Polypropylene (PP)/montmorillonite (MMT) nanocomposites were prepared by compounding maleic anhydride-g-polypropylene (MAPP) with MMT modified with alpha,omega-diaminododecane. Structural characterization confirmed the formation of characteristic amide linkages and the intercalation of MAPP between the silicate layers. In particular, X-ray diffraction patterns of the modified clay and MAPP/MMT composites showed 001 basal spacing enlargement as much as 1.49 nm. Thermogravimetric analysis revealed that the thermal decomposition of the composite took place at a slightly higher temperature than that of MAPP. The heat of fusion of the MAPP phase decreased, indicating that the crystallization of MAPP was suppressed by the clay layers. PP/MAPP/MMT composites showed a 20-35% higher tensile modulus and tensile strength compared to those corresponding to PP/MAPP. However, the elongation at break decreased drastically, even when the content of MMT was as low as 1.25-5 wt %. The relatively short chain length and loop structure of MAPP bound to the clay layers made the penetration of MAPP molecules into the PP homopolymer phase implausible and is thought to be responsible for the decreased elongation at break. (C) 2004 Wiley Periodicals, Inc.