Functionalization of living polyisobutylene: Preference for reduction over electrophilic addition

Polyisobutylene was synthesized using 2-chloro-2,4,4-trimethylpentane (TMPCl) as an initiator and TiCl₄ as a coinitiator. After taking a base sample, the living cation was reacted with 5 equivalents of (4-vinylphenyl)dimethylsilane (VPDMSi). It was observed that the cation preferred reduction by hydride elimination from VPDMSi compared to electrophilic addition of even a single vinyl group. It was postulated that the reduction of the cation in presence of strong Lewis acid such as TiCl₄ occurs readily before addition of cation to vinyl group. Thus saturated polyisobutylene was obtained with a terminal hydrogen group instead of chlorine group which is produced by conventional cationic polymerization.