Influence of the nature of the catalyst on the textural properties of organosilsesquioxane materials

The hydrolytic sol-gel polymerization of molecular organosilicon precursors with a 'rigid' geometry 1,4-C6H4[Si(OMe)(3)](2) (1) and a 'flexible' geometry 1,4-C6H4[CH2CH2Si(OMe)(3)](2) (2) was investigated varying the nature of the catalyst. They were hydrolyzed under nucleophilic catalysis using non-ionic species such as dimethylformamide (DMF), dimethylaminopyridine (DMAP), N-methylimidazole (NMI) and hexamethylphosphorotriamide (HMPT) in THF. The effect of the concentrations of both the precursor and the catalyst was studied. Molecular precursor 1 led always to hydrophobic solids with degrees of condensation lying in the range 55-67%. These solids were mainly microporous exhibiting high specific surface areas. The densities lay in the range 1.37-1.42 g cm(-3). By contrast, the precursor 2 led to hydrophobic solids with no significant specific surface area. Degrees of condensation ranged between 59 and 74% and the densities between 1.27 and 1.31 g cm(-3). The nature of the catalyst (ionic or non-ionic) involved in the hydrolytic sol-gel polymerization of molecular organosilicon precursors appeared to be of great influence on the textural properties of the resulting solids. (C) 2000 Elsevier Science Ltd All rights reserved.