Impact‐Resistant Underwater Adhesive Based on the Shear‐Stiffening Effect via Hydrophobic Protective B─O Bonds

ABSTRACT Adhesive failure under the combined conditions of water and impact not only leads to the separation of bonded objects but can also trigger severe economic losses, structural collapse, and even life‐threatening danger. Herein, we have developed an excellent impact‐resistant adhesive suitable for underwater applications by hydrophobic protective B─O bonds. This design enables rapid energy dissipation upon impact while the hydrophobic components protect the dynamic B─O bonds from hydrolysis, ensuring reliable underwater adhesion. The resulting adhesive achieves an adhesive strength of 1.01 MPa under dry conditions and retains over 90% of its strength under water, significantly outperforming the 3 m commercial adhesive (0.49 MPa). It also exhibits an impact force attenuation efficiency of up to 83.3%; when configured into a sandwich structure, the efficiency maintains high levels of 85.9% and 87.7% under dry and water‐immersed conditions, respectively, with excellent structural integrity. This work provides a straightforward and effective strategy for developing high‐performance underwater impact‐resistant adhesives.