TiO2 nanocomposites with high refractive index and transparency†

Transparent polymer nanocomposites with high refractive index were prepared by grafting polymer chains onto anatase TiO2 nanoparticles via a combination of phosphate ligand engineering and alkyneazide ‘‘click’’ chemistry. Highly crystalline TiO2 nanoparticles with 5 nm diameter were synthesized by a solvothermal method and used as high refractive index filler. The synthesized phosphate-azide ligand anchors strongly onto the TiO2 nanoparticle surface and the azide end group allows for attachment of poly(glycidyl methacrylate) (PGMA) polymer chains through an alkyne-azide ‘‘click’’ reaction. The refractive index of the composite material increased linearly from 1.5 up to 1.8 by increasing the loading of TiO2 particles to 30 vol % (60 wt %). UV-vis spectra show that the nanocomposites exhibited a transparency around 90% throughout the visible light range. It was also found that the PGMAgrafted TiO2 nanoparticles can be well dispersed into a commercial epoxy resin, forming transparent high refractive index TiO2-epxoy nanocomposites.