NMR CHARACTERIZATION OF HYBRID SILOXANE-OXIDE MATERIALS

Numerous hybrid siloxane-oxide systems have been prepared by sol-gel t echniques, using either monomeric species, such as substituted silicon alkoxides R'(4-x),Si(OR)(x), or OH-terminated poly(dimethylsiloxanes) (PDMS) cross-linked by metal alkoxides, M(OR)n with M=Si, Ti, or Zr. The properties of the materials are strongly related to the way the va rious components of the systems are distributed within the network. Mu ltinuclear Magnetic Resonance is a powerful technique to investigate t he whole elaboration process, from the solution to the final material. The evolution of the inorganic (Si-29, O-17 NMR) and organic (C-13, H -1 NMR) components can be characterized. NMR results on materials prep ared from hydrolysis of dimethyldiethoxysilane (CH3)(2)Si(OEt)(2) and a metal alkoxide, M(OR), with M = Si, Ti, or Zr, will be presented. Co condensation reactions between precursors can be evidenced in solution by Si-29 and O-17 solution NMR, while Si-29 and H-1 Magic Angle Spinn ing (MAS) NMR studies performed on the final materials give informatio n on the connectivity of the network and the mobility of the various s ites. Structural models have been proposed depending on the nature of the metal alkoxide.