Method of purifying a polymeric material of a type which includes (A) phenyl moieties; (B) carbonyl and/or sulphone moieties; and; (C) ether and/or thioether moieties. The method includes contacting the polymeric material with a solvent formulation which is at a temperature of greater than 100.degree. C. and a pressure above ambient pressure thereby to charge the solvent formulation with impurities derived from the polymeric material, and separating the charged solvent from the polymeric material.