Emulsion polymerization method for preparing aqueous dispersions of organic polymer particles

An emulsion polymerization method for preparing an aqueous dispersion of normally solid organic polymeric particles, said method comprising dispersing an oil phase comprising at least one monovinylidene aromatic carbocyclic monomer in an aqueous phase containing from about 0.5 to about 4 weight percent based on total monomer of a stabilizing emulsifier selected from the group consisting of water-soluble anionic surfactant, water-soluble non-ionic surfactants and mixtures thereof, and from about 0.2 to about 2 weight percent based on total monomer of a polymer of at least 20 weight percent of a sulfo ester of an .alpha.-methylene carboxylic acid and up to 80 weight percent of at least one ethylenically unsaturated monomer copolymerizable therewith selected from a group consisting of monovinylidene aromatic carbocyclic monomer, acrylate esters and acrylonitriles, said total monomer being capable of polymerization to form a water-insoluble polymer, and (2) subjecting the dispersion to emulsion polymerization conditions comprising free-radical type catalyst, temperature in the range from about 60.degree. to about 100.degree. C. and agitation of the dispersion.