PCL(2k)-PEG(5k)-COOH has a polyester, polycaprolactone (PCL), hydrophobic block and a PEG hydrophilic block. The carboxyl (COOH) is tethered to PEG which is reactive with amine in the presence of activating agent, such as HATU or EDC, to form a stable amide linkage. The polymer can self-assemble to form micelles in water and be used to encapsulate drugs in drug delivery. Reagent grade, for research purpose.