Jul.  30,  2020  47  US 2020/0241418 Al  ions such as tris(trifluoromethylsulfonyl)methide and tris  (perfluoroethylsulfonyl)methide.  [0093]  Also included are sulfonate ions having fluorine  substituted at a-position as represented by the formula ( dl-1)  and sulfonate ions having fluorine substituted at a-position  and trifluoromethyl at ~-position as represented by the  formula (dl-2).  [0088]  In formulae (dl) to (d3),  RA  is each independently  hydrogen or methyl. Z 1  is a single bond, phenylene,  -O-Z 11 , ----C(=0)-0-Z 11 - or  ----C(=0)-NH› Z11-,  wherein  Z 11  is a  C$_{1}$-C$_{6 }$ alkanediyl group,  C$_{2}$-C$_{6 }$ alkenediyl group, or phenylene group, which may contain a  carbonyl moiety, ester bond, ether bond or hydroxyl moiety.  z 2 A  is a single bond or ester bond.  zw  is a single bond or a  C$_{1 }$-C$_{12 }$ divalent group which may contain an ester bond,  ether bond, lactone ring, bromine or iodine. Z 3  is a single  bond, methylene, ethylene, phenylene, fluorinated phe› nylene,  ---O-Z 31 -,  ----C(=0)-0-Z 31 - or  -C(=0)-NH-Z 31 -, wherein  Z $^{31 }$is a C$_{1}$-C$_{6 }$ alkanediyl  group, C$_{2}$-C$_{6 }$ alkenediyl group, or phenylene group, which  may contain a carbonyl moiety, ester bond, ether bond or  hydroxyl moiety.  [0089]  In formula (d2), Rf$^{1 }$to R:t4 are each independently  hydrogen, fluorine or trifluoromethyl, at least one of Rf 1  to  R:t4 being fluorine. Preferably at least one of Rf $^{3 }$and R:t4 is  fluorine, most preferably both RF and R:t4 are fluorine.  [0090]  In formulae (dl) to (d3), R 21  to R 28  are each  independently a C$_{1 }$-C$_{20 }$ monovalent hydrocarbon group  which may contain a heteroatom, any two of R 23 , R $^{24 }$and  R$^{25 }$or any two of R 26 , R $^{27 }$and R$^{28 }$may bond together to  form a ring with the sulfur atom to which they are attached.  The monovalent hydrocarbon group may be straight,  branched or cyclic and examples thereof include C$_{1 }$-C$_{12 }$ alkyl,  CcC$_{12 }$ aryl, and  C$_{7}$-C$_{20 }$ aralkyl groups. In these  groups, some or all hydrogen may be substituted by C$_{1 }$-C$_{10 }$ alkyl, halogen, trifluoromethyl, cyano, nitro, hydroxyl, mer› capto,  C$_{1 }$-C$_{10 }$ alkoxy,  C$_{2}$-C$_{10 }$ alkoxycarbonyl, or  C$_{2}$-C$_{10 }$ acyloxy moiety, or some carbon may be replaced by a  carbonyl moiety, ether bond or ester bond.  [0091]  Examples of the sulfonium cation in formula (d2)  or ( d3) are as will be later exemplified for the cation of the  sulfonium salt having formula (1-1).  [0092]  In formula (dl),  M- is a non-nucleophilic counter  ion. Examples of the non-nucleophilic counter ion include  halide ions such as chloride and bromide ions; fluoroalkyl› sulfonate ions such as triflate, 1, 1, 1-trifluoroethanesulfonate,  and nonafluorobutanesulfonate; arylsulfonate ions such as  tosylate, benzenesulfonate, 4-fluorobenzenesulfonate, and  1,2,3,4,5-pentafluorobenzenesulfonate; alkylsulfonate ions  such as mesylate and butanesulfonate; imide ions such as  bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfo› nyl)imide and bis(perfluorobutylsulfonyl)imide; methide  [0096]  Examples of the monomer from which recurring  unit ( dl) is derived are shown below, but not limited thereto.  RA  and  M- are as defined above.  [0095]  In formula ( dl-2), R 32  is hydrogen, or a C$_{1 }$-C$_{30 }$ alkyl group,  C$_{2}$-C$_{30 }$ acyl group,  C$_{2}$-C$_{20 }$ alkenyl group,  C$_{6}$-C$_{20 }$ aryl group or  C$_{6}$-C$_{20 }$ aryloxy group, which may  contain an ether bond, ester bond, carbonyl moiety or  lactone ring. The alkyl, acyl and alkenyl groups may be  straight, branched or cyclic.  [0094]  In formula (dl-1), R 31  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 contain an ether bond, ester bond, carbonyl  moiety, lactone ring, or fluorine atom. The alkyl and alkenyl  groups may be straight, branched or cyclic.  -continued  (d2)  R23  I  +s-R24  I  R2s  (d3)  R26  I  +s-R 27  I  R2s  (dl-2)  (dl-1) 