Jul.  18,  2019  32  US 2019/0219920 Al  -continued  [0258]  As the structural unit (a2), a structural unit derived  from an acrylate ester which may have the hydrogen atom  bonded to the carbon atom on the a-position substituted with  a substituent is preferable.  [0259]  The structural unit (a2) is preferably a structural  unit represented by general formula (a2-1) shown below.  In the formula, R represents a hydrogen atom, an alkyl group  of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to  5 carbon atoms; Ya$^{21 }$represents a single bond or a divalent  linking group; La 21  represents ---0-, --COO-, --CON  (R’)-, ---OCO-, -CONHCO- or-CONHCS-; and R’  represents a hydrogen atom or a methyl group; provided  [Chemical Formula 35]  (a2-1)  R  ~ $_{Ya21 }$ I  La21  \ $_{Ra21 }$ (r-cr-3-2)  (r-cr-3-1)  (r-cr-2-4)  (r-cr-2-3)  (r-cr-2-2)  (r-cr-3-3)  (r-cr-3-4)  (r-cr-3-5)  -continued 