Insertion of novel optically active poly(amide-imide) chains containing pyromellitoyl-bis-l-phenylalanine linkages into the nanolayered silicates modified with l-tyrosine through solution intercalation

Article abstract of DOI:10.1016/j.polymer.2011.04.013

In the present investigation, for the first time, functional optically active poly(amide-imide) (PAI)/organonanosilica bionanocomposite films were successfully fabricated through solution intercalation technique. At the start, Cloisite Na⁺ and

Full text of DOI:10.1016/j.polymer.2011.04.013

Polymer 52 (2011) 2514e2523
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Insertion of novel optically active poly(amide-imide) chains containing
pyromellitoyl-bis-
L-phenylalanine linkages into the nanolayered silicates
modified with -tyrosine through solution intercalation
L
,
b
,
a
Shadpour Mallakpour a , Mohammad Dinari
*
a Organic Polymer Chemistry Research Laboratory, Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111, Islamic Republic of Iran
b Nanotechnology and Advanced Materials Institute, Isfahan University of Technology, Isfahan 84156-83111, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present investigation, for the first time, functional optically active poly(amide-imide) (PAI)/
organonanosilica bionanocomposite films were successfully fabricated through solution intercalation
Received 10 January 2011
Received in revised form
2 April 2011
technique. At the start, Cloisite Naþ and protonated form of
L-tyrosine amino acid were used for the
preparation of the novel chiral organoclay via ion-exchange reaction. Then, PAI containing phenylala-
nine amino acid was synthesized via solution polycondensation of N,N’-(pyromellitoyl)-bis-phenylala-
nine diacid chloride (5) with 4,40-diaminodiphenylsulfone (6). This polymer was end-capped with
amine end groups near the completion of the reaction to interact chemically with organoclay. Finally,
PAI/organ-nanosilica bionanocomposites films containing 5, 10 and 15% of organoclay were prepared via
solution intercalation method through blending of organoclay with the PAI solution. The nanostructures
and properties of the PAI/organoclay hybrids were investigated using Fourier transform infrared
spectroscopy, X-ray diffraction (XRD), scanning electron microscopy, field emission scanning electron
microscopy (FE-SEM), transmission electron microscopy (TEM) and thermogravimetry analysis (TGA)
techniques. XRD, FE-SEM and TEM results revealed the formation of exfoliated and intercalated orga-
noclay platelets in the PAI matrix. TGA results indicated that the addition of organoclay into the PAI
matrix increases in the thermal decomposition temperatures of the resulted bionanocomposites. The
transparency of the nanocomposite films decreased gradually by the addition of organoclay, and the
films became semitransparent as well as brittle at high loading of organoclay. Mechanical data indicated
improvement in the tensile strength and modulus with organoclay loading. The film containing
a 10 wt.%. of organoclay had a tensile strength of the order of 85.24 MPa relative to the 67.52 MPa of the
pure PAI.
Accepted 10 April 2011
Available online 19 April 2011
Keywords:
Organoclay
Chiral poly(amide-imide)
Bionanocomposite
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
[2e5]. The uniform dispersion of silicate layers is usually desirable
for maximum reinforcement of the materials [6]. Nanoclays have
Nanocomposites are an important class of new generation
materials, which typically reveal properties superior to those of
their individual components. To optimize the concert properties of
these materials, the dispersion of inorganic domain in the organic
matrix at nanolevel is enviable [1]. Nanocomposites based on
organic polymers and inorganic nanoclay minerals consisting of
silicate layers are amongst the most promising composite systems
several advantages over conventional microsized clays in polymer
composites: good mechanical and gas barrier properties, thermal
stability and conductivity properties without significant reduction
in other relevant properties, including toughness. An additional
benefit is the transparency because of their low filler loading, for
the reason that the clay content is below a critical loading level [7].
Incorporation of layered silicate into the polymeric matrix provides
several improvements in the physical and mechanical properties,
such as Young’s modulus, yield stress, heat deflection temperature,
permeability, and flammability. The superior mechanical properties
of the polymer/clay nanocomposites are achieved not only through
the molecular-level dispersion of the aluminosilicate layers but also
through the strong interactions between the polymer matrix and
the clay layers [4,8].
* Corresponding author. Nanotechnology and Advanced Materials Institute,
Isfahan University of Technology, Isfahan 84156-83111, Islamic Republic of Iran.
Tel.: þ98 311 391 3267; fax: þ98 311 391 2350.
E-mail addresses: mallak@cc.iut.ac.ir, mallak777@yahoo.com, mallakpour84@
alumni.ufl.edu (S. Mallakpour).
0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2011.04.013

S. Mallakpour, M. Dinari / Polymer 52 (2011) 2514e2523
2515
The incompatibility between organophilic polymer and the
hydrophilic layered silicates has been resolved through surface
modification of the nanoclays. This can be carried out via an ion-
exchange reaction of the surface sodium ions with organics
producing organically modified layered silicates. The replacement
of inorganic exchange cations by organic onium ions on surface of
clay not only serves to match the clay surface polarity with the
polarity of the polymer but also expands the interlayers of clay, thus
facilitating the penetration of polymer precursors or preformed
polymer. Depending on the charge density of nanoclay and the
onium ion surfactant, different arrangements of the onium ions are
possible [9]. The organomodification of clay is an important step in
the preparation of polymer/clay nanocomposites. This is usually
done by ion-exchange reactions between alkaline cations situated
inside clay galleries and organic cationic surfactant molecules, such
as ammonium and phosphonium cations [10,11].
a cation-exchange method in a green and environmentally friendly
process. The optically active PAI chains was produced by reacting of
N,N’-(pyromellitoyl)-bis-phenylalanine diacid chloride 5 with 4,40-
diaminodiphenylsulfone 6 in N,N-dimethyl acetamide (DMAc). The
amide chains were selectively end-capped with amine end groups
near the completion of the reaction to interact chemically with
modified organoclay. As a result, chemically combined and ther-
mally stable BNCFs were produced with permanent intercalating
effect. The organoclay and thin BNCFs obtained by evaporation of
the solvent were subjected for Fourier transfer infrared (FT-IR)
spectroscopy, X-ray diffraction (XRD), thermogravimetry analysis
(TGA) techniques and mechanical properties. The morphology of
the obtained materials was examined by scanning electron
microscopy (SEM), field emission scanning electron microscopy
(FE-SEM) and transmission electron microscopy (TEM) techniques.
Chiral phenomenons play vital roles in nature. Amino acids are
among the simplest chiral biomolecules that contain intra-
molecular hydrogen bonds and they serve as building blocks of
more complex peptides and proteins. Most of the naturally occur-
ring compounds for instance nucleic acids, proteins, and poly-
saccharides are chiral and optically active. Some of them show
characteristic functionalities such as molecular recognition ability
and catalytic activity, due to their specific chiral structure as rep-
resented by genes and proteins. Amino acid based synthetic
materials are also expected to show biocompatibility and biode-
gradability similar to those of polypeptides [12,13]. The use of
amino acid compounds in the hybrid materials increases the
biocompatibility of such system and allows interactions with bio-
logical systems [14,15]. In another hand, peptide-based systems
have been found to show nanoscale ordering into stable hierar-
chical superstructures administered by the formation of secondary
structures in the peptide segments. Positively charged amino acids
have a similarity in chemical structure with conventional modifiers
with alkylammonium cations. When compared with chemically
synthesized modifier, amino acid biosurfactants have the impor-
tant advantage of biodegradability, low toxicity and various
possible structures [16].
2. Experimental
2.1. Materials
The source clay, sodium montmorillonite (Cloisite Naþ), was
purchased from Southern Clay Products, Gonzales, Texas (USA). The
cation-exchange capacity (CEC) of Cloisite Naþ is 92.6 meq/100 g as
reported by suppliers. This compound was used without any
further purification. Pyromellitic dianhydride (benzene-1,2,4,5-
tetracarboxylic dianhydride) (1) (from Merck Chemical CO.,
Germany) was purified with acetic anhydride in boiling acetic acid.
4,40-Diaminodiphenylsulfone (6) was used as obtained without
further purification. DMAc was dried over BaO, and then distilled in
vacuum.
L-Tyrosine, L-phenylalanine, triethylamine (TEA) and
hydrochloric acid (HCl) were purchased from Merck Chemical Co.
(Germany) and were used as obtained without further purification.
2.2. Equipments
FT-IR spectra of the hybrid films were recorded with a Jasco-680
(Japan) spectrometer at a resolution of 4 cmꢀ1 and they were
scanned at wavenumber range of 400e4000 cmꢀ1. Vibration bands
were reported as wavenumber (cmꢀ1). Thin films of BNCFs were
made by evaporating solvent at 80 ꢁC and used for FT-IR analysis.
FT-IR spectra of Cloisite Naþ, organoclay and PAI were also collected
by making their pellets in KBr as a medium. The band intensities are
assigned as weak (w), medium (m), shoulder (sh), strong (s), and
broad (br). Proton nuclear magnetic resonance (1H NMR) spectra
were recorded on Bruker Avance 400 MHz spectrometer operating
polymer solution in DMSO-d6. The Proton resonances were desig-
nated as singlet (s) and multiplet (m). Inherent viscosities were
measured by a standard procedure using a Cannon-Fenske routine
viscometer (Germany) at the concentration of 0.5 g/dL at 25 ꢁC.
Specific rotations were measured by a Jasco Polarimeter (Japan).
TGA is performed with a STA503 win TA at a heating rate of 10 ꢁC/
min from 25 ꢁC to 800 ꢁC under nitrogen atmosphere. XRD patterns
In addition, the synthesis of macromolecules containing amino
acids is a subject of much interest. Because amino acids are natu-
rally occurring compounds, synthetic poly(
a-amino acids)s and
their copolymers would likely be biodegradable, biocompatible,
and nontoxic [17e19]. Moreover, amino acid based chiral copoly-
mers can incorporate crystallinity with the ability to form higher
ordered structures that exhibit improved solubility. Synthetic
macromolecules containing amino acids are potentially biode-
gradable because of the incorporation of amino acids, which can be
targeted for cleavage by enzymes such as proteases [20e22].
Poly(amide-imide)s (PAI)s contains both amide and heterocycle
imide structures along the main chain of the polymer backbone are
a kind of thermoplastic resin, have good high-temperature resis-
tance, outstanding mechanical properties, excellent oxidative
stability and hydrogen bonding interaction, being a promising
matrix candidate for hybrid materials [23e27]. They have been
widely used with electronic materials, adhesives, composite
materials, fiber, and film material. Comparing with the polyimide
and polyamide, the PAI own the better process ability and heat
resistant properties [3,26e30].
were recorded using CuK
(Germany) diffractometer operating at current of 100 mA and
a voltage of 45 kV. The diffractograms were measured for 2 , in the
range of 1.2e10ꢁ, using CuK
incident beam (
¼ 1.51418 Å). And
Bragg’s law n was used to compute the d-spacing. The
¼ 2d sin
a radiation on a Bruker, D8ADVANCE,
q
a
l
l
q
In the present study, for the first time, we wish to report the
synthesis and characterization of new optically active PAI/organo-
clay bionanocomposites films (BNCF)s which were prepared by
solution intercalation method through blending of organoclay with
the PAI solution for full dispersion of organoclay throughout the
dispersion morphology of the nanoparticles on PAI matrix was
observed using SEM (XL30, Philips) and FE-SEM (HITACHI S-4160).
TEM images were obtained using a Philips CM 120 microscope with
an accelerating voltage of 100 kV. The BNC films were first micro-
tomed into 60 nm ultra thin sections with a diamond knife using
Leica Ultracut UCT ultramicrotome. Tensile properties of the BNC
films were measured according to DIN procedure 53455 having
matrix. Cloisite Naþ and ammonium salt of
L-tyrosine amino acid
were used for the preparation of the novel chiral organoclay by

2516
S. Mallakpour, M. Dinari / Polymer 52 (2011) 2514e2523
+
+
+
+
Na Na
Na Na
O
O
-
Cl
NH3
NH2
OH
NH3
OH
+
H
H CH2
Cloisite Na+
-NaCl
HO
OH
H CH2
CH2
O
HCl
OH
OH
O
CH2
H
NH3
OH
OH
L-Tyrosine
Organoclay
Scheme 1. Spatial array of the intercalated protonated L-tyrosine amino acid ions in Cloisite Naþ
.
a crosshead speed of 5 mm minꢀ1 using Testometric Universal
Testing Machine M350/500.
protonated form of L-tyrosine amino acid and the mixture was
stirred at 60 ꢁC for 6 h under mechanically stirred. The precipitates
of novel modified clay were isolated by suction-filtration using
Whatman filter paper, placed in a 250-mL beaker again and washed
with 200 mL hot water. This process was repeated three times to
ensure the removal of excess ammonium salt of amino acid. The
final product obtained by filtration was dried under vacuum at
60 ꢁC for 8 h. The dried cake was ground and screened with a 325-
mesh sieve to obtain the organoclay.
2.3. Synthesis of organoclay
The organo-modified bionanoclay was prepared by a cation-
exchange method, which is a displacement of the sodium cations
of Cloisite Naþ with the positively charged
L-tyrosine amino acid.
The equation for calculating the intercalating amino acid used for
a cationic-exchange reaction is expressed as follows:
ꢀ
ꢁ
2.4. Monomer synthesis
92:6
100
X
ꢂ Y ꢂ 1:5 ¼
ꢂ 1 ꢂ 1000
MW of interclated amino acid
N,N’-(Pyromellitoyl)-bis- -phenylalanine diacid chloride 5 was
L
prepared by procedure reported elsewhere [31].
where 92.6/100 represents the CEC value per 100 g of Cloisite Naþ
nanoclay; 1.5 (>1) indicates the excess amount of intercalating
agent used; Y is the amount of nanoclay and X and MW represent
the amount and molecular weight of intercalating amino acid,
respectively. Typically, 2 g of Cloisite Naþ was mechanically stirred
with 100 mL of deionized water at 80 ꢁC for 3 h to swell the layered
silicates. The aqueous solutions of the tyrosine amino acid was
prepared separately by dissolving amino acid (1.5 times the CEC of
clay) in 50 mL of distilled water at 80 following by addition of
stoichiometric amount of concentrated HCl to the solution. Then
the dispersed clay solution was added to the solution of the
2.5. Synthesis of PAI and amine end-capped PAI
An optically active PAI was synthesized by the solution poly-
merization of diacid chloride 5 and aromatic diamine 6 at low
temperature. The measured amount of diamine 6 (0.36 mmol) was
placed in the flask followed by the addition of DMAc as a solvent
under an inert atmosphere. After complete mixing, stoichiometric
amount of diacid chloride 5 (0.36 mmol) was added again under
anhydrous conditions. To remove HCl from the PAI solution, after
O
O
O
O
O
O
O
NH2
CH2
*
AcOH
HO
HN
NH
HOOC
OH
O
O
+
HO
H
H
CH2
H
CH2
COOH
O
O
1
3
2
O
O
N
O
N
O
N
O
O
O
O
N
SOCl2
Reflux HO
OH
Cl
Cl
H
H
CH2
CH2
H
O
H
CH2
O
CH2
O
O
4
5
Scheme 2. Synthesis of chiral monomer 5.

S. Mallakpour, M. Dinari / Polymer 52 (2011) 2514e2523
2517
O
N
H CH2
O
N
O
O
O
Cl
Cl
+
NH2
S
NH2
H
CH2
O
O
O
5
6
DMAc
O
O
O
O
O
S
N
N
NH
NH
H2C
H
CH2
H
O
O
O
n
PAI 7
Diamine 6 in Excess
O
O
O
O
S
O
O
S
N
N
N
NH
H
NH
NH
H2C
H
CH2
H
O
H
O
O
O
n
Amine End-capped PAI
Scheme 3. Preparation of optically active amine end-capped PAI.
the reagents dissolved completely, stoichiometric amount of TEA
was added with constant stirring for 2 h. The polymerization
reaction after initial mixing of monomers was allowed to come to
ambient temperature after 1 h. While reaction between diamine
and diacid chloride is extremely fast, however, further 24 h were
given to the reaction mixture for its completion. The reaction
mixture was highly viscous and golden in color. The viscous solu-
tion was poured into 40 mL of methanol and the precipitated solid
was filtered off and dried at 80 ꢁC for 6 h under vacuum to yield
0.246 g (85%) of the solid PAI 7, and the specific rotation was
dispersion of organoclay platelets in the polymer matrix. Various
compositions (2, 5, 10 and 15 wt.%) of organoclay were prepared by
mixing various amounts of organoclay to the PAI solution. Thin
BNCFs of uniform thickness were obtained by pouring the hybrid
solutions into glass dishes, followed by solvent evaporation at high
temperature. These films were further dried at 80 ꢁC under reduced
pressure to a constant weight.
3. Results and discussion
measured (½a 2D5
¼ ꢀ134, measured at a concentration of 0.5 g/dL
ꢃ
3.1. Preparation of chiral organoclay
in DMF at 25 ꢁC).
Amine end-capped PAI chains was produced by adding excess
(1%) amount of diamine 6 near the end of the polymerization
reaction.
In this study, positively charged of L-tyrosine amino acid is
chosen to replace the chemically synthesized surfactant for modi-
fication of Cloisite Naþ. During this reaction, the Cloisite Naþ
changes from hydrophilic to organophilic and the interlayer space
of organoclay was increased. These phenomena causes enlarge in
the d-spacing which facilitates the entry of the host polymer
molecules into the organoclay gallery for further applications.
Scheme 1 illustrates the schematic of such an adsorption process.
This scheme only provides to accentuate the route of adsorption
and does not present information on the arranging in which the
adsorbent molecules are present along with ammonium ions ion-
ically bound on the surface.
Yellow solid; FT-IR (KBr): 3483(sh), 3367 (br), 3101 (w), 3029
(w), 2929 (w), 1776 (m), 1725 (s), 1590 (s), 1525 (m), 1455 (m), 1381
(m, br),1354 (m, br),1316 (m, br),1250 (m),1180 (sh),1150 (m),1105
(m), 956 (w), 917 (w), 835 (m), 727 (m, br), 700 (m, br), 613 (w), 579
(m, br) cmꢀ1
.
1H NMR (400 MHz, DMSO-d6, d, ppm): 3.5 (m, 2H, CH2), 5.2 (s, br,
1H, chiral center hydrogen), 7.1e7.3 (m, AreH), 7.7 (s, 2H,), 7.8
(s, 2H,), 8.2 (s, 2H, AreH), 10.3 (s, amide hydrogen) ppm.
Elemental analysis: calcd. for (C40H30N4O8S): C, 66.11%; H, 4.16%;
N, 7.71%; S, 4.41%. Found: C, 65.88%; H, 4.44%; N, 7.93%; S, 4.60%.
3.2. Synthesis of aromatic polymer
2.6. Preparation of the PAI/organoclay BNCFs
At first, an optically active monomer
according to the reported procedure as show in Scheme 2 starting
from pyromellitic dianhydride and -phenylalanine amino acid.
Then an optically active PAI 7 was synthesized by the step-growth
polymerization reactions of an equimolar mixture of monomer 5
5 was synthesized
The novel BNCFs were prepared by mixing the appropriate
amounts of the PAI and organoclay in DMAc as a solvent in a flask
for a particular concentration. The solution was agitated to high
speed stirring at 80 ꢁC for 2 h and then at 40 ꢁC for 20 h for uniform
L

2518
S. Mallakpour, M. Dinari / Polymer 52 (2011) 2514e2523
NH3
H
CH2
O
Organoclay + Amine End-capped PAI Chain
NH
HO
OH
NH
CH2
H
O
NH3
Scheme 4. Preparation of chiral PAI/organoclay BNCs.
with aromatic diamine 6 in dry DMAc (Scheme 3). The inherent
viscosity of the synthesized PAI was 0.37 dL/g and the yield was
85%. The resulting polymer showed optical rotation, which indi-
cated that, the polymer is optically active and chirality was intro-
duced into the backbone of the polymer. The specific rotation of this
bands of the Cloisite Naþ, but the presence of the amino acid is also
seen. The peaks at 1650e1400 cmꢀ1 of the intercalated materials
and comparison with the same wavenumber interval of the amino
acid and that of the nanoclay reveal that organic cations are in
the interlayer of Cloisite Naþ or on its outer surface. Bands in the
3500e2500 cmꢀ1 region of tyrosine are mostly observable in
the spectrum of the organoclay. The protonated amino acid ions
should be largely among the layers since after intercalation the
materials were intensively washed, thus excess of organic cation
were removed. Bands at 2918 and 1682 cmꢀ1 are attributed to CeH
stretching vibration of CH2 aliphatic and C]C aromatic segment,
polymer is ½a 2D5
¼ ꢀ134(0.05 g in 10 mL of DMF). The structure of
ꢃ
this polymer was confirmed as PAI using FT-IR spectroscopy, 1H
NMR and elemental analysis techniques.
3.3. Preparation of the PAI/organoclay BNCFs
respectively for the interlayered L-tyrosine amino acid. Bands of
The affinity between polymer matrix and organoclay is one of
the most important factors in achieving good exfoliation; to
a certain extent the affinity can be enhanced by optimizing the
structure of the organoclay for a given polymer matrix. Novel
optically active PAI/organoclay BNCFs containing 2, 5, 10 and 15% of
organoclay were successfully fabricated using functionalized
organoclay (COOH and OH) and amine end-capped PAI chains in
dry DMAc through solution intercalation technique (Scheme 4).
These new families of homogeneous transparent materials are the
combinations of organic polymers and layered silicates blended
with each other at ultrafine phase dimensions. The uniform
distribution of organically modified nanoclay in polymer matrices
can lead to physical, morphological, and mechanical property
enhancements in the resulting BNCFs.
carboxylic OH and the phenolic OH vibrations of tyrosine were
observed in both hybrid materials virtually unchanged just as the
C]O stretching mode and the OH groups of Cloisite Naþ were
consumed.
The FT-IR spectra of PAI (Fig. 1c) showed absorptions around
3360 cmꢀ1 (NeH), 3100 cmꢀ1 (aromatic CeH stretching),
2930 cmꢀ1 and 2857 cmꢀ1 (CH2 stretching) and two overlapped
3.4. Characterizations methods
3.4.1. FT-IR spectra
Any changes in the structure of the organoclay and BNCFs will
be observed through changes in the FT-IR spectra. The represen-
tative FT-IR spectra of the unmodified clay (Cloisite Naþ), organo-
clay, bulk PAI and PAI/organoclay BNCs materials are shown in
Fig. 1. Thin films of PAI and BNCs were made by evaporating solvent
at 80 ꢁC and used for FT-IR analysis. Fig. 1a and b shows the FT-IR
spectra of Cloisite Naþ and organoclay, respectively. In the spec-
trum of Cloisite Naþ the absorption band at 3626 cmꢀ1 is due to
eOH stretching of AleOH and SieOH. The broad band at 3440 cmꢀ1
results from the eOH stretching vibration of interlayer water. The
characteristic peaks at 1637 and 1040 cmꢀ1 is due to interlayer
water deformation vibrations and SieO stretching, respectively.
The infrared spectrum of the Cloisite Naþ also show bands in the
400e600 cmꢀ1 regions that are attributed to SieO and AleO
bending vibration. The spectrum of organoclay is dominated by the
Fig. 1. FT-IR spectra of (a) Cloisite Naþ, (b) organoclay, (c) PAI, (d) BNC5%, (e) BNC10%
and (f) BNC15%.

S. Mallakpour, M. Dinari / Polymer 52 (2011) 2514e2523
2519
Table 1
Basal spacing of Cloisite Naþ, organoclay and PAI/organoclay BNCFs.
Sample
2
q
(ꢁ)
d (001) Spacing (nm)
Cloisite Naþ
Organoclay
BNCF2%
BNCF5%
BNCF10%
BNCF15%
7.56
6.4
4.62
4.62
4.70
4.96
1.17
1.38
1.91
1.91
1.88
1.78
moiety (SO2 stretching). These FT-IR data confirm the formation of
the aromatic PAI.
Fig. 1def also shows the FT-IR spectra of PAI/organoclay BNCFs
containing 5,10 and 15% of organoclays, respectively. As the loading
of organoclay is increased, the intensities of organoclay bands
become more pronounced. From these Figs, it can be concluded
that the BNCFs not only have characteristic neat PAI bands, but also
have characteristic pick for organoclay.
3.4.2. 1H NMR spectra
1H NMR data of neat PAI is described in experimental section. In
the 1H NMR spectrum of PAI, appearances of the NeH protons of
amide group at 10.30 ppm indicate the presence of amide group in
the polymer chain. The absorption of aromatic protons appeared in
the range of 7.1e7.3 ppm and the peak at 8.20 ppm was assigned to
pyrimillitimide ring protons. The proton of the chiral center
appeared as multiplets in the range of 5.26e5.34 ppm. The
absorption of the diastrotopic hydrogens bonded to neighbor
carbon of chiral center appeared in the range of 3.40e3.59 ppm as
Fig. 2. XRD patterns of (a) Cloisite Naþ
, (b) organoclay, (c) BNC2%, (d) BNC5%,
(e) BNC10% and (f) BNC15%.
carbonyl (amide and imide’s C]O) absorptions at 1776, 1725, and
1663 cmꢀ1 respectively. Absorption at 1380 and 727 cmꢀ1 was
showed the presence of the imide heterocycle in this polymer.
Absorptions at 1251 and 1150 cmꢀ1 showed due to the sulfone
Fig. 3. SEM micrographs of (aec) Cloisite Naþ, (def) organoclay and (gei) pure PAI.

2520
S. Mallakpour, M. Dinari / Polymer 52 (2011) 2514e2523
Fig. 4. FE-SEM images of (aec) organoclay, (def) pure PAI and (gei) BNC10%.
two discrete multiplets peaks. The aforementioned results show
that PAI was synthesized successfully.
3.4.4. SEM and FE-SEM
The morphological images of the Cloisite Naþ, organoclay and
pure PAI were studied by SEM and FE-SEM. The morphology of
Cloisite Naþ before and after modification is shown in Fig. 3aef. The
Cloisite Naþ shows massive, aggregated morphology and in some
instances, there are some bulky flakes (Fig. 3aec). Figs. 3de3f show
the morphology of modified organoclay with tyrosine amino acid.
Organoclay has more fragments of smaller size and they are formed
with irregular shapes. The SEM images of pure PAI show the flake-
like structure and the high yield of organoclay (10%) that have the
smoother morphology than organoclay (Fig. 3gei). Fig. 4aei also,
shows the FE-SEM of organoclay, pure PAI and PAI/organoclay
(10%), respectively. The results demonstrate that organoclay is
homogeneously dispersed in PAI matrix.
3.4.3. XRD patterns
The most conventional technique used to analyze the organo-
clay and polymer/clay nanocomposites is XRD, which measure the
interlayer d-spacing. The layers were propped open upon swelling
in water and the basal distances became higher after the ion-
exchange process by the protonated amino acids compare to the
original clay. Fig. 2(aee) shows XRD patterns of Cloisite Naþ,
organoclay and different BNCs (BNC2%, BNC5%, BNC10% and
BNC15%) and the result are summarized in Table 1. The d-spacing of
pristine Cloisite Naþ is 1.17 nm calculated from the peak position
2
q
¼ 7.56ꢁ using Bragg’s equation. After the ion-exchange reaction
with ammonium salt of L-tyrosine amino acid, peak of the orga-
noclay shifted to a new position at 2
q
¼ 6.40ꢁ (d ¼ 1.38 nm). An
3.4.5. TEM
increase of the interlayer distance, leads to a shift of the diffraction
peak toward lower angles and confirmed that intercalation and
surface modification of Cloisite Naþ had taken place. This means
that the basic structures of the Cloisite Naþ is kept, the layers only
propped open, and the basal distances increased significantly,
providing evidence that intercalation has occurred. The presence of
2, 5,10 and 15 wt% of organoclay in the PAI matrix resulted in a shift
TEM is supplementary utilized as an effective means of devel-
oping insights into the internal structure and spatial distribution of
the various components, through direct visualization [4,32,33].
Structure of the organo-modified clay was directly investigated by
means of TEM. It has been reported that the layer-structure images
of untreated Cloisite Naþ can not be observed with TEM [34]. Unlike
unmodified Cloisite Naþ, nanoclay modified with protonated form
of the tyrosine amino acid show clear layer structures (Fig. 5a and
b). Intercalated structures with higher interfacial distance are
observed. In some places, there are some curved layers for modified
of this diffraction peak towards smaller angle 2
q
¼ 4.62e4.98ꢁ. It
corresponds to a d spacing of 1.78e1.91 nm, suggesting a degree of
intercalation of PAI into the organoclay galleries.

S. Mallakpour, M. Dinari / Polymer 52 (2011) 2514e2523
2521
Fig. 5. TEM micrograph of (aec) organoclay and (def) BNC10%.
nanoclay. Nevertheless, some bundles aggregates can be high-
lighted in certain regions.
three different molecular environments for the surfactant in the
organoclay: surfactant cations intercalated into the clay interlayers
through cation exchange and bound to surface sites via electrostatic
interaction; surfactant physically adsorbed on the external surface
of the clay; and surfactant molecules located within the clay
interlayer [34]. Therefore, the decomposition temperatures for
surfactants with different molecular environments will be different
from each other. Cloisite Naþ does not undergo thermally induced
changes in the temperature range of 100e610 ꢁC, therefore the
mass loss in this temperature range should be attributed to the
decomposition and/or evaporation of the tyrosine amino acid ions.
The TGA curves of PAI and PAI/organoclay BNCFs are shown in
Fig. 7 and the resulting TGA data are summarized in Table 2 that
including temperatures at which 5% (T5), 10% (T10) degradation
occur and char yield at 800 ꢁC. The initial decomposition temper-
atures of the nanocomposites with different organoclay contents
(5, 10 and 15%) are about 300 ꢁC. These values are related to the
decomposition of pristine polymer matrix. The char yields at 800 ꢁC
Fig. 5c and d also shows the typical TEM image of the 10 wt.%
BNCF in which the brighter region represents the polymer matrix
while the dark narrow stripes represent the stacked and interca-
lated stacked nanoparticles. TEM study of the BNC structure
revealed a coexistence of exfoliated and intercalated organoclay
layers. TEM observations have been complete by XRD analysis,
which gives information on the interlayer distance of the alumi-
nosilicate platelets. The nanoclay sheets were appraised to be about
1 nm thick and an average length of about 100 nm. It is referred to
intercalated layers structures where the inorganic layers maintain
the parallel registry of pristine silicates and are separated by ultra
thin (1.3e5 nm) PAI films. Because of the periodic parallel assembly
of the silicates, the intercalated structures give rise to XRD peaks. In
addition, it is referred to exfoliated layers structures where the
layers are much further apart (5 nm), and in general both the layer
registry and the parallel stacking are lost [35]. This TEM photograph
demonstrates that most of the organoclay layers were intercalated
and dispersed homogeneously into the PAI matrix.
3.4.6. Thermal analysis
The TGA curves for Cloisite Naþ and organoclay are shown in
Fig. 6. According to these data, decomposition of Cloisite Naþ occurs
in two steps: the mass loss before 100 ꢁC was attributed to the
desorption of water from the interlayer space, since, the maximum
decomposition starts at around 660 ꢁC due to dehydroxylation of
the layers and proceeds till around 700 ꢁC [36]. In comparison with
Cloisite Naþ, organoclay have lower mass loss before 100 ꢁC,
implying less free water in the modified Cloisite Naþ. In addition,
the presence of organic cations increases the number of decom-
position steps. Previous studies [34,37,38] showed that the
decomposition of an organoclay takes place in four steps: (1) water
desorption, (2) dehydration, (3) surfactant decomposition and loss
and (4) dehydroxylation of the organoclay. In addition, there are
Fig. 6. TGA thermograms of Cloisite Naþ and organoclay.

2522
S. Mallakpour, M. Dinari / Polymer 52 (2011) 2514e2523
Fig. 7. TGA thermograms (a) neat PAI, (b) BNC5% (c) BNC10% and (d) BNC15%.
Fig. 8. UVevis transmission spectra of (a) neat PAI, (b) BNC2%, (c) BNC5%, (d) BNC10%
and (e) BNC15%.
of the nanocomposites with different organoclay content are higher
than that of pure PAI. Char yield can be applied as decisive factor for
estimated limiting oxygen index (LOI) of the polymers based on
Van Krevelen and Hoftyzer equation [39].
3.4.8. Mechanical properties
The stressestrain curves of pure PAI and BNC materials with 5,10
and 15 wt. % organoclay are shown in Fig. 9. The BNCs were found to
be stiffer than the neat polymer and the elastic modulus increased
with increasing organoclay. The maximum modulus value was
observed with 10 wt. % organoclay in the polymer matrix, providing
more stiffness to the materials, since stiffness is a function of the
aspect ratio. A decreased attraction between the silicate layers caused
larger interlayer spacing between the silicate layers and more exfo-
liated nanolayers with a high aspect ratio. Another reason for the
enhancements in the tensile modulus of BNCs is the strong interac-
tion between the matrix and silicate layer via formation of hydrogen
and chemical bonding. The extent of the improvement of modulus
depends directly upon the average length of the dispersed clay
particles and hence the aspect ratio and excellent enhancement in
the modulus is attributed to the uniformly dispersed silicate layers
[4]. The results also indicated significant increase in tensile strength
of the BNC materials, relative to that of the neat PAI. The incorpora-
tion of organoclay into the polymer reinforced the polymer, giving
the observed increase in this important property. The intimate
blending of the two phases, presumably with the covalent bonding
between them, provides a combination of some of the best properties
of the two components [6]. The maximum stress at break (ultimate
strength) was found to increase initially with increase in organoclay
content, and at 10 wt% organoclay showed a maximum value of
85.24 MPa (relative to the 67.52 MPa of the neat PAI) representing
significant enhancement in tensile strength. Further addition of
organoclay decreased the strength because of increasing brittleness.
LOI ¼ 17:5 þ 0:4 CR
Where CR ¼ char yield.
The BNCF5%, BNCF10% and BNCF15% have LOI values around 35
which were calculated from their char yield at 800 ꢁC. On the basis
of LOI values, all BNCFs can be classified as self-extinguishing
nanocomposites (Table 2). This enhancement in the char forma-
tion is ascribed to the high heat resistance exerted by the organo-
clay, because the organoclay have high thermal stability, so the
incorporation of organoclay can improve the thermal decomposi-
tion rate of the nanocomposites, although the initial decomposition
temperature does not increase.
3.4.7. Optical clarity of the BNCFs
Even though layered silicates are microns in lateral size, they are
just 1 nm thick. Thus, when single layers are dispersed in a polymer
matrix, the resulting nanocomposite is optically clear in visible
light. Owing to the nanoscale distribution of organo-nanoclay in
the PAI matrix, optical transparency remains high at different
organo-nanoclay contents. Fig. 8(aee) shows the UVevisible
transmission spectra of pure PAI and BNC materials with 2, 5,10 and
15 wt % of organoclay. These films had a thickness of w50e55 mm.
The spectra of BNCF2% and BNCF5% in the visible regions
(400e700 nm) were slightly affected by the presence of the clay
and retained the high transparency, indicating that exfoliated BNC
materials might exist at low clay contents. Furthermore, BNCF10%
and BNCF15% had a lower transparency than BNCF2% and BNCF5%
resulting from agglomeration of the clay particles. The translucency
of the BNCF comes from the nanoscale dispersion of the organoclay
particles in the matrix polymer.
Table 2
Thermal properties of the PAI and different BNCFs.
Polymer
Decomposition
temperature (ꢁC)
Char yield (%)b
LOIc
a
a
T5
T10
PAI
281
296
305
317
298
307
318
348
43
49
51
55
34.7
37.1
38.0
39.5
BNC5%
BNC10%
BNC15%
a
Temperature at which 5 and 10% weight loss was recorded by TGA at heating
rate of 10 ꢁC minꢀ1 in a N2 atmosphere.
b
Weight percent of the material left undecomposed after TGA at maximum
temperature 800 ꢁC in a N2 atmosphere.
c
Limiting Oxygen Index (LOI) evaluating at char yield at 800 ꢁC.
Fig. 9. Stress versus strain curves of pure PAI and different BNC films.

S. Mallakpour, M. Dinari / Polymer 52 (2011) 2514e2523
2523
At high clay loading, silicate layers may stack together in the form of
Acknowledgments
tactoids and the intergallery space does not increase much so that
more chains can travel into the space between the layers. These large
size particles then deteriorated the properties of the composites.
Further addition of organoclay decreased the strength because of
increasing brittleness [9]. The above results on mechanical prop-
erties suggested considerable reinforcement, presumably from the
bonding between the PAI chains and the organoclay. However, the
higher the molecular weight of the polymer, the fewer the end
groups available for bonding to the ceramic phase. Perhaps, orga-
noclay platelets in excess of those linkable to PAI chains contribute
obviously to the final brittleness that was observed.
We wish to express our gratitude to the Research Affairs Divi-
sion Isfahan University of Technology (IUT), Isfahan, for partial
financial support. Further financial support from National Elite
Foundation (NEF), Iran Nanotechnology Initiative Council (INIC)
and Center of Excellency in Sensors and Green Chemistry Research
(IUT) is gratefully acknowledged.
References
[1] Zulfiqar S, Lieberwirth I, Ahmad Z, Sarwar MI. Polym Eng Sci 2008;48:
1624e33.
4. Conclusions
[2] Pereira D, Losada PP, Angulo I, Greaves W, Cruz JM. Polym Compos 2009;30:
436e44.
[3] Ranade A, Dsouza A, Gnade B. Polymer 2002;43:3759e66.
[4] Ray SS, Okamoto M. Prog Polym Sci 2003;28:1539e641.
[5] Chow W, Bakar A, Ishak Z, Karger-Kocsis J, Ishiaku U. Eur Polym J 2005;41:
687e96.
[6] Zulfiqar S, Sarwar MI. J Incl Phenom Macrocycl Chem 2008;62:353e61.
[7] Zanetti M, Camino G, Thomann R, Mulhaupt R. Polymer 2001;42:4501e7.
[8] Pavlidou S, Papaspyrides CD. Prog Polym Sci 2008;33:1119e98.
[9] Zulfiqar S, Rafique M, Shaukat MS, Ishaq M, Sarwar MI. Colloid Polym Sci
2009;287:715e23.
[10] Kim ES, Shim JH, Woo JY, Yoo KS, Yoon JS. J Appl Polym Sci 2010;117:809e16.
[11] Yoo Y, Paul DR. Polymer 2008;49:3795e804.
[12] Wulff G. Angew Chem Int Ed 1989;28:21e37.
[13] Okamoto Y. Prog Polym Sci 2000;25:159e62.
[14] Wathier M, Johnson CS, Kim T, Grinstaff MW. Bioconjugate Chem 2006;17:
873e6.
One successful approach to the synthesis of nanocomposites is the
dispersion or break-down of inorganic nanoclay minerals consisting
of layered silicates into nanoscale building blocks in the polymer
matrices. The selection ofmodifierisimportantbecause itcan enlarge
the nanoclay galleries as well as improve the compatibility between
nanoclay and the polymer. Organoclay when added to the PAI matrix
reinforces materials with improved compatibility between the two
phases. In this investigation, the incompatibility between organo-
philic polymer and the hydrophilic layered silicates was resolved
through surface modification of the Clouisite Naþ nanoclay. Inview of
that, at first, Cloisite Naþ and protonated form of
L-tyrosine amino
acid was used for preparation of the novel chiral organoclay via ion-
exchange reaction. Then, novel optically active PAI containing
phenylalanine amino acid was synthesized via solution poly-
condensation of N,N’-(pyromellitoyl)-bis-phenylalanine diacid chlo-
ride with 4,40-diaminodiphenylsulfone in DMAc and then it was
selectively end-capped with amine end groups near the completion
of the reaction to interact chemically with modified organoclay.
Finally, novel PAI/organ-nanosilica BNCFs with different composi-
tions of the organoclay were prepared via solution intercalation
method. The nanostructure and properties of the synthesized orga-
noclay and PAI/organoclay hybrids were investigated using different
techniques. XRD, FE-SEM and TEM results revealed the formation of
intercalated and exfoliated organoclay platelets in the PAI matrix.
Thermal stability of BNCFs increased compared with pristine PAI
by increasing organoclay content. Tensile strength and modulus
improved for BNCFs with optimum organoclay content (10 wt.%).
Enhancement in the mechanical properties results from the fine
dispersionof the nanoclay particularly upto10 wt. % inBNC materials.
The presence of amino acids as a biodegradable segment in
both novel organo-modified nanoclay and optically active PAI,
make the obtained BNCs materials more susceptible for better
biodegradation process. These findings are important and relevant
to the preparation of low-cost, biodegradable and biocompatible
chiral organoclay and novel BNCs for industrial applications.
[15] Pilkington-Miksa MA, Writer MJ, Sarkar S, Meng QH, Barker SE, Shamlou PA,
et al. Bioconjugate Chem 2007;18:1800e10.
[16] Gigante A, Chillemi C, Bevilacqua C, Greco F, Bisaccia F, Tamburro AM. J Mater
Sci Mater Med 2003;14:717e20.
[17] Sanda F, Endo T. Macromol Chem Phys 1999;200:2651e61.
[18] Mallakpour S, Khani M, Rafiemanzelat F. J Appl Polym Sci 2008;108:2975e82.
[19] Yujiang F, Guoping C, Junzo T, Tetsuya T. Mater Sci Eng C 2004;24:791.
[20] Okada M. Prog Polym Sci 2002;27:87e133.
[21] Birchall AC, Bush SM, North M. Polymer 2001;42:375e89.
[22] Nakanot OY. Chem Rev 1994;94:349e72.
[23] Liaw D, Hsu P, Liaw B. J Polym Sci Polym Chem 2001;39:63.
[24] Liaw D, Liaw B. Polymer 2001;42:839e45.
[25] Ma X, Lee NH, Oh HJ, Hwang JS, Kim SJ. Nanoscale Res Lett 2010;5:1846e51.
[26] Liaw D, Chen W. Polym Degrad Stabil 2006;91:1731e9.
[27] Babooram K, Francis B, Bissessur R, Narain R. Compos Sci Technol 2008;8:
617e24.
[28] Mallakpou S, Kowsari E. Polym Sci Part A Polym Chem 2003;41:3974e88.
[29] Banihashemi A, Tamami B, Abdolmaleki A. J Iran Chem Soc 2004;1:141e51.
[30] Yang CP, Chen RS, Hung KS, Woo EM. Polym Int 2002;51:406e16.
[31] Mallakpour SE, Hajipour AR, Sakineh Habibi S. J Appl Polym Sci 2002;86:
2211e6.
[32] Vaia RA, Liu W. J Polym Sci B Polym Phys 2002;40:1590e600.
[33] Kiliaris P, Papaspyrides CD. Prog Polym Sci 2010;35:902e58.
[34] Xi Y, Frost RL, He H, Kloprogge T, Bostrom T. Langmuir 2005;1:8675e80.
[35] Strawhecker KE, Manias E. Chem Mater 2000;12:2943.
[36] Xie W, Gao Z, Pan WP, Hunter D, Singh A, Vaia R. Chem Mater 2001;13:2979.
[37] Frost R, Xi Y, He H. J Colloid Interface Sci 2007;305:150e8.
[38] Mallakpou S, Dinari M. Appl Clay Sci 2011;51:353e9.
[39] Van Krevelen DW, Hoftyzer PJ. Properties of polymers. 3rd ed. New York:
Elsevier Scientific Publishing; 1976.