Supramolecular assembly of poly(ionic liquid) nanogel driven by host-stabilized charge transfer interaction

Article abstract of DOI:10.1002/pola.29516

Poly(ionic liquid) (PIL)-based nanogels, functionalized by naphthyl (Np), are fabricated via a facile one-step ternary crosslinking copolymerization in selective solvent. The size of PIL nanogels can be conveniently regulated through the feed ratio of IL monomer to crosslinker. The presence of Np groups in PIL nanogel is confirmed by using ultraviolet–visible (UV–vis), Fourier transform infrared, and X-ray photoelectron spectroscopy measurements. Through introducing cucurbit[8]uril (CB[8]) and bisviologen compound (DEDV) as the host molecule and electron acceptor, respectively, host-stabilized charge transfer (HSCT) interaction is achieved through utilizing Np containing PIL nanogel as the building block. The studies reveal that PIL nanogels can form schistose aggregates in the scale of micrometer via HSCT interaction. The aggregates will be broken in the presence a competitive guest molecule (amantadine) and can recover by adding another host molecule (CB[7]). HSCT interaction among CB[8], DEDV and PIL nanogel is investigated by dynamic light scattering, UV–vis, and Proton nuclear magnetic resonance. Our studies thus provided an applicable strategy for constructing dynamic polymer nanoparticles through noncovalent interaction.

Full text of DOI:10.1002/pola.29516

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Supramolecular Assembly of Poly(ionic liquid) Nanogel Driven By
Host-Stabilized Charge Transfer Interaction
1
1
2
2
1,2
1
Yuntao Tang, Ke Wang, Yong Zuo, Xi Chen, Yubing Xiong , Yumin Yuan
1
Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, Zhejiang Province, China
College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou 730070, China
2
Correspondence to: Y. Xiong (E-mail: yubing_xiong@163.com), Y. Yuan (E-mail: yuan42@hotmail.com)
Received 30 July 2019; Revised 18 September 2019; accepted 19 September 2019
DOI: 10.1002/pola.29516
ABSTRACT: Poly(ionic liquid) (PIL)-based nanogels, functionalized
by naphthyl (Np), are fabricated via a facile one-step ternary
crosslinking copolymerization in selective solvent. The size of
PIL nanogels can be conveniently regulated through the feed ratio
of IL monomer to crosslinker. The presence of Np groups in PIL
nanogel is confirmed by using ultraviolet–visible (UV–vis), Fourier
transform infrared, and X-ray photoelectron spectroscopy mea-
surements. Through introducing cucurbit[8]uril (CB[8]) and
bisviologen compound (DEDV) as the host molecule and electron
acceptor, respectively, host-stabilized charge transfer (HSCT) inter-
action is achieved through utilizing Np containing PIL nanogel as
the building block. The studies reveal that PIL nanogels can form
schistose aggregates in the scale of micrometer via HSCT interac-
tion. The aggregates will be broken in the presence a competitive
guest molecule (amantadine) and can recover by adding another
host molecule (CB[7]). HSCT interaction among CB[8], DEDV and
PIL nanogel is investigated by dynamic light scattering, UV–vis,
and Proton nuclear magnetic resonance. Our studies thus provided
an applicable strategy for constructing dynamic polymer
nanoparticles through noncovalent interaction. © 2019 Wiley Peri-
odicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019
KEYWORDS: charge transfer interaction; nanogel; poly(ionic liq-
uid); supramolecular assembly
1
4,15
INTRODUCTION Noncovalent interactions between different
building blocks can allow the self-assembly behaviors with
reversibility and versatile stimuli responses. Supramolecular
self-assembly mediated by non-covalent interactions thus has
attracted tremendous interests in the fields of polymer, smart
pumpkin shape.
Especially, CB[8] can form stable 1:1:1
ternary complexes, in which the donor and the acceptor are
both encapsulated in its cavity. The short distance between
the donor and the acceptor can enhance the CT interaction
Therefore, HSCT interaction mediated by CB[8] is
widely utilized in supramolecular self-assembly, and provides
access to various assemblies, such as vesicles, hydrogels, and
hierarchical nanoparticles.
used building blocks for supramolecular assembly are small
molecules and polymers with different structures.
is highly desired to explore versatile building blocks for new
applications of HSCT interaction.
1
6–20
greatly.
1
–3
material, life science, and so forth.
Till now, the most
widely developed noncovalent interactions include hydrogen
2
1,22
bonding, hydrophobic interaction, host–guest interaction, elec-
Presently, most of the widely
4
–7
trostatic interaction, π–π stacking, coordination, and so on.
2
3,24
These noncovalent interactions can endow the organized sys-
tems with micro/macrotransformation in response to external
stimuli, such as temperature, light, pH, magnetic field, electric-
ity, and compounds, which have found many potential applica-
tions in biomimetic material, controlled drug delivery,
Thus, it
From the point of view of structure, poly(ionic liquid)s (PILs),
comprising ionic liquid units in their side chains or backbones,
falls into the category of polyelectrolyte.
8
–11
actuators, and sensors.
2
5–28
However, PILs
Through host-stabilized charge transfer (HSCT) interaction,
more than one guest molecule can be accommodated into the
host molecule. Additionally, the as-formed complex can pro-
duce a confined environment, which benefits to get insight
into the new form of stereoisomerism, bimolecular reaction,
inherit some excellent performances deriving from ILs and
polymers, such as wide electrochemical window, high ion con-
ductivity, good processability, tunable structure, and polar-
2
9,30
ity.
Therefore, PILs have been rapidly developed since
3
1
they were first reported by Ohno and Ito. In the previous
studies, we have demonstrated a facile and universal one-step
technique to prepare PIL-based nanogels, which can be
1
2,13
and molecular recognition.
In the past two decades,
cucurbit[n]urils (CB[n]) have been popular host compounds
used as the building elements in view of their symmetrical
achieved
through
the
conventional
free
radical
Additional supporting information may be found in the online version of this article.
2019 Wiley Periodicals, Inc.
©
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copolymerization of IL monomers and crosslinkers in selective
calcium hydride for 4 h and distilled under normal pressure.
IL monomers, 4-vinylbenzyl triphenyl phosphonium chloride
(VBP-Ph), and 4-vinylbenzyltributyl phosphonium chloride (VBP-
3
2
solvent in the absence of stabilizers or surfactants. The
structure and size of as-obtained PIL-based nanogels can be
well regulated through changing the crosslinkers and IL
monomers. In the light of broadly tunable structure of ILs, we
also find that it is feasible to prepare stimuli-responsive PIL
nanogels by introducing different functional groups into IL
monomers. The as-formed PIL nanogels are of the stimuli
32,33
Bu) were prepared according to the reported protocols.
Unless stated otherwise, all other reagents, such as
triphenylphosphorus, tributylphosphorous, 2-naphthol, 4-chloro-
0
1-butanol, n-hexane, methacryloyl chloride, 4,4 -bipyridine,
1,4-dibromobutane, amantadine (AdNH ), carbamide, glyoxal
2
solution (40 wt %) and methanol were A.R. grade and used as
received without further treatment.
3
3–35
responses including light, redox, temperature, and pH.
Herein, novel PIL nanogel functionalized by naphthyl
Np) was synthesized via the as-reported one-step technique.
(
Through using CB[8] as a host molecule, charge transfer inter-
action between PIL-nanogel and a bisviologen compound is
achieved, which can be utilized to mediate supramolecular
assembly of PIL nanogel (Fig. 1). To the best of our knowl-
edge, HSCT complex using polymer nanogel as the building
block has not yet been reported in the literatures.
Characterization
Proton and carbon nuclear magnetic resonance ( H and
1
13
C
NMR) spectra were recorded on a Bruker AM spectrometer
ꢀ
(
400 MHz) at 25 C. Mass spectrometric (MS) measurements
were performed on an Agilent 6520 QTOF mass spectrometer
equipped with electrospray ionization (ESI) source in positive
and negative ion modes. Fourier transform infrared (FTIR)
spectra were conducted on a DIGIL FTS3000 spectropho-
tometer using KBr tables. Ultraviolet–visible (UV–vis)
absorption spectra were measured on a Shimadzu UV-
2500PC spectrophotometer using a 1.0 cm path length qua-
rtz cell. Thermogravimetric analysis (TGA) were surveyed
EXPERIMENTAL
Materials
Azobisisobutyronitrile (AIBN, 98%) was recrystallized from
methanol twice and stored in the fridge before use. To remove
the inhibitors, vinyl imidazole (VIm), 4-vinylbenzyl chloride
and ethylene glycol dimethacrylate (EGDMA) were distilled under
ꢀ
on a PerkinElmer TG/TGA 6300 at a heating rate of 10 C/min.
0
vacuum and stored in the fridge. N,N -dimethylformamide (DMF)
Dynamic light scattering (DLS) measurements were performed
ꢀ
ꢀ
was dried over calcium hydride overnight and distilled under
reduced pressure. Dichloromethane (CH Cl ) was dried over
at 25 C and a scattering angle of 90 on a commercial laser
light scattering (ALV/SP-125) equipped with an ALV-5000
2
2
FIGURE 1 Schematically illustration of supramolecular assembly of PIL nanogel mediated by HSCT interaction. [Color figure can be
viewed at wileyonlinelibrary.com]
2
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multidigital time correlator and ADLAS DPY425 solid-state
laser (output power = 22 mW at = 632.8 nm). The morphology
of the samples was observed by scanning electron microscopy
ppm, Fig. S3): 7.81–7.71 (m, 3H), 7.48–7.42 (t, 1H), 7.38–7.32
(t, 1H), 7.20–7.12 (m, 2H), 6.15 (s, 1H), 5.57 (s, 1H), 4.31–4.25
(t, 2H), 4.15–4.09 (t, 2H), 2.02–1.90 (m, 7H). C NMR (CDCl3,
100 MHz, δ ppm, Fig. S4): 167.5, 156.9, 136.4, 134.6, 129.4,
129.0, 127.7, 126.7, 126.3, 125.4, 123.6, 118.9, 106.6, 67.3,
1
3
(
SEM, JSM 6700F; Japan). The samples were prepared by
directly dropping the dilute sample solution on the substrate.
X-ray photoelectron spectroscopy (XPS) data were collected
using a PerkinElmer PHI-5702 multifunctional XPS (Physical
20 3
64.3, 26.0, 25.5, 18.3. MS (ESI) m/z: calculated for C18H O :
284.35, found: 284.17.
Electronics, Waltham, MA) with Al K radiation (1486.6 eV) as
α
0
0
the excitation source. The adventitious carbon 1 s peak was cal-
ibrated at 285 eV and used as an internal standard to compen-
sate for any charging effects.
Synthesis of 1,1 -(butane-1,4-diyl)bis(1-ethyl-4,4 -
0
bipyridine-1,1 -diium)bromide (DEDV)
Compound 1 was synthesized according to the procedure
described in the literature with a little modification (Fig. 2).
1
3
4
1
-4’-Bipyridine (6.25 g, 40 mmol), 1,4-dibromobutane (2.87 g,
Synthesis of 4-(Naphthalen-2-yloxy)butyl methacrylate
3 mmol) and acetonitrile (50 mL) were fed into a dried flask
First, 4-hydroxybutyl-2-naphthyl ether (HBNp) was synthesized
ꢀ
3
6
with a magnetic stirrer. The mixture was stirred at 70 C for
2
washed with acetonitrile (50 mL) and diethyl ether (50 mL)
successively. A yellow powder was obtained and dried under
vacuum (Yield: 5.24 g, 74.35%). H NMR (DMSO-d
δ ppm, Fig. S5): 9.24 (d, 4H), 8.85 (d, 4H), 8.65 (d, 4H), 8.02
according to the reported protocol. Typically, 2-naphthol
5.77 g, 40.02 mmol), 4-chloro-1-butanol (6.51 g, 59.96 mmol)
4 h to produce a precipitate. The precipitate was then
(
and potassium carbonate (11.06 g, 80.0 mmol) were fed into a
dried flask. Then, anhydrous DMF (50 mL) and potassium
iodide (catalytic amount) were added into the above flask. The
1
6
, 400 MHz,
ꢀ
mixture was stirred at 80 C for 30 h under nitrogen atmo-
1
3
(
d, 4H), 4.70 (s, 4H), 2.03 (d, 4H). C NMR (DMSO-d
6
,
sphere. After cooling to room temperature, the reaction mixture
was poured into deionized water (200 mL). White crude was
obtained by filtration and purified by column chromatography
1
1
3
00 MHz, δ ppm, Fig. S6): 153.0, 151.7, 146.1, 141.5, 126.1,
22.6, 60.1, 27.8. MS (ESI) m/z: calculated for C H N
68.28, found: 368.26.
2
+
:
24 28
4
2 2 f
using CH Cl as eluent (retention factor R : 0.36). The product
was obtained as a white powder (Yield: 1.31 g, 15.41%). mp:
ꢀ
1
In the following step, Compound
1 (3.25 g, 6 mmol),
1
7
7
2
1
1
06–109 C. H NMR (CDCl , 400 MHz, δ ppm, Fig. S1):
.79–7.69 (dd, 3H), 7.46–7.40 (t, 1H), 7.36–7.30 (t, 1H),
3
bromoethane (2.68 g, 25 mmol) were dissolved in dried DMF
ꢀ
(
100 mL) and stirred at 90 C for 48 h. The precipitate was
.17–7.11 (d, 2H), 4.17–4.10 (t, 2H), 3.80–3.72 (t, 2H),
1
3
obtained through filtration, and washed with hot DMF and
.00–1.92 (m, 2H), 1.86–1.77 (m, 2H).
3
C NMR (CDCl ,
2
acetonitrile (30 × 3 mL ) to get a buff powder (Yield: 1.48 g,
00 MHz, δ ppm, Fig. S2): 156.8, 134.5, 129.4, 128.9, 127.6,
26.7, 123.6, 118.9, 106.7, 67.7, 62.6, 29.6, 25.8. MS (ESI) m/z:
ꢀ
1
3
4
4
3.16%). mp: 246–249 C (decomposition). H NMR (DMSO-d
6
,
00 MHz, δ ppm, Fig. S7): 9.52–9.35 (m, 8H), 8.88–8.75 (m, 8H),
.87–4.66 (m, 8H), 2.15–2.03 (d, 4H), 1.63–1.54 (t, 6H). C NMR
O, 100 MHz, δ ppm, Fig. S8): 145.4, 127.2, 126.9, 60.9, 27.3,
16 2
calculated for C14H O : 216.28, found: 216.16.
13
For the preparation of 4-(naphthalen-2-yloxy)butyl methacry-
late (NpBMA), to a solution of HBNp (1.3 g, 6.0 mmol) and
(D
2
4+
34 4
15.5. MS (ESI) m/z: calculated for C28H N : 426.21, found:
triethylamine (1.22 g, 12.0 mmol) in CH
methacryloyl chloride (0.94 g, 8.99 mmol) in dried CH
10 mL) was added dropwise under stirring. The reaction
mixture was kept below 0 C for 1.0 h using ice–water bath.
Then, it was further stirred at room temperature for 24 h. The
2
Cl
2
(30 mL),
426.34.
2
Cl
2
(
Synthesis of cucurbit[8]uril (CB[8])
First, glycoluril was synthesized according to the literature
(Fig. 3). Typically, carbamide (18 g, 0.3 mol) was dissolved
ꢀ
3
7
reaction mixture was washed with saturated NaCl solution
in distilled water (25 mL) in a flask. Then, H SO (98%,
2
4
2
(
50 × 3 mL ). After that, the solution was dried over magne-
2.0 mL) was added slowly into the above solution. The solu-
ꢀ
sium sulfate, and the solvent was removed through rotary
tion was heated to 50 C and glyoxal solution (40 wt %,
evaporation. The crude product was further purified by col-
15.6 g, 0.11 mol) was added in 5 min using a constant pres-
sure funnel. The temperature was kept at 85 C for 2 h. After
ꢀ
umn chromatography, using CH
2
Cl
2
/petroleum ether as eluent
(
1:1, v/v, R = 0.32). The product was obtained as a light yel-
that, the reaction was stopped and the solution was cooled
down to room temperature. Then, the solution was
f
1
low liquid (Yield: 1.4 g, 72.51%). H NMR (CDCl , 400 MHz, δ
3
Br(CH ) Br
CH
3
CH
Br
2
2
4
N
N
N
N
(CH
2
)
4
N
N
CH CN
DMF
3
Br
Br
(
1)
N
Br
N
(CH2)4
Br
DEDV
N
N
Br
Br
FIGURE 2 Synthesis of bisviologen compound DEDV.
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O
O
O
O
O
H
O
H
HN
HN
NH
NH
N
N
N
N
CH
2
H
CH2
H
2
SO
4
(HCHO)
n
H
2
H N
NH
2
5 oC, 3 h
8
HCl (37%), 100 C
o
n
O
n = 5, 6, 7, 8
FIGURE 3 Synthesis of cucurbit[n]curls (CB[n]).
neutralized using NaOH solution (5.0 wt %). The precipitate
was obtained through filtration and washed by distilled water.
The product was dried under vacuum and obtained as white
EGDMA (0.476 g, 2.40 mmol), and AIBN (0.009 g, 0.055 mmol)
were dissolved in 30 mL absolute methanol, the mixture was
stirred at 70 C for 40 h in nitrogen atmosphere. To remove the
residual monomers, the as-prepared nanogel solutions were
first dialyzed against methanol thoroughly. Then, nanogel
solutions were further dialyzed against water. Finally, PIL-
based nanogel powder was obtained by lyophilization.
ꢀ
−1
powder (Yield: 9.37 g, 60%). FTIR (Fig. S9): N H (3300 cm
,
−
1
−1
−1
st), C O (1700 cm ), N H (1500 cm , ip; 800 cm , oop),
C N (1300 cm− , st).
1
In the following step, glycoluril (155 g, 1.09 mol), paraformal-
dehyde (70 g, 2.33 mol), and concentrated hydrochloric acid
(
1
Yield: 0.33 g, 40%). The as-prepared sample is defined as
N1P4E, in which N, P, and E are short for NpBMA, VBP-Ph,
(
37 wt %, 800 mL) were mixed in a three-necked flask. The
and EGDMA, respectively, and the numbers are the feeding
ratio of the corresponding monomers. The control sample
ꢀ
reaction was conducted at 100 C for 3 h. After that, the mix-
ture was cooled down to room temperature. The precipitate
1
P4E was prepared under the same conditions only without
(
mixture of CB[5] and CB[8]) was collected by filtration. The
feeding NpBMA. To determine the concentration of PIL
nanogels (calculated by Np group), Job’s plot was measured
through UV–vis at the absorbance of 328 nm using NpBMA
solution in CH OH:H O (3:1, v/v) as the samples. The fitted
resulting solution was concentrated and precipitated from
substantial methanol (1000 mL). The as-obtained white solid
(
mixture of CB[6] and CB[7]) was collected through filtration,
3
2
and washed with distilled water and acetone successively. The
2
equation is y = 14.88x–0.04 and the correlation coefficient R
crude product (CB[5] and CB[8]) was dried under vacuum at
is 0.9995.
ꢀ
80
C. In the next step, the mixture of CB[5] and CB
[
8] (100 g) was dissolved in hydrochloride (5 mol/L, 500 mL).
RESULTS AND DISCUSSION
The solution was boiled for 30 min (Be caution!). After that,
the solution was cooled down to room temperature and white
solid (CB[8]) was collected through filtration. The crude prod-
uct (CB[8]) was dried under vacuum at 80 C. The above
manipulations were repeated four times until CB[8] with high
Preparation and characterization of Np-grafted PIL
nanogel
ꢀ
First, Np group was introduced into methacrylate-based
monomer (NpBMA). Its structure was confirmed by NMR,
FTIR, and MS measurements. In addition, two phosphonium
IL monomers, VBP-Ph and VBP-Bu, were synthesized and used
as the comonomers. Subsequently, NpBMA was copolymerized
with EGDMA in the presence of phosphonium IL monomers,
which played the role of stabilizer in the polymerization pro-
cess. As illustrated in Figure S15(A), opalescent solutions
could be obtained under the above conditions. And there were
no precipitates after the copolymerization reaction. Strong
scattering light could be observed when the samples were
illuminated by a laser pointer (650 nm). The performance
demonstrates that there are many stable particles in the
1
purity (>95%, determined by H NMR) was obtained. mp:
ꢀ
1
~
470 C (decomposition). H-NMR (D
Fig. S10): 5.86–5.66 (d, 16H), 5.66–5.56 (s, 16H), 4.42–4.17
d, 16H).
2 4
SO , 400 MHz, δ ppm,
(
Preparation of Np-grafted PIL nanogels
Nanogels composed of different ILs were prepared according to
our previous methods (Fig. 4).
describes the typical synthesis of Np-grafted PIL nanogels.
NpBMA (0.107 g, 0.60 mmol), VBP-Ph (0.249 g, 0.60 mmol),
3
2,33
The following example
*
*
n
m
l
O
O
AIBN
+
+
O
O
O
O
In MeOH
O
O
o
6
0
C
O
PR
3
Cl
O
O
PR
O
3
Cl
O
O
*
*
l
FIGURE 4 Synthesis of Np-grafted PIL nanogels (R = Bu and Ph).
4
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solution. Since the host–guest interaction will be conducted in
water, the as-prepared Np-grafted PIL nanogel solutions were
dialyzed against methanol and water successively, which
could remove the unreacted monomers and exchange metha-
nol with water. As shown in Figure S11(B), the strong scatter-
ing light confirms that Np-grafted PIL nanogels are still stable
in water.
0.4
0
.5N1P4E
1N1P4E
2N1P4E
1P4E
0.3
0.2
0.1
0.0
NpBMA
The sizes of Np-grafted PIL nanogel were measured through
DLS and the results are summarized in Table 1. It can be
found that the sizes of PIL nanogels are in the range of
50–130 nm. With increasing the feed of phosphonium IL
monomer, PIL nanogel with smaller size can be obtained,
which is probably because poly(phosphonium IL) segments
play the role of stabilizer in the polymerization process. As a
result, the size of Np-grafted PIL nanogel can be mediated
through the feeding ratio of the monomers and the
crosslinker. Similar to our previous studies, the sizes of PIL
300
325
350
375
400
Wavelength (nm)
FIGURE 5 UV–vis spectra of PIL nanogels with different feeding
ratios in water and NpBMA in CH OH:H O (3:1, v/v). [Color
3
4,35
nanogels are still in a wide dispersity.
DLS results also
3
2
reveal that the substitution group in comonomers (VBP-Ph/
Bu) has little influence on the size of Np-grafted PIL nanogel.
In addition, the sizes of Np-grafted PIL nanogel become much
larger after they are transferred into water through dialysis. It
should be due to the stronger polarity of water than that of
methanol, which will result in the association of PIL nanogel
considering the presence of hydrophobic Np groups and
PEGDMA segments. Another interpret is that water can partly
shield the charges on the surface of PIL nanogels.
figure can be viewed at wileyonlinelibrary.com]
Figure 5, the strong absorption peaks at 313 nm and 327 nm
are ascribed to the π–π* transition of the naphthalene ring in
NpBMA. Similar absorption peaks can be observed in PIL
nanogels. The absorption enhances with increasing the feed of
NpBMA monomer in the copolymerization. Compared with the
typical absorption peaks in NpBMA, those in Np-grafted PIL
nanogels redshift a little. This shift is probably ascribed to the
difference in polarity between water and methanol. However, no
absorptions can be observed in the above region in 1P4E, which
is prepared in the absence of NpBMA monomer. Therefore, UV–
vis results confirm the successful introduction of Np groups into
PIL nanogel through the ternary copolymerization. The composi-
tion of PIL nanogels were also examined by XPS technique.
To confirm the presence of Np groups in PIL nanogel, UV–vis
measurement was conducted. Before the measurement, the
possible unreacted monomers in the as-prepared PIL nanogel
solution were removed by dialysis against methanol thor-
oughly. Then, the solutions were further dialyzed against
water to get PIL nanogel aqueous solution. Finally, Np-grafted
PIL nanogel powders were obtained by freeze-drying. The
monomer NpBMA was dissolved in the mixed solvent of meth-
anol and water (3:1, v/v) as the control sample. As showed in
As revealed in Figure 6, PIL nanogel is mainly composed of
carbon, oxygen, phosphorus, and chlorine besides hydrogen.
a
TABLE 1 Hydrodiameter and PDI of PIL Nanogels with Different Feeding Ratios Before and After Dialysis
b
c
c
d
d
Entry
Comonomer
Feeding ratio
D
h
(nm)
PDI
D
h
(nm)
PDI
0
0
0
1
1
1
2
2
0
1
.5N1P3E
.5N1P4E
.5N1P5E
N1P4E
VBP-Ph
VBP-Ph
VBP-Ph
VBP-Ph
VBP-Ph
VBP-Ph
VBP-Ph
VBP-Ph
VBP-Bu
VBP-Bu
0.5:1:3
0.5:1:4
0.5:1:5
1:1:4
130
103
83
0.34
0.21
0.32
0.30
0.48
0.22
0.42
0.36
0.46
0.48
159
131
113
191
162
79
0.59
0.62
0.71
0.51
0.32
0.39
0.42
0.48
0.65
0.79
113
87
N1P5E
1:1:5
N1P6E
1:1:6
50
N1P4E
2:1:4
122
102
114
129
236
180
160
185
N1P5E
2:1:5
.5N1B4E
N1B4E
0.5:1:4
1:1:4
a
c
Polymerization
conditions:
([EGDMA] + [NpBMA] + [Comonomer])/
In methanol.
d
[
AIBN] = 100:1, solvent: absolute methanol (30 mL), polymerization tem-
In water. In the abbreviation of samples, N, P/B, and E denote NpBMA,
VBP-Ph/Bu, and EGDMA, respectively, and the numbers denote the
molar feeding ratio of the corresponding monomers.
ꢀ
h
perature = 70 C. D , average hydrodynamic diameter; PDI, polydispersion
index.
b
The molar ratio of NpBMA:[Comonomer]:EGDMA.
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FIGURE 6 XPS survey spectrum of PIL nanogel (a) and the peaks of Cl2p (b) and P2p (c) orbits of PIL nanogel.
Both P and Cl come from phosphonium IL monomer. Thus,
XPS data indicate that phosphonium IL monomers also partici-
pate in the ternary copolymerization.
Moreover, the thermostability of nanogels was determined by
TGA. As shown in Figure S12, these PIL nanogels have good
ꢀ
thermostability and are stable below 250 C, due to the highly
ꢀ
crosslinked structure. The slight weight loss before 150 C
FTIR spectra of the as-prepared PIL nanogels with various
feeding ratios were recorded and exhibited in Figure 7. Some
typical vibration peaks ascribed to the groups in PIL nanogels
was probably owing to the evaporation of retained solvents.
The morphologies of PIL nanogels were observed through
SEM. As revealed in the images [Fig. 8(a,b)], the sizes of PIL
nanogel are around 100 nm. These sizes are a little smaller
than those measured by DLS, which is due to the absence of
solvent in SEM measurement. In addition, PIL nanogel aggre-
gate slightly after the solvent is removed. When PIL nanogel is
transferred into water, they aggregate obviously judging from
Figure 8(c,d). The results are consistent with DLS data, which
probably results from the strong polarity of water that can
shield the charges on the surface of PIL nanogel.
can be identified obviously, such as the peaks at 1720 and
1
1
630 cm− , attributed to the stretching vibration of the car-
bonyl group and aromatic benzene ring. The peak ascribed to
−1
C H bond (3054 cm , stretching vibration) of the vinyl
groups in the monomers disappeared after the crossing-
linking copolymerization. Therefore, FTIR results demonstrate
that all monomers have participated in the ternary copolymer-
ization, and Np containing PIL nanogels were produced.
Supramolecular assembly of PIL nanogels driven by HSCT
interaction
Since the charge transfer interaction between naphthalene
and viologen group can be stabilized by the cavity of cucurbit
1720
(
a)
b)
[
8]uril, tremendous host–guest supramolecular systems are
fabricated through using versatile small molecules and poly-
3
8
mers as the building blocks. To achieve the supramolecular
assembly of PIL nanogels, a bisviologen guest molecule
(DEDV), which can be embedded into two equivalents of CB
(
(c)
[
8]’s cavities and act as a link, was synthesized through a two-
step quaternization of viologen. Thereafter, HSCT supramolec-
ular interaction was investigated by H NMR using NpBMA as
(d)
1
a model compound. As demonstrated in Figure 9, the signals
of pyridinium hydrogens in DEDV emerge in the range from
3054
1630
8.5 to 9.2 ppm. After adding CB[8] into DEDV solution, the
4000 3500 3000 2500 2000 1500 1000
500
-1
above signals show an upfield shift and become broader. The
Wavenumber (cm )
behavior reveals that there exists interaction between CB
3
9
[
8] and DEDV. For the model molecule NpBMA, the signals
FIGURE 7 FTIR spectra of NpBMA and PIL nanogels with various
feeding ratios. (a) NpBMA; (b) 0.5N1P4E; (c) 0.5N1P3E; and
at 7.1–7.8 ppm result from the protons in naphthalene group.
When CB[8] and DEDV are introduced, the signals of Np pro-
ton in NpBMA show pronounced upfield shifts. Simulta-
neously, the signals of pyridinium protons in DEDV become
(d) 0.5N1P5E. All nanogel samples were prepared through
lyophilization after dialysis against water. [Color figure can be
viewed at wileyonlinelibrary.com]
6
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FIGURE 8 SEM images of PIL nanogels with different feeding ratios. (a) 1N1P5E in methanol; (b) 0.5N1P5E in methanol; (c) 1N1P5E in
water; (d) 0.5N1P5E in water; (e) 0.5N1P4E + DEDV+CB[8] in water; and (f) 0.5N1P4E + DEDV+CB[8]+AdNH in water.
2
much broader. Furthermore, the proton signals in Np and
pyridinium exhibit a downshield shift when AdNH is added
into the above solution as a competitive guest. At the same
time, these signals also become narrower. In view of the poor
solubility of NpBMA, the signals resulting from Np group still
keep broad. These performances further confirm that HSCT
interaction can be achieved in the above ternary system, and
can also be dissociated though introducing a competitive
guest.
2
Afterward, Np-grafted PIL nanogels were complexed CB
[
8] and DEDV in water under stirring. It has been reported
that CB[8] has very poor solvability in water, and can be only
dissolved in water in the presence of strong acid. As shown in
Figure 10, after adding DEDV and CB[8] into PIL nanogel solu-
tion, there are no CB[8] powders in the solution, and the clear
solution becomes a stable milky emulsion. It has been demon-
strated that the formation of charge transfer complex can
(
e)
(d)
4
0
greatly improve the solvability of CB[8] in water. Therefore,
the appearance of the solution shows the formation of ternary
complex among CB[8], DEDV and PIL nanogel. In addition, the
scattering light becomes much stronger after the addition of
CB[8] and DEDV. It should be attributed to the aggregation of
PIL nanogels due to the HSCT interaction. When AdNH2 is
introduced as a competitive guest molecule, the solution
(
c)
(b)
becomes clearer again. Since AdNH
8] than Np groups, HSCT complex among PIL nanogel, DEDV,
and CB[8] will disassociate and form CB[8]-AdNH complex.
2
is more affinitive to CB
(
a)
[
9.5
9.0
8.5
8.0
(ppm)
7.5
7.0
6.5
6.0
2
The existence of PIL nanogel can also be confirmed through
the Tyndall effect. When CB[7] was added into the above sys-
tem, the solution became opalescent. The behavior indicates
the formation of HSCT complex again, which results from the
δ
1
FIGURE 9 H NMR spectra (400 MHz) of (a) DEDV in D
2
O;
O;
(
(
[
(
b) NpBMA in CD
d) NpBMA + DEDV + CB[8] in D
8] + AdNH in D O. Concentrations: DEDV (3 mM), NpBMA
6 mM), CB[8] (6 mM), and AdNH (6 mM). [Color figure can be
3 2
OD/D O (3/1, v/v); (c) DEDV + CB[8] in D
2
4
1
stronger affinity of CB[7] to AdNH
2
than that of CB[8].
2
O; and (e) NpBMA + DEDV + CB
Therefore, HSCT complex of CB[8], DEDV, and PIL nanogel can
be recovered through introducing CB[7] as a competitive host
molecule. It is found that all PIL nanogels can form HSCT
2
2
2
viewed at wileyonlinelibrary.com]
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FIGURE 10 Photographs of association and dissociation of Np-grafted PIL-based nanogels. Concentrations: PIL nanogel (14 mM,
calculated by Np group), CB[8] (14 mM), DEDV (7 mM), and AdNH
2
(14 mM). [Color figure can be viewed at wileyonlinelibrary.com]
interaction with DEDV in the presence of CB[8]. The structure
of comonomers has no obvious influence on the interaction
except for the size of PIL nanogels. Therefore, 0.5N1P4E was
used in the following studies.
[8] cavity will be substituted by AdNH and HSCT complexes
2
are disassembled. The above size evolution can also be con-
firmed by SEM images. As illustrated in Figure 8(e), PIL
nanogels aggregate and form schistose morphology in the
scale of micrometer after the addition of DEDV and CB[8].
However, when AdNH2 is introduced, the supramolecular
complexes are dissociated and nanoparticles emerge [Fig. 8
The size evolution of PIL nanogel during the process of HSCT
interaction was monitored through DLS technique. As shown
in Figure 11, the average size of 0.5N1P4E in water is
(
f)], indicating that AdNH2 can break the HSCT interaction
131 nm. When CB[8] was added into the solution, the size of
among CB[8], DEDV, and PIL nanogel.
PIL nanogel increases to 217 nm, which is probably due to the
weak interaction between CB[8] and Np groups in PIL
HSCT interaction among Np-grafted PIL nanogel, DEDV, and
CB[8] is further investigated through UV–vis measurement.
Typically, the absorption band will have an obvious redshift
4
1
nanogel. After DEDV was added into the above solution, the
average size of the particles increased to 755 nm. The size
change is ascribed to the aggregation of PIL nanogels, which
results from encapsulating Np groups in PIL nanogel and pyri-
dine units in DEDV into the cavities of CB[8]. Since DEDV can
act as links in the process, PIL nanogels accumulate together
to form larger particles through the supramolecular interac-
tion. In addition, the size of PIL nanogel aggregates decreased
from 755 to 270 nm when AdNH2 is added into the above
solution. AdNH2 is a competition guest molecule and has
stronger affinity to CB[8] than Np. Therefore, Np units in CB
4
2
(~100 nm) due to HSCT interaction. To confirm the HSCT
interaction in CB[8]-DEDV-PIL nanogel ternary system, we
used NpBMA as a model molecule. As illustrated in the curves
of NpBMA and 0.5N1P4E (Fig. 12), there are no absorption
bands above 400 nm. For the control sample CB[8]+DEDV,
there are no obvious absorption peaks neither. However,
when DEDV and CB[8] are added into NpBMA solution, there
emerges strong absorption peaks above 400 nm, indicating
1.0
CB[8]+NpBMA+DEDV (H O)
2
0
.5N1P4E+CB[8]+DEDV+AdNH2
CB[8]+DEDV (H O)
2
0.8
0.5N1P4E+CB[8]+DEDV
NpBMA (CH OH:H O = 3:1)
3
2
0.5N1P4E
CB[8]+0.5N1P4E+DEDV (H O)
2
0
.5N1P4E (H O)
0.6
2
0.5N1P4E+CB[8]
0.4
0.2
0.0
350
400
450
500
550
600
650
10
100
1000
10000
Wavelength (nm)
Diameter (nm)
FIGURE 12 UV–vis spectra of CB[8] + DEDV, CB[8]+NpBMA
+ DEDV, CB[8] + 0.5N1P4E + DEDV, and NpBMA. Concentrations:
0.5N1P4E (2 mM, calculated by Np group), NpBMA (2 mM), CB
[8] (2 mM), and DEDV (1 mM). [Color figure can be viewed at
wileyonlinelibrary.com]
FIGURE 11 Size evolution of PIL nanogel in the process of HSCT
interaction. Concentrations: 0.5N1P4E (2 mM, calculated by Np
group), CB[8] (2 mM), DEDV (1 mM), and AdNH (2 mM). [Color
2
figure can be viewed at wileyonlinelibrary.com]
8
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the formation of CT interaction between naphthalene ring and
pyridine ring. For Np-grafted PIL nanogel sample (0.5N1P4E),
there is also an absorption band around 400 nm after intro-
ducing CB[8] and DEDV. The above performance illustrates
that there exists HSCT interaction between PIL nanogel and
DEDV in the presence of CB[8].
14 H. D. Correia, S. Chowdhury, A. P. Ramos, L. Guy,
G. J. F. Demets, C. Bucher, Polym. Int. 2019, 68, 572.
1
5 X. L. Ni, X. Xiao, H. Cong, Q. J. Zhu, S. F. Xue, Z. Tao, Acc.
Chem. Res. 2014, 47, 1386.
6 C. S. Y. Tan, J. del Barrio, J. Liu, O. A. Scherman, Polym.
Chem. 2015, 6, 7652.
1
1
7 U. Rauwald, O. A. Scherman, Angew. Chem. Int. Ed. 2008, 47,
3
950.
CONCLUSIONS
1
8 H. J. Kim, J. Heo, W. S. Jeon, E. Lee, J. Kim, S. Sakamoto,
Naphthyl functionalized PIL nanogels were facilely fabricated
through one-step ternary crosslinking copolymerization in
methanol. Considering the incorporation of phosphonium IL
monomers, stable nanogel solutions with tunable size could
be conveniently achieved through changing the feed ratio of
IL monomer and the crosslinker EGDMA. As a result, the
charge transfer interaction between Np group and DEDV mol-
ecules stabilized by CB[8] was accomplished. Since DEDV can
act as the links, supramolecular assembly through HSCT inter-
action is successfully achieved by using PIL nanogels as the
building blocks. In addition, the supramolecular aggregates of
PIL nanogel can be dissociated by adding a competitive guest
compound amantadine. Therefore, our studies provided a fea-
sible strategy for the fabrication of dynamic nanoparticles,
which has great potential applications in the smart material
areas. However, there is still a limitation using PIL nanogel as
the building block for host-guest interaction. That is, it is diffi-
cult to evaluate quantitatively the HSCT interaction due to the
highly crosslinked structure of PIL nanogel.
K. Yamaguchi, K. Kim, Angew. Chem. Int. Ed. 2001, 40, 1526.
19 K. Kim, Chem. Soc. Rev. 2002, 31, 96.
20 Y. Liu, R. Fang, X. Tan, Z. Wang, X. Zhang, Chem. A Eur. J.
2
012, 18, 15650.
21 Y. Xu, M. Guo, X. Li, A. Malkovskiy, C. Wesdemiotis, Y. Pang,
Chem. Commun. 2011, 47, 8883.
2
2 Y. H. Ko, K. Kim, J. K. Kang, H. Chun, J. W. Lee, S. Sakamoto,
K. Yamaguchi, J. C. Fettinger, K. Kim, J. Am. Chem. Soc. 2004,
1
26, 1932.
3 J. del Barrio, P. N. Horton, D. Lairez, G. O. Lloyd,
2
C. Toprakcioglu, O. A. Scherman, J. Am. Chem. Soc. 2013, 135,
1
1760.
2
4 Z. W. Ji, J. H. Liu, G. S. Chen, M. Jiang, Polym. Chem. 2014,
5
, 2709.
2
3
5 J. Yuan, D. Mecerreyes, M. Antonietti, Prog. Polym. Sci. 2013,
8, 1009.
2
6 W. Qian, J. Texter, F. Yan, Chem. Soc. Rev. 2017, 46, 1124.
7 J. Illescas, M. Casu, V. Alzari, D. Nuvoli, M. A. Scorciapino,
2
R. Sanna, V. Sanna, A. Mariani, J. Polym. Sci. Part A: Polym.
Chem. 2014, 52, 3521.
2
8 A. S. Shaplov, D. O. Ponkratov, Y. S. Vygodskii, Polym. Sci.
ACKNOWLEDGMENT
Series B 2016, 58, 73.
2
2
9 Y. Men, D. Kuzmicz, J. Yuan, Curr. Opin. Colloid Interface Sci.
014, 19, 76.
This work was supported by the National Natural Science
Foundation of China (Project Nos. 21774101 and 21474080).
3
0 M. M. Obadia, S. Fagour, Y. S. Vygodskii, F. Vidal, A. Serghei,
A. S. Shaplov, E. Drockenmuller, J. Polym. Sci. Part A: Polym.
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