Synthesis of SET-LRP-induced galactoglucomannan-diblock copolymers

Article abstract of DOI:10.1002/pola.26942

Polysaccharides are biorenewable and biodegradable starting materials for the development of functional materials. The synthesis of a monofunctional macroinitiator for single electron transfer-living radical polymerization was successfully developed from a wood polysaccharide-O-acetyl galactoglucomannan (GGM) using a beforehand synthesized amino-functional α-bromoisobutyryl derivative applying reductive amination. The GGM macroinitiator was employed to initiate a controlled radical polymerization of [2-(methacryloyloxy)ethyl] trimethylammonium chloride (MeDMA), methyl methacrylate (MMA), and N-isopropylacrylamide (NIPAM) using Cu⁰/Me₆-Tren as a catalyst. The either charged or amphiphilic GGM-b-copolymers with different chain lengths of the synthetic block were successfully synthesized without prior hydrophobization of the GGM chain and dimethyl sulfoxide (DMSO) or DMSO/water mixtures were used as solvents. This novel synthetic approach may find untapped potentials particularly for the development of polysaccharide-based amphiphilic additives for cosmetics or paints and for the design of novel temperature or pH responsive polymers with such potential applications as in drug delivery systems or in biocomposites. Copyright

Full text of DOI:10.1002/pola.26942

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Synthesis of SET–LRP-Induced Galactoglucomannan-Diblock Copolymers
1
1,2
3
1
4
1
Daniel Dax, Chunlin Xu, Otto L a˚ ngvik, Jarl Hemming, Peter Backman, Stefan Willf o€ r
1
˚
Process Chemistry Centre, c/o Laboratory of Wood and Paper Chemistry, Abo Akademi University, Porthansgatan 3,
˚
2
0500 Abo/Turku, Finland
2
Wallenberg Wood Science Center, KTH the Royal Institute of Technology, 10044 Stockholm, Sweden
3
˚
Process Chemistry Centre, c/o Laboratory of Organic Chemistry, Abo Akademi University, Biskopsgatan 8,
˚
2
0500 Abo/Turku, Finland
4
˚
Process Chemistry Centre, c/o Laboratory of Inorganic Chemistry, Abo Akademi University, Biskopsgatan 8,
˚
2
0500 Abo/Turku, Finland
Correspondence to: C. Xu (E-mail: cxu@abo.fi)
Received 31 May 2013; accepted 2 September 2013; published online 25 September 2013
DOI: 10.1002/pola.26942
ABSTRACT: Polysaccharides are biorenewable and biodegrad-
able starting materials for the development of functional mate-
rials. The synthesis of a monofunctional macroinitiator for
single electron transfer-living radical polymerization was suc-
cessfully developed from a wood polysaccharide-O-acetyl gal-
phobization of the GGM chain and dimethyl sulfoxide (DMSO)
or DMSO/water mixtures were used as solvents. This novel
synthetic approach may find untapped potentials particularly
for the development of polysaccharide-based amphiphilic addi-
tives for cosmetics or paints and for the design of novel tem-
perature or pH responsive polymers with such potential
applications as in drug delivery systems or in biocomposites.
actoglucomannan (GGM) using
a beforehand synthesized
amino-functional a-bromoisobutyryl derivative applying reduc-
tive amination. The GGM macroinitiator was employed to initi-
ate a controlled radical polymerization of [2-(methacryloyloxy)
ethyl]trimethylammonium chloride (MeDMA), methyl methac-
V
C
2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym.
Chem. 2013, 51, 5100–5110
0
rylate (MMA), and N-isopropylacrylamide (NIPAM) using Cu /
Me
6
-Tren as a catalyst. The either charged or amphiphilic
KEYWORDS: amphiphilic; biodegradability; biorenewable; block-
copolymer; O-acetyl galactoglucomannan; polysaccharide;
SET-LRP; stimuli-responsive
GGM-b-copolymers with different chain lengths of the syn-
thetic block were successfully synthesized without prior hydro-
INTRODUCTION An important challenge in times of increas-
ing demand of energy and raw materials for the chemical
industry is the effective use of natural resources. Because of
a simultaneous rise of prices it is hence not surprising that
polysaccharides have moved into the focus of many research
groups around the world. The natural occurring polysaccha-
rides such as cellulose, starch, and hemicelluloses represent
valuable biorenewable and biodegradable starting materials
for new and innovative chemical products. One of the prom-
ising hemicelluloses is O-acetyl galactoglucomannan (GGM)
from Norway spruce (Picea abies). Water soluble GGM can
be extracted from the wood matrix by pressurized hot-water
and the O-acetyl groups are located randomly at C2 and C3
7
position of the mannose units in the main chain. Native
GGM and modified GGMs have been studied in such applica-
8
9
10
11
tions as emulsions, films, barriers, and biocomposites.
To synthesize new GGM derivatives, the hydroxyl groups of
the polysaccharide chain have been randomly targeted by
1
0
introducing new functionalities or the reducing end was
1
2
selectively chemically modified. A novel and versatile way
of synthesizing polysaccharides grafted with hydrophobic
1
3
moieties is the use of polymerization techniques. A reactive
group able to start controlled radical polymerization can be
reacted with the hydroxyl groups of the polysaccharides. In a
consecutive polymerization a large variety of commercially
1
extraction (PHWE) or can be isolated from the wastewater
2
–5
of thermomechanical pulp processes by ultrafiltration.
GGM consists of a linear backbone of randomly distributed
1!4)-linked b-D-mannopyranosyl (Manp) and (1!4)-linked
b-D-glucopyranosyl (Glcp) units, with a-D-galactopyranosyl
1
4,15
13,16
available monomers, such as acrylates,
styrene, or methacrylates
acrylamides,
can be used. Different techni-
ques for controlled polymerization, such as atom transfer
1
7
18,19
(
6
20–22
(
Galp) units as single side units. GGM is partially acetylated
radical polymerization (ATRP)
and single electron
Additional Supporting Information may be found in the online version of this article.
2013 Wiley Periodicals, Inc.
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2
3,24
transfer-living radical polymerization (SET-LRP)
have
Methyl tert-butyl ether (MTBE) was obtained from Fluka.
Ethanol (ꢀ99.5 vol %) was purchased from Altia Oyj. Pyridine
and 1,4-dioxane were received from VWR. Acetone and tetra-
hydrofuran (THF) were obtained from J.T. Baker. Acetic anhy-
dride was purchased from Riedel-de Ha €e n. All the materials
were used without further purification unless mentioned
otherwise.
been applied to modify polysaccharides. SET-LRP has been
emphasized to be a powerful method for controlled radical
polymerization in different solvents, including water-based
mixtures. The metal-catalyzed reaction pathway of SET-LRP
is based on the reversible activation of a macroradical using
copper as a single electron donor. Therefore, elemental cop-
0
I
per (Cu ) or Cu salts, such as Cu S or Cu O in combination
2
2
Pressurized hot-water extracted GGM from Norway spruce
(Picea abies) was provided by The Finnish Forest Research
Institute Metla. GGM was obtained as a solution with concen-
tration of 30 wt.-%. The extract was further purified to
remove impurities and to narrow down the molar mass dis-
tribution [low polydispersity (PDI)]. Therefore, the concen-
trated GGM solution (330 mL) was diluted with water
(670 mL) and then precipitated in 9 L of ethanol at room
temperature. The white precipitate was filtrated off and con-
secutively washed with ethanol, acetone, and MTBE and
finally the solid GGM was freeze-dried. The purified GGM had
with
a
nitrogen-containing ligand, as for example
0
00 00
2
13
N,N,N ,N ,N -pentamethyldiethylenetriamine (PMDETA) or
3
Me -Tren, were applied.
6
Besides the polysaccharides grafted with synthetic polymers,
also the synthesis of block-structured copolymers has moved
into focus.
of the native polysaccharide chain is fully preserved in the
final products. The most studied approach for the synthesis of
block-copolymers of polysaccharides is the coupling of before-
hand synthesized end group functionalized synthetic polymers
2
5–27
In these well-defined copolymers, the integrity
2
8–30
3
21
at the reducing end of the polysaccharide chain.
This
a weight average molar mass (M ) of 7.1 3 10 g mol and
w
3
21
method implies long reaction times due to the lack of compat-
ibility of the two polymer blocks and laborious work-up and
purification steps are needed. Surprisingly, despite its high
potential, only a few synthetic pathways for amphiphilic poly-
saccharide block-copolymers using a polysaccharide macroini-
tiator have been described up to now.
of polysaccharides in organic solvents made hydrophobization
of the polysaccharide
could be performed. Although reversible acetylation and tri-
methylsilylation are common procedures to solubilize polysac-
charides in organic solvents, this strategy implies two
supplementary steps in the synthesis pathway.
copolymers in general and especially block-copolymers of
a number average molar mass (M ) of 4.8 3 10 g mol
n
(polydispersity ꢁ 1.5), as determined by HPSEC. The sugar
unit ratio of GGM was determined by acid methanolysis and
gas chromatography and was around 5–4:1:0.5–1.1 (Man:
3
7
4
Glc:Gal) and the degree of acetylation (DS ) ꢁ 0.20.
Ac
2
0,25
The poor solubility
Synthesis
2
0,31
Synthesis of Me -TREN
6
necessary before the polymerization
3
8
Me -TREN was synthesized as reported earlier. Formic acid
6
(
15.7 g of 98% (v/v) solution, 0.34 mol, 10 equiv.) and form-
aldehyde (6.8 g of 37% (v/v) solution, 0.23 mol, 6.7 equiv.)
were mixed in a round-bottled flask and cooled down to 0
2
5
Block-
ꢂ
3
2
C using an ice bath. Consecutively, tris(2-aminoethyl)amine
5 g, 0.034 mol, 1 equiv.) in 20 mL of H O were added drop-
(
polysaccharides have promising properties for the application
2
2
5
wise to the mixture and the temperature was kept below 4
as “green” structural and functional materials and hence
there is a need for more effective and diverse synthetic
routes. Amphiphilic polysaccharides have been shown to have
the ability to form well defined structures
surfactants, as well as foaming agents or active constituent
in thermo responsive nanoparticles.
copolymers containing sugar moieties were proved to have
potential application in controlled drug release systems. In
this study, we describe a versatile method to synthesize GGM-
b-copolymers using a GGM macroinitiator applying SET-LRP
ꢂ
C. After the addition of tris(2-aminoethyl)amine, the reac-
ꢂ
tion mixture was stirred for 1 h at 0 C and then slowly
ꢂ
ꢂ
3
3,34
heated up to 100 C. The reaction was kept at 100 C for
15 h and then the volatile compounds were evaporated under
reduced pressure. The pH of the orange residue was adjusted
to 10 using a 1 M NaOH solution. The crude product was col-
lected by extracting with dichloromethane and consecutively
and to act as
3
0
3
5
Amphiphilic block-
3
6
washed with a saturated NaCl solution and H O. After evapo-
2
ration of the organic solvent, the product was obtained as
clear yellow oil (1.4 g, 8.9 mmol, 26% yield).
0
with Cu as a copper source and Me -Tren as a ligand.
6
1
ꢂ
H NMR (600 MHz, CDCl , 25 C, d): 2.24 (s, 18 H, NAMe ),
3
2
2
.39 (tr, 6 H, NA(CH ACH ANAMe ) ), 2.62 (tr, 6 H,
EXPERIMENTAL
2 2 2 3
9
3
NA(CH ACH ANAMe ) .
2
2
2 3
Materials
Methyl methacrylate (MMA) (99%, Aldrich) and dimethyl sulf-
oxide (DMSO) (Merck) were distilled under reduced pressure
and then stored in argon atmosphere. Di-tert-butyl-dicarbon-
ate (97%), tris(2-aminoethyl)amine (96%), ethylenediamine
Preparation of tert-Butyl-N-(2-aminoethyl) carbonate
The synthesis of the amino functional coupling agent con-
taining the initiator group has been synthesized previously
and a similar synthesis route was applied. A solution of di-
2
0
(
EDA, ꢀ99.5%), sodium cyanoborohydride (NaBH CN, 95%),
tert-butyl-dicarbonate (BOC O) (17.5 g, 80 mmol) in 180 mL
3
2
a-bromoisobutyryl bromide (BIBB, 98%), triethylamine (Et
9
thyl]trimethylammonium chloride (MeDMA, 80 wt % in H O)
and the copper bars (99.999%) were purchased from Aldrich.
3
N,
of 1,4-dioxane was dropped into a stirred solution of ethyl-
enediamine (36 g, 600 mmol, 7.5 equiv.) in 180 mL of 1,4-
dioxane over a period of 5 h at room temperature. After
additional 48 h stirring at room temperature, the formed
9%), N-isopropylacrylamide (NIPAM), [2-(methacryloyloxy)e-
2
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ꢂ
GGM-b-pMeDMA: H NMR (600 MHz, D O, 35 C, d): 2.08–
2
precipitate was filtered off and the solvent was evaporated
at reduced pressure. To the residue 300 mL, distilled water
2
1
3 2
2.14 (s, 6 H, ACA(CH ) ABr). IR (cm ): 1640 (C@O
0
was added and the water-insoluble bis(N,N -tert-butyloxycar-
stretch).
4
0
bonyl)-1,2-diaminoethane was removed by filtration. The
product was extracted by dichloromethane from the aqueous
solution saturated with NaCl. The organic phase was dried
over Na SO and the solvent was evaporated under reduced
SET-LRP Using the GGM Macroinitiator
For the polymerizations, three different unsaturated mono-
mers (MeDMA, NIPAM, and MMA) were used. Before starting
2
4
pressure to give tert-butyl-N-(2-aminoethyl) carbonate (NH2-
the polymerizations, DMSO, H O, and MMA were distilled
2
BOC) (7.68 g, 48 mmol, 60% yield).
and kept under argon. A solution of Me -TREN (0.05 mol
6
2
1
L
) in DMSO was prepared and kept under argon. The poly-
1
ꢂ
H NMR (600 MHz, DMSO-d , 25 C, d): 1.36 ppm (s, 9 H,
6
merizations using the different monomers were conducted
under similar conditions; in the following the procedure is
exemplary shown for NIPAM.
(
CH ) ACA), 2.52 (tr, 2 H, ACH ANH ), 2.90 (tr, 2 H,
3 3 2 2
4
0
ACHANHA).
Amidation of a-Bromoisobutyryl bromide (BIBB) with
GGM-Br (49.4 mg, 0.01 mmol, 1 equiv.), five pieces of copper
and NIPAM (50 mg, 0.44 mmol, 44 equiv.) were introduced
in a Schlenk tube equipped with a magnetic stirrer. The tube
was consecutively degassed under argon (three cycles) and 3
NH -BOC
2
BIBB (16.6 g, 72 mmol, 1.5 equiv.) in 50 mL of THF was
slowly added to a solution of NH -BOC (7.68 g, 48 mmol, 1
2
equiv.) in THF (150 mL) in the presence of Et N (9.7 g, 96
3
mL of H O and 1 mL of DMSO were added. The reactants
2
mmol, 2 equiv.). The temperature during the addition of
ꢂ
were dissolved by stirring at 40 C and the solution was
ꢂ
BIBB was kept at 0 C. After 1 h, the addition was completed
again degassed carefully under argon (three cycles). To start
and the solution was stirred for 24 h at room temperature.
The formed triethylammonium bromide was filtered off as a
white solid. The organic solvent was removed under reduced
pressure and the crude product was redissolved in methanol
and precipitated into water saturated with Na CO . After
the polymerization, the Schlenk tube was transferred to an
ꢂ
oil bath (40 C) and then Me -Tren (100 lL of the previous
6
prepared solution, 1.15 mg, 0.005 mmol, 0.5 equiv.) was
added. After 30 h, the copper pieces were removed and the
reaction mixture was precipitated in cold acetone. The prod-
uct was collected by centrifugation and washed twice with
cold acetone. To remove copper residues, the product was
dissolved in distilled water and dialyzed against distilled
water. The purified copolymer was received after freeze-
drying.
2
3
drying the product was collected as a white solid (11.0 g,
3
1
5.6 mmol). The BOC-protected initiator (11.0 g, 35.6 mmol,
equiv.) was dissolved in 70 mL of ethyl acetate and hydro-
3
4
gen chloride gas was bubbled into the solution. An excess
of hydrogen chloride gas was formed by the addition of a
3
7% hydrogen chloride solution into concentrated H SO .
2 4
After the bubbling was completed the reaction mixture was
stirred for 1 h at room temperature. The organic solvent was
evaporated under reduced pressure. To the residue, 40 mL
of water was added and the insoluble fraction was filtered
off. The aqueous fraction was freeze-dried and yielded a
For the polymerization of MeDMA the same solvent mix-
ture was applied as for NIPAM, but for MMA, pure DMSO
(4 mL) was used. The GGM-b-pMMA derivatives were not
soluble in water and to remove solvent and copper resi-
dues the samples were swollen in water and transferred in
dialyses tubes with consecutive dialyses against distilled
water.
white solid (NH -Br) (7.2 g, 34.5 mmol, 72 % yield).
2
1
ꢂ
H NMR (600 MHz, D O, 25 C, d): 1.94 ppm (s, 6 H,
2
1
ꢂ
ACA(CH ) ), 3.17 (tr, 2 H, ACH ANH ), 3.55 (tr, 2 H,
GGM-b-pMeDMA: H NMR (600 MHz, D O, 35 C, d): 0.97–
3
2
2
2
2
4
1
ACH
2
ANHA).
1.52 (3 H, ACACH ), 1.95–2.37 (2 H, ACH ACA), 3.40 (9 H,
3
2
ANA(CH
3
)
3
), 3.95 (2 H, ANACH
2
A), 4.64 (2 H,
Synthesis of the GGM Macroinitiator
21
ANACH ACH A); IR (cm ): 2989 (v CAH), 1721 (v C@O
2
2
s
s
GGM (2.38 g, 0.50 mmol, 1 equiv.) was dissolved in 90 mL
H O and NH -Br (0.63 g, 3 mmol, 6 equiv.) was added. The
1
(
ester)), 1151 (v CAN). GGM-b-pMMA: H NMR (600 MHz,
s
2
2
ꢂ
DMSO-d , 35 C, d): 1.23 (3 H, ACACH ), 2.05 (2 H,
6
3
ꢂ
solution was heated up to 50 C and the pH was adjusted to
. Consecutively, NaBH CN (1.5 g, 23.9 mmol, 50 equiv.) was
21
ACH ACA), 3.59 (3 H, OACH ); IR (cm ): 2900 (v CAH),
2
3
s
4
1
3
1
727 (v C@O), 1242 (v CAO). GGM-b-pNIPAM: H NMR (600
s s
ꢂ
added to the solution and the reaction mixture was stirred
MHz, DMSO-d
6 3 2
, 35 C, d): 1.07 (6 H, ACHA (CH ) ), 1.20–
ꢂ
at 50 C. After 8 h NaBH
3
CN (1.5 g, 23.9 mmol, 50 equiv.)
1.68 (2 H, CH ACH), 1.79–2.21 (1 H, CH ACHA), 3.79–3.98
2
2
was added and the reaction was stirred for another 16 h at
21
(1 H, NHACHA), 6.90–7.43 (1 H, ANHA); IR (cm ): 2969–
ꢂ
50
C. The reaction was stopped and the reaction solution
2
875 (v CAH), 1642 (v C@O (amide).
s s
was precipitated in 800 mL of cold EtOH with a subsequent
filtration of the product. The solid product was re-dissolved
in H O and dialyzed against distilled H O. After freeze-
HPSEC
2
2
Native GGM and the GGM derivatives had different solubility
in water and organic solvents. To assure the reliability of the
results the HPSEC measurements were performed in water
for native GGM and its water-soluble derivatives and in THF
for the less water-soluble derivatives.
drying, a white solid was obtained (1.1 g, 0.23 mmol, 46%
1
13
yield). The product was analyzed by H and C NMR and
the results are presented in the result and discussion
section.
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TABLE 1 Reaction Conditions for the Polymerizations and the Molar Masses Determined by H NMR and HPSEC Measurements
a
b
21
c
21
Monomer
[M]/[I]
M
n,theo
.
(g mol
)
M
n,NMR (g mol
)
SEC
21
M
n
(g mol
)
M /M
w n
d
d
MeDMA
MeDMA
MeDMA
MMA
9
6,750
9,750
44,750
5,750
6,750
9,750
14,750
9,750
15,610
–
8,400
1.32
1.73
1.61
1.52
1.72
2.70
2.78
1.99
1.95
d
d
d
e
e
e
e
e
e
24
193
10
20
50
100
44
96
5,500
21,300
5,500
5,600
5,800
6,700
5,800
9,600
9,200
d
50,000
e
5,200
e
MMA
6,600
e
MMA
8,100
e
e
e
MMA
11,400
14,300
16,900
NIPAM
NIPAM
a
c
1
Monomer to GGM macroinitiator ratio.
Molar mass of the products determined by H NMR.
HPSEC results using 0.1 M NaNO
b
d
e
Theoretical molar mass of the GGM derivatives after polymerization
does not take conversion into account): M theo. 5 (([M]/[I]) 3 (molar
3
solution as eluent.
(
n
,
HPSEC results using THF as eluent (Mn,cal).
mass monomer) 1 (molar mass GGM)).
The weight- and number-average molar mass (M
w
and M
n
)
Mn;calðproductÞ5Mn;THFðproductÞ2½Mn;THFðGGMÞ2Mn;H2OðGGMÞꢃ
and molar mass distribution (MWD) of native GGM were
determined by HPSEC in on-line combination with a multian-
gle laser light scattering (MALLS) detector (miniDAWN,
Wyatt Technology, Santa Barbara, CA) and a refractive index
(1)
where Mn,cal (product) is the calculated value for the
number-average molar mass of the polymerization product
(
RI) detector (Shimadzu Corporation, Japan). A two-column
before acetylation, Mn,THF(product) is the measured M
of the acetylated polymerization product in THF,
n,THF(GGM) is the measured M value for acetylated GGM in
value of native GGM in
n
value
TM
system, 23 Ultrahydrogel linear 300 mm 3 7.8 mm col-
umn (Waters, Milford, MA), in series was used. 0.1 M NaNO
was used as the elution solvent. The flow rate was 0.5 mL
min . A dn/dc value of 0.150 mL g was used. The sam-
ples were filtered through a 0.22 lm nylon syringe filter
before injection. The injection volume was 100 lL. Astra
software (Wyatt Technology, Santa Barbara, CA) was used to
analyze the data.
M
3
n
THF, and Mn;H O(GGM) is the M
2
n
21
21
42
water.
NMR
The native GGM and the GGM-b-copolymers were analyzed
1
13
by H and C NMR measurements using a Bruker Avance
1
13
spectrometer (operation frequency: H: 600.13 MHz; C:
50.92 MHz). For the water-soluble products, D O was used
For the less water-soluble derivatives of GGM, the Mn was
determined by HPSEC with THF as eluent. To increase the
hydrophobicity of the samples they were acetylated before
the analysis. Therefore, 2 mg of material were treated with
2
7
1
2
as a solvent and the water insoluble products were dissolved
in DMSO-d . The temperature for all the experiments with
6
ꢂ
GGM was set to 35 C.
50 lL of pyridine and 250 lL of acetic acid anhydride at
ꢂ
0 C for 2 h. After allowing the excess acetic acid anhydride
1
Calibration of the H NMR Spectra
to react with added ethanol the volatile compounds were
evaporated. The derivatized sample was dissolved in 2 mL of
THF and filtered through a 0.45 lm PTFE syringe filter. Mn
of the acetylated products was determined using polystyrene
standards for calibration after recording retention volumes
with a SEDEX Model 85 ELSD detector (SEDERE, Alfortville,
France). A two-column system, 23 JordiGel DVB 500 Å 300
mm 3 7.8 mm (Jordi Labs, Mansfield, MA), in series was
used. THF containing 1% (v/v) acetic acid was used as elu-
To calibrate the proton spectra, the theoretical integration
value for the peak region from 3.2 to 4.4 ppm was deter-
mined. Beforehand, size exclusion chromatography for native
GGM, as well as a volumetric titration for the determination
of the acetyl-group content was performed. For the calcula-
3
tions, the number average molar mass (M
n
5 4.8 3 10
g
21
mol ) was used. The volumetric titration gave a value of
.16 mmol g (acetyl group per gram of GGM). The amount
2
1
1
of acetyl groups per GGM chain was calculated as shown in
eq 2:
21
tion solvent and the flow rate was 0.8 mL min . The data
were analyzed with Shimadzu software packages CLASS VP
6.1 and GPC for CLASS VP (Shimadzu Corporation, Japan).
n 5M 31:16=10005475031:16=100055:5
(2)
a
n
For the final evaluation of the results (Table 1), the molar
mass of the polymerization products before acetylation was
where Mn is the number average molar mass of GGM, n is
a
estimated by taking the measured M value of native GGM in
water into account (eq 1).
number of acetyl-groups per GGM chain (degree of acetyla-
tion). The degree of acetylation of GGM was 5.5 (referred to
n
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ꢂ
ꢂ
one GGM chain). The amount of sugar units in a GGM chain
C up to 100 C in nitrogen atmosphere. Aluminum pans,
with pinholes in the lid, were used in these tests. The heat
3
21
with a molar mass of 4.8 3 10 g mol containing 5.5 ace-
tyl groups per macromolecule was determined by eq 3,
knowing that the average molar mass of each anhydro-
2
1
flow signals (W g ) (the difference between the sample and
reference) were recorded.
2
1
monomer unit was M 5 162 g mol
.
s
ns5½Mn2na3Maꢃ=Ms5½475025:5343ꢃ=162527:6
where M is the number average molar mass of GGM, n
(3)
RESULTS AND DISCUSSION
n
a
is
Synthesis of the GGM Macroinitiator
the number of acetyl-groups per GGM chain, M
a
is the molar
To enable the synthesis of block-copolymers based on native
GGM, firstly a GGM macroinitiator was synthesized by intro-
ducing an amino-functional starter for SET-LRP at the reduc-
ing end of GGM. Therefore, a beforehand synthesized and
purified amino-functional a-bromoisobutyryl derivative [(1)
in Scheme 1] was reacted in a reductive amination with
mass of one acetyl-group and M is the average molar mass
s
of one sugar unit in GGM.
The total mass of the 5.5 acetyl groups was subtracted from
Mn and it was found that in average one GGM chain con-
sisted of 28 sugar units. For the determination of the theo-
retical value for the integration of the area between 3.2 and
3
GGM using NaBH CN as a reducing agent yielding in a mono-
functional GGM macroinitiator [(2) Scheme 1]. Solvent and
residue free GGM macroinitiator was obtained after dialyses
4.4 ppm in the proton NMR spectra, the amount of protons
showing a signal in this area had to be determined. Every
sugar unit is bearing seven protons, which can be detected
by proton NMR. 28 3 7 led to a total of 196 protons for one
GGM chain. There are two distinguished regions in the pro-
ton spectrum of GGM, the first from 3.2 to 4.4 ppm and the
other one from 4.6 to 5.5 ppm. The region between 4.6 and
1
13
and was analyzed by H NMR and C NMR (DEPT-135). The
1
H NMR spectra of native GGM and GGM macroinitiator are
shown in Figure 1. The signals of the anomeric protons (H-1
00
and H-1 ) of the sugar units, as well as the protons close to
the acetyl-groups (H-9), are situated in the region from 4.6
6
to 5.5 ppm. The CH groups (H-7) of the acetyl groups gave
3
5.5 ppm contains signals of the reducing end protons, as
signals from 2.11 to 2.28 ppm. In the spectra of the GGM
macroinitiator, the CH3 groups (H-12) in the neighborhood
of the bromine gave signals from 1.91 to 1.97 ppm and cor-
respond to six protons. The reaction conditions for the
reductive amination of GGM and the amino-functional a-bro-
moisobutyryl derivative had been optimized to minimize the
amount of the functionalized starter needed for the produc-
tion of the monofunctional GGM macroinitiator. The NMR
results of the three reductive aminations of this study were
compared (Fig. 2) and a decrease of one of the mannose
well as the protons in neighborhood of the acetyl groups,
resulting in 28 1 5.5 5 33.5 protons. Subtracting 33.5 pro-
tons from the total number of protons gave 162.5 protons,
which were taken as the theoretical value for the integration
of the peak region from 3.2 to 4.4 ppm. This value was set
constant for all the spectra evaluated in this work and it was
taken care that the products were solvent-free before meas-
1
uring the H NMR spectra.
FTIR
R
reducing end peaks (a-Manp ) at 5.23 ppm and a simultane-
The infrared spectroscopy measurements were performed
with a Bruker ALPHA series using the ALPHA platinum ATR
single reflection diamond ATR module. The samples were
directly placed on the ATR plate for measurement. The
results were evaluated using the software OPUS from Bruker.
3
ous increase of the signal belonging to the CH groups of the
SET-LRP starter at 1.94 ppm was observed for increasing
conversion.
When taking into account that the integration of the signals
of the CH3 groups equals exactly six protons when the a-
Manp peak had disappeared completely, we assume that no
R
TGA
The thermal stability of GGM and GGM-fatty acid derivatives
was investigated by DSC-TGA (Differential Scanning
Calorimetry-Thermal Gravimetric Analysis) (Q600, TA Instru-
ments). The samples were dried before thermal analysis. The
side reactions occurred and only the desired GGM macroini-
tiator was obtained in which the SET-LRP starter is situated
at the reducing end of GGM. GGM consists of a backbone of
randomly distributed mannose and glucose units and there-
fore glucose or mannose units are situated at the reducing
ꢂ
21
heating rate in the experiments was 10 C min up to 600
ꢂ
1
C under nitrogen. A platinum cup was used in these tests.
end. Nevertheless, for the H NMR evaluation of the GGM
R
The weight of the sample and the DTA signals (the difference
between the sample and reference temperature) were
recorded.
macroinitiator only the a-Manp was taken into account
R
R
R
because the b-Manp as well as the a-Glup and b-Glup are
overlapping with other signals of GGM and could hence not
be integrated separately. To prove the complete conversion
of all the reducing end peaks, DEPT-135 NMR spectra of
GGM and of the GGM macroinitiator were recorded (Fig. 3).
Differential Scanning Calorimetry
Differential scanning calorimetry (DSC; Q1000, TA Instru-
ments) measurements were performed in three cycles for
each sample. A first cycle was made to remove additional
In the DEPT-135 spectra the carbons of the acetyl-groups (C-
7) gave a signal at 21.44 ppm. In the GGM spectrum all the
carbons (C-2, 3, 4, 5, and 6) except for the anomeric carbons
gave signals in the peak region from 59.39 to 82.21 ppm.
ꢂ
water from the sample by heating up to 100 C. During the
ꢂ
second cycle the samples were cooled down to 280 C. The
ꢂ
21
heating rate for the third cycle was 10 C min from 280
5
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SCHEME 1 Protection of one amine group of EDA with subsequent amidation of BIBB and deprotection resulting in the amino-
functional starter for SET-LRP (1). Reductive amination of GGM and the amino-functional starter for SET-LRP (2).
0
0
The anomeric carbons (C-1 ) gave signals in the region from
the GGM-b-copolymers were obtained after polymerization of
the respective monomer as white solids. Dialyses against dis-
tilled water had to be performed to remove copper residues
from the crude products. The GGM-b-pMeDMA products with
9
1
2.73 to 106.16 ppm including the reducing end carbons (C-
R
R
), with a-Glup at 92.73 ppm and b-Glup at 98.07 ppm.
R
R
The a-Manp and b-Manp are overlapping and had signals
21
at 94.35 ppm. The synthesized GGM macroinitiator, which
different chain lengths of pMeDMA (up to 21,300 g mol
)
R
1
showed full conversion of the a-Manp in the H NMR spec-
trum, was measured by DEPT-135. At 31.61 ppm a new peak
appeared, which was assigned to the carbon of the CH3-
group of the starter (C-12). Furthermore, all the signals of
the reducing end carbons vanished, thus proving that the
desired GGM macroinitiator with a starter only at the reduc-
ing end of the GGM chain was successfully synthesized.
were highly soluble in water and hence the HPSEC analyses
could be performed in water. The molar masses of the GGM-
b-pMeDMA copolymers were rising accordingly to an
increase in the monomer amount at the start of the reaction.
The polydispersity values for most of the final products
were sufficiently low to assume a controlled living character
of the polymerization and to exclude the recombination of
the reactive chain ends as a side reaction (Table 1). In the
1
Polymerization
H NMR spectra, the characteristic polymer signals of
Different GGM-b-copolymers aiming at distinguished physico-
chemical properties (amphiphilic or charged) were success-
fully synthesized applying the previously designed
monofunctional GGM macroinitiator. To determine the most
suitable conditions for the polymerization of MeDMA, NIPAM,
and MMA using the GGM macroinitiator, atom transfer radi-
cal polymerizations (ATRP) and SET-LRP were performed.
pMeDMA could be assigned (Fig. 4). The GGM-b-pMMA prod-
ucts showed poor solubility in water when the PMMA chain
21
1
was larger than 2000 g mol and the H NMR spectra were
recorded in DMSO-d (Fig. 4). To determine the exact molar
6
mass, the previously acetylated GGM-b-pMMA products were
dissolved in THF and analyzed by HPSEC. Similar to the
GGM-b-pMeDMA, the GGM-b-pMMA copolymers showed
increasing molar masses for an increasing amount of mono-
mer in the reaction mixture. For a monomer to initiator ratio
(M/I) higher than 50 the polydispersity reached values over
2.7 probably caused by recombination of the active species
during the polymerization resulting in ABA-b-copolymer side
products (elution curves are shown in the Supporting Infor-
mation Figs. S1 and S2). One tentative explanation is that the
formation of micelles in the reaction mixture during the
polymerization was likely and, thus the pMMA chains accu-
mulated in the micelle core with progressing polymerization
time and pMMA chain length. This could lead to an accumu-
lation of the reactive chain ends in a relatively small volume
0
00 00
For the ATRP CuBr/PMDETA (N,N,N N ,N -pentamethyldie-
4
0
19
thylenetriamine) and CuBr/Bipyridine were previously
tested as catalyst systems using MMA and MeDMA, respec-
tively, as monomers. The resulting products had very low
molar masses and in both systems fast deactivation of the
catalyst was assumed to be the reason for insufficient con-
1
version of the monomers (determined by H NMR). A less
oxygen sensitive method to perform controlled radical poly-
0
merization was shown to be SET-LRP in which Cu is used
as a copper source and Me -Tren as a ligand (Scheme 2).
6
Me -Tren was synthesized beforehand by performing an
6
Eschweiler–Clarke reaction and was kept under argon. All
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FTIR Spectroscopy
The FTIR spectra for native GGM, the GGM macroinitiator
and the GGM-b-copolymers were recorded at room tempera-
ture (Fig. 5). The spectra of native GGM and the GGM macro-
initiator are similar due to the minor changes to the GGM
2
1
structure. The C@O band of the amide at 1640 cm
was
identified. In the spectrum of GGM-b-pNIPAM the amplifica-
2
1
tion of the bands of valence from 2875 to 2969 cm of the
21
methyl groups and the appearance of a signal at 1642 cm
vsC@O) assigned to the carbonyl group of the amide of pNI-
(
PAM prove the formation of the desired product. In the
measured spectrum of GGM-b-pMMA, also an amplification
2
1
of methyl group signals around 2900 cm
was observed.
Furthermore, the carbonyl stretch signal of the ester bond of
2
1
pMMA (v
s
C@O) could be identified at 1727 cm , as well as
1
FIGURE 1 H NMR spectra of native GGM and the monofunc-
ꢂ
tional GGM macroinitiator recorded in D
2
O at 35 C.
and, hence make recombination and the formation of ABA-b-
copolymers side products more probable. In literature in situ
micelle formation was descript for MMA and styrene when
4
3,44
water was used as a reaction medium.
improved solvent mixture or the beforehand hydrophobiza-
The use of an
2
0
tion of the GGM macroinitiator might enhance the molar
distribution of the AB-b-copolymers with a higher molar
1
mass. For the GGM-b-pNIPAM products, H NMR spectra
were recorded (Fig. 4) and the formation of the desired
product could be proven by the presence of the polymer
peaks in the region from 0.8 to 1.8 ppm, as well as by the
other characteristic signals of pNIPAM. The molar masses
were lower than expected and it might be possible to
achieve a higher molar mass after optimization of the reac-
tion conditions, for example, other solvent resp. solvent
mixtures.
1
FIGURE 2 Inset of the H NMR spectra for different conversions of
R
the mannose reducing end peak (a-Manp ) (A) and the CH -groups
3
from the a-bromoisobutyryl group (B). [Color figure can be viewed
in the online issue, which is available at wileyonlinelibrary.com.]
5
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the corresponding C-O stretch of the ester bond at 1242
2
1
cm (v
s
CAO).
In the spectrum of GGM-b-pMeDMA an amplification of the
21
methyl group signals around 2989 cm and the appearance
of the carbonyl group signal of the ester of pMeDMA at 1721
2
1
cm (v C@O) indicate the formation of the desired product.
s
Also the signal of the amine (v CAN) was observed at 1151
s
2
1
cm . The amplification of the OAH band in the spectrum of
GGM-b-pMeDMA compared to the GGM macroinitiator was
due to water, which was absorbed by the very hygroscopic
sample.
Differential Scanning Calorimetry
The GGM macroinitiator and the GGM-b-copolymers were
analyzed with DSC and no clear T values could be detected
g
(
Supporting information Fig. S4). It is likely that the materi-
als exhibit too weak T signals present under the detection
g
limit. The shift in the heat flow in the region from 21 to 24
ꢂ
C might originate from the GGM backbone. Further, the
ꢂ
water evaporation, seen at temperatures between 25 C and
ꢂ
ꢁ
80 C is interfering and possibly hiding the weak T sig-
g
nals. Trials with multiple cycles to remove water completely
did not succeed.
Thermal Stability
Thermal gravimetric analysis of the GGM macroinitiator and
the different GGM-b-copolymers was carried out. The GGM
macroinitiator showed a mass loss in two stages. The first
FIGURE 3 DEPT-135 spectra of native GGM and the synthe-
ꢂ
ꢂ
sized GGM macroinitiator recorded in DMSO-d
6
at 35 C.
stage in the temperature range between 21 and 210
C
SCHEME 2 Synthesis of the GGM-b-copolymers using [2(methacryloyloxy)ethyl]trimethylammonium chloride (MeDMA), N-isopro-
pylacrylamide (NIPAM), and MMA, respectively.
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ꢂ
from 210 to 600 C. GGM-b-pNIPAM, GGM-b-pMMA, and
GGM-b-pMeDMA showed a similar three-stage decomposition
behavior whereby the mass loss in the temperature range
ꢂ
from 21 to 210 C was due to the desorption of the incorpo-
rated water. Although all the samples were freeze-dried in
the same way before the measurement, the water content
was found to be between 4% for GGM-b-pMMA and 16% for
GGM-b-pMeDMA. This indicated that the GGM-b-pMeDMA
has more pronounced hygroscopic properties, whereas the
GGM-b-pMMA did not incorporate much water due to the
hydrophobic character of the pMMA chain. The second stage
ꢂ
of the slopes from 210 to 340 C was assigned to the decom-
position of the GGM part of the copolymers and the third
1
FIGURE 4 H NMR spectrum of GGM-b-pNIPAM in DMSO-d
6
,
GGM-b-pMeDMA in D O, and GGM-b-pMMA in DMSO-d
2
6
.
corresponded to a mass loss of around 10% and is due to
the desorption of water. In the second stage the GGM macro-
initiator was gradually decomposed in the temperature range
FIGURE 5 FTIR spectra of the GGM macroinitiator GGM-b-
pMMA, GGM-b-pMeDMA, and GGM-b-pNIPAM.
5
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PAM derivatives an application in drug delivery and con-
4
6
trolled release bioactive molecules is conceivable.
ACKNOWLEDGMENTS
D. Dax thanks the National Research Fund of Luxembourg
AFR) for granting him a scholarship. The Graduate School of
(
Biomass Refining (BIOREGS) is thanked for financial support.
C. Xu thanks the funding from Knut and Alice Wallenberg
Foundation via Wallenberg Wood Science Center, Sweden.
This work was also part of the activities at the Åbo Akademi
Process Chemistry Centre. O. L a˚ ngvik thanks Patrik Eklund
for the fruitful discussion supporting the work.
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