THERMODYNAMIC PROPERTIES OF POLY(ETHYLENE GLYCOL) WATER-SYSTEMS .1. APOLYMER SAMPLE WITH A NARROW MOLAR-MASS DISTRIBUTION

Liquid-liquid demixing experiments of a poly(ethylene glycol)/water sy stem have been performed. The polymer is characterized by a nominal mo lar mass of 6000 g mol(-1) and a narrow molar mass distribution. The c loud-point curve of the system and a large number of phase volume rati os at different polymer concentrations and temperatures have been meas ured. With these results the critical coordinates and the shadow curve of the system have been determined using the volume conservation equa tion. Generally, the system behaves like a binary:one. The miscibility gap is well described using the scaling theory up to temperatures of about 12 K above the lower critical point. The cloud-point and the sha dow curve of the system have been computed using the Flory-Huggins the ory. For the first time thermodynamic parameters have been used that a re calculated directly from the concentrations of coexisting phases ob tained by evaluation of phase volume ratio measurements. The examined forms of the interaction function g of the base molar free enthalpy of mixing Delta G(M) do not describe the system satisfactorily.