Hybrid polydimethylsiloxane-zirconium oxo nanocomposites. Part 1 Characterization of the matrix and the siloxane-zirconium oxo interface

Hybrid materials made from polydimethylsiloxane and zirconium oxo species have been synthesized. They exhibit a high degree of homogeneity and dispersion for Zr/Si molar ratios ranging between 0.2 and 0.9. These hybrid materials show good mechanical integrity and transparency. They have been characterized by Si-29, O-17 and C-13 MAS-NMR as well as FTIR, SAXS and dynamic mechanical analysis (DMA). These polydimethylsiloxane/zirconium oxopolymers are hybrids which consist of amorphous zirconium oxo domains of about one to two nanometers 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 approximatively 15-20 silicon atoms to 3 silicon atoms with increasing zirconium 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 zirconium content. The curing of these hybrid materials at 140 degrees C completes consolidation of the hybrid network, without affecting the overall characteristics of the organic-inorganic interface. Curing at 200 degrees C induces the loss of small silicic species and the increase of cross-linking points in the siloxane regions. For samples with a high zirconium content (Zr/Si = 0.9) curing at 200 degrees C also induces an increase in the number of the Zr-O-Si interface bonds.