Novel hyperbranched copolymers were prepared by the atom transfer radical copolymerization of N-(4-alpha-bromobutyryloxy phenyl) maleimide (BBPMI) with styrene in 1-methyl-2-pyrrolidone (NMP) using the complex of CuBr/2,2'-bipyridine as catalyst. The copolymerization behavior was investigated by comparison of the conversion of double bond of BBPMI determined by H-1 NMR with that of styrene. The hyperbranched structure of resulting copolymers was verified by gel permeation chromatography (GPC) coupled with multi-angle laser light scattering (MALLS). The influences of dosage of catalyst and monomer ratio on the polymerization rate and structure of the resulting polymers were also investigated. The glass transition temperature of the resulting hyperbranched copolymer increases with increasing mole fraction of BBPMI, f(BBPMI). The resulting copolymers exhibit improved solubility in organic solvents; however, they show lower thermal stabilities than their linear analogues. (c) 2006 Elsevier Ltd. All rights reserved.