Synthesis and properties of new fluorinated polyimides derived from an unsymmetrical and noncoplanar diamine

Article abstract of DOI:10.1002/cjoc.201200431

A new unsymmetrical and noncoplanar diamine containing trifluoromethyl and trimethyl groups, 1,4-bis(4-amino-2-trifluoromethylphenoxy)-2,3,5- trimethylbenzene (2), was synthesized using 2,3,5-trimethylhydroquinone and 2-chloro-5-nitrobenzotrifluoride as starting materials. A series of fluorinated poly(ether imide)s (PEIs) (4a-4d) were prepared from diamine 2 with four aromatic dianhydrides via a one-step high-temperature polycondensation procedure. The obtained PEIs were readily soluble in most organic solvents and could be solution-cast into flexible and strong films. The resulting thin films exhibited light color and good optical transparency with a cutoff wavelength of 356-376 nm. They also displayed good thermal stability with glass transition temperatures (T_g) above 281°C, 10% weight loss temperatures in the range of 482-486°C, and the weight residue more than 55% at 800°C in nitrogen. Moreover, they revealed low dielectric constants (2.77-2.93 at 1 MHz) and low moisture absorptions (0.41%-0.57%). A new unsymmetrical and noncoplanar aromatic diamine monomer has been successfully synthesized in high yield by a facile reaction route. New series of highly soluble fluorinated polyimides with moderate to high molecular weights have been prepared by a one-step polycondensation procedure. The resulting polyimides could be readily solution-cast into transparent and flexible films with light color, good optical transparency, moderate to high glass-transition temperatures, and low dielectric constants. The eminent combination of several properties guaranteed the obtained polyimides as potential high-temperature resistant materials for optical and photoelectric applications. Copyright

Full text of DOI:10.1002/cjoc.201200431

FULL PAPER
DOI: 10.1002/cjoc.201200431
Synthesis and Properties of New Fluorinated Polyimides De-
rived from an Unsymmetrical and Noncoplanar Diamine
Wang, Chenyi*,a(汪称意)
Zhao, Xiaoyana(赵晓燕)
Li, Guang*,b(李光)
a School of Material Science and Engineering, School of Petrochemical Engineering, Changzhou University,
Changzhou, Jiangsu 213164, China
b State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Material Science
and Engineering, Donghua University, Shanghai 201620, China
A new unsymmetrical and noncoplanar diamine containing trifluoromethyl and trimethyl groups, 1,4-bis(4-
amino-2-trifluoromethylphenoxy)-2,3,5-trimethylbenzene (2), was synthesized using 2,3,5-trimethylhydroquinone
and 2-chloro-5-nitrobenzotrifluoride as starting materials. A series of fluorinated poly(ether imide)s (PEIs) (4a—4d)
were prepared from diamine 2 with four aromatic dianhydrides via a one-step high-temperature polycondensation
procedure. The obtained PEIs were readily soluble in most organic solvents and could be solution-cast into flexible
and strong films. The resulting thin films exhibited light color and good optical transparency with a cutoff wave-
length of 356—376 nm. They also displayed good thermal stability with glass transition temperatures (Tg) above
281 ℃, 10% weight loss temperatures in the range of 482—486 ℃, and the weight residue more than 55% at 800
℃ in nitrogen. Moreover, they revealed low dielectric constants (2.77—2.93 at 1 MHz) and low moisture absorp-
tions (0.41%—0.57%).
Keywords fluorinated polyimides, solubility, optical transparency, dielectric constant
Introduction
devices, flexible solar cell, optical waveguides and so
on.[23] The coloration of aromatic PI films is mainly
caused by their highly conjugated aromatic structures
and/or the intra- and intermolecular charge-transfer
complex (CTC) formation. A strategy for obtaining less
colored or colorless PIs is to use diamines of lower
electron donatability as monomers or dianhydrides of
lower electron acceptability for weakening the intra-
and intermolecular CTC formation.[24] Reducing conju-
gation or introducing aliphatic dianhydride/diamine is
another method to lighten the color of PIs.[25] However,
the level of thermal stability of these PIs would be re-
duced in this way, because the aliphatic segments are
less stable.
Recently, considerable attention has been devoted to
the fluorinated PIs, especially the trifluoromethyl-
containing poly(ether imide)s (PEIs).[18,24,26-36] As well-
known, the bulky free volume and high electronegativ-
ity of the fluorinated groups could endow aromatic PIs
with many attractive features, such as good organo-
solubility, high optical transparency, light color as well
as low water uptake and dielectric constants.[37] Thus,
the develepment of novel trifluoromethyl substituted
monomers for functional PIs has become a subject of
intense research interest. As part of our continuing ef-
forts to develop soluble and colorless PIs with good
Since being first reported in 1908 and followed by
the introduction of the high molecular weight polymer
in the 1950s, polyimides (PIs) have found a wide range
of applications in advanced technologies because of
their good mechanical properties, high thermal stability,
and excellent electric properties.[1-12] However, most
commercial PIs exhibit very limited solubilities and
high melting points, thus presenting serious processing
difficulties. Therefore, the soluble precursor polymers,
poly(amic acid)s, are cast onto the substrates and ther-
mally cyclodehydrated at elevated temperature to yield
the insoluble PI films or coatings. One of the major
drawbacks of these precursors is that they are sensitive
to moisture or oxygen and must be kept refrigerated
during storage. Therefore, much effort has been spent
on synthesizing soluble PIs that reasonably maintain the
desired properties. Several successful approaches in-
cluding insertion of flexible linkage and bulky substitu-
ents on the main chain or utilization of noncoplanar or
unsymmetrical monomers have been developed.[13-22]
On the other hand, the wholly aromatic PIs often
have strong absorption in the visible region of their
UV-visible spectra and exhibit pale yellow or deep red-
dish yellow, which hinder their applications as optical
or optoelectronic materials in liquid crystal display
*
E-mail: wangcy1981@gmail.com, lig@dhu.edu.cn
Received May 3, 2012; accepted June 18, 2012; published online XXXX, 2012.
Chin. J. Chem. 2012, XX, 1—7
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1

Wang, Zhao & Li
FULL PAPER
thermal stability for advanced optical and optoelectron-
ics applications, the current work reports a new
trifluoromethyl-substituted diamine and a series of PEIs
containing bulky pendant groups and unsymmetrical
structures. These PEIs should have diminished intra-
and intermolecular CTC formation because of the de-
crease in electron-donating property of diamine moieties
caused by the electron-withdrawing trifluoromethyl
groups. Additionally, the incorporation of the bulky
trimethyl and trifluoromethyl groups and the formation
of noncoplanar structures due to the presence of ortho
links would also help reducing the aromatic conjugation.
Thus, the polymers would be expected to exhibit low
coloration, high optical transparency in the visible re-
gion, low dielectric constants and good solubility in or-
ganic solvents.
spectrophotometer at room temperature. The tensile
properties were performed on an Instron 3365 Tensile
Apparatus with a 5 kg load cell at a crosshead speed of
5 mm/min on strips approximately 40—60 um thick and
0.5 cm wide with a 2 cm gauge length. An average of at
least five individual determinations was used. The
dielectric property of the polymer films was determined
by the parallel-plate capacitor method with an Agilent
E4980A LCR Meters. Prior to test, gold electrodes were
vacuum-deposited on both surfaces of dried films. The
experiments were performed in a dry chamber. The
equilibrium water absorption was determined by the
weighing of the changes in vacuum-dried film speci-
mens before and after immersion in deionized water at
25 ℃ for 6 h.
Monomer synthesis
1,4-Bis(4-nitro-2-trifluoromethylphenoxy)-2,3,5-
trimethylbenzene (1) A mixture of 2,3,5-trimethyl-
hydroquinone (15.22 g, 0.10 mol), 2-chloro-5-nitroben-
zotrifluoride (45.11 g, 0.2 mol), potassium carbonate
(28.98 g, 0.021 mol) and DMAc (130 mL) was heated
to 130 ℃ for 12 h and then poured into methanol/water
(1∶3 by volume). The crude product was recrystallized
from DMF/ethanol (3∶2) to provide pale yellow crystal
solid (44.55 g, 84%), m.p. 256—257 ℃ by DSC at a
scan rate of 10 ℃/min. 1H NMR (DMSO-d6, 400 MHz)
δ: 8.64 (d, J＝2.8 Hz, 1H), 8.62 (d, J＝2.8 Hz, 1H),
8.32 (dd, J＝2.8, 9.2 Hz, 1H), 8.30 (dd, J＝2.8, 9.2 Hz,
1H), 6.91 (s, 1H), 6.80 (d, J＝9.2 Hz, 1H), 6.62 (d, J＝
9.2 Hz, 1H), 2.13 (s, 3H), 2.11 (s, 3H), 2.10 (s, 3H); IR
Experimental
Materials
2,3,5-Trimethylhydroquinone and 2-chloro-5-nitro-
benzotrifluoride were purchased from Alfa Aesar and
used as received. Commercially available aromatic
tetracarboxylic dianhydrides such as pyromellitic dian-
hydride (PMDA or 3a), 3,3',4,4'-biphenyltetracarboxylic
dianhydride (BPDA or 3b), 3,3',4,4'-benzophenone-
tetracarboxylic dianhydride (BTDA or 3c) and 4,4'-
oxydiphthalic dianhydride (ODPA or 3d) were all puri-
fied by recrystallization from acetic anhydride and then
dried in vacuo at 180 ℃ for 6 h. Commercially avail-
able N-methyl-2-pyrrolidinone (NMP), m-cresol, N,N-
dimethylacetamide (DMAc), N,N-dimethyl-formamide
(DMF), dimethyl sulfoxide (DMSO) and other solvents
were purified by distillation prior to use.
－
1
(KBr) v: 2928, 1611, 1532, 1347, 1269, 1144 cm .
Anal. calcd for C23H16F6N2O6: C 52.09, H 3.04, N 5.28;
found C 51.97, H 3.08, N 5.31.
1,4-Bis(4-amino-2-trifluoromethylphenoxy)-2,3,5-
trimethylbenzene (2) The intermediate dinitro com-
pound 1 (26.52 g, 0.05 mol) and 5% Pd/C (0.6 g) were
suspended in 250 mL of ethanol in a 500 mL flask. The
suspension solution was heated to refluxing, and 85%
hydrazine monohydrate (20 mL) was added dropwise to
the mixture over 0.5 h. After a further 6 h of refluxing,
the resultant clear, darkened solution was filtered hot to
remove Pd/C, and the filtrate was then distilled to re-
move the solvent. The crude product was purified by
recrystallization from ethanol to give white crystals
(19.05 g, 81%), m.p. 233—234 ℃ by DSC at a scan
Measurements
NMR spectra were measured on a Bruker AV400 in-
strument with dimethyl sulfoxide-d6 (DMSO-d6) or
CDCl3 as solvent and tetramethylsilane (TMS) as an
internal standard. FT-IR spectra were recorded on a
Nicolet NEXUS 670 spectrometer. Elemental analysis
was carried out on a Carlo-Erba 1106 system.
Weight-average molecular weights (Mw) and number
average molecular weights (Mn) were obtained via gel
permeation chromatography (GPC) on the basis of
polystyrene calibration using BI-MwA system as an
apparatus and THF as the eluent. Differential scanning
calorimetry (DSC) analysis was performed on a PE
Diamond DSC instrument at a heating rate of 20 ℃/
min in nitrogen atmosphere. Glass transition tempera-
tures were read at the middle of the transition in the heat
capacity from the second heating scan after quick cool-
ing from 360 ℃ at a cooling rate of 20 ℃/min. Ther-
mogravimetric analysis (TGA) of the polymer samples
was measured on a Netzsch TG 209F1 instrument at a
heating rate of 20 ℃/min in nitrogen atmosphere. Ul-
traviolet-visible (UV-vis) spectra of the polymer films
were recorded on a PerkinElmer Lambda 35 UV-vis
1
rate of 10 ℃/min. H NMR (DMSO-d6, 400 MHz) δ:
6.92—6.95 (m, 2H), 6.78 (dd, J＝2.8, 8.8 Hz, 1H), 6.68
(d, J＝8.8 Hz, 1H), 6.66 (dd, J＝2.8, 8.8 Hz, 1H), 6.57
(s, 1H), 6.18 (d, J＝8.8 Hz, 1H), 5.33 (s, 2H), 5.12 (s,
2H), 2.12 (s, 3H), 2.01 (s, 3H), 1.94 (s, 3H); IR (KBr) v:
－
1
3429, 3331, 3226, 2928, 1624, 1236, 1149 cm . Anal.
calcd for C23H20F6N2O2: C 58.72, H 4.29, N 5.96; found
C 58.60, H 4.33, N 6.01.
Polymer synthesis
The general procedure for the preparation of the
PEIs 4a—4d was illustrated as follows. Diamine 2 (2.0
2
www.cjc.wiley-vch.de
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, XX, 1—7

Synthesis and Properties of New Fluorinated Polyimides
mmol) and dianhydride monomer 3 (2.0 mmol) were
first dissolved in 20.0 mL of m-cresol in a 50 mL
three-necked round bottom flask. After the mixture was
stirred at room temperature for 30 min, isoquinoline (ca.
4 drops) was added, and further stirred for 3 h at 120 ℃.
Then the mixture was heated at 190 ℃ for 8 h. Water
formed during the imidization was continuously re-
moved with a stream of nitrogen. At the end of the reac-
tion, the mixture was cooled and precipitated into 300
mL ethanol. The polymer was separated by filtration
and washed with ethanol for several times and dried in a
vacuum oven at 120 ℃ for 10 h.
Scheme 1 Synthesis of aromatic diamine 2
F3C
H3C
HO
H3C
K2CO3
DMAc
OH
CH3
+
Cl
NO2
F3C
CF3 H3C
O
.
H2NNH2 H2O
O2N
O
NO2
Pd/C
H3C
CH3
1
F3C
CF3 H3C
O
Results and Discussion
H2N
O
NH2
Monomer synthesis
H3C
CH3
2
The new fluorinated diamine, 1,4-bis(4-amino-2-
trifluoromethylphenoxy)-2,3,5-trimethylbenzene, was
successfully synthesized in a two-step reaction using
2,3,5-trimethylhydroquinone and 2-chloro-5-nitrobenzo-
trifluoride as starting materials (Scheme 1). 1,4-Bis(4-
nitro-trifluoromethylphenoxy)-2,3,5-trimethylbenzene
(1), an intermediate dinitro-compound, was first synthe-
sized by the chloro-displacement reaction of 2-chloro-
5-nitrotrifluoromethylbenzene with 2,3,5-trimethylhy-
droquinone in the presence of potassium carbonate in
DMAc. Then, the aromatic diamine monomer 2 was
obtained by the catalytic reduction of intermediate dini-
tro-compounds 1 with hydrazine monohydrate and Pd/C
catalyst in refluxing ethanol in high yields. The chemi-
cal structures of the synthesized intermediate 1 and
1
Figure 1 FT-IR spectra of 1, 2, and PEI 4b.
diamine 2 were characterized by FTIR, H NMR and
elemental analysis. In the FTIR spectra (Figure 1), dini-
putations, exhibited remarkable twisting and noncopla-
nar structure. This chemical structure was designed to
impart several desirable properties to obtained polyim-
ides.
tro-compound 1 gave two characteristic bands at 1532
and 1347 cm － (NO2 asymmetric and symmetric
1
stretching). After reduction, the characteristic absorp-
tions of the nitro groups disappeared, and the amino
groups showed the pair of N—H stretching bands at the
－
1
1
Polymer synthesis
region of 3200—3500 cm . Figure 2 shows H NMR
spectra of 1 and 2, and the assignments of each proton
are given in the figure. The spectra agree well with the
desired molecular structure, and they confirm that the
nitro groups have been completely converted into amino
groups by the high field shift of the aromatic protons
(especially for the protons H-1, H-7, H-2 and H-6 ortho
to the amino group) and by the signals at δ 5.33 and
5.12 corresponding to the primary aromatic amine pro-
tons. Furthermore, the elemental analysis results also
agree with the calculated values for all the proposed
chemical composition.
Because of the introduction of bulky pendent groups
(trifluoromethyl and trimethyl groups) at the ortho-
position of ether linkage in diamine 2, to attain the
minimum energy of conformation, it is no doubtful that
the diamine monomer would possess a large kink non-
coplanar structure and dihedral angles between aromatic
phenyl rings. As shown in Figure 3, the molecular
model of diamine 2, simulated by semiempirical com-
PEIs 4a—4d were prepared conveniently from aro-
matic diamine 2 and various aromatic dianhydrides
3a—3d (PMDA, BPDA, BTDA and ODPA) via a
one-step, high-temperature solution polycondensation
procedure, as shown in Scheme 2. The polymerization
of diamine 2 with 3a—3d proceeded smoothly at 190
℃, and homogeneous, transparent, viscous polymer
solutions were produced. White or pale yellow, fibrous
polymer resins were obtained by the polymer solution
being poured into an excess of ethanol. The PEIs were
obtained in almost quantitative yields and the inherent
viscosities were between 0.62 and 0.80 dL/g in DMAc
solution summarized in Table 1. The weight-average
molecular weights (Mw) and number average molecular
weights (Mn) were measured based on GPC (Table 1).
The Mw and Mn values of the PIs dissolved in THF were
51500 to 71400 and 29400 to 42100, respectively. The
polydispersity index (PDI) of the 4 series was in the
range of 1.55—1.75. These data indicates that the ob-
Chin. J. Chem. 2012, XX, 1—7
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
3

Wang, Zhao & Li
FULL PAPER
Figure 2 1H NMR spectra of compounds 1 and diamine 2 in DMSO-d6.
completely here, and new peaks appear at δ 8.26 and
8.10—8.14 (Figure 4) which correspond to the protons
in the dianhydride units. All the results confirm the
complete imidization between diamine and dianhy-
drides.
Table 1 Inherent viscositiesa and GPC molecular weights of the
PEIs.
Figure 3 Minimum energy models of diamine 2.
GPC data
1
Polymer
ŋinh//(dL•g－
)
Mn×10－
2.94
Mw×10－
PDI
1.75
1.55
1.62
1.69
4
4
tained PEIs have moderate molecular weights and rela-
tively narrow PDI. Structural features of these polyim-
ides were characterized by FTIR and 1H NMR analysis.
All polyimides showed characteristic imide group ab-
4a
4b
4c
4d
0.62
0.77
0.69
0.80
5.15
3.68
5.72
3.34
5.42
sorptions around 1780 and 1725 cm－ (typical of imide
1
4.21
7.14
carbonyl asymmetrical and symmetrical stretch), 1380
(C—N stretch), and 1050 and 720 (imide ring deforma-
tion), together with some strong absorption bands in the
a Measured at a concentration of 0.5 g/dL in DMAc at 30 ℃.
region of 1100—1300 cm－ due to the C—O and C—F
1
Polymer solubility
1
stretching. A representative FTIR and H NMR spectra
The solubility of these fluorinated PEIs in different
organic solvents was measured (Table 2). They were
soluble and showed high dissolvability at a concentra-
tion of 10 wt% in most tested solvents. It is surprising
that PEI 4a and 4b, which were prepared from the very
rigid dianhydrides PMDA and BPDA, respectively,
could be quickly soluble in CHCl3, CH2Cl2 and THF at
of PEI 4b are illustrated in Figures 1 and 4, respectively.
The assignments of each proton designated in the H
NMR spectrum are in complete agreement with the
proposed polymer structures. The sharp peaks at δ 5.33
and 5.12 corresponding to the amine protons in H
NMR spectrum of diamine 2 (Figure 2b) disappear
1
1
4
www.cjc.wiley-vch.de
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, XX, 1—7

Synthesis and Properties of New Fluorinated Polyimides
Scheme 2 Synthesis of fluorinated PEIs 4a—4d
H3C
H3C
H3C
CF3
F3C
F3C
O
+ O
O
O
O
O
O
N
O
N
O
CF3
isoquinoline
8 h
O
O
Ar
Ar
H2N
O
O
NH2
190 ℃,
n
CH3
O
H3C
CH3
—
3a 3d
—
4a
2
4d
O
C
O
:
Ar
a
c
d
b
Figure 4 1H NMR spectrum of PEI 4b in CDCl3.
room temperature. It should be noted that the good
solubility of these polymers in low boiling point sol-
vents is a benefit to prepare the polymer films or coat-
ings at low processing temperatures, which is desirable
for advanced manufacturing applications. Apparently,
PEI 4a and 4b showed an improved solubility compared
with some fluorinated PEIs derived from the trifluoro-
methyl-substituted bis(ether amine)s and the same di-
anhydride monomers, especially in some low boiling
point solvents.[26-29] The enhancement of solubility of
these fluorinated PEIs was governed by the structural
modification through incorporation of the bulky groups
(trifluoromethyl and methyl groups) and noncoplanar
structures into their macromolecular backbone. This
kind of macromolecular architecture could decrease the
packing density and intermolecular interactions of mac-
romolecular chains, so that improve the solubility of
resultant polymers.
Optical and mechanical properties
As depicted in introduction, most commercially
aromatic PIs display rather deep yellow and strongly
absorption at UV-visible spectra because of their high
conjugated aromatic structures and/or the intra- and in-
termolecular CTC formation. Unlike the commercial PIs,
PEI 4a—4d films exhibited good transparency and light
color (Table 3). Figure 5 shows the UV-visible trans-
mittance spectra of PEIs films (about 40 µm thickness).
The cutoff wavelength of these films was in the range of
356—376 nm, and the transparency at 450 nm was
higher than 71%. Especially 4d, based on ODPA, dis-
played the best transparency and nearly colorless, with
83% of transmittance at 450 nm. For comparison, a
photograph of one piece of 4d film and one piece of
commercial Kapton are shown in Figure 6. The films
were photographed against a special background to
highlight the transparency. It is easy to find that 4d film
had much lighter color than Kapton film. The good op-
tical transparency and light color of these PEIs were
mainly attributed to the reducing of the conjugation and
intermolecular CTC formation along the PEI backbone.
The incorporation of the bulky pendant groups (tri-
fuoromethyl and trimethyl groups) and the noncoplanar
structure were effective to reduce the conjugation and
intermolecular CTC formation, so to improve the optical
Table 2 Solubility behavior of fluorinated PEIsa
Polymer NMP DMAc DMF DMSO CHCl3 CH2Cl2 THF Acetone
4a
4b
4c
4d
○
○
○
○
＋＋
＋
＋
＋
○
○
○
○
○
＋＋ ＋＋
＋＋ ＋＋
－
－
－
S
＋＋ ＋＋
○
○
○
○
○
○
○
○
○
a ○, 100 mg sample dissolved in 1 mL solvent (10 wt%); ＋＋,
soluble at 5 wt%; ＋, soluble at 1wt%; S, swelling; －, insolu-
ble.
Chin. J. Chem. 2012, XX, 1—7
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
5

Wang, Zhao & Li
FULL PAPER
properties. Moreover, the electron-withdrawing trifluo-
romethyl in the diamine moieties was presumably effec-
tive to decrease the CTC formation between polymer
chains in virtue of inductive effect (by decreasing the
electron-donating behavior of the diamine moieties) and
enhanced optical transparency.
4a—4d showed extra high Tg, and the values were all
above 281 ℃ (Figure 7a). PEI 4a based on rigid dian-
hydride PMDA even did not find the distinct Tg at de-
termined temperature region. Apparently, PEIs 4 series
had higher Tg values (30—50 ℃) compared with some
fluorinated PEIs derived from the trifluoromethyl-
substituted bis(ether amine)s and corresponding dian-
hydrides.[18,24,26-32] High Tg values mainly originated
from the introduction of trifluoromethyl and trimethyl
groups into the ortho-position of the ether linkages,
which hinder the rotation around C—O—C bond of the
two phenyl rings, and further increase the chain rigidity
and Tg values of these polymers. Typical TGA curves of
PEI 4b are shown in Figure 7b. 4a—4d exhibited good
Figure 5 UV-visible spectra of the PEI 4a—4d films.
Figure 6 Photographs of a piece of the Kapton film (35 µm
thickness) and a piece of the PEI 4d film (40 µm thickness ).
Table 3 Optical and mechanical properties of the PEI films
λcutoff
nm
/
Tensile
Elongation to
Initial
Polymer
T450/%
strength/MPa break/% modulus/GPa
4a
4b
4c
4d
358
374
376
356
71
80
75
83
79.5
80.1
74.6
67.2
5.5
8.4
2.3
2.3
2.1
1.8
5.4
Figure 7 DSC (a) curves of PEI 4a—4d and TGA (b) curves of
PEIs 4b at a heating rate of 20 ℃/min.
14.4
These PEI films were subjected to tensile tests, and
the results are also reported in Table 3. The mechanical
properties of 4a—4b, in general, are satisfactory. The
films had high tensile strength of 67.2—80.1 MPa, and
tensile moduli of 1.8—2.3 GPa, and they also gave
fairly medium values of elongation to break. Although
the intermolecular force was decreased by the introduc-
tion of bulky pendant groups and noncoplanar structure,
these PEIs still exhibited high tensile strength.
Table 4 Thermal properties of PEIs
T10b/℃
Dielectric
Water
absorp-
tion/%
Char
yieldc/%
Constant
(Dry, at
1 MHz)
a
Polymer Tg /℃
In N2 In air
4a
4b
4c
4d
No
312
295
281
482
486
484
483
481
485
483
485
55
58
58
55
2.84
2.77
2.93
2.86
0.43
0.41
0.57
0.52
Thermal properties
a From the second trace of DSC measurements conducted at a
heating rate of 20 ℃/min. b 10% weight loss temperature in TGA
at 20 ℃/min heating rate. c Residual weight retention at 800 ℃.
Thermal properties of these PEIs were investigated
by DSC and TGA. Table 4 summarizes the results. PEI
6
www.cjc.wiley-vch.de
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, XX, 1—7

Synthesis and Properties of New Fluorinated Polyimides
References
thermal stability with no significant weight loss up to
450 ℃. Their 10% weight loss temperatures (T10) in
nitrogen and in air atmospheres were recorded at 482—
486 and 481—485 ℃, respectively. They left more
than a 55% char yield at 800 ℃ in nitrogen. The TGA
data indicated that these fluorinated PEIs had fairly
high-thermal stability regardless of the introduction of
the trifluoromethyl and trimethyl groups.
[1] Ding, M. X. Prog. Polym. Sci. 2007, 32, 623.
[2] Bogert, M. T.; Renshaw, R. R. J. Am. Chem. Soc. 1908, 30, 1135.
[3] Chung, I. S.; Park, C. E.; Ree, M.; Kim, S. Y. Chem. Mater. 2001,
13, 2801.
[4] Kim, K. H.; Jang, S. Y.; Harris, F. W. Macromolecules 2001, 34,
8925.
[5] Liu, J. G.; Nakamura, Y.; Suzuki, Y.; Shibasaki, Y.; Ando, S.; Ueda,
M. Macromolecules 2007, 40, 7902.
[6] Han, S. H.; Misan, N.; Kim, S. J.; Doherty, C. M.; Hill, A. J.; Lee, Y.
M. Macromolecules 2010, 43, 7657.
Dielectric constant and water absorption
The dielectric constants and water absorption of
these PEI films were presented in Table 4. These
fluorinated PEI 4a—4d revealed dielectric constants in
the range of 2.77—2.93 at 1 MHz, which were much
lower than that of Kapton film (3.48 at 1 MHz). The
decreased dielectric property could mainly be attributed
to the introduction of bulky pendant groups (trifluoro-
methy and multi-methyl groups), which increased free
volume and loosened the polymer packing. In addition,
the strong electronegativity of fluorine atoms results in
permanent dipole moments of the trifluoromethyl
groups, thus decreasing the dielectric constant. PEI
4a—4d also had low water absorption of 0.41%—
0.57%. The low water absorption is attributed to the fact
that PEI 4a—4d contained the water proofing effect of
the trifluoromethyl and methyl groups. The low water
absorptions ensure that these fluorinated polyimides
have stable dielectric performance.
[7] Zhang, Q. X.; Naito, K.; Tanaka, Y.; Kagawa, Y. Macromolecules
2008, 41, 536.
[8] Chern, Y. T.; Ju, M. H. Macromolecules 2009, 42, 169.
[9] Dasgupta, B.; Sen, S. K.; Banerjee, S. J. Membr. Sci. 2009, 345,
249.
[10] Sen, S. K.; Banerjee, S. J. Membr. Sci. 2010, 365, 329.
[11] Chen, F.; Bera, D.; Banerjee, S.; Agarwal, S. Polym. Adv. Technol.
2012, 23, 951.
[12] Sen, S. K.; Banerjee, S. RSC Adv. 2012, 2, 6274.
[13] Liaw, D. J.; Chen, I. W.; Yang, M. C. Macromol. Chem. Phys. 2002,
15, 203.
[14] Babanzadeh, S.; Mahjoub, A. R.; Ataei, S. M. Polym. Degrad. Stabil.
2010, 95, 2492.
[15] Wang, C. Y.; Li, G.; Jiang, J. M. Chin. J. Chem. 2009, 27, 2255.
[16] Wang, C. Y.; Zhao, X. Y.; Li, G. Chin. J. Chem. 2012, 30, 1555.
[17] Wang, C. Y.; Li, G.; Zhao, X. Y.; Jiang, J. M. J. Polym. Sci., Part A:
Polym. Chem. Ed. 2009, 47, 3309.
[18] Shao, Y.; Li, Y. F.; Zhao, X.; Wang, X. L.; Ma, T.; Yang, F. C. J.
Polym. Sci., Part A: Polym. Chem. Ed. 2006, 44, 6836.
[19] Chern, Y. T.; Tsai, J. Y.; Wang, J. J. J. Polym. Sci., Part A: Polym.
Chem. Ed. 2009, 47, 2443.
[20] Wang, C. Y.; Li, G.; Jiang, J. M. Polymer 2009, 50, 1709.
[21] Lin, C. H.; Chang, S. L.; Cheng, P. W. J. Polym. Sci., Part A: Polym.
Chem. Ed. 2011, 49, 1331.
Conclusions
A new unsymmetrical and noncoplanar aromatic
diamine monomer has been successfully synthesized in
high yield by a facile reaction route. New series of
highly soluble fluorinated polyimides with moderate to
high molecular weights have been prepared by a one-
step high-temperature polycondensation procedure. The
resulting polyimides could be readily solution-cast into
transparent and flexible films with light color, good op-
tical transparency, moderate to high glass-transition
temperatures, and low dielectric constants. The eminent
combination of several properties guaranteed the ob-
tained polyimides as potential high-temperature resis-
tant materials for optical and photoelectric applications.
[22] Chung, I. S.; Kim, S. Y. Macromolecules 2000, 33, 3190.
[23] Hasegawa, M.; Horie, K. Prog. Polym. Sci. 2001, 26, 259.
[24] Chung, C. L.; Yang, C. P.; Hsiao, S. H. J. Polym. Sci., Part A:
Polym. Chem. Ed. 2006, 44, 3092.
[25] Liu, J. G.; He, M. H.; Zhou, H. W.; Qian, Z. G.; Wang, F. S.; Yang,
S. Y. J. Polym. Sci., Part A: Polym. Chem. Ed. 2002, 40, 110.
[26] Xie, K.; Zhang, S. Y.; Liu, J. G.; He, M. H.; Yang, S. Y. J. Polym.
Sci., Part A: Polym. Chem. Ed. 2001, 39, 2581.
[27] Yang, C. P.; Su, Y. Y. J. Polym. Sci., Part A: Polym. Chem. Ed.
2004, 42: 222.
[28] Hsiao, S. H.; Yang, C. P.; Huang, S. C. J. Polym. Sci., Part A: Polym.
Chem. Ed. 2004, 42, 2377.
[29] Yang, C. P.; Su, Y. Y.; Wu, K. L. J. Polym. Sci., Part A: Polym.
Chem. Ed. 2004, 42, 5424.
[30] Liaw, D. J.; Huang, C. C.; Chen, W. H. Polymer 2006, 47, 2337.
[31] Qiu, Z. Q.; Wang, J. H.; Zhang, Q. Y.; Zhang, S. B.; Ding, M. X.;
Gao, L. X. Polymer 2006, 47, 8444.
[32] Yang, F. C.; Zhao, J. J.; Li, Y. F.; Zhang, S. J.; Shao, Y.; Shao, H.;
Ma, T.; Gong, C. L. Eur. Polym. J. 2009, 45, 2053.
[33] Liu, Y.; Xing, Y.; Zhang, Y. H.; Guan, S. W.; Zhang, H. B.; Wang,
Y.; Wang, Y. P.; Jiang, Z. H. J. Polym. Sci., Part A: Polym. Chem.
Ed. 2010, 48, 3281.
[34] Ghosh, A.; Banerjee, S. High Perform. Polym. 2010, 22, 28.
[35] Kute, V.; Banerjee, S. Macromol. Chem. Phys. 2003, 204, 2105.
[36] Banerjee, S.; Madhra, M. K.; Salunke, A. K.; Jaiswal, D. K. Polymer
2003, 44, 613.
Acknowledgement
This work was supported by the National Natural
Science Foundation of China (No. 51103016), the
Natural Science Foundation of Jiangsu Province (No.
BK2011232 and BK2011241), the Grant-in-aid for
Youth Innovation Fundation of Changzhou University
(No. ZMF11020017 and ZMF1102037), and the Open-
ing Project of State Key Laboratory for Modification of
Chemical Fibers and Polymer Materials (No. LK1001).
[37] Dhara, M. G.; Banerjee, S. Prog. Polym. Sci. 2010, 35, 1022.
(Pan, B.; Lu, Z.)
Chin. J. Chem. 2012, XX, 1—7
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
7