polymeric chelating agents and metal chelates , particularly those of lanthanide metals and more specifically those of gd , useful as contrast agents in magnetic resonance imaging for therapeutic and diagnostic applications as well as clinical and biomedical research applications . the polymeric chelates are generated using ring - opening metathesis polymerization . polymers can have multiple sites for functionalization allowing for the synthesis of multimodal and targeted contrast agents . hydroxypyridonate - based chelating moieties are integrated into a romp - derived polymer . more specifically , the hopo - based chelating moiety is integrated into a benzonorbornadiene unit that constitutes the backbone of the polymer . the romp - derived polymer chelators can comprise multiple metal ions , particularly gd ions , in polymers of varying lengths to provide a series of agents with controlled relaxivites . polymer chelates include those that are water - soluble .