Gamma‐Radiation‐Induced Polymerization of Ethylene

Abstract The kineties and product characteristics of the Co60 gamma‐radiation‐induced polymerization of ethylene have been studied as a function of pressure, radiation intensity, and temperature. Experiments were carried out under conditions which ranged in pressure from 170 to 1360 atm., in temperature from 20° to 200°C., and in radiation intensity from 5.8 × 1014 to 8.5 × 105 rad./hr. Activation energies of 0.2 and 14.5 kcal./mole were determined for the temperature ranges 20° to 100°C and 120° to 200°C., respectively. Empirical relationships for the rate of polymerization and the radiation yield for the range of pressure and radiation intensity studied and for temperatures between 20 and 100°C., are as follows: Q = (1.39 ± 0.37) × 10−8e−200/RT p2.7I0.5; G = (3.50 ± 0.95)e−200RTp2.5I−0.5, where Q = polymerization rate, g./l.‐hr., G = radiation yield, molecules/100 e.v., P = pressure, atm., and I = radiation intensity, rad./hr. The 0.5 power dependence of the intensity on rate indicates a free radical mechanism. The polymers produced over the entire range of conditions were found to be completely soluble. Densities ranged from 0.95 g./cc. for material formed at 20°C. to 0.91 g./cc. for material formed at 120°C. The weight average molecular weight decreased from 1.5 × 1016 to 4.7 × 104 over the same temperature range. The molecular weight was found to increase with pressure and with decreasing radiation intensity. All polymers formed at temperatures below 120°C. had a melt index of < 0.06 g./10 min.