Swelling, melting point reduction and solubility of PEG 1500 in supercritical CO2.

The knowledge of the solubility of PEG 1500 as well as the swelling and melting point variation in supercritical CO(2) in a relatively high-pressure range is a necessary prerequisite to set-up pharmaceutical processes dealing with the polymer in the molten state. Experiments carried out in a pressurized view cell indicated that the PEG 1500 progressively decreases its melting point and increases its volume as a consequence of the absorption of the CO(2). The melting point depression was pronounced (from 46 to 28 degrees C) up to 8.7 MPa. Thereafter a constant value was attained. Analogously, under CO(2) the polymer increased its volume (about 34%) until 10 MPa; after this pressure, the polymer volume no longer increased. PEG 1500 showed solubility in SC-CO(2) at 35 and 55 degrees C in the 10-40 MPa range in the order of 10(-6)mole fraction. An empirical model based on solubility parameters was used to fit the experimental data and to predict the maximum concentration achievable by the polymer in the dense gas, as well as to quantify the polymer concentration at low pressures where the experimental determination may be extremely difficult.