SAS-PEG-SAS (PEG-bis-Succinimidyl Amido Succinate) is a linear homobifunctional polymer with two succinimide (NHS) groups and a C2 aliphatic amide between the PEG and the NHS ester key. The compound is capable of crosslinking with two amine molecules while maintaining water solubility and flexibility. It is a kind of NHS-PEG-NHS ester reagent.