Synthesis of polyurethane with asymmetric hard segments and its effect on room-temperature self-healing property of bitumen

Self-healing bitumen can significantly enhance the durability and service life of bituminous pavement, thereby reducing the need for frequent maintenance and repairs. In this study, isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), and isophorone diamine (IPDA) were utilized to design asymmetric dynamic hard segments, imparting self-healing properties to polyurethane even at room temperature. Particular emphasis was placed on hydrogen bonding, as its reversible formation serves as a primary mechanism for the self-healing characteristics of the material. During the synthesis of polyurethane (PU), two different composition ratios were employed to produce two types of PU with distinct chemical structures, molecular weights, and dynamic crosslink densities, which were characterized using NMR, FTIR, GPC, and DMA, respectively. Furthermore, these two PU types exhibited varying mechanical properties and glass transition temperatures, leading to differences in the rheological properties of the corresponding PU-modified bitumen. Dynamic frequency sweep test results indicated that bitumen modified with PU exhibiting higher molecular weight and narrower molecular weight distribution had superior rutting resistance and enhanced room-temperature self-healing capabilities. The underlying reasons for this improvement can be attributed to the hydrogen bonding present in the PU as well as the phase separation structure between the PU and bitumen.