Perfectly alternating amphiphilic poly(p-phenylene) graft copolymers by combination of controlled radical polymerization and suzuki coupling processes

Article abstract of DOI:10.1021/ma1000749

The preparation of amphiphilic poly(p-phenylene) (PP) possessing completely and perfectly alternating hydrophilic poly(ethylene oxide) (PEO) and hydrophobic polystyrene (PS) side chains is described. First, PS macromonomer with suitable functionality for polyphenylation was prepared by atom transfer radical polymerization (ATRP). The antagonist macromonomer, PEO, was synthesized by etherification reaction. Both macromonomers were reacted in the final stage via Suzuki cross coupling in the presence of Pd(PPh₃)4 as catalyst to form the desired amphiphilic graft copolymer (M_n: 32 400 g/mol and M_w/ M_n: 2.28). The intermediates obtained in various stages and graft copolymers were characterized by ¹H NMR and IR analysis. The optical absorption properties of the polymer were monitored with UV, and an additional absorption at around 280-320 nm evidenced the formation of PP chain. Thermal properties of PP were investigated by DSC. The thermogram displayed two transitions at 51.98 and 89.60 °C., indicating the presence of both PEO and PS structures in the copolymer. The perfectly alternating hydrophilic PEO and hydrophobic PS side chains were observed by AFM measurements to nanophase-separate in thin films.

Full text of DOI:10.1021/ma1000749

2
732 Macromolecules 2010, 43, 2732–2738
DOI: 10.1021/ma1000749
Perfectly Alternating Amphiphilic Poly(p-phenylene) Graft Copolymers by
Combination of Controlled Radical Polymerization and Suzuki Coupling
Processes
‡
Elif L. Sahkulubey, Yasemin Yuksel Durmaz, A. Levent Demirel, and Yusuf Yagci*
‡
‡
,‡
‡
Istanbul Technical University, Department of Chemistry, Maslak 34469, Istanbul, Turkey, and
‡
Chemistry Department, Koc University, Rumelifeneri Yolu, Sariyer, Istanbul 34450, Turkey
Received January 11, 2010; Revised Manuscript Received February 12, 2010
ABSTRACT: The preparation of amphiphilic poly(p-phenylene) (PP) possessing completely and perfectly
alternating hydrophilic poly(ethylene oxide) (PEO) and hydrophobic polystyrene (PS) side chains is
described. First, PS macromonomer with suitable functionality for polyphenylation was prepared by atom
transfer radical polymerization (ATRP). The antagonist macromonomer, PEO, was synthesized by ether-
ification reaction. Both macromonomers were reacted in the final stage via Suzuki cross coupling in the
presence of Pd(PPh ) as catalyst to form the desired amphiphilic graft copolymer (M : 32 400 g/mol and M /
3
4
n
w
1
n
M : 2.28). The intermediates obtained in various stages and graft copolymers were characterized by H NMR
and IR analysis. The optical absorption properties of the polymer were monitored with UV, and an additional
absorption at around 280-320 nm evidenced the formation of PP chain. Thermal properties of PP were
investigated by DSC. The thermogram displayed two transitions at 51.98 and 89.60 °C, indicating the
presence of both PEO and PS structures in the copolymer. The perfectly alternating hydrophilic PEO and
hydrophobic PS side chains were observed by AFM measurements to nanophase-separate in thin films.
Introduction
wide range of monomers. In our previous works, we reported the
synthesis of PPs with polystyrene (PS) side chains starting from
A great deal of interest has been paid to the conjugated
polymers because of their applications in electronic conductivity
ATRP initiators, namely, 1,4-dibromo-2,5-bis(bromomethyl)ben-
19
1
,2
zene or benzene-2,5-dibromomethyl-1,4-bis(boronic acid pro-
and optoelectronic devices such as light-emitting diodes (LEDs),
3
0
3
4
5
6
panediol diester).
transistors, solid-state lasers, waveguides, solar cells, and
7
Amphiphilic copolymers with hydrophilic and hydrophobic
segments have been extensively investigated because of their
unique self-organization characteristics and wide range of poten-
chemical and biomolecular sensors. Poly(p-phenylene)s (PPs)
are typical conjugated polymers in combination with excellent
mechanical properties and thermal and thermo-oxidative stabi-
lity. They are potentially one of the most useful polymers for
organic conducting materials because of their extended planar
conjugated π system, along with high strength and high heat
resistance. Other interesting and significant properties of PPs are
liquid crystallinity and photo- and electroluminescence. Cur-
rent methodologies for the direct synthesis of various PPs are
primarily based on nickel-
3
1
tial applications. In the area of polymer chemistry, amphiphilic
copolymers are identified to display various attractive properties
3
2,33
such as surface activity and aggregate formation.
Statistical
copolymer of PPs substituted with oligo(oxyethylene) side chains
were synthesized as a novel polymer electrolytes by Wegner and
8
9
3
4,35
36
coworkers.
Then, Zhang et al. reported amphiphilic PP
1
0-12
13
having nonpolar hexyloxy and polar oligo(ethyleneglycol) chains
at every other repeating unit. PPs having alternating sugar and
alkyl substituents were synthesized by Suzuki coupling and an
increased rotational flexibility of the main chain phenyl rings with
respect to the PP having only glucose substitutents has been
and palladium-mediated cross-
coupling reactions largely because of their preservation of regio-
chemistry and nearly quantitative yields.
8
-10,12
Unfortunately,
PPs are insoluble in many organic solvents, which limit their
processability. Therefore, attachment of conformationally mo-
bile alkyl side chains to the backbone has been important because
it has allowed the controlled synthesis of soluble and processable
PPs with high molecular weight. To improve the solubility of PPs,
a series of functionalized PPs pendant alkyl groups has been
37
demonstrated. However, in both cases, the hydrophobic groups
were short alkyl chains. Additionally, several reports in the
literature concern the preparation of amphiphilic poly(phenylene
ethylene)s (PPEs) possessing a hydrophobic alkyl side chain
3
8
39-41
14-17
together with polar, poly(ethylene oxide) (PEO),
nic
or catio-
reported.
Moreover, our group reported the synthesis of PP-
4
2,43
1
8
side chains. Computer simulations of polymers having
type graft copolymers by using the macromonomer technique
via controlled polymerizations such as atom transfer radical
chemically incompatible alternating side chains showed local
1
9-21
polymerization (ATRP)
or ring-opening polymerization
phase separation of the two different side chains without any
22-25
44,45
(
ROP).
Among various controlled radical polymerization methods
long-range order along the backbone.
To the best of our
knowledge, there are no examples of amphiphilic PPs with
alternating polymeric side chains.
2
6-29
developed in the past decade, ATRP
seems to be the most
extensively used method because of its easy manipulation, ability
to control molecular weight and structure, and applicability to a
Herein, we describe the synthesis and characterization of novel
alternating amphiphilic PP graft copolymers by Suzuki poly-
condensation reaction of hydrophilic PEO and hydrophobic PS
macromonomers through aryl dihalide and aryldiboronic acid
*Corresponding author. E-mail:yusuf@itu.edu.tr.
pubs.acs.org/Macromolecules Published on Web 02/23/2010
r 2010 American Chemical Society

Article
Macromolecules, Vol. 43, No. 6, 2010 2733
4
6
functional groups. The morphology of the synthesized PPs in
ultrathin films is interpreted in terms of local phase separation
between the two chemically incompatible side chains.
diol diester) was synthesized according to modified procedure.
1,3-Propanediol (10.5 mL, 144 mmol) and 10.8 g of boronic acid
were refluxed in dry benzene (200 mL) for 6 h under nitrogen
using a Dean-Stark trap. The reaction mixture was washed
several times with water and then dried over MgSO . The
4
solvent was removed in vacuo to afford a light-yellow solid.
Experimental Section
1
Recrystallization from hexane. Yield: 18%. m.p.: 116.3 °C. H
Materials. Styrene (S, 99%, Aldrich) was passed through a
basic alumina column to remove the inhibitor. 2,5-Dibromotoluene
NMR (CDCI
3
): 2.08-1.99 (t, 4H, O-CH
2
-CH
2
-CH
2
-O),
),
4
7
3
.17-4.13 (t, 8H, O-CH
2
-CH
2
-CH
.50 (s, 1H, aromatic), 7.65 and 7.68 (2H, aromatic). IR (cm ):
2
-O), 2.37 (s, 3H, CH-
3
(
PEO monomethylether (M : 2000, Fluka), sodium hydride
98%, Aldrich), N-bromosuccinimide (NBS, 99%, Merck),
1
n
053-3019 (aromatic CH stretching), 2955-2926 (aliphatic
(
97%, Aldrich), n-butyl lithium (n-BuLi (2.5 M solution in
qCH stretching), 1483 (aromatic CdC stretching), 1421
(
hexane), Acros), trimethylborate (g99%, Merck), 1,3-propane-
diol (g99%, Fluka), NaHCO (Aldrich), Pd(PPh ) (Merck),
2
vibration of Ph-B bond), 1392, 1372 (B-O in B(OH) ), 1297,
3
3 4
1
7
198, 1157, 1128, 1113 (C-O stretching), 1033, 1005, 925, 903,
24, 688.
benzoyl peroxide (Aldrich), CuBr (98%, Acros), 2,2 dipyridyl
bpy, g99% Acros), magnesium sulfate anhydrous (MgSO4,
g99.0%, Aldrich), and silicagel 90 (Fluka, 0.2 to 0.5 mm) were
used as received. Carbon tetrachloride (CCI , g99.0%, Aldrich)
(
Synthesis of Benzene-2-bromomethyl-1,4-bis(boronic acid pro-
panediol diester) (2). Benzene-2-bromomethyl-1,4-bis(boronic
acid propanediol diester was synthesized according to modified
procedure. Benzene-2-methyl-1,4-bis(boronic acid propane-
diol diester) (1.80 g, 6.9 mmol), NBS (1.5 g, 8.3 mmol), and
benzoyl peroxide (0.03 g, 0.14 mmol) were heated under reflux in
4
˚
was distilled over phosphorus pentoxide and stored over 4 A
molecular sieves. Hexane (95.0%, Carlo Erba) was distilled over
sodium wire. Tetrahydrofuran (THF, g 99.0%, Fluka) was
dried over potassium hydroxide and distilled over sodium wire
and benzophenone.
3
0
1
5 mL of CCl
filtered to remove succinimide and washed with a small amount
of CCl and CH Cl . The combined organic solutions were
washed several times with water and then dried over MgSO
4
under nitrogen for 24 h. The reaction mixture was
Synthesis of 1,4-Dibromo-2-(bromomethyl)benzene (1). 1,4-
Dibromo-2-(bromomethyl)benzene was synthesized according
4
2
2
3
0
.
to modified procedure. 2,5-Dibromotoluene, (5.0 g, 20 mmol),
NBS (3.9 g, 22 mmol), and benzoyl peroxide (0.10 g, 0.4 mmol)
were heated under reflux in 20 mL of CCl under nitrogen for
4
The solvent was removed by rotary evaporator. The product
was purified by passing through a silica gel column using
diethylether as an eluent. Finally, the product was obtained as
4
4
h. The reaction mixture was filtered to remove succinimide,
and the succinimide was washed with a supplementary amount
of CCl4 and finally with a little quantity of CH Cl . The
white crystals after recrystallizing twice from diethyl ether.
1
Yield: 30%. H NMR (CDCI
3
): 2.10-2.02 (m, 4H, O-
-O), 4.20-4.12 (m, 8H, O-CH -CH
-O), 4.89 (s, 2H, -CH -Br), 7.51 (bs, 1H aromatic),
2
2
combined organic solutions were washed several times with
water and than dried over MgSO . The solvent was removed
CH
CH
2
-CH
2
-CH
2
2
2
-
4
2
2
-
1
by rotary evaporator. The product was purified by passing
through a silica gel column using diethylether as an eluent.
Finally, the product was obtained as white crystals after recrys-
7.64 (1H aromatic), 7.73 (1H aromatic). IR (cm ): 3064
(aromatic CH stretching), 2956-2895 (aliphatic CH strecthing),
1481(aromatic CdC stretching), 1425 (vibration of Ph-B bond),
1393 (vibration of B-O), 1313-1150 (starching of C-O
linkages), 1097, 1023, 928, 822, 798, 724, 687, 653.
tallizing twice from petroleum ether (Yield: 38%). m.p.: 89.2 °C.
1
3 2
H NMR (CDCI ): 4.51 (s, 2H, CH Br), 7.25 (1H aromatic),
.35 (1H aromatic), 7.58 (1H aromatic). IR (cm ): 3053-2950
-
1
7
Preparation of Poly(ethylene oxide) Macromonomer (M1) by
Etherification Reaction. Sodium hydride (0.024 g, 1.1 mmol) was
added to PEO (2.0 g, 1.0 mmol) in dry 25 mL of THF, and the
reaction mixture was stirred at 0 °C under nitrogen for 30 min.
1,4-Diboromo-2-(bromomethyl)benzene (1) (0.66 g, 2.0 mmol)
in dry 10 mL of THF was added portionwise to the solution. The
mixture was kept stirring at room temperature for 24 h. The
solution was extracted with water, and the organic layer was
dried over anhydrous MgSO4 and CH Cl was removed by
(
aromatic and aliphatic CH stretching), 1488-1455 (aromatic
CdC stretching), 1380, 1270-951(C-H bending), 885, 876,
8
15, 719, 616.
Synthesis of Benzene-2-methyl-1,4-bis(boronic acid). Benzene-
-methyl-1,4-bis(boronic acid) was synthesized according to
2
1
5
modified procedure. 2,5-Dibromotoluene, (22 g, 87.0 mmol)
was heated under reflux in 140 mL of n-hexane under nitrogen
for 2 h. The solution was allowed to cool to room temperature
for 30 min. The reaction mixture was then cooled to -78 °C, and
n-BuLi (96 mL, 24 mmol) was added at that temperature. The
solution was stirred for an additional 1 h at -80 °C and then was
allowed to reach slowly room temperature for 3 h. After being
stirred at room temperature for 12 h, the solution was heated to
reflux temperature under nitrogen for 2 h. Then, the solution
was cooled to room temperature for 30 min. The reaction
mixture was further cooled to -78 °C, and trimethylborate
2
2
rotary evaporation. The mixture was precipitated in diethyl
ether, and the solid formed was collected after filtration and
dried at room temperature in a vacuum overnight. H NMR
1
(CDCI
4.55 (s, 2H, Ar-CH
7.64 (1H, aromatic). IR (cm ): 2946-2884 (aliphatic CH
stretching), 1466 (aromatic CdC stretching) 1360-1341 (CH2
vibration), 1279-1147 (C-O-C stretching of ether lineages),
1060, 1028, 960, 841.
3
): 3.34 (s, 3H, OCH
3
), 3.70 (m, 4H, O-CH
2 2
CH -O),
2
), 7.33 (1H aromatic), 7.37 (1H aromatic)
-
1
(
3 3
B(OCH ) ) (100 mL, 870 mmol) was added. The solution was
allowed to warm to room temperature for 3 h before the reaction
was quenched with the addition of 2 M HCl. The two phases
were separated, and the water phase was extracted with four
Preparation of Polystyrene Macromonomer (M2) by ATRP. A
Schlenk tube was charged with CuBr (0.040 g, 0.27 mmol), bpy
(0.13 g, 0.83 mmol), initiator (2) (0.090 g, 0.27 mmol), and
styrene (4.5 g, 24 mmol). Three freeze-pump-thaw cycles were
performed, and the tube was stirred in an oil bath at 110 °C for
50 min. After the given time, the mixture was diluted with THF.
Then, the copper complex was removed by passing through a
neutral alumina column, and THF was removed by rotary
evaporation. The mixture was precipitated in methanol, and
the solid was collected after filtration and dried at room
4
portions of diethyl ether and then dried over MgSO and
evaporated to yield the boronic acid as a white solid, which
was used without further purification. Yield: 50%. H NMR
1
(
aromatic), 7.56 (1H, aromatic), 7.73 (1H, aromatic). IR
CDCI
3 3
): 2.29 (3H, CH ), 7.90 (bs, 4H, OH), 7.38 (1H,
-
1
(
with stretching of aromatic CH), 2980 (aliphatic CH), 1488
cm ): 3202 (OH stretching of B(OH) as a broad peak overlap
2
(
(
aromatic CdC stretching), 1446 (vibration of Ph-B bond), 1388
), 1321 and 1110 (vibration of the bond B-O
temperature in a vacuum overnight (32%, Mn,GPC = 9150,
1
= 1.4). H NMR (CDCI
B-O in B(OH)
2
M /M
w
n
3
): 2.26-1.17 (aliphatic of PS,
and B-OH), 1023, 699.
Synthesis of Benzene-2-methyl-1,4-bis(boronic acid propane-
diol diester). Benzene-2-methyl-1,4-bis(boronic acid propane-
O-CH -CH -CH -O, Ar-CH ), 4.13 (t, 8H, O-CH ), 4.47
(bs, 1H, PhCH-Br), 6.47-6.57 (2H aromatic of PS), 7.04-7.46
-1
2
2
2
2
2
(3H aromatic of PS). IR (cm ): 3059-3026 (aromatic CH

2
734 Macromolecules, Vol. 43, No. 6, 2010
Sahkulubey et al.
stretching), 2924-2849 (aliphatic CH stretching), 1944-1601-
out-of-plane C-H deformation), 1583, 1493, 1452 (aromatic
CdC stretching), 1370, 1262, 1181, 1154, 1070, 1027, 907, 840,
Scheme 1. Synthesis of Aryl Dihalide (1) and Aryl Diboronic Acid (2)
Compounds by Using N-Bromosuccinimide (NBS) in the Bromination
Step
(
8
02, 756.
Synthesis of Amphiphilic Poly(p-phenylene) by Suzuki Poly-
condensation Reaction. A 100 mL three-necked round-bottomed
flask equipped with a condenser, a septum, nitrogen inlet-out-
let, and magnetic stirrer, was charged with 20 mL of 1 M
NaHCO solution and 30 mL of THF. The solvents were
3
previously degassed by bubbling nitrogen over a period of
3
2
0 min. The mixture was refluxed under nitrogen for 3 h. A
0 mL three-necked round-bottomed flask equipped in the
same way as the previous one was charged under inert atmo-
sphere with PS-based macromonomer (0.25 g, 0.028 mmol),
PEO-based macromonomer (0.07 g, 0.028 mmol), Pd(PPh )
3 4
-
4
(
0.7 mg, 5.8 Â 10 mmol), and 3 mL of the solvent mixture
introduced with a syringe through the septum. The reaction
was maintained with vigorous stirring and with the exclusion
of oxygen and light at reflux. After 48 h, a supplementary
amount of 5 mL of the solvent mixture was added through
the septum and stirred 1 day more. After this time, the polymer
was obtained by precipitation in methanol, and the solid was
collected after filtration and dried at room temperature in a
): 1.85-
Scheme 2. Preparation of Poly(ethylene oxide) (PEO) Macromonomer
(M1) by Etherification Reaction in Tetrahydrofuran (THF)
1
vacuum overnight (0.21 g, 66%,). H NMR (CDCI
3
1
.43 (m, aliphatic of PS), 3.64 (s, O-CH -CH -O of
2
2
-1
PEO), 7.20-6.57 (m, aromatic of PS and PP). IR (cm ):
059, 3025 (aromatic CH stretching), 2923, 2849 (aliphatic
3
CH stretching), 1937, 1867, 1798, 1665 (out-of-plane C-H
deformation), 1583, 1492, 1452 (aromatic CdC stretching),
1
7
390-1313 (CH
60.
Characterization. H NMR spectra of 5-10% (w/w) solu-
2
vibration), 1267-1125 (C-O-C stretching)
1
Results and Discussion
tions in CDCl
recorded at room temperature at 250 MHz on a Bruker DPX
50 spectrometer. Gel permeation chromatography (GPC)
3
with Si(CH
3
)
4
as an internal standard were
The overall strategy, as presented in Scheme 1, is based on the
preparation of functional precursors and macromonomers sui-
table for the phenylation process by Suzuki coupling. First, the
precursor (1) for the PEO-based macromonomer (M1) was
synthesized through bromination of methyl group of 2,5 dibro-
2
measurements were obtained from a Viscotek GPCmax Auto-
sampler system consisting of a pump, a Viscotek UV detec-
tor and a Viscotek differential refractive index (RI) detector.
Three ViscoGEL GPC columns (G2000HHR, G3000HHR, and
G4000HHR), (7.8 mm internal diameter, 300 mm length) were
used in series. The effective molecular weight ranges were
motoluene with N-bromosuccinimide (NBS) in CCl solution.
4
The ATRP initiator (2), namely, benzene-2-bromomethyl-1,4-
bis(boronic acid propanediol diester), was obtained by multiple
step reactions. For this purpose, benzene-2-methyl-1,4-bis-
4
56-42 800, 1050-107 000, and 10 200-2 890 000, respec-
tively. THF was used as an eluent at flow rate of 1.0 mL min
(
boronic acid) was synthesized from the same starting compound
-1
for 1 by using n-BuLi, followed by reaction with trimethylborate
at -78 °C. Refluxing of the diboronic acid compound with 1,3-
propanediol using a Dean-Stark trap afforded bis(boronic acid
propandiol diester). Apparently, the esterification reaction en-
hanced the solubility of the initial boronic acid compound in CCl4
and consequently esteems the subsequent bromination reaction
with NBS in this solvent. The FT-IR analysis of the related
at 30 °C. Both detectors were calibrated with PS standards
having narrow molecular weight distribution. Data were ana-
lyzed using Viscotek OmniSEC Omni-01 software. Molecular
weights were calculated with the aid of PS standards. FT-IR
spectra were recorded on a Perkin-Elmer FT-IR Spectrum One
B spectrometer. UV spectra were recorded on a Shimadzu UV-
1
601 spectrometer. Fluorescence measurements were carried
compounds indicated that the OH stretching of -B(OH) group
2
out using a Hitachi F-4500 fluorescence spectrophotometer,
and the excitation and emission spectra of PP were recorded in
CH Cl at room temperature. Differential scanning calorime-
-1
gives a broad peak at ∼3202 cm (Figure S1 of the Supporting
Information). The aromatic CH stretching is located at 3029
2
2
-1
cm . The vibration of phenyl boronic acid linkage Ph-B gives a
try (DSC) was performed on Perkin-Elmer Diamond DSC
calibrated with indium. Glass-transition temperatures were
measured after a first heating (from -50 to 150 °C) and cooling
-
1
strong peak at 1446 cm . The absorption bands at 1388 and
-
1
1
110 cm are assigned to the vibrations of the bonds B-O and
B-OH. After the esterification reaction, OH stretching of
boronic acid at 3202 cm completely disappeared, and the
(
from 150 to -50 °C) cycle. Thermograms were recorded
during the second heating cycle (from -50 to 300 °C) at
0 °C/min under nitrogen flow. DSC calibration was per-
formed with indium, and the transition temperature (T and
-
1
vibrations of Ph-B and B-O are still observed at 1421 and
1
-
1
1
392 cm , respectively. The structures of intermediates were also
g
1
confirmed by H NMR analysis (Figure S2 of the Supporting
Information). The peak at 7.90 ppm corresponding to boronic
acid protons completely disappeared after the ester formation
m
T ) was determined at the midpoint between upper and lower
intersection of the baseline with the tangent to the transition
step. For atomic force microscopy (AFM) measurements, PP
films were spin coated on silicon substrates from 0.5 to 1.0 mg/
(
Figure S2a of the Supporting Information). In the spectrum of
mL solutions in CH
2
Cl
2
. Hydrophilic silicon substrates were
bis(boronic acid propanediol diester), methylene and methyl
protons resonanced at 4.17 and 2.05 ppm, respectively (Figure S2b
of the Supporting Information). Bromination of methyl group of
benzene-2-methyl-1,4-bis(boronic acid propanediol diester) was
clearly evidenced by the shifting of the peak corresponding to the
obtained by UV-ozone treatment for 30-40 min. Height and
phase images were taken by NT-MDT Solver P47 in tapping
mode with ultra sharp Si cantilevers having force constant of
4
8 N/m.

Article
Macromolecules, Vol. 43, No. 6, 2010 2735
Table 1. Molecular Weight Characteristics of Poly(p-phenylene) and
Its Precursors
Scheme 3. Preparation of Polystyrene (PS) Macromonomer (M2) by
ATRP Using CuBr/Bipyridine (CuBr/bpy) Catalyst System
M
nNMR
(g/mol)
M
nGPC
(g/mol)
a
b
b
polymers
w n
M /M
c
d
PEO macromonomer
PS macromonomer
poly(p-phenylene)
a
2650
8250
nd
2400
9150
32400
1.03
1.40
2.28
e
f
g
h
1
b
Calculated by using H NMR spectra. Determined by GPC based
: number-average molecular weight; M
on polystyrene standards. M
n
w
:
c
weight-average molecular weight. Functionalization was performed by
etherification reaction. Molecular weight and molecular weight distri-
bution of starting PEO were measured as 2200 and 1.03, respectively.
d
Determined by using the ratio between aromatic protons of (1) and
Scheme 4. Synthesis of Amphiphilic Poly(p-phenylene) (PP) by Suzuki
1
e
methylene protons of PEO from H NMR spectrum. Polymerization
conditions; bulk, [M] /[CuBr] /[L]
= 86/1/3 at 110 °C. Bipyridine used
as a ligand. Determined by using the ratio between methylene protons
Polycondensation Reaction
0
0
0
f
1
g
of (2) and aromatic protons of PS from H NMR spectrum. Suzuki
polycondensation was performed using Pd(0) catalyst at 90 °C for 5
days. Not determined.
h
as well as aromatic protons of central benzene ring at 7.24-
7
9
.64 ppm. Functionalization efficiency of PEO was found to be
4%, as calculated by using the ratio between aromatic protons
to methylene protons of repeating units. Moreover, the aromatic-
CH groups are in the vicinity of O atoms of the first PEO
2
repeating unit, and the corresponding protons give a clear signal
at 4.55 ppm.
The ATRP of styrene using the CuBr/bpy catalytic system
provide PS as a second precursor preserving two boronic ester
functionalities, which is useful for Suzuki coupling in combina-
tion with PEO-based macromonomer (Scheme 3). The results of
polymerization are shown in Table 1. There is a good agreement
1
between molecular-weight-obtained GPC measurement and H
1
NMR calculation. Furthermore, H NMR spectrum of PS macro-
monomer indicates the boronic ester structure at the chain end as
showing a peak at 4.13 ppm corresponding to methylene protons
of boronic ester structures (Figure 1c).
Hydrophilic PEO- and hydrophobic PS-based macromono-
mers were reacted via Suzuki polycondensation in the presence
Pd(PPh ) as catalyst to form desired amphiphilic copolymer
1
Figure 1. H NMR spectra of (a) poly(p-phenylene) (PP) and (b) its
3
4
precursors poly(ethylene oxide) (PEO)-based macromonomer (M1)
and (c) polystyrenre (PS)-based macromonomers (M2) in CDCl .
3
(
Scheme 4). The structure of amphiphilic PP was investigated by
H NMR, GPC, UV, fluorescence, DSC, and the thin film
1
1
methyl protons at 2.47-4.89 ppm (Figure S2c of the Supporting
Information). The aromatic protons were noted at 7.25-7.68
ppm in all of the related spectra. After the bromination reaction,
the resulting initiator, 2, was used as an ATRP initiator and also
Suzuki coupling reagent.
morphology by AFM analysis. H NMR spectra of PP and its
precursors PEO- and PS-based macromonomers were collected
in Figure 1. Even if the protons of the PP backbone appear
together with aromatic protons of PS, the spectrum shows
characteristic signals of both macromonomers (Figure 1a).
Moreover, GPC traceof the PP was shifted tohigher molecular
weights (lower elution volume) as compared with that of starting
PEO- and PS-based macromonomer (Figure 2). GPC measure-
ment of PP was performed after the reprecipitation from metha-
nol. This treatment is expected to remove the unreacted PEO
macromonomer. However, unreacted PS would have remained in
the mixture because of the similar solubility behavior with the
resulting PP arising from its high PS character. The absence of a
peak corresponding PS macromonomer at high elution volume is
another indication for the successful coupling process. Because of
the comblike structure of the poly(phenylene)s obtained from the
corresponding macromonomers, the values of M and M /M
PEO-based macromonomer (M1) was obtained by etherifica-
tion reaction between 1 and monohydroxy functional PEO
(
Scheme 2). This macromonomer, having two bromine atoms
directly connected to the central benzene ring, is suitable for
Suzuki polycondensation with a diboronic ester in the presence of
palladium catalyst. As can be seen from Table 1, the molecular
weight of the polymer was slightly increased by the etherification
reaction. The observed increase is due the incorporation of the
aromatic group at the chain end. The polydispersity remained
unchanged, indicating that there was no degradation or coupling
during the etherification reaction. More reliable evidence of
1
functionalization of PEO was obtained by H NMR analysis.
n
w
n
The spectrum presented in Figure 1b contains characteristic
calibrated with linear standard polymers should be taken as a
minimum estimation.
4
7
bands of PEO at 3.34 (OCH ) and 3.70 ppm (O-CH CH -O)
3
2
2

2
736 Macromolecules, Vol. 43, No. 6, 2010
Sahkulubey et al.
Figure 2. (a) GPC traces of poly(p-phenylene) (PP) and its precursors
b) polystyrene (PS)-based macromonomer (M2) and (c) poly(ethylene
(
oxide) (PEO)-based macromonomers (M1).
Figure 4. (a) Normalized excitation and (b) emission fluorescence
spectra of poly(p-phenylene) (PP) in CH C at room temperature.
2 2
Figure 3. UV spectra of (a) poly(p-phenylene) (PP) and its precursors
(b) polystyrene (PS)-based macromonomers (M2) and (c) poly(ethylene
oxide) (PEO)-based macromonomer (M1) in CH Cl
2
2
.
Figure 5. DSC traces of (a) poly(p-phenylene) (PP) and its precursors
b) poly(ethylene oxide) (PEO)-based macromonomer (M1) and (c)
polystyrene (PS)-based macromonomers (M2).
(
UV absorption spectra of macromonomers and corresponding
PP registered in solutions withthe same concentrations are shown
in Figure 3. Whereas PEO-based macromonomer does not show
significant absorption, the PS-based macromonomer has intense
absorption at ∼262 nm. The UV spectrum of PP has a peak with
higher intensity at wavelengths close to that of PS-based macro-
monomer because of the presence of supplementary phenylene
rings in the main chain. Moreover, additional absorption at
around 280-320 nm is further evidence of the presence of PP
chain.
Furthermore, fluorescence properties of PP and macromono-
mers were investigated in Figure 4. Whereas PEO- and PS-based
macromonomers do not show any fluorescence properties, PP
shows the strong fluorescence properties. The excitation spec-
trum of PP had the maximum at 299 nm, and emission spectrum
obtained for the excitation wavelength at this value had a
maximum at 366 nm.
transition belongs to Tm of the PEO segment, and the latter is
consistent with T of PS segment.
g
Ultrathin films (thickness <20 nm) of PP spin coated on
silicon substrates from CH Cl solutions showed nanostructured
2
2
morphology at the top surface. Figure 6 shows the AFM height
and phase pictures of a 19.0 nm thick PP film. The top surface had
∼1 to 2 nm peak-to-peak roughness originating from circular
holes of ∼1 to 2 nm deep. Although the in-plane distribution of
these holes were not regular, the distance between the neighbor-
ing holes were on the average 65 ( 15 nm, as determined by
Fourier transformation of the AFM phase image. We attribute
such morphology to the presence of nanophase separation
between the PS and the PEO side chains of PP. Phase-separated
PS and PEO side chains tend to either side of the PP backbone.
The tendency of the PEO side chains for the underlying silicon
substrate and the PS side chains for the air/film interface then
orient the molecules in such a way that layers of PEO/PP
backbone/PS forms parallel to the substrate. Perfect alternation
of PEO and PS side chains on the backbone allows interdigitation
between same-type side chains of neighboring layers. An incom-
plete top surface layer of the film would then show holes whose
depth would be equal to the PS layer thickness. Rg of PS
Also, the thermal behavior of the polymers was investigated by
DSC (Figure 5). Glass-transition temperatures (T ) were mea-
g
sured after a first heating (from -50 to 150 °C) and cooling (from
1
50 °C to -50 °C) cycle. Thermograms were recorded during the
second heating cycle (from -50 to 300 °C) at 10 °C/min under
nitrogen flow. PS-based macromonomer shows a typical T at
g
9
9.57 °C, and low-molecular-weight-PEO-based macromonomer
exhibits only a melting temperature (T ) at 52.57 °C. PP
displayed two transitions at 51.98 and 89.60 °C. The first
m
macromonomers (M ≈ 8250-9150 g/mol) is ∼1 nm, which is
n

Article
Macromolecules, Vol. 43, No. 6, 2010 2737
Figure 6. (a) AFM height and (b) phase pictures of 19.0 nm thick poly(p-phenylene) (PP) film on silicon substrate.
Figure 7. AFM height and phase pictures of 10.6 nm thick poly(p-phenylene) (PP) films on (a-c) untreated silicon and on (d-f) UV-ozone treated
silicon: (a) height picture on untreated Si, (b) the surface roughness profile along the line shown in part a, (c) phase picture on untreated Si, (d) height
picture on UV-ozone treated Si, (e) the surface roughness profile along the line shown in part d, and (f) phase picture on UV-ozone treated Si.
in good agreement with the observed depths of the holes on the
top surface. The average distance of ∼65 nm between the holes
cannot be related to the molecular structure. This might arise
because of different solubility of PS and PEO in CH Cl and the
evaporation of the solvent during the spin coating process.
To check further the nanophase separation between the
perfectly alternating PEO and PS side chains and the influence
of the substrate interface in orienting the layers, we investigated
the morphology of even thinner films on untreated and UV-
ozone-treated silicon substrates. UV-ozone treatment makes the
silicon substrate surface more hydrophilic by the addition of
consisted of ∼5 nm thick smooth film on top of which there were
∼5 nm peak-to-peak undulations (Figure 7b), indicating an
incomplete and rough top surface. On the contrary, the PP film
having the same thickness on hydrophilic silicon substrate
showed a smooth ∼10 nm thick film between the circular holes.
The peak-to-peak roughness of the top surface was ∼1 nm
(Figure 7e). The difference in the roughness of the top surfaces
of PP films for different substrates is also clearly seen in the phase
pictures of Figure 7c,f. Another difference observed between the
two spin-coated films is in the smoothness of the circumference of
the large uncoated holes: the holes on untreated silicon have
rougher circumference including some kinks, whereas the holes
on hydrophilic silicon had smoother circumference. This shows
that the film on hydrophilic silicon is better equilibrated by the
tendency of the PEO side chains for the substrate such that the
incomplete top layers disappeared at the expense of enlarged
holes.
2
2
-
OH groups. The tendency of the hydrophilic PEO side chains
for the substrate will then be stronger. Figure 7 shows the AFM
height and phase pictures of 10.6 nm thick PP films on untreated
silicon wafers (a and c) and UV-ozone treated silicon wafers
(
0
d and f). Spin coating from relatively dilute PP solution (c=
.5 mg/mL) resulted in incomplete coverage. Uncoated circular
regions (holes) having diameter between 0.1 and 0.5 μm were
observed on both substrates. The PP film on untreated silicon
In summary, we have demonstrated the potential of Suzuki
cross coupling reactions as a versatile synthetic route to prepare

2
738 Macromolecules, Vol. 43, No. 6, 2010
Sahkulubey et al.
completely and perfectly alternating amphiphilic graft copoly-
mers. The well-defined macromonomers of hydrophilic PEO and
hydrophobic PS equipped with the opponent functional groups
were readily coupled in the presence of palladium catalyst. The
structures of such complexed graft copolymers have been fully
characterized. Because of the extended conjugation arising from
the polyphenylene formation, they exhibit a bathochromic shift
in both absorption and emission spectra. The perfectly alternat-
ing hydrophilic PEO and hydrophobic PS side chains were
observed by AFM measurements to nanophase separate in thin
films. The perfectly designed amphiphilic nature of the PP graft
copolymers, and the optical properties imply that they may find
many applications in various fields.
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