Enthalpies of solution of polyvinylacetate in chloroform,acetone, and methanol using titration calorimetry

Heats of mixing of the solvents chloroform, methanol, and acetone with their solutions in polyvinylacetate have been measured at 25°C using a titration calorimeter. Titration of pure solvent to solutions as well as titration of solutions to the pure solvent or to diluted solutions have been performed. The second method, called reverse titration, proved to be more sensitive than normal dilution titration at sufficiently low polymer concentration. Equations describing the relative sensitivity of both titration methods have been developed. The concentration range covered by the experiments is restricted to volume fractions of polyvinylacetate not higher than 0.1–0.15 due to the high viscosities of concentrated solutions. The interaction parameterX _H of the Flory-Huggins theory has been determined from the calorimetric data.X _H is positive for methanol solutions and negative for chloroform and acetone solutions reflecting endothermic and exothermic heat effects respectively.