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 tetraethoxysilane and a 1/1 mixture of dimethyldiethoxysilane and tetraethoxysilane (H2O/OEt = 0.5; pH = 2). The spectra recorded over several hours time period were simulated to follow quanti tatively the variations of residual 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 tetrafunctional Si units clearly demonstrates that co-condensation reactions occur to a large extent between the two alkoxides, and that these bonds are stable during the aging period.