STUDIES ON SOLVENT EVAPORATION AND POLYMER PRECIPITATION PERTINENT TO THE FORMATION OF ASYMMETRIC POLYETHERIMIDE MEMBRANES

The characteristics of solvent evaporation and polymer precipitation during the formation of asymmetric aromatic polyetherimide (PEI) membranes via the dry/wet phase inversion method are studied and the results are discussed with reference to membrane preparation. It is shown that the solvent evaporation from the surface of freshly cast films in early evaporation stages can be quantified by an empirical equation with two parameters. Analysis of the evaporation parameters partially explains the interaction effect of membrane preparation variables on membrane performance. The phase separation data for systems PEI/DMAc/H2O and PEI/NMP/H2O with and without LiNO3 additive are determined using the turbidimetric titration method. The kinetic data on solvent-nonsolvent exchange and additive leaching during polymer precipitation in nonsolvent water are measured. The results presented here offer a qualitative basis for the development of asymmetric PEI membranes. (C) 1995 John Wiley and Sons, Inc.