Polymer nanoparticles self-assembled from photo-, pH- and thermo-responsive azobenzene-functionalized PDMAEMA

Article abstract of DOI:10.1039/c5ra26894j

A series of amphiphilic azobenzene-functionalized poly(dimethylaminoethyl methacrylates) have been synthesized by quaternization between [3-(4-(4-bromo-butyloxy)phenyl)-trifluoromethyl]-diazene and the dimethylaminoethyl units of poly(dimethylaminoethyl m

Full text of DOI:10.1039/c5ra26894j

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PAPER
Polymer nanoparticles self-assembled from photo-, pH- and
thermo-responsive azobenzene-functionalized PDMAEMA
Tingting Yuan, Jie Dong, Guoxiang Han, Guojie Wang*
A series of amphiphilic azobenzene-functionalized poly (dimethylaminoethyl methacrylates) have been synthesized by
quaternization between [3-(4-(4-bromo-butyloxy)phenyl)-trifluoromethyl]-diazene and the dimethylaminoethyl units of
poly(dimethylaminoethyl methacrylate) (PDMAEMA). The azobenzene-functionalized polymers could self-assemble into
micellar nanoparticles in water. Upon UV light irradiation, the spherical nanoparticles could only swell a little. Although the
loaded Nile Red could not be released from the nanoparticles under UV light irradiation, the fluorescence intensity of Nile
Red changed reversibly when altering UV and visible light irradiation. At pH 3, the nanoparticles could be swelled greatly
and the loaded Nile Red could be released completely. At pH 10, the nanoparticles could be shrunk and the loaded Nile
Red could be released a little. At high temperature, the nanoparticles could be shrunk, where little of Nile Red could be
released from the nanoparticles, while the fluorescence intensity of Nile Red could change reversibly during the heating
and cooling process.
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
reported multiple responsive micellar nanoparticles self-
assembled from polymers comprised of photo-responsive
1. Introduction
pyrene-,
perylene-
and
nitrobenzyl-containing
In the past few decades, stimuli-responsive polymers that
respond to external stimuli such as light,1 temperature,2 pH
value3 and enzyme4 have attracted significant attention in
material science and technology due to their applications in
developing smart materials.5 Among them, stimuli-responsive
amphiphilic polymers which can self-assemble into
nanoparticles in aqueous media draw a lot of attention
because of their potential applications in catalysis,6
nanoreactors,7 logic gates,8 and drug delivery.9 Zhao’s group
designed a micellar system that could be dissociated upon UV
or near-infrared irradiation based on a diblock copolymer
comprising hydrophilic PEO and hydrophobic PNBM.10 Ren et
al. reported a pH-responsive dendritic star-block copolymer
PCL-b-PDMAEMA which could self-assemble into complex
micelles with bimodal size distribution in aqueous solution.11
Shi et al. prepared temperature-responsive multilayered
micelles formed from the complexation of PNIPAM-b-P4VP
block-copolymer and PS-b-PAA core-shell micelles.12 Most of
the stimuli-responsive nanoparticles reported so far are
focused on being responsive to a single stimulus. Multiple
stimuli-responsive systems, which can achieve more
functionalities and be modulated through more parameters,
may present many intriguing possibilities.13,14 We have ever
polymethacrylate
and
temperature/pH-responsive
poly(dimethylaminoethyl methacrylate) (PDMAEMA).15-19
Photo and pH responsive polymer nanoparticles self-
assembled from azobenzene and pyrene functionalized
polymers based on poly(acrylic acid) (PAA) have also been
explored.20,21 Here we report a photo-, pH- and thermo-
responsive polymer nanoparticle self-assembled from
azobenzene-functionalized PDMAEMA.
Poly(2-(N,
N-dimethylamino)ethyl
methacrylate)
(PDMAEMA) is
a
pH- and thermo-responsive polymer.22
PDMAEMA exhibits pH-responsive behavior because of the
protonation/deprotonation of amine groups in the polymer,
which is partially charged at neutral pH. In addition,
PDMAEMA also exhibits temperature-responsive behavior
because of the H-bonding interactions between the polymer
and water at low temperature (hydrophilic) and the
hydrophobic interactions between N,N-dimethylaminoethyl
groups at high temperature (hydrophobic).23 It is well known
that azobenzene undergoes trans to cis isomerization under
UV irradiation resulting in a shape change accompanied by an
increase in the dipole moment of the molecule.24-26 It is noted
that light is a clean and highly efficient stimulation source
which can be triggered from outside of the system and
controlled both spatially and temporally with great ease and
convenience.27 To achieve the triple-stimuli sensitive polymer,
light-sensitive azobenzene chromophore was incorporated
into temperature/pH sensitive polymer (PDMAEMA) through
quaternization with the dimethylaminoethyl unit. The
School of Materials Science and Engineering, University of Science and Technology
Beijing, Beijing 100083, China. *E-mail: guojie.wang@mater.ustb.edu.cn; phone:
86-10-62333619
† Electronic Supplementary Information (ESI) available: 1H NMR, GPC, UV/vis
absorption spectra and fluorescence spectra See DOI:10.1039/c000000x
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synthesized azobenzene-functionalized PDMAEMA could self- (THF, 8 mL), ethy 2-bromoisobutyrate (EBIB, 0.065 mL, 5.3 ×
assemble into nanoparticles in water, the morphological 10-4 mol) and dimethylaminoethyl methacrylate (DMAEMA,
changes of which under the stimulation were revealed by DLS 8.334 g, 5.3 × 10-2 mol) under a N2 atmosphere with a stirrer.
and TEM. Moreover, the properties of the loaded Nile Red, a The reaction mixture was deoxygenated more than three
hydrophobic dye, in the polymer nanoparticles were also times using freeze-pump-thaw cycles and sealed. Then the
explored under the stimulation of photo, pH and temperature flask was placed in an oil bath at 70 °C for 12 h. The solution
by absorption and fluorescence spectroscopy.
was diluted with dichloromethane and passed through an
alumina column to remove the copper salts. The polymer was
precipitated twice from an excess of hexane, filtered and dried
at 40 °
C under vacuum for 48 h. Yield : 72% 1H NMR (400 MHz,
2. Experimental
CDCl3) δ (ppm): 4.1 (t, 2H, OCH2CH2N(CH3)2), 2.6 (t, 2H,
OCH2CH2N(CH3)2), 2.3 (s, 6H, OCH2CH2N(CH3)2), 2.1-1.6 (broad,
2H, aliphatic main chain), 1.3-0.7 (broad, 3H CH3 main chain).
GPC: Mn= 2.0 × 104 g mol-1, PDI = 1.08.
2.1 Materials
2-(Dimethylamino)
(Trifluoromethyl) aniline, ethyl α-bromoisobutyrate (98%),
copper bromide (98%), 1,1,4,7,10,10-
ethy
methacrylate
(99%),
3-
Synthesis of 4-(3-trifluoromethylphenylazo) phenol (AZO-A)
hexamethyltriethylenetetramine (97%), Phenol from Aldrich
and the conventional reagents were used as received. All
atmosphere sensitive reactions were done under nitrogen.
Deionized water with a conductance below 10-6 S cm-1 was
used in the experiments.
：
3-(Trifluoromethyl) aniline (3.22 g, 20 mmol) was dissolved
in an aqueous solution of sodium nitrite (1.39 g in 7mL of
deionized water). The obtained solution was cooled to 0-5 °C
and then hydrochloric acid (6 mL) in 12 mL deionized water
was added slowly with stirring in ice bath. After a clear
solution of the diazonium salt was formed, the solution was
added dropwise into a solution of phenol (1.88 g, 20 mmol),
sodium hydroxide (1.2 g, 30 mmol) and deionized water (10
mL) at 0-5 °C. The mixture was vigorously stirred for 30 min in
ice bath and hydrochloric acid aqueous solution was added to
adjust the pH to 5-7. The solution was kept for 30 min, and
then the solid was filtered and dried under vacuum at room
temperature. After recrystallized from petroleum ether, the
2.2 Polymer Synthesis
Azobenzene-functionalized
PDMAEMA
was
prepared
according to the reported procedures.15,20 The synthetic route
is shown in Scheme 1.
CH3
CH3
H2C
C
C
O
CH2
C
C
O
x
O
O
CuBr, PMDETA, EBIB
THF, 65 , 24h
CH2
CH2
N
CH2
CH2
N
1
final yellow powder was obtained. Yield: 70%. m.p. 112 °C. H
H3C
CH3
H3C
CH3
NMR (400 MHz, CDCl3) δ (ppm): 8.120 (s, 1H, ArH), 8.028-8.047
(d, 1H, ArH), 7.883-7.905 (d, 2H, ArH), 7.665-7.684 (d, 1H,
ArH), 7.587-7.626 (t, 1H, ArH), 6.936-6.958 (d, 2H, ArH),
5.218(s, 1H, OH).
F3C
OH
N
OH
NH2
N
HCl , NaNO2
F3C
AZO-A
Synthesis
of
[3-(4-(4-bromo-butyloxy)phenyl)-
(AZO-B): 4-(3-
trifluoromethyl]-diazene
Br(CH2)4Br
acetone 63
N
N
O(CH2)4Br
Trifluoromethylphenylazo) phenol (0.532 g, 2 mmol) was
dissolved in acetone (50 mL), in which 1, 4-dibromobutane
(2.16 g, 10 mmol), K2CO3 (2.73 g, 20 mmol) and a catalytic
amount of KI (0.28 g) were added. The reaction mixture was
stirred at 65 °C for 24 h. Then the reaction mixture was cooled
to room temperature and poured into water (1.5 L). The
precipitate was collected by filtration. Purification of the crude
material was achieved by twice recrystallization from n-hexane
and then the orange crystal was obtained. Yield: 59%. m.p. 38
°C. 1H NMR (400 MHz, CDCl3) δ (ppm): 8.122 (s, 1H, ArH),
8.029-8.048 (d, 1H, ArH), 7.919-7.939 (d, 2H, ArH), 7.659-7.678
(d, 1H, ArH), 7.584-7.623 (t, 1H, ArH), 7.023-7.109 (d, 2H, ArH),
4.100-4.146 (t, 2H, OCH2CH2CH2CH2Br), 3.725-3.963 (t, 2H,
OCH2CH2CH2CH2Br), 1.978-2.051 (m, 2H, OCH2CH2CH2CH2Br),
1.830-1.905 (m, 2H, OCH2CH2CH2CH2Br).
，
， 24h
F3C
AZO-B
O(CH2)4Br
CH3
CH3
CH3
CH2
C
C
O
CH2
C
y
CH2
C
C
O
x
O
x
O
m
THF, 65 , 24h
C
O
O
N
N
CH2
CH2
CH2
CH2
N
CH2
CH2
N
N
Br
CH
H3C
H3C
CH3
3H3C
CH3
CH2
4
CF3
O
N
N
CF3
Scheme 1. Synthetic route of the azobenzene-functionalized
Synthesis
of
azobenzene-functionalized
PDMAEMA
polymer PDMAEMA-AZO
(PDMAEMA-AZO) with DF of 4%: The synthesized PDMAEMA
(0.314 g, 2 mmol) and AZO-B (0.16 g, 0.4 mmol) were dissolved
in THF (20 ml) and then stirred for 24 h at 65 °C. Then the
polymer PDMAEMA-AZO was precipitated from an excess of
hexane, filtered and dried at 40°C under vacuum for 48 h.
Yield: 73%. 1H NMR (400 MHz, CDCl3) δ (ppm): 7.017-8.113
PDMAEMA was synthesized via atom transfer radical
polymerization (ATRP). In a typical experiment, a 10 ml Schlenk
flask dried under vacuum were charged with CuBr (0.076 g,
5.3×
10-4 mol), 1,1,4,7,10,10-hexamethyltriethylenetetramine
(HMTETA, 0.144 g, 5.3×
10-4 mol), anhydrous tetrahydrofuran
2 | Poly., 2012, 00, 1-3
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(ArH), 4.385-4.415 (OCH2CH2CH2CH2), 4.023 (CH2CH2N(CH3)2), were determined by a gel permeation chromatography (GPC)
3.453 (OCH2CH2CH2CH2), 2.529 (CH2CH2N(CH3)2), 2.250 (Waters 1515) with styragel columns relative to polystyrene
(CH2CH2N(CH3)2), 1.969-2.101 (OCH2CH2CH2CH2), 1.790-1.880 standards using tetrahydrofuran (THF) as eluent. Fourier
(broad, 2H, aliphatic main chain), 0.868-1.395 (broad, 3H, CH3 transform infrared (FTIR) spectra were recorded on
main chain).
PerkinElmer spectrophotometer at room temperature.
Synthesis of PDMAEMA-AZO with DF of 9%: PDMAEMA Polymer nanoparticles were examined using a JEM 2010 TEM
(0.317 g, 2 mmol) and AZO-B (0.45 g, 1.11 mmol) were operating at 100 kV. The samples for TEM observation were
dissolved in THF (20 ml) and then stirred for 24 h at 65 °C. The prepared by placing 5 μL of nanoparticle solution onto carbon-
polymer was precipitated twice from an excess of hexane, coated copper TEM grid. Dynamic light scattering (DLS)
filtered and dried at 40°C under vacuum for 48 h. Yield: 78%. experiments and zeta-potentials were carried out on the
1H NMR (400 MHz, CDCl3) δ (ppm): 7.240-8.081 (ArH), 4.381- ALV/SP-150 spectrometer equipped with an ALV-5000 multi-
4.415 (OCH2CH2CH2CH2), 4.022 (CH2CH2N(CH3)2), 3.470 digital time correlator and a solid-state laser (ADLS DPY 425II,
(OCH2CH2CH2CH2),
(CH2CH2N(CH3)2), 1.977-2.103 (OCH2CH2CH2CH2), 1.792-1.883 The fluorescence spectra were recorded on
(broad, 2H, aliphatic main chain), 0.868-1.395 (broad, 3H, CH3 fluorescence spectrophotometer. The UV-vis spectra of the
main chain). samples were recorded by a JASCO V-570 spectrometer. A UV-
2.540
(CH2CH2N(CH3)2),
2.254 output power ca. 400 MW at λ = 632.8 nm) as the light source.
a
F-280
Synthesis of PDMAEMA-AZO with DF of 17%: PDMAEMA LED irradiator (LAMPLIC UVEC-4 , λ= 365 nm) and a VIS-LED
(0.264 g, 1.68 mmol) and AZO-B (0.3 g, 1.11 mmol) were irradiator (LAMPLIC UVEC-4 , λ= 450 nm) were used to induce
dissolved in THF (20 ml) and then stirred for 24 h at 65 °C. The the photo-isomerization of azobenzene.
polymer was precipitated twice from an excess of hexane, 2.5 Degree of Functionalization
filtered and dried at 40°C under vacuum for 48 h. Yield: 65%.
The degree of functionalization (DF) of PDMAEMA-AZO was
1H NMR (400 MHz, CDCl3) δ (ppm): 7.001-8.072 (ArH), 4.381-
determined by UV-vis spectroscopy. As the molar absorptivity
4.415 (OCH2CH2CH2CH2), 4.018 (CH2CH2N(CH3)2), 3.506
ε (λmax) in the range of 300 to 400 nm of the azobenzene
(OCH2CH2CH2CH2),
2.521
(CH2CH2N(CH3)2),
2.241
chromophores in the polymer was assumed to be almost the
same as that of the corresponding molecule [3-(4-(4-bromo-
butyloxy)phenyl)-trifluoromethyl]-diazene (AZO-B), the degree
of azobenzene-functionalization was calculated from the
absorption intensities of the azobenzene-functionalized
polymer and the compound AZO-B in THF.
(CH2CH2N(CH3)2), 1.956-2.101 (OCH2CH2CH2CH2), 1.794-1.881
(broad, 2H, aliphatic main chain), 0.861-1.224 (broad, 3H, CH3
main chain).
2.3 Preparation of Polymer Nanoparticles and Encapsulation of
Nile Red10,19
Preparation of polymer nanoparticles: The azobenzene- 2.6 Critical Aggregation Concentration
functionalized polymer PDMAEMA-AZO (2 mg) was first
The critical aggregation concentration (CAC) of the
dissolved in THF (1 mL). Then suitable amount of water (1 mL)
was added dropwise into the solution at a rate about 5-6 drop
min-1 with stirring to induce the formation of the
nanoparticles. After 3 h of stirring, more water (9 mL) was
added to quench the nanoparticles. THF was removed by
evaporation for 7 days at room temperature.
azobenzene-functionalized polymer PDMAEMA-AZO was
determined by the fluorescent method with Nile Red as a
probe. Polymer nanoparticles loaded with Nile Red in aqueous
solution were prepared with concentrations ranging from 0.5
mg mL-1 to 0.0001 mg mL-1. Then fluorescence measurements
were taken at an excitation wavelength of 550 nm and the
emission monitored from 560 to 750 nm. The maximum
fluorescence intensity emission was plotted against the
logarithm of polymer concentration to measure the critical
aggregation concentration.
Preparation of polymer nanoparticles loaded with Nile Red:
The azobenzene-functionalized polymer PDMAEMA-AZO (2
mg) and Nile Red (0.2 mg) were dissolved in THF (1 mL); 1 mL
of water was then added dropwise into the solution at a rate
about 5-6 drop min-1 with stirring to induce the formation of
nanoparticles and the simultaneous encapsulation of Nile Red.
The driving force for encapsulation of Nile red is the
hydrophobic interaction between the dye and hydrophobic
segments of the azobenzene-functionalized polymer. After 3 h
of stirring, more water (9 mL) was added to quench the
nanoparticles. THF was removed by evaporation and
precipitated NR was filtered by microfiltration (450 nm pore
filter). The polymer nanoparticles with different pH were
obtained by adding aqueous HCl or NaOH solutions to the
above solutions.
3. Results and Discussion
3.1 Synthesis and Characterization.
The azobenzene-functionalized polymer PDMAEMA-AZO has
been successfully synthesized as described in the following and
the procedure is shown in Scheme 1. The pH- and thermo-
responsive polymer PDMAEMA was first synthesized through
atom transfer radical polymerization (ATRP) of the monomer
DMAEMA, the number-average molecular weight (Mn) and
polydispersity index (PDI) of which were determined to be 2.0
× 104 g mol-1 and 1.08, respectively, by gel permeation
chromatography (GPC), shown in Figure S1. Then [3-(4-(4-
bromo-butyloxy)phenyl) -trifluoromethyl]-diazene was
synthesized and incorporated into PDMAEMA through
2.4 Instrumental Analysis
1H NMR spectra were recorded from CDCl3 solution on a
Bruker AM 400 spectrometer. The average molecular weights
and molecular weight distributions of the obtained polymers
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quaternization with the dimethylaminoethyl unit to achieve The UV-vis measurements were performed to examine the
the azobenzene-functionalized PDMAEMA with DF of 4%, 9% photoisomerization behavior of the azobenzene-functionalized
and 17%. The incorporation of trifluoromethyl group into polymer in THF. As shown in Figure 3, the absorption bands at
azobenzene was expected to obtain a large polarity change 352 and 442 nm were ascribed to the π-π* transition of the
during the process of photo-isomerization from trans to cis.20 trans form and n-π* transition of the cis form of the
azobenzene group, respectively. Upon UV light irradiation, the
absorption band at 352 nm became progressively weaker with
the increase of irradiation time, while the absorption band at
442 nm slightly increased, shown in Figure 3a. The changes of
the absorption bands induced by UV irradiation were
indicative of the photo-isomerization of the trans-azobenzene
to the cis-azobenzene. Then the polymeric solution was
exposed to visible light of 450 nm, and the opposite change of
UV-vis spectra could be observed, shown in Figure 3b, which
implied the process of back-conversion from cis to trans form.
Figure 1.1H NMR spectrum of PDMAEMA-AZO with DF of 4% in
CDCl3
100
Figure 3. UV-vis spectra of the azobenzene-functionalized
80
polymer (DF, 4%) in THF under irradiation of UV light (365 nm,
5 mW cm-2) (a) and visible light (450 nm, 7 mW cm-2) (b),
PDMAEMA
4% Azo
9% Azo
60
respectively.
40
20
0
3.3 Self-assembly of PDMAEMA-AZO in Water.
The synthesized azobenzene-functionalized polymers are
amphiphilic polymers composed of hydrophobic azobenzene
units and hydrophilic unquaternized PDMAEMA and
quaternized amine groups. When the azobenzene-
functionalized polymers dissolve in water at room
temperature and neutral pH, the random copolymers may self-
assemble into supramolecular multimolecular micelles,29,30
where the hydrophobic azobenzene units form the core and
the hydrophilic unquaternized PDMAEMA and quaternized
amine groups form the shell. As a strong evidence for self-
assembly behavior of amphiphilic polymers into nanoparticles,
CAC value of PDMAEMA-AZO with DF of 4% in aqueous
solution was measured to be 0.09 mg mL-1, shown in Figure 4a.
The CAC values of the copolymers with DF of 9% and 17% were
measured to be 0.05 and 0.04 mg mL-1, respectively, shown in
Figure S4. The CAC values decreased with the increase of the
functionalization degree, since the increased hydrophilicity
could enhance the thermodynamical stability of the self-
assembled nanoaggregates.31,32 Transmission electron
microscopy (TEM) and Dynamic light scattering (DLS) were
used to investigate the self-assembled nanostructures of the
polymer PDMAEMA-AZO. Figure 4b shows the TEM image of
the polymer nanoparticles, from which it can be seen that the
core-shell spherical structure with a diameter of approximately
120 nm was formed. Figure 4c shows the size distribution
20 30 40 50 60 70 80 90
Temperature / °C
Figure 2. Temperature dependence of optical transmittance at
500 nm for the aqueous solutions of PDMAEMA and
PDMAEMA-AZO with DF of 4% and 9%.
1
Figure 1 shows the typical H NMR spectrum of the polymer
PDMAEMA-AZO with DF of 4%. The FTIR spectra of PDMAEMA,
PDMAEMA-AZO with DF of 4%, 9% and 17% are shown in
Figure S3, from which it can be seen that a carbon-nitrogen
vibration peak from the ammonium groups at 3420 cm-1
increased with the increase of DF. The LCST curves of
PDMAEMA and PDMAEMA-AZO with DF of 4% and 9% are
shown in Figure 2. The LCST of the synthesized PDMAEMA was
measured to be 43°C, while the LCST of the copolymer
PDMAEMA-AZO with DF of 4% increased to 57°C and the LCST
of the copolymer with DF of 9% was too high to be detectable.
The LCST increased with the increase of the degree of
functionalization, since the functionalization endowed the
polymer with hydrophilic quaternary ammonium groups and
the increase of hydrophilicity of the polymer induced the
increase of LCST.28
3.2 Photo-responsive Properties of PDMAEMA-AZO in THF.
4 | Poly., 2012, 00, 1-3
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curve of the polymer nanoparticles obtained from DLS shown in Figure 5b, indicating the reversible isomerization
experiment, where the hydrodynamic diameter (Dh) of the from cis-azobenzene to trans-azobenzene. It should be noted
polymer nanoparticle was about 125 nm. The TEM images of that the absorption bands blue-shifted 2 nm compared with
the polymer assemblies from PDMAEMA-AZO with DF of 9% those in THF (shown in Figure 3), which confirmed that the
and 17% are shown in Figure S5 and S6, from which it can be azobenzene units formed H-aggregates in the nanoparticles.33
seen that the diameters of the nanoparticles from the two Figure 5c shows the TEM image of the nanoparticles after UV
polymers were approximately 120 nm and 130 nm, light irradiation, where the spherical morphology of polymer
respectively.
nanoparticles could be still observed and the size of the
nanoparticles increased to 125 nm. Figure 5d shows the DLS
curves of the nanoparticles before and after UV light
irradiation and then after visible light irradiation, from which it
can be seen that the Dh of nanoparticles increased from 125
nm to 138 nm under UV light irradiation, subsequently, when
visible light was applied, the Dh of nanoparticles could be
recovered (125 nm). The photo-responsive morphological
changes of nanoparticles self-assembled from the polymers
with DF of 9% and 17% are shown in Figure S5 and S6, from
which it can be seen that the spherical nanoparticles could be
also swollen a little after UV light irradiation. Under UV light
irradiation, the trans-azobenzene can be isomerized to the cis-
azobenzene, resulting in the increase of the polarity of
azobenzene. In this study, although the trifluoromethyl-
azobenzene with a large polarity change upon UV irradiation
was introduced,20 this polarity change is still insufficient, which
can not result in dissociation of the micellar aggregates,34
where the cis-azobenzene units still exist in the core.
Figure 4. (a) Plot of the maximum fluorescence emission
intensity of Nile Red (λex=550 nm) vs the log of concentration
of the polymer PDMAEMA-AZO (DF, 4%). Inset: Fluorescence
emission spectra of Nile Red in aqueous polymer solution with
different concentrations of the polymer. (b) and (c) TEM image
and DLS curve of the nanoparticles self-assembled from the
polymer PDMAEMA-AZO (DF, 4%).
3.4 Photo-responsive Behaviors of Nanoparticles .
To evaluate the photo-responsive properties of the polymer
nanoparticles, UV-vis spectrophotometer was employed to
monitor the absorption spectra upon irradiation of UV light
(365 nm, 5 mW cm-2) and visible light (450 nm, 7 mW cm-2).
Figure 5a shows the UV-vis absorption spectra of the polymer
nanoparticles self-assembled from the polymer with DF of 4%
upon UV light irradiation, from which it can be seen that the
intensity of the π-π* transition band at 350 nm decreased
while the intensity of the n-π* transition band at 440 nm
slightly increased with the increase of UV irradiation time,
indicating the isomerization from trans-azobenzene to cis-
azobenzene. The photostationary state for the copolymer with
DF of 4% was obtained after irradiating for 30 seconds. It is
noted that it took more time to reach the balance between cis
and trans when the degree of azobenzene functionalization
increased. For the copolymers with DF of 9% and 17%, the
photosationary time increased to 60s and 80s, respectively
(see ESI†). When the polymer solution was subsequently
exposed to visible light irradiation, the absorption band of π-
π* transition increased and the n-π* transition band decreased,
Figure 5. (a) and (b) UV-vis spectra of the nanoparticles from
the polymer PDMAEMA-AZO (DF, 4%) under irradiation of UV
light (365 nm, 5 mW cm-2) and visible light (450 nm, 7mW cm-
2), respectively. (c) TEM image of the nanoparticles after UV
irradiation. (d) DLS curves of the nanoparticles before and
after UV light irradiation and then after visible light irradiation.
Nile Red, a model hydrophobic dye, is well known for
monitoring the formation and disruption of the nanoparticles
under stimulation. Figure 6a shows the UV-vis absorption
spectral change of the nanoparticle self-assembled from the
polymer with DF of 4% loaded with Nile Red exposed to UV
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light for various time. Under UV light irradiation, a remarkable in sensor technology which requires no leakage of the
decrease of the absorption band at 350 nm was observed encapsulated substances for preventing environment from
accompanied by an increase of the absorbance at 440 nm due pollution and in catalyst system because the change of
to the trans-to-cis photoisomerization of azobenzene, while hydrophobicity might affect the activity of catalysts so as to
the absorption band of Nile Red changed little, as indicated no control the chemical reactions by light.39
leakage of Nile Red. Figure 6b shows the fluorescence intensity 3.5 pH-responsive Behaviors of Nanoparticles .
change of loaded Nile Red upon UV irradiation for different
It is well-known that PDMAEMA can be protonated in an acidic
time, from which it can be seen that the fluorescence intensity
aqueous solution, which leads to an increase of hydrophilicity,
of Nile Red decreased with increasing UV irradiation time since
while PDMAEMA chains can be shrunk in alkaline aqueous
the nanoparticles became more polar after UV irradiation.
solution because of the deprotonation of tertiary amine
groups.40 Figure 7a shows the DLS plots of the polymer
Figure 6c shows the fluorescence intensity of Nile Red
recovered to the initial value when the nanoparticles were
nanoparticles self-assembled from PDMAEMA-AZO with DF of
illuminated with visible light. Figure S9 shows the UV-vis
4% under acidic and alkaline conditions. Under acidic condition
spectra of the nanoparticles self-assembled from the polymers
(pH 3), the nanoparticles could be swollen, where the Dh of the
with DF of 9% and 17% loaded with Nile Red under UV light
nanoparticle increased to 300 nm, much larger than that in a
irradiation, where the photo-isomerization of azobenzene
neutral environment, resulted from the protonation of the
could be observed and no leakage of Nile Red occurred either,
tertiary amine groups in PDMAEMA segments and the increase
whereas the fluorescence intensity of loaded Nile Red changed
of hydrophilicity. Under alkaline condition (pH 10), the
reversibly when altering UV and visible irradiation (Figure S11).
nanoparticles were shrunk and then aggregated, where the Dh
It is known that Nile Red is an uncharged hydrophobic
of the nanoparticles increased to 400 nm. Figure 7b shows the
molecular whose fluorescence is strongly influenced by the
zeta potentials of the polymer nanoparticles were measured to
polarity of its environment, the emission of which can be
quenched when the environment becomes more polar.35,36
respectively. The potential increased with the decrease of pH
The fluorescence change of Nile Red could be resulted from
be 0.6, 34.3, 38.3 and 42.8 mV at pH 10, 7, 5 and 3,
value since more PDMAEMA could be protonated at lower pH.
the polarity change of azobenzene in the nanoparticle. Upon
The pH-responsive morphological changes of nanoparticles
UV light irradiation, the azobenzene could be isomerized to
self-assembled from the polymers with DF of 9% and 17% are
the cis form with a higher polarity, which would induce a
shown in Figure S5 and S6, from which it can be seen that the
decrease in emission of Nile Red,37,38 while the polarity and
nanoparticles were also swollen under acidic condition and
emission could be recovered when the cis form isomerized to
shrunk under alkaline condition.
the trans form upon visible irradiation. Although the photo
The controlled release of Nile Red at various pH from
stimulation had little effect on the release of Nile Red loaded
polymer nanoparticles were monitored through UV-vis
in the nanoparticles, the fluorescence intensity of Nile Red
absorption spectroscopy and fluorescence spectroscopy.
could change reversibly when altering UV and visible
Figure 7c shows the UV-vis absorption spectra of Nile Red
irradiation. The photo-responsive system may find applications
loaded in the polymer nanoparticles self-assembled from
PDMAEMA-AZO (DF, 4%) at different pH. At pH 10, the
absorbance of Nile Red decreased about 10% compared with
the initial value at pH 7, indicating that only some Nile Red
could be released from the nanoparticles and most of Nile Red
was still encapsulated in the nanoparticles. At pH 5, the
absorbance of Nile Red decreased about 75%, indicating that
the most Nile Red was released. At pH 3, the loaded Nile Red
could be released completely, since the absorbance
disappeared. Figure 7d shows the fluorescence change of Nile
Red under different pH. At pH 10, the fluorescence intensity of
Nile Red at 638 nm decreased about 10%, compared with the
intensity at pH 7. At pH 5, the fluorescence intensity of Nile
Red decreased about 75% and totally disappeared at pH 3,
which were consistent with the results of UV absorbance.
Since the polymer nanoparticles could be swelled at acidic
condition or under UV light irradiation, the combined
Figure 6. (a) UV-vis spectra of the nanoparticles self-assembled
stimulation of pH 5 and UV light irradiation could be applied to
from PDMAEMA-AZO (DF, 4%) loaded with Nile Red under UV
enhance the release of encapsulated molecules from the
light irradiation (365 nm, 5 mW cm-2). (b) and (c) Fluorescence
nanoparticles. Figure S10 shows that the release could be
spectra of the nanoparticles loaded with Nile Red under UV
enhanced indeed upon the combined stimulation compared
light irradiation (365 nm, 5 mW cm-2) and visible light
with those under single stimulation. The controlled release of
irradiation (450 nm, 7 mW cm-2), respectively.
Nile Red from the nanoparticles self-assembled from the
copolymers with DF of 9% and 17% could be also realized
6 | Poly., 2012, 00, 1-3
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ARTICLE
under pH stimulation just like that from the copolymer with DF change of loaded Nile Red in the nanoparticles of the
of 4%. It is noted that the random copolymer system provided copolymers with DF of 9% and 17% could be also observed
a burst release of encapsulated molecules at acidic pH, while a during the process of heating and cooling, shown in Figure S15.
sustained release could be achieved from carboxylic acid
functionalized copolymer micelles at basic pH.41
Figure 8. (a) and (b) TEM image and DLS curve of the
nanoparticles self-assembled from PDMAEMA-AZO with DF of
Figure 7. (a) and (b) DLS curves and zeta potentials of the
4% when heating to 60
(λex=550 nm ) of the nanoparticles loaded with Nile Red
through a heating process from 20 to 60 and the
C, respectively.
°C. (c) and (d) Fluorescence spectra
nanoparticles self-assembled from PDMAEMA-AZO with DF of
4% at different pH, respectively. (c) and (d) UV-vis absorption
and fluorescence spectra of Nile Red loaded in the
nanoparticles at different pH, respectively.
°C
subsequent cooling process from 60 to 20
°
3.6 Thermo-responsive Behaviors of Nanoparticles .
4. Conclusions
PDMAEMA, as we know, exhibits a reversible thermo-sensitive
phase transition in aqueous solution. Below LCST, PDMAEMA
is hydrophilic, while it exhibits hydrophobic above LCST since
the hydrogen bonding between the polymer chains and water
will be broken at high temperature. Figure 8a shows the TEM
image of the nanoparticles self-assembled from the copolymer
with DF of 4% when heated to 60 °C (above the LCST), from
which it can be seen that the size decreased to 80 nm, due to
the shrinkage of the nanoparticles where the hydrophobic
interactions between N,N-dimethylaminoethyl groups could be
dominated. Figure 8b shows the DLS curve of the nanoparticles
when heating to 60 °C, where the Dh decreased to 105 nm. The
thermo-responsive morphological changes of nanoparticles
self-assembled from the polymers with DF of 9% and 17% are
shown in Figure S5 and S6, from which it can be seen that the
nanoparticles were also shrunk at high temperature.
A
series of novel amphiphilic azobenzene-functionalized
polymers have been successfully prepared by incorporating
the photo-responsive azobenzene unit into the pH- and
thermo-responsive PDMAEMA through quaternization
reaction. The LCST increased with the increase of the
functionalization degree. The amphiphilic random copolymers
could self-assemble into micellar nanoparticles in water. The
CAC values decreased with the increase of the
functionalization degree. Upon UV light irradiation, the trans
azobenzene changed to the cis form and thus the polarity of
the nanoparticles increased, while the nanoparticle could only
swell a little. Although the loaded Nile Red in the polymer
nanoparticles could not be released under UV light irradiation,
the fluorescence intensity of Nile Red changed reversibly when
altering UV and visible light irradiation for the reversible
change of the polarity. Under acidic condition, the
nanoparticles swelled a lot due to the protonation of the
tertiary amine groups in PDMAEMA segments and the loaded
Nile Red could be released. Under alkaline condition, the
nanoparticles could be shrunk and aggregated owing to the
deprotonation of PDMAEMA segments and the loaded Nile
Red could be released only a little. When the temperature
increased, the nanoparticles shrank, while the Nile Red was
still encapsulated in the nanoparticles. The fluorescence
intensity of loaded Nile Red could be increased upon heating
and decreased upon cooling due to the reversible changes
between hydrophobicity and hydrophilicity of PDMAEMA. The
The absorbance and fluorescence of loaded Nile Red in the
polymer nanoparticles upon heating and cooling process were
also investigated. Upon heating to 60 °C, the absorption band
of Nile Red changed little, as indicated no leakage of Nile Red
(Figure S13). Figure 8c shows that the fluorescence intensity of
Nile Red loaded in nanoparticles of the copolymer with DF of
4% increased when increasing temperature from 20 to 60 °C
since the hydrophobicity of PDMAEMA increased.42 Figure 8d
shows that the fluorescence intensity could be recovered to
the initial value upon cooling due to the increase of
hydrophilicity of PDMAEMA. The reversible fluorescence
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28 H. Feil, Y. Bae, J. Feijen and S. Kim, Macromolecules, 1993, 26
2496-2500.
29 Y. Zheng, L. Zhong, W. Huang, Y. Zhou and D. Yan, J. Polym.
Sci. Polym. Chem., 2010, 48, 4428-4438.
30 W. Su, X. Luo, H. Wang, L. Li, J. Feng, X. Zhang and R. Zhuo,
Macromol. Rapid Commun., 2011, 32, 390-396.
,
polymer nanoparticles self-assembled from the photo-, pH-
and thermo-responsive azobenzene-functionalized PDMAEMA
may find their applications in the fields of sensing, catalysis,
separation and controlled release.
31 X. Liu, P. Ni, J. He and M. Zhang, Macromolecules, 2010, 43
4771-4781.
32 T. Noda, A. Hashidzume and Y. Morishima, Macromolecules,
2001, 34, 1308-1317.
Foundation of China (Grant No. 51373025 and 21074010), the 33 W. Su, K. Han, Y. Luo , Z. Wang, Y. Li and Q. Zhang, Macromol.
,
Acknowledgements
This work was supported by the National Natural Science
Chem. Phys., 2007, 208, 955-963.
Program for New Century Excellent Talents in University
(NCET-11-0582), and the Fundamental Research Funds for the
Central Universities (FRE-TP-12-004B).
34 Y. Zhao, Macromolecules, 2012, 45, 3647-3657.
35 P. Han, S. Li, C. Wang, H. Xu, Z. Wang, X. Zhang, J. Thomas
and M. Smet, Langmuir, 2011, 27, 14108-14111.
36 D. Sackett and J. Wolff, Anal. Biochem., 1987, 167, 228-234.
37 Z. Feng, L. Lin, Z. Yan and Y. Yu, Macromol. Rapid Commun.,
2010, 31, 640-644.
38 E. Blasco, B. Schmidt, C. Kowollik, M. Pinol and L. Oriol,
Polym. Chem., 2013, 4, 4506-4514.
39 X. Tong, G. Wang, A. Soldera and Y. Zhao. J. Phys. Chem. B,
2005, 109, 20281-20287.
40 X. Tang, X. Liang, L. Gao, X. Fan and Q. Zhou, J. Polym. Sci.
Polym. Chem., 2010, 48, 2564-2570.
41 D. Basak and S. Ghosh, ACS Macro Lett. 2013, 2, 799-804.
42 A. Goodwin, J. Mynar, Y. Ma, G. Fleming and J. Fréchet, J. Am.
Chem. Soc., 2005, 127, 9952-9953.
Notes and references
1
2
J. Gohy and Y. Zhao, Chem. Soc. Rev., 2013, 42, 7117-7129.
D. Roy, W. Brooks and B. Sumerlin, Chem. Soc. Rev., 2013, 42
7214-7243.
,
3
4
S. Dai, P. Ravib and K. Tam, Soft Matter, 2008, 4, 435-449.
J. Hu, G. Zhang and S. Liu, Chem. Soc. Rev., 2012, 41, 5933-
5949.
5
6
7
8
9
P. Theato, B. Sumerlin, R. O'Reilly and T. Epps, Chem. Soc.
Rev., 2013, 42, 7055-7056.
Y. Leng, J. Zhao, P. Jiang and J. Wang, ACS Appl. Mater.
Interfaces, 2014,
K. Kim, S. Meeuwissen, R. Nolte and J. Hest, Nanoscale, 2010,
, 844-858.
M. Motornov, J. Zhou, M. Pita, V. Gopishetty, I. Tokarev, E.
Katz and S. Minko, Nano. Lett., 2008, , 2993-2997.
Z. Ge and S. Liu, Chem .Soc. Rev., 2013, 42, 7289-7325.
6, 5947-5954.
2
8
10 J. Jiang, X. Tong, D. Morris and Y. Zhao, Macromolecules,
2006, 39, 4633-4640.
11 Y. Liu, J. Li, J. Ren, C. Lin and J. Leng, Mater. Lett., 2014, 127
,
8-11.
12 D. Xiong, Z. He, Y. An, Z. Li, H. Wang, X. Chen and L. Shi,
Polymer, 2008, 49, 2548-2552.
13 S. Ganta H. Devalapally, A. Shahiwala and M. Amiji, J. Control.
Release, 2008, 126, 187-204.
14 O. Bertrand, E. Poggi, J. Gohy and C. Fustin, Macromolecules,
2014, 47, 183-190.
15 J. Dong, Y. Wang, J. Zhang, X., S. Zhu, H. Yang and G. Wang,
Soft Matter, 2013, 9, 370-373.
16 J. Dong, R. Zhang, H. Wu, X. Zhan, H. Yang, S. Zhu and G.
Wang, Macromol. Rapid Commun., 2014, 35, 1255-1259.
17 H. Wu, J. Dong, C. Li, Y. Liu, N. Feng, L. Xu, X. Zhan, H. Yang
and G. Wang, Chem. Commun., 2013, 49, 3516-3518.
18 H. Wu, J. Dong, X. Zhan, H. Yang, Y. Zhao, S. Zhu and G. Wang,
RSC Adv., 2014, 4, 35757-35761.
19 Z. Cao, H. Wu, J. Dong and G. Wang, Macromolecules, 2014,
47, 8777-8783.
20 N. Feng, G. Han, J. Dong, H. Wu, Y. Zheng and G. Wang, J.
Colloid Interface Sci., 2014, 421, 15-21.
21 N. Feng, J. Dong, G. Han and G. Wang, Macromol. Rapid
Commun., 2014, 35, 721-726.
22 J. Niskanen, C. Wu, M. Ostrowski, G. Fuller, S. Hietala and H.
Tenhu, Macromolecules, 2013, 46, 2331-2340.
23 X. Liu, P. Ni, J. He and M. Zhang, Macromolecules, 2010, 43
4771-4781.
24 J. Gohy and Y. Zhao, Chem. Soc. Rev., 2013, 42, 7117-7129.
,
25 J. Wang, S. Wang, Y. Zhou, X. Wang and Y. He, ACS Appl.
Mater. Interfaces, 2015, , 16889-16895.
26 J. Wang, Y. Zhou, X. Wang and Y. He, RSC Adv., 2015, 5, 9476-
7
9481.
27 Y. Huang, R. Dong, X. Zhu and D. Yan, Soft Matter, 2014, 10
6121-6138.
,
8 | Poly., 2012, 00, 1-3
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Polymer nanoparticles self-assembled from photo-, pH- and
thermo-responsive azobenzene-functionalized PDMAEMA
Tingting Yuan, Jie Dong, Guoxiang Han, Guojie Wang＊
Polymer nanoparticles self-assembled from an amphiphilic azobenzene-functionalized
PDMAEMA have been constructed, the morphological changes of which under
stimulation of UV light, temperature and pH changes are demonstrated.
Acid
Self-assembly
x
O
y
O
m
O
O
Br
N
N
4
O
N
N
CF
3