Innovative route for the synthesis of hybrid nanocomposites by a single step organic and inorganic photopolymerization

The present paper focuses on the potentialities offered by derived hybrid sol-gel photomaterials to assess innovative UV-cured nanocomposites coatings. Organoalkoxysilane precursors with the general formula R'Si(OR)3 proved to be remarkably well-suited as molecular starting blocks in the synthesis of hybrid coatings. OR groups can be condensed to yield an inorganic network via sol-gel process while R' represents a polymerizable group, thus allowing the building of an organic photopolymer conjointly to the polysiloxane structure. There are today a number of industrial applications involving these hybrid precursors: abrasion resistant coatings for plastics, glass coatings exhibiting excellent adhesion, barrier effect coatings…[1]. Beside the well-referenced methods of elaboration of these materials by a thermal process, Radiation Curing has become an attractive route as it holds many assets in terms of environmental concerns. Generally, the methodology deals with the use of acrylate or epoxy alkoxysilanes: sol-gel reaction of this hybrid precursor leads in a first step to a liquid epoxy-based polysiloxane network that can be photopolymerized subsequently [2,3,4,5]. The present paper focuses on cationic photopolymerization as a synthetic reaction towards hybrid materials. In addition to the lack of knowledge in this field, an important driver is related to the classical advantages of this polymerization process: insensitivity to oxygen inhibition, dimensional stability, good adhesion to a range of substrates and post-reaction after irradiation. A novel one-step methodology for preparing hybrid coatings through the photopolymerization of a bifunctional hybrid precursor bearing both an organic epoxy function and alkoxysilane moieties or by combining this latter with a diepoxy resin is presented [6]. Through the in situ liberation of protic acids via photoinitiator photolysis, epoxy polymerization takes place concomitantly with hydrolysis and condensation of the reactive silanes. This straightforward method gives access to a stable, solvent-free and singlecomponent hybrid coating composition, which can be applied at room temperature and cured upon UV exposure.