Methacrylonitrile (or 2-Methylprop-2-enenitrile), MeAN in short, is a chemical compound that is an unsaturated aliphatic nitrile, widely used in the preparation of homopolymers, copolymers, elastomers, and plastics and as a chemical intermediate in the preparation of acids, amides, amines, esters, and other nitriles. MeAN is also used as a replacement for acrylonitrile in the manufacture of an acrylonitrile/butadiene/styrene-like polymer. It is a clear and colorless (to slightly yellow) liquid, that has a bitter almond smell. It is toxic by ingestion, inhalation, and skin absorption. Exposure and regulation Since MeAN is present in polymeric coating materials as found in many everyday use items, humans are exposed to it by skin absorption. Aside from this there is an occupational exposure, and low levels of MeAN are also present in the smoke of unfiltered cigarettes made from air-cured or flue-cured tobaccos. Due to the toxicity of MeAN, the U.S. Department of Health & Human Services has limited the concentration of methacrylonitrile-derived polymer in resinous and polymeric coating materials to 41%. Its use in food packaging is further limited to 0.5 mg per square inch of food-contact surface, and only 50 ppm, or 0.005% MeAN is permitted in chloroform-soluble coating components in water containers (21 CFR, § 175.300). A time-weighted average (TWA) threshold limit value of 1 ppm (3 mg/m3) for MeAN exposure was adopted by the American Conference of Governmental Industrial Hygienists. The National Cancer Institute (USA) nominated MeAN for research because of its potential for human exposure, the common features shared with the known carcinogen acrylonitrile and the shortcoming of knowledge in toxicity and carcinogenicity of MeAN. Structure and reactivity Methacrylonitrile is an acrylonitrile (AN) with an additional CH3 group on the second carbon. Polymerization does not require a catalyst and happens rapidly in the absence of a stabilizer. Because of its double bond, additional reactions are possible with biological molecules. The extra methyl group of MeAN lessens the electron-withdrawing effect caused by the nitrile so that reactions that form negative charge on the alpha carbon are faster with AN as the reactant. Inversely, reactions that form a positive charge on said carbon (i.g. Cytochrome-P450 oxidation of the double bond), are faster with MeAN as the reactant. As a result, in metabolism, MeAN conjugates less with glutathione (GSH) than AN, and is activated more easily. Synthesis Poly(acrylonitrile) is generally made via emulsion or solution polymerization. The commercial product can be stabilized by