Remarkable mechanical performance at low temperatures of hydroxy-terminated polybutadiene enhanced by hyperbranched polysiloxane

The inadequate mechanical properties and limited low temperature adaptability of Hydroxy-terminated polybutadiene (HTPB) impose constraints on its practical utilization in solid propellant applications. In the present investigation, a pioneering approach involved the synthesis of a novel hyperbranched polysiloxane, denoted as HBPSi-NH₂, which encompasses –NH₂ groups and Si–O–C chains. The HBPSi-NH₂ with its unique flexible Si–O–C segments, serving as the soft component in the crosslinked network, in conjunction with the curing agent TDI as the hard component, achieves a synergistic balance of rigidity and flexibility. The resulting HTPB composites not only demonstrate enhanced mechanical properties but also exhibit excellent low temperature adaptability. Remarkably, the HTPB composites exhibit excellent mechanical properties at both 25 °C (0.74 MPa ~ 2.08 MPa) and − 40 °C (1.77 MPa ~ 12.49 MPa). This enhancement can be ascribed to the abundant presence of functional groups, namely –OH and –NH₂. These active groups significantly augment the cross-linking density within the HTPB system, also promote the formation of numerous hydrogen bonds, enhancing the strength of HTPB. Simultaneously, the abundant presence of Si–O–C flexible chain segments within HBPSi-NH₂ enhances the reactivity of the HTPB molecular chains, not only improving the toughness of HTPB but also significantly reducing its T_g (− 65.95 °C to − 75.62 °C). Furthermore, this study establishes a pivotal direction for the design and synthesis of high-performance HTPB-PU materials.