Use of an acrylic dendron-containing monomer in the synthesis of a macroporous polymeric material

Article abstract of DOI:10.1007/s11167-005-0355-3

A procedure was developed for preparing a monolithic macroporous material by photoinitiated co-polymerization of glycidyl methacrylate, ethylene glycol dimethacrylate, and an acrylic comonomer containing a dendron with protected terminal amino groups. The

Full text of DOI:10.1007/s11167-005-0355-3

Russian Journal of Applied Chemistry, Vol. 78, No. 4, 2005, pp. 623 627. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 4, 2005,
pp. 629 633.
Original Russian Text Copyright
2005 by Khimich, Tennikova.
MACROMOLECULAR CHEMISTRY
AND POLYMERIC MATERIALS
Use of an Acrylic Dendron-containing Monomer
in the Synthesis of a Macroporous Polymeric Material
G. N. Khimich and T. B. Tennikova
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
Received July 26, 2004; in final form, December 2004
Abstract A procedure was developed for preparing a monolithic macroporous material by photoinitiated co-
polymerization of glycidyl methacrylate, ethylene glycol dimethacrylate, and an acrylic comonomer containing
a dendron with protected terminal amino groups. The macropore formation is provided by a blowing agent.
Dendrimers and superbranched polymers were syn-
thesized in the late 1980s. Active efforts are made
today to find applications for dendrimers. For this
purpose, numerous modified dendrons and dendrimers
have been synthesized. The use of dendritic mono-
mers as building blocks, along with linear monomers,
substantially expanded the possibilities of macromo-
lecular design and led to macromolecules of unusual
architecture [1]. Incorporation of bulky dendrons into
the polymer structure is of both basic and applied in-
terest. The high degree of functional substitution of
such polymers opens virtually unlimited opportunities
for further transformations, which can lead to novel
materials. Modification of the surface of macromole-
cules, with the aim to impart to them pronounced
lyophilic or lyophobic properties, is also possible.
However, only very few studies have been con-
cerned with the possibility of using dendrimers and
dendron-containing monomers for preparing modi-
fied sorbents [13, 14]. In particular, aliphatic highly
branched poly alcohols were used for preparing poly-
meric chiral stationary phases by postmodification
of a macroporous copolymer [13].
The use of vinyl monomers linked through spacers
to dendrons containing various terminal groups may
be a promising route to adsorption-active macroporous
polymers.
Monolithic sorbents, a new generation of stationary
phases, are prepared by copolymerization of mono-
mers containing active groups whose high reactivity
provides for easy functionalization of the internal
surface of the sorbent [15, 16]. Macroporous flow-
through layers based on a monolithic copolymer of
glycidyl methacrylate (GMA) and ethylene glycol
dimethacrylate (EDMA) were developed in the late
1980s early 1990s [17 21]. Dendron-containing
monomers seem promising for preparing functional-
ized macroporous polymers, since addition of even
a small amount of a dendron-containing monomer
allows the content of functional groups in the sorbent
to be sharply increased. By varying the level of gen-
eration and the chemical nature of substituents on the
external surface of a dendron molecule, and also by
varying the length of a spacer linking the dendron to
the acryloyl group, it is possible to control the charac-
teristics of the resulting sorbents.
Dendron-containing polymers of several types have
been synthesized: monodendrons with a polymer
chain in the focal point [2]; dumbbell-like hybrids
containing a polymer chain between two monoden-
drons [3, 4]; and dendron-containing polymers pre-
pared by polymerization of dendron-containing mono-
mers [5, 6].
The interest in dendron-containing polymers is
due to the possibility of obtaining new speciality
materials and using them in biology, medicine, and
medical diagnostics [7, 8]. In particular, dendrimers
are used for detecting oligonucleotides in DNA diag-
nostics [9, 10], and polynucleotide dendrimers with
fluorescent markers, in microchip DNA diagnostics
[11]. Dendritic polyvalent ions can be used to bind
proteins [12].
In the first step, we prepared an acrylic derivative
of a dendron containing Boc-protected amino groups
by controllable multistep synthesis:
1070-4272/05/7804-0623 2005 Pleiades Publishing, Inc.

624
KHIMICH, TENNIKOVA
OH
OH
O
O
(a)
HO
O
OH
OH
O
I
O
(b)
NH3Br
Br
Br
NH
II
O
O
O
O
O
O
O
O
O
NH
NH
NH
O
O
O
O
O
O
O
O
O
(c)
(d)
(e)
I + II
NH
O
NH
NH
O
NH
NH
HN
O
H2N
O
O
III
IV
V
Steps: (a) MeOH, H+; (b) Boc2O; (c) KHCO3, DMF; (d) NH2(CH2)2NH2; and (e) CH2=CHCOCl, NEt3.
Methyl 3,5-di(2-tert-butoxycarbonylaminoethoxy)-
benzoate III was prepared by alkylation of methyl
3,5-dihydroxybenzoate I with 2-(tert-butoxycarbonyl-
amino)ethyl bromide II. It is known that compound
III can be prepared in the presence of various cat-
alysts [15, 16, 22, 23]. We performed alkylation in
the presence of potassium carbonate, with DMF as
solvent [15]. The reaction occurs at 40 C within 16 h;
yield about 80%.
The porosity of monolithic sorbents depends on the
monomer ratio, blowing agents used, and polymeriza-
tion conditions [18]. Therefore, the participation of
a dendron-containing monomer in copolymerization
can affect the pore structure of the resulting material
and, in particular, cause its ordering.
Monolithic macroporous polymers were prepared
by radical photoinitiated copolymerization of EDMA,
GMA, and acrylic comonomer V containing a den-
dron of the first generation. The reaction was per-
formed in cyclohexanol (a solvent acting as blowing
agent [19]) using 2,2-dimethyl-2-hydroxyacetophen-
one (Darocure 1173) as initiator of radical polymeri-
zation [24, 25]:
The starting compounds, methyl 3,5-dihydroxyben-
zoate I and 2-(tert-butoxycarbonylamino)ethyl bro-
mide II, were prepared as follows: I, by esterification
of 3,5-dihydroxybenzoic acid with methanol in acid
solution [15]; II, by protection of the amino group of
2-bromoethylamine hydrobromide with di-tert-butyl
pyrocarbonate [16].
O
O
O
We prepared previously unknown dendron of the
first generation IV with the amino group at the focal
point and terminal Boc-amino groups. To do this,
methyl 3,5-di(2-tert-butoxycarbonylaminoethoxy)ben-
zoate was treated with excess ethylenediamine at
room temperature. The subsequent acylation of the
NH2 group in IV with acryloyl chloride in anhydrous
methylene chloride in the presence of triethylamine
at low temperature yielded dendritic monomer V. The
structures of the compounds prepared were confirmed
O
O
O
O
GMA
EDMA
OH
O
Darocure 1173
We prepared the copolymers containing 10 and
20 mol % V.
1
by H NMR spectroscopy.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 78 No. 4 2005

USE OF AN ACRYLIC DENDRON-CONTAINING MONOMER IN THE SYNTHESIS
625
1
1
The IR spectrum confirmed the involvement of
the acrylic dendron-containing monomer in the copo-
lymerization. The IR spectrum of the hybrid material
and CO (1690 cm , amide I; 1520 cm , amide II)
bonds.
A fragment of the assumed chemical structure of
the resulting macroporous polymer is shown below:
1
contains absorption bands of the N H (3340 cm )
>
O
>
O
>
>
O
O
O
O
O
O
O
O
H
O
O
N
O
O
N
N
O
O
H
O
H
<
<
<
<
<
<
O
NH
O
The pore structure of the materials obtained was
examined by electron microscopy. The polymer layers
have a homogeneous internal morphology of the pores.
Figure shows plane and cross-sectional electron mi-
crographs of the samples. The polymer containing
10 wt % dendritic monomer has a looser structure.
The time required for formation of such monolythic
macroporous materials is longer than that for syn-
thesis of GMA EDMA polymers.
EXPERIMENTAL
GMA was purchased from Fluka (Switzerland);
2,2-dimethyl-2-hydroxyacetophenone, from Merck
Schuchard (Germany); EDMA, cyclohexanol, 3,5-di-
hydroxybenzoic acid, (2-bromoethyl)amine hydrobro-
mide, and di-tert-butyl pyrocarbonate, from Sigma
Aldrich (Germany); and acryloyl chloride, from Rea-
khim (Russia).
Electron micrographs of microporous monolithic layers prepared by ternary copolymerization of GMA, EDMA, and
acrylic monomer. Acrylic monomer content, wt %: (a c) 10 and (d f) 20. (a, d) Planar and (b, c, e, f) cross-sectional.
Magnification: (a, b, d, e) 4800 and (c, f) 10000.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 78 No. 4 2005

626
KHIMICH, TENNIKOVA
1
The H NMR spectra were recorded on a Bruker
AC300 spectrometer (300 MHz), with deuterated ace-
tone as solvent.
0.06 ml (0.66 mmol) of acryloyl chloride. The mix-
ture was stirred for 30 min at 0 C and then for 3 h at
room temperature. The reaction course was monitored
by TLC. After the reaction was complete, 5 ml of
methylene chloride was added, and the mixture was
washed with water, dried over sodium sulfate, and
The structural homogeneity of the monoliths was
examined by scanning electron microscopy using a
JSM-35CF device with cathodic sputtering of a 50
100- gold layer.
1
concentrated; 0.151 g (44%) of V was obtained. H
NMR spectrum (acetone-d6), , ppm: 1.45 s [18H,
2C(CH3)3], 3.46 t (4H, 2CH2NH), 3.60 m (2H,
2CH2NH2), 3.82 s (4H, NHCH2CH2NH), 4.07 t (4H,
2OC_H2), 5.52 d.d (1H, CH2=CH), 5.88 d.d (1H,
CH2=CH), 6.3 d.d (1H, CH2=CH), 6.62 t (1H, Ar H),
7.05 d (2H, Ar H).
The IR spectra were measured with a Bruker IFS
88 spectrophotometer (KBr pellets). UV irradiation
was performed with a 125-W mercury lamp having a
broad radiation spectrum and constant intensity.
Methyl 3,5-di(2-tert-butoxycarbonylaminoeth-
oxy)benzoate III. A mixture of 2.82 g (0.017 mol) of
methyl 3,5-dihydroxybenzoate, 10.0 g (0.045 mol) of
2-(tert-butoxycarbonylamino)ethyl bromide, 10.58 g
(0.0765 mol) of potassium carbonate, and 25 ml of
DMF was stirred at 80 C for 4 h and left overnight.
The precipitate was filtered off, and the solution was
concentrated. The product was purified by preparative
adsorption column chromatography. Yield 5.08 g
(81.5%); colorless crystalline substance. 1H NMR
spectrum (acetone-d6), , ppm: 1.47 s [18H, 2C(C_H3)3],
3.47 m (4H, 2CH2NH), 3.86 s (3H, CO2C_H3), 4.10 m
(4H, 2OC_H2), 6.25 br.s (1H, N_HBoc), 6.76 t (1H,
Ar H), 7.13 d (2H, Ar H).
Found, %: C 58.23, H 7.68, N 10.27.
C26H40N4O8.
Calculated, %: C 58.19, H 7.51, N 10.44.
The radical polymerization of GMA, EDMA, and
acrylic monomer (molar ratios 5.4 : 4 : 0.6 and 4.8 :
4 : 1.2) in cyclohexane in the presence of 0.5% Daro-
cure 1173 was performed under the photoinitiation
conditions for 1 h. After the reaction was complete,
the polymers obtained were washed with ethanol and
dried at 100 C.
CONCLUSIONS
Found, %: C 57.98, H 7.81, N 6.21.
C22H34N2O8.
(1) A procedure was developed for preparing den-
dron of the first generation with the amino group at
the focal point and terminal Boc-amino groups and
an acrylic monomer derived from it.
Calculated, %: C 58.14, H 7.54, N 6.16.
Dendron IV. A solution of 1.5 g (3.28 mmol) of
methyl 3,5-di(2-tert-butoxycarbonylaminoethoxy)ben-
zoate III in 15 ml of methanol was slowly added drop-
wise to 20 ml of ethylenediamine. The mixture was
kept in the dark at room temperature for 3 days, after
which the solvent and excess ethylenediamine were
distilled off in a vacuum. The residue was dissolved
in chloroform, washed with water, dried with sodium
sulfate, and concentrated. Yield 1.06 g (67%); oily
(2) A monolithic material can be prepared by
photoinitiated ternary copolymerization of glycidyl
methacrylate, ethylene glycol dimethacrylate, and an
acrylic dendron-containing monomer in the presence
of Darocure in a cyclohexanol solution.
(3) Scanning electron microscopy shows that the
layers obtained have a homogeneous internal mor-
phologhy of pores.
1
substance. H NMR spectrum (acetone-d6), , ppm:
1.45 s [18H, 2C(C_H3)3], 3.42 (6H, 2CH2NH), 3.60 m
(2H, 2CH2NH2), 4.04 t (4H, 2OC_H2), 6.64 t (1H,
Ar H), 7.05 d (2H, Ar H).
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