US 9,052,592 B2  77  78  -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]  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.  In -COOR" and ---OC(=O)R" in Ra’ 21 , 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.  In the formulae, each Ra’ 21  independently represents a  hydrogen atom, an alkyl group, an alkoxy group, a halogen  *  I  Ra’21  --x:  ).CH2)  -;.!  n’  o" Ra,21  0  (a2-r-1)  (a2-r-2)  *  Ra’ 21  )SI  -;- Ra ,21-- A"  0  0  (a2-r-3)  (a2-r-4)  (a2-r-5)  (a2-r-6)  (a2-r-7) 