In this study, Ca2+-montmorillonite (Ca2+-MMT) and organo-montmorillonite (OMMT) were modified by three compatibilizers with different degrees of polarity [poly(ethylene glycol) (PEG), alkyl-PEG, and polypropylene (PP)-g-PEG]. PP/MMT nanocomposites were prepared by melt blending and characterized using X-ray diffraction and transmission electron microscopy. The results showed the degree of dispersion of OMMT in the PP/PP-g-PEG/OMMT (PMOM) nanocomposite was considerably higher than those in the PP/PEG/OMMT and PP/alkyl-PEG/OMMT nanocomposites, which indicated that the dispersion was relative to the compatibility between modified OMMT and PP matrix. Linear viscoelasticity of PP/MMT nanocomposites in melt states was investigated by small amplitude dynamic rheology measurements. With the addition of the modified MMT, the shear viscosities and storage modulus of all the PP/MMT nanocomposites decreased. It can be attributed to the plasticization effect of PEG segments in the three modifiers. This rheological behavior was different from most surfactant modified MMT nanocomposites which typically showed an increase in dynamic modulus and viscosity relative to the polymer matrix. The unusual rheological observations were explained in terms of the compatibility between the polymer matrix and MMT. In addition, the mechanical properties of PP/MMT nanocomposites were improved. A simultaneous increase in the tensile strength and toughness was observed in PP/PMOM nanocomposites. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013