Side-chain polypseudorotaxanes by threading cucurbit[7]uril onto poly-N-n-butyl-N′-(4-vinylbenzyl)-4,4′-bipyridinium bromide chloride: Synthesis, characterization, and properties

Article abstract of DOI:10.1002/pola.23981

A novel side-chain polypseudorotaxanes P4VBVBu/ CB[7] was synthesized from poly-Ar-n-butyl-N′-(4-vinylbenzyl)4,4′-bipyridinium bromide chloride (P4VBVBu) and cucurbit [7]uril (CB[7]) in water by simple stirring at room temperature. CB[7] beads are localiz

Full text of DOI:10.1002/pola.23981

Side-Chain Polypseudorotaxanes by Threading Cucurbit[7]uril onto
Poly-N-n-butyl-N0-(4-vinylbenzyl)-4,40-bipyridinium Bromide Chloride:
Synthesis, Characterization, and Properties
HUI YANG,1 YEBANG TAN,1,2 JINGCHENG HAO,1,2 HUABIAO YANG,1 FAWEN LIU1
1School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, People’s Republic of China
2The Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Jinan 250100,
People’s Republic of China
Received 18 November 2009; accepted 15 February 2010
DOI: 10.1002/pola.23981
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A novel side-chain polypseudorotaxanes P4VBVBu/
CB[7] was synthesized from poly-N-n-butyl-N0-(4-vinylbenzyl)-
4,40-bipyridinium bromide chloride (P4VBVBu) and cucurbit
[7]uril (CB[7]) in water by simple stirring at room temperature.
CB[7] beads are localized on viologen units in side chains of
polypseudorotaxanes as shown by 1H NMR, IR, XRD, and UV–
vis studies, and it is considered that the hydrophobic and
charge-dipole interactions are the driving forces. TGA data
show that thermal stability of the polypseudorotaxanes
increases with the adding of CB[7] threaded. DLS data show
that P4VBVBu and CB[7] could form polypseudorotaxanes, and
the average hydrodynamic radius of the polypseudorotaxanes
increases with increasing the concentration of CB[7]. The typi-
cal cyclic voltammograms indicate that the oxidation reduction
characteristic of P4VBVBu is remarkably affected by the addi-
tion of CB[7] because of the formation of polypseudorotaxanes
and the shielding effects of CB[7] threaded on the viologen
units of polypseudorotaxanes. With the increase of the concen-
tration of KBr or K2SO4, the formation of the polypseudorotax-
anes was inhibited due to the shielding effects of both Brꢀ or
SO24ꢀ to viologen ion and Kþ to CB[7] by UV–vis. 2010 Wiley
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Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2135–
2142, 2010
KEYWORDS: cucurbit[7]uril;
polyrotaxanes;
self-assembly;
water-soluble polymers
INTRODUCTION Supramolecular chemistry1,2 has ushered
polymer chemistry into a new era. Polypseudorotaxanes, in
which many cyclic molecular ‘‘beads’’ are threaded by a
long ‘‘string,’’ not only have their unique structures but
also have their unusual properties different from those of
conventional covalent polymers,1,3–5 such as potential use
as a material for molecular devices6–12 and catalysts.13–16
Since the earliest example of poly (ethylene glycol)
containing a-cyclodextrin threaded in aqueous media,17 a-,
b- and c-cyclodextrin, crown ether, and cyclophane have
been threaded onto a number of different linear polymer
backbones.18–28
cucurbit[6]uril as a molecular bead that have been also
reported.34,45–48
These investigations expend our understanding about side-
chain polypseudorotaxanes with CB[7] as a molecular bead.
Herein, we synthesized a novel water soluble side-chain
polypseudorotaxanes with CB[7] threaded on viologen pend-
ants attached to a main polymer chain. The thermal stability
of polypseudorotaxanes with CB[7] was investigated by TGA.
The average hydrodynamic radius (Rh), the distribution of
the hydrodynamic radius, and the oxidation reduction char-
acteristics were studied by DLS and cyclic voltammograms,
respectively. The binding constant was obtained and the
effects of salt on the formation of polypseudorotaxanes were
studied by UV–vis spectra.
Cucurbit[7]uril(CB[7]), a water soluble, barrel-shaped host,
consists of 7 glycoluril groups and 14 methylene bridges at
both ends. The two rims are formed by the glycoluril car-
bonyl oxygens, thereby are negatively charged, and they de-
velop ion-dipole interactions with cationic guests.29,30 Tak-
ing advantage of cucurbit[n]uril’s structure, various
mechanically interlocked molecules including rotaxanes and
poly(pseudo)rotaxanes have been synthesized by Kim,31–39
Buschmann40–42 and others.16,43,44 We previously synthe-
sized some side-chain polypseudorotaxanes containing
EXPERIMENTAL
Materials
CB[7] was prepared according to the literature.29,30 4,40-
dipyridyl (98%) and 4-vinybenzyl chlorine (90%) were
received from ACRO. Anhydrous acetonitrile (AR) and n-butyl
bromide (AR) were received from the Sinopharm Chemical
Reagent Co., (SCRC).
Correspondence to: Y. Tan (E-mail: ybtan@sdu.edu.cn)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 2135–2142 (2010) 2010 Wiley Periodicals, Inc.
SYNTHESIS OF POLYPSEUDOROTAXANES P4VBVBU/CB [7], YANG ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
Synthesis of N-n-butyl-4,40-bipyridinium
Synthesis of Polypseudorotaxanes P4VBVBu/CB[7]
Bromide (BuV)
P4VBVBu (0.5 g) was dissolved in water (200 mL) and CB[7]
(0.4 g) was added in the solution of P4VBVBu, and stirred
for 24 h at room temperature. The resulting solution was fil-
trated and the filtrate was concentrated and precipitated by
acetone and dried in vacuum to give polypseudorotaxanes
P4VBVBu/CB[7] (PC3, 0.85 g, 94%). The solid power of PC1 and
4,40-Dipyridyl (7.8 g, 0.05 mol) was dissolved in anhydrous
acetonitrile (40 mL) and stirred for 10 min at room temper-
ature. N-butyl bromide (1.71 g, 0.0125 mol) was slowly
dripped to the solution of 4,40-dipyridyl, and the mixture
ꢁ
was stirred for 40 h at 85 C. The reaction solution was con-
1
centrated by rotary evaporation method and filtrated, and
the yellow precipitate was purified with diethyl ether anhy-
drous and dried in vacuum to give N-n-butyl -4,40-bipyridi-
nium bromide (3.0 g, 81%). mp: 210.0 ꢁC. 1H NMR
(400 MHz, D2O, ppm) d: 0.87 (t, J ¼ 7.4 Hz, 3H, CH3), 1.30
(m, J ¼ 7.6 Hz, 2H, CH2CH3), 1.95 (m, J ¼ 7.4 Hz, 2H,
CH3CH2CH2), 4.57 (t, J ¼ 7.4Hz, 2H, NþCH2), 7.82 (d, J ¼ 6.2
Hz, 2H, PyH), 8.31 (d, J ¼ 6.5 Hz, 2H, PyH), 8.69 (d, J ¼ 6.2
Hz, 2H, PyH), 8.87 (d, J ¼ 6.8 Hz, 2H, PyH); IR (KBr, cmꢀ1) m:
1639 (CANþ), 1539 (C¼¼C and C¼¼N from viologen). Anal.
calcd for C14H17N2Br: C 57.37, H 5.84, N 9.56, C/N ¼ 7;
found C 54.02, H 5.47, N 9.00, C/N ¼ 7.
PC2 for the measurement of H NMR’XRD, TGA, and FTIR were
synthesized by the above method as shown in Table 1. 1H NMR
(D2O, 400 MHz, ppm) d: 0.92 (br, CH3), 1.35 (br, CH2CH3 and
CH2CH from the main chains of P4VBVBu), 1.99 (br, CH3CH2CH2
and CH2CH from the main chains of P4VBVBu), 4.21 (d, 14H
from CB[7]), 4.50 (br, NþCH2), 5.49 (s,14H from CB[7]), 5.66 (d,
14H from CB[7]), 5.88 (br, PhCH2), 6.77, 7.44 (br, Ph), 8.32, 8.49,
8.83, 8.95, 9.13 (br, PyH); IR (KBr, cmꢀ1) m: 1633 (CANþof
P4VBVBu), 1731 (C¼¼O of CB[7]).
Characterization
All 1H NMR experiments were performed on a Bruker
AVANCE400 NMR spectrometer. D2O was used for field-
frequency lock, and the observed 1H chemical shifts were
reported in parts per million (ppm) relative to an internal
standard (TMS, 0 ppm).
Synthesis of Monomer N-n-butyl-N0-(4-vinylbenzyl)-4,
40-bipyridinium Bromide Chloride (4VBVBu)
The mixing solution of 4-vinybenzyl chlorine (3.39 g, 0.02
mol) and BuV (1.47 g, 0.005 mol) in anhydrous acetonitrile
(40 mL) was stirred for 24 h at 80 ꢁC in the oil bath. The
resulting solution was filtrated and then the yellow precipi-
tate was purified with diethyl ether anhydrous and dried in
vacuum to give 4VBVBu (2.1 g, 90%). 1H NMR (D2O,
400 MHz, ppm) d: 0.91 (t, J ¼ 7.4 Hz, 3H, CH3), 1.35 (m, J ¼
7.6 Hz, 2H, CH2CH3), 2.0 (m, J ¼ 7.5 Hz, 2H, CH3CH2CH2),
4.70 (the signal of NþCH2 that overlapped with D2O), 5.35
(d, J ¼ 10.9 Hz, 1H, vinyl), 5.82–5.86(m, 3H, vinyl and
PhCH2), 6.78 (q, J ¼ 6.8 Hz, 1H, vinyl), 7.46 (d, J ¼ 8.2 Hz,
2H, Ph), 7.57 (d, J ¼ 8.2 Hz, 2H, Ph), 8.46 (t, J ¼ 6.6 Hz, 4H,
PyH), 9.04 (d, J ¼ 6.7 Hz, 2H, PyH), 9.95 (d, J ¼ 6.8 Hz, 2H,
PyH); IR (KBr, cmꢀ1) m: 1633 (CANþ), 1539 (C¼¼C and C¼¼N
from viologen), 1446 (C¼¼C from phenyl), 924, 725 (C¼¼C
from vinyl). Anal. Calcd for C23H26N2BrCll4H2O: C 53.33, H
6.60, N 5.41; found C 53.28, H 6.58, N 5.34.
FTIR was carried out on a Tensor 27 spectrometer (Bruker,
Switzerland) with sample prepared as KBr pellets. The spec-
tra were acquired in the frequency range 4000–400 cmꢀ1 at
a resolution of 4 cmꢀ1 with a total of 16 scans.
Elemental analyses (C, N, and H) were performed on Ele-
mentar Vario E1 III analyzer (German).
Thermal characteristics of samples were determined with
Thermogravimetric analyzer (TGA), which was performed
with a MettlerToledo SDTA-851 TGA system. The analysis
was performed with ꢂ10 mg of dried samples in a dynamic
nitrogen aꢁtmosphere (flow rate 50 mL/min) at a heating
rate of 10 C/min.
Multiangle laser light scattering (MALLS) measurements were
performed by the Wyatt Technology DAWN HELEOS 18 angle
(from 15ꢁ to 165ꢁ) light scattering detector using a Ga-As laser
(658 nm, 40 mW). The refractive index increments (dn/dc) of
Synthesis of Poly-N-n-butyl-N0-(4-vinylbenzyl)-4,
40-bipyridinium Bromide Chloride (P4VBVBu)
ꢁ
P4VBVBu in aqueous solution were determined at 25 C by an
4VBVBu (3.0 g) was added to a 3-neck flask and stirred with
a magnetic stir bar under an inert N2 atmosphere and
heated to 85 ꢁC with an oil bath. After thermal equilibrium
reached and the solution had been bubbled for 0.5 h, K2S2O8
was added and reacted for 24 h at this temperature to give
a crude product (2.58 g, 86%), which was dialyzed through
a semipermeable membrane with distilled water for 5 days.
The dialyzed aqueous was concentrated and precipitated
with acetone and dried in vacuum to give the polymer (1 g,
38.8%). 1H NMR (D2O, 400 MHz, ppm) d: 0.92 (br, CH3),
1.34 (br, CH2CH3 and CH2CH from the main chains), 1.99 (br,
CH3CH2CH2 and CH2CH from the main chains), 4.70 (the sig-
nal of NþCH2 that overlapped with D2O), 5.87 (br, PhCH2),
Optilab Rex interferometeric refractometer (Wyatt Technology)
at the wavelength of 658 nm, and the concentrations of
P4VBVBu determined in aqueous solution for Zimm plot were
3.3750 ꢃ 10ꢀ4, 6.6750 ꢃ 10ꢀ4, 1.0013 ꢃ 10ꢀ3, 1.3350 ꢃ
10ꢀ3, 1.6688 ꢃ 10ꢀ3, and 2.0025 ꢃ 10ꢀ3 g/mL.
DLS was performed on Dawn Heleos, Wyatt QELS and Opti-
lab DSP instrument. The water used for Light Scattering
measurements were all filtered through Millipore 0.45 lm
hydrophilic membranes before using. The concentrations of
P4VBVBu and guest of polypseudorotaxanes for the distribu-
tion of the hydrodynamic radius and the average hydrody-
namic radius were all 1 mg/mL.
6.68, 7.40 (br, Ph), 8.53, 8.93, 9.07 (br, PyH); IR (KBr, cmꢀ1
)
Data of X-ray Powder Diffraction (XRD) were collected on a
Max 2200PC power X-ray diffractometer (Rigaku, Japan)
with Cu-Ka (1.54051 Å) radiation (40 kV, 20 mA). Powder
m: 1633 (CANþ), 1447 (C¼¼C from phenyl), 1539 (C¼¼C and
C¼¼N from viologen).
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TABLE 1 The Composition and the Mw of Polymer and Polypseudorotaxanes P4VBVBu/CB [7]
The Molar Ratio of CB[7]
to Viologen Units of P4VBVBu
at the Time of Synthesis
Elemental Analyses
The Actual Molar
Ratio of CB[7] to Viologen
Units of P4VBVBu
Sample
C (wt %)
H (wt %)
N (wt %)
Mw (g molꢀ1
)
P4VBVBu
PC1
0
53.33
52.69
51.29
50.19
6.60
4.88
4.65
4.54
d
5.41
10.86
14.48
17.11
0a
0b
1.14 ꢃ 105c
1.36 ꢃ 105d
1.61 ꢃ 105d
1.90 ꢃ 105d
0.145
0.247
0.347
0.11a
0.21a
0.32a
0.08b
0.18b
0.29b
PC2
PC3
a
Determined by elemental analyses.
Determined by 1H NMR spectra.
Determined by static light scattering.
Calculated by the actual molar ratio of CB[7] to viologen units of
b
c
P4VBVBu determined by 1H NMR spectra.
samples were mounted on a sample holder and scanned
with a step size of 2h ¼ 0.02ꢁ between 2h ¼ 5ꢁ and 50ꢁ.
gen, and nitrogen as listed in Table 1, which was in good
agreement with the results of the H NMR spectra.
1
All electrochemical experiments were carried out in a standard
In static light scattering, we are able to obtain the weight-
average molar mass Mw, the second-order virial coefficient
A2, and the mean square radius hr2gi of polymer chains from
the angular dependence of the excess absolute scattering in-
tensity, known as the Rayleigh ratio R(h), on the basis of
ꢁ
three-electrode cell at room temperature (ꢂ25 C) using a CHI
760 dual channel electrochemical workstation (CHI instru-
ments). Mercury/mercurous sulfate electrode (MMSE) as refer-
ence electrode, Pt foil as counter electrode, and glassy carbon
electrode as working electrode were used in a standard three-
electrode cell. All solutions were purged with ultrapure nitro-
gen for about 20 min before electrochemical measurements.
ꢀ
ꢁ
KꢄC
1
1
¼
1 þ hrg2iq2 þ 2A2C
(1)
RðhÞ Mw
3
where K* ¼ 4p(dn/dc)2 n0/(NAk04) and q ¼ (4pn0/k0) sin(y/2),
with no, dn/dc, k0 and y being the solvent refractive index, the
specific refractive index increment, the wavelength of the inci-
The UV–vis spectra were measured by UV-4100 (Japan) at
ꢁ
25 C, and the range of scanning was from 200 to 600 nm.
dent light in vacuum and the scattering angle, respectively,49,50
.
RESULTS AND DISCUSSION
Figure 1 shows a typical static Zimm plot of P4VBVBu in water
solutions, where C ranges from 3.375 ꢃ 10ꢀ4 to 2.0025 ꢃ 10ꢀ3
g/mL. The date of static light scattering measurements indicated
that the weight-average molar mass Mw of P4VBVBu was 1.03
ꢃ 105 g/mol, and Mw of polypseudorotaxanes with CB[7] were
calculated by the actual mole ratio of CB[7]/P4VBVBu deter-
mined by 1H NMR spectra and the actual Mw of polymer deter-
mined by static light scattering.
Preparation of P4VBVBu and Polypseudorotaxanes
with CB[7] Threaded
Monomer 4VBVBu was prepared by 4-vinybenzyl chlorine
and BuV, which was synthesized by 4,40-dipyridyl and n-
butyl bromide, and the polymer P4VBVBu was prepared
using K2S2O8 as the initiator and 4VBVBu as the polymer
monomer in water under the inter N2 atmosphere by the
free radical polymerization as shown in Scheme 1. Side-chain
polypseudorotaxanes were easily achieved by self-assembly
of P4VBVBu with a certain amount of CB[7] in water at
room temperature for 24 h as shown in Scheme 2.
1H NMR Spectra
The host-guest interaction of P4VBVBu with CB[7] was
1
investigated by H NMR spectrum. Figure 2 are the 1H NMR
spectra of CB[7] (1 mg/mL), PC1 (2.46 mg/mL), PC2 (2.92
mg/mL), PC3 (3.38 mg/mL), P4VBVBu (2 mg/mL), and
monomer 4VBVBu (2 mg/mL). Upon formation of polypseu-
dorotaxanes, new broad signals appear at 4.21, 5.49, and
The polypseudorotaxanes with different degree of CB[7]
threaded were determined by elemental analyses as shown
in Table 1, while the actual mole ratio of CB[7]/P4VBVBu
were calculated via the weight percentages of carbon, hydro-
SCHEME 1 Synthesis of polymer P4VBVBu.
SCHEME 2 Synthesis of the side-chain polypseudorotaxanes.
SYNTHESIS OF POLYPSEUDOROTAXANES P4VBVBU/CB [7], YANG ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
of CB[7] threaded onto the side chains of the polymer can
be estimated by calculating the ratio of the peak area of i0 to
peak a (the side-chain methyl peak of P4VBVBu) in the 1H
NMR spectra, which indicates that the degree of threading of
polypseudorotaxanes P4VBVBu/CB[7] (the molar ratio of
CB[7] threaded to the viologen units of P4VBVBu) could be
controlled between 0 and 0.3 simply by adding a certain
amount of CB[7] into the solution of P4VBVBu.
FTIR Spectra
Figure 3 shows FTIR spectra of CB[7], polypseudorotaxanes
PC3 and P4VBVBu. The extreme bands at 1731 cmꢀ1 and 1633
cmꢀ1 as shown in Figure 3 are the characteristic absorption
peaks of C¼¼O of CB[7] and viologen unite of polymer P4VBVBu,
respectively. Also, the band at 1731 and 1633 cmꢀ1 are
observed in polypseudorotaxanes PC3 as shown in Figure 3. The
FTIR data are indirect proof for the existence of polypseudoro-
taxanes P4VBVBu/CB[7].
FIGURE 1 Typical Zimm plot for P4VBVBu in water.
5.66 ppm, which correspond to threaded CB[7]. Upon addi-
tion of CB[7], a part of the viologen proton signal (peak i
and h) of P4VBVBu are upfield shifted from 8.93 to 8.83
(peak i0) and from 8.53 to 8.32 (peak h0) as shown in Figure
2, while the signals (e, f, and g) of the benzyl protons, which
are located just outside of the CB[7], are downfield shifted
from 5.87, 6.68, 7.40 to 5.88, 6.77, 7.44. The other protons
(a, b, c, and d), which are located far from the CB[7], remain
unchanged or have a little change. With the adding of CB[7],
the areas of the peak i0 and h0 shielded by CB[7] increases as
shown with arrows in insert of Figure 2. The 1H NMR data
supports that the CB[7] beads threaded in the side chains of
P4VBVBu are located on the viologen units, and the amount
X-Ray Powder Diffraction (XRD)
Figure 4 shows the XRD patterns of P4VBVBu, CB[7] and
polypseudorotaxanes P4VBVBu/CB[7] with different degree of
CB[7] threaded. No sharp peaks reflected in the pattern of
polymer P4VBVBu show that it is a typical noncrystalline poly-
mer as shown in Figure 4. While comparing with polymer
P4VBVBu, CB[7] has crystal composition because there are
three sharper peaks (2h ¼ 12.8, 21.1, 27.8) in the XRD pattern
as shown in Figure 4. As the amount of CB[7] threaded
increases from 0 to 0.3 as shown in Figure 4, a new set of
peaks appear (2h ¼ 12.8, 27.8). The intensity of the peaks (2h
¼ 12.8, 21.1, 27.8) increase with increasing amount of CB[7]
FIGURE
2
1H NMR spectra of
CB[7] (1 mg/mL), PC1 (2.46 mg/
mL), PC2 (2.92 mg/mL), PC3 (3.38
mg/mL), P4VBVBu (2 mg/mL),
and monomer 4VBVBu (2 mg/
mL). Insert image shows a mag-
nified image of the increase of
peak i0 and h0.
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ARTICLE
FIGURE 3 FTIR spectra of CB[7], polypseudorotaxanes PC3,
and P4VBVBu.
threaded and approach that of pure CB[7] as shown in Figure
4. The increasing intensity suggests that the threading of CB[7]
may cause chain conformational changes of the polymer. Com-
pared with the parent polymer, the polypseudorotaxanes have
more regular chain conformation because of amount of the
threaded CB[7] beads (as shown in Fig. 8), and the regularity
of the chain conformation increases with increasing amount of
CB[7] threaded.
Thermal Properties
Figure 5 shows the TGA and DTGA curves of P4VBVBu,
CB[7] and polypseudorotaxanes with different degree of
CB[7] threaded (PC1, PC2, and PC3). The polypseudorotax-
anes P4VBVBu/CB[7] show three major mass loss steps
under nitrogen atmosphere. The first transition occurs near
325 ꢁC and may be associated with the loss of the side
chains of polymer, which are not threaded by CB[7], and this
decomposition temperature is somewhat higher than that of
P4VBVBu and increases with increasing the mole percentage
FIGURE 5 (a) TGA curves of polymer P4VBVBu, CB[7], and
polypseudorotaxanes with different degree of CB[7] threaded
(PC1, PC2, and PC3); (b) DTGA curves of P4VBVBu, CB[7], and
polypseudorotaxanes PC1, PC2, and PC3.
FIGURE 6 The distribution of the hydrodynamic radius of a (CCB[7]
¼ 0.69 mg/mL), b (CP4VBVBu ¼ 1 mg/mL), c (CP4VBVBu ¼ 1 mg/mL,
CCB[7] ¼ 0.23 mg/mL), d (CP4VBVBu ¼ 1 mg/mL, CCB[7] ¼ 0.46 mg/
mL), and e (CP4VBVBu ¼ 1 mg/mL, CCB[7] ¼ 0.69 mg/mL) in water.
FIGURE 4 XRD patterns of P4VBVBu, polypseudorotaxanes
PC1, PC2, PC3, and CB[7].
SYNTHESIS OF POLYPSEUDOROTAXANES P4VBVBU/CB [7], YANG ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 7 The average hydrodynamic radius (Rh) of a (CP4VBVBu
¼ 1 mg/mL), b (CP4VBVBu ¼ 1 mg/mL, CCB[7] ¼ 0.23 mg/mL), c
FIGURE 9 UV-vis absorption spectrum of 50 mg/L P4VBVBu in
absent and presence of CB[7] (10, 20, 30, 40, 50 lmol/L). Insert
shows a plot of the relative absorbance as a function of the ra-
tio of CB[7] to viologen unites of P4VBVBu.
(CP4VBVBu ¼ 1 mg/mL, CCB[7] ¼ 0.46 mg/mL), and d (CP4VBVBu
1 mg/mL, CCB[7] ¼ 0.69 mg/mL).
¼
of CB[7] (shown with arrows in Figure 5 (b)). This reason
may be that the van der Waals interaction of the side chains
are enhanced with increasing amount of CB[7] threaded. The
second transition occurs at 429 ꢁC and is loss of CB[7]
threaded, which is compared with the loss of pure CB[7]. Inter-
estingly, a new peak of the DTGA curve (the third transition of
polypseudorotaxanes P4VBVBu/CB[7]) is observed near 492 ꢁC
comparing with the curves of pure P4VBVBu and CB[7] and the
peak area increases with increasing the mole ratio of CB[7]. It is
considered that it is loss of the viologen shielded by CB[7],
which enhances the thermal stability of the viologen.
and the distribution of Rh and the average Rh of the poly-
pseudorotaxanes increase with the increasing CB[7] threaded
because the regularity of the polypseudorotaxanes chain con-
formation increases with increasing the amount of CB[7]
threaded as shown in Figure 8.
The Binding Constant of the Polypseudorotaxanes
by UV–Vis Spectra
Figure 9 shows UV–vis spectra of P4VBVBu (50 mg/L) and
P4VBVBu (50 mg/L) with different concentrations of CB[7]
(10, 20, 30, 40, 50 lM). The pattern of P4VBVBu exhibits a
strong absorption band centered around 260 nm, which is a
characteristic absorption peak of polyviologen and the absorp-
tion peak of CB[7] around 260 nm is inexistence. The date of
the experiment indicate that the intensity of the band
decreases with increasing amount of CB[7] threaded. Obvi-
ously, both P4VBVBu and CB[7] could form the polypseudoro-
taxanes by the host-guest interactions, and the viologen chro-
mophore is shielded by the threading of CB[7], which is in
accord with the results of 1H NMR and FTIR. The insert of
Figure 3 shows a plot of the relative absorbance (A/Ao, where
A is the corresponding absorbance intensity at 260 nm in pres-
ence of different equiv. of CB[7] and Ao is the absorbance in-
tensity in absent of CB[7]) as a function of the ratio of CB[7]
to viologen unites of P4VBVBu. The data show that both CB[7]
and P4VBVBu could reach equilibrium and form the polypseu-
dorotaxanes, when the molar ratio of CB[7] to the viologen
units of P4VBVBu is 0.4, and the binding constant of CB[7]
and the viologen units of P4VBVBu is 2 ꢃ 103 L/mol.
DLS Measurements
The distribution of the hydrodynamic radius and the average
hydrodynamic radius of P4VBVBu (1 mg/mL), CB[7] (0.69
mg/mL) and P4VBVBu (1 mg/mL) with different concentra-
tions of CB[7] (0.23, 0.46, 0.69 mg/mL) in water are
obtained by DLS as shown in Figure 6 and Figure 7. The
sizes of the aggregates in water increase with adding CB[7]
as shown in Figure 6, and the average hydrodynamic radius
of the aggregates also increases with the adding of CB[7] as
shown in Figure 7. These results indicate that P4VBVBu and
CB[7] are not simply mixed but form polypseudorotaxanes,
Electrochemistry of P4VBVBu and Polypseudorotaxanes
with CB[7]
Typical cyclic voltammograms curves of P4VBVBu (50 mg/L)
obtained in the absence and presence of CB[7] (10, 20, 30
lM) are shown in Figure 10, and the corresponding peak
potentials (Ep) are given in Table 2. The data indicate that
P4VBVBu undergoes two reversible one-electron reductions in
the absence of CB[7]. However, the addition of CB[7] produces
FIGURE 8 The model of conformational changes of the chain
with CB[7] threaded.
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ARTICLE
FIGURE 10 Cyclie voltammograms curves (0.05 v/s) of
a
FIGURE 11 The effects of salts on the formation of polypseu-
(CP4VBVBu ¼ 50 mg/L), b (CP4VBVBu ¼ 50 mg/L, CCB[7] ¼ 10 lmol/
L), c (CP4VBVBu ¼ 50 mg/L, CCB[7] ¼ 20 lmol/L), and d (CP4VBVBu
¼ 50 mg/L, CCB[7] ¼ 30 lmol/L).
dorotaxanes between CB[7] and P4VBVBu.
sity of P4VBVBu (50 mg/L) at 260 nm in absent of CB[7]) of
CB[7] threaded to viologen units of P4VBVBu, which indi-
cates the degree of the formation of the polypseudorotax-
anes, decreases with increasing the concentration of KBr or
K2SO4, and the molar ratio effected by the concentration of
K2SO4 decreases more quickly than KBr. It is considered that
the formation of the polypseudorotaxanes was inhibited by
the adding of salts because that the host-guest interactions
decease by the shielding effects of both Brꢀ or SO42ꢀ to violo-
gen ion and Kþ to CB[7], and the more inhibitory effect of
K2SO4 on the formation of polypseudorotaxanes than KBr
may be the result of more shielding effects of SO24ꢀ than Brꢀ.
a remarkable effect on the cyclic voltammograms of P4VBVBu,
which is that the peak potentials have a noticeable shift and
the peak areas have a marked decrease with increasing the
concentration of CB[7], because that the viologen units of the
polypseudorotaxanes formed P4VBVBu and CB[7] by the host-
guest interactions are shielded by CB[7] threaded.
The shift in peak potentials reflects relative binding affinities
of the guest of different redox states to the host.51 The much
larger negative shift observed in the peak potential for the first
oxidation reveals that the binding affinity of the fully reduced,
neutral species to CB[7] is considerably reduced. On the other
hand, the small negative shift in the Ep value of the second oxi-
dation of polypseudorotaxanes with CB[7] threaded indicates
that the cation radical form interacts slightly less strongly with
CB[7] compared with the dication form. Therefore, the voltam-
meric results clearly demonstrate that CB[7] are threaded in
the viologen units of P4VBVBu to form the polypseudorotax-
anes and have remarkable effect on the oxidation reduction
characteristic of the polypseudorotaxanes.
CONCLUSIONS
We synthesized a novel water soluble side-chain polypseu-
dorotaxanes with CB[7], which were localized on the violo-
gen units in side chains of the polymer. The structure of
polypseudorotaxanes with CB[7] was characterized by 1H
NMR, IR, XRD and UV-vis. DLS results showed that the aver-
age size of the aggregates in water increased with the
increasing of CB[7] threaded, and TGA data indicated that
the regularity of the polypseudorotaxanes chain conforma-
tion increased with increasing amount of CB[7] threaded,
which led to the increasing of the polypseudorotaxanes ther-
mal stability. The typical cyclic voltammograms showed that
the peak potentials had a noticeable shift and the peak areas
had a marked decrease with increasing the mole ratio of
CB[7] threaded. UV-vis data showed that both CB[7] and
P4VBVBu could form the polypseudorotaxanes with the
binding constant of 2 ꢃ 103 L/mol, and the formation of the
polypseudorotaxanes was inhibited by increasing the concen-
tration of KBr or K2SO4 due to the shielding effects of both
Brꢀ or SO24ꢀ to viologen ion and Kþ to CB[7].
Effect of Salts on the Formation of Polypseudorotaxanes
Figure 11 shows the molar ratio (1-Ao/A, where A is the cor-
responding absorbance intensity of P4VBVBu (50 mg/L) and
CB[7] (20lmol/L) at 260 nm in presence of different con-
centrations of KBr or K2SO4 and Ao is the absorbance inten-
TABLE 2 The Peak Potential for P4VBVBu (50 mg/L) in the
Absence and Presence of CB[7] (10, 20, 30 lmol L21
)
E1p (V)a
E2p (V)b
P4VBVBu (a)
P4VBVBu/CB[7] (b)
P4VBVBu/CB[7] (c)
P4VBVBu/CB[7] (d)
a
ꢀ0.818
ꢀ0.919
ꢀ0.934
ꢀ1.071
ꢀ0.656
ꢀ0.693
ꢀ0.712
ꢀ0.792
The authors are grateful for financial support from the
National Natural Science Foundation of China (No.
20674045), National Basic Research Program of China (973
Program, 2009CB930103) and Graduate Independent Inno-
vation Foundation of Shandong University (yzc09057).
The peak potential for the first oxidation process expressed in volts
vs. saturated calomel electrode.
b
The peak potential for the second oxidation process.
SYNTHESIS OF POLYPSEUDOROTAXANES P4VBVBU/CB [7], YANG ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
27 Huang, F.; Gibson H. W. Prog Polym Sci 2005, 30, 982–1018.
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