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pyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, cyclopentyl, n-hexyl, and cyclohexyl. Examples of the alkyl moiety in the C$_{1 }$-C$_{6 }$ alkoxy group R 4 are as exemplified above for the alkyl group. Examples of the alkyl moiety in the C$_{2}$-C$_{6 }$ acyloxy group R 4 are as exemplified above for the alkyl group, but of 1 to 5 carbon atoms. The C$_{2}$ -C$_{8 }$ alkenyl group represented by R 4 B may be straight, branched or cyclic, and examples thereof include vinyl, 1-propenyl, 2-propenyl, butenyl, hexenyl, and cyclohexenyl. Among others, R 4 is preferably selected from fluorine, chlorine, bromine, hydroxyl, amino, C$_{1 }$-C$_{3 }$ alkyl, C$_{1 }$-C$_{3 }$ alkoxy, C$_{2}$ -C$_{4 }$ acyloxy, -NR $^{4}$A-C(=0)-R, and -NR4A----C(=0)---0-R4B_ 

[0046] In formula (a), Rs is a C$_{1 }$-C$_{10 }$ alkyl group or CcC$_{10 }$ aryl group, which may be substituted with an amino, nitro, cyano, C$_{1 }$-C$_{12 }$ alkyl, C$_{1 }$-C$_{12 }$ alkoxy, C$_{2}$-C$_{12 }$ alkoxycarbonyl, C$_{2}$-C$_{12 }$ acyl, C$_{2}$-C$_{12 }$ acyloxy, hydroxyl moiety or halogen. 

[0047] Of the groups represented by Rs, the C$_{1 }$-C$_{10 }$alkyl group may be straight, branched or cyclic, and examples thereof include those exemplified above as the C$_{1 }$-C$_{6 }$ alkyl groups R 4 , R 4 A and R 4 B and n-heptyl, n-octyl, n-nonyl, n-decyl, norbomyl, and adamantyl. Examples of the CcC$_{10 }$ aryl group include phenyl, tolyl, xylyl, 1-naphthyl, and 2-naphthyl. The C$_{1 }$-C$_{12 }$ alkyl group may be straight, branched or cyclic, and examples thereof include those exemplified above as the C$_{1 }$-C$_{10 }$alkyl groups and n-undecyl and n-dodecyl. Examples of the alkyl moiety in the C$_{1 }$-C$_{12 }$ alkoxy group include those exemplified above as the C$_{1 }$-C$_{12 }$ alkyl groups. Examples of the alkyl moiety in the C$_{2}$ -C$_{12 }$ alkoxycarbonyl, C$_{2}$-C$_{12 }$ acyl or C$_{2}$-C$_{12 }$ acyloxy group include those exemplified above as the C$_{1 }$-C$_{12 }$alkyl groups, but of 1 to 11 carbon atoms. 

[0048] In formula (a), L1 is a single bond or a C$_{1 }$-C$_{20 }$ divalent linking group which may contain an ether bond, carbonyl moiety, ester bond, amide bond, sultone moiety, lactam moiety, carbonate moiety, halogen, hydroxyl moiety or carboxyl moiety. 

[0049] In formula (a), m is an integer of 1 to 5, n is an integer of Oto 3, lsm+ns5, and p is 1 or 2. 

[0050] Examples of the cation moiety in the monomer from which recurring units (a) are derived are shown below, but not limited thereto. Herein RA is as defined above. 

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