High Azide Content Hyperbranched Star Copolymer as Energetic Materials

A series of star azide copolymers (<i>b</i>-POBs) with hyperbranched polyether cores (HBPO-<i>c</i>) and short linear poly­(3,3′-bis-azidomethyl oxetane) arms (PBAMO-<i>a</i>) have been prepared. The polymers were characterized with FT-IR, ¹H NMR, quantitative ¹³C NMR, gel permeation chromatography, MALDI-TOF, and X-ray diffractometry. Due to hyperbranched structures, the crystallinity (<i>W</i>_c) of <i>b</i>-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 <i>b</i>-POBs demonstrated their remarkable energy level. Furthermore, <i>b</i>-POBs had good resistance to pyrolysis up to 230 °C (<i>T</i>_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 <i>b</i>-POBs was established by analyzing the relationship between the activation course in mechanical stimulus and its crystalline structure.