Synthesis of three different galactose-based methacrylate monomers for the production of sugar-based polymers

Article abstract of DOI:10.1016/j.carres.2016.06.008

Glycopolymers, synthetic sugar-containing macromolecules, are attracting ever-increasing interest from the chemistry community. Glycidyl methacrylate (GMA) is an important building block for the synthesis of sugar based methacrylate monomers and polymers. Normally, glycidyl methacrylate shows some advantages such as reactivity against nucleophiles or milder synthetic conditions such as other reactive methacrylate monomers. However, condensation reactions of glycidyl methacrylate with for instance protected galactose monomer leads to a mixture of two products due to a strong competition between the two possible pathways: epoxide ring opening or transesterification. In this paper, we propose two alternative routes to synthesize regiospecific galactose-based methacrylate monomers using the epoxy-ring opening reaction. In the first alternative route, the protected galactose is first oxidized to the acid in order to make it more reactive against the epoxide of GMA. In the second route, the protected sugar was first treated with epichlorohydrin followed by the epoxy ring opening reaction with methacrylic acid, to create an identical analogue of the ring-opening product of GMA. These two monomers were polymerized using conventional radical polymerization and were compared to the previously known galactose-methacrylate one. The new polymers show similar thermal stability but lower glass transition temperature (Tg) with respect to the known galactose methacrylate polymer.

Full text of DOI:10.1016/j.carres.2016.06.008

Carbohydrate Research 432 (2016) 50e54
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Note
Synthesis of three different galactose-based methacrylate monomers
for the production of sugar-based polymers
,
,
**
,
1
a
a
Jessica S. Desport a 1, Daniele Mantione a
, Monica Moreno , Haritz Sardon ,
ꢀ
ꢀ
María J. Barandiaran a, David Mecerreyes a
POLYMAT, University of the Basque Country UPV/EHU, Joxe Mari Korta Center, 20018, Donostia-San Sebastian, Spain
b Ikerbasque, Basque Foundation for Science, E-48011, Bilbao, Spain
,
b
,
*
a
ꢀ
a r t i c l e i n f o
a b s t r a c t
Article history:
Glycopolymers, synthetic sugar-containing macromolecules, are attracting ever-increasing interest from
the chemistry community. Glycidyl methacrylate (GMA) is an important building block for the synthesis
of sugar based methacrylate monomers and polymers. Normally, glycidyl methacrylate shows some
advantages such as reactivity against nucleophiles or milder synthetic conditions such as other reactive
methacrylate monomers. However, condensation reactions of glycidyl methacrylate with for instance
protected galactose monomer leads to a mixture of two products due to a strong competition between
the two possible pathways: epoxide ring opening or transesterification. In this paper, we propose two
alternative routes to synthesize regiospecific galactose-based methacrylate monomers using the epoxy-
ring opening reaction. In the first alternative route, the protected galactose is first oxidized to the acid in
order to make it more reactive against the epoxide of GMA. In the second route, the protected sugar was
first treated with epichlorohydrin followed by the epoxy ring opening reaction with methacrylic acid, to
create an identical analogue of the ring-opening product of GMA. These two monomers were poly-
merized using conventional radical polymerization and were compared to the previously known
galactose-methacrylate one. The new polymers show similar thermal stability but lower glass transition
temperature (Tg) with respect to the known galactose methacrylate polymer.
Received 16 May 2016
Received in revised form
24 June 2016
Accepted 26 June 2016
Available online 28 June 2016
Keywords:
Glycidyl methacrylate (GMA)
Isopropylidene-D-galactopyranose
AMC-2 catalyst
Epoxide ring opening
Free radical polymerization
© 2016 Elsevier Ltd. All rights reserved.
Glycopolymers, synthetic sugar-containing macromolecules, are
attracting ever-increasing interest from the chemistry community
due to their role as biomimetic analogues and their potential for
commercial applications. Glycopolymers play an important role in
many biological recognition events such as cell-cell adhesion,
development of new tissues and infectious behavior of virus and
bacteria. They have high potential in targeted drug delivery, tissue
engineering and synthesis of biocompatible materials. On the other
hand, there is a general trend to synthesize polymers using
renewable raw materials istead of oil based ones [1]. Counting the
fact that about 75% of biomass consists of carbohydrates [2], several
sugar based polymers have been synthesized over the years [3e5],
contributing to the developments and applications of bio-based
plastic materials [6e8]. Among the different glycopolymers,
galactose based ones have shown interesting performance as
extracellular matrices for tissue engineering, as antimicrobial
agents or as thermoresponsive materials [9].
In this work, a galactose based monosaccharide carrying ace-
tonide protecting groups will be envisaged as valuable precursor:
1,2:3,4-Di-O-isopropylidene-D-galactopyranose (DAGA). In order to
make this protected galactose polymerizable we coupled it with
bio-based methacrylate monomers such as glycidyl methacrylate
or methacrylic acid reagent [10]. From this precursor three different
methacrylic monomers are synthesized. The incorporation of a
polymerizable methacrylic group will be achieved through the use
of two different functional agents: glycidyl methacrylate (GMA) on
the one hand and epichlorohydrin plus methacrylic acid on the
other hand. Noteworthy that the first two are both coming from the
biggest biodiesel production side product: glycerol [1,11]. Exploring
the literature, a variety of different mechanisms are reported for the
* Corresponding author. POLYMAT, University of the Basque Country UPV/EHU,
ꢀ
Joxe Mari Korta Center, 20018, Donostia-San Sebastian, Spain.
** Corresponding author. POLYMAT, University of the Basque Country UPV/EHU,
ꢀ
Joxe Mari Korta Center, 20018, Donostia-San Sebastian, Spain.
E-mail
addresses:
daniele.mantione@ehu.es,
david.mecerreyes@ehu.es
(D. Mecerreyes).
1
These authors contributed equally.
http://dx.doi.org/10.1016/j.carres.2016.06.008
0008-6215/© 2016 Elsevier Ltd. All rights reserved.

J.S. Desport et al. / Carbohydrate Research 432 (2016) 50e54
51
reaction between an alcohol and GMA [12e19]. We can note that in
aqueous media, the reaction of GMA with alcohol groups is strongly
pH dependent and could lead to both products: the one resulting
from the epoxide ring opening and, the other, from the trans-
esterification of the methacrylic ester [16,18e21]. In organic sol-
vents, even if there are some exceptions in recent literature [13,22],
the predominant mechanism appear to be the unexpected trans-
esterification [16,17,20]. These different pathways result in product
formed by a mixture of two chemical compounds with a predom-
inance of the esterification one. The two products are methacrylic
monomers showing the presence or not of a spacer between the
sugar ring and the methacrylate group as shown in Fig. 1. It is worth
remarking that if the target product would be the one obtained by
transesterification, other routes with higher yield and higher atom
economy may be used instead of the glycidyl methacrylate one,
such as esterification using methacryloyl chloride or methacrylic
anhydride [8,23].
In order to confirm previous studies in organic solvent and to
exploit all the possible products, the reaction between DAGA and
GMA has been performed in bulk in the presence of trimethylamine
at 60 ꢀC (Fig. 1, route in the right). The resulted mixture of products
was analyzed by UPLC-QTOF and subsequently separated by flash
chromatographic column, confirming that the major product was 1
(Fig. 2a). It is interesting to note that the molecule resulting from
ring-opening mechanism was also detected in ratio 90/10: trans-
esterification product 1/ring opening product 5. It is worthwhile to
isopropylidene-D-galactopyranose is first oxidized with KMnO4 in
order to make it more reactive against the epoxide of GMA [24].
Consequently, the oxidized sugar 2 has been reacted with GMA in
the presence of a catalytic amount of an industrial catalyst called
AMC-2. Specifically designed to promote reactions of epoxides,
AMC-2 has shown efficiency in promoting the regiospecific ring-
opening reaction of GMA with carboxylic acid groups [25]. The
resulting product (3) was isolated by flash column chromatography
and characterized (Fig. 2b).
In the second route (Fig. 1 route in the left down side), the GMA
was split in two synthons, epichlorohydrin and methacrylic acid, to
create an identical analogue of the ring opening product of GMA.
Since the opening of epoxy-ring in the presence of AMC-2 catalyst
was successful for the reaction of carboxylic acid, a second strategy
where the epoxy function was grafted to DAGA [26] using
epichlorohydrin was tested, and made react with methacrylic acid
in the presence of AMC-2, leading to product 5 (Fig. 2c). It is worthy
to point out that in the two last examples of ring-opening no
mixture of isomers was observed, indicating that the use of AMC-2
catalyst allowed stereospecific opening of the epoxide. This was
deeply demonstrated by 1H and 13C NMR spectroscopy, using HSQC,
HMBC, DEPT at different temperatures, due to the high similarity of
the two possible regioisomers (Supporting information).
Therefore, using different synthetic routes, we were able to
synthesize three different methacrylate galactose monomers,
whose difference is found in the spacer between the methacrylate
and galactose groups. In order to compare the different properties
that the spacer could give to the final polymers, the monomers
were polymerized at 70 ꢀC using conventional radical polymeri-
zation in benzene with Azobisisobutyronitrile (AIBN) as thermal
initiator. After purification we were able to isolate and characterize
three polymers from monomers 1, 3 and 5, called HOMO-1, HOMO-
note that the only product detected is the one resulting from the
attached to the epoxide leading to a secondary alcohol.
a
In this paper, we propose two alternative routes to synthesize
galactose-based methacrylate monomers using the epoxy-ring
opening reaction (Fig. 1, routes in the left). In the first alternative
route (Fig.
1
route in the left upper side), 1,2:3,4-Di-O-
O
O
O
O
OH
O
O
O
O
O
O
O
O
(c)
3
O
OH
O
O
O
O
O
O
O
OH
O
O
O
O
O
O
2
(b)
O
OH
O
5
O
O
10%
90%
O
O
O
(a)
O
O
O
O
Cl
O
O
(d)
O
O
O
O
O
O
O
O
O
O
OH
OH
O
O
O
4
O
O
(e)
1
OH
O
O
O
O
O
5
Fig. 1. Synthesis strategies to produce methacrylate galactose-based monomers from transesterification and epoxy-ring opening mechanisms. Reagents and conditions: (a) NEt3,
60 ꢀC, 5 h; (b) NaOH, KMnO4, 45 ꢀC, 12 h; (c) GMA, AMC-2, DCE, 70 ꢀC, 3 h; (d) EPC, DCM, 80 ꢀC, 12 h; (e) MA, AMC-2, DCE, 70 ꢀC, 3 h.

Fig. 2. 13C NMR of methacrylate galactose-based monomers: a) monomer 1; b) monomer 3; c) monomer 5 in DMSO-d6.

J.S. Desport et al. / Carbohydrate Research 432 (2016) 50e54
53
3 and HOMO-5 respectively. First, we measured the molecular
weight by gel permeation chromatography (GPC) and secondly we
compared their thermal stability by thermogravimetric analysis
(TGA) and differential scanning calorimetry (DSC). In the three
cases we were able to obtain high molecular weight linear poly-
mers with valued of 55 kDa, 54 kDa and 39 kDa for HOMO-1,
HOMO-2 and HOMO-3 respectively [27,28]. In all the cases the
dispersity (Ð) values were between 1.5 and 1.7 which is the ex-
pected ones for a radical polymerization mechanism. To conclude,
as expected these 3 methacrylate monomers were polymerized by
conventional radical polymerization.
As shown in Fig. 3a all three polymers exhibit good stability
until 200 ꢀC. However, at higher temperatures, the new polymers,
HOMO-3 and HOMO-5, showed better thermal stability than the
previously known HOMO-1. Indeed, at 300 ꢀC, HOMO-1 has already
lost 53 wt% while HOMO-3 lost 25 wt% and HOMO-5 only 18 wt%.
These values demonstrate a higher stability of the new polymers
and a beneficial character of the introduced alcoholic spatial moi-
eties. These new polymers show a similar degradation profile of
most methacrylic polymers such as PMMA that exhibit a degrada-
tion temperature range between 300 and 400 ꢀC [29].
Furthermore, the three homopolymers were characterized by
DSC in order to evaluate their glass transition temperatures. It is
interesting to note the significant effect of the spacer between the
methacrylate group and the sugar on glass transition temperature
ranges. Indeed, we can observe a decrease in glass transition tem-
perature when the monomers were produced by ring opening, as
can be seen in Fig. 3b. Because of its cyclic nature, the protected
pendant sugar scaffold provides stiffness to the chains and as it can
be seen HOMO-1 exhibits a very high Tg around 113 ꢀC. However,
the presence of a short chain separating the methacrylate from the
sugar helps improving significantly the mobility of the polymer
chains and justifies the lower Tg of HOMO-3 and HOMO-5 around
65 ꢀC and 36 ꢀC respectively. We also believe that the planarity of
the extra carbonyl group in HOMO-3 can explain its higher Tg
compared to HOMO-5 [30].
In conclusion, in this work three different protected galactose
monomers were synthesized by the condensation of glycidyl
methacrylate and a protected galactose building block, 1,2:3,4-Di-
O-isopropylidene-D-galactopyranose (DAGA). The three monomers
presented similar methacrylic and protected galactose moiety and
the main difference was the spacer in between. The monomers
were polymerized and resulting galactose-polymethacrylates were
compared. The new polymers showed better thermal stability and
lower glass transition temperature (Tg) than the previously known
galactose polymer. Incorporation of these bio-based materials
could give added value to the resulting polymeric materials.
Preparation of waterborne polymeric binders and additives from
these monomers are under investigation.
1. Materials and methods
1.1. Materials
All reactants were used without prior purification. 1,2:3,4-Di-O-
isopropylidene-D-galactopyranose was obtained from Carbosynth
(UK). Glycidyl methacrylate, triethylamine, methacrylic acid, so-
dium hydroxide, azobisisobutyronitrile (AIBN) were coming from
Sigma-Aldrich. AMC-2, which is a mixture of 50% trivalent organic
chromium complexes and 50% phthalate esters, was purchased
from AMPAC Fine Chemicals. Solvents were purchased from Acros-
Organic and Sigma-Aldrich.
1.2. Instrumentation
1H NMR and 13C NMR spectra were recorded at ambient tem-
perature with a 400 MHz Bruker equipment whereas 2D-NMRs
were recorded with a 500 MHz equipment. An extra amount of
inhibitor (benzoquinone) was added in the tube when recording
spectra at high temperatures to prevent polymerization. TLC were
carried out on aluminium precoated plates (silica gel 40-60 Å
400 mesh, F254, Aldrich) using hexane/ethyl acetate 7:3 (v:v) as
eluent. The compounds were highlighted by spraying the TLC plates
with EtOH/H2SO4 9:1 (v:v) stain and heat.
Polymers glass transition temperature (Tg) was measured by
means of a differential scanning calorimeter, series DSC Q1000 (TA
Instruments). The scanning cycles consisted of first cooling to -
20 ꢀC at 10 ꢀC/min, then heating from ꢁ20 to 200 ꢀC at 10 ꢀC/min,
cooling again from 200 to ꢁ20 ꢀC at 10 ꢀC/min, and then heating to
200 ꢀC at a rate of 10 ꢀC/min. The results from the second heating
from ꢁ20 to 200 ꢀC will be presented herein. Thermogravimetric
analysis were carried out in a TGA Q500 (TA instruments) from
20 ꢀC to 800 ꢀC, using a heating rate of 10 ꢀC/min under a nitrogen
flow rate of 90 mL/min.
Polymers molecular weights were determined via gel perme-
ation chromatography using an Agilent technologies GPC system,
equipped with a mixed column (Shodex KD-806M), and a refractive
index detector. The analysis was performed at 1.0 mL/min flow rate
in dimethylformamide (DMF) at 40 ꢀC. Relative Mw was deter-
mined thanks to a conventional calibration obtained with poly-
styrene narrow standards.
Fourier Transform Infrared Spectroscopy (FTIR) measurements
were performed on a Brüker Alpha-p FTIR spectrometer. Spectra
were collected from 4000 to 250 cmꢁ1 with the following settings:
Fig. 3. a) Thermogravimetric analysis; b) Differential Scanning Calorimetry of HOMO-1, HOMO-3 and HOMO-5.

54
J.S. Desport et al. / Carbohydrate Research 432 (2016) 50e54
42 scans per sample and spectral resolution: 4 cmꢁ1
.
members of the Industrial Liaison Program in Polymerization in
Dispersed Media of Polymat (AkzoNobel, Allness, Arkema, BASF,
Foresa, Nuplex, Solvay, Stahl, Syntomer, Vinavil, Wacker). The work
was supported by EU through project FP7-PEOPLE-212-ITN
316832-OLIMPIA (Mantione D.). The authors thank for technical
and human support provided by SGIker of UPV/EHU and European
Ultra-Performance Liquid Chromatography (UPLC-Q-TOF) was
performed using a chromatograph from Acquity, equipped with a
diode array detector and coupled with a mass spectrometer (Wa-
ters, model SYNAPTTM G2 HDMSTM) with ESI ionization sources.
Analyses were conducted in positive ionization mode.
~
funding (ERDF and ESF). The authors thanks Inaki Gomez (POLY-
1.3. Reaction of oxidize-DAGA (2) and GMA: synthesis of 3
MAT UPV/EHU), Dr. Jose Ignacio Miranda (SGIker) and Dr. Patricia
Navarro Villaverde (SGIker) for useful and essential support.
2 (3.60 g, 13 mmol) was mixed with glycidyl methacrylate (3 g,
21 mmol) in 150 mL of 1,2-dichloroethane (DCE) in the presence of
1,5 wt%, in respect of the sugar, of AMC-2. A few ppm of benzo-
quinone was added to the media. The mixture was heated up to
70 ꢀC and stirred for 3 h. DCE (150 mL) was used to dilute the re-
action and the resulting organic phase was washed with distilled
water 3 ꢂ 50 mL. Solvent evaporation was performed after drying
over Na2SO4. Purification was completed by flash column chro-
matography (Hexane/Ethyl Acetate (EtOAc) from 7/3 to 1/1) to
obtain 3. Yield ¼ 2.45 g (45%) as a slightly yellow oil. Rf 0.42
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.carres.2016.06.008.
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0.5 g of monomer was dissolved in 10 mL of benzene. The re-
action mixture was purged with nitrogen for 20 min and then
heated up to 70 ꢀC. AIBN 1 wt% with respect to the sugar, dissolved
in benzene (ca. 0.1 mL) was added as a shot to initiate the poly-
merization. After 48 h of reaction, the polymer was precipitated in a
large amount of heptane. The product was filtered under vacuum,
then dissolved in THF and re-precipitated again in heptane. The
resulting fine powder was suction filtrated and dried for one night
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39e55.
Acknowledgement
[30] E.H. I, E.A.G.J. Brandrup, Polymer Handbook 2 Volumes Set, fourth ed., John
Wiley & Sons, Inc., 1999.
The authors acknowledge the financial support provided by the