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

Abstract

Nanostructured silicon-based hybrid materials were prepared by sol-gel hydrolysis/polycondensation of (MeO)_3−nSiMe_n–CC–C₆H₄–CC–SiMe_n(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 N₂), the cross-linking level of the Si–O–Si network of the solids (²⁹Si CPMAS spectroscopy) appears to be determinant for the anitropic organisation. For n = 2 the corresponding polymer –(–O–SiMe₂–CC–C₆H₄–CC–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 350 °C (DSC, IRTF).