Propargyl-PEG4-Sulfone-PEG4-t-butyl ester is a PEG derivative containing a propargyl group and t-butyl protected carboxyl group acid. The propargyl groups can be reacted with azide-bearing compounds or biomolecules via copper catalyzed azide-alkyne Click Chemistry to yield stable triazole linkages. The t-butyl protected carboxyl group (COOH) prevents self coupling or polymerization under standard acid/amine or acid/hydroxyl coupling conditions. The protected acid can be deprotected by acidic or basic hydrolysis. The hydrophilic PEG spacer increases solubility in aqueous media.