Determination of solvent-independent polymer–polymer interaction parameter by an improved inverse gas chromatographic approach

The solvent-dependence problem generally observed in the determination of polymer–polymer interaction parameters from inverse gas chromatography (IGC) measurements has been examined and resolved. The problem is mainly attributed to the use of different reference volumes in the calculations of χ12, χ13, and χ1(23) from the raw IGC data for different solvents. Upon selection of a common reference volume for all the solvents used, IGC data were found to be well described by the ternary version of the Flory–Huggins lattice theory; unique solvent-independent χ23 values were obtained. Our data on blends of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) have also confirmed the validity of the zero Δχ criterion suggested by Su and Patterson twenty odd years ago (Macromolecules, 10 (1977) 708) so long as a common reference volume is used in the data analysis. If the latter criterion is not satisfied, measured χ23 values still vary with the solvent used. However, it is uncertain whether the present approach can be applied to the situation in which the solvents used do not meet the zero Δχ criterion. The χ23 values obtained in the present work suggest that HDPE/LDPE blends may exhibit a closed-loop phase behavior.