WO2012163782A1 - Polyazole-based polymer films - Google Patents

Abstract

The invention relates to polyazole-based polymer films containing amorphous polysilicic acids, said films being 0 to 20 wt% soluble relative to the polyazole contents thereof at 130ºC and 1000 hPa in N, N-dimethylacetamide. The invention further relates to a method for the production thereof and to the use thereof, in particular for preparing polymer electrolyte membranes.

Description

 Polymer films based on polyazoles

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

Polyazoles, especially polybenzimidazole {PBI), as well as membranes and fibers made therefrom, have long been known. Polybenzimidazole is characterized by a high thermal and chemical resistance. Fibers from PBI are therefore u.a. used for fireproof fabrics. Crosslinked polymer films made of PBI are used, for example, as semipermeable membranes or as polymer electrolyte membranes for fuel cells.

In polymer membranes for gas separation, crosslinking often leads to an improvement in the selectivity with simultaneously reduced permeability. However, US Pat. No. 6,946,015 shows that cross-linking of PBI does not adversely affect the ratio of selectivity to permeability. In this case, the CO ₂ / CH ₄ selectivity in the crosslinked PBI membrane decreases even less with increasing permeability than with the uncrosslinked membrane. Addition of silica nanoparticles can increase the selectivity of the PBI membranes for CO ₂ or CH ₄ over N ₂ (Sadeghi, M. et al., Journal of Membrane Science, Vol. 331, pp. 30-30, 2009) ).

In a fuel cell, controlled oxidation of a fuel, such as hydrogen gas, converts chemical energy into electrical energy. For this purpose, the fuel and an oxidizing agent, such as oxygen, at two opposite electrodes, which by an electronically isolate separating membrane are 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 the preparation of proton-conducting polymer electrolyte membranes in which a basic polymer such as polybenzimidazole is doped with a strong acid such as phosphoric acid or sulfuric acid. Since then, numerous similar membranes of various polyazoles or polyazines have been developed for this application. The advantage of a fuel cell with such a membrane is that it can ■ be operated at temperatures above 100 ° C to about 200 ° C, because the polymer is sufficiently stable and the boiling point of the acid is well above 100 ° C. By increased compared to a fuel cell with a membrane of Perfluorsulfonsäurepolymer and water operating temperature, the catalyst activity is increased at the electrodes, reduces the sensitivity of the catalysts against carbon monoxide contamination in the fuel gas and made the waste heat with higher temperature technically better usable. The disadvantage of doping the polymer with a liquid electrolyte is that the mechanical stability of the membrane is considerably reduced.

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

The optimum operating temperature of such fuel cells based on PBI doped with phosphoric acid is about 160 ° C, and it is recommended to keep the operating temperatures always above 120 ° C and to keep the cells de-energized at lower temperatures. For mobile applications, such as in motor vehicles, but a broad temperature window is desirable, which starts at minus temperatures and reaches temperatures well above 100 ° C. For this it is advantageous if the liquid electrolyte always contains a small amount of water and does not completely dry out even at high operating temperatures above the boiling point to 200 ° C. This improves in particular the proton conductivity at low operating temperatures and thus influences the cold start of the

Fuel cell,

In the past, therefore, numerous attempts have been made to improve the retention capacity of the membranes for water by adding inorganic fillers. For example, reference is made to M. Helen et al. , Strategies for the design of membranes for fuel cells, Photo / Electrochemistry & Photobiology in the Environment, Energy and Fuel, 2006, 1. For this purpose, composites of basic polymers with a layer or framework silicate and doped with an inorganic niche acid used. For example, EP-B 1 177 247 describes membranes containing thermoplastic ion exchange polymers, preferably based on polysulfone, polyether ether ketone, polybenzimidazole or polyvinylpyridine, and phyllosilicates such as montmorillonite. These membranes can also contain phosphoric acid. WO-A-07101537 describes phosphoric acid-doped hybrid membranes containing a basic organic polymer such as polybenzimidazole and a silicate polymer intermixed at the molecular level. The silicate polymer is formed from a precursor monomer during membrane production. In the examples, tetraethoxysilane is used for this purpose. The membranes are covalently crosslinked by an additional reactive additive, which is evidenced by measurements of the solubility in N, N-dimethylacetamide. E. Quartarone et al. have carried out systematic investigations of phosphoric acid-doped polybenzimidazole composites with commercial precipitated silica (HiSil ™ T700 from PPG Silica Products), self-made mesoporous silica particles (SBA-15) or self-made imidazole-containing silica particles (Fuel Cells 09, 2009, No. 3 , Pp. 231-236). Their measurements of the proton conductivities show that all three fillers, even at a low concentration of about 5%, lead to significant increases in conductivity compared to the unfilled membranes (eg at 120 ° C. and 20% relative humidity with 5% by weight HiSil ™ filled PBI approx. 2 S / m compared to 0.1 S / m unfilled). However, higher concentrations in these studies did not result in an improvement, but rather in a deterioration of the properties. No tests were carried out in a fuel cell. Because the membranes produced were not cross-linked, sufficient long-term stability for operation in a fuel cell would not be ensured. The invention relates to polymer films based on polyazoles and amorphous polysilicic acids, which are 0 to 20 wt.% Soluble in terms of their Polyazolgehalt at 130 ° C and 1000 hPa in N, N-dimethylacetamide.

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, particularly preferably 0 to 5% by weight, soluble.

At room temperature and the pressure of the surrounding atmosphere, the polymer films according to the invention are preferably solids of any desired color. The glass transition point of the polymer films according to the invention is preferably above 150 ° C., more preferably above 200 ° C., in particular in the range from 250 to 500 ° C.

The polymer films of the present invention have the advantage that they are characterized by excellent hydrolysis stability and retain their structural integrity, even when stored in strong acids.

The polymer films according to the invention have the advantage that they have good mechanical stability even at high temperatures.

Furthermore, the polymer films according to the invention have the advantage that they are long-lasting under the usual conditions for the applications described. After doping with a strong acid, the polymer films according to the invention surprisingly have a significantly higher proton conductivity in the range from 0 to 100 ° C. than polymer films based on polyazoles without amorphous polysilicic acids but with the same acid content relative to the total mass of the film.

The polymer films according to the invention can be prepared by any desired method by mixing together the individual components and crosslinking of the mixture, the preparation preferably being carried out in several steps.

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

in a first step

a mixture comprising polyazoles (A), amorphous polysilicic acid (B), solvent component (C), optionally bridging reagents (D) and optionally further substances (E) is prepared,

in a second step

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

in a third step

if necessary, the coating obtained in the second step is brought into contact with bridging reagent (D) and allowed to crosslink, the solvent component being optionally completely or partially removed.

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

Examples of the polyazoles (A) used according to the invention are those which are based on building blocks selected from pyrrole, pyrazole, benzpyrazole, oxazole, benzoxazole, thiazole, benzothiazole, imidazole and benzimidazole and additionally aromatic or heteroaromatic groups, such as benzene, naphthalene, Pyridin, pyrimidine or pyrazine, may contain, wherein the building blocks may be substituted, such as by sulfonic acid, alkyl, alkenyl and fluoroalkyl radicals. The different groups may also be linked via imide, ether, thioether, sulfone or direct C-C bonds. Preferred examples of polyazoles (A) are all described in Q. Li et al. Progress in Polymer Science, 34, p. 453 (Scheme 1), 455 (Scheme 5, 6), 456 (Scheme 7) and 457 (Scheme 8) "High temperature proton exchange membranes based on polybenzimidazoles for fuel cells". (2009) mentioned polymers, which are to be included in the disclosure of the present invention.

The polyazoles (A) used according to the invention are particularly preferably those which are built up from components selected from imidazole, benzimidazole, pyridine, benzene and naphthalene, the different groups being bonded via imide, ether, sulfone or Bindings are linked and wherein the blocks may be substituted, such as by sulfonic acid, alkyl, alkenyl and fluoroalkyl radicals.

The polyazoles (A) used according to the invention and processes for their preparation are known. For example, see Q. Li et al. "High temperature proton exchange membranes based on polybenzimidazoles for fuel cells", Progress in Polymer Science, 34, pp. 449-477 (2009). The polyazoles (A) carry as end groups usually those of the monomers used for the preparation, such as amino and / or carboxylic acid groups and / or their esters, or by subsequent chemical reaction any introduced end groups, such as alkyl, aryl , Alkenyl, OH, epoxide, keto, aldehyde, ester, thiol, thioester, silyl, oxime, amide, imide, urethane, and urea groups.

In the inventively used polyazoles (A) are preferably those having a primary amino and / or carboxylic acid end groups, particularly preferably NH ₂ - and / or C00H- end group.

In particular, the polyazoles (A) used according to the invention are polybenzimidazoles, as described, for example, in Q. Li et al. Progress in Polymer Science, 34, p. 453 (Scheme 1), 455 (Scheme 5, 6), 456 (Scheme 7), 457 (Scheme 8) (2009, "High temperature proton exchange membranes based on polybenzimidazoles for fuel cells") ), very particularly preferably poly-2, 2 '- (m-phenylene) -5,5'-dibenzimidazole having primary amino and / or carboxylic acid end groups, more preferably having NH ₂ and / or COOH end groups. A) can be prepared in various known ways, for example by polymerization of diaminobenzidine and isophthalic acid and / or esters thereof Polybenzimidazoles (A) can contain amino and / or carboxylic acid groups and / or their esters as terminal groups, or any end groups introduced by subsequent chemical reaction, such as, for example, alkyl, aryl, alkenyl, OH, epoxide, keto, aldehyde, Ester, thiol, thioester, silyl, oxime, amide, imide, urethane and urea groups.

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, in each case measured on a 0.4% (w / v) solution, ie 0.4 g / 100 ml, of polyazole in H ₂ S0 ₄ (95-97% by weight) with an Ubbelohde viscometer at a temperature of 25 ° C. and a pressure of 1000 hPa.

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

Most preferably, (A) is poly-2,2'- (m-phenylene) -5,5'-dibenzimidazole having 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 S0 ₄ (95-97 wt.%) With an Ubbelohde viscometer at a temperature of 25 ° C and a pressure of 1000 hPa ,

The mixture according to the first step of the process according to the invention preferably contains at least 1% by weight, more preferably at least 5% by weight, in particular at least 10% by weight, of polyazole (A). The mixture preferably contains at most

90% by weight, particularly preferably at most 70% by weight, in particular at most 50% by weight, of polyazole (A). The amorphous polysilicic acid (B) used according to the invention can be of natural origin or can be produced synthetically, with synthetically prepared polysilicic acids being preferred as component (B).

Preferred natural polysilicic acids (B) which contain additional metal ions, such as, for example, Al, Na, K, Mg and / or Ca, are phyllosilicates, in particular from the group of montmorillonites, mica, steatites, bentonites, smectites, kaolinites, pyrophyllites , Vermiculites and chlorites, more preferably from the group of montmorillonites or bentonites.

Preferred synthetically produced polysilicic acids (B) are pyrogenic silicas, such as HDK * from Wacker Chemie AG, Aerosil ⁸ from Evonik and Cab-o-Sil * from Cabot, or precipitated silicas, such as, for example, SIPERNAT ⁸ from Evonik, Vulkasil ' ⁵ '. from Lanxess and HiSil ™ from PPG Silica Products, fumed silicas being particularly preferred.

For the application of the film of the invention as a polymer electrolyte membrane or for the separation of gases or liquids in particular the different surface properties of the amorphous polysilicic acids used are relevant. Pyrogenic silicic acids (B) preferably have a specific

Surfaces according to BET of 100 to 500 m ² / g are acidic with a pH in the range of preferably 2 to 4 and preferably have a low moisture of 0 to 2 wt.%.

Pyrogenic silicic acids (B) are preferably prepared by reacting volatile chlorosilane, such as tetrachlorosilane or methylchlorosilane, is introduced into a hydrogen flame. Hydrolysis at high temperatures of more than 1000 ° C with formed in situ water, silica and hydrogen chloride. The spherical primary silica particles have a smooth surface and an average particle size of about 5 to 50 nm. In the flame, the primary particles fuse tightly into larger units, the aggregates, having a size of preferably about 100-500 nm. The isolated primary particles therefore only exist for a short time in the actual reaction zone. On cooling, these aggregates form flaky agglomerates with a size of preferably 1-250 pm, which are also referred to as tertiary structures. These are open structured and therefore mesoporous. The small particle diameters of the primary particles sintered in the aggregates, together with the large accessible surface of the aggregates and agglomerates, lead to the high BET specific surface area. The high surface-to-mass ratio causes strong interparticle interactions based on attractive dispersion and dipole forces (see description according to DIN 53206 Part 1 (08/72)).

From a chemical point of view, fumed silica consists of highly pure amorphous silica and has the appearance of a loose white powder. It is made up of Si0 _4/2 tetrahedra. These tetrahedra are connected by siloxane bridges {Si-O-Si bonds). On average, every second Si atom on the surface carries a hydroxyl group and thus forms a silanol group.

The fumed silica so produced is hydrophilic and typically has an average of 1.5 to 2 silanol groups per 1 nm ² , is wetted by water, and can be dispersed in water. More difficult is the dispersion in nonpolar organic Solvents or polymers. Ideally, when making a composite with a polymer, the agglomerates are completely broken up and the aggregates are evenly distributed throughout the polymer matrix. The energy required for this is usually introduced in the technical process in the form of mechanical energy, for example by the shearing forces in a kneader or by extrusion,

The hydrophilic fumed silica can now be prepared by chemical reaction with reactive silanes, e.g. Chlorosilanes or hexamethyldisilazane be rendered hydrophobic. Hydrophobic silicic acid has water-repellent properties and is no longer dispersible in water.

The precipitated silicas (B) have a different surface chemistry than the pyrogenic silicas, in particular more hydroxyl groups, due to the preparation in a solution. They have BET specific surface areas of preferably 50 to 300 m ² / g, are preferably neutral to alkaline in aqueous solution with a pH in the range of preferably 6 to 10 and, after drying, have a higher residual moisture content of preferably 3 to 8 wt .%). Precipitated silicas are hydrophilic and typically carry on average 4 to 6 silanol groups per 1 nm ² on the surface.

The production of precipitated silicic acids is based on the monosilicic acid Si (OH) ₄ , which is stable for a long time at room temperature only in high dilution and tends to form with elimination of water amorphous silicon dioxide. The condensation of monosilicic acid proceeds via diciesilicic acid molecules, cyclic silicic acids, to form caged silicas, from which spherical polysilicic acids form, which serve as primary particles. be referred to. The solution thus obtained is referred to as silica sol. The formation of the primary particles varies at room temperature from seconds to minutes at pH values between 8 and 9, up to hours or days at pH values between 2 and 3. The particle diameter is dependent on the pH value of the reaction and can be 2 nm to 150 nm. The Si0 ₂ skeleton is essentially composed of irregularly linked Si0 ₄ tetrahedra and is bounded by a layer of hydroxyl-group-containing silicic acid units. This polysilicic acid is unstable against further condensation. The primary particles combine in the solution by forming oxygen bridge bonds to form a wide-meshed amorphous silica, the so-called silica gel. If the reaction takes place in an alkaline environment, gel formation is prevented and instead precipitated silica is formed. In this case, porous agglomerates with a size of a few μιη to about 40 μηι arise from the primary particles. At a high silica concentration in the solution, these can grow into even larger porous structures, the agglomerates themselves being the basic building blocks of the larger objects.

The monosilicic acids used for the production of precipitated silicas are often contaminated with metal ions. Therefore, precipitated silicas do not generally achieve the high purity of the fumed silicas.

The amorphous polysilicic acids (B) used according to the invention preferably have fractal silicate structures with an average aggregate diameter of preferably 50 to 500 nm, particularly preferably 50 to 200 nm. The amorphous polysilicic acids (B) used according to the invention preferably have a BET surface area of preferably 20 to 800 m ² / g, more preferably 100 to 500 m ² / g, in particular 200 to 400 m ² / g.

Preferred are polysilicic acids (B) which substantially do not contain additional metal ions, e.g. AI, Na, K, Mg and Ca.

The amorphous polysilicic acid (B) may be formed on the surface by organic groups such as from the group of the C 1 to C 20 alkyl, C 2 to C 3 alkenyl, C 1 to C 20 alkylamine and C 1 to C 20 alkylenediamine groups, C 1 to C 20 quaternary ammonium salts and nitrogen containing heterocyclic Compounds may be modified. For this purpose, organosilanes, preferably Aminosila- ne, such as (3-aminopropyl) trimethoxysilane or N- (2-aminoethyl) (3-aminopropyl) trimethoxysilane be connected by a condensation reaction to the surface of the amorphous polysilicic acid.

The amorphous polysilicic acids (B) are preferably those having hydrophilic surfaces, which are preferably provided with hydroxyl groups and / or amino groups, which are preferably attached via an organic spacer. The amount of these functional groups corresponds to the BET surface area of the polysilicic acids. It is preferably in the range from 0.1 to 3 mmol / g, particularly preferably in the range from 0.3 to

1.5 mmol / g, in particular 0.5 to 1.2 mmol / g.

The amorphous polysilicic acids (B) are preferably pyrogenic silicas, particularly preferably pyrogenic silicic acids. acids with hydrophilic surfaces, in particular hydrophilic pyrogenic silicas whose surfaces are provided with hydroxyl groups and / or amino groups.

The amorphous polysilicic acid (B) is in the first step of the process according to the invention in an amount of preferably 1 to 50 wt.%, Particularly preferably 2 to 35 wt.%, In particular 5 to 25 wt.%, Each based on the weight of the polyazole ( A).

The amorphous polysilicic acid (B) used according to the invention can be used in the form of a powder or a suspension having a liquid which is also used, for example, for the solvent component (C), the use in the form of a powder being preferred.

The solvent component (C) used in accordance with the invention may be any polar aprotic solvent which does not react with the further mixing constituents (A), (B), (D) and (E) under the process conditions, acids and in particular polyacids, if they solve the polyazole (A) in sufficient amount for the process, as well as their mixtures with rheological additives act.

The solvent components (C) used according to the invention preferably contain rheological additives,

Preferred examples of solvent component (C) are N, N-dimethylacetamide, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, polyphosphoric acid and mixtures thereof with rheological additives, where N, N-dimethylacetamide and phosphoric acid and mixtures thereof with rheological additives are particularly preferred.

The rheological additives which may be present in the solvent component (C) are preferably those which dissolve in (C) and adjust the viscosity of the mixture. If polar aprotic solvents are used, the rheological additives are preferably phosphates and phosphites, particularly preferably organic phosphates and phosphites, for example diethylhexyl phosphate (DEHPA) or dibutylphosphite, in particular diethylhexyl phosphate. When polyphosphoric acid is used as a solvent, the rheological additives are preferably water or ortho-phosphoric acid. These additives may be removed from the film along with the solvent in the third step, or they may remain in the film, which is preferred. Additives that remain in the film can have additional functions, for example, as a plasticizer or as a component of the liquid electrolyte.

Polyphosphoric acid is often used as solvent already in the production of polyazoles, so that polyazole (A) in the process according to the invention may optionally be used already in admixture with polyphosphoric acid, if this was not previously separated in the preparation of the polyazole, in which case the polyphosphoric optionally in Mixture with additives of component (C) corresponds.

The term solvent does not mean that all components of the mixture must dissolve completely in it. The solvent component (C) used according to the invention contains additives in amounts of preferably 0 to 60% by weight, more preferably 1 to 50% by weight, in particular 5 to 40% by weight.

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

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

Examples of bridging agents (D) which may be used according to the invention are compounds having at least two reactive groups, such as diglycidyl ether, polyfunctional organic acids or their halides and anhydrides, polyhalogenated organic compounds, dialdehydes or di-inyl compounds, and also reactive compounds, such as aldehyde reagents which can form methylol bridges with primary or secondary amino groups on the polymer.

Component (D) is preferably bisphenol A di-glycidyl ether, 1-butyldiglycidyl ether, ethylene glycol diglycidyl ether, terephthalic aldehyde, divinyl sulphone, dibromo-p-xylene, 3, 4-dichlorotetrahydrothiophene-l, 1-dioxide, dichloromethylphosphonic acid, paraformaldehyde and formaldehyde.

If a compound having at least two reactive groups is used as the bridging reagent (D) in the first step according to the invention, the amounts are preferably at least 0.1 mol, particularly preferably at least 1 mol, and preferably at most 10 mol, particularly preferably at most 5 mol , in each case based on 1 mol of polymer (A) used.

If an aldehyde reagent is used as the bridging reagent (D) in the first step according to the invention, this is used in an amount such that the molar ratio of aldehyde groups in (D) to primary or secondary amino groups in component (A) is between 0.1 and 10 , more preferably between 0.5 and 8, in particular between 1 and 5.

If bridging reagent (D) is used in the third step according to the invention, this is preferably carried out in the form of solutions or gases which preferably contain the bridging reagent in a concentration of from 1 to 50% by weight and which are brought into contact with the film.

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

In addition to the components (A), (B), (C) and optionally (D), further constituents (E) can now be used in the process according to the invention. In the optionally used further constituents (E) may be any and hitherto known substances act as they have been used for example in connection with polyazoles. Examples of such substances (E) are additives which increase the crosslinking density; Low concentration additives that can serve to modify the properties of the surface of the polymer film, such as surface tension; Additives that improve the durability of the mixture or the film; or additives that serve process optimization.

Examples of additives (E) which increase the crosslinking density are low molecular weight or polymeric crosslinker building blocks or particles which are not based on polyazoles and which carry more than one reactive group which can be incorporated into the network in the third step.

Examples of preferred low molecular weight crosslinker units (E) are di-, tri- and tetrahydroxy compounds, such as ethyleneglycol, dihydroxybenzene, glycerol, trihydroxybenzene and pentaerythritol, or compounds with more than two amino groups, such as diaminobenzidine or melamine. An example of a compound having NH and OH groups is hydroxyaniline.

Examples of additives (E) are surfactants, adhesion promoters or preservatives.

Examples of additives (E) which serve for process optimization are catalysts, initiators or free-radical formers or stabilizers. The type and amount of further constituents (E) which may be used depend primarily on the specific applications or conditions of the polymers according to the invention or those prepared according to the invention.

The mixture according to the first step of the invention contains further constituents {E) in amounts of preferably 0 to 30% by weight, particularly preferably 0 to 10% by weight. In the first step of the process according to the invention, preference is given to using no further constituents (E) apart from the additives (E) which serve for process optimization.

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.

A preferred variant of the method according to the invention (variant 1) is characterized in that

in a first step

a mixture comprising polyazoles (A), amorphous polysilicic acid (B), solvent component (C), bridging agents (D) and optionally further substances (E) is prepared,

in a second step

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

and

in a third step

Polyazole (A) is reacted with the bridging reagent (D), wherein any solvent component is partially or completely removed. A further preferred variant of the process according to the invention {variant 2) is characterized in that

in a first step

a mixture containing polyazole (A), amorphous polysilicic acid (B), solvent component (C) and optionally further substances (E) is prepared,

in a second step

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

and

in a third step

the film obtained in the second step is brought into contact with the bridging reagent (D) and polyazole (A) is reacted with bridging reagent (D), with any solvent component being wholly or partly removed.

A further preferred variant of the method according to the invention (variant 3) is characterized in that

in a first step

a mixture containing polyazole (A), amorphous polysilicic acid (B), solvent component (C) and optionally further substances (E) is prepared,

in a second step

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

and

in a third step

the solvent component (C) is completely or partially removed and the resulting polymer film is heated in the presence of oxygen to a temperature in the range of 200 to 500 ° C.

The mixture according to the first step of variants 1 to 3 according to the invention can be prepared by methods known per se are mixed, for example by simply mixing the individual constituents and, if appropriate, stirring., Whereby preferably polyazole (A) with solvent component (C) or the solvent from component (C) is mixed to form a premix (10) into which the amorphous polysilicic acid ( B), for example, as homogeneously as possible incorporated as a powder or as a suspension.

If the solvent component (C) contains rheological additives, these may be used together with the solvent or separately in the preparation of the premix (16).

The remaining ingredients are preferably added in any order after homogenization. For this purpose, the further constituents, such as the bridging reagent (D) used in variant 1 or optionally used further substances (E), can be dissolved separately in a part of the solvent component (C) or the solvent from component (C) and then Mixture of (M) and (B) are added.

To prepare the premix (M) in the first step of variants 1 to 3 according to the invention, the mixture is preferably stirred until the polyazole (A) is preferably more than 90% by weight, particularly preferably completely, in the solvent component ( C) or the solvent from component (C) has dissolved. The preparation of this premix (M) in the first step according to the invention is carried out at temperatures of preferably from 50 to 350.degree. C., more preferably from 100 to 300.degree. C., in particular from 150 to 250.degree. If polyazole was mixed only with solvent, the rheological additives can be used after the dissolution process, which are then stirred in preferably after cooling to room temperature. Thereafter, the amorphous polysilicic acid (B) is incorporated as homogeneously as possible into the premix (M). If necessary, the agglomerates of the amorphous polysilicic acids must be broken up. For this purpose, an evacuable mixing unit is preferably used, in which the mixture is mixed under reduced pressure of preferably 10 to 800 mbar, more preferably 50 to 500 mbar, with a sufficiently high energy input, which is to be determined experimentally. The mixing can also be carried out by means of batchwise and / or continuous mixing units, such as kneaders, dissolvers or planetary mixers.

An increased viscosity of the premixture (M) with amorphous polysilicic acid (B) facilitates the breaking up of the agglomerates of the amorphous polysilicic acid. Preference is given to viscosities of (M) + (B) in the range from 0.1 Pas to a few hundred Pas, which must be adapted to the particular mixing process. The viscosity is preferably adjusted via the solvent content of the premix (M), suitable additives for the solvent and the temperature during the mixing process. The incorporation of the amorphous polysilicic acid (B) into the premix (M) is preferably carried out in the temperature range from 0 to 100 ° C, if in this range a suitable viscosity of the mixture can be achieved.

The addition of the optionally remaining constituents to the mixture of (M) with (B) in the first step of variants 1 to 3 according to the invention can be carried out at the temperatures at which the premix (M) was prepared or at higher or lower temperatures, the optionally used bridging reagent (D) preferably at low temperature acids, such as 10 to 40 ° C, to avoid premature reactions.

The inventive step 1, in the variants 1 to 3 preferably at the pressure of the surrounding atmosphere, ie 900 to 1100 hPa, carried out with the exception of the incorporation of amorphous polysilicic acid (B), preferably at lower pressures of preferably 10 to 800 mbar, especially preferably 50 to 500 mbar, happens. It can also be performed at lower or higher pressures.

The partial steps of the first step of the inventive variants 1 to 3 carried out at 900 to 1100 hPa are preferably carried out in an inert gas atmosphere, such as under argon or nitrogen purge.

The first step of variants 1 to 3 according to the invention can be carried out continuously or batchwise.

In the mixture according to the first step of Va ^¬ variants 1 to 3 according to the invention is preferably a suspension or a paste. In the case of the suspension, preferably the polyazole (A) and optionally used bridging reagents (D) and / or further substances (E) are dissolved in the solvent component (C) and the amorphous polysilicic acid (B) is in the continuous phase serving solvent dispersed. The mixture of the first step is particularly preferably a suspension having a honey-type viscosity in the range from 1 to 100 Pas. 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 or by the doctor blade method. The chosen application method also depends on the desired layer thickness of the dry polymer film according to the third step of variants 1 to 3 according to the invention.

Examples of carriers which can be used in the second step of variants 1 to 3 according to the invention are all previously known carriers which are well wetted by the mixtures according to the invention, are largely resistant to the components contained in the mixtures and dimensional stability in the temperature range used exhibit. 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 strips, glass surfaces and siliconized papers.

In particular, when the polymer film is to be detached from the carrier after production, carriers are preferred which are chemically inert to the mixture according to the first step of variants 1 to 3 according to the invention.

If, in the second step of the process according to the invention, a carrier is used which is not removed after the third step according to the invention, for example a woven, nonwoven or textile, a coating is obtained. Preferred are in In such a case, substrates which, owing to the presence of reactive groups, such as, for example, hydroxyl or amino groups, allow covalent attachment of the coating to the substrate by the bridging reagent (D).

If the carrier is not removed, it may have a function which is part of the application of the polymer film of the invention. 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

 Fuel cell membrane, the mixture can be applied directly to the gas diffusion layer or the electrode thereon,

The carriers used are preferably those which are wetted by the mixture according to the first step of the inventive variants 1 to 3, wherein the contact angle of the mixture on the carrier is preferably less than 90 °, particularly preferably less than 30 ° , each measured with inert gas as the surrounding phase.

The second step according to the invention can be carried out continuously or discontinuously in variants 1 to 3.

For continuous application methods, polymer films such as poly (ethylene terephthalate) films or metal strips such as stainless steel are preferably used. For the batch process, glass plates are preferably used. The second step of variants 1 to 3 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 second step of variants 1 to 3 according to the invention is preferably carried out at temperatures below the boiling point of the solvent (C), particularly preferably in the temperature range from 10 to 80 ° C., in particular 15 to 40 ° C. If a polyacid is used as the solvent component (C), the application of the mixture to the support is preferably carried out in the temperature range of 150 to 200 ° C.

The second step of variants 1 to 3 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.

If component (C) contains a polar aprotic solvent in the mixture from the first step, this is preferably completely or partially removed in the third step of variants 1 to 3 according to the invention. If component (C) in the mixture of the first step contains a polyacid as solvent, it preferably remains in the film and, if appropriate, is later converted into an acid by hydrolysis.

If solvents are to be removed in the third step of the process according to the invention, then the customary processes known from the prior art for drying can be used. In this case, the polymer film is preferably used as far as heats the solvent or solvent mixture escapes without forming gas bubbles in the film.

The drying of the film in the third step of variant 1 according to the invention is preferably carried out at temperatures below the

Boiling point of the solvent (C) carried out, preferably at 40 to 150 ° C, more preferably at 60 to 130 ° C, especially at temperatures at which a crosslinking reaction is not or only delayed takes place. Drying can be accelerated by reducing the ambient pressure below 900 hPa. By subsequently increasing the temperature to preferably not more than 250 ° C., more preferably not more than 200 ° C., the reaction of the polyazole (A) with the bridging reagent (D) can be started or accelerated.

In the third step of Inventive Variant 2 according to the invention, bridging reagent (D) is added in order to allow the reaction of the polyazole (A) with the bridging reagent (D), wherein the optionally carried out drying can be carried out before or after addition of the component (D). If in the third

 Step of the process variant 2 solvent is to be removed wholly or partially, this is preferably done before addition of bridging reagent (D).

The drying of the film in the third step of the invention

Variant 2 is preferably carried out at temperatures of 40 to 250 ° C, particularly preferably at 80 to 200 ° C, in particular at 80 to 150 ° C. By reducing the ambient pressure below 900 hPa, drying can be accelerated. If the film is to be dried only after addition of component (D), which is not preferred, rather lower chosen in which a crosslinking reaction is not or only delayed takes place.

In the third step of process variant 2 according to the invention, bridging reagent (D) is added, for example by immersion, spraying or by gassing in the second

Step, optionally after prior drying, polymer film obtained. Subsequently, the crosslinking reaction can be accelerated by raising the temperature to preferably not more than 250 ° C., more preferably not more than 200 ° C.

Preferably, in the third process step of variant 2 according to the invention, the optionally completely or partially dried film is immersed on the support or as a self-supporting film in a bath containing a bridging reagent (D). The bath is preferably a polar liquid, such as, for example, water or an acid, for example orthophosphoric acid, in which preferably 1 to 50% by weight, particularly preferably 2 to 40% by weight, of bridging reagent (D) are dissolved. The bath may contain further additives, such as, for example, alcohols, in amounts of preferably 0 to 50% by weight, particularly preferably 0 to 20% by weight, which may serve to improve the stability of the solution. Instead of a bridging reagent (D), the bath may also contain radical formers or initiators (E) which initiate the crosslinking reaction in amounts of preferably from 1 to 40% by weight, particularly preferably from 2 to 20% by weight. Particular preference is given to baths which contain an alcohol-stabilized formaldehyde solution or an aqueous solution of 85% by weight orthophosphoric acid with paraformaldehyde.

The bath used according to the invention has a temperature of preferably below 200 ° C., particularly preferably 20 to 160 ° C., in particular 35 to 130 ° C, wherein higher temperatures accelerate both the diffusion of the bridging reagent (D) or the radical initiators (E) in the film and the crosslinking reaction.

Immersion in the bath may be carried out in an inert gas atmosphere, such as under argon or nitrogen purge, or even in the presence of oxygen, for example in air.

The necessary duration of the treatment of the film with Verbrückungs- reagents (D) in the third step, the invention Varian ^¬ te 2 is formed by the diffusion rate of the bridging reagent (D) is determined in the film and can not be sweepingly. The optimum duration can be determined experimentally depending on the temperature, the concentration of the bridging reagent in the bath and the material composition and thickness of the film.

The reaction of the invention in the third step of the variants 1 and 2 is preferably carried out in an inert gas atmosphere, such as under argon or nitrogen purge, but can optionally also in the presence of oxygen at ^¬ play, in air, to be performed.

The drying of the film in the third step of variant 3 according to the invention is preferably carried out at temperatures of 40 to 250 ° C, more preferably at 80 to 200 ° C, in particular at 80 to 150 ° C. By reducing the ambient pressure below 900 hPa, drying can be accelerated. Subsequently, the dried film can be detached from the carrier or, if the carrier has sufficient thermal stability to remain on this.

The heating of the polymer film at 200 ° C. to 500 ° C. in the third step of variant 3 according to the invention can be carried out by any desired methods known hitherto, for example in a hot-air oven or by contact with hot surfaces.

The maximum temperature in the third step of variant 3 according to the invention is limited primarily by the stability of the polymer and the economy of the process. It is preferably in the range of 250 and 400 ° C, particularly preferably 300 to 400 ° C.

The maximum duration of the heating in the third step of variant 3 according to the invention is limited primarily 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 heating of the polymer film to the maximum temperature in the third step of variant 3 according to the invention is carried out in the presence of oxygen, preferably 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. The heating of the polymer film to the maximum temperature in the third step of the inventive variant 3 is most preferably carried out in the presence of air. The desired thickness of the polymer film after the third step of process variants 1 to 3 depends on the requirements of the particular application. As semipermeable membranes, thin layers between 1 and 20 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 pm. If the polymer film contains polyphosphoric acid after the third step, the film thickness is preferably between 30 and 500 μm.

1 to 3 polymer films with a thickness of 1 to 500 μιη, more preferably from 5 to 200 μιτι, preferably produced in the third step of the process variants according to the invention.

As soon as the polymer film has sufficient mechanical stability, it can be detached from the carrier. This may be done after the third step or after the optional drying in the third step. The polymer film can also remain on the support, if this is for the

Application is desired.

The heating of the polymer film in the third step of process variants 1 to 3 according to the invention can be carried out by any desired and heretofore known methods, for example in a hot-air oven or by contact with hot surfaces,

The third step of variants 1 to 3 according to the invention can be carried out at different pressures, preferably at the pressure of the surrounding atmosphere, ie at 900 to 1100 hPa. The partial steps carried out in air in the third step of the process variants 1 to 3 according to the invention are preferably carried out 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 of the invention is to be carried out continuously, for example, a drying oven or heated rolls / belts, e.g. made of stainless steel or sintered metal, or a floating dryer can be used.

In the third step of variants 1 to 3 according to the invention, polymer films are now obtained which, in addition to the polyazoles, optionally have a residual amount of solvent and optionally further substances. The quality of the crosslinking of the polymer films obtained can be assessed by determining the N, N-dimethylacetamide-soluble fractions of polyazole in the polymer film.

The selection of the process variant according to the invention depends on the intended use of the polymer films according to the invention and in particular on whether they are used as rather thick or thin films. For example, for the crosslinking of a thick film, the bridging reagent (D) is preferably introduced in the first step into a mixture with the polyazole (A), that is to say variant 1 according to the invention is preferably carried out. If thin films are to be prepared from the polyazole, then the bridging reagent (D) can be prepared according to method Variant 2 are also supplied in the third step, for example by immersion or spraying with a solution containing a bridging reagent, or by gassing, for example with formaldehyde.

Especially for thin films of polybenzimidazole, process variant 3 has proven to be particularly simple to carry out,

The process according to the invention in variants 1 and 2 has the advantage that it can be carried out under mild temperature conditions and thus subsequent embrittlement of the polymer films is avoided. Also, the choice of other materials (E) for modifying the film properties is less limited than in a process in which the films are exposed to high thermal stress.

Due to the variability of the method according to the invention, the procedure can be customized depending on the desired end product and preferred production management.

The polymer films according to the invention or produced according to the invention can now be used for many purposes for which polymer films have hitherto also been used. Particularly preferred applications are polymer electrolyte membranes and semipermeable films.

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 the application as

Polymer electrolyte membrane can be in the third step of Variant variants 1 to 3 polymer obtained in a further step optionally carried out with a strong acid dope, unless this was not already used in a previous process step as a solvent. As strong acids should here acids with a pKs of preferably less than 4 are understood. It is also possible to combine such a further process step with the third step of process variant 2 and thus, for example, to introduce the bridging reagent (D) together with a strong acid into the polymer film.

Another object of the present invention are polymer electrolyte membranes based on polyazoles and amorphous polysilicic acids, which are soluble in terms of their Polyazolgehalt at 130 ° C and 1000 hPa in N, N-dimethylacetamide 0 to 20 wt.% That with a strong acid are doped.

Another object of the present invention is a process for the preparation of polymer electrolyte membranes

characterized in that

in a first step

a mixture comprising polyazoles (A), amorphous polysilicic acid (B), solvent component (C), optionally bridging reagents (D) and optionally further substances (E) is prepared,

in a second step

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

in a third step

optionally, contacting and crosslinking the coating obtained in the second step with bridging reagent (D) is left, wherein the solvent component is optionally completely or partially removed, and

in a fourth step

the film obtained in the third step is doped with a strong acid (F).

In a variant of the process according to the invention for the preparation of polymer electrolyte membranes, the third and fourth steps may coincide if in the third step bridging agent (D) is used and this is mixed with the strong acid (F) and the film is brought into contact with this mixture ,

In a further variant of the process according to the invention for the preparation of polymer electrolyte membranes, the solvent component (C) in the first step already contains a precursor of the strong acid. An example of such a precursor is polyphosphoric acid, which can also be used, for example, as a solvent for the production of polybenzimidazole. In such a case, in the fourth step, the precursor already contained in the film can be converted into a strong acid, for example, by contact with water.

In view of the stability of the polymer film and the safety precautions required for the handling of strong acids at high temperatures, the doping in the doping step carried out according to the invention is preferably carried out below 200 ° C., more preferably at 20 to 160 ° C., in particular at 35 to 130 ° C. , According to a variant of the optionally performed doping step, the polymer film according to the invention is immersed in a highly concentrated strong acid over a period of preferably at most 5 hours and more preferably 1 minute to 1 hour, wherein a higher temperature shortens the immersion time.

The amount of acid used in the doping step optionally carried out in this variant is usually from 5 to 10,000 times, preferably from 6 to 5000 times, more preferably from 6 to 1000 times, in each case based on weight the polymer (A) in the polymer film,

Alternatively, according to a further variant of the optionally performed doping step, a strong acid can be applied in a metered manner to the polymer film and the film is heated until the film has completely absorbed the acid. In this variant, the amount of acid used in the doping step according to the invention is usually from 2 to 10 times the amount, preferably from 3 to 8 times, in each case based on the weight of the polymer film.

According to a further variant of the optional doping step, the polymer film is pressed between two acid-impregnated gas diffusion electrodes for the production of a membrane electrode assembly. The amount of acid used in the doping step optionally carried out according to the invention in this variant 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. As strong acids in the doping step according to the invention are protic strong acids, such as 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 ), ortho-phosphoric acid (H ₃ PO 4), pyrophosphoric acid (H ₄ P ₂ O ₇ ), triphosphoric acid (H ₅ P ₃ Oi ₀ ) and metaphosphoric acid.

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

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

After doping with a strong acid, the polymer films according to the invention advantageously have a markedly higher here proton conductivity in the range of 0 to 100 ° C as polymer films based on polyazoles without amorphous polysilicic acids but the same acid content based on the total mass of the film.

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 invention or inventively produced polymer electrolyte membranes for the production of membrane electrode assemblies for fuel cells or electrolysis cells.

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

The polymer electrolyte membranes according to the invention have the advantage that when used in a high-temperature PEM fuel cell in a cold start at temperatures below 100 ° C, a higher electrical power is made possible.

Although the polyazole content of the membranes is low, they have high mechanical stability and excellent long-term thermal and chemical stability. In particular when using polyazoles having predominantly amino groups as terminal groups that are cross-linked via these end groups, surprisingly, homogeneous and flexible films are obtained,

Due to the different permeabilities and selectivities of the polymer films according to the invention for liquids and gases, they are outstandingly suitable as semipermeable membranes.

The invention therefore also relates to the use of the polymer according to the invention or of the polymer produced according to the invention) as a semipermeable membrane for the separation of liquids and gases.

In the following examples, all parts and percentages are by weight unless otherwise specified

Unless stated otherwise, the following examples are air at a pressure of the surrounding atmosphere, ie at about 1000 hPa, and at room temperature, ie about 20 ° C or a temperature, the reactants when combined at room temperature without additional heating or üh-

20 ment stops, carried out. The air used in the experiments contains 23% by weight of oxygen and 50% relative humidity. All viscosity data given in the examples refer to a temperature of 25 ° C.

The inherent viscosity was measured in the following examples as follows:

The polymer is first dried at 160 ° C for 2 h. 400 mg of the polymer thus dried are then dissolved for 4 hours at 80 ° C. in 100 ml of concentrated sulfuric acid (concentration 95-097% by weight). The inherent viscosity becomes from this 0.4% (w / v) solution according to ISO 3105 with an Ubbelohde viscometer at a temperature of 25 ° C determined.

The solubility of the polyazole portion of the polymer films produced was determined in the following examples as follows ("solubility test"):

A membrane piece of about 1 to 2 cm ^s is dried at 150 ° C to constant weight, weighed and then extracted for one hour at 130 ° C and 1000 hPa in about 10 g of N, -Dimethylacetamid. Thereafter, the membrane is again dried at 150 ° C to constant weight and then weighed.

The specific surface of the silicas used was measured by the BET method according to DIN 66131 and DIN 66132.

example 1

a) Preparation of amino-terminated polybenzimidazole

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

The polybenzimidazole thus prepared had an inherent viscosity of 0.70 dl / g. b) Preparation of a polymer solution of polybenzimidazole with 10% aminopropylsilyl-functionalized fumed silica

An aminopropylsilyl-functional fumed silica (BET: 300 m ² / g, functional group density: 1 mmol / g) was prepared according to Example 1 described in EP-B 1304332 on page 11, lines 10-21 with the modification that a hydrophilic silica having a specific surface area of 300 m * / g (available under the name Wacker ^HDK® T30 from Wacker Chemie AG, Germany) was used.

8.7 g of the amine-terminated polybenzimidazole prepared above were dissolved in 91.4 g of N, N-dimethylacetamide (DMAc) in a pressure reactor (Buchi Miniclave, 200 ml) with stirring at a temperature of 200 ° C. After cooling to Raumtempera- tur 15.0 g of this solution were Hauschild with 3.0 g of diethyl hexyl phosphate (DEHPA) and 0.13 g of the aminopropylsilyl -functional fumed silica (in an evacuable mixing unit Speedmixer DAC ^® 400.1 V-DP Fa., Germany).

 The following mixing program was used:

 Stage t [min] rpm

I 1 g DEHPA 1 1000

 2 2500

II 1 g DEHPA 1 1000

 2 2500

III 1 g DEHPA 1 1000

 2 2500

IV 0.14 g of aminopropylsilyl-functional 1 800 fumed silica

 1 1000

2 2500

The pressure during the mixing process was 500 mbar. c) Preparation and characterization of a cross-linked polybenzimidazole film with formalin solution

 The polymer solution from Example 1b was applied at room temperature by means of a film-drawing apparatus (0.6 mm gap height) to a polyethylene terephthalate support film having a thickness of 0.175 mm (commercially available under the trade name "Melinex 0" from Pütz GmbH, Germany) The film was separated from the support film for 10 minutes at 80 ° C., 100 ° C. and 30 minutes at 150 ° C. The film was then immersed in a 70 ° C. methanol-stabilized formalin solution (37% by weight of formaldehyde, 12% by weight of methanol, 51% by weight of water) was then placed in a circulating air drying cabinet for 1 h

Heated to 250 ° C hot air. The thickness of the film thus obtained was 50 to 55 μπι. The film thus obtained is hereinafter called film lc.

With this film, a solubility test was carried out according to the method described above. The weight loss after one hour in 130 ° C hot N, N-dimethylacetamide was 6%.

d) doping a membrane with phosphoric acid and determining the conductivity

From a piece (6 x 6 cm ² ) of the film lc, 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 45 min at 130 ° C in a drying oven. The film was cooled to room temperature and wiped with paper towels. From the swollen film, the weight and the thickness were again determined. He had taken about 6 times his weight. The degree of doping {Mass increase based on the weight of the swollen membrane) was 85% by weight. The thickness was 94 μηα.

One piece (20 × 10 mm ² ) of this swollen membrane was placed in a 4-point conductivity measuring cell (available under the designation "Type BT110" Fa. BekkTech LLC, USA) and heated in a cabinet to 150 ° C and then cooled to 0 ° C. The membrane impedance was determined by means of an impedance analyzer (available under the name "Model IM6ex" from Zahner-Elektrik, Germany). With the sample geometry (thickness, area), a membrane conductivity is obtained under almost dry conditions

1.0 S / m at 0 ° C, 35% rel. Humidity and 5.7 S / m at 150 ° C, 1% rel. Humidity. Moistening the circulating air in the climatic chamber, then reached at 125 ° C and 22% rel. Moisture has a higher conductivity of 10 S / m.

e) producing a membrane-electrode assembly

The 6 × 6 cm ² piece of the phosphoric acid-swollen membrane from Example 1d was thus between two commercially available gas diffusion electrodes, each with 4.0 mg / cm ² platinum loading (Johnson Matthey, type 4 mg Pt Blk, no Electrolysis, on Toray TGP-H-060, UK) that the platinum catalyst layers contacted the membrane. This membrane-electrode assembly was compressed for 4 hours between plane-parallel plates at a temperature of 160 ° C and a force of 1.3 kftf to a membrane-electrode assembly.

f) Fuel cell test of the membrane-electrode assembly

The membrane-electrode unit from Example 1e was usually installed in a test cell (quickCONNECT F25 from Balic-FuelCells GmbH, Germany) and fitted with a press cell. closed by force of 3.5 kN. The operation of the test cell was carried out on a MILAN test rig from Magnum Fuel Cell AG. Figure 1 shows the course of the current-voltage curve at 160 ° C. The gas flow for hydrogen was 196 nml / min and for air 748 nml / min. Unhumidified gases with atmospheric pressure were used. At a current of 0.5 A / cm ^2, a cell voltage of 0.500 mV was measured. Under the test conditions indicated, the MEA exhibited an impedance of 7.2 mQ over an area of 25 cm ² at a measurement frequency of 16 kHz.

Figure 1: Polarization curve of a membrane-electrode assembly according to the invention from Example le

Example 2

a) Preparation of polybenzimidazole with carboxylic acid end groups

101.8 g of 3, 3 ¹ -Diaminobenzidin {0.475 mol) (commercially available from Sigma-Aldrich, Germany) and 83.7 g of isophthalic acid

 (0.5 mol) (molar ratio 0.95, excess acid) were dissolved in

2.0 kg of polyphosphoric stirred and filled in a heatable reactor (5 1), which was purged with inert gas argon. The batch was heated to 190 ° C (jacket temperature) and stirred for 20 hours. The reaction product was precipitated in water, washed with it and neutralized in 550 g of a 10% strength by weight sodium bicarbonate solution. Thereafter, the polybenzimidazole was washed again with water, filtered off, dried at 130 ° C in vacuo and ground with an electric mill. The yield was 132.3 g.

The polybenzimidazole thus prepared had an inherent viscosity of 0.43 dl / g. b) Preparation of a polymer solution of carboxy-terminated polybenzimidazole with 20% hydrophilic fumed silica

9.8 g of the carboxy-terminated polybenzimidazole prepared above were dissolved in 90.2 g of Ν, Ν-dimethylacetamide (DMAc) in a pressure reactor (Büchi miniclave, 200 ml) with stirring at a temperature of 200 ° C. After cooling to room temperature, 15.0 g of this solution together with 3.0 g of diethylhexyl phosphate (DEHPA) and 0.3 g of hydrophilic fumed silica having a BET surface area of 200 m ² / g and a density of the existing silanol groups 0.6 mmol / g (commercially available under the name HDK ^® N20 from Wacker Chemie AG, Germany) in an evacuable mixing unit (speed mixer ^® DAC 400.1 V DP Fa. Hauschild, Germany) mixed.

 The following mixing program was used:

Stage t [min] rpm

I DEHPA 1 1000

 2 2500

II i g DEHPA 1 1000

 2 2500

III i g DEHPA 1 1000

 2 2500

IV 0.3 g of hydrophilic fumed silica 0.5 800

 1 1000

2 2500

The pressure during the mixing process was 50 mbar.

c) producing and characterizing a crosslinked film

The polymer solution from Example 2b was applied to a polyethylene terephthalate support film having a thickness of 0.175 mm at room temperature by means of a film-drawing apparatus (0.6 mm gap height) (commercially available under the trade name "Melinex O" from Pütz GmbH, Germany) After drying (10 minutes each at 80 ° C., 100 ° C. and 30 minutes at 150 ° C.), the film was separated from the carrier film the film was heated in air in a circulating drying oven for 240 minutes at 300 ° C. The thickness of the film thus obtained was 60 to 65 μm The film thus obtained is referred to below as film 2.

 With this film, a solubility test was carried out according to the method described above. The weight loss after one hour in 130 ° C hot N, N-dimethylacetamide was 1%.

d) doping a membrane with phosphoric acid and determining the conductivity

From a piece (6 x 6 cm ² ) of the film 2c, the weight and the thickness were determined. The piece of film was then placed in a Petri dish, covered with 85% strength by weight phosphoric acid in water in the Petri dish and heated for 60 minutes at 130 ° C. in a drying oven. The film was cooled to room temperature and wiped with paper towels. From the swollen film, the weight and the thickness were again determined. He had taken about 5 times his weight. The degree of doping {mass increase based on the weight of the swollen membrane) was 82.6 wt.%, The thickness was 92 μτη.

One piece (20 × 10 mm ² ) of this swollen membrane was placed in a 4-point conductivity measuring cell (available under the name "BTllO type" from BekkTech LLC, USA) and heated to 150 ° C. in a climate-controlled cabinet then cooled to 0 ° C. The membrane impedance was determined by means of an impedance analyzer (available under the name "Model IM6ex" from Zahner-Elektrik, Germany). With the sample geometry (thickness, area), a membrane conductivity is obtained under almost dry conditions 1.4 S / m at 0 ° C, 31% rel. Humidity and 7.3 S / m at 150 ° C, 0% rel. Humidity. If the circulating air is humidified in the climatic chamber, a higher conductivity of 19 S / m is achieved at 125 ° C and 21% relative humidity.

e) producing a membrane-electrode assembly

The 6 × 6 cm ² piece of the phosphoric acid-swollen membrane from Example 2d was so between two commercially available gas diffusion electrodes, each with 4.0 mg / cm ² platinum loading (Johnson Matthey, type 4 mg Pt Blk, no electro lyte on Toray TGP-H-060, UK) that the platinum catalyst layers contacted the membrane. This membrane-electrode assembly was compressed for 4 hours between plane-parallel plates at a temperature of 160 ° C and a force of 1.3 kN to a membrane-electrode assembly.

f) fuel cell test of the membrane electrode assembly

The membrane-electrode unit from Example 2e was installed in a conventional arrangement in a test cell (quickCONNECT F25 from the company Balastic-FuelCells GmbH, Germany) and sealed with a pressing force of 3.5 kN. The operation of the test cell was carried out on a MILAN test rig from Magnum Fuel Cell AG. Figure 2 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 0.522 mV was measured. Under the test conditions indicated, the MEA exhibited an impedance of 4.2 mQ over an area of 25 cm ² at a measurement frequency of 16 kHz. Figure 2: Polarization curve of a membrane electrode assembly of Example 2e according to the invention

Comparative Example 1

Conductivity of a thermally crosslinked film without silica a) 12.0 g of polybenzimidazole according to Example 1a were dissolved in 88.0 g of Ν, Ν-dimethylacetamide (DMAc) in a pressure reactor (Buchi miniclav, 200 ml) with stirring at a temperature of 200 ° C solved. After filtration and degassing, the solution was applied by means of a film-drawing device with a gap of 0.4 mm to a carrier film of polyethylene terephthalate PET having a thickness of 0.175 mm (commercially available under the trade name "Melinex O" from Pütz GmbH, Germany) The film was separated from the base film at 80 ° C., 10 minutes at 100 ° C. and 30 minutes at 150 ° C. It was then heated in a circulating air drying oven for 240 minutes in air at 300 ° C. The film thickness was 30 With this film, a solubility test was carried out according to the method described above The weight reduction after one hour in 130 ° C. hot N, -dimethylacetamide was 1%.

b) From a piece (6 x 6 cm 2) of the film prepared in Comparative Example la, 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 about 5 times his weight. The degree of doping (mass increase based on the weight of the swollen membrane) was 82.4 wt.%. The thickness was 45 pm. c) A piece (20 × 10 mm ² ) of the swollen membrane prepared above under a) was placed in a point-conductivity measuring cell (available under the name "Type BT110" Fa. BekkTech LLC, USA) and in a convection oven on 150 ° C. The membrane impedance was determined by means of an impedance analyzer (available under the name "Model IM6ex" from Zahner-Elektrik, Germany). With the sample geometry (thickness, area) is obtained under almost dry conditions, a membrane conductivity between 0.67 S / m at 0 ° C, 40% rel. Humidity and 5.1 S / m at 150 ° C, 1% rel. Humidity. Moistening the circulating air in the climatic chamber, then reached at 125 ° C and 21% rel. Humidity a higher conductivity of 9 S / m. All values are significantly lower than the conductivities measured in Example 2d.

Claims

claims 1. Polymer films based on polyazoles and amorphous polysilicic acids, which are soluble in terms of their Polyazolgehalt at 130 ° C and 1000 hPa in N, -Dimethylacetamid 0 to 20 wt.%. 2. Polymer films according to claim 1, characterized in that they are 0 to 10 wt.% Soluble in terms of their Polyazolgehalt at 130 ° C and 1000 hPa in N, N-dimethylacetamide. 3. Polymer films according to claim 1 or 2, characterized in that it is pyrogenic polysilicic acid in the amorphous polysilicic acid. 4. A process for the preparation of the polymer films according to the invention characterized in that in a first step a mixture comprising polyazoles (A), amorphous polysilicic acid (B), solvent component (C), optionally bridging reagents (D) and optionally further substances (E) is prepared, in a second step the mixture obtained in the first step is applied to a support, in a third step the coating obtained in the second step is optionally brought into contact with bridging reagent (D) and allowed to crosslink, the solvent component being optionally completely or partially removed. 5. Process according to Claim 4, characterized in that the polyazoles (A) are polybenzimidazoles. 6. The method according to claim 4 or 5, characterized in that solvent components (C) contain rheological additives. 7. Polymer electrolyte membranes based on polyazoles and amorphous polysilicic acids which, in terms of their Polyazolge- hold at 130 ° C and 1000 hPa in N, N-dimethylacetamide 0 to 20 wt.% Soluble, which are doped with a strong acid. 8. A process for the preparation of polymer electrolyte membranes, characterized in that in a first step a mixture comprising polyazoles (A), amorphous polysilicic acid (B), solvent component (C), optionally bridging reagents (D) and optionally further substances (E) is prepared, in a second step the mixture obtained in the first step is applied to a support, in a third step if appropriate, the coating obtained in the second step is brought into contact with bridging agent (D) and allowed to crosslink, the solvent component being optionally completely or partially removed, and in a fourth step the film obtained in the third step is doped with a strong acid (F). 9. Use of the polymer electrolyte membranes according to claim 7 or produced according to claim 8 for the production of membrane electrode assemblies for fuel cells or electrolysis cells. 10. membrane electrode assembly comprising at least one electrode and at least one Pölymerelektrolytmembran according to claim 7 or manufactured according to claim 8. 11. Use of the polymer films according to one or more of claims 1 to 3 or prepared according to one or more of claims 4 to 6 as a semipermeable membrane for the separation of liquids and gases.