Synthesis of novel glycidol copolymers with pendant alkene and hydroxyl groups

Article abstract of DOI:10.1002/cjoc.201300638

A series of linear poly glycidol copolymers, tethering with both alkene and hydroxyl groups, were prepared by a combination of anionic ring-opening polymerization (ROP) using specific reactions of ethoxy ethyl glycidyl ether (EEGE) and allyl glycidyl ether (AGE) firstly, and subsequently removal of the protection group of glycidol in EEGE to achieve the linear copolymer pendant with both hydroxyl groups and double bonds. The EEGE/AGE monomer reactivity ratio is measured to be 3.30/1.13. The chemical compositions of the as-synthesized polymers were characterized by ¹H NMR and GPC, and the glass transition temperatures (T_g) of as-synthesized polymers were determined by DSC. The final copolymers have abundant double bonds and hydroxyl as side groups. Furthermore, the ratio of the double bonds to hydroxyl groups can be controlled by the ratio of the starting materials in a wide range. A facile method is presented here to synthesize glycidol copolymers pendant with multiple different functional groups at a time, which has a potential application for further chemical modification and functionalization. Copyright

Full text of DOI:10.1002/cjoc.201300638

FULL PAPER
DOI: 10.1002/cjoc.201300638
Synthesis of Novel Glycidol Copolymers with Pendant Alkene
and Hydroxyl Groups
Siwei Liu,* Feng Zhang, Yi Zhang, and Jiarui Xu
PCFM Lab, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou,
Guangdong 510275, China
A series of linear poly glycidol copolymers, tethering with both alkene and hydroxyl groups, were prepared by a
combination of anionic ring-opening polymerization (ROP) using specific reactions of ethoxy ethyl glycidyl ether
(EEGE) and allyl glycidyl ether (AGE) firstly, and subsequently removal of the protection group of glycidol in
EEGE to achieve the linear copolymer pendant with both hydroxyl groups and double bonds. The EEGE/AGE
monomer reactivity ratio is measured to be 3.30/1.13. The chemical compositions of the as-synthesized polymers
1
were characterized by H NMR and GPC, and the glass transition temperatures (Tg) of as-synthesized polymers
were determined by DSC. The final copolymers have abundant double bonds and hydroxyl as side groups. Fur-
thermore, the ratio of the double bonds to hydroxyl groups can be controlled by the ratio of the starting materials in
a wide range.
Keywords amphiphiles, anions, ring-opening polymerization, glycidol copolymers, biomaterials
Introduction
these hydroxyl groups as a whole for such polymers. To
date, besides hydroxyl groups, only amino functional-
ities are accessible to be introduced in PEG chain via
the copolymerization of ethylene oxide. The linear co-
polymers comprising alkene were synthesized by Hol-
ger group through copolymerization of ethylene oxide
and allyl glycidyl ether.[19]
Poly(ethylene glycol) (PEG) is a kind of bio-func-
tional material with extensive applications in the fields
of food, pharmacology and biomedicine.[1-4] It has the
following advantages: a good solubility in water and
most organic solvents, unique anti-fouling[5-9] and
anti-bacteria properties,[10-13] low toxicity which is ap-
proved by US FDA, and so on. The PEG, however, only
has one or two active chemical group(s) (hydroxyl
group) at the end of its backbone, which limits its com-
bining ability with other functional molecules and sub-
sequently limits its practical applications in a variety of
application environments. To break through the limita-
tion, PEG has been designed and synthesized with a
great number of molecular structures, such as star-
shaped, branched, etc. Unfortunately, these methods
require very complex synthesis process and the number
of active groups in the resulting modified PEG is still
relatively low. Feng et al.[14] reported a series of den-
drimer-like poly(ethylene oxide)s with up to 384 exter-
nal hydroxyl groups; however, due to the steric problem,
the number of active hydroxyl groups is far below that
number. The star-shaped macromolecules containing
polyglycidol and poly(ethylene oxide) as arms synthe-
sized by Lapienis et al.[15-18] also have the same steric
problem. Probably, in such dendrimer-like or star-
shaped structure, due to the folding of the polymer
chains (or arms), some of the hydroxyl groups could not
be exposed out directly, thus decreasing the reactivity of
To tether multiple (different) functional groups to a
single polymer chain (or a single macromolecular)
analogous to PEG is one of important ways to widen
application of PEG derivatives. In addition, chemical
modification of an existing polymer via its active groups
is an easy and effective way to incorporate new proper-
ties into the original polymer, thus achieving new type
of functional material. There are some approaches to
attach functional groups onto PEG (or tether PEG to
other functional groups conversely). Yao’s group
grafted PEG onto the anterior surface of hydrophobic
acrylic intraocular lens by atmospheric pressure glow
discharge treatment to improve their biocompatibility.[20]
Due to the improved penetration of PEGylation proteins
into tissue, Molly introduced PEG segments onto fibro-
blast growth factor 2.[21] Su’s group modified a rigid
porous microsphere [poly(glycidyl methacrylate-divi-
nylbenzene)] with PEG to decrease the irreversible in-
teraction between microsphere and protein, and the re-
sults showed that the modified microsphere was ex-
pected to become a promising protein purification me-
dia.[22]
*
E-mail: liusiw@mail.sysu.edu.cn
Received August 22, 2013; accepted September 23, 2013; published online October 17, 2013.
Chin. J. Chem. 2013, 31, 1315—1320
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Liu et al.
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In this paper, a series of linear polymer, poly(ethoxy
ethyl glycidyl ether-co-allyl glycidyl ether) [P(EEGE-
co-AGE)], were synthesized firstly through anionic
ring-opening polymerization (ROP) by using AGE and
EEGE with the catalyst of triisobutylaluminum (i-Bu3Al)
and tetraoctylammonium bromide (NOct4Br).[23,24] The
obtained intermediate product was subsequently hydro-
lyzed and the linear polymer, P(Gly-co-AGE), pendant
with both hydroxyl groups and double bonds was gen-
erated. The motivation to design and synthesize this
kind of polymer is that, for one thing, we desire that the
as-synthesized polymers possess active hydroxyl groups
(for bio-compatibility and bio-application considera-
tions) as many as possible; for another, the as-synthe-
sized polymers should contain other active functional
groups which could be chemically modified further eas-
ily (e.g., introduction of DNA, RNA, drug molecules or
other bioactive molecules). That is, on a single analog
PEG chain, different kind of functional groups are in-
troduced at a time. From the synthetic route it can be
expected that the ratio of hydroxyl group to alkene
could be adjusted in a wide range to meet the practical
application demand.
magnesium sulfate for 1 h, and then filtrated. The col-
orless liquid product (EEGE) was obtained by vacuum
distillation (51 ℃/80 Pa) with a yield of 80%.
Copolymerization of EEGE with AGE
The typical procedure used for the copolymerization
of EEGE with AGE was as follows: a Schlenk tube
(about 20 mL in volume) was vacuumed at 120 ℃ for
1 h and cooled to room temperature and then to 0℃ in
argon atmosphere. Toluene (10.0 mL), EEGE (1.0 mL,
6.6 mmol), AGE (0.78 mL, 6.6 mmol), tetraoctylammo-
nium bromide (0.035 g, 0.06 mmol) and triisobutylalu-
minum (1.0 mol/L in toluene, 1.1 mL) were added into
the tube in argon atmosphere and the tube was sealed.
Then, the reaction was held at 0 ℃ for 12 h in argon
atmosphere. The reaction was terminated by addition of
a few drops of ethanol subsequently. After removal of
the solvents by rotary evaporation, the residue was dis-
solved in dichloromethane, dried by anhydrous sodium
sulfate and filtered. The final wax-like product was ob-
tained after complete removal of solvents under vacuum
at 50 ℃. The yield is near 100%.
Deprotection of the copolymer: P(EEGE-co-AGE)
The deprotection procedure was illustrated as fol-
lows. P(EEGE-co-AGE) (1.2 g) was dissolved into 100
mL ethanol which contained 3% (V/V) hydrochloric
acid (ca. 0.054 mol/L). After stirring for 4 h at room
temperature, the solution was neutralized by adding 50
mL of 1.0 mol/L sodium carbonate aqueous solution.
The reaction mixture was filtered. The filtrate was dis-
tilled off the solvent, and then dried at 50 ℃ for 12 h
under vacuum. The viscous liquid product was achieved
with the yield near 100%.
Experimental
Materials and measurements
Glycidol (2,3-epoxypropan-1-ol, 96%, Aldrich), tri-
isobutylaluminum (i-Bu3Al, 1.0 mol/L in toluene, Al-
drich), and tetraoctylammonium bromide (NOct4Br,
98%, Aldrich) were used as received. Allyl glycidyl
ether (AGE) purchased from Acros was distilled under
vacuum, and treated with triisobutylaluminum for 15
min in a glass flask equipped with PTFE stopcocks to
remove traces of impurities. Toluene was purified
through distillation over sodium chips under nitrogen
atmosphere before use. Other chemical reagents were
purchased from local chemical corporations and used as
received. FTIR spectra were recorded on a Nexus 670
Fourier transform infrared spectrometer (by Nicolet).
Results and Discussion
Chemical structure of the as-synthesized copolymers
The synthetic route for P(EEGE-co-AGE) and its
deprotection form is outlined in Figure 1. The first step,
the synthesis of EEGE, was order to protect the hy-
droxyl group of glycidol to avoid side reaction in the
subsequent experiments. Then, EEGE and AGE were
copolymerized to generate a linear copolymer, P(EEGE-
co-AGE), by using tetraoctylammonium bromide as the
initiator and triisobutylaluminum as the catalyst. Finally,
the polymer was hydrolyzed in ethanol containing hy-
drochloric acid for 4 h.
1
The H NMR spectroscopies were measured on a Mer-
cury-Plus 300 MHz (by Varian). The molecular weights
of the as-synthesized polymers were detected with a
Waters Breeze gel chromatography using dimethyl for-
mamide as the solvent and polystyrene as the standard.
Synthesis of 2,3-epoxypropyl-1-ethoxyethyl ether
(EEGE)
The protection for the hydroxyl group of glycidol
was performed following the procedure reported in the
literatures.[25,26] Glycidol (10.00 g) was dissolved into
ethyl vinyl ether (40 mL) in a 100 mL flask equipped
with a magnetic stirrer; 4-methylbenzenesulfonic acid
(0.25 g) was added in batch. In the feeding process, the
temperature of the mixture was controlled below 35 ℃
with a constant stirring for 3 h. Then saturated solution
of sodium bicarbonate aqueous (100 mL) was added.
The obtained organic layer was dried by anhydrous
Figures 2 and 3 are the 1H NMR spectra of a typical
copolymer before (measured in DMSO-d6) and after
(recorded in CD3OD) deprotection. The attribution of
each proton in the polymer is labeled in the figures.
After the protection groups of glycidol (in EEGE)
were eliminated, some proton peaks, e.g., δ 4.64－4.68
[proton 6 in P(EEGE-co-AGE), as shown in Figure 2]
disappeared. By comparing Figures 2 and 3, the charac-
teristic peaks of AGE (δ 5.7, 5.3 and 3.9) had no obvi-
ous changes during the deprotection procedure. The
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Synthesis of Novel Glycidol Copolymers with Pendant Alkene and Hydroxyl Groups
O
OH
O
(AGE)
O
4-methylbenzenesulfonic acid
O
O
+
NOct4Br/i-Bu3Al, 0 oC, 12 h
O
O
EEGE
O
O
O
m
EtOH/HCl
20 oC, 4 h
O
n
O
O
m
n
O
OH
O
the deprotection form
P(Gly-co-AGE)
P(EEGE-co-AGE)
Figure 1 The synthetic route for P(EEGE-co-AGE) and its deprotection form, P(Gly-co-AGE).
Figure 2 The 1H NMR spectrum of P(EEGE-co-AGE), recorded in DMSO-d6.
1
changes in the H NMR spectra indicate that a reaction
time of 4 h is suitable for the deprotection procedure of
P(EEGE-co-AGE).
ated. As seen in Table 1, the ratio of i-Bu3Al/NOct4Br
Table 1 The polymerization parameters and characterization
data of P(EEGE-co-AGE)
By varying the feed ratio of EEGE, AGE, initiator
and catalyst, a series of P(EEGE-co-AGE)s were syn-
thesized, as listed in Table 1. Through the investigation
of the self-polymerization of EEGE, Deffieux[23] found
that the self-polymerization process of EEGE greatly
depended on the ratio of i-Bu3Al/NOct4Br. The function
of the catalyst NOct4Br was mainly to initiate the co-
polymerization, and the other catalyst, i-Bu3Al, featured
prominently not only in initiating stage but also in the
copolymerization speed. Only when the ratio was
greater than 2, the self-polymerization of EEGE could
be carried out. When the ratio was increased up to 4, the
polymerization of EEGE could be happened in a quan-
titative manner. Furthermore, if the ratio was equal to 5,
high molecular weight of poly (EEGE) could be gener-
Run
1
[AGE]/(mol•L−1)
AGE/EEGEa
AGE/EEGEb
0.135
0.145
0.19
0.28
0.32
0.42
0.54
1
0.14
0.16
0.21
0.27
0.5
2
3
4
0.22
5
0.38
6
2
1
0.87
7
3
1.5
1.34
a Molar feed ratio; b Experimental molar ratio calculated by H
NMR. The molar ratio of i-Bu3Al to NOct4Br is 5, the concentra-
tion of EEGE is 2 mol/L, and the reaction time is 12 h in each run.
The yield is near 100% in all runs (calculated by weight).
1
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Liu et al.
FULL PAPER
Figure 3 1H NMR spectrum of the deprotection form of P(EEGE-co-AGE), recorded in CD3OD.
Table 2 Determined EEGE/AGE molar ratio at initial reaction
rates
used in all the seven experiments was greater than 4.
The yield of each experiment was in all cases near
100%, indicating that the polymerization was carried
out in a quantitative manner. The ratio of AGE to EEGE
in the P(EEGE-co-AGE) increased along with the in-
crease of the feed ratio of AGE to EEGE.
It should be pointed out that the values of AGE to
EEGE (molar ratio) in P(EEGE-co-AGE) were smaller
than their feed ratio. This might be due to the different
reactivity of AGE and EEGE in the copolymerization
process. To confirm this query, we measured the reac-
tivity ratios of AGE and EEGE in polymerization. In
order to accurately calculate the reactivity ratios, each
copolymerization was terminated when its conversion
rate was less than 10% (Table 2). The reactivity ratios
were calculated by the following Eq. (1):[27]
Sample
Rfeed ratio
1/11.4
1/7.6
Rpolymer
1/5.7
1/3.7
1/1.8
Conversionc/%
a
b
1
2
3
4
5
8.1
7.3
6.4
5.3
4.6
1/2.5
1/0.67
1/0.33
1/0.27
1/0.14
b
a The feed ratio of EEGE to AGE; The molar ratio of EEGE to
1
AGE in P(EEGE-co-AGE) is measured by H NMR; c The data
determined by gravimetric method.
After deprotection, there should be lots of hydroxyl
groups tethered to the P(EEGE-co-AGE) chains. This
can be verified from their infrared spectra (Figure 4). In
x
y1/2
y1/2
x
1
y1/2
(
)r－(
1
)r2＋(
－y1/2 )＝0
(1)
where x is the feed molar ratio (EEGE/AGE) of the co-
polymerization; y is the molar ratio of (EEGE/AGE) in
P(EEGE-co-AGE); r1 is the reactivity ratio of EEGE; r2
is the reactivity ratio of AGE.
Based on the experimental data, the reactivity ratios
for EEGE (r1＝3.30) and AGE (r2＝1.13) in this co-
polymerization were calculated. The considerable dif-
ference in the reactivity ratios indicates that the reactiv-
ity of EEGE is higher than that of AGE while involving
such anionic copolymerization. This could be another
evidence for the data in Table 1 that the molar ratio of
EEGE to AGE in P(EEGE-co-AGE) is lower than that
in starting materials.
Figure 4 The FT-IR spectra of P(EEGE-co-AGE) and the de-
protection production of P(EEGE-co-AGE).
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Synthesis of Novel Glycidol Copolymers with Pendant Alkene and Hydroxyl Groups
Table 3 Molecular weight, monomer composition and Tg of the as-synthesized P(EEGE-co-AGE) copolymers
c
Run
1
Composition (tha)
AGE55-co-EEGE35
AGE25-co-EEGE118
AGE59-co-EEGE59
AGE16-co-EEGE115
AGE19-co-EEGE118
AGE32-co-EEGE118
AGE89-co-EEGE59
Composition (expb)
AGE80-co-EEGE117
AGE15-co-EEGE54
AGE69-co-EEGE71
AGE6-co-EEGE41
AGE6-co-EEGE38
AGE9-co-EEGE34
AGE131-co-EEGE91
Mn (tha, g/mol) (×104)
Mn (expc, g/mol) (×104)
Mw/Mn Tg/℃
1.1
2.0
1.5
1.9
1.9
2.1
1.9
2.6
1.0
1.8
0.7
0.6
0.6
2.8
1.63
1.43
1.68
1.44
1.46
1.50
1.76
−94.3
−83.8
−83.5
−79.9
−74.7
−74.5
−73.7
2
3
4
5
6
7
a Theoretical values. Experimental data determined by 1H NMR (b) and GPC (c) in THF using a calibration with polystyrene as standards.
its deprotection form, the peaks around 3400 cm−1 be-
zation. After deprotection, the resultant polymer was a
come wide and strong, indicating a large number of hy-
droxyl groups exist in the deprotection form of the co-
polymer.
new type of amphiphilic copolymer pendant with func-
tional side groups with both alkene and hydroxyl group.
This method paved a way to synthesize glycidol co-
polymers with multiple different functional groups at a
time. The molar ratio of EEGE to AGE in the copoly-
mer could be controlled by varying the feed ratio of
EEGE and AGE as well as the reaction conditions, and
subsequently allowing the adjustment of the solubility
of the copolymer in water/organic phase. Due to the
coexistence of double bonds and hydroxyl groups in the
side chain, it provides the reactive sites in the copoly-
mer, just like a chemical reaction platform, for further
chemical modification and functionalization.[10,28-30]
Molecular weight of the as-synthesized polymers
The molecular weights of these as-synthesized
polymers were determined by gel permeation chroma-
tography (GPC). The data were composited in Table 3
(the experimental run in Table 1 had no relationship to
the run in Table 3). There are significant differences
between the theoretical values and experimental data.
For this kind of polymer, Deffieux[23] proposed that this
could be explained by the difference of hydrodynamic
volume of P(EEGE) and polyglycidol.
Thermal properties of the as-synthesized polymers
Acknowledgement
The glass transition temperature (Tg) of these
as-synthesized polymers was determined by differential
scanning calorimetry (DSC). The Tg values of P(EEGE-
co-AGE) with different chemical composition are in the
range of −73－−95 ℃. However, due to the limitations
of the instrument, Tg of the deprotection form of
P(EEGE-co-AGE), P(Gly-co-AGE), was not detected (it
might be lower than −100 ℃). From the given data of
Tg in Table 3, it can be seen that the variation of Tg
seems to be related somewhat with the changes of mo-
lecular weight (theoretical values) as well as the chemi-
cal composition. The Tg increases with increasing of the
molecular weight and the amount of AGE segments in
these copolymers. This result is basically the same as
the result obtained by Holger.[19] The obvious difference
between theoretical Mn and measured Mn is probably
due to two reasons: (a) the apparent difference between
PEG chain and polystyrene chain in structure (for GPC
detection); (b) some of the protons in the PEG chain
could not be detected by 1H NMR because of the entan-
glement of the polymer chains.
This study was supported by the National Natural
Science Foundation of China (No. 50903096), the De-
partment of Science Technology of Guangdong Prov-
ince (No. 2008B090500196), and the Fundamental Re-
search Funds for the Central Universities.
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