UV-Responsive Adhesive Based on Polystyrene-block-Poly(Ethyl Lipoate) Copolymer

Block copolymers (BCPs), capable of self-assembling into various nanoscale structures, are widely used in adhesives owing to their versatile properties. However, conventional BCP-based adhesives pose environmental concerns: they are petroleum-derived, non-degradable, and have a non-tunable adhesion strength. To address these challenges, a novel BCP is designed comprising a conventional hard segment, polystyrene (PS), and a green rubbery segment, poly(ethyl lipoate) (PEtLp), derived from the bio-based molecule α-lipoic acid. The PS-b-PEtLp is synthesized via the base-catalyzed ring-opening polymerization from thiol-terminated PS. Adhesion tests showed that PS-b-PEtLp with cylindrical nanostructures exhibited higher adhesion strength than that with lamellar structures. Importantly, the dynamic disulfide bonds in PEtLp enable a reversible and adjustable adhesion strength under UV light. Upon UV irradiation, the adhesion strength decreases by approximately half, facilitating easy separation from the adherends. Additionally, the selective depolymerization of the PEtLp block achieves 100% conversion, enabling the recovery of the monomer (EtLp) and macroinitiator (thiol-terminated PS). This study introduces a sustainable, degradable, and reusable adhesive derived from renewable resources, providing a promising solution to the environmental challenges associated with traditional petroleum-based adhesives.