Multiscale regulation of topological evolution and mechanical enhancement mechanisms in branched glycidyl azide polymer-based polyurethanes

The design of high-performance elastomeric networks from highly branched prepolymers represents a significant challenge in polymer science due to inherent topological complexities. Branched glycidyl azide polymer (BGAP), while serving as a functional candidate for energetic binders, typically exhibits restricted mechanical properties arising from steric hindrance, a high proportion of dangling chains, and topological looseness. This study develops a multiscale regulation strategy by optimizing the formulation-defined NCO/OH ratio (R = 5), replacing 20 wt% of BGAP with PET, and adding 1 wt% TMP. The strategy was systematically evaluated across 13 formulations using tensile testing, LF-NMR-derived cross-linked fraction A_c and crosslink density ν, and XPS/FTIR analysis of urethane-related signals at a plasticizer ratio of 0.3. Optimization achieves a 2.5-fold tensile strength increase to 1.19 MPa with >140% elongation at break, as ν rises from 4.563 × 10⁻⁴ to 6.443 × 10⁻⁴ mol/mL at A_c = 66.75%, accompanied by enhanced XPS –NH–/–NO₂ and FTIR N–H/C=O urethane-related signals. The observed cross-scale correlations (adjusted R² = 0.74-0.97 for the selected parameter pairs) suggest that molecular urethane-related signals are closely associated with effective network evolution and provide a basis for formulation-guided optimization of BGAP-based energetic binders.