Fluoro-containing poly(amide-imide)s with sterically hindered pendants: Synthesis and characterization

Article abstract of DOI:10.1016/j.jfluchem.2012.03.009

A structurally kinked fluorinated diacid, 2,6-bis(N-trimellitimido)-4- trifluoromethyl-4′-phenoxydiphenyl ether (TFPDPE) was synthesized and then used for preparing a new class of fluoro-containing poly(amide-imide)s via phosphorylation polyamidation with

Full text of DOI:10.1016/j.jfluchem.2012.03.009

Journal of Fluorine Chemistry 138 (2012) 34–41
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Fluoro-containing poly(amide-imide)s with sterically hindered pendants:
Synthesis and characterization
*
Hossein Behniafar , Farzin Zardoozi, Ali Rastkar
Chemistry Group, Faculty of Science, Islamic Azad University, Damghan Branch, Damghan, Iran
A R T I C L E I N F O
A B S T R A C T
A structurally kinked fluorinated diacid, 2,6-bis(N-trimellitimido)-4-trifluoromethyl-40-phenoxydiphe-
nyl ether (TFPDPE) was synthesized and then used for preparing a new class of fluoro-containing
poly(amide-imide)s via phosphorylation polyamidation with four diamines including 4,40-(oxidianiline,
2,6-diamino-4-trifluoromethyl)-40-phenoxydiphenyl ether, 1,5-bis(2-amino4-trifluoromethylphenoxy)-
naphthalene, and 2,20-bis(2-amino-4-trifluoromethylphenoxy)-1,10-binaphthyl. Chemical structure of
monomer TFPDPE as well as the resulted polymers was fully confirmed by IR and NMR spectroscopy.
Article history:
Received 15 January 2012
Received in revised form 29 February 2012
Accepted 7 March 2012
Available online 16 March 2012
Keywords:
¯
Limited viscosity numbers ([
¯
h
]’s) of the resulting polymers at 25 8C were measured. The values of Mw and
Mn were determined using gel-permeation chromatography (GPC). In addition, the absorption edge
values ( 0) obtained from their UV curves were determined, and all the resulting poly(amide-imide)s
Fluoropolymer
Trifluoromethyl group
Optical behavior
Heat stability
l
exhibited high optical transparency. The crystallinity of the polymers was estimated by wide-angle X-ray
diffraction (WXRD), and the resulted polymers exhibited nearly an amorphous nature. To study on the
surface morphologies, the scanning electron microscopy (SEM) images of the poly(amide-imide)s were
taken. Furthermore, solubility of the samples in various kinds of organic solvents was tested. From
differential scanning calorimetric (DSC) analyses, the polymers showed Tg’s between 304 and 328 8C.
Thermo-stability of the polymers was determined by thermogravimetric analysis (TGA), and the 10%
weight loss temperatures of the poly(amide-imide)s were found to be in the range of 548–553 8C.
ß 2012 Elsevier B.V. All rights reserved.
Organo-solubility
1. Introduction
the preparation of new classes of fluorine-containing polymers
using a large variety of fluorinated monomers [11–15]. The
High-performance polymers such as polyimides, polyamides
and poly(amide-imide)s with high glass transition temperature
(Tg), high thermal stability, good mechanical properties have been
identified for a variety of applications such as engineering plastics
of aerospace industries, optical and electronic devices and also as
films or membranes [1,2]. However, many completely aromatic
polymers do not display ideal properties, resulting from deficien-
cies in processability and solubility. Insolubility in common
organic solvents, intractability, infusibility and strong color often
limit their utility in various advanced technological applications.
To circumvent the limitations of aromatic polyimides and
poly(amide-imide)s some structural modifications often become
essential [3–5].
exceptional results corresponding to the synthesis of processable
fluoropolymers became more and more in course of time via
designing new chemical structures, and it seems that we have to
continue this research line for the future. Introduction of –CF3
group, as the most prominent representative among perfluoro
alkyl groups, into aromatic structure of a high-performance
polymer has been one of the most widely used strategies to
enhance processability along with a desired set of properties for
the resultant polymer [16–21]. This introduction modifies several
physical properties, e.g., increases solubility, thermal stability,
optical transparency and flame-resistance, while simultaneously
decreasing the crystallinity, dielectric constant, water absorption,
and color intensity. Moreover, owing to the presence of –CF3
substituents, the formation of charge-transfer complex, which
imparts deep yellow color to the polymer, is largely hindered, and
thus the color intensity is considerably reduced, making the
polyimide more suitable for some applications. On the other hand,
polymers with structurally hindered chains caused by local steric
crowding along the chains indicate improved processability
It has been demonstrated that introduction of fluorinated
substitutions within the aromatic polyimides and poly(amide-
imide)s can give these polymers many desirable properties,
making them suitable for a much wider range of applications
[6–10]. In this regard, considerable attention has been devoted to
relative to those of lacking steric hindrance because of
a
constrained macromolecular twisting [22–24,7]. These structural
congestions can be generally resulted from the presence of
* Corresponding author.
E-mail address: h_behniafar@du.ac.ir (H. Behniafar).
0022-1139/$ – see front matter ß 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2012.03.009

H. Behniafar et al. / Journal of Fluorine Chemistry 138 (2012) 34–41
35
Scheme 1. Synthesis of fluoro-containing monomer TFPDPE.
voluminous substituents in close places into a macromolecular
chain such as ortho positions of an aromatic ring.
structure of dinitro NFPDPE. In the IR spectrum of diamine AFPDPE
the characteristic absorption of nitro groups disappeared and the
characteristic bonds of amino groups at 3460 and 3375 cmꢀ1 (N–H
stretching) and 781 cmꢀ1 (N–H out of plane bending) appeared
after reduction. In the 1H NMR spectrum of diamine AFPDPE the
signals of aromatic protons appear in the range of 6.75–7.64 ppm,
and the characteristic resonance signal at 4.97 ppm is due to the
amino group. In the 13C NMR spectrum of diamine AFPDPE the
twelve aromatic carbons appeared their signals in the range of
110.7–152.2 ppm. Moreover, the quartets of the heteronuclear
13C–19F coupling appear in the region of 121.4–128.1 ppm. The
coupling constant of one-bond C–F is about 260 Hz and two-bond
is about 35 Hz, respectively.
Therefore, alongside our recent studies [25–30], this research
focuses on the synthesis of
containing fluoro-diacid, 2,6-bis(N-trimellitimido)-4-trifluoro-
methyl-40-phenoxydiphenyl ether (TFPDPE) via
three-step
a structurally hindered imide-
a
reaction. The diacid TFPDPE has been designed as a potentially
suitable monomer for poly(amide-imide)s, capable of imparting
good processability and high thermal stability at the same time.
The poly(amide-imide)s obtained from TFPDPE were characterized
by IR, NMR, solution viscometry, GPC, UV–vis, WXRD, organo-
solubility, SEM, DSC and TGA.
2. Results and discussion
2.2. Fluorinated diimide–diacid TFPDPE
2.1. Dinitro and diamine precursors
Scheme 1 (underside) shows the reaction to CF3-containing
diimide–diacid TFPDPE. In this reaction, ring-opening addition of
diamine AFPDPE to trimellitic anhydride in refluxing glacial acetic
acid results in the corresponding di(amic–acid) intermediate. Next,
an intramolecular cyclodehydration can give rise to the related
cyclic imide groups. The FT-IR spectrum of monomer TFPDPE
showed the characteristic absorption bands around 2400–
3600 cmꢀ1 (–OH, carboxylic acid), 1783 cmꢀ1 (imide C55O
asymmetrical stretching), and 1723 cmꢀ1 (imide C55O symmetrical
stretching and acid C55O stretching), confirming the presence of
imide ring and carboxylic acid groups in the structure. The 1H NMR
spectrum of TFPDPE presented three specified signals around the
downfield regions (8.14–8.50 ppm) due to the trimellitic acid
moiety. Moreover, the protons for the carboxylic acid groups are
observed at about 13.60 ppm in the form of a short and broad peak.
The 13C NMR spectrum of TFPDPE exhibited eighteen peaks of
various absorptions for aromatic carbons. In this spectrum,
carbons of carboxylic acid and imide groups were observed at
Scheme 1 (upside) shows the synthetic route to 2,6-diamino-4-
trifluoromethyl-40-phenoxydiphenyl ether (AFPDPE) by a two-step
process. In the first step, aromatic nucleophilic displacement of 4-
chloro-3,5-dinitrobenzotrifluoride with 4-phenoxyphenol in the
presence of anhydrous K2CO3 in DMF solvent resulted in 2,6-
dinitro-4-trifluoromethyl-40-phenoxydiphenyl ether (NFPDPE) as
a pale yellow solid. In the second step, this dinitro was reduced in
ethanol in the presence of hydrazine hydrate and a catalytic
amount of palladium on activated carbon at 80 8C to produce white
crystals of the fluorinated diamine AFPDPE. The structures of
dinitro NFPDPE and diamine AFPDPE were confirmed by IR and
NMR spectroscopic methods. In the IR spectrum of dinitro NFPDPE
the peaks attributed to the stretching vibrations of the bonds Ar–O
and C–F appeared at 1267, 1183, 1141, and 1101 cmꢀ1. Moreover,
absorptions appearing around 1322 and 1545 cmꢀ1 are due to
symmetric and asymmetric stretching of –NO2 groups, respective-
ly. In the 1H NMR spectrum of NFPDPE two hydrogens attached to
the nitro-containing ring (Ha) resulted in a singlet centralized at
8.42 ppm. Furthermore, in the 13C NMR spectrum, twelve peaks
corresponding to the twelve kinds of aromatic carbons appeared in
the range of 120.3–150.8 ppm. In this spectrum, the quartets of the
heteronuclear 13C–19F coupling appear in the region of 121.2–
128.1 ppm. The coupling constant of one-bond C–F is about 280 Hz
and two-bond is about 35 Hz, respectively. Thereby all these
spectral patterns are thoroughly in agreement with the proposed
about 164.0 ppm. Fig. 1 displays IR (top), 1H NMR (middle), and 13
NMR (bottom) spectra of the synthesized monomer.
C
2.3. Preparation of fluorinated poly(amide-imide)s
According to the phosphorylation technique first described by
Yamazaki and Higashi [31] a series of novel poly(amide-imide)s
were synthesized from diacid TFPDPE and various diamines as

36
H. Behniafar et al. / Journal of Fluorine Chemistry 138 (2012) 34–41
Fig. 1. IR (top), 1H NMR (middle), and 13C NMR (bottom) spectra of monomer TFPDPE.
shown in Scheme 2. It should be noted that the selection of the
diamine comonomers was well-advised as well. Three of them
possess CF3 group in their chemical structures. This in turn can
help the preparation of low-colored, optically transparent and
organo-soluble polymers when combining to diacid TFPDPE. In the
case of AFPBN, in addition to the presence of two trifluoromethyl
groups and two ether linkages in its structure, it profits greatly
from a twisting about the bond linking the two naphthyl rings. All
the polycondensations were homogeneously throughout the
reactions and afforded highly viscous polymer solutions with up
limited viscosity numbers in the range of 0.62–0.75 dL gꢀ1. These
values for all polymeric solutions were determined through the
extrapolation of the concentrations used to zero. Furthermore, the
poly(amide-imide)s had polydispersity index (PDI) values of about
two. The molecular weights of these polymers were high enough to
obtain flexible and tough thin films by casting from their
appropriate solutions.
The formation of the products was confirmed by FT-IR and NMR
spectroscopy methods. The FT-IR spectra of the CF3-containing
poly(amide-imide)s exhibited the characteristic amide bands at
about 3400 (N–H stretching) and 1650 (C55O stretching) cmꢀ1. The
resulting polymers also showed characteristic imide bands around
1780 and 1720 cmꢀ1 (asymmetrical and symmetrical C55O
to 90% yield. Limited viscosity numbers ([h]’s) of the resulting
poly(amide-imide)s in DMAc at 30 8C as well as the results of GPC
analyses are tabulated in Table 1. The obtained polymers had

H. Behniafar et al. / Journal of Fluorine Chemistry 138 (2012) 34–41
37
Scheme 2. Preparation of fluorinated poly(amide-amide)s.
Table 1
Some characteristics of the resulting poly(amide-imide)s.
a
b
b
d
(dL gꢀ1
)
Mw (g molꢀ1
)
Mn (g molꢀ1
)
PDIc
l0 (nm)
¯
¯
Polymer
[
h
]
TFPDPE/ODA
0.68
0.62
0.75
0.71
18,800
21,400
26,900
32,100
9300
11,500
12,500
13,600
2.02
1.86
2.15
2.36
379
374
375
378
TFPDPE/AFPDPE
TFPDPE/AFPN
TFPDPE/AFPBN
a
Measured in DMAc at 25 8C.
Measured by GPC in THF with polystyrene as a standard.
Polydispersity index.
b
c
d
Cut-off wavelength is defined as the point at which the light transmittance from the prepared thin films becomes less than 1%.
stretching vibrations, respectively) and 1380 (imide C–N stretch-
ing). In these spectra, lacking the highly broad absorption peak in
the region 2400–3500 cmꢀ1, related to acid O–H stretching,
indicates that no any TFPDPE monomer is present in the sample
composition. Instead, in the left side of this region a peak
corresponding to N–H stretching appeared at about 3400 cmꢀ1
as stated. In the 1H NMR spectra of the resulting poly(amide-
imide)s, the existing aromatic protons resonate in the region 7.1–
8.5 ppm. Among the aromatic protons, the protons adjacent to the
imide ring appeared at the farthest downfield. In addition, the
signals appeared at the most downfield region, about 10.50 ppm,
could be attributed to the protons of the amide linkages. Fig. 2
shows representative IR (top) and 1H NMR (bottom) spectra of the
poly(amide-imide)s TFPDPE/AFPDPE and TFPDPE/ODA, respective-
ly.
diffractograms clearly showed that the mentioned poly(amide-
imide)s were essentially amorphous, and no remarkable crystal
diffraction appeared in their WXRD curves. Apparently, the
laterally attached –O–Ph–O–Ph bulky group, which itself has been
2.4. Optical behavior
To investigate the optical behavior of the resulting fluoropo-
ly(amide-imide)s, their solutions (10ꢀ5 mol Lꢀ1 in DMSO) were
separately prepared, and then exposed to UV–vis rays. Over 80% of
irradiated light could be transmitted from all the solutions in the
wavelength range of 500–750 nm. Furthermore, the absorption
edge values (l0’s) are determined at below 380 nm. These
observations obviously show that the resultant fluoro-containing
macromolecules have high level of optical transparency in the UV–
vis light region. As mentioned earlier, the formation of charge-
transfer complex is largely prevented with –CF3 substituents, and
thereby the absorption intensity is remarkably lowered. The
spectra of the solutions were nearly identical with each other.
Table 1 (the last column) lists the values of l0 obtained from the
diluted solutions of the polymers in DMSO.
2.5. WXRD studies
The crystallinity of the resulting poly(amide-imide)s was
measured by wide-angle X-ray diffraction (WXRD) at room
Fig. 2. IR spectrum of polymer TFPDPE/AFPDPE (top), and 1H NMR spectrum of
temperature with 2
u
ranging from 58 to 408. The resulted
polymer TFPDPE/ODA (bottom).

38
H. Behniafar et al. / Journal of Fluorine Chemistry 138 (2012) 34–41
Table 2
Solubility of the resulting fluorinated poly(amide-imide)s.
Polymer
DMSO DMF DMAc NMP Pyridine THF Toluene
TFPDPE/ODA
++
++
++
++
++
++
++
++
++
++
++
++
++
+
ꢀ
ꢁ
ꢁ
ꢁ
ꢀ
ꢁ
ꢀ
ꢁ
TFPDPE/AFPDPE ++
++
++
++
TFPDPE/AFPN
TFPDPE/AFPBN
++
++
Qualitative solubility: 10 mg. mLꢀ1
.
DMSO, dimethylsulfoxide; DMF, N,N-dimethylformamide; DMAc, N,N-dimethyla-
cetamide; NMP, N-methyl-2-pyrrolidinone; THF, tetrahydrofuran.
++, soluble at room temperature; +, soluble on heating; ꢁ, partially soluble; ꢀ,
insoluble.
sandwiched between two ortho trimellitimido groups decreases
the chain–chain interactions, resulting in a decreasing crystallini-
ty. In fact, this structural crowding provides the chains a non-
coplanarity, leading to disordered kinked macromolecules. More-
over, the effect of the diamine comonomers on the crystallinity
amount could be observed by comparing the unequal shape of the
diffractograms obtained. By comparing the diffractograms
obtained, it is concluded that the amorphousness nature of
poly(amide-imide)s TFPDPE/ODA is somewhat lower than that of
the other ones. This might be attributed to the lesser macromo-
lecular prevention of diamine moiety against compactness in this
polymer.
Fig. 3. SEM image of poly(amide-imide)s TFPDPE/AFPDPE.
supported by WXRD analyses. Steric factors associated with the
previously mentioned bulky substituents could greatly destroy the
regularity of the macromolecular main chains and caused a high
degree of non-uniformity in microstructural order.
2.8. DSC measurements
2.6. Organo-solubility
Differential scanning calorimetry (DSC) was used to determine
the glass-transition temperature values (Tg’s) of the samples
obtained with a heating rate of 10 8C minꢀ1 under nitrogen.
Fig. 4(top) shows a typical DSC thermogram of poly(amide-imide)s
TFPDPE/AFPDPE. The Tg values were read at the middle of the first
break down observed in the DSC plots, and found to be in the range
of 304–328 8C. In general, molecular packing and chain rigidity are
among the main factors influencing on Tg values. In polymer
TFPDPE/AFPDPE the increased rotational barrier resulted from the
additional –CF3 and phenoxy substituents enhanced the Tg value
The solubility behavior of the resulting poly(amide-imide)s was
tested qualitatively in various organic solvents, and the results
were tabulated in Table 2. All the polymers were readily soluble in
high polar solvents such as DMSO, DMF, DMAc, and NMP at room
temperature. Except poly(amide-imide)s TFPDPE/ODA the remain-
der ones were dissolved even in pyridine as a moderate polar
solvent at room temperature. These structurally well-designed
polymers were even partially soluble in THF upon heating at about
70 8C. A steric overcrowding caused by the presence of –CF3 and –
O–Ph–O–Ph voluminous groups could be resulted in local non-
coplanarities along the chains, and consequently excellent
solubility could be observed in tested organic solvents. Moreover,
the presence of additional CF3 polar groups in poly(amide-amide)s
TFPDPE/AFPDPE, TFPDPE/AFPN and TFPDPE/AFPBN plays an
important role in solubility enhancement of these polymers. The
high organo-solubility of poly(amide-imide)s TFPDPE/AFPBN
might be also attributed the participation of the two twisted
binaphthyl rings, which provides more distortion of the chains. In
fact, the excellent organo-solubility of these polymers could be
interpreted based on a combination of steric and electronic effects.
The bulky arylene-ether pendant groups attached to the CF3-
containing backbone can inhibit the close packing of the
macromolecular chains and endow a large amount of polarity
due to the high electronegativity of fluorine atoms, and thereby
these fluoropoly(amide-imide)s show good organo-solubility,
particularly in polar solvents.
2.7. Surface morphology
A representative scanning electron microscopy (SEM) image of
poly(amide-imide)s TFPDPE/AFPDPE is shown in Fig. 3. As can be
seen, this image clearly shows an agglomerated spherical bulk with
non-equal packing, indicating a nearly non-uniformity in the
surface area of the samples. The SEM images of the other
poly(amide-imide)s showed even more disordered pattern, and
no specified shape could be detected for the arrangement of the
microstructures obtained. This kind of surface morphology might
be attributed to the same amorphous structures, which could be
Fig. 4. DSC plot of TFPDPE/AFPDPE (top) and TGA thermogram of TFPDPE/ODA
(bottom).

H. Behniafar et al. / Journal of Fluorine Chemistry 138 (2012) 34–41
39
Table 3
Thermal behavior of the resulting poly(amide-imide)s.
CYe (wt.%)
a
b
c
d
Polymer
T0 (8C)
Tg (8C)
Td5% (8C)
Td10% (8C)
TFPDPE/ODA
301
323
312
321
304
327
316
328
532
538
540
533
548
551
553
549
73
74
68
66
TFPDPE/AFPDPE
TFPDPE/AFPN
TFPDPE/AFPBN
a
Onset temperature, from DSC measurements in N2, defines the point at which the first deviation from the base line on the low temperature side is observed.
Glass-transition temperatures from the DSC traces in N2 at heating rate of 10 8C minꢀ1
b
c
.
Temperature of 5% weight loss, determined by TGA in N2 at a heating rate of 10 8C minꢀ1
Temperature of 10% weight loss, determined by TGA in N2 at a heating rate of 10 8C minꢀ1
.
d
e
.
Char yield: residual weight percentages at 600 8C, determined by TGA in N2 at a heating rate of 10 8C minꢀ1
.
relative to the Tg value of polymer TFPDPE/ODA up to 23 8C. A
further rotational barrier, and consequently higher Tg value could
be also observed by incorporation of rigid and kinked binaphthyl
units in polymer TFPDPE/AFPBN chains. Therefore, in addition to
diacid TFPDPE, the values of Tg were affected by diamine moieties
too, which shows the order AFPBN > AFPDPE > AFPN > ODA as
illustrated in Table 3.
4. Experimental
4.1. Materials
Trimellitic anhydride (TMA) and triphenyl phosphite (TPP)
were purchased from Aldrich Chemical Co. and used as received
without further purification. All other chemicals were purchased
from Merck Chemical Co. 4-Phenoxyphenol and 4-chloro-3,5-
dinitrobenzotrifluoride were used as received. 4,40-Oxydianiline
(ODA) was purified by recrystallization from ethanol before use.
Diamine AFPDPE was synthesized during the synthesis reaction of
the monomer TFPDPE. 1,5-Bis(2-amino4-trifluoromethylphenox-
y)naphthalene (AFPN) and 2,20-bis(2-amino-4-trifluoromethyl-
phenoxy)-1,10-binaphthyl (AFPBN) were synthesized and
purified by procedures reported elsewhere [29,32]. Reagent-grade
calcium chloride was dried under vacuum at 180 8C before use.
N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF),
dimethylsulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), and
pyridine were purified by distillation under reduced pressure over
2.9. Thermo-stability
The thermo-stability of the resulting fluorinated poly(amide-
imide)s were evaluated by thermogravimetric analysis (TGA)
under nitrogen atmosphere at a heating rate of 10 8C minꢀ1, and
corresponding weight loss temperatures of 5% and 10% (T5% and
T10%) were all determined from original TGA curves. All the
aromatic poly(amide-imide)s exhibited good thermal stability
with insignificant weight loss up to 550 8C in nitrogen. The T5% and
T10% values of the poly(amide-imide)s were measured in the ranges
of 532–540 and 548–553 8C, respectively. The amount of carbon-
ized residue (char yield) of these fluorinated polymers in nitrogen
atmosphere was up to 70% at 600 8C. The high char yields of these
polymers could be ascribed to their chemical structure, which has
high degree of aromaticity. Obviously, the data from thermal
analysis showed that these poly(amide-imide)s have fairly high
thermal stability in comparison with many of their analogs.
Furthermore, the diamine comonomers have no considerable
effect on the heat stabilities. Meanwhile, by comparing the data of
poly(amide-imide)s TFPDPE/ODA and TFPDPE/AFPDPE it is proved
that no undesired effect on the heat stability of the product could
be observed by the introduction of fluoro-containing substituent
into the structures. Typical TGA curves of representative poly(am-
ide-imide)s TFPDPE/ODA is shown in Fig. 4 (bottom). In addition,
the results obtained from these analyses are completely tabulated
in Table 3.
˚
calcium hydride and stored over 4-A molecular sieves. Hydrazine
monohydrate and 10% palladium on activated carbon were used as
received. Tetrahydrofuran (THF) and toluene were dried by sodium
before use.
4.2. Measurements
Melting points were determined in open capillaries with IA
9200 Series Digital Melting Point apparatus. FT-IR spectra were
recorded on a PERKIN ELMER RX I FT-IR spectrometer. The spectra
of solids were obtained using KBr pellets. 1H NMR spectra were
recorded with a Bruker AVANCE 500 NMR operated at 500 MHz in
dimethylsulfoxide-d6 (DMSO-d6) using tetramethylsilane as an
internal standard. 13C NMR spectra were also taken with the same
apparatus operated at 125 MHz. Viscosity numbers (hred) were
measured using an Ubbelohde viscometer with polymer solutions
in DMAc at 30 8C. These values were separately measured for
concentrations 0.10, 0.25, and 0.50 g dLꢀ1, and then plotted against
3. Conclusions
these concentrations. To determine limited viscosity numbers ([h])
A fluoro-containing diimide–diacid (TFPDPE) with high degree
of crowding in its chemical structure was successfully synthesized
and used to prepare a novel class of aromatic fluorinated
poly(amide-imide)s with kinked macromolecules. The incorpo-
ration of CF3 polar substituents as well as arylene-ether
voluminous groups, which are sandwiched between two ortho-
catenated trimellitimido groups could distort the macromolecu-
lar chains, and consequently increase their organo-solubility. On
the other hand, this new design could also endow a high degree of
optical transparency in the prepared solution of the products. In
addition, thermal stability of the resulting polymers was not
lowered by this structural modification. In summary, these fluoro-
containing poly(amide-imide)s displayed excellent organo-
solubility, low crystallinity, reasonable thermal stability and
glass transition temperatures, making them suitable for thermo-
forming processing.
a linear extrapolation was finally done to zero concentration as the
y-axis intersect [33]. Weight- and number-average molecular
weights of the resulting poly(amide-imide)s were determined by
gel-permeation chromatography (GPC). This chromatography was
performed on a Waters 150-C instrument using Styragel columns
and a differential refractometer detector. The molecular weight
calibration was carried out using polystyrene standards. Calibra-
tion and measurements were made at a flow rate of 1 mL minꢀ1
with tetrahydrofuran (THF) as the eluent. Cut-off wavelength
(absorption edge) values (l0) of the prepared solutions in DMSO at
a concentration of 10ꢀ5 mol Lꢀ1 were determined with a PERKIN
ELMER PTP-1 Peltier System Lambda 25 UV/VIS Spectrometer.
Wide-angle X-ray diffraction patterns were performed at room
temperatures with film specimens on a Bruker Advance D5 X-ray
diffractometer with Ni-filtered Cu/Ka radiation (30 kV, 25 mA). The

40
H. Behniafar et al. / Journal of Fluorine Chemistry 138 (2012) 34–41
morphologies of the samples were determined with a HITACHI S-
4160 scanning electron microscope (SEM). Thermal gravimetric
analysis (TGA) and differential scanning calorimetry (DSC) were
performed on a Mettler TA 5000 system (Columbus, OH) under
(C12), 121.44 (C*), 116.50 (C10), 115.88 (C6), 115.85 (C7), 110.68
(C2).
nitrogen atmosphere at a heating rate of 10 8C minꢀ1
.
4.3. Synthesis of 2,6-dinitro-4-trifluoromethyl-40-phenoxydiphenyl
ether (NFPDPE)
In a three-necked round bottom flask equipped with a nitrogen
inlet, 4-phenoxyphenol (1.8621 g, 10 mmol) and anhydrous
potassium carbonate (2.902 g, 21 mmol) were suspended in a
mixture of dry DMF (10 mL) and toluene (4 mL). The mixture was
then refluxed at 140 8C using a Dean-Stark trap to remove small
amount of water azeotropically. After most of the toluene was
distilled, 4-chloro-3,5-dinitrobenzotrifluoride (2.7055 g, 10 mmol)
was added when the mixture was cooled to 60 8C. The mixture was
then allowed to warm to 120 8C and kept for 6 h. After cooling to
25 8C, it was poured into 50 mL of CH3OH/H2O to give a yellow
solid. After filtration under reduced pressure, the crude product
was washed twice with hot water. After drying, the product was
recrystallized from DMF/H2O to give 3.1102 g of NFPDPE as a pale
yellow fine crystals (74% yield, m.p. = 83–85 8C).
4.5. Synthesis of 2,6-bis(N-trimellitimido)-4-trifluoromethyl-40-
phenoxydiphenyl ether (TFPDPE)
AFPDPE (3.6033 g, 10 mmol), trimellitic anhydride (4.8025 g,
25 mmol), and glacial acetic acid (50 mL) were poured into a
reaction flask. The heterogeneous mixture obtained was then
refluxed under N2 atmosphere for 15 h. Next, the reaction mixture
was filtered to give a yellow precipitate. The precipitate was
washed several times with hot ethanol to remove acetic acid
residue. The product obtained was purified by recrystallization
from DMF/H2O. The solid obtained (TFPDPE) was then dried under
reduced pressure at 100 8C for 24 h to afford 6.7313 g of yellow fine
crystals (95% yield, m.p. = 365–368 8C). Results of the IR, 1H NMR
and 13C NMR spectroscopy measurements of monomer TFPDPE are
detailed below in Section 3.
FT-IR (KBr; cmꢀ1): 1545, 1322 (–NO2 stretch), 1267, 1183, 1141,
1101 (C–F and C–O stretch). 1H NMR (DMSO-d6;
d, ppm): 8.42 (s,
2H, Ha), 7.87 (t, J = 9 Hz, 2H, He), 7.30 (t, J = 9 Hz, 1H, Hf), 7.22 (d,
J = 7 Hz, 2H, Hb), 7.05 (d, J = 9 Hz, 2H, Hd), 6.91 (d, J = 7 Hz, 2H, Hc).
13C NMR (DMSO-d6;
d, ppm): 150.78 (C9), 144.89 (C4), 143.25 (C5),
143.18 (C8), 141.91 (C3), 133.10 (C11), 131.22 (C2), 128.12 (C*),
2
125.73 (C*), 124.58 (C12), 123.53 (C*), 122.30 (C1, quartet, JC–
F = 35 Hz), 121.24 (C*), 120.71 (C10), 120.40 (C6), 120.35 (C7).
4.6. Synthesis of poly(amide-imide)s
A typical example of TPP-activated polycondensation is de-
scribed as follows. A mixture of TFPDPE (0.7086 g, 1 mmol), 2,6-
diamino-4-trifluoromethyl-40-phenoxydiphenyl ether (AFPDPE)
(0.3603 g, 1 mmol), CaCl2 (0.2 g), pyridine (1.2 mL), TPP (0.6 mL)
and NMP (5 mL) were heated while being stirred at 100 8C for 3 h.
The viscosity of the reaction solutions increased after 1 h, and an
additional 3.0 mL of NMP were added to the reaction mixture. At the
end of the reaction, the obtained polymer solution was trickled into
stirred methanol. The yellow-stringy polymer was washed thor-
oughly with hot water and methanol, collected by filtration, and
dried at 100 8C under reduced pressure. The calculated yield was
about 95%. The limited viscosity number of the polymer obtained
(TFPDPE/AFPDPE) was 0.62 dL/g. The other poly(amide-imide)s
were synthesized in a similar manner.
4.4. Synthesis of 2,6-diamino-4-trifluoromethyl-40-phenoxydiphenyl
ether (AFPDPE)
To a suspension of the purified dinitro compound (NFPDPE)
(4.2030 g, 10 mmol) and 10% Pd/C (0.02 g) in ethanol (15 mL),
hydrazine monohydrate (1.5 mL) was added dropwise to the stirred
mixtureat70 8Cwithin10 min. Aftercompleteaddition,themixture
was heated at the reflux temperature for another 2 h. The reaction
solution was filtered hot to remove Pd/C, and the filtrate was then
filtered cold to remove the solvent. The crude product was purified
by recrystallization from ethanol to give 2.7385 g of AFPDPE as a
pale-cream needles (76% yield, m.p. = 109–113 8C).
Acknowledgments
Financial support from the Research Council of Islamic Azad
University-Damghan branch (Ref No. 4409 projection/2 Tyr 1389)
is greatly acknowledged. The authors are also grateful to the Sharif
University of Technology for running the NMR spectra, Amir-Kabir
University of Technology for running the TGA and DSC analyses,
and University of Tehran for the SEM images.
FT-IR (KBr; cmꢀ1): 3460, 3375 (N–H stretch), 1618, 1590 (C55C
aromatic), 1223, 1199, 1163, 1116 (C–F and C–O stretch), 781 (N–H
out of plane bending). 1H NMR (DMSO-d6;
d, ppm): 7.64 (t, J = 6 Hz,
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