Dual role of novel highly efficient radical generators for UV/LED-activated polymerization processes

Abstract

This study reports novel diphenyliodonium tosylates (IODs) as highly effective photoinitiators for the radical polymerization of (meth)acrylates. The proposed compounds showed high photoinitiation efficiency in the polymerization process as one-component, as well as in two-component and three-component systems. The synthesized and developed derivatives were characterized by the presence of a nitro group attached to one of the phenyl rings, while the second aromatic ring was substituted by one of the halogen atoms (i.e. Br, Cl, F, and I). The introduction of two different electron withdrawing substituents into the chemical structure of iodonium salts is a new and unique approach in the design of novel asymmetrical IOD derivatives. The use of the proposed IODs as UV photoinitiators resulted in about 30% conversion of acrylate. The introduction of camphorquinone (CQ) to polymerizable compositions caused a shift in the absorption band of the photoinitiators and expanded the photoactivity of IODs to visible light. The proposed diphenyliodonium salts in combination with a light absorber (CQ) were highly active photoinitiators for radical polymerization upon LED illumination (conversion of about 30%–70%). The newly synthesized compounds can be promising alternatives to typical commercially available iodonium salt initiators (or co-initiators), which are commonly used in photopolymerization reactions.