Azido-PEG11-NHS ester is a PEG derivative that finds application in drug delivery research. Serving as a click chemistry reagent, it contains an Azide group capable of undergoing copper-catalyzed Azide-Alkyne Cycloaddition (CuAAc) with molecules bearing Alkyne groups. Additionally, it can participate in Strain-Promoted Alkyne-Azide Cycloaddition (SPAAC) with molecules containing DBCO or BCN groups.