Propargyl-PEG6-Ms is a PEG derivative containing propargyl and mesyl moieties. 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. Mesyl is a good leaving group and can be used for substitution reactions. The hydrophilic PEG spacer increases the water solubility of a compound in aqueous media.