A polymer membrane comprising a hydrogen bond donor polymer and a hydrogen bond acceptor polymer; wherein said hydrogen bond donor polymer is made of one or more monomers, and comprises: a hydrogen bond donor group being carboxyl, wherein from 75% to 100%, in number of the monomer units relative to the total number of monomer units in the polymer comprise such a hydrogen bond donor group; and a lateral substituent comprising at least one hydrophobic group selected from alkyl, cycloalkyl and aryl, wherein from 75% to 100%, in number of the monomer units relative to the total number of monomer units in the polymer comprise such a lateral substituent; said hydrogen bond donor polymer being selected from poly(methacrylic) acid (PMAA), poly(ethylacrylic) acid (PEAA), styrene-maleic acid copolymer (PSMA) and polyvinyl alcohol -polyvinyl acetate (PVAc) copolymers comprising from 75% to 100% of polyvinyl alcohol monomer, in number of polyvinyl alcohol monomer relative to the total number of monomer units in the copolymer; wherein said hydrogen bond acceptor polymer is made of one or more monomers, and comprises a hydrogen bond acceptor group being ether, wherein from 75% to 100% in number of the monomer units relative to the total number of monomer units in the polymer comprise such a hydrogen bond acceptor group; and a lateral substituent comprising at least one hydrophobic group selected from alkyl, cycloalkyl and aryl, wherein from 75% to 100% in number of the monomer units relative to the total number of monomer units in the polymer comprise such a lateral substituent; said hydrogen bond acceptor polymer being selected from polypropylene oxides, poloxamers which are polypropylene oxide -polyethylene oxide copolymers comprising from 50% to 100% of polypropylene oxide monomers, in number of polypropylene oxide monomer relative to the total number of monomer units in the poloxamer, and polyvinyl acetate (PVAc)-polyvinyl alcohol copolymers comprising from 75% to 100% of polyvinyl acetate (PVAc) monomers, in number of polyvinyl acetate (PVAc) monomer relative to the total number of monomer units in the copolymer; wherein said polymer membrane does not comprise any charged polymer, wherein the hydrogen bond donor polymer and the hydrogen bond acceptor polymer are bounded together by means of hydrogen bounds, and wherein the shear storage modulus G' of said polymer membrane, measured at 1 rad/s, is at least 0.5 N/m, preferably at least 1.0 N/m, more preferably at least 5.0 N/m. a hydrogen bond donor group being carboxyl, wherein from 75% to 100%, in number of the monomer units relative to the total number of monomer units in the polymer comprise such a hydrogen bond donor group; and a lateral substituent comprising at least one hydrophobic group selected from alkyl, cycloalkyl and aryl, wherein from 75% to 100%, in number of the monomer units relative to the total number of monomer units in the polymer comprise such a lateral substituent; said hydrogen bond donor polymer being selected from poly(methacrylic) acid (PMAA), poly(ethylacrylic) acid (PEAA), styrene-maleic acid copolymer (PSMA) and polyvinyl alcohol -polyvinyl acetate (PVAc) copolymers comprising from 75% to 100% of polyvinyl alcohol monomer, in number of polyvinyl alcohol monomer relative to the total number of monomer units in the copolymer; wherein said hydrogen bond acceptor polymer is made of one or more monomers, and comprises a hydrogen bond acceptor group being ether, wherein from 75% to 100% in number of the monomer units relative to the total number of monomer units in the polymer comprise such a hydrogen bond acceptor group; and a lateral substituent comprising at least one hydrophobic group selected from alkyl, cycloalkyl and aryl, wherein from 75% to 100% in number of the monomer units relative to the total number of monomer units in the polymer comprise such a lateral substituent; said hydrogen bond acceptor polymer being selected from polypropylene oxides, poloxamers which are polypropylene oxide -polyethylene oxide copolymers comprising from 50% to 100% of polypropylene oxide monomers, in number of polypropylene oxide monomer relative to the total number of monomer units in the poloxamer, and polyvinyl acetate (PVAc)-polyvinyl alcohol copolymers comprising from 75% to 100% of polyvinyl acetate (PVAc) monomers, in number of polyvinyl acetate (PVAc) monomer relative to the total number of monomer units in the copolymer; wherein said polymer membrane does not comprise any charged polymer, wherein the hydrogen bond donor polymer and the hydrogen bond acceptor polymer are bounded together by means of hydrogen bounds, and wherein the shear storage modulus G' of said polymer membrane, measured at 1 rad/s, is at least 0.5 N/m, preferably at least 1.0 N/m, more preferably at least 5.0 N/m.