Azido PEG amine, N3-PEG-NH2 (MW 3400) is a hetero-bifunctional PEG product with an azide and an amine group at the PEG terminus. N3-PEG-NH2 is an important cross-linker with PEG chains. The azide can be used for molecular conjugation through chemical reactions, and the amine can react with carboxylic acid or NHS ester.