Thermodynamics of polyolefin blends: small-angle neutron scattering studies with partially deuterated chains

Small-angle neutron scattering is used to evaluate the binary interaction parameter χ in molten blends of polyethylenes having different levels of ethyl branching along the backbone. The labelled chains were partially deuterated to minimize the isotope effect on χ. The present results for equal-volume-fraction binary blends at 150°C can be summarized as χ=0.4×10^?4+0.014ΔX²_br. The first term is from the hydrogen-deuterium isotope effect for chains labelled with about 33% deuterium. The second term is due to chemical composition differences, expressed here as the difference in X_br, the fraction of four-carbon repeat units having an ethyl branch. The observed contributions to χ are in reasonable accord with calculated estimates.