Studies on syntheses and morphology characteristic of chiral novel poly(ester-imide)/TiO2 bionanocomposites derived from l-phenylalanine based diacid

Article abstract of DOI:10.1016/j.polymer.2010.09.063

In this study, a new optically active poly(ester-imide) (PEI) was synthesized from the polymerization reaction of N,N′-(pyromellitoyl)-bis-l-phenylalanine diacid with 4,4′-thiobis(2-tert-butyl-5-methylphenol) using tosyl chloride, pyridine and N,N-dimethy

Full text of DOI:10.1016/j.polymer.2010.09.063

Polymer 51 (2010) 5369e5376
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Polymer
journal homepage: www.elsevier.com/locate/polymer
Studies on syntheses and morphology characteristic of chiral novel poly(ester-
imide)/TiO2 bionanocomposites derived from -phenylalanine based diacid
L
,
b
,
a
Shadpour Mallakpour a , Samaneh Soltanian
*
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:
Received 8 July 2010
Received in revised form
21 September 2010
Accepted 25 September 2010
Available online 1 October 2010
In this study, a new optically active poly(ester-imide) (PEI) was synthesized from the polymerization
reaction of N,N0-(pyromellitoyl)-bis- -phenylalanine diacid with 4,40-thiobis(2-tert-butyl-5-methyl-
L
phenol) using tosyl chloride, pyridine and N,N-dimethyl formamide as a condensing agent. The obtained
polymer and inorganic metal oxide bionanocomposites composed of poly(ester-imide)/titanium dioxide
were synthesized through ultrasonic irradiation. The formation of PEI was confirmed by 1H NMR, fourier
transform IR spectroscopy (FT-IR), specific rotation and elemental analysis. The resulting bionanocompo-
sites were characterized by FT-IR, powder X-ray diffraction (XRD), atomic force microscopy)AFM(, scanning
electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), transmission electron
microscopy (TEM) and thermogravimetric analysis (TGA). The TEM, SEM and FE-SEM results indicated that
the nanoparticles were dispersed homogeneously in PEI matrix on nanoscale. TGA confirmed that the heat
stability of the nanocomposite was improved in the presence of TiO2 nanoparticles.
Keywords:
Optically active polymer
Bionanocomposites
Poly(ester-imide)
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
ceramic in the sense that some shapes of TiO2 show a strong
interfacial bonding to alive tissue by way of the creation of a bio-
Composite materials containing polymeric and inorganic units
have been attracting considerable attention as new materials
because they have novel optical, [1e3] mechanical, [4] electronic
properties, [5] as well as cosmetic and medicine applications [6]. The
applications of inorganic particles and analogous hybrid polymer-
inorganic composite material became imperative when chemists,
material scientists and physicists recognized that reduction in
dimensions of the particles results in the manifestation of a new
crystal motif, or conceivably a new physical phenomenon that does
not exist in materials with larger particle sizes [7].
Nanocomposites including biocompatible polymer matrix and
inorganic nanoparticle filler symbolize a novel group of composite
biomaterials for tissue engineering, scaffolds and biomedical
implants and devices. Titanium dioxide (TiO2) is one of the most
studied metal oxides in recent years, since it is economical and
nontoxic material, which has high refractive index and possesses
the ability to absorb ultraviolet light. TiO2 can act as a bioactive
logically active hydroxyapatite layer on the material surface [8,9].
TiO2 nanoparticles crystallize into three polymorphic forms: rutile,
anatase and brookite. The rutile shape is stable at high tempera-
tures and is generally obtained when pure TiO2 crystal is produced.
Anatase structure is less stable and forms at lower temperatures
and is chemically and optically more active in environmental
remediation than rutile particles. Brookite form occurs only in
excessive conditions and is very rare. The anatase to rutile transi-
tion is an irreversible procedure and usually happens within
a temperature range of 500e1000 ꢀC [10]. Because of photocatalytic
effects of TiO2 nanoparticles, they could decay a variety of organic
chemicals such as aldehyde, toluene and polymers for instance
polyethylene [11,12], polypropylene [13], polyvinylchloride [14] and
polystyrene [15]. Addition of TiO2 in macromolecule matrix can
supply substantial enhancement in the weatherability and dura-
bility of polymer products [8].
Ultrasonic irradiation has been broadly used in chemistry, medi-
cine, cleaning, machining, jointing and preparing nanocomposites
[16e20]. Thisroutcancontrol thesizedistributionandmorphologyof
the nanosized particles. As was known, the aggregation of nano-
particles is decreased and its dispersivity is highly improved [21].
Poly(ester-imide)s (PEI)s contain both ester and heterocycle
imide structures along the main chain of the polymer backbone and
* 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 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.09.063

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S. Mallakpour, S. Soltanian / Polymer 51 (2010) 5369e5376
Scheme 1. Synthesis of diacid (4).
possess high thermal stabilities, and are used as high-strength and
high-modulus fibers, aswellashigh-performanceengineeringresins
[22], being a promising matrix candidate for hybrid materials. Chiral
polymers have attracted a large deal of interest in the applications of
fields for instance drug delivery, tissue engineering, dentistry and
chiral stationary phases for resolution of enantiomers in chromato-
graphic techniques [23e25] due to their promising properties.
In this work, a novel optically active PEI having good thermal
stability as well as good solubility in common organic solvent, was
prepared, by direct polycondensation of optically active natural
amino acid based diacid and an aromatic diol using Vilsmeier adduct
derived from tosyl chloride (TsCl) and N,N-dimethylformamide
(DMF) in pyridine (Py) as a condensing agent. Then optically active
poly(ester-imide)/titanium dioxide (PEI/TiO2) bionanocomposites
were synthesized under ultrasonic irradiation. The resulting bion-
anocomposites are characterized by various techniques including
FT-IR, XRD, TGA and their morphology were investigated by SEM,
FE-SEM, AFM and TEM analyses.
2. Experimental
2.1. Materials
All chemicals were purchased from Fluka Chemical Co.
(Buchs, Switzerland), Aldrich Chemical Co. (Milwaukee, WI),
Riedel-deHaen AG (Seelze, Germany) and Merck Chemical Co.
Nanosized TiO2 powder was purchased from nanosabz Co.
with average particle sizes of 30e50 nm. Pyromellitic dianhy-
dride (benzen-1,2,4,5-tetracarboxylic dianhydride) (1) (from
Merck Chemical CO., Germany) was purified by recrystallization
from acetic anhydride follow by sublimation. DMF was dried
over BaO, followed by fractional distillation.
4,40-thiobis(2-tert-butyl-5-methylphenol) (TTMP) were used as
obtained without further purification. Coupling agent ( -ami-
dopropyl-triethoxyl silicane) (KH550) obtained from Merck
Chemical Co.
L-phenylalanine,
g
Scheme 2. Synthesis of the PEI.

S. Mallakpour, S. Soltanian / Polymer 51 (2010) 5369e5376
5371
Fig. 1. Preparation of PEI/TiO2 bionanocomposites.
2.2. Equipments
a Philips X’PERT MPD with a copper target at 40 kV and 35 mA
and Cu Ka l ¼ 1.54 Å in the range 10e80ꢀ at the speed of 0.05ꢀ/
min. Atomic force microscopy)AFM(topographic images were
obtained using Digital Multimode Instruments Nanoscope III
(Digital Instrument Inc.,USA) with noncontact tapping mode with
a silica probe (NSC 11) and a frequency of 463 kHz. Transmission
electron microscopy (TEM) analyses were performed using a Phi-
lips CM 120 operating at 100 kV. Field emission scanning electron
microscopy (FE-SEM) was acquired by JSM-6700S Japan. Scanning
electron microscopy (SEM) was obtained on the microscope of
Cambridge Oxford (UK) 7060 with four-quadrant backscattered
electron detector and with resolution 1/38 eV. The reaction was
carried out on a MISONIX ultrasonic liquid processors, XL-2000
SERIES. Ultrasound was a wave of frequency 2.25 ꢂ104 Hz and
power 100 W.
Proton nuclear magnetic resonance (1H NMR, 500 MHz)
spectra were carried out at a Bruker (Germany) Avance 500
instrument at room temperature (RT) in dimethylsulphoxide-d6
(DMSO-d6) using TMS (Si(CH3)4) as an international reference.
Multiplicities of proton resonance were designated as singlet (s),
doublet (d), 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
frequencies are reported in wave numbers (cmꢁ1). Band intensi-
ties are assigned as weak (w), medium (m), shoulder (sh), strong
(s) and broad (br). Inherent viscosities were measured by using
a CannoneFenske Routine Viscometer (Germany) at the concen-
tration of 0.5 g/dL at 25 ꢀC. Specific rotations were measured by
a Jasco Polarimeter (Japan). Thermal gravimetric analysis (TGA)
data for polymers were taken on a STA503 WinTA instrument in
a nitrogen atmosphere at a rate of 20 ꢀC/min. Elemental analyses
were performed by Isfahan University, Isfahan, I.R. Iran. The XRD
patterns of the polymer and nanocomposites were recorded using
2.3. Monomer synthesis
N,N0-(pyromellitoyl)-bis-
L-phenylalanine diacid (4) was prepared
according to our previous works [26] and is shown in Scheme 1.
Fig. 2. FT-IR spectra of (a) pure TiO2 nanoparticles, (b) TiO2 nanoparticles modified by
Fig. 3. FT-IR spectra of (a) PEI/TiO2 (5 wt%), (b) PEI/TiO2 (10 wt%), (c) PEI/TiO2 (15 wt%),
KH550 (c) pure PEI (d) PEI/TiO2 (5 wt%).
(d) PEI/TiO2 (20 wt%), (e) PEI/TiO2 (25 wt%).

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S. Mallakpour, S. Soltanian / Polymer 51 (2010) 5369e5376
irradiated under ultrasound waves for 4 h. The resulting mixture was
centrifuged. The obtained solid was dried in vacuum at 80 ꢀC for 2 h.
3. Results and discussion
3.1. Fabrication of PEI/TiO2 bionanocomposites
Fabrication of PEI/TiO2 bionanocomposites was performed by an
ultrasonic irradiation technique [27]. The process is depicted in
Fig. 1. Under ultrasonic conditions, the coupling agent KH550
hydrolyzes to form hydroxyls and then polycondensation will occur
to form SieOeSi bonds. On the other hand hydroxyl group on the
surface of TiO2 will replace with OEt of the KH550 to link to it.
Commonly, the main effects of sonication are because of cavitation
or the growth and explosive disintegration of microscopic bubbles
on a microsecond timescale. At the same time, ultrasonic cavitation
can generate a rigorous environment of local temperature up to
5000 K and local pressure up to 500 atm [28]. Under such condi-
tions the modified TiO2 nanoparticles which have polar group of
coupling agent and OH group on the surface of TiO2, could be
dispersed completely in polymer matrix via different interactions
with the functional groups of the obtained PEI. Although the
resulting PEI has lots of polar groups such as carbonyl, nitrogen and
sulphur, but with respect to these functional groups they are not
much difference between FT-IR spectra of resulting bionono-
composites with that of pure PEI (Fig. 2) except for the TieOeTi
bands which proves the presence of TiO2 in the PEI matrix. Thus,
the relatively weak interaction is thought to be a hydrogen bond,
and also short-ranged steric and electrical interaction between
active sites of TiO2 and different functional groups of PEI. As a result
the polymer on the nanoparticle surface has a steric dispersing and
stabilizing effect, which can be observed from the photographs of
TEM and SEM.
Fig. 4. XRD curves of (a) PEI (b) pure TiO2 nanoparticles (c) PEI/TiO2 (10 wt%), (d) PEI/
TiO2 (15 wt%).
2.4. Polymer synthesis
PEI 6 was synthesized by the direct polycondensation reaction
of an equimolar mixture of diol 5 with diacid 4 in a system of TsCl/
Py/DMF as condensing agent (Scheme 2). For the polymerization of
optically active diacid with aromatic diol, a Vilsmeier adduct was
prepared by the following procedure: a solution of Py (0.20 ml;
2.5 ꢂ 10ꢁ3 mol) with TsCl (0.18 g; 9.75 ꢂ 10ꢁ4 mol) after 30 min
stirring at room temperature, was treated with DMF (0.09 ml;
1.22 ꢂ 10ꢁ3 mol) for 30 min and the mixture was added dropwise
to a solution of diacid (4) (0.10 g; 1.95 ꢂ 10ꢁ4 mol) in Py (0.20 ml).
The mixture was maintained at room temperature for 30 min and
then TTMP (5) (0.07 g; 1.95 ꢂ 10ꢁ4 mol) was added and the whole
solution was stirred at 120 ꢀC for 6 h. Then the viscous liquid was
precipitated in 30 ml of methanol to yield 0.14 g (86%) of the
polymer 6. The inherent viscosity of the resulting PEI was obtained
0.17 dL/g. The amalgamation of a chiral unit into the polymer
backbone was obtained by measuring the specific rotation of
3.2. Spectral data
FT-IR spectra of pure TiO2 nanoparticles (a), TiO2 modified by
KH550 (b), pure PEI (C), PEI/TiO2 (5 wt%) (d) are represented in Fig. 2.
In pure TiO2, OH stretching and bending bands are observed at 3423
and 1637 cmꢁ1, respectively. The broader bands at 3500 and
3422 cmꢁ1 were credited to hydroxyl groups on different sites and
some various interactions between hydroxyl groups on TiO2,
respectively [29]. A broad absorption peak at 500e800 cmꢁ1 is
assignedtothe TieOeTistretchingband. In the case of TiO2 modified
by KH550, The peak at 2870e2928 cmꢁ1 is attributed to CH
stretching band of KH550, that these stretching bands are not
observed in pure TiO2. The FT-IR spectrum of pure PEI showed the
characteristic absorptions of imide and ester groups around 1765
and 1725 cmꢁ1, which are related to carbonyls stretching of imide
andestergroups, respectively. Thepeaks at 1380and 727 cmꢁ1 show
the existence of the imide heterocycle in this polymer. FT-IR spec-
trum of PEI/TiO2 (5 wt%) is shown in Fig. 2(d), where the charac-
teristic peaks of pure PEI and TiO2 are still maintained, it may be
proved that the structure of PEI was affected by the presence of TiO2.
FT-IR spectrums of bionanocmposites with different amounts of
TiO2 (5, 10, 15, 20, 25 wt%) nanoparticles are shown in Fig. 3. From
these data it is clear that with increasing the amount of nano-
particles the intensity of absorption related to TieOeTi bonds was
enhanced.
polymer ð½a 2D5
ꢃ Þ. It was obtained to be þ22 (measured at a concen-
tration of 0.5 g/dL in DMF at 25 ꢀC).
FT-IR (KBr, cmꢁ1): 3438 (w, br), 3028 (w), 2959 (m), 2869 (w),
1765 (s), 1729 (s), 1638 (w), 1603 (w), 1525 (w), 1482 (w),1455
(w), 1380 (s), 1366 (m), 1217 (m), 1171 (m), 1093 (m), 1032 (w), 1010
(w), 728 (m). 1H NMR (500 MHz, DMSO-d6,
d, ppm): 0.9e1.2 (S,
18H), 2.15e2.24 (S, 6H), 3.42 (m, 2H), 3.62 (m, 2H), 5.58 (m, 2H),
6.75e7.16 (m, 14H, AreH), 8.26 (s, 2H), 9.66 (s, OH end group) ppm.
Elemental analysis: calcd. for (C50H46N2O8S): C, 71.92%; H, 5.55%;
N, 3.36%; S, 3.84%. Found: C, 71.42%; H, 5.57%; N, 3.76%; S, 3.99%.
2.5. Preparation of PEI/TiO2 bionanocomposites
The preparationofPEI/TiO2 bionanocompositeswascarried out by
the following procedure: TiO2 nanoparticles (0.3 g) was added into
acetone (10 mL), and 10 wt% of silane coupling agent (KH550) was
dissolved in H2O (10 mL). Then the mixture of nanoparticles and
KH550 wasirradiated under ultrasonicradiationfor 30 min, afterthat
centrifuged and dried. Different amounts of modified TiO2 nano-
particles (5, 10, 15, 20, 25 wt%) were mixed with the new PEI and the
mixture was dispersed in 20 mL of absolute ethanol and then
3.3. X-ray diffraction data
Fig. 4 shows XRD curves of PEI (a), pure TiO2 (b), PEI/TiO2 (10 wt
%) (c) and PEI/TiO2 (15 wt%) (d). The broad peak in XRD curve of PEI
shows that the PEI in the absence of TiO2 nanoparticles is

S. Mallakpour, S. Soltanian / Polymer 51 (2010) 5369e5376
5373
Fig. 5. SEM micrographs of (a and b) pure PEI, (c and d) PEI/TiO2 (10 wt%), (e) PEI/TiO2 (15 wt%).
amorphous. Presence of the non-coplanar and twisted units into
the backbone of polymer decreased the intermolecular forces
between the polymer chains and reduced the crystallinity of this
polymer. Fig. 4(b) shows anatase and rutile phase for pure TiO2
nano particles. The XRD patterns of PEI/TiO2 bionanocomposites (c)
and (d) show characteristic peaks of anatase and rutile of TiO2 and
PEI, respectively, indicating that the morphology of TiO2 nano-
particles has not been disturbed during the process. The wide weak
diffraction peak of PEI still exists, but its intensity decreases. The
average crystalline size of nano-TiO2, which has been determined
Fig. 6. FE-SEM micrographs of PEI/TiO2 (10 wt%).

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S. Mallakpour, S. Soltanian / Polymer 51 (2010) 5369e5376
Fig. 7. The two and three dimension AFM topography images of (a and b) pure PEI, (c and d) PEI/TiO2 (10 wt%), (e and f) PEI/TiO2 (15 wt%).
from the half-width of the diffraction using the DebyeeScherrer
equation, is approximately 15 nm. Sherrer’s equation is as follows:
[30]
good compatibility and homogeneous distribution of nanoparticles
in the polymer matrix. FE-SEM images of PEI/TiO2 (10 wt%) is
illustrated in Fig. 6. As can be seen, the bionanocomposite offered
a homogeneous microstructure and dispersed as global beads.
Surface topography of the bionanocomposites was investigated
by AFM. The three and two dimension AFM images of the pure PEI,
PEI/TiO2 (10 wt%) and PEI/TiO2 (15 wt%) are displayed in Fig. 7.
Compared with the surface morphology of pure PEI and surface
morphology of PEI bionanocomposites, a number of small bulges
are observed on the surface. The size of the bulge was enhanced
with an increase of TiO2 nanoparticles content in the PEI, therefore
the bulges should be TiO2 nanoparticles, indicating that some TiO2
nanoparticles exist at PEI surface and appear in nanoscale
comparing with smooth surface of pure PEI.
0:9
b
l
D ¼
cos
q
Where D is the crystallite size,
l
is wavelength of the radiation,
q is
the Bragg’s angle and
b is the full width at half maximum.
3.4. Morphology
Fig. 5 shows the SEM of pure PEI (a and b), PEI/TiO2 (10 wt%)
(d and c) and PEI/TiO2 (15 wt%) (e) nanocomposites, which indicates

S. Mallakpour, S. Soltanian / Polymer 51 (2010) 5369e5376
5375
Fig. 8. TEM micrographs of PEI/TiO2 (15 wt%).
LOI ¼ 17:5 þ 0:4CR
where CR ¼ char yield.
From these data it is clear that the PEI had a high decomposition
temperature of about 380 ꢀC, which was further improved when
TiO2 was introduced. Incorporation of inorganic nanoparticles in
polymer matrix improves its thermal stability. Increasing in the
thermal stability may consequence from the high thermal stability
of TiO2 network and the physical crosslink points of the TiO2
particles, which restricted the movement of the molecular chain of
PEI. The char yield of pure PEI at 800 ꢀC are 26%, whilst those of the
bionanocomposites (PEI/TiO2 5, 10, 15, 20, 25 wt%) at 800 ꢀC are in
the range of 41e62%, they were enhanced with an increase of TiO2
nanoparticles content in the PEI. The high weight residue of the PEI
can be arisen from the participation of thermally stable aromatic
rings and imide group in its repeating unit and the rigid architec-
ture of this polymer.
Fig. 9. TGA thermograms of PEI and PEI/TiO2 bionanocomposites under a nitrogen
atmosphere at heating rate of 20 ꢀC/min.
Fig. 8 shows the TEM micrographs of PEI/TiO2 (15 wt%) biona-
nocomposite. Some discrete TiO2 domains and homogeneously and
well-dispersed in PEI matrix are observed obviously. The nano
particle sizes of TiO2 are in the range of 30e70 nm.
5. Conclusions
In the present study, a novel thermally stable and optically
active PEI was successfully prepared by direct polycondensation
method. The polymerization was carried out by the reaction of
natural amino acid based diacid (4) with aromatic diol TTMP (5)
using TsCl/DMF/Py as condensing agent. The prepared PEI is ther-
mally stable and soluble in common organic solvents. Novel PEI/
TiO2 bionanocomposites were synthesized by ultrasonic method as
a simple and inexpensive route to prepare the polymer/nano-
particles, using TiO2 nanoparticles modified by KH550. The surface
modification of inorganic particles by similar molecular chains
to those of an organic matrix is a useful way to improve the
compatibility between the organic and the inorganic phases.
The modification would make the nanoparticles scatter within the
matrix more homogeneously. Moreover, the molecules grafted onto
the nanoparticles would interact with the matrix, thus the final
mechanical properties could be greatly improved. Morphology
study of resulting bionanocomposites showed well-dispersed TiO2
nanoparticles in the polymer matrix by AFM, SEM, FE-SEM and TEM
analyses. TGA studies indicated that thermal stability of the bion-
anocomposites has enhanced with increasing nanoparticles
content. FT-IR and XRD data also confirmed that TiO2 nanoparticles
are dispersed in the PEI matrix. Since this PEI has amino acid in its
polymer architecture, it could be categorized under environmen-
tally benign polymers and could be composted with organic wastes
and recycled to enrich the soil. Also, it has the potential to be used
as optically active packing materials in column chromatography for
the resolution of racemic mixtures. Polymers that are synthesized
from naturally occurring building blocks such as amino acids are
4. Thermal properties
The thermal properties of the PEI and PEI/TiO2 bionanocompo-
sites were evaluated by TGA at a heating rate of 20 ꢀC/min, under
a nitrogen atmosphere (Fig. 9). Table 1 shows the data for the
thermal degradation of the PEI and its bionanocomposites,
including the temperature at which 5% (T5) and 10% degradation
occurs (T10), char yield at 800 ꢀC and also limiting oxygen index
(LOI) [31].
Table 1
Thermal properties of the PEI and PEI/TiO2 bionanocomposites.
Polymer
T5 (ꢀC)a
T10 (ꢀC)b
Char Yield(%)c
LOId
PEI
387
394
408
412
417
424
410
417
423
425
429
433
26
41
53
55
57
62
27.9
33.9
38.7
39.5
40.3
42.3
PEI/TiO2 (5 wt%)
PEI/TiO2 (10wt%)
PEI/TiO2 (15 wt%)
PEI/TiO2 (20 wt%)
PEI/TiO2 (25 wt%)
a
Temperature at which 5% weight loss was recorded by TGA at heating rate of
20 ꢀC/min under a nitrogen atmosphere.
b
Temperature at which 10% weight loss was recorded by TGA at heating rate of
20 ꢀC/min under a nitrogen atmosphere.
c
weight percentage of material left undecomposed after TGA analysis at
a temperature of 800 ꢀC under a nitrogen atmosphere.
d
Limiting oxygen index (LOI) evaluating char yield at 800 ꢀC.

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We wish to express our gratitude to the Research Affairs Divi-
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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
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