Catalyst-transfer suzuki-miyaura coupling polymerization for precision synthesis of poly(p-phenylene)

Article abstract of DOI:10.1021/ma101073x

Catalyst-transfer Suzuki-Miyaura coupling polymerization of 2,5-bis(hexyloxy)-4-iodophenylboronic acid (1b) with ^tBu ₃PPd(Ph)Br (2) was investigated. When 1b was polymerized with 2 at 0 °C in the presence of 4 equiv of CsF, 8 equiv o

Full text of DOI:10.1021/ma101073x

Macromolecules 2010, 43, 7095–7100 7095
DOI: 10.1021/ma101073x
Catalyst-Transfer Suzuki-Miyaura Coupling Polymerization for
Precision Synthesis of Poly( p-phenylene)
Tsutomu Yokozawa,* Haruhiko Kohno, Yoshihiro Ohta, and Akihiro Yokoyama
Department of Material and Life Chemistry, Kanagawa University, Rokkakubashi, Kanagawa-ku, Yokohama
221-8686, Japan
Received May 14, 2010; Revised Manuscript Received July 19, 2010
ABSTRACT: Catalyst-transfer Suzuki-Miyaura coupling polymerization of 2,5-bis(hexyloxy)-4-iodophe-
nylboronic acid (1b) with tBu3PPd(Ph)Br (2) was investigated. When 1b was polymerized with 2 at 0 °C in the
presence of 4 equiv of CsF, 8 equiv of 18-crown-6, and a small amount of water (to dissolve CsF), poly-
( p-phenylene) (poly1b) with a narrow molecular weight distribution was obtained. The conversion-number
average molecular weight (Mn) and feed ratio-Mn relationships indicate that this polymerization proceeded
in a chain-growth polymerization manner. Matrix-assisted laser desorption ionization time-of-flight
(MALDI-TOF) mass spectra showed that poly1b with moderate molecular weight uniformly had a phenyl
group, derived from 2, at one end of each polymer chain and a hydrogen atom at the other, indicating
involvement of a catalyst-transfer mechanism. However, the molecular weight distribution of the polymer
gradually became broader with increase of the feed ratio of 1b to 2, and polymer chains with other end groups
were formed. Successive catalyst-transfer Suzuki-Miyaura coupling polymerization of 2-(7-bromo-9,9-
dioctyl-9H-fluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3) and then 1b yielded a well-defined
block copolymer of polyfluorene and poly( p-phenylene).
Introduction
of pinacol fluoreneboronate monomer 3 with aqueous Na2CO3
as a typical base but afforded polyphenylene with a broad
π-Conjugated polymers containing aromatic rings in the back-
bone are an attractive class of materials owing to their potential
applications as organic electronic materials in devices such as
field effect transistors (FETs),1,2 organic light-emitting diodes
(OLEDs),3 and photovoltaic cells.4 These polymers have gener-
ally been synthesized by conventional polycondensation with a
metal catalyst,5-7 and this approach results in a broad molecular
weight distribution. However, the development of catalyst-trans-
fer condensation polymerization has made it feasible to con-
trol the molecular weight, polydispersity, and end groups of
π-conjugated polymers.8,9 In catalyst-transfer Kumada-Tamao
coupling polymerization with a Ni catalyst, the synthesis of poly-
(3-alkylthiophene)s,8,10-12 poly( p-phenylene),13 and poly(N-alkyl-
pyrrole)14,15 shows the character of living polymerization, whereas
the polymerization leading to polyfluorene proceeds in a chain-
growth polymerization manner accompanied by chain transfer
reaction.15,16 Among these polymerizations, the catalyst-transfer
condensation polymerization leading to poly(3-alkylthiophene)s
has been extensively developed. For example, block copolythio-
phenes with different alkyl side chains,12,17-24 block copolymers of
polythiophene and other π-conjugated polymers,14,25-30 and block
copolymers of polythiophene and vinyl polymers31-40 have been
obtained. Isolable Ni initiators41-43 were found and applied to
production of polythiophene brushes from the surface.41,43-46
Furthermore, the mechanism of the catalyst-transfer condensation
polymerization of poly(3-alkylthiophene)s has been investigated.47,48
In the case of catalyst-transfer Suzuki-Miyaura coupling
polymerization, however, only polyfluorenes could be obtained
in a controlled manner.49,50 The polymerization of bromophe-
nylboronic acid monomer 1a with a Pd complex initiator 2 was
attempted under the same conditions used for the polymerization
molecular weight distribution.49 In the present paper, we focus
on the Suzuki-Miyaura coupling polymerization of iodophenyl-
boronic acid monomer 1b with 2 under various conditions. We
found that the polymerization using CsF/18-crown-6 and a small
amount of water instead of aqueous Na2CO3 proceeded in a
chain-growth polymerization manner to yield polyphenylene
with well-defined molecular weight and low polydispersity. The
polymer end groups were also well controlled: a phenyl group,
derived from 2, was present at one end and a hydrogen atom at
the other end (designated Ph/H). Furthermore, block copolymers
of polyfluorene and polyphenylene were synthesized by succes-
sive catalyst-transfer Suzuki-Miyaura coupling polymerization
of fluorene monomer 3 and then 1b in one pot (Scheme 1).
Experimental Section
1
Measurements. H and 13C NMR spectra were obtained on
JEOL ECA-600 and ECA-500 instruments using tetramethylsi-
lane (0.00 ppm in 1H NMR) and the midpoint of CDCl3 (77.0
ppm in 13C NMR) as internal standards, respectively. IR spectra
were recorded on a JASCO FT/IR-410. Column chromatogra-
phy was performed on silica gel (Kieselgel 60, 230-400 mesh,
Merck). Analytical thin-layer chromatography (TLC) was per-
formed on silica gel (silica gel 60 F254, aluminum sheets, Merck).
GC was performed on a Shimadzu GC-14B gas chromatograph
equipped with a GL Science dimethylsilicone fluid OV-101
column (3 m) and a flame ionization detector (FID). The Mn
and Mw/Mn values of polymers were measured with a TOSOH
HLC-8020 gel permeation chromatography (GPC) unit [eluent:
tetrahydrofuran (THF); calibration: polystyrene standards]
using two TSK-gel columns (2 Â Multipore HXL-M). Isolation
of poly1b for an NMR sample was carried out with a Japan
Analytical Industry LC-908 Recycling Preparative HPLC
(eluent: chloroform) using two TSK-gel columns (2 Â G
*Corresponding author. E-mail: yokozt01@kanagawa-u.ac.jp.
r 2010 American Chemical Society
Published on Web 08/06/2010
pubs.acs.org/Macromolecules

7096 Macromolecules, Vol. 43, No. 17, 2010
Yokozawa et al.
a
Scheme 1
Table 1. Polymerization of 1b with 2 by Using Aqueous Na2CO3
b
Mn
b
entry
temp (°C)
[1b]0/[2]0
Mw/Mn
1
2
3
40
reflux
reflux
50
20
50
22 200c
9 600
2.71c
1.87
1.79
17 900
a Polymerization was carried out in the presence of Na2CO3 in
THF-H2O ([1b]0 = 0.02 mol/L in THF, [Na2CO3]0 = 2 mol/L in
water, THF/water = 3/1 (v/v)). b Estimated by GPC based on poly-
styrene standards (eluent: THF). c Polymer was precipitated during
polymerization.
1b (1.75 g, 52%); mp 100.7-101.4 °C. IR (KBr): 3378, 2938,
1
2856, 1587, 1384, 1311, 1050, 881, 476 cm-1. H NMR (500
MHz, CDCl3) δ: 7.31 (s, 1 H), 7.24 (s, 1 H), 6.02 (s, 2 H), 4.01 (t,
J = 6.9 Hz, 2 H), 4.00 (t, J = 6.9 Hz, 2 H), 1.85-1.79 (m, 4 H),
1.54-1.43 (m, 4 H), 1.38-1.31 (m, 8 H), 0.91 (t, J = 7.4 Hz, 6
H). 13C NMR (126 MHz, CDCl3) δ: 158.3, 152.5, 122.4, 119.0,
91.4, 70.0, 69.3, 31.5, 31.4, 29.2, 25.7, 25.6, 22.6, 22.5, 14.0, 13.9.
Polymerization of 1b. Compound 2 (1.5 mg, 3.3 μmol) was
placed in a round-bottomed flask, and a vacuum was applied.
The flask was filled with argon, then THF (3 mL) was added,
and the solution was degassed with argon by using a diaphragm
pump. In a pear-shaped flask, 1b (28 mg, 0.063 mmol), CsF
(42 mg, 0.28 mmol), 18-crown-6 (140 mg, 0.53 mmol), and
naphthalene (7.5 mg, 0.059 mmol) as an internal standard were
charged, and THF (4.5 mL) and water (0.4 mL) were added. The
solution was similarly degassed. The polymerization was in-
itiated by addition of the solution in the pear-shaped flask to the
solution containing 2 in the round-bottomed flask with a
cannula at 0 °C. After 2 h at 0 °C, the reaction was quenched
with 12 mol/L hydrochloric acid. The solution was extracted
with dichloromethane, and the organic layer was dried over
MgSO4. The solution was concentrated under reduced pressure,
and the residue was purified by HPLC to remove 18-crown-6 to
yield poly1b (Mn = 6100, Mw/Mn = 1.24). 1H NMR (500 MHz,
CDCl3) δ: 7.10 (m, 2 H), 3.92 (m, 4 H), 1.68 (m, 4 H), 1.36 (m,
4 H), 1.28 (m, 8 H), 0.87 (t, J = 6.9 Hz, 6 H). 13C NMR (151 MHz,
CDCl3) δ: 150.1, 127.5, 117.3, 69.6, 31.7, 29.5, 25.8, 22.6, 14.0.
Block Copolymerization of 3 and 1b. Compound 2 (1.0 mg, 2.1
μmol) was placed in a round-bottomed flask, and a vacuum was
applied. The flask was filled with argon, THF (2 mL) was added,
and then the solution was degassed with argon by using a dia-
phragm pump. In a pear-shaped flask, 3 (23 mg, 0.042 mmol),
CsF (70 mg, 0.46 mmol), 18-crown-6 (0.29 g, 1.1 mmol), and
naphthalene (5.5 mg, 0.043 mmol) as an internal standard were
charged, and THF (4 mL) and water (0.6 mL) were added. The
solution was similarly degassed. The polymerization was in-
itiated by addition of the solution in the pear-shaped flask into
the solution containing 2 in the round-bottomed flask via a
cannula at 0 °C. The mixture was stirred at 0 °C for 4 h (con-
version of 3 = 94%, poly3: Mn = 7300, Mw/Mn = 1.19).
A solution of 1b (19 mg, 0.043 mmol) in THF (3 mL), which
had been degassed, in a pear-shaped flask was added to the
solution of poly3. The reaction mixture was stirred at 0 °C for 1 h
(conversion of 1b = 92%), and then the reaction was quenched
with 12 mol/L hydrochloric acid. The solution was extracted
with dichloromethane, and the organic layer was dried over
MgSO4, followed by concentration under reduced pressure to
give 18.2 mg (68%) of poly3-b-poly1b (Mn=13 000, Mw/Mn=1.29).
2000HHR). Matrix-assisted laser desorption ionization time-
of-flight (MALDI-TOF) mass spectra were recorded on a
Shimadzu/Kratos AXIMA-CFR plus in the reflectron or linear
mode by use of a laser (λ = 337 nm). Dithranol (1,8-dihydroxy-
9[10H]-anthracenone) was used as the matrix for the MALDI-
TOF mass measurements.
Materials. 1,4-Bis(hexyloxy)benzene was prepared by the
reported procedure.51 tBu3PPd(Ph)Br (2)52 and 2-(7-bromo-
9,9-dioctyl-9H-fluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxa-
borolane (3)53 were prepared according to the established pro-
cedures.49 Dry tetrahydrofuran (THF) and other reagents were
commercial products and were used without further purifi-
cation.
Synthesis of 1b. Monomer 1b was prepared by diiodination of
1,4-bis(hexyloxy)benzene, followed by boronation in a similar
manner to the literature method.54,55 A flask was charged
with glacial acetic acid (55 mL), H2SO4 (2 mL), water (9 mL),
and CCl4 (12 mL), and into the flask were added 1,4-bis-
(hexyloxy)benzene (5.04 g, 18.1 mmol), iodine (4.14 g, 16.3
mmol), and iodic acid (1.90 g, 10.8 mmol). The resulting mixture
was heated at 70 °C for 24 h. After this time, a solution of sodium
thiosulfate was added to remove any unreacted iodine. The
solution was extracted with diethyl ether and washed succes-
sively with 5% NaOH solution and water. The organic layer was
dried over MgSO4 and the solvent was removed under reduced
pressure. Column chromatography on silica gel with hexane,
followed by recrystallization from hexane, afforded 1,4-bis-
(hexyloxy)-2,5-diiodobenzene as a white powder (4.67 g, 49%);
mp 54.2-55.0 °C. IR (KBr): 2950, 2918, 2857, 1450, 1213, 849,
526 cm-1. 1H NMR (500 MHz, CDCl3) δ: 7.17 (s, 2 H), 3.93 (t,
J = 6.5 Hz, 4 H), 1.80 (quint, J = 6.5 Hz, 4 H), 1.53-1.47 (m,
4 H), 1.37-1.32 (m, 8 H), 0.91 (t, J = 7.0 Hz, 6 H). 13C NMR
(126 MHz, CDCl3) δ: 152.8, 122.7, 86.3, 70.3, 31.5, 29.1, 25.7,
22.6, 14.0.
The diiodinated product (4.03 g, 7.60 mmol) was placed in a
flame-dried flask, and the flask was evacuated and then filled
with argon. THF (40 mL) was added to the flask, and the
solution was cooled to -78 °C. Butyllithium (1.6 mol/L in hex-
ane, 4.8 mL, 7.7 mmol) was slowly added, and then the mixture
was stirred at that temperature. After 2 h, when the starting
material had been consumed, tri(isopropoxy)borane (3.4 mL, 15
mmol) was added at -78 °C, and the mixture was stirred at that
temperature for 2 h. The reaction was quenched with 1 mol/L
hydrochloric acid, and the product was extracted with diethyl
ether. The organic layer was washed with water and brine and
then dried over MgSO4, and the solvent was evaporated.
Recrystallization of the residue from ethyl acetate/hexane gave
Results and Discussion
Polymerization of 1b with Aqueous Na2CO3. The poly-
merization of 1b with 2 was first carried out by using aqueous
Na2CO3 as a base in THF in a similar manner to the case of
catalyst-transfer polymerization of 3 (Table 1). In the poly-
merization at 40 °C, poly1b was precipitated during the poly-
merization (entry 1), although the same polyphenylene that
was synthesized by catalyst-transfer Kumada-Tamao cou-
pling polymerization13 is soluble in THF. The precipitation

Article
Table 2. Polymerization of 1b with 2 by Using Various Basesa
Macromolecules, Vol. 43, No. 17, 2010 7097
Table 3. Polymerization of 1b with 2 at Various Temperaturesa
b
Mn
b
b
Mn
b
entry
base
time (h)
Mw/Mn
entry
temp (°C)
[1b]0/[2]0
time (h)
Mw/Mn
1
2
3
4
5
K3PO4
TBAF
CsFd
96c
120c
48c
4
2790
1550
3480
6400
6200
1.43
2.01
1.44
1.26
1.49
1
2
3
4
5
6
7
rt
0
0
60
60
80
100
60
80
20
3.5
5
18 300
16 100
21 200
15 500c
18 700
15 100c
5 300c
1.84
1.47
1.52
1.44
1.45
1.89
1.25
CsF/18-crown-6d,e
CsF/18-crown-6d
0
6
20
-20
-20
-50d
48
4
a Polymerization of 1b was carried out with 2 ([1b]0/[2]0 = 20) in the
presence of 4 equiv of base in THF ([1b]0 = 0.02 mol/L) at room
temperature. b Estimated by GPC based on polystyrene standards
(eluent: THF). c Monomer 1b remained. d 8 equiv of 18-crown-6 was
used. e A small amount of water was added (water/THF = 1/25 (v/v)).
60
48e
a Polymerization of 1b was carried out with 2 in the presence of 4 equiv
of CsF and 8 equiv of 18-crown-6 in THF ([1b]0 = 8.0 mmol/L) and
water (water/THF = 1/17 (v/v)). b Estimated by GPC based on polysty-
rene standards (eluent: THF). c Polymer was precipitated during po-
lymerization. d CsF was precipitated. e Monomer 1b remained.
might be responsible for the bimodal GPC elution curve of
the obtained poly1b. Since aqueous Na2CO3 was used, water
dissolved in THF might decrease the solubility of poly1b in
the reaction solvent, resulting in precipitation of poly1b. On
the other hand, polymerization under reflux proceeded
homogeneously to afford polymer with a monomodal GPC
trace. When the feed ratio of 1b to 2 ([1b]0/[2]0) was increased
from 20 to 50, the Mn value almost doubled from 9600 to
17 900 (entries 2 and 3). However, the molecular weight dis-
tribution was broad. Accordingly, we expected that poly1b
with a narrower molecular weight distribution would be
obtained when the polymerization was carried out homo-
geneously at lower temperature by using a nonaqueous base.
Study of Base. The polymerization of 1b with 2 was then
carried out by using various bases in THF at room tempera-
ture (Table 2). We first examined K3PO4, which was effective
for selective diarylation of dihaloarenes with arylboronic
acids via intramolecular Pd-catalyst transfer.56 However,
K3PO4 was not soluble in THF, and 1b remained unreacted
even after 96 h. The obtained polymer had low molecular
weight (entry 1). We next tried fluoride-mediated Suzuki-
Miyaura polymerization.57 When tetrabutylammonium
fluoride (TBAF), which is soluble in THF, was used, 1b
remained and low-molecular-weight polymer was obtained
(entry 2). The use of CsF dissolved in a small amount of
water gave similar results (entry 3). However, addition of 18-
crown-6 to the former reaction mixture accelerated the
polymerization, and 1b was consumed within 4 h. Further-
more, the molecular weight distribution narrowed to 1.26
(entry 4). We further checked the polymerization with CsF/
18-crown-6 in the absence of water, but the polymerization
became slower, affording poly1b with a broader molecular
weight distribution (entry 5). Consequently, it turned out
that CsF along with 18-crown-6 and a small amount of water
for dissolving CsF was the best base system for obtaining
poly1b with a narrow molecular weight distribution.
become apparent that 1b should be polymerized at 0 °C with
an [1b]0/[2]0 ratio of 80 or less.
Polymerization Behavior. With the optimized conditions in
hand, we studied the polymerization behavior and evaluated
the polymerization. We first analyzed the Mn and Mw/Mn
values of poly1b at each conversion in the polymerization of
1b with 2 ([1b]0/[2]0 = 30) at 0 °C. The Mn values increased in
proportion to the conversion, and the Mw/Mn ratios were
1.25 or less over the whole conversion range (Figure 1A),
indicating that 1b was polymerized in a chain-growth poly-
merization manner. When 1b was polymerized with vari-
ous feed ratios ([1b]0/[2]0), the Mn values of the polymer
increased linearly in proportion to [1b]0/[2]0 (Figure 1B). The
polydispersity, however, gradually increased with increasing
[1b]0/[2]0 ratio (see later discussion). The chain-growth nat-
ure of the polymerization was also examined by means of a
monomer-addition experiment. A fresh feed of 1b ([added
1b]0/[2]0 = 20) was added to the prepolymer ([1b]0/[2]0 = 40,
conversion = 98%, Mn = 11 600, Mw/Mn = 1.33) in the re-
action mixture. The GPC chromatogram of the product
clearly shifted toward the higher-molecular-weight region
(conversion=96%, Mn=16 500, Mw/Mn = 1.47) (Figure 2).
This result indicates that the added 1b was polymerized from
the polymer end group of the prepolymer due to the chain-
growth nature of this polymerization.
In the 1H NMR spectra of poly1b obtained at [1b]0/[2]0 =
20 and 50, the signals a, c, and d due to the terminal phenyl
group derived from initiator 2 were observed (Figure 3). On
the basis of the integral ratio of the phenylene proton signal b
in the repeat unit to the signal a of the terminal phenyl group,
the average values of degree of polymerization (DPn) of
poly1b obtained at [1b]0/[2]0 = 20 and 50 were estimated to
be 20 and 54, respectively. The DPns were in good agreement
with the feed ratios [1b]0/[2]0, implying that one initiator 2
molecule forms one polymer chain.
Effect of Polymerization Temperature. Using the above
conditions with CsF/18-crown-6, the polymerization was
carried out with increasing values of [1b]0/[2]0 ratio from
20 to 60 in order to obtain higher-molecular-weight polymer.
Indeed, the Mn value of the polymer increased almost 3-fold,
but the molecular weight distribution became broad (Table
3, entry 1), implying that side reactions took place at room
temperature. The polymerization was then examined at
lower temperature. When the polymerization was carried
out at [1b]0/[2]0 = 60 at 0, -20, and -50 °C, the polydis-
persity was narrower at 0 and -20 °C (entries 2 and 5),
whereas CsF was precipitated at -50 °C, leaving unreacted
1b (entry 7). The polymerization was then carried out at
[1b]0/[2]0 = 80 at 0 and -20 °C. At 0 °C, the reaction mixture
was homogeneous, whereas at -20 °C polymer was precipi-
tated during the polymerization (entries 3 and 6). When the
polymerization was carried out at 0 °C and [1b]0/[2]0 = 100,
polymer was also precipitated (entry 4). Consequently, it has
The polymer end groups were further analyzed by means
of matrix-assisted laser desorption ionization time-of-flight
(MALDI-TOF) mass spectrometry. The spectrum of poly1b
(Mn = 6100, Mw/Mn = 1.24, Figure 4A(a)), obtained by the
polymerization of 1b with 2 at [1b]0/[2]0 = 20, followed by
quenching with 12 mol/L HCl, contains only one series of
peaks, which correspond to the polymer with a phenyl group
at one end and a hydrogen atom at the other end (designated
as Ph/H) (Figure 4B). For example, the exact mass of a single
isotope of the 14-mer with Ph/H is expected to produce a
signal at 3944.99 Da, and in fact a signal was observed
at 3945.07 Da, as shown in the magnified spectrum in
Figure 4B. Since the Ph and H end groups are thought to
be derived from the Ph group of 2 and the Pd complex end
group by quenching, respectively, the results of the 1H NMR
and the MALDI-TOF mass spectra of poly1b indicate that
the polymerization of 1 with 2 involves the catalyst-transfer
polymerization mechanism.

7098 Macromolecules, Vol. 43, No. 17, 2010
Yokozawa et al.
Figure 1. Mn and Mw/Mn values of poly1b as a function of (A) monomer conversion, obtained by the polymerization of1b with 2 ([1b]0/[2]0 = 30), and
(B) the feed ratio of 1b to 2. All the polymerizations were carried out in the presence of 4 equiv of CsF and 8 equiv of 18-crown-6 in THF ([1b]0 = 8.0
mM) and water (water/THF = 1/17 (v/v)) at 0 °C. Mn and Mw/Mn values were determined by GPC based on polystyrene standards.
in hand, we tried to synthesize block copolymers of polyfluor-
ene and polyphenylene. McCullough and co-workers have
recently reported similar block copolymers synthesized by
means of Kumada-Tamao coupling polymerization.30 In
our previous paper, fluorene monomer 3 was polymerized by
using aqueous Na2CO3 as a base.49 For block copolymeriza-
tion of 1b and 3, it should first be examined whether the poly-
merization of 3 with the CsF/18-crown-6 base system, instead
of aqueous Na2CO3, proceeds in a catalyst-transfer mecha-
nism. The polymerization of 3 with 2 ([3]0/[2]0=10) was then
carried out in the presence of 4 equiv of CsF, 8 equiv of 18-
crown-6, and a small amount of water at 0 °C to yield poly3
with a narrow molecular weight distribution (Mn=3800, Mw/
Figure 2. GPC profiles of (a) prepolymer ([1b]0/[2]0 = 40, conversion =
98%, Mn = 11 600, Mw/Mn = 1.33) and (b) postpolymer ([added
1b]0/[2]0 = 20, conversion = 96%, Mn = 16 500, Mw/Mn = 1.47)
obtained in a monomer addition experiment.
Mn=1.28) (Scheme 2). Furthermore, the feasibility of block
copolymerization was also examined by means of a monomer-
addition experiment, in which a fresh feed of 3 ([added 3]0/[2]0 =
10) was added to the prepolymer ([3]0/[2]0 = 10, conversion =
92%, Mn=3700, Mw/Mn=1.28) in the reaction mixture. The
added 3 was smoothly polymerized (conversion=96%), and the
Mn value of the resulting polymer doubled, while a narrow
molecular weight distribution was maintained (Mn = 7300, Mw/
Mn=1.19).
The good result of the polymerization of 3 with CsF/18-
crown-6 prompted us to try block copolymerization. Be-
cause we have found that successive catalyst-transfer poly-
merizations should be conducted from a monomer with low
π-donor ability to a monomer with high π-donor ability,28
the fluorene monomer 3 was polymerized first in the presence
of 2 ([3]0/[2]0 = 20) and CsF/18-crown-6 at 0 °C for 4 h to
afford well-defined poly3 (conversion of 3=94%, poly3: Mn=
7300, Mw/Mn=1.19). Then 1.0 equiv of phenylene monomer 1b
was added to the reaction mixture, and the second polymeriza-
tion was conducted at 0 °Cfor1h(Scheme 1). The conversionof
1b reached 92%, and the GPC elution curve shifted toward the
Figure 3. 1H NMR spectra of poly1b, obtained at [1b]0/[2]0=(A) 20
higher-molecular-weight region, although with tailing toward
(Mn = 6100, Mw/Mn = 1.24) and (B) 50(Mn = 15 200, Mw/Mn = 1.51)
the low-molecular-weight region (Figure 5). The obtained poly-
mer showed Mn = 13000 and Mw/Mn = 1.29. These results
at 0 °C, in CDCl3 at 25 °C.
However, poly1b (Mn=17 300, Mw/Mn=1.43), obtained
by the polymerization at [1b]0/[2]0 =60, showed tailing to-
ward the low-molecular-weight region in the GPC chroma-
togram (Figure 4A(b)). The product in the tailing region was
isolated by means of HPLC, and the MALDI-TOF mass
spectrum was taken (Figure 4C). The main series of peaks
were similarly due to the polymer with Ph/H, but peaks of the
polymers with Ph/I and H/H were also observed as well as
other peaks that could not be assigned. Therefore, termina-
tion and chain transfer of the catalyst might occur to some
extent during propagation, resulting in the formation of low-
molecular-weight polymer, when high-molecular-weight
polymer is synthesized at a high [1b]0/[2]0 ratio.
indicate that the second monomer 1b was polymerized in a
chain-growth polymerization manner from the polymer end
group of the first polymer to yield diblock copolymer poly3-b-
poly1b.
The block copolymerization in the reverse order was also
examined, even though it is considered an inappropriate
polymerization order on the basis of our previous observa-
tions.28 Phenylene monomer 1b was polymerized first in the
presence of 2 ([1b]0/[2]0=20) and CsF/18-crown-6 at 0 °C for
1 h to afford poly1b (conversion of 1b = 97%, poly1b: Mn =
6870, Mw/Mn = 1.18). Equimolar 3 was then added to the
reaction mixture, and the polymerization was conducted at
0 °C. The conversions of 3 in 4 and 6 h were 23 and 26%,
respectively; the polymerization almost stopped. The GPC
profile of the polymer obtained at 6 h showed Mn=9110 and
Block Copolymerization. With two monomers that undergo
catalyst-transfer Suzuki-Miyaura coupling polymerization

Article
Macromolecules, Vol. 43, No. 17, 2010 7099
Figure 4. (A) GPC profiles of the polymer obtained at [1b]0/[2]0 = (a) 20 and (b) 60. (B) MALDI-TOF mass spectra of the polymer obtained at
[1b]0/[2]0 = 20. (C) MALDI-TOF mass spectrum of the product in the tailing part of the GPC profile (b).
Scheme 2
polymerization of fluorene monomer 3 and then p-phenylene
monomer 1b yielded block copolymer of polyfluorene and poly-
( p-pheneylene), which has many potential applications. Further
experiments are in progress to evaluate catalyst-transfer Suzuki-
Miyaura coupling polymerization of other monomers.
Acknowledgment. This work was partially supported by a
Grant-in-Aid (No. 21350067) for Scientific Research and a
Scientific Frontier Research Project from the Ministry of Educa-
tion, Culture, Sports, Science and Technology, Japan.
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