Silyl Glyoxylates as a New Class of High Performance Photoinitiators: Blue LED Induced Polymerization of Methacrylates in Thin and Thick Films

Abstract

Silyl glyoxylates are proposed here as a new class of high performance type I photoinitiators for free radical polymerization under air or in laminate (e.g., (meth)­acrylates) upon exposure to different near-UV (at 395 nm; at 405 nm) and blue (at 477 nm) LEDs. The new proposed photoinitiators can also be used in the presence of additives that can enhance their initiating ability: an iodonium salt and an amine or a phosphine. The silyl glyoxylate-based photoinitiating systems exhibit excellent polymerization performances upon blue LED light (at 477 nm) with exceptional bleaching properties compared to camphorquinone (CQ)-based systems. This can be highly worthwhile for the preparation of colorless polymers upon visible light. Real-time Fourier transform infrared spectroscopy (RT-FTIR) experiments are used to monitor the polymerization profiles. The involved chemical mechanisms are investigated by fluorescence, laser flash photolysis, electron spin resonance (ESR), and steady state photolysis experiments. Molecular orbital calculations are also carried out. The overall excited state processes and the chemical mechanisms involved in the initiation step are detailed.

2‐Oxo‐2(tert‐butyldimethylsilyl)Acetic Acid (DKSi‐COOH) as a New Water‐Soluble Visible Light Type I Photoinitiator for Free Radical Polymerization

“…The frontier orbitals (HOMO and LUMO) of DKSi and DKSi‐COOH were calculated by molecular orbital calculations (density functional theory [DFT] level) (Figure ). Similarly to DKSi, the presence of the Si atom in DKSi‐COOH and the participation of the Si d‐orbitals in the frontier orbitals lead to the decrease of the HOMO–LUMO energy gap and thus to a bathochromic shifted transition compared to alkyl phenylglyoxylates. Compared to DKSi, a similar cleavage process can be proposed for DKSi‐COOH in agreement with similar bond dissociation energies (BDEs) of the CC central bond (BDE(DKSi‐COOH) = 72.6 kcal mol −1 vs BDE(DKSi) = 71.6 kcal mol −1 by molecular orbital calculations at DFT level).…”

“…To determine the dissociation quantum yield of DKSi‐COOH, solutions of DKSi‐COOH and DKSi in acetonitrile were prepared with the same absorbance at 477 nm. Indeed, the dissociation quantum yield of DKSi was already reported in our previous study . The photolysis quantum yield is measured by following the bleaching of the UV–vis absorption of DKSi‐COOH and DKSi as a function of the irradiation time (Figure ).…”

“…Using the photolysis quantum yield of DKSi already reported in the literature by our group (ϕ DKSi = 0.43), ϕ DKSi‐COOH can be determined: ϕ DKSi‐COOH = 0.58. A high quantum yield is obtained for DKSi‐COOH and especially high for a visible light Type I PI.…”

“…Previously, we described alkyl(trialkylsilyl)glyoxylates (e.g., tert ‐butyl( tert ‐butyldimethylsilyl)glyoxylate [DKSi]; Scheme ) as new high‐performance photoinitiators (PIs) for the free radical polymerization of methacrylates under blue light irradiation . Nevertheless, for dental applications and especially for dental adhesives, it is crucial to develop new blue light PIs presenting good water solubility and excellent stability in acidic conditions.…”

Silyl glyoxylates as high‐performance photoinitiators for cationic and hybrid polymerizations: Towards better polymer mechanical properties

“…In this context, silyl glyoxylates were recently proposed as interesting structures of photoinitiators upon blue light. Indeed, in our previous work, we reported silyl glyoxylates as new photoinitiators for free radical polymerization of methacrylates upon blue light . In the present work, we will show that the system based on silyl glyoxylate in the presence of an iodonium salt can also initiate cationic polymerization under blue light irradiation.…”