  Vapor pressures were measured for the system chloroform/polyethylene oxide
(peo, weight average molar mass = 1000 kg/mol) at 25 degrees centigrade as a
function of the weight fraction w of the polymer by means of a combination of
head space sampling and gas chromatography. The establishment of thermodynamic
equilibria was assisted by employing thin polymer films. The degrees of
crystallinity alpha of the pure peo and of the solid polymer contained in the
mixtures were determined via dsc. An analogous degree of polymer insolubility,
beta, was calculated from the vapor pressures measured in this composition
range. The experiments demonstrate that both quantities and their concentration
dependence are markedly affected by the particular mode of film preparation.
These non-equilibrium phenomena are discussed in terms of frozen local and
temporal equilibria, where differences between alpha and beta are attributed to
the occlusion of amorphous material within crystalline domains. Equilibrium
information was obtained from two sources, namely from the vapor pressures in
the absence of crystalline material (gas/liquid) and from the saturation
concentration of peo (liquid/solid). The thermodynamic consistency of these
data is demonstrated using a new approach that enables the modeling of
composition dependent interaction parameters by means of two adjustable
parameters only.
