DE102010039900A1 - Porous polymer films based on nitrogen-containing aromatic polymers - Google Patents

Abstract

The invention relates to porous polymer films based on polymers which contain 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 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 are soluble in N, N-dimethylacetamide in terms of their polymer content at 130 ° C and 1000 hPa in 0 to 20 wt .-%, process for their preparation and their use, in particular for the representation of polymer electrolyte membranes.

Description

The invention relates to porous polymer films with a low extractable content based on 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 high thermal and chemical resistance. Therefore, fibers from PBI are 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 polymer membranes for gas separation, crosslinking often leads to an improvement in the selectivity with simultaneously reduced permeability. In US-BB 6,946,015 however, it is shown that the cross-linking of PBI does not adversely affect the selectivity to permeability ratio. 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 which is permeable to protons but not to the reactive gases. Materials used for this purpose are, for example, perfluorosulfonic acid polymers which have been swollen with water or basic polymers which contain strong acids as the liquid electrolyte.

EP-A 787 369 describes a process for producing 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 catalyst 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.

Recent studies show that the conductivity of phosphoric acid-doped PBI membranes can be significantly improved by a porous structure of the polymer matrix ( Mecerreyes et al. in Chem. Mater. 16 (2004) 604-607 ). Various methods for producing porous PBI films are known. In US 4,693,824 For example, the preparation of ultrafiltration membranes is described by immersion in a coagulation bath consisting of a mixture of liquids which dissolve the PBI differently well. In EP-A 954 544 For example, a process for producing a polymer electrolyte membrane based on a porous PBI layer is claimed. Again, a coagulation bath is used to create the porous structure. In US-A 4,828,699 the production of microporous PBI membranes by means of pore formers, which are added to the polymer solution as additives, described. Weber at al. use in Macromolecules 40 (2007) 1299-1304 Silica nanoparticles as placeholders for the pores.

By doping the polymer with a liquid electrolyte, the mechanical stability of the membrane is significantly reduced. 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 such as in Q. Li et al. "High temperature proton exchange membranes based on polybenzimidazoles for fuel cells", Progress in Polymer Science, 34 (2009) pp. 459-460 described covalently using bifunctionally reactive additives or ionically crosslinked by additives with polar groups. For this purpose, a solution which contains the basic polymer and a bridging reagent is used and then the bridging is carried out. As attack points for the bridging reagents serve mainly the NH groups of the imidazole. 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 rings having one or two ring nitrogen atoms, with a porosity of 2 to 90% based on the film volume and an average pore diameter of 0.5 μm to a maximum of 20%. 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.

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, the polymer films according to the invention are soluble in N, N-dimethylacetamide, preferably 0 to 10% by weight, particularly preferably 0 to 5% by weight.

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 the porosity can be carried out in the context of the invention by methods known in the art, such as. B. 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 containing one or two ring nitrogen atoms, polar aprotic solvent (B), pore formers (C), optionally bridging agents (D) and optionally other 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 which are 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 are different may be included in the polyvalent heteroaromatic cycles having one or two ring nitrogen atoms, such as phenylene or naphthalene groups, where the different groups may be linked via amide, imide, ether, thioether, sulfone or direct C-C bonds, like 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) (2009, "High temperature proton exchange membranes based on polybenzimidazoles for fuel cells") ) 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 above 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 having one or two ring nitrogens.

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 sulphonic acid, alkyl, alkenyl and fluoroalkyl radicals, 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, be on Q. Li et al. "High temperature proton exchange membranes based on polybenzimidazoles for fuel cells", Progress in Polymer Science, 34, pp. 449-477 (2009) such as WO 2008122893 directed.

The polymers (A) carry as end groups usually those of the monomers used for the preparation, such as amino and / or carboxylic acid groups and / or their esters, or by subsequent chemical reaction any end groups introduced, such. B. alkyl, aryl, alkenyl, OH, epoxy, 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, such as, for example, in US Pat Q. Li et al. Progress in Polymer Science, 34, p. 453 (Scheme 1), 455 (Scheme 5, 6), 456 (Scheme 7), 457 (Scheme 8) (2009, "High temperature proton exchange membranes based on polybenzimidazoles for fuel cells") ) in particular poly-2,21- (m-phenylene) -5,5'-dibenzimidazole having primary or secondary amino and / or carboxylic acid end groups, particularly preferably NH ₂ and / or COOH end groups, in particular more than 50% of all end groups are NH ₂ residues.

The polymers (A) used according to the invention have an inherent viscosity of preferably> 0.1 dl / g, more preferably from 0.1 to 2.5 dl / g, in particular from 0.3 to 1.5 dl / g, measured in each case a 0.4% (w / v) solution, ie 0.4 g / 100 ml, of polymer in H ₂ SO 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 SO 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 those in US-A 4,828,699 , Column 5, line 49 to column 6, line 11 called pore formers, which are to be included in the disclosure 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, in the polymer ( A) Leave cavities.

The pore formers (C) and polymer (A) used according to the invention are present 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 the pore former (C) salts can be used which are soluble in the solvent (B), such as preferably ammonium salts or salts of alkali and alkaline earth metals, more preferably their halides, carboxylates, sulfates, sulfonates, phosphates and phosphonates, in particular cetyltrimethylammonium bromide and sodium dodecyl sulfate ,

It is also possible to use low molecular weight esters as pore formers (C), such as esters of mono- 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 monopalmitate.

As pore formers (C) it is also possible to use alcohols and polyols, preferably alkanols and glycols, particularly preferably n-propanol, triethylene glycol and glycerol.

Polymers which do not mix at least partially with the polymer (A) and can subsequently be dissolved out of the film according to the invention are preferably used as pore formers (C), such as preferably polyolefins, polyethers, polyacrylates, polyvinyl esters, polyvinyl alcohols, polystyrenes, and the like Copolymers, more preferably polypropylene oxide, polyethylene oxide, poly (ethylene oxide-block-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.

Preferably, as the pore-forming agent (C), insoluble particles such as polymer particles, chalks and silica particles can also be used in the solvent (B).

In addition, organosilicon compounds such as polydialkylsiloxanes, phenyl / alkylsiloxanes, cyclic siloxanes, and organosilanes, particularly preferably, may be used as the pore former (C) preferably cyclohexadimethylsiloxane, cyclodecadimethylsiloxane and bis (aminopropyl) -terminated polydimethylsiloxane.

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) in amounts of preferably at least 5 wt .-%, particularly preferably at least 10 wt .-%, in particular at least 20 wt .-%, and at most 90 wt .-%, particularly preferably at most 80 wt .-%, in particular at most 70 Gew. -%, in each case based on the total amount of polymer (A) used.

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

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

Examples of bridging agents (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, terephthalic aldehyde, divinyl sulphone, α-dibromo-p-xylene, 3,4-dichlorotetrahydrothiophene-1,1-dioxide, dichloromethylphosphonic acid.

If bridging reagent (D) is used in the first step according to the invention, these are amounts of preferably at least 0.1 mol, more preferably at least 1 mol, and preferably not more than 10 mol, more preferably not more than 5 mol, in each case based on 1 mol of starting material Polymer (A). Preferably, no component (D) is used.

Bridging reagent (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) further substances (E) can be used in the first step according to the invention, which are different from the compounds (A) to (D), such. For example, fillers such as polymers or inorganic substances, which may for example change the mechanical properties or the absorption capacity for a liquid electrolyte in the polymer film according to the invention, or additives in low concentration such as surfactants, adhesion promoters or preservatives, which may serve the properties of the surface of the polymer film, such as the surface tension, or to improve the durability of the film or additives that serve the process optimization, such as catalysts, initiators or stabilizers.

• – Polyolefine, wie Polyethylen, Polypropylen, Polyisobutylen, Polynorbornen, Polymethylpenten, Poly(1,4-isopren), Poly(3,4-isopren), Poly(1,4-butadien), Poly(1,2-butadien),
• – Styrol(co)polymere wie Polystyrol, Poly(methylstyrol), Poly(trifluorstyrol), Poly(pentafluorostyrol),
• – N-basische Polymere wie Polyvinylcarbazol, Polyethylenimin, Poly(2-vinylpyridin), Poly(3-vinylpyridin), Poly(4-vinylpyridin),
• – (Het)arylhauptkettenpolymere, wie Polyetherketon PEK, Polyetheretherketon PEEK, Polyetheretherketonketon PEEKK, Polyetherketonetherketon-keton PEKEKK,
• – Polyethersulfone wie Polysulfon, Polyphenylsulfon, Polyetherethersulfon, Polyethersulfon PES, Polyphenylenether wie Poly(2,6-dimethyloxyphenylen), Poly(2,6-diphenyloxyphenylen), Polyphenylensulfid und
• – perfluorierte Polymere.

For the preparation of the porous polymer film according to the invention, in addition to the component (A), for example, further polymeric components (E) containing no polyvalent, heteroaromatic cycles with one or two ring nitrogen atoms can be used as part of a mixture or a copolymer and so-called hybrid materials are produced. Examples of optionally used polymers (E) are

• Polyolefins such as polyethylene, polypropylene, polyisobutylene, polynorbornene, polymethylpentene, poly (1,4-isoprene), poly (3,4-isoprene), poly (1,4-butadiene), poly (1,2-butadiene),
• Styrene (co) polymers such as polystyrene, poly (methylstyrene), poly (trifluorostyrene), poly (pentafluorostyrene),
• N-basic polymers such as polyvinylcarbazole, polyethylenimine, poly (2-vinylpyridine), poly (3-vinylpyridine), poly (4-vinylpyridine),
• - (Het) aryl main chain polymers, such as polyether ketone PEK, polyether ether ketone PEEK, polyether ether ketone ketone PEEKK, polyether ketone ether ketone ketone PEKEKK,
• Polyethersulfones such as polysulfone, polyphenylsulfone, polyether 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, these 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 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, these 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 and known per se methods, for example by simply mixing the individual components and optionally stirring, wherein preferably polymer (A) with solvent (B) to a premix (M) is mixed 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). Thereafter, the pore formers (C) and, optionally, bridging reagents (D) or further substances (E) may 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 from 50 to 350.degree. C., more preferably from 100 to 300.degree. C., in particular from 150 to 250.degree.

The addition of the optionally remaining constituents to the masterbatch (M) in the first step according to the invention is carried out at temperatures of preferably 15 to 300 ° C., particularly preferably 20 to 100 ° C., in particular 20 to 90 ° C.

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-type 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 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 well wetted by the mixtures according to the invention, are largely resistant to the components contained in the mixtures and have dimensional stability in the temperature range used. Examples of such carriers are polymer films such as poly (ethylene terephthalate), polyimide, polyethyleneimide, polytetrafluoroethylene and polyvinylidene fluoride films, metal surfaces such as stainless steel belts, 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 manufacturing a semi-permeable membrane, the mixture may be applied to an open-pored film or backing 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 helps to ensure 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, it can be used in the third step together with the Solvents (B) are wholly or partially removed from the film, wherein in the polymer film at the sites which had occupied the pore former (C), remain cavities. 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 of the invention at different pressures, preferably at the 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, for example, a drying oven or heated rolls / belts or a floating dryer can be used 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, such as when used as a polymer electrolyte membrane, the thickness of the dry polymer film is preferably between 20 and 200 microns.

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.

• i) Durch Verbrückungsreagenzien (D) wie beispielsweise Diglycidylether, mehrfachfunktionelle organische Säuren oder deren Halogenide und Anhydride, mehrfach halogenierte organische Verbindungen, Dialdehyde oder Divinylverbindungen, insbesondere beispielsweise Bisphenol-A-diglycidylether, 1,4-Butyldiglycidylether, Ethylenglycoldiglycidylether, Terephthaldehyd, Divinylsulphon, α-Dibrom-p-xylol, 3,4-Dichlortetrahydrothiophene-1,1-dioxid, Dichlormethylphosphonsäure und gegebenenfalls unter Verwendung von Katalysatoren (E) und/oder Initiatoren (E) können die Polymere (A) über die darin enthaltenen NH-Gruppen kovalent verbrückt werden. Die Verbrückungsreaktion kann durch Erhitzen des getrockneten Films gemäß drittem Schritt gestartet werden.

In the fourth step according to the invention, the polymer film is crosslinked. The networking can be started by any and known methods, some of which are exemplified here:

• 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, 1,4-butyl diglycidyl ether, ethylene glycol diglycidyl ether, terephthalic aldehyde, divinyl sulphone, α Dibromo-p-xylene, 3,4-dichlorotetrahydrothiophene-1,1-dioxide, dichloromethylphosphonic acid and optionally using catalysts (E) and / or initiators (E), the polymers (A) via the NH groups contained therein covalently be bridged. The bridging reaction can be started by heating the dried film according to the third step.

• ii) Eine radikalische Vernetzung ist möglich, wenn das Polymer (A) polymerisierbare funktionelle Gruppen, wie beispielsweise (Meth-)Acrylatester und Vinylether, aufweist. Diese Vernetzung wird vorzugsweise mittels freier Radikale bewirkt, welche durch durch UV-Licht, andere energiereiche elektromagnetische Strahlung, durch Elektronenstrahlen oder thermisch, gegebenenfalls unter Verwendung von Initiatoren (E), wie beispielsweise Peroxiden, erzeugt werden.

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 produced by UV light, other high-energy electromagnetic radiation, by electron beams or thermally, if appropriate using initiators (E), such as, for example, peroxides.

• iii) Bei den Polymeren (A), insbesondere wenn es sich um Polyazole handelt, kann auch ohne Verbrückungsreagenzien (D) durch ein ausreichend langes Erhitzen des Polymerfilms auf über 200°C in einer Sauerstoff-haltigen Umgebung eine ausreichende Vernetzung erreicht werden. Bevorzugt ist das Erhitzen an Luft. Es können jedoch auch andere Gasgemische verwendet werden, die vorzugsweise mehr als 1 Gew.-% Sauerstoff enthalten.

The crosslinking reaction in this case is preferably carried out in the absence of oxygen. 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 bridging reagents (D) by heating the polymer film sufficiently long to above 200 ° C. in an oxygen-containing environment. Preference is given to heating in air. However, other gas mixtures may also be used 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) remain. The boiling point or the decomposition temperature of the pore-forming agent is for this 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 and all known methods, such as 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 crosslinking of the polymer films obtained is assessed by determining the proportions of polymer soluble in N, N-dimethylacetamide in the polymer film.

In the method according to the invention, pore former (C) may have already been removed in the third step and / or fourth step, especially 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 during 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 process according to the invention, various methods for removing the pore-forming agent (C) from the crosslinked polymer can be used. 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 amount of pore former (C) used in the first step.

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 having a uniform pore distribution along the cross section and an average pore 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. As strong acids should here acids with a pK _s of preferably less than 4 are understood. 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 an average pore diameter of 0.5 .mu.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 are soluble in N, N-dimethylacetamide 0 to 20% by weight in terms of their polymer content at 130 ° C and 1000 hPa, the 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 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
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 in the sixth step, which may be carried out according to the invention, is preferably carried out below 200 ° C., more preferably at 20 to 160 ° C., in particular 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. 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 2 to 10 times the amount, preferably from 3 to 8 times, in each case based on the weight of the polymer film.

According to a further variant of the optionally performed sixth step, the polymer film for the production of a membrane-electrode unit is pressed between two acid-impregnated gas diffusion electrodes. 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 2 to 10 times the amount, preferably from 3 to 8 times, in each case 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 context of the present invention, "phosphorus-containing acids" is understood as meaning polyphosphoric acid, phosphonic acid (H ₃ PO ₃ ), orthophosphoric acid (H ₃ PO ₄ ), pyrophospharic acid (H ₄ P ₂ O ₇ ), triphosphoric acid (H ₅ P ₃ O ₁₀ ) and metaphosphoric acid.

Because the polymer (A) in the film of the present invention can be impregnated with a larger number of strong acid molecules as the strong acid concentration increases, the phosphorus acid, especially orthophosphoric acid, preferably has a concentration of at least 70% by weight and more 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 typically 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 inventively prepared for the production of membrane electrode assemblies 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 the separation of liquids and gases.

In the fuel cell, the porous polymer films according to the invention have the advantage that they allow a higher proton conductivity and thus a better electrical performance than compact membranes based on nitrogen-containing aromatic polymers. The mechanical stability and the long-term thermal and chemical stability are significantly improved by the crosslinking. The porous membrane matrix swells less when receiving the electrolyte as a compact membrane. This facilitates the manufacture of the membrane-electrode assemblies and reduces the mechanical stresses when operating 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 wt .-% oxygen and 50% relative humidity. 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 calculated from this 0.4% (w / v) solution according to ISO 3105 determined with a Ubbelohde viscometer at a temperature of 25 ° C.

The solubility of the proportion of nitrogen-containing aromatic polymers in the polymer films produced was determined in the following examples 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 in accordance with DIN EN 993-1 calculated with the formula P = 1 - ρ / ρ _P. Here, ρ is the measured density of the porous film determined by the buoyancy method at 20 ° C and 1000 hPa. ρ _P is the density of the compact polymer.

example 1

I) Preparation of amine-terminated polybenzimidazole

107.1 g of 3,3'-diaminobenzidine (0.5 mol) and 79.5 g of isophthalic acid (0.475 mol) (molar ratio 1.053, amine excess) were stirred into 2.0 kg of polyphosphoric acid and charged into a heatable reactor (5 l) , which was purged with inert gas argon. 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 wt .-% 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 Crosslinked Polybenzimidazole Porous Film

• a) 9.1 g of the polybenzimidazole (PBI) prepared above under I) were dissolved in 90.9 g of N, N-dimethylacetamide (DMAc) in a pressure reactor (Büchi miniclave, 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 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 ^TM DAC 150 SP, Fa. Hauschild & Co. KG, Germany) mixed for 10 min at 3500 U / min.

• b) Mit den unter a) erhaltenen Film wurde ein Löslichkeitstest nach dem oben beschriebenen Verfahren durchgeführt. Die Gewichtsabnahme nach einer Stunde in 130°C heißem N,N-Dimethylacetamid betrug 3%.

After degassing, the solution was applied by means of a film applicator with 0.4 mm gap height on a carrier film of polyethylene terephthalate (PET) with a thickness of 0.175 mm (commercially available under the trade name "Melinex O" at Pütz GmbH, Germany). 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 dryer at 100 ° C for 60 minutes and at 300 ° C for 360 minutes. 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 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 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 microns with a width of the distribution of ± 2 microns.

The determination of the density of the film by the buoyancy method in accordance with DIN EN 993-1 gave a value of ρ = 0.98 g / cm ³ at 20 ° C and 1000 hPa. From this, assuming that the film consists only of polybenzimidazole having a density ρ _P = 1.3 g / cm ³ , one calculates Porosity P of 25%.

Example 2

Doping a membrane with phosphoric acid and determining the conductivity

• a) From a piece (6 × 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 wt .-%.
• b) A piece (20 × 10 mm ² ) of the phosphoric acid-swollen membrane according to Example 2a was placed in a 4-point conductivity measuring cell (type BT110 Fa. BekkTech LLC, USA) and heated to 150 ° C in a convection 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 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-forming agent 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 example Porcer fraction, based on the polymer weight [wt .-%] measured density of polymer film [g / cm ³ ] Porosity of polymer film [%] Distribution of pore diameter [μm] Membrane conductivity at 150 ° C [S / m] V2 0 1.30 0 - 5.6 3.1 10 1.14 12 1.5 ± 0.5 8.0 3.2 20 1.06 18 2.5 ± 1 9.5 3.3 40 0.98 25 5 ± 2 11.3

Example 4

Producing a membrane electrode assembly

The 6 × 6 cm ² piece of phosphorus acid-swollen membrane from Example 2 was so between two commercially available gas diffusion electrodes, each with 3.0 mg / cm ² platinum loading (Johnson Matthey, type 3 mg Pt Blk, no electrolyte, Toray TGP-H-090, UK) that the platinum catalyst layers contacted the membrane. This membrane electrode assembly was left for 4 hours plane-parallel plates pressed 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 assembly of Example 4 was installed in a conventional arrangement in a test cell (quickCONNECT F25 Fa. 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. 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 mΩ over an area of 25 cm ² at a measurement frequency of 5.4 kHz. The associated quiescent voltage was 0.938 V. The diffusion of the gaseous hydrogen through the membrane was determined by supplying nitrogen at an anode voltage of 1 V at the anode 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 H ₂ penetration 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 the For comparison, the MEA curve with uncrosslinked compact membrane from counterexample 3, on the other hand, 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 .

: Polarization curve of a membrane-electrode unit 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 (V1)

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 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 (fluid NH 40 D, Wacker Chemie AG, Germany) were weighed into a polypropylene cup with screw cap and by means of a centrifugal mixer (Speedmixer ^TM DAC 150 SP, Hauschild & Co. KG, Germany) for 10 minutes at 3500 rpm.

• b) Mit diesem Film wurde ein Löslichkeitstest nach dem oben beschriebenen Verfahren durchgeführt. Dabei löste sich der Film vollständig auf.

After degassing, the solution was applied to a PET support film (Melinex O, 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, then separated from the carrier film and washed for 60 min at room temperature on a shaker with hexane. Finally, the film was heated again in a circulating air dryer at 100 ° C for 60 min. The thickness of the film thus obtained was 30 to 35 μm.

• b) This film was subjected to a solubility test by 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 cross-linked polybenzimidazole film

• a) 12.0 g of PBI according to Example 1 were dissolved in 88.0 g of DMAc in a pressure reactor (Büchi miniclave, 200 ml) with stirring at a temperature of 200 ° C. After filtration and degassing, the solution was applied to a PET support film (Melinex O, 0.175 mm) using a 0.4 mm gap film applicator. Thereafter, the film was in each case 10 min at 80 ° C and 100 ° C and 30 min at 150 ° C in a Heated circulating air dryer 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 μm.
• 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, N-dimethylacetamide 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 by the buoyancy method in accordance with DIN EN 993-1 gave a value of ρ _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 × 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, 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 absorbed 5.6 times his weight. The degree of doping (mass increase based on the weight of the swollen membrane) was 85 wt .-%.
• 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 measuring cell (type BT110 Fa. BekkTech LLC, USA) and heated to 150 ° C in a convection 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 in (Dashes) compared with Example 5. 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 .

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 6946015 BB [0003]
• EP 787369A [0005]
• US 4693824 [0006]
• EP 954544A [0006]
• US 4828699 A [0006, 0033]
• WO 2008122893 [0016, 0020]

Cited non-patent literature

• Mecerreyes et al. in Chem. Mater. 16 (2004) 604-607 [0006]
• Weber at al. use in Macromolecules 40 (2007) 1299-1304 [0006]
• Q. Li et al. "High temperature proton exchange membranes based on polybenzimidazoles for fuel cells", Progress in Polymer Science, 34 (2009) pp. 459-460 [0008]
• DIN EN 993-1 [0012]
• Q. Li et al. Progress in Polymer Science, 34, p. 453 (Scheme 1), 455 (Scheme 5, 6), 456 (Scheme 7), 457 (Scheme 8) (2009, "High temperature proton exchange membranes based on polybenzimidazoles for fuel cells") [0016]
• Q. Li et al. "High temperature proton exchange membranes based on polybenzimidazoles for fuel cells", Progress in Polymer Science, 34, pp. 449-477 (2009) [0020]
• Q. Li et al. Progress in Polymer Science, 34, p. 453 (Scheme 1), 455 (Scheme 5, 6), 456 (Scheme 7), 457 (Scheme 8) (2009, "High temperature proton exchange membranes based on polybenzimidazoles for fuel cells") [0023]
• ISO 3105 [0123]
• DIN EN 993-1 [0126]
• DIN EN 993-1 [0132]
• DIN EN 993-1 [0144]

Claims (12)

Porous polymer films based on polymers containing polyvalent, heteroaromatic cycles with one or two ring nitrogen atoms, with a porosity of 2 to 90% based on the film volume and a mean pore diameter of 0.5 .mu.m to a maximum of 20% of the film thickness 20 ° C and 1000 hPa, with the proviso that the porous polymer films in terms of their polymer content at 130 ° C and 1000 hPa in N, N-dimethylacetamide 0 to 20 wt .-% are soluble. Polymer films according to claim 1, characterized in that they are soluble in N, N-dimethylacetamide 0 to 10 wt .-% in terms of their polymer content at 130 ° C and 1000 hPa. Polymer films according to claim 1 or 2, characterized in that the polymers containing polyvalent, heteroaromatic cycles with one or two ring nitrogen atoms are polybenzimidazoles. Polymer films according to one or more of claims 1 to 3, characterized in that they have a porosity of 5 to 75%. Polymer films according to one or more of claims 1 to 4, characterized in that the average pore diameter is 0.5 to 50 microns. Process for the preparation of the porous polymer films according to the invention 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 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. A method according to claim 6, characterized in that in a fifth step pore-forming agent (C) is removed from the resulting film. Polymer electrolyte membranes based on polymers containing polyvalent, heteroaromatic cycles with one or two ring nitrogen atoms, having a porosity of 2 to 90% and a mean pore diameter of 0.5 to a maximum of 20% of the film thickness, each at 20 ° C and 1000 hPa, with the proviso that the porous polymer films are soluble in N, N-dimethylacetamide 0 to 20 wt% doped with a strong acid at 130 ° C and 1000 hPa in polymer content. Process for the production of polymer electrolyte membranes according to claim 8, characterized in that in a first step a mixture comprising polymers containing polyvalent, heteroaromatic cycles with one or two ring nitrogen atoms, (A), polar aprotic solvent (B), pore former (C), optionally In a second step, the mixture obtained in the first step is applied to a carrier, in a third step, the solvent (B) is completely or partially removed and in a fourth step of the crosslinked in the third step, if appropriate, in a fifth step pore-forming agent (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 the sixth step in the fourth or fifth step obtained polymer film is doped with a strong acid. 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. Membrane-electrode assembly containing at least one electrode and at least one polymer electrolyte membrane according to claim 8 or produced according to claim 9. Use of the polymer films according to one or more of claims 1 to 5 or produced by the process according to claim 6 or 7 as semipermeable membrane for the separation of liquids and gases.

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