Molecular weight distribution in radiation‐induced polymerization. I. γ‐radiation‐induced free‐radical polymerization of liquid styrene

Abstract

AbstractThe kinetics of γ‐radiation‐induced free‐radical polymerization of styrene were studied over the temperature range 0–50°C at radiation intensities of 9.5 × 104, 3.1 × 105, 4.0 × 105, and 1.0 × 106 rad/hr. The overall rate of polymerization was found to be proportional to the 0.44–0.49 power of radiation intensity, and the overall activation energy for the radiation‐induced free‐radical polymerization of styrene was 6.0–6.3 kcal/mole. Values of the kinetic constants, kp2/kt and ktrm/kp, were calculated from the overall polymerization rates and the number‐average molecular weights. Gelpermeation chromatography was used to determine the number‐average molecular weight M̄n, the weight‐average molecular weight M̄w, and the polydispersity ratio M̄w/M̄n, of the product polystyrene. The polydispersity ratios of the radiation‐polymerized polystyrene were found to lie between 1.80 and 2.00. Significant differences were observed in the polydispersity ratios of chemically initiated and radiation‐induced polystyrenes. The radiation chemical yield, G(styrene), was calculated to be 0.5–0.8.