This paper discusses a new process of preparing borane-terminated isotactic polypropylenes (i-PPs) via in situ chain transfer reaction, which avoids the use of B-H-containing chain transfer agent and thus can be carried out with Al-activated metallocene catalyst under mild reaction conditions. The chemistry centers on a consecutive chain transfer reaction, first to a trialkylborane-containing styrene derivative, 4-[B-(n-butylene)-9-BBN]styrene (B-styrene), then to hydrogen in the isoselective polymerization of propylene catalyzed by rac-Me2Si(2-Me-4-Ph-Ind)(2)ZrCl2/MAO. The borane-terminated i-PP thus obtained keeps the desired properties of a polymeric alkyl-9-BBN reagent and was used to initiate radical polymerization of methyl methacrylate (MMA) to prepare i-PP-b-PMMA diblock copolymer. (c) 2005 Wiley Periodicals, Inc.