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 functionalities were synthesized by the radical copolymerization of 4-(1-hydroxy-1-methylethyl)styrene with styrene. This copolymerization system was found to be ideal with r(1) = r(2) = 1. Selected macroinitiators with average functionalities of 8-73 were then used to synthesize the star-branched polyisobutylenes. Polymers with molecular weights up to (M) over bar(n) = 400,000 were obtained within 30-60-min reaction times, while under similar conditions the monofunctional 2-chloro-2,4,4-trimethylpentane initiator yielded (M) over bar(n) approximate to 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 branched polyisobutylene with (M) over bar(n) = 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.