PCL(2k)-PEG(1k)-COOH is a self-assembling polymer where the hydrophilic block (PEG) will face the water and the hydrophobic block (polycaprolactone (PCL)) will be shielded from the water. The hydrophobic core regions serve as reservoirs for hydrophobic drugs allowing high concentration delivery of hydrophobic drugs which exceeds their innate water solubility. The carboxylic acid moiety can be used for bioconjugation with peptide/protein/amino molecule in the presence of activating agent, such as HATU or EDC. Reagent grade, for research purpose.