Synthesis and postfunctionalization of rod-coil diblock and coil-rod-coil triblock copolymers composed of poly(3-hexylthiophene) and poly(4-(4′-N, N -dihexylaminophenylethynyl)styrene) segments

Article abstract of DOI:10.1021/ma301692b

Poly(3-hexylthiophene) (P3HT) with a bromobutyl functional group at the ω-chain-end (P3HT-C₄Br) and P3HT with bromobutyl functional groups at the α,ω-chain-ends (BrC₄-P3HT-C₄Br) were synthesized by selecting the appropriate initiators for the Grignard metathesis (GRIM) polymerization. The high end-functionality was confirmed by matrix assisted laser desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry. These polymers were efficiently reacted with the living anionic polymers of 4-(4′-N,N-dihexylaminophenylethynyl)styrene (DHPS) to yield novel rod-coil diblock and coil-rod-coil triblock copolymers composed of rigid P3HT and flexible poly(4-(4′-N,N-dihexylaminophenylethynyl)styrene) (PDHPS) segments. The expected structures of the block copolymers were confirmed by size exclusion chromatography (SEC), proton nuclear magnetic resonance (¹H NMR), and Fourier transform infrared (FT-IR) spectroscopies. Furthermore, the side chain alkynes of the PDHPS segments of both P3HT-b-PDHPS and PDHPS-b-P3HT-b-PDHPS were quantitatively functionalized by a [2 + 2] cycloaddition followed by a cycloreversion with tetracyanoethylene (TCNE), producing the corresponding block copolymers with donor-acceptor moieties in the flexible polystyrene segments. The formation of the new chromophores was confirmed by UV-vis spectroscopy and cyclic voltammetry (CV), which revealed strong intramolecular charge-transfer bands and redox activities ascribed to the formed donor-acceptor moieties. The thermal properties and surface morphology of the block copolymers were also evaluated by differential scanning calorimetry (DSC), atomic force microscopy (AFM) observations, and small-angle and wide-angle X-ray scattering (SAXS and WAXS). This is the first report about the development of P3HT-based block copolymers with tunable optoelectronic properties, which was achieved by the combined synthetic techniques of the GRIM polymerization, living anionic polymerization, and click postfunctionalization.

Full text of DOI:10.1021/ma301692b

Article
pubs.acs.org/Macromolecules
Synthesis and Postfunctionalization of Rod−Coil Diblock and Coil−
Rod−Coil Triblock Copolymers Composed of Poly(3-hexylthiophene)
and Poly(4-(4′‑N,N‑dihexylaminophenylethynyl)styrene) Segments
Hiroyuki Fujita,† Tsuyoshi Michinobu,‡,* Masatoshi Tokita,† Mitsuru Ueda,†
and Tomoya Higashihara†,§,*
†Department of Organic and Polymeric Materials, Graduate School of Science and Engineering, Tokyo Institute of Technology,
2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552, Japan
‡Global Edge Institute, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8550, Japan
§Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
S
* Supporting Information
ABSTRACT: Poly(3-hexylthiophene) (P3HT) with a bro-
mobutyl functional group at the ω-chain-end (P3HT-C4Br)
and P3HT with bromobutyl functional groups at the α,ω-
chain-ends (BrC4-P3HT-C4Br) were synthesized by selecting
the appropriate initiators for the Grignard metathesis (GRIM)
polymerization. The high end-functionality was confirmed by
matrix assisted laser desorption-ionization time-of-flight
(MALDI−TOF) mass spectrometry. These polymers were
efficiently reacted with the living anionic polymers of 4-(4′-
N,N-dihexylaminophenylethynyl)styrene (DHPS) to yield
novel rod−coil diblock and coil−rod−coil triblock copolymers composed of rigid P3HT and flexible poly(4-(4′-N,N-
dihexylaminophenylethynyl)styrene) (PDHPS) segments. The expected structures of the block copolymers were confirmed by
size exclusion chromatography (SEC), proton nuclear magnetic resonance (1H NMR), and Fourier transform infrared (FT-IR)
spectroscopies. Furthermore, the side chain alkynes of the PDHPS segments of both P3HT-b-PDHPS and PDHPS-b-P3HT-b-
PDHPS were quantitatively functionalized by a [2 + 2] cycloaddition followed by a cycloreversion with tetracyanoethylene
(TCNE), producing the corresponding block copolymers with donor−acceptor moieties in the flexible polystyrene segments.
The formation of the new chromophores was confirmed by UV−vis spectroscopy and cyclic voltammetry (CV), which revealed
strong intramolecular charge-transfer bands and redox activities ascribed to the formed donor−acceptor moieties. The thermal
properties and surface morphology of the block copolymers were also evaluated by differential scanning calorimetry (DSC),
atomic force microscopy (AFM) observations, and small-angle and wide-angle X-ray scattering (SAXS and WAXS). This is the
first report about the development of P3HT-based block copolymers with tunable optoelectronic properties, which was achieved
by the combined synthetic techniques of the GRIM polymerization, living anionic polymerization, and click
postfunctionalization.
separation of dissimilar segments.9 Since the flexible coil
segments tend to effectively assist the microphase separation by
preventing the aggregation of the crystalline P3HT domains,
the rod−coil types seem to be superior to the rod−rod types in
the sense of morphological control.
To synthesize well-defined rod−coil block copolymers
containing a P3HT segment, multistep and complex site
transformation reactions have been required because different
polymerization systems must, in general, be used for the
synthesis of each P3HT and coil segments. This difficulty has
limited the establishment of a general synthetic route to the
well-defined rod−coil block copolymers. Nevertheless, some
INTRODUCTION
■
There has been growing attention paid to poly(3-
alkylthiophene)s (PATs) in the field of polymer electronic
devices, such as organic field-effect transistors1 and organic
photovoltaic cells,2 because PATs are the best class of balanced
high-performance materials as p-type semiconductors in terms
of solubility, chemical stability, charge mobility, and commercial
availability. The discovery of the quasi-living GRIM polymer-
ization system, independently reported by Yokozawa et al.3 and
McCullough et al.,4,5 made it possible to synthesize a wide
variety of chain-end-functional polythiophene derivatives,6 their
block copolymers5,7 and star-branched polymers.8 Among
them, rod−coil block copolymers containing the poly(3-
hexylthiophene) (P3HT) moiety as a rod segment are of
particular interest due to their unique self-assembled structures
on a nanometer scale, originating from the microphase
Received: August 9, 2012
Revised: November 19, 2012
Published: November 30, 2012
© 2012 American Chemical Society
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rod−coil block copolymers composed of P3HT segments have
already been reported.10 We have also succeeded in synthesiz-
ing polystyrene-b-P3HT-b-polystyrene and poly(4-N,N-diphe-
nylaminostyrene)-b-P3HT-b-poly(4-N,N-diphenylaminostyr-
ene) by the combination of the GRIM polymerization and
living anionic polymerization techniques.11,12 The synthetic
methodology requires only two reaction steps, (a) the synthesis
of P3HT with 1,1-diphenylethylene (DPE) functional groups at
α,ω-chain-ends (DPE-P3HT-DPE) and (b) the linking reaction
of DPE-P3HT-DPE with 2 equiv of the living anionic
polystyrene or poly(4-N,N-diphenylaminostyrene). Because of
the living anionic polymerization system and reduced reaction
steps, the polydispersity indices (PDIs) of the final products are
relatively low (PDI < 1.2). Although significant purification
efforts are required to remove homopolymers used in excess
and/or unreacted in the linking reaction, the most advanta-
geous feature of this polymer/polymer linking method is the
high accuracy of individual polymer segments in the block
copolymers in terms of the molecular weights and molecular
weight distributions, as compared to other initiation methods
using end-functionalized polymers.
In addition to the excellent semiconducting characteristics of
P3HT, it is also expected that the coil segments show some
specific properties, especially when the applications to organic
solar cells are considered. Although the triphenylamine moiety,
previously adopted as a side chain of the coil segments, is redox
active and possesses p-type semiconducting features, the
absorption range is limited in the ultraviolet (UV) region.12
Also, the shallow lowest unoccupied molecular orbital
(LUMO) level of the triphenylamine unit generally hinders
the efficient energy transfer from P3HT to the coil segments.
To expand the absorption range into the visible-near-infrared
and lower the LUMO level, intramolecular charge-transfer
(CT) interactions are often used. Since aromatic amines are a
strong electron-donating group, the direct substitution by
electron-accepting moieties would result in a new low-energy
CT band due to the elevation of the highest occupied molecular
orbital (HOMO) level and reduction of the LUMO level.
However, electron-accepting units are usually unstable under
anionic polymerization conditions. Thus, the electron-accepting
moieties have not been introduced into the P3HT-based rod−
coil block copolymers.
polymers including polystyrenes, polyurethanes, polyacetylenes,
conjugated polymers, and aromatic polyamines were success-
fully functionalized by this method.17 In the previous studies of
the P3HT-based rod−coil block copolymers, the energy levels
of the coil segments were inevitably determined by the vinyl
monomer structures, and the number of available vinyl
monomers was limited from the synthetic standpoint. However,
such a polymer functionalization method based on the new
click chemistry would provide the desired (or varied) energy
levels of the coil segments, and this will lead to the fast energy
transfer from P3HT into the coil segments in organic solar
cells.
We now report the synthesis and postfunctionalization of
rod−coil diblock and coil−rod−coil triblock copolymers
c o m p o s e d o f P 3 H T a n d p o l y ( 4 - ( 4 ′ - N , N -
dihexylaminophenylethynyl)styrene) (PDHPS) segments,
P3HT-b-PDHPS and PDHPS-b-P3HT-b-PDHPS, respectively,
by the combination of the GRIM polymerization, living anionic
polymerization, and click postfunctionalization. The bromi-
nated polythiophene derivatives, P3HT-C4Br and BrC4−
P3HT-C4Br, were for the first time synthesized by selecting
the appropriate initiators, and the individual polythiophenes
were isolated. These polymers were then reacted with the living
anionic polymers of DHPS to produce the corresponding block
copolymers. Furthermore, the block copolymers were post-
functionalized with TCNE. The thermal, optical, and electro-
chemical properties as well as the thin film and bulk sample
morphology are comprehensively investigated. This study
established the general synthetic route to the P3HT-based
block copolymers with tunable optoelectronic and self-
assembling properties.
RESULTS AND DISCUSSION
■
Synthesis of Chain-end Functional P3HT. The chain-
end functionalization of P3HT is a very important step for
obtaining rod−coil block copolymers, because the terminal
functional groups are responsible for the introduction of the
coil segments. McCullough reported the chain-end functional-
ization of P3HT by terminating the quasi living P3HT-
Ni(dppp)Br (dppp = diphenylphosphinopropane) with the
Grignard reagent (R-MgX).6 However, the R-MgX type
significantly affected the final product structures as to whether
the monofunctionalization at the ω-terminal or difunctionaliza-
tion at the α,ω-termini takes place. This fact suggested the
difficulty in selectively synthesizing either the mono- or
difunctional P3HT derivatives. For instance, during the course
of our studies on the synthesis of DPE-P3HT-DPE,11 we could
not achieve the monofunctional P3HT with a DPE moiety,
probably because of the diffusion of the Ni(0) species to the
media after the monofunctionalization of P3HT-Ni(dppp)Br
with the Grignard reagent of 1-(4-bromopropylphenyl)-1-
phenylethylene (DPE-C4-MgBr), resulting in the occurrence
of difunctionalization in terms of the oxidative insertion of the
Ni(0) species to the α-chain-end.
Recently, another approach to construct donor−acceptor
chromophores in polymer side chains was proposed. That is
based on the formation of electron-accepting units during the
last stage of the polymer functionalization by high-yielding
addition reactions between electron-rich alkynes and strong
acceptor molecules, such as tetracyanoethylene (TCNE).13
A
[2 + 2] cycloaddition of the electron-deficient olefin of TCNE
to electron-rich alkynes, followed by a cycloreversion, yields
donor-substituted 1,1,4,4-tetracyanobuta-1,3-diene (TCBD)
chromophores.14 When alkynes are substituted by aromatic
amines, this reaction quickly proceeds under mild conditions
without any side reactions and byproducts. Accordingly, this
class of reactions is regarded as metal-free click chemistry.15
A
Luscombe and co-workers reported the efficient initiation
from an o-halotoluene based on a ligand exchange approach,
aimed at the synthesis of a defect-free regioregular P3HT.18 It
should be noted that the initiation using Ni(dppp)Cl2 causes
tail-to-tail dimer formation at the initiating site.3−5 On the basis
of this finding, we first intended to synthesize the monofunc-
tional P3HT, in which only the ω-chain-end was terminated by
P3HT-Ni(dppp)Br with R-MgX. The α-chain-end was capped
by the tolyl group. As can be seen in Scheme 1a, the ligand of
significant advantage of this reaction over the conventional click
chemistry reactions, such as the azide−alkyne cycloaddition,
thiol−ene reactions, and Diels−Alder reactions, is the
emergence of new functinonalities based on intramolecular
CT interactions. For example, an improved second-order
nonlinearity, metal ion sensitivity, and energy level tuning
ability were realized.16 This method is highly promising because
of its applicability to almost all polymers. Indeed, various
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Scheme 1. Synthesis of (a) 8, P3HT-C4Br, and (b) 9, BrC4-P3HT-C4Br
the trans-bromo(tolyl)bis(triphenylphosphine)nickel(II) com-
plex (1) was replaced with dppp in tetrahydrofuran (THF) at
room temperature to yield the monofunctional initiator, the cis-
bromo(tolyl)(dppp)nickel(II) complex (2). This was followed
by the initiation of 2-bromo-5-chloromagnesio-3-hexylthio-
phene (4) in THF, which was obtained by the Grignard
exchange reaction of 2,5-dibromo-3-hexylthiophene (3) with
isopropylmagnesium chloride (iPrMgCl). By terminating the
monofunctional living polymer (5) with 2-(4-bromobutyl)-5-
(chloromagnesio)thiophene (7), which was obtained by the
Grignard exchange reaction of 5-bromo-2-(4-bromobutyl)-
Table 1. Molecular Weights, Polydispersities, and
Composition of Polymers
P3HT: PSt
derivatives
Mn (g/mol)
a
a
polymer
1H NMR
SEC
PDI
(mol %) (wt %)
b
P3HT-C4Br (8)
9 800
11 000
12 500
31 300
42 300
10 700
10 600
40 900
1.11
1.06
1.06
1.15
1.11
1.05
1.05
−
−
49:51
−
−
29:71
24:76
−
c
PDHPS
−
d
b
e
P3HT-b-PDHPS (11)
P3HT-b-PTCNE (13)
BrC4−P3HT-C4Br (9)
32 800
d
b
40 400
8 800
49:51
−
−
f
PDHPS
−
20:80
i
thiophene (6) with PrMgCl, P3HT with the bromobutyl
d
d
b
PDHPS-b-P3HT-b-
PDHPS (12)
42 400
53 400
37:63
functional group at the ω-chain-end (8: P3HT-C4Br) was
successfully obtained. When Ni(dppp)Cl2 was used as the
initiator instead of 2, P3HT with the bromobutyl functional
groups at the α,ω-chain-ends (9: BrC4-P3HT-C4Br) was
obtained (Scheme 1b). The polymer structures were
e
PTCNE-b-P3HT-b-
PTCNE (14)
56 300
1.07
37:63
16:84
a
Calculated from the calibration using polystyrene standards.
b
Calculated from the peak intensity ratio between the thiophene
c
1
ring and alkyl groups. The coil segment used for the synthesis of 11
after capped with DPE. Calculated from the peak intensity ratio and
each molecular weight. The same composition ratios as the
corresponding precursor polymers. The coil segment used for the
characterized by SEC, H NMR, FT-IR, and MALDI−TOF
d
mass spectrometry. The selected data are summarized in Table
1.
e
f
In the SEC curves of 8 and 9 (Figure 1a for 8 and Figure 2a
for 9), unimodal peaks were observed, indicating the living
manner of the GRIM polymerization system. The estimated
molecular weights were ca. 10 000 and the polydispersity
indices (PDIs) were narrow (1.11). The 1H NMR spectrum of
8 is shown in Figure 3a. There is the characteristic singlet signal
d at 2.48 ppm, assignable to the three methyl protons of the
tolyl initiating site. Also, the triplet signal b ascribed to the two
methylene protons next to the terminal Br group is observed at
3.43 ppm. The peak intensity ratio d:b was determined to be
3.12:2.00, which is close to the theoretical value of 3:2. This
result indicates that the efficient initiation and monofunction-
alization reactions proceeded without any undesired chain-
transfer or termination reactions. The molecular weight of 8,
synthesis of 12 after capped with DPE.
(Figure 3b) also confirmed the progress of the efficient
difunctionalization reaction. The peak positions and integration
ratios were consistent with the chemical structure and the
estimated molecular weight of 9. Furthermore, the MALDI−
TOF mass spectra of 8 and 9 (Figure 4, parts a and b,
respectively) showed a series of peaks corresponding to the
calculated molecular ions or their protonated forms. In the case
of the monofunctional P3HT 8, the most intense molecular ion
peak was detected at m/z = 5297.4, which agreed well with the
theoretical value of the 30-mer ([M]+ = 5297.66, m = 30). The
protonated forms were also sometimes detected. A sharp peak
ascribed to the protonated 29-mer ([M + H+] = 5132.38, m =
29) was clearly observed. Accordingly, reasonable peak intervals
corresponding to the monomer repeat unit (166.28) were
1
calculated from the ratio of the H NMR peak intensities, was
1
close to that determined by SEC. The H NMR spectrum of 9
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Figure 1. SEC curves of (a) 8, P3HT-C4Br, (b) PDHPS, (c) crude
products after the coupling reaction of 8 with the living PDHPS, (d)
11, P3HT-b-PDHPS, after HPLC fractionation, and (e) 13, P3HT-b-
PTCNE.
Figure 3. 1H NMR spectra of (a) 8 and (b) 9 in CDCl3 at 25 °C. The
residual CHCl3 peak is marked.
Figure 2. SEC curves of (a) 9, BrC4−P3HT-C4Br, (b) PDHPS, (c)
crude products after the coupling reaction of 9 with the living PDHPS,
(d) 12, PDHPS-b-P3HT-b-PDHPS, after HPLC fractionation, and (e)
14, PTCNE-b-P3HT-b-PTCNE.
The living polymers were quenched with methanol, yielding
PDHPS. The time-dependent conversion of DHPS into
PDHPS was investigated from the polymerization experiments
in benzene at 25 °C. The representative SEC curves are shown
in Figure 5a and the results are summarized in Table 2. The
SEC curves of the products directly collected from a reaction
flask (before precipitation into methanol) at varying times
gradually shifted to higher molecular weight ranges, maintain-
ing the narrow PDI of <1.2, as the polymerization time was
extended. The molecular weights determined by SEC propor-
tionally increased up to 61 kDa by increasing the feed ratio of
[DHPS]/[sBuLi], as shown in Figure 5b.
Synthesis of Block Copolymers. It is well-known that
living anionic polymers rapidly undergo the high-yielding
nucleophilic substitution reaction with bromoalkyl groups in
polar solvents, such as THF. No side reactions, such as the
metal−halogen exchange reaction and single electron transfer
reaction, usually occur under strictly controlled conditions.21 It
should be noted that the reaction between a living anionic
polymer and a chain-end functionalized polymer with
bromoalkyl groups is also a very efficient process and,
accordingly, this can be used to prepare block and star-
branched copolymers, despite the considerable steric hindrance
of the polymer chains. It is thought that the efficiency is
achieved by the high nucleophilicity of the carbanion and the
sufficient electrophilicity of the bromoalkyl group.
found. This fact strongly supports the perfect substitution of
the α and ω-ends by the tolyl and 4-bromobutylthienyl groups,
respectively. In other words, there were no disubstituted
products with 4-bromobutylthienyl end groups. The MALDI−
TOF mass spectrum of the bifunctional P3HT 9 displayed a
similar peak profile. The most intense peak at 6256.4 was the
molecular ion peak of the 35-mer ([M]+ = 6256.06, m = 35),
whereas the peak of the 34-mer at 6091.3 was the protonated
form ([M + H+] = 6090.78, m = 34). The peak intervals were
consistent with the monomer repeat unit. All these results
suggested that both P3HT-C4Br and BrC4-P3HT-C4Br with the
highly controlled end-functionalities were successfully synthe-
sized by selecting the appropriate initiators of the GRIM
polymerization system.
Living Anionic Polymerization of DHPS. In order to
achieve the desired block copolymers, we first needed to
confirm the living nature of the anionic polymerization of
DHPS, although there is a report on its radical polymer-
ization.19 The living anionic polymerization of 4-
(phenylethynyl)styrene with sec-butyllithium (sBuLi) as an
initiator was previously reported.20 On the basis of this report,
s
DHPS was anionically polymerized with BuLi in benzene at
room temperature or in THF at −78 °C under a nitrogen
atmosphere in a glovebox (Scheme 2). Both polymerization
conditions afforded the corresponding living polymers
(PDHPS-Li) within 10 min, and no side reactions occurred.
According to Scheme 3, the synthesis of the rod−coil diblock
copolymer (11: P3HT-b-PDHPS) and coil−rod−coil triblock
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the desired ABA triblock copolymer (12) and the quenched
PDHPS (10), respectively, the undesired AB diblock
copolymer was also produced. This was probably due to an
insufficient reaction time or contamination of the monofunc-
tional P3HT precursor in 9. Nevertheless, HPLC fractionation
enabled isolation of the desired ABA triblock copolymer 12.
Neither the AB diblock copolymer nor PDHPS existed in the
SEC curve (see Figure 2d).
The chemical structures of the block copolymers were
characterized by spectroscopic methods. The 1H NMR
spectrum of 11 is shown in Figure 6. The complete
disappearance of the bromomethylene peak at 3.43 ppm
indicates the successful coupling followed by purification. By
comparing the signal intensities of the P3HT and PDHPS
segments as well as the tolyl protons at the α-chain end (2.48
ppm), the degrees of polymerization of P3HTand PDHPS were
determined to be 57 and 59, respectively. The theoretical
molecular weight of 9.5 kDa + 22.9 kDa + 0.4 kDa = 32.8 kDa
was calculated from these values. The Mn value determined by
SEC was 31.3 kDa, which showed an excellent agreement to the
1
value calculated from the H NMR spectrum. The SEC curve
revealed the very narrow PDI of 1.06 even after the polymer
coupling reaction. These characterization data are summarized
in Table 1. The IR spectrum of 11 also suggested the formation
of the block copolymer. The alkyne vibration peak was clearly
detected at 2208 cm−1. Furthermore, the elemental analysis
showed good agreement with the theoretical value calculated
for the P3HT:PDHPS composition of 57:59. Similar to 11, the
purified triblock copolymer 12 was also perfectly characterized.
Figure 4. MALDI−TOF mass spectra of (a) 8, P3HT-C4Br and (b) 9,
BrC4-P3HT-C4Br. Inset: Enlarged spectra of the most intense peaks.
1
The H NMR spectrum of 12 revealed the absence of the
bromomethylene peak and the block composition ratio (Figure
1SI, Supporting Information). The degrees of polymerization of
P3HT and PDHPS were 50 and 43, respectively. The molecular
weight calculated from this ratio was consistent with that
determined by SEC (Table 1). Elemental analysis again
supported the composition.
Scheme 2. Living Anionic Polymerization of DHPS
We were thus successful in synthesizing new rod−coil
diblock and coil−rod−coil triblock copolymers composed of
P3HT and PDHPS segments, 11 and 12, based on the coupling
approach.
Click Postfunctionalization. The obtained block copoly-
mers were further converted into new derivatives by click
postfunctionalization. An equivalent amount of the small
acceptor molecule, TCNE, was added to a dichloromethane
solution of 11 and 12 at 20 °C (Scheme 4). The added TCNE
rapidly underwent a [2 + 2] cycloaddition followed by a
cycloreversion to the side chain alkynes activated by the
dihexylaniline donor, forming the dihexylaniline-substituted
1,1,4,4-tetracyanobuta-1,3-diene (TCBD) chromophore. The
formation of this donor−acceptor chromophore can be
evaluated from the charge-transfer (CT) band in the visible
region. In order to confirm the quantitative addition, the
titration experiments of TCNE added to the solutions of 11
and 12 were performed, and the UV−vis spectral changes were
monitored. Upon the stepwise addition of TCNE, a new CT
band appeared at 480 nm in both cases of 11 and 12 (Figure
3SI, Supporting Information). The peak position of the CT
band was almost unchanged, while the intensities linearly
increased with the increasing amount of TCNE up to 1.0 equiv.
The addition of excess TCNE did not cause any spectral
changes in the visible region, suggesting the reaction
completion and the high chemical stability of the formed
donor−acceptor chromophores and P3HT moiety. Thus, the
copolymer (12: PDHPS-b-P3HT-b-PDHPS) was performed by
coupling the excess living anionic PDHPS (PDHPS-Li) with 8
(P3HT-C4Br) or 9 (BrC4-P3HT-C4Br), respectively, in THF at
25 °C for 1 h. The living anionic polymer, PDHPS-Li, was
capped with 1,1-diphenylethylene (DPE) to tune the
nucleophilicity before the coupling reaction. This step also
suppressed any undesired reactions, such as a metal−halogen
exchange reaction and single electron transfer reaction, as well
as the attack on the pendent alkyne groups. The success of the
coupling reaction was judged by the SEC curves. As can be seen
in Figure 1c, the crude product of the reaction between 8 and
10 showed two main peaks corresponding to the desired AB
diblock copolymer (11) and quenched PDHPS (10) used in
excess in the reaction. After the HPLC fractionation, the
analytically pure 11 was successfully isolated in 59% yield (see
Figure 1d). There were no residual peaks assignable to the
precursor polymers, 8 and 10. In the case of the triblock
copolymer 12 synthesis, three major peaks were observed in the
SEC curve of the crude product (Figure 2c). Although the
highest and lowest molecular weight peaks were derived from
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Figure 5. (a) SEC curves of the products directly obtained after various polymerization times without precipitation treatment and (b) plots of the
feed ratio of [Monomer]/[sBuLi] × conversion (%)/100 versus Mn and PDI values.
Table 2. Living Anionic Polymerization of DHPS
Mn (g/mol)
a
b
c
c
solvent
temp (°C)
time (min)
convn (%)
[DHPS]/[sBuLi] × convn (%)/100
calcd
SEC
PDI
benzene
benzene
benzene
benzene
benzene
benzene
THF
25
1
40
9.88
12.4
15.1
20.0
24.5
140
3890
4860
5910
7810
9550
3950
5360
6140
7750
9240
1.09
1.14
1.15
1.11
1.12
1.23
1.06
25
60
10
4
100
100
81
25
25
25
10
10
10
99
25
98
54300
61200
−78
100
25.8
10100
12500
a
b
Calculated from the peak intensity ratio of the polymer and monomer in the SEC curves. Calculated from the equation: Mn (calcd) = 57.1 (sBu-)
+ [DHPS]/[sBuLi] × convn (%)/100 × 387.6 + 1.0 (H). Calculated from the calibration using polystyrene standards.
c
block copolymers 11 (P3HT-b-PDHPS) and 12 (PDHPS-b-
P3HT-b-PDHPS) were postfunctionalized with one equivalent
of TCNE, yielding the new block copolymers 13 (P3HT-b-
PTCNE) and 14 (PTCNE-b-P3HT-b-PTCNE), respectively.
Note that no special purification processes were necessary due
to the use of the click chemistry reaction.
precursor polymer 11 was replaced by the strong cyano
vibration peak at 2213 cm−1 for the postfunctionalized polymer
13. This was also true for the case of the triblock copolymers
12 and 14. Moreover, the elemental analyses also supported
these polymer structures.
Thermal Properties. The thermal stability of all polymers
was investigated by a thermogravimetric analysis (TGA) at the
heating rate of 10 °C min−1 under flowing nitrogen. The end-
functional P3HT derivatives 8 and 9 possessed a high thermal
stability due to the rigid main chain. The 5% decomposition
temperatures (Td5%s) of 8 and 9 were determined to be 430
and 412 °C, respectively (Table 3). However, the sequential
modification of these P3HT derivatives gradually reduced the
thermal stability. The TGA curves of the block copolymers 11
and 12 displayed a single step decomposition with the Td5%
values of 391 and 376 °C, respectively (Figure 5SI, Supporting
Information). These values further decreased upon the TCNE
addition. The Td5% values of 13 and 14 were 331 and 336 °C,
respectively. However, for these polymers, the decomposition
proceeded in two steps. Consequently, the residual char
amounts at 500 °C were greater than those of the precursor
polymers.
The chemical structures of the postfunctionalized polymers
were fully characterized. The SEC curves of 13 and 14 revealed
a reasonable increase in the Mn values compared to the
corresponding precursor polymers (Table 1 and Figures 1e and
2e). The narrow PDIs of both polymers were retained. The 1H
NMR spectra were also employed to identify the chemical
structures and estimate the molecular weights. The block
copolymer 11 showed a singlet peak at 7.34 ppm for the four
protons ascribed to the tolane moiety, while this peak was
clearly split into two peaks of 7.45 (two protons) and 7.78 (two
protons) ppm after the postfunctionalization (Figure 7). A
similar peak splitting was observed for the aromatic protons of
14 (Figure 2SI, Supporting Information). This was due to the
pseudosymmetry breaking of the side chain chromophores by
the twisted TCBD moiety. Other peak profiles were similar to
those of the precursor polymers. A careful integration of each
peak allowed for the estimation of the molecular weights, which
were in fairly good agreement with the Mn values determined
by SEC (Table 1). The TCNE addition was also confirmed by
the IR spectra (Figure 4SI, Supporting Information). The weak
peak at 2208 cm−1 ascribed to the alkyne vibration of the
The transition temperatures of all the polymers were
estimated from the second heating scan of the differential
scanning calorimetry (DSC) thermograms at the scanning rate
of 10 °C min−1 under flowing nitrogen. The DSC curves of the
block copolymers are depicted in Figure 8. The end-functional
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Scheme 3. Synthesis of (a) 11, P3HT-b-PDHPS, and (b) 12, PDHPS-b-P3HT-b-PDHPS
the intermolecular interactions between the cyano groups.17c,24
The appearance of these phase transition temperatures ascribed
to both polymer segments suggests the possible microphase
separation in the thin film states (vide infra).
Optical and Electrochemical Properties. The UV−vis
absorption spectra of the block copolymers were measured
both in THF (0.1 g/L) and in the thin film state on a quartz
plate prepared by spin-coating from a 10 g/L toluene solution
at 1000 rpm for 1 min (Figure 9 and Table 4). Both the diblock
and triblock copolymers showed similar absorption maxima and
spectral shapes, originating from the same polymer segments.
However, there was a considerable difference between the
solution and thin film spectra. In the THF solution, the longest
wavelength absorption maxima (λmax) of 11 and 12 were
detected at 441−442 nm, which is derived from the P3HT
moiety (Figure 9, parts a and b). The absorption range of the
PDHPS segments was limited to the UV region. In contrast, 13
and 14 exhibited a strong intramolecular CT band at 477−478
nm due to the side chain donor−acceptor chromophore of the
PTCNE segments, which covers the entire P3HT absorption.
Therefore, the end absorption (λend) is determined by the CT
band. The TCNE-adducted polymers showed the bathochromi-
cally shifted λend values by about 120 nm relative to the
corresponding precursor polymers.
It is known that the crystalline P3HT aggregates result in a
dramatic bathochromic shift in their solution spectra. In order
to induce the self-assembly of the P3HT moiety, the spin-
coated thin films of the block copolymers were thermally
annealed at 160 °C for 1 h. The thin film spectra of the block
copolymers 11 and 12 revealed a dramatic shift in λmax to 523
nm (Figure 9, parts c and d). Additionally, typical vibrational
bands were detected as shoulder peaks at 550 and 604 nm.25
The λend values of these block copolymers thus shifted to about
650 nm, which corresponds to the narrow band gap of about
1
Figure 6. H NMR spectrum of 11 in CDCl3 at 40 °C. The residual
CHCl3 peak is marked.
P3HT derivatives, 8 and 9, displayed the two distinct melting
points (Tm) at 204−227 °C with the melting enthalpy (ΔHm)
of about 16 J/g (Table 3). This behavior is similar to that of the
previously reported P3HT derivative with a clicked initiator site
for the nitroxide-mediated radical polymerization.22 For the
diblock copolymer 11, both the Tm and ΔHm values decreased
compared to the precursor P3HT derivative 8. In particular, the
decrease in the melting enthalpy is significant. This is probably
due to the lower content of P3HT in 11 (29 wt %) than that of
the pristine P3HT, and accordingly, the ΔHm value of the
triblock copolymer 12 became even lower being affected by the
lowest P3HT content (20 wt %). The TCNE addition to the
block copolymers further lowered these values, but an
additional glass transition for the PTCNE segment appeared
at 120−129 °C.23 This new transition is most likely caused by
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Scheme 4. Click Postfunctionalization of Block Copolymers with TCNE
content of 24 wt %), while the thin film spectrum of the
triblock copolymer 14 was governed by the PTCNE segments
because of the low P3HT content (16 wt %). The most intense
band of these polymers at 486−487 nm originated from the
intramolecular CT of the PTCNE segments. The λend values of
both thin films were almost unchanged from the solution
spectra.
The thin films of the block copolymers were further
investigated by electrochemistry. Cyclic voltammograms
(CVs) of the cast films prepared on a glassy carbon electrode
were measured in CH3CN with 0.1 M (nC4H9)4NClO4 at 20
°C. The dihexylaniline-based oxidation potential appeared as a
single sharp peak, while the oxidation peak of the P3HT moiety
was broad. Thus, the diblock copolymer 11 showed the sharp
first oxidation peak ascribed to the dihexylaniline moieties,
while the second oxidation step was more broadened due to the
multielectron removal from the P3HT segment (Figure 10a).
These two oxidation events were initiated at the almost same
onset oxidation potential (Eox,onset) of 0.25 V (vs Fc/Fc+)
(Table 5). In contrast, the triblock copolymer 12 displayed only
the dihexylaniline-based oxidation with the Eox,onset of 0.24 V
(Figure 10b). The TCNE addition to the PDHPS segments
affected the redox potentials. Both 13 and 14 exhibited a new
reversible reduction potential with the onset reduction
potential (Ered,onset) of −0.84 V, ascribed to the side chain
TCBD moiety of the flexible coil segments. Because of the
efficient conjugation with the dihexylaniline moiety, the
oxidation of this donor unit became difficult. The dihexylani-
line-based oxidation of 13 and 14 occurred at about 0.7 V.
Thus, the redox sites of the first and second oxidation
potentials of 13 were inverted from those of 11. The P3HT-
based oxidation could not be detected even for 14.
1
Figure 7. H NMR spectrum of 13 in CDCl3 at 40 °C. The residual
CHCl3 peak is marked.
Table 3. Summary of Thermal Properties of Polymers
a
b
b
b
polymer
Td5% (°C)
Tg (°C)
Tm (°C)
ΔHm (J/g)
8
430
391
331
412
376
336
−
−
129
218, 227
203
16.1
3.1
11
13
9
197
1.9
−
−
120
204, 208
229
16.2
0.1
12
14
209
0.1
a
b
Determined by TGA. Determined by the second heating scan of
DSC thermograms.
1.9 eV. These results imply the oriented self-assembly of the
P3HT moieties. The thin films of the TCNE-adducted
polymers 13 and 14 also showed a slight bathochromic shift
in λmax by about 10 nm compared to the solution spectra. The
vibrational bands of the crystalline P3HT assembly were
definitely recognized for the diblock copolymer 13 (P3HT
The highest occupied molecular orbital (HOMO) levels
were calculated from the Eox,onset values based on the
assumption of Fc/Fc+ = −4.80 eV. The lowest unoccupied
molecular orbital (LUMO) levels were calculated from the
HOMO levels and the optical band gaps. As listed in Table 5,
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Figure 8. DSC curves of polymers (a) 11 and 13 and (b) 12 and 14 at a scan rate of 10 °C min−1 under flowing nitrogen.
Figure 9. UV−vis absorption spectra of (a) 11 and 13 and (b) 12 and 14 in THF (0.1 g/L) and (c) 11 and 13 and (d) 12 and 14 in thin film states
after thermal annealing at 160 °C for 1 h.
both the HOMO and LUMO levels were lowered by the
postfunctionalization using the TCNE addition reaction. In
particular, the energy level decrease is significant for the
conversion from 12 into 14. These polymers lacked the redox
activities of the P3HT moiety; the HOMO and LUMO levels
of P3HT were reported to be −5.17 and −3.27 eV,
respectively.26 This was simply caused by the relatively low
P3HT content and/or due to the preferential self-assembly of
the flexible coil segments (PDHPS for 12 and PTCNE for 14)
on the electrode surface, which enabled the selective redox
events. It should also be noted that the LUMO levels of 13 and
Table 4. Summary of Optical Properties of Polymers
in THF
film
λend
λmax
polymer (nm)
λend
(nm)
λmax
(nm)
opt. band gap
a
(nm)
(eV)
b
b
b
11
12
13
14
441
442
477
478
555
555
682
523, 550, 604
657
652
685
672
1.89
1.90
1.81
1.84
b
523, 550, 604
487
486
674
a
b
Calculated from λend. Shoulder.
Figure 10. CVs of (a) 11 and 13 and (b) 12 and 14 in thin film states on a glassy carbon electrode measured in CH3CN with 0.1 M n(C4H9)4NClO4
at 20 °C and the scan rate of 0.1 V/s.
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precursor polymer 12 showed better phase separation images in
the case of the triblock copolymers. This difference between the
diblock and triblock copolymers might be explained by the
composition of the two segments and the amorphous nature of
the coil segments. The latter nature could be assisted by the
weak intermolecular forces between the cyano groups. The
delicate balance of these parameters would control the most
stable structures.
Table 5. Summary of Redox Potentials and Energy Levels of
Polymers
a
b
c
polymer
Eox,onset (V)
Ered,onset (V) HOMO (eV)
LUMO (eV)
11
12
13
14
0.25
0.24
−
−
−0.84
−0.84
−5.05
−5.04
−5.12
−5.50
−3.22
−3.15
−3.43
−3.79
d
0.32, 0.68
0.70
a
Thin films on a glassy carbon electrode measured in CH3CN with 0.1
Small-Angle and Wide-Angle X-ray Scattering. Small-
angle and wide-angle X-ray scattering (SAXS and WAXS)
patterns were measured to support the self-assembly of the bulk
samples of block copolymers. For both measurements, bulk
samples were prepared by slow evaporation of the polymer
solutions in chloroform followed by annealing at 150 °C for 30
min under vacuum. The WAXS profiles of the block
copolymers 11 and 12 showed the typical diffraction peaks of
the crystalline P3HT segment (Figure 12, parts a and b).28 The
well-defined peak at 2θ = 5.3° (d = 1.67 nm) is ascribed to the
(100) reflection, which corresponds to the lamellar length
formed by the intralayer chain-to-chain stacking. Another peak
at 2θ = 23.4° (d = 0.380 nm) is the (010) reflection caused by
the π-stacking of the P3HT backbones. Broad peaks at 2θ =
19.1° (d = 0.465 nm) and 19.4 o (d = 0.458 nm) for 11 and 12,
respectively, are probably due to the amorphous halo
originating from the PDHPS segments. The postfunctionalized
block copolymers 13 and 14 still displayed the peak at 2θ =
23.7° (d = 0.375 nm), suggesting the remained π-stacking of
the P3HT backbones (Figures 6SI, parts a and b, Supporting
Information). All these results clearly indicate that the flexible
coil segments do not much interfere with the formation of the
crystalline P3HT domains.
M (nC4H9)4NClO4 at 20 °C at the scan rate of 0.1 V/s. Potentials
b
versus Fc/Fc+. Calculated from the equation: HOMO = -(Eox,onset
c
+4.8) (eV). Calculated from the equation: LUMO= HOMO + optical
d
band gap (eV). The onset potential of the second oxidation step.
14, originating from the TCBD moieties, are lower than that of
P3HT. This decrease in the LUMO levels, achieved by click
postfunctionalization, will facilitate the energy transfer from
P3HT to the coil segments.
Thin Film Morphology. To gain an insight into the surface
morphology, the thin films of the block copolymers were
visualized by atomic force microscopy (AFM) under ambient
conditions. The films were prepared on a Si substrate by spin-
coating from a 10 g/L toluene solution at 1000 rpm for 1 min
at room temperature, followed by exposure to toluene vapors at
room temperature. In addition to thermal annealing, solvent
annealing is a common technique to facilitate the microphase
separated structures of block copolymers.27 The AFM images
of 11−14 (1 × 1 μm2) are shown in Figure 11. As expected
from the thin film absorption spectra, the P3HT assembly was
thought to promote the phase separation. In the case of the
diblock copolymers 11 and 13, postfunctionalization resulted in
more well-defined phase separation images. In contrast, the
Figure 11. AFM phase images of (a) 11, (b) 12, (c) 13, and (d) 14 thin films after solvent annealing (toluene) at room temperature.
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functionalized by the click chemistry-type TCNE addition. This
click postfunctionalization could become a general route to the
P3HT-based rod−coil block copolymers with electron-accept-
ing units in the coil segments. Additionally, the thin film
properties of the block copolymers were evaluated from their
UV−vis spectra and CVs. The TCNE addition significantly
affected both the absorption spectra and redox activities.
Moreover, the AFM images and X-ray diffraction patterns
demonstrated the microphase separation and the existence of
P3HT crystalline domain in these block copolymers. All these
results reasonably suggest that they are an interesting class of
new P3HT-based block copolymers for advanced studies of
various organic devices. In particular, the application to organic
solar cells is promising because of the expanded absorption,
tunable energy levels for fast energy transfer between both
segments, and well-defined microphase separation. The organic
solar cells using the developed block copolymers is now being
fabricated, and their device performances will be evaluated in
due course.
Figure 12. WAXS profiles of (a) 11 and (b) 12 and SAXS profiles of
(c) 11 and (d) 12 in bulk samples after thermal annealing (150 °C, 30
min under vacuum).
EXPERIMENTAL SECTION
■
Materials. All chemicals (>98% purities) were purchased from
Aldrich, Japan, and used as received unless otherwise noted. Benzene
(superdehydrated, Wako Pure Chemical Industries, Ltd.) and
tetrahydrofuran (THF) (superdehydrated, Wako Pure Chemical
Industries, Ltd.) were used as received in a glovebox in a nitrogen
atmosphere. 2,5-Dibromo-3-hexylthiophene 3 was purchased from
Aldrich, Japan, and distilled under the reduced pressure just before use.
trans-Bromo(tolyl)bis(triphenylphosphine)nickel(II) complex, 1,29
and 2-(4-bromobutyl)thiophene30 were synthesized according to the
literature methods. 4-(4′-N,N-dihexylaminophenylethynyl)styrene
(DHPS) was synthesized by Sonogashira coupling between 4-
ethynylstyrene and N,N-dihexyl-4-iodoaniline.
The SAXS profiles of the block copolymers 11 and 12 are
shown in Figure 12, parts c and d. The diblock copolymer 11
showed a peak at 2θ = 0.320° (d = 27.6 nm), while the peak of
the triblock copolymer 12 was detected at 2θ = 0.508° (d =
17.4 nm). These peaks suggested the occurrence of the
microphase separation between the rod and coil blocks.
Furthermore, 12 displayed the weak shoulder peak centered
at 2θ = 1.05° (d = 8.4 nm), which can be assigned as the second
order reflection of the main peak. Taking into account the AFM
phase image of the thin film of 12, it is reasonable to conclude
that this triblock copolymer formed the lamellar structure in the
bulk state. In contrast, no higher order peaks were observed for
11, and the d-spacing value was by ca. 10 nm larger than that of
12. Therefore, it is thought that 11 formed a different type of
self-assembled structures. Dai and co-workers previously
reported the relationship between the P3HT content and the
microstructure of a rod−coil diblock copolymer, P3HT-b-
poly(2-vinylpyridine).9 They found that the microstructure and
d-spacing value of the block copolymer changed from spheres
or disorder micelles (30 nm) to hexagonal close-packed
cylinders (23.3 nm), lamellae (19.3 nm), and nanofibers (32
nm) with the increasing P3HT content. In our polymers, the
diblock copolymer 11 has higher P3HT content (29 wt %)
than the triblock copolymer 12 (20 wt %) with the lamellar
structure. Thus, 11 most likely formed a nanofiber structure
rather than a lamellar one, as also supported by the AFM phase
image of the thin films.
1
General Measurements. H NMR spectra were recorded on a
JEOL model AL300 or ECS400 spectrometer at 25 or 40 °C.
Deuterated chloroform was used as a solvent. Chemical shifts are
reported in ppm (parts per million) using either tetramethylsilane
(TMS) or residual solvent signals as an internal reference. Coupling
constants (J) are given in Hz. The resonance multiplicity is described
as s (singlet), d (doublet), t (triplet), and m (multiplet). Fourier
transform infrared (FT-IR) spectra were recorded on a JASCO FT/IR-
4100 spectrometer in the range from 4000 to 600 cm−1. MALDI−
TOF mass spectra were measured on a Shimadzu/Karatos AXIMA-
CFR mass spectrometer using 2,2′:5,2″-terthiophene as a matrix. Size
exclusion chromatography (SEC) was measured on a JASCO
GULLIVER 1500 equipped with a pump, an absorbance detector
(UV, λ = 254 nm), and three polystyrene gel columns based on a
conventional calibration curve using polystyrene standards. THF (35
°C) was used as a carrier solvent at the flow rate of 1.0 mL min−1 after
calibration with standard polystyrenes. Elemental analysis was
performed on a YANACO CHN corder MT-6. UV−vis spectra
were recorded on a JASCO V-670 spectrophotometer. Thermogravi-
metric analysis (TGA) and differential scanning calorimetry (DSC)
measurements were carried out on a Rigaku TG8120 and a Rigaku
DSC8230, respectively, under nitrogen flow at the scan rate of 10 °C
min−1. Electrochemistry measurements were carried out on a BAS
electrochemical analyzer model 612C at 25 °C in a classical three-
electrode cell. The working, reference, and auxiliary electrodes were a
glassy carbon electrode, Ag/AgNO3/CH3CN/(nC4H9)4NPF6, and a
Pt wire, respectively. All potentials are referenced to the ferrocene/
ferricinium (Fc/Fc+) couple used as an internal standard. Atomic force
microscopy (AFM) images were taken by a Seiko Instruments SPA-
400 with a stiff cantilever of Seiko Instruments DF-20. The SAXS and
WAXS patterns were measured using Cu Kα (λ = 1.5418 Å) radiation
with a Bruker AXS Nano-STAR-U and a Bruker D8 DISCOVER,
respectively. The two-dimensional scattering patterns were measured
using two-dimensional PSPC detectors, and the intensity was
CONCLUSIONS
■
The GRIM polymerization allowed for the synthesis of mono-
and difunctional P3HTs, i.e., P3HT-C4Br and BrC4-P3HT-
C4Br, respectively, by selecting the appropriate initiators. The
selective and high end-functionality of those polymers was
confirmed by MALDI−TOF mass spectrometry. On the other
hand, the living anionic polymerization of DHPS with the
initiator of sBuLi was demonstrated. By the coupling reaction of
PDHPS-Li with P3HT-C4Br or BrC4-P3HT-C4Br, novel rod−
coil diblock and coil−rod−coil triblock copolymers composed
of the P3HT and PDHPS segments were synthesized, and they
1
were characterized by SEC, H NMR, and FT-IR spectros-
copies. The obtained block copolymers were then quantitatively
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integrated azimuthally to obtain the scattering profile as a function of
the diffraction angle of 2θ. The bulk samples for SAXS and WAXS
measurements were prepared from polymer solutions in chloroform.
The solvent was evaporated slowly over 24 h, and then annealed at
150 °C for 30 min under vacuum.
precipitation. The benzene solution was then poured into methanol
(100 mL) to precipitate the polymer, followed by filtration and drying
under vacuum. Finally, PDHPS was obtained as a white solid. Yield:
0.641 g (91%). Mn = 9 710, PDI = 1.15. 1H NMR (300 MHz, CDCl3):
δ
(ppm) 0.88 (−CH3 , br, 6nH), 1.29−1.54 (N−
5-Bromo-2-(4-bromobutyl)thiophene (6). In a three-neck flask,
2-(4-bromobutyl)thiophene (10.0 g, 45.6 mmol) was placed and
dissolved in chloroform (150 mL) and acetic acid (75 mL). After
cooling to 0 °C, N-bromosuccinimide (8.43 g, 47.4 mmol) was added
at once. The reaction mixture was stirred at room temperature
overnight and poured into water (100 mL). After washing the organic
phase with water, sodium bicarbonate aq., and water again, it was dried
over magnesium sulfate. It was filtered and concentrated under
reduced pressure. Finally silica gel flash column chromatography
(eluent: hexane) of the crude product afforded analytically pure 6 as
colorless oil (10.7 g, 36.0 mmol, 79%). 1H NMR (300 MHz, CDCl3):
δ (ppm) 1.72−1.97 (−CH2CH2CH2Br, m, 4H), 2.78 (ArCH2−, t, J =
7.2 Hz, 2H), 3.41 (−CH2Br, t, J = 6.5 Hz, 2H), 6.55 (Ar, d, J = 3.6 Hz,
1H), 6.85 (Ar, d, J = 3.6 Hz, 1H). 13C NMR (75 MHz, CDCl3): δ
(ppm) 29.46, 29.88, 31.87, 33.29, 109.10, 124.85, 129.58, 146.38. Anal.
Calcd for [C8H10Br2S]: C, 32.24; H, 3.38. Found: C, 32.40; H, 3.45.
P3HT-C4Br (8). All the reactions were carried out in a glovebox
under purified N2 atmosphere. In a 300 mL flask, 3 (2.00 g, 6.13
mmol) and LiCl (0.580 g, 13.6 mmol) were dissolved in THF (100
mL). A THF solution of iPrMgCl (2 M x 3.40 mL = 6.80 mmol) was
then added to the solution and it was stirred at room temperature for
30 min to give the solution 4. In another flask, 1 (0.0770 g, 0.102
mmol) was dissolved in THF (20 mL), and dppp (84.0 mg, 0.204
mmol) was added. The solution was stirred at room temperature for
30 min to give the solution of 2. The solution of 2 was then added to
the solution of 4 at once to start the polymerization, and the mixture
was stirred for 15 min to give the solution of 5. In another flask, a THF
CH2CH2CH2CH2CH2− + −CH2CH−, br, 19nH) 3.23 (N−CH2−,
br, 4nH), 6.52 (Ar, br, 4nH), 7.36 (Ar, br, 4nH). IR (neat): 3029,
2952, 2925, 2855, 2208, 1601, 1520, 1464, 1400, 1367, 1294, 1254,
1226, 1195, 1181, 1135, 1107, 1017, 1004, 975, 948, 930, 917, 888,
864, 828, 811, 758, 722, 693, 675, 666, 653, 644, 628, 620, 607 cm−1.
Anal. Calcd for [(C28H37N1)25 + C4H9]: C, 86.73; H, 9.68; N, 3.59.
Found: C, 86.62; H, 9.55; N, 3.79.
Synthesis of P3HT-b-PDHPS (11). All the polymerizations and
reactions were carried out in a glovebox under purified N2 atmosphere
in THF at −78 °C. To a THF solution (10 mL) of DHPS (0.600 g,
1.55 mmol) was added a THF solution of Bu2Mg (1 M × 0.200 mL =
0.200 mmol), and the mixture was stirred for 10 min. Then, a
s
cyclohexane solution of BuLi (1 M × 0.060 mL = 0.060 mmol) was
added at one time to start the polymerization at −78 °C. After stirring
for 10 min, 1,1-diphenylethylene (32 mg, 0.18 mmol) was added and
allowed to stand for 5 min for end-capping. To this solution was added
a THF solution (20 mL) of 8 (0.300 g, 0.027 mmol) which was
completely dehydrated by adding a THF solution of Bu2Mg (1 M ×
0.200 mL = 0.200 mmol). After 30 min, the reaction was quenched by
adding ethanol. The solution was then poured into methanol/water
(200 mL/100 mL) to precipitate the polymer. After filtration, the
polymer was again dissolved in THF (20 mL) and poured into ethyl
acetate (200 mL) to remove excess homopolymers of PDHPS. The
crude polymer was further purified by HPLC fractionation to finally
yield the analytically pure P3HT-b-PDHPS (11). Yield: 0.323 g (59%).
Mn = 31 300, PDI = 1.06. 1H NMR (400 MHz, CDCl3): δ (ppm) 0.90
(−CH3, m, (3m+6n)H), 1.28−1.67 (Th−CH2CH2CH2CH2CH2− +
N−CH2CH2CH2CH2CH2− + −CH2CH−, m, (6m+19n)H), 1.71
(Th−CH2CH2−, m, 2mH), 2.48 (tolyl, s, 3H), 2.80 (ThCH2−, t, J =
7.8 Hz, 2mH), 3.20 (N−CH2−, br, 4nH), 6.49 (Ar, br, 4nH), 6.98
(Th, s, 1mH), 7.34 (Ar, br, 4nH). IR (neat): 3033, 2952, 2925, 2854,
2208, 2167, 1602, 1556, 1520, 1458, 1399, 1367, 1294, 1254, 1227,
1195, 1135, 1108, 1051, 1017, 1004, 976, 931, 889, 811, 759, 723, 699,
i
solution of PrMgCl (2 M x 0.510 mL = 1.02 mmol) was added to a
THF solution (10 mL) of 6 (0.304 g, 1.02 mmol) and LiCl (86.0 mg,
2.04 mmol), and the mixture was stirred at room temperature for 30
min to obtain the solution of 7. The solution of 7 was added to the
solution of 5 to terminate the polymerization. The solution was then
poured into methanol/water (3/1) to precipitate the polymer. After
filtration, the polymer was purified by Soxhlet extraction with
methanol, hexane, and chloroform. The chloroform solution was
passed through silica gel. After removal of the solvent, the polymer was
freeze-dried from its absolute benzene solution to afford P3HT-C4Br
671, 643, 632, 619, 607 cm−1. Anal. Calcd for [(C10H14S1)57
+
(C28H37N1)59 + C33H38S1]: C, 82.52; H, 9.29; N, 2.52. Found: C,
82.22; H, 9.20; N, 2.53.
Synthesis of PDHPS-b-P3HT-b-PDHPS (12). The synthesis of
the titled compound was carried out in the same procedure as 11
except for the use of 9 instead of 8. Yield: 0.217 g (49%). Mn = 40 900,
1
(8). Yield: 0.705 g (67%). Mn = 11 000, PDI = 1.11. H NMR (300
MHz, CDCl3): δ (ppm) 0.91 (−CH3, t, J = 6.9 Hz, 3mH), 1.27−1.46
(Th−CH2CH2CH2CH2−, m, 6mH), 1.66−1.76 (Th−CH2CH2−, m,
2mH), 2.48 (tolyl, s, 3H), 2.80 (ThCH2−, t, J = 7.8 Hz, 2mH), 3.43
(−CH2Br, t, J = 6.4 Hz, 2H), 6.97 (Th, s, 1mH). IR (neat): 3059,
2953, 2923, 2854, 2671, 1635, 1562, 1509, 1455, 1377, 1302, 1259,
1204, 1113, 1092, 1049, 1019, 922, 888, 821, 757, 724, 676, 661, 647,
633, 615 cm−1. Anal. Calcd for [(C10H14S1)57 + C15H17S1Br1]: C,
71.77; H, 8.41. Found: C, 70.47, H, 8.15.
1
PDI = 1.05. H NMR (400 MHz, CDCl3): δ (ppm) 0.88 (−CH3, m,
(3m+12n)H), 1.29−1.54 (Th−CH2CH2CH2CH2CH2− + N−
CH2CH2CH2CH2CH2− + −CH2CH−, m, (6m+38n)H), 1.71 (Th−
CH2CH2−, m, 2mH), 2.80 (ThCH2−, t, J = 7.4 Hz, 2mH), 3.21 (N−
CH2−, br, 8nH), 6.50 (Ar, br, 8nH), 6.98 (Th, s, 1mH), 7.34 (Ar, br,
8nH). IR (neat): 3039, 2952, 2925, 2854, 2208, 2167, 1602, 1520,
1462, 1399, 1367, 1294, 1254, 1227, 1195, 1135, 1107, 1053, 1017,
1003, 981, 930, 889, 828, 811, 759, 725, 700, 671, 654, 644, 619, 607
cm−1. Anal. Calcd for [(C10H14S1)50 + (C28H37N1)86 + C52H62S2]: C,
83.83; H, 9.39; N, 2.84. Found: C, 83.77; H, 9.35; N, 2.57.
Br-C4-P3HT-C4Br (9). The titled compound was synthesized in the
same way as 8 in a glovebox under purified N2 atmosphere except for
the use of Ni(dppp)Cl2 instead of 2. Yield: 0.167 g (63%). Mn
=
1
10 700, PDI = 1.11. H NMR (300 MHz, CDCl3): δ (ppm) 0.92
(−CH3, t, J = 6.6 Hz, 3mH), 1.35−1.44 (Th−CH2CH2CH2CH2CH2−,
m, 6mH), 1.69 (Th−CH2CH2−, m, 2mH), 2.81 (ThCH2−, t, J = 7.5
Hz, 2mH), 3.43 (−CH2Br, t, J = 6.3 Hz, 4H), 6.98 (Th, s, 1mH). IR
(neat): 3057, 2953, 2923, 2854, 2668, 1650, 1559, 1541, 1509, 1455,
1376, 1340, 1302, 1252, 1203, 1112, 1049, 1014, 920, 888, 821, 793,
Synthesis of P3HT-b-PTCNE (13). To a solution of 11 (82.1 mg,
0.147 mmol alkyne unit−1) in dichloromethane (14.7 mL) was added a
TCNE solution in 1,2-dichloroethane (0.149 mmol, 4.0 mL) under air.
The mixture was stirred at 20 °C for 1 h. After the solution was
evaporated, the crude product was dissolved in a small amount of THF
and poured into methanol, yielding 13 as a black solid. Yield: 100.6 mg
761, 724, 660, 616 cm−1. Anal. Calcd for [(C10H14S1)50
C16H20S2Br2]: C, 70.81, H, 8.31. Found: C, 69.91; H, 8.03.
+
1
(99.7%). Mn = 42 300, PDI = 1.15. H NMR (400 MHz, CDCl3): δ
(ppm) 0.90 (−CH3, m, (3m+6n)H), 1.34−1.74 (Th−
Anionic Polymerization of DHPS. All of the polymerizations of
DHPS were carried out in a glovebox under purified N2 atmosphere.
In a typical experiment, a benzene solution (10 mL) of DHPS (0.700
CH2 CH2 CH2CH2 CH2 −
+ N−CH2 CH2 CH2CH2CH2 − +
−CH2CH−, m, (8m+19n)H), 2.49 (tolyl, s, 3H), 2.80 (ThCH2−,
br, 2mH), 3.39 (N−CH2−, br, 4nH), 6.70 (Ar, br, 4nH), 6.97 (Th, s,
1mH), 7.44 (Ar, br, 2nH), 7.78 (Ar, br, 2nH). IR (neat): 3039, 2952,
2925, 2854, 2208, 2167, 1602, 1520, 1462, 1399, 1367, 1294, 1254,
1227, 1195, 1135, 1107, 1053, 1017, 1003, 981, 930, 889, 828, 811,
759, 725, 700, 671, 655, 644, 619, 607 cm−1. Anal. Calcd for
s
g, 1.81 mmol) was titrated with a cyclohexane solution of BuLi until
yellowish color appeared with stirring. A cyclohexane solution of sBuLi
(1.05 M × 0.0700 mL = 0.0735 mmol) was added to start the
polymerization. After the set polymerization time, ethanol was added
to quench the polymerization. SEC analysis was carried out before
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[(C10H14S1)57 + (C34H37N5)59 + C33H38S1]: C, 77.61; H, 7.55, N,
10.24. Found: C, 77.02; H, 7.46, N, 10.93.
(5) Iovu, M. C.; Sheina, E. E.; Gil, R. R.; McCullough, R. D.
Macromolecules 2005, 38, 8649−8656.
Synthesis of PTCNE-b-P3HT-b-PTCNE (14). To a solution of 12
(80.5 mg, 0.163 mmol alkyne unit−1) in dichloromethane (16.3 mL)
was added a TCNE solution in 1,2-dichloroethane (0.166 mmol, 4.0
mL) under air. The mixture was stirred at 20 °C for 1 h. After the
solution was evaporated, the crude product was dissolved in a small
amount of THF and poured into methanol, yielding 14 as a black
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Hirota, K.; Hashimoto, K. J. Am. Chem. Soc. 2008, 130, 7812−7813.
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1
solid. Yield: 100.2 mg (98.8%). Mn = 56 300, PDI = 1.07. H NMR
(400 MHz, CDCl3): δ (ppm) 0.90 (−CH3, m, (3m+12n)H), 1.33−
1.63 (Th−CH2CH2CH2CH2CH2− + N−CH2CH2CH2CH2CH2− +
−CH2CH−, m, (8m+38n)H), 2.80 (ThCH2−, br, 2mH), 3.39 (N−
CH2−, br, 8nH), 6.70 (Ar, br, 8nH), 6.98 (Th, s, 1mH), 7.45 (Ar, br,
4nH), 7.78 (Ar, br, 4nH). IR (neat): 3052, 2953, 2927, 2856, 2214,
1602, 1538, 1485, 1467, 1445, 1415, 1343, 1295, 1262, 1213, 1182,
1144, 1119, 1078, 1015, 975, 889, 820, 795, 760, 722, 688, 666 cm−1.
Anal. Calcd for [(C10H14S1)50 + (C34H37N5)86 + C52H62S2]: C, 78.15;
H, 7.46, N, 11.28. Found: C, 77.63; H, 7.42, N, 12.13.
(9) Dai, C. A.; Yen, W. C.; Lee, Y. H.; Ho, C. C.; Su, W. F. J. Am.
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ASSOCIATED CONTENT
* Supporting Information
■
(10) (a) Liu, J.; Sheina, E.; Kowalewski, T.; McCullough, R. D.
Angew. Chem., Int. Ed. 2002, 41, 329−332. (b) de Cuendias, A.; Le
Hellaye, M.; Lecommandoux, S.; Cloutet, E.; Cramail, H. J. Mater.
Chem. 2005, 15, 3264−3267. (c) Iovu, M. C.; Jeffries-EL, M.; Sheina,
E. E.; Cooper, J. R.; McCullough, R. D. Polymer 2005, 46, 8582−8586.
(d) Iovu, M. C.; Craley, R.; Jeffries-EL, M.; Krankowski, A. B.; Zhang,
R.; Kowalewski, T.; McCullough, R. D. Macromolecules 2007, 46,
4733−4735. (e) Sommer, M.; Lang, A. S.; Thelakkat, M. Angew.
Chem., Int. Ed. 2010, 47, 7901−7904. (f) Li, Z.; Ono, R. J.; Wu, Z.-Q.;
Bielawski, C. W. Chem. Commun. 2011, 47, 197−199.
S
1H NMR spectra of 12 and 14, UV−vis absorption spectra of
11 and 12 upon TCNE titration, FT-IR spectra and TGA
curves of 11−14, and WAXS and SAXS profiles of 13 and 14.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: (T.M.) michinobu.t.aa@m.titech.ac.jp; (T.H.)
thigashihara@polymer.titech.ac.jp.
■
(11) Higashihara, T.; Ohshimizu, K.; Hirao, A.; Ueda, M.
Macromolecules 2008, 41, 9505−9507.
(12) Higashihara, T.; Ueda, M. Macromolecules 2009, 42, 8794−8800.
(13) Michinobu, T. Chem. Soc. Rev. 2011, 40, 2306−2316.
(14) Kato, S.-i.; Diederich, F. Chem. Commun. 2010, 46, 1994−2006.
Notes
The authors declare no competing financial interest.
(15) (a) Qin, A.; Jim, C. K. W.; Lu, W.; Lam, J. W. Y.; Haussler, M.;
̈
Dong, Y.; Sung, H. H. Y.; Williams, I. D.; Wong, G. K. L.; Tang, B. Z.
Macromolecules 2007, 40, 2308−2317. (b) Killops, K. L.; Campos, L.
M.; Hawker, C. L. J. Am. Chem. Soc. 2008, 130, 5062−5064. (c) Becer,
C. R.; Hoogenboom, R.; Schubert, U. S. Angew. Chem., Int. Ed. 2009,
48, 4900−4908. (d) Inglis, A. J.; Sinnwell, S.; Stenzel, M. H.; Barner-
Kowollik, C. Angew. Chem., Int. Ed. 2009, 48, 2411−2414. (e) Singh,
I.; Zarafshani, Z.; Lutz, J.-F.; Heaney, F. Macromolecules 2009, 42,
5411−5413. (f) Lee, Y.-G.; Koyama, Y.; Yonekawa, M.; Takata, T.
Macromolecules 2009, 42, 7709−7717. (g) Hoyle, C. E.; Lowe, A. B.;
Bowman, C. N. Chem. Soc. Rev. 2010, 39, 1355−1387.
(16) (a) Li, Y.; Tsuboi, K.; Michinobu, T. Macromolecules. 2010, 43,
5277−5286. (b) Li, Y.; Ashizawa, M.; Uchida, S.; Michinobu, T.
Macromol. Rapid Commun. 2011, 32, 1804−1808. (c) Michinobu, T.;
Seo, C.; Noguchi, K.; Mori, T. Polym. Chem. 2012, 3, 1427−1435.
(17) (a) Li, Y.; Michinobu, T. Polym Chem. 2010, 1, 72−74.
(b) Fujita, H.; Tsuboi, K.; Michinobu., T. Macromol. Chem. Phys. 2011,
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ACKNOWLEDGMENTS
■
This work is partially supported by the Japan Science and
Technology Agency (JST), PRESTO program (JY 220176), a
Grant-in-Aid for Scientific Research from MEXT, Japan, and
the Takahashi Industrial and Economic Research Foundation.
The authors thank Satoru Genseki, Center for Advanced
Materials Analysis, Tokyo Institute of Technology, for the
elemental analyses.
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