Heats of solution and dilution for polyethylene oxide in several solvents

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Abstract
The Tian-Calvet microcalorimeter, as modified by Maron and Filisko, has been used to measure the heats of solution and dilution of a sample of polyethylene oxide (PEO) of M2 = ca. 6000 in chloroform, methylene chloride, and water. By applying the Maron theory to these measurements, it was found from the organic solvent data that the heat of fusion of the PEO sample is 57.1 cal/g polymer, independent of the solution concentration or the solvent used. However, the solution behavior in water was different because PEO in organic solvents exists as a random coil, whereas in water its conformation is helical. By combining the water and organic solvent data, it can be shown that conversion of the random coils to the helix involves the evolution of 39.3 cal of heat per gram of polymer. This heat evolution accounts, in all probability, for the solubility of PEO in water.