Block copolymer, method for producing a block copolymer, membrane, use of a membrane, and method for producing a membrane

Abstract

The present invention relates to a block copolymer having at least two different polymer blocks, wherein one polymer block is at least predominantly composed of a first, ion-conducting polymer, the ion-conducting polymer having ion-conductive functional groups, and one polymer block is at least predominantly composed of a second, mechanically flexible polymer, the mechanically flexible polymer having a lower glass transition temperature than the ion-conducting polymer. The present invention also relates to a method for producing a block copolymer, to a membrane and to the use of a membrane.

Description

[0001] DESCRIPTION

[0002] Block copolymer, process for producing a block copolymer, membrane, use of a membrane and process for producing a membrane

[0003] The invention relates to a block copolymer with at least two different polymer blocks.

[0004] The invention further relates to a process for producing such a block copolymer, as well as to a membrane and the use of a membrane. Furthermore, the invention relates to a process for producing a membrane.

[0005] As part of the energy transition, alternative methods for generating and storing electricity are increasingly being developed. Fuel cells represent an important area in this regard. These convert the chemical reaction energy of an input fuel and an oxidizing agent into electrical energy. In addition to hydrogen fuel cells, one group of fuel cells is the so-called direct alcohol fuel cells. Other relevant electrochemical processes include electrolysis processes and redox flow batteries.

[0006] Membranes, particularly ion exchange membranes, are used in such electrochemical processes. Such membranes are subject to stringent requirements. Firstly, they must be sufficiently chemically stable with respect to the surrounding media, depending on their intended application. Furthermore, such membranes are frequently exposed to mechanical stress. In electrochemical applications, a certain degree of conductivity combined with a low degree of swelling, i.e., a low volume expansion, is also required.

[0007] Due to their high ionic conductivity, special ion-conducting polymers, also known as ionomers, are used as the base material for the production of ion-conducting membranes. In addition to the properties described above, the highest possible conductivity is desired within the target temperature range of the respective application. Other desired properties include ion-selective transport within such an ionomer membrane, as well as the separation of the various reaction spaces at the electrodes and the prevention of reactant transfer, thus ensuring the highest possible impermeability.

[0008] For low-temperature applications, i.e., operating temperatures below 100°C, proton exchange membranes made of Nafion are often used. This is a sulfonated tetrafluoroethylene polymer (PTFE) developed by DuPont as a modification of Teflon. Specifically, it is an ionomer obtained by copolymerizing a nonpolar monomer with a polar monomer. To reduce the diffusion of reactants toward the cathode-anode side, relatively thick membranes (with a thickness > 50 μm) or membranes with special reinforcement layers and additives, marketed, for example, under the name Nafion XL, are usually used.

[0009] In principle, such polymers or membranes made of such polymers have proven effective as long as water is present during operation. At operating temperatures above 100 °C, sufficient hydration is no longer present, which is why sulfonated polymers generally exhibit significantly reduced conductivity for such applications, which prevents the use of the materials at such temperatures.

[0010] Phosphonated and phosphoric acid-doped polymers exhibit sufficient conductivity in the corresponding application, even at operating temperatures above 100°C. However, there is sometimes the problem that such doped ion-conducting polymers, such as polybenzimidazole, lose phosphoric acid at temperatures below 140°C or during frequent start-stop cycles, causing a decrease in ionic conductivity if no further doping takes place.

[0011] Polymers with ion-conductive groups often have a high glass transition temperature, meaning they are in a glassy state at typical application temperatures. Accordingly, the material tends to have brittle properties, so cracks can occur under certain stresses. For example, brittle cracks can form in membranes made of certain polymers, such as phosphonated terphenyl-based polymers, after the evaporation of water.

[0012] The object of the present invention is therefore to provide a polymer characterized by a favorable property profile and avoids the aforementioned disadvantages. Furthermore, a process for producing such a polymer is to be created.

[0013] This object is achieved by a block copolymer with at least two different polymer blocks, wherein one polymer block consists at least predominantly of a first, ion-conducting polymer, wherein the ion-conducting polymer has ion-conducting functional groups, and one polymer block consists at least predominantly of a second, mechanically flexible polymer, wherein the mechanically flexible polymer has a lower glass transition temperature than the ion-conducting polymer.

[0014] The invention is based on the idea of ​​combining an ion-conducting polymer and another polymer in a block copolymer. While the ion-conducting polymer has rather brittle material properties, the other, mechanically flexible polymer possesses greater ductility, particularly due to its lower glass transition temperature, so that mechanical stresses are absorbed by this polymer block. A further advantage of such a block copolymer is that, unlike an ion-conducting homopolymer, no stabilization with a polymer blend, for example, with polybenzimidazole (PBI), is required, so that no ion-conducting groups are lost through ionic cross-linking.Thus, the polymer block made of one ion-conducting polymer enables unproblematic ionic conductivity, while the other polymer block made of a second, mechanically flexible polymer ensures favorable mechanical properties. At the same time, the length of the individual polymer blocks can be adjusted virtually arbitrarily, so that the resulting block copolymer can be very precisely tailored in terms of its properties. The two polymer blocks are preferably covalently linked to one another.

[0015] The block copolymer can be a diblock copolymer. This means that each polymer chain has a section / block with the ion-conducting polymer and a section / block with the mechanically flexible polymer. In other words, the individual polymer chains have the structure AB. It is also possible for the block copolymer to be a triblock copolymer. This means that the polymer chains have a block on one polymer, then a block made of the other polymer, and another block made of the one polymer. One polymer and the other polymer can either be the mechanically flexible polymer or the ion-conducting polymer. In other words, such a triblock copolymer has the structure ABA or B-AB. It is also possible for the three polymer blocks of such a triblock copolymer to have different designs.Such a block copolymer can also have or consist of three different polymer blocks. In simple terms, the structure ABC can form. Alternatively, the block copolymer can also be a quadblock copolymer, in which the polymer chains alternately consist of a block on the mechanically flexible polymer, the ion-conducting polymer, the mechanically flexible polymer and the ion-conducting polymer, in other words they have an ABAB structure. A quadblock copolymer can also have two, three or four different polymer blocks. The polymer chains can also have more than four blocks. In general, these can then be referred to as multiblock copolymers. It has been found that triblock copolymers and quadblock copolymers orMultiblock copolymers can have more favorable properties than diblock copolymers due to the increased number of transitions between the different polymer blocks, in particular more favorable mechanical properties or lower swelling.

[0016] The mechanically flexible polymer preferably has higher ductility than the ion-conducting polymer. Ductility is a measure of deformability, particularly elongation at break. In other words, the mechanically flexible polymer can be deformed more than the ion-conducting polymer before it breaks. This applies in particular to temperatures below 120°C, preferably below 100°C, and most preferably at room temperature. This ensures a certain degree of deformability, allowing a membrane made from the block copolymer to be installed without the risk of brittle fracture. Especially at higher temperatures above 100°C and in the absence of moisture, mechanical flexibility can be ensured by the block made from the mechanically flexible polymer.

[0017] A polymer block can consist predominantly or essentially of a polymer if the proportion of the respective mechanically flexible or ion-conducting polymer is at least 50%, in particular at least 80%, preferably at least 90%, more preferably at least 95%, 98%, or 99%. The polymer blocks can also consist entirely of the respective mechanically flexible or ion-conducting polymer.

[0018] The object underlying the invention is further achieved by a process for producing such a block copolymer, which comprises the following steps:

[0019] - Providing a first starting monomer;

[0020] - Providing a second starting monomer;

[0021] - polymerization of the starting monomers to form a block copolymer having at least two different polymer blocks, wherein one polymer block consists at least substantially of a first (ion-conducting) polymer and wherein one polymer block consists at least substantially of a second, mechanically flexible polymer;

[0022] Functionalizing the first polymer so that it has an ionically conductive functional group. According to the invention, a block copolymer is thus produced by polymerizing two starting monomers. Subsequently, functionalization can take place so that the first polymer is provided with ionically conductive functional groups.

[0023] The invention further includes a process for producing a block copolymer comprising the following steps:

[0024] - Providing a first starting monomer;

[0025] - functionalizing the starting monomer so that it has an ion-conductive functional group;

[0026] - Providing a second starting monomer;

[0027] - Polymerization of the starting monomers to form a block copolymer having at least two different polymer blocks, wherein one polymer block consists at least substantially of a first, ion-conducting polymer, wherein the ion-conducting polymer has an ion-conducting functional group, and wherein one polymer block consists at least substantially of a second, mechanically flexible polymer.

[0028] This process is based on the idea of ​​functionalizing the starting monomer, ie providing it with appropriate functional groups that are ion-conductive after polymerization.

[0029] According to a preferred embodiment of the block copolymer according to the invention, the glass transition temperature of the mechanically flexible polymer is less than 80 °C, in particular less than 60 °C. Such a relatively low glass transition temperature is particularly suitable when the block copolymer is operated in conjunction with a low-temperature fuel cell / electrolyzer, particularly in the absence of humidification and / or in particular below 100 °C, preferably below 60 °C. This is the case, for example, with direct alcohol fuel cells.

[0030] The glass transition temperature of the mechanically flexible polymer can be less than 200 °C. Such a glass transition temperature results in the mechanically flexible polymer being mechanically flexible, i.e., not brittle, even at temperatures below 200 °C, making it suitable for use in high-temperature hydrogen fuel cells.

[0031] The glass transition temperature refers to a temperature at which the property profile of the corresponding polymer changes. Above the glass transition temperature, such a polymer is generally mechanically flexible, so that it can be easily deformed and the occurrence of brittle cracks can generally be avoided. If the glass transition temperature, also referred to as TG, is exceeded, the property profile changes. The polymer becomes hard and strong and loses ductility, so that brittle cracks can occur. The glass transition temperature can be measured using various methods. In dynamic mechanical analysis (DMA), a strong change in the elastic modulus or shear modulus is recorded. Another method for determining the glass transition temperature is differential scanning calorimetry (DSC), for example, according to DIN EN ISO 11357-2:2020-08.The measurement is carried out by determining the heat capacity as a function of temperature. Other measurement options are electrical relaxation spectroscopy or dilatometry. Preferably, the mechanically flexible polymer which forms a polymer block has a high hydrolysis resistance or is hydrolysis-resistant. In other words, it has a high chemical stability towards water. It is preferably stable even at extreme, i.e. very acidic or very basic, pH values ​​of up to pH 0 or 14. More preferably, it is resistant to alcohols, in particular to methanol and isopropanol. The mechanically flexible polymer can also be apolar or non-polar. In a further embodiment, it can contain no degradable or hydrolyzable functional groups.

[0032] Preferably, the mechanically flexible polymer is not an acrylate polymer. This embodiment is based on the consideration that acrylate polymers, i.e., polymers made of acrylate or comprising acrylate, have proven to be insufficiently stable or hydrolysis-resistant.

[0033] In a preferred embodiment, the mechanically flexible polymer contains no hydrolyzable groups. This means that such a mechanically flexible polymer exhibits high resistance to hydrolysis. Hydrolysis is a chemical reaction in which the bond of a molecule is broken by water. This is associated with far-reaching changes in the properties of the molecule / polymer.

[0034] In a specific embodiment, the mechanically flexible polymer can be a vinyl-based polymer, in particular polybutadiene, polyisoprene, polypropylene, polyvinylidene fluoride or polyvinyl fluoride, or a substituted styrenated polymer, in particular poly-4-n-octylstyrene.

[0035] Possible repeating units or starting monomers that can form the mechanically flexible polymer are shown in the figure below, where "n" represents an unbranched or branched alkyl chain, X a functional group that can be used for later functionalization or cross-linking.

[0036] Possible (starting) monomers which contain functional, ion-conducting groups or which can be converted into repeating units of an ion-conducting polymer by appropriate reactions after polymerization are shown in the figure below.

[0037]

[0038] 5 According to a preferred embodiment of the invention, the ion-conducting polymer can contain or consist of polyfluorostyrene, in particular polypentafluorostyrene and / or analogues thereof. Analogues are referred to as polyfluorostyrenes in which at least one fluorinated site is present on the aromatic compound. In a further embodiment, a fluorinated site, or a fluorine atom, on the aromatic compound can be replaced by substitution with an ion-conducting functional group. This can preferably be a nucleophilic substitution. The ion-conducting functional group can be a sulfonic acid and / or a phosphonic acid group and / or a precursor thereof. A precursor can be, for example, a sulfochloride group (-SO2Cl) or a superacidic sulfonimide group (SO2NHSO2CF3).

[0039] Examples of polystyrenes which have at least one fluorinated site on the aromatic per repeating unit are shown in the figure below.

[0040]

[0041] The ion-conductive functional groups of the ion-conducting polymer can comprise acidic functional groups, wherein the acidic functional groups include, in particular, sulfonic acid, sulfinic acid, phosphonic acid, or sulfonimide, or non-ionic forms thereof. The ion-conductive functional groups of the ion-conducting polymer can also comprise basic functional groups, wherein the basic functional groups include, in particular, primary, secondary, or tertiary amines, imidazoles, pyrazoles, benzimidazoles, pyridines, or quaternary functional groups, in particular ammonium and / or imidazolium and / or pyrazolium and / or pyridinium groups or cations, in particular tetraalkylphosphonium and / or tetraarylphosphonium and / or metallocene-based anion conductors.

[0042] It is possible that different functional groups are provided on the ion-conducting polymer, or that the ion-conducting polymer contains different functional ion-conducting groups. For example, the ion-conducting polymer can contain both acidic functional groups and basic functional groups.

[0043] The block of the ion-conducting polymer may have an ion-conducting functional group in each repeating unit or may have an ion-conducting functional group only in a part of the repeating units.

[0044] In a further embodiment, the block copolymer according to the invention can have at least two microphases, with one microphase consisting at least predominantly of the ion-conducting polymer and another microphase consisting at least predominantly of the mechanically flexible polymer. In other words, such a copolymer can therefore have microphase-separating properties, i.e., two different microphases are formed, with one microphase dominated by the ion-conducting polymer and the other microphase dominated by the mechanically flexible polymer. The microphases can also consist entirely of the mechanically flexible polymer or of the ion-conducting polymer.

[0045] In a further embodiment, the microphase made of the ion-conducting polymer can be continuous. This means that the microphase made of the ion-conducting polymer extends continuously through the entire block copolymer, so that a conductive connection exists between two outer surfaces of a membrane made from such a block copolymer. In other words, the microphase made of the mechanically flexible polymer is then embedded in such a continuous microphase. For example, corresponding inclusions can be distributed throughout the block copolymer.

[0046] Specifically, the microphase composed of the ion-conducting polymer can have a volume fraction of at least 35% or at least 50%, in particular at least 60%, preferably at least 70%. In such a case, a continuous microphase composed of the ion-conducting polymer can be formed. This creates continuous conductivity.

[0047] The microphase made of the ion-conducting polymer and / or the microphase made of the mechanically flexible polymer can be configured such that the distance between two opposing interfaces to another microphase is less than 200 nm, in particular less than 150 nm, preferably less than 100 nm, more preferably less than 75 nm, less than 50 nm, less than 35 nm, less than 25 nm, or less than 20 nm. In such a case, the two phases are in the nanometer range, which is why they are also referred to as nanophases.In other words, in this case the block copolymer forms a nanostructure, for example a bi-continuous nanostructure, wherein the individual regions, when viewed in a cross-sectional view, preferably have extensions in one direction of less than 200 nm, in particular less than 150 nm, preferably less than 100 nm, more preferably less than 75 nm, less than 50 nm, less than 35 nm, less than 25 nm or less than 20 nm. The distance between two opposing interfaces to another microphase is preferably at least 1 nm, in particular at least 2 nm, preferably at least 3 nm, more preferably 4 nm or 5 nm. Such a nanophase structure can be detected, for example, by high-angle annular dark-field imaging (HAADF) - scanning transmission electron microscopy (STEM).

[0048] If the block copolymer is a triblock copolymer or a quadblock copolymer or - generally speaking - a multiblock copolymer, the more frequent transitions between the individual polymer blocks and thus between the various micro- or nanophases compared to a diblock copolymer lead to a more intensive entanglement of the phases with each other, so that particularly favorable mechanical properties and / or low swelling of a membrane made from or consisting of the block copolymer result.

[0049] Preferably, the block copolymer does not have a lamellar structure. Rather, the microphases or nanophases can have a gyroidal structure. This simultaneously results in isotropic material properties, allowing for direction-independent ion transport or direction-independent conductivity.

[0050] The ratio of the number of repeating units of the block made of the ion-conducting polymer to the number of repeating units of the block made of the mechanically flexible polymer can be at least 10:90, in particular at least 25:75, preferably at least 50:50, and / or at most 90:10, in particular at most 75:25. In other words, it is possible to adjust the length ratios in the block copolymer depending on the respective requirements. If higher demands are placed on the mechanical flexibility of the block copolymer or a membrane made therefrom, the length of the block made of the mechanically flexible polymer can be increased and the length of the block made of the ion-conducting polymer can be reduced proportionally.If, however, conductivity is desired to be as high as possible and mechanical properties are relatively low, the length of the block made of the ion-conducting polymer can be increased and the length of the block made of the mechanically flexible polymer reduced. If two different microphases form, the volume ratio of the two microphases to each other also changes accordingly.

[0051] In a further embodiment, polymer blocks made of the ion-conducting polymer and / or polymer blocks made of the mechanically flexible polymer can be covalently and / or ionically cross-linked with each other or with each other. Such ionic or covalent cross-linking can significantly reduce the diffusion of the fuel and the oxidation product to the cathode side. In some cases, even complete diffusion can be prevented. Furthermore, higher power densities can sometimes be achieved in this way.

[0052] The ion-conducting polymer can contain or be coupled to partially or perfluoroaromatic compounds. Accordingly, the blocks of the ion-conducting polymer can be covalently cross-linked via their partially or perfluoroaromatic compounds.

[0053] These designs are based on the idea of ​​creating additional covalent crosslinking through a nucleophilic substitution reaction on the chain backbone using a difunctional crosslinker. Such additional covalent crosslinking requires the presence of partially or perfluoroaromatic compounds in which individual fluorine atoms can be nucleophilically substituted by a corresponding functional group. It has been shown that membranes consisting of such covalently crosslinked block copolymers are significantly more chemically stable, particularly toward secondary alcohols and toward compounds containing at least one secondary alcohol group. Furthermore, a significantly increased resistance to secondary alcohols and the reaction products in the fuel cell reaction, particularly ketones and water, has also been demonstrated.

[0054] The partially or perfluoroaromatic compound can be present in the main or side chain of the respective polymer. Examples of partially or perfluoroaromatic building blocks of ionomers / polymers that are suitable for covalent cross-linking are shown in the following figures. Although the figure refers to polymer main chains and side chains, the corresponding structures apply equally to both polymer blocks.

[0055] Specifically, the partially or perfluoroaromatic compound can contain a partially or perfluorinated phenyl unit or a partially or perfluorinated biphenyl unit. The covalent crosslinking can have the structure S-R-S, where each sulfur atom substitutes for a fluorine atom of a partially or perfluoroaromatic compound. R can represent a linear or branched saturated or unsaturated carbon chain, in particular in the form (CFbjx with x = 2 to 20, or a heteroaromatic chain, in particular poly- or oligoethylene glycol, or any aromatic, in particular 1,4-dimercaptobenzene, biphenyl-4,4'-dithiol or toluene-3,4-dithiol. In other words, the covalent crosslinking can be produced by a dithiol, so that at each end of the covalent crosslinking a sulfur atom takes the place of a fluorine atom of a partially or perfluoroaromatic compound.In principle, crosslinkers with more than two thiol groups are also conceivable for crosslinking, for example trimethylolpropane tris(3-mercaptopropionate).

[0056] The ion-conducting polymer can contain both acidic and basic functional groups, with ionic crosslinks being formed between the acidic and basic functional groups. Alternatively, the block copolymer according to the invention can be mixed with another basic polymer, such as polybenzimidazole, to form an acid-base blend. The resulting acid-base blend contains opposing functional groups that can be ionically crosslinked. One such possible crosslinking is shown in detail in the figure below.

[0057]

[0058] Covalent cross-linking of the polymer block made of the second, mechanically flexible polymer is also possible. For example, the unsaturated double bonds in polyisoprene or polybutadiene can be vulcanized, or a double bond within an aliphatic side chain can be used. Cross-linking can achieve additional elastomeric, reversible properties beyond mechanically flexible behavior. This explicitly ensures that the block copolymer and the materials consisting of this block copolymer return to their original shape after mechanical stress. Any known processes can be used for cross-linking, such as vulcanization. Possible examples of covalent cross-linking of the mechanically flexible polymer are shown in the figure below.

[0059]

[0060] The process according to the invention can be characterized in that cationic or anionic polymer initiators are used for the polymerization, and / or that the polymerization comprises an atom transfer (atom transfer radical polymerization - ATRP), a nitroxide mediation, and / or a reversible addition / fragmentation (reversible addition fragmentation change-transfer polymerization - RAFT). In a further embodiment, the polymer blocks made of the ion-conducting polymer can be covalently and / or ionically cross-linked with one another or with each other. Furthermore, the polymer blocks made of the mechanically flexible polymer can be covalently and / or ionically cross-linked with one another or with each other. The properties of the block copolymer can be further optimized through such cross-linking.

[0061] Preferably, two separate microphases are formed during polymerization, with one microphase consisting at least predominantly of the ion-conducting polymer and another microphase consisting at least predominantly of the mechanically flexible polymer.

[0062] In a further embodiment of the process according to the invention, a further functional modification can be carried out, in particular of the microphase made of the mechanically flexible polymer. In particular, as part of the further functional modification, further functional groups, in particular further ion-conductive functional groups, can be introduced into the mechanically flexible polymer. This can result in a further ion-conducting microphase. Specifically, functional groups which arise during polymerization, in particular double bonds in side chains of a polyisoprene / polybutadiene block, can be introduced by 1,2-addition, or by using corresponding apolar monomers which in particular comprise or consist of halides or unsaturated groups. These can be further functionalized.

[0063] By creating an additional microphase from a second ion-conducting polymer, which possesses its own conduction mechanism, the properties can be further optimized. In other words, a combination material can be created that exhibits specific microphases for the transport of protons / cations in both humidified and dry conditions. Humidified conditions, for example, occur at temperatures below 100°C at ambient pressure, whereas dry conditions exhibit temperatures above 100°C at ambient pressure.

[0064] Examples of further functional modifications are shown in the figure below.

[0065] Cross-linking

[0066] The further functional modification may comprise a partial or complete thiolation, in particular in an electrolyte solution and / or in a salt solution. Furthermore, the further functional modification may comprise an oxidation of the

[0067] thiol group to a sulfonic acid group.

[0068] The object underlying the invention is further achieved by a membrane comprising or consisting of a block copolymer as described above. The thickness of the membrane is preferably less than 100 pm, in particular less than 75 pm, preferably less than 50 pm. This embodiment is based on the consideration that membranes made of such a block copolymer have favorable properties, so that they can be made significantly thinner than, for example, a membrane made of Nafion or Nafion XL. The membrane preferably has a conductivity of at least 22 mS / cm, in particular of at least 25 mS / cm, preferably of at least 30 mS / cm, particularly preferably of at least 32 mS / cm.

[0069] The invention further relates to the use of such a membrane as a proton exchange membrane in a direct alcohol fuel cell, in particular in a direct methanol fuel cell or in a direct isopropanol fuel cell, or in a hydrogen fuel cell or in a hydrogen electrolyzer, to reduce fuel and oxidation product diffusion across the membrane and with increased resistance to solvents. Application in redox flow batteries is also conceivable.

[0070] Furthermore, the invention provides a method for producing a membrane, comprising the following steps:

[0071] - Providing a block copolymer, in particular as described above and / or produced by a process as described above;

[0072] - partial or complete thiolation of the polymer, in particular by nucleophilic substitution of a fluorine atom, preferably of a polyfluorostyrene, particularly preferably of a perfluorophenyl unit or a perfluorobiphenyl unit or a perfluoroterphenyl unit, which is arranged in particular in a side chain of the polymer;

[0073] - forming a membrane from the thiolated polymer, in particular forming a cross-link;

[0074] - Conversion of the thiol groups into ion-conducting sulfonic acid groups. This process is based on the consideration that partial or complete thiolation of a block copolymer, particularly on a perfluoroaromatic compound, leads to such polymers tending to crosslink. Such thiolated polymers are then no longer soluble in various solvents. The crosslinking that occurs during molding, for example, casting or doctor blade coating of a membrane, can be used to produce solvent-resistant membranes. An alcohol solution, particularly an ethanol solution, can be used as an auxiliary agent to mold the membrane. On the molded membrane, the thiol groups formed during thiolation can then be converted into ion-conducting sulfonic acid groups under appropriate oxidative conditions.This results in increased solvent resistance and, at the same time, favorable ion-conducting properties. Partial phosphonation can occur before the polymer is thiolated. In this case, partial phosphonation is carried out sequentially, followed by thiolation. Preferably, at least 30%, in particular at least 40%, preferably at least 50%, and / or at most 80%, in particular at most 70%, preferably at most 65%, of the repeating units of the ion-conducting polymer are phosphonated. In particular, the repeating units of the mechanically flexible polymer are sulfonated.

[0075] It is also possible that only some of the repeating units of the ion-conducting polymer are sulfonated.

[0076] Preferably, the thiolation of the polymer takes place in an electrolyte solution and / or in a salt solution.

[0077] For further details of the invention, reference is made to the dependent claims and to the description of the embodiments with reference to the drawings. The embodiments described with reference to the figures represent preferred block copolymers according to the present invention. The reaction schemes show preferred embodiments of the processes according to the invention, with the parameters mentioned (auxiliaries, temperature, or the like) showing optional embodiments of the respective processes. In the drawings:

[0078] Figure 1 shows the mesostructure of a POS-b-sPPFS block copolymer according to the invention;

[0079] Figure 2 Structure of the block copolymer from Figure 1 in HAADF-STEM images;

[0080] Figure 3 shows a reaction scheme for sequential partial phosphonation and complete thiolation with subsequent oxidation and protonation;

[0081] Figure 4 shows a reaction scheme for the preparation of POS-PPFS block copolymers which are phosphonated and cross-linked in the PPFS nanophase and sulfonated in the POS phase;

[0082] Figure 5 shows the mesostructure of the polymer from Figure 4;

[0083] Figure 6 the synthesis of polypentafluorostyrene-block-polyisoprene PPFS-b-PI;

[0084] Figure ? the reaction scheme of the functionalization of PPFS-b-PI by means of complete phosphonation and partial thiolation; Figure 8 a 19 F-NMR spectrum of PPFS-b-PI and the crude product after a Michaelis-Arbuzow reaction;

[0085] Figure 9 shows a reaction scheme for the functionalization of PPFS-b-PI by partial thiolation;

[0086] Figure 10 a 19 F-NMR spectrum of PPFS-b-PI and the crude product after thiolation with sodium hydrogen sulfide;

[0087] Figure 11 shows the reaction scheme of a synthesis of polyoctystyrene-block-polypentafluorstyrene POS-b-PPFS;

[0088] Figure 12 shows a reaction scheme of a functionalization of POS-b-PPFS by partial phosphonation;

[0089] Figure 13 a 19 F-NMR spectrum of POS-b-PPFS and the crude product after the Michaelis-Arbuzow reaction.

[0090] Figure 14 shows a scheme for the preparation of a membrane from a block copolymer with a crosslink and ion-conducting sulfonic acid groups.

[0091] Figure 1 initially shows a simulation of the microphase of a block copolymer according to the invention, specifically polyoctylstyrene-block-sulfonated polypentafluorostyrene (POS-b-sPPFS), depending on the respective block lengths used, i.e., the number of repeating units in the two blocks. Polyoctylstyrene forms a mechanically flexible polymer, whereas sulfonated polypentafluorostyrene forms an ion-conducting polymer. To synthesize the block copolymers, the various blocks were prepared by RAFT polymerization. The polymer block made of polypentafluorostyrene was subsequently modified with an acidic functional group as an example.

[0092] Using the Biovia Materials Studios software from Dassault Systemes, the mesostructure of the block copolymer (POS-b-sPPFS) was calculated for various block lengths based on the molecular volume of a repeating unit and the van Krevelen solubility parameter. Figure 1 visualizes the polymer structure and the corresponding microphase for a given block ratio. The ratio of the block lengths is reflected in the formation of continuous polar, sPPFS phases, which are required for high ionic conductivity. In general, the simulation of the microphases provides guidance for the subsequent synthetic production of block copolymers according to the invention.

[0093] The image above in Figure 1 shows the mesostructure of a block copolymer in which the polymer block of the mechanically flexible polymer contains n=200 repeating units, while the polymer block of the ion-conducting polymer contains m=50 repeating units. The mesostructure shows that the microphase of the mechanically flexible polymer (dark gray) dominates over the microphase of the ion-conducting polymer (light gray).

[0094] The middle figure shows the mesostructure of a block copolymer in which both polymer blocks each contain 50 repeating units. It can be seen that the distribution between the individual microphases is relatively uniform. The lower figure shows the mesostructure of a block copolymer in which the polymer block made of ion-conducting polymer contains 200 repeating units, while the polymer block made of mechanically flexible polymer contains 50 repeating units. It is clearly evident that the microphase made of the ion-conducting polymer dominates here.

[0095] Figure 2 shows the structure of the synthesized polymer and HAADF-STEM images at various scales. The bright areas correspond to the PWN-60 block, while the dark areas are caused by the microphase and nanophase separation of the octylstyrene block.

[0096] Figure 3 shows a reaction scheme for a further functional modification of the block copolymer. In the first step of a functional modification, a partial phosphonation of the polypentafluorostyrene block takes place. Specifically, the partial phosphonation is carried out using the Michaelis-Arbuzov reaction known from the literature. The block copolymer POS-b-PPFS (pentafluorostyrene units: 1 eq) was dissolved in DMAc and the phosphonating reagent tris(trimethylsilyl)phosphite (TSP, 0.7 eq) and stirred at 170 °C for 18 h. After cooling to room temperature, the crude product was precipitated in acetonitrile and filtered off. To remove the silyl ester, the filtrate was hydrolyzed in water at 100 °C for 18 h. The polymer was then dissolved in DMAc. Sodium hydrogen sulfide hydrate (5 eq) was dissolved in DMAc with stirring at 50 °C. Both mixtures were degassed with argon for several minutes to remove any remaining oxygen.The PWN60-b-POS solution was then added dropwise to the hydrogen sulfide solution at 50°C over 15 minutes under argon countercurrent and stirred for 20 minutes at 50°C.

[0097] The reaction solution of the partially thiolated block copolymer was purified by dialysis with water and ethanol to remove excess NaSH. The concentration of the polymer solution was determined gravimetrically. N-methylpyrolidone (NMP) was added to the mixture, and excess water and ethanol were removed under reduced pressure to produce a 10 wt% solution of the polymer. A polymer film was drawn from this solution using a doctor blade, and the membrane was pre-dried at 80 °C for 1.5 h, and the remaining solvent was evaporated at 110 °C for 18 h. The membrane was detached from the glass substrate in a water bath and placed in a mixture of aqueous H2O2 (30 wt%, 12 mL), formic acid (22 mL), and H2SO4 (95 wt%, 1.1 mL) at room temperature for 18 h. To ensure the most complete oxidation possible, the membrane and the reaction mixture were then heated to 60 °C for 6 h.The membrane was then removed and washed with deionized water until a neutral pH value was reached. The membrane of the block co-ionomer contains both phosphonic and sulfonic acid groups in the hydrophilic, proton-conductive nanophase. While proton conductivity is primarily ensured by the sulfonic acid groups upon sufficient wetting with water, conductivity is still present via the phosphonic acid groups in the dry state. The sulfonic acid groups, which are more acidic than phosphonic acid groups, can protonate the phosphonic acid groups, thereby increasing their proton conductivity.

[0098] An alternative embodiment of a further functional modification of the block copolymer is shown in Figure 4.

[0099] The block copolymer PPFS-Block-POS is first partially phosphonated.

[0100] After partial phosphonation, the block copolymer is dissolved in a dipolar aprotic solvent such as DMSO, and then a dithiol, for example, hexane-1,6-dithiol, is added to the solution along with the base DBU. The solvent is evaporated, and during evaporation, the dithiol crosslinks with the remaining para-fluorine positions of the unphosphonated PPFS units. Crosslinking fixes the nanophase-separated structure of the block copolymer. A covalently crosslinked membrane of the phosphonated block copolymer is obtained. The covalently crosslinked membrane is then immersed in concentrated sulfuric acid (96 wt%). This sulfonates the octylstyrene blocks. A covalently crosslinked membrane containing both continuous sulfonated and continuous phosphonated nanophases is obtained.

[0101] The expected nanophase structure is shown in Figure 5. The simulation shown is based on the previously proven nanophase structure. Cross-linking stabilizes / fixes the nanophase structure, enabling subsequent sulfonation of the previously nonpolar octylstyrene block while maintaining the nanostructure. If concentrated sulfuric acid or oleum is used for the sulfonation of the octylstyrene block, the thiol bridges of the cross-linking sites can be at least partially oxidized to sulfoxide or even sulfone bridges due to the oxidizing properties of concentrated sulfuric acid or oleum, which further chemically stabilizes the cross-linking bridges. Such a phosphonated and sulfonated membrane is presumably applicable as a proton conductor over a wider temperature range than sulfonated polymer membranes.At temperatures below 100°C, the sulfonated and phosphonated nanophases conduct, while at T>100°C, the phosphonated nanophase conducts protons. This is because phosphonic acids, unlike sulfonic acids, exhibit intrinsic conductivity, which becomes important when the lack of water at T>100°C prevents proton conduction in the sulfonated nanophase. In the inner interface between sulfonated and phosphonated nanophases, the sulfonic acid groups, which are more acidic than phosphonic acid groups, can also protonate the phosphonic acid groups, which contributes to a further increase in the proton conductivity of the phosphonic acid groups. Example 1.

[0102] Synthesis of polypentafluorostyrene-block-polyisoprene (PPFS-b-PI)

[0103] Pentafluorostyrene (here, an ion-conducting polymer) (50 eq), DDMAT (1 eq), and AIBN (0.2 eq) were dissolved in DMF, and the reaction mixture was degassed by three freeze-vacuum-thawing cycles to remove residual oxygen. The reaction mixture was stirred at 80 °C for 22 hours. The yellow solution was cooled to room temperature and precipitated in methanol. The yellow polymer was filtered off and dried at 60 °C overnight. The dried polymer was dissolved in tert-butyl methyl ether, and the precipitation and drying procedure was repeated. The yellow powder (macro chain transfer reagent, 1 eq) was dispersed in DMF, and isoprene (1000 eq) and dicumyl peroxide (0.2 eq) were added to the reaction mixture and degassed by two freeze-vacuum-thaw cycles. The mixture was transferred to a steel autoclave and filled with DMF (200 mL). The steel autoclave was sealed, and the atmosphere was rendered inert.The reaction mixture was stirred at 115 °C for three days. After cooling to room temperature, the steel autoclave was opened, and the precipitated block copolymer was separated from the DMF fraction. The block copolymer was dissolved in THF, concentrated, and precipitated in isopropanol. The fine, colorless solid was centrifuged, dried in air at room temperature for three days, and a slightly greenish, mechanically flexible block copolymer was obtained.

[0104] Using gel permeation chromatography (GPC) and end group analysis using 1 The molecular weight of the polypentafluorostyrene (PPFS) block and the PPFS-b-PI diblock were determined by H-NMR. These are listed in the table below. The results confirm the successful synthesis of PPFS-b-PI.

[0105]

[0106] The polymerization of the second block was also successfully carried out in a microwave reactor, using THF as the solvent instead of DMF. By varying the reaction time, the length of the polyisoprene block (here, a mechanically flexible polymer) could be successfully controlled.

[0107] Functionalization of PPFS-b-PI by complete phosphonation and partial thiolation

[0108] An example of a further functional modification of the block copolymer thus obtained is shown schematically in Figure 7.

[0109] The phosphonation of the PPFS block was carried out using the Michaelis-Arbuzov reaction known from the literature. The block copolymer PPFS-b-PI (1 eq) was dissolved in the phosphonating reagent tris(trimethylsilyl)phosphite (TSP, 10 eq) and stirred at 170 °C for 18 h. The crude product was precipitated in acetonitrile after cooling to room temperature and filtered off. To remove the silyl ester, the filtrate was hydrolyzed for 18 h at 100 °C in water and then at 50 °C in aqueous HCl (1 M). Figure 8 compares the 19 F-NMR of the starting material PPFS-b-PI and the phosphonated crude product confirms the almost complete phosphonation of the PPFS block.

[0110] Another example of functional modification, namely partial thiolation, is shown in Figure 9. Thiolation of the PPFS block forms the precursor to sulfonation and the formation of a sulfonimide. The block copolymer PPFS-b-PI (1.2 g, 3.1 mmol pentafluorostyrene units, 1 eq) was dissolved in THF (15 mL). Sodium hydrogen sulfide hydrate (0.9 g; 3.7 mmol, 1.2 eq) was dissolved in THF (15 mL) and water (2 mL) with stirring at 50 °C. Both mixtures were degassed by three freeze-vacuum-thaw cycles each to remove residual oxygen. The PPFS-b-PI solution was then added dropwise to the hydrogen sulfide solution at 50 °C over 30 minutes under argon countercurrent. After addition of degassed DMAc (15 mL) under argon, a dark green color of the reaction mixture was observed and stirred for 1 h at 50°C. After stirring for a further 18 h at room temperature, the crude product was precipitated in acetone.The crude product was filtered off and washed with saturated NaCl solution and cold water. After drying in air for three days, a colorless wax was obtained. Figure 10 compares the 19 F-NMRs of the starting product PPFS-b-PI and the 88% thiolated crude product.

[0111] Example 2

[0112] Synthesis of polyoctystyrene block polypentafluorostyrene (POS-b-PPFS)

[0113] Figure 11 shows an example of the synthesis of a block copolymer according to the invention (POS-b-PPFS).

[0114] DDMAT (1 eq) and AIBN (0.2 eq) were dissolved in 4-n-octylstyrene (75 eq), and the reaction mixture was degassed by three freeze-vacuum-thaw cycles to remove residual oxygen. The reaction mixture was stirred at 85 °C for 44 h. The viscous, yellowish crude product was taken up in ethyl acetate and precipitated in isopropanol. The viscous oil was separated, and remaining volatile solvents / monomers were removed by heating under high vacuum. The polyoctylstyrene (POS, macro-chain transfer reagent, 1 eq) was dissolved in pentafluorostyrene (75 eq) and added to AIBN (0.2 eq). The reaction mixture was heated at 85 °C for 66 h, yielding a solid polymer block. This was dissolved in THF, and the resulting solution was precipitated in isopropanol. The polymer was filtered off and dried overnight at 60 °C in a vacuum oven to obtain colorless POS-b-PPFS.

[0115] Using gel permeation chromatography (GPC) and end group analysis using 1 The molecular weight of the POS block and the POS-b-PPFS diblock was determined by H NMR spectroscopy. These are listed in the table below. The results confirm the successful synthesis of POS-b-PPFS.

[0116] Functionalization of POS-b-PPFS by partial phosphonation

[0117] An exemplary functional modification of this block copolymer is shown in Figure 12.

[0118] Partial phosphonation of the PPFS block was carried out using the Michaelis-Arbuzov reaction known from the literature. The block copolymer POS-b-PPFS (pentafluorostyrene units: 1 eq) was dissolved in DMAc and the phosphonating reagent tris(trimethylsilyl)phosphite (TSP, 0.7 eq) and stirred at 170 °C for 18 h. The crude product was cooled to room temperature and precipitated in acetonitrile and filtered off. To remove the silyl ester, the filtrate was hydrolyzed for 18 h at 100 °C in water and then at 50 °C in aqueous HCl (1 M). Figure 13 compares the 19 F-NMR of the starting product POS-b-PPFS and the phosphonated crude product confirms the 60% phosphonation of the PPFS block.

[0119] In an adapted conductivity measurement, which differs from the one described above in that the test membranes were previously immersed in water, a membrane based on the chemical structure shown in Figure 2 was tested. Compared to a PWN75 / PVDF blend membrane, which has a conductivity of 21 ± 1 mS / cm, the nanophase-separated membrane according to the invention showed an approximately 50% higher conductivity of 33 ± 2 mS / cm. Both membranes have a similar proton exchange capacity of approximately 1.25 and 1.22 mmol / g, respectively, and are therefore directly comparable. The water absorption of the two polymer membranes is also listed in Table 1. In general, the advantage of nanophase separation is also evident here, since the water absorption of the comparison membrane is approximately 60% higher than that of the block copolymer membrane.

[0120] Example 3

[0121] Preparation of a sulfonated block copolymer by thiolation of a PPFS-b-POS block copolymer with subsequent oxidation of the thiol groups to sulfonic acid groups. Thiolation of the PPFS block forms the precursor to sulfonation and the formation of a sulfonimide. The PPFS-b-POS block copolymer (2 g, 4.2 mmol pentafluorostyrene units, 1 eq) was dissolved in THF (10 mL). Sodium hydrogen sulfide hydrate (1.7 g; 20.9 mmol, 5 eq) was dissolved in DMAc (15 mL) with stirring at 50 °C. Both mixtures were degassed with argon for several minutes to remove any remaining oxygen. The PPFS-b-POS solution was then added dropwise to the hydrogen sulfide solution at 50°C over 15 minutes under argon countercurrent, and stirred for 20 minutes at 50°C. After a further 18 h of stirring at room temperature, a degree of thiolation of 91% (partial thiolation) was determined by 19F NMR.By reheating the reaction solution to 55 °C for 24 h, the degree of thiolation can be increased to 100 % (full thiolation).

[0122] The reaction solution of the partially thiolated block copolymer of the invention was purified by dialysis with water and ethanol to remove excess NaSH. The concentration of the polymer solution was determined gravimetrically. N-methylpyrolidone (NMP) was added to the mixture, and excess water and ethanol were removed under reduced pressure to produce a 10 wt% solution of the polymer. A polymer film was drawn from this solution using a doctor blade, and the membrane was pre-dried at 80 °C for 1.5 h, and the remaining solvent was evaporated at 110 °C for 18 h. The membrane was detached from the glass substrate in a water bath and immersed in a mixture of aqueous H2O2 (30 wt%, 12 mL), formic acid (22 mL), and H2SO4 (95 wt%, 1.1 mL) at room temperature for 18 h. To ensure the most complete oxidation possible, the membrane and the reaction mixture were then heated to 60 °C for 6 h.The membrane was then removed and washed with deionized water until a neutral pH value was reached. Sulfonation by oxidation of the thio group to the sulfonic acid group was confirmed by infrared spectroscopy. The conductivity at room temperature was determined according to an established literature procedure (Kerres, J.; Ullrich, A.; Haering, T.; Baldauf, M.; Gebhardt, U.; Preidel, W. Preparation, characterization, and fuel cell application of new acid-base blend membranes).

[0123] Journal of New Materials for Electrochemical Systems 2000, 3 (3), 229-239) 74.1 ± 4.4 mS / cm, while a commercial Nafion membrane (Nafion 211) has a conductivity of 69.7 ± 4.1 mS / cm. The water uptake in water after about 24 hours is 66% at 25 °C, 84% at 60 °C, and 92% at 85 °C. After three days in a water: acetone: isopropanol mixture (v:v:v 1:1:1) at 85 °C, a residual mass of 90 wt% of the initial membrane weight was determined. Due to incomplete thiolation / sulfonation and possible cross-linking reactions, the proton exchange capacity is 1.25 mmol(H + ) / g(polymer) slightly below the expected value of the chemical structure in Figure 5 (1.56 mmol(H + ) / g(polymer)), but still above that of a commercial Nafion membrane (about 0.91 mmol(H + ) / g(Nafion)).

Claims

CLAIMS 1. Block copolymer with at least two different polymer blocks, wherein one polymer block consists at least predominantly of a first, ion-conducting polymer, wherein the ion-conducting polymer has ion-conducting functional groups, and one polymer block consists at least predominantly of a second, mechanically flexible polymer, wherein the mechanically flexible polymer has a lower glass transition temperature than the ion-conducting polymer.

2. Block copolymer according to claim 1, characterized in that it is a diblock, a triblock or a quadblock copolymer.

3. Block copolymer according to claim 1 or 2, characterized in that the glass transition temperature of the mechanically flexible polymer is less than 80°C, in particular less than 60°C.

4. Block copolymer according to claim 1 or 2, characterized in that the glass transition temperature of the mechanically flexible polymer is less than 200°C.

5. Block copolymer according to one of the preceding claims, characterized in that the mechanically flexible polymer is not an acrylate polymer.

6. Block copolymer according to one of the preceding claims, characterized in that the mechanically flexible polymer does not contain any hydrolyzable functional groups.

7. Block copolymer according to one of the preceding claims, characterized in that the mechanically flexible polymer has apolar or nonpolar repeating units.

8. Block copolymer according to one of the preceding claims, characterized in that the mechanically flexible polymer is a vinyl-based polymer, in particular polybutadiene, polyisoprene, polypropylene, polyvinylidene fluoride or polyvinyl fluoride, or a substituted styrenated polymer, in particular poly-4-n-octylstyrene.

9. Block copolymer according to one of the preceding claims, characterized in that the ion-conducting polymer contains or consists of polypentafluorostyrene or analogues thereof.

10. Block copolymer according to one of the preceding claims, characterized in that ion-conductive functional groups of the ion-conductive polymer comprise acidic functional groups, wherein the acidic functional groups include in particular sulfonic acid, sulfinic acid, phosphonic acid or sulfonimide or non-ionic forms thereof.

11. Block copolymer according to one of the preceding claims, characterized in that the ion-conductive functional groups of the ion-conducting polymer comprise basic functional groups, wherein the basic functional groups comprise in particular primary, secondary or tertiary amines, imidazoles, pyrazoles, benzimidazoles, pyridines, or quaternary functional groups, in particular ammonium and / or imidazolium and / or pyrazolium and / or pyridinium groups, or cations, in particular tetraalkylphosphonium and / or tetraarylphosphonium and / or metallocene-based anion conductors.

12. Block copolymer according to one of the preceding claims, characterized in that the block of the ion-conducting polymer has an ion-conducting functional group in each repeating unit or has an ion-conducting functional group only in some of the repeating units.

13. Block copolymer according to one of the preceding claims, characterized in that it has at least two microphases, wherein one microphase consists at least predominantly of the ion-conducting polymer and another microphase consists at least predominantly of the mechanically flexible polymer.

14. Block copolymer according to claim 13, characterized in that the microphase is formed continuously from the ion-conducting polymer.

15. Block copolymer according to claim 13 or 14, characterized in that the microphase of the ion-conducting polymer has a volume fraction of at least 50%, in particular of at least 60%, preferably of at least 70%.

16. Block copolymer according to one of claims 13 to 15, characterized in that the microphase made of the ion-conducting polymer and / or the microphase made of the mechanically flexible polymer is / are designed such that the distance between two opposing interfaces to another microphase is less than 200 nm, in particular less than 150 nm, preferably less than 100 nm, more preferably less than 75 nm, less than 50 nm, less than 35 nm, less than 25 nm or less than 20 nm.

17. Block copolymer according to one of the preceding claims, characterized in that the ratio of the number of repeating units of the block made of the ion-conducting polymer to the number of repeating units of the block made of the mechanically flexible polymer is at least 10:90, in particular at least 25:75, preferably at least 50:50, and / or at most 90:10, in particular at most 75:

25.

18. Block copolymer according to one of the preceding claims, characterized in that polymer blocks made of the ion-conducting polymer and / or polymer blocks made of the mechanically flexible polymer are each covalently and / or ionically cross-linked with one another or with one another.

19. Block copolymer according to claim 18, characterized in that the ion-conducting polymer contains partially or perfluoroaromatic compounds or is coupled to it, and in that the blocks of the ion-conducting polymer are covalently cross-linked with one another via their partially or perfluoroaromatic compounds, wherein the partially or perfluoroaromatic compounds are contained in particular in the main chain or a side chain of the respective polymer, and / or wherein, in particular, the partially or perfluoroaromatic compounds contain a partially fluorinated or perfluorinated phenyl unit or a partially fluorinated or perfluorinated biphenyl unit.

20. Block copolymer according to claim 19, characterized in that the covalent crosslinks have the structure SRS, where the sulfur atoms substitute a fluorine atom of a partially or perfluoroaromatic compound and R stands for a linear or branched saturated or unsaturated carbon chain, in particular in the form (CH2)x with X = 2 - 20 or for a heteroaromatic chain, in particular poly- or oligoethylene glycol, or for any aromatic, in particular 1,4-dimercaptobenzene, biphenyl-4,4'-dithiol or toluene-3,4-dithiol.

21. Block copolymer according to one of claims 18 to 20, characterized in that the ion-conducting polymer contains both acidic and basic functional groups and that ionic crosslinks are formed between the acidic and basic functional groups.

22. Block copolymer according to one of claims 18 to 21, characterized in that covalent crosslinks are formed in the mechanically flexible polymer.

23. A membrane comprising or consisting of a block copolymer according to any one of the preceding claims.

24. Membrane according to claim 23, characterized in that the membrane has a conductivity of at least 22 mS / cm, in particular of at least 25 mS / cm, preferably of at least 30 mS / cm, particularly preferably of at least 32 mS / cm.

25. Use of a membrane according to claim 23 or 24 as a proton exchange membrane in a direct alcohol fuel cell, in particular in a direct methanol fuel cell or in a direct isopropanol fuel cell, or in a hydrogen fuel cell or in a hydrogen electrolyzer or in a redox flow battery, in particular for reducing fuel and oxidation product diffusion across the membrane and with increased resistance to solvents.

26. A process for producing a block copolymer according to any one of claims 1 to 22, comprising the following steps: Providing a first starting monomer; Providing a second starting monomer; Polymerization of the starting monomers to form a block copolymer having at least two different polymer blocks, wherein one polymer block consists at least substantially of a first polymer, and wherein one polymer block consists at least substantially of a second, mechanically flexible polymer; Functionalizing the first polymer so that it has an ion-conductive functional group.

27. A process for producing a block copolymer according to any one of claims 1 to 22, comprising the following steps: Providing a first starting monomer; Functionalizing the starting monomer so that it has an ion-conductive functional group; Providing a second starting monomer; Polymerization of the starting monomers to form a block copolymer having at least two different polymer blocks, wherein one polymer block consists at least substantially of a first, ion-conducting polymer, wherein the ion-conducting polymer has an ion-conducting functional group, and wherein one polymer block consists at least substantially of a second, mechanically flexible polymer.

28. A process according to claim 26 or 27, characterized in that the first starting monomer is pentafluorostyrene or an analogue thereof.

29. The process according to any one of claims 26 to 28, characterized in that cationic or anionic polymer initiators are used for the polymerization, and / or that the polymerization comprises an atom transfer (atom transfer radical polymerization - ATRP), a nitroxide mediation and / or a reversible addition / fragmentation (reversible addition fragmentation chain transfer polymerization - RAFT).

30. Process according to one of claims 26 to 29, characterized in that the polymerization is a (controlled) radical polymerization.

31. Method according to one of claims 26 to 30, characterized in that the polymer blocks made of the ion-conducting polymer are covalently and / or ionically cross-linked with one another.

32. Method according to one of claims 26 to 31, characterized in that the polymer blocks made of the mechanically flexible polymer are covalently and / or ionically cross-linked with one another or with each other, wherein, in particular, vulcanization takes place.

33. Process according to one of claims 26 to 32, characterized in that two separate microphases are formed during the polymerization, wherein one microphase consists at least predominantly of the ion-conducting polymer and another microphase consists at least predominantly of the mechanically flexible polymer.

34. Method according to one of claims 26 to 33, characterized in that a further functional modification, in particular of the microphase made of the mechanically flexible polymer, is carried out.

35. The method according to claim 34, characterized in that during the further functional modification, further functional groups, in particular ion-conductive functional groups, are introduced into the mechanically flexible polymer, so that a further ion-conductive microphase is formed.

36. The method according to claim 34 or 35, characterized in that the further functional modification comprises a partial or complete thiolation with the formation of thiol groups, in particular in an electrolyte solution.

37. The method according to claim 36, characterized in that the further functional modification further comprises an oxidation of at least part of the thiol group to a sulfonic acid group.

38. A method for producing a membrane, in particular a membrane according to claim 23 or 24, comprising the following steps: - Providing a block copolymer, in particular according to one of claims 1 to 22 and / or produced by a process according to one of claims 26 to 37; - partial or complete thiolation of the block copolymer to form thiol groups, in particular by nucleophilic substitution of at least one fluorine atom, preferably of a polyfluorostyrene, particularly preferably of a perfluorophenyl unit or a perfluorobiphenyl nyl unit or a perfluoroterphenyl unit, which is arranged in particular in a side chain of the polymer; - forming a membrane from the thiolated polymer, in particular forming a cross-link between the polymer chains; - Converting the thiol groups into ion-conducting sulfonic acid groups, in particular by oxidation.

39. The process according to claim 38, characterized in that the partial or complete thiolation of the polymer takes place in an electrolyte solution and / or in a salt solution.

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