Rapid Underwater Adhesion via Photo-Activated Chemically Cross-Linked Hybrid Network

Underwater adhesives with high bonding strength and rapid curing are increasingly needed for marine infrastructure, underwater sealing, and aquatic equipment repair. Despite recent progress in underwater adhesive technologies, critical formulation challenges such as solvent toxicity, poor initial adhesion to irregular surfaces, and weak performance in dynamic aqueous environments remain unresolved. In this study, we report a chemically hybrid adhesive network formed by phototriggered copolymerization of acrylate-functionalized polyurethane (PU) prepolymers and acrylic acid (AA), resulting in a single, covalently hybrid network that combines flexible, hydrogen-bond-rich polyurethane segments with rigid poly(acrylic acid) (PAA) domains. Unlike conventional systems that rely on solvent-based formulations or require ideal bonding conditions, our adhesive employs AA as a miscible reactive monomer and plasticizer, enabling good wettability, initial adhesion, and facile application on curved or rough surfaces under dynamic aquatic environments. Photo-cross-linking ensures rapid formation of robust hybrid structures of PU and PAA, providing both flexibility and rigidity for underwater adhesive bonding. The adhesive resists underwater turbulence and cures rapidly under UV irradiation, achieving lap-shear strength of ∼1.2 MPa within 5 s and ∼2.5 MPa within 20 s on glass substrates. This work offers a promising strategy for fast-curing, high-performance adhesives suitable for rapid repair and sealing on complex surfaces in dynamic underwater environments.