Preparation and characterization of soap-free carboxylated polystyrene latexes

Soap‐free carboxylated polystyrene latexes have been prepared by copolymerizing carboxylic monomers in a wide range of degree of neutralization using a slight amout of soap. In this polymerization system, the formation of particles seems to be explained by the precipitation of growing radicals formed in the aqueous phase. The degree of neutralization of carboxylic monomers has a great effect on the formation of particles, which may be attributed to a change in the hydrophilic nature of growing radicals formed in aqueous phase that governs the number and uniformity of particles. The number of particles increases remarkably with increasing the amount of soap to some extent, which may be attributed to the stabilization of primary particles formed by the precipitation of growing radicals with the adsorption of soap. The localization of carboxyl groups on the surface of particles seems to be governed by the electrostatic repulsion between carboxyl groups. The surface area occupied by a surface carboxyl group, however, is fairly small irrespective of the degree of neutralization of carboxylic monomers or the amount of soap, which indicates that the latexes are sufficiently stabilized with surface carboxyl groups.