Abstract: This invention relates to porous polyfluoroethylene (PTFE), shaped articles prepared therefrom, and to methods of preparing said articles.

Abstract: The present invention relates to a process for forming a foamed elastomeric polymer. The process involves forming a reverse emulsion of liquid droplets in a continuous liquid phase of polymer precursor and then polymerizing the precursor to entrap uniformly distributed droplets of the liquid in pores formed in the polymer bulk. The liquid in the pores is then removed under supercritical conditions.

Abstract: A structure of a microporous resin bonded to metal is prepared by a method, comprising, molding a resin composition comprising a polymer alloy consisting of polyether imide and polyphenylene ether and particles of aluminum borate or amorphous silica filler, wherein the particles of aluminum borate and amorphous silica have an aspect ratio of 10 or less and an average diameter of 0.01-100 .mu.m, the aluminum borate having the formula: nAl.sub.2 O.sub.3.mB.sub.2 O.sub.3, wherein n and m individually represent an integer of 1-100, and the amorphous silica having the formula: SiO.sub.2, into a shaped object, treating the molded resin composition with an aqueous alkaline solution to remove the filler, thereby creating micropores within the resin object, and depositing a metal film on a surface of the treated resin object.

Abstract: The present invention relates to porous crosslinked polymeric microbeads having cavities joined by interconnecting pores wherein at least some of the cavities at the interior of each microbead communicate with the surface of the microbead. The present invention also relates to a process for producing a porous, crosslinked polymeric microbead as well as the product of this process. This process involves combining an oil phase with an aqueous discontinuous phase to form an emulsion, adding the emulsion to an aqueous suspension medium to form an oil-in-water suspension of dispersed emulsion droplets, and polymerizing the emulsion droplets to form microbeads. At least 10% of the microbeads produced in accordance with the present invention are substantially spherical or substantially ellipsoidal or a combination of the two.

Abstract: The present invention relates to a process for forming a foamed elastomeric polymer. The process involves forming a reverse emulsion of liquid droplets in a continuous liquid phase of polymer precursor and then polymerizing the precursor to entrap uniformly distributed droplets of the liquid in pores formed in the polymer bulk. The liquid in the pores is then removed under supercritical conditions.

Abstract: Scaffold bodies and methods for their fabrication are disclosed, and, more particularly, fabrication of scaffold bodies by freeze-drying emulsion of polymer solutions are disclosed.

Abstract: This invention relates to porous polyfluoroethylene (PTFE), shaped articles prepared therefrom, and to methods of preparing said articles.

Abstract: A polymeric reticulated structure is prepared by mixing an ethylene-propylene copolymer having an ethylene content of at least 60% by weight or a thermoplastic block copolymer terminated with a crystalline ethylene block with a low molecular weight material. The low molecular weight material is trapped in the three-dimensional continuous network the copolymer forms.

Abstract: A coating powder consisting essentially of generally spherical particles ranging in size from less than 2 to about 40 microns, 75% of whose volume consists of particles of from about 2 to about 20 microns in size, is provided by dissolving the components of the coating powder in a supercritical fluid without the aid of a surfactant and spraying the solution into a zone whose pressure is less than that of the fluid. A very smooth continuous film of a cured thermosettable coating powder is achieved even when the film thickness is less than 1 mil, e.g., from about 0.2 and greater. The advantages of powder coatings may now be realized fully in the automobile and can industries.

Abstract: A novel processing technique is reported to bond non-woven fibers and, thus, prepare structural interconnecting fiber networks with different shapes for organ implants. The fibers are physically joined without any surface or bulk modification and have their initial diameter.

Abstract: A hydrophilic polymer alloy which has a permanent hydrophilic nature, a sufficient mechanical strength and a high safety and which is suitable for the formation of hydrophilic porous membranes manufacturable by an industrially advantageous process can be prepared by blending an amorphous hydrophilic copolymer (X) containing 10 mole % or more of an ethylene unit, 10 to 60 mole % of a vinyl alcohol unit and 1 mole % or more of a vinyl acetate unit with a polyolefin (Y). Furthermore, this polymer alloy is also suitable for the formation of hydrophilic (porous) fibers having a sufficient mechanical strength and antistatic function.

Abstract: A polymeric foam with continuous, open-cell pores containing living cells suitable for medical applications and methods for preparing these foams. The microporous foams are of controlled pore size that may be utilized in a variety of applications. In general, the foams are characterized in that the pores are continuous and open-celled. In preparing the foams, an organic polymer is melted and combined with a selected solid crystalline fugitive compound, that melts above about 25.degree. C. and/or that sublimates at above about 25.degree. C. or can be extracted, to produce a substantially isotropic solution. The solution is cooled under controlled conditions to produce a foam precursor containing the solidified fugitive composition dispersed through a matrix of the organic polymer. Crystals of fugitive composition are then removed by solvent extraction and/or sublimation, or a like process to produce microcellular foams having a continuous, open-cell structure.

Abstract: Biaxially oriented films from high molecular weight polyethylene are characterized by a gas permeable structure formed from random-arranged microfibrils. The films have coefficients of static friction and kinetic friction of not more than 1.0. The biaxially oriented films are further characterized by service smoothness as well as tensile (tangent) modulus and tensile strength. The films may be used for lamination, filter, or for packaging for moisture absorbers. The biaxially oriented films may be obtained by extracting a hydrocarbon plasticizer from a sheet formed from the high molecular weight polyethylene and a hydrocarbon plasticizer, stretching the resulting sheet to obtain an oriented film having a specific surface area of at least 70 m.sup.2 /g and a fibril structure, and heating the oriented film under a standard length constraint to reduce the oriented film in specific area by at least 20 m.sup.2 /g.

Abstract: The present invention is embodied in a method of producing a ceramic foam. The steps for producing the ceramic foam include first mixing a liquid pre-ceramic resin with a liquid phenolic resin, second allowing the resultant mixture to chemically foam, third curing the mixture for a time and at a temperature sufficiently to convert the mixture to a polymeric foam, and then heating the resultant polymeric foam for a time and at a temperature sufficiently to completely break-down polymers of the polymeric foam and convert the polymeric foam to a ceramic foam.

Abstract: Condensation polymerization followed by a supercritical extraction step can be used to obtain highly cross-linked nanoporous polymers with high surface area, controlled pore sizes and rigid structural integrity. The invention polymers are useful for applications requiring separation membranes.

Abstract: The present invention relates to porous crosslinked polymeric microbeads having cavities joined by interconnecting pores wherein at least some of the cavities at the interior of each microbead communicate with the surface of the microbead. Approximately 10% of the microbeads of the present invention are substantially spherical or substantially ellipsoid or a combination of the two. The present invention also relates to a process for producing a porous, crosslinked polymeric microbead as well as the product of this process. This process involves combining a continuous phase with an aqueous discontinuous phase to form an emulsion, adding the emulsion to an aqueous suspension medium to form an oil-in-water suspension of dispersed emulsion droplets, and polymerizing the emulsion droplets to form microbeads. Also included in the invention are modifications of the microbeads as well as methods for using the microbeads in a variety of applications.

Abstract: The invention provides a method for producing a microcellular foam of a curable material by replicating a dissolvable particle preform and leaching away the dissolvable particle preform to yield the microcellular foam. The foam can be a preceramic polymer microcellular foam which can be pyrolyzed to form a ceramic microcellular foam. A method for making a composite including steps of producing a ceramic microcellular foam which is subsequently infiltrated to form the composite is also provided as are microcellular foams, ceramic microcellular foams and composites prepared according to the method of the invention.

Abstract: The sol-gel polymerization of a phenolic-furfural mixture in dilute solution leads to a highly cross-linked network that can be supercritically dried to form a high surface area foam. These porous materials have cell/pore sizes .ltoreq.1000.ANG., and although they are dark brown in color, they can be classified as a new type of aerogel. The phenolic-furfural aerogel can be pyrolyzed in an inert atmosphere at 1050.degree. C. to produce carbon aerogels. This new aerogel may be used for thermal insulation, chromatographic packing, water filtration, ion-exchange, and carbon electrodes for energy storage devices, such as batteries and double-layer capacitors.

Abstract: Described is a continuous process for removing polyphosphoric acid from a polybenzazole dope filament, which comprises: (a) contacting the dope filament with water or a mixture of water and polyphosphoric acid under conditions sufficient to reduce the phosphorous content of the filament to less than about 10,000 ppm by weight; and then (b) contacting the dope filament with an aqueous solution of an inorganic base under conditions sufficient to convert at least about 50 percent of the polyphosphoric acid groups present in the filament to a salt of the base and the acid. It has been discovered that contacting the dope filament with a solution of a base after washing the filament to remove most of the residual phosphorous advantageously leads to an improvement in the initial tensile strength of the filament, as well as improved retention of tensile strength and/or molecular weight (of the polybenzazole polymer) following exposure to light and/or high temperatures.

Abstract: A novel processing technique is reported to bond non-woven fibers and, thus, prepare structural interconnecting fiber networks with different shapes for organ implants. The fibers are physically joined without any surface or bulk modification and have their initial diameter.

Abstract: A device for preventing adhesions or binding of tissue to tissue or of tissue to bone which comprises a composite of a first layer and a second layer, each of which comprises a biodegradable polymer. The first layer is selected from the group consisting of a non-porous layer and a porous layer having a pore size no greater than 3.mu.. The second layer has pores which have a pore size of from about 30.mu. to about 250.mu.. Such a composite device provides for tissue growth into the second layer, while the first layer acts as an adhesion-preventing barrier, and enables attachment of the device to tissue without suturing. Alternatively, the device comprises the first layer hereinabove mentioned and a second layer which is an adherence layer and which adheres to tissue and/or bone.

Abstract: A process for forming biocompatible porous matrices of bioabsorbable materials comprising:a) providing a bioabsorbable polymer;b) dissolving the bioabsorbable polymer in a volumetric orientation aid to yield a molten solution;c) solidifying the molten solution to yield an orientation matrix comprising first and second phases, the first phase being the bioabsorbable polymer and the second phase being the volumetric orientation aid; andd) removing the volumetric orientation aid while the solution is solid; to yield a biocompatible matrix of bioabsorbable polymer. Also matrices formed by the process and devices made with such matrices.

Abstract: A process for preparing high internal phase emulsions (HIPE) that can be polymerized to provide flexible, microporous, open-celled polymeric foam materials capable of absorbing aqueous fluids, especially aqueous body fluids such as urine. The HIPE is prepared using certain polyglycerol aliphatic ether emulsifiers that are less chemically complex and variable in composition than many prior HIPE emulsifiers, have higher levels of the desired interfacially active components, and have lower levels of components (e.g., sludge) that are insoluble or insufficiently soluble in the oil phase used to prepare the HIPE. These polyglycerol aliphatic ether emulsifiers provide HIPE having relatively uniform sized water droplets dispersed in the continuous oil phase.

Abstract: The sol-gel polymerization of a phenolic-furfural mixture in dilute solution leads to a highly cross-linked network that can be supercritically dried to form a high surface area foam. These porous materials have cell/pore sizes.ltoreq.1000.ANG., and although they are dark brown in color, they can be classified as a new type of aerogel. The phenolic-furfural aerogel can be pyrolyzed in an inert atmosphere at 1050.degree. C. to produce carbon aerogels. This new aerogel may be used for thermal insulation, chromatographic packing, water filtration, ion-exchange, and carbon electrodes for energy storage devices, such as batteries and double-layer capacitors.

Abstract: A blend of high-molecular and a low-molecular organic material contains the high-molecular organic material in a proportion smaller than that of the low-molecular organic material, and has a three-dimensionally continuous network skeleton structure formed by the high-molecular organic material. The structure preferably has an average cell or mesh diameter not exceeding 500 microns. The removal of the low-molecular organic material from the blend gives a functional porous material consisting of the high-molecular organic material. The replacement of the low-molecular organic material in the blend with a solid or liquid, or a mixture thereof, gives a functional composite material containing the solid or liquid, or their mixture in the network skeleton structure.

Abstract: Porous polymeric structures are provided along with a method to make such structures comprising heat-induced phase separation of a polymeric solution exhibiting a lower critical solution temperature.

Abstract: A method for making a particulate filled polymeric matrix composite film includes mixing a polymeric matrix material with a dispersion of particulate filler in a carrier liquid to form a casting composition and adjusting the viscosity of the casting composition to retard separation of the particulate filler from the composition. A layer of the viscosity-adjusted casting composition is cast on a substrate and the layer is consolidated to form the particulate filled polymer matrix composite film. Films made by the method include very thin, e.g less than 1.0 mil, fluoropolymeric matrix films highly filled with very small diameter, preferably spherical, particles for use as, e.g. dielectric substrate materials in laminar electrical circuits.

Abstract: A process of fabricating a porous silicone product utilizing a silicone emulsion capable of forming an elastomer by removal of water therefrom. The silicone emulsion comprises a water emulsion of an organopolysiloxane, a cross-linking agent, and a curing catalyst. The process comprises the steps of freezing the silicone emulsion, and drying the frozen silicone emulsion, whereby water is sublimed therefrom and the porous silicone product is obtained. The resulting porous silicone product is best utilized as a selective permeable membrane for separation of a liquid component from a liquid solution containing two or more liquid components.

Abstract: Biofoam is a rigid, microcellular organic foam made from organic materials derived from natural products and biological organisms. Starting materials include agar, agarose, gelatin, algin, alginates, gellan gum, and microcrystalline cellulose. The organic material is dissolved in a polar solvent, typically water, and the mixture is gelled. The water in the gel pores is replaced at least once with another solvent to reduce the pore size of the final biofoam. The solvent in the gel pores may be replaced several times. After the final replacement of solvent, the gel is frozen and freeze-dried to form a biofoam. Translucent biofoams are formed by selecting a final solvent that forms very small crystals. A variety of crystalline, fibrous, amorphous, or metallic additives may be incorporated into the foam structure to produce lightweight composite materials with enhanced strength and insulating properties.

Abstract: A process for preparation of latex of a hollow polymer which comprises adding a base, in the presence of a monomer, to latex containing carboxy-modified copolymer particles to make the pH of the latex 8 or more; adding a carboxyl group-containing monomer to make the pH of the latex 7 or less; and then polymerizing these monomers.

Abstract: Aqueous coating compositions for forming elastomeric films around active cores (e.g., drugs) comprising a dispersion of pre-crosslinked polyorganosiloxane latex particles, colloidal silica particles, and a water-dispersible organic material (e.g., polyethylene glycol) are disclosed and claimed. The elastomeric films formed by the coating compositions are used to control the rate of release of an active agent in the cores into an aqueous environment. Methods of formulating the coating compositions and active cores coated with the coating compositions are also disclosed.

Abstract: A method of making liquid toner for electrophotographic imaging by forming a mixture of a polyamide polymer, a good solvent therefor and a particulate pigment, heating the polymer/pigment/solvent mixture to form a solution thereof, cooling the resulting solution to precipitate fine polymer-encapsulated pigment particles of generally uniform size and morphology, removing the precipitated particles, removing the solvent and redispersing the resulting particles in dispersant medium along with a charge-control agent to form the liquid toner. A steric stabilizer can be added to the polymer-encapsulated pigment particle dispersion.

Abstract: Normally hydrophobic foams, such as polyurethane foams and polymerized water-in-oil emulsion foams, are rendered hydrophilic by means of treatment with simple surfactants and hydrophilizing agent salts. Thus, a surfactant-containing foam is treated with a solution of, for example, calcium chloride, and is dried to leave a substantially uniformly distributed residue of hydrated or hydratable calcium chloride on the surfactant-containing internal foam surfaces. In-use, the combination of surfactant and calcium chloride hydrate provides a hydrophilic surface to the foam. Other hydratable calcium or magnesium salts such as magnesium chloride can be used. The resulting hydrophilized foams are suitable for use in absorbent devices, including diapers, sanitary napkins, bandages, and the like.

Abstract: Stable high internal phase water-in-oil emulsions containing polymerizable vinyl monomers, crosslinking monomers and polymerization initiators are obtained by using saccharide fatty acid esters as surfactants. The amount of surfactants necessary to form stable high internal phase water-in-oil emulsions is decreased by using saccharide fatty acid esters as surfactants. Further, hydrophobic foams can be obtained by using saccharide fatty acid esters.

Abstract: A lightweight absorbent foam is produced using a high internal phase emulsion (HIPE), the production of which incorporates the use of capillary viscosity measurements as an in-line diagnostic for HIPE quality. The in-line diagnostics yield measurements of viscosity slope and amplitude. These measurements offer several advantages for monitoring emulsion quality, including stable high resolution measurement of hardware-independent parameters of the whole flow, without the need for sampling.

Abstract: A polyamide fiber comprised of (A) a thermoplastic aliphatic polyamide having copolymerized therein a polyalkylene oxide unit and having a melting point of at least 160.degree. C., and (B) a polyoxyalkylene glycol, wherein the ingredient (B) is finely dispersed in the ingredient (A). A polyamide fiber exhibiting a rate of moisture absorption of at least 3.5%/5 minutes at 25.degree. C. and R.H. 90% and/or a triboelectric voltage of not larger than 1.5 kV at 20.degree. C. and R.H. 40% is obtained by removing the ingredient (B) from the above-mentioned polyamide fiber by means of dissolution.

Abstract: An ultra-lightweight, open-pore foamed cellulose material with an increased surface area, having ion exchangeable functional groups introduced in it. The cellulose material presents a three-dimensional network structure which, upon swollen, has a particle diameter of 0.8 to 12.0 mm, a mean pore diameter of 0.1 to 1.7 mm, a specific surface area of 1.0 to 10.0 m.sup.2 /g, a true density of 1.4 to 1.6 g/cm.sup.3 and a porosity of 90% or greater. The ion exchangeable functional groups, for instance, may be cationic polyethyleneimine.

Abstract: Porous, polymer particles comprising a functionalized cross-linked copolymer having microporous regions and macroporous regions in the polymer matrix thereof, wherein the functional groups are essentially present only within the macroporous regions, as well as processes for preparing these particles based on a template polymerization technique followed by removal of the template polymer from the particles are disclosed. The particles of the invention are useful in chromatography, and in various analytical, diagnostic techniques and solid state peptide, DNA synthesis.

Abstract: A polyamide polymer and one of methanol, ethanol and 2-propanol are formed into a solution by heating at 70 degrees Celsius for approximately two hours, the resulting solution is cooled to precipitate the polymer as particles from said solution. Alternatively, a non-solvent to said polymer may be added to effect precipitation of said polymer particles. The solvent is removed and the particles isolated and dried to form a dry powder. Fine particulate material such as a pigment, may be included with the polymer and solvent in formation of the solution. The resulting solution may be cooled at a rapid rate to precipitate the particles as polymer-encapsulated pigment particles of generally uniform size and morphology, the surface characteristics such as surface area being controlled. The precipitated polymer particles may be classified when dispersed in a dispersant medium, as mono-dispersed particles.

Abstract: An improved asymmetric membrane fashioned from a polyimide for the liquid separation of solvents from lube oil. The membrane is based on a fully imidized polymer based on 5(6)-amino-1-(4'-aminophenyl)-1,3-trimethylindane polymer and benzophenone tetracarboxylic dianhydride.

Abstract: A method for forming fine polymer particles, including core/shell polymer composite particles and polymer-encapsulated liposome particles. A polymer solution is formed using a selective solvent which enables the polymer to be precipitated from the solution upon a change in condition thereof. The change in condition may be effected by lowering of the temperature of the solution and/or introducing a non-solvent to the solution. With respect to the formation of the polymer-encapsulated liposome particles, the liposome particles are included when the polymer solution is formed.

Abstract: A polymeric bead has now been developed to act as a support for other entities having a volume mean diameter of up to 250 microns and having a surface provided with pores which form at least 10% by area of the surface. At least one third of the total area of the pores is provided by pores having a larger size of at least 0.4 micron. A method for the manufacture of such polymeric beads involves using a water-in-oil-in-water emulsion technique in which the amount of water used in the preparation of the aqueous phase is not greater than 125 parts by weight per 265 parts by weight of the mixture of the polyester resin and monomer which is used.The porous beads provide an excellent base for carrying enzymes, bacteria and catalysts species useful in a wide range of applications.

Abstract: Disclosed is a process for the continuous preparation of high internal phase emulsions which are suitable for subsequent polymerization into polymeric foam materials that, upon dewatering, act as absorbents for aqueous body fluids. The process involves continuous introduction of a certain type of monomer-containing oil phase and a certain type of electrolyte-containing water phase into a dynamic mixing zone at relatively low water to oil phase ratios. Flow rates are then steadily adjusted to increase the water to oil ratio of the streams fed to the dynamic mixing zone while subjecting the dynamic mixing zone contents to shear agitation which is sufficient to thereby form a high internal phase emulsion that, upon subsequent polymerization, provides a foam having an average cell size of from about 5 to 100 microns. The formation of such a stable high internal phase emulsion is completed by feeding the contents of the dynamic mixing zone to and through a static mixing zone.

Abstract: A process for the preparation of optionally cellular elastic moldings by the reaction injection molding technique in closed molds, in which isocyanate prepolymers A) based ona) polyisocyanates of the diphenylmethane series andb) polyether polyols having a maximum hydroxyl functionality of 2.4 are reacted with a reactive component B) consisting essentially of aromatic, alkyl-substituted diamines, optionally with the addition of auxiliary agents and additives d).

Abstract: Fine particles of gelatin and amino acid used in the present invention are particularly suitable for use in combination with resins.Gelatin particles used in the present invention have the number-average molecular weight of 8,500 or less, and amino acid particles with the number-average molecular weight of 200 or less, so that efficient pulverization becomes possible and that gelatin and amino acid particles maintain their intrinsic properties as they are not subject to denaturation during pulverization. Resultant particles are neither too large nor too small but are uniform in size and are particularly suitable for use in combination with resins.

Abstract: Disclosed is a process for the continuous preparation of high internal phase emulsions which are suitable for subsequent polymerization into polymeric foam materials that, upon dewatering, act as absorbents for aqueous body fluids. The process involves continuous introduction of a certain type of monomer-containing oil phase and a certain type of electrolyte-containing water phase into a dynamic mixing zone at relatively low water to oil phase ratios. Flow rates are then steadily adjusted to increase the water to oil ratio of the streams fed to the dynamic mixing zone while subjecting the dynamic mixing zone contents to shear agitation which is sufficient to thereby form a high internal phase emulsion that, upon subsequent polymerization, provides a foam having an average cell size of from about 5 to 100 microns. The formation of such a stable high internal phase emulsion is completed by feeding the contents of the dynamic mixing zone to and through a static mixing zone.

Abstract: A method for altering a macroporous cross-linked hydrophobic copolymeric lattice produced by precipitation polymerization in a solvent of at least one monounsaturated ester monomer and at least one polyunsaturated ester monomer soluble therein, in order to render the hydrophobic copolymeric lattice hydrophilic. The method involves saponifying the hydrophobic copolymeric lattice by reacting the surface of the hydrophobic copolymeric lattice with an aqueous alkali. The surface can also be rendered hydrophilic by polymerizing an acrylate monomer onto the lattice in order to form a surface containing carboxylic acid sites. The carboxylic acid sites formed on the surface of the lattice are converted to carboxylate anions.

Abstract: A method to prepare uniform populations of macroscopic beads containing pores of at least 0.1 microns diameter is described. The beads consist essentially of a copolymer of a monoethylenically unsaturated monomer and a crosslinking polyethylenically unsaturated monomer, said resulting copolymer optionally being derivatized with functional groups, linking moieties, and/or affinity ligands. The macroporous beads are obtained by utilizing, as porogen in the polymerization reaction, porous inorganic particles which have been preabsorbed with a blowing agent. The blowing agent is not activated until after the polymerization takes place; when the blowing agent is activated, the organic polymer which isolates the inorganic porogen particles from each other in the bead is destroyed. Upon subsequent dissolution of the inorganic porogen, a network of pores throughout the organic copolymer-formed particle is formed. The resulting beads are useful in a variety of chromatographic, analytical and biomedical techniques.

Abstract: A microporous sheet comprising a polymeric matrix having a liquid insoluble, particulate, activated polysaccharide media dispersed therein; use of the sheet in affinity chromatography or ion-exchange chromatography or as a biochemical reactor or battery separator; processes for manufacturing the sheet; apparatus containing the microporous sheet as its active element; and methods for using such sheet.

Abstract: This invention relates to a process for the preparation of hydrophilic membranes by coagulation of a solution of at least one hydrophobic polymer and at least one hydrophilic polymer in a suitable solvent medium in a coagulation medium. The process according to the invention is characterized in that hydrophilic microfiltration and/or ultrafiltration membranes are prepared by cross-linking the hydrophilic polymer which is present in or on the obtained membrane matrix after the coagulation in an essentially non-swollen state and fixing same as such in or on the polymer matrix. Advantageously the solvents and the undesirable components of the coagulation medium are removed whereby the hydrophilic polymer is converted into an essentially non-swollen state prior to cross-linking. The removal of the undesirable components from the membrane takes place by means of a non-solvent for the hydrophilic polymer according to the invention.