Novel aromatic poly(amine-imide)s bearing a pendent triphenylamine group: Synthesis, thermal, photophysical, electrochemical, and electrochromic characteristics

Article abstract of DOI:10.1021/ma048774d

A new triphenylamine-containing aromatic diamine, N,N-bis(4-aminophenyl)-N′,N′-diphenyl-1,4-phenylenediamine, was synthesized from the animation reaction between 4-aminotriphenylamine and 4-fluoronitrobenzene and subsequent reduction of the dinitro intermediate. A series of novel aromatic poly(amine-imide)s with pendent triphenylamine units were prepared from the newly synthesized diamine and various tetracarboxylic dianhydrides by either a one-step or a conventional two-step polymerization process. All the poly(amine-imide)s were amorphous and readily soluble in many organic solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide, and chloroform. These polymers could be solution cast into transparent, tough, and flexible films with good mechanical properties. They had useful levels of thermal stability associated with relatively high glass transition temperatures (264-3520°C), 10% weight-loss temperatures in excess of 568°C, and char yields at 800°C in nitrogen higher than 63%. These polymers exhibited strong UV-vis absorption bands at 311-330 nm in NMP solution. The photoluminescence spectra showed maximum bands around 545-562 nm in the green region. The holetransporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the poly(amine-imide) films cast onto an indium-tin oxide (ITO)-coated glass substrate exhibited two reversible oxidation redox couples at 0.78 and 1.14 V versus Ag/ AgCl in acetonitrile solution. The poly(amine-imide) films revealed excellent stability of electrochromic characteristics, with a color change from the pale yellowish neutral form to the green and blue oxidized forms at applied potentials ranging from 0.78 to 1.14 V.

Full text of DOI:10.1021/ma048774d

Macromolecules 2005, 38, 307-316
307
Novel Aromatic Poly(Amine-Imide)s Bearing A Pendent Triphenylamine
Group: Synthesis, Thermal, Photophysical, Electrochemical, and
Electrochromic Characteristics
Shu-Hua Cheng,† Sheng-Huei Hsiao,‡ Tzy-Hsiang Su,† and Guey-Sheng Liou*,†
Department of Applied Chemistry, National Chi Nan University, 1 University Road,
Nantou Hsien 545, Taiwan, Republic of China, and Department of Chemical Engineering,
Tatung University, 40 Chungshan North Rd. 3rd Sec., Taipei 104, Taiwan, Republic of China
Received June 21, 2004; Revised Manuscript Received October 23, 2004
ABSTRACT: A new triphenylamine-containing aromatic diamine, N,N-bis(4-aminophenyl)-N′,N′-diphenyl-
1,4-phenylenediamine, was synthesized from the amination reaction between 4-aminotriphenylamine
and 4-fluoronitrobenzene and subsequent reduction of the dinitro intermediate. A series of novel aromatic
poly(amine-imide)s with pendent triphenylamine units were prepared from the newly synthesized diamine
and various tetracarboxylic dianhydrides by either a one-step or a conventional two-step polymerization
process. All the poly(amine-imide)s were amorphous and readily soluble in many organic solvents such
as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide, and chloroform. These polymers could be
solution cast into transparent, tough, and flexible films with good mechanical properties. They had useful
levels of thermal stability associated with relatively high glass transition temperatures (264-352 °C),
10% weight-loss temperatures in excess of 568 °C, and char yields at 800 °C in nitrogen higher than
63%. These polymers exhibited strong UV-vis absorption bands at 311-330 nm in NMP solution. The
photoluminescence spectra showed maximum bands around 545-562 nm in the green region. The hole-
transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical
methods. Cyclic voltammograms of the poly(amine-imide) films cast onto an indium-tin oxide (ITO)-
coated glass substrate exhibited two reversible oxidation redox couples at 0.78 and 1.14 V versus Ag/
AgCl in acetonitrile solution. The poly(amine-imide) films revealed excellent stability of electrochromic
characteristics, with a color change from the pale yellowish neutral form to the green and blue oxidized
forms at applied potentials ranging from 0.78 to 1.14 V.
Introduction
Aromatic polyimides are well accepted as advanced
materials for a thin-film application in microelectronic
devices and liquid crystal displays due to their out-
standing mechanical, chemical, thermal, and physical
properties.25,26 However, the technological applications
of most polyimides are limited by processing difficulties
because of high melting or glass transition temperatures
(Tg’s) and limited solubility in most organic solvents.
To overcome such a difficulty, polymer-structure modifi-
cation becomes necessary. One of the common approach-
es for increasing solubility and processability of poly-
imides without sacrificing high thermal stability is the
introduction of bulky, packing-disruptive groups into the
polymer backbone.27-34 Recently, we have reported the
synthesis of soluble aromatic polyamides and polyimides
bearing triphenylamine units in the main chain based
on N,N′-bis(4-aminophenyl)-N,N′-diphenyl-1,4-phenylene-
diamine,35,36 N,N′-bis(4-carboxyphenyl)-N,N′-diphenyl-
1,4-phenylenediamine,37 and 2,4-diaminotriphenyl-
amine,38 respectively. Because of the incorporation of
bulky, three-dimensional triphenylamine units along
the polymer backbone, all the polymers were amor-
phous, had good solubility in many aprotic solvents, and
exhibited excellent thin-film-forming capability.
Semiconducting, conducting, and light-emitting or-
ganic materials are showing increasing potential as
active components for a wide range of electronic and
optoelectronic devices. Arylamine-containing aromatics
have been used as hole-transporting molecules in the
optoelectronic fields, both in photoreceptor devices1 and
organic light emitting diodes (OLEDs).2,3 The redox
properties, ion transfer process, electrochromism, and
photoelectrochemical behavior of N,N,N′,N′-tetrasub-
stituted-1,4-phenylenediamines are of importance for
technological application.4-7 A new material with longer
life, higher efficiency, and appropriate HOMO energy
level is in increasing demand. In recent years, intensive
research efforts have been focused on the development
of new charge-transport polymers since they promise a
number of commercial advantages over low-molecular-
weight counterparts.8 One of the perceived advantages
is that polymer films can be more easily deposited over
a larger area and they are often flexible. Furthermore,
prevention of crystallization and phase-separation may
improve the device performance. Since triarylamine
derivatives have been widely used as hole-transport
compounds in organic photoconductors and electrolu-
minescent devices,9-15 many triarylamine macromol-
ecules have been developed, and some important results
have been obtained.16-24
In the present article, we report the synthesis of a
series of novel poly(amine-imide)s bearing pendent
triphenylamine groups based on a new diamine, N,N-
bis(4-aminophenyl)-N′,N′-diphenyl-1,4-phenylenedi-
amine (4). The general properties such as solubility,
crystallinity, and thermal and mechanical properties are
reported. The electrochemical, electrochromic, and pho-
toluminescence properties of these polymers prepared
* Author to whom correspondence should be addressed. E-
mail: gsliou@ncnu.edu.tw.
† National Chi Nan University.
‡ Tatung University.
10.1021/ma048774d CCC: $30.25 © 2005 American Chemical Society
Published on Web 12/22/2004

308 Cheng et al.
Macromolecules, Vol. 38, No. 2, 2005
3, 0.2 g of 10% Pd/C, 5 mL of hydrazine monohydrate, and
150 mL of ethanol was heated at reflux for 10 h. After being
cooled to room temperature, 150 mL of tetrahydrofuran (THF)
was added to dissolve the precipitate. The solution was filtered
to remove Pd/C catalyst, and the filtrate was distilled to
remove the solvent. The crude product was washed with
methanol and recrystallized from toluene in nitrogen and dried
in vacuo at 100 °C to give 7.02 g (yield: 89%) of light-beige
product; mp ) 245-247 °C measured by DSC at 2 °C/min. IR
by casting solution onto an indium-tin oxide (ITO)-
coated glass substrate are also described herein and are
compared with those of structurally related ones from
4,4′-diaminotriphenylamine.
Experimental Section
Materials. 4,4′-Diaminotriphenylamine (mp ) 186-187 °C)
was synthesized by hydrazine Pd/C-catalyzed reduction of 4,4′-
dinitrotriphenylamine resulting from the cesium fluoride-
assisted condensation of aniline with 4-fluoronitrobenzene
according to a reported procedure.39 Commercially available
aromatic tetracarboxylic dianhydrides such as pyromellitic
dianhydride (PMDA) (5a) (Chriskev), 3,3′,4,4′-benzophenone-
tetracarboxylic dianhydride (BTDA) (5c) (Chriskev), 4,4′-
oxydiphthalic dianhydride (ODPA) (5d) (TCI), and 3,3′,4,4′-
diphenylsulfonetetracarboxylic dianhydride (DSDA) (5e) (TCI)
were purified by recrystallization from acetic anhydride.
3,3′,4,4′-Biphenyltetracarboxylic dianhydride (BPDA) (5b)
(Chriskev) and 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane
dianhydride (6FDA) (5f) (Chriskev) were purified by vacuum
sublimation. Tetrabutylammonium perchlorate (TBAP) was
obtained from Acros and recrystallized twice from ethyl acetate
and then dried in vacuo prior to use. All other reagents were
used as received from commercial sources.
1
(KBr): 3368, 3457 cm-1 (N-H stretch). H NMR (DMSO-d6,
ppm): 7.21 (t, J ) 7.7 Hz, 4H, Hd), 6.92 (d, J ) 7.3 Hz, 4H,
Hc), 6.91 (t, J ) 7.5 Hz, 2H, He), 6.84 (d, J ) 8.6 Hz, 4H, Hf),
6.82 (d, J ) 8.9 Hz, 2H, Hb), 6.60 (d, J ) 8.9 Hz, 2H, Ha), 6.57
(d, J ) 8.6 Hz, 4H, Hg), 4.95 (s, 4H, -NH2). 13C NMR (DMSO-
d6, ppm): 147.9 (C5), 146.7 (C4), 145.6 (C12), 137.4 (C1), 136.4
(C9), 129.4 (C7), 127.4 (C10), 127.2 (C3), 122.2 (C6), 121.8 (C8),
118.0 (C2), 115.2 (C11). Anal. Calcd for C30H26N4 (442.55): C,
81.42%; H, 5.92%; N, 12.66%. Found: C, 81.14%; H, 6.01%;
N, 12.42%.
Monomer Synthesis. 4-Nitrotriphenylamine (1) and 4-Ami-
notriphenylamine (2). According to well-known chemistry,40,41
compound 1 (mp ) 144-145 °C; lit.42 141.5-142 °C) was
prepared by the aromatic nucleophilic amination of 4-nitro-
fluorobenzene and diphenylamine in N,N-dimethylformamide
(DMF) in the presence of sodium hydride. Subsequent reduc-
tion of 1 by means of hydrazine and Pd/C in refluxing ethanol
gave compound 2 (mp ) 148-149 °C). The molecular struc-
Polymer Synthesis. Poly(Amine-Imide) 6a by a Two-Step
Method via Thermal Imidization Reaction. The diamine mono-
mer 4 (0.6699 g, 1.514 mmol) was dissolved in 10 mL of DMAc
in a 50-mL round-bottom flask. Then, PMDA (0.3302 g, 1.514
mmol) was added to the diamine solution in one portion. Thus,
the solid content of the solution is approximately 10 wt%. The
mixture was stirred at room temperature for about 4 h to yield
a viscous polyamic acid solution. The inherent viscosity of the
resulting polyamic acid was 0.82 dL/g, measured in DMAc at
a concentration of 0.5 g/dL at 30 °C. The polyamic acid film
was obtained by casting from the reaction polymer solution
onto a glass plate and drying at 90 °C overnight under vacuum.
The polyamic acid in the form of film was converted to poly-
(amine-imide) 6a by successive heating under vacuum at 100
°C for 1 h, 200 °C for 1 h, and then 300 °C for 1 h. The inherent
viscosity of poly(amine-imide) 6a was 0.34 dL/g, measured at
a concentration of 0.5 g/dL in concentrated sulfuric acid at 30
°C. Anal. Calcd for (C40H24N4O4)n (624.64)n: C, 76.91%; H,
3.87%; N, 8.97%. Found: C, 76.24%; H, 4.05%; N, 8.93%. The
other poly(amine-imide)s 6b-6f were prepared by the one-
step method.
Poly(Amine-Imide)s 6b-6f by a One-Step Method. A typical
procedure is as follows. A stoichiometric mixture of diamine 4
(0.6638 g, 1.5 mmol) and dianhydride 5d (0.4654 g, 1.5 mmol)
and a few drops of isoquinoline in m-cresol (10 mL) were
stirred at ambient temperature under nitrogen. After the
solution was stirred for 5 h, it was heated to 200 °C and
maintained at that temperature for 15 h. After the solution
was allowed to cool to ambient temperature, the viscous
solution then was poured slowly into 300 mL of methanol with
stirring. The polymer that precipitated was collected by
filtration, washed thoroughly with hot methanol, and dried
at 150 °C for 15 h in vacuo. Precipitations from NMP into
methanol were carried out twice for further purification. The
poly(amine-imide) 6d was obtained having inherent viscosity
of 0.36 dL/g, measured at a concentration of 0.5 g/dL in NMP
at 30 °C. The IR spectrum of 6d (film) exhibited characteristic
imide absorption bands at 1775 (asymmetrical C-O), 1721
(symmetrical C-O), 1377 (C-N), and 739 cm-1 (imide ring
deformation). Anal. Calcd for (C46H28N4O5)n (716.74)n: C,
77.08%; H, 3.94%; N, 7.82%. Found: C, 76.43%; H, 4.01%; N,
7.62%. Poly(amine-imide)s 6b-6f were prepared by an analo-
gous procedure.
1
tures of 1 and 2 were confirmed by elemental, IR, H NMR,
and 13C NMR analyses.
N,N-Bis(4-nitrophenyl)-N′,N′-diphenyl-1,4-phenylenedi-
amine (3). A mixture of 1.77 g (0.070 mol) of sodium hydride
and 100 mL of DMF was stirred at room temperature. To the
mixture, 9.11 g (0.035 mol) of compound 2 and 10.12 g (0.071
mol) of 4-fluoronitrobenzene were added in sequence. The
mixture was heated with stirring at 110 °C for 15 h and then
precipitated into 700 mL of methanol. Recrystallization from
acetonitrile yielded 8.46 g of the desired dinitro compound 3
as dark red crystals in 48% yield; mp ) 219-220 °C measured
by DSC at 2 °C/min. IR (KBr): 1578, 1303 cm-1 (-NO2
1
stretch). H NMR (DMSO-d6, ppm): 8.20 (d, J ) 9.1 Hz, 4H,
Hg), 7.36 (t, J ) 8.1 Hz, 4H, Hd), 7.24 (d, J ) 9.1 Hz, 4H, Hf),
7.15 (d, J ) 8.8 Hz, 2H, Hb), 7.11 (t, J ) 7.9 Hz, 2H, He), 7.10
(d, J ) 7.9 Hz, 4H, Hc), 7.02 (d, J ) 8.8 Hz, 2H, Ha). 13C NMR
(DMSO-d6, ppm): 151.9 (C9), 147.0 (C5), 146.4 (C4), 142.1 (C12),
138.1 (C1), 130.0 (C7), 128.8 (C3), 125.8 (C10), 124.8 (C6), 124.0
(C8), 123.8 (C2), 122.3 (C11). Anal. Calcd for C30H22N4O4
(502.52): C, 71.70%; H, 4.41%; N, 11.15%. Found: C, 71.41%;
H, 4.40%; N, 11.02%. Crystal data: Dark red crystal grown
during the slow crystallization in acetonitrile, 0.35 × 0.25 ×
0.20 mm3, Triclinic P1 with a ) 11.1490(3), b ) 11.4860(3), c
) 11.6470(3) Å; R ) 70.2780(10)°, â ) 63.958(2)°, γ ) 73.576-
(2)°, where the density of crystal Dc ) 1.340 Mg/m3 for Z ) 2
and V ) 1245.38(6) Å3.
N,N-Bis(4-aminophenyl)-N′,N′-diphenyl-1,4-phenylenedi-
amine (4). In a 500-mL round-bottom flask equipped with a
stirring bar, a mixture of 8.88 g (0.018mol) of dinitro compound

Macromolecules, Vol. 38, No. 2, 2005
Novel Aromatic Poly(Amine-Imide)s 309
Scheme 1
Film Preparation. A polymer solution was made by the
dissolution of about 0.7 g of the poly(amine-imide) sample in
10 mL of NMP. The homogeneous solution was poured into a
9-cm glass Petri dish, which was placed in a 90 °C oven
overnight for the slow release of the solvent, and then the film
was stripped off from the glass substrate and further dried in
vacuo at 180 °C for 8 h. The obtained films were about 60-80
µm thick and were used for X-ray diffraction measurements,
tensile tests, solubility tests, and thermal analyses.
Results and Discussion
Monomer Synthesis. 4-Aminotriphenylamine (2)
was prepared by the condensation of diphenylamine
with 4-fluoronitrobenzene followed by hydrazine Pd/C-
catalytic reduction according to the synthetic route
outlined in Scheme 1. The new aromatic diamine having
a bulky pendent triphenylamine group, N,N-bis(4-
aminophenyl)-N′,N′-diphenyl-1,4-phenylenediamine (4),
was successfully synthesized by the amination reaction
of 2 with 4-fluoronitrobenzene followed by hydrazine Pd/
Measurements. Infrared spectra were recorded on a
PerkinElmer RXI FT-IR spectrometer. Elemental analyses
were run in an Elementar VarioEL-III. 1H and 13C NMR
spectra were measured on a Bruker Avance 500 MHz FT-NMR
system. The inherent viscosities were determined at a 0.5 g/dL
concentration using an Tamson TV-2000 viscometer at 30 °C.
Wide-angle X-ray diffraction (WAXD) measurements were
performed at room temperature (ca. 25 °C) on a Shimadzu
XRD-7000 X-ray diffractometer (40 kV, 20 mA), using graphite-
monochromatized Cu KR radiation. UV-vis spectra of the
polymer films were recorded on a Varian Cary 50 probe
spectrometer. An Instron universal tester model 4400R with
a load cell of 5 kg was used to study the stress-strain behavior
of the samples. A gauge length of 2 cm and a crosshead speed
of 5 mm/min were used for this study. Measurements were
performed at room temperature with film specimens (0.5 cm
width, 6 cm length), and an average of at least three replicates
was used. Thermogravimentric analysis (TGA) was conducted
with a PerkinElmer Pyris 1 TGA. Experiments were carried
out on approximately 6-8-mg film samples heated in flowing
nitrogen or air (flow rate ) 20 cm3/min) at a heating rate of
20 °C/min. DSC analyses were performed on a PerkinElmer
Pyris Diamond DSC at a scan rate of 20 °C/min in flowing
nitrogen (20 cm3/min). Thermomechanical analysis (TMA) was
conducted with a PerkinElmer TMA 7 instrument. The TMA
experiments were conducted from 50 to 350 °C at a scan rate
of 10 °C/min with a penetration probe 1.0 mm in diameter
under an applied constant load of 10 mN. Softening temper-
atures (Ts) were taken as the onset temperatures of probe
displacement on the TMA traces. Electrochemistry was per-
formed with a Bioanalytical System Model CV-27 potentiostat
and a BAS X-Y recorder. Voltammograms are presented with
the positive potential pointing to the left and with increasing
anodic currents pointing downward. Cyclic voltammetry was
conducted with the use of a three-electrode cell in which ITO
(polymer films area about 0.7 × 0.5 cm2) was used as a working
electrode. A platinum wire was used as an auxiliary electrode.
All cell potentials were taken with the use of a homemade Ag/
AgCl, KCl (sat.) reference electrode. The spectroelectrochemi-
cal cell was composed of a 1-cm cuvette, ITO as a working
electrode, a platinum wire as an auxiliary electrode, and a Ag/
AgCl reference electrode. Absorption spectra were measured
with a HP 8453 UV-vis spectrophotometer. Photolumines-
cence spectra were measured with a Jasco FP-6300 spectro-
fluorometer.
1
C-catalytic reduction. Elemental analysis, IR, and H
and 13C NMR spectroscopic techniques were used to
identify the structures of the intermediate compounds
1, 2, and 3 and the diamine monomer 4. The transfor-
mation of nitro to amino functionality could be moni-
tored by the change of IR spectra. The nitro groups of
compounds 1 and 3 gave two characteristic bands at
around 1580 and 1313 cm-1 (-NO2 asymmetric and
symmetric stretching). After reduction, the character-
istic absorptions of the nitro group disappeared and the
amino group showed the typical N-H stretching ab-
sorption pair in the region of 3300-3500 cm-1. Figure
1
1 illustrates the H NMR and 13C NMR spectra of the
diamine monomer 4. Assignments of each carbon and
proton are assisted by the two-dimensional NMR spec-
tra shown in Figures 2 and 3, and these spectra agree
well with the proposed molecular structure of 4. The
1H NMR spectra confirm that the nitro groups have
been completely transformed into amino groups by the
high-field shift of the aromatic protons and by the
resonance signals at around 5.0 ppm corresponding to
1
Figure 1. (a) H NMR and (b) 13C NMR spectra of diamine
monomer 4 in DMSO-d6.

310 Cheng et al.
Macromolecules, Vol. 38, No. 2, 2005
Figure 2. H-H COSY spectrum of diamine monomer 4 in DMSO-d6.
the amino protons. The molecular structure of dinitro
compound 3 was also confirmed by X-ray crystal analy-
sis acquired from the single crystal obtained by slow
crystallization of an acetonitrile solution of 3. As shown
in Figure 4, the dinitro compound 3 displays a propeller-
shaped configuration of the triphenylamine cores and
the benzene rings are not in the same plane. This
conformation will hinder the close packing of polymer
chains and enhance the solubility of formed poly(amine-
imide)s.
Polymer Synthesis. The one-step procedure starting
from aromatic diamines and tetracarboxylic dianhy-
drides in the presence of isoquinoline as a catalyst, as
well as conventional two-step process, involving a ring-
opening addition and subsequent thermal cyclodehy-
dration, are convenient methods for the preparation of
polyimides.25 New poly(amine-imide)s 6b-6f were syn-
thesized by the one-step method starting from diamine
monomer 4 with aromatic tetracarboxylic dianhydrides
5b-5f in the presence of a catalytic amount of isoquino-
line in refluxing m-cresol (Scheme 2). Due to less
solubility, poly(amine-imide) 6a was prepared by the
conventional two-step method via thermal imidization
reaction. The formation of poly(amine-imide)s was
confirmed with elemental analysis, IR spectroscopy, and
NMR spectroscopy. The results of elemental analysis
shown in Table 1 supported the formation of the
expected polymers. The IR spectra of these polymers
exhibited characteristic imide absorption bands at
around 1775 (asymmetrical C-O), 1720 (symmetrical
C-O), 1380 (C_N), and 740 cm-1 (imide ring deforma-
tion). The microstructures of these poly(amine-imide)s
were also verified by the high-resolution NMR spectra.
For a comparative study, a series of referenced poly-
(amine-imide)s 6a′-6f ′ were also synthesized from 4,4′-
diaminotriphenylamine and dianhydrides 5a-5f.
Basic Characterization. The X-ray diffraction stud-
ies of the poly(amine-imide)s indicated that all the
polymers were essentially amorphous. The qualitative
solubility properties of polymers 6a-6f are reported in
Table 2. On comparing with the corresponding poly-
(amine-imide)s 6′, the present series of poly(amine-
imide)s exhibited an enhanced solubility because of the
increased flexibility or free volume caused by the
introduction of a bulky pendent triphenylamine group
in the repeat unit. The excellent solubility makes these
poly(amine-imide)s potential candidates for practical
applications in spin- or dip-coating processes.
All the aromatic poly(amine-imide)s could afford
flexible and tough films. These films were subjected to
tensile testing, and the results are given in Table 3. The
tensile strengths, elongations to break, and initial
moduli of these films were in the ranges of 87-119 MPa,
8-12%, and 2.0-2.6 GPa, respectively.
The thermal properties of the poly(amine-imide)s
were investigated by TGA, DSC, and TMA. The results

Macromolecules, Vol. 38, No. 2, 2005
Novel Aromatic Poly(Amine-Imide)s 311
Figure 3. C-H COSY spectrum of diamine monomer 4 in DMSO-d6.
°C, respectively. The amount of carbonized residue (char
yield) of these polymers in nitrogen atmosphere was
more than 63% at 800 °C. The high char yields of these
polymers can be ascribed to their high aromatic content.
This outstanding thermal stability also renders advan-
tages in various applications. The glass-transition tem-
peratures (Tg) of all the polymers were observed in the
range of 264-352 °C by DSC and decreased with
decreasing rigidity of the tetracarboxylic dianhydride
used. When compared with the analogous poly(amine-
imide)s 6′, the 6 series of poly(amine-imide)s showed a
slightly decreased Tg that may be attributed to the
increased conformational flexibility or free volume
caused by the introduction of the bulky pendent tri-
phenylamine group in the repeat unit. These results are
consistent with those reported previously.35-37 All the
polymers indicated no clear melting endotherms up to
the decomposition temperatures on the DSC thermo-
grams. This result also supports the amorphous nature
of these triphenylamine-containing polymers. The soft-
ening temperatures (Ts) of the polymer film samples
were determined by the TMA method with a loaded
penetration probe. They were obtained from the onset
temperature of the probe displacement on the TMA
trace. A typical TMA thermogram for poly(amine-imide)
6d is illustrated in Figure 6. There is a large window
Figure 4. Molecular structure of dinitro compound 3 by
single-crystal X-ray analysis.
are summarized in Table 4. Typical TGA curves for poly-
(amine-imide) 6e are reproduced in Figure 5. All of the
poly(amine-imide)s exhibited a similar TGA pattern
with no significant weight loss below 500 °C both in air
and in nitrogen atmosphere. The 10% weight-loss tem-
peratures of the poly(amine-imide)s in nitrogen and air
were recorded in the range of 568-629 and 574-622

312 Cheng et al.
Macromolecules, Vol. 38, No. 2, 2005
Scheme 2. Synthesis of Poly(amine-imide)s by the One-step Method
Table 1. Inherent Viscosity and Elemental Analysis of Poly(Amine-Imide)s
poly(amine-imide)s elemental analysis (%) of poly(amine-imide)s
a
ηinh
formula
(formula weight)
code
(dL/g)
C
H
N
S
6a
0.34
(C40H24N4O4)n
(624.64)n
(C46H28N4O4)n
(700.74)n
(C47H28N4O5)n
(728.75)n
(C46H28N4O5)n
(716.74)n
(C46H28N4O6S)n
(764.80)n
(C49H28F6N4O4)n
(850.76)n
calcd
found
calcd
found
calcd
found
calcd
found
calcd
found
calcd
found
76.91
76.24
78.84
77.67
77.46
76.86
77.08
76.43
72.24
71.51
69.18
68.73
3.87
4.05
4.03
4.12
3.87
4.04
3.94
4.01
3.69
3.88
3.32
3.43
8.97
8.93
8.00
7.81
7.69
7.41
7.82
7.62
7.33
7.10
6.59
6.32
6b
6c
6d
6e
6f
0.39
0.35
0.36
0.32
0.29
4.19
4.07
a Measured at a polymer concentration of 0.5 g/dL in NMP at 30 °C (6a and 6b: measured in concentrated sulfuric acid).
between Tg or Ts and the decomposition temperature
of each polymer, which could be advantageous in the
processing of these polymers by the thermoforming
technique.
Optical and Electrochemical Properties. The
optical and electrochemical properties of the poly(amine-
imide)s were investigated by cyclic voltammetry, UV-
vis spectroscopy, and photoluminescence spectroscopy.
The results are summarized in Table 5. These polymers
(6b-6f) exhibited strong UV-vis absorption bands at
311-330 nm in NMP solution, assignable to the π-π*
transition resulting from the conjugation between the
aromatic rings and nitrogen atoms. Their photolumi-
nescence spectra in NMP solution showed maximum
bands around 545-562 nm in the green region. Figure
7 shows UV-vis absorption and photoluminescence
spectra of poly(amine-imide)s 6d, 6e, 6′d, and 6′e for
comparison. These polymers exhibited similar spectro-
grams while the PL intensity of the poly(amine-imide)s
6′ series is greater than that of the poly(amine-imide)s
6 series. This phenomenon possibly could be attributed
to the fact that the excited-state energy of the 6 series
is more likely released in a vibrational way because of
the greater conformational mobility. The cutoff wave-

Macromolecules, Vol. 38, No. 2, 2005
Novel Aromatic Poly(Amine-Imide)s 313
Table 2. Solubility of Aromatic Poly(Amine-Imide)s
solventsa
DMSO
polymer
NMP
DMAc
DMF
m-cresol
THF
chloroform
6a
6b
6c
6d
6e
6f
+h (-)b
+h (+h)
+ (+h)
+ (+h)
+ (+h)
+ (-)
( (-)
( (-)
+ (+h)
+ (+h)
+ (-)
+ (-)
( (-)
( (-)
+ (+h)
( (-)
+ (-)
+ (-)
( (-)
+h (-)
+h (-)
+ (+h)
+h (+h)
+h (+h)
+h (+h)
- (-)
( (+h)
+ (-)
( (-)
+ (-)
+ (-)
( (-)
+ (-)
+ (-)
+ (-)
+ (-)
+ (-)
( (-)
+h (+h)
+h (+h)
+h (+h)
+h (+h)
a Solubility: +, soluble at room temperature; +h, soluble on heating; (, partially soluble or swelling; -, insoluble even on heating.
b Data in parentheses are the solubility of analogous poly(amine-imide)s (6′) having the corresponding dianhydride residue as in the 6
series.
Table 3. Mechanical Properties of Poly(Amine-Imide)
Films
for poly(amine-imide)s 6e and 6′e are shown in Figure
8. There are two reversible oxidation redox couples at
E1/2 ) 0.78 and 1.14 V, respectively, for poly(amine-
imide) 6e and one reversible oxidation redox couple at
E1/2 ) 1.08 V for poly(amine-imide) 6′e in the oxidative
scan. Because of the stability of the films and the good
adhesion between the polymer and ITO substrate, the
poly(amine-imide) 6e exhibited excellent reversibility of
electrochromic characteristics by five continuous cyclic
scans between 0.0 and 1.35 V, changing color from pale
yellowish to green then blue at electrode potentials
ranging from 0.78 to 1.14 V. Comparing the electro-
chemical data, it was found that poly(amine-imide) 6e
is much more easily oxidized than poly(amine-imide) 6′e
(0.78 vs 1.08 V). The first electron removal for poly-
(amine-imide) 6e is assumed to occur at the nitrogen
atom on the pendent triphenyl unit, which is more
electron-rich than the nitrogen atom on the main-chain
triphenylamine group. The energy of the HOMO and
LUMO levels of the investigated poly(amine-imide)s can
be determined from the oxidation half-wave potentials
tensile strength elongation at break initial modulus
polymer
(MPa)
(%)
(GPa)
6a
6b
6c
6d
6e
6f
87
119
102
101
111
95
10
12
8
11
9
9
2.1
2.3
2.6
2.0
2.3
2.2
lengths (absorption edge; λ0) from the UV-vis absorp-
tion spectra are also included in Table 5. It revealed
that most of the visible region can be absorbed by poly-
(amine-imide)s 6a and 6e which show higher λ0 values.
This is consistent with the fact that the films of
polymers 6a and 6c appeared deep red-brown color. The
redox behavior was investigated with cyclic voltamme-
try conducted for the cast film on an ITO-coated glass
substrate as working electrode in dry acetonitrile (CH3-
CN) containing 0.1 M TBAP as an electrolyte under
nitrogen atmosphere. The typical cyclic voltammograms
Table 4. Thermal Properties of Aromatic Poly(Amine-Imide)s
Td at 5%
weight loss (°C)c
Td at 10%
weight loss (°C)c
char yield
(wt%)d
polymer
Tg (°C)a
Ts (°C)b
N2
air
N2
air
6a
6b
6c
6d
6e
6f
352 (-)
327 (314)
267 (314)
251 (290)
258 (292)
281 (291)
261 (310)
607
602
582
586
528
559
584
591
537
567
537
546
624 (606)
629 (613)
618 (590)
610 (608)
568 (546)
585 (581)
610 (596)
622 (619)
589 (590)
600 (611)
582 (577)
574 (571)
68 (70)
70 (68)
63 (67)
74 (66)
67 (60)
68 (63)
302 (331)e
294 (309)
264 (295)
305 (326)
286 (316)
a Midpoint temperature of baseline shift on the second DSC heating trace (rate 20 °C/min) of the sample after quenching from 400 °C.
b Softening temperature measured by TMA with a constant applied load of 10 mN at a heating rate of 10 °C/min. c Decomposition
temperature, recorded via TGA at a heating rate of 20 °C/min and a gas-flow rate of 30 cm3/min. d Residual weight percentage at 800 °C
in nitrogen. e Values in parentheses are data of analogous poly(amine-imide)s (6′) having the corresponding dianhydride residue as in the
6 series.

314 Cheng et al.
Macromolecules, Vol. 38, No. 2, 2005
Table 5. Optical and Electrochemical Properties of the Aromatic Poly(Amine-Imide)s
oxidation (V)
(vs Ag/AgCl)
λabs, max
λabs, onset
λPL
λ0
HOMO-LUMO
HOMOe
(eV)
LUMOf
(eV)
code
(nm)a
(nm)a
(nm)b
(nm)c
first
second
gapd (eV)
6ag
6b
6c
6d
6e
6f
-
330
316
324
311
326
314
304
-
387
388
385
390
385
378
385
-
562
555
545
556
546
534
547
661
577
588
499
608
508
456
549
-
-
-
-
-
0.78
1.14
3.20
3.20
3.22
3.18
3.22
3.28
3.22
5.08
5.08
5.08
5.09
5.10
5.36
5.38
1.88
1.88
1.86
1.91
1.88
2.08
2.16
0.78
0.78
0.79
0.80
1.06
1.08
1.13
1.13
1.14
1.14
-
-
6′d
6′e
a UV-vis absorption measurements in NMP (0.02 mg/mL) at room temperature. b PL spectra measurements in NMP (5 mg/mL) at
room temperature. c The cutoff wavelengths (λ0) from the transmission UV-vis absorption spectra of polymer films. d The data were
calculated by the equation: gap ) 1240/λonset
to ferrocene (4.8 eV). f LUMO ) HOMO - gap. g Poly(amine-imide) 6a is difficult to dissolve into the NMP solvent.
.
e The HOMO energy levels were calculated from cyclic voltammetry and were referenced
Figure 5. TGA thermograms of poly(amine-imide) 6e at a
scan rate of 20 °C/min.
Figure 7. Absorptions and PL spectra of poly(amine-imide)
6d, 6e (black and red solid line) and 6′d, 6′e (black and red
dash-dot line) in NMP solution.
Figure 6. TMA curve of poly(amine-imide) 6d with a heating
rate of 10 °C/min.
and the onset absorption wavelength, and the results
are listed in Table 5. For example, the oxidation half-
wave potential for poly(amine-imide)s 6e has been
determined as 0.78 V vs Ag/AgCl. The external fer-
rocene/ferrocenium (Fc/Fc+) redox standard E1/2 is 0.50
V vs Ag/AgCl in CH3CN. Assuming that the HOMO
energy for the Fc/Fc+ standard is 4.80 eV with respect
to the zero vacuum level, the HOMO energy for poly-
(amine-imide)s 6e has been evaluated to be 5.08 eV.
Electrochromic Characteristics. Electrochromism
of the poly(amine-imide) thin films was monitored by a
UV-vis spectrometer at different applied potentials.
The electrode preparations and solution conditions were
identical to those used in cyclic voltammetry. The typical
electrochromic absorption spectra of poly(amine-imide)s
Figure 8. Cyclic voltammograms of (a) ferrocene (b) poly-
(amine-imide) 6e (c) poly(amine-imide) 6′e film onto an in-
dium-tin oxide (ITO)-coated glass substrate in CH3CN con-
taining 0.1 M TBAP. Scan rate ) 0.1 V/s.
6e and 6′e are shown as Figures 9-11. When the
applied potential was increased positively from 0.65 to
0.98 V, the peak of characteristic absorbance at 320 nm
for poly(amine-imide) 6e decreased gradually while two
new bands grew up at 420 and 879 nm due to the first

Macromolecules, Vol. 38, No. 2, 2005
Novel Aromatic Poly(Amine-Imide)s 315
Figure 11. Electrochromic behavior of poly(amine-imide) 6′e
thin film (in CH3CN with 0.1 M TBAP as the supporting
electrolyte) at (a) 0, (b) 0.93, (c) 0.96, (d) 1.04, (e) 1.08, (f) 1.15,
(g) 1.19, (h) 1.23, and (i) 1.30 V.
Figure 9. Electrochromic behavior of poly(amine-imide) 6e
thin film (in CH3CN with 0.1 M TBAP as the supporting
electrolyte) at (a) 0.0, (b) 0.65, (c) 0.70, (d) 0.75, (e) 0.79, (f)
0.83, (g) 0.88, (h) 0.92, and (i) 0.98 V.
Figure 12. Potential step absorptometry of poly(amine-imide)
6e (in CH3CN with 0.1 M TBAP as the supporting electrolyte)
by applying a potential step (0 V D 0.98 V).
Figure 10. Electrochromic behavior of poly(amine-imide) 6e
thin film (in CH3CN with 0.1 M TBAP as the supporting
electrolyte) at (a) 1.01, (b) 1.05, (c) 1.10, (d) 1.14, (e) 1.20, (f)
1.28, and (g) 1.35 V.
electron oxidation. The new spectrum was assigned as
that of the cationic radical poly(amine-imide)+•. Mean-
while, the film color turned to the green (as shown in
Figure 9). When the potential was adjusted to a more
positive value, corresponding to the second electron
oxidation, the spectral change is shown as Figure 10.
The characteristic peaks for poly(amine-imide) +• disap-
peared and a new band grew at 656 nm. The new
spectrum was assigned as poly(amine-imide)2+. The film
color became deep blue. The electrochromic character-
istics of poly(amine-imide) 6′e was also shown in Figure
11. When the applied potential increased positively from
0.93 to 1.30 V, the peak of characteristic absorbance at
311 nm for poly(amine-imide) 6′e decreased gradually,
while new bands grew at 390, 486, and 777 nm. The
new spectrum was assigned as that of the cationic
radical poly(amine-imide)+• which appeared the comple-
mentary color of blue after oxidation.
Figure 13. Potential step absorptometry of poly(amine-imide)
6e (in CH3CN with 0.1 M TBAP as the supporting electrolyte)
by applying a potential step (0 V ∆ 1.35 V).
The color-switching times were estimated by applying
a potential step, and the absorbance profiles were
followed (Figures 12 and 13). The switching time was
defined as the time that was required to reach 90% of
the full change in absorbance after switching potential.
Thin films from poly(amine-imide) 6e would require 20
s at 0.98 V for switching absorbance at 420 and 879 nm
and 3 s for bleaching. When the potential was set at
1.35 V, thin films from poly(amine-imide) 6e would

316 Cheng et al.
Macromolecules, Vol. 38, No. 2, 2005
(11) Shirota, Y.; Okumoto, K.; Inada, H. Synth. Met. 2000, 111-
112, 387.
(12) Giro, G.; Cocchi, M.; Lalinowski, J.; Fattori, V.; Di Macro,
P.; Dembech, P.; Seconi, G. Adv. Mater. Opt. Electron. 2000,
9, 189.
require almost 7 s for coloration at 656 nm and 2 s for
bleaching. During five continuous cyclic scans between
0.0 and 1.35 V, the polymer films still exhibited excel-
lent stability of electrochromic characteristics.
(13) Thomas, K. R. J.; Lin, J. T.; Tao, Y. T.; Ko, C. W. Chem. Mater.
Conclusions
2002, 14, 1354.
(14) Thomas, K. R. J.; Lin, J. T.; Tao, Y. T.; Chuen, C. H. Chem.
Mater. 2002, 14, 2796.
(15) Okumoto, K.; Shirota, Y. Chem. Mater. 2003, 15, 699.
(16) Lu, J.; Hlil, A. R.; Sun, Y.; Hay, A. S. Chem. Mater. 1999,
11, 2501.
The new triphenylamine-containing aromatic di-
amine, N,N-bis(4-aminophenyl)-N′,N′-diphenyl-1,4-phe-
nylenediamine (4) was successfully synthesized in high
purity and good yields. The novel aromatic poly(amine-
imide)-bearing pendent triphenylamine groups were
prepared by the one-step or the two-step method start-
ing from diamines with various aromatic tetracarboxylic
dianhydrides. The introduction of the bulky, intrinsicly
electron-donating triphenylamine group could decrease
the HOMO energy levels and disrupt the copolanarity
of aromatic units in chain packing which increases the
between-chain spacing or free volume, thus enhancing
solubility of the formed poly(amine-imide)s. All the poly-
(amine-imide)s were amorphous in nature, as evidenced
by the WAXD and DSC analysis. These polymers could
afford tough and flexible films with good mechanical
properties and high thermal stability. All obtained poly-
(amine-imide)s revealed excellent stability of electro-
chromic characteristics, changing color from the pale
yellowish neutral form to the green and blue oxidized
forms when scanning potentials positively from 0.78 to
1.14 V. Thus, our novel poly(amine-imide)s have a great
potential as a new type of hole-transporting and elec-
trochromic materials due to their proper HOMO values
and excellent electrochemical and thermal stability.
(17) Ogino, K.; Kanegawa, A.; Yamaguchi, R.; Sato, H.; Kurjata,
J. Macromol. Rapid Commun. 1999, 20, 103.
(18) Li, H.; Geng, Y.; Tong, S.; Tong, H.; Hua, R.; Su, G.; Wang,
L.; Jing, X.; Wang, F. J. Polym. Sci., Part A: Polym. Chem.
2001, 39, 3278.
(19) Wang, X.; Nakao, M.; Ogino, K.; Sato, H.; Tan, H. Macromol.
Chem. Phys. 2001, 202, 117.
(20) Behl, M.; Hattemer, E.; Brehmer, M.; Zentel, R. Macromol.
Chem. Phys. 2002, 203, 503.
(21) Kim, Y.; Han, K.; Ha, C. S. Macromolecules 2002, 35, 8759.
(22) Nomura, M.; Shibasaki, Y.; Ueda, M.; Tugita, K.; Ichikawa,
M.; Taniguchi, Y. Macromolecules 2004, 37, 1204.
(23) Ego, C.; Grimsdale, A. C.; Uckert, F.; Yu, G.; Srdanov, G.;
Mullen, K. Adv. Mater. 2004, 14, 809.
(24) Chou, M. Y.; Leung, M. K.; Su, Y. L.; Chiang, C. L.; Lin, C.
C.; Kuo, C. K.; Mou, C. Y. Chem. Mater. 2004, 16, 654.
(25) Polyimides; Wilson, D., Stenzenberger, H. D., Hergenrother,
P. M., Eds.; Blackie: Glasgow and London, 1990.
(26) Polyimides: Fundamentals and Applications; Ghosh, M. K.,
Mittal, K. L., Eds.; Marcel Dekker: New York, 1996.
(27) Harris, F. W.; Hsu, S. L.-C. High Perform. Polym. 1989, 1, 1.
(28) Imai, Y. React. Funct. Polym. 1996, 30, 3.
(29) Hsiao, S. H.; Li, C. T. Macromolecules 1998, 31, 7213.
(30) Liou, G. S. J. Polym. Sci., Part A: Polym. Chem. 1998, 36,
1937.
(31) Eastmond, G. C.; Paprotny, J.; Irwin, R. S. Polymer 1999,
Acknowledgment. The authors are grateful to the
National Science Council of the Republic of China for
financial support of this work (Grant No. NSC 92-2216-
E-260-001).
40, 469.
(32) Eastmond, G. C.; Gibas, M.; Paprotny, J. Eur. Polym. J. 1999,
35, 2097.
(33) Reddy, D. S.; Chou, C. H.; Shu, C. F.; Lee, G. H. Polymer
2003, 44, 557.
(34) Myung, B. Y.; Ahn, C. J.; Yoon, T. H. Polymer 2004, 45, 3185.
(35) Liou, G. S.; Hsiao, S. H.; Ishida, M.; Kakimoto, M.; Imai, Y.
J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 2810.
(36) Liou, G. S.; Hsiao, S. H.; Ishida, M.; Kakimoto, M.; Imai, Y.
J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 3815.
(37) Liou, G. S.; Hsiao, S. H. J. Polym. Sci., Part A: Polym. Chem.
2003, 41, 94.
References and Notes
(1) Law, K. Y. Chem. Rev. 1993, 93.
(2) Mitschke, R. H.; Bauerle, P. J. Mater. Chem. 2000, 10, 1471
(3) Forrest, S. R. Chem. Rev. 1997, 97, 1793.
(4) Marken, F.; Hayman, C. M.; Bulman Page, P. C. Electrochem.
Commun. 2002, 4, 462.
(38) Hsiao, S. H.; Chen, C. W.; Liou, G. S. J. Polym. Sci., Part A:
(5) Marken, F.; Webster, S. D.; Bull, S. D.; Davies, S. G. J.
Electroanal. Chem. 1997, 437, 209.
Polym. Chem. 2004, 42, 3302.
(39) Oishi, Y.; Ishida, M.; Kakimoto, M.; Imai, Y.; Kurosaki, T. J.
Polym. Sci., Part A: Polym. Chem. 1992, 30, 1027.
(40) Gujadhur, R.; Venkataraman, D.; Kintigh, J. T. Tetrahedron
Lett. 2001, 42, 4791.
(6) Wadhawan, J. D.; Evans, R. G.; Banks, C. E.; Wilkins, S. J.;
France, R. R.; Oldham, N. J.; Fairbanks, A. J.; Wood, B.;
Walton, D. J.; Schroder, U.; Compton, R. G. J. Phys. Chem.
B 2002, 106, 9619.
(7) Davies, W. B.; Svec, W. A.; Ratner, M. A.; Wasielewski, M.
R. Nature 1998, 396, 60.
(41) Urgaonkar, S.; Xu, J. H.; Verkade, J. G. J. Org. Chem. 2003,
68, 8416.
(8) Akcelrud, L. Prog. Polym. Sci. 2003, 28, 875.
(9) Katsuma, K.; Shirota, Y. Adv. Mater. 1998, 10, 223.
(10) Shirota, Y.; Kinoshita, M.; Noda, T.; Okumoto, K.; Ohara, T.
J. Am. Chem. Soc. 2000, 122, 11021.
(42) Bergstrom, F. W.; Granara, I. M.; Erickson, V. J. Org. Chem.
1942, 7, 98.
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