Sorption of vapors of aromatic compounds by cross-linked polymer particles containing luminophores: A spectroscopic study

Article abstract of DOI:10.1134/S1070427210110200

Monodispersed core-shell particles 290-315 nm in diameter were prepared by seed emulsion copolymerization of styrene with divinylbenzene in the presence of luminophore-containing comonomers. The capability of the particles obtained to sorb toluene vapor was shown by solid-state ¹H and ¹³C NMR spectroscopy.

Full text of DOI:10.1134/S1070427210110200

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 11, pp. 1997−2005. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.Yu. Men’shikova, Yu.E. Moskalenko, A.V. Gribanov, N.N. Shevchenko, V.B. Faraonova, A.V.Yakimanskii,
M.Ya. Goikhman, N.L. Loretsyan, A.V. Koshkin, M.V. Alfimov, 2010, published in Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 11, pp. 1865−1873.
MACROMOLECULAR COMPOUNDS
AND POLYMERIC MATERIALS
Sorption of Vapors of Aromatic Compounds
by Cross-Linked Polymer Particles Containing
Luminophores: A Spectroscopic Study
a
a
a
a
A. Yu. Men’shikova , Yu. E. Moskalenko , A. V. Gribanov , N. N. Shevchenko ,
a
a
a
V. B. Faraonova , A. V. Yakimanskii , M. Ya. Goikhman ,
a
b
b
N. L. Loretsyan , A. V. Koshkin , and M. V. Alfimov
a
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
b
Photochemistry Center, Russian Academy of Sciences, Moscow, Russia
Received August 24, 2010
Abstract—Monodispersed core–shell particles 290–315 nm in diameter were prepared by seed emulsion
copolymerization of styrene with divinylbenzene in the presence of luminophore-containing comonomers. The
1
13
capability of the particles obtained to sorb toluene vapor was shown by solid-state Н and С NMR spectroscopy.
DOI: 10.1134/S1070427210110200
Growing attention to the development of sensor
materials for highly selective detection of organic
substances is dictated by the necessity for ensuring safety
at chemical enterprises and laboratories, for monitoring
of harmful impurities in the atmosphere and in air of
inhabited rooms, and also for medical diagnostics
To enhance the selectivity of sensor polymeric
materials with optical response on the presence of an
analyte, it seems appropriate to combine both these
approaches, i.e., to apply the molecular imprinting
technology to make molecular imprints with the
participation of luminophore-containing comonomers.
In this case, the radical copolymerization should
involve the formation of a complex of a template with
the luminophore which, in turn, is fixed in the cross-
linked polymer matrix owing to incorporation in the
polymer chain. After the synthesis completion and
template removal, an empty sensor site remains in the
immediate vicinity of the luminophore. Molecules
structurally similar to the template, when getting into
this site from the environment, can be detected by
changes in the fluorescence spectrum of the polymer
material. Two alternative approaches can be used for the
formation of a sensor polymer layer in the presence of
a template: polymerization of the monomers in a thin
layer directly on the detector of a sensor device [3–5]
or preparation of dispersions of particles uniform in
size, containing molecular imprints and luminophores,
by heterophase polymerization methods, followed by
application of these particles onto a sensor panel by
jet printing [14]. The latter approach seems to be more
technologically efficient, because it makes possible
[1, 2]. Introduction into relatively cheap polymer
matrices of luminophores whose fluorescence spectrum
changes upon complexation with organic compounds
(solvatochromic effect) is a promising approach to
the development of sensor materials with an optical
response on the presence of volatile organic compounds
in the gas phase [3–11]. Today the technology of
molecular imprinting has already been suggested for
the development of a new generation of highly selective
polymeric sorbents. In the process, template molecules
(target analyte or a structurally similar substance)
are introduced into the reaction mixture in the step
of formation of the cross-linked polymer matrix [5,
1
2]. Owing to various noncovalent interactions, these
molecules are fixed in the polymer matrix and, after the
synthesis completion, can be removed from it with the
formation of molecular imprints (molecular recognition
sites) complementary in the size, shape, and chemical
structure to definite organic molecules and hence
capable of their selective binding [13, 14].
1
997

1998
MEN’SHIKOVA et al.
large-scale production and formation of a bank of
polymer particles differing in the size, polymer matrix,
type of the incorporated luminophore, and nature of the
template used in the synthesis.
comonomers we used fluorescein dimethacrylate (MFl),
methacryloyloxyethylthiocarbamoyl Rhodamine
B
(MRB, Aldrich, Germany), and 2-methacryloyloxy de-
rivative of Nile Red (MNR), prepared by the reaction
of methacryloyl chloride with 2-OH derivative of Nile
Red, 9-diethylamino-2-hydroxy-5Н-benzo[a]phenoxa-
zin-5-one (NR–ОН) (Scheme 1).
The principally important points in the development
of sensor materials with optical response on vapors of
volatile organic substances are the accessibility of the
pore space of the polymer matrix to sorption of analyte
molecules and the occurrence of detectable changes in
the fluorescence spectrum of the indicator luminophore
incorporated in the polymer matrix upon interaction
with these molecules. In this connection, our goal was
to synthesize luminophore-containing cross-linked
monodisperse polymer particles using the molecular
imprinting technique, to study the capability of the
particles prepared for sorption of vapors of aromatic
NR–OH was prepared by the procedure described
previously [15] (Scheme 2).
1
The H NMR spectra, recorded with an Avance-400
NMR spectrometer (Bruker, Germany) at 20°C from
1
0% solutions in DMSO-d , contain a set of signals
6
unambiguously confirming the structure of NR–OH
and MNR. The NR–OH spectrum contains a broadened
singlet in the region of 10.42 ppm, corresponding to the
Н-2 proton of OH group, two doublets of equal intensity
at 7.96 and 7.87 ppm, belonging to Н-4 and Н-1 protons,
respectively, doublets at 7.08, 7.55, and 6.77 ppm,
belonging to Н-3, Н-7, and Н-8 protons, respectively,
and a singlet at 6.61 ppm, belonging to the Н-6 proton.
The aliphatic moiety of NR–OH is manifested as
a quartet at 3.48 ppm of 4H intensity, belonging to four
Н-9 and Н-11 protons, and a triplet at 1.15 ppm of 6Н
intensity, belonging to six Н-10 and Н-12 protons. In the
MNR spectrum, the signals corresponding to hydrogen
1
compounds (with toluene as example) by solid-state Н
13
and С NMR spectroscopy, and to compare the results
obtained with the data on changes in the fluorescence of
the layers of the same particles in benzene vapor.
EXPERIMENTAL
The monomers, styrene (Akros, St. Petersburg) and
MAA (98.5%, BASF, Germany), were purified by dis-
tillation following standard procedures. Divinylbenzene
atoms of the aromatic system and –N(Et) group do
2
(
DVB, 80%, Aldrich, Germany), polyvinylpyrrol-
not change appreciably their position compared to the
related signals in the NR spectrum. In addition, new
signals appear: two singlets at 5.9 and 6.1 ppm of
1H intensity and a singlet at 2.0 ppm of 3H intensity,
belonging to protons of the methylene (Н-2) and methyl
(Н-3) fragments of the methacrylate group, respectively.
Cross-linked monodisperse core–shell particles with
imprints of aromatic molecules and covalently bonded
luminophores in the surface layer (Fig. 1) were pre-
pared by seed emulsion copolymerization in an argon
idone of molecular weight 35000 ± 5000 (Farmakon,
St. Petersburg), and sodium dodecyl sulfate (Serva,
Germany) were used without additional purification.
The initiators were purified by double recrystalliza-
tion: K S O , from water with washing with ethanol;
benzoyl peroxide (BP), from chloroform into metha-
nol; 2,2’-azobis(isobutyronitrile) (AIBN), from ethanol.
Analytically pure grade Na S O ·5H О was used with-
2
2
8
2
2
3
2
out additional purification. As luminophore-containing
Scheme 1.
O
2
CH2
OH
O
1
CH3
4
5
3
CH3
8
7
9
N (Z)
N (Z)
+
1
2
1
3
O
Cl
N
O (E) 6
O
O (E)
O
1
0
N(Et)2
1
1
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 11 2010

SORPTION OF VAPORS OF AROMATIC COMPOUNDS
1999
Scheme 2.
NO
OH
OH
HCl, NaNO2
°C
0
.
N(Et)2
N(Et)2 HCl
2
OH
OH
NO
1
3
OH
7
(Z)
Dimethylformamide, Tb
N
4
8
+
11
12
N
O (E) 5
O
6
N(Et)2 HCl
OH
9
1
0
atmosphere. In the first step, following the procedure
described previously [16], we formed seeds (Table 1).
In so doing, as the main monomer we used hydrophobic
styrene ensuring rapid particle nucleation in the course
of emulsifier-free emulsion copolymerization and thus
formation of polymer dispersion with a narrow particle-
size distribution (PSD). In the first step, as functional
comonomer we used MAA, which enhanced the aggre-
gative stability of the resulting dispersions in alkaline
and neutral solutions owing to ionization of carboxy
groups of MAA units in the surface layer of the par-
ticles. As cross-linking agent we used DVB. In the first
step of the synthesis, its content in the monomer mixture
was varied in the interval 5–20 wt % relative to styrene,
and in the second step it was increased to 50 wt %, so as
to form a rigidly cross-linked polymer matrix and thus
to fix the structure of the molecular imprints formed. As
aromatic templates we used aromatic impurities pres-
ent in commercial DVB (20 wt %, mainly diethylben-
zenes). As a result, the content of aromatic impurities
was 10 wt % of the monomers forming the shell. In
the second step, we also introduced into the monomer
Luminophores
Molecular
imprints
Fig. 1. Scheme of the structure of a core–shell polymer particle
with molecular imprints of organic compounds and covalently
bonded luminophores in the shell.
Table 1. Synthesis conditions and size of monodisperse seeds
Copolymerization conditions
(
MAA + St)/H O
MAA /St
DVB/St
wt %
5
initiator/monomers
Sample
2
D, nm
Т, °С
pH0
Aa
B
80
80
10
3.6
2.0
K S O , 1.67
10.7
11.2
265
270
2
2
8
5.5
20
K S O , 2.45; BP, 0.05
2 2 8
a
Synthesis was performed in the presence of a chain-terminating agent, o-diaminodiphenyl disulfide, 0.155 mol % relative to styrene [16].
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 11 2010

2000
MEN’SHIKOVA et al.
Table 2. Synthesis conditions and size of cross-linked luminophore-containing core–shell particles
Luminophore/shell
Initiator/monomers
K S O , 2.0
D
h
Alcohol/water,
vol %
Sample
A-1
Т, °С
pH0
6.8
wt %
nm
40
MFl, 0.12
Ethanol, 20
290
290
13
13
2
2
8
Na S O ·5H О, 1.85
2
2
3
2
A-2
40
MRB, 0.12
K S O , 2.0
Ethanol, 5
6.7
2
2
8
Na S O ·5H O, 1.8
2
2
3
2
B-1
B-2
70
60
MNR, 0.12
MNR, 0.12
BP, 2.0
Ethanol, 20
6.8
6.8
310
315
20
22
AIBN, 2.0
Methanol, 20
mixture 0.12 wt % luminophore-containing comono-
mer (Table 2). The core-to-shell weight ratio was 70 :
to the surface layer of the seeds through the aqueous me-
dium, 5–20 vol % ethanol was added. In the second step
of the synthesis, the ratio of the comonomer mixture to
the aqueous ethanol phase was 5 wt%. After each step
of the synthesis, the residual monomers and aromatic
impurities (diethylbenzene) were removed by steam dis-
tillation, and then the polymeric dispersion was purified
to remove water-soluble impurities by threefold succes-
sive centrifugation and redispersion of the particles in
double-distilled water.
3
0, which was optimal for forming a continuous cross-
linked surface layer. Low shell thickness reduces to
a minimum the consumption of the luminophore-con-
taining comonomer and makes the sensor sites formed
with its participation more accessible to the analyte. In
all the experiments, using an ultrasonic bath, we prelimi-
narily prepared a thin emulsion of the monomer mixture
in an aqueous solution containing 2 wt % polyvinylpyr-
rolidone, effective as a steric stabilizer in heterophase
polymerization, and 0.234 wt % sodium dodecyl sulfate
as anionic emulsifier. To facilitate mass transfer of the
monomers of the second step from the emulsion drops
Thediameteroftheparticlesobtainedwasdetermined
by electron microscopy (JEM 100 S microscope, JEOL,
Japan) (Fig. 2).
To examine the structure of the particles obtained
(a)
(c)
(b)
(d)
Fig. 2. Electron micrographs of seeds (a) A and (b) B (Table 1) and core–shell particles (c) A-2 and (d) B-1 prepared on their basis
Table 2).
(
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SORPTION OF VAPORS OF AROMATIC COMPOUNDS
2001
and their sorption power toward aromatic compounds
sample with a fiber optic system.
1
(
with toluene as example), we used solid-state Н and
С NMR spectroscopy. The NMR spectra were recorded
Electron-microscopic examination of the polymer
particles obtained showed that narrow PSD was attained
already in the step of formation of seeds (Figs. 2a, 2b).
The same distribution was preserved after synthesis of
a rigidly cross-linked shell on them (Table 2; Figs. 2c,
1
3
with an Avance II-500 NMR spectrometer (Bruker,
1
Germany) operating at 500 MHz for Н and 125.7 MHz
13
for С. Polymer samples were packed in zirconium
rotors 4 mm in diameter. The spectra were recorded
at 20°С at a spinning frequency of 8 or 10 kHz. The
magic angle was adjusted with KBr, and the chemical
shifts were determined relative to external adamantane.
The 13С MAS NMR spectra were recorded following
the standard program of single-pulse excitation with 6 s
delays between π/2 pulses and proton decoupling. The
2
d). Comparison of the diameters of particles obtained
in the first and second steps of the synthesis allowed
estimation of the shell thickness, which varied in the
range 13–22 nm (Fig. 2, Table 2).
As initiator in the synthesis of samples A-1 and A-2
we used the redox system K S O /Na S O allowing the
2
2
8
2
2
3
radical polymerization to be performed at a relatively
low temperature (40°С), which increased the probability
of complex formation by the template and luminophore
in the second step of the synthesis and could ensure
the reaction of primary radicals with the luminophore-
containing monomers MFl and MRB already in the
dispersion medium, with the subsequent capture of
the propagating radicals by the seeds. However, A-1
particles did not have the characteristic yellow color,
and their layer exhibited no fluorescence. Apparently,
under the synthesis conditions the adsorption of MFl
1
13
H→ С СP–MAS NMR spectra were taken at a contact
time of 4 ms. The composite lines were resolved into
components using DMFIT program [17] on the basis of
mathematical simulation in which the ratio of the Gauss
and Lorentz functions xG/(1–x)L was taken equal to 0.5
for high-resolution lines and to 0.8 for broad lines.
Sorption of toluene vapor on polymeric particles was
performed by keeping it in a desiccator with an open
vessel with toluene for 24 h. The sorbed toluene was
detected by the appearance of the corresponding high-
1
13
resolution signals in the Н and С NMR spectra. For
(present as the monomer or incorporated in a propagating
quantitative interpretation of the sorption values, the
radical) by seeds is hindered, because MFl is capable of
ionization with the formation of carboxylate ion having
the like charge with the particle surface. On the contrary,
under the conditions of the synthesis of A-2 particles,
MRB cations were efficiently incorporated in the shell
of negatively charged particles, which is confirmed by
fluorescence of their layer in the region characteristic of
Rhodamine B.
intensities of the signals of the toluene CH groups
3
13
1
(
2 ppm in the Н spectrum and 21 ppm in the С NMR
spectrum) were compared with those of the signals of the
СH and CH groups in the polymer backbone (0–3 ppm
2
1
13
for Н and 35–57 ppm for С).
To prepare layers of polymer particles, onto cover
glass (Menzel–Glaser, 24 × 24 mm) we applied a drop
(
20 μl) of a 1 wt % polymer dispersion. The sample was
In synthesis of B-1 and B-2 samples with the
participation of a hydrophobic luminophore-containing
monomer, MNR, we used oil-soluble initiators BP and
AIBN, effecting polymerization only in the organic
phase, particle shell, which ensures the preset particle
morphologyandexcludesformationofnewnanoparticles
not bonded to the seeds. Indeed, samples B-1 and B-2
had thicker shell than samples A-1 and A-2 (Table 2).
However, with the peroxy initiator BP, the capability of
B-1 particle layer for fluorescence decreased by an order
of magnitude and the fluorescence maximum shifted
toward shorter wavelengths (Table 3, samples B-1, B-2).
This fact indicates that the synthesis under the action of
BP can be accompanied by oxidation of the luminophore
with the break of its conjugation system. Thus, the use
of a peroxy initiator in combination with luminophore-
left at 20°C for 24 h, which was sufficient for complete
drying.
To measure the fluorescence response on vapors
of organic compounds, the cover glass with a layer of
polymer particles was placed in a dark box of volume
1
.73 l together with a porous support wetted with
a volatile analyte (benzene, methanol, ethanol), so
that the concentration of its vapor was of the order of
1
anlayte vapor for 5–10 min, after which the support with
the analyte was withdrawn and the box was purged with
a fan. The optical response on the anlayte was recorded
by the fluorescence method with an SD2000 fiber optic
spectrofluorimeter (Ocean Optics, USA). The excitation
light of wavelength 390 nm was transmitted to the
00 ppm. The sample was kept in the presence of the
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 11 2010

2002
MEN’SHIKOVA et al.
Table 3. Optical responses of layers of core–shell particles on organic solvent vapors
Response
maximum
intensity, arb.
units
Luminophore-
containing
comonomer
Alcohol in
reaction mixture,
vol %
Fluorescence
maximum
wavelength, nm
Fluorescence
maximum intensity,
arb. units
Response
maximum
wavelength, nm
Sample
A-2
B-1
B-2
MRB
MNR
МНК
EtOH, 5
580
582
603
1565
155
602, benzene
561, benzene
+175
+18
EtOH, 20
MeOH, 20
1798
624, benzene
553, methanol
553, ethanol
+92
–74
–86
1
1
884
884
containing comonomers is not appropriate, whereas
the azo initiator used in the synthesis of B-2 particles
appeared to be quite efficient.
particles obtained are shown in Figs. 3 and 4. The
characteristic regions are those of the resonance of the
aromatic groups of the polymer (6–8 ppm for Н and
110–150 ppm for 13С) and aliphatic groups (0–5 and
1
Typical 13С and 1Н NMR spectra of the polymer
1
0–50 ppm, respectively). Comparative analysis of
the structure of the weakly cross-linked core (А) and
of core-shell particles (А-1, А-2) was performed using
1
the Н NMR spectra (Fig. 4, spectra 1–3). Notably, in
the spectrum of A-1 particles there are high-resolution
signals in the range 3.6–5.3 ppm (half-width 25 Hz),
whereas A-2 particles are characterized by the presence
of high-resolution signals at approximately 1 ppm (half-
width 40 Hz). Such small half-widths of lines are typical
of highly mobile fragments of organic compounds.
1
3
Comparative analysis of the С NMR spectra also
revealedthepresenceofhighlymobilegroupsmanifested
δ, ppm
δ, ppm
Fig. 3. 13С (1–3) CP–MAS and (4–7) MAS NMR spectra of
polymer particles: (1) seeds A; A-2 core–shell particles (2, 6)
before and (3, 7) after sorption of toluene; (4) A-1 and (5) B-1
core–shell particles. Toluene signals (21 and 126 ppm) are
marked with one asterisk, and side signals at a rotation rate of
1
Fig. 4. Н NMR spectra of polymer particles: (1) seeds A; (2)
A-1 and (3, 4) A-2 core–shell particles (2, 3) before and (4)
after toluene sorption. The toluene signals (2 and 7 ppm) are
marked with an asterisk.
8
kHz, with two asterisks.
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SORPTION OF VAPORS OF AROMATIC COMPOUNDS
2003
in the spectra of samples A-1 and A-2 in the ranges 60–
0 and 20–30 ppm, respectively (Fig. 3, spectra 4, 6).
It should be noted that these signals practically are not
1Н NMR spectra.
7
It should be noted that introduction into a polymer
matrixofsmallamountsofluminophoreswasnotreflected
in the NMR spectra of the polymers. The similarity of
the spectral characteristics of the polymers, irrespective
of the structure of the photoactive component, allowed
us to compare the spectra of different samples.
1
3
observed in the С CP–MAS NMR spectrum but are
1
3
well resolved in the С MAS NMR spectrum recorded
by the standard single-pulse excitation program. This
can also be accounted for by relatively high mobility
of the corresponding groups. To rule out the possible
assignment of these signals to organic solvents sorbed
from air, we additionally dried sample A-2 over NaOH,
After the sorption of toluene vapor with polymer
13
particles, toluene signals appear in the С NMR
spectra: the signal of the methyl group at ~21 ppm and
that of the aromatic ring at ~125 ppm (Fig. 3, spectra
13
after which the С MAS NMR spectrum did not change.
This fact suggests that the mobile groups detected are
bonded to the polymer matrix. It is known from the
literature [18] that high DVB content (about 50%) in
copolymerization with styrene ensures only 30–35%
3
, 7). The best resolved and suitable for quantitative
1
3
treatment are С MAS NMR spectra, but application of
the MAS technique to recording the spectra from nuclei
1
3
with a low sensitivity ( С) requires much time for the
measurement [19]. Therefore, our data were compared
with the results of calculating the toluene sorption from
1
effective cross-links. Thus, better resolution of the Н
and 13С MAS NMR spectra of A-1 and A-2 particles
relative to the spectrum of weakly cross-linked A cores
may be due to larger amount of terminal groups in
branched and cross-linked polymer chains of the shell.
1
3
the С СР–MAS NMR spectra. This technique allows
high resolution to be attained in a relatively short time.
The amount of toluene sorbed by A-2 particles,
estimated from the Н and 13С MAS NMR and 13
CP–MAS NMR spectra, was 0.37, 0.35, and 0.08
molecule per monomeric unit of the polymer chain,
The groups giving in the 13С MAS NMR spectrum
a signal at 60–70 ppm can be formed at the polymer
chain termini under the conditions of initiation of the
emulsion polymerization with the K S O /Na S O
1
С
2
2
8
2
2
3
1
respectively. The sorption values calculated from the Н
redox system as a result of attack of the monomers with
1
3
and С MAS NMR spectra are well consistent, whereas
the technique in which the intensity of the 13С NMR
signal is determined by the magnetization transfer from
protons gives considerably lower value.Asimilar pattern
was observed with samples B-1 and B-2: The toluene
–
primary SO · radicals or of radical transfer to solvent
4
molecules (water, ethanol), followed by attack of the
monomers by ·ОН or ·ОС Н radicals:
2
5
CH CH2
CH2
OH
CH2
OC
1
3
sorption, according to С MAS NMR data, was 0.26 and
O
2
H
5
0
.30 molecule per monomeric unit, whereas according to
1
3С СР–MAS NMR data it was as low as 0.03 and 0.06
molecule, respectively. Thus, the NMR data confirm that
samples А-2, B-1, and B-2 synthesized using different
initiators but having similar nature of the polymer
matrix and comparable particle size are characterized by
close values of toluene sorption. At the same time, high,
according to 13C MAS NMR data, values of toluene
sorption by polymer particles that are cross-linked
and incapable of swelling seem doubtful. To compare,
core–shell particles based on a copolymer of methyl
methacrylate with ethylene glycol dimethacrylate sorbed
lower alcohols from their saturated vapor in amounts of
SO3
The decreased content of ethanol in the reaction
mixture in synthesis of sample A-2 sample compared to
A-1 (Table 2) leads to disappearance of the signals of
alcohol and ether groups in the range 60–70 ppm from
13
the С NMR spectra as a result of lower probability
of formation of terminal ether groups in the polymer
and to appearance of high-resolution signals of mobile
terminal methyl and methylene groups at 20–30 ppm.
1
In the Н NMR spectrum, a change in the nature of
terminal groups in going from sample А-1 to А-2 is also
manifested as a shift of high-resolution signals from
0
13
.02–0.08 molecule per monomeric unit, according to
С NMR data [20]. For various samples, the ratio of
3
.6–5.3 to ~1 ppm (Fig. 4, spectra 2, 3).
On the contrary, with an oil-soluble initiator, BP, used
the sorption values calculated from the MAS and СР–
MAS spectra was in the range 1.03–2.85, whereas for
toluene sorption by particles with a polyaromatic matrix
in the synthesis of B-1 and B-2 particles, the signals of
1
3
aliphatic terminal groups are absent from the С and
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 11 2010

2004
MEN’SHIKOVA et al.
this ratio is considerably higher: 4.38–8.67. Apparently,
in the system under consideration, toluene sorption was
accompanied by toluene condensation from saturated
vapor on the surface of particles with the polyaromatic
matrix. This assumption is confirmed by the fact that,
after the contact with toluene vapor, the samples looked
with divinylbenzene in the presence of luminophore-
containing comonomers allows preparation of core–
shell particles of uniform size with the diameter in
the submicrometer range, containing in the shell both
luminophore groups and molecular imprints of aromatic
compounds.
13
wet. On the contrary, the С CP–МАS NMR spectra
give more reasonable sorption values close in the order of
magnitude to the amount of the template (diethylbenzene)
introduced in particle synthesis. However, the 1 С CP–
МАS NMR data can be used only as estimates, because
the magnetization transfer kinetics and, correspondingly,
the signal intensities in the spectra are largely determined
2) Methods of solid-state 1Н and 13С NMR
(
spectroscopy furnish important information both on
the structure of the polyaromatic cross-linked particles
formed and on their capability to sorb vapors of aromatic
compounds (with toluene as example). Increased values
of sorption of the aromatic solvent from its saturated
3
1
13
vapor, determined by Н and С MAS NMR compared
1
by the amount of Н nuclei and by their steric proximity
13
to С СР–MAS NMR, may be due to additional
13
to the С nuclei (Overhauser effect).
condensation of toluene vapor on the particle surface.
In the case of samples A-2 and B-2, with sufficient
amount of luminophore incorporated in the shell, the
layer of particles of these samples also showed optical
response on benzene (Table 3). The deviation of the
fluorescence intensity from the initial value during 5-min
monitoring did not exceed 12%, which is sufficient for
detection of this aromatic analyte but, at the same time,
suggests its relatively slow diffusion from the gas phase
into the cross-linked polymer shell of particles to sites
containing luminophore groups. The optical response
on benzene of a layer of A-2 particles was appreciably
higher than that of a layer of B-2 particles. This may be
due to smaller shell thickness, i.e., to better accessibility
of molecular imprints in the immediate vicinity of
the luminophore to diffusion of the analyte into them.
In addition, lower content of ethanol in the reaction
mixture in the course of synthesis of A-2 particles
decreases the probability of its redistribution from the
dispersion medium into the particle shell in the course
of the synthesis with the formation of the corresponding
molecular recognition sites in accordance with the
molecular imprinting technology. The latter assumption
was confirmed by detection of the fluorescence response
of a layer of B-2 particles on methanol and ethanol
in the gas phase (Table 3), whereas the layer of A-2
particles gave no response on lower alcohols. Hence,
the presence of a large amount of ethanol in the reaction
mixture negatively affects the sensor properties of the
particles formed toward the aromatic analyte.
(
3) Benzenevaporcauseschangesinthefluorescence
of a layer of particles containing luminophore groups in
the surface layer. A decrease in the alcohol content in the
reaction mixture in the course of formation of particle
shells increases the optical response of the particle
layer. The particles obtained show promise for the
development of sensor materials with optical response
on aromatic analytes.
ACKNOWLEDGMENTS
The study was financially supported by the Federal
Target Program “Research and Development in
Priority Directions of the Scientific and Technological
Complex of Russia in Years 2007–2012” (State Contract
nos. 02.513.12.3025 and 02.527.11.0009), Program
for Basic Research of the Presidium of the Russian
Academy of Sciences “Basics of Fundamental Studies
of Nanotechnologies and Nanomaterials,” and Russian
Federation President’s grants for young candidates of
sciences (MK–794.2009.3 and MK–6699.2010.3).
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