Article
Chem. Mater., Vol. 22, No. 23, 2010 6349
2. Experimental Section
Quaternization of 1-Alkylimidazole Using mPEG Iodide.
1-Methylimidazole (1.76 g, 21 mmol) was added to a nitrogen-
purged round-bottom flask containing mPEG12I (7.03 g, 10.7
mmol) in DMF (4 mL) and the mixture was stirred at 80 ꢀC under
nitrogen for 48 h. After cooling to room temperature, the reaction
mixture was added slowly to cold (∼ 0 ꢀC) Et2O with vigorous
stirring, which resulted in phase separation of the product. The top
Et2O layer was decanted off, and the product was repeatedly
washed with fresh Et2O, after which it was dried in vacuo for about
12 h to obtain 5.75 g of the pure IL. 1H NMR (400 MHz, CDCl3, δ):
3.38 (br s, 3H, OCH3), 3.55 (t, J = 4.6 Hz, CH2OCH3), 3.52-3.70
(br m, 44.9H, CH2CH2O), 3.92 (t, J = 4.6 Hz, 2H, NþCH2CH2O),
4.05 (s, 3H, NCH3), 4.59 (t, J = 4.6 Hz, 2H, NþCH2), 7.46 (t, J =
1.6 Hz, 1H, NCH), 7.77 (s, 1H, NþCH), 9.78 (s, 1H, NþCHN).
2.3. Synthesis of 1-Alkyl-3-methylimidazolium Iodides. CnMeImI
ILs were synthesized using 1-methylimidazole and 1-iodoalkanes,
using procedures similar to those reported previously.17 The alkyl
iodide (1-iodohexane, 1-iodobutane, or 1-iodopropane) was added
dropwise, over a period of 1 h, to 1-methylimidazole taken in a
round-bottom flask that was purged with dry nitrogen. The con-
tents of the flask turned green (or yellow) immediately upon adding
the alkyl iodide. The mixture was heated at 80 ꢀC for 48 h period,
and later cooled to room temperature and added dropwise to cold
Et2O with vigorous stirring. The top Et2O layer was decanted off,
and the extraction with Et2O was repeated several times. The
bottom layer was dried in vacuo at 50 ꢀC, for about 12 h, to obtain
a viscous liquid of high purity (determined using 1H NMR).
EtMeImI was recovered as a yellowish white powder after pre-
cipitation and washing with cold Et2O. The powder was dissolved in
chloroform, precipitated again in cold Et2O, filtered, and dried in
vacuo at 50 ꢀC for about 12 h.
2.1. Materials. Methoxy-terminated polyethylene glycols (CH3-
O(CH2CH2O)nH, mPEGn, Ænæ= 7, 12, and 16, CAS no. 9004-
74-4), p-toluenesulfonyl chloride (TsCl, CAS no. 98-59-9, 99%),
anhydrous sodium iodide (CAS no.7681-82-5, 99.999%), 1-methyl-
imidazole (CAS no. 616-47-7, 99%), 1-butylimidazole (CAS no.
4316-42-1, 98%), 1-iodoethane (CAS no. 75-03-6, 99%) 1-iodo-
propane (CAS no.107-08-4, 99%), 1-iodobutane (CAS no. 542-
69-8, 99%), 1-iodohexane (CAS no. 638-45-9, 98%), and lithium
iodide hydrate (CAS no. 85017-80-7, 98%), obtained from Sigma-
Aldrich, were used without further purification. 1-Ethyl-3-methylimi-
dazolium ethylsulfate (EtMeImEtSO4, ECOENG212, Solvent In-
novation) was vacuum-dried at 80 ꢀC before use. Anhydrous pyri-
dine, methylene chloride, acetone, N,N-dimethylformamide (DMF),
sodium bicarbonate, hydrochloric acid, sodium thiosulfate, and anhy-
drous sodium sulfate (all from Fisher), and diethyl ether (Et2O, Alfa
Aesar) were also used as received.
2.2. Synthesis of 1-(Methoxy PEG)-3-methylimidazolium Io-
dides (mPEGnMeImI). The synthesis of the mPEG12MeImI is
described here. The other three PEGylated ionic liquids were
synthesized in a similar manner.
Tosylation of methoxy-terminated poly(ethylene glycol).
mPEG12 (CH3O(CH2CH2O)12H, 17.56 g, 31 mmol) was mixed
with anhyd. pyridine (4.75 g, 60 mmol) in a round-bottom flask,
and a solution of TsCl (12.75 g, 67 mmol) in anhyd. CH2Cl2
(45 mL) was added dropwise to the flask while cooling the flask in an
ice-bath (∼ 0 ꢀC). A white precipitate formed immediately after the
addition of TsCl. After 1 h, the reaction mixture was warmed back
to room temperature. After 24 h of mixing at room temperature,
CH2Cl2 (50 mL) was added to the reaction flask and the resulting
mixture was stirred for 30 min, followed by sequential extractions
with satd. NaHCO3 soln. (3 ꢀ 30 mL), 1 M aq. HCl soln. (3 ꢀ
30 mL), and distilled water (3 ꢀ 30 mL). The organic layer was
dried over sodium sulfate, filtered, and concentrated by evaporation
of CH2Cl2 under vacuum. The resulting colorless liquid was dried
in vacuo for about 12 h. This liquid (17.71 g) contained about
89.3 mol % of mPEG12 tosylate and 10.7 mol % of the starting
mPEG12. The yield of mPEG12 tosylate, based on the initial
amount of mPEG12 was, therefore, ∼ 72%. The mixture was used
in the next step, without further purification. 1H NMR (400 MHz,
CDCl3, δ): 7.80 and 7.35 (A2B2 dd, J = 8.2 Hz, 4H, aryl ring), 4.16
(t, J = 4.8 Hz, 2H, CH2OTs), 3.5-3.8 (br m, CH2CH2O), 3.38 (s,
3.36H, OCH3), 2.45 (s, 3H, Ar-CH3).
Iodination of mPEG tosylate. NaI (8.79 g, 58.6 mmol) was
added in the dark, with vigorous stirring, to mPEG12 tosylate
(10.51 g, 13.6 mmol mPEG12 tosylate) dissolved in dry acetone
(50 mL), and the resulting yellow mixture was stirred for 24 h under
reflux at about 60 ꢀC. A yellow solid eventually settled down in the
reaction flask. After evaporating acetone using a rotary evapora-
tor, CH2Cl2 (60 mL) and distd. water (40 mL) were added to the
solid left behind in the flask. The mixture was stirred for 30 min at
room temperature. The organic and aqueous phases were sepa-
rated and the organic phase was extracted with 5% aq. Na2S2O3
soln. (3 ꢀ 50 mL). The organic phase was further washed with satd.
NaHCO3 soln. (3 ꢀ 50 mL) and with distd. water (3 ꢀ 50 mL) and
dried over sodium sulfate. The sodium sulfate was removed by
filtration and CH2Cl2 was evaporated under vacuum. The product
was further dried in a vacuum oven at 50 ꢀC to obtain 8.95 g of a
viscous liquid which contained 95.7 mol % of mPEG12 iodide and
4.3 mol % of mPEG12. This mixture was used in the next reaction
without further purification. 1H NMR (400 MHz, CDCl3, δ): 3.26
(t, J=6.9 Hz, 1.9H, CH2I), 3.37 (s, 3H, OCH3), 3.55 (t, J=4.6 Hz,
CH2OCH3), 3.52-3.71 (br m, CH2CH2O), 3.76 (t, J=6.9 Hz,
1.9H, OCH2CH2I).
EtMeImI: 1H NMR (400 MHz, CDCl3, δ): 1.64 (t, J = 7.4 Hz,
3H, NþCH2CH3), 4.13 (s, 3H, NCH3), 4.42 (q, J = 7.5 Hz, 2H,
NþCH2), 7.50 (apparent br d, J = 1.6 Hz, 2H, NCHCHNþ, 10.07
(s, 1H, NþCHN).
PrMeImI: 1H NMR (400 MHz, CDCl3, δ): 1.02 (t, J = 7.4 Hz,
3H, Nþ (CH2)2CH3), 2.0 (sx, J = 7.4 Hz, 2H, NþCH2CH2CH3),
4.14 (s, 3H, NCH3), 4.32 (t, J = 7.2 Hz, 2H, NþCH2CH2), 7.49 (s,
J = 1.6 Hz, 1H, NCH), 7.55 (s, J = 1.6 Hz, 1H, NþCH), 10.06 (s,
1H, NþCHN).
BuMeImI: 1H NMR (400 MHz, CDCl3, δ): 0.98 (t, J = 7.4 Hz,
3H, Nþ (CH2)3CH3), 1.41 (sx, J = 7.4 Hz, 2H, Nþ(CH2)2CH2-
CH3), 1.93 (qn, J = 7.4 Hz, 2H, NþCH2CH2CH2), 4.14 (s, 3H,
NCH3), 4.34 (t, J=7.4 Hz, 2H, NþCH2CH2), 7.40(t, J=1.7 Hz, 1H,
NCH), 7.48 (t, J=1.7 Hz, 1H, NþCH), 10.14 (s, 1H, NþCHN).
HexMeImI: 1H NMR (400 MHz, CDCl3, δ): 0.88 (t, J=7.0
Hz, 3H, Nþ(CH2)5CH3), 1.33 (brm, 6H, NþCH2CH2(CH2)3CH3),
1.93 (qn, J = 7.5 Hz, 2H, NþCH2CH2CH2), 4.13 (s, 3H, NCH3),
4.32 (t, J=7.5 Hz, 2H, NþCH2), 7.36 (t, J=1.7 Hz, 1H, NCH),
7.45 (t, J=1.7 Hz, 1H, NþCH), 10.17 (s, 1H, NþCHN).
2.4. Characterization. The chemical structures of the electro-
lytes were characterized using 1H NMR Spectroscopy. A Bruker
1
Avance 400 MHz NMR spectrometer was used to record H
NMR spectra of the salts in anhyd. deuterated chloroform (99.8
atom % D, 0.03% v/v tetramethylsilane, TMS), and chemical shifts
are expressed in parts per million relative to TMS. Thermal
degradation was studied using a Perkin-Elmer Pyris 1 Thermo-
gravimetric Analyzer. The sample (∼30 mg) was heated in a Pt pan,
under nitrogen purge, over a temperature range of 40-600 ꢀC, at a
rate of 15 ꢀC/min. Thermal phase behavior was studied using a TA
Instruments DSC Q100. The samples (10-15 mg) were weighed in
aluminum pans and sealed with lids that contained pin holes.
Thermal scans were performed in a nitrogen atmosphere over a
temperature range of -80 to 100 ꢀC (up to 120 ꢀC for CmCnImI).