Synthesizing and characterization of comb-shaped carbazole containing copolymer via combination of ring opening polymerization and nitroxide-mediated polymerization

Article abstract of DOI:10.1016/j.polymer.2010.03.001

The macro-TEMPO agent (poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl), PGTEMPO) was synthesized by anion ring-opening polymerization (ROP) of 4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (GTEMPO) using potassium t-butoxide as the initiator

Full text of DOI:10.1016/j.polymer.2010.03.001

Polymer 51 (2010) 1947e1953
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Polymer
journal homepage: www.elsevier.com/locate/polymer
Synthesizing and characterization of comb-shaped carbazole containing
copolymer via combination of ring opening polymerization and
nitroxide-mediated polymerization
Cheng Chang, Jian Zhu, Zhengbiao Zhang, Nianchen Zhou, Zhenping Cheng, Xiulin Zhu*
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow (Suzhou) University, Suzhou 215123, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 October 2009
Received in revised form
The macro-TEMPO agent (poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl), PGTEMPO) was
synthesized by anion ring-opening polymerization (ROP) of 4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-
oxyl (GTEMPO) using potassium t-butoxide as the initiator. The comb-shaped copolymer, PGTEMPO-g-PVBK,
was prepared via nitroxide-mediated free radical polymerization (NMP) using PGTEMPO as macro-TEMPO
agent and 9-(4-vinylbenzyl)-9H-carbazole (VBK) as the monomer. The polymerizations showed character-
istics of “living”/controlled behavior. The optical properties, thermal analysis and electrochemical properties
of the comb-shaped copolymers were investigated. The fluorescence and ultraviolet intensity and cyclic
voltammetries of the comb-shaped copolymers with different molecular weight showed a regular order.
Ó 2010 Elsevier Ltd. All rights reserved.
3
February 2010
Accepted 1 March 2010
Available online 10 March 2010
Keywords:
Carbazole
Comb-shaped copolymer
NMP
1. Introduction
successfully polymerized under controlled manner via ATRP and
xanthate-mediated controlled radical polymerization [25e27]. The
Polymers containing carbazole structure have attracted much
attention because of their characteristic hole transporting and
electroluminescence properties [1e3]. These polymers have been
used in wide range of functional materials, such as in the electro
photographic process and in light-emitting, photorefractive and
photovoltaic devices [4]. To fabricate such polymers, carbazole can
be easily introduced into chain of the polymer via polymerization
of carbazole containing monomers by free radical polymerization,
ZieglereNatta initiators, charge transfer and electrochemical
RAFT polymerization of N-ethyl-3-vinylcarbazole was successfully
realized by Endo et al. [28].
Till now, the homopolymerization of N-vinylcarbazole via
typical nitroxide-mediated free-radical polymerization still showed
negative result by Fukuda et al. [29], whereas the copolymerization
of N-vinylcarbazole with styrene under the same conditions
proceeded in a living fashion. Register’s group investigated the
nitroxide-mediated free-radical polymerization of N-ethyl-2-
vinylcarbazole. The results showed key characteristics of a living
polymerization [30]. Our group previously reported successfully
polymerization of 9-(4-vinylbenzyl)-9H-carbazole (VBK) via nitro-
xide-mediated living free-radical polymerization [31]. The poly-
merizations were confirmed under typical controlled features by
the linear increase in the molecular weight with the monomer
conversion while keeping the relative narrow molecular weight
distribution, and successful chain extension with styrene. The
fluorescence intensity of the polymer was apparently influenced by
chromophore concentration, and the maximum value was obtained
processes, as well as by g-radiation [5e7]. With the convenience
and versatilities of free radical polymerization, a number of poly-
mers with pendant carbazolyl groups have been prepared,
including polymethacrylate [5,8,9], polyacrylate [10,11] and poly-
styrene derivatives [12]. To further control over the structure of the
polymers with controlled molecular weights and molecular weight
distributions, the “living”/controlled free-radical polymerization
(
LFRP), such as atom transfer radical polymerization (ATRP) [13,14],
reversible addition-fragmentation chain transfer (RAFT) polymer-
ization [15,16] and nitroxide-mediated free-radical polymerization
ꢁ
5
when the carbazole unit concentration was around 8 ꢀ 10 mol/L.
Moreover, it was shown that the strong fluorescence of PVBK can be
quenched by methyl acrylate (MA).
(
NMP) [17e24], has been also used. N-vinylcarbazole was
In this work, comb-shaped copolymer (PGTEMPO-g-PVBK) with
PVBK as the side chain and polyether as the main chain was
successfully synthesized via the combination of ring opening
*
Corresponding author. Fax: þ86 512 65112796.
E-mail address: xlzhu@suda.edu.cn (X. Zhu).
0
032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.03.001

1948
C. Chang et al. / Polymer 51 (2010) 1947e1953
polymerization and nitroxide-mediated free-radical polymeriza-
tion techniques. The introduction of polyether chain structure into
carbazole containing materials improved its film forming abilities.
The fluorescence, ultraviolet absorbance intensity, and the oxida-
tion and reduction potential of the comb-shaped copolymer with
different molecular weight exhibited a regular order.
2.3. Anionic ring-opening polymerization of the epoxy monomer
(GTEMPO)
The anionic ring-opening polymerization of GTEMPO was
carried out using following procedure: The 25 mL kettle was vac-
ꢂ
uumed at 100 C for 24 h and cooled to room temperature and then
ꢂ
to ꢁ20 C. GTEMPO (0.456 g, 2 mmol), THF (2 mL) and Potassium t-
butoxide THF solution (40 mL of 1 M solution, 0.04 mmol) were
2
. Experimental sections
introduced successively into the kettle under an argon atmosphere.
ꢂ
The mixture was stirred for 24 h at 75 C for polymerization. After
2.1. Materials
that, the content was dissolved in 5 mL tetrahydrofuran and
precipitated into 200 mL hexane. The precipitated polymer
4
-Hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (HO-TEMPO)
(PGTEMPO) was collected by filtration. It was further purified by
(
98%, from Wuxi Fuan Chemical Plant, China) was recrystallized
two cycles of dissolution in tetrahydrofuran and precipitation into
hexane to yield an orange powder.
from n-hexane. 4-Vinylbenzyl chloride (Aldrich, 90%) and dibenzoyl
peroxide (BPO) (Aldrich) were purified by crystallization from
ethanol. Carbazole (analytical reagent), ascorbic acid (VC) (99.7%)
and sodium hydroxide (NaOH) (analytical reagent) were all
purchased from Shanghai Chemical Reagent Co. Ltd. and used as
received. Methanol (commercially available) was used as received.
N, N-Dimethylformamide (DMF) (analytical reagent), chloroform
2.4. Preparation of 9-(4-vinylbenzyl)-9H-carbazole (VBK)
9-(4-Vinylbenzyl)-9H-carbazole (VBK) was synthesized
according to reference [31]. Carbazole (8.4 g, 50 mmol) was mixed
with NaOH (2 g, 50 mmol) in DMF (100 mL) under vigorous stir. 4-
Vinylbenzyl chloride (7.6 g, 50 mmol) was added dropwise at room
temperature. The reaction was allowed to stir at room temperature
for 24 h. The reaction content was poured into a large amount of
deionized water. The product was precipitated and collected by
(
3
CHCl ) (analytical reagent), and tetrahydrofuran (THF) (analytical
reagent) were all purchased from Shanghai Chemical Reagent Co.
Ltd. and purified via standard method before used. All other
reagents were used as received unless otherwise noted.
filtration. It was purified by recrystallization from acetone to give
1
white crystal (85%). H NMR (DMSO-d
6
, tetramethylsilane) (ppm):
]CH), 5.64 (2H, CH ), 6.64 (1H,
]CH), 7.34, 7.12, 8.17, 7.42, 7.19, 7.62 (12H, AreH). Element.
Anal.: Calcd for C21 17N (%): C, 89.01; H, 6.05; N, 4.94. Found (%): C,
8.69; H, 6.11; N, 5.15. HPLC (Waters 515) indicated that the purity
of VBK was above 98.5%.
2.2. Preparation of 4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-
d 5.71(1H, CH
CH
2
]CH), 5.17(1H, CH
2
2
oxyl (GTEMPO)
2
H
The monomer 4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-
oxyl (GTEMPO) was prepared according to reference [32] (Scheme 1).
Epichlorohydrin (10 mL, 120 mmol) and tetrabutylammonium
hydrosulfate (1.5 g, 4.6 mmol) was added to a sodium hydroxide
aqueous solution (16 mL, 50 wt%). The mixture was vigorously stirred
for 10 min. A solution of 4-hydroxy-2,2,6,6-tetramethylpiperidin-N-
oxy (4.12 g, 24 mmol) in tetrahydrofuran (30 mL) was added as
droplets into the mixture. It was vigorously stirred for 12 h at room
temperature and then poured into ice water (200 mL). The mixture
was extracted with ethyl acetate (50 mL). The organic solution was
washed with deionized water (30 mL) and then extracted with ethyl
acetate again. After that, the organic solution was dried by anhydrous
magnesium sulfate. The crude product was obtained after removing
solvent by rotary evaporation under vacuum. It was purified by
column chromatography on silica oxide with mixed petroleum ether
and ethyl acetate (8:1, v/v) as an eluent. After further recrystallized
from hexane, the TEMPO-radical containing epoxy monomer, 4-gly-
cidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (GTEMPO), was iso-
lated as a red solid (yield 80%). The purity was 98% by HPLC. Element.
8
2
.5. General procedure for polymerization of VBK
A typical polymerization procedure was as follows (Scheme 2):
a mixture of VBK (0.566 g, 2 mmol), BPO (3.7 mg, 0.015 mmol),
PGTEMPO (4.6 mg, 0.02 mmol GTEMPO group), and VC (4.6 mg,
0
.02 mmol), DMF (3 mL) was added to a dried ampoule ([VBK]
0
/
[BPO] /[GTEMPO] /[VC] 130/1/1.3/1.3). The mixture was
0
0
0
¼
bubbled with argon for 20 min to eliminate the dissolved oxygen.
The ampoule was flame-sealed, and then transferred into an oil
bath held by a thermostat at the desired temperature (123 C) to
polymerize. After the desired polymerization time, the ampoule
was cooled by immersing it into iced water. Afterwards, it was
opened and the contents were dissolved in THF (2 mL), and
precipitated into methanol (200 mL). The polymer obtained by
filtration was dried under vacuum until constant weight at 50 C.
The monomer conversion was determined gravimetrically.
ꢂ
ꢂ
Anal.: Calcd for C12
3
H22NO (%): C, 63.13; H, 9.71; N, 6.14. Found (%): C,
6
2.52; H, 9.63; N, 5.71.
2
.5.1. Characterizations
1H NMR spectra were recorded on an INOVA 400 MHz nuclear
magnetic resonance instrument, using CDCl
solvent and tetramethylsilane (TMS) as the internal standard. The
molecular weights (M s) and polydispersities (PDI) of the polymers
3 6
or DMSO-d as the
n
were determined with a Waters 1515 gel permeation chromatog-
rapher (GPC) equipped with refractive index detector, using HR1,
HR3, and HR4 column with molecular weight range 100e500,000
calibrated with PS standard samples. THF was used as the eluent at
ꢁ
1
ꢂ
a flow rate of 1.0 mL min operated at 30 C. Elemental analysis of
C, H, and N were measured with an EA1110 CHNO-S instrument.
The purity of products was determined on high-performance liquid
chromatography (HPLC, Waters 515 pump with 2996 PAD) using
ꢁ1
acetonitrile as eluent at a flow rate of 1.0 mL min operated at
30 C. The UV absorption spectra of the samples in chloroform
Scheme 1. The synthesis route of 4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl
GTEMPO).
ꢂ
(

C. Chang et al. / Polymer 51 (2010) 1947e1953
1949
Scheme 2. The preparation route of comb-shaped copolymer (PGTEMPO-g-PVBK).
(
CHCl
3
) solution were determined on a shimadzu-RF540 spectro-
was almost constant during the process of the polymerization.
However, the extrapolation of the kinetic line does not cross origin
point, which should be caused by the slow initiation. The evolution
of molecular weights measured by gel permeation chromatograph
(Mn(GPC)s) of the polymers with conversions shown linearly rela-
tionship as shown in Fig. 3. These results are similar to the typical
living free radical polymerization behavior. However, the PDI of the
obtained comb-shaped copolymers is a bit broad, e.g., 1.59e1.87,
which may due to the low efficiency termination of propagating free
radicals in the multi-TEMPO polymerization.
photometer at room temperature. Thermal analysis of the polymers
was performed by differential scanning calorimetry (DSC) using
a
TA instruments DSC2010 with a heating/cooling rate of
ꢂ
ꢁ1
1
0 C min under a continuous nitrogen flow. FT-IR spectra were
recorded on a Perkin-Elmer 2000 FT-IR spectrometer. Cyclic vol-
tammetries were performed on a CHI631B electrochemical work-
station at a constant scan of 0.1 V/s. Measurements were carried out
in a conventional three-electrode cell. The working electrode was
a Pt electrode and counter electrode was an argentum mesh. The
0
0
.1 mmol polymers were dissolved in 10 mL chloroform containing
.1 M tetra-n-butylammonium hexafluorophosphate ((n-Bu) NPF
4
6
)
3.3. Optical properties of PGTEMPO-g-PVBK
as the supporting electrolyte.
Carbazole containing polymers were well known as photo-
3
. Results and discussion
conduct materials. The resulting polymer, PGTEMPO-g-PVBK, was
characterized in terms of their optical properties. Fig. 4 depicts the
UVevis absorption spectra of the monomer (VBK) and polymers
3.1. The polymerization of the epoxy monomer (GTEMPO)
(
PGTEMPO-g-PVBK). Both the monomer and corresponding poly-
mers showed absorption peaks at 294, 331 and 345 nm. The peak at
295 nm should be attributed to the * transition of benzene
ring. Another two peaks at 330 nm and 345 nm are the charac-
teristic of * transition of carbazole molecules [34]. As shown in
Fig. 4, the UV absorbance intensity was decreased with the
increasing of molecular weights of the polymers, which may due to
interaction of neighboring carbazolyl chromophores in the poly-
mers. Additionally, it can be observed that the comb-shaped
copolymer exhibited strong fluorescence emission both in solution
and film (Fig. 5). The polymer showed the strong monomeric
In order to synthesize comb-shaped copolymer via NMP tech-
nique, the multiple TEMPO agents should be prepared firstly. Due to
the high reactive property of TEMPO with free radical, these kinds of
compounds were generally synthesized in the dormant state [33].
Nishide H. et. al. reported the synthesizing of unprotected multi-
TEMPO containingpolymer, PGTEMPO [32]. Following thereference,
the epoxy group was introduced into TEMPO analog by the reaction
of 4-hydroxy-2,2,6,6-tetramethylpiperidin-N-oxy with epichloro-
hydrin in the presence of a phase transfer agent in this paper. 4-
glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (GTEMPO) was
obtained in mild yield (80%) after purification. Then, GTEMPO was
polymerized by ring opening of epoxy group under the initiating of
potassium t-butoxide in THF to afford PGTEMPO. Three PGTEMPOs
pep
pep
Table 1
Characterizations of the comb-shaped copolymers, (PGTEMPO-g-PVBK), with
different molecular weights.
(
macro-TEMPO agent) with different molecular weight were
obtained (showed in Table 1).
Macro-
TEMPO
agent
Molar ratio [VBK]
[TEMPO] /[VC]
0
/[BPO]
0
/
PGTEMPO-g-PVBKb
0
0
3
.2. The preparation of the comb-shaped copolymer (PGTEMPO-
a
g-PVBK)
M
mol)
n
(g/
PDI
Conv.
(%)
M
(g/
n
PDI mc nc
The PGTEMPO contained TEMPO moieties was used as macro-
TEMPO agent to conduct controlled free radical polymerization of 9-
4-vinylbenzyl)-9H-carbazole (VBK) with pendent carbazole group
by molar ratios of [VBK]
/[BPO] /[GTEMPO] /[VC]
and 65:1:1.3:1.3. A serial of comb-shaped copolymers (PGTEMPO-g-
PVBK) with various molecular weights were obtained as shown in
Table 1. Fig. 1 showed GPC curves of the polyethers and the corre-
sponding comb-shaped copolymers. As shown in Fig. 2, the corre-
mol)
4
4
5
080
740
010
1.35 130:1:1.3:1.3
65:1:1.3:1.3
1.59 130:1:1.3:1.3
81.3
81.3
77.7
79.5
81.3
77.7
15100 1.74 17 2.3
12550 1.70 1.8
13700 1.84 20 1.6
10580 1.80 1.1
16510 1.73 21 1.9
10230 1.84 0.9
(
0
0
0
0
¼ 130:1:1.3:1.3
6
5:1:1.3:1.3
1.59 130:1:1.3:1.3
5:1:1.3:1.3
6
a
b
c
ꢂ
Where polymerizations were all carried out in 75 C for 24 h.
Where polymerizations were all carried out in 123 C for 8 h.
m, n (Scheme 2) value were calculated from Mn(GPC) by assuming equal length of
ꢂ
0
sponding plot of ln([M] /[M]) versus the polymerization time was
linear, which indicated that the propagating radical concentration
each side chain.

1950
C. Chang et al. / Polymer 51 (2010) 1947e1953
PGTEMPO-3
14000
4.0
3.8
3.6
PGTEMPO-2
13000
12000
11000
10000
PGTEMPO-g-PVBK-3
PGTEMPO-g-PVBK-2
PGTEMPO-1
Mn
3.4
PDI
3.2
3
2
2
2
2
2
1
1
.0
.8
.6
.4
.2
.0
.8
.6
9
000
PGTEMPO-g-PVBK-1
8000
7000
6000
5000
4000
3000
2000
1000
0
1.4
1.2
1.0
0
10
20
30
40
50
60
70
80
Conversion (
)
10
12
14
16
18
20
22
24
26
28
30
Fig. 3. Evolution of Mn(GPC) and PDI with monomer conversion for polymerization of
VBK. Polymerization conditions are same as in Fig. 2.
Elution time(min)
Fig. 1. Evolution of GPC traces of the polyethers (1: Mn(GPC) ¼ 4080 g/mol, PDI ¼ 1.35;
: Mn(GPC) ¼ 4740 g/mol, PDI ¼ 1.59; 3: Mn(GPC) ¼ 5010 g/mol, PDI ¼ 1.59) and the
correspond comb-shaped copolymers (1: Mn(GPC) ¼ 10,230 g/mol, PDI ¼ 1.84; 2: M
13,700 g/mol, PDI ¼ 1.84; 3: Mn(GPC) ¼ 17,860 g/mol, PDI ¼ 1.87).
analysis (TGA) measurements. The results were shown in Fig. 6 and
Table 2, respectively. The glass transition temperatures (T ) of
g
2
n
(GPC)
¼
macro-TEMPO agents, PGTEMPO-1w3, with molecular weights of
ꢂ
4
080, 4740 and 5010 were 15.4, 22.7 and 25.3 C and thermal
fluorescence at 350 nm and 365 nm together with weak excimer
fluorescence at longer wavelength in DMF solution at room
temperature (Fig. 5A) [31]. Meanwhile, only the excimer fluores-
cence at 412 nm and 435 nm was found in film condition (Fig. 5B)
ꢂ
decomposition temperature (T
d
) were 285.9, 294.4 and 306 C,
respectively. After grafted with VBK, the glass transition tempera-
tures and thermal decomposition temperatures of the comb-sha-
g
ped copolymers were observably improved. The T of PGTEMPO-g-
[35,36]. Furthermore, the fluorescence intensity of the comb-sha-
ꢂ
PVBK-1w3 was increased to 74.2, 81.5 and 94.1 C, respectively.
Thus, the introduction of VBK would greatly improve the T of the
ped copolymers in the solution was lower than that of VBK
monomer, which may be attributed to the polymerizable double
bond in VBK is relatively weakly electron-deficient. Similar results
were found in the VBK homopolymer system and N-ethyl-3-
vinylcarbazole system [31,37]. The results in Fig. 5 also showed that
fluorescence intensities of the comb-shaped copolymers had an
increase trend with the increasing molecular weights of the poly-
mers at the same concentration of VBK moiety. This should be the
increasing of excimer concentration in VBK side chain with the
increase of molecular weights of the polymers.
g
polymers, which should be caused by the rigid structure of carba-
ꢂ
zole in PGTEMPO-g-PVBK. The sharp peak in about 175 C in Fig. 6
should be the melting point of carbazole containing structures [38].
The introduction of carbazole moiety in PGTEMPO-g-PVBK also
improved the thermal stability of the polymers. There were two
decomposition stages in the TGA curves of PGTEMPO-g-PVBK
polymers (Fig. 6). One should be the decomposition of PGTEMPO
ꢂ
main chain, which showed the T
d
values at about 218 C. The other
one should be attributed to the decomposition of PVBK chain at the
ꢂ
range of 388e397 C with different molecular weights of PVBK
chains. The decomposition temperatures of PGTEMPO chain in
comb-shaped copolymers were lower than that of their
3.4. Thermal properties of the polymers
The thermal properties of the polymers were investigated by
differential scanning calorimetry (DSC) and thermogravimetric
3.0
1
1
1
1
0
0
0
0
0
.6
.4
.2
.0
.8
.6
.4
.2
.0
1
8
6
4
2
0
00
2
.5
0
2.0
1.5
PGTEMPO-g-PVBK-1
PGTEMPO-g-PVBK-2
VBK
0
1.0
PGTEMPO-g-PVBK-3
0
0.5
0
0.0
260
280
300
320
340
360
380
0
1
2
3
4
5
6
7
8
9
10
Wavelength(nm)
Time(h)
Fig. 4. UVevis absorption spectra of VBK and PGTEMPO-g-PVBK with different
molecular weights (1: Mn(GPC) ¼ 10,230 g/mol, PDI ¼ 1.84; 2: Mn(GPC) ¼ 13,700 g/mol,
Fig. 2. Relationship of ln([M]
0
/[M]) and monomer conversion with polymerization
time for the NMP of VBK in THF at 123 C. [VBK]
ꢂ
0
/[BPO]
¼ 4080, PDI ¼ 1.35.
0
/[GTEMPO]
0
/
PDI ¼ 1.84; 3:
M
n(GPC)
¼
17,860 g/mol, PDI ¼ 1.87) in CHCl
3
solution at room
ꢁ
5
[VC]
0
¼ 130:1:1.3:1.3 [VBK]
0
¼ 0.5 mol/L. PGTEMPO: M
n
temperature. The concentration of carbazole moieties was 5 ꢀ 10 M for all cases.

C. Chang et al. / Polymer 51 (2010) 1947e1953
1951
8
DSC
6
4
2
0
PGTEMPO-g-PVBK-2
PGTEMPO-g-PVBK-3
PGTEMPO-g-PVBK-1
50
100
Temperature °C
150
200
100
TGA
PGTEMPO-g-PVBK-2
PGTEMPO-g-PVBK-1
80
60
PGTEMPO-g-PVBK-3
40
20
0
0
100
200
300
400
500
600
Fig. 5. The fluorescence spectra of PGTEMPO-g-PVBK with different molecular weights
Temperature C
°
(
1: Mn(GPC) ¼ 10,230 g/mol, PDI ¼ 1.84; 2: Mn(GPC) ¼ 13,700 g/mol, PDI ¼ 1.84; 3: M
n
(
GPC) ¼ 17,860 g/mol, PDI ¼ 1.87) at room temperature with excitation wavelength of
5
2
94 nm. A: In DMF solution, the concentration of carbazole moieties is 5 ꢀ 10ꢁ M; B:
Fig. 6. DSC and TGA of PGTEMPO-g-PVBK (1: Mn(GPC) ¼ 10,230 g/mol, PDI ¼ 1.84; 2: M
(GPC) ¼ 13,700 g/mol, PDI ¼ 1.84; 3: Mn(GPC) ¼ 17,860 g/mol, PDI ¼ 1.87).
n
In film.
homopolymers, which may be attributed to the interaction of
neighboring side chain in the polymers.
donating and accepting abilities upon the increasing of PVBK chain
molecular weight, e.g., easy electron-accepting and hard electron-
donating ability with increasing of PVBK chain length. Similar trend
was observed in CV curves of 4-vinyl-benzylcarbazole (VBK)
homopolymers (the polymers were synthesized according to our
previously work [31]), which was shown in the inset figure within
Fig. 7. The increasing in molecular weight of polymers should
increase the charge carrier’s mobility within them [39], which
would evidently improve the electron-accepting ability of the
3.5. Electrochemical properties of the polymers
The redox behavior of the polymers was studied by cyclic vol-
tammetry (CV), using a three-electrode cell in an anhydrous chlo-
roform solution with (n-Bu) NPF as the support electrolyte. A Pt
4
6
wire was used as the counter electrode and Ag/AgCl (0.1 M) as the
reference electrode. The scans were performed at a scan rate of
Table 2
ꢁ1
5
0 mV s at room temperature. The spectra are shown in Fig. 7 and
)a and the thermal decomposition temperature
The glass transition temperature (T
g
b
d
the results are summarized in Table 3. PGTEMPO (Mn(GPC) ¼ 4740 g/
mol, PDI ¼ 1.59) exhibited chemical reversible oxidation and
reduction peaks of 0.62 V and 0.45 V which due to the free radical of
the TEMPO. The voltammetries of three comb-shaped copolymers
all showed the good reversible oxidation and reduction processes.
On anodic sweep, the oxidative peak potentials for PGTEMPO-g-
PVBK-1, PGTEMPO-g-PVBK-2 and PGTEMPO-g-PVBK-3 were 0.50,
(T ) of the polymers.
Polymer c
M
PDI
T
/ C
ꢂ
/ C
ꢂ
T
d
n,GPC
g
PGTEMPO-1
PGTEMPO-2
PGTEMPO-3
4080
4740
5010
10230
13,700
17,860
1.35
1.59
1.59
1.84
1.84
1.87
15.4
22.7
25.3
74.2
81.5
94.1
285.9
294.4
306.0
218.8, 388.9
218.5, 397.6
218.5, 392.7
d
PGTEMPO-g-PVBK-1
PGTEMPO-g-PVBK-2e
PGTEMPO-g-PVBK-3d
0
.54 and 0.59 V, respectively. The peak values of reductive poten-
a
tials for these three polymers were 0.46, 0.48 and 0.55 V, respec-
tively. The magnitude of oxidative and reductive potential is
considered to reflect the electron-donating and electron-accepting
ability of the structure. The results showed that these comb-shaped
polymers showed obvious regular changes in their electron-
The glass transition temperature.
The thermal decomposition temperature.
Three polymers were obtained in the same reaction temperature, the same
b
c
reactant feed molar ratio, and the different reaction time.
d
Polymers prepared using PGTEMPO-3 as the macro-TEMPO agent.
Polymers prepared using PGETEMO-2 as the macro-TEMPO agent.
e

1952
C. Chang et al. / Polymer 51 (2010) 1947e1953
-
6
7
6
5
4
3
2
1
.0x10
.0x10
.0x10
.0x10
.0x10
.0x10
.0x10
have high HOMO levels so that efficient hole injection should occur
-
6
-6
.0x10
from indium tin oxide (ITO) anodes (work function about 5.0 eV)
making them potentially efficient emissive and/or hole trans-
porting materials for electronic devices. Furthermore, the HOMO,
LUMO and band gap increased with the molecular weight of the
polymers [39]. Thus, these parameters of the polymers can be
adjusted by varying the molecular weights of the polymers. This
should be favorable to the application of these polymers in elec-
tronic devices.
3
PVBK-3
PVBK-2
-
6
-6
2.0x10
1.0x10
-6
PVBK-1
-6
0
.0
-6
-6
-
1.0x10
-6
-6
-
2.0x10
-6
0.0
0.2
0.4
0.6
0.8
0.0
PGTEMPO-g-PVBK-3
PGTEMPO-g-PVBK-2
PGTEMPO-g-PVBK-1
-
6
4. Conclusions
-
1.0x10
2.0x10
3.0x10
4.0x10
-
6
-
-
-
The comb-shaped copolymers (PGTEMPO-g-PVBK) with poly-
ether main chain and poly(4-vinyl-benzylcarbazole) (PVBK) side
chain were synthesized by combination of ring opening polymeri-
zation and nitroxide-mediated polymerization. The graft poly-
merization of VBK from macro-TEMPO showed typical controlled
free radical polymerization behaviors. These comb-shaped copol-
ymers had intensity fluorescence emission at 350 nm and 365 nm
under the excitation of 294 nm light. The glass transition temper-
atures and decomposition temperatures of PGTEMPO were
improved by grafted of PGTEMPO with VBK to obtain PGTEMPO-g-
PVBK. Reversible oxidation and reduction behavior of the polymers
was investigated by cyclic voltammetry. The highest occupied
molecular orbital (HOMO) and lowest unoccupied molecular orbital
(LUMO) energy levels accompanied with band gaps could be
adjustable via molecular weights of the polymers, which should be
favorable to the application of these polymers in electronic devices.
PGTEMPO
-
6
-
6
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Potential/V
Fig. 7. Cyclic voltammograms of the polyether (PGTEMPO, Mn(GPC) ¼ 4740 g/mol,
PDI ¼ 1.59), PVBK and the comb-shaped copolymer with different molecular weight
(
PVBK1: Mn(GPC) ¼ 9860 g/mol, PDI ¼ 1.14; PVBK2: Mn(GPC) ¼ 12530 g/mol, PDI ¼ 1.21;
PVBK3: Mn(GPC) ¼ 14980 g/mol, PDI ¼ 1.24; PGTEMPO-g-PVBK-1: Mn(GPC) ¼ 10230 g/
mol, PDI ¼ 1.84; PGTEMPO-g-PVBK-2: Mn(GPC) ¼ 13700 g/mol, PDI ¼ 1.84; PGTEMPO-g-
PVBK-3: Mn(GPC) ¼ 17860 g/mol, PDI ¼ 1.87) in CHCl
3
solution. The concentration of
repeating units is 5 ꢀ 10 M in room temperature containing 0.1 M tetra-n-buty-
ꢁ
4
lammonium hexafluorophosphate (n-Bu) NPF ) as the supporting electrolyte.
4
6
typical carbazole functionalized hole transportation materials.
However, the difference of electron accepting and donating abilities
among different molecular weight polymer was obviously enlarged
in comb-shaped PVBK based polymers. The reason should due to
the particular assembly behavior of comb-shaped copolymers [40],
Acknowledgments
which may favor for the
pep stacking structure formation in the
current comb-shaped copolymers.
The financial support from the National Nature Science Foun-
dation of China (No.20874069 and 50803044) and the Specialized
Research Fund for the Doctoral Program of Higher Education
contract grant (No.200802850005) are gratefully acknowledged.
This work was also sponsored by Qing Lan Project and Program of
Innovative Research Team of Soochow University.
The highest occupied molecular orbital (HOMO) energy levels of
the polymer materials can be calculated from the onset oxidation
ox
potential (Eonset) based on the reference energy level of ferrocene
(
4.8 eV below the vacuum level) [41]:
ox
HOMO ¼ Eonset þ 4:8 ꢁ EFoc
where in EFoc was the potential of Foc(ferrocene)/Foc þ vs. Ag/AgCl.
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