Novel para-linked and CF3-substituted poly(amide-ether- imidazole)s: Solubility, optical and thermal properties

Article abstract of DOI:10.1016/j.jfluchem.2012.07.014

A new photoactive fluorinated diamine, 2-(4-trifluoromethylphenyl)-4,5- bis(4-(4-amino-2-trifluoromethylphenoxy)phenyl)imidazole (TFIA), was synthesized and used for preparation of novel fluorinated poly(amide-ether-imidazole)s (PAEIs) by using direct polycondensation of the diamine with various dicarboxylic acids. The resulting PAEIs were amorphous and had intrinsic viscosity [η] in the range of 0.68-0.80 dL/g. The weight average (M _w) and number average (M_n) molecular weights of one of the polymer, measured by GPC, were 18,600 g/mol and 11,500 g/mol, respectively. These polymers were readily soluble in a variety of organic solvents and formed low-colored and flexible thin films via solution casting. Their values of cut-off wavelength (λ₀) were in the range of 380-390 nm, and all PAEIs films exhibited high optical transparency. According to thermal analysis, these polymers exhibited glass transition temperatures (T _g)s in the range of 160-250°C, initial decomposition temperature (T_i) from 295 to 400°C and temperature of 10% weight loss (T _10%) from 400 to 490°C in N₂. These polymers exhibited strong UV-vis absorption at 310 nm in solution and in films and their fluorescence emission peaks appeared around 430-520 nm with the quantum yields in solution varied from 10% to 29%.

Full text of DOI:10.1016/j.jfluchem.2012.07.014

Journal of Fluorine Chemistry 144 (2012) 86–93
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Novel para-linked and CF3-substituted poly(amide-ether-imidazole)s:
Solubility, optical and thermal properties
*
Mousa Ghaemy , Farshad Rahimi Berenjestanaki
Polymer Chemistry Research Laboratory, Department of Chemistry, Mazandaran University, Babolsar, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
A new photoactive fluorinated diamine, 2-(4-trifluoromethylphenyl)-4,5-bis(4-(4-amino-2-trifluoro-
methylphenoxy)phenyl)imidazole (TFIA), was synthesized and used for preparation of novel fluorinated
poly(amide-ether-imidazole)s (PAEIs) by using direct polycondensation of the diamine with various
Received 6 May 2012
Received in revised form 3 July 2012
Accepted 25 July 2012
Available online 1 August 2012
dicarboxylic acids. The resulting PAEIs were amorphous and had intrinsic viscosity [h] in the range of
0.68–0.80 dL/g. The weight average (Mw) and number average (Mn) molecular weights of one of the
polymer, measured by GPC, were 18,600 g/mol and 11,500 g/mol, respectively. These polymers were
readily soluble in a variety of organic solvents and formed low-colored and flexible thin films via solution
Keywords:
Fluorinated polyamide
Direct polycondensation
Fluorinated diamine
Thermal properties
Solubility
casting. Their values of cut-off wavelength (l0) were in the range of 380–390 nm, and all PAEIs films
exhibited high optical transparency. According to thermal analysis, these polymers exhibited glass
transition temperatures (Tg)s in the range of 160–250 8C, initial decomposition temperature (Ti) from
295 to 400 8C and temperature of 10% weight loss (T10%) from 400 to 490 8C in N2. These polymers
exhibited strong UV–vis absorption at 310 nm in solution and in films and their fluorescence emission
peaks appeared around 430–520 nm with the quantum yields in solution varied from 10% to 29%.
ß 2012 Elsevier B.V. All rights reserved.
Fluorescent
1. Introduction
This study explores the synthesis and basic characterization of
several novel poly(amide-ether-imidazole)s having imidazol-
The chemistry of aromatic polyamides has undergone out-
standing developments in the last few years to overcome the
problem of processability due to their high glass-transition and
melting temperature [1,2]. Many novel diamine or diacid mono-
mers have been specially designed using different approaches,
such as incorporation of flexible or bridging functional groups [3–
6], bulky pendant groups [7–11], cardo groups [12–14], heterocy-
clic rings [15,16] and meta- or ortho-catenated as a less symmetric
aromatic units [17–19] to afford the success in preparation of
organosoluble polyamides. Recently, considerable attention has
been devoted to the synthesis of fluorine containing polymers.
Incorporation of the bulky fluorine groups serves to increase the
free volume of the polymers, thereby improving some properties
such as solubility, gas permeability, optical transparency and flame
resistance [20–23]. In addition, it also reduces the moisture
absorption, crystallinity, dielectric constant and color. Imidazole
ring is a useful n-type building block with high-electron affinity
and good thermal stability and has been successfully incorporated
in small molecules and polymers as the electron-transport
component of OLEDs [24–30].
trifluoromethyl moieties as well as aryl-ether unit in their
backbone. These PAs were prepared by direct polycondensation
of a new synthesized diamine, 2-(4-trifluoromethylphenyl)-4,5-
bis(4-(4-amino-2-trifluoromethylphenoxy)phenyl)
(TFIA), with various aromatic and aliphatic dicarboxylic acids.
TFIA and the intermediates were characterized by mass, FT-IR, 1
imidazole
H
and 13C NMR spectroscopy, and elemental analysis. The obtained
PAEIs were characterized by FT-IR, H NMR, elemental analysis and
viscosity measurements and their properties such as organosolu-
bility, thermal and photophysical are investigated and discussed.
2. Experimental
2.1. Materials
All materials and solvents were purchased either from Merck or
from Fluka Chemical Co. 4-(Trifluoromethyl)benzaldehyde, 2-
chloro-5-nitrobenzotrifluoride, 4,40-dimethoxybenzil, ammonium
acetate, hydrazine monohydrate, 10% Pd/C, potassium carbonate,
triphenyl phosphite (TPP), acetic acid, and all dicarboxylic acids, and
solvents such as dimethylformamide (DMF), dimethylsulfoxide
(DMSO), ethanol, methanol, acetone, hexamethylphosphoramide
(HMPA), and tetrahydrofuran (THF) were used without further
purification. N-methyl-2-pyrrolidone (NMP), N,N-dimethylaceta-
mide (DMAc), and pyridine were purified by distillation over
* Corresponding author. Tel.: +98 112 534 2353; fax: +98 112 534 2302.
E-mail address: ghaemy@umz.ac.ir (M. Ghaemy).
0022-1139/$ – see front matter ß 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jfluchem.2012.07.014

M. Ghaemy, F.R. Berenjestanaki / Journal of Fluorine Chemistry 144 (2012) 86–93
87
calcium hydride under reduced pressure. LiCl and CaCl2 were dried
at 180 8C in vacuum for 14 h.
2.2. Measurements
FT-IR measurements were performed on a Bruker-IFS48
spectrometer (Ettlingen, Germany). The spectra of solids were
obtained using KBr pellets. 1H NMR and 13C NMR spectra were
recorded in dimethyl sulfoxide-d6 (DMSO-d6) solution using a
Bruker Avance 400 MHz instrument (Germany), operated at
500 MHz for proton and 100 MHz for carbon using DMSO-d6,
and tetramethylsilane was used as an internal standard.
Elemental analysis was run in a Flash EA 1112 series analyzer.
Melting points were determined in open capillaries with IA 9200
Series Digital Melting Point apparatus. Differential scanning
calorimetry (DSC) and thermogravimetric (TGA) analyses were
recorded on a Stanton Redcraft STA-780 (London, UK) at heating
rate of 10 8C/min under N2 atmosphere. Glass transition tem-
peratures (Tg)s were read at the middle of the transition in the heat
capacity and were taken from the second heating scan after quick
cooling from 350 8C at a cooling rate of 200 8C/min. Intrinsic
viscosity [
polymer solutions in DMAc at 30 8C. To determine the values of
], at first three viscosity numbers ( red) were measured at
h] were measured using an Ubbelohde viscometer with
[
h
h
concentrations of 0.10, 0.25, and 0.50 g/dL in DMAc. These
viscosity numbers were plotted against the concentrations used,
and then the linear extrapolation was done. The values of [h] were
determined as the y-axis intersect. UV–vis absorption and
fluorescence emission spectra were recorded in NMP solution
and in polymer films on a Cecil 5503 and Perkin-Elmer LS-3B
spectrophotometers, respectively. Also, cut-off wavelength (ab-
sorption edge) values (l0) of the prepared thin films were
Scheme 1. Synthesis of target diamine TFIA.
determined. Weight and number-average molecular weights of
the one of the resulting PAs were determined by gel-permeation
chromatography (GPC). This chromatography was performed on a
Waters 150-C instrument using Styragel columns and a differen-
tial refractometer detector. The molecular weight calibration was
carried out using polystyrene standards. Calibration and mea-
surements were made at a flow rate of 1 mL/min with THF as the
eluent. Mass measurements of the synthesized compounds were
performed on a Bruker-BiFlex III MALDI-TOF spectrophotometer
(Bruker Daltonics, Billerica, MA).
2.5. 2-(4-(Trifluoromethyl)phenyl)-4,5-bis(4-hydroxyphenyl)
imidazole (TFIDO)
A
mixture of 4-(trifluoromethyl)benzaldehyde (1.00 g,
0.0057 mol), BHD (1.39 g, 0.0057 mol), ammonium acetate
(3.18 g, 0.041 mol) and 20 mL glacial acetic acid was refluxed
for 24 h under N2. On cooling, the white precipitate was collected
by filtration, washed with ethanol and dried in vacuum oven at
80 8C. The yield was 89% (2.10 g) with a melting point of 150 8C. FT
IR (KBr, cmꢀ1): 3031 (OH stretching), 1614 (C55N stretching), and
1521 (C55C stretching), 1252 (C–O–C stretching).1H NMR
2.3. Synthesis
The synthetic procedures for the synthesis of target diamine are
reported below and shown in Scheme 1.
(400 MHz, DMSO-d6):
d = 12.69 (1H NH, s), 9.67 (1H OH, s), 9.37
(1H OH, s), 8.25 (2H, d, J = 8 Hz), 7.81 (2H, d, J = 8 Hz), 7.35 (4H, dd,
J = 4 Hz), 6.69 (4H, dd, J = 4 Hz) ppm. C22H15F3N2O2: calculated C,
66.66%; H, 3.78%; N, 7.07%; found C, 66.63%; H, 3.81%; N, 7.04%. m/
e: 396.11, 397.11, 398.12.
2.4. 4,40-Dihydroxybenzil (BHD)
A mixture of 4,40-dimethoxybenzil (2.50 g, 0.0092 mol), glacial
acetic acid (25 mL), and HBr (30 mL) was refluxed for 12 h under
N2. After cooling, 5 mL HBr was added and mixture was refluxed for
another 12 h. Upon completion of the reaction (as witnessed by
TLC), the medium was poured into 200 mL deionized water. The
organic product was extracted with 220 mL ethyl acetate. The
organic phase was thoroughly washed with water in order to
remove all acids and then dried over magnesium sulfate. The
product was obtained as crystal after evaporation of the solvent in
a rotary evaporator. The yield after drying in a vacuum oven at
80 8C was 90% (1.79 g) with melting point of 120 8C. FT-IR (KBr,
cmꢀ1): 3031 (OH stretching), 1633 (C55O stretching), 1612 (C55C
stretching), 1226 (C–O–C stretching). 1H NMR (400 MHz, DMSO-
2.6. 2-(4-Trifluoromethylphenyl)-4,5-bis(4-(4-nitro-2-
trifluoromethylphenoxy)phenyl)imidazole (NTFI)
A mixture of TFIDO (1.00 g, 0.0025 mol), 2-chloro-5-nitroben-
zotrifluoride (1.127 g, 0.005 mol), potassium carbonate (1.40 g,
0.01 mol) and N, N-dimethyl acetamide (DMAc, 15 mL) was
refluxed for 8 h under N2, and then was poured into methanol/
water (1:1, v/v). The crude product was recrystallized from glacial
acetic acid and dried in a vacuum oven at 80 8C. The yield was 93%
(1.80 g) with a melting point of 159 8C. FTIR (KBr, cmꢀ1): 1522,
1328(–NO2), 1254 (C–O–C stretching) and 1621 (C55N stretching).
d6):
d
= 10.84 (2H OH, s), 6.91–7.77 (8H, m) ppm. C14H10O4:
1H NMR (400 MHz, DMSO-d6):
d = 8.50–8.52 (2H, dd, J = 8 Hz),
calculated C, 69.42%; H, 4.13%; N, 0%; found C, 69.38%; H, 4.16%; N,
0%. m/e: 242.06, 243.06, 244.06.
8.48–8.48 (2H, d, J = 2.7 Hz), 8.26–8.28 (2H, d, J = 8.4 Hz), 7.74–7.76
(2H, d, J = 8.4 Hz), 7.16–7.18 (2H, d, J = 8.4 Hz), 7.70–7.73 (4H, m),

88
M. Ghaemy, F.R. Berenjestanaki / Journal of Fluorine Chemistry 144 (2012) 86–93
7.20–7.23 (4H, m) ppm. C36H19F9N4O6: calculated C, 55.81%; H,
2.45%; N, 7.23%; found C, 55.83%; H, 2.47%; N, 7.20%. m/e: 774.12,
775.12, 776.12, 775.11.
into a large volume of methanol giving rise to a precipitate which
was washed thoroughly with hot water; it was then extracted with
hot methanol using a soxhlet extractor for 10 h to remove low
molecular weight fractions, and dried at 80 8C in a vacuum oven for
24 h.
2.7. 2-(4-Trifluoromethylphenyl)-4,5-bis(4-(4-amino-2-
trifluoromethylphenoxy)phenyl)imidazole (TFIA)
PAEI-a: Yield = 90%, [
H, imidazole), 3420 (N–H, amide), 1374 (C55N stretching) and 1227
(C–O–C). 1H NMR (400 MHz, DMSO-d6):
= 13.65 (1H, imidazole
h
] = 0.80 dL/g. FT-IR (KBr, cmꢀ1): 3550 (N–
3.50 mL hydrazine monohydrate was added drop-by-drop over a
30 min period to a mixture of NTFI (2.00 g, 0.0025 mmol), 0.5 g of
10% Pd/Cand 20 mLethanolandheated for5 h. Thereaction mixture
was then filtered while hot to remove Pd/C and heated to reduce the
volume of solvent. After cooling, the precipitate was isolated by
filtration, recrystallized from ethanol and dried in a vacuum oven at
80 8C.The yield was89%(1.58 g)withameltingpointof200 8C. FT-IR
(KBr, cmꢀ1): 3445–3318 (NH2), 1223 (C–O–C), 1621 (C55N), and
d
ring), 10.76 (2H, NH amide), 6.75–8.86 (22H, aromatic protons)
ppm. [C44H25F9N4O4]n: calculated C, 62.55%; H, 2.96%; N, 6.63%;
found: C, 62.59%; H, 2.99%; N, 6.58%.
PAEI-b: Yield = 92%, [
H, imidazole), 3438 (N–H, amide), 1378 (C55N stretching) and 1231
(C–O–C). 1H NMR (400 MHz, DMSO-d6):
= 13.70 (1H, imidazole
h
] = 0.68 dL/g. FTIR (KBr, cmꢀ1): 3546 (N–
d
ring), 10.63 (2H, NH amide), 7.09–8.57 (22H, aromatic protons)
ppm. [C44H25F9N4O4]n: calculated C, 62.55%; H, 2.96%; N, 6.63%;
found: C, 62.52%; H, 2.98%; N, 6.61%.
1492(C55C). 1H NMR (400 MHz, DMSO-d6):
d = 12.89 (1H, s), 8.28
(2H, d, J = 8 Hz), 7.83 (2H, d, J = 8 Hz), 7.5 (4H, m), 6.83–6.93 (10H,
m), 5.50(4H, s) ppm. 13C NMR (100 MHz, DMSO-d6): 111.0, 115.9,
116.9, 119.0, 121.6, 123.4, 123.6, 124.0, 125.3, 125.8, 126.1, 128.0,
128.9, 129.7, 129.9, 130.5, 134.4, 137.3, 142.1, 142.6, 144.0, 146.2,
157.7, 158.8, 161.4, 167.6. C36H23F9N4O2: calculated C, 60.50%; H,
3.22%; N, 7.84%; found C, 60.46%; H, 3.27%; N, 7.82%. m/e: 714.17,
715.17, 716.17, 715.16, 717.18.
PAEI-c: Yield = 89%, [
H, imidazole), 3494 (N–H, amide), 1398 (C55N stretching) and 1233
(C–O–C). 1H NMR (400 MHz, DMSO-d6):
= 13.65(1H, imidazole
h
] = 0.70 dL/g. FT-IR (KBr, cmꢀ1): 3543 (N–
d
ring), 10.63 (2H, NH amide), 7.10–8.57 (21 H, aromatic protons)
ppm. [C43H24F9N5O4]n: calculated C, 60.99%; H, 2.95%; N, 8.27%;
found: C, 60.95%; H, 2.97%; N, 8.25%.
PAEI-d: Yield = 90%, [
(N–H, imidazole), 3374 (N–H, amide), 1373 (C55N stretching) and
1239 (C–O–C). 1H NMR (400 MHz, DMSO-d6):
= 13.09 (1H,
h
] = 0.75 dL/g. FT-IR (KBr, cmꢀ1): 3558
3. Synthesis of PAEIs
d
imidazole ring), 10.45 (2H, NH amide), 6.07–7.90 (18H, aromatic
protons), 1.36–1.55 (8H, aliphatic protons) ppm. [C42H29F9N4O4]n:
calculated C, 61.16%; H, 3.51%; N, 6.79%; found: C, 61.19%; H,
3.57%; N, 6.74%.
General procedure for the preparation of PAEIs is described as
follows. In a 50 mL two-necked round-bottomed flask equipped
with a reflux condenser, a nitrogen gas inlet tube, and a magnetic
stirrer bar, a mixture of 1 mmol (0.714 g) diamine (TFIA), 1 mmol
of a dicarboxylic acid, 1.2 mL TPP, 1 mL pyridine, 0.6 g LiCl, 0.6 g
CaCl2 and 5.0 mL NMP was refluxed under a stream of N2 at 120 8C
for 12 h. After cooling, the obtained polymer solution was poured
PAEI-e: Yield = 91%, [
(N–H, imidazole), 3294 (N–H, amide), 1389 (C55N stretching),
and 1229 (C–O–C). 1H NMR (400 MHz, DMSO-d6):
= 13.04
h
] = 0.78 dL/g. FT-IR (KBr, cmꢀ1): 3487
d
Fig. 1. 1H NMR spectrum of TFIA in DMSO-d6.

M. Ghaemy, F.R. Berenjestanaki / Journal of Fluorine Chemistry 144 (2012) 86–93
89
[32] and has afforded the TFIDO. IR spectrum of TFIDO exhibited
absorption at 1614 cmꢀ1 due to C55N stretching vibration and 1H
NMR spectrum of this compound showed signals at 12.69 ppm and
in the region of 9.67–9.37 ppm related to the N–H of imidazole ring
and phenolic O–H groups, respectively. The chlorodisplacement
reaction between TFIDO and 2-chloro-5-nitrobenzotrifluoride in
presence of K2CO3 in DMAc afforded the dinitro compound NTFI.
The FT-IR spectrum of NTFI showed characteristic absorption
bands at 1522 cmꢀ1 (NO2 asymmetrical stretching) and 1328 cmꢀ1
(NO2 symmetrical stretching). The catalytic reduction of the nitro
groups by means of Pd/C-catalyzed hydrazine monohydrate in
ethanol afforded the target diamine. FT-IR spectrum of the diamine
(TFIA) showed the characteristic absorption bands of the primary
amine at 3318 and 3445 cmꢀ1 due to N–H stretching. The 1H NMR
spectrum of diamine showed signals at 12.89 related to the protons
of NH group in imidazole ring. The 1H NMR spectrum also
confirmed that the nitro groups have been completely transformed
into the amino groups by the high field shift of the aromatic
protons and by the signal at 5.50 ppm. The 1H NMR spectrum of
diamine is shown with descriptions in Fig. 1. These results clearly
confirmed that the diamine prepared here in is consistent with the
proposed structure.
4.2. Synthesis and characterization of PAEIs
A series of novel well-oriented macromolecules containing
imidazole and trifluoromethyl moieties in the backbone was
synthesized based on the phosphorylation polycondensation from
the diamine (TFIA) and various commercial available dicarboxylic
diacids such as terephthalic acid, isophthalic acid, pyridine-2,6-
dicarboxylic acid, adipic acid, and sebacic acid as shown in Scheme
2. The phosphorylation polycondensation as described for the first
time by Yamazaki et al. [33] was carried out by using triphenylpho-
sphite and pyridine as condensing agents. The polymerization
readily proceeded within a homogeneous solution in NMP and in
the presence of LiCl and CaCl2, and afforded highly viscous polymer
solutions with up to 92% yield. Since Yamazaki’s development,
many researchers have utilized the activated polyamidation using
the TPP activator and found that the addition of a small amount of
LiCl or CaCl2 enhances the molecular weight of the polyamides. The
Scheme 2. Polycondensation reaction of TFIA with different dicarboxylic acids.
(1H, imidazole ring), 10.40 (2H, NH amide), 6.09–7.78 (18H,
aromatic protons), 1.36–1.55 (16H, aliphatic protons) ppm.
[C46H37F9N4O4]n: calculated C, 62.72%; H, 4.20%; N, 6.36%; found:
C, 62.77%; H, 4.24%; N, 6.32%.
intrinsic viscosity [
25 8C as well as the results of GPC analyses for PAEI-e are tabulated
in Table 1. The values for all polymer solutions were
h] values of the prepared polymers in DMAc at
4. Results and discussion
[h]
determined through the extrapolation of the concentrations used
to zero [33]. The obtained polymers had limited viscosity numbers
in the range of 0.68–0.80 dL/g. The average molecular weights of
these polymers, except PAEI-e, were not detectable by GPC because
of their insolubility in THF eluent. The weight average (Mw) and
number average (Mn) molecular weights of the PAEI-e were
18,600 g/mol and 11,500 g/mol, respectively, high enough to
obtain flexible and tough thin films by casting from their DMF
solutions. The structures of the PAs were confirmed by means of
4.1. Synthesis and characterization of diamine (TFIA)
A new aromatic diamine was synthesized according to the
synthetic route depicted in Scheme 1. The preparation of BHD was
carried out according to the procedure given in the literature [31].
1H NMR spectrum of BHD showed a signal at 10.84 ppm related to
the phenolic hydroxyl. The reaction of BHD with 4-(trifluoro-
methyl)benzaldehyde in the presence of NH4OAc in glacial acetic
acid is a well known reaction for the preparation of imidazole ring
Table 1
Solubility behavior of PAEIs.
Polymer
[
h]a, dL/g
Mn, g/molb
Mw, g/molb
DMAc
DMF
NMP
DMSO
Py
THF
Methanol
HMPA
PAEI-a
PAEI-b
PAEI-c
PAEI-d
PAEI-e
0.80
0.68
0.70
0.75
0.78
–
–
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
ꢀ+
ꢀ+
ꢀ+
ꢀ+
++
ꢀꢀ
ꢀꢀ
–
++
++
++
++
++
–
–
–
–
–
–
–
11,500
18,600
ꢀꢀ
The solubility was determined by using 5 g sample in 100 mL of solvent.
Abbreviations: DMAc, N,N-dimethyl acetamide; DMF, N,N-dimethyl formamide; NMP, N-methyl pyrrolidone; DMSO, dimethyl sulfoxide; THF, tetrahydrofuran; Py, pyridine;
HMPA, hexamethylphosphoramide; ++: soluble at room temperature; ꢀ+: soluble on heating at 60 8C; ꢀꢀ: insoluble on heating at 60 8C.
a
Measured in DMAc at 25 8C.
Measured by GPC in THF with polystyrene as a standard.
b

90
M. Ghaemy, F.R. Berenjestanaki / Journal of Fluorine Chemistry 144 (2012) 86–93
Fig. 2. 1H NMR spectrum of PAEI-e in DMSO-d6.
FT-IR and 1H NMR spectroscopy methods. In general, FT-IR spectra
of the PAs showed the characteristic absorption bands around
3550 (N–H imidazole, stretching), 3370 (N–H amide, stretching),
1630 (C55O stretching), 1375 (C55N stretching of imidazole ring)
and around 1227 cmꢀ1 (C–O stretching). The 1H NMR spectra of the
resulting PAEIs a signal appeared at the most downfield region, in
the range of 13.04–13.70 ppm, can be attributed to the proton of
imidazole ring and in the range of 10.76–10.40 is related to the
protons of amide linkages. In addition to the signals in the region of
7.10–8.78 ppm related to the aromatic protons, PAEI-d and PAEI-e
also showed signals in the range of 3.83–3.93 and 1.36–1.55 ppm,
respectively, related to the aliphatic protons. Assignment of
protons in the spectra is consistent with the proposed chemical
structure of polymers. The 1H NMR spectrum of the representative
polymer, PAEI-e, is shown in Fig. 2.
the macromolecular backbones which led to the increased chain
distances and decreased chain interactions; consequently, the
solvent molecules were able to penetrate more easily into the
polymer chains and interact with the polar linkages of the PAEIs
backbone such as imidazole ring, ether and amide linkages.
Therefore, the presence of polar CF3 pendants and ether and
imidazole units in the main chains can contribute effectively in the
solubility of these PAEIs as compared with the solubility of
the previously reported polyamides [34,35]. These polymers can be
processed into thin colorless films by casting from their solutions.
The ease of solubility varies depending upon the dicarboxylic acids
used. The PAEI-e synthesized from sebacic acid with longer
aliphatic unit exhibited better solubility behavior in THF in
comparison with the other PAEIs.
5. Properties of PAEIs
Table 2
Photophysical properties of TFIA and PAEIs.
5.1. Solubility
Polymer
la.max (nm)
le.max (nm)
Ff (%)c
The solubility behavior of the prepared PAEIs was tested
qualitatively in various organic solvents at 5% (w/v), and the results
are summarized in Table 1. All the prepared PAEIs exhibited
excellent solubility in polar aprotic solvents such as NMP, DMAc,
DMF, DMSO, HMPA and pyridine at room temperature and in less
polar solvent such as THF at 60 8C. The good solubility of these
PAEIs should be the result of the introduction of the bulky phenyl
pendant with trifluoromethyl substitutes in polymer backbone.
When the CF3-substituted diamine TFIA is polymerized with
various aliphatic and aromatic dicarboxylic acids, the correspond-
ing PAEIs with ortho- and para-oriented CF3 moieties per repeat
unit would be an exceptional material from the solubility point of
view. Dense packing of the polymer chains was probably disturbed
by the bulky CF3 and phenyl containing-CF3 groups attached to the
main chains along with a good path in the direction of the bonds in
Solutiona
Filmb
Solutiona
Filmb
PAEI-a
PAEI-b
PAEI-c
PAEI-d
PAEI-e
TFIA
339
337
325
310
307
305
342
339
328
315
–309
–
520
502
489
452
445
405
522
509
492
455
450
–
9
10
22
20
24
34
l
a.max = maximum absorption wavelength. le.max = maximum emission wave-
length. The excitation wavelength was 320 nm.
a
Polymer concentration of 0.2 g/dL in NMP.
b
PAEIs thin films were made by dissolving about 0.5 g of the PAEI in 5 mL of NMP,
and the homogeneous solution in a glass culture dish was heated under vacuum in
three steps: at 50 8C for 1 h, 100 8C for 2 h, and 150 8C for 5 h. 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 8C for 10 h.
c
Fluorescence quantum yield relative to 0.1 N quinine sulfate in 1 N H2SO4 (aq)
(Ff = 0.55) as a standard.

M. Ghaemy, F.R. Berenjestanaki / Journal of Fluorine Chemistry 144 (2012) 86–93
91
Fig. 4. Fluorescence emission spectra of PAEIs.
(absorption edge or cut-off wavelength) of the resulting polymers
were found to be in the range of 380–390 nm. In these polymers,
the presence of CF3 groups in the structure of the repeating units
plays the main role in its excellent optical behavior. By inducing
separation of the macromolecular chains caused by –CF3 and bulky
phenyl groups, the formation of charge transfer complex, which
imparts deep color to the polymer, is largely hindered, and thus the
color intensity is considerably reduced. Generally, the results
obtained clearly show that the prepared thin films have low color
intensity and high level of optical transparency in the UV–vis light
region.
To investigate the emission properties of TFIA and PAEIs, an
excitation wavelength of 320 nm was used in all cases. The TFIA
showed strong blue fluorescent light in dilute (10ꢀ5 M) NMP
solution with maximum emission wavelength at le.max = 415 nm.
Photoluminescence (PL) spectra of the PAEI-a, PAEI-d, PAEI-e
(0.2 g/dL) and TFIA (10ꢀ5 M) in dilute NMP solutions are shown in
Fig. 4. To measure the PL quantum yields (
solutions (0.2 g/dL) in NMP were prepared. A 0.1 N solution of
quinine in H2SO4 ( f = 0.55) was used as reference according to the
Ff), dilute polymer
Fig. 3. Absorption (a) and transmission (b) spectra of PAEIe film.
F
literature [28]. The fluorescence spectra of these PAEIs in NMP
solutions exhibited broad emission peaks with the maxima in the
range of 430–520 nm and quantum yields in the range of 9–24%.
The aliphatic PAEIs, PAEI-e and PAEI-d, exhibit emission both in
5.2. Optical properties
To prepare crack-free and homogeneous thin films for the
measurement of optical properties, solutions of PAEIs were made
by dissolving about 0.5 g of the PAEI in 5 mL of NMP to afford an
approximate 10 wt.% solution. The homogeneous solution was
poured into a 9-cm diameter glass culture dish, which was heated
under vacuum at 50 8C for 1 h, 100 8C for 2 h, and 150 8C for 5 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 8C for 10 h. The photophysical
properties of the diamine (10ꢀ5 M) and PAEIs (0.2 g/dL) in dilute
NMP solutions were investigated by UV–vis and fluorescence
spectroscopy. Table 2 lists some important optical data obtained
from dilute solutions of the diamine and PAEIs in NMP and from
thin films of PAEIs. The TFIA showed strong UV absorption with
solution and in solid state at
24% and the aromatic PAEIs, PAEI (a–c), exhibited emission both in
solution and in solid state at e.max = 490–520 nm with f = 9–22%.
le.max = 445–455 nm with Ff = 20–
l
F
The blue shift and higher intensity of the photoluminescence peak
of the aliphatic polyamides compared with the aromatic polyam-
ide 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 [34–36].
5.3. Thermal properties
The thermal behavior data of these PAEIs were assessed by
using DSC and TGA analysis. DSC was used to determine the glass-
transition temperature values (Tgs) of the samples obtained with a
heating rate of 10 8C/min under nitrogen, Fig. 5(a). The Tg values
were taken as the midpoint of the change in slope of the baseline in
DSC curves. The DSC curves did not exhibit endothermic peak up to
350 8C which can be associated to the amorphous nature of the
PAEIs. Quenching from temperature of 350 8C to room temperature
yielded amorphous samples so that in most cases the Tgs could
easily be observed in the second heating traces of DSC. The
amorphous nature of these PAEIs can be attributed to their bulky
maximum at
resulting PAEIs in solutions and in films were nearly identical with
each other. The maximum absorption wavelength ( a.max) of all
PAEIs appeared in the range of 310–320 nm, which shows a
relatively small energy band gap for * transition. Fig. 3 shows
la.max = 298–305 nm. The absorption spectra of the
l
p
!
p
molar absorptivity spectrum of the representative polymer, PAEI-e,
film (top) and UV–vis transmission spectrum of the same polymer
film (bottom). The plateau region of the light transmittance in the
UV–vis spectrum was extended to about 800 nm, indicating high
degree of the film transparency. Moreover, the l0 values

92
M. Ghaemy, F.R. Berenjestanaki / Journal of Fluorine Chemistry 144 (2012) 86–93
Table 3
Thermal characteristic data of PAEIs.
Polymer
Tg (8C)a
Ti (8C)
T10% (8C)
C.Y. (%) at
600 8Cb
PAEI-a
PAEI-b
PAEI-c
PAEI-d
PAEI-e
250
242
248
180
160
400
390
320
300
295
490
460
420
405
400
68
58
58
37
35
Tg, glass transition temperature; decomposition temperature, recorded via TGA at
10 8C/min under N2 (20 cm3/min); Ti, temperature for 0% weight loss; T10%
,
temperature for 10% weight loss.
a
Midpoint temperature of baseline shift on the second DSC scan trace (10 8C/min,
under N2, 20 cm3/min) of the sample after quenching from 350 8C.
b
C.Y. = char yield: residual weight percentage at 600 8C in N2.
listed in Table 3. The Ti and T10% values of the aliphatic and aromatic
PAEIs stayed within 295–400 8C and 400–490 8C, respectively, and
the amount of carbonized residue (char yield) of these polymers
was from 35% to 68% at 600 8C in nitrogen atmosphere, depending
on the structure of diacid component, implying that these
polyamides possess reasonable thermal stability. The data from
thermal analysis show that the resulting polymers have fairly high
thermal stability. This explains that introduction of strong electron
negativity of –CF3 groups might have enhanced the polarity of the
polymer, which should restrict the movement of polymer-link and
led to better thermal stability than previously reported polyamides
[3,34].
6. Conclusion
A series of new optically active poly(amide-ether-imidazole)s
containing substituted imidazole ring and ether linkages in the
main chains and –CF3 side groups were successfully synthesized
from a new diamine monomer and various aromatic and aliphatic
dicarboxylic acids via direct polycondensation method. These
PAEIs exhibited excellent solubility in many polar aprotic organic
solvents and capability of forming colorless flexible thin films
through solution casting. Incorporating the bulky –CF3 side groups
linked in ortho and para positions and flexible aryl ether linkages
along the symmetrically oriented chains could change their
alignment, disrupting the copolanarity of aromatic rings due to
local macromolecular twisting, and highly increase the organo-
solubility of the polymers. Accordingly, all the polymeric low-
colored thin films were significantly flexible and showed high
optical transparency in the UV–vis light region. The PAEIs have also
exhibited fluorescence emission with the maxima in the region of
430–520 nm in solution and in solid state due to presence of
triphenyl imidazole unit in their backbones. In sum, these fluoro-
containing PAEIs displayed excellent organo-solubility, good film-
forming capability, reasonable thermal stability and Tg values
suitable for thermoforming processing.
Fig. 5. DSC (a) and TGA (b) curves of PAEIs under N2 at 10 8C/min.
pendent group which decreased the interchain interaction
resulting in loose polymer chain packaging and aggregates. The
Tg values of these polymers were in the range of 160–250 8C,
depending on the stiffness of the residue of diacids in the polymer
backbone, and the data are summarized in Table 3. 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 diamines and side chain-side chain
and side chain-main chain interactions enhanced Tg values.
However, Tg values of these polymers are comparable [35] and
lower than Tg values of the previously reported polyamides [34]
which can be due to presence of flexible ether linkages in the main
chains. As anticipated, the Tg values of these PAEIs 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. PAEIs obtained from aliphatic dicarboxylic acid such
as PAEI-d and PAEI-e, showed lower Tgs of 180 8C and 160 8C,
respectively, because of the presence of flexible aliphatic unit
between the aromatic amide units and low rotation barrier of their
diacid moieties, and the highest Tg of 250 8C was observed for PAEI-
a derived from terephthalic acid because of the highest rigidity
which inhibited the molecular motion.
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.jfluchem.
2012.07.014.
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decomposition temperatures (Ti) as well as weight loss tempera-
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