High pressure density, miscibility and compressibility of poly(lactide-co-glycolide) solutions in acetone and acetone + CO2 binary fluid mixtures

High pressure density, miscibility and compressibility of poly(lactide-co-glycolide) (PLGA) solutions in acetone and in acetone + CO2 mixtures were determined at 75, 100, 125 and 150 °C at pressures up to 400 bar. The experiments were carried out in a special variable-volume view-cell system which permits continuous real-time monitoring of the pressure, temperature, transmitted light intensity, and the position of a movable piston which allows continuous determination of the cell internal volume and, thus the solution density, as pressure is altered. The liquid–liquid (LL) phase boundaries are assessed from the variation of transmitted light intensity with pressure while the liquid–vapor (LV) or liquid–liquid–vapor (LLV) phase boundaries are assessed from the variation of density with pressure as, upon formation of vapor phase, the density shows an abrupt decrease and varies without a further change in pressure. Isothermal compressibilities are also evaluated from the variation of density with pressure by generating functional correlations of density with pressure. Data are reported for the PLGA:acetone:CO2 compositions with the ratios (in wt%) of 0:89:11, 5:84.5:10.5, 10:85:5, 10:80:10 and 10:90:0. The observations of phase boundaries, densities and the compressibilities are discussed in terms of the effect of varying the polymer concentration while maintaining the CO2:acetone ratio the same, or by varying the CO2:acetone ratio and maintaining the polymer concentration unchanged. These LL boundaries display lower solution temperature (LCST) behavior, and the densities and compressibilities display the complexities of the relative extent of the association of carbon dioxide with polymer versus acetone.

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► Continuous density data as a function of pressure are reported for PLGA–acetone–CO2 solutions.
► The LL and LLV boundaries have been determined.
► LL phase separation is shown to be LCST type.
► The effect of association of CO2 with PLGA vs. acetone on the density and compressibility of the solutions is discussed.