Conversion of B(NHCH3)3 into boron nitride and polyborazine fibres and tubular BN structures derived therefrom

Abstract

The reaction of ammonia with tris(methylamino)borane B(NHCH ₃ ) ₃ 1 or with a B(NHCH ₃ ) ₃ derived polyborazine 2 led to completely different processes. Compound 1 reacted spontaneously with NH ₃ to give mainly the borazine (CH ₃ NH) ₃ B ₃ N ₃ H ₃ and subsequently a BN prepolymer which was not processible. A polymer 2 obtained by heating 1 under argon could be spun into crude polyborazinic fibres. When 2 was heated under ammonia in order to obtain carbon free BN, it was partially dissociated into 1,3,5-trimethyl-2,4,6-tri(amino)borazine (NH ₂ ) ₃ B ₃ N ₃ (CH ₃ ) ₃ 3. The borazine 3 was fully characterised by multinuclear NMR spectroscopy, FTIR and mass spectrometry. The structure of 3 has been confirmed by a single crystal X-ray diffraction analysis. An illustration of the formation of 3 was the formation of BN tubes from crude fibres. These results were explained by the TGA curves of the polymer 2 under ammonia or nitrogen.