Abstract: A method for drying porous ultrafiltration membranes by the use of heat and possibly also at reduced pressure is characterized in that prior to the application of heat the pores of the membranes are at least partially filled with a solution of a water-soluble organic solid which swells the membranes and which has a melting point above 35.degree. C. in an organic solvent which is completely miscible with water and which does not change the membrane structure.

Abstract: Selectively permeable asymmetric membranes are disclosed which are suitable for use in hemodialysis processes and the like. The membranes are produced from hydrophobic and hydrophilic polymers, and include a three-layered structure including a first dense thin skin layer which includes uniform pores of a size whereby proteins having a molecular weight of at least that of albumin are substantially rejected therefrom, an intermediate second layer in the form of a sponge and having a higher diffusive permeability than the first layer, and a third layer with a finger-like structure which provides mechanical stability. These membranes are preferably formed in the shape of hollow fibers, with the first layer as the inner layer thereof.

Abstract: A membrane for hemodialysis is prepared by casting, extruding or spinning a solution of a polyether-polycarbonate block copolymer and a swelling agent having a molecular weight of about 1,000 to about 20,000 Daltons, then partially evaporating the solvent, gelling and washing. The membrane has a top cut-off value less than about 68,000 Daltons, and hence is substantially impermeable to albumin, but nonetheless provides high permeability to water and to other small molecules.

Abstract: Processes for producing semipermeable membranes in the form of hollow fibers are disclosed including extruding a solution of a block copolymer including at least one hydrophilic polymer and at least one hydrophobic polymer while simultaneously injecting a gaseous or vaporous center medium into the center bore of the hollow fiber extrudate, including coagulating the extrudate so formed therefrom. The preferred process includes using air or the components of air as the center medium and employing a polyethyleneoxide-polycarbonate block copolymer to form the hollow fiber membranes.

Abstract: Plasmapheresis membranes of hydrophilic polycarbonates are disclosed, comprising polycondensates of bisphenol A and a polyalkylene oxide. These membranes which have a regular pore structure with smoothly rounded pores with openings without sharp edges, have an average pore diameter of about 0.01 to 0.8.mu., a porosity preferably above 65%, and a thickness of between about 50 and 300.mu.. Processes for preparing these membranes are also disclosed, including casting a 3 to 20 weight percent polycarbonate polymer solution onto a smooth surface, contacting the layer with a gelling medium prior to precipitation of the membrane, and subsequent precipitation of the gelled layer to form the membrane.