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The cationic polymerization of isobutylene using 2‐phenyl‐2‐propanol (CumOH)/AlCl3OBu2 and H2O/AlCl3OBu2 initiating systems in nonpolar solvents (toluene, n‐hexane) at elevated temperatures (−20 to 30 °C) is reported. With CumOH/AlCl3OBu2 initiating system, the reaction proceeded by controlled initiation via CumOH, followed by β‐H abstraction and then irreversible termination, thus, affording polymers (Mn = 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; Mw/Mn = 2.3–3.5). H2O/AlCl3OBu2 initiating system induced chain‐transfer dominated cationic polymerization of isobutylene via a selective β‐H abstraction by free base (Bu2O). 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 H2O/AlCl3OBu2 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 (Mw/Mn = 2.5–3.5) at low reaction temperatures (from −40 to 10 °C), but became narrower (Mw/Mn ≤ 2.1) at temperatures higher than 10 °C. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Highly reactive polyisobutylenes with a desirable low Mn were obtained with RAlCl2 × OiPr2 initiating systems with high monomer concentrations at room temperature.

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