Miniemulsion polymerization of styrene in the presence of a water-insoluble blue dye

Relatively stable styrene (ST) miniemulsions were prepared by using a water-insoluble, low molecular weight blue dye as the cosurfactant. The data of the monomer droplet size, creaming rate and phase separation of the monomer as a function of time, were used to evaluate their shelf stability. The dye concentration in toluene can be determined by UV absorbance at 678 nm. This makes the dye molecule a potential probe for determining the loci of particle nucleation during miniemulsion polymerization. In the subsequent miniemulsion polymerization, latex particles were produced via both the monomer droplet nucleation and homogeneous nucleation. Approximately 60% of the original monomer droplets was successfully nucleated during polymerization based on the data of the weight percentage of dye incorporated into the final latex particles (P-dye) The parameter P-dye goes up with increasing [dye] (0.1% --> 1.0% based on total monomer), which is attributed to the increased resistance against diffusional degradation of the monomer droplets. This may greatly reduce the number of primary particles nucleated in the aqueous phase and, thereby, increase the degree of incorporation of dye into the final latex particles. Conductivity measurements during polymerization also support the mixed modes of particle nucleation. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.