N-dodecanethiol (RSH) was found efficient to initiate the radical copolymerization of methyl methacrylate (MMA) with N-cyclohexylmaleimide (NCMI) at 40-60 degrees C. The initial copolymerization rate, R-p increases respectively with increasing [RSH] and the mol fraction of NCMI in the comonomer feed, f(NCMI) The molecular weight of the copolymer decreases with increasing [RSH]. The initiator transfer constant of RSH was determined to be C-I, = 0.21. The apparent activation energy of the overall copolymerization was measured to be 46.9 kJ/mol. The monomer reactivity ratios were determined to be r(NCMI) = 0.32 and r(MMA) = 1.35. The glass transition temperature of the copolymer increases obviously with increasing f(NCMI) which indicates that adding NCMI may improve the heat resistance of plexiglass.