Layered silicate nanocomposites based on polyamide 6 and polypropylene have been prepared via static annealing experiments. The evolution of clay dispersion into the polymer matrices was monitored by wide angle X-ray diffraction analysis and transmission electron microscopy. The results have evidenced that the polymer diffusion inside the organoclay galleries is spontaneous and have elucidated the mechanism of nanostructured system formation under static conditions. Indeed, the exfoliation mechanism turned to be a two-step process consisting of polymer intercalation into the clay galleries and progressive layer delamination. Both steps have turned out to depend on thermodynamic and kinetic parameters. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2476-2483, 2010