Visible-Light-Curable Solvent-Free Acrylic Pressure-Sensitive Adhesives via Photoredox-Mediated Radical Polymerization

Owing to their excellent properties, such as transparency, resistance to oxidation, and high adhesivity, acrylic pressure-sensitive adhesives (PSAs) are widely used. Recently, solvent-free acrylic PSAs, which are typically prepared via photopolymerization, have attracted increasing attention because of the current strict environmental regulations. UV light is commonly used as an excitation source for photopolymerization, whereas visible light, which is safer for humans, is rarely utilized. In this study, we prepared solvent-free acrylic PSAs via visible light-driven photoredox-mediated radical polymerization. Three α-haloesters were used as additives to overcome critical shortcomings, such as the previously reported low film curing rate and poor transparency observed during additive-free photocatalytic polymerization. The film curing rate was greatly increased in the presence of α-haloesters, which lowered the photocatalyst loadings and, hence, improved the film transparency. These results confirmed that our method could be widely used to prepare general-purpose solvent-free PSAs—in particular, optically clear adhesives for electronics.