Addition polymerization of nitrile compounds by organotin catalysts

A study was made of the polymerization of NC(CH₂)_nCN (n = 1-4), fumaronitrile and tetracyanoethylene (TCNE) by organotin compounds such as, oxides and alkoxides, as catalysts. It was found that polymerization occurred with malononitrile, succinonitrile, fumaronitrile and TCNE, but not with glutaronitrile and adiponitrile. Initiation of the polymerization is by addition of the tin compounds to the CN bond leading to the formation of a SnN bond, and propagation is probably by insertion of this bond to CN bonds. Addition of the tin compounds occurred only to nitrile groups that were sufficiently activated by proximity to electron withdrawing groups. The mutual electron withdrawing effect of one nitrile on the other is sufficient to permit this addition if the nitriles are geminal or vicinal, otherwise no reasonable polymerization occurred. The polymerization of the nitrile bond leads to the formation of highly conjugated systems, which give a black colour to the polymers.