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 rang e 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 tempe rature. The P-V-T data can be described very accurately in terms of a corre sponding-states principle that depends on a single system-dependent paramet er. 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. Althoug h it is not possible to reproduce the asymmetry of the excess volume curves , the model accounts for the pressure dependence of the volume. No signific ant differences an found between predictions of the bare lattice-model and the model with hydrogen-bond interactions. (C) 2000 Elsevier Science Ltd. A ll rights reserved.