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

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.