Synthesis of novel chitin derivatives having poly(2-alkyl-2-oxazoline) side chains

Novel chitin derivatives having poly(2-alkyl-2-oxazoline) side chains, i.e., chitin-graft-poly(2-methyl-2-oxazoline) ( 4a ) and chitin-graft-poly(2-ethyl-2-oxazoline) ( 4b ), were synthesized by means of the reaction of ca. 50% deacetylated chitin ( 3 ) with living poly(2-methyl-2-oxazoline) ( 2a ) and poly(2-ethyl-2-oxazoline) ( 2b ), respectively. The reaction between amino groups of 3 and the oxazolinium active species of 2 was examined by changing molar ratios of the feed ([ 2 ]₀/[D -glucosamine units of 3] ₀, ranging from 1,0 to 9,9) under mild conditions (at 27°C in dimethyl sulfoxide (DMSO)). 4a having monodisperse poly(2-methyl-2-oxazoline) side chains on almost every D -glucosamine unit of the main chain was obtained in 35% yield. The number of poly(2-alkyl-2-oxazoline) side chains was roughly controlled by the molar feed ratio of 2 and 3 . 4 is soluble in water, N,N-dimethylformamide, and DMSO, and partially soluble in methanol, acetonitrile, and chloroform. 4 shows improved solubilities in organic solvents, compared with 3 or chitin. The molecular motion of 4b in aqueous solution was discussed by employing ¹H NMR analytical data measured with changing temperature and solvent. In D₂O and, especially, in DMSO, it is suggested that motion of the chitin backbone is restricted, compared with that of the poly(2-ethyl-2-oxazoline) side chain. The content of the side chain in 4 was calculated from the ¹H NMR spectra recorded in D₂O/CD₃CO₂D (vol. ratio 95:5) above 60°C.     

Grafting of Poly(2‐Oxazoline) Side Chains from Polyester Containing Oxazoline Units and Their Blends with Water Soluble Vinyl Polymers

Ternary polycondensation of thiomalic acid (TMA), adipic acid (ADA), and 1,5‐pentanediol (PD) at 80 °C proceeds to give polyester having pendent mercapto groups. After the mercapto groups are consumed quantitatively by a Michael addition with 2‐isopropenyl‐2‐oxazoline (IPOx) to create an initiation point for grafting, successive additions of methyl triflate (MeOTf) and 2‐oxazoline allow ring‐opening polymerization of 2‐oxazoline from the IPOx unit to give a graft copolymer with a M_n of 2.2 × 10⁴ ‐ 3.7 × 10⁴ and an molecular dispersity index (M_w/M_n = 1.9–2.6). The synthesized polyester‐based graft copolymer is water‐soluble and forms transparent blend films with poly(vinyl alcohol) (PVA) and poly(N‐isopropy acrylamide) (PNIPAM) using solvent cast methods. Differential scanning calorimetry measurements show that blends with PVA (<30% of the graft copolymer) show a single T_gs over the whole composition range. All scans for the blends with PNIPAM have a single T_gs that is between those of the parent polymers indicating that the graft copolymer shows excellent miscibility with PNIPAM, although the parent polyester, poly(TMA‐alt‐PD)‐co‐poly (ADA‐alt‐PD) does not exhibit such miscibility.     

Synthesis and assembly of novel chitin derivatives having amphiphilic polyoxazoline block copolymer as a side chain

The first synthesis of chitin derivatives with well-defined block copolymer side chains, i. e., chitin-graft-[poly(2-methyl-2-oxazoline)-block-poly(2-phenyl-2-oxazoline)] ( 5 ), chitin-graft-[poly(2-methyl-2-oxazoline)-block-poly(2-butyl-2-oxazoline)] ( 6 ), and chitin-graft-[poly(2-methyl-2-oxazoline)-block-poly(2-tert-butyl-2-oxazoline)] ( 7 ), was achieved by the reaction of partially deacetylated chitin ( 1 ) with living polyoxazoline block copolymers 2 – 4 . The graft copolymers 5 – 7 are associated into micelles above the critical micelle concentration (CMC). CMCs of 5 (0.01–0.02 wt.-%) are smaller than those (0.32–0.50 wt.-%) of ω-hydroxyl-terminated poly(2-phenyl-2-oxazoline)-block-poly(2-methyl-2-oxazoline) ( 2 -OH), which is a model block copolymer of the side chain segment of 5 . The self-aggregates of 5 – 7 are capable of forming a complex with hydrophobic low molecular weight substances such as pyrene and magnesium 1-anilinonaphthalene-8-sulfonate (ANS). Cryo-transmission electron microscopy showed that the graft copolymer 5 forms globular particles (diameter: 40 nm) and larger cylindrical aggregates (diameter: 40 nm, length: 80–200 nm). The average radius of gyration of the particles of 5 from the SANS analysis is 36 nm.     

Synthesis of a Poly(vinyl alcohol)‐Based Graft Copolymer Having Poly(ε‐caprolactone) Side Chains by Solution Polymerization

Poly(vinyl alcohol)‐graft‐poly(ε‐caprolactone) (PVA‐g‐PCL) was synthesized by ring‐opening polymerization of ε‐caprolactone with poly(vinyl alcohol) in the presence of tin(II) 2‐ethylhexanoate as a catalyst in dimethyl sulfoxide. The relationship between the reaction conditions of the solution polymerization and the chemical structure of the graft copolymer was investigated. The degree of substitution (DS) and degree of polymerization (DP) of the PCL side chains were roughly controlled by varying the reaction periods and feed molar ratios of the monomer and the catalyst to the backbone. PVA‐g‐PCL with a PCL content of 97 wt.‐% (DP = 22.8, DS = 0.54) was obtained in 56 wt.‐% yield. The graft copolymer was soluble in a number of organic solvents, including toluene, tetrahydrofuran, chloroform, and acetonitrile, which are solvents of PCL. The molecular motion of the graft copolymer from ¹H NMR measurements appears to be restricted to some extent at 27–50°C, however the ¹H NMR signal intensities measured at temperatures higher than ca. 50°C reflect the actual chemical structure of the graft copolymer as determined by elemental analysis. The graft copolymer having a short PCL side chain (DP = 4.4, DS = 0.15) was amorphous. The melting temperature of a sample with relatively high PCL content (DP = 22.8, DS = 0.54) was observed at 39°C. Thermogravimetric analysis revealed that the thermal stability of PVA was improved by introducing PCL side chains. The surface free energies of the air‐side of a graft copolymer film, as calculated by Owens' equation using contact angles, were comparable to that of PCL homopolymer.     

Glass transition temperatures in blends of poly(N-vinyl-2-pyrrolidone) with a copolymer of bisphenol A and epichlorohydrin or with poly(vinyl butyral)

Blends of poly(vinyl butyral) (PVB) and of a copolymer of bisphenol A and epichlorohydrin (Phenoxy) with poly(N-vinyl-2-pyrrolidone) (PVP) were prepared by solution casting. The glass transition temperatures T_g for different compositions of the blends were measured by differential scanning calorimetry (DSC). The T_g behaviour of PVB/PVP blends suggests the existence of a single phase for blends containing less than 50 wt.-% PVP, and of two phases in blends containing more than 50 wt.-% PVP. Phenoxy/PVP blends showed to be miscible over the entire composition range. It was found that the Gordon-Taylor equation predicts adequately the T_g-composition dependence with a K parameter equal to 0,5 and 1,25 for PVB/PVP and Phenoxy/PVP blends, respectively.     

1,3-Oxazoline intermediates in reactive processing applications, 1. Melt grafting of poly(ethene-co-methacrylic acid) with 2-substituted 1,3-oxazolines

A novel family of functional ethene copolymers with various side chains were prepared by melt grafting of poly(ethene-co-methacrylic acid), containing 3,00 and 4,25 mol-% of methacrylic acid, with 2-substituted 1,3-oxazolines such as 2-phenyl-1,3-oxazoline, 2-undecyl-1,3-oxazoline, 2-heptadecyl-1,3-oxazoline, and 4-(1,3-oxazolin-2-yl)phenyl 4-methoxybenzoate. ¹H NMR and FTIR studies of the polymer microstructures revealed that carboxylic acid groups reacted with 1,3-oxazolines within few minutes to form esteramide-coupled side chains in very high yields. Torque of the reaction mixture, mechanical and thermal properties of the graft copolymers were measured. In the case of 2-heptadecyl-esteramide-substituted polyethenes, the side-chain cocrystallization accounted for higher crystallinity of the resulting graft copolymers.     

Graft copolymerization of methyl methacrylate by lithium diisopropylamide-treated poly(vinyl propionate)

The anionic grafting of methyl methacrylate (MMA) onto poly(vinyl propionate) (PVPr) was achieved after treatment of the latter with lithium diisopropylamide (LDA). The percentage of grafting of the polymer was between 120 and 730%, no homopolymers being obtained. The degree of lithiation was determined to be 26 mol-% with respect to monomer units by means of deuterolysis. The hydrolysis of the graft copolymers results in the side-chain polymers (PMMA) and poly(vinyl alcohol) (PVA). The average number of branches in the graft copolymer increases from 1 to 7 with increasing percentage of grafting. M?_w/M?_n of the side chain poymer is between 2,0 and 6,7. The low reactivity of the lithium sites may be caused by aggregation of enolates, leading of the broadening of the molecular weight distribution.     

Synthesis, characterization and biocompatibility of poly(2-ethyl-2-oxazoline)-poly(D,L-lactide)-poly(2-ethyl-2-oxazoline) hydrogels

A novel thermoreversible hydrogel based on poly(2-ethyl-2-oxazoline)-derived amphiphilic triblock copolymer, poly(2-ethyl-2-oxazoline)-poly(D,L-lactide)-poly(2-ethyl-2-oxazoline) (PEOz-PLA-PEOz), was developed. The synthesis of PEOz-PLA-PEOz was carried out by coupling monohydroxylated PEOz-PLA diblocks with adipoyl chloride as coupling agent and dimethylamino pyridine as catalyst. The tube inverting and rheological tests showed that triblock copolymers had sol-gel-sol transition behavior with increasing temperature, and the gelation was found to be thermoreversible. The critical gelation concentration, the sol-gel transition temperature at a given concentration depended on the EOz/LA ratio and the molecular weight of PEOz. Scanning electron microscopy observation revealed that the resultant bulky gel exhibited an interconnected porous three-dimensional (3D) microstructure after freeze-drying. In addition, the hydrogels showed good cytocompatibility in vitro. MTT assays revealed that the human skin fibroblast cells encapsulated within the hydrogels were viable and proliferated inside the 3D scaffold. This newly described thermoreversible hydrogel demonstrated attractive properties to serve as cell matrix for a variety of tissue engineering applications or pharmaceutical delivery vehicles.     

Well-defined graft copolymers containing a poly(methacrylate) backbone and functional or block poly(vinyl ether) side chains

The anionic random copolymerization of methyl methacrylate (MMA) and 2-(1-acetoxyethoxy)ethyl methacrylate (AEEMA) was carried out using 1,1-diphenylhexyllithium (DPHL) as initiator, in the presence of LiCl ([LiCl]/[DPHL]₀ = 2), in tetrahydrofuran (THF), at –60°C. The resulting polymer, poly-(MMA-co-AEEMA), has a controlled molecular weight and a narrow molecular weight distribution (M_w/M_n = 1.05 ˜ 1.09). Without quenching, toluene, EtAlCl₂ and a functional monomer [2-acetoxyethyl vinyl ether (AcVE), 2-chloroethyl vinyl ether (ClVE) or 2-vinyloxyethyl methacrylate (VEMA)] were introduced into the above THF solution of the copolymer at 20°C. Every side chain of AEEMA unit of poly(MMA-co-AEEMA) was activated by EtAlCl₂ to induce the cationic polymerization of the functional monomer. THF, which was used as solvent in the preparation of the copolymer of MMA and AEEMA, acted as a Lewis base in the latter cationic polymerization, thus stabilizing the propagating site. By using this procedure, a controlled cationic polymerization of a functional monomer was achieved and a well-defined graft copolymer with functional side chains was obtained. Instead of a single functional monomer, the simultaneous addition of isobutyl vinyl ether (IBVE) and AcVE, ClVE or VEMA during the second step cationic polymerization process generated a graft copolymer with random copolymer side chains. Furthermore, a graft copolymer with block side chains could also be prepared by performing a block copolymerization during the second cationic grafting step by adding sequentially AcVE (ClVE or VEMA) and IBVE or vice versa. Every graft copolymer thus obtained possessed a high purity, controlled graft number and molecular weight as well as a narrow molecular weight distribution (M_w/M_n = 1.12 ˜ 1.25).     

The glass transition temperatures of homogeneous blends of polystyrene,poly(methyl methacrylate), and copolymers of styrene and methyl methacrylate

The glass transition temperatures T_g of homogeneous binary blends of the homo- and the statistical copolymers of the system poly(styrene-co-methyl methacrylate) were studied. Some of the blends, which are in the equilibrium phase separated, were forced into homogeneity. T_g (?) of the homopolymer blends (PS/PMMA)? follows the Fox equation, while T_g (x) of the pure copolymers P(S_xMMA_{1 ? x}) exhibits a minimum. This minimum can be effectively removed by blending the copolymers with small fractions (? ≈ 0,2) of one of the two homopolymers or a differently composed copolymer P(S_yMMA_{1 ? y}).     

Reactive poly(2-vinyl-4,4-dimethyl-5-oxazoione) and poly[(2-vinyl-4,4-dimethyl-5-oxazolone)-co-(methyl methacrylate)]s. Synthesis,characterization and chemical modification with 4-methoxy-4′-(β-aminoethoxy)biphenyl

Poly(2-vinyl-4,4-dimethyl-5-oxazolone) ( P₀ ) and poly[(2-vinyl-4,4-dimethyl-5-oxazolone)-co-(methyl methacrylate)]s with increasing content of methyl methacrylate units ( P₁–P₄ ) were synthesized and characterized. NMR spectra were discussed in terms of monomer sequence distribution and tacticity effects. The reaction of 4-methoxy-4′-hydroxybiphenyl ( 1 ) with 2-ethyl-2-oxazoline was utilized to prepare 4-methoxy-4′-(β-aminoethoxy)biphenyl ( 3 ) through the intermediate 4-methoxy-4′-[(N-propanoyl)-β-aminoethoxy]biphenyl ( 2 ). The homopolymer P ₀ and two copolymers P ₂ and P ₃ were functionalized with 4-methoxybiphenyl side groups by reaction with 3 via a ring-opening process in N,N-dimethylformamide (DMF) or 1,2-dichloroethane. The resulting copolymers P₅–P₈ were characterized by ¹H and ¹³C NMR. The highest degree of functionalized units was obtained in DMF at 80°C.     

Polymer synthesis based on 2-(hydroxyphenyl)-2-oxazolines

2-(Hydroxyphenyl)-2oxazolines(p- and n-isomers 1a and 1b ) were used for the synthesis of various polymers. Cationic polymerization of 2-methyl-2-oxazoline initiated with the N-methyl 2 -oxazolinium species 3 , Derived from 1 , Gave telechelic poly(N-acetylethylenimine) ( 5 ) having a hydroxyl group of different reactivity at both ends. Anionic polymerization of ethylene oxide induced by the lithium salt of 1, 7 , produced a poly(ethylene oxide) macromer, 9 , having a ringopening polymerizable 2-oxazoline group. The copolymer from 9 and 2-phenyl-2oxazoline, 10 , has been shown to have good properties as a nonionic polymeric surfactant in which the N-benzoylethylenimine main-chain behaves as a lipophilic group whereas the oxyethylene graftchains act as a hydrophilic group. Di-salt 11 derived from 1 was polymerized to give polymide 13 (“amphi-ionic polymerization”).     

Ester-carbonate interchange reaction in the solid state: synthesis of poly(ester-carbonate)

Poly(ethylene terephthalate-co-bisphenol A carbonate) was synthesized by ester-carbonate interchange reaction in the solid state. The polymerization reaction was carried out by heating two chemically distinct oligomers, namely, poly(aryl carbonate) and poly(ethylene terephthalate) in the temperature range of 180–230°C, during which period both chain extension as well as interchange reactions occurred. A copolymer of η_inh = 0.84 dL/g was obtained. With the progress of the interchange reaction the T_g of the copolymer slowly increases and reaches a maximum value of 102°C. The oligomer mixture, which exhibits initially two distinct T_m's, shows a single T_m at the end of the reaction. Formation of copoly(aryl ester-carbonate)s by an ester-carbonate interchange reaction was also found in the solid state at temperatures below 230°C. High molecular weight poly(aryl ester-carbonate)s with a T_g = 163°C and η_inh = 0.52 dL/g were prepared from the corresponding low molecular weight oligomers of poly(aryl ester) and poly(aryl carbonate)s.     

Nano‐Scale Molecular Shapes of Water‐Soluble Chitin Derivatives Having Monodisperse Poly(2‐alkyl‐2‐oxazoline) Side Chains

The molecular shapes and the sizes of structures formed by chitin derivatives with monodisperse poly(2‐alkyl‐2‐oxazoline) side chains were investigated using atomic force microscopy (AFM), cryo‐transmission electron microscopy (cryo‐TEM), and small‐angle neutron scattering (SANS) analyses. A ring structure with an outside diameter of 45–60 nm and a cross‐sectional diameter of 10–18 nm was observed in the AFM image for chitin‐graft‐poly(2‐methyl‐2‐oxazoline) 1d (DP of the side chain, 8.5; [side chain]/[glucosamine unit], 0.53). From the cryo‐TEM observation of the graft copolymer 1d in 0.5 wt.‐% D₂O solution, an average diameter of 40 nm for the particles was determined, with a narrow size distribution. SANS measurements of the 0.5 wt.‐% D₂O solution of 1d revealed that the outside diameter of the particles and the cross‐sectional diameter were 57 nm and 8 nm, respectively. The absolute weight average molecular weight of 1d was determined to be 5.4 × 10⁵ by static light scattering. From these results it was concluded that 1d can form a unimolecular ring structure in aqueous solution. However, graft copolymers with fewer side chains ( 1c ; [side chain]/[glucosamine unit], 0.30) and with more side chains ( 1e ; [side chain]/[glucosamine unit], 0.96) did not form rings but instead formed monodisperse unimolecular spherical particles of diameters of 28–36 nm by AFM. A graft copolymer 1f with relatively long side chains (DP of side chain, 19.6; [side chain]/[glucosamine unit], 1.00) was also observed as a spherical particle by AFM (diameter: 30–40 nm by AFM; 40 nm by SANS). On the other hand, an intermolecular aggregate formation (diameter of the aggregate: 36–143 nm) was observed for graft copolymers 1a and 1b having short side chains (DP of side chains, 5.6; [side chain]/[glucosamine unit], 0.35 and 0.48, respectively), with a spherical molecular particle of diameter 36 nm by the AFM analysis. Chitin‐graft‐poly(2‐ethyl‐2‐oxazoline) ( 2 ) (DP of side chains, 21.7; [side chain]/[glucosamine unit], 0.95) generated larger aggregates of diameter 100–400 nm by AFM. The complexation behavior of graft copolymer 1d with magnesium 8‐anilino‐1‐naphthalenesulfonate (ANS) and with N‐phenyl‐1‐naphthylamine (PNA) was also examined by fluorescence measurement in an aqueous solution. It was found that graft copolymer 1d complexed with both ANS and PNA, and the binding constants were calculated to be 7.5 × 10⁴ M ^?1 and 5.3 × 10⁴ M ^?1, respectively.

Chemical structure of chitin‐graft‐poly(2‐alkyl‐2‐oxazoline).     

Synthesis of a Novel Chitin Derivative Having Oligo(ε‐caprolactone) Side Chains in Aqueous Reaction Media

A chitin‐based graft copolymer, chitin‐graft‐oligo(ε‐caprolactone) ( 2 ), was synthesized via ring‐opening graft polymerization of (ε‐caprolactone (ε‐CL) to ca. 50% partially deacetylated chitin 1 catalyzed by tin(II) 2‐ethylhexanoate in the presence of water as a swelling agent. The graft copolymer with ca. 40 wt.‐% poly(ε‐CL) content was obtained by the reaction using the catalyst of 0.17 mol‐% and water of 130 mol‐%, respectively, to the ε‐CL monomer at 100°C for 20 h. The chemical structure of 2 was characterized by IR, ¹H and ¹³C NMR spectroscopies. The poly(ε‐CL) contents by IR were in accordance with those determined by ¹H NMR analysis. T₁ measurements of an aqueous solution of 2 suggested that the molecular motion of the hydrophobic poly(ε‐CL) side chains is restricted to some extent. On the other hand, it was demonstrated by ¹³C CP/MAS NMR that the mobility of the chitin skeleton of 2 in the solid‐state is higher than that of the partially deacetylated chitin. X‐ray diffraction diagrams showed that 2 is amorphous, indicating that the crystallinity due to the chitin main chain was reduced by introducing the oligo(ε‐CL) side chains.     

Thermal properties and crystallization behavior of poly(ether ether ketone ketone)/poly(ether biphenyl ether ketone ketone) copolymers

Thermal properties of poly(ether ether ketone ketone) (PEEKK)/poly(ether biphenyl ether ketone ketone) (PEDEKK) copolymers were investigated by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The glass transition temperature (T_g) increases from 154°C to 183°C as the content of PEDEKK units increases. The melting point (T_m) of the copolymers varied in the range between 314°C and 409°C and showed the behavior of eutectic type copolymer. From the investigation of the crystallization behavior of the copolymers, it was found that the cold-crystallization temperature (T_c′) of the amorphous copolymers assumes a maximum value for the copolymer with a mole fraction of the PEDEKK segment (n_B) of about 0.6, isothermally crystallized PEEKK and the PEEKK/PEDEKK copolymer exhibit double-melting behavior.     

Temperature-responsive graft copolymers for immobilization of enzymes

A graft copolymer was prepared by coupling of poly(acrylic acid-co-acrylamide) (monomer ratio 1:8,5) with poly(N-isopropylacrylamide) (PIPA) having an amino group at its end. The copolymer with the graft chains obtained [poly(AA-co-AAm)-g-PIPA] showed a temperature-responsive phase transition at 34°C in water, and at 26°C in 1-propanol/water (8:92 vol.-%). Lipase from wheat germ was covalently bound to the graft copolymer using a water-soluble carbodimide. The Arrhenius plots of the catalytic activity of the lipase immobilized to poly(AA-co-AAm)-g-PIPA had a bending point around 25 – 30°C in 1-propanol/water (8:92 vol.-%), which is consistent with the temperature-responsiveness of the carrier polymer. As for lipase immobilized to the graft copolymer poly(AA)-g-PIPA, on the contrary, there was no bending point in the temperature dependence of the catalytic activity, probably due to electrostatic repulsion between acrylic acid residues, which perturbs the aggregation of PIPA side chains. The graft copolymer prepared here can be used as a component of temperature-sensitive devices in various forms.     

Effect of structure on glass transition temperatures of poly(methacrylic ester)s with bulky side groups

The values of the vitreous transition temperature, T_g, of three poly(methacrylic ester)s having bulky side groups are correlated with structural effects. T_g has been obtained experimentally by means of differential calorimetry and by the tensiometric method suggested by Ferroni. The experimental values of T_g agree well with the calculated ones obtained by the method of Van Krevelen. The values of T_g determined by differential calorimetry are markedly affected by the heating rate and by the molecular weight of the fractions. The solubility parameters of the polymers studied have been estimated. Poly(p-tert-butylphenyl methacrylate), (BPh), exhibits higher values for the solubility parameter, the steric hindrance parameter σ and the glass transition temperature T_g than poly(p-tert-butylcyclohexyl methacrylate), (BCy), and poly(neopentyl methacrylate), (NPe). These results have been interpreted in terms of intermolecular forces and steric hindrance effects, which would be greater in BPh than in BCy and NPe.     

Glass transition temperatures of comb-like polymers. Poly(ethylene oxide)-polyacrylates and -polymethacrylates

A series of twelve poly(ethylene oxide) (PEO)-polyacrylates and -polymethacrylates with PEO side chains, ranging in molecular weight from 164 to 1000, was studied by differential scanning calorimetry in order to analyse the behaviour of the glass transition temperature. It is shown that the glass transition temperature T_g first decreases with increasing side-chain length to attain a constant value corresponding to the T_g of linear PEO. Contrary to the n-alkyl homologous polymers, the influence of the side-chain crystallization is weak and only appears for long side chains (number-average molecular weight M?_n > 450). The proposed reason is the higher content of amorphous side-chain units between the backbone and the crystallites in PEO as compared to alkyl chains. A relation predicting variations of T_g in comb-like polymers with the length of the side chains is proposed. This relation, based on variation of the T_g of the side chain with its length, fits the experimental results for n-alkyl and PEO side-chain polyacrylates and polymethacrylates using only one parameter characterizing the nature of the side chain.     

Synthesis of poly(vinyl alcohol)/poly(dimethylsiloxane) graft copolymer

Poly(vinyl acetate)/poly(dimethylsiloxane) graft copolymer ( 4a ), with a controlled poly(dimethylsiloxane) graft chain length, was synthesized by radical copolymerization of vinyl acetate with poly(dimethylsiloxane) ( 3 ) having a dimethylvinylsilyl end group. 3 was prepared by living anionic polymerization of hexamethylcyclotrisiloxane ( 1 ) with butyllithium and subsequent termination with chlorodimethylvinylsilane ( 2 ). Poly(vinyl alcohol)/poly(dimethylsiloxane) graft copolymer ( 4b ) was then synthesized by selective saponification of the poly(vinyl acetate) segments in the graft copolymer 4a with K₂CO₃ in methanol.