Development of a light-deactivatable PSA via photodimerization

Photoreactive pressure-sensitive adhesives (PSAs) were developed to create photodeactivatable resins. Coumarin-functionalized poly(2-ethylhexyl acrylate-cohydroxyethyl acrylate) was prepared via traditional free-radical polymerization followed by quantitative hydroxyl group esterification and studied as model photoactive PSAs. The polymers were solution-cast into films and photocrosslinked via dimerization of the coumarin derivatives with ultraviolet-A (UVA) light irradiation (> 300 nm). Ultraviolet-Visible (UV-Vis) spectroscopy indicated that approximately 60% of the coumarin groups photodimerized when exposed to 22 J cm(-2) of UVA irradiation. The formation of reversible coumarin crosslinks gelled the model PSA and reduced peel strength from 1.62 to 0.05 N/mm. UVC irradiation photocleaved the coumarin dimers, reducing the crosslink density and raising the peel strength to 0.10 N/mm. This reversibility of the coumarin photodimerization and consequent peel-strength modulation may provide a mechanism for the repeated use of these model adhesives.