methylstyrene.PMS. latex particles in an emulsifier-free emulsion were first synthesized by using 2,29-azobis-2-amidinopropane. dihydrochlorideV-50. as an initiator. Purification of the latexes by dialysis was followed inorder to remove residual monomer, initiator and electrolytes. The cationic polymethylstyrene. latexes were then oxidized in the presence of t-butyl hydroperoxide catalyzed by copper chloride at 608C under air. The degree of oxidation increased with reaction time, but the emulsions of highly oxidized poly methylstyrene. latexes were found to be unstable. An increase of oxidant concentration enhanced the rate of oxidation, while the catalyst concentration had little influence on it. The effect of reaction temperature and pH value on the catalytic oxidation of poly methyl-styrene. latexes was also investigated.