Copolymerizations of vinyl chloride (VC) and N-substituted maleimides (RMI) were carried out at 60℃ by using azobisisobutyronitrile as an initiator in tetrahydrofuran. It was found that copolymers contained more RMI than VC, not being concerned with monomer compositions. The monomer reactivity ratios were determined, and from these values, Q and e-values for RMI were calculated. In consequence of thermal analyses, these copolymers were decomposed at 300&acd