Effects of mixed surfactants on the styrene miniemulsion polymerization in the presence of an alkyl methacrylate

The influence of the mixed surfactants sodium dodecyl sulfate (SDS) and nonylphenol polyethoxylate with an average of 40 ethylene oxide units per molecule (NP-40) on the styrene (ST) miniemulsion polymerization in the presence of dodecyl methacrylate (DMA) and stearyl methacrylate (SMA) was investigated. Both Ostwald ripening and creaming could not be neglected for the miniemulsions stabilized by SDS/NP-40 in combination with DMA upon aging at 35 degrees C, whereas no appreciable Ostwald ripening and creaming were detected for the SMA containing miniemulsions. For both the DMA and SMA containing polymerizations at 80 degrees C, the rate of polymerization (R-p) decreases with increasing NP-40 concentration ([NP-40]). Incorporation of a small quantity of the extremely water-insoluble blue dye into the reaction system was applied to probe the particle nucleation loci. For the DMA containing polymerizations with [NP-40] = 0, 1.25, and 2.50 mM and the SMA polymerization with [NP-40] = 0 mM, homogeneous or micellar nucleation can not be ignored. On the other hand, the more hydrophobic SMA in combination with SDS/NP-40 effectively retards the particle nucleation occurring in the aqueous or micellar phase.