PTAD-PEG4-alkyne is a cleavable 4 unit PEG ADC linker used in the synthesis of antibody-drug conjugates (ADCs) [1]. PTAD-PEG4-alkyne is a click chemistry reagent, it contains an Alkyne group and can undergo copper-catalyzed azide-alkyne cycloaddition (CuAAc) with molecules containing Azide groups.