Nuclear magnetic resonance techniques for the structural characterization of siloxane-oxide hybrid materials

The objective of this paper is to discuss the appropriateness of various solution and solid state NMR techniques to describe structural aspects of siloxane-oxide hybrid systems prepared by sol-gel processes. Co-hydrolysis of organosilanes and metallic alkoxides can promote either self-condensation or co-condensation reactions between the different precursors, and this will control the structural homogeneity of the final network. Solution state Si-29 and O-17 NMR can give unique information on the formation and stability of co-condensing species. In the final gels, solid state Si-29 MAS used in conjunction with cross-polarization (CP) and related two-dimensional Si-29-H-1 heteronuclear NMR correlation techniques, provides detailed information on dipole-dipole coupled Si-29 and H-1 species among different molecular moieties. Finally, the use of O-17 MAS NMR with the newly developed MQ MAS sequence that provides a direct identification of the various oxo bridges will be discussed. (C) 2000 Elsevier Science Ltd All rights reserved.