The evolution of the various structural units incorporated in the hyperbranched polymers formed from AB_g polycondensation was investigated by the kinetic model. The various definitions for the degree of branching (DB) of hyperbranched polymers were reviewed and an improved definition was presented for the general AB_g polycondensation system. DB increased with increasing g at any specified conversion of A groups (x), and reached a maximum value of 1－e^－1 at full conversion of A group and infinite g. The z-average mean-square radius of gyration was almost independent of the variation in the g at any specified x. It only increased 0.1% with the variation in the g from 2 to infinite at x＝0.999. However, the z-average degree of polymerization became twice at the same condition. Such a phenomenon suggests that the outline of the hyperbranched polymers formed in the polycondensation of AB_g type monomers is almost independent of the g at any specified conversion, since that the radius of gyration is decided by the shape and distribution. The added structural units (or degree of polymerization) with increasing g must be distributed over interior of the molecules.

Key words: hyperbranched polymer, degree of branching, kinetic model