Well-Characterized Monodisperse Polystrene Latexes as Model Colloids

Abstract

Monodisperse polystyrene latexes prepared with persulfate initiator are stabilized by the sulfate endgroups of the polymer molecules. These latexes can be characterized by removing the adsorbed emulsifier and solute electrolyte by ion exchange or serum replacement and determining the surface sulfate groups by conductometric titration with base. However, these latexes sometimes contain surface hydroxyl groups formed by hydrolysis of sulfate groups or a side reaction of sulfate ion-radicals to form hydroxyl radicals. These hydroxyl groups can be determined by oxidation to the carboxyl form, followed by conductometric titration. The purpose of this paper is to describe the preparation of model colloids as well as characterization of industrial latexes. Model colloids with the same number of three different types of surface groups can be prepared to give particles stabilized only with sulfate endgroups, hydrolysis to give particles stabilized only with hydroxyl groups, and oxidation to give particles stabilized only with carboxyl groups. Examples of industrial latexes characterized by these methods include styrenebutadiene-acrylic acid and -methacrylic acid copolymers, ethyl acrylate-methyl methacrylate-acrylic acid copolymers, polyvinyl acetate prepared with polymethacrylic acid emulsifier, and vinyl acetate-butyl acrylate copolymers prepared by batch and semi-continuous polymerization.