Barium anionic initiators

With barium-containing anionic initiators [88] polybutadiene with a high trans content [89] and less then 5 % of vinyl double bonds can be synthesized. This rubber does not crystallize at room temperature but can undergo crystallization upon stretching. The properties of rubber, e. g., green strength, tackiness of the compound, as well as tensile strength of the vulcanizate, are much improved by strain-induced crystallization. 

These are usually reactions of anhydrous transition and B metal halides with dry alkali metal salts such as the sulphides, nitrides, phosphides, arsenides etc. to give exchange of anions. They tend to be very exothermic with higher valence halides and are frequently initiated by mild warming or grinding. Metathesis is described as a controlled explosion. Mixtures considered in the specific reference above include lithium nitride with tantalum pentachloride, titanium tetrachloride and vanadium tetrachloride, also barium nitride with manganese II iodide, the last reaction photographically illustrated. 

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