PCL(2k)-PEG(3k)-COOH is an amphipathic polymer which can self-assemble in water. The hydrophobic polycaprolactone (PCL) segment can be used to entrap hydrophobic therapeutics while the PEG block can form a tight shell around the core due to hydrogen bonds interaction with water. The carboxyl (COOH) can react with amino molecule (such as protein or peptide etc.) in the presence of activating agent, such as HATU or EDC. Reagent grade, for research purpose.