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[0128] Of the recurring units having formula (b), those units having a lactone ring as the polar group are most preferred. 

[0129] The polymer may further comprise recurring units of at least one type selected from recurring units having the formulae (cl) to (c3). 

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[0130] In formulae (cl) to (c3), RA is as defined above. Z 1 is a single bond, phenylene, ---O-Z 11 -, ----C(=O)-O› Z11- or----C(=O)-NH-Z 11 -, wherein Z 11 is a C$_{1}$-C$_{20 }$ alkanediyl group, C$_{2}$-C$_{20 }$ alkenediyl group or phenylene group, which may contain a carbonyl moiety (-CO-), ester bond (-COO-), ether bond (---0-) or hydroxyl moiety. Z 2 is a single bond or -Z$^{21}$-C(=O)-O› wherein Z$^{21 }$is a C$_{1 }$-C$_{20 }$divalent hydrocarbon group which may contain a heteroatom. Z 3 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, ---O-Z 31 -, ----C(=O)---0-Z$^{31}$-or-C(=O)-NH-Z 31 -, wherein Z$^{31 }$is a C$_{1 }$-C$_{6 }$ alkanediyl group, C$_{2}$-C$_{6 }$ alkenediyl group or phenylene group, which may contain a carbonyl moiety, ester bond, ether bond or hydroxyl moiety. 21 22 

[0131] In formula (cl), R and R are each indepen› dently a C$_{1 }$-C$_{20 }$monovalent hydrocarbon group which may contain a heteroatom. R 21 and R 22 may bond together to form a ring with the sulfur atom to which they are attached. [0132] Examples of the monovalent hydrocarbon group represented by R 21 and R 22 include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, cyclo› propyl, cyclopentyl, cyclohexyl, cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbomyl, and ada› mantyl, alkenyl groups such as vinyl, ally!, propenyl, bute› nyl, hexenyl, and cyclohexenyl, aryl groups such as phenyl, naphthyl, and thienyl, and aralkyl groups such as benzyl, 1-phenylethyl and 2-phenylethyl. Inter alia, aryl groups are preferred. In these hydrocarbon groups, some hydrogen may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, and a moiety containing a heteroatom such as oxygen, sulfur or nitrogen may inter› vene between carbon atoms, so that the group may contain a hydroxyl moiety, cyano moiety, carbonyl moiety, ether bond, ester bond, sulfonic acid ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride or haloalkyl moiety. 

[0133] In formula (cl), M- is a non-nucleophilic counter ion. Examples of the non-nucleophilic counter ion include 

