Evidence of ternary interaction parameters for polymer solutions in mixed solvents from headspace-gas chromatography

Partial vapor pressures of the volatiles have been measured for four solven t/precipitant/polymer systems at different temperatures. The high molecular weight compounds were polysulfone or polyethersulfone and the mixed solven t was either DMF/acetone or DMF/water. Systems containing the very powerful precipitant water exhibit a special phenomenon: Upon the addition of polym er to a mixed solvent of constant composition the partial vapor pressure of water increases by a factor of more than two before it falls to zero as th e volume fraction of the polymer approaches unity. This particular situatio n cannot be modeled using binary interaction parameters only, in contrast t o the results obtained with acetone as the precipitant. The present finding s are used to discuss the necessity of ternary interaction parameters and p ossibilities for their calculation from known binary interaction parameters . (C) 2000 Elsevier Science Ltd. All rights reserved.