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Examples of the non-nucleophilic counter ion M- include halide ions such as chloride and bromide ions; fluoroalkyl› sulfonate ions such as triflate, 1, 1, 1-trifluoroethanesulfonate, and nonafluorobutanesulfonate ions; arylsulfonate ions such as tosylate, benzenesulfonate, 4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate ions; alkylsul› fonate ions such as mesylate and butanesulfonate ions; sulfonimide ions such as bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide and bis(perfluorobutylsul- fonyl)imide ions; sulfonmethide ions such as tris(trifluorom› ethy lsulfony 1 )methide and tris(perfluoroethy lsulfonyl )me› thide ions. 

Also included are sulfonates having fluorine substituted at a-position as represented by the formula (K-1) and sul- fonates having fluorine substituted at a- and ~-positions as represented by the formula (K-2). 

In formula (K-1), R 61 is hydrogen, or a C$_{1}$-C$_{20 }$ straight, branched or cyclic alkyl group, C$_{2}$-C$_{20 }$straight, branched or 55 cyclic alkenyl group, or CcC$_{20 }$ aryl group, which may contain an ether, ester, carbonyl moiety, lactone ring, or fluorine atom. In formula (K-2), R 62 is hydrogen, or a C$_{1 }$-C$_{30 }$ straight, branched or cyclic alkyl group, C$_{2}$ -C$_{30 }$ straight, branched or cyclic acyl group, C$_{2}$-C$_{20 }$ straight, 60 branched or cyclic alkenyl group, CcC$_{20 }$ aryl group or CcC$_{20 }$ aryloxy group, which may contain an ether, ester, carbonyl moiety or lactone ring. 

Examples of the monomer from which recurring unit (f2) is derived are shown below, but not limited thereto. RA is as defined above. 

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