PLGA-PEG-NHS has a NHS ester group at the distal end of PEG block. The reagent is an amine-reactive amphiphilic AB diblock copolymer consisting of a hydrophilic block polyethylene glycol (PEG) and a hydrophobic block poly(lactide-co-glycolide) (PLGA). The hydrophobic block terminates with a hydroxyl group. PEGylated copolymers with biodegradable and biocompatible polyester segments can be useful to prepare core-shell micelles, nanoparticles and microspheres. The hydrolytic degradability of polyester segments depend on the molecular weight and the spacer between ester groups. PEG-PLGA with other MW and a variety of L to G ratio is also available.