Preparation of Highly Charged, Monodisperse Nanospheres

A two-stage shot growth emulsifier-free polymerization was applied to prepare styrene(St)/sodium styrenesulfonate (NaSS) latices. The latex particles prepared in the pure water medium were monodisperse and highly charged spheres, but their particle diameters were all higher than 120 nm. By using the two-stage shot growth copolymerization at 70°C in the mixed reaction medium of water and acetone, we successfully prepared monodisperse, highly charged nanospheres with the smallest particle diameter of 89 nm. As the acetone content in the mixed reaction medium was increased to an acetone/H2O ratio of around 0.125, the particle diameter decreased to minimum, and then the particle diameters increased with increasing acetone content in the mixed reaction medium. The conversion-time curves for the first stage emulsifier-free copolymerization of St/NaSS in the mixed reaction medium with varied acetone contents show that the polymerization rate first increased with increasing acetone content, and then decreased. The enhanced rate of polymerization in the lower acetone content results from the increase in the number of primary particle in the reaction medium. As the acetone content was further increased, the solubility of St in the reaction medium further increased, making the copolymerization somewhat like the dispersion polymerization and thus causing increased particle size.