Nanostructured hybrid materials obtained by UV curing and sol-gel processes involving alkoxysilane groups

Novel hybrid organic-inorganic coatings were obtained by photopolymerization and subsequent thermally induced condensation through sol-gel processes. Both radical (methacrylic) and cationic (epoxy) resins were considered as precursors of the organic phase; tetraethoxysilane (TEOS) was the precursor of the inorganic phase. The effect of the presence of a coupling agent was investigated. Real-time FT-IR analysis was used for evaluating the kinetics of photopolymerization. 29Si-NMR spectroscopy was used in order to evaluate the degree of condensation of alkoxysilane groups. The results showed the prevalence of Q3 e T2 structures indicating an incomplete condensation of the alkoxysilane groups. T1 and Q1 signals are not present, thus indicating that for each Si atom, two or more alkoxysilane groups take part to the condensation reaction. FE-SEM analyses evidenced a nanometric organization of the inorganic domains in the polymer matrix. The addition of the coupling agent was found to influence the morphology of the hybrid systems. DMTA and TGA analyses revealed an increase of the Tg values and of the thermal stability by increasing the coupling agent and TEOS content.