Apr. 18,  2019  34  US 2019/0113844 Al  may be incorporated in the base polymer. JP-A 2005-084365  discloses sulfonium and iodonium salts having a polymer› izable unsaturated bond capable of generating a sulfonic  acid. JP-A 2006-178317 discloses a sulfonium salt having  sulfonic acid directly attached to the main chain.  [0075]  The preferred recurring units (f) are recurring units  having the following formulae  (fl), (f2) and (f3). These units  are simply referred to as recurring units  (fl), (f2) and (f3),  which may be used alone or in combination of two or more  types.  [0072]  In another preferred embodiment, the base polymer  may further comprise recurring units ( d) selected from units  of indene, benzofuran, benzothiophene, acenaphthylene,  chromone, coumarin, and norbornadiene, or derivatives  thereof. Suitable monomers are exemplified below.  [0076]  Herein  RA  is each independently hydrogen or  methyl. Z$^{1 }$is a single bond, phenylene group,  ---O-Z 12 -,  or  ----C(=0)-Z$^{11}$-Z 12 -,  wherein Z 11  is -0- or  -NH-, and Z$^{12 }$is a C$_{1 }$-C$_{6 }$ alkylene, C$_{2}$ -C$_{6 }$ alkenylene or  phenylene group, which may contain a carbonyl, ester bond,  ether bond or hydroxyl moiety. Z 2  is a single bond, or  -Z$^{21}$-O----C(=O)-, wherein Z 21  is a C$_{1}$-C$_{12 }$ alkylene  group which may contain a carbonyl moiety, ester bond or  ether bond. Z 3  is a single bond, methylene, ethylene, phe› nylene or fluorinated phenylene group,  ---O-Z 32 -,  or  ----C(=0)-Z $^{31}$-Z32 -,  whereinZ$^{31 }$is-O-or-NH-,  and Z 32  is a C$_{1 }$-C$_{6 }$ alkylene, phenylene, fluorinated phe› nylene, trifluoromethyl-substituted phenylene, or C$_{2}$-C$_{6 }$ alk› enylene group, which may contain a carbonyl, ester bond,  ether bond or hydroxyl moiety. "A" is hydrogen or trifluo› romethyl.  [0077]  R$^{21 }$to R$^{28 }$are each independently a C$_{1 }$-C$_{20 }$mon› ovalent hydrocarbon group which may contain a heteroa› tom. Any two ofR 23 , R $^{24 }$andR$^{25 }$or any two ofR26 , R $^{27 }$and  R$^{28 }$may bond together to form a ring with the sulfur atom  to which they are attached.  [0078]  The monovalent hydrocarbon group may be  straight, branched or cyclic and examples thereof are as  exemplified above for R 4  to R 6  in formula (A). The sulfa- [0073]  Besides the recurring units described above, further  recurring units ( e) may be incorporated in the base polymer,  examples of which include styrene, vinylnaphthalene,  vinylanthracene, vinylpyrene, methyleneindene, vinylpyri› dine, and vinylcarbazole.  [0074]  In a further embodiment, recurring units (f) derived  from an onium salt having a polymerizable unsaturated bond  -continued  OH  (fl)  (f2)  R23  I  +s-R24  I  R2s  (fJ)  R26  I  +s-R 27  I  R2s 