Thermodynamics of polyvinyl chloride solutions: III. Solutions in tetrahydrofuran

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Abstract
Six samples of polyvinyl chloride (PVC), ranging in molecular weight from 23,200 to 155,400, were used to determine in tetrahydrofuran the intrinsic viscosities, molecular weights, and the polymer-solvent interaction parameters over a range of temperatures. The solutions were found to behave normally and to exhibit no evidence of “aggregate” formation. The molecular weights obtained were independent of temperature and agreed well with those measured in cyclohexanone and cyclopentanone. The interaction parameters observed were independent of concentration and molecular weight, and functions only of temperature. Again, the intrinsic viscosities are related to molecular weight by the Mark-Houwink equation between 20° and 50°C with a constant a and with a K linearly dependent on the temperature. The value of the temperature coefficient of the interaction parameter obtained by osmometry agrees well with that found by microcalorimetry and predicts that heats of mixing of completely amorphous polymer with solvent and heats of dilution are exothermic for this system. A comparison of solutions of PVC in cyclohexanone, cyclopentanone, and tetrahydrofuran shows that all are good solvents for PVC and that the order of solvent quality is cyclohexanone >cyclopentanone >tetrahydrofuran. Finally, the results obtained prove that the Maron theory of polymer solutions is applicable both qualitatively and quantitatively to solutions of PVC in all three solvents and that the agreement between theory and experiment extends to free-energy as well as to thermal measurements.

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