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[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. 

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[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. 

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[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. 

[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 

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