Synergistic Optimization of Cohesive Energy and Adhesive Force by Regulating End‐Capping Catechol and Chain Extender 4‐Aminophenyl Disulfide Toward Enhancing Bonding Strength of Hot‐Melt Polyurethane

ABSTRACT Vehicles and electronics rely on detachable and reusable hot‐melt adhesives, but they are hard to reach structural bonding strength to date. In this work, a strategy reconciling cohesive energy and adhesion force was developed to overcome the trade‐off relation between the bulk strength and bonding strength. Specifically, the prepolymer of polytetrahydrofuran ether glycol (PTMEG) capped by isophorone diisocyanate (IPDI) was deliberately extended by different content of 4‐aminophenyl disulfide (AD) and capped by 3,4‐dihydroxybenzaldehyde (DBD), aiming at manipulating the chain length and thereafter the aggregation state. It was found that the adhesive PU‐PAD1.4 has reached an ideal balance between cohesion and adhesion. This adhesive not only boasts high bonding strength and possesses re‐adhesion capabilities but also demonstrates exceptional adhesive performance on a variety of metal substrates, especially on aluminum, where its bonding strength reaches up to 12.13 MPa. Moreover, the self‐healing feature of PU‐PAD1.4 is particularly remarkable, as it can recover 98.28% of its original mechanical properties after being heated at 80°C for just 30 min, which is mainly due to the rapid reorganization of hydrogen and disulfide bonds. With its outstanding toughness and high strength, the PU‐PADx adhesive offers innovative solutions for environmentally friendly and high‐precision processing industries.