Hemicellulose-based multifunctional macroinitiator for single-electron- transfer mediated living radical polymerization

Article abstract of DOI:10.1021/bm101357k

A multifunctional macroinitiator for single-electron-transfer mediated living radical polymerization (SET-LRP) was designed from acetylated galactoglucomannan (AcGGM) by α-bromoisobutyric acid functionalization of the anomeric hydroxyl groups on the heteropolysaccharide backbone. This macroinitiator, with a degree of substitution of 0.15, was used in the SET-LRP of methyl acrylate, catalyzed by Cu⁰/Me₆-TREN in DMSO, DMF, or DMSO/H₂O in various concentrations. Kinetic analyses confirm high conversions of up to 99.98% and a living behavior of the SET-LRP process providing high molecular weight hemicelluloses/methyl acrylate hybrid copolymers with a brush-like architecture.

Full text of DOI:10.1021/bm101357k

Biomacromolecules 2011, 12, 253–259
253
Hemicellulose-Based Multifunctional Macroinitiator for
Single-Electron-Transfer Mediated Living Radical
Polymerization
†
†
,†
‡
Jens Voepel, Ulrica Edlund, Ann-Christine Albertsson,* and Virgil Percec
Fibre- and Polymer Technology, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden, and
Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia,
Pennsylvania 19104-6323, United States
Received November 15, 2010; Revised Manuscript Received December 3, 2010
A multifunctional macroinitiator for single-electron-transfer mediated living radical polymerization (SET-LRP)
was designed from acetylated galactoglucomannan (AcGGM) by R-bromoisobutyric acid functionalization of the
anomeric hydroxyl groups on the heteropolysaccharide backbone. This macroinitiator, with a degree of substitution
0
of 0.15, was used in the SET-LRP of methyl acrylate, catalyzed by Cu /Me
6
-TREN in DMSO, DMF, or DMSO/
2
H O in various concentrations. Kinetic analyses confirm high conversions of up to 99.98% and a living behavior
of the SET-LRP process providing high molecular weight hemicelluloses/methyl acrylate hybrid copolymers with
a brush-like architecture.
0
Scheme 1. Catalytic Cycle of SET-LRP Based on Cu in Polar
Solvents
Introduction
Single-electron-transfer mediated living radical polymeriza-
tion (SET-LRP) has emerged as a potent method to achieve
1
-3
living radical polymerization,
and the concept is currently
4
-12
being elaborated and explored with respect to mechanism,
polymer topology, and architecture,
as well as suitable monomers.
13-19
20-22
reaction conditions,
2
3-25
The metal-catalyzed syn-
thetic pathway involves the reversible activation of a halide-
terminated macroradical [P -X] into an active propagating chain
·. The metal catalyst is typically a Cu species, such as Cu ,
Cu O, or Cu S, which donates a single electron to the halide-
n
0
P
n
2
2
terminated chain, causing a heterolytic cleavage of the carbon-
halide bond via the formation of a radical anion that dissociates
into P
· and X- and enables propagation. The Cu species
1,2
I
n
generated in the SET process associate with an N-ligand to form
a Cu X/L complex. Fast disproportionation of this complex leads
I
0
II
to the formation of a Cu and a Cu X
the deactivation of the propagating macroradical generating the
dormant species [P -X]. The proposed SET-LRP cycle is
2
/L. The latter mediates
n
required for ATRP that form stronger complexes with Cu(I)X
species. Compared to ATRP, which involves the Cu(I)X
activating species, the SET-LRP is more robust in the sense
that the activation rate constant of propagation is not strongly
schematically outlined in Scheme 1.
Although recently introduced, SET-LRP has already been
proved a facile and versatile strategy for living radical polym-
2
erization. SET-LRP is viable for a range of monomers,
1
1
2
2,26,27
determined by the nature of the halide (X ) Cl, Br, or I). In
addition, SET-LRP can be successfully conducted without a
vigorous deoxygenation process by the addition of an extremely
small amount of reducing agent to the reaction mixture, allowing
for an economial approach to the synthesis of functional
including the commercially important acrylates,
acryl-
28,29
1,23,30
31
24,32-35
amides,
vinyl chloride,
styrene, methacrylates,
3
6
and methacrylic acid. A number of different ligands and
initiators have also been shown eligible for SET-LRP. The most
efficient initiators for SET-LRP and for Atom Transfer Radical
Polymerization (ATRP) must match the reactivity of the
propagating dormant chain. The most efficient solvents (dipolar
aprotic, alcohols, water and combinations of them) and ligands
13
macromolecules. This is considered a major advantage of SET-
LRP over ATRP, since the AGET (activator generated by
electron transfer) and ARGET (activator regenerated by electron
transfer) ATRP conducted under limited air require the addition
(
Me
plexes with Cu(II)X
mediate the disproportionation of Cu(I)X into Cu(0) and
Cu(II)X . Both differ from the nonpolar solvents and ligands
6
-TREN) for SET-LRP are those that form stronger com-
3
7,38
of excess reducing agent as oxygen scavenger.
tolerance to O of SET-LRP was further exemplified by its
immortal” nature. Despite repeated interruptions by O
reactivated SET-LRP provides polymers with narrow molecular
The high
2
rather than Cu(I)X species and therefore,
2
1
2
“
2
, the
2
12
weight distribution and excellent chain-end functionality. The
addition of O to ATRP would irreversibly oxidize the active
Cu(I)X species and terminate the polymerization process.
*
To whom correspondence should be addressed. E-mail: aila@kth.se.
Royal Institute of Technology (KTH).
University of Pennsylvania.
†
2
‡
10.1021/bm101357k
 2011 American Chemical Society
Published on Web 12/17/2010

2
54 Biomacromolecules, Vol. 12, No. 1, 2011
Voepel et al.
It was recently shown that markedly increased reaction rates,
Scheme 2. Representative Structural Unit of Acetylated
Galactoglucomannan
suppression of induction periods, and better control of the
polymer chain ends can be achieved in SET-LRP via a reducing
0
pretreatment of the catalyst surface to ensure high Cu avail-
ability rather than a combination of Cu
available on the surface of nonreduced Cu(0) catalyst.
2
O and Cu(0) that is
1
8
The versatility and controllability of the SET-LRP strategy
opens up a range of possibilities to use this method for the site-
specific controlled grafting from functionalized sites on mac-
romolecules thereby producing graft copolymers and brush-like
22,29,32
structure.
As such, the method is appealing for the design
of hybrid materials from macromolecules that do not otherwise
lend themselves to vinyl copolymerization, such as polymers
based on sugar moieties, known as polysaccharides. An
abundant, inexpensive, renewable, and green candidate from this
family is acetylated galactoglucomannan, a softwood hemicel-
lulose. We have previously demonstrated its viability and
versatility as a candidate for various chemical modifications and
Scheme 3. CDI (1) Assisted Coupling of R-bromoisobutyric Acid
(2) under CO
2
Expulsion to 3-bromo-1-(1H-imidazol-1-yl)-
3-methylbutan-1-one (3), Followed by Imidazole (4)-Catalyzed
Esterification of Acetylated Galactoglucomannan (5) to
R-Briba-AcGGM (6)
3
9-47
the development of functional materials.
Several attempts have been presented for the vinyl copolym-
erization with polysaccharides into glycopolymers, including
the controlled free radical polymerization with sugar deriva-
2
3
48
tives, covalent linkage of PMMA chains to cellulose, styrene
4
9
grafting on cellulose filter paper via reversible addition-
fragmentation chain transfer (RAFT), or the grafting onto
chitosan. However, these reactions have several drawbacks,
such as high reaction temperatures, water sensibility, low
conversions, and a risk for cross-linking.
5
0
Here, SET-LRP offers a unique opportunity of targeted
functionalization of the aforementioned acetylated galactoglu-
comannan. Being soluble in dimethyl sulfoxide (DMSO), N,N-
the imidazoyl-activated acid derivative. Following, 4.08 g imidazole
(
60 mmol, 4 equiv) were added as additional catalyst and the reaction
2
dimethylformamide (DMF) and H O this polysaccharide offers
mixture was heated to 50 °C. To this solution 2.60 g AcGGM (15 mmol
hexose units, 1 equiv) in 100 mL of DMSO were added under stirring
at 50 °C. The reaction was stopped after 60 to 120 min, was precipitated
in 2-propanol, followed by centrifugal collection and Soxhlet extraction
for 2 days with 2-propanol.
The macroinitiator is representatively shown in Scheme 4, including
half of the main chain repeating units with respect to the degree of
polymerization estimated by SEC. An average macroinitiator molecule
is expected to consist of approximately 40 sugar rings with three -Br
initiator moieties.
the chance to graft polymer chains from the backbone in a one
phase system. Thus, this method offers a new approach,
achieving brush-like architectures with equally long polymer
chains randomly distributed on the AcGGM backbone derived
in homogeneous media in contrast to earlier reports being
heterogeneous grafting from surfaces.
Experimental Section
Materials. N,N′-Carbonyldiimidazole (CDI) 97% (Aldrich), R-bro-
moisobutyric acid (RBrIBA) 98% (Aldrich), tris(2-aminoethyl)amine
6 6
Me -TREN Synthesis. Me -TREN was synthesized as reported
5
2
earlier. A total of 25.5 mL of 98% formic acid (0.45 mol, 10 equiv)
and 25 mL of 37% formaldehyde (0.30 mol, 6.65 equiv) were mixed
in a round-bottom flask kept in an ice bath. Tris(2-aminoethyl)amine
9
6% (Aldrich), formic acid g96% (Aldrich), formaldehydeaq 37% (Alfa
Aesar), dichloromethane 99.8% (Fisher), sodium chloride 99.5%
Merck), 2-propanol g99% (LabScan), methanol g99.8% (Labscan),
(
2
(6.58 g, 0.045 mol, 1 equiv) in 25 mL of H O were added dropwise to
copper wire (Gauge 20) (Fisher), acetone (Fischer, purum), and
dimethylacetamide 99.8% (Fisher) were used as received. Dimethyl
sulfoxide (DMSO) g99.5% (Fluka), N,N-dimethylformamide (DMF)
the solution, keeping the reaction mixture at 0 °C. After 60 min, the
ice bath was removed and the solution was allowed to warm up to
room temperature. Then the flask was heated to 100 °C and refluxed
overnight. After removing the volatiles at reduced pressure in a rotary
evaporator, the orange residue was adjusted to pH 10 with NaOHaq
(10% w/w). The crude product was extracted with dichloromethane,
99.8% (Fisher), and methyl acrylate (MA) 99.0% (Merck) were distilled
at reduced pressure prior to use.
O-Acetyl-galactoglucomannan (AcGGM) originating from spruce
(
Picea abies) was extracted from thermomechanical pulping process
2
the organic phase repeatedly washed with H O and NaCl solution and
water, fractionated by ultrafiltration and finally freeze-dried. The sugar
the product was recovered via rotary evaporation at reduced pressure.
Low pressure distillation yielded an oily, colorless liquid. The synthesis
5
1
composition was 17% glucose, 65% mannose, 15% galactose. The
-
1
1
average molecular weight was about 7500 g mol (DP ∼ 40), the
PDI was ∼1.3, and the degree of acetylation (DSAc) was 0.30, as
determined by size exclusion chromatography (SEC) calibrated with
MALDI-TOF-MS. A representative structure of AcGGM is shown in
Scheme 2.
of Me
ppm (tr, 6 H, CH
NMR (DMSO-d ): δ 57.43, 52.52, 45.64 ppm.
Polymerizations. Polymerizations were conducted in DMSO, DMSO/
O, or DMF. Ligand (Me -TREN), macroinitiator (Br-AcGGM), and
6
-TREN is shown in Scheme 5. H NMR (DMSO-d
6
): δ 2.50
1
3
2
2 3 2
), 2.26 (tr, 6 H, CH ), 2.12 (s, 18 H, N-(CH ) ); C
6
H
2
6
Esterification of AcGGM. The AcGGM macro initiator was
synthesized performing a N,N′-carbonyldiimidazole (CDI)-assisted
esterification of the hydroxyl groups of the polysaccharide backbone
as depicted in Scheme 3. In a first step, 9.73 g CDI (60 mmol, 4 equiv)
was reacted with 10.02 g R-bromoisobutyric acid (RBrIBA; 60 mmol,
monomer (methyl acrylate, MA) in a 1:10:2000 as well as a 1:10:4000
molar ratio were dissolved in DMSO or DMF. Typical amounts were
1.4 µL of Me -TREN (0.005 mmol), 50.95 mg Br-AcGGM (0.05 mmol
6
-Br), and 860 mg MA (10 mmol) in 3 mL of solvent. As catalyst, 6.25
or 12.5 cm of copper wire (20 gauge) was wrapped around the stirring
bar for all polymerizations. The solution was transferred to a Schlenk-
4
equiv) in 80 mL of DMSO at room temperature for 60 min to form

Mediated Living Radical Polymerization
Biomacromolecules, Vol. 12, No. 1, 2011 255
Scheme 4. Representative Structure of the Functionalized Macroinitiator Based on AcGGM
Scheme 5. Me
Eschweiler-Clarke Methylation, Reacting Tris(2-aminoethyl)amine
7) with Formaldehyde and Formic Acid in Excess
6
-TREN (8) is Synthesized via an
1H and 13C NMR spectra were recorded at 500 MHz on a Bruker
DMX-500 nuclear magnetic resonance spectrometer using Bruker
software. Samples of about 20 mg were dissolved in DMSO-d or D O
6 2
(
(
(
Larodan Fine Chemicals AB) in 5 mm o.d. sample tubes.
Thermograms were recorded by Differential Scanning Calorimetry
DSC) using a temperature- and energy-calibrated Mettler Toledo DSC
8
20 purged with nitrogen gas (80 mL/min). The samples were loaded
into 100 µL aluminum caps. Thermograms were recorded from -30
to 200 °C at a heating rate of 10 °C/min by a heating-cooling-heating
cycle. Glass transition temperatures were determined from the second
heating.
Scheme 6. SET-LRP of MA (9) with R-Briba-AcGGM (6) as
Macroinitiator
Results and Discussion
A macroinitiator based on the heteropolysaccharide acetylated
galactoglucomannan (AcGGM) was designed to enable the use
of SET-LRP as a new and powerful approach for the synthesis
of hybrid glycopolymers under benign conditions. The synthetic
route includes (1) esterification of the polysaccharide affording
bromine groups in R position linked to the backbone, (2) the
tube and degassed with six freeze-pump-thaw cycles, flushing with
nitrogen after thawing. Next, the tube was transferred to an oil bath at
2
5 °C and the stirring bar was dropped into the solution, starting the
polymerization. The proceeding polymerization, as schematically
illustrated in Scheme 6, was monitored via H NMR (for conversion)
0
1
Cu -catalyzed, living radical polymerization of a representative
vinyl monomer yielding graft copolymers with a brush-like
architecture. Reaction kinetics and molecular weights of the
resulting hybrid materials are herein elaborated.
and SEC (for molecular weight), taking samples with a steel syringe
at various times under constant nitrogen flow. Products were precipitated
in methanol and dried prior to SEC-measurements.
Esterification of AcGGM. The CDI-assisted esterification
was preferred to acid halides due to observed degradation of
the polysaccharide during the esterification experiments per-
formed with the acid halide. The AcGGM-macroinitiator was
synthesized via the imidazoyl-activated R-bromoisobutyric acid
Characterization. The molecular weights were determined from
filtered samples by Size Exclusion Chromatography (SEC) on a system
based on N,N-dimethylacetamide as eluent, with a flow rate of 0.5 mL/
min at 80 °C. Pullulan standards with narrow molecular weight
distributions were used for calibration.

2
56 Biomacromolecules, Vol. 12, No. 1, 2011
Voepel et al.
Polymerizations. Polymerizations were first conducted in
DMSO with a ligand/macroinitiator/MA molar ratio of 1/10/
2
000. Here, the macroinitiator concentration was constrained
by the limited solubility in the reaction mixture with increasing
monomer concentrations. As shown in Figure 2, the maximum
initiator concentration of 16.6 mmol/L resulted in a living
app
process with the apparent rate constant of propagation (k
p
)
-
1
of 0.0075 min up to 90% conversion. However, due to the
multifunctionality of the macroinitiator, at high conversion,
multiple propagating macroradicals can terminate by recombina-
tion and cause gelation when originating from different mac-
roinitiators. Accordingly, gel formation was observed at con-
versions of 60% and higher, growing adjacently to the copper
wire and outward, swollen in the reaction media. Occurring
cross-linking did slow down the process, resulting in a decrease
app
-1
of k
p
to 0.0038 min due to lowered mobility of the active
centers as well as hindered monomer diffusion. Still, the reaction
proceeded to almost full conversion, producing an insoluble
fraction. However, due to the gel formation, taken samples may
not be representative, which might explain the outliners in Figure
2
n
. The molecular weight (M ) of the soluble fraction increases
1
Figure 1. H NMR spectra of the natural AcGGM (bottom) and of the
linearly with reaction time and approaches 65000 g/mol at full
conversion.
macroinitiator (top).
Hence, further experiments were designed to achieve slower
reaction rates via lowering the radical concentration [P ·], thereby
suppressing gelation as an undesired side reaction. As discussed
earlier, reaction rates in SET-LRP can be enhanced by a
(
2
R-BrIBA) under CO and imidazole elimination in the first step.
The byproduct imidazole catalyzes the covalent coupling to the
AcGGM backbone via esterification.
The precipitated and thoroughly washed product was analyzed
reductive pretreatment of the Cu wire to increase the catalyst
1
by H NMR, as shown in Figure 1. Here, the methyl groups of
0
surface Cu availability and due to a larger amount of Cu(II)X
2
the coupled species shift dependent on their position on the
polysaccharide backbone at 1.96 and 1.82 ppm. Knowing that
the natural degree of acetylation is 0.3, the incorporated methyl
groups and thus the amount of coupled initiator can be quantified
in relation to the signal of the acetyl group at 2.17 ppm. Residual
traces of 2-propanol (around 4 ppm) and DMSO (at 2.71 ppm)
are visible but do not affect the quantitative evaluation of the
product.
Because the probability of having propagating sites situated
in the vicinity of another propagating macroradical in its active
state is increasing with the degree of substitution (DS), a
moderate DS was chosen. Thus, all polymerizations in this work
were conducted with a macroinitiator DS of 0.15, corresponding
to one R-bromine per 6.6 hexose units in average. SEC analysis
revealed a moderate degradation to ∼7000 g/mol.
generated by disproportionation with a substantial improvement
1
8
of the living polymerization process. Here, we focused on
reducing the rate of polymerization by decreasing the catalyst
concentration to avoid gelation.
To overcome the observed gel formation at high macro
initiator concentration, reaction conditions were adapted via
decreasing the initiator concentration to 4.16 mmol/L as well
as reducing monomer and ligand concentration by 50% and, in
addition, the Cu wire to 6.25 cm. However, this did not result
app
-1
in a decrease of k
Importantly, no gelation occurred even at full conversion (Figure
).
Following, a polymerization with a higher initiator/
p
being 0.0043 min here as well.
3
monomer ratio was conducted. Here, a further decrease of
the initiator concentration to 2.08 mmol/L was necessary to
avoid too high viscosity, making sampling impossible at
higher conversions. As seen in Figure 4, this resulted in a
6 6
Me -TREN Synthesis. Me -TREN was synthesized by
performing an Eschweiler-Clark reaction. Tris(2-aminoethyl)-
amine was 6-fold methylated, reacting it with excess formic
acid and formaldehyde under CO
app
-1
2
and H
2
O elimination.
significantly decreased k
p
of 0.0016 min . Nevertheless,
Extraction and purification resulted in a rather low final yield
the reaction proceeded living until complete conversion.
Increased viscosity and thus a nonrepresentative sampling
at high conversion is seen as the reason for the outliner at
2880 min. Expected graft yield corresponds to around three
PMA grafts per macroinitiator molecule which is reasonable
1
13
1
(
13%) but high purity, as proven with H and C NMR. H
NMR (DMSO-d ): δ 2.50 (tr, 6 H, CH ), 2.26 (tr, 6 H, CH ),
); C NMR (DMSO-d ): δ 57.43, 52.52,
6
2
2
13
2
.12 (s, 18 H, N-(CH
5.64 ppm.
)
3 2
6
4
Figure 2. Kinetic plots for SET-LRP of MA (L/I/M ) 1/10/2000), 12.5 cm Cu wire, and an initiator concentration of 16.6 mmol/L in DMSO.

Mediated Living Radical Polymerization
Biomacromolecules, Vol. 12, No. 1, 2011 257
Figure 3. Kinetic plots for SET-LRP of MA (L/I/M ) 1/10/2000), 6.25 cm Cu wire, and an initiator concentration of 4.16 mmol/L in DMSO.
Figure 4. Kinetic plots for SET-LRP of MA (L/I/M ) 1/10/4000), 6.25 cm Cu wire, and an initiator concentration of 2.08 mmol/L in DMSO.
Figure 5. Kinetic plots for SET-LRP of MA (L/I/M ) 1/10/2000), 6.25 cm Cu wire, and an initiator concentration of 4.16 mmol/L in a 90/10 (v/v)
2
DMSO/H O solution.
Figure 6. Kinetic plots for SET-LRP of MA (L/I/M ) 1/10/2000), 6.25 cm Cu wire, and an initiator concentration of 4.16 mmol/L in DMF.
app
-1
with respect to degree of substitution and steric effects. The
molecular weights are here however less than expected. This
is explained by the significant change in solubility parameters
that affects the hydrodynamic volume and thus the calculated
molecular weights.
k
p
decreases from 0.0035 to 0.0007 min during the
-
1
reaction as compared to 0.0043 min in pure DMSO. This
can be attributed to a decreased solubility of the dormant
chain end in the reaction mixture and, thus, a lowered
concentration of active propagating macroradicals. The
Protic solvents like water are not only tolerated in SET-
LRP but are actually shown to increase the rate of propagation
due to the increased disproportionation of Cu(I)X into Cu(0)
corresponding SET-LRP was conducted in DMF as well.
app
Here, almost complete conversion was observed with a k
of 0.0039 min .
p
-
1
2
,16
and Cu(II)X
2
.
Hence, a 90:10 (% v/v) DMSO/H
2
O solution
Polymerization in DMF (Figure 6) was observed to proceed
with significantly lower viscosity as compared to DMSO. The
molecular weight at full conversion is dramatically higher
than expected based on the calculated graft yield. A
contributing factor may be the tendency for agglomeration,
was evaluated for its applicability in the SET-LRP with an
AcGGM-derived macroinitiator. Figure 5 shows the kinetic
plots of this experiment. The reaction proceeds in a controlled
way until precipitation at around 80% conversion. However,

2
58 Biomacromolecules, Vol. 12, No. 1, 2011
Voepel et al.
Table 1. Comparative Solubility Data
(9) Rosen, B. M.; Percec, V. J. Polym. Sci., Part A: Polym. Chem. 2008,
4
6 (16), 5663–5697.
PMA-grafted
AcGGM at high
conversion
(
10) Jiang, X.; Fleischmann, S.; Nguyen, N. H.; Rosen, B. M.; Percec, V.
J. Polym. Sci., Part A: Polym. Chem. 2009, 47 (21), 5591–5605.
11) Guliashvili, T.; Percec, V. J. Polym. Sci., Part A: Polym. Chem. 2007,
45 (9), 1607–1618.
(12) Jiang, X. A.; Rosen, B. M.; Percec, V. J. Polym. Sci., Part A: Polym.
Chem. 2010, 48 (12), 2716–2721.
(13) Fleischmann, S.; Rosen, B. M.; Percec, V. J. Polym. Sci., Part A:
Polym. Chem. 2010, 48 (5), 1190–1196.
(14) Lligadas, G.; Percec, V. J. Polym. Sci., Part A: Polym. Chem. 2008,
unmodified
AcGGM
solvent
macroinitiator
(
a
b
d
H
2
O
++
+
--
a
a
a
DMSO
DMF
DMAc
THF
++
++
++
b
b
a
+
+
++
d
a
a
--
++
++
d
d
c
--
--
--
-
d
d
c
CHCl
3
--
-
4
6 (20), 6880–6895.
a
b
c
d
+
+, easily soluble. +, slightly soluble. -, agglomeration. --,
(
(
(
15) Nguyen, N. H.; Jiang, X.; Fleischmann, S.; Rosen, B. M.; Percec, V.
J. Polym. Sci., Part A: Polym. Chem. 2009, 47 (21), 5629–5638.
16) Nguyen, N. H.; Rosen, B. M.; Jiang, X.; Fleischmann, S.; Percec, V.
J. Polym. Sci., Part A: Polym. Chem. 2009, 47 (21), 5577–5590.
17) Rosen, B. M.; Jiang, X.; Wilson, C. J.; Nguyen, N. H.; Monteiro,
M. J.; Percec, V. J. Polym. Sci., Part A: Polym. Chem. 2009, 47 (21),
insoluble.
also observed during the synthesis and possibly preserved
in liquid media resulting in a marked increase in hydrody-
namic volume.
The poly(methyl acrylate), PMA, produced at high conver-
sion by the described SET-LRP approach using an AcGGM-
based macroinitiator have thermal properties similar to that
of conventional PMA as compared to unmodified AcGGM
that do not show any clear-cut glass transition. PMA derived
by AcGGM-initiated SET-LRP with an initiator concentration
of 4.16 mmol/L are amorphous with a glass transition
5
606–5628.
18) Nguyen, N. H.; Percec, V. J. Polym. Sci., Part A: Polym. Chem. 2010,
8 (22), 5109–5119.
(
(
4
19) Wright, P. M.; Mantovani, G.; Haddleton, D. M. J. Polym. Sci., Part
A: Polym. Chem. 2008, 46 (22), 7376–7385.
(20) Rosen, B. M.; Lligadas, G.; Hahn, C.; Percec, V. J. Polym. Sci., Part
A: Polym. Chem. 2009, 47 (15), 3940–3948.
(
21) Lligadas, G.; Percec, V. J. Polym. Sci., Part A: Polym. Chem. 2007,
4
5, 4684–4695.
(
22) Zhai, S.; Wang, B.; Feng, C.; Li, Y.; Yang, D.; Hu, J.; Lu, G.; Huang,
temperature (T
is typically amorphous with a T
g
) between 15.7 and 19.7 °C. Commercial PMA
X. J. Polym. Sci., Part A: Polym. Chem. 2010, 48 (3), 647–655.
(23) Sienkowska, M. J.; Rosen, B. M.; Percec, V. J. Polym. Sci., Part A:
Polym. Chem. 2009, 47 (16), 4130–4140.
5
3
g
around 6-9 °C. The
solubility properties for unmodified AcGGM, the AcGGM-
derived macroinitiator, and PMA-grafted AcGGM at high
conversion is summarized in Table 1.
(
(
(
(
(
24) Fleischmann, S.; Percec, V. J. Polym. Sci., Part A: Polym. Chem. 2010,
8 (10), 2236–2242.
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6 (38), 7181–7183.
4
4
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Sci., Part A: Polym. Chem. 2009, 47 (17), 4420–4427.
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Conclusions
The hemicellulose acetylated galactoglucomannan (AcGGM)
was successfully functionalized by R-bromoisobutyric acid to
a degree of substitution of 0.15 yielding a new and effective
multifunctional macroinitiator for SET-LRP. SET-LRP of MA
(29) Zoppe, J. O.; Habibi, Y.; Rojas, O. J.; Venditti, R. A.; Johansson,
0
L.-S.; Efimenko, K.; O I` sˇ terberg, M.; Laine, J. Biomacromolecules
was performed at 25 °C catalyzed by Cu /Me
6
-TREN and the
2
010, 11 (10), 2683–2691.
AcGGM-based macroinitiator yielding graft copolymers with
(
(
(
(
30) Hatano, T.; Rosen, B. M.; Percec, V. J. Polym. Sci., Part A: Polym.
Chem. 2009, 48 (1), 164–172.
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-
1
molecular weights ranging from 4300 to 263,000 g mol . The
initiator concentration is limited by the tendency of product
gelation. Kinetic analyses confirm the living character of the
polymerizations and reveal a more rapid propagation in DMSO
2
than in DMF or DMSO/H O (90:10% v/v) proceeding to almost
full conversions regardless of the solvent used. AcGGM-initiated
SET-LRP of MA is a powerful approach to the design of hybrid
graft glycopolymers.
4
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(
(
(
(
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Acknowledgment. The authors gratefully acknowledge KTH
and Formas (Project No. 243-2008-129) and for financial
support.
4
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