The Effects of the Temperature on the γ-Radiation-Induced Polymerization of Ethylene

Abstract

Abstract The gamma-radiation-induced polymerization of ethylene was carried out/over the wide range of temperature from 30 to 200°C at pressure ranging from 100 to 400kg./cm2 and at dose rates from 2×103 to 4×105 rad./hr. It was shown that the rate of polymerization is rapidly accelerated at 30°C, that the degree of acceleration decreases with an increase in the reaction temperature, and that above 100°C the rate is independent of the time. It was correspondingly shown that the molecular weight of the polymer increases with the reaction time, at 30°C, that its increment for a unit of time decreases with an increase in the temperature, and that the molecular weight is independent of the time above 100°C. By means of a kinetical discussion it was concluded that the rate of the termination reaction, which is almost eliminated at 30°C, increases with the temperature and attains a value comparable to that of initiation above 100°C. The dose rate exponents of the polymerization rate and molecular weight were shown to vary with the reaction temperature. Namely, the exponents were evaluated as 0.9 and 0 at 30°C, 0.8 and −0.1 at 100°C, and 0.7 and −0.2 at 140 and 200°C, for the polymerization rate and the molecular weight respectively. It was assumed from these high exponents that the termination may occur above 100°C in a first-order reaction to a considerable extent. Under a constant pressure, the polymer yield was shown to decrease with the temperature from 30 to 60–80°C, and then to increase at high temperatures from 80 to 200°C. On the other hand, the molecular weight of the polymer simply decreases with the temperature from 30 to 200°C. The chain transfer reaction is considered to be almost negligible at 30–70°C. The number of polymer chains for a constant reaction time and monomer concentration is independent of the temperature from 30 to 70°C, while it increases with the temperature from 70 to 200°C. The effects of pressure on the polymer yield and molecular weight were also investigated at 140°C.