University of Groningen

Synthesis and Application of Thermally Reversible Polymeric Networks from Vegetable OilsYuliati, Frita

DOI:10.33612/diss.127911343

IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.

Document VersionPublisher's PDF, also known as Version of record

Publication date:2020

Link to publication in University of Groningen/UMCG research database

Citation for published version (APA):Yuliati, F. (2020). Synthesis and Application of Thermally Reversible Polymeric Networks from VegetableOils. University of Groningen. https://doi.org/10.33612/diss.127911343

CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).

Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.

Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.

Download date: 22-05-2021

1

1 INTRODUCTION

Thermosets have a vast variety of applications in modern societies. However, repair

and reprocessing of these materials is often difficult. Furthermore, most are produced

from fossil resources. The use of fossil resources is under pressure due to

environmental concerns, fluctuating prices and uncertainties regarding future

availability. This thesis aims to contribute to solving these challenges, by providing

synthetic methodology for reprocessible thermosets from renewable resources. This

chapter provides a literature overview relevant to the work reported in this thesis.

The first part discusses various methods employed for self-healing polymeric systems.

The emphasis will be on methodology using the Diels-Alder reaction. Moreover, the

synthesis of biobased polymers based on vegetable oils is described.

2 CHAPTER 1

1.1 Self-healing polymers

Thermosetting polymers and composites are used in many applications, for

example in transportation, construction, electronics and sporting goods1.

Unfortunately, the materials have some major drawbacks, for example

mechanical properties degradation over time as a result of stresses and strains

build up. Damage usually starts with micro crack formation that is visually difficult

to detect. Larger cracks can be repaired by using adhesives; however, this may not

restore the original properties of the material1,2

. In this context, the design and

preparation of self-healing thermosets constitute a popular research area among

academic and industrial researchers.

In general, two self-healing methods can be distinguished. The first is known as

autonomous self-healing. Here, the polymers do not require external stimuli to

heal. This method is inspired by self-healing mechanisms operative within living

organisms3. Examples in the thermosetting field are self-healing epoxy resins

made by embedding microcapsules with dicyclopentadiene monomer and

separate capsules containing a Grubb catalyst. In the case of crack formation, the

capsules rupture, the monomer and catalyst are released and polymerization

occurs, leading to repair of the crack4–6

. The major drawback of this system is that

it is limited to a single healing action at a given specific spot in the sample. To

answer this challenge, new systems were developed by embedding a 3-

dimensional microvascular network containing dicyclopentadiene monomer in an

epoxy coating, and dispersing a Grubb catalyst into the substrate. When cracks

are formed, the monomer flows towards the fracture as a result of capillary

forces, polymerization occurs and the cracks are healed. This new system was

found to be able to perform 7 healing cycles. However, the healing ability is

limited by the availability of active catalyst, and as such the catalyst intake

determines to a large extent the maximum number of healing cycles7.

The second self-healing strategy involves the use of reversible polymerization

strategies, where the polymers can return to the monomeric, oligomeric, or non-

cross-linked state under certain external stimuli. Examples of this strategy

1

CHAPTER 1 3

involving covalent bond formation/breakage are the disulfide/thiol system, the

thermally reversible NO-C bonds, photo-induced reversibility, and the use of

reversible Diels-Alder chemistry2. The disulfide/thiol system was used for the

synthesis of reversible gels. Here, the disulfide was synthesized under oxidizing

conditions, and cleaved into two thiol groups via a reduction reaction8–10

. The NO-

C bonds in alkoxyamines have low bond dissociation energy, and were exploited

in synthesizing reversible grafts and cross-links of polymers via reversible radical

crossover of alkoxyamine units. The reaction was reversed by heating in anisole

solvent containing excess alkoxyamines11–13

. The proof of concept for the third

strategy, the photo-induced reversibility, was provided for the dimerization of

anthracene under photoirradiation ( > 350 nm), and cleaving of the dimer back

into anthracene during photoirradiation at < 300 nm14

.

Heat is a stimulus for Diels-Alder chemistry, which is easy to perform compared to

other options15

. Another advantage of this chemistry is that the reaction may be

carried out without a catalyst and yet with relatively fast kinetics16

. As a

consequence, the use of the Diels-Alder (DA) chemistry in thermosetting polymers

has attracted high attention in the last decades. The DA reaction is known to take

place at relatively low temperatures (from 20 oC to 90

oC)

17,18, and can be reversed

via the retro-Diels-Alder (rDA) reaction by increasing the temperature up to 200

oC

18,19, the actual temperature depending on the chemical structure of the

molecules involved. The decomposition of the DA adduct enables the polymers to

be reprocessed due to the absence of cross-linking points. Therefore, the use of

DA chemistry allows the synthesis of self-healing thermosetting polymers and

facilitates the recycling of this product 16,20,21

.

Besides the need for self-healing and recyclable polymers, the replacement of

fossil based feeds for renewable ones is also high on the research agenda. Among

the potentially attractive renewable feedstock for the chemical industry, oils and

fats from vegetable and animal origin are considered notably important. These

resources are available worldwide at relatively low cost and have multiple

applications22,23

. Synthetic methodology for polymers from vegetable oils have

been developed, including polymers based on DA reactions. The objective of this

4 CHAPTER 1

chapter is to provide an overview on the application of DA chemistry for the

synthesis and applications of reversible materials, with an emphasis on the use of

renewable feeds, particularly vegetable oils.

1.2 Thermally reversible polymers based on the DA reaction

The DA reaction is a cycloaddition between a conjugated diene and a dienophile

(a component with at least one bond), to form a six-membered ring (Figure 1.1).

Diene Dienophile

New bond

New bond

Figure 1.1. The Diels-Alder reaction24 a

The dienes should be in the cis configuration, and it is well established that cyclic

dienes display a higher reactivity than open forms. The electronic properties of

the substituents on both the diene and dienophiles have a major impact on the

reaction rates. In general, substituted dienes with electron-donating properties

leading to higher reaction rates for reactions with dienophiles with electron-

withdrawing substituents24,25

. Relevant examples of dienes and dienophiles are

given in Table 1.124,25

.

a

Figures describing chemical structures in this thesis were not prepared with

stereochemistry consideration for brevity reasons.

1

CHAPTER 1 5

Table 1.1. Representative dienes and dienophiles24

for the DA reaction.

The use of the DA reaction has been studied for various polymeric systems. Well

known combinations of dienes and dienophiles are furans-maleimides,

cyclopentadiene-cyclopentadiene, anthracene-maleimides, fulvene-fulvene,

fullerene-dienes and cyclopentadiene-dithioesters2,26

. Among these systems, the

furan-maleimide combination is the most studied, mainly due to the high

availability of reagents and relatively fast kinetics27

. Different strategies have been

investigated: (i) reacting multifunctional monomers in a direct DA cycloaddition;

(ii) utilizing DA linkages in cross-linkers or initiators to perform polymerization and

(iii) DA cycloaddition of pendant functional groups on linear polymers16

, see Figure

1.2 for details.

Dienes

Open Chain Outer Ring Inner-outer Ring Across Ring Inner Ring

OSiMe3

OMe

O

O

O

CH2

N

O

O

O

O

O

O

O

O O

O

Dienophiles

Acyclic Cyclic

CHO

COMe

CN

O

O

O

O

O

N

O

O

H2C C CHMe

HC CO2Me

OEt O

N

NN

O

O

Ph

Me2C S

Ph N O

ArN NCN

O

O

O

O

6 CHAPTER 1

Figure 1.2. Common strategies in implementing the DA chemistry in polymers: (i)

polymerization of multifunctional monomers via the DA reaction, (ii) utilizing cross-linkers

containing DA adducts, and (iii) cross-linking of linear polymers by using pendant

functional groups16,28–30

.

An early example of a cross-linked polymer synthesized with the first strategy (i in

Figure 1.2) involves the DA cycloaddition between a diene comprising 4 furan

moieties per molecule (4F) and a dienophile with 3 maleimide moieties per

molecule (3M) (Figure 1.3). The reaction formed a hard and fully transparent

polymeric material. The polymerization was performed in a solvent

(dichloromethane) at 24 – 95 oC. The mechanical properties of the polymer were

in the range of commercial epoxy and unsaturated polyesters. To understand the

healing capability of the polymer, some samples were scratched and subjected to

loads at directions perpendicular to the cracks during a scratch toughness

measurement. After failure, the samples were healed by heating them at about

150 oC. The healed samples were measured again and showed healing efficiencies

(defined as the ratio between the scratch toughness after and before healing) of

about 50%31

.

Thermally reversible bond

Irreversible bond

(i)

(ii)

(iii)

1

CHAPTER 1 7

Figure 1.3. A diene comprising 4 furans (4F); and dienophiles comprising 2 (2M and 2MP)

and 3 maleimides (3M)32

.

To avoid the use of solvents, the original dienophile was replaced by molecules

containing two maleimide moieties (2M and 2MP). The mechanical properties of

the resulting polymers (2M-4F and 2MP-4F) were determined and shown to have

lower Young’s modulus than that of 3M-4F. In addition, the polymeric materials

showed an average of 80% healing efficiency32

.

Besides the synthesis of cross-linked polymers, the first strategy is also applicable

to obtain linear polymers. An example involves the use of a molecule with 2 furan

units combined with a bismaleimide. A biobased monomer with two furan groups

was synthesized by reacting furfural and trehalose. The product was reacted with

a bismaleimide to produce a linear polymer. The optimum temperature for the DA

reaction was 70 oC, higher temperatures were shown to lead to lower yields due

to the occurrence of the retro-DA reaction33

.

Another interesting example of a linear polymer synthesized via the DA reaction

involves the use of cyclopentadiene as both diene and dienophile.

Cyclopentadiene is thermally labile and has to be stored at -20 oC to prevent

dimerization to dicyclopentadiene34

This property can be used to prepare new

reversible polymers (Figure 1.4). The reaction successfully generated a hard and

transparent polymeric material35

.

C O OO

O

4

NO

ON

O

O

O

O

N

N

O

O

3

N N

O

O O

O

4F 3M

2M2MP

8 CHAPTER 1

Figure 1.4 . Polymerization of a dicyclopentadiene-based monomer35

.

The second polymerization strategy (ii in Figure 1.2) comprises the use of DA

linkages in cross-linkers or initiators to perform an irreversible polymerization

reaction. The incorporation of such DA adducts in the cross-linker enables the

cross-linked polymer to be reprocessed upon heating. This strategy was applied in

a diamine cross-linker containing DA adducts at both ends (Figure 1.5). The cross-

linker was able to cure commercially available epoxy resins such as diglycidyl

ether bisphenol A (DGEBA) at 60 oC

28. The cross-linker was also used to cure TGAP

(trifunctional triglycidyl p-amino phenol). The best curing condition was at 80 oC

for 24 h, giving a conversion as high as 85%. However, higher curing temperature

lead to the retro-DA reaction and possibly also to Michael additions between the

maleimide groups and unreacted amines, which is known to occur at 70 oC. The

optimum condition for the rDA reaction was 150 oC for 10 min

29. Both epoxy

polymers were found to possess self-healing capabilities. Scratches of about 40

micrometer wide on the polymer surface completely disappeared after heating at

140 oC for 30 min and subsequent annealing at 75

oC for 5 h for the DGEBA-based

epoxy, and at 130 oC for 5.4 min for the TGAP-based polymer

28,29.

The third strategy (iii in Figure 1.2) uses DA active moieties as pendant groups on

monomers or linear polymers and further cross-linking of the polymers by making

use of the DA reaction. Examples include the use of furan groups attached to

epoxy resins, polymethacrylate, alternating polyketone, and EPM rubber; and

O

O

O

O

OO

O

O

O

O

O

O

O

O

O

O

O

O

120 oC

1

CHAPTER 1 9

NN

OO

NH2

NH2

O

O

O

O

Figure 1.5. A cross-linker containing amine groups (red) for irreversible bond formation

and the reversible DA adduct (blue)28,29

.

cross-linking them with the commercially available 1,1’-(methylene-di-1,4-

phenylene)bismaleimide. The resulting cross-linked polymers were found to show

reversible behavior upon a thermal treatment30,36–38

.

Polymers synthesized with the third strategy can be also be cross-linked by a

combination of the DA chemistry and another approach. A thermosetting polymer

was cross-linked with a conventional epoxy ring-opening reaction and the DA

reaction. The resin contained both epoxide groups at both ends and a pendant

furan group (Figure 1.6). It was cross-linked with a mixture of a traditional curing

agent (methylhexahydrophtalic anhydride) and a bismaleimide. The end-product

contained two types of bonds, namely thermally stable bonds from the reaction

product of epoxide and anhydride groups; and thermally reversible bonds from

the DA reaction between the furan and maleimide moieties. The Young’s and

flexural modulus of this polymer were found to be higher than those of

conventional epoxy polymers (2.5 GPa and 4.6 GPa, compared to 1.8 GPa and 2.6

GPa), although the tensile strength was somewhat lower (53 compared to 65

MPa)36

. Other polymers were synthesized, for example, by using modified

polymethacrylate38

and a Novolac epoxy resin37

. The latter produced a polymer

with a storage modulus of 2.37 GPa at 30 oC

37, lower than the Novolac resin cross-

linked conventionally with a methyl etherified amino resin39

. The high

functionality of the starting materials enabled high amounts of pendant furans

groups grafted along the backbone. The rDA reaction occurred upon heating,

allowing reprocessing37,38

. The Novolac-based polymer also showed self-healing

capabilities, as shown by healing scratches on polymer films by heating the

samples at 130 oC for 10 min and subsequent annealing at 60

oC for 24 h

37.

10 CHAPTER 1

N

O O

O

Figure 1.6. An epoxy resin containing epoxy groups (red) and pendant furans (blue)36

.

Earlier research in our group showed that pendant furan groups can be attached

to polyketones by the Paal-Knorr reaction of such polyketones with furfurylamine

(Figure 1.7). Reaction of the resulting polymer with bismaleimides by a DA

approach leads to cross-linked material with thermally reversible properties, even

after six heating and cooling cycles30

. Higher levels of furan groups attached to

the polyketones and the use of higher maleimide concentration resulted in higher

cross-link densities. Even though molecular reversibility was shown to be less than

quantitative, the mechanical properties were found to be completely reversible26

.

The Tg of the product can be increased by making use of free primary amines

which form hydrogen bonds with the carbonyl groups present in the backbone40

.

In addition, electric conductivity of the polymer can be enhanced by adding

carbon nanotubes as a filler to the formulation41

.

O

NH2

O

R

R

N

O

R

N

R

R

O

Paal-Knorr, 110 oC

O

R

R

N

O

R

N

R

R

O

N

N

RR R

O

N

O

O

O

N

O

O

O

R

O

R

R

N

R

N

RR

Diels-Alder, 50 oC

Retro-Diels-Alder, 150 oC

N N

O

OO

O

O

R

R

N

O

R

N

R

R

O

Figure 1.7. Synthesis route for polyketone-based thermally reversible thermosets40

.

1

CHAPTER 1 11

A similar strategy is applicable to EPM rubbers, for instance by the introduction of

pendant furan groups to the rubber, followed by cross-linking with a commercial

bismaleimide42

. The mechanical properties of the products were shown to be

tunable by using different types of bismaleimides43

. These resulting rubbers were

found to be fully thermally reversible, indicating that the Diels-Alder chemistry is

also applicable in this system.

The three strategies utilizing the DA and rDA reactions to prepare thermally

reversible and self-healing polymers have specific features that affect their

applicability. The first strategy uses relatively small molecules as monomers, that

will be detached from the polymeric structure during the rDA reaction, potentially

resulting in a dramatic decrease of the mechanical properties. This condition is

acceptable in the case of recycling, but potentially more cumbersome in the case

of healing processes. Similar issues occur with the second strategy, though to a

lower extent, because the thermally stable bonds will not be cleaved during

heating. The changes in mechanical properties during recycling or healing of a

polymer can be tailored by changing the composition of the thermally reversible

and irreversible bonds in the polymer. Furthermore, attention needs to be paid to

the temperature at which the irreversible bonds are formed. If it is in the range

where the rDA reaction occurs, the detachment of the DA adducts should be

taken into account in handling the polymer. On the other hand, the third strategy

only uses the DA and rDA reactions for network formation and disruption,

therefore the behavior of the thermosets is more predictable. In case of the rDA

reaction where the adducts are separated into the original DA pairs, the products

still consist of large molecules. Consequently, the decrease in mechanical strength

during heating is less dramatic than those in the previous strategies. These

consequences should be considered when selecting the best strategy for a given

application.

12 CHAPTER 1

1.3 Applications of thermally reversible polymers

Thermally reversible polymers offer new possibilities and advantages in many

applications. Here we describe some potential applications of the materials in

adhesives, coatings, and composites.

1.3.1 Removable adhesives from thermally reversible polymers

Thermosetting adhesives are potentially applicable in the aerospace, automotive,

electronics and medical industry. Removable adhesives are required when

disassembling of joined parts is an important aspect in the design, e.g. for

recycling, repair or upgrading of an expensive component. The use of removable

adhesives, for instance, a thermally reversible one, enables easy disassembling

without causing collateral damage to the components or the entire unit44,45

.

A number of strategies can be envisaged for the use of thermally reversible epoxy

adhesives, for example by incorporating a DA adduct in the epoxy resin or in the

cross-linker. A number of removable adhesives were designed using conventional

curing agents for cross linking in combination with modified resins, e.g. with

thermally labile DA adducts. The DA adducts can be inserted in the resin

structure44

, or utilized as a bridging structure between a linear polymer and

pendant oxiranes46

. When a non-modified commercial epoxy resin is preferred,

the DA adduct can also be incorporated in the cross-linker, e.g. in the diamine

used45

. These strategies gave adhesives with similar lap shear strengths as a

commercial adhesive (about 4 MPa and 2 MPa for the two strategies

respectively44,45

. The reversibility of these adhesives were examined by repeatedly

detaching and re-attaching the substrates bonded by the adhesives. It was found

that the bond strength was similar or even increased after several detaching-re-

attaching cycles44–46

.

A major concern for thermally reversible adhesives described above is the limited

temperature range of application. As such, alternatives with improved properties

using a different approach are required. A “lock” and “unlock” mechanism was

proposed to enable a removable adhesive to operate at higher temperature under

1

CHAPTER 1 13

“locked” condition. When it was “unlocked”, the adhesive could be removed by

heating. Such an adhesive was prepared from a DA adduct where the diene

component was integrated into a photoresponsive hexatriene (Figure 1.8). After

the DA reaction, the hexatriene is attached to the cyclohexene of the DA adduct.

Exposure of the polymer to ultraviolet light was shown to trigger ring closure of

the hexatriene while converting the cyclohexene part of the DA adduct into

cyclohexanes, and consequently prevented the retro DA reaction to happen.

When the system was exposed to visible light, the photoreaction occurred by

returning the hexatriene and also the cyclohexene of the DA adduct, and

therefore “unlocked” the adduct (enabling the rDA reaction to take place)47

.

Figure 1.8. A removable adhesive using a lock/unlock mechanism triggered by light.

Ultraviolet light promotes the ring closing of the hexatriene (blue), removing the

cyclohexene of the DA adduct (red) and prevents the rDA reaction. Visible light exposure

opens the hexatriene ring and enables the rDA reaction to occur47

.

N

O

CH3

SSCH3

O O

CH3

Cl

O

O

O

O

N

O

CH3

S

SCH3

O

O

CH3Cl

N

O

CH3

S S

O O

CH3

Cl

O

O

O

O

N

O

CH3

S

S

O

O

Cl

CH3

CH3

CH3

312 nm >435 nm

14 CHAPTER 1

1.3.2 Thermally reversible polymers for self-healing coatings

Coatings are used to protect their substrates from damage caused by the

environment, for example to prevent corrosion of metals. Since coatings usually

have a high surface to volume ratio, they are very susceptible to damage, which

will ultimately also lead to the damage of the substrate. Thermally reversible

polymers offer advantages for coating applications by allowing easy repair within

certain limits of damage48,49

.

Methacrylate-based polymers are widely used as coatings due to their fast curing

kinetics and good weather resistance. Augmenting self-healing properties into the

polymeric structure can be achieved by incorporation of a Diels-Alder adduct in

the polymer structure. A number of methods have been proposed for this

purpose. For example, furans were incorporated as pendant groups to a

methacrylate-based block copolymer and the resulting copolymer was

subsequently cross-linked with an aliphatic bismaleimide via a DA reaction50

. To

avoid the complications of using two components, incorporation of both pendant

furans and maleimides into a linear methacrylate backbone was also reported49

.

Both methods were shown to lead to self-healing polymers with interesting

properties49,50

.

Other polymers used extensively in the coating industry are epoxy resins and

polyurethanes. Epoxy coatings are applicable with minimum preparation and are

used for a wide range of applications, from primer to top coatings and

applications where chemical resistance is a key product property. Polyurethane

coatings are known for their high UV resistance, gloss retention, and color

stability. There is a high interest to incorporate self-healing properties into both

classes of coatings. An example is the use of strategy (ii) in Figure 1.2 using an

epoxy resin and a polyol. A thermally-responsive epoxy resin was synthesized by

reacting furfuryl glycidyl ether with aromatic or aliphatic bismaleimides, yielding a

diepoxy resin with two DA adducts between the oxirane groups50

. For

polyurethanes, the synthesis of a soybean oil-based polyol containing DA adducts

connecting the triglyceride structure with the alcohol groups is worth

mentioning51

. In both cases, the monomers were cross-linked using conventional

1

CHAPTER 1 15

amines and isocyanates, respectively50,51

, producing polymers with irreversible

and reversible bonds. Both epoxy and polyurethane coatings showed self-healing

properties without notable changes in other product properties, such as chemical

resistance against MEK for the epoxy, and gloss retention for the

polyurethane.50,51

Fouling caused by marine organisms is a major challenge for the development of

coatings for marine applications. Hyperbranched fluorinated polymers (HBFP)

cross-linked with poly(ethylene glycol) (PEG), possess good anti-biofouling

capabilities and have shown to be suitable for marine coatings. However,

durability is limited and this is considered a major disadvantage. The introduction

of DA adducts into the material in the form of furan groups into HBFP and

maleimides into PEG was shown to have a very positive effect on service life. The

coating prepared from furan-functionalized HBFP and maleimide-functionalized

PEG was cured at 60 oC for 24 h. It was shown to reheal after thermal reprocessing

and to have similar resistance to protein adsorption as a conventional HBFP-PEG

coating, confirming its anti-biofouling property52

.

1.3.3 Self-healing composites from thermally reversible polymers

Cross-linked polymers are important components in polymer composites. Defects

in such composites usually arise at the interface between the polymer matrix and

the reinforcement. At this interface, mechanical stress is transferred from the

matrix to the reinforcement. However, the difference in mechanical properties

between the materials may lead to stress concentration and eventually to crack

formation. Using thermally reversible polymers in the composite systems enables

easy repair of the cracks resulting in prolonged service life of the composite53,54

.

An effort to create rehealable interphases was made by introducing DA linkages

between the epoxy matrix and a typical reinforcement material (glass fiber). For

this purpose, furan groups were introduced into the epoxy matrix by mixing

DEGBA and furfuryl glycidyl ether (FGE), while the glass fibers were functionalized

with maleimides. The interfacial bond strength between the matrix and

reinforcement was measured by a micro-droplet single fiber pull-out testing. A

16 CHAPTER 1

single fiber was embedded into a droplet of the resin as a model of a composite,

then the fiber was pulled out, followed by healing of the composite. Debonding

between the matrix and the fiber was found to be possible at higher temperatures

and the interfacial bonds were shown to remain recoverable after five healing

cycles55

. A similar strategy was applied when using carbon instead of glass fibers,

however, the healing efficiency was found to decrease with the number of

debonding/healing cycles. During debonding, some furan groups were attached to

the fiber in the form of DA adducts. This resulted in a decrease in furan content in

the matrix, thus reduced the number of DA linkages at the interphase53

.

A novel nanocomposite with thermally reversible properties was prepared by

incorporating DA adducts into polyhedral oligomeric silesquioxanes (POSS). POSS

are organic-inorganic hybrid materials with an empirical formula of Rn(SiO1.5)n

(n=8, 10, 12), with R comprising organic groups (e.g. glycidyl, phenyl, cyclohexyl)

or organic-inorganic hybrids such as -OSiMe2OPh. DA adducts were incorporated

in the material by first reacting POSS with furfurylamine, and a subsequent

reaction with a bismaleimide. The thus obtained material was cracked and

subsequently heated at 135 oC and 150

oC for 30 min. The results suggest that

thermal healing was successful, provided that the damaged parts are in close

contact during heating56

.

1.3.4 Shape-memory polymers

The DA reaction is also found to be useful for the synthesis of recyclable shape-

memory polymers. A successful example involves incorporation of furan groups

into shape memory bisphenol-A type resins and subsequent cross-linking with a

maleimide linker. The thus produced epoxy polymers have shape memory

properties and can be recycled at temperatures above 120 oC

57. In another study,

modified poly(lactic acid) was functionalized with furan groups and cross-linked

with a flexible maleimide linker, producing a recyclable shape memory polymer58

.

The polymers were shown to be self-healing without the need for external forces

to close cracks59

.

1

CHAPTER 1 17

1.4 Vegetable oils as raw materials for thermally reversible

polymers

Vegetable oils are considered attractive resources for the synthesis of chemicals

and polymers. The feeds are available in high amounts (an average of 202 million

tons per year worldwide in 2016-201860) at relatively low cost (US$ 400 – 800 per

ton in 201961). Several studies on the utilization of vegetable oils for the synthesis

of thermally reversible polymers have been performed, for example using castor,

tung, soybean, linseed, and jatropha oils. Here we briefly describe some of these

studies.

Early in the 1970s, the first reports on the synthesis of DA adducts from safflower

oil were published. The oil contains up to 70% of linoleic acid, which may serve as

the diene in DA reactions after double bond isomerization. Maleic anhydride was

used as the dienophile. It was found that the dienophile is preferably present in

the trans,trans configuration, in contrast to common believe that the reaction

takes place when the dienophile is in the s-cis configuration62. In subsequent

studies, the isomerized linoleic ester was allowed to react with styrene (1-2

molecules of the latter per molecule of linoleic ester). The reaction was favored at

higher temperature, higher styrene input, and higher pressure, although a

considerable amount of side products were also formed63. Beside maleic

anhydride and styrene, acrylic, methacrylic, crotonic and cinnamic acids and their

esters may also serve as dienophiles. When performing the reaction between 160

to 220 oC, mixtures containing more than 45% of DA adducts were obtained, with

a relatively low content of the side products64. These reports suggest that DA

reactions with linoleic acid and its ester are well possible, and that polymers can

also be obtained via the DA reaction with proper dienophile selection.

Soybean oil is one of the most produced vegetable oils in the world. Its relatively

high content of unsaturated fatty acids23 enables various chemical modifications,

thus make it an attractive source for chemicals. Commercially available acrylated

epoxidized soybean oil (AESO) can be modified to obtain DA-active chemicals.

Furan groups were attached to AESO via a Michael addition with furfurylamine

18 CHAPTER 1

(Figure 1.9), and the product (AESO-FA) was subsequently reacted with a

bismaleimide and n-phenylmaleimide at 65 oC in different solvents (acetonitrile,

dimethylformamide, chloroform, and tetrachloroethane). It was found that

solvents influenced the Tg of the polymers obtained, and the temperature at

which the rDA occurred. The product with the highest Tg (74 oC) was synthesized

with an AESO-FA to bismaleimide ratio of 1 to 1 in tetrachloroethane65

.

Figure 1.9. Commercial AESO modified with furfurylamine via a Michael addition65

.

Oils obtained from the seed of the tung tree contain -eleostearic acid, an

interesting molecule with a conjugated triene. This makes the oil suitable for the

preparation of paints and varnishes, not at least because of its outstanding drying

property66

. Tung oil is also a potential precursor for synthesis of DA polymers, for

example, using the synthesis routes given in Figure 1.1067

. The first route involves

a direct polymerization with three types of bismaleimides, with and without

solvent (1,1,2,2-tetrachloroethane). The second route started with ester

aminolysis of the oil using an excess of furfurylamine, to attach furans at the ester

sites of the oil. The furan-functionalized triene was then cross-linked with three

different bismaleimides. It was found that the properties of the cross-linked

materials can be tailored by modifying the structure of the bismaleimides. Partial

O

OH

OO

O

O

O

O

OH OH

NH

O

O

O

NH

O

O

O

NH

O

O

O

OH

O OO

O

O

O

O

OH OH

O OOO

NH2

O

DMSO

30 oC

1

CHAPTER 1 19

O

O OO O

O

OO

O

O

O

O

N OO

N OO

NO O

R

OO

O

O

O

O

N OO

N OO

NO O

NH

O

O

NH

O

N OO

N O

O

O

RNO

O

ONH

O

NO O

Tu

ng

oil

(8

5 %

-ele

ost

ea

ric

aci

d)

Direct DA polymerisation with bismaleimide

Ester aminolysis(excess furfurylamine)

DA polymerization with bismaleimide

OR =

Figure 1.10. Two approaches of tung oil polymerization via DA reaction67

.

depolymerization by the retro-DA reaction was only possible for the materials

produced by the second route67

.

Epoxidized linseed oil is one of the few commercially available epoxidized

vegetable oils. It was shown to be a suitable starting materials for polymers with

DA linkages (Figure 1.11). The synthetic approach involves the introduction of

furan groups to the epoxidized oil by reaction with furfurylamine at temperatures

between 80 and 95 oC. Both ester aminolysis and epoxide ring opening reactions

occur, resulting in furan units attached at the epoxy and glyceride ester sites.

Subsequently, the materials are cross-linked with a bismaleimide, leading to a

linear DA polycondensation product with a glass transition temperature of 80-100

oC. TGA analysis showed that the polymer was thermally stable up to 250

oC.

Retro-DA reactions occurred at about 110 oC. It was proposed that the polymer is

suitable to be used for thermally reversible coatings and adhesives68

20 CHAPTER 1

O

O

O

OO

O OO

O OO

ONH2

(excess)

95 C

NH

O

O OH

NH

O

NH

O

O OH

NH

O

O

NH

O

O OH

NH

O

OH

NH

O

Figure 1.11. Reaction of epoxidized linseed oil with an excess of furfurylamine68

.

10-Undecenoic acid, the pyrolysis product of Castor oil, is an interesting

renewable chemical due to the presence of a terminal C-C double bond. Furan

groups may be introduced at both ends of the molecule whereas the combination

of one furan and one maleimide unit at each end is also possible (Figure 1.12). The

introduction of two furan groups was performed by the esterification of 10-

undecenoic acid with furfuryl alcohol and an ene reaction with furanmethanethiol

at the terminal double bond, resulting in monomer AA (a). An alternative

approach involves esterification of 10-undecenoic acid with an allyl alcohol

followed by an ene reaction at both alkenyl ends, producing monomer AA’ (b).

The synthesis of monomers with one furan and one maleimide unit at each end

was done by the esterification of 10-undecen-1-ol by a masked 4-

maleimidobutyric acid, followed by an ene reaction with furanmethanethiol at the

terminal double bond, producing monomer AB (c). Monomers AA and AA’were

polymerized with 1,6-bismaleimidohexane. Repeated heating and cooling cycles

revealed that all polymers show thermally reversible properties69,70

.

o

1

CHAPTER 1 21

CH2OH

O

OOH

CH2O

O

O

OSH

O

O

O

SO

CH2OH

O

CH2O

O

CH2

OSH

O

O

SO

S O

CH2 OH

NOH

O

O

OO

CH2OH

CH2O N

O

O

OO

O N

O

O

OO

SO

AA

AA'

AB

OSH

(a)

(b)

(c)

Figure 1.12. Synthesis of monomers based on the pyrolysis products of castor oil, to be

used for the synthesis of thermally reversible polymers69,70

.

Jatropha curcas oil, a non-edible oil, contains high amounts of unsaturated fatty

acids, and as such it is an interesting vegetable oil for further modifications.

Recent research in our group indeed showed that thermally reversible polymers

may be prepared from this oil (Figure 1.13). It involves epoxidation of the C-C

double bonds in the oil by performic acid, followed by a reaction with

furfurylamine to introduce furan groups. However, ester aminolysis also occurred

to a significant extent, leading to di- and mono-glycerides. The product was cross-

linked with a bismaleimide, resulting in a brittle solid product. Thermoreversibility

of the product was determined by a DSC analysis comprising a number of heating

and cooling cycles between 20 and 190 oC. Analysis suggests that the retro-DA

reaction occurs at about 125 oC in every cycle

71.

22 CHAPTER 1

NHO

O

OH

NH

O

NHO

O

O

O

O

O

O

O

O

NH

O

OH OH

NH

O

OH

NH

O

NN

O

O

O

O

Diels - Alder

retro - Diels - Alder

R1

O

OH

NH

N O

O

O

R2

O

O

O

NH

R1

O

OH

R2 =

Figure 1.13. Cross-linking of a furan-functionalized Jatropha curcas oil with a

bismaleimide71

.

1.5 Aim and scope of this thesis

The aim of this research is to prepare environmentally benign polymeric

materials based on vegetable oils and to investigate their possible applications.

The emphasis is on the synthesis of polymers with mechanical properties of that

of a cross-linked structure combined with the ability to be reprocessed to enable

straightforward repair and recycle. The selected strategy involves the

introduction of furan groups to vegetable oils, followed by cross-linking by the

thermally reversible Diels-Alder approach using bismaleimides.

The synthesis of suitable monomers with furan units from non-edible Jatropha oil

is described in Chapter 2. It entails a novel two-step approach involving

epoxidation and furan-functionalization, in contrast to a three-steps route

proposed in the literature (involving epoxidation, acrylation, and furan-

functionalization)65

. The major challenge is the limited chemoselectivity of the

reaction, leading to by-product formation. Experiments aimed to reduce by-

product formation, e.g. by tuning process conditions, are described.

1

CHAPTER 1 23

The furan-bearing monomers described in chapter 2 are used for the synthesis of

polymers by cross linking reactions with commercially available bismaleimides

(Chapter 3). Mechanical properties of the polymers could be tuned by varying

the chemical structure of the bismaleimide, and/or by using mixtures of aliphatic

and aromatic bismaleimide in various ratios. The influence of the bismaleimides

composition on the thermal reversibility of the obtained polymers is also

investigated. To determine whether the synthetic methodology is applicable for

a range of plant oils and not restricted to Jatropha oil only, additional

experiments with sunflower oil were performed.

Vegetable oils are also used as starting materials for the synthesis of epoxy

resins72–76

. Such polymers are typically more easy to synthesize compared to the

thermally reversible ones described in the previous chapter, though are not easy

to reprocess. In Chapter 4, the properties of thermally reversible and epoxy

polymers with similar structures are compared.

In the final chapter of this thesis, attempts are described to identify applications

and to further modify the polymers to extend the application range. The

thermally reversible polymers are tested as adhesives and their bond strengths

are compared with a commercially available adhesive. In addition, the use of

fillers is investigated to improve the mechanical properties. Finally the use of

these polymers in formulations with a thermosetting polyketone is investigated

to improve the self-healing properties.

References

1. Wu DY, Meure S, Solomon D. Self-healing polymeric materials: A review of recent

developments.Prog.Polym.Sci.2008;33(5):479-522. doi:10.1016/j.progpolymsci.2008.02.001

2. Bergman SD, Wudl F. Mendable polymers. J Mater Chem. 2008;18(1):41.

doi:10.1039/B713953P

3. Diesendruck CE, Sottos NR, Moore JS, White SR. Biomimetic Self-Healing. Angew Chemie Int

Ed. 2015;54(36):10428-10447. doi:10.1002/anie.201500484

4. White SR, Sottos NR, Geubelle PH, et al. Autonomic healing of polymer composites. Nature.

2001;409(6822):794-797. doi:10.1038/35057232

24 CHAPTER 1

5. Brown EN, Sottos NR, White SR. Fracture testing of a self-healing polymer composite. Exp

Mech. 2002;42(4):372-379. doi:10.1007/BF02412141

6. Brown EN, White SR, Sottos NR. Microcapsule induced toughening in a self-healing polymer

composite. J Mater Sci. 2004;39(5):1703-1710. doi:10.1023/B:JMSC.0000016173.73733.dc

7. Toohey KS, Sottos NR, Lewis JA, Moore JS, White SR. Self-healing materials with

microvascular networks. Nat Mater. 2007;6(8):581-585. doi:10.1038/nmat1934

8. Chujo Y, Sada K, Naka A, Nomura R, Saegusa T. Synthesis and Redox Gelation of Disulfide-

Modified Polyoxazoline. Macromolecules. 1993;26(5):883-887. doi:10.1021/ma00057a001

9. Tsarevsky N V., Matyjaszewski K. Reversible redox cleavage/coupling of polystyrene with

disulfide or thiol groups prepared by atom transfer radical polymerization. Macromolecules.

2002;35(24):9009-9014. doi:10.1021/ma021061f

10. Tsarevsky N V., Matyjaszewski K. Combining atom transfer radical polymerization and

disulfide/thiol redox chemistry: A route to well-defined (bio)degradable polymeric

materials. Macromolecules. 2005;38(8):3087-3092. doi:10.1021/ma050020r

11. Higaki Y, Otsuka H, Takahara A. Dynamic Formation of Graft Polymers via Radical Crossover

Reaction of Alkoxyamines. Macromolecules. 2004;37(5):1696-1701.

doi:10.1021/ma035518c

12. Higaki Y, Otsuka H, Takahara A. A thermodynamic polymer cross-linking system based on

radically exchangeable covalent bonds. Macromolecules. 2006;39(6):2121-2125.

doi:10.1021/ma052093g

13. Otsuka H, Aotani K, Higaki Y, Amamoto Y, Takahara A. Thermal reorganization and

molecular weight control of dynamic covalent polymers containing alkoxyamines in their

main chains. Macromolecules. 2007;40(5):1429-1434. doi:10.1021/ma061667u

14. Xu J-F, Chen Y-Z, Wu L-Z, Tung C-H, Yang Q-Z. Dynamic Covalent Bond Based on Reversible

Photo [4 þ 4] Cycloaddition of Anthracene for Construction of Double-Dynamic Polymers.

Angew Chem, Int Ed. 2007;36(2):14567. doi:10.1021/ol403015s

15. Bergman SD, Wudl F. Mendable polymers. J Mater Chem. 2008;18(1):41-62.

doi:10.1039/B713953P

16. Tasdelen MA. Diels–Alder “click” reactions: recent applications in polymer and material

science. Polym Chem. 2011;2(10):2133. doi:10.1039/c1py00041a

17. Jegat C, Mignard N. Effect of the polymer matrix on the thermal behaviour of a furan-

maleimide type adduct in the molten state. Polym Bull. 2008;60(6):799-808.

doi:10.1007/s00289-008-0913-y

18. Froidevaux V, Borne M, Laborbe E, Auvergne R, Gandini A, Boutevin B. Study of the Diels-

Alder and retro-Diels-Alder reaction between furan derivatives and maleimide for the

creation of new materials. RSC Adv. 2015;5:37742. doi:10.1039/c5ra01185j

19. Sanyal A. Diels-alder cycloaddition-cycloreversion: A powerful combo in materials design.

Macromol Chem Phys. 2010;211(13):1417-1425. doi:10.1002/macp.201000108

20. Toncelli C, Reus D De, Broekhuis AA, Picchioni F. Thermoreversibility in Polymeric Systems.

In: Self-Healing at the Nanoscale. CRC Press; 2011:199-248. doi:doi:10.1201/b11484-12

21. Gandini A. The furan/maleimide Diels-Alder reaction: A versatile click-unclick tool in

macromolecular synthesis. Prog Polym Sci. 2013;38(1):1-29.

doi:10.1016/j.progpolymsci.2012.04.002

22. Biermann U, Bornscheuer U, Meier M a R, Metzger JO, Schäfer HJ. Oils and fats as

renewable raw materials in chemistry. Angew Chemie - Int Ed. 2011;50(17):3854-3871.

doi:10.1002/anie.201002767

23. Montero De Espinosa L, Meier M a R. Plant oils: The perfect renewable resource for

polymer science?! Eur Polym J. 2011;47(5):837-852. doi:10.1016/j.eurpolymj.2010.11.020

24. Fringuelli F, Taticchi A. Diels–Alder Reaction: General Remarks. In: The Diels–Alder Reaction.

John Wiley & Sons, Ltd; 2001:1-28. doi:10.1002/0470845813.ch1

1

CHAPTER 1 25

25. Domingo LR, Aurell MJ, Pérez P, Contreras R. Quantitative characterization of the global

electrophilicity power of common diene/dienophile pairs in Diels–Alder reactions.

Tetrahedron. 2002;58(22):4417-4423. doi:10.1016/S0040-4020(02)00410-6

26. Toncelli C, Reus DC De, Picchioni F, Broekhuis AA. Properties of Reversible Diels – Alder

Furan / Maleimide Polymer Networks as Function of Crosslink Density. :157-165.

27. Amendola V, Meneghetti M. Self-Healing at the Nanoscale: Mechanisms and Key Concepts

of Natural and Artificial Systems. CRC Press; 2011.

28. Bai N, Saito K, Simon GP. Synthesis of a diamine cross-linker containing Diels–Alder adducts

to produce self-healing thermosetting epoxy polymer from a widely used epoxy monomer.

Polym Chem. 2013;4(3):724-730. doi:10.1039/C2PY20611K

29. Bai N, Simon GP, Saito K. Characterisation of the thermal self-healing of a high crosslink

density epoxy thermoset. New J Chem. 2015;39(5):3497-3506. doi:10.1039/C5NJ00066A

30. Zhang Y, Broekhuis AA, Picchioni F. Thermally self-healing polymeric materials: The next

step to recycling thermoset polymers? Macromolecules. 2009;42(6):1906-1912.

doi:10.1021/ma8027672

31. Chen X, Dam MA, Ono K, et al. A thermally re-mendable cross-linked polymeric material.

Science. 2002;295(5560):1698-1702. doi:10.1126/science.1065879

32. Chen X, Wudl F, Mal AK, Shen H, Nutt SR. New thermally remendable highly cross-linked

polymeric materials. Macromolecules. 2003;36(6):1802-1807.

33. Teramoto N, Arai Y, Shibata M. Thermo-reversible Diels–Alder polymerization of

difurfurylidene trehalose and bismaleimides. Carbohydr Polym. 2006;64(1):78-84.

doi:10.1016/j.carbpol.2005.10.029

34. Huertas D, Florscher M, Dragojlovic V. Solvent-free Diels–Alder reactions of in situ

generated cyclopentadiene. Green Chem. 2009;11(1):91. doi:10.1039/b813485e

35. Murphy EB, Bolanos E, Schaffner-Hamann C, Wudl F, Nutt SR, Auad ML. Synthesis and

characterization of a single-component thermally remendable polymer network: Staudinger

and stille revisited. Macromolecules. 2008;41(14):5203-5209. doi:10.1021/ma800432g

36. Tian Q, Yuan YC, Rong MZ, Zhang MQ. A thermally remendable epoxy resin. J Mater Chem.

2009;19(9):1289. doi:10.1039/b811938d

37. Li J, Zhang G, Deng L, et al. Thermally reversible and self-healing novolac epoxy resins based

on Diels-Alder chemistry. J Appl Polym Sci. 2015;132(26):n/a-n/a. doi:10.1002/app.42167

38. Amalin Kavitha A, Singha NK. A tailor-made polymethacrylate bearing a reactive diene in

reversible diels–alder reaction. J Polym Sci Part A Polym Chem. 2007;45(19):4441-4449.

doi:10.1002/pola.22195

39. Zhao S, Zhang G, Sun R, Wong C. Multifunctionalization of novolac epoxy resin and its

influence on dielectric, thermal properties, viscoelastic, and aging behavior. J Appl Polym

Sci. 2014;131(8). doi:10.1002/app.40157

40. Araya-Hermosilla R, Broekhuis AA, Picchioni F. Reversible polymer networks containing

covalent and hydrogen bonding interactions. Eur Polym J. 2014;50:127-134.

doi:10.1016/J.EURPOLYMJ.2013.10.014

41. Araya-Hermosilla R, Pucci A, Raffa P, et al. Electrically-Responsive Reversible

Polyketone/MWCNT Network through Diels-Alder Chemistry. Polymers. 2018;10(10).

doi:10.3390/polym10101076

42. Polgar LM, van Duin M, Broekhuis AA, Picchioni F. Use of Diels–Alder Chemistry for

Thermoreversible Cross-Linking of Rubbers: The Next Step toward Recycling of Rubber

Products? Macromolecules. 2015;48(19):7096-7105. doi:10.1021/acs.macromol.5b01422

43. Polgar LM, Cerpentier RRJ, Vermeij GH, Picchioni F, Duin M van. Influence of the chemical

structure of cross-linking agents on properties of thermally reversible networks. Pure Appl

Chem. 2016;88(12):1103-1116. doi:10.1515/pac-2016-0804

44. Aubert JH. Note: Thermally removable epoxy adhesives incorporating thermally reversible

diels-alder adducts. J Adhes. 2003;79(6):609-616. doi:10.1080/00218460309540

26 CHAPTER 1

45. Kuang X, Liu G, Dong X, Liu X, Xu J, Wang D. Facile fabrication of fast recyclable and multiple

self-healing epoxy materials through diels-alder adduct cross-linker. J Polym Sci Pol Chem.

2015:n/a-n/a. doi:10.1002/pola.27655

46. Luo K, Xie T, Rzayev J. Synthesis of thermally degradable epoxy adhesives. J Polym Sci Pol

Chem. 2013;51(23):4992-4997. doi:10.1002/pola.26926

47. Asadirad AM, Boutault S, Erno Z, Branda NR. Controlling a polymer adhesive using light and

a molecular switch. J Am Chem Soc. 2014;136(8):3024-3027. doi:10.1021/ja500496n

48. Pratama P a., Peterson AM, Palmese GR. The role of maleimide structure in the healing of

furan-functionalized epoxy–amine thermosets. Polym Chem. 2013;4(18):5000-5006.

doi:10.1039/c3py00084b

49. Kötteritzsch J, Stumpf S, Hoeppener S, Vitz J, Hager MD, Schubert US. One-component

intrinsic self-healing coatings based on reversible crosslinking by diels-alder cycloadditions.

Macromol Chem Phys. 2013;214(14):1636-1649. doi:10.1002/macp.201200712

50. Wouters M, Craenmehr E, Tempelaars K, Fischer H, Stroeks N, van Zanten J. Preparation

and properties of a novel remendable coating concept. Prog Org Coat. 2009;64(2-3):156-

162. doi:10.1016/j.porgcoat.2008.09.023

51. Amato DN, Strange G a, Swanson JP, et al. Synthesis and evaluation of thermally-responsive

coatings based upon Diels-Alder chemistry and renewable materials. Polym Chem.

2013;5(1):69. doi:10.1039/c3py01024d

52. Imbesi PM, Fidge C, Raymond JE, Cauët SI, Wooley KL. Model Diels-Alder studies for the

creation of amphiphilic cross-linked networks as healable, antibiofouling coatings. ACS

Macro Lett. 2012;1(4):473-477. doi:10.1021/mz200137m

53. Zhang W, Duchet J, Gérard JF. Self-Healable Interfaces Based on thermo-reversible Diels-

Alder Reactions in Carbon Fiber Reinforced Composites. J Colloid Interf Sci. 2014;430:61-68.

doi:10.1016/j.jcis.2014.05.007

54. Peterson AM. Development of remendable polymer composites using a thermoreversible

reaction. iDEA: DREXEL LIBRARIES E-REPOSITORY AND ARCHIVES. June 2011.

https://idea.library.drexel.edu/islandora/object/idea%3A3534.

55. Peterson AM, Jensen RE, Palmese GR. Thermoreversible and remendable glass-polymer

interface for fiber-reinforced composites. Compos Sci Technol. 2011;71(5):586-592.

doi:10.1016/j.compscitech.2010.11.022

56. Xu Z, Zhao Y, Wang X, Lin T. A thermally healable polyhedral oligomeric silsesquioxane

(POSS) nanocomposite based on Diels-Alder chemistry. Chem Commun. 2013;49:6755-6757.

doi:10.1039/c3cc43432j

57. Fan M, Liu J, Li X, Zhang J, Cheng J. Recyclable Diels-Alder furan/maleimide polymer

networks with shape memory effect. Ind Eng Chem Res. 2014;53(42):16156-16163.

doi:10.1021/ie5028183

58. Yamashiro M, Inoue K, Iji M. Recyclable Shape-memory and Mechanical Strength of

Poly(lactic acid) Compounds Cross-linked by Thermo-reversible Diels-Alder Reaction. Polym

J. 2008;40(7):657-662. doi:10.1295/polymj.PJ2008042

59. Heo Y, Sodano HA. Self-Healing Polyurethanes with Shape Recovery. Adv Funct Mater.

2014;24(33):5261-5268. doi:10.1002/adfm.201400299

60. Vegetable oil projections: Production and trade. https://www.oecd-

ilibrary.org/docserver/cdca305d-

en.pdf?expires=1577621846&id=id&accname=guest&checksum=D278C1958BDDE9437E2C

6322414CDAC6. Published 2019. Accessed December 29, 2019.

61. OECD/FAO Agricultural Outlook 2018-2027. doi:10.1787/agr-outl-data-en

62. Sastry GS., Murthy BG., Aggarwal J. Diels-Alder adducts from safflower oil fatty acids: I.

Maleic Anhydrine as Dienophile. J Am Oil Chem Soc. 1971;48(11):686-688.

doi:10.1007/BF02638520

1

CHAPTER 1 27

63. Balakrishna RS, Murthy BGK, Aggarwal JS. Diels-Alder adducts from safflower oil fatty acids:

II. Styrene as Dienophile. J Am Oil Chem Soc. 1971;48(11):689-692.

doi:10.1007/BF02638521

64. Sastry GSR, Murthy BGK, Aggarwal JS. Diels-alder adducts from safflower fatty acids: III.

Acrylic and related acid dienophiles. J Am Oil Chem Soc. 1972;49(3):192-195.

doi:10.1007/BF02633794

65. Frias CF, Fonseca AC, Coelho JFJ, Serra AC. Straightforward functionalization of acrylated

soybean oil by Michael-addition and Diels–Alder reactions. Ind Crops Prod. 2015;64:33-38.

doi:10.1016/j.indcrop.2014.10.050

66. Li F, Larock RC. Thermosetting polymers from cationic copolymerization of tung oil:

synthesis and characterization. J Appl Polym Sci. 2000;78(5):1044-1056. doi:10.1002/1097-

4628(20001031)78:5<1044::AID-APP130>3.0.CO;2-A

67. Lacerda TM, Carvalho AJF, Gandini A. Two alternative approaches to the Diels–Alder

polymerization of tung oil. RSC Adv. 2014;4(51):26829-26837. doi:10.1039/c4ra03416c

68. Gandini A, Lacerda TM, Carvalho AJF. A straightforward double coupling of furan moieties

onto epoxidized triglycerides: synthesis of monomers based on two renewable resources.

Green Chem. 2013;15(6):1514. doi:10.1039/c3gc40358k

69. Vilela C, Cruciani L, Silvestre AJD, Gandini A. Reversible polymerization of novel monomers

bearing furan and plant oil moieties: a double click exploitation of renewable resources. RSC

Adv. 2012;2(7):2966. doi:10.1039/c2ra20053h

70. Vilela C, Cruciani L, Silvestre AJD, Gandini A. A double click strategy applied to the reversible

polymerization of furan/vegetable oil monomers. Macromol Rapid Commun.

2011;32(17):1319-1323. doi:10.1002/marc.201100246

71. Iqbal M. Synthesis and Properties of Bio-based and Renewable Polymeric Products. 2014.

https://www.rug.nl/research/portal/files/12356126/Complete_dissertation.pdf.

72. Stemmelen M, Lapinte V, Habas JP, Robin JJ. Plant oil-based epoxy resins from fatty

diamines and epoxidized vegetable oil. Eur Polym J. 2015;68:536-545.

doi:10.1016/j.eurpolymj.2015.03.062

73. Shibata M, Teramoto N, Makino K. Preparation and properties of biocomposites composed

of epoxidized soybean oil, tannic acid, and microfibrillated cellulose. J Appl Polym Sci.

2011;120(1):273-278. doi:10.1002/app.33082

74. Lyon D, Chrysanthos M, Gottis P, Lancelin MJM. Thèse Novel biobased epoxy networks

-property relationships Présentée devant Le

grade

75. Takahashi T, Hirayama K, Teramoto N, Shibata M. Biocomposites composed of epoxidized

soybean oil cured with terpene-based acid anhydride and cellulose fibers. J Appl Polym Sci.

2008;108(3):1596-1602. doi:10.1002/app.27866

76. Liu Z, Erhan SZ. Ring-Opening Polymerization of Epoxidized Soybean Oil. J Am Oil Chem Soc.

2010;87(4):437-444. doi:10.1007/s11746-009-1514-0

28 CHAPTER 1