A new family of thermoplastic nanocomposites based on isotactic polypropylene (iPP) and inorganic fullerene-like tungsten disulfide (IF-WS2) has been successfully prepared. A very efficient dispersion of IF-WS2 material was obtained by mixing in the melted polymer without using modifiers or surfactants. The addition of IF-WS2 nanoparticles induces a remarkable enhancement of the thermal stability of iPP, as well as an increase in the crystallization rate of the matrix when compared with pure iPP. The nucleating efficiency of IF-WS2 solid lubricant nanoparticles on the alpha-phase of iPP reaches very high values (60-70%), the highest values observed hitherto for polypropylene nanocomposites. The incorporation of IF-WS2 has also been observed to increase the size and stability of the crystals formed. The melting behavior of the nanocomposites indicates the formation of more perfect crystals as determined by differential scanning calorimetry and time-resolved synchrotron X-ray scattering experiments. The new nanocomposites show an increase in the storage modulus with respect to pure iPP measured by dynamic mechanical analysis. (c) 2007 Wiley Periodicals, Inc.