Thioctic Acid-Based Solvent-Free and Recoverable Adhesive for Dry/Wet Environments

Metal adhesive synthesis typically involves heating and solvents, and the resultant adhesives lack degradability and suffer from recycling and sustainable problems. Herein, we developed a solvent-free and chemically degradable biobased adhesive (p(Elp-TA)+PVP) from thioctic acid (TA), its derivative (Elp), and polyvinylpyrrolidone (PVP). Through a rapid acid-triggered cationic ring-opening polymerization of dithiolane at ambient conditions, p(Elp-TA)+PVP adhesive could build up a strong lap shear strength of 1123 kPa in air and an underwater lap shear strength of 534 kPa to the copper plate. Molecular dynamics simulations show that compared to p(Elp-TA), the presence of an appropriate amount of PVP can significantly enhance the binding energy of the adhesive molecules to the metal substrate, and the rapid adhesion of p(Elp-TA)+PVP molecules to metal substrates was achieved through a synergistically dynamic adaptive network enhanced by hydrogen bonding, reversible dynamic bonding, and metal coordination bonding at 40 ps. More importantly, the applied p(Elp-TA)+PVP adhesive could be easily degraded and reverted to its small-molecular-weight lipoic acid species. Upon exposure to dithiothreitol, a green reducing agent, the average molecular weight of the adhesive could quickly decrease from 1603 kDa to 274 Da. This green adhesive constructed by a simple method provides a promising general strategy for developing a controlled degradable and recoverable adhesive from natural resources.