Propargyl-NH-PEG3-C2-NHS ester is a non-cleavable 3 unit PEG ADC linker used in the synthesis of antibody-drug conjugates (ADCs). Propargyl-NH-PEG3-C2-NHS ester is a click chemistry reagent, it contains an Alkyne group and can undergo copper-catalyzed azide-alkyne cycloaddition (CuAAc) with molecules containing Azide groups.