We have measured the equation of state surface for the mixtures poly(4-hydroxystyrene) + ethanol, and + tetrahydrofuran below 40 MPa. The results obey a superposition principle that makes it possible to build a master curve once the p-V-T surface is known at a given pressure. The master curve depends on a single system-dependent parameter that, for the two systems studied, takes almost the same value. The results have been analyzed with a lattice fluid model that includes the existence of hydrogen bonds. Even though the model describes the composition dependence of the excess volume, it underestimates the pressure dependence of the density. While the inclusion of hydrogen bonds in the model has a negligible influence on the predictions for the system with tetrahydrofuran, it improves significantly the predictions for the system with ethanol.

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The equation of state of acetonitrile + benzene has been measured over the whole composition range and for 298.15 I T/K I 328.15 and 0.1 I p/MPa I 40.0. The pressure dependence of several excess properties has been calculated from the experimental data. The system shows high values of GE, higher than in other systems formed by benzene with a polar and rigid molecule. The P(x) curves are s-shaped, though l P l is relatively small. The reS8ltS have been used to test the predictive capacity of a generalized van der Waals equation (Deiters' one) and a lattice-with-holes model.

The equation of state of poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol) (PEGÈPPGÈPEG) ] water has been measured in the sol phase at 298.15 K and up to 40 MPa. For the sake of comparison two mixtures of (PEG ] PPG) ] water, with the same PEG : PPG ratio as the copolymer, have been measured. The di †erences found between the data of the copolymer and the blend solutions are well beyond the experimental precision, the compressibility for the copolymer mixtures being larger than for the blend one. Contrary to previous non-aqueous mixtures, the aqueous ones present deviations with respect to the corresponding states equation proposed by the group of Sanchez (I. C. Sanchez, J. Cho and W. J. Chen, Macromolecules, 1993, 26, 4234). The surface tension c results show that both PEGÈPPGÈPEG and PPG are surface active, leading to a strong decrease of c with respect to that of water even for very low polymer concentrations. The behaviour of the spinodal pressure of the system is discussed in terms of the compressibility and the surface tension data.