The microemulsion (M.E.) and conventional emulsion (C.E.) copolymerizations of styrene (STY) with methyl methacrylate (MMA) are carried out at 70 degrees C by employing n-pentanol (PA) and n-octanol (OA), respectively, as cosurfactants along with sodium lauryl sulfate (SLS), as surfactant in the reaction media, and potassium persulphate (KPS) as initiator. The copolymers are characterized by FTIR, NMR, TG/DTA, and GPC techniques. The reactivity ratios are evaluated by employing Fineman-Ross (F-R), Kellen-Tudos (K-T), and Mayo-Lewis integration (M-L-I) methods. The K-T method yields the apparent reactivity ratios, 0.73 (r(STY)), 0.39 (r(MMA)) and 0.55(r(STY)), 0.50 (r(MMA)), respectively, for the M.E. and C.E. copolymerizations of STY and MMA with PA as the cosurfactant present in the reaction media. And the K-T method yields the apparent reactivity ratios, 0.56 (r(STY)), 0.43 (r(MMA)) and 0.42 (r(STY)), 0.51 (r(MMA)) respectively, for the M.E. and C.E. copolymerizations of STY and MMA with OA as the cosurfactant present in the reaction media. (C) 2007 Wiley Periodicals, Inc.