Hyperbranched polyborate modified HTPB adhesives with enhanced performance and lower glass transition temperature

Abstract

Hydroxyl-terminated polybutadiene (HTPB) adhesive has a low polarity main chain, resulting in poor compatibility with energetic components and a lack of energy-contributing groups, thus offering a limited energy contribution to propellants. Despite the diverse modification methods available for HTPB, they often suffer from harsh reaction conditions, decreased performance post-modification, and limited modification pathways. In this study, simple “one-pot polycondensation” was employed to synthesize a hyperbranched polyborate (HBPB) with a B–O–C backbone structure for the modification of HTPB-based adhesives. The modified HBPB/HTPB adhesive exhibited excellent mechanical properties at both room and low temperatures. Compared to pure HTPB, the tensile strength at room temperature increased by 198%, and at low temperatures, the increase reached 941%. Additionally, the adhesion strength improved by 214%, enhancing the adhesive bonding effect and reducing the occurrence of “debonding” issues. Moreover, HBPB's unique three-dimensional topological structure and flexible chains imparted better low-temperature adaptability to HTPB, lowering the glass transition temperature (T_g) by 16.03 °C. The numerous active terminal groups increased the crosslinking density, thereby enhancing the strength of the HTPB system and significantly improving the performance of the composite material. This study addresses the shortcomings of existing adhesives in terms of polarity and low-temperature adaptability, providing an effective technical pathway for the further development of adhesives for solid propellants.