Synthesis of well-defined rod-coil block copolymers containing trifluoromethylated poly(phenylene oxide)s by chain-growth condensation polymerization and atom transfer radical polymerization

Article abstract of DOI:10.1002/pola.23859

Well-defined trifluoromethylated poly(phenylene oxide)s were synthesized via nucleophilic aromatic substitution (S_NAr) reaction by a chain-growth polymerization manner. Polymerization of potassium 4-fluoro-3-(trifluoromethyl)phenolate in the presence of an appropriate initiator yielded polymers with molecular weights of ～4000 and polydlspersity indices of <1.2, which were characterized by ¹H nuclear magnetic resonance spectroscopy and gel permeation chromatography. Initiating sites for atom transfer radical polymerization (ATRP) were Introduced at the either side of chain ends of the poly(phenylene oxide), and used for ATRP of styrene and methyl methacrylate, yielding well-defined rod-coil block copolymers. Differential scanning calorimetry study indicated that the well-defined trifluoromethylated poly(phenylene oxide)s showed high crystallinity and were immiscible with polystyrene.

Full text of DOI:10.1002/pola.23859

Synthesis of Well-Defined Rod-Coil Block Copolymers Containing
Trifluoromethylated Poly(phenylene oxide)s by Chain-Growth
Condensation Polymerization and Atom Transfer Radical Polymerization
YUN JUN KIM,* MYUNGEUN SEO, SANG YOUL KIM
Department of Chemistry, KAIST, Gwahangno 335, Yuseong-gu, Daejeon 305-701, Korea
Received 21 September 2009; accepted 26 November 2009
DOI: 10.1002/pola.23859
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Well-defined
trifluoromethylated poly(phenylene
ide), and used for ATRP of styrene and methyl methacrylate,
yielding well-defined rod-coil block copolymers. Differential scan-
ning calorimetry study indicated that the well-defined trifluoro-
oxide)s were synthesized via nucleophilic aromatic substitution
(SNAr) reaction by a chain-growth polymerization manner. Poly-
merization of potassium 4-fluoro-3-(trifluoromethyl)phenolate in
the presence of an appropriate initiator yielded polymers with
molecular weights of ꢀ4000 and polydispersity indices of <1.2,
which were characterized by 1H nuclear magnetic resonance
spectroscopy and gel permeation chromatography. Initiating
sites for atom transfer radical polymerization (ATRP) were intro-
duced at the either side of chain ends of the poly(phenylene ox-
methylated poly(phenylene oxide)s showed high crystallinity and
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were immiscible with polystyrene. 2010 Wiley Periodicals, Inc.
J Polym Sci Part A: Polym Chem 48: 1049–1057, 2010
KEYWORDS: atom transfer radical polymerization; block copoly-
mers; chain-growth condensation polymerization; poly(pheny-
lene oxide)
INTRODUCTION Macromolecules with well-defined struc-
tures have been of recent interests, partly because they can
be a basic building block for nanostructured organic materi-
als. For example, self-assembled pattern of diblock copoly-
mer thin films has been utilized for nanopatterning in an
attempt to overcome the resolution limit of traditional
photolithographic technique.1 Much of diblock copolymer
studies have been focused on the diblock copolymers
obtained by living or controlled chain polymerization of two
different kinds of vinyl monomers.2 Recently, rod-coil block
copolymers consisting of condensation and addition blocks
have been studied, but most of them do not have a precisely
defined condensation block mainly because of synthetic diffi-
culties.3 However, a recent development of chain-growth con-
densation polymerization (CGCP) has opened an easy access
for rod-coil block copolymers containing condensation and
addition blocks.4
produced well-defined rod-coil block copolymers, which is
expected to show interesting self-assembly behaviors due to
the large incompatibility between the rod and the coil
segments.9
An interesting class of poly(phenylene oxide)s is a fluorine-
containing poly(phenylene oxide), promising material for
optoelectronic applications. The introduction of fluorine is
important because it provides low optical loss, birefringence,
dielectric constant, and moisture absorption.10 Previously we
have found that a trifluoromethyl group at the ortho position
of the leaving group (i.e., F or NO2) facilitates a nucleophilic
aromatic substitution (SNAr) reaction, and we synthesized a
number of poly(phenylene oxide)s containing trifluoromethyl
groups which show excellent optical properties.11 Here, we
report the synthesis of well-defined poly(phenylene oxide)s
by using a phenoxide monomer containing the trifluoro-
methyl group with appropriate initiators for CGCP. Also, syn-
thesis of rod-coil block copolymers containing trifluorome-
thylated poly(phenylene oxide) block is presented.
Poly(phenylene oxide), composed of phenyl rings and ether
linkages, is a high-performance condensation polymer with
excellent physical properties and finds applications in many
areas.5 A variety of materials including the blend of poly-
(phenylene oxide)s and styrenic polymers are commercially
available due to the high miscibility between two kinds of
polymers.6 By using the CGCP technique, well-defined poly-
(phenylene oxide)s with narrow polydispersities have been
synthesized.7 In addition, use of orthogonal initiators for
CGCP and atom transfer radical polymerization (ATRP)8 has
EXPERIMENTAL
Materials
4-Fluoro-3-(trifluoromethyl)phenol (Fluorochem), 4-fluoro-3-
(trifluoromethyl)aniline (Aldrich), 4-nitro-3-(trifluoromethyl)-
benzonitrile (2, Aldrich), 2-bromoisobutyryl bromide (Al-
drich), and 2,20-bipyridine (bpy, Aldrich) were used as
received. Phenol was distilled under reduced pressure. 2-
*Present address: Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706.
Correspondence to: S. Y. Kim (E-mail: kimsy@kaist.ac.kr)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 1049–1057 (2010) 2010 Wiley Periodicals, Inc.
POLY(PHENYLENE OXIDE) BLOCK COPOLYMERS, KIM, SEO, AND KIM
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
Nitrobenzotrifluoride (3) was recrystallized from methanol/
hexane. Dimethyl sulfoxide (DMSO) and N,N-dimethylforma-
mide (DMF) were stirred in the presence of calcium hydride
overnight and then distilled under reduced pressure. Methyl
methacrylate (MMA) and Styrene (Aldrich) was passed
through a column filled with neutral alumina, stirred in the
presence of calcium hydride overnight, and then distilled
under reduced pressure before use. Copper(I) chloride
(CuCl) was washed with glacial acetic acid and absolute
ethanol, and dried in vacuo. 4,40-Di-(5-nonyl)-2,20-bipyridine
(dnbpy) was synthesized as reported previously. Methanol
(HPLC grade), dichloromethane (HPLC grade), tetrahydro-
furan (THF, HPLC grade), cyclohexane (HPLC grade), and ani-
sole (anhydrous grade) were used without further purifica-
tion. Polystyrene standards were purchased from Senshu
Scientific. Other commercially available reagent grade chemi-
cals were used without further purification.
ꢁC, ppm): 162.66, 161.21 (qd, J ¼ 258.9 Hz, J ¼ 2.1 Hz),
150.13 (d, J ¼ 3.6 Hz), 147.01, 128.91 (d, J ¼ 9.1 Hz),
126.09 (q, J ¼ 34.4 Hz), 123.65 (dq, J ¼ 272.3 Hz, J ¼ 1.2
Hz), 121.84 (dq, J ¼ 4.6 Hz, J ¼ 2.0 Hz), 119.61 (dq, J ¼ 33.3
Hz, J ¼ 13.9 Hz), 118.60 (d, J ¼ 22.3 Hz), 116.68. EI HRMS
(m/z): calcd for C13H8F4N2O, 284.0573; found, 284.0572
[M]þ.
Syntheses of Poly(phenylene oxide)s via CGCP
(CF3PPO3 and CF3PPO4)
All the polymerizations were carried out under dry argon
atmosphere. A typical polymerization procedure was exem-
plified with the synthesis of CF3PPO3. A dried, 100 mL
three-necked flask was equipped with a mechanical stirrer
and a Dean-Stark trap connected to a water-cooled con-
denser. 1 (3.02 g, 13.9 mmol), 3 (0.177 g, 0.924 mmol), and
DMSO (55 mL) were added to the flask. The polymerization
ꢁ
mixture was stirred at 120 C. To investigate the polymeriza-
Potassium 4-Fluoro-3-(trifluoromethyl)phenoxide) (1)
4-Fluoro-3-(trifluoromethyl)phenol (14.1 g, 78.3 mmol) was
stirred in methanol (30 mL) in a 250 mL flask. Potassium
hydroxide (4.26 g, 76.0 mmol) dissolved in methanol (70
mL) was slowly added to the flask at 0 ꢁC, and the mixture
was stirred at room temperature for an additional hour. Af-
ter excess solvent was evaporated, oil-like product was
poured into dichloromethane. The white powder was fil-
tered, washed with dichloromethane, and dried in vacuo
tion kinetics, small portion of the reaction mixture was taken
via syringe (previously purged with argon) under dry argon
atmosphere at a certain time interval. For the NMR measure-
ment, each crude mixture was added to tetrahydrofuran-d8.
For the GPC measurement, each crude mixture was added to
tetrahydrofuran and passed through a 0.2 lm filter before
injection. After the polymerization was complete, the solu-
tion was poured into vigorously stirred distilled water. The
resulting polymer was filtered, washed with distilled water,
and dried in vacuo.
ꢁ
(13.9 g, 81% yield). m.p. 73–75 C.
1H NMR (400.13 MHz, DMSO-d6, 25 ꢁC, ppm): 6.67 (t, J ¼
10.6 Hz, 1H), 6.20–6.10 (2H). 13C NMR (100.62 MHz, DMSO-
d6, ppm): 167.97, 144.59 (d, J ¼ 229.5 Hz), 124.00 (dq, J ¼
271.6 Hz, J ¼ 1.5 Hz), 121.85 (d, J ¼ 6.0 Hz), 116.32 (d, J ¼
19.7 Hz), 115.76 (dq, J ¼ 29.9 Hz, J ¼ 12.4 Hz), 113.10 (dq,
J ¼ 3.9 Hz, J ¼ 1.6 Hz).
Using the aforementioned procedure, CF3PPO4 was synthe-
sized from 1 (2.14 g, 9.79 mmol), 4 (0.186 g, 0.653 mmol),
and DMSO (40 mL).
Synthesis of the Macroinitiator CF3PPO3Br
A 100 mL three-necked flask was equipped with a Dean-
Stark trap connected to a water-cooled condenser. CF3PPO3
(1.50 g, 0.577 mmol), 4-aminophenol (0.252 g, 2.31 mmol),
K2CO3 (0.399 g, 2.89 mmol), DMF (35 mL), and benzene
(18 mL) were ꢁadded to the flask. The reaction mixture was
heated to 140 C for 24 h at which the benzene was brought
to reflux. After the reaction was complete, the solution was
poured into vigorously stirred distilled water. The product
was filtered, washed with distilled water and methanol
repeatedly, and dried in vacuo.
40-Hydroxy-4-fluoro-3-(trifluoromethyl)azobenzene) (4)
4-Fluoro-3-(trifluoromethyl)aniline (5.07 g, 28.3 mmol) and
50 mL of 2 N HCl (aq) was placed in a 100 mL flask. The
mixture was stirred at 0 ꢁC while sodium nitrite (2.34 g,
33.9 mmol) in distilled water (10 mL) was added slowly.
The mixture became homogenous, which was indicative of
the formation of diazonium salt. Then, aqueous sodium
phenoxide solution, prepared by dissolving phenol (3.19 g,
33.9 mmol) and sodium hydroxide (2.72 g, 67.9 mmol) in
distilled water (10 mL) was slowly added to the flask. The
reaction mixture was stirred at room temperature for addi-
tional 2 h. The resulting precipitate was filtered, washed
with distilled water, and dried in vacuo. After the precipitate
was added into ethyl acetate (200 mL), insoluble compound
was filtered. Excess solvent in the filtrate was evaporated to
give orange-colored product which was further purified by
silica column chromatography using ethyl acetate/n-hexane
(1/8) as an eluent, and then recrystallized from dichlꢁorome-
thane/cyclohexane (6.90 g, 86% yield). m.p. 121–122 C.
The amine-terminated CF3PPO3 (0.800 g, 0.295 mmol) was
added into a dried 50 mL flask with triethylamine (0.120 g,
1.18 mmol) and THF (20 mL). 2-Bromoisobutyryl bromide
(0.272 g, 1.18 mmol) in THF (3 mL) was slowly added to
the flaꢁsk at room temperature. Then, the mixture was stirred
at 60 C for 24 h. After the reaction was complete, the solu-
tion was poured into vigorously stirred distilled water. The
resulting CF3PPO3Br was filtered, washed with distilled
water and methanol repeatedly, and dried in vacuo.
CF3PPO3Br was further purified by the reprecipitation in
methanol.
1
ꢁ
H NMR (400.13 MHz, tetrahydrofuran-d8, 50 C, ppm): 8.92
(s, 1H), 8.15 (dd, J ¼ 6.73 Hz, J ¼ 2.37 Hz, 1H), 8.14–8.09
(m, 1H), 7.87–7.82 (m, 2H), 7.45 (t, J ¼ 9.44 Hz, 1H), 6.92–
6.87 (m, 2H). 13C NMR (100.62 MHz, tetrahydrofuran-d8, 50
Synthesis of the Macroinitiator CF3PPO4Br
CF3PPO4 (0.600 g, 0.240 mmol) was added into a dried
50 mL flask with triethylamine (0.0971 g, 0.960 mmol) and
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ARTICLE
Characterization
1H NMR and 13C NMR spectra of the synthesized compounds
were recorded on a Bruker Fourier Transform AVANCE 400
(400.13 MHz for 1H and 100.62 MHz for 13C) spectrometer.
Chemical shift of NMR was reported in part per million
(ppm) using residual proton resonance of solvent as internal
reference. Splitting patterns designated as s (singlet), d (dou-
blet), q (quartet), dd (doublet of doublet), dq (doublet of
quartet), qd (quartet of doublet), m (multiplet), and br
(broaden). Electron impact high-resolution mass (EI HRMS)
spectra of the synthesized compounds were obtained with a
Micromass Autospec Ultima mass spectrometer. Gel Permea-
tion Chromatography (GPC) traces were obtained with Visco-
tek T60A equipped with UV detector and packing column
(PLgel 10 lm MIXED-B) using tetrahydrofuran as an eluent
at 35 ꢁC. Number (Mn) and weight (Mw) average molecular
weights of the polymers were calculated on the basis of
polystyrene standards. Differential scanning calorimetry
(DSC) analyses were performed on a TA Q100 instrument.
Melting (Tm) and/or glass (Tg) transition temperatures of the
synthesized compounds weꢁre obtained with the DSC instru-
ment at a heating rate of 5 C/min in N2.
SCHEME 1 Self-polymerization of the monomer 1.
THF (15 mL). 2-Bromoisobutyryl bromide (0.221 g, 0.960
mmol) in THF (2 mL) was slowly added to the flask at room
temperature. Then, the mixture was stirred at 60 ꢁC for
24 h. After the reaction was complete, the solution was
poured into vigorously stirred distilled water. The product
was filtered, washed with distilled water and methanol
repeatedly, and dried in vacuo. CF3PPO4Br was further puri-
fied by the reprecipitation in methanol.
Synthesis of CF3PPO-b-PMMA
A typical polymerization procedure was exemplified with the
ATRP of MMA from CF3PPO3Br macroinitiator (Table 2,
Entry 1). CuCl (0.0139 g, 0.140 mmol), bpy (0.0437 g, 0.280
mmol), and MMA (3.50 g, 35.0 mmol) was placed in a dried
Schlenk flask under dry argon atmosphere. The mixture was
diluted with anisole (3.7 mL), stirred until it became homo-
geneous, and then degassed by ‘‘freeze-pump-thaw’’ cycles.
After deoxygenated anisole solution of the CF3PPO3Br
macroinitiator (0.200 g, 0.0700 mmol) was added to the
flask via gastight syringe under dry argon atmosphere, three
more ‘‘freeze-pump-thaw’’ cycles were performed. Then, the
RESULTS AND DISCUSSION
Synthesis of Well-Defined Poly(phenylene oxide)s
For the synthesis of well-defined poly(phenylene oxide)s
containing trifluoromethyl groups via SNAr reaction, potas-
sium 4-fluoro-3-(trifluoromethyl)phenolate (1) was chosen
as an appropriate AB0 type monomer. Because the reactivity
of the fluorine is suppressed by the electron-rich phenoxide
group at the para position of the phenyl ring, self-polymer-
ꢁ
flask was immersed in an oil bath thermostatted at 90 C. At
a proper monomer conversion below 50%, the polymeriza-
tion mixture was cooled to room temperature and diluted
with THF. After the solution was passed through a small col-
umn of alumina and a 0.2 lm filter, it was poured into n-hex-
ane. The resulting precipitate was filtered, washed with n-
hexane, and dried in vacuo. Reprecipitation in hot methanol
yielded the desired CF3PPO-b-PMMA block copolymer.
ꢁ
ization of the monomer 1 does not proceed below 140 C in
DMSO or N,N-DMF. However, once the phenoxide group is
transformed into ethereal oxygen, the fluorine is activated by
the trifluoromethyl group at ortho position and polymeriza-
tion proceeds (Scheme 1).
Synthesis of CF3PPO-b-PS
A typical polymerization procedure was exemplified with the
ATRP of styrene from CF3PPO4Br macroinitiator (Table 2,
Entry 4). CuCl (0.0374 g, 0.377 mmol), dnbpy (0.308 g,
0.755 mmol), and styrene (3.93 g, 37.7 mmol) was placed in
a dried Schlenk flask under dry argon atmosphere. The mix-
ture was diluted with anisole (4.3 mL), stirred until it
became homogeneous, and then degassed by ‘‘freeze-pump-
thaw’’ cycles. After deoxygenated anisole solution of the
CF3PPO4Br macroinitiator (0.200 g, 0.0755 mmol) was
added to the flask via gastight syringe under dry argon
atmosphere, three more ‘‘freeze-pump-thaw’’ cycles were
performed. Then, the flask was immersed in an oil bath ther-
On the basis of the previous results, CGCP of the monomer 1
was investigated using different B type initiators shown in
Scheme 2 and 3. Polymerization was conducted in DMSO at
a total concentration of 5 wt %. The ratio between the
monomer ([M]) and the initiator ([I]) was 15, and the reac-
ꢁ
tion temperature was 120 C to avoid self-polymerization of
the monomer.
Initiators for CGCP should react with the monomers at tem-
peratures where self-polymerization does not occur. 4-Nitro-
3-(trifluoromethyl)benzonitrile (2) was selected as an initia-
tor because it possesses a nitro leaving group strongly acti-
vated by the trifluoromethyl group as well as the nitrile
ꢁ
mostatted at 110 C. At a proper monomer conversion below
50%, the polymerization mixture was cooled to room tem-
perature and diluted with THF. After the solution was passed
through a small column of alumina and a 0.2 lm filter, it
was poured into methanol. The resulting precipitate was fil-
tered, washed with methanol, and dried in vacuo. The poly-
meric mixture was stirred in cyclohexane overnight. Filtra-
tion of insoluble precipitates and evaporation of the filtrate
yielded the desired CF3PPO-b-PS block copolymer.
SCHEME 2 CGCP of the monomer 1 in the existence of initia-
tors 2 and 3.
POLY(PHENYLENE OXIDE) BLOCK COPOLYMERS, KIM, SEO, AND KIM
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 1 (a) Evolution of GPC traces for polymerization of the monomer 1 in the existence of 3 in DMSO. Total concentration
was 5 wt % and [1]/[3] was 15. (b) Number-average molecular weight Mn (circles) and PDI (Mw/Mn, triangles) as a function of
overall monomer conversion. Theoretical Mn (line) was calculated from the conversion. (c) ln([M]0/[M]) versus time plot (circles).
The line was obtained by linear regression.
group. However, GPC analysis of the polymer CF3PPO2 syn-
thesized by the polymerization of 1 in the presence of the
initiator 2 showed trimodal molecular weight distribution,
indicating that the polymerization did not proceed in a con-
trolled manner. The origin of the poor controllability was
attributed to a transetherification reaction at the ether link-
age between the initiator 2 and the repeating unit. The
transetherification is likely to occur because the ether link-
age is strongly activated by the trifluoromethyl group and
the nitrile group as well. It will produce a polymer termi-
nated with a phenoxide group which can grow further via a
step-growth manner or which can form a macrocycle via
intramolecular cyclization. These side reactions disturb the
controlled polymerization behavior, resulting in the trimodal
molecular weight distribution as suggested by the previous
study.7(b)
a fluorine leaving group (B0) activated by the trifluoromethyl
group at ortho position of the phenyl ring for CGCP. Also,
the initiator contains a phenolic hydroxyl group on the
other side which can be used for post-modification of the
synthesized polymer. The azobenzene group in the middle
of the olecule acts not only as a bridge between two
functionalities but as
photoisomerization.14
a stimuli-responsive moiety via
Polymerization of the monomer 1 in the presence of the ini-
tiator 4 was conducted under the same condition for the
polymerization with the initiator 3 (Scheme 3). The polymer-
ization proceeds in a controlled chain-growth manner illus-
trated by the linear increase of the molecular weight with
conversion which well matches the theoretical values, nar-
row PDIs throughout the polymerization, and the linear plot
of ln([M]0/[M]) versus time (Fig. 2). It is interesting to
observe that the phenolic hydroxyl group did not participate
in the polymerization and remained intact. Table 1 summa-
rizes characterization results of the synthesized polymers.
Because 2-nitrobenzotrifluoride (3) contains a fluorine leav-
ing group solely activated by the trifluoromethyl group, the
synthesized polymer is expected to show higher tolerance
towards the transetherification reaction when 3 is used as
an initiator. Figure 1(a) shows the evolution of the GPC
traces of the polymer CF3PPO3 synthesized by polymeriza-
tion of the monomer 1 with the initiator 3. GPC analysis
reveals that the molecular weight increases linearly with
conversion and the experimental values are close to the the-
oretical ones, assuming quantitative initiation. The molecular
weight distributions decrease with conversion, and at the
end of the reaction, are relatively narrow [Fig. 1(b)]. In addi-
tion, the plot of ln([M]0/[M]) versus time is linear indicating
a constant number of propagating species throughout the
reaction [Fig. 1(c)]. These data support that the polymeriza-
tion proceeds in a controlled chain-growth manner.12
Figure 3 shows 1H NMR spectra of CF3PPO3 and CF3PPO4
in THF-d8. All protons in the initiator and the repeating units
1
are clearly visible. Especially, H NMR spectrum of CF3PPO4
shows a peak at 8.8 ppm corresponding to the phenolic pro-
ton confirming that the phenolic hydroxyl group remains in
the polymer [Fig. 3(b)].
Multifunctional initiators have an advantage in introducing
useful functionalities into the polymer chains.13 In this
regard, a multifunctional initiator 4 was synthesized by
diazotization of 4-fluoro-3-(trifluoromethyl)aniline followed
by coupling with phenol (Scheme 3). The initiator 4 contains
SCHEME 3 Synthesis of azobenzene-containing multifunctional
initiator 4 and CGCP of the monomer 1 using 4.
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ARTICLE
FIGURE 2 (a) Number-average molecular weight Mn (circles) and PDI (Mw/Mn, triangles) as a function of overall monomer conver-
sion for polymerization of the monomer 1 with 4 in DMSO at 120 ꢁC. Total concentration was 5 wt % and [1]/[4] was 15. Theoretical
Mn (line) was calculated from the conversion. (b) ln([M]0/[M]) versus time plot (circles). The line was obtained by linear regression.
The CGCP of 1 was also attempted at an increased feed ratio
relative to 3 ([1]/[3] ¼ 30) in DMSO at 120 ꢁC. However,
the mixture became heterogeneous at the last stage of poly-
merization. The 1H NMR spectrum indicated that the mono-
mer conversion was about 80% (theoretically calculated Mn
of the polymer ¼ ꢀ4 ꢂ 103). The GPC trace showed a peak
which was accompanied by a small shoulder in higher mo-
lecular weight region [Fig. 4(a), 72 h]. The continued poly-
merization of the heterogeneous mixture was not controlla-
ble. The shoulder peak intensified, and not only the main
peak but also the shoulder peak shifted toward higher mo-
lecular weight region [Fig. 4(a), 96 h]. These polymerization
behaviors implied the growths of polymer chains in two dif-
ferent phases, that is, one from the solution phase and the
other from the precipitated solid phase. It was believed that
the rigid, rod-like poly(phenylene oxide) had a limited solu-
bility in DMSO above certain molecular weight. The poly-
(phenylene oxide) showed a good solubility in THF, and was
also soluble in anisole and DMF on heating. The synthesis of
high molecular weight poly(phenylene oxide) was also
attempted in DMF considering its better solubility in DMF
than in DMSO. The molecular weight could be increased to
ꢀ4 ꢂ 103 with maintaining narrow PDI of 1.14 [Fig. 4(b), 96
h]. However, the polymerization could not be complete
within reasonable time (monomer conversion: ꢀ80% for
96 h) because of the polymer solubility issues and slow
polymerization kinetics.
Block Copolymerization by ATRP
For the synthesis of rod-coil block copolymers, atom transfer
radical polymerization (ATRP) was considered because intro-
duction of an ATRP initiator into the synthesized poly(pheny-
lene oxide)s can be readily achieved. Scheme 4 shows syn-
thetic routes for the poly(phenylene oxide)s bearing ATRP
initiating sites.
TABLE 1 CGCP of the Monomer 1 in the Presence of Different
Initiators
PDIa
a
a
Entry
Initiator
Mn
Mw
CF3PPO1
CF3PPO3
CF3PPO4
a
None
2.0 ꢂ 103
2.6 ꢂ 103
2.5 ꢂ 103
4.0 ꢂ 103
2.8 ꢂ 103
2.9 ꢂ 103
2.0
3
4
1.09
1.14
FIGURE 3 1H NMR spectra of (a) CF3PPO3 and (b) CF3PPO4
(400 MHz, THF-d8, 50 ꢁC).
Determined by GPC using polystyrene standards (THF).
POLY(PHENYLENE OXIDE) BLOCK COPOLYMERS, KIM, SEO, AND KIM
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 4 (a) Evolution of GPC traces for polymerization of the
monomer 1 in the existence of 3 (a) in DMSO and (b) in DMF.
Total concentration was 5 wt % and [1]/[3] was 30.
CF3PPO3, which contains a fluorine leaving group at the chain
end, was reacted with 4-aminophenol via SNAr reaction using
potassium carbonate as a base. When the reaction was con-
ducted in DMF at 140 ꢁC, amine-terminated CF3PPO3 was
exclusively produced presumably because the amine group was
not reactive enough as a nucleophile compared to the phenox-
ide ions in the given reaction condition. A slightly shifted but
unimodal GPC trace was observed after the reaction, suggesting
no side reaction such as transetherification occurred (data not
shown). Subsequent amide formation between the amine-termi-
nated CF3PPO3 and 2-bromoisobutyryl bromide in the pres-
ence of triethylamine produced CF3PPO3 bearing an ATRP ini-
tiator at the chain end (CF3PPO3Br).
FIGURE
5
1H NMR spectra of (a) CF3PPO3Br and (b)
CF3PPO4Br (400 MHz, THF-d8, 50 ꢁC).
ducted using CF3PPO3Br and CF3PPO4Br macroinitiators.
Scheme 5 shows the structures and synthetic schemes of the
resulting CF3PPO-b-PMMA and CF3PPO-b-PS copolymers.
Table 2 summarizes the ATRP conditions and the characteri-
zation results for the block copolymers. To monitor the poly-
merization behavior, some of the polymerization mixture
was taken during ATRP, and analyzed by NMR and GPC. The
feed ratio of monomer to macroinitiator was 500. The poly-
merization was stopped at a monomer conversion of <50%
to avoid radical-radical coupling reactions.
For CF3PPO4, which contains a phenolic hydroxyl group,
introduction of an ATRP initiator was simply achieved by
esterification of CF3PPO4 with 2-bromoisobutyryl bromide.
The reaction produced CF3PPO4Br bearing an ATRP initia-
tor at the chain end. 1H NMR spectra of CF3PPO3Br and
CF3PPO4Br in THF-d8 are shown in Figure 5.
Reaction conditions for ATRP of MMA15 and styrene16 have
been well developed in previous studies. We utilized halogen
exchange system (R-Br/CuCl) to facilitate faster initiation
than propagation.17 ATRP of MMA was conducted at 90 C in
ꢁ
the presence of CuCl and 2,20-bipyridine (bpy) in 50% (v/v)
To demonstrate the feasibility of block copolymerization,
ATRP of methyl methacrylate (MMA) and styrene was con-
of anisole as a solvent. When one equivalent of CuCl/bpy
SCHEME 4 Synthesis of ATRP
macroinitiators CF3PPO3Br and
CF3PPO4Br containing poly(phe-
nylene oxide) CF3PPO3 and
CF3PPO4, respectively.
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ARTICLE
SCHEME 5 Synthesis of block copolymers consisting of poly(phenylene oxide)s via ATRP.
ꢁ
complex relative to the macroinitiator CF3PPOBr used, poly-
merization proceeded slowly. GPC analysis showed that some
portion of the macroinitiator did not participate in the poly-
merization although the growing CF3PPO-b-PMMA main-
tained narrow molecular weight distributions during the
polymerization. When the amount of the catalyst increased
to two equivalents, polymerization proceeded more rapidly,
and it was possible to obtain a block copolymer with high
molecular weight (entry 1). Unreacted macroinitiators still
remained after the polymerization, but they were readily
removed by reprecipitation of the crude product in hot
methanol, yielding a pure block copolymer with narrow
polydispersity [Fig. 6(a)]. The molar ratio of two kinds of
repeating units, MMA to PPO, in the block copolymer was
determined as 15:1 by 1H NMR. Given the GPC data (total
Mn of the block copolymer: ꢀ1.8 ꢂ 104), it was estimated
that PMMA block has Mn of ꢀ1.6 ꢂ 104. CF3PPO4Br also
successfully produced a high molecular weight CF3PPO-b-
PMMA copolymer with narrow polydispersity using the same
ATRP condition (entry 2).
the slow polymerization rate in anisole at 110 C. When the
ATRP of styrene was carried out in the presence of
CF3PPO3Br using 5 equivalent of CuCl/dnbpy complex, the
polymerization mixture became viscous after 36 h. The GPC
analyses indicated that the CF3PPO-b-PS copolymer had a
high molecular weight, but relatively broad molecular weight
distribution (entry 3). Furthermore, significant amount of
CF3PPO3Br macroinitiator was remained without initiation.
CF3PPO3Br might not be suitable in the controlled polymer-
ization of styrene presumably because of the amide bond next
to the initiating site. It has been reported that the amide type
ATRP initiators generally have poor efficiency and can produce
polymers with high polydispersities.18 When CF3PPO4Br was
used as a macroinitiator, high molecular weight block copoly-
mer was obtained as well as the molecular weight distribution
was narrow [entry 4 and Fig. 6(b)]. The block copolymer was
extracted with cyclohexane to remove any unreacted macroini-
tiators. The molar ratio of styrene to phenylene oxide in the
block copolymer was determined as 14:1 by 1H NMR (esti-
mated Mn of PS block: 1.7 ꢂ 104).
For the synthesis of CF3PPO-b-PS copolymer from
CF3PPO3Br or CF3PPO4Br, we used CuCl/4,40-di-(5-nonyl)-
2,20-bipyridine (dnbpy) catalyst system which has been
known to induce the well-controlled, homogeneous ATRP of
styrene.16 Excess amount of catalyst is required because of
Thermal Properties of the Polymers and Miscibility
Between the Blocks
DSC studies were carried out to evaluation thermal transi-
tions of the synthesized polymers and miscibility between
the blocks. DSC thermograms of CF3PPO3 and block
TABLE 2 ATRP of Vinyl Monomers from the Poly(phenylene oxide) Macroinitiators
a
a
Entry
Monomer
MMA
Initiator
Catalyst
[M]:[I]:[Cu]:[ligand]
Mn
Mw
PDIa
1b
2b
3d
4d
a
CF3PPO3Br
CF3PPO4Br
CF3PPO3Br
CF3PPO4Br
CuCl/bpyc
CuCl/bpyc
CuCl/dnbpye
CuCl/dnbpye
500:1:2:4
500:1:2:4
500:1:5:10
500:1:5:10
d
1.8 ꢂ 104
1.6 ꢂ 104
2.2 ꢂ 104
1.9 ꢂ 104
2.2 ꢂ 104
1.8 ꢂ 104
2.9 ꢂ 104
2.3 ꢂ 104
1.20
1.17
1.35
1.24
Styrene
Determined by GPC using polystyrene standards (THF).
Polymerization was carried out in 50% (v/v) of anisole at 110 ꢁC for
36 h and the resulting polymer was purified by extraction with
b
Polymerization was carried out in 50% (v/v) of anisole at 90 ꢁC for 1
h and the resulting polymer was purified by reprecipitation in hot
methanol.
cyclohexane.
e
4,40-Di-(5-nonyl)-2,20-bipyridine.
c
Bipyridine.
POLY(PHENYLENE OXIDE) BLOCK COPOLYMERS, KIM, SEO, AND KIM
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
glass transition corresponding to that of PMMA, indicating
that both blocks are miscible [Fig. 7(b)]. However, CF3PPO-
b-PS showed two thermal transitions corresponding to the
glass transition of polystyrene block and the melting transi-
tion of CF3PPO block, respectively [Fig. 7(c)]. This tendency
is clearly different from the conventional PPOTM, which is
completely miscible with polystyrene regardless of molecular
weight and composition.
CONCLUSIONS
Well-defined poly(phenylene oxide)s containing trifluoro-
methyl groups were synthesized via CGCP. By using the appro-
priate polymerization conditions such as initiator and reaction
temperature, trifluoromethylated poly(phenylene oxide)s with
desired molecular weights and narrow molecular weight distri-
bution were readily obtained. Furthermore, block copolymers
consisting of poly(phenylene oxide)s were synthesized by
introducing initiators for ATRP at the chain end. Subsequent
ATRP of styrene or methyl methacrylate produced well-defined
block copolymers. Thermal transitions of synthesized poly
(phenylene oxide)s and their block copolymers suggest that the
poly(phenylene oxide)s are highly crystalline due to the well-
defined architecture and they are immiscible with polystyrene.
FIGURE 6 THF-GPC chromatograms of (a) CF3PPO-b-PMMA
(Table 2, Entry 1) and (b) CF3PPO-b-PS (Table 2, Entry 4) mea-
sured by UV detector at the flow rate of 1 mL/min.
copolymers consisting of the CF3PPO segment are shown in
Figure 7. CF3PPO3 shows a large endothermal transition at
220 ꢁC which was assigned as melting transition [Fig. 7(a)].
In contrast to the previously reported amorphous poly(phe-
nylene oxide) containing trifluoromethyl group which shows
a glass transition at 108 ꢁC,V11(c) the well-defined architec-
ture achieved by CGCP might attribute to the highly crystal-
line nature of CF3PPO3.7(b) CF3PPO-b-PMMA in which
PMMA has much higher molecular weight showed only one
This work was supported by National Research Foundation
(NRF) through NRL (R0A-2008-000-20121-0) and ERC
(R11-2007-050-04001-0) programs, and by the Ministry of
Environment, Republic of Korea through contract No.
20090192091001-B0-0-001-0-0-2009.
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