Polyether oligomers (M-n = 200-2000) were respectively esterified by succinic anhydride and fatty sebacoyl chloride to synthesize corresponding intermediate diacids, and experimental results of melt polycondensations based on these two kinds of intermediates were compared. The reasons for affecting higher molecular weight products to be achieved in polymerization with prepolymers based on succinic anhydride esterification were theoretically analyzed. Light scattering measurements showed that copolyanhydrides with higher molecular weights exceeding 8 x 10(4) (weight-average) were synthesized from the intermediate diacids prepared by a new method using fatty diacid chlorides to undergo esterification with polyether. Synthesized intermediates were characterized by H-1-NMR and infrared spectroscopy. Intrinsic viscosity of the polymers were measured to display the advancement of polymerization. The properties of polymers were investigated by X-ray diffraction and differential scanning calorimetry analysis as well.