High strength and rapid self-healing daidzein-based polyhydroxyurethanes for high temperature-resistant adhesives†

Polyhydroxyurethanes (PHUs) are considered a sustainable and safer alternative to traditional toxic isocyanate-based polyurethanes (PUs). There are two important characteristics of PHUs, which are their mechanical and self-healing properties. However, these two features are contradictory properties difficult to optimize simultaneously. In this work, a strong and rapid self-healing bio-based PHU network was prepared based on carbonated daidzein (DZ-BCC) and amines. The self-healing properties are tailored by using aminopropyl-terminated polydimethylsiloxane (H₂N-PDMS-NH₂) as a soft segment, increasing the chain mobility. The high crosslinking density of networks and the benzopyran ring structure in daidzein give the resulting PHUs a strength of up to 28.3 MPa. Despite their excellent mechanical properties, these materials show rapid self-healing capability, chemical recyclability, and remarkable reprocessing efficiency. Notably, 94% of the original tensile strength can be recovered after self-healing for 30 min at 150 °C. In addition, the prepared materials have the potential to be used as adhesives in wood and glass bonding, achieving lap shear strengths of up to 6.4 MPa and 3.4 MPa, respectively. Moreover, bonded glasses with PHUs exhibit excellent high-temperature resistance, maintaining stability up to 150 °C. This study presents bio-based PHUs derived from daidzein with good mechanical and dynamic performance simultaneously, and broadens their applications in high temperature-resistant adhesives.