Styrene miniemulsion polymerization initiated by 2,2 '-azobisisobutyronitrile

The effects of various parameters on the dodecyl methacrylate (DMA) or stea ryl methacrylate (SMA) containing styrene miniemulsion polymerizations were investigated. These parameters include the type of initiators [2,2'-azobis isobutyronitrile (AIBN) vs. sodium persulfate (SPS)], the size of the homog enized monomer droplets, the AIBN concentration, and the SDS concentration. A small quantity of a water-insoluble dye was also incorporated into the p olymerization system to study the related particle nucleation mechanisms. T he oil-soluble AIBN promotes nucleation in the monomer droplets, whereas ho mogeneous nucleation predominates in the reaction system with the water-sol uble SPS. Homogeneous nucleation, however, cannot be ruled out in the DMA o r SMA containing polymerizations with AIBN as the sole initiator. Increasin g the level of AIBN or SDS enhances formation of particle nuclei via homoge neous nucleation. The reaction kinetics is primarily controlled by the comp etitive events of monomer droplet nucleation and homogeneous nucleation. (C ) 1999 John Wiley & Sons, Inc.