WO2011003539A1

WO2011003539A1 - Method for stabilizing nitrogen-containing polymers

Info

Publication number: WO2011003539A1
Application number: PCT/EP2010/003973
Authority: WO
Inventors: Silvia Rybka-Krafft; Jörg BELACK
Original assignee: Basf Se
Priority date: 2009-07-09
Filing date: 2010-07-01
Publication date: 2011-01-13

Abstract

The invention relates to a method for stabilizing polyazole polymers, comprising the following steps: a) producing a film comprising polyazoles having at least one amino group in a repeat unit, b) treating the film from step a) with a solution comprising (i) at least one strong acid and (ii) at least one stabilizing reagent, in particular at least one bridging and/or cross-linking reagent, wherein the total content of stabilizing reagent in the solution ranges from 0.01 to 30 wt.-%, c) carrying out the stabilizing reaction in the membrane obtained according to step b), d) additionally optionally doping of the membrane obtained according to step c) using a strong acid or concentration of the strong acid that is present by withdrawing water that is present. The polyazole-polymer membranes obtained in this way are characterized in particular by high conductivity and very good stability. They are therefore particularly suitable for use in fuel cells.

Description

Process for the stabilization of nitrogen-containing polymers

The present invention relates to a method for the stabilization of

nitrogenous polymers by reaction with suitable reagents, in particular by bridging and / or crosslinking, and the use of such stabilized materials in polymer electrolyte membranes (PEM), membrane

Electrode units and PEM fuel cells.

Polymer electrolyte membranes (PEM) are already known and will

especially used in fuel cells. Sulfonic acid-modified polymers, in particular perfluorinated polymers, are frequently used here.

A prominent example of this is Nafion ™ by DuPont de Nemours, Willmington USA. For the proton conduction is a relatively high water content in the membrane

which is typically 4 to 20 molecules of water per sulfonic acid group. The necessary water content, but also the stability of the polymer in

Compound with acidic water and the reaction gases hydrogen and

Oxygen, the operating temperature of the PEM fuel cell stacks usually limited to 80 - 100 ⁰ C. Under pressure, the operating temperatures can be increased to> 120 ° C. Otherwise, higher operating temperatures can not be realized without a power loss of the fuel cell.

For technical reasons, however, higher operating temperatures than

100 ⁰ C desirable in the fuel cell. The activity of the noble metal based catalysts contained in the membrane electrode assembly (MEU) is significantly better at high operating temperatures. In particular, at the

Use of so-called reformates from hydrocarbons significant amounts of carbon monoxide contained in the reformer gas, which usually must be removed by a complex gas treatment or gas cleaning. At high operating temperatures, the tolerance of the catalysts to the CO impurities increases to several vol .-% CO.

Furthermore, heat is generated during the operation of fuel cells. However, cooling of these systems to below 80 ⁰ C can be very expensive. Depending on

Power output, the cooling devices can be made much simpler. This means that in fuel cell systems that are operated at temperatures above 100 ^° C, the waste heat can be made significantly more usable and thus the fuel cell system efficiency can be increased through electricity-heat coupling. In order to reach these temperatures, membranes with new conductivity mechanisms are generally used. One approach for this is the use of membranes, which show an electrical conductivity without the use of water. A first development in this direction is shown for example in WO 96/13872. Thus, WO 96/13872 discloses the use of acid-doped

Polybenzimidazole membranes produced by a casting process.

A new generation of acidic polyazole membranes, which also exhibit electrical conductivity without the use of water, is described in WO 02/088219. The acidic polyazole membranes disclosed in WO 02/088219 already show a favorable property profile.

However, due to the applications targeted for PEM fuel cells, the mechanical properties of the acidic polyazole membranes must always be improved. Thus, such membranes are still relatively soft and therefore only limited mechanical load, the mechanical stability decreases with increasing temperature, which can lead to durability problems already in the upper part of the typical operating window (about 160 ° C-180 ° C). It is therefore desirable to improve the mechanical properties, in particular the

Membrane stability with high conductivity.

The mechanical stabilization, for example by bridging or

Vernetzungsreationen, is already well known in polymer technology.

The problem here, however, is that even if a polymer per se has a sufficient mechanical strength, it may happen that the mechanical strength of the polymer by impregnation / doping with a strong acid - for the purpose of conferring proton conductivity - decreases to an insufficient degree.

First approaches to improve the stability of acidic polyazole membranes can be found in WO 00/44816 and WO 02/070592. In this case, first solutions of the polyazole polymers are prepared in an aprotic, polar, organic solvent and the solution with a

Provide bridging reagent. After formation of a film, the organic solvent is removed and the bridging reaction is carried out. Subsequently, the film is doped with a strong acid and used. The obtained

Polyazole membranes show improved physical and chemical

Resistance, which manifests itself, for example, in mechanical strength and improved dissolving behavior in strong acids. However, it has been found that, with the aid of the methods known hitherto, bridging or crosslinking of polyazole polymers is possible, but new limits arise through the use of aprotic, polar, organic solvents. In particular, high molecular weight polyazole polymers are only partially soluble in the abovementioned organic solvent or

insoluble.

It is an object of the present invention to provide better possibilities for stabilization, in particular for mechanical stabilization, of

proton-conducting, acidic polyazole membranes based on polyazole polymers show. In addition, the good property profiles of acidic polyazole membranes, in particular with regard to conductivity, to be maintained or even improved. Furthermore, the membranes should be relatively inexpensive to produce in a relatively simple manner.

These and other objects, which emerge directly from the contexts discussed above, are solved by a method having all the features of present claim 1. The dependent subclaims describe particularly expedient variants of the method. Furthermore, the membranes and membrane-electrode assemblies obtainable by the process and their use in fuel cells are protected.

The present invention is a process for the stabilization, in particular for bridging and / or crosslinking, of polyazole polymers, comprising the following steps:

a) Preparation of a film comprising polyazoles having at least one

Amino group in a repeat unit,

b) treating the film of step a) with a solution comprising (i)

at least one strong acid and (ii) at least one stabilizing reagent, wherein the total content of stabilizing reagents in the solution is in the range 0.01 to 30% by weight, preferably 0.01 to 15% by weight, c ) Carrying out the stabilization reaction in the membrane obtained according to step b) directly or in a subsequent processing step of

Membrane in the PEM fuel cell, such. B. a membrane-electrode unit,

d) if appropriate, additional doping of the membrane obtained according to step c) with a strong acid or concentration of the strong acid present by removal of water present. With the help of the above method are first acidic and

proton-conducting polyazole membranes based on stabilized, in particular bridged and / or crosslinked, high molecular weight polyazole polymers accessible. The hitherto known high molecular weight polyazole polymers were either unstabilized or bridged and / or crosslinked; the previously known stabilized, or bridged and / or crosslinked, polyazole polymers do not comprise high molecular weight polyazole polymers.

Furthermore, acidic, proton-conducting, high-molecular-weight polyazole polymers are available with the aid of the above method for the first time

have improved modulus of elasticity and improved elongation at break. Both

Properties are particularly important for use as a polymer electrolyte membrane for fuel cells of great importance.

In addition, the conductivities of the membranes of the invention are extremely high. The stabilization of the membrane according to the invention in solution leads

in particular to a higher conductivity than the stabilization of the same membrane under air or gas atmosphere.

Finally, the method according to the invention can be carried out in a comparatively simple manner on an industrial scale and cost-effectively.

Film comprising polyazoles

For the purposes of the present invention, polyazoles are understood as meaning those polymers in which the repeating unit in the polymer is preferably

contains at least one aromatic ring having at least one nitrogen atom. The aromatic ring is preferably a five- or six-membered ring having one to three nitrogen atoms which may be fused to another ring, especially another aromatic ring. Individual nitrogen heteroatoms can also be replaced by oxygen, phosphorus and / or sulfur atoms. The heterocyclic aromatic rings are preferably present in the polymer backbone but may be present in the side chain. Particular preference is given to those basic polymers which comprise in the repeat unit unsaturated five-membered or six-membered aromatic units containing in the nucleus 1-5 nitrogen atoms or in addition to nitrogen atoms one or more other heteroatoms.

The polyazoles according to the invention have at least one amino group in a repeat unit. In this case, the amino group as the primary amino group (NH ₂ group), as a secondary amino group (NH group) or as a tertiary group, which are either part of a cyclic, optionally aromatic structure or part of a substituent on the aromatic unit.

Due to the amino group in the repeating unit, the polymer is basic and the repeating unit may preferably be substituted by the amino group

Stabilizing react. With regard to the reactivity towards the stabilizing reagent, the amino group in the

Repeating unit preferably a primary or secondary amino group, more preferably a cyclic secondary amino group, the

suitably belongs to the core of the azole repeating unit.

The production of a film or a film comprising polyazoles is already known. The preparation takes place - for example as in WO 2004/024797

described - and includes the steps:

A) mixing one or more aromatic tetra-amino compounds with one or more aromatic carboxylic acids or their esters containing at least two acid groups per carboxylic acid monomer, or mixing one or more aromatic and / or heteroaromatic Diaminocarbonsäuren, in polyphosphoric under Formation of a solution and / or dispersion

B) applying a layer using the mixture according to step A) on a support,

C) heating of the sheet / layer obtainable according to step B) under inert gas to temperatures of up to 350 ⁰ C, preferably up to 280 ⁰ C to form the polyazole polymer,

D) hydrolysis of the polymer film formed in step C) (until it is self-supporting),

E) detaching the polymer film formed in step D) from the carrier,

F) removing the existing polyphosphoric acid or phosphoric acid and

Drying.

The aromatic and heteroaromatic tetra-amino compounds used according to the invention are preferably 3,3 ', 4,4'-tetraaminobiphenyl, 2,3,5,6-tetraaminopyridine, 1, 2,4,5-tetraaminobenzene, 3 , 3 ', 4,4'-tetraaminodiphenylsulfone, 3,3', 4,4'-tetraaminodiphenyl ether, 3,3 ', 4,4'-tetraaminobenzophenone, 3,3', 4,4'-tetraaminodiphenylmethane and 3,3 ', 4,4'- Tetraaminodiphenyldimethylmethan and salts thereof, in particular their mono-, di-, tri- and tetrahydrochloride derivatives. The aromatic carboxylic acids used according to the invention are dicarboxylic acids and tricarboxylic acids and tetracarboxylic acids or their esters or their anhydrides or their acid chlorides. The term aromatic

Carboxylic acids equally includes heteroaromatic carboxylic acids.

Preferably, the aromatic dicarboxylic acids are um

Isophthalic acid, terephthalic acid, phthalic acid, 5-hydroxyisophthalic acid, 4-hydroxyisophthalic acid, 2-hydroxyterephthalic acid, 5-aminoisophthalic acid, 5-N ₁ N-dimethylaminoisophthalic acid, 5-N, N-diethylaminoisophthalic acid, 2,5-dihydroxyterephthalic acid, 2,6-dihydroxyisophthalic acid, 4,6-dihydroxyisophthalic acid, 2,3-dihydroxyphthalic acid, 2,4-dihydroxyphthalic acid. 3,4-dihydroxyphthalic acid, 3-fluorophthalic acid, 5-fluoroisophthalic acid, 2-fluoroterephthalic acid, tetrafluorophthalic acid, tetrafluoroisophthalic acid,

Tetrafluoroterephthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, diphenic acid, 1,8-dihydroxynaphthalene-3,6-dicarboxylic acid, diphenyl ether-4,4'-dicarboxylic acid, benzophenone 4,4'-dicarboxylic acid, diphenylsulfone-4,4'-dicarboxylic acid, biphenyl-4,4'-dicarboxylic acid, 4-trifluoromethylphthalic acid, 2,2-bis (4-carboxyphenyl) hexafluoropropane, 4,4'-stilbenedicarboxylic acid, 4 - Carboxycinnamic acid, or their C1 -C20-alkyl esters or C5-C12-aryl esters, or their acid anhydrides or their acid chlorides. The aromatic tri-, tetracarboxylic acids or their C 1 -C 20 -alkyl esters or C 5 -C 12 -aryl esters or their acid anhydrides or their acid chlorides are preferably 1, 3,5-benzenetricarboxylic acid (trimesic acid), 1, 2,4-benzenetricarboxylic acid (trimellitic acid), (2-carboxyphenyl) iminodiacetic acid, 3,5,3'-biphenyltricarboxylic acid, 3,5,4'-biphenyltricarboxylic acid.

The aromatic tetracarboxylic acids or their C 1 -C 20 -alkyl esters or C 5 -C 12 -aryl esters or their acid anhydrides or their acid chlorides are preferably 3,5,3 ', 5'-biphenyltetracarboxylic acid (3,5,3 ', 5'-biphenyltetracarboxylic acid), 1, 2,4,5-benzenetetracarboxylic acid, benzophenonetetracarboxylic acid, 3,3', 4,4'-biphenyltetracarboxylic acid, 2,2 ', 3,3'-biphenyltetracarboxylic acid, 1, 2.5 , 6-Naphthalenetetracarboxylic acid, 1, 4,5,8-naphthalenetetracarboxylic acid.

The heteroaromatic carboxylic acids used according to the invention are heteroaromatic dicarboxylic acids and tricarboxylic acids and

Tetracarboxylic acids or their esters or their anhydrides. Heteroaromatic carboxylic acids are aromatic systems which contain at least one nitrogen, oxygen, sulfur or phosphorus atom in the aromatic.

Preferably it is pyridine-2,5-dicarboxylic acid, pyridine-3,5- dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5-pyridinedicarboxylic acid, 3,5-pyrazoldicarboxylic acid, 2,6-pyrimidinedicarboxylic acid, 2,5-pyrazinedicarboxylic acid, 2,4, 6-pyridine tricarboxylic acid, benzimidazole-5,6-dicarboxylic acid and their C1-C20-alkyl esters or C5-C12 aryl esters, or their

Acid anhydrides or their acid chlorides.

The content of tricarboxylic acid or tetracarboxylic acid (based on the dicarboxylic acid used) is between 0 and 30 mol%, preferably 0.1 and 20 mol%, in particular 0.5 and 10 mol%.

The aromatic and heteroaromatic diaminocarboxylic acids used according to the invention are preferably diaminobenzoic acid and its mono- and dihydrochloride derivatives.

In step A), mixtures of at least 2 different aromatic carboxylic acids are preferably used. Particular preference is given to using mixtures which, in addition to aromatic carboxylic acids, are also heteroaromatic

Contain carboxylic acids. The mixing ratio of aromatic carboxylic acids to heteroaromatic carboxylic acids is between 1:99 and 99: 1, preferably 1:50 to 50: 1.

These mixtures are, in particular, mixtures of N-heteroaromatic dicarboxylic acids and aromatic dicarboxylic acids. Non-limiting examples thereof are isophthalic acid, terephthalic acid, phthalic acid, 2,5-dihydroxyterephthalic acid, 2,6-dihydroxyisophthalic acid, 4,6-dihydroxyisophthalic acid, 2,3-dihydroxyphthalic acid, 2,4-dihydroxyphthalic acid, 3,4-dihydroxyphthalic acid, 1,4 Naphthalenedicarboxylic acid, 1, 5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, diphenic acid, 1,8-dihydroxynaphthalene-3,6-dicarboxylic acid, diphenyl ether-4,4'-dicarboxylic acid,

Benzophenone-4,4'-dicarboxylic acid, diphenylsulfone-4,4'-dicarboxylic acid, biphenyl-4,4'-dicarboxylic acid, 4-trifluoromethylphthalic acid, pyridine-2,5-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, pyridine-2 , 6-dicarboxylic acid, pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5-pyridinedicarboxylic acid, 3,5-pyrazoldicarboxylic acid, 2,6-pyrimidinedicarboxylic acid, 2,5-pyrazinedicarboxylic acid.

The polyphosphoric acid used in step A) is

Commercially available polyphosphoric acids such as these are available, for example, from Riedel-de Haen. The polyphosphoric acids H _{n + 2} P _n O ₃ n ₊ i (n> 1) usually have a content calculated as P ₂ O ₅ (acidimetric) of at least 83%. Instead of a solution of the monomers, it is also possible to produce a dispersion / suspension. The mixture produced in step A) has a weight ratio of polyphosphoric acid to sum of all monomers of 1: 10,000 to 10,000: 1, preferably 1: 1000 to 1000: 1, in particular 1: 100 to 100: 1, on.

The layer formation according to step B) takes place by means of measures known per se (casting, spraying, doctoring) which are known from the prior art for polymer film production. Suitable carriers are all suitable carriers under the conditions as inert. In addition to these inert supports, however, other supports, such as polymeric films, fabrics and fleeces, which bond to the layer formed in step B) and form a laminate are also suitable. To adjust the viscosity, the solution may optionally be treated with phosphoric acid (concentrated phosphoric acid, 85%). This allows the viscosity to be adjusted to the desired value and the formation of the membrane can be facilitated.

The layer produced according to step B) has a thickness which is matched to the subsequent use and is not subject to any restriction. Usually, the layer formed has a thickness between 1 and 5000 μm, preferably between 1 and 3500 μm, in particular between 1 and 100 μm.

The polyazole-based polymer formed in step C) contains recurring azole units of the general formula (I) and / or (II) and / or (III) and / or (IV) and / or (V) and / or (VI) and / or (VII) and / or (VIII) and / or (IX) and / or (X) and / or (XI) and / or (XII) and / or (XIII) and / or (XIV)

wherein

Ar are the same or different and represent a tetravalent aromatic or heteroaromatic group which may be mononuclear or polynuclear,

Ar ^{1 are the} same or different and represent a divalent aromatic or heteroaromatic group which may be mononuclear or polynuclear,

Ar ^{2 are the} same or different and, for a two- or three-membered aromatic or heteroaromatic group which may be mononuclear or polynuclear, Ar ^{3 are the} same or different and are a trivalent aromatic or heteroaromatic group which may be mononuclear or polynuclear,

Ar ^{4 are the} same or different and represent a trivalent aromatic or heteroaromatic group which may be mononuclear or polynuclear, Ar ^{5 are the} same or different and represent a tetravalent aromatic or heteroaromatic group which may be mononuclear or polynuclear,

Ar ^{6 are the} same or different and are for a divalent aromatic or

heteroaromatic group, which may be mononuclear or polynuclear,

Ar ^{7 are the} same or different and are for a divalent aromatic or

heteroaromatic group, which may be mononuclear or polynuclear,

Ar ^{8 are the} same or different and for a trivalent aromatic or

heteroaromatic group, which may be mononuclear or polynuclear,

Ar ^{9 are the} same or different and are a two- or three- or vierbindige

aromatic or heteroaromatic group which may be mononuclear or polynuclear,

Ar ^{10 are the} same or different and represent a divalent or trivalent aromatic or heteroaromatic group which may be mononuclear or polynuclear,

Ar ^{11 are the} same or different and are for a divalent aromatic or

heteroaromatic group, which may be mononuclear or polynuclear,

X is the same or different and is oxygen, sulfur or a

Amino group which represents a hydrogen atom, a 1-20 carbon atoms group, preferably a branched or unbranched

Carries alkyl or alkoxy group, or an aryl group as a further radical,

R is the same or different for hydrogen, an alkyl group and a

aromatic group is and

n, m are each an integer greater than or equal to 10, preferably greater than or equal to 100.

Preferred aromatic or heteroaromatic groups are derived from benzene, naphthalene, biphenyl, diphenyl ether, diphenylmethane, diphenyldimethylmethane, bisphenone, diphenylsulfone, quinoline, pyridine, bipyridine, pyridazine, pyrimidine, pyrazine, triazine, tetrazine, pyrol, pyrazole, anthracene, benzopyrrole, benzotriazole,

Benzooxathiadiazole, benzooxadiazole, benzopyridine, benzopyrazine,

Benzopyrazidine, benzopyrimidine, benzopyrazine, benzothazine, indolizine, quinolizine, pyridopyridine, imidazopyrimidine, pyrazinopyrimidine, carbazole, aciridine, phenazine, benzoquinoline, phenoxazine, phenothiazine, acridizine, benzophthyne, phenanthroline and phenanthrene, which may optionally be substituted from.

Here, the substitution pattern of Ar ¹ , Ar ⁴ , Ar ⁶ , Ar ⁷ , Ar ⁸ , Ar ⁹ , Ar ¹⁰ , Ar ^{11 is} arbitrary, in the case of phenylene, for example, Ar ¹ , Ar ⁴ , Ar ⁶ , Ar ⁷ , Ar ⁸ , Ar ⁹ , Ar ¹⁰ , Ar ^{11 are} ortho, meta and para-phenylene. Particularly preferred groups are derived from benzene and biphenylene, which may optionally also be substituted. Preferred alkyl groups are short chain alkyl groups of 1 to 4

Carbon atoms, such as. For example, methyl, ethyl, n- or i-propyl and t-butyl groups.

Preferred aromatic groups are phenyl or naphthyl groups. The

Alkyl groups and the aromatic groups may be substituted.

Preferred substituents are halogen atoms such as. As fluorine, amino groups, hydroxy groups or short-chain alkyl groups such as. For example, methyl or ethyl groups.

Preference is given to polyazoles having repeating units of the formula (I) in which the radicals X within a repeating unit are identical.

The polyazoles can in principle also have different recurring

Have units that differ, for example, in their remainder X.

Preferably, however, it has only the same X radicals in a repeating unit.

Other preferred polyazole polymers are polyimidazoles, polybenzothiazoles, polybenzoxazoles, polyoxadiazoles, polyquinoxalines, polythiadiazoles, poly (pyridines), poly (pyrimidines), and poly (tetrazapyrenes).

In a further embodiment of the present invention, the polymer containing recurring azole units is a copolymer or a blend containing at least two units of the formulas (I) to (XIV) which differ from each other. The polymers can be present as block copolymers (diblock, triblock), random copolymers, periodic copolymers and / or alternating polymers.

In a particularly preferred embodiment of the present invention, the polymer containing recurring azole units is a polyazole which contains only units of the formula (I) and / or (II).

The number of repeating azole units in the polymer is preferably an integer greater than or equal to 10. Particularly preferred polymers contain at least 100 recurring azole units.

In the context of the present invention, polymers containing recurring benzimidazole units are preferred. Some examples of the extremely expedient Polymers contain recurring benzimidazole units and are represented by the following formulas:

In the last formula, the azole units and the two fluorinated moieties can be linked in any order. The preparation can be carried out as a polymer, static copolymer or block copolymer.

Furthermore, in the above formulas, n and m, each independently, are an integer greater than or equal to 10, preferably greater than or equal to 100.

The procedure according to the invention is suitable in principle for all polyazoles, irrespective of the molecular weight. However, it has proven particularly useful for the stabilization of high molecular weight polyazoles, which is not obtainable in any other way. High molecular weight polyazoles, but especially polybenzimidazoles, are characterized by a high molecular weight, which, measured as

Intrinsic viscosity, at least 1.8 dl / g, preferably at least 2.0 dl / g,

particularly preferably at least 2.5 dl / g. The upper limit is preferably not more than 8.0 dl / g, more preferably not more than 6.8 dl / g, particularly preferably not more than 6.5 dl / g. The molecular weight is thus significantly higher than that of commercial polybenzimidazole (IV <1, 1 dl / g).

The determination of the intrinsic viscosity is carried out as described below: For this purpose, the polymer is first dried at 160 ^° C. for ² hours. 100 mg of the polymer thus dried are then heated for ⁴ h at 80 ⁰ C in 100 ml of

concentrated sulfuric acid (at least 96% by weight). The inherent or

intrinsic viscosity is determined from this solution according to ISO 3105 (DIN 51562, ASTM D2515) with an Ubbelhode viscometer at a temperature of 25 ° C.

Insofar as the mixture according to step A) also tricarboxylic acids or

Containing tetracarboxylic acid, thereby a branching / crosslinking of the polymer formed along the main chain is achieved. This contributes to the improvement of the mechanical property.

In a variant of the process, by heating the mixture from step A) to temperatures of up to 350 ^° C., preferably up to 280 ^° C., the formation of oligomers and / or polymers can already be effected. Depending on the selected temperature and duration, subsequent to the heating in step C) be waived partially or completely. This variant is also suitable for producing the films required for step a), preferably comprising high molecular weight

Polyazoles, suitable.

It has also been shown that when using aromatic

Dicarboxylic acids (or heteroaromatic dicarboxylic acids) such as isophthalic acid, terephthalic acid, 2,5-dihydroxyterephthalic acid, 4,6-dihydroxyisophthalic acid, 2,6-dihydroxyisophthalic acid, diphenic acid, 1,8-dihydroxynaphthalene-3,6-dicarboxylic acid, diphenyl ether-4,4'- Dicarboxylic acid, benzophenone-4,4'-dicarboxylic acid,

Diphenylsulfone-4,4'-dicarboxylic acid, biphenyl-4,4'-dicarboxylic acid, 4-trifluoromethylphthalic acid, pyridine-2,5-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-2, 4-dicarboxylic acid, 4-phenyl-2,5-pyridinedicarboxylic acid, 3,5-pyrazoldicarboxylic acid, 2,6-pyrimidinedicarboxylic acid, 2,5-pyrazinedicarboxylic acid, the temperature in step C) - or if the formation of oligomers and / or polymers already in step A) is desired - in the range of up to 300 ⁰ C, preferably between 100 ⁰ C and 250 ⁰ C, is favorable.

The treatment of the polymer layer produced according to step C) to produce the film required for step b) can be carried out in several ways.

In a variant (variant A), the existing polyphosphoric acid or

Leave phosphoric acid in the membrane, as it does not interfere with further processing. In this case, the treatment of the generated according to step C)

Polymer layer takes place in the presence of moisture at temperatures and for a sufficient time until the layer has sufficient strength for the

intended use. The treatment can be carried out so far that the membrane is self-supporting, so that it can be detached from the carrier without damage (step E). The steps D) and E) can also take place simultaneously or briefly on each other. Furthermore, it is possible to combine steps D) and E) with the measures of steps b), c) and if necessary d). Thus, for example, the hydrolysis in step D) by treatment of the formed in step C)

Polymer film with the solution comprising (i) at least one strong acid and (ii) at least one stabilizing reagent, in particular at least one

Bridging and / or cross-linking reagent, wherein the total content of stabilizing reagent in the solution in the range 0.01 to 30 wt .-% and wherein the total amount of stabilizing reagents based on the film present in the polyazole preferably in Range from 0.01 to 100 mol%. The implementation of the stabilization reaction according to step c) can with a thermal drying or concentration of the existing acid can be combined.

The treatment of the polymer film in step D) is carried out at temperatures above 0 ⁰ C and below 150 ⁰ C, preferably at temperatures between 10 ⁰ C and 120 ⁰ C, in particular between room temperature (20 ⁰ C) and 90 ⁰ C, in the presence of

Moisture or water and / or water vapor and / or water-containing phosphoric acid of up to 85%. The treatment is preferably carried out under

Normal pressure, but can also be done under the action of pressure. It is essential that the treatment is carried out in the presence of sufficient moisture, whereby the present polyphosphoric acid by partial hydrolysis

Training low molecular weight polyphosphoric acid and / or phosphoric acid contributes to the solidification of the polymer film. Due to the hydrolysis step, a SoI-GeI transition takes place, which is responsible for the particular shape of the membrane.

The partial hydrolysis of the polyphosphoric acid in step D) leads to a

Solidification of the polymer film so that it becomes self-supporting and further leads to a decrease in the layer thickness.

The intra- and intermolecular structures present in the polyphosphoric acid layer according to step B) lead to an ordered one in step C)

Membrane formation, which is responsible for the good properties of the polymer film formed.

The upper temperature limit of the treatment according to step D) is generally 180 ^° C. In the case of extremely short exposure to moisture, for example extremely superheated steam, this steam may also be hotter. Essential for the

Upper temperature limit is the duration of the treatment.

The partial hydrolysis (step D) can also be carried out in climatic chambers in which the hydrolysis can be controlled in a controlled manner under defined action of moisture. Here, the moisture by the temperature or saturation of the

contacting environment such as gases such as air, nitrogen, carbon dioxide or other suitable gases, or steam can be adjusted specifically. The duration of treatment depends on the parameters selected above.

Furthermore, the treatment duration of the membrane depends on its thickness. As a rule, the treatment duration is between a few seconds to

Minutes, for example under the action of superheated steam, or up to whole days, for example in air at room temperature and low relative humidity. The treatment time is preferably between 10 seconds and 300 hours, in particular 1 minute to 200 hours.

If the partial hydrolysis is carried out at room temperature (20 ° C.) with ambient air having a relative humidity of 40-80%, the treatment duration is between 1 and 200 hours.

The polymer film obtained according to step D) is preferably self-supporting, i. it can be released from the carrier without damage according to step E) and then optionally further processed directly.

In this respect, the polymer film obtained according to step C) on the support

is further processed, for example, to a composite membrane, step D) can be waived in whole or in part.

Insofar as the polyphosphoric acid or phosphoric acid present after step C) is left in the membrane (variant A), the treatment of the film in step b) can be carried out in a hydrolysis bath analogously to step D). In this case, the polyphosphoric acid or phosphoric acid present in the membrane is completely or at least partially replaced by the solution comprising (i) at least one strong acid and (ii) at least one stabilizing reagent, in particular at least one bridging and / or cross-linking reagent. The stabilization reaction according to step c) can be carried out in the hydrolysis bath or afterwards, preferably immediately thereafter. Depending on the stability of the membrane, the treatment can be carried out in a hydrolysis bath on a carrier or else the carrier can already be removed beforehand, so that step E) can possibly be omitted or

is preferred.

This variant is also the subject of the present invention.

In a further variant (variant B), the existing polyphosphoric acid or phosphoric acid is removed from the membrane. For this purpose, the treatment of the polymer layer produced according to step C) takes place in the presence of moisture at temperatures and for a sufficient time until the layer has sufficient strength for further handling. Thus, the hydrolysis in step D) and the detachment in step E) can also take place simultaneously. This simplification of Hydrolysis is particularly possible if the existing polyphosphoric acid or phosphoric acid is to be completely removed and need not be present for the treatment in step b), since a fresh solution comprising a strong acid is fed again later in step b).

Insofar as the still contained in the polymer film polyphosphoric acid or

Phosphoric acid according to step F) to be removed, this can be done by means of a treatment liquid in the temperature range between room temperature (20 ⁰ C) and the boiling temperature of the treatment liquid (at atmospheric pressure).

As a treatment liquid in the sense of the invention and in the sense of step F) are present at room temperature [ie 20 ⁰ C] liquid present solvent selected from the group of alcohols, ketones, alkanes (aliphatic and cycloaliphatic), ethers (aliphatic and cycloaliphatic), Glycols, esters, carboxylic acids, wherein the above group members may be halogenated, water and mixtures thereof used.

Preferably, C 1 -C 10 alcohols, C 2 -C 5 ketones, C 1 -C 10 alkanes

(aliphatic and cycloaliphatic), C2-C6 ethers (aliphatic and

cycloaliphatic), C2-C5 esters, C1-C3 carboxylic acids, dichloromethane, water and mixtures thereof.

Subsequently, the introduced in step F) treatment liquid is removed again. This is done, preferably by drying, the parameters

Temperature and the ambient pressure depending on the partial vapor pressure of the treatment liquid can be selected. Usually, the drying is carried out at atmospheric pressure and temperatures between 20 ⁰ C and 200 ⁰ C. A gentler drying can also be done in vacuo. Instead of drying can also be blotted into the membrane and thus be freed of excess treatment liquid. The order is not critical.

The preparation of the film comprising polyazoles can also be carried out by varying the above method. The following steps are carried out: i) reaction of one or more aromatic tetra-amino acids

Compounds with one or more aromatic carboxylic acids or their esters which contain at least two acid groups per carboxylic acid monomer, or of one or more aromatic and / or

heteroaromatic diaminocarboxylic acids in the melt at temperatures of up to 350 ⁰ C ₁ is preferably up to 300 ⁰ C, ii) dissolving the solid prepolymer obtained in step i) in

polyphosphoric

iii) heating the solution obtainable according to step ii) under inert gas

Temperatures of up to 300 ° C, preferably up to 280 ⁰ C to form the dissolved polyazole polymer.

iv) forming a membrane using the solution of the polyazole polymer according to step iii) on a support and

v) treatment of the membrane formed in step iv) until it is self-supporting.

In addition to the above variation, formation can also be achieved by the following steps:

I) dissolving polymers, in particular polyazoles in polyphosphoric acid,

II) heating the solution obtainable according to step I) under inert gas

Temperatures of up to 400 ⁰ C,

III) forming a membrane using the solution of the polymer according to step II) on a support and

IV) treatment of the membrane formed in step III) until it is self-supporting.

In both variations, steps E) and F) are still carried out after steps v) and IV), whereby both variants A) and B) are also possible.

The preferred embodiments of the respective named raw materials and process parameters are already given in steps A), B), C) and D) and are also valid for this variant.

Film comprising polyazoles and other blend components

In addition to the above-mentioned preferably high molecular weight polyazole may also be a blend of one or more, preferably high molecular weight

Polyazoles be used with another polymer. The blend component essentially has the task of improving the mechanical properties and reducing the material costs. A preferred blend component is polyethersulfone as described in German Patent Application No. 10052242.4.

Among the preferred polymers which can be used as a blend component include polyolefins such as poly (chloroprene), polyacetylene, polyphenylene, poly (p-xylylene), polyarylmethylene, polyarmethylene, polystyrene, polymethylstyrene, polyvinyl alcohol, polyvinyl acetate, polyvinyl ether, polyvinylamine, Poly (N-vinylacetamide), polyvinylimidazole, polyvinylcarbazole, polyvinylpyrrolidone, Polyvinylpyridine, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene,

Polyhexafluoropropylene, copolymers of PTFE with hexafluoropropylene, with

Perfluoropropyl vinyl ether, with trifluoronitrosomethane, with sulfonyl fluoride vinyl ether, with

Carbalkoxy perfluoroalkoxy vinyl ether, polychlorotrifluoroethylene, polyvinyl fluoride,

Polyvinylidene fluoride, polyacrolein, polyacrylamide, polyacrylonitrile, polycyanoacrylates,

Polymethacrylimide, cycloolefinic copolymers, in particular from norbornene;

Polymers with C-O bonds in the main chain, for example

Polyacetal, polyoxymethylene, polyether, polypropylene oxide, polyepichlorohydrin,

Polytetrahydrofuran, polyphenylene oxide, polyether ketone, polyester, in particular

Polyhydroxyacetic acid, polyethylene terephthalate, polybutylene terephthalate,

Polyhydroxybenzoate, polyhydroxypropionic acid, polypivalolactone, polycaprolactone,

Polymalonic acid, polycarbonate;

Polymers with C-S bonds in the main chain, for example polysulfide ethers,

Polyphenylene sulfide, polyethersulfone;

Polymers with C-N bonds in the main chain, for example

Polyimines, polyisocyanides, polyetherimine, polyaniline, polyamides, polyhydrazides,

Polyurethanes, polyimides, polyazoles, polyazines;

Liquid crystalline polymers, especially Vectra and

Inorganic polymers, for example polysilanes, polycarbosilanes, polysiloxanes,

Polysilicic acid, polysilicates, silicones, polyphosphazenes and polythiazyl.

For use in fuel cells having a continuous use temperature above 100 ^° C., preference is given to those blend polymers which have a glass transition temperature or Vicat softening temperature VST / A / 50 of at least 100 ^° C., preferably at least 150 ^° C. and very particularly preferably at least 180 ^° C. , Here are polysulfones having a Vicat softening temperature VST / A / 50 of 180 ⁰ C to 230 ⁰ C are preferred.

Preferred polymers include polysulfones, especially polysulfone having aromatics in the backbone. According to a particular aspect of the present invention, preferred polysulfones and polyethersulfones

a melt volume rate MVR 300/21, 6 is less than or equal to 40 cm ^3/10 min, especially less than or equal to 30 cm ^3/10 min and particularly preferably less than or equal to 20 cm ^3/10 min measured in accordance with ISO 1133rd

Film comprising polyazoles and other additives (additives)

To further improve the later performance characteristics of the preferably high molecular weight polyazole film or the acidic Polyazole membrane even more fillers, especially proton-conductive fillers are added.

Non-limiting examples of proton-conductive fillers are

Sulfates such as: CsHSO ₄ , Fe (SO ₄ ) ₂ , (NH ₄ ) ₃ H (SO ₄ ) 2, LiHSO ₄ , NaHSO ₄ , KHSO ₄ ,

RbSO ₄ , LiN ₂ H ₅ SO ₄ , NH ₄ HSO ₄ ,

Phosphates such as Zr ₃ (PO ₄ ) ₄ , Zr (HPO ₄ ) ₂ , HZr ₂ (PO ₄ ) ₃ , UO ₂ PO ₄ .3H ₂ O, H ₈ UO ₂ PO ₄ ,

Ce (HPO ₄ ) ₂ , Ti (HPO ₄ ) ₂ , KH ₂ PO ₄ , NaH ₂ PO ₄ , LiH ₂ PO ₄ , NH ₄ H ₂ PO ₄ , CsH ₂ PO ₄ , CaHPO ₄ , MgHPO ₄ , HSbP ₂ O ₈ , HSb ₃ P ₂ Oi ₄ , H ₅ Sb ₅ P ₂ O ₂₀ ,

Polyacid such as H ₃ PW ₁₂ O ₄₀ .n H ₂ O (n = 21-29), H ₃ SiW ₁₂ O ₄₀ .nH ₂ O (n = 21-29), H _x WO ₃ ,

HSbWO ₆ , H ₃ PMo ₁₂ O ₄₀ , H ₂ Sb ₄ O ₁₁ , HTaWO ₆ , HNbO ₃ , HTiNbO ₅ , HTiTaO ₅ , HSbTeO ₆ , H ₅ Ti ₄ O ₉ , HSbO ₃ , H ₂ MoO ₄

Selenites and arsenides such as (NH ₄ ) ₃ H (SeO ₄ ) ₂ , UO ₂ AsO ₄ , (NH ₄ ) ₃ H (SeO ₄ ) ₂ , KH ₂ AsO ₄ ,

Cs ₃ H (SeO ₄ ) ₂ , Rb ₃ H (SeO ₄ ) ₂ ,

Phosphides such as ZrP, TiP, HfP

Oxides such as Al ₂ O ₃ , Sb ₂ O ₅ , ThO ₂ , SnO ₂ , ZrO ₂ , MoO ₃

Silicates such as zeolites, zeolites (NH ₄ +), phyllosilicates, framework silicates, H-natrolites,

H-mordenites, NH ₄ -alcines, NH ₄ -sodalites, NH ₄ -gallates, H-montmorillonites, other condensation products of orthosilicic acid Si (OH) ₄ and their salts and esters, polysiloxanes of the general formula H ₃ Si (O-) SiH ₂ -) _n -O-SiH ₃ , especially others

Clay minerals, such as montmorillonites, bertonites, kaolinites, pyrophillites, talc, chlorites, muscovites, mica, smectites, halosites,

Vermiculites and hydrotalcites.

Acids such as HCIO ₄ , SbF ₅

Fillers such as carbides, in particular SiC, Si3N4, fibers, in particular

Glass fibers, glass powders and / or polymer fibers, fleece or fabric, preferably based on polyazoles and / or polyaryletherketones or polyarylethersulfones, also partially crosslinked. The fillers may also be partially or completely modified, based on the aromatic fraction, by charged groups, in which connection sulphonic acid groups,

Phosphonic acid groups, phosphate groups or other anionic or cationic charged groups are particularly suitable.

These additives can be used in the proton-conducting polymer membrane in conventional

However, the positive properties, such as high

Conductivity, long life and high mechanical stability of the membrane are not affected too much by the addition of too large amounts of additives should be. In general, the membrane comprises at most 80% by weight, preferably at most 50% by weight and more preferably at most 20%

% By weight of additives. The additives may be present in different particle shapes and particle sizes or even mixtures, but more preferably in the form of nano-particles (particles with a size of 1 to 100 nm).

Crosslinking Solution and Reaction

The treatment of the film comprising preferably high molecular weight polyazoles with a solution comprising (i) at least one strong acid and (ii) at least one stabilizing reagent, preferably at least one bridging and / or cross-linking reagent, takes place in step b).

The stabilizing reagent used according to the invention, in particular the bridging and / or crosslinking reagents, is a compound having a functional group which reacts with the polyazole,

in particular is capable of reacting with the existing amino group of the polyazole. Insofar as the stabilizing reagent is a bridging reagent, it preferably has at least two functional groups in the molecule which are capable of reacting with the polyazole, in particular with the amino group. Furthermore, this is an organic compound.

Insofar as the stabilizing reagent is a crosslinking reagent, it preferably has at least three functional groups which are capable of reacting with the polyazole, in particular with the amino group, in the molecule. Furthermore, this is an organic compound.

As a stabilizing reagent, in particular bridging and / or

Crosslinking reagent, organic compounds used must have sufficient stability against the present in the solution strong acid. Furthermore, they must have sufficient solubility in the strong acid. The solubility must therefore be sufficient for the solution in step b) to be capable of producing a total content of stabilizing reagent, in particular a bridging and / or crosslinking reagent, in the range from 0.01 to 30% by weight, preferably 0, 1 to 25 wt .-%, preferably 0.5 to 15 wt .-%, in particular 1 to 5 wt .-%, to be contained, wherein the total amount of

Stabilizing reagents, based on the polyazole present in the film, preferably in the range of 0.01 to 100 mol%, preferably 10 to 80 mol%, in particular 15 to 65 mol%. The stabilizing reagent used according to the invention are compounds having a functional group which can react with the polyazole, in particular with the amino group of the polyazole present. The stabilizing reagent used is preferably substances which have at least one epoxide group per molecule.

The stabilizing reagents which have at least one epoxide group per molecule are preferably organic compounds of the formula (A)

Preference is furthermore given to compounds of the formula (B)

in which an aldehyde is combined with an epoxide.

In addition, bridging reagents which have at least two epoxide groups, more preferably at least 3, have proven particularly useful

Have epoxide groups, per molecule and preferably satisfy the formula (II)

In the above formulas, R ^{1 represents} a hydrocarbon group of 1 to 30 carbon atoms, preferably a straight-chain or branched one

Lower alkylene group having 1 to 30 carbon atoms, a straight-chain or branched lower alkoxy group having 1 to 30 carbon atoms or a

aromatic system having 4 to 20 carbon atoms, where the abovementioned radicals (i) may be substituted by one or more nitro groups, oxygen atoms, epoxide groups or aryl groups, (ii) in which individual, non-adjacent carbon atoms are replaced by heteroatoms, in particular nitrogen, oxygen, And (iii) in which one or more hydrogen atoms, in particular in the epoxide groups, are replaced by a halogen or an alkyl, in particular a lower alkyl, or an alkoxyl, in particular a lower alkoxy, or aryl group, preferably one

Aryl group having 4 to 20 carbon atoms, substituted or substituted. Aryl group in the context of the present invention are also understood as meaning heteroaryls having 4 to 20 carbon atoms, in particular preferred aryls being in particular phenyl, naphthyl and indenyl.

The term lower alkyl or lower alkoxy means an alkyl or alkoxy group having 1 to 15 carbon atoms.

The term aryl or heteroaryl means an aryl or heteroaryl of 4 to 20

Carbon atoms. The heteroatoms are usually from the group of

Oxygen, nitrogen and / or sulfur atoms selected.

Hydrogen atoms present in the formulas, in particular in the epoxide groups, may be replaced or substituted by a halogen or a lower alkyl group.

Examples of R ¹ are the following groups.

In the above formulas, m, k and I are the same or different and each represents an integer of 1 to 6.

Particularly preferred in the case of the monofunctional epoxide compounds of the formula (A) are:

Phenol (EO) 5 glycidyl ether (54140-67-9, Denacol EX-145) and Lauryl Alcohol

(EO) 15 glycidyl ether (86630-59-3, Denacol-EX-171).

The bridging reagents which have at least two epoxide groups per molecule are particularly preferably resorcinol diglycidyl ether (compound formula III, trade name, for example Denacol EX-201)

Further, non-limiting examples of preferred compounds containing at least two epoxide groups u. a .:

The crosslinking reagents which have at least three epoxide groups per molecule are preferably organic compounds of the formula (III)

Particularly preferred bridging reagents are bis-phenol-A-glycidyl ether [BPAGDE] and 1,4-butyl diglycidyl ether.

Further advantageous examples of epoxide components are:

The solution according to step b) according to the invention contains 0.01 to 30 wt .-% of stabilizing reagent, in particular bridging and / or crosslinking reagent, wherein the total amount of stabilizing reagents based on the polyazole present in the film preferably in the range of 0.01 to 100 mol%.

If the proportion of bridging or crosslinking agent chosen too low, the polymer membrane is not sufficiently stabilized, the proportion is too high, the membrane is brittle and the fracture toughness is insufficient.

The stabilization is preferably carried out by heating, advantageously under inert gas, to temperatures of up to 250 ^° C., preferably to temperature ranges from 100 ^° C. to 160 ^° C., conveniently for a period of 5 minutes to 120 minutes, preferably 5 minutes to 30 minutes, more preferably 10 mins. Optionally, the stabilized film at temperatures of 20 ⁰ C to 80 ⁰ C, especially preferably 60 ^° C., be postconditioned in an acidic solution for 10 minutes to 60 minutes.

The implementation of the stabilization reaction, in particular the bridging or crosslinking, according to step c) can also by irradiation with

electromagnetic waves (e.g., photochemical reaction, IP and / or UV irradiation), electrons, or thermal. In a thermal

Reaction, it is advantageous to carry out the reaction in a temperature range of 20 ⁰ C (room temperature) to 200 ⁰ C. The reaction time is from a few minutes to several hours, depending on the reactivity of the reagent. The stabilization reaction can be carried out in one or more stages.

The stabilization is described below by way of example with reference to a modification of a polybenzimidazole with a monofunctional epoxide compound and by means of a bridging with an epoxy compound of the formula (IIa) with the

Polybenzimidazole of formula (I) shown schematically.

In the above formulas, R ^{1 has} the meaning given above.

The strong acid used according to the invention are protic acids, preferably phosphoric acid and / or sulfuric acid.

In the context of the present description, "phosphoric acid" 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 Oio), metaphosphoric acid, and the like Derivatives, in particular organic derivatives, such as cyclic organo-phosphoric acids, and their derivatives, such as acid esters.

The phosphoric acid, in particular orthophosphoric acid, preferably has a concentration of at least 80 wt .-%, more preferably a concentration of at least 90 wt .-%, even more preferably a concentration of at least 95 wt .-% and most preferably a concentration of at least 98% by weight. The data refers to the effective

Concentration of the acid in the membrane or in the hydrolysis.

In the solution according to step b) other components (except acid & stabilizing reagent) may be present. For example, the additives mentioned at the outset can be added. Furthermore, additional catalysts for a stabilization reaction can be added, such as small amount of strong acids, starter reagents or activating metal ions, peroxides or other substances that react with the invention

Positively influence stabilizing reagents. For further adaptation for later use, after stabilization or bridging and / or crosslinking, an additional doping of the membrane can take place. In this case, the additives mentioned at the beginning can be added or the degree of doping can be carried out by further addition of the stated strong acids. Furthermore, the membrane existing water, for example by concentration of the strong acid present, be withdrawn.

The acidic polyazole membrane according to the invention based on stabilized, in particular bridged and / or crosslinked, preferably high molecular weight, polyazole polymers forms an acid-base complex with the acid and is therefore proton-conducting even without the presence of water. This so-called

Grotthus conductivity mechanism allows use in high-temperature fuel cells, with a continuous operating temperature of min. 120 ^° C., preferably min. 140 ⁰ C, in particular min. 160 ⁰ C. The membrane of the invention can therefore be used as an electrolyte for electrochemical cells, in particular fuel cells.

The acidic polyazole membrane according to the invention based on stabilized, in particular bridged and / or crosslinked, preferably high molecular weight, polyazole polymers is distinguished by improved mechanical properties. Thus, a membrane of the invention shows an E modulus of at least 3 MPa, suitably of at least 4 MPa, preferably of at least 5 MPa, more preferably of at least 6 MPa, desirably of

at least 7 MPa, in particular of at least 8 MPa. Furthermore, the membranes according to the invention exhibit an elongation at break of at least 85%, preferably of at least 200%.

The tensile elongation properties are determined preferably with a Zwick Z010 standard tension gauge, whereby the following procedure has proven particularly useful. The samples are first conveniently cut into 1, 5 cm wide and 12 cm long strips. It is preferable to prepare and measure 2 to 3 samples per sample and then to average the results. The thickness of the samples is preferably determined with a Mitutoyo Absolute Digmatic thickness gauge at 3 points and averaged (preferably at the beginning, middle and end of the strip). The measurement is preferably carried out as follows. Of the

Sample strip is clamped and held for 1 min at a pre-load of 0.1 N. Subsequently, the measurement is carried out automatically at a drawing speed of preferably 5 mm / min, preferably at RT, until the modulus of elasticity (MPa) has been determined (automatic procedure by means of the Zwick software TextExpert (verse 11)) 30 mm / min until the tearing of the sample strip is measured, and after completion of the measurement, the fracture toughness (kJ / m 2) and the elongation at break (%) are determined. The proton conductivity of the stabilized membranes is between 50 and 220 mS / cm at 160 ^° C., preferably at least 90-220 mS / cm, more preferably between 150 and 220 mS / cm.

The proton conductivities are measured by means of impedance spectroscopy (Zahner IM5 or IM6 spectrometer) and a 4-point measuring cell. A particularly preferred procedure is as follows.

For sample preparation, approximately 3.5 ^* 7 cm pieces are expediently cut out and the membrane samples are rolled a total of 10 times with a roller-shaped weight of 500 g to remove supernatant acid. The thickness of the samples is favorably with a Mitutoyo type "Absolute, Digmatic"

Thickness gauge determined and averaged at 3 points (beginning, middle and end of the sample strip). The sample is expediently fixed in the measuring cell, as shown in the figure (FIG. 1).

They denote:

(1): l.

(3): U ₊

(5): U-

(7): U

(9): connector

(11): Pt wire

(13): seal

(15): membrane

(17): Pt plate

The screws of the test cell are preferably tightened hand-tight and the cell is conveniently transferred to a controlled oven, which proceeds with the according to Table 1 a temperature, frequency program.

Table 1 :

The oven program is started and there are impedance spectra with a Zahner electrics impedance spectrometer IM6 with a 4-point dry cell at 20 ⁰ C to 160 ⁰ C and - conversely - from 160 ⁰ C to 20 ⁰ C, preferably in 20 ⁰ C.

Measured steps, wherein conveniently before the measurement, a holding time of 10 minutes takes place. The spectrum is stored and preferably evaluated according to the literature known methods of Bode and Niquist. The proton conductivity here is calculated according to:

I (distance of contacts) = 2 cm, b (diaphragm width) = 3.5 cm, d = membrane thickness (cm), R = measured resistance (ohm)

The acidic polyazole membranes according to the invention based on stabilized, especially bridged and / or crosslinked, preferably high molecular weight polyazole polymers are also characterized by increased stability when used as a proton-conducting membrane in high-temperature fuel cells. In the operation of such systems has been shown that, especially in phosphoric acid systems, the stability of the acidic

Polyazole membranes should be further improved. The membranes of the invention are characterized by such improved stability and are preferably insoluble in 99% phosphoric acid over the temperature range of 85 ° C to 180 ⁰ C. Insoluble in this context means that in an excess of the present acid, the swelling does not exceed 300% and no dissolution of the self-supporting film occurs.

Additional applications also include use as an electrolyte for

Display element, an electrochromic element or various sensors.

Another object of the present invention is also the preferred

Use of the polymer electrolyte membrane according to the invention in the single cell (MEU) for a fuel cell.

The single cell for a fuel cell contains at least one membrane according to the invention and two electrodes, between which the proton-conducting membrane is sandwiched.

The electrodes each have a catalytically active layer and a

Gas diffusion layer for supplying a reaction gas to the catalytically active Shift up. The gas diffusion layer is porous so that reactive gas can pass through.

The polymer electrolyte membrane of the present invention can be used as the electrolyte membrane. In addition, you can the electrolyte membrane and a

Prepare precursor for a single cell (MEU) with one or both catalytically active layers. Furthermore, one can also prepare the single cell by fixing the gas diffusion layer to the precursor.

Another subject of the present invention is a fuel cell having a plurality of individual cells (MEU ^'s ) each containing a membrane prepared by the above method and two electrodes sandwiching the membrane therebetween.

The stabilization according to the invention can also be carried out after preparation of an MEU from a membrane. For this purpose, a doping of the membrane with the stabilizing agent preferably takes place as described above. The

Stabilization reaction according to step c) or the activation of the stabilizing component, however, preferably takes place subsequently within the sandwiched MEU.

The stabilization reaction according to step c) can also be carried out here by irradiation with electromagnetic waves (for example photochemical reaction, IR and / or UV irradiation), electrons or thermally. In a thermal reaction, it is advantageous to the reaction in one

Temperature range of 20 ⁰ C (room temperature) to 240 ⁰ C to perform.

Particularly preferably, the stabilization takes place at 160-200 ^° C. The

Reaction time is from a few minutes to several hours, depending on the reactivity of the reagent. The stabilization reaction in an MEU can be carried out in one or more stages (temperature ramp).

Below, the invention is further illustrated by several examples, without this being intended to limit the inventive concept.

Examples

Route i for carrying out a stabilization according to the invention

(Stabilization of washed-out polyazole films):

A film or a film comprising preferably high molecular weight polyazoles and a strong acid is particularly in a bath with an aqueous solvent, more preferably pure water, at a temperature between 0 ° and 90 ⁰ C. preferably 40 - 70 ⁰ C, inserted. In this case, the acid contained in the film is diluted by dilution of solvent or completely washed out. The acid can be exchanged for 1 - 100% percent against water. Of the

Exchange of solution may vary depending on the temperature and

Concentration of the solvent from a few minutes to several

Take hours. Particular preference is given to wash-outs which do not take more than one to 120 minutes. Subsequently, the treated film is removed from the bath and the supernatant solvent on the surface, z. B. by blotting with a flow sheet removed.

The film is then placed in another bath which contains an organic solvent, preferably DMAc or NMP, as well as at least one of the stabilizing agents according to the invention. The bath particularly preferably contains 0.01 to 30% by weight of the stabilizing component. In the bath, a doping of the film takes place by solvent exchange, the previously introduced aqueous solvent being replaced by an organic solution containing at least one stabilizing agent. In this case, a temperature of at least ⁰ ° C., but at most 120 ^° C. is used with particular preference. The film remains there for a period of one minute to 24 hours. The temperature must be below the temperature at which the stabilizing agent is activated. The film is then removed from the bath and the supernatant

Solvent may be re-absorbed with a cloth but may remain on the surface. Then proceed according to route I a or route I b.

Route I a (Organic Solvent Route):

The film is then by treatment at 70 - 200 ⁰ C between two carrier films (eg polyethylene terephthalate (250 microns) or glass plates) in a heating oven for a time of one minute to 24 hours, more preferably 100 - 160 ⁰ C at a Duration of up to 10 hours, treated with stabilization taking place. A stepwise increase and / or decrease in the temperature in the oven is possible. The film is carried out after

Stabilization taken from the solution and can (i) directly

further processed / used, or (ii) preferably over a period of 30 min - 24 hours in a bath of phosphoric acid with a concentration of 30 - 99%, particularly preferably 30 - 85%, conditioned. These

Conditioning, for example, is important to adjust the concentration of the acid in the film for specific uses.

Route I b (stabilization in an acid medium, advantage of higher conductivities of the membranes): The film is then transferred to another bath, which preheated, preferably 70 - 200 ⁰ C _{1 contains} a strong acid, or an acid mixture and is left there for several minutes to several hours, the

Stabilization according to the invention takes place directly in a liquid, acidic medium. The concentration of the acid is between 10 and 99%, particularly preferably 30-85%.

The film is removed from the solution after stabilization has taken place and can be (i) directly further processed / used or (ii) preferably over a period of 30 minutes to 24 hours in a bath of phosphoric acid with a concentration of 30-99%, particularly preferably 30-85%, are conditioned. This conditioning is important, for example, to adjust the concentration of the acid contained in the film for specific uses.

Route II for carrying out a stabilization according to the invention

(Stabilization of PA containing polyazole films):

A film or a film comprising preferably high molecular weight polyazoles and at least one strong acid is placed in a bath which contains a strong acid and one of the stabilizing reagents according to the invention. The bath particularly preferably contains 0.01-30% by weight of the stabilizing substance. Within the bath, a doping of the film takes place by solvent exchange, wherein the previously introduced aqueous solvent is exchanged with the acidic solution with the stabilizing agent. In this case, a temperature of at least 0 ^° C., but at most 120 ^° C., is used with particular preference. The film is then removed from the bath and any excess solvent can be re-absorbed, but also remain on the surface of the film. Then proceed according to route IIa or route IIb.

Route IIa (oven treatment as a film):

The film is then by treatment at 70 - 200 ⁰ C between two carrier films (eg polyethylene terephthalate (250 microns) or glass plates) from one minute to 24 hours, more preferably 100 - 160 ⁰ C for a period of up to 10 hours treated, wherein the stabilization according to the invention takes place. A stepwise increase and / or decrease in the temperature in the oven is possible.

Route IIb (stabilization in acidic solution, preferred method):

The film is then transferred to another bath, which preheated, preferably 70 - 200 ⁰ C, a strong acid, or an acid mixture and is left there for several minutes to several hours, the

stabilization according to the invention directly in a liquid, acidic medium

takes place. The concentration of the acid is between 10 and 99%, particularly preferably 30-85%.

Table 1 shows the differences in the conductivities of various membranes which were prepared either by the already known procedure (route Ia; comparison) or else by the method according to the invention (route I b).

Table 1

Example 4

The stabilized membranes of the invention are further distinguished by improved long-term stability. For this purpose, a membrane electrode assembly (MEA) is prepared from the membrane together with two electrodes (as described below), preferably loaded with Pt catalyst. The membrane is then within the MEU in a single cell measurement strongly oxidative conditions

exposed. As a measure of stability, the voltage at open terminals (OCV, Open circuit potential, also open circuit voltage). The method for producing an MEA from a membrane and two gas diffusion electrodes by eg hot pressing is known to the expert and state of the art.

The single measuring cell is heated for the measurement to 160 ⁰ C, supplied with about 3 - 5 L / h of hydrogen gas on the anode side and about 5 L / h of air on the cathode side and retracted. The original voltage of the cell and the cell resistance (impedance spectroscope from Zahner) are measured. The measurement of the original voltage by means of impedance spectroscopy is also known to experts and state of the art. Subsequently, the cell without gas supply is kept at 160 ° C kept under atmospheric conditions. The determination of the OCV is repeated 2 to 3 times a week. An incoming damage to the membrane in the MEA is due to a sinking initial stress and / or increasing cell resistance

demonstrated. The stand-by test is terminated when the cell voltage drops below 800 mV. At the beginning of the measurement, this is typically about 1000 mV. The membrane of the invention improves the stability against the

present conditions and delays the decline of the OCV decisively. A comparison membrane (standard PBI / PA) shows a drop in OCV to below 800 mV after approximately 250 h (+/- 50 h) residence time in the cell under the conditions indicated. The stabilized membranes degrade depending on the proportion

Stabilizing reagent within 800 - 1000 h, so factor 3 - 4 slower.

Table 2

Table 2 shows the decrease of OCV for standard membranes in an MEA (MEA 1 and MEA 2) compared to a membrane stabilized with 0.5% by weight of pentaerythritol polyglycidyl ether on Route Ia. The decrease to OCV = 800 mV takes place on average for the standard membranes at 250 h, while the stabilized membrane drops only after about 1200 h below this value.

Claims

claims:

A process for stabilizing polyazole polymers, comprising the following steps:

a) Preparation of a film comprising polyazoles having at least one

Amino group in a repeat unit,

b) treating the film of step a) with a solution comprising (i)

at least one strong acid and (ii) at least one stabilizing reagent, in particular at least one bridging and / or cross-linking reagent, wherein the total content of stabilizing reagent in the solution is in the range 0.01 to 30% by weight, c ) Carrying out the stabilization reaction in the according to step b)

obtained membrane,

d) if appropriate, additional doping of the membrane obtained according to step c) with a strong acid or concentration of the strong acid present by removal of water present.

2. The method according to claim 1, characterized in that the polyazole has a molecular weight (measured as intrinsic viscosity) of at least 1, 8 dl / g.

3. The method according to claim 1, characterized in that the solution in step b) comprises at least one strong, protic acid, in particular based on phosphoric acid and / or sulfuric acid.

4. The method according to claim 3, characterized in that the

Phosphoric acid polyphosphoric acid, phosphonic acid (H ₃ PO ₃ ),

Orthophosphoric acid (H ₃ PO ₄ ), pyrophosphoric acid (H ₄ P ₂ O ₇ ), triphosphoric acid (H5P3O10), metaphosphoric acid and derivatives, in particular organic derivatives, such as cyclic organo-phosphoric acids, and their derivatives, such as acid esters.

5. The method according to claim 1, characterized in that the solution in step b) comprises at least one stabilizing reagent which has at least one functional group, preferably an epoxide group, per molecule which is capable of reacting with the polyazole.

6. The method according to claim 5, characterized in that the

Stabilizing reagent has at least two and / or at least three functional groups, preferably epoxide groups, per molecule which can react with the polyazole.

7. The method according to claim 6, characterized in that as stabilizing reagent has at least two epoxide groups per molecule and represented by the formula (II)

wherein R ^{1 represents} a hydrocarbon group having 1 to 30 carbon atoms, preferably a straight-chain or branched lower alkylene group having 1 to 30 carbon atoms, a straight-chain or branched lower alkoxy group having 1 to 30 carbon atoms or an aromatic system having 4 to 20 carbon atoms, wherein the above-mentioned radicals (I) may be substituted by one or more nitro groups, oxygen atoms, epoxide groups or aryl groups, (ii) in which individual, non-adjacent

Carbon atoms can be replaced by heteroatoms, in particular nitrogen, oxygen, phosphorus and / or sulfur, and (iii) in which one or more hydrogen atoms, in particular in the epoxide groups, by a halogen or an alkyl, in particular a lower alkyl, or an alkoxyl -, In particular, a lower alkoxy group, or aryl group, preferably an aryl group having 4 to 20 carbon atoms, replaced or may be substituted.

8. membrane, obtainable by a process according to claim 2.

9. Membrane according to claim 8, characterized in that it has an E-modulus of at least 3 MPa.

10. A membrane according to claim 8 or 9, characterized in that it has an elongation at break of at least 85%.

11. Use of a membrane according to one or more of claims 8 to 10 for the preparation of a membrane electrode assembly.

12. membrane electrode assembly comprising at least one membrane according to one or more of claims 8 to 10.

13. Use of a membrane electrode assembly according to claim 12 for

Production of a fuel cell.

14. Fuel cell comprising at least one membrane-electrode unit according to claim 12.