Maleimide PEG amine (Maleimide-PEG-NH2) is a thiol reactive heterobifunctional PEG derivative. Maleimide groups react with sulfhydryl groups at pH 6.5~7.5 at room temperature to form stable thioether bonds, while primary amine groups on the other end can react with NHS, -COOH and other amine reactive molecues.