t-Boc-N-Amido-PEG4-azide is a PEG derivative containing an azide group and Boc-protected amino group. The hydrophilic PEG spacer increases solubility in aqueous media. The azide group can react with alkyne, BCN, DBCO via Click Chemistry to yield a stable triazole linkage. The Boc group can be deprotected under mild acidic conditions to form the free amine.