The present invention provides hydmoxyapatite-targeting, multiarm polymer reagents suitable for reaction with biologically active agents to form conjugates, the polymeric reagents comprising one or more polymer chains and a plurality of hydroxyapatile-targeting moieties located at the terminus of one or more of the polymer chains. The multiarm polymers are optionally divided or separated by one or more degradable linkages into polymer segments having a molecular weight suitable for renal clearance. The polymeric reagents of the invention can have a substantially linear structure, although branched or multiarm structures are contemplated as well. The invention is suited for applications in which use of a high molecular weight polymer is desired, such as a total polymer number average molecular weight of at least about 30,000 Da for linear polymers and 20,000 Da for multiarm polymers. Each structure includes one or more linkages capable of degradation in vivo. The use of multiple hydroxyapatite-targeting moieties on each polymer molecule enhances the ability of the polymer reagent to selectively target and bind to hydroxyapatite surfaces, which in turn, can increase the concentration of biologically active moiety delivered to the bone site.
