Abstract: The present invention provides a biodegradable, biocompatible polymer that is capable of forming particles (micelles), vesicles, surfaces and membranes, and other structures in which a biologically active agent, e.g. a drug, can be incorporated in such a way that its release to the host can be controlled to a high degree of accuracy, or in where surfaces of the formed polymers can be used to increase the hemeo compatibility of biomaterials. The present invention provides polymer compounds comprising at least one biodegradable polyester having a terminal functional group based on hydrophilic moieties from a phospholipid.