Three types of novel N-[4-(N＇-substituted aminocarbonyl)phenyl] maleimide (RPhMI : N-substituent (R) = phenyl, cyclohexyl, and cyclododecyl) were synthesized and homopolymerized under several conditions. In the copolymerizations of RPhMI (M-1) with styrene (ST; M-2) or methyl methacrylate (MMA; M-2), monomer reactivity ratios and Alfrey-Price Q, e values were determined. All homopolymers decomposed without softening and melting points. The initial degradation temperatures (T-d) of poly(RPhMI)s were over 320 degrees C. The glass transition temperatures (T-g) of RPhMI copolymers were much higher than those of N-phenylmaleimide (PhMI)-ST, PhMI-MMA, N-cyclohexylmaleimide (CHMI)-ST, and CHMI-MMA copolymers. Thermal stability of the terpolymers of RPhMI with ST and acrylonitrile (AN) was higher than that of ST-AN copolymers, i.e., AS resin.