Poly(glycidyl methacrylate) polymer brushes were grafted onto TiO2 nanoparticle surfaces via a combination of phosphate ligand engineering and Cu-catalyzed alkyne-azide "click" reaction. The grafted TiO2 nanoparticles are compatible with a commercial epoxy resin enabling the preparation of thick (1 mm) transparent high-refractive index TiO2/epoxy nanocomposites. In order to maximize the volumetric loading and thereby the refractive index of nanocomposites, the minimum graft densities that can lead to high optical transparency were identified. It was found that, when the graft density was too low to form polymer brushes, the dispersion of the grafted particles changed from a dispersed state to an agglomerated state. The transition of the dispersion state was in good agreement with the theoretical prediction from a parametric model. This good agreement will facilitate the design and fabrication of transparent polymer nanocomposites filled with grafted nanoparticles. With 30 wt% loading of TiO2 nanoparticles, the refractive index of TiO2/epoxy nanocomposites increased from 1.5 for neat epoxy to 1.62. The transparency of the prepared nanocomposites can be well predicted by the Raleigh scattering model. Published by Elsevier Ltd.