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 newly formed bonds are amides, imines or secondary amines. Applicable for reversible or permanent crosslinking with PEG. PEG tritylthio derivatives feature a protected thiol at one chain end. Trityl groups are easily removed with acid. Pure TFA or TFA/DCM mixtures cleave trityl from thiols quantitatively.