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In the formulas, R andA’ are the same as defined above; and each of c to e independently represents an integer of 1 to 3. -Structural Unit (a2L): 

Examples of the structural unit (a2L) include structural units represented by the aforementioned general formula ( a2- 0) in which the R$^{28 }$group has been substituted with a lactone- containing cyclic group. Specific examples include structural units represented by general formulas ( a2-1) to ( a2-5) shown below. 

[Chemical Formula 32] 

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In the formulas, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; each R’ independently represents a hydrogen atom, an alkyl group, an alkoxy group, a haloge- nated alkyl group, a hydroxy group, -COOR", -OC(=O) R", a hydroxyalkyl group, or a cyano group, wherein R" represents a hydrogen atom or an alkyl group; R$^{29 }$represents a single bond or a divalent linking group; s" represents an integer of0 to 2;A" represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; and m represents 0 or 1. 

In general formulas (a2-1) to (a2-5), R is the same as defined above. 

As the alkyl group, alkoxy group, halogenated alkyl group, ----COOR",---OC(=O)R" andhydroxyalkylgroup forR’, the same alkyl groups, alkoxy groups, halogenated alkyl groups, --COOR", ---OC(=O)R" and hydroxyalkyl groups as those described above as the substituent which a -SO$_{2}$ - contain- ing cyclic group may have, can be mentioned. 

In terms of industrial availability, R’ is preferably a hydro› gen atom. 

The alkyl group for R" may be any of linear, branched or cyclic. 

When R" is a linear or branched alkyl group, it preferably has 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms. 

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