Polymer/TiO2 nanoparticles composites have been prepared either by the 'grafting from' method or by the direct mixing of components, and their mechanical properties were compared. The 'grafting from' method is a process in two steps. First, the ATRP-initiator molecule, 2-bromo-2-methyl-propionic acid 11-phosphono-undecyl ester, is covalently grafted onto the surface of TiO2 nanoparticles through the phosphonic group, as evidenced by FTIR spectroscopy. In a second step, styrene is polymerized at the particle surface leading to a solid material. By comparison with the values obtained for the hybrid mixed composites, the hardness and the Young's modulus are increased, the maximum penetration depth decreased and the recovery capability improved for the hybrid grafted composites as proved by nano-indentation and nanoscratch experiments. (C) 2014 Elsevier B.V. All rights reserved.