Kinetics of styrene miniemulsion polymerization stabilized by nonionic surfactant alkyl methacrylate

The effects of various reaction parameters on the styrene miniemulsion poly merizations stabilized by nonylphenol polyethoxylate with an average of 40 ethylene oxide units per molecule (NP-40) and dodecyl methacrylate (DMA) at 80 degrees C were investigated. These parameters include the concentration s of DMA ([DMA]), NP-40 ([NP-30]), sodium persulfate ([SPS]), and 2,2'-azob isisobutyronitrile ([AIBN]). A water-insoluble dye was also incorporated in to the reaction system to gain a better understanding of the related partic le nucleation mechanisms. The polymerization rate decreases with increasing [DMA], whereas it increases with increasing [NP-40], [SPS] and [AIBN]. Sev eral competitive events (e.g, coalescence among the monomer droplets, nucle ation in the monomer droplets and micelles, formation of particle nuclei in water, and particle growth) occur simultaneously in the course of polymeri zation. This is due to the fact that the steric stabilization effect provid ed by NP-40 is greatly reduced at 80 degrees C and the CMC of the miniemuls ion is far below the NP-30 concentrations used in this work. Mixed modes of particle nucleation are operative in this reaction system, but monomer dro plet nucleation becomes more important by increasing [DMA] or decreasing [N P-40], [SPS] and [AIBN]. (C) 1999 Elsevier Science Ltd. All rights reserved .