Maleimide-PEG-Poly(lactide-co-glycolide)-COOH (Mal-PEG-PLGA-COOH) is a functional amphiphilic block copolymer with maleimide capped PEG and amine capped PLGA. Mal-PEG-PLGA-NH2 can self assemble into micelles/nanoparticles. Maleimide on the micelle surface can conjugate with thiol, SH, sulfhydryl or mercapto group to form a disulfide bond. COOH group on the PLGA block can be used for drug conjugation or micellar core modification. Hydrophobic drugs is encapsulated in the PLGA core for targeted drug delivery.