Mechano-responsive hydrogen-bonding array of thermoplastic polyurethane elastomer captures both strength and self-healing

Self-repairable materials strive to emulate curable and resilient biological tissue; however, their performance is currently insufficient for commercialization purposes because mending and toughening are mutually exclusive. Here, we report a carbonate-type thermoplastic polyurethane elastomer that self-heals at 35 °C and exhibits tensile strength of 43 MPa. This elastomer is as strong as footwear soles. Distinctively, it has abundant carbonyl groups in soft-segments and is fully amorphous with negligible phase separation due to poor hard-segment stacking. It operates in dual mechano-responsive mode through a reversible disorder-to-order transition of its hydrogen-bonding array; it heals when static and toughens when dynamic. In static mode, non-crystalline hard segments promote dynamic exchange of disordered carbonyl hydrogen-bonds for self-healing. The amorphous phase forms stiff crystals when stretched through a transition that orders inter-chain hydrogen bonding. The phase and strain fully return to the pre-stressed state after release to repeat healing process.<b><br> </b>

自修复材料（Self-repairable materials）旨在模拟可修复且具有弹性的生物组织；然而目前其性能尚未达到商业化应用标准，原因在于修复与增韧二者不可兼得。本研究报道了一种碳酸酯型热塑性聚氨酯弹性体（carbonate-type thermoplastic polyurethane elastomer），该材料可在35℃下实现自修复，拉伸强度达43 MPa，其强度与鞋底材料相当。其独特之处在于软段（soft-segments）中含有大量羰基，且由于硬段（hard-segments）堆叠能力较弱，材料呈完全无定形态，相分离程度可忽略不计。该材料通过氢键阵列（hydrogen-bonding array）的可逆无序-有序转变，实现双重力学响应模式：静态时完成自修复，动态时实现增韧。静态模式下，非晶态硬段可促进无序羰基氢键的动态交换，从而实现自修复；受拉伸时，无定形相通过链间氢键有序化的转变，形成刚性晶体结构。外力释放后，其相结构与应变可完全恢复至预拉伸前的状态，从而可重复进行自修复过程。