PCL(5k)-PEG(3k)-COOH is a micelle-forming polymer for drug encapsulation in drug delivery system. The polymer has terminal carboxyl which can react with amine molecule to form a stable amide linkage in presence of activator, such as HATU or EDC. The polyester hydrophobic block, polycaprolactone (PCL), can be degraded via hydrolysis attack on the ester bonds. Reagent grade, for research purpose.