Synthetic route effect on macromolecular architecture: From block to gradient copolymers based on acryloyl galactose monomer using RAFT polymerization

Article abstract of DOI:10.1021/ma201208u

Statistical, gradient, and block copolymer containing 2-(2′,3′, 4′,6′-tetra-O-acetyl-β-d-galactosyloxy)ethyl acrylate (AcGalEA) glycomonomer and styrene (S) were synthesized by RAFT polymerization using S-methoxycarbonylphenylmethyl dodecyltrithiocarbonat

Full text of DOI:10.1021/ma201208u

ARTICLE
pubs.acs.org/Macromolecules
Synthetic Route Effect on Macromolecular Architecture: From Block to
Gradient Copolymers Based on Acryloyl Galactose Monomer Using
RAFT Polymerization
Pierre Escalꢀe,†,‡ S. R. Simon Ting,‡ Abdel Khoukh,† Laurent Rubatat,† Maud Save,† Martina H. Stenzel,*,‡
and Laurent Billon*,†
†IPREM Equipe de Physique et Chimie des Polymꢁeres, UMR 5254 CNRS, Universitꢀe de Pau et des Pays de L’Adour, Hꢀelioparc,
2 Avenue du Prꢀesident Angot, 64053 Pau Cedex, France
‡Centre for Advanced Macromolecular Design, School of Chemical Engineering, University of New South Wales,
Sydney NSW 2052, Australia
S Supporting Information
b
ABSTRACT: Statistical, gradient, and block copolymer con-
taining 2-(20,30,40,60-tetra-O-acetyl-β-D-galactosyloxy)ethyl
acrylate (AcGalEA) glycomonomer and styrene (S) were
synthesized by RAFT polymerization using S-methoxycarbo-
nylphenylmethyl dodecyltrithiocarbonate (MCPDT) as con-
trol agent. The block copolymer was synthesized by a two-stage
experiment, whereas the statistical and gradient copolymers
were obtained in one-pot synthesis. Results obtained from the
size exclusion chromatography (SEC) and the nuclear magnetic
resonance (NMR) reveal that the polymers synthesized by
RAFT were controlled. The kinetic of each synthetic route was
investigated, and the reactivity ratio of both monomers was estimated by in situ NMR experiments: rAcGalEA = 0.07 ( 0.01 and rS =
0.7 ( 0.1. Moreover the AcGalEA moieties were deacetylated to achieve potential amphiphilic bioactive copolymer. The
preparation of three different macromolecular architectures to form honeycomb porous films by breath figure process was
investigated using atomic force microscopy (AFM).
’ INTRODUCTION
acrylamide galactose derivative with N-acryloylmorpholine.
Polymer chains with a very slight gradient microstructure were
prepared, and reactivity ratio of the monomers was not investi-
gated to control the gradient profile.
In this article, we report for the first time the synthesis of
amphiphilic copolymer with a gradient architecture by reversible
additionꢀfragmentation chain-transfer (RAFT) polymerization
using a trithiocarbonate control agent (Scheme 1). A compre-
hensive characterization of the polymer chain architecture was
conducted and the synthetic methodology effect on the macro-
molecular architecture was also investigated. A particular effort in
the determination of reactivity ratio of AcGalEA and S mono-
mers was made considering that any values for this kind of
monomer are indeed available in the literature.
In recent years, glycopolymers (i.e., polymers carrying pen-
dant carbohydrate moieties) have received increasing attention
due to the numerous biological mechanisms in which carbo-
hydrates are implicated. The biological mechanisms include cell-
to-cell recognition, inflammation, signal transmission and infec-
tion.1ꢀ4 Glycopolymers could be also used for drug delivery
nanoreactors, radio-labeled sugarꢀnucleotide donors, surfaces
modifications, and cell surface receptor.5ꢀ10
These polymers can be obtained by postpolymerization glyco-
sylation reaction or polymerization of galactose containing mono-
mers.11ꢀ21 Various controlled living polymerization techniques
such as ring-opening metathesis polymerization (ROMP),22,23
living anionic polymerization,24 nitroxide-mediated radical po-
lymerization (NMP),18,20,25ꢀ29 atom transfer radical polymeri-
zation (ATRP),19,30ꢀ34 and reversible additionꢀfragmentation
chain-transfer polymerization (RAFT)11ꢀ15,35ꢀ39 were employed
for the synthesis of homopolymers, block copolymers, and hyper-
branched polymers. To date, only Charreyre et al. reported the
synthesis of gradient glycopolymer architectures by the RAFT
process.40 In this work, biotin end-functionalized hydrophilic
glycopolymers were synthesized using copolymerization of an
Moreover, we studied the ability of different architectures such
as block, statistical, and gradient to form potential bioactive
honeycomb porous surface. Highly organized porous surfaces
can be obtained by fast evaporation of solvent in appropriate
Received: May 27, 2011
Revised:
July 4, 2011
Published: July 14, 2011
r
2011 American Chemical Society
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Scheme 1. Structure of S-Methoxycarbonylphenylmethyl Dodecyltrithiocarbonate (MCPDT) RAFT Agent and 2-(20,30,40,60-
Tetra-O-acetyl-β-D-galactosyloxy)ethyl Acrylate (AcGalEA) Glycomonomer
conditions.41,42 This simple, inexpensive, and robust bottom-up
mechanism of pattern formation is known as the breath figure
approach (BFA). This phenomenon occurs when vapor con-
denses onto a cold solid or liquid surface.43,44 The created breath
figure template can be trapped by a polymer solution yielding to a
porous film. The pores are the result of empty water drop-
lets. The regular arrays of pores may be favored by Bꢀenardꢀ
Marangoni convection taking place in solution presenting a
thermal gradient.45,46 Several parameters such as polymer con-
centration, solvent, substrate, inert gas flow, chain-end function-
ality, and relative humidity can induce the control of pores
ordering and diameters.47ꢀ50 Honeycomb films from BFA could
find potential applications such as superhydrophobic surface,
microelectronic, optoelectronic, photonics, sensors, photovol-
taic, and also for biomedical applications.51ꢀ57 Indeed, bioactive
moieties that are immobilized onto a surface might serve for
protein immobilization or for screening devices.6,58
Reaction was left for 48 h. The final suspension was filtered in order to
remove the molecular sieves and washed three times with saturated salt
solution. The resulting organic phase was removed under reduced
pressure and purified by flash chromatography using 254 nm UV
detection and cyclohexane/ethyl acetate (3:2) as eluent. The final
solution was placed under reduced pressure for 48 h. Purity of the
crystallized product was confirmed by mass spectroscopy and 1H NMR
(see Figures SI-1 and SI-2 in Supporting Information). ESI-MS (in
methanol) calculated for C19H30O12N + NH4+ m/z, 464.20; found, m/z
464.18. 1H NMR (CDCl3, 400 MHz) δ (ppm): 1.98, 2.02, 2.05, 2.15 (s,
12H, 4 CH3), 4.53 (d, anomeric 1H), 5.0, 5.2 (dd, 2H, CH sugar
moiety), 5.4 (d, 1H, CH sugar moiety), 5.8 (m, 1H, vinylic H), 6.1 (m,
1H, vinylic H), 6.4 (m, 1H, vinylic H). 13C NMR (CDCl3, 400 MHz)
δ (ppm): 20.56, 20.64 (s, 12C, 4 CH3), 61.27 (s, 1C, CH2ꢀC(O)dO),
63.27 (s, 1C, CH2ꢀCH2ꢀC(O)dO), 66.98, 68.61, 70.84 (s, 3C, sugar
moiety CH), 67.41 (s, 1C, CHꢀCH2ꢀOCH3), 101.29 (s, 1C, Oꢀ
((CH2)2)ꢀOꢀCH), 128.08 (s, 1C, CH2dCH), 130.27 (s, 2C,
CH2dCH), 166.12 (s, 1C, C(O)dO).
Herein, an acetyl galactosyloxyethyl acrylate (AcGalEA)
(Scheme 1) was used considering its potential bioactivity after
deacetylation, whereas styrene (S) was chosen as comonomer to
afford a sufficient hydrophobic part to the copolymer. Indeed, all
the synthesized copolymers were highly hydrophobic in order to
favor honeycomb porous film formation. As mentioned in several
works on honeycomb porous films, to enhance pore regularity,
the hydrophobic fraction in the polymer need to be substantial to
ensure the sufficient surface tension of the water droplet and
consequently to avoid coalescence of the droplets. AFM analysis
was used to reveal the quality of the porous film.
Synthesis of S-Methoxycarbonylphenylmethyl Dodecyltrithiocar-
bonate (MCPDT). MCPDT RAFT agent was synthesized as reported
previously with slight modifications.59 1-Dodecanethiol (6.41 g, 3.17 ꢁ
10ꢀ2 mol) was suspended in 43 mL of distilled water and cooled in an ice
bath. This was followed by the addition of potassium hydroxide (1.82 g,
3.25 ꢁ 10ꢀ2 mol) before 6.5 mL of carbon disulfide was introduced
dropwise into the suspension. A yellow emulsion was observed during
the addition of carbon disulfide. Methyl R-bromophenyl acetate (5.0 g,
2.19 ꢁ 10ꢀ2 mol) was eventually added dropwise into the yellow
emulsion, and a condenser was attached onto the single neck round-
bottom flask, after which the reaction vessel was heated to 80 °C for 12 h.
Upon cooling, the water phase was separated from the organic phase and
washed with methylene chloride (3 ꢁ 20 mL). The yellow solution of all
the organic phases were concentrated under reduced pressure to give a
yellow oil. The yellow oil was further purified through a column using
toluene as the eluent with the product exiting at an Rf value of 0.8. The
combined fractions were dried under reduced pressure and high vacuum
to yield a bright yellow oil and upon cooling in the fridge gave a bright
’ EXPERIMENTAL SECTION
Materials. β-D-Galactose pentaacetate (98%), 2-hydroxyethyl acry-
late (HEA, 98%), boron trifluoride diethyl etherate (purum, dist.), and
dichloromethane (DCM, 99.5%) were purchased from Aldrich. Ethyl
acetate (ACS reagent, g99.5%) and cyclohexane (ACS reagent, g99%)
for flash chromatography were used as purchased from Aldrich. Styrene
(S, Aldrich, 99%) was freshly deinhibited using an inhibitor remover
column from Aldrich before use. 1-Dodecanethiol (g98%), potassium
hydroxide (97.0%), carbon disulfide (ACS reagent, g99.9%), methyl
R-bromophenyl acetate (97%), 2,20-azobis(2-methylpropionitrile) (g98%),
and N,N-dimethylacetamide (HPLC grade) were also purchased from
Aldrich and used directly. Sodium methoxide in methanol (MeONa 0.5
M in MeOH, Aldrich) was used as received.
1
yellow solid. The reaction conversion (60%) was obtained using H
NMR by observing the integrals from the proton shift of 4.51 to 5.75
ppm. ESI-MS (CH2Cl2) calculated for C22H34O2S3 + Ag+ m/z, 533.08;
found, m/z 533.30. 1H NMR (CDCl3, 300 MHz) δ (ppm): 0.81 (t, 3H,
CH3), 1.19 (s, 18H, CH3ꢀC9H18ꢀ(CH2)2ꢀS), 1.61 (m, 2H,
CH2ꢀCH2ꢀS), 3.26 (t, 2H, CH2ꢀS), 3.68 (s, 3H, OꢀCH3), 5.75 (s,
1H, SꢀCHꢀ(Ph)ꢀC(O)dO), 7.27 (m, 5H, ArH5). 13C NMR
(CDCl3, 75.5 MHz) δ (ppm): 14.53 (1C, CH3), 23.09 (1C,
CH3ꢀCH2), 28.23, 29.30, 29.48, 29.74, 29.82, 29.94, 30.02, 30.11
(8C, C8H16 ꢀCH2ꢀS), 32.32 (1C, CH3ꢀCH2ꢀCH2), 37.72 (1C,
CH2ꢀS), 53.60 (1C, OꢀCH3), 58.19 (1C, SꢀCH(Ph)ꢀC(O)dO),
125.70, 128.62, 129.15, 129.29, 129.44, 133.64 (6C, ArC), 169.90 (1C,
CH(Ph)ꢀC(O)dO), 222.40 (1C, SdC(S)ꢀS).
Synthesis. Synthesis of 2-(20,30,40,60-Tetra-O-acetyl-β-D-galacto-
syloxy)ethyl Acrylate (AcGalEA). β-D-Galactose pentaacetate (10.0 g,
2.60 ꢁ 10ꢀ2 mol) and 2-hydroxyethyl acrylate HEA (6.0 mL, 0.052 mol)
were introduced into a 250 mL round-bottom flask with dried 3 Å mole-
cular sieves. Dichloromethane (100 mL) was dried overnight and intro-
duced in the flask, and the mixture was purged under nitrogen for
30 min. Then, boron trifluoride (16.0 mL, 0.129 mol) was slowly added
during 30 min while maintaining the flow of nitrogen through the flask.
RAFT PolymerizationofAcGalEA First Block (Experiment3 inTable 1).
AcGalEA (4.5 ꢁ 10ꢀ1 g, 1.0 ꢁ 10ꢀ3 mol) and MCPDT (4.3 ꢁ 10ꢀ3 g,
1.0 ꢁ 10ꢀ5 mol) were introduced into a 5 mL one-neck round-bottom
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Table 1. Experimental Conditions for the Synthesis of PS-b-PAcGalEA, PS-co-PAcGalEA, and PS-b-P(AcGalEA-grad-S) by RAFT
Polymerization Using MCPDT as Control Agent
Mn(SEC,
a
[AcGalEA]0
[S]0
(mol Lꢀ1
[CTA]0
[AIBN]0
(mol Lꢀ1
time
calib PS)
(g molꢀ1
expt
polymer
PAcGalEA
T (°C)
(mol Lꢀ1
)
)
(mol Lꢀ1
)
)
(min)
conv (%)
)
Mw/Mn
1c
2c
3c
4c
5b
6c
7c
8c
90
70
60
60
90
90
90
90
0.70
0.70
0.69
7.10 ꢁ 10ꢀ3 8.7 ꢁ 10ꢀ4
6.90 ꢁ 10ꢀ3 1.7 ꢁ 10ꢀ3
6.90 ꢁ 10ꢀ3 2.7 ꢁ 10ꢀ3
4.37 ꢁ 10ꢀ3 1.8 ꢁ 10ꢀ3
4.54 ꢁ 10ꢀ2 5.3 ꢁ 10ꢀ3
1.15 ꢁ 10ꢀ2 1.4 ꢁ 10ꢀ3
3.66 ꢁ 10ꢀ2 4.7 ꢁ 10ꢀ3
145
480
82
15 720
16 220
14 520
16 150
7 560
1.21
1.15
1.17
1.57
1.23
1.32
1.26
1.18
PAcGalEA
94
PAcGalEA
960
88
PAcGalEA-b-PS
PS
2.16
8.14
1200
360
17
50
PS-b-PAcGalEA
PS-co-PAcGalEA
PS-b-P(AcGalEA-grad-S)
0.58
1.59
200
18
55d
10 320
13 300
10 270
6.36
8.16
1440
450
4.3 ꢁ 10ꢀ2
5.1 ꢁ 10ꢀ3
53S/ 36AcGalEA
a [CTA]0 corresponds to the initial concentration of chain transfer agent which is MCPDT RAFT agent in the case of experiments 1, 2, 3, 5, 7, and 8;
PAcGalEA macro-RAFT agent in the case of experiment 4 and PS macro-RAFT agent for experiment 6. b Polymerization was carried out in bulk.
c Polymerization was carried out in DMAc. d The conversion corresponds to the global conversion.
flask. AIBN was introduced by first preparing a solution of AIBN in
DMAc (7.2 ꢁ 10ꢀ3 g in 1 mL) and taking the appropriate quantity
(91 μL). Then DMAc (9 mL) was added to dissolve the mixture. The
solution was degassed for 45 min using nitrogen and introduced into a
preheated oil bath at 60 °C. At the end of the polymerization, a part of
the crude solution was dissolved in CDCl3 for 1H NMR analysis.
AcGalEA conversion was determined using the integration of a mono-
mer vinylic proton at 6.15 ppm with the integration of the CH from the
Chain Extension of PS Macro-RAFT Agent with AcGalEA (Experi-
ment 6 in Table 1). Purified PS from experiment 3 (8 ꢁ 10ꢀ2 g, 8 ꢁ 10ꢀ6
mol, Mn (SEC,PS calibration) = 7560 g/mol, Mw/Mn = 1.23) and AcGalEA
(0.18 g, 4 ꢁ 10ꢀ4 mol) were measured into a 5 mL one-neck round-
bottom flask. A solution of AIBN in DMAc was first prepared by
dissolving 1.58 ꢁ 10ꢀ2 g of AIBN in 2.0 g of DMAc. Then 0.02 g of the
freshly prepared solution and 0.62 g of DMAc were added to the flask.
After purging the mixture under nitrogen for 45 min, the flask was
introduced in a preheated oil bath at 90 °C for 200 min. At the end of the
reaction, a part of the crude solution was analyzed in 1H NMR. AcGalEA
conversion was calculated using the integration of one monomer vinylic
proton at 6.15 ppm with the integration of the CH from the galactose of
galactose of both monomer and polymer (3Hmonomer + 3Hpolymer
+
1Hstyrene, 5.7ꢀ7.6 ppm). Finally, the resulting PAcGalEA block was
purified by precipitation in diethyl ether and dried overnight under
reduce pressure.
Chain Extension of PAcGalEA Macro-RAFT Agent with S (Experi-
ment 4 in Table 1). PAcGalEA macro-RAFT agent (6.9 ꢁ 10ꢀ2 g, 4.75 ꢁ
10ꢀ6 mol, Mn (SEC,PS calibration) = 14 520 g molꢀ1, Mw/Mn = 1.17) and S
(1.75 ꢁ 10ꢀ1 g, 1.7 ꢁ 10ꢀ3 mol) were introduced into a 5 mL one-neck
round-bottom flask. AIBN (2.6 ꢁ 10ꢀ3 g) was dissolved in DMAc
(1 mL), and the appropriate amount of this solution was introduced in
the flask (85.7 μL). The reaction mixture was degassed with nitrogen for
45 min and subsequently introduced into an oil bath at 60 °C. At the end
of the polymerization a part of the crude solution was withdrawn to
determined S conversion by 1H NMR. S conversion was calculated using
the integration of the vinylic protons (2Hmonomer, 5.0ꢀ5.7 ppm) of the
monomer with the integration of the aromatic protons of both monomer
and polymer (6Hmonomer + 5Hpolymer, 6.1ꢀ7.3 ppm). The resulting
PAcGalEA-b-PS was purified by precipitation in diethyl ether, filtered,
and dried under reduced pressure overnight.
RAFT Polymerization of S First Block (Experiment 5 in Table 1). S (1.2
g, 1.2 ꢁ 10ꢀ2 mol) and MCPDT (2.9 ꢁ 10ꢀ2 g, 6.5 ꢁ 10ꢀ5 mol)
were measured into a 5 mL one-neck round-bottom flask. A solution of
AIBN in DMAc was prepared by dissolving 1.32 ꢁ 10ꢀ2 g of AIBN in
9.60 ꢁ 10ꢀ1 g of DMAc. The sufficient quantity of this solution (0.09 g)
was withdrawn and introduced into the flask. The reaction mixture
was thoroughly degassed for 45 min using nitrogen before it was sealed
and placed into a preheated oil bath at 90 °C. Several aliquots were
withdrawn at time intervals during polymerization and directly dis-
solved in CDCl3 for conversion determination using 1H NMR analysis.
S conversion was calculated using the integration of the vinylic
protons (2Hmonomer, 5.0ꢀ5.7 ppm) of the monomer with the inte-
gration of the aromatic protons of both monomer and polymer
(6Hmonomer + 5Hpolymer, 6.1ꢀ7.3 ppm). The final PS-macro-RAFT
agent was purified by precipitation in methanol, filtered, and dried under
reduced pressure at room temperature for 48 h before using it as a
macro-RAFT agent.
both monomer and polymer (3Hmonomer + 3Hpolymer + 1Hstyrene,
5.7ꢀ7.6 ppm). The remaining solution was purified two times by
precipitation in methanol and subsequently dried under reduce pressure
overnight to yield a slightly yellow powder.
RAFT Copolymerization of Styrene and AcGalEA (Experiment 7 in
Table 1). In a typical experiment, AcGalEA (1.0 g, 2.3 ꢁ 10ꢀ3 mol),
styrene (0.94 g, 9.0 ꢁ 10ꢀ3 mol), and MCPDT (2.2 ꢁ 10ꢀ2 g, 5.2 ꢁ
10ꢀ5 mol) were introduced in a 5 mL one-neck round-bottom flask.
Moreover, a solution of AIBN (1.7 ꢁ 10ꢀ2 g) was first prepared in
DMAc (1.98 g). Then the appropriate amount of AIBN was introduced
in the flask, and 0.23 g of DMAc was also added. To follow the kinetic
polymerization, several aliquots at time intervals were withdrawn and
subsequently characterized by 1H NMR in order to determine individual
conversion of both monomers. The final crude solution was precipitated
in methanol, filtered, and dried under reduced pressure overnight,
yielding to a slightly yellow fine powder.
Synthesis of Gradient Copolymer Made of Styrene and AcGalEA
(Experiment 8 in Table 1). In a first step styrene (1.04 g, 1 ꢁ 10ꢀ2 mol)
and MCPDT (2.3 ꢁ 10ꢀ2 g, 5.3 ꢁ 10ꢀ5 mol) were introduced in a
10 mL one-neck round-bottom flask. Then, a solution of AIBN (1.3 ꢁ
10ꢀ2 g) in DMAc (0.96 g) was prepared, and the appropriate amount
was introduced into the flask. The reaction mixture was thoroughly
purged with nitrogen for 45 min and sealed. Polymerization was
carried out at 90 °C, and aliquots were taken at periodic intervals for
the determination of styrene conversion. During the homopolymer-
ization of styrene, a solution of AcGalEA (1.0 g, 2.3 ꢁ 10ꢀ3 mol) in
DMAc (2.1 g) was purged and subsequently withdrawn in a syringe.
At the end of a defined time of the stage one, the solution of AcGalEA
in DMac was slowly added using a pump with a rate of 0.5 mL hꢀ1
.
After 4 h 30 min, the addition of the solution was complete, and
the reaction was left for 1 h. Several aliquots were taken along and
after the addition of the solution in order to monitor the conversion
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Table 2. Experimental Conditions for 1H NMR in Situ
Experiment for Conventional Copolymerization of AcGalEA
and Styrene Using AIBN as Initiator
[AcGalEA]0
expt
(mol Lꢀ1
)
[S]0 (mol Lꢀ1
)
[AIBN]0 (mol Lꢀ1
)
1
2
3
4
0.62
0.21
1.00
1.65
1.35
1.93
1.06
0.42
0.02
0.02
0.02
0.02
1
of both styrene and AcGalEA monomers using H NMR in CHCl3.
The final solution was purified by precipitation in methanol, and the
resulting solid was isolated by vacuum filtration and dried for 48 h
under vacuum, yielding a fine and slightly yellow powder.
Figure 1. Pseudo-first-order kinetic (closed symbol) and conversion
plot (open symbol) for the RAFT polymerization of AcGalEA in DMAc
using MCPDT at different temperatures: (9) 90, (2) 70, and (b) 60 °C
(experiments 1, 2, and 3 in Table 1). [AcGalEA]/[MCPDT] = 100 for
each kinetic.
NMR in Situ Copolymerization of AcGalEA and Styrene for Reactiv-
ity Ratio Determination (Experiments 1ꢀ4 in Table 2). In experiment 1,
AcGalEA (0.14 g, 3 ꢁ 10ꢀ4 mol) and styrene (0.07 g, 6.8 ꢁ 10ꢀ4 mol)
were introduced into a hemolyse tube. AIBN was prepared by first dis-
solving 1.7 ꢁ 10ꢀ2 g of purified AIBN in 2 g of DMAc and transferring
0.2 g into the reaction mixture. For this in situ experiment, two NMR
tubes were used. The first one which contains the purged reaction
mixture was introduced in the second tube which contains the deuter-
ated DMSO. The tubes were sealed with rubber septa and subsequently
introduced in the NMR apparatus preheated at 90 °C. By the same
method, several kinetics were performed with different [AcGalEA]0/
[S]0 ratio (Table 2).
Deacetylation. A solution of purified copolymer from experiment 4,
5, or 6 in Table 1 (3 ꢁ 10ꢀ6 mol) in a mixture of CHCl3ꢀCH3OH (1:1,
8 mL) was degassed at room temperature under nitrogen for 30 min.
Then, 1 mL of a freshly prepared 1 M solution of NaOMe in MeOH was
added. After ∼10 s, a white precipitate was observed and disappeared
straight away. The reaction was left for 1 h, and the solvents were reduce
under reduced pressure. Then, the final solution was purified by pre-
Figure 2. Size exclusion chromatograms of PAcGalEA macro-RAFT
agent and of the resulting PAcGalEA-b-PS obtained in DMAc at 60 °C
(experiment 4 in Table 1).
1
cipitation in methanol, filtered, and dried, yielding a fine powder. H
NMR and FTIR were used to confirm that the successful deprotection of
acetyl groups on the galactose moieties.
Atomic Force Microscopy (AFM). Measurements were performed
with an Innova AFM (Veeco Instrument Inc.). The images were scanned
in tapping mode under ambient conditions and recorded either as
topography images (Figure 9). Rectangular silicon cantilevers from Veeco-
probes (MMP-12100ꢀ10) with a resonance frequency of about 150 kHz
were used.
Optical Microscopy. Pictures were taken in reflection with a Leica
DM/LM microscope equipped with ꢁ50 optic and a Leica DFC280
video camera. The regular image treatments were performed with the
Image Manager IM50 software.
Honeycomb Film Preparation. The preparation of the honey-
comb film using the breath figure method was conducted in a
Perspex glovebox with relative humidity between 35 and 40% at
room temperature (22ꢀ25 °C). The humid air flow was set at
2 L minꢀ1. For each copolymer, two series of solution were prepared:
(1) copolymers in CS2 at 5 g Lꢀ1 and (2) a copolymer/linear PS
(Mn = 20 000 g molꢀ1) mixture (1:1, w/w) in CS2 at 5 g Lꢀ1. For
the film formation, 100 μL of the solutions was cast on a glass
substrate in the Perspex box.
Analysis. Nuclear Magnetic Resonance (NMR) Spectroscopy.
NMR spectra were recorded using a Br€uker 400 MHz spectrometer at
’ RESULTS AND DISCUSSION
1
25 °C. H and 13C measurements were performed at frequencies of
Synthesis of Block Copolymer. Two synthetic approaches
were investigated for the synthesis of block copolymers.
First, homopolymerization kinetics of AcGalEA using MCPDT
and AIBN at different temperatures was performed. Inhibition
periods were observed for all three temperature performed
(Figure 1). Nevertheless, this period decrease from 320 min at
60 °C to 100 min at 70 °C and, finally, to 50 min at 90 °C.
Moreover, we performed the chain extension of a PAcGalEA first
block (Mn = 14 500 g/mol, Mw/Mn = 1.17) in DMAc at 60 °C
with styrene. SEC chromatograms of this chain extension
showed that the reinitiation of the PAcGalEA first block is not
completed (Figure 2). Considering the problem of reinitiation,
we also investigated the synthesis of a PS first block and subse-
quently chain extended with AcGalEA. The homopolymerization
400.13 and 100.6 MHz, respectively. Deuterated chloroform CDCl3 was
used as solvent.
Mass Spectrometry. Mass spectra were recorded using a LTQ-FTMS
Orbitrap VELOS from Thermofisher (precision <3 ppm). The sample
was dissolved in methanol before the characterization.
Size Exclusion Chromatography (SEC). Characterizations of the
polymers were performed at 30 °C with THF as eluent at a flow rate
of 1 mL minꢀ1. The SEC system was equipped with three Waters Styragel
columns HR 0.5, 2, and 4 working in series (separation range 1 ꢁ
102ꢀ3 ꢁ 106 g molꢀ1) and a refractive index detector ERC 7515-A. The
number-average molar molecular weight (Mn) and the dispersity (D =
Mw/Mn) were derived against a calibration derived from PS standards.
All polymers samples were prepared at 5 g Lꢀ1 concentrations and
filtered through PVDF 0.45 μm filters.
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Figure 3. Size exclusion chromatograms of PS obtained at different monomer conversion during the polymerization of styrene in bulk at 90 °C
(experiment 5 in Table 1) (left). Size exclusion chromatograms of PS macro-RAFT agent and of the resulting PS-b-PAcGalEA obtained in DMAc at
90 °C. Experimental conditions of experiment 6 are reported in Table 1.
of styrene using MCPDT and AIBN in bulk at 90 °C was
controlled as a constant radical concentration with time and a
linear dependence of the molecular weight with conversion were
observed (see Figure SI-3 in Supporting Information). The SEC
chromatograms of PS samples shifted toward high molecular
mass with increasing conversion (Figure 3, left). Moreover, the
SEC traces of the chain extension of this PS macro-RAFT agent
did not shown any shoulder, indicating a better reinitiation in
comparison to the chain extension of a PAcGalEA first block
(Figure 3, right). One explanation could be that during the pre-
equilibrium of the RAFT process the R radical formed was more
stable in the case of the reinitiation of PS as the phenyl group
stabilizes the radical, whereas in the case of a PAcGalEA chain
Figure 4. Pseudo-first-order kinetic (b) and conversion plots (0) of
RAFT copolymerization of styrene and AcGalEA in DMAc at 90 °C
using MCPDT as control agent and AIBN as initiator. The experimental
extension polymerization the radical might be destabilized by the
presence of the attractive carboxyl group.60
One-Pot Synthesis of Gradient Copolymers. Studies have
shown that amphiphilic block copolymers are able to form
honeycomb porous film using the appropriate conditions and
also to create hierarchically structured porous film at the nano-
and micrometer scale.61,62 The final aim of this work was to
develop a new methodology to synthesize bioactive polymer in
one-pot synthesis, which is time- and cost-saving in comparison
to the usual two-step procedure for the synthesis of block
copolymer. Nonetheless, the synthesized copolymer needs to
be able to form porous structure via the breath figure process.
One-pot synthesis of gradient copolymers requires the knowl-
edge of the reactivity ratios of monomers. Indeed, considering
two monomers A and B with the corresponding reactivity ratios
rA and rB, the consumption rate for each monomer is driven by
the MayoꢀLewis equation:
conditions are reported in Table 1.
methods.64ꢀ66 The evolution of the AcGalEA monomer fraction
versus the global conversion along the copolymerization is
shown in Figure SI-4A. For the Skeist method this evolution
was fitted for each initial composition in order to determine the
reactivity ratios. The monomer reactivity ratios for the AIBN
conventional radical copolymerization of S and AcGalEA were
rS = 0.7 ( 0.1 and rAcGalEA = 0.07 ( 0.01. These values reveal that
styrene is much more reactive than the glycomonomer. The
profile of FS in function of the initial composition in styrene
monomer fS is shown Figure SI-4B. Considering the reactivity
ratio obtained and also that a high hydrophobic fraction is
required for honeycomb film formation in order to reduce the
surface tensions of the water droplet during the breath figure
mechanism, spontaneous gradient copolymer with this require-
ment could not be obtained. Indeed, with an initial fraction of
S close to 80%, the composition of the obtained copolymer will
be 80% in PS due to the azeotropic curve. The RAFT copolym-
erization of S (80 mol %) and AcGalEA (20 mol %) was
investigated using MCPDT as chain transfer agent and AIBN
as initiator in DMAc at 90 °C (experiment 5 Table 1). The first-
order kinetic plot shows a linear plot with a high concentration of
radical generated at the beginning of the reaction (Figure 4).
Moreover, the evolution of the number-average mole-
cular weight with conversion increases linearly showing a con-
trolled polymerization as the growing chains were constant
through the reaction (Figure 5). The molecular weights
were determined using PS calibration. This can explain the
observed deviation with the theoretical values given that the
2
df1
df2
r1f1 þ f1f2
F1
F2
¼
¼
ð1Þ
2
r2f2 þ f1f2
Depending on the reactivity ratios and on the initial fraction for
both monomers, the instantaneous copolymer composition is
affected.63
The reactivity ratios of both monomers have not been studied,
and no values of the reactivity ratios are available in the literature.
Considering that, we investigated the reactivity of both mono-
mers using in situ NMR experiments. Experiments were con-
ducted in several initial mixtures of S and AcGalEA; we followed
the kinetics in conventional radical polymerization using AIBN at
90 °C (Figure SI-4A).
The monomer reactivity ratios were estimated with the Skeist
equation but also with the FinemanꢀRoss and KelenꢀTudos
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Figure 5. Evolution of number-average molar mass for P(AcGalEA-co-S) vs conversion (X). Dotted line is the theoretical Mn, (b) represents the Mn
using PS calibration, and (0) represents the polydispersity index (PDI) (left). Size exclusion chromatograms of P(AcGalEA-co-S) obtained at different
monomer conversion during the copolymerization of S and AcGalEA in bulk at 90 °C (right).
Figure 6. Pseudo-first-order kinetic of styrene (9) and AcGalEA (b) and conversion plots of styrene (0) and AcGalEA (O) of RAFT copolymerization
of styrene and AcGalEA in DMAc at 90 °C using MCPDT as control agent and AIBN as initiator (left). Instantaneous fraction of AcGalEA in the
copolymer as a function of the normalized chain length (right). The experimental conditions are reported in Table 1.
Figure 7. Evolution of number-average molar mass for PS-b-P(AcGalEA-grad-S) vs conversion (X). Dotted line is the theoretical Mn, (b) represents
the Mn using PS calibration, and (0) represents the polydispersity index (PDI) (left). Size exclusion chromatograms of PS-b-P(AcGalEA-grad-S)
obtained at different monomer conversion during the copolymerization of styrene and AcGalEA in bulk at 90 °C (right).
hydrodynamic volume of the AcGalEA units differs largely from
the styrene units.29
commonly used by Billon and co-workers67ꢀ70 (see experiment
8 from Table 1). In this method, the S was polymerized first
followed by the slow addition of the AcGalEA monomer by the
mean of a pump. Figure 6 (left) showed the first-order kinetic
plot of the semibatch copolymerization. For both monomers, a
linear evolution with time was observed. The evolution of the
molar fraction of AcGalEA in the copolymer for each sample
versus the normalized chain length showed an “S-shaped” curve
associated with a slight increase of the instantaneous AcGalEA
molar fraction in the copolymer up to 12% (Figure 6, right).
Moreover, the evolution of number-average molar masses
determined using SEC increases linearly with conversion, in-
dicating a controlled process (Figure 7, left). The Mw/Mn of
the copolymers reduces to 1.18 at 53% and 36% of conversion
for respectively S and AcGalEA. SEC chromatograms showed
The final purified copolymer is composed of 15% of AcGalEA
monomer units. As expected, the final composition was closed
to the initial composition in AcGalEA monomer. In conclusion
from this part, gradient profile composition could not be
obtained by batch polymerization with aim to have a highly hydro-
phobic chain. Nevertheless, considering the high difference in
reactivity of both monomers, hydrophilic spontaneous gradient
copolymer could be obtained and will be the objective of future
research. Indeed in this case, the hydrophilic copolymer could be
used as a model for micellization and lectins complexation.
Considering those previous results, we investigated the other
way to make copolymer with a gradient profile and with a
high hydrophobic fraction, by means of a semibatch technique
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Figure 8. 1H NMR spectra in CDCl3 of PAcGalEA-b-PS (top), P(AcGalEA-co-S) (middle), and PS-b-P(S-grad-AcGalEA) (bottom) between 3.0ꢀ
7.6 ppm (A) and 3.3ꢀ5.5 ppm (B).
Figure 9. AFM topography images (10 ꢁ 10 μm) of honeycomb porous films from PS-b-PGalEA, PS-b-P(S-grad-GalEA), and P(S-co-GalEA) in CS2 at
5 g Lꢀ1 (from A to C, upper line). AFM topography images of honeycomb films obtained with mixture of PS-b-PGalEA, PS-b-P(S-grad-GalEA), or P-
(S-co-GalEA) with linear PS (1:1 w/w) (from A to C, bottom line).
closely symmetrical curves at the end of the polymerization,
confirming the control of the reaction with a minimum amount
of dead chains (Figure 7, right).
sugar cycle. As is shown in Figure 8A,B, the signal b differs
from block to statistical or gradient profile. In summary, for the
sugar moieties, the anomeric and CH protons from the cycle
are highly sensitive to their environment. Moreover, resonances of
the aromatic protons from the styrene were also affected by the
environment as the profile of the spectra slightly changes for each
chain architecture (Figure 8A,B).
The influence of the synthetic methodology on macromole-
1
cular chain architecture was investigated by H NMR. Indeed,
1
depending on its environment, particular effects on H NMR
shifting for the anomeric proton of the sugar moieties were ob-
served. Two types of signal were attributed to this anomeric
proton: 4.34 and 4.31 ppm in the case of statistical and gradient
profile, respectively, and a more deblinded signal at 4.62 ppm was
observed in the case of block copolymer (signal c Figure 8A,B).
The difference between the two types of signals was followed by
2D HSQC NMR experiments (see Figure SI-5 in the Supporting
Information). This shift of the 1H signal for the anomeric proton
was attributed to the environment of the sugar moieties. The
signal at 4.62 ppm for block copolymer corresponds to AcGa-
lEA/AcGalEA/AcGalEA triads, whereas the signal at ∼4.3 ppm for
statistical and gradient copolymer corresponds to S/AcGalEA/S
triads. Another consequence of the synthetic methodology on
the chain architecture was observed for the CH protons from the
Deacetylation of PS-b-PAcGalEA, P(S-co-AcGalEA), and
PS-b-P(AcGalEA-grad-S) to PS-b-PGalEA, P(S-co-GalEA),
and PS-b-P(GalEA-grad-S) Copolymers. FT-IR and 1H NMR
were empolyed to confirm deprotection occurred. The carbonyl
band at 1740 cmꢀ1 decreased sharply, and the broad hydroxyl
band at 3400 cmꢀ1 appeared after the deprotection (see Figure
1
SI-6 in the Supporting Information). H NMR experiments of
the deprotection was also confirmed by the complete disappear-
ance of the signal from the CH3 of the protective acetyl group
(at 2.10, 2.05, 1.95, and 1.6 ppm; 4 ꢁ CH3). Moreover, the CH
signals from the sugar cycle completely disappeared, pointing
out the complete deacetylation (4.98, 5.15, and 5.38 ppm) (see
Figure SI-7 in the Supporting Information). Indeed, if residual
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protection function were still present, the three signals should be
present.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: laurent.billon@univ-pau.fr (L.B.); m.stenzel@
unsw.edu.au (M.H.S.).
Honeycomb Porous Films. Syntheses of copolymers with a
high hydrophobic fraction were performed in order to study their
abilities to form honeycomb porous film. Atomic force micro-
scopy (AFM) was used to observe the quality of the pores array.
Images recorded in topographic mode are displayed in Figure 9.
The PS-b-PAcGalEA block copolymer exhibit pore sizes of
650 nm on average, with a slight irregular array. Moreover, a sec-
ond porosity appears in the walls of the honeycomb film (Figure 9A,
top). This second porosity was early described by Beattie et al.
with PS-b-PAA block copolymer and was attributed to the
formation of water-swollen inverse aggregates.71 Wong et al.
attributed this nanoporosity to the excess of water encapsulated
’ ACKNOWLEDGMENT
Authors thank the FrenchꢀAustralian Science and Technol-
ogy (FAST) Program FR080066 for financial support. CNRS
and the French Ministry of Research are thanked for funding M.
S., L.B., and L.R. Rꢀegion Aquitaine is acknowledged for P.E. PhD
funding. The authors also thank G. Clisson for his help on SEC
analyses, H. Preud’homme for mass spectroscopy in IPREM, and
I. Jacenyik and M. R. Whittaker for the management in CAMD.
within the pores.72 Insertion of linear PS (Mn = 20 000 g molꢀ1
;
Mw/Mn = 1.2; 1:1 w/w) slightly enhanced the regularity of the
hexagonal array, and the second porosity is still present and is
perfectly distributed around the bigger pores (Figure 9A, bot-
tom). The PS-b-P(S-grad-AcGalEA) copolymer showed a good
ability to form honeycomb films as the hexagonal array formed by
the pores is regular with pores ranging from 250 to 300 nm. The
introduction of linear PS enables the enhancement of the regular-
ity over a larger area (Figure 9B, top and bottom). Note that in
the case of this polymer the second porosity was not present.
Concerning the statistical copolymer P(S-co-AcGalEA), the result-
ing film is highly irregular with pore sizes ranging from 50 to
300 nm (Figure 9C, top). The mixture with PS poorly enhances
the regularity of the array and the homogeneity of the pores
diameters (Figure 9C, bottom).
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