O-17 NMR INVESTIGATION OF CHEMICAL HOMOGENEITY IN HYBRID SYSTEMS

O-17 NMR experiments using enriched water were performed to follow the hydrolysis-condensation process of dimethyldiethoxysilane tetraethoxy silane and a 1/1 mixture of dimethyldiethoxysilane and tetraethoxysila ne (H2O/OEt = 0.5; pH = 2). The spectra recorded over several hours ti me period were simulated to follow quanti tatively the variations of r esidual water, hydroxyl groups (Si-(OH)-O-17) and oxo bridges (Si-O-17 -Si). Presence of a resonance signal due oxo bridges between di- and t etrafunctional Si units clearly demonstrates that co-condensation reac tions occur to a large extent between the two alkoxides, and that thes e bonds are stable during the aging period.