Exploring the advantages of oxygen-tolerant thiol-ene polymerization over conventional acrylate free radical photopolymerization processes for pressure-sensitive adhesives

UV light-induced polymerization is one of the most efficient methods to produce pressure-sensitive adhesives (PSAs) in lamination processes, as it is simple and easily scalable. Among the wide variety of monomers used in light-induced polymerizations, acrylates and/or methacrylates are typically used as the main components due to their versatility and their high reactivity. However, as radical polymerization is not tolerant to the presence of oxygen, O2 inhibitors must be added, which increases the final cost of the laminate adhesive. In this work, we exploit the oxygen insensitivity of thiol-click reactions and evaluate their potential for use in fast and inexpensive UV curable resins for lamination processes. After some preliminary investigations that demonstrate the need for a radical inhibitor to extend the shelf life of the noncured resin, we confirm the insensitivity of this reaction to the presence of oxygen. After evaluating the effect of several parameters, including the effect of thiol functionality, vinyl ester structure, and the addition of an acrylate, we demonstrate the design of a formulation with competitive adhesive performance compared to conventional photopolymerized acrylic PSAs. Materials with relatively high gel content (66%), intermediate crosslinking (swelling degree 391%), and low Tg were obtained using a bifunctional thiol, an aliphatic vinyl monomer, and a polyurethane-based diacrylate. This formulation has good potential for the replacement of acrylate-based adhesives because it is capable of polymerization in short times and in the presence of oxygen and possesses fast adhesion to the substrate and a very good adhesive/cohesive ratio. UV light-induced polymerization is one of the most efficient methods to produce pressure-sensitive adhesives in lamination processes, as it is simple and easily scalable. Acrylates and/or methacrylates are typically used as the main components, however, O2 inhibitors are needed, which increases the final cost. In this work, we exploit the oxygen insensitivity of thiol-click reactions, evaluate their potential for use in fast and inexpensive UV curable resins, and demonstrate the design of a formulation with competitive adhesive performance compared to conventional acrylic PSAs.