Photoinduced Ionic Polymerization. VI. Molecular Weight Distribution in Cationic Polymerization of α-Methylstyrene

Abstract

The photoinduced cationic polymerization of α-methylstyrene was carried out in dichloromethane solution using pyromellitic dianhydride as an electron acceptor, and the molecular weight distributions of the resulting polymer were measured by gel-permeation chromatography. It was found that the molecular weight distribution was bimodal at low monomer concentration and low temperature. The lower molecular weight peak, which increased with decreasing monomer concentration and temperature, was assigned to the free-ion polymerization, and the higher-molecular weight one to the ion-pair polymerization. It was shown that the molecular weight of the polymer produced by the free-ion polymerization decreased with decreasing monomer concentration, but was not affected by temperature, while that of the polymer produced by the ion-pair polymerization decreased with increasing temperature, but was not affected by the monomer concentration. The propagation mechanism was discussed in connection with the conventional catalytic and radiation-induced polymerizatson.