Dual Dynamic Cross-Linking HTPB Polyurethane Elastomers with Disulfide and Cu-MOF Coordination Interactions

Abstract Hydroxyl-terminated polybutadiene-based polyurethane (HTPB-PU) elastomers are often constrained by insufficient mechanical strength, poor intrinsic damage-recovery capability, and inadequate long-term durability, which restrict their application as high-performance binders for composite solid propellants. Herein, a dual-dynamic network integrating reversible disulfide exchange and Cu-MOF-mediated metal coordination was developed to enhance the mechanical robustness and recoverability of HTPB-PU elastomers. Dynamic disulfide bonds were introduced using 4,4′-diaminodiphenyl disulfide, while Cu-MOFs were incorporated as multifunctional coordination nodes to construct a hierarchically dynamic HTPB-PU network. Structural characterization and systematic performance evaluation demonstrated that this coupled dual-dynamic network achieved exceptional synergistic optimization of multiple key properties. The tensile strength reached 11.50 MPa, corresponding to 8.65 times the value of unmodified HTPB-PU, while the tensile toughness was enhanced by approximately 24.72-fold. These substantial improvements were accompanied by remarkable cyclic fatigue resistance, with 75.2% stress retention after repeated loading at 500% strain, as well as excellent thermally responsive self-healing performance, with more than 95% of the mechanical strength recovered after treatment at only 60 °C for 2 h. The exceptional performance originated from reversible S–Cu coordination, which directly coupled the disulfide-exchange and metal-coordination networks to promote energy dissipation, stress redistribution and dynamic network reconstruction. This coupled dual-dynamic-network design effectively reconciles the traditionally competing requirements of strength, toughness, fatigue resistance, and self-healing capability, establishing a promising molecular-engineering paradigm for advanced HTPB-based solid-propellant binders.