DE102010029990A1 - Polymer films based on polyazoles - Google Patents

Abstract

The invention relates to polymer films based on polyazoles which, based on their polyazole content at 130 ° C. and 1000 hPa, are 0 to 20% by weight soluble in N, N-dimethylacetamide, processes for their production and their use as polymer electrolyte membranes for the production membrane electrode assemblies for fuel cells and as a semi-permeable membrane for separating liquids and gases.

Description

The invention relates to polymer films based on polyazoles, processes for their preparation and their use, in particular for the preparation of polymer electrolyte membranes.

Polyazoles, especially polybenzimidazole (PBI), and membranes made therefrom have long been known. Crosslinked polymer films of polybenzimidazole (PBI) are characterized by high thermal and chemical resistance and are therefore used, for example, as semipermeable membranes such as, inter alia US-A 4,020,142 described or as polymer electrolyte membranes for fuel cells as in EP-B 1 165 670 disclosed.

In membranes for gas separation, crosslinking often leads to an improvement of the selectivity with simultaneously reduced permeability. In US 6,946,015 BB 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. These are the fuel and an oxidizing agent, such as. As oxygen, at two opposite electrodes, which are separated by an electronically insulating membrane supplied. 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 a proton-conducting polymer electrolyte membrane in which a basic polymer such as polybenzimidazole is doped with a strong acid such as phosphoric acid or sulfuric acid. 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 doping the polymer with a liquid electrolyte is that the mechanical stability of the membrane is considerably reduced. This can be like in EP-B 1 165 670 described by a cross-linking of the polymer are partially compensated. So that the operating time is not limited by this crosslinking, there is a requirement that the long-term stability of the crosslinking in the hot and strongly acidic environment of a fuel cell membrane corresponds to the stability of the polybenzimidazole.

Polybenzimidazoles were from H. Vogel and CS Marvel in "Polybenzimidazoles, new thermally stable polymers", Journal of Polymer Science 50 (154) p. 511-539 (1961). synthesized and characterized. Particularly preferred for the preparation of polymer electrolyte membranes is the poly-2,2 '- (m-phenylene) -5,5'-bibenzimidazole. The polymer chains of the polybenzimidazoles are generally soluble in a polar, aprotic solvent such as N, N-dimethylacetamide or in acids. However, by permanently heating the pure polymer at 500 ° C in a nitrogen atmosphere, Vogel and Marvel already observed that the polymer tends to be insoluble and suspected incipient crosslinking by free radicals. Such low crosslinking would not be sufficient for a good mechanical stability of the liquid electrolyte swollen PBI films. Membranes of PBI are therefore usually such. In US 4,020,142, A . EP 1 373 379 B . EP 1 425 336 B or WO 05076401 A 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. Bisphenol A diglycidyl ethers and 1,4-butyl diglycidyl ethers are used as particularly preferred bridging reagents. However, ethers are easily radically oxidized at elevated temperature and can be cleaved by acids. Therefore, the long-term stability of the bridging is limited. Loud EP-B 1 373 379 These membranes are in need of improvement in terms of their mechanical strength and in particular the fracture toughness is still insufficient. It is therefore proposed to carry out the reaction of the polymer with the bridging reagent, which preferably has at least two epoxide groups or isocyanate groups per molecule, in the presence of a specific catalyst. However, the long-term stability of bridging is not improved by this measure.

Polybenzimidazole is characterized by exceptionally high thermal and chemical resistance. The crosslinking by additional additives therefore always involves the risk that the bridging over the additive is less stable in the long term than the pure PBI and therefore that the mechanical stability of such a crosslinked PBI membrane slowly decreases, especially in an aggressive environment such as in a fuel cell.

The present invention relates to polymer films based on polyazoles, which are soluble in N, N-dimethylacetamide 0 to 20 wt .-% in terms of their Polyazolgehalt at 130 ° C and 1000 hPa, which can be prepared by that
in a first step
a mixture containing polyazole (A), polar aprotic solvent (B) and optionally further substances (C) 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 heated in the presence of oxygen to a temperature in the range of 200 to 500 ° C.

Another object of the present invention is a process for the preparation of polymer films based on polyazoles, characterized in that
in a first step
a mixture containing polyazole (A), polar aprotic solvent (B) and optionally further substances (C) 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 heated in the presence of oxygen to a temperature in the range of 200 to 500 ° C.

With regard to their polyazole 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, more preferably 0 to 5% by weight, in particular 0 to 2% by weight, soluble.

The polyazoles (A) used in accordance with the invention may be any and all known polyazoles which, in addition to the azole building block, contain at least one further aromatic or heteroaromatic compound.

Examples of the polyazoles (A) used according to the invention are those based on monomers selected from pyrrole, pyrazole, benzpyrazole, oxazole, benzoxazole, thiazole, benzothiazole, imidazole and benzimidazole, and additionally aromatic or heteroaromatic groups, such as phenylene, naphthalene -, pyridine, pyrimidine or pyrazine groups. The different groups can also be linked via amide, imide, ether, thioether or direct CC bonds. The polyazoles (A) used according to the invention and processes for their preparation are already known. For example, be on H. Vogel, CS Marvel "Polybenzimidazoles, new thermally stable polymers", Journal of Polymer Science 50 (154) p. 511-539 (1961) referred to in the disclosure of the present invention.

The polyazoles (A) can be prepared by various and known methods and carry as end groups usually 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 as B. alkyl, aryl, alkenyl, OH, epoxy, keto, aldehyde, ester, thiol, thioester, silyl, oxime, amide, imide, urethane and urea groups.

In the inventively used polyazoles (A) are preferably those having 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 groups.

The polyazoles (A) are particularly preferably polybenzimidazoles (such as, for example, in US Pat H. Vogel, CS Marvel "Polybenzimidazoles, new thermally stable polymers", Journal of Polymer Science 50 (154) p. 511-539 (1961) described), in particular poly-2,2 '- (m-phenylene) -5,5'-dibenzimidazole with 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 are NH ₂ residues.

Polybenzimidazole (A) can be prepared by various and known methods, such as by polymerization of diaminobenzidine and isophthalic acid and / or their esters. Polybenzimidazoles (A) may have as end groups 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 polyazoles (A) used according to the invention may have a different number of amino and / or carboxylic acid end groups. Preferably, the component (A) used according to the invention contains at least in part polyazoles having at least 3 NH ₂ and / or COOH end groups, more preferably more than 20% of the polyazoles carry 4 NH ₂ groups per molecule.

The polyazoles (A) used according to the invention have an inherent 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, measured in each case a 0.4% (w / v) solution, ie 0.4 g / 100 ml, of polyazole in H ₂ SO ₄ (95-97%) with an Ubbelhode 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).

Most preferably (A) is 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 polyazole in H ₂ SO ₄ (95-97%) with an Ubbelhode 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 of polyazole (A), more preferably at least 5% by weight of polyazole, especially at least 10% by weight. The mixture preferably contains at most 90% by weight, particularly preferably at most 70% by weight, in particular at most 50% by weight, of polyazole (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) and (C).

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.

In addition to the components (A) and (B), the mixtures according to the first step of the invention contain further substances (C), such as. For example, organic compounds which do not contain groups which are reactive toward NH groups, inorganic substances such as metal oxides or additives such as, for example, surfactants or adhesion promoters, which contain no NH-reactive groups and can serve to improve the properties of the surface of the crosslinked polymer film. such as the surface tension, to modify.

If further substances (C) are used, these are preferably inorganic substances.

The mixture according to the first step of the invention contains further substances (C) in amounts of preferably 0 to 90 parts by weight, more preferably 0 to 50 parts by weight, in particular 0 to 20 parts by weight, in each case based on 100 parts by weight of polyazole. The mixture preferably contains no further substances (C).

The mixtures in the first step preferably contain no further constituents in addition to polyazoles (A), solvents (B) and optionally further substances (C).

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 can be prepared by any desired methods known per se, for example by simply mixing the individual constituents in any order and, if appropriate, stirring.

The first step according to the invention is carried out at temperatures of preferably 20 to 350.degree. C., particularly preferably 100 to 300.degree. C., in particular 150 to 250.degree.

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.

In the first step according to the invention, the mixture is preferably stirred until the polyazole (A) has more preferably completely, more preferably completely, dissolved in the solvent (B) to more than 90% by weight. If desired, portions of component (A) and / or (C) that did not dissolve in solvent (B) may remain in the solution or be filtered off.

The mixture according to the first step is preferably a solution, a suspension or a paste. In the case of the solution, the polyazole (A) and optionally used further substances (C) is dissolved in the solvent (B). In the case of suspension, particles of the polyazole (A) and / or other materials (C) are dispersed in the continuous phase solvent. The mixture of the first step is particularly preferably a solution, in particular having 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 selected application method also depends on the desired layer thickness of the dry polymer film according to the third step of the invention.

Examples of carriers which can be used in the second step of the invention are all previously known carriers which are well wetted by the mixtures according to the invention, substantially resistant to the components (A), (B) and, if appropriate, (C) contained in the mixtures. are and have dimensional stability in the applied temperature range. 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 processes, polymer films such as poly (ethylene terephthalate) films or metal belts 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 impairing the homogeneity of the film.

The polymer film can be dried 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 50 to 150 ° C, especially 80 to 150 ° C.

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 1 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 1 to 500 μm, more preferably from 5 to 200 μm.

Before carrying out the fourth step according to the invention, the dried polymer film can now be removed from the carrier in accordance with the third step or, if the carrier has sufficient thermal stability, remain thereon.

The heating of the polymer film at 200 ° C to 500 ° C 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.

The maximum temperature in the fourth step of the invention is limited primarily by the stability of the polymer and the economics of the process. It is preferably below 450 ° C and more preferably below 400 ° C.

The temperature in the fourth step according to the invention is preferably in the range from 250 to 400.degree. C., more preferably from 300 to 400.degree.

The maximum duration of heating in the fourth step according to the invention is limited mainly by economic aspects. Annealing takes place over a period of preferably 1 second to 24 hours, more preferably 1 minute to 10 hours, in particular 1 to 4 hours.

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 is carried out in the presence of oxygen, preference being given to using a gas mixture which contains more than 1% by weight of oxygen, more preferably more than 5% by weight of oxygen, in particular more than 10% by weight of oxygen contains. The fourth step according to the invention is very particularly preferably carried out in the presence of air.

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.

A variant of the fourth step according to the invention is that the third and the fourth step continuously merge into each other, in the z. B. the coated carrier remains in the drying apparatus and this is heated to a temperature according to the fourth step.

In the fourth step of the invention, polymer films are now obtained which have a polyazole fraction, optionally a residual amount of solvent and optionally further substances. The quality of the polymer films obtained is assessed by determining the N, N, -dimethylacetamide soluble proportions of polyazole in the polymer film.

The polymer films according to the invention or produced according to the invention can now be used for all purposes for which polymer films have hitherto 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 step can be doped with a strong acid in a fifth step, if appropriate.

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

According to a variant of the optionally performed fifth step, the polymer film 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 (D) used in the fifth process step optionally carried out is usually from 5 to 10000 times, preferably from 6 to 5000 times, more preferably from 6 to 1000 times, in each case based on the weight of the polymer (A) in the polymer film.

Alternatively, according to a further variant of the fifth step which may be carried out, 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 the acid (D) used in the fifth invention optionally carried out In this variant, the process step is usually 2 to 10 times the amount, preferably 3 to 8 times the amount, in each case based on the weight of the polymer film.

According to another variant of the fifth step, if necessary, the polymer film is pressed between two acid-impregnated gas diffusion electrodes for the production of a membrane-electrode assembly. In this variant, the amount of acid (D) used in the fifth process step optionally carried out in this variant is usually 2 to 10 times the amount, preferably 3 to 8 times, in each case based on the weight of the polymer film.

Strong acids in the fifth step according to the invention are protic strong acids (D), such as, 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 ), pyrophosphoric acid (H ₄ P ₂ O ₇ ), triphosphoric acid (H ₅ P ₃ O ₁₀ ) and metaphosphoric acid.

Because the polyazole (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-containing 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 fifth 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 fifth step is proton-conducting and therefore can preferably be used as electrolyte for fuel 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.

Another object of the invention are polymer electrolyte membranes based on polyazoles, which are soluble in terms of their Polyazolgehalt at 130 ° C and 1000 hPa in N, N-dimethylacetamide 0 to 20 wt .-%, which can be prepared by that
in a first step
a mixture containing polyazole (A), polar aprotic solvent (B) and optionally further substances (C) is produced,
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,
in a fourth step
the polymer film obtained in the third step is heated in the presence of oxygen to above 200 to 500 ° C and
in a fifth step
the polymer film obtained in the fourth step is doped with a strong acid.

Another object of the present invention is a process for the preparation of polymer electrolyte membranes based on polyazoles, characterized in that
in a first step
a mixture containing polyazole (A), polar aprotic solvent (B) and optionally further substances (C) 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,
in a fourth step
the polymer film obtained in the third step is heated in the presence of oxygen to a temperature in the range of 200 to 500 ° C, and
in a fifth step
the polymer film obtained in the fourth step is doped with a strong acid.

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.

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.

The polymer films of the invention have the advantage that they have a high mechanical stability and excellent thermal and chemical long-term stability.

The method according to the invention has the advantage that it is easy to carry out.

Furthermore, the process according to the invention has the advantage that largely insoluble polymer films can be produced without the use of bridging reagents.

In the following examples, all parts and percentages are by weight unless otherwise specified. Unless indicated otherwise, the following examples are at a pressure of the surrounding atmosphere, ie at about 1000 hPa, and at room temperature, ie about 20 ° C or a temperature which is adjusted when adding the reactants at room temperature without additional heating or cooling , carried out. All viscosity data given in the examples should refer to a temperature of 25 ° C.

The air used in the experiments contains 23% by weight of oxygen and 50% of relative humidity.

In the following examples, the solubility of the polyazole portion of the polymer films produced was 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 dimethylacetamide. After one hour, the membrane is again dried at 150 ° C and then weighed.

In the following examples, the inherent viscosity was measured 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 an Ubbelhode viscometer at a temperature of 25 ° C.

example 1

a) Preparation of amine-terminated polybenzimidazole

107.1 g of 3,3'-diaminobenzidine (0.5 mol) (commercially available from Sigma-Aldrich, Germany) 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 in a heated reactor (5 1) filled, 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 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.

b) Preparation of carboxy-terminated polybenzimidazole

The preparation of the polymer was carried out as described above under a) with the difference that the 3,3'-diaminobenzidine is reacted with 1.053 times (molar) of isophthalic acid (excess acid).

The polybenzimidazole thus prepared had an inherent viscosity of 0.43 dl / g.

Example 2

• a)
• aa) 12.0 g of polybenzimidazole according to Example 1a were dissolved in 88.0 g of N, N-dimethylacetamide (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 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). After drying (10 min at 80 ° C, 10 min at 100 ° C and 30 min at 150 ° C), the film was separated from the carrier film. It was then heated in a convection oven for 240 min in 300 ° C hot air. The film thickness was 30 to 35 μm. The film thus obtained is hereinafter referred to as film 2a.
• from) 12.0 g of polybenzimidazole according to Example 1b were dissolved in 88.0 g of N, N-dimethylacetamide (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 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). After drying (10 min at 80 ° C, 10 min at 100 ° C and 30 min at 150 ° C), the film was separated from the carrier film. It was then heated in a convection oven for 240 min in 300 ° C hot air. The film thickness was 30 to 35 μm. The film thus obtained is referred to below as film 2b.
• b) In order to be able to assess the mechanical stability of the polymer films film 2a and film 2b obtained in a) above, tensile stress measurements were carried out. 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 film 2a ruptured at a tension of 142 N / mm ² and an elongation of 4
• c) From the polymer film 2a, the soluble Polyazolanteil was determined according to the solubility test described above. The weight difference was 1%.

Example 3

Dependence of the cross-linking on the cross-linking temperature

12.0 g of polybenzimidazole according to Example 1a were dissolved in 88.0 g of N, N-, dimethylacetamide (DMAc) in a pressure reactor (Buchi Miniclave, 200 ml) with stirring at a temperature of 200 ° C. After filtration and 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). After drying (10 min at 80 ° C, 10 min at 100 ° C and 30 min at 150 ° C), the film was separated from the carrier film. Subsequently, the film thus prepared was heated in a circulating air dryer for 480 min at 200 ° C in air. This example is repeated with the modification that the film produced in each case is heated in a circulating air dryer for 480 min at the temperatures shown in Table 1 in air. Table 1: Temperature in ° C Duration in min Soluble polyazole content in% by weight (solubility test) 200 480 10.0 250 480 17 300 480 1 315 480 1

Example 4

12.0 g of polybenzimidazole according to Example 1a were dissolved in 88.0 g of N, N-dimethylacetamide (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 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). After drying (10 min at 80 ° C, 10 min at 100 ° C and 30 min at 150 ° C), the film was separated from the carrier film. Subsequently, the thus prepared Film in a convection oven at 300 ° C for a period of 30 minutes in air. This example is repeated with the modification that the film produced in each case in a convection oven at 300 ° C for the time specified in Table 2 is heated in air. Table 2: Temperature in ° C Duration in min Soluble polyazole content in% by weight (solubility test) 300 30 48 300 60 24 300 120 5 300 240 1

Comparative Example 1

The procedure described in Example 2aa is repeated with the modification that the last step is carried out for 300 min at 300 ° C in an argon atmosphere instead of air. The argon-heated film almost completely dissolved. Its soluble Polyazolanteil according to the solubility test described above was 79 wt .-%.

Example 5

Dependence of Crosslinking on the End Groups of the Polymer The procedure described in Example 2aa is repeated except that the last step is performed for 360 min at 300 ° C in air (film 5a).

The procedure described in Example 2ab is repeated with the modification that the last step is performed for 360 min at 300 ° C in air (film 5b).

The soluble content according to the above-described solubility test of the polymer film 5a with the amine-terminated polymer of Example 1a was less than 1%, the soluble content of the polymer film 5b with the carboxy-terminated polymer of Example 1b was 4%.

Example 6

Doping a membrane with phosphoric acid

• a) From a piece (6 × 6 cm ² ) of the film 2a produced in Example 2, the weight and the thickness were determined. Subsequently, the film piece was placed in a Petri dish, covered with 85 wt.% Phosphoric acid in water in the Petri dish 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 six times his weight. The degree of doping (mass increase based on the weight of the swollen membrane) was 86% by weight.
• b) A piece (2.0 x 10 mm ² ) of the swollen membrane prepared above under a) was placed in a 4-point conductivity cell (available under the designation "Type BT110" from BekkTech LLC, USA) and embedded in heated to 150 ° C in a convection oven. The membrane impedance was determined by means of an impedance analyzer (available under the name "Model IM6ex" from Zahner-Elektrik, Germany). The sample geometry (thickness, area) gives a membrane conductivity of 5 S / m at 150 ° C.

Example 7

Producing a membrane electrode assembly

The 6 × 6 cm ² piece of phosphorus acid swollen membrane from Example 6 was between two commercially available gas diffusion electrodes, each with 3.0 mg / cm ² platinum loading (Johnson Matthey, type 3mg Pt Blk, no electrolyte, on Toray TGP-H-120, UK) that the platinum Catalyst layers touched the membrane. This membrane-electrode sandwich was pressed 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 8

Fuel cell test of the membrane-electrode assembly

The membrane-electrode unit from Example 7 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. 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. At a current of 0.5 A / cm ² , a cell voltage of 0.511 mV was measured. Under the specified test conditions, the MEA exhibited an impedance of 4.4 mΩ over an area of 25 cm ² at a measuring frequency of 7.8 kHz.

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 4020142 A [0002, 0006]
• EP 1165670 B [0002, 0005]
• US 6946015 BB [0003]
• EP 787369A [0005]
• EP 1373379 B [0006, 0006]
• EP 1425336 B [0006]
• WO 05076401 A [0006]

Cited non-patent literature

• H. Vogel and CS Marvel in "Polybenzimidazoles, new thermally stable polymers", Journal of Polymer Science 50 (154) p. 511-539 (1961) [0006]
• H. Vogel, CS Marvel "Polybenzimidazoles, new thermally stable polymers", Journal of Polymer Science 50 (154) p. 511-539 (1961) [0012]
• H. Vogel, CS Marvel "Polybenzimidazoles, new thermally stable polymers", Journal of Polymer Science 50 (154) p. 511-539 (1961) [0015]
• ISO 3105 [0091]

Claims (10)

Polymer films based on polyazoles, which are soluble in N, N-dimethylacetamide 0 to 20 wt .-% in terms of their Polyazolgehalt at 130 ° C and 1000 hPa, which can be prepared by that in a first step a mixture containing polyazole (A), polar aprotic solvent (B) and optionally further substances (C) 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 heated in the presence of oxygen to a temperature in the range of 200 to 500 ° C. Polymer films according to claim 1, characterized in that they are soluble in N, N-dimethylacetamide 0 to 5 wt .-% in terms of their Polyazolgehalt at 130 ° C and 1000 hPa. Polymer films according to claim 1 or 2, characterized in that the polyazoles (A) are polybenzimidazoles. Polymer films according to one or more of claims 1 to 3, characterized in that solvent (B) is N, N-dimethylacetamide. Process for the preparation of polymer films based on polyazoles, characterized in that in a first step a mixture containing polyazole (A), polar aprotic solvent (B) and optionally further substances (C) 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 heated in the presence of oxygen to a temperature in the range of 200 to 500 ° C. Polymer electrolyte membrane based on polyazoles, which are soluble in terms of their Polyazolgehalt at 130 ° C and 1000 hPa in N, N-dimethylacetamide 0 to 20 wt .-%, which can be prepared by containing a mixture in a first step Polyazole (A), polar aprotic solvent (B) and optionally other substances (C) 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, in a fourth step, the polymer film obtained in the third step is heated in the presence of oxygen to above 200 to 500 ° C and doped in a fifth step of the polymer film obtained in the fourth step with a strong acid becomes. Process for the preparation of polymer electrolyte membranes based on polyazoles, characterized in that in a first step a mixture containing polyazole (A), polar aprotic solvent (B) and optionally further substances (C) 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, in a fourth step the polymer film obtained in the third step is heated in the presence of oxygen to a temperature in the range of 200 to 500 ° C, and in a fifth step the polymer film obtained in the fourth step is doped with a strong acid. Use of the polymer electrolyte membranes according to claim 6 or produced according to claim 7 for the production of membrane electrode assemblies for fuel cells. Membrane-electrode assembly containing at least one electrode and at least one polymer film according to claim 6 or produced according to claim 7. Use of the polymer films according to one or more of claims 1 to 4 or prepared by the process according to claim 5 as a semipermeable membrane for the separation of liquids and gases.

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