Steric Hindrance-Induced Microphase Structure Evolution and Synergistic Performance Optimization of High-Performance Polybutadiene-Based Polyurethane Elastomers

The segmental compatibility between soft and hard segments, along with the resulting microphase separation behavior, critically influences the mechanical and thermal properties of polyurethane elastomers (PU). In this work, we propose a steric hindrance-based molecular design strategy to regulate the microphase structure of nonpolar polybutadiene-based PU. Multiscale characterization and molecular simulations reveal that introducing chain extenders with moderate steric hindrance effectively disrupts the ordered packing of hard segments. This leads to the formation of an interfacial transition-type microphase separation (ITMS) structure. The unique interfacial state enhances interfacial compatibility and morphological uniformity, thereby improving tensile strength, toughness, and energy dissipation. The optimized sample, PU-2, achieved a tensile strength of 14.3 MPa, a toughness of 23.5 MJ·m⁻³, and tan δ_max above 1.0. It also exhibited stable performance under dynamic loading, together with water resistance, electrical insulation, and biocompatibility. These results highlight ITMS as a design strategy for optimizing PU with nonpolar soft and rigid hard segments.