Borylborazines as new precursors for boron nitride fibres

A variety of borylborazine-based polymers were successfully converted into boron nitride fibres via the preceramic polymer route. In this procedure, four monomers were polycondensed into highly tractable polymers which could be easily melt-spun into fine-diameter green fibres. These polymeric filaments were then transformed into boron nitride fibres after a well-defined heat-treatment at 1800 °C in a controlled atmosphere. All the resulting ceramic fibres were mechanically tested. In particular, results showed that the promising mechanical properties for two of the polymer-derived fibres were closely related to the structural units of the corresponding preceramic polymers.

Schematic representation of a borylborazine molecular precursor of high performance BN fibres. A series of borylborazine-based polymers have been prepared by thermal or chemical route. Function of the polycondensation and of the kind of monomer, the polymers display different structure established from the linkage of borazine units through direct B–N bonds or 3 atoms “–N–B–N–” bridges. This study demonstrated that high melt-spinning ability, which influences in a large extent the mechanical properties of the resulting BN fibres, is directly linked to a good stretching ability of the polymer; the latter being enhanced by the presence of flexible 3 atom bridges within the polymer.Figure optionsDownload as PowerPoint slide