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[0128] Among the examples, a constitutional unit repre› sented by Formula (a0-1-1) is preferable as the constitu› tional unit (aO). 

[0129] [In the formula, R represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a halogenated alkyl group having 1 to 5 carbon atoms. Va 01 represents a divalent hydrocarbon group which may have an ether bond, and nao1 represents Oto 2. Ya$^{1 }$represents a carbon atom. Xa 1 represents a group that forms a cyclopentyl group or a cyclohexyl group together with Ya 1 . Some or all hydrogen atoms in this cyclopentyl group or cyclohexyl group may be substituted with substituents. Ra 001 represents a phenyl group or a naphthyl group. 

[0130] In Formula (a0-1-1), as the alkyl group having 1 to 5 carbon atoms as R, a linear or branched alkyl group having 1 to 5 carbon atoms is preferable, and specific 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 isopentyl group, and a neopentyl group. The halogenated alkyl group having 

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1 to 5 carbon atoms is a group in which some or all hydrogen atoms of the above-described alkyl group having 1 to 5 carbon atoms have been substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and a fluorine atom is particularly preferable. As R, a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms is preferable, a hydrogen atom or a methyl group is more preferable, and a methyl group is particularly preferable in terms of industrial availability. 01 

[0131] In Formula (a0-1-1), Va represents a divalent hydrocarbon group which may have an ether bond. The divalent hydrocarbon group as Va 01 may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. 

[0132] The aliphatic hydrocarbon group as the divalent hydrocarbon group represented by VaOl may be saturated or unsaturated, but it is preferable that the aliphatic hydrocar› bon group is saturated. 

[0133] More specific examples of the aliphatic hydrocar› bon group include a linear or branched aliphatic hydrocar› bon group and an aliphatic hydrocarbon group having a ring in the structure thereof. 

[0134] The linear aliphatic hydrocarbon group has prefer› ably 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, still more preferably 1 to 4 carbon atoms, and most preferably 1 to 3 carbon atoms. 

[0135] As the linear aliphatic hydrocarbon group, a linear alkylene group is preferable. Specific examples thereof include a methylene group [-CH$_{2}$ -], an ethylene group [-(CH 2 ) 2 -], a trimethylene group [-(CH 2 )$_{3}$ -], a tetram› ethylene group [-(CH$_{2}$ ) 4 -], and a pentamethylene group [-(CH2)s-l- 

[0136] The branched aliphatic hydrocarbon group has preferably 2 to 10 carbon atoms, more preferably 3 to 6 carbon atoms, still more preferably 3 or 4 carbon atoms, and most preferably 3 carbon atoms. 

[0137] As the branched aliphatic hydrocarbon group, branched alkylene groups are preferred, and specific examples thereof include alkylalkylene groups, for example, alkylmethylene groups such as -CH(CH$_{3}$ )-, --CH (CH 2 CH$_{3}$)-, ----C(CH$_{3}$ ) 2 -, ----C(CH$_{3}$)(CH 2 CH$_{3}$)-, ----C(CH$_{3}$)(CH 2 CH 2 CH$_{3}$)-, and ----C(CH 2 CH$_{3}$ ) 2 -; alkyl› ethylene groups such as ----CH(CH$_{3}$)CH 2 -, -CH(CH$_{3}$)CH (CH$_{3}$)-, -C(CH 3 ) 2 CH 2 -, -CH(CH 2 CH$_{3}$)CH 2 -, and ----C(CH 2 CH$_{3}$ ) 2 ----CH 2 -; alkyltrimethylene groups such as ----CH(CH$_{3}$)CH 2 CH 2 -, and ----CH 2 CH(CH$_{3}$)CH 2 -; and alkyltetramethylene groups such as -CH(CH$_{3}$ ) CH 2 CH 2 CH 2 -, and ----CH 2 CH(CH$_{3}$)CH 2 CH 2 -. As the alkyl group in the alkylalkylene group, a linear alkyl group having 1 to 5 carbon atoms is preferable. 

[0138] Examples of the aliphatic hydrocarbon group con› taining a ring in the structure thereof include an alicyclic hydrocarbon group (a group in which two hydrogen atoms have been removed from an aliphatic hydrocarbon ring), a group in which the alicyclic hydrocarbon group is bonded to the terminal of the above-described linear or branched aliphatic hydrocarbon group, and a group in which the alicyclic hydrocarbon group is interposed in the above› described linear or branched aliphatic hydrocarbon group. The linear or branched aliphatic hydrocarbon group is the same as defined for the above-described linear aliphatic hydrocarbon group or the above-described branched ali› phatic hydrocarbon group. 

