PP/PP-g-MA/MMT/EOR blend nanocomposites were prepared in a twin-screw extruder at fixed 30 wt % elastomer and 0 to 7 wt % MMT content. Elastomer particle size and shape in the presence of MMT were evaluated at various PP-g-MA/organoclay masterbatch ratios of 0, 0.5, 1.0, and 1.5. The organoclay dispersion facilitated by maleated polypropylene serves to reduce the size of the elastomer dispersed phase particles and facilitates toughening of these blend nanocomposites. The rheological data analysis using modified Carreau-Yasuda model showed maximum yield stress in extruder-made nanocomposites compared with nanocomposites of reactor-made TPO. Increasing either MMT content or the PP-g-MA/organoclay ratio can drive the elastomer particle size below the critical particle size below which toughness is dramatically increased. The ductile-brittle transition shift toward lower MMT content as the PP-g-MA/organoclay ratio is increased. The D-B transition temperature also decreased with increased MMT content and masterbatch ratio. Elastomer particle sizes below similar to 1.0 mu m did not lead to further decrease in the D-B transition temperature. The tensile modulus, yield strength, and elongation at yield improved with increasing MMT content and masterbatch ratio while elongation at break was reduced. The modified Mori-Tanaka model showed better fit to experimental modulus when the effect of MMT and elastomer are considered individually. Overall, extruder-made nanocomposites showed balanced properties of PP/PP-g-MA/MMT/EOR blend nanocomposites compared with nanocomposites of reactor-made TPO. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012