Polymer composition, membrane containing said composition, method for the production and uses thereof

Abstract

The composition described comprises 30 to 99.5% by weight of a sulfonated aromatic polyether ketone which has an ion-exchange capacity of from 1.3 to 4.0 meq (—SO 3 H)/g of polymer, and from 0.5 to 70% by weight of a polybenzimidazole. This composition can, as can a sulfonated polyether ketone of PEK type, be processed to give membranes, preferably used in fuel cells.

What is claimed is:  
     
         1 . A composition comprising from 30 to 99.5% by weight of a sulfonated aromatic polyether ketone which has an ion-exchange capacity of from 1.3 to 4.0 meq (—SO 3 H)/g of polymer, and from 0.5 to 70% by weight of a polybenzimidazole.  
     
     
         2 . A composition as claimed in  claim 1 , wherein the sulfonated polyether ketone has the repeat unit of formula I  
       —[Ar 1 —O—Ar 2 —CO]—  (I),  
       where Ar 1  and Ar 2 , independently of one another, are bivalent, aromatic or heteroaromatic radicals, unsubstituted or substituted with one or more monovalent organic groups inert under usage conditions, and where at least a portion of the radicals Ar 1  and Ar 2  have substitution by radicals of the formula —(SO 3 ) w M, where M is a metal cation of valency w, an ammonium cation or in particular hydrogen, and w is an integer, in particular 1 or 2.  
     
     
         3 . A composition as claimed in  claim 2 , wherein Ar 1  and Ar 2  are naphthylene or in particular phenylene.  
     
     
         4 . A composition as claimed in  claim 2 , wherein Ar 1  and Ar 2  have substitution by from one to four amino, alcohol, ether, alkyl, aryl, sulfonyl, phosphonyl, carbonyl, nitro or carboxylic acid groups, and/or the nitrogen atoms of the polybenzimidazole have substitution by these groups.  
     
     
         5 . A composition as claimed in  claim 1 , wherein the sulfonated polyether ketone has an ion-exchange capacity of from 1.6 to 2.9 meq (—SO 3 H)/g of polymer.  
     
     
         6 . A composition as claimed in  claim 1 , wherein the polybenzimidazole has repeat structural units of the formula II  
       
         
           
           
               
               
           
         
       
       where Ar″ is a tetravalent aromatic radical, Ar′ is a bivalent aromatic radical and R is hydrogen or an inert monovalent organic radical.  
     
     
         7 . A composition as claimed in  claim 6 , wherein Ar″ is 1,2,4,5-phenylene or 3,4,3′,4′-biphenylene, Ar′ is 1,3- or 1,4-phenylene and R is hydrogen.  
     
     
         8 . A composition as claimed in  claim 2 , wherein the proportion of the polybenzimidazole is selected depending on the degree of sulfonation of the sulfonated polyether ketone according to formula III below:  
       percent by weight of polybenzimidazole=9.4 x− 12.4±(9.4 x− 12.4)×0.5  (III),  
       where x is the ion-exchange capacity of the sulfonated polyether ketone in meq (—SO 3 H)/g of polymer.  
     
     
         9 . A composition as claimed in  claim 1 , wherein the type and amount of the polybenzimidazole and of the sulfonated polyether ketone are selected in such a way as to permit preparation of a solution in N-methylpyrrolidone with a viscosity of from 500 to 5000 mPas (measured at 80° C. in a solution of the polymer in NMP using a Couette rotary viscometer).  
     
     
         10 . A sulfonated aromatic polyether ketone of PEK type which has an ion-exchange capacity of from 1.3 to 4.0 meq (—SO 3 H)/g of polymer.  
     
     
         11 . A membrane comprising the polyether ketone as claimed in  claim 10  or the composition as claimed in  claim 1 .  
     
     
         12 . A membrane as claimed in  claim 11 , which has a thickness of at least 5 μm, in particular of at least 30 μm.  
     
     
         13 . A membrane as claimed in  claim 11 , which has an ion-conductivity, mesured in contact with liquid water at room temperature with the aid of 4-pole impedance spectroscopy at a phase angle |θ|<1°, of not less than 50 mS/cm.  
     
     
         14 . A membrane as claimed in  claim 11 , which remains mechanically stable after treatment for 72 hours in boiling water at 100° C.  
     
     
         15 . A membrane as claimed in  claim 11 , which has a modulus of elasticity (determined as gradient of the tangent at 1.2 MPa) in the dry state of at least 600 MPa at 23° C. and 50% relative humidity.  
     
     
         16 . A membrane as claimed in  claim 11 , which has a modulus of elasticity (determined as gradient of the tangent at 1.2 MPa) in water at 60° C. of at least 90 MPa, and an ultimate elongation of more than 200%.  
     
     
         17 . A membrane as claimed in  claim 11 , which has a residual solvent content of less than 0.5% by weight.  
     
     
         18 . A membrane as claimed in  claim 11 , which has a proton-conductivity of more than 50 mS/cm in contact with water at room temperature.  
     
     
         19 . A process for producing the membrane as claimed in  claim 11 , which comprises 
 a) preparing a solution comprising from 30 to 99.5% by weight of a salt of a sulfonated polyether ketone and from 0.5 to 70% by weight of a polybenzimidazole or of the PEK-type sulfonated polyether ketone by dissolving the polymer(s) in a suitable organic solvent, in particular dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide or N-methyl-2-pyrrolidone, and    b) shaping this solution by processes known per se, such as casting, doctoring, spraying or centrifugal processes, to give a membrane.    
     
     
         20 . The process for producing a membrane as claimed in  claim 19 , wherein, after the membrane has been produced, it is freed from residual solvent and, as appropriate, from other water-soluble impurities present by washing in water or in a dilute acid of from 0.1 to 20% strength, for example nitric acid, sulfuric acid or phosphoric acid.  
     
     
         21 . The process for producing a membrane as claimed in  claim 19 , wherein the membrane is dried by heating until the residual content of solvent is less than 0.5% by weight.  
     
     
         22 . The process for producing a membrane as claimed in  claim 19 , wherein the solution comprising from 30 to 99.5% by weight of the salt of the sulfonated polyether ketone and from 0.5 to 70% by weight of the polybenzimidazole is introduced into an absorbent web and the solvent is then removed by evaporation.  
     
     
         23 . The use of the membrane as claimed in  claim 11  for application in fuel cells, in particular for application in direct methanol fuel cells.  
     
     
         24 . The use of the membrane as claimed in  claim 11  for application in high-performance capacitors.  
     
     
         25 . The use of the membrane as claimed in  claim 11  for application in electrodialysis or in ultrafiltration.