PCL(4k)-PEG(1k)-COOH is a linear amphipathic polymer with carboxyl terminal which can react with amine in the presence of activator, such as HATU or EDC, to form a stable amide bond. The hydrophobic polycaprolactone (PCL) can be hydrolyzed on the ester bonds. The self-assembling polymer forms micelles which can be used to entrap hydrophobic drugs for nanomedicine. Reagent grade, for research purpose.