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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
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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)
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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.