Influence of Copolymer Composition and Curing on Toughness of Isotactic Polypropene Blended Together with Metallocene-EPDM and Ethene/Propene/Vinylcyclohexane Terpolymers

Abstract

Ethene/propene terpolymers containing either 1-vinylcylohexene-4 (VCHen) or vinylcyclohexane (VCHan) as termonomer component were prepared using MAO-activated rac-Me2Si(2-MeBenz[e]Ind)2ZrCl2 (MBI). Propene content was varied between 26 and 72 wt.-% with less than 1 mol-% termonomer incorporation. Blends containing 85 vol.-% isotactic polypropene (i-PP) and 15 vol.-% of the two EP terpolymer families were prepared by melt-compounding in a twin-screw kneader at 200°C to examine the role of sulfur-mediated crosslinking of the unsaturated EPDM terpolymer phase in comparison to the corresponding blends containing non-crosslinked saturated EP/VCHan terpolymers. The observed glass temperature (Tg) depression of the Tg of EP(D)M phases with respect to the Tg of the corresponding bulk EP(D)M was attributed to the presence of thermally induced stresses in both blend systems. Blends of i-PP with crosslinked EPDM showed smaller Tg depression with respect to those of iPP/EPM blends containing non-crosslinked EP and EPM dispersed phases. Morphology differences were detected for i-PP/EPM and dynamically vulcanized i-PP/EPDM blends by means of atomic force microscopy (AFM). The crosslinked i-PP/EPDM blends exhibited significantly improved low temperature toughness as compared to the corresponding non-crosslinked i-PP/EPM blends. Curing of the EPDM elastomer phase in i-PP/EPDM (85 vol.-%/15 vol.-%) blends afforded significantly improved toughness/stiffness balance and a wider toughness window with respect to the corresponding i-PP/EPM and i-PP/EP blends without sulfur-cured rubber phases.