Poly 2?-aminoborazines

The structure of this compound has been confirmed by X-ray analysis 172>. The first s-diazadiborines were obtained by pyrolysis of tris(t-butyl-amino)borane 166 167). Other less hindered tris(amino) boranes form aminoborazines or poly(aminoborazines) the nature of the product depends on pyrolysis time and utilized temperature 175>. Exocyclic B—N bonding appears to contribute to the stability of 1,3-diamino-diazaborines thereby explaining their chemical stability as compared to that of the corresponding tetraorganocompounds. 

A poly(aminoborazine), precursor for hexagonal boron nitride obtained by reaction of borazine B3N3H6 with ammonia, and its pyrolysis derivatives have been extensively characterised by and B MAS NMR. ... 

Two-step synthetic routes to poly(/i-aminoborazines) from /i-chloroborazines involve initial nucleophilic reaction of the /i-chloroborazine with appropriate linking reagents followed by a deamination reaction of the as-obtained /i-aminoborazine. The 5-tiichloroborazine undergoes nucleophilic attack by ammonia or amine derivatives on the boron atom linked to chlorine atoms. For the same reasons previously quoted a tertiary amine (e.g., Et3N) must be added to precipitate the corresponding hydrochloride. 

The preparation of high surface area boron nitride powders and foams from various molecular precursors has been studied. The highest specific areas were obtained using the poly-borazylenic precursor. However the difference with the measured surface area of the samples prepared from the polyhaloborazinic precursor was specially related to an enhanced micro-porosity of the samples prepared from the borazinic precursor. Curiously, the samples obtained from aminoborazinic precursors always exhibited a smaller specific surface area. This has been related to the ability of this precursor to melt and stay under a waxy form at... 

The reactions of [NP(NMe2)2]a[NPX(NMe2) ]b(NPX2) (X=C1, NH2) with B3N3Me3NH2 or B3N3Me3Cl3 followed by NHj have been utilized to generate poly(phosphazenes) with B-aminoborazine substituents. Pyrolysis of these polymers gave over 50% ceramic yield... 

In a two-step synthesis procedure, the B-trichloroborazine reacts with ammonia or amine derivatives as linking reagents to form B-aminoborazines which are subsequently thermolyzed at moderate temperatures to generate poly[B-aminoborazine] [25 7]. Pioneering works in this chemistry have described the preparation of B-aminoborazine-type polymers through a two-step procedure [31,32,34], but no attention has been given to the materials as BN precursors. 

In the 1970s, Tanigushi et al. reported the preparation of boron nitride fibers from a melt-spinnable poly[B-aminoborazine] (Eq. 14.4) [25], However, Uttle information has been provided and the lack of reproducibihty in the melt-spinning process rendered the production of BN fibers difficult. 

The second approach which generates poly(fi-aminoborazines) is based on the reaction of 5-chloroborazine derivatives with linking reagents such as silazanes in an one-step synthesis procedure. The earliest successful efforts to prepare poly[5-aminoborazine] according to this one-step synthesis procedure are those made by Paine et al. [38] They have synthesized a large variety of polymers by reaction of 5-chloroborazine derivatives with disilazanes. 

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