Synthesis and characterization of transparent PDMS-metal-oxo based organic anorganic nanocomposites

Poly(dimethylsiloxane)(PDMS)-metal-oxo nanocomposites have been prepared as transparent monoliths from dimethyldiethoxysilane (DMDES) and metal alkoxides, M(OR)(n), where M = Al(III), Ge(IV), Sn(IV), Ti(IV), Zr(IV), Nb(V), and Ta(V). An accurate structural analysis of these hybrid materials has been performed by FTIR, Raman, and multinuclear NMR (H-1, C-13, and Si-29) spectroscopies, SAXS, and DSC measurements. These techniques show that all the hybrid systems present a structure based on amorphous metal-oxo nanodomains embedded within the siloxane network. However, a strong influence of the cross-linking metal nature on the size of the metal-oxo nanoparticles and on the extent of the interface between inorganic domains and the siloxane component has been found. Spectroscopic measurements reveal a more important nanophase separation for the PDMS systems incorporating AI(III), Ti(IV), or Zr(IV) species as cross-linking agent than for the ones crosslinked with Nb(V), Ta(V), or Ge(IV) (in which 45% of the silicon atoms are spatially near a metal species).