Dec. 17, 2020  4  US 2020/0393760 Al  pyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl,  n-pentyl, cyclopentyl, n-hexyl, and cyclohexyl. Examples of  the alkyl moiety in the C$_{1 }$-C$_{6 }$ alkoxy group R 4  are as  exemplified above for the alkyl group. Examples of the alkyl  moiety in the C$_{2}$-C$_{6 }$ acyloxy group R 4  are as exemplified  above for the alkyl group, but of  1  to 5 carbon atoms. The  C$_{2}$ -C$_{8 }$ alkenyl group represented by  R 4 B  may be straight,  branched or cyclic, and examples thereof include vinyl,  1-propenyl, 2-propenyl, butenyl, hexenyl, and cyclohexenyl.  Among others, R 4  is preferably selected from fluorine,  chlorine, bromine, hydroxyl, amino,  C$_{1 }$-C$_{3 }$ alkyl,  C$_{1 }$-C$_{3 }$ alkoxy,  C$_{2}$ -C$_{4 }$ acyloxy,  -NR $^{4}$A-C(=0)-R,  and  -NR4A----C(=0)---0-R4B_  [0046]  In formula (a), Rs is a  C$_{1 }$-C$_{10 }$ alkyl group or  CcC$_{10 }$ aryl group, which may be substituted with an amino, nitro,  cyano,  C$_{1 }$-C$_{12 }$ alkyl,  C$_{1 }$-C$_{12 }$ alkoxy,  C$_{2}$-C$_{12 }$ alkoxycarbonyl,  C$_{2}$-C$_{12 }$ acyl,  C$_{2}$-C$_{12 }$ acyloxy, hydroxyl moiety or halogen.  [0047]  Of the groups represented by Rs, the C$_{1 }$-C$_{10 }$alkyl  group may be straight, branched or cyclic, and examples  thereof include those exemplified above as the C$_{1 }$-C$_{6 }$ alkyl  groups R 4 ,  R 4 A  and  R 4 B  and n-heptyl, n-octyl, n-nonyl,  n-decyl, norbomyl, and adamantyl. Examples of the  CcC$_{10 }$ aryl group include phenyl, tolyl, xylyl, 1-naphthyl, and  2-naphthyl. The C$_{1 }$-C$_{12 }$ alkyl group may be straight,  branched or cyclic, and examples thereof include those  exemplified above as the C$_{1 }$-C$_{10 }$alkyl groups and n-undecyl  and n-dodecyl. Examples of the alkyl moiety in the C$_{1 }$-C$_{12 }$ alkoxy group include those exemplified above as the C$_{1 }$-C$_{12 }$ alkyl groups. Examples of the alkyl moiety in the C$_{2}$ -C$_{12 }$ alkoxycarbonyl,  C$_{2}$-C$_{12 }$ acyl or  C$_{2}$-C$_{12 }$ acyloxy group  include those exemplified above as the C$_{1 }$-C$_{12 }$alkyl groups,  but of  1  to  11  carbon atoms.  [0048]  In formula (a),  L1  is a single bond or a C$_{1 }$-C$_{20 }$ divalent linking group which may contain an ether bond,  carbonyl moiety, ester bond, amide bond, sultone moiety,  lactam moiety, carbonate moiety, halogen, hydroxyl moiety  or carboxyl moiety.  [0049]  In formula (a), m is an integer of  1  to 5, n is an  integer of Oto 3, lsm+ns5, and p is  1  or 2.  [0050]  Examples of the cation moiety in the monomer  from which recurring units (a) are derived are shown below,  but not limited thereto. Herein  RA  is as defined above.  0  -w› H  -continued  RA  -WH  -w› H  L 