A polymer comprises at least one functional group of the formula (I) bound to one of the termini and/or to the backbone of the polymer, or a salt thereof. # indicates the point of attachment to the terminus and/or to the polymer backbone; A is a chemical bond or a divalent moiety selected from the group consisting of C1-C6 alkylene, —O—(C2-C6 alkylene), —C(═O)—O—(C2-C6 alkylene), —NR3—(C2-C6 alkylene) and C(═O)—NR3—(C2-C6 alkylene), where the C2-C6 alkylene part is attached to Q; Q is a divalent moiety selected from the group consisting of —O—, —NH— and —S—; and X is a divalent moiety selected from the group consisting of linear C1-C10 alkylene, linear C2-C6 alkenylene, C4-C7 cycloalkylene, arylene and alkarylene, wherein the linear C1-C10 alkylene, the linear C2-C6 alkenylene, the C4-C7 cycloalkylene, the arylene and the alkarylene may be substituted.