Porous membrane, method for manufacturing a porous membrane, and separation method

Abstract

To provide a porous membrane capable of suitably separating predetermined components from a material to be filtered, a method for manufacturing a porous membrane, and a separation method. [Solution] A porous membrane comprising a porous body and a polymer having a crosslinked structure on the porous body between a first monomer containing a positively charged cationic group and a second monomer containing a pH-responsive anionic group.

Description

[Technical Field]

[0001] The present invention relates to a porous membrane, a method for manufacturing a porous membrane, and a separation method. [Background technology]

[0002] Conventionally, the technology described in Patent Document 1 is known as a porous membrane. Specifically, Patent Document 1 discloses a negatively charged microporous membrane composed of a porous substrate and a cross-linked coating, wherein the cross-linked coating is prepared from a solution containing polysaccharides and an anionic polymer. According to Patent Document 1, this negatively charged microporous membrane is useful for processing fluids containing positively charged species, such as proteins. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 4532748 [Overview of the project] [Problems that the invention aims to solve]

[0004] Regarding the configuration disclosed in Patent Document 1, when filtering a material to be filtered by a microporous membrane and recovering components captured by the microporous membrane, methods such as using a salt concentration gradient to perform ion exchange between the captured components and salt ions, or using a pH gradient to change the charge of the captured components, can be considered. However, when using a salt concentration gradient, there is a concern that impurities such as salt may mix with the captured components, and when using a pH gradient, there is a possibility that the captured components may be degraded. On the other hand, when separating a specific component from a material to be filtered, it is desirable that the operation be carried out quickly. Thus, there is a need for a technology that can suitably separate a specific component from a material to be filtered.

[0005] The present invention is a technology completed based on the above circumstances, and relates to providing a porous membrane capable of suitably separating a predetermined component from a filtered body, a method for manufacturing the porous membrane, and a separation method.

Means for Solving the Problems

[0006] The present invention is a porous membrane including a porous body and a polymer having a crosslinked structure of a first monomer containing a cationic group having a positive charge and a second monomer containing an anionic group having pH responsiveness on the porous body.

[0007] Further, the present invention is a method for manufacturing a porous membrane including a step of bringing a porous body into contact with a mixture including a first monomer containing a cationic group having a positive charge, a second monomer containing an anionic group having pH responsiveness, and a crosslinking agent.

[0008] Further, the present invention is a separation method in which, in a step of filtering a filtered body with the above porous membrane, acidic protein and basic protein are separated from the filtered body by changing the charge of the porous membrane according to pH.

Effects of the Invention

[0009] According to the present invention, it becomes possible to provide a porous membrane capable of suitably separating a predetermined component from a filtered body, a method for manufacturing the porous membrane, and a separation method.

Modes for Carrying Out the Invention

[0010] <Embodiment> Embodiments of the present invention will be described in detail. The porous membrane and the like described below are for embodying the technical idea of the present invention, and the present invention is not limited to the following unless specifically described.

[0011] (Porous Membrane) The porous membrane serves as a member for filtering the filtered object. The porous membrane includes a porous body and a polymer having a crosslinked structure of a first monomer containing a cationic group having a positive charge and a second monomer containing an anionic group having pH responsiveness on the porous body. The upper side of the porous body may mean the upstream side in the flow direction of the filtered object. For example, when the filtered object flows from above the porous membrane through its interior and downward, the polymer is disposed on the upper side of the porous body. A part (or most) of the polymer may penetrate into the interior of the porous body.

[0012] The porous membrane has pH responsiveness, with its charge changing according to pH. The porous membrane is negatively charged (or uncharged) when the pH is in the neutral range, and positively charged when the pH is below the neutral range (on the acidic side of the neutral range). In the present technology, this neutral range may be a range where the pH is 6.0 or more and 8.0 or less, a range where the pH is 6.5 or more and 7.5 or less, or when the pH is 7.0 (when the pH is neutral). From the viewpoint of preferably separating a predetermined component from the filtered object, the isoelectric point of the porous membrane is preferably 2.0 or more and 7.0 or less, more preferably 3.0 or more and 6.0 or less, still more preferably 4.0 or more and 5.5 or less, and even more preferably 4.5 or more and 5.0 or less. The porous membrane may be negatively charged (or uncharged) when the pH is on the basic side of the isoelectric point, and positively charged when the pH is on the acidic side of the isoelectric point.

[0013] The material to be filtered contains components to be recovered (target components). These target components are components contained in the liquid passing through the porous membrane or components captured by the porous membrane. For example, the material to be filtered contains one or more components from among amino acids, peptides, proteins, nucleic acids, viruses, macromolecules, and other components. The material to be filtered may also contain buffers, solvents, etc. Furthermore, the material to be filtered may contain a first component and a second component with a higher isoelectric point than the first component as target components. Each component has a negative charge at pH levels higher than its isoelectric point and a positive charge at pH levels lower than its isoelectric point. For convenience, components in the material to be filtered may be referred to as acidic components (first component) if their isoelectric point is less than 7, and basic components (second component) if their isoelectric point is 7 or higher.

[0014] For example, the material to be filtered may contain acidic proteins and basic proteins as target components. Examples of acidic proteins include albumin (such as BSA and HSA), pepsinogen, insulin, nucleases, fibrinogen, α-globulin, β-globulin, and γ-globulin. Examples of basic proteins include lysozyme, thaumatin, cytochrome C, ribonuclease, trypsinogen, chymotrypsinogen, α-chymotrypsin, histones, protamine, polylysine, and monellin. The molecular weight of the target components in the material to be filtered is not particularly limited, but may be between 500 Da and 500 kDa, between 800 Da and 200 kDa, or between 1 kDa and 100 kDa. The target components may be biological components related to living organisms, such as proteins.

[0015] The porous membrane can be used as a porous membrane for filtering a material to be filtered (for example, a material containing biological components). The porous membrane can be used in a variety of applications, such as food and beverages, pharmaceuticals, cosmetics, diagnostic reagents, water purification agents, and for testing and research. Furthermore, the porous membrane may constitute a filtration unit together with a holding member to hold the porous membrane and a receiving member to receive the material to be filtered.

[0016] The porous body is not particularly limited as long as it is made of a material that forms a porous structure to which polymers can be attached. Examples of porous bodies include membrane filters, fiber filters, and other filters (wherein a filter is defined as a membrane). The material of the porous body is not particularly limited as long as it can to which polymers can be attached, but examples include nitrocellulose, cellulose mixed esters, cellulose acetate, polyethylene, polypropylene, polyester, polyethylene, polyvinyl chloride, polyvinylidene fluoride, polysulfone, polyethersulfone, and nylon. Among these, from the viewpoint of suitably separating predetermined components from the material to be filtered, hydrophilic materials are preferred as porous bodies, and polyethersulfone membrane filters are more preferred. From the same viewpoint, the pore size of the porous body is preferably 0.03 μm to 1.2 μm, more preferably 0.1 μm to 0.8 μm, and even more preferably 0.22 μm to 0.65 μm.

[0017] The polymer is a pH-responsive polymer whose charge changes depending on the pH. The polymer is negatively charged (or uncharged) when the pH is in the neutral range, and positively charged when the pH is below the neutral range (when it is acidic). The isoelectric point of the polymer is preferably 2.0 to 7.0, more preferably 3.0 to 6.0, even more preferably 4.0 to 5.5, and most preferably 4.5 to 5.0.

[0018] The polymer is a copolymer formed by polymerizing a first monomer and a second monomer, wherein the monomers are crosslinked with a crosslinking agent to cover a porous body. The monomers to be crosslinked may be of the same type or different types. The structure of the copolymer is not particularly limited, but examples include linear structures such as random copolymers and block copolymers, branched structures such as graft copolymers, and network structures.

[0019] The first monomer contains a cationic group having a positive charge. The first monomer may be a monomer represented by the following general formula (1). R 1 -R 2 -R 3 (1) (Where R 1 is a cationic group, R 2 is a spacer group, R 3 represents an unsaturated group.)

[0020] R 1 Regarding, the cationic group is a functional group having a positive charge. As the cationic group (R 1 ), there is no particular limitation, and examples thereof include a quaternary ammonium group, a tertiary amino group, a secondary amino group, or a primary amino group. Among these, as the cationic group (R 1 ), a quaternary ammonium group is preferable from the viewpoint that the positive charge is not affected by pH. The quaternary ammonium group is not particularly limited, and examples thereof include a trimethylammonium group, a triethylammonium group, a tripropylammonium group, a methyldiethylammonium group, an ethyldimethylammonium group, a methyldipropylammonium group, a dimethylbenzylammonium group, a diethylbenzylammonium group, a methyldibenzylammonium group, an ethyldibenzylammonium group, a dimethyloctadecylammonium group, and a dimethyloleylammonium group. Among these, as the quaternary ammonium group, a trimethylammonium group is preferable from the viewpoint of preferably separating a predetermined component from the filter medium.

[0021] The first monomer may include a quaternary ammonium group (cationic R 1 ) located at one end and an unsaturated carbon-carbon double bond (unsaturated group R 3 ) located at the other end. Regarding R 3 , the first monomer includes an unsaturated group which is a functional group containing an unsaturated carbon-carbon double bond. The unsaturated group (R 3The group is not particularly limited, and examples include acrylic group, methacrylic group, allyl group, styryl group, vinyl group, crotonyl group, isocrotonyl group, itaconyl group, etc. Among these, the unsaturated group (R 3 As for the group, terminal alkenyl groups are preferred due to their high reactivity in radical reactions, and methacrylic groups are more preferred.

[0022] R 2 Regarding the spacer group, it is not particularly limited, but it may be at least one element from carbon, oxygen, and nitrogen in the main chain (one end of which is R 1 It is joined, and the other end is R 3 It may also be included as a part bonded to (R). 2 The spacer group (R) may contain one or more of the following bonds: ether bonds, ester bonds, amide bonds, and urethane bonds. 2 The number of elements in the main chain of the ) is not particularly limited, but due to its high reactivity in radical reactions, an integer between 1 and 10 is preferred, an integer between 1 and 5 is more preferred, and an integer between 2 and 4 is even more preferred. Also, a spacer group (R 2 Of the bonds contained in ), ester bonds are preferred due to their high resistance to weak acids and weak bases.

[0023] Specifically, examples of the first monomer include [2-(acryloyloxy)ethyl]trimethylammonium chloride, (3-acrylamidopropyl)trimethylammonium chloride, [2-(methacryloyloxy)ethyl]trimethylammonium chloride, (3-acrylamidopropyl)trimethylammonium chloride, [3-(methacryloylamino)propyl]trimethylammonium chloride, (vinylbenzyl)trimethylammonium chloride, diallyldimethylammonium chloride, and 3-sulfopropyl methacrylate potassium salt. Among these, [2-(methacryloyloxy)ethyl]trimethylammonium chloride is preferred as the first monomer from the viewpoint of suitably separating a predetermined component from the material to be filtered.

[0024] The second monomer contains a pH-responsive anionic group. The second monomer may also be the monomer represented by the following general formula (2). R 4 -R 5 -R 6 (2) (Here, R 4 R is an anionic group. 5 R is a spacer base, 6 (This represents an unsaturated group.)

[0025] R 4 Regarding this, anionic groups are functional groups that have a negative charge by releasing hydrogen atoms and ionizing when the pH is in the neutral range, and the negative charge decreases when the pH is acidic above the neutral range as this ionization is suppressed. Anionic group (R 4 The group is not particularly limited, and examples include carboxyl groups, phenol groups, and sulfonamide groups. Among these, anionic groups (R 4 As for the carboxyl group, a carboxyl group is preferred from the viewpoint of suitably separating a predetermined component from the material to be filtered.

[0026] The second monomer is a carboxyl group (anionic group R) located at one end. 4 ) and the unsaturated carbon-carbon double bond located at the other end (unsaturated group R 6 ) and may also be provided. 6 Regarding the second monomer, it has an unsaturated group, which is a functional group containing an unsaturated carbon-carbon double bond. 6 The group is not particularly limited, and examples include acrylic group, methacrylic group, allyl group, styryl group, vinyl group, crotonyl group, isocrotonyl group, itaconyl group, etc. Among these, the unsaturated group (R 6 As for the group, terminal alkenyl groups are preferred due to their high reactivity in radical reactions, and methacrylic groups are more preferred.

[0027] R 5 Regarding the spacer group, it is not particularly limited, but it may be at least one element from carbon, oxygen, and nitrogen in the main chain (one end of which is R 4 It is joined, and the other end is R6 It may also be included as a part bonded to (R). 5 The spacer group (R) may contain one or more of the following bonds: ether bonds, ester bonds, amide bonds, and urethane bonds. 5 The number of elements in the main chain of (R) is not particularly limited, but due to its high reactivity in radical reactions, an integer between 1 and 20 is preferred, an integer between 4 and 10 is more preferred, and an integer between 6 and 8 is even more preferred. Also, a spacer group (R) 5 The bond contained in ) is preferably an ester bond due to its high resistance to weak acids and weak bases. Spacer group (R 5 ) is a spacer base (R 2 The structure may have a longer main chain (more elements) than ).

[0028] Specifically, examples of the second monomer include 2-carboxyethyl acrylate, 2-carboxyethyl methacuacrylate, 2-(acryloxy)ethyl succinate, 2-(methacryloyloxy)ethyl succinate, and 1-(2-acryloyloxyethyl) phthalate. Among these, 2-(methacryloyloxy)ethyl succinate is preferred as the second monomer from the viewpoint of suitably separating a predetermined component from the material to be filtered.

[0029] The polymer obtained by polymerizing the first monomer and the second monomer as described above exhibits a change in charge depending on the pH, for example, in the pH range from neutral to acidic. In the neutral pH range, the anionic group is ionized, so the molecule as a whole is negatively charged (or uncharged). However, as the pH decreases from the neutral range, the ionization of the anionic group is suppressed, while the charge of the cationic group does not change, so the molecule as a whole becomes positively charged. Due to this property of the polymer, the entire porous membrane exhibits similar pH responsiveness. The polymer and its manufacturing method described in this technology can be used, for example, as described in Japanese Patent Application Publication No. 2020-143183.

[0030] The crosslinking agents constituting the crosslinked structure are not particularly limited, but examples include aromatic divinyl compounds, diacrylate compounds linked by alkyl chains, diacrylate compounds linked by alkyl chains containing ether bonds, diacrylate compounds linked by chains containing aromatic groups and ether bonds, polyester-type diacrylates, and polyfunctional crosslinking agents. Examples of diacrylate compounds linked by alkyl chains containing ether bonds include diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol #400 diacrylate, polyethylene glycol #600 diacrylate, dipropylene glycol diacrylate, and the above compounds in which the acrylate is replaced with methacrylate. Among these, as crosslinking agents, diacrylate compounds linked by alkyl chains containing ether bonds are preferred from the viewpoint of excellent reactivity with the first monomer and second monomer, and suppression of adverse effects on the separation of predetermined components from the material to be filtered, polyethylene glycols having a polyethylene glycol skeleton are more preferred, and polyethylene glycol #400 diacrylate is even more preferred.

[0031] Polymerization initiators used when polymerizing monomers are not particularly limited, but include, for example, organic peroxides such as benzoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, cumene hydroperoxide, tert-butyl peroxide, tert-butyl peroxylaurate, tert-butyl peroxyisopropyl carbonate, tert-butyl peroxyacetate, and diisopropylbenzene hydroperoxide; and azobisisobutyronitrile. Examples include azo compounds such as azobis(2,4-dimethylvaleronitrile), azobis(2-methylpropionnitrile), azobis(2-methylbutyronitrile), 4,4'-azobis(4-cyanobutanoic acid), dimethylazobis(2-methylpropionate), azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], and azobis{2-methyl-N-[2-(1-hydroxybutyl)]-propionamide}; and persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate. Among these, persulfates are preferred as polymerization initiators due to their high radical generation ability in solution, and ammonium persulfate is more preferred.

[0032] The first monomer and the second monomer may have the same skeleton. Also, two or three of the first monomer, the second monomer, and the crosslinking agent may have the same skeleton. This same skeleton may be a methacrylic group (methacryloyl group) or a methacryloyl group (methacryloyloxy group) in which a methacrylic group is bonded to an oxygen atom.

[0033] From the viewpoint of suitably separating a predetermined component from the material to be filtered, the molar ratio of the first monomer to the second monomer is preferably in the range of 15:85 to 60:40, more preferably in the range of 20:80 to 55:45, even more preferably in the range of 20:80 to 50:50, even more preferably in the range of 20:80 to 45:55, even more preferably in the range of 25:75 to 40:60, and even more preferably in the range of 25:75 to 35:65.

[0034] (Method for manufacturing porous membranes) A method for manufacturing a porous membrane includes a mixing step of mixing materials such as monomers to obtain a mixture, and a contact step of bringing a porous body into contact with the mixture after the mixing step to obtain a contact body.

[0035] In the mixing step, a first monomer containing a positively charged cationic group, a second monomer containing a pH-responsive anionic group, and a crosslinking agent are mixed to obtain a mixture. At this time, a polymerization initiator and a solvent are mixed together so that they are included in the mixture. The solvent is not particularly limited, but examples include aprotic polar solvents such as dimethyl sulfoxide, dimethylformamide, and N-methylpyrrolidone; protic polar solvents such as water, organic acids (formic acid, acetic acid, propionic acid, butyric acid, etc.) and alcohols (methanol, ethanol, propanol, etc.); and aprotic nonpolar solvents such as hexane. These solvents may be used individually or in combination of two or more. Among these, protic polar solvents are preferred as solvents from the viewpoint of high solubility in materials such as monomers and chemical resistance of porous membranes, and water is more preferred. The temperature during mixing is not particularly limited, but from a similar viewpoint, it is preferably 0 degrees Celsius or higher and 60 degrees Celsius or lower, more preferably 10 degrees Celsius or higher and 50 degrees Celsius or lower, and even more preferably 20 degrees Celsius or higher and 40 degrees Celsius or lower.

[0036] In the mixing step, the first monomer and the second monomer are mixed so that the molar ratio is within a predetermined range. From the viewpoint of suitably separating the predetermined components from the material to be filtered, this molar ratio is preferably in the range of 15:85 to 60:40, more preferably in the range of 20:80 to 55:45, even more preferably in the range of 20:80 to 50:50, even more preferably in the range of 20:80 to 45:55, even more preferably in the range of 25:75 to 40:60, and even more preferably in the range of 25:75 to 35:65.

[0037] In the mixture, when the total amount of substance of the first monomer, the second monomer, and the crosslinking agent is 100 ml, the amount of substance of the first monomer is preferably 10 ml to 50 ml, more preferably 15 ml to 40 ml, and even more preferably 15 ml to 30 ml, from the viewpoint of suitably separating a predetermined component from the material to be filtered. From a similar viewpoint, the amount of substance of the second monomer relative to the total amount of substance of 100 ml is preferably 25 ml to 75 ml, more preferably 35 ml to 65 ml, and even more preferably 45 ml to 55 ml. From a similar viewpoint, the amount of crosslinking agent relative to 100 ml of total substance is preferably 10 ml to 45 ml, more preferably 15 ml to 40 ml, and even more preferably 20 ml to 35 ml.

[0038] In the contact process, a porous material is brought into contact with the mixture to obtain a contact material. The method of contact is not particularly limited, but for example, the porous material may be immersed in the mixture.

[0039] The method for manufacturing a porous membrane may also include a heating step in which the contact body is heated after the contact step, a cleaning step in which the contact body is washed after the heating step, and a drying step in which the contact body is dried at a lower temperature than the heating step after the cleaning step.

[0040] (Separation method) The separation method involves separating the target component from the material to be filtered using a porous membrane. This separation method includes a filtration step in which the material to be filtered is filtered through a porous membrane.

[0041] In the filtration process, the charge of the porous membrane is changed according to the pH to separate the first component (e.g., acidic protein) and the second component (e.g., basic protein) from the material to be filtered. Specifically, the filtration process includes a first filtration step in which the material to be filtered is passed through a porous membrane that is negatively charged (or uncharged), and a second filtration step in which a buffer solution with a pH on the acidic side (acidic buffer solution) is passed through the porous membrane.

[0042] In the first filtration step, the acidic component (acidic protein), which is the first component of the material to be filtered, selectively passes through the negatively charged porous membrane and is recovered as filtrate (filtered liquid). The basic component (basic protein), which is the second component, is selectively adsorbed and captured by the porous membrane (polymer). In the second filtration step, the pH is changed to the acidic side from the neutral range by the acidic buffer solution, causing the charge of the porous material to change from negatively charged (or uncharged) to positively charged. Due to this change in the charge of the porous material, the basic component that was captured by the porous membrane flows out of the porous membrane and is recovered as filtrate. In this way, the first and second components are separated and recovered from the material to be filtered.

[0043] The separation method may also include a stacking step in which multiple (two or more) porous membranes are stacked and set in a holder (a holding member that holds the porous membranes) before the filtration step, and a pretreatment step in which a buffer solution is passed through the porous membrane after the stacking step and before the filtration step. The pretreatment step may include a washing step in which an acidic buffer solution is passed through the porous membrane to wash it, and an equilibration step in which, after the washing step, a neutral buffer solution with a pH in the neutral range (or a basic buffer solution with a pH in the basic range) is passed through the porous membrane to make the porous membrane negatively charged (or uncharged). Furthermore, the separation method may include an intermediate filtration step between the first and second filtration steps in the filtration process in which a neutral buffer solution or a basic buffer solution is passed through the porous membrane. In the intermediate filtration step, acidic components are further flushed out from the porous membrane, improving the recovery rate of acidic components. Furthermore, the separation method may involve recovering the first component in the first filtration step, selectively adsorbing and capturing the second component, which has a larger molecular weight than the first component, onto a porous membrane, and then recovering the second component in the second filtration step. [Examples]

[0044] The following are specific examples of the present invention, but these are not intended to limit the present invention.

[0045] The materials used are listed below. • Porous material Polyethersulfone membrane filter (47mm diameter, 0.45μm pore size, 90-100μm thickness, manufactured by Toyo Roshi Co., Ltd.) • First monomer [2-(methacryloyloxy)ethyl]trimethylammonium chloride (80% aqueous solution, manufactured by Tokyo Chemical Industry Co., Ltd.) • Second monomer 2-(methacryloyloxy)ethyl succinate (manufactured by SIGMA-ALDRICH) • Crosslinking agent Polyethylene glycol #400 diacrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) • Polymerization initiator Ammonium persulfate (manufactured by Kanto Chemical Co., Ltd.) • Component 1 (acidic protein) Bovine serum albumin (BSA, molecular weight 66.5 kDa, isoelectric point 4.7, manufactured by SIGMA-ALDRICH) • Second component (basic protein) Lysozyme (Lyz, derived from egg white, molecular weight 14.3 kDa, isoelectric point 11, manufactured by Fujifilm Wako Pure Chemical Corporation)

[0046] <Example 1> To 20 mL of ultrapure water, 0.2 g of polyethylene glycol #400 diacrylate, 0.146 g of 80% aqueous solution of [2-(methacryloyloxy)ethyl]trimethylammonium chloride, 0.262 g of 2-(methacryloyloxy)ethyl succinate, and 0.13 g of ammonium persulfate were added separately and mixed at room temperature (25°C) to dissolve each material and obtain a mixture (mixing step).

[0047] After dissolution, a polyethersulfone membrane filter was immersed in the mixture to obtain a contact body (contact step). The membrane filter (contact body) was removed with tweezers and heat-treated at 90°C for 10 minutes. After heat treatment, the membrane filter was washed with water for 10 minutes and dried in a 70°C dryer for 30 minutes to obtain the porous membrane of Example 1.

[0048] <Example 2> The porous membrane of Example 2 was obtained in the same manner as in Example 1, except that the amount of 2-(methacryloyloxy)ethyl succinate was changed to 0.131 g.

[0049] <Example 3> The porous membrane of Example 3 was obtained in the same manner as in Example 1, except that the amount of [2-(methacryloyloxy)ethyl]trimethylammonium chloride in an 80% aqueous solution was changed to 0.073 g and the amount of 2-(methacryloyloxy)ethyl succinate was changed to 0.1965 g.

[0050] <Example 4> The porous membrane of Example 4 was obtained in the same manner as in Example 1, except that the amount of [2-(methacryloyloxy)ethyl]trimethylammonium chloride in the 80% aqueous solution was changed to 0.073 g.

[0051] <Example 5> The porous membrane of Example 5 was obtained in the same manner as in Example 1, except that the amount of [2-(methacryloyloxy)ethyl]trimethylammonium chloride in an 80% aqueous solution was changed to 0.073 g and the amount of 2-(methacryloyloxy)ethyl succinate was changed to 0.3275 g.

[0052] <Comparative Example 1> A porous membrane of Comparative Example 1 was obtained in the same manner as in Example 1, except that 2-(methacryloyloxy)ethyl succinate was not used.

[0053] <Comparative Example 2> A porous membrane of Comparative Example 2 was obtained in the same manner as in Example 2, except that 0.074 g of the neutral monomer N-(methoxymethyl)methacrylamide (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of an 80% aqueous solution of [2-(methacryloyloxy)ethyl]trimethylammonium chloride.

[0054] <Comparative Example 3> A porous film of Comparative Example 3 was obtained in the same manner as in Example 2, except that 0.096 g of diacetone acrylamide (manufactured by Tokyo Chemical Industry Co., Ltd.), a neutral monomer, was used instead of 2-(methacryloyloxy)ethyl succinate.

[0055] [Evaluation of porous membranes (selective separation test of proteins)] A filter material was prepared by dissolving 120 ppm each of BSA and lysozyme (12 mg of BSA and 12 mg of lysozyme) in 100 mL of pH 7, 50 mM MES buffer (manufactured by Dojin Chemical Laboratories Co., Ltd.). Next, the porous membranes prepared in each of the above examples and comparative examples were punched out into circles with a diameter of 25 mm, and two of these punched-out membrane filters were stacked to form a laminate, which was then set in a holding member (ADVANTEC, plastic holder, PP-25) (hereinafter, this laminate will simply be referred to as a membrane filter).

[0056] (Protein isolation) Next, the following steps were performed in order. Step 1: 5 mL of pH 3, 50 mM phosphate buffer (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was passed through the membrane filter for washing. A quantitative dispensing pump (manufactured by Tokyo Rikakikai Co., Ltd., model number MP-2000) was used for dispensing the solution (this same quantitative dispensing pump was used for dispensing the solution in subsequent steps as well). Step 2: 5 mL of MES buffer solution at pH 7 and 50 mM was passed through a membrane filter and equilibrated. Step 3: 1 mL of the material to be filtered (a 120 ppm solution of BSA / lysozyme) was passed through a membrane filter to flush out the BSA and collect it as filtrate A, while the lysozyme was adsorbed onto the membrane filter. Step 4: 1 mL of pH 7, 50 mM MES buffer was passed through a membrane filter, and the BSA was further flushed out of the membrane filter and collected as filtrate B. Step 5: 1 mL of pH 3, 50 mM phosphate buffer was passed through the membrane filter once to flush out the lysozyme, which was then collected as filtrate C. Step 6: Step 5 was repeated and the filtrate D was collected. By performing the above steps, BSA was recovered in filtrates A and B (total 2 mL), and lysozyme was recovered in filtrates C and D (total 2 mL).

[0057] The filtrates A through D and the blank solution were analyzed using a ULC (Waters Corporation, ACQUITY UPLC H-Class) under the following conditions: phosphate buffer as the mobile phase, flow rate of 0.4 mL / min, column temperature of 30°C, and column type ACQUITY UPLC Protein BEH SEC Column, 1.7 μm, 4.6 mm × 150 mm. The recovery rate was calculated from the peak areas of BSA and lysozyme in the absorbance at 280 nm using the following formula. For the blank solution, steps 1 through 3 were performed without setting a membrane filter in the holding member, and the filtrate after step 3 (corresponding to filtrate A) was used. BSA recovery rate (%) = (peak area of ​​BSA in filtrate A + peak area of ​​BSA in filtrate B) / peak area of ​​BSA in blank solution × 100 Lysozyme recovery rate (%) = (Peak area of ​​lysozyme in filtrate C + Peak area of ​​lysozyme in filtrate D) / Peak area of ​​lysozyme in blank solution × 100 Lysozyme adsorption rate (%) = (Peak area of ​​lysozyme in blank solution - Peak area of ​​lysozyme in filtrate A - Peak area of ​​lysozyme in filtrate B) / Peak area of ​​lysozyme in blank solution × 100

[0058] The above is summarized in Table 1. In Table 1, each material is shown in molecular weight (mOL). "Total molecular weight" is the total molecular weight of the first monomer, second monomer, and crosslinking agent in the mixture. "First monomer:Second monomer" is the molecular weight ratio of the first monomer to the second monomer. Regarding the recovery rate of BSA, "-" means that lysozyme was recovered along with BSA in filtrates A and B and could not be separated.

[0059] [Table 1] *1: Instead of the first monomer, the neutral monomer N-(methoxymethyl)methacrylamide is used. *2: Instead of the second monomer, diacetone acrylamide, a neutral monomer, is used.

[0060] According to the examples, predetermined components could be suitably separated from the material to be filtered.

Claims

1. Porous material and A porous membrane comprising a polymer having a crosslinked structure on the porous body, comprising a first monomer containing a positively charged cationic group and a second monomer containing a pH-responsive anionic group.

2. The porous membrane according to claim 1, wherein the first monomer comprises a quaternary ammonium group located at one end and an unsaturated carbon-carbon double bond located at the other end.

3. The porous membrane according to claim 1 or 2, wherein the second monomer comprises a carboxyl group located at one end and an unsaturated carbon-carbon double bond located at the other end.

4. The porous membrane according to claim 1 or 2, wherein the molar ratio of the first monomer to the second monomer is 15:85 to 60:

40.

5. The porous membrane according to claim 1 or 2, wherein it is negatively charged when the pH is in the neutral range and positively charged when the pH is below the neutral range.

6. A method for producing a porous film, comprising the step of contacting a porous body with a mixture comprising a first monomer containing a positively charged cationic group, a second monomer containing a pH-responsive anionic group, and a crosslinking agent.

7. The method for producing a porous membrane according to claim 6, comprising mixing the first monomer and the second monomer in a molar ratio in the range of 15:85 to 60:

40.

8. The method for producing a porous membrane according to claim 6 or 7, wherein the mixture comprises a polymerization initiator and a solvent.

9. A separation method comprising the step of filtering an object to be filtered with a porous membrane according to claim 1 or 2, wherein the charge of the porous membrane is changed according to the pH to separate acidic proteins and basic proteins from the object to be filtered.

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