Jul.  30,  2020  61  US 2020/0241414 Al  [0091]  In a further embodiment, recurring units  (I)  derived  from an onium salt having a polymerizable unsaturated bond  may be incorporated in the base polymer. Specifically, the  base polymer may 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.  [0089]  In another preferred embodiment, the base polymer  may further comprise recurring units ( d) selected from units  derived from indene, benzofuran, benzothiophene, acenaph› thylene, chromone, coumarin, and norbomadiene, or deriva› tives thereof. Suitable monomers are exemplified below.  [0092]  to In formulae (fl) to (f3),  RA  is independently  hydrogen or methyl. Z 1  is a single bond, phenylene group,  ---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, ester bond, ether bond or hydroxyl moiety. Z $^{2 }$is a  single  bond,  -Z $^{21}$----C(=0)---0-, -Z $^{21}$---0- or  -Z $^{21}$-0----C(=0)-,  wherein  Z 21  is a C$_{1}$-C$_{12 }$alkanediyl  group which may contain a carbonyl moiety, ester bond or  ether bond. "A" is hydrogen or trifluoromethyl. Z $^{3 }$is a single  bond, methylene, ethylene, phenylene, fluorinated phe› nylene,  ---O-Z 11 -,  ----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, phenylene group, fluorinated  phenylene group, or trifluoromethyl-substituted phenylene  group, which may contain a carbonyl moiety, ester bond,  ether bond or hydroxyl moiety. The alkanediyl and alk› enediyl groups may be straight, branched or cyclic.  [0093]  In formulae (fl) to (f3), R$^{21 }$to R$^{28 }$are each inde› pendently a C$_{1 }$-C$_{20 }$ monovalent hydrocarbon group which  may contain a heteroatom. The monovalent hydrocarbon  groups may be straight, branched or cyclic, and examples  thereof include C$_{1 }$-C$_{12 }$alkyl groups, C$_{6}$-C$_{12 }$aryl groups, and  C$_{7}$-C$_{20 }$ arallcyl groups. In these groups, some or all of the  hydrogen atoms may be substituted by C$_{1 }$-C$_{10 }$alkyl groups,  halogen, trifluoromethyl, cyano, nitro, hydroxyl, mercapto,  C$_{1 }$-C$_{10 }$ alkoxy groups, C$_{2}$-C$_{10 }$ alkoxycarbonyl groups, or  [0090]  Furthermore, recurring units (e) may be incorpo› rated in the base polymer, which are derived from styrene,  vinylnaphthalene, vinylanthracene, vinylpyrene, methyl› eneindene, vinylpyridine, and vinylcarbazole.  (fJ)  (f2)  (fl)  -continued  XR’  0  0  0  0  -0:•  C(  0  0 