US 10,698,314 B2  91  92  -continued  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).  Examples of the monomer from which recurring unit (f2)  is derived are shown below, but not limited thereto.  RA  is as  defined above.  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.  (K-1)  (K-2) 