EFFECT OF SURFACE-WATER AND BASE CATALYSIS ON THE SILANIZATION OF SILICA BY (AMINOPROPYL)ALKOXYSILANES STUDIED BY X-RAY PHOTOELECTRON-SPECTROSCOPY AND C-13 CROSS-POLARIZATION MAGIC-ANGLE-SPINNING NUCLEAR-MAGNETIC-RESONANCE

Two varieties of silica, viz., Davisil and Cab-O-Sil M-5, were silanized with 3-(triethoxysilyl)-l-propanamine (APTES) and 3-(dimethylethoxysilyl)-1-propanamine (APDMES) in toluene with or without base catalysis by triethylamine. The two silicas were either used as such in their hydrated form or thermally dehydrated at 200 or 400-degrees-C prior to silanization. Making use of the carbon compositions derived from X-ray photoelectron spectroscopy, the surface coverages of the two silanes were estimated by the application of Kovats' formula. While APTES was found to form multilayers on either silica, APDMES formed monolayer or submonolayer coverages on the hydrated and dehydrated silicas, respectively. High-resolution XPS studies in the N(1s) binding energy region indicated that the presence of the base reduced the interaction of the amino moieties of the (aminopropyl)silylated silicas with the silica surface silanols, while surface water promoted such interactions. The X-ray photoelectron spectroscopy (XPS) studies were corroborated with cross-polarization/magic angle spinning C-13 nuclear magnetic resonance studies on the silanized silicas. XPS studies on the nonsilanized silica samples revealed carbon contamination even when the silicas were heated to 400-degrees-C. The amount of surface water in these hydrated/dehydrated silica samples could be computed through the O(1s) binding energy peak intensities recorded in the XPS.