The present disclosure provides a compound having a constituent unit represented by general formula (1) and having a number average molecular weight of 1,000-3,000 (inclusive). (R1 is a group represented by formula (2), R2 is H, a group represented by formula (2), a C1-20 substitutable
hydrocarbon group, a C2-20 substitutable heterocycle-containing group, or a group obtained by substitution of a
methylene group in these groups, R3 and R4 are H,
halogen, or a C1-5 substitutable
alkyl group, which are bonding sites, group Agt, which are-O-or the like, and R101 is H or a C1-20
hydrocarbon group) (L1 is a C1-5 substituted alkylene group, R11 and R12 are H,
halogen, or C1-5 substituted or unsubstituted
alkyl groups, and n1 is 1 or 0).