Facile synthesis of soluble aromatic poly(amide amine)s via C-N coupling reaction: Characterization, thermal, and optical properties

Article abstract of DOI:10.1002/pola.26910

Aromatic poly(amide amine)s (APAAs), as novel high-performance polymers, have been obtained by the condensation polymerization of N,N′-bis(4- bromobenzoyl)-p-phenylenediamine with two different primary aromatic diamines via palladium-catalyzed aryl amination reaction. The structures of the polymers are characterized by means of FTIR, 1H NMR spectroscopy, and elemental analysis, the results show a good agreement with the proposed structures. DSC and TGA measurements exhibit that polymers possess high glass transition temperature (T_g > 240°C) and good thermal stability with high decomposition temperatures (T₅ > 400°C). These novel polymers also display good solubility. In addition, due to its special structure, APAA-2 is endowed with significantly strong photonic luminescence in N,N-dimethylforma-mide and good electroactivity.

Full text of DOI:10.1002/pola.26910

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ARTICLE
Facile Synthesis of Soluble Aromatic Poly(amide amine)s via C–N
Coupling Reaction: Characterization, Thermal, and Optical Properties
Guanjun Chang,1 Li Yang,1 Junxiao Yang,1 Yawen Huang,1 Ke Cao,1
Lin Zhang,2 Runxiong Lin3
1State Key Laboratory Cultivation Base for Nonmetal Composite and Functional Materials and School of Material Science and
Engineering, Southwest University of Science and Technology, Mianyang 621010, People’s Republic of China
2Joint Laboratory for Extreme Conditions Matter Properties, Southwest University of Science and Technology and
Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, People’s Republic of China
3Engineering Research Center of High Performance Polymer and Molding Technology, Ministry of Education,
Qingdao University of Science and Technology, Qingdao 266042, People’s Republic of China
Correspondence to: G. Chang (E-mail: gjchang@mail.ustc.edu.cn)
Received 23 May 2013; accepted 14 August 2013; published online 10 September 2013
DOI: 10.1002/pola.26910
ABSTRACT: Aromatic poly(amide amine)s (APAAs), as novel high-
performance polymers, have been obtained by the condensation
polymerization of N,N’-bis(4-bromobenzoyl)-p-phenylenediamine
with two different primary aromatic diamines via palladium-
catalyzed aryl amination reaction. The structures of the polymers
are characterized by means of FTIR, 1H NMR spectroscopy, and
elemental analysis, the results show a good agreement with the
proposed structures. DSC and TGA measurements exhibit that
polymers possess high glass transition temperature (Tg > 240 ꢀC)
and good thermal stability with high decomposition temperatures
(T5 > 400 ꢀC). These novel polymers also display good solubility.
In addition, due to its special structure, APAA-2 is endowed with
significantly strong photonic luminescence in N,N-dimethylforma-
C
V
mide and good electroactivity.
2013 Wiley Periodicals, Inc. J.
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KEYWORDS: aromatic poly(amide amine)s; high-performance
polymer; palladium-catalysis; soluble; photoluminescence
processability and solubility in order to broaden the scope of
the technological applications of these materials.10–13 In
addition, there is currently a huge research effort directed
toward exploiting the special high performance characteris-
tics of the aramids to obtain electro- or photoluminescent
materials, reverse osmosis, gas or ion-exchange membranes,
optically active (OA) materials, nanocomposites, and so on
with superior thermomechanical performances.14–17
INTRODUCTION Aramids form a relevant family of polymers
that in the past decades have attracted great interest of
many research groups, at both the academic and industrial
levels, not only as high-performance materials but also for
their peculiar conformational and physicochemical behav-
iors.1–4 They are finding increasing demand for use as advan-
tageous replacements for metals or ceramics in currently
used goods, or even as new materials in novel technological
applications.5–8 In particular, as a type of high-performance
polymer, poly(p-phenylene terephthalamide) (PPPT) is the
earliest, simplest, and best known commercial aramid
(Scheme 1). Its transformed materials have applications in
advanced coatings, fabrics, and fillers, as advanced compo-
sites in the aerospace and armament industry, as asbestos
substitutes, electrical insulation, bullet-proof body armor,
industrial filters, and protective and sport clothing, among
others.9 However, the extremely high glass transition temper-
atures of the commercial aramids, which lie above their
decomposition temperatures, and their poor solubility in
common organic solvents give rise to processing difficulties
and limit their applications.8,9 As a consequence, recent
basic and applied research has focused on enhancing their
The catalytic amination reaction of arylene halides with pri-
mary amines using palladium complexes has become an
important synthetic procedure for a variety of arylene amines
including pharmaceuticals, electronic materials, and ligands
for metal catalysts.18–20 This reaction has become a widely
used practical synthetic method for C[sbond]N bond forma-
tion. In addition, the Pd-catalyzed aryl amination has also
been applied to polycondensation reactions to give various
polyamines, poly(imino arylene)s and poly(imino ketone)s
with no or scarcely crosslinked structures.21–25 In this article,
the idea is to use Pd-catalyzed aryl amination to synthesize
new types of polymers, and two aromatic poly(amide amine)s
(APAAs) have been obtained by the polycondensation of
C
V
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ferrocene (with a highest occupied energy molecular orbital
(HOMO) energy level, EHOMO 5 ca. 4.8 eV) as an external
standard.
Synthesis of N,N’-Bis(4-bromobenzoyl)-p-
phenylenediamine
A three-necked flask equipped with a magnetic stirrer, a con-
denser and an addition funnel was charged with p-phenyl-
enediamine (4.65 g, 0.05 mol), triethylamine (11.11 g, 0.11
mol), and washed with 250 mL of tetrahydrofuran. The
4-bromobenzoyl chloride (24.15 g, 0.11 mol) was added
SCHEME 1 The structures of APAA and traditional PPPT.
N,N0-bis(4-bromobenzoyl)-p-phenylenediamine with primary
aromatic diamines using the catalytic system generated from
tris(dibenzylideneacetone)dipalladium (0) Pd2(dba)3 and 2,20-
bis(diphenylphosphino)-1,10-binaphthyl (BINAP). The synthe-
sized APAAs can be considered as a hybrid structure of ara-
mids and polyanilines. It is expected that the polycondensation
of aramids and polyanilines would result in new soluble poly-
mers (Scheme 1). Functional amine groups on a APAAs back-
bone also serve as sites for further chemical modification,
graft copolymerization, or crosslinking. Furthermore, the Pd-
catalyzed aryl amination method provides a facile synthetic
route to construct novel structural polymers containing N-aryl
moieties. Interchain hydrogen bonding, thermal behaviors, sol-
ubility, and photoluminescence properties as well as electroac-
tivity of the APAAs are also investigated in detail.
ꢀ
dropwise to the solution (25 C) under nitrogen. The precip-
itate which formed was isolated by filtration and rinsed with
both water and methanol to remove salts and excess
4-bromobenzoic acid. Recrystallization of the crude product
from N-methylpyrrolidone (NMP) afforded N,N’-bis(4-bromo-
benzoyl)-p-phenylenediamine as a white crystalline powder.
Yield: 91%; FTIR spectrum (KBr pellet, cm21): 3308
(N[sbond]H), 1647 (C[dbond]O), 843 (p-disubstituted ben-
zene); 1H NMR (300 MHz, DMSO-d6): d 5 7.74 (d, J 5 8.7
Hz, 8H), 7.90 (d, J 5 8.7 Hz, 4H), 10.33 (s, 2H) ppm; 13C
NMR (75 MHz, DMSO-d6): d 5 120.7, 125.2, 129.7, 131.3,
134.0, 134.8, 164.2 ppm; Anal. Calcd. for C20H14Br2N2O2
(474.15): C, 50.63; H, 2.95; N, 5.91. Found: C 50.60, H 2.96,
N 5.90.
EXPERIMENTAL
Synthesis of Aromatic Poly(amide amine)s
Materials
A typical synthesis of a APAAs was conducted in a three-
necked flask (50 mL) equipped with a magnetic stirrer, a
nitrogen outlet, inlet, and water-cooled condenser, added
to which are N,N’-bis(4-bromobenzoyl)-p-phenylenediamine
(5.0 mmol), primary aromatic diamines (5.0 mmol), sodium
tert-butoxide (14.0 mmol), tris(dibenzylideneacetone)dipal-
ladium(0) Pd2(dba)3 (0.05 mmol), BINAP (0.15 mmol), and
N,N-dimethylacetamide (DMAc) (15 mL). The reaction mix-
ture was flushed with high purity nitrogen and the flask
Tris(dibenzylideneacetone)-dipalladium(0) (Pd2(dba)3) and
BINAP were purchased from Alfa Aesar a Johnson Matthey
Company in USA. N,N0-bis(4-bromobenzoyl)-p-phenylenedi-
amine was synthesized in our laboratory. p-Phenylenedi-
amine, 4-aminopheyl ether, and sodium tert-butoxide were
purchased from J & K Technology. The rest materials and
reagents were obtained from different commercial sources
and used without further purification.
ꢀ
was immersed in a 130 C oil bath for 10–12 h. The result-
Measurements
ing polymer solution was allowed to slowly cold to room
temperature, filtered, and subsequently poured into metha-
nol, the powder precipitate was filtered, washed with
methanol several times, and then dried at 100 ꢀC under
vacuum.
FTIR spectra were recorded on a Nicolt 6700 FTIR spec-
trometer. Elemental analysis was measured on a Vario EL III.
1H NMR was performed on AVANCE 300 MHz NMR spec-
trometers in dimethylsulfoxide (DMSO)-d6. The molecular
weights and molecular weight distributions were estimated
by gel permeation chromatography (GPC) on a Wyatt DAWN
HELEOS using N,N-dimethylformamide (DMF) (adding 1%
APAA-1: Yield: 93%; FTIR spectrum (KBr pellet, cm21):
1
3320 (N[sbond]H), 1694 (C[dbond]O), 1306 (C[sbond]N); H
ꢀ
LiBr) as an eluent, testing temperature 50 C. The glass tran-
NMR (300 MHz, DMSO-d6): d 5 7.03 (d, J 5 8.4 Hz, 4H),
7.18 (s, 4H), 7.71 (m, 4H), 7.85 (d, J 5 8.7 Hz, 4H), 8.52 (s,
2H), 9.89 (s, 2H) ppm; Anal. Calcd. for (C26H20N4O2)n
(420.48)n: C, 74.28; H, 4.76; N, 13.33; Found: C, 74.16; H,
4.78; N, 13.30.
sition temperature was obtained by DSC curves at a rate of
21
ꢀ
10 C min under flowing nitrogen gas. Thermo gravimetric
analysis was performed on a Setarma TG-92 at a heating
21
ꢀ
rate of 10 C min under oxygen and nitrogen atmosphere.
Absorption spectra were detected on a SHIMADZU UV-3150
UV–vis–NIR sprectrophotometer. Fluorescent emission spec-
tra were collected on a PerkinElmer LS-55 fluorescence spec-
trometer. The cyclic voltammograms were obtained with a
Zennium IM6 electrochemical workstation (Zahner, Germany)
using a normal three-electrode cell with a Pt working elec-
trode, a Pt wire counter electrode, and a Ag=AgCl reference
electrode in 1.0 M H2SO4 at a scan rate of 20 mV s21, using
APAA-2: Yield: 82%; FTIR spectrum (KBr pellet, cm21):
1
3317 (N[sbond]H), 1698 (C[dbond]O), 1304 (C[sbond]N); H
NMR (300 MHz, DMSO-d6): d 5 7.00 (t, J 5 9.0 Hz, 8H),
7.19 (d, J 5 9.0 Hz, 4H), 7.70 (d, J 5 7.5 Hz, 4H), 7.85 (d, J
5 8.7 Hz, 4H), 8.56 (s, 2H), 9.90 (s, 2H) ppm; Anal. Calcd.
for (C32H24N4O3)n (512.58)n: C, 75.00; H, 4.69; N, 10.94;
Found: C, 74.92; H, 4.70; N, 10.92.
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SCHEME
2 Synthesis
of
N,N’-bis(4-bromobenzoyl)-p-
phenylenediamine.
RESULTS AND DISCUSSION
Design, Synthesis, and Characterization of Polymers
The N,N’-bis(4-bromobenzoyl)-p-phenylenediamine, as the
monomer, was synthesized by the condensation of 4-
bromobenzoyl chloride with p-phenylenediamine via amida-
tion reaction. The synthetic route to N,N’-bis(4-bromoben-
zoyl)-p-phenylenediamine is shown in Scheme 2. The
structure of N,N’-bis(4-bromobenzoyl)-p-phenylenediamine
was characterized by FTIR, 1H NMR, and elemental analysis,
and the results showed a good agreement with the proposed
structure.
FIGURE 1 1H NMR (300 MHz) spectra of APAAs recorded in
DMSO-d6.
During the synthesis of polymers, the effect of concentration
and temperature on the molecular weight could be followed.
Taking APAA-2 as an example, upon increasing the tempera-
ture from 70 to 160 ꢀC, Mn and Mw increases at first and then
decreases, while upon increasing the concentration from 20 to
35%, Mn and Mw botꢀh increased. It is implied in Table 2 that a
temperature of 130 C and a concentration of 35% are more
suitable for the palladium-catalyzed polycondensation to pro-
duce these polymers with higher molecular weights.
The accepted mechanism of the Pd-catalyzed amination
involves oxidative addition of the aromatic halides to a palla-
dium(0) species to form an arylene palladium(II) halide. By
inductive effect or by resonance, this step should be favored
for an arylene bromide substituted with an electron-
withdrawing group in the para position. In addition, reactions
of electron-deficient aromatic halides and electron-rich amines
give high yields in the amination protocol.20,26 Thus, we
attempted to do polycondensation of N,N’-bis(4-bromoben-
zoyl)-p-phenylenediamine as electron-poor arylene halides
with two different electron-rich primary aromatic diamines
(Scheme 3). As expected, the proposed polymers were success-
fully obtained with high yields and high molecular weights.
Interchain Hydrogen Bonding
The radial distribution function (RDF) is a useful method in
the structural investigation of both solid and liquid packing
(local structure) for studying specific interactions such as
hydrogen bonding.27,28 The interactions between the
[Sbond]C[dbond]O groups and the [sbond]NH groups in the
amide and amine moieties of the APAA can be investigated by
means of the RDF, gA-B(r), where A and B are [sbond]C[d-
bond]O and [sbond]NH groups, respectively. The inset in Fig-
ure 2 displays the RDF of the hydrogen atoms of the amine
group (NH) relative to the oxygen atoms of the carbonyl
groups (C[dbond]O). It can be observed that the distance
between the NH groups and the CO groups of APAA-1 and
APAA-2 are about 2.18 and 2.39 Å, respectively, which indi-
cates a strong interaction between these groups. A number of
interchain hydrogen bonds are formed. Figure 2 demonstrates
the interchain hydrogen-bonding interactions between the
[sbond]C[dbond]O and [sbond]NH groups of APAAs.
The synthesized polymers were characterized by FTIR, 1H
NMR, and elemental analysis. The results were in good agree-
ment with the proposed structures. As an example, the 1H
NMR spectra of APAA-1 and APAA-2 are shown in Figure 1
(DMSO-d6). The molecular weights of the reprecipitated poly-
mers were measured by GPC (calibrated by polystyrene stand-
ards). The Mn and Mw values are exhibited in Table 1, with
increasing molecular weights, the polydispersity increases
drastically (Table 1).
Moreover, hydrogen-bonding interactions of polymers have
frequently been studied by FTIR spectroscopy.29 Therefore,
FTIR of APAAs (KBr pellets) were recorded, giving results to
TABLE 1 Molecular Weights and the Yields of Aromatic Poly
(amide amine)sa
Polymer Code
Mn
Mw
Mw=Mn
Yield (%)
APAA-1
APAA-2
a
30,400
25,500
98,300
68,900
3.23
2.72
93
82
SCHEME 3 Synthesis of aromatic poly(amide amine)s (APAAs)
via Pd-catalyzed aryl amination.
The polymer solutions in DMF were calibrated by GPC polystyrene
standards.
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TABLE 2 Different Experimental Conditions for APAA-2
Concentration
Temperature of Monomers
Mw= Yield
Run (ꢀC)
(%)
Mn
Mw
Mn
(%)
a
1
2
3
4
5
a
70
15
15
25
35
35
–
–
–
–
100
100
130
160
4,200 8,900 2.12 69
9,800 23,100 2.36 79
25,500 68,900 2.70 82
16,800 56,600 3.37 86
–, There is no polymer formed.
FIGURE 3 FTIR spectra at different temperatures of APAA-1.
[Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
corroborate the proposed structures. Typical FTIR spectra at
different temperatures are shown in Figure 3. The character-
istic absorptions for amine groups t (NH) appeared between
3318 and 3422 cm21. Obviously, because of hydrogen bond-
ing, a significant lowering of the absorption frequency of the
bands t (NH) are observed, and the hydrogen-bonding
interactions decrease with the temperature increasing. This
effect is known to be a function of the degree and strength
of the hydrogen bonding.30 This clearly indicates that
N[sbond]HꢁꢁꢁO[dbond]C interactions from neighboring mole-
cules (Scheme 4). Comparing the frequencies of the NH bond
of traditional PPPT (ca. 3300 cm21),9 with those observed in
the APAAs (ca. 3305 cm21), a slight shift to higher frequen-
cies is observed. This suggests that the hydrogen bonding in
APAAs is weaker than that in PPPT. We assumed that the
introduction of amine units gave rise to much more hydro-
gen donors in polymer chains, in other words, the hydrogen
acceptors were relatively decreased, which would further
result in lower degree of hydrogen bonds relative to the tra-
ditional PPPT.31
Thermal Behaviors
The thermal properties of APAAs were evaluated via ther-
mogravimetric analysis (TGA) and the data are summarized
in Table 3. The synthesized polymers displayed high thermal
ꢀ
stability and a high char yield in nitrogen at 800 C. Typical
TGA traces in oxygen and nitrogen are shown in Figure 4 for
APAAs. TGA curves revealed that the polymers were ther-
mally stable at up to 400 ꢀC. The 50% weight losses took
place at over 800 ꢀC in nitrogen. The APAAs showed higher
decomposition temperatures in nitrogen than that in oxygen.
Compared with APAA-2, APAA-1 exhibited better thermal sta-
bility. Char yield is an easy and important measurement
which correlates to the ability to sustain combustion. For
FIGURE 2 Hydrogen bonds between the [sbond]CO[sbond]
group and the [sbond]NH[sbond] group of the APAA-1 (a) and
the APAA-2 (b). [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
SCHEME 4 The hydrogen-bonding interactions of aromatic
poly(amide amine)s. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
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TABLE 3 Thermal Analysis Data for APAAs
Char Yield
at 800 ꢀCd
a
b
c
Polymer Code
APAA-1
O2=N2
T5
T10
T50
O2
N2
O2
N2
502
570
461
528
550
598
529
568
783
31
67
25
57
>800
775
APAA-2
>800
a
T5: temperature of 5% weight loss.
b
c
T
10: temperature of 10% weight loss.
T
50: temperature of 50% weight loss.
d
The remaining of the polymer at 800 ꢀC.
ꢀ
these two polymers, the char yield in nitrogen at 800 C was
up to 57% (Table 3).
FIGURE 5 DSC curves of aromatic poly(amide amine)s in nitro-
gen. [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
Differenꢀtial scanning calorimetry (DSC) of these polymers up
to 250 C exhibited a single Tg. Two representative DSC ther-
mograms of the polymers are shown in Figure 5. The polymers
displayed high Tgs ranging from 248 to 275 ꢀC. The Tgs are
higher than those of the related poly(ether ketone)s (PEKs)
APAAs were obtained. The wide-angle X-ray diffraction pat-
terns of the polymers over the 2h range of 5-30ꢀ are dis-
played in Figure 6. Polymer APAA-1 exhibited the most
noticeable diffractions peaks at 2h 5 12.6ꢀ (A, d 5 7.0 Å),
ꢀ
which range from 129 to 167 C and lower than those of ara-
ꢀ
mids which amount to 292–319 C. Moreover, APAA-1 also dis-
played a visible melting temperature Tm (350 ꢀC). While the
observed Tm value is significantly lower than that of PPPT (Tm
5 570 ꢀC) and slightly higher than that of poly(ether ether
ketone) (PEEK), which has a Tm of 343 ꢀC.32 This can be
explained by the hydrogen bonding in APAAs which is weaker
than that in aramids while PEKs have no hydrogen bonding.
Wide-Angle X-Ray Diffraction
The crystallization characteristic of the PPPT results from its
chemical structure. The wholly aromatic structure with all-
para substitutions creates stiff rod-like macromolecules, hav-
ing a high cohesive energy and a high crystallization tend-
ency due to the very favorable intramolecular hydrogen
bonds.9 Compared with the structure of PPPT, the amine
groups were introduced in the polymer chain, and the novel
FIGURE 4 TGA curves of aromatic poly(amide amine)s in oxy-
gen and nitrogen. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
FIGURE 6 WAXD diffractograms intensity versus Bragg angle
graph for (a) APAA-1 and (b) APAA-2.
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FIGURE 7 Hydrogen bonding between solvent and APAA. [Color figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
18.0ꢀ (C, d 5 4.8 Å), 24.4ꢀ (B, d 5 7.0 Å), and 28.9ꢀ (D, d 5
3.0 Å), which are quite similar to the (200), (110), (200),
and (211) reflections [Figure 6(a)]. The reflection B in the
scattering pattern is exactly in a double distance on the scat-
tering vector coordinates as A and can be considered as a
second-order one but related to the same correlation period
as A.33,34 Obviously, the ether groups hindered chain packing
and reduced the level of ordering, thus leading to the amor-
phous nature of APAA-2 ([Figure 6(b)]. The amorphous
nature of APAA-2 was also reflected in its good solubility. By
comparing WAXD of APAA-2 with APAA-1, the latter polymer
exhibited semicrystalline behavior, and we can conclude that
insertion of ether group groups into the repeating units of
the polymers resulted in a significant increase of the amor-
phous nature of the polymer.
mers in 1 mL of organic solvents at room temperature and
50 C (Table 4). The polymers could be easily soluble in high
ꢀ
polar solvents, such as DMAc, DMSO, NMP, and DMF. By com-
paring APAA-1 with APAA-2, the latter polymer exhibited
better solubility, and this was reflected in its amorphous
nature. The two APAAs both showed improved solubility
compared with aramids.9
Optical and Photoluminescence Properties
Light-emitting phenomenon is a characteristic of lumines-
cence materials. Outstanding luminescence properties of ara-
mids make these polymers suitable for the production of
specifically polymer light-emitting diodes (PLEDs). There is
currently much research directed toward the preparation of
blue light-emitting polymers, because blue light can be con-
verted to green or red using the proper dyes, which means a
blue PLED alone is capable of generating all colors, while
green or red cannot emit blue light by this method. In this
article, the UV spectra of APAA-1 and APAA-2 were first
investigated in DMF. As displayed in Figure 8(a), the two
Solubility
The APAAs can be considered as hybrid structure of aramids
and polyaniline. It was expected that the combination of ara-
mids and polyaniline would result in improved solubility. In
addition, the hydrogen bonding between solvent and the
APAAs could be formed, which has been proved by molecu-
lar simulation (Figure 7). Because of their hydrogen bonding
interactions, APAAs demonstrated good solubility in most
organic solvents.
TABLE 4 Solubility of Polymers
Polymer Code
DMAc
DMSO
DMF
NMP
CHCl3
a
b
APAA-1
APAA-2
a
1 1
1 1
1 1
1 –
1 1
1 1
1 –
1 1
1 1
1 1
These novel polymers showed different solubility behavior in
different organic solvents. Polymer solubility was qualita-
tively determined by the dissolution of 5 mg of solid poly-
1 1, Solid polymer was completely dissolved at room temperature.
1 –, Solid polymer was completely dissolved at 50 ꢀC.
b
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FIGURE 8 (a) Overlay of the absorbance curves of APAA-1 and APAA-2. (b) Fluorescence spectra of APAA-1 and APAA-2 in DMF
(kexc 5 360 nm; excitation and emission slits 5 5.0 and 5.0 nm, respectively). (c) Fluorescence images of APAA-1 and APAA-2 (kexc
5 365 nm) in DMF. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
polymers gave rise to similar UV absorption bands. However,
the long wavelength absorption maximum (359 nm) of
APAA-1 was 16-nm bathochromic shift compared with that
of APAA-2, implying that the relative flexible ether group
structure of APAA-2 might freely rotate in the polymer
chains and thus restrict the conjugation of the pheny unit.
Moreover, we found that APAA-2 exhibited significantly
strong photonic luminescence in DMF [Figure 8(c)]. As
shown in Figure 8(b), the emission maximum of APAA-2 at
440 nm was bathochromic shift relative to that of APAA-1
(420 nm) with a dramatic increase in intensity. The fluores-
cence quantum yields (UF) of APAA-1 and APAA-2 deter-
mined in DMF solutions using quinine sulfate (UF 5 55% in
1 M H2SO4) as standard are 7.5 and 34.2%, respectively.2 It
is suggested that the intensity of the photonic emission is
heavily depend upon the structures of the polymers. As com-
pared to APAA-1, there is a “push-pull” p-electron mode in
APAA-2, in which the oxygen atom of the ether moiety serves
as the electron donor and the electron-deficient groups of
amide act as the electron acceptor. Hence, the polymer will
undergo an intramolecular charge transfer from the donor to
the acceptor upon excitation by light.
The energy levels of the HOMO and LUMO were determined
by measuring the electrochemical properties of the polymers
using cyclic voltammetry (CV) with
a standard three-
electrode. A platinum (Pt) electrode was modified with a
polymer film by means of dip-coating, and was used as the
working electrode. A Pt wire was used as the counter elec-
trode, and Ag=AgCl (4.0 M KCl) served as the reference elec-
trode. The CV measurements were carried out in a 1.0 M
H2SO4 electrolyte at room temperature at a scan rate of 20
mV s21. The scanned cyclic voltammograms are shown in
Figure 9. The redox process of APAA-1 was very weak under
our experimental conditions [Figure 9(a)]. In contrast, the
TABLE 5 Electrochemical Data of Polymers
HOMOb
(eV)
LUMOc
(eV)
a
Polymer
Code
konset
Eg
Eonset
(nm)
(eV)
(eV)
d
APAA-1
APAA-2
a
420
385
2.95
3.22
–
–
–
0.48
–5.28
–2.06
Optical band gap calculated from the UV–Vis absorption onset.
b
The HOMO energy levels were calculated from cyclic voltammetry
FIGURE 9 CV measurements of (a) APAA-1 and (b) APAA-2 con-
and were referenced to ferrocene (4.8 eV).
ducted in aqueous H2SO4 (1.0 M) at a scan rate of 20 mV s21
.
c
LUMO levels of the polymer were estimated from the optical band
[Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
gaps and the HOMO energies.
d
Not measured due to weak signals.
WWW.MATERIALSVIEWS.COM
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8 A. Arun, K. Dullaert, R. J. Gaymans, Macromol. Chem. Phys.
2009, 210, 48–59.
oxidation process of APAA-2 had an onset at 0.48 V and gave
a peak at 0.60 V. The oxidation was pseudoreversible and
gave the corresponding reduction peak at 0.50 V. The energy
levels of the HOMO and the LUMO were thus estimated from
the cyclic voltammograms and the onset of the absorption
spectra. The results are summarized in Table 5. The APAA-2
has relatively lower energy levels, which means that a better
hole transporting ability can be expected.35
ꢁ
ꢁ
~
9 J. M. Garcıa, F. C. Garcıa, F. Serna, J. L. de la Pena, Prog.
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CONCLUSIONS
13 G. Huang, S. Zhang, D. Li, M. Zhang, G. Zhang, J. Yang,
Polym. Int. 2013, 62, 411–418.
Two novel APAAs have been successfully synthesized by a Pd-
catalyzed polycondensation of N,N’-bis(4-bromobenzoyl)-p-
phenylenediamine with different primary aromatic amines.
These polymers can be considered as a new class of high-
performance polymers with high thermal stability (Tg > 240
ꢀC and T5 > 400 ꢀC). Their good solubilities broaden the
scope of the technological applications of these materials.
Moreover, APAA-2 displays significantly strong photonic lumi-
nescence in DMF and good electroactivity, which warrants its
potential applications for photoluminescent devices. This
work does not only deepen our systemic understanding of the
synthetic strategy of Pd-catalyzed polycondensation but also
provide new perspectives for generating polymers with ther-
mal stability, good solubility, and well optical properties.
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This research was financially supported by the National Natural
Science Foundation of China (No. 21202134), the Research
Fund for the Doctoral Program of Southwest University of Sci-
ence and Technology (No. 12zx7129), Science and Technology
Development Foundation of China Academy of Physics Engi-
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