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-0----C(=O)- in a ring skeleton thereof. When the lactone ring is counted as the first ring, a lactone-containing cyclic group in which the only ring structure is the lactone ring is called a monocyclic group, whereas a lactone-containing cyclic group containing other ring structure is called a poly- cyclic group regardless of the structure of the other rings. The lactone-containing cyclic group may be either a monocyclic group or a polycyclic group. 

The lactone-containing cyclic group in the constituent unit (a2) is not particularly limited, and any optional lactone- containing cyclic group can be used. Specifically, examples thereof include groups represented by the following general formulae (a2-r-1) to (a2-r-7), respectively. 

[Chemical formula 34] 

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In the formulae, each Ra’ 21 independently represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen 

atom, a halogenated alkyl group, a hydroxyl group, --COOR", ---OC(=O)R", ahydroxyalkyl group, or a cyano group; R" represents a hydrogen atom, an alkyl group, a lactone-containing cyclic group, a carbonate-containing cyclic group, or a -S0$_{2}$--containing cyclic group; A" rep› resents an alkylene group having 1 to 5 carbon atoms, which may contain an oxygen atom (---0-) or a sulfur atom (-S-), an oxygen atom, or a sulfur atom; n’ represents an integer of O to 2; and m’ represents O or 1. 

In the general formulae (a2-r-1) to (a2-r-7), the alkyl group in Ra’ 21 is preferably an alkyl group having 1 to 6 carbon atoms. The alkyl group is preferably linear or branched. Spe› cifically, examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an iso› pentyl group, a neopentyl group, and a hexyl group. Of these, a methyl group or an ethyl group is preferable, with a methyl group being especially preferable. 

The alkoxy group in Ra’$^{21 }$is preferably an alkoxy group having 1 to 6 carbon atoms. The alkoxy group is preferably linear or branched. Specifically, examples thereof include a group in which the alkyl group exemplified above as the alkyl group in Ra’$^{21 }$and an oxygen atom (-0-) are connected to each other. 

Examples of the halogen atom in Ra’$^{21 }$include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, with a fluorine atom being preferable. 

Examples of the halogenated alkyl group in Ra’$^{21 }$include a group in which some or all hydrogen atoms of the alkyl group in Ra’$^{21 }$are substituted with a halogen atom. The halogenated alkyl group is preferably a fluorinated alkyl group, and espe› cially preferably a perfluoroalkyl group. 21 

In -COOR" and ---OC(=O)R" in Ra’ , each R" is a hydrogen atom, an alkyl group, a lactone-containing cyclic group, a carbonate-containing cyclic group, or a -S0$_{2}$ -› containing cyclic group. 

The alkyl group in R" may be linear, branched, or cyclic, and the number of carbon atoms thereof is preferably 1 to 15. 

In the case where R" is a linear or branched alkyl group, the number of carbon atoms thereof is preferably 1 to 10, and more preferably 1 to 5. Above all, R" is especially preferably a methyl group or an ethyl group. 

In the case where R" is a cyclic alkyl group, the number of carbon atoms thereof is preferably 3 to 15, more preferably 4 to 12, and most preferably 5 to 10. Specifically, examples thereof include a group in which one or more hydrogen atoms are eliminated from a monocycloalkane, which may or may not be substituted with a fluorine atom or a fluorinated alkyl group; and a group in which one or more hydrogen atoms are eliminated from a polycycloalkane such as a bicycloalkane, a tricycloalkane, and a tetracycloalkane. More specifically, examples thereof include a group in which one or more hydrogen atoms are eliminated from a monocycloalkane such as cyclopentane and cyclohexane; and a group in which one or more hydrogen atoms are eliminated from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane, and tetracyclododecane. 

Examples of the lactone-containing cyclic group in R" include the same groups as those represented by the general formulae (a2-r-1) to (a2-r-7), respectively. 

The carbonate-containing cyclic group in R" is the same as a carbonate-containing cyclic group to be described later. Specifically, examples thereof include groups represented by general formulae (ax3-r-1) to (ax3-r-3), respectively. 

The -S0$_{2}$--containing cyclic group in R" is the same as a -S0$_{2}$--containing cyclic group to be described later. 

