Mal NHS ester contains a maleimide and PFP ester end group. Maleimides react with thiol groups within the pH range of 6.5 to 7.5 and form stable thioether bonds. PFP is an activated ester which can readily react with amine-bearoing molecules to form stable amide bonds. It is less prone to hydrolysis than NHS ester.
Axispharm offers 3000+ PEG Linkers with high purity. Different kinds of PEG Reagents may be available by custom synthesis.