9510 Zhao et al.
Macromolecules, Vol. 38, No. 23, 2005
R-(p-Toluenesulfonyl)-ω-methoxytris(oxyethylene), tetra-
(ethylene glycol) monomethyl ether (R-hydro-ω-methoxytet-
rakis(oxyethylene), TrEG), and penta(ethylene glycol) mono-
methyl ether (R-hydro-ω-methoxypentakis(oxyethylene), PEG)
were prepared by use of the same procedures reported in the
literature.37
r-(p-Toluenesulfonyl)-ω-methoxytris(oxyethylene). 1H
NMR (CDCl3) δ (ppm): 7.77 (d, 2H, RO3SC(CH)2), 7.32 (d, 2H,
H3CC(CH)2), 4.14 (t, 2H, SO3CH2), 3.67 (t, 2H, SO3CH2CH2),
3.61-3.49 (m, 8H, OCH2), 3.35 (s, 3H, OCH3), 2.43 (s, 3H,
ArCH3). 13C NMR (CDCl3) δ (ppm): 144.75 (CH3C(CH)2),
132.97 (SO2C(CH)2), 129.78 (CH3C(CH)2), 127.95 (SO2C(CH)2),
71.86 (CH3OCH2), 70.71, 70.53, 70.51, 69.20 (OCH2), 68.64
(SO3CH2), 59.00 (OCH3), 21.6 (CH3C(CH)2). MS (ES) m/z 341.1
([M + Na]+).
Tetra(ethylene glycol) Monomethyl Ether (r-Hydro-
ω-methoxytetrakis(oxyethylene), TrEG). 1H NMR (CDCl3)
δ (ppm): 3.78-3.41 (m, 16H, OCH2), 3.35 (s, 3H, OCH3), 2.60
(t, 1H, -OH). 13C NMR (CDCl3) δ (ppm): 72.66 (CH2OCH3),
71.73 (HOCH2CH2O), 70.45, 70.36, 70.33, 70.26, 70.03 (-CH2-
OCH2CH2OCH2CH2OCH2CH2OCH3), 61.51 (HOCH2-), 58.84
(-OCH3). MS (ES) m/z 231.1 ([M + Na]+).
Penta(ethylene glycol) Monomethyl Ether (r-Hydro-
ω-methoxypentakis(oxyethylene), PEG). 1H NMR (CDCl3)
δ (ppm): 3.73-3.51 (m, 20H, OCH2); 3.36 (s, 3H, -OCH3), 2.67
(t, 1H, -OH). 13C NMR (CDCl3) δ (ppm): 72.57 (CH2OCH3),
71.59 (HOCH2CH2O), 70.33, 70.30, 70.21, 69.92 (CH2O-
(CH2CH2O)3OCH2CH2OCH3), 61.32 (HOCH2CH2O), 58.75
(OCH3). MS (ES) m/z 275.1 ([M + Na]+).
Synthesis of 4-Vinylbenzyl Methoxytris(oxyethylene)
Ether (TEGSt). Tri(ethylene glycol) monomethyl ether (16.58
g, 0.101 mol) was added into a three-necked flask containing
dry THF (50 mL) followed by addition of NaH (6.08 g, 0.152
mol). After the mixture was stirred at room temperature under
N2 atmosphere for 1 h, a solution of 4-vinylbenzyl chloride
(10.76 g, 70.5 mmol) in dry THF (20 mL) was added dropwise.
The reaction mixture was refluxed for 20 h. The mixture was
then poured into a 250 mL beaker and neutralized by adding
a dilute HCl aqueous solution. The mixture was then placed
in a separatory funnel to allow phase separation. The organic
phase was separated, and the aqueous layer was extracted
with diethyl ether four times. The organic phase and extracts
were combined and dried over anhydrous Na2SO4. The solvents
were removed by a rotavapor, and purification by column
chromatography (1:1 ethyl acetate/hexanes) afforded 9.99 g of
pure product as a nearly colorless liquid (51% yield). 1H NMR
(CDCl3) δ (ppm): 7.36 (d, 2H, aromatic), 7.28 (d, 2H, aromatic),
6.69 (dd, 1H, CH2dCH-), 5.72 (dd, 1H, CHHdCH-), 5.21 (dd,
1H, CHHdCH-,), 4.53 (s, 2H, (CH)2C-CH2-), 3.51-3.67 (m,
12H, -OCH2CH2O-), 3.35 (s, 3H, OCH3). 13C NMR (CDCl3) δ
(ppm): 137.85 (OCH2C(CH)2), 136.90 (CH2CHC(CH)2), 136.51
(CH2CHC(CH)2), 127.90 ((CH)2CCH2O), 126.16 (CH2CHC-
(CH)2), 113.70 (CH2CHC(CH)2), 72.90 ((CH)2CCH2O), 71.90
(CH3OCH2), 70.60, 70.51, 69.34 (CH2O), 59.01 (CH3OCH2). IR
(cm-1): 2870 (CH2 and CH3, ether), 1628 (CHdCH2), 1512
(aromatic CdC), 1454 (CH2), 1107 (C-O-C). MS (ES) m/z
303.1 ([M + Na]+).
Synthesis of 4-Vinylbenzyl Methoxytetrakis(oxyeth-
ylene) Ether (TrEGSt). A procedure similar to the synthesis
of TEGSt was used to prepare TrEGSt. The crude product was
purified by column chromatography (4:1 ethyl acetate/hex-
anes), giving a nearly colorless liquid (72% yield). 1H NMR
(CDCl3) δ (ppm): 7.37 (d, 2H, aromatic), 7.28 (d, 2H, aromatic),
6.69 (dd, 1H, CH2dCH-), 5.72 (dd, 1H, CHHdCH-), 5.21 (dd,
1H, CHHdCH-), 4.53 (s, 2H, (CH)2C-CH2-), 3.67-3.50 (m,
16H, -OCH2CH2O-), 3.35 (s, 3H, OCH3). 13C NMR (CDCl3) δ
(ppm): 137.83 ((CH)2CCH2O), 136.89 (CH2CHC(CH)2), 136.48
(CH2CHC(CH)2), 127.88 ((CH)2CCH2O), 126.14 (CH2CHC-
(CH)2), 113.68 (CH2CHC(CH)2), 72.88 ((CH)2CCH2O), 71.87
(CH2OCH3), 70.58, 70.55, 70.46, 69.33 (CH2O), 58.97 (CH3-
OCH2). IR (cm-1): 2870 (CH2 and CH3, ether), 1628 (CHdCH2),
1512 (aromatic CdC), 1454 (CH2), 1107 (C-O-C); MS (ES)
m/z 347.2 ([M + Na]+).
contain a hydrogen atom attached to a carbon located
R to the nitrogen atom have been proven to be highly
effective in the controlled polymerizations of a wide
variety of monomers including styrenics, acrylates, and
acrylamides.16 The advantage of these second-genera-
tion NMRP initiators over TEMPO-based systems is
also shown by the very low polydispersities, typically
1.05-1.15. In the present work, we used TPPA to
prepare homopolymers and diblock copolymers of TEGSt,
TrEGSt, and PEGSt. Although the polymerization of
TrEGSt by R,R′-azobis(isobutyronitrile) was reported for
making biocompatible materials35 and similar polysty-
renics containing oligo(ethylene glycol) groups (x ) 3
and 7 in Scheme 1) were grown from the surface by
surface-initiated TEMPO-mediated radical polymeriza-
tion to form protein-resistant polymer brushes,36 the
thermosensitive properties of the polymers in water
were not investigated. In the current work, the phase
transitions of homopolymers and diblock copolymers of
the three monomers were studied by cloud point mea-
surements and variable temperature 1H NMR spectros-
copy.
Experimental Section
Materials. Tri(ethylene glycol) monomethyl ether (95%),
ethylene glycol, di(ethylene glycol) (99%), and anisole (99.7%)
were purchased from Aldrich and used as received. 4-Vinyl-
benzyl chloride (tech., 90%), p-toluenesulfonyl chloride (p.a),
and NaH (60% dispersion in mineral oil) were obtained from
Acros and used as received. Tetrahydrofuran (THF) was
distilled from sodium and benzophenone and stored in a
solvent storage bottle prior to use. All other chemical reagents
were purchased from either Aldrich or Fisher and used without
further purification.
Characterization. Gel permeation chromatography (GPC)
was carried out at room temperature using a PL-GPC 20 (an
integrated GPC system from Polymer Laboratories, Inc.) with
a refractive index detector, one PLgel 5 µm guard column
(50 × 7.5 mm), and two PLgel 5 µm mixed-C columns (each
300 × 7.5 mm, linear range of molecular weight from 200 to
2 000 000 according to Polymer Laboratories). The data were
processed using Cirrus GPC/SEC software (Polymer Labora-
tories). THF was used as the carrier solvent at a flow rate of
1.0 mL/min. Standard monodisperse polystyrenes (Polymer
Laboratories) were used for calibration. The 1H (300 MHz) and
13C NMR (75 MHz) spectra were recorded on a Varian Mercury
300 NMR spectrometer, and the residual solvent proton signal
was used as the internal standard. Mass spectroscopy was
performed in the Mass Spectroscopy Center in the Chemistry
Department at the University of Tennessee at Knoxville on a
Micromass Quattro II tandem electrospray spectrometer run
in the positive ion electrospray mode or using fast atom
bombardment (FAB). Variable temperature 1H NMR (400
MHz) spectra were recorded on a thermoregulated Bruker
Avance 400 using solutions of polymers in D2O (99.9 D atom
%) with a concentration of 10 mg/mL. An acquisition of 32
scans was performed with an acquisition time of 4 s per scan,
a pulse of 10 µs, and a recycle delay of 1 s. For each
temperature, the solution was equilibrated for 20 min. Cloud
points of thermosensitive homopolymers and diblock copoly-
mers in aqueous solutions (0.5% (w/w) for homopolymers and
1.0% for diblock copolymers) were measured by placing the
solutions in the water bath of a Fisher Scientific Isotemp
refrigerated circulator. Temperature was increased at a step
of 1 °C. At each temperature, the polymer solutions were
allowed to equilibrate with the water bath for 3 min. The cloud
point was recorded when the polymer solution became cloudy.
IR spectra were recorded on a BIO-RAD FTS-60A Fourier
transform infrared instrument. The samples were prepared
by adding several drops of a solution of the compound in
chloroform on a NaCl plate and drying in a vacuum at room
temperature for 10 min.