Synthesis, structure and properties of cross-linked R(SiO1.5)/SiO2 (R = 3-glycidoxypropyl) porous organic inorganic hybrid networks dried at ambient pressure.

Highly porous organic inorganic hybrid networks have been prepared from tetraethoxysilane (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) precursors by drying at ambient pressure. Hydrolysis-condensation reactions of the alkoxy groups on the precursors provide the inorganic network and polymerization of the epoxy group on GPTMS, the organic network. The effects of varying the molar ratios, water/OR, and TEOS/GPTMS (precursor ratio) on the gel structure were investigated. Infrared spectroscopy, thermal analysis, nitrogen adsorption measurements, and tunneling electron microscopy were used to characterize the structure and porosity features of the hybrids. At low precursor ratios, the organic networking is characterized by highly cross-linked polymer chains of low molecular weight and at high precursor ratios it consists of mainly linear chains of high molecular weight. Organic networking reinforces the inorganic network at high precursor ratios and the monoliths effectively withstand the stress produced during drying at ambient pressure. But as the proportion of the organic precursor increases, there is a higher shrinkage of the gel network, increasing the density of the dried gel. Variation in precursor ratio affects the volume of larger pores, while varying water content influences the volume of smaller pores. Monolithic gels with low shrinkage and density could be prepared through ambient pressure drying by this method.