Designed Monomers and Polymers 13 (2010) 207–220 brill.nl/dmp
Synthesis and Characterization of New Optically Active Poly(amide-imide)s Based on N,N -(Pyromellitoyl)-bis-L-Amino Acids and 1,3,4-Oxadiazole Moieties Khalil Faghihi ∗ and Hassan Moghanian Organic Polymer Chemistry Research Laboratory, Department of Chemistry, Faculty of Science, Arak University, Arak 38156, Iran Abstract New optically active poly(amide-imide)s derived from chiral N,N -(pyromellitoyl)-bis-L-amino acids (3a–f) and 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (BAO) (8) were synthesized by direct polycondensation. Chiral N,N -(pyromellitoyl)-bis-L-amino acids were obtained by the reaction of pyromellitic dianhydride with two equimolar of L-alanine (2a), L-valine (2b), L-leucine (2c), L-isoleucine (2d), L-phenyl alanine (2e) and L-2-aminobutyric acid (2f) in acetic acid. The polycondensation reaction proceeded through the in situ formation of an Vilsmeier adduct by dissolving tosyl chloride (TsCl) in a mixed solvent of pyridine and DMF. The resulting thermally stable poly(amide-imide)s were obtained in good to high yields and inherent viscosities ranging between 0.31 and 0.55 dl/g. The structures of the new polymers were confirmed by elemental analysis and spectral methods (FT-IR, 1 H-NMR). Optical activity and thermal behavior investigated by polarimetric measurements and thermogravimetric analysis, respectively. © Koninklijke Brill NV, Leiden, 2010 Keywords Poly(amide-imide), 1,3,4-oxadiazole, polycondensation, optically active polymer, chiral amino acid
1. Introduction Aromatic polymers such as polyimides and polyamides are thermally stable polymers which have received much interest over the past decades due to increasing demands for high-performance polymers as replacement for ceramics or metals in the microelectronic, aerospace and automotive industries [1–3]. They are difficult to process due to their insolubility in organic solvents and infusibility [4–9]. Considerable effort has been made to improve their processing properties by structural modifications. One such method is the synthesis of copolymers. Poly(amide-imide)s (PAIs) are a class of high-performance polymers, which show excellent mechani*
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DOI:10.1163/138577210X12634696333514
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cal and thermal properties and are also solvent resistant [4, 10]. There is a growing interest in PAIs for a variety of applications, as they retain good mechanical properties at high temperatures and are more processable than other aromatic thermostable polymers, such as polyamides and polyimides [11]. Optically active compounds have attracted much attention because living systems are chiral. Proteins and nucleic acids possess chiral characteristic structures that are related closely to their functions. Because of the chirality, living organisms usually show different biological responses to one or the other of a pair of enantiomers or optical isomers whether they are drugs, pesticides or wastes. Synthesis and characterization of optically active polymers has been a challenging theme in the field of polymer synthesis in recent years for their important applications of optically active polymers as catalysts for asymmetric synthesis [12, 13] and as chiral stationary phases (CSP) for the direct optical resolution of enantiomers [14–17]. Optically active polymers can be obtained by polymerization of optically active monomers or by stereo-selective polymerization of racemic or prochiral monomers using optically active catalysts. Recently, we have synthesized a variety of optically active polymers by incorporation of optically active segments in polymer’s backbone. In addition of optical properties of these polymers, the solubility of them was improved without significant loss of mechanical and thermal properties [18–22]. On the other hand, it was shown that aromatic polymers containing 1,3,4oxadiazole rings in the main chain exhibit high thermal resistance in oxidative atmosphere, good hydrolytic stability, low dielectric permittivity, high toughness and other special properties which are determined by the electronic structure of this particular heterocycle [23–27]. The incorporation of oxadiazole and imide rings together with flexible groups into the polymer chain is expected to provide a combination of high-performance properties and processability, particularly in thin films and coatings. Here we present the research on the synthesis and characterization of new optically active PAIs containing 1,3,4-oxadiazole rings in the main chain, which were obtained by direct polycondensation reaction of 2,5-bis(4-aminophenyl)1,3,4-oxadiazole (7) with six chiral N,N -(pyromellitoyl)-bis-L-amino acids (3a–f) using tosyl chloride (TsCl), pyridine (Py) and dimethylformamide (DMF) as condensing agent. 2. Experimental 2.1. Materials All chemicals were purchased from Fluka and Aldrich. Pyromellitic dianhydride was purified by recrystallization from acetic anhydride and then dried in vacuo at 125◦ C for 12 h. Acetic anhydride was purified by distillation under reduced pressure.
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2.2. Measurements IR spectra were recorded on a Galaxy series FT-IR 5000 spectrophotometer. Band intensities are assigned as weak (w), medium (m), strong (s) and band shapes as shoulder (sh), sharp (s) and broad (br). 1 H-NMR and 13 C-NMR spectra were recorded on a Bruker 300 MHz instrument. Inherent viscosity was measured by a standard procedure using a Technico® viscometer. Specific rotations were measured by an A-Kruss polarimeter. Thermogravimetric analysis (TGA) data for polymers were recorded on a Mettler TA4000 System under N2 atmosphere at a rate of 10◦ C/min. Elemental analyses were performed using Vario EL equipment at Arak University. 2.3. Monomer Synthesis 2.3.1. Synthesis of N,N -(pyromellitoyl)-bis-L-amino Acid (3a–f) Pyromellitic dianhydride (1,2,4,5-benzenatetracarboxylic acid 1,2,4,5-dianhydride) 1 (4.36 g, 20.00 mmol), 40.00 mmol L-amino acids 2a–f, 80 ml acetic acid and a stirring bar were placed into a 250-ml round-bottomed flask. The mixture was stirred at room temperature overnight and refluxed for 4 h. The solvent was removed under reduced pressure, and the residue was dissolved in 100 ml cold water, then the solution was decanted and 5 ml concentrated HCl was added. A white precipitate was formed, filtered off, and dried to give compounds N,N -(pyromellitoyl)-bis-Lamino acid (3a–f). Diacid (3a): 1 H-NMR (300 MHz, DMSO-d6 , δ, ppm): 13.5 (s, br, 2H), 8.39– 8.40 (d, 1H, J = 9 Hz), 8.26 (s, 1H), 8.04–8.07 (d, 1H, J = 9 Hz), 4.91 (q, 1H), 1.55 (d, 3H). FT-IR (KBr): 2500–3400 (s, br), 1728 (s, sh), 1722 (s, br), 1604 (w, sh), 1487 (w, sh), 1423 (s, sh), 1384 (s), 1290 (s), 1095 (m), 927 (m), 731 (s), 655 (m), 532 (w) cm−1 . Diacid (3b): 1 H-NMR (300 MHz, DMSO-d6 , δ, ppm): 13.64 (s, br, 2H), 8.51– 8.54 (d, 1H, J = 9 Hz), 8.25 (s, 1H), 8.02–8.05 (d, 1H, J = 9 Hz), 5.02 (d, 1H), 2.32 (m, 1H), 1.06–1.08 (d, 3H), 0.83–0.85 (d, 3H). FT-IR (KBr): 2500–3400 (m, br), 1782 (m, sh), 1722 (s, br), 1487 (w), 1384 (s), 1290 (s), 1095 (w), 929 (m), 733 (s), 609 (w), 532 (w) cm−1 . Diacid (3c): 1 H-NMR (300 MHz, DMSO-d6 , δ, ppm): 13.07 (s, br, 2H), 8.51– 8.54 (d, 1H, J = 9 Hz), 8.41 (s, 1H), 8.02–8.05 (d, 1H, J = 9 Hz), 4.78–4.83 (dd, 1H, J = 6, 3 Hz), 1.52 (m, 2H), 1.49 (m, 1H), 0.85–0.87 (d, 6H). FT-IR (KBr): 2500–3400 (m, br), 1780 (m, sh), 1733 (s, br), 1485 (w), 1380 (s), 1295 (s), 1095 (w), 920 (m), 743 (s), 609 (w), 533 (w) cm−1 . Diacid (3d): 1 H-NMR (300 MHz, DMSO-d6 , δ, ppm): 13.39 (s, br, 2H), 8.38– 8.41 (d, 1H, J = 9 Hz), 8.27 (s, 1H), 8.02–8.05 (d, 1H, J = 9 Hz), 4.53–4.56 (d, 1H), 2.36–2.38 (m, 1H), 1.46–1.52 (m, 2H), 1.00–1.06 (d, 3H), 0.77–0.82 (t, 3H). FT-IR (KBr): 2400–3500 (s, br), 1778 (s, sh), 1722 (s, br), 1379 (s), 1286 (s), 1093 (m), 929 (w), 733 (m), 538 (w) cm−1 . Diacid (3e): 1 H-NMR (300 MHz, DMSO-d6 , δ, ppm): 13.57 (s, br, 2H), 8.33– 8.53 (d, 1H, J = 6 Hz), 8.19 (s, 1H), 7.94–7.97 (d, 1H, J = 6 Hz), 7.15 (s, 5H),
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5.12–5.17 (dd, 1H, J = 9, 3 Hz), 3.46–3.52 (dd, 1H, J = 9, 3 Hz), 3.29–3.35 (dd, 1H, J = 9, 3 Hz). FT-IR (KBr): 2400–3500 (s, br), 1770 (s, sh), 1720 (s, br), 1383 (s), 1278 (s), 1091 (m), 925 (w), 731 (m), 539 (w) cm−1 . Diacid (3f): 1 H-NMR (300 MHz, DMSO-d6 , δ, ppm): 13.45 (s, br, 2H), 8.37– 8.40 (d, 1H, J = 9 Hz), 8.26 (s, 1H), 8.01–8.04 (d, 1H, J = 9 Hz), 4.66–4.71 (dd, 1H, J = 6, 3 Hz), 2.01–2.19 (m, 2H), 0.82–0.87 (t, 3H). FT-IR (KBr): 2400–3500 (s, br), 1780 (s, sh), 1720 (s, br), 1604 (m), 1487 (m), 1383 (s), 1284 (s, sh), 1082 (s), 879 (s), 729 (s), 638 (m), 472 (w), 314 (w) cm−1 . 2.3.2. Synthesis of N -(4-nitrobenzoyl)-4-nitrobenzohydrazide (6) Into a 100-ml round-bottomed flask fitted with a magnetic stirrer was placed a solution of 4-nitrobenzoyl chloride (10 g, 53.9 mmol) and triethylamine (4 ml) in 40 ml dry dimethylacetamide (DMAc). The reaction mixture was cooled in an ice water bath. To this solution, 6 ml hydrazine monohydrate was added drop-wise. The mixture was stirred in ice bath for 2 h and at room temperature overnight. The mixture was poured into 100 ml water. The precipitate was collected by filtration and washed thoroughly with water and dried at 100◦ C to yield 6 (6.5 g, 73%). Mp 290–292◦ C, FT-IR: 3221 (s, br), 3111 (w), 1619 (s), 1587 (s), 1529 (s), 1465 (s), 1348 (s), 1261 (w), 1109 (w), 837 (m), 715 (m) cm−1 . 2.3.3. Synthesis of 2,5-Bis(4-nitrophenyl)-1,3,4-oxadiazole (7) Into a 50-ml round-bottomed flask, 4 g (12.0 mmol) N -(4-nitrobenzoyl)-4nitrobenzohydrazide, 30 ml phosphoryl trichloride and a stirring bar were placed. The stirrer was started and the mixture was refluxed for 12 h. The reaction mixture was cooled to room temperature, poured into ice–water and precipitated. The precipitate was filtered, washed with water and then dried to afford 7 (3.5 g, 87%). Mp > 300◦ C, FT-IR: 3109 (w), 1612 (m), 1583 (s), 1515 (s), 1469 (m), 1350 (s), 1109 (w), 866 (m), 717 (m) cm−1 . 2.3.4. Synthesis of 2,5-Bis(4-aminophenyl)-1,3,4-oxadiazole (BAO) (8) 2,5-Bis(4-nitrophenyl)-1,3,4-oxadiazole (2 g, 6.4 mmol), 0.2 g 10% Pd–C and 50 ml ethanol were introduced into a 100-ml round-bottomed flask to which 12 ml hydrazine monohydrate was added drop-wise over a period of 1 h at 85◦ C. After the complete addition, the reaction was continued at reflex temperature for another 5 h. Then, the mixture was filtered to remove the Pd–C and the filtrate was poured into water. The product was filtered off, washed with water and dried to afford 8 (1.2 g, 74%). Mp 260–261◦ C, FT-IR: 3325 (m), 3215 (m), 1608 (s), 1493 (s), 1438 (w), 1273 (w), 1178 (m), 1080 (w), 831 (w), 746 (w) cm−1 . 1 H-NMR (DMDO-d6 ): δ = 7.71 (d, J = 8.7, 4H), 6.69 (d, J = 8.7, 4H), 5.86 (s, 4H) ppm. 13 C-NMR (DMDO-d6 ): δ = 168.6, 157.2, 133.0, 118.8, 115.4 ppm. 2.4. Polymer Synthesis Polymer 8a, as an example of synthesis of PAIs, was prepared by the following procedure: a pyridine (0.20 ml) solution of TsCl (0.18 g, 9.5 × 10−4 mol) after 30 min stirring at room temperature was treated with DMF (0.07 ml, 9.0 × 10−4 mol)
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for additional 30 min. The reaction mixture was added drop-wise to a solution of N,N -(pyromellitoyl)-bis-L-alanine (3a) (0.137 g, 3.8 × 10−4 mol) in pyridine (0.20 ml). The mixture was maintained at room temperature for 30 min, and then to this mixture, a solution of 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (7) (0.096 g, 3.8 × 10−4 mol) in pyridine (0.30 ml) was added drop-wise and the whole solution was stirred at room temperature for 30 min and at 100◦ C for 2 h. As the reaction proceeded, the solution became viscous, then was precipitated in 20 ml methanol, filtered off and dried in vacuum to yield 0.196 g (89%) of the polymer 9a. PAIs 9a–f were analyzed using FT-IR spectroscopy with KBr pellets. 9a: 3317 (m, br), 3067 (w), 2941 (w), 1774 (m), 1722 (s, br), 1606 (m), 1525 (m), 1496 (s), 1383 (sh), 1251 (m), 1157 (m), 1076 (w), 1016 (w), 939 (w), 846 (m), 729 (m), 565 (w) cm−1 . 9b: 3331 (m, br), 3099 (w), 2968 (w), 1776 (m), 1722 (s, br), 1604 (s), 1496 (s), 1383 (sh), 1315 (m), 1251 (m), 1180 (m), 1076 (m), 1012 (w), 914 (w), 846 (m), 727 (m), 563 (w) cm−1 . 9c: 3352 (m, br), 2960 (m), 1776 (m), 1724 (s, br), 1606 (s), 1496 (s), 1411 (w), 1356 (sh), 1317 (w), 1251 (w), 1182 (w), 1084 (w), 844 (w), 727 (w), 565 (w) cm−1 . 9d: 3331 (m, br), 3107 (w), 2968 (w), 1776 (m), 1722 (s, br), 1606 (m), 1527 (m), 1496 (s), 1383 (sh), 1253 (m), 1182 (m), 1078 (m), 1014 (w), 914 (w), 846 (m), 729 (m), 565 (w) cm−1 . 9e: 3369 (m, br), 3030 (w), 2928 (w), 1776 (m), 1724 (s, br), 1604 (m), 1525 (m), 1497 (s), 1381 (sh), 1317 (m), 1249 (m), 1180 (m), 1105 (w), 914 (w), 842 (m), 727 (m), 563 (w) cm−1 . 9f: 3350 (m, br), 3068 (w), 2972 (w), 1776 (m), 1724 (s, br), 1604 (m), 1496 (s), 1413 (w), 1353 (sh), 1248 (m), 1180 (m), 1068 (m), 960 (w), 842 (m), 725 (m), 565 (w) cm−1 . 3. Results and Discussion 3.1. Monomer Synthesis As shown in Scheme 1, the asymmetric diimide-diacids 3a–f were synthesized by the condensation reaction of pyromellitic dianhydride 1 with two equimolars of Lalanine (2a), L-valine (2b), L-leucine (2c), L-isoleucine (2d), L-phenyl alanine (2e) and L-2-aminobutyric acid (2f) in an acetic acid solution according to the reported procedure [19]. The yields and some physical properties of these compounds are shown in Table 1. The chemical structure and purity of the optically active diimide-diacids 3a–f were determined using elemental analysis, FT-IR and 1 H-NMR spectroscopy. As an example, the FT-IR spectrum of N,N -(pyromellitoyl)-bis-L-2-aminobutyric acid (3f) showed a broad peak between 2500 and 3500 cm−1 , which was assigned to the COOH groups and two absorption bands at 1776 and 1726 cm−1 due to carbonyl
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Scheme 1. Synthesis of asymmetric diimide-diacids 3a–f.
Table 1. Synthesis of chiral diimide-diacid derivatives 3a–f Entry
Amino-acid compound
R
Mp (◦ C)
Yield (%)
a [α]D 25
3a 3b 3c 3d 3e 3f
L-Alanine
CH3 (CH3 )2 CH (CH3 )2 CHCH2 (C2 H5 )(CH3 )CH PhCH2 CH3 CH2
303–305 276–278 318–320 279–282 305–307 295–297
78 85 87 88 90 85
−6.5 −3.0 +0.2 −8.0 +0.2 +12.1
L-Valine L-Leucine L-Isoleucine L-Phenylalanine L-2-Aminobutyric
acid
a Measured at a concentration of 0.5 g/dl in EtOH at 25◦ C.
of imide (asymmetrical and symmetrical C=O stretching vibration), and bands at 1383, 1113 and 731 cm−1 (imide ring deformation) (Fig. 1). The 1 H-NMR spectrum of diimide-diacid 3f showed peaks between 0.85 and 0.90 ppm as a triplet, which were assigned for two CH3 (a), and peaks between 2.10 and 2.17 ppm as a multiplet, which was assigned to the CH2 (b) and between 4.72 and 4.77 ppm as a doublet of doublet (J = 6 and 3 Hz), which was assigned to the CH(c) proton, which is a chiral center. The peak at 8.35 ppm was assigned to aromatic protons (e). Also a broad peak in 13.25 ppm was assigned to COOH groups (Fig. 2). Also, 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (8) was synthesized using a three-step reaction. At first N -(4-nitrobenzoyl)-4-nitrobenzohydrazide (6) was prepared from condensation of two equivalents of 4-nitrobenzoyl chloride (4) with hydrazine monohydrate (5) in the presence of triethylamine in DMAc solution (Scheme 2). Then N -(4-nitrobenzoyl)-4-nitrobenzohydrazide (6) was cyclized to 2,5-bis(4nitrophenyl)-1,3,4-oxadiazole (7) with phosphorus oxychloride as anhydrous re-
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Figure 1. FT-IR spectrum of N,N -(pyromellitoyl)-bis-L-2-aminobutyric acid 3f.
Figure 2. 1 H-NMR spectrum of N,N -(pyromellitoyl)-bis-L-2-aminobutyric acid 3f.
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agent under reflux conditions. Finally, 7 was reduced using Pd/C to produce 8 (Scheme 2). The chemical structure and purity of 8 was determined by elemental analysis, FT-IR and 1 H-NMR spectroscopic techniques. The 1 H-NMR spectrum of 8 showed a peak at 5.86 ppm, which was assigned to the H(c) protons of the NH2 groups. Peaks at δ = 6.60 and δ = 7.72 were assigned to the H(b) and H(a) protons of the phenyl rings (Fig. 3).
Scheme 2. Synthesis of 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (8).
Figure 3. 1 H-NMR spectrum of 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (8).
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3.2. Polymer Synthesis PAIs 9a–f were synthesized by direct polycondensation reaction of an equimolar mixture of diacids 3a–f with 8 using TsCl/Py/DMF as condensing agent (Scheme 3). In this report of the polycondensation of aliphatic–aromatic diacids and 2,5bis(4-aminophenyl)-1,3,4-oxadiazole, a Vilsmeier adduct was prepared by dissolving TsCl in a mixed solvent of pyridine and DMF. The polycondensation was carried out according to reported procedure [28, 29]. The synthesis and some physical properties of these new optically active PAIs are listed in Table 2. All of the polymers were obtained in good to high yields (78–89%) with moderate inherent viscosities (0.31–0.55 dl/g) and show optical rotation and, therefore, they are optically active.
Scheme 3. Synthesis of PAIs 9a–f.
Table 2. Synthesis and some physical properties of PAIs 9a–f Imide-diacid
Polymer
Yield (%)
ηinh (dl/g)a
a [α]D 25
3a 3b 3c 3d 3e 3f
9a 9b 9c 9d 9e 9f
89 84 81 78 85 87
0.55 0.47 0.31 0.40 0.44 0.49
86.2 80.9 110.2 117.5 97.7 105.4
a Measured at a concentration of 0.5 g/dl in DMSO at 25◦ C.
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3.3. Polymer Characterization The elemental analysis values of the resulting polymers are in good agreement with the calculated values for the proposed structures (Table 3). The solubility of PAIs was tested quantitatively in various solvents. The solubility of the PAIs is listed in Table 4. Most of the PAIs are soluble in organic polar aprotic solvents such as DMF, N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), 1-methyl-2-pyrrolidone (NMP), and polar protic solvents such as H2 SO4 at room temperature, and are insoluble in solvents such as chloroform, methylene chloride, methanol, ethanol and water. Table 3. Elemental analysis of PAIs 9a–f Polymer
Formula
C (%)
H (%)
N (%)
9a
C30 H20 N6 O7 (576.52)n
Calcd Found
62.50 61.25
3.50 3.77
14.58 14.37
9b
C34 H28 N6 O7 (632.62)n
Calcd Found
64.55 63.10
4.46 4.69
13.28 13.49
9c
C36 H32 N6 O7 (660.68)n
Calcd Found
65.45 64.50
4.88 4.70
12.72 12.93
9d
C36 H32 N6 O7 (660.68)n
Calcd Found
65.45 64.38
4.88 4.94
12.72 12.54
9e
C42 H28 N6 O7 (728.71)n
Calcd Found
69.23 68. 17
3.87 3.63
11.53 11.32
9f
C32 H24 N6 O7 (604.57)n
Calcd Found
63.57 62.10
4.00 4.22
13.90 14.06
Table 4. Solubility of PAIs 9a–f Solvent
9a
9
9c
9d
9e
9f
H2 SO4 DMAc DMSO DMF NMP MeOH EtOH CHCl3 CH2 Cl2 H2 O
+ + + + + − − − − −
+ + + + + − − − − −
+ + + + + − − − − −
+ + + + + − − − − −
+ + + + + − − − − −
+ + + + + − − − − −
+, soluble at room temperature; −, insoluble at room temperature.
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The structures of these polymers were confirmed as PAIs by means of FT-IR, spectroscopy and elemental analyses. The representative FT-IR spectrum of PAI 9a is shown in Fig. 4. The FT-IR spectra of the polymer exhibited characteristic absorption bands at 1774 and 1722 cm−1 for the imide ring (asymmetric and symmetric C=O stretching vibration), 1383 cm−1 (C–N stretching vibration). The absorption band at 3317 cm−1 corresponds to the N–H stretching. The others spectra show a similar pattern. The FT-IR spectra of the polymers show an absorption peak at 3050– 3070 cm−1 characteristic of the aromatic C–H stretching vibrations. The bands at 2960–2870 cm−1 are due to the aliphatic C–H stretching. The 1 H-NMR spectrum of PAI 9f (Fig. 5) shows peaks that confirm its chemical structure. It shows a peak for CH3 (Hf ) that appears at 0.91 ppm. A peak for CH2 (He ) appears as broad peak at 2.20 ppm according to its coupling with CH3 (Hf ) and CH (Hd ). The proton of the chiral center (Hd ) appeared at 4.90 ppm. The aromatic protons related to phenyl groups of oxadiazole unit and pyromellitic ring appeared in the region of 8.03, 7.78 (Ha and Hb ) and 8.38 ppm (Hg ), respectively. The peak in the region of 10.34 ppm is assigned to N–H of amide groups in the main chain. The decaying peak related to carboxylic acid protons and appearing peaks related 1 H-NMR
Figure 4. FT-IR spectrum of PAI 9a.
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Figure 5. 1 H-NMR spectrum of PAI 9f.
to amide groups, oxadiazole moiety and pyromellitic ring protons in the polymer chain, confirmed the proposed structure of PAIs 9a–f. 3.4. Thermal Properties The thermal stability of the polymers 9a and 9e was characterized by TGA conducted in nitrogen at a heating rate of 10◦ C/min. In all cases, the thermal stability was very good. The temperature at which the decomposition began was never under 300◦ C. The highest thermal stability was found for PAI 9e. This behavior could be a consequence of the phenyl group present in the side-chain of polymer. Typical TGA curves of representative polymers are shown in Fig. 6. The 5 and 10% weight loss temperatures together with char yield at 600◦ C for PAIs 9a and 9e have been calculated from their thermograms. From these data it is clear that the resulting polymers are thermally stable. The thermo analyses data of PAIs 9a and 9b are summarized in Table 5. 4. Conclusion The present study involved the synthesis of several new optically active PAIs (9a–f) by the direct polycondensation reaction of 2,5-bis(4-aminophenyl)-1,3,4oxadiazole (8) with six asymmetric imide-diacids 3a–f and tosyl chloride (TsCl)/pyridine (Py)/dimethylformamide (DMF) as condensing agent. These PAIs
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Figure 6. TGA curves of PAIs 9a and 9e. Table 5. Thermal properties of PAIs 9a and 9e Polymer
T5 (◦ C)
T10 (◦ C)
Char yield (%)c
9a 9e
325–330 350–355
370–375 385–390
56.3 52.11
T5 , T10 , temperature at which 5 or 10% weight loss was recorded TGA at a heating rate of 10◦ C/min in N2 ; char yield, weight percentage of material left after TGA analysis at a maximum temperature of 600◦ C in N2 .
were soluble in various organic solvents and had moderate to good thermal stability. Since the resulting polymers optically active and have good thermal stability, they have the potential to be used as a chiral stationary phase in chromatography for the separation of racemic mixtures. References 1. K. L. Mittal, Polyimides. Synthesis, Characterization and Application. Plenum, New York, NY (1984). 2. J. M. Abadie and B. Sillion, Polyimides and other High Temperature Polymers. Elsevier, New York, NY (1991). 3. C. Feger, M. M. Khojasteh and S. M. Htoo, Advances in Polyimide Science and Technology. Technomic, Lancaster, PA (1993). 4. P. E. Cassidy, Thermally Stable Polymers. Marcel Dekker, New York, NY (1980). 5. A. Banihashemi and H. Firoozifar, Eur. Polym. J. 39, 281 (2003). 6. J. Preston and F. Dobinson, J. Polym. Sci. B 2, 1171 (1964). 7. G. Bier, Adv. Chem. Ser. 91, 612 (1969). 8. J. Preston, in: Encyclopedia of Polymer Science and Technology, H. F. Mark, N. M. Bikales, C. G. Overberger and G. Menges (Eds), Vol. 111, p. 81. Wiley-Interscience, New York, NY (1988).
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9. J. Lin and D. C. Sherrington, Adv. Polym. Sci. 111, 177 (1994). 10. J. P. Critchley, G. J. Knight and W. W. Wright, Heat Resistant Polymers. Plenum Press, New York, NY (1983). 11. A. V. R. Reddy, P. R. Sreenivasulu and P. S. Anand, Eur. Polym. J. 34, 1441 (1998). 12. A. Akelah and D. C. Sherrington, Polymer 24, 1369 (1983). 13. J. H. Liu, J. Appl. Polym. Sci. 53, 176 (1994). 14. K. Saigo, T. Shiwaku, K. Hayashi, K. Fukoja, M. Sukegawa, Y. Chen, N. Yonezawa and M. Hasegawa, Macromolecules 23, 2830 (1990). 15. K. Saigo, N. Nakamura, Y. Suzuki, L. Fang and M. Hasegawa, Macromolecules 23, 3722 (1990). 16. Y. Chen and J. J. Lin, J. Polym. Sci. Part A: Polym. Chem. 30, 2699 (1992). 17. Y. Chen and H. H. Tseng, J. Polym. Sci. Part A: Polym. Chem. 31, 1719 (1993). 18. K. Faghihi, J. Appl. Polym. Sci. 109, 74 (2008). 19. D. J. Liaw, F.-C. Chang, J. H. Liu, K. L. Wang, K. Faghihi, S. H. Huang, K. R. Lee and J. Y. Lai, Polym. Degrad. Stabil. 92, 323 (2007). 20. K. Faghihi and A. Mirsamie, Chin. J. Polym. Sci. 23, 63 (2005). 21. K. Faghihi, Polym. J. 37, 449 (2005). 22. K. Faghihi, K. Zamani, A. Mirsamie and S. Mallakpour, Polym. Int. 53, 1226 (2004). 23. B. Schulz, M. Bruma and L. Brehmer, Adv. Mater. 9, 601 (1997). 24. I. Sava, M. D. Iosip, M. Bruma, C. Hamciuc, J. Robison, L. Okrasa and T. Pakula, Eur. Polym. J. 39, 725 (2003). 25. M. Bruma, E. Hamciuc, B. Schulz, T. Köpnick, Y. Kaminorz and J. Robison, Macromol. Symp. 199, 511 (2003). 26. I. Sava, I. A. Ronova and M. Bruma, Polym. J. 38, 940 (2006). 27. M. Bruma and T. Köpnick, Adv. Colloid. Interface Sci. 116, 277 (2005). 28. S. Mallakpour and M. Koladoozan, J. Appl. Polym. Sci. 104, 1248 (2007). 29. S. Mallakpour and M. Koladoozan, Eur. Polym. J. 43, 3444 (2007).
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