Thermodynamics of mixing for statistical copolymers of ethylene and α-olefins

The melt-state interactions that govern phase behavior in polyolefin blends were evaluated by small-angle neutron scattering (SANS) and compared with earlier results for structurally similar model polymers. The materials are statistical copolymers of ethylene with a range of propylene, 1-butene, 1-hexene, and 1-octene contents, made by metallocene catalysis. They are modestly polydisperse (M_w/M_n - 2) and not available in deuterated form, thus requiring modification of the procedures used for the nearly monodilperse and easily deuterated model polymers. The SANS intensity expression for polydisperse components was confirmed independently, and two experimental procedures, employing binary and ternary blends with deuterated model components, were used. The interactions obey a solubility-parameter formalism, in agreement with the earlier studies. Moreover the values of δ - δ_ref obtained for the α-olefm copolymers were found to depend only on w, the weight fraction of α-olefin comonomer. Finally, this δ - δ_ref vs w relationship is the same as that found earlier for model copolymers with different side-chain sequencing, indicating that variations in comonomer sequencing have little effect on the mutual solubility of statistical olefin copolymers.