MICROCALORIMETRIC DETERMINATION OF THE CRITICAL CONCENTRATION AND THE MOLECULAR DIMENSIONS OF POLYVINYL ACETATE IN SOLUTION

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Abstract
Heats of mixing of polyvinyl acetate fractions with s-tetrachloroethane and methanol have been determined for the low concentration region. At the lowest concentrations the graphs of ΔH vs. volume fraction are linear as predicted by the van Laar, Scatchard, and Hildebrand theory. As the concentration increases, an inflection point appears, the enthalpy increment being smaller for a short concentration interval and then resuming its former value up to the limit of the range studied. The position of the critical interval depends on the solvent employed and on the molecular weight of the fraction. An equation, based on Flory's theory, has been developed for predicting the critical concentration from intrinsic viscosity. Assuming that, at the critical concentration, the molecules are just coming into contact, it is possible to calculate the diameter of the sphere equivalent to a molecule. Comparison of the dimensions obtained from the critical concentration and the root-mean-square end-to-end distance of the molecule calculated by the Flory equation leads to agreement within 10%.

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