Some experimental studies on enthalpy and entropy effects in equilibrium swelling of polyoxypropylene elastomers

Abstract

Measurements on the equilibrium swelling of some polyoxypropylene elastomers by a series of solvents are reported with the purpose of distinguishing entropy and enthalpy effects in the thermodynamics of the swelling process. Values of the X parameter have been obtained, and from direct measurements of the heat of swelling in a Tian-Calvet microcalorimeter, the x H, or enthalpy interaction parameter, has been obtained. The values of x S, the corresponding entropy parameter, are then deduced and it is shown that there is a linear relation (or ‘compensation effect’) between the x H and x S terms. In no solvent can the x S term be neglected. Diffusion calculations have been made in which it is shown that heats of mixing of liquids in thin layers can be accurately measured in the microcalorimeter without use of stirring and its consequent difficulties.