Preparation and Interfacial Enhancement of Polyether-Modified HTPB-Based Polyurethane Based on Step-Growth Polymerization and Microphase Structure Control

To improve the interfacial performance between hydroxyl-terminated polybutadiene (HTPB)-based polyurethanes and polar propellants, this study addresses the intrinsic polarity mismatch between the two components and proposes a facile chemical modification strategy based on the step-growth copolymerization method, in which polar polyether segments are incorporated into the HTPB backbone. This approach features low cost, simple processing, and promising scalability for practical applications. Poly(propylene oxide) diol (N210), polytetrahydrofuran (PTMEG), and polyethylene glycol (PEG) were employed as representative polyethers to modify HTPB, and a series of polyether-modified HTPB-based polyurethane films and bonded assemblies were prepared accordingly. The effects of polyether type and content on the microphase structure, mechanical properties, surface polarity, and interfacial adhesion strength of the materials were systematically investigated using Fourier-transform infrared spectroscopy, scanning electron microscopy, mechanical testing, contact angle measurements, and debonding tests of bonded specimens. The results demonstrate that N210 significantly enhances the elongation at break of the material (up to 623%) while markedly increasing surface polarity, as evidenced by a decrease in the water contact angle from 113.8° to 80.1°. The N210-modified liner exhibits outstanding interfacial adhesion potential, with the failure mode dominated by cohesive fracture within the propellant. In contrast, PTMEG-modified HTPB polyurethane enables a balanced combination of mechanical properties over a relatively wide composition range (10–30 wt%), while improving interfacial adhesion through optimization of the interfacial structure. The N210- and PTMEG-modified systems enhance interfacial bonding via two distinct mechanisms, namely “polarity–toughness enhancement” and “mechanical balance preservation–interface optimization,” respectively. These results highlight the effectiveness of polyether copolymerization in tailoring the interfacial performance of HTPB-based polyurethanes with polar propellants and provide valuable guidance for the rational design and selection of liner materials.