Synthesis and kinetics of non-isothermal degradation of acetylene terminated silazane

Article abstract of DOI:10.1016/j.cclet.2010.10.001

Novel acetylene terminated silazane compounds, with three types of substituent, were synthesized by the aminolysis of dichlorosilane with 3-aminophenylacetylene (3-APA). Thermal property of the compounds is studied by thermogravimetry analysis (TGA). It s

Full text of DOI:10.1016/j.cclet.2010.10.001

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Chinese Chemical Letters 22 (2011) 139–142
www.elsevier.com/locate/cclet
Synthesis and kinetics of non-isothermal degradation of acetylene
terminated silazane
Wei Jian Han a,b, Li Ye a,b, Ji Dong Hu a, Tong Zhao a,
*
a Laboratory of Advanced Polymer Materials, Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100190, China
b Graduate University of the Chinese Academy of Sciences, Beijing 100190, China
Received 4 May 2010
Abstract
Novel acetylene terminated silazane compounds, with three types of substituent, were synthesized by the aminolysis of
dichlorosilane with 3-aminophenylacetylene (3-APA). Thermal property of the compounds is studied by thermogravimetry analysis
(TGA). It shows that the acetylene terminated silazane has high temperature resistance. The char yield at 1000 8C is 77.6, 81.9 and
68.7 wt% for methyl, vinyl, and phenyl substituted silazane, respectively. The pyrolysis kinetics of the silazane is investigated by
non-isothermal thermogravimetric measurement. The pyrolysis undergoes three stages, which is resolved by PEAKFIT. The kinetic
parameters are calculated by the Kissinger method. The role of functionalities on the thermal resistance is discussed. The vinyl-
silazane exhibits higher thermal stability because of higher cross-linking density.
# 2010 Tong Zhao. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Silazane; Thermal properties; Pyrolysis kinetics
Various silazane compounds have been synthesized as a precursor for silicon carbonitride ceramics[1], surface
modifiers [2] and additives for silicone rubbers [3,4]. Xie and Wang [3] developed a method to suppress the reversion
of polysiloxanes with a polysilazane crosslinker by which the heat resistance of room temperature-vulcanized (RTV)
silicone rubbers is improved. Silazane derivatives effectively impede the rearranging degradation of polysiloxane
main chain by the removal of trace water or Si–OH groups with the reactive Si–N bond, and thus can improve the
thermal stability of silicone rubbers.
Acetylene-contained silicon polymer have also been attractive for enhancing the thermal stability of polymer [5].
Keller and co-workers synthesized high-temperature elastomers from silarylene–siloxane–diacetylene linear
polymers [5]. There is great interest to develop Si–N and acetylenyl containing polymers. Xu and co-workers
synthesized 1,3-bis(phenylethynyl)disilazane as a crosslinker for silicon rubber [6]. However, to the best of our
knowledge, the information of thermal decomposition kinetic of these compounds is very limited.
In this article, we report the synthesis of a novel acetylene terminated silazane compound with various substituent
on silicon. The effect of the functionalities on thermal properties are studied by thermogravimetric analyzer (TGA),
* Corresponding author.
E-mail address: tzhao@iccas.ac.cn (T. Zhao).
1001-8417/$ – see front matter # 2010 Tong Zhao. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2010.10.001

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W.J. Han et al. / Chinese Chemical Letters 22 (2011) 139–142
and PEAKFIT. The kinetics parameters are studied using and Kissinger method. The role of substituent on the thermal
properties is discussed.
1. Experimental
All experiments were carried out under a nitrogen atmosphere. Solvents were distilled from sodium/benzophenone
prior to use. Other chemicals were purchased from Aldrich or Acros Co. and used as received. 1H NMR and 29Si NMR
spectra were obtained on a Bruker DM 300 MHz spectrometer using CDCl3 as solvent. FT-IR spectra were recorded
on a Bruker 27 spectrometer. TGAwas carried out on a Netzsch STA 409PC instrument with ramping rates of 5, 10, 20,
and 30 8C/min from room temperature (RT) to 1000 8C in nitrogen atmosphere.
Synthesis of di-(3-acetylenephenylamino)dimethylsilane (1a): The compound was prepared by traditional
aminolysis procedure (Scheme 1). A three neck flask equipped with a condenser and a magic stirrer bar was charged
with dry toluene (50 mL) and dichlorodimethylsilane (0.1 mol, 12.1 mL). After cooled down to À10 8C, 3-
aminophenylacetyele (0.2 mol, 11.3 mL) dissolved in toluene (30 mL) was added dropwise to the above mixture. The
aminolysis reaction produced a white precipitation as observed immediately. The mixture was stirred for 1 h at
À10 8C, and then warmed to room temperature for 4 h. The slurry was filtered under nitrogen atmosphere, and a
colorless solution was obtained. After removing the solvent under vacuum, 2.46 g white solid was obtained (85%
yield). FT-IR: (KBr, cmÀ1): 3374 (n N–H, s), 3289 (nCBC–H, w), 3025 (nPh–H, w), 2983 (nC–H, w), 2103 (nCBC, w), 1619
(nC=C, w), 1253 (nSi–CH3, s), 955 (gSi–N, s), 787 (gSi–C, s); 1H NMR (300 MHz, CDCl3): d 0.42 (s, 6 H), 3.01 (s, 2 H),
3.74 (s, 2 H), 6.82, 6.96, 7.15 (m, 8 H). 29Si NMR (ppm): À10 (Me2Si–N).
Di-(3-acetylenephenylamino)methylvinylsilane (1b) and di-(3-acetylenephenylamino)diphenylsilane (1c) were
prepared similar to 1a, but using MeViSiCl2 and Ph2SiCl2 (Ph: phenyl) , respectively. Compound 1b was obtained as
yellow viscous liquid (yield: 65%). FT-IR: (KBr, cm-1): 3380 (nN–H, s), 3289 (nCBC–H, w), 3025 (nPh–H, w), 2983 (nC–H
,
w), 2103 (nCBC, w), 1405 (dSi–C=C, w), 1253 (nSi-CH3, s), 960 (gSi–N–C s), 787 (gSi–C, s); 1H NMR (300 MHz, CDCl3): d
0.48 (s, 3 H), 3.02 (s, 2 H), 3.73 (s, 2 H), 6.01, 6.20 (m, 3 H), 6.79, 6.91, 7.05, 7.19 (m, 8 H). 29Si NMR (ppm): À22
(MeViSi–N). Compound 1c was obtained as a white solid (yield: 59%). FT-IR (KBr, cmÀ1): 3366 (n=N–H, w), 3289
(nCBC–H, w), 3025 (nph–H, w), 2983 (nC–H, w), 2103 (nCBC, w), 1253 (nSi–CH3, s), 957 (gSi–N–C s), 787 (gSi–C, s); 1H NMR
(300 MHz, CDCl3): d 3.01 (s, 2 H), 4.15 (s, 2 H), 6.87, 6.99, 7.40, 7.68 (m, 18 H). 29Si NMR (ppm): À29 (Ph2Si–N).
2. Results and discussion
A series of novel acetylene terminated silazanes (1a, 1b, 1c), having different substituents on silicon were prepared
by the aminolysis of dichlorosilane and 3-aminophenylacetylene according to Scheme 1. All di-(3-acetylenephe-
nylamino)silanes, abbreviated as APSN, are tractable and can be dissolved in common solvents, such as toluene,
hexane and tetrahydrofuran (THF). The cured monomers (2a, 2b, 2c) were prepared by the following procedure:
[()TD$FIG]
(200 8C, 2 h), (230 8C, 2 h), (250 8C, 4 h) in N2 atmosphere.
Scheme 1. Synthesis protocol for di-(3-acetylenephenylamino)silane compounds.

[()TD$FIG]
W.J. Han et al. / Chinese Chemical Letters 22 (2011) 139–142
141
100
95
90
85
80
75
70
65
2b
2a
2c
200
400
600
800
1000
Temperature (ºC)
Fig. 1. TGA profiles for cured di-(3-acetylenephenylamino)silane compounds.
The thermal stability of the cured compounds was examined by thermogravimetric analysis. TGA curves of the
cured compounds are shown in Fig. 1. The shape of TGA curves indicate that decomposition rate of 2b is much lower
than those of 2a and 2c. As shown in Fig. 1, T10 of 2b is 499.6 8C, which is the highest among the three compounds.
And the residual weight of 2b was 10% higher than those of 2a, indicating the enhancement in the thermal stability of
2b. This should be attributed to the increase in cross-linking density by the polymerization of vinyl groups and
acetylene groups. Compared with other acetylene-contained silicon polymers, the residual weight of silazanes is
lower, because the Si–N bond is not as stable as Si–C bond in the pyrolysis process.
In order to intensive study the thermal resistance of compounds with different pendent groups, weight loss data
from the pyrolysis of compounds in a nitrogen atmosphere were obtained at four heating rates. It was found that the
thermal decomposition process has three main regions above 200 8C. Trick et al. developed a model to predict the
pyrolysis reaction of phenolic/carbon composite [7], which also has different decomposition stage in the different
temperature. He used software PEAKFIT to separate the thermogravimetric weight loss data to three major regions,
and calculate the kinetic parameters of each separated region. So the same method was used to separate the
overlapping peaks, and Kissinger method was employed to calculate the kinetic parameters of each peak based on their
peak temperatures.
The resulting peak separation for the typical decomposition is shown in Fig. 2 and summarized in Table 1. The
kinetic parameters was calculated by the Kissinger method and listed in Table 2. As shown in Table 1 and Table 2, it is
easy to evaluate the influence of substituted groups on the thermal resistance of silazanes at each separated region base
[()TD$FIG]
Fig. 2. Peak separation of the 2a–c mass loss data obtained at 10 8C minÀ1 Gaussian curves fit to the mass loss peaks.

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W.J. Han et al. / Chinese Chemical Letters 22 (2011) 139–142
Table 1
Temperature and Percent areas under curve of each separated peak.
Sample
Heating rate
(8C minÀ1
Peak 1
Peak 2
Peak 3
)
Peak center
Percent area
Peak center
Percent area
Peak center
Percent area
(8C)
under curve (%)
(8C)
under curve (%)
(8C)
under curve (%)
2a
5
452.9
483.1
504.3
517.7
–
42.2
48.1
54.4
50.8
46.5
69.3
65.7
63.1
62.2
65.8
30.0
35.8
31.1
39.7
34.9
552.6
567.1
581.9
595.5
–
28.7
22.6
26.1
24.55
26.6
13.9
17.0
18.9
22.8
18.4
64.8
59.0
62.9
55.0
59.9
625.9
653.3
687.4
698.0
–
29.1
29.3
19.5
24.7
26.9
16.8
17.3
18.0
14.9
15.9
5.2
10
20
30
Average
2b
2c
5
494.2
508.9
523.4
539.1
–
588.9
602.1
614.8
630.2
–
677.9
702.5
713.3
725.1
–
10
20
30
Average
5
493.2
515.1
525.0
535.4
–
575.9
597.7
610.7
616.5
–
678.3
693.9
709.5
725.6
–
10
5.2
20
6.0
30
5.3
Average
5.3
Table 2
Apparent global kinetic parameter of the pyrolysis of monomers.
E (kJ/mol)
A (L/min)
K (sÀ1
)
2a
2b
2c
Stage 1
Stage 2
Stage 3
Stage 1
Stage 2
Stage 3
Stage 1
Stage 2
Stage 3
119.63
238.80
157.80
197.57
271.62
288.16
208.85
255.98
288.36
4.61E7
0.2516
0.4068
0.2211
0.4036
0.4396
0.3832
0.4277
0.4271
0.3831
2.85E14
1.75E8
1.13E13
1.26E16
2.58E15
7.37E13
2.39E15
2.60E15
on this novel method. In the first stage, 2c and 2b exhibited higher activation energy than 2a indicated the steric effect
of phenyl group of 2c and higher cross-linked density of 2b suppressed the retroversion reaction. All of the three cured
compounds show the similar activation energy in the second region. But 2c has the largest weight lose in the second
region which is due to the high molecular weight of phenyl group, so the total weight lost of 2c is lower than other two
monomers. Compared with 2a, 2b with vinyl substituted retain more weight residue and higher peak temperature at the
second and third regions, indicating the high temperature decomposition of 2b was retarded by the higher cross-
linking density induced by the cross-linking reaction of vinyl groups. The above results show vinyl-substituted
monomer has better thermal stability than those compounds with methyl and phenyl substituted.
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