Influence of ionic liquid on selective polycondensation of a new diamine-bisphenol: Synthesis and properties of polyamides and their composites with modified nanosilica

Article abstract of DOI:10.1016/j.polymer.2013.05.043

This work reports that imidazolium-based ionic liquids (ILs) are very efficient solvents and catalysts for the selective synthesis of novel high performance polyamides (PAs) from a new diamine-bisphenol. Direct polycondensation of the diamine-bisphenol was carried out with various dicarboxylic acids by using mixture of: (1) triphenylphosphite (TPP)/N-methylpyrolidone (NMP)/pyridine (Py)/LiCl; and (2) IL/TPP. The PAs were obtained in no more than 2.5 h at 110 C, which is considerably shorter than the conventional direct polycondensation, with mass-average molar mass (M _w) up to 61,000 g mol^-1, glass transition temperatures (T_g) up to 325 C and 10% weight loss temperatures (T_10%) up to 511 C (in N₂) and 456 C (in air). Nanocomposites of these PAs with modified nanosilica (mNS) showed that strong chemical bonding between inorganic particles and the polymer matrix contributed to the enhanced thermal and mechanical properties. The photoluminescence intensity of the PAs increased and the spectra red shifted with increasing mNS content. The PAs and nanocomposites were tested for their extraction capability of metal ions such as Cr³⁺, Co²⁺, Zn²⁺, Pb²⁺, Cd ²⁺, Hg²⁺ and Fe³⁺ from aqueous solutions either individually or in the mixture.

Full text of DOI:10.1016/j.polymer.2013.05.043

Polymer xxx (2013) 1e13
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Influence of ionic liquid on selective polycondensation of a new
diamine-bisphenol: Synthesis and properties of polyamides and their
composites with modified nanosilica
*
Mehdi Taghavi, Mousa Ghaemy , Seyed Mojtaba Amini Nasab, Marjan Hassanzadeh
Polymer Chemistry Research Laboratory, Department of Chemistry, University of Mazandaran, Babolsar 47416-95447, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
This work reports that imidazolium-based ionic liquids (ILs) are very efficient solvents and catalysts for
the selective synthesis of novel high performance polyamides (PAs) from a new diamine-bisphenol.
Direct polycondensation of the diamine-bisphenol was carried out with various dicarboxylic acids by
using mixture of: (1) triphenylphosphite (TPP)/N-methylpyrolidone (NMP)/pyridine (Py)/LiCl; and (2) IL/
TPP. The PAs were obtained in no more than 2.5 h at 110 ꢀC, which is considerably shorter than the
conventional direct polycondensation, with mass-average molar mass (Mw) up to 61,000 g molꢁ1, glass
transition temperatures (Tg) up to 325 ꢀC and 10% weight loss temperatures (T10%) up to 511 ꢀC (in N2) and
456 ꢀC (in air). Nanocomposites of these PAs with modified nanosilica (mNS) showed that strong
chemical bonding between inorganic particles and the polymer matrix contributed to the enhanced
thermal and mechanical properties. The photoluminescence intensity of the PAs increased and the
spectra red shifted with increasing mNS content. The PAs and nanocomposites were tested for their
extraction capability of metal ions such as Cr3þ, Co2þ, Zn2þ, Pb2þ, Cd2þ, Hg2þ and Fe3þ from aqueous
solutions either individually or in the mixture.
Received 20 February 2013
Received in revised form
30 April 2013
Accepted 5 May 2013
Available online xxx
Keywords:
Ionic liquids
Polyamide
Nanocomposite
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
aromatic PAs, many researchers have focused on development of
structurally modified PAs with increased solubility and better
In recent years much attention has been given to reusability of
solvents and catalysts for the development of cost-effective pro-
tocols [1]. Ionic liquids (ILs) are organic salts that are liquid at
ambient temperatures and act much like good organic solvents
dissolving both polar and nonpolar species [2,3]. Since the concept
of green chemistry has emerged, much attention has been paid to
organic chemistry processes involving ILs as non-volatile, easily
recyclable reaction media of high thermal and chemical stabilities.
These characteristics have made them as potential green solvents
for preparing polymers with various polymerization mechanisms
[4,5]. Most polycondensation studies were relative to the synthesis
of aromatic polymers such as polyamides, polyimides, poly-
hydrazides or polyoxadiazoles in a range of conventional ionic
liquids [6e9]. Polyamides (PAs) are one of the high-performance
polymeric materials and are characterized by thermo oxidative
stability, good mechanical properties, and outstanding solvent
resistance [10e12]. However, because of difficulty in processing
processability through introducing bulky side groups [13e18]
flexible units [19e21] and breaking symmetry and regularity of
the polymer chain [22e24]. Organic-inorganic hybrid materials
have been paid on much attention in the last decades due to the
synergetic effect of organic and inorganic components in nano-
scales. The combination of organic and inorganic components is
expected to provide remarkable and complementary properties,
which cannot be obtained with
a single material [25e27].
Compared to composites containing larger dispersed particles,
nanocomposites have the advantage of achieving the optimal
properties at relatively low filler content, resulting in a lower
density and better surface smoothness and transparency. The ad-
vantages in mechanical properties of nanocomposites, such as the
higher modulus and yield stress, are usually accompanied by an
increase in melt viscosity and a change in rheological behaviour
[28e32]. In this paper, for the first time, synthesis and character-
ization of new polyamides from a tetrafunctional compound con-
taining both eNH2 and eOH groups is described. The PAs were
synthesized selectively from the diamine-bisphenol compound in
the mixture of IL/TPP without using Py/NMP/LiCl which is required
in the conventional direct polycondensation. The PAs which were
* Corresponding author. Tel.: þ98 112 5342353; fax: þ98 112 5342350.
E-mail address: ghaemy@umz.ac.ir (M. Ghaemy).
0032-3861/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2013.05.043
Please cite this article in press as: Taghavi M, et al., Influence of ionic liquid on selective polycondensation of a new diamine-bisphenol:
Synthesis and properties of polyamides and their composites with modified nanosilica, Polymer (2013), http://dx.doi.org/10.1016/
j.polymer.2013.05.043

2
M. Taghavi et al. / Polymer xxx (2013) 1e13
obtained in IL and bearing reactive phenolic hydroxyl groups were
used in preparation of composites chemically bounded with
modified NS particles. The PAs and nanocomposites were charac-
terized by using FT-IR, NMR, XRD and AFM techniques and their
properties such solubility, thermal, photophysical, mechanical and
ability for removal of environmentally toxic heavy metal ions were
investigated.
(0.20 g/dL) in DMSO. To measure the photoluminescence (PL)
quantum yields (Ff), dilute PAs solutions (0.2 g/dL) in NMP were
prepared. A 0.10 N solution of quinine in H2SO4 (Ff ¼ 0.53) was used
as a reference [33]. To prepare crack-free and homogeneous thin
films for the measurement of optical properties, solutions were
made by dissolving about 0.5 g of polymer in 5 mL DMF to afford an
approximate 10 wt% solution. The homogeneous solution was
poured into a 9 cm-diameter glass culture dish, heated under
vacuum at 50 ꢀC for 2 h, 100 ꢀC for 5 h, and 150 ꢀC for 3 h to
evaporate the solvent slowly. Polymer films were self-stripped off
from the glass surface by soaking in water. The polymer films were
further dried in vacuum oven at 170 ꢀC for 10 h. X-ray powder
diffraction patterns were recorded by an X-ray diffractometer (GBC
MMA instrument) with Be-filtered Cu K (1.5418 Aꢀ) operating at
2. Experimental
2.1. Materials
All chemicals were purchased from Fluka and Merck Chemical
Co. (Germany). Ammonium acetate, hydrazine monohydrate, 10%
palladium on activated carbon, (3-chloropropyl)trimethoxysilane
(CTMS), terephthalic acid, isophthalic acid, pyridine-2,6-
dicarboxylic acid, 4,40-sulfonyldibenzoic acid, adipic acid and se-
bacic acid were used as received. N-methyl-2-pyrrolidone (NMP),
N,N-dimethylacetamide (DMAc), and pyridine (Py) were purified by
distillation under reduced pressure over calcium hydride and
stored over 4 Å molecular sieves. NS was purchased from Nissan
Chemical Co. (Tokyo, Japan). Characteristic data for NS particles are
absorption bands at 3397 and 1106 cmꢁ1 related to hydroxyl
and SieOeSi groups, respectively. 4,40-dihydroxy benzyl was syn-
thesized and characterized recently in our research laboratory [23].
All ionic liquids were prepared by using previously reported
procedure [33].
35.4 kV and 28 mA. The 2q
scanning range was set between 4ꢀ and
50ꢀ at a scan rate of 0.05ꢀ pers. Atomic force microscopic (AFM)
Easy Scan 2 Flex AFM (Swiss Co), was used to investigate the surface
phase and topography of the nanocomposites. Branson S3200
(50 kHz, 150 W) ultrasonic bath was used for better dispersion of
nanoparticles. To determine the tensile properties of the polymers,
strips (5 mm in width and 30 mm in length) were cut from polymer
films of 30e50 mm thickness on a MTS CriterionÔ Universal Test
Systems at 20 ꢀC. Mechanical clamps were used and an extension
rate of 5 mm minꢁ1 was applied using a gauge length of 10 mm. At
least six samples were tested for each polymer and the average
values are reported. The solideliquid extraction of Hg2þ, Cd2þ, Ni2þ
,
Co2þ, Cu2þ, Cr3þ and Fe3þ as their nitrate salts was carried out at
pH ¼ 7e8 from metal aqueous solutions either individually or in
the mixture. Approximately 50 mg of the appropriate polymer
powder was shaken with 50 mL of an aqueous solution of the metal
salt for a week at 25 ꢀC (equilibrium was assessed in less than three
days). The initial concentration of salts was 20 mg Lꢁ1. After
filtration, the concentration of each metal cation in the liquid phase
was determined by atomic absorption (BRAIC WFX-130 AA), and
direct information regarding the extraction percentages of metal
ions by polymers was obtained by using a calibration curve made
from standard solutions of 5, 10, and 20 ppm for each metal salts.
2.2. Measurements
Proton and carbon nuclear magnetic resonance (1H NMR and 13
C
NMR) spectra were recorded on a 400 MHz Bruker Avance DRX
instrument (Germany) using DMSO-d6 as solvent and tetramethyl
silane as an internal standard. Proton resonances are designated as
singlet (s), doublet (d), and multiplet (m). FT-IR spectra were
recorded using a Bruker Tensor 27 spectrometer on KBr pellets over
the range of 400e4000 cmꢁ1. Elemental analyses performed by a
CHN-600 Leco elemental analyzer. Melting point (uncorrected) was
measured with a Barnstead Electrothermal engineering LTD 9200
apparatus. Inherent viscosities (at a concentration of 0.5 g/dL) were
measured with an Ubbelohde suspended-level viscometer at 25 ꢀC
using NMP as solvent. Quantitative solubility was determined using
0.05 g of a polymer in 0.5 mL of solvent. For the moisture absorption
measurement, 200 mg polymer powder was dried at 120 ꢀC for 8 h
and then placed in an open space with a relative humidity of 80%.
The samples were weighed periodically over the course of 48 h. The
GPC measurements were conducted at 30 ꢀC with a PerkineElmer
instrument equipped with a differential refractometer detector. The
columns used were packed with a polystyrene/divinylbenzene
copolymer (PL gel MIXED-B from Polymer Laboratories) with DMF
as fluent at a flow rate of 1 mL/min. Calibration of the instrument
was done with monodisperse polystyrene standards. Thermogra-
vimetric analysis (TGA) was performed with the DuPont In-
struments (TGA 951) analyzer at a heating rate of 10 ꢀC/min under
N2 (20 cm3/min) and in air in temperature range of 30e650 ꢀC.
Differential scanning calorimeter (DSC) was recorded on a Perkin
Elmer pyres 6 DSC under nitrogen atmosphere (20 cm3/min) at a
heating rate of 10 ꢀC/min. Glass-transition temperatures (Tg) values
were read at the middle of the transition in heat capacity and ꢀwere
taken from the second heating scan after cooling from 350 Cꢁt1o
2.3. Monomer synthesis
2.3.1. Synthesis of 2,4-bis(4-nitrophenoxy)benzaldehyde (1)
In a 500 mL round-bottomed two-necked flask equipped with a
condenser, a magnetic stir bar and a nitrogen gas inlet tube, a
mixture of 1.38 g (10 mmol) 2,4-dihydroxy benzaldehyde, 2.82 g
(20 mmol) 1-fluoro-4-nitrobenzene, and 2.76 g (20 mmol) anhy-
drous potassium carbonate in 10 mL dry DMSO was refluxed at
120 ꢀC for 12 h. After completion of the reaction (as witnessed by
TLC test), the solution was cooled to room temperature. The reac-
tion mixture was poured into 400 mL deionized water. The
resulting yellowish powder was collected by filtration, washed
with water repeatedly, dried in a vacuum oven and then recrys-
tallization from ethanol. The yield of the reaction was 93% (3.55ꢁg1),
and the melting point was 152e156 ꢀC. FT-IR (KBr disk) at cm
:
3105 (CeH aromatic), 2842 (CeH aldehyde), 1684 (C]O aldehyde),
1583 (C]C), 1522, 1350 (NO2) and 1229 (CeOeC). 1H NMR
(500 MHz, DMSO-d6,
d
in ppm): 7.08 (d, 1H, AreH, J ¼ 2.1 Hz), 7.19
(dd,1H, AreH, J ¼ 8.0 Hz), 7.29e7.38 (m, 4H, AreH), 8.03 (d,1H, Are
H, J ¼ 8.5 Hz), 8.26e8.34 (m, 4H, AreH), 10.16 (s,1H, CeH aldehyde).
Elemental analysis calculated for C19H12N2O7: C, 60.00%; H, 3.18%;
N, 7.37% and found: C, 59.98%; H, 3.25%; N, 7.32%.
room temperature (w30 ꢀC) at a cooling rate of 20 ꢀC min
.
Ultraviolet-visible and fluorescence emission spectra were recor-
ded on a Cecil 5503 (Cecil Instruments, Cambridge, UK) and Per-
kineElmer LS-3B spectrophotometers (Norwalk, CT, USA) (slit
width ¼ 2 nm), respectively, using a dilute polymer solution
2.3.2. Synthesis of 4,40-(2-(2,4-bis(4-nitrophenoxy)phenyl)-1H-
imidazole-4,5-diyl) diphenol (2)
In a 500 mL round-bottomed two-necked flask equipped with a
condenser, a magnetic stir bar and a nitrogen gas inlet tube, a mixture
Please cite this article in press as: Taghavi M, et al., Influence of ionic liquid on selective polycondensation of a new diamine-bisphenol:
Synthesis and properties of polyamides and their composites with modified nanosilica, Polymer (2013), http://dx.doi.org/10.1016/
j.polymer.2013.05.043

M. Taghavi et al. / Polymer xxx (2013) 1e13
3
of 3.8 g (0.01 mol) 2,4-bis(4-nitrophenoxy)benzaldehyde, 2.1 g
(0.01 mol) 4,40-dihydroxy benzil, 2.42 g (0.07 mol) ammonium acetate
and 50 mL glacial acetic acid was refluxed for 24 h. Upon cooling, the
white precipitate was collected by filtration and washed with ethanol
and water. The yield of the crude product was 5.5 g (91%). The crude
product was recrystallized from ethanol to afford white solid with
melting point 312e315 ꢀC. FT-IR (KBr disk) at cmꢁ1: 3208e3550 (OH
and NH imidazole), 3115 (CeH aromatic), 1615 (C]N), 1588 (C]C),
2.4.2. Direct polycondensation using TPP/IL
Into a 50 mL three-necked round-bottomed flask fitted with a
water cooled condenser, a mechanical stirrer and a nitrogen gas
inlet tube, a mixture of compound 3 (1 mmol, 0.54 g), a dicarboxylic
acid (1 mmol), 1,3-dipropyl imidazolium bromide {[1,3-(pr)2im]Br}
(0.70 g), and TPP (1.29 mmol) was placed. The mixture was heated
at 110 ꢀC for 2.5 h, the solution became viscous as the reaction
proceeded. The reaction mixture was then cooled to room tem-
perature and the resulting polymers were precipitated in 100 mL
methanol. The precipitate was filtered and washed with hot water,
and then was further purified by washing with refluxing methanol
for 24 h in a Soxhlet apparatus to remove the low molecular weight
oligomers. The inherent viscosity (hinh) of the resulting PAs,
measured at a concentration of 0.5 g/dL in NMP at 25 ꢀC, was be-
tween 0.52 and 0.91 dL gꢁ1. The above procedure was used for the
preparation of all PAs, as shown in Scheme 1.
1521, 1352 (NO2),1266 and 1228 (CeO).1H NMR (DMSO-d6,
d inppm):
6.49 (dd,1H, AreH, J ¼ 8.2 Hz), 6.61 (d,1H, AreH, J ¼ 2.4), 6.68 (d, 2H,
AreH, J ¼ 8.4 Hz), 6.70 (d, 2H, AreH, J ¼ 8.4 Hz), 6.96 (d, 1H, AreH,
J ¼ 8.2 Hz), 7.04 (d, 2H, AreH, J ¼ 8.4 Hz), 7.18 (d, 2H, AreH, J ¼ 8.4 Hz),
7.29 (d, 2H, AreH, J ¼ 8.4 Hz), 7.53(d, 2H, AreH, J ¼ 8.4 Hz), 8.21 (d, 2H,
AreH, J ¼ 8.4 Hz), 8.27 (d, 2H, AreH, J ¼ 8.4 Hz), 9.46 (s, 1H, OH
phenol), 9.70 (s, 1H, OH phenol), 12.10 (s, 1H, NH imidazole ring). 13
C
NMR (100 MHz, DMSO-d6,
d in ppm): 108.07, 110.59, 112.69, 115.65,
116.11, 118.78, 120.11, 124.77, 124.83, 126.66, 127.90, 129.29, 130.20,
130.53, 133.03, 135.96, 142.95, 143.15, 143.79, 147.40, 156.48, 156.90,
158.01, 158.84 and 162.34. Elemental analysis calculated for
PA1: Yield ¼ 88% and hinh ¼ 0.72 dL/g. FT-IR (KBr disk) at cmꢁ1
:
3194e3483 (OH, NH amide and NH imidazole), 3094 (CeH ar-
omatic), 1682 (C]O amide), 1611 (C]N), 1543 (C]C), 1252 and
C33H22N4O8: C, 65.78%; H, 3.65%; N, 9.30% and found: C, 65.71%; H,
3.68%; N, 9.29%.
1214 (CeO). 1H NMR (DMSO-d6,
d in ppm): 6.20e8.08 (m, 23H,
AreH), 9.50 (s, 1H, OH phenol), 9.66 (s, 1H, OH phenol), 10.48 (s,
1H, NH amide), 10.59 (s, 1H, NH amide), 13.63 (s, 1H, NeH,
2.3.3. Synthesis of 4,40-(2-(2,4-bis(4-aminophenoxy)phenyl)-1H-
imidazole-4,5-diyl) diphenol (3)
imidazole
ring).
Elemental
analysis
calculated
for
To a 250 mL round-bottomed three-necked flask equipped with
a dropping funnel, a reflux condenser and a magnetic stir bar,
(C41H28N4O6)n: C, 73.21%; H, 4.17%; N, 8.33%. Found: C, 73.16%; H,
4.20%; N, 8.33%.
6.02
g
(0.01 mol) 4,40-(2-(2,4-bis(4-nitrophenoxy)phenyl)-1H-
PA2: Yield ¼ 83% and hinh ¼ 0.67 dL/g. FT-IR (KBr disk) at cmꢁ1
:
imidazole-4,5-diyl)diphenol and 0.2 g palladium on activated
carbon (Pd/C, 10%), were dispersed in 80 mL ethanol. The sus-
pension solution was heated to reflux, and 8 mL of hydrazine
monohydrate was added slowly to the mixture. After a further 5 h
of reflux, the solution was filtered hot to remove Pd/C, and the
filtrate was cooled to give white crystals. The product was
collected by filtration and dried in vacuum oven at 80 ꢀC. The yield
of the reaction was 81% (4.4 g), and the melting point was 273e
275 ꢀC. FT-IR (KBr disk) at cmꢁ1: 3222e3546 (OH, NH2 and NH
imidazole), 3111 (CeH aromatic), 1615 (C]N), 1588 (C]C), 1258
3250e3559 (OH, NH amide and NH imidazole), 3039 (CeH ar-
omatic), 1666 (C]O amide), 1610 (C]N), 1522 (C]C), 1256 and
1217 (CeO). 1H NMR (DMSO-d6,
d in ppm): 6.08e7.99 (m, 23H,
AreH), 9.44 (s, 1H, OH phenol), 9.65 (s, 1H, OH phenol), 10.43 (s,
1H, NH amide), 10.59 (s, 1H, NH amide), 13.51 (s, 1H, NeH,
imidazole
ring).
Elemental
analysis
calculated
for
(C41H28N4O6)n: C, 73.21%; H, 4.17%; N, 8.33%. Found: C, 73.09%;
H, 4.29%; N, 8.30%.
PA3: Yield ¼ 89% and hinh ¼ 0.91 dL/g. FT-IR (KBr disk) at cmꢁ1
:
3272e3538 (OH, NH amide and NH imidazole), 3066 (CeH ar-
omatic), 1671 (C]O amide), 1607 (C]N), 1517 (C]C), 1258 and
and 1236 (CeO). 1H NMR (DMSO-d6,
d in ppm): 5.03 (s, 2H, NH),
5.40 (s, 2H, NH), 6.06 (dd, 1H, AreH, J ¼ 8.0 Hz), 6.28 (d, 1H,
J ¼ 2.4 Hz), 6.51 (d, 2H, AreH, J ¼ 8.4 Hz), 6.58 (dd, 2H, AreH,
J ¼ 8.4 Hz), 6.62 (s, 1H, AreH), 6.65e6.69 (m, 4H, AreH), 6.76 (dd,
2H, AreH, J ¼ 8.40), 6.92 (d, 2H, AreH, J ¼ 8.20), 7.01 (dd, 2H, Are
H, J ¼ 8.40), 7.22 (dd, 2H, AreH, J ¼ 8.40), 9.43 (s, 1H, OH phenol),
9.61 (s, 1H, OH phenol), 13.92 (s, 1H, NH imidazole ring). 13C NMR
1213 (CeO). 1H NMR (DMSO-d6,
d in ppm): 6.20e8.33 (m, 22H,
AreH), 9.49 (s, 1H, OH phenol), 9.65 (s, 1H, OH phenol), 10.99 (s,
1H, NH amide), 11.08 (s, 1H, NH amide), 13.52 (s, 1H, NeH,
imidazole
ring).
Elemental
analysis
calculated
for
(C40H27N5O6)n: C, 71.32%; H, 4.01%; N, 10.40%. Found: C, 71.16%;
H, 4.37%; N, 10.37%.
(100 MHz, DMSO-d6,
d
in ppm): 104.15, 106.77, 107.93, 114.40,
PA4: Yield ¼ 90% and hinh ¼ 0.66 dL/g. FT-IR (KBr disk) at cmꢁ1
:
115.23, 115.66, 115.74, 120.69, 121.93, 124.70, 124.85, 126.98, 127.65,
129.56, 130.10, 133.10, 133.45, 144.38, 144.86, 146.39, 149.70,
156.77, 157.73, 159.96 and 160.71. Elemental analysis calculated for
3285e3561 (OH, NH amide and NH imidazole), 3068 (CeH ar-
omatic), 1687 (C]O amide), 1608 (C]N), 1519 (C]C), 1256 and
1219 (CeO). 1H NMR (DMSO-d6,
d in ppm): 6.43e8.34 (m, 27H,
C
33H26N4O4: C, 73.06%; H, 4.80%; N, 10.33% and found: C, 73.01%;
AreH), 9.51 (s, 1H, OH phenol), 9.67 (s, 1H, OH phenol), 10.55 (s,
1H, NH amide), 10.59 (s, 1H, NH amide), 13.51 (s, 1H, NeH,
H, 4.93%; N, 10.29%.
imidazole
ring).
Elemental
analysis
calculated
for
2.4. PAs synthesis
(C47H32N4O8S)n: C, 69.46%; H, 3.94%; N, 6.90%. Found: C, 69.37%;
H, 4.01%; N, 6.90%.
2.4.1. Direct polycondensation using TPP/NMP/Py/LiCl
PA5: Yield ¼ 93% and hinh ¼ 0.52 dL/g. FT-IR (KBr disk) at cmꢁ1
:
Into a 50 mL three-necked round-bottomed flask equipped with a
condenser, a mechanical stirrer and a nitrogen gas inlet tube,
monomer 3 (1 mmol, 0.54 g), a dicarboxylic acid (1 mmol), and LiCl
(0.30 g) were dissolved in a mixture of Py (1 mL), TPP (1.20 mmol),
and NMP (5 mL). The mixture was heated at 50 ꢀC for 6 h and at 70 ꢀC
for 4 h with stirring under dry N2 atmosphere. The homogeneous
solution was poured into a 9 cm diameter glass culture dish, which
was heated under vacuum at 80 ꢀC for 1 h, 100 ꢀC for 2 h, and 140 ꢀC
for 5 h to evaporate the solvent slowly. Polymer films were self-
stripped off from the glass surface by soaking in water. The poly-
mer films were further dried in a vacuum oven at 160 ꢀC for 6 h.
3255e3519 (OH, NH amide and NH imidazole), 3052 (CeH ar-
omatic), 1677 (C]O amide), 1612 (C]N), 1523 (C]C), 1251 and
1206 (CeO). 1H NMR (DMSO-d6,
d in ppm): 1.63 (m, 4H, CeH),
2.32 (t, 4H, CeH), 6.68e8.25 (m, 19H, AreH), 9.40 (s, 1H, OH
phenol), 9.55 (s, 1H, OH phenol), 10.53 (s, 1H, NH amide), 10.59
(s, 1H, NH amide), 13.40 (s, 1H, NeH, imidazole ring). Elemental
analysis calculated for (C39H32N4O6)n: C, 71.78%; H, 4.91%; N,
8.59%. Found: C, 71.68%; H, 5.04%; N, 8.55%.
PA6: Yield ¼ 96% and hinh ¼ 0.61 dL/g. FT-IR (KBr disk) at cmꢁ1
:
3258e3526 (OH, NH amide and NH imidazole), 3060 (CeH ar-
omatic), 1668 (C]O amide), 1609 (C]N), 1518 (C]C), 1251 and
Please cite this article in press as: Taghavi M, et al., Influence of ionic liquid on selective polycondensation of a new diamine-bisphenol:
Synthesis and properties of polyamides and their composites with modified nanosilica, Polymer (2013), http://dx.doi.org/10.1016/
j.polymer.2013.05.043

4
M. Taghavi et al. / Polymer xxx (2013) 1e13
Scheme 1. Synthesis of target monomer (3), preparation of polyamides with different dicarboxylic acids (PA1-PA-6) and chemically bonded nanocomposites (NCPA1-NCPA6).
1207 (CeO). 1H NMR (DMSO-d6,
d in ppm): 1.30 (m, 8H, CeH),
ethanol using a soxhlet extraction method to remove any unreacted
materials. The obtained nanocomposites dried under reduced
pressure at 60 ꢀC for 12 h.
1.57 (m, 4H, CeH), 2.32 (t, 4H, CeH), 6.64e8.18 (m, 19H, AreH),
9.40 (s, 1H, OH phenol), 9.51 (s, 1H, OH phenol), 10.49 (s, 1H, NH
amide), 10.52 (s, 1H, NH amide), 13.46 (s, 1H, NeH, imidazole
ring). Elemental analysis calculated for (C43H40N4O6)n: C,
72.88%; H, 5.65%; N, 7.91%. Found: C, 72.83%; H, 5.70%; N, 7.89%.
A certain amount (5, 10, 15 and 20 wt%) of NCPAs in DMF was
stirred in an ultrasonic water bath for 1 h to form a homogeneous
dispersion. The mixture was further stirred for 24 h at 60 ꢀC,
forming a viscose solution which was casted into flat-bottom glass
plate. The casted nanocomposite was heated under nitrogen at-
mosphere at different temperatures of 70 ꢀC, 100 ꢀC, 200 ꢀC for 1 h
each and at 250 ꢀC for 2 h, forming film of NCPAs with thicknesses
of around 3 mm.
2.5. Surface modification of NS particles (mNS)
Silane coupling agent of (3-chloropropyl)trimethoxysilane
(CTMS), as shown in Scheme 1, was introduced to ensure good
dispersion and improvement of interface between NS particles and
PAs. The surface modification of NS particles was carried out as
follows [34]. A suspension of 1 g activated NS particles in 30 mL dry
toluene was sonicated in 150 W ultrasonic water bath for 1 h, then
in a 50 mL round bottomed flask equipped with a reflux condenser,
an argon gas inlet tube and a magnetic stir bar, 1 g CTMS in dry
toluene (10 mL) was added to this sonicated suspension solution
and stirred at 80 ꢀC for 4 h, and then left at room temperature for
24 h. Finally, the separated solid was washed with diethyl ether and
then was further purified by washing with refluxing dichloro-
methane using a soxhlet extraction method and dried under
reduced pressure at 60 ꢀC for 12 h. The yield was 1.4 g of covalently
anchored CTMS moieties. The modified NS particles (6, Scheme 1)
were kept at 60 ꢀC in order to protect the nanoparticles surface
from water.
3. Results and discussion
3.1. Synthesis and characterization of diamine-bisphenol (3)
This manuscript reports selective polycondensation of a new
diamine-bisphenol monomer with several commercial aliphatic
and aromatic dicarboxylic acids in imiazolium-based ILs. For this
purpose, compound 3 containing diamine and dihydroxyl groups
were synthesized in three steps. As illustrated in Scheme 1, com-
pound
1
was successfully synthesized from 1-fluoro-4-
nitrobenzene and 2,4-dihydroxy benzaldehyde as starting mate-
rials by the nucleophilic fluorodisplacement reaction. Compound 1
reacted with 4,4-dihydroxy benzil and ammonium acetate in a
well-known classical but convenient synthetic method for the
formation of imidazole ring. The target monomer, compound 3, was
obtained by catalytic reduction of the nitro groups of compound 2
by using hydrazine hydrate and Pd/C in refluxing ethanol. The
structure of these compounds was identified by elemental analysis,
FT-IR and 1H NMR spectroscopy. FT-IR spectrum of compound 1 in
Fig. 1 shows the absorption bands of nitro group at 1522 and
1350 cmꢁ1 and carbonyl of aldehyde group at 1681 cmꢁ1. 1H NMR
spectrum of compound 1 showed proton of aldehyde group at
10.160 ppm. After reaction, the disappearance of absorption band at
1681 cmꢁ1 and signal at 10.16 ppm confirmed the consumption of
aldehyde group. New signals were observed at 13.91 ppm and at
2.6. Preparation of mNS/PA nanocomposites (NCPA)s
0.1 g of one of the PAs was dissolved in 20 mL dry NMP by
stirring in an ultrasonic water bath. Then a certain amount of mNS
particles (5, 10, 15 and 20 wt% based on weight of PA) was added to
the resulting solution and the mixture stirred further for 30 min at
70 ꢀC. After irradiation, 0.2 g K2CO3 was added and the mixture was
continuously stirred at 80 ꢀC for 5 h under argon atmosphere. At the
end of the reaction, the mixture was allowed to cool and after
filtration the solid was further purified by washing with refluxing
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(NO2 asymmetric and symmetric stretchings, respectively) dis-
appeared and the absorption bands of primary amino groups of
compound 3, as shown in Fig. 1, were observed at 3473 cmꢁ1 and
3386 cmꢁ1 with the bending vibrations in the region of 1560e
1640 cmꢁ1. As shown in Fig. 2, 1H NMR spectrum of compound 3
showed the characteristic resonance of different protons of two
amine groups at 5.03 and 5.40 ppm and two hydroxyl groups at
9.43 and 9.60 ppm. 13C NMR spectrum of compound 3 showed 25
different carbons for the aromatic and heterocyclic rings.
3.2. Synthesis and characterization of PAs and nanocomposites
As an extension of studies in developing organosoluble high-
performance polymers, a simple and efficient method is reported
for the selective polymerization of a new diamine-bisphenol
monomer with commercial dicarboxylic acids in ILs as activator
and solvent. The polycondensation reaction proceeded selectively
and efficiently in the mixture of ILs/TPP without using NMP/Py/LiCl
mixture which is required when using traditional method by
Yamazaki [35]. The ambient temperature ILs, especially those based
on 1,3-dialkylimidazolium cations, have gained considerable in-
terest as promising alternative green solvents in polymer synthesis
[4,36e38]. This investigation also used room temperature ILs,
thermally stable near the process temperature and good solvents
for the initial materials and for the resulting polymer, which were
prepared simply from the commercially available starting materials
such as N-trimethylsilylimidazole and alkyl halides [33]. Thus,
different symmetrical 1,3-dialkylimidazolium ILs bearing Br, PF4ꢁ
and BFꢁ6 anions, shown in Table 1, were prepared and used as
polycondensation agents. These ILs were all very viscous liquids at
room temperature and soluble in polar solvents such as water and
methanol allowing for the complete isolation of the obtained
polymers. To determine the effect of the nature of ILs on the yield
and viscosity of the polymer, the synthesis of aromatic PA3 was
carried out in different ILs at a constant reaction temperature of
110 ꢀC. Table 1 compares the yield and viscosity of PA3 in different
ILs. Although PA3 was soluble in all ILs, the viscosity of the polymer
decreased when the alkyl chain length in the IL increased. This may
be explained by the decrease in the polarity of the IL, resulting in a
Fig. 1. FT-IR spectra of compounds 1 and 3, PA3, mNS and NCPA3-10%.
9.43e9.60 ppm in the spectrum of compound 3, as shown in Fig. 2,
which are related to NeH of imidazole ring and OeH of hydroxyl
groups, respectively. After reduction of nitro groups of compound 2,
the two characteristic absorption bands at 1521 and 1352 cmꢁ1
Fig. 2. 1H NMR spectrum of monomer (3) in DMSO-d6.
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M. Taghavi et al. / Polymer xxx (2013) 1e13
Table 1
The influence of IL cation and anion upon yield and inherent viscosity (hinh) of PA3.
a
Polymer
IL structure
IL
Yield (%) hinh
PA3
[1,3-Isopropyl2im]Br 80
0.76
PA3
PA3
[1,3-Propyl2im]Br
[1,3-Butyl2im]Br
89
77
0.91
0.86
PA3
PA3
PA3
[1,3-Pentyl2im]Br
[1,3-Hexyl2im]Br
[1,3-Heptyl2im]Br
75
83
89
0.67
0.66
0.63
Fig. 3. Optimum conditions for the synthesis of PA3 in IL.
such as the non-volatility of ILs, low reaction time, no environ-
mental pollution, and no need to remove chemicals such as NMP,
LiCl and Py which are essential for conventional direct poly-
condensation. The reason for the selective polycondensation of
diamine-bisphenol (compound 3) can be suggested to be due to
formation of phenolic salt as a result of reaction between phenolic
hydroxyl groups and the ionic liquid, while the amine groups
remain free to react with the carboxylic acids to give polyamide.
The PAs obtained in IL/TPP mixture were brown powder with good
yields (80e96%) after removal of low molecular weight fractions by
using hot methanol extraction. Inherent viscosities of these PAs in
NMP (0.5 g/dL) were in the range of 0.52e0.91 dL/g. The elemental
analysis results were in good agreement with the calculated per-
centages for carbon, hydrogen and nitrogen contents in PAs
repeating units. The weight average molecular weights (Mw) of
these PAs were in the range of 44755e61368 g/mol with distribu-
tion index of 1.69e2.03. The results are listed in Table 2. ILs possess
low vapour pressure and, in contrast to volatile organic solvents,
can be used at high temperature and under vacuum. Thus, the
relatively high molecular weights of these polymers can be due to
the fact that ILs can dilute highly viscous polymer solutions and
facilitate the elimination of the byproduct under N2 flow, thus
shifting the equilibrium. The 1H NMR spectrum of PA3, Fig. 4, shows
the NeH proton of amide groups at 10.99e11.08 ppm, NeH proton
of imidazole ring at 13.52 ppm and phenolic hydroxyl groups at
9.48e9.65 ppm. The signals of aromatic and aliphatic protons
appeared in the range of 6.58e8.88 ppm and 1.25e2.25 ppm,
respectively.
PA3
[1,3-Butyl2im]BF4
[1,3-Butyl2im]PF6
67
66
0.63
0.61
PA3
a
Measured at a concentration of 0.5 g/dL in NMP at 25 ꢀC.
decreased solubility of polymer. The highest viscosity of PA3 was
obtained when [1,3-(Pr)2im]þ Br was used as the reaction medium,
and this IL was also selected for the synthesis of other PAs. The
optimum polycondensation time (2.5 h) was determined by
measuring the yield and viscosity of PA3 in the selected IL and at
the selected temperature (110 ꢀC). These results are shown in Fig. 3,
and the synthetic procedure and polymers designation are shown
in Scheme 1. The decrease in viscosity of PA3, as shown in Fig. 3, can
be as a result of thermal degradation of the polymer chains at 110 ꢀC
in longer reaction times.
A dark colour and insoluble material (PA100) was obtained when
direct polycondensation of compound 3 with terephthyalic acid
was conducted in the mixture of TPP/NMP/Py/LiCl. This thermoset
material (PA100) has been formed through cross-linking reactions
between carboxylic acid groups of terephthalic acid and amino and
hydroxyl groups of compound 3. This demonstrates the beneficial
effect of ILs in the synthesis of thermoplastic PAs selectively from a
diamine-bisphenol compound, in addition to other useful factors
PA/mNS composites with covalent bonds between organic and
inorganic phases have been successfully prepared. NS were first
activated in methanesulfonic acid media for 12 h, and then CTMS
Table 2
Average molecular weights, viscosity and solubility of PAs and nanocomposites.
Code
hinh (dL/g)a
Mn (g/mol)
Mw (g/mol)
Moisture absorption (%)
DMSO
DMAc
DMF
NMP
Py
THF
CH3CN
m-cresol
PA1
PA2
PA3
PA4
PA5
PA6
NCPA1-5%
NCPA6-5%
NCPA6-10%
PA100
0.72
0.67
0.91
0.66
0.52
0.61
e
32,219
30,081
36,357
29,301
26,811
22,051
e
56,920
54,223
61,368
53,984
49,124
44,755
e
13.51
12.88
14.61
12.47
11.34
12.11
e
þþ
þþ
þþ
þþ
þþ
þþ
e
þþ
þþ
þþ
þþ
þþ
þþ
e
þþ
þþ
þþ
þþ
þþ
þþ
e
þþ
þþ
þþ
þþ
þþ
þþ
e
þ
ꢂ
ꢂ
ꢂ
ꢂ
þ
þ
e
e
e
e
e
e
e
e
e
e
e
e
e
e
þ
þ
þ
þ
þ
þ
þ
þþ
þþ
e
þþ
þþ
e
e
e
e
e
ꢂ
ꢂ
ꢂ
ꢂ
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
GPC measurement at 30 ꢀC with DMF as fluent at 1 mL/min and monodisperse polystyrene as standard for instrument calibration.
PA100: This PA was prepared in the mixture of TPP/NMP/Py/LiCl.
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Fig. 4. 1H NMR spectrum of PA3 in DMSO-d6.
molecules were linked to the silica surface via SieOeSi covalent
bonds. This was achieved by condensation of hydroxyl groups (e
OH) on the surface of activated silica with the hydrolysable
methoxy groups (eOCH3) of CTMS. FT-IR spectrum of mNS in Fig. 1
presents a few absorption bands; around 1100 cmꢁ1 can be
assigned to the characteristic vibration bands of SieO link, at
3400 cmꢁ1 to the characteristic stretching vibration of hydroxyl
group (eOH) on the surface of NS, at 1380 cmꢁ1 to the bending and
at 2906e2857 cmꢁ1 to the stretching vibrations of CeH of organic
methylene. In addition, characteristic absorption band at 1040e
1180 cmꢁ1 broadens which reveals that a new absorption band of
SieOeSi has formed due to the contribution of interaction between
siloxane and NS. The above interpretations, and also the insolubility
of the nanocomposites in organic solvents (Table 2), are enough to
suggest that CTMS is chemically bound on the surface of NS. PA/
mNS composite was prepared from chloroedisplacement reaction
of mNS with the hydroxyl groups of PAs. FT-IR spectrum of NCPA3-
10% nanocomposite, Fig. 1, exhibited the characteristic absorption
bands of the amide group in the regions of 3407 cmꢁ1 (NeH
stretching) and 1671 cmꢁ1 (C]O stretching), and SieOeSi band at
1040e1150 cmꢁ1. As shown in Scheme 1, it is suggested that co-
valent bonds can be formed between polymer matrix and mNS
through substitution reaction of phenolic groups in the polymer
backbones with the chlorine atom on the surface of mNS. It was not
possible to obtain 1H NMR spectrum from composite samples due
to their insolubility in organic solvents. X-ray scattering is well-
suited for many polymer/inorganic composites. X-ray diffraction
(XRD) technique has been used to investigate the nature of the
nanocomposites with respect to pure PAs. XRD patterns for pure
PA1, NS, mNS and nanocomposites (NCPA1-5% and NCPA1-15%) are
shown in Fig. 5. According to the XRD patterns for pure PAs and NS,
they are considered totally amorphous in nature which do not show
any sharp diffraction peaks. XRD patterns of mNS and nano-
composites containing 5% and 15% mNS (NCPA1-5% and NCPA1-
15%) showed sharp diffraction peaks which might be related to
small structural order in the mNS, Scheme 1 (6). The number of
these sharp peaks increased with increasing mNS content in the
Fig. 5. X-ray diffraction patterns of PA (1, 3, and 5), NS, mNS, NCPA1-(5% and 15%).
polymer matrix. To study the electrochemical behaviour of PAs and
nanocomposites, modified graphite-polymer paste as working
electrode was examined by cyclic voltammetry (CV) and the results
in Fig. 6 reveal that the polymers are oxidized at a potential of 0.5e
0.8 V. The two anodic peaks at the forward scan of potential, at 0.6
and 0.8 V, may be related to the oxidation of the eOH groups and
imidazole ring, respectively. The CV curves show that PA1 has
higher electrochemical oxidation potential in comparison with the
nanocomposites. The intensity of oxidation peak of eOH groups in
the polymer backbone in the region of 0.6 V decreased with
increasing the amount of mNS from 5 wt% to 20 wt%. Therefore, it
can be concluded that the eOH groups in the polymer backbone are
the main sites for chemical bond formation with mNS, and also for
electrochemical oxidation to occur. The oxidized products are
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3.4. Photophysical properties
The photophysical properties of PAs and nanocomposites were
investigated by using UVevis and fluorescence spectroscopy. The
absorption and fluorescence spectra of PAs and nanocomposites
films are shown in Fig. 7. The absorption spectra of PAs in dilute
NMP solution (0.2 g/dL) and in films, Fig. 7A, were nearly identical
and the maximum absorption wavelengths (lab) were in the range
of lab ¼ 302e317 nm, as listed in Table 3, which shows a relatively
small energy band gap for
p / p* transition. Reasonably, this could
be attributed to the all aromatic structure possessing substituted
imidazole pendant attached to the aromatic backbone. To investi-
gate the fluorescence emission of PAs, an excitation wavelength of
320 nm was used in all cases. The fluorescence emission spectra of
PAs are shown in Fig. 7B. The solution and thin films of PAs showed
broad fluorescent emission spectra with the maximum wave-
lengths in the range of lem ¼ 421e499 nm and Ff ¼ 12e38%, as
listed in Table 3. The aliphatic PAs (PA5 and PA6) exhibited blue
emission (lem ¼ 421e445 nm) with the highest Ff values of 31% and
38%, respectively. The aromatic PAs exhibited green emission
Fig. 6. Cyclic voltammograms of PA1 and NCPA1-(5%e20%) with modified CPE.
formed irreversibly during forward scan and there is not cathodic
peak at the backward scan.
(lem ¼ 480e490 nm) and Ff in the range of 12e17%. The blue shift
and higher intensity of PL of semi-aromatic PAs compared with the
PL of aromatic PAs could be attributed to the effectively reduced
conjugation and capability of charge transfer complex formation by
aliphatic diacids in comparison with the electron-donating amino
unit and the strongly electron-accepting aromatic diacid unit [41].
The absorption and emission spectra of the representative nano-
composite films are shown in Fig. 7(A and B). Table 3 lists some
important photophysical data obtained from films and suspension
solution of composites containing 5 wt% mNS. The nanocomposites
showed absorption at lab ¼ 315e329 nm, emission at lem ¼ 441e
503 nm and Ff ¼ 22e41%. As can be seen in Fig. 7B and in Table 3,
similar to aliphatic PAs their nanocomposites (NCPA5-5% and
NCPA6-5%) also showed blue shift with Ff of 39% and 41%,
respectively, in comparison with the nanocomposites of aromatic
PAs which showed green shift with Ff ¼ 16e22%.
3.3. Properties of PAs and nanocomposites
3.3.1. Solubility and moisture absorption
As a general rule, high solubility is a desired prerequisite for
polymer processing. The solubility behaviour of these PAs and
nanocomposites was qualitatively tested in various organic sol-
vents, and the results are summarized in Table 2. All PAs prepared
in the mixture of TPP/IL exhibited excellent solubility in polar
aprotic solvents such as NMP, DMAc, DMF, DMSO and even in less
polar solvents like pyridine, THF, and m-cresol, while PA100 which
was prepared in the mixture of TPP/NMP/Py/LiCl did not dissolve in
the above mentioned solvents. In previous reports, comparable
aramids with almost the same backbone structure, showed very
low solubility in organic solvents [39] or were practically insoluble
[40]. The good solubility should be due to presence of different
functional groups in the polymer backbone such as bulky hetero-
cyclic pendant, ether linkage, hydroxyl groups, and unsymmetrical
structure. These factors and also the amorphous nature contributed
to the enhanced solubility of these PAs through better penetration
of solvent molecules, formation of H-bonding and dipoleedipole
interaction with polar molecules of organic solvents. In addition,
the solubility varies depending upon the dicarboxylic acid used.
The PAs which were synthesized from aliphatic dicarboxylic acids
(PA5 and PA6) exhibited better solubility behaviour in less polar
solvents such as THF and m-cresol. The presence of methylene units
instead of rigid phenyl improves the solubility of these PAs. Com-
posites of aliphatic PA6 with 5 wt% mNS showed partial solubility in
highly polar solvents by heating at 60 ꢀC which can be due to so-
lution of low molecular weight oligomer component. However,
composites containing more than 5 wt% mNS did not dissolve in
these solvents which confirm they have definitely formed cross-
linked network structure through chemical reaction between e
CH2Cl groups in the mNS and hydroxyl groups in the polymer
backbone. The water uptake determines the final application of
high performance materials. The absorbed water diminish Tg and
influence mechanical and electrical properties, but in membrane
technology, greater water uptake implied better performance. The
results showed moisture intake of these PAs ranged from 11.34% to
14.61%, as listed in Table 2. These PAs are partially hydrophilic
materials because of the presence of bulky pendant which increase
the free volume and their polar amide and free hydroxyl groups
which interact effectively with water molecules.
3.5. Mechanical properties
The tensile stressestrain curve is a tool to provide data on
toughness (area under the curve), ultimate tensile strength, ulti-
mate elongation at break and Young’s modulus. Typical stresse
strain curves of PAs and the nanocomposites are illustrated in Fig. 8
and the corresponding tensile data are summarized in Table 4. An
average of five individual measurements was used for each sample.
These PAs showed tensile strength in the range of 48e88 MPa,
elongation to break of 14e26%, and initial modulus of 1.61e
2.47 GPa. The PA10 which was prepared in the mixture of TPP/Py/
NMP/LiCl, as explained in section 3.2, is a highly crosslinked ma-
terial and showed very brittle characteristics with low elongation
(0.6%) and high Young’s modulus (6.0 GPa), as listed in Table 4. The
area under the stressestrain curve is used to measure the fracture
energy or static toughness of the polymer and depends on the
molecular weight and intermolecular interactions. PA1 showed the
highest tensile strength and toughness due to higher molecular
weight and more symmetrical structure of terephthalic unit in
comparison with the other PAs. PA5 and PA6 showed the lowest
strength and elongation due to presence of aliphatic chain in the
backbone and lower molecular weights in comparison with the
other PAs. From Table 4, we can see the noticeable trend of tensile
strength of specimens increased when increasing the mNS amount.
The tensile strength of PA1 increased from 88 MPa to 110 MPa for
NCPA1-20%, and simultaneously, the tensile elongation decreased
from 26% to 9%. The enhancement of tensile strength corresponds
to the forecast, as mentioned before, that NS could play a
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Fig. 7. UVevis and fluorescence spectra of PAs, NCPA1-10% and NCPA6-10%.
reinforcing role in the composite. It might be ascribed to the
presence of chemical interactions between mNS and hydroxyl
groups in the PAs chains and formation of cross-links. As we know,
elongation at break is a crucial parameter to judge the plasticity or
ductility of the polymer. Generally, the addition of inorganic par-
ticles into polymers, and in this case formation of cross-links,
lowers the elongation at break.
Table 3
Optical properties data of PAs and nanocomposite.
Code
lab (nm)a
lem (nm)a
lab (nm)b
lem (nm)b
Ffc (%)
PA1
PA2
PA3
PA4
PA5
PA6
NCPA1-5%
NCPA2-5%
NCPA3-5%
NCPA4-5%
NCPA5-5%
NCPA6-5%
NCPA6-10%
NCPA6-15%
NCPA6-20%
314.75
313.25
311.50
310.25
307.50
302.50
321.25
320.00
318.25
317.25
315.00
315.50
e
498.00
495.25
496.25
480.25
442.75
421.00
502.50
499.25
496.25
487.00
454.00
440.75
e
317.00
315.75
315.00
311.50
308.25
302.25
329.50
326.25
324.25
321.25
320.25
317.50
318.75
320.75
321.50
499.00
497.25
497.25
483.75
445.25
423.25
502.75
500.25
499.00
488.00
453.75
443.50
449.25
451.25
452.25
17
15
14
12
31
38
22
20
17
16
39
41
e
3.6. Thermal properties
The thermal behaviour data of these PAs and nanocomposites
were assessed by using DSC, DMTA and TGA analysis. Fig. 9 shows DSC
curves of PAs, neither crystallization exotherms nor melting endo-
therms were observed in the range of 35e400 ꢀC, so that these PAs
were considered to be essentially amorphous. The amorphous nature
of these PAs can be attributed to their bulky pendant group which
decreased the inter-chain interaction resulting in loose polymerchain
packaging and aggregates. The Tg values were read at the middle of
the first break down observed in the DSC curves, and found to be in
the range of 188e325 ꢀC, as listed in Table 4. In general, molecular
packing and chain rigidity are among the main factors influencing on
Tg values. Therefore, the increased rotational barrier caused by the
bulky pendant in the monomer 3 and side chain-side chain and side
chain-main chain interactions enhanced Tg values. As anticipated, the
Tg values of these PAs also depend on the stiffness of dicarboxylic acid
component in the polymer chain and the increasing order of Tg
generally correlated with that of chain rigidity. PA5 and PA6 obtained
from aliphatic dicarboxylic acid, showed lower Tg values (204 ꢀC and
188 ꢀC, respectively) because of the presence of flexible aliphatic unit
and their low rotation barrier, and the highest Tg value of 325 ꢀC was
observed for PA1 derived from terephthalic acid. Tg values of com-
posites showed dependence on the amount of mNS particles. As
shown in Table 4, composites of aromatic PAs containing more than
5 wt% mNS did not show Tg up to 400 ꢀC, while Tg of PA1 increased
from 325 ꢀC to 344 ꢀC when contains 5 wt% mNS.
e
e
e
e
e
e
Polymer concentration of 0.20 g/dL in NMP.
a
UVevisible absorption and fluorescence emission spectra of the PAs and
nanocomposites (5% NS) in solution.
b
UVevisible absorption and fluorescence emission spectra of the PAs and
nanocomposites (5% NS) in films
c
Fluorescence quantum yield relative to 10ꢁ5 M quinine sulphate in 1 N H2SO4
(aq) (Ff ¼ 0.55) as a standard.
The viscoelastic behaviour of representative PAs and nano-
composites was determined by using DMTA. Tan
d curves are
shown in Fig. 10A. Measurement of tan values was carried out to
d
relate the viscoelastic behaviour and PAs molecular structure and
mNS content in the composites. The increase in the Tg (peak tem-
peratures in the tan
d curves) values indicates that a change in the
viscoelastic behaviour of the nanocomposite films from liquid like
to solid-like occurs. As already has been discussed, mNS particles
and PA chains have definitely been involved in reactions of cross-
Fig. 8. Tensile stress vs. strain (%) of PAs and NCPAs nanocomposites.
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10
M. Taghavi et al. / Polymer xxx (2013) 1e13
Table 4
Thermal and mechanical properties of PAs and nanocomposites.
Code
Tensile (MPa)a
Modulus (GPa)
Elongation (%)
Tg (ꢀC)b
T10 (ꢀC)c
T10 (ꢀC)c
C. Y.d
C. Y.d
LOI (%)e
PA1
88.41
117.19
71.08
71.67
59.38
56.85
47.72
97.54
101.63
104.90
110.76
e
2.47
6.00
2.10
2.18
1.94
1.78
1.61
2.51
2.67
2.92
3.12
e
25.82
0.90
22.73
23.58
24.17
15.28
14.14
20.21
16.06
10.80
8.73
e
325.36
e
511.25
532.49
498.08
471.91
501.47
462.60
447.15
528.24
533.58
539.03
538.79
530.65
525.84
530.03
517.43
460.71
455.81
489.26
450.19
430.04
451.70
416.67
407.33
475.51
488.58
495.04
506.43
482.72
471.75
484.34
434.18
423.00
63.11
70.65
58.49
51.05
58.68
40.91
41.28
72.40
73.39
75.00
75.18
69.45
62.24
71.39
51.55
50.14
e
42.74
45.76
40.90
37.92
40.97
33.86
34.01
46.46
46.86
47.50
47.57
45.28
42.40
46.06
38.12
37.56
PA10
e
PA2
PA3
PA4
PA5
304.42
260.17
310.64
203.76
188.24
344.39
e
e
e
e
e
PA6
e
NCPA1-5%
NCPA1-10%
NCPA1-15%
NCPA1-20%
NCPA2-10%
NCPA3-10%
NCPA4-10%
NCPA5-10%
NCPA6-10%
10.24
15.08
17.63
24.00
16.49
12.53
17.44
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
231.85
206.06
e
e
e
e
PA1’: This PA was prepared in the mixture of TPP/NMP/Py/LiCl.
a
Film stored in a 80% relative humidity atmosphere before tensile test.
b
c
Tg was recorded by DSC at 10 ꢀC/min in N2.
T10% was recorded by TGA at 10 ꢀC/min in N2 and in air, respectively.
C.Y. ¼ Char yield, weight% of material left at 800 ꢀC in N2 and in air, respectively.
Limiting oxygen index percent evaluating at char yield 800 ꢀC.
d
e
links formation. These immobilize the polymer chains at elevated
temperatures. The Tg values of the representative PAs (PA1 and PA5)
were in the range of 205 ꢀC and 320 ꢀC, respectively, and also for the
nanocomposites (NCPA5-10% and NCPA1-5%) were 235 ꢀC and
340 ꢀC. These values were in good agreement with Tg values of
these polymers measured by DSC method. Thermoplastic response
of PAs and their nanocomposites was determined by plotting
storage modulus against testing temperature. Fig. 10B shows the
storage modulus values as a function of varying wt% of mNS par-
ticles. It was observed that with increasing wt% of mNS particles the
value of storage modulus of composite increases.
Fig. 11A presents TGA curves of the PAs, and the corresponding
10% weight loss temperatures (T10%) determined from the original
curves in N2 (447e511 ꢀC) and air (407e456 ꢀC) are listed in Table 4.
Char yield (CR) can be used as criteria for evaluating limiting oxy-
gen index (LOI) of the polymers in accordance with Van Krevelen
and Hoftyzer equation [42], LOI ¼ 17.5 þ 0.4CR. In general, when
the LOI of a polymer is higher than 26% it is considered to be
flammable. For these PAs, LOI values were calculated based on their
char yields at 650 ꢀC. According to Table 4, thermal stability of the
aromatic PAs in N2 appeared in the 472e511 ꢀC range in terms of
T10% values, compared to 447e463 ꢀC for the aliphatic PAs. This can
Fig. 9. DSC curves of PAs and NCPA1-5% and NCPA1-10% under N2 at 10 ꢀC/min.
Fig. 10. DMTA curves of tan
d (A) and storage modulus (B) of PA (1, 5) and NCPA1-(5% and 10%).
Please cite this article in press as: Taghavi M, et al., Influence of ionic liquid on selective polycondensation of a new diamine-bisphenol:
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M. Taghavi et al. / Polymer xxx (2013) 1e13
11
Fig. 11. TGA curves of (A) PA (1, 3 and 5), and (B) NS, mNS, NCPA1-(5%, 15% and 20%) under N2 and air at 10 ꢀC/min.
be pertained to the rigid structure of aromatic diacids compared to
the flexible structure of aliphatic diacids. Fig. 11B shows TGA curves
of NS, mNS and composites containing 5, 15 and 20 wt% mNS
particles, and the thermal data extracted from the original curves
are listed in Table 4. The T10% value of NCPA1-20% in comparison
with the same pure PA1 has increased from 511 ꢀC to 539 ꢀC with
the char yield from 63% to 76% in N2. It is clear that the existence of
inorganic material in polymer matrix and its chemical interactions
with the polymer shifted decomposition temperature towards
higher temperatures indicating enhanced thermal stability of the
composite with mNS loading.
3.7. Extraction of metal cations from aqueous solution
Heavy metals are toxic because they are present as ions in an
aqueous system and can be readily absorbed into the human body.
Fig. 12. AFM images of NCPA1-10% (A) before and (B) after absorption of HgII.
Please cite this article in press as: Taghavi M, et al., Influence of ionic liquid on selective polycondensation of a new diamine-bisphenol:
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12
M. Taghavi et al. / Polymer xxx (2013) 1e13
Thus, the removal of metal ions from water has become an
important and widely studied area. In these experiments, the
presence of imidazole rings, amide linkages and hydroxyl groups in
the backbones of solid PAs can acted as hosts for the adsorption and
formation of complex with the target metal ion. After filtration, the
concentration of metal ions in the filtrate was determined by
atomic absorption spectroscopy and by using a calibration curve
made from standard solutions of metal salts. The amount of
adsorbed ions was calculated using the following equation:
phases, points to future applications in the fields of membrane
preparation for cation transport, water decontamination and in
sensing materials, among other applications.
4. Conclusions
The design and synthesis of novel thermally stable PAs with
improved solubility based on unsymmetrical aromatic diamine-
bisphenol containing beneficial heterocyclic ring such as imid-
azole was the main objective of this work. Therefore, an aromatic
tetrafunctional compound containing both eNH2 and eOH groups
was synthesized, characterized and used for preparation of PAs in
direct selective polycondensation in IL/TPP without using NMP/Py/
LiCl. These PAs with Mw in the range of 44,755e56,920 g/mol
exhibited high thermal stability based on their Tg and T10% values
which varied from 188 ꢀC to 325 ꢀC and from 407 ꢀC to 456 ꢀC in air,
respectively, depending on the rigidity of the polymer backbone.
These results support that such a modification of the polymer
structure can be used as an effective strategy for imparting fluo-
rescence emission in the visible light region and enhancing the
processability of aramids while maintaining the high thermal sta-
bility. These PAs with reactive hydroxyl groups in the backbone
were also used in the preparation of chemically bonded reinforced
composite materials with the surface modified NS. As compared
with the pure PAs, the mNS/PAs nanocomposites are significantly
strengthened by increasing the tensile strength and have an
improved thermal stability. The solubility, thermal and tensile
properties of the nanocomposites showed dependence on the
amount of mNS particles. The results also demonstrated that these
PAs and particularly their composite with mNS can act efficiently as
chelating agent for heavy metal ions.
½ðC0 ꢁ CAÞ ꢃ Vꢄ
Qt
¼
(1)
W
where Qt is the amount of metal ions adsorbed into the unit of the
composites (mg gꢁ1), C0 and CA are the concentrations of metal ions
in the initial solution and in the aqueous phase after adsorption,
respectively (mg mLꢁ1), V is the volume of the initial solution (mL)
and w is the weight of the polymer (g). Selectivity coefficient of
adsorption of metal ions in the solution was studied in the mixture
by batch procedure. The distribution coefficients (kd) of ions were
determined by the following equation (1):
½ðC0 ꢁ CA0Þ ꢃ Vꢄ
Kd
¼
(2)
CA ꢃ W
The extraction selectivity,
a
, is the ratio of two distribution co-
efficients as shown in equation (2). The HgII cation was taken as the
reference, as it has the highest distribution coefficient.
nþ
Kdm
a
¼
(3)
KdHg2þ
As the synthesized PAs are insoluble in water and showed highly
moisture absorptive, therefore only PA3 and its composite with
20 wt% mNS (NCPA3-20%) has been used in solideliquid extraction.
Fig. 12 shows AFM images taken from surface of sample before and
after adsorption of Hg2þ. The difference in these images which is
observed by their appearance and the size of the particles (w25 nm
and w87 nm before and after metal ion adsorption, respectively)
reveal that the surface of sample is fully covered with layer of
absorbed substance. The results for distribution coefficient and
selectivity in the mixture of metal ions in solution are shown in
Table 5. As can be seen in this table, the extraction level of these
cations Hg2þ, Cd2þ, Ni2þ, Co2þ, Cu2þ, Cr3þ and Fe3þ by solid nano-
composite (NCPA3-20%) increased almost three times in comparison
with the absorption level by PA3. This increase in the metal ions
extraction can be suggested to be due to formation of network
structure in the nanocomposite materials which raise the amount of
entrapped metal ions inside the entangled macromolecular chains.
Also, the selective adsorption of Hg2þ cation in the mixture solution
of all cations is the highest which is similar with the results obtained
for each ion individually. It is clear from the results, selectivity factor,
that the quantitative separation of Hg2þ cation from the rest of the
cations is possible. The extraction level of these cations especially
mercury from aqueous media by the PAs and solid nanocomposite
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Please cite this article in press as: Taghavi M, et al., Influence of ionic liquid on selective polycondensation of a new diamine-bisphenol:
Synthesis and properties of polyamides and their composites with modified nanosilica, Polymer (2013), http://dx.doi.org/10.1016/
j.polymer.2013.05.043