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Boron Nitride Fibers Prepared from Symmetric and Asymmetric Alkylaminoborazines
Author(s) -
Toury B.,
Miele P.,
Cornu D.,
Vincent H.,
Bouix J.
Publication year - 2002
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/1616-3028(200203)12:3<228::aid-adfm228>3.0.co;2-u
Subject(s) - materials science , fourier transform infrared spectroscopy , raman spectroscopy , boron nitride , polymer , scanning electron microscope , ceramic , ultimate tensile strength , composite material , chemical engineering , optics , physics , engineering
The thermolysis of 2,4,6‐[(CH 3 ) 2 N] 3 B 3 N 3 H 3 ( 1 ), 2,4‐[(CH 3 ) 2 N] 2 ‐6‐(CH 3 HN)B 3 N 3 H 3 ( 2 ), and 2‐[(CH 3 ) 2 N]‐4,6‐(CH 3 HN) 2 B 3 ‐N 3 H 3 ( 3 ) led to polyborazines 4 , 5 , and 6 respectively. The polymers display direct B–N bonds between borazinic B 3 N 3 rings and, in addition, a proportion of –N(CH 3 )– bridges for 5 and 6 , as clearly underlined by 13 C NMR spectroscopy. Melt‐spinning of these three polymeric precursors exemplified that their ease of processing increases in the order 4 < 5 < 6 . Nevertheless, polyborazine filaments could be prepared from each of them and a subsequent thermal treatment up to 1800 °C resulted in the formation of crystalline hexagonal boron nitride fibers, which were characterized by X‐ray diffraction analysis, Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. Scanning electron microscopy (SEM) images showed that the ceramic fibers are circular and dense without major defects. The mechanical properties for 4 ‐derived fibers could not be measured because of their brittleness, whereas measurements on 5 ‐ and 6 ‐derived fibers gave tensile strength σ R = 0.51 GPa, Young’s modulus E = 67 GPa, and σ R = 0.69 GPa, E = 170 GPa, respectively. The improvement in mechanical properties for ceramic fibers prepared respectively from 4 , 5 , and 6 could be explained to a large extent by the improvement of the processing properties of the preceramic polymers. This evolution could be related to the increased ratio of bridging –N(CH 3 )– groups between the B 3 N 3 rings within the polymers 4 , 5 , and 6 and therefore to the functionalities of the starting monomers 1 , 2 , and 3 .