MICROCALORIMETRIC STUDIES OF POLYVINYL ACETATE SOLUTIONS

Abstract

A relation between intrinsic viscosity and the sign of heat of mixing of a linear polymer in different solvents has been predicted by Alfrey, Bartovics, and Mark. To verify this, the intrinsic viscosities and heats of mixing at one concentration for two samples of polyvinyl acetate in six solvents were determined. The heats of mixing have been measured with a Tian–Calvet microcalorimeter especially designed for slow processes and having a sensitivity of one thousandth of a calorie per hour. The results generally agree with the above prediction. Furthermore, the heats of mixing of two fractions of polyvinyl acetate in three solvents have been measured over a range of low concentrations to study the behavior of the quantity B from the theory of van Laar, Scatchard, and Hildebrand on energy of mixing of nonelectrolytes. It was found that B goes through a minimum at low concentrations when the mixing process is exothermic. This effect may be explained by the existence of a critical concentration below which entanglement between macromolecules ceases. For a poor solvent, B seems to be constant at high dilution.