The use of high‐energy irradiation in an investigation of the mechanism and kinetics of emulsion polymerization

Abstract

Abstract The emulsion polymerization of styrene initiated by γ‐rays was studied using competitive particle growth and conventional techniques. With γ‐rays, the rate of free‐radical generation is independent of temperature, and the absorption of energy is uniform throughout the system. From the competitive growth experiments, the particle growth rates were similar to those of persulfate ion‐initiated systems and quite different from those of benzoyl peroxide‐initiated systems. From the conventional experiments, the number of particles increased approximately as the square of the emulsifier concentration for both γ‐ray and persulfate ion‐initiated polymerizations. With γ‐rays, the number of particles decreased with increasing temperature; the opposite was observed for persulfate. This may be explained by the relative rates of free‐radical generation of each system; for γ‐rays this rate is independent of temperature, while for persulfate, the activation energy for initiator decomposition is greater than that for polymerization propagation. For the γ‐ray system, the calculated values of k p increased with increasing particle size; the activation energy was 7.2 (σ = 0.59) kcal./mole. The calculated values of k t at 50°C. were 10 4 –10 5 l./mole/sec.