Tetrazine-PEG4-SS-NHS is a cleavable 4 unit PEG ADC linker used in the synthesis of antibody-drug conjugates (ADCs). Tetrazine-PEG4-SS-NHS is a click chemistry reagent, it contains a Tetrazine group that can undergo an inverse electron demand Diels-Alder reaction (iEDDA) with molecules containing TCO groups.