A new apparatus has been built to measure transport and thermodynamic properties in polymer-solvent systems using a pressure decay sorption technique. The equipment has been constructed and has been used to obtain preliminary data on molten polypropylene with supercritical isobutane and carbon dioxide. A model has been developed to describe the experiment. This model has been solved using an explicit finite difference technique and has been used in conjunction with the experimental data to extract both diffusivities and solubilities.