Anion-exchange polymer membrane and method for synthesizing same by electron bombardment

Abstract

The invention relates to a method for preparing an anion-exchange polymer membrane which contains a crosslinked ionomer, which method comprises the electron bombardment of an ionomer in the form of a film, the ionomer being a block polymer of formula (A-B)n-A, the symbol A representing a polyvinylaromatic block bearing quaternary amine groups, the symbol B representing a hydrogenated block of a poly(1,3-diene) or of a copolymer comprising monomer units of a 1,3-diene and of a vinylaromatic monomer, n being an integer equal to or greater than 1. The membrane intended for use in a fuel cell or electrolyzer has good resistance to alkaline media.

Description

[0001] Anion exchange polymer membrane and its synthesis process by electron bombardment

[0002] The field of the present invention is that of the processes for synthesizing an anion exchange polymer membrane containing an ionomer and intended for use in an electrolyzer or a fuel cell.

[0003] The core of a fuel cell and electrolyzer consists of two electrodes, an anode and a cathode, an electrolytic layer separating them, and a catalyst located at the interfaces between the electrolytic layer and each electrode. Fuel cells and electrolyzers include a membrane that forms the electrolytic layer. One of the membrane's components is the ionomer, a polymer containing ionic or ionizable groups. The presence of these ionic or ionizable groups in the polymer is essential to give the polymer the ionic conductivity necessary for the transfer of anions from the cathode to the anode. The most common ionic or ionizable groups in polymers used in anion-exchange membrane fuel cells are quaternary amines, imidazolinium, phosphonium, and sulfonium.Ionomers whose ionic groups are quaternary amines or imidazoliums are generally obtained from halogenated polymers that are modified by reaction with a tertiary amine or an imidazole. For example, see document WO 2019010290, which describes the reaction between a tertiary amine and the previously bromoalkylated aromatic motifs of rigid blocks constituting a block polymer in which the rigid blocks are linked together by a soft block. It is also known from the document "Energy Technol. 2017, 5, 929-936" to synthesize an ionomer bearing imidazolinium groups by reacting 1-methylimidazole with a styrene-vinylbenzyl chloride copolymer.

[0004] When used in a fuel cell or electrolyzer, the anion exchange membrane is generally exposed to a highly alkaline environment, which is very aggressive to ionomers, consequently reducing the membrane's lifespan. Therefore, it is a concern to find new anion exchange membranes that can better withstand these alkaline environments to extend their lifespan.

[0005] The Plaintiff has discovered a process that solves the problems mentioned.

[0006] Thus, a first object of the invention is a process for preparing an anion exchange polymer membrane containing a crosslinked ionomer, which process comprises electron bombardment of an ionomer in the form of a film, the ionomer being a block polymer of formula (I), (AB)nA (I), the symbol A representing a polyvinylaromatic block bearing quaternary amine groups, the symbol B representing a hydrogenated block of a poly(1,3-diene) or of a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1.Another object of the invention is an anion exchange polymer membrane containing a crosslinked ionomer, the crosslinked ionomer being a block polymer of formula (I) crosslinked by electron bombardment (AB)nA (I), the symbol A representing a polyvinylaromatic block bearing quaternary amine groups, the symbol B representing a hydrogenated block of a poly(1,3-diene) or a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1, which membrane is capable of being obtained by the process according to the invention.

[0007] The invention also relates to a crosslinked ionomer, a block polymer of formula (I) crosslinked by electron bombardment.

[0008] The invention also relates to a fuel cell or an electrolyzer containing a membrane according to the invention.

[0009] Detailed description of the invention

[0010] The polymers mentioned in the description can be of fossil origin or bio-based. In the latter case, they can be derived, partially or entirely, from biomass or obtained from renewable raw materials derived from biomass. Similarly, they can also come from the recycling of previously used materials; that is, they can be derived, partially or entirely, from a recycling process, or even obtained from raw materials themselves derived from a recycling process.

[0011] The terms "membranes" and "films" are well known to those skilled in the technical field. It is well understood that a membrane is a structure as defined by IUPAC in "IUPAC Recommendations 1996." Similarly, and in accordance with the definition given by IUPAC, the term "film" is understood according to the definition given by IUPAC in "IUPAC Recommendations 1996."

[0012] The useful ionomer in the process according to the invention is a block polymer bearing quaternary amine groups of formula (I) (AB)nA (I), the symbol A representing a polyvinylaromatic block bearing ionic groups which are quaternary amines, the symbol B representing a hydrogenated block of a poly(1,3-diene) or of a copolymer comprising monomeric units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1.

[0013] According to any one of the embodiments of the invention, the block polymer of formula (I) is preferably a linear polymer.

[0014] Preferably, n is equal to 1, in which case the block polymer of formula (I) is a triblock. The triblock then has the formula ABA, where the symbol A represents a polyvinylaromatic block bearing quaternary amine groups and the symbol B represents a hydrogenated block of a homopolymer of a 1,3-diene or of a copolymer comprising monomeric units of a 1,3-diene and a vinylaromatic monomer. The polyvinylaromatic block of the ionomer can be a block of a homopolymer of a vinylaromatic monomer or a block of a copolymer of two or more vinylaromatic monomers. The vinylaromatic monomer of the polyvinylaromatic block of the ionomer is also called the "first vinylaromatic." In the present invention, vinylaromatic monomer means a monomer of formula Ar-CH=CH2 or Ar-CR=CH2, the symbol Ar representing an aryl group, substituted or not, and the symbol R an alkyl group such as methyl.The aryl group, represented by the symbol Ar, is preferably a phenyl group or a phenyl group substituted with an alkyl group having 1 to 4 carbon atoms. Examples of vinylaromatic monomers useful for the purposes of the invention include styrene, styrene substituted with an alkyl group in the para, meta, ortho, or alpha positions. The alkyl group is preferably an alkyl group having 1 to 4 carbon atoms. The polyvinylaromatic block is preferably a polystyrene block, a polyalphamethylstyrene block, or a styrene-alphamethylstyrene copolymer block. The styrene-alphamethylstyrene copolymer block may be stochastic, tapered, or block-type.

[0015] The polyvinylaromatic block of the ionomer is also characterized by the presence of quaternary amine groups. The polyvinylaromatic block of the ionomer typically contains vinylaromatic monomer units bearing a quaternary amine group. The vinylaromatic monomer unit bearing a quaternary amine group is typically a monomer unit in which the aryl group is linked to a quaternary amine group via a saturated hydrocarbon chain. In other words, the aromatic ring of a vinylaromatic monomer unit bearing a quaternary amine group is substituted by a saturated hydrocarbon chain, specifically an alkyl chain substituted with a quaternary amine group.The saturated hydrocarbon chain substituted with a quaternary amine group, present in the block represented by the symbol A, is preferably a linear chain containing 1 to 10 carbon atoms, more preferably a linear chain containing 2 to 8 carbon atoms. In this application, a linear chain is understood to be an acyclic and unbranched chain. Preferably, the quaternary amine group is N-alkylpiperidinium. More preferably, the quaternary amine group is N-methylpiperidinium. The quaternary amine groups are preferably N-alkylpiperidinium, more preferably N-methylpiperidinium.

[0016] As is known, the polyvinylaromatic block bearing quaternary amine groups is obtained by a two-step modification of the aryl groups: a haloalkylation reaction of the aromatic ring to form a halogenated polymer, followed by a reaction with a tertiary amine to form the ionomer. See, for example, patent application WO 2010010290.

[0017] According to the invention, the block represented by the symbol B is a hydrogenated block of a poly(1,3-diene) or a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer. The vinylaromatic monomer or a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer is also referred to as "second vinylaromatic".

[0018] A hydrogenated block of a poly(1,3-diene) or a copolymer comprising monomeric units of a 1,3-diene and a vinylaromatic monomer is defined as a block in which the 1,3-diene monomer units are reduced to more than 95%, preferably more than 98%, and more preferably more than 99% by mole of the 1,3-diene monomer units. The hydrogenation reaction of a poly(1,3-diene) or a copolymer comprising monomeric units of a 1,3-diene and a vinylaromatic monomer is a well-known reaction. For example, reference can be made to documents EP 1840993 Bl, US 5239010, US 5468574 and US 20070021569 which describe the selective hydrogenation of a poly(l,3-diene) or a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer of a block polymer of formula (I).

[0019] The term "a 1,3-diene" refers to one or more 1,3-dienes. "Several" refers to at least two. The 1,3-diene preferably contains 4 to 8 carbon atoms. The 1,3-diene is preferably 1,3-butadiene, isoprene, or a mixture of 1,3-butadiene and isoprene, and more preferably 1,3-butadiene.

[0020] According to a first embodiment, the block represented by the symbol B is a hydrogenated block of poly(1,3-diene). In the present invention, poly(1,3-diene) is understood to be a polymer whose constituent units are the monomeric units of a 1,3-diene. Poly(1,3-diene) is preferably a homopolymer of a 1,3-diene, in which case the constituent units of poly(1,3-diene) are monomeric units of a single 1,3-diene. Poly(1,3-diene) is more preferably a homopolymer of 1,3-butadiene.

[0021] According to a second variant, the block represented by the symbol B is a hydrogenated block of a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer. The copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer may be statistical or gradient.

[0022] The vinylaromatic monomer constituting the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer may or may not be the same as the vinylaromatic monomer of the polyvinylaromatic block. The vinylaromatic monomer constituting the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer is preferably styrene. The 1,3-diene constituting the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer is preferably 1,3-butadiene.

[0023] The copolymer comprising monomeric units of a 1,3-diene and a vinylaromatic monomer preferably contains monomeric units of a vinylaromatic monomer in which the aryl group, preferably phenyl, is substituted by an alkyl chain substituted with a quaternary amine group. Preferably, the 1,3-diene and the vinylaromatic monomer of the copolymer comprising monomeric units of a 1,3-diene and a vinylaromatic monomer are 1,3-butadiene and styrene, respectively. The copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer is advantageously a copolymer of a 1,3-diene and a vinylaromatic monomer, copolymer in which some or all of the vinylaromatic monomer units have the aryl group, preferably phenyl, substituted by an alkyl chain substituted by a quaternary amine group.The alkyl chain substituted with a quaternary amine group present in the block represented by the symbol B is preferably a linear chain containing 1 to 10 carbon atoms, more preferably a linear chain containing 2 to 8 carbon atoms. Advantageously, it is identical to the saturated hydrocarbon chain substituted with a quaternary amine group present in the block represented by the symbol A. The molar content of vinylaromatic monomer units and vinylaromatic monomer units bearing a quaternary amine group in the hydrogenated block of a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer varies preferably in the range of 1% to 25%, more preferably from 5% to 20% of the repeating units constituting the hydrogenated block.

[0024] According to any one of the embodiments of the invention, the block represented by the symbol B is preferably a hydrogenated block of a homopolymer of 1,3-butadiene or a hydrogenated block of a copolymer of 1,3-butadiene and styrene, copolymer in which all or part of the monomer units of styrene have the phenyl group substituted by an alkyl chain substituted by a quaternary amine group, said alkyl chain substituted by a quaternary amine group present in the block represented by the symbol B is preferably a linear chain containing 1 to 10 carbon atoms, more preferably a linear chain containing 2 to 8 carbon atoms.

[0025] In the block polymer ionomer of formula (I), the block represented by the symbol B preferentially represents 50% to 90% by mass of the total mass of the block polymer ionomer of formula (I), more preferably 60% to 80% by mass of the total mass of the block polymer ionomer of formula (I).

[0026] According to any one of the embodiments of the invention, the quaternary amine group is preferably of formula (II) or (III) N + (RI)3(II) The Ri atoms, whether identical or different, are alkyl, with R2 representing an unbranched, saturated or unsaturated divalent hydrocarbon chain containing 3 to 5 carbon atoms and potentially interrupted by one or more heteroatoms selected from oxygen, nitrogen, and sulfur. In formulas (II) and (III), the bond attaching the nitrogen atom to the monomeric units of the ionomer, specifically via the alkyl chain substituted with a quaternary amine group, is not shown. Furthermore, the quaternary amine group is of formula (III), preferably N-alkylpiperidinium, and more preferably N-methylpiperidinium.

[0027] The proportion of quaternary amine groups in the block polymer of formula (I) can vary widely and is adjusted by those skilled in the art according to the desired performance of the anion exchange membrane, particularly based on the desired trade-off between water uptake and ionic conductivity. It is known that increasing the proportion of a group in an ionomer is beneficial for the ionic conductivity of the membrane containing that ionomer, but tends to decrease the membrane's stability in highly alkaline environments. Preferably, the proportion of quaternary amine groups in the ionomer is greater than or equal to 0.1 meq / g of ionomer (meq / g, milliequivalents per gram) and less than or equal to 1 meq / g of ionomer, the ionomer being the block polymer of formula (I). The counterions of the quaternary amine groups are preferably halide anions, and more preferably bromide anions.

[0028] The average molar mass of the block polymer ionomer of formula (I) can vary widely and is chosen by those skilled in the art according to the desired performance of the anion exchange membrane, particularly based on the desired compromise between mechanical properties and its ability to be formed into a film. Preferably, the number-average molar mass of the block polymer ionomer of formula (I) is greater than 20,000 g / mol and less than 500,000 g / mol in polystyrene equivalent (values ​​determined by steric chromatography (SEC) coupled with a refractometer).

[0029] The average molar mass of the block represented by the symbol A can vary widely and is chosen by those skilled in the art according to the desired performance of the proton exchange membrane, particularly the desired compromise between the membrane's mechanical and electrical resistance properties. It is known that increasing its average molar mass is beneficial for the membrane's mechanical properties, while decreasing it tends to lower the membrane's electrical resistance. Preferably, the number-average molar mass of the block represented by the symbol A is greater than 1000 g / mol and less than 100,000 g / mol in polystyrene equivalent (values ​​determined by steric chromatography (SEC) coupled with a refractometer).

[0030] The number-average molar masses of the block polymer ionomer of formula (I) are the number-average molar masses of the block polymer before the introduction of quaternary amine groups into the block polymer. Similarly, the number-average molar masses of the block represented by the symbol A are the number-average molar masses of the block represented by the symbol A before the introduction of quaternary amine groups into the block polymer.

[0031] The ionomer, a block polymer of formula (I), can be prepared from a starting block polymer. The number-average molar mass of the ionomer can be determined from the number-average molar mass of this starting block polymer, as previously mentioned. The starting block polymer differs from the block polymer of formula (I) in that the aromatic rings are not substituted with groups containing a quaternary amine group, and the 1,3-diene monomer units are not reduced. To prepare the ionomer, the 1,3-diene monomer units of the starting block polymer are selectively hydrogenated, and then the vinylaromatic monomer units of the starting block polymer are modified first by a haloalkylation reaction of the aromatic rings, followed by a reaction with a tertiary amine, hereafter referred to as the quaternization reaction.The reagent used in the haloalkylation reaction is typically a haloalkene. In the haloalkene, the halogen atom and the double bond are preferentially located at opposite ends of the haloalkene's carbon chain. The haloalkene preferentially contains 2 to 10 carbon atoms, and more preferably 4 to 8 carbon atoms. The carbon chain of the haloalkene is preferentially linear.

[0032] The tertiary amine used in the quaternization reaction is preferably of formula (IV) or (V) N (RI)3(IV) The Ri atoms, whether identical or different, are alkyl, with R2 representing a divalent, unbranched hydrocarbon chain, saturated or unsaturated, containing 3 to 5 carbon atoms and potentially interrupted by one or more heteroatoms chosen from oxygen, nitrogen, and sulfur. The tertiary amine is preferably of formula (V), more preferably N-alkylpiperidine, and even more preferably N-methylpiperidine.

[0033] Typically, the block polymer is a thermoplastic elastomer, preferably a triblock. According to any one of the embodiments of the invention, the starting block polymer is preferably a linear polymer.

[0034] The starting block polymer can be a commercial product, available for example from Kraton or Kuraray, or can be prepared according to any of the known synthesis processes described below:

[0035] - a) anionic polymerization of 1,3-diene or its copolymerization with the second vinylaromatic initiated by a dilithiated compound such as the diisopropenylbenzene and sec-butyllithium adduct described for example in document EP1237941 or 1,1,4,4-tetraphenyl-1,4-dilithiobutane, followed by the polymerization of the first vinylaromatic to form a triblock polymer, the synthesis of block polymers containing more than 3 blocks being able to be carried out by successively continuing the polymerization of 1,3-diene and where appropriate of the second vinylaromatic and that of the first vinylaromatic;

[0036] - b) anionic polymerization of the first vinylaromatic initiated by a monolithic compound such as butyllithium, followed by the polymerization of 1,3-diene or its copolymerization with the second vinylaromatic, then reaction with a coupling agent, for example a dichlorosilane to form a triblock, the synthesis of block polymers containing more than 3 blocks being able to be carried out by successively carrying out the polymerization of the first vinylaromatic and that of 1,3-diene and where appropriate of the second vinylaromatic before the coupling reaction.

[0037] A person skilled in the art understands that the methods of preparing the starting block polymer can lead to mixtures containing the starting block polymer. They understand that the method of preparing the starting block polymer according to process b) can lead to the formation of a mixture containing the starting block polymer, a polyvinylaromatic compound, and a diblock formed in the third, first, and second steps described in the process, respectively. Similarly, they understand that process a) can lead to a mixture containing the starting block polymer and a homopolymer or copolymer of a 1,3-diene formed in the first step.

[0038] For the modification of vinylaromatic monomer units, one can, for example, refer to document WO 2010010290; for the hydrogenation reaction, one can, for example, refer to document WO 03008467. Alternatively, the ionomer, block polymer of formula (I), can be prepared from a commercial product, available, for example, from the Kraton company, for example under the name "Kraton G", or from the Kuraray company, for example under the trade name "SEPTON", which commercial product is an already hydrogenated block polymer which differs from the ionomer in that it does not carry quaternary amine groups.

[0039] When one of these methods of preparing the starting block polymer results in a mixture containing the starting block polymer, the hydrogenation and modification reactions of the vinylaromatic monomer units are generally carried out on the mixture containing the starting block polymer. In cases where the hydrogenation and modification reactions of the vinylaromatic monomer units are carried out on the mixture containing the starting block polymer, the ionomer is obtained as a mixture and is generally used without being isolated from this mixture.

[0040] The ionomer, before electron beam crosslinking, is in film form. It is known that a polymer can be film-formed by coating. It is also known, for example from patent application WO 2019010290, that ionomers with quaternary amine ionic groups are poorly soluble, or even insoluble, in many solvents. Due to this low solubility or insolubility, forming a film from the ionomer by coating a solution of the ionomer can be problematic. To overcome this problem, the film is generally prepared by coating not from the ionomer itself, but from its precursor, the halogenated polymer.

[0041] The halogenated polymer can be applied as a film by depositing a solution of the halogenated polymer onto the surface of a substrate to coat it, followed by drying, a step involving the evaporation of the solvent in the solution or dispersion. Typically, a solution of the halogenated polymer is prepared that can be spread onto a flat surface of a substrate to form a polymer layer by coating the substrate. The temperature at which the coating is carried out is chosen by those skilled in the art, taking into account factors such as the viscosity of the halogenated polymer solution and the boiling point of the solvent in the halogenated polymer solution. The coating is preferably applied at a temperature close to ambient temperature, typically 20°C to 25°C, or at a temperature above ambient temperature but below the boiling point of the solvent in the halogenated polymer solution.The concentration of the polymer solution is adjusted by a person skilled in the art, taking into account the solubility of the halogenated polymer in the solution solvent and the viscosity of the solution. The solvent for the halogenated polymer solution is chosen by a person skilled in the art, taking into account the solubility of the halogenated polymer in that solvent and its boiling point. The concentration of the halogenated polymer solution generally ranges from 1 to 15% by mass of solids. The solvent for the halogenated polymer solution preferably has a relatively low boiling point, typically less than or equal to 100°C, to allow for easy removal from the polymer layer, particularly by evaporation under vacuum, air currents, or an inert gas such as nitrogen or argon. Suitable solvents include, for example, ethers, mixtures of ethers and alcohols, and halogenated solvents.The solvent is preferably chosen from tetrahydrofuran, mixtures of tetrahydrofuran and an alcohol, or chloroform, with ethanol being the preferred alcohol. Drying to remove the solvent from the halogenated polymer solution is generally carried out under vacuum, with a stream of air, or with an inert gas such as nitrogen or argon, preferably at a temperature ranging from ambient temperature (23 °C) to the boiling point of the solvent, preferably lowered by 15 °C, with a stream of air or an inert gas. The thickness of the spread layer after drying is preferably less than or equal to 110 pm, more preferably less than or equal to 90 pm. It is preferably greater than or equal to 50 pm.

[0042] Once the halogenated polymer is in film form, it is immersed in a bath of tertiary amine solution to modify the vinylaromatic monomer units and thus form the ionomer in film form. Preferably, the ionomer is then rinsed and dried. Once recovered, it is exposed to electron beam bombardment, which crosslinks the ionomer.

[0043] During electron bombardment, the crosslinking of the ionomer is caused by the radiochemical effect of the irradiation. Electron bombardment is preferably carried out in the absence of a crosslinking agent (chemical curing agent). The electron bombardment dose can vary widely and is adjusted by a person skilled in the art according to the film thickness and the desired compromise between membrane properties such as lifetime, water absorption, and ionic conductivity. Preferably, the electron bombardment dose is greater than 50 kGy and less than 5000 kGy. More preferably, the electron bombardment dose is greater than 100 kGy and less than 3000 kGy, preferably less than 2000 kGy. Electron bombardment can be carried out under air or under an inert atmosphere, generally nitrogen, preferably under an inert atmosphere, more preferably under nitrogen.Doses can be delivered in a single irradiation sequence or in several consecutive irradiation sequences, depending on the power of the electron bombardment device used. Electron bombardment results in a cross-linked ionomer in the form of a film.

[0044] The crosslinked ionomer, another object of the invention, is an electron-bombed crosslinked block polymer, the block polymer being any one of the block polymers of formula (I) defined in the process relating to the preparation of an anion-exchange polymer membrane and which is in accordance with the invention. The crosslinked ionomer constitutes all or part, preferably all, of the membrane intended for use in a fuel cell or electrolyzer. The electron-bombed crosslinked ionomer confers to the membrane containing it improved properties with respect to water uptake and lifespan while preserving ionic conductivity properties.

[0045] The membrane, another object of the invention and capable of being obtained by the process according to the invention, is an anion exchange polymer membrane containing the crosslinked ionomer.

[0046] In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 36:

[0047] Mode 1: A process for preparing an anion-exchange polymer membrane containing a crosslinked ionomer, which process comprises electron bombardment of an ionomer in the form of a film, the ionomer being a block polymer of formula (I), (AB)nA (I), the symbol A representing a polyvinylaromatic block bearing quaternary amine groups, the symbol B representing a hydrogenated block of a poly(1,3-diene) or of a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1.

[0048] Mode 2: Process according to mode 1 in which the block polymer of formula (I) is linear.

[0049] Mode 3: Process according to mode 1 or 2 in which the block polymer of formula (I) is a triblock.

[0050] Mode 4: Process according to any one of modes 1 to 3 in which the 1,3-diene is 1,3-butadiene, isoprene or a mixture thereof.

[0051] Mode 5: A process according to any one of modes 1 to 4 in which the polyvinylaromatic block is a polystyrene block, a polyalphamethylstyrene block or a styrene-alphamethylstyrene copolymer block.

[0052] Mode 6: Process according to any one of modes 1 to 5 in which poly(1,3-diene) is a homopolymer of 1,3-butadiene.

[0053] Mode 7: A process according to any one of modes 1 to 6 in which the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer is a copolymer of a 1,3-diene and a vinylaromatic monomer, copolymer in which some or all of the vinylaromatic monomer units have the aryl group substituted by an alkyl chain substituted by a quaternary amine group.

[0054] Mode 8: Process according to mode 7 in which the aryl group is the phenyl group.

[0055] Mode 9: A process according to any one of modes 1 to 8 in which the molar content of vinylaromatic monomer units and vinylaromatic monomer units bearing a quaternary amine group in the hydrogenated block of a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer varies in the range of 1% to 25%, preferably 5% to 20% of the repeating motifs constituting the hydrogenated block.

[0056] Mode 10: A process according to any one of modes 1 to 9 in which the 1,3-diene and the vinylaromatic monomer of the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer are respectively 1,3-butadiene and styrene.

[0057] Mode 11: Process according to any one of modes 1 to 10 in which the block represented by the symbol B represents from 50% to 90% by mass of the total mass of the block polymer of formula (I), preferably from 60% to 80% by mass of the total mass of the block polymer of formula (I).

[0058] Mode 12: A process according to any one of modes 1 to 11, wherein the block represented by the symbol B is a hydrogenated block of a homopolymer of 1,3-butadiene or a hydrogenated block of a copolymer of 1,3-butadiene and styrene, a copolymer in which all or part of the monomer units of styrene have the phenyl group substituted by an alkyl chain substituted by a quaternary amine group. Mode 13: A process according to any one of modes 1 to 12, wherein the proportion of quaternary amine groups in the block polymer of formula (I) is greater than or equal to 0.1 meq / g of block polymer of formula (I) and less than or equal to 1 meq / g of block polymer of formula (I).

[0059] Mode 14: Process according to any one of modes 1 to 13 in which the quaternary amine groups are N-alkylpiperidinium.

[0060] Mode 15: Process according to any one of modes 1 to 14 in which the quaternary amine groups are N-methylpiperidinium.

[0061] Mode 16: A process according to any one of modes 1 to 15 in which the electronic bombardment is carried out in the absence of a crosslinking agent.

[0062] Mode 17: A method according to any one of modes 1 to 16 in which the electronic bombardment dose is greater than 50 kGy and less than 5000 kGy.

[0063] Mode 18: A method according to any one of modes 1 to 17 in which the electronic bombardment dose is greater than 100 kGy and less than 3000 kGy.

[0064] Mode 19: A method according to mode 18 in which the electronic bombardment dose is less than 2000 kGy.

[0065] Mode 20: Anion exchange polymer membrane containing a crosslinked ionomer, the crosslinked ionomer being an electron-bombed (AB)nA(I) block polymer of formula (I), the symbol A representing a polyvinylaromatic block bearing quaternary amine groups, the symbol B representing a hydrogenated block of a poly(1,3-diene) or a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1.

[0066] Mode 21: Membrane according to mode 20 in which the block polymer of formula (I) is linear.

[0067] Mode 22: Membrane according to mode 20 or 21 in which the block polymer of formula (I) is a triblock.

[0068] Mode 23: Membrane according to any one of modes 20 to 22 in which the 1,3-diene is 1,3-butadiene, isoprene or a mixture thereof.

[0069] Mode 24: Membrane according to any one of modes 20 to 23 in which the polyvinylaromatic block is a polystyrene block, a polyalphamethyl styrene block or a styrene-alphamethylstyrene copolymer block.

[0070] Mode 25: Membrane according to any one of modes 20 to 24 in which poly(l,3-diene) is a homopolymer of 1,3-butadiene.

[0071] Mode 26: Membrane according to any one of modes 20 to 25 in which the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer is a copolymer of a 1,3-diene and a vinylaromatic monomer, copolymer in which some or all of the vinylaromatic monomer units have the aryl group substituted by an alkyl chain substituted by a quaternary amine group.

[0072] Mode 27: Membrane according to any one of modes 20 to 26 in which the aryl group is the phenyl group.

[0073] Mode 28: Membrane according to any one of modes 20 to 27 in which the molar content of vinylaromatic monomer units and vinylaromatic monomer units bearing a quaternary amine group in the hydrogenated block of a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer varies in a range of 1% to 25%, preferably 5% to 20% of the repeating motifs constituting the hydrogenated block.

[0074] Mode 29: Membrane according to any one of modes 20 to 28 in which the 1,3-diene and the vinylaromatic monomer of the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer are respectively 1,3-butadiene and styrene.

[0075] Mode 30: Membrane according to any one of modes 20 to 29 in which the block represented by the symbol B represents from 50% to 90% by mass of the total mass of the block polymer of formula (I), preferably from 60% to 80% by mass of the total mass of the block polymer of formula (I).

[0076] Mode 31: Membrane according to any one of modes 20 to 30 in which the block represented by the symbol B is a hydrogenated block of a homopolymer of 1,3-butadiene or a hydrogenated block of a copolymer of 1,3-butadiene and styrene, copolymer in which all or part of the monomer units of styrene have the phenyl group substituted by an alkyl chain substituted by a quaternary amine group.

[0077] Mode 32: Membrane according to any one of modes 20 to 31 in which the proportion of quaternary amine groups in the block polymer of formula (I) is greater than or equal to 0.1 meq / g of block polymer of formula (I) and less than or equal to 1 meq / g of block polymer of formula (I).

[0078] Mode 33: Membrane according to any one of modes 20 to 32 in which the quaternary amine groups are N-alkylpiperidinium.

[0079] Mode 34: Membrane according to any one of modes 20 to 22 in which the quaternary amine groups are N-methylpiperidinium.

[0080] Mode 35: crosslinked lonomer, electron-bombed block polymer of formula (I), (AB)nA (I), the symbol A representing a polyvinylaromatic block bearing quaternary amine groups, the symbol B representing a hydrogenated block of a poly(1,3-diene) or a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1.

[0081] Mode 36: Fuel cell or electrolyzer containing a membrane defined according to any one of modes 20 to 34 or a membrane capable of being obtained by the process defined in any one of modes 1 to 19. The aforementioned features of the present invention, as well as others, will be better understood from the following description of several illustrative examples of embodiments of the invention.

[0082] Examples

[0083] The cross-linked ionomer constituting a membrane according to the invention is prepared from a commercial product according to the following sequence of steps:

[0084] 1) Bromoalkylation of the commercial product to prepare a brominated polymer, a polymer in which the vinylaromatic monomer units are substituted by an alkyl group substituted with a bromine atom,

[0085] 2) the formation of a film of the brominated polymer by coating,

[0086] 3) the reaction of a tertiary amine with the brominated polymer, which is in the form of a film, to form the ionomer, which is also in the form of a film.

[0087] 4) the electronic bombardment of the film obtained at the end of step 3.

[0088] The commercial product, "G1652" from Kraton, is a hydrogenated triblock polymer with a polybutadiene core and polystyrene end blocks, the hydrogenation of the butadiene units exceeding 99%. Table 1 shows the composition of the commercial product and its macrostructure (number-average molar mass Mn measured by size-exclusion chromatography, PS calibration).

[0089] Table 1:

[0090] Step 1: Bromoalkylation of the commercial product according to the following procedure:

[0091] Place the polymer and the dichloromethane solvent in a bottle under agitation until completely dissolved (approximately 2 hours at room temperature (23°C)) then place the bottle at 5°C for 12 hours;

[0092] Allow the polymer solution to be bubbled through nitrogen at 5°C for 10 min;

[0093] Cool the solution to 0°C in an ice bath for 30 min;

[0094] With stirring, add trifluoroacetic acid drop by drop (0.6 acid / styrene equivalent) in less than 1 min at 0°C (yellow / orange color);

[0095] Leave under agitation for 30 minutes at 0°C (yellow / orange colouring);

[0096] After the stirring time, allow the solution to return to room temperature;

[0097] Add the 6-bromo-l-hexene alkene drop by drop using a syringe pump for 45 min (the solution turns red), while stirring;

[0098] Leave under agitation for an additional 90 minutes at room temperature (23°C) (colour becomes dark red);

[0099] Add methanol as a reaction stopper (decolorization of the medium);

[0100] Neutralize by fractional addition of a KOH solution in methanol (IM), until pH reaches 7-8 (formation of a little precipitate and decolorization from whitish to mauve);

[0101] Coagulate in methanol (3 times the reaction volume) by pouring the methanol drop by drop into the vortex and then recover the polymer using a filter;

[0102] Wash the polymer by pouring it into a bath of deionized water under agitation for 10 min (to remove the salts) then recover the polymer using a filter;

[0103] Retrieve the polymer and let it dry for 24 hours in an oven at 40°C, 150 mbar.

[0104] The levels in the brominated polymer of the ethylene, butylene, styrene and substituted styrene motifs are measured by NMR analysis and are shown in Table 2; the term "substituted styrene" refers to styrene motifs substituted by an alkyl group substituted by a bromine atom.

[0105] Table 2:

[0106] Step 2: Formation of a brominated polymer film by coating:

[0107] Five Fl to F5 films are prepared according to the following procedure: a) a solution containing the brominated polymer in toluene is prepared, b) the solution is poured onto a flat polytetrafluoroethylene (PTFE) support framed by two spacers of a height of 1200 pm to form a layer of solution 1200 pm thick by passing a squeegee, c) the solvent is evaporated at room temperature for 120 minutes under air sweep to dry the layer d) the film is recovered from its support and the film is peeled off its support.

[0108] The films have a thickness of 90 to 110 µm.

[0109] Step 3: Reaction of a tertiary amine with the brominated polymer, which is in the form of a film:

[0110] Prepare a 20%w solution of N-methylpiperidine in deionized water;

[0111] In a glass container (such as a beaker, jar, or other glass container), pour the solution up to the 3 / 4 of the volume;

[0112] Using tweezers, gently immerse the film, avoiding the formation of air bubbles and / or it folding back on itself;

[0113] Place a glass lens over the container to isolate it from the external environment; Leave the film submerged for 72 hours at room temperature;

[0114] Replace the solution with deionized water to wash the film. The water is replaced twice a day for two days;

[0115] Place the film on a PTFE support and place the assembly in an oven at 40°C, 150 mbar overnight.

[0116] The levels in the ionomer of the ethylene, butylene, styrene and substituted styrene motifs are those of the brominated polymer measured by NMR analysis and shown in Table 2.

[0117] Step 4: Electron bombardment of the ionomer in the form of a film:

[0118] The films, with the exception of film Fl, are exposed to electron bombardment (using the EBLab200 device from manufacturer Skan Stein AG). For each film, the absorbed radiation doses are listed in Table 3. Doses are expressed in kilogray (kGy). Since the device can deliver a maximum of 300 kGy per pass, for doses exceeding 300 kGy, the films are exposed in multiple passes.

[0119] 1 dose of 300 kGy and a dose of 200 kGy for dose 2;

[0120] 3 doses of 300 kGy for dose 3;

[0121] 4 doses of 300 kGy and one dose of 200 kGy for dose 4.

[0122] Table 3:

[0123] The five other films, F6 to F10, are from the company Dioxide Materials. They consist of a commercial ionomer, Sustainion 37-50 grade T, described in "Energy Technol. 2017, 5, 929-936" as the reaction product between 1-methylimidazole and a copolymer of styrene and vinylbenzyl chloride. It is not a block copolymer of formula (I).

[0124] For the preparation of the films, Table 4 indicates the solvent used and the mass concentration of polymer in the solution, the polymer being the brominated polymer for films Fl to F5. Films F6 to F10 are made of the Sustainion membrane with a thickness of 50 µm.

[0125] Table 4:

[0126] Films F2 to F5 and F7 to F8, as well as films Fl and F6, are subjected to alkaline degradation under the conditions described below to evaluate their lifespan as anion exchange membranes. Their water absorption and anion conductivity capacities are also measured. The results are shown in Table 5.

[0127] The F9 and F10 films could not be evaluated from the point of view of their stability, since the electronic bombardment caused them to break.

[0128] Conditions for alkaline degradation:

[0129] The film is immersed in an aqueous potassium hydroxide solution in which the hydroxide ion (HO⁻) is considered the active species. The etching conditions are carried out under stirring in a reaction volume of 500 mL at a KOH concentration of 5 mol / L and a temperature of 80°C. The residual mass of the membrane after 300 hours of immersion allows for estimation of the membrane degradation rate. Measurement of ionic conductivity:

[0130] To determine the ionic conductivity of the prepared membrane, its electrochemical impedance is measured across the plane of the membrane at 30°C and 30% relative humidity, the measurement parameters being an amplitude variation of 50 mV, an applied potential of 0V.

[0131] To measure conductivity, the halide counter-ions are replaced by hydroxide anions according to the following procedure:

[0132] The cross-linked ionomer, in the form of a film and thus forming a membrane, is immersed for 24 hours at room temperature (23°C) in a solution of IM potassium hydroxide in demineralized water to perform ion exchange between bromide and hydroxide ions. It is then soaked for 15 minutes in a demineralized water solution to remove excess hydroxide ions.

[0133] The water intake is 100% by mass.

[0134] The ionic conductivity is then measured.

[0135] Table 5:

[0136] Films F2 to F5 are membranes according to the invention and are prepared according to a process according to the invention. Films F6 to F10 are not membranes according to the invention, nor are they prepared according to a process according to the invention, as the ionomer constituting the membrane is not of formula (I). Film Fl is not a membrane according to the invention because film Fl has not been exposed to electron bombardment. Film F6 is also not a membrane according to the invention for the following two reasons: the ionomer is not of formula (I) and the film has not been exposed to electron bombardment.

[0137] Compared to a non-conforming membrane that has not undergone electron bombardment, the membranes according to the invention exhibit significantly less alkali degradation, as well as a better compromise between water absorption, ionic conductivity, and resistance to alkali degradation. "Sustainion" membranes that have undergone electron bombardment under the same conditions as the membranes according to the invention have lower resistance to alkali degradation or even become too fragile and therefore unusable for the alkali degradation test.

Claims

Demands 1. A process for preparing an anion-exchange polymer membrane containing a crosslinked ionomer, which process comprises electron bombardment of an ionomer in the form of a film, the ionomer being a block polymer of formula (I), (AB)nA (I), the symbol A representing a polyvinylaromatic block bearing quaternary amine groups, the symbol B representing a hydrogenated block of a poly(l,3-diene) or a copolymer comprising monomeric units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1.

2. A method according to claim 1 wherein the block polymer of formula (I) is linear.

3. A method according to claim 1 or 2 wherein the block polymer of formula (I) is a triblock.

4. A method according to any one of claims 1 to 3 wherein the polyvinylaromatic block is a polystyrene block, a polyalphamethyl styrene block or a styrene-alphamethylstyrene copolymer block.

5. A method according to any one of claims 1 to 4 wherein poly(l,3-diene) is a homopolymer of 1,3-butadiene.

6. A process according to any one of claims 1 to 5 wherein the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer is a copolymer of a 1,3-diene and a vinylaromatic monomer, copolymer wherein some or all of the vinylaromatic monomer units have the aryl group substituted by an alkyl chain substituted by a quaternary amine group.

7. A process according to any one of claims 1 to 6 wherein the molar content of vinylaromatic monomer units and vinylaromatic monomer units bearing a quaternary amine group in the hydrogenated block of a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer varies in the range of 1% to 25%, preferably from 5% to 20% of the repeating motifs constituting the hydrogenated block.

8. A method according to any one of claims 1 to 7 wherein the 1,3-diene and the vinylaromatic monomer of the copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer are respectively 1,3-butadiene and styrene.

9. A method according to any one of claims 1 to 8 wherein the block represented by the symbol B represents from 50% to 90% by mass of the total mass of the block polymer of formula (I), preferably from 60% to 80% by mass of the total mass of the block polymer of formula (I).

10. A method according to any one of claims 1 to 9 wherein the proportion of quaternary amine groups in the block polymer of formula (I) is greater than or equal to 0.1 meq / g of block polymer of formula (I) and less than or equal to 1 meq / g of block polymer of formula (I).

11. A method according to any one of claims 1 to 10 wherein the quaternary amine groups are N-alkylpiperidinium, preferably N-methylpiperidinium.

12. A method according to any one of claims 1 to 11 in which the electronic bombardment is carried out in the absence of a crosslinking agent.

13. Anion exchange polymer membrane containing a crosslinked ionomer, the crosslinked ionomer being a block polymer of formula (I) crosslinked by electron bombardment (AB)nA (I), the symbol A representing a polyvinylaromatic block bearing quaternary amine groups, the symbol B representing a hydrogenated block of a poly(1,3-diene) or a copolymer comprising monomer units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1, which membrane is capable of being obtained by the process defined in any one of claims 1 to 12.

14. Crosslinked ionomer, block polymer of formula (I) crosslinked by electron bombardment, (AB) n-A (I), the symbol A representing a polyvinylaromatic block bearing quaternary amine groups, the symbol B representing a hydrogenated block of a poly(l,3-diene) or a copolymer comprising monomeric units of a 1,3-diene and a vinylaromatic monomer, n being an integer equal to or greater than 1.

15. Fuel cell or electrolyzer containing a membrane defined in claim 13 or a membrane that can be obtained by the process defined in any one of claims 1 to 12.

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