PCL(5k)-PEG(2k)-COOH is a self-assembling block copolymer with polycaprolactone (PCL) as hydrophobic segment and PEG as hydrophilic block. The carboxyl is reactive with amine, such as protein or peptide, in the presence of activating agent (HATU/EDC) to form a stable amide linkage. Reagent grade, for research purpose.