Multi-Scale Hydrogen Bonding and Microphase Separation Synergistically Engineered Polyurethane-Polyurea (PU-PUa) as High-Performance Binder

Driven by the rising frequency of extreme climatic events and the escalating demand for sustainable infrastructure, modern pavement materials must deliver enhanced resilience, structural stability, and environmental adaptability. This study presents the design and synthesis of a novel polyurethane-polyurea (PU-PUa) pavement binder, engineered via a synergistic framework combining nanoscale microphase separation and a hierarchical hydrogen-bonding network. Utilizing a streamlined, one-step synthesis approach involving an aliphatic isocyanate, a polyaspartic ester, polytetramethylene ether glycol, and 1,4-butanediol, the PU-PUa copolymer achieves distinct nanoscale phase separation between its hard and soft segments. Fourier transform infrared (FTIR) spectroscopy verifies the successful formation of characteristic PU-PUa moieties and a multi-scale hydrogen-bonding network, while DSC and DMA reveal SSC-dependent soft-segment mobility, crystallization/melting behavior, and viscoelastic relaxation. These intra- and inter-segmental interactions, together with thermally activated soft-segment transitions, establish the structural foundation for the macro-performance enhancement of the system. Comprehensive evaluations demonstrate that the PU-PUa binder exhibits excellent mechanical and highly tunable properties. Rheological measurements indicate that increasing the soft segment content (SSC) or incorporating an appropriate diluent concentration significantly lowers the system viscosity, thereby enhancing processing workability during mixing and paving. Contact angle goniometry reveals that the surface hydrophobicity of PU-PUa can be effectively regulated by adjusting the SSC, offering a viable strategy to optimize moisture damage resistance. Moreover, curing behavior analyses show that the polymerization kinetics are strictly governed by both the SSC and environmental temperature, where a lower SSC or elevated curing temperature accelerates strength development. Mechanically, the PU-PUa binder displays desirable surface hardness (>80 Shore A) and exceptional aggregate adhesion (>2 MPa), ensuring robust bonding stability and resistance to traffic-induced abrasion. Characterized by balanced tensile performance, the elongation at break of the binder can be tailored from 90% to 161%, while its tensile strength varies between 6.4 MPa and 17.8 MPa at intermediate temperatures, manifesting excellent resilience and cracking resistance. Overall, this molecular-to-macroscopic design strategy establishes the PU-PUa copolymer as a highly promising, durable binder for next-generation resilient pavement infrastructures.