Ionic liquid catalyzed synthesis and characterization of heterocyclic and optically active poly (amide-imide)s incorporating l-amino acids

Article abstract of DOI:10.1007/s00726-010-0667-3

N,N′-Pyromelliticdiimido-di-l-alanine (1), N,N′- Pyromelliticdiimido-di-l-phenylalanine (2), and N,N′-Pyromelliticdiimido- di-l-leucine (3) were prepared from the reaction of Pyromellitic dianhydride with corresponding l-amino acids in a mixture of glacia

Full text of DOI:10.1007/s00726-010-0667-3

Amino Acids (2011) 40:533–542
DOI 10.1007/s00726-010-0667-3
ORIGINAL ARTICLE
Ionic liquid catalyzed synthesis and characterization
of heterocyclic and optically active poly (amide-imide)s
incorporating L-amino acids
Saeed Zahmatkesh
Received: 16 May 2010 / Accepted: 16 June 2010 / Published online: 7 July 2010
Ó Springer-Verlag 2010
Abstract N,N0-Pyromelliticdiimido-di-L-alanine (1), N,
N0-Pyromelliticdiimido-di-L-phenylalanine (2), and N,N0-
Pyromelliticdiimido-di-L-leucine (3) were prepared from
the reaction of Pyromellitic dianhydride with correspond-
ing L-amino acids in a mixture of glacial acetic acid and
pyridine solution (3/2 ratio) under refluxing conditions. A
series of poly (amide-imide)s containing L-amino acids
were prepared from the synthesized dicarboxylic acids with
two synthetic aromatic diamines in an ionic liquid (IL) as a
green, safe and eco-friendly medium and also reactions
catalysis agent. Evaluation of data shows that IL is the
better polyamidation medium than the reported method and
the catalysis stand on the higher inherent viscosities of the
obtained PAIs and the rate of polymerizations beyond the
greener reaction conditions and deletion of some essential
reagents in conventional manners. Characterization were
Introduction
The synthesis and application of optically active polymers
are the newly considerable topics, which have been paid
more attention recently (Zahmatkesh and Hajipour 2009).
Most of the natural polymers are optically active and have
special chemical activities, such as catalytic properties that
exist in genes, proteins, and enzymes. Some other appli-
cations are construction of chiral media for asymmetric
synthesis, chiral stationary phases for resolution of enan-
tiomers in chromatographic techniques (Akelah and
Sherrington 1981), chiral liquid crystals in ferroelectrics
and nonlinear optical devices (Wulff 1989). These syn-
thetic polymers based on optically pure aminoacids can
induce crystallinity with their ability to form higher
ordered structures that exhibit enhanced solubility charac-
teristics. These properties have caused them to be good
candidate for drug delivery systems, biomimetic systems,
biodegradable macromolecules, biomaterials, and also as
chiral purification media (Mallakpour et al. 1998). So,
more considerations to improve different synthetic proce-
dures of optically active polymers exist. Recently, we have
synthesized optically active polymers by different methods
(Zahmatkesh and Hajipour 2010).
1
performs by means of IR, MS and H NMR spectroscopy,
elemental analysis, specific rotation, thermogravimetric
analysis and differential scanning calorimetric techniques.
Molecular weights of the obtained polymers were evalu-
ated viscometrically, and the measured inherent viscosities
were in the range 0.43–0.85 dL/g. These polymers were
readily soluble in many organic solvents. These polymers
still kept good thermal stability with glass transition tem-
peratures in the range of 94–154°C, and the decomposition
temperature under the nitrogen atmosphere for 10%
weight-loss temperatures in excess of 308°C.
Polycondensation reactions to prepare polyamides are
traditionally performed in aprotic polar high-boiling-point
organic solvents such as N-methyl-2-pyrrolidone (NMP)
(Caouthat et al. 2007), N,N-dimethyacetamide (DMAc)
(Zulfiqar et al. 2008), N,N-dimethyformamide (DMF)
(Mallakpour and Yousefian 2008), which are generally
cause several ecological disadvantages and over cost on
synthetic methods. In this regard, replacing or removing
hazardous materials is one of the recent environmental
issues (Talawar et al. 2009). Recently, ionic liquids (ILs)
have been of interest in many fields of chemistry because
Keywords Biodegradable ꢀ Amino acid ꢀ
Green chemistry ꢀ Poly (amide-imide) ꢀ Ionic liquid
S. Zahmatkesh (&)
Department of Science, Payame Noor University (PNU),
Tehran, Iran
e-mail: zahmatkesh1355@yahoo.com
123

534
S. Zahmatkesh
1
1,280, 1,250, 1,170, 1,060, 1,015, 930, 850, 730, 630; H
of their exclusive properties such as solubility, nonvola-
tility, high reactivity, low flammability, and possibility of
recycling, etc. (Shi et al. 2007). Nonvolatile nature and
stability at high temperature make the ILs excellent can-
didates for the use as polycondensation reactions medium
(Shaplov et al. 2008). Furthermore, it has been shown that
ILs have catalytic effect on the polymerization progresses,
resulting the removal of some of the additives which
are essential in conventional polymerization methods
(Mallakpour and Kowsari 2006).
NMR d (ppm): 1.60 (d, 6H), 4.98 (q, 2H), 8.45 (s, 2H), 13.7
(s, 2H); MS (m/z): 360, 345, 317, 316, 315 (100%), 288,
271, 244, 243, 199, 173, 172, 145, 135, 128, 75, 74, 45.
Elemental analysis: calculated for C16H12N2O8: C (56.47%),
H (3.55%), N (8.23%); found C (56.39%), H (3.60%), N
(8.19%).
N,N0-Pyromelliticdiimido-di-L-phenylalanine (2)
In the present article, the synthesized dicarboxylic acids
containing L-amino acids (Hajipour et al. 2007) were directly
polycondensed with the two synthetic aromatic diamines
(Hajipour et al. 2007) in an ionic liquid medium to produce a
series of organosoluble poly (amide-imide)s. The properties
of these polymers, such as specific rotation, viscosity, solu-
bility, and thermal stability also discussed herein.
Cream; Yield (%) = 98; m.p. (°C) [250; [a]2D5 = -4.08;
IR (cm-1): 3,400–2,280, 1,775, 1,750–1,680, 1,495, 1,450,
1,380, 1,365, 1,275, 1,095, 940, 920, 870, 825, 730, 695;
1H NMR d (ppm): 3.30 (dd, 2H), 3.50 (dd, 2H), 5.20 (dd,
2H), 7.15 (s, 10H), 8.25 (s, 2H), 13.60 (s, 2H); MS (m/z):
364, 343, 318, 315, 149, 148 (100%), 103, 91, 77, 65, 51,
44. Elemental analysis: calculated for C28H20N2O8: C
(65.62%), H (3.93%), N (5.47%); found C (65.55%), H
(4.02%), N (5.38%).
Materials and methods
N,N0-Pyromelliticdiimido-di-L-leucine (3)
Pyromellitic dianhydride (Merck) was recrystallised from
acetic anhydride. Triphenyl phosphite (TPP) was purified
by distillation under reduced pressure. The other chemicals
(Merck) were used as received. 1H NMR spectra were
recorded on 300 MHz instrument, using DMSO-d6 as
solvent and tetramethylsilane as shift reference (tube
diameter, 5 mm). IR spectra were recorded on a Shimadzu
IR-435 instrument, using KBr pellets. Mass spectra were
recorded on a Fisons (UK) mass spectrometer Model
Trio 1000. Specific rotations were measured by a JASCO
P-1030 Polarimeter. Thermogravimetric analyses (TGA)
were recorded on a Mettler TGA-50 with heating rate of
10°C min-1 under air atmosphere. Differential scanning
calorimetry (DSC) analyses were recorded on a Mettler
DSC-30 under nitrogen atmosphere. Inherent viscosities of
polymer solution (0.5% w/v) in DMF were determined at
25°C by a standard procedure using a Cannon-Fenske
Routine viscometer (Cannon, Mainz, Germany). Melting
points were measured in open capillaries with a Qallenkamp
instrument.
White; Yield (%) = 98; m.p. (°C) = 235–237(d); [a]D25
=
?6.08; IR (cm-1): 3,200, 2,920, 1,765, 1,700, 1,555, 1,480,
1,385, 1,235, 1,180, 1,145, 1,080, 925, 855, 810, 725, 620;
1H NMR d (ppm): 1.00 (d, 12H), 1.50 (m, 2H), 1.90 (ddd,
2H), 2.20 (ddd, 2H), 4.88 (dd, 2H), 8.50 (s, 2H), 13.20 (s,
2H); MS (m/z): 447, 444, 402, 401, 399, 383, 371, 370,
257, 344, 343, 331, 315, 313, 287, 269, 255, 243, 229, 225,
199, 128, 114, 99, 75, 69, 53, 44, 43 (100%). Elemental
analysis: calculated for C22H24N2O8: C (59.45%), H
(5.44%), N (6.30%); found C (59.33%), H (5.52%), N
(6.21%).
N-Phthalicimido-L-phenylalanine (4)
White; Yield (%) = 98; m.p. (°C) = 232; [a]2D5 = ?0.5;
IR (cm-1): 3,450–2,600, 1,765–1,705, 1,505, 1,425, 1,380,
1
1,275, 1,102, 945, 865, 725; H NMR d (ppm): 3.40 (dd,
1H), 3.50 (dd, 1H), 5.15 (dd, 1H), 7.20 (s, 5H), 7.85 (s,
4H), 13.40 (s, 1H); MS (m/z): 295 (Mꢀ?), 251, 249, 232,
149, 148 (100%), 147, 131, 130, 117, 105, 104, 92, 91, 89,
77, 76, 65, 51.
Monomer synthesis
Diacid synthesis (Hajipour et al. 2007)
Diamine synthesis (Hajipour et al. 2007)
The acidic compounds (1–4) were prepared by the reported
procedure.
Compounds (5, 6) were prepared by the reported
procedure.
N,N0-Pyromelliticdiimido-di-L-alanine (1)
4-Phenyl-2,6-bis(4-nitrophenyl) pyridine
Yield (%) = 92; m.p. (°C) [250; [a]2D5 = ?2.76; IR
Yield (%) = 60; m.p. (°C)[250; IR (cm-1): 1,585, 1,543,
1,510, 1,375, 1,345, 1,090, 845, 815, 750, 740; H NMR d
1
(cm-1): 3,400–2,700, 17,650–1,570, 1,455, 1,380, 1,365,
123

Synthesis and characterization of heterocyclic and optically active poly (amide-imide)s
535
Preparation of polymers
(ppm): 7.56–7.62 (m, 8H), 7.77–7.79 (s, 2H), 8.07 (dd,
2H), 8.37–8.44 (m, 3H); MS (m/z): 399, 398, 397(Mꢀ?,
100%), 351, 306, 305, 304, 302, 152, 151.
The polymers (PAI1–6) were prepared by the modified pro-
cedure which is mentioned in the section of model compound
preparation by using the mentioned starting materials.
4-(p-Methylthiophenyl)-2,6-bis(4-nitrophenyl) pyridine
Yellow; Yield (%) = 55; m.p. (°C) [250; IR (cm-1):
3,400, 1,590, 1,545, 1,510, 1,425, 1,375, 1,345, 1,095, 850,
PAI1 (using diacid 1 and diamine 5)
Light yellow; Yield (%) = 95; g0inh (dL g-1) = 0.56;
[a]2D5 = ?11.25; IR (cm-1): 3,390, 3,040, 2,900, 1,780,
1,715, 1,595, 1,520, 1,490, 1,450, 1,380, 1,360, 1,320,
1,245, 1,180, 1,125, 1,075, 1,015, 930, 830, 755, 725, 685;
1H NMR d (ppm): 1.70 (d, 6H), 5.05 (q, 2H), 7.30 (m, 1H),
7.50 (d, 2H), 7.70 (d, 4H), 8.00 (d, 2H), 8.10 (s, 2H), 8.25
(d, 4H), 8.35 (s, 2H), 10.3 (s, 2H); CHNS: Calculated for
(C39H27N5O6)n (661.669) C (70.79%), H (4.11%), N
(10.58%); found C (70.51%), H (4.25%), N (10.32%).
1
805, 750, 725, 680; H NMR d (ppm): 2.61 (s, 3H), 7.47
(d, 2H), 8.05 (d, 2H), 8.20 (s, 2H), 8.45 (d, 4H), 8.65
(d, 4H); MS (m/z): 445, 444, 443 (Mꢀ?, 100%), 415, 413,
397, 383, 367, 353, 352, 351, 337, 336, 335, 303, 302, 291,
252, 227, 207, 176, 167, 151, 145, 133, 117, 97, 73, 69, 57, 55.
4-Phenyl-2,6-bis(4-aminophenyl) pyridine (5)
Yield (%) = 92; m.p. (°C) = 155; IR (cm-1): 3,335,
3,200, 1,620, 1,580, 1,535, 1,505, 1,440, 1,385, 1,280,
1
PAI2 (using diacid 2 and diamine 5)
1,235, 1,175, 825, 750, 680; H NMR d (ppm): 7.00–8.20
(m, 15H), 3.99 (NH2, s, 4H); MS (m/z): 340, 338, 337
(Mꢀ?, 100%), 336, 322, 245, 169.
Light yellow; Yield (%) = 95; g0inh (dL g-1) = 0.73;
[a]2D5 = ?12.35; IR (cm-1): 3,380, 3,050, 2,900, 1,770,
1,725, 1,590, 1,535, 1,490, 1,450, 1,385, 1,350, 1,315,
4-(p-Methylthiophenyl)-2,6-bis(4-aminophenyl)
pyridine (6)
1
1,245, 1,180, 1,105, 945, 845, 760, 725, 695; H NMR d
(ppm): 3.65 (dd, 4H), 5.30 (dd, 2H), 7.20 (s, 11H), 7.55
(d, 2H), 7.75 (d, 4H), 8.03 (d, 2H), 8.15 (s, 2H), 8.28 (s,
2H), 8.35 (d, 4H), 10.20 (s, 2H); CHNS: Calculated for
(C51H35N5O6)n (813.865) C (75.26%), H (4.33%), N
(8.60%); Found C (74.87%), H (4.40%), N (8.57%).
Bright yellow; Yield (%) = 90; m.p. (°C) = 130–132; IR
(cm-1): 3,350, 3,280, 1,620, 1,580, 1,535, 1,510, 1,480,
1
1,430, 1,405, 1,375, 1,295, 1,235, 1,175, 1,090, 800; H
NMR d (ppm): 2.50 (s, 3H), 5.41 (s, 4H), 6.65 (d, 4H), 7.4
(d, 2H), 7.75 (s, 2H), 7.90 (d, 2H), 8.00 (d, 4H); MS (m/z):
386, 385, 383 (Mꢀ?, 100%). 368, 366, 336, 192, 117.
PAI3 (using diacid 3 and diamine 5)
Light yellow; Yield (%) = 95; g0inh (dL g-1) = 0.85;
[a]2D5 = ?15.80; IR (cm-1): 3,350, 3,005, 2,950, 1,765,
1,720, 1,590, 1,515, 1,490, 1,375, 1,350, 1,315, 1,245,
Preparation of model compound (7)
A mixture of N-phethalic imido-L-phenyl alanine (4)
(0.295 g, 1.0 mmol) and 4-(p-methylthiophenyl)-2,6-bis(4-
aminophenyl) pyridine (6) (1.914 g, 0.5 mmol) were dis-
solved in 0.33 g of [1-methyl-3-propyl imidzolium]Br,
then 0.33 mL (1.25 mmol) of triphenyl phosphite (TPP)
was added. The whole solution was heated at 110°C for
2.5 h. The solution becomes more viscous by progress of
the reaction. The resulting product was dissolved in 3 mL
of DMF and was poured into 30 mL of stirring methanol/
H2O, followed by filtration. It was washed several times
with methanol and vacuum dried. Yellow; Yield (%) = 95;
m.p. (°C) = 154; [a]D25 = ?5.65; IR (cm-1): 3,350, 1,735,
1,710, 1,600, 1,510, 1,485, 1,420, 1,375, 1,310, 1,240,
1,175, 1,080, 950, 815, 730; 1H NMR d (ppm): 2.55
(s, 3H), 3.40 (m, 2H), 3.65 (dd, 2H), 5.25 (dd, 2H), 7.20
(s, 10H), 7.4 (d, 2H), 7.75 (d, 4H), 7.82 (s, 8H), 8.00 (d,
2H), 8.13 (s, 2H), 8.30 (d, 4H), 10.2 (s, 2H). MS (m/z): 384,
383, 337, 234, 207, 149, 148, 126, 98, 94, 85, 69, 60, 57, 55
(100%).
1
1,175, 1,075, 945, 840, 755, 715, 690; H NMR d (ppm):
0.92 (d, 12H), 1.52 (br, 2H), 2.05 (br, 2H), 2.30 (br, 2H),
5.20 (dd, 2H), 7.40 (m, 1H), 7.55 (d, 2H), 7.75 (d, 4H),
8.05 (d, 2H), 8.12 (s, 2H), 8.30 (d, 4H), 8.40 (s, 2H), 10.2
(s, 2H); CHNS: calculated for (C45H39N5O6)n (745.831) C
(72.47%), H (5.27%), N (9.39%), S (8.20%); found C
(72.26%), H (5.32%), N (9.31%).
PAI4 (using diacid 1 and diamine 6)
Bright yellow; Yield (%) = 95; g0inh (dL g-1) = 0.43;
[a]2D5 = ?19.56; IR (cm-1): 3,380, 2,900, 1,770, 1,720,
1,595, 1,510, 1,492, 1,425, 1,380, 1,375, 1,312, 1,240,
1
1,178, 1,080, 1,005, 940, 812, 755, 725, 690; H NMR d
(ppm): 0.90 (d, 6H), 2.55 (s, 3H), 5.05 (m, 2H), 7.40
(d, 2H), 7.70 (d, 4H), 8.00 (d, 2H), 8.10 (s, 2H), 8.30 (d,
4H), 8.40 (s, 2H), 10.20 (s, 2H); CHNS: calculated for
(C40H29N5O6S)n (707.762) C (67.88%), H (4.13%), N
123

536
S. Zahmatkesh
Scheme 1 Preparation of
diacids (1–3)
O
O
O
O
O
HOAc/Py(3:2)
Reflux
HOOC
N
N
+ 2 L-Amino acid
COOH
O
O
R
R
O
O
O
R= CH3; PhCH2; (CH3)2CHCH2
1
2
3
Fig. 1 1H NMR of diacid 1
(9.89%), S (4.53%); found C (67.63%), H (4.21%), N
(9.78%), S (4.36%).
1,725, 1,655, 1,595, 1,510, 1,490, 1,450, 1,420, 1,380,
1,310, 1,235, 1,185, 1,095, 1,010, 940, 810, 745, 720,
1
685; H NMR d (ppm): 2.05 (s, 3H), 3.25–3.42 (m, 4H),
PAI5 (using diacid 2 and diamine 6)
5.3 (dd, 2H), 7.10–7.60 (m, 10H), 7.85 (d, 2H), 8.05
(d, 4H), 8.17 (s, 2H), 8.30 (s, 2H), 8.40 (d, 4H), 8.55
(s, 2H), 10.60 (s, 2H); CHNS: calculated for
(C52H37N5O6S)n (859.958) C (72.63%), H (4.34%), N
Bright yellow; Yield (%) = 95; g0inh (dL g-1) = 0.48;
[a]2D5 = ?20.54; IR (cm-1): 3,360, 3,005, 2,880, 1,766,
123

Synthesis and characterization of heterocyclic and optically active poly (amide-imide)s
537
O
C
(8.14%), S (3.73%); found C (72.55%), H (4.46%), N
(7.96%), S (3.68%).
NH4OAC
HOAC/T
+
CH3
ArCHO
2 O2N
O2N
N
NO2
N2H4.H2O Pd/C
DMF/EtOH/ reflux
PAI6 (using diacid 3 and diamine 6)
Bright yellow; Yield (%) = 95; g9inh (dL g-1) = 0.63;
[a]2D5 = ?21.43 IR (cm-1): 3,390, 3,008, 2,995, 1,770,
1,720, 1,595, 1,512, 1,475, 1,420, 1,375, 1,350, 1,315,
Ar
N
H2N
NH2
SMe
1
1,245, 1,175, 1,170, 1,050, 945, 815, 750, 715, 685; H
NMR d (ppm): 0.90–1.00 (d, 12H), 1.55 (br, 2H), 2.05 (br,
2H), 2.30 (br, 2H), 2.55 (s, 3H), 5.07 (br, 2H), 7.42 (d, 2H),
7.75 (d, 4H), 7.96 (s, 2H), 8.10 (d, 2H), 8.30 (d, 4H),
8.50 (s, 2H), 10.20 (s, 2H); CHNS: calculated for
(C46H41N5O6S)n (791.924) C (69.77%), H (5.22%), N
(8.84%), S (4.05%); found C (69.59%), H (5.34%), N
(8.75%), S (3.93%).
Ar
,
Ar:
5
6
Scheme 2 Preparation of diamines (5, 6)
Fig. 2 1H NMR spectrum of
diamine 6
Scheme 3 Preparation of
model compound 7
H2N
NH2
O
N
HOOC
TPP/IL
N
2
+
2.5 h, 110 oC
O
4
SMe
O
O
O
O
N
N
N
N
N
H
H
O
O
SMe
7
123

538
S. Zahmatkesh
Fig. 3 1H NMR of the model
compound (7)
Scheme 4 Ionic liquid
catalyzed synthesis of PAI1–6
O
O
O
O
N
COOH
HOOC
N
TPP/IL
H2N
N
NH2
+
R
2.5 h, 110 oC
R
Ar
O
O
O
N
O
O
O
*
N
N
N
N
*
H
H
n
R
R
Ar
PAI1-6
R: CH3; PhCH2; (CH3)2CHCH2 , Correspondingly
Ar: Ph; CH3SPh, Correspondingly
Results and discussion
Table 1 Optimization of the direct polycondensation in IL on PAI1
We synthesized the optically active diimide-diacid mono-
mers (1–3) from condensation of pyromellitic dianhydride
with the corresponding L-amino acids (1:2) in a refluxing
solution of acetic acid/pyridine (3:2) (Scheme 1). IR
spectra of these compounds showed the characteristic
absorptions at around 3,400–2,250 cm-1, peculiar to car-
boxylic acid groups, and two peaks at around 1,770 and
1,700 cm-1, peculiar to carbonyl stretching of imide and
acid moieties. All of these compounds exhibited strong
absorptions at 1,388 and 725 cm-1, which indicates the
presence of the cyclic imide group in these monomers. The
corresponding peaks included acidic groups at around
Temperature
TPP/monomer
g9inh (dL g-1
)
[a]2D5
100
110
120
100
110
120
100
110
120
2
0.31
0.35
0.35
0.37
0.56
0.60
0.34
0.39
0.39
?12.56
?12.11
?10.43
?12.43
?11.25
?6.53
2
2
2.5
2.5
2.5
3
?13.67
?11.02
?5.67
3
3
123

Synthesis and characterization of heterocyclic and optically active poly (amide-imide)s
539
Table 2 Comparison between IL catalyzed and the conventional reported (Hajipour et al. 2007) method
Polymer
IL catalyzed method
The conventional reported method
Viscosity
Specific
rotation
Reaction
time
Reaction
temperature
Viscosity
Specific
rotation
Reaction
time
Reaction
temperature
PAI1
PAI2
PAI3
PAI4
PAI5
PAI6
0.56
0.73
0.85
0.43
0.48
0.63
?11.25
?12.35
?15.80
?19.56
?20.54
?21.43
2.5 h
2.5 h
2.5 h
2.5 h
2.5 h
2.5 h
110°C
110°C
110°C
110°C
110°C
110°C
0.49
0.40
0.97
0.36
0.45
0.38
?3.84
?4.04
?6.88
?4.80
?4.60
?9.52
1 h then 3 h
1 h then 3 h
1 h then 3 h
1 h then 3 h
1 h then 3 h
1 h then 3 h
25°C then 1008C
25°C then 100°C
25°C then 100°C
25°C then 100°C
25°C then 100°C
25°C then 100°C
1
Fig. 4 a H NMR spectrum of
1
PAI3. b H NMR spectrum of
PAI6
1
1
Table 3 Solubility of PAI1–6
13.4 ppm have been detected by H NMR. H NMR of
diimide-diacid 1 is presented in Fig. 1. Mass spectra
showed the appropriate molecular ion peaks and/or
fragments.
Polymer
DMAc
DMF
NMP
DMSO
H2SO4
PAI1
PAI2
PAI3
PAI4
PAI5
PAI6
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
There are several methods for preparation of the pyri-
dine ring, but the Chichibabin method is one of the best
(Scheme 2). IR spectra of dinitro compounds showed
characteristic bands of nitro groups at around 1,345 and
1,540 cm-1. In addition C=C and C=N bands of phenyl
and pyridine rings at 1,590 cm-1 were presented. 1H NMR
? soluble at room temperature
123

540
S. Zahmatkesh
Model compound (7) was prepared via direct polycon-
densation in [1-methyl-3-propyl imidzolium]Br both as
solvent and catalyst outlined in Scheme 3. In addition to
provide a safe and green reaction medium, IL has also
catalytic effect on polymerization reaction because the
amidation did not progress in the absence of either IL or
TPP and the existence of both IL and TPP at the same time
was essential for the condensation. The IR spectrum of the
model compound (7) showed amide bands at 3,350 cm-1
(N–H stretching), 1,710 cm-1 (C=O stretching) and
1,600 cm-1 (combined N–H bending and C–N stretching).
In its 1H NMR spectrum an amidic proton was observed at
ca. 10.3 ppm (Fig. 3) and its elemental analysis data
(C58H43N5O6S)938.072 are given below:
Table 4 Thermal properties of PAI1–6
Polymer
T10% (°C)a
Tgb
Ch.Yc
PAI1
PAI2
PAI3
PAI4
PAI5
PAI6
a
350
345
340
320
340
308
125
154
98
5.9
0.0
19.0
4.7
94
128
112
14.8
6.0
Temperature of 10% weight loss, obtained from TGA
Glass transition temperature, obtained from DSC
Char yield percentage at 600°C, obtained from TGA
b
c
spectra showed the corresponding peaks which confirmed
the formation of pyridine rings. 1H NMR spectrum of
diamine 6 is shown in Fig. 2. Mass spectra showed the
appropriate molecular ion peaks and fragments. Hydrazine
monohydrate with the catalytic amount of palladium on
charcoal (10%) was used for reduction. IR spectra of dia-
mines (5, 6) showed characteristic bands of amino group at
ca. 3,350–3,200 cm-1 (N–H stretching) and 1,620 cm-1
Calculated C 74.26%, H 4.62%, N 7.4%, S 3.42%;
Found C 74.17%, H 4.72%, N 7.31%, S 3.31%.
Polymerization of diacids (1–3) with stoichiometric
amount of different aromatic diamines (5, 6) was carried
out in [1-methyl-3-propyl imidzolium]Br both as solvent
and catalyst outlined in Scheme 4. In addition to provide
a safe and green reaction medium, IL has also catalytic
effect on polymerization reaction because polyamidation
did not progress in the absence of either IL or TPP and
the existence of both IL and TPP at the same time was
essential for the polycondensation. In optimizing the
1
(N–H out-of-plane bending). H NMR spectra of diamines
(5, 6) showed NH2 protons at ca. (4.0 and 5.4 ppm).
Molecular ion peaks and fragment peaks were shown by MS.
Fig. 5 a TGA/DSC diagrams of PAI3. b TGA/DSC diagrams of PAI6
123

Synthesis and characterization of heterocyclic and optically active poly (amide-imide)s
541
polycondensation it is found that higher reaction temper-
ature cause higher viscosity and lower specific rotation
and more TPP/monomer ratio cause lower viscosity; the
results are shown in Table 1. A comparison between this
method and the conventional method (Hajipour et al.
2007) proves that the PAs prepared via direct polycon-
densation in IL encompass higher inherent viscosities and
specific rotations (Table 2). Furthermore, the use of IL
causes reduced overall cost of synthesis and cleaner
reaction. All polyamidations proceeded in a homogeneous
system throughout the reaction, and the polyamides were
isolated in quantitative yields. Inherent viscosities of the
polymers ranged from 0.43 to 0.85 dL/g, indicative of the
formation of high molecular weights. The structures of
these polyamides were confirmed by IR spectroscopy. The
Conclusions
Replacement of the toxic volatile organic solvents with
several ecological disadvantages by a green, safe and eco-
friendly reaction medium is the main aspect of this inves-
tigation. Therefore, direct polycondensations of diacids
(1–3) and two aromatic diamines (5, 6) have been inves-
tigated in IL medium, which acts as a green solvent and a
reaction catalyst. Comparison with the reported direct
method (Hajipour et al. 2007) indicates that IL in combi-
nation with TPP is the superior polyamidation agent. On
the other hand, in the case of IL catalyzed polyamidation,
removal of some chemicals such as NMP, CaCl2 and Py,
which are essential in conventional methodologies,
decreases the cost of polymerization as well as the envi-
ronmental pollutions, considerably. Here six heterocyclic
thermally stable and optically active PAIs with admirable
inherent viscosities (0.43–0.85) and optical activity
(?11.25–?21.43) were synthesized by phosphorylation
polycondensation in an IL media. The properties of these
polymers make them attractive for practical applica-
tions such as processable optically active polymeric
materials.
1
polymers (PAI1–6) were characterized by IR, H NMR,
and CHNS analyses. The presence of amidic bands at ca.
3,350 cm-1 (N–H stretching), 1,720 cm-1 (C=O stretch-
ing) and ca. 1,595 cm-1 (combined N–H bending and
C–N stretching) in the IR spectra and the amidic proton at
1
ca. 10.25 ppm in the H NMR spectra confirm the amidic
1
structure. H NMR spectra of PAI3 and PAI6 are shown
in Fig. 4.
The color of PAIs ranges from bright yellow to yellow.
The inherent viscosities of the polymers are in the range of
0.43–0.85 dL/g, indicating moderate to high molecular
weight. Transparent, flexile and tough films could be
obtained from these polymers by casting from solution of
polymers in DMF solvent, which shows good mechanical
strength of the films and consequently high molecular
weight. One of the major objectives of this work is to
improve the solubility. The solubility behavior of the new
aromatic polyamides was determined at concentration of 5%
(W/V) in a number of solvents. Table 3 shows that these
polymers are readily soluble in common polar aprotic sol-
vents. The other objective was to study the optical activity of
polymers from three different L-amino acids, which showed
that L-leucine is one of the best and cause maximum rotation
of the polarized light.
Acknowledgments We gratefully acknowledge the funding support
received for this project from Payame Noor University.
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