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

Waterborne polyurethane with a combination of high strength, toughness, and self-healing efficiency is attractive in many fields, but the development of such materials remains challenging due to the contradictions of these properties. In this work, a cross-linked waterborne polyurethane (DWPU) was successfully prepared by introducing a cross-linking agent containing reversible disulfide and acylhydrazone bonds on the linear backbone. The dual network of acylhydrazone covalent cross-linking and hydrogen bonding improves the stability of the polyurethane network and provides excellent mechanical properties for the elastomers, while the synergistic action of dynamic acylhydrazone bonds, disulfide bonds, and hydrogen bonds imparts outstanding self-healing performance. As a result, DWPU exhibits excellent tensile strength (49.34 MPa), exceptional Young's modulus (305.4 MPa), satisfactory toughness (214.8 MJ m–3), and rapid self-healing efficiency (over 90%). Thanks to the abundant polar groups, DWPU presents tough adhesion strength in bonding various substrates, such as aluminum, glass fiber, and epoxy resin. In addition, it has a good transparency and inherent blue fluorescence. By integration of the self-healing ability and fluorescence properties, the self-healing process of the materials could be traced by detecting the change in fluorescence intensity of crack positions. This study not only provides a simple way for the preparation of high-performance and multifunctional environmentally friendly waterborne polymers but also broadens their application fields in optical anti-counterfeiting, protective coatings, smart devices, and so on.