Synthesis and characterization of soluble polyimides based on a new fluorinated diamine: 4-Phenyl-2,6-bis[3-(4'-amino-2'-trifluoromethyl-phenoxy) phenyl] pyridine

Article abstract of DOI:10.1016/j.jfluchem.2010.03.008

A new kind of pyridine-containing aromatic diamine monomer, 4-phenyl-2,6-bis[3-(4'-amino-2'- trifluoromethyl-phenoxy) phenyl] pyridine (m-PAFP), was successfully synthesized by a modified Chichibabin reaction of 3-(4'-nitro-2'-trifluoro-methyl-phenoxy)-acetophenone with benzaldehyde, followed by a catalytic reduction. A series of fluorinated pyridine-bridged aromatic poly(ether-imide)s were prepared from the resulting diamine monomer with various aromatic dianhydrides via a conventional two-step thermal or chemical imidization method. The inherent viscosities values of these polyimides were in the range of 0.56-1.02 dL/g, and they could be cast and thermally converted into transparent, flexible, and tough polyimide films. The polyimides displayed higher solubility in polar solvents such as NMP, DMSO and m-cresol. The polyimides had good thermal stability, with the glass transition temperatures (T_g) of 187-211 °C, the temperatures at 5% weight loss of 511-532 °C, and the residue at 800 °C in air was higher than 50%. These films also had dielectric constants of 2.64-2.74 at 10 MHz and low water uptake 0.53-0.66%. Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous. Moreover, the polymer films of these novel polyimides showed outstanding mechanical properties with the tensile strengths of 90.1-96.6 MPa, elongations at breakage of 8.9-10.7% and tensile modulus of 1.65-1.98 GPa.

Full text of DOI:10.1016/j.jfluchem.2010.03.008

Journal of Fluorine Chemistry 131 (2010) 724–730
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis and characterization of soluble polyimides based on a new
fluorinated diamine: 4-Phenyl-2,6-bis[3-(40-amino-20-trifluoromethyl-phenoxy)
phenyl] pyridine
*
Tao Ma, Shujiang Zhang, Yanfeng Li , Fengchun Yang, Chenliang Gong, Jiujiang Zhao
State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Institute of Biochemical Engineering & Environmental Technology,
Lanzhou University, Lanzhou 730000, China
A R T I C L E I N F O
A B S T R A C T
A new kind of pyridine-containing aromatic diamine monomer, 4-phenyl-2,6-bis[3-(40-amino-20-
trifluoromethyl-phenoxy) phenyl] pyridine (m-PAFP), was successfully synthesized by a modified
Chichibabin reaction of 3-(40-nitro-20-trifluoro-methyl-phenoxy)-acetophenone with benzaldehyde,
followed by a catalytic reduction. A series of fluorinated pyridine-bridged aromatic poly(ether-imide)s
were prepared from the resulting diamine monomer with various aromatic dianhydrides via a
conventional two-step thermal or chemical imidization method. The inherent viscosities values of these
polyimides were in the range of 0.56–1.02 dL/g, and they could be cast and thermally converted into
transparent, flexible, and tough polyimide films. The polyimides displayed higher solubility in polar
solvents such as NMP, DMSO and m-cresol. The polyimides had good thermal stability, with the glass
transition temperatures (Tg) of 187–211 8C, the temperatures at 5% weight loss of 511–532 8C, and the
residue at 800 8C in air was higher than 50%. These films also had dielectric constants of 2.64–2.74 at
10 MHz and low water uptake 0.53–0.66%. Wide-angle X-ray diffraction measurements revealed that
these polyimides were predominantly amorphous. Moreover, the polymer films of these novel
polyimides showed outstanding mechanical properties with the tensile strengths of 90.1–96.6 MPa,
elongations at breakage of 8.9–10.7% and tensile modulus of 1.65–1.98 GPa.
Article history:
Received 18 November 2009
Received in revised form 16 March 2010
Accepted 16 March 2010
Available online 25 March 2010
Keywords:
Fluorinated polyimides
Monomer synthesis
Solubility
Thermal properties
ß 2010 Elsevier B.V. All rights reserved.
1. Introduction
Pyridine is a heteroaromatic molecule with rigidity and
polarizability. New kinds of heteroaromatic diamine or dianhy-
dride holding pyridine unit have been designed and synthesized,
and the novel heteroaromatic polymers with good thermostability
and processability have been obtained derived from those
monomers containing pyridine nucleus structures at the same
time [17–23]. Considering the rigidity based on pyridine ring have
contributions for the thermal stability, chemical stability of the
resulting polymer at elevated temperature [24], as well as
polarizability resulting from nitrogen atom in pyridine ring could
be suitable to improve their solubility.
Aromatic polyimides are well known as materials of high
performance for their excellent thermal stabilities, chemical
resistance and electric properties [1–4]. During the past decade,
interests in these polymers have risen in response to increasing
technological applications in a variety of fields such as aerospace,
automobile, and microelectronics, etc. [5–8]. However, their
applications have been limited in some fields because aromatic
polyimides are normally insoluble in common organic solvents
and high melting point.
Solubilization of the polyimides has been targeted by several
methods, such as introduction of flexible linkage [9,10], bulky units
in the polymer backbone [11,12], bulky pendent substituents
[13,14], or noncoplanar moieties [15,16]. Among these approaches,
introduction of bulky pendent substituents and heteroaromatic
rings into polyimide chains has been considered to be efficient,
which can provide not only enhanced solubility but also good
thermostability and processability.
Polyimides containing hexafluoroisopropylidene or pendent
trifluoromethyl groups are of special interest [25,26]. It was found
that the incorporation of CF3 into polymer backbones resulted in an
enhanced solubility and optical transparency together with a
lowered dielectric constant, which attributed to low polarizability
of the C–F bond and the increasing in free volume. The fluorinated
polyimides also provided other merits such as good thermal and
low moisture absorption.
In this paper, a new aromatic, pyridine-containing ether
diamine with trifluoromethyl pendent group, 4-phenyl-2,6-
bis[3-(40-amino-20-trifluoromethyl-phenoxy) phenyl] pyridine
(m-PAFP), had been designed and synthesized as a potentially
* Corresponding author. Tel.: +86 931 8912528; fax: +86 931 8912113.
E-mail address: liyf@lzu.edu.cn (Y. Li).
0022-1139/$ – see front matter ß 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2010.03.008

T. Ma et al. / Journal of Fluorine Chemistry 131 (2010) 724–730
725
convenient condensation monomer to form pyridine-containing
polyimides. Meanwhile, a new series of pyridine-containing
polyimides were synthesized from the resulting diamine monomer
with several aromatic dianhydrides by a two-step procedure, and
the polyimides obtained were characterized in detail. Furthermore,
to investigate the effect of trifluoromethyl substituents and the
nonlinear structure on the polymer solubility, the polyimides
derived from m-PAFP were compared with analogous polyimides
derived from a pyridine-containing diamine monomer, PAFP [27],
and polyimides derived from a non-fluorinated pyridine-contain-
ing diamine monomer, PAPP, reported by Wang et al. [28], as
shown in Fig. 1.
2. Results and discussion
2.1. Monomer synthesis
Among several methods for the preparation of a pyridine ring,
modified Chichibabin is one of the best methods that offer some
advantages such as good yield, available starting materials, and the
potential for introducing different substituents in the pyridine ring
[19]. As shown in Scheme 1, the diamine monomer (m-PAFP) was
obtained through
a three-step synthetic route. Firstly, the
nucleophilic substitution reaction of 3-hydroxyacetophenone with
2-chloro-5-nitrotrifluoromethylbenzene in the presence of potas-
sium carbonate in DMF gave the intermediate compound m-NFAP.
Then the dinitro compound m-PNFP was prepared via a modified
Chichibabin reaction from benzaldehyde and m-NFAP. Finally, the
novel diamine monomer m-PAFP was obtained by the reduction of
m-PNFP with hydrazine monohydrate catalyzed by Pd/C. The new
aromatic diamine monomer is pure enough for polymerization
with commercial aromatic dianhydride monomers to prepare
polyimides.
The structures of m-PAFP and the intermediates were
confirmed by elemental analysis, mass spectrometry, IR spectra,
and 1H NMR and 13C NMR spectroscopy. Fig. 2 shows the FT-IR
spectra of m-NFAP, m-PNFP and the diamine monomer (m-PAFP).
The FT-IR spectrum of m-PNFP showed two characteristic bands at
1531 and 1351 cmꢀ1 (–NO2 asymmetric and symmetric stretch-
ing), while the characteristic absorptions of the nitro groups
disappeared and the amino group showed a pair of N–H stretching
absorptions in the region of 3300–3500 cmꢀ1 in the FT-IR
spectrum of diamine. Fig. 3 presents the 1H NMR and 13C NMR
spectra of the diamine monomer m-PAFP in CDCl3. In the 1H NMR
spectroscopy of the diamine, the signals in the range of 7.58–
6.81 ppm were ascribed to the protons of the aromatic rings and
the signal in 3.81–3.40 ppm were ascribed to the protons of –NH2
group. In the 13C NMR spectra, all the carbon-13 atoms of diamine
showed 20 main signals, which resonated in the regions of 158.8–
113.0 ppm. The 13C NMR spectroscopy showed one quartet
because of heteronuclear C–F coupling. The quartet was centered
at 114 ppm by the CF3 carbon C20, and the one-bond C–F coupling
constant was 268 Hz. The CF3-attached carbon C19 was centered at
120 ppm, and the constant was about 90 Hz by two-bond C–F
coupling. All the spectroscopic data obtained and the elemental
analyses were in good agreement with the expected structures.
Fig. 1. PAPP and PAFP diamine monomers and polyimides.
solid dianhydride monomer into the equimolar amounts of
diamines in anhydrous NMP, and stirred for 24 h at room
temperature. Either thermal or chemical imidization procedures
were chosen to form polyimides. Merits of the former were easy for
preparation of polyimide films, whereas the latter was suited for
the preparation of soluble polyimides. The experimental data of
the isolated polyimides obtained have been summarized in Table 1.
According to the data from Table 1, the resulting polyimides all get
2.2. Polymer synthesis
The diamine monomer was reacted with three kinds of
commercially available aromatic dianhydrides, PMDA, ODPA,
and BTDA, to give the corresponding poly(ether-imide)s as shown
in Scheme 2.
The new polyimides were synthesized using two-step methods,
which were carried out via poly(amic acid)s intermediate. In our
case, the poly(amic acid)s were prepared by gradually adding the
Scheme 1. Preparation of diamine monomers.

726
T. Ma et al. / Journal of Fluorine Chemistry 131 (2010) 724–730
Scheme 2. Synthesis of the polyimides.
0.56 to 1.02 dL/g, which indicated formation of high molar masses.
Fig. 4 demonstrates IR spectra of polyimides. All the polyimides
exhibited characteristic imide group absorptions around 1770
(asymmetrical C55O stretching) and 1715 cmꢀ1 (symmetrical C55O
stretching), 1375 cmꢀ1 (C–N stretching), and together with some
strong absorption bands in the region of 1300–1100 cmꢀ1 (C–O
stretching). There was no existence of the characteristic absorption
bands of the amide group near 3200–3365 cmꢀ1 (N–H stretching),
indicating polymers had been fully imidized.
Fig. 2. FT-IR spectra of m-NFAP, m-PNFP, and m-PAFP.
high yields (95–98%), and elemental analyses show that composi-
tions found of the repeating unit of them can agree with those
calculated of that of them well as shown in Scheme 2. Meanwhile,
the inherent viscosities values of these polyimides ranged from
2.3. Solubility of the resulting polyimides
The solubility of the PIs was determined by dissolving 10 mg of
polymers into 1 mL of organic solvent at room temperature or
upon heating, as shown in Table 2. It can be seen that all the
polyimides exhibited good solubility in common organic solvents,
such as NMP, DMSO, DMAc, DMF and m-cresol, even at room
temperature in most cases. The good solubility should be resulted
from both the flexibility of ether groups and the bulk pendent
trifluoromethylphenyl group in the polyimide structure, which
decreased the interaction between polymer chains. In addition, the
solubility varies depending upon the dianhydride used. PI-2
possesses the better solubility at room temperature, because of the
presence of the flexible ether groups, respectively. It can be seen
that the good solubility of PI-2 in THF indicates their potential
applications in areas where temperature is sensitive.
As shown in Table 2, the PI series obtained via chemical
imidization could be dissolved in organic polar solvents even at
room temperature in most cases. However the PI series prepared
via thermal imidization had poorer solubility than those prepared
Table 1
Physical properties and elemental analysis of the polyimides.
Polyimide Yield hinh
Composition of Elemental analysis (%)
(%)
(dL/g) repeating unit
C
H
N
PI-1
PI-2
PI-3
95
0.56
1.02
0.98
C47H23N3F6O6
C53H27N3F6O7
C54H27N3F6O7
Calcd.
67.93 2.77 5.06
Found 68.01 2.60 5.11
98
96
Calcd.
68.30 2.90 4.51
Found 68.46 3.20 4.50
Calcd.
68.48 2.85 4.44
Found 68.56 2.68 4.77
Fig. 3. 1H and 13C NMR spectra of m-PAFP.

T. Ma et al. / Journal of Fluorine Chemistry 131 (2010) 724–730
727
Fig. 4. FT-IR spectra of polyimides.
Fig. 5. Wide-angle X-ray diffraction curves of the polyimides.
chemical. The difference insolubility of PI between thermal and
chemical imidization can be explained by the imidization reaction
mechanism [29,30].
radiation, 2u ranging from 08 to 808, using the polyimide films
From Table 2, we summarized the results and compared with
polyimides reported [27,28]. It can be seen all the resulted FPIs
exhibited good solubility in common organic solvents. A compar-
ison of the solubility of FPIs shows that PI-1, PI-2 and PI-3 have
better solubility in strong polar solvents, even at room tempera-
ture. According to the comparison in Table 2, FPI exhibited
comparable solubility, which was better than that of non-
fluorinated PIs. This indicates that introduction of trifluoromethyl
group, despite its position, can enhance solubility of polyimides.
obtained by thermal cyclodehydration as samples, and the results
were shown in Fig. 5. The X-ray diffraction curves of the polyimides
express a set of wider diffraction peaks, these should be evidences
that indicate the polyimides holding heterogenous morphology,
and should also be a reason that could obtain transparent films
from these polyimides. The polyimide based on PI-1 shows some
crystalline character and exhibits two peaks around 148 and 178,
which indicate a little of crystalline morphologies in the resulting
polyimide. These should be related to rigidity and planar structure
of the polymer chains, as well as due to the more efficient packing
of polymer chains containing pyromellitimide unit. The polyimides
based on PI-2 and PI-3 show amorphous patterns, and this is
because the presence of flexible ether link induces looser chain
packing and reveals a large decrease in crystallinity. Therefore, the
amorphous nature of the resulting polyimides would endow them
a good solubility.
2.4. X-ray diffraction data
The crystallinity of the polyimides was examined by wide-angle
X-ray diffraction analysis with graphite monochromatized Cu K
a
Table 2
Solubility of polyimidesa.
2.5. Thermal properties of the polyimides
Polymer
Solventb
NMP
DSC and TGA were applied to evaluate the thermal properties
of the polyimides, the DSC and TGA curves of the polyimides are
shown in Figs. 6 and 7, respectively, and thermal analysis data
from the TGA and DSC curves of the polyimides are summarized in
Table 3. DSC revealed that rapid cooling from 400 8C to room
temperature produced predominantly amorphous samples, so
that Tg of polymer could be easily read in the second heating trace
of DSC. The data in Table 3 represents that Tg values of these PIs are
in the range of 187–211 8C. As we expected, the Tg values of these
polyimides depended on the structure of the dianhydride
component and decreased with increasing flexibility of the
polyimide backbones according to the applied structure of the
dianhydride. PI-2, obtained from ODPA, showed a lower Tg
because of the presence of a flexible ether linkage between the
phthalimide units. PI-1, derived from PMDA, exhibited the highest
Tg because of the effect of the rigid polymer backbone. In
comparison with analogous polyimides derived from a pyridine-
containing diamine monomer, PAFP and PAPP, reported by Shang
et al. and Wang et al. [27,28]. The Tg values of these polyimides are
lower than analogous polyimides (Tg, 268–338 and 258–312 8C),
which suggests that the nonlinear structure in the polymer
DMSO
DMAc
DMF
m-Cresol
CHCl3
THF
PI-1c
++
++
++
+
+
++
++
++
+ꢀ
+ꢀ
++
++
++
+ꢀ
+ꢀ
+ꢀ
+ꢀ
++
+
+ꢀ
+ꢀ
+ꢀ
+ꢀ
+ꢀ
+ꢀ
+ꢀ
++
+
+ꢀ
+
+ꢀ
+
PI-2c
+
PI-3c
+
+ꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
++
+ꢀ
ꢀꢀ
+ꢀ
ꢀꢀ
ꢀꢀ
++
PI-1d
PI-2d
PI-3d
6FPI-1e
6FPI-2e
6FPI-3e
PI-af
+ꢀ
+ꢀ
+ꢀ
+ꢀ
++
+
++
+
+ꢀ
++
+
+ꢀ
++
+
+ꢀ
ꢀꢀ
+ꢀ
+ꢀ
+ꢀ
ꢀꢀ
+ꢀ
+ꢀ
+ꢀ
+
+ꢀ
+ꢀ
+
+ꢀ
+
+ꢀ
+ꢀ
+ꢀ
+ꢀ
+
PI-bf
PI-cf
+ꢀ
+ꢀ
+ꢀ
a
Qualitative solubility was determined with 10 mg of polymer in 1 mL of solvent;
++, soluble at room temperature; +, soluble on heating; +ꢀ, partially soluble on
heating; ꢀꢀ, insoluble.
b
NMP, N-methylpyrrolidone; DMAC, N,N-dimethylacetamide; DMF, N,N-
dimethylformamide; DMSO, dimethylsulfoxide.
c
Measured by chemical cyclization polyimide derived from the corresponding
poly(amic acid)s.
d
Measured by thermal cyclization polyimide derived from the corresponding
poly(amic acid)s.
e
Results reported by Shang et al. in the literature [27].
f
Results reported by Wang et al. in the literature [28].

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T. Ma et al. / Journal of Fluorine Chemistry 131 (2010) 724–730
Table 3
Thermal properties of the polyimides.
Polyimides
Thermal propertiesa
Tg (8C)
Td (8C)
T5 (8C)
T10 (8C)
Rw (%)
PI-1
PI-2
PI-3
211
187
203
364
382
370
511
532
531
550
596
588
57
57
58
a
Tg: determined by DSC curve; Td: decomposition-starting temperature; T5: the
temperature at 5% weight loss in air; T10: the temperature at 10% weight loss in air;
Rw: residual weight retention at 800 8C.
90.1–96.6 MPa, 8.9–10.7%, and 1.65–1.98 GPa, respectively, indi-
cating that they are strong and tough materials.
2.7. Dielectric properties
The dielectric constant values of the polyimide films at 1 MHz
and 10 MHz at 25 8C, which is summarized in Table 5. As shown in
Table 5, the dielectric constants of FPIs at 1 and 10 MHz were in the
range of 2.84–2.98 and 2.64–2.74, respectively. In this study, all
polyimide samples were prepared with the same curing process.
Obviously, the dielectric constants for each sample are quite
different, and strongly depend on the chemical structure. The
fluorinated polyimide films FPIs exhibited lower dielectric con-
stants. This may be explained by the increase in free volume and
decrease in polarizability. The incorporation of the bulky
trifluoromethylphenyl group prohibits close packing of the
polymer chains and reduces interchain charge transfer of the
highly polar dianhydride groups, in addition, the large fluorine
atoms increase the free volume fraction in the polymer, thereby
essentially reducing the number of polarizable groups in a unit
volume. The large electron negativity of the C–F bond also lowered
the electronic polarization in the polymer. Polyimides based on m-
PAFP have lower dielectric constants compared with conventional
polyimides such as PMDA/ODA polyimide film (3.44 at 10 MHz)
and those of many fluorinated polyimides (6FDA–MPD: 3.0; 6FDA–
7FMDA: 2.9; TFDA-p-APB: 2.89) [4,30].
Fig. 6. DSC curves of the polyimides.
backbone decreased the intermolecular interactions, thus leading
to a decreased Tg value.
For the thermal stability of the polyimides, Table 3 gives the
temperature of 5% and 10% weight loss in air, respectively, i.e. T5
and T10 values. The T5 and T10 values of the polyimides were in the
range 511–532 and 550–596 8C in air, and the amount of residue of
all polyimides at 800 8C in air was higher than 50%, especially, the
polyimide derived from m-PAFP–BTDA had the highest residue
yield up to 58%. The data from thermal analysis show that the
resulting polyimides have fairly high thermal stability.
2.6. Mechanical properties
High-quality polyimide films could be prepared by casting the
poly(amide acid) solutions on glass plates followed by the thermal
curing in the following procedure 80 8C overnight, 110, 150, 180,
210, 230, and 250 8C for 30 min at each temperature. These films
were subjected to tensile tests. Table 4 shows the mechanical
properties of the polyimides, including the tensile strength, tensile
modulus, and elongation at break. Polyimide films had tensile
strengths, elongation at break, and tensile modulus in the ranges of
The water uptake of these polyimides was investigated, and the
results are listed in Table 5. The data indicate that polyimides
exhibited low water uptake. The reason is the structure of the CF3
group.
Table 4
Mechanical properties of the polyimides.
Polyimide
Tensile
strength
(MPa)
Tensile
modulus
(GPa)
Elongation at
breakage (%)
PI-1
PI-2
PI-3
90.1
96.6
95.5
1.98
1.65
1.84
8.9
10.7
9.9
Table 5
Dielectric properties and water uptake.
Polyimide
Dielectric
constant
(1 MHz)a
Dielectric
constant
(10 MHz)a
Water
uptakeb (%)
PI-1
PI-2
PI-3
2.91
2.84
2.98
2.69
2.64
2.74
0.63
0.52
0.66
a
Measured by Agilent 4291B at room temperature (dry dielectric constant).
b
Water uptake was the immersion of the films in water at 25 8C for 24 h, followed
Fig. 7. TGA curves of the polyimides.
immediately by weighing.

T. Ma et al. / Journal of Fluorine Chemistry 131 (2010) 724–730
729
3. Conclusions
FT-IR (KBr): 1691 cmꢀ1 (C55O stretching) and 1521, 1349 cmꢀ1
(C–NO2 stretching) and 1335 cmꢀ1 (C–N stretching) and 1161,
1135, 1114 cmꢀ1 (C–F and C–O stretching). 1H NMR (300 MHz,
A new pyridine-containing aromatic diamine monomer, 4-
phenyl-2,6-bis[3-(40-amino-20-trifluoromethyl-phenoxy) phenyl]
pyridine (m-PAFP) was successfully synthesized, which led to a
number of novel fluorinated polyimides by two-step polycondensa-
tion method via reacting with various aromatic dianhydrides. The
resulted polyimides exhibited good solubility in many organic
solvents and could be cast into transparent, tough, and flexible films.
The novel polyimides obtained have fairly high Tg values, excellent
thermal stability in air, as well as good dielectric properties.
CDCl3):
J = 1.2 Hz, 1H), 7.66 (s, 1H), 7.58 (t, J1 = 8.4, J2 = 7.2 Hz, 1H), 6.30 (d,
J = 9.0 Hz, 2H), 2.59 (s,3H). 13C NMR (400 MHz, CDCl3):
(ppm)
d (ppm) 8.61 (s, 1H), 8.31 (d, J = 2.4 Hz, 1H), 7.69 (d,
d
196.53, 160.34, 154.57, 142.17, 139.54, 130.88, 128.86, 125.98,
125.06, 123.95, 119.85, 117.36, 114.81 MS (EI): 325(M+). Elem.
Anal. Calcd. for C15H10F3NO4: C 55.39%, H 3.10%, N 10.29%, while
Found C 54.96%, H 2.98%, N 9.95%.
4.3.2. 2,4-Phenyl-2,6-bis[3-(40-nitro-20-trifluoromethyl-phenoxy)
phenyl] pyridine (m-PNFP)
4. Experimental
31.68 g (0.05 mol) of m-NFAP, 2.65 g (0.025 mol) of benzalde-
hyde, 25.05 g (0.325 mol) of ammonium acetate and 40 mL of
glacial acetic acid were placed into a 100 mL three-necked flask
equipped with a mechanical stirrer and a reflux condenser. The
mixture was refluxed with stirring for 4 h. Then the precipitated
solid was filtered off and washed thoroughly with water. After
drying under vacuum at 60 8C, 8.96 g of yellow powder of m-PNFP
was obtained. The yield is 50%, and the melting point is 95–97 8C.
FT-IR (KBr): 3086 cmꢀ1 (C–H stretching) and 1531, 1351 cmꢀ1
(C–NO2 stretching) and 1334 cmꢀ1 (C–N stretching) and 1160,
1137, 1116 cmꢀ1 (C–F and C–O stretching). 1H NMR (300 MHz,
4.1. Materials
Commercially available 3-hydroxyacetophenone (Shanghai
Chemical Reagents Corp., China), 2-chloro-5-nitrotrifluoromethyl-
benzene (Acros), benzaldehyde (Beijing Chemical Reagents Corp.,
China), potassium carbonate (Fuchen Chemical Reagents Corp.,
Tianjin, China), hydrazine monohydrate (Shanghai Chemical
Reagents Corp., China), and 10% Pd/C (Acros) were used without
further purification. 4,40-Oxydiphthalic anhydride (ODPA; Shang-
hai Nanxiang Chemical, China) and 3,30,4,40-benzophenonetetra-
carboxylic dianhydride (BTDA; Beijing Chemical Reagents, China)
were recrystallized from acetic anhydride before use. Pyromellitic
dianhydride (PMDA; Beijing Chemical Reagents, China) was
purified by sublimation at 200–220 8C. N,N-Dimethylformamide
(DMF), and N-methyl-2-pyrrolidone (NMP) were purified by
distillation under reduced pressure over calcium hydride and
DMSO-d6):
d (ppm) 8.45 (s, 2H), 8.32 (d, J = 10.5 Hz, 2H), 8.26 (d,
J = 1.2 Hz, 2H), 8.20 (s, 2H), 8.03 (d, J = 8.8, 2H), 7.93 (s, 2H) 7.86 (t,
J1 = 5.4, J2 = 4.2 Hz, 2H), 7.68 (t, J1 = 2.4, J2 = 2.7 Hz, 2H), 7.55 (d,
J = 2.4 Hz, 1H), 7.38 (d, J = 4.4 Hz, 2H), 7.16 (t, J = 4.8 Hz, 2H). 13C
NMR (400 MHz, DMSO-d6):
d (ppm) 160.23, 159.66, 157.61,
155.04, 149.99, 144.78, 141.90, 131.28, 131.20, 130.54, 128.83,
124.91, 123.64, 122.03, 121.65, 120.16, 119.46, 118.31, 117.50,
114.57. MS (EI): 717(M+). Elem. Anal. Calcd. for C37H21F6N3O6: C
61.93%, H 2.95%, N 5.86%, while Found C 61.02%, H 2.88%, N 5.78%.
´
˚
were stored over 4-A molecular sieves. Reagent-grade potassium
carbonate was dried in vacuo at 130 8C for 12 h before use. All other
solvents were obtained from various commercial sources and used
without further purification.
4.3.3. 3,4-Phenyl-2,6-bis[3-(40-amino-20-trifluoromethyl-phenoxy)
phenyl] pyridine (m-PAFP)
4.2. Measurements
To a 250 mL three-necked flask equipped with a dropping
funnel and a reflux condenser, 7.17 g (0.01 mol) of m-PNFP, 0.2 g of
palladium on activated carbon (Pd/C10%), and 100 mL of anhy-
drous ethanol were added, and after heating to refluxing
temperature with stirring, 10 mL of hydrazine monohydrate was
added dropwise in 2 h. After addition of hydrazine monohydrate
was finished, the mixture was refluxed for additional 8 h. Then, the
mixture was filtered and the resultant solid was extracted using
enough ethanol. On concentrating all the ethanol solution, yellow
precipitation was appeared, which was filtered off and recrys-
tallized from ethanol to get 5.71 g of needle crystal of m-PAFP. The
yield is 87%, and the melting point is 81–83 8C.
1H NMR and 13C NMR spectra were measured on a JEOL EX-400
spectrometer and JEOL EX-300 spectrometer using tetramethylsi-
lane as the internal reference. FT-IR spectra (KBr) were recorded on
a Nicolet Nexus 670 FT-IR spectrometer. Elemental analyses were
determined by a PerkinElmer model 2400 CHN analyzer. DSC
testing was performed on a PerkinElmer DSC 7 or Pyris 1
differential scanning calorimeter at a scanning rate of 20 8C/min
in flowing nitrogen (30 cm/min), and the Tg values were read at the
DSC curves at the same time. TGA was conducted with a TA
Instruments TGA 2050, and the experiments were carried out with
approximately 10-mg samples in flowing air (flow rate = 100 cm3/
min) at a heating rate of 20 8C/min. WaXD measurements were
FT-IR (KBr): 3453, 3379 cmꢀ1 (N–H stretching) and 1156, 1127,
performed at room temperature (ca. 25 8C) on
a
Siemens
1116 cmꢀ1 (C–F and C–O stretching). 1H NMR (300 MHz, CDCl3):
d
Kristalloflex D5000 X-ray diffractometer with nickel-filtered Cu
(ppm) 7.58 (d, J = 2.4, 2H, Hf), 7.84 (s, 2H, He), 7.73 (d, J = 1.8 Hz, 2H,
Hc), 7.71 (s, 2H, Hd), 7.49–7.42 (m, 4H, Hb, Hg), 7.38 (s, 1H, Ha),
7.11 (d, J = 5.1 Hz, 2H, Hh), 7.02–6.95 (m, 4H, Hi, Hk), 6.81 (d,
J = 3.9 Hz, 2H, Hj), 3.81–3.40 (m, 4H, Hl). 13C NMR (400 MHz,
´
˚
Kx radiation (wavelength = 1.5418 A) at 40 kV and 30 mA.
4.3. Synthesis of the monomer
CDCl3):
d (ppm) 158.76 (C10), 156.67 (C7), 154.10 (C5), 142.54
4.3.1. 1,3-(40-Nitro-20-trifluoromethyl-phenoxy)-acetophenone
(m-NFAP)
(C17), 141.23 (C4), 138.78 (C14), 134.84 (C8), 129.84 (C1, C2),
129.14 (C12), 128.21 (C3), 127.18 (C13), 125.57 (C16), 122.78
(C15), 122.58–119.70 (C19), 119.06 (C6), 118.40 (C11), 117.16
(C9), 116.68 (C18), 113.00–114.81 (C20). MS (EI): 657(M+). Elem.
Anal. Calcd. for C37H25F6N3O2: C 67.58%, H 3.83%, N 6.39%, while
Found C 66.96%, H 3.98%, N 6.95%.
In a 250 mL three-necked flask equipped with a nitrogen inlet,
6.82 g (0.05 mol) of 3-hydroxyacetophenone, 11.2 g (0.05 mol) of 2-
chloro-5-nitro trifluoromethyl-benzene, 6.9 g (0.05 mol) of potas-
sium carbonate, and 100 mL of N,N-dimethylformamide (DMF) was
stirred at 100 8C for 8 h. Then, it was poured into 500 mL of ice/water
to give brown precipitates. The crude product was obtained by
filtration, washed with water, and dried in vacuum overnight. After
recrystallization from ethanol, 15.4 g of m-NFAP was obtained. The
yield is 95%, and the melting point is 64–68 8C.
4.4. Polyimide synthesis
The diamine monomer was reacted with three kinds of
commercially available aromatic dianhydrides, PMDA, ODPA, and

730
T. Ma et al. / Journal of Fluorine Chemistry 131 (2010) 724–730
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BTDA to give the corresponding poly(ether-imide)s, as shown in
Scheme 2. A typical example of polymerization is as follows.
To a stirred solution of 1.3146 g (2.0 mmol) of m-PAPP in 3.4 mL
NMP was added 0.6444 g (2.0 mmol) of BTDA. The mixture was
stirred at room temperature for 24 h under nitrogen atmosphere,
forming a viscous solution of poly(amide acid) (PAA) precursor in
NMP. Either thermal or chemical imidization procedures were
chosen to form polyimides. Chemical imidization was carried out by
adding 3 mL of a mixture of acetic anhydride/pyridine (2/1, v/v) into
the PAA solution with stirring at ambient temperature for 1 h, then
the mixture was stirred at 100 8C for 4 h to yield a homogeneous
polyimide solution, which was poured slowly into ethanol to give a
fibrous precipitate, which was collected by filtration, washed
thoroughly with hot methanol, and dried at 80 8C in vacuum
overnight. For the thermal imidization, the PAA solution was spread
on a glass plate and the solvent was removed at 80 8C overnight.
Imidization was carried out by thermalcyclodehydration of the
poly(amic acid) film by sequential at 110, 150, 180, 210, 230 and
250 8C for 30 min each. Polyimide film was stripped from the glass
substrate by immersing the glass plates in hot water.
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The authors are grateful for the research support from the
Natural Science Foundation of Gansu Province (No. 096RJZA047)
and the State Key Laboratory of Applied Organic Chemistry of
People’s Republic of China.
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