Free-radical copolymerizations; of N,N-diethylaminodithiocarbamoylmethylstyrene (inimer: DTCS) with a methyl methacrylate (MMA)/zinc chloride (ZnCl2) complex were carried out under UV light irradiation. DTCS monomers play an important role in this copolymerization system as an inimer that is capable of initiating living radical polymerization of the vinyl group. The reactivity ratios (r(1) = 0.56 and r(2) = 0.52: DTCS [M-1]; MMA [M-2]) obtained for this copolymerization system were different from a corresponding model system (alternating copolymer) of a styrene and MMA/ZnCl2 complex (r(1) = 0.25 and r(2) = 0.056). It was found that the hyperbranched copolymers produced exhibited a random branching structure. It was found that the Lewis acid ZnCl2 formed the complex not only with MMA but also with the carbamate group of inimer. (C) 2003 Wiley Periodicals, Inc.