Mal-PEG-SCM (MW 20000) is a linear heterobifunctional PEG compound featuring maleimide and N-hydroxysuccinimide (NHS) ester groups. It serves as an essential PEGylated crosslinker. The maleimide group reacts with thiols, such as SH or sulfhydryl groups, while SCM stands for succinimidyl carboxymethyl, which can react with primary amines. The maleimide possesses a reactive C=C double bond, which is sensitive to light and oxygen.