Synthesis of novel polyfluorene-derived task-specific ionic liquid

Article abstract of DOI:10.1080/00397910500212676

The synthesis and characterization of a novel polymerizable ionic liquid derived from polyfluorene, poly[3-methyl-1-(4-(9-methyl-fluorene)-butyl)- imidazolium hexafluorophosphate] (PFIL), are described. Copyright Taylor & Francis, Inc.

Full text of DOI:10.1080/00397910500212676

Synthetic Communicationsw, 35: 2609–2613, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500212676
Synthesis of Novel Polyfluorene-Derived
Task-Specific Ionic Liquid
Dingjun Zhang and Lei Chen
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical
Physics, Chinese Academy of Sciences, Lanzhou, China and Graduate
School of the Chinese Academy of Sciences, Beijing, China
Jianmin Chen, Yongming Liang, and Huidi Zhou
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical
Physics, Chinese Academy of Sciences, Lanzhou, China
Abstract: The synthesis and characterization of a novel polymerizable ionic
liquid derived from polyfluorene, poly[3-methyl-1-(4-(9-methyl-fluorene)-butyl)-
imidazolium hexafluorophosphate] (PFIL), are described.
Keywords: Characterization, ionic liquids, polyfluorene, synthesis
Besides interesting properties as alternative green media, ionic liquids are also
quite promising electrolyte materials because of their unique properties, such
as high ionic density, pretty high ionic conductivity, good mechanical
property, and high thermal stability.[1–6] Very recently a new class of ionic
liquid, polymerizable ionic liquid, has been developed.[7,8] The polymerizable
ionic liquids (PILs) are quite attractive because of their potential application to
electrolyte materials. They have many remarkable advantages over common
ionic liquids, such as good mechanical property and no chance of
leakage.[9,10] These derivatives combine the ionic liquid–type part (to be as
close as possible to classic ionic liquids and maintain the corresponding
Received in Japan March 18, 2005
Address correspondence to Jianmin Chen, State Key Laboratory of Solid Lubrica-
tion, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou
730000, China. E-mail: chenjm@ns.lzb.ac.cn
2609

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D. Zhang et al.
properties) with an extra function of the polymer (to be designed for the
specific purpose).[11–15] Another very attractive possibility is to develop
such ionic liquids as task-specific materials. One of the important tasks to
improve their application as functionalized materials is the synthesis of
suitable polymerizable ionic liquids.
Preparation and characterization of task-specific ionic liquids have been
reported from our laboratory. Besides intrinsic academic interest, the work
assumes importance because some of these compounds have been found to
display specific optoelectronic activity.[16] Work on PIL materials is relatively
unknown. As an extension, we report herein the synthesis of a novel polymer-
izable ionic liquid derived from polyfluorene, poly[3-methyl-1-(4-(9-methyl-
fluorene)-butyl)-imidazolium hexafluorophosphate] (PFIL).
As a preliminary study of polymerizable ionic liquid, we synthesized
a novel polymerizable ionic liquid containing polyfluorene (Scheme 1).
9-Methyfluorene was converted into the corresponding 9-methyl-9-(4-bromo-
butyl)-fluorene upon treatment with lithium butyl and 1,4-dibromobutane at
2788C under a nitrogen atmosphere. 9-Methyl-9-(4-bromobutyl)-fluorene
was purified by silica-gel column chromatography and eluted by hexane. The
solution of 9-methyl-9-(4-bromobutyl)-fluorene and 1-methylimidazole in
tetrahydrogenfuran (THF) was refluxed for 8–10 h to give the corresponding
monomeric ionic liquid with high purity in a good yield. Metathesis of
Scheme 1. Synthetic route for PF. Reagents and conditions: 1) BuLi, CH3I, THF;
2) n-BuLi, Br(CH2)4Br, THF; 3) 1-methylimidazole, THF, sodium hexafluorophos-
phate, H2O; and 4) FeCl3, CHCl3.

Novel Ionic Liquid
2611
obtained imidazolium bromide salt with sodium hexafluorophosphate in water
gave a high yield (93%)of the corresponding hexafluorophosphate salt upon ion
exchanging. The final target compound we describe in this article was obtained
via cross-linking at the 2,7-positions of the fluorene unit by chemical oxidation.
The procedure involved the use of the FeCl3 catalytic polymerization system as
reported by Fukuda and coworkers.[17] To the best of our knowledge this is the
first report for the synthesis of a poly(fluorene)-containing polymerizable ionic
liquid derivative. GPC analyses was attempted but led to strong absorption of
the polymer on the columns.
EXPERIMENTAL
The melting points of the synthetic products were determined on a X-6
melting-point measurement device and are uncorrected. The infrared (IR)
spectra were recorded on a Perkin-Elmer 325 instrument (KBr disk or liquid
1
film). The H NMR spectra were recorded on a Bruker-400 FT NMR (400-
MHz) spectrometer in DMSO-d6 or CDCl3, using tetramethylsilane as an
internal standard. The reagents and solvents were commercially purchased
and used without further treatment.
9-Methyl-fluorene
A solution of fluorene (1.0 g, 6 mmol) in dry THF (20 ml) was treated under
nitrogen at 2788C with 2 ml of n-BuLi (2.86 M in hexane) over a 45-min
period. After addition, the temperature was allowed to rise to room tempera-
ture and stirring continued for 1 h. The mixture was then cooled to 2788C and
treated with a solution of 0.37 ml (6 mmol) of methyliodide in THF (5 ml). The
temperature was then allowed to rise to room temperature and the mixture was
stirred overnight. The red solution obtained was neutralized with 5% HCl and
THF was evaporated in vacuo. Extraction of the aqueous phase with chloro-
1
form yielded a light-yellow solid (0.8 g, 75%). Bp: 908C/0.75 mmHg, H
NMR (300 MHz, CDCl3, ppm): d 7.2–7.8 (m, 8H), 4.03 (q, 1H), 1.55 (d, 3H).
9-Methyl-9-(4-bromobutyl)-fluorene[18]
To a solution of 1.0 g of 9-methylfluorene in 20 ml of THF at 2788C, 2 ml of
n-BuLi (2.86 M in hexane) was added dropwise. The mixture was stirred at
2788C for 1 h, and warmed to room temperature for another 2 h. On cooling to
2788C again, 1.5 g of 1,4-dibromobutane in 10 cm3 of THF was added to the
mixture. The solution was allowed to warm to room temperature and stirred
overnight. THF was removed, and the residue was poured into water and
extracted with chloroform. The organic extracts were washed with brine and

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D. Zhang et al.
dried over magnesium sulfate. After removing the solvent, the product was purified
by silica-gel column chromatography and eluted by hexane to afford 1.3 g (72%) of
slightly yellowish oil. 1H NMR (300 MHz, CDCl3) d (ppm): 7.773–7.791
(d, J ¼ 7.2 Hz, 2H), 7.240–7.546 (m, 6H), 3.377–3.411 (t, J ¼ 6.8, 2H), 1.804–
1.875 (m, 2H), 1.252–1.522 (m, 5H), 0.854–0.872 (m, 2H).
Synthesis of Ionic Liquid Monomer: 1-Methyl-3-[4-(9-methyl-9-
fluorene)-butyl]-imidazolium Hexafluorophosphate
Asolutionof9-methyl-9-(4-bromobutyl)-fluorene(3 mmol)and1-methylimid-
azole (3.1 mmol) in THF was refluxed for 10 h and filtered. The precipitate
was thoroughly rinsed with THF. The residue was rinsed with diethyl
ether (20 ml) and dried in vacuo to give 2 g (85% yield) of product as a
white waxy solid, 1-methyl-3-[4-(9-methyl-9-fluorene)-butyl]-imidazolium
bromide.
Sodium hexafluorophosphate (3.1 mmol) was added to a magnetically
stirred solution of the imidazolim bromide prepared previously (3 mmol) in
20 mL of water. After 30 min, the precipitated solid was separated by filtration
and washed with water. The product obtained was dried in vacuo at 1008C
overnight to give a white solid (1.3 g, 93%) of compound 3. Mp: 65–678C.
1H NMR (400 MHz, DMSO-d6) d (ppm): 7.582–7.825 (m, 2H), 4.120–
4.211 (t, J ¼ 7.2 Hz, 2H), 3.843 (s, 3H), 2.074–2.098 (s, 2H), 1.904–1.927
(m, 2H).
Preparation of Polymerizable Ionic Liquid: Poly[1-methyl-3-[4-(9-
methyl-9-fluorene)-butyl]-imidazolium Hexafluorophosphate]
1-Methyl-3-[4-(9-methyl-9-fluorene)-butyl]-imidazolium hexafluorophosphate
(0.3 g) was mixed with 0.74 g of FeCl3 in CHCl3 under an argon atmosphere.
The mixture was stirred for 72 h at room temperature. The reaction mixture
was quenched by adding it to methanol. The precipitated solid was
separated by filtration, washed with methanol, and dried at room temperature
under vacuum overnight to afford 0.19 g (66%) of light-yellow powder. Mp:
87–898C. Elemental analytical results calc. for C22H23N2PF6: C, 57.02%;
1
N, 6.05%; H, 4.97%; found: C, 56.10%; N, 4.20%; H, 3.77%. H NMR
(400 MHz, DMSO-d6) d (ppm): 7.582–7.825 (m, 2H), 4.275–4.321
(t, J ¼ 9.2, 2H), 3.843 (s, 3H), 2.074–2.098 (s, 2H), 1.904–1.927 (m, 2H).
ACKNOWLEDGMENTS
The authors are grateful to the National Natural Science Foundation of China
(Grant No. 59925513), the National Basic Research Priority Program of

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2613
China (No. G1999065005), and “Top Hundred Talents Program” of Chinese
Academy of Sciences for financial support.
REFERENCES
1. Wilkes, J. S.; Zaworotko, M. J. J. Chem. Soc. Chem Commun. 1992, 965.
2. Fuller, J.; Breda, A. C.; Carlin, R. T. J. Electrochem. Soc. 1997, 67, 144.
3. (a) Forsyth, M.; Sun, J.; Zhou, F.; MacFarlane, D. R. Electrochim. Acta 2003, 48,
2129; (b) Ohno, H.; Yoshizawa, M.; Ogihara, W. Electrochim. Acta 2003, 48,
2079; (c) Hirao, M.; Ito, K.; Ohno, H. Electrochim. Acta 2000, 45, 1291.
4. Tiyapiboonchaiya, C.; MacFarlane, D. R.; Sun, J.; Forsyth, M. Macromol. Chem.
Phys. 2002, 203, 1906.
5. Yoshizawa, M.; Hirao, M.; Ito-Akita, K.; Ohno, H. J. Mater. Chem. 2001, 11,
1057.
6. Ohno, H.; Ito, K. Chem. Lett. 1998, 751.
7. Takanori, F.; Takuzo, A. Science 2003, 300, 2072.
8. Yoshizawa, M.; Ohno, H. Electrochim. Acta 2001, 46, 1723.
9. Fuller, J.; Breda, A. C.; Carlin, R. T. J. Electroanal. Chem. 1998, 29, 459.
10. Washiro, S.; Yoshizawa, M.; Nakajimaa, H.; Ohnoa, H. Polymer 2004, 45, 1577.
´
11. Anjaiah, S.; Chandrasekhar, S.; Gree, R. Tetrahedron Lett. 2004, 45, 569.
12. Wasserscheid, P.; Keim, W. Angew. Chem., Int. Ed. Engl. 2000, 39, 3772.
13. Sheldon, R. Chem. Commun. 2001, 2399.
14. (a) Schoefer, S. H.; Kaftzik, N.; Wasserscheid, P.; Kragl, U. Chem. Commun. 2001,
´
425; (b) Lozano, P.; Diego, T.; Carrie, D.; Vaultier, M.; Iborra, J. L. Chem.
Commun. 2002, 692.
15. Davis, J. H.; Forrester, H. J. Tetrahedron Lett. 1999, 40, 1621.
16. (a) Welton, T. Chem. Rev. 1999, 99, 2071; (b) Earle, M. J.; Seddon, K. R. Pure
Appl. Chem. 2000, 72, 1391.
17. Fukuda, M.; Sawada, K.; Yoshino, K. J. Polym. Sci., Part A: Polym. Chem. 1993,
31, 2465.
18. Liu, B.; Chen, Z. K.; Yu, W. L.; Lai, Y. H.; Huang, W. Thin Solid Films 2003, 63,
332.