Macromolecules, Vol. 38, No. 1, 2005
Hyperbranched Glycopolymers 11
Table 1. Homopolymerization of 3-O-Acryloyl-1,2:5,6-di-O-isopropylidene-r-D-Glucofuranoside (AIGlc) with CuBr/
PMDETA at 60 °C in Ethyl Acetate (50 wt %)a
c
[M]0/[I]0
time (h)
convb (%)
Mn, calcd
Mn,GPCd (Mw/Mn)
Mn,GPC-VISCOe (Mw/Mn)
Mn, MALDIf (Mw/Mn)
15
20
18
48
73
88
93
33
84
3400
5500
14600
10300
26300
4100 (1.05)
5900 (1.09)
13400 (1.09)
9300 (1.06)
24200 (1.14)
3200 (1.14)
5400 (1.09)
13600 (1.11)
9400 (1.13)
29200 (1.12)
6600 (1.13)
18500 (1.25)
14800 (1.17)
30900 (1.37)
50
72
100
100
48
120
a Solution polymerization with ethyl 2-bromoisobutyrate; [I]0:[CuBr]0:[PMDETA]0 ) 1:1:1. b Monomer conversion as determined by 1H
NMR. c Theoretical number-average molecular weight as calculated from the monomer conversion. d Determined by GPC using THF as
eluent with PtBuA standards. e Determined by GPC-viscosity measurement. f Determined by MALDI-TOF MS measurement.
isopropylidene units), 4.05, 4.25, 5.29, 5.87 (7H, sugar moiety),
5.85-6.50 (3H, three vinyl protons). 13C NMR (CDCl3): δ )
165.05 (CdO), 131.6 (CH2)), 128.09 (CH)), 27.18, 27.07,
26.56, 25.59 (CH3 in isopropylidene groups).
white powder in a quantitative yield (75 mg, yield ) 88%),
which was insoluble in water, methanol, and acetone and
completely soluble in DMSO. The deprotection was done in a
similar way in the case of linear poly(AIGlc), which gave water-
soluble glycopolymers.
Atom Transfer Radical Polymerization of AIGlc. All
polymerizations were carried out in a round-bottom flask
sealed with a plastic cap. A representative example is as
follows: Ethyl 2-bromoisobutyrate (0.0254 g, 0.127 mmol) was
added to a round-bottom flask containing CuBr(I) (0.0178 g,
0.127 mmol), PMDETA (0.0219 g, 0.127 mmol), and AIGlc (0.80
g, 2.54 mmol) in ethyl acetate (0.80 g, 50 wt % to AIGlc). As
soon as the initiator was added to the mixture, the color
changed into green, indicating the start of the polymerization.
The flask was placed in an oil bath at 60 °C for 48 h.
Conversion of the double bonds, as detected by 1H NMR, was
88%. The content in the flask was viscous which was dissolved
in THF. The solution was passed through a silica column, and
the polymer was precipitated from THF into hexane. Finally,
the product was freeze-dried from dioxane and dried under
vacuum at room temperature. The polymer had Mn ) 5900
and Mw/Mn ) 1.09 according to conventional GPC, Mn ) 6600
and Mn/Mw ) 1.13 according to GPC/visosity using universal
calibration, and Mn ) 5400 and Mw/Mn ) 1.09 according to
MALDI-TOF MS measurement.
Characterization. The linear and branched polymers
obtained from AIGlc were characterized by conventional GPC
and GPC/viscosity using THF as eluent at a flow rate of 1.0
mL/min at room temperature. A conventional THF-phase GPC
system was used to obtain apparent molecular weights. GPC
system I; column set: 5 µm PSS SDV gel, 102, 103, 104, 105 Å,
30 cm each; detectors: Waters 410 differential refractometer
and Waters photodiode array detector operated at 254 nm.
Narrow PtBuA standards (PSS, Mainz) were used for the
calibration of the column set I. Molecular weights of the
branched polymers were determined by the universal calibra-
tion principle37 using the viscosity module of the PSS-
WinGPC scientific V 6.1 software package. Linear PMMA
standards (PSS, Mainz) were used to construct the universal
calibration curve. GPC system II; column set: 5 µm PSS SDV
gel, 103 Å, 105 Å and 106 Å, 30 cm each; detectors: Shodex
RI-71 refractive index detector; Jasco Uvidec-100-III UV
detector (λ ) 254 nm); Viscotek viscosity detector H 502B. A
1-methyl-2-pyrrolidone (NMP)-phase GPC system was used to
obtain apparent molecular weights of the hydrolyzed polymers.
GPC system III; column set: two PSS GRAM 7 µm, 1000 and
100 Å columns thermostated at 70 °C; detectors: Waters 486
UV detector (λ ) 270 nm), and Bischoff RI-detector 8110. 50
µL of the sample diluted in NMP (containing 0.05 M LiBr) were
injected at a flow rate of 1 mL/min. Linear PS standards were
used for calibration.
MALDI-TOF mass spectrometry was performed on a
Bruker Reflex III instrument equipped with a 337 nm N2 laser
in the reflector mode and 20 kV acceleration voltage. 2,5-
Dihydroxybenzoic acid (Aldrich, 97%) was used as a matrix.
Samples were prepared from THF solution by mixing matrix
(20 mg/mL) and polymer (10 mg/mL) in a ratio of 4:1. The
number-average molecular weights of the polymers were
determined in the linear mode.
1H and 13C NMR spectra were recorded with a Bruker AC-
250. FT-IR spectra were recorded on a Bruker Equinox 55
spectrometer. The elemental analyses were performed by Ilse
Beetz Mikroanalytisches Laboratorium (Kulmbach).
A mixture of linear poly(AIGlc)s with various molecular
weights was used as comparison in the solution viscosity
studies. Molecular weight for this sample: Mn ) 13 800 and
Mw/Mn ) 1.64 (determined by GPC/viscosity using universal
calibration) as shown in Figure S-1 (see Supporting Informa-
tion).
Self-Condensing Vinyl Copolymerization. A represen-
tative example for the copolymerization (γ ) [AIGlc]0/[BPEA]0
) 1) is as follows: BPEA (0.3995 g, 1.592 mmol) was added to
a round-bottom flask containing CuBr(I) (0.004 78 g, 0.0318
mmol), PMDETA (0.005 49 g, 0.0318 mmol), AIGlc (0.5 g, 1.592
mmol), and ethyl acetate (0.5 g, 50 wt % to AIGlc). As soon as
BPEA was added to the mixture, the color changed into green,
indicating the start of the polymerization. The flask was placed
in an oil bath at 60 °C for 4 h. The mixture was completely
solidified after 4 h when the conversion reached a certain level.
Conversion of the double bonds, as detected by 1H NMR, was
90%. After the mixture was dissolved in THF, and was passed
through a silica column, the polymer was precipitated from
THF into hexane. Then the product was freeze-dried from
dioxane and finally dried under vacuum at room temperature
to yield a white powder. The polymer had Mn ) 7800 and Mw/
Mn ) 1.43 according to conventional GPC and Mn ) 9200 and
Mw/Mn ) 2.84 according to GPC/viscosity using universal
calibration. The resulting polymer was soluble in chloroform,
THF, and acetone but insoluble in methanol, hexane, and
water.
Deprotection. Transformation of randomly branched poly-
(AIGlc) into branched poly(3-O-acryloyl-R,â-D-glucopyranoside)
(AGlc) was achieved under mild acidic conditions. The branched
poly(AIGlc) (γ ) 1; 85 mg) was dissolved in 80% formic acid
(10 mL) and stirred for 48 h at room temperature. Then, 4
mL of water was added, and it was stirred for another 3 h.
The solution was dialyzed using Spectra/PorR (MWCO: 1000)
against Millipore water for 2 days. The solution was evapo-
rated under reduced pressure, and the resulting polymer was
freeze-dried from dioxane and dried under vacuum. The
deprotected hyperbranched polymer (γ ) 1) was obtained as
Results and Discussion
Effect of Polymerization Conditions on the Ho-
mopolymerization of AIGlc. To find the suitable
polymerization conditions for the synthesis of highly
branched glycopolymers by SCVCP, we first investi-
gated the effect of polymerization conditions on ATRP
of AIGlc. In a previous paper, we have demonstrated
that the synthesis of randomly branched polymers by
SCVCP of tert-butyl acrylate with BPEA was achieved
using CuBr/PMDETA catalyst system.38 Hence, the
CuBr/PMDETA catalyst system was employed for ATRP
of AIGlc. When AIGlc was polymerized using CuBr/
PMDETA with ethyl 2-bromoisobutyrate ([M]0/[I]0 ) 20)
at 60 °C in ethyl acetate, as shown in Table 1, the
1
conversion reached 88% (as determined by H NMR)