PCL(2k)-PEG(2k)-COOH is a micelle-forming polymer for hydrophobic 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 polycaprolactone (PCL) can be degraded by hydrolysis on the ester bonds. Reagent grade, for research purpose.