Highly reactive polyisobutylenes via AlCl₃OBu₂‐coinitiated cationic polymerization of isobutylene: Effect of solvent polarity, temperature, and initiator

Abstract

Abstract The cationic polymerization of isobutylene using 2‐phenyl‐2‐propanol (CumOH)/AlCl 3 OBu 2 and H 2 O/AlCl 3 OBu 2 initiating systems in nonpolar solvents (toluene, n ‐hexane) at elevated temperatures (−20 to 30 °C) is reported. With CumOH/AlCl 3 OBu 2 initiating system, the reaction proceeded by controlled initiation via CumOH, followed by β‐H abstraction and then irreversible termination, thus, affording polymers ( M n = 1000–2000 g mol −1 ) with high content of vinylidene end groups (85–91%), although the monomer conversion was low (≤35%) and polymers exhibited relatively broad molecular weight distribution (MWD; M w / M n = 2.3–3.5). H 2 O/AlCl 3 OBu 2 initiating system induced chain‐transfer dominated cationic polymerization of isobutylene via a selective β‐H abstraction by free base (Bu 2 O). Under these conditions, polymers with very high content of desired exo ‐olefin terminal groups (89–94%) in high yield (>85%) were obtained in 10 min. It was shown that the molecular weight of polyisobutylenes obtained with H 2 O/AlCl 3 OBu 2 initiating system could be easily controlled in a range 1000–10,000 g mol −1 by changing the reaction temperature from −40 to 30 °C. The MWD was rather broad ( M w / M n = 2.5–3.5) at low reaction temperatures (from −40 to 10 °C), but became narrower ( M w / M n ≤ 2.1) at temperatures higher than 10 °C. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012