PCL(1k)-PEG(5k)-NHS is a monofunctional block copolymer with terminal N-Hydroxysulfosuccinimide (NHS) ester which is reactive with amine (NH2). The copolymer consists of hydrophobic polycaprolactone (PCL) and hydrophilic PEG block which can self-assemble in water to form micelles used for controlled release drug delivery. Reagent grade, for research purpose.