Joanna Potakowska

Lucyna Herczyńska

Roman Jantas

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Preparation and cross-linking properties of methacrylated sucrose

ORI GIN AL PA PER
Preparation and cross-linking properties
of methacrylated sucrose
Roman Jantas • Lucyna Herczyn´ska •
Joanna Potakowska
Received: 26 January 2011 / Revised: 29 May 2011 / Accepted: 29 May 2011 /
Published online: 17 June 2011
 The Author(s) 2011. This article is published with open access at Springerlink.com
Abstract By interfacial esterification of sucrose with methacryloyl chloride, an
ester derivative of sucrose—methacryloyloxysucrose was prepared, which contains
vinyl side groups. The structure of methacrylated sucrose (MS) was determined by
means of FTIR, 1H NMR, and 13C NMR spectra. The MS was used as new cross-
linker to cross-link poly(2-hydroxyethyl methacrylate). The influence of the
amounts of cross-linking agent on the swelling behavior of these hydrogels was
studied. Differential scanning calorimetry (DSC) was used for measuring the dif-
ferent states of water in hydrogel materials. DSC date showed that the content of
freezing water in hydrogel decreased with growth of MS percentage.
Keywords Sucrose  Methacrylated sucrose  Cross-linker  Hydrogels 
Freezing water
Introduction
Sucrose and its derivatives are of interest as potentially useful substrates in the
chemical and biological fields [1]. Due to its low price and high production, sucrose
could be particularly important for this purpose. To develop new applications of
sucrose and its derivatives, chemical modifications of sucrose have been investi-
gated. Sucrose esters are very interesting compounds because the properties of
sucrose can be modified to extend the use of this sugar by incorporating different
R. Jantas (&)  L. Herczyn´ska
Department of Physical Chemistry of Polymers, Technical University of Ło´dz´,
90-924, Ło´dz´, Poland
e-mail: rojan@p.lodz.pl
J. Potakowska
Tricomed SA, 93-493 Ło´dz´, Poland
123
Polym. Bull. (2011) 67:1865–1874
DOI 10.1007/s00289-011-0526-8
groups into the sucrose molecule. They are used in the industries of detergents,
cosmetics, pharmaceuticals, as well as in the food sector as non toxic emulsifiers
[2]. In early studies, a number of authors [3–6] have demonstrated the suitability of
the method for the esterification of unprotected sucrose of acid chlorides. The
possibility of using water as an alternative solvent for the esterification of sucrose
instead of organic solvents such as N,N-dimethylformamide, dimethylsulfoxide, or
pyridine has been studied [5]. In some cases, an aqueous solution of NaOH was used
[6]. Enzymes have been also used as catalysts in the synthesis of carbohydrate (in
particular sucrose) esters. The enzymatic regioselective synthesis of sucrose-10-
methacrylate from sucrose and vinyl methacrylate using subtilisin Carlsberg, a
readily available bacterial serine protease, has been described in article [7]. Also
Potier et al. [8] have obtained sucrose monomethacrylate in the reaction between
sucrose and trifluorethyl methacrylate using Proteinase N enzyme as catalyst. The
nonselective synthesis of methacrylated sucrose (MS) proposed in article [9]
consisted of transesterification of sucrose with glycidyl methacrylate in DMSO in
the presence of 4-(N,N-dimethylamino)pyridine as catalyst. Polymerizable or
amphiphilic sucrose esters have been obtained regioselectively with a good yield
[10, 11]. Schotten–Baumann’s interfacial esterification is commonly known in
organic chemistry as a method for the preparation of esters from alcohols and acid
chlorides. Thus, it seems to be of interest to use this method to prepare sucrose
esters.
Synthetic hydrogels based on poly(2-hydroxyethyl methacrylate) (PHEMA) have
been tested for their use as suitable synthetic materials because of their superior
biocompatibility, high permeability to small molecules (i.e., tissue metabolites) and
hydrophilic properties [12]. The cross-linkers, which remain in the resulting
hydrogels, usually show high toxicity. Therefore, it was necessary to develop an
alternative, biodegradable, and low-toxicity cross-linker. In order to overcome these
obstacles, we developed a novel cross-linker of sucrose with side vinyl groups.
The aim of this study was to prepare a sucrose derivative, containing reactive
double bonds—methacryloyloxysucrose, by Schotten–Baumann’s esterification of
sucrose with methacryloyl chloride (Scheme 1) and to characterize the obtained
product and its use as biodegradable cross-linker for cross-linking of poly(2-
hydroxyethyl methacrylate).
O
O
OH
OH
OH
O
OH
OH
OH
OH
OH O
O
R1O
OR1
OR1
O
OR1
OR1
OR1
OR1
R1O
CH2 CCOCl
CH3
C C
CH3
CH2
O
R1  =      H orsucrose
aqueous solution of KOH/MEK
                   -80C
Scheme 1 Esterification of sucrose with MCl
1866 Polym. Bull. (2011) 67:1865–1874
123
Experimental
Materials
Sucrose trade product (available on the market) was used without additional
purification. 2-Hydroxyethyl methacrylate (HEMA, Aldrich Chem., Co.) was
purified by distillation under reduced pressure and the fraction of by 87–89 C/
5 mmHg was collected. Methacryloyl chloride (MCl) was prepared by treating
methacrylic acid with thionyl chloride, b.p. 98–99 C/760 mm Hg. Organic
solvents: methyl ethyl ketone (MEK and toluene, Aldrich Chem., Co.) were dried
and purified by common methods.
Synthesis of MS
The MS was prepared according to a previously reported modified procedure for
synthesis of methacrylated starch [13].
Solution A
Aqueous solution of sucrose: 0.5 mol dm-3 groups OH: 1 vol.
Aqueous solution of KOH: 3 mol dm-3: 1 vol.
Methyl ethyl ketone: 1 vol.
Solution B
Methacryloyl chloride: 1.5 mol equiv. (to the hydroxyl groups in sucrose).
Methyl ethyl ketone: 1.1 vol.
Toluene: 0.2 vol.
Solution A was introduced into a three-neck flask provided with a stirrer and a
thermometer, cooled down to -8 C, and then solution B was added dropwise. The
process was carried out with intensive stirring for 40 min and then the reaction
mixture was left for separation. The upper organic layer was separated from the
aqueous lower one in which only sucrose esterified to a low degree remained. Next,
the organic layer was dried over anhydrous MgSO4. The product was precipitated
with heptane and purified by dissolving in THF and reprecipitating with heptane. It
was dried for a short time under vacuum at room temperature, protected against day
light. The obtained MS has degree of substitution (DS) equal to 6.5. Yield was 49%
based on DS equal to 6.5.
Synthesis of cross-linked PHEMA
The free-radical polymerization of HEMA in the presence of AIBN as initiator and
variable amounts of the cross-linking agent was carried out for 24 h, gradually raising
the process temperature from 40 to 75 C. Typical course of this process was as
follows: 4.4 cm3 of HEMA, 0.02 g AIBN, and the cross-linking agent in amounts
ranging from 0.5 to 5.0 wt% in relation to the monomer were placed by means
of a syringe between two glass plates separated by a silicon spacer
Polym. Bull. (2011) 67:1865–1874 1867
123
(120 9 50 9 0.9 mm). The glass plates were siliconized with a dimethyldichloros-
ilane. The polymerization was carried out in a laboratory drier under the following
conditions: 2 h at 40 C, 4 h at 55 C, and 18 h at 75 C. The gradual temperature
raising prevented blister formation in the cross-linked PHEMA samples. After
removal of the glass plates, the films obtained were dried at 75 C. The samples were
cut out from the films with the dimensions 15 9 10 9 0.9 mm for investigating their
swelling behavior.
Before the examination of all, the samples were immersed in a large excess of
ethanol for about 48 h at 25 C to remove the noncross-linked material and then
were dried at room temperature for about 24 h, and further dried in a 60 C under
vacuum to a constant weight.
Photopolymerization
A thin layer of MS was applied onto a KBr plate by evaporation of the solvent from
the MS solution in chloroform and then dried at room temperature under vacuum.
The layer obtained was irradiated with a L6/58 quartz tube (37.5 W) without filter
from a distance of 20 cm. The conversion of double bonds in MS during UV
irradiation was investigated by FTIR spectroscopy. The absorption peak of the
[C=C\ at 1638 cm-1 was used to calculate its conversion while the absorption
peak of the carbonyl group at 1728 cm-1 was used as standard. The conversion of
double bonds was calculated according to Eq. 1
% Conversion ¼ ðA1638=A1728Þ0  ðA1638=A1728ÞtðA1638=A1728Þ0
 100 ð1Þ
where (A1638/A1728)0 and (A1638/A1728)t are the ratio of absorbance at 1638 cm
-1 to
that of 1728 cm-1 before and after different irradiation times, respectively.
Measurements
Infrared spectra were recorded using a Perkin-Elmer 2000 Fourier transform
infrared (FTIR) instrument. 1H-NMR and 13C-NMR spectra were obtained using a
Bruker DPX 250 MHz spectrometer with DMSO-d6 (for sucrose) or CDCl3 (for
MS) as solvent and TMS as an internal reference.
Differential scanning calorimetry (DSC) was performed using a Perkin-Elmer
DSC-7 instrument with a heating rate of 20 C min-1 from -30 to 200 C in
nitrogen atmosphere. The MS sample of about 5 mg was placed in an aluminum pan
and aluminum cover was crimped on.
About 2–4 mg hydrogel sample which had been preswollen at room temperature
was quickly cooled to -60 C and equilibrated for 10 min. The sample was slowly
heated at a program rate of 10 C min-1 up to 40 C.
The DS of the MS was determined by titration method. The procedure in detail is
as follows: 0.2 g of the sample was weighed accurately and placed in 250 cm3 flask.
Twenty milliliters of distilled water was added to flask and stirred overnight at room
temperature. Thirty milliliters of 0.1 M NaOH was added and heated at 60 C for
1868 Polym. Bull. (2011) 67:1865–1874
123
2 h under reflux condenser. After cooling to room temperature, titration was
conducted with 0.1 M HCl using phenolphthalein as indicator [14].
The swelling of cross-linked PHEMA versus time was examined by determining
the amount of absorbed swelling agent (water). About 0.18 g samples were
immersed in excess water at 25 C for various periods of time. The swollen samples
were dried with a filter paper and weighed. The degree of swelling was calculated
using the following expression:
Degree of swelling ¼ ½ðWt  W0Þ=W0 ð2Þ
where Wt and W0 are weights of the sample at time t and zero (the dry state),
respectively.
Results and discussion
The FTIR spectra of sucrose and MS (DS = 6.5) are shown in Fig. 1a, b. In the
spectrum of the esterification product, one can observe a strong absorption band at
1728 cm-1 which can be ascribed to the valence vibration of[C=O. An absorption
band corresponding to [C=C\ appears at 1638 cm-1. In addition, there is also a
distinct absorption band within the range from 3640 to 3150 cm-1 derived from
hydroxyl groups, which indicates an incomplete esterification of sucrose.
Figure 2a, b shows the 1H NMR spectra of sucrose and the MS. In spectrum
(Fig. 2b) one can observe multiplets derived from methacryloyl group at 1.94 ppm
(methyl proton, Hb) as well as at 5.45 and 6.14 ppm (protons at the double bond,
Ha).
4000 3200 2400 1800 1400 1000 600
Wave number, cm-1
Tr
a
n
sm
ita
nc
e,
 %
a)
b)
>C=C<
=C<
-OH
Fig. 1 The FTIR spectra of a sucrose and b MS
Polym. Bull. (2011) 67:1865–1874 1869
123
The formation of the MS is also confirmed by the respective 13C NMR spectrum
(Fig. 3b). Here, the signals of methacryloyl group are detected at 166.5 (C16), 135.2
(C14), 126.8 (C13), and 19.0 (C15) ppm.
The sucrose has eight hydroxyl groups, the maximum possible DS is 8.0. The
determination of DS by titration involved complete basic hydrolysis of the ester
linkages and titration of the excess alkali. DS for MS is 6.5 was determined by
means of the method for starch esters.
Preliminary observation shows that MS is susceptible to the action of UV
radiation. After irradiation of the sample under investigation, one can observe a
broadening of the absorption band of the carbonyl group at 1728 cm-1 (the area of
this band is approximately constant) while the intensity of the absorption band of
CH2=C\(m = 1638 cm
-1) is decreased. This is probably due to cleavage of double
bonds by UV radiation and the formation of cross-linking in the molecule which
results in a product insoluble in organic solvents. This process is illustrated in Fig. 4
showing the conversion of CH2=C\ versus irradiation time.
Fig. 2 The 1H NMR spectra of a sucrose and b MS
1870 Polym. Bull. (2011) 67:1865–1874
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Figure 5 shows the curves illustrating the swelling of PHEMA networks in water
obtained with various amounts (0.5–5.0 wt%) of MS. As can be seen, the
equilibrium swelling is reached after about 24 h. Its value decreases with increasing
amount of MS used in the initial reaction mixture.
Fig. 3 The 13C NMR spectra of a sucrose and b MS
0
20
40
60
80
100
0 50 100 150 200 250 300 350
Irradiation time, min
C
on
ve
rs
io
n,
 %
 
Fig. 4 The conversion of
CH2=C\ versus irradiation time
Polym. Bull. (2011) 67:1865–1874 1871
123
The MS was characterized by DSC analysis. In the first heating cycle of MS an
exothermic peak can be observed within the temperature range 63–165 C. This
exotherm probably results from the thermal polymerization of double bonds of the
MS leading to cross-linked product what is confirmed by the disappearance of the
peak in the MS sample during the second cycle of heating.
Differential scanning calorimetry can provide information about the states of
water in the swollen hydrogels. In general, the state of water in the polymer
hydrogel can be divided into free water, freezing bound water, and nonfreezing
bound water [15, 16]. Free water is the freezing water, which does not take part in
hydrogen bounding with polymer chains and shows a similar transition temperature
and enthalpy of fusion in the DSC curves, as pure water does. Freezing bound water
is the water which interacts weakly with polymer molecules and has a melting
endotherm below 0 C. Bound water is the nonfreezing water as it is immobilized
from hydrogen bounds with polymer chains. These water molecules are immobi-
lized and show no freezing peak. The water structure data of the hydrogels are listed
in Table 1.
It can be seen from Fig. 6 that for the hydrogel with 0.5 wt% of cross-linker the
endothermic peak was separated into two peaks, one remaining at close to 0 C, and
the other shifting to about -40 C. These two peaks indicate the existence of the
two types of water in the hydrogel, the free water and the freezing bound water.
It has been found that the hydrogel with 0.5 wt% of cross-linker contain more
freezing water including the free water and the freezing bound water, while the
hydrogels with 3.0 and 5.0 wt% of MS, respectively are occupied mainly by the
nonfreezing bound water.
0
0,1
0,2
0,3
0,4
0,5
0,6
0 5 10 15 20 25 30
Time, h
D
eg
re
e 
of
 sw
el
lin
g,
 g
/g
Fig. 5 Swelling curves of
PHEMA cross-linked with
various amounts of MS: circle
0.5 wt%, square 3.0 wt%,
diamond 5.0 wt%
Table 1 Calculated freezing water and nonfreezing bound water in swollen hydrogels from DSC results
Hydrogels Mass % MS
in the gel
g-water/g-swollen gel Freezing water/
total water (%)
Nonfreezing bound
water/total water (%)
Total
water
Freezing
water
Nonfreezing
bound water
Gel1 0.5 0.490 0.231 0.259 47.14 52.86
Gel2 3.0 0.257 0.060 0.197 23.35 76.65
Gel3 5.0 0.215 0.022 0.193 10.23 89.77
1872 Polym. Bull. (2011) 67:1865–1874
123
Conclusions
The studies performed have shown that the esterification of sucrose with MCl by
Schotten–Baumann’s method results in formation of MS. The MS was used as new
cross-linker to cross-link poly(2-hydroxyethyl methacrylate). DSC date showed that
the content of freezing water in hydrogel decreased with growth of MS percentage.
It has been found that the high-hydration hydrogel contain relatively more freezing
water, while the low-hydration hydrogels are occupied mainly by the nonfreezing
bound water. The differences between the DSC results were explained by a
structural transformation during cooling. There are two states of water in the
unfrozen hydrogel, i.e., unfrozen water and disordered water which is mainly
formed in narrow apertures in the hydrogel. The degree of equilibrium swelling of
the hydrogels prepared depends on the quantity of the cross-linker used.
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Preparation and cross-linking properties of methacrylated sucrose

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