We investigate the properties of polymer nanocomposites consisting of narrow disperse spherical nanoparticles that are coated with narrow disperse polymers. These nanoparticles can be homogeneously dispersed in a polymer matrix. The structure of the polymer-coated nanoparticles was examined by using small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), and was related to the viscoelastic properties of the nanocomposites. We observe a systematic retardation of the polymer relaxation dynamics with increasing particle loading. Nanoparticle aggregation leading to the formation of chain-like structures causes a strong reinforcement effect. (C) 2018 Published by Elsevier Ltd.