Thermal behaviour of the copolymers of acrylonitrile with methyl acrylate and itaconic acid or its derivatives

Article abstract of DOI:10.1016/j.mencom.2013.09.013

Itaconic acid monoesters and monoamides, such as 2-carbamoylmethacrylic acid, N-octyl-2-carbamoylmethacrylic acid and 2-methoxy- carbonylmethacrylic acid, smoothed the peak of heat release upon the thermal cyclization of acrylonitrile copolymers with commensurable effectiveness, and they can serve as competitive substitutes for itaconic acid in the synthesis of carbon fiber precursors.

Full text of DOI:10.1016/j.mencom.2013.09.013

Mendeleev
Communications
Mendeleev Commun., 2013, 23, 277–278
Thermal behaviour of the copolymers of acrylonitrile
with methyl acrylate and itaconic acid or its derivatives
Andrei V. Shlyakhtin,* Dmitrii A. Lemenovskii and Ilya E. Nifant’ev
Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation.
Fax: +7 495 939 1671; e-mail: shlyahtinav@mail.ru
DOI: 10.1016/j.mencom.2013.09.013
Itaconic acid monoesters and monoamides, such as 2-carbamoylmethacrylic acid, N-octyl-2-carbamoylmethacrylic acid and 2-methoxy-
carbonylmethacrylic acid, smoothed the peak of heat release upon the thermal cyclization of acrylonitrile copolymers with commensurable
effectiveness, and they can serve as competitive substitutes for itaconic acid in the synthesis of carbon fiber precursors.
The production of carbon fibers is an important area of applica­
O
O
O
O
tions of acrylonitrile­containing copolymers; on a global scale,
0% carbon fibers are produced with the use of these copolymers.
H2C
H2C
H2C
H2C
9
OH
OH
OH
OH
NH
OH
In this case, homo­polyacrylonitrile (homo­PAN) is not used for
the production of carbon fibers because of a sharp exothermic
effect at the first stage of the heat treatment of the polymer (PAN
precursor), when the cyclization of nitrile groups occurs to finally
impair the quality (strength) of the carbon fiber obtained. To solve
this problem, comonomers (acids which smooth the peak of heat
release) are introduced into the PAN precursor. For this purpose,
itaconic, acrylic and methacrylic acids are most frequently used.
In addition to acid comonomers, neutral comonomers such as
methyl acrylate (MA) and methyl methacrylate are introduced
into the PAN precursor to improve the plasticity of the co­
NH2
OMe
C8H17
O
O
O
O
1
2
3
4
provided the precise control of temperature and homogeneity of
the reaction mixture.
The molecular­weight characteristics and the composition of
the obtained polymers were determined by gel filtration chromato­
graphy and H NMR spectroscopy, respectively. Table 1 indicates
‡
1
that the itaconic comonomers are inserted to approximately the
same degrees. In this case, the yield of a copolymer with itaconic
1
–3
polymer.
Recently, the use of the mono­ and biderivatives of itaconic
acid (the monoalkyl esters of itaconic acid, the methyl ester of
Table 1 Composition and molecular­weight characteristics of test polymers.
3
­aminocarbonylbut­3­enoic acid and the methyl ester of 3­car­
Initial composition
(mol%)
Composition
(mol%)b
bamoylbut­3­enoic acid) as comonomers instead of itaconic acid
was reported. The experimental data demonstrated that, quali­
tatively, the copolymers obtained are highly competitive with
copolymers with itaconic acid in terms of their capability for
Co­
mono­
mer
Yield
Mnc
PDc
(
%)
Acrylo­
nitrile
Comono­
mer
Comono­
mer
MA
MA
thermal cyclization.4–7 In this case, a systematic comparison
–a
100
97
97
97
97
–
2
2
2
2
–
1
1
1
1
–
–
71
57
69
79
70
47800 2.38
42600 2.34
41800 2.19
46300 2.10
46100 2.20
1
2
3
4
1.7 1.2
1.7 0.9
1.6 1.2
1.6 0.9
between the thermal cyclization parameters of copolymers with
itaconic acid and copolymers based on itaconic acid monoesters
and monoamides obtained under identical conditions was not
reported in the literature. Due to the presence of two carboxyl
groups in itaconic acid, it is possible to vary the structure of its
derivatives over a wide range with the retention of an acidic
fragment. In this study, we compared the thermal behaviours of
homo­PAN and acrylonitrile copolymers with MA and itaconic
acid 1 and also with its mono derivatives: 2­carbamoylmethacrylic
acid 2, N­octyl­2­carbamoylmethacrylic acid 3 and 2­methoxy­
a
Homo­PAN. b The concentrations of comonomers were determined by
the integration of signals in the H NMR spectra of copolymers (solvent,
DMSO­d ): the methylene group of a polymer chain (br., 2.23–1.82 ppm),
the methyl group of MA (3.69 ppm), the methyl group of 4 (3.59 ppm), the
methyl group of 3 (0.85 ppm) and the amide group of 2 (7.58, 6.83 ppm). For
the determination of the itaconic acid 1 content, the solution of a polymer in
DMSO­d was treated with an Et O solution of diazomethane and evaporated
1
6
6
2
†
carbonylmethacrylic acid 4. All of the copolymers were obtained
under identical conditions by solution polymerization which
in vacuo, and the concentration of methylated carboxyl groups was deter­
c
mined as in the case of MA. Mn is the number­average molecular weight,
and PD is polydispersity. Analysis was conducted on a GPC­120 chromato­
graph from PolymerLabs at 50°C in DMF containing 0.1 wt% LiBr at a
†
1
The structures of compounds 2–4 were determined by H NMR spectro­
scopy (Bruker Avance 400 instrument, CDCl solutions). Compounds 2–4
3
–1
flow rate of 1 cm min . For the separation, two columns PLgel 5 m MIXED
B [M = (5×102)–(1×107)] were used. The solution of a polymer in the eluent
3
8–10
–3
were synthesized employing published procedures.
As the starting
with a polymer concentration of 1 mg cm was prepared for the analysis.
reagent for the synthesis, itaconic anhydride was used, which was prepared
as follows: 10.0 g of itaconic acid (Aldrich, 99%) and 50 ml of thionyl
chloride were placed in a 100­ml round­bottom flask. A reflux condenser
with a calcium chloride tube was attached to the flask, and the contents of
the flask was stirred on boiling (76°C) for 6 h. The homogeneous reaction
mixture was cooled and added to a tenfold amount of carbon tetrachloride.
Calibration was performed with standard PMMA samples.
‡
Synthesis of homo-PAN. A magnetic anchor, 9.3 ml of DMSO, 3.0 ml
(0.046 mol) of acrylonitrile and 7.5 mg of azo(bis)isobutyronitrile (AIBN)
were placed in a 15­ml glass ampoule. The ampoule was filled with argon
and sealed. Then, the ampoule was kept at 70°C for 6 h and opened; the
resulting polymer solution was poured out into water, and the obtained
polymer was filtered off.
The crystals formed were washed with CCl (3×50 ml) and dried on a glass
4
filter and then in vacuo. Yield, 5.51 g (64%).
©
2013 Mendeleev Communications. All rights reserved.
– 277 –

Mendeleev Commun., 2013, 23, 277–278
Table 2 Characteristics of the DSC profiles of acrylonitrile homo­ and
copolymers with MA and 1–4.
2
1
1
0
5
0
5
0
Start of
Comonomer
Peak tem­
perature/°C
End of
effect/°C
DH/J g–1
effect/ºC
–a
1
2
3
4
241.6
144.3
143.0
153.2
173.1
272.8
286.9
287.5
286.1
288.1
299.1
319.7
320.6
319.3
321.3
1185.9
1176.2
1193.0
1211.5
1136.3
a
Homo­PAN.
2
0
60 100 140 180 220 260 300 340
of nitrile groups, and the reaction mechanism changed from
radical to ion one (Scheme 1).
initiates the process of cyclization, and itaconic acid contains
two carboxyl groups, exothermic effects come into play at a lower
temperature for itaconic acid and compound 2. DSC profiles
1
,11,12
Since the amide group also
T/°C
4
Figure 1 DSC profile of homo­PAN.
(Figure 2, curves 2–4) exhibit a weakly pronounced maximum at
2
70°C, which was not observed in the case of a copolymer with
itaconic acid; this fact suggests the more uniform introduction of
itaconic acid into the copolymer.
1
2
Me
O
Me
N
Me
O
Me
NH
(1)
C
C
C
C
C
O
H
N
N
N
N
O
N
N
N
N
N
+
3
4
Me
Me
N
Me
Me
N
(2)
C
C
N
2
0
60 100 140 180 220 260 300 340
Scheme 1 Cyclization of the nitrile groups of PAN via (1) ion and (2)
radical mechanisms.
T/°C
Figure 2 DSC profiles of acrylonitrile copolymers with MA and (1) 1,
2) 2, (3) 3 and (4) 4.
(
Thus, based on the experimental DSC data, we can conclude
that the introduction of itaconic acid 1 and its mono derivatives
2–4, which contain carboxyl groups, into the PAN copolymer
leads to the broadening of an exothermic peak, and these co­
monomers exert comparable effects on the heat release peaks of
the copolymers.
acid was somewhat lower than the yield of copolymers with
itaconates 2–4. It is interesting that the homopolymer obtained
under the same conditions was almost identical to copolymers
with 2–4 in terms of molecular­weight characteristics and yields.
Figures 1 and 2 show the DSC profiles of homo­PAN and the
copolymers of acrylonitrile with MA and itaconic acid 1 or its
derivatives 2–4, respectively. Table 2 summarizes the comparative
This work was supported by the Ministry of Education and
Science of the Russian Federation (state contract no. 14.513.11.0033).
§
characteristics of the DSC profiles.
It is well known that the DSC profiles of both homo­PAN and
an acrylonitrile copolymer with MA are narrow peaks. It is
References
2
1
P. Morgan, Carbon Fibers and their Composites, Taylor & Francis Group,
evident that the introduction of itaconic acid 1 and its derivatives
Boca Raton, 2005, pp.121−130.
2
–4 leads to the broadening of the heat release peak, and the
2 V. Ya. Varshavskiy, Uglerodnye volokna (Carbon Fibers), 2007, pp. 97−113
in Russian).
(
above comonomers exhibited comparable effects (Figures 1 and 2,
Table 2). The start of the exothermic peaks of terpolymer is moved
to the low temperature region, while the end, to the high tem­
perature region. Obviously, the cyclization reaction enthalpies
DH of homo­ and terpolymers are about the same because the
comonomer content is small, and the compositions of polymers
are approximately identical (Figures 1 and 2, Table 2).
3
4
5
X. Huang, Materials, 2009, 2, 2369.
A. Ju, Sh. Guang and H. Xu, Carbon, 2013, 54, 323.
Y. Li, B. Li, G. Zhang, X. Liu andY. Bai, Chinese Patent, 101413153 A
2
0090422, 2009.
6 Q. Chen, G. Zhang, X. Liu, Y. Xi, Y. Li and Y. Liu, Hecheng Xianwei,
2010, 39, 27.
7
Y. Li, G. Zhang, B. Li, Y. Bai, X. Liu and Zh. Yang, Chinese Patent,
01158060 A 20080409, 2008.
1
The heat release peak was broadened due to the fact that
compounds 1–4 decrease the activation energy of the cyclization
8
9
B. Baker, R. Schaub and J. Williams, J. Org. Chem., 1952, 17, 116.
A. Zilkha and U. Golik, J. Org. Chem., 1963, 28, 2007.
1
1
1
0 D. Grobelny, US Patent, 5679688 A1, 1997.
1 T. Sun, Y. Hou and H. Wang, J. Appl. Polym. Sci., 2010, 118, 462.
2 Q. Ouyang, L. Cheng, H. Wang and K. Li, Polym. Degrad. Stab., 2008,
Synthesis of copolymers. A magnetic anchor, 9.3 ml of DMSO, 3.0 ml
–4
(
4
0.046 mol, 97 mol%) of acrylonitrile, 86 ml of MA (9.5×10 mol, 2 mol%),
.7×10–4 mol of monomer 2, 3 or 4 (1 mol%) and 7.5 mg of AIBN were
9
3, 1415.
placed in a 15­ml glass ampoule. The ampoule was filled with argon and
sealed. Then, the ampoule was kept at 70°C for 6 h and opened; the
resulting polymer solution was poured out into water, and the obtained
polymer was filtered off.
§
The DSC analysis was conducted on a DSC­823e instrument from
–1
Mettler Toledo in an atmosphere of N at a heating rate of 5 K min .
Received: 10th June 2013; Com. 13/4136
2
–
278 –