The new approach for preparation of hyperbranched polymers from commercially available A(2) and BB'(2) type monomers was further extended to synthesize hyperbranched copolymers. In this work, hyperbranched copoly(sulfone-amine)s were prepared by polyaddition of piperazine (B-2) and N-ethylethylenediamine (BB'(2)) to divinylsulfone (A(2)) The polymerization mechanism was investigated with FTIR and LC-MSD. During the copolymerization, secondary-amino groups of piperazine and N-ethylethylenediamine react rapidly with vinyl groups of divinylsulfone within 50 s, and then the residual vinyl groups react with primary-amino groups resulting in hyperbranched copoly(sulfone-amine)s. The crystallization behaviors of the resulting polymers were characterized with DSC and X-ray diffraction. When the initial mole ratio of B-2 to BB'(2) is equal to or higher than three, r greater than or equal to 3, resulting copolymers are semi-crystalline, while those with r < 3 are amorphous. Interestingly, the resulting polymers with r = 3 exhibit the highest melting temperature comparing with other semi-crystalline samples. The degree of branching of hyperbranched copolymers was determined by H-1 NMR. (C) 2001 Elsevier Science Ltd. All rights reserved.