Mal-PEG4-(PEG3-DBCO)-(PEG3-TCO) is a cleavable 10 unit PEG ADC linker used in the synthesis of antibody-drug conjugates (ADCs)[1]. Mal-PEG4-(PEG3-DBCO)-(PEG3-TCO) is a click chemistry reagent, it contains a TCO group that can undergo an inverse electron demand Diels-Alder reaction (iEDDA) with molecules containing Tetrazine groups.