PCL(1k)-PEG(1k)-NH2 possesses two dissimilar block of polymers, i.e. hydrophobic polycaprolactone (PCL) and hydrophilic PEG blocks. The terminal amine is reactive with NHS ester to form a stable amide linkage. Upon dispersion in water, the polymer self-assembles with the PCL being shielded from water by the PEG. The PCL core can be used to encapsulate hydrophobic drugs. On the other hand, the PEG shell not only provides protection against degradation but also enables a stealth behavior which is a prerequisite for successful in vivo translation of nanomedicine to achieve long blood circulation and targeted delivery. Reagent grade, for research purpose.