Phase Behavior of Isotactic Polypropylene−Poly(ethylene/ethylethylene) Random Copolymer Blends

Abstract

The melt-state phase behavior of isotactic polypropylene (i-PP) blended with a series of poly(ethylene/ethylethylene) random copolymers has been investigated using small-angle neutron scattering (SANS). These PEExx copolymers, where xx is the percentage of ethylethylene (EE) units, were prepared by hydrogenation of anionically polymerized polybutadienes with controlled amounts of 1,2 addition. Random phase approximation (RPA) fits to the scattering data for blends of i-PP with a deuterated, low molecular weight PEE90 at 180 °C indicate a statistical segment length for i-PP that is 10% less than that reported previously. Scattering from blends of i-PP with higher molecular weight PEE90 and PEE73 at 180 °C can be quantitatively fit using the RPA theory with χ as the only adjustable parameter, indicating melt miscibility. PEE46 and PEE62 are strongly and marginally immiscible, respectively, with i-PP at 180 °C. These results establish a “window” in EE content in which these random copolymers can form single phase mixtures with i-PP.