Highly reactive polyisobutylenes via AlCl 3OBu 2-coinitiated cationic polymerization of isobutylene: Effect of solvent polarity, temperature, and initiator

Abstract

The cationic polymerization of isobutylene using 2-phenyl-2-propanol (CumOH)/AlCl 3OBu 2 and H 2O/AlCl 3OBu 2 initiating systems in nonpolar solvents (toluene, n-hexane) at elevated temperatures (-20 to 30 °C) is reported. With CumOH/AlCl 3OBu 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;bsubesubbsubesub& = 2.3-3.5). H;bsubesubbsubesubbsubesub& initiating system induced chain-transfer dominated cationic polymerization of isobutylene via a selective ;beta&-H abstraction by free base (Bu;bsubesub&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;bsubesubbsubesubbsubesub initiating system could be easily controlled in a range 1000-10,000 g mol;bsupesup& by changing the reaction temperature from -40 to 30 °C. The MWD was rather broad (M;bsubesubbsubesub = 2.5-3.5) at low reaction temperatures (from -40 to 10 °C), but became narrower (M;bsubesubbsubesub a;circ 2.1) at temperatures higher than 10 °C. © 2011 Wiley Periodicals, Inc.