Influence of kinetic parameters on the textural and chemical properties of silsesquioxane materials obtained by sol-gel process

The hydrolytic sol-gel polymerization of a 'rigid' molecular precursor 1,4-C6H4 [Si(OMe)(3)](2) 1 and a more 'flexible' one 1,4-C6H4[CH2CH2Si(OMe)(3)](2) 2 was investigated varying the experimental conditions. Two solvents, MeOH and THF, were employed. The influence of the catalyst has been determined by using TBAF (tetrabutylammonium fluoride) or NH4F as nucleophilic catalysts, NH4OH and NaOH as basic catalysts and HCl as acid catalyst. The effect of concentration;of the precursor was also studied. Molecular precursor I led always to hydrophilic solids with similar degrees of condensation (63-67%). In all cases high specific surface areas and poor chemical reactivity towards Cr(CO)(6) were observed and the solvent had an influence on the porosity. By contrast, the precursor 2 led to hydrophobic solids and the texture, the de,gree of condensation and the reactivity with Cr(CO), were strongly dependent on the solvent, the catalyst and the concentration. In MeOH no significant specific surface areas were observed, whereas in THF a high specific surface area was observed with TBAF catalysis at both precursor concentrations studied. Degrees of condensation were higher in THF. All the kinetic parameters involved in the hydrolytic sol-gel polymerization of molecular organosilicon precursors were of importance on the properties of the resulting solids, the main factor being the geometry of the organic unit.