Study of the Hyflon AD80 perfluorinated copolymer by inverse gas chromatography

The perfluorinated copolymer of tetrafluoroethylene and perfluoromethoxydioxole, Hyflon® AD80x, is investigated by inverse gas chromatography. C₅–C₁₃ n-alkanes are used as sorbates, for which the specific retention volume, the solubility coefficient at infinite dilution, and the excess thermodynamic functions are calculated in the temperature range 30–115°C. The solubility coefficients of the hydrocarbons in the studied polymer are shown to be lower than those in amorphous Teflons AF1600 and AF2400, a finding that is consistent with the difference between the glass-transition temperatures of these polymers. The correlation between excess partial molar enthalpies and critical volumes of n-alkanes testifies that the upper limit for the size of the free-volume element in this polymer is 613 ų. Mixing of n-alkanes with Hyflon AD80 is thermodynamically disadvantageous (\(\bar G_1^{E,\infty } \) > 0) and becomes even less advantageous with an increase in the size of hydrocarbon molecules. Excess entropy mainly contributes to the high values of excess free energy, thus indicating a higher order in the system containing the glassy polymer than that in systems in which the polymer occurs in the rubberlike state.