CATIONIC POLYMERIZATION OF HYDROCARBON MONOMERS UNDER THE EFFECT OF COMPLEXES OF ACYL HALIDES WITH LEWIS-ACIDS .2. EFFECT OF THE POLARITY OF THE SOLVENT ON THE MECHANISM OF INITIATION

The polarity of the solvent significantly affects polymerization of isobutylene under the effect of complexes of acetyl bromide with aluminum bromide of 1:2 (Ac-2) and 1:1 (Ac-1) composition. Going from hexane to the more polar CH2Cl2 is accompanied by an increase in the polymerization rates in both cases, a decrease in the molecular weight and molecular-weight distribution, and an increase in the ratio of C-Br/C=C groups in polyisobutylenes in both cases. In contrast to hexane, in CH2Cl2 the mechanism of initiation of the Ac-2 complex becomes nonselective, and only 42% of all of the polyisobutylenes contain head CO groups. The degree of efficiency of initiation by Ac-2 in CH2Cl2 is 100% (in comparison to 8.5% in hexane). The mechanism of initiation of polymerization by the Ac-1 complex is the same in hexane and in CH2Cl2. Polyisobutylenes containing no head carbonyl groups are obtained in both cases.