The formation of membranes from two systems has been studied. In the system polyurethane-dimethylformamide-water, the mechanism for the formation of the sponge-like structure proves to be a liquid-liquid phase separation with nucleation and growth of the diluted phase. This mechanism has been confirmed for the system modified polystyrene-polyisoprene-polystyrene/o-dichlorobenzene/(methanol-water). Crystallization and gelation is discussed. The membranes prepared showed hyperfiltration activity. The mechanism proposed here is believed to be valid for other systems, too.
Koenhen, D. M., Mulder, M. H. V., & Smolders, C. A. (1977). Phase separation phenomena during the formation of asymmetric membranes. Journal of applied polymer science, 21(1), 199-215. https://doi.org/10.1002/app.1977.070210118