Modification of anti-cancer drugs with poly(ethylene glycol)(PEG),e.g.directly linking PEG to hydrophobic drugs and conjugating drugs to PEG-block copolymers (PEG-polyDeug),has been shown to significantly improve the physicochemical and biological properties of various drug delivery systems [1].PEG-polyDrugs are generally synthesized by conjugating anticancer drugs via cleavable bonds onto the polymer backbones.However,this method has several disadvantages including incomplete conjugation,side reactions and broad polydispersity.