Tetramethoxysilane polycondensation

Further examination has shown that the acid content should be small in order for the solution to become spinnable in the course of hydrolysis and polycondensation. It has been found (4 ) that very large concentrations at more than 0.15 in the [HCl]/[Metal alkoxide] ratio of acid catalyst produce round-shaped particles in the tetra-ethoxysilane (7) and tetramethoxysilane solutions, and so no spinnability appears. 

Tang et al. used columns packed with a slurry of beads suspended in supercritical C02. This packed column was filled with a dilute sol solution prepared by hydrolysis and polycondensation of tetramethoxysilane and ethyltri-methoxysilane precursors. The column was dried using supercritical C02 and heated first to 120 °C for 5 h followed by another 5 h at a temperature of 250 °C [108-110]. Column efficiencies of 127,000 and 410,000 plates/m were reported... 

An aqueous solution of salt monomer 9PME was mixed with tetramethoxysi-lane, yielding a gel, which was then vacuum-dried forming a precursor powder composed of silica gel and the salt monomer. This was subjected to high-pressure polycondensation under 235 MPa at 230 °C for 5 h, producing polyimide-silica hybrid molding. By varying the ratio of tetramethoxysilane to the salt... 

The continuous demand for new materials have moved to the investigation of polyimides containing metal atoms. Although many polyimide formulations have been reported containing inorganic fillers, of instance silica, it seems that not more than 10% of silica can be incorporated to the composite material at molecular level. Therefore, methods have been outlined to get hybrid polyimides by the sol-gel process. It implies the combination of polyimide with classical precursors of silica employed in the sol-gel methods, particularly tetraethoxysilane and tetramethoxysilane, which lead to silicon oxide through hydrolysis and polycondensation. 

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