Abstract: Provided is a compound (Z) represented by the formula (1) or (2) below. In the formulas (1) and (2), Xs in each of the formulas (1) and (2) are each independently a carboxy group, a carboxylate group, or a monovalent group represented by the formula (3); at least one of Xs in each of the formulas (1) and (2) is a carboxy group or a carboxylate group; and at least one of Xs in each of the formulas (1) and (2) is a monovalent group represented by the formula (3) —C(O)—Y-(AO)n—R (3). In the formula (3), —Y— is —O—, —NH—, or —S—; A is a C2-C4 alkylene group; R is a hydrogen atom or a C1-C15 monovalent hydrocarbon group in which a hydrogen atom is optionally substituted with a C1-C10 alkoxy group; n is an integer of 4 to 1000; at least one of n As is an ethylene group; and when the formulas (1) and (2) each have multiple monovalent groups represented by the formula (3), each of —Y—, A, R, and n is the same or different among the monovalent groups.