Synthesis and characterization of new imidazole and fluorene-bisphenol based polyamides: Thermal, photophysical and antibacterial properties

Article abstract of DOI:10.1016/j.reactfunctpolym.2012.12.005

A new para-linked diether-diamine, 9,9-bis{4-[2-(4,5-diphenylimidazol-2-yl) -4-aminophenoxy] phenyl}fluorene (III), bearing fluorene-bisphenol and two ortho-linked diaryl-substituted imidazole rings were synthesized by the catalytic reduction of the nitro

Full text of DOI:10.1016/j.reactfunctpolym.2012.12.005

Reactive & Functional Polymers 73 (2013) 555–563
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Reactive & Functional Polymers
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Synthesis and characterization of new imidazole and fluorene–bisphenol based
polyamides: Thermal, photophysical and antibacterial properties
a
a
a
Mousa Ghaemy a, , Bahareh Aghakhani , Mehdi Taghavi , Seyed Mojtaba Amini Nasab ,
⇑
Mojtaba Mohseni b
a Polymer Chemistry Research Laboratory, Department of Chemistry, University of Mazandaran, Babolsar, Iran
b Department of Biology, University of Mazandaran, Babolsar, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 October 2012
Received in revised form 25 December 2012
Accepted 26 December 2012
Available online 2 January 2013
A
new para-linked diether-diamine, 9,9-bis{4-[2-(4,5-diphenylimidazol-2-yl)-4-aminophenoxy]
phenyl}fluorene (III), bearing fluorene–bisphenol and two ortho-linked diaryl-substituted imidazole rings
were synthesized by the catalytic reduction of the nitro groups of compound (II), 9,9-bis{4-[2-(4,5-diph-
enylimidazol-2-yl)-4-nitrophenoxy]phenyl}fluorene, by using hydrazine monohydrate in the presence of
Pd/C. Compound (II) was synthesized by the nucleophilic chloro displacement reaction of the synthesized
2-(2-chloro-5-nitrophenyl)-4,5-diphenyl-1H-imidazole with 9,9-bis(4-hydroxyphenyl)fluorene in reflux-
ing DMAc in the presence of potassium carbonate. This diamine was condensed directly with aliphatic
and aromatic diacids via the Yamazaki–Higashi phosphorylation method in the presence of trip-
henylphosphite (TPP), pyridine (Py) and halide salt to give high molecular polyamides (PAs). The synthe-
Keywords:
Polyamides based on imidazole and
fluorene–bisphenol rings
Solubility
sized PAs were obtained in quantitative yields with inherent viscosities between 0.51 and 0.76 dL gÀ1
.
Thermal stability
The structures of diamine and PAs were characterized by elemental analysis, FT-IR and NMR spectros-
copy, and properties of PAs were investigated by using differential scanning calorimetry (DSC), thermo-
gravimetric analysis (TGA), and UV–visible and fluorescence spectroscopy. The PAs showed good
solubility in aprotic and polar organic solvents, with high thermal stability exhibiting the glass transition
temperatures (Tgs) and 10% weight loss temperatures (T10%) in the range of 226–330 °C and 400–466 °C in
air, respectively, and fluorescence emission with maximum wavelengths (kem) in the range of 417–
473 nm with quantum yields (Uf) of 9–35%. Two of these polymers together with compounds (II) and
(III) were also screened for antibacterial activity against Gram positive and Gram negative bacteria.
Ó 2012 Elsevier Ltd. All rights reserved.
Photophysical properties
Antibacterial activity
1. Introduction
mechanical properties to any great extent. Imidazole ring and its
derivatives such as lophine, 2,4,5-triphenylimidazole, are useful
Polyamides offer excellent physical and chemical properties,
thermal and oxidative stability, flame resistance, and superior
mechanical and dielectric properties [1,2]. However, for many
applications polyamides need to have good film-forming ability
and adequate organo-solubility. In order to achieve these require-
ments, structural modifications of polyamides often became essen-
tial [3]. Therefore, research on aromatic polyamides with
heterocycles in the main chain [4–9] and in the pendant structure
[10,11] is widespread in the scientific literature. Among these ap-
proaches, introducing bulky pendent substituents and heteroaro-
matic rings into polymers chains has been considered to be
efficient, which can provide not only enhanced solubility but also
good thermal stability. If these groups are carefully chosen, they
are likely to increase solubility without affecting thermal and
n-type building blocks with high electron affinity and good thermal
stability and has been successfully incorporated in small molecules
and polymers as the electron-transport component [12–17]. More-
over, imidazole and its derivatives are fairly extensively studied due
to new possibilities for their application in medicine as biologically
active substances [18–22]. However, the use of antimicrobial
agents blended in a polymer matrix can give rise to the migration
towards the surface of the antibacterial agent and therefore the
antimicrobial activity decreases during the lifetime of the polymer
application. For this reason, in the last years, several research
groups have tested the use of different antimicrobial agents cova-
lently bonded to the polymer chain, and the vast majority of litera-
ture focuses on olefin-containing imidazole monomers [23–30].
Fluorene has a violet fluorescence and its derivatives are precursor
to other useful fluorene compounds such as pharmaceuticals, dyes,
and also used in preparation of many commercially important
derivatives. Polyfluorene polymers are electrically conductive and
⇑
Corresponding author. Tel.: +98 112 534 2353; fax: +98 112 534 2302.
E-mail address: ghaemy@umz.ac.ir (M. Ghaemy).
1381-5148/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.reactfunctpolym.2012.12.005

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M. Ghaemy et al. / Reactive & Functional Polymers 73 (2013) 555–563
electroluminescent, and have been much investigated for use as a
luminophore in organic light-emitting diodes [31]. For all the rea-
sons reported above the preparation of polyamides with good solu-
bility, thermal stability and photophysical properties look very
interesting. Prompted by these observations and in continuation
of our research on polyamides, we hereby report the synthesis
and characterization of a new diamine containing substituted imid-
azole and fluorene–bisphenol rings and its use in preparation of a
series of polyamides. These polymers are expected to show high
thermal stability and photoluminescence properties due to pres-
ence of lophine and fluorene structures in the backbone, and must
also have good solubility in organic solvents as a result of presence
of hetero-aromatic and ether linkages in the polymer chains. Be-
cause of the presence of substituted imidazole (lophine) in these
polymers, they were also tested for antibacterial activity against
Gram positive and Gram negative bacteria.
7.91 (d, 1H, J = 8.20 Hz), 8.25 (dd, 1H, J = 8.20 Hz), 8.65 (d, 1H,
J = 8.20 Hz), 12.98 (s, 1H, NAH imidazole). Elemental analysis cal-
culated for C21H14ClN3O2: C, 67.20%; H, 3.73%; N, 11.20% and
found: C, 67.00%; H, 3.65%; N, 11.35%.
2.2.2. 9,9-Bis{4-[2-(4,5-diphenylimidazol-2-yl)-4-
nitrophenoxy]phenyl}fluorene (II)
A mixture of 10 mmol (3.50 g) 9,9-bis(4-hydroxyphenyl)fluo-
rene, 20 mmol (7.5 g) 2-(2-chloro-5-nitrophenyl)-4, 5-diphenyl-
1H-imidazole and 20 mmol (2.76 g) anhydrous potassium carbon-
ate in 20 mL of dry DMAc was refluxed at 130 °C for 12 h and then
cooled. The mixture was poured into water and the precipitate was
collected by filtration and recrystallized from ethanol. The yield of
product was 9.87 g (96%) with mp = 295–298 °C. FT-IR (KBr disk) at
cmÀ1: 3453 (NAH imidazole), 3062 (CAH aromatic), 1622 (C@N),
1580 (C@C), 1532, 1345 (NO2) and 1243 (CAO). 1H NMR (DMSO-
d6, d in ppm): 6.98 (d, 2H, J = 9.2 Hz), 7.17–7.52 (m, 34H), 7.97 (d,
2H, J = 7.6 Hz), 8.19 (dd, 2H, J = 9.2 Hz), 8.92 (d, 2H, J = 2.8 Hz),
12.57 (s, 2H, NAH imidazole). Elemental analysis calculated for
2. Experimental
2.1. Materials
C67H44N6O6: C, 78.21%; H, 4.28%; N, 8.17% and found: C, 78.09%;
H, 4.27%; N, 8.12%.
All chemicals were purchased from Fluka and Merck Chemical
Co. (Germany), through a local agency. Ammonium acetate, 9,9-
bis(4-hydroxyphenyl)fluorene, hydrazine monohydrate and 10%
palladium on activated carbon, and reagent grade diacids such as
terephthalic acid, isophthalic acid, pyridine-2,6-dicarboxylic acid,
adipic acid and sebacic 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 cal-
cium hydride and stored over 4 Å molecular sieves.
2.2.3. 9,9-Bis{4-[2-(4,5-diphenylimidazol-2-yl)-4-aminophenoxy]
phenyl}fluorene (III)
A 10 mmol (10.28 g) compound II and 0.4 g palladium on acti-
vated carbon (Pd/C, 10%) were dispersed in 120 mL ethanol. The
suspension solution was heated to reflux, and 12 mL hydrazine
monohydrate was slowly added to the mixture. After a further 6 h
reflux, the solution was filtered hot to remove Pd/C and the filtrate
was cooled to precipitate white crystals. The product was collected
by filtration and dried in vacuum at 90 °C. The yield of product was
8.03 g (83%) with mp = 184–186 °C. FT-IR (KBr disk) at cmÀ1: 3437
(NAH imidazole), 3362, 3212 (NH2), 3032 (CAH aromatic), 1607
(C@N), 1491 (C@C) and 1221 (CAO). 1H NMR (DMSO-d6, d in
ppm): 5.20 (s, 4H), 6.60 (dd, 2H, J = 7.6 Hz), 6.68 (d, 2H,
J = 8.8 Hz), 6.80 (d, 2H, J = 8.8 Hz), 6.90 (d, 4H, J = 9.2 Hz), 7.14–
7.41 (m, 30H), 7.85 (d, 2H, J = 7.2 Hz), 11.94 (s, 2H, NAH imidazole).
13C NMR (100 MHz, DMSO-d6, d in ppm): 1 (63.41), 2 (114.46), 3
(115.89), 4 (116.44), 5 (120.90), 6 (122.54), 7 (123.77), 8 (126.25),
9 (126.84), 10 (127.42), 11 (127.94), 12 (128.21), 13 (128.52), 14
(128.63), 15 (128.97), 16 (129.09), 17 (131.48), 18 (139.30), 19
(139.77), 20 (142.53), 21 (143.38), 22 (146.12), 23 (151.38), 24
(157.56). Elemental analysis calculated for C67H48N6O2: C, 83.06%;
H, 4.96%; N, 8.68% and found: C, 83.14%; H, 5.05%; N, 8.64%.
2.2. Diamine synthesis
The synthetic pathway leading to the synthesis of target dia-
mine is outlined in Scheme 1.
2.2.1. 2-(2-Chloro-5-nitrophenyl)-4,5-diphenyl-1H-imidazole (I)
A mixture of 10 mmol (1.86 g) 2-chloro-5-nitrobenzaldehyde,
10 mmol (2.1 g) benzil, 70 mmol (5.39 g) ammonium acetate and
20 mL glacial acetic acid was refluxed for 24 h. On cooling, the pre-
cipitated white solid was collected by filtration and washed with
ethanol and water. The yield of product was 3.55 g (95%) with
mp = 218–220 °C. FT-IR (KBr disk) at cmÀ1: 3453 (NAH imidazole),
3124 (CAH aromatic), 1532, 1345 (NO2) and 1684 (C@N). 1H NMR
(DMSO-d6, d in ppm): 7.34–7.38 (m, 6H), 7.54 (d, 4H, J = 8.20 Hz),
Scheme 1. Synthesis of target diamine (III).

M. Ghaemy et al. / Reactive & Functional Polymers 73 (2013) 555–563
557
2.3. Polymer synthesis
ArAH, J = 8.0 Hz), 7.56 (s, 1H, ArAH), 7.71 (m, 2H, ArAH), 7.88
(m, 4H, ArAH), 8.12 (d, 1H, ArAH, J = 7.2 Hz), 8.20 (d, 2H, ArAH,
J = 8.0 Hz), 8.48 (m, 2H, ArAH), 8.57 (m, 1H, ArAH), 8.63 (m, 1H,
ArAH), 10.63 (s, 2H, NAH amide), 12.22 (s, 2H, NAH imidazole
ring). Elemental analysis calculated for (C75H50N6O4)n: C, 81.97%;
H, 4.55%; N, 7.65%. Found: C, 81.88%; H, 4.69%; N, 7.70%.
The following general procedure, as is illustrated in Scheme 2,
was used for the preparation of polyamides from diamine (III)
and different aliphatic and aromatic dicarboxylic acids. Diamine
(III) (1 mmol, 0.97 g), a dicarboxylic acid (1 mmol), and lithium
chloride (0.30 g) were dissolved in a mixture of pyridine (1 mL),
triphenylphosphite (TPP) (1.20 mmol), and NMP (5 mL). The reac-
tion mixture was heated at 120 °C for 12 h with stirring under
dry N2 atmosphere. The mixture was then cooled to room temper-
ature and the resulting polymers were precipitated in 200 mL
methanol. The precipitate was filtered and washed with hot water,
and then was further purified by washing with methanol for 1 day
in a Soxhlet apparatus to remove the low molecular weight frac-
PA3: Yield 89% and ginh (dL/g) = 0.66. FT-IR (KBr disk) at cmÀ1
:
3437 (NAH imidazole), 3282 (NAH amide), 3058 (CAH aromatic),
1665 (C@O amide), 1607 (C@N), 1498 (C@C) and 1230 (CAOAC).
1H NMR (DMSO-d6, d in ppm): 6.80 (d, 4H, ArAH, J = 7.6 Hz), 7.10
(m, 6H, ArAH), 7.09–7.37 (m, 18H, ArAH), 7.48 (d, 4H, ArAH,
J = 8.4 Hz), 7.51 (s, 1H, ArAH), 7.73 (m, 2H, ArAH), 7.86 (m, 4H,
ArAH), 8.11–8.25 (m, 2H, ArAH, J = 7.8 Hz), 8.43 (m, 2H, ArAH),
8.59 (m, 1H, ArAH), 8.66 (m, 1H, ArAH), 10.60 (s, 2H, NAH amide),
12.28 (s, 2H, NAH imidazole ring). Elemental analysis calculated
for (C74H49N7O4)n: C, 80.80%; H, 4.46%; N, 8.92%. Found: C,
80.71%; H, 4.57%; N, 8.86%.
tions. The inherent viscosity (ginh) of the polymers was measured
at a concentration 0.5 g/dL in NMP at 25 °C and was in the range
of 0.51–0.76 dL/g.
PA1: Yield 92% and ginh (dL/g) = 0.76. FT-IR (KBr disk) at cmÀ1
:
PA4: Yield 91% and ginh (dL/g) = 0.51. FT-IR (KBr disk) at cmÀ1
:
3426 (NAH imidazole), 3273 (NAH amide), 3062 (CAH aromatic),
1664 (C@O amide), 1607 (C@N), 1495 (C@C) and 1229 (CAOAC).
1H NMR (DMSO-d6, d in ppm): 6.89 (d, 4H, ArAH, J = 7.2 Hz), 7.02
(m, 6H, ArAH), 7.11–7.34 (m, 18H, ArAH), 7.44 (d, 4H, ArAH,
J = 7.08 Hz), 7.59 (s, 1H, ArAH), 7.72 (m, 2H, ArAH), 7.92 (m, 4H,
ArAH), 8.12 (d, 1H, ArAH, J = 7.2 Hz), 8.23 (d, 2H, ArAH,
J = 8.2 Hz), 8.47 (m, 2H, ArAH), 8.58 (m, 1H, ArAH), 8.62 (m, 1H,
ArAH), 10.60 (s, 2H, NAH amide), 12.23 (s, 2H, NAH imidazole
ring). Elemental analysis calculated for (C75H50N6O4)n: C, 81.97%;
H, 4.55%; N, 7.65%. Found: C, 81.84%; H, 4.63%; N, 7.62%.
3429 (NAH imidazole), 3270 (NAH amide), 3055 (CAH aromatic),
2934 (CAH aliphatic), 1671 (C@O amide), 1609 (C@N), 1487 (C@C)
and 1220 (CAOAC). 1H NMR (DMSO-d6, d in ppm): 1.65 (m, 4H,
CAH), 2.31 (t, 4H, CAH), 6.82 (d, 4H, ArAH, J = 8.0 Hz), 6.84 (m,
6H, ArAH), 7.23–7.38 (m, 22H, ArAH), 7.47 (d, 4H, ArAH,
J = 7.6 Hz), 7.63 (d, 2H, ArAH, J = 8.8 Hz), 7.81 (distorted d, 2H,
ArAH), 8.25 (s, 2H, ArAH), 10.14 (s, 2H, NAH amide), 12.18 (s,
2H, NAH imidazole ring). Elemental analysis calculated for (C73-
H54N6O4)n: C, 81.26%; H, 5.01%; N, 7.79%. Found: C, 81.17%; H,
5.13%; N, 7.73%.
PA2: Yield 86% and ginh (dL/g) = 0.70. FT-IR (KBr disk) at cmÀ1
:
PA5: Yield 94% and ginh (dL/g) = 0.57. FT-IR (KBr disk) at cmÀ1
:
3418 (NAH imidazole), 3275 (NAH amide), 3066 (CAH aromatic),
1664 (C@O amide), 1605 (C@N), 1500 (C@C) and 1226 (CAOAC).
1H NMR (DMSO-d6, d in ppm): 6.87 (d, 4H, ArAH, J = 7.2 Hz), 7.03
(distorted d, 5H, ArAH), 7.17–7.35 (m, 19H, ArAH), 7.45 (d, 4H,
3426 (NAH imidazole), 3276 (NAH amide), 3051 (CAH aromatic),
2931 (CAH aliphatic), 1671 (C@O amide), 1607 (C@N), 1487 (C@C)
and 1221 (CAOAC). 1H NMR (DMSO-d6, d in ppm): 1.31 (m, 8H,
CAH), 1.60 (m, 4H, CAH), 2.31 (t, 4H, CAH), 6.80 (d, 4H, ArAH,
Scheme 2. Polycondensation reaction of diamine (III) with different dicarboxylic acids.

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M. Ghaemy et al. / Reactive & Functional Polymers 73 (2013) 555–563
J = 8.4 Hz), 6.80 (m, 6H, ArAH), 7.17–7.33 (m, 22H, ArAH), 7.43 (d,
4H, ArAH, J = 7.2 Hz), 7.66 (d, 2H, ArAH, J = 9.2 Hz), 7.86 (distorted
d, 2H, ArAH), 8.23 (s, 2H, ArAH), 10.04 (s, 2H, NAH amide), 12.13
(s, 2H, NAH imidazole ring). Elemental analysis calculated for (C77-
H62N6O4)n: C, 81.48%; H, 5.47%; N, 7.41%. Found: C, 81.44%; H,
5.52%; N, 7.40%.
100 rpm. The compounds sensitivity of the strains was assayed
for positive or negative growth after 24–48 h.
3. Results and discussion
3.1. Synthesis and characterization of diamine and polymers
2.4. Measurements
The objective of this study was two folds: synthesis and charac-
terization of a new diamine bearing particular functional groups
for optical and antibacterial activity such as imidazole and fluorene
moieties and its use in preparation of corresponding polyamides.
The synthetic procedure for the preparation of diamine (III) is
shown in Scheme 1. Condensation of benzil with 2-chloro-5-nitro-
benzaldehyde and ammonium acetate is a classical but convenient
synthetic method for preparation of triaryl imidazole. The dinitro
compound (II) was successfully synthesized by nucleophilic chlo-
rodisplacement reaction between 9,9-bis(4-hydroxyphenyl)fluo-
rene and compound (I) in DMAc in the presence of K2CO3. The
diamine (III) was obtained by catalytic reduction of the dinitro
compound (II) by using hydrazine hydrate and Pd/C in refluxing
ethanol. The chemical structure of the synthesized compounds I–
III was identified by elemental analysis, FT-IR and 1H and 13C
NMR spectroscopy. The formation of imidazole ring in compound
(I) was evident from the signal around 12.00 ppm of 1H NMR spec-
trum. The nitro groups in compounds (I) and (II) were evident from
the FT-IR peaks at 1532 and 1345 cmÀ1 (ANO2 asymmetric and
symmetric stretching). After reduction, the absorption peaks of
NO2 groups disappeared and the primary amino group showed
the typical absorption pair at 3362 and 3212 cmÀ1, as shown in
Fig. 1. The 1H (A) and COSY (B) NMR spectra of diamine (III) con-
firms the complete transformation of nitro groups into the amine
groups by the high field shift of the aromatic protons and by the
appearance of characteristic signals of amine group’s protons at
5.20 ppm, as shown in Fig. 2. The 13C NMR spectrum of this com-
pound, Fig. 3, shows 24 different carbons for the aromatic segment
and heterocyclic rings. The elemental analysis results are also in
good agreement with the calculated percentages of carbon, hydro-
gen and nitrogen contents in the intermediates and diamine (III)
structures.
1H and 13C NMR spectra were recorded on a 400 MHz Bruker
and 100 MHz, respectively, (Ettlingen, Germany) instrument using
DMSO-d6 as solvent and tetramethyl silane as an internal standard.
Elemental analyses performed by a CHN-600 Leco elemental ana-
lyzer. Melting point (uncorrected) was measured with a Barnstead
Electrothermal engineering LTD 9200 apparatus. Inherent viscosi-
ties (at a concentration of 0.5 g/dL) were measured with an Ubbe-
lohde suspended-level viscometer at 25 °C using NMP as solvent.
Qualitative solubility was determined using 0.05 g of the polymer
in 0.5 mL of solvent. Thermogravimetric analysis (TGA) was per-
formed with the DuPont Instruments (TGA 951) analyzer well
equipped with a PC at a heating rate of 10 °C/min under nitrogen
atmosphere (20 cm3/min) and in the temperature range of 30–
650 °C. Differential scanning calorimetry (DSC) was recorded on a
Perkin Elmer pyris 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 capac-
ity and were taken from the second heating scan after cooling from
350 °C at a cooling rate of 20 °C minÀ1. Ultraviolet–visible and fluo-
rescence emission spectra were recorded on a Cecil 5503 (Cecil
Instruments, Cambridge, UK) and Perkin-Elmer LS-3B spectropho-
tometers (Norwalk, CT, USA) (slit width = 2 nm), respectively,
using a dilute polymer solution (0.20 g/dL) in DMSO.
2.5. Antibacterial assay
The in vitro biocidal screening, antibacterial activities of the
synthesized compounds was assayed onto LB (Luria–Bertani) med-
ium contained: BactoTM tryptone, 10.0 g LÀ1
; yeast extract,
5.0 g LÀ1; sodium chloride, 5.0 g LÀ1; and glucose, 1.0 g LÀ1. The
medium was dispensed into universal bottles and sterilised at
121 °C for 15 min. A 0.04 g of intermediate compounds (II) and
(III) and polyamides PA1 and PA5 were dissolved separately in
20 mL DMSO to generate 2 mg mLÀ1 working solutions which were
The new PAs were synthesized by phosphorylation polyconden-
sation between diamine (III) and various commercially available
aromatic and aliphatic dicarboxylic acids in NMP using TPP and
pyridine as condensing agents at 120 °C in N2 (Scheme 2). All the
polycondensation reactions proceeded readily in a homogeneous
solution. Since Yamazaki et al.’s [32] development, many
researchers have utilized the activated polyamidation using the
filter sterilised using a 0.22
work solutions were added into LB medium to give a final concen-
tration of 1–300
g mLÀ1 as required. The antibacterial activities of
lm Ministart (Sartorius). The sterilized
l
the compounds were compared with known antibiotic tetracycline
at the same concentration. The minimum inhibitory concentration
(MIC) test of the newly synthesized compounds were determined
in vitro against microorganisms including the two Gram-negative
bacteria Escherichia coli PTCC1533 and Pseudomonas aeruginosa
PTCC 1707, and two Gram-positive bacteria Staphylococcus aureus
ATCC 25923 and Bacillus subtilis PTCC 1156. MIC is typically re-
ported as the lowest concentration of antimicrobial activity that
completely inhibits growth over a set period of incubation relative
to a control containing no antimicrobial. For the synthesized com-
pounds investigated, the amount of bacterial growth at each com-
pound concentration was reported. Late exponential phase of the
bacteria were prepared by inoculating 1% (v/v) of the cultures into
the fresh LB medium and incubating on an orbital shaker at 37 °C
and 100 rpm overnight. Before using the cultures, they were stan-
dardized with a final cell density of approximately 108 cfu mLÀ1. A
1% (v/v) inoculums of each culture was inoculated into the LB
medium containing different concentrations of the synthesised
compounds and incubated on the orbital shaker at 37 °C and
Fig. 1. FT-IR spectrum of diamine (III) and PA1.

M. Ghaemy et al. / Reactive & Functional Polymers 73 (2013) 555–563
559
Fig. 2. 1H (A) and COSY (B) NMR spectra of diamine (III) in DMSO-d6.
Fig. 3. 13C NMR spectrum of diamine (III) in DMSO-d6.
TPP activator and found that the addition of a small amount of LiCl
or CaCl2 enhances the molecular weight of the polyamides. All PAs
remained soluble in the reaction medium, thus permitting an in-
crease of their molecular weight and giving viscous solutions.

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M. Ghaemy et al. / Reactive & Functional Polymers 73 (2013) 555–563
Stringy and tough precipitates formed when the viscous polymer
solutions were trickled into the stirring methanol. As shown in Ta-
ble 1, the inherent viscosities of polymers were in the range of
0.51–0.76 dL/g. The elemental analysis values were in good agree-
ment with the calculated ones. For obtaining light colored PAs, a
lower capability of charge transfer is indispensable. An effective
way of depressing the charge transfer of polymers is introducing
non-conjugated segments into the backbone. Thus, PA4 and PA5
were synthesized from adipic acid and sebacic acid, respectively.
This could effectively reduce the conjugation and capability of
charge transfer and led to enlarged band gaps of the PAs. FT-IR
spectrum of the representative polymer PA1 is shown in Fig. 1.
These polymers exhibited characteristic absorption bands around
3300 cmÀ1 (NAH stretching), 1420 cmÀ1 (NAH bending), near
1220 cmÀ1 (aryl ether stretching) and at 1670 cmÀ1 (C@O, amide).
1H NMR spectrum of the representative polymer PA5 is illustrated
in Fig. 4, where all the peaks could be readily assigned to the pro-
tons in the repeating unit. In the 1H NMR spectra of these poly-
mers, the NAH proton of amide groups appeared in the region of
10.04–10.63 ppm, while the NAH proton of imidazole ring ap-
peared at the most downfield region of 12.13 ppm.
the polymers were made by dissolving about 0.50 g of the samples
in 6 mL of NMP. These solutions were poured into a 5-cm glass Pet-
ri dish, which was heated under vacuum at 50 °C for 1 h, 100 °C for
2 h, and 150 °C for 5 h to evaporate the solvent slowly. By being
soaked in distilled water, the flexible and transparent thin films
with almost no color was self-stripped off from the glass surface.
The obtained films were then used to investigate the optical prop-
erties of the PAs. The excitation wavelength was 310 nm in all
cases. The maximum emission wavelength (kem) of the diamine
was observed at 385 nm, around 460–473 nm for the aromatic
PAs (PA1, PA2 and PA3) and around 417–431 nm for the aliphatic
PAs (PA4 and PA5). In addition, the PAs exhibited a slightly red-
shifted emission in the solid state when compared with that mea-
sured in NMP solutions, possibly due to an increased interchain
interaction in the film form. The emission intensity of aliphatic
and aromatic PAs was not the same, which confirms that the fluo-
rescence intensity is affected by incorporation of alkyl and phenyl
groups into the polymer main chain. To measure the photolumi-
nescence (PL) quantum yields (Uf), dilute polymer solutions
(0.2 g/dL) in NMP were prepared. A 0.10 N solution of quinine in
H2SO4 (Uf = 0.55) was used as a reference.
The Uf values were 35% and 27% for the aliphatic PA5 and PA4,
respectively, and in the range of 9–12% for the aromatic PAs. The
blue shift and higher fluorescence quantum yield of the aliphatic
PAs compared with the aromatic PAs could be attributed to re-
duced conjugation and capability of charge-transfer complex for-
mation by the aliphatic diacids with the electron-donating
diamine moiety in comparison to the stronger electron-accepting
aromatic diacids [33].
3.2. Properties of polyamides
3.2.1. Solubility
The solubility behavior of these polymers was tested qualita-
tively in various organic solvents, and the results are summarized
in Table 1. The polyamides were readily soluble in polar organic
solvents such as NMP, DMAc, DMF, and DMSO at room tempera-
ture. The good solubility associated with these polymers could be
attributed to the presence of propeller-shaped fluorene–bisphenol
structure, bulky pendent triaryl imidazole group, and ether linkage
sequences in the repeat unit. These factors increase the chain dis-
tance and decrease the interaction of the polymer chains; conse-
quently, the solvents molecules are able to penetrate easily and
interact with the polar groups and to solubilize the polymer chains.
The solubility also varies depending upon the dicarboxylic acid
used. The polyamides synthesized from aliphatic dicarboxylic acids
PA4 and PA5 exhibited better solubility behavior in less polar sol-
vents such as THF, m-cresol and Py.
3.2.3. Thermal properties
The thermal behavior data of these polymers were assessed by
using DSC and TGA analysis. DSC was used to determine the glass-
transition temperature (Tg) values of the PAs. The DSC curves were
recorded at heating rate of 10 °C/min in N2 are shown in Fig. 6.
Melting endothermic peak was not observed by DSC in the temper-
ature range of 50–350 °C, so that the PAs were considered to be
essentially amorphous. The amorphous nature of these PAs can
be attributed to their bulky pendent group which decreased the in-
ter-chain interaction resulting in loose polymer chain packaging
and aggregates. The Tg values were read at the midpoint of the
change in slope of the baseline of DSC curves, and found to be in
the range of 226–330 °C, as listed in Table 3. In general, molecular
packing and chain rigidity are among the main factors influencing
on Tg values. The increased rotational barrier caused by the bulky
pendant in diamines and side chain-side chain and side chain-main
chain interactions led to enhanced Tg values. However, the
presence of flexible bond such as amide and particularly ether link-
ages in the main chain of these PAs reduced the rigidity of their
backbones and consequently Tg of these polymers reached to a rea-
sonable and obtainable values in the range of 226–330 °C. There-
fore, Tg values of these polymers are affected by these two
opposite key factors; bulky pendants and flexibility of the main
3.2.2. Photophysical properties
The UV–vis absorption and photoluminescence (PL) spectra of
the diamine (2 Â 10–5 M) and PAs (0.1 g/dL) in dilute NMP solu-
tions are shown in Fig. 5A and B, respectively. The photophysical
data for PAs in solution and in solid state were summarized in Ta-
ble 2. The diamine and PAs showed strong UV–vis absorption
bands with maxima (kab) in the region of 305–314 nm which was
assigned to a
p–
pà transition resulting from the conjugation sys-
tems of aromatic rings in the main chain and in the pendent group.
By comparing the absorption spectra, a slightly red shift of 9 nm is
observed in PAs spectra due to expansion of
gate the optical properties of thin films of these PAs, solutions of
p system. To investi-
Table 1
Solubility of synthesized PA1–PA5.
Code
Solvent
Yield (%)
ginh (dL/g)a
DMAc
DMF
NMP
DMSO
Py
THF
–
CHCl3
CH3CN
m-cresol
PA1
PA2
PA3
PA4
PA5
92
86
89
91
94
0.76
0.70
0.66
0.51
0.57
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
–
–
–
–
–
–
–
–
–
–
+
+
++
++
+
++
++
+
+
++, Soluble at room temperature; +, soluble on heating at 60 °C; , partially soluble on heating at 60 °C; –, insoluble on heating at 60 °C.
a
Measured at a polymer concentration of 0.5 g/dL in NMP at 25 °C.

M. Ghaemy et al. / Reactive & Functional Polymers 73 (2013) 555–563
561
Fig. 4. 1H NMR spectrum of PA5 in DMSO-d6.
Fig. 5. UV–vis (A) and fluorescence (B) spectra of diamine (III) in solution and PA (1–5) films. Inside images: dilute solutions (2 Â 10À5 M) of (1) dinitro (II) and (2) diamine
(III), and (3) PA5 (0.1 g/dL) in DMSO.
chain by ether linkages. The Tg values also depend on the stiffness
of diacid residue in the polymer main chain and the increasing or-
der of Tg generally correlated with that of chain rigidity. Therefore,
among all the prepared PAs, PA4 and PA5 based on aliphatic dicar-
boxylic acid showed the lowest Tg values and those based on the
aromatic dicarboxylic acids such as PA(1–3) exhibited the highest
Tg values.
Thermal stability of these PAs was evaluated by TGA under N2
and air atmosphere at a heating rate of 10 °C minÀ1 and the curves
are shown in Fig. 7. The data, extracted from the original TGA
curves, in Table 3, show the temperature of 10% weight loss
(T10%) in the range of 419–492 °C in N2 atmosphere and in the
range of 396–466 °C in air, depending on the structure of diacid
Table 2
Photophysical properties data of PA1–PA5.
c
Polymer
kabs (nm)a
kem (nm)a
kabs (nm)b
kem (nm)b
Uf (%)
PA1
PA2
PA3
PA4
PA5
311
311
311
303
300
467
460
455
429
416
314
313
313
308
306
473
463
461
431
417
12
11
9
27
35
Polymer concentration of 0.20 g/dL in NMP.
a
UV–visible absorption and fluorescence emission spectra of the PAs in solution.
UV–visible absorption and fluorescence emission spectra of the PAs in films.
Fluorescence quantum yield relative to 10À5 M quinine sulfate in 1 N H2SO4 (aq)
b
c
(Uf = 0.55) as a standard.

562
M. Ghaemy et al. / Reactive & Functional Polymers 73 (2013) 555–563
component in the polymer backbone. The residual weights for the
resulting PAs were in the range of 36–63% at 750 °C in N2. Char
yield (CR) can be used as criteria for evaluating limiting oxygen in-
dex (LOI) of the polymers in accordance with Van Krevelen and
Hoftyzer equation [34]; LOI = 17.5 + 0.4CR. For all the PAs, LOI val-
ues calculated based on their CR at 700 °C. Due to the reasons
which have been explained above, the thermal stability of these
PAs are observed in order of PA(1–3) > PA(4 and 5). According to
Table 3, it is clear that aromatic PAs have better thermal stability
and higher LOI values as compared to the aliphatic PAs.
shown good activity against all tested bacteria particularly against
S. aureus. The diamine compound (III) was less active in inhibition
particularly for P. aeruginosa and S. aureus in comparison with the
dinitro (II) and the polymers. The results indicate that electron-
donating groups such as ANH2 decrease the antibacterial effect
of the imidazole-containing compounds. As can be seen from the
results in Table 4, it is revealed that the dinitro (II) inhibited the
growth of bacteria S. aureus at a low concentration of 50
and the rest of bacteria at 100
g mLÀ1 whereas the growth inhib-
itory effects of the diamine and PA1 on most bacteria were shown
at high concentration of 150 and 200
g mLÀ1 (Fig. 8). The results
l
g mLÀ1
l
l
indicated that the presence of electron withdrawing groups is nec-
essary for the antimicrobial activity of the synthesized compounds.
3.2.4. Antibacterial activity
The newly synthesized compounds were screened in vitro
against an assortment of two Gram-positive bacteria S. aureus
and B. subtilis and two Gram-negative bacteria E. coli and P. aerugin-
osa. In addition, the finding towards inhibition of microorganisms
was correlated with a standard antibiotic tetracycline and the
screening results are summarized in Table 4. Only an aromatic
and an aliphatic of the prepared polymers were tested for antibac-
terial activities. The antibacterial screening revealed that all the
tested compounds dinitro (II), diamine (III), PA1 and PA5 showed
moderate to good inhibition. The antibacterial screening indicated
that among the tested bacterial strains, good inhibitory results
were obtained against E. coli. As regards the relationships between
the structures of the heterocyclic scaffold and the detected anti-
bacterial properties, it showed varied biological activity. The anti-
bacterial activity seemed to be dependent on the heterocyclic
moiety as well as on the nature of substituent. Although the imid-
azole-containing compounds themselves are observed active. The
activity was further enhanced by the presence of nitro substituent
on the imidazole moiety. The nitro substituted compound has
Fig. 7. TGA curves of PA1, PA3 and PA5 under a N2 and air atmosphere at a heating
rate of 10 °C/min.
Table 4
Minimum inhibitory concentration (MIC) of the compounds (l
g mLÀ1) against some
bacteria.
Strain
Minimum inhibitory concentration (
l
g mLÀ1
PA1
)
Diamine (III)
Dinitro (II)
PA5
Tetracycline
E. coli
150
200
200
150
100
100
50
100
150
150
150
150
150
100
150
25
50
10
25
P. aeruginosa
S. aureus
B. subtilis
100
Fig. 6. DSC curves of PA (1–5) under a N2 atmosphere at a heating rate of 10 °C/min.
Table 3
Thermal properties of the PAs.
Code
Tg (°C)a
T10 (°C)b
T10 (°C)c
Char yieldd
LOI (%)e
PA1
PA2
PA3
PA4
PA5
330
316
305
234
226
492
476
460
428
419
466
450
433
401
396
63
57
46
36
39
43
40
36
32
33
a
b
c
Glass transition temperature was recorded at a heating rate of 10 °C/min in N2.
Temperature at which 10% weight loss was recorded by TGA in N2.
Temperature at which 10% weight loss was recorded by TGA in air.
d
Percentage weight of material left undecomposed after TGA analysis at
a
temperature of 800 °C in N2.
Fig. 8. Minimum inhibitory concentration of dinitro (II), diamine, PA1 and PA5
against some bacteria.
e
Limiting oxygen index percent evaluating at char yield 800 °C.

M. Ghaemy et al. / Reactive & Functional Polymers 73 (2013) 555–563
563
[9] F.A. Bottino, G. Di Pasquale, L. Scalia, A. Pollicino, Polymer 42 (2001) 3323–
3332.
The role of electron withdrawing group in improving antimicrobial
activities is supported by the studies of Sharma et al. [35,36].
[10] M. Ghaemy, R. Alizadeh, React. Funct. Polym. 71 (2011) 425–432.
[11] M. Ghaemy, M. Bazzar, J. Appl. Polym. Sci. 116 (2010) 64–71.
[12] M. Ghaemy, S.M. Amini Nasab, React. Funct. Polym. 70 (2010) 306–313.
[13] Y. Pan, X. Tang, Eur. Polym. J. 44 (2008) 408–414.
[14] Y. Pan, X. Tang, L. Zhu, Y. Huang, Eur. Polym. J. 43 (2007) 1091–1095.
[15] N. Fridman, M. Kaftory, S. Speiser, Sens. Actuators B 126 (2007) 107–115.
[16] A. Mikroyannidis, D. Panayiotis, V.I. Panayiotis, K. Spiliopoulos, Syn. Met. 145
(2004) 87–93.
[17] K. Feng, F.L. Hsub, D. Van DerVeer, K. Bota, R. Xiu, J. Photochem. Photobiol. A
Chem. 165 (2004) 223–228.
[18] J. Pandey, V.K. Tiwari, S.S. Verma, V. Chaturvedi, S. Bhatnagar, S. Sinha, A.N.
Gaikwad, R.P. Tripathi, Eur. J. Med. Chem. 44 (2009) 3350–3355.
[19] D. Zampieri, M.G. Mamolo, E. Laurini, G. Scialino, E. Banfi, L. Vio, Bioorg. Med.
Chem. Lett. 16 (2008) 4516–4522.
[20] J.Z. Vlahakis, R.T. Kinobe, K. Nakatsu, W.A. Szarek, I.E. Crandall, Bioorg. Med.
Chem. Lett. 16 (2006) 2396–2406.
[21] E.R. Kenawy, F.I. Abdel-Hay, A.A. El-Magd, Y. Mahmoud, J. Bioact. Compat. Pol.
20 (2005) 95–111.
[22] S. Khabnadideh, Z. Rezaei, A. Khalafi-Nezhad, R. Bahrinajafi, R. Mohamadi, A.A.
Farrokhroz, Bioorg. Med. Chem. Lett. 13 (2003) 2863–2865.
[23] M. Colonna, C. Berti, E. Binassi, M. Fiorini, S. Sullalti, F. Acquasanta, M. Vannini,
D. Di Gioia, I. Aloisio, S. Karanam, D.J. Brunelle, React. Funct. Polym. 72 (2012)
133–141.
[24] H.I. Chang, M.S. Yang, M. Liang, React. Funct. Polym. 70 (2010) 944–950.
[25] E.B. Anderson, T.E. Long, Polymer 51 (2010) 2447–2454.
[26] D. Kalita, S. Sarmah, S.P. Das, D. Baishya, A. Patowary, S. Baruah, N.S. Islam,
React. Funct. Polym. 68 (2008) 876–890.
4. Conclusions
In this study, a series of novel photoactive PAs containing bulky
imidazole pendant and fluorene–bisphenil rings and aryl ether
linkages in the main chain have been successfully prepared by di-
rect phosphorylation polycondensation of a new aromatic diamine
with various aromatic and aliphatic dicarboxylic acids. These re-
sults support that such a modification of the polymer structure
can be used as an effective strategy for imparting fluorescence
emission in the visible light region and enhancing the processabil-
ity of aramids, while maintaining the high thermal stability. These
polymers with inherent viscosities in the range of 0.51–0.76 dL/g
exhibited high enough molecular weight to give tough and flexible
thin films by solution casting. Their Tg values varied from 226 °C to
330 °C and their thermal stability based on 10% weight loss tem-
perature varied from 226 °C to 330 °C, depending on the rigidity
of the polymer backbone. Some of the synthesized compounds
were tested for antibacterial activity and the results indicated that
the presence of electron withdrawing groups is necessary for the
antimicrobial activity. In general, these compounds exhibited good
antibacterial activity and can be further developed for application
as effective antimicrobial agent.
[27] B. Yu, F. Zhou, C. Wang, W. Liu, Eur. Polym. J. 43 (2007) 2699–2707.
[28] N. Preethi, H. Shinohara, H. Nishide, React. Funct. Polym. 66 (2006) 851–855.
[29] H. Shinohara, H. Shibata, D. Wöhrle, H. Nishide, Macromol. Rapid. Commun. 26
(2005) 467–470.
[30] L. Cen, K.G. Neoh, E.T. Kang, Langmuir 19 (2003) 10295–10303.
[31] E. Zhou, J. Cong, M. Zhao, L. Zhang, K. Hashimoto, K. Tajima, Chem. Commun.
48 (2012) 5283–5285.
References
[32] N. Yamazaki, M. Matsumoto, F. Higashi, J. Polym, Polym. Chem. Ed. 13 (1975)
1373–1380.
[33] G.S. Liou, C.W. Chang, Macromolecules 41 (2008) 1667–1674.
[34] D.W. Van-Krevelen, Properties of Polymers, fourth ed., Elsevier Scientific
Publishing, 2008.
[35] D. Sharma, B. Narasimhan, P. Kumar, V. Judge, R. Narang, E. De Clercq, J.
Balzarini, Eur. J. Med. Chem. 44 (2009) 2347–2353.
[36] P. Sharma, N. Rane, V.K. Gurram, Bioorg. Med. Chem. Lett. 14 (2004) 4185–
4190.
[1] J.M. Garcıa, F.C. Garcıa, F. Serna, J.L. de la Peña, Prog. Polym. Sci. 35 (2010) 623–
686.
[2] C.P. Yang, J.H. Lin, J. Polym. Sci. Part A: Polym. Chem. 34 (1996) 341–348.
[3] J.E. Flood, J.L. White, J.F. Fellers, J. Appl. Polym. Sci. 27 (1982) 2965–2985.
[4] J. Tan, C. Wang, W. Peng, G. Li, J.M. Jiang, Polym. Bull. 62 (2009) 195–207.
[5] K. Faghihi, Z. Mozaffari, J. Appl. Polym. Sci. 108 (2008) 1152–1157.
[6] A. Abdolmaleki, Polym. Degrad. Stab. 92 (2007) 292–298.
[7] R.R. Pal, P.S. Patil, M.M. Salunkhe, N.N. Maldar, P.P. Wadgaonkar, Polym. Int. 54
(2005) 569–575.
[8] S.H. Hsiao, C.P. Yang, C.W. Chen, G.S. Liou, Eur. Polym. J. 41 (2005) 511–517.