Synthesis of pyridine-based poly(N-arylenebenzimidazole sulfone)

Article abstract of DOI:10.1016/j.cclet.2012.04.028

Poly(N-arylenebenzimidazole pyridine sulfone) (PNABIPS) has been prepared via the aromatic nucleophilic displacement reaction of 2,6-bis(2-benzimidazoly) pyridine (BBP) with bis(4-fluorophenyl) sulfone. BBP was synthesized by reaction of 2,6-pyridinedicarboxylic acid with 1,2-phenylenediamine in polyphosphoric acid. The chemical structure of BBP was confirmed by FT-IR, HRMS, ¹H NMR and ¹³C NMR. The characterization of the polymer was performed with FT-IR, ¹H NMR, elemental analysis, GPC, XRD, DSC, TGA and solubility tests. The polymer was obtained in quantitative yield with M _n value 12,600 and M_w value 28,300, respectively. DSC and TGA measurements show that the glass transition temperature (T_g) is 312 °C and 5% weight loss temperature is 434°C in nitrogen and 545°C in air, respectively. In addition, the novel polymer exhibits good solubility, which can be dissolved in common organic solvent at room temperature.

Full text of DOI:10.1016/j.cclet.2012.04.028

Available online at www.sciencedirect.com
Chinese Chemical Letters 23 (2012) 871–874
www.elsevier.com/locate/cclet
Synthesis of pyridine-based poly(N-arylenebenzimidazole sulfone)
Ye Wei Xu a, Jie Tang b, Guan Jun Chang a, Fang Hua Zhu a, Lin Zhang a,
*
a Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
b School of Chemistry and Chemical Engineering, Mianyang Normal University, Mianyang 621000, China
Received 19 March 2012
Available online 9 June 2012
Abstract
Poly(N-arylenebenzimidazole pyridine sulfone) (PNABIPS) has been prepared via the aromatic nucleophilic displacement
reaction of 2,6-bis(2-benzimidazoly)pyridine (BBP) with bis(4-fluorophenyl) sulfone. BBP was synthesized by reaction of 2,6-
pyridinedicarboxylic acid with 1,2-phenylenediamine in polyphosphoric acid. The chemical structure of BBP was confirmed by FT-
IR, HRMS, 1H NMR and 13C NMR. The characterization of the polymer was performed with FT-IR, 1H NMR, elemental analysis,
GPC, XRD, DSC, TGA and solubility tests. The polymer was obtained in quantitative yield with Mn value 12,600 and Mw value
28,300, respectively. DSC and TGA measurements show that the glass transition temperature (Tg) is 312 8C and 5% weight loss
temperature is 434 8C in nitrogen and 545 8C in air, respectively. In addition, the novel polymer exhibits good solubility, which can
be dissolved in common organic solvent at room temperature.
# 2012 Lin Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Polybenzimidazoles; Poly(N-arylenebenzimidazole pyridine sulfone); Thermal properties; Solubility
In a wide definition poly(benzimidazole)s (PBIs) refer to a large family of aromatic heterocylic polymers
containing benzimidazole units. As an amorphous thermoplastic polymer, the aromatic nuclei of PBIs provide the high
thermal stability, excellent chemical resistance, retention of stiffness and toughness [1]. However, the rigid backbones
of the molecules result in poor solubility in common organic solvents and limit their application. Thereby more efforts
have been made to modify the polymer structures to improve the solubility without sacrificing the desirable properties
[2–11]. Due to the rigidity and polarizability of pyridine rings, introducing pyridine rings into the main chain of a
synthetic polymer could improve the solubility and thermal stability [12–14]. However, the synthesized
polybenzimidazoles containing pyridine rings have N–H groups, and the concentration of N–H sites gradually
and continuously decreases as time increases under air atmosphere at 350 8C [15].
Hay et al. firstly reported that the N–H group in benzimidazoles could undergo a C–N coupling reaction with
activated halides to give linear polymers with high molecular weight under appropriate temperature, and the
N-substituted homopolymers and copolymers have very high glass transition temperature and thermal stability
[16,17]. In addition, pursuing to improve the processability of PBIs, sulfonyl groups in the PBI polymers would
increase solubility and flexibility, which allow further processing, modification and production of films with good
mechanical properties [18].
* Corresponding author.
E-mail addresses: zhlmy@sina.com, xywchem@sina.com (L. Zhang).
1001-8417/$ – see front matter # 2012 Lin Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2012.04.028

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Y.W. Xu et al. / Chinese Chemical Letters 23 (2012) 871–874
Base on these, in this paper, the synthesis of 2,6-bis(2-benzimidazoly)pyridine is reported along with the
preparation of poly(N-arylenebenzimidazole pyridine sulfone) from the N–H sites in benzimidazole ring and bis(4-
fluorophenyl) sulfone. Due to the incorporation of pyridine and sulfonyl groups in the PBI backbone, the resulting
polymer exhibits good thermal resistance, high glass transition temperature values and good solubility in organic
aprotic solvents.
1. Experimental
The chemicals and reagents, unless otherwise specified, were purchased from Acros and TCI Chemical Co. and
used as received. All the solvents were further purified before use.
Scheme 1 shows the synthesis route of 2,6-bis(2-benzimidazoly)pyridine (BBP) and poly(N-arylenebenzimidazole
pyridine sulfone) (PNABIPS). The synthesis of BBP was performed via the reaction of 2,6-pyridinedicarboxylic acid
with 1,2-phenylenediamine in polyphosphoric acid, PPA, as the condensation agent and solvent. PPA is a very
convenient dehydration agent for the preparation of benzimidazole from acid in a single step. PNABIPS was prepared
from BBP with bis(4-fluorophenyl) sulfone under the existence of anhydrous potassium carbonate at 210 8C.
BBP: white solid. Yield: 95%. mp: 353 8C. UV recorded in CH3CN lmax at 325 nm. FT-IR (KBr pellet, cmÀ1):
3167, 3057, 1624, 1601. 1H NMR (300 MHz, DMSO-d6): d 13.0 (s, 2H), 8.34 (t, 2H), 8.18 (t, 1H), 7.76 (s, 4H), 7.33 (s,
4H). 13C NMR (75 MHz, DMSO-d6): d 150.5, 147.8, 144.2, 139.2, 134.4, 123.7, 122.2, 121.4, 119.7, 111.8. MS
(MALDI-TOF): m/z: calcd. for C19H13N5 311.3402; found: 311.1175.
PNABIPS: dark solid. Yield: 92%. FT-IR (KBr pellet, cmÀ1): 3057, 1624, 1601, 1188. 1H NMR (300 MHz, DMSO-
d6): d 8.18 (d, 2H), 7.84 (m, 1H), 7.70 (s, 4H), 7.32 (s, 4H), 6.87 (m, 4H), 6.61 (m, 4H). Anal. Calcd. for C31H19N5O2S
(525.142): C, 70.84; H, 3.62; N, 13.33. found: C, 70.53; H, 3.65; N, 13.30.
2. Results and discussion
The molecular weight of the reprecipitated polymer was measured by GPC (calibrated by polystyrene standards).
The Mn value is 12,600 and the Mw value is 28,300, respectively. Polydispersity index (PDI) is 2.25. The wide-angle X-
ray diffraction pattern of PNABIPS over the 2u range of 5–608 is investigated. Despite the presence of the rigid phenyl
ring, the polymer reveals essentially amorphous pattern. Because the polymer studied here is completely
noncrystalline, any crystalline melting peaks have not been observed in the differential scanning calorimetry (DSC)
study.
DSC thermogram of the polymer is shown in Fig. 1. A single glass transition temperature of PNABIPS is obtained,
and the resulting polymer shows Tg is 312 8C, which lower than that of traditional PBIs (Tg > 400 8C) [1]. This
decrease in Tg could be correlated to the elimination of hydrogen bonding after the N-substitution.
The synthesized polymer exhibits high thermal stability. Fig. 2 shows the primary thermogravimetric curve
obtained by dynamic TGA of PNABIPS. 5% weight loss temperature is 430 8C in nitrogen and 545 8C in air, and 5%
H
a
H2N
H2N
N
N
HOOC
COOH
N
N
N
N
H
O
S
N
N
N
N
F
F
N
O
O
S
b
n
O
Scheme 1. Synthesis of BBP and PNABIPS. Reagents and condition: (a) PPA, 200 8C, 6 h; and (b) K2CO3/sulfolane, 210 8C, 10 h.

Y.W. Xu et al. / Chinese Chemical Letters 23 (2012) 871–874
873
EXO
PNABIPS
312 oC
0
50
100 150 200 250 300 350 400
Temperature (ºC)
Fig. 1. DSC of polymer in nitrogen.
110
100
90
80
70
60
50
40
30
20
PNABIPS in N
2
PNABIPS in air
0
200
400
600
800
1000
Temperature (ºC)
Fig. 2. TGA of polymer in nitrogen and in air.
weight loss temperature in air higher than that in nitrogen. The result may be attributed to the oxidation of PNABIPS.
The end groups of PNABIPS may have N–H groups of benzimidazole rings, and hydrogen abstraction from the N–H
groups initiated to form more stable quinone and benzonitrile structures in air atmosphere before decomposition [15].
TG curves reveal that the polymers is thermally stable at up to 400 8C, and the 50% weight losses take place at over
900 8C in nitrogen. Char yield is an easy and important measurement which correlates to the ability to sustain
combustion. For the polymer the char yield at 600 8C is up to 60%.
PNABIPS exhibits good solubility behavior in different organic solvents. The solubility was qualitatively
determined by the dissolution of 10 mg of solid polymer in 1 mL of organic solvent at room temperature. The polymer
could be easily soluble in high polar solvent, such as dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP) and
dimethylformamide (DMF), while partially soluble in common organic solvents, such as dimethyl sulfoxide (DMSO),
dichloromethane (CHCl2) and chloroform (CHCl3). The polymer shows improved solubility compared with
previously reported traditional PBI which is only soluble after heating in highly polar organic solvents. Compared with
traditional PBIs which are only soluble after heating in highly polar organic solvents [1], PNABIPS displays the
improved solubility. The difference in solubility was attributed to the presence of sulfonyl and pyridine groups in the
PBI backbone, which hinder dense chain packing, thereby reducing the interchain interactions and enhancing
solubility.
In conclusion, a convenient synthetic route has designed to prepare bis(benzimidazolyl) derivative containing
pyridine group in high yield and high purity. It has been used as condensation monomer, in combination with bis(4-
fluorophenyl) sulfone, to yield novel poly(N-arylenebenzimidazole pyridine sulfone) (PNABIPS). The reaction of the
reactive benzimidazole N–H sites and the combination of sulfonyl and pyridine groups along with the polymer

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Y.W. Xu et al. / Chinese Chemical Letters 23 (2012) 871–874
backbone remarkably endow the current polymers with some special characteristics, such as good thermal resistance,
high glass transition temperature values and good solubility in common organic solvents. Intensive studies on the
synthesis of poly(N-arylenebenzimidazole pyridine sulfone)s are in progress.
Acknowledgments
This work was supported by the Science and Technology Development Foundation of China Academy of
Engineering Physics (No. 2009A0302021) and the Foundation of Double-Hundred Talents of China Academy of
Engineering Physics (No. ZX8078).
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