Synthesis of novel aromatic ether polymers containing perfluorocyclobutyl and triazole units via click chemistry

Article abstract of DOI:10.1016/j.jfluchem.2008.04.012

The synthesis and characterization of a novel class of linear aromatic ether polymers containing perfluorocyclobutyl and triazole unites is described. These polymers were prepared from the click chemistry (the copper-catalyzed Huisgen's 1,3-dipolar cycloa

Full text of DOI:10.1016/j.jfluchem.2008.04.012

Journal of Fluorine Chemistry 129 (2008) 1003–1010
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Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis of novel aromatic ether polymers containing perfluorocyclobutyl
and triazole units via click chemistry
Rong-Xing Yao a,b, Lei Kong a,b, Zeng-Shen Yin a,b, Feng-Ling Qing a,c,
*
a College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, 2999 North Renmin Lu, Shanghai 201620, China
b State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University, 2999 North Renmin Lu, Shanghai 201620, China
c 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:
The synthesis and characterization of a novel class of linear aromatic ether polymers containing
perfluorocyclobutyl and triazole unites is described. These polymers were prepared from the click
chemistry (the copper-catalyzed Huisgen’s 1,3-dipolar cycloaddition) of new monomer 1,2-bis(4-
azidomethylphenoxy) perfluorocyclobutane and bisethynyl compounds.
Received 24 March 2008
Received in revised form 23 April 2008
Accepted 23 April 2008
Available online 4 May 2008
ß 2008 Elsevier B.V. All rights reserved.
Keywords:
Click chemistry
Perfluorocyclobutane (PFCB)
Fluorinated polymer
1. Introduction
needs high temperature (>150 8C) and long reaction time [4].
Recently, our group has applied click chemistry for the synthesis of
The Huisgen 1,3-dipolar cycloadditions of azides and terminal
alkynes were shown to be the most effective and versatile and thus
became the prime example of click chemistry that was introduced
by Sharpless and co-workers in 2001 [1]. Because of their high
selectivity, near-perfect reliability, high yields, and exceptional
tolerance towards a wide range of functional groups and reaction
conditions, click chemistry have recently attracted increased
attention in organic synthesis and, in particular, have gained
popularity in material synthesis. Click chemistry is widely used in
polymer synthesis as well as in the modification of surfaces
nanometer- and mesoscale structures [2]. Fluoropolymers keep
attractive in the development of advanced materials with high
thermal and oxidative stability, chemical resistance and superior
electrical insulating ability [3]. In recent years, partially fluorinated
polymers containing perfluorocyclobutane (PFCB) rings have been
developed [4]. PFCB aromatic ether polymers, combining the
engineering thermoplastic nature of polyaryl ethers and the
stability of fluorocarbon segments, exhibit excellent processability,
optical transparency, high temperature performance and low
dielectric constants. PFCB polymers are generally obtained by the
fluorinated polymer containing perfluorocyclobutane (PFCB) rings.
The Huisgen 1,3-dipolar cycloaddition of poly(ethylene glycol)
diazides and 1,2-bis(4-ethynylphenoxy)perfluorocyclobutane in
the presence of copper(I) at 80 8C provided alternating copolymers
in high yields (Scheme 1). These novel polymers showed good
thermal stability and solubility in common organic solvents [5].
Here we describe the synthesis of a novel class of linear aromatic
ether polymers containing perfluorocyclobutyl and triazole unites
from the click chemistry of 1,2-bis(4-azidomethylphenoxy) per-
fluorocyclobutane and bisethynyl compounds.
2. Experimental
2.1. Materials
THF was distilled under nitrogen over sodium. DMSO, acetoni-
trile, and acetone were dried over calcium hydride, and distillated
before use. Granular zincs were activated with 0.1 M hydrochloric
acid, washed with ethanol and ether, and dried at 120 8C under
vacuum for 4 h. Other reagents or materials were used as received.
thermal [2p + 2p] cyclopolymerization of aryl trifluorovinyl ethers
in bulk or solution. However, this polymerization process generally
2.2. Measurements
Melting point ranges were determined on a WRS-2A capillary
melting point apparatus (uncorrected). Elemental analysis was
carried out on a Carlo-Erba 1106 system. Infrared spectra were
* Corresponding author. Tel.: +86 21 54925187; fax: +86 21 64166128.
E-mail address: flq@mail.sioc.ac.cn (F.-L. Qing).
0022-1139/$ – see front matter ß 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2008.04.012

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R.-X. Yao et al. / Journal of Fluorine Chemistry 129 (2008) 1003–1010
Scheme 1.
obtained on Thermo Electron Corporation Nicolet 380 FT-IR
spectrophotometer. MS spectra were recorded on a Finnigan-
MAT-8430 instrument using EI ionization at 70 eV. 1H NMR
(400 MHz) and 13C NMR (100 MHz) were recorded on a Bruker
AM-400 spectrometer with Me4Si (1H NMR) and CDCl3 (13C NMR) as
internal standard. 19F NMR (376 MHz) was collected with CFCl3 as
external standard. Relativemolecularweights and molecular weight
distributions were measured by gel permeation chromatography
(GPC) system equipped with a Waters 1515 Isocratic HPLC pump, a
Waters 2414 refractive index (RI) detector, a Waters 2487 dual-
2.4. Synthesis of 1-methyl-4-trifluorovinyloxybenzene 2
To a 500 mL dry three-necked flask equipped with a magnetic
stirrer, a thermometer and a condenser under nitrogen was added
compound 1 (95.0 g, 0.33 mol) slowly over 1 h to a stirring mixture
of granular Zn (26.0 g, 0.40 mol) in acetonitrile (350 mL) at 80 8C.
The reaction mixture was refluxed for 12 h and then evaporated;
the crude product was extracted from the salts successively with
hexane, concentrated, and distilled to give 2 as a colorless liquid
(39.2 g, 63%): b.p. 31–32 8C (ca. 8 mmHg). 1H NMR (400 MHz,
wavelength
l
absorbance detector and a set of Waters Styragel
CDCl3)
s). 19F NMR (376 MHz, CDCl3)
film, cmÀ1):
3040, 2960, 2930, 2855, 1833, 1611, 1507, 1314,
d
: 7.16 (2H, d, J = 8.42 Hz), 6.99 (2H, d, J = 8.44 Hz), 2.33 (3H,
columns (HR3, HR4 and HR5, 7.8 mm  300 mm). GPC measure-
d
: À120.1, À127.1, À133.6. IR (thin
ments were carried out at 35 8C using DMF as eluent at a flow rate of
n
1.0
mL/min. The system was calibrated with polystyrene standards.
1284, 1278, 1195, 1168, 1140, 1017, 820, 739.
Differential scanning calorimetry (DSC)was conductedon a NetZSch
(German) DSC 204 F1 system under nitrogen calibrated with indium
and zinc standards. Initial sample weight was set as 1–2 mg for each
operation. The specimen was heated from 25 to 280 8C at a heating
rate of 10 8C/min. 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 under nitrogen atmosphere
from 25 to 700 8C. Wide-angle X-ray diffraction (WAXD) patterns
were obtained at room temperature on a Rigaku D/Max-2550
powder diffractometer with a scanning speed of 5 8/min, and the
2.5. Synthesis of 1,2-bis(4-methylphenoxy)perfluorocyclobutane 3
Compound 2 (38.0 g, 0.20 mol) was heated neat at 160 8C for
36 h in a 50 mL single-necked round-bottom flask under N2. The
product was purified by column chromatography on silica gel
(petroleum ether/ethyl acetate = 90/1) to give 3 as clear oil (34.5 g,
91%). 1H NMR (400 MHz, CDCl3)
19F NMR (376 MHz, CDCl3)
: À128.3, À128.8, À129.8, À130.3,
À130.4, À130.7, À131.1, À131.2. MS (EI): m/z 377, 376, 375, 269,
188, 168, 141, 108, 91, 77, 65. IR (thin film, cmÀ1):
3039, 2958,
d: 7.00–7.12 (8H, m), 2.31 (6H, s).
d
patterns were recorded in the 2
u
range of 5–608.
n
2928, 2867, 1611, 1596, 1508, 1455, 1402, 1382, 1319, 1285, 1266,
1197, 1170, 1116, 1019, 962, 899, 815, 754.
2.3. Synthesis of 1-(2-bromo-1,1,2,2-tetrafluoroethoxy)-4-
methylbenzene 1
2.6. Synthesis of 1,2-bis(4-
To a 500 mL three-necked flask equipped with a magnetic
stirrer, a nitrogen inlet, a condenser, and a Dean-Stark azeotropic
distillation assembly was added p-cresol (54.0 g, 0.50 mol),
potassium hydroxide (80%, 35.0 g, 0.50 mol), DMSO (250 mL)
and toluene (100 mL). The reaction mixture was refluxed for about
48 h until no water was existed in the separator. The solution was
cooled to room temperature, and 1, 2-dibromotetrafluoroethane
(156.0 g, 0.60 mol) was added dropwise under cooling by ice
water. The solution was stirred at 20 8C for 12 h and then for at
35 8C for 10 h. Then the reaction mixture was diluted with water
(800 mL) and extracted with dichloromethane. The organic phase
was washed three times with water, dried over MgSO4. The
solution was distilled under ambient pressure and then reduced
pressure to give 1 as a colorless liquid (100.8 g, 70%): b.p. 42–44 8C
bromomethylphenoxy)perfluorocyclobutane 4
A mixture of compound 3 (30.1 g, 0.08 mol), N-bromosuccini-
mide (NBS, 28.5 g, 0.16 mol) and dry CCl4 (350 mL) was stirred and
refluxed under the light of two ‘‘IR 275 W’’ lamps until the starting
material was complete transformed (ca. 1–3 h). The reaction
mixture was cooled to room temperature, succinimide was filtered
off and the solvent was removed on a rotary evaporator to give
crude product. The crude product was recrystallized from ethanol
to afford compound 4 as white solid (39.6 g, 93%): m.p. 98.4–
99.3 8C. 1H NMR (400 MHz, CDCl3)
(4H, dd, J = 8.0 Hz, 8.5 Hz), 4.45 (4H, s). 13C NMR (100 MHz, CDCl3)
: 34.6, 120.6, 120.9, 132.8, 132.9, 137.4, 154.5. 19F NMR (376 MHz,
d: 7.34–7.38 (4H, m), 7.04–7.15
d
CDCl3)
d
: À127.7, À127.9, À128.4, À128.6, À129.5, À130.1, À130.7,
(ca. 8 mmHg). 1H NMR (400 MHz, CDCl3)
d
: 7.17 (2H, d, J = 8.48 Hz),
À131.3, À131.6. IR (KBr, cmÀ1):
n 3042, 2970, 2927, 2856, 1608,
7.11 (2H, d, J = 8.56 Hz), 2.36 (3H, s). 19F NMR (376 MHz, CDCl3)
d
:
1508, 1322, 1288, 1265, 1198, 1177, 1117, 1018, 963, 833, 603. MS
À67.8, À85.9. IR (thin film, cmÀ1):
n
3040, 2959, 2929, 2854, 1597,
(EI): m/z 456, 455, 454, 453, 187, 106, 90, 89, 78. Anal. Calcd for
C18H12Br2F6O2: C, 40.48; H, 2.26. Found: C, 39.96; H, 2.25.
1508, 1328, 1220, 1196, 1164, 1127, 1101, 1020, 932, 844, 778.

R.-X. Yao et al. / Journal of Fluorine Chemistry 129 (2008) 1003–1010
1005
Scheme 2. Synthesis of 1,2-bis(4-methylazidophenoxy)perfluorocyclobutane 5.
2.7. Synthesis of 1,2-bis(4-
combined organic layer was washed with saturated brine solution
(80 mL), dried and concentrated in vacuo. The residue was purified
by column chromatography on silica gel using petroleum ether/
ethyl acetate (10: 1) as eluent to give compound 5 as colorless
azidomethylphenoxy)perfluorocyclobutane 5
To a 250 mL single-necked flask equipped with a reflux
condenser and a magnetic stirrer were added compound 4
(37.5 g, 0.07 mol) and NaN3 (9.1 g, 0.14 mol) in DMF (180 mL).
The reaction mixture was stirred at 90 8C for 24 h. After the
mixture was cooled to room temperature, the solution was
diluted with water and extracted with ether (3 mL Â 80 mL). The
liquid (21.5 g, 67%). 1H NMR (400 MHz, CDCl3)
m), 7.10–7.21 (4H, dd, J = 8.4 Hz, 8.5 Hz), 4.32 (4H, s). 13C NMR
(100 MHz, CDCl3) : 56.3, 120.7, 121.0, 132.0, 134.7, 135.1, 154.6.
19F NMR (376 MHz, CDCl3)
d: 7.28–7.31 (4H,
d
d
: À127.8, À128.2, À128.5, À128.8,
À129.5, À130.2, À130.8, À131.1, À131.5. IR (neat, cmÀ1):
n 3045,
2930, 2878, 2099, 1610, 1508, 1449, 1422, 1317, 1263, 1202, 1171,
1120, 1018, 962. MS (EI): m/z 401, 388, 106, 104, 89, 90, 91, 78, 77,
51. Anal. Calcd for C18H12F6N6O2: C, 47.17; H, 2.64; N, 18.34.
Found: C, 47.47; H, 2.69; N, 18.43.
2.8. Synthesis of bisethynyl compounds 6a–e
To a solution of the benzenediol (0.05 mol) in dry acetone
(120 mL) was added excess anhydrous K2CO3 (40.0 g) and the
reaction mixture was refluxed for 0.5 h. Then propargyl bromide
(13.1 g, 0.11 mol) was added dropwise over 2 h to the above
reaction mixture. The resulting mixture was refluxed for 20 h and
then cooled, filtered and the filtrate was evaporated. The residue
was dissolved in CH2Cl2 (150 mL) and the solution was washed
with water (3 mL Â 40 mL) followed by saturated brine solution
(40 mL). The organic layer was dried over anhydrous MgSO4 and
then concentrated in vacuo. The residue was purified by column
chromatography on silica gel using petroleum ether/ethyl acetate
(8: 1) as eluent to give 6a–e.
Compound 6a: colorless liquid (7.5 g, 81%). 1H NMR (400 MHz,
CDCl3)
(1H, t, J = 4.45 Hz), 4.65 (4H, d, J = 2.40 Hz), 2.50 (2H, t, J = 2.40 Hz).
IR (neat, cmÀ1):
3284, 3032, 2916, 2868, 2122, 1595, 1495, 1470,
d: 7.12 (1H, t, J = 7.25 Hz), 6.54 (2H, dd, J = 4.45 Hz), 6.49
n
1368, 1302, 1235, 1201, 1112, 1017, 935, 834, 695.
Compound 6b: white solid (7.9 g, 86%): m.p. 48.2–48.6 8C. 1H
NMR (400 MHz, CDCl3)
d
: 6.93 (4H, s), 4.65 (4H, d, J = 2.40 Hz), 2.51
3289, 3033, 2922, 2866, 2121,
(2H, t, J = 2.40 Hz). IR (KBr, cmÀ1):
n
1604, 1507, 1451, 1366, 1299, 1222, 1202, 1105, 1028, 923, 827.
Compound 6c: white solid (11.3 g, 73%): m.p. 80.0–80.5 8C. 1H
NMR (400 MHz, CDCl3)
d: 7.14 (4H, m), 6.86 (4H, m), 4.66 (4H, d,
J = 2.40 Hz), 2.51 (2H, t, J = 2.40 Hz), 1.64 (6H, s). IR (KBr, cmÀ1):
n
3285, 3035, 2967, 2870, 2116, 1604, 1508, 1454, 1364, 1297, 1264,
1221, 1182, 1028, 830.
Compound 6d: white solid (10.4 g, 72%): m.p. 90.5–90.8 8C. 1
NMR (400 MHz, CDCl3) d: 7.79 (4H, d, J = 7.12 Hz), 7.04 (4H, d,
H
Fig. 1. 1H NMR (a), 13C NMR (b) and 19F NMR (c) spectra of compound 5.

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R.-X. Yao et al. / Journal of Fluorine Chemistry 129 (2008) 1003–1010
Scheme 3. Synthesis of bisethynyl compounds 6a–f.
J = 7.12 Hz), 4.78 (4H, d, J = 2.40 Hz), 2.57 (2H, t, J = 2.40 Hz),. IR
(KBr, cmÀ1):
3289, 3065, 2923, 2868, 2123, 1647, 1598, 1506,
1452, 1417, 1373, 1309, 1232, 1166, 1020, 929, 845.
1508, 1461, 1432, 1382, 1320, 1304, 1263, 1201, 1171, 1113, 1047,
1013, 961, 823. Mn = 62230, Mw = 78715, PI = 1.26.
n
Compound 7c: 82%. 1H NMR (400 MHz, CDCl3)
d
: 8.30 (2H, s),
7.42 (4H, br), 7.27 (4H, br), 7.10 (4H, br), 6.92 (4H, br), 5.63 (4H, s),
5.10 (4H, s), 1.57 (6H, s). 13C NMR (100 MHz, CDCl3)
: 33.5, 44.1,
55.0, 64.0, 116.8, 120.8, 121.4, 127.9, 129.9, 130.5, 132.4, 136.4,
Compound 6e: pale white solid (12.3 g, 75%): m.p. 180.0–
181.3 8C. 1H NMR (400 MHz, CDCl3)
d
: 7.85 (4H, d, J = 7.12 Hz), 7.02
(4H, d, J = 7.12 Hz), 4.66 (4H, d, J = 2.40 Hz), 2.48 (2H, t, J = 2.40 Hz).
IR (KBr, cmÀ1):
3283, 3272, 3098, 2923, 2868, 2129, 1592, 1581,
d
n
145.6, 146.0, 154.4, 158.7. 19F NMR (376 MHz, CDCl3)
n 3137, 3070, 2938, 2876, 1595, 1508, 1491,
1459, 1384, 1321, 1305, 1263, 1199, 1177, 1150, 1119, 1047, 1018,
962, 819. Mn = 64656, Mw = 78604, PI = 1.22.
d
: À127 to
1492, 1457, 1417, 1386, 1311, 1297, 1242, 1143, 1107, 1072, 833.
2.9. Synthesis of 1,2-bis(4-ethynylphenoxy)-perfluorocyclobutane 6f
Compound of 6f was prepared according to the reference [5].
2.10. General procedure for polymerization
À132. IR (KBr, cmÀ1):
Compound 7d: 75%. 1H NMR (400 MHz, CDCl3)
d
: 8.35 (2H, s),
7.69 (4H, br), 7.40 (4H, br), 7.24 (4H, br), 7.17 (4H, br), 5.63 (4H, s),
5.24 (4H, s). 13C NMR (100 MHz, CDCl3)
: 54.9, 64.2, 117.3, 121.1,
d
121.6, 127.6, 129.9, 132.3, 134.5, 134.8, 136.4, 145.3, 154.2, 164.4,
195.0. 19F NMR (376 MHz, CDCl3)
n 3138, 3066, 2928, 2876, 1647, 1600, 1508, 1462, 1421, 1310,
d
: À127 to À132. IR (KBr, cmÀ1):
CuSO4Á5H2O (7 mg, 5 mol%) and sodium ascorbate (12 mg,
10 mol%) dissolved in H2O (10 mL) were added dropwise to a
solution of bisethynyl compound 6a–f (0.50 mmol) and 1,2-bis(4-
1251, 1204, 1169, 1116, 1048, 1013, 962, 928, 848, 770.
Mn = 53608, Mw = 64376, PI = 1.20.
azidomethylphenoxy)perfluorocyclobutane
5
(229 mg,
Compound 7e: 69%. 1H NMR (400 MHz, CDCl3)
d
: 8.30 (2H, s),
7.84 (4H, br), 7.46 (4H, br), 7.25–7.18 (8H, br), 5.61 (4H, s), 5.21
(4H, s). 13C NMR (100 MHz, CDCl3)
: 54.9, 64.4, 118.3, 121.1, 121.6,
0.50 mmol) in DMSO (15 mL). The reaction mixture was stirred
at 45 8C overnight. The solvent was decanted to leave a gum
residue in the flask. The residue was then stirred in H2O (20 mL)
and concentrated ammonia (5 mL) for another 1 h. The mixture
was filtered and the resulting filter cake was washed with H2O
(3 mL Â 20 mL). The filter cake was then dissolved in DMSO,
filtered again and precipitated into a 2:1 solution of water and
methanol. The solid was separated and washed repeatedly with
aqueous methanol before dried in a vacuum oven. The desired
polymers 7a–f were obtained as pale yellow solids, respectively.
d
127.6, 129.8, 132.1, 132.5, 136.4, 136.5, 145.0, 154.5, 164.8. 19F
NMR (376 MHz, CDCl3)
3070, 2958, 2870, 1593, 1509, 1495, 1464, 1318, 1292, 1258, 1203,
d
: À127 to À132. IR (KBr, cmÀ1):
n 3141,
Compound 7a: 75%. 1H NMR (400 MHz, CDCl3)
d: 8.32 (2H, s),
7.61–7.54 (4H, br), 7.38–7.27 (4H, br), 7.10–7.05 (1H, br), 6.84
(1H, br), 6.55 (2H, d), 5.76 (4H, s), 5.18 (4H, s). 13C NMR (100 MHz,
CDCl3) d: 55.0, 64.1, 104.4, 110.1, 120.6, 121.2, 127.4, 128.9, 131.9,
132.5, 136.4, 146.0, 154.5, 161.9. 19F NMR (376 MHz, CDCl3)
d:
À127 to À132. IR (KBr, cmÀ1):
n 3138, 3075, 2944, 2876, 1596,
1509, 1491, 1463, 1432, 1384, 1319, 1304, 1263, 1201, 1176, 1149,
1113, 1048, 1017, 958, 899, 820. Mn = 72102, Mw = 85290,
PI = 1.18.
Compound 7b: 78%. 1H NMR (400 MHz, CDCl3)
d
: 8.25 (2H, s),
7.37 (4H, br), 7.18 (4H, br), 6.92 (4H, br), 5.59 (4H, s), 5.03 (4H, s).
13C NMR (100 MHz, CDCl3)
: 54.9, 64.4, 118.4, 121.1, 121.6, 127.4,
d
129.7, 132.7, 136.5, 146.2, 154.0, 155.4. 19F NMR (376 MHz, CDCl3)
d
: À127 to À132. IR (KBr, cmÀ1):
n
3137, 3075, 2938, 2869, 1606,
Fig. 2. IR spectrum of monomer 6e.

R.-X. Yao et al. / Journal of Fluorine Chemistry 129 (2008) 1003–1010
1007
1177, 1151, 1107, 1049, 1017, 963, 834, 718. Mn = 51499, Mw =
61457, PI = 1.19.
potassium 4-methylphenolate with BrCF2CF2Br followed by
dehalogenation with zinc. Although a series of p-substituted
aromatic trifluorovinyl ethers were prepared [6], to the best of our
knowledge, there was no report about the synthesis of 1-methyl-4-
Compound7f: 67%. 1HNMR (400 MHz, CDCl3)
d
:8.64(2H, s), 7.91
(4H, br), 7.40 (4H, br), 7.27 (8H, br), 5.65 (4H, s). 13C NMR (100 MHz,
CDCl3) : 54.9, 121.1, 121.3, 121.5, 124.6, 129.8, 129.9, 132.7, 132.8,
d
trifluorovinyloxybenzene 2. The thermal [2p + 2p] cyclodimeriza-
136.4, 136.6, 148.3, 153,9, 154.0, 154.2. 19F NMR(376 MHz,CDCl3)
n 3137, 3046, 2946, 2928, 2847, 1614,
1560, 1510, 1496, 1459, 1320, 1266, 1201, 1169, 1117, 1045, 1017,
958, 839, 772. Mn = 29070, Mw = 35968, PI = 1.24.
d:
tion of 2 at 160 8C provided 1,2-bis(4-methylphenoxy)perfluor-
ocyclobutane 3 in 91% yield. The light-induced bromination of 3
with N-bromosuccinimide gave compound 4 in 93% yield [7].
Finally, treatment of 4 with NaN3 provided the desired compound
5 in 67% yield. There was a strong stretch vibration at 2100 cmÀ1 in
the IR spectrum of compound 5. The structure of 5 was further
confirmed by 1H NMR, 13C NMR and 19F NMR spectra (Fig. 1).
À127 to À132. IR (KBr, cmÀ1):
3. Results and discussion
3.1. Synthesis and characterization of 1,2-bis(4-
3.2. Synthesis of bisethynyl compounds 6a–f
azidomethylphenoxy)perfluorocyclo-butane 5
The monomers 6a–e were prepared from the phenols and
propargyl bromide in the presence of K2CO3 (Scheme 3). They were
The synthesis of compound 5 was outlined in Scheme 2.
Compound 2 was synthesized in high purity by treatment of
Scheme 4. Synthesis of polymers 7a–e via click chemistry.
Scheme 5. Synthesis of polymer 7f via click chemistry.

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R.-X. Yao et al. / Journal of Fluorine Chemistry 129 (2008) 1003–1010
characterized by FT-IR which showed the characteristic absorption
owing to –H bond of the propargyl groups near 3285 cmÀ1. The
absorption owing to the CBB C appeared as a weak band at about
2120 cmÀ1. The typical IR spectrum of 6e was shown in Fig. 2. The
monomer 6f was prepared from 4-bromophenol through five
steps and the detailed procedures were reported in our published
paper [5].
3.3. Synthesis and characterization of polymers 7a–f
The polymers containing perfluorocyclobutyl and triazole
unites 7a–f were obtained in 67–82% from the click reactions of
monomers 5 and 6a–f respectively (Schemes 4 and 5). Click
reactions were carried out in a 3:2 solvent ratio of DMSO to H2O
using 5 mol% CuSO4Á5H2O with 10 mol% sodium ascorbate as
the in situ reducing agent to generate the active Cu(I) species [8].
The reaction temperature played key role in the formation of
fluorinated polymers. It was found that the polymers with
reasonable molecular weight were obtained when the click
reactions were carried out at 45 8C.
A particularly useful method of characterization available for
PFCB polymers is FT-IR spectrum. A strong sharp band near
960 cmÀ1 is diagnostic for the presence of perfluorocyclobutyl
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. The monomers 5 and 6f and polymer 7f all
have PFCB groups which were confirmed in their IR spectra
(Fig. 3). The perfluorocyclobutyl groups in PFCB polymers were
characterized further by 19F NMR (Fig. 4), in which fluorine
signals of these groups were presented from À127 to À132 ppm.
The 1,2-disubstituted perfluorocyclobutyl group was further
identified in the 13C NMR spectrum of polymers 7a–f by the
presence of several separated multiplets near 121 ppm. These
unresolved cyclobutyl carbon signals showed that both cis and
trans geometric isomers were all coupled to each nonequivalent
fluorine atom attached to the cyclobutyl ring. The aromatic
carbons of polymers 7a–f adjacent (ipso) and ortho to the
perfluorocyclobutyl ether linkage did give separate signals
dictated by the 1,2-disubstituted cis/trans configuration of the
ring: the ipso carbon signals near 154.0 (presumably trans) and
154.2 ppm (cis) (Fig. 4c). The 1,2,3-triazole rings of the polymer
were characterized by signals near 8.3 ppm of the triazole
protons in the 1H NMR spectrum (Fig. 4a), and signals at 148.3
Fig. 4. 1H NMR (a), 19F NMR (b) and 13C NMR (c) spectra of polymer 7f.
and 124.6 ppm of triazole carbons in the 13C NMR spectrum
(Fig. 4c). The triazole ring was confirmed further by the presence
of C–H of 1,2,3-triazole ring stretch vibration near 3135 cmÀ1 in
the FT-IR spectrum (Fig. 3).
Table 1
Solubility of PFCB polymers
Polymers Acetone THF CHCl3 Conc. H2SO4 NMP DMAc DMSO DMF
a
Æ
Æ
Æ
–
Æ
Æ
Æ
–
Æ
Æ
Æ
–
Æ
Æ
Æ
Æ
Æ
Æ
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
7b
7c
7d
7e
7f
–
–
–
Æ
+
–
Fig. 3. IR spectra of monomers 5, 6f and polymer 7f.
Note: (+) Soluble; (Æ) swell; (–) insoluble.

R.-X. Yao et al. / Journal of Fluorine Chemistry 129 (2008) 1003–1010
1009
Table 2
Physical properties of PFCB polymers
Mna
Mwa
(Mw/Mn)a
Tg (8C)
Td (8C)
b
b
Polymers
7a
7b
7c
7d
7e
7f
72,102
62,230
64,656
53,608
51,499
29,070
85,290
78,715
78604
64,376
61,457
35,968
1.18
1.26
1.22
1.20
1.19
1.24
91
106
98
–
340
345
332
334
339
370
–
156
a
GPC in DMF vs. polystyrene at 35 8C.
DSC and TGA at 10 8C/min in N2.
b
3.4. Properties of polymers
3.4.1. Solubility of polymers
Fig. 6. DSC curves of polymers 7a–f.
The solubility of the PFCB polymers in common organic solvent
was determined quantitatively by dissolving 5.0 mg of solid
polymers in 1.0 mL of solvents (Table 1). It can be seen that these
perfluorocyclobutyl-containing polymers showed good solubility
in dipole organic solvents, such as NMP, DMAc, DMSO and DMF.
But they can not dissolve or can just swell in acetone, THF and
CHCl3 with the exception of polymer 7f which can be dissolved in
THF because of two PFCB groups in one repeating unit that make
the polymer backbone more flexible. Polymers 7a–f can swell in
conc. H2SO4 owing to the effect of hydrogen bonds between the
solution and the polymers.
3.4.2. Molecular weights and their distributions of PFCB polymers
The corresponding data of GPC analysis in DMF for 7a–f were
listed in Table 2. The molecular weights were reduced from 7a to
7f. The shorter the repeating unit of the polymer chain was, the
higher the molecular weight was. All the polydispersities of
fluoropolymers 7a–f were about 1.2 which indicated that the click
chemistry was efficient for polymerization.
Fig. 7. Wide-angle X-ray diffraction patterns of polymers 7a–f.
3.4.3. Thermal properties of polymers
Thermal properties of the PFCB polymers were evaluated by
means of thermo-gravimetric analysis (Fig. 5) and differential
scanning calorimetry (Fig. 6). The resulting data are listed in
Table 2. The polymers 7a–e started to decompose at about 340 8C,
and there were the second stage of weight loss at 420 8C, which
might be caused by the decomposition of triazole rings. The values
of Tg were determined from the DSC curves. The molecular
structure of 7b is more rigid than 7a, so its Tg is higher. It is a little
difficult to determine the Tg of polymers 7d and 7e, because there is
no apparent transformation in their DSC curves. The polymer 7f
contains more fluorine than others, which makes higher Tg and Td.
The curves of DSC (Fig. 6) also showed that all PFCB polymers
mostly were amorphous, which had been further confirmed by the
X-ray of these polymers (Fig. 7).
4. Conclusion
A novel monomer 1,2-bis(4-azidomethylphenoxy) perfluoro-
cyclobutane was prepared. The click chemistry of 1,2-bis(4-
azidomethylphenoxy) perfluorocyclobutane and bisethynyl com-
pounds provided a novel class of linear aromatic ether polymers
containing perfluorocyclobutyl and triazole unites. The resulting
polymers mostly are amorphous and have good solubility in most
dipole solvents and thermal stability.
Acknowledgments
We are grateful to National Natural Science Foundation of
China, the Program for Changjiang Scholars and Innovative
Research Team in University (No. IRT0526) and Shanghai
Municipal Scientific Committee for the financial support.
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