The present invention relates to micelle-forming poly(ethylene oxide)-block-poly(ester) block copolymers having reactive groups on the polyester block therein. The biodegradability of these copolymers and their biocompatibilities with a large number of bioactive agents make them suitable as carriers for various bioactive agents. The bioactive agents, such as DNA, RNA, oligonucleotide, protein, peptide, drug and the like, can be coupled to the reactive groups on the polyester block of the copolymer.
