ARTICLE IN PRESS UNCORRECTED PROOF Pyrolysis of poly[2,4,6-tri(methylamino)borazine] and its conversion into BN fibers S. Bernard *, D. Cornu, P. Miele *, H. Vincent, J. Bouix Laboratoire des Multimate ´riaux et Interfaces, UMR CNRS 5615, Universite ´ Lyon 1, 43, boulevard du 11 novembre 1918, ba ˆtiment Berthollet, F-69622 Villeurbanne Cedex, France Received 3 September 2001; accepted 23 April 2002 / 12 / Abstract / 13 / / 14 / The pyrolysis process of poly[2,4,6-tri(methylamino)borazine]-based fibers has been studied in detail. The condensation of / 15 / polymer leads to infusible fibers with a three-dimensional polymeric network from 70 to 400 8C. A polymer  /mineral transition / 16 / occurs since 400 to give amorphous hydrogenated fibers at 1000 8C. The chemical conversion process is complete at 1400 8C and / 17 / the BN fibers crystallize up to 1800 8C. # 2002 Published by Elsevier Science B.V. / 18 / Keywords: PolyMAB; BN fibers; Cross-link; Polymer  /mineral transition; Ceramization; Crystallization / 19 / 1. Introduction / 20 / Hexagonal boron nitride (h -BN) is known as aniso- / 21 / tropic material with interesting thermal and electric / 22 / properties, good resistance to oxydation and high / 23 / mechanical properties [1]. This ceramic is predominantly / 24 / produced via powder-metallurgical process. Difficulties / 25 / inherent to this traditional powder-based technique for / 26 / manufacturing complex forms of h -BN (fibers-rein- / 27 / forced composites, nanocomposites and coating) can / 28 / be overcome by the use of preceramic polymers [2  /4]. / 29 / They offer several important advantages such as a low / 30 / impurity level, homogeneous element distribution and / 31 / flexible forming methods. / 32 / There are two majors polymeric precursors for the / 33 / fabrication of boron nitride fibers: polyborazylenes and / 34 / polyborazines. Concerning the former, Sneddon and co- / 35 / workers [5] have studied the conversion process of / 36 / polyborazylene into boron nitride ceramic and shown / 37 / that a spinnable oligomer can be obtained by linking / 38 / dipentylamino groups to the polymer backbone. BN / 39 / fibers with poor mechanical properties were produced / 40 / [6]. For the latter, Kimura et al. have prepared BN fibers / 41 / with high mechanical properties from a mixture of / 42 / tri(methylamino)borazine and laurylamine [7]. / 43 / Following a similar approach, a particularly useful / 44 / family of preceramic borazine-based polymers, polyalk- / 45 / ylaminoborazines, was investigated as precursors of BN / 46 / fibers in our laboratory [8,9]. In this paper, a poly[2,4,6- / 47 / tri(methylamino)borazine] (PolyMAB) schematically il- / 48 / lustrated in Fig. 1 is prepared by thermal condensation / 49 / of 2,4,6-tri(methylamino)borazine (MAB) as it was / 50 / detailed in Section 3. / 51 / The polymer is spun by conventional melt-spinning / 52 / technique into crude fibers which are pyrolyzed under / 53 / specific conditions into BN fibers. The fiber diameter / 54 / reduces by half after the pyrolysis process up to 1800 8C / 55 / as shown in Fig. 2. / 56 / Up to now, the mechanisms which govern both the / 57 / fabrication of the ceramic fibers and the evolution of / 58 / their behavior during pyrolysis annealing are not well- / 59 / established. In this study, the conversion of polybor- / 60 / azine fibers into ceramic fibers is studied by TGA, GC / / 61 / MS, FTIR and XRD analysis to provide an under- / 62 / standing of the obtaining of carbon-free boron nitride / 63 / fibers. c:/3b2/3B2_Batch_Print/in/JOM11358.3d[x] Tuesday, 21st May 2002 17:7:29 3 * Corresponding authors. 4 E-mail addresses: sbernard@univ-lyon1.fr (S. Bernard), 5 miele@univ-lyon1.fr (P. Miele). 6 7 8 9 10 11 Journal of Organometallic Chemistry 00 (2002) 1  /7 www.elsevier.com/locate/jorganchem 1 0022-328X/02/$ - see front matter # 2002 Published by Elsevier Science B.V. 2 PII:S0022-328X(02)01543-7