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Examples of the non-nucleophilic counter ion M- include ~~l}~:;t~~~!~~~c~ a~~~~!:,a~f, t~::fiir~~~~~:!c:i1~~~!~ and nonafluorobutanesulfonate; arylsulfonate ions such as tosylate, benzenesulfonate, 4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate; alkylsulfonate ions such as mesylate and butanesulfonate; imidates such as bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfo- nyl)imide and bis(perfluorobutylsulfonyl)imide; methidates such as tris(trifluoromethylsulfonyl)methide and tris(per› fluoroethylsulfonyl)methide. 

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). 

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In formula (K-1), R 51 is hydrogen, or a C$_{1}$-C$_{20 }$ straight, branched or cyclic alkyl group, C$_{2}$-C$_{20 }$straight, branched or 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 52 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, 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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-continued 

(K-1) 

(K-2) 

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-continued 

