Heats of solution and dilution for polyvinyl chloride in cyclohexanone and tetrahydrofuran

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Abstract
Heats of solution and dilution for polyvinyl chloride (PVC) in cyclohexanone and tetrahydrofuran have been measured at 30°C for samples ranging in molecular weight from 23,200 to 155,400, as well as for several polymers with special histories. The results show that normal PVC is a mixture of crystalline and glassy phases. The degree of crystallinity is relatively low, ca. 20%, and decreases with increase in molecular weight. Annealing does not modify the crystallinity significantly, but quenching from the melt can reduce it to low levels and possibly even to zero. A tentative method is presented for estimating the degree of crystallinity from residual heats obtained from heat of solution measurements. These residual heats are independent of concentration or solvent used and are properties only of the polymer. Also, Maron theory λ's have been calculated from the heat of dilution data, and these agree with the λ's evaluated from osmometry. This agreement confirms the Maron theory argument that heats of solution and dilution are determined by the temperature coefficient of the polymer-solvent interaction parameter and not by the parameter itself, as claimed by the Flory-Huggins theory and its various extensions and modifications.