Multifunctional Waterborne Polyurethane with Robustness,\nAdhesiveness, and Self-Healability Based on a Dual Cross-Linked Network\nContaining Multiple Dynamic Bonds

Waterborne polyurethane with a combination\nof high strength, toughness,\nand self-healing efficiency is attractive in many fields, but the\ndevelopment of such materials remains challenging due to the contradictions\nof these properties. In this work, a cross-linked waterborne polyurethane\n(DWPU) was successfully prepared by introducing a cross-linking agent\ncontaining reversible disulfide and acylhydrazone bonds on the linear\nbackbone. The dual network of acylhydrazone covalent cross-linking\nand hydrogen bonding improves the stability of the polyurethane network\nand provides excellent mechanical properties for the elastomers, while\nthe synergistic action of dynamic acylhydrazone bonds, disulfide bonds,\nand hydrogen bonds imparts outstanding self-healing performance. As\na result, DWPU exhibits excellent tensile strength (49.34 MPa), exceptional\nYoung’s modulus (305.4 MPa), satisfactory toughness (214.8\nMJ m<sup>–3</sup>), and rapid self-healing efficiency (over\n90%). Thanks to the abundant polar groups, DWPU presents tough adhesion\nstrength in bonding various substrates, such as aluminum, glass fiber,\nand epoxy resin. In addition, it has a good transparency and inherent\nblue fluorescence. By integration of the self-healing ability and\nfluorescence properties, the self-healing process of the materials\ncould be traced by detecting the change in fluorescence intensity\nof crack positions. This study not only provides a simple way for\nthe preparation of high-performance and multifunctional environmentally\nfriendly waterborne polymers but also broadens their application fields\nin optical anti-counterfeiting, protective coatings, smart devices,\nand so on.