Poly(arylene ether)s with trifluoromethyl groups via meta-activated nitro displacement reaction

Article abstract of DOI:10.1016/j.polymer.2010.08.003

New poly(arylene ether)s with pendent trifluoromethyl groups were synthesized from 2,2'-bis(trifluoromethyl)-4,4'-dinitro-1,1'-biphenyl with several bisphenols. The nitro leaving group activated by the trifluoromethyl group at meta position was quantitati

Full text of DOI:10.1016/j.polymer.2010.08.003

Polymer 51 (2010) 4477e4483
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Polymer
journal homepage: www.elsevier.com/locate/polymer
Poly(arylene ether)s with trifluoromethyl groups via meta-activated nitro
displacement reaction
,
b
c
c,
**
Im Sik Chung a , Kyoung Hoon Kim , Yoon Sub Lee , Sang Youl Kim
*
a BioNanotechnology Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), 52 Eoeun-Dong, Yuseong-Gu, Daejeon 305-333, Republic of Korea
b Computational Chemistry Laboratory, Advanced Materials R&D, LG Chem. Ltd. Research Park, 104-1 Moonji-Dong, Yuseong-Gu, Daejon, 305-380, Republic of Korea
c Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong-Dong, Yuseong-Gu, Daejeon 305-701, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
New poly(arylene ether)s with pendent trifluoromethyl groups were synthesized from 2,20-bis(tri-
fluoromethyl)-4,40-dinitro-1,10-biphenyl with several bisphenols. The nitro leaving group activated by the
trifluoromethyl group at meta position was quantitatively displaced with phenolate ions, resulting in
high molecular weight polymers. The quantum mechanical calculation of the energy state suggested that
the nitro displacement reaction activated by the trifluoromethyl group at meta position is an energeti-
cally favorable process. The polymers having weight average molecular weight of 42,100e95,000 g/mol
and molecular weight distribution of 2.65e2.95 were obtained. The polymers were amorphous
and dissolved in a wide range of organic solvents. Transparent and flexible films were obtained by
solution casting. The resulting polymers are thermally stable, and Tgs of the polymers are in the range of
176e199 ꢀC depending on their molecular structure. All of the synthesized polymers show refractive
indices in the range of 1.592e1.624 with low birefringence below 0.006.
Article history:
Received 23 June 2010
Received in revised form
29 July 2010
Accepted 3 August 2010
Available online 10 August 2010
Keywords:
Poly(arylene ether)s
SNAr reaction
Trifluoromethyl group
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
[10e16], mostof them are notsuitable for the synthesisof linearhigh
molecular weight polymers through polycondensation [17,18].
Nucleophilic aromatic substitution (SNAr) reaction has been
utilized in commercial production of poly(arylene ether)s, one of
high-performance engineering plastics with excellent hydrolytic,
thermal and dimensional stability along with good mechanical
properties [1]. The SNAr reaction requires a leaving group activated
with an electron withdrawing group [2], and sulfone, ketone, and
imide groups are used as activating groups for SNAr reaction to
make poly(ether sulfone)s, poly(ether ketone)s, and poly(ether
imide)s respectively [3e5]. Various heterocyclic rings have been
also used as an activating group to produce high molecular weight
poly(arylene ether)s [6].
The activating groups in SNAr reaction are generally electron
withdrawing groups, and they stabilize the negative charge devel-
oped during the transition state largely through conjugation [7e9].
So, the electron withdrawing group at meta position of the leaving
group is less effective than the same group at ortho or para position,
and therefore activating groups at ortho or para position are
generally required to obtain high molecular weight polymers. Even
though there are a few examples of meta-activated SNAr reaction
It has been reported that the trifluoromethyl group at ortho or
para position activates fluoro or nitro groups for displacement by
phenoxides [19e26]. The steric congestion caused by bulky tri-
fluoromethyl group at ortho position of the nitro leaving group
significantly affects the formation of a Meisenheimer complex with
release of steric strain [27e32]. The perfluoroalkyl activation in
SNAr reaction provides an effective way to incorporate fluorines
into the polymer chains, which may improve many physical prop-
erties of polymers such as dielectric constant, moisture absorption,
and solubility [33e38].
In the previous work [39], we have found that trifluoromethyl
groups and ether linkages are stable in the nitro displacement
reaction even at 190 ꢀC, and the displacement reaction occurs
quantitatively without any side reactions which are frequently
observed during the nitro displacement reaction at high tempera-
ture due to the reactive nitrite ion by-product [40e46]. Further-
more, the nitro group activated by trifluoromethyl group at meta
position undergoes the displacement reaction quantitatively at
high temperature, and the trifluoromethylated poly(biphenylene
oxide)s were successfully synthesized through meta-activated
nucleophilic nitro displacement reaction [47].
* Corresponding author. Tel.: þ82 42 879 8448; fax: þ82 42 879 8594.
** Corresponding author. Tel.: þ82 42 350 2834; fax: þ82 42 350 2810.
E-mail addresses: cis123@kribb.re.kr (I.S. Chung), kimsy@kaist.ac.kr (S.Y. Kim).
In this study, new poly(arylene ether)s with pendent tri-
fluoromethyl groups were prepared from 2,20-bis(trifluoromethyl)-
0032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.08.003

4478
I.S. Chung et al. / Polymer 51 (2010) 4477e4483
4,40-dinitro-1,10-biphenyl through meta-activated nucleophilic
nitro displacement reaction, and their properties were investigated.
CF3
CH3
O2N
NO2
HO
C CH3
CH3
+
2. Experimental section
2 eq.
F3C
1
2.1. Materials
1) K2CO3, NMP/toluene
140 oC, 4 h
5-Bromo-2-nitrobenzotrifluoride (Marshallton) was used as
received. 4-tert-Butylphenol was sublimed at 90 ꢀC in vacuum.
2,2-Bis(40-hydroxyphenyl)propane (Bisphenol A, Aldrich) was
recrystallized from toluene, 2,2-bis(40-hydroxyphenyl)hexa-
fluoropropane (Bisphenol AF, Aldrich) was recrystallized from
toluene/ethyl acetate (v/v ¼ 95/5), and 4,40-biphenol (Aldrich) was
2) 175 oC, 4 h
CF3
CH3
H3C C
CH3
CH3
C CH3
CH3
O
O
recrystallized from ethanol/water (v/v
¼
60/40). Potassium
carbonate (K2CO3) was dried in vacuo at 150 ꢀC for 24 h prior to use.
N-Methyl pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), and
N,N-dimethyl formamide (DMF) were stirred in the presence of
P2O5 overnight and then distilled under reduced pressure. Toluene
was stirred in the presence of CaH2 overnight and then distilled
under nitrogen. Other commercially available reagent grade
chemicals were used without further purification.
F3C
2
Scheme 1. Model reaction.
from benzene/diethyl ether (v/v ¼ 1/2), and then sublimed at
120 ꢀC in vacuo to give pale yellow solid (52.3 g, 0.138 mol, 74.6%
yield).: m.p. 140e141 ꢀC (lit [48]. m.p. 138e140 ꢀC). IR (KBr, cmꢁ1):
3071 (aromatic CeH); 1593 (aromatic C]C); 1529, 1351 (NO2);
1190e1120 (CeF). 1H NMR (DMSO-d6, 400 MHz, ppm): 8.61 (dd, 2H,
J ¼ 8.32 Hz, J ¼ 2.32 Hz), 8.59 (d, 2H, J ¼ 2.18 Hz), 7.81 (d, 2H,
J ¼ 8.35 Hz). 13C NMR (DMSO-d6, 100 MHz, ppm): 147.90, 140.90,
133.30, 128.54 (q, J ¼ 32.1 Hz), 126.67, 122.44 (q, J ¼ 273.6 Hz),
121.37 (q, J ¼ 5.82 Hz). HRMS (m/e): calc. for C14H6N2O4F6,
328.0232; found, 380.0257.
2.2. General measurements
Fourier-transform infrared (FTIR) spectra of the compounds
were obtained with a Bruker EQUINOX-55 Spectrophotometer
using a KBr pellet or film. Nuclear magnetic resonance (NMR)
spectra of synthesized compounds were recorded on Bruker Four-
ier Transform AVANCE400 spectrometers (400 MHz for 1H and
100 MHz for 13C). Chemical shift of NMR was reported in part per
million (ppm) using tetramethylsilane as an internal reference.
Splitting patterns designated as s (singlet), d (doublet), t (triplet), q
(quartet), dd (doublets of doublet), m (multiplet), and br (broaden).
High-resolution mass spectra (HRMS) of the synthesized
compounds were obtained with a Jeol JMS-SX-102 mass spec-
trometer. Intrinsic viscosity data were obtained in N,N-dimethyla-
cetamide (DMAc) with a Canon-Ubbelohde type viscometer at
30 ꢀC. Size exclusion chromatography (SEC) diagrams were
obtained with Senshu SSC-7100 equipped with RI detector and high
temperature packing column (SUS-316) using o-dichlorobenzene
as an eluent at 85 ꢀC. Number and weight average molecular weight
of the polymers were calculated on the basis of polystyrene stan-
dards. Thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC) and were performed on a TA 2200 thermal
analyzer system. Melting points (m.p.) of the synthesized
compounds and Tgs of the polymers were obtained with DSC
instrument at a heating rate of 10 ꢀC/min in N2. TGA measurements
were conducted at a heating rate of 10 ꢀC/min in N2 and air. The
refractive indices of the synthesized polymers were measured with
a Metricon 2010 prism coupler. The light source was a HeeNe laser
of 632.8 nm wavelength, i.e., 474.08 THz frequency. The refractive
index (n) of films was measured in transverse electric (TE) and
transverse magnetic (TM) modes by choosing the appropriate
polarization of the incident laser beam, giving the in-plane
refractive index (nTE ¼ nxy) and the out-of-plane refractive index
(nTM ¼ nz), respectively.
2.4. Model reaction of 1 with 4-tert-butylphenol (2)
A 25 mL three-necked flask equipped with an argon inlet,
DeaneStark trap, and condenser was charged with 1 (0.7212 g,
1.897 mmol), 4-tert-butylphenol (0.5700 g, 3.794 mmol), K2CO3
(0.7865 g, 5.691 mmol), 6 mL of NMP, and 5 mL of toluene. The
reaction mixture was heated to 140 ꢀC for 4 h at which the toluene
was brought to reflux. The toluene was periodically removed from
the DeaneStark trap, and fresh dry toluene was added to the
reaction mixture to ensure dehydration of the system. The
temperature was raised to 175 ꢀC and the reaction mixture was
stirred for 4 h. The product was precipitated into water and then
filtered. Further purification was carried out by short-path silica gel
column chromatography using ethyl acetate/n-hexane (v/v ¼ 1/2)
as an eluent to give colorless 2 (1.062 g, 1.810 mmol, 95.4% yield):
F3C
-O
X
+
F3C
O
-
X
2.3. 2,20-Bis(trifluoromethyl)-4,40-dinitro-1,10-biphenyl (1)
F3C
X-
O
+
Activated copper (94.0 g, 1.48 mol) was added to a solution of
2-bromo-5-nitrobenzotrifluoride (100 g, 0.37 mol) in 200 mL of
DMF. The reaction mixture was stirred mechanically at 150 ꢀC for
6 h, then cooled and poured into vigorously stirred water. The
yellow precipitate was filtered, washed with water and 1N HCl
solution, and dried in vacuo. The crude product was recrystallized
A
B
C
D
X = F, NO2
X
F
NO2
F
NO2
Link meta meta ortho ortho
Scheme 2. 4 Sets of the reaction for quantum mechanical calculation.

I.S. Chung et al. / Polymer 51 (2010) 4477e4483
4479
Table 1
CF3
Reaction energy in gas phase (values in kcal/mol).a
O2N
NO2
HO
X
OH
No.
A
B
C
D
+
HF/6-31G*
45.4(13.1)
37.1(13.4)
38.0(14.2)
39.6(38.2)
ꢁ13.6(9.8)
ꢁ11.4(9.7)
ꢁ9.72(11.7)
ꢁ9.73(34.2)
43.6
34.9
35.9
37.5
ꢁ26.6
ꢁ26.1
ꢁ24.4
ꢁ25.0
F3C
HF/6-311G*//HF/6-31G*
HF/6-311G(2d)//HF/6-31G*
HF/6-311G(2df)//HF/6-31G*
1) K2CO3, NMP/toluene
140 oC, 4 h
a
2) 175 oC, 14 h
The values in parenthesis are the energy difference of reactants and
intermediate.
CF3
F3C
FTIR (KBr, cmꢁ1): 3092, 2887 (aromatic and aliphatic CeH); 1590,
1478 (aromatic C]C); 1251 (CeOeC); 1170e1110 (CeF). 1H NMR
(CDCl3, 400 MHz, ppm): 7.42 (d, 2H, J ¼ 2.62 Hz), 7.25 (d, 2H,
J ¼ 8.32 Hz), 7.13 (d, 2H, J ¼ 8.47 Hz); 7.44 (d, 4H, J ¼ 7.57 Hz), 7.04
(d, 4H, J ¼ 7.51 Hz); 1.37 (s, 18H). 13C NMR (CDCl3, 100 MHz, ppm):
157.63, 153.32, 147.31, 133.36, 130.87, 130.40 (q, J ¼ 32.7 Hz), 126.23,
123.42 (q, J ¼ 273.0 Hz), 119.52, 119.10, 115.63 (q, J ¼ 5.41 Hz); 34.33,
31.37. HRMS (m/e): calc. for C34H32O2F6, 586.2306; found, 586.2321.
O
X
O
n
X = C(CH3)2 (P1), C(CF3)2 (P2), nil (P3)
Scheme 3. Polymerization.
2.7. Poly(arylene ether) from 1 and 4,40-biphenol (P3)
2.5. Poly(arylene ether) from 1 and Bisphenol A (P1)
The same procedure used for P1 was repeated with 1.393 g
(3.644 mmol) of 1, 0.6823 g (3.664 mmol) of 4,40-biphenol, 1.519 g
(10.99 mmol) of K2CO3, 8 mL of NMP (1.796 g, 97.2% yield).: FTIR
(Thin film, cmꢁ1): 3011 (aromatic CeH); 1591, 1492 (aromatic C]
C); 1251 (CeOeC); 1170e1100 (CeF). 1H NMR (DMSO-d6, 400 MHz,
100 ꢀC, ppm): 7.74 (d, 4H, J ¼ 7.76 Hz), 7.22 (d, 4H, J ¼ 7.94 Hz); 7.48
(s, 2H), 7.40 (d, 4H, J ¼ 8.21 Hz), 7.34 (d, 4H, J ¼ 8.17 Hz). 13C NMR
(DMSO-d6, 100 MHz, 100 ꢀC, ppm): 157.34, 154.84, 135.72, 133.97,
130.79, 128.96 (q, J ¼ 30.1 Hz), 128.22, 123.33 (q, J ¼ 272.5 Hz),
120.51, 120.04, 115.38 (br).
A 25 mL three-necked flask equipped with an argon inlet,
mechanical stirrer, DeaneStark trap, and condenser was charged
with 1.212 g (3.188 mmol) of 1, 0.7278 g (3.188 mmol) of Bisphenol
A, 1.322 g (9.565 mmol) of K2CO3, 8 mL of NMP, and 5 mL of toluene.
The reaction mixture was heated to 140 ꢀC for 4 h at which the
toluene was brought to reflux. The toluene was periodically
removed from the DeaneStark trap, and fresh dry toluene was
added to the reaction mixture to ensure dehydration of the system.
The temperature was raised to 175 ꢀC and the reaction mixture was
stirred for 14 h. The polymer was precipitated into a 400 mL of
vigorously stirred methanol/water (v/v ¼ 1/1) mixture and then
filtered. The precipitated polymer was washed with hot water and
methanol repeatedly, and dried in vacuo at 100 ꢀC for 24 h (1.682 g,
96.6% yield). Further purification was carried out by dissolving the
polymers in N,N-dimethylacetamide, filtering the polymer solution,
and then precipitating it into methanol.: FTIR (Thin film, cmꢁ1):
3070e2880 (aromatic and aliphatic CeH); 1592,1491 (aromatic C]
C); 1248 (CeOeC); 1170e1100 (CeF). 1H NMR (DMSO-d6, 400 MHz,
100 ꢀC, ppm): 7.45e7.32 (br, 8H), 7.30 (br, 2H), 7.05e7.03 (br, 4H);
1.71 (s, 6H). 13C NMR (DMSO-d6, 100 MHz, 100 ꢀC, ppm): 157.26,
153.01, 146.43, 133.86, 130.47, 129.14 (q, J ¼ 30.2 Hz), 128.34, 123.24
(q, J ¼ 271.8 Hz), 120.11, 119.06, 115.16 (br); 41.83, 30.43.
3. Results and discussion
3.1. Model reaction
The
monomer,
2,20-bis(trifluoromethyl)-4,40-dinitro-1,10-
biphenyl (1), was synthesized by the Ullmann reaction of 5-bromo-
2-nitrobenzotrifluoride with copper in DMF [48]. The crude
product was recrystallized from benzene/diethyl ether. In order to
study the reactivity of the monomer, model reaction was conducted
with 1 and 4-tert-butylphenol (Scheme 1). 1 and two equivalents of
4-tert-butylphenol were reacted in the presence of K2CO3 as a base
in NMP as a solvent at 20 w/v % of solid content. Toluene as an
azeotrope was used during the initial stage of polymerization to
remove water by the phenoxide generation. During the initial stage
of model reaction, the reaction temperature was maintained at
140 ꢀC, and the water generated by deprotonation of the 4-tert-
butylphenol was removed through DeaneStark trap. The reaction
mixture was heated to 175 ꢀC to complete the displacement
2.6. Poly(arylene ether) from 1 and bisphenol AF (P2)
The same procedure used for P1 was repeated with 1.012 g
(2.662 mmol) of 1, 0.8950 g (2.662 mmol) of Bisphenol AF, 1.1048 g
(7.988 mmol) of K2CO3, 8 mL of NMP (1.701 g, 97.7% yield).: FTIR
(Thin film, cmꢁ1): 3031 (aromatic CeH); 1592, 1468 (aromatic C]
C); 1250 (CeOeC); 118e1090 (CeF). 1H NMR (DMSO-d6, 400 MHz,
100 ꢀC, ppm): 7.49 (br, 8H), 7.40 (br, 2H), 7.20 (br, 4H). 13C NMR
(DMSO-d6, 100 MHz, 100 ꢀC, ppm): 158.20, 155.80, 134.00, 131.79,
131.76, 130.93, 129.57 (q, J ¼ 30.2 Hz), 123.22 (q, J ¼ 271.8 Hz),
122.166, 118.55, 116.67 (br); 123.90 (q, J ¼ 282.4 Hz), 63.40 (m).
Table 3
Physical properties of the synthesized polymers.
a
d
e
Polymer
[
h]
Mnb/103
Mwb/103
PDIc
Td5 (ꢀC)
Tg (ꢀC)
(dL/g)
In N2
In Air
P1
P2
P3
0.63
0.42
0.60
33.7
14.3
30.8
95.0
42.1
81.6
2.82
2.95
2.65
493
481
502
451
428
463
176
181
199
Table 2
Reaction energy using SCRF calculation (values in kcal/mol).
a
Intrinsic viscosity, measured at a concentration of 0.5 g/dL in DMAc at 30 ꢀC.
No.
A
B
C
D
b
Determined by GPC using o-dichlorobenzene as eluent at 85 ꢀC with polystyrene
HF/6-31G*
4.27
ꢁ10.2
ꢁ10.8
ꢁ6.24
ꢁ12.8
1.14
ꢁ9.67
ꢁ5.13
ꢁ23.3
ꢁ25.9
ꢁ21.2
ꢁ29.5
standards.
HF/6-311G*//HF/6-31G*
HF/6-311G(2d)//HF/6-31G*
HF/6-311G(2df)//HF/6-31G*
ꢁ6.57
ꢁ2.05
ꢁ6.62
c
Polydispersity Index ¼ Mw/Mn.
d
e
5% weight loss temperature measured by TGA with a heating rate of 10 ꢀC/min.
Measured by DSC with a heating rate of 10 ꢀC/min.
ꢁ11.1

4480
I.S. Chung et al. / Polymer 51 (2010) 4477e4483
reactivity of the compound
1 compared to 4-nitro-2-tri-
fluoromethylbiphenyl is caused by the strong electron withdrawing
character of the nitro leaving group and trifluoromethyl group
attached to the other aromatic ring of the biphenyl structure.
3.2. Quantum mechanical calculation
In order to understand the unusual reaction behavior of a nitro
leaving group, quantum mechanical calculation for the energy state
of 4 sets of the reaction (Scheme 2) in gas and solution phase was
carried out at Hartree-Fock level using the HF/6-31G(d) and 3 more
models as a basis set and initial molecular geometries optimized in
vacuo with GAUSSIAN98 program. SCRF (Self Consistent Reaction
Field) calculations for solution phase were also performed by the
PCM (Polarizable Continuum Model) [49]. The solvent was NMP at
298 K (dielectric constant
3
¼ 32.2). The results of calculations in gas
and solution phase are summarized in Tables 1 and 2, respectively.
In the case of meta-activated aryl moiety A and B, the energy
differences of reactants and intermediate in gas phase were
calculated, but the calculation for C and D which contain ortho
activated aryl moieties were unsuccessful due to the difficulty of
obtaining optimized molecular geometry of the intermediate.
A showed higher energy difference (3e4 kcal/mol) between the
reactant and the intermediate than B, which implies that the nitro
leaving group is more susceptible to the displacement reaction than
the fluorine when they are activated by trifluoromethyl group at
meta position. However, the energy differences between the reac-
tant and the product in gas phase were not reasonable because of
the uncertainty caused by the fluoride anions in the products.
SCRF calculations were also carried out by following the PCM/DIR
procedure using NMP (dielectric constant
3
¼ 32.2) as a solvent. In
Fig. 1. FTIR spectra of monomer 1, model compound 2, and polymer P1.
the case of D known as the most reactive one, the products are more
stable (over 20 kcal/mol) than the reactants, but in the case of A, the
products and the reactants had similar energy state, indicating that
A procedure is not energetically favorable. In the case of B, the
products are more stable (c.a. 10 kcal/mol) than the reactants. The
calculated energy values of B and C shows that the reaction of B is
slightly more favorable than that of C which is also known to occur
rapidly [21e26]. These calculation results suggest that B procedure,
nitro displacement reaction activated by the trifluoromethyl group
at meta position, is an energetically favorable process.
reaction. Conversion was complete within 4 h at 175 ꢀC, and the
isolation yield was 95%. The spectroscopic analyses of the model
compound 2 showed the successful formation of the ether linkages
without any degradation of trifluoromethyl groups. In our previous
report [47], the model meta-activated SNAr reaction, which is the
reaction of 4-nitro-2-trifluoromethylbiphenyl with 4-tert-butyl-
phenol, is complete at 175 ꢀC for 12 h. It seems that the higher
1
Fig. 2. H NMR Spectra of polymer P1 (DMSO-d6, 400 MHz, 100 ꢀC, ppm).

I.S. Chung et al. / Polymer 51 (2010) 4477e4483
4481
13
Fig. 3. C NMR Spectra of polymer P1 (DMSO-d6, 100 MHz, 100 ꢀC, ppm).
3.3. Synthesis of poly(arylene ether)s
spectrum of monomer 1 show the absorption bands at 1529 and
1351 cmꢁ1 corresponding to nitro (eNO2) stretching, the FTIR
spectra of model compound 2 and the corresponding polymers
show the absorption band around 1250 cmꢁ1 corresponding to aryl
ether (PheOePh) stretching generated in the polymer-forming
reaction without any trace of nitro stretching. 1H and 13C NMR
spectra show all expected proton and carbon peaks, respectively,
without any signals corresponding to the nitro and hydroxyl end
groups. Representative 1H and 13C NMR spectra with the corre-
sponding assignment of P1 are shown in Figs. 2 and 3, respectively.
Based on the successful result of the model reaction and the
quantum mechanical calculation, we carried out the polymeriza-
tion at 175 ꢀC. Dinitro monomer 1 was polymerized with Bisphenol
A, Bisphenol AF, and 4,40-Biphenol according to the conventional
poly(arylene ether) synthesis, with K2CO3 as a base in NMP, to make
P1, P2, and P3, respectively (Scheme 3). The solid content was
maintained over 20 w/v%, and toluene as an azeotrope was used
during the initial stage of polymerization to remove water by the
phenoxide generation. After bisphenoxide generation and dehy-
dration for 4 h, the polymerization mixtures were heated to 175 ꢀC,
and reacted for 14 h at this temperature. The pale yellow polymers
were precipitated in water/methanol (v/v ¼ 1/1) mixture.
3.4. Properties of the polymers
The synthesized polymers exhibit good solubility in common
organic solvents. The solubility of the synthesized poly(arylene
ether)s is summarized inTable 4. All of the synthesized polymers are
well dissolved inpolar aprotic solvents such as NMP, DMAc and DMF.
P1 and P2 are also soluble in dimethyl sulfoxide (DMSO), tetrahy-
drofuran (THF), chlorobenzene, and 1,1,2,2-tetrachloroethane at
room temperature. P3 shows lower solubility than P1 and P2
presumably due to its more rigid structure. It is soluble in DMSO,
o-dichlorobenzene, and 1,1,2,2-tetrachloroethane at elevate
temperature, and partially soluble in THF and chlorobenzene, but
insoluble in chloroform and toluene. However, all polymers are
insoluble in acetone, ethyl acetate, benzene, cyclohexane, and
methanol. Transparent, pale yellow, and flexible films are prepared
by solution casting from N,N-dimethylacetamide solutions of the
polymers.
The polymerization results are summarized in Table 3. The
intrinsic viscosity values of P1, P2, and P3 are 0.63, 0.42, and
0.60 dL/g, respectively. The SEC data for the polymers indicate
formation of high molecular weight polymers. Weight average
molecular weight and polydispersity of P1, P2, and P3 are 95000,
42100, and 82100 g/mol, and 2.82, 2.95, and 2.65, respectively. The
polydispersity values are within the expected range for condensa-
tion polymerization.
The structures of the polymers were confirmed by FTIR, 1H NMR,
and 13C NMR spectroscopy, which indicated the formation of ether
linkages without degradation of trifluoromethyl groups. All of the
FTIR spectra of dinitro monomer 1, model compound 2, and poly-
mers show the absorption bands at 1140e1060 cmꢁ1 correspond-
ing to trifluoromethyl (CeF) stretching (Fig. 1.). While the FTIR
Table 4
Solubility of the synthesized polymers.a
Polymer
NMP
DMAc
DMF
DMSO
THF
CHCl3
TCE
CB
ODCB
Toluene
P1
P2
P3
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þ
þþ
þþ
ꢂ
ꢂ
ꢂ
ꢁ
þþ
þþ
þ
þþ
þþ
ꢂ
þþ
þþ
þ
ꢂ
ꢂ
ꢁ
Abbreviations: NMP (N-methyl pyrrolidone), DMAc (N,N-dimethylacetamide), DMF (N,N-dimethyl formamide), DMSO (dimethyl sulfoxide), THF (tetrahydrofuran), CHCl3
(chloroform), TCE (1,1,2,2-tetrachloroehtane), CB (chlorobenzene), ODCB (o-dichlorobenzene).
a
þþ: Soluble at room temperature, þ: soluble on heating, ꢂ: partially soluble, ꢁ: insoluble.

4482
I.S. Chung et al. / Polymer 51 (2010) 4477e4483
4. Conclusions
The nitro leaving group activated by trifluoromethyl group at
P1
P2
P3
meta position undergoes SNAr reaction quantitatively. The
quantum mechanical calculation for the energy state suggests that
the nitro displacement reaction is an energetically favorable
process. High molecular weight poly(arylene ether)s were prepared
from
2,20-bis(trifluoromethyl)-4,40-dinitro-1,10-biphenyl
with
several bisphenols. The synthesized polymers were amorphous and
dissolved well in a wide range of organic solvents regardless of the
position of trifluoromethyl pendent groups. They showed good
thermal stability as well as low refractive index and birefringence.
0
100
200
Temperature (oC)
300
400
Acknowledgment
Fig. 4. DSC curves of the polymers (Heating rate: 10 ꢀC/min, in N2 flow).
This work was supported by the National Research Foundation
of Korea through NRL (R0A-2008-000-20121-0) and ERC (R11-
2007-050-04001-0), Nano/Bio Science and Technology Program
(2005-01321, MEST, Korea), and the KRIBB Research Initiative
Program.
Thermal properties of the poly(arylene ether)s were evaluated
by TGA and DSC, and the results are summarized in Table 3.
Thermal analyses show that the polymers have high thermal
stability. Dynamic TGA shows 5% weight loss occurred for P1, P2,
and P3 at 493, 481, and 502 ꢀC in nitrogen, and 451, 428, and 463 ꢀC
in air, respectively. None of the poly(arylene ether)s showed crys-
tallization or melt transition in DSC measurement. The Tgs of the
polymers depends on the structure of bisphenol comonomer unit
(Fig. 4.). The Tgs of P1, P2, and P3 are 176, 181, and 199 ꢀC, respec-
tively. The Tg of P3 approaches that of PPOÔ (Tg ¼ 210 ꢀC [50]) even
though they do not have any pendent group near the ether linkage.
P1 display a Tg comparable to that of the poly(arylene ether) made
from bisphenol A and 4,40-dibromobiphenyl by Ullmann conden-
sation (Tg ¼ 166 ꢀC [51], 175 ꢀC [52]). It seems that the presence of
two trifluoromethyl groups appears to have minimal effect on Tg in
this case. However, while the Tg of P3 are comparable to that of the
poly(arylene ether) made from 3,30-bis(trifluoromethyl)-4,40-dini-
trobiphenyl and 4,40-biphenol, P1 and P2 display about 10 ꢀC
higher Tgs than those of the poly(arylene ether) from 3,30-bis(tri-
fluoromethyl)-4,40-dinitrobiphenyl with bisphenol A or bisphenol
AF (Tg ¼ 167 ꢀC [27]).
References
[1] Cotter RJ. In: Cotter RJ, editor. Engineering plastics: a handbook of polyaryl
ethers. Amsterdam: Gordon and Breach Publishers; 1995. p. 1e52.
[2] Theil F. Angew Chem Int Ed 1999;38:2345e7.
[3] Kricheldorf HR. In: Kricheldorf HR, editor. Handbook of polymer synthesis.
New York: Marcel Dekker; 1992. p. 545e615.
[4] Mati S, Mandal B. Prog Polym Sci 1986;12:111e53.
[5] Chung IS, Eom HJ, Kim SY. Polym Bull 1998;41:631e7.
[6] Labadie JW, Hedrick JL, Ueda M. In: Labadie JW, Hedrick JL, editors. Step
growth polymers for high-performance materials, new synthetic method (ACS
symposium Series 624). Washington, D.C: ACS; 1996. p. 210e25.
[7] Bunnett JF, Zahler RE. Chem Rev 1951;49:273e412.
[8] Bartoli G, Todesco PE. Acc Chem Res 1977;10:125e32.
[9] Terrier F. Nucleophilic aromatic displacement: the influence of the nitro
group. New York: VCH Publishers; 1991 [chapter 1].
[10] Bartoli G, LaTrofa A, Naso F, Todesco PE.
J Chem Soc Perkin Trans I;
1972:2671e2.
[11] Kornblum N, Cheng L, Kerber RC, Kestner MM, Newton BN, Pinnick WP, et al.
J Org Chem 1976;41:1560e4.
[12] Idoux JP, Madenwald ML, Garcia BS, Chu DL, Gupton JT.
1985;50:1876e8.
J Org Chem
In-plane and outeof plane refractive indices (nxy and nz) of the
polymers were measured using a prism coupling waveguide tech-
nique with a laser beam having 632.8 nm wavelength (474.58 THz),
and the results are summarized in Table 5. All of the synthesized
polymers show refractive indices (nav) in the range of 1.592e1.624
[13] Tamai S, Yamaguchi K, Ohta M. Polymer 1996;37:3683e92.
[14] Eastmond GC, Paprotny J. J Mater Chem; 1997:1321e6.
[15] Hawker CJ, Chu F. Displacement of the fluorine-leaving groups activated by
ketone and sulfone group at the meta position was utilized in the synthesis of
hyperbranched polymers that does not require complete conversion.
Macromolecules 1996;29:4370e80.
[16] Himmelberg P, Fossum E.
J
Polym Sci Part
A
Polym Chem
with low birefringence (
a material at optical frequencies can be estimated from the
refractive index n according to Maxwell’s equation,
y n2. The
value at 1 MHz has been evaluated as
y 1.10 n2av, including an
additional contribution of approximately 10% from the infrared
absorption [53]. The values estimated from average refractive
D) below 0.006. A dielectric constant (3) of
2005;43:3178e87.
[17] Beek Dv, Fossum E. Recently, displacement of the fluorine-leaving
groups activated by ketone and sulfone group at the meta position was
utilized in the synthesis of linear polymers. Macromolecules
2009;42:4016e22.
[18] Kaiti S, Himmelberg P, Williams J, Abdellatif M, Fossum E. Macromolecules
2006;39:7909e14.
3
3
3
3
[19] Labadie JW, Hedrick JL. Macromolecules 1990;23:5371e3.
[20] Kim SY, Labadie JW. Polym Prepr (Am Chem Soc Div Polym Chem) 1991;32
(1):164e5.
[21] Banerjee S, Maier G, Burger M. Macromolecules 1999;32:4279e89.
[22] Banerjee S, Maier G. Chem Mater 1999;11:2179e84.
[23] Maier G. Prog Polym Sci 2001;26:3e65.
[24] Lee MS, Kim SY. Macromol Rapid Commun 2005;26:52e6.
[25] Banerjee S, Komber H, Häussler L, Voit B. Macromol Chem Phys
2009;210:1272e82.
[26] Ghosh A, Banerjee S, Komber H, Lederer A, Häussler L, Voit B. Macromolecules
2010;43:2846e54.
indices of the resulting polymer films were in the range of
2.81e2.90. The low dielectric constants may be attributed to the
existence of the trifluoromethyl groups in the main chain.
Table 5
Refractive indices of the synthesized polymers.a
b
c
d
Polymer
nxy
nz
nav
De
3f
dg
(mm)
P1
P2
P3
1.6210
1.6030
1.6238
1.6184
1.5917
1.6194
1.6201
1.5992
1.6223
0.0026
0.0059
0.0044
2.89
2.81
2.90
5.8
4.3
4.1
[27] Carter KR, Kim SY, Labadie JW. Polym Prepr (Am Chem Soc Div Polym Chem)
1993;34(1):415e6.
[28] Park SK, Kim SY. Macromolecules 1998;31:3385e7.
[29] Lee HS, Kim SY. Macromol Rapid Commun 2002;23:665e71.
[30] Kim YJ, Chung IS, Kim SY. Macromolecules 2003;36:3809e11.
[31] Lee MS, Kim SY. Macromolecules 2005;38:5844e5.
[32] Kim YJ, Kakimoto M, Kim SY. Macromolecules 2006;39:7190e2.
[33] Hougham G. In: Hougham G, Cassidy PE, Johns K, Davidson T, editors. Fluo-
ropolymers (Part 2). New York: Plenum Press; 1999. p. 233e76.
[34] Chung IS, Kim SY. Macromolecules 2000;33:3190e3.
a
Measured at 632.8 nm (474.58 THz).
nxy: In-plane refractive index.
nz: Out-of plane refractive index.
b
c
d
e
f
nav: Average refractive index (nav ¼ (2 nav þ nav)/3).
D
: Birefringence (
D
¼ nxy ꢁ nz).
Dielectric constant estimated from the refractive index:
Film thickness.
3
y 1.10 n2av
.
g

I.S. Chung et al. / Polymer 51 (2010) 4477e4483
4483
[35] Chung IS, Park CE, Ree M, Kim SY. Chem Mater 2001;13:801e2806.
[44] Takekoshi T. Polym J 1987;19:191e202.
[36] Liu B, Hu W, Matsumoto T, Jiang Z, Ando S. J Polym Sci Part A Polym Chem
2005;43:30183029.
[45] In IS, Eom HJ, Kim SY. Polymer (Korea) 1998;22:544e52.
[46] In I, Kim SY. Polymer 2006;47:4549e65.
[37] Choi H, Chung IS, Hong K, Park CE, Kim SY. Polymer 2008;49:2644e9.
[38] Kim YJ, Seo M, Kim SY. J Polym Sci Part A Polym Chem 2010;48:1049e57.
[39] Chung IS, Kim SY. Macromolecules 2000;33:9474e6.
[40] Williams FJ, Donahue PE. J Org Chem 1977;42:3414e9.
[47] Chung IS, Kim SY. J Am Chem Soc 2001;123:11071e2.
[48] Rogers HG, Gaudiana RA, Hollinsed WC, Kalyanaraman PS, Manello JS,
McGowan C, et al. Macromolecules 1985;18:1058e68.
[49] Cossi M, Barone V, Cammi R, Tomasi J. Chem Phys Lett 1996;255:327e35.
[50] Hay AS. J Polym Sci Part A Polym Chem 1998;36:505e17.
[51] Jurek M, McGrath JE. Polym Prepr (Am Chem Soc Div Polym Chem) 1987;28
(1):180e1.
[52] Farnham AG, Johnson RN. US Patent 3,332,909; 1990.
[53] Doses D, Lee H, Yoon DY, Swallen JD, Rabolt JF. J Polym Sci Part B Polym Phys
1992;30:1321e7.
[41] Markezich RL, Zamek OS, Donahue PE, Williams FJ.
J Org Chem
1977;42:3435e6.
[42] Takekoshi T, Wirth JG, Heath DR, Kochanowski JE, Manello JS, Webber MJ. J
Polym Sci Part A Polym Chem 1980;18:3069e80.
[43] White DM, Takekoshi T, Williams FJ, Relles HM, Donahue PE, Klopfer HJ,
et al. J Polym Sci Part A Polym Chem 1981;19:1635e58.