Synthesis of solvent-free acrylic pressure-sensitive adhesives via visible-light-driven photocatalytic radical polymerization without additives

Research on solvent-free acrylic pressure-sensitive adhesives (PSAs) has tremendously grown over the last few decades due to the stringent regulations to control volatile organic compound emissions. They are mostly prepared in the presence of photoinitiators using high-energy UV light that causes several issues such as those associated with radiation safety. Herein, for the first time, solvent-free acrylic PSAs were prepared through visible-light-driven photocatalytic free radical polymerization. Importantly, we found that the use of N-vinyl-based monomers noticeably enhances the rate and conversion of polymerizations, thereby eliminating the need for additives (e.g. alpha-haloester and sacrificial electron donor) that are usually required for photoredox-mediated free radical polymerization, but concurrently needs an additional purification process to remove residues. Combined experiments and quantum chemical calculations suggest that N-vinyl-based monomers facilitate electron transfer between monomers and photocatalysts, which is responsible for the enhanced rate and converison of polymerization. Viscoelasticity, mechanical strength and adhesion performance of acrylic PSAs were well adjusted in a broad range by controlling the monomer composition, suggesting that our new method would replace the existing photoinitiated free radical polymerization.