Designing Macromolecules on Nanoparticle Surfaces: In Situ Formation of Silica Grafted with Star Chains

Herein, we report the synthesis and characterization of asymmetric 3-arm homostar (3h-star) and 3-miktoarm star (3 mu-star) chains grafted on silica nanoparticles simultaneously with the formation of silica. We employed high-vacuum anionic polymerization techniques to synthesize well-defined omega-triethoxysilyl (TEOS)-terminated (PS)(2)PS, (PS)(2)PI, and (PS)(2)PI-b-PS macromonomers (polystyrene (PS) and polyisoprene (PI)), which upon hydrolysis/condensation of the terminal TEOS yielded the grafted silica nanoparticles. The molecular characteristics of the precursors (PS)(2)PS-TEOS, (PS)(2)PI-TEOS, and (PS)(2)PI-b-PS-TEOS were determined by proton nuclear magnetic resonance (NMR) spectroscopy and size-exclusion chromatography (SEC). The formation of 3h-star and 3 mu-star@SiO2 nanoparticles was demonstrated by Fourier transform infrared spectroscopy, 29Si solid-state NMR, transmission electron microscopy, thermogravimetry, and dynamic light scattering. Blends of 3h-star and 3 mu-star@SiO2 with a thermoplastic elastomer (TPE) (PS-b-PI-b-PS), synthesized by anionic polymerization, were obtained by the evaporation of solutions containing the TPE and the grafted nanoparticles. The role of 3h-star and 3 mu-star@SiO2 in the mechanical properties and morphological features of the polymer matrices was examined by tensile testing and scanning electron microscopy. This synthetic methodology controls the molecular characteristics, particle size, and grafting density of nanoparticles and enhances the mechanical properties of the final nanocomposites.