Izod impact strength was determined as a function of temperature for polypropylene (PP)/ethylene-co-octene elastomer (EOR) blends and nanocomposites to determine the effect of PP molecular weight. elastomer MFI, EOR octene content and MMT content on the ductile-brittle (D-B) transition temperature. The D-B transition temperature decreases with increased molecular weight of the PP (H = high, M = medium and L = low) and the addition of MMT. The D-B transition temperature also decreases as the elastomer particle size is decreased, and at a fixed elastomer particle sizes, the D-B transition varies as H-PP < M-PP < L-PP. The H-PP based materials show a smaller decrease in the D-B transition temperature compared to L-PP based materials in the presence of MMT. Elastomers having a melt flow index (MFI) in the range of 0.5-1.0 showed a significant decrease in the D-B transition temperature for both L-PP and H-PP nanocomposites. The D-B transition temperature also decreases with increasing octene content of the elastomer. (C) 2011 Elsevier Ltd. All rights reserved.