Copolymerizations have been carried out with styrene (STY) as monomer 1 and with ethyl (EMA), n-butyl (BMA), or lauryl (LMA) methacrylate as monomer 2. A pulsed UV laser was used to photoinitiate the polymerizations to low conversion. The resultant copolymers were analyzed for composition and molecular weight. Propagation rate constants were obtained as a function of composition for each of the copolymerizations, as well as reactivity ratios for the copolymerization of STY with EMA (r1 = 0.62, r2 = 0.35) and with BMA (r1 = 0.72, r2 = 0.45). None of the copolymerizations conformed to the Mayo-Lewis model with respect to their propagation rate constants. The results were interpreted using a penultimate model for propagation. Homopropagation rate constants for each of the monomers were also determined at several temperatures, allowing Arrhenius expressions to be formulated.