A fluorinated polymer [polymer] comprising recurring units derived from at least the following monomers: (i) 5 to 50 % by weight of a fluorinated monomer [monomer] containing at least one -SO 2 X functionality, preferably having the formula of CF 2 =CF-O-(CF 2 CF(CF 3)O) m -(CF 2) n SO2X wherein m is 0 or 1, n is an integer between 0-10, and X is selected from F, OH, and O - Me +, wherein Me + indicates an alkali metal ion or an ammonium cation of formula NR 4 + where each R independently represents a hydrogen atom or a monovalent organic radical selected from aliphatic radicals having from 1 to 8 carbon atoms and arylic or alicyclic radicals having from 3 to 8 carbon atoms; (ii) a non-functional fluorinated monomer [monomer] having at least one ethylene unsaturation, wherein said non-functional fluorinated monomer is selected from the group consisting of: - C 2 -C 8 perfluoroolefins, preferably tetrafluoroethylene or hexafluoropropylene; - vinylidene fluoride; - C 2 -C 8 chloro- and/or bromo- and/or iodo-fluoroolefines, such as - chlorotrifluoroethylene (CTFE) and bromotri-fluoroethylene; - fluoroalkylvinylethers of formula CF 2 =CFOR f1 in which R f1 is a C 1 -C 6 fluoroalkyl, e.g. -CF 3, -C 2 F 5, -C 3 F 7; and - fluoro-oxyalkylvinylethers of formula CF 2 =CFOR O1, in which R O1 is a C 1 -C 12 fluorooxyalkyl having one or more ether groups, like perfluoro-2-propoxypropyl; and (iii) a fluorinated polyfunctional compound having the general formula: (CR 1 R 2 =CFCF 2 -O) a -R f -( c -CF=CR 3 R 4) b wherein: a is an integer equal to or larger than 1, preferably a is 1, 2, or 3; b is 0 or 1 and the sum of a and b is an integer equal to or larger than 2; c is 0 or 1; R 1, R 2, R 3 and R 4 are independently selected from F, H, alkyl, alkoxy, polyoxy alkyl, perfluoroalkyl, perfluoroalkoxy or perfluoropolyoxy alkyl, preferably F; and R f represents a hydrocarbon group or fluorocarbon group having at least two carbon atoms, wherein the hydrocarbon group refers to a non-fluorinated group containing carbon and hydrogen atoms, as well as optional elements other than carbon and hydrogen such as oxygen, nitrogen, sulphur and silicon, and wherein the fluorocarbon group refers to a chemical group having carbon and fluorine atoms, that can optionally contain a heteroatom selected from O, N and S. (i) 5 to 50 % by weight of a fluorinated monomer [monomer] containing at least one -SO 2 X functionality, preferably having the formula of CF 2 =CF-O-(CF 2 CF(CF 3)O) m -(CF 2) n SO2X wherein m is 0 or 1, n is an integer between 0-10, and X is selected from F, OH, and O - Me +, wherein Me + indicates an alkali metal ion or an ammonium cation of formula NR 4 + where each R independently represents a hydrogen atom or a monovalent organic radical selected from aliphatic radicals having from 1 to 8 carbon atoms and arylic or alicyclic radicals having from 3 to 8 carbon atoms; (ii) a non-functional fluorinated monomer [monomer] having at least one ethylene unsaturation, wherein said non-functional fluorinated monomer is selected from the group consisting of: - C 2 -C 8 perfluoroolefins, preferably tetrafluoroethylene or hexafluoropropylene; - vinylidene fluoride; - C 2 -C 8 chloro- and/or bromo- and/or iodo-fluoroolefines, such as - chlorotrifluoroethylene (CTFE) and bromotri-fluoroethylene; - fluoroalkylvinylethers of formula CF 2 =CFOR f1 in which R f1 is a C 1 -C 6 fluoroalkyl, e.g. -CF 3, -C 2 F 5, -C 3 F 7; and - fluoro-oxyalkylvinylethers of formula CF 2 =CFOR O1, in which R O1 is a C 1 -C 12 fluorooxyalkyl having one or more ether groups, like perfluoro-2-propoxypropyl; and - C 2 -C 8 perfluoroolefins, preferably tetrafluoroethylene or hexafluoropropylene; - vinylidene fluoride; - C 2 -C 8 chloro- and/or bromo- and/or iodo-fluoroolefines, such as - chlorotrifluoroethylene (CTFE) and bromotri-fluoroethylene; - fluoroalkylvinylethers of formula CF 2 =CFOR f1 in which R f1 is a C 1 -C 6 fluoroalkyl, e.g. -CF 3, -C 2 F 5, -C 3 F 7; and - fluoro-oxyalkylvinylethers of formula CF 2 =CFOR O1, in which R O1 is a C 1 -C 12 fluorooxyalkyl having one or more ether groups, like perfluoro-2-propoxypropyl; and (iii) a fluorinated polyfunctional compound having the general formula: (CR 1 R 2 =CFCF 2 -O) a -R f -( c -CF=CR 3 R 4) b wherein: a is an integer equal to or larger than 1, preferably a is 1, 2, or 3; b is 0 or 1 and the sum of a and b is an integer equal to or larger than 2; c is 0 or 1; R 1, R 2, R 3 and R 4 are independently selected from F, H, alkyl, alkoxy, polyoxy alkyl, perfluoroalkyl, perfluoroalkoxy or perfluoropolyoxy alkyl, preferably F; and R f represents a hydrocarbon group or fluorocarbon group having at least two carbon atoms, wherein the hydrocarbon group refers to a non-fluorinated group containing carbon and hydrogen atoms, as well as optional elements other than carbon and hydrogen such as oxygen, nitrogen, sulphur and silicon, and wherein the fluorocarbon group refers to a chemical group having carbon and fluorine atoms, that can optionally contain a heteroatom selected from O, N and S.