US 10,222,696 B2  76  75  chromone, coumarin, and norbornadiene, or derivatives  thereof. Suitable monomers are exemplified below.  erating a sulfonic acid. JP-A 2006-178317 discloses a sul› fonium salt having sulfonic acid directly attached to the  main chain.  In a preferred embodiment, the base polymer may further  comprise recurring units of at least one type selected from  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.  Herein R 51 , R $^{55 }$andR$^{59 }$each are hydrogen or methyl. R52  is a single bond, phenylene, -O-R 63 -, or ----C(=O)› Y1 -R  63  -, wherein Y 1  is -0- or -NH-, and R $^{63 }$is a  C$_{1 }$-C$_{6 }$ straight, branched or cyclic alkylene or alkenylene  group which may contain a carbonyl, ester, ether or hydroxyl  moiety, or phenylene group. R 53 , R 54 , R 56 , R 57 , R 58 , R 60 ,  R 61 , and R 62  are each independently a C$_{1}$-C$_{12 }$ straight,  branched or cyclic alkyl group which may contain a carbo- nyl, ester or ether moiety, or a C$_{6}$-C$_{12 }$ aryl group, C$_{7}$ -C$_{20 }$ aralkyl group or mercaptophenyl group. A $^{1 }$is a single bond,  -A$^{0}$-C(=O)---0-, -A$^{0}$-O-or-A$^{0}$-O-C(=O)-, wherein  A $^{O }$is a C$_{1 }$-C$_{12 }$ straight, branched or cyclic alkylene group  which may contain a carbonyl, ester or ether moiety. A 2  is  hydrogen or trifluoromethyl. Z$^{1 }$is a single bond, methylene,  ethylene, phenylene, fluorinated phenylene, -O-R  64 -,  or  ----C(=O)-Z$^{2}$-R 64 -, wherein Z 2  is -0- or -NH-,  and R$^{64 }$is a C$_{1}$-C$_{6 }$ straight, branched or cyclic alkylene or  alkenylene group which may contain a carbonyl, ester, ether  or hydroxyl moiety, or phenylene, fluorinated phenylene or  trifluoromethyl-substituted phenylene group.  M- is a non› nucleophilic counter ion, and fl, f2 and f3 are numbers in the  range: 0sfls0.5, 0sf2s0.5, 0sf3s0.5, and 0<fl+f2+f3s0.5.  Examples of the monomer from which recurring unit (fl)  is derived are shown below, but not limited thereto.  M- is as  defined above.  Besides the recurring units described above, further recur› ring units ( e) may be incorporated in the base polymer,  examples of which include styrene, vinylnaphthalene,  vinylanthracene, vinylpyrene, methyleneindene, vinylpyri› dine, and vinylcarbazole.  In a further embodiment, recurring units  (f)  derived from  an onium salt having a polymerizable carbon-carbon double  bond may be incorporated in the base polymer. JP-A 2005- 084365 discloses sulfonium and iodonium salts having a  polymerizable carbon-carbon double bond capable of gen- CObb  0  0  0  0  \  \-j  \--j(__  I  (fl)  (f2)  R56  I  +s-Rs7  I  Rss  (fJ) 