NANOSTRUCTURED MATERIALS BASED ON POLYHEDRAL AND BRIDGED SILSESQUIOXANES

R. J. J. WILLIAMS

Praga

Simposio; 71st Prague Meeting on Macromolecules; 2007

Monofunctional polyhedral oligomeric silsesquioxanes (POSS) have been used to modify different types of polymer networks. In most cases, a polymerization-induced phase separation takes place leading to a dispersion of a POSS-rich phase in the polymer network. We will show that the nature of the organic inert group and the pre-reaction of the functional group can be used to control morphologies generated in POSS-modified epoxies. An example where large amounts of a monofunctional POSS can be introduced to an acrylic formulation without any evidence of phase separation will be discussed. Mechanical and thermal properties of the resulting hybrid materials will be analyzed. Narrow distributions of POSS can be synthesized in one step starting from organotrialkoxysilanes bearing hydroxyl groups in beta position with respect to tertiary amines. When this precursor is co-condensed with tetraethoxysilane (TEOS), soluble functionalized-silica can be obtained. This product can be covalently bonded to the surface of silica and the resulting modified-silica used as a support of a metallocene catalyst. The activity of the supported catalyst for ethylene polymerization was similar than the activity found in the homogeneous reaction. Bridged silsesquioxanes can be synthesized by the hydrolysis and condensation of monomers containing an organic bridging group joining two trialkoxysilyl groups. When the organic bridge contains urea groups, the material exhibits photoluminescence arising from processes taking place both in inorganic and organic domains. We will show that the photoluminescence spectra can be varied by controlling the relative rates between the self-assembly of organic bridges and the inorganic polycondensation. Specific dies can be covalently bonded to the structure during the synthesis producing a significant variation of the emission spectra. When bulky pendant groups are present in the organic bridge, a nanostructuration at different levels takes place due to the need to accommodate the bulky group in the structure. We will discuss examples of the nanostructures obtained when the pendant group is a dodecyl chain or a cyclohexyl ring.