An Amphibious Adhesive with Excellent Underwater Adhesion Enabled by Hydrophobic Microphase-Separation Reinforcement

Developing amphibious adhesives that bond strongly under dry, wet, and hydrothermal conditions remains challenging. Inspired by mussels and barnacles, we designed a bionic adhesive by introducing a catechol-grafted chain extender and an amino-terminated fluorinated polyimide chain extender to polyurethane. Catechol groups strengthen interfacial anchoring, while fluorinated polyimide segments induce hydrophobic microphase separation, displace interfacial water, and improve thermal stability. Tuning the fluorinated polyimide molecular weight optimized the phase structure and adhesion. The optimal PU1.4 showed a tensile strength of 62 MPa and a toughness of 320 MJ·m-3. It achieved 8.2 MPa lap-shear strength on Fe and retained >85% adhesion at 100 °C. PU1.4 also delivered 7.3 MPa wet adhesion and 3.8 MPa underwater adhesion on Fe, while maintaining >90% strength after 10 rebonding cycles and >92% after 5 recycling cycles. This study offers a molecular design strategy for multifunctional amphibious adhesives in underwater repair, waterproof sealing, and harsh hydrothermal bonding.