Competitive complexation in the cationic polymerization of isobutylene in a nonpolar medium

The cationic polymerization of isobutylene coinitiated by Al(i‐Bu)Cl2(Al) was carried out in mixed butane–butene fractions at −50 °C. The expected polymerization processes induced by the trace of moisture with Al system in the presence of a small amount of external electron‐donor modifiers, such as methyl acrylate (MA) and dimethyl sulfoxide (DMSO), were obtained. The experimental results showed that these polymerizations produced polymers with relatively high number‐average molecular weights and narrow molecular weight distributions (1.5–2.2). That the gel permeation chromatography traces of the polymers depended on the types and concentrations of external donors suggested that there existed competitive complexation reactions of various electron donors (H2O, MA, and DMSO) with the Al Lewis acid. The roles of external electron donors were to take part in the initiation step by competitive complexation and to modify the reactivity of the growing chain ends in the propagation step by mediation and/or solvation, which impaired the high reactivity of the original growing chain ends. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2209–2214, 2002 Cationic polymerizations of isobutylene by the H2O/Al(i‐Bu)Cl2 system in the presence of methyl acrylate (MA) and/or dimethyl sulfoxide (DMSO) led to polymers with high molecular weights and narrow molecular weight distributions. There existed competitive complexation of H2O, MA, or DMSO with Al(i‐Bu)Cl2. The roles of MA or DMSO were to take part in the initiation step by competitive complexation and to modify the reactivity of growing chain ends in the propagation step by mediation and/or solvation.