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[0238] Each ofRs 1 and Rs$_{3 }$ in formula (a) more preferably represents a hydrogen atom, an alkyl group or a halogen atom, and especially preferably a hydrogen atom, a methyl group, an ethyl group, a trifluoromethyl group (-CF 3 ), a hydroxym› ethyl group (----CH$_{2}$---0H), a chloromethyl group (----CH$_{2}$- Cl), or a fluorine atom (-F). Rs$_{2 }$ more preferably represents a hydrogen atom, an alkyl group, a halogen atom, or an alkylene group (forming a ring together with Ls), and espe› cially preferably a hydrogen atom, a methyl group, an ethyl group, a trifluoromethyl group (-CF$_{3}$ ), a hydroxymethyl group (-CH$_{2}$-OH), a chloromethyl group (----CH$_{2}$----Cl), a fluorine atom (-F), a methylene group (forming a ring together with Ls), or an ethylene group (forming a ring together with Ls)- 

[0239] As the divalent linking group represented by Ls, an alkylene group, a divalent aromatic cyclic group, -COO› L1-, -O-L 1 -, -L 1 -O-, and a group formed by combining two or more of these groups are exemplified, wherein L 1 represents an alkylene group, a divalent aliphatic hydrocar› bon cyclic group, a divalent aromatic cyclic group, or a group obtained by combining an alkylene group and a divalent aromatic cyclic group, which may further be substituted with a fluorine atom or the like. 

[0240] Ls preferably represents a single bond, ----COO-L 1 - (L 1 is preferably an alkylene group having 1 to 5 carbon atoms, and more preferably a methylene group or a propylene group), or a group represented by a divalent aromatic cyclic group. 

[0241] The alkyl group ofRs$_{4 }$ to Rs$_{6 }$ is preferably an alkyl group having 1 to 20 carbon atoms, more preferably an alkyl group having 1 to 10 carbon atoms, and especially preferably an alkyl group having 1 to 4 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, or at-butyl group. 

[0242] The monovalent aliphatic hydrocarbon cyclic group represented by Rss and Rs$_{6 }$ is preferably a monovalent ali› phatic hydrocarbon cyclic group having 3 to 20 carbon atoms, which group may be monocyclic such as a cyclopentyl group or a cyclohexyl group, or may be polycyclic such as a norbo› nyl group, an adamantyl group, a tetracyclodecanyl group, or a tetracyclododecanyl group. 

[0243] The ring formed by bonding Rss to Rs$_{6 }$to each other is preferably a ring having 3 to 20 carbon atoms, which may be monocyclic such as a cyclopentyl group or a cyclohexyl group, or may be polycyclic such as a norbonyl group, an adamantyl group, a tetracyclodecanyl group, or a tetracy› clododecanyl group. When Rss and Rs$_{6 }$ form a ring by bond› ing to each other, Rs$_{4 }$ preferably represents an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group or an ethyl group. 

[0244] The monovalent aromatic cyclic group represented by Rss and Rs$_{6 }$is preferably an aromatic cyclic group having 6 to 20 carbon atoms, e.g., a phenyl group and a naphtyl group are exemplified. When eitherone ofRss and Rs$_{6 }$is a hydrogen atom, the other is preferably a monovalent aromatic cyclic group. 

[ 0245] A monomer corresponding to the repeating unit rep› resented by formula (a) can be synthesized according to an ordinary synthesizing method of a polymerizable group-con› taining ester without any restriction. 

[0246] The specific examples of the repeating units repre› sented by formula (a) are shown below, but the invention is not restricted thereto. 

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<img src='content_image/890716.jpg'>

<img src='content_image/890717.jpg'>

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