The miscibility and structure in polypropylene/layered silicate nanocomposites is systematically investigated utilizing a maleic-anhydride grafted polypropylene with a low degree of functionalization acting as the compatibilizer. The morphology of the hybrids can be modified from phase separated to almost completely exfoliated in a controlled way by varying the ratio alpha of the compatibilizer to the organophilized clay; this ratio alpha is found to be the most important parameter in determining the final structure whereas exfoliated structures can be obtained for alpha values of 9 or higher. Furthermore, utilization of a "masterbatch" procedure can enhance the degree of exfoliation even for smaller values of alpha; in that case, polypropylene is essentially mixed with the already dispersed "hairy" platelets. Investigation of the thermal stability of the micro- and nanocomposites shows that high degree of exfoliation is vital in increasing the temperature that the polymer starts to degrade. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2683-2695, 2008