The microemulsion (ME) and conventional emulsion (CE) copolymerizations of methyl methacrylate (MMA) with acrylonitrile (AN) are carried out at 70degreesC by employing n-butyl cellosolve as cosurfactant along with sodium lauryl sulfate as surfactant in the reaction medium and potassium persulfate as initiator. The copolymers are characterized by FTIR, NMR, TG/DTA, and GPC techniques. The reactivity ratios are evaluated by employing Fineman-Ross, Kellen-Tudos (K-T), and Mayo-Lewis integration methods. The K-T method yields reactivity ratios, r(MMA) and r(AN), for the ME copolymerization of MMA and AN of 1.06 +/- 0.01 and 0.14 +/- 0.01, and those for the CE copolymerization of MMA and AN are 2.19 +/- 0.01 and 0.14 +/- 0.01, respectively. (C) 2004 Wiley Periodicals, Inc.