THERMODYNAMICS OF MIXING FOR STATISTICAL COPOLYMERS OF ETHYLENE AND ALPHA-OLEFINS

The melt-state interactions that govern phase behavior in polyolefin b lends were evaluated by small-angle neutron scattering (SANS) and comp ared with earlier results for structurally similar model polymers. The materials are statistical copolymers of ethylene with a range of prop ylene, l-butene, l-hexene, and 1-octene contents, made by metallocene catalysis. They are modestly polydisperse (M-w/M-n similar to 2) and n ot available in deuterated form, thus requiring modification of the pr ocedures used for the nearly monodisperse and easily deuterated model polymers. The SANS intensity expression for polydisperse components wa s 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 delta - delta(ref) o btained for the alpha-olefin copolymers were found to depend only on t o, the weight fraction of alpha-olefin comonomer. Finally, this delta - delta(ref) vs w relationship is the same as that found earlier for m odel copolymers with different side-chain sequencing, indicating that variations in comonomer sequencing have little effect on the mutual so lubility of statistical olefin copolymers.