Polymerization induced by ionizing radiation at low temperatures. II. Effects of change of phase and heterogeneity on the polymerization of styrene and 2,4‐dimethylstyrene

Abstract

Abstract The radiation‐induced polymerizations of undiluted styrene and of 2,4‐dimethylstyrene have been studied in the solid, partially solid, and completely liquid states. The results may be compared with solution polymerizations covering a similar temperature range reported in the previous paper. 1 In addition to the interesting information obtained from the rate data for the solid phase, decidedly unusual effects of temperature on rate have been found by studying the systems in the vicinities of the melting points. For styrene, in the solid state (below −30.5°C.), the rate increases with temperature (Δ E a = 6–7 kcal./mole), having a maximum value when the system is partially solid. The rate drops rapidly above the melting point to a minimum, and then rises in a normal manner with temperature (Δ E a = 9–10 kcal./mole). For 2,4‐dimethylstyrene, in the solid monomer (−120 to −65°C.), the rate increases with temperature (Δ E a = 1 kcal./mole), having, like styrene, a maximum value at the melting point where the system is a solid–liquid mixture. The rate drops precipitously above the melting point. In the liquid state, the rate also increases with temperature (Δ E a = 1 kcal./mole). Similar effects have been observed in the polymerization of styrene–benzene and styrene–ethylbenzene mixtures. Enhanced rates have also been observed at the melting temperatures of these mixtures.