PCL(4k)-PEG(5k)-NHS is an amphipathic polymer with NHS ester which can react with amine (NH2) via amide linkage formation. The block copolymer contains a hydrophobic polycaprolactone (PCL) block chemically attached to a hydrophilic PEG block. Upon dispersion in water, the polymer self assembles to form micelles which can encapsulate drugs for drug delivery. Reagent grade, for research purpose.