EQUATION OF STATE OF HYDROGEN-BONDED POLYMER-SOLUTIONS - POLY(PROPYLENE GLYCOL) PLUS N-HEXANE AND POLY(PROPYLENE GLYCOL) PLUS ETHANOL

We have measured the equation of state surface over the whole composit ion range for the mixtures poly(propylene glycol) + ethanol and poly(p ropylene glycol) + n-hexane up to 40 MPa. The excess volume for the sy stem with ethanol is negative, decreasing in magnitude with increasing pressure. For the system with n-hexane, the excess volume becomes pos itive at high pressure and presents a complex shape with two changes i n curvature along the composition axis. The p-rho-T data obey a superp osition principle that makes it possible to build a master curve once the p-rho-T surface is known at a given pressure. The master curve dep ends on a single system-dependent parameter. The results have been ana lyzed with a lattice fluid model. The inclusion of hydrogen bond contr ibutions in the model does not improve the prediction of the p-rho-T d ata for the system with n-hexane, while it makes a significant contrib ution in the system with ethanol, especially in ethanol-rich mixtures.