Polymerization of Isobutyleneby GaCl3orFeCl3/Ether Complexes in Nonpolar Solvents.

The carbocationic polymerization of isobutylene (IB),co-initiatedby GaCl3or FeCl3·dialkyl ether 1:1 complexeshas been investigated in hexanes in the −20 to 10 °C temperaturerange. In contrast to AlCl3·diisopropyl ether (AlCl3·i-Pr2O) complexes,(1) GaCl3·i-Pr2O and FeCl3·i-Pr2O readily co-initiate polymerization with 2-chloro-2,4,4-trimethylpentane(TMPCl) or tert-butyl chloride (t-BuCl) in the presence or absence of proton trap. In the absenceof proton trap, chain transfer to monomer readily proceeded, resultingin close to complete monomer conversion and up to 85% exo-olefinicend group content. Diisopropyl ether complexes gave the highest polymerizationrates, while nonbranched alkyl ether complexes were completely inactive.A polymerization mechanism is proposed to involve ether-assisted protonelimination to yield PIB exo-olefin, and the abstracted proton cansubsequently start a new polymer chain by protonation of IB. AlternativelyPIB+may be deactivated by ion collapse to yield PIBCl,which can be reactivated by the Lewis acid. The reasons for the differencein behavior between the Ga and Fe catalysts and the Al-based catalystsare described. [ABSTRACT FROM AUTHOR]