Synthesis and characterization of new optically active copoly(amid-imide)s based on N-phthalimido-l-aspartic acid and aromatic diamines

Article abstract of DOI:10.1016/j.cclet.2009.12.007

In this article, six new optically active copoly(amide-imide)s (10a-f) were synthesized through the direct polycondensation reaction of N-phthalimido-l-aspartic acid (4) with 1,5-diamino naphthalene (8), 3,4-diamino benzophenone (9) in the presence of therphthalic acid (7), fumaric acid (6) and adipic acid (5) as a second diacid in a medium consisting of N-methyl-2-pyrrolidone, triphenyl phosphite, calcium chloride and pyridine. The resulting copolymers were fully characterized by means of FT-IR spectroscopy, elemental analyses, inherent viscosity, solubility tests and UV-vis spectroscopy. Thermal properties of resulting copolymers (10a-c) containing three different second diacid in the main chain were compared by using TGA and DTG thermograms.

Full text of DOI:10.1016/j.cclet.2009.12.007

Available online at www.sciencedirect.com
Chinese Chemical Letters 21 (2010) 407–411
www.elsevier.com/locate/cclet
Synthesis and characterization of new optically active
copoly(amid-imide)s based on N-phthalimido-L-aspartic
acid and aromatic diamines
Khalil Faghihi a, , Hamidreza Alimohammadi
b
*
a Polymer Research Laboratory, Department of Chemistry, Faculty of Science, Islamic Azad University, Branch Arak, Iran
b Yaung Research Club, Islamic Azad University, Branch Arak, Iran
Received 19 August 2009
Abstract
Inthisarticle, sixnewopticallyactivecopoly(amide-imide)s(10a–f)weresynthesizedthroughthedirectpolycondensationreaction
of N-phthalimido-L-aspartic acid (4) with 1,5-diamino naphthalene (8), 3,4-diamino benzophenone (9) in the presence of therphthalic
acid (7), fumaric acid (6) and adipicacid (5) as a second diacid in a medium consistingof N-methyl-2-pyrrolidone, triphenyl phosphite,
calciumchlorideandpyridine.The resultingcopolymerswere fullycharacterizedbymeansofFT-IRspectroscopy, elementalanalyses,
inherent viscosity, solubility tests and UV–vis spectroscopy. Thermal properties of resulting copolymers (10a–c) containing three
different second diacid in the main chain were compared by using TGA and DTG thermograms.
# 2009 Khalil Faghihi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: High-performance polymers; Copoly(amide-imide)s; Direct polycondensation
Aromatic polyimides (PIs) are well known for their excellent thermal stabilities, electric insulation and chemical
resistance properties. However, their applications are limited because of their high softening or melting temperatures
and insoluble nature in the most organic solvents [1]. To overcome these drawbacks, PI structures are often modified.
One of this method is synthesis of copolymers such as poly(amide-imide)s and copoly(amide-imide)s to improve the
processing ability [2–5]. PAIs have the advantages of both PAs and PIs and possess thermal stability balanced with
processability. In this article six new copoly(amide-imide)s (10a–f) were synthesized through the direct
polycondensation reaction of N-phthalimido-L-aspartic acid (4) with 1,5-diamino naphthalene (8), 3,4-
diaminobenzophenone (9) in the presence of therphthalic acid (7), fumaric acid (6) and adipic acid (5) as a
second diacid in a medium consisting of N-methyl-2-pyrrolidone, triphenyl phosphite, calcium chloride and pyridine.
1. Experimental
1H NMR and 13C NMR spectra were recorded on a Bruker 300 MHz instrument (Germany). Fourier transform
infrared (FT-IR) spectra were recorded on Galaxy Series FT-IR 5000 spectrophotometer (England). Inherent
* Corresponding author.
E-mail address: k-faghihi@araku.ac.ir (K. Faghihi).
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.2009.12.007

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K. Faghihi, H. Alimohammadi / Chinese Chemical Letters 21 (2010) 407–411
viscosities were measured by using an Ostvald viscometer. Specific rotations were measured by an A-Kruss
polarimeter. Thermal Gravimetric Analysis (TGA and DTG) data were taken on a Mettler TA4000 System under N2
atmosphere at a rate of 10 8C/min. Elemental analyses were performed by Vario EL equipment. UV–vis absorptions
were recorded at 25 8C in the 200–800 nm with a PerkinElmer Lambda 15 spectrophotometer in DMF solution by
using cell lengths of 1 cm.
1.1. Synthesis of N-phthalimido-L-aspartic acid (4)
Into a 100 mL round-bottomed flask with a stirring bar were placed (2.22 g, 0.015 mol) of phthalic anhydride (1),
(1.995 g, 0.015 mol) of L-aspartic acid (2) and 25 mL of acetic acid. The mixture was stirred at room temperature
overnightandthenrefluxed4 h.Thesolventwasremovedunderreducedpressureandthen5.0 mLcoldwaterwasaddedto
theresidue. Awhiteprecipitatewasformedthenitwashedwithcoldwateranddriedunderreducedpressuretogive3.74 g
25
(94%) of compound (4). Mp: 227–230 8C, ½aꢀD þ 100 (c 0.6 DMF). FT-IR(KBr): 2500–3400 (m, br), 1778 (w), 1728 (s,
br), 1469 (w), 1423 (m, sh), 1392 (s), 1300 (m), 1197 (m), 1107 (w), 1085 (w), 1024 (w), 956 (w), 893 (m), 869 (w), 719
(m), 634 (m), 532 (w) cmꢁ1. 1H NMR (300 MHz, DMSO-d6): d 12.54 (s, br, 2H), 7.87–7.94 (m, 4H), 5.12–5.17 (t, 1H),
2.88–3.17 (m, 2H). 13C NMR (300 MHz, DMSO-d6): d 171.93, 170.38, 167.47, 135.38, 131.59, 123.91, 48.32, 34.24.
1.2. Copolymer synthesis
Into a 100 mL round-bottomed flask were placed a mixture of diacid (4) (0.002 mol), second diacid (5–7)
(0.002 mol), diamine (8–9) (0.004 mol), 0.60 g of calcium chloride, 1.0 mL of triphenyl phosphite, 1.0 mL of pyridine
and 4.0 mL NMP. The mixture was heated for 1 h at 60 8C, 2 h at 90 8C and then refluxed at 130 8C for 8 h until a
viscous solution was formed. Then it was cooled to room temperature and 30 mL of methanol was added to reaction
mixture. The precipitate was formed, filtered off and washed with methanol. The resulting polymers (10a–f) were
dried under vacuum.
2. Results and discussion
2.1. Monomer synthesis
N-Phthalimido-L-aspartic acid (4) was synthesized by the condensation reaction of one equimolar of phthalic
anhydride (1) with one equimolar of L-aspartic acid (2) in an acetic acid solution (Scheme 1).
The chemical structure of diacid (4) was confirmed by FT-IR, 1H NMR and 13C NMR spectroscopy. In the FT-IR
spectrum of diacid (4) peaks appearing at 2500–3400 cmꢁ1 (acid O–H stretching), 1778 cmꢁ1 (C O asymmetric
imide stretching), 1728 cmꢁ1 (C O acid and symmetric imide stretching), 1392 and 719 cmꢁ1 (imide characteristic
ring vibration) confirmed the presence of imide ring and carboxylic groups in this compound. The 1H NMR spectrum
of diacid (4) was shown in Fig. 1. H(a) protons relevant to O–H carboxylic groups and peaks between 7.87 and 8.94
related to aromatic protons. Peaks in region 5.12–5.17 as a triplet which were assigned to the CH(c) proton as a chiral
center and peaks between 2.88–3.17 were assigned to aliphatic CH2(d) as the diastereotopic hydrogen’s.
Scheme 1. Synthetic routs of diacid (4).

K. Faghihi, H. Alimohammadi / Chinese Chemical Letters 21 (2010) 407–411
409
Fig. 1. 1H NMR of diacid (4).
Scheme 2. Synthetic route of copoly(amide-imide)s (10a–f).
The 13C NMR spectrum of diacid (4) showed 8 signals, including three carbons in carboxylic acids and imide rings
that appeared in region of 167.47–171.93 ppm, three carbons related to aromatic ring that appeared in region of
123.91–135.38 ppm and also two carbons relevant to chiral center and diastereotopic center that appeared in 48.32 and
1
34.24 ppm, respectively. Peaks in H NMR, 13C NMR spectra along with elemental analyses data confirmed the
proposal structure of compound (4).
Copolymer synthesis: Copoly(amide-imide)s (10a–f) were synthesized by the direct solution polycondensation
reaction of an equimolar mixture of diacid (4), an equimolar mixture of diacid (5–7) with two equimolars mixture of
aromatic diamines (8–9) by using triphenyl phosphate (TPP) and pyridine as condensing agents (Scheme 2). The
synthesis and some physical properties of these PAIs (10a–f) are given in Table 1. All of the copolymers were obtained
in moderate to good yields and had inherent viscosities between 0.21–0.72 dLgꢁ1
.
2.2. Polymer characterization
These polymers were confirmed as CoPAIs by using FT-IR spectroscopy and elemental analyses. The resulting
polymers had absorption band between 1776 and 1665 cmꢁ1 due to imide and amide carbonyl groups. Absorption
bands around 1384 cmꢁ1 and 719 cmꢁ1 demonstrated the presence of the imide heterocyclic absorption in these
polymers. Also absorption band of amide group appeared at 3338 cmꢁ1 (N–H stretching). The elemental analysis
values of the resulting polymers were in good agreement with the calculated values for the proposed structures. The

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K. Faghihi, H. Alimohammadi / Chinese Chemical Letters 21 (2010) 407–411
Table 1
Synthesis and some physical properties of copoly(amide-imide)s (10a–f).
hinh (dL/g)a
25
b
Copolymer
Diamine
Second diacid
Yield (%)
½aꢀD
10a
10b
10c
10d
10e
10f
8
8
8
9
9
9
5
6
7
5
6
7
78
94
86
92
88
91
0.72
0.29
0.27
0.25
0.21
0.23
+183.0
+91.0
+191.0
+116.0
+175.0
+166.0
a,bMeasured at a concentration of 0.5 g//dL in DMF at 25 8C.
Fig. 2. UV–vis spetra of resulting polymers (10a–f) and diacid (4).
UV–vis absorption spectra of CoPAI (10a–f) and monomer in DMF are shown in Fig. 2. Monomer (4) showed a strong
absorption band around 232–274 nm in DMF solution, which assigned to the p!p* transition of the carbonyl
chromospheres. Also UV–vis absorption spectra of CoPAI (10a–f) showed a bathochromic shift in compare to
monomer (4) at 320–370 nm. The bathochromic shift in UV–vis spectra show complete converting of diacid
functional groups in monomer to amide functional groups in resulting polymers. The specific rotations of these PAIs
were in the range of +91.0 to +183.0. These characteristics indicated that optically active PAIs (10a–f) are promising
materials for optical applications.
The solubility of resulting polymers (10a–f) was investigated with 0.01 g polymeric samples in 2 mL of a solvent.
All these PAIs were soluble in organic solvents such as N,N-dimethyl formamide (DMF), N,N-dimethyl acetamide
(DMAc), dimethyl sulfoxide (DMSO) and N-methyl-2-pyrolidone (NMP) at room temperature and were insoluble in
solvents such as ethanol, methanol, tetrahydrofurane (THF), acetone and water.
2.3. Thermal properties
The thermal properties of three samples of resulting polymers (10a–c) containing three different of second diacids
such as adipic, fumaric and terephthalic acid were investigated by using TGA and DTG in nitrogen atmosphere at a
rate of heating of 10 8C/min, and thermal data are summarized in Table 2. These polymers exhibited good resistance to
thermal decomposition, up to 260–400 8C in nitrogen, and began to decompose gradually above this temperature. T5
for these polymers ranged from 260 to 390 8C and T10 for them ranged from 350 to 400 8C, and residual weights at
600 8C ranged from 9.6 to 52% in nitrogen, respectively. According to the results, thermal stability of these polymers
related to the second diacid units in the main chain. Thermal stability of polymer (10b) with terephthalic acid was
higher than two other polymers, because this polymer has a rigid aromatic structure in the main chain. Also polymer
containing fumric acid (10c) has higher thermal stability in compare to polymer (10a) with adipic acid as second
diacid. Fig. 3 shows TGA curves of CoPAIs (10a), (10b) and (10c).

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Table 2
Thermal behavior of PAs 7a–f.
Polymer
T5 (8C)a
T10 (8C)b
Char yieldc (%)
10a
10b
10c
265–270
390–395
380–385
355–360
400–405
395–400
52.0
22.1
9.6
a,bTemperature at which 5% and 10% weight loss was recorded by TGA at heating rate of 10 8C/min in N2, respectively. cPercentages weight of
material left undecomposed after TGA analysis 600 8C.
Fig. 3. TGA thermograms of CoPAIs (10a–c).
3. Conclusion
In this work, six new optically active copoly(amide-imide)s (10a-f) were prepared. The presence of trimellitic
rings, therphthalic, fumaric and adipic acids moieties into the backbone increased solubility of these polymers in
common organic solvent in compare to aromatic polyimide. These properties could make these PAs attractive for
practical applications, such as processable high-performance engineering plastics.
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