Copolymerization of styrene and butadiene in emulsion. II. Relative rates of crosslinking and propagation

For the styrene–butadiene emulsion copolymerization (71 parts butadiene:29 parts styrene) the ratio of the rate coefficients for crosslinking, kx, and propagation, kp, have been determined at 5, 15, and 25°C by using an adaption of the method of Morton and co‐workers. These ratios yield a value of 4.85 kcal/mole for the difference in activation energy between crosslinking and propagation, Ex − Ep. Since the relative frequency of crosslinking and propagation depends upon the copolymer composition, and hence upon the free monomer ratio and the temperature, the range of application of these data is more limited than in a simple homopolymerization.