cis-Selective polymerizations of isoprene with the catalysts composed of η5-C5H4(R)TiCl3 (1; RH, 2; tert-Bu) and methylaluminoxane were investigated. Both catalysts showed remarkable catalytic activities for the polymerization of isoprene. The polymerization activities were strongly affected by the substituent introduced on cyclopentadienyl ring. Introduction of bulky tert-butyl group was found to be effective for enhancement of polymerization activity, but the cis-content of polyisoprene prepared by the 2/MAO catalyst was lower than that by 1/MAO catalyst. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1841–1844, 2004
