Preparation of polypropylene/silica composites by in-situ sol–gel processing using hyperbranched polyethoxysiloxane

Based on a volatile-free silica liquid precursor polymer—hyperbranched polyethoxysiloxane (PEOS), an industrial compatible in situ sol–gel process for the preparation of polymer/silica nanocomposites has been developed. It has been shown that in the presence of a catalyst water vapor induced a fast conversion of liquid PEOS to solid silica in polypropylene (PP) melt in a twin-screw microcompounder. Solid state NMR showed that the in situ conversion of PEOS proceeded to a large extent. With small amounts of PEOS this procedure yielded PP/silica composites with particle size less than 100 nm. The particle size increased with the PEOS amount blended with PP. Nevertheless, the particles were observed to be homogeneously dispersed within the polymer matrix. PP/silica composites prepared by in situ sol–gel technology showed improved thermal properties, but almost not affected mechanical properties in comparison with pure PP.