The effect of the sterically hindered base 2,6-di-tert-butyl-pyridine (DtBP) on the polymerization of α-methylstyrene (αMeSt initiated by “H2O”/BCl3in a wide temperature range) has been investigated. αMeSt polymerizations carried out under identical conditions except in the presence of DtBP give much lower yield, much higher molecular weight, and noticeably narrower distributions than those obtained in the absence of this hindered base. The possibility of DtBP acting as an inhibitor is ruled out. Yields, molecular weights, and molecular weight distributions virtually do not change by changing DtBP concentration from 1.0 × 10−1to 1.0 × 10−3M. Differences in conversion levels do not explain the observed phenomena. PaMeSt samples obtained in the presence of trace amount of DtBP were of much higher molecular weight than those prepared in the absence of hindered pyridine, even at the same conversion level. These findings are explained by proposing that DtBP is a specific proton scavenger able to trap protons emerging during chain transfer to monomer, and that other elementary events remain unaffected by the presence of this hindered base.