HYBRID POLYDIMETHYLSILOXANE-ZIRCONIUM OXO NANOCOMPOSITES. PT.1. CHARACTERISATION OF THE MATRIX AND THE SILOXANE-ZIRCONIUM OXO INTERFACE

Hybrid materials made from polydimethylsiloxane and zirconium oxo species were synthesised. They exhibit a high degree of homogeneity and dispersion for Zr/Si molar ratios ranging between 0.2 and 0.9, and show good mechanical integrity and transparency. They were characterised by 29Si, 17O and 13C MAS-NMR as well as by FTIR, SAXS and dynamic mechanical analysis. These polydimethylsiloxane/zirconium oxopolymers are hybrids consisting of amorphous zirconium oxo domains of about one to two nm in diameter. The mean correlation distance between the zirconium-oxo domains decreases from about 6 to 2 nm when the Zr/Si ratio increases. The siloxane species (chains and loops) have an average chain length that decreases from about 15-20 Si atoms to 3 Si atoms with increasing Zr content. The interface between siloxane and zirconium oxo domains is composed primarily of Zr-O-Si(CH3)2 bonds and hydrogen bonds, their relative proportion being a function of the Zr content. Curing at 140 C consolidates the hybrid network without affecting the overall characteristics of the organic-inorganic interface. Curing at 200 C induces the loss of small silicic species and increases cross-linking points in the siloxane regions. For samples with a high Zr content (Zr/Si = 0.9), curing at 200 C also increases the number of Zr-O-Si interface bonds. 56 refs.