The amine functional group at one end of the PEG linker molecule allows for selective and covalent attachment to other molecules with complementary functional groups, such as carboxylic acids or activated esters, aldehydes and epoxides. 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.