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Researchers found that newly synthesized biphenyl iodonium salts exhibit enhanced light absorption and can serve as highly efficient photoinitiators for UV-LED photopolymerizations.
Diaryliodonium salts play an important role as highly efficient photoinitiators in the field of photopolymerizations. They can rapidly photodecompose to produce free radicals and super acids; thus, can initiate highly efficient photocuring of acrylic and epoxy monomers and resins. However, the absorption of commercialized diphenyliodonium salts is poorly matched with popular LED light sources, and the participation of sensitizers is usually required to achieve efficient photoexcitation. Here, researchers synthesized five new phenyl biphenyl iodonium salts with different electron-pushing and electron-withdrawing substituents, e.g., methoxy and CN, at the biphenyl substituent.
The results demonstrate that all synthesized iodonium salts have strong absorption in the range (λmax = 258–352 nm; εmax = 21,300–29,900 M？1 cm？1). The photochemistry of these synthesized iodonium salt is strongly influenced by substituents on the biphenyl ring. All iodonium salts can undergo rapid photolysis under light excitation, with higher quantum yield of photoacid generation reaching 0.25 and can quickly initiate cationic photopolymerization of epoxy monomers. Furthermore, free radicals are generated during photolysis, which can successfully trigger free radical polymerization. These iodonium salts with good absorbance in the UVA band demonstrate their potential as excellent photoinitiators under 365–405 nm LED excitation.
Source: Progress in Organic Coatings Volume 188, March 2024, 108209
Source: european-coatings
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