The effect of 2,6-di-tert-butyl-pyridine (DtBP) on isobutylene polymerization induced by AlCl3in n-hexane, CH2Cl2, and n-hexane/CH2Cl2mixtures has been investigated. Polymerization carried out in the presence of DtBP invariably yielded much reduced yields, much elevated molecular weights, and noticeably narrower molecular weight dispersities than those carried out under identical conditions except in the absence of this hindered pyridine. As expected, conversions increase while [Mbar]n's decrease and [Mbar]w/[Mbar]n's broaden with increasing [AlCl3] in the absence of DtBP; however, in the presence of DtBP, increasing [AlCl3]'s lead to increased conversions, increasing [Mbar]n's, and narrowing [Mbar]w/[Mbar]n's. At constant [AlCl3], increasing [DtBP] tends to decrease yields but at the same time increases [Mbar]nand narrow [Mbar]w/[Mbar]n. Directionally these effects remain similar by changing the polarity of the medium. The proposition of proton scavenging during chain transfer to monomer by the hindered pyridine helps to explain these observations.