A method for synthesizing extended poly(amino acids) conjugated to imaging agents, such as DTPA, is disclosed. The amino acid is initially conjugated to the imaging agent at the monomer stage, followed by formation of the corresponding N-carboxyanhydride. The method utilizes catalyzed ring opening polymerization of the N-carboxyanhydride of the amino acid-imaging agent monomer allowing the formation of a poly(amino acid) backbone having 100% imaging agent conjugation if desired. However, the present method also permits the degree of conjugation to be controlled by copolymerizing the N-carboxyanhydride of the amino acid-imaging agent monomer with one or more unconjugated monomers, i.e. N-carboxyanhydrides of the same or of other amino acids. Various imaging agents may be employed, and new hybrid random, block, and mixed copolymers may be prepared.