| Abstract: | The emulsion polymerization of styrene was studied using the nonionic surfactant Triton X-405 (octylphenoxy polyethoxy ethanol). Two separate nucleation periods were noted in these polymerizations resulting in bimodal final latex particle size distributions. The partitioning of the surfactant between the phases was found to play the major role in determining the nucleation mechanism(s) in these polymerizations. Although the total concentration of the emulsifier was always added at a level above its critical micelle concentration (CMC) based on the water phase in the recipe, it was found that the portion of the surfactant initially present in the aqueous phase was below its CMC due to the partitioning. This CMC was also found to increase with increasing total surfactant 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 attributed to homogeneous nucleation, while the second was attributed to micellar nucleation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3813–3825, 1997 |
