The carbocationic polymerization of isobutylene (IB), co-initiated by GaCl3 or FeCl3 dialkyl ether 1:1 complexes has been investigated in hexanes in the -20 to 10 degrees C temperature range. In contrast to AlCl3 diisopropyl ether (AlCl3 center dot i-Pr2O) complexes,(1) GaCl3 center dot i-Pr2O and FeCl3 center dot 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 absence of proton trap, chain transfer to monomer readily proceeded, resulting in close to complete monomer conversion and up to 85% exo-olefinic end group content, Diisopropyl ether complexes gave the highest polymerization rates, while nonbranched alkyl ether complexes were completely inactive. A polymerization mechanism is proposed to involve ether assisted proton elimination to yield PIB exo-olefin, and the abstracted proton can subsequently start a new polymer chain by protonation of IB. Alternatively PIB+ may be deactivated by ion collapse to yield PIBCl, which can be reactivated by the Lewis acid. The reasons for the difference in behavior between the Ga and Fe catalysts and the Al-based catalysts are described.