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

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48 B. Charleux, R. Faust 3.3 Macromonomers A macromonomer is a macromolecule with a reactive end group that can be homopolymerized or copolymerized with a small monomer by cationic, anionic, free-radical, or coordination polymerization (macromonomers for stepgrowth polymerization will not be considered here). The resulting species may be a star-like polymer (homopolymerization of the macromonomer), a comblike polymer (copolymerization with the same monomer), or a graft polymer (copolymerization with a different monomer) in which the branches are the macromonomer chains. Macromonomers have been synthesized by living cationic polymerization by three different techniques: by the use of a functional initiator, employing functional capping agent or by chain end modification. 3.3.1 Synthesis of Macromonomers by Living Cationic Polymerization 3.3.1.1 Synthesis Using a Functional Initiator This technique is the simplest as it generally requires only one step since the polymerizable function is incorporated via the initiator fragment. To obtain welldefined macromonomers with one polymerizable end group per chain, controlled length and narrow MWD, the following criteria should be fulfilled: – initiation only from the initiator (no protic or direct initiation); – living polymerization conditions (especially no transfer to the monomer); – during the polymerization the functional group should remain unreacted or it needs to be protected. 3.3.1.1.1 Poly(vinyl ethers) Most of the reported poly(vinyl ether) macromonomers have been prepared with a methacrylate end group which can be radically polymerized and which is non-reactive under cationic polymerization conditions [71–73] . Generally, the synthesis was based on the use of the functional initiator 30, which contains a methacrylate ester group and a function able to initiate the cationic polymerization of vinyl ethers. Such initiator can be obtained by the reaction of HI and the corresponding vinyl ether. With initiator 30 the polymerization of ethyl vinyl ether (EVE) was performed using I 2 as an activator in toluene at –40 °C. The MW increased in direct proportion with conversion, and narrow MWD (M w/M n= 1.05–1.15) was obtained. The chain length could be controlled by the monomer to initiator feed ratio. Three poly(EVE) macromonomers of different length were prepared by this method: M n=1200, 5400, and 9700 g mol –1 . After complete
Synthesis of Branched Polymers by Cationic Polymerization 49 conversion and quenching with methanol (acetal w end group), 1 H and 13 C NMR spectroscopy was used to demonstrate the structural integrity of the macromonomers and to determine the value of F n for the -methacrylate end group. The latter was always very close to 1, indicating that one methacrylate end group was incorporated per molecule. Radical homopolymerization and copolymerization with MMA initiated by AIBN in benzene solution or in bulk led to high MW graft (co)polymers. Macromonomers of the same monomer, EVE, were prepared using initiator 32 bearing an allylic function [73, 74]. This reactive group remained intact during the polymerization and could be further transformed into the corresponding oxirane by peracid oxidation. This epoxy end group can be polymerized by ring-opening polymerization. (32) Other vinyl ethers were also polymerized with initiator 30 under the same experimental conditions [75]. For instance, SiVE and 2-(trimethylsilyloxy)ethyl vinyl ether provided hydrophobic macromonomers which could be desilylated under suitable conditions to obtain the corresponding water-soluble poly(HOVE) without any side reaction of the methacrylate end group. 3.3.1.1.2 Poly(silyl vinyl ether) (30) X=1 (31) X=Cl Poly(silyl vinyl ether) macromonomers with a styrenic polymerizable function [76, 77] were prepared by the so-called aldol group transfer polymerization of tert-butyldimethylsilyl vinyl ether. The polymerization proceeded by activation of the aldehyde in the functionalized initiator p-formylstyrene (33) by ZnCl 2 or ZnBr 2 in THF or CH 2Cl 2 at 30 °C. Initiation was found to be fast and quantitative. The products, macromonomers of poly(tert-butyldimethylsilyl vinyl ether) with an aldehyde w end group, were analyzed by SEC and 1 H NMR spectroscopy. The polymerization was shown to be living resulting in MWs controlled by the monomer to initiator feed ratio and narrow MWD (M w/M n
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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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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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142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

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