This article reports the synthesis of atom transfer radical polymerization (ATRP) of active initiators from well-defined silica nanoparticles and the use of these ATRP initiators in the grafting of poly(n-butyl acrylate) from the silica particle surface. ATRP does not require difficult synthetic conditions, and the process can be carried out in standard solvents in which the nanoparticles are suspended. This "grafting from" method ensures the covalent binding of all polymer chains to the nanoparticles because polymerization is initiated from moieties previously bound to the surface. Model reactions were first carried out to account for possible polymerization in diluted conditions as it was required to ensure the suspension stability. The use of n-butyl acrylate as the monomer permits one to obtain nanocomposites with a hard core and a soft shell where film formation is facilitated. Characterization of the polymer-grafted silica was done from NMR and Fourier transform infrared spectroscopies, dynamic light scattering, and DSC.