Different Solvent Free Synthetic Routes to Organic/Inorganic Hybrid Materials

The sol-gel chemistry in low-temperature conditions can be used to produce organicinorganic materials nanocomposite from the in-situ formation of silica-rich phase in a polymer matrix. Different synthetic routes have been proposed: i) hydrolysis and condensation reactions of silane end capped oligomers, ii) polymerization of hydroxyethyl methacrylate, HEMA in presence of preformed functionalized silica nanoparticles, and iii) simultaneous hydrolysis and condensation of tetraethoxysilane and polymerization of hydroxyethymeth-acrylate. Rheological investigations made during the polymerization of these three systems display many differences. Time for gelation was chosen as the time at which the loss factor, tanδ is independent on the testing frequency, or the time at which the system displays an elastic response. Vitrification phenomenon is associated with a tanδ peak. In some cases vitrification of the inorganic-rich phase interfered with the observation of gelation and the appearance of a non soluble fraction in a good solvent like tetrahydrofurane can help for attribution. During radical chain-polymerization of HEMA a classical Trommsdorff-effect was observed. It can be at the same time than the macrogelation in the case of neat HEMA or delayed by the presence of grafted SiO2 nanoparticles. During simultaneous synthesis of inorganic and organic phases, vitrification of the inorganic-rich phase occured just after macrogelation of the system. Final morphologies are strongly dependent on the occurrence of these different structural transformations.