Synthesis and characterization of fluorinated polyimides derived from novel unsymmetrical diamines

Article abstract of DOI:10.1016/j.jfluchem.2010.03.014

Two kinds of aromatic, unsymmetrical diamines with ether-ketone group, 3-amino-4'-(4-amino-2- trifluoromethylphenoxy)-benzophenone and 4-amino-4'-(4-amino-2-trifluoromethylphenoxy)-benzophenone, were successfully synthesized with two different synthetic r

Full text of DOI:10.1016/j.jfluchem.2010.03.014

Journal of Fluorine Chemistry 131 (2010) 767–775
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis and characterization of fluorinated polyimides derived from novel
unsymmetrical diamines
*
Fengchun Yang, Yanfeng Li , Tao Ma, Qianqian Bu, Shujiang Zhang
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
Two kinds of aromatic, unsymmetrical diamines with ether–ketone group, 3-amino-40-(4-amino-2-
trifluoromethylphenoxy)-benzophenone and 4-amino-40-(4-amino-2-trifluoromethylphenoxy)-benzo-
phenone, were successfully synthesized with two different synthetic routes. Then, they were
polymerized with 4,40-oxydiphthalic anhydride, 3,30,4,40-benzophenone tetracarboxylic dianhydride,
and 2,20-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride to form a series of fluorinated
polyimides via a conventional two-step thermal or chemical imidization method. The resulting
polyimides were characterized by measuring their solubility, viscosity, mechanical properties, IR-FT, and
thermal analysis. The results showed that the polyimides had inherent viscosities of 0.48–0.68 dl/g and
were easily dissolved in bipolarity solvents and common, low-boiling point solvents. Meanwhile, the
resulting strong and flexible polyimide films exhibited excellent thermal stability, e.g., decomposition
temperatures (at 10% weight loss) are above 575 8C and glass-transition temperatures in the range of
218–242 8C. The polymer films also showed outstanding mechanical properties, such as tensile strengths
of 86.5–132.8 MPa, elongations at break of 8–14%, and initial moduli of 1.32–1.97 GPa. These
outstanding combined features ensure that the polymers are desirable candidate materials for advanced
applications.
Article history:
Received 15 January 2010
Received in revised form 23 March 2010
Accepted 24 March 2010
Available online 31 March 2010
Keywords:
Fluorinated polyimide
Solubility
Unsymmetrical diamine
ß 2010 Elsevier B.V. All rights reserved.
1. Introduction
enhance the solubility of aromatic polymers make them pro-
cessability.
Polyimides (PIs) represent a class of high performance polymers
that combine high thermal stability, chemical resistance, excellent
electrical and mechanical properties, and so they have been widely
used in many applications such as aerospace, microelectronics,
optoelectronics and composites [1,2]. For these applications it is
desirable to use polyimides that are soluble in spin coating and
casting processes. However, most of wholly aromatic polyimides
have high melting or softening temperatures (Ts’s), and are
insoluble in most organic solvents because of the rigidity of the
backbone and strong interchain interactions. Those properties
make them generally intractable or difficult to process. Thus, many
studies have focused on designing such chemical structures of the
rigid aromatic backbone so as to obtain aromatic polymers that are
processable by conventional techniques, while maintaining desir-
able properties. For example, bulky lateral substituents [3–5],
flexible linkages [6–8], noncoplanar biphenyl moieties [9,10] as
well as unsymmetrical structures [11–13] have been used to
Most of the approaches for soluble polyimides are aimed at
reduction of several types of chain–chain interaction, such as chain
packing (e.g., crystallinity), charge transfer and electronic polariza-
tion interactions. As well known, introduction of geometrically or
molecularly unsymmetrical diamine components into the poly-
imide main chain has led to new polyimides with improved
solubility, melt processability and other desirable properties
[14–19]; additionally, fluorination is also known for increasing
intermolecule space while enhancing the solubility, optical trans-
parency and lower moisture absorption of polyimides [6,20,21].
In this work, we synthesize two kinds of new aromatic
unsymmetrical diamine monomers, 3-amino-40-(4-amino-2-tri-
fluoromethylphenoxy)-benzophenone (m-AAFP) and 4-amino-40-
(4-amino-2-trifluoromethylphenoxy)-benzophenone
(p-AAFP),
which have been designed as potentially convenient condensation
monomers for polyimides, capable of imparting solubility and
good thermal properties at the same time. Then, a series of all-
aromatic, organosoluble polyimides bearing unsymmetrical ether
structure were synthesized from the two diamines with three
different kinds of commercial dianhydrides. The characterizations
of the two diamines and related intermediates, as well as the
* Corresponding author.
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.2010.03.014

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F. Yang et al. / Journal of Fluorine Chemistry 131 (2010) 767–775
Scheme 1. Synthesis of diamine m-AAFP and p-AAFP.
resulting polyimides based on the two diamines were carried out
by means of FT-IR, DSC, TGA and elemental analysis methods.
We designed two different routes to synthesize NNFP. m-NNFP and
p-NNFP were successfully synthesized by the Friedel-Crafts reaction
(route 1). In the route 2, the intermediate dinitro compoundm-NNFP
and p-NNFP were synthesized by a nucleophilic chloro-displace-
ment reaction of 2-chloro-5-nitrotrifluoromethylbenzene with
m-NHB or p-NHB in the presence of potassium carbonate in
N,N-dimethylacetamide (DMAc). Both the para nitro-group and the
ortho trifluoromethyl group activated the chlorine atom for
displacement; therefore, the chlorine-displacement reaction of
2. Results and discussion
2.1. Monomer synthesis
The diamines with the ether–ketone group, m-AAFP and p-AAFP,
were prepared according to a well-developed method (Scheme 1).
Scheme 2. Synthesis of the polyimides.

F. Yang et al. / Journal of Fluorine Chemistry 131 (2010) 767–775
769
Fig. 1. 1H NMR spectra of m-AAFP and p-AAFP.
2-chloro-5-nitrobenzotrifluoride by the phenoxide anion was
readily carried out even at 80 8C. Diamine m-AAFP or p-AAFP was
readily obtained in high yields by the reduction of NNFP with SnCl2/
HCl in refluxing ethanol.
reacting stoichiometric amounts of diamine monomer AAFP with
aromatic dianhydrides at a concentration of 15% solids in NMP.
The ring-opening polyaddition at room temperature for 24 h
yielded poly(amic acid)s (PAA), followed by sequential heating to
300 8C or mixture of Ac2O/Py to obtain the corresponding
polymers. Transformation from poly(amic acid) to polyimide
was possible via the thermal or chemical cyclodehydration; the
former were easy to handle and cast into thin films, and the latter
was suited to prepare soluble polyimides. In general, it is well
known that CF3 groups can decrease the nucleophilicity of
aromatic amines, thus, reaction rate is lower than corresponding
nonfluorinated monomer. In our work, we rised temperature to
80 8C for another 4 h to compensate for the deficiency. The
chemical structures of polyimides were characterized by FT-IR,
and element analysis.
NMR and MS analysis were used to confirm the structures of the
intermediates and the diamine monomers, m-AAFP and p-AAFP.
Fig. 1 shows 1H NMR spectrum, the absorption signals of aromatic
protons of m-AAFP or p-AAFP appeared in the range of 7.3–
8.6 ppm. In the 13C NMR spectrum (Fig. 2) the carbon 13 atoms in
m-AAFP and p-AAFP showed 18 and 16 signals, respectively, which
resonated in the regions of 110–195 ppm. For the 3F-diamine
compound AAFP, the large quartet centered at about 123 ppm was
due to the CF3 carbon. The one-bond C–F coupling constant in this
case was 273 Hz. The 3F-attached carbon also exhibited a clear
quartet centered at about 120 ppm with a smaller coupling. All the
spectroscopic data obtained agreed with the expected structures.
All of the polyimides could form tough and transparent films,
and showed characteristic imide absorption bands at 1782–
1776 cmꢀ1 attributed to the asymmetrical carbonyl stretching
vibrations, and 1725–1718 cmꢀ1 attributed to the symmetrical
carbonyl stretching vibrations. The absorption at 1383–1374 cmꢀ1
was assigned to C–N stretching, and the C–O multiple stretching
2.2. Polymer synthesis
New polyimides were prepared from m-AAFP or p-AAFP
and commercially available aromatic dianhydrides, such as
ODPA, BTDA and 6FDA, via a conventional two-step procedure
as shown in Scheme 2. The polymerization was carried out by
absorptions were also detected in the range of 1300–1100 cmꢀ1
There was no existence of the characteristic absorption bands of
.

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F. Yang et al. / Journal of Fluorine Chemistry 131 (2010) 767–775
Fig. 2. 13C NMR spectra of m-AAFP and p-AAFP.
Table 1
Physical properties and elemental analysis of the polyimides.
Polyimide
Yield (%)
Inherent viscosity(dl/g)
Composition of repeating unit
Elemental analysis (%)
C
H
N
F-PI-1
F-PI-2
F-PI-3
F-PI-4
F-PI-5
F-PI-6
97
96
98
98
97
97
0.52
0.58
0.68
0.48
0.62
0.51
C36H17F3N2O7
C37H17F3N2O7
C39H17F9N2O6
Calcd.
Found
66.88
66.75
2.65
2.73
4.33
4.35
Calcd.
Found
67.48
67.53
2.60
2.64
4.25
4.41
Calcd.
Found
60.01
59.81
2.20
2.24
3.59
3.57
C36H17F3N2O7
Calcd.
Found
66.88
66.94
2.65
2.59
4.33
4.29
C37H17F3N2O7
C39H17F9N2O6
Calcd.
Found
67.48
67.57
2.60
2.64
4.25
4.19
Calcd.
Found
60.01
60.12
2.20
2.17
3.59
3.50

F. Yang et al. / Journal of Fluorine Chemistry 131 (2010) 767–775
771
Fig. 3. Mechanism of thermal and chemical imidization.
Table 2
Solubility of the polyimides.
Solvents
Polyimidesa
F-PI-1
F-PI-2
F-PI-3
F-PI-4
F-PI-5
F-PI-6
NMP
++
++
++
++
+
++
++
++
+
++
++
++
++
+
++
++
++
++
+
++
+
++
++
++
++
+
DMAc
DMF
++
++
+ꢀ
+
DMSO
THF
+
CHCl3
Toluene
+ꢀ
+
+ꢀ
+ꢀ
+ꢀ
+
+
+ꢀ
++
+
+
a
Measured by chemical cyclization polyimide derived from the corresponding poly(amic acid)s. Qualitative solubility was determined with as 10 mg of polymer in 1 ml of
solvent. ++, soluble at room temperature; +, soluble on heating; +ꢀ, partial soluble on heating; ꢀ, insoluble on heating.

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F. Yang et al. / Journal of Fluorine Chemistry 131 (2010) 767–775
the amide group near 3200–3363 (N–H stretching) and 1650–1674
(C55O stretching) cmꢀ1. In addition to the IR spectra, the elemental
analysis values of the polymers generally agreed well with the
calculated values for the proposed structures. Table 1 shows the
element analysis data for the new polyimides, which are in good
agreement with the calculated values for the proposed chemical
structures.
As shown in Fig. 3 the difference of PI between thermal and
chemical imidization can be explained by the imidization
reaction mechanism. PAA was synthesized by dianhydride and
diamine via a polyaddition reaction in the amidetype polar
solvent at room temperature. This kind of PAA was an unstable
polymer; the hydroxyl group of the carboxylic acid group and
amino group of amide in PAA caused a nucleophilic substitution
reaction to take place with the carbonyl group of PAA at room
temperature or in the heating process. The former was a
reversible reaction, which could reduce to form anhydride and
amine, and the latter was an irreversible reaction, which would
dehydrate to form imide. At room or low temperature, the
equilibrium of the former becomes PAA solution with little
chance to occur later. Although PAA solution was heated, the
reversible and irreversible reactions increased with temperature,
and more anhydride ends and amine ends in PAA were produced.
These ends of anhydride and amine still could regenerate to amic
acid. However, the ketone group was an electrophilic group,
which condensed to the amine group to form an imine group;
therefore, PAA with the ketone group is connected with imine
linkage to form nonlinear or cross-linking PI during thermal
imidization. The cross-linking reaction increased with a higher
concentration of PAA after most solvents were volatilized in
the imidization. If PAA is tested with Ac2O/Py via chemical
imidization, causing the Ac2O to react with amic acid to form
amide–anhydride, then the imide is formed by a nucleophilic
reaction of the amide–anhydride group with separating acetic
acid. According to the preceding description, this type of cross-
linking was due to the ketone group of PAA being connected with
the imine group by thermal imidization.
Fig. 5. TGA curve of the polyimides.
2.3. Solubility
The solubilities of the resulting polyimides by chemical
imidization were investigated for the samples in different organic
solvents. The solubility behavior of these polymers in different
solvents is presented in Table 2. These polymers from m-AAFP and
p-AAFP exhibited good solubility behavior in polar solvents such as
DMSO, DMF, DMAc, NMP, THF and toluene. The good solubility
might be attributed to the more bent chain structure of the
polyimides. The bulky CF3 groups could loosen the packing of the
polyimide backbone chains, resulting in the increase of free
volume in the polymers. On the other hand, the unsymmetrical
structure could result in the random head-to-tail, head-to-head
and tail-to-tail triad orientation in consecutive repeating units
along the polymer main chain (Fig. 4). These three structures are
naturally different in rigidity and degree of bending, but because
they all should be present mixed up along polymer chains, they
lead to backbone randomization. This backbone randomization
should make a contribution to the high solubility of polymers. In
summary, the bulky CF3 groups and the unsymmetrical structure
could increase the disorder in the chains and hinder dense chain
stacking, thus reducing the chain–chain interactions to enhance
solubility. It should be noted that good solubility in low-boiling-
point solvents is critical for preparing polyimide films or coatings
at a relatively low processing temperature, which is desirable for
advanced microelectronics manufacturing applications.
Table 3
DSC and TGA of the non-cross-linked polyimides, nonfluorinated polyimides and
fluorinated polyimides.
Polyimidea
Thermal properties
b
c
c
c
c
Tg (8C)
Td (8C)
T5 (8C)
T10 (8C)
Rw (%)
F-PI-1
231
238
218
224
242
222
232
237
260
248
251
242
577
590
567
552
586
560
546
540
525
588
575
564
567
584
568
564
575
572
545
538
523
582
573
558
590
603
589
575
600
582
570
561
535
608
618
582
50
54
58
52
54
56
17
31
5
F-PI-2
F-PI-3
F-PI-4
F-PI-5
F-PI-6
NC-PI-1
NC-PI-2
NC-PI-3
NF-PI-1
NF-PI-2
NF-PI-3
56
48
50
a
Measured samples were obtained by thermal imidization method.
b
c
Tg was measured by DSC at a heating rate of 10 8C/min in nitrogen.
Td, decomposition-starting temperature; T5 and T10, temperature at a 5 or 10%
Fig. 4. Three different triad structures.
weight loss. Rw, residual weight (%) at 800 8C in nitrogen.

F. Yang et al. / Journal of Fluorine Chemistry 131 (2010) 767–775
773
Scheme 3. Synthesis of the non-cross-linked polyimides, nonfluorinated polyimides and fluorinated polyimides.
2.4. Thermal properties and mechanical properties
licity than fluorinated monomer, the molecular weight of
nonfluorinated polyimides are higher than fluorinated polyimides
and (2) the cross-linking reaction play an important role in thermal
stabilization of polymer. As shown in Table 4, all the polyimides
can be processed into clear, flexible and tough films, the polyimide
films had tensile strengths of 86.5–132.8 MPa, elongations at break
of 8–14% and tensile modulus of 1.32–1.97 GPa, which indicated
strong and tough materials.
DSC and TGA methods were applied to evaluate the thermal
properties of the polyimides; the TGA curves of the polyimides are
shown in Fig. 5, 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 the polymer
could be easily read in the second heating trace of DSC. The Tg
values of PI-1 to PI-6 were in the range of 218–242 8C. As we
expected, the Tg values of these polyimides depend on the
structure of the different component and decreased with increas-
ing flexibility of the polyimide backbones according to the applied
structure of the monomer. For the thermal stability of the
2.5. Moisture uptakes
Polyimide materials usually show higher moisture uptakes
than the hydrocarbon polymers because of the presence of imide
groups. The moisture absorption of aromatic polyimides can be
up to 3.0–3.5% depending on the chemical structures of polymer
and the relative humidity of the surrounding environments,
which have a significant influence on the dielectric properties of
polymers. For instance, polyimides derived from PMDA or 6FDA
with ODA show moisture uptakes of 2.3–2.7 wt% and 1.3–
1.64 wt%, respectively. Also, some fluorinated polyimides were
reported to absorb moisture of <1%. However, there was not a
quantitative linear relationship between the fluorine content and
moisture uptake for polyimide materials. Table 4 compares the
moisture uptakes of the polyimides derived from diamine m-
AAFP or p-AAFP with three dianhydrides. The moisture uptakes of
polyimides were measured at 0.41–0.67%. The moisture absorp-
tion of polyimides might be related to several factors including
the chemical structures, the introduction of fluorinated groups
and of other functional groups, the geometrical packing of the
polymer chains as well as film-processing parameters, and so
forth in which the chemical structure and the presence of
functional groups in polymer might be the major concern factors.
The trifluoromethyl groups possess amphiprotoc features, which
inhibit the absorption of moisture molecules on the surface of the
fluorinated polymers. On the other hand, the bulky trifluor-
omethyl groups could loosen the packing of the polyimide
backbone chains, resulting in the increase of free volume in the
polymers that ensure the polymer to entrap some of the water
molecules. These two opposing effects of the trifluoromethyl
groups are offsetted, to some extent, resulting in fluorinated
polyimides with lower moisture absorption than the correspond-
ing polyimides derived from unfluorinated diamines. Fig. 5
shows the moisture uptakes of non-cross-linked polyimides
polyimides, Table
3 gives the temperatures of the initial
decomposition and 5 and 10% gravimetric losses in nitrogen.
The temperatures of the initial decomposition were determined to
be in the range of 552–590 8C for all polyimides tested. The
temperatures of 10 and 5% gravimetric losses of the polyimides
reached 564–575 and 575–603 8C in nitrogen. Also, the char yields
at 800 8C for all the polymers were in the range of 50–58 wt%. As
shown in Table 3 and Scheme 3, the thermal stabilization of non-
cross-linked polyimides (NC-PI-1–NC-PI-3) is worse than cross-
linked polyimides (F-PI-1–F-PI-3 and NF-PI-1–NF-PI-3). But the
thermal stabilization of nonfluorinated polyimides (NF-PI-1–NF-
PI-3) and fluorinated polyimides (F-PI-1–F-PI-3) did not show
significant difference, generally, the thermal stabilization of
fluorinated polyimides is better than nonfluorinated polyimides
because of the existing of CF3, we think it may attribute to two
reasons: (1) it is well known that CF3 groups can decrease the
nucleophilicity of aromatic amines due to their strong electroneg-
ativity, thus, the nonfluorinated monomer has better nucleophi-
Table 4
Mechanical properties and water absorption of the polyimides.
Polymer
Tensile
Elongation
(%)
Modulus
(GPa)
Water
strength (MPa)
absorption (%)
F-PI-1
F-PI-2
F-PI-3
F-PI-4
F-PI-5
F-PI-6
126.6
132.8
117.5
116.5
86.5
12
8
1.46
1.78
1.32
1.37
1.97
1.74
0.44
0.44
0.67
0.52
0.63
0.41
10
13
11
14
104.2

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F. Yang et al. / Journal of Fluorine Chemistry 131 (2010) 767–775
Table 5
The water absorption comparison of non-cross-linked polyimides, nonfluorinated polyimides and fluorinated polyimides.
Polyimides
Non-cross-linked polyimides
Nonfluorinated polyimides
Fluorinated polyimides
NC-PI-1
0.32
NC-PI-2
0.63
NC-PI-3
0.41
NF-PI-1
1.08
NF-PI-2
1.32
NF-PI-3
0.86
F-PI-1
0.44
F-PI-2
0.44
F-PI-3
0.67
Water absorption (%)
(NC-PI-1–NC-PI-3), nonfluorinated polyimides (NF-PI-1–NF-PI-
3) and fluorinated polyimides (F-PI-1–F-PI-3). The fluorinated
polyimides and non-cross-linked polyimides shown lower
moisture uptakes than of nonfluorinated polyimides, it indicates
that the CF3 group plays a main role in moisture uptakes
(Table 5).
4.3. Monomer synthesis
4.3.1. (4-Nitro-2-trifluoromethylphenoxy)-phenoxy ether (NFPP)
2-Chloro-5-nitrotrifluoromethylbenzene (9.02 g, 0.04 mol) and
phenol (3.76 g, 0.04 mol) were first dissolved in 40 ml of DMF in a
100-ml flask with stirring. After the mixture was completely
dissolved, potassium carbonate (5.56 g, 0.04 mol) was added to it
in one portion. After 30 min of stirring at room temperature, the
mixture was heated at 60 8C for 4 h. The obtained mixture was
poured into 300 ml of distilled water. The precipitated solid was
collected by filtration and dried in vacuo at 60 8C for 12 h. The
crude product was purified by column chromatography over silica
gel (4:1 petroleum ether/ethyl acetate), 10.52 g was obtained
(92%). 1H NMR (CDCl3, ppm): 8.60 (s, 1H), 8.32–8.29 (dd, 1H), 7.50–
7.46 (t, 2H), 7.34–7.31 (t, 1H), 7.14–7.12 (d, 2H), 6.95–6.93 (d, 2H).
Low MS (m/e) 282.2, Calcd. 283 for C13H8F3NO3.
3. Conclusions
Two kinds of aromatic unsymmetrical diamines with CF3 group,
3-amino-40-(4-amino-2-trifluoromethylphenoxy)-benzophenone
and 4-amino-40-(4-amino-2-trifluoromethylphenoxy)-benzophe-
none, were successfully synthesized by two different synthetical
routes and polymerized with various aromatic tetracarboxylic acid
dianhydrides. The resulting polyimides exhibit good solubility,
excellent thermal stability and balanced mechanical properties.
The introduction of unsymmetrical structures and trifluoromethyl
groups in polyimides results in dramatic changes in their
properties, especially in the improvement of solubility and
lowered moisture uptakes.
4.3.2. 3-Nitro-40-methoxy-benzophenone (m-NMB) and 4-nitro-40-
methoxy-benzophenone (p-NMB)
18.5 g (0.1 mol) of m-nitrobenzoyl chloride was gradually
added to a mixture of 60 ml of benzene, 10.8 g (0.1 mol) of phenyl
methyl ether and 16.0 g (0.12 mol) of anhydrous aluminum
chloride at 10–12 8C with continuous stirring. After addition, the
mixture was slowly heated to 40 8C and stirred for 2 h. Finally, the
resulting reaction mixture was allowed to cool to room tempera-
ture and poured into 500 ml of a water solution of hydrochloric
acid (5%) to precipitate out white solids. The solids was collected by
filtrating, and washed with hot methanol to give 23.0 (92%) g of
white powder. 1H NMR (CDCl3, ppm): 8.63 (s, 1H), 8.47–8.44 (dd,
1H), 8.16–8.14 (d, 1H), 7.82–7.80 (d, 2H), 7.74–7.70 (t, 1H), 7.57–
7.55 (d, 2H). Low MS (m/e) 257.07, Calcd. 257 for C14H11NO4.
p-NMB was prepared from p-nitrobenzoyl chloride in CH2Cl2.
1H NMR (CDCl3, ppm): 8.35–8.32 (d, 2H), 7.90–7.87 (d, 2H), 7.83–
7.80 (d, 2H), 7.01–6.98 (d, 2H), 3.91 (t, 3H). Low MS (m/e) 257.07,
Calcd. 257 for C14H11NO4.
4. Experimental
4.1. Materials
Commercially available 2-chloro-5-nitrotrifluoromethylben-
zene, m-nitrobenzoyl chloride, p-nitrobenzoyl chloride (Shanghai
Chemical Reagents Corp., China), phenol, phenyl methyl ether
(Fuchen Chemical Reagents Corp., Tianjin, China). 4,40-Oxy-
diphthalic anhydride (ODPA, Shanghai Nanxiang Chemical Co.,
China), 3-nitro-benzoyl chloride, 3,30,4,40-benzophenonetetracar-
boxylic dianhydride (BTDA, Beijing Chemical Reagents Corp.,
China) and 2,20-bis(3,4-dicarboxyphenyl) hexafluoropropane dia-
nhydride (6FDA, Aldrich) were recrystallized from acetic anhy-
dride before use. N,N-dimethylacetamide (DMAc) and N-methyl-
2-pyrrolidone (NMP) were purified by distillation under reduce
4.3.3. 3-Nitro-40-hydroxy-benzophenone (m-NHB) and 4-nitro-40-
hydroxy-benzophenone (p-NHB)
˚
pressure over calcium hydride and stored over 4 A molecular
sieves. All other solvents were obtained from various commercial
sources and used without further purification.
A 500 ml one-necked flask equipped with stir bar and reflux
condenser was charged with 12.8 g (0.05 mol) of m-NMP, 160 ml of
glacial acetic acid and 60 ml of HBr (48%). This solution was
refluxed for 20 h till only one spot in TLC and allowed to cool to
room temperature. The orange solution was extracted with 200 ml
of CH2Cl, the organic layer was washed with 150 ml of water and
dried over MgSO4. The solvent was removed, to give 10.1 (93%) g of
white powder of compound 3-nitro-40-hydroxy-benzophenone
(m-NHB). 1H NMR (CDCl3, ppm): 8.58 (s, 1H), 8.44–8.42 (dd, 1H),
8.11–8.09 (d, 1H), 7.83–7.81 (d, 2H), 7.72–7.68 (t, 1H), 7.01–6.98
(d, 2H). Low MS (m/e) 243.05, Calcd. 243 for C13H9NO4.
p-NHB: 1H NMR (CDCl3, ppm): 8.35–8.32 (d, 2H), 7.90–7.87 (d,
2H), 7.79–7.76 (d, 2H), 6.95–6.92 (d, 2H). Low MS (m/e) 243.05,
Calcd. 243 for C13H9NO4.
4.2. Measurements
The inherent viscosities of the resulting polyimides were
measured with an Ubbelohde viscometer at 30 8C. FT-IR spectra
(KBr) were recorded on a Nicolet Nexus 670 FT-IR spectrometer. 1H
NMR and 13C NMR spectra were measured on a JEOLEX-300
spectrometer with tetramethylsilane as the internal reference.
Elemental analyses were determined with a PerkinElmer model
2400 CHN analyzer. DSC testing was performed on a PerkinElmer
DSC 7, differential scanning calorimeter at a scanning rate of 10 8C/
min in flowing nitrogen (30 cm3/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. The mechanical properties
were measured on an Instron 1122 tensile apparatus with
100 mm ꢁ 5 mm specimens in accordance with GB 1040-79 at a
drawing rate of 100 mm/min.
4.3.4. 3-Nitro-40-(4-nitro-2-trifluoromethylphenoxy)-benzophenone
(m-NNFP) and 4-nitro-40-(4-nitro-2-trifluoromethylphenoxy)-
benzophenone (p-NNFP)
2-Chloro-5-nitrotrifluoromethylbenzene (9.02 g, 0.04 mol) and
m-NHB (7.72 g, 0.04 mol) were first dissolved in 100 ml of DMF in a

F. Yang et al. / Journal of Fluorine Chemistry 131 (2010) 767–775
775
250-ml flask with stirring. After the mixture was completely
dissolved, potassium carbonate (5.56 g, 0.04 mol) was added to it in
one portion. After 30 min of stirring at room temperature, the
mixture was heated at 60 8C for 4 h. The obtained mixture was
poured into 300 ml of distilled water. The precipitated solid was
collected by filtration and dried in vacuum at 60 8C for 12 h. The
crude product was purified by column chromatography over silica
gel (4:1 petroleum ether/ethyl acetate), 15.52 g was obtained (90%).
9.7 g (0.05 mol) of m-nitrobenzoyl chloride was gradually
added to a mixture of 60 ml of benzene, 14.2 g (0.05 mol) of NFPP
and 8.0 g (0.06 mol) of anhydrous aluminum chloride at 10–12 8C
with continuous stirring. After addition, the mixture was slowly
heated to 40 8C and stirred for 2 h. Finally, the resulting reaction
mixture was allowed to cool to room temperature and poured into
500 ml of a water solution of hydrochloric acid (5%) to precipitate
out white solids. The solids were collected by filtrating, and
washed with hot methanol to give 15.32 g (71%) of yellow powder.
1H NMR (DMSO-d6, ppm): 8.63 (s, 1H), 8.62 (s, 1H), 8.49–8.47 (dd,
1H), 8.43–8.40 (d, 1H), 8.17–8.15 (d, 1H), 7.94–7.92 (d, 2H), 7.77–
7.73 (t, 1H), 7.26–7.24 (d, 2H), 7.15–7.13 (d, 1H). Low MS (m/e)
432.31, Calcd. 432 for C20H11F3N2O6.
polyimide PI-1 (ODPA–m-AAFP) is used as an example to
illustrate the general synthetic route used to produce the
polyimides. To a solution of 0.3722 g (1.0 mmol) of diamine
AAFP in 5.0 ml of CaH2-dried NMP, 0.3099 g (1.0 mmol) of ODPA
was added in one portion. The solution was stirred at room
temperature under N2 for 24 h to yield a viscous poly(amic acid)
(PAA) solution. PAA was converted into a polyimide with thermal
or chemical imidization methods. For the thermal imidization
method, the PAA solution was cast onto a clean glass plate and
heated (80 8C/3 h, 120 8C/30 min, 150 8C/30 min, 180 8C/30 min,
210 8C/30 min, 250 8C/30 min, 300 8C/1 h) to produce a fully
imidized polyimide film. Chemical imidization was carried out by
the addition of an equimolar mixture of acetic anhydride and
pyridine to the aforementioned PAA solution (with mechanical
stirring) at the ambient temperature for 30 min and via heating
at 80 8C for 4 h. The polyimide solution was poured into
methanol. The precipitate was collected by filtration, washed
thoroughly with methanol, and dried at 80 8C in vacuo to give the
following.
PI-2 (BTDA and m-AAFP), PI-3 (6FDA and m-AAFP), and PI-10
(ODPA and p-AAFP), PI-20 (BTDA and p-AAFP), PI-30 (BTDA and p-
AAFP) were synthesized by a similar method.
p-NNFP was prepared by the similar method. 1H NMR (DMSO-
d6, ppm): 8.63 (s, 1H), 8.62 (s, 1H), 8.49–8.47 (dd, 1H), 8.43–8.40
(d, 1H), 8.17–8.15 (d, 1H), 7.94–7.92 (d, 2H), 7.77–7.73 (t, 1H),
7.26–7.24 (d, 2H), 7.15–7.13 (d, 1H). Low MS (m/e) 432.31, Calcd.
432 for C20H11F3N2O6.
Acknowledgement
The authors acknowledge the financial support of the Research
Foundation of the State Key Laboratory of Applied Organic
Chemistry.
4.3.5. 3-Amino-40-(4-amino-2-trifluoromethylphenoxy)-
benzophenone (m-AAFP) and 4-amino-40-(4-amino-2-
trifluoromethylphenoxy)-benzophenone (p-AAFP)
A mixture consisting of 21.6 g (0.05 mol) of m-NNFP, 58.0 g
(0.3 mol)ofanhydrousSnCl2 and500 mlof95%C2H5OH wasputinto
a reaction flask, with stirred while 20 ml of concentrated HCl was
added slowly. After addition of hydrochloric acid was finished, the
mixture was refluxed for 12 h. Excess ethanol was evaporated, and
the remaining solution was poured into 400 ml of distiller water, the
mixing solution was basified with 15% NaOH solution to form a
precipitate, and the precipitate was filtrated off, washing with water
and methanol, recrystallized from toluene to get a yellow product
16.4 g (88%). 1H NMR (DMSO-d6, ppm): 7.74–7.72 (d, 2H), 7.18–7.14
(t, 1H), 7.02–7.00 (d, 1H), 6.98–6.96 (d, 2H), 6.95 (s, 1H), 6.91 (s, 1H),
6.88–6.86 (dd, 1H), 6.82–6.78 (m, 2H). 13C NMR (DMSO-d6, ppm):
195.0, 162.0, 148.8, 146.6, 140.7, 138.1, 132.0, 131.4, 128.8, 124.0,
118.5, 117.6, 116.9, 115.6, 114.3, 110.,7. Low MS (m/e) 372.34, Calcd.
372 for C20H15F3N2O2. FT-IR(KBr): 3419, 3333 (NH stretch), 1271,
1238, 1159, 1122 cmꢀ1 (C–O and C–F stretch).
p-AAFP was prepared by the similar method. 1H NMR (DMSO-
d6, ppm): 7.62–7.59 (d, 2H), 7.51–7.48 (d, 2H), 6.99–6.83 (m, 6H),
6.83–6.80 (d, 2H). 13C NMR (DMSO-d6, ppm): 192.3, 161.1, 153.6,
146.5, 141.1, 132.9, 132.5, 131.4, 124.0, 123.9, 118.6, 115.6, 122.6,
110.7. Low MS (m/e) 372.34, Calcd. 372 for C20H15F3N2O2. FT-
IR(KBr): 3448, 3359 (NH stretch), 1263, 1232, 1168, 1127 cmꢀ1 (C–
O and C–F stretch).
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The polyimides were synthesized from various dianhydrides
and diamine AAFP via a two-step method. The synthesis of