Hydroboration polymerization of low molecular weight allyl-telechelic polyisobutylene with narrow molecular weight distribution gave a novel stable organoboron segmented block copolymer by using tripylborane as a boron monomer. The chain transformation reaction of the copolymer was also examined. The reaction with alpha,alpha-dichloromethyl methyl ether (DCME) gave the corresponding polyisobutylene segmented poly(alcohol).