Polymer-based additives containing zwitterionic sites for membranes based on vinylidene fluoride (VDF) polymers

Abstract

The present invention relates to a composition suitable for producing membranes based on vinylidene fluoride (VDF) polymers, to porous membranes thereof, to a method for their production, and to their use, in particular for the filtration of aqueous phases. The composition, comprising a vinylidene fluoride (VDF) polymer and a polymeric additive containing zwitterionic moieties, provides excellent hydrophilization performance for the membranes produced.

Description

Technical Field

[0001] The present invention relates to a composition suitable for the production of a film based on a vinylidene fluoride (VDF) polymer, a porous film thereof, methods for producing them, and their use, in particular for the filtration of aqueous phases. The present invention also relates to a copolymer suitable for use as a hydrophilic additive for said film.

Background Art

[0002] A porous membrane is a thin object, and its important property is the ability to control the permeation rate of chemical species through itself. This feature is utilized in applications such as separation applications (water and gas).

[0003] Fluorinated polymers are widely used in the production of microfiltration membranes and ultrafiltration membranes due to their excellent mechanical strength, high chemical resistance, and thermal stability. Among them, partially fluorinated polymers based on vinylidene fluoride (VDF) are particularly convenient for controlling the porosity and morphology of said membranes. Membranes made from vinylidene fluoride polymers [polymer (VDF)] are essentially hydrophobic, and therefore have water repellency and low water permeability, and fouling of particles and proteins is likely to occur on their surfaces. Hydrophobicity prevents water from penetrating the fluoropolymer membrane, so higher pressure is required for water permeability and more energy is consumed. Fouling temporarily or permanently reduces the flow of water permeating through the membrane in, for example, an ultrafiltration or microfiltration process.

[0004] The ability of water to permeate through a porous VDF polymer membrane is generally improved by making the inner surface of the internal pores more hydrophilic. Furthermore, since proteins and other adhering substances are essentially hydrophobic, it is generally recognized that better fouling resistance can be obtained when the hydrophilicity of the VDF polymer membrane increases.

[0005] Multiple strategies have been adopted to hydrophilize the porous VDF polymer membrane, which results in making the membrane more water-permeable and imparting fouling resistance. Among the approaches pursued, approaches based on grafting hydrophilic species onto the membrane surface, incorporating hydrophilic comonomers into the main chain of the vinylidene fluoride polymer, blending hydrophilic additives, etc. can be mentioned. These approaches are outlined, for example, in Surface Modifications for Antifouling Membranes, Chemical Reviews, 2010, Vol. 110, No. 4, p. 2448-2471. Using zwitterionic structures to hydrophilize PVDF-based membranes is part of these approaches and is very interesting.

[0006] WO 2015 / 070004 pamphlet discloses a zwitterion-containing membrane in which a selected layer formed from a statistical copolymer containing zwitterionic repeating units and hydrophobic repeating units, such as p(MMA-s-SBMA), is disposed on a support layer formed from a porous PVDF membrane. However, nothing is described about the durability of the resulting membrane or its resistance to chemical aging.

[0007] US Patent Application Publication No. 2018 / 0001278, which discloses a comb-shaped and random zwitterionic copolymer (such as p(MMA-r-SBMA)) useful for enhancing the hydrophilicity of PVDF-based membranes, proposes a hydrophilic additive for PVDF-based membranes. The resulting PVDF membrane with the additive shows excellent fouling resistance and improved permeability compared to the PVDF membrane. However, to obtain such results, a relatively large amount of zwitterionic additive is required, which may impair the mechanical resistance, chemical resistance, and economic attractiveness of the PVDF membrane.

[0008] There is a need to develop a highly permeable porous membrane having a controlled pore size and exhibiting fouling-resistant behavior. Further, the membrane needs to exhibit high thermal and chemical stability that can guarantee durability. Also needed are additives having high thermal and chemical stability that can hydrophilize a PVDF membrane in which the additives are dispersed. In addition, these additives need to be easily and permanently incorporated into a vinylidene fluoride polymer membrane in order to enhance their hydrophilicity, water permeability, and fouling-resistant behavior over the long term without impairing the inherent properties of the vinylidene fluoride polymer having high mechanical, thermal, and chemical properties. Finally, the additives need to be very efficient hydrophilizing agents for use in moderation, such that the adverse effects on the mechanical, thermal, and chemical resistance of the porous PVDF membrane due to their excessive presence are avoided.

Brief Description of the Drawings

[0009]

Figure 1

Summary of the Invention

[0010] All of this requirement and more are - at least one vinylidene fluoride (VDF) polymer [polymer (VDF)], and - at least one zwitterionic repeating unit [unit (R ZW )] derived from at least one ethylenically unsaturated monomer having at least two ionic groups, at least one of which is a cationic group [group (C+)], at least one of which is an anionic group [group (A-)], and further comprising at least one hydroxyl group, in at least one polymer [polymer (N-ZW)], is satisfied by a first aspect of the invention relating to a composition [composition (C)] comprising.

[0011] A second aspect of the invention is Step (i): preparing the composition (C); Step (ii): processing the composition obtained in step (i) to thereby obtain a film; and Step (iii): treating the film obtained in step (ii), which usually includes contacting the film with a non-solvent medium [medium (NS)] to thereby obtain a porous film, relates to a method for producing a porous film, which comprises.

[0012] The third aspect is - at least one vinylidene fluoride polymer [polymer (VDF)], and - at least one zwitterionic repeating unit [unit (R ZW )] derived from at least one ethylenically unsaturated monomer having at least two ionic groups, at least one of which is a cationic group [group (C+)], at least one of which is an anionic group [group (A-)], and further including at least one hydroxyl group, relates to a porous film, which comprises.

[0013] The porous film can be obtained from the above composition (C) and can be produced by the above method.

[0014] The fourth aspect of the present invention relates to a method for separating an aqueous medium, which method comprises contacting the aqueous medium with the above porous film.

[0015] The fifth aspect of the present invention relates to a copolymer (N-ZW) comprising a zwitterionic repeating unit (R ZW ) derived from 3-((3-acrylamidopropyl)dimethylammonio)-2-hydroxypropane-1-sulfonate (AHPS) and a repeating unit (R N ) derived from at least one monomer selected from the list consisting of alkyl (meth)acrylate, vinyl acetate, and N,N-dimethylacrylamide. The copolymer is suitable for use in the composition (C) for producing the above film by the above method.

[0016] The Applicant has surprisingly found that the composition (C) detailed above is particularly effective for use in the manufacture of membranes, providing very good permeation performance in the filtration and separation processes of aqueous media while maintaining compatibility with the water-induced coagulation processes typical of membrane manufacture.

[0017] Polymer (VDF) Within the framework of the present invention, the expressions "vinylidene fluoride polymer" and "polymer (VDF)" are used to refer to polymers that typically contain repeating units derived from vinylidene fluoride as the main repeating unit component. Therefore, polymer (VDF) is usually a polymer essentially made up of repeating units where more than 50 mol% of the repeating units are derived from vinylidene fluoride (VDF).

[0018] Polymer (VDF) may further contain repeating units derived from at least one fluorinated monomer different from VDF and / or may further contain repeating units derived from a fluorine-free monomer (also called a "hydrogenated monomer"). The term "fluorinated monomer" is intended herein to mean an ethylenically unsaturated monomer containing at least one fluorine atom. The fluorinated monomer may further contain one or more other halogen atoms (Cl, Br, I).

[0019] In particular, polymer (VDF) is usually selected from among addition polymers that contain repeating units derived from VDF and, optionally, repeating units derived from at least one fluorine atom-containing ethylenically unsaturated monomer different from VDF, and this at least one ethylenically unsaturated monomer is usually selected from the group consisting of: (a) C 2 ~C 8 perfluoroolefins such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoroisobutylene; (b) vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutylene (HFIB), of the formula CH 2 =CH-Rf1 (wherein R f1 is a C 1 ~C 6 perfluoroalkyl group) perfluoroalkyl ethylene and the like, a hydrogen-containing C different from VDF 2 ~C 8 fluoroolefin; (c) C such as chlorotrifluoroethylene (CTFE) 2 ~C 8 chloro and / or bromo-containing fluoroolefin; (d) the formula CF 2 =CFOR f1 (wherein R f1 is a CF 3 (PMVE), C 2 F 5 or C 3 F 7 such as, a C 1 ~C 6 perfluoroalkyl group) perfluoroalkyl vinyl ether (PAVE); (e) especially the formula CF 2 =CFOCF 2 OR f2 (wherein R f2 is -CF 2 CF 3 , -CF 2 CF 2 -O-CF 3 and -CF 3 such as, a C 1 ~C 3 perfluoro(oxy)alkyl group) perfluoromethoxyalkyl vinyl ether-containing, the formula CF 2 =CFOX 0 (wherein X 0 is a C containing one or more ether oxygen atoms 1 ~C 12 perfluorooxyalkyl group) perfluorooxyalkyl vinyl ether; and (f) the formula:

Chemical formula

[0020] Vinylidene fluoride polymer [polymer (VDF)] preferably (a’) at least 60 mol%, preferably at least 75 mol%, more preferably 85 mol% of repeating units derived from vinylidene fluoride (VDF); (b’) optionally, 0.1 to 30 mol%, preferably 0.1 to 20 mol%, more preferably 0.1 to 15 mol% of repeating units derived from a fluorinated monomer different from VDF; and (c’) optionally, 0.1 to 10 mol%, preferably 0.1 to 5 mol%, more preferably 0.1 to 1 mol% of repeating units derived from one or more hydrogen-containing comonomers; and is a polymer containing the above, and all of the above mol% are based on the total moles of the repeating units of the polymer (VDF).

[0021] The fluorinated monomer is advantageously vinyl fluoride (VF 1 ), trifluoroethylene (VF 3) selected from the group consisting of chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(methyl)vinyl ether (PMVE), perfluoro(ethyl)vinyl ether (PEVE), and perfluoro(propyl)vinyl ether (PPVE), perfluoro(1,3-dioxole), and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD). Preferably, possible additional fluorinated monomers are selected from chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF3), and tetrafluoroethylene (TFE).

[0022] The selection of the hydrogenated comonomer is not particularly limited, and α-olefins, (meth)acrylic monomers, vinyl ether monomers, and styrenic monomers can be used. However, in order to optimize chemical resistance, embodiments in which polymer (F) essentially does not contain repeating units derived from the hydrogenated comonomer are preferred.

[0023] Therefore, the vinylidene fluoride polymer [polymer (VDF)] is more preferably (a’) at least 60 mol%, preferably at least 75 mol%, more preferably 85 mol% of repeating units derived from vinylidene fluoride (VDF); (b’) optionally, a fluorinated monomer different from VDF in an amount of 0.1 to 30 mol%, preferably 0.1 to 20 mol%, more preferably 0.1 to 15 mol%; preferably, vinyl fluoride (VF 1 ), chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), tetrafluoroethylene (TFE), perfluoromethyl vinyl ether (MVE), trifluoroethylene (TrFE), and a fluorinated monomer selected from the group consisting of mixtures thereof; consisting essentially of, and all of the above mol% are based on the total moles of the repeating units of polymer (VDF).

[0024] In addition to the repeating units, defects, end chains, impurities, chain inversions or branches, etc. may further exist in the polymer (VDF) without substantially modifying the behavior and properties of these components on the polymer (VDF).

[0025] Non-limiting examples of polymers (VDF) useful in the present invention include those made from homopolymers of VDF, VDF / TFE copolymers, VDF / TFE / HFP copolymers, VDF / TFE / CTFE copolymers, VDF / TFE / TrFE copolymers, VDF / CTFE copolymers, VDF / HFP copolymers, VDF / TFE / HFP / CTFE copolymers, etc. can be specifically mentioned.

[0026] The VDF homopolymer is particularly advantageous for use as the polymer (VDF) in the composition (C).

[0027] The melt index of the polymer (VDF) is preferably at least 0.01, preferably at least 0.05, more preferably at least 0.1 g / 10 min, advantageously less than 50, preferably less than 30, more preferably less than 20 g / 10 min when measured according to ASTM test number 1238, carried out at 230 °C under a piston load of 2.16 kg.

[0028] The melt index of the polymer (VDF) is preferably at least 0.1, preferably at least 1, more preferably at least 5 g / 10 min, advantageously less than 70, preferably less than 50, more preferably less than 40 g / 10 min when measured according to ASTM test number 1238, carried out at 230 °C under a piston load of 5 kg.

[0029] The melt index of the polymer (VDF) is advantageously at least 0.1, preferably at least 0.5, more preferably at least 1 g / 10 min, advantageously less than 30, preferably less than 20, more preferably less than 10 g / 10 min when carried out at 230 °C under a piston load of 21.6 kg and measured according to ASTM test number 1238.

[0030] The polymer (VDF) advantageously has a melting point (T m ) of at least 120 °C, preferably at least 125 °C, more preferably at least 130 °C, up to 190 °C, preferably up to 185 °C, more preferably up to 180 °C when measured by DSC at a heating rate of 10 °C / min according to ASTM D3418.

[0031] Polymer (N-ZW) containing zwitterionic repeating units The composition (C) usually contains at least one zwitterionic repeating unit [unit (R ZW )] derived from at least one ethylenically unsaturated monomer containing at least two ionic groups, at least one of which is a cationic group [group (C+)], at least one of which is an anionic group [group (A-)], and further containing at least one hydroxyl group, and contains at least one polymer [polymer (N-ZW)].

[0032] Usually, the zwitterionic repeating unit (R ZW) is derived from at least one ethylenically unsaturated monomer which is electrically neutral overall but contains a number of groups (C+) equal to the number of groups (A-), and further contains at least one hydroxyl group. The cationic charge can be provided by at least one onium cation or inium cation of nitrogen such as ammonium cation, pyridinium cation, and imidazolinium cation; phosphorus such as phosphonium; and / or sulfur such as sulfonium. The anionic charge can be provided by at least one carbonate, sulfonate, phosphate, phosphonate, phosphinate, or ethenolate anion, etc. Suitable zwitterionic monomers include, but are not limited to, betaine monomers, which are zwitterionic and contain an onium atom having no hydrogen atom and not adjacent to an anionic atom.

[0033] In some embodiments, the unit (R ZW ) is derived from at least one monomer selected from the list consisting of: a) Hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl acrylates or methacrylates, acrylamides or methacrylamides, typically: - Sulfohydroxypropyl dimethylammonioethyl acrylate, - Sulfohydroxypropyl dimethylammonioethyl methacrylate, - Sulfohydroxypropyl dimethylammoniopropyl acrylamide, - Sulfohydroxypropyl dimethylammoniopropyl methacrylamide; b) Heterocyclic betaine monomers containing at least one hydroxyl group, typically: - Sulfobetaines derived from piperazine, - Sulfobetaines derived from 2-vinylpyridine and 4-vinylpyridine, - Sulfobetaines derived from imidazolium; and c) Hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl styrenes.

[0034] In a preferred embodiment, the unit (R ZW ) is derived from at least one monomer selected from the list consisting of: [Chemical formula] [Chemical formula] [Chemical formula]

[0035] In a preferred embodiment, the unit (R ZW ) is derived from at least one monomer selected from the list consisting of: - Sulfohydroxypropyldimethylammonioethyl acrylate, - Sulfohydroxypropyldimethylammonioethyl methacrylate (SHPE), - Sulfohydroxypropyldimethylammoniopropyl acrylamide (AHPS), and - Sulfohydroxypropyldimethylammoniopropyl methacrylamide (SHPP).

[0036] In a more preferred embodiment, the unit (R ZW ) is derived from sulfohydroxypropyldimethylammoniopropyl acrylamide (AHPS).

[0037] In some embodiments, the polymer (N-ZW) further comprises a repeating unit [unit (R ZW )] different from the unit (R N ) derived from at least one ethylenically unsaturated monomer having no ionizable group.

[0038] In some embodiments, the unit (R N) is derived from at least one monomer selected from the list consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, vinyl acetate, and N,N-dimethylacrylamide [unit (R N~1 )]. Preferably, the unit (R N~1 ) is derived from methyl methacrylate, ethyl methacrylate, or a mixture thereof. More preferably, the unit (R N~1 ) is derived from methyl methacrylate.

[0039] In some other embodiments, the unit (R N ) is derived from at least one monomer selected from the list consisting of 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2-hydroxyethyl acrylate (HEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, poly(ethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate, and poly(ethylene glycol) ethyl ether acrylate [unit (R N~2 )]. Preferably, the unit (R N~2 ) is derived from 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, or a mixture thereof. More preferably, the unit (R N~2 ) is derived from 2-hydroxyethyl methacrylate (HEMA).

[0040] In still some other embodiments, the unit (R N ) is from at least one monomer selected from the list consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, vinyl acetate, and N,N-dimethylacrylamide [unit ((R N~1)], and at least one monomer selected from the list consisting of 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2-hydroxyethyl acrylate (HEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, poly(ethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate, and poly(ethylene glycol) ethyl ether acrylate [unit (R N~2 )]. Preferably, the unit (R N~1 ) is derived from methyl methacrylate, ethyl methacrylate, or a mixture thereof, and the unit (R N~2 ) is derived from 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, or a mixture thereof. More preferably, the unit (R N~1 ) is derived from methyl methacrylate, and the unit (R N~2 ) is derived from 2-hydroxyethyl methacrylate (HEMA).

[0041] In some preferred embodiments, the polymer (N-ZW) of the present disclosure comprises a repeating unit (R ZW ) derived from (AHPS), (SHPP), (SHPE), or a mixture thereof, and a repeating unit (R N~1 ) derived from methyl methacrylate.

[0042] In some other preferred embodiments, the polymer (N-ZW) of the present disclosure comprises a repeating unit (R ZW ) derived from (AHPS) and a repeating unit (R N~1 ) derived from methyl methacrylate.

[0043] In still some other preferred embodiments, the polymer (N-ZW) of the present disclosure comprises a repeating unit (R ZW) and repeating unit (R) derived from methyl methacrylate N~1 ) and repeating unit (R) derived from 2-hydroxyethyl methacrylate (HEMA) N~2 ) are included.

[0044] The polymer (N-ZW) of the composition (C) according to the present disclosure usually contains 0.1 to 30 mol%, preferably 0.1 to 20 mol%, more preferably 0.1 to 7 mol%, still more preferably 0.1 to 5 mol% of unit (R) based on the total number of moles of the repeating units of the polymer (N-ZW). ZW ) is included.

[0045] Also, the polymer (N-ZW) of the composition (C) according to the present disclosure usually contains 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more, still more preferably 95 mol% of unit (R) based on the total number of moles of the repeating units of the polymer (N-ZW). N ) is included.

[0046] When repeating unit (R) N~1 ) and repeating unit (R) N~2 ) are present, the polymer (N-ZW) usually contains 0.1 to 50 mol%, preferably 0.1 to 40 mol%, more preferably 0.1 to 30 mol%, still more preferably 0.1 to 20 mol% of repeating units (R) ZW ) and (R) N~2 ) based on the total number of moles of the repeating units of the polymer (N-ZW).

[0047] The polymer (N-ZW) according to the present invention is a homopolymer or a copolymer. This is preferably a copolymer containing repeating unit (R) ZW ) and repeating unit (R) N ). When it is a copolymer, it is a block copolymer, a branched copolymer, or a statistical copolymer. Good results were obtained with the polymer (N-ZW) being a statistical copolymer.

[0048] Unless otherwise indicated, when molar mass is mentioned, the reference is to the weight-average molar mass expressed in g / mol. The latter can be determined by gel permeation chromatography (GPC) equipped with light scattering detection (DLS or MALLS) or refractive index detection, depending on the polymer (N-ZW), using an aqueous eluent or an organic eluent (such as dimethylacetamide, dimethylformamide, etc.). There is no particular limitation on the molar mass of the polymer (N-ZW). However, the weight-average molar mass (Mw) of the polymer (N-ZW) ranges from about 5,000 to about 3,000,000 g / mol, typically from about 8,000 to about 1,000,000 g / mol, more typically from about 10,000 to 500,000 g / mol, and even more typically from 20,000 to 200,000 g / mol.

[0049] The polymer (N-ZW) of the present disclosure can be obtained by any polymerization process known to those skilled in the art. For example, the polymer (N-ZW) can be obtained by radical polymerization or copolymerization or controlled radical polymerization in an aqueous solution, a dispersion medium, an organic solution, or an organic / aqueous solution (miscible phase).

[0050] The ethylenically unsaturated monomer having no ionizable group for inducing the unit (R N ) can be obtained from commercial suppliers.

[0051] The ethylenically unsaturated monomer having at least two ionic groups for inducing the unit (R ZW ), at least one of which is a cationic group [group (C+)], at least one of which is an anionic group [group (A-)], and further containing at least one hydroxyl group, can be obtained from commercial suppliers or can be synthesized according to methods known to those skilled in the art.

[0052] The unit (R ZWFor inducing ), suitable ethylenically unsaturated monomers can be obtained by reacting sodium 3-chloro-2-hydroxypropane-1-sulfonate (CHPSNa) with an ethylenically unsaturated monomer having a tertiary amino group starting from dimethylaminopropylmethacrylamide according to the following reaction scheme as described in US Patent Application Publication No. 2008 / 0045420 for the synthesis of SHPP:

Chemical formula

[0053] unit (R ZW ) In order to obtain a suitable ethylenically unsaturated monomer from which the ) is derived, another ethylenically unsaturated monomer having a tertiary amino group can be added to the reaction with CHPSNa:

Chemical formula

[0054] unit (R ZW ) A suitable ethylenically unsaturated monomer from which the ) is derived can also be obtained by reacting sodium 3-chloro-2-hydroxypropane-1-sulfonate (CHPSNa) with an ethylenically unsaturated monomer having a pyridine group or an imidazole group:

Chemical formula

[0055] In relation to the ethylenically unsaturated monomer, the expression "derived from" expressing the repeating unit (RZW) is intended to define both the repeating unit (RZW) directly obtained from the polymerization of the ethylenically unsaturated monomer and the same repeating unit (RZW) obtained by modification of an existing polymer.

[0056] Therefore, the repeating unit (R ZW) can be obtained by modifying a polymer containing repeating units having a tertiary amino group by reaction with sodium 3-chloro-2-hydroxypropane-1-sulfonate (CHPSNa), which is called a precursor polymer. A similar modification is described in WO 2008 / 125512 pamphlet using sodium 3-chloropropane-1-sulfonate instead of CHPSNa: [Chemical formula]

[0057] Similarly, the repeating unit (R ZW ) can be obtained by modifying a polymer (called a precursor polymer) containing repeating units having a tertiary amino group, a pyridine group, an imidazole group, or a mixture thereof by reaction with sodium 3-chloro-2-hydroxypropane-1-sulfonate (CHPSNa).

[0058] Since the polymer (N-ZW) is used as an additive for the polymer (VDF), the polymer (VDF) is usually present in a larger amount than the polymer (N-ZW) in the composition (C). Usually, the weight ratio of polymer (N-ZW) / polymer (VDF) is at least 1 / 99 wt / wt, preferably at least 3 / 97 wt / wt, more preferably at least 5 / 95 wt / wt, and / or this is less than 50 / 50 wt / wt, preferably less than 40 / 60 wt / wt, preferably less than 30 / 70 wt / wt.

[0059] The composition (C) may optionally contain at least one additional component. The additional raw materials are preferably selected from the group consisting of non-solvents (water, alcohol...), co-solvents (such as ketones), pore formers, nucleating agents, fillers, salts, surfactants.

[0060] When used, the pore-forming agent is typically added to the composition (C) in an amount in the range of usually 1% to 30% by weight, preferably 2% to 20% by weight, based on the total weight of the composition (C). Suitable pore-forming agents are, for example, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and polyethylene glycol (PEG).

[0061] When used, the salt is typically added to the composition (C) in an amount in the range of usually 0.5% to 20% by weight, preferably 1% to 10% by weight, based on the total weight of the composition (C). Suitable salts are, for example, NaCl, LiCl, LiClO 4 , and LiCF 3 SO 3 .

[0062] Liquid medium In some embodiments, the composition (C) further comprises at least one liquid medium [medium (L)] comprising at least one organic solvent [composition (C L )].

[0063] The term "solvent" is used herein in its ordinary sense, i.e., to denote a substance that can dissolve another substance (solute) to form a uniformly dispersed mixture at the molecular level. In the case of a polymer solute, it is common practice to refer to a solution of the polymer in the solvent when the resulting mixture is transparent and no phase separation is observed in the system. Phase separation is interpreted as the point, often referred to as the "cloud point", at which the solution becomes turbid or cloudy due to the formation of polymer aggregates.

[0064] Typically, in the composition (C L ), the medium (L) comprises at least one solvent (S) for the polymer (VDF).

[0065] The medium (L) typically is - More specifically, aliphatic hydrocarbons including paraffin, such as especially pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane or cyclohexane, and naphthalene and aromatic hydrocarbons, more specifically aromatic hydrocarbons, such as especially benzene, toluene, xylene, cumene, a petroleum fraction composed of a mixture of alkylbenzenes; - More specifically, aliphatic or aromatic halogenated hydrocarbons including perchlorinated hydrocarbons, such as especially tetrachloroethylene, hexachloroethane; - Partially chlorinated hydrocarbons, such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane, trichloroethylene, 1-chlorobutane, 1,2-dichlorobutane, monochlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,4-trichlorobenzene or a mixture of different chlorobenzenes; - Aliphatic, alicyclic or aromatic ether oxides, more specifically diethyl oxide, dipropyl oxide, diisopropyl oxide, dibutyl oxide, methyl tert-butyl ether, dipentyl oxide, diisopentyl oxide, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether benzyl oxide; dioxane, tetrahydrofuran (THF); - Dimethyl sulfoxide (DMSO); - Glycol ethers, such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether; - Glycol ethers esters, such as ethylene glycol methyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, etc.; - Alcohols containing polyhydric alcohols, such as methyl alcohol, ethyl alcohol, diacetone alcohol, ethylene glycol, etc.; - Ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, etc.; - Linear or cyclic esters, such as isopropyl acetate, n-butyl acetate, methyl acetoacetate, dimethyl phthalate, γ-butyrolactone, etc.; - Linear or cyclic carboxamides, such as N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, dimethylformamide (DMF), diethylformamide or N-methyl-2-pyrrolidone (NMP), etc.; - Organic carbonates, such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, ethyl methyl carbonate, ethylene carbonate, vinylene carbonate; - Phosphate esters, such as trimethyl phosphate, triethyl phosphate (TEP), etc.; - Ureas, such as tetramethyl urea, tetraethyl urea, etc.; - Methyl 5-dimethylamino-2-methyl-5-oxopentanoate (commercially available under the trade name Rhodialsov Polarclean®) It contains at least one organic solvent selected from the group consisting of.

[0066] The following are particularly preferred: N-methyl-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), methyl 5-dimethylamino-2-methyl-5-oxopentanoate (commercially available under the trade name Rhodialsov Polarclean®), and triethyl phosphate (TEP).

[0067] The medium (L) may further comprise at least one additional liquid component that is different from the solvent (S) (or, in other words, the non-solvent).

[0068] The additional liquid component that does not have the ability to dissolve the polymer (VDF) is typically present in an amount lower than the level required to reach the cloud point, typically in an amount of 0.1% to 40%, preferably 0.1 wt% to 20 wt%, based on the total weight of the medium (L) of the composition (C L ) and may be added to the composition (C L ).

[0069] Without being bound by this theory, the addition of the non-solvent to the composition (C L ) is generally understood to be beneficial, advantageously, in increasing the rate of separation / coagulation in the process of manufacturing the porous membrane and / or in promoting coagulation by removal of the solvent (S) by evaporation.

[0070] Typically, the composition (C L ) comprises a total amount of polymer (N-ZW) and polymer (VDF) of at least 1 wt%, more preferably at least 3 wt%, even more preferably at least 5 wt%, based on the total weight of the medium (L), polymer (N-ZW), and polymer (VDF), and / or the composition (C L ) preferably comprises the medium (L), polymer (N-ZW), and polymer (VDF), and / or the composition (C LBased on the total weight of ), it contains a total amount of polymer (N-ZW) and polymer (VDF) of up to 60% by weight, more preferably up to 50% by weight, and even more preferably up to 30% by weight.

[0071] Conversely, the amount of the medium (L) in the composition (C L ) is at least 40% by weight, preferably at least 50% by weight, and even more preferably at least 70% by weight, based on the total weight of the medium (L), polymer (N-ZW), and polymer (VDF), and / or the amount of the medium (L) in the composition (C L ) is at most 99% by weight, preferably at most 97% by weight, and even more preferably at most 95% by weight, based on the total weight of the medium (L), polymer (N-ZW), and polymer (VDF).

[0072] The composition (C L ) may optionally contain at least one additional component. The additional component is preferably selected from the group consisting of a pore former, a nucleating agent, a filler, a salt, and a surfactant.

[0073] When used, the pore former is typically added to the composition (C L ) in an amount of usually 0.1% to 30% by weight, preferably 0.5% to 20% by weight, based on the total weight of the composition (C L ). Suitable pore formers are, for example, polyvinyl alcohol (PVA), cellulose acetate, polyvinylpyrrolidone (PVP), and polyethylene glycol (PEG).

[0074] Method for manufacturing a porous membrane The second aspect of the present invention relates to a method for manufacturing a porous membrane, and the method includes: Step (i): preparing the composition (C) defined above; Step (ii): processing the composition obtained in step (i) to obtain a membrane; Step (iii): treating the membrane obtained in step (ii), which usually includes contacting the membrane with a non-solvent medium [medium (NS)] to obtain a porous membrane. including.

[0075] The porous membrane can be produced by a solvent-free method that combines processing the composition (C) by melt extrusion in step (ii) and performing (salt) leaching by contacting the membrane with an extraction medium in step (iii), and optionally stretching the membrane during or after leaching, thereby obtaining a porous membrane in the form of either a flat membrane or hollow fibers.

[0076] In step (i), the composition (C) is prepared by mixing the polymer in the melt in the presence of a salt or a pore-forming agent.

[0077] Typically, the porous membrane can be obtained from the continuous extrusion of the prepared composition (C) by mixing the polymer in the melt in the presence of a salt and then performing salt leaching using, for example, immersion in hot water.

[0078] Depending on the nature of the extrusion die (flat die, tubular die, spinneret, etc.) and the processing conditions, flat membranes, tubular membranes, hollow fiber membranes, and capillary fiber membranes can be produced using this solvent-free method.

[0079] According to the first embodiment, in step (ii), the composition (C) is typically processed by casting, whereby a membrane is obtained.

[0080] According to the second embodiment of step (ii), the composition (C) is processed by casting to obtain a tubular membrane.

[0081] As described above, in some embodiments, the composition (C) further comprises at least one liquid medium [medium (L)] comprising at least one organic solvent [composition (C L )]. Usually, in the composition (C L ), the medium (L) comprises at least one solvent (S) for the polymer (VDF).

[0082] Therefore, in some embodiments, the method for producing a porous membrane is Step (i): preparing the composition (C L ) defined above; Step (ii): processing the composition obtained in step (i) to thereby obtain a film; Step (iii) treating the film obtained in step (ii), which usually includes contacting the film with a non-solvent medium [medium (NS)] to thereby obtain a porous film; comprising.

[0083] In step (i), the composition (C L ) is produced by any prior art. For example, the medium (L) may be added to the polymer (VDF) and the polymer (N-ZW), or preferably, the polymer (VDF) and the polymer (N-ZW) may be added to the medium (L), or further, the polymer (VDF), the polymer (N-ZW), and the medium (L) may be mixed simultaneously.

[0084] Any suitable mixing device can be used. Preferably, the mixing device is selected to reduce the amount of air trapped in the composition (C L ) that can cause defects in the final film. The mixing of the polymer (VDF), the polymer (N-ZW), and the medium (L) can conveniently be carried out in a sealed container, optionally maintained under an inert atmosphere. An inert atmosphere, more precisely a nitrogen atmosphere, has been found to be particularly advantageous for the production of the composition (C L ).

[0085] In step (i), the mixing time and stirring speed required to obtain a transparent and homogeneous composition (C L ) can vary widely depending on the dissolution rate of the components, temperature, efficiency of the mixing device, viscosity of the composition (C L ), etc.

[0086] In step (ii) of the method of the present invention, prior art can be used for processing the composition (C L ) to obtain a film.

[0087] In step (ii), the composition (CL ) is typically processed by casting, whereby a film is obtained.

[0088] Casting usually includes solution casting, which typically uses a casting knife, drawdown bar, or slot die to spread a uniform film of the composition (C L ) over a suitable substrate.

[0089] In step (ii), the temperature at which the composition (C L ) is processed by casting may or may not be the same as the temperature at which the composition (C L ) is mixed under stirring.

[0090] Different casting techniques are used depending on the final form of the film to be produced.

[0091] If the final product is a flat film, the composition (C L ) is typically cast as a film onto one side of a flat support substrate, typically a plate, belt or cloth or another microporous support membrane, using a casting knife, drawdown bar or slot die.

[0092] According to a first embodiment of step (ii), the composition (C L ) is processed by being cast onto a flat support substrate to give a flat film.

[0093] According to a second embodiment of step (ii), the composition (C L ) is processed by casting to give a tubular film.

[0094] According to a variant of this second embodiment of the invention, the tubular film is produced using a spinneret, and this technique is generally also called the "spinning method". Hollow fibers and capillary membranes can be produced by the spinning method.

[0095] The term "spinneret" refers to at least two concentric capillaries, i.e., the composition (C LAs used herein, an annular nozzle is meant to include a first outer capillary for the passage of (

[0096] According to this variant of the second embodiment of the invention, the composition (C L ) is typically pumped through a spinneret, usually together with at least one support fluid (so-called "bore fluid"). The support fluid functions as a support for the casting of the composition (C L ) and keeps the holes of the hollow fiber precursor or capillary precursor open. The support fluid may be a gas, or preferably a non-solvent medium [medium (NS)], or a mixture of medium (NS) and medium (L). The choice of the support fluid and its temperature depends on the required properties of the final membrane, since they can have a significant impact on the size and distribution of the pores in the membrane.

[0097] Step (iii) typically includes the step of contacting the membrane obtained in step (ii) with a non-solvent medium [medium (NS)] to thereby obtain a porous membrane.

[0098] Such a step of contacting with medium (NS) is usually effective for precipitating and then solidifying the composition (C L ) that constitutes the membrane in step (ii) to form a porous membrane.

[0099] The membrane can be precipitated in the medium (NS) by immersion in a bath of medium (NS), often referred to as a coagulation bath.

[0100] As an alternative (or usually before immersion in the coagulation bath), the contact of the membrane with medium (NS) can be achieved by exposing the membrane to a gas phase containing the vapor of the medium (NS).

[0101] Typically, for example, a gas phase is prepared by at least partially saturating with vapor of a medium (NS), and the membrane is exposed to the gas phase. For example, air with a relative humidity higher than 10%, usually higher than 50% (i.e., containing water vapor) can be used.

[0102] Before contacting with the non-solvent medium (by any of the techniques described above), the membrane can be exposed to air and / or a controlled atmosphere for a predetermined residence time in a state where the medium (NS) is substantially absent. Such an additional step may be beneficial for forming a skin on the exposed surface of the membrane by an alternative mechanism.

[0103] For example, in the spinning method, this can be achieved by arranging an air gap in the path followed by the hollow tubular precursor spun before being placed in the coagulation bath.

[0104] According to a particular embodiment, in step (iii), the coagulation / precipitation of the composition (C L ) can be promoted by cooling. In this case, the cooling of the membrane obtained in step (ii) can typically use any conventional technique.

[0105] Usually, when the coagulation / precipitation is thermally induced, the solvent (S) of the medium (L) of the composition (C L ) is preferably a "latent" solvent [solvent (LT)], that is, a solvent that acts as an active solvent for the polymer (VDF) only when heated above a specific temperature and cannot solubilize the polymer (VDF) below said temperature.

[0106] When the medium (L) contains a latent solvent or solvent (LT), steps (i) and (ii) of the method of the present invention are usually carried out at a temperature high enough to maintain the composition (C L ) as a homogeneous solution.

[0107] For example, in step (ii), according to this embodiment, the film can typically be processed at a temperature included in the range of 60°C to 250°C, preferably 70°C to 220°C, more preferably 80°C to 200°C. In step (iii), the film can typically be precipitated by cooling to a temperature of less than 100°C, preferably less than 60°C, more preferably less than 40°C.

[0108] Cooling can be performed by bringing the film obtained in step (ii) into contact with a cooling fluid, which may be a gaseous fluid (i.e., cooled air or a cooled conditioning atmosphere) or a liquid fluid.

[0109] In the latter case, since it is common to use the medium (NS) detailed above, the phenomena of precipitation induced by a non-solvent and precipitation induced by heat may occur simultaneously.

[0110] However, even in a situation where precipitation is thermally induced, it is generally understood that an additional step of contacting with the medium (NS), for example, a step of ending precipitation and promoting the removal of the medium (L), is performed.

[0111] When the medium (L) contains both the solvent (S) and a non-solvent for the polymer (VDF), at least a certain degree of selective evaporation of the solvent (S) can be used to promote the coagulation / precipitation of the polymer (VDF). In this case, the solvent (S) and the non-solvent component of the medium (L) are typically selected such that the solvent (S) has a significantly higher volatility than the non-solvent. As a result, under usually controlled conditions, the solvent (S) gradually evaporates and the polymer (VDF) precipitates, and as a result, the film and the medium (NS) actually come into contact.

[0112] Composition (C L ) When present in the pores, the pore-forming agent is usually at least partially removed from the porous film in the medium (NS) in step (iii) of the method of the present invention, if not completely.

[0113] In all of these approaches, the temperature gradient between steps (ii) and (iii), and the properties of the non-solvent (NS) and the solvent (L), such as the presence of the non-solvent in the solvent (L), are all parameters that are generally understood to be known to those skilled in the art for controlling the morphology of the final porous membrane, such as its average porosity.

[0114] The method of the present invention may include additional post-treatment steps, such as steps of rinsing and / or stretching the porous membrane, and / or drying it.

[0115] For example, the porous membrane can be further rinsed using a liquid medium miscible with the solvent (L).

[0116] Furthermore, the porous membrane can be advantageously stretched to increase its average porosity.

[0117] Typically, the porous membrane is advantageously dried at a temperature of at least 30 °C.

[0118] Drying can be carried out under air or an improved atmosphere, for example typically under an inert gas from which moisture has been removed (water vapor content less than 0.001% v / v). Drying can alternatively be carried out under vacuum.

[0119] For the purposes of the present invention, the term "non-solvent medium [medium (NS)]" means a medium consisting of one or more liquid substances that cannot dissolve the polymer (VDF) of the composition (C) or (C L ) and which advantageously promotes the coagulation / precipitation of the polymer (VDF) from the liquid medium of the composition (C L ).

[0120] The medium (NS) typically includes water and, optionally, an alcohol or polyalcohol, preferably a short-chain aliphatic alcohol having, for example, 1 to 6 carbon atoms, more preferably at least one organic solvent selected from methanol, ethanol, isopropanol, and ethylene glycol.

[0121] The medium (NS) is generally selected among those miscible with the medium (L) used for the preparation of the composition (C L ).

[0122] The medium (NS) may further contain the solvent (S) detailed above.

[0123] More preferably, the medium (NS) consists of water. Water is the cheapest non-solvent medium and can be used in large quantities.

[0124] Porous membrane In a third aspect, the present invention relates to - at least one vinylidene fluoride polymer [polymer (VDF)], and - at least one zwitterionic repeating unit [unit (R ZW )] derived from at least one ethylenically unsaturated monomer having at least two ionic groups, at least one of which is a cationic group [group (C+)], at least one of which is an anionic group [group (A-)], and further containing at least one hydroxyl group, contained in at least one polymer [polymer (N-ZW)], relates to a porous membrane containing.

[0125] The expression "porous membrane" is used according to its normal meaning in this technical field. That is, it is used to represent a membrane containing pores, i.e., voids or cavities of any shape and size.

[0126] As described above, the porous membrane of the present invention can be obtained from the composition (C) or (C L ) detailed above, and / or can be manufactured using the method detailed above.

[0127] The porous membrane of the present invention may be in the form of a flat membrane or in the form of a tubular membrane.

[0128] In applications where a compact module with a large surface area is required, hollow fiber membranes are particularly advantageous, while flat membranes are generally preferred when a high flux is required.

[0129] Flat membranes preferably have a thickness included in the range of 10 μm to 200 μm, more preferably 15 μm to 150 μm.

[0130] Tubular membranes typically have an outer diameter greater than 3 mm. Tubular membranes having an outer diameter included in the range of 0.5 mm to 3 mm are typically referred to as hollow fiber membranes. Tubular membranes having a diameter less than 0.5 mm are typically referred to as capillary membranes.

[0131] Membranes containing pores uniformly distributed throughout their thickness are generally known as symmetric (or isotropic) membranes; membranes containing pores non-uniformly distributed throughout their thickness are generally known as asymmetric (or anisotropic) membranes.

[0132] The porous membrane according to the present invention may be either a symmetric membrane or an asymmetric membrane.

[0133] Asymmetric porous membranes typically consist of one or more layers containing pores non-uniformly distributed throughout their thickness.

[0134] Asymmetric porous membranes typically include an outer layer containing pores having an average pore diameter smaller than the average pore diameter of the pores in one or more inner layers.

[0135] The porous membrane of the present invention preferably has an average pore diameter of at least 0.001 μm, more preferably at least 0.005 μm, still more preferably at least 0.01 μm. The porous membrane of the present invention preferably has an average pore diameter of at most 50 μm, more preferably at most 20 μm, still more preferably at most 15 μm.

[0136] Suitable techniques for measuring the average pore diameter in the porous membrane of the present invention are described, for example, in Handbook of Industrial Membrane Technology, edited by PORTER.Mark C., Noyes Publications, 1990, pp. 70-78.

[0137] The porous membrane of the present invention typically has a gravimetric porosity of 5% to 90%, preferably 10% by volume to 85% by volume, more preferably 30% to 90%, based on the total volume of the membrane.

[0138] For the purposes of the present invention, the term "gravimetric porosity" is intended to mean the fraction of voids with respect to the total volume of the porous membrane.

[0139] Suitable techniques for determining the gravimetric porosity in the porous membrane of the present invention are described, for example, in SMOLDERS K., et al. Terminology for membrane distillation. Desalination. 1989, vol. 72, pp. 249-262.

[0140] The porous membrane of the present invention may be a self-supporting porous membrane or any porous membrane supported on a substrate and / or including a backing layer.

[0141] The porous membrane includes at least one layer containing at least one polymer (VDF) and at least one polymer (N-ZW).

[0142] The porous membrane supported on a substrate can typically be obtained by laminating a pre-formed porous membrane to the substrate and / or the backing, or by directly manufacturing the porous membrane on the substrate and / or the backing.

[0143] Thus, the porous membrane may consist of only the layer containing polymer (VDF) and polymer (N-ZW), or may include additional layers.

[0144] In particular, the porous membrane of the present invention may further include at least one substrate. The substrate may be partially or completely interpenetrated by the porous membrane of the present invention.

[0145] The properties of the substrate / backing material are not particularly limited. The substrate is usually made of a material that has a minimal impact on the selectivity of the porous membrane. The substrate layer is preferably made of a non-woven material, such as a polymeric material like polypropylene, glass, or glass fiber.

[0146] In some embodiments, the porous membrane of the present invention - at least one substrate layer, preferably a non-woven substrate, - at least one top layer, and - at least one layer between the at least one substrate layer and the at least one top layer, comprising at least one polymer (VDF) and at least one polymer (N-ZW). is a porous composite membrane assembly comprising.

[0147] A typical example of such a porous composite membrane assembly is the so-called thin film composite (TFC) structure typically used for reverse osmosis or nanofiltration applications.

[0148] Non-limiting examples of top layers suitable for use in the porous composite membrane assembly of the present invention include those made from polymers selected from the group consisting of polyamide, polyimide, polyacrylonitrile, polybenzimidazole, cellulose acetate, and polyolefin.

[0149] The porous membrane layer comprising polymer (VDF) and polymer (N-ZW) may further include one or more additional components. However, embodiments in which the porous membrane comprises at least one layer consisting essentially of polymer (VDF) and polymer (N-ZW) are preferred, and it is understood that additives and / or residues of pore formers may be present in an amount not exceeding 10% by weight of the layer.

[0150] In the porous membrane, since the polymer (N-ZW) is used as an additive to the polymer (VDF), it is generally understood that the polymer (VDF) is present in a greater amount than the polymer (N-ZW). Usually, the weight ratio of polymer (N-ZW) / polymer (VDF) is at least 1 / 99 wt / wt, preferably at least 3 / 97 wt / wt, more preferably at least 5 / 95 wt / wt, and / or less than 50 / 50 wt / wt, preferably less than 40 / 60 wt / wt, preferably less than 30 / 70 wt / wt.

[0151] Method for separating an aqueous medium A fourth aspect of the present invention relates to a method for separating an aqueous medium, the method comprising contacting the aqueous medium with the porous membrane described above.

[0152] All features described above in relation to the porous membrane of the present invention are applicable with respect to its use in the methods described herein.

[0153] Depending on the average pore size, the porous membrane of the present invention has different uses and can also be applied to various separation processes such as microfiltration, ultrafiltration, reverse osmosis, etc., which are very different in relation to the size of the "blocked" / rejected substances, and their properties can be various.

[0154] The expression "aqueous medium" is not particularly limited and encompasses all media containing water, such as biological fluids, natural fluids, or synthetic mixtures.

[0155] The method for separating an aqueous medium of the present invention can be particularly applied to the desalination of brackish water and seawater, wastewater treatment / regeneration, can be used in the food industry, and can also be completed for the separation and purification of chemical and biological products.

[0156] According to a particular embodiment, the aqueous phase may in particular be an aqueous phase containing one or more contaminants.

[0157] The aqueous phase may be a particulate suspension of contaminants, i.e., a suspension containing chemical or physical contaminants (e.g., inorganic particles such as sand, sandstone, metal particles, ceramics; organic solids such as polymers, paper fibers, plant and animal residues; biological contaminants such as bacteria, viruses, protozoa, parasites).

[0158] The separation method of the present invention can be used to filter biological solutions (e.g., biofilms, viruses, other large molecules) and / or buffer solutions (e.g., solutions that may contain small amounts of solvents such as DMSO or other polar aprotic solvents).

[0159] For example, the separation method of the present invention may be a method for purifying biological fluids such as blood, particularly in an extracorporeal blood circuit or a dialysis filter. In this case, the porous membrane used usually has an average pore size of 0.001 to 5 μm and may be in the form of a tubular or hollow fiber membrane.

[0160] Alternatively, the separation method of the present invention may be a method for filtering a water suspension from suspended particles, in which case the porous membrane used usually has an average pore size of 5 μm to 50 μm.

[0161] Hereinafter, the present invention will be described in connection with the following examples, but the scope is merely illustrative and is not intended to limit the scope of the present invention.

[0162] Particularly suitable copolymers A fifth aspect of the present invention relates to a zwitterionic copolymer (N-ZW) comprising a zwitterionic repeating unit (R ZW ) derived from 3-((3-acrylamidopropyl)dimethylammonio)-2-hydroxypropane-1-sulfonate (AHPS) and a repeating unit (R N ) derived from at least one monomer selected from the list consisting of alkyl (meth)acrylate, vinyl acetate, and N,N-dimethylacrylamide. The copolymer is suitable for use in the composition (C) for producing the above-described membrane by the above-described method.

[0163] In a preferred embodiment, the copolymer (N-ZW) comprises zwitterionic repeating units (R ZW ) derived from 3-((3-acrylamidopropyl)dimethylammonio)-2-hydroxypropane-1-sulfonate (AHPS) and repeating units (R N ) derived from methyl methacrylate.

[0164] The copolymer is particularly suitable for use in the composition (C) for producing the above-described membrane by the above-described method.

[0165] In some other embodiments, the aforementioned copolymer further comprises repeating units derived from at least one monomer selected from the list consisting of 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2-hydroxyethyl acrylate (HEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, poly(ethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate, and poly(ethylene glycol) ethyl ether acrylate.

[0166] In some preferred embodiments, the copolymer of the present invention comprises repeating units derived from methyl methacrylate, repeating units derived from 3-((3-acrylamidopropyl)dimethylammonio)-2-hydroxypropane-1-sulfonate (AHPS), and repeating units derived from 2-hydroxyethyl methacrylate (HEMA).

[0167] Experiment Raw materials PVDF SOLEF® 1015 supplied by Solvay Specialty Polymers was used as the VDF homopolymer.

[0168] The following solvent reactants and solvents were obtained from Sigma Aldrich and used as received: N-[3-(dimethylamino)propyl]acrylamide (DMAPA), 3-chloro-2-hydroxy-1-propanesulfonic acid, sodium salt (CHPSNa), 2,2’-azobis(2-methylbutyronitrile) (AMBN), methyl methacrylate (MMA), 3-((2-(methacryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate (SPE), dimethyl sulfoxide (DMSO), and N-methyl-2-pyrrolidone (NMP).

[0169] Determination of molar mass Gel permeation chromatography was performed at 40 °C using a Jasco PU-2080 Plus HPLC pump equipped with two SHODEX KD-804 columns and a Jasco Refractive index-4030 detector. The mobile phase was composed of 1.5% LiBr in DMF and the flow rate was 1.0 mL / min. A 100 μL sample (concentration of approximately 5.0 mg / mL) was injected and calibration was performed using narrow standards of PMMA. M w is the weight-average molar mass and is expressed in g / mol units.

Example

[0170] Synthesis of 3-((3-acrylamidopropyl)dimethylammonio)-2-hydroxypropane-1-sulfonate (AHPS) AHPS was synthesized according to the following scheme.

Chemical formula

[0171] The synthesis was carried out by reacting N-[3-(dimethylamino)propyl]acrylamide (DMAPA) with 3-chloro-2-hydroxy-1-propanesulfonic acid, sodium salt (CHPSNa) in 50% water in the presence of hydroquinone monomethyl ether (MEHQ) which inhibits polymerization.

[0172] To a four-necked round-bottom flask equipped with mechanical stirring, temperature control, and a reflux condenser, 60 g of water and 0.02 g (mmol) of MEHQ were added with stirring. Subsequently, 43.53 g (221 mmol) of crystalline solid CHPSNa was added from a powder funnel, and the temperature was raised to 60 °C. Then, liquid DMAPA was added at a constant flow rate over 20 minutes. The maximum temperature reached 76 °C. Finally, the reaction mixture was heated to 90 °C, and the pH was maintained at 10 for 4 hours at this temperature by adding 50 wt% aqueous sodium hydroxide solution as needed (typically 0.14 g). Following the conversion, HPLC was performed, and the structure of the product was 1 confirmed by 13 1H and

[0173] Synthesis of poly(MMA-stat-AHPS) 95 / 5 mol / mol The statistical copolymer poly(methyl methacrylate-stat-3-((3-acrylamidopropyl)dimethylammonio)-2-hydroxypropane-1-sulfonate) was prepared by free radical polymerization using 2,2’-azobis(2-methylbutyronitrile) (AMBN) as the initiator. (-MMA = 95 mol% - AHPS = 5 mol%)

[0174] To a 500 mL kettle reactor equipped with a water condenser and mechanical stirring, at room temperature (22 °C), 7.5 g (18.73 mmol) of methyl methacrylate (MMA) solution (25 wt% in DMSO), 88.3 g of dimethyl sulfoxide (DMSO, purity 99%), and 5.80 g (9.86 mmol) of 3-((3-acrylamidopropyl)dimethylammonio)-2-hydroxypropane-1-sulfonate aqueous solution (AHPS content 50.0 wt%) were charged. The mixture was degassed by nitrogen bubbling for 50 minutes while raising the temperature of the reaction medium to 70 °C. 15.16 g (1.5 mmol) of AMBN solution (2% in DMSO) was further introduced under a nitrogen blanket. Then, 67.5 g (168.57 mmol) of MMA solution was added within 4 hours (flow rate 0.28 g / min), and the reaction medium was stirred at 70 °C for an additional 8 hours.

[0175] Subsequently, to determine the conversion rates of MMA and AHPS 1 Samples for 1H NMR analysis were taken. Results: MMA monomer conversion rate = 99.9%; AHPS monomer conversion rate = 84.4%. M W = 37200 g / mol

[0176] Synthesis of poly(MMA-stat-SPE) 95 / 5 mol / mol Into a 500 mL kettle reactor equipped with a water condenser and mechanical stirring, at room temperature (22 °C), 75 g (187.30 mmol) of methyl methacrylate (MMA) solution (25 wt% in DMSO), 92.5 g of dimethyl sulfoxide (DMSO, purity 99%), and 55.1 g (9.5 mmol) of 3-((2-(methacryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate (SPE) (5% in DMSO) solution were added. While raising the temperature of the reaction medium to 70 °C, the mixture was degassed for 50 minutes by nitrogen bubbling. Then, 15.16 g (1.5 mmol) of AMBN solution (2% in DMSO) was introduced under a nitrogen blanket. The reaction was carried out at 70 °C for 10 hours with stirring.

[0177] Subsequently, to determine the conversion rates of MMA and SPE 1 Samples for 1H NMR analysis were taken. Results: MMA monomer conversion rate = 98.1%; SPE monomer conversion rate = 94.1%. M W = 69000 g / mol

[0178] Fabrication of membranes containing zwitterionic additives The membranes were cast from a dope solution containing a blend of PVDF SOLEF® 1015 and the synthesized zwitterionic p(MMA-s-SPE) or (MMA-s-AHPS) copolymer in dimethyl sulfoxide (DMSO) or N-methyl-2-pyrrolidone (NMP), and immersed in a coagulation bath to induce phase separation (NIPS for non-solvent induced phase separation).

[0179] General method for preparing dope solution To prepare the dope solution, the zwitterionic additive was dissolved in NMP at about 65 °C, and PVDF was added. The resulting mixture was then stirred at 65 °C overnight. Several zwitterionic copolymer:PVDF ratios were fixed at 5 / 95, 10 / 90, and 20 / 80 wt / wt. A total of 0.5 g of polymer was included in 4.5 g of solvent.

[0180] The dope solution was degassed in a vacuum oven set at 40 °C for 24 hours. The dope solution was cast onto a glass plate using an adjustable film coating apparatus set to a gate size of 200 μm, and the polymer blend was precipitated by immersing it in a deionized water bath at room temperature for 20 minutes. After this time, the resulting film was transferred to a fresh deionized water bath and stored for at least overnight before use. As a control, 0.5 g of PVDF was dissolved in 4.5 g of NMP, and an additive-free PVDF film was produced following the NIPS procedure described above.

[0181] Hydrophilicity evaluation by contact angle measurement The hydrophilicity of the surface is usually evaluated by the water contact angle (WCA). That is, the contact angle of a water droplet on the sample surface is evaluated. Due to the absorption phenomenon, this method is not very suitable for measuring the contact angle of porous hydrophilic samples. Therefore, the contact angle was measured by the captive air bubble (CAB) method. In practice, this method measures the contact angle of a bubble on a surface immersed in a liquid, in this case water. Since the membrane is already wet, swelling and absorption are suppressed.

[0182] Theoretically, the air contact angle (ACA) and WCA are complementary. This means that an increase in ACA corresponds to an increase in hydrophilicity. WCA (°) = 180 - ACA (°).

[0183] The principle of the CAB method is shown in Figure 1.

[0184] The measurement of the air contact angle (ACA) was performed at room temperature using an adjusted environmental control chamber filled with deionized water (1) (DI water). Before analysis, the wet sample (2) was wound onto a 15×15 mm glass substrate and fixed to the sample holder (3) with double-sided tape. Then, the sample was immersed in deionized water, and 2 μL of air bubbles (4) were dropped onto the sample surface using a J-shaped syringe (5).

[0185] The contact angle measurement was performed using an optical tensiometer (Attension (registered trademark) Theta Flex supplied by BIOLIN) equipped with a high-quality monochromatic low-temperature LED (6) and a high-resolution (1984×1264) digital camera (7). The image acquisition parameters were set to 5 frames per second (FPS) and a minimum acquisition time of 60 seconds. The instrument was calibrated using a calibration ball (CA = 143.15°) with an allowable error of 0.03°.

[0186] The obtained contact angle values are the average of five measurements taken on the same sample. The error bars represent the standard deviation between measurements (Std) with the addition of the standard deviation during measurement.

[0187] Chemical aging of the film Using sodium hydroxide (NaOH) The film (sample size approximately 2×2 cm) was immersed in 20 mL of a sodium hydroxide (NaOH) solution with a pH of 11.5 (0.003 mol / L) at room temperature for one week. Stirring was not performed.

[0188] Using sodium hypochlorite (NaOCl) The film (sample size approximately 2×2 cm) was immersed in 20 mL of a sodium hypochlorite (NaOCl) solution with a concentration of 5000 ppm and a pH of 8 at room temperature for one week. Stirring was not performed. The NaOCl solution was prepared by diluting a commercially available 5% available chlorine solution and adjusting the pH to 8 by adding hydrochloric acid HCl. Aging was performed in the dark, and the aging solution was exchanged at least every two days.

[0189] Results As described above, an increase in the air contact angle (ACA) corresponds to an increase in the hydrophilicity of a given membrane.

[0190] The following table summarizes the ACA values measured for PVDF membranes with or without copolymer-based additives, and PVDF membranes aged or not aged with NaOH or NaOCl. Table 1 includes the results for membranes cast from NMP-containing dope solutions.

[0191]

Table 1

[0192] Comparing the ACA values measured for membranes without any additives (membrane 0), which are lower than the ACA values of membranes containing additives (membranes 1 - 6) in Table 1, it can be seen that the effect of the additives on the hydrophilicity of the PVDF membrane is clearly shown.

[0193] Furthermore, the results in Table 1 show that aging of the membrane in NaOH or NaOCl does not have an adverse effect on the hydrophilicity of the PVDF membrane containing additives. In fact, the ACA values measured for membranes containing additives aged in NaOH or NaOCl beforehand are still higher than the ACA values measured for membranes without additives after aging under the same conditions.

[0194] At a low additive content, i.e., a PVDF / additive composition of 95 / 5, surprisingly, an ACA value of 163° can be reached when AHPS is present in the additive (see membrane 4). To obtain a similar ACA value, i.e., 160°, with an additive containing SPE, a higher additive content, i.e., a PVDF / additive composition of 80 / 20, is required (compare membrane 3 and membrane 4).

[0195] From the results in Table 1, it is clear that changing the zwitterionic monomer involved in copolymerization with MMA from SPE to AHPS improves the hydrophilic ability of the resulting copolymer-based additive.

[0196] In other words, the high hydrophilicity of the PVDF-based membrane can be achieved with fewer additives when adding an additive containing an amphoteric ionic repeating unit further containing a hydroxyl group, compared to adding a similar additive containing an amphoteric ionic repeating unit not containing a hydroxyl group.

[0197] The excellent hydrophilicity of the PVDF-based membrane can be achieved with fewer additives, thus avoiding the adverse effects on the mechanical, thermal, and chemical resistance of the porous PVDF membrane due to an excessive abundance of the additive.

Claims

1. - At least one vinylidene fluoride (VDF) polymer [polymer (VDF)], and - having at least two ionic groups, at least one of which is a cationic group [group (C+)], at least one of which is an anionic group [group (A-)], and further containing at least one hydroxyl group, a zwitterionic repeating unit [unit (R ＺＷ )] derived from at least one ethylenically unsaturated monomer, and at least one polymer [polymer (N-ZW)] containing the same, A composition [composition (C)] containing

2. The polymer (VDF) is selected from the group consisting of polymers containing repeating units derived from VDF and optionally repeating units derived from at least one fluorine atom-containing ethylenically unsaturated monomer different from VDF, the composition (C) according to claim 1.

3. The at least one fluorine atom-containing ethylenically unsaturated monomer is as follows: (a) C2-C8 perfluoroolefins such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoroisobutylene; (b) Hydrogen-containing C2-C8 fluoroolefins different from VDF, such as vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutylene (HFIB), perfluoroalkyl ethylene of the formula CH2=CH-Rf1 (wherein Rf1 is a C1-C6 perfluoroalkyl group); (c) C2-C8 chloro- and / or bromo-containing fluoroolefins such as chlorotrifluoroethylene (CTFE); (d) Perfluoroalkyl vinyl ethers (PAVE) of the formula CF2=CFORf1 (wherein Rf1 is a C1-C6 perfluoroalkyl group such as CF3 (PMVE), C2F5 or C3F7); (e) Perfluorooxyalkyl vinyl ethers of the formula CF2=CFX0 (wherein X0 is a C1-C12 perfluorooxyalkyl group containing one or more ether oxygen atoms), including perfluoromethoxyalkyl vinyl ethers of the formula CF2=CFOCF2ORf2 (wherein Rf2 is a C1-C3 perfluoro(oxy)alkyl group such as -CF2CF3, -CF2CF2-O-CF3 and -CF3); and (f) Formula: 【Chemical 1】 (wherein Rf3, Rf4, Rf5, and Rf6 are each equal to or different from one another and independently are a fluorine atom or a C1-C6 perfluoro(oxy)alkyl group optionally containing one or more oxygen atoms such as -CF3, -C2F5, -C3F7, -OCF3, or -OCF2CF2OCF3) of (per)fluorodioxole The composition (C) according to claim 2, selected from the group consisting of **Claim 4** The polymer (VDF) is (a') at least 60 mol% of repeating units derived from vinylidene fluoride (VDF); (b') optionally, 0.1 to 30 mol% of repeating units derived from a fluorinated monomer different from VDF; and (c') optionally, 0.1 to 10 mol% of repeating units derived from one or more hydrogen-containing comonomers; is a polymer comprising The composition (C) according to claim 2, wherein all of the aforementioned mol% are based on the total moles of the repeating units of the polymer (VDF). **Claim 5** Unit (R ＺＷ ) consists of the following list: a) a hydroxyalkyl sulfonate or phosphonate of a dialkylammonium alkyl acrylate or methacrylate, acrylamide or methacrylamide; b) a heterocyclic betaine monomer containing at least one hydroxyl group; and c) a hydroxyalkyl sulfonate or phosphonate of a dialkylammonium alkyl styrene The composition (C) according to any one of claims 1 to 3, derived from at least one monomer selected from **Claim 6** The polymer (N-ZW) further contains a repeating unit [unit (R ＺＷ ), which is different from the unit (R Ｎ ), and is derived from at least one ethylenically unsaturated monomer having no ionizable group. The composition (C) according to any one of claims 1 to 5. **Claim 7** Unit (R Ｎ ) is - At least one monomer [unit (R Ｎ～１ ))] selected from the list consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, vinyl acetate, and N,N-dimethylacrylamide; - 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2-hydroxyethyl acrylate (HEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, poly(ethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate, and at least one monomer selected from the list consisting of poly(ethylene glycol) ethyl ether acrylate [unit (R Ｎ～２ )]; At least one monomer selected from the list consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, vinyl acetate, and N,N-dimethylacrylamide [unit (R Ｎ～１ )], and at least one monomer selected from the list consisting of 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2-hydroxyethyl acrylate (HEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, poly(ethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate, and poly(ethylene glycol) ethyl ether acrylate [unit (R Ｎ～２ )]; The composition (C) according to claim 6, derived from **Claim 8** The polymer (N-ZW) contains units (R ＺＷ ) in an amount of 0.1 to 30 mol% based on the total number of moles of the repeating units of the polymer (N-ZW), and the composition (C) according to claim 6 or 7. **Claim 9** The polymer (N-ZW) contains units (R Ｎ ), in an amount of 70 mol% or more, based on the total number of moles of the repeating units of the polymer (N-ZW). The composition (C) according to any one of claims 6 to 8. **Claim 10** The polymer (N-ZW) comprises repeating units (R Ｎ～１ ), and 0.1 to 50 mol% of the repeating units (R ＺＷ ) and (R Ｎ～２ ) based on the total number of moles of the repeating units of the polymer (N-ZW), the composition (C) according to any one of claims 7 to 9. **Claim 11** The polymer (VDF) is present in an amount greater than the polymer (N-ZW) in the composition (C), and the weight ratio of polymer (N-ZW) / polymer (VDF) is at least 1 / 99 wt / wt and / or less than 50 / 50 wt / wt. The composition (C) according to any one of claims 1 to 10. **Claim 12** At least one liquid medium [medium (L)] containing at least one organic solvent, and further comprising [composition (C Ｌ ), the composition (C) according to any one of claims 1 to 11. **Claim 13** The composition comprises a total amount of at least 1% by weight of polymer (N-ZW) and polymer (VDF) based on the total weight of the medium (L), polymer (N-ZW), and polymer (VDF), and / or the composition (C Ｌ ) comprises a total amount of polymer (N-ZW) and polymer (VDF), and / or the composition (C Ｌ ) comprises a total amount of polymer (N-ZW) and polymer (VDF) of at most 60% by weight based on the total weight of the medium (L), polymer (N-ZW), and polymer (VDF), and / or the composition (C), the composition (C) according to claim 12. **Claim 14** Step (i): preparing the composition (C) according to any one of claims 1 to 13; Step (ii): processing the composition provided in step (i) to thereby provide a film; and Step (iii): treating the membrane provided in step (ii), which typically involves contacting the membrane with a non-solvent medium [medium (NS)] to thereby provide a porous membrane. A method for producing a porous membrane, comprising: **Claim 15** - at least one vinylidene fluoride polymer [polymer (VDF)], and - having at least two ionic groups, at least one of which is a cationic group [group (C+)], at least one of which is an anionic group [group (A-)], and further containing at least one hydroxyl group, a zwitterionic repeating unit [unit (R ＺＷ )] derived from at least one ethylenically unsaturated monomer, and at least one polymer [polymer (N-ZW)] containing the same, A porous membrane comprising: **Claim 16** A method for separating an aqueous medium, comprising contacting the aqueous medium with the porous membrane according to claim 15. **Claim 17** A zwitterionic repeating unit (R) derived from 3-((3-acrylamidopropyl)dimethylammonio)-2-hydroxypropane-1-sulfonate (AHPS) ＺＷ ), and a repeating unit (R) Ｎ ) derived from at least one monomer selected from the list consisting of alkyl (meth)acrylate, vinyl acetate, and N,N-dimethylacrylamide, a copolymer (N-ZW).

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