Emulsion polymerization of styrene: double emulsion effect

Five independent sets of experiments have been performed in this work and s ome experimental evidence is presented to gain an insight into the reaction mechanisms of emulsion polymerization of styrene (St) stabilized by anioni c emulsifier sodium dodecyl sulfate (SDS). Existence of water-in-oil-in-wat er (w/o/w) reverse micelles or double emulsion droplets is evidenced from t he critical micelle concentration (cmc) measurement and the observation of w/o/w double emulsion experiment. Existence of monomer droplets at high mon omer conversion and relatively low mass ratio of St/PSt in the swollen poly styrene (PSt) latex particles are demonstrated from the experiments of swel ling of latex particles and the St emulsion polymerization. The increased u niformity and stability of the monomer emulsion is most likely due to the l ong pre-emulsification period and/or accumulation of PSt. This will then de crease the monomer droplet degradation, induce the formation of double mono mer emulsion droplets and promote the apparent monomer-starved condition du ring polymerization. As a result, during polymerization the current polymer ization system deviates from the conventional Smith-Ewart model, that is, t he emulsion polymerization data show a distinct maximum R-p, the increase o f N-p up to 20-50% conversion and a continuous increase in d(w) in Interval s II and III. (C) 2000 Published by Elsevier Science Ltd.