Synthesis of Linear High Molar Mass Glycidol-Based Polymers by Monomer-Activated Anionic Polymerization

Article abstract of DOI:10.1021/ma902286a

Linear polyglycidols of high molar masses were prepared by the monomer-activated anionic polymerization of the corresponding protected monomers, ethoxyethyl glycidyl ether and tert-butyl glycidyl ether, using a system composed of tetraoctylammonium bromide as initiator and triisobutylaluminum as monomer activator. The aluminic compound was used in 1.5-5-fold excess compared to the initiator. Linear poly(ethoxyethyl glycidyl ether) and poly(teri-butyl glycidyl ether), with narrow chain dispersity and controlled high molar masses, up to 85 000 g/mol, were prepared at 0 °C in a few hours. Deprotection of hydroxyl functions by acidic treatment of the polymers was shown to proceed quantitatively and cleanly affording the corresponding linear polyglycerol and validating the use of these protecting groups. The copolymerization of protected glycidols with propylene oxide and butene oxide was also investigated with the goal to broaden the scope of this synthetic approach to various polyethers and copolyethers.

Full text of DOI:10.1021/ma902286a

1778 Macromolecules 2010, 43, 1778–1784
DOI: 10.1021/ma902286a
Synthesis of Linear High Molar Mass Glycidol-Based Polymers by
Monomer-Activated Anionic Polymerization
Matthieu Gervais, Anne-Laure Brocas, Gabriel Cendejas, Alain Deffieux,* and
Stephane Carlotti*
ꢀ
ꢁ
Laboratoire de Chimie des Polymeres Organiques, Universite of Bordeaux, CNRS-ENSCBP,
16 avenue Pey Berland, 33607 Pessac, France
Received October 15, 2009; Revised Manuscript Received January 8, 2010
ABSTRACT: Linear polyglycidols of high molar masses were prepared by the monomer-activated anionic
polymerization of the corresponding protected monomers, ethoxyethyl glycidyl ether and tert-butyl glycidyl
ether, using a system composed of tetraoctylammonium bromide as initiator and triisobutylaluminum as
monomer activator. The aluminic compound was used in 1.5-5-fold excess compared to the initiator. Linear
poly(ethoxyethyl glycidyl ether) and poly(tert-butyl glycidyl ether), with narrow chain dispersity and
controlled high molar masses, up to 85 000 g/mol, were prepared at 0 °C in a few hours. Deprotection of
hydroxyl functions by acidic treatment of the polymers was shown to proceed quantitatively and cleanly
affording the corresponding linear polyglycerol and validating the use of these protecting groups. The
copolymerization of protected glycidols with propylene oxide and butene oxide was also investigated with the
goal to broaden the scope of this synthetic approach to various polyethers and copolyethers.
Introduction
remained limited to low polymerization degrees. The syntheses of
high molar mass polyglycidol and of copolymers with high molar
Polyglycidol, a water-soluble polymer, and its copolymers are
of great interest for biomedical applications due to their biocom-
patibility and high hydroxyl functionality.1-3 Moreover, glycidol
can constitute a significant economical issue for this sector as far
as it is readily obtained from glycerol, a byproduct of the
synthesis of biodiesel.4
mass polyglycidol block are of great interest to increase the
contribution of polyglycidol to the final properties. Recently,
other glycidol protecting groups have been reported, including
the tert-butyl ether group.13 One interest of tert-butyl glycidyl
ether (tBuGE) deals with its commercial availability, in contrast
to EEGE. However, the same limitations are observed in the
anionic polymerization of tBuGE that allows exclusively the
preparation of low molar mass polymers.13 The preparation of
polyglycidol combining high molar mass and a narrow molar
mass distribution fromanefficient initiating system still remains a
challenge to enlarge the scope of applications, especially in the
biomedical field.
The present study deals with the use of tetraalkylammonium
salts as initiatorsin the presence of triisobutylaluminum(i-Bu3Al)
as activator for the homopolymerization of EEGE and tBuGE
and for their copolymerization with hydrophobic propylene
oxide (POx) or butene oxide (BOx).
Hyperbranched polyglycidols have been recently prepared
directly from glycidol by anionic5-7 or cationic8-10 polymeriza-
tions by combining reactions of epoxide groups and hydroxyl
functions. The hyperbranched polymers obtained can reach high
molar masses; however, their structure is not well-controlled. The
synthesis of linear polyglycidols requires a protection of the
monomer hydroxyl function prior the polymerization. The most
generally used protection method reported first by Spassky11
consists in the preparation of ethoxyethyl glycidyl ether (EEGE)
by reaction of glycidol with ethyl vinyl ether. The efficiency and
ease of the monomer protection step and its deprotection by
acidic treatment make EEGE a good candidate as monomer for
the synthesis of linear polyglycidols. Many polymerization stu-
dies of EEGE have been conducted using both anionic and
coordinated type polymerizations.11-18 Coordinated polymeri-
zation using diethylzinc/water or calcium amide alkoxide allows
to get high molar mass poly(ethoxyethyl glycidyl ether)
(PEEGE), but with either multimodal and/or broad molar mass
distributions. Anionic processes involving the use of alkali metal
salts and/or phosphazene base initiators permit the synthesis of
PEEGE with molar masses limited to 30 000 g/mol due to chain
transfer to monomer, as confirmed recently.18 Despite this draw-
back, a series of block and random copolymers based on glycidol
and ethylene oxide,15,19-22 propylene oxide,23 lactide,22 styrene,12,24
2-vinylpyridine,12 and 4-vinylpyridine25 have been synthesized to
add the hydrophilic behavior and the high functionality of
polyglycidol to these polymers. However, the polyglycidol part
Experimental Section
Materials. Triisobutylaluminum (1 mol/L in toluene, Aldrich)
was used without further purification. 2,3-Epoxypropan-1-ol
(glycidol, 96%, Aldrich) and ethyl vinyl ether (99% Aldrich)
were used as received. Propylene oxide (99%, Fluka), butene
oxide (99%, Aldrich), andtert-butylglycidyl ether (99%, Aldrich)
were purified over CaH2, distilled under vacuum, and stored for
15 min in a glass flask equipped with PTFE stopcocks in the
presence of i-Bu3Al to remove traces of impurities. They were
finally distilled under vacuum and stored under vacuum at RT in
calibrated glass tubes until use. Toluene (98%, J.T. Baker) was
purified with polystyryllithium seeds. It was distilled under
vacuum and then stored in calibrated glass tubes under vacuum.
Tetraoctylammonium bromide (NOct4Br) (98%, Aldrich) was
solubilized into dried toluene and stored in calibrated glass tubes
fitted with PTFE stopcocks. Ethoxyethyl glycidyl ether was
synthesized from glycidol and ethyl vinyl ether as already
*Corresponding author. E-mail: carlotti@enscpb.fr.
pubs.acs.org/Macromolecules
Published on Web 01/22/2010
r 2010 American Chemical Society

Article
Macromolecules, Vol. 43, No. 4, 2010 1779
Scheme 1. Protection and Polymerization of Ethoxyethyl Glycidyl Ether
Table 1. Polymerization of Ethoxyethyl Glycidyl Ether (EEGE) Using NOct4Br/i-Bu3Al (Toluene, 0 °C)
Mn exp (g/mol)
yielda (%)
time (h)
Mn thb (g/mol)
SECc
osmod
Mw/Mn
c
run
[i-Bu3Al]/[NOct4Br]
[EEGE] (mol/L)
1
2
3
4
5
6
2
2
3
4
4
5
0.5
2
1.5
0.5
1
63
68
70
100
100
100
18
28
24
9
19
15
18 900
68 000
35 000
10 000
30 000
100 000
18 000
50 000
35 000
10 300
29 600
85 000
1.03
1.18
1.30
1.06
1.06
1.27
11 000
31 000
2
a Determined gravimetrically. b Mn th = [EEGE]0/[NOct4Br] ꢀ MEEGE ꢀ yield. c Determined by size exclusion chromatography in tetrahydrofuran
using a calibration with polystyrene standards. d Determined by osmometry in toluene.
reported26 with a yield of 90%, dried with CaH2, and distilled
prior to use.
1, 2, 3, 5, 6, 3.35-3.75 ppm; 4, 1.17 ppm; 7, 1.35-1.65 ppm; 8,
triplet at 0.90 ppm.
Procedures. All (co)polymerizations were performed between
0 and 25 °C under argon in a glass reactor equipped with a
magnetic stirrer and fitted with PTFE stopcocks. As an example
a polymerization reactor was flamed under vacuum and cooled
prior introduction of 32 mL of toluene and 6 mL of EEGE (39.4
mmol) through connected glass tubes. Then, 0.87 mL (0.19
mmol) of a toluene solution of NOct4Br (C = 0.22 M) followed
by 0.77 mL (0.77 mmol) of i-Bu3Al solution in toluene (C = 1
M) were added via a syringe under argon. The polymerization
was allowed to proceed for 19 h at 0 °C and then stopped by
addition of ethanol. The yield (100%) was determined gravime-
trically after complete drying of the polymer under vacuum at
50 °C. Mn(SEC) = 29600 g/mol, Ip = 1.06. 1H NMR of PEEGE:
-O-CH2(1)-CH(2)[CH2(3)-O-CH(4)-CH3(5)-O-CH2(6)-
CH3(7)]: 1, 2, 3, 6, 3.35-3.75 ppm; 4, quadruplet at 4.75 ppm; 5,
1.27 ppm; 7, 1.17 ppm.
Deprotection of PEEGE was carried out in ethanol with 3%
HCl and stirred for 4 h. The polymer was then evaporated under
reduced pressure and finally dried under vacuum. Deprotection
of PtBuGE was done in ethanol with 3% HCl under stirring for
24 h at 60 °C. After neutralization by adding sodium carbonate,
ethanol was evaporated under reduced pressure and polyglyci-
dol finally dried under vacuum. 1H NMR of polyglycidol:
O-CH2(1)-CH(2)[CH2(3)-OH]-O: 1, 2, 3, 3.60-3.85 ppm.
Analysis. Polymer molar masses were determined by size
exclusion chromatography (SEC) at 40 °C using tetrahydrofur-
an (THF) as eluent. Measurements in THF were performed on a
PL GPC50 integrated system with RI and UV detectors and
three TSK columns: G4000HXL (particles of 5 μm, pore size of
˚
200 A, and exclusion limit of 400 000 Da), G3000HXL (particles
˚
of 5 μm, pore size of 75 A and exclusion limit of 60 000 Da),
˚
G2000HXL (particles of 5 μm, pore size of 20 A and exclusion
Polymerization of tBuGE, following the same procedure, was
carried out with 1 mL of tBuGE (7 mmol), 6 mL of toluene, 0.14
mL (0.045 mmol) of NOct4Br solution in toluene (C = 0.32 M),
and 0.09 mL (0.09 mmol) of i-Bu3Al solution in toluene (C = 1
M) for 3 h at 0 °C. Mn(SEC) = 20 000 g/mol, Ip = 1.02. H
NMR of PtBuGE: -O-CH2(1)-CH(2)[CH2(3)-O-[CH3-
(4)]3]: 1, 2, 3, 3.35-3.70 ppm; 4, 1.17 ppm.
limit of 10 000 Da) at an elution rate of 1 mL/min. Polystyrene
were used as standards. Measurements in dimethylformamide
(DMF) were performed on a similar apparatus with the same
kind of columns, elution rate, and standards.
1
1H (400 MHz) NMR measurements of the polymers and
€
copolymers were performed on a Bruker Avance 400 spectro-
meter, in CDCl3 or D2O at room temperature.
A typical copolymerization of EEGE and POx was carried
out with 2 mL (28.6 mmol) of POx, 1.8 mL (11.8 mmol) of
EEGE, 20 mL of toluene, and 0.78 mL (0.17 mmol) of NOct4Br
solution in toluene (C = 0.22 M) and 0.85 mL (0.85 mmol) of
i-Bu3Al solution in toluene (C = 1 M) for 3 h at -30 °C. Yield:
100%, Mn(SEC) = 21 000 g/mol, Ip = 1.30, DPEEGE/DPPOx
(NMR) = 0.32. 1H NMR of P(EEGE-co-POx): -O-CH2(1)-
CH(2)[-CH2(3)-O-CH(4)-CH3(5)-O-CH2(6)-CH3(7)]-
co-O-CH2(8)-CH(9)[CH3(10)]: 1, 2, 3, 6, 8, 9, 3.35-3.75
ppm; 4, quadruplet at 4.75 ppm; 5, 1.27 ppm; 7 and 10, 1.17
ppm.
Copolymerization of tBuGE and BOx was carried out with
1 mL (11.6 mmol) of BOx, 1 mL (7 mmol) of tBuGE, 16 mL of
toluene, 0.38 mL (0.08 mmol) of NOct4Br solution in toluene
(C = 0.22 M), and 0.17 mL (0.17 mmol) of i-Bu3Al solution in
toluene (C = 1 M) for 8 h at -30 °C. Yield: 100%, Mn(SEC) =
21 000 g/mol, Ip = 1.16, DPtBuGE/DPBOx (NMR) = 0.57.
1H NMR of P(t-BuGE-co-BOx): -O-CH2(1)-CH(2)[-CH2-
(3)-O-C(CH3)3(4)]-co-O-CH2(5)-CH(6)[-CH2(7)-CH3(8)]:
Osmometric measurements were performed on a Gonotec
Osmomat 090 device in toluene with a Tac 5 kDa membrane.
Osmotic pressures were measured for each sample at five con-
centrations: 0.2, 0.5, 1, 2, and 5 mg/mL.
Results and Discussion
Polymerization of Ethoxyethyl Glycidyl Ether. A binary
initiating system constituted of NOct4Br as initiator and
i-Bu3Al as catalyst/activator has been recently reported by us
for the controlled anionic polymerization of epoxides27-30 in
hydrocarbon media. This system was investigated for the
polymerization of EEGE, as a protected form of glycidol (see
Scheme 1).
As indicated in Table 1, polymerization of EEGE proceeds
in toluene at low temperature, for [i-Bu3Al]/[NOct4Br] ratios
ranging from 2 to 5. However, quantitative polymerization
requires the use of ratios higher than 3. Whereas at a ratio of
4 the polymerization of EEGE is achieved up to quantitative

1780 Macromolecules, Vol. 43, No. 4, 2010
Gervais et al.
Figure 1. Conversion (filled squares) and ln[M]0/[M] (open circles) versus time plots for the polymerization of ethoxyethyl glycidyl ether (EEGE)
(toluene, 0 °C, [EEGE]=0.5 M, [NOct4Br]=7 ꢀ 10-3 M, [i-Bu3Al]/[NOct4Br]=2 (9) or 4 (O)).
Scheme 2. Complexation of Triisobutylaluminum by Oxygens of
Poly(EEGE) Chains
Figure 2. Evolution of molar masses and molar mass distribution (Ip)
versus conversion in the polymerization of (EEGE) (toluene, 0 °C,
final molar masses remains in good agreement with theore-
tical values at the obtained conversion. Indeed, the PEEGE
molar mass increases linearly with the monomer conversion
[EEGE] = 0.5 M, [NOct4Br] = 7 ꢀ 10-3 M, [i-Bu3Al]/[NOct4Br] = 2).
conversion when medium molar mass polymers are targeted
(runs 4 and 5, Table 1), this ratio should be raised to 5 for
high molar mass PEEGE (100 000 g/mol). The increase of the
monomer concentration also favors fast reactions. This
shows that more i-Bu3Al is required to trigger the EEGE
polymerization compared to propylene oxide.27
up to the final yield, whereas molar mass distribution
remains narrow (see Figure 2). This behavior can be ex-
plained by a living-like reaction, without termination and
transfer, in which the i-Bu3Al fraction used to trigger the
reaction is trapped by complexation with the oxygen of
poly(EEGE) chain, as illustrated in Scheme 2.
Experimental molar masses, determined by SEC on the
basis of a polystyrene calibration, are in the range of the
calculated ones, assuming the formation of one PEEGE
chain per NOct4Br. A good correlation between SEC PS
molar masses and PEEGE ones was shown by osmometry
measurements performed on PEEGE samples with molar
masses ranging from 10 000 to 30 000 g/mol (see Table 1).
The use of higher [i-Bu3Al]/[NOct4Br] ratio and high mono-
mer concentration (>2 mol/L) to speed up the reaction
resulted in a broadening of the molar mass distribution,
suggesting the contribution of side reactions in these condi-
tions, probably some transfer to i-Bu3Al as already explained
for propylene oxide.27 Concerning the transfer to monomer
observed with conventional initiation like potassium alkox-
ides, precisely described by Keul and Moeller,18 which limits
the molar masses, it was not observed with the initiating
system we have used. Indeed, no characteristic peaks of
allylic end groups at 4, 5, and 6.6 ppm appeared in the H
NMR spectra of all protected polyglycidol synthesized (see
Figure S1 given as Supporting Information).
EEGE polymerization kinetics were carried out by dila-
tometry. Typical conversion vs time curves are plotted
Figure 1 for [i-Bu3Al]/[NOct4Br] ratios 2 and 4 as well as
ln([M]0/[M]) vs time for a ratio equal to 4. For 2 equiv of
[i-Bu3Al], the monomer consumption levels off at about 60%
conversion and does not reach completion, although the
In contrast, for 4 equiv of i-Bu3Al, a linear consumption,
up to 90%, of EEGE is observed in a few minutes, at 0 °C,
yielding PEEGE of 10 000 g/mol with a dispersity of 1.11.
The ([M]0 - [M]/[M]0) = f(t) plot follows a linear rate law up
to high EEGE conversion, whereas the ln([M]0/[M]) vs time
plot is not linear. This suggests an apparent zero monomer
order for the propagation reaction as already proposed for
the monomer-activated mechanism of propylene oxide,27
illustrated for EEGE in Scheme 3.
Kinetics of the EEGE activated anionic polymerization
can be expressed by the equation Rp = kp[NOct4Br]0[M*],
where kp is the propagation rate constant and M* represents
the trialkylaluminum activated monomer. At initial polym-
erization time [M*] can be approximated to [Al]0
-
[NOct4Br]0 considering that 1 equiv of i-Bu3Al is quantita-
tively trapped in the 1:1 aluminate complex27 and that
complexation of i-Bu3Al by the poly(EEGE) chain is negli-
gible.
1
All the results agrees with the formation of a 1:1 initiating
and propagating complex of low basicity, which strongly
minimizes transfer reactions to monomer, and of high nu-
cleophilicity due to the activation role of the excess of Lewis
acid, allowing fast reactions at low temperatures.
The regioregularity and stereospecificity of PEEGE chains
were examined by 13C NMR. As can be seen Figure 3 at 65
and 79 ppm corresponding respectively to methylene and

Article
Macromolecules, Vol. 43, No. 4, 2010 1781
Figure 3. 13C NMR spectra of PEEGE synthesized in the presence of the NOct4Br/i-Bu3Al initiating system (run 4 Table 1, [i-Bu3Al]/[NOct4Br] = 4,
toluene, 0 °C, [EEGE] = 0.5 mol/L).
Scheme 3. Mechanism for the Monomer-Activated Anionic Polymerization of Ethoxyethyl Glycidyl Ether Initiated by the NOct4Br/i-Bu3Al System
methine groups of the polymer backbone, no small side
peaks indicative of head-to-head and tail-to-tail irregulari-
ties, as reported for regioirregular poly(propylene oxide),31
are detected close to the two mentioned chemical shifts. This
indicates a highly regioregular insertion of EEGE in agree-
ment with an anionic polymerization mechanism. The split-
ting of the methylene signal into two main peaks of almost
same intensity, at 64.9 and 65.2 ppm, can be attributed to the
presence of meso and racemic EEGE diads. The methine
peak resolution in a multiplet, between 78.7 and 79.2 ppm,
also points out the presence of different stereosequences.
This confirms the formation of atactic PEEGE and the
absence of stereoregulation during the EEGE polymeriza-
tion in presence of the NOct4Br/i-Bu3Al initiating system.
Polymerization of tert-Butyl Glycidyl Ether. Following the
same strategy and conditions, the polymerization of tert-
butyl glycidyl ether has been carried out in presence of
NOct4Br/i-Bu3Al. Typical polymerization results are col-
lected in Table 2.
Compared to EEGE, polymerization of tBuGE proceeds
more readily and goes to completion in a few hours using
only 2 equiv of triisobutylaluminum with respect to the
tetraoctylammonium bromide initiator. This can be ex-
plained by the presence of a single oxygen atom on the

1782 Macromolecules, Vol. 43, No. 4, 2010
Table 2. Polymerization of tert-Butyl Glycidyl Ether (t-BuGE) with NOct4Br/i-Bu3Al (Toluene, 0 °C)
Gervais et al.
yielda (%)
Mn thb (g/mol)
Mn expc (g/mol)
Mw/Mn
c
run
[i-Bu3Al]/[NOct4Br]
[t-BuGE] (mol/L)
time (h)
1
2
3
4
5
1.5
2
2
3
4
1
1
1
1
3
3
3
3
54
100
100
100
100
16 000
10 000
20 200
30 000
65 000
20 000
14 000
20 000
26 000
52 000
1.13
1.15
1.02
1.15
1.37
3
7d
a Determined gravimetrically. b Mn th = [t-BuGE]/[NOct4Br] ꢀ Mt-BuGE
.
c Determined by SEC in THF using a calibration with PS standards. d The
temperature was left to increase up to 25 °C.
Figure 4. 1H NMR analysis of poly(EEGE) (run 5 Table 1) and poly(tBuGE) (run 4 Table 2) before (in CDCl3) and after (in D2O) acidic deprotection.
tBuGE and on PtBuGE units, without counting the oxygen
atom of the reactive and reacted epoxide function, which is
moreover greatly hindered by its tert-butyl substituent. This
strongly limits complexation of the aluminum compound by
the chain. PtBuGE experimental molar masses determined
by SEC on the basis of a polystyrene calibration are in the
range of calculated ones, and dispersities remain narrow for
a molar mass up to 26 000 g/mol or slightly broad for a
sample at 52 000 g/mol. This indicates that no significant side
reaction occurs during propagation. But the preparation of
much higher molar masses starting with this monomer
appeared more problematic than EEGE. Polymer solubility
difficulties appeared in many solvents and can be one reason.
Despite this limitation, the data reported and its commercial
availability make tBuGE a first ranked raw material for the
synthesis of linear polyglycidol by the reported polymeriza-
tion system, assuming that the deprotection step would
proceed cleanly.
Deprotection of Poly(EEGE) and Poly(tBuGE) units. Both
Figure 5. SEC chromatograms and apparent molar mass (polystyrene
calibration) of a PEEGE prepared using NOct4Br/i-Bu3Al (1/5) as
initiating system before and after deprotection using HCl/ethanol (3/97
acetal14 and tert-butyl32 protecting groups of glycidol units
respectively in PEEGE and PtBuGE can be removed by
acidic treatment although the deprotection conditions are
quite different. Acetal groups of PEEGE can be quantita-
tively removed by treatment of the polymer in an acidic
in volume).
ethanol solution (3 vol % of HCl) in 4 h at room temperature.
Removal of the tert-butyl groups of PtBuGE using the same

Article
Macromolecules, Vol. 43, No. 4, 2010 1783
Table 3. Copolymerization of EEGE with Propylene Oxide (Toluene, [M] = 2 M, -30 °C, [i-Bu3Al]/[NOct4Br] = 5, 3 h) and of tBuGE with
Butene Oxide (Toluene, [M] = 2 M, -30 °C, [i-Bu3Al]/[NOct4Br] = 2, 8 h)
theoretical composition
DPEEGE-DPPOx
DPEEGE/DPPOx
expb
Mn thc
(g/mol)
Mn exp f
(g/mol)
a
f
run
DPEEGE/DPPOx tha
conversiong (%)
Mw/Mn
1
2
3
4
5
69-168
69-168
65-262
132-155
137-172
0.41
0.41
0.25
0.85
0.80
0.32
0.44
0.22
0.84
0.82
19 800
19 800
25 000
28 000
30 000
21 000
15 000
25 000
31 000
36 000
100
100
100
100
100
1.30
1.43
1.58
1.41
1.34
theoretical composition
DPtBuGE-DPBOx
DPtBuGE/DPBOx
expb
Mn the
(g/mol)
Mn exp f
(g/mol)
d
f
run
DPtBuGE/DPBOx thd
conversiong (%)
Mw/Mn
6
7
42-69
87-144
0.61
0.55
0.52
0.60
10 000
21 700
12 000
21 000
100
100
1.14
1.16
a DPEEGE = [EEGE]/[NOct4Br], DPPOx = [POx]/[NOct4Br]. b Determined by 1H NMR. c Mn th = ([EEGE]/[NOct4Br] ꢀ MEEGE þ [POx]/[NOct4Br] ꢀ
MPOx) ꢀ conversion. d DPtBuGE = [tBuGE]/[NOct4Br], DPBOx = [BOx]/[NOct4Br]. e Mn th = ([tBuGE]/[NOct4Br] ꢀ MtBuGE þ [BOx]/[NOct4Br] ꢀ
MBOx) ꢀ conversion. f Determined by SEC in THF using a calibration with PS standards. g Determined gravimetrically.
acidic ethanol solution requires 24 h at 60 °C. The 1H NMR
spectra of PEEGE and PtBuGE synthesized by the mono-
mer-activated approach and of the corresponding depro-
tected polyglycidol are shown Figure 4.
proceeds to complete monomers consumption even at low
[NOct4Br]/[i-Bu3Al] ratio, yielding copolymers with similar
average composition as the comonomer feed, experimental
molar masses in the range of theoretical ones, and low
dispersities. A further study will focus on the structures of
the copolymers prepared by this approach as well as their
properties.
SEC analysis carried out in DMF on protected and
deprotected polyglycidol shows no peak broadening in
agreement with a clean deprotection step (Figure 5). The
apparent polyglycidol molar mass are higher than that of the
initial PEEGE, although the repetitive unit decreases from
146 to 74 g/mol, leading to a loss of around half of the
polymer molar mass. This may be explained by the difference
of hydrodynamic volume of PEEGE and polyglycidol.
Copolymerization Studies. The copolymerization of
EEGE and tBuGE with other epoxides has been investigated
to examine the possibility of synthesizing copolyethers of
various hydrophilicity or amphiphilicity. Typical results for
the copolymerization of EEGE with propylene oxide, mixed
at the same time, are collected in Table 3. Copolymerizations
go to completion, and the copolymers analyzed by SEC show
a monomodal distribution (see Figure S2 given as Support-
ing Information) and experimental molar masses close to
theoretical values. The broadening of dispersities in compar-
ison with hompolymerization results can be attributed to the
high NOct4Br/i-Bu3Al ratio used (1/5), necessary to quanti-
tatively polymerize EEGE, which induces a very high reac-
tivity for POx and results in a slight contribution of transfer
reaction.27 The reactivity ratios between EEGE and POx
were determined in a series of copolymerization experiments
Conclusion
The anionic polymerization of protected glycidols (ethoxyethyl
glycidyl ether and tert-butyl glycidyl ether) in the presence of a
binary initiating system consisting of tetraoctylammonium bromide
(NOct4Br) and an excess of triisobutylaluminum (i-Bu3Al) has been
investigated. This method allows the controlled syntheses of
PEEGE and PtBuGE of high molar masses, up to 85 000 g/mol
as shown for PEEGE, in short reaction time, at 0 °C. A 1:1 initiating
or propagating complex of weak basicity is believed to be formed,
which suppresses transfer reactions to monomer. Fast polymeriza-
tions at low temperatures support a high nucleophilicity of the
system due to the monomer-activation role of the excess of Lewis
acid. Its amount required to trigger the reaction and get quantitative
yields depends on the glycidyl derivative used as protected form of
glycidol, probably in relation to the number of oxygen atoms
contained in the epoxide side group. After a clean and quantitative
acidic deprotection, polyglycidol as well as a large variety of
copolymers of glycidol with controlled molar masses can be
obtained, offering new opportunities of applications, in particular
in the field of biomaterials.
€
stopped at low conversion, using the Kelen-Tudos meth-
od.33 This yields rPOx = kPOxPOx/kPOxPEEGE = 3.58 and
rPEEGE = kPEEGEPEEGE/kPEEGEPOx = 0.18. These values
indicate, in living-like conditions, the formation of copoly-
mers with a gradient composition constituted by a predomi-
nant incorporation of POx units at the beginning of the
chains and EEGE units at the end. This should yield after
release of the hydroxyl groups of the glycidol units copoly-
mers with an amphiphilic character. A quantitative depro-
tection was achieved following the procedure discussed
Supporting Information Available: 1H NMR spectrum of
PEEGE (Figure S1), SEC chromatogram in THF of a P(POx-ran-
EEGE) (Figure S2), and 1H NMR spectrum of P(POx-ran-EEGE)
(Figure S3). This material is available free of charge via the Internet
at http://pubs.acs.org.
References and Notes
1
(1) Kainthan, R. K.; Gnanamani, M.; Ganguli, M.; Ghosh, T.;
Brooks, D. E.; Maiti, S.; Kizhakkedathu, J. N. Biomaterials
2006, 27, 5377–5390.
(2) Klajnert, B.; Walach, W.; Bryszewska, M.; Dworak, A.; Shcharbin,
D. Cell Biol. Int. 2006, 30, 248–252.
(3) Kainthan, R. K.; Janzen, J.; Levin, E.; Devine, D. V.; Brooks, D. E.
Biomacromolecules 2006, 7, 703–709.
(4) Tesser, R.; Santacesaria, E.; Di Serio, M.; Di Nuzzi, G.; Fiandra, V.
above as confirmed by H NMR spectroscopy of a poly-
(propylene oxide-co-glycidol) copolymer (Figure S3 given as
Supporting Information). A preliminary study of the beha-
vior in solution of this copolymer showed the formation of
micelles in water.
In a similar way tBuGE was copolymerized with butene
oxide a monomer of lower reactivity than propylene oxide
and with a more pronounced hydrophobic character with the
objective to enlarge the scope of this synthetic approach to
other copolymers based on cyclic ethers. Copolymerization
results are collected in Table 3. Again, copolymerization
Ind. Eng. Chem. Res. 2007, 46, 6456–6465.
(5) Sandler, S. R.; Berg, F. R. J. Polym. Sci., Part A-1: Polym. Chem.
1966, 4, 1253–1259.
(6) Walach, W.; Trzebicka, B.; Justynska, J.; Dworak, A. Polymer
2004, 45, 1755–1762.

1784 Macromolecules, Vol. 43, No. 4, 2010
Gervais et al.
(7) Wurm, F.; Nieberle, J.; Frey, H. Macromolecules 2008, 41, 1184–1188.
(8) Royappa, A. T.; Vogt, M. L.; Sharma, V. J. Appl. Polym. Sci. 2004,
91, 1344–1351.
(9) Tokar, R.; Kubisa, P.; Penczek, S.; Dworak, A. Macromolecules
1994, 27, 320–322.
(10) Kubisa, P. J. Polym. Sci., Part A: Polym. Chem. 2003, 41, 457–468.
(11) Taton, D.; Le Borgne, A.; Sepulchre, M.; Spassky, N. Macromol.
Chem. Phys. 1994, 195, 139–148.
(21) Dimitrov, P.; Utrata-Wesolek, A.; Rangelov, S.; Walach, W.;
Trzebicka, B.; Dworak, A. Polymer 2006, 47, 4905–4915.
(22) Dimitrov, P.; Porjazoska, A.; Novakov, C. P.; Cvetkovska, M.;
Tsvetanov, C. B. Polymer 2005, 46, 6820–6828.
(23) Dimitrov, P.; Rangelov, S.; Dworak, A.; Tsvetanov, C. B. Macro-
molecules 2004, 37, 1000–1008.
(24) Dworak, A.; Panchev, I.; Trzebicka, B.; Walach, W. Macromol.
Symp. 2000, 153, 233–242.
€
(12) Toy, A. A.; Reinicke, S.; Muller, A. E.; Schmalz, H. Macromole-
cules 2007, 40, 5241–5244.
(25) Mendrek, S.; Mendrek, A.; Adler, H.-J.; Dworak, A.; Kuckling, D.
J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 1782–1794.
(26) Fitton, A. O.; Hill, J.; Jane, D. E.; Millar, R. Synthesis 1987, 1140–
1142.
(27) Labbe, A.; Carlotti, S.; Billouard, C.; Desbois, P.; Deffieux, A.
Macromolecules 2007, 40, 7842–7847.
€
(13) Erberich, M.; Keul, H.; Moller, M. Macromolecules 2007, 40, 3070–
3079.
(14) Dworak, A.; Baran, G.; Trzebicka, B.; Walach, W. React. Funct.
Polym. 1999, 42, 31–36.
(15) Li, Z.; Li, P.; Huang, J. J. Polym. Sci., Part A: Polym. Chem. 2006,
44, 4361–4371.
(16) Halacheva, S.; Rangelov, S.; Tsvetanov, C. Macromolecules 2006,
39, 6845–6852.
(28) Rejsek, V.; Sauvanier, D.; Billouard, C.; Desbois, P.; Deffieux, A.;
Carlotti, S. Macromolecules 2007, 40, 6510–6514.
(29) Billouard, C.; Carlotti, S.; Desbois, P.; Deffieux, A. Macromole-
cules 2004, 37, 4038–4043.
(17) (a) Dimitrov, P.; Rangelov, S.; Dworak, A.; Haraguchi, N.; Hirao,
A.; Tsvetanov, C. Macromol. Symp. 2004, 215, 127–140. (b)
Dimitrov, P.; Hasan, E.; Rangelov, S.; Trzebicka, B.; Dworak, A.;
Tsvetanov, C. Polymer 2002, 43, 7171–7178.
(30) Carlotti, S.; Labbe, A.; Rejsek, V.; Doutaz, S.; Gervais, M.;
Deffieux, A. Macromolecules 2008, 41, 7058–7062.
(31) Schilling, F. C.; Tonelli, A. E. Macromolecules 1986, 19, 1337–
1343.
(18) Hans, M.; Keul, H.; Moeller, M. Polymer 2009, 50, 1103–1108.
(19) Kaluzynski, K.; Petrula, J.; Lapienis, G.; Basko, M.; Bartczak, Z.;
Dworak, A.; Penczek, S. J. Polym. Sci., Part A: Polym. Chem. 2001,
39, 955–963.
(32) Greene, T. W.; Wuts, P. G. M. In Protective Groups in Organic
Chemistry, 3rd ed.; Wiley: New York, 1999; pp 65-67.
€
€
(33) Tudos, F.; Kelen, T.; Folde-Berezsnich, T.; Turcsanyi, B. J. Macromol.
Sci., Chem. 1976, A10, 1513–1540.
(20) Penczek, S.; Petrula, J.; Kaluzynski, K. J. Polym. Sci., Part A:
Polym. Chem. 2004, 42, 432–443.
(34) Fox, T. G. Bull. Am. Phys. Soc. 1956, 1, 123–124.
(35) Gordon, M.; Taylor, J. S. J. Appl. Chem. 1952, 493–500.