Control of regioselectivity and main-chain microstructure in cationic polymerization of cyclopentadiene

The control of regioselectivity in the cationic polymerization of cyclopent adiene (CPD) was examined with initiating systems consisting of the HCl add uct of CPD (1; initiator) and a Lewis acid (activator/catalyst). Among a se ries of metal halides as catalysts, weak Lewis acids such as ZnX2 (X = Cl, Br, I) gave the highest [1,4]-contents (64, 70, and 76%, respectively). In particular, the 1/ZnBr2 system induced controlled polymerization to give po ly(CPD)s with narrow molecular weight distributions (MWDs) (M-w/M-n = 1.3-1 .5) and relatively high regioselectivity ([1,4] = 70%). In contrast, SnCl4, TiCl4, and other strong Lewis acids resulted in less controlled microstruc tures ([1,4] = 45-50%). Other reaction parameters, e.g., solvents, additive s, and temperatures, did not dramatically affect regioselectivity, giving 5 5-60% [1,4]-contents almost invariably.