Propargyl-O-C1-amido-PEG2-C2-NHS ester is a nonclaevable 2-unit PEG linker for antibody-agent-conjugation (ADC). Propargyl-O-C1-amido-PEG2-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.