A new route has been developed to produce PP/silica nanocomposites starting from porous PP reactor powder and making use of sol-gel chemistry. Silica-like, nano-sized particles were prepared in the pores of the PP reactor powder with a controlled degree of adhesion between PP and silica. Magic-angle spinning (MAS) 29SiNMR spectra showed that the chemical building blocks of the silica-like clusters are of Q3 and Q4-type. For (vinyl triethoxy silane (VTES)-grafted PP)/silica nanocomposites, VTES was grafted via solid-state modification (SSM) in porous PP particles. Subsequently, silica particles were prepared by sol-gel technology in the VTES-grafted PP. MAS 29Si NMR and FT-IR spectroscopy showed that the grafted VTES becomes part of the in-situ formed silica particles. The study on the mechanical properties of (VTES-graftedPP)/silica nanocomposites showed that the silica particles improved the impact toughness of PP by a factor of 2, when there is no chemical interactionbetween the particles and the matrix, while for (VTES-grafted PP)/silica nanocomposites the impact toughness decreased. This indicates that chemical bonding betweenthe filler particles and the PP-matrix results in brittle failure and supports the hypothesis that debonding is necessary for improving the impact toughness of PP with inorganic fillers.