Synthesis of novel nanostructured chiral poly(amide-imide)s containing dopamine and natural amino acids

Article abstract of DOI:10.1007/s12039-012-0351-0

Four new thermally stable and optically active poly(amide-imide)s (PAI)s with good inherent viscosities were synthesized from the direct polycondensation reaction of N,N^′-(pyromellitoyl)-bis-L-α-amino acids with 3,5-diamino-N-(3,4-dihydroxy-phe

Full text of DOI:10.1007/s12039-012-0351-0

c
J. Chem. Sci. Vol. 125, No. 1, January 2013, pp. 203–211. ꢀ Indian Academy of Sciences.
Synthesis of novel nanostructured chiral poly(amide-imide)s containing
dopamine and natural amino acids
SHADPOUR MALLAKPOURa,b,∗ and AMIN ZADEHNAZARIa
aOrganic Polymer Chemistry Research Laboratory, Department of Chemistry,
bNanotechnology and Advanced Materials Institute, Isfahan University of Technology,
Isfahan, 84156-83111, Islamic Republic of Iran
e-mail: mallak@cc.iut.ac.ir; mallakpour84@alumni.ufl.edu; mallak777@yahoo.com
MS received 8 January 2012; revised 16 March 2012; accepted 25 May 2012
Abstract. Four new thermally stable and optically active poly(amide-imide)s (PAI)s with good inherent vis-
cosities were synthesized from the direct polycondensation reaction of N,Nꢁ-(pyromellitoyl)-bis-L-α-amino
acids with 3,5-diamino-N-(3,4-dihydroxy-phen-ethyl)benzamide in a medium consisting of a molten salt, tetra-
butylammonium bromide, and triphenyl phosphite as the activator. The polymerization reactions produced a
series of novel PAIs containing dopamine segment in the side chain in high yield with inherent viscosities
between 0.33 and 0.49 dL/g. The obtained polymers were typically characterized by means of FT-IR, 1H NMR
spectroscopy, elemental analyses, powder X-ray diffraction, field emission scanning electron microscopy, inher-
ent viscosity, and solubility tests. Thermal properties and flame retardant behaviour of the PAIs were also inves-
tigated using thermal gravimetric analysis (TGA and DTG) and limiting oxygen index (LOI). Data obtained by
thermal analysis revealed that these polymers showed good thermal stability. Furthermore, high char yield in
TGA and good LOI values indicated that the obtained polymers were capable of exhibiting good flame retardant
properties.
Keywords. Thermally stable; green chemistry; optically active polymers; tetrabutylammonium bromide.
1. Introduction
In recent years, environmentally-friendly reaction
processes have been vigorously studied from the stand-
point of green chemistry. Most recently, ionic liquids
(IL)s have gained much attention as green reaction sol-
vents for organic synthesis.8,9 When an IL is used as a
reaction medium, the solute is solvated by ions, where
the reaction proceeds under quite different conditions as
compared to using water or common organic solvents.10
The solvent power of ILs can be tuned by designing
the structure of cations and anions and choosing appro-
priate combinations of them. For example, ILs con-
taining quaternary ammonium cation such as molten
tetrabutylammonium bromide (TBAB) salt is not only
used as reaction solvent, but also exhibit catalytic pro-
perties.11–14 This molten ionic salt has very high sol-
ubility in water and polar organic solvents. Utilization
of this property enables recovery and reuse of it, after
extracting the product. This can help to reduce the waste
of traditional solvents which are rarely reused. It was
also used as reaction medium in several step-growth
polymerization reactions.15–17
Polymers play an important role in the development
of materials for industrial applications such as bio-
chemical science and in the pharmaceutical industry
due to their exceptional properties.1 They are rela-
tively inexpensive, can be functionalized to achieve
required optical, electronic, or mechanical properties,
and have demonstrated compatibility with various pat-
terning methods. They can be ‘nanostructured’ since
they exhibit pertinent structural features down at the
nanometer length scale. Nanostructured polymers are
currently gaining world-wide interest, because of their
unique properties and promising potential applications
in many areas such as biosensors, integrated optics,
drug delivery systems, and molecular electronics.2–4
There are many ways to produce nanostructured poly-
mers including self-assembling method, Langmuir–
Blodget technique, layer-by-layer technique, etc.5–7
Numerous studies concerned with the synthesis and
characterization of optically active polymers have been
∗For correspondence
203

204
Shadpour Mallakpour and Amin Zadehnazari
carried out, mainly in the past few decades, because of 2.2 Techniques
their chiroptical and stereospecific properties.18 They
Proton nuclear magnetic resonance (1H NMR,
are used as catalysts for asymmetric synthesis,19 as
a chiral stationary phase (CSP) for enantioselective
separation in high performance liquid chromatogra-
phy (HPLC),20 electrodes for enantioselective recogni-
tion for performing bioelectro synthesis,21 microwave
absorbents,22 membrane separation technology,23 liq-
uid crystals,24 and nonlinear optics.25,26 A direct and
effective way for synthesizing chiral polymers is to
introduce chiral elements into the polymer backbone
or side chains. Some groups have made large con-
tributions to this significant research field, including
Okamoto and co-workers,27 Masuda et al.,28 Yashima
et al.,29 Aoki and co-workers,30 etc. In the poly-
condensation reactions our group uses amino acids
as chiral inducting agents. These materials are natu-
rally occurring compounds and synthetic polymers
based on amino acids are expected to be biodegradable
and biocompatible. In addition to optical properties of
these polymers, the solubility of them was improved
without significant loss of mechanical and thermal
properties.31
400 MHz) spectra were carried out at a Bruker
(Germany) Avance 500 instrument at room tempera-
ture (RT) in N,Nꢁ-dimethylsulphoxide-d6 (DMSO-d6).
Multiplicities of proton resonance were designated as
singlet (s), doublet (d), triplet (t), and multiplet (m).
FT-IR spectra were recorded on a spectrophotometer
(Jasco-680, Japan). The spectra of solids were obtained
using KBr pellets. The vibrational transition frequen-
cies are reported in wavenumbers (cm−1). Band inten-
sities are assigned as weak (w), medium (m), strong
(s), and broad (br). Inherent viscosities were mea-
sured by using a Cannon Fenske Routine Viscometer
(Germany) at the concentration of 0.5 g dL−1 at 25◦C.
Specific rotations were measured by a Jasco Polarime-
ter (Japan). Thermal gravimetric analysis (TGA) is
performed with a STA503 win TA at a heating rate of
20◦C min−1 from 25◦C to 800◦C under nitrogen atmo-
sphere. The X-ray diffractograms of polymers were
recorded using an X-ray diffraction (XRD) (Bruker,
D8ADVANCE, Germany) with a copper target at
40 kV and 35 mA and Cu Kα λ = 1.54 Å in the range
of 10-80◦ at the speed of 0.05◦ min−1. The morphology
of the polymers was observed using field emission
scanning electron microscope (FE-SEM) (HITACHI S-
4160). The effect of ultrasonic radiation on the size of
polymer particles was investigated by MISONIX ultra-
sonic liquid processors, XL-2000 SERIES. Ultrasound
was a wave of frequency 2.25 × 104 Hz and power
100 W.
Based on our previous studies, we describe here the
preparation and basic characterization of a series of
novel heat resistant and optically active nanostructured
poly(amide-imide)s (PAI)s containing amino acid and
dopamine moiety in a medium consisting of molten
TBAB salt and triphenyl phosphite (TPP) by reaction
of 3,5-diamino-N-(3,4-dihydroxyphenethyl)benzamide
with four different N,Nꢁ-(pyromellitoyl)-bis-L-amino
acids.
2.3 Monomer synthesis procedure
3,5-Diamino-N-(3,4-dihydroxyphenethyl)benzamide
(4) as a diamine monomer was prepared according to
our published article and is shown in scheme 1.32
N,Nꢁ-(pyromellitoyl)-bis-L-amino acids 7a–7d were
prepared in quantitative yields by the condensa-
tion reaction of pyromellitic dianhydride (1,2,4,5-
benzene-tetra-carboxylicacid-1,2,4,5-dianhydride) with
L-leucine,33 L-isoleucine,34 L-valine,35 and L-alanine36
in acetic acid solution.
2. Experimental
2.1 Materials
All chemicals used in this study were obtained com-
mercially from Fluka Chemical Co. (Switzerland),
Aldrich Chemical Co. (Milwaukee, WI) and Merck
Chemical Co. (Germany). Dopamine hydrochloride (3-
hydroxytyraminium chloride), 3,5-dinitrobenzoyl-
chloride, N,Nꢁ-dimethylacetamide (DMAc), N-methyl2-
pyrrolidone (NMP), and propylene oxide from
Merck were used for the synthesis of mediators.
2.4 Polymer synthesis procedure
Propylene oxide was used as acid scavenger. N,Nꢁ- The PAIs were prepared by the following procedure: for
dimethylformamide (DMF) (d = 0.94 g cm−3 at 20◦C), the synthesis of PAI8a, A mixture of 0.10 g (2.25 ×
and DMAc as solvent (d = 0.94 g cm−3 at 20◦C) were 10−4 mol) of diacid 7a, 0.064 g (2.25 × 10−4 mol) of
distilled over barium oxide under reduce pressure. diamine 4 and 0.29 g of TBAB (9.00 × 10−4 mol) was
Other reagents were used without further purification.
ground until a powder was formed. After the mixture

Synthesis of nanostructured chiral poly(amide-imide)s
205
O2N
NO2
NH3.Cl
CH2
O2N
NO2
H2C
C
O
DMAc, Propylene oxide
+
0 °C
NH
CH2
C
O
HO
H2C
Cl
OH
1
2
HO
OH
H2N
NH2
3
Hydrazine, Pd/C
EtOH
C
O
NH
CH2
H2C
HO
OH
4
Scheme 1. Synthetic rute of diamine 4.
was completely ground, it was transferred into a 25 mL,
PAI8c: FT-IR (KBr, cm−1): 3,420 (m, br, NH and
round-bottom flask and then 0.23 mL (9.00 × 10−4 mol) OH stretching), 3,100 (w, C-H aromatic), 2,964 (w, C-
of TPP was added to the mixture which was heated until H aliphatic), 2,932 (w, C-H aliphatic), 1,776 (m, C=O
a homogeneous solution was formed. Then, the solu- imide, asymmetric stretching), 1,722 (s, C=O imide,
tion was stirred for 12 h at 120◦C, and the viscous solu- symmetric stretching), 1,647 (s, C=O amide, stertch-
tion was precipitated in 15 mL of methanol. The yellow ing), 1,599 (s), 1,554 (s), 1,446 (s), 1,382 (s, CNC
solid was filtered off and dried to give 0.168 g (92%) of axial stretching), 1,213 (m, CNC transverse stretching),
PAI8a. The other PAIs, PAI8b-PAI8d were prepared by 1,077 (m), 879 (m), 762 (m), 727 (s, CNC out-of-plane
a similar procedure.
bending), 689 (w).
PAI8a: FT-IR (KBr, cm−1): 3,338 (m, br, NH and
Elemental analysis: calculated for (C35H33N5O9)n: C,
OH stretching), 3,098 (w, C-H aromatic) 2,960 (m, C- 62.96%; H, 4.98%; N, 10.49%. Found: C, 62.46%; H,
H aliphatic), 2,873 (w, C-H aliphatic), 1,775 (m, C=O 5.00%; N, 10.58%.
imide, asymmetric stretching), 1,722 (s, C=O imide,
PAI8d: FT-IR (KBr, cm−1): 3,409 (m, br, NH and
symmetric stretching), 1,647 (m, C=O amide, stertch- OH stretching), 3,100 (w, C-H aromatic), 2,961 (w, C-
ing), 1,599 (s), 1,449 (s), 1,382 (s, CNC axial stretch- H aliphatic), 2,932 (w, C-H aliphatic), 1,774 (m, C=O
ing), 1,116 (m, CNC transverse stretching), 1,078 (w), imide, asymmetric stretching), 1,719 (s, C=O imide,
960 (m), 879 (m), 821 (m), 726 (s, CNC out-of-plane symmetric stretching), 1,647 (m, C=O amide, stertch-
bending), 691 (w).
ing), 1,600 (s), 1,559 (m), 1,448 (s), 1,383 (s, CNC
1
PAI8b: H-NMR (400 MHz, DMSO-d6, ppm): 0.92 axial stretching), 1,152 (m, CNC transverse stretching),
(t, 6H, CH3, distorted), 1.02–1.03 (d, 6H, CH3, J = 1,076 (m), 879 (m), 764 (m), 727 (s, CNC out-of-plane
3.68 Hz), 1.52 (m, 4H, CH2), 1.70 (m, 2H, CH), 2.29 bending), 690 (w).
(t, 2H, CH, distorted), 2.68 (t, 2H, CH, distorted), 4.71–
4.72 (d, 2H, CH, J = 5.80 Hz), 6.42–6.43 (d, 1H, Ar-H,
J = 5.92 Hz), 6.58 (s, 1H, Ar-H), 6.63–6.64 (d, 1H, Ar-
H, J = 6.40 Hz), 7.90 (s, 2H, Ar-H), 8.18 (s, 1H, Ar-H),
3. Results and discussion
8.29 (s, 2H, Ar-H), 8.55 (s, 1H, OH), 8.61 (s, 1H, OH),
8.66 (s, 1H, NH), 10.24 (s, 2H, NH).
3.1 Monomer synthesis
Elemental analysis: calculated for (C37H37N5O9)n: C,
63.88%; H, 5.36%; N, 10.07%. Found: C, 63.22%; H,
5.24%; N, 10.13%.
Diamine monomer 4 was synthesized by using a
two-step reaction according to our previous work

206
Shadpour Mallakpour and Amin Zadehnazari
O
O
O
O
O
O
O
NH
OH
*
COOH
HO
NH
Glacial acetic acid
R.T
H2N
COOH
*
O
+
R
H
H
HOOC
R
*
O
O
R
H
5
6a-6d
O
O
Reflux
15h
COOH
*
HOOC
*
N
O
N
O
R
H
R
H
7a-7d
O
O
O
O
C
C
*
NH
NH
N
O
N
O
*
n
Molten TBAB/TPP
R
H
R
+
H
7a-7d
4
12 h, 120°C
-H2O
C
O
8a-8d
NH
CH3
CH3
CH3
CH3
CH2
CH2
R:
H2C
CH3
CH2
CH3
CH3
HO
a: Leu b: Ile c: Val d: Ala
Scheme 2. Synthesis of PAIs 8a–8d.
OH
(scheme 1).32 Diacid monomers were synthesized by based diamine (4) in molten TBAB in the presence
the condensation reaction of an equimolar amount of of TPP (scheme 2). This IL was selected because it
pyromellitic dianhydride (1) and different amino acids proved to be the most valuable among those employed
[L-leucine (6a), L-isoleucine (6b), S-valine (6c), and L- in our recent works.15–17 Runs in IL were carried out
alanine (6d)] in refluxing acetic acid solution, as shown by thermal heating technique. The entire polycondensa-
in scheme 2.33–36
tion reaction readily proceeds in a homogeneous solu-
tion and after stringy work-up tough and precipitates
were formed. The syntheses and some physical prop-
erties of these new PAIs (8a–8d) are given in table 1.
All the polymers were obtained in high yields (85–
92%), and the inherent viscosities were 0.33–0.49 dL/g
which were measured in DMF solutions. Also, the
resulting polymers showed yellow colour. All of them
are optically active, because they have a chiral cen-
tre from amino acid residue in their pendant groups.
The structure of the PAIs was confirmed by FT-IR
3.2 Polymer synthesis
The direct polycondensation of a dicarboxylic acid and
diamine in a conventional organic solvent is one of
the well-known methods for PAI synthesis. The use of
environmentally benign reaction media is very impor-
tant in view of today’s environment-conscious attitudes.
The utilization of organic solvents, which are most
often used for conventional polymerization media, has
numerous disadvantages: they may be flammable, toxic,
and volatile, which increases the potential hazard of
environmental pollution due to solvent loss. The use of
green solvents such as ILs appears to eliminate these
1
and H NMR spectroscopy, and elemental analysis
technique.
3.3 Polymer characterization
drawbacks, while retaining the advantages of common The FT-IR spectra of all polymers showed absorp-
organic solvents or even ensuring better conditions. So, tions around 1719–1776 cm−1, commonly attributed to
in this research we tried to eliminate common organic the asymmetric and symmetric stretches of carbonyl
solvents such as NMP, DMAc, and DMF and per- groups. The presence of imide heterocycle in these
formed the polymerization reaction under green condi- polymers was revealed by absorption around 1382 and
tions to report a simple, safe, and efficient method for 726 cm−1 which belong to carbonyl bendings of imide.
synthesis of several optically active PAIs via direct Bands of amide N–H and hydroxyl groups appeared at
polycondensation reaction of several natural amino around 3338–3420 cm−1. A representative FT-IR spec-
acid-based diacids (7a–7d) with an aromatic dopamine- trum for PAI8b is illustrated in figure 1. The structure of

Synthesis of nanostructured chiral poly(amide-imide)s
207
Table 1. Synthesis and some physical properties of PAI8a-PAI8d prepared in molten TBAB.
25,b
25
Diacid
Polymera
Yield (%)
Inherent viscosityb (dL/g)
[α]Na,589 (deg.)b
[α]Hg (deg.)c
Colour
7a
7b
7c
7d
PAI8a
PAI8b
PAI8c
PAI8d
92
87
88
85
0.35
0.43
0.49
0.33
−30.41
−29.38
−31.12
−23.15
−18.90
−16.93
−25.46
−16.65
Yellow
Yellow
Yellow
Yellow
aPolymers were precipitated in methanol
bMeasured at a concentration of 0.5 g dL−1 in DMF at 25◦C
cMeasured without filter
PAI8b was also confirmed with 1H NMR spectroscopy on their chemical structure. Thus, the introduction of
1
(figure 2). In the H NMR spectrum of this polymer, flexible linkages and polar functional groups into the
appearances of the N–H protons of amide groups at 8.66 main chain or the side chain of aromatic polymers
and 10.24, as two singlet peaks, and OH groups at 8.55 greatly enhances molecular mobility and provides bet-
and 8.61 ppm as two singlet peaks, respectively, indi- ter solubility. One of the main objectives of this study
cate the presence of amide groups in the polymer’s side was producing modified PAIs with improved solubili-
chain as well as main chain and hydroxyl groups in the ty. Due to the presence of bulky groups as well as
polymer’s side chain. These data was compared with hydroxyl functional groups in the polymer side chain,
those of the diamine monomer 4. In the 1H NMR spec- these PAIs have good solubility in different organic
trum of diamine monomer 4, the protons of hydroxyl solvents. The solubility of obtained PAIs (8a–8d) was
1
groups appeared at about 8.60 ppm.32 In the H NMR investigated as 0.01 g of polymeric sample in 2 mL
spectrum of PAI8b, the resonance of aromatic protons solvent. All of the polymers are soluble in organic
appeared in the range of 6.42–8.29 ppm. The proton of solvents such as DMF, DMAc, DMSO, NMP, pyri-
the chiral centre appeared as doublet at 4.71–4.72 ppm. dine, and in H2SO4 at room temperature and pheno-
lic solvents such as m-cresol, and are insoluble in sol-
vents such as methanol, ethanol, acetone, chloroform,
methylene chloride, and water. The polymer solutions
are very stable, and no gelation, phase separation, or
precipitation was observed after storage for several
weeks.
3.4 Organosolubility of PAIs
It is well-known that the dissolution of polymers
depends not only on their physical properties, but also
Figure 2. 1H NMR (400 MHz) spectrum of PAI8b in
DMSO-d6 at RT.
Figure 1. FT-IR spectrum of PAI8b.

208
Shadpour Mallakpour and Amin Zadehnazari
Table 2. Thermal properties of PAIs (8b) and (8c)a.
Polymer
Ta5 (◦C)
Ta10 (◦C)
Char yield (%)b
LOI (%)c
ꢀHcomb (kJ/g)
PAI6b
PAI6c
325
332
376
405
42.2
45.1
34.4
35.5
23.2
22.5
aTemperature at which 5 and 10% weight loss was recorded by TGA at a heating rate of 20◦C min−1 in a nitrogen atmosphere
bPercentage weight of material left undecomposed after TGA analysis at maximum temperature 800◦C in a nitrogen atmo-
sphere
cLimiting oxygen index (LOI) evaluating at char yield at 800◦C
3.5 Thermal stability of PAIs
factor for estimating the limiting oxygen index (LOI) of
polymers according to Van Krevelen equation:37
The thermal properties of two PAIs (8b) and (8c) were
examined by TGA and derivative of thermaogravimet-
ric (DTG) in a nitrogen atmosphere at a heating rate of
20◦C min−1 and the thermal behaviour data are sum-
marized in table 2. Typical TGA curves of representa-
tive PAIs 8b and 8c in nitrogen atmospheres are shown
in figure 3. The thermal stability of the polymers was
studied on the basis of 5 and 10% weight losses (T5
and T10, respectively) of the polymers and the residue at
800◦C. These polymers exhibit good resistance to ther-
mal decomposition, up to 325◦C in nitrogen, and began
to decompose gradually above that temperature. The
good thermal stability of resulting polymers is due to
the introduction of high rigid pyromellitoyl group into
the PAI backbone. T5 for these polymers ranged from
325 to 332◦C and the 10% weight loss temperatures of
these polymers in nitrogen were recorded in the range
of 376–405◦C. The concentration of carbonized residue
(char yield) of these polymers in a nitrogen atmosphere
was more than 40% at 800◦C. The high char yields of
these polymers can be ascribed to their high aromatic
content. The char yield can be applied as a decisive
LOI = 17.5 + 0.4CR (where CR = Char yield) .
PAIs 8b and 8c had LOI values around 42, which were
calculated from their char yield. A polymer having LOI
more than 28 is considered as effective flame retardant.
There is also an interesting relationship between
the LOI and heat of combustion according to Johnson
equation:38
8000
LOI =
,
ꢀHcomb
where ꢀHcomb is the specific heat of combustion in J/g.
So, in the case of these polymers (PAI8b and PAI8c),
ꢀHcomb is 23.2 and 22.5, respectively.
3.6 XRD analysis
XRD scans with 2θ ranging from 10◦ to 80◦ for pow-
der specimens were obtained for the synthesized PAIs
(8b) and (8c). As indicated by X-ray diffractograms of
Figure 3. TGA thermograms of PAIs (8b) and (8c).
Figure 4. XRD patterns of PAI8b and PAI8c.

Synthesis of nanostructured chiral poly(amide-imide)s
209
Figure 5. FE-SEM micrographs of PAI8b (a and b) and PAI8c (c and d).
these polymers in figure 4, the weak reflection centred FE-SEM images of PAI8b and PAI8c. FE-SEM obser-
at a 2θ value around 20◦ was characteristic of the amor- vation revealed that PAIs self-organized into nanopat-
phous polymers. This is because the presence of hetero- terns. As can be seen from these images, the aver-
cyclic imide groups and aromatic structures in the poly- age diameter of polymeric particles is in the range of
mer chain which reduce intermolecular forces between 32–56 nm, shape of them is spherical, and they are
the polymer chains, causing a decrease in crystallinity distributed uniformly and randomly.
of all the polymers. On the whole, new wholly aromatic
PAIs showed amorphous behaviour.
It is well-known that ultrasounic irradiation is a
well-established method for particle size reduction
in dispersions and emulsions as well as generation
and application of nano-size materials, because of the
potential in the deagglomeration and the reduction
of primaries. As most nanomaterials are still fairly
3.7 Morphological studies
Morphological characterization of PAIs was studied expensive, this aspect is of high importance for the
by FE-SEM. Shown in figure 5 are the respective commercialization of product formulations containing
Figure 6. FE-SEM micrographs of PAI8b (a and b) and PAI8c (c and d) after sonication process.

210
Shadpour Mallakpour and Amin Zadehnazari
nanomaterials.39 Here, powders of polymers have been constructing chiral media for asymmetric synthesis,
subjected to irradiation with high-intensity ultrasound CSPs for resolution of racemic mixtures by chromato-
for one hour while suspended in ethanol. The homoge- graphic techniques, and in related fields.
neous suspension was placed in a 60◦C oven overnight
to evaporate most of the solvent. Then the semidried Acknowledgements
polymer powder was further dried in vacuo at 80◦C
The authors gratefully acknowledge the financial
for 8 h. The resulting images from FE-SEM confirmed
support from the Research Affairs Division, Isfahan
that after ultrasonic irradiation the size of polymeric
University of Technology (IUT). The financial support
nanoparticles was decreased (23–28 nm) (figure 6).
from National Elite Foundation (NEF) and Center of
Excellence in Sensors and Green Chemistry Research
(IUT) is also gratefully acknowledged.
4. Conclusions
References
The present study involved the design and synthesis of
new optically active nanostructured polymeric materi-
als from the solution polycondensation reaction of 3,5-
diamino-N-(3,4-dihydroxy-phen-ethyl)benzamide with
four N,Nꢁ-(pyromellitoyl)-bis-L-α-amino acids (8) in
molten TBAB as an efficient medium and in the pres-
ence of TPP as an activating agent. The reaction condi-
tions open an important alternative to the use of volatile
organic solvents. This study shows that we can simply
replace the molten ionic salts with traditional volatile
and flammable organic solvents in polycondensation
reaction between a diamine containing hydroxyl groups
and diacids without any reaction of hydroxyl group
with acid. The main advantage of this technique is that
molten TBAB act as a simple, cheap, safe and excellent
medium with a high solubilizing power for the poly-
merization reactions that increase chemical reactivi-
ty and thus lead to better results in comparison with
conventional solvents. The easy work-up procedures
and recyclability of this molten salt used as the reac-
tion medium makes the method amenable for scale-up
operations. Because the resulting polymers had opti-
cally pure L-amino acid moieties, they showed opti-
cal rotations and were optically active. The presented
results also clearly reveal that incorporating the imide
group into the polymer main chain as well as combina-
tion of the wholly aromatic backbone and several func-
tional groups especially hydroxyl groups remarkably
enhanced the thermal stability and solubility of the new
polymers and a nice balance of these properties (ther-
mal stability versus solubility) was observed for these
polymers. Morphology study of resulting polymers by
FE-SEM showed that the polymeric particles are nano-
sized. The effect of ultrasonic intensity on the PAIs par-
ticle size was also studied. FE-SEM images showed
that size of particles was decreased. Thermal stabili-
ty, optical activity, and organosolubility of these poly-
mers make them potential candidates for future high
performance applications in high-powered materi-
als, processable high-performance engineering plastics,
1. Chanda M 2008 Industrial polymers, specialty poly-
mers, and their applications, Salil K Roy (ed) (Kolkata
West Bengal, India: CRC Press)
2. Huang L, Peng Z, Guo Y and Porter A L, 2010 J. Bus.
Chem. 7 15
3. Reis C P, Neufeld R J, Ribeiro A J and Veiga F 2006
Nanomedicine 2 8
4. Mohanraj V J and Chen Y 2006 Trop. J. Pharm. Res. 5 1
5. Muccini M, Murgia M and Biscarini F 2001 Adv. Mater.
13 355
6. Biederman H 2000 RF Vacuum 59 594
7. Maurer R 1992 J. Mater. Sci. 27 6279
8. Rogers R D, Seddon K R (eds) 2003 Ionic liquids as
green solvents: Progress and prospects (Washington,
DC, USA: ACS Symposium Series)
9. Kim D H, Im J K, Kim D W, Cheong M, Kim H S and
Mukherjee D K 2011 J. Chem. Sci. 123 467
10. Dupont J, de Souza R F and Suarez P A Z 2002 Chem.
Rev. 102 3667
11. Ranu B C, Das A and Samanta S 2002 J. Chem. Soc.,
Perkin Trans. 1 1520
12. Liu Z, Zhang G, Sun H, Jiang H, Zhao C, Xu D, Li H,
Sun X and Na H 2012 Polym. Int. 61 565
13. Kissane M, McNamara O A, Mitchell D, Coppert D M,
Moynihan H A, Lorenz K T and Maguire A R 2012
Tetrahedron Lett. 53 403
14. Nagarapu L, Cheemalapati V N, Karnakanti S and Bantu
R 2010 Synthesis 19 3374
15. Mallakpour S and Rafiee Z 2007 Polymer 48 5530
16. Mallakpour S and Rafiee Z 2007 Eur. Polym. J. 43 1510
17. Mallakpour S and Zadehnazari A 2010 High. Perform.
Polym. 22 567
18. Ikai T and Okamoto Y 2010 In Chiral recognition in
separation methods: Mechanisms and applications, A
Berthod (ed) (London, New York: Springer Heidelberg
Dordrecht) p. 34
19. Okamoto Y, Haruhiko M, Motoshi I, Koichi H, Heimei
Y 1986 J. Polym. Sci. Part C, Polym. Symp. 74 125
20. Nakano T 2001 J. Chromatogr. A 906 205
21. Chen Z, Takei Y, Deore B A and Nagaoka T 2000
Analyst 125 2249
22. Petrov V M and Gagulin V V 2001 Inorg. Mater. 32 135
23. Ulbricht M 2006 Polymer 47 2217
24. Shibaev V, Bobrovsky A, Boiko N 2003 Prog. Polym.
Sci. 28 729

Synthesis of nanostructured chiral poly(amide-imide)s
211
25. Singer K D, Petschek R G, Ostroverkhov V and Twieg 32. Mallakpour S, Hatami M, Ensafi A A and Karimi-Maleh
R J 2003 J. Polym. Sci., Part B: Polym. Phys. 41
2744
26. Kauranen M, Verbiest T, Maid J J and Persoons A 1996
Synth. Met. 81 117
27. Okamoto Y 2009 J. Polym. Sci., Part A: Polym. Chem.
47 1731
28. Liu R, Sanda F and Masuda T 2008 J. Polym. Sci., Part
A: Polym. Chem. 46 4175
H 2011 Chin. Chem. Lett. 22 185
33. Mallakpour S E, Hajipour A R and Habibi S 2001 Eur.
Polym. J. 37 2435
34. Mallakpour S and Shahmohammadi M H 2004 J. Appl.
Polym. Sci. 92 951
35. Mallakpour S and Shahmohammadi M H 2005 Iran.
Polym. J. 14 473
36. Faghihi K, Foroughifar N and Mallakpour S 2004 Iran.
Polym. J. 13 93
29. Miyabe T, Iida H, Banno M, Yamaguchi T and Yashima
E 2011 Macromolecules 44 8687
37. Van Krevelen D W 1975 Polymer 16 615
30. Inoue M, Teraguchi M, Aoki T, Hadano S, Namikoshi T, 38. Johnson P R 1974 J. Appl. Polym. Sci. 18 491
Marwanta E and Kaneko T 2009 Synth. Met. 159 854
31. Mallakpour S and Zadehnazari A 2011 eXPRESS Polym.
Lett. 5 142
39. Mason T J and Lorimer J P 2002 Applied sonochemistry:
Uses of power ultrasound in chemistry and processing
(Verlag GmbH and Co. KGaA: Wiley-VCH)