-continued  -continued  110  US 10,323,113 B2  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).  (K-2)  (K-1)  Rs2_0  >--CF2-S03- F3C  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.  fo,Q_  c~s~o+s-0  ~I  ~  fo,¢_  C~SO;o+s-0  ~  I  ~  109 