Development of a Light-Deactivatable PSA Via Photodimerization

ABSTRACT

Photoreactive pressure-sensitive adhesives (PSAs) were developed to create photodeactivatable resins. Coumarin-functionalized poly(2-ethylhexyl acrylate-co-hydroxyethyl 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.

Keywords:

• Coumarin
• Photodimerization
• PSA
• UV crosslinking

Notes

The authors acknowledge financial support from the Virginia Tech Center for Adhesive and Sealant Science (CASS) and the Adhesive and Sealant Council Education Foundation. They also acknowledge support by the U.S. Army Research Laboratory and the U.S. Army Research Office under Grant Number DAAD19-02-1-0275 Macromolecular Architecture for Performance (MAP) MURI.