N-(Amino-PEG2)-N-bis(PEG3-azide) is a branched PEG derivative containing azide and amine moieties. The azide can react with alkyne, BCN, DBCO via Click Chemistry to yield a stable triazole linkage. An amine is reactive with carboxylic acids, activated NHS esters, carbonyls (ketone, aldehyde) etc. The hydrophilic PEG spacer increases solubility in aqueous media.