Synthesis and characterization of block copolythiophene with hexyl and triethylene glycol side chains

Article abstract of DOI:10.1016/j.polymer.2011.06.037

A well-defined diblock copolythiophene, poly(3-hexylthiophene)-b-poly(3-(2- (2-(2-methoxyethoxy)ethoxy)ethoxy)methylthiophene) (P3HT-b-P3TEGT) was successfully synthesized by a Grignard metathesis (GRIM) polymerization. The structure of the block copolymer was confirmed by size exclusion chromatography (SEC), ¹H NMR spectroscopy, differential scanning calorimetry (DSC), ultraviolet-visible (UV-vis) spectroscopy and fluorescence spectroscopy. The self-assembled structure of the block copolythiophene was investigated by atomic force microscopy (AFM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and synchrotron grazing incidence X-ray scattering (GIXS). These analyses found that the block components in films form vertically oriented lamellar structure via phase separation. Furthermore, both the phases were found to consist of molecular multi-layers respectively, in which the layers stack in the out-of-plane of the film. The P3HT phase exhibited crystalline, which is originated from the π-π stacked thiophene backbones. In contrast, the poly(3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methylthiophene) (P3TEGT) phase revealed amorphous. Overall, the amphiphilic nature of P3HT-b-P3TEGT successfully demonstrated to lead to well-defined self-assembly structure in films.

Full text of DOI:10.1016/j.polymer.2011.06.037

Polymer 52 (2011) 3687e3695
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Synthesis and characterization of block copolythiophene with hexyl and
triethylene glycol side chains
,
c
,
,
,
Tomoya Higashihara a 1, Kaoru Ohshimizu a 1, Yecheol Ryo b 1, Takuya Sakurai a, Ayumi Takahashi a,
Shuichi Nojima a , Moonhor Ree , Mitsuru Ueda
,
b,
a,
*
*
*
a Department of Organic and Polymeric Materials, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1-H-120, O-okayama, Meguro-Ku,
Tokyo 152-8552, Japan
b Division of Advanced Materials Science, Department of Chemistry, Center for Electro-Photo Behaviors in Advanced Molecular Systems, BK School of Molecular Science,
and Polymer Research Institute, Pohang University of Science & Technology (POSTECH), Pohang 790-784, Republic of Korea
c PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A
well-defined diblock copolythiophene, poly(3-hexylthiophene)-b-poly(3-(2-(2-(2-methoxyethoxy)
Received 25 April 2011
Received in revised form
13 June 2011
Accepted 19 June 2011
Available online 25 June 2011
ethoxy)ethoxy)methylthiophene) (P3HT-b-P3TEGT) was successfully synthesized by Grignard
a
metathesis (GRIM) polymerization. The structure of the block copolymer was confirmed by size exclusion
chromatography (SEC), 1H NMR spectroscopy, differential scanning calorimetry (DSC), ultraviolet-visible
(UV-vis) spectroscopy and fluorescence spectroscopy. The self-assembled structure of the block copo-
lythiophene was investigated by atomic force microscopy (AFM), transmission electron microscopy
(TEM), small-angle X-ray scattering (SAXS), and synchrotron grazing incidence X-ray scattering (GIXS).
These analyses found that the block components in films form vertically oriented lamellar structure via
phase separation. Furthermore, both the phases were found to consist of molecular multi-layers
respectively, in which the layers stack in the out-of-plane of the film. The P3HT phase exhibited crys-
Keywords:
Block copolymer
Polythiophene
Phase separation
talline, which is originated from the
p p stacked thiophene backbones. In contrast, the poly(3-(2-(2-(2-
ꢀ
methoxyethoxy)ethoxy)ethoxy)methylthiophene) (P3TEGT) phase revealed amorphous. Overall, the
amphiphilic nature of P3HT-b-P3TEGT successfully demonstrated to lead to well-defined self-assembly
structure in films.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
first block copolythiophene, poly(3-hexylthiophene)(P3HT)-b-
poly(3-dodecylthiophene), based on a Grignard metathesis (GRIM)
Well-defined block copolymers self-assemble into various types
of well-ordered nanostructures such as lamellae, cylinders and
spheres, on a variety of substrates after being cast from a number of
polymerization, various block copolythiophenes have been widely
synthesized [21]. Yokozawa et al. synthesized P3HT-b-poly(3-(2-(2-
methoxyethoxy)ethoxy)methylthiophene) having both hydro-
phobic and hydrophilic side chains, although its morphological
study was not reported [22]. We reported the synthesis and self-
assembled structure of P3HT-b-poly(3-phenoxymethylthiophene)
which showed a nanofibril structure after solvent annealing [23].
Tajima et al. also synthesized and characterized P3HT-b-poly(3-(2-
ethylhexyl)thiophene) [24,25]. The block copolymers showed
wormlike morphology after thermal annealing observed by Atomic
Force Microscopy (AFM). Jenekhe et al. synthesized and charac-
terized crystallineecrystalline poly(3-butylthiophene)-b-poly(3-
octylthiophene) and the block copolymer showed nanowire
structures observed by TEM [26]. However, clear periodical nano-
structures such as lamella, cylinders and so on, have not been
observed so far. To facilitate self-assembly and pursue the clear
microphase-separated nanostructures, samples of conjugated block
solvents and thermal annealing [1e7]. Especially,
p-conjugated
polymers based on regioregular polythiophene are attractive
materials due to their potential applications as organic electronic
devices such as thin film transistors [8e13], light-emitting diodes
[14], and photovoltaic cells [15e20]. Thus, by combining their
possibility with the fascinating self-assembling property of block
copolymers, the synthesis and morphology of all-conjugated,
roderod block copolymers have been intensively investigated
during the last 3e4 years [21e26]. Since McCullough reported the
* Corresponding authors. Tel./fax: þ82 81 3 5734 2127.
E-mail addresses: snojima@polymer.titech.ac.jp (S. Nojima), ree@postech.edu
(M. Ree), ueda.m.ad@m.titech.ac.jp (M. Ueda).
1
These authors equally contributed to this work.
0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2011.06.037

3688
T. Higashihara et al. / Polymer 52 (2011) 3687e3695
copolymers containing both hydrophilic and hydrophobic conju-
gated blocks will be effective [27e29].
purified by silica gel column chromatography (eluent: hexane and
ethyl acetate) to give 3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)
methylthiophene (1) as a clear oil (6.86 g, 44%). 1H NMR (300 MHz,
In this paper, we synthesized block copolythiophene, poly(3-
hexylthiophene)-b-poly(3-(2-(2-(2-methoxyethoxy)ethoxy)
ethoxy)methylthiophene) (P3HT-b-P3TEGT), having hydrophobic
hexyl side chains and hydrophilic tri(ethylene glycol) side chains.
Its self-assembled structure was also investigated for the first time.
The combination of hydrophobic/hydrophilic segments, for which
the corresponding monomers are specially designed, induced the
formation of a clear self-assembled structure, as confirmed by AFM,
TEM, SAXS and GIXS.
CDCl3, ppm, 25 ꢁC):
d
¼ 7.28 (q, ArH, 1H),7.21 (m, ArH, 1H), 7.07 (q,
ArH,1H), 4.57 (s, eCH2eOe, 2H), 3.69e3.60 (m, alkyl,10H), 3.54 (m,
eOeCH2eCH2e, 2H), 3.37 (s, eCH3, 3H). 13C NMR (300 MHz, CDCl3,
ppm, 25 ꢁC):
d
¼ 139.8, 127.4, 125.8, 122.7, 72.2, 70.8, 70.7, 69.6, 68.6,
59.0. Anal. Calcd. for C12H20O4S; C, 55.36; H, 7.74; O, 24.58; S, 12.32.
Found: C, 55.42; H, 7.83.
2.3. Synthesis of 2-bromo-3-(2-(2-(2-methoxyethoxy)ethoxy)
ethoxy)methylthiophene (2)
2. Experimental section
N-Bromosuccinimide (4.64 g, 26.1 mmol) was added to a stirred
solution of 1 (6.79 g, 26.1 mmol) in THF (100 mL) at 0 ꢁC under
nitrogen atmosphere, and the mixture was stirred at room
temperature overnight. The solvent was evaporated and hexane
was added to the mixture. After stirring for 1 h, succinimide was
filtrated and the filtrate was removed by evaporation under
reduced pressure. The residue was purified by silica gel column
chromatography (eluent: hexane and ethyl acetate) to give 2-
bromo-3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methyl-
2.1. Materials
Tetrahydrofuran (THF) was dried over sodium benzophenone
and distilled before use under nitrogen. 2-Bromo-3-hexyl-5-
iodothiophene was prepared according to the literature [30]. 2-
Bromo-5-iodo-3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methyl-
thiophene was prepared (Scheme 1) by modifying the procedure
previously reported [31]. Lithium chloride was dried by a heat-gun
under reduced pressure and used under nitrogen. All other
reagents and solvents were used without further purification.
thiophene (2) as a clear oil (7.93 g, 90%). 1H NMR (300 MHz, CDCl3,
ppm, 25 ꢁC):
d
¼ 7.22 (d, ArH, 1H), 6.99 (d, ArH, 1H), 4.50 (s,
eCH2eOe, 2H), 3.68e3.59 (m, alkyl,10H), 3.54 (m, eOeCH2eCH2e,
2H), 3.37 (s, eCH3, 3H). 13C NMR (300 MHz, CDCl3, ppm, 25 ꢁC):
2.2. Synthesis of 3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)
methylthiophene (1)
d
¼ 138.2, 128.3, 126.0, 111.2, 72.0, 70.6, 70.5, 69.4, 67.1, 59.1. Anal.
Calcd. for C12H19BrO4S; C, 42.48; H, 5.65; Br, 23.55; O, 18.86; S, 9.45.
Found: C, 43.53; H, 5.70.
Triethyleneglycol monomethyl ether (9.84 g, 59.9 mmol) was
dropped to a stirred solution of NaH (4.8 g, 120.0 mmol) in THF
(110 mL) at room temperature with a stream of nitrogen. The
reaction mixture was stirred for 1 h, and then a solution of 3-
bromomethylthiophene was added to the mixture. The 3-
bromomethylthiophene was prepared as follows.
2.4. Synthesis of 2-bromo-5-iodo-3-(2-(2-(2-methoxyethoxy)
ethoxy)ethoxy)methylthiophene (3)
To a stirred solution of 2 (7.93 g, 23.4 mmol) in CH2Cl2 (80 mL) at
0
ꢁC were added iodine (3.05 g, 12.0 mmol) and iodobenzene
N-Bromosuccinimide (18.0 g, 101.1 mmol) and benzoyl peroxide
(0.2 g, 0.82 mmol) was slowly added to a stirred solution of 3-
methylthiophene (9.82 g, 100.0 mmol) and benzoyl peroxide (0.2 g,
0.82 mmol) in benzene (150 mL) at 100 ꢁC, and the mixture was
refluxedfor1h. Thesolventwasevaporatedandhexanewasaddedto
the mixture. After stirring for 30 min, succinimide was filtrated and
the filtrate was removed by evaporation under reduced pressure.
The reaction was continued for 12 h and quenched by the
addition of water and then the reactant was extracted. The organic
layer was washed with brine, and dried over anhydrous MgSO4.
After the drying agent was removed by filtration, the residue was
diacetate (3.88g, 12.0 mmol) successively, and the mixture was
stirred for 12 h. Then 10% aqueous Na2S2O3 solution was added, and
the mixture was extracted with CHCl3. The organic layer was
washed with brine and water, and dried over anhydrous MgSO4.
After the drying agent was removed by filtration, the solvent was
removed by evaporation under reduced pressure. The residue was
purified by silica gel column chromatography (eluent: hexane and
ethyl acetate) and then purified by distillation under reduced
pressure to give 2-bromo-5-iodo-3-(2-(2-(2-methoxyethoxy)
ethoxy)ethoxy)methylthiophene as a pale yellow oil (9.02 g, 83%).
1H NMR (300 MHz, CDCl3, ppm, 25 ꢁC):
d
¼ 7.18 (s, ArH, 1H), 4.44 (s,
eCH2eOe, 2H), 3.68e3.58 (m, alkyl,10H), 3.55 (m, eOeCH2eCH2e,
O
O
2H), 3.38 (s, eCH3, 3H). 13C NMR (300 MHz, CDCl3, ppm, 25 ꢁC):
d
¼ 140.6, 138.0, 113.7, 72.1, 70.8, 70.7, 70.7, 70.6, 69.7, 66.8, 59.2.
Anal. Calcd. for C12H18BrIO4S; C, 30.99; H, 3.90; Br, 17.18; I, 27.28; O,
13.76; S, 6.89. Found: C, 30.90; H, 3.73.
Br
HO
O
O
O
O
NBS, BPO
Benzene
NaH
THF
O
S
S
2.5. Synthesis of poly(3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)
methylthiophene) (P3TEGT)
S
1
A round-bottomed flask equipped with a three-way stopcock
was charged with lithium chloride (0.21 g, 4.95 mmol) and was
heated by a heat-gun under reduced pressure. After the flask was
cooled to room temperature under a nitrogen atmosphere, 3
(447 mg, 0.961 mmol) and THF (20 mL) were added, and the
mixture was stirred at 0 ꢁC for 30 min. To the mixture was added
iPrMgCl (2.0 M solution in THF, 0.528 mL, 1.05 mmol) via a syringe,
and the mixture was stirred for 30 min. Then, a suspension of
Ni(dppp)Cl2 (12.0 mg, 0.0222 mmol) in dry THF (5.0 mL) was added
to the mixture via a syringe, and then the mixture was stirred at
O
O
O
O
I2, Ph(OAc)2I
CHCl3
NBS
THF
O
O
O
O
Br
I
Br
S
S
2
3
Scheme 1. Synthesis of 2-bromo-5-iodo-3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)
methylthiophene (3).

T. Higashihara et al. / Polymer 52 (2011) 3687e3695
3689
40 ꢁC for 12 h. The polymerization was quenched by the addition of
5M HCl solution and the mixture was extracted with CHCl3. The
organic layer was washed with water, dried over anhydrous MgSO4,
and concentrated under reduced pressure. Hexane was added to
the residue. The insoluble material was filtered and washed by
Soxhlet extraction using methanol and hexane, and finally extrac-
ted using CHCl3. The solvent was removed by evaporation under
reduced pressure to give P3TEGT (Mn ¼ 16500, polydispersity
indice (PDI) ¼ 1.61) as a purple solid (0.185 g, 75%). 1H NMR
a Jasco V-560 UV/VIS spectrophotometer over a wavelength range
of 300e800 nm. Fluorescence spectra of polymer solution in CHCl3
were taken on a Jasco FP-750 spectrofluorometer over a wave-
length range of 500e700 nm. TEM images of the bulk films were
obtained using a JEOL JEM-1010BS instrument operated at 80 kV
accelerating voltage. The block copolymer bulk sample was
prepared by slowly evaporating in a 50 mL vial from a toluene
solution (0.04 wt%) at room temperature for 3 days and drying
under vacuum. The bulk sample was microtomed at ꢀ110 ꢁC and
the cut film with a thickness of 60 nm on a copper grid was stained
with a vapor of OsO4 crystals at room temperature for 90 min. The
TEM image of the thin film was obtained using the same instrument
operated at 80 kV accelerating voltage. The thin film was prepared
by drop casting from a dilute toluene solution onto a copper grid
coated with carbon, followed by slow evaporation to promote
phase separation at room temperature for 2 days. Finally, the film
was well dried at room temperature under vacuum for 24 h. The
film was stained in the same way aforementioned. The self-
assembled structure was also investigated using synchrotron
SAXS, which was performed at beam line BL-10C of Photon Factory
in High Energy Accelerator Research Organization, Tsukuba Japan.
Details of the equipment and instrumentation were described
elsewhere [32]. The scattered intensity was recorded with a one-
dimensional position-sensitive proportional counter (PSPC), by
which isotropic scattering from the sample was obtained as
(300 MHz, CDCl3, ppm, 25 ꢁC):
d
¼ 7.22 (s, ArH, 1H), 4.63 (s,
eCH2eOe, 2H), 3.73e3.56 (m, alkyl, 10H), 3.48 (m, eOeCH2eCH2e,
2H), 3.31 (s, eCH3, 3H).
2.6. Synthesis of poly(3-hexylthiophene)-b-poly(3-(2-(2-(2-
methoxyethoxy)ethoxy)ethoxy)methylthiophene) (P3HT-b-P3TEGT)
A round-bottomed flask equipped with a three-way stopcock
was charged with lithium chloride (0.21 g, 4.95 mmol) and was
heated by a heat-gun under reduced pressure. After the flask was
cooled to room temperature under a nitrogen atmosphere, 2-
bromo-3-hexyl-5-iodothiophene (440 mg, 1.180 mmol) and THF
(20 mL) were added, and the mixture was stirred at 0 ꢁC for 30 min.
To the mixture was added iPrMgCl (2.0 M solution in THF, 0.648 mL,
1.296 mmol) via a syringe, and the mixture was stirred for 30 min at
0
ꢁC. Then, a suspension of Ni(dppp)Cl2 (10.0 mg, 0.0184 mmol) in
dry THF (5.0 mL) was added to the mixture via a syringe. The
polymerization continued for 9.5 min at room temperature, and
then a solution of Grignard exchanged compound 3 in dry THF
(5 mL) was added to the mixture. The Grignard exchanged
compound 3 solution was prepared as follows.
a function of s (¼ (2/
l
) sin
q
;
l
: X-ray wavelength (¼ 0.1488 nm); 2
q:
scattering angle). The alternating distance of the structure was
evaluated from the angular position of the SAXS peak. GIXS
measurements were conducted at the 4C1 and 4C2 beamlines
[33e35] of the Pohang Accelerator Laboratory at Pohang University
of Science & Technology. The film samples coated with 40e60 nm
thickness on silicon substrates were mounted on a home-made z-
axis goniometer equipped in a vacuum chamber. The incident angle
ai of the X-ray beam was set at 0.15ꢁ, which is between the critical
angles of the films and the Silicone substrate (ac,f and ac,s). Scat-
tering data were measured at a sample-to-detector distance of
120.4 mm using an X-ray radiation source of 0.138 nm wavelength
and a two-dimensional (2D) charge-coupled detectors (CCD) (Mar,
USA). All scattering measurements were carried out at 25 ꢁC. Each
measurement was collected for 30e120 s.
A round-bottomed flask equipped with a three-way stopcock
was charged with lithium chloride (0.11 g, 2.59 mmol), and heated
by a heat-gun under reduced pressure. The flask was cooled to
room temperature under a nitrogen atmosphere, compound 3
(257 mg, 0.553 mmol) and THF (5 mL) were added, and the mixture
i
was stirred at 0 ꢁC for 30 min. To the mixture was added PrMgCl
(2.0 M solution in THF, 0.304 mL, 0.609 mmol) via a syringe, and the
mixture was stirred for 30 min at 0 ꢁC.
The polymerization of the second monomer was continued for
4 h at room temperature and quenched by addition of 5M HCl
solution. Then, the polymer solution was poured into a mixture
solution of methanol (300 mL) and water (100 mL), and the residue
was filtered and purified via a Soxleht extraction with methanol.
The residue was extracted again with chloroform using a Soxhlet
apparatus. Chloroform was removed by evaporation under reduced
pressure, and the polymer was dried overnight under reduced
pressure to give P3HT-b-P3TEGT (Mn ¼ 18200, PDI ¼ 1.45) as
a purple solid (0.273 g, 81%). 1H NMR (300 MHz, CDCl3, ppm, 25 ꢁC):
3. Results and discussion
3.1. Synthesis of P3TEGT and P3HT-b-P3TEGT
For a reference of the target block copolymer, P3HT-b-P3TEGT,
we synthesized P3TEGT homopolymer by modifying the reported
procedure [22]. The obtained P3TEGT was characterized by SEC and
1H NMR spectroscopy. It was found that P3TEGT has a Mn of 16500
and a PDI of 1.16. The homopolymer is soluble in common solvents
such as toluene, CHCl3, THF, and acetone.
To obtain clear nanostructures from diblock copolythiophenes,
generally a high contrast in polarity as well as uniformity of the
block structures are preferable. We synthesized P3HT-b-P3TEGT by
nickel-catalyzed coupling polymerization of the corresponding 2,5-
dihalogenated thiophene derivatives (Scheme 2) sequentially [21].
The polymer yield was relatively high (>80%). Table 1 summarizes
the results of the synthesis of the block copolymers. Although the
PDIs of the block copolymers were not very low (Fig. 1), their
number average molecular weight (Mn) could be controlled by
changing the feed ratio of the two monomers and the initiator.
Furthermore, the feed molar ratios of the two monomers are almost
the same as those in the block copolymers, as confirmed by 1H
NMR. The repeating monomer units of P3HT and P3TEGT segments
in the block copolymers were calculated from the integration of the
d
¼ 7.26 (s, Ar H, 1H), 6.98 (s, ArH, 1H), 4.67 (s, eCH2eOe, 2H),
3.75e3.61 (m, alkyl, 10H), 3.53 (m, eOeCH2eCH2e 2H),3.35 (s,
eCH3 (P3TEGT), 3H), 2.80 (t, eCH2 (P3HT), 2H), 1.71 (s, CH2eCH2,
2H), 1.49e1.28 (m, alkyl, 6H), 0.91 (s, eCH3 (P3HT), 3H).
2.7. Measurements
The 1H NMR spectrum was recorded with a Bruker DPX300S
spectrometer. Number- and weight-average molecular weights (Mn
and Mw) were measured by size exclusion chromatography (SEC)
on a Jasco GULLIVER 1500 system equipped with two polystyrene
gel columns (Plgel 5 mm MIXED-C) eluted with CHCl3 at a flow rate
of 1.0 mL minꢀ1 calibrated by standard polystyrene samples.
Thermal analysis was performed on a Seiko EXSTAR 6000 DSC 6200
at a heating rate of 20 ꢁC/min for differential scanning calorimetry
(DSC) under nitrogen. Ultraviolet-visible (UV-vis) absorption
spectra of polymer thin films and solution in CHCl3 were taken on

3690
T. Higashihara et al. / Polymer 52 (2011) 3687e3695
Scheme 2. Synthesis of P3HT-b-P3TEGT.
methylene proton signals (a and b) next to the thiophene ring of
both segments in the 1H NMR spectrum (Fig. 2). Therefore, we
successfully synthesized the objective block copolythiophene
without a problem. The polymer is soluble in common solvents
such as toluene, CHCl3, and THF.
show bright-orange fluorescence with maximum emission wave-
lengths of 568 and 571 nm.
3.3. Bulk morphology of P3HT-b-P3TEGT
The DSCprofilesof P3TEGTandP3HT-b-P3TEGT (run 1) areshown
in Fig. 3. P3TEGT shows no Tm and no grass transition temperature
(Tg) in the range of 0e250 ꢁC. P3HT was found to reveal a melting
point (Tm) at 240 ꢁC (data not shown). P3HT-b-P3TEGT shows the Tm
at 196 ꢁC andnoTg. The observation of a single Tm, which is originated
from the P3HT block, is an indication that the block components in
the diblock copolymer underwent phase separation.
To investigate the bulk morphology of P3HT-b-P3TEGT (run 2),
TEM images of its cross section were observed. The sample was
prepared by slowly evaporating the copolymer solutions in toluene
for 2 days at room temperature followed by drying under vacuum.
The bulk sample was then microtomed, and the cut film with
a thickness of 60 nm was selectively stained with OsO4 only for the
P3TEGT segment for TEM observation. Fig. 7 shows a TEM image, in
which the bright and dark parts represent the P3HT-rich and
P3TEGT-rich domains, respectively. Both domains construct
a continuous lamellae-like structure to show a striped pattern in the
TEM image, which may arise from the self-assembly of P3HT-b-
P3TEGT.
The self-assembled structure in the bulk film was further
examined by SAXS using the same sample (run 2) of the P3HT-b-
P3TEGT film for TEM observation. A representative SAXS curve
obtained is shown in Fig. 8. The SAXS curve has a diffuse scattering
peak, which is reminiscent of the crystallized lamellar morphology
usually formed in weakly segregated crystalline-amorphous
3.2. UV-vis and fluorescence spectra of P3HT-b-P3TEGT
The optical properties of P3HT-b-P3TEGT (run 1) were investi-
gated by UV-vis and fluorescence spectroscopy. The solution-state
UV-vis spectra of P3HT, P3TEGT and P3HT-b-P3TEGT show the
maximum absorptions (lmax) for the
and 449 nm, respectively (Fig. 4). The lmax of P3TEGT is 24 nm
p p
* transition at 453, 429
ꢀ
shorter than that of crystalline P3HT, which suggests that the P3HT
chain has a higher
p-stacking conformation with a longer conju-
gation length, and that P3TEGT has a more coil-like conformation
with a shorter conjugation length. On the other hand, P3HT-b-
P3TEGT has a middle lmax between those of P3HT and P3TEGT. In
a film state, the lmax values of P3TEGT and P3HT-b-P3TEGT are
bathochromically shifted to 455 and 520 nm, respectively,
compared to those in a solution state due to a higher degree of
ordering of the P3HT segments in all polymers (Fig. 5). The shoulder
at 610 nm of P3HT-b-P3TEGT is related to vibronic absorption and is
an indicator of the high degree of P3HT ordering, despite the
presence of the covalently-bonded amorphous P3TEGT segment.
The lmax value of P3HT-b-P3TEGT (520 nm) is between those of
P3HT (555 nm) and P3TEGT (455 nm). These results suggest the
formation of a block copolymer. The chloroform solution of P3HT
shows a bright-orange fluorescence with a maximum emission
wavelength of 570 nm, when excited at 453 nm corresponding to
the onset of the
spectrum (Fig. 6). The solutions of P3TEGT and P3HT-b-P3TEGT also
p p
* transition of the electronic absorption
ꢀ
Table 1
Synthesis of P3HT-b-P3TEGT.a
b
b
run
Mn
PDI
nc
mc
n/m (%) c
Yield (%)
1
2
18200
15000
1.45
1.34
63
28
30
40
68/32
41/59
81
84
a
[LiCl]/[M] ¼ 5 THF ¼ 25 mL [i-PrMgCl]/[M] ¼ 1.1.
Determined by SEC (CHCl3, PSt standard).
Determined by 1H NMR.
b
c
Fig. 1. SEC profiles of Homo P3TEGT and P3HT-b-P3TEGT (run 1).

T. Higashihara et al. / Polymer 52 (2011) 3687e3695
3691
Fig. 2. 1H NMR spectrum of P3HT-b-P3TEGT in CDCl3 (run 1).
diblock copolymers [36]. That is, even if the microdomain structure
is formed after slow evaporation of the solvent, it will be subse-
quently destroyed by the crystallization of P3HT blocks to yield the
crystallized lamellar morphology consisting of thin P3HT lamellar
crystals and amorphous P3HT þ P3TEGT layers. The alternating
distance of this morphology evaluated from the SAXS peak position
is 16.7 nm. Thus, the SAXS result is qualitatively consistent with the
TEM observation and clearly shows that the self-assembled struc-
ture is formed in this system.
calculated to be 29.4 nm and 27.4 nm, respectively. The driving
force for the clear and periodic lamellae-like morphology of the
P3HT-b-P3TEGT film, compared to other block copolythiophenes
which often show non-periodic worm-like or nanofibril
morphology, might be the large
g parameter due to the high
contrast of hydrophobic and hydrophilic side chains, although
g
parameter between P3HT and P3TEGT has not been determined in
this study.
With the AFM and TEM results, the P3HT-b-P3TEGT thin films
were further studied by GIXS analysis using synchrotron radiation
sources. Fig. 10a and A show the representative 2D grazing inci-
dence small angle and wide angle X-ray scattering (GISAXS and
GIWAXS) patterns respectively, which were measured from the
block copolymer films coated on silicon substrates. From these 2D
scattering patterns, out-of-plane and in-plane scattering profiles
have been extracted respectively and the resulting scattering
profiles are shown in Fig. 10b and c and B and C.
3.4. Thin film morphology of P3HT-b-P3TEGT
The thin film morphology was also investigated in detail by
AFM, TEM, and GIXS. The solution of P3HT-b-P3TEGT (run 1) dis-
solved in toluene was cast on a mica substrate, and then it was
slowly evaporated to promote phase separation at room tempera-
ture for 2 days. The surface profile of the specimen was investigated
using AFM. Fig. 9a and b show AFM tapping-mode phase contrast
images, where the bright and dark parts represent the P3HT-rich
and P3TEGT-rich domains, respectively. Both domains construct
a continuous lamellar structure which would be induced by the
crystalline nature of P3HT domains as well as the side chains having
different polarity of hydrophobicity and hydrophilicity. Fig. 9c
shows the TEM images of the thin film sample cast from a toluene
solution, treated in the same way for AFM observation. The
continuous and periodic lamellar structure could be observed by
TEM, very similar to AFM observation. The average alternating
distances of the lamellar structure observed by AFM and TEM were
As can be seen in Fig. 10 a and b, the out-of-plane GISAXS profile
is featureless. In contrast, the in-plane GISAXS profile clearly shows
a scattering spot at 2qf ¼ 0.305ꢁ and a board shoulder peak from
2
qf ¼ 0.6ꢁe0.8ꢁ (Fig. 10a and c). These scattering results indicate
that in the film the diblock copolymer molecules underwent phase
separation in the blocks and formed lamellar structure whose
lamellae stack along a direction in the film plane (i.e., vertically
oriented lamellar structure). The scattering spot in the low angle
region is determined to have a d-spacing of 25.9 nm. This d-spacing
Fig. 3. DSC thermograms of P3TEGT and P3HT-b-P3TEGT (run 1).
Fig. 4. UV-vis spectra of P3HT-b-P3TEGT (run 1), P3TEGT and P3HT in chloroform.

3692
T. Higashihara et al. / Polymer 52 (2011) 3687e3695
Fig. 5. UV-vis spectra of P3HT-b-P3TEGT (run 1), P3TEGT and P3HT in films.
Fig. 7. TEM image of P3HT-b-P3TEGT film (run 2).
value is comparable to the interspacing of the morphological
textures observed in the AFM (29.4 nm) and TEM images (27.4 nm)
described in the earlier section. Thus, the scattering spot is assigned
as the first order reflection of the lamellar structure formed in the
film. The long period of the lamellar structure is 25.9 nm. The
shoulder peak at 2qf ¼ 0.6e0.8ꢁ can be assigned as the second order
reflection of the lamellar structure.
plane but such orientation has a certain level of variation. In
particular, the first order peak appears at af ¼ 4.81ꢁ and 2qf ¼ 0ꢁ,
giving a d-spacing of 1.65 nm. The d-spacing value is equivalent to
the layer thickness of the multi-layer structure formed in P3HT
films [19,20,41]. Thus, such multi-layer structure was formed in the
phase separated P3HT phases of the lamellar structure in the film;
the layer thickness in the multi-layer structure is 1.65 nm.
With the above scattering information, we attempted to further
analyze the GISAXS data quantitatively by using a GIXS formula
[37,38] with a lamellar structure model [39,40]. As can be seen in
Fig. 10c the in-plane scattering profile is satisfactorily fitted by
analysis using the GIXS formula with a lamellar structure model
(Fig. 11). This analysis found that the higher order reflections of the
vertically oriented lamellar structure are sensitively dependent on
the thicknesses of phase-separated P3HT and 3TEGT block layers in
the structure. The higher order reflections are weakened and
broadened when the layer thicknesses of both the phase-separated
two blocks are close each other. Taking into account this fact and
the diblock copolymer’s chemical composition and molecular
weight, the analysis ultimately found that in the lamellar structure
the P3HT phase has a layer thickness of 13.7 nm while the 3TEGT
phase has a layer thickness of 12.2 nm (Fig. 11). On the other hand,
the measured GIWAXS pattern reveals four periodic scattering arcs
along the af direction at 2qf ¼ 0ꢁ whose relative af positions from
the specular reflection position are 1, 2, 3, and 4 (Fig. 10A and B).
This scattering feature is indicative of a well-ordered multi-layer
structure whose layers stack along a direction normal to the film
The GIWAXS pattern also shows several peaks along the 2qf
direction at af ¼ 0ꢁ (Fig. 10A and C). A peak appears at 2qf ¼ 3.38ꢁ
and its d-spacing is determined to be 2.34 nm. This peak is not
easily discernible in the out-of-plane scattering profile because of
heavy overlapping with the very strong reflection from the verti-
cally oriented multi-layer structure formed in the P3HT phase as
well as the tail of the specular reflection of the main beam
(Fig. 10B). However, its second order peak is discernible around
af ¼ 6.76ꢁ but very weak in intensity (Fig. 10B). These results
Fig. 6. Fluorescence spectra of P3HT-b-P3TEGT (run 1), P3TEGT and P3HT in
chloroform.
Fig. 8. SAXS curve of P3HT-b-P3TEGT film (run 2).

T. Higashihara et al. / Polymer 52 (2011) 3687e3695
3693
Fig. 9. AFM tapping-mode phase images of the P3HT-b-P3TEGT (run 1) thin film cast from a solution in toluene in the area of 2 ꢂ 2
P3TEGT thin film cast from a solution in toluene (C).
mm (A) and (B) and TEM image of the P3HT-b-
suggest that in the film the phase separated P3TEGT block phases
are also composed of multi-layer structure whose layers stack
mainly along the out-of-plane of the film. Another peak is observed
at 2qf ¼ 4.81ꢁ (d-spacing ¼ 1.65 nm) in the in-plane scattering
profile (Fig. 10C), which corresponds to the first order reflection
from the multi-layer structure formed in the P3HT phase. The
observation of this peak in the in-plane scattering profile again
confirms that the orientation of the multi-layer structure formed in
a
A
b
B
c
C
Fig. 10. (a) 2D GISAXS and (A) GIWAXS patterns of P3HT-b-P3TEGT (run 1) films coated on silicon substrates, which were measured at
a
i ¼ 0.15ꢁ at room temperature. (b) Out-of-
plane scattering profile extracted from the scattering pattern in (a) along the af direction at 2qf ¼ 0.08ꢁ; (c) in-plane scattering profiles extracted from the scattering pattern in (a)
along the 2qf direction at af ¼ 0.16ꢁ. (B) Out-of-plane scattering profile extracted from the scattering pattern in (A) along the af direction at 2qf ¼ 0.0ꢁ; (C) in-plane scattering profiles
extracted from the scattering pattern in (A) along the 2qf direction at af ¼ 0.16ꢁ.

3694
T. Higashihara et al. / Polymer 52 (2011) 3687e3695
Fig. 11. Schematic representation of the lamellar structure of the P3HT-b-P3TEGT (run 1) in thin films, in which the phase-separated P3HT and P3TEGT lamellae are composed of
molecular multi-layers.
the P3HT phase is not perfect normal to the film plane but has
a certain level of variation. An anisotropic arc type of peak is clearly
observed 2qf ¼ 19.91ꢁ (d-spacing ¼ 0.40 nm) (Fig. 10A and C). Its d-
spacing value is relatively shorter than the mean interdistances
between the side groups in the phase separated two block phases
and the mean interdistance of the polymer backbones. Further-
more, the P3HT block phase shows a melting transition as discussed
in the earlier section. The thiophene backbone units in P3HT are
4. Conclusions
We successfully prepared a diblock copolythiophene of P3HT-b-
P3TEGT, which possesses hydrophobic hexyl and hydrophilic tri-
ethylene glycol side chains, based on GRIM polymerization. The
formation of the expected block copolymers was confirmed by SEC
and 1H NMR analyses. Optical data from UV-vis spectroscopy and
fluorescence spectroscopy also supported the expected block
structures. DSC thermograms of P3HT-b-P3TEGTshowed a single Tm,
which was originated from the P3HT block, indicating the existence
ofphaseseparation. Theself-assembledstructureof P3HT-b-P3TEGT
was investigated by TEM and SAXS using the block copolymer bulk
film. As a result, a continuous lamellae-like structure could be
observed byTEM. In addition, the SAXS curvehad a diffuse scattering
peak, also indicating that a self-assembled structure was formed in
the system. Furthermore, the AFM, TEM and GIXS analysis collec-
tively found that the diblock copolymer molecules in thin films
undergo phase separation, interestingly forming vertically oriented
lamellar structure. The P3HT-b-P3TEGT of this study successfully
demonstrated that the amphiphilic nature as well as the crystalline
nature of P3HT blocks leads to well-defined self-assembly structure
in thin films of the diblock copolymer. The P3HT phase is richly
crystalline, which is composed of molecular multi-layer structure
whose layers stack along a direction normal to the film plane. The
known to pack well via their
p p interaction [19,20,41]. Taking into
ꢀ
account these facts, the scattering peak at 2qf ¼ 19.91ꢁ can be
assigned as a reflection from the
in the phase separated P3HT phase.
pꢀp stacked thiophene backbones
In addition, the GIWAXS pattern reveals weak, broad isotropic
scattering ring over 11e25ꢁ (Fig. 10A and C). This broad isotropic
ring can be deconvoluted into three reflection peaks at least. One of
those is the reflection at 2qf ¼ 19.91ꢁ, which was discussed above.
The other two ring peaks are centered at 2qf ¼ 15.40 and 17.41ꢁ.
Considering the chain packing situations in the P3HT and P3TEGT
phases, one at 2qf ¼ 15.40ꢁ (d-spacing ¼ 0.52 nm) can be assigned
to the mean interdistance of the side groups between the P3TEGT
block chains while the other at 2qf ¼ 17.41ꢁ (d-spacing ¼ 0.46 nm)
can be assigned to the mean interdistance of the side groups
between the P3HT block chains.
From the above GIWAXS analysis results, a molecular packing
model in the P3HT lamellar layer and in the P3TEGT lamellar layer
are developed and shown in Fig. 11.
crystalline nature is attributed to the
backbones. In contrast, the P3TEGT phase is amorphous but still able
pꢀ
p stacked thiophene

T. Higashihara et al. / Polymer 52 (2011) 3687e3695
3695
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Dr. K. Ohshimizu especially thanks a research fellowship for
young scientists from the Japan Society for the Promotion of Science
(JSPS). This work was supported by Global COE Program, Education
and Research Center for Material Innovation, MEXT, and Japan
Science and Technology Agency (JST), PRESTO program (JY220176).
The technical supports of Mr. Jun Koki and Mr. Ryohei Kikuchi, Center
for Advanced Materials Analysis, Tokyo Institute of Technology, for
the TEM operation are gratefully acknowledged. The SAXS
measurement has been performed under the approval of Photon
Factory Advisory Committee (No. 2010G014). M.R. acknowledges the
financial supports of the National Research Foundation of Korea
(Center for Electro-Photo Behaviors in Advanced Molecular Systems
(2010-0001784)) and of the Ministry of Education, Science & Tech-
nology (MEST) (BK21 Program and World Class University Program
(R31-2008-000-10059-0)). The synchrotron X-ray scattering
measurements at Pohang Accelerator Laboratory were supported by
MEST, POSCO and POSTECH Foundation.
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