Surface modification of poly(ethylene-butyl acrylate) copolymers by microwave methodology and functionalization with 4-dimethylamino-N-(2-hydroxyethyl)-1,8-naphthalimide for acidity sensing

Article abstract of DOI:10.1016/j.reactfunctpolym.2016.08.009

A new procedure was developed for functionalization in the solid phase by using microwave irradiation. Heterogeneous chemical modification of poly(ethylene-butyl acrylate) copolymer (EBA), hydrolysis, chlorination, and Schotten–Baumann reactions were monitored by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. EBA was superficially functionalized by a previously synthesized fluorescent dye, 4-dimethylamino-N-(2-hydroxyethyl)-1,8-naphthalimide, and the depth profile of the functionalized polymer was determined by confocal Raman spectroscopy. The new functionalized materials were also evaluated as an acidic pH sensor by determining the change in the spectroscopic properties of absorption and fluorescence with pH of the solution and vapor phases. To improve the wettability of the EBA surface, oxygen plasma treatment was used and the response time of the solid sensor was analyzed.

Full text of DOI:10.1016/j.reactfunctpolym.2016.08.009

Reactive and Functional Polymers 107 (2016) 78–86
Contents lists available at ScienceDirect
Reactive and Functional Polymers
journal homepage: www.elsevier.com/locate/react
Surface modification of poly(ethylene-butyl acrylate) copolymers by
microwave methodology and functionalization with
4
-dimethylamino-N-(2-hydroxyethyl)-1,8-naphthalimide for
acidity sensing
S. Fernández-Alonso, T. Corrales, J.L. Pablos, F. Catalina ⁎
Departamento de Química Macromolecular Aplicada, Instituto de Ciencia y Tecnología de Polímeros (CSIC), C/Juan de la Cierva, 3, 28006 Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 June 2016
Received in revised form 25 August 2016
Accepted 28 August 2016
Available online 30 August 2016
A new procedure was developed for functionalization in the solid phase by using microwave irradiation. Hetero-
geneous chemical modification of poly(ethylene-butyl acrylate) copolymer (EBA), hydrolysis, chlorination, and
Schotten–Baumann reactions were monitored by attenuated total reflection Fourier transform infrared (ATR-
FTIR) spectroscopy. EBA was superficially functionalized by a previously synthesized fluorescent dye, 4-
dimethylamino-N-(2-hydroxyethyl)-1,8-naphthalimide, and the depth profile of the functionalized polymer
was determined by confocal Raman spectroscopy. The new functionalized materials were also evaluated as an
acidic pH sensor by determining the change in the spectroscopic properties of absorption and fluorescence
with pH of the solution and vapor phases. To improve the wettability of the EBA surface, oxygen plasma treat-
ment was used and the response time of the solid sensor was analyzed.
Keywords:
Surface functionalization
Microwave
Ethylene-butyl acrylate copolymers
Naphthalimide sensor
Plasma treatment
© 2016 Elsevier B.V. All rights reserved.
1
. Introduction
An effective approach to develop an applicable solid sensor is to
the surface of EBA. The sequence of reactions carried out is shown in
Fig. 1.
The introduction of specific functional groups to polymer surfaces by
well-defined, classical organic chemical reactions usually involves ionic
or polar reactions rather than free radical reactions. Therefore, the poly-
mer surfaces suitable for this type of modification must have sites that
are vulnerable to electrophilic or nucleophilic attack.
modify the surface of the material that already has excellent bulk prop-
erties. A grafted surface can be produced primarily by either graft poly-
merization of monomers or a covalent coupling reaction of existing
polymer molecules onto the substrate polymer surface. Many chemical
and physical methods [1] such as plasma, e-beam, and sputtering have
been used to modify the structure of polymer surfaces and in particular
polyethylenes [2]. Most of these techniques are based on the use of
high-energy sources that can ultimately damage the polymer surfaces
either chemically or physically. Moreover, these methods are usually
not versatile enough to allow the design of structurally and chemically
modified surfaces through the control of the distribution of chemical
functionalities throughout the surface. In an earlier work, we described
the microwave-assisted chemical modification of poly(ethylene-butyl
acrylate) copolymers [3] (EBA) in solution to bind coumarin derivatives
through the acrylic comonomer. In this study, organic functionalities
were introduced onto EBA as the polymer substrate in a controlled man-
ner by performing a sequence of chemical reactions on the surface. In
the heterogeneous phase, hydrolysis, chlorination, and Schotten–
Baumann reactions were used to graft a naphthalimide derivative to
The modification of the EBA surface opens the possibility to chemi-
cally bond numerous organic structures having a terminal group capa-
ble of reacting with the functional groups present on the substrate
polymer surface. Recently, polymers containing photosensitive func-
tional groups have gained significant attention [4,5,6]. A number of pub-
lications have appeared concerning 1,8-naphthalimide derivatives as a
special class of environmentally sensitive fluorophores. Their strong
fluorescence and good photostability have promoted their applications
in a number of areas such as coloration of polymers [7,8], as laser active
media [9], fluorescence markers in biology [10], anticancer agents [11],
light-emitting diodes [12], photoinduced electron transfer sensors [13,
14], fluorescence switchers [15], electroluminescent materials [16,17],
liquid crystal displays [18], ion probes [19], and pH sensors [20].
Hence, in this study, we synthesized a hydroxyl derivative, 4-
dimethylamino-N-(2-hydroxyethyl)-1,8-naphthalimide (DMAN) to
react with the superficial chlorine acids of the modified EBA to
functionalize the polyolefin material with a sensor probe (EBA-
DMAN), as shown in Fig. 1. The surface functionalization was studied
by attenuated total reflection Fourier transform infrared (ATR-FTIR)
⁎
Corresponding author.
E-mail address: fcatalina@ictp.csic.es (F. Catalina).
http://dx.doi.org/10.1016/j.reactfunctpolym.2016.08.009
381-5148/© 2016 Elsevier B.V. All rights reserved.
1

S. Fernández-Alonso et al. / Reactive and Functional Polymers 107 (2016) 78–86
79
Fig. 1. Heterogeneous reaction sequence for surface modification of EBA using microwave methodology.
spectroscopy and confocal Raman spectroscopy (CRS) [21] to determine
the depth profile of the functionalized polymer.
Furthermore, the new functionalized materials were evaluated as an
acidic pH sensor by determining the change in the spectroscopic prop-
erties of absorption and fluorescence with pH. To improve the wettabil-
ity of the surface, EBA-DMAN films were treated with oxygen plasma
Confocal Raman Spectroscopy (CRS). A Renishaw inVia Raman mi-
croscope, working in a confocal mode and connected to an Olympus
BH2 microscope was used for measuring the Raman spectra. The
beam from the 785 line of a He–Ne laser (laser power 320 mW at
100%) was focused by 100× magnifying length objective (numerical ap-
erture (NA) value of 0.85) in the confocal mode and a charge-coupled
device (CCD) camera as detector. Raman light was dispersed by a
diffraction grating with 1200 lines/mm using a Raman holographic
notch filter.
[22]. The plasma-treated materials (EBA-pl-DMAN) exhibited a lower
response time for environmental changes of pH in solution and vapors
because of surface oxidation.
The depth profile of the sample was obtained by focusing the micro-
scope stepwise at fixed 1-μm intervals within the polymer film and re-
cording 10 accumulative spectra at each step (accumulation time, 3 min
per spectrum). The depth resolution of the confocal arrangement in air
was previously checked using a sample of silica as a reference material.
Ultraviolet (UV) spectroscopy was used for the quantitative determi-
nation of DMAN moieties anchored to EBA in a PerkinElmer Lambda 35
spectrometer. DMAN surface loading was determined by measuring the
absorbance at the peak maximum of absorption band. This was translat-
ed into quantitative DMAN content per unit area by rearrangement of
the Beer–Lambert law. Each material was assessed in quintuplicate.
Fluorescence spectra were recorded using a PerkinElmer LS 55 fluo-
rescence spectrometer. Fluorescence emission spectra of the probe
were recorded in the range of 490–700 nm using the maximum of the
longest-wavelength absorption band as excitation wavelength. All the
spectra were corrected using the response curve of the photomultiplier.
2
. Experimental
2
.1. Materials, reagents, and film preparation
Poly(ethylene-co-butyl acrylate) copolymer (EBA) with 7% (w/w) of
−
1
butyl acrylate (0.924 g ml of density) was supplied by Repsol compa-
ny (Madrid, Spain). EBA films of 100 μm thickness and 50 × 50 mm
dimension were prepared by compression molding in automatic Press
ATLAS T8 plates with a maximum pressure of 2 tons and temperature
of 190 °C. The thickness of the films was controlled by specific-size spac-
er rings.
The following chemicals and solvents were purchased and used as
received unless otherwise indicated: 4-bromo-1,8-naphthalic anhy-
dride (Aldrich, 95%), 2-propanol (Scharlau, 99.5%), sodium hydroxide
(
Panreac, 98–100%), hydrochloric acid (VWR Chemicals, 37%), ultrapure
The fluorescence quantum yields (ϕ
F
) were measured relatively to cou-
MilliQ water (Millipore), diiodomethane (Aldrich, ≥99.5%), dichloro-
methane (Aldrich, ≥99.9%), phosphorus pentachloride (Aldrich, ≥98%),
triethylamine (Aldrich, ≥99%), 2-aminoethanol (Aldrich, 99%), ethanol
F
marin 6 (ϕ = 0.78 in ethanol) [23].
1
H- and 13C-nuclear magnetic resonance (NMR) spectra were
recorded on Varian-Mercury 400 MHz and Bruker 300 MHz NMR
spectrometers using hexadeuterated dimethyl sulfoxide (DMSO-d
(
VWR Chemicals, 99.95%), dimethylformamide (DMF, Scharlau,
9.8%), ethyl acetate (Aldrich, ≥99.5%), hexane (Carlo Erba Reagents,
9%), hexadeuterated dimethylsulfoxide (DMSO-d Euriso-top,
6
) as
9
9
9
9
the solvent. Chemical shifts were reported in parts per million (ppm).
1
13
,
H NMR and C NMR chemical shifts were referenced to DMSO-d
(39.52 ppm) as standard.
6
6
9.8%), potassium carbonate (Panreac, 99%), and coumarin 6 (Aldrich,
8%).
Mass spectra (MS) were recorded on a HP 5973-MSD spectrometer.
2
.2. Spectroscopic characterization
2.3. pH measurements and spectroscopic detection of acid in solution and
vapors
ATR-FTIR was used to characterize the polymer films of EBA before
and after MW reactions. ATR-FTIR spectra were obtained using a
PerkinElmer BX-FTIR spectrometer coupled with a MIRacle™ ATR ac-
cessory from PIKE Technologies, and interferograms were obtained
from 32 scans. The degree of hydrolysis and modifications of the EBA
films were determined using ATR-FTIR and accessories with the same
value of pressure.
The pH was measured at room temperature (23 °C) by using a
Mettler Toledo SevenGo Duo pro meter with an InLab Expert Pro ISM-
ID67 electrode that was previously calibrated with standard buffers.
The sensing measurements of the solutions of DMAN and surface-mod-
ified films of EBA-DMAN were performed using HCl solution in the
water:ethanol (4:1) mixture as solvent.

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S. Fernández-Alonso et al. / Reactive and Functional Polymers 107 (2016) 78–86
Acid titration by ultraviolet–visible (UV–Vis) and fluorescence spec-
trometry in aqueous solution and vapors was performed as follows. The
The EBA film was placed in a 30-ml microwave test tube, and the test
tube was then filled with a solution of 0.5 M NaOH in isopropanol. The
temperature of the solution was fixed at 65 °C under stirring at
600 rpm for 6 h. After completion of the heterogeneous reaction at
−
4
titration of the solution with DMAN (water:ethanol 4:1, 10 M) was
carried out by adding dilute HCl to increase the acidity from pH 8 to
pH 0.5. After each addition, the solutions were allowed to equilibrate
for 10 min, the pH was measured, and UV–Vis and fluorescence spectra
were recorded.
In the case of functionalized materials (EBA-DMAN and EBA-pl-
DMAN), the films were cut into strips of dimension 1 × 4 cm and dipped
into 100 ml of water (Millipore-Q) using a homemade support that is
slotted into the cell holder of the spectrophotometers. To study the ef-
fect of increasing the acidity of the medium beyond the pH scale, vials
containing 50 ml of HCl at pH 7 to −1.1 (12 M HCl, 37%) were prepared.
Strips of the film were immersed in these vials, starting from the vial
with the lowest acid concentration, and the UV–Vis and fluorescence
spectra were recorded for each pH after a conditioning time of 2 h.
The fluorescence detection of acidic vapors was performed by adding
–
room temperature, the EBA-COO film was separated from the medium
and neutralized in a microwave-assisted second step by adding 30 ml of
aqueous HCl solution (0.1 M) to the polymer and maintaining the mix-
ture at 50 °C for 1 h. The resulting hydrolyzed EBA-COOH film was then
washed repeatedly with distilled water and dried under vacuum over-
night. The surface modification of EBA to EBA-COO– and EBA-COOH
was confirmed and evaluated by ATR-FTIR spectroscopy (Fig. 3).
The EBA-COOH film and phosphorus pentachloride (50 mg,
0.24 mmol) were placed in a 30-ml microwave reactor containing
2 2
20 ml of CH Cl anhydrous solution. Acid chlorination was carried out
under microwave irradiation at 55 °C under magnetic stirring at
600 rpm. After 90 min, the EBA-COCl film was washed with dichloro-
methane and dried under vacuum overnight. The reaction between su-
perficial acid groups and EBA-COCl was quantitative and confirmed by
ATR-FTIR spectroscopy (Fig. 3).
1
00 μl of HCl (12 M HCl 37%) over a cotton fragment to avoid direct con-
tact and placing it at the bottom of a sealed spectrophotometric cuvette,
where the functionalized EBA film is disposed.
2.7. Functionalization of EBA-COCl with DMAN
2
.4. Microwave equipment
Superficially chlorinated EBA film, EBA-COCl, and 25 mg of DMAN
The microwave equipment used in this study was an Anton Paar
2 2
were placed in a vial containing 20 ml of CH Cl and 500 μl of
Monowave™ 300 microwave synthesis reactor equipped with an infra-
red sensor (IR pyrometer). All reactions were performed in pressure-re-
sistant 30-ml test tubes sealed with silicon septum with a magnetic
stirring bar. The progress of the reactions was observed by an integrated
CCD camera, which directly focuses on the reaction vial.
triethylamine (TEA) under microwave at 55 °C for 15 h under magnetic
stirring at 600 rpm. The vial was then rapidly cooled down with com-
pressed air to room temperature, and the modified EBA-DMAN film
was washed repeatedly with dichloromethane and dried under vacuum
overnight. The reaction was confirmed by ATR-FTIR and UV–Vis spec-
troscopy (Fig. 3).
2
.5. Plasma treatment and characterization by contact angle measurements
and atomic force microscopy
2.8. Synthesis of N-(2-hydroxyethyl)-4-dimethylamino-1,8-naphthalimide
The films were plasma-treated using an RF-Expanded Plasma Clean-
er PDC-002 coupled with a PlasmaFlo PDC-FMG gas mixer obtained
from Harrick Plasma and a Varian SH-110 vacuum pump. Samples
were placed inside the Pyrex chamber (6″ diameter × 6.52″ length),
and both sides of all films were treated with high RF power (30 W to
the RF coil) for 30 min with oxygen plasma. Gas flow rates and chamber
pressure can be altered by manual pressure and flow regulators, and
stabilized pressure was fixed at 250 mTorr (0.33 mbar).
N-(2-hydroxyethyl)-4-bromo-1,8-naphthalimide (compound 1)
and N-(2-hydroxyethyl)-4-dimethylamino-1,8-naphthalimide (com-
pound 2) were synthesized following the procedure (Fig. 2) described
in refs. [25,26] and using a novel reaction [27] for dimethylamination
of compound 1.
In a pressure-resistant microwave test tube, a mixture of 4-bromo-
1,8-naphthalic anhydride (1.4 g, 0.005 mol) and ethanol amine (0.4 g,
0.005 mol) in ethanol (15 ml) was heated at 85 °C and stirred at
600 rpm for 2 h. The resulting mixture was cooled at 5 °C. The solid
product obtained was filtered and washed with 30 ml of cold ethanol
thrice and then identified as N-hydroxyethyl-4-bromo-1,8-
Changes in the wettability of plasma-treated polymer surfaces were
observed after the determination of water contact angle (CA) by the ses-
sile drop method. CA measurements were performed at 25 °C using a
KSV instruments LTD CAM 200 Tensiometer and MilliQ water as wetting
solvent. Surface energy was determined using two liquids (water and
methylene iodide) for the measurements. On the basis of Owens–
naphthalimide (compound 1) after drying. Yield 90% (1.4 g). M.p.:
1
206 ± 2°. H NMR (δ
H
6 4
ppm) (300 MHz, DMSO-d , Me Si): δ 8.42 (dd,
J = 13.9, 7.9 Hz, 2H), 8.20 (d, J = 7.9 Hz, 1H), 8.10 (d, J = 7.8 Hz, 1H),
d
Wendt's method [24], the surface energy (γ) and its dispersive (γ )
7.89 (t, J = 7.9 Hz, 1H), 4.81 (s, 1H), 4.10 (t, J = 6.4 Hz, 2H), 3.61
p
13
and polar (γ ) parts were calculated using the CAM 200 software.
C 6 4
(t, J = 5.9 Hz, 2H). C NMR (δ ppm) (100.6 MHz, DMSO-d , Me Si):
Surface morphology and roughness of the EBA films modified with
DMAN before and after oxygen plasma treatment were examined
by atomic force microscopy (AFM) using a Nanoscope IV system
δ 162.90, 162.85, 132.41, 131.42, 131.24, 130.80, 129.61, 128.98,
128.67, 128.14, 122.70, 121.92, 57.71, 41.95. FTIR (wavenumbers,
−
1
−1
−1
cm ): νOH3386 cm ; νC \\ H3066 cm
aromatic stretch vibration;
ν
C_O 1692, 1658 cm ; νN \\ C_O 1611 cm−1; νC \\ C 1585, 1568 cm
−
1
−1
(
Digital Instruments) working in tapping mode with a triangular
microfabricated cantilever having a length of 115–135 mm, 1- to 10-
Ohm-cm phosphorous (n)-doped Si pyramidal tip, and a nominal spring
constant of 20–80 N m . The mean roughness value (Ra) represents
the arithmetic average of the deviations from the center plane of the
sample, which was determined using standard Digital Instruments
software.
aromatic ring chain vibrations. Elemental analysis, theoretical values:
%C 52.52; %H 3.15; %N 4.38; experimental values: %C 52.42; %H 3.25;
%N 4.25; EI–MS m/z: 321.0 (M ).
In a pressure-resistant microwave test tube, 1 g of compound 1
(0.003 mol), 4.35 ml of triethylamine (0.03 mol), and 10 ml of
DMF:water (1:1) solution were added. The mixture was heated at
−
1
+
120 °C and stirred at 600 rpm for 12 h. After completion of the reaction,
2
.6. Surface modification of EBA films by hydrolysis (EBA-COOH) and acid
the vial was cooled with water to room temperature. The mixture was
extracted with ethyl acetate (4 × 50 ml), and the organic layer was
chlorination (EBA-COCl)
2 3
dried over K CO . The solvent was evaporated under reduced pressure,
EBA (7% of BA) film was cut into strips (1 × 4 cm) and hydrolyzed in
the solid state by a modified procedure of the method reported previ-
ously [3] to conduct the heterogeneous reaction in a microwave reactor.
which was purified by silica gel column chromatography using ethyl
acetate:hexane (2:1) as eluent to obtain an orange solid product,
which is identified as N-(2-hydroxyethyl)-4-dimethylamino-1,8-

S. Fernández-Alonso et al. / Reactive and Functional Polymers 107 (2016) 78–86
81
Fig. 2. Reaction pathway and mechanism for the synthesis of N-(2-hydroxyethyl)-4-dimethylamino-1,8-naphthalimide (DMAN, compound 2).
naphthalimide. Yield: 84%, M.p. = 135 ± 2 °C. 1H NMR (δ
400 MHz, DMSO-d , Me Si): δ 8.51 (dd, J = 8.5, 1.1 Hz, 1H), 8.45 (dd,
J = 7.3, 1.1 Hz, 1H), 8.34 (d, J = 8.3 Hz, 1H), 7.75 (dd, J = 8.5, 7.3 Hz,
ppm)
with 10 equiv. of triethylamine in DMF:water (1:1) yielding compound
2 in 90%.
H
(
6
4
1
6
H), 7.21 (d, J = 8.3 Hz, 1H), 4.81 (t, J = 6.0 Hz, 1H), 4.13 (t, J =
.6 Hz, 2H), 3.59 (q, J = 6.5 Hz, 2H), 3.08 (s, 6H). 13C NMR (δ
ppm)
, Me Si): δ 163.69, 163.03, 156.41, 132.12,
31.32, 130.41, 129.56, 124.90, 124.16, 122.37, 113.43, 112.91, 57.87,
3.2. Microwave-assisted surface hydrolysis, acid chlorination, and
functionalization of EBA with naphthalimide groups
C
(
100.6 MHz, DMSO-d
6
4
1
4
1
The functionalization of EBA (7% content of BA) was carried out fol-
lowing the sequence of reactions shown in Fig. 1. The different modifi-
cations of EBA, hydrolysis of butyl ester, acid chlorination, and
esterification with DMAN were accomplished successfully in solution
under microwave irradiation. All the modified EBA films were isolated
and characterized by ATR-FTIR spectroscopy (Fig. 3).
−
1
−1
4.35, 41.51. FTIR (wavenumbers, cm ): νOH 3474 cm ; νC_O
680 cm and 1628 cm , νC \\ C 1575 cm aromatic ring chain vibra-
−
1
−1
−1
tions. Elemental analysis, theoretical value: %C 67.59; %H 5.67; %N 9.85;
experimental values: %C 67.09; %H 5.88; %N 9.88. EI-MS m/z: 285.0
+
(
M ).
Fig. 3 shows the characteristics of vibrational bands of the species
formed after each functionalization step as described above in the syn-
thesis section. As shown in Fig. 3, butyl ester on the surface was hydro-
lyzed by microwave irradiation under heterogeneous conditions, and
the degree of hydrolysis was determined by ATR-FTIR as described ear-
lier [3] and by using the butyl ester and carboxylate bands. The obtained
curves are plotted in Fig. 4.
3
. Result and discussion
3
.1. Synthesis of N-(2-hydroxyethyl)-4-dimethylamino-1,8-naphthalimide
The synthesis route to obtain N-(2-hydroxyethyl)-4-
dimethylamino-1,8-naphthalimide is presented in Fig. 2. In the first
step, the condensation of 4-bromo-1,8-naphthalic anhydride with 2-
hydroxyethylamine under microwave irradiation in ethanol at 85 °C
afforded compound 1 in high yield at a shorter reaction time than con-
ventional conditions. It has been observed [28] that for various amines,
imidation of naphthalimides under reflux required 4–16 h. Our results
show that the microwave method reduced the reaction time and im-
proved the yield from 72–85% (under conventional conditions) to 96%.
In the second reaction step (Fig. 2), an interesting observation was
made while we were optimizing the reaction conditions for the nucleo-
philic substitution reaction of compound 1 with 2-methoxyethylamine.
When the reaction was carried out in DMF, surprisingly,
dimethylamination product (DMAN, compound 2) was also produced.
In the absence of the primary amine, DMAN was obtained in very
good yield. This reaction has been described [27,29] as a convenient
method for the introduction of a dimethylamino group in aromatic
compounds through chlorinated derivatives of heterocycles or aro-
The spectra at different hydrolysis reaction times show the growth
of bands because of the increase in carboxylate content, introduced to
the surface of the polyolefin film. This confirms the hydrolysis of the
surface with treatment time. Thus, the carboxylate content can be
used to follow the modification of EBA surface by ATR-FTIR.
After reacting sodium hydroxide solution (0.5 M) in isopropanol for
6 h at 65 °C, the conversion of butyl ester to carboxylate (Fig. 4) reaches
a value of 83.3% (5.83% of butyl ester content). In our experimental con-
dition, 1.17% of butyl ester remained in the EBA composition after hy-
drolysis in the superficial thickness of the film analyzed by ATR-FTIR.
As found in the hydrolysis reactions carried out in bulk with EBA [3]
and ethylene vinyl acetate (EVA) copolymers [32], a plateau was
reached in the hydrolysis conversion when the reaction times are longer
than 6 h.
The determination of the acid content by ATR-FTIR suggested the
−
1
carboxylic acid band at 1703 cm is attributed to the overlapping of
−
1
the carbonyl butyl ester band at 1735 cm . The asymmetric stretch
−
1
matics using bases such as KOH or K
2
CO
3
, and although the reaction
band of the carboxylate group at 1580 cm could therefore be more
convenient to follow the hydrolysis conversion.
mostly proceeds slowly, it results in good yields.
In our experimental conditions, dimethylamination resulted in the
formation of compound 2 in good yield. On the contrary, when no
base was added, the reaction did not proceed. Also, the presence of
water seemed to be crucial for the amination, and this fact could be at-
tributed to a better solvation of the base. The reaction and the plausible
mechanisms for the amination are illustrated in Fig. 2.
The reaction starts with a base-assisted cleavage of DMF to form the
required dimethylamine [30,31], which acts as the nucleophile for the
formation of the required product. DMF is an easy substitute for
dimethylamine, and the reaction occurs in a shorter period of time
and produces high yields with microwave irradiation. The best condi-
tions were noted under microwave irradiation for 12 h at 850 W and a
ceiling temperature of 120 °C of a mixture of compound 1 together
After protonation of the carboxylate groups in a microwave-assisted
second step (HCl aq. solution 0.1 M, 50 °C, 1 h), the acid groups present
in EBA-COOH were converted to acid chloride under microwave
heating. After 1.5 h of reaction with phosphorus pentachloride, the
transformation was quantitative, as shown by the band at 1793 cm−
1
,
which corresponds to ν(C_O) acyl chloride (EBA-COCl) and the disap-
−
1
pearance of the acid band at 1703 cm (Fig. 3).
Finally, functionalization was carried out by reacting EBA-COCl with
the previously obtained N-(2-hydroxyethyl)-4-dimethylamino-1,8-
naphthalimide derivative. The degree of functionalization increased
with reaction time (3 h: 45%; 5 h: 60%; 7 h: 70%; and 10 h: 83%). After
reacting for 15 h at 55 °C, no acyl halide band in the functionalized
−
1
EBA-DMAN film could be detected at 1793 cm , suggesting that the

82
S. Fernández-Alonso et al. / Reactive and Functional Polymers 107 (2016) 78–86
7
6
8
9
3
4
5
2
1
EBA
EBA-COO
EBA-COOH
EBA-COCl
EBA-DMAN
DMAN
-
2000
1800
1600
1400
1200
1000
2000
1800
1600
1400
1200
1000
-
1
-1
Wavenumbers (cm )
Wavenumbers (cm )
Fig. 3. ATR-FTIR spectra in the region between 2000 and 1000 cm of EBA (7% of BA content) and the surface-modified EBA materials: (1) 1735 cm−1
ν(C_O) butyl ester (EBA), (2)
−
1
165 cm−
1
ν
(C \\ O) aliphatic ester (EBA), (3) 1568 cm and (4) 1413 cm−1 are assigned to νas(COO \\ ) and νs(COO \\ ) of carboxylate anion, respectively, (EBA-COO ), (5) 1703 cm
−1
−
−1
1
ν
−
1
−1
−1
(C_O) carboxylic acid (EBA-COOH), (6) 1793 cm
aromatic ring (EBA-DMAN), and (9) 1167 cm
ν
(C_O) acyl chloride (EBA-COCl), (7) 1730 cm
ν
(C_O) naphthalimide (EBA-DMAN), (8) 1644 cm
ν
(C_C) naphthalimide
−
1
ν( C\\ O) aliphatic ester (EBA-DMAN).
reaction was quantitative and the content of naphthalimide on the sur-
face remained constant after several washes with dichloromethane.
The amount of naphthalimide superficially bonded to the EBA was
determined spectrophotometrically through the measurement of ab-
sorbance at the peak maximum of the absorption band and using the
absorption coefficient of N-(2-hydroxyethyl)-4-dimethylamino-1,8,-
To obtain the depth profile of the films, a Raman microscope was fo-
cused stepwise (1 μm) from near the surface down to the center of each
film, and the 1000- to 1800-cm region of the spectrum was recorded
at each step. In addition to the typical EBA polymer peaks, new charac-
teristic bands emerged for graphitic material EBA-DMAN.
−
1
The degree of modification as a function of depth was obtained from
the relative intensity of the naphthalimide bands and ν(C \\ C) aromatic
4
−1
naphthalimide in water:ethanol (4:1 w/w) (ε445 = 1.02 × 10 mol
−
1
−1
l cm ). Analysis of EBA-DMAN by UV spectroscopy provided a mea-
sure of the surface content of DMAN per unit area of polymer, and a con-
ring vibrations at 1585 cm with respect to the ν(C \\ C) aliphatic chain
−
1
−1
vibrations of the EBA at 1296 cm . Hence, signals [I (1585 cm )/I
−
2
−1
centration value of 2.4 ± 0.20 μg cm
was calculated for the EBA-
(1296 cm )] lead to the relative depth profile, which is depicted in
DMAN film hydrolyzed after 6 h. For the materials with a lower initial
degree of hydrolysis, a good correlation was observed between increas-
ing the extent of acid chlorination on EBA and increased content of
DMAN bonded to the EBA.
Fig. 5.
The shape of the curve shown in Fig. 5 confirms that the EBA has not
only been modified at the surface, but a gradient of DMAN was also
formed across the first 20 μm of film thickness until the naphthalimide
Raman bands are negligible. Relative degrees of hydrolysis of the EBA
and the subsequent functionalization are a function of the depth with-
out any interface between the pure EBA layers and functionalized layers.
This behavior has been described by other authors using this technique
to modify polyvinyl chloride (PVC) [34] and in the nitration of polysty-
rene [35] without any swelling of the polystyrene film. In our reaction
conditions of hydrolysis (6 h at 65 °C using 0.5 M NaOH in isopropanol),
3
.3. Depth profiling of the functionalization by CRS
Chemical functionalization of EBA-DMAN polymer films was studied
using Raman microscopy. Both physical and chemical surface modifica-
tion reactions generally result in the formation of a concentration gradi-
ent of the modifying groups through the film, and we used CRS to
characterize the depth profile [33] of DMAN anchored to the EBA-
DMAN films.
1.0
Initial
Depth ( m)
7
0.8
-
EBA-COO
6
5
4
3
2
1
0.6
1560
1590
Wavenumbers (cm
1620
-1
)
0.4
0.2
EBA (7% BA ester)
0
0
5
10
Depth ( m)
15
20
0
50 100 150 200 250 300 350 400 450
Time (min.)
Fig. 5. Relative depth profile of functionalization calculated from the evolution of the
Raman band ν(C \\ C) aromatic ring vibrations of naphthalimide at 1585 cm
−
1
(inset)
Fig. 4. Relationship between the percentages of surface hydrolysis degree of butyl ester (▪)
and carboxylate formation (•) and reaction time in EBA films (7% content in BA)
determined from the ATR-FTR spectra.
versus depth. Spectra of a functionalized EBA-DMAN film (100 μm) were recorded using
confocal Raman spectroscopy and normalized with respect to the intensity of the ν(C \\ C)
band at 1296 cm− of the aliphatic chain vibrations of the EBA.
1

S. Fernández-Alonso et al. / Reactive and Functional Polymers 107 (2016) 78–86
83
the polyolefin film did not swell, and hence, the extent of hydrolysis
83.3% of butyl ester content of EBA) is confined to the first 20 μm
from the surface down to the film center as the DMAN depth profile.
CRS is a useful technique to measure the functionalization of poly-
mer surface through the depth profile using Raman absorption band
characteristics of the anchored functionalities.
Table 1
Parameters for N-(2-hydroxyethyl)-4-dimethylamino-1,8-naphthalimide (DMAN) in
solution and bonded to the polymer film (EBA-DMAN) determined according to pH de-
pendence by UV–Vis absorption and fluorescence spectroscopy
(
(a)
.
Parameter
DMAN
EBA-DMAN
λ
ABS-acid
332, 346 nm
4.08 (332 nm)/4.05 (346 nm)
305, 360 nm
445 nm
4.01 (445 nm)
1.41
327, 348 nm
−
(
b)
Log εacid
λ
λ
Isobestic
370 nm
402 nm
–
−0.88
480 nm
488 nm
3
.4. Effect of pH on the absorption and fluorescence properties of DMAN and
ABS-base
EBA-DMAN
(b)
Log εbase
(c)
pK
a
Light excitation of DMAN elicits an electron donor–acceptor interac-
λ
λ
ϕ
FLU-acid
548 nm
550 nm
FLU-base
tion between the unbound electron pair of the nitrogen atom at C-4 po-
sition toward the electron-accepting peri-carboximide groups [36,37].
This intramolecular electron charge transfer (ICT) results in a long-
wavelength broad absorption band with absorption maxima at 445
and 402 nm for DMAN (Fig. 6A) and EBA-DMAN (Fig. 6B), respectively.
Upon acidification, the maximum intensity of the band decreases from
pH approximately 3 to 0 (Fig. 6C). When the aromatic amine of the
naphthalimide derivative is protonated at low pH values, the electron-
withdrawing effect leads to fluorescence quenching (Fig. 6D). This effect
can also be observed for the DMAN bonded to the surface of EBA (Fig.
(f)
FLU-(solvent)
0.032 (water:ethanol, 4:1, v/v) water:ethanol
0
0
.035 (ethanol)
.85 (hexane)
(4:1, v/v) bb ethanol ⋘ hexane
(g)
Δν
4290.1
4425.7
a
Measured at 10−4 M in water:ethanol (4:1, v/v). The subscripts “acid” and “base” refer
to the limiting value of a given parameter when the acid or base condition is increased, re-
spectively. Fluorescence emission spectra were obtained by excitation at λMAX
.
b
c
−1
−1
ε, molar absorptivity in M cm
Obtained [37] by analyzing the pH dependence of the absorbance (A) at a given wave-
.
length according to the equation log[(Aacid − A)/(A − Abase)] = pH − pK
a
.
f
F
Relatively to coumarin 6 (ϕ = 0.78 in ethanol).
Stokes shift (νFLU-νABS) in frequency (cm ).
g
−1
6
B). The effect of pH on the absorbance and fluorescence of DMAN
and EBA-DMAN is illustrated in Fig. 6.
For EBA-DMAN, the decrease in absorbance and the corresponding
quenching of fluorescence due to the amine protonation occurs at
lower pH values than that obtained for DMAN (Fig. 6C and F). This fact
could be due to the hydrophobic characteristic of the EBA surface.
Hence, EBA-DMAN films were used to evaluate the molarity of HCl
aqueous solutions in the interval of 1–12 M with the change in absor-
bance (Fig. 6B) and fluorescence (Fig. 6E) characteristics as a function
of pH [38]. Table 1 summarizes some spectroscopic parameters obtain-
ed from the spectra.
marked hypsochromic shift of 40–60 nm without a decrease in intensity
and maintaining the Stokes shift (Table 1). The fluorescence quantum
yield of DMAN is low in polar and base–neutral media, but is drastically
increased to 0.85 in hexane. These results are in agreement with those
obtained by other authors [37] for N-methyl-4-dimethylamino-1,8-
naphthalimide. The corresponding fluorescence quantum yields of
EBA-DMAN were not determined because of difference between the
functionalized film and the fluorescence standard used in solution, but
the relative fluorescence intensities of EBA-DMAN were in the same in-
tensity order: water:ethanol (4:1, v/v) bb ethanol ⋘ hexane.
When the DMAN chromophore is bonded to the EBA through the 2-
hydroxyethyl group, the absorption and fluorescence maxima exhibit a
DMAN
EBA-DMAN
402 nm
4
45 nm
C
0
0
0
.6
.4
.2
HCl 0.75M
HCl 1M
HCl 3M
HCl 5M
HCl 7M
HCl 8M
HCl 9M
HCl 10M
HCl 11M
HCl 12M
346 nm
332 nm
348 nm
EBA-DMAN
0.6
.5
0.4
.3
0.2
A
B
327 nm
DMAN
0
1.4
0.7
0.0
0
0
0
.1
.0
4
00
600
300
400
500
-1
0
1
2
3
Wavelength (nm)
Wavelength (nm)
pH
F
D
HCl 0.75M
HCl 1M
HCl 3M
HCl 5M
HCl 7M
HCl 8M
HCl 9M
HCl 10M
HCl 11M
HCl 12M
3
2
1
00
00
00
0
E
EBA-DMAN
DMAN
300
250
200
2
1
00
00
0
150
100
DMAN
EBA-DMAN
50
0
5
00
550
600
650
700
4
50
500
550
600
-1
0
1
2
3
Wavelength (nm)
Wavelength (nm)
pH
Fig. 6. Spectroscopic characteristics as a function of pH of acid media: Absorption of DMAN (A) and EBA-DMAN (B) and fluorescence of DMAN (D) and EBA-DMAN (E). Comparison of the
absorption (C) and fluorescence (F) changes with pH for DMAN and EBA-DMAN.

84
S. Fernández-Alonso et al. / Reactive and Functional Polymers 107 (2016) 78–86
The pK
a
of EBA-DMAN has a negative value (−0.88) and is lower
that the change in morphology is the result of the ion bombardment and
ablation of the polymer surface layer.
than that of DMAN (1.41), as the dimethylamine protonation of EBA-
DMAN occurs at lower pH than that observed for DMAN (Fig. 6).
The EBA-DMAN material acts as an extreme acidity sensor by its
absorbance and fluorescence characteristics. The sensor activity of
EBA-DMAN was effective under several acid–water wash cycles (until
3.6. Plasma treatment of EBA-DMAN films and response time to acid media
The changes in fluorescence emission with HCl (37%, 12 M) as a
function of time are shown in Fig. 8A and B for EBA-DMAN and EBA-
pl-DMAN, respectively.
The oxygen plasma treatment substantially decreased the response
time of the DMAN fluorescence in strong acid medium (HCl, 12 M)
from 80 min for EBA-DMAN to 30 min for EBA-pl-DMAN (Fig. 8C), to-
gether with a larger decay of fluorescence in the plasma-treated film.
The increase in hydrophilicity imparted by the oxidative plasma on
the film surface facilitates the penetration of proton into the coordina-
tion sphere of the DMAN functional groups anchored to the first
4
–5 cycles), but with a prolonged response time (~2 h). Also, reversibil-
ity was observed with lower recovery of the fluorescence after the
fourth cycle. One possibility to decrease the response time to acid
media is to increase the hydrophilicity of the EBA surface though oxygen
plasma treatment. In the next section, we report the results obtained
from EBA-DMAN before and after plasma treatment as a sensor of
acidity.
3
.5. Plasma treatment of EBA-DMAN films and characterization
2
0 μm of the film. The remaining nonprotonated DMAN chromophore
To enhance the hydrophilic characteristic of the functionalized EBA,
after acid treatment was higher for the EBA-DMAN film, as the residual
fluorescence intensity is stronger than that observed for the EBA-pl-
DMAN film. This fact confirms a deeper penetration of protons into
the plasma treatment material. Also, the reversibility of dimethylamine
protonation after washing with water was compared for both materials.
Again, the extent of deprotonation is lower for EBA-DMAN (Fig. 8D), as
the fluorescence intensity of EBA-pl-DMAN (Fig. 8E) was totally recov-
ered after washing with distilled water. Thus, oxygen plasma treatment
improved the sensitivity of the functionalized EBA surface to the acid
medium.
The response time of functionalized films to the extremely acidic en-
vironment was also studied in the vapor phase, it was observed that the
spectroscopic characteristics of DMAN bonded to the polymer were sen-
sitive to the acid vapor medium. It was necessary to maintain the film
for approximately 1 h to observe the effective change in absorption
and fluorescence properties. The results are shown in Fig. 9.
Both functionalized materials are sensitive to HCl vapors through
their ICT absorption bands at the longest wavelength (Fig. 9A and B).
The plasma-treated EBA-pl-DMAN film exhibits better behavior in fluo-
rescence decay after 120 min of vapor treatment (Fig. 9D) than the un-
treated EBA-DMAN film (Fig. 9C). The vapor penetration into the surface
materials was improved by the surface oxidation induced by the
plasma.
the EBA-DMAN films were exposed to oxygen plasma for 30 min. Plas-
ma treatment causes cleavage of macromolecular chains, generation of
free radicals and oxygen-containing functionalities, and subsequent
rearrangement of modified chains [39]. Plasma treatment can induce
several surface changes [40], with serious impacts on consequent
applications such as alterations in biocompatibility and antibacterial
properties [41].
These processes have a significant effect on surface wettability. The
content of DMAN bonded to the polymer remained constant after the
treatment, but important changes were observed in the water CA. The
obtained results are summarized in Table 2.
The plasma-treated film EBA-pl-DMAN exhibited a hydrophilic char-
acteristic because of the presence of oxidative species on the surface
42]. The value of the water CA of EBA (7% BA), 106.5°, changed to
2.6° for EBA-DMAN, and after 30 min of treatment with oxygen plasma
EBA-pl-DMAN), this value further decreased to 41°. The measured CAs
[
9
(
were then used to calculate the polar, disperse, and total surface ener-
gies of the modified EBA films. The change in the total surface energy
p
d
(
γ) and its polar (γ ) and dispersive (γ ) components of the modified
EBA films was calculated by Owens–Wendt's method. The variation in
the values of the total, polar, and disperse solid surface energies (Table
) of EBA-DMAN before and after oxygen plasma treatment, EBA-pl-
2
DMAN, shows that the total surface energy of EBA-DMAN increases
The hydrophilicity of the EBA surface clearly improved the sensor ac-
tivity of the DMAN chromophore bonded to the surface.
−
1
−1
from 30.91 mN m
for untreated film to 62.39 mN m
for oxygen
plasma-treated film EBA-pl-DMAN. Compared with the untreated film,
plasma-treated films have higher total surface energy, particularly for
the polar component.
The change in EBA-DMAN surface structure and the topography
after oxygen plasma modification were imaged and measured by AFM.
The AFM images of the untreated and oxygen plasma-treated films are
presented in Fig. 7.
In this study, we have described a useful procedure to modify and
functionalize the polyolefin copolymer EBA, thereby opening the possi-
bility of anchoring numerous interesting structures containing func-
tionalities capable of reaction with acid chlorine groups introduced by
microwave irradiation. The functionalized surface films of EBA-DMAN
act as strong acid sensors in both solution and vapor phases. The post-
functionalization treatment with oxygen plasma decreased the
response time to the acid media and increased the penetration of pro-
tons into the material. This functionalization with dimethylamine
naphthalimide derivatives such as those used in this study or other fluo-
rescence probes could result in a variety of film sensors of significant
interest in environmental applications.
a
The average roughness (R ) of untreated films was 12.5 nm, and
their surface pattern was relatively smooth. After 30 min of oxygen plas-
ma treatment, the treated EBA-pl-DMAN exhibited high density of
height features distributed on the surface (Fig. 7). As expected, the aver-
age roughness was increased to 35.5 nm. The mean surface roughness of
EBA-pl-DMAN was increased by approximately three times, confirming
4. Conclusions
Table 2
In conclusion, we have demonstrated that microwave irradiation al-
p
d
Contact angle (CA) and total (γ), polar (γ ), and disperse (γ ) surface energy data for EBA
7% of BA content) and the surface-modified EBA materials.
lows rapid and efficient attachment of hydroxyl naphthalimide func-
tionalities to superficially acid-chlorinated ethylene-butyl acrylate
copolymers (EBA-COCl). The previous modifications of EBA (7% of BA)
films (hydrolysis and acid chlorination) occur efficiently in a heteroge-
neous phase under our experimental conditions.
CRS was a useful technique to measure the functionalization of the
polymer surface through the depth profile, and the results demonstrat-
ed that the heterogeneous modification was confined to the first 20 μm
from the surface down to the film center.
(
a
Static CA (°)
Water
Surface energy (mN m−1)
p
d
Diiodomethane
γ
γ
γ
EBA
106.5
85.9
92.6
41.0
55.0
66.6
60.8
51.5
29.38
29.51
30.91
62.39
0.38
4.99
2.33
28.44
29.00
24.53
28.58
33.95
EBA-COOH
EBA-DMAN
EBA-pl-DMAN
a
Calculated using Owens–Wendt's method [24].

S. Fernández-Alonso et al. / Reactive and Functional Polymers 107 (2016) 78–86
85
Fig. 7. AFM images and surface roughness (Ra) of the modified polymer films: EBA-DMAN and oxygen plasma-treated EBA-pl-DMAN.
The surface-modified films with N-(2-hydroxyethyl)-4-
fluorescence because of the amine protonation of EBA-DMAN films occurs
at lower pH values than that obtained for DMAN, and the solid sensor was
used to evaluate the molarity of HCl solutions in the interval of 1–12 M.
Oxygen plasma treatment of the functionalized films increased ap-
preciably the hydrophilic characteristic of the surface (EBA-pl-DMAN),
dimethylamino-1,8-naphthalimide (EBA-DMAN) at a concentration of
−
2
2
.4 ± 0.20 μg cm determined by UV-spectroscopy exhibited properties
as a reversible acidity sensor (until 4–5 cycles). The decrease in absor-
bance (ICT absorption band) and the corresponding quenching of
1.0
EBA-pl-DMAN
A
EBA-DMAN
B
C
4
00
00
0
Time
HCl (37 %)
400
200
0
Time
HCl (37 %)
0.5
EBA-pl-DMAN
EBA-DMAN
2
0.0
450
500
550
600
650
450
500
550
600
650
0
10
20 30 40
50 60
70 80
Wavelength (nm)
Wavelength (nm)
Time (min.)
EBA-pl-DMAN
D
EBA-DMAN
E
F
600
400
200
0
600
400
200
0
Initial
Initial
Washed with water
Washed with water
+
HCl (37 %)
+
HCl (37 %)
450
500
550
600
650
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
Fig. 8. Fluorescence decay with time for EBA-DMAN (A) and oxygen plasma-treated EBA-pl-DMAN (B) films using HCl (37% w/w, 12 M) aqueous solution. Response time comparison
between both materials (C) and reversibility of dimethylamine protonation of the functionalized surfaces of EBA-DMAN (D) and EBA-pl-DMAN (E) after washing with distilled water
and (F) fluorescence cells with EBA-pl-DMAN film, initial and after 30 min.

86
S. Fernández-Alonso et al. / Reactive and Functional Polymers 107 (2016) 78–86
0.4
0.3
0.2
0.1
A
324 nm
B
EBA-pl-DMAN
EBA-DMAN
0.6
0.4
0.2
0.0
3
24 nm
Time
HCl vapor
Time
HCl vapor
4
00 nm
4
00 nm
300
400
500
300
400
500
Wavelength (nm)
Wavelength (nm)
6
00
C
EBA-DMAN
D
EBA-pl-DMAN
300
200
100
0
Initial
500
Initial
400
300
200
100
0
HCl vapor
20 minutes
HCl vapor
20 min.
1
1
450
500
550
600
650
700
500
600
700
Wavelength (nm)
Wavelength (nm)
Fig. 9. Absorption changes with HCl vapors as a function of time (0–120 min) for functionalized films of EBA-DMAN (A) and EBA-pl-DMAN (B). Light blue fluorescence (488 nm) decreases
after 120 min of vapors treatment for EBA-DMAN (C) and EBA-pl-DMAN (D). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of
this article.)
[
[
[
12] W. Zhu, C. Hu, K. Chen, H. Tian, Synth. Met. 96 (1998) 151.
13] H. Tian, J. Gan, K. Chen, J. He, Q. Song, X. Hou, J. Mater. Chem. 12 (2002) 1262.
14] I. Grabchev, J.M. Chovelon, Polym. Adv. Technol. 14 (2003) 601.
and the DMAN content bonded to the polymer remained constant after
the treatment. The plasma treatment decreased the response time of the
DMAN fluorescence to a strong acid medium (from 80 min for EBA-
DMAN to 30 min for EBA-pl-DMAN in HCl, 12 M) and thus improved
reversibility.
[15] L. Jia, Y. Zhang, X. Guo, X. Qian, Tetrahedron Lett. 45 (2004) 3969.
[
[
[
16] W. Zhu, M. Hu, R. Yao, H. Tian, J. Photochem. Photobiol. A. 154 (2003) 169.
17] I. Grabchev, I. Moneva, V. Bojinov, S. Guittonneau, J. Mater. Chem. 10 (2000) 1291.
18] I. Grabchev, J.M. Chovelon, X. Qian, J. Photochem. Photobiol. A. 158 (2003) 37.
DMAN films bonded to the polymer were sensitive to the acid vapor
medium, and the films treated with plasma (EBA-pl-DMAN) exhibited a
better behavior in fluorescence decay, confirming that vapor penetra-
tion into the surface materials was improved by the surface oxidation
induced by the plasma.
This new procedure using microwave reactions in a heterogeneous
phase opens up the possibility to attach numerous interesting struc-
tures to polyolefin surfaces for application in materials of significant
value such as environmental solid sensors.
[19] F. Cosnard, V. Wintgens, Tetrahedron Lett. 39 (1998) 2751.
[20] P.L. Shuai Zheng, T.E.R. Mark Lynch, T.S. Moody, H.Q.N. Gunaratne, A.P. de Silva,
Photochem. Photobiol. Sci. 11 (2012) 1675.
[
21] S. Hajatdoost, M. Olsthoorn, J. Yarwood, Appl. Spectrosc. 51 (1997) 1784.
[22] P. Slepicka, Z. Malá, S. Rimpelova, N.S. Kasalkova, V. Svorcik, React. Funct. Polym. 95
(2015) 71.
[
[
[
23] G. Reynolds, K. Drexhage, Opt. Commun. 13 (1979) 222.
24] G.K. Owens, R.C. Wendt, J. Appl. Polym. Sci. 13 (1969) 1741.
25] H. Tian, J. Gan, K. Chen, J. He, Q.L. Song, X.Y. Hou, J. Mater. Chem. 12 (2002) 1262.
[26] Y.Q. Tian, B.R. Shumway, C. Youngbull, A.K.Y. Jen, R.H. Johnson, D.R. Meldrum, Sens.
Actuators B Chem. 147 (2010) 714.
[
[
27] Y.H. Cho, J.C. Park, Tetrahedron Lett. 38 (1997) 8331.
28] S. Rouhani, K. Ghraranjig, M.H. Nezhad, Green Chem. Lett. Rev. 7 (2014) 174.
Acknowledgments
[29] A. Agarwal, P.M.S. Chauhan, Synth. Commun. 34 (2004) 2925.
[
[
[
30] Y. Wan, M. Alterman, M. Larhed, A. Hallberg, J. Org. Chem. 67 (2002) 6232.
31] A. Sharma, V.P. Mehta, E. Van der Eycken, Tetrahedron 64 (2008) 2605.
32] M. Tang, J. Hou, L. Lei, X. Liu, S. Guo, Z. Wamg, K. Chen, Int. J. Pharm. 400 (2010) 66.
This study was supported by MINECO (Project Ref. MAT2012-
3
1709). S. Fernández-Alonso thanks MINECO for a pre-doctoral fellow-
[33] S. Hajatdoost, J. Yarwood, J. Appl. Spectrosc. 50 (1996) 558.
[
[
[
34] J. Sacristán, C. Mijangos, H. Reinecke, J. Spelle, J. Yarwood, Macromolecular 33
2000) 6140.
35] J. Sacristán, H. Reinecke, C. Mijangos, S. Spell, J. Yarwood, Macromol. Chem. Phys.
203 (2002) 678.
36] M.S. Alexiou, V. Tychopoulos, S. Ghorbanian, J.H.P. Tyman, R.G. Brown, P.I. Brittain, J.
Chem. Soc. Perkin Trans. 2 (1990) 837.
ship linked to the project.
(
References
[
[
[
1] L.S. Penn, H. Wang, Polym. Advan. Technol. 5 (1994) 809.
2] S.M. Desai, R.P. Singh, Adv. Polym. Sci. 169 (2004) 231.
3] L. López-Vilanova, I. Martinez, T. Corrales, F. Catalina, React. Funct. Polym. 85 (2014)
[37] P.A. Panchencko, O.A. Fedorova, Y.V. Fedorov, Russ. Chem. Rev. 82 (2014) 155.
[38] K.A. Connors, Binding Constants: The Measurement of Complex Stability, Wiley,
New York, 1987.
28.
[
[
[
4] V. Gaud, F. Rougé, Y. Gnanou, React. Funct. Polym. 72 (2012) 521.
5] M. Kondo, K. Goto, Y. Dozono, N. Kawatsuki, React. Funct. Polym. 73 (2013) 1567.
6] F. Gicogna, S. Coiai, C. Pinzino, F. Ciardelli, E. Passaglia, React. Funct. Polym. 72
[39] N. Slepičková Kasálková, P. Slepička, Z. Kolská, P. Sajdl, L. Bačáková, S. Rimpelová, V.
Švorčík, Nucl. Instrum. Meth. B 272 (2012) 391.
[40] P. Slepička, S. Trostová, N. Slepičková Kasálková, Z. Kolská, P. Sajdl, V. Švorčík, Plas-
ma Process. Polym. 9 (2012) 197.
(2012) 885.
[
[
[
7] I. Grabchev, R. Betcheva, J. Photochem. Photobiol. A. 73 (2001) 142.
8] K. Wang, W. Huang, P. Xia, C. Gao, D. Yan, React. Funct. Polym. 52 (2002) 143.
9] E. Martin, R. Weigand, A. Pardo, J. Lumin. 68 (1996) 157.
[41] P. Slepička, N. Kasálková-Slepičková, J. Siegel, Z. Kolská, L. Bačáková, V. Švorčík, Bio-
tech. Adv. 33 (2015) 1120.
[42] Y. Zheng, J. Miao, F. Zhang, C. Cai, A. Koh, T. Simmons, React. Funct. Polym. 100
(2016) 142.
[
[
10] W. Stewart, J. Am. Chem. Soc. 103 (1981) 7615.
11] S. Banerjee, E.B. Veale, C.M. Phelan, S.A. Murphy, G.M. Tocci, L.J. Gillespie, D.O.
Frimannsson, J.M. Kelly, T. Gunnlaugsson, Chem. Soc. Rev. 42 (2013) 1601.