Strong, Water-Resistant, Self-Healing Waterborne Polyurethane Achieved by Rigid-Flexible Design and Dynamic Networks

The development of high-performance waterborne polyurethane (WPU) coatings that combine robust mechanical strength with multiple functionalities remains a significant challenge. Herein, we propose a “rigid–flexible” molecular design strategy to fabricate multifunctional WPU coatings by simultaneously incorporating a rigid disulfide-containing dynamic chain extender (APDS) and a flexible siloxane-based chain extender (BATD) into the polymer backbone. This synergistic design promotes the formation of a microphase-separated structure and the construction of a dynamic bonding network. The resulting optimal material (SSWPU2–3) exhibits overall performance, including a high tensile strength of 49.19 MPa, water resistance (a water contact angle of 85.6° and a water absorption of 5.12%), and self-healing capability (72.7% recovery at 80 °C). As a demonstration of practical application, the coating enhances the surface gloss, hydrophobicity, and abrasion resistance of leather while retaining its self-healing functionality. This work provides a versatile and scalable approach for designing sustainable, multifunctional polymeric coatings suitable for high-end leather finishing and other flexible substrates.