Multiarm-star polyisobutylenes by living carbocationic polymerization

This article describes the synthesis of high molecular weight multiarm-star branched polyisobutylenes by living polymerization, using multifunctional initiators, and their initial characterization. First, macrointiators carrying tert-hydroxy function-alities were synthesized by the radical copolymerization of 4-(1-hydroxy-1-methylethyl)-styrene with styrene. This copolymerization system was found to be ideal with r1 ≡ r2 ≡ 1. Selected macroinitiators with average functionalities of 8–73 were then used to synthesize the star-branched polyisobutylenes. Polymers with molecular weights up to M̄n = 400,000 were obtained within 30–60-min reaction times, while under similar conditions the monofunctional 2-chloro-2,4,4-trimethylpentane initiator yielded M̄n ≈ 10,000 in 20 min. This can be viewed as an indirect proof that simultaneous multiple initiation took place with the macroinitiators. Under controlled conditions a branchedpolyisobutylene with M̄n = 375,000 and MWD = 1.2, and theoretically calculated 23 arms, with no detectable side products was obtained under living conditions in 60 min; the molecular weight of this polymer increased linearly with time. The branched structure of the polymers were demonstrated by SEC-LLS analysis and core destruction of selected samples.