Boc amine PEG crosslinker is a Boc-protected amine group in one segment, and other functional groups in the other segment. BOC (tert-butoxycarbonyl) protecting group is the most common amine protecting group in non-peptide chemistry. Under acidic conditions, the Boc protecting group is easily removed, releasing free amines that can be used for conjugation with amine-reactive biomolecules.