Emulsion polymerization of styrene: double emulsion effect

Abstract

Five independent sets of experiments have been performed in this work and some experimental evidence is presented to gain an insight into the reaction mechanisms of emulsion polymerization of styrene (St) stabilized by anionic emulsifier sodium dodecyl sulfate (SDS). Existence of water-in-oil-in-water (w/o/w) reverse micelles or double emulsion droplets is evidenced from the critical micelle concentration (cmc) measurement and the observation of w/o/w double emulsion experiment. Existence of monomer droplets at high monomer conversion and relatively low mass ratio of St/PSt in the swollen polystyrene (PSt) latex particles are demonstrated from the experiments of swelling of latex particles and the St emulsion polymerization. The increased uniformity and stability of the monomer emulsion is most likely due to the long pre-emulsification period and/or accumulation of PSt. This will then decrease the monomer droplet degradation, induce the formation of double monomer emulsion droplets and promote the apparent monomer-starved condition during polymerization. As a result, during polymerization the current polymerization system deviates from the conventional Smith–Ewart model, that is, the emulsion polymerization data show a distinct maximum Rp, the increase of Np up to 20–50% conversion and a continuous increase in dw in Intervals II and III.