mPEG(5k)-PCL(10k)-COOH is a widely used micelle-forming polymer for drug encapsulation in nanomedicine. 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 PCL is biodegradable via hydrolytic attack on the ester bonds. Reagent grade, for research purpose.