Mechanism of emulsion polymerization of styrene with persulfate as activator in the absence and presence of mercaptan and a retarder

Abstract

Abstract With the use of persulfate containing radioactive sulfur it is shown that the termination reaction of the polymerization of styrene is a coupling of the free radical chains. In the presence of m ‐dinitrobenzene as a retarder evidence has been presented that the termination reaction is a disproportionation and not a combination of two free radical chains. Mercaptan in the emulsion polymerization of styrene acts solely as a chain transfer agent. Any chemical reaction between persulfate and mercaptan does not contribute to the initiation. In the presence of detergent the rate of initiation of the polymerization of styrene is equal to the rate of thermal dissociation of persulfate: Thus, any reaction between persulfate with monomer and detergent does not contribute to the initiation. The much smaller rate of initiation in the absence of detergent is attributed to the slight solubility of styrene, the concentration of the monomer being so small that it cannot capture all the free radicals. The effect of the detergent is a physical one, by its solubilizing action it increases the solubility of the monomer in the water layer to such an extent that the “activator” now becomes 100% efficient.