A series of star azide copolymers (b-POBs) with hyperbranched polyether cores (HBPO-c) and short linear poly(3,3'-bis-azidomethyl oxetane) arms (PBAMO-a) have been prepared. The polymers were characterized with FT-IR, H-1 NMR, quantitative C-13 NMR, gel permeation chromatography, MALDI-TOF, and X-ray diffractometry. Due to hyperbranched structures, the crystallinity (We) of b-POBs was significantly decreased, and the processability was greatly improved. The enthalpy of formation, obtained by oxygen bomb calorimetric measurements, high azide content, and heats of decomposition of b-POBs demonstrated their remarkable energy level. Furthermore, b-POBs had good resistance to pyrolysis up to 230 degrees C (T-5%), and their mechanical sensitivities were also obviously lower than that of the PBAMO homopolymer, showing their good safety properties. Moreover, the mechanism for sensitivity reduction of b-POBs was established by analyzing the relationship between the activation course in mechanical stimulus and its crystalline structure.