A NaPSS-b-PS was prepared via a two-stage stable free-radical polymerization using a mixture of ethylene glycol and water as the medium. Styrene emulsion polymerization was conducted using a mixture of NaPSS-b-PS and SDS. Results showed that there is little aggregation among particles. Two other NaPSSs with different sulfonation fractions were also compared. Comparisons were made using relationships, such as $ {\overline n} $ versus Dv, chain growing time versus SDS content, and Dv versus SDS content. Characteristic behaviors of various NaPSSs on entry were revealed. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012