Methyltetrazine-PEG4-SS-PEG4-methyltetrazine is a cleavable 8 unit PEG ADC linker used in the synthesis of antibody-drug conjugates (ADCs)[1]. Methyltetrazine-PEG4-SS-PEG4-methyltetrazine 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.