J.A. Perdigon-Melon et al. / Journal of Organometallic Chemistry 657 (2002) 98Á
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106
105
NHCH3), 3.3Á
/
2.66 (m, br, NH cycle); 11B, dꢂ
27.9 (s, br, NHCH3).
/
25.77 (s,
4. Conclusion
br); 13C, dꢂ
/
The precursor P IV was obtained reacting TCB with
aniline as reported in the literature [26]. The tri anilino
aminoborazine (C6H5NHBNH)3 was prepared with a
45% yield due to its poor solubility in C6H5CH3. The
Porous boron nitride could be prepared from poly-
meric precursors and the physical properties of the
obtained ceramic supports could be adapted to the
required utilisation conditions. Higher specific areas
were obtained from polyborazylene derived precursor.
The preceramisation conditions were shown to be very
independent of the obtained sample and, using the same
precursor, the surface of the porous BN could be two
times higher following different ceramisation protocols.
No microporous structure could be obtained as de-
scribed in the literature. The porous substrates were
composed of broad pores, widely open to the surface of
the sample that could be interesting to depose an active
part of noble metal to prepare a catalyst. The commonly
obtained specific area of about 30 m2 gꢀ1 could be
related to the surface of the powder used in literature
and attempts would be made to prepare noble metal
deposed on the new BN porous supports. The behaviour
of aminoborazine derived precursors showed that the
better results were obtained from the compounds
exhibiting the lower ceramic yield. However, this low-
ering was shown to be difficult to be obtained using very
broad amino group which were known to be hard to
strip from the polymer. A future study would be to
prepare some catalyst samples using first BN foam and
an impregnation technique with Pt or Pd precursor and
other attempts would be made to incorporate the noble
metal precursor into the polymer before the expansion
and the ceramisation of the samples.
1
AAB was characterised using H-NMR. IR (cmꢀ1): n
3421, 3278 (NH); 2922, 3032 (CH); 1501 (CH); 1429
(BN stretch.); 1231 (NC); 1028 (NH); 696 (BN bend);
1H-NMR (ppm): d 3.80 (s, br, 1H, (BNHC6H5); 6.77,
6.94, 7.24 (m, br, 5H, (NHC6H5)), 3.67 (m, br ,3H (NH
cycle)); 11B-NMR (ppm): d 25.2 (s, br). The ceramic
yield was 19.4% up to 1000 8C; it was consistent with
the theoretical weight loss of 21% when AAB was
converted into BN.
The precursor P V was obtained using the same
method [26]. The tribenzylaminoborazine (C6H5CH2-
NHBNH)3 was prepared with a 30% yield. It was
purified by recrystallisation from a chlorobenzene solu-
1
tion. The BAB was characterised using H-NMR. IR
(cmꢀ1): n 3440, 3240 (NH); 2910, 3025 (CH); 1495
(CH); 1443 (BN stretch.); 1028 (NH); 713 (BN bend);
1H-NMR (ppm): d 2.73 (s, br, 1H, (C6H5CH2NHB);
3.12, 3.15 (m, br, 2H, (BNHCH2C6H5); 7.19, 7.27, 7.37
(m, br, 5H, (NHCH2C6H5)), 4.2, 4.32 (m, br, 3H(NH
cycle)); 11B-NMR (ppm): d 30.10 (s, br). The ceramic
yield determined using TGA was 25.6% which was very
high but the residue was black and carbon containing,
so this value was not taken into account and confirmed
the poor ‘living group’ character of the benzyl group.
3.4. Preceramisation and ceramisation conditions
The crude foams after the expanding treatment were
transformed into ceramic by a two steps thermal and
chemical treatment using two different apparatus. First,
a preceramisation was performed from r.t. up to
1000 8C in classic ovens fitted with a silica tube, this
operation was run under reactive ammonia flow (1 L
hꢀ1) up to 600 8C and then under nitrogen flow.
Ammonia was used to strip the organic parts of the
copolymer, as shown in previously [25]. Two heating
rates were used, the standard heating used for ceramic
fibres production Protocol A: 18 minꢀ1 up to 600 8C
and then 58 minꢀ1 up to 1000 8C and a more rapid
preceramisation protocol B: heating rate of 200 8C hꢀ1
under a 6 l hꢀ1 ammonia flow up to 600 8C and then
under nitrogen. Then the fibres were transferred into a
high temperature oven where they were heated up to
1800 8C with a heating rate of 108 minꢀ1 under a
nitrogen atmosphere. The ammonia gas used was from
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Alfagaz Electronic grade N36 (99.96%; H2OB
CnH2n 1 ppm) used without further purification and
nitrogen was from ‘air liquid’ N21 grade (99.999%,
H2OB3 ppm, O2B0.2 ppm).
/100 ppm,
B
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