Abstract: Fully aromatic polyamide (aramid) resins can be cast into ultraporous and microporous membranes by forming a solution of the resin in an amount sufficient to cast a coherent membrane, diluting the solution with a liquid pore modifier which is a nonsolvent for the resin so as to produce a metastable dispersion of the resin, adding a precipitant to form a turbid casting dope, casting the dope onto a surface, and gelling the so-cast film.

Abstract: Mono-layer thin film membranes are provided which are ultraporous. Such mono-layers are formed having a thickness on the order of about 1.2 to 150 nanometers, by a variety of polymerization, cross-linking, and film treatment processes to achieve the development of controlled pore sizes in the ultraporous size range corresponding to a molecular weight cutoff values of from about 500 to about 1,000,000. Such thin film mono-layer membranes are ordinarily supported on a microporous support material, desirably a microporous polymer membrane having a smooth, microporous skin with pore sizes in the range of from about 0.1 microns to about 3 microns, preferably from about 0.1 microns to about 0.5 microns, in diameter. There may be an intermediate gel layer. These membranes are useful for ultrafiltration, dialysis, and molecular separations.