Effects of carboxylic monomers on the styrene miniemulsion polymerizationsstabilized by SDS/alkyl methacrylates

The effects of a small amount of carboxylic monomers (AA and MAA) on the st yrene miniemulsion polymerizations stabilized by SDS/DMA or SDS/SMA are stu died. A mixed mode of particle nucleation (monomer droplet nucleation and h omogeneous nucleation) is operative during polymerization. Formation of par ticle nuclei in the aqueous phase predominates in the SDS/SMA stabilized po lymerization in the absence of carboxylic monomers. The relatively stable m onomer droplets exhibiting an extremely large droplet surface area become t he primary particle nucleation loci when a small amount of AA or MAA is use d as the comonomer. On the other hand, homogeneous nucleation plays a cruci al role in the polymerizations stabilized by SDS/DMA. The experiment using the less hydrophilic MAA as the comonomer shows an intermediate behavior in the polymerization kinetics. A mechanistic model is proposed for the enhan ced monomer droplet nucleation in the polymerizations containing carboxylic monomers. (C) 2000 Elsevier Science Ltd. All rights reserved.