The copolymerization of N-cyclohexylmaleimide (CHMI) and methylmethacrylate (MMA) with azobisisobutyronitrile as the initiator was investigated. Infrared spectroscope was applied to determine the copolymer compositions of the copolymers synthesized at 60, 70, 80, and 90 degrees C while the conversions of the copolymerizations were controlled to be below 10%. According to the Mayo-Lewis equation, the reactivity ratios of N-cyclohexylmaleimide and methylmethacrylate were calculated. It was proved that N-cyclohexylmaleimide was less reactive, and the optimum temperature of the copolymerization was 80 degrees C.