A novel hyperbranched copolymer (HBCP), with a number-average molecular weight from 11000 to 25000, was successfully prepared by the direct condensation polymerization of a unimolecular 3-armed 4-N-methylbenzamide pentamer (TMA-3MAB(5)) as a hard segment (B-3 monomer), with amine-functionalized poly(propylene oxide) (PPOx) (x: degree of s polymerization, 32 or 64) (A(2) monomer) at both ends as a soft segment, and investigated its possibility as a thermoplastic elastomer. The highly pure B-3 molecule, TMA-3MAB(5), was quantitatively obtained by the step-growth reaction of 4-(N-methylamino)benzoic acid (MAB) using thionyl chloride as the condensation reagent and trimesic acid (TMA) as the core molecule in N-methylpyrrolidone (NMP) at 20 degrees C for 0.5 h for each step. The HBCP showed two glass transitions corresponding to imperfectly segregated PPO-rich and polybenzamide hard segment-rich domains, and the film showed good mechanical properties (Young's Modulus T-M 0.25-4.0 MPa, elongation at break E-B 133-1470%), which were controlled by the fraction of the hard segment.