Synthesis and characterization of some organosilicon derivatives of poly 2-hydroxyethyl methacrylate with cubane as a cross-linking agent

Article abstract of DOI:10.1016/j.jorganchem.2005.07.068

Some silyl ether derivatives of 2-hydroxyethyl methacrylate (HEMA) were prepared. The Et₃Si, Ph₃Si and Me₃Si groups together with cubane-1,4-dicarboxylic acid (CDA) were covalently linked with HEMA. The silyl-linked HEMA are abbreviated as TETMA, TPhMA and TMEMA, respectively. CDA linked to two HEMA groups is the cross-linking agent (CA). Free radical copolymerization and cross-linking copolymerization of the resulting monomers with 2-hydroxyethyl methacrylate (HEMA) with the various ratios of CA as cross-linking agent, were carried out using AIBN as initiator at the temperature ranges 60-70 °C. The cross-linking copolymers were identified by FT-IR spectroscopy. The glass transition temperature (T _g) of the network polymers was determined calorimetrically. The T_g of network polymers increases with increase of cross-linking degree. All monomers and polymers were identified by spectroscopic methods. These silyl derivatives modified methacrylate polymer properties.

Full text of DOI:10.1016/j.jorganchem.2005.07.068

Journal of Organometallic Chemistry 690 (2005) 4755–4760
www.elsevier.com/locate/jorganchem
Synthesis and characterization of some organosilicon derivatives
of poly 2-hydroxyethyl methacrylate with cubane as a
cross-linking agent
*
Mohammad G. Assadi , Mehrdad Mahkam, Zohreh Tajrezaiy
Chemistry Department, Azerbaijan University of Tarbiat Moallem, Tabriz, km 35 Tabriz-Marageh, Tabriz 35751379, Iran
Received 6 April 2005; received in revised form 5 July 2005; accepted 20 July 2005
Available online 2 September 2005
Abstract
Some silyl ether derivatives of 2-hydroxyethyl methacrylate (HEMA) were prepared. The Et3Si, Ph3Si and Me3Si groups together
with cubane-1,4-dicarboxylic acid (CDA) were covalently linked with HEMA. The silyl-linked HEMA are abbreviated as TETMA,
TPhMA and TMEMA, respectively. CDA linked to two HEMA groups is the cross-linking agent (CA). Free radical copolymeri-
zation and cross-linking copolymerization of the resulting monomers with 2-hydroxyethyl methacrylate (HEMA) with the various
ratios of CA as cross-linking agent, were carried out using AIBN as initiator at the temperature ranges 60–70 °C. The cross-linking
copolymers were identified by FT-IR spectroscopy. The glass transition temperature (Tg) of the network polymers was determined
calorimetrically. The Tg of network polymers increases with increase of cross-linking degree. All monomers and polymers were iden-
tified by spectroscopic methods. These silyl derivatives modified methacrylate polymer properties.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Cross-linking; Silyl group; Copolymerization; Cubane
1. Introduction
tivity parameters, mechanical, thermal and surface
properties, as well as photochemical reactivity [1–8].
On the other hand, some silyl derivatives of polymers
such as acrylates and styrene showed membrane proper-
ties [9]. One of the important properties of these mem-
branes is selectivity with reference to oxygen. The
membrane usually showed high oxygen permeability
and a reasonably high perm selectivity of oxygen against
nitrogen and carbon dioxide. The permeability behavior
was attributed to a high affinity of oxygen molecules to
Si atoms and the relatively large free volumes between
the polymers, resulting from the restricted mobility of
the side chain in the repeat units. Thus, this type of poly-
mers may be applicable to the biosensor electrode mem-
brane as their chemical and physical properties are
appropriate. In this way, silyl methacrylate was also
used in contact lens. These lenses with silyl chain have
Attaching the organosilyl groups to macromolecular
chains as a 2-hydroxyethyl methacrylate (HEMA) poly-
mer should lead to important modifications of polymer
properties. The combination of versatility and tailored
molecules has relatively easily made acrylic and metha-
crylic esters prime candidates for diverse applications.
Polymers containing organosilyl groups are an interest-
ing research field in polymer and silicon chemistry.
Attaching the organosilyl groups to macromolecular
chains should lead to important modifications of poly-
mer properties such as gas permeability and perm selec-
*
Corresponding author. Tel.: +98 411 4439467; fax: +98 4524991.
E-mail address: mgalehassadi@yahoo.com (M.G. Assadi).
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.07.068

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M.G. Assadi et al. / Journal of Organometallic Chemistry 690 (2005) 4755–4760
interesting properties with reference to polymer without
the silyl group. The selectivity of organosilicon methac-
rylates with reference to oxygen is an important factor in
these properties, where some silyl derivatives of methac-
rylate polymers used in contact lens were patented. On
the other hand, silyl methacrylates have been extensively
used in photolithographic applications [10]. A process
for producing a controlled drug-release contact lens,
containing a first member which forms a front fact of
the lens and a second member which forms a rear face
of the lens, the first and second members defining a
space in the contact lens, which entails (a) preparing
the first and second members from a non-cross-linked
polymer; (b) bonding the prepared first and second
members by melt pressing; and (c) cross-linking the
bonded members by hydration treatment, wherein the
non-cross-linked polymer is obtained from a polymeriz-
able methoxy silicone compound and another monomer
copolymerizable therewith [11]. For these reasons in the
present work, we report the synthesis and properties of
2-hydroxyethyl methacrylate (HEMA) polymers modi-
fied with some silyl groups. The methacryloyloxyethyl
ester of Et3Si, Me3Si, and Ph3Si was synthesized and
polymerized with HEMA. Free radical cross-linking
copolymerization of the silyl derivatives of HEMA with
the various CA ratios produced silyl pendent network
polymers. The DSC analysis showed that the attaching
of silyl group in copolymer reduces the Tg value. Influ-
ences of different factors such as cross-linking and
attaching silyl group were studied.
10 °C/min in air. The molecular weights (Mw and Mn)
were determined by using a Waters 501 gel permeation
chromatograph fitted with 102 and 103 nm Waters
Styragel columns. THF was used as an elution solvent
at a flow rate of 1 ml/min and polystyrene standards
were employed for calibration.
4. Monomers synthesis
4.1. 2-Propenoic acid, 2-methyl-2-[(triphenylsilyl)oxy]-
ethyl ester (TPhMA)
A mixture of 3 g (23 mmol) HEMA and 3.5 g
(34 mmol) triethylamine in 50 ml dried THF was treated
in a drop wise manner with a solution of 6.7 g (23 mmol)
triphenylchlorosilane in 10 ml dried THF under dry ar-
gon at room temperature. After (3 h) stirring at room
temperature the reaction mixture was filtered. Then
THF was removed under reduced pressure to produce
a nearly colorless oily residue. The residue was chro-
matographed over silica gel by CH2Cl2 to yield 35% of
TPhMA. IR (neat, cmꢀ1): 2985, 2930, 1722, 1257, 837,
1131, 1168. 1H NMR (CDCl3, ppm): 1.95 (s, 3H,
–CH3), 4.06 (t, J = 4 Hz, 2H, –CH2O), 4.35 (t,
J = 4 Hz, 2H, –COOCH2), 5.57 (m, 1H, @CH2), 6.10
(m, 1H, @CH2), 7.39–7.68 (m, 15H, phenyl-H). 13C
NMR (CDCl3, ppm): 17.10 (–CH3), 60.80 (–CH2O),
64.48 (–COOCH2), 124.46 (@CH2), 134.94 (@C),
166.10 (–COO), 126.73, 128.52, 132.58, 134.14
(C-phenyl). m/z (EI) : 388 (M)+ (6%), 311 (95%), 105
(90%).
2. Experimental
4.2. 2-Propenoic acid, 2-methyl-2-[(triethylsilyl)oxy]-
ethyl ester (TETMA)
Synthesis of monomers and copolymerization were
carried out under dry argon to exclude oxygen and
moisture from the reaction systems.
A mixture of 3 g (23 mmol) HEMA and 3.5 g
(34 mmol) triethylamine in 50 ml dried THF was treated
in a drop wise manner with a solution of 3.5 g (23 mmol)
triethylchlorosilane in 10 ml dried THF under dry argon
at room temperature. After (6 h) stirring at room tem-
perature the reaction mixture was filtered. Then THF
was removed under reduced pressure to produce a
nearly colorless oily residue. The residue was purified
by chromatographic method over silica gel by CH2Cl2
to yield 35% of TETMA. IR (neat, cmꢀ1): 2955, 1722,
1241, 814. 1H NMR (CDCl3, ppm): 0.54–0.60 (q,
J = 8 Hz, 6H, –SiCH2), 0.90–0.94 (t, J = 8 Hz, 9H
(–CH3 of ethyl (CH3–CH2Si), 1.91 (s, 3H, –CH3), 3.81
(t, J = 4 Hz, 2H, –CH2O), 4.19 (t, J = 4 Hz, 2H,
–COOCH2), 5.52 (m, 1H, @CH2), 6.09 (m, 1H,
@CH2). 13C NMR (CDCl3, ppm): 4.30 (–SiCH2), 6.63
(–CH3 of ethyl (CH3–CH2Si)), 18.31 (–CH3), 60.90
(–CH2O), 65.93 (–COOCH2), 125.53 (@CH2), 136.23
(@C), 167.49 (–COO). m/z (EI): 215 (M ꢀ Et)+(18%),
171 (26%), 143 (10%), 115 (15%).
3. Materials
Cubane-1,4-bis(methacryloyloxyethyl)carboxylate
(CA), was prepared by the method described in the liter-
ature [12]. The solvents and reagents were purchased
from Merck and Fluka Co. Et3SiCl, Me3SiCl, and
Ph3SiCl were used as received. Initiator of a,a0-
azobis(isobutyronitrile) (AIBN) was purified by crystal-
lization from methanol.
3.1. Measurements
1H NMR and 13C NMR spectra were recorded on a
Brucker 400 AC spectrometer in CDCl3. The IR spectra
were recorded on a Shimadzu FT IR-408 spectropho-
tometer.The DSC curves was obtained on a TGA/
SDTA 851 calorimeter at heating and cooling rates of

M.G. Assadi et al. / Journal of Organometallic Chemistry 690 (2005) 4755–4760
4757
5. 2-Propenoic acid, 2-methyl-2-[(trimethylsilyl)oxy]ethyl
ester (TMEMA)
6.3. Synthesis of poly(HEMA-TETMA, 1:1) (VII)
In a Pyrex glass ampoule, a mixture of 0.52 g
(4 mmol) of HEMA, 0.02 g (0.01 M) of AIBN and
1.00 g (4 mmol) of TETMA was dissolved in 25 ml of
dioxane. Then the ampoule was degassed, sealed under
vacuum and started to polymerize at 60–70 °C, with stir-
ring, for about 72 h. Then the viscous solution was
poured from the ampoule in to 150 ml of cold water,
the precipitate was collected and dried under vacuum
at room temperature to give 0.2 g of copolymer. IR
(neat, cmꢀ1): 3440 2954, 1730, 1273, 801. 1H NMR
(CDCl3, ppm): 0.60–1.13 (–SiCH2–CH3), 1.78–1.87 (b,
CH2, CH3), 3.57–3.89 (–CH2O, –COOCH2), 4.81 (b,
1H, OH).
Mixture of 3 g (23 mmol) HEMA and 3.5 g
(34 mmol) triethylamine in 50 ml dried THF was treated
in a drop wise manner with a solution of 2.5 g
(23 mmol) trimethylchlorosilane in 10 ml dried THF
under dry argon at room temperature. After (5 h) stir-
ring at room temperature, the reaction mixture was fil-
tered and the solvent was removed under reduced
pressure to produce a nearly colorless oily residue.
The residue was chromatographed over silica gel by
CH2Cl2 to yield 35% of TMEMA. IR (neat, cmꢀ1):
1
2959, 1721, 1252, 843. H NMR (CDCl3, ppm): 0.19
(s, 6H, –SiCH3), 2.02 (s, 3H, –CH3), 3.90 (t, J = 4 Hz,
2H, –CH2O), 4.29 (t, J = 4 Hz, 2H, –COOCH2), 5.64
(m, 1H, @CH2), 6.20 (m, 1H, @CH2). 13C NMR
(CDCl3, ppm): 2.30 (–SiCH3), 18.35 (–CH3), 60.88
(–CH2O), 65.90 (–COOCH2), 125.40 (@CH2), 136.10
(@C), 167.30 (–COO). m/z (EI): 187(M ꢀ Me)+(10%),
143 (20%), 116 (15%), 103 (20%).
7. Cross-linking polymerization
7.1. Cross-linked copolymerization of TETMA and
HEMA with CA (VIII, IX)
In two Pyrex glass ampoules, a mixture of 1 g
(4 mmol) of TETMA, 0.52 g (4 mmol) of HEMA and
specific mol percentage of CA (5% and 10%) was
polymerized at 60–70 °C in a thermostatic water bath,
using 2,2-azobisisobutyronitrile (AIBN) as initiator
([I] = 0.01 M), and dried dioxane as solvent
([M] = 1.0 M). After the specified time (72 h), the pre-
cipitated network polymer (0.30 g) was collected,
washed with methanol or water and dried in vacuum.
IR (neat, cmꢀ1): 3540, 2952, 1730, 1264, 845.
6. Polymer synthesis
6.1. Synthesis of poly(HEMA-TMEMA, 1:1) (I)
In a Pyrex glass ampoule, a mixture of 0.52 g
(4 mmol) of HEMA, 0.02 g (0.01 M) of AIBN and
0.80 g (4 mmol) of TMEMA was dissolved in 25 ml of
dioxane. Then the ampoule was degassed, sealed under
vacuum and started to polymerization at 60–70 °C, with
stirring, for about 72 h. Then the viscous solution was
poured from the ampoule in to 150 ml of cold water,
the precipitate was collected and dried under vacuum
at room temperature to give 0.2 g of copolymer. IR
(neat, cmꢀ1): 3440 2954, 1732, 1264, 900. 1H NMR
(CDCl3, ppm): 0.71 (s, –SiCH3), 0.92–1.98 (b,
CH2,CH3), 3.58–3.96 (–CH2O, –COOCH2), 4.86 (b,
1H, OH).
7.2. Cross-linked copolymerization of TPhMA and
HEMA with CA (V, VI)
In two Pyrex glass ampoules, a mixture of 1 g
(2.6 mmol) of TPhMA, 0.4 g (2.6 mmol) of HEMA
and specific mol% of CA (5% and 10%), in the presence
of AIBN ([I] = 0.01 M) as initiator, and dried dioxane as
solvent ([M] = 1.0 M) were polymerized at 60–70 °C in a
thermostatic water bath. After the 72 h, the precipitated
network polymer (0.28 g) was collected and washed with
heptane and dried in vacuum. IR (neat, cmꢀ1): 3540,
2952, 1730, 1260, 845.
6.2. Synthesis of poly(HEMA-TPhMA, 1:1) (IV)
In a Pyrex glass ampoule, a mixture of 0.52 g
(4 mmol) of HEMA, 0.02 g (0.01 M) of AIBN and
1.55 g (4 mmol) of TPhMA was dissolved in 25 ml of
dioxane. Then the ampoule was degassed, sealed under
vacuum and started to polymerize at 60–70 °C, with stir-
ring for about 72 h. Then the viscous solution was
poured from the ampoule into 150 ml of cold heptane,
the precipitate was collected and dried under vacuum
at room temperature to give 0.2 g of copolymer. IR
(neat, cmꢀ1): 3444, 3053, 2945, 1727, 1589, 1486, 1266,
873. 1H NMR (CDCl3, ppm): 0.87–1.85 (b, CH3,
CH2), 2.89 (b, 1H, OH), 3.71–3.96 (–CH2O,
–COOCH2), 7.27–7.66 (m, 15H, phenyl-H).
7.3. Cross-linked copolymerization of TMEMA and
HEMA with CA (II, III)
In two Pyrex glass ampoules, a mixture of 1 g
(5 mmol) of TMEMA, 0.65 (5 mmol) of HEMA and
specific mol percentage of CA (5% and 10%), in the pres-
ence of 2,2-azobisisobutyronitrile (AIBN) as an initia-
tor, and dried dioxane as solvent ([M] = 0.1 M) was
polymerized at 60–70 °C in a thermostatic water bath.
After 72 h, the precipitated network polymer (0.34 g)

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M.G. Assadi et al. / Journal of Organometallic Chemistry 690 (2005) 4755–4760
was collected with methanol or water and washed with
cold methanol and dried in vacuum. IR (neat, cmꢀ1):
3430, 2960, 1730, 1264, 850.
the form of oligomeric compounds and polymers.
Although many physical properties of cubane have been
measured, until about 10 years ago, cubane was consid-
ered just a laboratory curiosity of interest only to aca-
demics. Recently, however, the possible applications in
industry, materials science, medicine and polymer have
come to light. The copolymers were synthesized by
free-radical polymerization. In this way, we synthesized
cross-linked copolymer with HEMA and silyl deriva-
tives by using cross-linking agent of cubane (CA)
(Scheme 1). These copolymers were identified by DSC
analysis and IR spectra. By regulating the cross-linking
percentage of the silyl copolymers, we can improve poly-
mer properties. Cubane are not inherently toxic. They
are considered as biologically stable, lipophilic plat-
forms on which a wide choice of substituents in a variety
of well defined spatial relationships can be installed.
Also, a cubane derivative has been known for its versa-
tility and may be pharmaceutical basis for future appli-
cation of cubane and its derivatives. In the recent
research, we used copolymers of cubane as a carrier of
some drugs, for example, indomethacine, ibuprofen,
and olsalazine [9]. Gel permeation chromatography
(GPC) was used to determine the number and weight-
average molecular weights of copolymers and the result
is listed in Table 1. The copolymer composition was cal-
8. Results and discussion
In this work, we synthesized some organosilicon
derivatives of HEMA, which Et3Si, Me3Si and Ph3Si
groups are as a side chain. These monomers were pre-
pared by using Et3SiCl, Me3SiCl and Ph3SiCl in the
presence of Et3N as a base in THF with 2-hydroxyethyl-
methacrylate. For synthesis of new modified polymers,
we used two methods: copolymerization and cross-
linked copolymerization. In copolymerization, the
TMEMA, TETMA, and TPhMA monomer was copoly-
merized with HEMA in dioxane at 70 °C using AIBN as
the radical polymerization initiator with a ratio of 1:1.
In cross-linking copolymerization, cubane-1,4-dicarbox-
ylic acid (CDA) linked to two 2-hydroxyethyl methacry-
late (HEMA) group was used as a cross-linking agent
(CA). Because the cubane frame is rigid, substituents
have precise spatial arrangements to one another. The
distance across the cube (the body diagonal) is almost
the same as that between the para positions of a benzene
ring. Due to their well-defined dimensionality and rigid
geometry, cubane could prove to be important building
blocks in the developing world of nanoarchitecture, in
1
culated from the H NMR spectra data. In the past few
decades, 1H NMR spectroscopic analysis has been
Scheme 1. Preparation of cross-linked polymers containing silyl group.

M.G. Assadi et al. / Journal of Organometallic Chemistry 690 (2005) 4755–4760
4759
VII
Table 1
DSC and GPC data of copolymers
Table 3
Solubility of polymers
Copolymer
Percent of CA
Mw
6589
–
–
22,000
–
Mw/Mn
Tg (°C)
Solvents
I
IV
I
II
III
IV
V
–
1.36
–
–
–
95
138
150
70
Acetone
CH2Cl2
THF
EtOH
DMF
+
–
–
+
+
+
+
+
–
–
–
–
+
+
5
10
–
5
–
95
–
VI
VII
VIII
IX
10
–
5
–
–
1.43
–
105
100
120
138
+, soluble; ꢀ, insoluble.
7138
–
–
10
–
EtOH, MeOH, and DMF (see Table 3). In addition to
the above properties, in loading of drugs to polymers
it has been shown that it is a balance between hydro-
philic and lipophilicity of polymer. Since most of drug
molecules have a lipophile structure, therefore, the pres-
ence of lipophile groups on the polymer chain increases
drug loading. The silyl groups that we used in this work
are lipophile groups; therefore, synthesis of silyl deriva-
tive of polymers and copolymers could be important
case in drug delivery systems. All of products were iden-
tified by spectroscopic methods. We also identified
monomers by 1H NMR, 13C NMR, and Mass spectros-
copy. A typical spectrum of 1H NMR and 13C NMR are
shown in Figs. 1 and 2, respectively.
established as a powerful tool for the determination of
copolymer compositions because of its simplicity, rapid-
ity and sensitivity [13,14]. The molar composition of
HEMA and silyl derivatives in copolymer was calcu-
lated from the ratio integrated intensities of the silyl pro-
tons refer to the protons of ethyl or hydroxyl groups.
The molar composition of TPhMA and TETMA was
calculated from the following equations, where x and
y are the mole fractions of HEMA and TPhMA, TET-
MA, respectively [15] (see Table 2).
For TPhMA:
x þ y ¼ 100;
Area at 7:2–7:6 ppm
15y
8.1. Identification of network polymer
¼
;
Area at 3:7–3:9 ppm 4x þ 4y
15 15y
The resulting network polymers swell and become
soft if they are exposed to solvents such as H2O and
most organic solvents without dissolving. In the
FT-IR spectra, absorption of C–Si bond appeared in
the region of 1258–1270 and 837–900 cmꢀ1 refer to
stretching, and bending vibration, respectively, absorp-
tion in the region 1730 cmꢀ1 refer to the stretching of
carbonyl bond. In this way, we characterized cross-
linked copolymers.
¼
;
6:8 4x þ 4y
x ¼ 41%; y ¼ 59%.
For TETMA:
Area at 0:6–1:1 ppm
15y
2x þ 2y
¼
;
Area at 3:5 ppm
4:4
15y
¼
;
2
2x þ 2y
x ¼ 30%; y ¼ 70%.
The important effects of silyl groups is decreasing of
Tg and increasing of solubility. Decreasing of Tg can
cause increasing of polymer flexibility, and improve its
properties. One of the important cases in polymer indus-
try is solubility of them; therefore, we showed that
attaching of silyl group to hydroxyethylmethacrylate
could increase the solubility of them, in which that
copolymer TETMA with HEMA was dissolved in
Table 2
The molar compositions of copolymers I, IV, VII
Copolymer
Ratio of
monomers
Time/h
Percent of
HEMA
Percent of
silyl
I
IV
VII
1:1
1:1
1:1
72
72
72
40
41
30
60
59
70
1
Fig. 1. H NMR of TETMA.

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Fig. 2. 13C NMR of TETMA.
8.2. Thermal behavior
Polymethacrylates dissolved difficulty in many solvents.
This effect can be an important case in industrial proce-
dures. In this work, we synthesized and identified novel
organosilicon monomers, and polymers of methacrylate.
Differential scanning calorimetry (DSC) was evalu-
ated. The glass transition temperature (Tg) was deter-
mined from the DSC thermograms. The values are
given in Table 1. It appears that with increasing cross-
linking degree, which would decrease the flexibility of
the chains and the ability of the chains to undergo seg-
mental motion, which would increase the Tg values
[12]. The Tg value of the homopolymer without the silyl
group would be higher than Tg value of the copolymer.
The silyl group as a plasticizer increases the flexibility of
hard polymers and reduces its Tg. It seems that incorpo-
ration of silyl groups in side chains of polymer reduced
the intermolecular interaction of chains and cause
decreasing of Tg.
Acknowledgement
The office of research vice chancellor Azarbaijan Uni-
versity of Tarbiat Moallem has supported this work.
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