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 Boc (tert-butyloxycarbonyl)-protected amino group is stable in a wide range of conditions (including highly basic environments) but may be easily removed by (strong) acids such as TFA or at low pH in water to release the primary amine.