Novel processable precursor for BN by the polymer-derived ceramics route

doi:10.1016/j.ceramint.2011.04.021

Ceramics International

Volume 37, Issue 8, December 2011, Pages 3005-3009

https://doi.org/10.1016/j.ceramint.2011.04.021 Get rights and content

Abstract

Novel precursors polymerized from (alkylamino)borazines (AAB) were synthesized and transformation of processable poly-AAB to boron nitride (BN) was researched. The AAB monomers of the type (BNH)₃(NHR)₃ were synthesized via ammolysis of 2,4,6-trichloroborazine (TCB) with different propylamines under mild conditions. The specially designed monomers served as molecular precursors for BN by the polymer-derived ceramics route. The processability of the polymeric precursors varied with propylamino-groups of AAB linked with boron atoms on (BNH)₃. The good processability of the poly[2,4,6-tris(iso-propylamino)borazine] (PTPⁱAB) was proven by melt-spinning it into polymer fiber. Furthermore, the PTPⁱAB gave a ceramic yield of about 53 wt% in Ar at 1200 °C by TGA. Based on FTIR, Raman, XRD, XPS and elemental analysis, the pyrolytic product of PTPⁱAB showed a composition of BN_1.07. In addition, the BN illustrated excellent oxygen resistance in air.

Introduction

In view of their high temperature stability, enhanced oxidation resistance and low density, boron nitride (BN) matrix composites embedded with BN fiber are deemed to be potential candidates for aircraft and space applications [1], [2]. However, preparation of BN fiber is difficult using conventional powder routes [3]. The polymer-derived ceramics (PDCs) route [4], [5], [6], [7], which offers homogeneous element distribution, low impurity level and good processability, is an elegant method for fabricating BN fiber [8]. It is worth noting that the PDCs method allows the design and control of the reactivity of moleculars to lead to soluble and fusible preceramic polymers. As far as we know (alkylamino)borazine (AAB) monomers synthesized from 2,4,6-trichloroborazine (TCB) were regarded as attractive molecular precursors for BN fiber to date [9], [10], [11].

It is known that the processability of polymeric precursors derived from AAB monomers was strongly dependent on the substituent alkylamino groups linked with boron atoms [10], [12]. Therefore, it is possible to adjust the processability of the preceramic polymers by substituting chlorine atoms on TCB with different alkylamines. However, it was inconvenient to synthesize AABs using gaseous alkylamines and TCB to lead to processable polymers due to quantitative measurement of these gaseous alkylamines, which need extraordinarily low temperature.

With the aim to facilitate the synthesis, two AABs for BN polymeric precursors have been synthesized using different liquid propylamines and TCB in our earlier work [13], respectively. Importantly, the synthesis of these monomers is under mild conditions without extraordinarily low temperature. In the present work, various polymeric precursors from above two AABs were obtained by thermal condensation. Moreover, processability of these polymers was tested by hand drawing technique. Finally, based on a combination of XRD, elemental analysis (EA), XPS, FTIR and Raman techniques, BN derived from the processable precursor was characterized.

Section snippets

Experimental

All samples described in this investigation were manipulated in a dry nitrogen atmosphere. Toluene as a solvent was purified by distillation with sodium.

Two molecular monomers were synthesized by aminolysis of TCB with n-propylamine and iso-propylamine, respectively, as reported in a previous investigation [13]. In a Schlenk flask, n-propylamine (or iso-propylamine, the same below) was slowly dropped into the solution of TCB and triethylamine in toluene under vigorous stirring. The white

Characterization of the polymeric precursors

The synthetic route of poly(alkylamino)borazines was shown in Scheme 1. It was found that both reactions between TCB and different propylamines proceeded as expected [13]. The effect of monomer and reaction temperature on the properties of polymeric precursors was investigated and the results were given in Table 1.

Clearly, there was no visible difference between polymers obtained from TPAB monomer. When the temperature was increased from 150 to 250 °C, they were all light yellow liquid with

Conclusions

Two poly(alkylamino)borazine precursors were synthesized by thermal condensation of different 2,4,6-tris(propylamino)borazines. Moreover, the properties of the preceramic polymers such as softening point and solubility were greatly effected by polymerization temperature. The processability of these two kinds of polymers was significantly influenced by propylamino-groups linked with boron atoms due to the steric hindrance effect. Furthermore, the poly[2,4,6-tris(iso-propylamino)borazine]

Acknowledgement

The work was financially supported by National High technology Research and Development of China (no. 2006AA03A217).

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Novel processable precursor for BN by the polymer-derived ceramics route

Abstract

Introduction

Section snippets

Experimental

Characterization of the polymeric precursors

Conclusions

Acknowledgement

Mater. Sci. Eng. A: Struct.

Ceram. Int.

Mater. Lett.

Chin. Chem. Lett.

J. Eur. Ceram. Soc.

Ceram. Int.

Synthetic routes to boron nitride

Chem. Rev.

A new polyborazine-based route to boron nitride fibers

J. Mater. Chem.

Structural and mechanical behavior of boron nitride fibers derived from poly[(methylamino)borazine] precursor: optimization of the curing and pyrolysis procedures

J. Am. Ceram. Soc.

Amine-modified polyborazylenes: second-generation precursors to boron nitride

Chem. Mater.

Polymer-derived ceramics: 40 years of research and innovation in advanced ceramics

J. Am. Ceram. Soc.

Polymer-derived SiBN fiber for high-temperature structural/functional applications

Chem. Eur. J.