10  US 10,394,127 B2  9  and Rs$_{6 }$ may be bonded to  each other to form  a ring.  However,  Rss  and Rs$_{6 }$ do not represent a hydrogen  atom at  the same time in any  case.  General Formula  (V)  will be described in  more detail.  Examples of the alkyl  group of each of Rsi  to Rs$_{3 }$ in  General Formula  (V) preferably include  an alkyl group  having 20 or less carbon  atoms, such as a methyl  group, an  ethyl group, a propyl  group, an isopropyl  group, an n-butyl  group, a sec-butyl  group, a hexyl group,  a  2-ethylhexyl  group, an octyl group,  and a dodecyl group,  which may have  a  substituent, more preferably  include an alkyl group  having  8 or less carbon atoms,  and particularly preferably  include  an alkyl group having  3 or less carbon atoms.  The alkyl group included  in an  alkoxycarbonyl  group is  preferably the same  alkyl group as that in  each ofRsi to Rs$_{3 }$ described above.  The cycloalkyl group  may be monocyclic  or polycyclic.  Preferred examples  thereof include a monocyclic  cycloalkyl  group having 3 to  10  carbon atoms, such  as a  cyclopropyl  group, a cyclopentyl  group, and a cyclohexyl  group, which  may have a substituent.  Examples of the halogen  atom include a fluorine  atom, a  chlorine atom, a bromine  atom and an iodine  atom, with the  fluorine atom being  particularly preferable.  Preferred examples  of the substituent  in each group  described above can  include an alkyl group,  a cycloalkyl  group, an aryl group,  an amino group, an  amido group, a  ureido group, a urethane  group, a hydroxyl group,  a carboxyl  group, a halogen atom,  an alkoxy group, a  thioether group,  an acyl group, an acyloxy  group, an alkoxycarbonyl  group,  a cyano group, and  a nitro group, and  the substituent  preferably has 8 or  less carbon atoms.  Furthermore,  in a case where Rs$_{2 }$ represents an alkylene  group and is bonded  to Ls to form a ring,  preferred examples  of the alkylene group  include an alkylene  group having  1  to  8 carbon atoms, such  as a methylene group,  an ethylene  group, a propylene  group, a butylene  group, a hexylene  group, and an octylene  group. The alkylene  group is more  preferably an alkylene  group having  1  to  4  carbon atoms,  and particularly preferably  an alkylene group having  1  or 2  carbon atoms. A ring  formed by the bonding  of Rs$_{2 }$ and Ls  is  particularly preferably  a 5- or  6-membered ring.  Rsi and Rs$_{3 }$ in Formula (V) are  each more preferably  a  hydrogen atom, an  alkyl group, or a  halogen atom, and  particularly 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$_{2 }$ is more preferably  a  hydrogen atom, an  alkyl group, a halogen  atom, or an  alkylene group (which  is bonded to Ls to  form a ring), and  particularly 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), a fluorine atom  (-F), a methylene  group (which is  bonded to Ls to form  a ring), or an ethylene  group (which is  bonded to Ls to form  a ring).  Examples of the divalent  linking group represented  by Ls  include an alkylene  group, a divalent aromatic  cyclic group,  -COO-Li-, ---0-Li-,  and a group formed  by combining  two or more thereof.  Here, Li represents  an alkylene group,  a  cycloalkylene group,  a divalent aromatic  cyclic group, and  a group formed by  combining an alkylene  group with a  divalent aromatic cyclic  group.  Ls is preferably a  single bond, a group  represented by  -COO-Li-,  or a divalent aromatic  cyclic group. Li is  preferably an alkylene  group having  1  to 5 carbon atoms,  and more preferably  a methylene group  or a propylene  That is, in General Formula  (S), the moiety represented  by  -L-SO$_{3}$ - represents a moiety  capable of generating  a sul› fonic acid group as  the leaving group represented  by wi at  the terminal leaves,  L is a polyvalent linking  group formed  of a non-metal atom,  and more specific  examples of the  moiety include those  configured by the combination  of the  following structural  units.  (In the formula, wi  represents a group capable  of leaving  by an acid, and L  represents a linking  group formed of a  polyvalent non-metal  atom which is necessary  to link a  structural unit represented  by General Formula  (S) to a  polymer skeleton.)  The side chain structure  included in the repeating  unit (a)  is preferably  represented by General  Formula (S).  The aralkyl group represented  by each ofRss and Rs$_{6 }$ may  be monocyclic or polycyclic,  or may have a substituent.  The  aralkyl group preferably  has 7 to 21 carbon  atoms, and  examples thereof include  a benzyl group and  a  1-naphthyl› methyl group.  The aryl group represented  by each of  Rss  and Rs$_{6 }$ is  preferably an aryl group  having 6 to 20 carbon  atoms, may  be monocyclic or  polycyclic, or may  have a substituent.  Examples thereof  include a phenyl  group, a 1-naphthyl  group, a 2-naphthyl  group, a  4-methylphenyl  group, and a  4-methoxyphenyl  group. In a case where  any one ofRss and  Rs$_{6 }$ is a hydrogen atom,  the other is preferably  an aryl group.  Furthermore,  the ring formed by  the mutual bonding  of  Rss  and Rs$_{6 }$is preferably a ring  having 3 to 20 carbon  atoms,  may be monocyclic,  such as a cyclopentyl  group and a  cyclohexyl group, and  may be the ring which  is polycyclic,  such as a norbornyl  group, an adamantyl  group, a tetracy› clodecanyl group,  and a  tetracyclododecanyl  group. In a  case where  Rss  and Rs$_{6 }$ are bonded to each  other to form a  ring, Rs$_{4 }$ is preferably an alkyl  group having  1  to 3 carbon  atoms, and more preferably  a methyl group or  an ethyl  group.  The cycloalkyl group  represented by each  ofRss and Rs$_{6 }$ is preferably a cycloalkyl  group having 3 to  20 carbon  atoms, may be a cycloalkyl  group which is monocyclic,  such  as a  cyclopentyl group and  a  cyclohexyl group, and  may be  a cycloalkyl group  which is polycyclic,  such as a norbomyl  group, an adamantyl  group, a  tetracyclodecanyl  group, and  a  tetracyclododecanyl  group.  The alkyl group of  each of Rs$_{4 }$ 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  particularly  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, and a  t-butyl group.  Suitable examples  of the trivalent linking  group repre› sented by Ls in a case  where Ls is bonded  to Rs$_{2 }$ to form a  ring include a group  obtained by eliminating  arbitrary one  hydrogen atom from  the  above-described specific  examples  of the divalent linking  group represented by  Ls- group. The divalent  aromatic cyclic group  is preferably a  1,4-phenylene group,  a  1,3-phenylene group,  a 1,2-phe› nylene group, or a  1,4-naphthylene  group, and more pref› erably a 1,4-phenylene  group.  General Formula (S):  I  -C-,  I 