Monodisperse micron-sized cross-linked polystyrene particles. VI. Understanding of nucleated particle formation and particle growth

The procedure of nucleated particle formation and particle growth in disper sion polymerization was studied with the intention of understanding the pro duction of monodisperse polystyrene particles cross-linked with urethane ac rylate (UA). The time required for the formation of primary particles was d etermined exactly from the turbidity measurement of the reaction mixture wi th the polymerization time. It could be found that differing from conventio nal divinyl crosslinkers, such as divinylbenzene, UA had a boundary concent ration where the association and coagulation of preformed nuclei with other oligomers and/or nuclei effectively took place until the primary particle formed. Similarly to linear polystyrene particles, the particle number dens ity of the primary particles cross-linked with UA remained constant to the final particles. This observation verifies the suggestion that the primary particles crosslinked with UA readily absorbed the monomers from the medium during the stage of particle growth.