Polyglycidol as a scaffold for multifunctional

polyethers

Von der Fakultät für Mathematik, Informatik und

Naturwissenschaften der RWTH Aachen University zur

Erlangung des akademischen Grades eines Doktors der

Naturwissenschaften genehmigte Dissertation

vorgelegt von

M. Sc. RWTH

Fabian Marquardt

aus Rüdersdorf

Berichter: Universitätsprofessor Dr. Martin Möller

Universitätsprofessor Dr. Andrij Pich

Tag der mündlichen Prüfung: 23. Oktober 2018

Diese Dissertation ist auf den Internetseiten der

Universitätsbibliothek verfügbar.

I hereby declare that I have created this work completely

on my own and used no other sources or tools than the ones

listed, and that I have marked any citations accordingly.

Hiermit versichere ich, dass ich die vorliegende Arbeit

selbstständig verfasst und keine anderen als die

angegebenen Quellen und Hilfsmittel benutzt, sowie Zitate

kenntlich gemacht habe.

Aachen, October 2018

Fabian Marquardt

Contents

i

Contents

Abstract ......................................................................................................... v

Überblick ................................................................................................... vii

Acknowledgements ................................................................................. ix

Publications ............................................................................................... xi

Chapter 1

Introduction & Motivation ..................................................................... 1

1.1 Motivation ....................................................................................... 3

1.2 Scope of the thesis ......................................................................... 4

1.3 References ....................................................................................... 5

Chapter 2

From Glycidol to Functional Polyethers ............................................ 9

2.1 Glycidol – Synthesis & Usage ..................................................... 9

2.2 Polymerization of Glycidol ....................................................... 10

2.3 Functionalization of Polyglycidol ............................................ 15

2.4 References .................................................................................... 21

Chapter 3

Straightforward Synthesis of Phosphate Functionalized Linear

Polyglycidol ............................................................................................... 33

3.1 Introduction ..................................................................................... 33

Contents

ii

3.2 Experimental Section ................................................................. 34

3.3 Results and Discussion .............................................................. 38

3.4 Conclusions ................................................................................. 46

3.5 References .................................................................................... 46

Chapter 4

Novel Antibacterial Polyglycidols: Relationship between

Structure and Properties ........................................................................ 51

4.1 Introduction................................................................................. 51

4.2 Experimental Section ................................................................. 54

4.3 Results and Discussion .............................................................. 64

4.4 Conclusions ................................................................................. 76

4.5 References .................................................................................... 77

Chapter 5

Homoserine Lactone as a Structural Key Element for

Multifunctional Polyglycidols ............................................................. 83

5.1 Introduction................................................................................. 83

5.2 Experimental Section ................................................................. 85

5.3 Results and Discussion .............................................................. 88

5.4 Conclusions ................................................................................. 92

5.5 References .................................................................................... 93

Chapter 6

Light-induced Cross-linking and Post-cross-linking

Modification of Polyglycidol ............................................................... 97

6.1 Introduction................................................................................. 97

6.2 Experimental Section ................................................................. 99

6.3 Results and Discussion ............................................................ 104

6.4 Conclusions ............................................................................... 112

6.5 References .................................................................................. 113

Contents

iii

Chapter 7

Summary ................................................................................................... 119

Additional Information ....................................................................... 121

A.1 Phosphate Functionalized Polyglycidols ......................... 121

A.2 Antibacterial Polyglycidols ................................................. 126

A.3 Homoserine Lactone Functionalized Polyglycidol ........ 140

A.4 Post-cross-linking Modification ........................................ 145

List of Abbreviations ............................................................................. 151

List of Figures ......................................................................................... 153

List of Schemes ....................................................................................... 159

List of Tables ........................................................................................... 163

Curriculum Vitae .................................................................................... 165

Abstract

v

Abstract

In this thesis, various multifunctional polyglycidols are synthesized via

post-polymerization modification protocols. Every functionalized

polyglycidol is meticulously characterized by appropriate analytical

methods in regard to its degree of functionalization, molecular weight,

molecular weight distribution and purity. All syntheses are optimized

to give maximum control on the degree of functionalization, high

yields and pure products.

The introduction of pendant diethyl phosphate groups into poly-

glycidol is achieved by straightforward reaction of the hydroxymethyl

side groups with diethyl chlorophosphate. The degree of function-

alization is controlled by the ratio of hydroxymethyl groups attached

to the polyether backbone to the organophosphorus reagent. Removal

of one and both ethyl groups is accomplished by dealkylation with

sodium iodide or bromotrimethylsilane, respectively.

The synthesis of cationic/hydrophobic polyglycidols with various

structures is presented. Functional polyethers are examined in regard

to their antimicrobial properties against E. coli and S. aureus. Poly-

glycidol with statistically distributed cationic and hydrophobic groups

(cationic to hydrophobic balance 1:1) is compared to (a) polyglycidol

with a hydrophilic modification at the cationic functionality, (b)

polyglycidol with cationic as well as hydrophobic groups at every

repeating unit, and (c) polyglycidol with a cationic to hydrophobic

balance of 1:2. Structure-property relationships are presented.

The usage of bio-based building blocks for polymer synthesis is

investigated by functionalization of polyglycidol with homoserine

lactone. The resulting polyethers with lactone groups in the side chains

Abstract

vi

are converted to cationic/hydrophilic polymers by ring-opening

reaction with 3-(dimethylamino)-1-propylamine, followed by quarter-

nization with methyl iodide.

The light-induced cross-linking of functional polyglycidol and its post-

cross-linking modification are presented. Linear polyglycidol is first

functionalized with a tertiary amine in a two-step reaction. The

dimethylaminopropyl functional polyglycidol is cross-linked in an UV-

light-induced reaction, using camphorquinone as a Type II photo-

initiator. The cross-linked polyglycidol is further functionalized by

quaternization with various organoiodine compounds. Aqueous

dispersions of the cross-linked polymers are investigated in regard to

their size and zeta potential. Dried polymer films are evaluated

concerning the thermal transitions and chemical transformations.

Überblick

vii

Überblick

In dieser Arbeit werden diverse multifunktionelle Polyglycidole an-

hand polymeranaloger Reaktionsprotokolle synthetisiert. Alle funktio-

nalisierten Polyglycidole werden durch geeignete analytische Metho-

den sorgfältig in Hinblick auf ihren Grad der Funktionalisierung, ihr

Molekulargewicht, der Molekulargewichtsverteilung und ihrer Rein-

heit charakterisiert. Alle Syntheseprotokolle werden optimiert, so dass

sie maximale Kontrolle über den Grad der Funktionalisierung, hohe

Ausbeuten und reine Produkte geben.

Die Einführung von Diethylphosphatgruppen an die Polyglycidol-

hauptkette erfolgt durch Reaktion der Hydroxymethyl-Seitengruppen

des Polyglycidols mit Diethylchlorphosphat. Der Grad der Funktio-

nalisierung wird über das Verhältnis der Hydroxymethylgruppen zum

Organophosphat kontrolliert. Entfernen von einer und beiden

Ethylgruppen wird durch Dealkylierung mit Natriumiodid, respektive

Bromtrimethylsilan erreicht.

Die Synthese kationisch/hydrophob funktionalisierter Polyglycidole

mit diversen Strukturen wird präsentiert. Die funktionellen Polyether

werden hinsichtlich ihrer antimikrobiellen Eigenschaften gegen E. coli

und S. aureus untersucht. Ein Polyglycidol mit statistisch verteilten

kationischen und hydrophoben Gruppen (Verhältnis kationisch:hy-

drophob von 1:1) wird mit (a) einem Polyglycidol mit einer hydro-

philen Modifikation an der kationischen Funktionalität, (b) einem

Polyglycidol mit kationischen und hydrophoben Gruppen an jeder

Wiederholungseinheit und (c) einem Polyglycidol mit kationischen

und hydrophoben Gruppen im Verhältnis von 1:2 verglichen. Der

Einfluss der Struktur auf die Eigenschaften wird gezeigt.

Überblick

viii

Die Verwendung biobasierter Bausteine in der Polymersynthese wird

durch Funktionalisierung von Polyglycidol mit Homoserin-Lacton

untersucht. Der Polyether mit Lactongruppen in den Seitenketten wird

durch eine ringöffnende Reaktion mit 3-Amiopropyldimethylamin

und anschließender Quaternisierung mit Methyliodid in ein katio-

nisch/hydrophiles Polymer umgewandelt.

Die lichtinduzierte Vernetzung und anschließende chemische Modifi-

kation von funktionalisiertem Polyglycidol wird präsentiert. Lineares

Polyglycidol wird zuerst in einer Zweistufenreaktion mit einem tertiä-

ren Amin funktionalisiert. Das 3-Dimethylaminopropyl funktionelle

Polyglycidol wird unter Verwendung von Campherchinon als Typ-II-

Photoiniator in einer UV-lichtinduzierten Reaktion vernetzt. Das

vernetzte Polyglycidol wird durch Quaternisierung mit verschiedenen

Organoiod-Verbindungen weiter funktionalisiert. Wässrige Dispersio-

nen der vernetzten Polymere werden hinsichtlich Größe und Zeta-

potential untersucht. Getrocknete Polymerfilme werden in Bezug auf

ihre thermischen Übergange, sowie ihrer chemischen Umwandlung

evaluiert.

Acknowledgements

ix

Acknowledgements

The present work was accomplished at the Institute for Technical and

Macromolecular Chemistry and the DWI - Leibniz Institute for Inter-

active Materials from January 2014 to February 2018 under the

supervision of Prof. Dr. Martin Möller. I want to thank Prof. Dr.

Martin Möller for the opportunity to be a part of his research group

and the possibility to work on an interesting research topic. Great

thanks go to my subgroup leader Dr. Helmut Keul, who taught me a

lot about polymer chemistry, beginning from when he first supervised

me during my Master thesis. Though our work approaches differ, I

enjoyed working with him and having him as a companion on the

journey to a successful PhD thesis. Next, I want to thank Dr. Jens

Köhler, my lab partner for sparking my interest in polymer chemistry

during one of the research works I did for him during my studies and

all the fruitful discussions and fun that followed. I also thank my other

fellow colleagues for making my stay at the institute a pleasant one.

Special thanks go to Rainer Haas, the gear that keeps the chroma-

tography running, for all the measurements he did.

I also want to thank all co-authors that contributed to my publications.

Thanks to Cornelia Stöcker and Justin Lange for supporting me with

their manpower during their research works. Thank you to Dr.

Elisabeth Heine and Rita Gartzen for the performance and evaluation

of antimicrobial measurements and the fruitful discussions that

followed. Thanks to Dr. Michael Bruns for the performance and

evaluation of XPS measurements. Thanks to Dr. Walter Tillmann for

the IR spectroscopy measurements. Special thanks to Prof. Yusuf

Acknowledgements

x

Yagci for the inspiration to develop the synthetic protocol presented

in chapter 6.

Besonderer Dank gilt meiner Familie, die mich immer unterstützt hat

und mir die Freiheit gegeben hat, alles in meinem Leben so zu

gestalten, wie ich es für richtig halte.

Publications

xi

Publications

Parts of this thesis are published and have been presented at

conferences.

Publications

1. Marquardt, F.; Keul, H.; Möller, M. Straightforward synthesis

of phosphate functionalized linear polyglycidol, Eur. Polym. J.

2015, 69, 319–327. (see Chapter 3)

2. Marquardt, F.; Stöcker, C.; Gartzen, R.; Heine, E.; Keul, H.;

Möller M. Novel Antibacterial Polyglycidols: Relationship

between Structure and Properties, Polymers 2018, 10, 96. (see

Chapter 4)

3. Marquardt, F.; Mommer, S.; Lange, J.; Jeschenko, P. M.;

Keul, H., Möller, M. Homoserine Lactone as a Structural Key

Element for the Synthesis of Multifunctional Polymers,

Polymers 2017, 9, 130. (see Chapter 5)

4. Marquardt, F.; Bruns, M.; Keul, H.; Yagci, Y.; Möller, M.

Light-induced cross-linking and post-cross-linking

modification of polyglycidol, Chem. Commun. 2018, 54, 1647.

(see Chapter 6)

Publications

xii

Poster Presentations

1. Ring-Opening of D,L-Homocysteine Thiolactone Functionalized

Polyglycidols: Adjustment of Antimicrobial Properties, Marquardt,

F.; Stöcker, C.; Keul, H.; Heine, E.; Möller M., Warwick

Polymer Conference 2016, Warwick (United Kingdom).

2. Homoserine lactone: A structural key element for multifunctional

polymers, Marquardt, F.; Keul, H.; Möller M., Brightlands

Rolduc Polymer Conference 2017, Kerkrade (Netherlands).

Chapter 1

1

Chapter 1

Introduction & Motivation

In 1600 B.C. ancient Mesoamericans were producing natural rubber

by harvesting latex from the Panama rubber tree (Castilla elastica) and

processing it with liquid extracted from the tropical white morning-

glory (Ipomoea alba).1 3500 years later Baekeland presented the first fully

synthetic resin (Bakelite, a phenol formaldehyde resin) by poly-

condensation of phenol with formaldehyde under acidic conditions.2

This milestone and Staudinger’s groundbreaking work on the theory

of polymerization3 paved the way for the large-scale industrial

production of polymers in the 1950s. Today, life without synthetic

polymers and the respective products seems unthinkable, emphasized

by an increase in polymer production from 1.5 Mt in 1950 to ~322 Mt

in 2015.4 The most commonly produced polymers are polyethylene

(PE) and polypropylene (PP).4 The field of application of PE is

dependent on its degree of crystallinity.5 Low-density PE is used in,

e.g. reusable bags, trays and containers and food packaging, while high-

density PE is used as a material for toys, housewares, shampoo bottles,

or pipes. PP is used as a material for food packaging, pipes and

automotive parts.6 Other polymers, such as polyvinyl chloride (PVC)7

are used in construction, polyethylene terephthalate (PET) is used as a

material for bottles8, and polystyrene (PS) is processed to plastic cups,

egg trays and other packaging material.9 These commodity polymers

account for ~90% of the global demand on plastics (Table 1.1).10

Chapter 1

2

Table 1.1: Industrially processed polymers, their abbreviation and fields of

application.

Polymer Field of application

Polyethylene

(PE)

Low density PE: reusable bags, trays and containers;

agricultural films; food packaging films; cable

sheathing

High density PE: toys; shampoo bottles; milk

bottles; housewares; pipes

Polypropylene

(PP)

Food packaging; snack wrappers; living hinges;

pipes; ropes; centrifuge tubes; automotive parts

Polyvinyl chloride

(PVC)

Window profiles; pipes; flooring; roof sheeting;

cable insulation; pleather; slip-proof surfaces

Polyethylene

terephthalate

(PET)

Bottles for carbonated drinks, juices, cleaners, etc.;

textile fibers; carrier foils; vascular implants

Polystyrene

(PS)

Plastic cups; egg trays; packaging material;

disposable cutlery; insulation; model making

Monomers used in the synthesis of these polymers are derived from

fossil hydrocarbons and the resulting materials lack specialization, due

to the absence of functional groups and/or the difficulty of post-

polymerization functionalization.11 In contrast to synthetic polymers,

natural polymers, such as polysaccharides, nucleic acids and peptides,

are multifunctional and exhibit highly specialized properties.12

Polysaccharides are derived from monosaccharides by enzyme

catalyzed polymerization, resulting in polydisperse polymers with

various potential complex structures based on the functionality of the

monomer.13,14 Peptides and nucleic acids are sequentially polymerized,

yielding monodisperse linear polymers with specific monomer

sequences.15-19 The similarity between all these biopolymers is the

possibility to create a vast amount of structures with very specific

applications from a limited number of building blocks.20 In the case of

peptides, the polymer is derived from the sequence-controlled

polymerization of amino acids, under the formation of peptide bonds.

The properties of the formed polyamide are dependent on the

functionality of each amino acid incorporated.21 In nature peptides are

Chapter 1

3

part of diverse, complex structures, such as enzymes, hormones,

antibodies, toxins, collagen, keratin, spider silk, etc.

As nature has always been an inspiration for scientists in the

development of systems in polymer and materials science, mimicking

of biopolymers has been the objective of extensive research.22,23

Poly(meth-)acrylates are an interesting scaffold for the synthesis of

functional polymers and thus, a promising candidate as a platform for

biomimetic polymers.24 Polymethacrylates have been functionalized

with catechol moieties to mimic the adhesion mechanism of mussels.25

The incorporation of di- and monohydroxyl catechols resulted in a

simple coatability of the biomimetic polymer on various surfaces and

excellent antifouling properties. Imitation of antimicrobial peptides

was achieved by functionalization of poly(meth-)acrylates with cat-

ionic and hydrophobic moieties.26,27 The prepared polymers exhibited

excellent antimicrobial behavior against bacterial and fungal biofilms.

Nature has demonstrated, how different functionalities and substi-

tution patterns in α-polyamides lead to a variety of complex, special-

ized properties. Based on this concept synthetic chemists have shown

that the properties of poly(meth-)acrylates can be tailored by intro-

duction of functional groups in the side chains. As an alternative to

these polymers, this thesis wants to evaluate the influence of a flexible,

hydrophilic polyether main chain on the properties of the functional

polymer.

1.1 Motivation

In recent years, the field of functional polymers has received an

increased interest due to the enhanced demands of modern

technology.28 Polymer scaffolds that allow the introduction of multiple

functionalities to the same polymer backbone are promising

candidates for the preparation of complex, specialized materials. The

motivation for this thesis is the presentation of polyglycidol as a

suitable, future-oriented alternative to poly(meth-)acrylates. Poly-

glycidol is a highly functionalized polyether with a hydroxyl func-

tionality in every repeating unit, allowing various post-polymerization

modifications.29 It is soluble in aqueous media, non-toxic towards cells

and licensed by the Food & Drug Administration (FDA).30,31 Addi-

Chapter 1

4

tionally, the glycidol monomer can be synthesized from renewable

resources.32 Enhancement of the polyglycidol library may prove as an

important stepping stone towards more complex, specialized

polymers.

1.2 Scope of the thesis

In chapter 2 a literature review of polyglycidol is presented. The

synthesis and various polymerization techniques of the glycidol

monomer, as well as the various post-polymerization functionalization

protocols of polyglycidol are discussed.

Phosphorus-containing compounds are of great interest for the

preparation and functionalization of polymers, as they show attractive

properties for the biomedical field. In chapter 3 polyglycidol is

functionalized with pendant diethyl phosphate groups in a controlled

manner. Removal of one and both ethyl groups is presented to prepare

phosphate diester and phosphate monoester functionalities,

respectively.

Polymers with pendant cationic and hydrophobic functionalities

exhibit antimicrobial properties and are an attractive alternative to low

molecular weight biocides, due to an enhanced chemical stability.

Chapter 4 shows the introduction of cationic and hydrophobic groups

into polyglycidol by various post-polymerization functionalization

protocols. Specific microstructures are prepared and compared in

regard to their antibacterial activity against the Gram-negative E. coli

and the Gram-positive S. aureus.

The utilization of bio-based materials in polymers is a huge milestone

on the way to a greener chemistry. In chapter 5 homoserine lactone

is established as a bio-based building block for the preparation of

multifunctional polyglycidols. The homoserine lactone ring is first

attached to the side chain, opened by a primary amine, and sub-

sequently quaternized to prepare cationic/hydrophilic polyethers.

Chapter 1

5

Chapter 6 introduces the concept of post-cross-linking modification.

Polyglycidol is first functionalized with a 3-(dimethylamino)-1-propyl-

amine in a two-step reaction. The functional polyether is then cross-

linked in a light-induced reaction, using camphorquinone as a Type II

photoinitiator. Further functionalization of the cross-linked poly-

glycidol with various organoiodine compounds yields cationic/hydro-

phobic, cationic/hydrophilic and cationic/superhydrophobic poly-

ether particles.

1.3 References

1. Hosler, D.; Burkett, S.L.; Tarkanian, M.J. Prehistoric

polymers: Rubber processing in ancient mesoamerica. Science

1999, 284, 1988.

2. Baekeland, L.H. The synthesis, constitution, and uses of

bakelite. J. Ind. Eng. Chem. 1909, 1, 149.

3. Staudinger, H. Über Polymerisation. Berichte d. D. Chem.

Gesellschaft 1920, 53, 1073.

4. PlasticsEurope. Plastic - the facts 2016: An analysis of

european plastics production, demand and waste data. 2016.

5. Vasile, C.; Pascu, M. Practical guide to polyethylene. Rapra

Technology Limited: Shawbury, Shrewsbury, Shropshire,

UK, 2005.

6. Maddah, H.A. Polypropylene as a promising plastic: A

review. American Journal of Polymer Science 2016, 6, 1.

7. Patrick, S.G. Practical guide to polyvinyl chloride. Rapra

Technology Limited: Shawbury, Shrewsbury, Shropshire,

UK, 2005.

8. ILSI Europe Report on packaging materials: 1. Polyethylene

terephthalate (PET) for food packaging applications.

Brussels, Belgium, 2000.

9. Gurman, J.L.; Baier, L.; Levin, B.C. Polystyrenes: A review

of the literature on the products of thermal decomposition

and toxicity. Fire and Materials 1987, 11, 109.

10. Andrady, A.L.; Neal, M.A. Applications and societal benefits

of plastics. Philos. Trans. R. Soc. B 2009, 364, 1977.

Chapter 1

6

11. Geyer, R.; Jambeck, J.R.; Law, K.L. Production, use, and fate

of all plastics ever made. Sci. Adv. 2017, 3, e1700782.

12. Hardy, J.G.; Römer, L.M.; Scheibel, T.R. Polymeric materials

based on silk proteins. Polymer 2008, 49, 4309.

13. Woods, R.J. Three-dimensional structures of oligo-

saccharides. Curr. Opin. Struct. Biol. 1995, 5, 591.

14. Aravamudhan, A.; Ramos, D.M.; Nada, A.A.; Kumbar, S.G.

Natural polymers. In Natural and synthetic biomedical polymers,

2014; pp 67.

15. Saxena, T.; Karumbaiah, L.; Valmikinathan, C.M. Proteins

and poly(amino acids). In Natural and synthetic biomedical

polymers, 2014; pp 43.

16. Weber, A.L.; Miller, S.L. Reasons for the occurrence of the

twenty coded protein amino acids. J. Mol. Evol. 1981, 17, 273.

17. Dickerson, R.; Drew, H.; Conner, B.; Wing, R.; Fratini, A.;

Kopka, M. The anatomy of a-, b-, and z-DNA. Science 1982,

216, 475.

18. Brautigam, C.A.; Steitz, T.A. Structural and functional

insights provided by crystal structures of DNA polymerases

and their substrate complexes. Curr. Opin. Struct. Biol. 1998, 8,

54.

19. McCulloch, S.D.; Kunkel, T.A. The fidelity of DNA

synthesis by eukaryotic replicative and translesion synthesis

polymerases. Cell Res. 2008, 18, 148.

20. Lutz, J.F.; Ouchi, M.; Liu, D.R.; Sawamoto, M. Sequence-

controlled polymers. Science 2013, 341, 1238149.

21. Berg, J.M.; Tymoczko, J.L.; Stryer, L. Chapter 3. Protein

structure and function. In Biochemistry, W. H. Freeman: New

York, 2002.

22. Hwang, J.; Jeong, Y.; Park, J.M.; Lee, K.H.; Hong, J.W.; Choi,

J. Biomimetics: Forecasting the future of science,

engineering, and medicine. Int. J. Nanomedicine 2015, 10, 5701.

23. Carlini, A.S.; Adamiak, L.; Gianneschi, N.C. Biosynthetic po-

lymers as functional materials. Macromolecules 2016, 49, 4379.

24. Coessens, V.; Pintauer, T.; Matyjaszewski, K. Functional

polymers by atom transfer radical polymerization. Prog. Polym.

Sci. 2001, 26, 337.

Chapter 1

7

25. Duan, J.; Wu, W.; Wei, Z.; Zhu, D.; Tu, H.; Zhang, A.

Synthesis of functional catechols as monomers of mussel-

inspired biomimetic polymers. Green Chem. 2018.

26. Qu, Y.; Locock, K.; Verma-Gaur, J.; Hay, I.D.; Meagher, L.;

Traven, A. Searching for new strategies against polymicrobial

biofilm infections: Guanylated polymethacrylates kill mixed

fungal/bacterial biofilms. J. Antimicrob. Chemother. 2016, 71,

413.

27. Kurtz, C.; Neenan, T.X. Antimicrobial compositions and

methods. US 6482402 B1, 2002.

28. Braun, D.; Cherdron, H.; Rehahn, M.; Ritter, H.; Voit, B.

Functional polymers. In Polymer synthesis: Theory and practice,

2013; pp 375.

29. Thomas, A.; Müller, S.S.; Frey, H. Beyond poly(ethylene

glycol): Linear polyglycerol as a multifunctional polyether for

biomedical and pharmaceutical applications. Biomacromolecules

2014, 15, 1935.

30. Frey, H.; Haag, R. Dendritic polyglycerol: A new versatile

biocompatible material. Rev. Mol. Biotechnol. 2002, 90, 257.

31. Kainthan, R.K.; Janzen, J.; Levin, E.; Devine, D.V.; Brooks,

D.E. Biocompatibility testing of branched and linear

polyglycidol. Biomacromolecules 2006, 7, 703.

32. Sutter, M.; Silva, E.D.; Duguet, N.; Raoul, Y.; Metay, E.;

Lemaire, M. Glycerol ether synthesis: A bench test for green

chemistry concepts and technologies. Chem. Rev. 2015, 115,

8609.

8

Chapter 2

9

Chapter 2

From Glycidol to Functional

Polyethers

Polyglycidol was first mentioned by Richter in 1877 as an unwanted

product in the synthesis of glycidol from epichlorohydrin.1 Since then,

many protocols for the controlled polymerization of glycidol have

been reported to receive polyglycidol in various topologies and molar

masses.2 This chapter gives a brief overview on the synthesis and

different polymerization techniques of glycidol, and the diverse

possibilities to functionalize polyglycidol.

2.1 Glycidol – Synthesis & Usage

Glycidol or 2,3-epoxypropan-1-ol is an organic compound that is used

in the syntheses of functional epoxides, glycidyl ethers, esters and

amines.3 It is also used as a demulsifier and as a stabilizer for natural

oils and vinyl polymers.4,5 Glycidol contains both an epoxide and a

hydroxyl functional group and can be synthesized via various

protocols. Industrial production is based on the hydrolysis of

epichlorohydrin under alkaline conditions6 (Scheme 2.1a) or the

epoxidation of allyl alcohol with hydrogen peroxide and a

homogenous or heterogeneous catalyst based on titanium7, tungsten8

or vanadium9 (Scheme 2.1b). Non-racemic glycidols (optically pure

(R)- and (S)-glycidols) can be prepared by asymmetric epoxidation

Chapter 2

10

using titanium(IV) isopropoxide, diisopropyl tartrate and cumene

peroxide.10,11 However, the endeavor of a “greener” chemistry, and

thus, metal-free and environmentally friendly processes has led to a

new approach in the synthesis of glycidol by decarboxylation of

glycerol carbonate (glycerol carbonate prepared from glycerol and

carbon dioxide) in the presence of ionic liquids (Scheme 2.1c).12-14

Scheme 2.1: Synthesis of glycidol by (a) hydrolysis of epichlorohydrin,

(b) epoxidation of allyl alcohol, and (c) decarboxylation of glycerol

carbonate.

2.2 Polymerization of Glycidol

Glycidol is used as monomer in the preparation of polyglycidol (PG),

a highly functionalized polyether with a hydroxyl group in every

repeating unit.15 The polymer is soluble in aqueous media, non-toxic,

biocompatible and licensed by the Food and Drug Administration

(FDA).16,17 Synthesis of polyglycidol is possible by means of anionic,

cationic, enzymatic, and coordination type polymerization, yielding

linear, star-shaped, and branched polyethers in various molecular

masses.

2.2.1 Anionic polymerization

The anionic ring-opening polymerization of epoxides is based on the

initiation step by formation of an alkoxide species from the corres-

ponding alcohol and the following propagation step by nucleophilic

attack on the epoxide.18 In case of glycidol the initiation step is

composed of the deprotonation of a mono- or polyfunctional alcohol

by an alkali metal alkoxide. The reactivity of the formed initiator

mainly depends on the nature of the counter-ion. The initiator acts as

a nucleophile and attacks the epoxide ring of the glycidol, cleaving the

Chapter 2

11

CH2―O bond, and generating a secondary alkoxide unit which can

propagate the chain growth to form polyglycidol. However, the pri-

mary hydroxyl group facilitates an intramolecular transfer reaction

with the secondary alkoxide, leading to two possible propagation sites,

and thus, the formation of branched polyglycidols.19,20

Scheme 2.2: Mechanism of the anionic ring-opening polymerization of

glycidol.

Nevertheless, the intramolecular transfer does not occur on every

hydroxyl functionality so that primary as well as secondary hydroxyl

groups are found in the polymer chains of the branched polyether

(Scheme 2.3). Branched polyglycidols have been successfully syn-

thesized with molecular weights of Mn ≤ 6000 g mol–1 and narrow

molecular weight distributions.21 To control the molecular weight and

polydispersity of the branched polyglycidol Sunder et al. used a partially

deprotonated trifunctional initiator and the slow monomer addition

technique.22,23 The use of a low molecular weight polyglycidol as

macroinitiator allowed the preparation of branched polyglycidols with

Mn ≤ 24,000 g mol–1 under controlled conditions, due to a higher

concentration of active reaction sides.24

Non-branched polyglycidols are received by inhibition of the intra-

molecular transfer reaction. Therefore, the hydroxyl group of the

glycidol is functionalized with a suitable protecting group prior to poly-

merization. Common protected monomers include ethoxyethyl glyci-

dyl ether (EEGE), tert-butyl glycidyl ether (tBuGE) and allyl glycidyl

ether (AGE) (Scheme 2.4a).25 EEGE is prepared by reaction of gly-

cidol with ethyl vinyl ether, using p-toluenesulfonic acid as a catalyst.26

Chapter 2

12

Scheme 2.3: Synthesis of branched polyglycidol with primary (blue) and

secondary (red) hydroxyl groups along the polymer chain.

Though, tBuGE and AGE are commercially available, EEGE is

predominantly used in the synthesis of linear polyglycidol, because the

acetal group can be easily removed after polymerization under mild

acidic conditions (Scheme 2.4b). Recently, tetrahydropyranyl glycidyl

ether (TGE) has been discussed as an alternative to EEGE

(Scheme 2.4a).27 The first successful polymerization of EEGE was

reported by Taton et al.28 Under usage of cesium hydroxide as initiator

in bulk they received poly(ethoxyethyl glycidyl ether) (P(EEGE)) with

molecular weights of Mn = ~30,000 g mol–1 and a broad molecular

weight distribution (Ð = ~1.5). The implementation of different

initiator systems, such as cesium and potassium alkoxides29,30 or sec-

BuLi/phosphazene base t-BuP431, allowed the synthesis of poly-

glycidols with narrow molecular weight distributions. However, higher

molecular weight polyglycidols could not be prepared by usage of alkali

metal based initiators. The basicity of the propagating alkoxide at the

chain end causes proton abstraction from the monomer, leading to the

formation of allylic end groups and limiting the molecular weight.32

Gervais et al. presented the anionic polymerization of EEGE in the

presence of a binary initiating system, containing tetraoctylammonium

bromide as initiator and an excess of triisobutylaluminum (iBu3-Al).33

The reaction mechanism comprises (i) complexation of the initiator by

iBu3-Al, and (ii) nucleophilic activation of the oxirane by complexation

with iBu3-Al.34 The reaction protocol allows the polymerization of

EEGE at low temperatures, yielding PG with a molecular weight of

Mn ≤ 85,000 g mol–1 with a narrow molecular weight distribution

(Ð ≥ 1.03).

Chapter 2

13

Scheme 2.4: a) Protected glycidol monomers used in the polymerization of

polyglycidol. b) Synthesis of linear polyglycidol from EEGE using potassium

alkoxide as initiator.

The controlled polymerization of EEGE is not limited to the pre-

paration of linear polyglycidol. Changing the initiator system from a

monofunctional to a multifunctional alkoxide allows the synthesis of

star-shaped polyglycidols. Hans et al. prepared 4-arm-star shaped poly-

glycidol with Mn = ~2300 g mol–1, using the tetrafunctional di-

(trimethylolpropane) and potassium methanolate as initiator system.35

This concept was transferred by Schmitz et al. to synthesize 3-arm- and

6-arm-star shaped polyglycidols from trifunctional (trimethylol-

propane) and hexafunctional (dipentaerythritol) initiators.36

2.2.2 Cationic polymerization

The first synthesis of branched polyglycidol copolymers by cationic

copolymerization with 1,3-dioxolane was reported by Goethals et al.37

In general, the cationic polymerization of glycidol is carried out by

initiation with Lewis acids (SnCl4, BF3 · Et2O) or Brønsted acids (triflic

acid, trifluoroacetic acid). Dependent on the initiator the polyether is

either formed by an activated monomer, or active chain-end mecha-

nism (Scheme 2.5).38 Brønsted acids facilitate the active chain-end

mechanism. The protonation of the monomer leads to a positive

partial charge in the methylene and methine groups of the glycidol.

Chapter 2

14

Reaction with a second monomer causes scission in the first oxirane

unit and the formation of primary hydroxyl groups in the resulting

polyglycidol.39 Lewis acids promote the activated monomer mecha-

nism, causing the addition of protonated monomer to the hydroxyl

group of the glycidol. This addition does not only form primary, but

also secondary hydroxyl groups in the polyglycidol side chains. Since

the activated monomer can add to any hydroxyl group in the polyether,

branching is unavoidable.

As an approach towards a “greener” chemistry Mohammadifar et al.

presented the cationic polymerization of glycidol with citric acid.

Starting from citric acid as a trifunctional core, branched polyglycidols

with narrow molecular weight distributions were prepared at ambient

conditions.40 Recently, Dadkhah et al. have described the use of

ascorbic acid as an activator for the cationic polymerization of glycidol

to prepare low molecular weight, hyperbranched polyglycidols.41

Scheme 2.5: Cationic polymerization of glycidol by active chain-end

mechanism (top) and activated monomer mechanism (bottom).

2.2.3 Coordination polymerization

Anionic ring-opening polymerization is the most commonly used

protocol for the synthesis of polyglycidol. Though, the control during

this process is high, the degree of polymerization and the resulting

molecular weight are limited. Coordination polymerization with

organometallic catalysts allows the synthesis of high molecular weight

Chapter 2

15

linear polyglycidol by polymerization of EEGE.42 Haout et al.

introduced diethylzinc/water as an initiating system which has since

then successfully been used in the preparation of polyglycidols with

molecular weights of up to Mn = 1,450,000 g mol–1.43,44 However, the

coordination polymerization of EEGE is not well-controlled, leading

to high molecular weight distributions (Ð = 1.8).45

2.2.4 Enzymatic polymerization

Studies on the enzymatic polymerization of glycidol were reported by

Soeda et al.46,47 Using various lipase enzymes as biocatalysts, poly-

glycidols with molecular weights of Mn = 900 g mol–1 were prepared.

Nevertheless, the low reaction rates and the occurrence of macrocycle

formation demand further work to make this protocol a viable type of

polymerization for the formation of polyethers from glycidol.

2.3 Functionalization of Polyglycidol

The introduction of functional groups into polyglycidol is possible

before or after the polymerization. Pre-polymerization protocols

include the usage of functional glycidyl ether monomers25,48-55, or the

-end-functionalization by utilization of suitable initiator systems.33,56-

64 Post-polymerization functionalization comprises the -end-

functionalization, and the backbone functionalization by reaction with

the pendant hydroxyl groups in every repeating unit of the

polyglycidol. Due to the focus of this work, only post-polymerization

functionalization techniques will be described. Further information on

pre-polymerization functionalization protocols can be found in the

respective references.

-End-functionalization of polyglycidol

-End-functionalization of polyglycidol comprises the reaction of end

hydroxyl group(s) with an appropriate reactant. In hyperbranched

polyglycidols multiple hydroxyl groups are present at the surface which

can be targeted by post-polymerization functionalization protocols

(Scheme 2.6). The synthesis of -end-functionalized linear

polyglycidol is realized by reaction of the end hydroxyl group of

Chapter 2

16

P(EEGE) after polymerization, followed by removal of the acetal

groups under acidic conditions. Various protocols for successful end-

capping have been presented.

End-functionalization of hyperbranched polyglycidol with tertiary

amine groups was presented by Salazar et al.65 The hydroxyl groups

were reacted with tosyl chloride under alkaline conditions, followed by

reaction with diethylamine or di-n-pentylamine, respectively, to

prepare tertiary amine-terminated polyglycidols (Scheme 2.6, A). The

synthesized polyethers were successfully used as ligands in the copper-

catalyzed oxidative coupling of terminal acetylenes. Schubert et al.

reported the functionalization with methyl and trimethylsilyl moities.66

Methyl groups were introduced by methylation of the hydroxyl func-

tionalities with methyl iodide (Scheme 2.6, B).67,68 Silylation was per-

formed using hexamethyldisilazane and catalyzed with iodine (Scheme

2.6, C).69 Both functionalization techniques were used to study the

effect of hydrogen bonding in hyperbranched polyglycidols in a broad

molecular weight range on the melt rheology. Türk et al. described the

preparation of polyanionic polyglycidols as new heparin analogues.70

Sulfate and carboxylate moieties were introduced by reaction with a

sulfur trioxide pyridine complex (Scheme 2.6, D), or sodium chloro-

acetate (Scheme 2.6, E), respectively. Hyperbranched polyglycidols,

carrying anionic functionalities were also reported by Weinhart et al.71

The functionalization was performed by 1,3-dipolar cycloaddition of

azide-terminated polyglycidol with anionic sulfonate, carboxylate,

phosphonate, and bisphosphonate alkynes (Scheme 2.6, I).72 Additio-

nally, phosphate functionalization was achieved by reaction with

chloro diethylphosphite, followed by in situ oxidation and ethyl ester

hydrolysis (Scheme 2.6, F). All polyanions were examined in regard to

their L-selectin inhibition. Yu et al. used the 1,3-dipolar cycloaddition

to react choline phosphate and phosphatidyl choline alkynes with azide

functionalized polyglycidol. The prepared zwitterionic polyethers were

used as biomembrane adhesives.73 The first synthesis of azide-

terminated PG was reported by Roller et al.74 The synthetic protocol

comprised the functionalization of polyglycidol with mesyl chloride,

followed by nucleophilic substitution with sodium azide (Scheme 2.6,

G). The azide moieties could further be reacted to the corresponding

amine by reaction with triphenylphosphane (Scheme 2.6, H).

Chapter 2

17

Scheme 2.6: -End-functionalization of hyperbranched polyglycidol.

Chapter 2

18

Amine-terminated PG was functionalized with catechol groups by

Krysiak et al. to study their adsorption mechanism on titan dioxide

surfaces.75 Therefore, the catechol functionalities were introduced by

amide coupling with 3,4-dihydroxyhydrocinnamic acid in various

degrees of functionalization (Scheme 2.6, J). Branched polyglycidol

functionalized with viologen chromophores to study the photo- and

electrochromic performance were reported by Cao et al.76 Esteri-

fication with chloroacetyl chloride, followed by quaternization of 4,4’-

bipyridyl lead to polyglycidols which could repeatedly be colorized by

UV-light and bleached with oxygen (Scheme 2.6, K). Additionally, the

polyether responded with reversible color changes to pulsed electrical

stimuli. Stiriba et al. used esterification with palmitoyl chloride to

functionalize linear and hyperbranched polyglycidols.77 The amphi-

philic PGs were compared in regard to their nanocapsule formation

capabilities. Linear and star-shaped polyglycidols were functionalized

with vinyl sulfonate groups by Haamann et al.78-80 Vinyl sulfonate

groups were introduced by reaction with 2-chloro-ethanesulfonyl

chloride. Various model reactions with primary amines confirmed the

successful functionalization.

The -end-functionalization of linear polyglycidol has been used in

the preparation of various copolymers. Mendrek et al. reported a

protocol to end-cap P(EEGE) with 2-chloropropionyl and 2-

bromopropionyl units.81 The functionalized polyethers were used as

macroinitiators for the atom transfer radical polymerization (ATRP)

of N-isopropylacrylamide. Removal of the acetal groups gave

polyglycidol-block-poly(N-isopropylacrylamide) copolymers with

controlled composition and narrow molecular weight distribution. The

end-functionalization of linear P(EEGE) with methacrylic acid

anhydride was presented by Thomas et al.82 The methacrylate

functionalized macromonomers were polymerized by ATRP and

deprotected under acidic conditions to receive poly(methacrylate)-

graft-polyglycidol copolymers. Another approach to receive meth-

acrylate containing macromonomers involves the end-capping of

linear polyglycidol with propargyl bromide, followed by 1,3-cyclo-

additon with azido hexyl methacrylate.83 Graft-copolymers were pre-

pared by radical polymerization with AIBN as initiator. Meyer et al.

used the end-capping of linear polyglycidol to introduce L-alanine as

Chapter 2

19

an endgroup.84 Therefore, P(EEGE) was first ω-end-functionalized by

anionic ring-opening reaction with glycidyl phthalimide. The

phthalimide was converted to the amine via hydrazinolysis and

subsequently reacted with L-alanine N-carboxyanhydride.

2.3.2 Backbone functionalization of polyglycidol

The backbone functionalization of polyglycidol comprises the reaction

of hydroxyl groups along the main chain with an appropriate reactant.

Various protocols have been reported to target these functional groups

randomly, or in a controlled manner.85,86

Hydroxyl groups can be esterified by reaction with a carboxylic acid.

Dworak et al. presented a method to randomly functionalize linear

polyglycidol with acetate moieties by reaction with acetic anhydride

(Scheme 2.7, A).87 The ester was introduced to hydrophobically

modify the polyglycidol and control its lower critical solution

temperature. Groll et al. used the esterification to introduce thiol

groups to the polyglycidol backbone.88 The polyglycidol was reacted

with 3,3’-dithiodipropionic acid, using DCC/DMAP as a catalyst

system, followed by reduction of the disulfide with TCEP (Scheme

2.7, B). The received thiol functionalized polyethers were used in the

preparation of nanogels to study the degradation behavior of these

gels. A protocol to convert the hydroxyl groups of the polyglycidol to

thiol groups was presented by Southan et al. (Scheme 2.7, C).89

Therefore, the polyglycidol was first esterified by reaction with tosyl

chloride. The tosylated polyether was reacted with triphenyl-

methanethiol, and deprotected under acidic conditions. Poly(ethylene

oxide)-co-polyglycidylthiol copolymers were successfully used in inkjet

printing. Erberich et al. functionalized polyglycidol with alkyne moieties

by nucleophilic substitution with propargyl bromide.25 The alkyne

functionalities were further reacted with azido sugar in a 1,3-dipolar

cycloaddition (Scheme 2.7, D). The introduction of urethane groups

to polyglycidol block-copolymers was presented by Dimitrov et al.90

The hydroxyl groups were reacted with ethyl isocyanate, using

dibutyltin dilaurate as catalyst (Scheme 2.7, E). The poly(ethyl glycidyl

carbamate) was used in a cross-linking reaction with a diacyl chloride

reagent by Utrata-Wesolek et al. to study the thermoresponsive behavior

of the received hydrogels.91 Backes et al. used the same protocol to

Chapter 2

20

synthesize amphiphilic block copolymers based on polyglycidol by

functionalization with various C12–C16 alkyl isocyanates (Scheme 2.7,

F).92 The copolymers were investigated in regard to their thermal

behavior, exhibiting three reversible thermal transitions. A different

protocol to introduce carbamates to polyglycidol was presented by

Theiler et al.93 Hydroxyl groups are reacted with phenyl chloroformate

under alkaline conditions to generate phenyl carbonates (Scheme 2.7,

G). The phenyl carbonate moieties can then act as active esters in the

nucleophilic substitution with primary amines, yielding carbamate

groups. Hydrophilic, hydrophobic and cationic amines were

introduced in the polyglycidol and examined in regard to their

antimicrobial activity. The same method was used by Ozdemir et al. in

the synthesis of polyglycidol based double-comb copolymers.94 Beezer

et al. presented a protocol for the amino-oxy functionalization of

polyglycidol (Scheme 2.7, H).95 The polyether was reacted with N-

oxyphthalimide in a Mitsonubu reaction, followed by hydrazinolysis of

the oxyphthalimide groups. The reaction protocol allowed the

introduction of the amino-oxy species in a defined ratio. Kaluzynski et

al. presented three different types of post-polymerization modifica-

tion.96 Functionalization with phosphoric acid was carried out by

reaction with phosphorus oxychloride in triethyl phosphate and

subsequent hydrolysis of the phosphorus dichloride (Scheme 2.7, I).

However, the reaction is not controllable, leading to the formation of

diesters and thus, to intra- and intermolecular cross-linking.97

Carboxylic acid groups were introduced by reaction of polyglycidol

with ethyl bromoacetate and hydrolysis under alkaline conditions

(Scheme 2.7, J). Additionally, polyglycidol was reacted with 1,3-

propane sultone to yield sulfonic acid functionalized polyethers

(Scheme 2.7, K). The functionalization of linear polyglycidol with

sulfate groups was performed by Malineni et al.98 The hydroxyl side

groups were reacted with a sulfur trioxide triethylamine complex and

the resulting poly(glycidyl sulfate) was used as part of a heparin-

mimetic copolymer (Scheme 2.7, L). Penczek et al. presented the

functionalization of polyglycidol with 2-diethyl-phosphonoethyl

acrylate.99 Dealkylation of the phosphonic ester groups gave the

corresponding phosphonic acid, while hydrolysis of the carboxylic

ester gave the carboxylic acid, allowing the simultaneous introduction

Chapter 2

21

of two functionalities (Scheme 2.7, M). The controlled addition of

phosphonic acid groups to the polyglycidol backbone was presented

by Köhler et al.100 The hydroxyl groups were reacted with diethyl vinyl

phosphonate in a base catalyzed Michael addition and subsequently

dealkylated (Scheme 2.7, N). The phosphonate functionalized

polyglycidols were used as macroinitiators in the graft-copolymeri-

zation of ε-caprolactone, leading to an enhancement of the hydrolytic

degradability of the poly(caprolactone).101-104 Additionally, phosphonic

acid and acrylate functionalized polyglycidols were prepared and

examined as UV-active adhesion promoters for a hydrogel coating on

stainless steel wires.105

Scheme 2.7: Backbone functionalization of polyglycidol.

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Chapter 2

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Chapter 2

32

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Chapter 3

33

Chapter 3

Straightforward Synthesis of

Phosphate Functionalized

Linear Polyglycidol

3.1 Introduction

Phosphorus containing compounds are of great interest for the

preparation and functionalization of polymeric materials. Thus, a

variety of polymers was synthesized by either (co-)polymerization of

monomers carrying the phosphorus atom or by post-polymerization

modification of polymers with phosphorus based reagents.1,2

Polyphosphates and polyphosphonates show attractive properties for

the biomedical field, due to their biodegradability, blood compatibility,

and strong interactions with dentin, enamel and bone.3-6 Hence, the

synthesis of phosphate and phosphonate functionalized polymers, e.g.

poly(acrylates), poly(vinylalcohols), and poly(acrylamides) has been

achieved by polymerization of the respective monomers or by polymer

analogous reactions.7-10 Introduction of the phosphonate moiety

allows the preparation of precursors for the corresponding

phosphonic acid.11,12 Phosphonic acids are known to show strong

interactions with metal oxides, leading to various applications, such as

adhesion promotion or corrosion inhibition.13-16

Chapter 3

34

Köhler et al. presented the post-polymerization functionalization of

polyglycidol with diethyl vinylphosphonate and subsequent

dealkylation of the pendant phosphonate groups.17 This method

allowed the tailoring of the amount of phosphonate/phosphonic acid

groups introduced into the polyglycidol backbone. The phosphonate

functionalized polyglycidols were used as macroinitiators in the graft-

copolymerization of ε-caprolactone, enhancing the hydrolytic degrada-

bility of the poly(caprolactone) formed.18,19 Additionally, multifunc-

tional polyglycidols carrying phosphonic acid and acrylate groups were

prepared and examined as UV-active adhesion promoters for a

hydrogel coating on stainless steel wires.20

Introduction of phosphate groups into polyglycidol follows two

different approaches. Babu et al. prepared phosphate functionalized

monomers based on glycidol, which were polymerized by anionic ring-

opening polymerization using a Zn(II) catalyst and tetrabutylammo-

nium bromide as initiator yielding polymers with fairly high molecular

weights.21 Weinhart et al. synthesized dendritic polyglycidol phosphate

by functionalization with chloro diethylphosphite followed by in situ

oxidation.22 However, this approach uses an excess of the phosphor-

ylation agent and allows no control of the degree functionalization.

Herein, a straightforward approach for the introduction of pendant

phosphate groups into linear polyglycidol is presented. The synthetic

pathway involves the partial phosphorylation of polyglycidol with

diethyl chlorophosphate and subsequent dealkylation of the pendant

phosphate groups. Additional functionalities can be introduced into

the remaining hydroxy groups to prepare tailor-made polymers,

carrying diethylphosphate, ethylphosphate or phosphoric acid groups.

3.2 Experimental Section

3.2.1 Materials

Potassium tert-butoxide (1 M solution in THF, Aldrich), diethyl

chlorophosphate (>97%, Aldrich), pyridine (99.5%, dry over

molecular sieve, Acros), 4-dimethylaminopyridine (>98%, Fluka),

sodium iodide (99.9+%, anhydrous, Chempur), 2-hexanone (98%,

Chapter 3

35

Aldrich), bromotrimethylsilane (≥97%, Aldrich), and dichloro-

methane (≥99.8%, anhydrous, Aldrich) were used as received.

Diglyme was distilled over sodium before use. 3-Phenyl-1-propanol

(99%, Aldrich) was stirred with calcium hydride for 24 h and distilled.

Ethoxyethyl glycidyl ether (EEGE) was synthesized from 2,3-

epoxypropan-1-ol (glycidol) and ethyl vinyl ether according to Fitton et

al.23, purified by distillation, and stored under a nitrogen atmosphere

over molecular sieve (3 Å).

All reactions were carried out in a nitrogen atmosphere. Nitrogen

(Linde 5.0) was passed over molecular sieve (4 Å) and finely distributed

potassium on aluminum oxide.

3.2.2 Measurements

1H NMR, 13C NMR, and proton decoupled 31P NMR spectra were

recorded on a Bruker DPX-400 FT-NMR spectrometer at 400, 101,

and 162 MHz, respectively. Dimethyl sulfoxide (DMSO-d6) and

deuterium oxide (D2O) were used as solvents. The residual solvent

signal was used as internal standard. 31P {1H} NMR spectra were

referenced against 85% H3PO4 as external standard. Coupling

constants Jxy are given in Hz.

FTIR spectra were recorded on a Thermo Nicolet Nexus 470 FTIR

spectrometer at 25 °C. The samples were prepared as KBr pellets and

scanned over a range of 400–4000 cm–1.

DSC measurements were performed on a Netzsch DSC 204

differential scanning calorimeter under a nitrogen atmosphere.

Samples were prepared in perforated closed aluminum pans using

5 mg of the sample. The sample was heated and cooled with a rate of

10 °C min–1 in a range of 25–250 °C. The heat flow was measured as

a function of the temperature. Transitions were reported during the

second heating cycle and first cooling cycle.

Autotitration was performed with a Metrohm Titrando 905 connected

to a conductivity module. 0.1 N HCl and 0.1 N NaOH were used as

acid and base, respectively. The concentration of the sample was

5 mg mL–1 in water and the titrant was added with a drop rate of

14 µL min–1.

Molecular weights (Mn,SEC) and molecular weight distributions (Đ)

were determined by size exclusion chromatography (SEC). SEC

Chapter 3

36

analyses were carried out with DMF or water as eluent. SEC with DMF

(HPLC grade, VWR) as eluent was performed using an Agilent 1100

system equipped with a dual RI-/Visco detector (ETA-2020, WGE).

The eluent contained 1 g L–1 LiBr (≥99%, Aldrich). The sample

solvent contained traces of distilled water as internal standard. One

pre-column (8x50 mm) and four GRAM gel columns (8x300 mm,

Polymer Standards Service) were applied at a flow rate of

1.0 mL min–1 at 40 °C. The diameter of the gel particles measured

10 µm, the nominal pore widths were 30, 100, 1000 and 3000 Å.

Calibration was achieved using narrowly distributed poly(methyl

methacrylate) standards (Polymer Standards Service). Results were

evaluated using the PSS WinGPC UniChrom software (Version 8.1.1).

Preparative SEC with THF (HPLC grade, Merck) as eluent was

performed using two HPLC pumps (PU-2087plus, Jasco) equipped

with a refractive index detector (RI-2031plus, Jasco). The sample

solvent contained toluene (15 drops per 100 mL THF, p.a., Aldrich)

as internal standard. One pre-column (50x20 mm) and two SDplus gel

columns (300x20 mm, SDplus, MZ Analysentechnik) were applied at

a flow rate of 3.0 mL min–1 at 20 °C. The diameter of the gel particles

measured 10 µm, the nominal pore widths were 500 and 104 Å.

Dialysis was performed in methanol using Biotech CE Tubing

(MWCO: 100–500 D, 3.1 mL cm–1, Spectrumlabs). The membrane

was washed for 15 min in water before use to remove the sodium azide

solution.

3.2.3 Syntheses

Synthesis of poly(glycidol diethylphosphate-co-glycidol) (P(GDEP-co-G)) (3a–d)

Polyglycidol (PG24) (2) (1.488 g, 20.09 mmol OH) was dissolved in

pyridine (13.94 mL) and 4-dimethylaminopyridine (4-DMAP) (0.247 g,

2.01 mmol) and diethyl chlorophosphate (DECP) (2.600 g,

15.07 mmol) were added. The reaction mixture was stirred for 20 h at

room temperature. The solvent was removed under reduced pressure,

the residue redissolved in dichloromethane and precipitated in

pentane/diethyl ether (1:1 v/v). The product was purified by dialysis

in methanol. A yellowish viscous liquid was obtained. P(GDEP22-co-G8)

3c: yield 38%. Functionalized polyglycidols 3a, 3b, and 3d were

Chapter 3

37

synthesized following the same protocol. The reagent ratios and

reaction conditions are summarized in Table A.1.1 of appendix A.1. 1H NMR (400 MHz, DMSO-d6) (3c): = 1.25 (t, 3JHH

= 7.0 Hz,

POCH2CH3), 1.73–1.83 (m, ArCH2CH2), 2.57–2.65 (m, ArCH2CH2),

3.32–3.69 (m, ArCH2CH2CH2, OCH2CH(CH2OH)O, OCH2CH-

(CH2OP)O), 3.88–4.15 (m, POCH2CH3, OCH2CH(CH2OP)O), 4.55

(br. s, CHCH2OH groups), 7.12–7.31 (m, ArCH2CH2) ppm. 13C NMR

(101 MHz, DMSO-d6) (3c): = 15.9 (d, 3JCP =6.2 Hz, POCH2CH3),

30.9 (ArCH2CH2), 31.6 (ArCH2CH2), 60.8 (OCH2CH(CH2OH)O),

63.3 (d, 2JCP = 5.3 Hz, POCH2CH3), 66.0 (OCH2CH(CH2OP)O), 68.1–

69.5 (ArCH2CH2CH2, OCH2CH(CH2OH)O, OCH2CH(CH2OP)O),

77.5 (OCH2CH(CH2OP)O), 80.0 (OCH2CH(CH2OH)O), 125.8 (Ar),

128.3 (Ar), 141.7 (Ar) ppm. 31P {1H} NMR (162 MHz, DMSO-d6)

(3c): = -0.97 ppm. IR (KBr) (3c): υmax = 3412 (w), 2984 (m), 2910

(m), 1446 (w), 1394 (w), 1369 (w), 1266 (s), 1032 (vs), 979 (s), 871 (w),

819 (w), 752 (w), 526 (w) cm–1.

Synthesis of poly(glycidol ethylphosphate-co-glycidol) (P(GEP-co-G)) (4a–d)

P(GDEP22-co-G8) (3c) (0.196 g, 0.83 mmol DEP) was dissolved in 2-

hexanone (20 mL) and sodium iodide (0.149 g, 0.99 mmol) was added.

The reaction mixture was stirred under reflux for 48 h. The solvent

was removed and the product dried under reduced pressure. A

brownish solid was obtained. P(GEP22-co-G8) 4c: yield 97%. 4a, 4b, and

4d were synthesized following the same protocol. The reagent ratios

and reaction conditions are summarized in Table A.1.2 of appendix

A.1. 1H NMR (400 MHz, D2O) (4c): = 1.21–1.32 (m, POCH2CH3),

1.85–1.95 (m, ArCH2CH2), 2.66–2.75 (m, ArCH2CH2), 3.52–3.83 (m,

ArCH2CH2CH2, OCH2CH(CH2OH)O, OCH2CH(CH2OP)O), 3.84–

4.07 (m, POCH2CH3, OCH2CH(CH2OP)O), 7.24–7.40 (m, ArCH2-

CH2) ppm. 13C NMR (101 MHz, D2O) (4c): = 15.8 (POCH2CH3),

30.4 (ArCH2CH2), 31.5 (ArCH2CH2), 60.8 (OCH2CH(CH2OH)O),

62.3 (POCH2CH3), 64.4 (OCH2CH(CH2OP)O), 67.2–69.0 (ArCH2-

CH2CH2, OCH2CH(CH2OH)O, OCH2CH(CH2OP)O), 78.4 (OCH2-

CH(CH2OP)O), 79.8 (OCH2CH(CH2OH)O), 126.0 (Ar), 128.7 (Ar)

ppm. 31P {1H} NMR (162 MHz, D2O) (4c): = 0.60 ppm. IR (KBr)

(4c): υmax = 3436 (s), 2979 (m), 2940 (m), 1642 (w), 1467 (w), 1394 (w),

1237 (s), 1059 (vs), 951 (s), 830 (m), 772 (w), 553 (m) cm–1.

Chapter 3

38

Synthesis of poly(glycidol phosphate-co-glycidol) (P(GP-co-G)) (5a–d)

P(GDEP22-co-G8) (3c) (0.409 g, 1.73 mmol DEP) was dissolved in dry

dichloromethane (35 mL) and bromotrimethylsilane (0.91 mL,

6.92 mmol) was added over 1 h at 0 °C using a syringe pump. The

reaction was allowed to warm to room temperature and stirred for a

further 17 h. Water (20 mL) was added and the reaction mixture was

vigorously stirred for 2 h. The mixture was repeatedly washed with

dichloromethane (3 x 20 ml), the aqueous phase was separated and the

solvent removed. The product was dried under reduced pressure at

50 °C. A brownish viscous liquid was obtained. P(GP22-co-G8) 5c: yield

91%. 5a, 5b, and 5d were synthesized following the same protocol.

The reagent ratios and reaction conditions are summarized in Table

A.1.3 of appendix A.1. 1H NMR (400 MHz, D2O) (5c): = 1.85–1.93

(m, ArCH2CH2), 2.66–2.72 (m, ArCH2CH2), 3.49–3.88 m, ArCH2CH2-

CH2, OCH2CH(CH2OH)O, OCH2CH(CH2OP)O), 3.90–4.17 (m,

OCH2CH(CH2OP)O), 7.23–7.41 (m, ArCH2CH2) ppm. 13C NMR

(101 MHz, D2O) (5c): = 30.0 (ArCH2CH2), 31.1 (ArCH2CH2), 60.5

(OCH2CH(CH2OH)O), 64.7 (OCH2CH(CH2OP)O), 68.4–70.3

(ArCH2CH2CH2, OCH2CH(CH2OH)O, OCH2CH(CH2OP)O), 77.7

(OCH2CH(CH2OP)O), 79.6 (OCH2CH(CH2OH)O), 125.8 (Ar),

128.4 (Ar), 141.8 (Ar) ppm. 31P {1H} NMR (162 MHz, D2O) (5c): =

-0.12 ppm. IR (KBr) (5c): υmax = 2944 (m), 2889 (m), 2318 (w), 1666

(w), 1464 (w), 1349 (w), 1044 (vs), 873 (w), 484 (m) cm–1.

3.3 Results and Discussion

In this chapter, an easy and straightforward protocol for the controlled

functionalization of linear polyglycidol with pendant phosphate

groups is presented. The synthetic pathway involves the phospho-

rylation of linear polyglycidol (PG) with diethyl chlorophosphate

(DECP) under alkaline conditions in the presence of a nucleophilic

catalyst. The phosphate groups are subsequently dealkylated using

either sodium iodide for removal of one ethyl group or bromo-

trimethylsilane for removal of both ethyl groups, respectively.

Chapter 3

39

3.3.1 Functionalization of polyglycidol (2) with diethyl chlorophosphate

Linear polyglycidol (2) was prepared by anionic ring-opening

polymerization of ethoxyethyl glycidyl ether using 3-phenyl-1-

propanol as initiator followed by removal of the acetal protecting

groups under acidic conditions. A polyalcohol with 24 repeating units

(PG24) and Mn,SEC = 2700 g mol–1 was obtained with a narrow

molecular weight distribution (Ð = 1.17). The NMR and SEC analyses

of PG24 (2) can be found in appendix A.1 (Fig. A.1.1–A.1.3).

PG24 was reacted with various amounts of DECP and catalytic

amounts of 4-dimethylaminopyridine (4-DMAP) in pyridine at room

temperature with ratios of DECP to hydroxy groups of 0.25, 0.50,

0.75, and 1.0 (Scheme 3.1). The synthesized poly(glycidyl diethyl

phosphate-co-glycidol)s (P(GDEP-co-G)) (3a–d) were purified by

dialysis in methanol and characterized by 1H, 13C, 31P {1H} NMR

spectroscopy, FTIR spectroscopy and SEC analysis.

Scheme 3.1: Functionalization of linear polyglycidol with diethyl

chlorophosphate.

1H and 13C NMR spectra of P(GDEP-co-G) in DMSO-d6 show

characteristic signals of the ethyl groups adjacent to the phosphorus

atom, proving the successful phosphorylation of PG24. In the 1H NMR

spectrum the signals appear as a triplet at δ = 1.25 ppm (Signal 11) and

as a multiplet at δ = 3.88–4.15 ppm (Signal 10) (Fig. 3.1a). This

multiplet also contains the methylene group of the glycidol repeating

unit adjacent to the phosphate group. In the 13C NMR spectrum the

characteristic signals appear as doublets at δ = 15.9 ppm and δ =

63.3 ppm, respectively (Fig. 3.1b). The phosphorus NMR spectrum

shows a distinctive signal at δ = -0.97 ppm, which was assigned to the

diethyl phosphate side group of P(GDEP-co-G) (Fig. 3.1c).

The number of diethyl phosphate groups attached to PG24 (2) was

calculated by comparing the signal intensity of the phenyl group of the

Chapter 3

40

3-phenyl-1-propanol (Signal 1–3), which was used as initiator in the

synthesis of 2, with signal 11. The degree of functionalization (FDEP)

and absolute molecular weights (Mn,NMR) were calculated likewise using

the 3-phenyl-1-propyl end group as an internal reference. The 1H

NMR spectra of all phosphate functionalized polyglycidols are similar,

differing only in the relative intensity of the signals.

Figure 3.1: 1H NMR (a), 13C NMR (b) and 31P {1H} NMR (c) spectra of

P(GDEP22-co-G8) (3c) measured in DMSO-d6.

FTIR spectra of P(GDEP-co-G) exhibit characteristic absorption bands

of the diethyl phosphate groups.25 The asymmetric stretching vibration

of P―O―C groups gives a very strong broad band at 1032 cm–1.

Additionally a strong band at 979 cm–1 is found, which is distinctive

for ethyl phosphates. The stretching vibration of the P═O group

shows a band at 1266 cm–1 (Fig. A.1.10, appendix A.1). The signals are

Chapter 3

41

consistent with literature and verify the successful functionalization of

PG24 with DECP.

SEC analysis using DMF as eluent confirms the synthesis of P(GDEP-

co-G) with molecular weight distributions of 1.23 ≤ Đ ≤ 1.44.

However, purification by dialysis in methanol led to fractionation of

the functionalized polymers. The high and low molecular weight

fractions were separated by preparative SEC with THF as eluent. 1H

NMR spectroscopy of those fractions showed that phosphate

functionalized polyglycidol was obtained in both cases. The SEC

analysis of P(GDEP22-co-G8) (3c) and of fractions separated by

preparative SEC can be found in Figure 3.2.

Figure 3.2: DMF-SEC traces of P(GDEP22-co-G8) (3c) (black line) and

fractions separated by preparative SEC with THF as eluent (red and blue

dotted lines).

At this point some observations during purification of P(GDEP-co-G)

(3a–d) should be mentioned. As shown in table 3.1 the degrees of

functionalization obtained for 3a–c were in excellent agreement with

the ratios adjusted in the feed. However, the functionalization of all

hydroxy groups of 2 was not possible, reaching a maximum degree of

functionalization of 87%. P(GDEP-co-G) purified by dialysis in

methanol (3a–d) shows slight deviations from the theoretical degree

Chapter 3

42

of functionalization since the dialysis leads to fractionation of the

polymers due to diffusion of lower molecular weight fractions through

the dialysis membrane. The starting degree of polymerization of

polyglycidol (2) was Pn = 24, however the samples of 3a–d show a

degree of polymerization of Pn = 38 for 3a, Pn = 34 for 3b and Pn =

30 for 3c and 3d.

To prove this assumption a higher molecular weight polyglycidol

(Mn,SEC = 7100 g mol–1, Đ = 1.30) was functionalized with DECP with

a ratio of DECP to hydroxy groups of 0.50. The degree of

functionalization in the product was in perfect agreement with the

ratio adjusted in the feed. The purification by dialysis in methanol did

not lead to a fractionation of the polymer.

The SEC traces of higher molecular weight polyglycidol and its

phosphate functionalized equivalent can be found in appendix A.1

(Fig. A.1.6, appendix A.1).

Table 3.1: Ratio of diethyl chlorophosphate (DECP) to hydroxyl groups,

degree of functionalization (FDEP) and molecular weight (Mn,NMR) calculated

from 1H NMR and SEC data of linear P(GDEP9-co-G29) (3a), P(GDEP

16-co-G18)

(3b), P(GDEP22-co-G8) (3c), P(GDEP

26-co-G4) (3d).

Polymer ratio

[DECP]

/[OH]

FDEP a

[%]

Mn,NMR a

[g mol–1]

Mn,SEC b

[g mol–1]

Đ b Yield c

[%]

3a 0.25 24 4176 5000 1.30 23

3b 0.50 47 4832 5200 1.29 41

3c 0.75 73 5352 5000 1.29 38

3d 1.00 87 5897 5200 1.44 27

a Degree of functionalization of hydroxyl groups with DECP (FDEP) and molecular weight (Mn,NMR) calculated from 1H NMR with an accuracy of integration of ± 5%. b Number average molecular weight (Mn,SEC) and molecular weight distribution (Đ) determined by size exclusion chromatography (SEC) using narrowly distributed P(MMA) standards in DMF. c Yield of P(GDEP

x-co-Gy) obtained after dialysis in MeOH for two days.

3.3.2 Monodealkylation of P(GDEP-co-G) (3a–d)

Monophosphoric acids can be easily prepared by a highly selective

method using sodium iodide or lithium bromide as a dealkylating

reagent.26,27 According to this synthetic protocol P(GDEP-co-G) (3a–d)

Chapter 3

43

were reacted with sodium iodide in 2-hexanone under reflux (Scheme

3.2). The synthesized poly(glycidyl ethyl phosphate-co-glycidol)

(P(GEP-co-G)) (4a–d) were characterized by 1H, 13C, 31P {1H} NMR

spectroscopy and DSC analysis (Table 3.2).

Scheme 3.2: Synthesis of poly(glycidyl ethyl phosphate-co-glycidol) (4a–d).

1H and 13C NMR spectra of P(GEP-co-G) (4a–d) in D2O present

characteristic signals of the ethyl group adjacent to the phosphorus

atom of P(GEP-co-G). In the 1H NMR spectrum the signals appear as

a multiplet at δ = 1.21–1.31 ppm (Signal 11) and as a multiplet at δ =

3.84–4.07 ppm (Signal 10) (Fig. 3.3a). The second multiplet also

contains the methylene group of the glycidol repeating unit adjacent

to the phosphate. In 13C NMR spectrum the characteristic signals

appear at δ = 15.8 ppm and δ = 62.3 ppm, respectively (Fig. A.1.4,

appendix A.1). The phosphorus NMR spectrum shows a distinctive

signal at δ = 0.60 ppm, which was assigned to P(GEP-co-G). (Fig. A.1.5,

appendix A.1)

The number of ethyl phosphate groups attached to PG24 (2) was

calculated as described previously. In comparison with the 1H NMR

spectra of P(GDEP-co-G) (3a–d) the relative intensity of signals of the

ethyl groups adjacent to the phosphorus atom is halved.

FTIR spectra of P(GEP-co-G) (4a–d) exhibit characteristic absorption

bands of the ethyl phosphate groups.25 The stretching vibration bands

of the P═O, P―O―C, and P―O―Et groups are found at 1237 cm–1,

1059 cm–1, and 951 cm–1, respectively, and are in good agreement with

the absorption bands of P(GDEP-co-G) (Fig. A.1.10, appendix A.1).

Additionally, a broad band at 1642 cm–1 is observed, which is

distinctive for the P―OH group, and confirms the successful

monodealkylation of P(GDEP-co-G) (3a–d).

Chapter 3

44

Table 3.2: Degree of functionalization (FEP) and molecular weight (Mn,NMR)

calculated from 1H NMR of linear P(GEP9-co-G29) (4a), P(GEP

16-co-G18) (4b),

P(GEP22-co-G8) (4c) and P(GEP

26-co-G4) (4d).

Polymer FEP a

[%]

Mn,NMR a

[g mol–1]

4a 24 3778

4b 47 4231

4c 73 4577

4d 87 5005

a Degree of functionalization of hydroxyl groups with ethyl phosphate groups (FEP) and molecular weight (Mn,NMR) calculated from 1H NMR with an accuracy of integration of ± 5%.

Figure 3.3: 1H NMR spectra of P(GEP22-co-G8) (4c) (top) and P(GP

22-co-G8)

(5c) (bottom) measured in D2O.

In all experiments 100 % conversion of diethyl phosphate groups is

reached after 48 h according to 31P analysis (Fig. A.1.5, appendix A.1).

Chapter 3

45

3.3.3 Dealkylation of P(GDEP-co-G) (3a–d)

The synthesis of poly(glycidyl phosphate-co-glycidol) (P(GP-co-G) (5a–

d) was achieved by conversion of P(GDEP-co-G) (3a–d) with

bromotrimethylsilane in dichloromethane as solvent (Scheme 3.3).

After stirring at room temperature for 17 h, the silalyted intermediates

were hydrolyzed with water. Washing with dichloromethane gave

P(GP-co-G) (5a–d) in yields of 81–94%. The P(GP-co-G)s (5a–d) were

characterized by 1H, 13C, 31P {1H} NMR spectroscopy (Table 3.3).

Scheme 3.3: Synthesis of poly(glycidyl phosphate-co-glycidol) (5a–d) by

dealkylation of P(GDEP-co-G) (3a–d).

The successful dealkylation of P(GDEP-co-G) was proven by the

absence of the characteristic diethyl phosphate signals at δ = 1.21–

1.31 ppm and δ = 3.84–4.07 ppm in the 1H NMR spectra (Fig. 3.3b)

and the signals at δ = 15.8 ppm and δ = 62.3 ppm in the 13C NMR

spectra (Fig. A.1.8, appendix A.1). In the 31P {1H} NMR spectrum a

signal appears at δ = -0.12 ppm, which was assigned to P(GP-co-G)

(5a–d) (Fig. A.1.9, appendix A.1).

FTIR spectra of P(GP-co-G) confirm the successful dealkylation by

absence of the distinctive ethyl phosphate absorption band at 940–

985 cm–1. Additionally, two broad bands at 2318 cm–1 and 1666 cm–1

are found, which are characteristic for phosphoric acid groups (Fig.

A.1.10, appendix A.1).

The titration curve of P(GP22-co-G8) (5c) was recorded in a pH range

of 2.0 to 11 using 0.1 N hydrochloric acid and 0.1 N sodium hydroxide

solution, respectively (Fig. A.1.7, appendix A.1). The graph shows two

equivalent points at pH = 5.13 and pH = 9.53, distinctive for the

deprotonation of the diprotic phosphate group. The phosphate group

shows acid dissociation constants of pKa,1 = 2.33 and pKa,2 = 7.80,

which are in good agreement with the pKa values of phosphoric acid.28

Chapter 3

46

Table 3.3: Degree of functionalization (FP) and molecular weight (Mn,NMR)

calculated from 1H NMR of P(GP9-co-G29) (5a), P(GP

16-co-G18) (5b), P(GP22-

co-G8) (5c) and P(GP26-co-G4) (5d).

Polymer FP a

[%]

Mn,NMR a

[g mol–1]

5a 24 3320

5b 47 3416

5c 73 3456

5d 87 3681

a Degree of functionalization of hydroxyl groups with dihydrogen phosphate groups (FP) and molecular weight (Mn,NMR) calculated from 1H-NMR with an accuracy of integration of ± 5%.

In all experiments conversions of diethyl phosphate groups of 100%

were reached after 17 h according to 31P analysis (Fig. A.1.9, appendix

A.1).

3.4 Conclusions

In this chapter, a synthetic strategy for the preparation of polyglycidols

with pendant phosphate groups has been developed. The successful

synthesis was confirmed by 1H, 13C, 31P {1H} NMR spectroscopy,

FTIR spectroscopy, and SEC analysis. Diethyl phosphate groups were

subsequently (mono-)dealkylated. This method allows tailoring of the

concentration of pendant phosphate/phosphoric acid groups intro-

duced into polyglycidol.

3.5 References

1. Monge, S.; Canniccioni, B.; Graillot, A.; Robin, J.J.

Phosphorus-containing polymers: A great opportunity for

the biomedical field. Biomacromolecules 2011, 12, 1973.

2. Wang, Y.C.; Yuan, Y.Y.; Du, J.Z.; Yang, X.Z.; Wang, J.

Recent progress in polyphosphoesters: From controlled

synthesis to biomedical applications. Macromol. Biosci. 2009, 9,

1154.

Chapter 3

47

3. Renier, M.L.; Kohn, D.H. Development and characterization

of a biodegradable polyphosphate. J. Biomed. Mater. Res. 1997,

34, 95.

4. Huang, S.W.; Wang, J.; Zhang, P.C.; Mao, H.Q.; Zhuo, R.X.;

Leong, K.W. Water-soluble and nonionic polyphosphoester:

Synthesis, degradation, biocompatibility and enhancement of

gene expression in mouse muscle. Biomacromolecules 2004, 5,

306.

5. Wang, S.; Wan, A.C.; Xu, X.; Gao, S.; Mao, H.Q.; Leong,

K.W.; Yu, H. A new nerve guide conduit material composed

of a biodegradable poly(phosphoester). Biomaterials 2001, 22,

1157.

6. Mou, L.; Singh, G.; Nicholson, J.W. Synthesis of a

hydrophilic phosphonic acid monomer for dental materials.

Chem. Commun. 2000, 345.

7. Moszner, N.; Salz, U.; Zimmermann, J. Chemical aspects of

self-etching enamel-dentin adhesives: A systematic review.

Dent. Mater. 2005, 21, 895.

8. Macarie, L.; Ilia, G. Poly(vinylphosphonic acid) and its

derivatives. Prog. Polym. Sci. 2010, 35, 1078.

9. Schott, H.; Bretzger, W. Funktionalisierung heterogen-

vernetzter Polyvinylalkohol-Gele. Makromol. Chem. 1988, 189,

2847.

10. Moszner, N.; Zeuner, F.; Pfeiffer, S.; Schurte, I.;

Rheinberger, V.; Drache, M. Monomers for adhesive

polymers, 3. Synthesis, radical polymerization and adhesive

properties of hydrolytically stable phosphonic acid

monomers. Macromol. Mater. Eng. 2001, 286, 225.

11. Wagner, T.; Manhart, A.; Deniz, N.; Kaltbeitzel, A.; Wagner,

M.; Brunklaus, G.; Meyer, W.H. Vinylphosphonic acid

homo- and block copolymers. Macromol. Chem. Phys. 2009,

210, 1903.

12. Ingratta, M.; Elomaa, M.; Jannasch, P. Grafting

poly(phenylene oxide) with poly(vinylphosphonic acid) for

fuel cell membranes. Polym. Chem. 2010, 1.

Chapter 3

48

13. Guerrero, G.; Mutin, P.H.; Vioux, A. Anchoring of

phosphonate and phosphinate coupling molecules on titania

particles. Chem. Mater. 2001, 13, 4367.

14. Pellerite, M.J.; Dunbar, T.D.; Boardman, L.D.; Wood, E.J.

Effects of fluorination on self-assembled monolayer forma-

tion from alkanephosphonic acids on aluminum: Kinetics

and structure. J. Phys. Chem. B 2003, 107, 11726.

15. Demadis, K.D.; Papadaki, M.; Raptis, R.G.; Zhao, H.

Corrugated, sheet-like architectures in layered alkaline-earth

metal R,S-hydroxyphosphonoacetate frameworks: Applica-

tions for anticorrosion protection of metal surfaces. Chem.

Mater. 2008, 20, 4835.

16. Gawalt, E.S.; Avaltroni, M.J.; Danahy, M.P.; Silverman, B.M.;

Hanson, E.L.; Midwood, K.S.; Schwarzbauer, J.E.; Schwartz,

J. Bonding organics to ti alloys: Facilitating human osteoblast

attachment and spreading on surgical implant materials.

Langmuir 2003, 19, 200.

17. Koehler, J.; Keul, H.; Möller, M. Post-polymerization

functionalization of linear polyglycidol with diethyl

vinylphosphonate. Chem. Commun. 2011, 47, 8148.

18. Koehler, J.; Marquardt, F.; Keul, H.; Moeller, M.

Phosphonoethylated polyglycidols: A platform for tunable

enzymatic grafting density. Macromolecules 2013, 46, 3708.

19. Koehler, J.; Marquardt, F.; Teske, M.; Keul, H.; Sternberg,

K.; Moeller, M. Enhanced hydrolytic degradation of

heterografted polyglycidols: Phosphonoethylated monoester

and polycaprolactone grafts. Biomacromolecules 2013, 14, 3985.

20. Koehler, J.; Kuehne, A.J.C.; Piermattei, A.; Qiu, J.; Keul,

H.A.; Dirks, T.; Keul, H.; Moeller, M. Polyglycidol-based

metal adhesion promoters. J. Mater. Chem. B 2015, 3, 804.

21. Babu, H.V.; Muralidharan, K. Polyethers with phosphate

pendant groups by monomer activated anionic ring opening

polymerization: Syntheses, characterization and their

lithium-ion conductivities. Polymer 2014, 55, 83.

22. Weinhart, M.; Groger, D.; Enders, S.; Dernedde, J.; Haag, R.

Synthesis of dendritic polyglycerol anions and their efficiency

toward L-selectin inhibition. Biomacromolecules 2011, 12, 2502.

Chapter 3

49

23. Fitton, A.O.; Hill, J.; Jane, D.E.; Millar, R. Synthesis of simple

oxetanes carrying reactive 2-substituents. Synthesis 1987,

1140.

24. Hans, M.; Gasteier, P.; Keul, H.; Moeller, M. Ring-opening

polymerization of ε-caprolactone by means of mono- and

multifunctional initiators: Comparison of chemical and enzy-

matic catalysis. Macromolecules 2006, 39, 3184.

25. Socrates, G. Infrared characteristic group frequencies. John Wiley &

Sons: Chichester, New York, Brisbane, Toronto, 1980.

26. Kluger, R.; Taylor, S.D. Mechanisms of carbonyl

participation in phosphate ester hydrolysis and their

relationship to mechanisms for the carboxylation of biotin. J.

Am. Chem. Soc. 1991, 113, 996.

27. Krawczyk, H. A convenient route for monodealkylation of

diethyl phosphonates. Synth. Commun. 1997, 27, 3151.

28. Riedel, E.; Janiak, C. Anorganische Chemie. 7th Edition ed.;

Walter de Gruyter: Berlin, New York, 2007.

Chapter 4

51

Chapter 4

Novel Antibacterial

Polyglycidols: Relationship

between Structure and

Properties

4.1 Introduction

Contamination by microorganisms such as bacteria, fungi and algae is

a key issue in medicine1, pharmaceutical production2, water purifica-

tion systems3, food packaging4 and various other fields.5,6 Artificial

materials lack defense against microbial growth, allowing microbes to

attach to the surface and form a biofilm.7 One way to prevent the

biofilm formation is the usage of disinfectants to keep the surface

sterile. Common disinfectants include low molecular weight sub-

stances such as alcohols, aldehydes, quaternary ammonium com-

pounds, silver compounds, peroxygens and bisphenols.8 However,

these classes of antimicrobial substances need to be applied regularly,

leading to the development of resistance in the microbial strains.9

Another way to prevent microbial growth is the coating of surfaces

with antimicrobial substances that either kill microorganisms on

contact or repel the attachment of microbes.10 Nevertheless, the

leaching of biocides from those coatings causes the same previously

mentioned problems. An attractive alternative to low molecular weight

Chapter 4

52

biocides are antimicrobial polymers, because they are non-volatile,

chemically stable and can be used as non-releasing additives.11 These

polymers are prepared either by (co-)polymerization of functionalized

monomers or by post-polymerization functionalization.12 Though, the

antimicrobial properties are derived from a variety of functionalities

such as biguanides13,14, benzoate esters and benzaldehydes15 or poly-

(acrylic acid)16, the most common active moieties are based on a

combination of quaternary ammonium, pyridinium or phosphonium

groups and hydrophobic functionalities.17-19 The proposed and com-

monly accepted mechanism for these types of polymers features the

electrostatic interaction between the cationic moieties and the nega-

tively charged bacterial cell membrane and the disruption of the cell

membrane by the hydrophobic groups, leading to leakage and subse-

quently cell death20,21. However, due to the heterogeneity and bacterial

strain specificity of the cell wall composition the efficacy of antimicro-

bial polymers is species dependent. The outer part of the cell wall of

Gram-positive bacteria is composed of about 90% peptidoglycan. In

Gram-negative bacteria the peptidoglycan layer accounts for approxi-

mately 20% of the cell envelope, being located between outer mem-

brane and inner cell membrane. Before reaching the inner cell mem-

brane polymers interact with the negatively charged components of

the outer part of the bacterial cell envelope, e.g. teichoic acids in the

thick peptidoglycan layers of Gram-positive bacteria, and phospho-

lipids and lipopolysaccharides in the outer membrane of Gram-

negative bacteria.22,23 The effectiveness of the antimicrobial cationic/

hydrophobic polymers is dependent on various factors.24 One factor

is the molecular weight of the polymer. Ikeda et al. synthesized poly-

methacrylates with pendant biguanide units and various molecular

weights and tested the antimicrobial activity against Staphylococcus

aureus, reaching an optimal activity at molecular weights between 50–

100 kDa.25 Kanazawa et al. showed an increase in biocidal activity of

poly[tributyl(4-vinylbenzyl)phosphonium chloride] against S. aureus

with increasing molecular weight.26 Based on the described mechanism

they assume that a higher molecular weight and a consequential higher

charge density enhance the adsorption of the polymers to the cell

membrane. A stronger adsorption leads to a stronger disruption of the

cell membrane and thus, to a higher activity of the polymer. However,

Chapter 4

53

Lienkamp et al. found that when the molecular weight reaches a

threshold value, the efficacy of the polymers decreases.27 Additionally,

Locock et al. reported the reverse effect on guanylated polymeth-

acrylates.28 The presented polymers showed higher antimicrobial acti-

vity at lower molecular weights, proving that the efficacy of antimicro-

bial polymers does not exclusively depend on their molecular weight.

A second factor for the antimicrobial behavior is the alkyl chain length

of the hydrophobic moiety. However, the optimal alkyl chain length is

different for different types of polymers. Pasquier et al. prepared

branched poly(ethylene imine)s with pendant ammonium and alkyl

functionalities, ranging from C6 to C16. An increase in the alkyl chain

length lead to an increase in the antimicrobial activity against E. coli.29

The activity was further enhanced by He et al., attaching the hydro-

phobic chain directly to the ammonium group.30 The opposite influ-

ence of aliphatic side chains was reported by Xu et al. on comb-like

ionenes.31 Here, a decrease in the alkyl chain length lead to an increase

in the antimicrobial activity against E. coli. On the other hand Chen et

al. prepared poly(propylene imine) dendrimers with alkyl chains rang-

ing from C8 to C16, showing a parabolic dependence between the bio-

cidal effect and the alkyl chain length, with the highest activity at C10.32

In this chapter, the preparation of various antimicrobial polymers

based on polyglycidol with quaternary trimethylammonium groups as

the cationic moiety and dodecyl chains as the hydrophobic part is

presented. Polyglycidol is a highly functional polymer with a hydroxy

group in every repeating unit, allowing various further modifica-

tions.33,34 It is non-toxic, soluble in aqueous media, and licensed by the

Food and Drug Administration (FDA).35,36 The cationic and hydro-

phobic side chain functionalities were distributed statistically along the

polymer backbone (cationic to hydrophobic ratio of 1:1). This func-

tionalized polyglycidol was compared to (i) a polyglycidol modified

with hydrophilic hydroxyethyl functionalities at the cationic center, (ii)

a polyglycidol with cationic and hydrophobic moieties at every repeat-

ing unit, and (iii) a polyglycidol with a cationic to hydrophobic balance

of 1:2. All polymers were tested in regard to their antimicrobial proper-

ties against Escherichia coli and Staphylococcus aureus to examine a possible

relationship between the structure and the biocidal effect of the

polymer.

Chapter 4

54

4.2 Experimental Section

4.2.1 Materials

Potassium tert-butoxide (1 M solution in THF), diglyme (≥99%, extra

dry, over molecular sieves), pyridine (99.5%, extra dry, over molecular

sieves), phenyl chloroformate (>97%), 4-nitrophenyl chloroformate

(>98), 3-(dimethylamino)-1-propylamine (99%), N-(3-aminopropyl)-

diethanolamine (>90%), dodecylamine (98%), 4-dimethylamino-

pyridine (>98%), DL-homocysteine thiolactone hydrochloride (98%),

triethylamine (≥99.5%, anhydrous), dodecyl acrylate (>98%), methyl

iodide (>99%), tetrahydrofuran (99.8%, stabilizer free, extra dry),

chloroform (99.9%, extra dry, over molecular sieves), N,N-dimethyl-

formamide (99.8%, extra dry, over molecular sieves), methanol

(≥99.8%, p.a.) and dichloromethane (≥99.8%, anhydrous) were used

as received.

3-phenyl-1-propanol (99%) was stirred with calcium hydride for 24 h

and then distilled. Ethoxyethyl glycidyl ether (EEGE) was synthesized

from 2,3-epoxypropan-1-ol (glycidol, 96%) and ethyl vinyl ether (99%)

according to Fitton et al.37, purified by distillation, and stored under a

nitrogen atmosphere over a molecular sieve (3 Å). Polyglycidol (PG)

(1) was synthesized according to literature.38

Water-sensitive reactions were carried out in a nitrogen atmosphere.

Nitrogen (Linde 5.0) was passed over a molecular sieve (4 Å) and finely

distributed potassium on aluminum oxide.

4.2.2 Bacteria

To determine the antibacterial activity polymers were tested against the

Gram-negative bacterium Escherichia coli (DSM498) and the Gram-

positive bacterium Staphylococcus aureus (ATCC6538). Overnight cul-

tures of E. coli and S. aureus with defined bacterial count in Mueller-

Hinton broth (pH = 7.4 ± 0.2) were used as inoculate in the

antibacterial test.

4.2.3 Antibacterial tests for polymer solutions

The antibacterial activity of the polymers in solution was determined

by measuring the minimal inhibitory concentration (MIC) using the

Chapter 4

55

test bacteria mentioned above. Suspensions of strains with known

colony forming units (CFU; 1‒2 · 106 CFU mL–1) were incubated at

37 °C in nutrient solutions (Mueller-Hinton Broth, MHB) with differ-

ent concentrations of the polymer samples. The polymer samples were

solubilized in bidistilled water and added to the nutrient solution at a

constant ratio of 1:10. The growth of the bacteria was followed during

the incubation over 20 h by measuring the optical density at 612 nm

every 30 min (with 1400 s of shaking at 100 rpm per 30 min cycle by

using a microplate reader/incubator (TECAN Infinite 200 Pro) The

testing is performed with defined concentrations specifically for each

polymer until within the monitoring time of 20 h no bacterial growth

curve is recorded. All experiments were performed in triplicate dupli-

cates and MIC determination was repeated on 3 different days. The

polymers were not sterilized. Sterile controls (defined polymer concen-

trations in nutrient solution without bacteria) were assessed in every

growth curve monitoring testing series. MICs were determined accord-

ing to broth microdilution in 96-well microtitre plates.39 Antimicrobial

polymer testing reference polymers/controls ε-polylysine and poly-

hexanide (poly(hexamethylene biguanide)) were used.

The minimal inhibitory concentration (MIC) corresponds to the

concentration of the test substance at which a complete inhibition of

the growth of the inoculated bacteria was observed by comparison

with control samples without test substance.

4.2.4 Hemolytic Activity

Hemolytic activity was assessed according to literature.40 Human ery-

throcytes (from healthy donors, red blood cells (RBC), 0, Rh positive,

citrate-stabilized) were obtained by centrifugation (3500 rpm, 12 min)

to remove plasma, washed 3 times in PBS, and diluted in PBS to obtain

a stock solution of 2.5–3.0 · 108 mL–1 RBC. Solutions of defined poly-

mer concentration (250 µL) were pipetted into 250 μL of the stock

solution; the final amount of RBC being 1.2–1.5 · 108 RBC mL–1. The

RBC were exposed for 60 min at 37 °C under 3D-shaking, centrifuged

thereafter (4000 rpm, 12 min), and the absorption of the supernatant

(diluted tenfold in PBS) was determined at 414 nm in a microplate

reader. As reference solutions (i) PBS for determining spontaneous

hemolysis and (ii) 1% Triton X-100 for 100% hemolysis (positive

Chapter 4

56

control) were used. Hemolysis was plotted as a function of polymer

concentration and the hemolytic activity was defined as the polymer

concentration that causes 50% hemolysis of human RBC relative to

the positive control (HC50).

4.2.5 Measurements

1H NMR and 13C NMR were recorded on a Bruker DPX-400 FT-

NMR spectrometer at 400 and 101 MHz, respectively. Deuterated

chloroform (CDCl3), deuterated dimethyl sulfoxide (DMSO-d6),

deuterated acetone (acetone-d6) and deuterated methanol (MeOD)

were used as solvents. The residual solvent signal was used as internal

standard. Coupling constants Jxy are given in Hz.

Molecular weights (Mn,SEC) and molecular weight distributions (Đ)

were determined by size exclusion chromatography (SEC). SEC

analyses were carried out with DMF as eluent. SEC with DMF (HPLC

grade) as eluent was performed using an Agilent 1100 system equipped

with a dual RI-/Visco detector (ETA-2020). The eluent contained

1 g L–1 LiBr (≥99%, Aldrich). The sample solvent contained traces of

distilled water as internal standard. For cationic samples the eluent

contained 2 g L–1 LiBr and 2 g L–1 tris(hydroxymethyl)aminomethane

(TRIS, ultrapure grade, ≥99.9%). One pre-column (8x50 mm) and

four GRAM gel columns (8x300 mm) were applied at a flow rate of

1.0 mL min–1 at 40 °C. The diameter of the gel particles measured

10 µm, the nominal pore widths were 30, 100, 1000 and 3000 Å.

Calibration was achieved using narrowly distributed poly(methyl

methacrylate) standards (Polymer Standards Service). Results were

evaluated using the PSS WinGPC UniChrom software (Version 8.1.1).

Dialysis was performed in methanol using Biotech CE Tubing

(MWCO: 100–500 D, 3.1 mL cm–1) and Biotech RC Tubing (MWCO:

1 kD, 6.4 mL cm–1), respectively. The membrane was washed for

15 min in water before use to remove the sodium azide solution.

4.2.6 Syntheses

Synthesis of poly(glycidyl phenyl carbonate) (P(GPC)27) (2)

PG27 (1) (2.018 g, 27.24 mmol OH) was dissolved in pyridine

(18.87 mL), and a solution of phenyl chloroformate (4.692 g,

Chapter 4

57

29.97 mmol) in dichloromethane (17.5 mL) was added in 30 min at

0 °C using a syringe pump. The reaction mixture was allowed to warm

to room temperature and stirred for 20 h. The precipitate was removed

by filtration. The solution was washed with water (15 mL), 1 M HCl

solution (aq.) (3 · 15 mL), and saturated NaCl solution (aq.) (15 mL).

The organic phase was dried over Na2SO4, filtrated, and the solvent

removed under reduced pressure. Polymer 2 was obtained as a brown

viscous liquid (3.650 g, 69%). Mn,NMR = 5243 g mol–1, Mn,SEC =

4800 g mol–1, Ð = 1.14. 1H NMR (400 MHz, CDCl3) (2): δ = 1.79 (m,

ArCH2CH2), 2.57 (t, 3JHH = 7.8 Hz, ArCH2CH2), 3.45–3.87 (m, ArCH2-

CH2CH2, OCH2CH(CH2OC=OOPh)O), 4.08–4.42 (m, OCH2CH-

(CH2OC=OOPh)O), 6.98–7.29 (m, ArCH2CH2, (OC=OOPh)O)

ppm. 13C NMR (101 MHz, CDCl3) (2): δ = 31.2 (ArCH2CH2), 32.3

(ArCH2CH2), 67.7–69.4 (ArCH2CH2CH2, OCH2CH(CH2OC=O-

OPh)O), 77.4 (OCH2CH(CH2OC=OOPh)O), 121.0 (OC=OOPh)O),

126.1 (ArCH2, OC=OOPh)O), 128.4 (ArCH2), 128.5 (ArCH2), 129.6

(OC=OOPh)O), 141.8 (ArCH2), 151.1 (OC=O-OPh)O), 153.6

(OC=OOPh)O) ppm.

Synthesis of poly(glycidyl 3-dimethylaminopropylcarbamate-co-glycidyl dodecyl-

carbamate) (P(GDMAPA15-co-GDDA

12)) (3)

P(GPC)27 (2) (1.509 g, 7.77 mmol carbonate) was dissolved in tetra-

hydrofuran (15 mL) and a solution of 3-(dimethylamino)-1-propyl-

amine (0.397 g, 3.89 mmol) and dodecylamine (0.721 g, 3.89 mmol) in

tetrahydrofuran (15 mL) was added in 1 h at 0 °C using a syringe pump.

The reaction was allowed to warm to room temperature and stirred

for 42 h. The solvent was removed under reduced pressure and the

polymer purified by dialysis in methanol. Polymer 3 was obtained as a

yellowish viscous liquid (1.153 g, 62%). Mn,NMR = 6459 g mol–1,

Mn,SEC = 7600 g mol–1, Ð = 1.38. 1H NMR (400 MHz, CDCl3) (3): δ =

0.84 (t, 3JHH = 7.0 Hz, NHCH2CH2(CH2)9CH3), 1.21 (s, NHCH2CH2-

(CH2)9CH3), 1.34–1.51 (m, NHCH2CH2(CH2)9CH3), 1.54–1.68 (m,

NHCH2CH2CH2N(CH3)2), 1.77–1.89 (m, ArCH2CH2), 2.16 (s, NH-

CH2CH2CH2N(CH3)2), 2.27 (t, 3JHH = 6.7 Hz, NHCH2CH2CH2N-

(CH3)2), 2.63 (t, 3JHH = 7.6 Hz, ArCH2CH2), 3.01–3.11 (m, NHCH2-

CH2(CH2)9CH3), 3.12–3.21 (m, 2H, NHCH2CH2CH2N(CH3)2), 3.45–

3.79 (m, ArCH2CH2CH2, OCH2CH(CH2OC=ONHR)O), 3.86–4.36

Chapter 4

58

(m, OCH2CH(CH2OC=ONHR)O), 5.88 (br. s, NH), 6.17 (br. s, NH),

7.09–7.25 (m, ArCH2CH2) ppm. 13C NMR (101 MHz, CDCl3) (3): δ =

14.2 (NHCH2CH2(CH2)9CH3), 22.7 (NHCH2(CH2)10CH3), 27.0 (NH-

CH2CH2CH2N(CH3)2, 27.5–32.0 (NHCH2(CH2)10CH3, ArCH2CH2),

39.9 (NHCH2(CH2)10CH3), 41.2 (NHCH2CH2CH2N(CH3)2), 45.5

(NHCH2CH2CH2N(CH3)2), 57.6 (NHCH2CH2CH2N(CH3)2), 64.2–

70.0 (ArCH2CH2CH2, OCH2CH(CH2OC=ONHR)O), 78.0 (OCH2-

CH(CH2OC=ONHR)O), 125.8 (ArCH2), 128.4 (ArCH2), 128.5

(ArCH2), 141.9 (ArCH2), 156.7 (OCH2CH(CH2OC=ONHR)O) ppm.

Synthesis of poly(glycidyl 3-aminopropyldiethanolcarbamate-co-glycidyl dodecyl-

carbamate) (P(GAPDEA16-co-GDDA

11)) (4)

P(GPC)27 (2) (0.707 g, 3.51 mmol carbonate) was dissolved in tetra-

hydrofuran (10 mL) and a solution of N-(3-aminopropyl)diethanol-

amine (0.284 g, 1.75 mmol), and dodecylamine (0.325 g, 1.75 mmol)

in tetrahydrofuran (5 mL) was added in 1 h at 0 °C using a syringe

pump. The reaction was allowed to warm to room temperature and

stirred for 42 h. The solvent was removed under reduced pressure and

the polymer purified by dialysis in methanol. Polymer 4 was obtained

as a colorless viscous liquid (0.655 g, 66%). Mn,NMR = 7337 g mol–1,

Mn,SEC = 14,100 g mol–1, Ð = 3.56. 1H NMR (400 MHz, MeOD) (4):

δ = 0.92 (t, 3JHH = 7.0 Hz, NHCH2CH2(CH2)9CH3), 1.31 (s, NHCH2-

CH2(CH2)9CH3), 1.44–1.59 (m, NHCH2CH2(CH2)9CH3), 1.62–1.76

(m, NHCH2CH2CH2N(CH2CH2OH)2), 1.85–1.92 (m, ArCH2CH2),

2.55–2.74 (m, CH2N(CH2CH2OH)2), 3.06–3.14 (m, NHCH2CH2-

(CH2)9CH3), 3.15–3.23 (m, NHCH2CH2CH2N(CH2CH2OH)2), 3.62 (t, 3JHH = 5.4 Hz, CH2N(CH2CH2OH)2), 3.66–3.81 (m, ArCH2CH2-CH2,

OCH2CH(CH2OC=ONHR)O), 4.00–4.34 (m, OCH2CH(CH2O-

C=ONHR)O), 7.17–7.32 (m, ArCH2CH2) ppm. 13C NMR (101 MHz,

MeOD) (4): δ = 14.6 (NHCH2CH2(CH2)9CH3), 23.8–30.9 (NH-

CH2CH2(CH2)9CH3), 28.2 (NHCH2CH2CH2N(CH2CH2OH)2), 33.1

(NHCH2CH2(CH2)9CH3), 40.1 (NHCH2CH2CH2N(CH2CH2OH)2),

42.0 (NHCH2CH2(CH2)9CH3), 53.6 (CH2N(CH2CH2OH)2), 57.6

(CH2N(CH2CH2OH)2), 60.8 (CH2N(CH2CH2OH)2), 65.3–79.3

(ArCH2CH2CH2, OCH2CH(CH2OC=ONHR)O), 129.4 (ArCH2),

129.6 (ArCH2), 158.7 (OCH2CH(CH2OC=ONHR)O) ppm.

Chapter 4

59

Synthesis of poly(glycidyl 3-trimethylaminopropylcarbamate-co-glycidyl dodecyl-

carbamate) (P(GTMAPA15-co-GDDA

12)) (5)

P(GDMAPA15-co-GDDA

12) (3) (0.147 g, 0.34 mmol ―NMe2) was dissolved

in THF (3.0 mL). Methyl iodide (0.058 g, 0.41 mmol) was added and

the solution was stirred for 20 h at room temperature. Excess methyl

iodide and the solvent were removed under reduced pressure and the

polymer purified by dialysis in methanol. Polymer 5 was obtained as a

yellowish crystalline solid (0.205 g, 89%). Mn,NMR = 10,111 g mol–1,

Mn,SEC = 4400 g mol–1, Ð = 1.18. 1H NMR (400 MHz, DMSO-d6) (5):

δ = 0.74–0.90 (m, NHCH2CH2(CH2)9CH3), 1.20 (s, NHCH2CH2-

(CH2)9CH3), 1.30–1.44 (m, NHCH2CH2(CH2)9CH3), 1.72–1.91 (m,

NHCH2CH2CH2N+(CH3)3, ArCH2CH2), 2.55–2.62 (m, 3JHH = 7.6 Hz,

ArCH2CH2), 2.85–2.99 (m, NHCH2CH2(CH2)9CH3), 3.00–3.17 (m,

NHCH2CH2CH2N+(CH3)3, NHCH2CH2CH2N+(CH3)3), 3.26–3.43

(m, NHCH2CH2CH2N+(CH3)3), 3.44–3.74 (m, ArCH2CH2CH2,

OCH2CH(CH2OC=ONHR)O), 3.82–4.19 (m, OCH2CH(CH2O-

C=ONHR)O), 7.10–7.30 (m, ArCH2CH2) ppm. 13C NMR (101 MHz,

DMSO-d6) (5): δ = 13.8 (NHCH2CH2(CH2)9CH3), 22.0–28.9 (NH-

CH2(CH2)10CH3), 26.2 (NHCH2CH2CH2N+(CH3)3), 31.2 (NHCH2-

(CH2)10CH3), 37.3 (NHCH2CH2CH2N+(CH3)3), 52.2 (NHCH2CH2-

CH2N+(CH3)3), 63.2 (NHCH2CH2CH2N+(CH3)3), 68.6–77.0 (ArCH2-

CH2CH2, OCH2CH(CH2OC=ONHR)O), OCH2CH(CH2OC=O-

NHR)O), 125.5 (ArCH2), 128.9 (ArCH2), 141.5 (ArCH2), 156.0

(OCH2CH(CH2OC=ONHR)O) ppm.

Synthesis of poly(glycidyl 3-aminopropyldiethanolmethylcarbamate-co-glycidyl

dodecylcarbamate) (P(GAPDEMA16-co-GDDA

11)) (6)

P(GAPDEA16-co-GDDA

11) (4) (0.216 g, 0.47 mmol ―NEtOH2) was

dissolved in THF (2.5 mL). Methyl iodide (0.081 g, 0.57 mmol) was

added and the solution was stirred for 20 h at room temperature.

Excess methyl iodide and the solvent were removed under reduced

pressure and the polymer purified by dialysis in methanol. Polymer 6

was obtained as a slightly yellow solid (0.238 g, 84%). Mn,NMR =

9608 g mol–1, Mn,SEC = not measurable. 1H NMR (400 MHz, MeOD)

(6): δ = 0.96 (t, 3JHH = 6.3 Hz, NHCH2CH2(CH2)9CH3), 1.35 (s,

NHCH2CH2(CH2)9CH3), 1.48–1.65 (m, NHCH2CH2(CH2)9CH3),

1.88–1.99 (m, ArCH2CH2), 2.05–2.23 (m, NHCH2CH2CH2N+(CH3-

Chapter 4

60

(CH2CH2OH)2)), 2.70–2.78 (m, ArCH2CH2), 3.09–3.20 (m,

NHCH2CH2(CH2)9CH3), 3.24–3.42 (m, NHCH2CH2CH2N+(CH3-

(CH2CH2OH)2)), 3.51–3.96 (m, ArCH2CH2CH2, OCH2CH(CH2-

OC=ONHR)O, CH2N+(CH3(CH2CH2OH)2)), 4.02–4.42 (m, OCH2-

CH(CH2OC=ONHR)O, CH2N+(CH3(CH2CH2OH)2)), 7.20–7.36 (m,

ArCH2CH2) ppm. 13C NMR (101 MHz, MeOD) (6): δ = 14.5

(NHCH2CH2(CH2)9CH3), 23.7–31.0 (NHCH2CH2(CH2)9CH3), 28.0

(NHCH2CH2CH2N+(CH3(CH2CH2OH)2), 33.0 (NHCH2CH2(CH2)9-

CH3), 38.9 (NHCH2CH2CH2N+(CH3(CH2CH2OH)2)), 42.0 (NHCH2-

CH2(CH2)9CH3), 50.9 (NHCH2CH2CH2N+(CH3(CH2CH2OH)2), 56.8

(NHCH2CH2CH2N+(CH3(CH2CH2OH)2), 62.8–79.1 (ArCH2CH2-

CH2, OCH2CH(CH2OC=ONHR)O), 65.4 (CH2N+(CH3(CH2CH2-

OH)2), 129.4 (ArCH2), 129.6 (ArCH2), 158.7 (OCH2CH(CH2OC=O-

NHR)O) ppm.

Synthesis of poly(glycidyl-4-nitrophenyl carbonate) (P(GNPC)27) (7)

PG27 (1) (2.012 g, 27.16 mmol OH) was dissolved in pyridine

(18.85 mL). The 4-nitrophenyl chloroformate (6.023 g, 29.88 mmol)

was dissolved in dichloromethane (20 mL) and added to the polymer

solution via syringe pump in 30 min at 0 °C. The solution was stirred

for 20 h at room temperature. The crude product was washed with

water (30 mL), 1 M HCl (aq.) (3 · 30 mL), and saturated NaCl solution

(aq.) (30 mL). The organic phase was separated, dried over Na2SO4

and precipitated in cold MeOH. The solvent was removed under

reduced pressure and polymer 7 was obtained as a colorless solid

(5.782 g, 89%). Mn,NMR = 6458 g mol–1, Mn,SEC = 6600 g mol–1, Ð =

1.41. 1H NMR (400 MHz, DMSO-d6) (7): δ = 1.69–1.83 (m,

ArCH2CH2), 2.54–2.61 (m, ArCH2CH2), 3.54–3.95 (m, ArCH2CH2-

CH2, OCH2CH(CH2OC=OOArNO2)O), 4.15–4.56 (d, CH2OC=O-

OArNO2), 7.08–7.25 (m, ArCH2CH2), 7.42 (s, CH2OC=OOArNO2),

8.18 (s, CH2OC=OOArNO2) ppm. 13C NMR (101 MHz, DMSO-d6)

(7): δ = 30.8 (ArCH2CH2), 31.6 (ArCH2), 68.2 (OCH2CH(CH2OC=O-

OArNO2)O), 76.4 (OCH2CH(CH2OC=OOArNO2)O), 76.5 (ArCH2-

CH2CH2), 76.6 (OCH2CH(CH2OC=OOArNO2)O), 122.3 (CH2O-

C=OOArNO2), 125.2 (CH2OC=OOArNO2), 125.7 (ArCH2), 128.2

(ArCH2), 128.3 (ArCH2), 141.6 (ArCH2), 145.0 (CH2OC=OOAr-

NO2), 152.0 (OC=OO), 155.1 (CH2OC=OOArNO2) ppm.

Chapter 4

61

Synthesis of poly(glycidyl homocysteine thiolactonylcarbamate) (P(GHCTL)27) (8)

P(GNPC)27 (7) (1.020 g, 4.26 mmol carbonate) was dissolved in DMF

(10 mL), and 4-(dimethylamino)pyridine (0.053 g, 0.43 mmol) and DL-

homocysteine thiolactone hydrochloride (0.655 g, 4.26 mmol) were

added. The mixture was cooled to 0 °C and triethylamine (0.862 g,

8.52 mmol) was added over 1 h via syringe pump. The solution was

stirred for 20 h at room temperature. DMF was removed under

reduced pressure at 50 °C and the crude product was precipitated in

MeOH. Drying under reduced pressure at 50 °C gave polymer 8 as a

slightly yellow solid (0.694 g, 75%). Mn,NMR = 5865 g mol–1, Mn,SEC =

6900 g mol–1, Ð = 1.44. 1H NMR (400 MHz, DMSO-d6) (8): δ = 1.74–

1.83 (m, ArCH2CH2), 2.00–2.48 (m, C=OSCH2CH2CHR), 2.60 (t, 3JH,H = 7.5 Hz, ArCH2CH2), 3.17–3.45 (m, C=OSCH2CH2CHR), 3.47–

3.75 (m, ArCH2CH2CH2, OCH2CH(CH2OC=ONHR)O), 3.86–4.23

(m, CH2OC=ONHR), 4.26–4.42 (m, C=OSCH2CH2CHR), 7.14–7.29

(Ar), 7.55 (br s, NH) ppm. 13C NMR (101 MHz, DMSO-d6) (8): δ =

26.5 (C=OSCH2CH2CHR), 29.8 (C=OSCH2CH2CHR), 30.9

(ArCH2CH2), 31.6 (ArCH2), 59.9 (CH2OC=ONHR), 63.7, 68.7, 77.2

(ArCH2CH2CH2, OCH2CH(CH2OC=ONHR)O), 79.2 (C=OSCH2-

CH2CHR), 128.3 (ArCH2), 128.4 (ArCH2), 156.0 (OC=ONHR), 205.7

(C=OSCH2CH2CHR) ppm.

Synthesis of P(GDDAc)27 (9)

To a mixture of P(GHCTL)27 (8) (0.301 g, 1.386 mmol HCTL) and

dodecyl acrylate (0.833 g, 3.464 mmol) in chloroform (3.0 mL), 3-

(dimethylamino)-1-propylamine (0.353 g, 3.464 mmol) was added in

30 min via syringe pump at room temperature. The mixture was stirred

for 20 h at room temperature. Chloroform was removed under re-

duced pressure. Dialysis in acetone gave 9 as a colorless, viscous liquid

(0.628 g, 81%). Mn,NMR = 15,115 g mol–1, Mn,SEC = 15,300 g mol–1, Ð =

1.36. 1H NMR (400 MHz, CDCl3) (9): δ = 0.82 (t, 3JH,H = 6.8 Hz,

CH2CH2(CH2)9CH3), 1.20 (s, CH2CH2(CH2)9CH3), 1.48–1.69 (m,

CH2CH2N(CH3)2, CH2CH2(CH2)9CH3, ArCH2CH2), 1.76–2.08 (m,

CHCH2CH2SCH2), 2.15 (s, CH2N(CH3)2), 2.22–2.37 (m, CH2N-

(CH3)2), 2.43–2.61 (m, CHCH2CH2SCH2CH2), 2.64–2.78 (m, CHCH2-

CH2SCH2CH2), 3.07–3.37 (m, NHCH2CH2CH2N(CH3)2), 3.41–3.75

(m, ArCH2CH2CH2, OCH2CH(CH2OC=ONHR)O), 3.77–4.07 (m,

Chapter 4

62

CH2OC=ONHCH), 4.10–4.41 (m, O=COCH2CH2), 7.09–7.23 (m,

Ar), 7.76 (br. s, NH) ppm. 13C NMR (101 MHz, CDCl3) (9): δ = 14.1

(CH2CH2(CH2)9CH3), 22.7–31.9 (CH2CH2(CH2)9CH3, CHCH2CH2S-

CH2, ArCH2CH2), 26.8 (CHCH2CH2SCH2CH2), 28.2 (CH2CH2N-

(CH3)2), 28.6 (CHCH2CH2SCH2CH2), 34.7 (CHCH2CH2SCH2CH2),

38.7 (NHCH2CH2CH2N(CH3)2), 45.5 (CH2N(CH3)2), 54.1 (NHCH),

57.9 (CH2N(CH3)2), 64.9 (O=COCH2CH2), 125.9 (ArCH2), 128.3

(ArCH2), 128.5 (ArCH2), 140.0 (ArCH2), 156.4 (OC=ONH), 171.5

(CHC=ONH), 172.0 (CH2C=OO) ppm.

Synthesis of P(GDDAc, q)27 (10)

P(GDDAc)27 (9) (0.431 g, 0.770 mmol ―NMe2) was dissolved in THF

(9.0 mL), and methyl iodide (0.131 g, 0.923 mmol) was added. The

solution was stirred at room temperature for 20 h. Removal of THF

and excess methyl iodide under reduced pressure and dialysis in

methanol gave polymer 10 as a slightly yellow solid (0.475 g, 88%).

Mn,NMR = 18,947 g mol–1, Mn,SEC = 11,800 g mol–1, Ð = 1.36. 1H NMR

(400 MHz, CDCl3) (10): δ = 0.81 (t, 3JH,H = 6.5 Hz, CH2CH2(CH2)9-

CH3), 1.05–1.32 (m, CH2CH2(CH2)9CH3), 1.46–1.62 (m, CH2CH2-

(CH2)9CH3), 1.85–2.25 (m, CH2CH2N+(CH3)3, ArCH2CH2, CHCH2-

CH2SCH2), 2.39–2.64 (m, CHCH2CH2SCH2CH2), 2.66–2.82 (m,

CHCH2CH2SCH2CH2), 3.05–3.50 (m, NHCH2CH2CH2N+(CH3)3),

3.51–3.83 (m, ArCH2CH2CH2, OCH2CH(CH2OC=ONHR)O), 3.84–

4.50 (m, CH2OC=ONHCH, O=COCH2CH2), 7.08–7.24 (m, Ar), 7.77

(br. s, NH) ppm. 13C NMR (101 MHz, CDCl3) (10): δ = 14.1

(CH2CH2(CH2)9CH3), 22.6–31.9 (CH2CH2(CH2)9CH3, CHCH2CH2S-

CH2, ArCH2CH2), 26.7 (CHCH2CH2SCH2CH2), 28.3 (CH2CH2N+-

(CH3)3), 28.6 (CHCH2CH2SCH2CH2), 34.8 (CHCH2CH2SCH2CH2),

40.1 (NHCH2CH2CH2N+(CH3)3), 53.8 (CH2N+(CH3)3, NHCH), 64.9

(CH2N+(CH3)3, O=COCH2CH2), 156.5 (OC=ONH), 172.1 (CHC=O-

NH), 172.8 (CH2C=OO) ppm.

Synthesis of P(GDMAPA14-co-GDDADDAc

13) (11)

P(GNPC)27 (7) (0.541 g, 2.26 mmol carbonate) was dissolved in DMF

(11 mL) and 3-(dimethylamino)-1-propylamine (0.115 g, 1.13 mmol)

was added in 30 min via syringe pump. The mixture was stirred for

20 h at room temperature. DL-homocysteine thiolactone hydro-

Chapter 4

63

chloride (0.174 g, 1.13 mmol) and 4-(dimethylamino)pyridine (0.013 g,

0.11 mmol) were added. The mixture was cooled to 0 °C, and triethyl-

amine (0.229 g, 2.26 mmol) was added over 1 h via syringe pump. The

solution was stirred for 20 h at room temperature. DMF was removed

under reduced pressure at room temperature. The crude product was

dissolved in chloroform, and dodecyl acrylate (0.680 g, 2.83 mmol) was

added. The mixture was cooled to 0 °C, and dodecylamine (0.525 g,

2.83 mmol) was added in 30 min using a syringe pump. After stirring

for 20 h at room temperature, the solvent was removed and the crude

product was purified by dialysis in acetone. Polymer 11 was received

as a slightly yellow, viscous liquid (0.469 g, 48%). Mn,NMR =

11,631 g mol–1, Mn,SEC = 10,800 g mol–1, Ð = 1.36. 1H NMR

(400 MHz, CDCl3/acetone-d6 (6:4)) (11): δ = 0.81 (t, 3JH,H = 6.6 Hz

CH2CH2(CH2)9CH3), 1.20 (s, CH2CH2(CH2)9CH3), 1.38–1.50 (m,

NHCH2CH2(CH2)9CH3), 1.51–1.64 (m, OCH2CH2(CH2)9CH3), 1.70–

1.86 (m, CH2CH2N(CH3)2), 1.88–2.01 (m, CHCH2CH2SCH2), 2.29–

2.77 (m, CH2N(CH3)2, CHCH2CH2SCH2CH2), 2.97–3.30 (m,

NHCH2CH2CH2N(CH3)2, NHCH2CH2(CH2)9CH3), 3.44–3.79 (m,

ArCH2CH2CH2, OCH2CH(CH2OC=ONHR)O), 3.90–4.34 (m,

CH2OC=ONHR, CH2OC=ONHCH, O=COCH2CH2), 7.07–7.24

(m, Ar) ppm. 13C NMR (101 MHz, CDCl3/acetone-d6 (6:4)) (11): δ =

13.5 (CH2CH2(CH2)9CH3), 22.1–31.4 (CH2CH2(CH2)9CH3, CHCH2-

CH2SCH2, ArCH2CH2, CH2CH2N(CH3)2), 34.2 (CHCH2CH2SCH2-

CH2), 38.4 (NHCH2CH2CH2N(CH3)2), 39.0 (NHCH2CH2(CH2)9-

CH3), 43.7 (CH2N(CH3)2), 53.3 (NHCH), 56.0 (CH2N(CH3)2), 64.2

(O=COCH2CH2), 127.8 (ArCH2), 127.9 (ArCH2), 155.9 (OC=ONH),

156.2 (OC=ONH), 171.4 (CHC=ONH), 172.1 (CH2C=OO) ppm.

Synthesis of P(GTMAPA14-co-GDDADDAc

13) (12)

P(GDMAPA14-co-GDDADDAc

13) (11) (0.179 g, 0.20 mmol ―NMe2) was

dissolved in THF (2.0 mL), and methyl iodide (0.036 g, 0.25 mmol)

was added. The solution was stirred at room temperature for 20 h.

Removal of THF and excess methyl iodide under reduced pressure

and dialysis in methanol gave polymer 12 as a slightly yellow solid

(0.203 g, quant.). Mn,NMR = 13,476 g mol–1, Mn,SEC = 9400 g mol–1, Ð =

1.41. 1H NMR (400 MHz, CDCl3/acetone-d6 (6:4)) (12): δ = 0.80 (t, 3JH,H = 6.8 Hz CH2CH2(CH2)9CH3), 1.18 (s, CH2CH2(CH2)9CH3),

Chapter 4

64

1.36–1.48 (m, NHCH2CH2(CH2)9CH3), 1.50–1.66 (m, OCH2CH2-

(CH2)9CH3), 1.74–2.01 (m, CH2CH2N+(CH3)3, CHCH2CH2SCH2),

2.42–2.89 (m, CHCH2CH2SCH2CH2), 2.94–3.45 (m, NHCH2CH2-

CH2N+(CH3)3, NHCH2CH2(CH2)9CH3), 3.49–3.81 (m, ArCH2CH2-

CH2, OCH2CH(CH2OC=ONHR)O), 3.87–4.38 (m, CH2OC=O-

NHR, CH2OC=ONHCH, O=COCH2CH2), 7.03–7.23 (m, Ar) ppm. 13C NMR (101 MHz, CDCl3/acetone-d6 (6:4)) (12): δ = 13.4 (CH2CH2-

(CH2)9CH3), 22.1–31.3 (CH2CH2(CH2)9CH3, CHCH2CH2SCH2, Ar-

CH2CH2, CH2CH2N(CH3)2), 34.2 (CHCH2CH2SCH2CH2), 38.9 (NH-

CH2CH2(CH2)9CH3), 43.0 (NHCH2CH2CH2N+(CH3)2), 53.0 (CH2N+-

(CH3)3), 53.8 (NHCH), 64.1 (CH2N(CH3)2, O=COCH2CH2), 127.8

(ArCH2), 127.9 (ArCH2), 141.3 (ArCH2), 155.9 (OC=ONH), 156.4

(OC=ONH), 171.3 (CHC=ONH), 171.4 (CH2C=OO) ppm.

4.3 Results and Discussion

In this chapter, the synthesis and characterization of various novel

cationic/hydrophobic functionalized polyglycidols is presented. The

functional polyethers are evaluated in regard to their antibacterial acti-

vity against E. coli and S. aureus, induced by different microstructures.

Thereto, a polyglycidol with statistically distributed cationic and hydro-

phobic groups (cationic–hydrophobic ratio of 1:1) was compared to

(a) a polyglycidol with a hydrophilic modification at the cationic moie-

ties; (b) a polyglycidol with cationic and hydrophobic functionalities at

every repeating unit; and (c) a polyglycidol with a cationic–hydro-

phobic balance of 1:2 (Fig. 4.1).

Linear polyglycidol was synthesized by anionic ring-opening poly-

merization of ethoxyethyl glycidyl ether with 3-phenyl-1-propanol as

initiator, followed by removal of the acetal protecting groups under

acidic conditions.38 Polyglycidol with 27 repeating units (PG27 (1)) and

Mn,SEC = 2900 g mol–1 was obtained with a narrow molecular weight

distribution (Ð = 1.13). 1H, 13C NMR spectra and SEC analysis of

PG27 (1) can be found in the supporting information (Fig. A.2.1–A.2.3,

appendix A.2).

Chapter 4

65

Figure 4.1: Comparison of various cationic/hydrophobic functionalized poly-

glycidols in regard to their antibacterial activity against E. coli and S. aureus to

examine the structure–property relationship.

4.3.1 Synthesis of P(GTMAPA15-co-GDDA

12) (5) and P(GAPDEMA16-co-

GDDA11) (6)

The general approach for the functionalization of linear polyglycidol

with cationic and hydrophobic groups starts with the introduction of

active ester functionalities to the polymer backbone. The active esters

allow the reaction with primary amines under the selective formation

of carbamate moieties. Quaternization of introduced tertiary amines

gave the cationic component.

Chapter 4

66

PG27 (1) was reacted with phenyl chloroformate in pyridine/

dichloromethane at room temperature (Scheme 4.1a). For purification,

poly(glycidyl phenyl carbonate)27 (2) was washed with water, 1 M HCl

solution (aq.), and saturated NaCl solution (aq.) to remove pyridine

hydrochloride and excess pyridine. The successful functionalization

was confirmed by 1H NMR, 13C NMR spectroscopy (Fig. A.2.4–A.2.5,

appendix A.2), and SEC analysis (Fig. A.2.12, appendix A.2). The

introduced phenyl carbonate groups are excellent electrophiles for the

substitution reaction with non-functionalized, primary amines.

P(GPC)27 (2) was subsequently reacted with dodecylamine (DDA) and

3-(dimethylamino)-1-propylamine (DMAPA) or N-(3-aminopropyl)-

diethanolamine (APDEA) in THF at room temperature in a 1:1 ratio

(Scheme 4.1b). The prepared poly(glycidyl 3-dimethylaminopropyl-

carbamate-co-glycidyl dodecylcarbamate) (P(GDMAPA15-co-GDDA

12)) (3)

and poly(glycidyl 3-aminopropyldiethanolcarbamate-co-glycidyl do-

decylcarbamate) (P(GAPDEA16-co-GDDA

11)) (4) were purified by dialysis

in methanol and characterized by 1H NMR, 13C NMR spectroscopy

(Fig. A.2.6–A.2.9, appendix A.2), and SEC analysis (Fig. A.2.13–

A.2.14, appendix A.2).

Scheme 4.1: Synthetic pathway to P(GTMAPA15-co-GDDA

12) (5) and

P(GAPDEMA16-co-GDDA

11) (6). (a) Functionalization of PG27 (1) with phenyl

chloroformate, pyridine/DCM, rt, 20 h; (b) Reaction of P(GPC)27 (2) with

DDA and DMAPA/APDEA, THF, rt, 42 h; (c) Quaternization of tertiary

amines with methyl iodide, THF, rt, 20 h.

In both cases, the different functional groups are statistically

distributed along the polyglycidol backbone. However, the higher

reactivity of DMAPA and APDEA in comparison to DDA leads to a

Chapter 4

67

slightly uneven ratio of functionalities. P(GDMAPA15-co-GDDA

12) (3) and

P(GAPDEA16-co-GDDA

11) (4) were further reacted with an excess of

methyl iodide in THF at room temperature to quaternize the tertiary

amine moieties (Scheme 4.1c). The synthesized P(GTMAPA15-co-GDDA

12)

(5) and P(GAPDEMA16-co-GDDA

11) (6) were purified by dialysis in metha-

nol and analyzed by 1H NMR, 13C NMR, and SEC analysis. 1H and 13C NMR spectra of P(GTMAPA

15-co-GDDA12) (5) in DMSO-d6

show characteristic signals of the dodecyl and trimethylpropyl-

ammonium groups adjacent to the carbamate moieties, proving the

successful functionalization of PG27 (1). In the 1H NMR spectrum

(Fig. 4.2a), the characteristic signals of the dodecyl functionality appear

as three multiplets at δ = 0.74–0.90 (Signal 20), δ = 1.30–1.44 (Signal

18), and δ = 2.85–2.99 ppm (Signal 17), and a singlet at δ = 1.20 ppm

(Signal 19). The trimethylpropylammonium groups are shown as three

multiplets δ = 1.72–1.91 (Signal 11), δ = 3.00–3.17 (Signal 10/13), and

δ = 3.26–3.43 ppm (Signal 12). A multiplet at δ = 3.82–4.19 ppm

(Signal 9/16) shows the methylene group of the glycidol repeating unit.

In the 13C NMR spectrum (Fig. A.2.10, appendix A2), the distinctive

signals of the dodecyl groups are found at δ = 13.8 (Signal 23), δ =

22.0–28.9 (Signal 22), and δ = 31.2 ppm (Signal 21). The representative

signals of the trimethylpropylammonium functionality are shown at

δ = 26.2 (Signal 13), δ = 37.3 (Signal 12), δ = 52.2 (Signal 15), and δ

= 63.2 ppm (Signal 14). Further, the signal of the carbamate groups

can be found at δ = 156.0 ppm (Signal 11/19).

The number of DMAPA and DDA groups attached to PG27 (1) was

calculated by comparing the signal intensity of one methylene group

of the 3-phenyl-1-propanol (Signal 4) used in the synthesis of 1 with

signals 10/11/13 and signals 18–20, respectively. The absolute

molecular weight (Mn,NMR) was calculated using the 3-phenyl-1-propyl

end group as an internal reference (Mn,NMR = 10,111 g mol–1). Full

functionalization of PG27 (1) was reached.

SEC analysis using DMF as eluent confirms the synthesis of

P(GTMAPA15-co-GDDA

12) (5) with Mn,SEC = 4400 g mol–1 and a molecular

weight distribution of Ð = 1.18 (Fig. A.2.15, appendix A.2). However,

due to the amphiphilic nature of this polymer and resulting

interactions with the column, the molecular weight measured by SEC

Chapter 4

68

analysis is lower than the molecular weight calculated from the 1H

NMR spectrum.

Figure 4.2: 1H NMR spectra of P(GTMAPA15-co-GDDA

12) (5) measured in

DMSO-d6 (a) and P(GAPDEMA16-co-GDDA

11) (6) measured in MeOD (b).

1H and 13C NMR spectra of P(GAPDEMA16-co-GDDA

11) (6) were

measured in MeOD due to the poor solubility of the polymer in

DMSO-d6. In the 1H NMR spectrum (Fig. 4.2b), this leads to a shift

of all signals to lower field. Thus, the characteristic signals for the

dodecyl functionality and the cationic moiety can be found in analogy

to P(GTMAPA15-co-GDDA

12) (5). Additionally, the signals of the hydroxy-

ethyl group can be found in the multiplets at δ = 3.51–3.96 (Signal 13)

and δ = 4.02–4.42 ppm (Signal 14). In the 13C NMR spectrum (Fig.

A.2.11, appendix A.2), the signals are also shifted to lower fields in

comparison with P(GTMAPA15-co-GDDA

12) (5), except for signals of the

methyl group and methylene group adjacent to the cationic moiety that

are shifted to higher fields. The methyl group can be found at δ =

Chapter 4

69

50.9 ppm (Signal 17) and the methylene group is found at δ =

56.8 ppm (Signal 14). Additionally, the hydroxyethyl group is shown

at δ = 65.4 ppm (Signal 15/16). The number of functionalities and the

absolute molecular weight was calculated as described previously

(Mn.NMR = 9608 g mol−1). Both spectra confirm the successful

synthesis of P(GAPDEMA16-co-GDDA

11) (6).

SEC analysis of P(GAPDEMA16-co-GDDA

11) (6) using DMF was not

possible. SEC analysis of the precursor P(GAPDEA16-co-GDDA

11) (4) con-

firmed the successful synthesis with Mn,SEC = 14,100 g mol–1 and a

molecular weight distribution of Ð = 3.56 (Fig. A.2.14, appendix A.2).

However, hydrogen bonding between polymer molecules leads to the

generation of polymer aggregates and, thus, a high molecular weight

and a broad distribution.

4.3.2 Synthesis of P(GDDAc, q)27 (10)

The previous part showed that phenyl carbonates are excellent

electrophiles for the substitution reaction of non-functionalized,

reactive, primary amines. For the reaction with homocysteine

thiolactone the electrophilicity of the carbonate needs to be higher

than that of the carbonyl group of the thiolactone ring to prevent the

reaction of the homocysteine thiolactone with itself. We have shown

in our previous work that 4-nitrophenyl carbonates show a higher

reactivity compared to phenyl carbonates in aminolysis reactions and

are suitable for the reaction with functional, primary amines.41,42

PG27 (1) was reacted with 4-nitrophenyl chloroformate in pyridine/

dichloromethane at room temperature (Scheme 4.2a). For purification,

poly(glycidyl 4-nitrophenyl carbonate)27 (7) was washed with water,

1 M HCl solution (aq.), and saturated NaCl solution (aq.) to remove

pyridine hydrochloride and excess pyridine, and precipitated in metha-

nol. The successful functionalization was confirmed by 1H, 13C NMR

spectroscopy (Fig. A.2.16–A.2.17, appendix A.2), and SEC analysis

(Fig. A.2.23, appendix A.2). P(GNPC)27 was afterwards reacted with DL-

homocysteine thiolactone hydrochloride in DMF at room temperature

using catalytic amounts of 4-DMAP and Et3N as a base (Scheme 4.2b).

The resulting poly(glycidyl homocysteine thiolactonylcarbamate)27

(P(GHCTL)27) (8) was purified by precipitation in methanol and charac-

terized by 1H, 13C NMR spectroscopy (Fig. A.2.18–A.2.19, appendix

Chapter 4

70

A.2), and SEC analysis (Fig. A.2.24, appendix A.2). In a one-pot reac-

tion, P(GHCTL)27 (8) was reacted with DMAPA under ring-opening in

CHCl3 at room temperature, and the generated thiol was converted

with dodecyl acrylate in a thiol-ene reaction. The synthesized

P(GDDAc)27 (9) was purified by dialysis in acetone and characterized by 1H NMR, 13C NMR spectroscopy (Fig. A.2.20–A.2.21, appendix A.2),

and SEC analysis (Fig. A.2.25, appendix A.2). P(GDDAc)27 (9) was

subsequently quaternized with methyl iodide in THF at room

temperature. The crude product was dialyzed in methanol to remove

excess methyl iodide, and P(GDDAc, q) (10) was described by 1H, 13C

NMR spectroscopy, and SEC analysis.

Scheme 4.2: Synthetic pathway to P(GDDAc, q)27 (10). (a) Functionalization of

PG27 (1) with 4-nitrophenyl chloroformate, pyridine/DCM, rt, 20 h; (b)

Reaction of P(GNPC)27 (7) with DL-homocysteine thiolactone hydrochloride,

4-DMAP, Et3N, DMF, rt, 20 h; (c) Ring-opening reaction with DMAPA,

followed by thiol-ene reaction with dodecyl acrylate, CHCl3, rt, 20 h; (d)

Quaternization of tertiary amines with methyl iodide, THF, rt, 20 h.

P(GDDAc, q)27 (10) exhibits characteristic signals of the introduced

functionalities in the 1H and 13C NMR spectra measured in DMSO-d6.

In the 1H NMR spectrum (Fig. 4.3a), the trimethylpropylammonium

group is described by two multiplets at δ = 1.85–2.25 (Signal 13) and

δ = 3.05–3.50 ppm (Signals 12/14/15). The dodecyl acrylate moiety is

shown as a triplet at δ = 0.81 ppm (Signal 23) and two multiplets at δ

= 1.05–1.32 (Signal 22) and δ = 1.46–1.62 ppm (Signal 21). Two

multiplets at δ = 2.39–2.64 (Signals 17/19) and δ = 2.66–2.82 ppm

(Signal 18) are distinctive for the methylene groups adjacent to the

thioether. The signals at δ = 3.84–4.50 ppm (Signals 10/11/20) show

Chapter 4

71

the methylene groups adjacent to the ester functionality and the single

proton adjacent to the carbamate moiety. The multiplet also contains

the methylene groups of the PG repeating unit adjacent to the

carbamate. In the 13C NMR spectrum (Fig. A.2.22, appendix A.2), the

distinctive signals can be found at δ = 28.3 (Signal 15), δ = 40.1 (Signal

14), δ = 53.8 (Signal 17), and δ = 64.9 ppm (Signal 16) for the

trimethylpropylammonium functionality; at δ = 14.1 (Signal 26), δ =

22.6–31.9 (Signals 24/25), and δ = 64.9 ppm (Signal 23) for the

dodecyl acrylate; and at δ = 26.7, δ = 28.6 (Signal 18–20) and δ =

34.8 ppm (Signal 21) for the methylene groups adjacent to the

thioether.

Figure 4.3: 1H NMR spectra of P(GDDAc, q)27 (10) measured in CDCl3 (a) and

P(GTMAPA14-co-GDDADDAc

13) (12) measured in CDCl3/acetone (6:4) (b).

Chapter 4

72

The number of functionalities and the absolute molecular weight were

calculated as described previously (Mn.NMR = 18,947 g mol−1). Both

spectra confirm the successful synthesis of P(GDDAc, q) (10).

SEC analysis using DMF as eluent also confirms the successful

synthesis of P(GDDAc, q)27 (10) with Mn,SEC = 11,800 g mol−1 and a

molecular weight distribution of Ð = 1.36 (Fig. A.2.26, appendix A.2).

4.3.3 Synthesis of P(GTMAPA14-co-GDDADDAc

13) (12)

The preparation of P(GTMAPA14-co-GDDADDAc

13) (12) combines both

previously described synthetic approaches. In a one-pot synthesis,

P(GNPC)27 (7) was first reacted with DMAPA in DMF at room

temperature for 20 h (Scheme 4.3a). After full conversion of the

primary amine (monitored by 1H NMR spectroscopy), 4-DMAP, DL-

homocysteine thiolactone hydrochloride, and triethylamine were

added, and the reaction was stirred for another 20 h at room tem-

perature. The crude product was reacted without further purification

with dodecylamine and dodecyl acrylate in chloroform at room

temperature (Scheme 4.3b). The crude product was purified by dialysis

in acetone and P(GDMAPA14-co-GDDADDAc

13) (11) characterized by 1H

NMR, 13C NMR spectroscopy (Fig. A.2.27–A.2.28, appendix A.2), and

SEC analysis (Fig. A.2.30, appendix A.2).

P(GDMAPA14-co-GDDADDAc

13 (11) was subsequently quaternized with

methyl iodide in THF at room temperature, purified by dialysis in

methanol, and characterized by the previously described methods

(Scheme 4.3c).

Due to the strong amphiphilic nature of P(GTMAPA14-co-GDDADDAc

13)

(12), 1H and 13C NMR spectroscopy were performed in a mixture of

CDCl3 and acetone-d6. In the 1H NMR spectrum (Fig. 4.3b), the

distinctive signals of the hydrophobic moiety are found at δ = 0.80

(Signal 14/22), δ = 1.18 (Signal 13/21), δ = 1.36–1.48 (Signal 12), and

δ = 1.50–1.66 ppm (Signal 20). The methylene group adjacent to the

ester is shown at δ = 3.87–4.38 ppm (Signal 19). This signal also

includes the methylene groups (Signal 9/25) and the single proton

(Signal 10) adjacent to the carbamate moieties. Specific signals of the

cationic functionalities are found at δ = 1.74–2.01 (Signal 27) and δ =

2.94–3.45 ppm (Signal 26/28/29). The shift of the signals of all

functional groups is in good comparison with the polymers described

Chapter 4

73

earlier. In the 13C NMR spectrum, the shifts of the various signals are

also in good comparison to the previously characterized cationic/

hydrophobic polymers (Fig. A.2.29, appendix A.2). Both spectra

confirm the successful synthesis of P(GTMAPA14-co-GDDADDAc

13) (12).

Scheme 4.3: Synthetic pathway to P(GTMAPA14-co-GDDADDAc

13) (12). (a) (I)

Reaction of P(GNPC)27 (7) with DMAPA, DMF, rt, 20 h, (II) Reaction with DL-

homocysteine thiolactone hydrochloride, 4-DMAP, Et3N, DMF, 20 h; (b)

Ring-opening reaction with dodecylamine, followed by thiol-ene reaction with

dodecyl acrylate, CHCl3, rt, 20 h; (c) Quaternization of tertiary amines with

methyl iodide, THF, rt, 20 h.

The number of functionalities and the absolute molecular weight were

calculated as described previously (Mn.NMR = 13,476 g mol–1).

Although, the integral values shown in the 1H NMR spectra are too

low to be accurate for a polyether with 27 repeating units, the ratio of

hydrophobic to cationic moieties is accepted as accurate. The absolute

values of hydrophobic to cationic groups is extrapolated to match the

expected number of repeating units. Fractionation towards lower

molecular weights is excluded based on the method of purification.

SEC analysis using DMF as eluent also confirms the successful synthe-

sis of P(GTMAPA14-co-GDDADDAc

13) (12) with Mn,SEC = 9400 g mol–1 and

a molecular weight distribution of Ð = 1.41 (Fig. A.2.31, appendix A.2)

4.3.4 Antibacterial Efficacy

To assess the influence of the microstructure of the functional

polyglycidols on their antibacterial efficacy, the minimal inhibitory

Chapter 4

74

concentrations of the four synthesized polymers against E. coli and S.

aureus were determined (Table 4.1). In comparison to the other three

polymers (6, 10, and 12) P(GTMAPA15-co-GDDA

12) (5)—with cationic and

hydrophobic groups statistically distributed at the polyglycidol

backbone—exhibited the lowest MIC against both E. coli and S. aureus.

A hydrophilic functionalization at the quaternary amine (P(GAPDEMA16-

co-GDDA11) (6)) does not affect the efficacy against E. coli, but slightly

impairs the efficacy against S. aureus.

Table 4.1: Minimal inhibitory concentration against E. coli and S. aureus and

hemolytic activity of functional polyglycidols with defined microstructures

P(GTMAPA15-co-GDDA

12) (5), P(GAPDEMA16-co-GDDA

11) (6), P(GDDAc, q)27 (10),

P(GTMAPA14-co-GDDADDAc

13) (12).

Polymer Mn,NMR a

[g mol–1]

MIC100 b,c

[µg mL–1]

HC50 d

[µg mL–1]

E. coli S. aureus

5 10,111 30 20 >>500 f

6 9608 30 30 100

10 18,947 30 >200 <10

12 13,476 200 d >200‒500 e <10

a Molecular weight (Mn,NMR) calculated from 1H NMR with an accuracy of integration of ±5%; b Minimum inhibitory concentration which prevents the visible growth of 100% of the bacteria within 20 h monitoring time; c Inoculum size = 1–2 · 106 CFU·mL−1; d HC50: concentration causing 50% lysis (hemolysis) of red blood cells (RBCs) relative to Triton X-100 (positive control, 100%), linear polyglycidol PG27 (1) HC50 >> 500 µg mL–1; e Non-growth value due to turbidity of solution caused by the polymer; f 10–500 µg mL–1 of polymer 5 causing agglutination of RBC, and about 6% (at 10 µg mL–1) –40% (at 500 µg mL–1) hemolysis.

When the cationic and the hydrophobic residues are located at every

repeating unit of the polymer and are connected by a short spacer

(P(GDDAc, q)27 (10)), the efficacy against E. coli remains the same as for

5 and 6. However, the efficacy against S. aureus decreases significantly

by a factor of 10. The molecular weight of polymer 10 is approximately

twice as high as the molecular weight of polymers 5 and 6. Thus, the

higher MIC values in the case of S. aureus compared to E. coli might

result from a sieving effect by the thick peptidoglycan layer of the

Gram-positive bacterium. This was also discussed by Lienkamp et al.43

Chapter 4

75

In polymer 10, the hydrophobic and cationic residues are connected

by a spacer and are not directly linked to each other. Opposite to the

resulting antibacterial effect of the latter (polymer 10), functionalized

branched poly(ethylene imine)s (PEI) with amphiphilic grafts had

better antibacterial properties against S. aureus than PEI with randomly

linked cationic and hydrophobic grafts. However, best results were

obtained with the cationic residue directly linked to the aliphatic

residue without a spacer in between.30 Thus, an influence of the kind

of polymer backbone on the polymer architecture and of the kind of

amphiphilic functionality on the antibacterial effect can be discussed.

Enhancing the hydrophobic share in comparison to the cationic

functionality (P(GTMAPA14-co-GDDADDAc

13) (12) with two hydrophobic

residues in the same polymer segment, connected by a spacer) leads to

a decrease of efficacy by a factor of 10 for both E. coli and S. aureus.

The high amount of hydrophobic residues induces aggregation in

aqueous media, which might lead to a partial unavailability of func-

tional groups of the polymer. Thus, interaction with the bacterial cell

envelope is impaired, since a certain amount of cationic charge is

necessary to initiate the binding to the bacterial cell envelope as the

first step in the cascade of amphipathic polymers’ mode of action.

Compared to the 1:2 ratio of cationic to hydrophobic residues in

polymer 12, branched PEI with functionalities introduced via

carbonate coupler chemistry and a higher ratio of cationic to hydro-

phobic residues resulted in higher efficacies in the case of E. coli.29

Furthermore, azetidinium functionalized poly(vinylamine)s with a

higher ratio of hydrophobic to cationic moieties resulted in better

antibacterial efficacies against E. coli and against S. aureus.44 Thus,

apparently there is a strong influence of the polymer backbone and the

structure of the cationic and hydrophobic side chains on the micro-

structure and the efficacy besides the hydrophilic to lipophilic balance

of the respective polymer.

Additionally, polymers functionalized with amphiphilic couplers

where the cationic moiety was directly linked to the hydrophobic

residue exhibited the lowest MIC compared to randomly distributed

cationic and hydrophobic groups linked via a spacer. Ganewatta et al.

refer to a “same-centered” repeat unit structure with the hydrophobic

moiety being directly accompanied by the charged moiety, i.e., the

Chapter 4

76

functional groups not being spatially separated over the backbone,

leading to an amphiphilic balance at the monomer level.45

4.3.5 Hemolytic Activity

To understand the selectivity of polymers 5, 6, 10, and 12 to affect

bacterial cells and mammalian cells, a hemolysis test was performed,

and the concentration required for 50% lysis of human red blood cells

(RBCs) was determined (HC50, Table 4.1). Linear polyglycidol PG27 (1)

did not show any significant lysis of RBCs even at the highest

concentration (500 μg mL–1) tested. For polymer 5 at the concen-

trations tested (10–500 µg mL–1), no HC50 value could be given at the

tested concentrations (10–500 µg mL–1). Hemolysis amounted to a-

bout 6% at 10 µg mL–1, 30% at 30 µg mL–1, and 40% at 500 µg mL–1.

However, agglutination of RBCs occurred at tested concentrations.

HC50 value for polymer 6 amounted to 100 μg mL–1. The higher value

of HC50 compared to the MIC100 against E. coli and S. aureus

(30 µg mL–1) proved that polymer 6 has a selectivity to differentiate

between mammalian cells and bacterial cell walls. For comparison, the

HC50 values of polymers 10 and 12 were below the lowest concen-

tration (10 µg mL–1) tested and thus, had a low selectivity for bacterial

cell envelopes.

4.4 Conclusions

Various novel cationic/hydrophobic functionalized polyglycidols were

successfully synthesized. A polyglycidol with statistically distributed

cationic and hydrophobic groups (cationic–hydrophobic ratio of 1:1),

a polyglycidol with a hydrophilic modification at the cationic moieties,

a polyglycidol with cationic and hydrophobic functionalities at every

repeating unit, and a polyglycidol with a cationic–hydrophobic balance

of 1:2 were characterized by 1H NMR, 13C NMR spectroscopy, and

SEC analyses and evaluated in regard to their antibacterial activity.

Antibacterial polyglycidols with statistic distribution of cationic and

hydrophobic residues are equally active against a Gram-negative and a

Gram-positive bacterial strain. In contrast to this, the efficacy of

amphipathic poly(ethylene imine)s is higher by a factor of 10 against

Chapter 4

77

Gram-positive bacteria than against Gram-negative ones. However,

antibacterial polyglycidols are equally or better active against E. coli

than against S. aureus. The best efficacy against both bacterial strains

resulted from the polyglycidol with statistic distribution of the cationic

and hydrophobic residues with polymer 6, showing also the best

selectivity to differentiate between mammalian cells and bacterial cell

walls compared with the other polymers tested in this study.

When cationic and hydrophobic residues are located in the same

polyglycidol repeating unit being connected by a spacer, the impact on

the cell envelope of S. aureus is significantly less effective than against

E. coli. The outer part of the cell envelope of Gram-positive bacteria is

composed of a thick peptidoglycan layer with integrated lipoteichoic

acids followed by the inner cell membrane. Here, a sieving effect might

be discussed, retarding the interaction of this polymer with the

underlying cell membrane. Additionally, the vicinity of the cationic and

hydrophobic groups in these polyglycidols compared to those

prepared with statistic distribution of cationic and hydrophobic

residues might disturb the interaction cascade of amphipathic

polymers with the components of the cell envelope.

Changing the hydrophilic–lipophilic balance (HLB) to a higher lipo-

philic–cationic ratio in amphipathic polyglycidol with statistically

distributed cationic and hydrophobic residues leads to a decrease in

efficacy in the same order of magnitude against both bacterial strains

E. coli and S. aureus. Antimicrobial efficacy of an amphipathic polymer

strongly depends on its HLB, the microstructure induced by the type

of polymer backbone, and the distribution and kind of the cationic and

hydrophobic functionalities.

4.5 References

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2. Spellberg, B.; Powers, J.H.; Brass, E.P.; Miller, L.G.;

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7. Siedenbiedel, F.; Tiller, J.C. Antimicrobial polymers in

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19. Palermo, E.F.; Kuroda, K. Chemical structure of cationic

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20. Ioannou, C.J.; Hanlon, G.W.; Denyer, S.P. Action of disin-

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21. Jennings, M.C.; Minbiole, K.P.; Wuest, W.M. Quaternary

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25. Ikeda, T.; Hirayama, H.; Yamaguchi, H.; Tazuke, S.;

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26. Kanazawa, A.; Ikeda, T.; Endo, T. Polymeric phosphonium

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Hayball, J.D.; Qu, Y.; Traven, A.; Griesser, H.J.; Meagher, L.;

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potent antimicrobial polymers with low hemolytic activity.

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29. Pasquier, N.; Keul, H.; Heine, E.; Moeller, M.; Angelov, B.;

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44. Chattopadhyay, S.; Heine, E.T.; Keul, H.; Moeller, M.

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Chapter 5

83

Chapter 5

Homoserine Lactone as a

Structural Key Element for

Multifunctional Polyglycidols

5.1 Introduction

In recent years, the increasing resource shortage and the consequential

sustainable awareness has led to a change of mindset of chemists

towards bio-based and renewable resources. The development of

enzymatic polymer synthesis1, multifunctional high performance

fibers2, membranes for water purification3 and transparent substrates

for use in electronics from wood4,5, or amino-acid based ionic liquids6,

and asymmetric building blocks7 are results of this rethinking process.

Another approach towards sustainability involves the utilization of

bio-based by-products. Glycerol is a readily available, major by-

product in the production of biodiesel and thus, used as a starting

material for the synthesis of monomers, such as epichlorohydrin and

glycidol8, or building blocks, as glycerol carbonate (Scheme 5.1).9

Glycidol acts as the monomer in the synthesis of linear, branched and

star-like polyglycidols.10-12 Polyglycidol is soluble in aqueous media,

shows no toxicity towards cells and is licensed by the FDA.13,14 It is a

highly functionalized polymer with a hydroxy group in every repeating

unit, allowing various further modifications.15,16 Hans et al. presented

Chapter 5

84

the application of polyglycidol as a multifunctional macroinitiator for

the ring-opening polymerization of -caprolactone.17,18 The reaction

was carried out by chemical and enzymatic catalysis, leading to densely

and loosely grafted polyglycidols, respectively. The loosely grafted

polymers showed enhanced hydrolytic degradation of the poly(capro-

lactone) side chains, allocated to the free hydroxy groups of the poly-

glycidol backbone.

Scheme 5.1: Strategies for the synthesis of glycerol carbonate and glycidol

from glycerol.9

The hydrolytic degradation of poly(caprolactone) was further

increased by functionalization of the polyglycidol macroinitiator with

phosphonate/phosphonic acid groups.19,20 Polyglycidol was function-

alized in a Michael-type addition with diethylvinyl phosphonate and

subsequent dealkylation of the pendant phosphonate groups.21 Addi-

tionally, multifunctional polyglycidols carrying phosphonic acid and

acrylate moieties were examined as UV-active adhesion promoters for

a hydrogel coating on stainless steel wires.22

Recently, a synthetic strategy for the post-polymerization function-

alization of polyglycidol with pendant phosphate groups by reaction

with diethyl chlorophosphate was developed (see chapter 3).23 The

diethyl phosphate moieties were subsequently (mono-)dealkylated.

This method allowed the tailoring of the concentration of pendant

phosphate/phosphoric acid groups introduced into the polyglycidol.

In this chapter, a strategy for the introduction of homoserine lactone

as a bio-based building block into polyglycidol is presented. The

synthetic protocol comprises (i) functionalization of polyglycidol with

homoserine lactone, (ii) ring-opening of the lactone with an amine, and

(iii) investigation of further modification possibilities.

Chapter 5

85

5.2 Experimental Section

5.2.1 Materials

Potassium tert-butoxide (1 M solution in THF, Aldrich), diglyme

(≥99%, extra dry, over molecular sieves, Acros Organics), pyridine

(99.5%, extra dry, over molecular sieves, Acros Organics), 4-

nitrophenyl chloroformate (>98%, TCI), 3-(dimethylamino)-1-

propylamine (99%, Acros Organics), DL-homoserine lactone hydro-

bromide (99%, Sigma-Aldrich), 4-dimethylaminopyridine (>98%,

Fluka), triethylamine (≥99.5%, anhydrous, Sigma-Aldrich), methyl

iodide (>99%, Sigma-Aldrich), tetrahydrofuran (99.8%, stabilizer free,

extra dry, Acros Organics), chloroform (99.9%, extra dry, over

molecular sieves, Acros Organics), N,N-dimethylformamide (99.8%,

extra dry, over molecular sieves, Acros Organics), methanol (≥99.8%,

p.a., CHEMSOLUTE®) and dichloromethane (≥99.8%, anhydrous,

Sigma-Aldrich) were used as received.

3-Phenyl-1-propanol (99%, Aldrich) was stirred with calcium hydride

for 24 h and distilled. Ethoxyethyl glycidyl ether (EEGE) was

synthesized from 2,3-epoxypropan-1-ol (glycidol) and ethyl vinyl ether

according to Fitton et al.24, purified by distillation, and stored under a

nitrogen atmosphere over molecular sieve (3 Å).

Water-sensitive reactions were carried out in a nitrogen atmosphere.

Nitrogen (Linde 5.0) was passed over molecular sieve (4 Å) and finely

distributed potassium on aluminum oxide.

5.2.2 Measurements

1H NMR and 13C NMR spectra were recorded on a Bruker DPX-400

FT-NMR spectrometer at 400 and 101 MHz, respectively. Deuterated

dimethyl sulfoxide (DMSO-d6), deuterated dimethylformamide

(DMF-d7) and deuterium oxide (D2O) were used as solvents. The

residual solvent signal was used as internal standard. Coupling

constants Jxy are given in Hz.

Molecular weights (Mn,SEC) and molecular weight distributions (Đ)

were determined by size exclusion chromatography (SEC). SEC

analyses were carried out with DMF (HPLC grade, VWR) as eluent.

SEC was performed using an Agilent 1100 system equipped with a

Chapter 5

86

dual RI-/Visco detector (ETA-2020, WGE). The eluent contained

1 g L–1 LiBr (≥99%, Aldrich). The sample solvent contained traces of

distilled water as internal standard. One pre-column (8x50 mm) and

four GRAM gel columns (8x300 mm, Polymer Standards Service)

were applied at a flow rate of 1.0 mL min–1 at 40 °C. The diameter of

the gel particles measured 10 µm, the nominal pore widths were 30,

100, 1000 and 3000 Å. Calibration was achieved using narrowly

distributed poly(methyl methacrylate) standards (Polymer Standards

Service). Results were evaluated using the PSS WinGPC UniChrom

software (Version 8.1.1).

Dialysis was performed in methanol using Biotech CE Tubing

(MWCO: 100–500 D, 3.1 mL cm–1, Spectrumlabs). The membrane

was washed for 15 min in water before use to remove the sodium azide

solution.

5.2.3 Syntheses

Synthesis of poly(glycidyl-4-nitrophenylcarbonate)26 (P(GNPC)26) (2)

PG26 (1) (0.990 g, 13.36 mmol OH) was dissolved in pyridine

(9.28 mL). 4-Nitrophenyl chloroformate (2.963 g, 14.70 mmol) was

dissolved in DCM (9.0 mL) and added to the polymer solution via

syringe pump in 30 min at 0 °C. The solution was stirred for 20 h at

room temperature. The crude product was washed with water (30 mL),

1 M HCl (aq.) (3 · 30 mL) and saturated NaCl solution (aq., 30 mL).

The organic phase was separated, dried over Na2SO4 and precipitated

in cold MeOH. The solvent was removed under reduced pressure and

polymer 2 was obtained as a colorless solid (2.922 g, 91%). Mn,NMR =

6219 g mol–1, Mn,SEC = 6100 g mol–1, Ð = 1.37. 1H-NMR (400 MHz,

DMSO-d6): δ = 1.69–1.83 (m, ArCH2CH2), 2.54–2.61 (m, ArCH2CH2),

3.68–3.72 (m, ArCH2CH2CH2, OCH2CH(CH2OC=OOArNO2)O),

4,26–4.42 (d, CH2OC=OOArNO2), 7.12–7.21 (m, ArCH2CH2), 7.41

(s, CH2OC=OOArNO2), 8.17 (s, CH2OC=OOArNO2) ppm. 13C

NMR (101 MHz, DMSO-d6): δ = 30.8 (ArCH2CH2), 31.6 (ArCH2),

68.3 (OCH2CH(CH2OC=OOArNO2)O), 76.4 (OCH2CH(CH2O-

C=OOArNO2)O), 76.5 (ArCH2CH2CH2), 76.6 (OCH2CH(CH2O-

C=OOArNO2)O), 122.3 (CH2OC=OOArNO2), 125.2 (CH2OC=O-

OArNO2), 125.7 (ArCH2), 128.2 (ArCH2), 128.3 (ArCH2), 141.6

Chapter 5

87

(ArCH2), 145.0 (CH2OC=OOArNO2), 152.0 (OC=OO), 155.1

(CH2OC=OOArNO2) ppm.

Synthesis of poly(glycidyl homoserine lactonylcarbamate)26 (P(GHSL)26) (3)

Polymer 2 (1.000 g, 4.181 mmol OH) was dissolved in DMF (20 mL)

and 4-(dimethylamino)pyridine (0.051 g, 0.418 mmol) and DL-

homoserine lactone hydrobromide (0.761 g, 4.181 mmol) were added.

The mixture was cooled to 0 °C and triethylamine (0.846 g,

8.361 mmol) was added over 1 h via syringe pump. The solution was

stirred for 20 h at room temperature. DMF was removed under

reduced pressure at 50 °C and the crude product was precipitated in

MeOH. Drying under reduced pressure at 50 °C gave polymer 3 as a

colorless solid (0.648 g, 77%). Mn,NMR = 5247 g mol–1, Mn,SEC = 6900

g mol–1, Ð = 1.36. 1H NMR (400 MHz, DMF-d7): δ = 1.81–1.90 (m,

ArCH2-CH2), 2.27–2.45 (m, NHCHCH2), 2.49–2.63 (m, NHCHCH2),

2.65–2.71 (m, ArCH2CH2), 3.61–3.86 (m, ArCH2CH2CH2, OCH2CH-

(CH2OC=OR)O), 4.09 (s, OCH2CH(CH2OC=OR)O), 4.20–4.37 (m,

NHCHCH2, OCH2CH(CH2OC=OR)O), 4.37–4.49 (m, NHCHCH2-

CH2), 4.51–4.66 (m, NHCHCH2CH2), 7.23–7.36 (m, ArCH2CH2),

7.66 (s, NH) ppm. 13C NMR (101 MHz, DMF-d7): δ = 28.7

(NHCHCH2), 31.6 (ArCH2CH2), 32.2 (ArCH2), 50.3 (NHCHCH2),

65.7 (NHCHCH2CH2), 64.7, 69.5, 78.0 (ArCH2CH2CH2, OCH2CH-

(CH2OR)O), 128.7 (ArCH2), 128.8 (ArCH2), 156.6 (OC=ONH), 175.8

(NHCHC=OO) ppm.

Synthesis of P(GHSL,o)26 (4)

Polymer 3 (0.263 g, 1.307 mmol HSL) was dissolved in DMF

(4 mL) and 3-(dimethylamino)-1-propylamine (0.339 g, 3.268 mmol)

and 4-(dimethylamino)pyridine (0.016 g, 0.131 mmol) were added. The

mixture was stirred for 20 h at room temperature. DMF was removed

under reduced pressure at 50 °C and the crude product was precipi-

tated in diethyl ether. Dialysis in MeOH gave 4 as a slightly yellow solid

(0.373 g, 94%). Mn,NMR = 7887 g mol–1, Mn,SEC = 8900 g mol–1, Ð =

1.32. 1H NMR (400 MHz, DMSO-d6): δ = 1.41–1.58 (m, NHCH2-

CH2CH2NMe2), 1.66–1.77 (m, ArCH2CH2, NHCHCH2CH2OH), 2.09

(s, NMe2), 2.18 (m, NHCH2CH2CH2NMe2), 2.55–2.61 (m, ArCH2-

CH2), 3.03–3.10 (m, NHCH2CH2CH2NMe2), 3.47–3.73 (m, ArCH2-

Chapter 5

88

CH2CH2, OCH2CH(CH2OR)O, NHCHCH2CH2OH), 3.81–4.25 (m,

OCH2CH(CH2OR)O, NHCHCH2CH2OH), 7.14–7.36 (m, ArCH2,

NH), 7.81–8.02 (m, NH) ppm. 13C NMR (101 MHz, DMSO-d6): δ =

26.9 (NHCH2CH2CH2NMe2), 31.0 (ArCH2CH2), 31.7 (ArCH2CH2),

35.1 (NHCHCH2CH2OH), 37.2 (NHCH2CH2CH2NMe2), 45.2

(NMe2), 52.2 (NHCHCH2CH2OH), 56.8 (NHCHCH2CH2OH), 57.7

(NHCH2CH2CH2NMe2), 63.8, 68.7, 77.8 (ArCH2CH2CH2, OCH2CH-

(CH2OR)O), 125.8 (ArCH2), 128.3 (ArCH2), 128.4 (ArCH2), 141.8

(ArCH2), 156.0 (OC=ONH), 171.9 (CHC=ONH) ppm.

Synthesis of P(GHSL,o,q)26 (5)

Polymer 4 (0.250 g, 0.824 mmol ―NMe2) was dissolved in MeOH

(5 mL) and methyl iodide (0.175 g, 1.236 mmol) was added. The

solution was stirred under reflux for 20 h. Removal of MeOH and

excess methyl iodide under reduced pressure at 50 °C gave polymer 5

as a yellow solid (0.324 g, 88%). 1H NMR (400 MHz, D2O): δ = 1.95–

2.08 (m, ArCH2CH2, NHCH2CH2CH2NMe3, NHCHCH2CH2OH),

2.66–2.74 (m, ArCH2CH2), 3.18 (s, NMe3), 3.25–3.47 (m, NHCH2CH2-

CH2NMe3), 3.72–3.87 (m, ArCH2CH2CH2, OCH2CH(CH2OR)O,

NHCHCH2CH2OH), 4.12–4.37 (m, OCH2CH(CH2OR)O, NHCH-

CH2CH2OH), 7.33–7.42 (m, ArCH2) ppm. 13C NMR (101 MHz,

D2O): δ = 22.8 (NHCH2CH2CH2NMe3), 33.8 (NHCHCH2CH2OH),

36.2 (NHCH2CH2CH2NMe3), 52.8 (NHCHCH2CH2OH), 53.2

(NMe3), 58.0 (NHCHCH2CH2OH), 64.2 (NHCH2CH2CH2NMe3),

64.5 (OCH2CH(CH2OR)O), 68.8, 76.6, 77.3 (ArCH2CH2CH2, OCH2-

CH(CH2OR)O), 128.2 (ArCH2), 128.8 (ArCH2), 141.0 (ArCH2), 157.5

(OC=ONH), 174.7 (CHC=ONH) ppm.

5.3 Results and Discussion

In this chapter, homoserine lactone derived from the bio-based

building block homoserine is presented as the structural key element.

Polyglycidol is functionalized with homoserine lactone in a two-step

reaction to prepare multifunctional polyethers.

Chapter 5

89

5.3.1 Functionalization of polyglycidol (1) with DL-homoserine lactone

hydrobromide

Linear polyglycidol was prepared by anionic ring-opening polymeri-

zation of ethoxyethyl glycidyl ether with 3-phenyl-1-propanol as

initiator and removal of the acetal protecting groups under acidic

conditions.18 A polyglycidol with 26 repeating units (PG26) and

Mn,SEC = 3100 g mol–1 was obtained with a narrow molecular weight

distribution (Ð = 1.14). The 1H, 13C NMR spectra and SEC analysis

of PG26 (5) can be found in the supporting information (Fig. A.3.1–

A.3.3, appendix A3).

In preliminary experiments it was observed that phenyl carbonates are

excellent electrophiles for the substitution reaction with non-

functionalized, primary amines. For the reaction with functionalized

amines, such as homoserine lactone, the electrophilicity of the

carbonate needs to be higher than the electrophilicity of the carbonyl

group of the lactone ring. Phenyl carbonates are not electrophilic

enough, leading to a reaction of the homoserine lactone with itself. In

hydrolysis reactions 4-nitrophenyl carbonates react faster by a factor

of five compared to phenyl carbonates.25 We expected an equal

increase in reactivity for the aminolysis reaction.

Scheme 5.2: Synthetic pathway to P(GHSL)26 (3). a) Functionalization of PG26

(1) with 4-nitrophenyl chloroformate, pyridine/DCM, rt, 20 h. b) Reaction of

P(GNPC)26 (2) with DL-homoserine lactone hydrobromide, 4-DMAP, Et3N,

DMF, rt, 20 h.

PG26 (1) was reacted with 4-nitrophenyl chloroformate in pyridine/

DCM at room temperature (Scheme 5.2a). For purification poly-

(glycidyl-4-nitrophenylcarbonate)26 (2) was washed with water, 1 M

HCl solution (aq.), and saturated NaCl solution (aq.) to remove excess

Chapter 5

90

pyridine and pyridine hydrochloride, and precipitated in methanol.

The successful functionalization was confirmed by 1H, 13C NMR

spectroscopy (Fig. A.3.4–A.3.5, appendix A.3), and SEC analysis (Fig.

A.3.7, appendix A.3). P(GNPC)26 was subsequently reacted with DL-

homoserine lactone hydrobromide in DMF at room temperature using

catalytic amounts of 4-(dimethylamino)pyridine (4-DMAP) and Et3N

as a base (Scheme 5.2b). The prepared poly(glycidyl homoserine lac-

tonylcarbamate)26 (P(GHSL)26) (3) was purified by precipitation in

methanol and characterized by 1H, 13C NMR spectroscopy, and SEC

analysis. 1H and 13C NMR spectra of P(GHSL)26 (3) in DMF-d7 show characteris-

tic signals of the homoserine lactonyl groups adjacent to the carbamate

moieties, proving the successful functionalization of PG26. In the 1H

NMR spectrum (Fig. 5.1) the characteristic signals of the lactonyl

functionality appear as four multiplets at δ = 2.27–2.45 and 2.49–2.63

(Signal 11) ppm for one methylene group and δ = 4.37–4.49 and 4.51–

4.66 (Signal 12) ppm for the other methylene group. A multiplet at δ =

4.20–4.37 ppm (Signal 9, 10) shows the methylene group of the

glycidol repeating unit and the single proton of the lactone ring

adjacent to the carbamate moiety. In the 13C NMR spectrum (Fig.

A.3.6, appendix A.3) the distinctive signals of the homoserine lactone

are found at δ = 28.7 (Signal 13), 50.3 (Signal 12) and 65.7 (Signal 14)

ppm. Additionally, the specific signal of the carbamate groups is found

at δ = 156.6 ppm (Signal 11).

Figure 5.1: 1H NMR spectrum of P(GHSL)26 (3) measured in DMF-d7.

Chapter 5

91

The number of HSL groups attached to PG26 (1) was calculated by

comparing the signal intensity of one methylene group of the 3-

phenyl-1-propanol (Signal 5) used in the synthesis of 1 with signal 11

and 12. The absolute molecular weight (Mn,NMR) was calculated

likewise using the 3-phenyl-1-propyl end group as an internal reference

(Mn,NMR = 5247 g mol–1). Full functionalization of PG26 (1) was

reached.

SEC analysis using DMF as eluent confirms the synthesis of P(GHSL)26

(3) with Mn,SEC = 6900 g mol–1 and a molecular weight distribution of

Ð = 1.36 (Fig. A.3.8, appendix A.3).

5.3.2 Ring-opening of P(GHSL)26 (3)

P(GHSL)26 (3) was reacted with 3-(dimethylamino)-1-propylamine

(DMAPA) and 4-DMAP as a nucleophilic catalyst in a ring-opening

reaction in DMF at room temperature (Scheme 5.3a). The synthesized

P(GHSL,o)26 (4) was purified by precipitation in diethyl ether, followed

by dialysis in MeOH and characterized by 1H, 13C NMR spectroscopy

and SEC analysis (Fig. A.3.9–A.3.11, appendix A.3).

Scheme 5.3: Synthetic pathway to P(GHSL,o,q)26 (5). a) Addition of DMAPA

to P(GHSL)26 (3), DMF, rt, 20 h. b) Quaternization of P(GHSL,o)26 (4) with MeI,

MeOH, reflux, 20 h.

1H and 13C NMR spectra in DMSO-d6 exhibit characteristic signals for

the DMAPA group and the opened lactone. In the 1H NMR spectrum

the distinctive signals of the DMAPA functionality appear as two

multiplets at δ = 1.41–1.58 ppm (Signal 14) and δ = 3.03–3.10 ppm

(Signal 13) and a multiplet at δ = 2.18 ppm (Signal 15). The singlet at

Chapter 5

92

δ = 2.09 ppm (Signal 16) represents the methyl groups vicinal to the

amine. The characteristic signals of the opened lactone appear as two

multiplets at 1.66–1.77 ppm (Signal 11) and 3.81–4.25 ppm (Signal 10).

The second multiplet also contains the methylene groups of the

polyglycidol repeating unit adjacent to the carbamate. In the 13C NMR

spectrum the distinctive signals appear at δ = 26.9 (Signal 17), 37.2

(Signal 16), 45.2 (Signal 19) and 57.7 (Signal 18) ppm for the DMAPA

group and at δ = 35.1 (Signal 13), 52.2 (Signal 12) and 56.8 (Signal

14) ppm for the opened lactone. The number of DMAPA moieties

attached to PG26 was calculated as described previously.

SEC analysis using DMF as eluent confirms the successful ring-

opening of P(GHSL)26 (3) with Mn,SEC = 8900 g mol–1 and a molecular

weight distribution of Ð = 1.32.

5.3.3 Quaternization of P(GHSL,o)26 (4)

As a model reaction for further functionalization, the quaternization

of P(GHSL,o)26 (4) was conducted with methyl iodide in methanol under

reflux (Scheme 5.3b). The solvent and excess methyl iodide were re-

moved under reduced pressure and P(GHSL,o,q)26 (5) characterized by 1H and 13C NMR spectroscopy (Fig. A.3.12–A.3.13, appendix A.3). 1H and 13C NMR spectra in D2O show distinctive signals of the

quaternary amine functionality. In the 1H NMR the singlet at δ =

3.18 ppm (Signal 16) represents the methyl groups vicinal to the amine

and the multiplet at δ = 3.25–3.47 ppm (Signal 15) shows the

methylene groups adjacent to the amine and the carbamate. The third

methylene group appears at δ = 1.95–2.08 (Signal 14) ppm. In the 13C

NMR spectrum the characteristic signals of the quaternary amine

moiety appear at δ = 22.8 (Signal 17), 36.2 (Signal 16), 53.2 (Signal 19)

and 64.2 (Signal 18) ppm. Both spectra confirm the successful

quaternization of P(GHSL,o)26 (4).

5.4 Conclusions

In this chapter, a synthetic strategy using homoserine lactone for the

preparation of multifunctional polyethers was developed. The strategy

includes the functionalization of linear polyglycidol with homoserine

Chapter 5

93

lactone. The successful synthesis was confirmed by 1H, 13C NMR

spectroscopy, and SEC analysis. Homoserine lactone groups were

subsequently opened by addition of 3-(dimethylamino)-1-propylamine

and the tertiary amine was quaternized with methyl iodide.

Future work will further exploit the possibility of the introduction of

multifunctionality into polymers this synthetic strategy offers.

5.5 References

1. Kobayashi, S.; Makino, A. Enzymatic polymer synthesis: An

opportunity for green polymer chemistry. Chem. Rev. 2009,

109, 5288.

2. Walther, A.; Timonen, J.V.; Diez, I.; Laukkanen, A.; Ikkala,

O. Multifunctional high-performance biofibers based on

wet-extrusion of renewable native cellulose nanofibrils. Adv.

Mater. 2011, 23, 2924.

3. Ma, H.Y.; Burger, C.; Hsiao, B.S.; Chu, B. Ultra-fine cellulose

nanofibers: New nano-scale materials for water purification.

J. Mater. Chem. 2011, 21, 7507.

4. Zhu, H.L.; Xiao, Z.G.; Liu, D.T.; Li, Y.Y.; Weadock, N.J.;

Fang, Z.Q.; Huang, J.S.; Hu, L.B. Biodegradable transparent

substrates for flexible organic-light-emitting diodes. Energ.

Environ. Sci. 2013, 6, 2105.

5. Fang, Z.; Zhu, H.; Preston, C.; Han, X.; Li, Y.; Lee, S.; Chai,

X.; Chen, G.; Hu, L. Highly transparent and writable wood

all-cellulose hybrid nanostructured paper. J. Mater. Chem. C

2013, 1, 6191.

6. Tao, G.H.; He, L.; Liu, W.S.; Xu, L.; Xiong, W.; Wang, T.;

Kou, Y. Preparation, characterization and application of ami-

no acid-based green ionic liquids. Green Chem. 2006, 8, 639.

7. Calaza, M.I.; Cativiela, C. Heterocycles from amino acids. In

Amino acids, peptides and proteins in organic chemistry, Hughes,

A.B., Ed. WILEY-VCH Verlag & KGaA: Weinheim,

Germany, 2011; Vol. 3, pp 83.

8. Sutter, M.; Silva, E.D.; Duguet, N.; Raoul, Y.; Metay, E.;

Lemaire, M. Glycerol ether synthesis: A bench test for green

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chemistry concepts and technologies. Chem. Rev. 2015, 115,

8609.

9. Sonnati, M.O.; Amigoni, S.; de Givenchy, E.P.T.; Darmanin,

T.; Choulet, O.; Guittard, F. Glycerol carbonate as a versatile

building block for tomorrow: Synthesis, reactivity, properties

and applications. Green Chem. 2013, 15, 283.

10. Gosecki, M.; Gadzinowski, M.; Gosecka, M.; Basinska, T.;

Slomkowski, S. Polyglycidol, its derivatives, and polyglycidol-

containing copolymers—synthesis and medical applications.

Polymers 2016, 8.

11. Mohammadifar, E.; Bodaghi, A.; Dadkhahtehrani, A.;

Nemati Kharat, A.; Adeli, M.; Haag, R. Green synthesis of

hyperbranched polyglycerol at room temperature. ACS

Macro Lett. 2016, 6, 35.

12. Dworak, A.; Slomkowski, S.; Basinska, T.; Gosecka, M.;

Walach, W.; Trzebicka, B. Polyglycidol - how is it synthesized

and what is it used for? Polimery 2013, 58, 641.

13. Kainthan, R.K.; Janzen, J.; Levin, E.; Devine, D.V.; Brooks,

D.E. Biocompatibility testing of branched and linear

polyglycidol. Biomacromolecules 2006, 7, 703.

14. Frey, H.; Haag, R. Dendritic polyglycerol: A new versatile

biocompatible material. Rev. Mol. Biotechnol. 2002, 90, 257.

15. Keul, H.; Möller, M. Synthesis and degradation of biomedical

materials based on linear and star shaped polyglycidols. J.

Polym. Sci. Pol. Chem. 2009, 47, 3209.

16. Thomas, A.; Müller, S.S.; Frey, H. Beyond poly(ethylene

glycol): Linear polyglycerol as a multifunctional polyether for

biomedical and pharmaceutical applications. Biomacromolecules

2014, 15, 1935.

17. Hans, M.; Keul, H.; Moeller, M. Poly(ether-ester) conjugates

with enhanced degradation. Biomacromolecules 2008, 9, 2954.

18. Hans, M.; Gasteier, P.; Keul, H.; Moeller, M. Ring-opening

polymerization of ε-caprolactone by means of mono- and

multifunctional initiators: Comparison of chemical and

enzymatic catalysis. Macromolecules 2006, 39, 3184.

19. Koehler, J.; Marquardt, F.; Teske, M.; Keul, H.; Sternberg,

K.; Moeller, M. Enhanced hydrolytic degradation of

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heterografted polyglycidols: Phosphonoethylated monoester

and polycaprolactone grafts. Biomacromolecules 2013, 14, 3985.

20. Koehler, J.; Marquardt, F.; Keul, H.; Moeller, M.

Phosphonoethylated polyglycidols: A platform for tunable

enzymatic grafting density. Macromolecules 2013, 46, 3708.

21. Koehler, J.; Keul, H.; Möller, M. Post-polymerization

functionalization of linear polyglycidol with diethyl

vinylphosphonate. Chem. Commun. 2011, 47, 8148.

22. Koehler, J.; Kuehne, A.J.C.; Piermattei, A.; Qiu, J.; Keul,

H.A.; Dirks, T.; Keul, H.; Moeller, M. Polyglycidol-based

metal adhesion promoters. J. Mater. Chem. B 2015, 3, 804.

23. Marquardt, F.; Keul, H.; Möller, M. Straightforward synthesis

of phosphate functionalized linear polyglycidol. Eur. Polym. J.

2015, 69, 319.

24. Fitton, A.O.; Hill, J.; Jane, D.E.; Millar, R. Synthesis of simple

oxetanes carrying reactive 2-substituents. Synthesis 1987,

1987, 1140.

25. Marlier, J.F.; O'Leary, M.H. Carbon kinetic isotope effects on

the hydrolysis of aryl carbonates. J. Am. Chem. Soc. 1990, 112,

5996.

Chapter 6

97

Chapter 6

Light-induced Cross-linking

and Post-cross-linking

Modification of Polyglycidol

6.1 Introduction

The continuous advancement in technological and medical applica-

tions leads to a high demand in materials with well-defined, tailored

properties.1 The properties of a given polymer are among others

defined by its architecture, morphology, molecular weight, as well as

type and degree of functionalization.2 Though, most of the polymer

characteristics are generated during the polymerization process, post-

polymerization modification is also possible.3 One approach is the

modification of functional groups of a polymer by subsequent reac-

tion(s) after the polymerization.4 Hydrophilic polymers carrying car-

boxylic acid, amine or hydroxy groups in the main or side chains are

an interesting platform for the synthesis of multifunctional materials.5

An excellent example for this class of polymers is polyglycidol. Every

repeating unit of the polyglycidol carries a hydroxy moiety, leading to

water solubility and a high degree of functionalization. Additionally,

linear and branched polyglycidols are biocompatible and certified by

the Food and Drug Administration (FDA).6,7 The hydroxy groups can

be reacted with various compounds to modify the properties of the

Chapter 6

98

polyether, e.g. introduction of phenyl carbonates and subsequent reac-

tion with primary amines, phosphorylation with diethyl chlorophos-

phate or phosphonoethylation via Michael-addition with vinyl phos-

phonate.8-10

A second approach to modify the polymer properties after the poly-

merization is cross-linking. Chemical cross-linking is based on the

reaction of a functional group in the polymer with a suitable multifunc-

tional cross-linking agent. Various protocols have been reported from

the reaction of carboxylic acid moieties with carbodiimides11,12 or aziri-

dines13,14, to the ring-opening of epoxides with amines and thiols15,16,

and the toolbox of “click chemistry”, e.g. the alkyne-azide [3+2]-cyclo-

addition and the thiol-ene reaction.17-19 Radiation cross-linking is based

on the generation of radicals by irradiation with UV-light20, electron

beams, X-rays or -rays.21 The photoinduced radical generation pro-

cess has received renewed interest as it meets a wide range of economic

and ecological expectations. The major use of this process involves

photopolymerization which has been the basis of numerous conven-

tional applications in coatings, adhesives, inks, printing plates, optical

waveguides, and micro-electronics.22,23 In these applications, the

radicals are generated by using photoinitiators via homolytic cleavage

of covalent bonds (Type I) and H-abstraction type (Type II) reactions.

Certain aromatic carbonyl compounds such as benzoin and deriva-

tives, benzyl ketals, acetophenones, aminoalkyl phenones, O-acyl-

oximino ketones, hydroxyalkyl ketones, acylphosphine oxides and

acylgermanes act as Type I photoinitiators and upon absorption of light

spontaneously undergo “α-cleavage”, generating free radicals. Type II

photoinitiators, belonging to the class of aromatic ketones, such as

benzophenone, thioxanthones, benzil, and quinones, generate radicals

by a bimolecular reaction. Their triplet excited states readily react with

hydrogen donors, such as alcohols, ethers, amines, and thiols thereby

producing radicals. Among various Type II photoinitiators, thioxan-

thones (TX) and camphorquinone (CQ) derivatives were widely used

due to the more favorable absorption characteristics in near UV and

visible range.24-32 The overall mechanism of their radical generation

process is represented in Scheme 1.

Chapter 6

99

Scheme 6.1: Photoinduced radical generation process by camphorquinone in

the presence of hydrogen donors.

In this chapter, a straightforward protocol for the light-induced cross-

linking and subsequent post-cross-linking modification of polyglycidol

is presented. The synthetic pathway comprises (i) functionalization of

linear polyglycidol (PG) with phenyl chloroformate under alkaline

conditions, (ii) substitution of the phenoxy groups of the introduced

phenyl carbonates with 3-(dimethylamino)-1-propylamine (DMAPA),

(iii) cross-linking of tertiary amine groups of the functionalized

polymer in a light-mediated reaction using camphorquinone as the

photoiniator and (iv) post-cross-linking quaternization with various

organoiodine compounds.

6.2 Experimental Section

6.2.1 Materials

Phenyl chloroformate (>97%, Fluka), pyridine (99.5%, dry over mole-

cular sieve, Acros Organics), dichloromethane (99.8%, anhydrous,

Sigma-Aldrich), 3-(dimethylamino)-1-propylamine (99%, Acros

Organics), tetrahydrofuran (99.8%, extra dry, stabilizer free, Acros

Organics), camphorquinone (99%, Acros Organics), N,N-dimethyl-

formamide (99.8%, VWR), methyl iodide (99%, Sigma-Aldrich), 1-

iodooctane (>97%, TCI), triethylene glycol monomethyl ether (95%,

Sigma-Aldrich), and 1H, 1H, 2H, 2H-heptadecafluorodecyl iodide

(>98%, TCI) were used as received.

Ethoxyethyl glycidyl ether (EEGE) was synthesized from 2,3-epoxy-

propan-1-ol (glycidol) and ethyl vinyl ether according to Fitton et al.33,

Chapter 6

100

purified by distillation, and stored under a nitrogen atmosphere over

molecular sieve (3 Å).

1-Iodo-3,6,9-trioxadecane was synthesized from the corresponding

tosylate by reaction with sodium iodide.34 The tosylate was prepared

according to literature from tri(ethylene glycol) monomethyl ether and

tosyl chloride.35

Water-sensitive reactions were carried out in a nitrogen atmosphere.

Nitrogen (Linde 5.0) was passed over molecular sieve (4 Å) and finely

distributed potassium on aluminum oxide.

6.2.2 Measurements

1H NMR and 13C NMR spectra were recorded on a Bruker DPX-400

FT-NMR spectrometer at 400 and 101 MHz, respectively. Chloroform

(CDCl3) and deuterated dimethyl sulfoxide (DMSO-d6) were used as

solvents. The residual solvent signal was used as internal standard.

Coupling constants Jxy are given in Hz.

FTIR spectra were recorded on a Thermo Nicolet Nexus 470 FTIR

spectrometer at 25 °C. The samples were prepared as KBr pellets and

scanned over a range of 400–4000 cm–1.

DSC measurements were performed on a Netzsch DSC 204 differen-

tial scanning calorimeter under a nitrogen atmosphere. Samples were

prepared in perforated closed aluminum pans using 5 mg of the

sample. The sample was heated and cooled with a rate of 10 °C min–1

in various temperature ranges. The heat flow was measured as a

function of the temperature. Transitions were reported during the

second heating cycle.

Molecular weights (Mn,SEC) and molecular weight distributions (Đ)

were determined by size exclusion chromatography (SEC). SEC with

DMF (HPLC grade, VWR) as eluent was performed using an Agilent

1100 system equipped with a dual RI-/Visco detector (ETA-2020,

WGE). The eluent contained 1 g L–1 LiBr (≥99%, Aldrich). The

sample solvent contained traces of distilled water as internal standard.

One pre-column (8x50 mm) and four GRAM gel columns (8x300 mm,

Polymer Standards Service) were applied at a flow rate of

1.0 mL min–1 at 40 °C. The diameter of the gel particles measured

10 µm, the nominal pore widths were 30, 100, 1000 and 3000 Å.

Calibration was achieved using narrowly distributed poly(methyl

Chapter 6

101

methacrylate) standards (Polymer Standards Service). Results were

evaluated using the PSS WinGPC UniChrom software (Version 8.1.1).

Dynamic light scattering was performed on an ALV system equipped

with a helium-neon laser (633 nm, 35 mW, JDS Uniphase), a

goniometer (CGS-8F, ALV), two avalanche photodiodes (SPCM-

CD2969, Perkin Elmer), a light scattering electronics unit (LSE-5003,

ALV), a digital hardware correlator (ALV 5000), an external

programmable thermostate (Julabo F32) and an index-match bath

filled with toluene. All measurements were recorded pseudo cross-

correlated at room temperature.

Zeta potential measurements were performed on a Zetasizer Nano ZS

(Malvern Instruments) at room temperature using folded capillary

cells.

XPS measurements were performed using a K-Alpha+ XPS

spectrometer (Thermo Fisher Scientific, East Grinstead, UK). Data

acquisition and processing using the Thermo Avantage software is

described elsewhere.36 All samples were analyzed using a micro-

focused, monochromated Al Kα X-ray source (30–400 µm spot size).

The spectra were fitted with one or more Voigt profiles (binding

energy uncertainty: ± 0.2 eV). The analyzer transmission function,

Scofield sensitivity factors37, and effective attenuation lengths (EALs)

for photoelectrons were applied for quantification. EALs were

calculated using the standard TPP-2M formalism.38 All spectra were

referenced to the C 1s peak of hydrocarbon at 285.0 eV binding energy

controlled by means of the well-known photoelectron peaks of

metallic Cu, Ag, and Au.

Dialysis was performed in methanol and water using Biotech CE

Tubing (MWCO: 100–500 D, 3.1 mL cm–1, Spectrumlabs) and Biotech

RC Tubing (MWCO: 8–10 kD, 3.3 mL cm–1, Spectrumlabs),

respectively. The membrane was washed for 15 min in water before

use to remove the sodium azide solution.

Polymer films were prepared on Si-wafers by evaporation of water

from the aqueous dispersions at 50 °C in vacuo.

Chapter 6

102

6.2.3 Syntheses

Poly(ethoxyethyl glycidyl ether) (P(EEGE)) and polyglycidol (PG) (1)

were synthesized according to literature.39 The results of the chemical

analyses for PG27 are summarized in Figure A.4.1–A.4.3 of appendix

A.4.

Synthesis of poly(glycidyl phenyl carbonate) P(GPC)27 (2)

Polyglycidol (PG27) (1) (2.018 g, 27.24 mmol OH) was dissolved in

pyridine (18.87 mL) and a solution of phenyl chloroformate (4.692 g,

29.97 mmol) in dichloromethane (17.50 mL) was added in 30 min at

0 °C using a syringe pump. The reaction mixture was allowed to warm

to room temperature and stirred for 20 h. The precipitate was removed

by filtration. The solution was washed with water (15 mL), 1 M HCl

solution (aq.) (3 · 15 mL), and sat. NaCl solution (aq.). The organic

phase was dried over Na2SO4, filtrated and the solvent removed under

reduced pressure. Precipitation in methanol gave P(GPC)27 (2) as a

brown viscous liquid (3.629 g, 69%). Mn, NMR = 5243 g mol–1, Mn, SEC =

4400 g mol–1, Ð = 1.15. 1H NMR (400 MHz, CDCl3) (2): δ = 1.82–

1.92 (m, ArCH2CH2), 2.66 (t, 2H, 3JHH = 7.7 Hz ArCH2CH2), 3.48–

3.93 (m, ArCH2CH2CH2, OCH2CH(CH2OC=OOPh)O), 4.15–4.48

(m, OCH2CH(CH2OC=OOPh)O), 7.05–7.39 (m, ArCH2CH2,

(OC=OOPh)O) ppm. 13C NMR (101 MHz, CDCl3) (2): δ = 31.2

(ArCH2CH2), 32.3 (ArCH2CH2), 67.7‒ 69.4 ArCH2CH2CH2, OCH2-

CH(CH2OC=OOPh)O), 77.4 (OCH2CH(CH2OC=OOPh)O), 121.0

(OC=OOPh)O), 126.1 (Ar, OC=OOPh)O), 128.4 (Ar), 128.5 (Ar),

129.6 (OC=OOPh)O), 141.8 (Ar), 151.1 (OC=OOPh)O), 153.6

(OC=OOPh)O) ppm.

Synthesis of poly(3-(dimethylamino)-1-propyl glycidyl carbamate) P(GDMAPA)27 (3)

P(GPC)27 (2) (1.422 g, 7.32 mmol carbonate) was dissolved in tetra-

hydrofuran (18.0 mL) and a solution of 3-(dimethylamino)-1-propyl-

amine (DMAPA) (0.436 g, 4.27 mmol) in tetrahydrofuran (10.0 mL)

was added in 1 h at 0 °C using a syringe pump. The reaction was

allowed to warm to room temperature and stirred for 42 h. The solvent

was removed under reduced pressure and the polymer purified by

dialysis in methanol. P(GDMAPA)27 (3) was obtained as a slightly yellow,

Chapter 6

103

viscous liquid (1.194 g, 81%) Mn, NMR = 5461 g mol–1, Mn, SEC =

6200 g mol–1, Ð = 1.21. 1H NMR (400 MHz, CDCl3) (3): δ = 1.51–

1.67 (m, NHCH2CH2CH2N(CH3)2), 1.77–1.86 (m, ArCH2CH2), 2.14

(s, NHCH2CH2CH2N(CH3)2), 2.25 (t, 2H, 3JHH = 7.0 Hz, NHCH2CH2-

CH2N(CH3)2), 2.60 (t, 3JHH = 7.6 Hz, ArCH2CH2), 3.04–3.19 (m,

NHCH2CH2CH2N(CH3)2), 3.46–3.70 (m, ArCH2CH2CH2, OCH2CH-

(CH2OC=ONHR)O), 3.88–4.27 (m, OCH2CH(CH2OC=ONHR)O),

5.83–6.34 (m, NH), 7.06–7.24 (m, ArCH2CH2) ppm. 13C NMR

(101 MHz, CDCl3) (3): δ = 27.5 (NHCH2CH2CH2N(CH3)2, 31.2

(ArCH2CH2), 32.2 (ArCH2CH2), 39.7 (NHCH2CH2CH2N(CH3)2),

45.4 (NHCH2CH2CH2N(CH3)2), 57.5 (NHCH2CH2CH2N(CH3)2),

64.3‒ 69.9 (ArCH2CH2CH2, OCH2CH(CH2OC=ONHR)O), 77.9

(OCH2CH(CH2OC=ONHR)O), 125.8 (Ar), 128.3 (Ar), 128.5 (Ar),

141.9 (Ar), 156.7 (OCH2CH(CH2OC=ONHR)O) ppm. FTIR (3):

υmax = 3322 (w), 2923 (m), 2853 (m), 2816 (w), 2765 (w), 1690 (s), 1537

(m), 1461 (m), 1255 (s), 1138 (m), 1039 (m), 849 (w), 780 (w) cm–1.

Light-promoted cross-linking of P(GDMAPA)27 (3)

P(GDMAPA)27 (3) (0.336 g, 1.66 mmol ―NMe2) was dissolved in N,N-

dimethylformamide (12 mL) and camphorquinone (0.276 g,

1.66 mmol) was added. The mixture was irradiated for 20 h with a

25 W solarium lamp emitting light at 400–500 nm at room

temperature. The polymer was purified by dialysis in methanol

followed by dialysis in water. The cross-linked product [P(GDMAPA)27]X

(4) was obtained as an opaque, aqueous dispersion. FTIR (4): υmax =

3324 (w), 2926 (m), 2854 (m), 1699 (s), 1535 (m), 1461 (m), 1251 (s),

1117 (m), 1076 (m), 836 (w), 780 (w) cm–1.

Quaternization of [P(GDMAPA)27]X (4) with MeI

Methyl iodide (0.026 g, 0.178 mmol) was added to an aqueous disper-

sion of 5 (4.5 mg mL–1, 22 µmol mL–1 ―NR3) and the mixture was

stirred for 24 h at 40 °C. The product was purified by dialysis in water.

[P(GTMAPA)27]X (5) (TMAPA: 3-(trimethylamino)-1-propylamine) was

obtained as an opaque, aqueous dispersion.

Chapter 6

104

Quaternization of [P(GDMAPA)27]X (4) with 1-iodooctane

Without the purification step a solution of [P(GDMAPA)27]X (4) in DMF

(28 mg mL–1, 138 µmol mL–1 ―NR3) was reacted with 1-iodooctane

(0.199 g, 0.830 mmol) for 20 h at 100 °C. The polymer was purified by

dialysis in methanol followed by dialysis in water. [P(GODMAPA)27]X (6)

(ODMAPA: 3-(octyldimethylamino)-1-propylamine) was obtained as

an opaque, aqueous dispersion.

Quaternization of [P(GDMAPA)27]X (4) with 1-iodo-3,6,9-trioxadecane

Without the purification step a solution of [P(GDMAPA)27]X (4) in DMF

(28 mg mL–1, 138 µmol mL–1 ―NR3) was reacted with 1-iodo-3,6,9-

trioxadecane (0.228 g, 0.830 mmol) for 20 h at 100 °C. The polymer

was purified by dialysis in methanol followed by dialysis in water.

[P(GPDMAPA)27]X (7) (PDMAPA: 3-(PEG-dimethylamino)-1-propyl-

amine) was obtained as an opaque, aqueous dispersion.

Quaternization of [P(GDMAPA)27]X (4) with 1H, 1H, 2H, 2H-heptadecafluoro-

decyl iodide

Without the purification step a solution of [P(GDMAPA)27]X (4) in DMF

(28 mg mL–1, 138 µmol mL–1 ―NR3) was reacted with 1H, 1H, 2H,

2H-heptadecafluorodecyl iodide (0.476 g, 0.830 mmol) for 20 h at

100 °C. The polymer was purified by dialysis in methanol followed by

dialysis in water. [P(GFDMAPA)27]X (8) (FDMAPA: fluorinated 3-

(dimethylamino)-1-propylamine) was obtained as an opaque, aqueous

dispersion.

6.3 Results and Discussion

In this chapter, a novel approach for the synthesis and characterization

of various, novel cationic/hydrophilic, cationic/hydrophobic and

cationic/superhydrophobic functionalized, cross-linked polyglycidols

is presented. The polyglycidol microgels are prepared by func-

tionalization of polyglycidol with phenyl chloroformate to have an

active ester unit that is subsequently reacted with 3-(dimethylamino)-

1-propylamine (DMAPA). The generated tertiary amine moieties are

cross-linked in a light-promoted reaction with CQ as photoinitiator

Chapter 6

105

and quaternized with various organoiodine compounds. The aqueous

dispersions and films are characterized.

6.3.1 Functionalization of polyglycidol (1) with DMAPA

Linear polyglycidol was prepared by anionic ring-opening

polymerization of ethoxyethyl glycidyl ether using 3-phenyl-1-propa-

nol as initiator and subsequent removal of the acetal protecting groups

under acidic conditions. A polyalcohol with 27 repeating units (PG27)

and Mn,SEC = 2500 g mol–1 was obtained with a narrow molecular

weight distribution (Ð = 1.13). The NMR and SEC analysis of PG27

(1) can be found in the supporting information (Fig. A.4.1–A.4.3,

appendix A.4).

Scheme 6.2: Synthetic pathway to P(GDMAPA)27 (3). (a) Functionalization of

PG27 (1) with phenyl chloroformate, pyridine/DCM, rt, 20 h. (b) Reaction of

P(GPC)27 (2) with 3-(dimethylamino)-1-propylamine, THF, rt, 42 h.

Afterwards, PG27 (1) was reacted with an excess of phenyl chloro-

formate in pyridine/DCM at room temperature. The synthesized

poly(glycidyl phenyl carbonate) (P(GPC)27) (2) was washed with water,

1 M HCl solution (aq.), and saturated NaCl solution (aq.) to remove

excess pyridine and pyridine hydrochloride and purified by

precipitation in methanol (Scheme 6.2a). The successful function-

alization was confirmed by 1H, 13C NMR spectroscopy (Fig. A.4.4–

A.4.5, appendix A.4) , and SEC analysis (Fig. A.4.7, appendix A.4).

P(GPC)27 (2) was reacted with DMAPA in THF at room temperature

(Scheme 6.2b). The prepared poly(3-(dimethylamino)-1-propyl

glycidyl carbamate), P(GDMAPA)27 (3) was purified by dialysis in

methanol and characterized by 1H, 13C NMR spectroscopy, FTIR

spectroscopy, and SEC analysis.

Chapter 6

106

P(GDMAPA)27 (3) shows characteristic signals of the introduced 3-

(dimethylamino)-1-propyl groups in the 1H and 13C NMR spectra

measured in CDCl3. In the 1H NMR spectrum (Fig. 6.1) the distinctive

signals are shown as two multiplets at δ = 1.51–1.67 ppm (Signal 11)

and δ = 3.04–3.19 ppm (Signal 10), a singlet at δ = 2.14 ppm (Signal

13) and a triplet at δ = 2.25 ppm (Signal 12). A multiplet at δ = 3.88–

4.27 ppm (Signal 9) shows the characteristic signal of the methylene

groups of the glycidol repeating unit adjacent to the carbamate

moieties. In the 13C NMR the 3-(dimethylamino)-1-propyl groups are

distinguished by signals at δ = 27.5 (Signal 13), 39.7 (Signal 12), 45.4

(Signal 15) and 57.5 (Signal 14) ppm (Fig. A.4.6, appendix A.4).

Additionally, the specific signal of the carbamate groups is found at

δ = 156.7 ppm (Signal 11).

Figure 6.1: 1H NMR spectrum of P(GDMAPA)27 (3) measured in CDCl3.

The number of DMAPA groups attached to PG27 (1) was calculated

by comparing the signal intensity of the phenyl group of the 3-phenyl-

1-propanol (Fig. 6.1, Signal 1–3) used in the synthesis of 1 with signal

11 of P(GDMAPA)27 (3). The absolute molecular weight (Mn,NMR) was

calculated likewise using the 3-phenyl-1-propyl end group as an

internal reference.

FTIR spectra of P(GDMAPA)27 (3) exhibit characteristic absorption

bands of the 3-(dimethylamino)-1-propyl groups.40 The symmetric

C―H stretching vibrations of the methyl groups of the tertiary amine

give two weak bands at 2816 and 2765 cm–1. Additionally, two strong

bands are found at 1690 and 1537 cm–1, which are distinctive for

carbamate moieties (Fig. 6.2a).

Chapter 6

107

SEC analysis using DMF as eluent confirms the synthesis of

P(GDMAPA)27 (3) with Mn,SEC = 6200 g mol–1 and a narrow molecular

weight distribution of Ð = 1.21 (Fig. A.4.8, appendix A.4).

Figure 6.2: FTIR spectra of P(GDMAPA)27 (3) (a) and [P(GDMAPA)27]X (4) (b).

6.3.2 Light-promoted cross-linking of P(GDMAPA)27 (3)

The cross-linking of P(GDMAPA)27 (3) was performed in a light-

promoted reaction in DMF using CQ as Norrish Type II photoiniator

and a 25 W solarium lamp (λ = 400–500 nm) as the light source

(Scheme 6.3a). Light-induced activation of the CQ leads to the

formation of triplet state CQ (3CO*) that abstracts hydrogen from the

methyl groups of the tertiary amine.41 Intermolecular recombination

of the aminoalkyl radicals leads to the cross-linked product

[P(GDMAPA)27]X (4). Although hydrogen abstraction from the polyether

groups present in the structure is also possible, its occurrence is less

likely due to the steric effect and higher reaction rates of the tertiary

amine groups. However, even if the hydrogen abstraction from the

polyether groups would happen, coupling would essentially yield the

same networked structure. [P(GDMAPA)27]X (4) was purified by dialysis

in methanol to remove the remaining CQ and its coupling products.

Chapter 6

108

Complete removal of the photoinitiator was monitored by UV/VIS

spectroscopy (Fig. A.4.9, appendix A.4). The cross-linked polymer was

subsequently dialyzed in water to exchange the solvent, yielding an

opaque dispersion showing a Tyndall effect. Polymer particles were

stable in dispersion. However, upon drying coalescence of the particles

leads to the vanishing of the particle structure and a non-redispersable,

solid coating. [P(GDMAPA)27]X (4) was characterized by FTIR spec-

troscopy, dynamic light scattering, DSC and XPS.

Scheme 6.3: Synthesis of cross-linked, cationic polyglycidols (5–8). (a) Cross-

linking of P(GDMAPA)27 (3) with camphorquinone, hυ, DMF, rt, 20 h. (b)

Quaternization of [P(GDMAPA)27]X (4) with MeI, H2O, 40 °C, 24 h, or

quaternization of [P(GDMAPA)27]X (4) with 1-iodooctane/1-iodo-3,6,9-trioxa-

decane/1H, 1H, 2H, 2H-heptadecafluorodecyl iodide, DMF, 100 °C, 20 h.

FTIR spectroscopy confirms the successful cross-linking of

P(GDMAPA)27 (3) by absence of the distinctive absorption bands of the

methyl functionalized tertiary amines at 2816 and 2765 cm–1 (Fig.

6.2b). No other difference in the absorption bands is observed

(compare Fig. 6.2a and Fig. 6.2b).

Microgel 4 was analyzed by DLS. A hydrodynamic radius of Rh =

198.8 ± 14.4 nm with a PDI of 0.443 ± 0.061 was found. Additionally,

a zeta potential of 14.0 ± 2.9 mV (Table 6.1, entry 1) indicated a

growing stability of the aqueous dispersion.

The successful cross-linking of P(GDMAPA)27 (3) is further confirmed

by DSC measurements. In general cross-linking of a polymer restricts

the chain mobility, leading to an increase in the glass transition

Chapter 6

109

temperature.42 For polymer 3 and microgel 4 an increase from Tg =

-7.7 °C to Tg = 70.8 °C was observed. DSC curves are found in the

supporting information (Fig. A.4.10a/b, appendix A.4).

Table 6.1: Hydrodynamic radii (Rh), polydispersity indices (PDI), zeta

potentials and glass transition temperatures (Tg) of P(GDMAPA)27 (3),

[P(GDMAPA)27]X (4), [P(GTMAPA)27]X (5), [P(GODMAPA)27]X (6), [P(GPDMAPA)27]X

(7), [P(GFDMAPA)27]X (8).

Entry Polymer Rh

[nm]

PDI Zeta

potential

[mV]

Tg

[°C]

1 [P(GDMAPA)27]X

(4)

198.8 ±

14.4

0.443 ±

0.061

14.0 ±

2.9

70.8

2 [P(GTMAPA)27]X

(5)

268.2 ±

15.9

0.365 ±

0.149

37.0 ±

2.7

120.0

3 [P(GODMAPA)27]X

(6)

77.9 ±

0.7

0.443 ±

0.029

36.3 ±

3.5

79.6

4 [P(GPDMAPA)27]X

(7)

330.1 ±

11.5

0.513 ±

0.098

42.1 ±

1.9

49.7

5 [P(GFDMAPA)27]X

(8)

243.1 ±

25.1

0.144 ±

0.103

39.0 ±

5.2

95.0

6.3.3 Quaternization of [P(GDMAPA)27]X (4)

[P(GDMAPA)27]X (4) was quaternized with various organoiodine

compounds to prepare cationic/hydrophilic, cationic/hydrophobic

and cationic/superhydrophobic microgels (Scheme 6.3b). The quater-

nization with methyl iodide was performed in an aqueous dispersion

of [P(GDMAPA)27]X (4) at 40 °C for 24 h. Purification by dialysis in water

gave [P(GTMAPA)27]X (5) as an opaque, aqueous dispersion. Quarter-

nization of [P(GDMAPA)27]X (4) with 1-iodooctane, 1-iodo-3,6,9-trioxa-

decane and 1H, 1H, 2H, 2H-heptadecafluorodecyl iodide was

performed in DMF at 100 °C for 20 h. Due to the low solubility of the

organoiodine compounds and the low reaction rates the quaternization

was not possible in water. Purification by dialysis in methanol,

followed by a solvent exchange by dialysis in water gave

[P(GODMAPA)27]X (6), [P(GPDMAPA)27]X (7) and [P(GFDMAPA)27]X (8) as

Chapter 6

110

opaque, aqueous dispersions. The quaternized polymer dispersions

were characterized by DLS, DSC and XPS measurements.

DLS measurements of the aqueous polymer dispersions show

differences in the hydrodynamic radius and PDI dependent on the

quaternization agent, compared to the non-quaternized starting

material. [P(GTMAPA)27]X (5) exhibits an increase in the hydrodynamic

radius to Rh = 268.2 ± 15.9 nm with a PDI of 0.365 ± 0.149 (Table

6.1, entry 2). Quaternization with octyl iodide leads to more compact

particles with Rh = 77.9 ± 0.7 nm and no change in the polydispersity

of the particles (Table 6.1, entry 3). For [P(GPDMAPA)27]X (7) Rh

increases to 330.1 ± 11.5 nm with a PDI of 0.513 ± 0.098 (Table 6.1,

entry 4). [P(GFDMAPA)27]X (8) shows an increased hydrodynamic radius

of Rh = 243.1 ± 25.1 nm. The PDI decreases to 0.144 ± 0.103,

indicating collapsed fluorinated side chains and the formation of more

uniform particles (Table 6.1, entry 5). The zeta potential increases to

~40 mV for all samples, confirming the successful quaternization.

Additionally, the introduction of cationic charges and thus,

intermolecular repulsive forces leads to a higher stability of the

polymer dispersions.

The quaternization of [P(GDMAPA)27]X (4) and ammonium salt

formation causes the modification of the glass transition temperature

of the cross-linked polymers 5, 6, 7 and 8. Quaternization with methyl

iodide causes an increase from Tg = 70.8 °C to Tg = 120 °C. The

introduction of octyl groups leads to a slight increase of the glass

transition temperature to Tg = 79.6 °C. Functionalization with

poly(ethylene glycol) moieties decreases Tg to 49.7 °C, due to the high

chain mobility of the PEG side groups. Quaternization with 1H, 1H,

2H, 2H-heptadecafluorodecyl iodide leads to a higher glass transition

temperature of Tg = 95.0 °C (Fig. A.4.10c–f, appendix A.4).

In-depth chemical characterization of the [P(GDMAPA)27]X (4),

[P(GTMAPA)27]X (5), [P(GODMAPA)27]X (6) and [P(GPDMAPA)27]X (7) and

[P(GFDMAPA)27]X (8) was performed by XPS (Fig. 6.3 and Fig. A.4.11,

appendix A4). The C 1s region of polymers 4–8 shows a dominant

signal for the C―O bonds of the polyether backbone at 286.4 eV

which in this particular case cannot be distinguished from C―N bonds

of the tertiary amine.43 Additionally, the carbamate moieties show a

distinctive C 1s peak at 289.5 eV for the O―(O═C)―N group.44,45

Chapter 6

111

Figure 6.3: High-resolution XPS spectra of the C 1s region (top left), the O 1s

region (top right), the N 1s region (bottom left), and the I 3d5/2 region (bottom

right) of P[(GDMAPA)27]X (4), P[(GTMAPA)27]X (5), P[(GODMAPA)27]X (6),

P[(GPDMAPA)27]X (7), and P[(GFDMAPA)27]X (8).

Chapter 6

112

In good agreement with literature the corresponding O 1s peaks at

532.1 eV (C═O groups) and 533.1 eV (C―O groups) corroborate

these assignments.43,45 However, the very weak peak at C 1s =

287.8 eV which usually is attributed to C═O and O―C―O groups

cannot be assigned unambiguously, but might be due to contamination

residues. The N 1s region of all cross-linked polymers show the C―N

bond of the carbamate group at 400.0 eV. The quaternized polymers,

moreover, reveal an additional peak at 402.5 eV for the NR4+ bond,

clearly evidencing the successful functionalization of [P(GDMAPA)27]X

(4).46 These findings are supported by the corresponding I 3d5/2 =

618.5 eV peak stemming from the I--counterion of the ammonium

groups in polymers 4–8. Finally, [P(GFDMAPA)27]X (8) exhibits a C 1s

peak at 292.0 eV and the corresponding F 1s = 689.2 eV peak assigned

to the CF2―CF2 group, additionally proving the successful func-

tionalization of [P(GDMAPA)27]X (4).47

6.4 Conclusions

In this chapter, a synthetic strategy to functionalize polyglycidol after

cross-linking was developed. First, linear polyglycidol was func-

tionalized with pendant tertiary amine groups at every repeating unit.

The successful functionalization was confirmed by 1H NMR, 13C

NMR spectroscopy, and SEC analysis. Polyglycidol was cross-linked

at the methyl groups of the tertiary amines in a light-induced reaction

using CQ as a photoinitiator. The cross-linked polymer was further

quaternized by reaction with four different organoiodine compounds

to obtain cationic/hydrophobic, cationic/hydrophilic and cationic/

superhydrophobic polyether particles. Aqueous dispersions of all

polyglycidols were evaluated by DLS and zeta potential measurements.

Polymer films were further evaluated by DSC and XPS. All analytical

methods confirm the successful cross-linking of the functional

polyglycidol and post-cross-linking modification. The simple strategy described here can be extended to other

polyglycidols and functional groups with the purpose of tuning the

hydrophilic to hydrophobic balance for specific bio applications.

Further studies in this line are now in progress.

Chapter 6

113

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47. Vesel, A.; Mozetic, M.; Zalar, A. XPS characterization of

PTFE after treatment with rf oxygen and nitrogen plasma.

Surf. Interface Anal. 2008, 40, 661.

Chapter 7

119

Chapter 7

Summary

In this work, various functionalities have been introduced to the

polyglycidol backbone. First, a synthetic strategy for the preparation

of polyglycidols with pendant phosphate groups by reaction of the

hydroxymethyl side groups with diethyl chlorophosphate has been

developed. The successful synthesis was confirmed by 1H, 13C, 31P

{1H} NMR spectroscopy, FTIR spectroscopy, and SEC analysis.

Diethyl phosphate groups were subsequently (mono-)dealkylated by

reaction with sodium iodide or bromotrimethylsilane, respectively.

The reaction protocol allows the tailoring of pendant phosphate/

phosphoric acid groups introduced into polyglycidol.

Secondly, various novel cationic/hydrophobic functionalized

polyglycidols were successfully synthesized. A polyglycidol with

statistically distributed cationic and hydrophobic groups (cationic to

hydrophobic ratio of 1:1), a polyglycidol with a hydrophilic modifica-

tion at the cationic moieties, a polyglycidol with cationic and hydro-

phobic functionalities at every repeating unit, and a polyglycidol with

a cationic to hydrophobic balance of 1:2 were characterized by 1H

NMR, 13C NMR spectroscopy, and SEC analyses and evaluated in

regard to their antibacterial activity. Antibacterial polyglycidols with

statistic distribution of cationic and hydrophobic residues are equally

active against a Gram-negative and a Gram-positive bacterial strain.

The best efficacy against both bacterial strains resulted from

Chapter 7

120

polyglycidol with statistic distribution of the cationic and hydrophobic

groups (cationic to hydrophobic ratio of 1:1). If cationic and hydro-

phobic residues are located in the same repeating unit connected by a

spacer, the impact on the cell envelope of S. aureus is significantly less

effective than against E. coli. Changing the cationic to hydrophobic

balance to a higher hydrophobic content in amphipathic polyglycidol

with statistically distributed cationic and hydrophobic residues leads to

a decrease in efficacy against both bacterial strains.

Thirdly, the usage of bio-based building blocks in the synthesis of

functional polyglycidols was investigated. Linear polyglycidol was

functionalized with homoserine lactone in a two-step reaction. The

successful synthesis was confirmed by 1H, 13C NMR spectroscopy, and

SEC analysis. Homoserine lactone groups were subsequently opened

by addition of 3-(dimethylamino)-1-propylamine and the tertiary

amine was quaternized with methyl iodide.

In the last chapter, the concept of post-cross-linking functionalization

of polyglycidol has been presented. Therefore, linear polyglycidol was

functionalized with pendant tertiary amine groups at every repeating

unit in a two-step reaction. The successful functionalization was

confirmed by 1H NMR, 13C NMR spectroscopy, and SEC analysis.

Polyglycidol was cross-linked at the methyl groups of the tertiary

amines in a UV-light-mediated reaction with camphorquinone as a

Type II photoinitiator. The cross-linked polymer was quaternized by

reaction with four different organoiodine compounds to obtain

cationic/hydrophobic, cationic/hydrophilic and cationic/superhydro-

phobic polyether particles. Aqueous dispersions of all polyglycidols

were evaluated by DLS and zeta potential measurements. Polymer

films were further evaluated concerning their thermal properties by

DSC and their chemical structure by XPS. All analytical methods

confirm the successful cross-linking of the functional polyglycidol and

the subsequent post-cross-linking modification.

Appendix A

121

Appendix A

Additional Information

A.1 Phosphate Functionalized Polyglycidols

A.1.1 Synthesis of polyglycidol, PG24

Figure A.1.1: 1H NMR spectrum of PG24 (2) measured in DMSO-d6.

Figure A.1.2: 13C NMR spectrum of PG24 (2) measured in DMSO-d6.

Appendix A

122

Figure A.1.3: DMF-SEC traces of PG24 (2)

A.1.2 Synthesis of poly(glycidyl diethyl phosphate-co-glycidol) (P(GDEP-co-G))

(3a–d)

Table A.1.1: Synthesis of linear P(GDEP-co-G) (3a–d) (t = 20 h, T = rt):

Reagent ratios and yields after dialysis in MeOH.

Polymer PG

[mmol

OH]

DECP

[mmol]

4-DMAP

[mmol]

Pyridine

[mmol]

Yield a

[%]

3a 23.53 5.88 2.35 202.36 23

3b 23.46 11.73 2.35 201.76 41

3c 20.09 15.07 2.01 172.77 38

3d 13.16 13.16 1.32 113.18 27

a Yield obtained after purification by dialysis in MeOH for two days.

Appendix A

123

A.1.3 Synthesis of poly(glycidyl ethyl phosphate-co-glycidol) (P(GEP-co-G))

(4a–d)

Table A.1.2: Synthesis of linear P(GEP-co-G) (4a–d) (t = 48 h, T = 130 °C):

Reagent ratios and yields.

Polymer P(GEP-co-G)

[mmol DEP]

NaI

[mmol]

2-Hexanone

[mL]

Yield

[%]

4a 0.24 0.29 20 99

4b 0.45 0.54 20 100

4c 0.83 0.99 20 97

4d 0.15 0.18 20 97

Figure A.1.4: 13C NMR spectrum of P(GEP22-co-G8) (4c) measured in D2O.

Figure A.1.5: 31P NMR spectrum of P(GEP22-co-G8) (4c) measured in D2O.

Appendix A

124

A.1.4 SEC trace of higher molecular weight polyglycidol (PG100) and its

phosphate functionalized equivalent (P(GDEP50-co-G50)

Figure A.1.6: DMF-SEC traces of PG100 (black) and P(GDEP50-co-G50) (red).

A.1.5 Titration curve of P(GP22-co-G8) (5c)

Figure A.1.7: Titration curve of P(GP22-co-G8) (5c).

Appendix A

125

A.1.6 Synthesis of poly(glycidyl ethyl phosphate-co-glycidol) (P(GP-co-G))

(5a–d)

Table A.1.3: Synthesis of linear P(GP-co-G) (5a–d) (t = 17 h, T = rt): Reagent

ratios and yields.

Polymer P(GP-co-G)

[mmol DEP]

TMSBr

[mmol]

DCM

[mL]

Yield

[%]

5a 0.43 1.72 10 92

5b 3.06 12.23 35 81

5c 1.73 6.92 20 91

5d 0.33 1.32 5.0 94

Figure A.1.8: 13C NMR spectrum of P(GP22-co-G8) (5c) measured in D2O.

Figure A.1.9: 31P NMR spectrum of P(GP22-co-G8) (5c) measured in D2O.

Appendix A

126

A.1.7 IR Analysis

Figure A.1.10: FTIR analysis of P(GDEP22-co-G8) (3c) (blue), P(GEP

22-co-G8)

(4c) (red) and P(GP22-co-G8) (5c) (black).

A.2 Antibacterial Polyglycidols

A.2.1 Synthesis of linear polyglycidol (1)

Figure A.2.1: 1H NMR spectrum of PG27 (1) measured in DMSO-d6.

Appendix A

127

Figure A.2.2: 13C NMR spectrum of PG27 (1) measured in DMSO-d6.

Figure A2.3: DMF-SEC traces of PG27 (1).

Appendix A

128

A.2.2 Synthesis of P(GTMAPA15-co-GDDA

12) (5) and P(GAPDEMA16-co-

GDDA11) (6)

Figure A.2.4: 1H NMR spectrum of P(GPC)27 (2) measured in CDCl3.

Figure A.2.5: 13C NMR spectrum of P(GPC)27 (2) measured in CDCl3.

Figure A.2.6: 1H NMR spectrum of P(GDMAPA15-co-GDDA

12) (3) measured in

CDCl3.

Appendix A

129

Figure A.2.7: 13C NMR spectrum of P(GDMAPA15-co-GDDA

12) (3) in CDCl3.

Figure A.2.8: 1H NMR spectrum of P(GAPDEA16-co-GDDA

11) (4) in MeOD.

Figure A.2.9: 13C NMR spectrum of P(GAPDEA16-co-GDDA

11) (4) in MeOD.

Appendix A

130

Figure A.2.10: 13C NMR spectrum of P(GTMAPA15-co-GDDA

12) (5) measured in

DMSO-d6.

Figure A.2.11: 13C NMR spectrum of P(GAPDEMA16-co-GDDA

11) (6) measured

in MeOD.

Appendix A

131

Figure A.2.12: DMF-SEC traces of P(GPC)27 (2).

Figure A.2.13: DMF-SEC traces of P(GDMAPA15-co-GDDA

12) (3).

Appendix A

132

Figure A.2.14: DMF-SEC traces of P(GAPDEA16-co-GDDA

11) (4).

Figure A.2.15: DMF-SEC traces of P(GTMAPA15-co-GDDA

12) (5).

Appendix A

133

A.2.3 Synthesis of P(GDDAc, q)27 (10)

Figure A.2.16: 1H NMR spectrum of P(GNPC)27 (7) measured in DMSO-d6.

Figure A.2.17: 13C NMR spectrum of P(GNPC)27 (7) measured in DMSO-d6.

Figure A.2.18: 1H NMR spectrum of P(GHCTL)27 (8) measured in DMSO-d6.

Appendix A

134

Figure A.2.19: 13C NMR spectrum of P(GHCTL)27 (8) measured in DMSO-d6.

Figure A.2.20: 1H NMR spectrum of P(GDDAc)27 (9) measured in CDCl3.

Figure A.2.21: 13C NMR spectrum of P(GDDAc)27 (9) measured in CDCl3.

Appendix A

135

Figure A.2.22: 13C NMR spectrum of P(GDDAc, q)27 (10) measured in CDCl3.

Figure A.2.23: DMF-SEC traces of P(GNPC)27 (7).

Appendix A

136

Figure A.2.24: DMF-SEC traces of P(GHCTL)27 (8).

Figure A.2.25: DMF-SEC traces of P(GDDAc)27 (9).

Appendix A

137

Figure A.2.26: DMF-SEC traces of P(GDDAc, q)27 (10).

A.2.4 Synthesis of P(GTMAPA14-co-GDDADDAc

13) (12)

Figure A.2.27: 1H NMR spectrum of P(GDMAPA14-co-GDDADDAc

13) (11)

measured in CDCl3/acetone-d6.

Appendix A

138

Figure A.2.28: 13C NMR spectrum of P(GDMAPA14-co-GDDADDAc

13) (11)

measured in CDCl3/acetone-d6.

Figure A.2.29: 13C NMR spectrum of P(GTMAPA14-co-GDDADDAc

13) (12)

measured in CDCl3/acetone-d6.

Appendix A

139

Figure A.2.30: DMF-SEC traces of P(GDMAPA14-co-GDDADDAc

13) (11).

Figure A.2.31: DMF-SEC traces of P(GTMAPA14-co-GDDADDAc

13) (12).

Appendix A

140

A.3 Homoserine Lactone Functionalized Polyglycidol

A.3.1 Synthesis of PG26 (1)

Figure A.3.1: 1H NMR spectrum of PG26 (1) measured in DMSO-d6.

Figure A.3.2: 13C NMR spectrum of PG26 (1) measured in DMSO-d6.

Figure A.3.3: DMF-SEC traces of PG26 (1).

Appendix A

141

A.3.2 Functionalization of polyglycidol (1) with DL-homoserine lactone

hydrobromide

Figure A.3.4: 1H NMR spectrum of P(GNPC)26 (2) measured in DMSO-d6.

Figure A.3.5 13C NMR spectrum of P(GNPC)26 (2) measured in DMSO-d6.

Figure A.3.6: 13C NMR spectrum of P(GHSL)26 (3) measured in DMF-d7.

Appendix A

142

Figure A.3.7: DMF-SEC traces of P(GNPC)26 (2).

Figure A.3.8: DMF-SEC traces of P(GHSL)26 (3).

Appendix A

143

A.3.3 Ring-opening of P(GHSL)26 (3)

Figure A.3.9: 1H NMR spectrum of P(GHSL,o)26 (4) measured in DMSO-d6.

Figure A.3.10: 13C NMR spectrum of P(GHSL,o)26 (4) measured in DMSO-d6.

Appendix A

144

Figure A.3.11: DMF-SEC traces of P(GHSL,o)26 (4).

A.3.4 Quaternization of P(GHSL,o)26 (4)

Figure A.3.12: 1H NMR spectrum of P(GHSL,o,q)26 (5) measured in D2O.

Appendix A

145

Figure A.3.13: 13C NMR spectrum of P(GHSL,o,q)26 (5) measured in D2O.

A.4 Post-cross-linking Modification

A.4.1 Synthesis of linear polyglycidol (1)

Figure A.4.1: 1H NMR spectrum of PG27 (1) measured in DMSO-d6.

Figure A.4.2: 13C NMR spectrum of PG27 (1) measured in DMSO-d6.

Appendix A

146

Figure A.4.3: DMF-SEC traces of PG27 (1).

A.4.2 Synthesis of P(GDMAPA)27 (3)

Figure A.4.4: 1H NMR spectrum of P(GPC)27 (2) measured in CDCl3.

Appendix A

147

Figure A.4.5: 13C NMR spectrum of P(GPC)27 (2) measured in CDCl3.

Figure A.4.6: 13C NMR spectrum of P(GDMAPA)27 (3) measured in CDCl3.

Figure A.4.7: DMF-SEC traces of P(GPC)27 (2).

Appendix A

148

Figure A.4.8: DMF-SEC traces of P(GDMAPA)27 (3).

A.4.3 Determination of camphorquinone concentration by UV/Vis

spectroscopy

Figure A.4.9: UV/Vis spectra of [P(GDMAPA)27]X (4) (black) after dialysis in

methanol and after addition of 1% of the amount of camphorquinone used

during the reaction (red).

Appendix A

149

A.4.4 DSC measurements

Figure A.4.10: DSC curves of the second heating cycle of P(GDMAPA)27 (3) (a),

P[(GDMAPA)27]X (4) (b), P[(GTMAPA)27]X (5) (c), P[(GODMAPA)27]X (6) (d),

P[(GPDMAPA)27]X (7) (e) and P[(GFDMAPA)27]X (8) (f).

Appendix A

150

A.4.5 F 1s XPS measurement

Figure A.4.11: High-resolution XPS spectra of the F 1s region of

P[(GDMAPA)27]X (4) and P[(GFDMAPA)27]X (8).

List of Abbreviations

151

List of Abbreviations

AGE allyl glycidyl ether

AIBN azobisisobutyronitrile

APDEA N-(3-aminopropyl)-diethanolamine

APDEMA N-(3-aminopropyl)-diethanolmethylammonium

ATRP atom transfer radical polymerization

CFU colony forming unit

Ð dispersity (Mw/Mn)

DCC N,N'-dicyclohexylcarbodiimide

DCM dichloromethane

DDA dodecylamine

DECP diethyl chlorophosphate

DEP diethyl phosphate

DLS dynamic light scattering

DMAP dimethylaminopyridine

DMF N,N-dimethylformamide

DMSO dimethylsulfoxide

DSC differential scanning calorimetry

E. coli Escherichia coli

EEGE ethoxyethyl glycidyl ether

EP ethyl phosphate

eq. equivalent(s)

FDA Food and Drug Administration

FDMAPA fluorinated 3-(dimethyl-amino)-1-propylamine

FTIR Fourier-transform infrared spectroscopy

HC hemolytic concentration

List of Abbreviations

152

HCTL homocysteine thiolactone

HSL homoserine lactone

J coupling constant

MHB Mueller-Hinton broth

MIC minimum inhibitory concentration

Mn number average molecular weight

NMR nuclear magnetic resonance (spectroscopy)

NPC 4-nitrophenyl carbonate

ODMAPA 3-(octyldimethylamino)-1-propylamine

P phosphate

PBS phosphate-buffered saline

PC phenyl carbonate

PDI polydispersity index

PDMAPA 3-(PEG-dimethylamino)-1-propylamine

PE polyethylene

PEG polyethylene glycol

PEI polyethylenimine

PET polyethylene terephthalate

PG polyglycidol

PP polypropylene

PS polystyrene

PVC polyvinyl chloride

RBC red blood cells

S. aureus Staphylococcus aureus

SEC size exclusion chromatography

tBuGE tert-butyl glycidyl ether

TCEP tris(2-carboxyethyl)phosphine

TGE tetrahydropyranyl glycidyl ether

THF tetrahydrofuran

TMAPA trimethylammoniumpropylamine

TX thioxanthones

UV ultraviolet

XPS X-ray photoelectron spectroscopy

δ chemical shift

List of Figures

153

List of Figures

Figure 3.1: 1H NMR (a), 13C NMR (b) and 31P {1H} NMR (c) spectra

of P(GDEP22-co-G8) (3c) measured in DMSO-d6. 40

Figure 3.2: DMF-SEC traces of P(GDEP22-co-G8) (3c) (black line) and

fractions separated by preparative SEC with THF as eluent (red and

blue dotted lines). 41

Figure 3.3: 1H NMR spectra of P(GEP22-co-G8) (4c) (top) and P(GP

22-

co-G8) (5c) (bottom) measured in D2O. 44

Figure 4.1: Comparison of various cationic–hydrophobic func-

tionalized polyglycidols in regard to their antibacterial activity against

E. coli and S. aureus to examine the structure–property relationship.

65

Figure 4.2: 1H NMR spectra of P(GTMAPA15-co-GDDA

12) (5) measured

in DMSO-d6 (a) and P(GAPDEMA16-co-GDDA

11) (6) measured in MeOD

(b). 68

Figure 4.3: 1H NMR spectra of P(GDDAc, q)27 (10) measured in CDCl3

(a) and P(GTMAPA14-co-GDDADDAc

13) (12) measured in CDCl3/acetone

(6:4) (b). 71

Figure 5.1: 1H NMR spectrum of P(GHSL)26 (3) measured in DMF-d7.

90

Figure 6.1: 1H NMR spectrum of P(GDMAPA)27 (3) measured in CDCl3.

106

List of Figures

154

Figure 6.2: FTIR spectra of P(GDMAPA)27 (3) (a) and [P(GDMAPA)27]X

(4) (b). 107

Figure 6.3: High-resolution XPS spectra of the C 1s region (top left),

the O 1s region (top right), the N 1s region (bottom left), and the

I 3d5/2 region (bottom right) of P[(GDMAPA)27]X (4), P[(GTMAPA)27]X (5),

P[(GODMAPA)27]X (6), P[(GPDMAPA)27]X (7), and P[(GFDMAPA)27]X (8).

111

Figure A.1.1: 1H NMR spectrum of PG24 (2) measured in DMSO-d6.

121

Figure A.1.2: 13C NMR spectrum of PG24 (2) measured in DMSO-d6.

121

Figure A.1.3: DMF-SEC traces of PG24 (2). 122

Figure A.1.4: 13C NMR spectrum of P(GEP22-co-G8) (4c) measured in

D2O. 123

Figure A.1.5: 31P NMR spectrum of P(GEP22-co-G8) (4c) measured in

D2O. 123

Figure A.1.6: DMF-SEC traces of PG100 (black) and P(GDEP50-co-G50)

(red). 124

Figure A.1.7: Titration curve of P(GP22-co-G8) (5c). 124

Figure A.1.8: 13C NMR spectrum of P(GP22-co-G8) (5c) measured in

D2O. 125

Figure A.1.9: 31P NMR spectrum of P(GP22-co-G8) (5c) measured in

D2O. 125

Figure A.1.10: FTIR analysis of P(GDEP22-co-G8) (3c) (blue), P(GEP

22-

co-G8) (4c) (red) and P(GP22-co-G8) (5c) (black). 126

Figure A.2.1: 1H NMR spectrum of PG27 (1) measured in DMSO-d6.

126

Figure A.2.2: 13C NMR spectrum of PG27 (1) measured in DMSO-d6.

127

Figure A2.3: DMF-SEC traces of PG27 (1). 127

List of Figures

155

Figure A.2.4: 1H NMR spectrum of P(GPC)27 (2) measured in CDCl3.

128

Figure A.2.5: 13C NMR spectrum of P(GPC)27 (2) measured in CDCl3.

128

Figure A.2.6: 1H NMR spectrum of P(GDMAPA15-co-GDDA

12) (3)

measured in CDCl3. 128

Figure A.2.7: 13C NMR spectrum of P(GDMAPA15-co-GDDA

12) (3) in

CDCl3. 129

Figure A.2.8: 1H NMR spectrum of P(GAPDEA16-co-GDDA

11) (4) in

MeOD. 129

Figure A.2.9: 13C NMR spectrum of P(GAPDEA16-co-GDDA

11) (4) in

MeOD. 129

Figure A.2.10: 13C NMR spectrum of P(GTMAPA15-co-GDDA

12) (5)

measured in DMSO-d6. 130

Figure A.2.11: 13C NMR spectrum of P(GAPDEMA16-co-GDDA

11) (6)

measured in MeOD. 130

Figure A.2.12: DMF-SEC traces of P(GPC)27 (2). 131

Figure A.2.13: DMF-SEC traces of P(GDMAPA15-co-GDDA

12) (3). 131

Figure A.2.14: DMF-SEC traces of P(GAPDEA16-co-GDDA

11) (4). 132

Figure A.2.15: DMF-SEC traces of P(GTMAPA15-co-GDDA

12) (5). 132

Figure A.2.16: 1H NMR spectrum of P(GNPC)27 (7) measured in

DMSO-d6. 133

Figure A.2.17: 13C NMR spectrum of P(GNPC)27 (7) measured in

DMSO-d6. 133

Figure A.2.18: 1H NMR spectrum of P(GHCTL)27 (8) measured in

DMSO-d6. 133

Figure A.2.19: 13C NMR spectrum of P(GHCTL)27 (8) measured in

DMSO-d6. 134

List of Figures

156

Figure A.2.20: 1H NMR spectrum of P(GDDAc)27 (9) measured in

CDCl3. 134

Figure A.2.21: 13C NMR spectrum of P(GDDAc)27 (9) measured in

CDCl3. 134

Figure A.2.22: 13C NMR spectrum of P(GDDAc, q)27 (10) measured in

CDCl3. 135

Figure A.2.23: DMF-SEC traces of P(GNPC)27 (7). 135

Figure A.2.24: DMF-SEC traces of P(GHCTL)27 (8). 136

Figure A.2.25: DMF-SEC traces of P(GDDAc)27 (9). 136

Figure A.2.26: DMF-SEC traces of P(GDDAc, q)27 (10). 137

Figure A.2.27: 1H NMR spectrum of P(GDMAPA14-co-GDDADDAc

13) (11)

measured in CDCl3/acetone-d6. 137

Figure A.2.28: 13C NMR spectrum of P(GDMAPA14-co-GDDADDAc

13) (11)

measured in CDCl3/acetone-d6. 138

Figure A.2.29: 13C NMR spectrum of P(GTMAPA14-co-GDDADDAc

13) (12)

measured in CDCl3/acetone-d6. 138

Figure A.2.30: DMF-SEC traces of P(GDMAPA14-co-GDDADDAc

13) (11).

139

Figure A.2.31: DMF-SEC traces of P(GTMAPA14-co-GDDADDAc

13) (12).

139

Figure A.3.1: 1H NMR spectrum of PG26 (1) measured in DMSO-d6.

140

Figure A.3.2: 13C NMR spectrum of PG26 (1) measured in DMSO-d6.

140

Figure A.3.3: DMF-SEC traces of PG26 (1). 140

Figure A.3.4: 1H NMR spectrum of P(GNPC)26 (2) measured in

DMSO-d6. 141

Figure A.3.5 13C NMR spectrum of P(GNPC)26 (2) measured in

DMSO-d6. 141

List of Figures

157

Figure A.3.6: 13C NMR spectrum of P(GHSL)26 (3) measured in DMF-

d7. 141

Figure A.3.7: DMF-SEC traces of P(GNPC)26 (2). 142

Figure A.3.8: DMF-SEC traces of P(GHSL)26 (3). 142

Figure A.3.9: 1H NMR spectrum of P(GHSL,o)26 (4) measured in

DMSO-d6. 143

Figure A.3.10: 13C NMR spectrum of P(GHSL,o)26 (4) measured in

DMSO-d6. 143

Figure A.3.11: DMF-SEC traces of P(GHSL,o)26 (4). 144

Figure A.3.12: 1H NMR spectrum of P(GHSL,o,q)26 (5) measured in

D2O. 144

Figure A.3.13: 13C NMR spectrum of P(GHSL,o,q)26 (5) measured in

D2O. 145

Figure A.4.1: 1H NMR spectrum of PG27 (1) measured in DMSO-d6.

145

Figure A.4.2: 13C NMR spectrum of PG27 (1) measured in DMSO-d6.

145

Figure A.4.3: DMF-SEC traces of PG27 (1). 146

Figure A.4.4: 1H NMR spectrum of P(GPC)27 (2) measured in CDCl3.

146

Figure A.4.5: 13C NMR spectrum of P(GPC)27 (2) measured in CDCl3.

147

Figure A.4.6: 13C NMR spectrum of P(GDMAPA)27 (3) measured in

CDCl3. 147

Figure A.4.7: DMF-SEC traces of P(GPC)27 (2). 147

Figure A.4.8: DMF-SEC traces of P(GDMAPA)27 (3). 148

Figure A.4.9: UV/Vis spectra of [P(GDMAPA)27]X (4) (black) after

dialysis in methanol and after addition of 1% of the amount of

camphorquinone used during the reaction (red). 148

List of Figures

158

Figure A.4.10: DSC curves of the second heating cycle of

P(GDMAPA)27 (3) (a), P[(GDMAPA)27]X (4) (b), P[(GTMAPA)27]X (5) (c),

P[(GODMAPA)27]X (6) (d), P[(GPDMAPA)27]X (7) (e) and P[(GFDMAPA)27]X

(8) (f). 149

Figure A.4.11: High-resolution XPS spectra of the F 1s region of

P[(GDMAPA)27]X (4) and P[(GFDMAPA)27]X (8). 150

List of Schemes

159

List of Schemes

Scheme 2.1: Synthesis of glycidol by (a) hydrolysis of epichlorohydrin,

(b) epoxidation of allyl alcohol, and (c) decarboxylation of glycerol

carbonate. 10

Scheme 2.2: Mechanism of the anionic ring-opening polymerization

of glycidol. 11

Scheme 2.3: Synthesis of branched polyglycidol with primary (blue)

and secondary (red) hydroxyl groups along the polymer chain. 12

Scheme 2.4: a) Protected glycidol monomers used in the

polymerization of polyglycidol. b) Synthesis of linear polyglycidol from

EEGE using potassium alkoxide as initiator. 13

Scheme 2.5: Cationic polymerization of glycidol by active chain-end

mechanism (top) and activated monomer mechanism (bottom). 14

Scheme 2.6: -End-functionalization of hyperbranched polyglycidol.

17

Scheme 2.7: Backbone functionalization of polyglycidol. 21

Scheme 3.1: Functionalization of linear polyglycidol with diethyl

chlorophosphate. 39

Scheme 3.2: Synthesis of poly(glycidyl ethyl phosphate-co-glycidol)

(4a–d). 43

Scheme 3.3: Synthesis of poly(glycidyl phosphate-co-glycidol) (5a–d)

by dealkylation of P(GDEP-co-G) (3a–d). 45

List of Schemes

160

Scheme 4.1: Synthetic pathway to P(GTMAPA15-co-GDDA

12) (5) and

P(GAPDEMA16-co-GDDA

11) (6). (a) Functionalization of PG27 (1) with

phenyl chloroformate, pyridine/DCM, rt, 20 h; (b) Reaction of

P(GPC)27 (2) with DDA and DMAPA/APDEA, THF, rt, 42 h; (c)

Quaternization of tertiary amines with methyl iodide, THF, rt, 20 h.

66

Scheme 4.2: Synthetic pathway to P(GDDAc, q)27 (10). (a)

Functionalization of PG27 (1) with 4-nitrophenyl chloroformate,

pyridine/DCM, rt, 20 h; (b) Reaction of P(GNPC)27 (7) with DL-

homocysteine thiolactone hydrochloride, 4-DMAP, Et3N, DMF, rt,

20 h; (c) Ring-opening reaction with DMAPA, followed by thiol-ene

reaction with dodecyl acrylate, CHCl3, rt, 20 h; (d) Quaternization of

tertiary amines with methyl iodide, THF, rt, 20 h. 70

Scheme 4.3: Synthetic pathway to P(GTMAPA14-co-GDDADDAc

13) (12). (a)

(I) Reaction of P(GNPC)27 (7) with DMAPA, DMF, rt, 20 h, (II)

Reaction with DL-homocysteine thiolactone hydrochloride, 4-DMAP,

Et3N, DMF, 20 h; (b) Ring-opening reaction with dodecylamine,

followed by thiol-ene reaction with dodecyl acrylate, CHCl3, rt, 20 h;

(c) Quaternization of tertiary amines with methyl iodide, THF, rt, 20 h.

73

Scheme 5.1: Strategies for the synthesis of glycerol carbonate and

glycidol from glycerol. 84

Scheme 5.2: Synthetic pathway to P(GHSL)26 (3). a) Functionalization

of PG26 (1) with 4-nitrophenyl chloroformate, pyridine/DCM, rt, 20 h.

b) Reaction of P(GNPC)26 (2) with DL-homoserine lactone

hydrobromide, 4-DMAP, Et3N, DMF, rt, 20 h. 89

Scheme 5.3: Synthetic pathway to P(GHSL,o,q)26 (5). a) Addition of

DMAPA to P(GHSL)26 (3), DMF, rt, 20 h. b) Quaternization of

P(GHSL,o)26 (4) with MeI, MeOH, reflux, 20 h. 91

Scheme 6.1: Photoinduced radical generation process by

camphorquinone in the presence of hydrogen donors. 99

Scheme 6.2: Synthetic pathway to P(GDMAPA)27 (3). (a) Func-

tionalization of PG27 (1) with phenyl chloroformate, pyridine/DCM,

List of Schemes

161

rt, 20 h. (b) Reaction of P(GPC)27 (2) with 3-(dimethylamino)-1-

propylamine, THF, rt, 42 h. 105

Scheme 6.3: Synthesis of cross-linked, cationic polyglycidols (5–8). (a)

Cross-linking of P(GDMAPA)27 (3) with camphorquinone, hυ, DMF, rt,

20 h. (b) Quaternization of [P(GDMAPA)27]X (4) with MeI, H2O, 40 °C,

24 h, or quaternization of [P(GDMAPA)27]X (4) with 1-iodooctane/1-

iodo-3,6,9-trioxa-decane/1H, 1H, 2H, 2H-heptadecafluorodecyl

iodide, DMF, 100 °C, 20 h. 108

List of Tables

163

List of Tables

Table 1.1: Industrially processed polymers, their abbreviation and

fields of application. 2

Table 3.1: Ratio of diethyl chlorophosphate (DECP) to hydroxyl

groups, degree of functionalization (FDEP) and molecular weight

(Mn,NMR) calculated from 1H NMR and SEC data of linear P(GDEP9-co-

G29) (3a), P(GDEP16-co-G18) (3b), P(GDEP

22-co-G8) (3c), P(GDEP26-co-G4)

(3d). 42

Table 3.2: Degree of functionalization (FEP) and molecular weight

(Mn,NMR) calculated from 1H NMR of linear P(GEP9-co-G29) (4a),

P(GEP16-co-G18) (4b), P(GEP

22-co-G8) (4c) and P(GEP26-co-G4) (4d).

44

Table 3.3: Degree of functionalization (FP) and molecular weight

(Mn,NMR) calculated from 1H NMR of P(GP9-co-G29) (5a), P(GP

16-co-

G18) (5b), P(GP22-co-G8) (5c) and P(GP

26-co-G4) (5d). 46

Table 4.1: Minimal inhibitory concentration against E. coli and S.

aureus and hemolytic activity of functional polyglycidols with defined

microstructures P(GTMAPA15-co-GDDA

12) (5), P(GAPDEMA16-co-GDDA

11)

(6), P(GDDAc, q)27 (10), P(GTMAPA14-co-GDDADDAc

13) (12). 74

Table 6.1: Hydrodynamic radii (Rh), polydispersity indices (PDI), zeta

potentials and glass transition temperatures (Tg) of P(GDMAPA)27 (3),

[P(GDMAPA)27]X (4), [P(GTMAPA)27]X (5), [P(GODMAPA)27]X (6),

[P(GPDMAPA)27]X (7), [P(GFDMAPA)27]X (8). 109

List of Tables

164

Table A.1.1: Synthesis of linear P(GDEP-co-G) (3a–d) (t = 20 h, T =

rt): Reagent ratios and yields after dialysis in MeOH. 122

Table A.1.2: Synthesis of linear P(GEP-co-G) (4a–d) (t = 48 h, T =

130 °C): Reagent ratios and yields. 123

Table A.1.3: Synthesis of linear P(GP-co-G) (5a–d) (t = 17 h, T = rt):

Reagent ratios and yields. 125

Curriculum Vitae

165

Curriculum Vitae

Personal Details

Name Fabian Marquardt

Date of Birth October 20th, 1987

Place of Birth Rüdersdorf, Germany

Citizenship German

Education

Jan 2014 – Feb 2018 PhD in Polymer Chemistry with Prof.

Dr. M. Möller, DWI - Leibniz Institute for Interactive Materials, Rheinisch-Westfälische Technische Hochschule, Aachen (Germany)

Nov 2013 Master of Science RWTH Aachen (1.7,

good), Rheinisch-Westfälische Techni-

sche Hochschule, Aachen (Germany)

July 2011 Bachelor of Science RWTH Aachen (2.8,

satisfactory), Rheinisch-Westfälische

Technische Hochschule, Aachen

(Germany)