Conjugate comprises at least one carboxyl group-containing compound and an oligomer, where the oligomer: comprises peptidically crosslinked monomer units； is formed from more than 50%, relative to the number of monomer units, of epsilon -lysine monomer units； or comprises at least 10 consecutive monomer units that are formed from at least up to 70%, relative to the number of monomer units, of epsilon -lysine monomer units. Independent claims are included for: (1) the preparation of the conjugate comprising providing the oligomers, as above per se, and conjugating at least one optionally activated carboxylic group-containing compound to the oligomer； and (2) a kit, for preparing pharmaceutical composition (preferably a therapeutic or image enhancing composition), comprising the above conjugate.
