The effectiveness as impact modifier of two in situ maleated metallocene copolymers, a metallocene polyethylene, (mPE1) and a metallocene ethylene-propylene (mEPDM) and three commercial maleated copolymers (mPE2-g-MA, EPDM-g-MA, and mEPR-g-MA) were studied in binary and ternary blends carried out in an inter-meshing corotating twin-screw extruder with polyamide-6 (PA) as matrix (80 wt %). Also, the effects of the grafting degree, viscosity ratio, and crystallinity of the dispersed phases on the morphological and mechanical properties of the blends were investigated. A significant improvement of the compatibility of these grafted copolymers with PA6 was shown by FTIR spectroscopy, capillary rheometry, and scanning electron microscopy (SEM) in all reactive blends. The tensile strength values of the mEPR-g-MA/PA2 binary blend showed the highest strain hardening. The results obtained in this work indicated that the effectiveness of the grafted copolymers as impact modifier depends on the morphology of the blends and a combination of tensile properties of the blend components such as Young's modulus, Poisson ratio, and break stress. (c) 2007 Wiley Periodicals, Inc.