High yield production of high molecular weight poly(ethylene glycol)/α-cyclodextrin polyrotaxanes by aqueous one-pot approach

Article abstract of DOI:10.1016/j.polymer.2012.04.038

An easy, one-pot, high-yield preparation of high molecular weight polyrotaxanes (PRs) from poly(ethylene glycol) (PEG) and α-cyclodextrin (α-CD) by click chemistry is presented with novel water soluble and clickable end-capping agents containing quaternary ammonium and propargyl groups. The threading numbers of α-CD on the PEG chain were investigated by means of ¹H NMR spectroscopy and gel permeation chromatography (GPC). When M_n of the PEG axis is 35 kDa, the yield is up to 614 mg per 100 mg PEG axis and the average number of α-CDs on each PEG axis is 193. Wide-angle X-ray diffraction (WAXD) revealed that PRs form a column-type crystalline structure. The prepared PR possesses terminal alkyne groups which can connect with functional molecules to make the PR more useful. As a typical example, fluorescent rhodamine B has been successfully installed on the PR terminals.

Full text of DOI:10.1016/j.polymer.2012.04.038

Polymer 53 (2012) 2884e2889
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
High yield production of high molecular weight poly(ethylene glycol)/
a-cyclodextrin polyrotaxanes by aqueous one-pot approach
Haiyan Sun, Jin Han, Chao Gao*
MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, 38 Zheda Road,
Hangzhou 310027, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 January 2012
Received in revised form
An easy, one-pot, high-yield preparation of high molecular weight polyrotaxanes (PRs) from poly(-
ethylene glycol) (PEG) and
soluble and clickable end-capping agents containing quaternary ammonium and propargyl groups. The
-CD on the PEG chain were investigated by means of 1H NMR spectroscopy and
threading numbers of
gel permeation chromatography (GPC). When M of the PEG axis is 35 kDa, the yield is up to 614 mg per
00 mg PEG axis and the average number of -CDs on each PEG axis is 193. Wide-angle X-ray diffraction
WAXD) revealed that PRs form a column-type crystalline structure. The prepared PR possesses terminal
a-cyclodextrin (a-CD) by click chemistry is presented with novel water
15 April 2012
a
Accepted 22 April 2012
Available online 9 May 2012
n
1
a
(
Keywords:
High molecular weight polyrotaxanes
One-pot approach
alkyne groups which can connect with functional molecules to make the PR more useful. As a typical
example, fluorescent rhodamine B has been successfully installed on the PR terminals.
Ó 2012 Elsevier Ltd. All rights reserved.
Alkyl stoppers
1. Introduction
threading PR by photocyclodimerization of terminal 9-anthryl
groups of the poly(propylene glycol) axis in the presence of
g-
In the early 1990s, Harada [1e8] first reported the preparation of
stable necklace-like supramolecules, polyrotaxanes (PRs), by end-
capping the terminal of the pseudo-polyrotaxanes (pseudo-PRs)
formed via inclusion complexation between linear polyethylene
CDs [27]. Hadziioannou et al. tried to prepare -CDs/PEG PR with
a
sodium picrylsulfonate as capping agent in water in one pot, but the
yield was much lower than that in two pots [28]. Yui et al. utilized
polyethylenimine (PEI)-b-PEG-b-PEI copolymer as the axis to
elaborate PR in aqueous solution capped with 9-anthraldehyde
(AN) by forming Schiff base bond at lower pH 4.4 [29]. Takata
et al. prepared PRs by threading diamineterminated PEG with
glycol (PEG) and a-cyclodextrin (a-CD) with bulky stoppers. Since
then, pseudo-PRs with various topologies [9e15] and PRs capped
with various bulky stoppers [16e22] were elaborated. Two-steps
are generally required to prepare PRs: formation of pseudo-PRs in
water and end-capping in organic solvent [23e26]. Although great
progress has been made with such a two-step strategy, some big
problems still remain to be addressed, such as low yield of PR and
pristine or permethylated
a-CDs in water or organic solvent,
respectively, and employing a bulky isocyanate as the stopper
[30e32], and proved the convenience and efficiency of the one-pot
strategy. Our group utilized click chemistry via the one-pot protocol
sparse threading percentage of
a
-CDs on PEG, due to the strong and
to prepare “full CD” PR capped by b-CD in water at room temper-
quick dethreading inclination of the axle from the pseudo-PR
during the end-capping process in an organic solvent. Conse-
quently, it is difficult to obtain the high CD coverage ratio of PRs in
large-scale, which poses an obstacle to the deep study on the
property and potential application of PRs. Therefore, it is urgently
calling for a novel strategy to efficiently prepare PRs.
ature with high yield, up to 320 mg PR/100 mg PEG-4600 axis [33].
Further modification of PRs via click chemistry afforded a series of
amphiphilic “sliding supramolecular polymer brushes” and novel
biocompatible amino acids-functionalized PRs [34,35], showing the
great potential of PR functionalization. However, so far whatever in
the two pot or the one-pot strategy, both the yield and the inclusion
ratio of CD threading on axis are relatively low for the high
molecular weight of PEG axis.
Recently, a one-pot strategy showing great advance has been
presented, which directly carries out end-capping reaction in
aqueous solution of pseudo-PRs. Harada et al. prepared
g-CD-
To meet such a challenge, highly water-soluble, novel quater-
nary ammonium salt stoppers are synthesized in this paper, and
used to facilely and efficiently prepare high molecular weight PRs
by the one-pot click chemistry-based strategy. Because of the
ultrahigh reactivity of the alkyl stoppers, a record high yield of PRs
*
Corresponding author.
E-mail addresses: chaogao@zju.edu.cn, cgao18@gmail.com (C. Gao).
0
032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2012.04.038

H. Sun et al. / Polymer 53 (2012) 2884e2889
2885
is achieved. More importantly, end-capping reaction with multi-
alkynyl stoppers can install alkynyl groups on PR terminals,
2.4. Synthesis of water-soluble di-alkyne quaternary ammonium
salt (DAS)
which can be utilized for further modification.
TMEDA (2.92 g, 25.1 mmol) was dissolved in 20 mL DMF. The
solution was cooled in an ice bath and then added dropwise with
propargyl bromide (6.25 g, 52.9 mmol) under magnetic stirring.
The reaction system was kept at room temperature for 10 h and
followed by pouring into acetone (80 mL). The white precipitates
were collected and washed twice with acetone, then dried under
2
. Experimental section
2.1. Materials
Poly(ethylene glycol) (PEG) (HO-PEG1-OH, M
n
¼ 35 kDa), HO-
ꢀ
PEG2-OH (M
n
¼ 12 kDa), (t)-sodium
L
-ascorbate (98%), valeryl
vacuum at 30 C for 24 h, affording DAS as hygroscopic white
1
chloride (98%), and rhodamine B (RhB, 95%) were purchased from
SigmaeAldrich. 2-Azidoethanol, 4-(2-azidoethoxy)-4-oxobutanoic
acid (Carboxylic azide), diazido-terminated PEG1 (N
diazido-terminated PEG2 (N -PEG2-N ), and azido-functionalized
RhB (RhB-N ) were prepared according to the Ref. [33,36] Prop-
argyl bromide (97%), N,N,N ,N ,N -pentamethyldiethylenetriamine
powder. Yield: 8.33 g, 94.2%. H NMR (300 MHz, DMSO-d
6
):
), 4.10(m, 4H, CH
NMR (75 MHz, O):
N), 55.51 (CHCCH NCH
), 55.02 (CH CH
d
4.59
(m, 4H, CHCCH
3.24(m, 12H, N(CH
2
), 4.20 (m, 2H, CHCCH
2
2
CH ),
2
13
3
-PEG1-N
3
),
3
)
2
).
C
D
2
d
83.88
CCH),
3
3
(CHCCH
2
N), 70.41 (CHCCH
2
2
2
CH
2
NCH
2
0
0
3
55.35 (CH
2
CH
2
N CH
2
CH
2
2
2
N CH
2
CH
2
), 52.22
0
00 00
0
(CH
3
N ).
0
0
(
(
9
PMDETA, 98%), and N,N,N ,N -tetramethylethylenediamine
TMEDA, 99%) were acquired from Alfa Aesar. -Cyclodextrin ( -CD,
9%) was provided by Shanxi Liquan Chemical Co., Ltd. DMSO,
CuSO $5H O and all the other materials used were obtained from
Sinopharm Chemical Reagent Co., Ltd. DMF, Triethylamine (TEA)
were dried over CaH and distilled prior to use.
a
a
2.5. Synthesis of water-soluble tri-alkyne quaternary ammonium
salt (TAS)
4
2
A mixture of DMF (70 mL) and PMDETA (7.05 g, 40.7 mmol) was
2
ꢀ
charged to a 150 mL flask and kept at 0 C. Then, propargyl bromide
14.54 g, 123,3 mmol) was added dropwise. After being stirred at
(
2.2. Instruments
room temperature for 48 h, the mixture was poured into acetone to
yield white precipitate. The precipitate was collected, washed twice
Gel permeation chromatography (GPC) was recorded on Perkin
Elmer HP 1100, using LiBr/DMF 0.01 mol/L as eluent at a flow rate of
1
calibration at 70 C. H NMR (300 MHz) measurements were
carried out on a Varian Mercury plus 300 NMR spectrometer using
3 6
CDCl or DMSO-d as solvent. Fourier transform infrared (FT-IR)
spectra were recorded on a PE Paragon 1000 spectrometer (film or
KBr disk). Wide-angle X-ray diffraction (WAXD) patterns were
obtained by using Rigaku X-ray diffractometer D/max-2200/PC
ꢀ
with acetone, and then dried under vacuum at 30 C for 24 h. TAS
1
was obtained as hygroscopic white powder. Yield: 19.36 g, 90.3%. H
mL/min, RI-WAT 150CVt þ as detector and linear polystyrene as
0
NMR (300 MHz, DMSO-d
6
):
d
4.75 (s, 2H, CHCCH
2
N ), 4.67 (s, 4H,
ꢀ
1
0
0
0
CHCCH
H, CH
s, 3H, CH
2
N and CHCCH
2
N ), 4.31(s, 1H, CHCCH
2
N ), 4.28e4.24 (m,
N and CHCCH
and N (CH
N ), 85.04 (CHCCH
0
00
8
(
(
2
CH
2
N CH
2
CH
2
), 4.22 (m, 2H, CHCCH
2
2
N ), 3.37
0
00
13
3
N ), 3.31 (m, 12H, N(CH
3
)
2
3
)
2
). C NMR
0
00
75 MHz, DMSO-d
6
):
d
82.26 (CHCCH
2
2
N
and
0
0
0
CHCCH
5.50(N(CH
2
N), 72.36 (CHCCH
2
N
and CHCCH
2
N), 71.54 (CHCCH
2
N ),
0
0
0
5
3
)
2
and N (CH
CH
0
2
N), 49.94 (CHCCH N ).
3
)
2
), 55.35 (CH
2
CH
2
N CH
2
CH
2
), 55.02
equipped with Cu Ka radiation (40 kV, 20 mA) at the rate of 5.0
0
0
00
(CH
2
CH
2
N CH
2
2
), 53.71 (CH
3
N ), 51.34 (CHCCH
2
N
and
deg/min. The samples for atomic force microscopy (AFM)
measurement were prepared by spin-coating sample solutions
onto freshly cleaved mica substrates at 1000 rpm, and the images
were taken in the tapping mode on an NSK SPI3800. Transmission
electron microscopy (TEM) measurements were performed on
a JEOL JEM2010 electron microscope at 200 kV. Thermal gravita-
tional analysis (TGA) was carried out using a PerkineElmer Pyris 6
CHCCH
2
3 3
2.6. Synthesis of PR with N -PEG1-N via one-pot strategy (PR1A)
Typically, an aqueous solution (100 mL) of N
3 3
-PEG1-N (1.00 g,
0.028 mmol) and -CD (12.00 g, 12.94 mmol) was ultrasonically
a
ꢀ
TGA instrument with a heating rate of 20 C/min under a nitrogen
agitated at room temperature for 5 min and then stirred overnight
to form pseudo-PR1A. To this mixture, TAS (89.5 mg, 0.17 mmol,
flow (30 mL/min). Fluorescence lifetimes were measured on Edin-
burgh instruments FLS 920. A flash lamp (nF900, 2.5 ns) was used
to excite the samples and reconvolution fitting was utilized as the
data analysis method with instrument respond function. Fourier
transform infrared (FTIR) spectra were recorded on a PE Paragon
the molar ratio of alkyne to eN
0.56 mmol), PMDETA (120.5
3
m
was 6:1), CuSO
L, 0.58 mmol) and (t)-sodium L-
4 2
$5H O (141.2 mg,
ascorbate (224.1 mg, 1.12 mmol) were added successively under
nitrogen atmosphere. After reacting at room temperature for 10
min-24 h in darkness, the precipitate was collected by centrifu-
1000 spectrometer (KBr disk and film).
ꢀ
gation, washed with 300 mL hot water (60 C) for more than 5
ꢀ
2.3. Synthesis of water-soluble mono-alkyne quaternary
times and then dried under vacuum at 65 C for 24 h, affording
1
ammonium salt (MAS)
PR1A as white powder. Yield: 357e614 mg/100 mg PEG axis.
NMR (300 MHz, DMSO-d ):
2,4), 3.49 (m, 2H, CH of PEG), 3.55e3.79 (br overlapped, 18H, H-
H
6
d 3.22e3.40 (br overlapped, 12H, H-
A 50 mL CHCl
3
solution of triethylamine (5.64 g, 55.7 mmol) was
2
prepared in a 100 mL flask and cooled in an ice bath. Then, prop-
argyl bromide (5.52 g, 46.8 mmol) was added dropwise to the
solution under magnetic stirring. After being kept in darkness at
room temperature for 6 h, the mixture was poured into ethyl ether
3,5,6), 4.46 (m, 6H, OH-6), 4.78 (m, 6H, H-1), 5.41e5.51 (m, 12H,
OH-2,3).
In other experiments, PEG2 was used instead of PEG1, and
other stoppers such as TAS and DAS were used instead of MAS. In
(
200 mL). The collected precipitate was washed twice with ethyl
n
the sample code “PRnX”, “n” represents M of PEG axis, 35 (1) or
12 (2) kDa and “X” denotes the stoppers, MAS (A), DAS (B) or
TAS (C).
ꢀ
ether, and then dried under vacuum at 30 C for 24 h, affording
hygroscopic white powder. Yield: 9.80 g, 95.6%. H NMR (300 MHz,
1
DMSO-d
CH CH ), 1.21 (m, 9H, CH
CHCCH N), 70.91 (CHCCH
.73 (CH CH N).
6
):
d
4.29 (s, 2H, CHCCH
2
), 3.95 (s,1H, CHCCH
2
), 3.33 (m, 6H,
). C NMR (75 MHz, D O): 81.22
N), 53.91 (CH CH N), 48.15 (CHCCH N),
The hydroxyl groups of PR can be converted to other functional
moieties for the application purpose. We prepared valeryl chloride
modified PR (PR-VC) according to the protocols reported in Ref.
[37], as shown in Supporting information.
13
2
3
2
CH
3
2
d
(
7
2
2
3
2
2
3
2

2886
H. Sun et al. / Polymer 53 (2012) 2884e2889
2.7. Synthesis of RhB-modified polyrotaxane (RhB-PR)
alkynes as stoppers for the preparation of high molecular weight
PRs. Their molecular structures are shown in Scheme 1.
PR1C (100.1 mg) was dissolved in 5 mL of dry DMAc containing
The stoppers can be easily prepared by dropwise adding prop-
argyl bromide into the DMF solution of tertiary amines. This effi-
cient one-step process from commercial and inexpensive starting
materials makes large-scale production of the quaternary ammo-
nium salts readily accessible. The stopper structures were
ꢀ
8
wt% LiCl under N
2
. Then, the mixture was heated at 60 C. To the
3
mixture, CuBr (26.3 mg), PMDETA (32.3 mg), RhB-N (100.2 mg)
were added successively. After stirring overnight in darkness, the
reaction system was poured into acetone. The collected red
precipitate was dissolved in DMAc and poured into acetone
1
13
1
confirmed by H and C NMR spectroscopy. In the H NMR spec-
trum of MAS (Figure S1), the protons of the propargyl group locate
at 3.95 and 4.29 ppm, and the ethyl protons appear at 1.21 and
3
repeatedly until RhB-N could not be detected by UVeVis spec-
trometer in the concentrated washing solution. The precipitate
ꢀ
1
(
RhB-PR1C) was dried under vacuum at 35 C for 24 h to afford red
3.33 ppm. In the H NMR spectrum of DAS (Figure S2), the protons
powder. Yield: 95.8 mg.
of alkynyl group and methyl appears at 4.20 and 3.24 ppm,
1
respectively. In the H NMR spectrum of TAS (Fig. 1(A)), the prop-
0
argyl group connected to the middle nitrogen atom (N ) exhibits its
3
. Results and discussion
methylene and alkyne proton signals at 4.75 (signal F) and 4.31
(
signal G) ppm, respectively, the other two propargyl groups at the
3
.1. Design and synthesis of alkyl end-capping reagents
0
0
two end nitrogen atoms (N and N ) show the methylene and alkyne
proton signals at 4.67 (signal C) and 4.22 (signal B) ppm, respec-
tively, and the integration ratio of signal F to signal C is 1:2, indi-
cating all the three tertiary amino groups are quaternized. In the
NMR spectrum of TAS (Fig.1(B)), the carbon signals of alkynyl group
It has been recognized that end-capping reagents play a crucial
role in the synthesis of PRs. All of the reported stoppers are almost
aryl molecules, except few ones such as cage-like molecules of
adamantine and cyclodextrin derivatives. Their molecular sizes are
big enough to prevent the threaded CDs from dethreading.
However, those bulky molecules are generally less reactive,
resulting in slow end-capping and thus low yield during the PR
synthesis. For instance, alkyne-functionalized rhodamine B can be
used as the stopper to prepare PR via click chemistry, but the yield
13
C
0
at N locate at 82.26 (signal D) and 71.54 (signal B) ppm, the carbon
0
0
signals of alkynyl group at N and N appear at 85.04 (signal C) and
2.36 (signal A) ppm, and the carbon atoms labeled as “G, H, I, J”
7
which originally belong to PMDETA still can be observed.
is only 4.47 mg per 100 mg PEG-4600 [38]; when the
used as the stopper, high yield was achieved up to 320 mg PR per
00 mg PEG-4600 via click-end capping, but the yield is quite low
b
-CD was
3.2. Synthesis and characterization of PRs
1
The one-pot preparation of PRs was carried out in water via
for the higher molecular weight axis PEG 12 kDa [33]. Accordingly,
we shift our attention to alkyl stoppers. Because the end-capping is
carried out in water in the one-pot click chemistry approach, the
stoppers should be water soluble. So we designed alkyl ammonium
a two-step procedure: 1) formation of pseudo-PR from a-CD and
diazide-terminated PEG; 2) end-capping of pseudo-PR with bulky
quaternary ammonium salt reagents via Cu(I)-catalyzed azide-
alkyne click reaction (Scheme 1). Typically, an aqueous solution of
3 3
N -PEG-N
Water
Pseudo-PR
4 2
CuSO ·5H O
Stopper =
(t)-sodium L-ascorbate
PMDETA
α-CD
N
N
N
PR
MAS
DAS
TAS
Stopper =
Br
N
Br
N
Br
N
N
Br
N
Br
N
Br
3 3
N -PEG-N =
O
O
N
3
O
O
O
O
O
O
N
3
n
O
O
Scheme 1. Synthetic protocol of quaternary ammonium salt-capped PR via chick chemistry.

H. Sun et al. / Polymer 53 (2012) 2884e2889
2887
A
B
Fig. 1. (A) 1H NMR spectrum of tri-alkyne quaternary ammonium salt in DMSO-d
, (B) 13C NMR spectrum of tri-alkyne quaternary ammonium salt in DMSO-d
.
6
6
A
B
c
a
b
OH
H
H O
2
6
H
4
5
O
H
2
H
PEG
HO
3
1
H
OH
H
O
DMSO
H-3,5,6
OH-2,3
H
1
OH-6
H-2,3
6
5
4
3
2
7.4
7.6
7.8
8.0
8.2
8.4
ppm
Elution time (min)
Fig. 2. (A) 1H NMR spectrum of the polyrotaxane prepared from PEG 35 kDa, mono-alkyne quaternary ammonium salt and
a-CD in DMSO. (B) Typical GPC curves of (a) PR1A-VC, (b)
PR1B-VC, and (c) PR1C-VC.
a
-CD and N
3
-PEG-N
3
was sonicated for 5 min and then stirred
prepared quaternary ammonium salts were excellent end-capping
reagents with seemly bulkiness, solubility and reactivity. As far as
we know, the achieved yield is the record ever reported for the
preparation of PRs [39e41], since the highest yield of PRs prepared
from PEG 35 kDa in previous reports is w343 mg/100 mg PEG axis
and the corresponding NCD is 100 [23]. In addition, the yields for
overnight at room temperature to generate pseudo-PR. To this
mixture, bulky quaternary ammonium salt reagents and catalyst for
click coupling were added successively under N
the precipitates were collected by centrifugation and washed with
hot water repeatly to remove free
stopper to yield pure PR.
2
. After 10 min-24 h,
3 3
a-CD, N -PEG-N and unreacted
PRs made from PEG 12 kDa and a-CD are also quite high (Table 1),
indicating the comparability of our method.
The structure of PR was characterized by 1H NMR and WAXD.
1
The H NMR spectrum of the present PR (Fig. 2(A)) was very similar
with those of the samples previously reported [33,38]. The inte-
gration ratio of the proton signal at 3.49 ppm (hydrogen atom in the
Table 1
Selected reaction conditions and results for the preparation of quaternary ammo-
nium stopper capped PRs.
1
repeat unit of PEG) to that at 4.78 ppm (H of a-CD) can be utilized
to calculate the average number of -CD in each PR (NCD), which is
a very important parameter for PRs. NCD was calculated according
to the Eq. (1) and the values are listed in Table 1.
a
Run Samplea Rb
Yield
N
Coverage
N
CD
(GPC)
CD
c
ratio (%)d
e
(mg/100 mg PEG axis) (NMR)
1
2
3
4
5
6
PR1A
PR1B
PR1C
PR1C
PR2A
PR2C
10 556
10 541
1
2
143
128
169
193
75
35.9
32.2
42.6
48.5
55.0
50.4
82
56
102
/
/
/
NCD ¼ M
ꢂ IH1
(1)
HOꢁPEGꢁOH
591
614
6
6 ꢂ IPEG
10 620
490
Herein, IH1 is the integration of H
1
peak of
a-CD, IPEG is that of
2
69
proton signal of PEG repeat unit, and MPEG is the molecular weight
of PEG axis. For the sample, PR1C (entry 4 of Table 1), the value of
a
n
In sample code “PRnX”, “n” represents M of PEG axis, 35 kDa (1) or 12 kDa (2)
and “X” denotes the stoppers, mono-alkyne quaternary ammonium salt (A), di-
N
CD is ca. 193 and the corresponding coverage ratio, which is the
alkyne quaternary ammonium salt (B) or tri-alkyne quaternary ammonium salt (C).
b
ratio of NCD to the theoretical maximum amount of -CDs threaded
a
The molar feed ratio of stoppers to azide unit.
c
The number of the threaded a
-CDs per axis calculated from 1H NMR method.
by the axis, equals ca. 48%. For other samples, use of MAS (entry 1)
and DAS (entry 2) stoppers and the reaction with a varied molar
ratio of the stopper and the azide groups (entry 1e4 in Table 1) all
resulted in relatively high yields and big NCDs, implying that the
d
The ratio of NCD to the theoretical maximum amount of
axis.
a-CDs threaded by the
e
n
NCD was calculated according to M of corresponding valeryl chloride-modified
PR obtained from GPC.

2888
H. Sun et al. / Polymer 53 (2012) 2884e2889
B
A
b
a
a
2
102
b
c
d
e
10
20
30
40
3000
2500
2000
1500
1000
)
500
2
(degree)
Wavenumber (cm-
1
Fig. 3. (A) WAXD patterns of a) PR1C, b) PR1B, c) PR1A, d) PR2C, e) native
a-CD. (B) FT-IR spectra of (a) RhB-N
3
and (b) RhB-PR1C.
M
n
ꢁ 2M ꢁ M
A
M
N3ꢁPEGꢁN3
NCD
¼
(2)
(2486.10 g/mol) denote the
0
a
ꢁCD
PR1C
0
where M
n
, M , MN3-PEG-N3, and M
A
a
ꢁCD
molecular weights of PR-VC, the stopper, the axis N
valeryl chloride modified -CD bead, respectively. The resulted
CDs are generally smaller than those calculated from H NMR
3 3
-PEG-N and
DMAc
CuBr
N
3
a
=
RhB-N
3
1
N
PMDETA
o
0 C
method. For instance, in entry 3 (Table 1), the NCD obtained through
GPC method is 102, which is smaller than that calculated from H
6
1
NMR result, 169. The difference may be attributed to, (1) incom-
plete modification of PRs, namely, the molecular weight of valeryl
chloride modified
smaller than that used in the eq (2) (M
the interaction between PR and GPC column, (3) the different
conformation between linear PS standard and PR.
a
-CD bead in the practical reaction system is
N
N
N
0
¼ 2486.10 g/mol), (2)
RhB-PR1C
a
ꢁCD
WAXD is utilized to elucidate the structure of inclusion
complexes in the solid state and explore the existence of pseudo-
PRs and PRs [42,43]. As shown in Fig. 3(A), the WAXD patterns of
Scheme 2. Synthetic protocol of RhB modified-PR via click chemistry.
pseudo-PR1A and PR1A show strong and sharp diffraction peaks at
ꢀ
2q
¼ 20 , demonstrating that
a-CDs are stacked along the PEG chain
In order to characterize the molecular weight of PR by means of
axis to form the necklace structure and in other words, PRs possess
a column crystalline structure. Thermal properties of PRs were
studied by TGA (Figure S3). The initial decomposition temperature
gel permeation chromatography (GPC), PR1A, PR1B and PR1C with
PEG axis of 35 kDa were treated with valeryl chloride to improve
their solubility in DMF, according to the Ref. [33] It is interesting to
note that GPC analysis of all the samples against linear polystyrene
standards resulted in typical symmetric Gaussian distribution
curves (Fig. 2(B)) with narrow polydispersities (polydispersity
index, PDI, 1.18e1.61), indicating that we successfully synthesized
host-guest supramolecular polyrotaxanes. Additionally, NCD can
also be calculated according to Eq. (2) based on the GPC result.
ꢀ
of PRs is higher than that of a-CD (ca. 300 C), implying that the
thermal stability of PRs has little difference comparing to the
starting materials.
It should be highlighted that the PRs with multi-alkynyl stop-
pers can be further functionalized, which will extensively facilitate
the application of PRs. Azido-functionalized rhodamine B (RhB-N3)
was used to functionalize the PRs by click coupling the azide group
B
A
8
7
6
5
00
00
00
00
600
500
400
300
200
100
0
PR35000-RhB
RhB
RhB-N
3
400
300
200
100
0
560
600
640
680
720
0
20
40
60
80
-
7
Wavelength (nm)
Concentration (10 mol/L)
ꢁ
5
Fig. 4. (A) Fluorescence emission spectra of RhB-PR1C in DMSO solution with gradient concentrations from 0.05 mg/mL to 9.8 ꢂ 10 mg/mL (along the arrow) by step-wise
3
dilution. (B) Fluorophores concentration versus fluorescence emission intensity of RhB, RhB-N , RhB-PR1C in DMSO solution. All the fluorescence emission spectra were excited
at 564 nm and the emission peak points were at 587 nm. The emission slit was 3 nm.

H. Sun et al. / Polymer 53 (2012) 2884e2889
2889
with the terminal alkyne groups of PRs (Scheme 2). In the FT-IR
spectrum of the RhB-PR1C (Fig. 3B-b), the characteristic absorp-
Appendix A. Supplementary material
ꢁ1
tion peak of azido group of RhB-N
3
at 2102 cm (Fig. 3B-a) cannot
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.polymer.2012.04.038.
be observed, implying the occurrence of the click reaction. The
presence of RhB fluorophores was confirmed by the fluorescent
measurements (Fig. 4(A)). All of the samples were excited at
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Acknowledgment
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Financial supports from the National Natural Science Founda-
tion of China (No. 51173162 and No. 20974093), Qianjiang Talent
Foundation of Zhejiang Province (2010R10021), the Fundamental
Research Funds for the Central Universities (2011QNA4029),
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