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Photoinduced Redox Initiation System for Delayed-Onset Radical UV-Curable Adhesives on Opaque Substrates
Naoya Machida1, Ataru Daimon1, Daisuke Aoki1
1Department of Pure and Applied Chemistry, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba278-8510, Japan.
Abstract:
Conventional radical ultraviolet (UV) curing requires optically transparent substrates owing to the rapid termination of propagating radicals, limiting its use in opaque or geometrically complex assembly cases. We report a photoinduced redox initiation system for delayed-onset radical UV-curable adhesives combining a coumarin-based photobase generator (Cou-TMG) with dilauroyl peroxide (LP). Upon UV irradiation, Cou-TMG releases 1,1,3,3-tetramethylguanidine, which reacts with LP through a redox process that continuously generates radicals, sustaining polymerization after irradiation stops. Optimized photobase generator loading and irradiation dose provide an open time sufficient for substrate lamination (low C═C conversion immediately after UV irradiation) and endow substantial postpolymerization capability (higher C═C conversion after 1 h), contrasting conventional radical UV curing systems. The delayed-onset, radical UV-curable adhesives are applicable to various multifunctional acrylates. Specifically, trimethylolpropane triacrylate-based adhesives achieve a high lap-shear strength of 4.4 MPa on aluminum, and the present system further bonds Cu, Fe, polycarbonate, and glass substrates.
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