The hydroxy group on one side of this PEG crosslinker is able to undergo esterification reactions with acids for reversible pegylation. It also enables further derivatization or replacement with other reactive functional groups. The protected hydrazine may be liberated by treating the Boc group with acid. The hydrazine group is used to conjugate carbonyl compounds like aldehydes or ketones with the formation of hydrolysable and pH sensitive hydrazone links.