WO2012025380A1

WO2012025380A1 - Porous polymer films based on nitrogenous aromatic polymers

Info

Publication number: WO2012025380A1
Application number: PCT/EP2011/063737
Authority: WO
Inventors: Eckhard Hanelt; Martin Bortenschlager; Tobias Halbach; Stefan Haufe; Manfred HÖLZL; Maria Leute
Original assignee: Wacker Chemie Ag
Priority date: 2010-08-27
Filing date: 2011-08-10
Publication date: 2012-03-01
Also published as: DE102010039900A1

Abstract

The invention relates to porous polymer films based on polymers comprising polyvalent, heteroaromatic cyclenes comprising one or two ring nitrogen atoms, having a porosity, based on the film volume, of 2 to 90% and having a mean pore diameter of 0.5 μm to no more than 20% of the film thickness, each at 20°C and 1000 hPa, characterized in that the porous polymer films are 0 to 20 wt % soluble based on the polymer content thereof at 130°C and 1000 hPa in N, N-dimethylacetamide. The invention further relates to a method for producing same and to the use thereof, in particular for preparing polymer electrolyte membranes.

Description

Porous polymer films based on nitrogen-containing aromatic polymers

The invention relates to porous polymer films with a small extra-share on the basis of nitrogen-containing aromatic polymers, processes for their preparation and their use, in particular for the preparation of polymer electrolyte membranes. Nitrogen-containing aromatic polymers, in particular polybenzimidazole (PBI), as well as membranes and fibers produced therefrom, have long been known. Polybenzimidazole is characterized by a high thermal and chemical resistance, fibers from PBI are therefore u.a. used for fireproof fabrics. Crosslinked polymer films of PBI are used, for example, as semipermeable membranes or as polymer electrolyte membranes for fuel cells.

In the case of polymer membranes for gas separation, crosslinking frequently leads to an improvement in the selectivity with simultaneously reduced permeability. However, US Pat. No. 6,946,015 shows that cross-linking of PBI does not adversely affect the ratio of selectivity to permeability. In this case, the CO ₂ / CH ₄ selectivity in the crosslinked PBI membrane decreases even less with increasing permeability than with the uncrosslinked membrane,

In a fuel cell, controlled oxidation of a fuel, such as hydrogen gas, converts chemical energy into electrical energy. For this purpose, the fuel and an oxidant, such as oxygen, are supplied to two opposing electrodes which are separated by an electronically insulating membrane. The membrane contains an electrolyte that is permeable to protons but not to the reactive gases. Materials used for this purpose are, for example, perfluorosulfonic acid polymers which are swollen with water or basic polymers which contain strong acids as liquid electrolyte,

EP-A 787 369 describes a process for preparing proton-conducting polymer electrolyte membranes in which a basic polymer such as polybenzimidazole is doped with a strong acid such as phosphoric acid or sulfuric acid. Since then, numerous similar membranes of various polyazoles or polyazines have been developed for this application. The advantage of a fuel cell with such a membrane is that it can be operated at temperatures above 100 ° C to about 200 ° C, because the polymer is sufficiently stable and the boiling point of the acid is well above 100 ° C. By increased compared to a fuel cell with a membrane of Perfluorsulfonsäurepolymer and water operating temperature, the catalyst activity is increased at the electrodes, reduces the sensitivity of the catalysts against carbon monoxide contamination in the fuel gas and made the waste heat with higher temperature technically better usable. The disadvantage of such a membrane compared to a membrane which uses water as the electrolyte, is the significantly lower ionic conductivity in the temperature range below 90 ° C. One of the reasons for this is that part of the acid is so strongly bound to the basic polymer that it is not available for ionic conduction. More recent investigations show that the conductivity of phosphoric acid-doped PBI membranes can be markedly improved by a porous structure of the polymer matrix (Meceryes et al., Chem. Mater., 16 (2004) 604-607). They are various methods for producing porous PBI films known. US Pat. No. 4,693,824 describes, for example, the production of ultrafiltration membranes by immersion in a coagulation bath which consists of a mixture of liquids which dissolve the PBI differently. EP-A 954 544 claims a process for producing a polymer electrolyte membrane based on a porous PBI layer. Again, a coagulation bath is used to create the porous structure. US Pat. No. 4,828,699 describes the preparation of microporous PBI membranes by means of pore formers added to the polymer solution as additives. Weber at al. used in Macromolecules 40 (2007) 1299-1304 Silica nanoparticles as placeholders for the pores. By doping the polymer with a liquid electrolyzer ^¬ th the mechanical stability of the membrane is substantially redu ^¬ sheet. This effect, which determines the lifetime of compact membranes, is even more pronounced in porous membranes. An improvement of the mechanical properties of the porous membranes is therefore desirable.

Compact membranes of PBI are commonly used as described, for example, in Q. Li et al. "High-temperature proton exchange membra- nes based on polybenzimidazoles for fuel cells", Progress in Polymer Science, 34 (2009) pp. 459-460 covalently using bifunctionally reactive additives or ionically crosslinked by additives with polar groups A solution containing the basic polymer and a bridging reagent is used, followed by bridging, using mainly the NH groups of the imidazole as the target for the bridging reagents.Preferred bridging reagents for a covalent bond are diglycidyl ethers, polyfunctional organic acids, or their halides and anhydrides, polyhalogenated organic compounds, dialdehydes or divinyl compounds,

The present invention relates to porous polymer films based on polymers containing polyvalent, heteroaromatic cycles with one or two ring nitrogen atoms, with a porosity of 2 to 90% and an average pore diameter of 0.5 to 20%, based on the film volume. the film thickness, each at 20 ° C and 1000 hPa, with the proviso that the porous polymer films with respect to their polymer content at 130 ° C and 1000 hPa in N, N-dimethylacetamide are 0 to 20 wt.% Soluble.

The solubility of the porous polymer films according to the invention in N, N-dimethylacetamide is a measure of the degree of crosslinking of the polymers. With regard to their polymer content at 130 ° C. and 1000 hPa in N, N-dimethylacetamide, the polymer films according to the invention are preferably 0 to 10% by weight, particularly preferably 0 to 5% by weight, soluble.

The average pore diameter is defined in the invention as the maximum of the distribution of the average diameter of the individual pores, wherein the average diameter of the single pore is determined as the diameter of a sphere with the same volume as the pore at 20 ° C and 1000 hPa.

The determination of porosity can be carried out within the scope of the invention by methods known in the art, e.g. according to DIN EN 993-1.

Another object of the present invention is a process for the preparation of the porous polymer films according to the invention characterized in that

in a first step

a mixture comprising polymers (A) which contain polyvalent, heteroaromatic rings having one or two ring nitrogen atoms, polar aprotic solvent (B), pore formers (C), optionally bridging agents (D) and optionally further substances (E),

in a second step

the mixture obtained in the first step is applied to a support,

in a third step

the solvent (B) is completely or partially removed

and

in a fourth step

the polymer film obtained in the third step is crosslinked, with the proviso that, depending on the type of pore-forming agent (C), it is completely or partially removed in the third step, in the fourth step and / or after the fourth step. The polyvalent, heteroaromatic cycles with one or two ring nitrogen atoms in the polymers (A) are preferably five- or six-membered rings.

The polymers containing polyvalent, heteroaromatic cycles having one or two ring nitrogens are preferably substantially linear polymers containing five- or six-membered heteroaromatic rings having one or two nitrogen atoms in the ring in the main chain. Examples of the component (A) used according to the invention are those based on building blocks selected from pyrrole, pyrazole, benzpyrazole, oxazole, benzoxazole, thiazole, benzothiazole, imidazole, benzimidazole, pyridine, pyrimidine and pyrazine and additionally aromatic or heteroaromatic groups, which may be different from the polyvalent heteroaromatic rings containing one or two ring nitrogen atoms, such as phenylene or naphthalene groups, the different groups being amide, imide, ether, thioether, sulfone - or direct CC bonds can be linked, such as all in Q. Li et al. Progress in Polymer Science, 34, p. 453 (Scheme 1), 455 (Scheme 5, 6), 456 (Scheme 7), 457 (Scheme 8) "High temperature proton exchange membranes based on polybenzimidazoles for fuel cells". (2009) as well as in WO

2008122893, p.14, line 1-20 (formula 1) mentioned polymers, which are to be included in the disclosure of the present invention. The component (A) used according to the invention is preferably composed of polymers which are synthesized from building blocks selected from pyrrole, pyrazole, benzpyrazole, oxazole, benzoxazole, imidazole, benzimidazole, pyridine, pyrimidine, pyrazine, benzene and naphthalene, the different groups via imide, ether, sulfone, thioether or direct C-C bonds are linked and wherein the blocks may be substituted, such as by sufonic acid, alkyl, alkenyl and fluoroalkyl radicals, with the proviso that the polymers (A) contain polyvalent, heteroaromatic cycles with one or two ring nitrogen atoms.

The component (A) used according to the invention is particularly preferably polymers which are built up from building blocks selected from imidazole, benzimidazole, pyridine, benzene and naphthalene, the different groups being bonded via imide, ether, sulfone or direct carbonyl groups. Bindings are linked and wherein the blocks may be substituted, such as by sulfonic acid, alkyl, alkenyl and Fluoroalkyl- with the proviso that the polymers (A) contain polyvalent, heteroaromatic cycles with one or two ring nitrogen atoms. In particular, the polymers (A) are polyazoles.

The component (A) used according to the invention and processes for their preparation are known. For example, see Q. Li et al. "High temperature proton exchange membranes based on polybenzimidazoles for fuel cells", Progress in Polymer Science, 34, pp. 449-477 (2009) and WO 2008122893.

The polymers (A) usually carry as end groups of the monomers used for the preparation, such as amino and / or

Carboxylic acid groups and / or their esters, or by subsequent chemical reaction optionally introduced end groups, such as. Alkyl, aryl, alkenyl, OH, epoxide, keto, aldehyde, ester, thiol, thioester, silyl, oxime, amide, imide, urethane and urea groups.

The polymers (A) used according to the invention are preferably those having primary or secondary amino and / or carboxylic acid end groups, more preferably NH ₂ and / or COOH end groups, in particular more than 50% of all end groups NH ₂ radicals are.

The polymers (A) are particularly preferably polybenzimidazoles, as described, for example, in Q. Li et al. Progress in Polymer Science, 34, S, 453 (Scheine 1), 455 (Scheme 5, 6), 456 (Scheme 7), 457 (Scheme 8) (2009 ), in particular poly-2, 2 '- (m-phenylene) - 5, 5'-dibenzimidazole with primary or secondary amino and / or carboxylic acid end groups, particularly preferably NH ₂ and / or COOH end groups, wherein in particular more than 50% of all end groups are NH ₂ radicals.

The polymers (A) used according to the invention have an intrinsic viscosity of preferably> 0.1 dl / g, particularly preferably from 0.1 to 2.5 dl / g, in particular from 0.3 to 1.5 dl / g, in each case measured on a 0.4% (w / v) solution, ie 0.4 g / 100 ml, of polymer in H ₂ S0 ₄ (95-97%) with an Ubbelohde viscometer at a temperature of 25 ° C and a Pressure of 1000 hPa.

The component (A) used according to the invention has a molecular weight Mw of preferably 1,000 to 300,000 g / mol, particularly preferably 4,000 to 150,000 g / mol, measured in each case as absolute molecular weight by GPC coupled with static light scattering (mobile phase: DMAc) with 1% LiBr).

Component (A) is very particularly preferably poly-2, 2 '- (m-phenylene) -5,5'-dibenzimidazole having amino and / or carboxylic acid end groups and an inherent viscosity of 0.3 to 1.5 dl / g measured on a 0.4% (w / v) solution, ie 0.4 g / 100 ml, of polymer in H ₂ S0 ₄ (95-97%) with an Ubbelohde viscometer at a temperature of 25 ° C. and a pressure of 1000 hPa.

The mixture according to the first step of the invention preferably contains at least 1% by weight, more preferably at least 5% by weight, in particular at least 10% by weight, of component (A). The mixture preferably contains at most 90% by weight, particularly preferably at most 70% by weight, in particular at most 50% by weight, of component (A). Examples of the solvents (B) used according to the invention are all polar aprotic solvents which do not react with the other mixture constituents (A), (C), (D) and (E) under the process conditions.

Preferred examples of solvent (B) are N, N-dimethylacetamide, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone or mixtures of the abovementioned solvents, with N, N-dimethylacetamide being particularly preferred.

The term solvent does not mean that all components of the mixture must dissolve completely in it.

The mixture according to the first step of the invention contains solvent (B) in amounts of preferably from 10 to 99% by weight, more preferably from 30 to 95% by weight, in particular from 50 to 90% by weight.

As a pore-forming agent (C), all previously known pore-forming agents can be used.

Examples of pore formers (C) used according to the invention are the pore formers mentioned in US Pat. No. 4,828,699, column 5, line 49 to column 6, line 11, which belong to the disclosure content of the present invention.

The pore formers (C) used are preferably liquid or solid substances which are finely dispersible in the polymer (A) but not or only slightly soluble at 20 ° C. and 1000 hPa and after removal, for example by dissolution, washing or evaporation , leave voids in the polymer (A). The pore formers (C) and polymer (A) used according to the invention are present in different phases at 20 ° C. and 1000 hPa after mixing, preferably in different phases. The pore formers (C) used according to the invention are soluble under process conditions in the polymer (A) in amounts of preferably 0 to 10% by weight, more preferably 0 to 5% by weight, in particular 0 to 1% by weight. If the pore formers (C) used according to the invention are removed by evaporation from the film according to the invention, they have a boiling point or decomposition point which is preferably at least 10 ° C., more preferably at least 20 ° C., above the boiling point of the solvent (B) used in the first step. In each case, the boiling point or decomposition point of pore former (C) is at most 100 ° C., more preferably at most 60 ° C., above the boiling point of solvent (B), at 1000 hPa. The pore formers (C) used according to the invention are preferably chemically inert to the components (A), (B), (D) and (E) under the respective process conditions.

Preferably, as pore formers (C) salts can be used which are soluble in the solvent (B), such as ammonium salts or salts of alkali metals and alkaline earth metals, particularly preferably their halides, carboxylates, sulfates, sulfonates, phosphates and phosphonates, in particular cetyltrimethylammoni - bromide and sodium dodecyl sulfate.

Preference is given to using low molecular weight esters as pore formers (C), such as esters of monocarboxylic and dicarboxylic acids, esters of phosphoric acid, esters of saccharides and fatty acids, particularly preferably dibutyl phthalate, dimethyl phthalate, diphenyl phthalate, triphenyl phosphate, sorbitan monolaurate and sorbitan arabonalmitate. Alcohols and polyols may preferably also be used as pore formers (C), such as preferably alkanols and glycols, particularly preferably n-propanol, triethylene glycol and glycerol.

It is also possible to use, as pore formers (C), polymers which at least partially do not mix with the polymer (A) and can subsequently be dissolved out of the film according to the invention, such as preferably polyolefins, polyethers, polyacrylates, polyvinyl esters, polyvinyl alcohols, Polystyrenes, and their copolymers, particularly preferably polypropylene oxide, polyethylene oxide, poly (ethylene oxide-HlocJc-propylene oxide) and poly (vinyl alcohol-co-vinyl acetate). These polymers may carry functional end groups, such as fatty acid residues or saccharides, which enhance pore formation due to their polarity.

Preference is given to using insoluble particles, such as polymer particles, chalks and silica particles, in the solvent (B) as pore formers (C). In addition, organosilicon compounds, such as preferably polydialkylsiloxanes, phenyl / alkylsiloxanes, cyclic siloxanes and organosilanes, particularly preferably cyclohexadimethylsiloxane, cyclodecadimethylsiloxane and bis (aminopropyl) -terminated polydimethylsiloxane, can preferably be used as pore formers (C).

Pore formers (C) are preferably organosilicon compounds. The organosilicon compounds (C) are preferably polydialkylsiloxanes, phenyl / alkylsiloxanes, cyclic siloxanes and organosilanes, particularly preferably cyclohexadimethylsiloxane, cyclodecadimethylsiloxane and bis (aminopropyl) -terminated polydimethylsiloxane, in particular bis (aminopropyl) -terminated polydimethylsiloxane.

In the first step according to the invention, pore formers (C) are used in amounts of preferably at least 5% by weight, more preferably at least 10% by weight, in particular at least 20% by weight, and at most 90% by weight, particularly preferably at most 80% by weight, in particular at most 70% by weight, based in each case on the total amount of polymer (A).

Pore formers (C) are commercially available products or can be prepared by methods commonly used in chemistry.

In addition to the components (A), (B) and (C), the mixtures according to the first step of the invention may contain bridging agents (D) which react with component (A) after the second step and thus crosslink the component ( A) effect. Such bridging reagents (D) are already known and may be, for example, compounds which bear reactive groups with respect to ring nitrogen atoms and / or end groups of the polymer (A).

Examples of bridging reagents (D) used according to the invention are compounds having at least two reactive groups, such as diglycidyl ether, polyfunctional organic acids or their halides and anhydrides, polyhalogenated organic compounds, dialdehydes or divinyl compounds. Component (D) is preferably bisphenol A diglycidyl ether, 1,4-butyl diglycidyl ether, ethylene glycol diglycidyl ether, terephthalaldehyde, divinyl sulphone, α-dibromo-p-xylene, 3-dichloro-tetrahydrothiophene-1,1-dioxide, dichloro - methylphosphonic acid.

If bridging reagent (D) in the first invention

Step is used, they are amounts of preferably at least 0.1 mol, more preferably at least 1 mol, and preferably at most 10 mol, more preferably at most 5 mol, each based on 1 mol of polymer (A). Preferably, no component (D) is used.

Bridging Reagents (D) are commercially available products or can be prepared by methods commonly used in chemistry.

In addition to the components (A), (B), (C) and optionally

(D) can in the first step according to the invention further substances

(E) which are different from the compounds (A) to (D), such as. Fillers such as polymers or inorganic substances which may, for example, alter the mechanical properties or the receptivity to a liquid electrolyte in the polymer film of the invention, or low concentration additives such as surfactants, adhesion promoters or preservatives which may serve to enhance the properties of the surface of the polymer film, such as improve the surface tension, or the durability of the film or additives that are used for process optimization, such as catalysts, initiators or stabilizers,

For the preparation of the porous polymer film according to the invention, in addition to the component (A), for example, further polymeric components (E) which do not contain polyvalent, heteroaromatic Cy clen with one or two ring nitrogen atoms, used as part of a mixture or a copolymer and so-called hybrid materials are produced, examples of optionally used polymers (E)

Polyolefins, such as polyethylene, polypropylene, polyisobutylene, polynorbornene, polymethylpentene, poly (1, isoprene), poly (3, 4-isoprene), poly (1, butadiene), poly (1, 2-butadiene),

Styrene (co) polymers such as polystyrene, poly (methylstyrene), poly (trifluorostyrene), poly (pentafluorostyrene),

N-basic polymers such as polyvinylcarbazole, polyethyleneimine, poly (2-vinylpyridine), pol (3-vinylpyridine), poly (4-vinylpyridine),

- (Het) aryl main chain polymers, such as polyether ketone PEK, polyether ether ketone PEEK, polyether ether ketone ketone PEE K, polyether ketone ether ketone ketone PEKEK ,.

Polyethersulfones such as polysulfone, polyphenylsulfone, polyethe- ether sulfone, polyethersulfone PES, polyphenylene ethers such as poly (2,6-dimethyloxyphenylene), poly (2,6-diphenyloxyphenylene), polyphenylene sulfide and

- perfluorinated polymers,

If polymeric components (E) are used in the first step according to the invention, they are amounts of preferably 1 to 200 parts by weight, more preferably 10 to 100 parts by weight, in each case based on 100 parts by weight of component (A). Preferably, no polymeric components (E) are used.

For the preparation of such hybrid materials, it is also possible to add to the mixture of polymer (A) and solvent (B) inorganic components (E), for example metal oxides. Preferred inorganic components (E) are silicon oxides, silicates such as scaffold silicates or phyllosilicates or silicic acids, zeolites, Aluminosilicates, titanium oxides, titanates, zirconium oxides, zirconium phosphates and heteropolyacids such as tungstophosphoric acid. These inorganic components (E) may also be in the form of particles which may be mesoporous and may be modified at the surface or in the pores by functional inorganic or organic groups such as, for example, sulfonic, phosphonic, amino or imidazole groups.

The other polymeric and inorganic components (E) listed above may be provided with reactive groups to allow covalent crosslinking with component (A),

If inorganic components (E) are used in the first step according to the invention, they are amounts of preferably 1 to 200 parts by weight, more preferably 10 to 100 parts by weight, in each case based on 100 parts by weight of component (A). Preferably, no inorganic components (E) are used.

The components used according to the invention may each be one type of such a component as well as a mixture of at least two types of a respective component.

The mixture according to the first step preferably contains no further substances beyond the components (A), (B), (C), (D) and (E). The mixture according to the first step can be prepared by any desired methods known per se, for example by simply mixing the individual constituents and, if appropriate, stirring, preferably using polymer (A) with solvent (B) is mixed to a premix (M) and then the remaining ingredients are added in any order to this premix. In this case, the further constituents, such as the pore former (C), optionally used bridging reagents (D) or further substances (E) can be dissolved separately in one part of the solvent (B) and subsequently added to the premix (M).

To prepare the masterbatch (M) in the first step according to the invention, the mixture is preferably stirred until the polymer (A) has preferably dissolved more than 90% by weight, particularly preferably completely, in the solvent (B). Afterwards, the pore formers (C) and, if desired, bridging reagents (D) or further substances (E) can be added. If desired, portions of component (A), (C), (D) and / or other materials (E) which have not dissolved in solvent (B) may remain in the solution or be filtered off.

The preparation of this premix (M) in the first step according to the invention is carried out at temperatures of preferably 50 to 350.degree. C., particularly preferably 100 to 300.degree. C., in particular 150 to 250.degree.

The addition of the optionally remaining constituents to the premix (M) in the first step according to the invention is added

Temperatures of preferably 15 to 300 ° C, more preferably 20 to 100 ° C, in particular 20 to 40 ° C carried out.

The first step according to the invention is preferably carried out at the pressure of the surrounding atmosphere, ie 900 to 1100 hPa. It can also be performed at lower or higher pressures. The first step according to the invention is preferably carried out in an inert gas atmosphere, such as under argon or nitrogen purge. The first step according to the invention can be carried out continuously or discontinuously.

The mixture according to the first step is preferably a solution, a dispersion or a paste. In the case of the solution, all components are dissolved in the solvent (B). In the case of dispersion, particles of component (A) and / or the pore former (C) and / or components (D) and (E) are dispersed in the continuous phase solvent. The mixture of the first step is particularly preferably a dispersion in which droplets or particles of the pore-forming agent (C) are dispersed in the solution of component (A) and solvent (B), in particular with a honey-like viscosity. The application of the mixture obtained in the first step of the invention on a support can be carried out with all suitable, previously known discontinuous and continuous application methods. Preferably, the application is carried out by pouring out the mixture on a planar substrate, by application with a roller or slot die, by the doctor blade method or spin coating. The chosen application method also depends on the desired layer thickness of the polymer film according to the third step of the invention. Examples of carriers which can be used in the second step according to the invention are all previously known carriers, which are wetted well by the mixtures according to the invention, largely resistant to the compounds present in the mixtures. components and have dimensional stability in the applied temperature range. Examples of such supports are polymer films such as poly (ethylene terephthalate), polyimide, polyethylene lenimid, polytetrafluoroethylene and polyvinylidene fluoride films, metal surfaces such as stainless steel strips, glass surfaces and siliconized papers.

In particular, when the polymer film is to be removed from the carrier after the preparation, carriers are preferred which are chemically inert to the mixture according to the first step.

The application can also be carried out on a functional carrier, which is part of the respective application. For example, in the case of the production of a semipermeable membrane, the mixture can be applied to an open-pore film or a support fabric. When used as a fuel cell membrane, the mixture can be applied directly to the gas diffusion layer or the electrode thereon. Preferably, the carriers used are those which are wetted by the mixture according to the first step, wherein the contact angle of the mixture on the carrier is preferably less than 90 °, particularly preferably less than 30 °, in each case measured with inert gas as the surrounding Phase.

The second step according to the invention can be carried out continuously or discontinuously.

For continuous application methods, polymer films such as poly (ethylene terephthalate) films or metal strips such as stainless steel are preferably used. For the batch process, glass plates are preferably used. The second step of the invention is preferably carried out at temperatures below the boiling point of the solvent (B), more preferably in the temperature range of 10 to 80 ° C, in particular 15 to 40 ° C.

The second step of the invention is preferably carried out at the pressure of the surrounding atmosphere, ie 900 to 1100 hPa. It can also be performed at lower or higher pressures.

The second step according to the invention is preferably carried out in air in a low-dust environment or in a clean room environment, which contributes to ensuring a constant film quality.

For the removal of the solvent in the third step according to the invention, the customary processes known from the prior art for drying can be used. In this case, the polymer film is preferably heated to the extent that the solvent or

Solvent mixture escapes without forming gas bubbles in the film. If pore former (C) is a liquid with a low boiling point or a substance with a low decomposition temperature, this can be mixed with the solvent (B) in part or in part in the third step

Removed film, wherein in the polymer film at the sites that had the pore former (C) occupied, cavities remain. The boiling point or the decomposition temperature of the pore-forming agent (C) for this purpose is preferably from 10 to 100 ° C higher than the boiling point of the solvent (B) at a pressure of 1000 hPa.

The polymer film can be dried in the third step according to the invention at different pressures, preferably in the case of Pressure of the surrounding atmosphere, ie at 900 to 1100 hPa, or under reduced pressure.

The third step of the invention is preferably carried out at temperatures below the boiling point of the solvent (B), more preferably at 40 to 150 ° C, in particular 80 to 150 ° C. However, it can also be carried out at a higher temperature, so that the crosslinking reaction may already begin during the drying.

The third step according to the invention is preferably carried out in air in a low-dust environment or in a clean room environment, which contributes to ensuring a constant film quality.

The third step according to the invention can be carried out continuously or discontinuously.

If the third step according to the invention is to be carried out continuously, it is possible, for example, to use a drying oven or heated rolls / belts or a floating dryer in order to remove the solvent by means of warm wind.

The desired thickness of the dry polymer film depends on the requirements of the particular application. As semipermeable membranes, thin layers between 3 and 20 μm are preferred, especially when the film is mechanically supported by a porous support. As a self-supporting film, for example when used as a polymer electrolyte membrane, the thickness of the dry polymer film is preferably between 20 and 200 μm. In the third step according to the invention, preference is given to producing polymer films having a thickness of from 3 to 500 μm, particularly preferably from 10 to 200 μm. Before carrying out the fourth step according to the invention, the dried polymer film can now be removed from or left on the carrier in accordance with the third step, with the proviso that the carrier has sufficient thermal stability if it is to be thermally crosslinked in the fourth step.

In the fourth step according to the invention, the polymer film is crosslinked. The crosslinking can be started by any desired and known processes, some of which are listed here by way of example: i) By bridging reagents (D) such as diglycidyl ether, polyfunctional organic acids or their halides and anhydrides, polyhalogenated organic compounds, dialdehydes or divinyl compounds in particular, for example, bisphenol A diglycidyl ether, 1-butyl diglycidyl ether, ethylene glycol diglycidyl ether, terephthalaldehyde, divinyl sulphone, α-dibromo-p-xylene, 3,4-dichlorotetrahydrothiophene-1,1-dioxide, dichloromethylphosphonic acid and, if appropriate, using Catalysts (E) and / or initiators (E) can be covalently bridged by the polymers (A) via the NH groups contained therein. The bridging reaction can be started by heating the dried film according to the third step. The temperature in the fourth step according to the invention in the case of the crosslinking type i) is preferably in the range from 20 to 300 ° C., more preferably from 50 to 250 ° C. ii) Free-radical crosslinking is possible when the polymer (A) has polymerizable functional groups such as (meth) acrylate esters and vinyl ethers. This crosslinking is preferably effected by means of free radicals which are generated by UV light, other high-energy electromagnetic radiation, electron beams or thermally, optionally with the use of initiators (E), such as peroxides. The crosslinking reaction is preferred in this case

Exclusion of oxygen carried out. The temperature of process variant ii) according to the invention depends on the type of crosslinking reaction and is preferably in the range from 20 to 300 ° C., more preferably between 20 and 200 ° C. iii) In the case of the polymers (A), in particular in the case of polyazoles, sufficient crosslinking can be achieved even without the use of bridging reagents (D) by heating the polymer film sufficiently long to above 200 ° C. in an oxygen-containing environment become. Preference is given to heating in air. However, it is also possible to use other gas mixtures which preferably contain more than 1% by weight of oxygen.

The temperature of variant iii) in the fourth step according to the invention is preferably in the range from 100 ° C to 400 ° C, more preferably between 200 ° C and 300 ° C.

If the pore former (C) was not or only partially removed in the third step, it can be completely or partially removed from the film when heated in the fourth step, with voids in the polymer film at the sites occupied by the pore former (C) urückbleiben. The boiling point or the decomposition temperature of the pore-forming agent lies to the sem purpose below the temperature used in the fourth step.

The heating of the polymer film in the fourth step can be carried out by any desired methods known hitherto, for example in a hot-air oven or by contact with hot surfaces. This step can be carried out in the case of the crosslinking types i) and ii) in an inert gas atmosphere, such as under argon or nitrogen purge, or as in cross-linking type iii) also in the presence of oxygen, for example in air.

The fourth step according to the invention is preferably carried out at the pressure of the surrounding atmosphere, ie 900 to 1100 hPa. It can also be performed at lower or higher pressures.

The fourth step according to the invention can be carried out continuously or discontinuously.

For example, in a continuous process, the polymer film may be passed over heatable stainless steel or sintered metal rolls. If in the fourth step according to the invention only one heating of the polymer film is carried out, the third and the fourth step can take place simultaneously or continuously merge into one another.

In the fourth step according to the invention, polymer films are now obtained which, in addition to the nitrogen-containing aromatic polymers, optionally have a residual amount of solvent and optionally further substances. The quality of the crosslinking of the resulting polymer films is determined by the determination of in Ν, Ν-dimethylacetamide soluble proportions of polymer in the polymer film assessed.

In the process according to the invention, pore former (C) may already have been removed in the third step and / or fourth step, in particular if the pore former (C) used in the first step is volatile, so that the formation of the porous structure of the polymer film already occurs of the third or fourth step. If this is not the case, a fifth step must be carried out in the method according to the invention in order to remove the pore-forming agent (C) from the resulting film.

In the optionally performed fifth step of the inventive method, various methods for

Removal of the pore-forming agent (C) can be applied from the crosslinked polymer. For example, the film obtained in the fourth step may be immersed in a solvent bath and thus the pore former dissolved out of the film, or evaporated by further heating of the film of pore formers.

The porous films produced according to the invention are free of pore formers (C) or contain these in residual amounts of preferably up to 50% by weight, more preferably up to 20% by weight, in particular up to 10% by weight, based in each case on the first step used amount of pore-forming agent (C).

The porosity of the polymer films according to the invention, based on the film volume, is characterized by a free volume which is preferably at least 5%, particularly preferably at least 20%, and at most 90%, particularly preferably at most 75%. Preference is given to films with a uniform pore distribution along the cross section and a middle pore distribution. diameter which is less than 20 of the film thickness, more preferably less than 10% of the film thickness, in particular less than 5% of the film thickness. The films according to the invention preferably have mean pore diameters of 0.5 to 50 μm, more preferably 1 to 20 μm, in particular 1 to 5 μm.

The polymer films according to the invention or produced according to the invention can now be used for all purposes for which hitherto porous polymer films have also been used.

Depending on the intended use, the polymer film according to the invention can be modified in further process steps by methods known per se. For use as a polymer electrolyte membrane, the polymer film obtained in the fourth or fifth step can be doped with a strong acid in an optional sixth step. Strong acids are to be understood here as acids having a p _a of preferably less than 4. It is also possible to combine such a further process step with a preceding step and thus, for example, to introduce a bridging reagent into the polymer film together with a strong acid.

Another object of the invention are polymer electrolyte membranes, based on polymers containing polyvalent, heteroaromatic cycles with one or two ring nitrogen atoms, with a porosity based on the film volume of 2 to 90% and a mean pore diameter of 0.5 m to a maximum of 20% of the film thickness, each at 20 ° C and 1000 hPa, with the proviso that the porous polymer films in relation to their

Polymer content at 130 ° C and 1000 hPa in N, N-dimethylacetamide 0 to 20 wt.% Are soluble, which are doped with a strong acid. Another object of the present invention is a process for the preparation of polymer electrolyte membranes

characterized in that

in a first step

a mixture containing polymers which contain polyvalent heteroaromatic rings containing one or two ring nitrogen atoms, (A), polar aprotic solvent (B), pore formers (C), optionally bridging reagents (D) and optionally further substances (S)

in a second step

the mixture obtained in the first step is applied to a support,

in a third step

the solvent (B) is completely or partially removed

and

in a fourth step

the polymer film obtained in the third step is crosslinked, optionally

in a fifth step

Pore former (C) is removed,

with the proviso that, depending on the type of pore-forming agent {C), it is completely or partially removed in step 3, in step 4 and / or after step 4, and

in a sixth step

the polymer film obtained in the fourth and fifth steps, respectively, is doped with a strong acid.

With regard to the stability of the polymer film and the safety precautions required for the handling of strong acids at high temperatures, doping is carried out in the sixth step, which may be carried out according to the invention. preferably below 200 ° C, more preferably at 20 to 160 ° C, especially at 35 to 130 ° C.

According to a variant of the optionally performed sixth step, the polymer film according to the invention is immersed in a highly concentrated strong acid over a period of preferably at most 5 hours and more preferably 1 minute to 1 hour, wherein a higher temperature shortens the immersion time.

In this variant, the amount of acid used in the sixth process step which may optionally be carried out in accordance with the invention is usually from 5 to 10,000 times, preferably from 6 to 5000 times, more preferably from 6 to 1000 times, in each case based on Weight of the polymer (A) in the polymer film.

Alternatively, according to another variant of the optional sixth step, a strong acid may be metered onto the polymer film and the film heated until the film has completely absorbed the acid. The amount of acid used in the present invention optionally performed sixth method step is in this variant usually 2- to 10-fold amount, preferably the 3- to 8-fold amount, based on the weight of the polymer ^¬ films.

According to a further variant of the optionally performed sixth step, the polymer film is pressed between two acid-impregnated gas diffusion electrodes for the production of a membrane electrode unit. The amount of acid used in the sixth process step, which may optionally be carried out according to the invention, in this variant is usually cherweise 2 to 10 times, preferably 3 to 8 times the amount, each based on the weight of the polymer film.

Strong acids in the sixth step of the invention are protic strong acids, for example phosphorus-containing acids and sulfuric acid. In the present invention, the term "phosphorus-containing acids" lyphosphorsäure Po, phosphonic acid (H ₃ P0 _3), orthophosphoric acid (H ₃ PO _4), pyrophosphoric acid (HP ₂ 0 _7), triphosphoric acid (H ₅ P ₃ O ₀ ) and metaphosphoric acid.

Because the polymer (A) in the film according to the invention can be impregnated with a larger number of molecules of strong acid with increasing concentration of the strong acid, the phosphorus-containing acid, in particular orthophosphoric acid, preferably has a concentration of at least 70% by weight, and especially preferably at least 85% by weight in water.

The optionally performed sixth process step according to the invention is carried out at the pressure of the surrounding atmosphere, ie 900 to 1100 hPa. It can also be performed at lower or higher pressures.

The polymer electrolyte membrane obtained according to the invention in the sixth step is proton-conducting and can therefore preferably be used as electrolyte for fuel cells or electrolysis cells. The polymer electrolyte is not limited to the use for cells, but may for example also be used as the electrolyte for a display element, an electrochromic element or various sensors.

Each individual cell in a fuel cell usually contains a polymer electrolyte membrane according to the invention and two Electrodes between which the polymer electrolyte membrane is sandwiched. The electrodes each have a catalytically active layer and a porous gas diffusion layer.

Another object of the invention is the use of the polymer electrolyte membranes according to the invention or prepared according to the invention for the production of membrane electrode units for fuel cells or electrolysis cells.

Another object of the invention is a membrane-electrode assembly containing at least one electrode and at least one inventive or inventively prepared polymer electrolyte membrane.

Due to the different permeabilities and selectivities of the polymer films according to the invention for liquids and gases, they are excellently suited as a semipermeable membrane. The invention therefore also relates to the use of the polymer films according to the invention or the polymer films produced according to the invention as a semipermeable membrane for separating liquids and gases. In the fuel cell, the porous polymer films according to the invention have the advantage that they permit a higher proton conductivity and thus a better electrical performance than Compact membranes based on nitrogenous aromatic polymers. The mechanical stability and the long-term thermal and chemical stability are significantly improved by the cross-linking. The porous membrane matrix swells less during absorption of the electrolyte than a compact membrane. This facilitates the production of the membrane-electrode assembly. and reduces the mechanical stresses during operation in a fuel cell,

In the following examples, all parts and percentages are by weight unless otherwise specified. Unless otherwise indicated, the following examples are air at ambient atmospheric pressure, ie, at about 1000 hPa, and at room temperature, ie, about 20 ° C, or a temperature resulting from combining the reactants at room temperature without additional heating or Cooling stops, carried out. The air used in the experiments contains 23% by weight,% oxygen and 50% relative

Moisture, All viscosity data given in the examples refer to a temperature of 25 ° C.

Inherent viscosity was measured in the following examples as follows:

The polymer is first dried at 160 ° C for 2 h. 400 mg of the thus dried polymer are then dissolved for 4 hours at 80 ° C in 100 ml of concentrated sulfuric acid (concentration 95- 97 wt.%). The inherent viscosity is determined from this 0.4% (w / v) solution according to ISO 3105 with an Ubbelohde viscometer at a temperature of 25 ° C. The solubility of the proportion of nitrogen-containing aromatic polymers in the polymer films produced has been described in the following Examples determined as follows ("solubility test"):

The membrane piece is dried at 150 ° C., weighed and extracted for one hour at 130 ° C. and 1000 hPa in N, N-dimethylacetamide. Thereafter, the membrane is again dried at 150 ° C to constant weight and then weighed. To determine the distribution of the pores, sections perpendicular to the film plane were examined with a scanning electron microscope. The pore size distributions were statistically evaluated by image analysis to obtain the average pore diameter and the width of the distribution.

The porosity P is calculated from the density of the porous film on the basis of DIN EN 993-1 with the formula P = 1 - p / pp. Here, p is the measured density of the porous film, which was determined by the buoyancy method at 20 ° C and 1000 hPa. p _P is the density of the compact polymer.

example 1

I) Preparation of amine-terminated polybenzimidazole

107.1 g of 3, 3 ¹ -Diaminobenzidin (0.5 mol) and 79.5 g isophthalic acid (0.475 mole) (1.053 molar ratio, excess of amine) were stirred in 2.0 kg of polyphosphoric acid and heated in a reactor (5 1 ), which was purged with inert gas argon de ^¬ . The batch was heated to 190 ° C (jacket temperature) and stirred for 20 hours. The reaction product was precipitated in water, washed with it and neutralized in 550 g of a 10% strength by weight sodium bicarbonate solution. Thereafter, the polybenzimidazole was washed again with water, filtered off, dried at 130 ° C in vacuo and ground with an electric mill. The yield was 132.3 g.

The polybenzimidazole thus prepared had an inherent viscosity of 0.70 dl / g.

II) Preparation of a porous film of crosslinked polybenzimidazole a) 9.1 g of the above under I) prepared polybenzimidazole (PBI) were dissolved in 90.9 g of N, N-dimethylacetamide (DMAc) in a pressure reactor (Buchi iniclave, 200 ml) with stirring at a temperature of 200 ° C. , Thereafter, the solution was filtered and degassed. 10.341 g of this polymer solution and as a pore former 0.377 g of bis (aminopropyl) -terminated polydimethylsiloxane having a molecular weight of 2900 g / mol (available under "fluid NH 40 D" Wacker Chemie AG, Germany) were weighed in a polypropylene cup with screw cap and by means of a Centrifugal mixer (Speedmixer ™ DAC 150 SP, Hauschild & Co. KG, Germany) mixed for 10 min at 3500 U / min.

After degassing, the solution was applied to a polyethylene terephthalate (PET) support film having a thickness of 0.175 mm (commercially available under the trade name "Melinex 0" from Pütz GmbH, Germany) by means of a film-drawing apparatus with 0.4 mm gap height The film was heated for 10 minutes at 80 ° C. and 100 ° C. for 30 minutes at 150 ° C. in a circulating air drying oven, then separated from the carrier film and washed with hexane at room temperature on a shaker for 60 minutes in a circulating air drying oven for 60 minutes at 100 ° C. and for 360 minutes at 300 ° C. The thickness of the film thus obtained was 30 to 35 μm.

b) With the film obtained under a), a solubility test was carried out according to the method described above. The weight loss after one hour in 130 ° C hot N, N-dimethylacetamide was 3%.

The mechanical stability of this polymer film was assessed by tensile stress measurements. For this purpose, film samples with a length of 6 cm and a width of 1 cm were placed in a measuring apparatus The company Zwick GmbH & Co. (model Z010 TN, sample holder 8106) clamped and pulled apart at a speed of 5 cm / min. The polymer film ruptured at a tension of 73 N / mm ² and an elongation of 4%.

The investigation of a section perpendicular to the plane of the film with a scanning electron microscope showed that the pores are closed and distributed almost uniformly over the film cross-section. They have an average pore diameter of 5 pm with a width of the distribution of ± 2 pm.

The determination of the density of the film according to the buoyancy method based on DIN EN 993-1 gave a value of p =

0.98 g / cm ³ at 20 ° C and 1000 hPa. From this, assuming that the film consists only of polybenzimidazole having a density p _{P =} 1.3 g / cm ³ , a porosity P of 25% is calculated.

Example 2

Doping a membrane with phosphoric acid and determining the conductivity

a) From a piece (6 x 6 cm ² ) polymer film from Example 1, the weight and the thickness was determined. Subsequently, the film piece was placed in a Petri dish, covered with 85% orthophosphoric acid and heated for 30 min at 150 ° C in a drying oven. After cooling to room temperature, the film was removed and wiped with paper towels. From the swollen film, the weight and the thickness were again determined. He had taken up 5.7 times his weight. The degree of doping (mass fraction of the acid based on the weight of the swollen membrane) was 85% by weight. b) A piece (20 × 10 mm ² ) of the phosphoric acid-swollen membrane according to Example 2a was placed in a 4-point conductivity cell (type BT110 Fa. BekkTech LLC, USA) and heated in a convection oven to 150 ° C. , The membrane impedance was determined by means of an impedance analyzer (model IM6ex from Zahner-Elektrik, Germany). The sample geometry (thickness, area) yields a membrane conductivity of 11.3 S / m at 150 ° C.

Example 3

Dependence of the membrane conductivity and the porosity on the proportion of pore formers

The procedure described in Example 1 is repeated with the modification that different proportions of pore formers based on the polymer fraction (PBI) according to Table 1 were used. The results are summarized in Table 1. For comparison, the compact membrane without pores from Comparative Example 2 is listed.

All films were doped with orthophosphoric acid as described in Example 2a so that they had an equal doping level of 85% by weight. The membrane conductivities measured as in Example 2b can also be taken from Table 1.

Table 1

Porosity-measured porosity distribution of membrane play proportion, density of the polyder pore-based polymer polymer film diameter polymer film [%] [μπι] at 150 ° C weight [g / cm ³ ] [S / m] [Wt. %]

0 1, 30 0 5,6 1 10 1,14 12 1,5 ± 0,5 8,0

2, 5 ± 1

2 20 1.06 18 9.5 3 5 ± 2

40 0.98 25 11, 3

Example 4

Producing a membrane electrode assembly

The 6 × 6 cm ² piece of the phosphoric acid-swollen membrane from Example 2 was thus between two commercially available gas diffusion electrodes, each with 3.0 mg / cm ² platinum loading (Johnson Matthey, type 3mg Pt Blk, no electrolytes on Toray TGP-H-090, UK) that the platinum catalyst layers contacted the membrane. This membrane-electrode assembly was compressed for 4 hours between plane-parallel plates at a temperature of 160 ° C and a force of 1.3 kN to a membrane-electrode assembly.

Example 5

Fuel cell test of the membrane-electrode assembly

The membrane-electrode unit from Example 4 was installed in a conventional arrangement in a test cell (quickCONNECT F25 from. Baltic-FuelCells GmbH, Germany) and sealed with a pressing force of 3.5 kN. The operation of the test cell was carried out on a MILAN test rig from Magnum Fuel Cell AG. Figure 1 shows the course of the current-voltage curve at 160 ° C. The gas flow for hydrogen was 196 nml / min and for air

748 nml / min. Unhumidified gases with atmospheric pressure were used. For this membrane-electrode assembly, a cell voltage of 0.536 V was measured at a current of 0.5 A / cm ² . Under the specified test conditions, it exhibited an impedance of 4.0 mQ over a surface area of 25 cm ² at a measurement frequency of 5.4 kHz. The associated rest voltage was 0.938 V. The diffusion of the gaseous hydrogen through the membrane was determined by supplying nitrogen at an externally given voltage of IV at the anode nitrogen and hydrogen at the cathode and the ion current of the H ⁺ formed at the anode Ions back to the cathode was measured. This so-called H2 passage was only 1.4 mA / cm ² for the crosslinked membrane even in continuous operation after a few hours. This is a value that is also common for compact membranes.

In contrast, the curve of the MEA with uncrosslinked compact membrane from counterexample 3 shown for comparison in FIG. 1 has a quiescent voltage of only 0.777 V and the H ₂ passage measured for this MEA was clearly too high at 23 mA / cm ² .

Figure 1: Polarization curve of a membrane-electrode assembly according to the invention (solid line) in the fuel cell. For comparison, the curve of a membrane electrode assembly having the uncrosslinked compact membrane of Comparative Example 3 (dashes) prepared in the same manner is shown.

Comparative Example 1 (VI)

Producing and characterizing a porous film of polybenzimidazole without crosslinking

a) 9.1 g of PBI according to Example 1 were dissolved in 90.9 g of DMAc in a pressure reactor (Büchi miniclave, 200 ml) with stirring at a temperature of 200 ° C. Thereafter, the solution was filtered and degas. 10.341 g of this polymer solution and as a pore former 0.377 g bis (aminopropyl) -terminated polydimethylsiloxane having a molecular weight of 2900 g / mol (fluid NH 40 D, Wacker Chemie AG, Germany) were weighed into a polypropylene cup with screw cap and by means of a centrifugal mixer (SpeedmixerT DAC 150 SP, Hauschild & Co. KG,

Germany) for 10 min at 3500 rpm.

After degassing, the solution was applied to a PET carrier film (Melinex 0) by means of a 0.4 mm gap film applicator.

0.175 mm). Thereafter, the film was heated for 10 min at 80 ° C and 100 ° C and 30 min at 150 ° C in a convection oven, then separated from the carrier film and washed for 60 min at room temperature on a shaker with hexane. Finally, the film was again heated in a circulating air drying cabinet at 100 ° C. for 60 minutes. The thickness of the film thus obtained was 30 to 35 \ im.

b) This film was subjected to a solubility test according to the method described above. The film completely dissolved.

In an attempt to dope the membrane with phosphoric acid as in Example 2a, it partly dissolved. The membrane is therefore not suitable for a test in the fuel cell.

Comparative Example 2 (V2)

Producing and characterizing a compact film made of networked! polybenzimidazole

a) 12.0 g of PBI according to Example 1 were dissolved in 88.0 g of DMAc in a pressure reactor (Buchi Miniclave, 200 ml) with stirring at a Temperature of 200 ° C dissolved. After filtration and degassing, the solution was applied to a PET support film (elinex 0, 0.175 mm) using a 0.4 mm gap film applicator. Thereafter, the film was heated for 10 min at 80 ° C and 100 ° C and 30 min at 150 ° C in a convection oven and then separated from the carrier film. Finally, the film was heated again in a convection oven 240 min at 300 ° C. The thickness of the film thus obtained was 30 to 35 μπι.

b) This film was subjected to a solubility test by the method described above. The weight loss after one hour in 130 ° C hot N, -Dimethylacetamid was 1%.

The mechanical stability of this polymer film was assessed by tensile stress measurements. For this purpose, film samples having a length of 6 cm and a width of 1 cm were clamped in a measuring apparatus from Zwick GmbH & Co. (model Z010 TN, sample holder 8106) and pulled apart at a speed of 5 cm / min. The polymer film ruptured at a tension of 142 N / mm ² and an elongation of 4%.

Sections were examined with a scanning electron microscope. The film has a homogeneous structure without pores.

The determination of the density of the film according to the buoyancy method based on DIN EN 993-1 gave a value of p _{P =} 1.3 g / cm ³ at 20 ° C and 1000 hPa.

Comparative Example 3 (V3) Doping a membrane with phosphoric acid and determining the conductivity

a) From a piece (6 x 6 cm ² ) of the polymer film of Comparative Example 2, the weight and the thickness was determined. Subsequently, the film piece was placed in a Petri dish, with

Overcoated 85% orthophosphoric acid and heated for 30 min at 150 ° C in a drying oven. After cooling to room temperature, the film was removed and wiped with paper towels. From the swollen film again the weight and the thickness were determined. He had absorbed 5.6 times his weight. The degree of doping (mass increase based on the weight of the swollen membrane) was 85% by weight.

b) A piece (20 × 10 mm ² ) of the phosphoric acid-swollen membrane according to Comparative Example 3a was placed in a 4-point conductivity cell (type BT110 from BekkTech LLC, USA) and heated to 150 ° C. in a circulating air oven , The membrane impedance was determined by means of an impedance analyzer (model IM6ex from Zahner-Elektrik, Germany). The sample geometry (thickness, area) yields a membrane conductivity of 5.6 S / m at 150 ° C.

c) From the membrane was prepared as in Example 4, an MEA, which was tested as in Example 5 in the fuel cell. The measured polarization curve is compared with Example 5 in Figure 1 (bars). The quiescent voltage of this MEA was only 0.777 V and the H ₂ passage measured for this MEA was clearly too high at 23 mA / cm ² .

Claims

claims

1. Porous polymer films based on polymers containing polyvalent heteroaromatic cycles with one or two ring nitrogen atoms, having a porosity of from 2 to 90% based on the film volume and a mean pore diameter of from 0.5 μm to a maximum of 20% of the film thickness, each at 20 ° C and 1000 hPa, with the proviso that the porous polymer films with respect to their polymer content at 130 ° C and 1000 hPa in N, N-dimethylacetamide 0 to 20 wt,% are soluble.

2. Polymer films according to claim 1, characterized in that they are soluble in terms of their polymer content at 130 ° C and 1000 hPa in N, -Dimethylacetamid 0 to 10 wt.%. 3. Polymer films according to claim 1 or 2, characterized in that it is polybenzimidazoles in the polymers containing polyhydric, heteroaromatic cycles with one or two ring nitrogen atoms. 4. Polymer films according to one or more of claims 1 to

3. characterized in that they have a porosity of 5 to 75%.

5. Polymer films according to one or more of claims 1 to 4, characterized in that the average pore diameter

0.5 to 50 pm.

6. Process for the preparation of the porous polymer films according to the invention

characterized in that

in a first step

a mixture containing polymers containing polyvalent heteroaromatic cycles with one or two ring nitrogen atoms Part (A), polar aprotic solvent (B), pore-forming agent (C), optionally bridging agents (D) and optionally other substances (E) is prepared,

in a second step

the mixture obtained in the first step is applied to a support,

in a third step

the solvent (B) is completely or partially removed

and

in a fourth step

the polymer film obtained in the third step is crosslinked, with the proviso that, depending on the type of pore-forming agent (C), it is completely or partially removed in the third step, in the fourth step and / or after the fourth step.

7. The method according to claim 6, characterized in that in a fifth step pore-forming agent (C) is removed from the resulting film. 8. polymer electrolyte membranes based on polymers containing polyvalent, heteroaromatic cycles with one or two ring nitrogen atoms, with a porosity based on the film volume of 2 to 90% and an average pore diameter of 0.5 μι to a maximum of 20% of the film thickness, respectively at 20 ° C and 1000 hPa, with the proviso that the porous polymer films with respect to their polymer content at 130 ° C and 1000 hPa in N, N-dimethylacetamide are 0 to 20 wt.% Soluble with a strong acid are doped. 9. A process for producing polymer electrolyte membranes according to claim 8, characterized in that

in a first step a mixture comprising polymers which contain polyvalent, heteroaromatic rings containing one or two ring nitrogen atoms, (A), polar aprotic solvent (B), pore formers (C), optionally bridging agents (D) and optionally further substances (E),

in a second step

the mixture obtained in the first step is applied to a support,

in a third step

the solvent (B) is completely or partially removed

and

in a fourth step

the polymer film obtained in the third step is crosslinked, optionally

in a fifth step

Pore former (C) is removed,

with the proviso that, depending on the type of pore-forming agent (C), it is completely or partially removed in the third step, in the fourth step and / or after the fourth step, and

in a sixth step

10. Use of the polymer electrolyte membranes according to claim 8 or produced according to claim 9 for the production of membrane electrode assemblies for fuel cells or electrolysis cells.

11. Membrane electrode unit comprising at least one electrode and at least one polymer electrolyte membrane according to claim 8 or produced according to claim 9.

12. Use of the polymer films according to one or more of claims 1 to 5 or prepared by the process according to claim 6 or 7 as a semipermeable membrane for the separation of liquids and gases,