Results of the copolymerization of 4-chloro-3-nitrostyrene (4-CNS) with acrylic and vinylic monomers in bulk or in solution are reported together with some related physico-chemical characterizations, i.r. and n.m.r. data, d.s.c., and solubility properties. These experiments allowed us to characterize the high reactivity of 4-CNS and its main effects (inhibition or retardation) on the copolymerizations studied. In all cases, and more particularly with methacrylic derivatives, copolymerization proceeded slowly, and at limited conversion rates; the copolymer compositions reveal preferential incorporation of 4-CNS. For methyl methacrylate copolymerization no significant induction time was detected, indicating a retarding effect on the kinetics due to 4-CNS.