Effect of substituted groups on the living anionic polymerization of 2-vinylcarbazole derivatives

Article abstract of DOI:10.1016/j.polymer.2013.08.042

To study the effect of the substituents in the N-position of the carbazole on anionic polymerization, 2-vinylcarbazole derivatives of 9-butyl-2- vinylcarbazole (NBu2VCz), 9-phenyl-2-vinylcarbazole (NPh2VCz), and 9-(pyridin-2-yl)-2-vinylcarbazole (NPy2VCz) were synthesized. The anionic polymerization of NBu2VCz and NPh2VCz using s-BuLi was performed at -78 C with a 100% yield, but the polymerization of NBu2VCz showed a broader molecular weight distribution (M_w/M_n = 1.23) than NPh2VCz (M _w/M_n = 1.11). The anionic polymerization of NPy2VCz using s-BuLi and DPM-K had a yield below 5%. In particular, the living anionic polymerization of NPh2VCz with s-BuLi/styrene ([s-BuLi/St]₀ = 0.33) shows a narrower M_w/M_n. The block copolymerization of NPh2VCz with styrene, α-methylstyrene (α-MeSt), and 2-vinylpyridine (2VP) was achieved successfully. The resulting block copolymers of PNPh2VCz-b-P2VP with f_PNPh2VCz = 17.7, 34.6, 48.1, 62.4, and 82.9 were synthesized for investigation of living characteristics.

Full text of DOI:10.1016/j.polymer.2013.08.042

Polymer 54 (2013) 5615e5625
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Effect of substituted groups on the living anionic polymerization
of 2-vinylcarbazole derivatives
Nam-Goo Kang, Yoon-Hyung Hur, Mohammad Changez, Beom-Goo Kang, Yong-Guen Yu,
*
Jae-Suk Lee
Department of Nanobio Materials and Electronics, School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST),
123 Cheomdan-gwagiro, Buk-gu, Gwangju 500-712, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
To study the effect of the substituents in the N-position of the carbazole on anionic polymerization, 2-
vinylcarbazole derivatives of 9-butyl-2-vinylcarbazole (NBu2VCz), 9-phenyl-2-vinylcarbazole (NPh
2VCz), and 9-(pyridin-2-yl)-2-vinylcarbazole (NPy2VCz) were synthesized. The anionic polymerization of
NBu2VCz and NPh2VCz using s-BuLi was performed at ꢀ78 ꢁC with a 100% yield, but the polymerization
of NBu2VCz showed a broader molecular weight distribution (Mw/Mn ¼ 1.23) than NPh2VCz (Mw/
Mn ¼ 1.11). The anionic polymerization of NPy2VCz using s-BuLi and DPM-K had a yield below 5%. In
particular, the living anionic polymerization of NPh2VCz with s-BuLi/styrene ([s-BuLi/St]0 ¼ 0.33) shows
Received 19 May 2013
Received in revised form
9 August 2013
Accepted 16 August 2013
Available online 24 August 2013
Keywords:
a narrower Mw/Mn. The block copolymerization of NPh2VCz with styrene, a-methylstyrene (a-MeSt), and
Living anionic polymerization
Carbazole derivatives
Block copolymers
2-vinylpyridine (2VP) was achieved successfully. The resulting block copolymers of PNPh2VCz-b-P2VP
with fPNPh2VCz ¼ 17.7, 34.6, 48.1, 62.4, and 82.9 were synthesized for investigation of living characteristics.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
electronics. The carbazole-containing polymer is a representative
electron donor and it will be an electron donating block in ambi-
The polymers containing carbazole moieties have been widely
studied as an important functional material for organic electronics,
such as organic lighting emitting diodes (OLED), photovoltaic cells,
and transistors, because of their excellent hole-transportation and
photoconductivity. Various types of carbazole-containing polymers
with different structures such as i) polymers with a carbazole
moiety in the conjugated main chain, ii) polymers with a carbazole
moiety isolated from the conjugated main chain or non-conjugated
main chain, and iii) polymers with a carbazole group in the side
chain have been synthesized [1]. Currently, the control of device
behavior by adjusting the balance of holes and electrons is a key
issue for maximizing performance in organic electronics [2]. The
photophysical and electrical performance of devices based on
conducting polymer-casted films, such as carbazole, oxadiazole,
and thiophene polymers, are affected by aggregation and film
morphologies [3,4]. The synthesis of controlled block copolymers
consisting of electron donating and accepting blocks is very
important for the improvement of device performance by
self-assembly of block copolymers in the application of organic
polar block copolymer consisting of electron donating and
accepting blocks. Accordingly, the well-defined carbazole poly-
mers, as a representative hole-transporting material, need to be
synthesized by living polymerization.
In general, poly(N-vinylcarbazole) can be synthesized by radical,
cationic, zielger-natta, electrochemical polymerization as well as g-
radiation [1]. However, anionic polymerization of N-vinylcarbazole
(NVK) and its derivatives is difficult and complicated due to side
reactions. The anionic polymerization of NVK has not been
accomplished due to the high electron density in the NeCH]CH2
group caused by the presence of the strong electron donor nitrogen
atoms adjoining the vinyl group. Nevertheless, a few groups ach-
ieved successful anionic polymerization of NVK using the organo-
metallic lithium di-n-butylcuprate of R2CuLi [5] or tert-butyllithium
(t-BuLi) [6], but the molecular weight and molecular weight dis-
tribution were not controlled. In addition, there are some successful
anionic polymerizations of carbazole derivatives as reported pre-
viously in Chart 1.
To overcome the limitations of anionic polymerization of NVK
and to improve the electronic properties, different types of carba-
zole derivatives, based on methacrylate and styrene as a main
chain, were designed and synthesized. Anionic polymerizations of
methacrylate-based carbazole derivatives such as 2-(9-carbazolyl)
* Corresponding author. Tel.: þ82 62 715 2306; fax: þ82 62 715 2304.
E-mail address: jslee@gist.ac.kr (J.-S. Lee).
0032-3861/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2013.08.042

5616
N.-G. Kang et al. / Polymer 54 (2013) 5615e5625
ethylmethacrylate (CzMA) [7] and 2-(3-nitrocarbazolyl)ethyl
methacrylate (NCzMA) [8] were controlled using potassium naph-
thalide/1,1-diphenylethylene or diphenylmethyl potassium in the
presence of diethylzinc. The anionic polymerization of CzMA pro-
duced a narrow molecular weight distribution and living nature,
but the polymerization of NCzMA did not. The 9-acrylylcarbazole
[9] was synthesized by introducing a carbonyl group in the N-po-
sition of the carbazole between the vinyl and carbazole, and the
anionic polymerization using n-butyllithium was conducted in
toluene below 0 ꢁC. However, at most, 80% conversion was ach-
ieved, and living nature was not reported. The anionic polymeri-
zation of the carbazole-containing styrene derivatives 4-(9-
carbazolylmethyl)styrene [10] and 9-(4-vinyelphenyl)carbazole
[11] was performed successfully with quantitative yields, but they
were not completely controlled, resulting in a broad molecular
weight distribution. Recently, poly(9-(4-vinylphenyl)carbazole)-b-
poly(2-vinylpyridine) [11] and poly(2-(9-carbazolyl)ethyl methac-
rylate) end-capped with fullerene [7c] were utilized for studying
nonvolatile switching characteristics, and both demonstrated
excellent non-volatile memory characteristics.
The fused-styrene types of carbazole derivatives, N-ethyl-2- and
N-ethyl-3-vinylcarbazole, were designed by introducing a vinyl
group directly into the phenyl moiety of the carbazole and
substituting an ethyl group into the N-position of the carbazole, and
their anionic polymerizations were successfully performed [12]. The
anionic polymerization of N-ethyl-2-vinylcarbazole showed a living
nature, controlled molecular weight, and narrow polydispersity.
However, the living characteristics of poly(N-ethyl-3-vinylcarbazole)
during anionic polymerization were deteriorated gradually due to
the low stability of the carbanion. Recently, the successful conditions
of the anionic polymerization of poly(9-phenyl-2-vinylcarbazole)
(PNPh2VCz) were used for the synthesis of well-defined ambipolar
block copolymers of PNPh2VCz/(2-phenyl-3-(3-(4-(1-phenylvinyl)
phenyl)propoxy)pyridine)(2-phenyl pyridi- ne)2iridium-b-poly(2-
phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole) with controlled
molecular weights (MW) and narrow molecular weight distribution
(MWD) [13]. However, the anionic polymerization of 9-phenyl-2-
vinylcarbazole (NPh2VCz) was not investigated for complete char-
acterization and nucleophilicity by block copolymerization with
The possibility of anionic polymerization of each carbazole de-
rivative (a)e(c) was studied using various initiators such as alkyl
lithium (n-BuLi or s-BuLi), s-BuLi/styrene, and DPM-K in THF
at ꢀ78 ꢁC in order to control Mn and Mw/Mn. Among the three
carbazole derivatives, the block copolymerization of NPh2VCz with
various vinyl monomers was performed to investigate the living
nature and reactivity.
2. Experimental section
2.1. Materials
Phenyl boronic acid (Boron Molecular, >97%), 4-chloro-3-
nitrobenzaldehyde (TCI, >95%), K2CO3 (Aldrich, 99%), tetrakis (tri-
phenyl phosphine) palladium(0) (Pd(PPh3)4, Aldrich), anhydrous
toluene (Aldrich, 99.8%), triphenyl phosphine (Aldrich, 99%), anhy-
drous 1,2-dichlorobenzene (Aldrich, 99%), bromobenzene (Aldrich,
>99%), copper (Aldrich, 99%, powder), nitrobenzene (Aldrich, 99%),
methyl triphenyl phosphonium bromide (Aldrich, 98%), potassium
tert-butoxide solution (Aldrich, 1.0 M in tetrahydrofuran), 1-
bromobutane (Aldrich, 99%), sodium hydroxide (Aldrich, >98%,
pellets), tetraoctylammonium bromide (Aldrich, >98%), acetone
(Aldrich, >99.9%), and 2-bromopyridine (Aldrich, 99%) were used as
received. s-BuLi (Aldrich, 1.4 M in cyclohexane) and n-BuLi (Aldrich,
2.0 M in cyclohexane) were used as received, and diphenylmethyl
potassium (DPM-K) was prepared by the reaction of 1,1-
diphenylmethane (DPM) and naphthalenide potassium (Naph-K)
prepared with naphthalene and potassium in THF at room tem-
perature for 2 days [14]. All initiators were stored at ꢀ30 ꢁC in
ampoules equipped with break-seals. Styrene (St, Aldrich, 99.9%),
a-
methylstyrene ( -MeSt, Aldrich, 99%), and 2-vinylpyridine (2VP,
a
Aldrich, 97%) were passed through an alumina column, dried for
24 h over anhydrous CaH2, and distilled under reduced pressure.
Tetrahydrofuran (THF, Fisher, GR grade) was distilled under N2 after
refluxing with sodium for 5 h.
2.2. Synthesis of monomer
2.2.1. Synthesis of 4-formyl-2-nitrobiphenyl and 9H-carbazole-2-
carbaldehyde
other vinyl monomers such as styrene,
a-methylstyrene, and 2-
vinylpyridine. Additionally, the effect of various substituents in the
N-position of the carbazole on the anionic polymerization of the 2-
vinylcarbazole derivative could not be reported.
For the synthesis, purification, and characterization, we fol-
lowed the previously reported work [15].
In this study, we focus on overcoming the limits of the anionic
polymerization of NVK caused by the high electron density of ni-
trogen atoms and on investigating the effect of different sub-
stituents on the anionic polymerization of carbazole derivatives.
The investigated substituents included butyl as an alkyl, phenyl as
an aryl, and pyridyl as a heteroatom group at the nitrogen of the
carbazole. The monomers (a) 9-butyl-2-vinylcarbazole (NBu2VCz),
(b) 9-phenyl-2-vinylcarbazole (NPh2VCz), and (c) 9-(pyridin-2-yl)-
2-vinylcarbazole (NPy2VCz) were synthesized, as shown in Fig. 1.
2.2.2. Synthesis of 2-vinyl-9H-carbazole
A solution of potassium tert-butoxide (72.0 ml, 72.0 mmol, 1.0 M
in tetrahydrofuran) was added slowly to a solution of methyl tri-
phenyl phosphonium bromide (31.0 g, 87.0 mmol) in THF (100 ml)
under a nitrogen atmosphere at 25 ꢁC, and the mixture was allowed
to react with constant stirring for 3 h. The 9H-carbazole-2-
carbaldehyde (10.9 g, 55.7 mmol) was dissolved in THF (50 ml)
and added slowly to the mixture of methyl triphenyl phosphonium
and potassium tert-butoxide in THF at 0 ꢁC, and the mixture was
Fig. 1. The structure of three different 2-vinylcarbazole derivatives: (a) 9-butyl-2-vinylcarbazole (NBu2VCz), (b) 9-phenyl-2-vinylcarbazole (NPh2VCz) [13], and (c) 9-(pyridin-2-yl)-
2-vinylcarbazole (NPy2VCz).

N.-G. Kang et al. / Polymer 54 (2013) 5615e5625
5617
stirred for 12 h. The reaction was quenched with 2 N HCl and
extracted with ether. The organic layer was washed with H2O three
times and dried over anhydrous Na2SO4. After removing the solvent
by evaporation, the crude product was purified by column chro-
matography on silica gel with hexane/ethyl acetate ¼ 9/1 and then
recrystallized from methanol to provide 2-vinyl-9H-carbazole
(7.50 g, 69.7% yield) as a brown solid. 1H NMR spectra (CDCl3,
hexane and hexane/ethyl acetate ¼ 9/1 to provide 9-phenyl-2-
vinylcarbazole (7.84 g, 54.8% yield) as a yellowish viscous liquid.
1H NMR spectra (CDCl3, 400 MHz),
d
(ppm): 8.09 (q, 2H), 7.6 (m,
4H), 7.48 (t, 1H), 7.38 (t, 4H), 7.7 (m, 1H), 6.82 (q, 1H), 5.81 (d, 1H),
5.25 (d, 1H). 13C NMR (CDCl3, 100 MHz),
(ppm): 141.4, 141.2, 137.5,
d
135.7, 129.9,127.5, 127.2, 125.9,123.1,120.3,120.0,118.3, 113.4, 109.7,
107.6. Element Anal. Calc. for C20H15N: C, 89.19; H, 5.61; N, 5.20%.
Found: C, 89.07; H, 5.64; N, 5.29%. m/z (EI) 268.90 (Mþ).
400 MHz),
d (ppm): 8.02 (q, 2H), 8.07 (s, 1H), 7.44 (d, 3H), 7.39 (d,
1H), 7.25e7.20 (m,1H), 6.86 (q,1H, vinyl), 5.84 (d,1H, vinyl), 5.28 (d,
1H, vinyl). m/z (EI) 193.10 (Mþ).
2.2.6. Synthesis of 9-(pyridin-2-yl)carbazole-2-carbaldehyde
A mixture of 9H-carbazole-2-carbaldehyde (7.6 g, 38.9 mmol),
2-bromopyridine (12.3 g, 78.0 mmol), copper (Cu) (0.4 g, 6.3 mmol),
and potassium carbonate (K2CO3) (8.1 g, 58.0 mmol) in nitroben-
zene (150 ml) was reacted under nitrogen atmosphere at 180 ꢁC for
48 h. After complete reaction, the mixture was cooled and filtered.
Nitrobenzene and 2-bromopyridine were removed by distillation
under reduced pressure. The resulting mixture was extracted with
dichloromethane and H2O, washed with H2O three times, and dried
over anhydrous Na2SO4. After concentration of the crude product,
column chromatography on silica gel with dichloromethane gave
9-(pyridin-2-yl)carbazole-2-carbaldehyde (9.40 g, 88.7% yield). 1H
2.2.3. Synthesis of 2-vinyl-9-butylcarbazole
To the mixture of 2-vinyl-9H-carbazole (3.80 g, 19.7 mmol),
tetraoctylammonium bromide (0.34 g, 3 mol%), and sodium hy-
droxide (1.57 g, 39.3 mmol) in acetone (100 ml), 1-bromobutane
(4.45 ml, 41.4 mmol) was added under nitrogen atmosphere at
25 ꢁC. The mixture was reacted at 50 ꢁC until the complete con-
sumption of 2-vinyl-9H-carbazole. After the reaction, the solution
was filtered, extracted with dichloromethane and H2O, washed
with H2O three times, and dried over anhydrous Na2SO4. After
concentration of the crude product, column chromatography on
silica gel with hexane gave 2-vinyl-9-butylcarbazole (4.80 g, 93.0%
yield) as a yellow viscous liquid. 1H NMR spectra (CDCl3, 400 MHz),
NMR spectra (CDCl3, 400 MHz),
8.37 (s, 1H), 8.25 (d, 1H), 8.19 (d, 1H), 8.0 (t, 1H), 7.86 (q, 2H), 7.67 (d,
1H), 7.55 (t, 1H), 7.38 (m, 2H). 13C NMR (CDCl3, 100 MHz),
(ppm):
d (ppm): 10.1 (s, 1H), 8.78 (d, 1H),
d
(ppm): 8.03 (q, 2H), 7.47e7.33 (m, 4H), 7.22 (t, 3H), 6.92 (q, 1H,
vinyl), 5.85 (d, 1H, vinyl), 5.28 (d, 1H, vinyl), 4.30 (t, 2H), 1.86 (m,
2H), 1.42 (m, 2H), 0.95 (t, 3H). 13C NMR (CDCl3, 100 MHz),
(ppm):
d
192.4, 151.1, 149.9, 141.2, 139.4, 138.8, 134.4, 129.4, 128.0, 122.5,
121.9, 121.5121.3, 120.5, 119.2, 113.1, 111.4. Element Anal. Calc. for
d
141.0, 140.8, 137.9, 135.3, 125.6, 122.7, 120.3, 118.8, 117.2, 113.1, 108.7,
106.6, 42.8, 31.1, 20.6, 13.9. Element Anal. Calc. for C18H19N: C,
86.70; H, 7.68; N, 5.62%. Found: C, 86.25; H, 7.81; N, 5. 94%. m/z (EI)
249.00 (Mþ).
C18H12N2O: C, 79.39; H, 4.44; N, 10.29; O, 5.88%. Found: C, 79.12; H,
4.65; N, 10.99; O, 5.24%. m/z (EI) 272.0 (Mþ).
2.2.7. Synthesis of 9-(pyridin-2-yl)-2-vinylcarbazole
A solution of methyl triphenyl phosphonium bromide (24.1 g,
67.5 mmol) in THF (100 ml) under nitrogen atmosphere was added
slowly to a potassium tert-butoxide solution (81.0 ml, 81.0 mmol,
1.0 M in tetrahydrofuran) at 25 ꢁC, and the mixture was allowed
to react with constant stirring for 3 h. 9-phenylcarbazole-2-
carbaldehyde (9.20 g, 33.8 mmol) dissolved in THF (50 ml) was
added slowly to the mixture of methyl triphenyl phosphonium and
potassium tert-butoxide in THF at 0 ꢁC, and the mixture was stirred
for 12 h. The reaction was quenched with 2 N HCl and extracted
with dichloromethane. The organic layer was washed with water
three times and dried over anhydrous Na2SO4. After removing the
solvent by evaporation, the crude product was purified by column
chromatography on silica gel with dichloromethane to provide 9-
(pyridin-2-yl)-2-vinylcarbazole (8.0 g, 87.5% yield) as a yellowish
2.2.4. Synthesis of 9-phenylcarbazole-2-carbaldehyde
The mixture of 9H-carbazole-2-carbaldehyde (11.2 g,
57.0 mmol), bromobenzene (12.0 ml, 114.0 mmol), copper (Cu)
(0.6 g, 9.4 mmol), and potassium carbonate (K2CO3) (11.8 g,
86.0 mmol) in nitrobenzene (220 ml) was reacted under nitrogen
atmosphere at 180 ꢁC for 48 h. After complete reaction, the solution
was cooled and filtered. The nitrobenzene was removed by distil-
lation under reduced pressure, extracted with dichloromethane
and H2O, washed with H2O three times, and dried over anhydrous
Na2SO4. After concentration of the crude product, column chro-
matography on silica gel with dichloromethane gave 9-phenyl
carbazole-2-carbaldehyde (14.4 g, 93.2% yield). 1H NMR spectra
(CDCl3, 400 MHz),
1H), 7.76 (dd,1H), 7.58 (t, 2H), 7.51e7.43 (m, 4H), 7.37 (d,1H), 7.30 (t,
1H). 13C NMR (CDCl3, 100 MHz),
(ppm): 192.36, 142.59, 140.56,
d (ppm): 10.03 (s, 1H), 8.21e8.14 (dd, 2H), 7.87 (s,
viscous liquid. 1H NMR spectra (CDCl3, 400 MHz),
d (ppm): 8.7 (d,
d
1H), 8.05 (q, 2H), 7.85 (m, 2H), 7.74 (d, 1H), 7.58 (d, 1H), 7.41 (t, 2H),
136.81, 134.12, 130.10, 128.39, 128.03, 127.81, 127.08, 122.27, 121.63,
121.29, 120.60, 120.56, 111.36, 110.20. Element Anal. Calc. for
7.26 (m, 2H), 6.83 (q, 1H), 5.78 (d, 1H), 5.24 (d, 1H). 13C NMR (CDCl3,
100 MHz),
d (ppm): 151.6, 149.6, 139.9, 138.4, 137.6, 135.9, 126.1,
C
19H13NO: C, 84.11; H, 4.83; N, 5.16; O, 5.90%. Found: C, 84.47; H,
124.0, 121.2, 120.9, 120.1, 119.2, 119.0, 113.3, 111.0, 109.0. Element
Anal. Calc. for C19H14N2: C, 84.42; H, 5.22; N, 10.36%. Found: C,
84.11; H, 5.31; N, 10.58%. m/z (EI) 270.0 (Mþ).
4.26; N, 5.78; O, 5.49%. m/z (EI) 271.00 (Mþ).
2.2.5. Synthesis of 9-phenyl-2-vinylcarbazole
A solution of potassium tert-butoxide solution (127.0 ml,
127.0 mmol, 1.0 M in tetrahydrofuran) was added slowly to a so-
lution of methyl triphenyl phosphonium bromide (37.9 g,
87.0 mmol) in THF (120 ml) under nitrogen atmosphere at 25 ꢁC,
and the mixture was allowed to react with constant stirring for 3 h.
9-phenylcarbazole-2-carbaldehyde (14.4 g, 53.1 mmol) dissolved in
THF (50 ml) was added slowly to the mixture of methyl triphenyl
phosphonium bromide and potassium tert-butoxide in THF at 0 ꢁC,
and the mixture was stirred for 12 h. The reaction was quenched
with 2 N HCl and extracted with dichloromethane. The organic
layer was washed with H2O three times and dried over anhydrous
Na2SO4. After removing the solvent by evaporation, the crude
product was purified by column chromatography on silica gel with
2.3. Anionic polymerization
2.3.1. Living anionic polymerization of NPh2VCz with n- or s-BuLi
The anionic polymerization of NPh2VCz in THF was conducted
under high vacuum conditions (10ꢀ6 mmHg) at ꢀ78 ꢁC in a glass
apparatus equipped with break-seals, in the typical method.
NPh2VCz and initiators were prepared and divided in THF under
reduced vacuum conditions. n-BuLi or s-BuLi in heptane was
transferred into the reaction flask, and the solution was stabilized
at ꢀ78 ꢁC. NPh2VCz in THF was added to the initiator solution,
polymerized at ꢀ78 ꢁC, and terminated with methanol. After
termination, the polymers were precipitated in excess methanol,
dried, dissolved in benzene, and freeze-dried.

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N.-G. Kang et al. / Polymer 54 (2013) 5615e5625
2.3.2. Living anionic polymerization of NB2VCz and NPy2VCz with
s-BuLi
apparatus equipped with break-seals, in the typical method.
NPy2VCz and initiators were prepared and divided in THF under
reduced vacuum conditions. DPM-K in THF was transferred into the
reaction flask, and the solution was stabilized at ꢀ78 ꢁC. NPy2VCz
in THF was added to the initiator solution, polymerized at ꢀ78 ꢁC,
and terminated with methanol. After termination, the polymers
were precipitated in excess methanol, dried, dissolved in benzene,
and freeze-dried.
The anionic polymerization of NB2VCz and NPy2VCz with s-BuLi
in THF was performed under high vacuum conditions (10ꢀ6 mmHg)
at ꢀ78 ꢁC, following the procedure of the living anionic polymeri-
zation of NPh2VCz with s-BuLi. After polymerization, purification
was conducted as described above.
2.3.3. Living anionic polymerization of NPh2VCz with s-BuLi/
styrene
2.4. Block copolymerization
s-BuLi in heptane was transferred into the reaction flask, and the
solutionwas stabilized at ꢀ78 ꢁC. The initiation system, using a mole
ratio of styrene in THF and s-BuLi in heptane (3:1), was prepared by
living anionic polymerization at ꢀ78 ꢁC for 30 min and was used for
the anionic polymerization of NPh2VCz at ꢀ78 ꢁC for 110 min. The
reaction was terminated with methanol. After polymerization, pu-
rification was performed as described above. The polymers were
characterized by NMR and SEC. NPh2VCz (MW: 20,100 g/mol, MWD:
1.05, Table 1, Run 5) Tg: 186.2 ꢁC. Td: 389.3 ꢁC.1H NMR spectra (CDCl3,
2.4.1. Block copolymerization of NPh2VCz with a-MeSt
The initiator, s-BuLi, was transferred to the reactor, and the so-
lution was stabilized at ꢀ78 ꢁC. Styrene in THF ([s-BuLi]/[St] ¼ 0.33)
was introduced to prepare the initiator of s-BuLi/St. The NPh2VCz
was introduced into the initiation solution at ꢀ78 ꢁC and poly-
merized for 40 min. Before the addition of a-MeSt, a portion of the
living PNPh2VCz was withdrawn to an attached receiver for the
characterization of the homopolymer. Sequentially, -MeSt was
a
400 MHz),
and carbazole of NPh2VCz), 6.5e5.7 (carbazole of NPh2VCz), 2.5e1.6
(eCHeCH2e of main chain),1.5e0.8 (eCHeCH2e of main chain). 13
NMR (CDCl3, 100 MHz), (ppm): 141.1e139.8, 137.6e136.9, 129.8e
d
(ppm): 8.1e7.5 (carbazole of NPh2VCz), 7.5e6.5 (phenyl
added as the second monomer into the living PNPh2VCz solution,
the copolymerization was conducted at ꢀ78 ꢁC for 30 min, and the
reaction was terminated with methanol. After polymerization,
purification was performed as described above.
C
d
128.9, 127.1e125.9, 125.4e124.7, 123.6e123.1, 121.5e120.8, 120.4e
118.7, 110.2e109.2, 45.0e38.5.
2.4.2. Block copolymerization of 2VP with NPh2VCz
The initiator DPM-K was transferred to the reactor, and the so-
lution was stabilized at ꢀ78 ꢁC. The 2VP was introduced into the
initiation solution at ꢀ78 ꢁC and was polymerized for 30 min.
Before the addition of NPh2VCz, a portion of the living 2VP was
withdrawn to an attached receiver for the characterization of the
homopolymer. Sequentially, NPh2VCz was added as the second
monomer into the living 2VP solution, the copolymerization was
conducted at ꢀ78 ꢁC for 40 min, and the reaction was terminated
with methanol. After polymerization, purification was performed
as described above.
2.3.4. Living anionic polymerization of NB2VCz and NPy2VCz with
s-BuLi/styrene
The anionic polymerization of NB2VCz and NPy2VCz with s-
BuLi/Styrene in THF was conducted under high vacuum conditions
(10ꢀ6 mmHg) at ꢀ78 ꢁC, following the procedure of the living
anionic polymerization of NPh2VCz with s-BuLi. After polymeri-
zation, purification was performed as described above.
2.3.5. Living anionic polymerization of nPy2VCz with DPM-K
The anionic polymerization of NPy2VCz in THF was conducted
under high vacuum conditions (10ꢀ6 mmHg) at ꢀ78 ꢁC in a glass
2.4.3. Block copolymerization of NPh2VCz with 2VP
The initiator, s-BuLi, was transferred to the reactor, and the so-
lution was stabilized at ꢀ78 ꢁC. Styrene in THF ([s-BuLi]/[St] ¼ 0.33)
was introduced to prepare the initiator of s-BuLi/St. The NPh2VCz
was introduced into the initiation solution at ꢀ78 ꢁC and poly-
merized for 40 min. Before the addition of 2VP, a portion of the
living PNPh2VCz was withdrawn to an attached receiver for the
characterization of the homopolymer. Sequentially, 2VP was added
as the second monomer into the living PNPh2VCz solution, the
copolymerization was conducted at ꢀ78 ꢁC for 30 min, and the
reaction was terminated with methanol. After polymerization,
purification was performed as described above. The polymers were
characterized by NMR and SEC. 1H NMR spectra (CDCl3, 400 MHz),
Table 1
Living anionic polymerization of NBu2VCz, NPh2VCz, and NPy2VCz with various
initiators in THF at ꢀ78 ꢁC.
Initiator (I) Carbazole
derivatives (M)
M/I
Time Polymer
Yield (%)
Mn ꢂ 10ꢀ3
Mw/Mnb
Mmol
mmol
mmol min Calcda Obsdb
n-BuLi
0.044
s-BuLi
0.039
NPh2VCz
1.62
1
2
36.82 60
33.33 30
9.9
9.0
4.3
9.5 1.19
100
100
1.30
8.7 1.11
3.9 1.06
s-BuLi/St
3
4
5
6
0.079/0.15 1.27
0.038/0.13 1.32
0.017/0.15 1.20
0.026/0.17 3.22
16.08 70
34.74 70
70.59 70
123.85 70
100
100
100
100
d
(ppm): 8.5e8.1 (pyridine of 2-vinylpyridine), 7.9e7.5 (carbazole of
9.4 10.8 1.06
19.8 20.1 1.05
33.4 31.4 1.07
NPh2VCz), 7.5e6.6 (pyridine of 2-vinylpyridine and phenyl and
carbazole of NPh2VCz), 6.6e5.7 (pyridine of 2-vinylpyridine and
carbazole of NPh2VCz), 2.6e1.2 (eCHeCH2e of main chain of 2-
vinylpyridne), 2.2e0.9 (eCHeCH2e of main chain of carbazole
s-BuLi
NBu2VCz
1.92
7
8
9
0.095
s-BuLi/St
0.035/0.11 1.54
s-BuLi
20.21 40
44.00 70
33.77 60
23.28 70
61.47 60
5.1
7.4 1.23
100
100
e
and 2-vinylpyridne). 13C NMR (CDCl3, 100 MHz),
d (ppm): 164.6e
11.3 15.2 1.27
163.6, 149.8e148.2, 141.1e140.1, 137.6e136.7, 136.1e134.7, 129.5e
128.9, 126.9e125.9, 125.1e124.5, 123.8e122.4, 121.3e118.8, 109.9e
109.1, 45.1e38.4.
NPy2VCz
1.79
0.053
9.1
6.6
e
e
e
e
s-BuLi/St
10 0.061/0.21 1.42
DPM-K
e
2.5. Characterizations
11 0.034
2.09
16.6 37.1 1.63
5
a
Mn (calcd) ¼ (MW of 2-vinylcarbazole derivatives) ꢂ [2-vinylcarbazole de-
rivatives]/[Initiator] ꢂ yield of polymers (%).
The molecular weights (MW) of the polymers were estimated
using size exclusion chromatography (SEC, Waters M 77251, M 510)
with four columns (HR 0.5, HR 1, HR 3, and HR 4, Waters Styragel
columns run in series). The pore sizes of the columns were 50, 100,
b
Mn (observed) and Mw/Mn were obtained by SEC calibration using a polystyrene
standard in tetrahydrofuran (THF) containing 2% triethylamine (C2H5)3N as an
eluent at 40 ꢁC.

N.-G. Kang et al. / Polymer 54 (2013) 5615e5625
5619
103, and 104 Å, respectively, with a refractive index detector at a
3.2. Effect of substitutes on the anionic polymerization of NBu2VCz,
flow rate of 1.0 ml/min using THF containing 2% (C2H5)3N as the
elution solvent at 40 ꢁC and calibrated with styrene standards
(American Polymer Standards Corp.). The 1H and 13C NMR spectra
(JEOL JNMLA400WB) were measured using CDCl3 as the solvent.
The chemical shifts were referenced to tetramethylsilane (TMS) at
0 ppm. The thermal properties were characterized using ther-
mogravimetric analysis (TGA, TA-2050) and differential scanning
calorimetry (DSC, TA2010) at 10 ꢁC/min. The absorption
spectra were measured using a UV/Vis spectrophotometer (Varian
spectrometer, Carry1E). The photoluminescence (PL) spectra
were characterized using a Hitachi F-7000 fluorescence spectro
photometer.
NPh2VCz, and NPy2VCz
The results of the anionic polymerization of NBu2VCz, NPh2VCz,
and NPy2VCz in THF using s-BuLi at ꢀ78 ꢁC are shown in Table 1. In
the anionic polymerization of NBu2VCz and NPh2VCz by s-BuLi
at ꢀ78 ꢁC, the solution maintained a purple color during initiation
and propagation. After termination with methanol, white solid
polymers were obtained with 100% yield by precipitation in excess
methanol (Table 1, Run 2 and 9). However, in the anionic poly-
merization of the pyridine-substituted NPy2VCz, the initiated so-
lution was red and quickly changed to orange due to the side
reaction of the carbanion of NPy2VCz initiated with s-BuLi (Table 1,
Run 9). In general, the anionic polymerization of pyridine-
containing monomers such as 2- or 4-vinylpyridine and 2-(4-
vinylphenyl)pyridine using alkyl lithium as an initiator under-
went the side reaction wherein the strong nucleophilicity of s-BuLi
and the living polymer end make an amine anion (Nꢀ) from the
pyridine moiety as reported previously [17].
2.6. Measurement of TEM images
The each block copolymer of PNPh2VCz-b-P2VP with 9-phenyl-
2-vinylcarbazole volume fraction of fPNPh2VCz ¼ 17.7, 34.6, 48.1, 62.4,
and 82.9 as 2VB01, 2VB02, 2VB03, 2VB04, and 2VB05, respectively
was dissolved in THF at concentration of 2.0 mg/ml. This resulting
solution was stirred for 24 h at 25 ꢁC. For TEM measurement, TEM
samples were prepared on 400 mesh carbon-coated copper grid by
drop-coating and annealed at 240 ꢁC under reduced pressure
(10ꢀ1 mmHg) for 24 h. In order to improve the contrast of TEM
images, P2VP blocks in PNPh2VCz-b-P2VP were selectively stained
by I2 vapor for 10 h. TEM images of block copolymers were obtained
at an acceleration voltage of 120 kV, using high resolution-
transmission electron microscopy (HR-TEM, JEOL JEM-2100) for
the study of microphase separation.
3.3. Effect of initiators on the anionic polymerization of NBu2VCz,
NPh2VCz, and NPy2VCz
The anionic polymerization of NPh2VCz was conducted with n-
BuLi, s-BuLi, and s-BuLi/styrene as summarized in Table 1, Run 1e6,
and shown in Scheme 2. All initiation systems using n-BuLi, s-BuLi,
and s-BuLi/styrene gave quantitative yields within 70 min, but the
Mw/Mn was controlled differently depending on the initiator, n-BuLi
(1.19), s-BuLi (1.08), and s-BuLi/styrene (1.05) [13].
3. Results and discussion
The degree of aggregation in solution and the relative reactivity
of the various alkyl lithium compounds as initiators for the anionic
polymerization of styrene play a decisive role in anionic polymer-
ization. Specifically, the less associated alkyllithiums are more
reactive as initiators in this order: methyllithium > s-BuLi > i-
PrLi > i-BuLi > n-BuLi > t-BuLi [18]. Accordingly, the anionic
polymerization of NPh2VCz was optimized using initiation by s-
BuLi/styrene ([s-BuLi]0/[St]0 ¼ 0.33) to control the Mn and to ach-
ieve a narrow Mw/Mn (below 1.1). To confirm that the calculated Mn
is in good agreement with the observed Mn, the anionic polymer-
ization was performed using different molar ratios of NPh2VCz to s-
BuLi/styrene in the molecular weight (Mn) range of 3900e31,400 g/
mol (Table 1, Run 3e6). The good linear correlation between the Mn
and the feed ratio of NPh2VCz to s-BuLi/styrene proved the living
nature of poly(9-phenyl-2-vinylcarbazole) (PNPh2VCz) as observed
in Fig. 2.
3.1. Synthesis of vinyl-containing carbazole derivatives
Various synthesis methods of carbazole derivatives containing a
variety of electrophiles at the 2-position of the carbazole have been
studied [16]. Among these methods, for the synthesis of 2-
formylcarbazole, reductive cyclization using triphenyl phosphine
in 1,2-dichlorobenzene was selected in this study because of the
simple procedure, easy purification, and high yield [15]. To syn-
thesize the three different carbazole derivatives of NBu2VCz,
NPh2VCz, and NPy2VCz, the Ullmann coupling reaction was per-
formed to substitute the pyridine and phenyl to the nitrogen of the
carbazole and the Wittig reaction was utilized to convert the formyl
to a vinyl group, as shown in Scheme 1. The details of synthesis
were described in the experimental section.
Scheme 1. Synthesis of (a) 9-butyl-2-vinylcarbazole (NBu2VCz), (b) 9-phenyl-2-vinylcarbazole (NPh2VCz), and (c) 9-(pyridin-2-yl)-2-vinylcarbazole (NPy2VCz). i) bromobenzene or
2-bromopyridine, Cu/bronze, K2CO3 in nitrobenzene at 180 ꢁC; ii) Methyl triphenyl phosphonium bromide, potassium tert-butoxide in THF at 25 ꢁC; and iii) 1-bromobutane, NaOH,
tetraoctylammonium bromide in acetone at 60 ꢁC.

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N.-G. Kang et al. / Polymer 54 (2013) 5615e5625
Scheme 2. Living anionic polymerization of NPh2VCz using s-BuLi and s-BuLi/styrene.
The anionic polymerization of NBu2VCz was performed with s-
shown in Table 2. Each block copolymerization was achieved within
70 min and had a 98e100% yield.
BuLi and s-BuLi/styrene as summarized in Table 1, Run 7e8. All
initiation systems using s-BuLi and s-BuLi/styrene gave quantitative
yields within 70 min, but these two initiation conditions resulted in
broad Mw/Mn, which were 1.23 for s-BuLi and 1.27 for s-BuLi/sty-
rene. In the case of anionic polymerization of NPy2VCz using s-BuLi,
s-BuLi and the carbanion formed by s-BuLi from the vinyl group of
NPy2VCz during initiation and propagation created an amine anion
(Ne) from the pyridine moiety by their strong nucleophilicity. This
anionic polymerization of NPy2VCz using s-BuLi and s-BuLi/styrene
resulted in 0% yield in Table 1, Run 910. To avoid this side reaction,
the previous reported initiating method [14a] using diphe-
nylmethyl potassium (DPM-K) as a weak initiator was utilized for
the controlled polymerization of NPy2VCz. The reaction solution
initiated by DPM-K at ꢀ78 ꢁC was purple and was maintained for
60 min, but the trace amount of polymer obtained was less than 5%
after termination and precipitation with methanol. Before per-
forming the polymerization using DPM-K, it was expected that the
initiation system using DPM-K would control the anionic poly-
From the results of the homopolymerization of NPh2VCz using
s-BuLi/styrene, the feasibility of the block copolymerization of
NPh2VCz and styrene using s-BuLi was already confirmed (Table 2,
Run 1). These results showed that the nucleophilicity of living
PNPh2VCz is weaker than that of living polystyrene. The two block
copolymerizations of
MeSt (Table 2, Run 2 and 3) verified that the nucleophilicity of living
PNPh2VCz is not strong enough to initiate -MeSt by the GPC trace
of PNPh2VCz-b-P -MeSt, as shown in Fig. 3a. To compare the
a-MeSt with nPh2VCz and NPh2VCz with a-
a
a
nucleophilicity of living PNPh2VCz with that of living poly(2-
vinylpyridine) (P2VP), the two sequential block copolymeri
zations of either NPh2VCz as the first monomer and 2VP as the
second, or the opposite sequential order, were also performed
(Table 2, Run 4e9). We denote the materials with the volume
fraction of PNPh2VCz in the block copolymer of PNPh2VCz-b-P2VP
(fPNPh2VCz) ¼ 17.7, 34.6, 48.1, 62.4, and 82.9 as 2VB01, 2VB02, 2VB03,
2VB04, and 2VB05, respectively (Table 2, Run 4e8).
merization of NPy2VCz with a
b
-carbon chemical shift (119.1 ppm)
The block copolymers containing pyridine units are important
and versatile because the lone pairs in the nitrogen atom of the
pyridine generate a variety of applications such polymeric templates
for metal nanoparticles, nanocomposites, quaternizations, and li-
gands of metalated complexes [19]. Additionally, the heterocycles
containing an electron-withdrawing imine (eC]Ne) nitrogen, such
as pyridine, quinoxaline, and thiadiazole, produce the n-type poly-
mer materials. Therefore, the pyridine moieties in the block co-
polymers play the role of electron acceptors [20]. For these
applications, the PNPh2VCz-b-P2VP in which the block of PNPh
2VCz is a donor unit and P2VP is an acceptor was synthesized with a
controlled Mn and a narrow Mw/Mn by sequential living anionic
polymerization. With the resulting block copolymer of PNPh2VCz-b-
P2VP (2VB01, Table 2, Run 4), the clear shift in the SEC profile from the
homopolymer of PNPh2VCz to the block copolymer of PNPh2VCz-b-
P2VP confirmed the successful sequential living anionic polymeri-
zation, as shown in Fig. 3b. In addition, other resulting block co-
polymers of PNPh2VCz-b-P2VP with fPNPh2VCz ¼ 34.6, 48.1, 62.4, and
82.9 (2VB02, 2VB03, 2VB04, and 2VB05) also demonstrated the shift
in the SEC profile as that of 2VB01. The observed MW of each block
copolymer was in good agreement with the calculated MW. However,
the SEC profile of P2VP-b-PNPh2VCz synthesized by the opposite
sequential polymerization showed incomplete block copolymeriza-
tion, as shown in Fig. 3c.
between that of 2-vinylpyridine (118.1 ppm) and that of MMA
(125.3 ppm). Nevertheless, the DPM-K did not control the anionic
polymerization of NPy2VCz because the nucleophilicity of DPM-K is
too weak to initiate NPy2VCz efficiently (Table 1, Run 11). The detail
study on successful anionic polymerization of NPy2VCz using
various conditions will be conducted in the future.
3.4. Block copolymerization of NPh2VCz with various monomers
For studying the reactivity and living nature of PNPh2VCz, the
block copolymers of NPh2VCz with a-methylstyrene (a-MeSt) and
2-vinylpyridine (2VP) were synthesized by sequential anionic
polymerization using s-BuLi/St as an initiator in THF at ꢀ78 ꢁC, as
From the results of the block copolymerization of NPh2VCz with
a
-MeSt and 2VP by sequential anionic polymerization, the nucle-
ophilicity of living poly(9-phenyl-2-vinylcarbazole) was estimated
in this order: living poly( -methylstyrene) > living poly(9-phenyl-
a
2-vinylcarbazole) > living poly(2-vinylpyridine), as shown in Fig. 4.
3.5. Study of microphase separation
The resulting block copolymers of PNPh2VCz-b-P2VP (2VB01e
2VB05) were used for the study of their phase separation behaviors
Fig. 2. Molecular weight (Mn) and molecular weight distribution (Mw/Mn) vs. the feed
ratio of NPh2VCz to s-BuLi/styrene.

N.-G. Kang et al. / Polymer 54 (2013) 5615e5625
5621
c
Table 2
Block copolymerization of NPh2VCz with various monomers in THF at ꢀ78 ꢁC for 70 min.
Initiator (I)
1st monomer (M1)
2nd monomer (M2)
M1/I, M2/I
Block copolymer (homopolymer)
Yield of polymer, %
fPNPh2VCz
Mn ꢂ 10ꢀ3
calcda
Mw/Mn
b
mmol
mmol
mmol
obsdb
s-BuLi
0.042
St
4.5
NPh2VCz
1.22
1
2
3
107.1, 29.0
30.3, 29.7
15.4, 23.3
66.1(35.7)
15.5(11.1)
6.8(4.1)
67.5(36.1)
15.9(10.8)
8.9(3.7)
1.06(1.03)
1.11(1.08)
1.05(1.07)
100
99
21.3
50.9
39.8
a
-MeSt
NPh2VCz
1.13
a-MeSt
0.038
s-BuLi/St
0.081/0.16
1.15
NPh2VCz
1.25
1.89
98
NPh2VCz
1.39
1.28
2.80
1.58
2.04
2VP
3.82
2VP
6.45
2.42
3.02
0.95
0.42
NPh2VCz
0.94
4
5
6
7
8
0.058
0.043
0.051
0.024
0.026
DPM-K
0.052
24.0, 111.2
29.8, 56.3
54.9, 59.2
65.8, 39.6
78.5, 16.2
18.2(6.5)
18.5(5.7)
1.06(1.07)
1.05(1.08)
1.05(1.06)
1.08(1.07)
1.06(1.08)
98
99
99
99
99
17.7
34.6
48.1
62.4
82.9
31.4(13.4)
20.9(14.7)
21.8(17.7)
22.8(21.1)
30.6(12.8)
21.9(14.1)
20.4(17.9)
23.6(21.8)
9
111.9, 18.1
12.6(7.7)
12.3(10.2)
1.36(1.06)
100
19.7
a
b
c
Mn (calcd) ¼ (MW of 1st monomer) ꢂ [1st monomer]/[initiator] þ (MW of 2nd monomer) ꢂ [2nd monomer]/[initiator].
Mn (obsd) and Mw/Mn were measured by SEC calibration using a polystyrene standard in THF containing 2% (C2H5)3N as the eluent at 40 ꢁC.
Block copolymer composition was determined by means of 1H NMR spectroscopy. Denote entry 4 (2VB01), entry 5 (2VB02), entry 6 (2VB03), entry 7 (2VB04), and entry 8
(2VB05).
in THF by transmission electron microscopy (TEM), as shown in
Fig. 5. The dark regions represent the P2VP block, and the white
regions are the PNPh2VCz block in PNPh2VCz-b-P2VP. As the vol-
ume fraction of PNPh2VCz in the block copolymer was increased,
the morphology of the various block copolymers gradually
changed, as shown in Fig. 5aee.
P2VP and PNPh2VCz of homopolymer are highly soluble in THF
but P2VP is more soluble than PNPh2VCz. The solubility of the
polymers in given solvent system depends on several parameters
including molecular weight and volume fraction. In self-assembly
process of block copolymers, relative parameters of block seg-
ments in block copolymer with respect to environments such as
solvent characteristics, temperature, pH, etc, play dominant role in
aggregation behavior in solution as well as in bulk. In addition,
annealing temperature is very significant to form final morphol-
ogies of the block copolymer aggregates [21].
At 82.9% mole fraction of P2VP in the block copolymer of
PNPh2VCz-b-P2VP (2VB01), micelles-typed structure with P2VP
shell was formed as shown in Fig. 5a because THF is slightly more
favorable to P2VP segment. However, as the volume fraction of
PNPh2VCz increases in the block copolymer (2VB03 and 2VB04),
the TEM images of phase separation of PNPh2VCz were observed in
Fig. 5c and d. The TEM image of block copolymer (2VB02) in Fig. 5b
showed the dark spherical shape region of P2VP stained by I2 vapor
and very undistinguishable phase separation. At 48.1 mol % of the
PNPh2VCz in PNPh2VCz-b-P2VP (2VB03), spherical shape of ag-
gregation was disappeared and distinguishable phase separation
like lamellar structure was clearly observed in Fig. 5c.
As further increasing volume of PNPh2Vz in 2VB04 and 2VB05,
more expansion of PNPh2Vz was appeared along with expansion
of P2VP chain as shown in Fig. 5d and e. Most probably, with
increasing the mole fraction of PNPh2Vz, both PNPh2VCz and P2VP
segments in the block copolymer (2VB04 and 2VB05) become
closer and THF became equally favorable to both two PNPh2VCz
and P2VP blocks. As a result, the two blocks of PNPh2VCz and P2VP
are in more solvated state, which leads to expiation of the both
coils of PNPh2Vz and P2VP. In addition, depending on increasing
volume fraction of carbazole units in block copolymers, spinodal
separation behaviors for the 2VB04 with fPnPh2VCz ¼ 62.5 and
2VB05 with 82.9 were observed, as shown in Fig. 5d and e, instead
of the classical phase like spherical, cylindrical, or lamellar struc-
ture. In general, the blending of two different polymers, rod-coil,
and liquid crystalline containing block copolymers usually
showed spinodal phase separation [22]. Even though 2VB4 and
2VB5 are a coilecoil block copolymer, a rigid mesogen-like phenyl
carbazoles in 2VB4 and 2VB5 formed aggregation, crystallization,
and incompatibility between two different blocks, which have an
effect on the spinodal morphology possibly as reported similarly
by Jen [23].
3.6. Thermal behavior
The thermal characteristics of the block copolymers (2VB01,
2VB02, 2VB03, 2VB04, and 2VB05) and homopolymer (PNPh2VCz
and P2VP) were measured by thermogravimetric analysis (TGA),
Fig. 3. SEC profile of the block copolymers of NPh2VCz with
a-methylstyrene and 2-vinylpyridine: (a) PNPh2VCz-b-Pa-MeSt; (b) PNPh2VCz-b-P2VP (2VB01, dotted line: PNPh2VCz
and sold line: PNPh2VCz-b-P2VP); and (c) P2VP-b-PNPh2VCz.

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N.-G. Kang et al. / Polymer 54 (2013) 5615e5625
Fig. 4. The increasing nucleophilicity order of living poly(a-methylstyrene), living poly(9-phenyl-2-vinylcarbazole), and living poly(2-vinylpyridine).
shown in Fig. 6a, and differential scanning calorimeter (DSC),
shown in Fig. 6b.
3.7. Measurement of optical properties
These block copolymers showed high thermal stability with an
onset of decomposition (5% weight loss). The decomposition tem-
perature (Td) of the block copolymers was little different as shown
in Fig. 6a and Table 3. The increasing mol % of PNPh2VCz in the
block copolymers increased the decomposition temperature from
377.6 ꢁC (2VB01) to 388.5 ꢁC (2VB05). The different block co-
polymers from 2VB01 to 2VB05 gave rise to two glass transition
temperatures (Fig. 6b and Table 3). Even though the mol% of
PNPh2VCz in the block copolymers increased, the Tg was showed
similarly. The high decomposition temperature (Td) and glass
transition temperature (Tg) of the polymers could improve the
stability of organic electronic devices.
Fig. 7a shows the normalized UV-Vis absorption spectra of the
block copolymers of poly(9-phenyl-2-vinylcarbazole)-b-poly(2-
vinylpyridine) (PNPh2VCz-b-P2VP) in chloroform. The absorption
spectra of the block copolymers (2VB01e2VB05) exhibited various
bands in the UV and visible region from 250 to 351 nm that origi-
nated from the 9-phenyl-2-vinylcarbazole and 2-vinylpyridine
structures. The maximum absorption wavelength
(lmax) of
250 nm resulted from the pyridine units of P2VP and the phenyl
units of NPh2VCz. The peaks at 300, 327, and 343 nm were caused
by the carbazole units of NPh2VCz and can be assigned to spin
allowed
p-p* transitions. All carbazole-containing block co-
polymers showed different absorption intensities because the five
Fig. 5. TEM images of PNPh2VCz-b-P2VP block copolymers at 2.0 mg/ml concentration in THF, annealed at 240 ꢁC under reduced pressure (10ꢀ1 mmHg) for 48 h (a) 2VB01
(fPNPh2VCz ¼ 17.7), (b) 2VB02 (34.5), (c) 2VB03 (48.1), (d) 2VB04 (62.4), and (e) 2VB05 (82.9). The dark regions stained with I2 vapor are P2VP.

N.-G. Kang et al. / Polymer 54 (2013) 5615e5625
5623
Fig. 6. (a) Decomposition temperature and (b) glass transition temperature of 2VB01, 2VB02, 2VB03, 2VB04, 2VB05, PNPh2VCz, and P2VP.
Table 3
poly(2-vinylpyridine) (P2VP), with the lone pair of electrons in the
nitrogen atom, is attractive because the -electron-deficient pyri-
The decomposition temperature and glass transition temperature of block co-
polymers (2VB01e2VB05) and homopolymer (PNPh2VCz).
p
dine moiety increases the electron affinity and can improve the
electron-transporting properties [24]. However, this P2VP has very
weak electron-transporting properties. Fig. 7b shows the PL spectra
of PNPh2VCz-b-P2VP in chloroform. The block copolymers
(2VB01e2VB05) showed three emission maxima at 353, 367, and
434e445 nm. As the PNPh2VCz units increased in the block co-
polymers, the absorption at 367 nm increased and the absorption at
353 nm decreased. In the case of 2VB04 and 2VB05, the absorption
at 353 nm disappeared because the PNPh2VCz units dominated the
structure of the block copolymers and the electrochemical prop-
erties. In addition, the increasing PNPh2VCz shifted the maximum
in the PL spectra from 445 to 434 nm. In the photoluminescence
spectra of the block copolymers (2VB01e2VB05), the maxima at
353 and 367 nm were not quenched, even though the carbazole
units of PNPh2VCz were increased in the block copolymer due to
the unsynchronized energy balance of the holes and electrons by
the very weak pyridine. In the future, the energy balance of
PNPh2VCz will be studied with different electron-transporting
materials in detail for the fabrication of organic electronic devices.
Glass transition
Decomposition temp. (Td, ꢁC)
temp. (Tg, ꢁC)
1st Tg
2nd Tg
P2VP
103.4
102.7
104.2
105.5
105.6
103.8
e
e
364.4
377.6
374.5
384.4
385.8
388.5
384.9
2VB01
2VB02
2VB03
2VB04
2VB05
PNPh2VCz
181.3
180.9
177.3
178.1
179.3
183.6
different block ratios of NPh2VCz:P2VP of 17.7:82.3, 34.6:65.4,
48.1:51.9, 62.4:37.6, and 82.9:17.1 dominated the polymer struc-
ture. In particular, as the block ratio of the NPh2VCz was increased,
the intensity of the absorption in the range of 280e351 nm grad-
ually increased, but the absorption in the range of 250e280 nm
decreased.
In general, carbazoles and their derivatives have been widely
used in organic electronics as hole-transporting materials (p-type)
because of their stable holes, high charge carrier mobilities, and
high thermal and photochemical stabilities [1]. The pyridine-
containing polymers with an imine (eC]Ne) structure have
been used as electron-transporting materials (n-type). In particular,
4. Conclusions
The 9-butyl-2-vinylcarbazole (NBu2VCz), 9-phenyl-2-vinyl
carbazole (NPh2VCz), and 9-(pyridin-2-yl)-2-vinylcarbazole (NPy
Fig. 7. UV-vis absorption (a) and photoluminescence (b) spectra of the block copolymers (2VB01e2VB05) in chloroform.

5624
N.-G. Kang et al. / Polymer 54 (2013) 5615e5625
Chart 1. Literature survey of the anionic polymerization of carbazole derivatives: (a) N-vinylcarbazole [6], (b) 2-(9-carbazolyl)ethyl methacrylate [7], (c) 2-(3-nitrocarbazolyl)ethyl
methacrylate [8], (d) 9-Acrylyl carbazole [9], (e) 4-(9-carbazolyl)methylstyrene [10], (f) 9-(4-vinylphenyl)carbazole [11], (g) N-ethyl-3-vinylcarbazole [12], and (h) N-ethyl-2-
vinylcarbazole [12].
2VCz) were designed and synthesized successfully as a 2-vinyl-
carbazole derivative. Only nBu2VCz and nPh2VCz were poly-
merized anionically using s-BuLi and s-BuLi/styrene. The anionic
polymerization of nPh2VCz with an Mw/Mn of 1.05e1.11 was
more controlled than that of NBu2VCz with an Mw/Mn of 1.23e
1.27. On the other hand, the anionic polymerization of NPy2VCz
was not controlled due to the nucleophilic attack of s-BuLi and
the carbanion on the pyridine, as well as insufficient initiating
by the weakly nucleophilic diphenylmethyl potassium (DPM-K).
With these results, we proved that the anionic polymerization
and living characteristics were affected by a kind of substituent,
the nucleophilicity of living polymers, a kind of initiator, delo-
calization by resonance, etc. From the block copolymerization of
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