Propargyl-PEG8-t-butyl ester is a PEG reagent with an alkyne group and a t-butyl group. The alkyne group enables the formation of triazole linkage with azide-bearing compounds or biomolecules; copper is required as a catalyst. The t-butyl group can be hydrolyzed under acidic conditions. The hydrophicility of the molecule is improved by having 8 units of PEG.