138  US 9,612,535 B2  137  a trifluoromethyl group is preferred, and a hydrogen atom or  a methyl group is particularly preferred.  Ab represents a single bond, an alkylene group, a divalent  linking group having a monocyclic or polycyclic cycloalkyl  structure, an ether bond, an ester bond, a carbonyl group or  a divalent linking group in which these groups are com› bined. Ab is preferably a single bond and a divalent linking  group represented by -Ab$_{1}$-CO$_{2}$-.  Ab$_{1 }$ is a straight or branched alkylene group, or a mono› cyclic or polycyclic cycloalkylene group, and preferably a  methylene group, an ethylene group, a cyclohexylene group,  an adamantylene group or a norbonylene group.  V represents a group having the structure shown by any  one of Formulas (LCl-1) to (LCl-16).  The repeating unit having a lactone group usually has an  optical isomer, but any optical isomer may be used. In  addition, one kind of optical isomer may be used alone, or  a plurality of optical isomers may be used in mixtures. When  one kind of optical isomer is mainly used, the optical purity 20  ( ee) thereof is preferably 90% or more, and more preferably  95% or more.  The content of the repeating unit having a lactone group  is in a range of preferably 15 to 60 mo! %, more preferably  20 to 50 mo! %, and still more preferably 30 to 50 mo! %,  based on the total repeating units of the resin (Ab).  Hereinafter, specific examples of the repeating unit hav› ing a lactone group will be shown, but the present is not  limited thereto.  (In the formulas, Rx represents CH$_{3}$, CH$_{2}$OH, or CF$_{3}$)  Rx  I  --+CH2-C+- I  C=O  I  0  0  -&o  !Yo  -continued 