π–π Interactions for Dramatically Enhanced Cohesion and Underwater Adhesion in Pressure-Sensitive Adhesives

The achievement of underwater bonding and maintaining bond stability are significant challenges due to interfacial water and hydration weakening adhesive bonds. In this study, a dry pressure-sensitive adhesive (PSA) was successfully developed through a one-step synthesis involving the random copolymerization of ethylene glycol phenyl ether acrylate (PEA), 2-ethylhexyl acrylate (2-EHA), and acrylic acid (AA). This PSA displayed good hydrophobicity, moderate Young’s modulus, and tensile strength, forming strong interfacial bonds with various substrates in water. The effect of the aromatic monomer PEA content on the adhesive properties, shear properties, and heat resistance of PSA was systematically investigated. Notably, at 10 mol % PEA content (P-AEP10), the PSA exhibited remarkable mechanical strength and bond strength, with an elastic modulus of 0.5353 MPa and tensile strength of 0.6882 MPa. The underwater peel strengths were 936.7 N/m (SS) and 1569.3 N/m (PET). The results indicate that π–π interactions significantly enhance the cohesive strength of the copolymer, enabling P-AEP10 to maintain excellent adhesive performance in water at 80 °C, with the static shear failure time extended to 880 h at room temperature. Additionally, the results obtained from underwater repair experiments demonstrated that the PSA did not exhibit secondary leakage for a period of 100 days following the repair procedure, thereby further substantiating its suitability for underwater repair and bonding applications. In conclusion, this study offers significant theoretical support and a practical foundation for the development and utilization of dry PSAs.