High-Strength, Durable, and Complex Environment-Applicable Thiourea-Based Polyurethane Underwater Adhesive Fabricated via a Reactive Deep Eutectic Solvent Strategy

High-performance underwater adhesives are essential for marine engineering. But their application is hindered by hydration layer interference, poor durability, and organic solvent pollution. In this work, the reactive deep eutectic solvent (DES) was formed via intermolecular hydrogen bonding reactions between thiourea and trioctylmethylammonium chloride (TOMAC), providing a mild and green strategy to introduce thiourea into the polyurethane (Thiourea-PU) adhesive. Thiourea functions as a “polar hydrophobic” hydrogen-bonding motif, which is beneficial to underwater adhesion. On the other hand, by utilizing the reaction between isocyanate groups and water molecules, Thiourea-PU adhesive disrupted the hydration layer and enhanced cohesive strength. It exhibited strong underwater adhesion on various substrates, reaching a maximum strength of 7.88 MPa on steel. And its strength can retain 90% of the maximum value after 6 months of water immersion. Meanwhile, Thiourea-PU adhesive exhibited outstanding stability in harsh environments (e.g., simulated seawater, acidic, and alkaline conditions). The incorporation of TOMAC endowed the adhesive with extremely high antibacterial efficacy (≥99.9999%). This work provides a reactive DES strategy for the fabrication of high-performance Thiourea-PU underwater adhesive with excellent durability, strong adhesion, complex environment resistance, and antibacterial property, holding broad application potential.