Oxidative Polymerization of 2,6-Dimethylphenol to Form Poly(2,6-dimethyl-1,4-phenyleneoxide) in Water

Article abstract of DOI:10.1002/anie.200352764

Green polymerization: The simple stirring of 2,6-dimethylphenol with an excess of oxidant or a catalytic amount of a copper complex in an alkaline aqueous solution yields poly (2,6-dimethyl-1,4-phenyleneoxide), a commercially important polymer (see scheme). The formed polymer was easily separated as an off-white powder by filtration.

Full text of DOI:10.1002/anie.200352764

Communications
Polymerization
Oxidative Polymerization of 2,6-Dimethylphenol
To Form Poly(2,6-dimethyl-1,4-phenyleneoxide)
in Water**
Kei Saito, Takahiro Tago, Toru Masuyama, and
Hiroyuki Nishide*
One of the critical factors in realizing a green chemical
reaction process involves the choice of water as the reaction
[
1]
solvent, particularly for polymer production on a large scale.
The oxidative polymerization of 2,6-dimethylphenol (1;
[
2]
DMP), reported in 1959 by A. S. Hay and his GE group,
provides a convenient and industrial method to prepare
poly(2,6-dimethyl-1,4-phenyleneoxide) (2; PPO), an impor-
tant plastic in engineering. This polymerization proceeds at
room temperature and is an ideal atom-economical reaction
that does not require any leaving groups (Scheme 1). How-
ever, the polymerization is carried out in organic solvents
such as toluene and benzene under oxygen. Therefore, both a
solvent-recovery process and an antiexplosive reactor are
needed for the industrial production. Herein we report the
first oxidative polymerization of DMP to form PPO in water
as a green chemical process.
Although the preparation of PPO has been studied in
[
3–5]
detail,
the polymerization solvent, except for a few studies in
there has been no report in which water was used as
[
6,7]
aqueous–organic biphasic solvents.
The oxidation of
DMP in water is well-known to give predominantly DPQ
(
3), which is formed by the CÀC coupling of two monomeric
[6,8]
phenols (Scheme 1).
There is another unsolved problem
associated with polymerization in water: The dimer of DMP is
insoluble, even in an alkaline aqueous solution, and the
molecular weight of the formed PPO remains very low. We
have now succeeded in oxidatively polymerizing DMP to
form high-molecular-weight PPO in water. DMP was vigo-
rously stirred in an alkaline aqueous solution with an oxidant
in air. In this reaction, the DMP monomer was insoluble in
water but it dissolved in water when an equimolar amount of
[
9]
base (NaOH) was added. The formed dimer and the
following oligomers and polymers were insoluble in the
alkaline aqueous solution, and the reaction mixture became
heterogeneous immediately after the addition of the oxidant
(see a photograph of the polymerization in water in the
Supporting Information). The precipitated product could be
[
*] K. Saito, T. Tago, T. Masuyama, Prof. Dr. H. Nishide
Department of Applied Chemistry, Waseda University
Tokyo 169-8555 (Japan)
Fax: (+813)3209-5522
E-mail: nishide@waseda.jp
[
**] This work was partially supported by Grants-in-Aid for Scientific
Research (No. 13450384) and for the 21COE Research “Practical
Nano-Chemistry” from MEXT, Japan. We thank Dr. Kenichi Oyaizu
for productive discussions.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
730
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DOI: 10.1002/anie.200352764
Angew. Chem. Int. Ed. 2004, 43, 730 –733

Angewandte
Chemie
presence of a copper catalyst (e.g. [Cu-
tmeda)]; Table 1, entry 7) and oxygen or an
(
excess of a metal oxide (e.g., MnO ; Table 1,
2
entry 8) without the formation of DPQ in
the same alkaline medium at 508C. The
former catalytic reaction could be improved
by tuning the conditions.
Phenol derivatives such as 2,6-diphenyl-
phenol were also polymerizable in the basic
solution to form the corresponding PPO
derivatives such as poly(2,6-diphenyl-1,4-
Scheme 1. Oxidative polymerization of 2,6-dimethylphenol in water.
phenyleneoxide) (Table 1, entry 9).
separated as an off-white powder from the reaction mixture
by simple filtration after the polymerization, and the recov-
ered alkaline aqueous solution could be used repeatedly for
One of the reasons for using alkaline water as the solvent
is a significant decrease in the oxidation potential of phenols.
The pH value of the aqueous phase of the reaction mixture
was 13.5 ([NaOH] = 0.5m). Cyclic voltammograms in the
alkaline aqueous solution (Figure 1, inset) showed irreversi-
ble oxidation peaks of the phenol groups of DMP and 4-(2,6-
dimethylphenoxy)-2,6-dimethylphenol (dimer), and their
oxidative potentials were estimated to be 0.26 and 0.12 V
1
the polymerization. The product was identified as PPO by H-
1
3
,
C NMR, and IR spectroscopy. The 10%-thermal-degrada-
tion temperature (Td10%) and glass-transition temperature
[
10]
(
T ) were determined to be 4018C and 2088C, respectively,
g
by TG and DSC and were found to be comparable with those
[
11]
of the commercial values.
Some examples of the polymerization are given in Table 1.
The control reaction (Table 1, entry 1) showed that the
oxidation of DMP did not proceed without the addition of
base. Another control reaction (Table 1, entry 2) revealed
that the oxidation of DMP with an equal amount of base and
potassium ferricyanide in water predominantly gave DPQ
and a small amount of the phenyleneoxide oligomer (M =
n
2
[6,8]
4
.0 ” 10 , M /M = 1.5) as previously reported.
We found
w
n
that the oxidation of DMP resulted in polymerization at an
optimal temperature of 508C in the presence of excess base
[
12]
(
relative to the monomer) (Table 1, entry 5); significantly,
[
13]
DPQ formation was suppressed to less than 0.4%.
The
addition of a surfactant as an emulsifier was effective: High-
4
molecular-weight PPO (M > 10 ) was obtained almost quan-
n
titatively (98%) by the addition of sodium n-dodecyl sulfate
(
Table 1, entry 6). Upon addition of the surfactant, the
reaction mixture became a latex, but the polymer could also
be separated by a simple filtration after being salted out.
The use of potassium ferricyanide as an oxidant is not
adequate from the point of view of a green process. However,
DMP was also oxidatively polymerized to give PPO in the
Figure 1. Radical concentration determined by SQUID. Inset: Cyclic
voltammograms a) DMP in water with sodium hydroxide (0.5m),
b) dimer of DMP in water with sodium hydroxide (0.5m), and c) DMP
in CH Cl with pyridine (3.0m). Phenol concentration: 0.01m; scan
2
2
À1
rate: 25 mVs
.
[
a]
Table 1: Oxidative polymerization of 2,6-dimethylphenol in water.
Entry
ArOH
Oxidant or catalyst
[mmol]
NaOH
[mmol]
SDS
[mmol]
T
[8C]
Yield [%]
PPO
[
b]
[c]
[d]
3
[e]
n
[
mmol]
DPQ
PPO
M [/10 ]
M /M
w
n
1
2
3
4
5
6
7
8
9
50
50
50
1.0
1.0
1.0
50
1.0
0.5
K [Fe(CN) ]
100
100
100
0
50
250
50
50
50
50
50
50
0
0
0
0
RT
RT
RT
RT
50
50
50
50
70
0.1
74
66
24
0.4
0.4
0.2
0
0
23
32
74
76
98
67
24
96
3
6
K [Fe(CN) ]
0.4
1.6
3.9
3.5
13
2.9
5.0
6.9
1.5
1.6
2.3
2.0
1.8
1.7
4.0
1.8
3
6
K [Fe(CN) ]
3
6
K [Fe(CN) ]
2.0
3
6
[
g]
K [Fe(CN) ]
2.0
2.0
5.0
10
1.0
0
3
6
K [Fe(CN) ]
0.1
5.0
0
3
6
[
f]
[Cu(tmeda)]Cl2
MnO2
K [Fe(CN) ]
0.5
0.9
3
6
[
a] All the polymerizations were carried out in water (100 mL) under air (except entry 7, which was carried out under oxygen), 6 h. [b] DMP, except
entry 9, which was studied with 2,6-diphenylphenol. [c] Sodium n-dodecyl sulfate. [d] Determined by UV/Vis absorption at lmax =421 nm.
e] Determined by gel-permeation chromatography relative to polystyrene standards in chloroform. [f] tmeda=N,N,N’,N’-tetramethylethylenedi-
amine. [g] The molecular weight was determined to be 3.4”10 by NMR spectroscopic analysis (terminal phenolic group content).
[
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Communications
À1
À1
(
vs. SCE), respectively. The former value is much lower than
determined to be 54000m cm in toluene using pure DPQ. The
amount of formed DPQ is given as a percentage of the feed amount of
DMP.
that of DMP (1.31 V) in a basic organic solvent such as
dichloromethane involving pyridine as the base. The oxida-
tive potential for the dimer was lower than that of the DMP
monomer, suggesting that the oxidation potential of the
terminal phenolic group becomes lower as the polymerization
progresses.
The ESR spectrum of the polymerization mixture was
recorded: The signal at g = 2.0044 was ascribed to the organic
phenoxyl radical. After filtering the powder product from the
mixture and quickly washing with alkaline water, it was
transferred to the capsule of a SQUID magnetometer to
SQUID magnetic measurement: The magnetization and static
magnetic susceptibility were measured with a Quantum Design
MPMS-7 SQUID magnetometer. Powder samples for the measure-
ment were prepared as follows: The polymerizations of DMP with
potassium ferricyanide were carried out as described above for 0.05,
0.5, 1, 3, and 6 h. After these reaction times, the powder product was
filtered, quickly washed with alkaline water, and transferred to the
capsule of the SQUID magnetometer. The magnetization was
measured from 0.5 to 7 T at 1.8, 2, 2.5, 3, 5, 20, and 200 K. The
static magnetic susceptibility was measured from 1.8 to 200 K in a
field of 0.5 T.
[
14]
determine the radical concentration of the powder product.
The radical concentration in the polymerization reaction
Figure 1) was maintained at approximately 20% per poly-
Received: September 2, 2003 [Z52764]
(
[
15]
mer molecule or per polymer terminal phenolic group. The
polymerization mechanism of DMP in the water is described
below.
DMP is dissolved in the basic aqueous phase to form the
phenolate anion, and is oxidized to the phenoxyl radical. The
CÀO coupling of two phenoxyl radicals gives the dimer. The
Keywords: green chemistry · oxidation · polymerization ·
radicals · water chemistry
.
[1] a) C.-J. Li, T.-H. Chan, Organic Reactions in Aqueous Media,
Wiley, New York, 1997; b) P. Tundo, P. Anastas, D. S. Black, J.
Breen, T. Collins, S. Memoli, J. Miyamoto, M. Polyakoff, W.
Tumas, Pure Appl.Chem. 2000, 72, 1207 – 1228; c) J. M. Desi-
mone, Science 2002, 297, 799 – 803.
2] a) A. S. Hay, H. S. Blanchard, G. F. Endres, J. W. Eustance, J.
Am. Chem. Soc. 1959, 81,6335 – 6336; b) A. S. Hay, J.Polym . Sci.
1962, 58, 581 – 591; c) A. S. Hay, Macromolecules 1969, 2, 107 –
formed dimer and oligomer are insoluble in the alkaline
aqueous solution, and the reaction mixture becomes hetero-
geneous. However, the terminal phenolic groups located at
the water interface are oxidized to give the polymeric
phenoxyl radicals, which are redistributed to the high-
molecular-weight polymer in the solid that precipitates from
the water.
In summary, we have described the polymerization of
DMP to form PPO in water. The oxidative polymerization of
phenols in alkaline water has the potential to become a
convenient green polymerization procedure.
[
1
08; d) A. S. Hay, J. Polym. Sci. Part A 1998, 36, 505 – 517.
3] a) E. Tsuchida, M. Kaneko, H. Nishide, Makromol. Chem. 1972,
[
1
1
51, 221 – 234; b) E. Tsuchida, H. Nishide, Makromol. Chem.
975, 176, 1349 – 1358; c) E. Tsuchida, H. Nishide, Adv.Polym.
Sci. 1977, 24,1 – 87; d) K. Oyaizu, Y. Kumaki, K. Saito, E.
Tuschida, Macromolecules 2000, 33, 5766 – 5769.
[4] D. Aycock, V. Abolins, D. M. White, Encyclopedia of Polymer
Science and Engineering, Vol.13 , 2nd ed., Wiley, New York,
1986, pp. 1 – 30.
[
5] a) W. Koch, W. Risse, W. Heitz, Makromol.Chem.Suppl. 1985,
12, 105 – 123; b) E. Tuschida, F. Suzuki, E. Shouji, K. Yamamoto,
Macromolecules 1994, 27, 1057 – 1060; c) P. J. Baesjou, W. L.
Driessen, G. Challa, J. Reedijk, J. Am. Chem. Soc. 1997, 119,
12590 – 12594; d) H. A. M. van Aert, M. H. P. van Gendersen,
G. J. M. L. van Steenpaal, L. Nelissen, E. W. Meijer, Macro-
molecules 1997, 30, 6056 – 6066; e) H. Higashimura, K. Fujisawa,
Y. Moro-oka, M. Kubota, A. Shiga, A. Terahara, H. Uyama, S.
Kobayashi, J. Am. Chem. Soc. 1998, 120, 8529 – 8530.
Experimental Section
Oxidative polymerization DMP in water with K [Fe(CN) ] (Table 1,
3
6
entry 6): DMP (0.122 g, 1 mmol) was dissolved in water (100 mL)
containing sodium hydroxide (2.00 g, 50 mmol) and sodium n-dodecyl
sulfate (29 mg, 0.1 mmol). Potassium ferricyanide (0.658 g, 2 mmol)
was added to the solution, and the mixture was vigorously stirred
(3000 rpm) under air at 508C for 6 h. The polymer was obtained as an
off-white powder (98%) by filtration after salting out by the addition
of sodium chloride (5.84 g, 0.25 mol) and by washing with water.
[6] a) G. D. Staffin, C. C. Price, J. Am. Chem. Soc. 1960, 82, 3632 –
3634; b) C. C. Price, N. S. Chu, J. Polym. Sci. 1962, 61, 135 – 141.
[7] a) H. Komoto, K. Ohmura, Makromol. Chem. 1973, 166, 57 – 68;
b) V. Percec, T. D. Shaffer, J. Polym. Sci. Polym. Lett. Ed. 1986,
24, 439 – 446; c) K. Mühlbach, V. Percec, J. Polym. Sci. Polym.
Chem. Ed. 1987, 25, 2605 – 2627; d) R. Ikeda, J. Sugihara, H.
Uyama, S. Kobayashi, Macromolecules 1996, 29, 8702 – 8705;
e) H. Yonami, H. Uyama, S. Kobayashi, J.Macromol.Sci ., Pure
Appl.Chem. 1999, 36, 719 – 730; f) Y. M. Chung, W. S. Ahn, P. K.
Lim, J. Mol. Catal. A 1999, 148, 117 – 126.
1
H NMR: (500 MHz, CDCl , TMS): d = 6.44 (2H, s; HAr), 2.09 ppm
3
1
3
(
1
s, 6H; CH ); C NMR: (125 MHz, CDCl , TMS): d = 16.8, 114.5,
3
3
À1
32.5, 145.4, 154.7 ppm; IR (KBr): n˜ C-O-C = 1186 cm . The reactions
described in Table 1, entries 1–5, 8, and 9 were carried out analo-
gously.
Oxidative polymerization of DMP in water with [Cu(tmeda)]
(
(
Table 1, entry 7): A solution [Cu(tmeda)] (0.250 g, 5 mmol) in water
10 mL) was added to a solution of DMP (6.10 g, 50 mmol), sodium
hydroxide (2.00 g, 50 mmol), and sodium n-dodecyl sulfate (1.45 g,
mmol) in water (90 mL). The mixture was then vigorously stirred
3000 rpm) in oxygen at 508C for 6 h. After salting out with sodium
5
(
[8] C. G. Haynes, A. H. Turner, W. A. Waters, J. Chem. Soc. 1956,
2823 – 2831.
À1
chloride (29.2 g, 1 mol), the product was obtained by filtration. The
reprecipitation from chloroform to methanol gave an off-white
[9] The solubility of DMP in aqueous NaOH (0.5m) is < 61 gL
.
[10] Td10% and T were for the polymer described in Table 1, entry 6.
g
1
13
polymer (67%). The H, C NMR, and IR spectra were similar to
those described above.
[11] F. E. Karasz, H. E. Bair, J. M. O'Reilly, J.Polym.Sci.Part A-2
1968, 6, 1141 – 1148.
UV/Vis spectral detection of DPQ: A sample of the filtered
product (1.2 mg) was removed and dissolved in toluene (10 mL). This
solution gave a UV/Vis absorption with the maximum at 421 nm,
which was ascribed to DPQ. The molar extinction coefficient e was
[12] The formation of DPQ in water was hardly affected by
temperature, in contrast to the case in organic solvents. G. F.
Endres, A. S. Hay, J. W. Eustance, J. Org. Chem. 1963, 28, 1300 –
1305.
732
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Angew. Chem. Int. Ed. 2004, 43, 730 –733

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[
13] The yield of DPQ was determined by the UV/Vis absorption at
lmax = 421 nm. The formation of DPQ was suppressed dramat-
ically. By comparison, conventional polymerization methods
(
e.g., catalyzed by a copper–amine complex in toluene at room
temperature) give DPQ in 3–5% yield. a) F. J. Viersen, G.
Challa, Recl. Trav. Chim. Pays-Bas 1990, 109, 97 – 102; b) F. J.
Viersen, J. Renkema, G. Challa, J. Reedijk, J.Polym.Sci.Part A
1992, 30, 901 – 911.
[
[
14] Normalized plots of magnetization versus the ratio of the
magnetic field and effective temperature for the powder product
1
obeyed a theoretical curve corresponding to the S = = Brillouin
2
function (S = spin quantum number). This showed no contribu-
tion of the contaminants such as the potassium ferricyanide
oxidant to the measurement of the radical concentration.
15] The half-life of the phenoxyl radical was determined to be
approximately 4 min by ESR spectroscopic analysis of the
powder sample.
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