Mussel‐Inspired Catechol‐Functionalized Waterborne Polyurethane Pressure‐Sensitive Adhesives With Enhanced Wet Adhesion

ABSTRACT Waterborne polyurethane (WPU) pressure‐sensitive adhesives are relatively environmentally friendly but often suffer from poor water resistance due to hydrophilic groups. In this study, a catechol‐functionalized internal emulsifier (HEA‐LDA) was synthesized via the aza‐Michael addition of levodopa (LDA) and hydroxyethyl acrylate (HEA) and incorporated into WPU dispersions. A micelle‐peripheral in situ crosslinking strategy was employed to orient catechol groups toward the micellar shell, enabling oxidative crosslinking after film formation to enhance cohesion and interfacial adhesion. The effects of HEA‐LDA content on particle size, storage stability, water resistance, and peel adhesion were systematically investigated and compared with dopamine‐modified WPU (WPU‐DA). The results showed that HEA‐LDA effectively regulated micelle size and improved emulsion stability, water resistance, and adhesive performance. At an LDA/DMPA molar ratio of 1:1, WPU‐LDA exhibited optimal performance, achieving 180° peel strengths of 39.79 N/25 mm and 37.33 N/25 mm on stainless steel under dry and wet conditions, respectively. Sodium periodate‐induced oxidative crosslinking further increased peel strength on pigskin from 18.79 N/25 mm to 34.47 N/25 mm. Compared with pure WPU and WPU‐DA, WPU‐LDA showed lower weight loss and swelling ratios, demonstrating a biomimetic molecular design strategy for highly water‐resistant and strongly adhesive WPU pressure‐sensitive adhesives.