ROLE OF THE NONIONIC SURFACTANT TRITON X-405 IN EMULSION POLYMERIZATION .1. HOMOPOLYMERIZATION OF STYRENE

The emulsion polymerization of styrene was studied using the nonionic surfactant Triton X-405 (octylphenoxy polyethoxy ethanol). Two separat e nucleation periods were noted in these polymerizations resulting in bimodal final latex particle size distributions. The partitioning of t he surfactant between the phases was found to play the major role in d etermining the nucleation mechanism(s) in these polymerizations. Altho ugh the total concentration of the emulsifier was always added at a le vel above its critical micelle concentration (CMC) based on the water phase in the recipe, it was found that the portion of the surfactant i nitially present in the aqueous phase was below its CMC due to the par titioning. This CMC was also found to increase with increasing total s urfactant because the distribution of the surfactant (varying ethylene oxide chain length) depended on the partitioning between the phases. Under these conditions, the first of the two nucleation periods was at tributed to homogeneous nucleation, while the second was attributed to micellar nucleation. (C) 1997 John Wiley & Sons, Inc.