The solubilities of 4,4'-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA), which are the representative monomers for an aromatic polyimide, were measured in supercritical carbon dioxide (scCO(2)) using the semi-batch flow method to clarify the entrainer effect of acetone. The investigations were carried out at 323 K and 20.0 MPa with concentrations of acetone as high as approximately 20 mol%. Although the solubilities of both ODA and PMDA increased with increasing acetone concentrations, the entrainer effects of acetone on both monomer solubilities in scCO(2) were lower than those of N,N-dimethylformamide, which was investigated in previous work. However, the addition of about 10 mol% of acetone increased the solubilities of ODA and PMDA by approximately 10- and 20-fold, respectively, compared with their solubilities in pure scCO(2). Moreover, the solubilities were predicted using the Peng-Robinson equation of state. (C) 2012 Elsevier Ltd. All rights reserved.