Effect of dose rate on radiation‐induced polymerization of styrene adsorbed on silica gel

Abstract

AbstractThe effect of dose rate on the rate of polymerization and molecular weight distribution of radiation‐induced polymerization of styrene adsorbed on silica gel was studied in a wide dose rate range of 4.4 × 104 to 3 × 108 rad/hr by γ rays of 60Co and electron beams with a Cockcroft‐Walton‐type accelerator. Dose rate dependence on the initial rate of polymerization was about 1 below 3 × 107 rad/hr, and it decreased gradually at high dose rates. Throughout the dose rate range, graft polymerizations and homopolymerizations by cationic and radical mechanisms proceeded simultaneously. Dose rate dependence of the cationic polymerization was 1 below 3 × 107 rad/hr, while dose rate dependence of the radical polymerization was 0.65 below 3 × 107 rad/hr. At high dose rates, molecular weight and fraction of graft polymer decreased, and fraction of cationic polymerization increased. A very high‐molecular‐weight graft polymer was formed above 4.4 × 105 rad/hr at the initial stage of the polymerization. The dose rate dependence of this polymerization was larger than 1 and decreased with increase in dose rate. The polymerization seems to be related to an excitation of monomer or growing chain.