A new approach for preparation of highly branched copolymers from A(2), B-2, and BB'(2) type monomers was reported in this work. Highly branched copoly(sulfone-amine)s were synthesized by polyaddition of piperazine (B-2) and 1-(2-aminoethyl)piperazine (BB'2) to divinyl sulfone (A(2)). The polymerization mechanism was investigated with FTIR and LC-MSD. During the polymerization, secondary amino groups of B-2 and BB'(2) monomers react rapidly with vinyl groups of A(2) monomers within 40 s, and then the residual A groups react with B' groups resulting in highly branched copoly(sulfone-amine)s. Thermal properties and the aggregation structure of resulting polymers were characterized with DSC and X-ray diffraction, respectively. When the initial mole ratio of B-2 to BB'(2) (r) is equal to or higher than three (r greater than or equal to 3 or B/B' greater than or equal to 3.5), resulting branched copolymers are semicrystalline, while copolymers in the case of r < 3 are amorphous. The degree of branching (DB) of the highly branched copoly(sulfone-amine)s was defined and determined by H-1 NMR. The degree of branching of the products increased with decreasing the fed ratio of piperazine to 1-(2-aminoethyl)piperazine. The ratio of the inherent viscosity to the molecular weight decreased with increasing the degree of branching.