The present disclosure concerns biologically active materials, particularly materials that comprise a biodegradeable polymer linked to a biologically active agent. The disclosure further concerns materials known as polymer-drug conjugates that typically contain a therapeutic agent, for instance a bioactive cytotoxic drug linked to a polymer backbone. The linkage typically is a convalent linkage. However, in some embodiments the disclosure concerns other polymer conjugates including those where the biologically active agent is an imaging agent, such as a tyrosinamide, a diagnostic agent, or a targeting agent, such as biotin.