The application of liquid-liquid separation as a means of polymer-solvent separation was studied. Phase separation experiments were performed with ethene-propene-diene terpolymer (EPDM) solved in hexane, using propene as an antisolvent. The results were interpreted using a thermodynamic model based on the Sako-Wu-Prausnitz (SWP) equation of state. The description of homogeneous polymers is unambiguous, but for heterogeneous polymers further development of the SWP theory is required. It was found that the model shows promising results with respect to multicomponent polymer systems. However, the description of the interaction between the components is still unsatisfactory. Therefore, an empirical model was developed to describe the experimental results. A flowsheet model was constructed to describe a novel EPDM process containing a liquid-liquid countercurrent extraction column. The effects of temperature, pressure, antisolvent concentration, and number of theoretical equilibrium stages were studied. With respect to variable costs, liquid-liquid extraction is a cost-effective option in the purification of rubber polymer solutions.