Preferential evaporation of precipitants from polymer solutions in mixed solvents

Partial vapor pressures were measured for the volatiles of solutions of pol ysulfone or polyethersulfone in mixtures of N,N-dimethylformamide (DMF, sol vent) and water or acetone (precipitants) by means of headspace gas chromat ography. The results demonstrate that the enrichment of water in the gas ph ase increases exponentially with rising polymer concentration, in contrast to that of acetone which remains constant. The reinforced expulsion of wate r resulting from the presence of polymers is theoretically conceivable and should be useful in the field of separation techniques.