Dual-Dynamic Waterborne Polyurethane Coating with Alkaline-Triggered Rapid Self-Healing and High Mechanical Robustness

The development of self-healing waterborne polyurethane (WPU) coatings that integrate rapid damage repair with robust mechanical performance remains challenging, primarily due to the inherent trade-off between dynamic bond mobility and network rigidity. Herein, a dual-dynamic WPU coating system was developed by using a custom-synthesized Schiff base chain extender that incorporated both imine (C═N) and disulfide (S–S) bonds into the WPU backbone. This molecular design enabled the WPU coating to achieve a 98% repair ratio at room temperature (RT) within 30 min under mild alkaline conditions (pH 10). Furthermore, the coating exhibited enhanced mechanical properties, including an adhesion strength of 2.8 MPa and a pencil hardness of 2H, attributable to its high cross-linking density and the incorporation of rigid aromatic segments. The remarkable mechanical properties of the coating were supported by the intrinsic strength of the WPU casting film, which demonstrated a tensile strength of 3.02 MPa, a Young’s modulus of 367.5 MPa, and an 88.9% recovery of its original tensile strength after healing. This work offers a viable approach to fabricating high-strength, highly self-healing waterborne polyurethane (WPU) coatings, showing strong potential for use in alkaline-relevant settings such as marine protective coatings, where pH-triggered, on-demand self-healing provides a clear functional benefit.