mPEG(2k)-PCL(2k)-COOH has a polycaprolactone (PCL) hydrophobic block and a PEG hydrophilic block. The terminal carboxyl 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.