Novel fluorinated poly(aryl ether)s derived from 1,2-bis(4-(4-fluorobenzoyl)phenoxy)-hexafluorocyclobutane

Article abstract of DOI:10.1016/j.jfluchem.2008.03.006

Two novel poly(aryl ether)s were prepared from 1,2-bis(4-(4-fluorobenzoyl)-phenoxy)-hexafluorocyclobutane and aromatic bisphenols by the aromatic nucleophilic substitution reaction in a polar aprotic solvent. These polymers have good thermal stability up to 341 °C with 10% weight loss in inert atmosphere and good solubility in common organic solvents such as THF, DMAc, DMF and DMSO.

Full text of DOI:10.1016/j.jfluchem.2008.03.006

Journal of Fluorine Chemistry 129 (2008) 498–502
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Novel fluorinated poly(aryl ether)s derived from
1,2-bis(4-(4-fluorobenzoyl)phenoxy)-hexafluorocyclobutane
You Zhou a, Feng-Ling Qing a,b,
*
a College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, 2999 North Renmin Lu, Shanghai 201620, China
b Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Two novel poly(aryl ether)s were prepared from 1,2-bis(4-(4-fluorobenzoyl)-phenoxy)-hexafluorocy-
clobutane and aromatic bisphenols by the aromatic nucleophilic substitution reaction in a polar aprotic
solvent. These polymers have good thermal stability up to 341 8C with 10% weight loss in inert
atmosphere and good solubility in common organic solvents such as THF, DMAc, DMF and DMSO.
ß 2008 Elsevier B.V. All rights reserved.
Received 10 January 2008
Received in revised form 12 March 2008
Accepted 12 March 2008
Available online 22 March 2008
Keywords:
Perfluorocyclobutane
Fluorinated poly(aryl ether)s
Soluble polymers
Thermally stable polymers
1. Introduction
Therefore, a novel aromatic monomer containing a perfluor-
ocyclobutane group, 1,2-bis(4-(4-fluorobenzoyl)phenoxy)-hexa-
Poly(aryl ether)s are a class of high performance materials
known for their excellent combination of chemical, physical and
mechanical properties. This class of advanced material is currently
receiving considerable attention for potential application in the
aerospace, optics, electronics and other high technology fields.
However, it is difficult for conventional poly(aryl ether)s to be used
as thin films and coating materials because of their poor solubility.
In addition, their poor solubility makes the polymerization
condition difficult. Therefore, a great deal of effort has been
focused on the preparation of soluble poly(aryl ether)s [1–4].
Fluorinated poly(aryl ether)s, specially perfluorocyclobutane
(PFCB)-containing poly(aryl ether)s have been explored [5–7] for
a variety of applications, such as high performance structure
coating, interlayer dielectrics, circuit board laminas, dielectric
wave guides and optical cladding layer [8], because the PFCB
aromatic ether polymers, combining the stability of fluorocarbon
segments and the engineering thermoplastic nature of polyaryl
ethers, exhibit good solubility, excellent processability and optical
transparency, high temperature performance and low dielectric
constants [9–11].
fluorocyclobutane 6, was designed and synthesized in our
laboratory, and two novel fluorinated poly(aryl ether)s were
prepared by polycondensation of 6 with aromatic diphenols. The
solubility of the resulting poly(aryl ether)s in several common
organic solvents was tested. The polycondensation process,
corresponding composition and structure, as well as physical
and thermal properties of the polymers were investigated.
2. Experimental
2.1. Materials
Ether (Et2O) was freshly distilled under nitrogen over sodium.
Acetonitrile (MeCN), DMAc and fluorobenzene were distilled over
CaH2. DMF was stirred over MgSO4 overnight at room temperature,
and then vacuum distilled. Zinc granular was treated with 5%
aqueous hydrochloric acid for several minutes, and then washed
with water, ethanol and ether successively, and dried in vacuum.
4,40-Dihydroxybenzophenone (DHBP) was recrystallized from
acetone. Resorcinol was sublimed before use. Other reagent and
materials were used as received.
2.2. Analysis
* Corresponding author at: Key Laboratory of Organofluorine Chemistry,
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin
Lu, Shanghai 200032, China. Tel.: +86 21 54925187; fax: +86 21 64166128.
E-mail address: flq@mail.sioc.ac.cn (F.-L. Qing).
1H NMR (400 MHz), 19F NMR (376 MHz) and 13C NMR (162 MHz)
spectra were recorded on a Bruker AM 400 spectrometer system.
0022-1139/$ – see front matter ß 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2008.03.006

Y. Zhou, F.-L. Qing / Journal of Fluorine Chemistry 129 (2008) 498–502
499
Chloroform-d and dimethyl sulphoxide-d6 were used as the solvent
and chemical shifts reported were internally referenced to Me4Si
(0 ppm) and CFCl3 (0 ppm) for 1H and 19F nuclei, respectively.
Infrared spectra were obtained on Thermo Electron Corporation
Nicolet380FT-IRspectrophotometer. MSspectrawererecordedona
Finnigan MAT-8430 instrument with electron-impact ionization at
70 eV. Relative molecular weights and molecular weight distribu-
tions were measured by gel permeation chromatography (GPC)
system equipped with a Waters 1515 Isocratic HPLC pump, a Waters
2414 refractive index detector (RI), a Waters 2487 dual-wavelength
absorbance detector and a set of Waters Styragel columns(HR3, HR4
and HR5, 7.8 mm ꢀ 300 mm). GPC measurements were carried out
at 35 8C using DMF as eluent with a 1.0 ml/minflow rate. The system
was calibrated with polystyrene standards. Dynamic thermo-
gravimetric analysis (TGA) was performed on NetZSch (German)
TGA 209 F1 system on powder samples at a heating rate of 10 8C/min
in N2. The wide-angle X-ray diffraction (WXRD) was conducted on a
mixture was then warmed to 90 8C to remove excess thionyl
chloride. After removal of the trace quantities of thionyl chloride in
vacuum, compound 5 was obtained and used directly for the next
step without further purification. Fluorobenzene (20 ml) was then
added to dissolve the mixture of compound 5 and anhydrous
aluminium trichloride (2.39 g and 17.88 mmol). The reaction
mixture was stirred at 90 8C for 12 h. Water was added to quench
the reaction and then ether was added. The organic layers were
washed with water, dried and concentrated in vacuo. The residue
was purified by column chromatography on silica gel (petroleum
ether:ethyl acetate = 85:15) to afford 1.06 g (42%) of compound 6
as a white solid. 1H NMR (CDCl3, 400 MHz, ppm):
J = 8.8 Hz, 4H), 7.37 (d, J = 8.8 Hz, 4H), 7.72–7.76 (m, 4H), 7.83 (d,
d 7.30 (t,
J = 8.8 Hz, 4H). 19F NMR (CDCl3, 376 MHz, ppm):
d
ꢁ121.1, ꢁ120.5,
ꢁ115.8, ꢁ115.2 and ꢁ105.6. 13C NMR (DMSO, 100 MHz, ppm):
d
118.4, 118.6, 120.5, 135.0, 135.3, 135.4, 136.2, 136.6, 157.2, 166.3,
168.8 and 195.8. IR (KBr, cmꢁ1):
n 3080, 1662, 1600, 1505, 1417,
Rigaku D/max-2500 X-ray diffractometer with Cu Ka1 radiation,
1377, 1279, 1232, 1156, 1041, 1001, 929, 854, 764, 678 and 596.
operated at 40 kV and 300 mA. The solubility was determined by
immersing 0.1 g polymer in various solvents (1.0 g) at 25 8C with
magnetic stirring.
MS(EI): m/z 554, 459, 312, 199, 188, 123 and 95.
2.4. Polymerization
A typical example for polymer P1 is given as follows [13]. To a
100 ml three-neck round-bottom flask equipped with a stirrer, a
Dean–Stark trap and condenser, and a nitrogen inlet were added
compound 6 (0.592 g and 1.0 mmol) and 4,40-dihydroxybenzophe-
none (0.214 g and 1.0 mmol). Then DMAc (15 ml), toluene (12 ml)
and potassium carbonate (0.290 g, 2.1 mmol) were charged to the
reaction flask. Under an atmosphere of nitrogen, the solution was
heated to reflux (140 8C) to dehydrate the system. The reaction
mixturewaskept refluxinguntilthe presenceofwater wasnolonger
observed in the Dean–Stark trap. This usually took between 6 and
8 h. Upon dehydration, the polymerization was carried out at 180 8C
for approximately 12 h, and the reaction was terminated about the
point where the viscosity increased dramatically. When the reaction
mixture became too viscous, DMAc (2–3 ml) was added. The
reaction mixture was diluted with about an equimolar volume of
DMAc and filtered to remove the inorganic salts. The polymer
solution was then coagulated in approximately 10ꢀ volume of a 4/1
(v/v) mixture of methanol/water, washed with methanol, water,
then dried in a vacuum oven for 24 h. Polymer P2 was obtained in a
similar way as to polymer P1.
2.3. Synthesis and characterization of the fluorinated monomer
2.3.1. Synthesis of 1,2-bis(4-bromophenoxy)-perfluorocyclobutane 2
Compound 2 was prepared using published procedures [5–7].
1H NMR (CDCl3, 400 MHz, ppm):
d
7.44–7.50 (m, 4H), 7.05 (d,
J = 8.4 Hz, 2H), 7.00 (d, J = 8.8 Hz, 2H). 19F NMR (CDCl3, 376 MHz,
ppm):
d
ꢁ126.7, ꢁ128.0, ꢁ128.6, ꢁ129.5, ꢁ130.1, ꢁ130.2, ꢁ130.8,
ꢁ131.3 and ꢁ131.4.
2.3.2. Synthesis of 1,2-bis(4-formylphenoxy)-hexafluorocyclobutane
3
Compound 3 was prepared using published procedures [12]. 1H
NMR (CDCl3, 400 MHz, ppm):
d 7.16 (d, J = 8.8 Hz, 2H), 7.28 (d,
J = 7.6 Hz, 2H), 7.82–7.86 (m, 4H), 9.89 (s, 1H), 9.91 (s, 1H). 19F NMR
(CDCl3, 376 MHz, ppm): ꢁ132.1, ꢁ131.7, ꢁ130.2, ꢁ129.6, ꢁ128.9,
ꢁ128.3, ꢁ127.7, ꢁ127.56 and ꢁ126.9.
2.3.3. Synthesis of 4,4’-((1,2,3,3,4,4-hexafluorocyclobutane-1,2-
diyl)bis(oxy))-dibenzoic acid 4
To a 250 ml three-neck round-bottom flask equipped with a
P1: 72.3% yield; 1H NMR (CDCl3, 400 MHz, ppm):
d 7.75 (m,
thermometer,
a sealed mechanical stirrer, and a pressure-
12H), 7.15 (m, 12H). 19F NMR (CDCl3, 376 MHz, ppm):
d
ꢁ105,
equalizing dropping funnel were charged a mixture of compound
3 (2.870 g and 7.10 mmol), pyridine (60 ml) and a solution of
sodium carbonate (0.318 g and 3.00 mmol) in water (20 ml). The
reaction mixture was cooled to 5 8C, and a solution of KMnO4
(2.467 g and 15.62 mmol) in water (60 ml) was added dropwise.
After complete addition the reaction was maintained at 5 8C with
vigorous stirring for 4 h. Then the mixture was stirred at 40 8C for
12 h. The precipitated MnO2 was filtered off and the filtrate was
concentrated to about 50 ml under reduced pressure. The solution
was acidified with dilute hydrochloric acid, and the product was
filtered and washed with water and dried to afford 2.860 g (92%) of
ꢁ110, ꢁ115, ꢁ117, ꢁ120 and ꢁ121. IR (KBr, cmꢁ1): 3060, 1653,
1590, 1497, 1241, 928, 857, 766, 677 and 502.
P2: 83% yield; 1H NMR (CDCl3, 400 MHz, ppm):
d 7.75 (m, 8H),
7.41 (s, 1H), 7.15 (m, 8H), 6.96 (m, 3H). 19F NMR (CDCl3, 376 MHz,
ppm):
d
ꢁ105, ꢁ110, ꢁ115, ꢁ117, ꢁ120 and ꢁ121. IR (KBr, cmꢁ1):
3066, 1597, 1480, 1227, 929, 855, 767, 680 and 593.
3. Results and discussion
3.1. Synthesis and characterization of 1,2-bis(4-(4-
4 as a white solid. 1H NMR (DMSO, 400 MHz, ppm):
J = 8.4 Hz, 2H), 7.38 (d, J = 8.0 Hz, 2H), 8.01–8.06 (m, 4H), 13.10 (s,
1H), 13.16 (s, 1H). 19F NMR (DMSO, 376 MHz, ppm):
d 7.30 (d,
fluorobenzoyl)phenoxy)-hexafluorocyclobutane 6
d
ꢁ130.9,
The synthesis of compound 6 was outlined in Scheme 1.
Compound 2 was prepared from 4-bromophenol using published
procedures [5–7]. Treatment of 3 with t-BuLi followed by addition
of DMF gave known aldehyde 3 [12]. Oxidation of 3 with KMnO4 in
water and pyridine gave 4 in quantitative yield. Then, 4,40-
((1,2,3,3,4,4-hexafluorocyclobutane-1,2-diyl)bis(oxy))-dibenzoic
acid 4 was converted into corresponding chloride 5 with thionyl
chloride. As compound 5 is readily hydrolyzed to acid in air, it was
prepared and immediately used without further isolation and
ꢁ130.3, ꢁ130.1, ꢁ129.7, ꢁ129.6, ꢁ128.9, ꢁ128.0, ꢁ127.4 and
ꢁ126.9.
2.3.4. Synthesis of 1,2-bis(4-(4-fluorobenzoyl)phenoxy)-
hexafluorocyclobutane 6
In a flame dried three-neck round-bottom flask compound 4
(1.95 g and 4.47 mmol) and thionyl chloride (20 ml) were charged.
The reaction mixture was stirred at 75 8C for 3 h. The reaction

500
Y. Zhou, F.-L. Qing / Journal of Fluorine Chemistry 129 (2008) 498–502
Scheme 1. Synthesis of 1,2-bis(4-(4-fluorobenzoyl)phenoxy)-hexafluorocyclobutane 6.
purification [14]. The next step involved a Friedel–Crafts acylation
reaction between 5 and fluorobenzene. Typically, anhydrous
aluminium trichloride (4.0 equiv.) was used as a catalyst and
fluorobenzene (10.0 equiv.) was used as a reactant and solvent. The
crude product was purified by flash column chromatography, and
then recrystallized twice to afford polymer grade monomer 6 in
42% yield. It is noteworthy that hexafluorocyclobutyl fluorine
signals in 19F NMR (between ꢁ115 and ꢁ121 ppm) of compound 6
appear downfield than that of compounds 2, 3 and 4 (between
ꢁ126 and ꢁ132 ppm). This result showed that 4-fluorobenzyl
group has more electron-withdrawing character than that of
bromo and formyl groups.
as shown in Scheme 2. The reaction temperature was maintained
at 140 8C and water (formed during phenoxide formation) was
removed by azeotropic distillation with toluene. The reaction was
allowed to continue at this temperature for 6–8 h with vigorous
stirring. Upon completion of bisphenoxides formation and
dehydration (6–8 h), the reaction temperature was raised to
180 8C to effect the nucleophilic displacement. High molar mass
polymers were obtained within 12 h as judged by the dramatic
increase of the viscosity of the reaction medium. At completion of
the reaction, the hot reaction mixture was poured into a mixture of
methanol and water. The polymer that coagulated was filtered and
washed with methanol, and then washed several times with hot
water to remove any inorganic impurities, dried in a vacuum at
110 8C for 24 h.
3.2. Synthesis of poly(aryl ether)s
The molecular weights of the fluorinated poly(aryl ether)s
determined by GPC in DMF using polystyrene as standard are in the
range of 10253–13494 for Mn and of 11277–14519 for Mw with
the Mw/Mn values of 1.08–1.10 (Table 1). This indicated that the
The polymerization of the aromatic difluoride 6 with aromatic
bisphenols (resorcinol and DHBP) was carried out in DMAc/toluene
solvent mixture in the presence of anhydrous potassium carbonate
Scheme 2. Synthesis of fluorinated poly(aryl ether)s.

Y. Zhou, F.-L. Qing / Journal of Fluorine Chemistry 129 (2008) 498–502
501
Table 1
Table 2
GPC analysis of the fluorinated poly(aryl ether)s
Solubility of the fluorinated poly(aryl ether)sa
Polymer
Mn
Mw
Mw/Mn
Polymer DMF NMP DMAc DMSO CHCl3 THF 30% 30%
Conc.
HCl NaOH H2SO4
P1
P2
13,494
10,253
14,519
11,277
1.08
1.10
P1
P2
++
++
++
++
++
++
++
++
++
++
++
++
ꢁꢁ
ꢁꢁ
ꢁꢁ
ꢁꢁ
+ꢁ
+ꢁ
GPC in DMF vs. polystyrene at 35 8C.
a
++: Soluble at room temperature in 2 h; +ꢁ: soluble at room temperature in
12 h; ꢁꢁ: insoluble at refluxing.
diagnostic for the presence of hexafluorocyclobutyl group. This
easily resolved absorption has proven to be a useful analytical tool
since this region in the IR is rarely occupied by other functionalities
[3] (Fig. 1). In addition, the hexafluorocyclobutyl groups in polymer
P1 were characterized further by 19F NMR (Fig. 2), in which
fluorine signals of these groups were presents from ꢁ109 to
ꢁ121 ppm. The signals at ꢁ105 ppm could be attributable to the
terminal fluorine group of polymer. The 19F NMR chemical shifts of
polymer P1 was similar to that of monomer 6. As polymer P1 was
obtained by the coagulation from polymer solution followed by
wash with methanol, there was no unreacted monomer 6 in
polymer P1.
3.3. Solubility of poly(aryl ether)s
Table 2 shows the solubility of the fluorinated poly(aryl ether)s
determined quantitatively by dissolving 0.1 g of solid polymer in
1.0 g of organic solvents. It can be seen that the perfluorocyclo-
butyl-containing fluorinated poly(aryl ether)s possessed good
solubility in common organic solvents, such as NMP, DMAc, DMSO,
DMF, THF and chloroform. The good solubility could be resulted
from the presence of PFCB group and aryl ether linkages [15].
The WAXD patterns of the fluorinated poly(aryl ether)s are
shown in Fig. 3. They showed that both the polymers were
amorphous. No crystalline or semi-crystalline phase was detected.
This might be interpreted by the presence of perfluorocyclobutyl
groups, which decreased the intra- and inter-polymer chain
interactions, resulting in loose polymer chain packaging and
aggregates. The amorphous phase endows some special features to
poly(aryl ether)s, such as good solubility in solvents.
Fig. 1. FT-IR spectra of the fluorinated poly(aryl ether)s.
medium molecular weight polymers were formed. The Mn and Mw
of polymer P1-2 were not high, which might be due to the low
reactivity of the monomer 6. The chemical structures of poly(aryl
ether)s were characterized by FT-IR, 1H NMR, and 19F NMR. All of
the poly(aryl ether)s showed characteristic absorption bands at
1227–1241 cmꢁ1 and 1653–1655 cmꢁ1 due to aryl ether linkages
and C O, respectively, and a strong sharp band near 928 cmꢁ1 is
3.4. Thermal properties of poly(aryl ether)s
Thermal properties of the fluorinated polymers were evaluated
by means of thermo-gravimetric analysis (TGA). The results are
Fig. 2. 1H NMR (A) and 19F NMR (B) spectra of P1.
Fig. 3. Wide-angle X-ray diffraction patterns of the poly(aryl ether)s.

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Y. Zhou, F.-L. Qing / Journal of Fluorine Chemistry 129 (2008) 498–502
Table 3
Crafts acylation reaction between 5 and fluorobenzene. The
aromatic nucleophilic substitution reaction between 1,2-bis(4-
(4-fluorobenzoyl)phenoxy)-hexafluorocyclobutane and aromatic
bisphenols provides novel poly(aryl ether)s containing the PFCB
group. The aryl ether linkages and PFCB group serve to increase
the solubility of polymers. Meanwhile, the resulting polymers
possessed good thermal stability and reasonable molecular
weight.
Thermal properties of the fluorinated poly(aryl ether)s
Polymer
Tf (8C)a
Ts (8C)a
Rw (%)b
P1
P2
285
279
341
324
51.5
33.1
a
Measured at 10 8C/min in N2; Tf: 5% weight loss at the first stage; Ts: 10% weight
loss at the second stage.
b
Residual weight retention at 8008C.
Acknowledgments
We are grateful to National Natural Science Foundation of China
(NO. 20325210), the Ministry of Education of China and Shanghai
Municipal Scientific Committee for the financial support.
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A novel fluorinated monomer, 1,2-bis(4-(4-fluorobenzoyl)-
phenoxy)-hexafluorocyclobutane 6 was prepared by the Friedel–