PURPOSE: To efficiently fractionate poly(perfluoroalkyl ether) depending on mol.wt. at low cost by bringing poly(perfluoroalkyl ether) into contact with carbon dioxide to extract and successively exposing the extract to pressures which are decreased stepwise.

CONSTITUTION: The solubility of poly(perfluoroalkyl ether) depending on mol.wt. to carbon dioxide in a supercritical or subcritical state varies with temp. and pressure same as other material. The higher the pressure, or the lower the temp. in a range of about >100kg/cm2, poly(perfluoroalkyl ether) of the higher mol.wt. can be dissolved. By using this property, successive extraction from higher mol.wt. to lower mol.wt. can be performed by successively raising the temp. under constant pressure. When the pressure is successively decreased, sharp fractionation for mol.wt. can be performed by varying the temp. of each extracting tank according to the mol.wt. to be fractionated.