Bio-Derived Urushiol-Polycaprolactone Polyurethane Coatings with Hydrolysis-Induced Surface Renewal for Sustainable Marine Antifouling of Static Infrastructure

Conventional self-polishing antifouling coatings rely heavily on petroleum-based polymers and hydrodynamic shear force, rendering them ineffective for stationary marine infrastructure while raising environmental concerns. Natural urushiol offers a promising bio-based alternative, yet its hyper-reactive conjugated side chains lead to uncontrollable auto-oxidation and severe storage failure—creating a sharp paradox between non-intended self-curing and target-controlled degradation. Herein, we report a sustainable, hydrolysis-driven static self-polishing polyurethane (PU) coating that resolves this fundamental dilemma. By stabilizing the volatile urushiol framework and integrating hydrolytically degradable poly(ε-caprolactone) (PCL) soft segments, the resulting PU architecture completely overcomes structural instability while achieving tailored microphase separation. This optimized molecular network grants the coating excellent thermal stability, strong substrate adhesion, high impact resistance, and superior flexibility. Crucially, controlled hydrolysis of the PCL backbones drives uniform, layer-by-layer surface renewal under static seawater conditions without requiring shear flow. The erosion kinetics can be further fine-tuned across a broad dynamic range by incorporating natural rosin. Driven by this continuous self-renewing interface, the coating exhibits exceptional broad-spectrum resistance against representative marine biofouling, achieving anti-adhesion efficiencies of 87.83% against Bacillus sp. and up to 99.41% against Nitzschia closterium. This work provides a sustainable natural molecular design strategy for bio-based static self-polishing coatings.