In Situ Formation of Silica Nanoparticles Decorated with Well-Defined Homopolymers and Block Copolymers

Grafting non-polar polymer chains on the surface of polarnanoparticles(e.g., silica) is an effective way to enhance particle/matrix interactionsand thus promote their homogeneous dispersion within a non-polar matrix,which leads to improved mechanical properties. Current grafting methodshave not yet produced nanoparticles with well-defined polymers onthe surface and high grafting density. Here, we employed anionic polymerizationhigh vacuum techniques to synthesize omega-triethoxysilyl polystyrene(PS-TEOS) and PS-b-PI macromonomers followed by hydrolysis/condensationof macromonomers, leading to the in situ formation of grafted (graftingthrough) silica nanoparticles with either PS or polystyrene-b-polyisoprene (PS-b-PI) chains. The molecularcharacteristics of the precursors PS-TEOS and PS-b-PI-TEOS were determined by proton nuclear magnetic resonance, sizeexclusion chromatography, and matrix-assisted laser desorption/ionizationtime-of-flight. The formation of PS (PS@SiO2 NPs) and PS-b-PI (PS-b-PI@SiO2 NPs) nanoparticleswas verified by Fourier transform infrared spectroscopy, Si-29 solid-state NMR, transmission electron microscopy, thermogravimetricanalysis, and dynamic light scattering. Blends of PS@SiO2 with commercially available PS and PS-b-PI@SiO2 with anionically synthesized thermoplastic elastomer (PS-b-PI-b-PS) were obtained either in meltby extrusion or in solution by evaporation. The role of polymer@SiO2 on the mechanical properties and morphological features ofthe matrices was examined by tensile testing and scanning electronmicroscopy. The proposed general method controls the molecular weight,chemical composition, particle size, and grafting density of nanoparticlesand effectively improves the mechanical characteristics of the twofamilies of PS-based nanocomposites.