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

Synthesis of Branched Polymers by Cationic Polymerization 43
promoter (in order to accelerate the initiation step) in the presence of tetrahydrothiophene
as a nucleophile. The graft copolymer obtained therefrom had
M n =105,000 g mol –1 with broad MWD (M w /M n =2.5) and the authors stated
that better defined polymers could be prepared by improving the initiating system.
3.1.2.2
Poly(silyl vinyl ether) Branches
Triflated poly(methyl phenyl silylene)
Aldol group transfer polymerization of tert-butyldimethylsilyl vinyl ether [62]
was initiated by pendant aldehyde functions incorporated along a poly(methyl
methacrylate) (PMMA) backbone [63]. This backbone was a random copolymer
prepared by group transfer polymerization of methyl methacrylate (MMA) and
acetal protected 5-methacryloxy valeraldehyde. After deprotection of the aldehyde
initiating group, polymerization proceeded by activation with zinc halide
in THF at room temperature. The reaction led to a graft copolymer with PMMA
backbone and poly(silyl vinyl ether) or, upon hydrolysis of the tert-butyldimethylsilyl
groups, poly(vinyl alcohol) branches.
3.1.2.3
Poly(isobutylene) Branches
Grafting IB from PS backbone containing tert-benzylic acetate initiating sites
was described by Jiang and Fréchet [64]. The backbone was obtained by chemical
modification of PS shown in Scheme 8.
Polymerization of IB from the PS macroinitiator was accomplished with BCl 3
as coinitiator in CH 2Cl 2 at –78 °C. Due to the living nature of the polymerization
of IB, high grafting efficiencies (~85%) were reported. The resulting ~15%
homoPIB was most probably due to initiation from adventitious moisture or direct
initiation (haloboration).
A similar multifunctional macroinitiator was obtained by Puskas [65] in a
radical copolymerization of S and 4-(1-hydroxy-1-methylethyl)styrene. The
macroinitiator was then used to initiate the living cationic polymerization of IB.
With relatively short backbone and 8–23 branches with M n =10,000–
20,000 g mol –1 , starlike structures, spherical in shape were obtained. The structure
was verified by core destruction followed by SEC analysis of the surviving
arms.