A mixture of sodium polystyrene suffonate (NaPSS) and anionic surfactant, sodium dodecyl sulfate (SDS), was used as the emulsifier in the emulsion polymerization of styrene at 60 degrees C. The latexes prepared were stable, bearing the better resistance to the addition of electrolyte, and have the larger values in particle size and the higher polymerization rates than those counterparts prepared using SDS only. The NaPSS was prepared by a series of process: a concentrated cyclohexane solution of an anionically polymerized polystyrene (PS) was sulfonated with sulfuric acid at 80 degrees C, and then neutralized and purified through dialysis. The data of average polymer number per particle (n(p)) were found useful in investigating the surfactant content effect on the entry of radicals into particles, where the latex particle size plays an important role. (c) 2007 Elsevier Ltd. All rights reserved.