Microwave-assisted synthesis and characterization of optically active poly (ester-imide)s incorporating l-alanine

Article abstract of DOI:10.1007/s00726-009-0336-6

Pyromellitic dianhydride (1) was reacted with L-alanine (2) to result [N,N'-(pyromellitoyl)-bis-l-alanine diacid] (3). This compound (3) was converted to N,N'-(pyromellitoyl)-bis-l-alanine diacyl chloride (4) by reaction with thionyl chloride. The microwave-assisted polycondensation of this diacyl chloride (4) with polyethyleneglycol-diol (PEG-200) and/or three synthetic aromatic diols furnish a series of new PEIs and Co-PEIs in a laboratory microwave oven (Milestone). The resulting polymers and copolymers have inherent viscosities in the range of 0.31-0.53 dl g^-1. These polymers are optically active, thermally stable and soluble in polar aprotic solvents such as DMF, DMSO, NMP, DMAc, and sulfuric acid. All of the above polymers were fully characterized by IR spectroscopy, ¹H NMR spectroscopy, elemental analyses, specific rotation and thermal analyses. Some structural characterizations and physical properties of these optically active PEIs and Co-PEIs have been reported.

Full text of DOI:10.1007/s00726-009-0336-6

Amino Acids (2010) 38:1253–1260
DOI 10.1007/s00726-009-0336-6
ORIGINAL ARTICLE
Microwave-assisted synthesis and characterization of optically
active poly (ester-imide)s incorporating L-alanine
Saeed Zahmatkesh Æ Abdol R. Hajipour
Received: 26 November 2008 / Accepted: 28 July 2009 / Published online: 23 August 2009
Ó Springer-Verlag 2009
Abstract Pyromellitic dianhydride (1) was reacted with
L-alanine (2) to result [N,N0-(pyromellitoyl)-bis-L-alanine
diacid] (3). This compound (3) was converted to
N,N0-(pyromellitoyl)-bis-L-alanine diacyl chloride (4) by
reaction with thionyl chloride. The microwave-assisted
polycondensation of this diacyl chloride (4) with polyeth-
yleneglycol-diol (PEG-200) and/or three synthetic aro-
matic diols furnish a series of new PEIs and Co-PEIs in a
laboratory microwave oven (Milestone). The resulting
polymers and copolymers have inherent viscosities in the
range of 0.31–0.53 dl g-1. These polymers are optically
active, thermally stable and soluble in polar aprotic sol-
vents such as DMF, DMSO, NMP, DMAc, and sulfuric
acid. All of the above polymers were fully characterized by
Introduction
Due to the increasing demands for high-performance
polymers as a replacement for ceramics or metals in the
microelectronic, aerospace and automotive industries,
thermally stable polymers have received much interest over
the past decade. Polyimides and their copolymers are cer-
tainly one of the most useful classes of high-performance
polymers, which have found many applications in indus-
tries (Mittal 1984). Aromatic polyimides are an important
class of heterocyclic polymers with remarkable heat
resistance and superior mechanical and electrical proper-
ties, and also durability (Banihashemi and Abdolmaleki
2004). Poor thermoplastic fluidity and solubility are the
major problems in wide application of polyimides. This
makes it impossible for most polyimides to be directly
processed in their imidized forms; thus, their applications
have been restricted in some fields. Processable engineer-
ing plastics possessing moderately high softening temper-
atures and/or solubility in some organic solvents are
required for practical use. Therefore, various efforts have
been focused on the preparation of soluble and/or ther-
moplastic polyimides, while still maintaining the excellent
thermal and mechanical properties. Typical approaches
have been employed to improve the processability of these
polyimides including the incorporation of flexible links
(Tamai et al. 1996), bulky pendant or cardo groups (Hsiao
and Li 1998), kinked or unsymmetrical structures (Li et al.
1999), and spiro-skeletons (Reddy et al. 2003) into the
polymer chain. These modifications lower the melting
temperature and lead to soluble and amorphous polymers.
In general, amorphous polymers have a lower softening
temperature (Tg) and improved solubility with respect to
their crystalline analogs. Some of the block copolymers
composed of polyethers and polyamides have already been
1
IR spectroscopy, H NMR spectroscopy, elemental analy-
ses, specific rotation and thermal analyses. Some structural
characterizations and physical properties of these optically
active PEIs and Co-PEIs have been reported.
Keywords Optically active ꢀ Poly (ester-imide) ꢀ
Microwave-assisted ꢀ Pyromellitic dianhydride
S. Zahmatkesh (&)
Department of Science, Payame Noor University (PNU),
Tehran, Iran
e-mail: zahmatkesh1355@yahoo.com
A. R. Hajipour
Department of Pharmacology, University of Wisconsin,
Medical School, 1300, University Avenue, Madison,
WI 53706-1532, USA
123

1254
S. Zahmatkesh, A. R. Hajipour
commercialized as thermoplastic elastomers (Legge et al.
1987). A number of synthetic routes for polyether–poly-
imide block copolymers have been known (Noshay and
McGrath 1977). Ether linkages inserted in the main chains
provide them with significantly lower energy of internal
rotation.
recrystallized from acetic anhydride. The other chemicals
(Merck) were used as received. Micro SYNTH oven
(Milestone) was used to perform reactions. 1H NMR
spectra were recorded on 300 MHz instrument, using
DMSO-d6 as solvent and tetramethylsilane as shift refer-
ence (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 vis-
cosities of polymers were measured by a standard proce-
dure using a KPG Cannon Fenske routine viscometer at
25°C using DMF as solvent. Melting points were measured
in open capillaries with a Qallenkamp instrument.
The synthesis and application of optically active poly-
mers are the newly considerable topics which have been
paid more attention recently (Hajipour et al. 2008). 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 applications are
construction of chiral media for asymmetric synthesis,
chiral stationary phases for resolution of enantiomers in
chromatographic techniques (Akelah and Sherrington
1981), chiral liquid crystals in ferroelectrics and nonlinear
optical devices (Wulff 1989). These synthetic polymers
based on optically pure aminoacids can induce crystallinity
with their ability to form higher ordered structures that
exhibit enhanced solubility characteristics. These proper-
ties have caused them to be good candidate for drug
delivery systems, biomimetic systems, biodegradable
macromolecules, biomaterials, and also as chiral purifica-
tion media (Mallakpour et al. 1998). So, more consider-
ations to improve different synthetic procedures of
optically active polymers exist. Recently, we have syn-
thesized optically active polymers by different methods
(Hajipour et al. 2005). Organic reactions assisted by
microwave irradiation have gained special attention. The
reactions are very fast and are completed within short times
(Hajipour et al. 2000). Recently, we have used microwave
irradiation to synthesis organic compounds as well as
macromolecules (Mallakpour et al. 1998).
Monomer synthesis
N,N0-Pyromelliticdiimido-di-L-alanine (3)
Into a 25 ml round-bottomed flask, 2.523 g (7.83 9 10-3
mol) of Pyromellitic dianhydride (1), 1.397 g (1.57 9
10-2 mol) of L-alanine (2), a mixture of acetic acid/pyri-
dine (10 ml, 3:2) and a stirring bar were placed. The
mixture was stirred at r.t. for 2 h and then refluxed for 15 h.
The solvents were removed under reduced pressure. 5 ml
of cold concentrated HCl was added. A white precipitate
was formed, filtered off, and washed with hot water. The
solid was dried to leave 2.593 g (92%) of diacid 3
(Scheme 1). m.p. (°C) [250. [a]2D5 = ?2.8 (0.050 g in
10 ml DMF). IR (KBr): 3,400–2,700, 1,765–1,570, 1,455,
1,380, 1,365, 1,280, 1,250, 1,170, 1,060, 1,015, 930, 850,
730, 630 cm-1. 1H NMR (300 MHz, DMSO-d6) d: 1.60 (d,
6H), 4.98 (q, 2H), 8.45 (s, 2H), 13.7 (s, 2H) ppm. MS
(m/z): 360, 345, 317, 316, 315 (100%), 288, 271, 244, 243,
199, 173, 172, 145, 135, 128, 75, 74, 45.
In this research, we report the synthesis and character-
ization of some PEIs and Co-PEIs by microwave-assisted
polycondensation method in a laboratory microwave oven.
These polymers showed good optical activity (?25.2 to
?60.3) and also because of the presence of benzophenone
moiety, the polymers containing it, can potentially be
photolabile (Guo et al. 2004). The photolabile polymers are
potentially able to be used as affinity columns for protein
purification (Guo et al. 2004).
Synthesis of N,N0-(pyromellitoyl)-bis-L-alanine diacyl
chloride (4)
The outstanding characteristics of these polymers
include thermal stability, good solubility, improved optical
activity and being photolabile. Here, we have also inves-
tigated the effect of catalyst, irradiation power, and time of
irradiation on optical activity and viscosity of polymers.
Into a 25-ml round-bottomed flask were placed 0.36 g
(1.0 9 10-3 mol) of diacid (3), 5 ml (an excess amount) of
thionyl chloride and two drops of DMF. The mixture was
refluxed for 2 h. Unreacted thionyl chloride was removed
under reduced pressure and the residue was washed with
n-hexane, to leave 0.38 g (96.0%) of white crystals
(Scheme 1). mp(dp): 150°C. [a]2D5 = ?3.2° (0.050 g in
10 ml DMF). IR (KBr): 3,450, 2,990, 1,805, 1,780, 1,720,
1,590, 1,465, 1,390, 1,380, 1,180, 1,170, 1,110, 1,080, 920,
905, 830, 730, 600 cm-1. Elemental analysis: Calculated
Materials and methods
Pyromellitic dianhydride (Merck) and 3,30,4,40-benzophe-
nonetetracarboxylic-3,30,4,40-dianhydride (Merck) were
123

Microwave-assisted synthesis and characterization
1255
O
Scheme 1 Preparation of
Diacid 3 and diacyl chloride 4
O
O
O
O
O
O
AcOH/Py(3:2)
N
N
O
OH
O
2
H2N
+
HO
OH
H3C
CH3
O
O
O
CH3
O
O
3
4
O
O
O
SOCl2
N
N
O
Cl
Cl
3
reflux/2h
H3C
CH3
O
for C16H10N2O6Cl2, C (48.38%), H (2.54%), N (7.05%);
found C (48.29%), H (2.58%), N (6.96%).
phenol, 10 ml of DMF and a stirring bar were placed. The
mixture was stirred at r.t. for 2 h and then refluxed for 10 h.
The solvents were removed under reduced pressure. A
yellow precipitate was formed, filtered off, and washed
thoroughly with hot water. The solid was dried to leave
3.70 g (94%) of diol (6) (Scheme 2). mp [ 300°C. IR
(KBr): 3,450, 1,780, 1,708, 1,660, 1,600, 1,518, 1,450,
Synthesis of N,N0-(pyromellitoyl)-bis-p-aminophenol (5)
Into a 25 ml round-bottomed flask, 2.523 g (7.83 9 10-3
mol) of Pyromellitic dianhydride (1), 1.711 g
(1.57 9 10-2 mol) of p-amino phenol, 10 ml of DMF and
a stirring bar were placed. The mixture was stirred at r.t. for
2 h and then refluxed for 10 h. The solvents were removed
under reduced pressure. A bright yellow precipitate was
formed, filtered off, and washed thoroughly with hot water.
The solid was dried to leave 2.974 g (95%) of diol (5)
(Scheme 2). mp [ 300°C. IR (KBr): 3,420, 1,710, 1,705,
1,560, 1,510, 1,490–1,410, 1,405, 1,260, 1,140, 995, 815,
720 cm-1. 1H NMR (300 MHz, DMSO-d6) d: 6.91 (d, 4H),
7.25 (d, 4H), 8.31 (s, 2H), 9.76 (s, 2H) ppm. Elemental
analysis: Calculated for C22H12N2O6, C (66.00%), H
(3.02%), N (7.00%); found C (65.9%), H (3.10%), N
(6.95%).
1
1,390, 1,250, 1,207, 1,120, 866, 824, 715 cm-1. H NMR
(300 MHz, DMSO-d6) d: 6.89 (d, 4H), 7.21 (d, 4H), 8.15
(br, 4H), 8.25 (s, 2H), 9.71 (s, 2H) ppm. Elemental anal-
ysis: Calculated for C29H16N2O7, C (69.05%), H (3.20%),
N (5.55%); found C (68.94%), H (3.26%), N (5.45%).
Synthesis of dihydroxy-[7a, 14c] dihydro-naphto[2,1-b]
naphtha[1’,2’: 4, 5] furo[3,2-d] furan (7)
Into a 50 ml round-bottomed flask, 3.20 g (0.02 mol) of
2,7-naphthalene diol, 15 ml (0.01 mol) of glyoxal (30%)
and 15 ml of AcOH were placed. To the stirring mixture
4 ml of H2SO4 (conc.) was added dropwise. It stirred for
24 h and then poured into water to precipitate. After re-
crystalization from EtOH and drying at 70°C, 2.55 g (74%)
of white diol (7) was left (Scheme 2). mp = 301°C. IR
(KBr): 3,500–3,200, 1,640, 1,530, 1,460, 1,370, 1,210,
Synthesis of N,N0-(3,30,4,40-benzophenonetetracarboxylic)-
3,30,4,40-diimido-bis-p-aminophenol (6)
Into a 25 ml round-bottomed flask, 2.521 g (7.83 9 10-3
mol) of 3,30,4,40-benzophenonetetracarboxylic-3,30,4,40-
dianhydride, 1.711 g (1.57 9 10-2 mol) of p-amino
1,070, 830 cm-1. H NMR (250 MHz, DMSO-d6) d: 9.82
1
(s, 2H), 6.98–7.77 (m, 8H), 5.58–5.60 (d, 2H), 3.55 (s, 2H)
ppm. 13C NMR (250 MHz, DMSO-d6) d: 156.6, 156.5,
O
O
O
O
O
O
Scheme 2 Preparation of diols
DMF
O
O
HO
+ 2 H2N
OH
N
N
OH
reflux
O
O
O
O
5
O
O
O
O
O
O
DMF
reflux
O
O
+ 2
H2N
OH
HO
N
N
OH
O
O
HO
6
OH
OH
HO
2
H2SO4
AcOH
+
CHOCHO
O
O
7
123

1256
S. Zahmatkesh, A. R. Hajipour
132.3, 131, 130.6, 124.8, 117.6, 116.3, 114.9, 108.8, 106.3,
48.8 ppm.
PEI3: White-gray; Yield (%) = 78; g9inh (dl g-1) =
0.53; [a]2D5 = ?60.3; IR (KBr): 3,380, 1,785–1,705, 1,630,
1,565, 1,450, 1,380, 1,205, 1,160, 1,055, 955, 920, 825,
1
Synthesis of polymers
720 cm-1. H NMR (300 MHz, DMSO-d6) d: 1.70 (br,
6H), 5.45 (br, 3H), 5.75 (br, 1H), 6.95 (br, 2H), 7.30 (br,
The PEIs (1, 2, and 3) were prepared by microwave-
assisted polycondensation using the following general
procedure:
2H), 7.65 (br, 2H), 7.95 (br, 4H), 8.32 (br, 2H) ppm. Ele-
mental analysis: calculated for (C38H22N2O10)n
C
(68.48%), H (3.30%), N (4.20%); Found C (68.41%), H
(3.36%), N (4.18%).
General procedure for polymerization of PEI1: Into a
porcelain dish, a mixture of diacid chloride (4) (0.397 g,
1.0 mmol) and DABCO (0.222 g, 2.0 mmol) as a catalyst
was placed. After grounding the reagents for 5 min, diol 5
(0.400 g, 1.0 mmol) was added and the mixture was ground
for further 5 min. 0.25 ml of O-cresol as a solvent was
added, and the mixture was ground for 5 min. The reaction
mixture was irradiated in a laboratory microwave oven
(Micro SYNTH, Milestone) for 20 min (600 W, Interval:
10 s/min). The resulting homogenous glassy compound film
was isolated by adding methanol/H2O (80:20) and triturat-
ing, followed by filtration. It was washed several times with
methanol and vacuum dried. White-gray; Yield (%) = 85;
g9inh (dl g-1) = 0.35; [a]2D5 = ?31.5; IR (KBr): 3,380,
1,800–1,700, 1,600, 1,510, 1,455, 1,395–1,360, 1,250,
1,205, 1,175, 1,140, 1,100, 1,095, 1,050, 910, 850, 810,
720 cm-1. Elemental analysis: calculated for C38H20N4O12,
C (62.81%), H (3.05%), N (7.71%); Found, C (62.69%), H
(3.18%), N (7.63%).
Synthesis of copolymers
The Co-PEIs (4, 5, and 6) were prepared by microwave-
assisted polycondensation using the following general
procedure:
General procedure for polymerization of Co-PEI4: Into a
porcelain dish, a mixture of diacid chloride (4) (0.397 g,
1.0 mmol) and DABCO (0.222 g, 2.0 mmol) as a catalyst
was placed. After grounding the reagents for 5 min, poly-
ethyleneglycol-diol (PEG-200) (0.100 g, 5 9 10-4 mol)
was added and the mixture was ground for further 5 min.
0.25 ml of O-cresol as a solvent was added, and the mixture
was ground for 5 min. The reaction mixture was irradiated
in a laboratory microwave oven (Micro SYNTH, Mile-
stone) for 5 min (600 W, Interval: 10 s/min). Diol 5
(0.200 g, 5 9 10-4 mol) and 0.25 ml of O-cresol was
added and the mixture was ground for further 5 min. The
reaction mixture was irradiated in a laboratory microwave
oven (Micro SYNTH, Milestone) for 20 min (600 W,
Interval: 10 s/min). The resulting homogenous glassy
compound film was isolated by adding methanol/H2O
(80:20) and triturating, followed by filtration. It was washed
several times with methanol and vacuum dried. Gray; Yield
(%) = 81; g9inh (dl g-1) = 0.39; [a]2D5 = ?38.4; IR (KBr):
3,380, 1,780–1,750, 1,715, 1,650, 1,600, 1,580, 1,510,
The other PEIs (2, 3) were prepared by the same pro-
cedure using the appropriate diols (Scheme 3).
PEI2: Gray; Yield (%) = 80; g9inh (dl g-1) = 0.45;
[a]2D5 = ?45.2; IR (KBr): 3,385, 1,780, 1,720, 1,705,
1,650, 1,565, 1,510, 1,430, 1,375, 1,240, 1,200, 1,150,
1,105, 820, 720 cm-1. Elemental analysis: calculated for
(C45H24N4O13)n C (65.22%), H (2.92%), N (6.76%); Found
C (65.10%), H (3.02%), N (6.93%).
Scheme 3 preparation of
polymers (PEI1–3)
O
O
O
O
DABCO/O-cresol
N
N
O
Cl
HO Ar
OH
+
Cl
MW (20 min/ 600 W)
H3C
CH3
O
4
O
O
O
O
Ar
N
N
O
*
O
*
O
H3C
CH3
O
PEI1,PEI2, PEI3
O
O
O
N
O
O
O
Ar:
N
N
N
O
O
O
O
O
123

Microwave-assisted synthesis and characterization
1257
1,455, 1,400–1,380, 1,240–1,210, 1,160, 1,110, 1,095, 870,
850, 805, 715 cm-1. Elemental analysis: calculated for
C62H46N6O23, C (59.90%), H (3.73%), N (6.76%); Found,
C (59.96%), H (3.64%), N (6.87%).
IR spectrum of this diacid shows the characteristic
absorptions at around 3,400–2,250 cm-1, peculiar to car-
boxylic acid groups, two peaks at around 1,765 and
1,700 cm-1, peculiar to carbonyl stretching of imide
and acid moieties, and exhibits strong absorptions at 1,380
and 730 cm-1, that indicates the presence of the cyclic
The other Co-PEIs (5, 6) were prepared by the same
procedure using the appropriate diols (Scheme 4).
Co-PEI5: Gray; Yield (%) = 76; g9inh (dl g-1) = 0.31;
[a]2D5 = ?25.2; IR (KBr): 3,385, 1,785–1,745, 1,715,
1,655, 1,595, 1,570, 1,505, 1,450, 1,390, 1,240–1,205,
1,150, 1,105, 1,075, 880, 845, 800, 720 cm-1. Elemental
analysis: calculated for (C69H50N6O24)n C (61.51%), H
(3.73%), N (6.25%); Found C (61.72%), H (3.60%), N
(6.40%).
1
imide group. H NMR of diimide-diacid 1 is presented in
Fig. 1. The corresponding peaks included acidic groups at
1
around 13.7 ppm have been detected by H NMR. Mass
spectra showed the appropriate molecular ion peaks and/or
fragments. The chlorination was completed after 2 h, when
the mixture was completely dissolved in refluxing thionyl
chloride.
Co-PEI6: Pale green; Yield (%) = 80; g9inh
(dl g-1) = 0.48; [a]2D5 = ?50.2; IR (KBr): 3,380, 1,780–
1,735, 1,720, 1,650, 1,580, 1,560, 1,460, 1,395, 1,215–1,205,
1,150, 1,100, 870, 840, 805, 720 cm-1. Elemental analysis:
calculated for (C62H48N4O21)n C (62.83%), H (4.08%), N
(4.73%); Found C(63.15%), H(3.88%), N(4.88%).
DMF plays a catalytic role in this reaction. The char-
acteristic peak at around 1,805 cm-1 is due to the acyl
chloride carbonyl group. The acyl chloride will decompose
on heating at 150°C, so its mass spectrum did not show the
molecular ion peak by EI technique.
This monomer is the source of chirality in the corre-
sponding polymers. Diol 7 was prepared as mentioned in
the experimental part (Fig. 2).
Results and discussion
The dark purple solids turned to white needle crystals
after recrystallization from EtOH (Scheme 2). In the
preparation of diols 5 and 6 after stirring at r.t. for 2 h, the
corresponding amic acids formed which turned to the cor-
responding imide rings after 10 h reflux. These diols were
yellow powders, which showed high melting points, low
solubility, and very low vapor pressure so that we could not
run their mass spectra by EI technique.
We synthesized the diimide-diacid [N,N0-Pyromellitic-
diimido-di-L-alanine (3)] by the condensation reaction of
dianhydride (1) with L-alanine (2) in 1:2 molar ratio in
refluxing acetic acid/pyridine (3:2). Washing the residue
with cold water yields a gummy layer which breaks by
adding concentrated HCl into a white solid (Scheme 1).
O
O
Scheme 4 Preparation of
copolymers (Co-PEI4–6)
O
O
DABCO / O-cresol
MW (5 min/ 600 W)
N
N
OH
HO
1
+
2
Cl
Cl
R
CH3
CH3
O
O
R: CH2CH2OCH2CH2OCH2CH2OCH2CH2
O
O
O
O
O
O
O
H3C
O
O
Cl
O
N
N
O
N
N
O
1
Cl
O
CH3
O
O
O
CH3
CH3
A
DABCO / O-cresol
HOArOH
O
1
*
A
+ 1
MW (20 min/ 600 W)
O
O
O
O
O
O
O
Ar
N
N
N
N
R
O
O
O
*
O
n
CH3
CH3
CH3
O
CH3
O
O
O
Co-PEI4, Co-PEI5, Co-PEI6
123

1258
S. Zahmatkesh, A. R. Hajipour
Fig. 1 1H NMR spectrum of diacid (3)
Fig. 3 1H NMR spectrum of diol 6
an example, the IR of Co-PEI6 showed the C=O asym-
metric stretching of imide group at 1,780 cm-1, the C=O
symmetric stretching of imide and ester groups at
1,725 cm-1, C–N stretching at 1,380 cm-1, C–O–C
stretching at 1,280–1,030 cm-1. All of these PEIs and Co-
PEIs exhibited strong absorption at 1,380 and 720 cm-1
,
which shows the presence of the heterocyclic imide groups.
As an example, the 1H NMR spectrum of PEI3 is presented
which shows peaks that confirmed its chemical structure
(Fig. 4). The elemental analyses results are also in good
agreement with calculated/expected percentages of carbon,
hydrogen and nitrogen contents in the polymer-repeating
units. The colors of these polymers range from white–grey
to grey. Transparent, flexile and tough films could be
obtained from these polymers by casting from solution of
polymers in DMF, which shows good mechanical strength
of the films and consequently high molecular weight.
One of the major objectives of this work is to study the
solubility and the flexibility of these polymers by incor-
porating the soft segment in the polymer backbone. Their
solubility was tested qualitatively in various solvents and
the results are summarized in Table 2. Having soft
Fig. 2 IR spectrum of diol 7
In IR spectra, the characteristic peaks at around
1
3,400 cm-1 and in H NMR, the peaks at around 9.7 ppm
show the phenolic (OH) groups. These diols are good can-
didates to improve the thermal stability of the corresponding
polymers. Figure 3 shows 1H NMR spectrum of diol 6.
The resulting homogenous glassy compound films were
isolated by adding methanol/H2O (80:20) and triturating,
followed by filtration. It was washed several times with
methanol and vacuum dried. To optimize the polymeriza-
tion conditions, we did six experiments on PEI1. The
optimum condition is as follows: Power = 600 W;
Time = 20 min with interval times of 10 s/min of running.
It is found that at higher power, the lower viscosity and
lower specific rotation are obtained; which can be attrib-
uted to polymer degradation. At lower power, the higher
specific rotation but lower viscosity is obtained; the results
are shown in Table 1.
Table 1 Optimization of microwave-assisted polycondensation on
PEI1
Power
Time (min)
Interval
(10 s/min)
g9inh
[a]2D5
(dl g-1
)
800
800
600
600
400
300
10
10
10
20
20
20
-
?
?
?
?
?
0.17
0.22
0.30
0.35
0.29
0.20
?16.7
?20.6
?23.0
?31.5
?33.1
?35.7
All the polymers were obtained in quantitative yields
with moderate inherent viscosities (0.31–0.53 dl g-1) and
optical rotation. The formation of PEIs and Co-PEIs was
confirmed by IR spectroscopy and elemental analysis. As
123

Microwave-assisted synthesis and characterization
1259
Table 3 Thermal behavior of PEIs and Co-PEIs
Polymer
Decomposition
temperature (°C)
Ta5%
Decomposition
temperature (°C)
Tb10%
Char
yield
(%)c
Tg
(°C)d
PEI1
400
395
380
355
370
375
430
415
390
365
380
385
0.2
2.0
0.4
0.0
0.0
0.0
-
PEI2
-
PEI3
-
Co-PEI4
Co-PEI5
Co-PEI6
a
170
190
180
Temperature at which 5% weight loss was recorded by TGA at a
heating rate of 10°C/min under air atmosphere
b
Temperature at which 10% weight loss was recorded by TGA at a
heating rate of 10°C/min under air atmosphere
Fig. 4 1H NMR spectrum of PEI3
c
Percentage weight of material left after TGA analysis at maximum
temperature 600°C under air atmosphere
d
Table 2 Solubility of PEIs and Co-PEIs
Glass transition temperature
Solvents PEI1 PEI2 PEI3 Co-PEI4 Co-PEI5 Co-PEI6
NMP
?
?
?
?
??
??
??
??
??
-
??
??
??
??
??
-
??
??
??
??
??
-
??
??
??
??
??
-
DMSO
DMAc
DMF
?
?
?
?
H2SO4
CH2Cl2
CHCl3
EtOH
MeOH
H2O
??
-
??
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Concentration: 5 mg ml-1; ??, soluble at room temperature; ?,
soluble upon heating; -, insoluble
segments in the polymer backbone will increase the solu-
bility, so here Co-PEIs showed very good solubility; all of
them are soluble in polar aprotic solvents such as DMF,
DMAc, DMSO, NMP and also H2SO4 at room tempera-
ture. They are insoluble in solvents, such as chloroform,
methylene chloride, methanol, ethanol and water. These
polymers showed good optical activity (?25.2 to ?60.3)
and also because of the presence of benzophenone moiety,
the polymers containing it, can potentially be photolabile.
In compare to PEIs, Co-PEIs showed higher viscosities
and better solubility. The thermal properties of these
polymers were evaluated by means of TGA/DTG (under air
atmosphere) and DSC (under nitrogen atmosphere). These
polymers show similar decomposition behavior. They
showed two different decomposition maxima. Table 3
summarizes the thermal properties of them. These poly-
mers exhibited good resistance to thermal decomposition.
(5% weight loss: 355–400°C and 10% weight loss: 365–
430°C). Tg values of Co-PEIs are from 170–190°C. TGA/
DTG thermogram of PEI1 is represented in Fig. 5.
Fig. 5 TGA/DTG thermogram of PEI1 under air atmosphere
TGA and DSC thermograms of Co-PEI4 are represented
in Fig. 6. DSC thermogram of PEI1 did not show a clear
Tg, but expectedly that of Co-PEI4, since soft segment in
the polymer backbone which cause an increase in phase
separation along with decreasing thermooxidative stability
have shown a Tg value of about 170°C.
Conclusions
A series of optically active PEIs and Co-PEIs, having
inherent viscosities of 0.31–0.53 dl g-1 were synthesized
for the first time by microwave-assisted polycondensation
123

1260
S. Zahmatkesh, A. R. Hajipour
Fig. 6 TGA/DTG and DSC
thermograms of Co-PEI4
of optically active N,N0-Pyromelliticdiimido-di-L-alanine
(3) as a diacid having a preformed imide rings as an
‘‘enlarged’’ monomer containing two chiral L-alanine
groups with polyethyleneglycol-diol (PEG-200) and/or
three synthetic aromatic diols. These polymers showed
optical activity (?25.2 to ?60.3) and also because of the
presence of benzophenone moiety, the polymers containing
it, can potentially be photolabile. Co-PEIs showed better
solubility than PEIs. These polymers showed good thermal
stability.
corresponding carbonyl compounds under microwave irradia-
tion. Synlett 5:740–742
Hajipour AR, Zahmatkesh S, Zarei A, Khazdooz L, Ruoho AE (2005)
Synthesis and characterization of novel optically active poly
(amide-imide)s via direct amidation. Eur Polym J 41:2290–2296
Hajipour AR, Zahmatkesh S, Parniyan Roosta, Ruoho AE (2009)
Synthesis and characterization of new optically active poly
(azo-ester-imide)s via interfacial polycondensation. Amino acids
36(3):511–518
Hsiao SH, Li CT (1998) Synthesis and characterization of new
adamantane-based polyimides. Macromolecules 31(21):7213–
7217
Legge NR, Holden G, Schroeder HE (1987) Thermoplastic elasto-
mers. Hanser, New York
Acknowledgments We gratefully acknowledge the funding support
received for this project from the Payame Noor University (PNU), IR
Iran and Grant GM 33138 (AER) from the National Institutes of
Health, USA. Further financial support from Center of Excellency in
Chemistry Research (IUT) is gratefully acknowledged.
Li F, Ge JJ, Honigfort PS, Fang S, Chen JC, Harris FW et al (1999)
Dianhydride architectural effects on the relaxation behaviors and
thermal and optical properties of organo-soluble aromatic
polyimide films. Polymer 40:4987–5002
Mallakpour SE, Hajipour AR, Khoee S, Sheikholeslami B (1998) A
new method for producing optically active polybutadiene. Polym
Int 47:193–197
Mittal KL (1984) Polyimides: synthesis, characterization and appli-
cation. Plenum, New York
References
Noshay A, McGrath IE (1977) Block copolymers. Academic Press,
New York
Akelah A, Sherrington DC (1981) Application of functionalized
polymers in organic synthesis. Chem Rev 81:557–587
Banihashemi A, Abdolmaleki A (2004) Novel aromatic polyimides
derived from benzofuro[2, 3-b]benzofuran-2, 3, 8, 9-tetracarb-
oxylic dianhydride (BBTDA). European Polymer Journal
40:1629–1635
Guo LW, Hajipour AR, Gavala ML, Grant JE, Ruoho AE (2004)
FASEB J 18:A587
Hajipour AR, Mallakpour SE, Khoee S (2000) An efficient, fast and
selective oxidation of aliphatic and benzylic alcohols to the
Reddy DS, Chou CH, Hsu CF, Lee GH (2003) Synthesis and
characterization of soluble poly(ether imide)s based on 2, 20-
bis(4-aminophenoxy)-9, 90-spirobifluorene. Polymer 44:557–563
Tamai S, Yamaguchi A, Ohta M (1996) Melt processible polyimides
and their chemical structures. Polymer 37:3683–3692
Wulff G (1989) Main-chain chirality and optical activity in polymers
consisting of CC chains. Angew Chem Int Engl Ed 28:21–37
123