Grafting polymeric chains on the surface of nanoparticles is an effective way to enhance particle-matrix interaction and their homogeneous dispersion within the matrix, leading to improved physical and mechanical properties. However, current methods for grafting polymeric chains onto nanoparticles have not produced well-defined polymers with high grafting density. Here, we employed anionic polymerization high vacuum techniques to synthesize in-situ grafted silica nanoparticles with either polystyrene (PS), polystyrene-b-polyisoprene (PS-b-PI) or 3- miktoarm star polymers (3-µ stars polymer) ((PS)2PS, (PS)2PI, and (PS)2PI-b-PS) by hydrolysis/condensation of ω-tetraethyl orthosilicate (TEOS) of PS, PS-b-PI and 3-µ star polymers. The molecular characteristics of the precursors PS-TEOS was determined by 1H NMR, SEC, and MALDI-ToF, and  PS-b-PI-TEOS, and 3-µ star polymer-TEOS were determined by 1H NMR, SEC. The synthesis of PS (PS@SiO2 NPs), PS-b-PI (PS-b-PI@SiO2 NPs), and 3-µ star polymer ((PS)2PS)@SiO2, (PS)2PI)@SiO2, and (PS)2PI-b-PS@SiO2 NPs) nanoparticles was verified by FT-IR, 29Si solid-state NMR, TEM, TGA, and DLS. Blends of PS@SiO2 with commercially available PS and PS-b-PI@SiO2 and 3-µ star polymer@SiO2 with anionically synthesized thermoplastic elastomer (PS-b-PI-b-PS), were obtained either in melt by extrusion or in solution by evaporation.

The role of polymer@SiO2 on the mechanical properties and morphological features of the matrices was examined by tensile testing and SEM. The proposed method controls the molecular weight, chemical composition, particle size and grafting density of nanoparticles and effectively improves the mechanical characteristics of the two families of PS-based nanocomposites.