A reusable visible light initiation system for radical polymerizations in water

Abstract

Photo-initiated free radical polymerization is extensively used in 3D printing and integrated circuit fabrication. Recent advancements have prioritized the development of initiation systems capable of operating under visible light; however, the lack of recyclability in conventional catalysts and initiators remains a significant barrier to sustainability. In this work, we report a visible-light-active radical initiation system based on 4-nitrophenylacetylene (4-NA) with diphenyliodonium chloride (Ph2ICl) as the co-catalyst. Under 420 nm irradiation, this system successfully mediated both free radical and reversible additionfragmentation chain transfer (RAFT) polymerization of N,N-dimethylacrylamide (DMA) in aqueous media at ambient temperature. Spectroscopic analysis revealed the mechanistic pathway: light-induced electron transfer between a DMA monomer and excited 4-NA generates an α-aminoalkyl radical and a 4-NA radical anion. Subsequent electron transfer between the 4-NA radical anion and the co-catalyst regenerates the 4-NA, completing the catalytic cycle. Notably, the water-insolubility of 4-NA facilitates straightforward purification; the catalyst can be recovered via centrifugation and reused.