US 10,915,021 B2  83  84  Also included are a sulfonate ion which is fluorinated at  a-position as represented by the formula (F-1) and a  sulfonate ion which is fluorinated at a- and ~-positions as  represented by the formula (F-2).  Illustrative, non-limiting examples of the iodonium cation  of formula ( d5) are given below.  In formula (F-1), R 19  is hydrogen, or a C$_{1}$-C$_{20 }$ alkyl  group, C$_{2}$-C$_{20 }$ alkenyl group or C$_{6}$-C$_{20 }$ aryl group, which  may have an ether bond, ester bond, carbonyl moiety,  lactone ring or fluorine atom. Herein the alkyl and alkenyl  groups may be straight, branched or cyclic.  In formula (F-2), R 20  is hydrogen, or a C$_{1}$-C$_{30 }$ alkyl  group, C$_{2}$ -C$_{30 }$acyl group, C$_{2}$ -C$_{20 }$alkenyl group,  CcC$_{20 }$ aryl  group or C$_{1 }$-C$_{20 }$ aryloxy group, which may have an ether  bond, ester bond, carbonyl moiety or lactone ring. Herein the  alkyl, acyl and alkenyl groups may be straight, branched or  cyclic.  Examples of the recurring units (dl) are given below, but  not limited thereto. Notably  RA  is as defined above.  Examples of the non-nucleophilic counter ion represented  by  M- include halide ions such as chloride and bromide  ions; fluoroalkylsulfonate ions such as triflate, 1, 1, 1-trifluo› romethanesulfonate,  and  nonafluorobutanesulfonate;  arylsulfonate ions  such as tosylate, benzenesulfonate,  4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenze› nesulfonate; alkylsulfonate ions such as mesylate and  butanesulfonate; imide ions such as bis(trifluoromethyl› sulfonyl)imide, bis(perfluoroethylsulfonyl)imide and bis  (perfluorobutylsulfonyl)imide; and methide ions such as  tris( trifluoromethy lsulfonyl )methide and tris(perfluoroethy 1- sulfonyl )methide.  Examples of the recurring units (d2) are given below, but  not limited thereto. Notably  RA  is as defined above.  (F-2)  01:’  ~S~  F3C  r  V  V  S03- RA  F3C~CF2  ¢  0  0  !03- usu 