A Strategy of Thiolactone\nChemistry to Construct Strong\nand Tough Self-Healing Supramolecular Polyurethane Elastomers via\nHierarchical Hydrogen Bonds and Coordination Bonds

Abstract

Self-healing elastomers with extended service life and\nenhanced\nreliability have attracted extensive attention in recent years due\nto their broad application in fields such as protective coatings,\nwearable electronics, shape memory materials, and health-care monitoring.\nHowever, it is challenging to simultaneously optimize the mechanical\nproperties (strength and toughness) and self-healing capacity of the\nelastomers. Herein, thiolactone chemistry was delicately used as a\nbridge to address this conundrum by incorporating 2-ureido-4[1<i>H</i>]-pyrimidinone (UPy) motifs and imidazole ligands into\nthe side chains of linear polyurethane. The synergistic cross-linking\nof UPy H-bonds and Zn²⁺-imidazole coordination afforded\na robust supramolecular network to significantly improve the strength.\nMeanwhile, these dynamic cross-linking points acted as sacrificial\nbonds for energy dissipation under external stress, which played a\ndominant role in toughening. Therefore, the resultant elastomer (PU-Im-UPy-Zn)\nexhibited a tensile strength of 9.1 MPa, a breaking elongation of\n989%, and toughness up to 62.1 MJ m^–3. In addition,\nthe reversible exchange of hierarchical hydrogen bonds (single H-bonds\nbetween the carbamate groups and quadruple H-bonds of the UPy dimers)\nand coordination bonds as well as the high mobility of side chains\nwere conducive to repairing under mild conditions. The superficial\nscratches completely disappeared at 60 °C, and a satisfactory\nhealing efficiency of 78% was observed after 24 h. This work provides\nsome insights into future design of self-healable supramolecular polyurethane\nelastomers integrated with conspicuous strength and toughness.