Polymerization of Nitriles by Organotin Catalysts

The polymerization of the nitrile groups of polyacrylonitrile, polymethacrylonitrile and poly‐α‐cyanoethyl acrylate by organotin compounds was studied. The reaction, which was accompanied by color formation, was found to depend on the concentration and nature of the initiator, temperature, solvent and time of reaction. In the series Pb, Sn and Si, the organometallic derivatives of the former showed the strongest catalyst activity. A series of di‐ and higher nitriles, including benzal malononitrile, 1,1,3,3‐tetracyanopropane, α‐(2‐cyanoethyl) acrylonitrile and Diels Alder adduct of tetracyanoethylene with anthracene, was also polymerized to dark colored polymers. The mechanism of the polymerization is thought to consist of the addition of the organotin compound to the nitrile groups followed by cyclization leading to the formation of conjugated C=N double bonds. Evidence for this mechanism was obtained from the reaction of model compounds, such as 1,3‐dicyanobutane‐1‐carboxylic acid ester, with tributyltin methoxide.