Synthesis of amphiphilic poly((R,S)-β-malic acid)-graft-poly(ε-caprolactone): "grafting from" and "grafting through" approaches

Article abstract of DOI:10.1021/ma047928m

The synthesis of novel amphiphilic graft copolyeaters baaed on Hydrophobic poly(ε-caprolactone) (PCL) segmente grafted all along a hydrophilic poly((R,S)-β-malic acid) (PMLA) backbone is proposed. These PMLA-g-PCL graft copolymers have been prepared in a controlled way using either the "grafting through" or the "grafting from" technique. Both approaches involve two different well-controlled ring-opening polymerization (ROP) mechanisms: anionic ROP of β-lactones, i.e., benzyl or allyl β-malolactonate (MLABz or MLAAllyl), and living ROP of ε-caprolactone (CL) through a so-called coordination-insertion mechanism. The grafting through approach relies upon the anionic copolymerization of MLABz and ω-malolactonate-PCL macromonomer as initiated by potassium carboxylic acid salt in the presence of 1 equiv of 18-crown-6 ether. The second route follows a four-step synthesis involving the anionic ROP of MLABz and MLAAllyl, the conversion of allylic groups into pendant hydroxyl functions owing to a free-radical reaction with thioethanol in the presence of 2,2′-azobis(2-methylpropionitrile), and then the CL polymerization as initiated from these pendant -OH groups after adequate activation into aluminum alkozide active species. Whatever the synthetic approach, the final step consiste of the deprotection of the MLABz repeating units along the backbone via a soft catalytic hydrogenation reaction. The amphiphilic character of the so-prepared graft copolyesters has been evidenced by some preliminary interfacial tension experiments using the pendant drop method.

Full text of DOI:10.1021/ma047928m

Macromolecules 2005, 38, 3141-3150
3141
Synthesis of Amphiphilic Poly((R,S)-â-malic
acid)-graft-poly(ꢀ-caprolactone): “Grafting From” and “Grafting Through”
Approaches
Olivier Coulembier,† Philippe Dege´e,† Pascal Gerbaux,‡ Pascale Wantier,‡
Christel Barbaud,§ Robert Flammang,‡ Philippe Gue´rin,§ and Philippe Dubois*,†
Laboratory of Polymeric and Composite Materials (LPCM) and Laboratoire de Chimie Organique,
University of Mons-Hainaut, Place du Parc 20, 7000 Mons, Belgium, and Laboratoire de Recherche sur
les Polyme`res, UMR C7581 CNRS, Universite´ Paris Val-de-Marne, Rue Henry Durant 2-8,
94320 Thiais, France
Received October 7, 2004; Revised Manuscript Received January 24, 2005
ABSTRACT: The synthesis of novel amphiphilic graft copolyesters based on hydrophobic poly(ꢀ-
caprolactone) (PCL) segments grafted all along a hydrophilic poly((R,S)-â-malic acid) (PMLA) backbone
is proposed. These PMLA-g-PCL graft copolymers have been prepared in a controlled way using either
the “grafting through” or the “grafting from” technique. Both approaches involve two different
well-controlled ring-opening polymerization (ROP) mechanisms: anionic ROP of â-lactones, i.e., benzyl
or allyl â-malolactonate (MLABz or MLAAllyl), and living ROP of ꢀ-caprolactone (CL) through a so-
called coordination-insertion mechanism. The grafting through approach relies upon the anionic
copolymerization of MLABz and ω-malolactonate-PCL macromonomer as initiated by potassium
carboxylic acid salt in the presence of 1 equiv of 18-crown-6 ether. The second route follows a four-step
synthesis involving the anionic ROP of MLABz and MLAAllyl, the conversion of allylic groups into pendant
hydroxyl functions owing to a free-radical reaction with thioethanol in the presence of 2,2′-azobis(2-
methylpropionitrile), and then the CL polymerization as initiated from these pendant -OH groups after
adequate activation into aluminum alkoxide active species. Whatever the synthetic approach, the final
step consists of the deprotection of the MLABz repeating units along the backbone via a soft catalytic
hydrogenation reaction. The amphiphilic character of the so-prepared graft copolyesters has been evidenced
by some preliminary interfacial tension experiments using the pendant drop method.
Introduction
mers,4 poly(â-malic acid) (PMLA) is an attractive water-
soluble aliphatic polyester with carboxylic acid pendant
groups that has proven to be biocompatible and de-
gradable in vivo into malic acid, a nontoxic molecule.5,6
Gue´rin et al. reported on the anionic polymerization of
a large range of protected and/or functional malo-
lactonates (including optically active derivatives) yield-
ing a high molecular weight (co)poly(â-malic acid)-based
structure.7 More recently, some of us reported on the
controlled synthesis of well-defined biodegradable and
biocompatible amphiphilic poly((R,S)-hexyl â-malo-
lactonate)-graft-poly((R,S)-â-malic acid) graft copoly-
mers (PMLAHex-g-PMLA) according to a four-step
strategy.8 It involves first the anionic ring-opening co-
polymerization of (R,S)-benzyloxypropyl â-malolactonate
and (R,S)-hexyl â-malolactonate initiated by tetraethyl-
ammonium benzoate, followed by the selective removal
of the benzyloxy function, which generated a free
pendant hydroxyl function suitable to initiate the ring-
opening polymerization (ROP) of (R,S)-benzyl â-malo-
lactonate (MLABz). The final step relied upon the
selective removal of benzyloxy protective groups of
MLABz repeating units of the grafts.
For about 40 years, living ionic polymerization has
been the main technique for the synthesis of controlled
macromolecular architectures with narrow molecular
weight distribution. Nowadays, despite the continuing
development of new strategies for the synthesis of well-
defined (co)polymers, ionic polymerization remains the
most reliable method for the synthesis of a wide variety
of model (co)polymers.1 For instance, most block copoly-
mers with complex molecular architectures and tunable
properties are selectively prepared by ionic polymeri-
zation.2 Similarly, graft copolymers can be obtained by
ionic copolymerization through various pathways
referred to as the “grafting onto”, “grafting from”,
and “macromonomer” technique (also called “grafting
through”). The grafting onto method involves the reac-
tion between nucleophilic end groups of living “side”
chains and electrophilic sites along the main polymer
chain or backbone.3 In the grafting from approach, the
backbone behaves as a polymeric multi-initiation site
from which side chains are polymerized. Finally, the
macromonomer approach brings in the polymerization
of a regular monomer and a preformed side chain
bearing a polymerizable end group.
This paper focuses on the controlled synthesis of novel
amphiphilic biodegradable and biocompatible poly((R,S)-
â-malic acid)-graft-poly(ꢀ-caprolactone) graft copolymers
(PMLA-g-PCL) as obtained by either the macromonomer
or the grafting from technique. The former method
consists of the anionic ring-opening copolymerization of
MLABz and ω-malolactonate-PCL macromonomer
(MLA-PCL) initiated by potassium 11-hydroxy-
dodecanoate added with 1 equiv of 18-crown-6 ether
In response to the demand for new biocompatible and
biodegradable materials based on synthetic (co)poly-
* To whom correspondence should be addressed. E-mail:
philippe.dubois@umh.ac.be.
† LPCM, University of Mons-Hainaut.
‡ Laboratoire de Chimie Organique, University of Mons-
Hainaut.
§ Universite´ Paris Val-de-Marne.
10.1021/ma047928m CCC: $30.25 © 2005 American Chemical Society
Published on Web 03/16/2005

3142 Coulembier et al.
Macromolecules, Vol. 38, No. 8, 2005
Scheme 1. Synthesis of PMLA-g-PCL Graft Copolymers through the Macromonomer Technique
Scheme 2. Synthesis of PMLA-g-PCL Graft Copolymers through the Grafting From Method
(HDD) in THF, followed by the selective removal of
benzyloxy protective groups (Scheme 1). The second
route follows a four-step strategy involving the an-
ionic copolymerization of (R,S)-allyl â-malolactonate
(MLAAllyl) and MLABz, followed by the conversion of
allylic functions into pendant hydroxy groups able to
initiate the ꢀ-caprolactone (CL) ring-opening polymer-
ization (ROP) after activation by AlEt3, and finally the
deprotection of the MLABz repeating units along the
backbone (Scheme 2). To demonstrate the amphiphilic
character of the resulting PMLA-g-PCL graft copoly-
mers, preliminary interfacial tension measurements
using the pendant drop method are also reported.
Experimental Section
Materials. MLABz and MLAAllyl were synthesized accord-
ing to the aspartic route and purified as previously reported.9
They were stored at -18 °C, then distilled under reduced
pressure, and dried by three successive azeotropic distillations
of toluene just before use. CL (Acros, 99%) was dried over

Macromolecules, Vol. 38, No. 8, 2005
Synthesis of PMLA-g-PCL 3143
calcium hydride at room temperature for 48 h and then
distilled under reduced pressure. Aluminum triisopropoxide
(Al(OiPr)3; Aldrich, 98%) was purified by sublimation under
reduced pressure and rapidly dissolved in dry toluene as
previously described.10 The accurate concentration of the
initiator solution was determined by back complexiometric
aqueous titration of Al3+ with standard solutions of Na2EDTA
and ZnSO4 at pH 4.8.10 11-Hydroxydodecanoic acid (Aldrich,
97%) and 18-crown-6 (Acros, 99%) were dried by three suc-
cessive azeotropic distillations of toluene. Potassium (Acros,
98%), naphthalene (Acros, 99%), trimethylsilyldiazomethane
(2 N in hexane from Aldrich), methanol (Aldrich, 99.93%),
2-mercaptoethanol (Acros, 99%), 2,2′-azobis(2-methylpropio-
nitrile) (Acros, 98%), N,N′-dicyclohexylcarbodiimide (Acros,
99%), 4-(dimethylamino)pyridine (Acros, 99%), triethylalumi-
num (1.8 M in toluene from Fluka), Pd/C (10 wt % from
Aldrich), and hydrogen (Air Liquide, N50) were used without
further purification. Toluene (Labscan, 99%) was dried by
refluxing over CaH2 and distilled under a nitrogen atmosphere.
Tetrahydrofuran (Labscan, 99%) was first dried on 4 Å
molecular sieves at room temperature for 72 h, then added to
low molecular weight ω-lithium styrylpoly(styrene), and dis-
tilled under reduced pressure just before use.
PCL (4.7 × 10-2 g, 0.65 × 10-4 mol) was typically conducted
in a previously flame-dried and nitrogen-purged round-bottom
flask equipped with a three-way stopcock and a septum by
initiation with the complex formed between potassium 11-
hydroxydodecanoate and 18-crown-6 ether (0.1 mL, 1.0 × 10-5
mol) in THF (3 mL) at 0 °C. After 4 h, the polymerization was
stopped by adding a few drops of aqueous HCl (0.1 mol‚L-1).
After evaporation of the solvent, the product was dissolved in
dichloromethane (20 mL) and extracted three times each with
a saturated aqueous KCl solution (3 × 20 mL) and with
deionized water (3 × 20 mL). Finally, the organic layer was
poured into 8 volumes of cold heptane (160 mL). The polymer
was recovered by filtration and dried under reduced pressure
at 40 °C until a constant weight was obtained (yield 89%).
Molecular parameters were determined by size exclusion
chromatography (SEC) with reference to polystyrene standards
(Mn(PS) ) 8000 g‚mol-1, Mw/Mn ) 1.4) by potentiometric
titration of carboxylic acid end groups (Mn ) 5400 g‚mol-1
)
and 1H NMR (CDCl3, δ (ppm); see Figure B in the Supporting
Information for signal assignation): 1-1.2 (m, 18Hj), 1.25 (m,
6Hh), 1.6 (m, 4Hb+d), 2.3 (t, 2He), 3.5 (t, 2Hi), 4.1 (t, 2Hf).
Anionic Ring-Opening Copolymerization of MLABz
and MLA-PCL. Copolymerization of MLABz (e.g., 0.33 g, 1.6
× 10-3 mol, 89 mol %) and MLA-PCL (e.g., 0.14 g, 1.9 × 10-4
mol, 11 mol %) was typically conducted in a previously flame-
dried and nitrogen-purged round-bottom flask equipped with
a three-way stopcock and a septum by initiation with the
complex formed between potassium 11-hydroxydodecanoate
and 18-crown-6 ether (0.5 mL, 5.0 × 10-5 mol) in THF (8 mL)
at 0 °C for 3.5 h and then at room temperature for 20.5 h.
After 24 h, the copolymerization was stopped by adding a few
drops of aqueous HCl (0.1 mol‚L-1). After evaporation of the
solvent, the product was dissolved in dichloromethane (20 mL)
and extracted three times each with a saturated aqueous KCl
solution (3 × 20 mL) and with deionized water (3 × 20 mL).
Finally, the organic layer was poured into a large excess of
cold heptane (160 mL). The copolymer was recovered by
filtration and dried under reduced pressure at 40 °C until a
constant weight was obtained (yield 99%). As determined by
SEC with reference to polystyrene standards, Mn(PS) ) 6300
g‚mol-1 and Mw/Mn ) 2.3. 1H NMR (CDCl3, δ (ppm); see Figure
C in the Supporting Information for signal assignation): 1.0-
1.2 (m, 6Hh), 1.3-1.8 (m, 18Hj+6Hb+c+d), 2.4 (t, 2He), 2.7-3.1
(m, 2Hm), 3.65 (t, 2Hi), 4.1 (t, 2Hf), 5.0-5.2 (m, 2Hn), 5.5 (m,
1Hl), 7.3 (s, 5Ho).
Synthesis of MLA-PCL. The ROP of CL (1 g, 8.77 × 10-3
mol) was initiated by aluminum triisopropoxide in toluene
solution (concentration 1 mol‚L-1, 1.75 mL) at 0 °C for an
initial monomer concentration of 0.2 mol‚L-1 (Vtolu ) 42 mL)
and an initial monomer-to-initiator molar ratio of 5. After 3
h, a few drops of HCl aqueous solution (0.1 mol‚L-1) was added,
and the R-isopropoxy-ω-hydroxypoly(ꢀ-caprolactone) (PCL-OH)
was selectively recovered by precipitation in cold heptane (yield
97%). Aluminum residues were extracted as previously de-
scribed (Mn ) 630 g‚mol-1, Mw/Mn ) 1.07 as determined by
size exclusion chromatography using the Mark-Houwink
parameters; see hereafter).11 Malolactonic acid (MLA) was
obtained by selective hydrogenation of MLABz in acetone at
room temperature using 20 wt % Pd/C and hydrogen. After 7
h, the reaction medium was filtered on Celite, and MLA was
recovered by flash distillation of the solvent (yield >99%). In
a previously flame-dried and nitrogen-purged round-bottom
flask, 177 mg (1.5 × 10-3 mol) of malolactonic acid and 155
mg (7.5 × 10-4 mol) of N,N′-dicyclohexylcarbodiimide were first
dried under vacuum for 30 min, then solubilized in 8 mL of
dry THF, and kept under a nitrogen atmosphere under
vigorous stirring at room temperature for 6 h. The reaction
medium rapidly turned white due to the formation of insoluble
dicyclohexylurea. In a second previously flame-dried and
nitrogen-purged round-bottom flask, 104 mg of PCL-OH (1.7
× 10-4 mol) and 38 mg of 4-(dimethylamino)pyridine (3.1 ×
10-4 mol) were dried by three successive azeotropic distillations
of toluene and dissolved in 8 mL of dry THF before being
transferred into malolactonic anhydride suspension through
a previously flamed and nitrogen-purged capillary. After a 48
h reaction time, the precipitated dicyclohexylurea was filtered
off, and the macromonomer (MLA-PCL) was selectively
recovered by precipitation into cold heptane (160 mL), filtered,
and dried under reduced pressure at 40 °C until a constant
weight was obtained (yield 62%, Mn ) 730 g‚mol-1, Mw/Mn )
1.07). 1H NMR (CDCl3, δ (ppm); see Figure A in the Supporting
Information for signal assignation): 0.8-0.9 (d, 6Hh), 1.3-1.45
(m, 2Hc), 1.45-1.9 (m, 4Hb+d), 2.4 (t, 2He), 3.55-3.9 (dd, 2Hk+k′),
4-4.2 (t, 2Hf), 4.25-4.4 (m, 3Hg+a), 4.85 (t, 1Hj).
Anionic Ring-Opening Copolymerization of MLABz
and MLAAllyl. Copolymerization of MLABz (e.g., 0.86 g, 4.2
× 10-3 mol, 93 mol %) and MLAAllyl (e.g., 0.05 g, 3.2 × 10-4
mol, 7 mol %) was typically conducted in a previously flame-
dried and nitrogen-purged round-bottom flask equipped with
a three-way stopcock and a septum by initiation with the
complex formed between potassium 11-hydroxydodecanoate
and 18-crown-6 ether (0.9 mL, 9.0 × 10-5 mol) in THF (20 mL)
at 0 °C. After 260 min, the copolymerization was stopped by
adding a few drops of aqueous HCl (0.1 mol‚L-1). After
evaporation of the solvent, the product was dissolved in
dichloromethane (20 mL) and extracted three times each with
a saturated aqueous KCl solution (3 × 20 mL) and with
deionized water (3 × 20 mL). Finally, the organic layer was
poured into 8 volumes of cold heptane (160 mL). The copolymer
was selectively recovered by filtration and dried under reduced
pressure at 40 °C until a constant weight was obtained (yield
92%). As determined by SEC with reference to polystyrene
standards, Mn(PS) ) 2900 g‚mol-1 and Mw/Mn ) 1.5. 1H NMR
(CDCl3, δ (ppm)): 0.8-1.8 (m, 18Hb), 2.3 (t, 2Hc), 2.7-3.0 (m,
2He), 3.6 (t, 2Ha), 4.55 (m, 2Hh), 5-5.2 (s, 2Hf), 5.25 (s, 2Hj),
5.55 (m, Hd), 5.8 (m, 1Hi) and 7.3 (s, 5Hg). Mn ) 8100 g‚mol-1
Anionic Ring-Opening Polymerization of MLA-PCL.
In a previously flame-dried and nitrogen-purged round-bottom
flask, 1.0 g (7.8 × 10-3 mol) of naphthalene was mixed with
0.37 g (9.5 × 10-3 mol) of potassium and 39 mL of dry THF.
After an overnight reaction, a deep green-colored solution of
potassium naphthalene radical anion was obtained (concentra-
tion 0.2 mol‚L-1). In another previously flame-dried and
nitrogen-purged round-bottom flask, 0.52 g (1.97 × 10-3 mol)
of 18-crown-6 ether and 0.43 g (1.97 × 10-3 mol.) of 11-
hydroxydodecanoic acid were dissolved in 10 mL of dry THF
and then mixed with a stoichiometric amount of the potassium
naphthalene radical anion in THF solution (10.0 mL, 1.97 ×
10-3 mol, [HDD] ) 0.1 mol‚L-1). The polymerization of MLA-
1
could be calculated from the H NMR spectrum as discussed
in the Results and Discussion.
Methylation of Poly(benzyl â-malolactonate-co-allyl
â-malolactonate), r-Hydroxy, ω-Carboxylic Acid. In a
previously flame-dried and nitrogen-purged round-bottom flask
equipped with a three-way stopcock and a septum, 0.5 g of
poly(benzyl â-malolactonate-co-allyl â-malolactonate), R-
hydroxy, ω-carboxylic acid (6.3 × 10-5 mol, Mn(NMR) ) 8100

3144 Coulembier et al.
Macromolecules, Vol. 38, No. 8, 2005
g‚mol-1, Mw/Mn ) 1.5) was dried by three successive azeotropic
distillations of toluene (3 × 10 mL) and then dissolved in a
mixture of 25 mL of toluene and 2.5 mL of anhydrous
methanol. Trimethylsilyldiazomethane (5.7 × 10-4 mol, 0.3
mL, 9 equiv compared to the content of carboxylic acid end
groups) was added while gas evolution was allowed through a
connected oil valve. After 3 h, the reaction was stopped by the
addition of a few drops of acetic acid in aqueous solution (0.1
mol‚L-1), and the volatiles were removed under reduced
pressure. The copolymer was recovered by precipitation into
8 volumes of cold heptane (160 mL), filtered, and dried under
reduced pressure at 40 °C until a constant weight was obtained
(yield 86%). 1H NMR (CDCl3, δ (ppm); see Figure 4 for signal
assignation): 0.8-1.8 (m, 18Hb), 2.3 (t, 2Hc), 2.7-3.0 (m, 2He),
3.5 (s, 3Hk), 3.6 (t, 2Ha), 4.55 (m, 2Hh), 5-5.2 (s, 2Hf), 5.25 (s,
2Hj), 5.5 (m, Hd), 5.8 (m, 1Hi) and 7.3 (s, 5Hg).
Conversion of Poly(benzyl â-malolactonate-co-allyl
â-malolactonate) Allylic Functions to Hydroxyl Pendant
Groups. In a previously flame-dried and nitrogen-purged
round-bottom flask equipped with a three-way stopcock and
a septum, 0.46 g of poly(benzyl â-malolactonate-co-allyl â-malo-
lactonate), R-hydroxy, ω-methyloxycarbonyl (5.6 × 10-5 mol,
Mn(NMR) ) 8100 g‚mol-1, Mw/Mn ) 1.5) was dried by three
successive azeotropic distillations of toluene (3 × 10 mL) and
mixed with 13 mg of 2,2′-azobis(2-methylpropionitrile) (AIBN)
(7.8 × 10-5 mol). After 1 h under reduced pressure, the
polymer/AIBN mixture was solubilized in 6 mL of dry toluene
and mixed with 0.125 mL of mercaptoethanol (1.8 × 10-3 mol).
The reaction was carried out at 70 °C for 24 h. Then the
copolymer was recovered by precipitation into cold ethanol (60
mL) and dried under reduced pressure at 40 °C until a
constant weight was obtained (yield 91%). As determined by
SEC with reference to polystyrene standards, Mn(PS) ) 2600
g‚mol-1 and Mw/Mn ) 1.6. 1H NMR (CDCl3, δ (ppm); see Figure
5 for signal assignation): 0.8-1.7 (m, 18Hb), 1.85 (m, 2Hi′), 2.45
(t, 2Hc), 2.5 (t, 2Hk′), 2.65 (t, 2Hj′), 2.8-3.1 (m, 2He), 3.4-3.9
(m, 2Ha+3Hk+2Hl′), 4.2 (m, 2Hh), 5.1-5.25 (s, 2Hf), 5.6 (m,
Hd), and 7.3 (s, 5Hg).
pressure (10 mmHg) before recovery of the polymer by
extensive drying at 40 °C under reduced pressure (yield 92%).
1H NMR (CD3COCD3, δ (ppm)): 1.2-1.4 (m, 18Hb + 2Hi′
+
6H), 1.55 (m, 4HPCL), 2.3 (t, 2HPCL), 2.9-3.1 (m, 2He), 3.55 (t,
2Ha), 4.1 (t, 2HPCL), 5.5 (s, Hd).
Characterization. 1H NMR (300 MHz) spectra were
recorded using a Bruker AMX-300 apparatus at room tem-
perature in CDCl3 except as otherwise mentioned (30 mg/0.6
mL). SEC was performed in THF at 35 °C using a Polymer
Laboratories liquid chromatograph equipped with a PL-DG802
degasser, an isocratic HPLC pump, LC 1120 (flow rate 1 mL/
min), a Rheodin manual injection (loop volume 200 µL, solution
concentration 2 mg/mL), a PL-DRI refractive index detector,
and four columns: a PL gel 10 µm guard column and three PL
gel mixed-B 10 µm columns (linear columns for separation of
MWPS ranging from 500 to 106). Molar masses and their
distribution were calculated with reference to polystyrene
standards. The surface tensions were determined using a drop
shape analysis system, DSA 10 Mk2, equipped with a ther-
mostated chamber and a circulator, Thermo Haake DC 10.
Mass spectrometry measurements were performed on a Waters
QToF2 apparatus equipped with an orthogonal electrospray
ionization (ESI) source (Z-spray) operated in positive ion mode.
ω-Hydroxy-PCL and MLA-PCL macromonomer were dis-
solved in acetonitrile to approximately achieve 10-4 mol‚L-1
concentration, as estimated from the molar mass determined
by 1H NMR spectroscopy. The solutions were infused into the
ESI source at a rate of 5 µL‚min-1 with a Harvard syringe
pump. Typical ESI conditions were capillary voltage 3.1 kV,
cone voltage 80 V, source temperature 80°C, and desolvation
temperature 120 °C. Dry nitrogen was used as the ESI gas.
The quadrupole was set to pass ions from 100 to 3000 Th, and
all ions were transmitted into the pusher region of the time-
of-flight analyzer where they were mass-analyzed with a 1 s
integration time. Data were acquired in continuum mode until
acceptable averaged data were obtained.
Results and Discussion
Ring-Opening Polymerization of E-Caprolactone Us-
ing Poly(benzyl â-malolactonate-co-propyl-3-thioethan-
2-ol â-malolactonate) Macroinitiator. In a previously
flame-dried and nitrogen-purged round-bottom flask equipped
with a three-way stopcock and a septum, 0.425 g of poly(benzyl
â-malolactonate-co-propyl-3-thioethan-2-ol â-malolactonate)
(6.3 × 10-5 mol, Mn ) 6700 g‚mol-1, Mw/Mn ) 1.6) was dried
by three successive azeotropic distillations of toluene (3 × 10
mL). Then the dried polymer was reacted with 1.2 equiv of
triethylaluminum relative to the hydroxy content (2.3 × 10-4
mol, 11 mL) in toluene at 50 °C for 2 h while ethane evolved
through a connected oil valve. After the mixture was cooled
to room temperature, 2 mL of ꢀ-caprolactone (1.8 × 10-2 mol)
was added and polymerized for 72 h. The polymerization was
stopped by adding a few drops of a HCl aqueous solution (0.1
mol‚L-1). Aluminum residues were removed by washing the
organic phase three times with an aqueous solution of ethyl-
enediaminetetraacetic acid (EDTA) buffered at pH 4.8 (0.1
mol‚L-1) (3 × 20 mL) and with deionized water (3 × 20 mL).
The organic layer was finally poured into a large excess of cold
heptane (160 mL). The copolymer was recovered by filtration
and dried under reduced pressure at 40 °C until a constant
weight was obtained (yield 94%). As determined by SEC with
reference to polystyrene standards, Mn(PS) ) 14000 g‚mol-1
(Macro)monomer Preparation. MLABz and
MLAAllyl have been synthesized through a well-
established three-step procedure starting from racemic
aspartic acid.9 Global yields depend on the â-substituted
â-malolactone reaching 30% and 60% for MLABz and
MLAAllyl, respectively.
MLA-PCL was obtained by esterification of MLA
with PCL-OH. Well-defined low molecular weight PCL-
OH chains were synthesized by initiating the ROP of
CL by Al(OiPr)3 in toluene at 0 °C for an initial [CL]0/
[Al(OiPr)3]0 molar ratio of 5 (eq a, Scheme 3). Under
such prevailing conditions, the polymerization of CL was
demonstrated to be perfectly living and characterized
by an average number of active sites per aluminum
atom close to 1.12 After complete monomer conversion
and hydrolysis of the aluminum alkoxide active sites,
PCL-OH with a narrow polydispersity index was iso-
lated. As determined by SEC by reference to a polysty-
rene standard calibration, using the Mark-Houwink
relationship [η] ) KMa for PS and PCL (KPS ) 1.25 ×
10-4 dL g-1, aPS ) 0.707, KPCL ) 1.09 × 10-3 dL g-1
,
1
and Mw/Mn ) 1.8. H NMR (CDCl3, δ (ppm)): 1.4 (m, 18Hb +
aPCL ) 0.600), a molecular weight of 630 and a polydis-
persity index of 1.07 were calculated. MLA was prepared
by selective catalytic hydrogenation of MLABz under
mild experimental conditions (see eq b, Scheme 3). Then
esterification between PCL-OH and MLA was carried
out using N,N′-dicyclohexylcarbodiimide (DCCI) and
4-(dimethylamino)pyridine (DMAP) as water scavenger
and catalyst, respectively (eq c, Scheme 3).
2Hi′), 1.65-1.8 (t, 4HPCL), 2.4 (t, 2HPCL), 2.9 (m, 2He), 3.65 (t,
2Ha+k), 4.1 (t, 2HPCL), 5.1 (s, 2Hf), 5.5 (m, Hd), 7.25 (s, 5Hg).
Mn ) 6400 g‚mol-1 for the PCL blocks was calculated from
the 1H NMR spectrum as discussed in the Results and
Discussion.
Removal of Benzyl Ester Protective Groups. In a
round-bottom flask, 0.18 g of the graft copolymer above was
dissolved in 250 mL of acetone at room temperature, and the
resulting solution then mixed with 0.04 g of Pd/C (10 wt %). A
continuous flow of hydrogen was bubbled into the solution for
10 h. After filtration through Celite, a clear copolymer solution
was obtained. The solvent was evaporated under reduced
1
As evidenced by H NMR spectroscopy, PCL chains
are quantitatively end-capped with a malolactonate
moiety. Indeed, the signal corresponding to the R-

Macromolecules, Vol. 38, No. 8, 2005
Synthesis of PMLA-g-PCL 3145
Scheme 3. Synthesis of MLA-PCL
hydroxymethylene-PCL end group (-CH2OH) at 3.6
ppm completely disappeared (see Figure A given in the
Supporting Information). A further confirmation for the
quantitative esterification of the polyester hydroxyl end
groups comes from spectrometry measurements. Figure
1 shows the ESI mass spectra of both PCL-OH (Figure
1A) and MLA-PCL (Figure 1B).
monomer to homopolymerize and thus the reactivity of
the terminal malolactonate moiety toward anionic ROP
have been investigated. The anionic polymerization of
MLA-PCL was carried out according to previously
established experimental conditions that strongly limit
the occurrence of undesirable transfer and termination
reactions by proton abstraction.14 By reducing both the
polymerization temperature to 0 °C and the initial
concentration in monomer to 0.2 mol‚L-1, the polymer-
ization of MLABz as initiated in THF by potassium 11-
hydroxydodecanoate in the presence of HDD is “living”
and proceeds selectively through the O-alkyl cleavage
of the endocyclic ester bond of malolactonate monomer.
Accordingly, the anionic homopolymerization of MLA-
PCL macromonomer (0.2 mol‚L-1) was initiated by HDD
in THF at 0 °C for an initial monomer-to-initiator molar
ratio of 7 (DPtheor ) 7). After 4 h of reaction time, the
1H NMR spectrum of the polymerization product is
characterized by the disappearance of cyclic malolacto-
nate methine protons at 4.9 ppm (see Figure B in the
Supporting Information). Complete consumption of the
macromonomer was further confirmed by SEC. Indeed
the molecular weight distribution of the polymerization
product is monomodal and shifted to lower retention
volume compared to that of MLA-PCL macromonomer
(Figure 2). Assuming the selective formation of poly-
(MLA-PCL) R-hydroxydodecanoate, ω-carboxylic acid,
nonaqueous potentiometric titration of carboxylic acid
functions has been carried out to determine the average
molar mass. P(MLA-PCL) was solubilized in a toluene/
methanol (8/2) solution at room temperature and ti-
trated by tetramethylammonium hydroxide solution.
The resulting average molar mass (Mn) of 5400 g‚mol-1
agrees very well with the theoretical Mn of 5300 g‚mol-1
(Mn,theor ) ((DPtheor)(Mn,MLA-PCL) + MWHDA, where
Mn,MLA-PCL and MWHDA are the molar masses of MLA-
PCL (Mn ) 730 g‚mol-1, as determined by ESI mass
spectrometry (ESI-MS) analysis) and 11-hydroxy-
dodecanoic acid, respectively). Therefore, the cyclic
malolactonate moiety is selectively and quantitatively
fixed at the PCL chain end group and, more impor-
tantly, is active in anionic ring-opening polymerization.
One of the main features of the ESI mass spectrum
of PCL-OH is that the mass difference between two
consecutive peaks is ca. 114.07, i.e., the molecular
weight of the CL repeating unit, -C(O)(CH2)5O- (exact
mass 114.0681). The most intense signal, detected at
i
m/z 653.38, corresponds to PrO[C(O)(CH2)5O]5H‚Na+
cation, which possesses five CL repeating units together
with isopropoxy and hydroxy end groups. This agrees
with the expected macromolecular structure and the
SEC data (Mn ) 630 g‚mol-1, Mw/Mn ) 1.07). In-depth
analysis of the mass spectrum reveals the presence of
additional mass distributions that could be identified
as iPrO[C(O)(CH2)5O]5H‚K+ (noted “a” in Figure 1A) and
iPrO[C(O)(CH2)5O]5H‚H+ (noted “b” in Figure 1A).
In the case of MLA-PCL macromonomer, doubly
charged species are clearly detected since the mass
difference between two consecutive signals reaches ca.
57.04 (114.0681/2 ) 57.034). The maximum in the ESI
mass spectrum appears at m/z 729.42, but it could not
be unambiguously attributed as the molecular ion
distribution of doubly charged species is strongly de-
pendent on the oligomer molar mass. In other words,
oligomers of lower molar mass can carry fewer charges
than those of higher molar mass.13 Such a behavior upon
ESI ionization probably arises from the covalent binding
of the malolactonate moiety at the PCL chain extremity.
Regardless of the assignment of specific signals, the
most important feature is that no residual PCL-OH
could be detected in the ESI mass spectrum (neither
singly or doubly charged species), thus confirming the
completion of the esterification reaction as attested by
the following polymerization experiments.
Synthesis of PMLA-g-PCL through the Macro-
monomer Technique. Before study of the graft co-
polymer synthesis, the efficiency of MLA-PCL macro-

3146 Coulembier et al.
Macromolecules, Vol. 38, No. 8, 2005
Figure 1. ESI mass spectra (Waters QToF2) of PCL-OH (A) and MLA-PCL (B) used as intermediates in the synthesis of poly-
((R,S)-â-malic acid)-graft-poly(ꢀ-caprolactone) graft copolymers through the macromonomer technique (1 mg/1 mL in acetonitrile).
Accordingly, the next step can rely upon the investiga-
tion of the graft copolyester synthesis.
According to the two-step strategy depicted in Scheme
1, poly((R,S)-benzyl â-malolactonate)-graft-poly(ꢀ-capro-
lactone) graft copolymers (PMLABz-g-PCL) of various
compositions were synthesized by initiating the anionic
ring-opeining copolymerization of a mixture of MLABz
and MLA-PCL by HDD in THF for an initial comono-
mer-to-initiator ratio of 40 and an initial total comono-
mer concentration ([MLABz + MLA-PCL]0) of 0.2
mol‚L-1 (Table 1). As already mentioned, to drastically
reduce the occurrence of undesirable transfer and
termination reactions, copolymerizations were initiated
at 0 °C. Due to the quite long reaction time required

Macromolecules, Vol. 38, No. 8, 2005
Synthesis of PMLA-g-PCL 3147
Table 2. Molecular Characteristics of Amphiphilic
PMLA-g-PCL Obtained by the Macromonomer Technique
fPCL(NMR)a
FPCL(NMR)b
entry
sample
(%)
(%)
1
2
3
PMLA-g-PCL1
PMLA-g-PCL2
PMLA-g-PCL3
4.5
5.0
10.0
15.5
16.0
28.7
a fPCL(NMR) ) experimental PCL molar fraction in PMLA-g-
PCL graft copolymers ) 100[I4.1/(I4.1 + 2I5.5)] (see Figure 3).
b FPCL(NMR) ) experimental PCL weight fraction in PMLA-g-PCL
grafts copolymers ) [Mn,MLA-PCL(fPCL(2I4.2)/100I3.6)]/[(Mn,MLA-PCL
-
(fPCL(2I4.2)/100I3.6)) + (206(1 - fPCL)(2I4.2)/100I3.6)].
Figure 2. SEC traces of MLA-PCL (full line) (Mn,PS ) 850,
Mw/Mn ) 1.07) and its homopolymer P(MLA-PCL) as obtained
by anionic polymerization (square full line) (Mn,PS ) 8000, Mw/
Mn ) 1.4).
Table 1. Molecular Characteristics of PMLABz-g-PCL As
Obtained by Ring-Opening Copolymerization of MLABz
and MLA-PCL Initiated by Potassium
11-Hydroxydodecanoate Mixed with HDD in THF for
[MLABz + MLA-PCL]0 ) 0.2 mol‚L-1and [MLABz +
MLA-PCL]0/[HDD] ) 40
[MLABz]/
[MLA-PCL]
c
at the
reaction yield
Mn,exp
Mw/
c
entry starta copolymerb time (h)
(%)
(g‚mol-1
)
Mn
Figure 3. 1H NMR spectrum in (CD3)2CO of PMLA-g-PCL
obtained by catalytic hydrogenation of PMLABz-g-PCL (entry
3, Table 2).
1
2
3
66/1
49/1
8/1
21/1
19/1
9/1
3.5
3.5
25
72
72
99
2000
2000
6300
1.3
1.4
2.3
a Initial MLABz/MLA-PCL macromonomer molar ratio.
b MLABz/MLA-PCL macromonomer molar ratio as determined
by 1H NMR from the relative intensity of the methylene oxycar-
bonyl protons of MLABz and the methylene protons of PCL. c As
determined by SEC with reference to polystyrene standards.
Synthesis of PMLA-g-PCL through the Grafting
From Technique. As shown in Scheme 2, the first step
in the synthesis of PMLA-g-PCL graft copolymers
through the grafting from technique involves the anionic
ring-opening copolymerization of MLAAllyl and MLABz
using HDD as initiator in THF at 0 °C for a comonomer
concentration of 0.2 mol‚L-1. After selective derivati-
zation of the carboxylic acid end groups in methyl
ester,14 the second step consists of the conversion of
pendant allylic functions into hydroxy groups by reac-
tion with mercaptoethanol in the presence of AIBN in
toluene at 70 °C. The third step implies the controlled
ROP of CL initiated by the as-formed pendant hydroxyl
functions, previously activated by AlEt3. The fourth and
last step corresponds to the selective deprotection of the
benzyl ester groups by catalytic hydrogenation.
Two poly(benzyl â-malolactonate-co-allyl malolacto-
nate) (P(MLABz-co-MLAAllyl)) graft copolymers were
synthesized from different initial comonomer molar
fractions, while the targeted copolymer molar mass was
kept constant (Mn,theor ) 10000 g‚mol-1) (Table 3).
Assuming that each chain of P(MLABz-co-MLAAllyl) is
end-capped by a hydroxyl group at one end and a
carboxylic acid function at the other chain end, the
experimental molar mass can be calculated by 1H
NMR spectroscopy (Mn,exp) from the relative intensity
of the methine protons within the main polyester chain
at 5.5 ppm (-CH(COOR)CH2COO-) and the terminal
methylene protons at 0.8-1.7 ppm (HOCH2(CH2)9CH2-
COO-). The molar composition of each copolymer was
determined from the relative intensity of R-vinylic
methylene protons at 4.6 ppm (-CO2CH2CHdCH2) and
the methylene protons of the poly(malolactonate) re-
peating units at 2.9 ppm (-CH(CO2R)CH2CO2-). The
for higher MLA-PCL molar fraction in the feed (entry
3 in Table 1), the temperature was allowed to increase
to room temperature after ca. 3.5 h at 0 °C. These
operating conditions directly affect the molecular weight
distribution of the copolymer, which broadens. The
copolymer composition was determined by 1H NMR
spectroscopy from the relative intensity of CL repeating
methylene unit protons at 4.1 ppm (-CO2CH2(CH2)4-)
and the methylene protons of the MLABz repeating
units at 5.1 ppm (-CO2CH2C6H5). It comes out that the
resulting graft copolymers are characterized by a higher
MLA-PCL macromonomer content compared to that of
the feed, indicating that MLA-PCL reacts faster than
MLABz in such experimental conditions.
The second step in the synthesis of the amphiphilic
PMLA-g-PCL graft copolymers consists of the catalytic
hydrogenation of benzyl ester functions anchored all
along the poly(malolactonate) backbone (see Table
2).14,15 1H NMR spectra of the as-obtained copolymers
recorded in (CD3)2CO show the complete disappearance
of benzylic protons, i.e., no signal from 6 to 9 ppm,
attesting for the quantitative deprotection reactions (see
Figure 3). As previously reported,14 the generated
carboxylic acid functions form strong hydrogen bonding
with the ester carbonyl functions, at least in a solvent
such as acetone-d6 ((CD3)2CO), so that no resonance
signal typical of carboxylic acid protons around 10 ppm
could be detected at low field.

3148 Coulembier et al.
Table 3. Molecular Characteristics of
P(MLABz-co-MLAAllyl) Synthesized by Ring-Opening
Copolymerization of MLABz and MLAAllyl by Potassium
11-Hydroxydodecanoate Mixed with 18-Crown-6 Ether in
THF at 0 °C for [MLABz + MLAAllyl]0 ) 0.2 mol‚L-1
Macromolecules, Vol. 38, No. 8, 2005
Table 4. Molecular Characteristics of
P(MLABz-co-MLAO-H) Copolymers As Obtained by
Reaction of P(MLABz-co-MLAAllyl) with
Mercaptoethanol Using AIBN in Toluene at 70°C for
24 ha
b
b
b
[MLABz]/
[MLAAllyl]
Mn,exp
fMLAAllyl fMLAOH Mw/
c
entry
sample
(g‚mol-1
)
(%)
(%)
Mn
polym
time convna Mn,theor
at the
co-
Mn,exp
Mw/
Mn
b
e
1
2
3
4
P(MLABz-co-MLAAllyl) 1
P(MLABz-co-MLAOH) 1
P(MLABz-co-MLAAllyl) 2
P(MLABz-co-MLAOH) 2
8100
7000
8400
9200
7.6
1.5
1.6
1.2
1.3
(g‚mol-1
)
startc polymerd (g‚mol-1
)
f
entry (min)
(%)
5.1
13
13
1
2
260
340
92
100
9200
10000
14/1
8/1
13/1
8/1
8100
8400
1.5
1.2
a Entries 1 and 3 refer to entries 1 and 2, respectively, in Table
3, i.e., to the copolymers before methylation). b As determined by
1H NMR spectroscopy: Mn(P(MLABz-co-MLAAllyl)) ) (9Ie/Ib)[(Ih/
Ie)MWMLAAllyl + (1 - Ih/Ie)MWMLABz]; Mn(P(MLABz-co-MLAOH))
) (2Id/Ic)[(Ii/2Id)MWMLAOH + (1 - Ii/2Id)MWMLABz]; fMLAAllyl ) 100Ih/
Ie and fMLAOH ) 100Ii/2Id. c As determined by SEC using PS
standards.
a Global comonomer conversion as determined by gravimetry.
b Mn,theor ) [MLABz + MLAAllyl]0/[HDD]0(convn)(MWMLABzfMLABz
+ MWMLAAllylfMLAAllyl) + MWHDD, where fMLABz and fMLAAllyl are the
molar fractions of MLABz and MLAAllyl in the copolymer,
respectively, and MWMLABz and MWMLAAllyl are the molar masses
of MLABz and MLAAllyl, respectively. c Initial MLABz/MLAAllyl
molar ratio. d MLABz/MLAAllyl molar ratio as determined by
1H NMR from the relative intensity of the methylene oxycarbon-
yl protons of MLABz and the R-vinylic methylene protons of
MLAAllyl. e As determined by 1H NMR spectroscopy: Mn,exp ) [9I3/
I0.8-1.7][(I4.6/I3)MWMLAAllyl + (1 - I4.6/I3)MWMLABz]. f As determined
by SEC using PS standards.
Figure 5. 1H NMR spectrum in CDCl3 of P(MLABz-co-MLA-
OH) (entry 4 in Table 4).
4) displaying a typical signal at 3.5 ppm characteristic
of the ω-methyl ester end groups (Hk).
The second step involves the conversion of allylic
functions into hydroxyl ones by reaction with mercapto-
ethanol, leading to poly(benzyl â-malolactonate-co-
propyl-3-thioethan-2-ol â-malolactonate) random copoly-
mers (P(MLABz-co-MLA-OH)) (entries 2 and 4 in Table
4). This reaction was carried out in toluene at 70 °C for
24 h using AIBN as radical promoter.16,17 1H NMR
spectroscopy attests for the completion of the homolytic
reaction by the disappearance of allylic protons at 5.8
and 5.35 ppm (Hi and Hj in Figure 4) to the benefit of
R-hydroxyl methylene (Hl′ in Figure 5) and R-thioether
methylene (Hk′ in Figure 5) protons from the short
lateral chains at 3.6 and 2.6 ppm, respectively, and by
the shift of methylene R-allylic protons (Hh) from 4.55
down to 4.3 ppm. Taking into account the inherent
experimental error of 1H NMR spectroscopy, the conver-
sion of allylic functions into hydroxy groups does not
detrimentally affect the molecular parameters (Mn and
Mw/Mn) of the so-obtained copolymers (Table 4).
Figure 4. 1H NMR spectrum in CDCl3 of P(MLABz-co-
MLAAllyl) as obtained by anionic ring-opening copolymeriza-
tion of (R,S)-benzyl â-malolactonate and (R,S)-allyl â-malolac-
tonate, followed by methylation of carboxylic end groups (entry
1, Table 4)
comonomer compositions at the start and in the copoly-
mers are very close to each other, while the experimen-
tal molar masses of the copolymers are only slightly
lower than predicted values. This can be explained by
1
the inherent experimental error of H NMR spectros-
copy. The monomodal molecular weight distributions
are quite narrow according to SEC.
To avoid undesirable side reaction with triethyl-
aluminum that will be used for activating the CL ROP
in a next step, the carboxylic acid end groups of
P(MLABz-co-MLAAllyl) chains were reacted first with
an excess of trimethylsilyldiazomethane for 1 h at room
temperature in toluene/methanol (9/1).14 Figure 4 shows
the 1H NMR spectrum of the resulting R-hydroxy,
ω-methyl ester P(MLABz-co-MLAAllyl) (entry 1 in Table
In the next step, the polymerization of CL was
initiated by the hydroxy functions attached all along the
poly(malonate) backbone after adequate activation by
adding a slight excess of triethylaluminum ([AlEt3]0/

Macromolecules, Vol. 38, No. 8, 2005
Synthesis of PMLA-g-PCL 3149
Figure 6. SEC traces of P(MLABz-co-MLAOH) 2 (1) (entry 4 in Table 4) and polymalolactonate-graft-poly(ꢀ-caprolactone) graft
copolymer as obtained by the grafting from technique, PMLABz-g-PCL 2 (2) (entry 2 in Table 5).
Table 5. Molecular Characteristics of PMLABz-g-PCL Synthesized by Ring-Opening Polymerization of CL from
P(MLABz-co-MLAOH)a
b
c
c
d
fPCL,theor
(%)
fPCL,exp
(%)
Mn,PCL,exp
Mn,copo
d
entry
sample
macroinitiator backbone
[CL]0/[OH]0
(g‚mol-1
)
(g‚mol-1
)
Mw/Mn
1
2
PMLABz-g-PCL 1
PMLABz-g-PCL 2
P(MLABz-co-MLAOH) 1
P(MLABz-co-MLAOH) 2
142
34
89.7
66.0
93.7
86.4
6400
2200
14000
3700
1.8
1.6
a Entries 1 and 2 refer to entries 2 and 4 in Table 4. b Theoretical molar fraction of PCL. c The experimental PCL molar fraction (fPCL,exp
)
and molar mass (Mn,PCL,exp) have been determined from 1H NMR spectra: fPCL,exp ) 100[I4.1/(I4.1 + I5.1)] and Mn,PCL,exp ) 114.14(I4.1/I3.6).
d As determined by SEC using PS standards.
[OH]0 ) 1.2). The lactone ROP has been carried out in
toluene at room temperature for an initial CL concen-
tration of 1 mol‚L-1 and for [CL]0/[OH]0 initial molar
ratios of 142 and 34 starting from P(MLABz-co-MLA-
OH) copolymers 1 and 2, respectively. After a 72 h
reaction time, a few drops of a HCl aqueous solution
(0.1 mol‚L-1) was added, and PMLABz-g-PCL graft
copolymers were recovered by precipitation from a large
excess of heptane. The grafting of the PCL segments
onto the P(MLABz-co-MLAOH) copolymers was attested
by SEC, which, for instance, shows the shift of the trace
of the PMLABz-g-PCL 2 graft copolymer to lower elution
volume compared to that of P(MLABz-co-MLAOH) 2
Figure 7. Time dependence of the IFT of a 2 g‚L-1 PMLA-
1
copolyester (Figure 6). Again H NMR spectra allowed
g-PCL 3 chloroform solution in water at 25 °C (entry 3 in Table
determination of the copolymer composition and PCL
graft molar masses (Table 5).
2).
The last step in the synthesis of amphiphilic PMLA-
g-PCL graft copolymers relies upon the selective cata-
lytic hydrogenation of benzyl ester functions. As evi-
denced by 1H NMR spectroscopy from the relative
intensity of benzyloxycarbonyl protons at 7.3 ppm and
the methine repetitive protons at 5.55 ppm, only 40%
of the protective groups could be removed, even under
intensive hydrogenation for 20 h. Compared to the data
related to the graft copolymers obtained by the macro-
monomer technique, such a behavior typically observed
for PMLABz-g-PCL graft copolymer characterized by a
much higher grafting density can only be explained
by some screening effect of PCL grafts toward the
heterogeneous catalytic hydrogenation, limiting there-
fore the access to the benzylic moieties along the main
backbone.
3 (entry 3 in Table 2) in chloroform was dipped into
Millipore Milli-RO water. Figure 7 shows the time
evolution of the chloroform/water interfacial tension
(IFT) induced by the investigated graft copolymer. At
25 °C, the IFT values drop from 29 to 4 mN/m,
demonstrating the tensioactive properties of this new
type of amphiphilic graft copolymers.
In conclusion, we have reported two new synthetic
approaches for grafting hydrophobic poly(ꢀ-caprolactone)
chains onto a highly hydrophilic poly((R,S)-â-malic acid)
backbone. Both the grafting from and grafting through
(i.e., macromonomer) techniques were successful and
allowed for controlling the graft copolyester composition
and molecular weight. As expected, these graft copoly-
esters display amphiphilic properties as attested by pre-
liminary interfacial tension measurements. The tensio-
active behavior of these new graft copolymers and their
ability to form micelles in aqueous media are under
current investigation and will be the subject of a
forthcoming paper.
Preliminary Interfacial Tension Measurements.
The amphiphilic character of these new biocompatible
PMLA-g-PCL graft copolymers is evidenced by interfa-
cial tension measurements. Purposely and as a repre-
sentative example, a 2 g‚L-1 solution of PMLA-g-PCL

3150 Coulembier et al.
Macromolecules, Vol. 38, No. 8, 2005
(5) Vert, M. CRC Crit. Rev. Ther. Drug Carrier Syst. 1986, 2,
291.
Acknowledgment. This work was partially sup-
ported by both the Re´gion Wallonne and the
Fonds Social Europe´en in the frame of the Objectif
1-Hainaut: Materia Nova program. O.C. is grateful to
FRIA for his Ph.D. grant. The LPCM thanks the Service
Fe´de´raux des Affaires Scientifiques, Techniques et
Culturelles for general support in the frame of Grant
PAI-5/03. P.G.sFNRS Research Associatesthanks the
Fonds National pour la Recherche Scientifique for
financial support in the acquisition of the Micromass
QToF2 instrument and for continuing support.
(6) Fournie´, Ph.; Dumurado, D.; Gue´rin, Ph.; Braud, C.; Vert,
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Supporting Information Available: 1H NMR spectra of
MLA-PCL, poly(MLA-PCL), and PMLABz-g-PCL (PDF).
This material is available free of charge via the Internet at
http://pubs.acs.org.
(12) Lo¨fgren, A.; Albertsson A. C.; Dubois Ph.; Je´roˆme R. Rev.
Macromol. Chem. Phys. 1995, C35 (3), 379.
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MA047928M