Preparation of polymers for AEM water electrolysis with reduced tendency to swell

Abstract

The invention is concerned with the preparation of anion-conducting polymers intended for use in alkaline membrane water electrolysis. Specifically, the intention is to reduce the tendency of anion-conducting polymers to swell in alkaline aqueous solutions, without severely impairing the specific anion conductivity of these polymers. This is achieved by adding a further reactant to the reaction mixture. In total, the polymer is prepared from three reactants, namely from 4,4-bis(4-hydroxy-3,5-dimethylphenyl)-1-methylpiperidine (formula I), from 4,4'-difluorobenzophenone (formula II), and from 4,4'- dihydroxybenzophenone (formula III) or from bis(4-hydroxy-3,5-dimethylphenyl)methanone (formula IV).

Description

[0001] Preparation of polymers for AEM water electrolysis with reduced tendency to swell

[0002] The invention is concerned with the preparation of anion-conducting polymers intended for use in alkaline membrane water electrolysis.

[0003] Water electrolysis describes the decomposition of water H2O into hydrogen H2 and oxygen O2 by means of electric current. Water electrolysis can be conducted in alkaline medium and in acidic medium. Alkaline water electrolysis uses a basic electrolyte, and acidic water electrolysis uses an acidic electrolyte. The electrolyte serves for ion exchange and at the same time contains the water to be split. Water electrolysis is performed using an electrochemical cell.

[0004] Alkaline membrane water electrolysis (or anion exchange membrane water electrolysis - AEMWE) is one particular method for water electrolysis. It takes place in a basic medium and is conducted in the presence of an anion exchange membrane. AEMWE is considered to be a technology for the sustainable production of "green" hydrogen, provided that the electrical energy required is obtained from renewables. Against this background, work is currently underway for the technical deployment of alkaline membrane water electrolysis on the industrial scale.

[0005] An overview of the construction of the electrochemical cells currently used in AEMWE and the materials used in these cells is provided by:

[0006] Miller, Hamish Andrew et al.: Green hydrogen from anion exchange membrane water electrolysis: a review of recent developments in critical materials and operating conditions. Sustainable Energy Fuels, 2020, 4, 2114 DOI: 10.1039 / c9se01240k

[0007] Particularly for the production of the membranes used in AEMWE, polymers exhibiting conductivity for anions, more precisely for hydroxide ions (OH ), are required.

[0008] Polymers exhibiting conductivity for anions are known inter alia from WO 2021 / 013694 A1 , EP4032934A1 and EP4059988A1. They are suitable for the production of anion exchange membranes (AEMs). These membranes can in turn be used in alkaline water electrolysis.

[0009] An essential property qualifying a polymer as suitable as a membrane material in AEMWE is firstly its high specific conductivity for hydroxide ions (OH ).

[0010] In a technical context, it is additionally of particular interest that the polymer as far as possible does not swell in an aqueous alkaline solution: Swelling is understood to be the increase in the volume of an electrochemical cell component that has been produced from the polymer, this swelling being attributable to the penetration of the alkaline solution into the polymer. The membrane in AEMWE as a matter of principle comes into sustained contact with alkaline solution, since the aqueous alkaline solution (usually potassium hydroxide solution KOH) is used as electrolyte.

[0011] The increase in volume caused by the swelling of the polymer is usually accompanied by an anisotropic change in shape of the electrochemical cell component produced from the polymer. In the case of the membrane, this change in shape leads to leaks at the cell, which should be avoided as far as possible in the interest of operational safety of the system: The water electrolysis produces gaseous hydrogen and oxygen, which are kept separate by the membrane. If the membrane becomes leaky due to the swelling, hydrogen and oxygen mix and form highly explosive oxyhydrogen gas.

[0012] A more in-depth description of the swelling process of anion-conducting polymers can be found in:

[0013] Qiongjuan Duan, Shanhai Ge, Chao-Yang Wang: Water uptake, ionic conductivity and swelling properties of anion-exchange membrane, Journal of Power Sources, Volume 243, 2013, Pages 773-778, ISSN 0378-7753, https: / / doi.org / 10.1016 / jjpowsour.2013.06.095.

[0014] Qiongjuan Duan's team was concerned with the swelling of anion exchange membranes that takes place within fuel cells. No water electrolysis is performed in fuel cells, and instead water is synthesized with the release of electrical energy. Since there are no alkaline conditions here, the swelling of the polymers by neutral water was investigated.

[0015] In addition to the physical swelling, the anion-conducting polymers used in AEMWE are also chemically attacked by the base. This degrades the polymer over a relatively long period of time.

[0016] The anion-conducting polymers disclosed in WO 2021 / 013694 A1 and EP4032934A1 were investigated in these documents only with respect to their swelling stability in deionized water. In contrast, the degradation of the polymers as a result of basic stress was not investigated. In this respect, a statement concerning the long-term stability of these polymers in the basic electrolyte is not possible.

[0017] EP4059988A1 investigated the long-term stability of various anion-conducting polymers in potassium hydroxide solution at 80°C. A polymer known from WO 2021 / 013694 A1 was also compared therein, see Membrane #1 from Example 27.

[0018] It should be mentioned here that, besides the swelling during electrolysis operation, swelling of the anion- conducting polymers used therefor also causes difficulties as early as during the production of the anion exchange membrane: For instance, AEMs are frequently coated with catalysts or catalytically active materials in order to increase the efficiency of the electrolysis. In addition to the catalytically active material, the catalyst layers produced in this process also contain binders which immobilize the catalytically active material on the membrane. Anion-conducting polymers are also used as binders. If the anion-conducting polymer swells when applying the catalyst layer, this results in a defective coating which makes it highly difficult to install the coated membrane in the cell. However, it should be noted in this context that the swelling of the ion-conducting polymer during the production of the anion exchange membrane is usually caused by organic solvents used in the membrane production. These solvents are generally no longer relevant during AEMWE operation.

[0019] From the point of view of the manufacturers and users of anion exchange membranes intended for alkaline water electrolysis, it is therefore important that the anion-conducting polymers from which the AEMs are produced do not swell either in the organic solvents used in the production or in the alkaline aqueous solutions used as electrolyte.

[0020] This invention is primarily concerned with those measures that concern the swelling during electrolysis. Specifically, the intention is to reduce the tendency of anion-conducting polymers to swell in alkaline aqueous solutions, without severely impairing the specific anion conductivity of these polymers.

[0021] This object is achieved by preparing the polymers as follows: a) providing a reaction mixture containing:

[0022] • a first reactant, namely 4, 4-bis(4-hydroxy-3,5-dimethylphenyl)-1 -methylpiperidine;

[0023] • a second reactant, namely 4,4'-difluorobenzophenone;

[0024] • a third reactant, which is 4,4'-dihydroxybenzophenone and / or bis(4-hydroxy-3,5- dimethylphenyl) methanone;

[0025] • at least one first solvent;

[0026] • at least one deprotonating agent; b) exposing the reaction mixture to heat so that the reaction mixture adopts a temperature of between 140°C and 180°C; c) separating water off from the reaction mixture; d) obtaining a precursor from the reaction mixture; e) washing the precursor; f) drying the washed precursor; g) providing an alkylating reagent; h) contacting the alkylating reagent with the washed and dried precursor; i) obtaining the polymer.

[0027] Such a process is a first subject of the invention.

[0028] The invention is based on the unexpected finding that, by adding a further reactant to the reaction mixture, a polymer is obtained which has increased swelling resistance in alkaline solution compared to a polymer which was prepared without this additional reactant. It is also surprising that the anion conductivity of the polymer obtained via the additional reactant is hardly lower than that of a conventional polymer which - apart from the additional reactant - is based on the same starting materials.

[0029] Specifically, the polymer is prepared from three reactants. The first reactant is 4,4-bis(4-hydroxy-3,5- dimethylphenyl)-1-methylpiperidine, which is represented in formula I.

[0030] The piperidine group present in this unit is positively charged as a result of quaternization and thus accounts for the intrinsic anion conductivity of the polymer.

[0031] The second reactant is 4,4'-difluorobenzophenone of formula II:

[0032] This unit serves for the equimolar employed weight of hydroxide compound (units I and III or IV) and fluorine compound. Accordingly, the employed weight of unit II is chosen depending on the employed weight of units I and 111 / IV.

[0033] The use of units (I) and (II) is known from WO 2021 / 013694 A1.

[0034] According to the invention, a further, third reactant is provided in the reaction mixture, which may be used either in methylated form or unmethylated.

[0035] In its simple, unmethylated form, the third reactant is 4,4'-dihydroxybenzophenone, which is represented in formula (III).

[0036] Alternatively, the third reactant used may be bis(4-hydroxy-3,5-dimethylphenyl)methanone, represented in formula (IV).

[0037] The unit represented in formula (IV) is the methylated form of (III). Of course, the third reactant used may also be a mixture of unit (III) and unit (IV).

[0038] Apart from the selection of the reactants present in the reaction mixture provided, the preparation process according to the invention corresponds to the conventional preparation of anion-conducting polymers with a piperidine group, by way of polycondensation and subsequent quaternization.

[0039] As with any chemical reaction, the three reactants here should also be provided in a suitable molar ratio with respect to each other. In a particularly preferred embodiment of the invention, the molar amounts u, v, w are selected such that the relationships of formulae (V) and (VI) are observed:

[0040] 100-c

[0041] It = V ■

[0042] 100 (V)

[0043] In the relationships of formulae (V) and (VI), in each case u is the molar amount of the first reactant, v is the molar amount of the second reactant and w is the molar amount of the third reactant. If a mixture of units (III) and (IV) is used as third reactant, w describes the molar amount of the mixture of units (III) and (IV). The total molar amount, that is to say the size of the mixture, is scaled via the molar amount w of the third reactant. In theory, it is also possible to scale via all units, since the molar amounts are related to each other via the formulae (V) and (VI).

[0044] The letter c in the formulae is a rational number between 0 and 15 in both formulae (V) and (VI). It is important that c represents the same number in both formulae. The number c defines a replacement factor. This means that between 0% and 15% of the molar amount of the first reactant u is replaced by the molar amount of the third reactant w. The number c may for example be 5 or 10. From the addition of formulae (V) and (VI), it follows that the sum total of the molar amounts u and w corresponds to the molar amount v. The first reactant and the third reactant therefore together take up the same stoichiometric proportion of the reaction mixture as the second reactant.

[0045] The molar amounts u, v, w indicated here describe the optimal stoichiometry, which corresponds to an equimolar employed weight. Of course, it is possible to deviate from the optimal stoichiometry and to actually add individual reactants in deficit or in excess. However, this is not preferred because this leads to shorter polymer chains: The molar mass of the polymers obtained is then too low, as, therefore, is their viscosity. As a result, the membrane becomes too soft and cannot be assembled so well. In addition, the membrane becomes more susceptible to mechanical degradation, in which the backbone of the polymer is cleaved. If the polymer chain is shorter from the start, there will be less time before the chain length falls below a critical value at which the membrane becomes brittle. If the chain length already falls below the critical chain length from the outset due to an employed weight that deviates significantly from formula (V) or (VI), there is the risk of it no longer being possible to cast a membrane from the polymer solution obtained. In particular, a homogeneous coating of the substrate used during membrane casting is no longer obtained. For these reasons, the reactants are preferably actually provided in the optimal stoichiometric ratio in the reaction mixture.

[0046] The deprotonating agent is partly consumed in the reaction, but is not incorporated into the polymer. Preferably, the deprotonating agent is an alkali metal carbonate, very particularly preferably lithium carbonate or sodium carbonate or potassium carbonate or mixtures thereof.

[0047] After the polymerization of the three reactants has ended, a precursor is obtained. The precursor is to a large extent still dissolved in the first solvent, especially at the reaction temperature. The precursor can be recovered from the reaction mixture by discharging it into distilled water. In order to purify it of solvent, unconverted reactant and unconverted deprotonating agent, the precursor is washed with water and then dried so as to remove the washing water again. Washing and drying is easiest to perform when the precursor is subjected to shearing in the crude state, in the washed state or at the latest during drying. The precursor is comminuted in the process. The shearing of the precursor may be effected with a mixer or a blender or a kneader.

[0048] The precursor is not yet conductive for anions. In order for it to be so, it must be quaternized. This is preferably done by at least partially dissolving the precursor, after washing and drying, in a second solvent and contacting it with the alkylating reagent in the presence of the second solvent. The quaternization is preferably effected at slightly elevated temperature, for example in the range from 30°C to 60°C.

[0049] The alkylating reagent used is preferably a haloalkane such as for example iodomethane or bromomethane. Mixtures of these are also usable as alkylating reagent. The process requires up to two solvents, namely a first solvent, which is present in the reaction mixture and in which the polymerization is conducted, and a second solvent, in which the quaternization is effected. The two solvents may be identical or different. The first and / or the second solvent is preferably a substance selected from the group consisting of N,N-dimethylacetamide (DMAC), N,N- dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), acetonitrile (ACN), ethanol (EtOH), methanol (MeOH). It is of course also possible to use mixtures of these substances as solvent. Particular preference is given to using DMAC or NMP as first solvent and DMSO, ACN or EtOH as second solvent.

[0050] Since the anion-conducting polymer is prepared according to the invention from three reactants, the product is a terpolymer. Due to the similarity of the units (III) and (IV), a polymer which is prepared from all four units I, II, III, IV is also considered to be a terpolymer.

[0051] The structure of the terpolymer cannot be described with sufficient precision. This is because the synthesis involves a polycondensation reaction. The 4,4'-difluorobenzophenone (II) acts as an electrophile, with fluorine as the leaving group. Either the first reactant (I) or the third reactant (III) and / or (IV) can act as nucleophile. The actual structure of the polymer chain is therefore statistically distributed. In addition, the chain length and the length of a single repeating unit of the terpolymer depends on the selected amount of reactants used.

[0052] One theoretically possible structure of the terpolymer obtained is represented in formula VII:

[0053] Since both the number of repeating units n and the number and sequence of units within the repeating unit can vary greatly, the product actually obtained will contain a multitude of different terpolymers.

[0054] On account of the barely representable complexity of the product, a polymer obtainable by the process according to the invention is a further subject of the invention.

[0055] After the quaternization, the polymer obtained is anion-conductive and sufficiently resistant in alkaline solution. It can therefore be used in alkaline membrane water electrolysis. This use is a further subject of the invention. The use is made by conducting alkaline membrane water electrolysis in the presence of the polymer prepared. A process for producing hydrogen and oxygen by electrolysis of water in a basic medium, conducted in the presence of the polymer, is therefore a further subject of the invention.

[0056] Specifically, an anion exchange membrane (AEM) can be produced from the polymer. The polymer forms the anion-conducting membrane material. The polymer may be mixed with other materials. An anion exchange membrane containing a polymer obtained according to the invention is therefore a further subject of the invention.

[0057] A further subject of the invention is a composition which contains at least one third solvent and a polymer which is obtained according to the invention and is at least partially dissolved in said solvent.

[0058] Such a composition is viscous and is used for the production of an anion exchange membrane from the polymer. This is done by applying the composition to a substrate and drying it. During the drying, the third solvent evaporates, with the result that the film-forming polymer precipitates and forms a layer on the substrate. As substrate, use may for example be made of a glass plate. Detached from the glass plate, the layer is used as an AEM. Such a procedure is known as "membrane casting".

[0059] The third solvent used in the composition may be the same as the first solvent present in the reaction mixture and / or the second solvent used in the quaternization. However, the third solvent may also be different from these solvents.

[0060] Moreover, the composition may additionally contain at least one particulate electrocatalyst. Electrocatalysts accelerate electrochemical reactions without themselves being consumed in the process. A composition containing an electrocatalyst is referred to as a "catalyst ink" or "catalyst paste", depending on its viscosity.

[0061] The catalyst ink / paste is also applied to a substrate and dried to form a solid catalyst layer on the substrate. The catalyst layer is formed by the anion-conducting polymer precipitated out from the solution and by the particulate electrocatalyst dispersed therein. In the simplest case, the role of substrate is performed by an anion exchange membrane, so that the latter receives a catalytically active layer. The electrocatalyst is immobilized on the AEM via the anion-conducting polymer serving as binder. A layered body obtained in this way is also referred to as a "catalyst coated membrane" (CCM). A process for producing a CCM is disclosed in WO 2023 / 088714 A1 . In said document, a catalyst ink is prepared from an ionomer and an electrocatalyst, is sprayed directly onto an AEM and is dried. The anion-conducting polymer described here can be processed analogously.

[0062] Examples

[0063] The invention shall now be elucidated in more detail with reference to synthesis examples. The polymers prepared in the examples are then investigated with respect to their anion conductivity, ion exchange capacity and tendency to swelling. In the figure: Figure 1 : shows the relative swelling (dimensional change) of the membranes according to the invention compared to the conventional membrane, in each case in the X and Y directions.

[0064] 1 . Production of an AEM from conventional polymer (not part of the invention)

[0065] An anion-conducting polymer was synthesized in accordance with Examples 1 to 3 of WO 2021 / 013694 A1. The polymer was used to cast an anion exchange membrane in accordance with Example 4 of the said WO document. The sample designation was MEM007.

[0066] 2.1 Preparation of the precursor with c = 5 of a polymer according to the invention (part of the invention)

[0067] The synthesis was conducted in a 2 L jacketed glass reactor, with a blade stirrer shaft, a water separator, and under nitrogen counterflow. At the start of the synthesis, 0.667 mol (226.77 g) of 4,4-bis(4-hydroxy- 3, 5-dimethylphenyl)-1 -methylpiperidine, 0.035 mol (7.52 g) of dihydroxybenzophenone, 0.702 mol (153.27 g) of difluorobenzophenone, 1.544 mol (213.58 g) of potassium carbonate and 1250 mL of dimethylacetamide were initially charged and stirred at 90 rpm at room temperature under nitrogen counterflow for 30 minutes. The temperature of the thermostat was then increased to 165°C. The temperature was maintained at 165°C jacket temperature for 19 h. The internal temperature of the reaction mixture was 160°C. The water formed was discharged from the system over the entire time period via the water separator under a nitrogen stream. The hot reaction mass was then discharged in portions from the reactor into ultrapure water (~20°C) with turbulent flow, under intense shearing. In total, the approx. 1400 mL of reaction mixture was discharged into approx. 6000 mL of water. The material was then washed six times with in each case 2000 mL of ultrapure water (60°C). The washed, white polymer material was then dried in a vacuum drying cabinet at 80°C for 72 h at 200 mbara (800 mbar negative pressure). The final weight was 87%.

[0068] 2.2 Preparation of the precursor with c = 10 of a polymer according to the invention (part of the invention)

[0069] The synthesis was conducted in a 2 L jacketed glass reactor, with a blade stirrer shaft, a water separator, and under nitrogen counterflow. At the start of the synthesis, 0.632 mol (226.77 g) of 4,4-bis(4-hydroxy- 3, 5-dimethylphenyl)-1 -methylpiperidine, 0.070 mol (15.04 g) of dihydroxybenzophenone, 0.702 mol (153.27 g) of difluorobenzophenone, 1.544 mol (213.58 g) of potassium carbonate and 1250 mL of dimethylacetamide were initially charged and stirred at 90 rpm at room temperature under nitrogen counterflow for 30 minutes. The synthesis was conducted analogously to that described under 2.1 . The final weight was 82%. 3.1 Quaternization of the with c = 5 of the inve

[0070] The precursor obtained in 2.1 was quaternized analogously to Example 3 of WO 2021 / 013694 A1 . This afforded an anion-conducting polymer.

[0071] 3.2 Quaternization of the precursor with c = 10 (part of the invention)

[0072] The precursor obtained in 2.2 was quaternized analogously to Example 3 of WO 2021 / 013694 A1 . This afforded an anion-conducting polymer.

[0073] 4.1 Preparation of an AEM from the polymer according to the invention with c = 5 (part of the invention)

[0074] The polymer solution obtained from 3.1 was passed through a filtration apparatus with 1 pm PTFE filter fabric. The polymer solution was then applied to a PET film using a coating bar. The coating bar moved at a constant 5 mm / s. The PET film was located on a 70°C hot heating bench during the process. For drying, the PET film remained on the heating bench together with the applied polymer film for 1 h. The sample designation was MB47.

[0075] 4.2 Preparation of an AEM from the polymer according to the invention with c = 10 (part of the invention)

[0076] The polymer solution obtained from 3.2 was passed through a filtration apparatus with 1 pm PTFE filter fabric. The polymer solution was then applied to a PET film using a coating bar. The coating bar moved at a constant 5 mm / s. The PET film was located on a 70°C hot heating bench during the process. For drying, the PET film remained on the heating bench together with the applied polymer film for 1 h. The sample designation was MB48.

[0077] 5. Determination of the behaviour

[0078] In addition to the change in polarity and resulting changes in the solubility behaviour and subsequent processing, swelling is in particular an important influencing parameter which is influenced by the structural change (5 mol% or 10 mol% of difluorobenzophenone in the polymer according to the invention).

[0079] Three membrane pieces (flat form, dimensions 25 mm x 15 mm) were prepared using a punch from each of the AEMs produced under 1 and 4.1 and 4.2.

[0080] The membrane pieces were all dried at 50°C for 24 h at atmospheric pressure and their sizes were then measured using a light microscope. The membrane pieces were then stored in 1 M KOH solution (60°C) in a shaking water bath for 24 h. The membrane pieces were then stored twice, in each case at 60°C in ultrapure water in a shaking water bath for 30 minutes. The ultrapure water was then exchanged once again with fresh water and measurement was performed at 20°C to 25°C within the following 30 minutes. The sizes of the membrane pieces were again measured using a light microscope. The dimensional change results from the difference in the recorded data between the respective wet membrane piece and the dried membrane piece.

[0081] Figure 1 shows the data averaged from three individual measurements in each case of the relative swelling (dimensional change) of the material produced according to the invention compared to the conventionally produced material.

[0082] The material MB0047 (c = 5) produced according to the invention is 13.6% less swollen in the X direction and 1 1 .7% less swollen in the Y direction, compared to the conventionally produced material MEM007. For MB48 (c = 10) the effect is amplified yet further: The swelling decreases by 20.0% in the X direction and by 18.5% in the Y direction.

[0083] 6. Determination of the ion exchange capacity for MEM007 and MB47

[0084] The ion exchange capacity (I EC) is a parameter for determining the degree of quaternization of the material. In other words, the IEC is used to determine the number of charged groups within the polymer. The comparative material from WO 2021 / 013694 A1 provides a theoretical IEC value of 1 .681 mmol / g. The measured IEC values typically lie at a degree of quaternization of 99 - 100 (+ / - 1)%. In the material MB47 produced according to the invention, a degree of quaternization of 97.5 (+ / - 0.6)% was measured. The slight decrease in the IEC may be attributable to a reduction in functional groups as a result of incorporating the unit of formula (III) into the polymer skeleton. 7. Determination of the anion for MB47

[0085] The conductivity (C) of the membrane for hydroxide ions (OH ) is a further indicator of how efficiently the membrane performs in electrolysis. A low ion conductivity leads to a higher resistance in the cell, which leads to voltage losses which in turn reduce the efficiency of the electrolysis as a result of the heat loss arising.

[0086] The conductivity C and the IEC correlate with each other because the conductivity C is significantly dependent on the number of charged groups in the polymer. However, the conductivity C measurements are subject to higher fluctuations than the IEC measurements.

[0087] The conductivity C is not measured directly, but rather the sheet resistance.

[0088] For the determination, three membrane pieces are punched out of the membrane MB47 and then ion exchanged in hydroxide form. The membrane is measured using a 4-point method.

[0089] The obtained conductivity C values of the material according to the invention correspond to -95% of the conventional material (cyclic voltammetry CV). The decrease in the conductivity can be accounted for by the decrease in charged groups. This is due to the replacement of 5% of the compound bearing the quaternary nitrogen of formula (I) by the unit of formula (III) and / or (IV).

[0090] 8. Conclusion

[0091] As a result of the use of the additional unit III and as a result of the substitution of 5% or 10% of unit (I) with unit (III) (and / or IV), a polymer is obtained the swelling behaviour of which in KOH is reduced compared to a material that was produced exclusively from (I) and (II) in a stoichiometric ratio of 1 :1 .

[0092] However, these measures result in a reduction in the charged groups in the membrane, which manifests in a decrease in the ion conductivity thereof. However, since new applications can be opened up as a result of reduced swelling (e.g. installation of larger membranes in electrolysers, better coating with catalysts due to better adhesion), this disadvantage is tolerable.

Claims

Claims1 . Process for preparing a polymer, comprising the following steps: a) providing a reaction mixture containing:• a first reactant, namely 4, 4-bis(4-hydroxy-3,5-dimethylphenyl)-1 -methylpiperidine (formula I);• a second reactant, namely 4,4'-difluorobenzophenone (formula II);• at least one first solvent;• at least one deprotonating agent; b) exposing the reaction mixture to heat so that the reaction mixture adopts a temperature of between 140°C and 180°C; c) separating water off from the reaction mixture; d) obtaining a precursor from the reaction mixture; e) washing the precursor; f) drying the washed precursor; g) providing an alkylating reagent; h) contacting the alkylating reagent with the washed and dried precursor; i) obtaining the polymer; characterized in that the reaction mixture additionally contains a third reactant, wherein the third reactant is 4,4'-dihydroxybenzophenone (formula III) and / or bis(4-hydroxy-3,5- dimethylphenyl)methanone (formula IV).

2. Process according to Claim 1 , wherein the reaction mixture is provided in such a way that the three reactants are each present at least in a molar amount u, v, w, where u is the molar amount of the first reactant, v is the molar amount of the second reactant and w is the molar amount of the third reactant, characterized in that the following applies for u, v and w.w = v ■ — (VI)100 in which c is a rational number between 0 and 15 which is selected so as to be identical in formula (V) and formula (VI).

3. Process according to Claim 1 or 2, characterized in that the precursor and / or the washed precursor and / or the washed and dried precursor is subjected to shearing.

4. Process according to any of Claims 1 to 3, characterized in that the washed and dried precursor is contacted with the alkylating reagent in the presence of a second solvent, wherein the washed and dried precursor is at least partially dissolved in the second solvent.

5. Process according to any of Claims 1 to 4, characterized in that the deprotonating agent is an alkali metal carbonate.

6. Process according to Claim 5, characterized in that the deprotonating agent is selected from the group consisting of: lithium carbonate, sodium carbonate, potassium carbonate.

7. Process according to any of Claims 1 to 6, characterized in that the alkylating reagent is a haloalkane.

8. Process according to any of the preceding Claims 1 to 7, characterized in that the first solvent and / or the second solvent is selected from the group consisting of N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), acetonitrile (ACN), ethanol (EtOH), methanol (MeOH).

9. Polymer obtainable by a process according to any of Claims 1 to 8.

10. Use of the polymer according to Claim 9 in alkaline membrane water electrolysis.11 . Process for producing hydrogen and oxygen by electrolysis of water in a basic medium, conducted in the presence of a polymer according to Claim 9.

12. Anion exchange membrane containing a polymer according to Claim 9.

13. Composition at least containing the following components: i) a third solvent; ii) a polymer according to Claim 9 which is at least partially dissolved in the solvent.

14. Composition according to Claim 13, additionally containing iii) at least one particulate electrocatalyst.

15. Process for producing an anion exchange membrane according to Claim 12, in which a composition according to Claim 13 and / or according to Claim 14 is provided, applied to a substrate and dried.

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