Studies on rate of emulsion polymerization of butadiene‐styrene (75:25) as a function of amount and kind of emulsifier used. III. Effect of amount of soap on rate of polymerization

The rate of emulsion copolymerization of butadiene‐styrene (75:25) has been studied at 50°C. as a function of the amount of soap. The following soaps were investigated: potassium myristate, potassium laurate, sodium caprate, sodium salt of dispropor‐ tionated rosin acids, and a commercial soap (largely sodium palmitate, oleate, and stearate). The initial rate of polymerization is decreased as the amount of soap is decreased, but the rate after about 25% conversion becomes almost independent of the amount of soap. If the concentration of soap in the aqueous phase is less than the critical concentration for micelle formation the initial rate is extremely small and becomes about equal to the rate in the absence of emulsifier. The initial rate with varying amounts of different detergents is approximately proportional to the amount of solu‐ bilization by the soap or other detergent solution. The data confirm Harkins' theory that solnbilization by soap micelles is a major factor in the initial stages of emulsion polymerization.