UV curing and sol-gel based chemistry: towards nanocomposite coatings in a one step process

The synthesis of organic-inorganic sol-gel coatings was performed using alkoxysilanes bearing either an epoxy or a methacrylate reactive function. These hybrid materials combine numerous advantages such as good adhesion to substrates, abrasion and chemical resistance. Usually, they are synthesized through the successive conventional sol-gel process and organic polymerization. This paper first presents an original organic-inorganic one-step synthesis of ambifunctional alkoxysilane precursors bearing an epoxy or methacrylate function. The UVgenerated Brönsted acids from a cationic photoinitiator (PI) were found to be effective in catalyzing alkoxysilane sol-gel polycondensation reactions and initiating the ring-opening reaction of the epoxy functions of TRIMO. Combination of both a radical and a cationic photoinitiator enabled the dual cure of a methacrylate organoalkoxysilane precursor (MAPTMS). These bifunctional hybrid precursors were then mixed with organic resins and the corresponding coatings were characterized. Competition between the formation of inorganic and organic networks was studied using Fourier transform infrared spectroscopy (FTIR). 29Si solid state NMR measurements and thermo-mechanical analyses were also performed with a view to correlate structure and properties of the UV–cured hybrid coatings.