Formation and Depolymerization of Oligomers during Thermal Cracking of Silicon-Containing Carbamates

Article abstract of DOI:10.1002/cplu.201900245

Polymerization reactions in the thermal cracking of N-substituted carbamates to produce the corresponding isocyanates significantly reduce the yield of isocyanates and thus vastly hinder the industrial application of such non-phosgene routes. Herein, we tried to recycle the oligomers generated during the thermal cracking of 3-ethylcarbamatopropyltriethoxysilane (CPTS) to produce 3-isocyanatopropyltriethoxysilane (IPTS). Firstly, the polymerized substrates of the pyrolysis reaction were analyzed by NMR, IR, MALDI-TOF-MS and TG, indicating the pyrolysis substrates were mixtures of CPTS (25 wt%), polyureas (74 wt%), imines, and other compounds (<1 wt %). The polyureas were generated by reaction of CPTS and IPTS. Then, the depolymerization of these polyureas was realized via alcoholysis in the presence of urea. It was found that the urea not only provides a carbonyl group source, but also forms hydrogen bonds with polyureas. In addition, NH₃ co-produced can also modify the reaction system microenvironment, which might be favorable for the dissociation of polyureas. With optimized conditions, more than 96 % of polymerized substrates could be reverted to CPTS for secondary cracking.

Full text of DOI:10.1002/cplu.201900245

Accepted Article
Title: Formation and Depolymerization of Oligomers during Thermal
Cracking of Silicon-Containing Carbamates
Authors: Peixue Wang, Dawei Zhou, Yuqing Fei, Yan Long, and
Youquan Deng
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ChemPlusChem
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Formation and Depolymerization of Oligomers during Thermal
Cracking of Silicon-Containing Carbamates
[a, c]
[a,b]
[a,b]
[a,b]
[a, c]
Peixue Wang,*
Dawei Zhou,
Yuqing Fei
Yan Long,
and Youquan Deng *
Abstract: The polymerization reactions in the thermal cracking of N-
substituted carbamates for the corresponding isocyanates
were significantly reducing the yield of isocyanates, which vastly
hinder such non-phosgene route into industrial application. Herein,
we tried to recycle the oligomers generated during the thermal
cracking of 3-ethylcarbamatopropyl-triethoxysilane (CPTS) for 3-
isocyanatopropyltriethoxysilane (IPTS). Firstly, the polymerized
substrates of pyrolysis reaction were analyzed by NMR, IR, MALDI-
TOF-MS and TG, indicating the pyrolysis substrates were mixtures
of CPTS (25 wt%), polyureas (74 wt%), imines and others (< 1 wt%).
The oligomers were mainly polyureas generated by reaction of
CPTS and IPTS. Then, the depolymerization of these polyureas was
realized via alcoholysis in the presence of urea. It was found that the
urea not only provides the source of carbonyl, but also forms H-bond
technology for isocyanate chemicals has become a focused
issue. With the development of pyrolysis technology,
carbonylation of nitrogenous compounds to carbamate for
pyrolysis has become the most promising route for the
[8-11]
preparation of isocyanates.
In order to improve the rate of
pyrolysis, this process usually conducted at high temperatures.
Probably because the higher cracking temperature, the
polymerization reactions between N-substituted carbamates and
[12-14]
isocyanates were easy to occur.
The formation of polyureas,
isocyanurate trimer and polycarbodiimide will significantly
reduce the yield of isocyanates, which vastly hinder the
[15]
industrial application of thermal cracking process.
By
providing a source of carbonyl and alkoxy, it is hoped that these
oligomers formed during pyrolysis reactions could be converted
into the corresponding carbamates. In our previous work, the
polyureas could be successfully degraded in the existence of
with polyureas. In addition, NH
reaction system microenvironment, which might be favorable for the
dissociation of polyureas. With optimized conditions, 96%
3
co-produced can also modify the
[
16,
>
DEC or urea, the corresponding carbamates yields over 95%.
1
7]
polymerized substrates could be back into CPTS for secondary
cracking.
Recently, we studied the formation and depolymerization of
polymers generated during thermal cracking diethyl
hexamethylenedicarbamate (EHDC). The polymers could be
successfully converted by the alcoholysis reaction in the
presence of ethyl carbamate. However, only 50% polymers
could be back into EHDC due to the complexity and diversity of
Introduction
[18]
polymers.
In the process of preparing IPTS by thermal
Isocyanates as important organic synthetic intermediates were
main raw materials for the synthesis of polyurethane, which
could be widely used in polyurethane oligomer materials (such
as pesticide, paint, dyes etc.).
isocyanatopropyltriethoxysilane (IPTS) was
organic silane coupling agent, which contains two different kinds
of active group ie. isocyanate group (NCO) and ethoxy (OC ).
IPTS was widely used in polyethylene crosslinking, surface
treatment of glass fiber reinforced plastics (such as unsaturated
resins, polyethylene, polypropylene resins), surface moisture-
proof treatment of electronic components, surface treatment of
cracking of CPTS, it was found that the thermal stability of IPTS
was lower than that of other common diisocyanate (such as MDI,
TDI, HDI). The polymerization reaction was easier to take place
even in the low temperature (150 °C). It is a wonderful idea that
the use of inhibitors can suppress the occurrence of some side
reactions, since it is almost impossible to avoid all the side
reactions completely. Herein, we tried to recycle the oligomers
generated during the CPTS thermal cracking (Scheme 1).
[1-3]
Among them, 3-
a
new type of
2
H
5
[4, 5]
inorganic silicon filler, special coatings and adhesives.
Besides, IPTS plays a significant coupling role in improving the
product mechanical, electrical, water resistant, anti-aging
properties. At the moment, this kind of coupling agent mainly
produced through the reaction of 3-aminopropyltriethoxysilane
[6, 7]
(
APTS) with phosgene or triphosgene.
The use of toxic
solvents and raw materials; by-product hydrogen chloride and
purification difficulty has limited its mass production. For this
reason, the research and development of non-phosgene
Scheme 1 Regenerated carbamate from the thermal cracking polymers
via the alcoholysis reaction in the presence of urea.
[
a]
Dr. P. Wang, D. Zhou, Y. Fei, Y. Long, Pro. Y. Deng, State Key
Laboratory for Oxo Synthesis and Selective Oxidation, State Key
Laboratory of Solid Lubrication, Centre for Green Chemistry and
Catalysis, Lanzhou Institute of Chemical Physics, Chinese Academy
of Sciences, Lanzhou, 730000, China. E-mail: ydeng@licp.cas.cn;
Fax: +86-931-4968116; Tel: +86-931-4968116
D. Zhou, Y. Fei, Y. Long, University of Chinese Academy of
Sciences, Beijing 100049, China.
Dr. P. Wang, Qingdao Center of Resource Chemistry & New
Materials, Qingdao, 266100, China. E-mail: peixuew@licp.cas.cn
Electronic Supplementary Information (ESI) available. See
DOI: 10.1039/b000000x/
In this work, the polymerized substrates obtained at different
pyrolysis conditions were tested by NMR, IR, MALDI-TOF-MS
and TGA, the possible structure and composition of the
oligomers were determined. The depolymerization of oligomers
was realized by a simple green catalytic process using urea as
an additional carbonyl. The impact of reaction parameters of
reaction time, temperature, and NH pressure was investigated
3
for the degradation of oligomers. This route avoids the waste of
raw materials and can produce huge economic benefits in the
[
b]
c]
[
†
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commercial production, which is in line with the concept of green
chemistry.
Results and Discussion
Formation of silicon-containing oligomers at different
conditions
The results of the formation of silicon-based oligomers at
different temperatures with or without catalysts were listed in
Table 1 and Figure 1. From the preliminary results, it can be
seen that the polymerization rate increased with the increase of
-
1
-1
temperature from 150 °C to 190 °C (5% h to 19% h ). At the
same temperature and time (150 °C, 6 h), the introduction of the
Figure 1 Impact of reaction temperature, time and catalyst on
oligomer formation.
SnO(C
4
H
9
)
2
catalyst could also accelerate the rate of
polymerization (entries 1, 2). Although the polymerization rate in
low temperature was low, the rate of pyrolysis also decreased.
In comparison, the oligomers yield was increased due to the
cracking reaction time was prolonged. For example, the
oligomers yield was 26% at 190 °C, 1.2 h, while the oligomers
yield was 36% at 150 °C, 6 h (entries 2, 6). From the above
results, it could be concluded that the formation of oligomers
was influenced by time, temperature and catalyst, but
temperature was probably the biggest factor. Besides, the
corresponding yield of IPTS was decreased with the rising
cracking temperature (entries 2, 4, 6), since most of the CPTS
were rectified with the IPTS fast at high temperature. The
catalyst can not only increase the yield of IPTS but also the yield
of oligomers, proper cracking temperature and catalyst must be
selected to obtain high yield of IPTS.
Characterization results of silicon-containing oligomers
In order to explore the component of the polymerized
substrates collected at 150 °C with SnO(C
4
H
9
)
2
catalyst
denoted as O-150Cat), IR spectroscopy was employed
Figure 2). The characteristic absorption peak of C=O (1700
(
(
-1
cm ) was observed in the O-150Cat, which attributed to
carbonyl of remaining pyrolytic precursors CPTS (Figure
-1
2
d). Whereas the band at 1640 cm was assigned to
carbonyl group in the urea structure, indicating the urea
derivates was formed in the thermal cracking process.
Contrasted with free C=O (Figure 2c), the absorption peak
moves towards low wave number affected by hydrogen
bonds. Compared with IR spectra of pure IPTS (Figure 2c),
-1
no N=C=O absorption peak (2269 cm ) was discovered in
-
1
-1
the O-150Cat. In addition, peaks at 955 cm , 771 cm were
the stretching vibrations of Si-C, while the correlation
[
a]
Table 1 Oligomers preparation under different conditions
-
1
[19]
absorption band at 1074 cm was belonging to Si-O-Si.
Tem. Time Oligomer Isocyanate
[
b]
Entry
Catalyst
None
Mn
(°C)
(h)
yield
yield
The absorption peaks of Si in the O-150Cat without obvious
displacement, demonstrating that the structure of alkoxyl
silicon was not changed significantly. Besides, the peaks at
about 156 ppm in 13C NMR (Figure S1-S6) also indicated
the formation of the polyurea linkage.
1
2
3
4
5
6
150
150
170
170
190
190
6
32%
5%
404
614
655
810
697
814
SnO(C
4
H
9
9
9
)
)
)
2
2
2
6
36%
27%
31%
29%
26%
60%
14%
33%
3%
None
3.5
2
SnO(C
4
H
None
1.5
1.2
SnO(C
4
H
11%
[
a] Reaction conditions: 30 g CPTS, 1 wt.% SnO(C
b] Determined by TOF-MS.
4 9 2
H ) , 1.8 mmHg.
[
Figure 2 IR spectra of the (a) APTS, (b) CPTS, (c) IPTS, (d) O-
150Cat.
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The oligomers obtained at different conditions were
further studied by IR (Figure 3). The polyureas absorption
substrate (CPTS) remains in the oligomers obtained at
150 °C. However, there are few substrate residual in
oligomers obtained at high temperature due to the
separation of substrate at high temperature is relatively
complete (Figure S7-S10). As shown in Figure 5A, the
m/z=316 (293+23=M+Na) corresponds to the residual of
the cracking precursor CPTS in the oligomers. The
m/z=491 (468+23=M+Na) corresponds to the diuret formed
by amine and isocyanate (Scheme 2). By the integrating
area, we got that the ratio of the CPTS, dipolyurea,
tripolyurea, tetraplurea in the O-150 was 25:41:26:7. The
repetitive unit (959-491=468) is 468 Da, which is equal to
-
1
-1
peak at 1560 cm and 1640 cm becomes sharp with
raising thermal cracking temperature and introducing
catalyst, which indicated that the addition of catalyst and
high temperature was conducive to the formation of
-
1
polyureas. Moreover, a new absorption peak at 2215 cm
was detected in the oligomers O-190Cat, which should be
derived from an imine structure RN=C=NR formed by two
2
isocyanate to take off the CO .
the formula weight of the diuret.
540+23=M+Na) corresponds to the allophanate formed by
CPTS and IPTS (Figure 5B). In addition, the repetitive unit
563-316=247, 1029-782=247) is 247 Da, which is equal to
While the m/z=563
(
(
the formula weight of the IPTS. The ratio of the CPTS,
dipolyurea, tripolyurea, tetraplurea, pentaplurea in the O-
1
50Cat was 26:38:10:10:8:8. By accurate determination of
molecular weight, it can determine the existence of CPTS
and polyureas in the oligomer.
Figure 3 Comparison of IR spectra of the oligomers obtained at
different conditions.
The thermal properties of oligomers obtained at different
conditions were monitored by TGA (Figure 4). The
decomposition temperature of these oligomers was about
2
00 °C. It can be found that the decomposition temperature
of oligomers obtained at high temperature is higher than
that obtained at low temperature. At the same thermal
cracking temperature, the oligomers obtained with the
catalyst have a higher decomposition temperature than the
oligomers obtained without the catalyst. This may be due to
a higher degree of polymerization at higher temperatures
and catalysts.
Figure 5 MALDI-TOF MS spectrum of the oligomers (A) O-150
and (B) O-150Cat.
Figure 4 TGA curves of the oligomers.
The average molecular weights of the oligomers were
determined by MALDI-TOF mass spectrometer. Figure 5A
was the oligomers obtained without catalyst, while Figure
5
B was the oligomers obtained with SnO(C
4 9 2
H ) catalyst.
The purity of the sample is not high, a small amount of
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Scheme 2 The structures found in the oligomers.
[c]
12
None
[a] Reaction conditions: 1 g O-150Cat, 3 mmol Carbonyl sources,
.1 g NaOC , 6.9 g ethanol, 180 °C, 8 h. [b] GC yield of CPTS
Urea
0
96%
Depolymerization of silicon-containing oligomers
0
2 5
H
Firstly, the depolymerization of silicon-containing oligomers
was proceeding in the absence of carbonyl source. Only 16%
yield of CPTS was received (entry 1), manifesting that the
additional carbonyl source was needed for the degradation of
silicon-containing oligomers. Secondly, three carbonyl sources
urea, EC and DEC were selected for the depolymerization
reaction. Carbonyl sources (urea, EC, DEC) mainly provide
carbonyl for the formation of carbamate (CPTS) through the
alcoholysis of polyureas. Excess EC and DEC almost remained
constant in the reaction system, while the excess urea would
based on oligomers. [c] 5 mmol urea.
Influence of reaction conditions
The effects of the temperature, ethanol amount and time on
the depolymerization of oligomers were investigated (Table 3).
The yield of CPTS increased rapidly with elevating temperature
(
entries 1-3). But declined slightly with further raising the
temperature to 200 C (entry 4), which probably because of the
thermal decomposition of oligomers at high temperature
(
confirmed by TGA). The yield of CPTS increased fastly at the
3
react with ethanol to form ethyl carbamate and NH . The yields
beginning 8 h and then tends to be stable with prolong reaction
time (entries 3, 5 and 6). Besides, the impact of the ethanol
amount on the yield of CPTS was also considered (entries 3 and
of CPTS were 83%, 75% and 43% respectively, demonstrating
that urea as carbonyl source works best (entries 2-4). When
DEC was used as carbonyl source, a large amounts of silicon
containing by-products were generated. For EC and urea, one
possible difference was the amount of ammonia released during
the reaction process. The quantity of ammonia released with
urea was twice of EC. It was hypothesized that the released
ammonia would change the microenvironment of the reaction
system. Generally, silicon compounds could be reacted with
alkali. Ammonia released converts the reaction system to
alkaline environment, which might be advantageous to the
depolymerization reaction. In order to certify this possibility,
7-9). The yield of CPTS increased from 79% to 96% as the
ethanol amount charged from 50 mmol to 150 mmol, and then
the yield of CPTS increased tinily with further increase the
alcohol amount to 200 mmol. Besides, the oligomers prepared at
various conditions were also depolymerized under the optimized
conditions (entries 10-14). The oligomers obtained at high
temperature show a decrease in the yield of CPTS, declaring
that the depolymerization of oligomers obtained at high
temperature became difficult. This may be due to the oligomers
formed at high temperature have large average molecular
weight (Table 1) disadvantage for the alcoholysis process.
Besides, the oligomers obtained with the catalyst display a good
yield of CPTS than the oligomers obtained without catalyst. It
was possibly due to the organotin catalyst has some catalytic
effect for the alcoholysis of oligomers.
3
about 0.2 MPa NH was introduced into the catalytic system
before the reaction. Fortunately, the yield of CPTS was
increased noticeably (entries 5-7). However, when the pressure
of NH
to 77% (entry 8). One possible reason was that too much NH
inhibits the reaction from going in the positive direction. To
further prove the role of NH , a strong base C ONa was
3
was increased to 0.5 Mpa, the yield of CPTS decreased
3
[
a]
3
2
H
5
Table 3 Oligomer depolymerization under different conditions
added in the reaction system, and the yields of CPTS were also
improved (entries 9-11). The purpose of oligomers
depolymerization was to obtain pure CPTS for the secondary
cracking. In order to avoid the introduction of other impurities
Tem. Time
Amount of
ethanol (mmol)
Yield
[b]
Entry Substrates
(
C)
(h)
(%)
1
2
3
4
5
6
7
8
9
O-150Cat
O-150Cat
O-150Cat
O-150Cat
160
170
180
200
180
180
180
180
180
180
180
180
180
180
8
150
150
150
150
150
150
50
25%
77%
95%
92%
71%
96%
79%
92%
96%
90%
72%
83%
50%
70%
(
2 5
NaOC H catalyst was difficult to remove), the high efficiently
8
8
depolymerization of oligomer was achieved using less excessive
urea as a catalyst and carbonyl source (entry 12).
[
a]
Table 2 Optimization the depolymerization conditions
8
Carbonyl
sources
NH
3
Yield
Entry
Catalyst
[
b]
(Mpa)
0
(%)
O-150Cat
O-150Cat
O-150Cat
O-150Cat
O-150Cat
O-150
4
1
2
3
4
5
6
7
8
9
None
None
None
None
None
None
None
None
None
Urea
EC
16%
83%
75%
43%
92%
84%
54%
77%
96%
87%
76%
12
8
0
0
8
100
200
150
150
150
150
150
DEC
Urea
EC
0
8
0.2
0.2
0.2
0.5
0
10
8
DEC
Urea
Urea
EC
11
O-170
8
12
13
14
O-170Cat
O-190
8
C
C
C
2
2
2
H
H
H
5
5
5
ONa
ONa
ONa
8
1
0
1
0
O-190Cat
8
1
DEC
0
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[
a] Reaction conditions: 1 g oligomers, 5 mmol Carbonyl sources. [b]
GC yield of CPTS based on oligomers.
Possible dissociation mechanism
Because the oligomer produced during thermal cracking
process is
a mixture, its structure, degree of polymerization
(
molecular weight distribution) is far different. Here we take
allophanate and diuret as examples, the related mechanism
might be that the carbonyl of polyurea would be attacked by the
activated nucleophilic alkoxy leading to the amido bond
dissociation to give the CPTS or APTS intermediate, and the
APTS would react with the activated ethanol and urea to form
[
18]
carbamate (Scheme 3).
source for the reaction, hydrogen bond between urea (EC or
NH ) and polyurea may be beneficial to the dissociation of
polyurea (Scheme S1).
In addition to providing a carbonyl
Scheme 3 The possible dissociation of diuret and allophanate.
3
[
20-21]
For the samples of O-150Cat + urea
3
EC or NH ), the characteristic absorption peaks of C=O–N–H
(
Conclusions
-
1
(
1570 cm ) in polyurea derivatives shifted to lower wavenumber
-
1
1
565 cm , which confirmed the formation of hydrogen bonds
The possible polymerization reactions in the process of CPTS
thermal cracking and the structure of the corresponding
oligomers were investigated. IR and MALDI-TOF-MS results
indicated the existence of substrate (CPTS), polyureas, imines
and others in the oligomers. The polyureas mainly comes from
the polymerization reaction between isocyanates and
carbamates. Fortunately, these oligomers were successfully
degraded using urea as carbonyl and catalyst. Recycling of
oligomerized substrates will have important significance for
achieving the non-phosgene synthesis of isocyanates.
(
Figure 6). On the other hand, the alkaline environment caused
by NH was conducive to the activation of ethanol and the
3
formation of alkoxy.
Experimental Section
Chemicals
3-ethylcarbamatopropyl-triethoxysilane (CPTS) was synthesized from 3-
aminopropyltriethoxysilane (APTS), urea and ethanol [See supporting
information]. APTS, dibutyltin oxide (SnO(C4H9)2, purity >98.5%), IPTS,
C2H5ONa, ethyl carbamate (EC) and diethyl carbonate (DEC) were
purchased from Shanghai Macklin Biochemical Co., Ltd. Urea and
ethanol were purchased from Sinopharm Chemical Reagent Co., Ltd.
NH3 (purity >99.9%) was supplied by Qingdao dehai weiye technology
Co., Ltd.
Figure 6 Comparison of IR spectra of the oligomers with
different carbonyls.
Synthesis of silicon-containing oligomers in the process of thermal-
cracking
The experiment was conducted in a 250 mL two-necked flask configured
with a thermocouple, an electromagnetic stirrer, a Wechsler rectification
column (15 cm) and a condenser-west tube. The reactor was connected
with the oil pump (1.8 mmHg) for eliminating co-product ethanol. 30 g
CPTS and 0.3 g SnO(C4H9)2 catalyst were added into the flask, and the
cleavage reaction performed at 150-190 °C for 1-6 h under atmospheric-
vacuum condition until no liquid refluxed in the rectification column.
Under the same vacuum conditions, the higher the cracking temperature,
the shorter the cracking time. After reaction finished, the remnants were
diluted with ethanol and detected by Agilent gas chromatography (GC
6
5
820) equipped with hydrogen flame ionization detector (FID) and a SE-
4 capillary column (biphenyl was the internal standard). The prepared
oligomers are denoted as O-TCat, T is the reaction temperature, Cat is
the SnO(C4H9)2 catalyst.
Depolymerization of silicon-containing oligomers via alcoholysis
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As a typical reaction process, 1.0 g O-150Cat, 0.3 g urea and 6.9 g
ethanol were added into the 90 mL stainless steel reactor, the reaction
proceeded at 180 °C for 8 h under magnetic stirrer. The analysis of the
products using a similar procedure as described above.
Characterization of the silicon-containing oligomers
1H NMR and 13C NMR of the oligomers were characterized by Bruker
Advance 2B (400 MHz, DMSO). Fourier-transform infrared (FTIR)
spectra of the oligomers were collected with a Bruker tensor 27 from 500
-
1
to 4000 cm at room temperature. The MALDI-TOF MS measurement
was proceed using a Bruker micoTOF-Q II smart beam MALDI-TOF
mass spectrometer operated in positive ion mode. Thermal analysis
(TGA) measurement was performed on a METTLER TG1 system under
N2 (50 mL/min) at a heating rate of 10 °C/min from 30 °C to 800 °C.
Acknowledgements
This work was supported by National Natural Science
Foundation of China (No. 21802148, 21761132014) and CAS
"Light of West China" Program.
Conflictofinterest
The authors declare no conflict of interest.
Keywords: carbamates • depolymerization • oligomers • silicon •
urea
Reference
[
[
[
[
1] C.S. Schollenberger, US2871218, 1959.
2] J. Disteldorf, R. Gras, H. Schnurbusch, US4413079, 1983.
3] D.J. Goldwasser, R.W. Oertel, US4567236, 1986.
4] X. Chen, Y. Liu, F. Qin, L. Kong, H. Zou. J Chromatogr. A 2003, 1010, 185-
194.
[5] H. Nishi, K. Ishibuchi, K. Nakamura, H. Nakai, T. Sato. J. pharm Biomed
Anal. 1995, 13, 1483-1492.
[6] A. Kurashima, A.Machiya, G. Yamaguchi. US4654428, 1987.
[7] U. Takashi, O. Hiroya, S. Takashi, S. Masaaki. EP0864574, 1998.
[8] P. Uriz, M. Serra, P. Salagre, S. Castillon, C. Claver, E. Fernandez,
Tetrahedron Lett. 2002, 43, 1673-1676.
[
[
[
9] Y. Dai, Y. Wang, J. Yao, Q. Wang, L. Liu, G. Wang, Catal. Lett. 2008, 123,
3
07–316.
10] M. J. Hyun, M. Shin, Y. J. Kim, Y. W. Suh, Res. Chem. Intermediat. 2016,
2, 57-70.
11] M. Ammar, Y. Cao, P. He, L. Wang, J. Chen, H. Li, Chinese Chem. Lett.
017, 28, 1583-1589.
4
2
[12] D. W. Duff, G. E. Meciel, Macromolecules 1991, 24, 651-658.
[13] G. Lewandowski, E. Milchert, J. Hazard. Mater. 2005, 119, 19-24.
[14] A. Lapprand, F. Boisson, F. Delolme, F. Méchin, J.-P Pascault. Polym.
Degrad. Stabil. 2005, 90, 363-373.
[
15] P. Wang, S. Liu, Y. Deng. Chin. J. Chem. 2017, 35, 821-835.
16] J. Shang, S. Liu, X. Ma, L. Lu, Y. Deng, Green Chem. 2012, 14, 2899-
[
2
906.
17] Q. Li, P. Wang, S. Liu, Y. Fei, Y. Deng, Green Chem. 2016, 18, 6091–
098.
18] D. Zhou, P. Wang, Y. Fei, Y. Long, Y. Deng, Catal. Sci. Technol. 2019, 9,
282-2290.
19] P. Tingaut, O. Weigenand, H. Militz, B. D. Jeso, G. Sebe. Holzforschung
005, 59, 397-404.
[
[
[
6
2
2
[
20] P. I. Dalko, L. Moisan, Angew. Chem. Int. Ed. 2004, 43, 5138-5175.
21] Y. Takemoto, Org. Biomol. Chem. 2005, 3, 4299-4306.
[
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ChemPlusChem
10.1002/cplu.201900245
FULL PAPER
FULL PAPER
Peixue Wang*, Dawei Zhou, Yuqing Fei, Yan Long
and Youquan Deng *
Page No. – Page No.
Formation and Depolymerization of Oligomers
during Thermal Cracking of Silicon-Containing
Carbamates
The polymerization reactions in the process of CPTS thermal
cracking and the structure of the corresponding oligomers were
investigated. IR and MALDI-TOF-MS results indicated the existence
of substrate (CPTS), polyureas, imines and others in the oligomers.
The polyureas mainly comes from the polymerization reaction
between isocyanates and carbamates. Fortunately, these oligomers
were successfully degraded using urea as carbonyl and catalyst.
This article is protected by copyright. All rights reserved.