Multifunctional Photobleaching Visible Radical/Cationic Photoinitiators Based on 5-Membered Aromatic Heterocyclic-Bis-Chalcone-Oxime Esters

Three photobleachable photoinitiators (PIs) with bis-chalcone-based oxime esters (PBAs) are designed and synthesized, including the electron donor (D) of a 5-membered aromatic heterocyclic (furan, thiophene, and pyrrole), electron acceptors (A) of cyclopentanone carbonyl, and oxime acrylate for visible photopolymerization. The mechanism for the generation of oxygen alkyl radicals, 5-membered aromatic heterocyclic radicals, and vinyl radicals demonstrates that PBAs are characterized by type I and type II PIs. Real-time Fourier-transform infrared (FT-IR) spectroscopy indicates that PBAs, effective one-component PIs, are able to rapidly initiate the photopolymerization of the double-bonded monomer when exposed to LED@385∼455 nm. In particular, PBA3 with pyrrole as D exhibits the highest double-bond conversion efficiency and photobleaching characteristics, and its acetonitrile solution completely fades within 8 min under LED@455 nm exposure. Moreover, the colorless bulk acrylate materials with thicknesses of up to 40 mm are produced through photopolymerization initiated by PBA3. Furthermore, PBA3/Iod as a two-component PI efficiently initiates hybrid photopolymerization of the double-bonded monomer and epoxy monomer to form an interpenetrating polymer network. Notably, PBA3 exhibits only a 1.9% migration ratio from polymerization films under illumination (60 min). Consequently, the research results provide an innovative avenue for the structural optimization of photobleaching PIs and extend their applicability to the field of deep photocuring.