142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

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50 B. Charleux, R. Faust second example [77], macromonomers with DP n up to 28 were prepared. After reacting the terminal aldehyde with a silyl ketene acetal (1-methoxy-2-methyl- 1-trimethylsilyloxy propene) to provide a more stable ester end group, tertbutyldimethylsilyl ether side groups were hydrolyzed to the corresponding alcohol leading to heterotelechelic poly(vinyl alcohol) with a polymerizable styryl a end group and an ester w end group. (33) Such hydrophilic macromonomers (DP n =7–9) were radically homopolymerized and copolymerized with styrene [78] using AIBN as an initiator at 60 °C in deuterated DMSO in order to follow the kinetics directly by 1 H NMR analysis. The macromonomer was found to be less reactive than styrene (r M=0.9 for the macromonomer and r S=1.3 for styrene). Polymerization led to amphiphilic graft copolymers with a polystyrene backbone and poly(vinyl alcohol) branches. The hydrophilic macromonomer was also used in emulsion polymerization and copolymerized onto seed polystyrene particles in order to incorporate it at the interface. 3.3.1.1.3 Polystyrene and Poly(p-methylstyrene) Using functional initiator 31, polystyrene and poly(p-MeS) macromonomers bearing a terminal methacrylate group [79] could be prepared by living cationic polymerization in CH 2Cl 2 at –15 °C in the presence of SnCl 4 and n-Bu 4NCl. To obtain an a end-functionality (F n) close to 1, mixing of the reagents was carried out at –78 °C. When mixing was performed at –15 °C, the functionality was lower than 1 which was ascribed to a side-reaction, initiation by protons eliminated following intramolecular alkylation. The resulting oligomers could be clearly observed by SEC analysis at low conversion. After complete conversion of the monomers, the polymerization was quenched with methanol and macromonomers with a chloride w end group were recovered. A polystyrene macromonomer with DP n =18 (M w /M n =1.16 and F n =0.94) and a poly(p-MeS) macromonomer with DP n =24 (M w /M n =1.14 and F n =0.97) were reported. 3.3.1.1.4 Poly(a-methylstyrene) A similar procedure was also used for the synthesis of methacrylate functional poly(a-MeS) [80]. Thus, 31 was used in conjunction with SnBr 4 in CH 2 Cl 2 at – 78 °C, to obtain the macromonomer with M n s substantially (~50%) higher than the theoretical value. This was probably due to the formation of terminated low MW oligomers with indanyl end group structure. The eliminated proton was as-
Synthesis of Branched Polymers by Cationic Polymerization 51 sumed to remain unreactive and did not initiate new polymer chains, since the functionality of the polymer was found to be close to unity. Allylation of the wend of the living polymer was also accomplished by quenching with excess allyltrimethylsilane. In a related development, four arm poly(a-MeS), functionalized with methacrylate end groups, has been synthesized by coupling reaction of a-methacryloyloxy functional living poly(a-MeS), obtained by the procedure given above, with tetrafunctional silyl enol ethers 25 [81]. 3.3.1.1.5 Poly(b-pinene) b-Pinene which is a main component of natural turpentine can be polymerized by living cationic isomerization polymerization [82] (Scheme 10) using TiCl 3(OiPr) as a Lewis acid in conjunction with n-Bu 4NCl in CH 2Cl 2 at –40 °C. When initiator 31 was used, polymerization led to a poly(b-pinene) macromonomer with a methacrylate function at the a end and a chlorine atom at the w chain end [83]. Three macromonomers were prepared with DP n=8, 15, and 25 respectively; they had narrow MWD (M w/M n=1.13–1.22) and the reported functionality was close to 1 (F n=0.90–0.96). A macromonomer made of a block copolymer of p-MeS and b-pinene was also prepared by sequential living cationic polymerization of both monomers under the same experimental conditions. The first block had 12 p-MeS units and the second had 11 b-pinene units as evaluated by 1 H NMR spectroscopy. The homopolymer and block copolymer macromonomers were copolymerized with MMA by free-radical polymerization in benzene at 60 °C using AIBN as an initiator; typical concentration were [MMA]=1.2 mol l –1 and [macromonomer]=0.020 mol l –1 . MMA was completely converted in 18 h and the macromonomers conversion reached more than 70% as determined by 1 H NMR. Incomplete conversion was explained by steric hindrance. Free-radical copolymerization resulted in high MW graft copolymers with PMMA backbone and relatively rigid, nonpolar poly(b-pinene) branches. Scheme 10
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142 Advances in Polymer Science Edi
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Branched Polymers I Volume Editor:
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Volume Editor Dr. Jacques Roovers I
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Preface While books have been writt
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Poly(macromonomers): Homo- and Copo
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Author Index Volumes 101-142 Author
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Author IndexVolumes 101-142 231 Dun
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Subject Index Addition-fragmentatio
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Subject Index 241 Microphases 11z,
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