Sol-gel process-influence of ageing on the textural properties of organosilsesquioxane materials

The hydrolytic sol-gel polymerization of a variety of molecular precursors with a "rigid'' geometry 1,4-C6H4[Si(OMe)(3)](2) 1 and a "flexible'' geomet ry (MeO)(3)Si-(CH2)(10)-Si(OMe)(3) 2 was investigated varying the nature of the catalyst, the temperature and the length of ageing. The reactions were performed using ionic and nonionic catalysts. The ionic ones were a nucleo phile [tetrabutylammonium fluoride (TBAF)] or acid (HCl) and the non-ionic one was dimethylaminopyridine (DMAP). The solvent was THF. In all cases, th e length of ageing had a minor effect on the level of condensation at silic on atoms of the different xerogels. Only a small increase was observed. In contrast, the specific surface area, the porosity and the pore size were hi ghly dependent on the length of ageing. The longer ageing times favoured th e formation of mesoporous solids with high specific surface areas and narro w pore size distribution.