UV-Triggered Coumarin-PDMS Dimerization for Robust and Easy-Cleaning Polyurethane Coatings

Conventional strategies to enhance the hydrophobicity of polyurethane (PU) coatings typically rely on fragile micro/nanostructures or irradiation-induced crosslinking, both of which suffer from poor controllability and often compromise mechanical robustness. Herein, we report a UV-triggered crosslinking strategy based on coumarin chemistry that enables precise, controllable network formation, thereby simultaneously enhancing the hydrophobicity, adhesion strength, and thermal stability of polydimethylsiloxane (PDMS)-based PU coatings. A series of coumarin-functionalized PDMS-PU coatings (HNP-PDMS-PUx) was prepared by blending coumarin-grafted PDMS (HNP) with PDMS-PU elastomers. Upon 365 nm UV irradiation, the coumarin moieties dimerize, forming a dense, chemically crosslinked “brush-like” structure on the coating surface. The optimal coating (HNP-PDMS-PU3/1) exhibited a significant increase in water contact angle from 108° to 129° on average, reaching a maximum of 134°. The UV-treated coating also showed enhanced adhesion strength (a 45% increase) and improved thermal stability, while maintaining good flexibility (F7 rating) and abrasion resistance (contact angle remained at 126° after 30 cycles). Moreover, the coating demonstrated excellent easy-cleaning performance against both liquid and solid contaminants. This work provides a photochemical strategy that replaces uncontrollable or irreversible crosslinking methods with a controllable UV-triggered approach, enabling synergistic enhancement of multiple properties.