Anion exchange membrane and its method of production.

Abstract

The invention relates to an anion exchange membrane containing a polymer ionomer bearing pendant imidazolium ionic groups attached to the polymer via a group resulting from a cycloaddition reaction between a 1,3-dipolar compound and an unsaturated polymer. The 1,3-dipolar compound is an aromatic nitrile oxide substituted with an imidazole functional group, and the unsaturated polymer is a polymer containing diene monomer units. The membrane, intended for use in a fuel cell or electrolyzer, has the advantage of being prepared by a process involving steps that can be carried out in the absence of solvent.

Description

Title of the invention: Anion exchange membrane and its method of obtaining.

[0001] The field of the present invention is that of anion exchange membranes containing an ionomer and intended for use in an electrolyzer or a fuel cell.

[0002] The core of a fuel cell and an electrolyzer consists of two electrodes, an anode and a cathode, an electrolytic layer separating the two electrodes, and a catalyst located at the interfaces of the electrolytic layer with each electrode. Fuel cells and electrolyzers include a membrane that constitutes the electrolytic layer. One of the constituent elements of the membrane is the ionomer, a polymer bearing ionic or ionizable groups.

[0003] A key step in the preparation of the membrane is the shaping of the ionomer into a film. The process generally described for forming a film of the ionomer is a coating process that requires dissolving the ionomer.

[0004] Polymers bearing imidazolium ionic groups are described as good candidates for forming anion-exchange membranes. These ionomers, which are generally prepared from a halogenated polymer and a compound bearing an imidazole functional group, are very poorly soluble, or even insoluble, in many solvents. As described in patent application WO 2019010290, the very low solubility or insolubility of these ionomers, which is attributed to ionic interactions present in the ionomer, makes the coating process problematic. To overcome this problem, the film is prepared by coating not from the ionomer, but from its precursor, the halogenated polymer. The halogenated polymer film is then immersed in a bath, a solution of the compound bearing an imidazole functional group, to lead to the formation of the ionomer film.This series of steps must be followed by further steps of rinsing the film and drying before the membrane can be used.

[0005] The inventors have discovered a new membrane which contains an ionomer whose ionic groups are imidazoliums and whose chemical structure makes it possible to overcome the difficulties mentioned in the preparation of the membranes of the prior art.

[0006] An object of the invention relates to an anion exchange membrane containing an ionomer, a polymer bearing pendant imidazolium ionic groups which are attached to the polymer via a group resulting from the cycloaddition reaction between a 1,3-dipolar compound and an unsaturated polymer, the 1,3-dipolar compound being an aromatic nitrile oxide substituted with an imidazole function, the unsaturated polymer being a polymer containing monomeric units of a diene.

[0007] Another object of the invention is a method for preparing an anion exchange membrane according to the invention, which method comprises the following steps a), b), c) and d): - a) the preparation of a polymer bearing pendant imidazole functions by a cycloaddition reaction of the 1,3-dipolar compound and the unsaturated polymer, - b) the incorporation of a haloalkane into the polymer bearing pendant imidazole functions by thermomechanical mixing, - c) a heat treatment of the mixture obtained in step b) to convert the imidazole functions into imidazolium ionic groups, - d) shaping the ionomer obtained at the end of step c) into a film, steps b), c) and d) being carried out in bulk.

[0008] The invention also relates to an ionomer, a polymer bearing pendant imidazolium ionic groups which are attached to the polymer via a group resulting from the cycloaddition reaction between a 1,3-dipolar compound and an unsaturated polymer, the 1,3-dipolar compound being an aromatic nitrile oxide substituted by an imidazole function, the unsaturated polymer being a polymer containing monomeric units of a diene.

[0009] The invention also relates to a method for preparing an ionomer according to the invention which includes steps a) to c) of the method for preparing an anion exchange membrane according to the invention.

[0010] The invention also relates to a fuel cell or electrolyzer which contains a membrane according to the invention. Detailed description

[0011] In the present description, any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​greater than "a" and less than "b" (i.e., bounds a and b excluded) while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​from "a" to "b" (i.e., including the strict bounds a and b).

[0012] The polymers mentioned in the description may be of fossil origin or bio-based. In the latter case, they may be partially or totally derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, they may also come from the recycling of materials already used, that is to say that they can be, partially or totally, from a recycling process, or even obtained from raw materials themselves from a recycling process.

[0013] The terms "membranes" and "films" are well known to those skilled in the art in this technical field. It should be noted that, as is well known, a membrane is a structure as defined by IUPAC in "IUPAC Recommendations 1996". Also as is well known, 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".

[0014] The anion exchange membrane according to the invention has as its essential characteristic that it contains an ionomer which is a polymer bearing pendant imidazolium ionic groups. Preferably, the counterions of the imidazolium ionic groups are halide anions, preferably bromides, or hydroxide anions.

[0015] The pendant imidazolium ionic groups are attached to the constituent polymer of the membrane via a group resulting from the cycloaddition reaction between an aromatic nitrile oxide substituted by an imidazole function and a polymer containing monomeric units of a diene.

[0016] The polymer containing monomer units of a diene, an unsaturated polymer useful for the purposes of the invention, is a polymer that includes, in a well-known manner, carbon-carbon double bonds. The unsaturated polymer may be a homopolymer of a diene or a copolymer of a diene.

[0017] The diene is preferably a 1,3-diene. The unsaturated polymer is preferably a homopolymer of a 1,3-diene or a copolymer of a 1,3-diene. The unsaturated polymer is then preferably chosen from homopolymers of a 1,3-diene, copolymers of several 1,3-dienes, copolymers of a 1,3-diene and a vinylaromatic monomer, and copolymers of a 1,3-diene and ethylene. When the unsaturated polymer is a copolymer of a 1,3-diene, it may be statistical, random, block, or tapered.

[0018] As 1,3-dienes, 1,3-dienes with 4 to 20 carbon atoms are preferentially suitable, more preferably 1,3-butadiene and isoprene, even more preferably 1,3-butadiene.

[0019] Styrene, or styrenes substituted at the alpha, ortho, meta, or para positions by an alkyl group, are preferably suitable as vinylaromatic monomers. The styrene may be substituted by one or more alkyl groups, which may be identical or different. The alkyl group may contain one or more carbon atoms, in particular one to four carbon atoms. The vinylaromatic monomer is preferably styrene.

[0020] Copolymers of several 1,3-dienes, that is, copolymers of at least two 1,3-dienes, are known to be copolymers whose constituent monomer units are the monomer units of said several 1,3-dienes. Examples of copolymers of several 1,3-dienes include copolymers of 1,3-butadiene and isoprene, copolymers of 1,3-butadiene and piperylene, and copolymers of isoprene and piperylene.

[0021] As is well known, homopolymers of a 1,3-diene and copolymers of several 1,3-dienes can be prepared in solution, dispersion, or emulsion. They can be prepared by anionic polymerization, by coordination polymerization, for example in the presence of a Ziegler-Natta type catalyst or in the presence of a metallocene, or by radical polymerization.

[0022] Copolymers of a 1,3-diene and a vinylaromatic monomer are well-known copolymers, as are their methods of preparation. They can be prepared in solution, dispersion, or emulsion, particularly in solution or dispersion by anionic polymerization or in emulsion by radical polymerization. Examples include 1,3-butadiene-styrene copolymers, isoprene-styrene copolymers, and 1,3-butadiene-isoprene-styrene copolymers. The proportion of vinylaromatic monomer units, preferably styrene, in the copolymer can vary considerably and is adjusted by those skilled in the art according to the desired properties of the copolymer. It is typically greater than 0% and less than 95% by mol, the percentage being calculated relative to the number of moles of the copolymer.It is preferably less than 75% by mole, more preferably less than 50% by mole, the percentage being calculated in relation to the number of moles of the copolymer.

[0023] Copolymers of 1,3-diene and ethylene are also known polymers, as are their synthesis processes, for example, described in patent applications EP 1 092 731, WO 200754223, WO 200754224, WO 2017103543, and WO 2017103544. Copolymers of 1,3-diene, preferably 1,3-butadiene, and ethylene preferably contain more than 50 mole percent of ethylene. Advantageously, they contain between 50 and 90 mole percent of ethylene units.

[0024] The 1,3-dipolar compound useful for the purposes of the invention is an aromatic nitrile oxide substituted with an imidazole group. Aromatic nitrile oxides are compounds well known to react by cycloaddition, in this case [3+2], with double bonds, as described in the book "Nitrile Oxides, Nitrones and Nitronates in Organic Synthesis, Novel Strategies in Synthesis", 2nd Edition, Henry Feuer, 2008, Wiley-Interscience Edition. Aromatic nitrile oxides substituted with an imidazole group are known compounds from patent application WO 2015059269. Aromatic nitrile oxides substituted with Imidazole groups are also known from patent application WO 2015059269 for reacting with the carbon-carbon double bonds of an unsaturated polymer via cycloaddition. Cycloaddition allows imidazole groups to be grafted onto the polymer, as illustrated in the following diagram on a monomer unit of 1,3-butadiene, with IMIDAZ denoting the imidazole group. The wavy line in the diagram of the 1,3-dipolar compound symbolizes the attachment of the imidazole group to the aromatic ring substituted with nitrile oxide. It is through the group formed by the cycloaddition reaction between the 1,3-dipolar compound and the unsaturated polymer that the imidazole groups are attached to the modified polymer.

[0025] The imidazole function preferably has the formula 177-imidazol-l-yl or 2-alkyl-177-imidazol-l-yl. The alkyl group substituting for the carbon atom at position 2 of the imidazole ring is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group. Advantageously, the imidazole function has the formula 177-imidazol-l-yl or the formula 2-alkyl-177-imidazol-1-yl, which is preferably 2-methyl-177-imidazol-1-yl.

[0026] The 1,3-dipolar compound preferentially corresponds to formula (I) in which one of the symbols Ri to R5 represents a group containing the imidazole function, the other symbols a hydrogen atom or an alkyl, knowing that one of the Ri and R5 is different from a hydrogen atom. CNO (I)

[0027] Preferably, R4 represents the group containing the imidazole function. R4 is preferably a (177-imidazol-l-yl)alkyl or (2-alkyl-177-imidazol-l-yl)alkyl group, more preferably a (177-imidazol-l-yl)methyl or (2-alkyl-177-imidazol-l-yl)methyl group. R4 is even more preferably a 177-imidazol-l-yl)methyl or (2-methyl-177-imidazol-l-yl)methyl group.

[0028] Preferably, in formula (I), R3 and R5 are each an alkyl group and R2 is a hydrogen atom. The alkyl groups R3 and R5 are preferably methyl or ethyl groups, more preferably methyl groups.

[0029] The 1,3-dipolar compound is advantageously the compound 2,4,6-trimethyl-3-((2-methyl-l / / -imidazol-l-yl)methyl)benzo-nitrile oxide or the compound 2,4,6-triethyl-3-((2-methyl-l / / -imidazol-l-yl)methyl)benzo-nitrile oxide, respectively of formula (lia) and (Ilb). (W

[0030] In the process, another object of the invention, for preparing the membrane according to the invention, step a) consists of preparing a polymer bearing imidazole functional groups by a grafting reaction of the 1,3-dipolar compound onto the unsaturated polymer. The grafting reaction between a polymer containing monomeric units of a diene and a 1,3-dipolar compound such as a nitrile oxide is a well-known [3+2] cycloaddition reaction of the 1,3-dipolar compound onto the carbon-carbon double bonds of the diene monomeric units of the polymer. Since the 1,3-dipolar compound used in the present invention is a compound which, in addition to the dipole, bears a chemical functional group, in this case an imidazole functional group, the reaction allows the grafting of pendant chemical functional groups, imidazole functional groups, onto the polymer. The grafting reaction is typically carried out at a temperature above ambient (23°C), preferably at a temperature above 60°C.

[0031] According to a first embodiment of the invention, the grafting reaction is carried out in solution. The polymer thus modified can be separated from its solution by any type of means known to those skilled in the art, and in particular by a steam stripping operation.

[0032] According to a second embodiment of the invention, the grafting reaction is carried out in bulk, for example in internal mixers, extruders, ovens, or presses. It is then generally preceded by bulk mixing so that the 1,3-dipolar compound is incorporated into the unsaturated polymer. Step a) can be carried out by incorporating the The 1,3-dipolar compound is incorporated into the unsaturated polymer at a mixer temperature below 60°C, followed by the grafting reaction under pressure or in an oven at temperatures ranging from 80°C to 200°C. Alternatively, step a) can be carried out by incorporating the 1,3-dipolar compound into the unsaturated polymer at a mixer temperature above 60°C, with the grafting reaction occurring simultaneously with the incorporation. When the grafting reaction is performed in bulk, it is preferably carried out in the presence of an antioxidant of the unsaturated polymer.

[0033] According to a first preferred embodiment of the second embodiment, step a) is a reactive extrusion step of a mixture of the unsaturated polymer and the 1,3-dipolar compound, at the end of which the 1,3-dipolar compound is grafted onto the polymer. Step a) is then typically a reactive extrusion process as described in patent application WO 2018115703.In this variant, the unsaturated polymer and the 1,3-dipolar compound feed a twin-screw extruder that conventionally comprises a barrel, a feed zone, a mixing zone, a set of two augers, and a die. The extrusion temperature, the setpoint temperature applied inside the extruder, particularly at the barrel, is preferably above 100°C. More preferably, the extrusion temperature in the zone extending from the mixing zone to the end of the auger set closest to the die is between 110 and 140°C. This temperature range provides the best compromise between grafting efficiency and productivity. Productivity is governed by the polymer flow rate in the extruder, which is itself adjusted according to the desired residence time of the polymer in the extruder from the mixing zone to the extruder die.Residence times are typically short, at most 5 minutes, and preferably less than 5 minutes. Residence times ranging from 30 seconds to 2 minutes can be sufficient to achieve both good grafting yield and precise control of the grafting rate, thus ensuring good process reproducibility. Reactive extrusion can be carried out without the need for specific atmospheric conditions inside the barrel. Typically, extrusion takes place under ambient air. At the extruder outlet, after passing through the die, the polymer is recovered, in which some or all of the diene monomer units have reacted with the 1,3-dipolar compound.

[0034] According to a second embodiment, step a) takes place in two phases, a first phase during which the unsaturated polymer and the 1,3-dipolar compound are mixed, typically at a temperature below 60°C, for example in an external mixer such as a roller tool, and a second phase during which the mixture resulting from the first phase is heated to a The temperature is maintained at 80°C to 200°C, preferably 100°C to 170°C, in a press or oven, for the time required to perform the grafting. At the end of the second phase, the polymer is recovered, in which some or all of the diene monomer units have reacted with the 1,3-dipolar compound. Such a process is described, for example, in patent application WO 2015059269.

[0035] According to a third embodiment of the second, step a) is carried out by thermomechanical mixing of the unsaturated polymer and the 1,3-dipolar compound, for example in an internal mixer, until a maximum mixing temperature of 110 to 180°C, preferably between 140 and 170°C, is reached. After thermomechanical mixing, the polymer is recovered, in which some or all of the diene monomer units have reacted with the 1,3-dipolar compound. Following this step, the modified polymer can be extruded to form granules, in order to facilitate its storage before use in step b), as described, for example, in patent application WO 2018115704.

[0036] Step a) is advantageously carried out in bulk. The grafting reaction of step a) is preferably carried out in bulk according to the second embodiment, advantageously according to the first variant, the second variant or the third variant, most advantageously according to the first variant which proves to be more efficient with regard to grafting yield and also more productive.

[0037] The amount of 1,3-dipolar compound useful in step a) can vary considerably. It is indexed to the grafting yield and the number of imidazole functions desired to be grafted onto the unsaturated polymer. The grafting yield, which is the ratio between the amount of 1,3-dipolar compound grafted onto the unsaturated polymer and the amount of 1,3-dipolar compound used in step a), is typically greater than or equal to 50% and can reach values ​​greater than or equal to 80%, particularly when step a) is implemented according to the first variant, the amount of 1,3-dipolar compound grafted onto the unsaturated polymer being able to be determined by NMR analysis. The number of imidazole functions desired to be grafted onto the unsaturated polymer is typically greater than or equal to 0.5 mmol per gram of unsaturated polymer. Preferably, it is greater than 0.5 mmol per gram of unsaturated polymer and less than 3.5 mmol per gram of unsaturated polymer. The amount of the 1,3-dipolar compound used in step a) is preferably greater than 0.5 milliequivalents of imidazole function per gram of unsaturated polymer, more preferably greater than 0.6 milliequivalents of imidazole function per gram of unsaturated polymer. It is also preferably less than 4.2 milliequivalents of imidazole function per gram of unsaturated polymer.

[0038] At the end of step a), a polymer is therefore obtained which carries pendant imidazole functions in a quantity which is preferably greater than or equal to 0.5 mmole per gram of polymer, more preferably greater than 0.5 mmole per gram of polymer and less than 3.5 mmoles per gram of polymer.

[0039] Step b) consists of incorporating a haloalkane, also called a haloalkane, into the polymer resulting from step a), a polymer bearing pendant imidazole groups. The incorporation is carried out by bulk mixing, for example in an internal or external mixer, which aims to distribute the haloalkane as uniformly as possible within the polymer bearing pendant imidazole groups along its chain without the use of a solvent. At the end of step b), a mixture is obtained containing the polymer bearing pendant imidazole groups and the haloalkane.

[0040] The amount of haloalkane used in step b) is indexed to the rate of imidazole function grafting of the functional polymer obtained at the end of step a), in other words to the number of imidazole functions carried by the polymer at the end of step a), or to the amount of 1,3-dipolar compound used in step a). Preferably, in step b) the amount of haloalkane is 1 to 2 molar equivalents of imidazole functions carried by the polymer at the end of step a) or is 1.2 to 2.4 molar equivalents of 1,3-dipolar compound used in step a).

[0041] The haloalkane can be an iodoalkane, a chloroalkane or a bromoalkane. It is preferably a bromoalkane. The hydrocarbon chain constituting the haloalkane can be linear, branched, or cyclic. In the haloalkane, the halogen atom can substitute for any of the carbon atoms in the hydrocarbon chain constituting the haloalkane. The haloalkane is chosen by those skilled in the art based on the desired performance compromise of the process, which may include, for example, minimizing or avoiding the emission of volatile compounds during step b) or step c), controlling the amount of haloalkane to be introduced in step b), and obtaining the best ionomer yield. A person skilled in the art will be able to choose the haloalkane based in particular on its physicochemical and chemical properties such as its vapor pressure, boiling point, molar mass, density and reactivity towards imidazole functions, which properties have an impact on this compromise.Preferably, the haloalkane contains at least 6 carbon atoms. Advantageously, the haloalkane contains fewer than 12 carbon atoms. Also preferably, the haloalkane contains only one halogen atom. Particularly suitable as haloalkanes are iodohexanes, bromohexanes, chlorohexanes, iodoheptanes, bromoheptanes, chloroheptanes, iodooctanes, bromooctanes, chlorooctanes, iodononanes, bromononanes, chlorononanes, iododecanes, bromodecanes, and chlorodecanes, preferably with a linear chain and bearing the halogen atom at the end of the carbon chain. Only one haloalkane may be used. or a mixture of haloalkanes, preferably a single haloalkane for reasons of process simplification.

[0042] Step c), which follows step b), consists of forming an ionomer by reacting the imidazole groups of the polymer with the haloalkane, a quaternization reaction. In this application, the quaternization reaction is defined as the reaction that allows the formation of an ionic group, the imidazolium cation, with the halide anion as the counter-ion. The heat treatment in step c) consists of heating the mixture obtained at the end of step b) to a temperature sufficient to carry out the quaternization reaction. A person skilled in the art adjusts the temperature at which the heat treatment is carried out, taking into account the reactivity of the haloalkane to the quaternization reaction and the thermal stability of the reactants and reaction products. In step c), the heat treatment is carried out at a temperature generally above 10°C, preferably above 30°C.The heat treatment is preferably carried out at a temperature below 100°C. Step c) which follows step b) is also carried out in bulk.

[0043] According to one embodiment of the invention, step b) and step c) are carried out in the same device which allows steps b) and c) to be carried out. The device useful for this embodiment may be an internal mixer or an extruder which provides mechanical work to uniformly incorporate the haloalkane into the polymer bearing pendant imidazole functions and which also provides heat to the mixture formed from the polymer bearing pendant imidazole functions and the haloalkane to allow the quaternization reaction.

[0044] According to another embodiment of the invention, steps b) and c) are carried out in different devices, a first device such as a roller tool or an extruder allowing the haloalkane to be incorporated into the polymer bearing pendant imidazole functions at a temperature below the quaternization reaction temperature, a second device which brings the mixture formed of the polymer bearing pendant imidazole functions and the haloalkane to a temperature allowing the quaternization reaction.

[0045] At the end of step c), an ionomer is therefore obtained whose ionic groups are imidazoliums. The content of the imidazolium ionic groups is preferably greater than or equal to 0.5 mmol per gram of ionomer, more preferably greater than 0.5 mmol per gram of ionomer and less than 3.5 mmol per gram of ionomer.

[0046] Step d) of the process according to the invention consists of putting the ionomer, a polymer obtained at the end of step c), into the form of a film intended to form part or all of an anion exchange membrane. Step d) is also carried out in bulk. Any device known for putting a polymer into the form of a film The absence of solvent can be exploited. Examples include calenders, roller nozzles positioned at the extruder outlet, and presses. To facilitate its formation into a film, the ionomer can be heated to soften it. The film preferably has a thickness of less than 1 mm, more preferably a thickness greater than 10 µm, and preferably less than 500 µm.

[0047] As is well known to those skilled in the art, a membrane is primed with water before being put into operation in an assembly constituting a fuel cell or an electrolyzer. Primed watering the membrane is generally part of the break-in or activation process. Typically, during this primed watering, the counterions of the membrane's constituent ionomer, which are halides, can be replaced by hydroxide anions, which are known to have much better ionic mobility than halide anions. See, for example, the article Energy Environ Sci 2014, 7, 3135.

[0048] The replacement of halide counterions by hydroxide anions can be achieved by impregnating the ionomer film of the membrane with an aqueous solution, for example, by bringing the ionomer film into contact with an aqueous solution containing hydroxide anions, such as an aqueous solution of a strong base. Suitable strong bases include potassium hydroxide, sodium hydroxide, and preferably potassium hydroxide. Preferably, the replacement of halide counterions by hydroxide anions is carried out during the membrane break-in or activation process.

[0049] The membrane according to the invention can be used in a fuel cell or an electrolyzer, preferably in an electrolyzer.

[0050] The ionomer used to prepare the membrane is prepared by steps a), b), and c) of the process according to the invention relating to the preparation of an anion exchange membrane, step a) advantageously being by mass. The ionomer is a polymer whose essential characteristic is to bear pendant imidazolium ionic groups, preferably in a concentration greater than or equal to 0.5 mmol per gram of polymer, more preferably greater than 0.5 mmol per gram of polymer and less than 3.5 mmol per gram of polymer. The pendant imidazolium ionic groups are attached to the polymer via a group resulting from the cycloaddition reaction between the 1,3-dipolar compound and the unsaturated polymer. The counterions of the imidazolium ionic groups are halide anions, preferably bromide anions.

[0051] In the preparation of the membrane according to the invention, the elimination of the step of immersion in a solution of a haloalkane to carry out the quaternization reaction is made possible thanks to the chemical structure of the ionomer and its method of preparation which can be carried out in bulk.

[0052] In summary, the invention can be implemented according to any one of embodiments 1 to 33:

[0053] Mode 1: Anion exchange membrane containing an ionomer, polymer bearing pendant imidazolium ionic groups which are attached to the polymer via a group resulting from the cycloaddition reaction between a 1,3-dipolar compound and an unsaturated polymer, the 1,3-dipolar compound being an aromatic nitrile oxide substituted by an imidazole function, the unsaturated polymer being a polymer containing monomeric units of a diene.

[0054] Mode 2: Membrane according to mode 1 in which the unsaturated polymer is a homopolymer of a 1,3-diene or a copolymer of a 1,3-diene.

[0055] Mode 3: Membrane according to mode 1 or 2 in which the unsaturated polymer is selected from homopolymers of a 1,3-diene, copolymers of two or more 1,3-dienes, copolymers of a 1,3-diene and a vinylaromatic monomer and copolymers of a 1,3-diene and ethylene.

[0056] Mode 4: Membrane according to mode 3 in which the vinylaromatic monomer is styrene.

[0057] Mode 5: Membrane according to any one of modes 1 to 4 in which the diene is 1,3-butadiene or isoprene.

[0058] Mode 6: Membrane according to any one of modes 1 to 5 in which the diene is 1,3-butadiene.

[0059] Mode 7: Membrane according to any one of modes 1 to 6 in which the imidazole function has the formula l / 7-imidazol- l-ylc.

[0060] Mode 8: Membrane according to any one of modes 1 to 6 in which the imidazole function is of formula 2-alkyl-l / 7-imidazol-l-ylc.

[0061] Mode 9: Membrane according to mode 8 in which the imidazole function is of formula 2-methyl-l / / -imidazol-1-yl.

[0062] Mode 10: Membrane according to any one of the modes 1 to 9 in which the 1,3-dipolar compound corresponds to formula (I) in which one of the symbols Ri to R5 represents a group containing the imidazole function, the other symbols a hydrogen atom or an alkyl, knowing that one of the Ri and R5 is different from a hydrogen atom.

[0063] Mode 11: Membrane according to mode 10 in which R4 represents the group containing the imidazole function.

[0064] Mode 12: Membrane according to mode 10 in which R4 is a (177-hnidazol- l-yl)alkyl group.

[0065] Mode 13: Membrane according to mode 10 in which R4 is a (2-alkyl-177-imidazol-l-yl)alkyl group.

[0066] Mode 14: Membrane according to mode 10 in which R4 is a (1H-imidazol-l-yl)methyl or (2-alkyl-177-imidazol-l-yl)methyl group.

[0067] Mode 15: Membrane according to any one of modes 10 to 14 in which Rb R3 and R5 are each an alkyl and R2 is a hydrogen atom and R4 represents the imidazole function.

[0068] Mode 16: Membrane according to any one of modes 10 to 15 in which Rb, R3 and R5 are methyl or ethyl.

[0069] Mode 17: Membrane according to any one of modes 1 to 16 in which the 1,3-dipolar compound is the compound 2,4,6-trimethyl-3-((2-methyl-177-imidazol-1-yl)methyl)benzo-nitrile oxide or the compound 2,4,6-triethyl-3-((2-methyl-177-imidazol-1-yl)methyl)benzo-nitrile oxide.

[0070] Mode 18: A method for preparing an anion exchange membrane defined in any one of modes 1 to 17 which comprises the following steps a), b), c) and d): - a) the preparation of a polymer bearing pendant imidazole functions by a cycloaddition reaction of the 1,3-dipolar compound and the unsaturated polymer, - b) the incorporation of a haloalkane into the polymer bearing pendant imidazole functions by thermomechanical mixing, - c) a heat treatment of the mixture obtained in step b) to convert the imidazole functions into imidazolium ionic groups, - d) the shaping of the ionomer, obtained at the end of step c), in the form of a film, steps b), c) and d) being carried out in bulk.

[0071] Mode 19: Method according to mode 18 in which step a) is carried out in mass.

[0072] Mode 20: A process according to mode 18 or 19 in which the unsaturated polymer is defined in mode 2 or 3.

[0073] Mode 21: Process according to any one of modes 18 to 20 in which the diene is 1,3-butadiene or isoprene.

[0074] Mode 22: Process according to any one of modes 18 to 21 in which the haloalkane is a bromoalkane.

[0075] Mode 23: Process according to any one of modes 18 to 22 in which the haloalkane contains a single halogen atom.

[0076] Mode 24: A process according to any one of modes 18 to 23 in which the amount of the 1,3-dipolar compound used in step a) is greater than 0.5 milliequivalent of imidazole function per gram of unsaturated polymer and less than 4.2 milliequivalents of imidazole function per gram of unsaturated polymer.

[0077] Mode 25: A process according to mode 24 in which the amount of the 1,3-dipolar compound used in step a) is greater than 0.6 milliequivalent of imidazole function per gram of unsaturated polymer.

[0078] Mode 26: A process according to any one of modes 18 to 25 in which at step b) the amount of haloalkane is 1 to 2 molar equivalents of imidazole functions carried by the polymer at the end of step a) or is 1.2 to 2.4 molar equivalents of 1,4-dipolar compound used in step a).

[0079] Mode 27: Process according to any one of modes 18 to 26 in which in step c) the mixture obtained in step b) is brought to a temperature above 30°C.

[0080] Mode 28: lonomer, polymer bearing pendant imidazolium ionic groups which are attached to the polymer via a group resulting from the cycloaddition reaction between a 1,3-dipolar compound and an unsaturated polymer, the counterions of the imidazolium ionic groups being halide anions, the 1,3-dipolar compound being an aromatic nitrile oxide substituted by an imidazole function, the unsaturated polymer being a polymer containing monomeric units of a diene.

[0081] Mode 29: lonomer according to mode 28 in which the 1,3-dipolar compound is defined in any one of modes 10 to 17.

[0082] Mode 30: lonomer according to mode 28 or 29 in which the unsaturated polymer is defined at any one of modes 2 to 3.

[0083] Mode 31: lonomer according to any one of modes 28 to 30 in which the diene is 1,3-butadiene or isoprene.

[0084] Mode 32: A process for preparing an ionomer defined according to any one of modes 28 to 31, which process comprises steps a) to c) defined in any one of modes 18 to 27.

[0085] Mode 33: Fuel cell or electrolyzer which contains a membrane defined in any one of modes 1 to 17.

[0086] The aforementioned features of the present invention, as well as others, will be better understood upon reading the following description of several examples of embodiments of the invention, given by way of illustration. Examples

[0087] In the examples, the 1,3-dipolar compound substituted with an imidazole function is 2,4,6-trimethyl-3-((2-methyl-l / / -imidazol-l-yl)methyl)benzonitrile oxide. It is prepared according to the procedure described in patent application WO 2015059269.

[0088] Nuclear magnetic resonance (NMR): The prepared polymers are characterized by 'H NMR and 13C NMR spectrometry. NMR spectra were recorded on a Brüker Avance III 500 MHz spectrometer equipped with a 5 mm BBFOz-grad "broadband" cryo-probe. The quantitative ¹H NMR experiment used a single 30° pulse sequence and a 5-second repetition delay between acquisitions. 64 to 256 accumulations were performed. The quantitative ¹³C NMR experiment used a single 30° pulse sequence with proton decoupling and a 10-second repetition delay between acquisitions. 1024 to 10240 accumulations were performed. The two-dimensional ¹H / ¹³C experiments were used to determine the structure of the copolymers. The ¹H chemical shift axis was calibrated with respect to the protonated impurity of the solvent (CDC¹³) at δm = 7.20 ppm. The chemical shift axis 13C is calibrated with respect to the solvent signal (CDC13) at ônc = 77 ppm.

[0089] SEC 3D Analysis: Size exclusion chromatography (SEC) separates macromolecules in solution according to their size using columns filled with a porous gel. The macromolecules are separated according to their hydrodynamic volume, with the largest being eluted first. Combined with three detectors (3D), a refractometer, a viscometer, and a 90° light scattering detector, SEC allows for the determination of the absolute molar mass distribution of a polymer. The various absolute molar masses, number average (Mn), weight average (Mw), and dispersity (D = Mw / Mn) can also be calculated.

[0090] Each sample is solubilized in tetrahydrofuran (+ 1% vol. of diisopropylamine + 1% vol. of triethylamine) at a concentration of approximately 1 g / L. Then the solution is filtered through a 0.45 µm porosity filter before injection.

[0091] The apparatus used is a WATERS Alliance e2695 chromatograph. The elution solvent is tetrahydrofuran (+ 1% vol. of diisopropylamine + 1% vol. of triethylamine), the flow rate is 1 mL / min, and the system temperature is 35°C. A set of three columns, "PL Gel Mixed B-LS" from Agilent, is used. The injected volume of the polymer sample solution is 100 pL. The detection system used, "MALS DAWN 8+, Viscostar and T-Rex" from WYATT, is composed of a differential refractometer, a differential viscometer and a 90° light scatter detector.

[0092] The haloalkane is TCI's 1-bromooctane (99% purity), the press is a Carver brand, the microextruder is a twin-screw with recirculation, Xplore brand, equipped with a sleeve with an internal volume of 15 cm3, the chamber volume being 3 cm3, the screw speed being 100 rpm (revolutions / minute).

[0093] Example 1: preparation of an ionomer, polybutadiene bearing pendant imidazolium ionic groups (or imidazolium functions)

[0094] Preparation of a polybutadiene bearing imidazole functions (step a):

[0095] The polymer containing monomer units of a diene is a strong cis polybutadiene containing 97% cis 1,4-butadiene units, commercial product "BR Synteca 63" of the Synthos company.

[0096] The 1,3-dipolar compound (1.308 g with a mass purity of 60%, corresponding to 3.1 mmol of compound) is incorporated in several stages (5 times) into polybutadiene (1.251 g - 23.1 mmol of butadiene monomer unit) in a microextruder for a residence time in the barrel of 3 min at 120°C. The mixture is collected at the extruder outlet in the form of a rod. This mixing phase is followed by heat treatment at 120°C for 10 minutes under pressure of 3 to 4 bar. A functional imidazole polybutadiene is obtained, the polybutadiene modified by the grafting reaction with the 1,3-dipolar compound.

[0097] Preparation of a polybutadiene bearing imidazolium groups (steps b) and c)):

[0098] The imidazole functional polybutadiene (1.95 g) is introduced into a microextruder. 1-Bromooctane (0.75 g - 3.9 mmol) is then added to the microextruder at the screw head to be incorporated into the imidazole functional polybutadiene. The residence time in the barrel is 17 h at a temperature between 39°C and 49°C. A polybutadiene bearing imidazolium groups is recovered at the extruder outlet in the form of a rod, as confirmed by NMR analysis. The results are shown in Table 1. The polymer contains 0.54 mmol of imidazolium ionic groups per gram of polymer.

[0099] Example 2: preparation of a polybutadiene ionomer bearing imidazolium groups

[0100] Steps a) and b) are carried out as in Example 1. Step c) differs from step c) of Example 1 in that the residence time in the sheath is 45 h at a temperature between 37 °C and 45 °C. A polybutadiene bearing imidazolium functional groups is recovered, as confirmed by NMR analysis. The results are shown in Table 1. The polymer contains 0.71 mmol of imidazolium ionic groups corresponding to formula 1 per gram of polymer.

[0101] Formula (1):

[0102] Table 1: Molar content in 1 e polymer (% mol) at the end of step c) Example 1 at the end of step c) Example 2 cis l,4-butadiene 91.3 86.4 imidazole function grafted 4.1 6.3 imidazolium function grafted 4.6 7.3

[0103] Example 3: preparation of an ionomer, poly(l,3-butadiene-co-ethylene) bearing pendant imidazolium ionic groups (or imidazolium functions)

[0104] Preparation of poly(1,3-butadiene-co-ethylene), a polymer containing monomer units of a 1,3-diene:

[0105] The ethylene-1,3-butadiene copolymer (EBR) is prepared according to the following procedure: The metallocene [{Me2SiFlu2Nd(p-BH4)2Li(THF)}]2 is prepared according to the procedure described in patent application WO 2007054224. BOMAG butyl methylmagnesium (20% in heptane, at 0.88 mol L') comes from Chemtura and is stored in a Schlenk tube under an inert atmosphere. The ethylene, of N35 grade, comes from the company Air Liquide and is used without prior purification. 1,3-Butadiene is purified over alumina guards. The methylcyclohexane (MCH) solvent from BioSolve is dried and purified on an alumina column in a solvent fountain from mBraun and used under an inert atmosphere. The polymerization reaction is carried out under an inert atmosphere in a 90 L stainless steel reactor equipped with a stainless steel stirring paddle. Temperature control is achieved using an oil bath. Thermostatically controlled and connected to a double-insulated jacket. This reactor has all the necessary inputs and outputs for handling. In a 90 L stainless steel reactor, 64 L of MCH and a solution of BOMAG (27 mmol) in MCH (0.01 mol / L) are introduced. The reactor is heated to 80°C, and the monomers are added at a controlled rate to maintain a constant monomer mixture composition in the polymerization medium. The ethylene flow rate is set at 40 g / min, butadiene is injected independently, and its flow rate is controlled by the ethylene flow rate at a butadiene / ethylene mass ratio of 1.26. When the reactor reaches a pressure of 8.8 bar, the catalytic system (5.16 mmol of Nd), prepared according to the protocol described below, is introduced into the polymerization medium. The polymerization reaction, conducted at 80°C, is stopped with methanol when approximately 5 to 6 kg of polymer have formed; the polymer is then recovered after a stripping step. The polymer is then dried on a screw conveyor equipped with a single screw at 150°C.

[0106] The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from the metallocene, [Me2Si(Flu)2Nd(q-BH4)2Li(THF)], the co-catalyst, butylloctylmagnesium (BOMAG), and a preforming monomer, 1,3-butadiene. It is prepared according to a preparation method in accordance with paragraph II.1 of patent application WO 2017093654 A1: In an 80 L reactor containing 54.5 L of methylcyclohexane previously degassed with nitrogen, 936 mL of a butylctylmagnesium in heptane solution (0.933 M, 870 mmol) and 254 g of the complex {(Me2Si(Ci3H8)2)Nd(-BH4)2Li(THF)}2 (number of moles of Nd, nNd = 399 mmol), prepared according to patent application WO2007 / 054224 (complex 1), are successively introduced. 1.9 kg of 1,3-butadiene (also referred to hereafter as butadiene) are added to the reactor at 50°C. The reactor is then heated to 80°C for 5 h with stirring. The resulting catalytic solution is stored at -5°C.

[0107] The copolymer thus prepared is analyzed by SEC and NMR. Table 2 shows: -the microstructure of the copolymer, the units being expressed as a molar percentage calculated relative to the total number of moles of ethylene, butadiene and 1,2-cyclohexane units (designated in Table 2 as "cycle"), - its number-average molar mass, Mn, expressed in g / mol and the dispersity, D.

[0108] Table 2: 1,4-Butadiene Units 1,2-Butadiene Units Cycle Unit Ethylene Unit Mn (SEC) IP 10 21 6 61 236200 1.4

[0109] Preparation of a poly(L3-butadiene-co-ethylene) bearing imidazole functions (step a):

[0110] The 1,3-dipolar compound (72 g) of 60% purity by mass is incorporated in several stages (4 times) into the copolymer (57 g) on ​​a roller tool (external mixer 23°C) by carrying out a total of 12 wallet passes to obtain a homogeneous mixture. This mixing phase is followed by heat treatment at 120°C for 10 minutes in the press under 10 t (tonnes) of charge. A functional imidazole copolymer is recovered, the copolymer modified by the grafting reaction with the 1,3-dipolar compound. [YES] Preparation of a poly(l,3-butadiene-co-ethylene) bearing imidazolium functions (steps b) and c)):

[0112] The imidazole functional copolymer (2.1 g) is introduced into the microextruder, the 1-bromooctane (0.90 g) is then added to the microextruder at the screw head to be incorporated into the imidazole functional copolymer, the residence time in the barrel is 30 minutes at 80°C. The mixture formed is collected at the outlet of the extruder in the form of a rod. This mixing phase is followed by heat treatment at 90°C for 17 hours in a press under 3 to 4 bars of pressure. A poly(1,3-butadiene-co-ethylene) containing imidazolium ionic groups is obtained as a film 180 µm thick. A test sample of 180 µm thickness is taken to create a membrane. To determine the ionic conductivity of the membrane, its electrochemical impedance is measured across the membrane plane at 30°C and 30% relative humidity. The measurement parameters are a 50 mV amplitude change and a 0 V applied potential. Prior to this, the halide counterions are replaced by hydroxide anions according to the following procedure: The ionomer film is immersed for 24 h at room temperature (23°C) in a potassium hydroxide solution in demineralized water to perform the ion exchange between bromide and hydroxide ions. It is then soaked for 15 min in demineralized water to remove excess hydroxide ions. The water absorption is 100% by mass. The measured ionic conductivity is 13.45 mS / cm.

Claims

Demands

1. Anion exchange membrane containing an ionomer, polymer bearing pendant imidazolium ionic groups which are attached to the polymer via a group resulting from the cycloaddition reaction between a 1,3-dipolar compound and an unsaturated polymer, the 1,3-dipolar compound being an aromatic nitrile oxide substituted with an imidazole function, the unsaturated polymer being a polymer containing monomeric units of a diene.

2. Membrane according to claim 1 in which the unsaturated polymer is a homopolymer of a 1,3-diene or a copolymer of a 1,3-diene.

3. Membrane according to claim 1 or 2 wherein the unsaturated polymer is selected from homopolymers of a 1,3-diene, copolymers of two or more 1,3-dienes, copolymers of a 1,3-diene and a vinylaromatic monomer and copolymers of a 1,3-diene and ethylene.

4. Membrane according to any one of claims 1 to 3 wherein the imidazole function is of formula l / / -imidazol-l-yl.

5. Membrane according to any one of claims 1 to 3 wherein the imidazole function is 2-alkyl-l / / -imidazol-l-yl, preferably 2-methyl-l / / -imidazol-1-yl.

6. Membrane according to any one of claims 1 to 5, wherein the 1,3-dipolar compound corresponds to formula (I), in which one of the symbols Ri to R5 represents a group containing the imidazole function, the other symbols a hydrogen atom or an alkyl group, wherein one of the Ri and R5 is not a hydrogen atom. CNO R 5 R1 JJ J ^2 (I) Rg

7. Membrane according to claim 6 in which R4 represents the group containing the imidazole function.

8. Membrane according to claim 6 or 7 wherein R4 is a (l / / -imidazol-l-yl)alkyl or (2-alkyl-l / / -imidazol-l- yl)alkyl, preferably a (l / / -imidazol-l-yl)methyl or (2-alkyl-l / / -imidazol-l-yl)methyl group.

9. Membrane according to any one of claims 6 to 8 wherein Rh, R3 and R5 are each an alkyl and R2 is a hydrogen atom.

10. Membrane according to any one of claims 6 to 9 wherein Rb, R3 and R5 are methyl or ethyl.

11. Membrane according to any one of claims 1 to 10 wherein the 1,3-dipolar compound is the compound 2,4,6-trimethyl-3-((2-methyl-l / / -imidazol-l-yl)methyl)benzo-nitrile oxide or the compound 2,4,6-triethyl-3-((2-methyl-l / / -imidazol-l-yl)methyl)benzo-nitrile oxide.

12. A method for preparing an anion exchange membrane as defined in any one of claims 1 to 11 comprising the following steps a), b), c) and d): - a) the preparation of a polymer bearing pendant imidazole functions by a cycloaddition reaction of the 1,3-dipolar compound and the unsaturated polymer, - b) the incorporation of a haloalkane into the polymer bearing pendant imidazole functions by thermomechanical mixing, - c) a heat treatment of the mixture obtained in step b) to convert the imidazole functions into imidazolium ionic groups, - d) the shaping of the ionomer, obtained at the end of step c), in the form of a film, steps b), c) and d) being carried out in bulk.

13. A process according to claim 12 wherein the haloalkane, preferably a bromoalkane, contains a single halogen atom.

14. A process according to any one of claims 12 to 13 wherein the amount of the 1,3-dipolar compound used in step a) is greater than 0.5 milliequivalent of imidazole function per gram of unsaturated polymer, preferably greater than 0.6 milliequivalent of imidazole function per gram of unsaturated polymer, and less than 4.2 milliequivalents of imidazole function per gram of unsaturated polymer.

15. A process according to any one of claims 12 to 14 wherein in step b) the amount of haloalkane is 1 to 2

16.

17.

18.

19.

20. molar equivalent of imidazole functions carried by the polymer at the end of step a) or is 1.2 to 2.4 molar equivalent of 1,4-dipolar compound used in step a). lonomer, polymer bearing pendant imidazolium ionic groups which are attached to the polymer via a group resulting from the cycloaddition reaction between a 1,3-dipolar compound and an unsaturated polymer, the counterions of the imidazolium ionic groups being halide anions, the 1,3-dipolar compound being an aromatic nitrile oxide substituted with an imidazole function, the unsaturated polymer being a polymer containing monomeric units of a diene. lonomer according to claim 16 wherein the 1,3-dipolar compound is defined in any one of claims 6 to 11. lonomer according to claim 16 or 17 wherein the unsaturated polymer is defined in any one of claims 2 to 3. A process for preparing an ionomer as defined in any one of claims 16 to 18, comprising steps a) to c) as defined in any one of claims 12 to 15. Fuel cell or electrolyzer which contains a membrane as defined in any one of claims 1 to 11.