Boron-nitrogen polymer precursors

There is great interest in developing molecular precursors for boron-nitrogen polymers and boron nitride solid state materials, and one general procedure is described in this report. Combinations of B-trichloroborazene and hexamethyldisilazane lead to formation of a gel which, upon thermolysis, gives hexagonal boron nitride. The BN has been characterized by infrared spectroscopy, x-ray powder diffraction and transmission electron microscopy. 

One attractive molecular species upon which polymeric boron nitride precursors could be based is the ring-compound borazine, BaNsHe The compound is easily made and has both the correct boron/nitrogen ratio and a hexagonal structure. Indeed, Paine and Paciorek have each demonstrated the use of linked polyborazine gels or polymers as precursors for boron nitride. 

B-Aminoborazines are of particular interest for fundamental studies. In these compounds, boron is bonded to three nitrogen atoms with two different types of environment. B-Aminoborazines are also useful precursors for the synthesis of thermally stable polymers. Quite a few polycondensates of aminoborazines and copolymerisates with organic difunctional molecules have been described 4>. Of major interest are difunctional borazines yielding linear polycondensates. The condensation of l,3,5-tris(2,6-dimethylphenyl)-2,4-dichloroborazine (cf. Section II.2.5) with aliphatic, aromatic, and heterocyclic diamines, as well as the preparation of the same linear polyborazines by transamination of 1,3,5-tris(2,6-dimethylphenyl)2,4-bis(diethyl-amino)borazine with diamines was studied 139). 

Boron tribromide in dichloromethane (1.0 M, 10 mL) was added to a solution of 24 (1.50 g, 2.00 mmol) in diehloromethane (30 mL) at room temperature under nitrogen. The resulting mixture was refluxed for 12 h. After reaetion, the mixture was washed with saturated NaHCOs solution, 5% Na2S03 solution, and brine. The organic layer was dried over MgS04, and the solvent was removed by evaporation. The residue was dissolved in a small amount of chloroform and poured into a large excess of hexane to precipitate the polymer. The polymer was collected by filtration with suction and dried under vacuum at r.t. for 6h. The precursor polymer 25 was obtained as a yellow solid. 

Boron, carbon and nitrogen from this polymer can not only react with the zirconium to form solids but also with the release of oxygen and hydrogen. Thermal dynamic calculations were carried out for the pyrolysis of [Zr(acac)2(C4HgO)2] and ZrB precursor with a B/Zr molar ratio of 2. Solids formed in the systems... 

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