Sulfonated polystyrene (S–PS), which is of considerable scientific and technological interest, has been traditionally prepared by the sulfonation of preformed polystyrene. This report describes the preparation and properties of S–PS prepared by emulsion copolymerization of styrene and sodium styrene sulfonate. S–PS prepared by copolymerization gave solubility, solution behavior and thermal characteristics that are consistent with an ionomeric structure. The solubility characteristics indicated some chain-to-chain sulfonate heterogeneity. Thermal analysis studies indicated that the glass transition does not increase with increasing sulfonate content. This is contrary to what has been observed for S–PS prepared by sulfonation and suggests that the S–PS prepared by copolymerization is fundamentally different in structure than S–PS prepared by sulfonation of polystyrene.