Poly B-vinylborazine or 2-Ethenylborazine Homopolymer

The procedure described below gives lightly cross-linked, pure poly(B-vinyl-borazine) (an inorganic analog of polystyrene) in good yields. 

056-g sample of AIBN (2 -azobisisobutyronitrile) is placed into a one-piece 100-mL flask (such as Chemglass AF-0S22-02) equipped with a Teflon vacuum stopcock and a magnetic stir bar, and the flask is evacuated at — 196°C. A 1.69-g (15.9 mmol) sample of B-vinylborazine (prepared by the procedure described above) is vacuum distilled into the flask. Three freeze-pump-thaw cycles are performed in order to remove any traces of oxygen. The stopcock is closed and the reaction flask is removed to a shielded hood where it is heated in an oil bath at 70°C for about 3 h, at which point the material is sufficiently viscous that the stir bar stops. Then 5 mL of benzene is condensed into the flask and the solution is heated at 70°C for another 9 h. Slow addition of the benzene solution into 40 mL of pentane under inert atmosphere aflbrds the precipitation of 0.73 g (43.2% yield) of poly(B-vinyl-borazine). The polymer is filtered under nitrogen and dried in vacuo for about 5 min. 

Poly(B-vinylborazine) is an air-sensitive white solid. Lightly cross-linked, freshly prepared samples are soluble and thermally stable in most dry aprotic solvents, such as benzene and ethers. If stored as a solid at room temperature, the polymer may become insoluble in several hours, but in benzene or glyme solution it is stable and can be used as a stock solution. The polymer decomposes rapidly in contact with water and alcohols. 

For a review of borazine chemistry see Gmelin Handbush der Anorganishen Cheme, Borazine and Its Derivatives, Springer-Verlag, New York, 1978, p. 48. 

in Hydrides of Boron and Silicon, Cornell University Press, Ithaca, NY, 1933, p. 94. 

Molecular weights, as determined by SEC/LALLS, of representative materials that are prepared as described above are Mn = 13,900, Mw = 39,250, and Mw/Mn = 2.82. 

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