The rheology, morphology. thermal and mechanical properties of blends containing low molecular weight polypropylene (PP) and metallocene-based ethylene-a-olefin copolymers (ECs) have been investigated. Evaluation of the thermo-theological properties of the blends showed that they are immiscible, both in the solid and melt state, over the whole range of compositions. Rheological properties were correlated to blend morphology, by using the Palieme emulsion model. The resulting low values of interfacial tension confirmed excellent compatibility between the phases.Addition of ECs in PP resulted in significant ductility improvement. The transition from plastic to elastomeric properties coincided with phase inversion. The butene-based EC was found to be the most beneficial in terms of impact properties.Fine morphologies, with sub-micron sizes of the dispersed phase, were obtained upon post-extrusion shearing of the blends. (C) 2003 Elsevier Ltd. All rights reserved.