Nanocomposite coatings via simultaneous organic-inorganic photo-induced polymerization: synthesis, structural investigation and mechanical characterization

Hybrid sol-gel films were prepared via a simultaneous organic-inorganic UV-curing process using a diaryliodonium salt as a superacid photogenerator. In this single-step procedure, an epoxy functionalized reactive resin mixed with a variable amount of either of two epoxy trialkoxysilane precursors was UV-irradiated, causing both the initiation of epoxy ring-opening copolymerization and the catalysis of trialkoxysilyl sol-gel reactions. The concomitant photo-induced sol-gel process was found to have a significant effect on the two related propagation mechanisms in competition for the oxirane ring-opening - the active chain-end and the activated monomer mechanisms - as proved by a systematic examination of the hybrid material microstructure through Si-29 and C-13 solid-state NMR spectroscopy. The effect of the oxo-silica network generation on the epoxy reaction kinetics was also evaluated using real-time Fourier transform infrared spectroscopy upon varying the epoxysilane structure and its concentration. Thermal and dynamic mechanical analyses were systematically performed on these hybrids, by studying thoroughly their structure-property interdependence. Other mechanical characterizations through tribological and scratch tests suggested that the present photopolymer-silica hybrid material provides a powerful tool to tailor mechanical property profiles. (C) 2010 Society of Chemical Industry