Polymer additives comprising zwitterionic moieties for use in films based on polyvinylidene fluoride

Abstract

The present invention relates to a composition suitable for the manufacture of a film based on a polyvinylidene fluoride (VDF) polymer, a porous film thereof, a method for its manufacture and its use, in particular for the filtration of an aqueous phase. The composition comprising a polyvinylidene fluoride (VDF) polymer and a polymer additive comprising a zwitterionic moiety provides an excellent hydrophilic performance of the manufactured film.

Description

[0001] The present invention relates to a composition suitable for the manufacture of membranes based on vinylidene fluoride (VDF) polymers, to porous membranes thereof, to a method for the manufacture thereof and to the use thereof, in particular for the filtration of an aqueous phase. The present invention also relates to a copolymer suitable for use as a hydrophilic additive of said membranes. BACKGROUND

[0002] Porous membranes are thin objects whose key property is their ability to control the rate of permeation of chemical species through themselves. This feature is exploited in applications like separation applications (water and gases).

[0003] Due to their good mechanical strength, high chemical resistance and thermal stability, fluorinated polymers are widely used for the preparation of microfiltration and ultrafiltration membranes. Among them, partially fluorinated polymers based on vinylidene fluoride (VDF) are particularly convenient in controlling the porosity and the morphology of said membranes. Membranes made of vinylidene fluoride polymers [polymer (VDF)] are hydrophobic by nature and thus have a water repellency, a low water permeability and are subject to fouling by particles, proteins on their surface. The hydrophobicity hinders the permeation of water into the fluoropolymer membrane and thus the water permeability requires higher pressure and consumes more energy. Fouling temporarily or permanently reduces the permeate flux of water through the membrane, for example in ultrafiltration or microfiltration processes.

[0004] The ability to permeate water through porous VDF polymer membranes is generally improved by making the inner surface of the internal pores more hydrophilic. Moreover, it is generally accepted that increasing the hydrophilicity of VDF polymer membranes provides better resistance to fouling, since proteins and other contaminants are hydrophobic by nature.

[0005] Several strategies have been employed to make porous VDF polymer membranes hydrophilic and thus more water permeable and resistant to fouling. Among the methods that have been employed, one can cite methods based on grafting of hydrophilic species on the surface of the membrane, incorporation of hydrophilic comonomers in the backbone of the vinylidene fluoride polymer, incorporation of hydrophilic additives, etc... These methods are reviewed for example in Surface Modifications for Antifouling Membranes, Chemical Reviews, 2010, vol. 110, no. 4, pages 2448-2471. The use of zwitterionic structures to make PVDF-based membranes hydrophilic is part of these methods and is the most sought after.

[0006] WO 2015 / 070004 discloses zwitterionic membranes, wherein a selective layer formed from a statistical copolymer comprising zwitterionic repeating units and hydrophobic repeating units, such as p(MMA-s-SBMA), is arranged on a support layer formed from a porous PVDF membrane. However, neither the durability of the resulting membranes nor their resistance to chemical ageing is mentioned.

[0007] A hydrophilic additive for PVDF-based membranes is proposed in US 2018 / 0001278, which discloses comb and random zwitterionic copolymers (e.g. p(MMA-r-SBMA)) useful to enhance the hydrophilicity of PVDF membranes. The resulting additive- loaded PVDF membranes show good resistance to fouling and improved permeability compared to PVDF membranes. However, to obtain such results, a relatively high amount of zwitterionic additive is required, which can compromise the mechanical, chemical resistance of the PVDF membrane and its economic attractiveness.

[0008] There is a need to develop porous membranes with controlled pore size and showing high permeability and antifouling properties. Moreover, the membranes should show high thermal and chemical stability, which can ensure durable properties. There is also a need for additives with high thermal and chemical stability, able to make the PVDF membranes in which they are dispersed hydrophilic. In addition, these additives must be easily and durably incorporated into the vinylidene fluoride polymer membranes in order to improve their hydrophilicity, water permeability and antifouling properties in the long term, without compromising the inherent properties of the vinylidene fluoride polymers, which are high mechanical, thermal and chemical properties. Finally, the additives must be very effective hydrophilic agents in order to be used sparingly, thus avoiding any adverse effects on the mechanical, thermal and chemical resistance of the porous PVDF membranes due to their too high presence. SUMMARY

[0009] The first aspect of the present invention meets all these needs and more, the first aspect of the present invention relating to a composition [composition (C)] comprising:

[0010] - at least one vinylidene fluoride (VDF) polymer [polymer (VDF)], and

[0011] - at least one polymer [polymer (N-ZW)] comprising zwitterionic repeating units [units (R ZW )] derived from at least one ethylenically unsaturated monomer having at least two ionic groups, at least one of these ionic groups being a cationic group [group (C+)] and at least one of these ionic groups being an anionic group [group (A-)].

[0012] The second aspect of the present invention relates to a process for manufacturing a porous membrane, the process comprising: - providing a porous support membrane [membrane (S)] comprising a plurality of pores having a pore size [size (D)], and - providing a composition [composition (C)] comprising: - at least one vinylidene fluoride (VDF) polymer [polymer (VDF)], and - at least one polymer [polymer (N-ZW)] comprising zwitterionic repeating units [units (R ZW )] derived from at least one ethylenically unsaturated monomer having at least two ionic groups, at least one of these ionic groups being a cationic group [group (C+)] and at least one of these ionic groups being an anionic group [group (A-)], and - mixing the porous support membrane [membrane (S)] and the composition [composition (C)] to obtain a porous membrane [membrane (M)] having a pore size [size (D)] and comprising the composition [composition (C)] in the pores of the porous support membrane [membrane (S)].

[0013] Step (i): preparing a composition (C);

[0014] Step (ii): processing the composition provided in step (i) thereby providing a film; and,

[0015] Step (iii): processing the film provided in step (ii), typically comprising contacting the film with a non-solvent medium [medium (NS)] thereby providing a porous membrane.

[0016] A third aspect of the present application relates to a porous membrane comprising:

[0017] - at least one vinylidene fluoride polymer [polymer (VDF)], and

[0018] - at least one polymer [polymer (N-ZW)] comprising zwitterionic repeating units [units (R ZW )] derived from at least one ethylenically unsaturated monomer having at least two ionic groups, at least one of these ionic groups being a cationic group [group (C+)] and at least one of these ionic groups being an anionic group [group (A-)].

[0019] The porous membrane can be obtained from a composition (C) as described above and manufactured by a method as described above.

[0020] A fourth aspect of the present application relates to a method of separating an aqueous medium, the method comprising contacting the aqueous medium with a porous membrane as described above.

[0021] A fifth aspect of the present application relates to a copolymer (N-ZW) comprising zwitterionic repeating units (R ZW ) derived from 3-((3-acrylamidopropyl)dimethylammonio)-2-hydroxypropane-1 -sulfonate (AHPS) and repeating units (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 a composition (C) for manufacturing a membrane as described above by a method as described above.

[0022] The present applicant has surprisingly found that a composition (C) as detailed above is particularly effective for manufacturing a membrane providing outstanding permeation properties during aqueous medium filtration and separation processes while still being compatible with the typical water-induced coagulation process specific to membrane manufacturing.

[0023] Polymer (VDF)

[0024] The expressions "vinylidene fluoride polymer" and "polymer (VDF)" are used in the framework of the present application to designate a polymer comprising repeating units derived from vinylidene fluoride, typically as the main repeating unit constituent. Thus, a polymer (VDF) is typically a polymer consisting mainly of repeating units more than 50% by moles of which are derived from vinylidene fluoride (VDF).

[0025] The polymer (VDF) can further comprise repeating units derived from at least one fluorinated monomer different from VDF, and / or can further comprise repeating units derived from a non-fluorinated monomer, also called "hydrogenated monomer". The term "fluorinated monomer" is hereby intended to mean an ethylenically unsaturated monomer comprising at least one fluorine atom. The fluorinated monomer can further comprise one or more other halogen atoms (CI, Br, I).

[0026] In particular, the polymer (VDF) is typically selected from polyaddition polymers comprising repeating units derived from VDF, and optionally repeating units derived from at least one ethylenically unsaturated monomer comprising one or more fluorine atoms different from VDF, typically selected from the group consisting of:

[0027] (a) C2-C8 perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoroisobutene;

[0028] (b) hydrogen-containing C2-C8 fluoroolefins different from VDF, such as vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutene (HFIB), perfluoroalkyl ethylenes having the formula CH2=CH-R f1 wherein R f1 is a C1-C6 perfluoroalkyl group;

[0029] (c) C2-C8 chloro- and / or bromo-containing fluoroolefins, such as chlorotrifluoroethylene (CTFE);

[0030] (d) perfluoroalkyl vinyl ethers (PAVE) having the formula CF2=CFOR f1 wherein R f1 is a C1-C6 perfluoroalkyl group, such as CF3(PMVE), C2F5 or C3F7;

[0031] (e) perfluoroalkoxy vinyl ethers having the formula CF2=CFOX0, wherein X0 is a C1-C 12 perfluoroalkoxy group comprising one or more ether oxygen atoms, notably including perfluoromethoxyalkyl vinyl ethers having the formula CF2=CFOCF2OR f2 wherein R f2 is a C1-C3 perfluoro(oxy)alkyl group, such as -CF2CF3, -CF2CF2-O-CF3 and -CF3; and

[0032] (f) (per)fluoro-methylenes having the formula:

[0033]

[0034] wherein each of R f3 , R f4 , R f5 and R f6 is, independently of the others, a fluorine atom, a C1-C6 perfluoro(oxy)alkyl group, such as -CF3, -C2F5, -C3F7, -OCF3or -OCF2CF2OCF3.

[0035] The vinylidene fluoride polymer [polymer (VDF)] is preferably a polymer comprising:

[0036] (a’) at least 60% by moles, preferably at least 75% by moles, more preferably 85% by moles of recurring units derived from vinylidene fluoride (VDF);

[0037] (b’) optionally from 0.1 to 30% by moles, preferably from 0.1 to 20% by moles, more preferably from 0.1 to 15% by moles of recurring units derived from a fluorinated monomer different from VDF; and

[0038] (c’) optionally from 0.1 to 10% by moles, preferably from 0.1 to 5% by moles, more preferably from 0.1 to 1% by moles of recurring units derived from one or more hydrogenated monomers,

[0039] All the above % by moles refer to the total number of moles of recurring units of the polymer (VDF).

[0040] The fluorinated monomer is advantageously selected in the group consisting of vinyl fluoride (VF1); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl) vinyl ethers such as perfluoro(methyl) vinyl ether (PMVE), perfluoro(ethyl) vinyl ether (PEVE) and perfluoro(propyl) vinyl ether (PPVE); perfluoro(1,3-methylenedioxy) ; perfluoro(2,2-dimethyl-1,3-methylenedioxy) (PDD). Preferably, the possible additional fluorinated monomer is selected from chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF3) and tetrafluoroethylene (TFE).

[0041] The choice of the one or more hydrogenated monomers is not particularly limited; alpha-olefins, (meth)acrylic monomers, vinyl ether monomers, styrene monomers can be used; however, in order to optimize the chemical resistance, the embodiment wherein the polymer (F) is substantially free of recurring units derived from the one or more hydrogenated comonomers is preferred.

[0042] Thus, the vinylidene fluoride polymer [polymer (VDF)] is more preferably a polymer consisting essentially of:

[0043] (a') at least 60% by moles, preferably at least 75% by moles, more preferably 85% by moles of recurring units derived from vinylidene fluoride (VDF);

[0044] (b') optionally from 0.1 to 30% by moles, preferably from 0.1 to 20% by moles, more preferably from 0.1 to 15% by moles of a fluorinated monomer different from VDF; said fluorinated monomer is preferably selected in the group consisting of vinyl fluoride (VF1), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), perfluoromethylvinyl ether (MVE), trifluoroethylene (TrFE) and mixtures thereof, all the above % by moles referring to the total number of moles of recurring units of the polymer (VDF).

[0045] In addition to said recurring units, the polymer (VDF) can additionally present defects, end chains, impurities, chain inversions or chain branching, etc., which do not substantially alter the properties and characteristics of the polymer (VDF).

[0046] As non-limiting examples of polymers (VDF) useful in the present application, mention can be made notably of 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.

[0047] VDF homopolymers are particularly advantageous for use as polymer (VDF) in the composition (C).

[0048] The melt index of the polymer (VDF) is advantageously at least 0.01, preferably at least 0.05, more preferably at least 0.1 g / 10 min and advantageously less than 50, preferably less than 30, more preferably less than 20 g / 10 min, when measured according to ASTM test n. 1238 at 230°C under a piston load of 2.16 kg.

[0049] The melt index of the polymer (VDF) is advantageously at least 0.1, preferably at least 1, more preferably at least 5 g / 10 min and advantageously less than 70, preferably less than 50, more preferably less than 40 g / 10 min when measured according to ASTM test number 1238 at 230°C under a piston load of 5 kg.

[0050] 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 and advantageously less than 30, preferably less than 20, more preferably less than 10 g / 10 min when measured according to ASTM test number 1238 at 230°C under a piston load of 21.6 kg.

[0051] The polymer (VDF) advantageously has a melting point (Tm) advantageously at least 120°C, preferably at least 125°C, more preferably at least 130°C and at most 190°C, preferably at most 185°C, more preferably at most 180°C when determined by DSC at a heating rate of 10°C / min according to ASTM D3418. m ).

[0052] Polymer (N-ZW) comprising zwitterionic repeat units

[0053] The composition (C) generally comprises at least one polymer [polymer (N-ZW)] comprising zwitterionic repeat units [units (R ZW )] derived from at least one ethylenically unsaturated monomer having at least two ionic groups, at least one of these ionic groups being a cationic group [group (C+)] and at least one of these ionic groups being an anionic group [group (A-)], and further comprising at least one hydroxyl group.

[0054] Generally, the zwitterionic repeat units (R ZW ) are derived from at least one ethylenically unsaturated monomer, the overall charge of which is neutral, but contains a number of groups (C+) equal to the number of groups (A-), and further comprises at least one hydroxyl group. One or more cationic charges can be contributed by at least one onium or inium cation of nitrogen, such as ammonium, pyridinium and imidazolinium cations; phosphorus, such as phosphonium; and / or sulfur, such as sulfonium. One or more anionic charges can be contributed by at least one carbonate, sulfonate, phosphate, phosphonate, phosphinite, or vinylenolate anion, etc. Suitable zwitterionic monomers include, but are not limited to, betaine monomers, which are zwitterionic and contain an onium atom that does not bear a hydrogen atom and is not adjacent to an anionic atom.

[0055] In some embodiments, the units (R ZW) derived from at least one monomer selected from the list consisting of:

[0056] a) a hydroxyalkyl sulfonate or phosphonate of a dialkylammonium alkyl acrylate or methacrylate, acrylamido or methacrylamido, typically:

[0057] - sulfobutylhydroxypropyl dimethylammonium ethyl acrylate,

[0058] - sulfobutylhydroxypropyl dimethylammonium ethyl methacrylate,

[0059] - sulfobutylhydroxypropyl dimethylammonium propyl acrylamide,

[0060] - sulfobutylhydroxypropyl dimethylammonium propyl methacrylamide;

[0061] b) a heterocyclic betaine monomer comprising at least one hydroxyl group, typically

[0062] - a sulfobetaine derived from piperazine,

[0063] - a sulfobetaine derived from 2-vinylpyridine and 4-vinylpyridine,

[0064] - a sulfobetaine derived from imidazolium, and

[0065] c) a hydroxyalkyl sulfonate or phosphonate of a dialkylammonium alkyl styrene.

[0066] In some preferred embodiments, the unit (R ZW ) derived from at least one monomer selected from the list consisting of:

[0067]

[0068]

[0069]

[0070] In preferred embodiments, the unit (R ZW ) derived from at least one monomer selected from the list consisting of:

[0071] - sulfobutylhydroxypropyl dimethylammonium ethyl acrylate,

[0072] - sulfobutylhydroxypropyl dimethylammonium ethyl methacrylate (SHPE),

[0073] - sulfobutylhydroxypropyl dimethylammonium propyl acrylamide (AHPS), and

[0074] - sulfobutylhydroxypropyl dimethylammonium propyl methacrylamide (SHPP).

[0075] In more preferred embodiments, the units (R ZW ) are derived from sulfobutyl dimethylammonium propyl acrylamide (SBP).

[0076] In some embodiments, the polymer (N-ZW) further comprises repeating units [units (R ZW )] derived from at least one ethylenically unsaturated monomer without ionizable groups, different from the units (R N ).

[0077] In some embodiments, the units (R N ) are 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, [units (R N-1 ]. Preferably, the units (R N-1 ) are derived from methyl methacrylate, ethyl methacrylate or mixtures thereof. More preferably, the units (R N-1 ) are derived from methyl methacrylate.

[0078] In some other embodiments, the units (R N ) are 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, [units (R N-2 ]. Preferably, the units (R N-2 ) are derived from 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate or mixtures thereof. More preferably, the units (R N-2 ) are derived from 2-hydroxyethyl methacrylate (HEMA).

[0079] In some other embodiments, the units (R N ) are 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, [units (R N-1)] and at least one monomer selected from the list of the following: 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, unit (R) N-1 ) Derived from methyl methacrylate, ethyl methacrylate, or mixtures thereof and unit (R N-2 It is derived from 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, or mixtures thereof. More preferably, unit (R) N-1 ) is derived from methyl methacrylate and the unit (R) N-2 It is derived from 2-hydroxyethyl methacrylate (HEMA).

[0080] In some preferred embodiments, the polymer (N-ZW) disclosed herein comprises repeating units (R) derived from (AHPS), (SHPP), (SHPE), or mixtures thereof. ZW ) and repeating units derived from methyl methacrylate (R N-1 ).

[0081] In some other preferred embodiments, the polymer (N-ZW) disclosed herein comprises repeating units (R) derived from (AHPS). ZW ) and repeating units derived from methyl methacrylate (R N-1 ).

[0082] In some other preferred embodiments, the polymer (N-ZW) disclosed herein comprises repeating units (R) derived from (AHPS). ZW ), repeating units derived from methyl methacrylate (R) N-1 ) and repeating units (R) derived from 2-hydroxyethyl methacrylate (HEMA) N-2 ).

[0083] The polymer (N-ZW) of the composition (C) disclosed herein typically comprises, in molar amounts from 0.1% to 30% of the total number of repeating units relative to the polymer (N-ZW), preferably from 0.1% to 20% of molar amounts, more preferably from 0.1% to 7% of molar amounts, and even more preferably from 0.1% to 5% of molar amounts of units (R). ZW ).

[0084] Furthermore, the polymer (N-ZW) of the composition (C) according to the present disclosure generally comprises 70% or more by mole, preferably 80% or more by mole, more preferably 90% or more by mole and even more preferably 95% or more by mole of units (R N ) relative to the total number of moles of repeating units of the polymer (N-ZW).

[0085] When the repeating unit (R N-1 ) and the repeating unit (R N-2 ) are present, the polymer (N-ZW) generally comprises from 0.1% to 50% by mole, preferably from 0.1% to 40% by mole, more preferably from 0.1% to 30% by mole and even more preferably from 0.1% to 20% by mole of the repeating units (R ZW ) and (R N-2 ) relative to the total number of moles of repeating units of the polymer (N-ZW).

[0086] The polymer (N-ZW) according to the present application is a homopolymer or a copolymer. It is preferably a copolymer comprising repeating units (R ZW ) and repeating units (R N ). When it is a copolymer, it is a block copolymer, a branched copolymer or a statistical copolymer. Good results are obtained in the case where the polymer (N-ZW) is a statistical copolymer.

[0087] When referring to the molar mass, the weight average molar mass expressed in g / mol will be intended, unless otherwise specified. The latter can be determined by gel permeation chromatography (GPC) with light scattering detection (DLS or alternatively MALLS) or refractive index detection, using aqueous eluent or organic eluent (e.g. dimethylacetamide, dimethylformamide, etc.) depending on the polymer (N-ZW). The molar mass of the polymer (N-ZW) is not particularly limited. However, the weight average molar mass (Mw) of the polymer (N-ZW) is in the range 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, even more typically 20,000 to 200,000 g / mol.

[0088] The polymer (N-ZW) of the present disclosure can be obtained by any polymerization method known to the person of ordinary skill. For example, the polymer (N-ZW) can be obtained by free radical polymerization or copolymerization or controlled radical polymerization in aqueous solution, dispersion medium, organic solution or organic / aqueous solution (miscible phase).

[0089] The unit (R NThe ethylenically unsaturated monomers without ionizable groups of the unit (R

[0090] The unit (R ZW ) of the ethylenically unsaturated monomers with at least two ionic groups and further comprising at least one hydroxyl group can be obtained from commercial sources or synthesized according to methods known to the person of ordinary skill in the art, at least one of these ionic groups being a cationic group [group (C+)] and at least one of these ionic groups being an anionic group [group (A-)].

[0091] The unit (R ZW ) of suitable ethylenically unsaturated monomers can be obtained by reaction of 3-chloro-2-hydroxypropane-1 -sulfonic acid sodium salt (CHPSNa) with ethylenically unsaturated monomers bearing tertiary amino groups, as described in US20080045420 with respect to the synthesis of SHPP, starting from dimethylaminopropyl methacrylamide according to the reaction scheme:

[0092]

[0093] Other ethylenically unsaturated monomers bearing tertiary amino groups can be involved in the reaction with CHPSNa to obtain suitable ethylenically unsaturated monomers of the unit (R ZW ) of suitable ethylenically unsaturated monomers:

[0094]

[0095] Suitable ethylenically unsaturated monomers of the unit (R ZW ) can also be obtained by reaction of 3-chloro-2-hydroxypropane-1 -sulfonic acid sodium salt (CHPSNa) with ethylenically unsaturated monomers bearing pyridine or imidazole groups:

[0096]

[0097] The expression "derived from" linking the repeating unit (RZW) to the ethylenically unsaturated monomer is intended to define both the repeating unit (RZW) obtained directly from polymerization of the ethylenically unsaturated monomer and the same repeating unit (RZW) obtained by modification of an existing polymer.

[0098] Thus, the repeating unit (R ZW ) can be obtained by modification of a polymer comprising repeating units bearing tertiary amino groups, referred to as precursor polymers, by reaction with 3-chloro-2-hydroxypropane-1 -sulfonic acid sodium salt (CHPSNa). A similar modification is described in WO 2008125512, with 3-chloropropane-1 -sulfonic acid sodium salt instead of CHPSNa:

[0099]

[0100] Similarly, the repeating unit (R ZW ) can be obtained by modifying a polymer comprising repeating units bearing tertiary amino groups, pyridyl groups, imidazolyl groups or mixtures thereof, referred to as a precursor polymer, by reaction with 3-chloro-2-hydroxypropane-1 -sulfonic acid sodium salt (CHPSNa).

[0101] Since the polymer (N-ZW) is used as an additive to the polymer (VDF), in the composition (C), the polymer (VDF) is generally present in a significant amount relative to the polymer (N-ZW). Typically, the weight ratio 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.

[0102] The composition (C) can optionally comprise at least one additional ingredient. Said additional ingredient is preferably selected in the group consisting of non-solvents (water, alcohol...), co-solvents (e.g. ketones), pore-forming agents, nucleating agents, fillers, salts, surfactants.

[0103] When used, pore-forming agents are typically added to the composition (C) in an amount ranging generally from 1 to 30% by weight, preferably from 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).

[0104] When used, salts are typically added to the composition (C) in an amount ranging generally from 0.5 to 20% by weight, preferably from 1 to 10% by weight, based on the total weight of the composition (C). Suitable salts are for example NaCI, LiCI, LiCI04and LiCF3SO3.

[0105] Liquid medium

[0106] In some embodiments, the composition (C) further comprises at least one liquid medium [medium (L)], the at least one liquid medium comprising at least one organic solvent, [composition (C L )].

[0107] The term "solvent" is used herein in its usual meaning, i.e. it designates a substance capable of dissolving another substance (solute) to form a mixture that is homogeneously dispersed at the molecular level. In the case of a polymeric solute, it is customary to refer to a solution of the polymer in the solvent when the resulting mixture is transparent and there is no visible phase separation in the system. The point at which phase separation occurs, often referred to as the "cloud point", is considered to be the point at which the solution of polymer aggregates becomes hazy or cloudy.

[0108] Typically, in the composition (C L ) the medium (L) comprises at least one solvent (S) for the polymer (VDF).

[0109] The medium (L) typically comprises at least one organic solvent chosen in the group comprising:

[0110] - aliphatic hydrocarbons, including more particularly paraffins, such as in particular pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane or cyclohexane, and naphthalene and aromatic hydrocarbons and more particularly aromatic hydrocarbons, such as in particular benzene, toluene, xylene, cumene, petroleum fractions consisting of a mixture of alkylbenzenes;

[0111] - aliphatic or aromatic halogenated hydrocarbons, including more particularly perhalogenated hydrocarbons, such as in particular tetrachloroethylene, hexachloroethane;

[0112] - partially halogenated 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;

[0113] - aliphatic, cycloaliphatic or aromatic ether oxides, more particularly diethyloxide, 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);

[0114] - dimethyl sulfoxide (DMSO);

[0115] - 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 monobutyl ether;

[0116] - glycol ether esters, such as ethylene glycol methyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate;

[0117] - alcohols, including polyols, such as methanol, ethanol, diacetone alcohol, ethylene glycol;

[0118] - ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone;

[0119] - linear or cyclic esters, such as isopropyl acetate, n-butyl acetate, methyl acetoacetate, dimethyl phthalate, gamma-butyrolactone;

[0120] - linear or cyclic carboxamides, such as N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, dimethylformamide (DMF), diethylformamide or N-methyl-2-pyrrolidone (NMP);

[0121] - organic carbonates, such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, ethyl methyl carbonate, vinyl carbonate, vinylene carbonate;

[0122] - phosphates, such as trimethyl phosphate, triethyl phosphate (TEP);

[0123] - ureas, such as tetramethyl urea, tetraethyl urea;

[0124] - methyl-5-dimethylamino-2-methyl-5-oxopentanoate (commercially available under the trade name Rhodialsov ).

[0125] The following are particularly preferred: N-methyl-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), methyl-5-dimethylamino-2-methyl-5-oxopentanoate (commercially available under the trade name Rhodialsov ) and triethyl phosphate (TEP).

[0126] The medium (L) can further comprise at least one additional liquid component (or in other words, non-solvent) different from the solvent (S).

[0127] The additional liquid component, which does not have the ability to dissolve the polymer (VDF), can be added to the composition (C L ) in an amount generally lower than the level required to reach the cloud point, typically in an amount of from 0.1 to 40% by weight, preferably from 0.1 to 20% by weight, based on the total weight of the medium (L) of the composition (C L ).

[0128] Without being bound by this theory, it is generally understood that the addition of the additional liquid component to the composition (C LThe addition of a non-solvent in the composition (C) can be advantageously beneficial in increasing the rate of phase separation / coagulation in the process of manufacturing a porous membrane and / or to facilitate coagulation by evaporation of the solvent (S).

[0129] 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 medium (L), polymer (N-ZW) and polymer (VDF), and / or the composition (C L ) preferably comprises a total amount of polymer (N-ZW) and polymer (VDF) of at most 60 wt.%, more preferably at most 50 wt.%, even more preferably at most 30 wt.%, based on the total weight of medium (L), polymer (N-ZW) and polymer (VDF) and / or the composition (C L ).

[0130] Conversely, the amount of medium (L) in the composition (C L ) is at least 40 wt.%, preferably at least 50 wt.%, even more preferably at least 70 wt.%, based on the total weight of medium (L), polymer (N-ZW) and polymer (VDF), and / or the amount of medium (L) in the composition (C L ) is at most 99 wt.%, preferably at most 97 wt.%, even more preferably at most 95 wt.%, based on the total weight of medium (L), polymer (N-ZW) and polymer (VDF).

[0131] The composition (C L ) can optionally comprise at least one additional ingredient. Said additional ingredient is preferably selected in the group consisting of pore-forming agent, nucleating agent, filler, salt, surfactant.

[0132] When used, pore-forming agents are typically added to the composition (C L ) in an amount ranging typically from 0.1 to 30% by weight, preferably from 0.5 to 20% by weight, based on the total weight of the composition (C L ). Suitable pore-forming agents are for example polyvinyl alcohol (PVA), cellulose acetate, polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG).

[0133] Method of manufacturing a porous membrane

[0134] The second aspect of the present invention relates to a method for manufacturing a porous membrane, said method comprising:

[0135] Step (i): preparing a composition (C) as defined above;

[0136] Step (ii): processing the composition provided in step (i) so as to provide a thin film; and,

[0137] Step (iii): processing the thin film provided in step (ii), typically comprising contacting the thin film with a non-solvent medium [medium (NS)], so as to provide a porous membrane.

[0138] The porous membrane can be prepared by a solvent-free process combining the processing of the composition (C) by melt extrusion in step (ii) and the (salt) leaching by contacting the thin film with an extractant medium in step (iii), optionally stretching the thin film during or after the leaching and thereby providing a porous membrane in the form of a flat thin film or hollow fiber.

[0139] In step (i), the composition (C) is prepared by mixing the polymer in the form of a melt in the presence of a salt or a pore-forming agent.

[0140] Typically, the porous membrane can be obtained from continuous extrusion of the composition (C) prepared by mixing the polymer in the form of a melt in the presence of a salt followed by salt leaching using for example immersion in hot water.

[0141] Depending on the nature of the extrusion die (flat die, tubular die, spinneret...) and the processing conditions, this solvent-free process can be used to prepare flat, tubular, hollow fiber and capillary fiber membranes.

[0142] According to a first embodiment, in step (ii), the composition (C) is typically processed by casting so as to provide a thin film.

[0143] According to a second embodiment of step (ii), the composition (C) is processed by casting so as to provide a tubular thin film.

[0144] As mentioned, in some embodiments, the composition (C) further comprises at least one liquid medium [medium (L)] comprising at least one organic solvent, [composition (C L )]. Typically, in the composition (C L ), the medium (L) comprises at least one solvent (S) for the polymer (VDF).

[0145] Thus, in some embodiments, the process for manufacturing a porous membrane comprises:

[0146] Step (i): preparing a composition (C L ) as defined above;

[0147] Step (ii): processing the composition provided in step (i) so as to provide a thin film; and,

[0148] Step (iii): processing the film provided in step (ii), typically comprises contacting the film with a non-solvent medium [medium (NS)], thereby providing a porous membrane.

[0149] In step (i), the composition (C L ) is manufactured by any conventional technique. For example, the medium (L) can be added to the polymer (VDF) and the polymer (N-ZW), or preferably, the polymer (VDF) and the polymer (N-ZW) are added to the medium (L), or even the polymer (VDF), the polymer (N-ZW) and the medium (L) are mixed simultaneously.

[0150] Any suitable mixing device can be used. Preferably, the mixing device is chosen to reduce the amount of air entrained in the composition (C L ), such entrainment can lead to defects in the final membrane. Mixing of the polymer (VDF), the polymer (N-ZW) and the medium (L) can conveniently be carried out in a sealed vessel, optionally under an inert atmosphere. An inert atmosphere and more precisely a nitrogen atmosphere has been found to be particularly advantageous for manufacturing the composition (C L ).

[0151] In step (i), the mixing time and the stirring rate required to obtain a clear homogeneous composition (C L ) can vary widely depending on the dissolution rate of the components, the temperature, the efficiency of the mixing device, the viscosity of the composition (C L ), etc.

[0152] In step (ii) of the process of the application, conventional techniques can be used for processing the composition (C L ) to provide a film.

[0153] In step (ii), the composition (C L ) is typically processed by casting, thereby providing a film.

[0154] Casting typically involves solution casting, wherein a uniform film of the composition (C L ) is spread onto a suitable support, typically using a casting knife, a draw down bar or a slot die.

[0155] In step (ii), the temperature at which the composition (C L ) is processed by casting can be the same as the temperature at which the composition (C L ) is mixed under stirring or can be different.

[0156] Depending on the final form of the membrane to be manufactured, different casting techniques are used.

[0157] When the final product is a flat membrane, the composition (C L ) is typically cast into a thin film by means of a casting knife, a stretching bar or a slot die onto a flat support substrate, typically a plate, a belt or a fabric, or another microporous support membrane.

[0158] According to a first embodiment of step (ii), the composition (C L ) is processed by casting onto a flat support substrate to provide a flat thin film.

[0159] According to a second embodiment of step (ii), the composition (C L ) is processed by casting to provide a tubular thin film.

[0160] According to a variant of this second embodiment of the application, a spinneret is used to manufacture the tubular thin film, a technique otherwise commonly referred to as the "spinning method". Hollow fibers and capillary membranes can be manufactured according to the spinning method.

[0161] The term "spinneret" is hereby understood to mean an annular nozzle comprising at least two concentric capillaries: a first outer capillary for the passage of the composition (C L ) and a second inner capillary (commonly referred to as the "lumen") for the passage of a support fluid, also called "bore fluid".

[0162] According to this variant of the second embodiment, the composition (C L ) is typically pumped through the spinneret together with at least one support fluid, the so-called "bore fluid". The support fluid acts as a support for the casting of the composition (C L ) and keeps the pores of the hollow fiber or capillary precursor open. The support fluid can be a gas, or preferably a non-solvent medium [medium (NS)] or a mixture of medium (NS) and medium (L). The choice of support fluid and of its temperature depends on the desired properties of the final membrane, as they can have a significant influence on the size and distribution of the pores in the membrane.

[0163] Step (iii) typically comprises a step of contacting the thin film provided in step (ii) with a non-solvent medium [medium (NS)], thereby providing a porous membrane.

[0164] This step of contacting with the medium (NS) is typically effective in precipitating and solidifying the composition (C L ) constituting the thin film of step (ii) into a porous membrane.

[0165] The thin film can be precipitated in the medium (NS) by immersion in a bath of said medium (NS), which is commonly referred to as a coagulation bath.

[0166] As an alternative (or generally before immersion in the coagulation bath), the contact of the film with the medium (NS) can be achieved by exposing said film to a gas phase comprising a vapour of said medium (NS).

[0167] Typically, the gas phase is prepared for example by at least partial saturation with a vapour of the medium (NS) and said film is exposed to said gas phase. For example, air having a relative humidity higher than 10%, typically higher than 50% (i.e. comprising water vapour) can be used.

[0168] Before the contact with the non-solvent medium (by any of the techniques explained above), the film can be exposed to air and / or a controlled atmosphere during a given residence time in the substantial absence of said medium (NS). This additional step can be beneficial to the formation of a skin on the exposed surface of the film by alternative mechanisms.

[0169] For example, in a spinning process, this can be achieved by applying an air gap in the path followed by the hollow tubular precursor of the spinning before entering the coagulation bath.

[0170] According to certain embodiments, in step (iii), the coagulation / precipitation of the composition (C L ) can be promoted by cooling. In this case, the cooling of the film provided in step (ii) can typically use any conventional technique.

[0171] Typically, when the coagulation / precipitation is induced by heat, the solvent (S) of the medium (L) of the composition (C L ) is advantageously a “latent” solvent [solvent (LT)], i.e. a solvent that only behaves as an active solvent for the polymer (VDF) when heated above a certain temperature and that is not able to dissolve the polymer (VDF) below said temperature.

[0172] When the medium (L) comprises a latent solvent or a solvent (LT), steps (i) and (ii) of the process of the application are generally carried out at a temperature high enough to maintain the composition (C L ) as a homogeneous solution.

[0173] For example, in step (ii), according to this embodiment, the film can typically be processed at a temperature comprised between 60°C and 250°C, preferably between 70°C and 220°C, more preferably between 80°C and 200°C, and in step (iii), the film can typically be precipitated by cooling to a temperature lower than 100°C, preferably lower than 60°C, more preferably lower than 40°C.

[0174] The cooling can be achieved by contacting the film provided in step (ii) with a cooling fluid, which can be a gaseous fluid (i.e. cooled air or cooled modified atmosphere) or which can be a liquid fluid.

[0175] In this latter case, the medium (NS) is generally used as detailed above, so that the phenomena of non-solvent-induced and heat-induced precipitation can occur simultaneously.

[0176] However, it is generally understood that even in the case of heat-induced precipitation, an additional step of contact with a medium (NS) is performed, for example, in order to complete the precipitation and to facilitate the removal of the medium (L).

[0177] In the case where the medium (L) comprises both a solvent (S) and a non-solvent for the polymer (VDF), the selective evaporation of at least part of the solvent (S) can be used to facilitate the coagulation / precipitation of the polymer (VDF). In this case, the solvent (S) and the non-solvent components of the medium (L) are typically chosen so as to ensure that the solvent (S) has a higher volatility than the non-solvent, so that the solvent (S) is generally evaporated gradually under controlled conditions, causing the polymer (VDF) to precipitate, and thus the actual contact of the film with the medium (NS).

[0178] When present in the composition (C L ) in step (iii) of the process of the application, the pore-forming agent is generally at least partially, if not totally, removed from the porous film in the medium (NS).

[0179] In all these processes, it is generally understood that the temperature gradient during steps (ii) and (iii), the nature of the medium (NS) and of the medium (L), including the presence of a non-solvent in the medium (L), are parameters known to those of ordinary skill in the art for controlling the morphology of the final porous film, including its average porosity.

[0180] The process of the application can comprise additional post-treatment steps, such as a step of rinsing and / or stretching the porous film and / or a step of drying the porous film.

[0181] For example, the porous film can be additionally rinsed with a liquid medium miscible with the medium (L).

[0182] In addition, the porous film can advantageously be stretched so as to increase its average porosity.

[0183] Generally, the porous film is dried at a temperature advantageously of at least 30°C.

[0184] The drying can be performed under air or under a modified atmosphere, for example in an inert gas, typically removing the moisture (water vapour content less than 0.001% v / v). The drying can alternatively be performed under vacuum.

[0185] For the purposes of the present application, the term "non-solvent medium [medium (NS)]" means a medium comprising one or more solvents that are not capable of dissolving the composition (C) or (CL ) of the liquid medium of the composition (C L ) and advantageously facilitates the coagulation / precipitation of the polymer (VDF) from the composition (C

[0186] The medium (NS) typically comprises water and optionally at least one organic solvent chosen from alcohols or polyols, the organic solvent(s) being preferably aliphatic alcohols with short chains, for example from 1 to 6 carbon atoms, more preferably methanol, ethanol, isopropanol and ethylene glycol.

[0187] The medium (NS) is generally chosen among those that are miscible with the medium (L) used to prepare the composition (C L ).

[0188] The medium (NS) can further comprise a solvent (S) as detailed above.

[0189] More preferably, the medium (NS) consists of water. Water is the least expensive non-solvent medium and can be used in large quantities.

[0190] Porous membrane

[0191] A third aspect of the application relates to a porous membrane comprising:

[0192] - at least one vinylidene fluoride polymer [polymer (VDF)], and

[0193] - at least one polymer [polymer (N-ZW)] comprising zwitterionic repeating units [units (R ZW )] derived from at least one ethylenically unsaturated monomer having at least two ionic groups and further comprising at least one hydroxyl group, at least one of these ionic groups being a cationic group [group (C+)] and at least one of these ionic groups being an anionic group [group (A-)].

[0194] The expression "porous membrane" is used according to its usual meaning in the art, i.e. to designate a membrane comprising pores, i.e. voids or cavities, of any shape and size.

[0195] As mentioned, the porous membrane of the application is obtainable from the composition (C) or (C L ) as detailed above and / or manufactured using the method as detailed above.

[0196] The porous membrane of the application can be in the form of a flat membrane or in the form of a tubular membrane.

[0197] Flat membranes are generally preferred when high fluxes are required, while hollow fiber membranes are particularly advantageous in applications where compact modules with high surface area are required.

[0198] The flat membrane preferably has a thickness comprised between 10 pm and 200 pm, more preferably between 15 pm and 150 pm.

[0199] The tubular membrane typically has an outer diameter greater than 3 mm. The tubular membrane having an outer diameter comprised between 0.5 mm and 3 mm is typically referred to as hollow fiber membrane. The tubular membrane having a diameter less than 0.5 mm is typically referred to as capillary membrane.

[0200] The membrane containing pores uniformly distributed throughout its thickness is generally referred to as symmetric (or isotropic) membrane; the membrane containing pores non-uniformly distributed throughout its thickness is generally referred to as asymmetric (or anisotropic) membrane.

[0201] The porous membrane according to the present application can be a symmetric membrane or an asymmetric membrane.

[0202] The asymmetric porous membrane typically consists of one or more layers containing pores non-uniformly distributed throughout its thickness.

[0203] The asymmetric porous membrane typically comprises an outer layer containing pores having an average pore size smaller than the average pore size of the pores in the inner layer(s).

[0204] The porous membrane of the present application preferably has an average pore size of at least 0.001 pm, more preferably of at least 0.005 pm, and even more preferably of at least 0.01 pm. The porous membrane of the present application preferably has an average pore size of at most 50 pm, more preferably of at most 20 pm, and even more preferably of at most 15 pm.

[0205] Suitable techniques for determining the average pore size in the porous membrane of the present application are described, for example, in the Handbook of Industrial Membrane Technology, edited by PORTER, Mark C. Noyes Publications, 1990. pp. 70-78.

[0206] The porous membrane of the present application typically has a gravimetric porosity comprised between 5% and 90%, preferably between 10% and 85%, more preferably between 30% and 90%, by volume based on the total volume of the membrane.

[0207] For the purposes of the present application, the term "gravimetric porosity" is intended to mean the fraction of voids with respect to the total volume of the porous membrane.

[0208] Suitable techniques for determining the gravimetric porosity in the porous membranes of the present application are described, for example, in Terminology for membrane distillation by SMOLDERS, K., et al. Desalination. 1989, vol. 72, p. 249-262.

[0209] The porous membranes of the present application can be free-standing porous membranes or porous membranes supported on a substrate and / or comprising a backing layer.

[0210] The porous membranes comprise at least one layer comprising at least one polymer (VDF) and at least one polymer (N-ZW).

[0211] The porous membranes supported on a substrate are typically obtainable by laminating said substrate and / or backing with a pre-formed porous membrane or by manufacturing the porous membrane directly on said substrate and / or said backing.

[0212] The porous membranes can thus consist of only one layer comprising a polymer (VDF) and a polymer (N-ZW) or can comprise additional layers.

[0213] In particular, the porous membranes of the present application can further comprise at least one substrate. The substrate can be partially or completely interpenetrated by the porous membranes of the present application.

[0214] The nature of the substrate / backing is not particularly limited. The substrate is generally composed of a material having a minimal impact on the selectivity of the porous membranes. The substrate layer is preferably composed of a non-woven material, a polymeric material such as, for example, polypropylene, glass, glass fibers.

[0215] In some embodiments, the porous membranes of the present application are porous composite membrane assemblies comprising:

[0216] - at least one substrate layer, preferably a non-woven substrate,

[0217] - at least one top layer, and

[0218] - between said at least one substrate layer and said at least one top layer, at least one layer comprising at least one polymer (VDF) and at least one polymer (N-ZW).

[0219] Typical examples of such porous composite membrane assemblies are so-called thin film composite (TFC) structures, which are typically used for reverse osmosis or nanofiltration applications.

[0220] Non-limiting examples of top layers suitable for use in the porous composite membrane assemblies of the present application include those made from a polymer selected from the group consisting of polyamides, polyimides, polyacrylonitriles, polybenzimidazoles, cellulose acetate, and polyolefins.

[0221] The porous membrane layer comprising polymer (VDF) and polymer (N-ZW) can additionally comprise one or more than one additional component. However, embodiments wherein the porous membrane comprises at least one layer consisting essentially of polymer (VDF) and polymer (N-ZW) are preferred, it being understood that residues of additives and / or pore formers can be present in an amount not exceeding 10 wt.% of said layer.

[0222] In the porous membrane, polymer (N-ZW) is used as an additive to polymer (VDF), so it is generally understood that polymer (VDF) is present in a significant amount relative to polymer (N-ZW). Typically, the weight ratio 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.

[0223] Method of separating an aqueous medium

[0224] A fourth aspect of the present application relates to a method of separating an aqueous medium, said method comprising contacting said aqueous medium with a porous membrane as described above.

[0225] All the features described above in relation to the porous membrane of the present application apply in relation to its use in the method described herein.

[0226] Depending on its average pore size, the porous membrane of the present application has different uses and can be applied to various separation processes, such as microfiltration, ultrafiltration, reverse osmosis, which differ greatly in terms of the size of the "rejected" / rejected entities, which can be of any nature.

[0227] The expression "aqueous medium" is not particularly limited and encompasses all media comprising water, including biological fluids, natural fluids or synthetic mixtures.

[0228] The method of separating an aqueous medium of the present application can be applied, inter alia, to the desalination of brackish water and seawater, to the treatment / recycling of wastewater, can be used in the food industry and can ultimately be used for the separation and purification of chemical and biological products.

[0229] According to certain embodiments, the aqueous phase can be, inter alia, a water-based phase comprising one or more contaminants.

[0230] The aqueous phase can be a suspension of particles of contaminants, i.e. a suspension comprising chemical or physical contaminants (e.g. inorganic particles, such as sand, grit, metal particles, ceramics; organic solids, such as polymers, paper fibers, plant and animal residues; biological contaminants, such as bacteria, viruses, protozoa, parasites).

[0231] The separation method of the present application can be used for filtering biological solutions (e.g. bioburden, viruses, other macromolecules) and / or buffered solutions (e.g. solutions that can contain small amounts of solvents like DMSO or other polar aprotic solvents).

[0232] For example, the separation method of the present application can be a method for purifying biological fluids, such as blood, in particular in extracorporeal blood circuits or dialysis filters. In this case, the porous membrane used typically has an average pore size from 0.001 to 5 pm and can be in the form of a tubular or hollow fiber membrane.

[0233] In addition, the separation method of the present application can be a method for filtering aqueous suspensions from suspended particles, in particular; in this case, the porous membrane used typically has an average pore size from 5 pm to 50 pm.

[0234] The present application will now be described in connection with the following examples, the scope of which is merely illustrative and not intended to limit the scope of the present application.

[0235] Particularly suitable copolymers

[0236] A fifth aspect of the present application relates to a copolymer (N-ZW) comprising zwitterionic repeating units (R ZW ) derived from 3-((3-acrylamidopropyl)dimethylammonio)-2-hydroxypropane-1 -sulfonate (AHPS) and repeating units (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) to manufacture the membrane as described above by the method as described above.

[0237] 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.

[0238] The copolymer is particularly suitable for use in the composition (C) to manufacture the membrane as described above by the method as described above.

[0239] In some other embodiments, the copolymer as previously described further comprises repeat 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.

[0240] In some preferred embodiments, the copolymer of the present application comprises repeat units derived from methyl methacrylate, repeat units derived from 3-((3- acrylamidopropyl)dimethylammonio)-2-hydroxypropane-1 -sulfonate (AHPS), and repeat units derived from 2-hydroxyethyl methacrylate (HEMA).

[0241] Experiments

[0242] Raw materials

[0243] PVDF provided by Solvay Specialty Polymers 1015 was used as VDF homopolymer.

[0244] 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).

[0245] Molar mass determination

[0246] Gel permeation chromatography was performed at 40 °C using a Jasco PU-2080 Plus HPLC pump equipped with 2 SHODEX KD-804 columns and a Jasco Refractive index-4030 detector. The mobile phase consisted of 1.5% LiBr in DMF and the flow rate was 1.0 mL / min. 100 μL of sample (concentration of about 5.0 mg / mL) was injected and a calibration was obtained with PMMA narrow standards. M w is the weight average molar mass expressed in g / mol.

[0247] Examples

[0248] 3-((3-acrylamidopropyl)dimethylammonio)-2-hydroxypropane-1 -sulfonate (AHPS) synthesis

[0249] AHPS was synthesized according to the following scheme

[0250]

[0251] The synthesis was carried out by reacting N-[3-(dimethylamino)propyl]acrylamide (DMAPA) and 3-chloro-2-hydroxy-1 -propanesulfonic acid sodium salt (CHPSNa) in 50% water in the presence of hydroquinone monomethyl ether (MEHQ) to inhibit polymerization.

[0252] In a four necked round bottom flask, equipped with mechanical stirring, temperature control and reflux condenser, 60 g of water and 0.02 g (mmol) of MEHQ were added under stirring. Then 43.53 g (221 mmol) of crystalline solid CHPSNa were added through a powder funnel and the temperature was raised to 60°C. Then liquid DMAPA was added in a steady stream over 20 minutes, keeping the maximum temperature at 76°C. The reaction mixture was finally heated to 90°C and kept at this temperature during 4 hours, while the pH was kept at 10 by adding a 50 wt% sodium hydroxide solution in water when necessary (typically 0.14 g). The conversion was followed by HPLC and the reaction was stopped by cooling the reactor to room temperature. 1 H and 13 C NMR confirmed the product structure.

[0253] Synthesis of poly(MMA-stat-AHPS) 95 / 5 mol / mol

[0254] 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 initiator. -MMA = 95 mol% - AHPS = 5 mol%

[0255] In a 500 mL tank reactor equipped with a water condenser and mechanical stirring, at room temperature (22 °C), were introduced 7.5 g (18.73 mmol) of methyl methacrylate (MMA) solution (25 wt% in DMSO), 88.3 g of dimethyl sulfoxide (DMSO, 99% purity) and 5.80 g (9.86 mmol) of 3-((3-acrylamidopropyl)dimethylammonio)-2-hydroxypropane-1 -sulfonate solution in water (AHPS content 50.0 wt%). The mixture was degassed by bubbling nitrogen for 50 minutes, while the temperature of the reaction medium was raised to 70 °C. Further 15.16 g (1.5 mmol) of AMBN solution (2% in DMSO) were introduced under a nitrogen blanket. Then, 67.5 g (168.57 mmol) of MMA solution were added in 4 hours (flow rate of 0.28 g / min) and the reaction medium was stirred for further 8 hours at 70 °C.

[0256] After that, a sample was taken for 1 H NMR analysis to determine MMA and AHPS conversion.

[0257] Results: MMA monomer conversion = 99.9%; AHPS monomer conversion = 84.4%.

[0258] M W = 37200 g / mol

[0259] Synthesis of poly(MMA-stat-SPE) 95 / 5 mol / mol

[0260] In a 500 mL tank reactor equipped with a water condenser and mechanical stirring, at room temperature (22 °C), were introduced 75 g (187.30 mmol) of methyl methacrylate (MMA) solution (25 wt% in DMSO), 92.5 g of dimethyl sulfoxide (DMSO, 99% purity) and 55.1 g (9.5 mmol) of 3-((2-(methacryloyloxy)ethyl)dimethylammonio)propane-1 -sulfonate (SPE) solution (5% in DMSO). The mixture was degassed by bubbling nitrogen for 50 minutes, while the temperature of the reaction medium was raised to 70 °C. Then 15.16 g (1.5 mmol) of AMBN solution (2% in DMSO) were introduced under a nitrogen blanket. The reaction was carried out at 70 °C under stirring for 10 hours.

[0261] After that, a sample was taken for 1 H NMR analysis to determine MMA and SPE conversion. Results: MMA monomer conversion = 98.1%; SPE monomer conversion = 94.1%.

[0262] M W = 69000 g / mol

[0263] Preparation of membranes containing zwitterionic additives

[0264] Membranes were cast from dope solutions containing PVDF 1015 and synthesized zwitterionic p(MMA-s-SPE) or (MMA-s-AHPS) copolymers in blends in dimethylsulfoxide (DMSO) or N-methyl-2-pyrrolidone (NMP) were cast from dope solutions and immersed in coagulation bath in order to induce phase separation (NIPS stands for non-solvent induced phase separation).

[0265] General method for preparing dope solutions

[0266] To prepare the dope solutions, the zwitterionic additive was dissolved in NMP at about 65 °C and PVDF was added. The resulting mixture was then stirred overnight at 65 °C. Several zwitterionic copolymer: PVDF ratios were fixed at 5 / 95, 10 / 90 and 20 / 80 wt. / wt., with a total of 0.5 g of total polymer in 4.5 g of solvent.

[0267] The dope solutions were degassed in a vacuum oven set at 40 °C for 24 h. The dope solutions were cast on glass plates using an adjustable film applicator set at a 200 pm gate size, and the polymer blends were precipitated by immersion in a DI water bath at room temperature for 20 min. After this period of time, the resulting membranes were moved to a fresh DI water bath and stored overnight at least before use. As a control, PVDF membranes without additives were manufactured by dissolving 0.5 g of PVDF in 4.5 g of NMP and following the NIPS procedure explained above.

[0268] Hydrophilicity evaluation by contact angle measurements

[0269] Surface hydrophilicity is usually evaluated by water contact angle (WCA), i.e. by evaluating the contact angle of a water droplet on the surface of the sample. This method is not suitable for measuring the contact angle of porous hydrophilic samples due to absorption phenomena, so the contact angle is measured by the Captive Air Bubble (CAB) method. In fact, this method measures the contact angle of a bubble at the surface immersed in a liquid (in this case water), and since the membrane is already wet, swelling and absorption are inhibited.

[0270] Theoretically, the air contact angle (ACA) and the WCA are complementary, which means that increasing the ACA corresponds to increasing the hydrophilicity.

[0271] WCA (°) = 180 - ACA (°).

[0272] Figure 1 The principle of the CAB method is illustrated.

[0273] Air contact angle (ACA) measurements were performed at room temperature using an adapted environmental controlled chamber filled with deionized water (1) (DI water). Before analysis, wet samples (2) were wrapped on a 15x15 mm glass substrate, fixed on a sample holder (3) with double sided tape. The sample was then immersed in DI water and 2 pL of a bubble (4) was dropped on the sample surface using a J-shaped syringe (5).

[0274] Contact angle measurements were performed on an optical tensiometer (Theta Flex, provided by Biolin Scientific) equipped with a high-quality monochromatic cold light LED (6) and a high-resolution (1984 x 1264) digital camera (7). Image acquisition parameters were set to 5 frames per second (FPS) and the minimum acquisition time was 60 s. The instrument was calibrated using a calibration sphere (CA = 143.15°) with an accepted error of 0.03°.

[0275] The contact angle values obtained are the average of 5 measurements on the same sample. Error bars represent the standard deviation (Std) between measurements, added during the measurement process.

[0276] Chemical aging of the membranes

[0277] With sodium hydroxide (NaOH)

[0278] Membranes (sample size of about 2x2 cm) were immersed in 20 mL of sodium hydroxide (NaOH) solution at pH = 11.5 (0.003 mol / L) for one week at room temperature. No stirring was applied.

[0279] With sodium hypochlorite (NaOCl)

[0280] Membranes (sample size of about 2x2 cm) were immersed in 20 mL of sodium hypochlorite (NaOCl) solution at a concentration of 5000 ppm and pH = 8 for one week at room temperature. No stirring was applied. The NaOCl solution was prepared by dilution of a 5% active chlorine commercial solution and the pH was adjusted to 8 by addition of hydrochloric acid HCI. The aging was performed in the dark and the aging solution was changed at least every 2 days.

[0281] Results

[0282] As mentioned previously, an increase in the air contact angle (ACA) corresponds to an increase in the hydrophilicity of a given membrane.

[0283] The ACA values measured on PVDF membranes with or without copolymer additives and aged or not in NaOH or NaOCl are compiled in the following table. Table 1 contains the results on membranes cast from dope solutions containing NMP.

[0284] ​Table 1 : Air contact angle (ACA°) measured from films cast from NMP stock solutions

[0285]

[0286] As can be seen from Table 1, when comparing the ACA values measured for the film without any additive (Film 0) to the ACA values measured for any of the films containing any additive (Films 1 to 6), it is clear that the additives have an impact on the hydrophilicity of the PVDF films.

[0287] In addition, the results of Table 1 show that aging the films in NaOH or NaOCl does not adversely affect the hydrophilicity of the PVDF films containing the additives. In fact, the ACA values measured for any of the films containing any additive that were previously aged in NaOH or NaOCl are still higher than the ACA values measured for the film without additive that was aged under similar conditions.

[0288] For the composition PVDF / additive with low additive content, i.e. 95 / 5, the presence of AHPS in the additive surprisingly leads to an ACA value of 163° (see Film 4). To obtain a similar ACA value, i.e. 160°, with an additive comprising SPE, a higher additive content composition PVDF / additive, i.e. 80 / 20, is required (compare Film 3 to Film 4).

[0289] From the results of Table 1, it is clear that when the zwitterionic monomer involved in the copolymerization with MMA is changed from SPE to AHPS, the hydrophilic power of the resulting copolymer additive is enhanced.

[0290] In other words, when adding an additive comprising a zwitterionic repeating unit that further comprises a hydroxyl group, a high hydrophilicity of the PVDF-based film can be obtained with less additive than when adding a similar additive comprising a zwitterionic repeating unit that does not comprise any hydroxyl group.

[0291] A good hydrophilicity of the PVDF-based film can be reached with less additive, thereby avoiding adverse effects on the mechanical, heat and chemical resistance of the porous PVDF film due to the presence of too much of said additive.

Claims

1. A composition (C) comprising: - at least one vinylidene fluoride (VDF) polymer [polymer (VDF)], and - at least one polymer [polymer (N-ZW)] comprising zwitterionic repeating units [units (R ZW )] derived from at least one ethylenically unsaturated monomer having at least two ionic groups, at least one of these ionic groups being a cationic group [group (C+)] and at least one of these ionic groups being an anionic group [group (A-)], and further comprising repeating units [units (R ZW )] derived from at least one ethylenically unsaturated monomer free of ionizable groups, different from units (R N )], wherein units (R N ) are derived from methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate and butyl acrylate, and wherein polymer (N-ZW) comprises from 0.1 to 7% by moles of units (R ZW ) relative to the total number of moles of repeating units of polymer (N-ZW).

2. The composition (C) according to claim 1, wherein The polymer (VDF) is chosen from the group consisting of polymers comprising recurring units derived from VDF, and optionally recurring units derived from at least one olefinically unsaturated monomer containing one or more fluorine atoms different from VDF, generally chosen from the group consisting of: (a) C2-C8 perfluoroolefins; (b) hydrogen-containing C2-C8 fluoroolefins different from VDF; (c) C2-C8 chloro- and / or bromo-containing fluoroolefins; (d) perfluoroalkyl vinyl ethers (PAVE) of the formula CF2=CFOR f1 wherein R f1 is a C1-C6 perfluoroalkyl group; (e) perfluorooxyalkyl vinyl ethers having the formula CF2=CFOX0, wherein X0is a C1-C 12 perfluorooxyalkyl; and (f) (per)fluorodioxoles of formula: wherein each of R f3 , R f4 , R f5 and R f6 is the same as or different from each other and is independently a fluorine atom, a C1-C6 perfluoro(oxy)alkyl group optionally containing one or more oxygen atoms.

3. The composition (C) according to claim 2, wherein The polymer (VDF) is a polymer comprising: (a') at least 60% by moles of recurring units derived from vinylidene fluoride (VDF); (b') optionally from 0.1 to 30% by moles of recurring units derived from a fluorinated monomer different from VDF; and (c') optionally from 0.1 to 10% by moles of recurring units derived from one or more hydrogenated monomers, All the above by moles refer to the total number of moles of recurring units of the polymer (VDF).

4. The composition (C) according to claim 3, wherein component (a') is at least 75% by moles of recurring units derived from vinylidene fluoride (VDF).

5. The composition (C) according to claim 3, wherein component (a') is 85% by moles of recurring units derived from vinylidene fluoride (VDF).

6. The composition (C) according to claim 3, wherein component (b') is from 0.1 to 20% by moles of recurring units derived from a fluorinated monomer different from VDF.

7. The composition (C) according to claim 3, wherein component (b') is from 0.1 to 15% by moles of recurring units derived from a fluorinated monomer different from VDF.

8. The composition (C) according to claim 3, wherein component (c') is from 0.1 to 5% by moles of recurring units derived from one or more hydrogenated monomers.

9. The composition (C) according to claim 3, wherein component (c') is from 0.1 to 1% by moles of recurring units derived from one or more hydrogenated monomers.

10. The composition (C) according to any one of claims 1 to 9, wherein, Units (R ZW ) are derived from at least one monomer selected from the list consisting of: a) a hydroxyalkyl sulfonate or phosphonate of a dialkylammonium alkyl acrylate or methacrylate, acrylamido or methacrylamido; b) a heterocyclic betaine monomer comprising at least one hydroxyl group; and c) a hydroxyalkyl sulfonate or phosphonate of a dialkylammonium alkyl styrene.

11. The composition (C) according to claim 10, wherein the hydroxyalkyl sulfonate or phosphonate is chosen from: - sulfobydroxypropyl dimethyl ammonioethyl acrylate, - sulfobydroxypropyl dimethyl ammonioethyl methacrylate, - sulfobydroxypropyl dimethyl ammoniopropyl acrylamide, - sulfobydroxypropyl dimethyl ammoniopropyl methacrylamide.

12. The composition (C) according to claim 10, wherein the heterocyclic betaine monomer is chosen from: - sulfobetaines derived from 2-vinylpyridine and 4-vinylpyridine, - sulfobetaines derived from 2-vinylpyridine and 4-vinylpyridine, - sulfobetaines derived from imidazolium.

13. The composition (C) according to claim 1, wherein The polymer (N-ZW) comprises from 0.1 to 5% by moles of units (R ZW ) relative to the total number of moles of repeating units of the polymer (N-ZW).

14. The composition (C) according to claim 1, wherein The polymer (N-ZW) contains 70% or more by mole of the unit (R N ) relative to the total moles of the repeating units of the polymer (N-ZW).

15. The composition (C) according to claim 14, wherein The polymer (N-ZW) contains 80% or more by mole of the unit (R N ) relative to the total moles of the repeating units of the polymer (N-ZW).

16. The composition (C) according to claim 14, wherein The polymer (N-ZW) contains 90% or more by mole of the unit (R N ) relative to the total moles of the repeating units of the polymer (N-ZW).

17. The composition (C) according to claim 14, wherein The polymer (N-ZW) contains 95% or more by mole of the unit (R N ) relative to the total moles of the repeating units of the polymer (N-ZW).

18. The composition (C) according to claim 1, wherein The polymer (N-ZW) comprises repeating units (R N-1 ) and comprises from 0.1 % to 50% by moles of repeating units (R ZW ) and (R N-2 ) relative to the total number of moles of repeating units of the polymer (N-ZW).

19. The composition (C) according to claim 18, wherein The polymer (N-ZW) comprises repeating units (R N-1 ) and comprises from 0.1 % to 40% by moles of repeating units (R ZW ) and (R N-2 ) relative to the total number of moles of repeating units of the polymer (N-ZW).

20. The composition (C) according to claim 18, wherein The polymer (N-ZW) comprises repeating units (R N-1 ) and comprises from 0.1 % to 30% by moles of repeating units (R ZW ) and (R N-2 ) relative to the total number of moles of repeating units of the polymer (N-ZW).

21. The composition (C) according to claim 18, wherein The polymer (N-ZW) comprises repeating units (R N-1 ) and comprises from 0.1 % to 20% by moles of repeating units (R ZW ) and (R N-2 ) relative to the total number of moles of repeating units of the polymer (N-ZW).

22. The composition (C) according to any one of claims 1 to 9, wherein, In composition (C), the polymer (N-ZW) is present in a significant amount relative to the polymer (VDF).

23. The composition (C) according to claim 22, wherein In composition (C), the weight ratio polymer (N-ZW) / polymer (VDF) is at least 1 / 99 wt. / wt.

24. The composition (C) according to claim 22, wherein In composition (C), the weight ratio polymer (N-ZW) / polymer (VDF) is at least 3 / 97 wt. / wt.

25. The composition (C) according to claim 22, wherein In composition (C), the weight ratio polymer (N-ZW) / polymer (VDF) is at least 5 / 95 wt. / wt.

26. The composition (C) according to claim 22, wherein In composition (C), the weight ratio polymer (N-ZW) / polymer (VDF) is less than 50 / 50 wt. / wt.

27. The composition (C) according to claim 22, wherein In composition (C), the weight ratio polymer (N-ZW) / polymer (VDF) is less than 40 / 60 wt. / wt.

28. The composition (C) according to claim 22, wherein In composition (C), the weight ratio polymer (N-ZW) / polymer (VDF) is less than 30 / 70 wt. / wt.

29. The composition (C) according to any one of claims 1 to 9, further comprising at least one liquid medium [medium (L)], which comprises at least one organic solvent, [composition (C L )].

30. The composition (C) according to claim 29, comprising a total amount of polymer (N-ZW) and polymer (VDF) of at least 1 wt.% based on the total weight of 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) of at most 60 wt.% based on the total weight of medium (L), polymer (N-ZW) and polymer (VDF) and / or the composition (C L ).

31. The composition (C) according to claim 30, comprising a total amount of polymer (N-ZW) and polymer (VDF) of at least 3 wt.% based on the total weight of medium (L), polymer (N-ZW) and polymer (VDF).

32. The composition (C) according to claim 30, comprising a total amount of polymer (N-ZW) and polymer (VDF) of at least 5 wt.% based on the total weight of medium (L), polymer (N-ZW) and polymer (VDF).

33. The composition (C) according to claim 30, which comprises a total amount of polymer (N-ZW) and polymer (VDF) of at most 50 wt.%, based on the total weight of medium (L), polymer (N-ZW) and polymer (VDF) and / or composition (C L ).

33. The composition (C) according to claim 30, which comprises a total amount of polymer (N-ZW) and polymer (VDF) of at most 50 wt.%, based on the total weight of medium (L), polymer (N-ZW) and polymer (VDF) and / or composition (C L ).

34. The composition (C) according to claim 30, which composition (C L ) comprises at most 30 wt.% of the total amount of polymer (N-ZW) and polymer (VDF) based on the total weight of medium (L), polymer (N-ZW) and polymer (VDF) and / or composition (C L ).

35. The composition (C) according to claim 2, wherein the C2-C8 perfluoroolefin is selected from tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoroisobutylene.

36. The composition (C) according to claim 2, wherein the hydrogen-containing C2-C8 fluoroolefin, which is different from VDF, is selected from vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutylene (HFIB), and has the formula CH2=CH-R. f1 Perfluoroalkyl ethylene, wherein R f1 It is a C1-C6 perfluoroalkyl group.

37. The composition (C) according to claim 2, wherein the C2-C8 chlorofluoroolefin is selected from chlorotrifluoroethylene (CTFE).

38. The composition (C) according to claim 2, wherein the perfluoroalkyl vinyl ether (PAVE) of formula CF2=CFOR f1 , wherein R f1 is a C1-C6 perfluoroalkyl group selected from CF3 (PMVE), C2F5 or C3F7.

39. The composition (C) according to claim 2, wherein the perfluorooxyalkyl vinyl ether of the formula CF2=CFOX0, wherein X0 is a C1-C3 perfluoro(oxy)alkyl group comprising one or more ether oxygen atoms. 12 perfluorooxyalkyl group selected from perfluoromethoxyalkyl vinyl ethers of the formula CF2=CFOCF2OR f2 wherein R f2 is a C1-C3 perfluoro(oxy)alkyl group.

40. The composition (C) according to claim 39, wherein the perfluoromethoxyalkyl vinyl ether is of formula CF2=CFOCF2OR wherein R is a C1-C3 perfluoro(oxy)alkyl group selected from -CF2CF3, -CF2CF2-O-CF3 and -CF3. f2 f2 - CF2CF2-O-CF3 and -CF3.​ 41. The composition (C) according to claim 2, wherein the C1-C6 perfluoro(oxy)alkyl group comprising one or more oxygen atoms is selected from -CF3, -C2F5, -C3F7, -OCF3 or -OCF2CF2OCF3.

42. A process for manufacturing a porous membrane, said process comprising: Step (i): preparing a composition (C) according to any one of claims 1 to 41 ; Step (ii): processing the composition provided in step (i), thereby providing a thin film; and, Step (iii): processing the thin film provided in step (ii), typically comprising contacting the thin film with a non-solvent medium [medium (NS)], thereby providing a porous membrane.

43. A porous membrane comprising: - at least one vinylidene fluoride polymer [polymer (VDF)], and - at least one polymer (N-ZW). - at least one polymer [polymer (N-ZW)] comprising zwitterionic repeating units [units (R ZW )] derived from at least one ethylenically unsaturated monomer having at least two ionic groups, at least one of these ionic groups being a cationic group [group (C+)] and at least one of these ionic groups being an anionic group [group (A-)], and further comprising repeating units [units (R ZW )] derived from at least one ethylenically unsaturated monomer without ionizable groups, different from units (R N )], wherein units (R N ) are derived from methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate and butyl acrylate, and wherein polymer (N-ZW) comprises from 0.1 to 7% by moles of units (R ZW ) relative to the total number of moles of repeating units of polymer (N-ZW).

44. A method of separating an aqueous medium, the method comprising contacting the aqueous medium with the porous membrane of claim 43.

45. A copolymer (N-ZW) comprising a zwitterionic repeating unit (R) derived from 3-((3-acrylamidopropyl)dimethylammonium)-2-hydroxypropane-1-sulfonate (AHPS). ZW ) and repeating units (R) derived from at least one monomer selected from the list of the following. N ): (meth)acrylate alkyl ester, wherein the copolymer (N-ZW) comprises units (R) in the molar percentage of the total number of repeating units relative to the copolymer (N-ZW) from 0.1% to 7% by molar. ZW ).

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