t-Boc-aminooxy-PEG3-propargyl is a crosslinker containing a propargyl group and t-Boc-aminooxy group. The propargyl group can be reacted with azide-bearing compounds or biomolecules via copper catalyzed azide-alkyne Click Chemistry to yield a stable triazole linkage. PEG Linkers may be useful in the development of antibody drug conjugates.