Organisation and reactivity of silicon-based hybrid materials with various cross-linking levels

Nanostructured silicon-based hybrid materials were prepared by sol-gel hydrolysis/polycondensation of (MeO)(3-n)SiMen-Cequivalent toC(6)H(4)-Cequivalent toC-SiMen(OMe)(3-n)(n=0, 1, 2) precursors. Their organisation was evaluated by birefringence measurements (microscopy under polarised light) and evidences the possibility of self-association of the macromolecular units in the sol step and reorientation processes in the ageing step. In contrast to the texture (porosimetry with N-2), the cross-linking level of the Si-O-Si network of the solids (Si-29 CPMAS spectroscopy) appears to be determinant for the anitropic organisation. For n=2 the corresponding polymer-(O-SiMe2-Cequivalent toC(6)H(4)-Cequivalent toC-SiMe2) is crystallised and demonstrates the strong ability of the organic units to self-associate. This is also suggested by partial polymerisation of the acetylenic moieties of the organic units in the solid state up to 350degreesC (DSC, IRTF).