Design of Novel Photoinitiators for Radical and Cationic Photopolymerizations under Near UV and Visible LEDs (385, 395, and 405 nm).

Abstract

Three novel photoinitiators, namely (2,2′-bithiophen-5-yl)(4-(N,N′dimethylaminophenyl)ketone, 5,10-dimethoxybenzo[j]fluoranthene and 6,6′-(((1E,1′E)-(2,5-bis(octyloxy)-1,4-phenylene)bis(ethene-2,1-diyl))bis(4,1-phenylene))bis(1,3,5-triazine-2,4-diamine) applicable to different near UV or visible LEDs (385 nm, 395 nm, 405 nm or cold white LED) have been developed. When incorporated into multicomponent photoinitiating systems PISs (in the presence of iodonium salt (and optionally N-vinyl carbazole) or amine/alkyl halide couples), they exhibit quite excellent photoinitiating abilities for the cationic polymerization CP of epoxides or the free radical polymerization FRP of methacrylates under air. Compared to the corresponding camphorquinone-based systems, the newly developed photoinitiating systems display noticeably higher polymerization efficiencies under air (epoxide conversions = 31−55% vs ∼0%, halogen lamp exposure; methacrylate conversion = 56−66% vs 0−8%, LED irradiation). These systems are very interesting to overcome the oxygen inhibition. The photochemical mechanisms have been studied by steady state photolysis, electron spin resonance spin trapping, fluorescence, cyclic voltammetry, and laser flash photolysis techniques.

Iron complexes as photoinitiators for radical and cationic polymerization through photoredox catalysis processes

“…(a,b)]. As reported in previous related studies, reactive initiating species are Ph • and Ph‐NVK • for FRP, cations (Ph‐NVK + ) and possibly the oxidized form of the photocatalyst for CP in irradiated FeCs/Iod or FeCs/Iod/NVK systems according to reactions 1–6 (Scheme ). In FeCs/EDB/R′‐Cl, aminoalkyl (EDB (H) • ), and R′ • radicals are likely formed as indicated in reactions 7–11 (Scheme ) to initiate the FRP (as also described in other systems).…”

2,2,2-trifluoroacetophenone-based D-π-A type photoinitiators for radical and cationic photopolymerizations under near-UV and visible LEDs

“…6(a)]. 8,39,50 When mixing with Iod, the key step is the photoinduced electron transfer (PET) process between the PI/Iod photoredox pair. The PET from the excited dye ( 1 PI) to iodonium (Ph 2 I 1 ) leads to the dye radical cation (PI •1 ) and neutral radical (Ph • ), as shown in the ESR-ST curve in Figure 6(b).…”

“…The FRP should work according to the reactions (r 1 and r 4 ) by comparing with other photoinitiating systems. 41,50,54,55 …”

Visible Light Induced Cationic Polymerization of Epoxides by Using Multiwalled Carbon Nanotubes

“…General strategies to conduct cationic polymerization at the visible range involve the oxidation of free radicals by onium salts (also called free‐radical promoted cationic polymerization), the formation of charge transfer complexes, and electron transfer reaction within the exciplexes of polynuclear aromatic compounds and onium salts. Lalevee et al have shown that various dyes, silanes, and polythiophenes can efficiently induce a reduction in onium salts, even at a visible range.…”