Polymer–diluent interactions. III. Polyethylene—diluent interactions

Abstract

The interactions between polyethylene and a number of hydrocarbon diluents were characterized on the basis of the Flory‐Huggins interaction parameter χ and the closely related heat of mixing parameter B. The evaluations of these parameters were based on Flory's statistical‐thermodynamic treatment of the effect of diluents on the melting points of crystalline polymers. Necessary for each evaluation was a single microscopic determination of the depressed melting point of polyethylene in its mixture with a given diluent as indicated by the disappearance of the last visible traces of crystallinity upon slow heating. Each mixture was diluted to an extent that the volume fraction of diluent approximated unity. This permitted the use of a simplified form of the Flory equation. The data obtained from the study of thirty diluents were utilized in an attempt to correlate diluent structure with solvency. Generally, the various types of hydrocarbon diluents can be rated in the following order of increasing solvency: aromatic, alkylaromatic, aliphatic, alicyclic. In addition, it was demonstrated that the value of B for a given diluent can be reliably estimated as a function of a new parameter which is calculated from the diluent structure, density, and an estimated value of the ionization energy. This new parameter also correlates well with the solubility parameter δ_T.