Molecular weight distribution studies, 2. Radiation‐induced polymerization of solid α‐methylstyrene

Abstract The radiation‐induced post ‐ and “in‐source” solid state polymerizations (the polymerizations occurred after and during the γ‐irradiation, resp.) of α‐methylstyrene were studied. Post‐polymerizations studied at −30°C, occurred only in pure and “dry” monomer. At a constant initial radiation dose of 2,5 Mrad (2,5.10 4 J/kg), the rate of polymerization increased, although slightly, with increasing conversion. With increasing initial radiation dose of up to 7,4 Mrad (7,4.10 4 J/kg) and post‐polymerized for 8 h, resp., the percentage of polymer yield per unit radiation dose decreased with increasing conversion. The GPC chromatograms of the polymer samples obtained showed a peak at 27,4 elution counts resulting from ionic polymerization and a shoulder at 29,0 counts from free radical polymerization. In the case of the “in‐source” polymerization, studied at −30 and −40°C, the “wet” monomer yielded rates of polymerization lower than those from “dry” monomer. GPC analysis of the polymer samples obtained at −40°C from both “dry” and “wet” monomer showed bimodal distributions, the higher molecular weight peak resulting from ionic polymerization. At increased conversions, the positions of both GPC peaks remained unchanged, whereas the heights and hence the ionic and free radical polymerization contribution changed, the ionic contribution decreasing. At −30°C polymerization temperature only one peak at 27,3 elution counts resulting from ionic polymerization was obtained.