STRUCTURAL INFLUENCE OF THE CARBON-CHAIN LENGTH IN HYBRID MATERIALS OBTAINED FROM ZIRCONIUM N-PROPOXIDE AND DIOLS

Zirconium n-propoxide Zr(OPrn)(4) has been chemically modified by 1,3-propanediol and 1,3-butanediol with molar ratio r = 0.5, 1 and 2. The properties of the hybrid organic-inorganic materials obtained after drying at 100 degrees C for 24 hours have been measured by thermal analysis, X-ray diffraction, infra-red spectroscopy and C-13 NMR with cross-polarisation at magic angle spinning. Chemical modification of the zirconium precursor at a molecular level has been clearly detected, with a bridging coordination mode for both diols. If the coordination mode of the diols cannot be changed by increasing the carbon chain length, it was found using C-13 CP MAS NMR that the local order is much more well-defined when the reactivity of both OH groups are not the same. Thus, using 1,3-butanediol which has a primary and a secondary OH group, it is possible to obtain after complete modification (r = 2) a highly homogeneous hybrid polymer which transforms directly into tetragonal zirconia below 400 degrees C. With other diols (1,2-ethanediol and 1,3-propanediol), the hybrid materials transform into tetragonal zirconia above 400 degrees C through a decomposition process involving several steps. Then playing with the carbon chain length and/or the steric hindrance around the OH groups provides an easy way to monitor the ultrastructure of these hybrid materials, and allows a better control of the gel --> oxide transformation.