The cationic polymerization of isobutyl vinyl ether was examined with transition-metal ate complexes with trityl cation as initiators. The initiators were generated by the reaction of triphenylmethyl chloride [trityl chloride (TrCl)] with ate complexes of Nb, Mo, and W with lithium cation, which were obtained in situ by the reaction of the transition-metal halides with anionic reagents (organolithium or lithium amide). When the polymerization was initiated with a mixture of TrCl and Li+[NbH5(NnBuPh)](-), the resulting poly(isobutyl vinyl ether)s had narrow molecular weight distributions (weight-average molecular weight/number-average molecular weight = 1.13-1.20). Although the polymerization was supposed to be initiated by the electrophilic attack of the trityl cation, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of the resulting poly(isobutyl vinyl ether)s revealed the presence of H at the alpha-chain end. (c) 2006 Wiley Periodicals, Inc.