Equation of state of a blend of water-soluble polymers:: poly(propylene glycol) plus poly(ethylene glycol)

We have measured the equation of state surface of the blend poly(propylene glycol) (PPG) + poly(ethylene glycol) (PEG) over the whole composition range up to 40 MPa. The excess volume of the blend is negative, except for PPG-rich mixtures, and becomes more positive with increase in pressure or temperature. The P-V-T data can be described very accurately in terms of a corresponding-states principle that depends on a single system-dependent parameter. Moreover, the effect of pressure on the volume has been found to be the same as that of a chemically dissimilar blend, and slightly different from that of a triblock copolymer with the same relative content of PEG and PPG. The results have been analysed in terms of a lattice-fluid model. Although it is not possible to reproduce the asymmetry of the excess volume curves, the model accounts for the pressure dependence of the volume. No significant differences an found between predictions of the bare lattice-model and the model with hydrogen-bond interactions. (C) 2000 Elsevier Science Ltd. All rights reserved.