Microemulsion (ME) and conventional emulsion (CE) copolymerizations of styrene (STY) with n-butyl methacrylate (BMA) were carried out at 70 degrees C in an inert atmosphere by employing sodium lauryl sulfate as a surfactant, n-heptanol as a cosurfactant, and potassium persulfate as a free-radical initiator. Five different compositions of the monomer mixtures were employed in the initial reaction mixtures, and the copolymerization reactions were arrested at lower conversions. The copolymers made were characterized using FTIR, NMR, TG/DTA, GC, and GPC techniques. The compositions of the copolymers were evaluated from (HNMR)-H-1 spectral data. The reactivity ratios for the RIE and CE copolymerizations of styrene with n-butyl methacrylate were evaluated by the Fineman-Ross (F-R), Kelen-Tudos (K-T), and Mayo-Lewis (M-L) methods. The Fineman-Ross method yielded the reactivity ratios of styrene (r(STY)) and n-butyl methacrylate (r(BMA)) as 0.17 +/- 0.02 and 0.60 +/- 0.02 for ME copolymerization of styrene and n-butyl methacrylate, respectively. The r(STY) and r(BMA) for CE copolymerization of styrene and n-butyl methacrylate were obtained as 0.31 +/- 0.02 and 0.55 +/- 0.02, respectively.