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tible to deprotection with acid, typically ethoxyethoxy, prior to polymerization, and the polymerization be followed by deprotection with weak acid and water. Alternatively, the hydroxyl group may be replaced by an acetyl, formyl, pivaloyl or similar group prior to polymerization, and the polymerization be followed by alkaline hydrolysis. 

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. 

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Besides the recurring units described above, further recur› ring units (e) which are derived from styrene, vinylnaph› thalene, vinylanthracene, vinylpyrene, methyleneindene, vinylpyridine, and vinylcarbazole may be incorporated in the base polymer. 

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› erating a sulfonic acid. JP-A 2006-178317 discloses a sul- fonium salt having sulfonic acid directly attached to the main chain. 

The preferred recurring units (f) include recurring units having formula (fl), recurring units having formula ( f2 ), and recurring units having formula (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 RA is each independently hydrogen or methyl. Z 1 is a single bond, phenylene, ---O-Z 11 -, or ----C(=O)› Z12-Z11-, wherein Z 11 is a straight, branched or cyclic C$_{1 }$-C$_{6 }$ alkylene group or straight, branched or cyclic C$_{2}$-C$_{6 }$ alkenylene group which may contain a carbonyl, ester, ether or hydroxyl moiety, or phenylene group, Z$^{12 }$is ---0- or -NH-. Rs1, Rs2, Rs3, Rs4, Rss, R66’ Rs7, and Rss are each independently a straight, branched or cyclic C$_{1 }$-C$_{12 }$ alkyl group which may contain a carbonyl, ester or ether moiety, or a CcC$_{12 }$ aryl, C$_{7}$-C$_{20 }$ aralkyl, or mercaptophenyl group. Z $^{2 }$is a single bond, -Z$^{21}$----C(=O)-O-, -Z$^{21}$---0-, or -Z $^{21}$-O----C(=O)-, wherein Z $^{21 }$is a straight, branched or cyclic C$_{1 }$-C$_{12 }$ alkylene group which may contain a car› bonyl, ester or ether moiety. Z $^{3 }$is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, ---O-Z 31 -, or ----C(=0)-Z$^{32}$-Z 31 -, wherein Z$^{31 }$is a straight, branched or cyclic C$_{1 }$-C$_{6 }$ alkylene group or straight, branched or cyclic C$_{2}$ -C$_{6 }$ alkenylene group which may contain a carbo› nyl, ester, ether or hydroxyl moiety, or a phenylene, fluori› nated phenylene or trifluoromethyl-substituted phenylene group, Z 32 is -0- or -NH-. A$^{1 }$is hydrogen or trifluo› romethyl. M- is a non-nucleophilic counter ion. 

Examples of the monomer from which recurring unit (fl) is derived are shown below, but not limited thereto. RA and M- are as defined above. 

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