Maleic anhydride grafted polypropylene (PP-g-MA) and organically modified clay composites were prepared in a plasticorder. PP-g-MAs, including Polybond PB3150, Polybond PB3200, Polybond PB3000, and Epolene E43, with a wide range of maleic anhydride (MA) concentrations and molecular weights were used. The structure was investigated with X-ray diffraction (XRD) and transmission electron microscopy (TEM). PP-g-MA compatibilizers gave rise to similar degrees of dispersion beyond the weight ratio of 3/1, with the exception of E43, which had the highest MA content and the lowest molecular weight. The thermal instability and high melt index were responsible for the ineffective modification by E43. Furthermore, PP-g-MA with a lower molecular weight and a higher melt index had to be compounded at a lower mixing temperature to achieve a reasonable level of torque for clay dispersion. Polypropylene/organoclay nanocomposites were then modified with different levels of PP-g-MA compatibilizers with twin-screw extruder. The polypropylene/E43/clay system, as shown by XRD patterns and TEM observations, yielded the poorest clay dispersion of the compatibilizers under investigation. The curves of the relative complex viscosity also revealed a systematic trend with the extent of exfoliation and showed promise for quantifying the hybrid structure of the nanocomposites. The mechanical properties and thermal stability were determined by dynamical mechanical analysis and thermogravimetric analysis, respectively. Atthough PP-g-MA with a lower molecular weight led to better clay dispersion in the polypropylene nanocomposites, it caused deterioration in both the mechanical and thermal properties of the hybrid systems. (c) 2005 Wiley Periodicals, Inc.