Membrane electrode assemblies and fuel cells with long lifetime

A proton-conducting polymer membrane based on copolymers comprising (I) polybenzoxazoles and (II) polybenzimidazoles, obtainable by a process comprising the steps of

• (i) mixing (a) one or more aromatic diamino dihydroxy compounds with (b) one or more aromatic carboxylic acids or esters thereof comprising at least two acid groups per carboxylic acid monomer,
• or
• mixing one or more aromatic and/or heteroaromatic amino hydroxy carboxylic acids in polyphosphoric acid to form a solution and/or dispersion,
• (ii) heating the mixture from step (i), to temperatures in the range from 120° C. up to 300° C. and polymerizing until attainment of a polybenzoxazole polymer having an intrinsic viscosity of up to 1.5 dl/g,
• (iii) mixing (a) one or more aromatic tetramino compounds with (b) one or more aromatic carboxylic acids or esters thereof comprising at least two acid groups per carboxylic acid monomer,
• or
• mixing one or more aromatic and/or heteroaromatic diamino carboxylic acids in polyphosphoric acid to form a solution and/or dispersion,
• (iv) heating the mixture from step (iii), to temperatures in the range from 120° C. up to 300° C. and polymerizing until attainment of a polybenzimidazole polymer having an intrinsic viscosity of up to 1.5 dl/g,
• (v) combining the polybenzoxazole polymer obtained in step (ii) and the polybenzimidazole polymer obtained in step (iv) and heating until attainment of an intrinsic viscosity of more than 1.5 dl/g, to form a polybenzoxazole-polybenzimidazole block polymer,
• (vi) applying a layer using the mixture according to step (v) to a support or to an electrode,
• (vii) at least partially hydrolyzing the polyphosphoric acid present in the layer from step (vi) by contacting with water and/or aqueous media,
• (viii) detaching the self-supporting membrane formed from the support.