The present invention provides methods for purifying polymers. In each embodiment of the invention disclosed herein, a supercritical fluid is contacted with an organic solution that includes a polymer to be purified dissolved in an organic solvent. The supercritical fluid extracts the organic solvent from the organic solution. Impurities such as residual monomers and process solvents are removed with the organic solvent and supercritical fluid, thereby purifying the polymer. The methods of the invention are particularly suitable for use in the purification of biodegradable polymers for use in pharmaceutical applications.