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Abstract
One-pot synthesis of organic-inorganic hybrid materials under light requires specific photoinitiating systems which are able to release several different initiating species after light absorption. In this paper, the reaction mechanism of a photocyclic three-component initiating system based on isopropylthioxanthone as photoinitiator and an iodonium salt and a thiol as co-initiators was studied. It is shown that this system enables simultaneous release of both radicals and protons which are able to initiate a free radical photopolymerization and the hydrolysis-condensation of a sol-gel network, respectively. Time-resolved investigations by laser flash photolysis show that the initiating species are produced within two concomitant cyclic reaction mechanisms depending on the relative quantities of the co-initiators. Protons resulting from the secondary dark reaction of the photocyclic systems are detected at the microsecond scale by means of a proton-sensitive molecular probe, and corresponding quantum yields are measured. Finally, synthesis of organic, inorganic, and hybrid materials under LED light at 395 nm is evaluated with respect to the mechanistic considerations demonstrating the dual initiating character of the system.
Highlights
Polymeric materials can be synthesized under light using various processes such as free radical photopolymerization (FRP)2-8, cationic ring opening photopolymerization2-7,9-12, anionic photopolymerization4-5,7,13, thiol-ene step growth reaction14-15, photoclick polymerization16-17 or hybrid organic-inorganic curing18-22
Several types of photoinitiating systems (PISs) have been developed in order to optimize the conversion of light into chemical energy and to improve the initial quantum yield in reactive species
It has been reported to act as both efficient photosensitizer for iodonium salts to trigger the cationic polymerization or sol-gel process, and effective type II photoinitiator for free radical polymerization, owing to its attracting photochemical and redox properties
Summary
Among the materials formed under light, organic/inorganic hybrid materials present interesting properties due to the elegant combination of the properties of organic polymers and inorganic materials through the in-situ formation of interpenetrated network or generation of chemical bonds between organic and inorganic components.. Among the materials formed under light, organic/inorganic hybrid materials present interesting properties due to the elegant combination of the properties of organic polymers and inorganic materials through the in-situ formation of interpenetrated network or generation of chemical bonds between organic and inorganic components.18-22 They are conventionally synthesized through a two-step process: a first sol-gel thermal reaction produces a liquid organic based polysilicate network which is further photopolymerized, leading to a solid cross-linked hybrid system. As a matter the photoinitiating system responsible for simultaneous generation of radical and proton initiating species becomes definitely essential in the design and synthesis of poly(meth)acrylates-based hybrid materials
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