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Where the recurring units of formula (3) are incorporated, units having lactone ring as the polar group are most preferably used. 

While the polymer is characterized by comprising recur› ring units having formulae (2) and (3), optionally recurring units having the general formula (dl) or (d2) may also be incorporated. 

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Herein R $^{1}$a, R100 , R 200 , and R $^{300 }$as defined above. L’ is a C$_{2}$-C$_{5 }$ alkylene group. RY is a straight C$_{1 }$-C$_{20 }$or branched or cyclic C$_{3}$-C$_{20 }$monovalent hydrocarbon group which may be substituted with or separated by a heteroatom. A is hydrogen or trifluoromethyl. L" is a single bond or a straight C$_{1 }$-C$_{20 }$ or branched or cyclic C$_{3}$ -C$_{20 }$ divalent hydrocarbon group which may be substituted with or separated by a heteroatom, mis O or 1, n is O or 1, with the proviso that n is O when L" is a single bond. 1$_{a }$ 

In formulae (dl) and (d2), R is as defined and exem› plified above. L’ is a C$_{2}$-C$_{5 }$ alkylene group, preferably ethylene, propylene or butylene. A is hydrogen or trifluo› romethyl, preferably trifluoromethyl. RY is a straight C$_{1 }$-C$_{20 }$ or branched or cyclic C$_{3 }$-C$_{20 }$ monovalent hydrocarbon group, examples of which are as described above for R $^{1 }$to R$^{5 }$in formula (1 ). L" is a single bond or a straight C$_{1 }$-C$_{20 }$or branched or cyclic C$_{3}$-C$_{20 }$ divalent hydrocarbon group, examples of which are as described above for L in formula (1). R 100 , R $^{200 }$and R$^{300 }$are as described above. 

Illustrative structures of the anion moiety in formula (dl) include those described in JP-A 2010-113209 and JP-A 2007-145797. Illustrative structures of the anion moiety in formula ( d2) wherein A is hydrogen include those described in JP-A 2010-1160. Illustrative structures of the anion moi› ety in formula (d2) wherein A is trifluoromethyl include those described in JP-A 2010-077404. 

While the polymer is characterized by comprising recur- ring units having formulae (2) and (3), and optionally recurring units having formula (dl) or (d2), other recurring units, typically recurring units of the structure having a hydroxyl group protected with an acid labile group may be further copolymerized. The recurring units of the structure having a hydroxyl group protected with an acid labile group are not particularly limited as long as the unit has one or more structures each having protected hydroxyl wherein the protective group is decomposed under the action of acid to generate a hydroxyl group. Of these, recurring units of the structure having the general formula ( e 1) are preferred. 

(dl) 50 

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(d2) 

(el) 

