Synthesis and characterization of polyketones containing pendant carbazoles

Article abstract of DOI:10.1016/j.polymer.2011.02.030

Condensation of 9-(4-aminobenzene)-carbazole with 4,4′- difluorobenzophenone afforded a carbazole-functionalized poly(aryl amino ketone) (PAK-Cz). Similarly, a series of poly(ether ether ketone)s (PEEK-Cz) and poly(arylene ether ketone)s (PAEK-Cz) contain

Full text of DOI:10.1016/j.polymer.2011.02.030

Polymer 52 (2011) 1731e1737
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Synthesis and characterization of polyketones containing pendant carbazoles
,
Zheng Chen a b, Robert J. Ono b, Kelly M. Wiggins b, Honglei Cui a, Changru Rong a,
,
a,
**
Christopher W. Bielawski b , Zhenhua Jiang
*
a Department of Chemistry, Jilin University, Changchun, Jilin, PR China
b Department of Chemistry & Biochemistry, The University of Texas, Austin, TX 78712, United States
a r t i c l e i n f o
a b s t r a c t
Condensation of 9-(4-aminobenzene)-carbazole with 4,40-difluorobenzophenone afforded a carbazole-
functionalized poly(aryl amino ketone) (PAK-Cz). Similarly, a series of poly(ether ether ketone)s (PEEK-
Cz) and poly(arylene ether ketone)s (PAEK-Cz) containing pendant carbazoles were synthesized from the
copolymerization of 9-(4-aminobenzene)-carbazole, 4,40-difluorobenzophenone and 4,40-biphenol or
4,40-isopropylidenebiphenol, respectively. The aforementioned polymers exhibited polystyrene equiva-
lent number average molecular weights of up to 36 kDa, and were found to be thermally stable with high
decomposition (Td) (469e569 ꢀC) and glass transition temperatures (Tg) (155e256 ꢀC). UVevis absorp-
tion and fluorescence spectra revealed that these materials exhibited highly efficient (Ff ¼ 0.41e0.66)
yellowegreen emission (lem ¼ 500e514 nm) in solution.
Article history:
Received 20 January 2011
Received in revised form
14 February 2011
Accepted 18 February 2011
Available online 1 March 2011
Keywords:
Poly(arylene ether ketone)
Carbazole
Ó 2011 Elsevier Ltd. All rights reserved.
Fluorescence
1. Introduction
of materials, potentially with tunable physical or electronic
properties, or facilitate access to analogous materials in a more
On account of their unique electronic, electrochemical, and
optical properties, polymers containing carbazole moieties in
their main or side chains have been widely studied for use in
a broad range of applications including photoconduction, elec-
troluminescence, and photorefraction [1e5]. From a synthetic
standpoint, there are generally three distinct methods for incor-
porating carbazole units into a polymeric material: polymeriza-
tion via the carbazole’s 1) 3,6-positions [6e9], 2) 2,7-positions
[10], or 3) 9-position (see Fig. 1). The first two approaches are
efficient manner. Selected examples of such methods include the
syntheses of poly(carbazolylacetylene)s from N-alkynylated
carbazoles (A), the ring opening metathesis polymerization of
carbazole-functionalized norbornene derivatives (B), and the
ring-opening polymerization of oxazole-functionalized carbazoles
(C) (Scheme 1) [14e16].
Inspired by a report by Hay [17] in which carbazole-based poly
(ether sulfone) analogs (D; Scheme 1) were prepared via nucleo-
philic aromatic substitution (SNAr) condensation of bis(4-fluo-
rophenyl)sulfone with 3,30-bicarbazole, we developed an interest
in the use of SNAr-type polycondensation chemistry to prepare
polymeric materials with pendant carbazoles [12]. In particular, we
envisioned using analogous methodology to incorporate the
desirable optical properties of carbazoles into industrially relevant
thermoplastics such as poly(ether ether ketone)s (PEEKs) and poly
(arylene ether ketone)s (PAEKs), polymers which are commonly
synthesized via SNAr-type polycondensation chemistry [18]. Poly-
mers encompassing the useful thermal and mechanical properties
of PEEK and PAEK, in combination with the optical properties
inherent to carbazole, may find utility in many of the aforemen-
tioned applications.
frequently utilized for the preparation of
which bear carbazole units in their main chains, often synthesized
through host of transition metal-mediated cross-coupling
p-conjugated polymers
a
reactions [6e10]. Polymerization reactions that belong to the third
category are generally used to afford polymers with pendant
carbazole moieties, and commonly utilize radical, ionic, or ring-
opening polymerizations of appropriate N-functionalized mono-
mers, including N-vinylcarbazole [11], carbazole acrylates and
methacrylates [12], or carbazole epoxides [13], respectively. Other
polymerization methods that afford polymers with pendant
carbazoles are less common, but further development of alterna-
tive polymerization methods may enable access to a broader range
Herein we report the synthesis of a series of copolymers con-
taining carbazoles in their side chains via the condensation of 9-(4-
aminobenzene)-carbazole with 4,40-difluorobenzophenone. To the
best of our knowledge, the methods described are the first exam-
ples of preparing polymers featuring pendant carbazolyl groups via
* Corresponding author.
** Corresponding author.
E-mail addresses: bielawski@cm.utexas.edu (C.W. Bielawski), jiangzhenhua@
email.jlu.edu.cn (Z. Jiang).
0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2011.02.030

1732
Z. Chen et al. / Polymer 52 (2011) 1731e1737
delta (d) units and expressed in parts per million (ppm) downfield
9
H
from tetramethylsilane using the residual solvent as an internal
standard. For 1H NMR: CDCl3, 7.26 ppm. For 13C NMR: CDCl3,
77.0 ppm. Coupling constants (J) are expressed in hertz. Gel
permeation chromatography (GPC) was performed at room
temperature on a home-built system equipped with a Beckman
Coulter System Gold 126 Solvent Module, two fluorinated poly-
styrene columns (Viscotek IMBHW-3078 and I-MBLMW-3078)
arranged in series, and a Beckman Coulter System Gold 168 Diode
N
8
1
7
2
6
3
5
4
Fig. 1. The structure and numbering system of carbazole.
Array Detector (
l
¼ 254 nm). Molecular weight and polydispersity
data are reported relative to polystyrene standards in tetrahydro-
furan (THF). FT-IR spectra were obtained in KBr matrices and were
measured on a Nicolet Impact 410 Fourier transform infrared
spectrometer. Differential scanning calorimetry (DSC) was per-
formed using a Mettler-Toledo DSC823e under an atmosphere of
nitrogen at a heating/cooling rate of 10 ꢀC minꢁ1. Thermogravi-
metric analysis (TGA) were performed using a TGA/SDTA85ꢁ11e
SNAr polycondensation chemistry. Likewise, the use of readily
accessible primary amines, such as 9-(4-aminobenzene)-carbazole,
as a difunctional comonomer in SNAr polycondensations was
hitherto unknown, and represents a new synthetic strategy that
may find broad applicability in the preparation of other conden-
sation polymers. The carbazole-based copolymers synthesized
were found to have good solubilities in organic solvents, high glass
transition temperatures, high thermal stabilities, and high molec-
ular weights, all of which could be modified by varying the carba-
zole content. The optical properties of the polymers were also
examined, and led us to conclude that the desirable emissive
characteristics of carbazole were preserved upon polymerization
using the methodology described below.
under an atmosphere of nitrogen at a heating rate of 10 ꢀC min
.
UVevis absorption spectra were measured using a Perkin Elmer
Lambda 35 spectrometer. Emission spectra were recorded using
a QuantaMaster Photon Technology International fluorometer.
2.2. Synthetic procedures and characterization data
2. Experimental section
2.2.1. Synthesis of model compound 1
A three-necked flask equipped with a mechanical stirrer,
a nitrogen inlet, a DeaneStark trap, and a condenser was charged
with 9-(4-aminophenyl)-carbazole (2.58 g, 10.0 mmol), 4-fluo-
robenzophenone (4.40 g, 22.0 mmol), and K2CO3 (1.52 g,11.0 mmol).
Tetramethylene sulfone (TMS) (30 g) and 10 mL of toluene were then
added. After heating the reaction mixture at 140e150 ꢀC for 2 h and
subsequent removal of toluene, the reaction temperature was
increased to between 198 and 202 ꢀC. After 4e5 h at this tempera-
ture, the solution was poured into a large excess of distilled water
(300 mL) with vigorous stirring. A greeneyellow powder precipi-
tated and was subsequently collected by vacuum filtration, washed
with hot deionized water (5 ꢂ 300 mL) and ethanol (3 ꢂ 300 mL),
then dried under vacuum at 80 ꢀC for 10 h to afford the desired
product as a yellow powder (5.07 g; 82% yield). m.p. 175 ꢀC (DSC).
MALDI-TOF MS calcd for C44H30N2O2 [Mþ]: 618.2; found: 618.6. IR
(KBr, cmꢁ1): 1450, 1519, 1602 (Ar, C]C), 1662 (AreCOeAr). 1H NMR
2.1. General considerations
All solvents were purchased from Fisher Scientific and used
without additional purification unless otherwise noted. Tetra-
methylene sulfone (TMS) was obtained from the Jinzhou Oil
refinery and purified before use. The compounds 9-(4-nitro-
phenyl)-carbazole (NO2eAreCz) and 9-(4-aminophenyl)-carbazole
(NH2eAreCz) were prepared according to literature procedures in
comparable purity and yield [19]. All other chemicals were
purchased from Aldrich, Alfa Aesar, Acros, or TCI, and were used as
received. 1H and 13C{1H} NMR spectra were recorded using a Bruker
510 NMR spectrometer (500 MHz). Chemical shifts are reported in
C C
NCH2CH2
C O
(CH2)3
n
n
H
N
n
(300 MHz, CDCl3): d 7.36e7.27 (m, 6H), 7.66e7.40 (m, 6H), 7.96e7.75
(m, 16H), 8.16 (d, 2H, J ¼ 8.8 Hz). 13C NMR (75 Hz, CDCl3):
d 195.19,
Si
N
N
150.49, 144.85, 140.66, 137.87, 134.54, 132.51, 132.32, 132.13, 132.07,
129.75,128.30,128.26,127.33,125.98,123.39,122.69,120.37,120.09,
118.56, 109.65. Anal calcd C44H30N2O2: C, 85.41; H, 4.89; N, 4.53.
Found: C, 85.22; H, 4.76; N, 4.44.
N
A
C
B
2.2.2. Synthesis of PAK-Cz
A flask was charged with 9-(4-aminophenyl)-carbazole (2.58 g,
10.0 mmol), 4,40-difluorobenzophenone (2.18 g, 10.0 mmol), tetra-
methylene sulfone (30 g), K2CO3 (1.52 g, 11.0 mmol) and toluene
(10 mL) as an azeotropic agent to remove the water generated
during the polycondensation reaction. After heating the reaction
mixture to 136e150 ꢀC for 2 h and subsequent removal of toluene,
the reaction temperature was increased to 198e202 ꢀC. When the
solution viscosity increased significantly (which required approxi-
mately 4e5 h), the solution was poured into a large excess of
distilled water (300 mL) with vigorous stirring. The precipitated
solids were collected and washed repeatedly with hot deionized
water (5 ꢂ 300 mL) and ethanol (3 ꢂ 300 mL), and then dried under
reduced pressure at 80 ꢀC for 10 h to afford the desired polymer as
a yellow powder (3.49 g; 80% yield). IR (KBr, cmꢁ1): 3040 (AreH),
1650 (AreCOeAr), 1592, 1500, 1454 (Ar, C]C), 1309 (NAr3), 1280
O
S
O
N
n
D
N
Scheme 1. Selected examples of polymers which incorporate 9-substituted carbazole
units.

Z. Chen et al. / Polymer 52 (2011) 1731e1737
1733
N
N
when R = H
NH2
N
C
O
C
O
O
C
1
F
R
O
C
N
N
n
when R = F
PAK-Cz
Scheme 2. Preparation of model compound 1 (top) and PAK-Cz (bottom). Conditions: K2CO3, tetramethylene sulfone, toluene, 200 ꢀC.
(NeC). 1H NMR (400 MHz, CDCl3):
8.20e8.95 (br).
d
7.60e7.12 (br), 7.93e7.62 (br),
(NeC), 1240, 1080 (AreOeAr). 1H NMR (CDCl3):
(CH3)2eAr), 6.98e7.06 (m), 7.13e7.17 (t), 7.25e7.31 (m), 7.40e7.47
(q), 7.55 (d), 7.77e7.84 (m), 8.14 (d, J ¼ 4.4).
d
1.71 (s, AreC
2.2.3. Representative copolymerization procedure (Synthesis of
PAEK-Cz 80%)
2.2.4. Representative copolymerization procedure (synthesis of
A flask was charged with 9-(4-aminophenyl)-carbazole (2.58 g,
10.0 mmol), 4,40-difluorobenzophenone (1.70 g, 8.0 mmol), 4,40-
dihydroxy-2,2-diphenylpropane (BPA) (0.456 g, 2.0 mmol), tetra-
methylene sulfone (TMS) (30 g), K2CO3 (1.52 g, 11.0 mmol) and
toluene (10 mL) as an azeotropic agent to remove the water
generated during the polycondensation reaction. After heating the
reaction mixture to 136e150 ꢀC for 2 h and subsequent removal of
toluene, the reaction temperature was increased to between 198
and 202 ꢀC. When the solution viscosity increased significantly
(which required approximately 4e5 h), the solution was poured
into a large excess of distilled water (300 mL) with vigorous stir-
ring. The precipitated solids were collected and washed repeatedly
with hot deionized water (5 ꢂ 300 mL) and ethanol (3 ꢂ 300 mL),
and then dried under reduced pressure at 80 ꢀC for 10 h to afford
the desired polymer as a yellow powder (3.57 g; 83% yield). IR (KBr,
cmꢁ1): 3040 (AreH), 2963 (eCH3), 1650 (AreCOeAr), 1592, 1500,
1454 (Ar, C]C), 1309 (NAr3), 1280 (NeC), 1240, 1080 (AreOeAr). 1H
PEEK-Cz 80%)
A
flask was charged with 9-(4-aminobenzene)-carbazole
(2.58 g, 10.0 mmol), 4,40-difluorobenzophenone (1.70 g, 8.0 mmol),
biphenol (BP) (0.22 g, 2.0 mmol), tetramethylene sulfone (TMS)
(30 g), K2CO3 (1.52 g, 11.0 mmol) and toluene (10 mL) as an azeo-
tropic agent to remove the water generated during the poly-
condensation reaction. After heating the reaction mixture to
136e150 ꢀC for 2 h and subsequent removal of toluene, the reaction
temperature was increased to between 198 and 202 ꢀC. When the
solution viscosity had increased significantly (which required
approximately 4e5 h), the reaction mixture was poured into a large
excess of distilled water (300 mL) with vigorous stirring. The
precipitated solids were collected by vacuum filtration, and washed
repeatedly with hot deionized water (5 ꢂ 300 mL) and ethanol
(3 ꢂ 300 mL), and then dried under reduced pressure at 80 ꢀC for
10 h to afford the desired product as a yellow powder (3.17 g; 78%
yield). IR (KBr, cmꢁ1): 3040 (AreH), 1650 (AreCOeAr), 1593, 1493,
1452 (Ar, C]C), 1313 (NAr3), 1277 (NeC), 1228, 1110, 1012
NMR (400 MHz, CDCl3):
d 1.71 (s), 7.10e7.03 (br), 7.22e7.11(br),
7.34e7.27 (br), 7.50e7.38 (br), 7.61e7.53 (br), 7.90e7.74 (br),
8.18e8.10 (br).
2.2.3.1. PAEK-Cz 60%. IR (KBr, cmꢁ1): 3040 (AreH), 2963 (eCH3),
1650 (AreCOeAr), 1592, 1500, 1454 (Ar, C]C), 1309 (NAr3), 1280
(NeC), 1240, 1080 (AreOeAr). 1H NMR (CDCl3):
d 1.71 (s, AreC
(CH3)2eAr), 7.00e7.06 (m), 7.15e7.19 (q, J1 ¼9.6, J2 ¼ 19.6), 7.28 (br),
7.43e7.48 (m), 7.55e7.57 (br), 7.77e7.87 (m), 8.14 (d, J ¼ 4.4).
2.2.3.2. PAEK-Cz 40%. IR (KBr, cmꢁ1): 3040 (AreH), 2963 (eCH3),
1650 (AreCOeAr), 1592, 1500, 1454 (Ar, C]C), 1309 (NAr3), 1280
(NeC), 1240, 1080 (AreOeAr). 1H NMR (CDCl3):
d 1.71 (s, AreC
(CH3)2eAr), 6.98e7.06 (m), 7.13e7.17 (t), 7.25e7.31 (m), 7.41e7.48
(q), 7.56 (d), 7.77e7.87 (m), 8.15 (d, J ¼ 4.4).
2.2.3.3. PAEK-Cz 20%. IR (KBr, cmꢁ1): 3040 (AreH), 2963 (eCH3),
1650 (AreCOeAr), 1592, 1500, 1454 (Ar, C]C), 1309 (NAr3), 1280
Fig. 2. FT-IR spectra (KBr) of NH2eAreCz (top), 1 (middle), and PAK-Cz (bottom).

1734
Z. Chen et al. / Polymer 52 (2011) 1731e1737
Fig. 3. 1H NMR spectra (CDCl3) of (A) model compound 1 and (B) PAK-Cz (CDCl3).
(AreOeAr). 1H NMR (400 MHz, CDCl3):
(br), 7.35e7.27 (br), 7.51e7.38 (br), 7.61e7.54 (br), 7.77e7.87 (br),
8.18e8.11 (m).
d
7.10e7.03 (br), 7.22e7.11
stretching bands between 3200 cmꢁ1 and 3500 cmꢁ1 attributed to
the AreNH2 groups found in the starting material (NH2eAreCz)
were no longer present in the IR spectrum of 1. In addition, a new,
sharp absorption band corresponding to the carbonyl stretching
2.2.4.1. PEEK-Cz 60%. IR (KBr, cmꢁ1): 3040 (AreH), 1650
(AreCOeAr), 1593, 1493, 1452 (Ar, C]C), 1313 (NAr3), 1277 (NeC),
frequency of the aryl ketone appeared at approximately 1650 cmꢁ1
.
The 1H NMR spectrum of 1 also revealed signals consistent with the
assigned structure and the disappearance of the NH2 signal
1228, 1110, 1012 (AreOeAr). 1H NMR (400 MHz, CDCl3):
d
7.05 (br),
7.13 (s), 7.28 (br), 7.42 (br), 7.55 (br), 7.8e7.86 (br), 8.12 (br).
(
d
¼ 5.44 ppm; DMSO-d6) of NH2eAreCz (see Fig. 3). Competitive
imine formation was not observed by 1H NMR or FT-IR spectros-
copy. Collectively, these spectroscopic data suggested to us that 1
was successfully synthesized.
2.2.4.2. PEEK-Cz 40%. IR (KBr, cmꢁ1): 3040 (AreH), 1650
(AreCOeAr), 1593, 1493, 1452 (Ar, C]C), 1313 (NAr3), 1277 (NeC),
1228, 1110, 1012 (AreOeAr). 1H NMR (400 MHz, CDCl3):
d
7.06 (t,
Building on the aforementioned results, we shifted our attention
toward the synthesis of polymeric materials. A series of poly-
condensation reactions were performed using conditions similar to
those described above with the exception that an equimolar
amount (relative to NH2eAreCz) of ditopic 4,40-difluor-
obenzophenone was used in lieu of its mono-fluorinated analog
(see Scheme 2). Following 6e7 h of stirring toluene solutions of
these monomers at elevated temperatures (2 h at 140e150 ꢀC and
then 4e5 h at 200 ꢀC), polymeric materials (i.e., PAK-Cz) were
isolated in 80% yield by pouring the respective reaction mixtures
into an excess of water and ethanol, followed by collection of the
precipitated solids via filtration. While this methodology was
similar to conventional SNAr-type polycondensations typically used
for the synthesis of polyketones [20], the use of NH2eAreCz as
a monomer (instead of a diol) was expected to afford polymers with
triarylamine moieties in their main chains.
Limited solubility in common organic solvents precluded
molecular weight determination of the materials isolated from the
aforementioned polymerization reactions by gel permeation chr-
omatography (GPC) (eluent ¼ THF); however, characterization by
FT-IR and 1H NMR spectroscopy (CDCl3) led us to conclude that PAK-
Cz was successfully formed. For instance, as shown in Fig. 2, the FT-IR
spectra of 1 and PAK-Cz shared similar features, all of which were
consistent with their proposed structures (see Scheme 2). The 1H
J ¼ 8), 7.13 (s), 7.27e7.31 (m), 7.41e7.47 (m), 7.56 (d, J ¼ 8), 7.81e7.87
(q, J1 ¼ 8, J2 ¼ 17.6), 8.14 (d, J ¼ 7.2).
2.2.4.3. PEEK-Cz 20%. IR (KBr, cmꢁ1): 3040 (AreH), 1650
(AreCOeAr), 1593, 1493, 1452 (Ar, C]C), 1313 (NAr3), 1277 (NeC),
1228, 1110, 1012 (AreOeAr). 1H NMR (400 MHz, CDCl3):
d 7.07 (t,
J ¼ 8), 7.14 (s), 7.25e7.33 (m), 7.42e7.48 (m), 7.55 (d, J ¼ 8),
7.80e7.85 (q, J1 ¼ 8, J2 ¼ 17.5), 8.12 (d, J ¼ 7.1).
3. Results and discussion
In
a
preliminary experiment, 9-(4-aminophenyl)-carbazole
equiv of 4-fluo-
(NH2eAreCz) [19] was treated with
2
robenzophenone in tetramethylene sulfone (TMS) in the presence
of excess potassium carbonate (Scheme 2). The use of sufficiently
elevated reaction temperatures (140e150 ꢀC) and toluene as a co-
solvent (30 vol%) facilitated the azeotropic removal of water
generated during the condensation reaction. After 4e5 h, the
reaction mixture was poured into water, and the precipitated solids
were collected by filtration, washed with water and ethanol, and
then dried under reduced pressure to afford the desired model
compound 1 in 82% isolated yield. As shown in Fig. 2, FT-IR spec-
troscopy (KBr) confirmed that the characteristic symmetric
O
C
O
C
O
C
N
TMS, Toluene
K2CO3, 200 °C
N
N
+
HO-Ar-OH
O
Ar O
F
F
+
x
y z
NH2
Ar =
Ar =
PEEK-Cz
CH3
C
CH3
PAEK-Cz
Scheme 3. Copolymerization of NH2eAreCz with various diols to form PEEK-Cz (Ar ¼ phenyl) or PAEK-Cz (Ar ¼ 2, 2-diphenylpropyl). TMS ¼ tetramethylene sulfone.

Z. Chen et al. / Polymer 52 (2011) 1731e1737
1735
Table 1
Table 3
Solubility characteristics of PEEK-Cz, PAEK-Cz, and PAK-Cz in Common Solvents.a
UVevis absorption and emission data of various polyketones containing carbazole.a
PEEK-Cz
PAK-Cz PAEK-Cz
Polymer
lmax (nm)
3
(mgꢁ1 cmꢁ1 mL)
lem (nm)
Ffb
PAK-Cz
389
389
388
387
384
295
390
389
389
384
27.01
30.00
27.01
14.20
8.46
16.82
9.66
7.67
510
508
505
500
509
370
508
511
508
514
0.55
0.49
0.59
0.41
0.66
0.08
0.59
0.59
0.48
0.59
Solvent 0% 20% 40% 60% 80% 100%
80% 60% 40% 20% 0%
PAEK-Cz 80%
PAEK-Cz 60%
PAEK-Cz 40%
PAEK-Cz 20%
PAEK-Cz 0%c
PEEK-Cz 80%
PEEK-Cz 60%
PEEK-Cz 40%
PEEK-Cz 20%
NMP
DMF
DMSO
THF
CHCl3
DMAc
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁþ þþ þþ ꢁþ ꢁþ
ꢁþ þþ þþ þþ þþ
ꢁþ
ꢁþ
ꢁ
þ
þ
þ
þ
ꢁþ ꢁþ
ꢁþ ꢁþ
ꢁþ þþ þþ
þ
þ
þþ
þþ
ꢁþ
þ
þ
þþ þþ ꢁþ ꢁþ
ꢁþ þþ þþ þþ þþ
ꢁþ þþ þþ þþ þþ
ꢁþ þþ þþ ꢁþ ꢁþ
ꢁ
þþ þþ ꢁþ ꢁþ
ꢁþ þþ þþ
þ
þþ
a
5.67
2.33
Solubility was determined by studying mixtures of sample to solvent in ratios
that were equivalent to 1.0 g Lꢁ1. Definitions: þþ, Soluble at room temperature; þ,
soluble upon heating; ꢁþ, slightly soluble; ꢁ, insoluble even upon heating. The
percentages denoted in the table indicate the molar quantity of carbazole in the
a
Absorption and emission spectra were recorded under ambient conditions in
CHCl3 at a polymer concentration of 4 mg mLꢁ1
.
polymer. NMP
¼
N-methyl-2-pyrrolidone. DMF
¼
dimethylformamide.
b
Fluorescence quantum yields (Ff) were determined relative to quinine bisulfate
DMSO ¼ dimethylsulfoxide. THF ¼ tetrahydrofuran. DMAc ¼ N-dimethylacetamide.
in H2SO4.
c
See Ref. [24].
NMR spectra of the model compound 1 and the isolated polymer
PAK-Cz are shown in Fig. 3. As was the case in the FT-IR analyses, the
disappearance of the signal attributable to the AreNH2 group of
NH2eAreCz (5.44 ppm, DMSO-d6) in the 1H NMR spectrum of PAK-
Cz suggested to us that the primary amino groups of the monomer
were no longer present in appreciable quantities in the isolated
material, presumably having reacted to form triarylamines. More-
over, comparison of the 1H NMR spectra of PAK-Cz and 1 also
revealed similar features between the two compounds, and the peak
broadening observed in the spectrum of PAK-Cz was consistent with
the formation of a polymeric material sharing similar molecular
connectivity to that of 1.
From a practical perspective, functional polymers should not
only be mechanically and thermally robust but also be readily
amenable to common processing conditions. In general, good
solubility in organic solvents facilitates polymer processing and
enables the use of spin- or dip-coating methodologies to prepare
films. With the goal of enhancing the processability of the afore-
mentioned copolymers in mind, we reasoned that integrating PEEK
or PAEK with PAK-Cz should result in a hybrid material that
exhibits both the desirable physical properties and processing
advantages of PEEK and/or PAEK [18] while preserving the useful
optical properties of carbazole. Thus, subsequent efforts were
directed toward copolymerization reactions involving NH2eAreCz
and 4,40-difluorobenzophenone with various bisphenol monomers
to form statistical copolymers containing mixtures of amine and
ether linkages in the corresponding polymer’s backbone.
As depicted in Scheme 3, two series of copolymers were
synthesized: the first employed 4,40-biphenol (BP) to form analogs
of PEEK which featured pendant carbazole units (PEEK-Cz), and the
second employed 4,40-isopropylidenebiphenol (BPA) to form
analogs of PAEK which also featured pendant carbazole units
(PAEK-Cz). In general, the copolymerization reactions employed
similar conditions as the preparation of PAK-Cz, albeit with the
addition of the comonomer (BP or BPA) in various stoichiometries
(see below). The progress of the copolymerization was monitored
by GPC; when no further increase in molecular weight was
observed, the reaction was purified using a similar procedure as
that described for PAK-Cz to obtain the statistical copolymers
PEEK-Cz or PAEK-Cz, typically in >80% isolated yield. To prepare
polymers with different carbazole contents, the molar feed ratios of
NH2eAreCz to BP or BPA were varied. Based on these molar feed
ratios, the expected final carbazole contents in the copolymers
were 100%, 80%, 60%, 40% and 20%, respectively, where a value of
100% denotes materials that did not contain BP or BPA.
With various PEEK-Cz and PAEK-Cz copolymers in hand, we
next sought to qualitatively measure their solubilities in a variety of
solvents. As summarized in Table 1, the solubilities exhibited by the
PAEK-Cz and PEEK-Cz copolymers varied as a function of carbazole
Table 2
Molecular weight and thermal properties of various polyketones containing
carbazole.a
polymerb
Mn (kDa)
Mw (kDa)
Mw/Mn
d,f
Tg (ꢀC)
e,f
Td (ꢀC)
PAK-Czb
e
e
e
256
227
216
193
163
184
166
155
163
542
534
569
560
562
469
511
526
534
PEEK-Cz 80%
PEEK-Cz 60%
PEEK-Cz 40%
PEEK-Cz 20%c
PAEK-Cz 80%
PAEK-Cz 60%
PAEK-Cz 40%
PAEK-Cz 20%
1.3
22
20
e
2.1
58
40
e
1.6
2.6
2.0
e
3.2
4.4
6.0
36
6.3
8.2
12
90
1.9
1.9
2.0
2.5
a
The Mn, Mw, and Mw/Mn values were determined by GPC in THF and are reported
relative to polystyrene standards.
b
The abbreviations PAK, PEEK and PAEK refer to poly(amino aryl ketone), poly
(ether ether ketone), and poly(arylene ether ketone), respectively, and the Cz
percentages indicate percent composition of NH2eAreCz added to the copoly-
merization feed.
c
Molecular weight characteristics could not be determined due to limited solu-
bility in THF.
d
Determined by DSC.
Defined as the temperature at which 5% mass loss was observed, as determined
e
by TGA.
Fig. 4. UVevis absorption spectra of PAK-Cz (PAEK-Cz 100%), PAEK-Cz 80e20% and
PAEK (PAEK-Cz 0%) in CHCl3.
f
Heating rate ¼ 10 ꢀC minꢁ1; atmosphere ¼ N2.

1736
Z. Chen et al. / Polymer 52 (2011) 1731e1737
Fig. 5. UVevis absorption spectra of PAK-Cz (PEEK-Cz 100%), and PEEK-Cz 80e20% in
CHCl3.
Fig. 7. Fluorescence spectra of PAK-Cz (PEEK-Cz 100%), and PEEK-Cz 80e20% in
CHCl3.
content. While PAEK-Cz 0% (zero carbazole content) exhibited
good solubility in all of the solvents tested, the solubility of the
PAEK-Cz copolymers decreased as the percent composition of
carbazole increased. PAEK-Cz 20%, in particular, displayed good
solubility in a range of solvents, including CHCl3, dimethylaceta-
mide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethylformamide
(DMF), and tetrahydroduran (THF), and sturdy, transparent films of
this material were obtained via drop casting. In contrast, while
PEEK-Cz 0% was insoluble in most solvents except sulfuric acid, the
solubility of the copolymer increased with carbazole content.
Collectively, these results suggested to us that the solubility of the
PAEK-Cz and PEEK-Cz materials could be adjusted by varying the
feed ratios of the carbazole and dihydroxylated monomers used in
their respective syntheses.
The relatively high solubilities of the PAEK-Cz and PEEK-Cz
copolymers described above enabled analysis of their molecular
weights by gel permeation chromatography (GPC). As summarized
in Table 2, low molecular weights were measured for copolymers
having high carbazole content (i.e., PAEK-Cz 80e40%). These data
suggested to us that the introduction of bulky and conformationally
restrictive triarylamine units into the polymer main chains may
challenge the formation of high molecular weight material. Like-
wise, polymer molecular weight increased as the carbazole content
was reduced. As summarized in Tables 1 and 2, the molecular
weights of the copolymers qualitatively mirrored their respective
solubilities, with the most soluble polymers exhibiting the highest
molecular weights. For example, PEEK-Cz 60%, PEEK-Cz 40%, and
PAEK-Cz 20%, which were among the copolymers displaying the
highest solubilities in the solvents studied, also exhibited the
highest number average molecular weights (Mns). Presumably,
precipitation of poorly soluble polymers during the polymerization
reactions prevented further growth. In contrast, relatively soluble
polymers may remain in solution for longer periods of time,
enabling the formation of comparatively high molecular weight
polymers.
With a broad range of copolymers in hand, efforts shifted
toward examining the thermal properties of these materials by
differential scanning calorimetry (DSC) and thermogravimetric
analysis (TGA). As summarized in Table 2, the glass transition
temperatures (Tg) of the copolymers were measured in the range of
155e227 ꢀC, and increased with carbazole composition. For
example, PAK-Cz, which featured the highest carbazole content for
any of the copolymers analyzed, exhibited a high Tg (265 ꢀC). The
measured Tg values represented
a remarkable increase over
commercial PEEK or PAEK, which typically exhibit Tgs at 143 and
130 ꢀC, respectively [21]. The decomposition temperatures (Td),
defined as the temperature at which 5% mass loss was observed,
were also measured for the aforementioned copolymers and were
found to be greater than 469 ꢀC. In general, the PAEK-Cz series of
copolymers were less thermally stable than their PEEK-Cz analogs,
presumably due to the instability associated with the former’s
aliphatic isopropylidene linkages [22]. Overall, however, all of the
copolymers showed excellent thermal stabilities, indicating that
the thermal properties of these materials were not compromised
upon incorporation of the carbazole moieties.
Finally, to determine whether the optical properties inherent to
carbazole were retained upon incorporation into various copoly-
mers, the PAK-Cz and the series of PAEK-Cz and PEEK-Cz copoly-
mers were characterized by UVevis absorption and fluorescence
spectroscopies. As shown in Table 3, minimal variability was
observed in the UVevis absorption maxima of the copolymers in
Fig. 6. Fluorescence spectra of PAK-Cz (PAEK-Cz 100%), PAEK-Cz 80e20% and PAEK
(PAEK-Cz 0%) in CHCl3.

Z. Chen et al. / Polymer 52 (2011) 1731e1737
1737
chloroform, with all values falling within 5 nm of the optical
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Acknowledgment
This work was supported by the National Science Foundation of
China (50803025) and the Robert A. Welch Foundation (F-1621).