Hydrophilic filter membrane with pendant hydrophilic groups, and related methods of preparation and use

Abstract

To provide: hydrophilic polymers (including in the form of a filter membrane that includes hydrophilic polymer) having pendant ionic groups; methods of making the hydrophilic polymer with pendant ionic groups and derivative membranes and filters; and a method of using the filter membranes for filtering a fluid such as a liquid chemical to remove unwanted material from the fluid.SOLUTION: A porous polymeric filter membrane includes a hydrophilic polymer that includes: a polymer backbone; pendant hydrophilic groups selected from hydroxyl groups, amine groups, carboxylic groups, or a combination thereof; and pendant ionic groups that are different from the pendent hydrophilic groups.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The following description relates to a porous polymer filter membrane containing a hydrophilic polymer having pendant ionic groups, a method for producing the filter membrane and a filter including such a filter membrane, and a method for removing unwanted substances from a fluid using the filter membrane for filtering a fluid such as a chemical solution.

Background Art

[0002] Filter products are used to remove unwanted substances from the flow of useful fluids and are essential instruments in modern industries. Useful fluids processed using filters include water, liquid industrial solvents and process fluids, industrial gases used in manufacturing or processing (e.g., in semiconductor manufacturing), and medical or pharmaceutical liquids. Unwanted substances removed from the fluid include impurities and contaminants such as particles, microorganisms, and dissolved chemical species. Specific examples of filter applications include use in liquid substances for the manufacture of semiconductors and microelectronic devices.

[0003] To perform the filtering function, a filter includes a filter membrane that serves to remove unwanted substances from the fluid passing through the filter membrane. The filter membrane may, if necessary, be in the form of a flat sheet, which sheet may be wound (e.g., spirally), and may be flat, pleated, or disk-shaped. Alternatively, the filter membrane may be in the form of hollow fibers. The filter membrane can be housed or supported within a housing such that the fluid to be filtered enters through the inlet of the filter and necessarily passes through the filter membrane before passing through the outlet of the filter.

[0004] The filter membrane can be constructed with a porous structure having an average pore size that can be selected based on the use of the filter, i.e., the type of filtration performed by the filter. Typically, the pore size is in the micron or sub-micron range, for example, from about 0.001 microns to about 10 microns. Membranes having an average pore size of from about 0.001 to about 0.05 microns may be classified as ultrafiltration membranes. Membranes having a pore size between about 0.05 microns and about 10 microns may be referred to as microporous membranes.

[0005] Filter membranes having a pore size in the micron or sub-micron range can be effective for removing unwanted substances from fluid flow by either a sieving mechanism or a non-sieving mechanism, or both. The sieving mechanism is a form of filtration that removes particles from the liquid flow by mechanically retaining the particles on the surface of the filter membrane, which acts to mechanically impede the movement of the particles, retain the particles within the filter, and mechanically impede the flow of particles through the filter. Typically, the particles may be larger than the pores of the filter. The "non-sieving" filtration mechanism is a form of filtration in which the filter membrane retains suspended particles or dissolved substances contained in the fluid flow through the filter membrane by means other than mechanical means, for example, including an electrostatic mechanism in which fine particles or dissolved impurities are electrostatically attracted and retained on the filter surface and removed from the fluid flow. The particles may be dissolved or may be solids having a particle size smaller than the pores of the filter medium.

[0006] Removing ionic substances such as dissolved anions or cations from a solution is important in many industries such as the microelectronics industry where very low concentrations of ionic contaminants and particles can affect the quality and performance of microprocessors and memory devices. Dissolved ionic substances can be removed by passing them through a microporous filter membrane made of a polymeric material that attracts the dissolved ionic substances via a non-sieving filtration mechanism. Examples of such microporous membranes include those made from chemically inert, low surface energy polymers such as ultrahigh molecular weight polyethylene ("UPE"), polytetrafluoroethylene, nylon, and the like. Nylon filter membranes are specifically used in various different filtration applications in the semiconductor processing industry due to the ability to form nylon into a filter membrane with high permeability and the good non-sieving filtration behavior of nylon.

Summary of the Invention

[0007] Filtration membranes made of hydrophilic polymers such as nylon are used in various filtration applications in the semiconductor and microelectronics industries. Nylon can be formed into a filtration membrane that exhibits high permeability, hydrophilicity, and good non-sieving filtration performance. Nylon polymers have inherent surface charges that depend on the type of nylon and contribute to the non-sieving filtration characteristics of the nylon polymer. If additional charge functionality can be added to the membrane while minimizing the overall flow characteristics and loss of filtration characteristics to the membrane, the non-sieving filtration characteristics of hydrophilic polymers such as nylon can be improved.

[0008] One common form of modifying the surface of a polymer is to graft functional (ionic) groups onto the polymer surface. However, techniques for grafting ionic charge groups onto polymers are not necessarily effective for grafting onto all types of polymers. Many grafting techniques use a hydrophobic photoinitiator. For grafting functional groups onto a polymer having a hydrophobic surface, such as polyethylene, the use of a hydrophobic photoinitiator can function well. For other polymers, especially polymers such as nylon that exhibit a hydrophilic surface, these techniques are not very effective even if useful.

[0009] This specification discloses a new technique for grafting ionic groups onto hydrophilic polymers. This technique involves applying a hydrophobic photoinitiator to the surface of a hydrophilic polymer in solution, optionally followed by a drying step, and then re-wetting the surface with a monomer solution. These techniques can reliably attach a relatively high level of photoinitiator to the surface of the hydrophilic polymer. The level of photoinitiator presented on the surface is useful or advantageously high in terms of making the hydrophilic polymer (as part of a filter membrane) effective as a filter membrane and is sufficient for grafting charged monomers onto the hydrophilic surface. The step of chemically bonding ionic groups to the hydrophilic polymer of the filter membrane has no substantial effect on the amount of fluid (flow rate or flux) that can pass through the filter membrane. That is, the amount of fluid (speed or flow rate) that can pass through the filter membrane is not substantially adversely affected by chemically adding ionic groups to the filter membrane. At the same time, the filtration performance of the filter membrane, particularly the non-sieving filtration performance evaluated by dye binding ability, particle retention rate, and metal ion removal rate, can be significantly improved.

[0010] In one aspect, a porous polymer filter membrane comprises a hydrophilic polymer including a polymer backbone, a pendant hydrophilic group selected from a hydroxyl group, an amine group, a carboxylic acid group, or a combination thereof, and a pendant ionic group different from the pendant hydrophilic group.

[0011] In another aspect, a method for grafting ionic groups onto a hydrophilic polymer is disclosed. The method includes contacting a hydrophilic polymer with a photoinitiator solution containing a solvent and a photoinitiator to dispose the photoinitiator on the surface of the hydrophilic polymer, contacting the surface with a monomer solution containing a charged monomer containing an ionic group after disposing the photoinitiator on the surface by contacting the surface with the photoinitiator solution, and exposing the surface to electromagnetic radiation such that the ionic groups are grafted onto the hydrophilic polymer.

[0012] A method for preparing a porous polymer filter membrane includes a hydrophilic polymer having grafted ionic groups. The method includes contacting the membrane with a photoinitiator solution containing a solvent and a photoinitiator to dispose the photoinitiator on the surface of the membrane, contacting the surface with a monomer solution containing a charged monomer containing an ionic group after disposing the photoinitiator on the surface by contacting the surface with the photoinitiator solution, and exposing the surface to electromagnetic radiation such that the ionic groups are grafted onto the hydrophilic polymer.

Brief Description of the Drawings

[0013]

Figure 1

Modes for Carrying Out the Invention

[0014] The following description relates to a novel and inventive method for chemically bonding, i.e., “grafting,” ionic groups onto a hydrophilic polymer, a hydrophilic polymer material containing pendant ionic groups, a filter membrane, a filter member, and a filter containing such a hydrophilic polymer material, and a method for removing unwanted substances from a fluid using a filter membrane or a filter member for filtering the fluid.

[0015] The Applicant has determined that there are certain specific technical problems associated with chemically bonding charged ("ionic") chemical groups to hydrophilic polymers by means of a certain chemical grafting technique that involves the use of photoinitiators. Many of these techniques involve contacting the polymer surface with a solution containing a charged reactive compound (e.g., a "charged monomer") and a photoinitiator, and then exposing the polymer and the solution to electromagnetic radiation. The charged monomer includes a reactive moiety (e.g., an unsaturated moiety) and a charged chemical group that chemically bonds to the polymer. When the solution containing the charged monomer, the polymer, and the photoinitiator is exposed to radiation, the photoinitiator initiates a chemical reaction between the unsaturated moiety and the hydrophilic polymer. By that reaction, the unsaturated moiety is chemically bonded to the polymer, i.e., "grafted" to the polymer.

[0016] The ionic group can be any group. The pendant ionic group is different from the pendant hydrophilic group. In certain embodiments where the hydrophilic polymer is included in a filter membrane, the ionic group can be effective for improving the filtration performance of the filter membrane, particularly the non-sieving filtration performance of the filter membrane. Examples of ionic groups that can be included in the described hydrophilic polymers, particularly hydrophilic polymers included in filter membranes, include cationic nitrogen-containing ionic groups, anionic sulfur-containing ionic groups, and anionic phosphorus-containing ionic groups, examples of which include their chemical counterparts (e.g., salts or acids). As a specific example, the pendant ionic group can be a cationic nitrogen-containing cyclic aromatic group, a cationic imidazole or a cationic amine, or an anionic phosphonic acid group or an anionic sulfonic acid group.

[0017] When using these techniques to bond charged monomers to hydrophilic polymers, there are certain specific technical problems. Conventional photoinitiators (e.g., benzophenone and benzophenone derivatives) are hydrophobic and are not essentially attracted to the hydrophilic surface of the hydrophilic polymer. The resulting problem is to place an effective amount of the hydrophobic photoinitiator on the surface of the hydrophilic polymer.

[0018] This specification discloses a new technique capable of chemically bonding, i.e., grafting, a charged monomer to a hydrophilic polymer or an article made from a hydrophilic polymer (including but not limited to a porous filter membrane). This technique generally involves disposing a photoinitiator on the surface of the hydrophilic polymer, then disposing the charged monomer on that surface, and then exposing the photoinitiator and the charged monomer present on the surface of the hydrophilic polymer to radiation. The radiation initiates a reaction between the unsaturated moiety and the hydrophilic polymer in the photoinitiator, whereby the unsaturated moiety is chemically bonded, i.e., "grafted", to the polymer, and as a result, the resulting hydrophilic polymer contains charged (ionic) chemical groups chemically bonded to the hydrophilic polymer via covalent chemical bonds.

[0019] A more specific example of the method is grafting ionic groups onto a porous filter membrane (e.g., a hydrophilic porous filter membrane) made to contain a hydrophilic polymer. This method involves chemically bonding the charged chemical groups of the charged monomer to the hydrophilic polymer surface of the filter membrane, preferably including the inner pore surface of the membrane. The method includes contacting the filter membrane with a photoinitiator solution containing a solvent and a photoinitiator to dispose the photoinitiator on the surface including the inner pore surface of the hydrophilic polymer, and optionally removing an excess amount of the photoinitiator solution from the surface, for example, by a rinsing (using water) step, a drying (solvent evaporation) step, or both a rinsing step and a drying step. After contacting the surface with the photoinitiator solution and optionally removing the excess photoinitiator solution from the surface, the charged monomer is disposed on the surface, and the surface (having the photoinitiator and the charged monomer) is exposed to electromagnetic radiation to react the charged monomer with the hydrophilic polymer and chemically bond it to the hydrophilic polymer via covalent chemical bonds, i.e., graft it to the hydrophilic polymer.

[0020] For a certain conventional grafting method, this specification uses a hydrophobic photoinitiator to chemically bond a charged (ionic) chemical group to a hydrophilic polymer. As used herein, the term "hydrophilic" for describing a hydrophilic polymer refers to a polymer that attracts water molecules due to the presence of a sufficient amount of hydrophilic pendant functional groups bonded to the polymer backbone, such as hydroxyl groups (-OH), carboxyl groups (-COOH), amino groups, (-NH 2 ), or similar functional groups bonded to the polymer backbone. In some embodiments, the pendant hydrophilic groups are selected from the group consisting of hydroxyl groups, amine groups, carboxylic acid groups, or combinations thereof. When a hydrophilic polymer is formed on a porous filter membrane, these hydrophilic groups assist in the absorption of water into the porous filter membrane.

[0021] Exemplary hydrophilic polymers are nylon polymers, including polyamide polymers. This is generally understood to include copolymers and terpolymers that typically contain repeating amide groups in the polymer backbone. Generally, nylon resins and polyamide resins include copolymers of diamines and dicarboxylic acids, or homopolymers of lactams and amino acids. Nylons suitable for use in the manufacture of the filter membranes described herein are copolymers of hexamethylenediamine and adipic acid (nylon 66), copolymers of hexamethylenediamine and sebacic acid (nylon 610), homopolymers of polycaprolactam (nylon 6), and copolymers of tetramethylenediamine and adipic acid (nylon 46). Nylon polymers are available in a variety of grades, which vary considerably in molecular weight and other properties within the range of about 15,000 to about 42,000 (number average molecular weight).

[0022] In some embodiments, the polymer or article thereof (e.g., the porous filter membrane) may be made entirely of a hydrophilic polymer or entirely of a nylon polymer, may consist of a hydrophilic polymer such as a nylon polymer, or may consist essentially of a hydrophilic polymer and is not blended with another polymer that is non-hydrophobic or non-nylon. The polymer may not be fluorinated and does not require other types of polymers such as fluoropolymers, perfluoropolymers, polyolefins (e.g., polyethylene, polypropylene), and may be specifically excluded. As used herein, a material that "consists essentially of" a specified component or material is a material that contains the described component or material and other materials in amounts less than a trace, e.g., at least 98, 99, 99.5, 99.9, or 99.99 weight percent of the specified component or material, and any other component or material in an amount of 2, 1, 0.5, 0.1, or 0.01 weight percent or less. Alternatively, if useful or desired, the polymer (or filter membrane or other article) may include an amount of a non-hydrophilic polymer blended with the hydrophilic polymer, e.g., a small amount (less than 50, 40, 30, 20, 10, or 5 weight percent) of a non-hydrophilic monomer.

[0023] According to the described method, the photoinitiator is disposed on the surface of the hydrophilic polymer, e.g., the surface of a porous filter membrane or other article containing the hydrophilic polymer. By suitable techniques, the photoinitiator can be dissolved in a solvent to form a photoinitiator solution, which is then applied to the hydrophilic polymer to dispose the photoinitiator on the surface. The photoinitiator may be dissolved in a liquid solvent that may be water, an organic solvent, or a combination of an organic solvent and water to form a photoinitiator solution. The photoinitiator solution is then contacted with the polymer by any useful method such as spraying, submersion, dipping, adsorption, etc.

[0024] The solvent of the photoinitiator solution can be any solvent effective for dissolving the photoinitiator and delivering the photoinitiator to the surface of the hydrophilic polymer, such as the surface of a hydrophilic porous polymer membrane. For a hydrophilic polymer and a hydrophobic photoinitiator, the solvent should preferably be compatible with each of the two components of the polymer and the photoinitiator in order to effectively bring a large amount of the hydrophobic photoinitiator into good contact with the surface of the hydrophilic polymer, including contact with the internal pores of a filter membrane made of the hydrophilic polymer. To achieve this, the solvent of the exemplified photoinitiator solution described may contain at least some amount of water, but at the same time is a solvent capable of dissolving a useful amount of the photoinitiator. Including water as part of the photoinitiator solvent can be effective for making the solvent more polar and can make the delivery (e.g., precipitation) of the hydrophobic photoinitiator from the solvent to the hydrophilic polymer more efficient. Furthermore, exposing a hydrophilic polymer such as nylon to a more concentrated, e.g., pure organic solvent, may easily cause deformation of the polymer membrane during handling, so water may improve the web handling property of the membrane in the process.

[0025] The term "solvent" refers to any liquid effective for containing a useful amount of dissolved photoinitiator, and the liquid is for carrying the dissolved photoinitiator to the surface of a hydrophilic polymer or an article made to include a hydrophilic polymer, such as the surface of a polymer filter membrane including the internal pore surface. The solvent can include an organic solvent, water, or both. Examples of organic solvents include alcohols, particularly lower alcohols (C1 - C5 alcohols), and isopropanol and methanol are useful examples.

[0026] Exemplary solvents for the photoinitiator solution include blends of organic solvents and water, such as blends of methanol and water or isopropanol and water, i.e., blends of water and lower (C1 - C4) alcohols, consisting of or essentially consisting of these. Combinations of lower alcohols such as isopropanol or methanol with water can be particularly effective for dissolving hydrophobic initiators such as benzophenone (or its derivatives), while at the same time being very effective for wetting the surface of hydrophilic polymers such as the surface of a porous filter membrane made of a hydrophilic polymer (including the internal pore surface). Due to the effectiveness of the above solvent mixture for dissolving hydrophobic photoinitiators (such as benzophenone or its derivatives) and wetting hydrophilic substrates, it is possible to effectively deliver a useful amount of hydrophobic photoinitiator to the surface of hydrophilic polymers including the internal pore surface of a porous hydrophilic filter membrane using the solvent mixture. The relative amounts of the organic solvent (e.g., lower alcohols such as methanol, isopropanol, or mixtures thereof) and water in the solvent may be any effective amount, for example, the ratio of water:organic solvent (weight:weight) may range from 10:90 to 90:10, 20:80 to 80:20, for example, 30:70 to 70:30, or 40:60 to 60:40.

[0027] The photoinitiator can be any photoinitiator that effectively responds to radiation (e.g., ultraviolet light) to initiate the reaction between the reactive groups of the charged monomers described herein and the hydrophilic polymer. Examples include photoinitiators known in the chemical art as "type II" photoinitiators. Known useful examples of type II photoinitiators include benzophenone and benzophenone derivatives.

[0028] The amount of photoinitiator in the photoinitiator solution can be any amount (concentration) that is high enough for the photoinitiator solution to deliver the desired, useful, or maximum amount of photoinitiator to the hydrophilic polymer surface. The application amount and the application method should desirably be sufficient to place an effective amount of photoinitiator on the polymer surface to react a large amount of charged monomer with the polymer surface. The useful amount of photoinitiator in the photoinitiator solution can be, for example, in the range of up to 5 weight percent, such as 0.1 or 0.5 weight percent to 4.5 weight percent, or 1 or 2 weight percent to 3 or 4 weight percent.

[0029] The photoinitiator solution can be applied to the surface of the hydrophilic polymer by any useful technique such as spraying the photoinitiator solution onto the hydrophilic polymer or immersing or dipping the hydrophilic polymer in the photoinitiator solution. Desirably, the entire surface of the article containing the hydrophilic polymer can be contacted with and wetted by the photoinitiator solution, including, for example, all the inner surfaces of a porous filter membrane. If necessary, the application process may include operating on the hydrophilic polymer or the article containing the hydrophilic polymer, for example, by rolling or squeezing a porous filter medium to wet all the surfaces of the porous filter medium. In some embodiments, the photoinitiator solution contains 0.1 to 2 weight percent of benzophenone or a benzophenone derivative, water, and one or more of isopropanol and methanol. In some embodiments, the photoinitiator solution contains 20 to 80 parts by weight of isopropanol and 80 to 20 parts by weight of isopropanol based on 100 parts by weight of the total amount of isopropanol and water.

[0030] Thereafter, if desired, a portion of the photoinitiator solution on the surface of the hydrophilic polymer surface may be removed, but at the same time, an effective amount of the photoinitiator solution is left on the surface. The photoinitiator solution may be present in an amount greater than necessary, and the excess amount may be removed by any one of a number of optional techniques for mechanical removal. Examples of techniques for removing excess photoinitiator solution for a porous filter membrane include dripping, squeezing, wringing, folding, or rolling the filter membrane using mechanical force or pressure such as a roller, rinsing with a spray or a water bath (e.g., using deionized water), or evaporating the solvent from the photoinitiator solution present on the hydrophilic polymer surface by using one or more of an air stream or heat, e.g., a fan or an "air knife" dryer, heat, or a combination thereof.

[0031] By one optional step of removing excess photoinitiator solution, for example, a hydrophilic polymer that is a porous hydrophilic filter membrane and contains a photoinitiator solution in contact with its surface may be rinsed using water, such as deionized water. The rinsing step can be carried out by any useful technique such as spraying the rinsing (e.g., deionized) water onto the hydrophilic polymer or submerging or dipping the hydrophilic polymer in water (e.g., deionized water), whereby at least a portion of the excess photoinitiator solution (including its organic solvent) is removed from the hydrophilic polymer surface. In the rinsing step, the useful amount of photoinitiator to remain on the surface of the hydrophilic polymer should preferably be considered when reducing the amount of solvent from the photoinitiator solution remaining on the hydrophilic polymer surface.

[0032] The rinsing step or the mechanical drying step or both may optionally be carried out, and in an optional further step of removing a part of the photoinitiator solution from the surface of the hydrophilic monomer, the photoinitiator solution is used to treat a hydrophilic polymer (for example, a porous hydrophilic filter membrane) in contact with the surface, and the solvent of the photoinitiator solution is removed by drying the solvent by evaporation, so that an amount of photoinitiator concentrated on the surface of the hydrophilic polymer can be left. This type of drying step for evaporating the solvent of the photoinitiator solution on the surface of the hydrophilic polymer can be carried out by heating the photoinitiator solution, passing a stream of air or another gaseous fluid over the photoinitiator solution, or leaving it for a time effective to evaporate a desired amount of the solvent of the photoinitiator solution under ambient conditions, for example, in air at room temperature, so as to evaporate the solvent from the photoinitiator solution. Desirably, a significant amount of the solvent, such as at least 40, 50, 70, or 90 weight percent of the solvent, can be evaporated and removed from the photoinitiator solution. As a result, the concentrated amount of photoinitiator remains distributed fairly uniformly on the surface of the hydrophilic polymer, preferably over the entire surface including, for example, the pores inside a porous filtration membrane.

[0033] Optionally, if desired, after the drying step, the hydrophilic polymer with the photoinitiator present on the surface may be re-wetted with water, for example, deionized water, by spraying deionized water onto the hydrophilic polymer, by immersing the hydrophilic polymer in deionized water, or by any other technique effective to re-wet the photoinitiator without removing the photoinitiator from the surface of the hydrophilic polymer.

[0034] According to the described method, after arranging the photoinitiator on the surface of the hydrophilic polymer (with an optional drying or wetting step), the next step can be to arrange the charged monomer in combination with the photoinitiator on that surface. The charged monomer can be arranged on the surface where the photoinitiator has been previously arranged by any useful technique, and a useful example is to bring the surface into contact with a monomer solution containing the charged monomer dissolved in a solvent. Specific examples of such techniques include spraying, immersion, dipping, adsorption, etc. After successfully arranging the charged monomer in combination with the photoinitiator on the surface, the surface (having the photoinitiator and the charged monomer) is exposed to radiation to initiate a chemical reaction that chemically bonds the charged monomer to the hydrophilic polymer (via a covalent chemical bond). This process is often chemically referred to as "grafting".

[0035] The charged monomer may be a reactive compound containing a reactive moiety such as an unsaturated moiety (e.g., vinyl, acrylate, methacrylate, etc.) and an ionic moiety that may be anionic or cationic.

[0036] Examples of suitable cationic charged monomers include acrylates, methacrylates, acrylamides, methacrylamides, amines (e.g., primary amines, secondary amines, tertiary amines, and quaternary amines), and vinyl types having the functionality of quaternary ammonium, imidazolium, phosphonium, guanidinium, sulfonium, or pyridinium. Examples of suitable acrylate monomers include 2-(dimethylamino)ethyl acrylate hydrochloride and [2-(acryloyloxy)ethyl]trimethylammonium chloride. Examples of suitable methacrylate monomers include 2-aminoethyl methacrylate hydrochloride, N-(3-aminopropyl)methacrylate hydrochloride, 2-(dimethylamino)ethyl methacrylate hydrochloride, [3-(methacryloylamino)propyl]trimethylammonium chloride solution, and [2-(methacryloyloxy)ethyl]trimethylammonium chloride. Examples of suitable acrylamide monomers include acrylamidopropyltrimethylammonium chloride. Examples of suitable methacrylamide monomers include 2-aminoethyl methacrylamide hydrochloride, N-(2-aminoethyl)methacrylamide hydrochloride, and N-(3-aminopropyl)-methacrylamide hydrochloride. Other suitable monomers include diallyldimethylammonium chloride, allylamine hydrochloride, vinylimidazolium hydrochloride, vinylpyridinium hydrochloride, and vinylbenzyltrimethylammonium chloride.

[0037] Suitable anionic monomers include acrylates, methacrylates, acrylamides, methacrylamides, and vinyl types having the functionality of sulfonic acid, carboxylic acid, phosphonic acid, or phosphoric acid. Examples of suitable acrylate monomers include 2-ethylacrylic acid, acrylic acid, 2-carboxyethyl acrylate, 3-sulfopropyl acrylate potassium salt, 2-propylacrylic acid, and 2-(trifluoromethyl)acrylic acid. Examples of suitable methacrylate monomers include methacrylic acid, sodium 2-methyl-2-propene-1-sulfonate, mono-2-(methacryloyloxy)ethyl maleate, and 3-sulfopropyl methacrylate potassium salt. An example of a suitable acrylamide monomer is 2-acrylamido-2-methyl-1-propanesulfonic acid. An example of a suitable methacrylamide monomer is 3-methacrylamidophenylboronic acid. Other suitable monomers include vinylsulfonic acid (or sodium vinylsulfonate), and vinylphosphonic acid (and its salts).

[0038] Other suitable monomers are N-(hydroxymethyl)acrylamide (HMAD), (3-acrylamidopropyl)trimethylammonium chloride (APTAC), and (vinylbenzyl)trimethylammonium chloride (VBTAC).

[0039] The type of solvent used in the monomer solution can be any that is effective for dissolving the monomer solution and delivering a useful amount of the charged monomer to the surface of the hydrophilic polymer. Suitable solvents for the monomer solution are water or water with an organic solvent added. The solvent can contain an organic solvent, water, or both. Examples of organic solvents include alcohols, particularly lower alcohols (C1-C5 alcohols), and useful examples are isopropanol, methanol, and hexylene glycol. The particular solvent used for a specific process, monomer solution, and charged monomer can be based on factors such as the type and amount of the charged monomer in the monomer solution, the type of hydrophilic polymer, and other factors. In a solvent containing both water and an organic solvent, the organic solvent can be included in any amount, for example, in an amount less than 90, 75, 50, 40, 30, 20, or 10 weight percent. As an example, a useful solvent composition can contain 1 to 10 weight percent of hexylene glycol in water.

[0040] The amount of charged monomer in the monomer solution can be any amount (concentration) that is sufficiently high to deliver the desired, useful, or maximum amount of charged monomer to the hydrophilic polymer surface. The amount of the monomer solution, the concentration of the charged monomer in the monomer solution, and the method used to apply the monomer solution to the hydrophilic polymer should be sufficient to place an effective amount of charged monomer on the polymer surface to react a desirable amount of charged monomer with the hydrophilic polymer surface. A useful amount of monomer in the monomer solution can range, for example, up to 5 or 10 weight percent, such as 0.5 to 5 weight percent, or 1 or 2 weight percent to 3 or 4 weight percent. In some embodiments, the charged monomer includes vinylimidazole, 2-acrylamido-2-methylpropanesulfonic acid, (3-acrylamidopropyl) trimethylammonium chloride, vinylsulfonic acid, vinylphosphonic acid, acrylic acid, (vinylbenzyl) trimethylammonium chloride, or polydiallyldimethylammonium chloride. In some embodiments, the monomer solution includes 0.5 to 10 weight percent charged monomer dissolved in 90 to 99.5 weight percent deionized water, based on the total weight of the monomer solution.

[0041] After the monomer solution has been effectively delivered to the surface of the hydrophilic polymer (including a photoinitiator pre-disposed thereon), the hydrophilic polymer (having the photoinitiator and the charged monomer on its surface) is typically exposed to ultraviolet electromagnetic radiation in the spectrum, or another energy source effective to initiate a chemical reaction in the photoinitiator, and the reactive portion of the charged monomer reacts with the hydrophilic polymer by that chemical reaction and chemically (covalently) bonds to the hydrophilic polymer.

[0042] The amount of ionic groups capable of binding to the hydrophilic polymer is described in terms of the amount of reactive monomers chemically bound to the hydrophilic monomer or the filter medium containing the hydrophilic monomer, but can be any useful amount, for example, an amount effective for enhancing the non-sieving filtration function of the hydrophilic filter membrane to which the ionic groups are bound. Preferably, the presence and amount of pendant ionic groups do not have a substantial or unacceptable level of detrimental effect on other properties of the filter membrane, such as flow characteristics.

[0043] For example, articles or compositions containing such a polymer, such as a hydrophilic polymer to which ionic groups are chemically bound by using a grafting technique involving a photoinitiator, or a filter membrane made of this polymer, may contain (although preferably in very small amounts) an analytically detectable (residual) amount of the photoinitiator.

[0044] In various examples of the methods and apparatuses herein, the hydrophilic polymer can be included in a porous filter membrane. As used herein, a "porous filter membrane" is a porous solid containing a porous (e.g., microporous) connecting pathway extending from one surface of the membrane to the opposite surface of the membrane. The pathway generally provides a tortuous tunnel or passage through which the liquid to be filtered is to pass. All particles larger than the pores contained in this liquid are prevented from entering the microporous membrane or are trapped within the pores of the microporous membrane (i.e., removed by a sieving-type filtration mechanism) when the fluid containing the particles passes through the microporous membrane. Particles smaller than the pores may also be trapped or absorbed in the pore structure and removed, for example, by a non-sieving filtration mechanism. The liquid and a reduced amount of particles or dissolved substances, to the extent possible, pass through the microporous membrane.

[0045] The exemplary porous polymer filter membranes described herein (which can be considered either before or after the step of grafting ionic groups onto its surface) can be characterized by physical properties including pore size, bubble point, and porosity.

[0046] The porous polymer filter membrane may have any pore size that enables the filter membrane to function as a filter membrane. For example, it may include pores of a size (average pore size) that may be regarded as a microporous polymer filter membrane or an ultrafiltration membrane as described herein. Examples of useful or suitable porous membranes can have an average pore size in the range of about 0.001 microns to about 1 or 2 microns, for example, 0.01 to 0.8 microns, and the pore size is selected based on one or more factors including the particle size or type of impurities to be removed, the requirements of pressure and pressure drop, and the viscosity requirements of the liquid being treated by the filter. The ultrafiltration membrane can have an average pore size in the range of 0.001 microns to about 0.05 microns. The pore size is often reported as the average pore size of the porous material, which can be measured by known techniques such as Mercury Porosimetry (MP), Scanning Electron Microscopy (SEM), Liquid Displacement (LLDP), or Atomic Force Microscopy (AFM).

[0047] The bubble point is also a known property of the porous membrane. By the bubble point test method, a sample of the porous polymer filter membrane is immersed and wetted in a liquid with a known surface tension, and a gas pressure is applied to one side of the sample. The gas pressure is gradually increased. The minimum pressure at which gas flows through the sample is called the bubble point. Useful bubble points for useful or suitable porous polymer filter membranes according to this specification can be in the range of 2 to 400 psi, for example, 20 to 200 psi, when measured using hydrofluoroether (HFE) 7200 at a temperature of 20 to 25 degrees Celsius. In some embodiments, the bubble point may be within the range of 5 to 200 psi when measured using HFE 7200 at a temperature of 20 to 25 degrees Celsius.

[0048] The described porous polymer filter layer may have any porosity that effectively makes the porous polymer filter layer as described herein. Exemplary porous polymer filter layers can have a relatively high porosity, such as at least 60, 70, or 80 percent porosity. As used herein, and in the technical field of porous bodies, the "porosity" (sometimes referred to as the void fraction) of a porous body is a measure of the void (i.e., "empty") space within the object as a percentage of the total volume of the object, and is calculated as the volume fraction of the voids of the object relative to the total volume of the object. An object with 0 percent porosity is completely solid.

[0049] The described porous polymer filter membrane can be in the form of a sheet or hollow fiber having any useful thickness, such as a thickness in the range of 5 to 100 microns, such as 10 or 20 microns to 50 or 80 microns.

[0050] The described filter membrane can be useful for filtering a liquid to remove undesirable substances (such as contaminants or impurities) from the liquid to produce a high-purity liquid for use as a material in industrial processes. The filter membrane can be useful for removing dissolved or suspended contaminants or impurities from the liquid flowing through the coated filter membrane by either a sieving mechanism or a non-sieving mechanism, preferably by combining both mechanisms of non-sieving and sieving. The hydrophilic filter membrane itself (before the ionic groups are attached) may exhibit effective sieving and non-sieving filtration characteristics, as well as desired flow characteristics. The same hydrophilic filter membrane further comprising the chemically bonded pendant ionic groups described can exhibit equivalent sieving filtration characteristics, useful or equivalent (not overly decreased) flow characteristics, and improved (e.g., substantially improved) non-sieving filtration characteristics.

[0051] The filter membranes of the present specification can be useful in any type of industrial process that requires a high-purity liquid substance as an input. Non-limiting examples of such processes include processes for preparing microelectronic devices or semiconductor devices, and specific examples thereof include methods of filtering liquid process substances (such as solvents or solvent-containing liquids) used in semiconductor photolithography. Examples of contaminants present in process liquids or solvents used for preparing microelectronic devices or semiconductor devices may include metal ions dissolved in the liquid, solid fine particles suspended in the liquid, and gelled or coagulated substances present in the liquid (such as those generated during photolithography).

[0052] Specific examples of the described filter membranes include those that can be used, for example, to filter liquid solvents or other process liquids used in semiconductor photolithography methods, or to purify chemical solutions or useful chemical solutions used in semiconductor or microelectronic manufacturing applications. Some specific, non-limiting examples of solvents that can be filtered using the described filter membranes include n-butyl acetate (nBA), isopropyl alcohol (IPA), 2-ethoxyethyl acetate (2-EEA), xylene, cyclohexanone, ethyl lactate, methyl isobutyl carbinol (MIBC), methyl isobutyl ketone (MIBK), isoamyl acetate, undecane, propylene glycol methyl ether (PGME), and propylene glycol monomethyl ether acetate (PGMEA). The exemplified filter membranes described contain solvents that contain water, amines, or both, such as NH 4OH, tetramethyl ammonia hydroxide (TMAH), and equivalent solutions, etc., may be effective for removing metals from bases and aqueous bases that may contain water in some cases. In some embodiments, tetramethylammonium hydroxide (TMAH) or NH 4 A liquid containing a solvent selected from OH passes through a filter having the membrane described herein to remove metals from the solvent. In some embodiments, when a solvent-containing liquid is passed through a membrane to remove metals from the solvent-containing liquid, the concentration of metals in the solvent-containing liquid is reduced.

[0053] The described filter membrane containing pendent ionic groups chemically bonded to a hydrophilic polymer can also be characterized in terms of the dye-binding ability of the filter membrane. Specifically, a charged dye can be bound to the surface of the filtration membrane. The amount of dye that can bind to the filtration membrane can be quantitatively evaluated based on the difference in the absorption readings of the membrane measured at the absorption frequency of the dye by spectroscopy. The dye-binding ability can be calculated by using a negatively charged dye or a positively charged dye. According to the described preferred filter membrane, a filter membrane made using a hydrophilic polymer with pendent ionic groups as described can have a dye-binding ability for positively charged dyes, negatively charged dyes, or both, and the dye-binding ability is greater than that of an equivalent filter membrane containing the same hydrophilic filter membrane but no pendent ionic groups. That is, a filter membrane made using a hydrophilic polymer without pendent ionic groups has a lower (e.g., significantly less) dye-binding ability than the same filter membrane containing a hydrophilic polymer with pendent ionic groups as described.

[0054] A coated filter membrane made using a hydrophilic polymer with pendent ionic groups has at least 1 microgram per square centimeter (μg / cm 2 ), for example 1, or 10, 20, or 50 μg / cm 2It may have the ability to bind dyes to larger methylene blue dyes. Alternatively, or additionally, the described coated filter membrane has at least 1 μg / cm 2 , for example, 1, 10, 20, or 50 μg / cm 2 and may have the ability to bind dyes to Ponceau S dyes exceeding this amount.

[0055] Alternatively, or additionally, the dye-binding ability of the filter membrane of the present specification can be evaluated in terms of being improved compared to an equivalent filter membrane made using a hydrophilic polymer that is the same except for not containing the pendant ionic groups described herein. The exemplary filter membranes of the present invention can exhibit a dye-binding ability that is at least 10, 25, 50, or 100 percent improved compared to the dye-binding ability of the same hydrophilic filter membrane without pendant ionic groups. That is, a filter membrane made using a hydrophilic polymer and containing the described pendant ionic groups has a greater (e.g., significantly greater) dye-binding ability, for example, at least 10, 25, 50, or 100 percent greater dye-binding ability, compared to the same filter membrane (in terms of pore size, porosity, thickness, etc.) made using the same hydrophilic polymer but without ionic pendants from that hydrophilic polymer.

[0056] The particle retention rate can be evaluated by assessing the number of test particles removed from the fluid stream by a membrane placed in the fluid stream. In one method, a sufficient supply aqueous solution of 0.1% Triton X-100 containing 8 ppm of polystyrene particles (0.025 μm green fluorescent polymer microspheres, available from ThermoFisher SCIENTIFIC) is passed through the membrane at a constant flow rate of 7 milliliters per minute to achieve monolayer coating rates of 0.5, 1, and 2%, and the permeate is collected to evaluate the particle retention rate. The concentration of polystyrene particles in the permeate can be calculated from the absorbance of the permeate. Then, the particle retention rate is calculated using the following formula. TIFF2025081341000002.tif16170

[0057] In a preferred embodiment of the described composite membrane, the composite membrane can exhibit a retention rate exceeding 90% for monolayer coating rates of 0.5%, 1.0%, 1.5%, and 2.0%, and can also exceed 95% for monolayer coating rates of 0.5% and 1.0%. By having this level of retention rate, these examples of the composite membrane of the present invention exhibit a higher retention rate level compared to many currently commercially available filter membranes, such as flat sheets and hollow fiber equivalent filter membranes made of UPE. These exemplary composite membranes also enable useful, good, or very good flow rates (low flow times) and exhibit mechanical properties that allow the composite membrane to be assembled into a filter cartridge or filter product.

[0058] Furthermore, the described filter membrane can be characterized by the flow velocity or flux of the liquid flowing through the filter membrane. The flow velocity must be high enough so that the filter membrane is efficient and effective in filtering the flow of the fluid through the filter membrane. The flow velocity, or alternatively the resistance to the flow of the liquid through the filter membrane considered, can be evaluated in terms of the flow velocity or flow time (the reciprocal of the flow velocity). The filter membranes described herein containing a hydrophilic polymer with pendant ionic groups preferably have a relatively low flow time in combination with a relatively high bubble point and good filtration performance (evaluated, for example, by particle retention rate, dye binding ability, or both). A useful or suitable flow time can be, for example, less than about 6,000 seconds / 500 mL, such as less than about 4,000 or 2,000 seconds / 500 mL.

[0059] The water flow time of the membrane can be determined by cutting the membrane into a 47 mm disc, wetting it with water, and then placing the disc in a filter holder attached to a reservoir for holding a certain amount of water. The reservoir is connected to a pressure regulator. Water flows through the membrane under a differential pressure of 14.2 psi (pounds per square inch). After reaching equilibrium, the time it takes for 500 ml of water to flow through the membrane is recorded.

[0060] Preferably, the flow time of the filter membrane made using a hydrophilic polymer and having the pendant ionic groups described is approximately equal to, and not significantly greater than, the flow time of the same filter membrane that does not contain pendant hydrophilic groups. In other words, having ionic groups in the hydrophilic polymer of the filter membrane does not substantially negatively affect the flow characteristics of the filter membrane, and further, the filtration function of the filter membrane, particularly the non-sieving filtration function of the membrane as evaluated by, for example, dye-binding ability, particle retention rate, or both, can be further improved. According to a preferred filter membrane, the measured flow time of the filter membrane of the present specification containing a hydrophilic polymer and pendant ionic groups can differ (e.g., can be greater) from the flow time of the same hydrophilic polymer without grafted ionic groups by 30 percent or less, for example 20 percent, 10 percent, 5 or 3 percent or less.

[0061] The described filter membrane can be housed in a larger filter structure such as a multilayer filter assembly or a filter cartridge used in a filtration system. In a filtration system, for example, the filter membrane is placed within a filter housing as part of a multilayer filter assembly or as part of a filter cartridge, and the filter membrane is exposed to the flow path of a chemical solution, passing at least a portion of the flow of the chemical solution through the filter membrane, such that the filter membrane removes a certain amount of impurities or contaminants from the chemical solution. The structure of the multilayer filter assembly or filter cartridge can include one or more of various additional materials and structures for supporting the composite filter membrane within the filter assembly or filter cartridge for passing the composite filter membrane when filtering a fluid by flowing the fluid from a filter inlet through the composite membrane (including the filter layer) and through a filter outlet. The filter membrane supported by the filter assembly or filter cartridge can be in any useful form, such as a pleated cylinder, a cylindrical pad, one or more non-pleated (flat) cylindrical sheets, a pleated sheet, etc.

[0062] An example of a filter structure including a pleated cylindrical filter membrane can be prepared to include the following components, any of which may or may not be essential to be included in the filter structure. The components include a rigid or semi-rigid core that supports the pleated cylindrical coated filter membrane at the inner opening of the pleated cylindrical coated filter membrane, a rigid or semi-rigid cage that supports or surrounds the outside of the pleated cylindrical coated filter membrane outside the filter membrane, optional end pieces or "packs" located at each of the two opposing ends of the pleated cylindrical coated filter membrane, and a filter housing including an inlet and an outlet. The filter housing can be of any useful and desired size, shape, and material, and is preferably made from a suitable polymeric material.

[0063] As an example, FIG. 1 shows a filter member 30 that is a product of a pleated cylindrical member 10 and end pieces 22 and other optional members. The cylindrical member 10 includes a filter membrane 12 as described herein and is pleated. The end piece 22 is attached (e.g., "potted") to one end of the cylindrical filter member 10. The end piece 22 can preferably be made from a melt-processable polymeric material. A core (not shown) can be disposed in the inner opening 24 of the pleated cylindrical member 10, and a cage (not shown) can be disposed around the outside of the pleated cylindrical member 10. A second end piece (not shown) can be attached ("potted") to the second end of the pleated cylindrical member 30. Next, the pleated cylindrical member 30 having the two opposing potted ends as well as optional core and cage can be disposed within a filter housing configured such that all of the fluid entering the inlet and exiting the outlet necessarily passes through the filter membrane 12 before exiting the filter at the outlet.

Example

[0064] Example 1 Benzophenone dissolved in a mixture of deionized water and isopropanol for grafting monomers onto nylon In this example, a method of using a 50:50 mixture of deionized water to isopropanol as a solvent for benzophenone during surface modification of nylon is described as being superior to 100% isopropanol.

[0065] A nylon membrane with an HFE average bubble point of 107 psi, a water flow time of 1220 seconds / 500 mL, and a thickness of 165 μm was surface modified using the following two methods. In the first experiment, an unmodified nylon membrane was cut into 47 mm diameter specimens. In step 1, the specimens were immersed in a 100% isopropanol (IPA) solution of 0.5% benzophenone. Then, in step 2, the specimens of the nylon membrane wetted with IPA were immersed in 100% deionized water. Then, in step 3, the deionized water exchange membrane was immersed in a monomer solution to absorb the negatively charged monomer, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), into the membrane. In step 4, the specimens were removed from the monomer solution and immediately placed between two transparent polyethylene sheets and passed through a Fusion Systems broadband UV lamp at a speed of 12 feet per minute. In step 5, the UV-cured membrane specimens were washed with water, washed twice in methanol, and then dried. During this process, the 47 mm nylon specimens were visibly deformed due to the time spent in the benzophenone and isopropanol solutions. In the second experiment, 1.0% benzophenone was dissolved in 49 g of isopropanol and then diluted with 50 g of deionized water. This solution was used to replace the 100% isopropanol solution of 0.5% benzophenone used in step 1 of the first experiment. The remaining steps 2-5 were repeated as in the first experiment. The nylon membrane specimens in the second experiment could be modified without visible deformation.

[0066] Example 2 Nylon surface modified with negatively charged AMPS monomer In this example, the surface modification of a nylon membrane with a negatively charged monomer, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), will be described.

[0067] A negatively charged nylon membrane was generated by surface modification. The surface modification was achieved by covalently grafting a negatively charged monomer, AMPS, onto the membrane surface using a photoinitiator. First, an unmodified nylon membrane similar to that in Example 1 was cut into specimens with a diameter of 47 mm, and then immersed in a 50% isopropanol / 50% deionized aqueous solution of 0.5% benzophenone. Next, the membrane was exchanged in a 100% deionized water solution. Then, the exchanged membrane was immersed in an AMPS monomer solution (Table 1A) to allow the membrane to absorb the monomer solution. The specimen was taken out of the monomer solution and immediately placed between two transparent polyethylene sheets and passed through a Fusion Systems broadband UV lamp at a speed of 12 feet per minute. The UV-cured membrane specimen was washed with water, washed twice in methanol, and then dried. The original membrane's HFE average bubble point was measured to be 107 psi, and its bubble point was not affected by the surface modification. When the percentage increase rate of the flow time due to surface modification was evaluated, it was 14%. Table 1A AMPS monomer solution TIFF2025081341000003.tif18170

[0068] Example 3 Nylon surface modified with a negatively charged VPA monomer In this example, the surface modification of a nylon membrane with a negatively charged monomer, Vinyl Phosphonic Acid (VPA), will be described.

[0069] A negatively charged nylon membrane was generated by surface modification. The surface modification was achieved by covalently grafting a negatively charged monomer, VPA, to the membrane using a photoinitiator. First, an unmodified nylon membrane similar to that of Example 1 was cut into 47-mm diameter specimens, which were then immersed in a 50% isopropanol / 50% deionized aqueous solution of 0.5% benzophenone. Next, the membranes were exchanged in a 100% deionized water solution. Then, the exchanged membranes were immersed in the VPA monomer solution (Table 1B) to allow the monomer solution to be absorbed into the membranes. The specimens were removed from the monomer solution and immediately placed between two transparent polyethylene sheets and passed through a Fusion Systems broadband UV lamp at a rate of 12 feet per minute. The UV-cured membrane specimens were washed with water, washed twice in methanol, and then dried. The HFE average bubble point of the original membrane was measured to be 107 psi, and that bubble point was not affected by the surface modification. When the percent increase in flow time due to the negatively charged surface modification was evaluated, it was 0.0%. Table 1B VPA Monomer Solution TIFF2025081341000004.tif15170

[0070] Example 4 Quantification of the Dye-Binding Ability of the Negatively Charged Nylon Membrane In this example, a method for approximating the degree of negative charge present in the treated porous nylon membrane will be described by evaluating the uptake rate of a positively charged dye molecule, methylene blue.

[0071] This method is used to evaluate the amount of charge imparted to the surface-modified nylon membrane. First, each specimen (e.g., the specimens of Example 2 and Example 3) is wetted again in isopropanol and immediately placed into a 50 mL conical tube containing 50 mL of a diluted (0.00075% weight percentage) methylene blue dye (Sigma Aldrich) supply solution. The tube is capped and rotated for 2 hours. After 2 hours of rotation, the membrane specimen is taken out from the methylene blue solution and placed into a 50 mL conical tube containing 50 mL of 100% isopropanol solution. The tube is capped and rotated for 0.5 hour. After rotation in isopropanol, visually confirm that the membrane specimen is dyed blue, and dry the specimen. Measure the UV absorbance of the diluted methylene blue supply solution and compare it with the UV absorbance of the solution in which the specimen was placed and rotated. By determining the difference in UV absorbance between the rotated solution and the original solution, the final "Dye-Binding Capacity" (DBC) is calculated and expressed in μg / cm 2 This numerical value is an approximation of the level of charged functional groups on the surface of the membrane and correlates with the level of the membrane ion exchange capacity. The DBC of the base nylon for methylene blue is 0.0 μg / cm 2 When determining the DBC of the nylon surface of Example 2 modified with negatively charged AMPS, it was 43.88 μg / cm 2 When determining the DBC of the nylon membrane surface of Example 3 modified with VPA, it was 14.3 μg / cm 2 Example 5

[0072] Example 5 Nylon surface modified with positively charged APTAC monomer In this example, the surface modification of the nylon membrane with the positively charged monomer, (3-acrylamidopropyl) trimethylammonium chloride (APTAC), will be described.

[0073] A positively charged nylon membrane was generated by surface modification. The surface modification was achieved by covalently grafting a positively charged monomer, APTAC, onto the membrane using a photoinitiator. First, an unmodified nylon membrane similar to that in Example 1 was cut into specimens with a diameter of 47 mm, and then immersed in a 50% isopropanol / 50% deionized aqueous solution of 0.5% benzophenone. Next, the membrane was exchanged in a 100% deionized water solution. Then, the exchanged membrane was immersed in an APTAC monomer solution (Table 1C) to allow the monomer solution to be absorbed into the membrane. The specimen was taken out of the monomer solution and immediately placed between two transparent polyethylene sheets and passed through a Fusion Systems broadband UV lamp at a speed of 12 feet per minute. The UV-cured membrane specimen was washed with water, washed twice in methanol, and then dried. The original membrane's HFE average bubble point was measured to be 107 psi, and its bubble point was not affected by the surface modification. When the percent increase rate of the flow time due to the positively charged surface modification was evaluated, it was 13.8%. Table 1C APTAC monomer solution TIFF2025081341000005.tif19170

[0074] Example 6 Nylon surface modified with a positively charged IM monomer In this example, the surface modification of a nylon membrane with a positively charged monomer, 1-vinyl imidazole (IM), will be described.

[0075] A positively charged nylon membrane was generated by surface modification. The surface modification was achieved by covalently grafting a positively charged monomer, IM, onto the membrane using a photoinitiator. First, an unmodified nylon membrane similar to that of Example 1 was cut into specimens with a diameter of 47 mm, and then immersed in a 50% isopropanol / 50% deionized aqueous solution of 0.5% benzophenone. Next, the membrane was exchanged in a solution of 100% deionized water. Then, the exchanged membrane was immersed in an IM monomer solution (Table 1D) to allow the monomer solution to be absorbed into the membrane. The specimen was taken out of the monomer solution and immediately placed between two transparent polyethylene sheets and passed through a Fusion Systems broadband UV lamp at a speed of 12 feet per minute. The UV-cured membrane specimen was washed with water, washed twice in methanol, and then dried. The original membrane's HFE average bubble point was measured to be 107 psi, and its bubble point was not affected by the surface modification. When the percent increase rate of the flow time due to IM surface modification was evaluated, it was 0.0%. Table 1D IM monomer solution TIFF2025081341000006.tif14170

[0076] Example 7 Nylon surface modified by air-dried grafting with positively charged APTAC monomer In this example, the surface modification of a nylon membrane using a positively charged monomer, (3-acrylamidopropyl) trimethylammonium chloride (APTAC), by grafting with an air-dried photoinitiator will be described.

[0077] A positively charged nylon membrane was generated by surface modification. The surface modification was achieved by covalently grafting a positively charged monomer, APTAC, to the membrane using a photoinitiator. First, an unmodified nylon membrane similar to that of Example 1 was cut into specimens with a diameter of 47 mm. Next, the membrane was taken out of the solution and dried at room temperature without moving it. Then, the dried membrane was immersed in the APTAC monomer solution (Table 1E) to suck the monomer solution into the membrane. The specimen was taken out of the monomer solution and immediately placed between two transparent polyethylene sheets and passed through a broadband UV lamp of Fusion Systems at a speed of 12 feet per minute. The UV-cured membrane specimen was washed with water, washed twice in methanol, and then dried. The HFE average bubble point of the original membrane was measured to be 107 psi, and the bubble point was not affected by the surface modification. When the percentage increase rate of the flow time due to the positively charged surface modification was evaluated, it was 1.6%. Table 1E APTAC monomer solution TIFF2025081341000007.tif18170

[0078] Example 8 An alkali-primed nylon surface modified by air-dried grafting with a positively charged APTAC monomer. In this example, the surface modification of an alkali-primed nylon membrane using a positively charged monomer, (3-acrylamidopropyl) trimethylammonium chloride (APTAC), by grafting with an air-dried photoinitiator will be described.

[0079] A positively charged nylon membrane was generated by surface modification. The surface modification was achieved by covalently grafting a positively charged monomer, APTAC, to the membrane using a photoinitiator. First, an unmodified nylon membrane similar to that of Example 1 was cut into specimens with a diameter of 47 mm, and then immersed in a solution of deionized water (DIW) adjusted to pH 11 with 1 M sodium hydroxide. Then, the membrane was taken out of the solution and dried at room temperature without moving. Next, the membrane was immersed in a 50% isopropanol / 50% deionized water solution of 0.5% benzophenone. Then, the membrane was taken out of the solution and dried at room temperature without moving. Next, the dried membrane was immersed in an APTAC monomer solution (Table 1F) to suck the monomer solution into the membrane. The specimen was taken out of the monomer solution and immediately placed between two transparent polyethylene sheets and passed through a Fusion Systems broadband UV lamp at a speed of 12 feet per minute. The UV-cured membrane specimen was washed with water, washed twice in methanol, and then dried. The original membrane's HFE average bubble point was measured to be 107 psi, and its bubble point was not affected by the surface modification. When the percentage increase rate of the flow time due to the positively charged surface modification was evaluated, it was 9.4%. Table 1F APTAC monomer solution TIFF2025081341000008.tif19170

[0080] Example 9 Quantification of the dye-binding ability of the positively charged nylon membrane In this example, a method for approximating the degree of positive charge present in the treated porous nylon membrane by evaluating the uptake rate of a negatively charged dye molecule, Ponceau S, will be described.

[0081] This method is used to evaluate the amount of charge imparted to a surface-modified nylon membrane. First, each specimen (e.g., specimens of Examples 5, 6, 7, and 8) is soaked again in isopropanol and immediately placed into a 50 mL conical tube containing 50 mL of a diluted (0.005% weight percentage) Ponceau S red dye (Sigma Aldrich) supply solution, the tube is capped, and rotated for 2 hours. After 2 hours of rotation, the membrane specimen is removed from the Ponceau S solution and placed into a 50 mL conical tube containing 50 mL of 100% isopropanol solution, the tube is capped, and rotated for 0.5 hour. After rotation in isopropanol, visually confirm that the membrane specimen has been dyed red and dry the specimen. Measure the UV absorbance of the Ponceau S supply solution and compare it with the UV absorbance of the solution in which the specimen was placed and rotated. By determining the difference in UV absorbance between the solution in which it was rotated and the original solution, the final "Dye-Binding Capacity" (DBC) is calculated and expressed in μg / cm 2 This numerical value is an approximation of the level of charged functional groups on the surface of the membrane and correlates with the level of the membrane's ion exchange capacity. The DBC of Ponceau S for a nylon-based membrane is 34.5 μg / cm 2 When the DBC of a nylon surface modified with positively charged APTAC was determined, it was 48.90 μg / cm 2 When the DBC of a nylon surface modified with positively charged APTAC and using an air-dried photoinitiator was determined, it was 47.44 μg / cm 2 When the DBC of a nylon surface modified with positively charged APTAC, alkali priming, and a dried photoinitiator was determined, it was 62.32 μg / cm 2 When the DBC of a nylon surface modified with IM was determined, it was 99.61 μg / cm 2 It was as follows.

[0082] Example 10 Quantification of the Filter Retention Rate of G25 Beads for Nylon Membranes, Negatively Charged Nylon Membranes, and Positively Charged Membranes In the following examples, it is demonstrated that the retention characteristics of the membrane can be maintained or improved by additionally introducing charged functional groups onto the nylon membrane.

[0083] For a nylon membrane, a nylon membrane modified with negative charges using the same method as in Example 2, and a nylon membrane modified with positive charges using the same method as in Example 5, the filter retention rate of G25 beads (0.025 μm green fluorescent polymer microspheres, Fluoro-Max) was determined. A supply solution of 8 ppb G25 beads using 0.1% Triton-X (Sigma) was prepared in deionized water and the pH was adjusted to 10.6. Nylon membrane specimens were cut and the membranes were fixed to 47 mm filter assemblies. The membrane assemblies containing the nylon membranes were flushed with deionized water and then flushed with a 0.1% aqueous solution of Triton-X in deionized water adjusted to pH 10.6. The solution prepared with G25 and Triton-X at pH 10.6 was filtered through the membranes at monolayer calculated bead loadings of 0.5, 1, and 2%, and the filtrates were collected. The collected filtrate samples were compared with the 8 ppb G25 bead 0.1% Triton-X supply solution by calculating the G25 bead concentration using a fluorescence spectrophotometer. The percent removal rate for various monolayers of the membrane can be calculated. The nylon membrane modified with positive charges showed an improved G25 bead retention rate when compared to the unmodified nylon membrane. The results are shown in Table 1H, retention rates (%) for monolayer 0.5, 1, and 2 of the metal removal rate in water. Table 1G Filter Retention Rate of G25 Beads TIFF2025081341000009.tif31170

[0084] Example 11 Quantification of Metal Removal Rates in DIW Using the Original Nylon Membrane and the Negatively Charged Nylon Membrane In the following examples, it is demonstrated that the metal removal characteristics of the membrane can be improved by additionally introducing negatively charged functional groups onto the nylon membrane.

[0085] A negatively charged nylon membrane was prepared using the same method as in Example 2 and cut into a plurality of 47 mm membrane specimens. These membrane specimens were washed several times with 0.35% HCl and then conditioned by immersion in 0.35% HCl overnight and equilibrated with deionized water. For each sample, one 47 mm membrane specimen was fixed to a clean PFA 47 mm single stage filter assembly (Single Stage Filter Assembly, Savillex). The membrane and filter assembly were flushed with DIW. An aqueous metal standard (SCP Science) containing 21 metals was added to DIW to achieve a target concentration of 5 ppb for each metal. To determine the filtration metal removal efficiency, the metal-added DIW was passed through each filter-containing corresponding 47 mm filter assembly at 10 mL / min, and the filtrate was collected in a clean PFA bottle at 100 mL. The metal concentrations of the metal-added DIW and filtrate samples were determined using inductively coupled plasma mass spectrometry (ICP-MS). The results are shown in Table 1H, the metal removal rate (%) of the metal removal rate in water. Table 1H Metal removal rate in water JPEG2025081341000010.jpg122170

[0086] In a first aspect, the porous polymer filter membrane comprises a hydrophilic polymer comprising a polymer backbone, a pendant hydrophilic group selected from the group consisting of a hydroxyl group, an amine group, a carboxylic acid group, and combinations thereof, and a pendant ionic group different from the pendant hydrophilic group.

[0087] A second aspect according to the first aspect, wherein the pendant ionic group is effective to improve the non-separation filtration performance of the filter membrane as compared to a filter membrane that is otherwise the same except that it does not contain the pendant ionic group.

[0088] A third aspect according to the first or second aspect, wherein the polymer backbone is a polyamide.

[0089] The fourth aspect according to any one of the first to third aspects, wherein the ionic group is a cationic nitrogen-containing group, an anionic sulfur-containing group, or an anionic phosphorus-containing group.

[0090] The fifth aspect according to any one of the first to fourth aspects, wherein the ionic group is a cationic nitrogen-containing cyclic aromatic group.

[0091] The sixth aspect according to any one of the first to fourth aspects, wherein the ionic group is a cationic imidazole or a cationic amine.

[0092] The seventh aspect according to any one of the first to fourth aspects, wherein the ionic group is an anionic phosphonic acid or an anionic sulfonic acid.

[0093] The eighth aspect according to any one of the first to seventh aspects, further comprising a residual photoinitiator.

[0094] The ninth aspect according to any one of the first to eighth aspects, wherein the porous polymer filter membrane has a porosity of at least 60 percent.

[0095] The tenth aspect according to any one of the first to ninth aspects, wherein the porous polymer filter membrane has a pore diameter in the range of 0.001 to 1.0 micron.

[0096] In the eleventh aspect, the filter cartridge includes the membrane according to any one of the first to tenth aspects.

[0097] In the twelfth aspect, the filter includes the membrane according to any one of the first to tenth aspects.

[0098] In the thirteenth aspect, a method of using the filter membrane according to any one of the first to tenth aspects includes passing a solvent-containing liquid through the membrane.

[0099] In a 14th aspect, a method of grafting an ionic group onto a hydrophilic polymer includes contacting the hydrophilic polymer with a photoinitiator solution containing a solvent and a photoinitiator to dispose the photoinitiator on the surface of the hydrophilic polymer; after disposing the photoinitiator on the surface by contacting the surface with the photoinitiator solution, contacting the surface with a monomer solution containing a charged monomer; and exposing the surface to electromagnetic radiation to graft the ionic group onto the hydrophilic polymer, wherein the charged monomer contains an ionic group.

[0100] A 15th aspect according to the 14th aspect, wherein the hydrophilic polymer is a porous polymer filter membrane.

[0101] A 16th aspect according to the 14th or 15th aspect, wherein the solvent contains an organic solvent and water.

[0102] A 17th aspect according to any one of the 14th to 16th aspects, including at least partially drying the surface by evaporation of the solvent after contacting the surface with the photoinitiator solution, and contacting the membrane with the monomer solution after at least partially drying the photoinitiator solution.

[0103] A 18th aspect according to any one of the 14th to 17th aspects, wherein the photoinitiator is benzophenone or a benzophenone derivative.

[0104] A 19th aspect according to any one of the 14th to 18th aspects, wherein the photoinitiator solution contains 0.1 to 2 weight percent of benzophenone or a benzophenone derivative, and the photoinitiator solution contains water and one or more of isopropanol and methanol.

[0105] A 20th aspect according to any one of the 14th to 19th aspects, wherein the charged monomer contains vinyl imidazole, 2-acrylamido-2-methylpropanesulfonic acid, (3-acrylamidopropyl) trimethylammonium chloride, vinylsulfonic acid, vinylphosphonic acid, acrylic acid, (vinylbenzyl) trimethylammonium chloride, or polydiallyldimethylammonium chloride.

Claims

1. 1. A porous polymer filter membrane comprising: A hydrophilic polymer, A polymer backbone; pendant hydrophilic groups selected from the group consisting of hydroxyl groups, amine groups, carboxylic acid groups, or combinations thereof; a pendant ionic group different from the pendant hydrophilic group; A hydrophilic polymer comprising 1. A porous polymeric filter membrane comprising:

2. 10. The filter membrane of claim 1, wherein the pendent ionic groups are effective to improve the non-sieving filtration performance of the filter membrane over an otherwise identical filter membrane that does not include the pendent ionic groups.

3. 3. The filter membrane of claim 1 or 2, wherein the polymer backbone is a polyamide.

4. 4. The filter membrane of claim 1, wherein the ionic group is a cationic nitrogen-containing group, an anionic sulfur-containing group, or an anionic phosphorus-containing group.

5. 5. The filter membrane of claim 1, wherein the ionic group is a cationic nitrogen-containing cyclic aromatic group.

6. 5. The filter membrane of claim 1, wherein the ionic group is a cationic imidazole or a cationic amine.

7. 5. The filter membrane according to claim 1, wherein the ionic group is an anionic phosphonic acid or an anionic sulfonic acid.

8. 8. The film of claim 1 further comprising a residual photoinitiator.

9. 9. The membrane of any of claims 1 to 8, wherein the porous polymeric filter membrane has a porosity of at least 60 percent.

10. 10. The membrane of any of claims 1 to 9, wherein the porous polymeric filter membrane has a pore size in the range of 0.001 to 1.0 microns.

11. A filter cartridge comprising the membrane of any one of claims 1 to 10.

12. A filter comprising a membrane according to any one of claims 1 to 10.

13. 11. A method of using a filter membrane according to any one of claims 1 to 10, comprising passing a solvent-containing liquid through the membrane.

14. A method for grafting ionic groups onto a hydrophilic polymer, comprising the steps of: contacting the hydrophilic polymer with a photoinitiator solution comprising a solvent and a photoinitiator to dispose a photoinitiator on a surface of the hydrophilic polymer; contacting the surface with a photoinitiator solution to dispose a photoinitiator on the surface, and then contacting the surface with a monomer solution that includes a charged monomer; exposing the surface to electromagnetic radiation to graft ionic groups onto the hydrophilic polymer; Including, The method wherein the charged monomer comprises an ionic group.

15. The method of claim 14, wherein the hydrophilic polymer is a porous polymeric filter membrane.

16. 16. The method of claim 14 or 15, wherein the solvent comprises an organic solvent and water.

17. 17. A method according to any one of claims 14 to 16, comprising: After contacting the surface with the photoinitiator solution, at least partially drying the surface by evaporation of the solvent; contacting the film with a monomer solution after at least partially drying the photoinitiator solution; The method includes:

18. 18. The method of any of claims 14 to 17, wherein the photoinitiator is benzophenone or a benzophenone derivative.

19. 19. The method of any of claims 14 to 18, wherein the photoinitiator solution comprises 0.1 to 2 weight percent benzophenone or a benzophenone derivative, and the photoinitiator solution comprises water and one or more of isopropanol and methanol.

20. 20. The method of any of claims 14 to 19, wherein the charged monomer comprises vinylimidazole, 2-acrylamido-2-methylpropanesulfonic acid, (3-acrylamidopropyl)trimethylammonium chloride, vinylsulfonic acid, vinylphosphonic acid, acrylic acid, (vinylbenzyl)trimethylammonium chloride, or polydiallyldimethylammonium chloride.

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