Synthesis and characterization of all-conjugated diblock copolymers consisting of thiophenes with a hydrophobic alkyl and a hydrophilic alkoxy side chain

Article abstract of DOI:10.1016/j.polymer.2011.06.030

Novel thiophene-based all-conjugated block copolymers consisting of 3-hexylthiophene and 3-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}thiophene were synthesized using the Grignard metathesis (GRIM) polymerization method in the presence of Ni(dppp)Cl₂. Favorable transfer of the catalytic site from an electron-poor precursor to an electron-rich monomer was found to produce the block copolymer. The molecular weights of the copolymers increased slightly with increasing polymerization temperature (10.1 × 10³ M _n (35 °C) → 11.1 × 10³ M_n (55 °C)), suggesting that transit of the catalytic site was accelerated at high temperatures. Size exclusion chromatography, UV-vis and photoluminescence spectroscopies, and cyclic voltammetry measurements confirmed that the polymers were block copolymers. The blocks were associated and organized relative to one another in adjacent chains.

Full text of DOI:10.1016/j.polymer.2011.06.030

Polymer 52 (2011) 3704e3709
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Polymer
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Synthesis and characterization of all-conjugated diblock copolymers consisting
of thiophenes with a hydrophobic alkyl and a hydrophilic alkoxy side chain
1
2
*
Jinseck Kim , Ayyanar Siva , In Young Song, Taiho Park
Department of Chemical Engineering, Polymer Research Institute, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel thiophene-based all-conjugated block copolymers consisting of 3-hexylthiophene and 3-{2-[2-(2-
methoxyethoxy)ethoxy]ethoxy}thiophene were synthesized using the Grignard metathesis (GRIM)
polymerization method in the presence of Ni(dppp)Cl2. Favorable transfer of the catalytic site from an
electron-poor precursor to an electron-rich monomer was found to produce the block copolymer. The
molecular weights of the copolymers increased slightly with increasing polymerization temperature
(10.1 ꢀ 103 Mn (35 ꢁC) / 11.1 ꢀ 103 Mn (55 ꢁC)), suggesting that transit of the catalytic site was accel-
erated at high temperatures. Size exclusion chromatography, UVevis and photoluminescence spectros-
copies, and cyclic voltammetry measurements confirmed that the polymers were block copolymers. The
blocks were associated and organized relative to one another in adjacent chains.
Received 26 March 2011
Received in revised form
14 June 2011
Accepted 19 June 2011
Available online 25 June 2011
Keywords:
Conjugated diblock copolymer
Thiophene
Ó 2011 Elsevier Ltd. All rights reserved.
Grignard metathesis polymerization
1. Introduction
crystallineecrystalline diblock copolymers. This novel method was
extended to monomers other than thiophene and its derivatives,
Since McCullough developed the Grignard metathesis (GRIM)
polymerization [1] of poly(3-hexylthiophenes) (P3HT), P3HT has
been employed widely in organic electronic and photonic applica-
tions, such as organic field-effect transistors (OFETs) [2] and organic
photovoltaic (OPV) devices [3]. These materials display relatively
such as 1,4-dibromo-2,5-dialkoxy-benzene (5) [9], 2,5-dibromo-1-
alkyl-1H-pyrrole [10], 2,7-dibromo-N-alkyl-substituted carbazole
[11], and 2,7-dibromo-9-dialkylfluorene [11]. During the propaga-
tion step, reductive elimination yielded a thiopheneethiophene
bond via intramolecular transfer of the nickel to the chain end by
oxidative insertion into the thiophene-bromine bond. Therefore,
controlling intramolecular transfer was a key to obtain a well-
defined block copolymer with a narrow molecular weight distri-
bution. Yokozawa et al. demonstrated that the order of addition of
the monomers played a crucial role in the successful transfer of the
catalyst from one block to the next [9]. The initial polymerization of
high hole mobilities (mh ¼ 10ꢂ2 cm2 Vꢂ1
s
ꢂ1) and low bandgaps
(DEg ¼ 1.9 eV) [4]. A product of the GRIM polymerization method
was prepared by magnesium halogen exchange of 2,5-dibromo-3-
hexylthiophene with CH3MgCl followed by addition of a Ni cata-
lyst to afford P3HTs with a narrow molecular weight distribution
and high regioregularity. Extensive independent studies of the
polymerization mechanism by McCullough [5] and Yokozawa [6]
revealed that the polymerization reaction displayed characteristics
reminiscent of a quasi-living process. Tajima et al. [7] and others [8]
have described the successful synthesis of thiophene-based all-
conjugated diblock copolymers, such as poly(3HT-b-(3(2-
ethylhexyl)thiophene)) [7] (1) as a crystalline-amorphous diblock
copolymer, and poly(3HT-b-(3(4-octylphenyl)thiophene)) [8a] (2)
and poly(-(3-buylthiophene)-b-(3-octylthiophene)) [8b] (3) as
the more strongly
p-rich thiophene monomer, followed by addition
of the p-phenylene monomer, resulted in a broad molecular weight
distribution. Meanwhile, reversing the order of polymerization led
to well-controlled polymerization with a narrow molecular weight
distribution. Recently, we reported synthesis of a novel thiophene-
based all-conjugated diblock copolymer (4) with hydrophobic and
hydrophilic side chains. This polymer formed a polymeric vesicle
with a crystalline interior and an amorphous exterior [12]. Herein,
we report the synthesis of novel all-conjugated thiophene-based
amphiphilic diblock copolymers. We used a second monomer [13]
(10) with a {2-[2-(2-methoxyethoxy)ethoxy]ethoxy} side chain
rather than an alkyl chain to produce a rod-rod-type amphiphilic
diblock copolymer. This allowed us to investigate the intramolecular
transfer of the catalyst from the growing chain end to the strongly
* Corresponding author. Tel.: þ82 54 279 2394; fax: þ82 54 279 8298.
E-mail addresses: drasiva@gmail.com (A. Siva), taihopark@postech.ac.kr (T. Park).
1
Present address: LG Chem. Research Park, 104-1, Moonji-Dong, Yoseong-Gu,
Daejeon 305-360, Republic of Korea.
2
Present address: Department of Inorganic Chemistry, School of Chemistry,
p-rich thiophene monomer, in contrast with the case of 5, as the
Madurai Kamaraj University, Palkalai Nagar, Madurai 625 021, Tamilnadu, India.
0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2011.06.030

J. Kim et al. / Polymer 52 (2011) 3704e3709
3705
alkoxy side chain enhanced the
p
-electron character of the thio-
ionization potential (IP) value of which is 4.8 eV for the Fc/Fcþ redox
system.
phene. In addition, the copolymers were expected to show a broad
white light absorption spectrum and a low bandgap due to the
electron-rich side chain (Fig. 1).
2.3. Poly(3-hexylthiophene), P3HT
Methylmagnesium bromide (5.3 mL, 1M solution in butylether,
5.25 mmol) was slowly added to a solution of 2,5-dibromo-3-
hexylthiophene (1.63 g, 5 mmol) (11) in anhydrous THF (20 mL)
at room temperature and the mixture was heated at 60 ꢁC for 1 h.
Ni(dppp)Cl2 (14 mg, 0.025 mmol) dispersed in anhydrous
THF(1 mL) was added and the solution was stirred at 60 ꢁC for
overnight. The mixture was poured into 200 mL of methanol and
precipitate was filtered. Soxhlet extractions were performed with
methanol (to remove monomer and salts), hexanes (to remove
catalyst and oligomers), and chloroform. The chloroform fraction
was reduced and dried in vacuo to afford 0.454 g (54%) of the title
2. Experimental details and measurements
2.1. Materials and reagents
2,5-Dibromo-3-hexylthiophene (11) and 2,5-dibromo-3-{2-[2-
(2-methoxyethoxy)ethoxy]ethoxy}thiophene (10) were synthe-
sized according to the previously reported procedures.[5d,13b] All
other chemical reagents were purchased from Aldrich Co. and used
without further purification except for tetrahydrofuran (THF)
which is purified using a J.C. Meyer solvent dispensing system.
polymer as a violet film. 1H NMR (CDCl3):
d[ppm] 6.98 (s, 1H), 2.80
(t, 2H), 1.71 (m, 2H), 1.36 (m, 6H), 0.91 (t, 3H).
2.2. Characterization
1H NMR spectra were recorded on a Bruker DPX-300 (300 MHz)
FT NMR system operating at 300 MHz. Number-average (Mn) and
weight-average (Mw) molecular weights were determined by size
exclusion chromatography (SEC) using the SHIMADZU LC solution,
chloroform as the eluent, and a calibration curve of polystyrene
standards. The UVeVis absorption spectra were measured using
a Carry 5000 UVeVis-near infrared double beam spectrophotom-
eter, and photoluminescence (PL) spectra of the copolymers were
measured on a Jasco FP-6500 spectrometer. Cyclic voltammetry
was performed using a POWERLAB/AD instrument model system in
a three-electrode cell with a 0.1 M Bu4NBF4 solution in acetonitrile
at a scan rate of 50 mV sꢂ1. A glassy carbon disk (w0.05 cm2) coated
with a thin polymer film was used as the working electrode. A
platinum wire and an Ag/AgNO3 electrode were used as the
counter- and reference electrodes, respectively. All measurements
were calibrated against an internal standard of ferrocene (Fc), the
2.4. P3HT-b-PMET block copolymers 6
Methylmagnesium bromide (4 mL, 1 M solution in bytylether,
4 mmol) was slowly added to a solution of 2,5-dibromo-3-
hexylthiophene (1.30 g, 4 mmol) (11) in anhydrous THF (40 mL)
at room temperature and the mixture stirred for 1 h. To the mixture
was added a suspension of Ni(dppp)Cl2 (43 mg, 0.08 mmol) in THF
(1 mL) via a syringe, and the mixture was stirred at room temper-
ature for 1 h. After this, solution mixture (1 mmol) (13) was
transferred to the THF solutions of 14 which had been prepared by
treatment of 10 (0.404 g, 1.00 mmol) in THF (10 mL) with methyl-
magnesium bromide (1 mL, 1 M solution in butylether, 1 mmol) at
different temperatures (BC1: 35ꢁ, BC2: 45ꢁ, BC3: 55 ꢁC). Each
solution was stirred for overnight. The resulting mixtures were
poured into 200 mL of methanol and precipitate was filtered.
Soxhlet extractions were performed with methanol (to remove
monomer and salts), hexanes (to remove catalyst and oligomers),
and chloroform. The chloroform fraction was reduced and dried in
vacuo and reprecipitated in methanol.
BC1: viscous violet colored solid, 125.3 mg (30% yield) 1H NMR
(CDCl3): d[ppm] 6.98 (br, 2.24H), 4.34 (br, 2.38H), 3.95 (br, 2.26H),
3.80e3.52 (m, 9.53H), 3.35 (br, 3.40H), 2.80 (br, 1.61H), 1.70 (br,
2.14H), 1.35 (br, 7.21H), 0.91 (br, 3.00H).
BC2: viscous violet colored solid, 172.3 mg (42% yield) 1H NMR
(CDCl3): d[ppm] 6.98 (br, 2.03H), 4.34 (br, 2.37H), 3.95 (br, 2.25H),
3.80e3.52 (m, 10.88H), 3.35 (br, 3.73H), 2.80 (br, 1.50H), 1.70 (br,
1.60H), 1.35 (br, 7.03H), 0.91 (br, 3.00H).
BC3: viscous violet colored solid, 171.6 mg (41% yield) 1H NMR
(CDCl3): d[ppm] 6.98 (br, 1.95H), 4.34 (br, 2.35H), 3.95 (br, 2.19H),
3.80e3.52 (m, 11.28H), 3.35 (br, 3.87H), 2.80 (br, 1.46H), 1.70 (br,
1.47H), 1.35 (br, 6.55H), 0.91 (br, 3.00H).
2.5. Poly(3-[2-[2(2-methoxyethoxy)ethoxy]ethoxy]thiophene)
(PMET)
Methylmagnesium bromide (5.3 mL, 1 M solution in butylether,
5.25 mmol) was slowly added to a solution of 2,5-dibromo-3-{2-[2-
(2-methoxyethoxy)ethoxy]ethoxy}thiophene (10) (2.00 g, 5 mmol)
in anhydrous THF (20 mL) at room temperature and the mixture
was heated at 60 ꢁC for 1 h. Ni(dppp)Cl2 (14 mg, 0.025 mmol)
dispersed in anhydrous THF(1 mL) was added and the solution was
stirred at 60 ꢁC for overnight. The mixture was poured into 200 mL
of methanol and precipitate was filtered. Soxhlet extractions were
performed with methanol (to remove monomer and salts), hexanes
(to remove catalyst and oligomers), and chloroform. The chloro-
form fraction was reduced and dried in vacuo to afford 0.467 g
Fig. 1. Structures of the thiophene-based all-conjugated diblock copolymers reported
in the literature (1e5) and synthesized here (6).

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J. Kim et al. / Polymer 52 (2011) 3704e3709
(38%) of the title polymer as a violet colored solid. 1H NMR (CDCl3):
[ppm] 6.98 (s, 1H), 4.34 (br, 2H), 3.95 (br, 2H), 3.80e3.52 (m, 10H),
3.35 (br, 3H).
Table 1
Molecular weights of the prepolymers, copolymers, and ratios of the blocks.
d
Polymers
Temp
(ꢁC)
103 Mn (g/mol)
Ratio (3HT:MET)b
a
(Mn/Mw
)
by GPCc
by NMRd
P3HT Precursor
(13)
r.t.
5.5 (1.24)
e
e
3. Results and discussion
BC1
BC2
BC3
PMET
P3HT
35
45
55
r.t.
r.t.
10.1 (1.64)
10.8 (1.68)
11.1 (1.73)
21.4 (1.32)
38.6 (1.26)
64:36
60:40
59:41
e
47:53
45:55
44:56
e
3.1. Synthesis and characterization
The synthesis of the monomers and block copolymers are out-
lined in Fig. 2. The thiophene-based derivative (9) having a hydro-
philic 2-[2-(2-methoxyethoxy)ethoxy]ethoxy substituent was
synthesized by copper (I)-mediated substitution of 3-
bromothiophene (7), followed by NBS bromination in THF at
cryogenic temperatures.
e
e
a
Determined by SEC in chloroform using a polystyrene standard.
Indicates the molar ratio of the monomer units of the 11 (3HT) and 10 (MET)
b
block polymers.
c
Estimated from the molecular weights of the repeated units and the degree of
polymerization in each block.
d
Estimated from the integral of the proton peaks at 3.35 (eOCH3) and 0.91
To prepare the amphiphilic block copolymers, the active
hydrophobic GRIM product (12) was prepared in situ by magnesium
halogen exchange of 11 (4.0 mmol) with CH3MgBr, followed by
polymerization at room temperature in the presence of a Ni catalyst
(Ni(dppp)Cl2) to obtain the P3HT living prepolymer (13) in the first
step. Three separate solutions containing the hydrophilic active
GRIM product (14) from 10 (1.0 mmol) were prepared by reaction
with CH3MgBr. Equal amounts (1.0 mmol) of the P3HT living pre-
polymer (13) were added to the three reaction solutions of the
GRIM product (14) (1.0 mmol). Polymerization of the three identical
compositions was conducted at 35, 45, and 55 ꢁC overnight to
afford the three block copolymers, BC1, BC2, and BC3, respectively.
The polymerization results are summarized in Table 1. The polymer
molecular weights and distributions (Mn/Mw) were determined by
size exclusion chromatography (SEC) against polystyrene standards
using CHCl3 as the eluent.
(eCH3) ppm.
weight of the P3HT living prepolymer (13) was 5.5 kDa (Mn), which
increased after reaction of the GRIM product (14) with the second
monomer. The monomer apparently did not decompose, and the
block copolymers were successfully synthesized. This result was
observed despite the report of Murso et al. [14] that monomer
decomposition occurred at high temperatures by reaction with
CH3Br generated in the metathesis reaction. Monomer decompo-
sition also demonstrated that transferring of the catalytic site from
a weaker electron-poor precursor (13) to a stronger electron-rich
monomer (14) favored production of copolymers with narrow
molecular weight distributions [9].
Interestingly, the molecular weights of the copolymers
increased slightly with increasing polymerization temperature at
the second step (10.1 ꢀ 103 Mn (35 ꢁC) / 10.8 ꢀ 103 Mn
(45 ꢁC) / 11.1 ꢀ 103 Mn (55 ꢁC)). This result suggested that trans-
ferring the catalytic site from the electron-poor precursor (13) to
the electron-rich monomer, relatively, was accelerated at high
temperatures. The temperature-dependent polymerization was
consistent with reports in the literature [15]. The molecular weight
distributions of the copolymers fell in the range 1.64e1.73 Mn/Mw,
which was slightly larger than the distributions of the homopoly-
mers, e.g., the P3HT prepolymer (1.24 Mn/Mw), P3HT (1.26 Mn/Mw)
with a large molecular weight (38.6 ꢀ 103 Mn), or PMET (1.32 Mn/
Mw). This was mainly ascribed to a shift toward a high molecular
weight polymer distribution, as seen in Fig. 3.
Fig. 3 shows the SEC chromatograms of the P3HT living pre-
polymer (13) and the resulting block copolymers. The molecular
The block ratios of the copolymers, calculated using the value for
Mn obtained from SEC measurements, were in the range
64:36e59:41 (3HT:MET). This range was close to the expected
value (50:50). On the other hand, the ratio estimated from 1H-NMR
Fig. 2. Synthetic scheme for preparing the hydrophilic monomer (10), and the quasi-
living copolymerization of the block copolymers (BC, 6) at various temperatures (35,
45, and 55 ꢁC).
Fig. 3. GPC elution curves of the prepolymer (P3HT) 13 and the block copolymers BC1,
BC2, and BC3.

J. Kim et al. / Polymer 52 (2011) 3704e3709
3707
Table 2
spectra, in which a methoxy peak (eOCH3) in the PMET block and
a methyl peak (eCH3) in the P3HT block appeared at 3.35 and
UVeVis absorption and emission data for P3HT, BC1, BC3, and PMET in chloroform
and in film.
0.91 ppm, respectively, provided
a range of 47:53e44:56
Polymers
Absorption
Emission
(3HT:MET). The value of Mn for the copolymers obtained from SEC
measurements was relative and assumed a random coil configu-
ration, and the ratios obtained from the 1H NMR spectra may have
been more reliable than those derived from SEC measurements.
The expected values may have been sensitive to differences in the
reactivities of the two monomers. Indeed, Mn (38.6 kDa Mn) for
P3HT was larger than that (21.4 kDa Mn) of PMET under identical
polymerization conditions.
Solution
(CHCl3)
Film
Solution
(CHCl3)
Film
a
b
a
b
c
c
Amax
D
Eopt
Amax
(nm)
D
(eV)
Eopt
lmax
lmax
(nm)
(eV)
(nm)
(nm)
P3HT
BC1
BC3
450
487
e
1.90
1.81
e
521
563
e
1.86
1.44
e
578
580
620
657
653
651
654
721
PMET
578
1.71
650
1.44
a
Absorption maximum wavelength.
Optical bandgap calculated at long wavelength absorption onset point.
Photoluminescence (PL) maximum wavelength. Excited at 420 nm.
3.2. Photophysical properties
b
c
To further investigate the structures and organizational associ-
ation among blocks in adjacent chains, optical studies of the block
copolymers were conducted in solution [1 ꢀ10ꢂ5 M] and film using
by UVevis spectroscopy, as shown in Fig. 4 (Table 2). We couldn’t
observe any new peaks or changes of shapes up to this concen-
tration [16]. The absorption maximum (Amax) of PMET was 578 nm
in a chloroform solution (Fig. 4(a)) and 650 nm in the film state
(Fig. 4(b)), higher than the values (450 nm in chloroform and
521 nm in film) for P3HT. This observation indicated that intro-
ducing an alkoxy side chain led to a lower bandgap due to the
mesomeric effect [17]. Meanwhile, both homopolymers (P3HT and
PMET) exhibited 71e72 nm red shifts at Amax in transitioning from
solution to film, indicating that the increased effective conjugation
length was governed not by the side chains, but by the nature of the
main backbones of the homopolymers.
Films were prepared by spin-casting, followed by annealing at three
different temperatures (50, 100, and 150 ꢁC), and the absorbance
properties were measured. For PMET, Amax appeared at 650 nm at
35 ꢁC, but it decreased slightly to 619 nm (Fig. 4(c)). For P3HT, the
absorption spectra revealed an additional absorption peak at
610 nm. This peak originated from the P3HT crystalline structure,
which featured p-p interactions among the P3HT blocks [18]. As the
annealing temperature increased, an additional peak (610 nm) was
observed (Fig. S1). Similar results were observed in the absorption
spectra of BC1 (Fig. 4(d)), (see Fig. S2 for BC2 and BC3). The peak
intensityat 610 nmwas enhanced at higherannealing temperatures,
indicating the preparation of two distinctive well-separated blocks,
which associated with one another and organized the adjacent
chains at high temperatures.
A comparison of the photoluminescence (PL) of P3HT, PMET, and
the block copolymers clearly supported the association and orga-
nization among blocks in adjacent chains (Fig. 5). The emission
maxima (lmax) of PMET, excited at 420 nm, were 657 nm in chlo-
roform (Fig. 5(a)) or 721 nm in film (Fig. 5(b)) and were higher than
The full width at half-maximum of the absorption band of the
block copolymer BC1 (228 nm) was greater than the corresponding
values for the homopolymers (P3HT ¼ 123 nm and PMET ¼ 145 nm)
in chloroform (Fig. 4(a)). This was consistent with a structure in
which the block copolymer contained intact P3HT and PMET units.
The solid-state properties of the block copolymer were studied.
Fig. 4. Normalized UVeVis absorption spectra. (a) P3HT, BC1, and PMET in chloroform. (b) P3HT, BC1, and PMET in film. (c) Temperature dependence of PMET in film.
(d) Temperature dependence of BC1 in film.

3708
J. Kim et al. / Polymer 52 (2011) 3704e3709
Fig. 5. Normalized photoluminescence (PL). (a) P3HT, BC1, BC3, and PMET in chloroform. (b) P3HT, BC1, BC3, and PMET in film. (c) Temperature dependence of BC1 in films.
(d) Temperature dependence of BC3 in films.
those (578 nm in chloroform and 653 nm in film) of P3HT due to the
mesomeric effect of the alkoxy side chain [17]. PMETexhibited a red
shift of 64 nm at lmax in transitioning from solution to film, and this
red shift was 11 nm smaller than the red shift observed in P3HT.
This indicated that the flexible side chains slightly hampered
ordering of the PMET blocks in the copolymer, as observed by
photoluminescent emission. The emission spectra of the block
copolymers, BC1 and BC3, showed some differences, depending on
the block ratios (Fig. 5(a)). BC1 (53% of the PMET block ratio) gave
chloroform. The potentials were calibrated against an internal
ferrocene (Fc) standard. It should be noted that the oxidation
potential, measured by cyclic voltammetry, was the lowest among
the independently oxidizable species in the polymer chain. Thus,
the oxidation potential may be strongly affected by the electronic
properties of the P3HT and PMET blocks. The PMET block of BC1
having the alkoxy side chains on was more electron-rich than the
P3HT block having the alkyl substituents. Thus, the oxidation
behavior of BC1 may be dominated by the properties of the PMET
block. Indeed, the initial oxidation of BC1 occurred at a potential
(e0.22 V) at which PMET began to oxidize, even though the onset
potential for BC1 was determined to be 0.083 V, based on its major
oxidation slope, as shown in Fig. 6. The oxidation potential of BC1 at
the peak maximum was 0.67 V, similar to that of P3HT (0.65 V). This
result indicated that oxidation occurred separately at each block,
for instance, the PMET block was oxidized at a lower voltage and
the P3HT block was oxidized at a higher voltage. The block copol-
ymers, therefore, were well-prepared. The electrochemical
a
lmax of 582 nm with a shoulder at 620 nm. However, the emission
at 620 nm was dominant in BC3, which contains 56% PMET block.
This observation was ascribed to the high flexibility of the PMET
block, which increased the ordering among the
p-p interactions
between P3HT blocks. The peak at 582 nm is characteristic of
p-
stacking in P3HT [19]. Similar trends were observed in the emission
spectra of the film states (Fig. 5(b)). Annealing of BC1 and BC3
clearly demonstrated PMET block-assisted organization of the P3HT
block in the copolymers, as shown in Fig. 5(c) and (d), respectively.
bandgap (
DEelec), which indicated the energy difference between
3.3. Electrochemical properties
The electrochemical properties of BC1 were investigated using
cyclic voltammetry (CV), and the resulting data for P3HT and PMET
are summarized in Table 3. The polymer film was coated onto
a
glassy carbon disk by dropping the polymer solution in
Table 3
Electrochemical properties of P3HT, PMET, and BC1.
Oxidation
Reduction
Epeak
(V)
Eon
(V)
EHOMO
(eV)
Epeak
(V)
Eon
(V)
ELUMO
(eV)
DEelec
(eV)
P3HT
BC1
PMET
0.65
0.67
0.060
0.35
0.083
ꢂ0.22
5.2
4.9
4.6
ꢂ1.45
ꢂ1.35
ꢂ1.32
ꢂ1.31
ꢂ1.19
ꢂ1.11
3.5
3.6
3.7
1.67
1.27
0.89
Fig. 6. Cyclic voltammograms of P3HT, PMET, and BC1, relative to a ferrocene internal
standard.

J. Kim et al. / Polymer 52 (2011) 3704e3709
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3709
onset potentials of oxidation and reduction, varied depending on
the chemical nature of the polymer. Eelec of PMET was 0.89 eV,
which was clearly lower than that of P3HT (1.67 eV). However,
discrepancies between Eelec and Eopt (the optical bandgap in the
film) were observed, especially in BC1, in agreement with reports
by others [20]. These discrepancies were ascribed to the hydrophilic
electrolytes present during the CV measurements, although this
topic requires further investigation.
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7271e3.
We successfully synthesized thiophene-based amphiphilic all-
conjugated block copolymers consisting of P3HT and PMET
blocks, as confirmed by SEC measurements. The polymerization
reaction via a Grignard metathesis (GRIM) in the presence of
Ni(dppp)Cl2 exhibited quasi-living characteristics, indicating the
successful transfer of
a catalytic site from an electron-poor
precursor to an electron-rich monomer, relatively. The molecular
weights of the block copolymers increased slightly with increasing
polymerization temperature without decomposition of the active
sites. UVevis, PL, and CV measurements of P3HT, PMET, and the
block copolymers clearly supported the association and organiza-
tion of the two blocks in adjacent chains.
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Acknowledgment
[10] Yokoyama A, Kato A, Miyakoshi R, Yokozawa T. Macromolecules 2008;41:
7271e4.
This work was supported by the Energy R&D program grant
(20093020010040) funded by the MKE, by the Mid-career
Researcher Program and the Basic Science Research Program
through a National Research Foundation of Korea (NRF) grant
funded by the MEST (No. 2010-0027732, No. 2009-0093462), and
by the second stage of a BK21 (Brain Korea 21) grant.
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Appendix. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.polymer.2011.06.030.
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