Synthesis and characterization of new polyesters based on 2,5-bis[(4-chloro carboxyanilino) carbonyl] pyridine and aromatic diols

Article abstract of DOI:10.1016/j.cclet.2009.08.002

Six new polyesters 7a-f were synthesized through the solution polycondensation reaction of diacid chloride 5 with six aromatic diols 6a-f in N,N-dimethyl acetamide (DMAc) as solvent in the presence of pyridine as base. The polycondensation reaction produced a series of novel polyester containing pyridyl moiety in the main chain in high yields with inherent viscosities between 0.35 and 0.54 dL/g. The resulted polymers were fully characterized by means of FT-IR spectroscopy, elemental analyses, inherent viscosity and solubility tests. Thermal properties of these polymers were investigated by using thermal gravimetric analysis (TGA) and differentional thermal gravimetric (DTG). The glass-transition temperatures of these polyesters were recorded between 130 and 170 °C by differential scanning calorimetry (DSC) and the 10% weight loss temperatures were ranging from 390 to 450 °C under nitrogen.

Full text of DOI:10.1016/j.cclet.2009.08.002

Available online at www.sciencedirect.com
Chinese Chemical Letters 21 (2010) 13–17
www.elsevier.com/locate/cclet
Synthesis and characterization of new polyesters based
on 2,5-bis[(4-chloro carboxyanilino) carbonyl] pyridine
and aromatic diols
Khalil Faghihi
Polymer Research Laboratory, Department of Chemistry, Faculty of Science, Islamic Azad University, Branch Arak, Arak, Iran
Received 30 March 2009
Abstract
Six new polyesters 7a–f were synthesized through the solution polycondensation reaction of diacid chloride 5 with six aromatic
diols 6a–f in N,N-dimethyl acetamide (DMAc) as solvent in the presence of pyridine as base. The polycondensation reaction
produced a series of novel polyester containing pyridyl moiety in the main chain in high yields with inherent viscosities between
0
.35 and 0.54 dL/g. The resulted polymers were fully characterized by means of FT-IR spectroscopy, elemental analyses, inherent
viscosity and solubility tests. Thermal properties of these polymers were investigated by using thermal gravimetric analysis (TGA)
and differentional thermal gravimetric (DTG). The glass-transition temperatures of these polyesters were recorded between 130 and
170 8C by differential scanning calorimetry (DSC) and the 10% weight loss temperatures were ranging from 390 to 450 8C under
nitrogen.
#
2009 Khalil Faghihi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: High-performance polymers; Polyesters; Pyridyl moiety; Aromatic diols
High-performance, high temperature polymers such as aromatic polyimides, poly(amide-imide)s, polyamides,
polyesters are characterized by their excellent balance of thermal and mechanical properties which makes them useful
materials for engineering applications [1]. However, these polymers particularly those with para-substituted rings
exhibit poor processability and limited solubility in organic solvents. Therefore, many efforts have been made to create
structurally modified aromatic polymers having increased solubility and processability with retention of their high
thermal stability. It is known that the solubility of polymers often increases when flexible bonds, large pendent groups
or polar constituents incorporated into the polymer backbone [2,3]. In our pervious papers we described synthesis of
different polyamides, poly(amide-imide)s and polyesters containing heterocyclic moieties in the main chain such as
hydantoin derivatives with improved solubility and thermal properties [4,5]. In this paper, synthesis and
characterization of a new series of polyesters containing pyridyl ring was studied by the solution polycondensation
reaction of 2,5-bis[(4-chlorocarboxyanilino) carbonyl] pyridine 5 with six aromatic diols such as hydroquinone 6a,
0
2,7-dihydroxy naphthalene 6b, bisphenol A 6c, 1,4-dihydroxy anthraquinone 6d, 4,4 -dihydroxyphenyl sulfone 6e and
phenol phethalein 6f in N,N-dimethyl acetamide (DMAc) as solvent in the presence of pyridine as base. These
E-mail address: k-faghihi@araku.ac.ir.
1001-8417/$ – see front matter # 2009 Khalil Faghihi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2009.08.002

14
K. Faghihi / Chinese Chemical Letters 21 (2010) 13–17
polymers have a heterocyclic aromatic ring such as pyridyl moiety in the main chain for improving thermal stability
and also solubility in organic solvents in comparison with aromatic polyesters.
1
. Experimental
All chemicals were purchased from Merck Chemical Co. (Germany) and Aldrich (USA). Fourier transform
infrared (FTIR) spectra were recorded on Galaxy series FTIR 5000 spectrophotometer (England). Spectra of solids
ꢀ
1
were performed by using KBr pellets. Vibrational transition frequencies are reported in wave number (cm ). Band
intensities are assigned as weak (w), medium (m), shoulder (sh), strong (s) and broad (br). Inherent viscosities were
measured by a standard procedure by using a Technico Regd Trad Merk Viscometer. Thermal gravimetric analysis
(
min. Differential scanning calorimetric analysis was performed on differential scanning calorimeter (Du Pont 910) at a
TGA and DTG) data for polymers were taken on a Mettler TA4000 System under N atmosphere at a rate of 10 8C/
2
heating rate of 10 8C/min. Elemental analyses were performed by Arak Petrochemical Company, Arak, Iran.
2
,5-Bis[(4-carboxyanilino) carbonyl] pyridine 4: This new diacid was synthesized by using a two-step reaction as
shown in Scheme 1 [6].
,5-Bis[(4-chlorocarboxyanilino) carbonyl] pyridine 5: Into a 100 mL round-bottomed flask were placed 2.02 g
5.00 mmol) of diacid 4 and 20 mL of thionyl chloride. The mixture was heated in an oil bath up to 100 8C until the
2
(
suspension mixture converted to a clear solution. Then the solution was stirred overnight at room temperature.
Unreacted thionyl chloride was removed under reduced pressure, and the residue was washed with dry n-hexane three
times, this yielded to a yellow precipitate 5. This compound has no melting point and will decompose over 250 8C. FT-
IR (KBr): 3076(w), 1780(m), 1755(s), 1722(s), 1602(m), 1510(m), 1379(s), 1188(m), 1151(m), 1097(m), 970(w)
ꢀ
1
cm . Analysis: Calcd. for C H N O Cl : C, 57.03; H, 2.93; N, 9.49; found: C, 57.25; H, 2.80; N, 9.40.
2
1
13
3
4
2
Polymer synthesis: Taking polymer 7a as an example: into a 25 mL round-bottomed flask which was placed in an
0
ice bath, 0.026 g (0.24 mmol) of hydroquinone 6a was dissolved in 0.8 mL of N,N -dimethyl acetamide (DMAc). Then
.5 mL of pyridine and 0.106 g (0.24 mmol) of diacid chloride 5 was added to the flask. The reaction mixture was
0
stirred for 1 h in ice bath. Then the ice bath was removed and a reflux system was set up. The mixture was again stirred
at room temperature overnight and then was heated at 80 8C for 12 h until viscose solution was formed. After cooling
down to room temperature, 25 mL of methanol was added and stirred, a white-yellow precipitate was formed which
was filtered-off and thoroughly washed with methanol and finally dried under vacuum at 60 8C for 12 h to leave
0
.101 g (88%) of solid polymer 7a.
2
. Results and discussion
Monomer synthesis: 2,5-Bis[(4-chlorocarboxyanilino) carbonyl] pyridine 5 as a new monomer containing pyridyl
moiety was synthesized by using a three-step reaction. At first 2,5-pyridine dicarboxylic acid 1 was converted to 2,5-
pyridine dicarbonyl dichloride 2. Diacid 4 was prepared by condensation reaction of 2,5-pyridine dicarbonyl
dichloride 2 with two equivalent of 4-amino benzoic acid 3 in extra pure tetrahydrofuran (THF). Then diacid 4 was
converted to 2,5-bis[(4-chlorocarboxyanilino) carbonyl] pyridine 5 by reaction with thionyl chloride in the presence of
pyridine (Scheme 1).
1
The chemical structure and purity of diacid 4 were proved with elemental analysis, H NMR, and FT-IR
spectroscopy [6]. Also the chemical structure and purity of diacid chloride 5 as new compound were proved with
elemental analysis and FT-IR spectroscopy. The measured results in elemental analyses of diacid 5 closely
Scheme 1. Synthetic route of 2,5-bis[(4-chlorocarboxyanilino) carbonyl] pyridine 5.

K. Faghihi / Chinese Chemical Letters 21 (2010) 13–17
15
Scheme 2. Synthetic route of polyesters 7a–f.
corresponded to the calculated ones, demonstrating that the expected compound was obtained. In the FT-IR spectrum
ꢀ
1
of compound 5 disappearing a broad peak at 2500–3100 cm confirmed a complete conversion of diacid 4 to diacid
chloride 5. On the other hand, because of the electron withdrawing character of the Cl groups, carbonyl peaks of the
diacid chloride 5 in comparison with diacid 4, were shifted to a higher frequency.
Polymer synthesis: PAs 7a–f were synthesized by solution polycondensation reaction of an equimolar mixture of
0
diacid chloride 5 with six aromatic diols 6a–f in N,N -dimethyl acetamide (DMAc) and in presence of pyridine as base
(
Scheme 2). The syntheses and some physical properties of these new polyesters 7a–f are given in Table 1. The entire
polycondensation reaction readily proceeded to the homogeneous solutions while tough and stringy precipitates
formed as the viscous polymeric solutions were obtained in good yields.
Polymer characterization: The syntheses and some physical properties of polyesters 7a–f are summarized in
Table 1. These polymers had inherent viscosities around 0.35–0.54 dL/g and showed white to yellow crystals. These
polymers confirmed as polyester with FT-IR spectroscopy and elemental analyses (Table 2). A representative FTIR
spectrum of polyester 7a is shown in Fig. 1. FT-IR spectrum shows that the carbonyl peak of polymer shift to lower
ꢀ
1
frequency in comparison with diacid chloride 5 and stretching OH peak at 2500–3100 cm of diacid disappeared.
The elemental analysis of the resulted polymers was in good agreement with the calculated values for the proposed
structures. The solubility of these polymers was investigated with 0.01 g polymeric samples in 2 mL of solvent. All
polymers were dissolved in polar aprotic solvents such as DMF, DMAC, DMSO and NMP at room temperature and are
insoluble in solvents such as chloroform, methylene chloride, methanol, ethanol and water.
Thermal properties: The thermal properties of polyesters 7a–f were investigated by TGA and DTG in a nitrogen
atmosphere at a heating rate of 10 8C/min and the thermal data are summarized in Table 2. The initial decomposition
temperatures of 5% and 10% weight losses (T and T ) and the char yields at 600 8C are summarized in Table 2. These
5
10
polymers exhibited good resistance to thermal decomposition up to 340–415 8C in nitrogen, and began to decompose
gradually above those temperatures. T for these polymers from 340 to 415 8C and T for all polymers ranged from
5
10
390 to 450 8C, and the residual weight for these polymers at 600 8C ranged from 17 and 68% in nitrogen (Fig. 2). In the
DSC experiments, there is no melting endotherm in the DSC thermograms. Glass-transition temperatures of these
polymers were found to be in the range of 130–170 8C.
Table 1
Synthesis and some physical properties of polyester 7a–f.
a
Aromatic Diols
Polymer
Yield (%)
hinh (dL/g)
6a
6b
6c
6d
6e
6f
7a
7b
7c
7d
7e
7f
88
89
91
89
90
80
0.35
0.52
0.54
0.43
0.41
0.43
a
Measured at a concentration of 0.5 g/dL in DMF at 25 8C.

16
K. Faghihi / Chinese Chemical Letters 21 (2010) 13–17
Table 2
Thermal behavior of PAs 7a–f.
a
b
c
d
Char Yield (%)
Polymer
Tg (8C)
T
5
(8C)
T10 (8C)
7a
7b
7c
7d
7e
7f
135
130
155
130
170
160
365–370
340–345
395–400
405–410
415–420
340–345
390–395
405–410
420–430
415–420
450–455
390–495
17
40
25
60
68
55
a
The glass-transition temperatures (Tg) were measured by DSC.
b,c
2
Temperature at which 5% and 10% weight loss was recorded by TGA at heating rate of 10 8C/min in N respectively.
Percentage weight of material left undecomposed after TGA analysis 600 8C.
d
Fig. 1. FTIR Spectrum of Polyster 7a.
Fig. 2. TGA and DTG of Polyester 7e.
3
. Conclusion
This work involved the syntheses of several new polyesters 7a–f through the solution polycondensation reaction of
diacid chloride 5 with six aromatic diols 6a–f in N,N-dimethyl acetamide (DMAc) as solvent in the presence of

K. Faghihi / Chinese Chemical Letters 21 (2010) 13–17
17
pyridine as base. These new polymers were soluble in various organic solvents and had good thermal stability. The
presence of pyridyl segments as a hetrocyclic ring into the backbone increased the solubility of these polymers. These
properties could make these polyesters attractive for practical applications, such as processable high-performance
engineering plastics.
References
[
[
[
[
[
[
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