Protected versus unprotected dextran macroinitiators for ATRP synthesis of Dex-g-PMMA

Protected Versus Unprotected Dextran Macroinitiatorsfor ATRP Synthesis of Dex-g-PMMA

LUDOVIC DUPAYAGE, CECILE NOUVEL, JEAN-LUC SIX

Laboratoire de Chimie Physique Macromoleculaire, UMR 7568 CNRS-Nancy University, ENSIC,

BP 20451, 54001 Nancy cedex, France

Received 1 July 2010; accepted 21 September 2010

DOI: 10.1002/pola.24409

Published online 18 November 2010 in Wiley Online Library (wileyonlinelibrary.com).

ABSTRACT: The synthesis of amphiphilic dextran-g-poly(methyl

methacrylate) glycopolymers (Dex-g-PMMA) is studied using

‘‘grafting from’’ concept and atom transfer radical polymeriza-

tion. Two strategies have been examined to control the macro-

molecular parameters of such glycopolymers. One is involving

four steps including a protection/deprotection approach and the

second one only two steps. The introduction of initiators group

onto a protected acetylated dextran (and directly onto dextran)

was achieved resulting in protected DexAcBr (and in unpro-

tected DexBr). These two types of polysaccharidic macroinitia-

tors differ in term of solubility (hydrophilic DexBr vs.

hydrophobic DexAcBr) and of position of the initiators groups

on the glucosidic units (which are the sites of the future grafts).

When evaluated as macroinitiators for ATRP of MMA, control

was achieved in both cases but DexBr gave much faster poly-

merization and lower average grafting efficiency compared with

DexAcBr or model initiator. Advantages and drawbacks of both

pathways have finally been discussed. VC 2010 Wiley Periodicals,

Inc. J Polym Sci Part A: Polym Chem 49: 35–46, 2011

KEYWORDS: ATRP; polysaccharides; amphiphiles; biopolymers;

glycopolymer; DMSO

INTRODUCTION Natural polysaccharides are very suitablecandidates for biomedical applications, because they arerenewable, biodegradable and biocompatible materials.Nevertheless, the choice of polysaccharide is very dependingon the aimed biomedical application, because it has to bebiocompatible toward the cells of the surrounding medium.1

For example, dextran has largely been used as blood plasmaexpander2–4 or for drug delivery system.5 However naturalpolysaccharide lacks some essential properties and has to bemodified. Grafting synthetic polymer onto natural polysac-charide is one of the best ways to combine both advantagesof natural and synthetic polymers for a wide range of appli-cations. Such a copolymer can be called a grafted glycopoly-mer.6–8 As example given, cellulose has already been modi-fied with various synthetic polymer chains for genedelivery,9 or to produce smart hydrogel,10 potential drugnanocarriers,11 dendronized polymers,12 or cellulose mem-brane for hemodialysis.1

The best route to control the parameters of such grafted gly-copolymers is the well-known ‘‘grafting from’’ method ifusing a controlled polymerization. In this way, the copolymerpollution caused by nongrafted homopolymer could beavoided. Recently comb-like glycopolymers with well-definedarchitecture such as polylactide-grafted dextran (Dex-g-PLA)7,13 were developed in our laboratory by this strategy.Synthesized using controlled ring opening polymerization(ROP) of D,L-Lactide, these copolymers could be used as bio-

compatible and biodegradable surfactants.14,15 Going frompolyester grafts to polyvinylic ones, controlled radical poly-merizations have recently appeared as very attractive tomodify polysaccharides compared with previous conven-tional polymerization techniques investigated in the last cen-tury.16 In particular, atom transfer radical polymerization(ATRP) has emerged as a robust method for preparation ofmany well-defined polymers with controlled architecture ina wide variety of solvents and compatible with a largeamount of functionalities.17–19 Numerous studies have al-ready shown how to use ATRP for grafting from polysac-charidic surface20–27 (mainly in cellulose20–25) or in hetero-geneous conditions.28 Nevertheless, due to the poorsolubility of most polysaccharides, considerably less articleshave reported the synthesis via ATRP of such products in ho-mogeneous conditions, which enable a better control of thearchitecture. To overcome this problem two strategies hasbeen developed. One is the use of hydrophobically protectedpolysaccharide as macroinitiator.6,9,11,12,29 Thus syntheticpathway is including protection/deprotection steps or usinghydrophobic derivatives of natural polyssacharides. Theother consists in carrying out the ATRP directly from unpro-tected polysaccharidic macroinitiators of natural polysaccha-rides. Indeed these problems of solubility have considerablyhampered extensive use of ATRP from unprotected polysac-charide macroinitiators (cellulose,1,30–32 pullulan,33 or dex-tran33,34 macroinitiators).

Correspondence to: C. Nouvel (E-mail: [email protected])

Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 49, 35–46 (2011) VC 2010 Wiley Periodicals, Inc.

SYNTHESIS OF Dex-g-PMMA BY ATRP, DUPAYAGE, NOUVEL, AND SIX 35

To diversify the available glycopolymers, we lately extendour Dex-g-PLA ‘‘grafting from’’ synthetic pathway carried outin homogeneous conditions to the synthesis of poly(methylmethacrylate)-grafted dextran copolymers (Dex-g-PMMA)using ATRP as controlled polymerization.6 On one hand, westudied first the protection/deprotection pathway calledroute A (Scheme 1).6 In the first step, the dextran OH func-tions were partially acetylated. The second step consisted inlinking initiator groups by reaction of 2-bromoisobutyrylbromide (BiBB) with the unprotected OH functions. Third,the ATRP of methyl methacrylate (MMA) was carried out inDMSO from the resulting dextran derivative (called DexAcBr)used as a macroinitiator. Finally, the cleavage of the acetategroups led to the expected glycopolymers. However, weinvestigated more recently ATRP carried out in DMSO,directly from unprotected dextran macroiniators calledDexBr (route B, Scheme 1). This second way is morestraightforward since it only requires two steps. But the sol-ubility of the DexBr macroinitiator used in this study is verysimilar to initial dextran and limits the number of solventavailable for ATRP of MMA essentially to DMSO. To ourknowledge, they were the first poly(methyl methacrylate)-grafted dextran copolymers synthesized by ATRP.

In this article, synthesis of both types of macroinitiator (pro-tected DexAcBr and unprotected DexBr) has been first exam-ined in details in term of solubility, of number and positionof the initiator groups on the glucosidic unit (that is the oneof the future grafts) and at last, of stability dextran back-bone. Second, experimental conditions used in route A wereapplied to DexBr macroiniators but they needed to beadapted due to very high polymerization rate. Then, the con-trol of the ATRP from both types of polysaccharidic macroi-nitiator has been compared in the same solvent (DMSO).Finally, advantages and drawbacks of both pathways will bediscussed. To our knowledge, it will be the first article to es-tablish the comparison between protected and unprotectedstrategies for brush-like glycopolymers synthesis.

EXPERIMENTAL

MaterialsDextran T40 [Mn ¼ 33.800 g/mol, a polydispersity index (I) ¼1.27, as characterized by size exclusion chromatography coupledto multiangle laser light scattering (SEC-MALLS) in water (0.1 MNaNO3, 6.15 � 10�3 M NaN3)] was purchased from PharmaciaBiotech and dried under reduced pressure at 100 �C for onenight. Dextran T40 was also analyzed by SEC-MALLS usingDMSO (0.1 M NaNO3) as eluent and was estimated to have Mn

¼ 38.000 g/mol and I ¼ 1.10. Triethylamine (NEt3), ethyl2�bromoisobutyrate (EBiBr), 2-bromoisobutyryl bromide(BiBB), 2,2’-dimethylaminopyridine (DMAP), and copper bro-mide (Cu(I)Br) were purchased from Aldrich while copperdibromide (Cu(II)Br2) was obtained from Fluka. All of thosewere used without further purification. Methyl methacrylate(MMA, Aldrich 99%) and DMSO (DMSO, Fischer scientific 99%)were vacuum distilled from CaH2 and stored under nitrogenatmosphere. Pyridine (Aldrich) was dried over BaO and filteredbefore use. N-(n-propyl)-2-pyridylmethanimine (n-Pr-PMI)35 and2-Bromoisobutyryl anhydride (BriBA)36 were prepared using lit-erature procedures with slight modifications. Dialysis mem-branes were purchased from Spectra Por (MWCO: 6000–8000).

All along the syntheses, dextran stability was checked by testexperiments where dextran underwent all the reaction stepsfor route A, without addition of anhydride in the first step,of BiBB in the second step or for route B without BriBA inthe first step (Scheme 1). Resulting samples were then ana-lyzed by SEC-MALLS in water (0.1 M NaNO3, 6.15 � 10�3 MNaN3) and compared with initial dextran. No difference wasobserved between the molecular weight distribution profilesof the resulting dextran products and the one of the initialdextran testifying that degradation observed would be onlydue to the reactant used during macroinitiator synthesis.

Synthesis of Dextran MacroinitiatorsProtected macroinitiators DexAcsAcBrsBr were synthesized intwo steps as previously described.6 In the first step, the

SCHEME 1 The two synthetic

pathways of Dex-g-PMMA: syn-

thetic scheme includes steps 1 to

4 (Protected Route A) or only 1’

and 2’ (Unprotected Route B).

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA

36 WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

dextran OH functions were partially acetylated. The secondstep consisted in linking initiator groups by reaction of BiBBwith the unprotected OH functions. The s is the modificationyield (that is the number of acetate (sAc) or of initiatorgroups (sBr) for 100 OH of the initial dextran).

Unprotected Macroinitiator DexBrsBrOne gram of dextran (6.2 mmol of glucosidic units, 18.5mmol of OH) was dissolved in DMSO (18 mL). 0.11 g ofDMAP (0.05 mol per mol of OH) was dissolved in 4.5 mL ofdried pyridine (3 mol per mol of OH) and then added to thedextran solution. To obtain a dextran derivative with sBr of20%, 2.4 g of BriBA (7.6 mmol) was then slowly introducedat 0�C during half an hour and the reaction was left at roomtemperature for 20 h. The polymer was precipitated twice inacetone and the product was filtrated, washed, and dried at50 �C under vacuum during 24 h. The sBr (%) was evaluatedby 1H NMR in DMSO-d6 using eq. 1 where ABr is the area ofthe singlet around 1.9 ppm, which is methyl protons fromthe initiator group. As previously for DexAcBr,6 the globalarea from 4 to 5.7 ppm (called A4!5.7), corresponded to 4protons (the coupling of the initiator group on anyOH induced the shift of the glucosidic H supported by thesame C).

sBr ð%Þ ¼ ABr

A4!5:7

� �� 4� 100

18: (1)

ATRP OF MMAFrom Model InitiatorIn a typical experiment, 14 mL of MMA (0.13 mol), 18 mL ofDMSO, and 1.4 mL of anisole (0.01 mol, used as NMR refer-ence) have been introduced in a reactor under nitrogenatmosphere. Next, Cu(I)Br (193 mg, 1.35 mmol) andCu(II)Br2 (30 mg, 0.13 mmol) have been added in additionwith appropriated amount of n-Pr-PMI. After 10 min of stir-ring, the reaction mixture was degassed by three freeze-pump-thaw cycles and the reactor was then immersed in athermostated oil bath at the reaction temperature (60 or 30�C). The initial MMA/anisole ratio ([MMA]0/[Anisole]0) wasestimated by 1H NMR analysis of an immediate aliquot. Poly-merization was started by adding 0.2 mL of EBiBr (1.35mmol). To follow the conversion yield and the evolution ofmolar masses, samples have been taken at different timesthroughout the reaction. Monomer conversion was deter-mined by 1H NMR in CDCl3 using eq. 2 from the area of bothsinglet of MMA methylene protons (AMMA, at 5.5 and 6 ppm)and that of some anisole protons (AAnisole, 3H at 6.8 ppm).

conversion ð%Þ ¼ 1� 3� AMMA

2� AAnisole� ½Anisole�0

½MMA�0� 100: (2)

Catalyst residues were removed by passing through a shortsilica column using THF as eluent. Crude PMMA has beenprecipitated twice from petroleum ether and dried overnightat 50 �C under vacuum. Purified product was then analyzedboth by SEC-MALLS using THF as eluent and by 1H NMR inCDCl3.

From the DexAcBr MacroinitiatorExperimental protocol is already published.6 For example, incase of DexAc71Br6, typical experimental conditions were asfollows: [MMA]0 ¼ 4 M, [Anisole]0 ¼ 0.4 M, [MMA]0/[Br]0/[n-Pr-PMI]0/[Cu(I)Br]0/[Cu(II)Br2]0 ¼ 100/1/2/1/0.1 (molarratio), where [Br]0 is the initial concentration of bromide(here [initiator group]0). To follow the conversion yield andthe evolution of molar masses, samples have been taken atdifferent times throughout the reaction. Monomer conversionwas determined by 1H NMR in CDCl3 using previous eq. 2.For each sample, catalyst residues were removed as previ-ously described. Crude sample was purified by precipitationtwice by petroleum ether and then dried overnight at 50 �Cunder vacuum. The purified product was called DexAc-g-PMMA.

From the DexBr MacroinitiatorDexBr has been dissolved in DMSO. Then predeterminedamounts of n-Pr-PMI, Cu(I)Br and finally Cu(II)Br2 were suc-cessively introduced in the reactor, whilst a solution of ani-sole (0.1 M) in MMA was prepared separately. Each mixturewas degassed by three freeze-pump-thaw cycles after a 10min stirring, and then the reactor was heated at convenienttemperature (that is 45 or 60 �C). Afterward an appropriatevolume of the anisole solution (0.4 M in MMA) wastransferred in the reactor with a canula. At this time, thepolymerization was started. For example in case of DexBr4.3,typical experimental conditions were as follows: 45 �C,[MMA]0 ¼ 4 M, [Anisole]0 ¼ 0.4 M, [MMA]0/[Br]0/[n-Pr-PMI]0/[Cu(I)Br]0/[Cu(II)Br2]0 ¼ 100/1/2/1/0.1 (molarratio), where [Br]0 is the initial concentration of bromide(here [initiator group]0). The evolutions of conversion yieldand of molar masses were followed as above. Catalyst resi-dues were removed as previously described. Crude samplewas purified by precipitation twice by petroleum ether anddried overnight at 50 �C under vacuum. The purified productwas called Dex-g-PMMA.

In this article, DexAAc-g-PMMA and DexA-g-PMMA (or DexB-g-PMMA) mean copolymers obtained after the three firststeps or the four steps through route A of Scheme 1 (or twosteps through route B ), respectively.

Cleavage of the PMMA Grafts from Dextran BackboneTo study the PMMA grafts, the dextran backbone ofDexAAc-g-PMMA or of DexB-g-PMMA (500 mg) was com-pletely degraded using 60 mL of THF/(1 M KOH-MeOH) (2/1 v/v) under stirring at room temperature for 72 h. Therecovered mixture was then neutralized with 1 M HCl. Afterevaporation of THF and methanol, PMMA chains were solubi-lized in toluene and the solution was filtered to remove KCl.PMMA was recovered by precipitation with petroleum ether,filtrated, and was then dried overnight at 50 �C under vac-uum. The polymers were analyzed by 1H NMR in DMSO-d6to prove the absence of the dextran backbone. The molarmasses of PMMA chains and their distribution were thencharacterized by SEC-MALLS in THF. We have alreadyreported,6 that under these hard basic conditions, no degra-dation of PMMA chain was observed and the stability of the

ARTICLE


methyl ester of each monomer unit was ascertained by 1HNMR analyses.

SaponificationDexAc, DexAcBr, DexBr, or DexAAc-g-PMMA (500 mg) weredissolved in 10 mL of DMSO/MeOH mixture (1/1 v/v). KOH(1 M in MeOH) was then added with a molar ratio equal to0.06 mol of KOH per mol of ester function onto the dextranderivative (DexAc, DexAcBr, DexBr, or DexAAc-g-PMMA). Af-ter 2 h of stirring at room temperature, the obtained productwas purified by dialysis and freeze-dried. Hydrolyzed prod-ucts called HDexAc, HDexAcBr, HDexBr, or DexA-g-PMMAhave been recovered after the saponification of DexAc, Dex-AcBr, DexBr, or DexAc-g-PMMA, respectively.

The stability of PMMA and dextran parts during this reaction(case of DexAc, DexAcBr, or DexAAc-g-PMMA) has alreadybeen proven by experiments on PMMA and on initial dextranwith similar mild basic conditions.6

Characterizations1H NMR spectra were recorded on a Bruker Avance 300 ap-paratus (300.13 MHz, 25 �C) in DMSO-d6 or CDCl3.

Size exclusion chromatography analyses of dextran and HDexderivatives (HDexAc, HDexAcBr, or HDexBr) were performedin water (0.1 M NaNO3–6.15 10�3 M NaN3 ) at room temper-ature using a Waters HPLC pump (Waters 410) equippedwith a DG-1310 degazer, a serial set of SB-806-HQ, SB-805-HQ, SB-804-HQ OHPack columns, and SB-OH Pack guard col-umn (Shodex). Elution (0.7 mL min�1) was dually monitoredby multiangle laser light scattering (MALLS) and differentialrefractometry (Waters 410).

In the case of PMMA chains, analysis was similar but wasperformed at room temperature using a Merck HPLC pump(L-6200A) equipped with a degazer, three PLgel 5 lm col-umns [100 Å, 300 � 7.5 mm; 1000 Å, 300 � 7.5 mm, andguard columns, 50 � 7.5 mm (all columns from Polymer lab-oratories)]. THF was used as eluent, at elution rate 0.7 mLmin�1. Two detectors were used online: a multiangle lightscattering detector (MALLS) and differential refractometry(Merck RI-71). Solutions (10 mg mL�1) were prepared bydissolution in the eluent and were left under vigorous stir-ring for 24 h. Filtration of these solutions was carried outright before injection.

Refractive index increments (dn/dc) of 0.087 and of 0.145were used for PMMA in THF, for dextran in water,respectively.

RESULTS AND DISCUSSION

Macroinitiators SynthesisAs described in Scheme 1, route A, bromoisobutyryl groupsas initiator groups have been introduced onto dextran, byreacting BiBB on acetylated dextran (DexAc) in THF as pub-lished previously.6 But the direct reaction carried out ontodextran was not successful in DMSO, DMF, or Bamford mix-ture.37 That is why we adapted the procedure of the dextranacetylation by using as bromo reagent 2-bromoisobutanoicanhydride (BriBA), which has already been tested onto b-

cyclodextrin.36 The presence of initiator groups onto DexBrwere attested by both NMR and FTIR spectroscopies: peakat 1.9 ppm (or at 31 ppm) observed on 1H NMR (13C NMRrespectively) spectrum corresponded to methyl of the initia-tors groups while FT-IR spectrums displays the appearanceof the carbonyl vibration band at 1734 cm�1 and methylstretching band at 1279 cm�1. As previously for DexAcBrmacroinitiator, the yield in initiator groups (sBr, number ofinitiator group per 100 OH of the initial dextran) was calcu-lated from 1H NMR spectrum and using eq. 1. The influenceof the amount of BriBA anhydride compared with the OH ofthe dextran was studied. In this way, sBr could be varied line-arly from 0 to 10% (higher was not aimed) by increasingthis BriBA/OH molar ratio (Fig. 1). Nevertheless, the molarratio of bromo reagent required to attain a specific sBr ishigher for DexBr synthesis compared with the DexAcBr.6

Solubility of Both Types of MacroinitiatorsTo produce Dex-g-PMMA glycopolymers with similar parame-ters via routes A or B, we suggest using DexAcBr and DexBrmacroinitiators with the same amount of initiator groups.But, both macroinitiator types are completely different interm of solubility. While DexBr solubility is very similar todextran at least in the used range of modification (sBr below10%), it is for DexAcBr very depending on global yield ofmodification (sAc þ sBr). In our conditions (high values of sAcaround 70% and limited amount of initiators groups –sBrbelow 13%), DexAcBr is hydrophobic and soluble like itsprecursor DexAc in less polar solvents (acetone, chloroform)or even in solvent with low polarity such THF or toluene.Nevertheless it is perfectly soluble in DMSO.

In view of glycopolymer synthesis by ‘‘grafting from’’ strat-egy, this difference of solubility is very important as that isthe limiting parameter to find an adequate solvent for

FIGURE 1 Influence of the used bromo reagent/(OH of initial

dextran) molar ratio on sBr. (sBr is the yield in initiator groups

for 100 OH of the initial dextran and was calculated from 1H

NMR). l DexAcBr and ^ DexBr were synthesized through

route A (respectively route B) from DexAc71 (respectively from

dextran).



polymerization of the selected monomer. This difficulty isespecially high in case of glycopolymers synthesis whenpolymers constituting the graft and the backbone have notthe same solubility. In our case for example, direct graftingof MMA from dextran requires to find a common solvent ofboth grafts and dextran (that is DMSO) or to use a protectedmacroinitiator through a protection/deprotection pathway tomodify the solubility character of the macroinitiator.

Reactivity OrderThe position of the protective/initiators groups onto the dex-tran influences the one of the grafts into the final copolymer.Consequently, the reactivity of each alcohol function carriedby dextran has to be studied in both cases to presume thestructure of macroinitiators and of the resulting copolymers.Indeed in polysaccharides, each hydroxyl group has generallya specific reactivity38 due to steric and electronic effects (SeeFig. 2 for notation of dextran OH). In case of dextran, reactiv-ity of OH functions has often been studied towards classicalesterification39 and is very depending on the nature of usedreagent.39–41 Nevertheless, the OH carried by the carbonatom C2 of dextran, which is noted in the following text OH2,is often the most reactive. This high reactivity is related toits high basicity due to its hydrogen bonding with the O car-ried by carbon atom C1. In case of dextran esterifica-tion,39,41–43 reported reactivity was the following: OH2 >

OH4 > OH3. In such cases, reactivity of OH4 could beexplained by the formation of intramolecular H bondingbetween OH4 of one glucosidic unit with the ester group ofthe next glucosidic unit. Even if the chemistry of reagent isvery important, reactions conditions could modify the rea-gent electrophilic character and thus the OH reactivityorder.44 OH2 was notability highly reactive in the presence ofpyridine, as in our cases (acetylation for the synthesis ofDexAc and introduction of initiator groups for the synthesisof DexBr). To our knowledge, no information was publishedabout esterification with the reagents used in this work.

Based on our previous attribution of the NMR dextran reso-nance signals,45 1H NMR spectra in DMSO-d6 of variousDexAc (sAc) and DexBr (sBr) were compared in the modifica-tion ranges used. Assuming that each glucose unit exhibitsthe same accessibility and overlooking the reactivity changeswith the substitution of one OH function, the study of 1H

NMR spectra of slightly modified dextrans with differentmodification yields allows us to determine the OH functionsto be first substituted.

As shown in Figure 3, one can observe a strong modificationof the shapes of the glucosidic protons multiplet [3–4 ppm]and of the peaks surrounding the anomeric proton one [4.2–5.7 ppm] with increasing substitution degrees. As previouslyreported,6 acetylation of any OH shifts the signal of the glu-cosidic proton carried by the C linked to the acetate groupfrom 3 ppm (glucosidic protons area) to 4.3 ppm [close tothe anomeric H peak, Fig. 3(a)]. The same phenomenon wasobserved when initiator groups are introduced by ester link-age onto the backbone either onto DexAc (second step, routeA) or onto dextran [first step route B, Fig. 3(b)]. All of thismakes precise attribution very difficult at high modificationyield. That is why we limited the study to lowest substitu-tion yield of dextran considering only the lowest sAc and sBr(below 12%). In both cases, the change in peaks between4.2 and 5.7 ppm proves that the area of OH2 peak is the firstto predominantly decrease. That indicates the high reactivityof OH2 for reaction of dextran with acetic and 2-bromoisobu-tanoic anhydrides. Moreover, in case of reaction with BriBA[Fig. 3(b)], it seems that OH4 is preferentially modified com-paratively to OH3 at slightly higher modification yield(around 5–10%). Similar trend is not so clear for reactionwith acetic anhydride even at moderate sAc (11% < sAc<32%). Thus, OH reactivity order is most probably OH2 >

OH4 >OH3 for introduction of initiators groups using BriBA,in agreement with the order reported in case of esterifica-tion like acetylation.39,41–43 To conclude, reactivity is verysimilar in both cases despite the more bulky anhydride usedfor direct introduction of initiator groups onto dextran.

Finally, from this reactivity order, one can imagine the posi-tion of initiators groups and thus of the future grafts forboth types of macroinitiators. However, in case of route A,DexAcBr macroinitiators are issued from DexAc having highsubstitution yield (>70% in our case), so the initiator groupsposition could only be located on OH3 or OH4. However, incase of route B, DexBr are modified at very low yield(<10%) and certainly only on OH2.

Macroinitiator StabilityDextran stability has already been checked all along the syn-thesis of DexAcBr and only the two first steps (protection byacetylation and introduction of initiators group) werefounded to be damageable for dextran backbone.6 Therefore,it was interesting to evaluate and compare the stability ofdextran through route B, wherein only the macroinitiatorsynthesis could be degrading as polymerization conditionshave already been proved as harmless.6 Several dextranderivatives (DexAc and DexAcBr) were saponified as in theprevious study,6 under mild basic conditions during 2 h inDMSO/MeOH with a small amount KOH. No degradation ofdextran chains has already been evidenced under these basicconditions. Therefore cleavage of all the ester bonds led tothe so-called ‘‘hydrolyzed’’ DexAc, DexAcBr, and DexBr namedHDexAc, HDexAcBr, and HDexBr, respectively. After the

FIGURE 2 Structure of dextran.

ARTICLE


treatment, these products were analyzed by SEC-MALLS inwater and compared to initial dextran (Table 1, Fig. 4). Incase of route A (Scheme 1), the various HDexAc showed a

slight hydrolysis of the dextran backbone depending on theamount of anhydride used.6 Moreover, HDexAcBr resultsascertained a further degradation of dextran chains during

FIGURE 3 1H NMR spectra (in

DMSO-d6) of different protected

dextrans. (a) Acetylated dextran

DexAcsAc (sAc varying from 11 to

71%). (b) DexBrsBr (sBr varying

from 3 to 9.9%).



the second step of route A and the extent of this degradationincreased with the amount of BiBB used [Table 1 and Fig.4(a)]. In case of HDexBr, the results showed a degradation ofthe dextran backbone depending on the BriBA/OH molar ra-tio used: the lower was the anhydride molar ratio per OH ofthe dextran (BriBA/OH), the higher were the resulting molarmasses. At worst, when this molar ratio was 0.3, the Mn ofthe recovered HDexBr7.0 were roughly divided by 2 com-pared with that of dextran (Table 1). Indeed this degradationis even worse compared with route A as lower molecularmasses of the dextran backbone were obtained for theHDexBr7.0 compared with that (Mn ¼ 32.800 g/mol)observed when 0.3 mol of acetic anhydride was used per OHdextran.6

Polymerization from Both Macroinitiators ComparisonKineticsOnce macroinitator synthesis was achieved, we examined thepolymerization from both types of macroinitiators. To com-pare them, polymerizations have to be carried out in thesame conditions. The solubility of the dextran derivativemacroinitiators and of the PMMA limits the number ofsolvent usable for homogeneous ATRP of MMA, essentiallyto DMSO. Polymerization conditions have been studiedin this solvent, first with a model initiator ethyl2�bromoisobutyrate (EBiBr) and then from both macroini-tiators. Here, we will compare controlled polymerizationsfrom a variety of macroinitiators carried out in same orclosely related conditions. Results are given in Table 2, exam-ples of kinetics curves on Figure 5(a) and of molar masseson Figure 5(b).

However experimental conditions optimized with EBiBr asmodel initiator were founded to be perfectly effective to con-trol the polymerization initiated from DexAcBr. Polymeriza-tion was carried out at 60 �C with [MMA]0 ¼ 4 M and

[MMA]0/[Br]0/[n-Pr-PMI]0/[Cu(I)Br]0/[Cu(II)Br2]0 ¼ 100/1/2/1/0.1 (molar ratio). Both kinetics curves for model initia-tor and DexAc71Br6.0 for instance (entries 1 and 2 of Table2) gives linear and similar first–order kinetics semilogarithmplot [Fig. 5(a)]. Similar results have been obtained for all theDexAcBr macroinitiators in Table 2.6 However, all the assayscarried out in similar conditions from unprotected macroini-tiators DexBr resulted in a very quick polymerization withgel formation after only 30 min due to intermolecular cou-pling between growing chains. After this period, conversionreached 90 %. Therefore we optimized the conditions toobtain a controlled ATRP from DexBr and finally two condi-tions were founded. First, the total amount of Cu(I)Br rela-tive to initiator groups concentration was increased whilstkeeping constant Cu(II)/Cu(I) molar ratio. This is supposedto encourage chain deactivation and thus to reduce the win-dow of time available for propagation.46 Nevertheless, it wasnecessary to increase [CuIBr]0/[Br]0 molar ratio up to 2.5[case of DexBr5.6, entry 5, Table 2 and Fig. 5(a)] to preventgel formation. In such conditions, obtained kinetics curvewas linear up to a least 80 % of conversion but a delay pe-riod of 20 min appeared, which is common of ATRP poly-merization carried out with high amount of catalytic system.Second, polymerization temperature was reduced to 45 �C todecrease both ATRP equilibrium and radical concentration,and thus polymerization rate: DexBr4.3 (entry 6, Table 2) isgiven as example in Figure 5(a). It can be seen on Figure5(a) that in both previous cases, the polymerization rateremained considerably higher (about 54% of conversion af-ter 60 min) compared to that of ATRP from DexAcBr. Thiscould be explained by the higher polarity of the surroundingmedium when making a polymerization from an unprotectedDexBr macroinitiator. Indeed the second option (polymeriza-tion at 45 �C) is preferable since less copper is necessary tocarry out this polymerization, which is better for

TABLE 1 Stability of the Dextran During Synthesis

Name Mna (g/mol) Ia anhydride/OHb BriBBr/ORc BriBA/ORd

T40 33,800 1.27 - -

HDexAc62 28,700 1.18 0.7 0.0

HDexAc62Br12.8 25,600 1.25 0.7 0.3

HDexAc70 28,200 1.21 0.7 0.0

HDexAc70Br12.7 19,200 1.38 0.7 0.2

HDexAc70Br15.2 16,000 1.45 0.7 0.3

HDexBr0.8 21,600 1.22 0.02

HDexBr2.7 17,400 1.22 0.10

HDexBr4.3 16,900 1.19 0.15

HDexBr4.6 17,100 1.21 0.20

HDexBr5.1 16,400 1.24 0.25

HDexBr7.0 16,100 1.40 0.30

a Determined by SEC-MALLS in water (0.1M NaNO3 � 6.15 10�3 M NaN3) using dn/dc¼0.145.b Acetic anhydride/OH molar ratio used (route A, see ref. 6).c BriBBr/OR molar ratio used (route A, see ref. 6).d BriBA/OH molar ratio used (route B).

ARTICLE


environmental and economical issues. In addition, increasingthe initial molar ratio of Cu(II)/Cu(I) turned out to beinefficient even with high value (0.8 for instance) as gel for-mation was not suppressed at the end. Thus all polymeriza-tions from DexBr were done at 45 �C and have beencontrolled.

Indeed in all cases, control of the polymerization was ascer-tained by SEC-MALLS analysis of PMMA grafts after theirdeliberate cleavage from dextran backbone. In all cases, SECchromatograms attested the presence of only one population.Number average molecular weight Mn of the grafts werevery similar in both cases. They increased linearly with con-version and could be compared with theoretical Mn ofPMMA grafts [calculated from conversion and [MMA]0/[Br]0ratio, Fig. 5(b)]. Polydispersity indexes remained below 1.1except for polymerization carried out from DexBr5.6 at 60 �Cwith high initial load of copper. Higher polydispersities inthis latter case revealed a less perfect control compared withthe other polymerizations.

Average Grafting Efficiency (Eff)As shown on Figure 5(b), experimental molecular massesare considerably higher than the theoretical ones due to lowinitiator efficiency whatever the macroinitiator. Indeed simi-lar behavior was observed with polymerization carried outfrom the model initiator where an almost constant efficiencywas evaluated to 67%. This low initiation efficiency is cer-tainly due to side reactions at the first stage of the reaction.Those could have originated from primary coupling of radi-cal issued from the initiator and/or from the more labileCABr bond end groups at the beginning of the reaction47

resulting in the penultimate effect, also called back straineffect. In case of macroinitiators based on dextran, the com-parison between experimental and theoretical Mn of PMMAgrafts allowed us to evaluate an average grafting efficiency(Eff) for each macroinitiator as given in Table 2. Indeed, thisgrafting efficiency was the average efficiency for each initia-tor group carried by the polysaccharide chain. In case ofDexAcBr macroinitiators, Eff was found around 55% slightlylower to the value obtained with the model initiator (EBiBr).In the used range, we suggested that the amount of initiatorsgroups had low influence on the grafting efficiency or on thekinetics. Probably there was little steric hindrance betweenthe initiator groups onto DexAcBr, due to their relatively lownumber per macroinitiator chain (<20 initiator groups perdextran chain). For DexBr macroinitators, Eff could be eval-uated around 25% whatever the macroinitiator. With theseunprotected macroinitiators, values were very similar inboth conditions of polymerization (i.e., 60 �C with high initialload of copper or 45 �C with usual amount of copper). Thisis considerably lower compared to the estimated value withDexAcBr around 55%. Such a difference between the twotypes of macroinitiator is quite surprising. Even if increaseof surrounding medium polarity with DexBr induces a fasterpolymerization and thus a higher influence of penultimateeffect, other factors should be considered. The most realisticexplanation for this difference resides in chemical incompati-bility between hydrophilic dextran backbone and ratherhydrophobic MMA and PMMA grafts. Because of this differ-ence, accessibility of inner initiator sites (inside dextran coil)to MMA is lower than those located at the surface. Conse-quently, only initiator group near the surface of the macroi-nitiator coil would be accessible to MMA monomers, whichtend to segregate outside the coil. In addition the PMMAarms would prefer to extend away from the macroinitiatorcoil (Scheme 2). Therefore, the CABr groups at termini ofthe PMMA arms are away from the congested coil and havemore opportunity to access the monomer and catalytic com-plex than the uninitiated inner CABr bonds. As a result, theinitiator groups inside the coil have very little chance to ini-tiate a graft, which reduces average grafting efficiency (Eff).This incompatibility would not be observed so much in caseof DexAcBr macroinitiator because its hydrophobicity ismore comparable in polarity to PMMA arms. Thus, all initiat-ing sites (C-Br) inner and at the coil periphery have a similarenvironment and opportunity to react with catalyst, which isessential to obtain a high Eff. Such a phenomenon has al-ready been observed in case of star copolymers synthesized

FIGURE 4 Aqueous SEC chromatograms of initial dextran and

several dextran derivatives, which have been deprotected:

HDexAcsAc, HDexAcsAcBrsBr, or HDexBrsBr: (a) route A and (b)

route B.



via ATRP using the arm-first method from a noncleavablecore, including poly(divinylbenzene) and poly(tert-butyl acry-late).48 In that case, average efficiency during the secondgeneration was depending on the chemical nature of thissecond generation of arms. Efficiency was lowered from 100to 30% when the chemical compatibility of the second gen-eration of arms to the first generation of arms decreased.

ATRP Equilibrium ConstantsIn each case, ATRP equilibrium constant (Keq) can be eval-uated from the slope of the kinetics semilogarithmic plotthat is the apparent propagation rate constant (kapp)obtained from kinetics curve (eq 3). Their values are givenon Table 2. We checked that in our conditions [Cu(II)Br2]0corresponds to the [Cu(II)Br2]threshold,

6,9,49,50 which is suffi-cient to assume a near constant ratio of both [Cu(II)Br2] and[Cu(I)Br] throughout the polymerization, at least in the timerange where lnð½M�0

½M�tÞ vs time remains linear. In addition, [Br],[Cu(I)], and [Cu(II)] should be close to their initial concen-trations ([Br]0, [Cu(I)]0, and [Cu(II)]0). Therefore, based onMatyjasweski’s equation (eq 3), kapp can be related to theinitial bromide concentration ([Br]0) and to the initial coppermolar ratio (½CuðIIÞ�0½CuðIÞ�0 ):

ln

½M�0½M�t

!¼ kpKeqEff

½Br�0½CuðIÞ�0½CuðIIÞ�0

t ¼ kapp � t (3)

where Eff is the average grafting efficiency and Keq ¼ kactkdeact

with kact and kdeact, the rate constants of activation and deac-tivation, respectively.

As already done by Matyjasweski and coworkers,50 andusing available free radical propagation rate constants (kp ¼833 or 569 L mol�1 s�1 at 60 �C (at 45 �C), respectively, Ta-ble 2),51,52 the kinetics data from ATRP allows thus an esti-mation of equilibrium constant (Keq) for ATRP of MMA inDMSO for each polymerization kinetics. Results are resumedin Table 2. Indeed these values for a same macroinitiatortype are very variable (from 1.6 � 10�7 to 2.2 � 10�7 forDexAcBr and from 1.4 � 10�6 to 3.9 � 10�6 for DexBr).

This just indicates some uncertainty in their determination,probably due to little variation of Eff. Thus only the magni-tudes of their value are to be taken into account. In case ofpolymerization from DexAcBr, Keq are similar to value of po-lymerization from model EBiBr, which is of classical order ofvalue for ATRP of MMA.50 To the reverse, polymerizationfrom DexBr gives equilibrium constant values about 10 timeshigher. This increase of Keq for ATRP is not surprising sincemedium polarity rise when going from case of DexAcBr toDexBr, even when the polymerization temperature is reducedfrom 60 to 45 �C. This is perfectly coherent with theincrease of polymerization rate from DexAcBr to DexBr,keeping constant all the conditions (expect temperature orinitial load of copper total amount). Indeed, DexBr containshigher number of free OH compared with DexAcBr. In addi-tion being more hydrophilic, DexBr still contains highamount of water even after drying (4.5 wt % compared with1 wt % for DexAcBr) strongly linked to the dextran back-bone through hydrogen bonds via its remaining free OH. Allof this contributes to increase the surrounding medium po-larity and consequently the Keq value.

CONCLUSION

The synthesis of amphiphilic grafted glycopolymers (Dex-g-PMMA) made of an hydrophilic dextran backbone and hydro-phobic poly(methyl methacrylate) grafts was studied using‘‘grafting from’’ concept and ATRP. Two strategies have beenexamined to control the macromolecular parameters of suchglycopolymers: route A is involving four steps including aprotection/deprotection approach and route B is morestraightforward as it only requires two steps. Our aims wereto compare advantages and drawbacks of both routes for thesynthesis of polyvinylic-grafted polysaccharides.

The introduction of initiator groups onto a protected acety-lated dextran (and directly onto dextran) was achieved yield-ing protected DexAcBr (and unprotected DexBr, respectively).In each case, the average number of initiator groups couldbe tuned in some range. The dextran backbone stability

TABLE 2 Polymerization of MMA from Various Initiators in DMSO

Entry (macro)Initiator Temp. [RBr]0 (mol L�1) Effa kappb (mol�1s�1) kp

c (L mol�1s�1) Keqd

1 EiBr 60 �C 4.1.10�2 0.67 4.1.10�5 833 1.8.10�7

2 DexAc71Br6 60 �C 3.8.10�2 0.53 3.7.10�5 833 2.2.10�7

3 DexAc62Br12.8 60 �C 3.9.10�2 0.55e 2.9.10�5 833 1.6.10�7

4 DexAc70Br4.4 60 �C 2.0.10�2 0.55e 1.7.10�5 833 1.8.10�7

5 DexBr5.6 60 �C 4.0.10�2 0.22 1.8.10�4 833 2.5.10�6

6 DexBr4.3 45 �C 3.9.10�2 0.23 2.2.10�4 569 3.9.10�6

7 DexBr5.1 45 �C 3.0.10�2 0.28 6.8.10�5 569 1.4.10�6

Anisole/MMA ¼ 1/10(v:v); [MMA]0 ¼ 4 mol/L.

Conditions of synthesis: [MMA]0/[Br]0/[CuIBr]0/[Cu

IIBr2]0/[n-Pr-PMI]0 ¼100/1/1/0.1/2; except for entry 5: [MMA]0/[Br]0/[Cu

IBr]0/[CuIIBr2]0/[n-Pr-

PMI]0 ¼ 100/1/2.5/0.25/5.a Average efficiency evaluated by the ratio MnExp/MnTh where MnTh is

the theoretical Mn of PMMA chains or grafts calculated from conversion

and [MMA]0/[Br]0 ratio. MnExp is the experimental Mn of chains or grafts

evaluated by SEC-MALLS in THF.

b Apparent propagation rate, that is the slope of the kinetics semilog-

arithmic plot.c Free radical propagation rate constants obtained from ref. 51.d Estimated from kapp thanks to equation kpKeqEff

½Br�0 ½CuðIÞ�0½CuðIIÞ�0 ¼ kapp as pre-

viously reported.6

e Real efficiency not determined - average grafting efficiency of various

DexAcBr macroinitiators.

ARTICLE


during the synthesis of macroinitiator has been appraised byboth routes. Both routes resulted in a slight hydrolysis ofdextran but unprotected route B was founded to be moredamageable. Indeed this degradation effect could certainlybe reduced for some strongest polysaccharidic backboneslike pullulan or cellulose or using milder conditions.

At last, two types of polysaccharidic macroinitiators havebeen synthesized. They are different in term of solubility(DexAcBr is soluble in large range of solvents from polar toapolar ones when hydrophilic DexBr is only soluble in dex-tran solvent). Positions of the initiator groups on the differ-ent OH of glucosidic unit are also quite different, resulting incopolymers having grafts either on OH2 (route B) or on OH3

or OH4 (route A). This difference in grafts position may havean influence on properties of such copolymers.

When evaluated as macroinitiator for ATRP of MMA inDMSO, DexBr gave much faster polymerization compared toDexAcBr, which is having similar behaviour to the model ini-tiator. To obtain a controlled polymerization from DexBr, ithas to be performed at lower temperature or with higherinitial amount of copper. In addition, the average grafting ef-ficiency was much lower compared to model initiator, due tochemical incompatibility between hydrophilic DexBr andhydrophobic PMMA graft. These results showed the impor-tance of backbone macroinitiator for the synthesis of graftedglycocopolymer. Thus, the density of grafting, that is a highnumber of initiator groups resulting in sterically confinedenvironments, is not the only important parameter to controlthe polymerization. Hydrophilic character of the macroinitia-tor could also be fundamental on polymerization behavior.Therefore if protection/deprotection route A seems longer, ithas many advantages in addition to a higher stability of dex-tran backbone and grafting efficiency. Polymerization fromDexAcBr in DMSO is much slower compared to DexBr, which

FIGURE 5 Kinetics of ATRP of MMA in DMSO using EBiBr,

DexAcBr or DexBr as (macro)initiators: Anisole/MMA ¼ 1/10

(v:v); [MMA]0 ¼ 4 mol L�1; [MMA]0/[Br]0 ¼ 100/1 and [Cu(I)Br]0/

[Cu(II)Br2]0/[n-Pr-PMI]0 ¼ 1/0.1/2 (molar ratio): (a) ln([M]0/[M]t)

versus time (b) evolution of experimental Mn (full symbols,

dotted line) and polydispersity index I (open symbols, plain

line) versus theoretical Mn (plain line). ^: EBiBr, [Br]0/[Cu(I)Br]0

¼ 1 (molar ratio) at 60 �C. n: DexAc71Br6.0, [Br]0/[Cu(I)Br]0 ¼ 1

(molar ratio) at 60 �C. ~: DexBr4.3, [Br]0/[Cu(I)Br]0 ¼ 1 (molar

ratio) at 45 �C. l: DexBr5.6, [Br]0/[Cu(I)Br]0 ¼ 2.5 (molar ratio) at

60 �C.

SCHEME 2 Hypothetical growth of PMMA grafts from both

ATRP macroinitiators types.



makes it less sensitive and facilitates its controls whenchanging MMA by another hydrophobic monomer. In fact,the main advantage is the solubility of DexAcBr in a broadvariety of solvent depending on the graft solubility, includingapolar solvent like toluene or xylene. Thus, it is possible togenerate copolymers having more hydrophobic grafts thanPMMA, which enlarge the variety of monomers availablecompared with DexBr macroinitiators, where monomershave to be water-soluble or soluble in DMSO.

Finally each route appears to have advantages and draw-backs for synthesis of polyvinylic-grafted polysaccharide andboth routes are complementary depending of the nature ofthe graft you want to produce. Indeed the difference of solu-bility of both types of macroinitiator enables the polymeriza-tion of a very broad variety of monomers from water-solubleto the most apolar monomers. This would give us versatilemethods to prepare by ATRP a wide range of comblike deriv-atives based on polysaccharide usable for a many applica-tions. For use as emulsifiers, both amphiphilic Dex-g-PMMAglycopolymers have already showed in preliminary studyability to reduce interfacial tension between water and co-polymer solution in chloroform by more than 10 mN/m.

The authors express their highest gratitude to Marie-ChristineGrassiot for help in SEC measurements and Olivier Fabre forNMR measurements. Ludovic Dupayage was supported by agrant of the French Ministry in charge of Research.

REFERENCES AND NOTES

1 Yan, L.; Ishihara, K. J Polym Sci Part A: Polym Chem 2008,

46, 3306�3313.

2 Thoren, L. In Blood stubstitutes and Plasma Expanders;

Jamieson, G. A.; Greenwalt, T. J.; A. R. Liss., Eds.; New York,

1978; pp 265.

3 Dellacherie, E. In Polysaccharides in medicinal applications;

Dumitriu, S.; Basel, N. Y., Eds.; Marcel Dekker, Inc: Hong-Kong,

1996, pp 525–544.

4 Marchant, R. E.; Yuan, S.; Szakalas-gratzl, G. J. Biomater Sci

Polym Ed 1994, 6, 549–564.

5 Mehvar, R. J. Controlled Release 2000, 69, 1–25.

6 Dupayage, L.; Save, M.; Dellacherie, E.; Nouvel, C.; Six, J.-L.

J Polym Sci Part A: Polym Chem 2008, 46, 7606–7620.

7 Nouvel, C.; Frochot, C.; Sadtler, V.; Dubois, P.; Dellacherie, E.;

Six, J.-L. Macromolecules 2004, 37, 4981–4988.

8 Nouvel, C.; Ydens, I.; Degee, P.; Dubois, P.; Dellacherie, E.;

Six, J.-L. J Polym Sci Part A: Polym Chem 2004, 42, 2577–2588.

9 Xu, F. J.; Ping, Y.; Ma, J.; Tang, G. P.; Yang, W. T.; Li, J.;

Kang, E. T.; Neoh, K. G. Bioconjugate Chem 2009, 20,

1449–1458.

10 Xu, F. J.; Zhu, Y.; Liu, F. S.; Nie, J.; Ma, J.; Yang, W. T. Bio-

conjugate Chem 2010, 21, 456–464.

11 Yan, Q.; Yuan, J.; Zhang, F.; Sui, X.; Xie, X.; Yin, Y.; Wang,

S.; Wei, Y. Biomacromolecules 2009, 10, 2033–2042.

12 Ostmark, E.; Harrison, S.; Wooley, K. L.; Malmstrom, E. E.

Biomacromolecules 2007, 8, 1138–1148.

13 Nouvel, C.; Ydens, I.; Degee, P.; Dubois, P.; Dellacherie, E.;

Six, J.-L. J Polym Sci Part A: Polym Chem 2004, 42,

2577–2588.

14 Raynaud, J.; Choquenet, B.; Marie, E.; Dellacherie, E.; Nou-

vel, C.; Six, J. L.; Durand, A. Biomacromolecules 2008, 9,

1014–1021.

15 Nouvel, C.; Raynaud, J.; Marie, E.; Dellacherie, E.; Six, J. L.;

Durand, A. J. Colloid Interface Sci 2009, 330, 337–343.

16 Jenkins, D. W.; Hudson, S. M. Chem Rev 2001, 101,

3245–3272.

17 Coessens, V.; Pintauer, T.; Matyjaszewski, K. Prog Polym Sci

2001, 26, 337–377.

18 Matyjaszewski, K.; Xia, J. Chem Rev 2001, 101, 2921–2990.

19 Kamigaito, M.; Ando, T.; Sawamoto, M. Chem Rev 2001,

101, 3689–3745.

20 Carlmark, A.; Malmstroem, E. J Am Chem Soc 2002, 124,

900–901.

21 Carlmark, A.; Malmstroem, E. E. Biomacromolecules 2003,

4, 1740–1745.

22 Lindqvist, J.; Malmstroem, E. J Appl Polym Sci 2006, 100,

4155–4162.

23 Zhou, Q.; Greffe, L.; Baumann, M. J.; Malmstroem, E.; Teeri,

T. T.; Brumer, H. Macromolecules 2005, 38, 3547–3549.

24 Plackett, D.; Jankova, K.; Egsgaard, H.; Hvilsted, S. Bioma-

cromolecules 2005, 6, 2474–2484.

25 Westlund, R.; Carlmark, A.; Hult, A.; Malmstrom, E.; Saez, I.

M. Soft Matter 2007, 3, 866–871.

26 Liu, P.; Su, Z. Carbohydrate Polymers 2005, 62, 159–163.

27 El Tahlawy, K.; Hudson, S. M. J Applied Polymer Sci 2003,

89, 901–912.

28 Coskun, M.; Temuez, M. M. Polym Int 2005, 54, 342–347.

29 Ifuku, S.; Kadla, J. F. Biomacromolecules 2008, 9,

3308–3313.

30 Sui, X.; Yuan, J.; Zhou, M.; Zhang, J.; Yang, H.; Yuan, W.;

Wei, Y.; Pan, C. Biomacromolecules 2008, 9, 2615–2620.

31 Meng, T.; Gao, X.; Zhang, J.; Yuan, J.; Zhang, Y.; He, J.

Polymer 2009, 50, 447–454.

32 Lin, C.-X.; Zhan, H.-Y.; Liu, M.-H.; Fu, S.-Y.; Zhang, J.-J. Car-

bohydr Polym 2009, 78, 432–438.

33 Bontempo, D.; Masci, G.; De Leonardis, P.; Mannina, L.;

Capitani, D.; Crescenzi, V. Biomacromolecules 2006, 7,

2154–2161.

34 Patrizi, M. L.; Piantanida, G.; Coluzza, C.; Masci, G. Eur

Polym J 2009, 45, 2779–2787.

35 Haddleton, D. M.; Crossman, M. C.; Dana, B. H.; Duncalf, D.

J.; Heming, A. M.; Kukulj, D.; Shooter, A. J. Macromolecules

1999, 32, 2110–2119.

36 Ohno, K.; Wong, B.; Haddleton, D. M. J Polym Sci Part A:

Polym Chem 2001, 39, 2206–2214.

ARTICLE


37 Bamford, C. H.; Middleton, I. P.; Al-Lamee, K. G. Polymer

1986, 27, 1981–1985.

38 Haines, A. H. Adv Carbohydr Chem Biochem 1976, 33,

11–109.

39 Arranz, F.; San Roman, J.; Sanchez-Chaves, M. Macromole-

cules 1987, 20, 801–806.

40 Goodlett, V. W. Anal Chem 1965, 37, 431–432.

41 Arranz, F.; Sanchez-Chaves, M. Polymer 1988, 29, 507–512.

42 Sanchez-Chaves, M.; Arranz, F. Polymer 1997, 38,

2501–2505.

43 Sanchez-Chaves, M.; Arranz, F. Polymer 1996, 37,

4403–4407.

44 De Belder, A. In 26- Polysaccharides in medicinal applica-

tions; Dumitriu, S., Ed.; Marcel Dekker Inc.: New York, Basel,

Hong-Kong, 1996; pp 505–523.

45 Nouvel, C.; Dubois, P.; Dellacherie, E.; Six, J.-L. Biomacro-

molecules 2003, 4, 1443–1450.

46 Sumerlin, B. S.; Neugebauer, D.; Matyjaszewski, K. Macro-

molecules 2005, 38, 702–708.

47 Matyaszewski, K.; Wang, J.-L.; Grimaud, T.; Shipp, D. A.

Macromolecules 1998, 31, 1527–1534.

48 Min, K.; Gao, H.; Matyjaszewski, K. J Am Chem Soc 2005,

127, 3825–3830.

49 Zhang, H. Q.; Klumperman, B.; Ming, W. H.; Fischer, H.; van

der Linde, R. Macromolecules 2001, 34, 6169–6173.

50 Pyun, J.; Jia, S.; Kowalewski, T.; Patterson, G. D.; Matyjas-

zewski, K. Macromolecules 2003, 36, 5094–5104.

51 Beuermann, S.; Buback, M. Prog Polym Sci 2002, 27,

191–254.

52 Van Herk, A. M. Macromol Theor Simul 2000, 9, 433–441.



Documents

Protected versus unprotected dextran macroinitiators for ATRP synthesis of Dex-g-PMMA