THERMODYNAMIC CHARACTERIZATION BY INVERSE GAS-CHROMATOGRAPHY OF A 50-PERCENT METHYL,50-PERCENT TRIFLUOROPROPYL POLYSILOXANE

Poly[methyl(3,3,3-trifluoropropyl)siloxane] with a 50% substitution of trifluoropropyl radical has been studied by inverse gas chromatography (IGC) between 90 and 180-degrees-C. Both packed and capillary columns have been used, the latter prepared with and without cross-linking of the polymer. Flory-Huggins solute-polymer interactions parameters and partial molar enthalpies and free energies of solution and mixing were calculated for 21 substances (ketones, alcohols, aromatic and saturated hydrocarbons, nitriles, esters, and dimethylaniline). Nitriles, tertiary amines, and ketones behave as good solvents. Aromatic hydrocarbons are moderate solvents if a hydrocarbon chain is not attached to the aromatic ring, while alcohols and alkanes are nonsolvents in the temperature range considered, although solubility increases slightly with temperature. The thermodynamic functions vary linearly with the number of carbon atoms of the alkyl chain in homologous series. The solubility parameter of the polymer varies linearly with temperature from about 7.9 (cal cm-3)1/2 at 90-degrees-C to 7.4 (cal cm-3)1/2 at 180-degrees-C. A value of 8.2 (cal cm-3)1/2 may be deduced for delta-2 at 25-degrees-C. No meaningful difference was found between values deduced form V(g) data obtained on packed or capillary columns, cross-linked or not.