Thermoresponsive supramolecular dendronized polymers

Article abstract of DOI:10.1002/asia.201100528

Combining the concepts of supramolecular polymers and dendronized polymers provides the opportunity to create bulky polymers with easy structural modification and tunable properties. In the present work, a novel class of side-chain supramolecular dendroni

Full text of DOI:10.1002/asia.201100528

FULL PAPERS
DOI: 10.1002/asia.201100528
Thermoresponsive Supramolecular Dendronized Polymers
Jiatao Yan,[a, b] Wen Li,[a] Kun Liu,[a] Dalin Wu,[a] Feng Chen,[a] Peiyi Wu,*[b] and
Afang Zhang*[a]
Abstract: Combining the concepts of
supramolecular polymers and dendron-
ized polymers provides the opportunity
to create bulky polymers with easy
structural modification and tunable
properties. In the present work, a novel
class of side-chain supramolecular
dendronized polymethacrylates is pre-
pared through the host–guest interac-
tion. The host is a linear polymethacry-
late (as the backbone) attached in each
repeat unit with a b-cyclodextrin (b-
CD) moiety, and the guest is constitut-
ed with three-fold branched oligoethy-
lene glycol (OEG)-based first- (G1)
and second-generation (G2) dendrons
with an adamantyl group core. The
host and guest interaction in aqueous
solution leads to the formation of the
supramolecular polymers, which is sup-
ported with H NMR spectroscopy and
spectroscopy, and compared with their
counterparts formed from individual b-
CD and the OEG dendritic guest. The
effect of polymer concentration and
molar ratio of host/guest was exam-
ined. It is found that the polar interior
of the supramolecules contribute signif-
icantly to the thermally-induced phase
transitions for the G1 polymer, but this
effect is negligible for the G2 polymer.
Based on the temperature-varied
proton NMR spectra, it is found that
the host–guest complex starts to de-
compose during the aggregation pro-
cess upon heating to its dehydration
temperature, and this decomposition is
enhanced with an increase of solution
temperature.
1
dynamic light scattering measurements.
The supramolecular formation was also
examined at different host/guest ratios.
The water solubility of hosts and guests
increases upon supramolecular forma-
tion. The supramolecular polymers
show good solubility in water at room
temperature, but exhibit thermorespon-
sive behavior at elevated temperatures.
Their thermoresponsiveness is thus in-
vestigated with UV/Vis and 1H NMR
Keywords: cyclodextrins
·
dendrimers · host–guest systems ·
polymers · supramolecular chemis-
try
Introduction
Supramolecular polymers have received considerable inter-
est during recent decades in areas such as chemistry and ma-
terials science.[1] Different types of supramolecular poly-
mers, including main-chain[2] and side-chain supramolecular
polymers,[3] have been reported, and these polymers possess
dynamic and living characteristics, thus providing an alterna-
tive and easier route to tune the polymer structures com-
pared with their covalent counterparts. Up to now, much
emphasis has been put on the control of supramolecular
morphologies through structural design. Recently, there has
been increasing interest in developing supramolecular poly-
mers with functions,[4] such as self-healable plastics,[5] photo-
voltaic materials,[6] and hydrogels for drug delivery.[7,8]
Supramolecular polymers are constituted from monomeric
units by means of highly directional non-covalent forces,
such as metal coordination,[6] hydrogen-bonding,[9] as well as
p–p,[10] ionic,[11] or hydrophobic interactions.[12] Among
these, one prominent example, which is based on the princi-
[a] J. Yan, Dr. W. Li, K. Liu, D. Wu,+ F. Chen, Prof. A. Zhang
Department of Polymer Materials
Shanghai University
Chengzhong Street 20, Shanghai 201800 (China)
Fax : (+86)21-69982827
E-mail: azhang@shu.edu.cn
[b] J. Yan, Prof. P. Wu
The Key Laboratory of Molecular Engineering of Polymers
Ministry of Education
Department of Macromolecular Science and Laboratory of Advanced
Materials
Fudan University
Handan Street 220, Shanghai 200433 (China)
E-mail: peiyiwu@fudan.edu.cn
[+] Current address:
Department of Chemistry
University of Basel
Klingelbergstrasse 80, CH-4056 Basel (Switzerland)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201100528.
3260
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 3260 – 3269

ple of hydrophobic interactions, is the inclusion complexa-
tion between the host cyclodextrins (CDs) and the guest hy-
drophobic moieties of appropriate size.[13] CDs are cyclic oli-
gosaccharides composed of six, seven, or eight d(+)-glucose
units (named a-, b-, or g-CD, respectively), and the molecu-
lar geometry affords to them a hydrophobic inner cavity of
different sizes.[14] Various molecules, fitted into the cavity
size of CDs, can form supramolecular inclusion complexes
with different binding constants,[15] and this binding differ-
ence is especially interesting in tuning the assembly by com-
petition inclusion between CDs and guest molecules.[16]
Threading of CDs by a linear polymer chain to form poly-
rotaxanes or polypseudorotaxanes has been intensively stud-
ied[13b] for supramolecular hydrogels[17] or bio-related appli-
cations.[18] Supramolecular inclusion polymers for stimuli-re-
sponsiveness, mainly based on a linear polymer architecture,
have also been brought to attention recently.[19]
Dendronized polymers are a novel class of cylindrical
polymers with branched dendrons pendent at each repeating
unit of a linear polymer main-chain.[20] The structural char-
acteristics of these polymers include high rigidity, easy func-
tionalization, and more importantly, bulkiness of individual
molecules having dimensions in the range of 3–7 nm.[21]
Based on these attributes, dendronized polymers have
drawn significant interest and have been utilized for DNA
wrapping,[22] helix formation,[23] self-assembly,[24] catalytic
supports,[25] nanomaterials,[26] and so on. These polymers are
typically constructed through a covalent linkage between
the polymer main-chain and the pendent dendrons, and are
prepared using either the macromonomer[27] or attach-to
route.[28] Despite the significant progress in the synthetic
strategies, the tedious synthetic procedure remains a major
drawback for this promising class of polymers. In contrast to
the covalent congeners, supramolecular dendronized poly-
mers (SDPs) combine the structural characteristics of cova-
lent dendronized polymers and the structure variability of
supramolecular polymers, thus forming a promising class of
bulky supramolecular polymers. Recently, SDPs have re-
ceived much attention though most are based on weak inter-
actions, such as metal coordination[29] and acid–base interac-
tions.[30]
Thermoresponsive polymers[31] are one of the most attrac-
tive stimuli-responsive polymers, and have shown promising
applications in various areas.[32] These polymers possess a
lower critical solution temperature (LCST) in aqueous solu-
tions, and their chains start to dehydrate below this temper-
ature, followed by chain collapse and then formation of
mesoglobules or aggregates, which is a an entropy-driven as-
sociation process of the polymer solute.[33] Up to now, most
thermoresponsive polymers have had a linear architecture
and are constructed through covalent linkages. To avoid the
slow phase transition in cooling and the significant hysteresis
caused by strong hydrogen bonding in polyacrylamides, oli-
goethylene glycol (OEG)-based comb-like (co)polymers[34]
and dendrimers[35] were developed. These OEG-derivatives
do not possess sites for strong hydrogen-bonding formation,
and thus show small hysteresis. However, to achieve sharp
and fast phase transitions in both heating and cooling pro-
cesses with small hysteresis remains a challenge.
We recently reported a series of OEG-based first- (G1) to
third-generation (G3) dendronized polymethacrylates, which
show fast and sharp transitions upon heating and cooling
with small hysteresis.[36] Their phase-transition temperatures
are easily tunable in the range of 32–658C, and mostly de-
pendent on polymer peripheral groups.[37] Furthermore, the
dendronization architecture results in these polymers exhib-
iting dehydration of the interior part at a much higher tem-
perature than that of the peripheral units,[38] and this hetero-
geneous dehydration may offer the possibility to fabricate
molecular devices on the individual molecule level. To com-
bine the structural advantages from both covalent dendron-
ized polymers and supramolecular polymers, the present
contribution describes a novel construction of thermores-
ponsive polymers through the supramolecular strategy using
host and guest interactions (Figure 1). The host is a linear
polymethacrylate (as the backbone) attached in each repeat
unit with a b-cyclodextrin (b-CD) moiety, and the guest is
three-fold branched oligoethylene glycol (OEG)-based G1
and G2 dendrons with an adamantyl (Ada) core. b-CD and
adamantane are selected as both can form inclusion com-
plexes in water with a high binding constant in the range of
1ꢁ105 mÀ1. The inclusion complexation was investigated by
1H NMR spectroscopy and dynamic light scattering meas-
urements. The supramolecular polymers show good solubili-
ty in water at room temperature, but exhibit characteristic
thermoresponsive behavior at elevated temperature. Their
thermoresponsiveness is thus investigated using UV/Vis and
1H NMR spectroscopy. The effect of polymer concentration
and molar ratio of host/guest was examined. Temperature-
Abstract in Chinese:
1
varied H NMR spectroscopy was utilized to investigate the
thermally induced dehydration and dissociation process.
Chem. Asian J. 2011, 6, 3260 – 3269
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3261

P. Wu, A. Zhang et al.
FULL PAPERS
mer concentration in polymeri-
zation media is a prerequisite
for obtaining a high-molar-mass
polymer.
Supramolecular Dendronized
Polymers (SDPs) by Host–
Guest Inclusion Complexation
Figure 1. Illustration of side-chain supramolecular dendronized polymers (SDPs) prepared through host–guest
inclusion and their collapse in water.
Mixing OEG-based dendron
guests (G1-Ada or G2-Ada)
with host polymer poly(5) in
aqueous solution at room tem-
Results and Discussion
perature formed clear solutions, where the strong host–guest
inclusion complexation between b-CD and adamantane moi-
eties is supposed to induce dendritic guests anchoring to the
CD polymer, thus forming the side-chain SDPs (Figure 1,
step one).
Host and Guest Synthesis
The OEG-based dendritic guests G1-Ada and G2-Ada were
effectively synthesized in two steps, starting from their cor-
responding dendron methyl ester 1a and 2a (Scheme 1).[39]
These esters were first saponified in the presence of LiOH
into the corresponding dendritic acid 1b and 2b, which were
then coupled with 1-adamantaneamine by EDC/HOBt strat-
egy[40] to form the corresponding dendritic guests. The host
polymer with the b-cyclodextrin (b-CD) moiety appended
was obtained by directly polymerizing the CD-based mono-
mer, similar to literature methods (Scheme 2).[41] Here,
mono-6-deoxy-6-amino-b-CD (3) was treated with active
ester 4 in a mixed solvent of N,N-dimethylformamide
(DMF) and methanol to form the macromonomer 5, which
was subjected to free radical polymerization in highly con-
centrated DMF solutions and afforded linear CD polymer
poly(5) with a well-defined structure. The high CD mono-
The first evidence for the complexation between OEG-
based dendritic guests and the CD polymer was the change
in the water solubility at room temperature. CD polymer
poly(5) itself dissolves very slowly in water owing to its
strong intermolecular hydrogen bonds, but dissolves quickly
in the presence of G1-Ada or G2-Ada. This may be ex-
plained by the inclusion between the adamantane moiety
from the guest and the CD moiety in the host polymer, lead-
ing to the CD polymer covered with water-soluble OEG
dendrons thus, retarding intermolecular interactions of the
CD polymer. Alternatively, the guest G1-Ada becomes
more water-soluble in the presence of poly(5), which can be
understood by the hydrophobic adamantane moiety being
included inside the CD cavity with the hydrophilic OEG
dendron remaining in the aque-
ous environment. The complex-
ation of G2-Ada and poly(5) in
aqueous solution to form supra-
molecular dendronized poly-
mers was therefore examined
by 1H NMR spectroscopy, and
the spectra are shown in
Figure 2. For comparison, the
proton NMR spectrum from
the complexation of the same
guest dendron (G2-Ada) with
individual b-CD is also includ-
ed. Upon addition of one equiv-
alent of poly(5) (based on CD
moieties) to the G2-Ada aque-
ous solution, all the proton sig-
nals from G2-Ada become
broader and the corresponding
signal heights decrease, with
the methylene and methine
proton signals from the ada-
Scheme 1. Synthesis procedures for OEG-based dendritic guests G1-Ada and G2-Ada. Reagents and condi-
tions: a) 1a or 2a, LiOH·H2O, MeOH/H2O, À5 to 258C, 12 h, (97% and 75% for 1b and 2b, respectively);
b) 1b or 2b, 1-adamantaneamine, EDC, HOBt, TEA, DCM, À15–258C, overnight (56% and 71% for G1-
Ada and G2-Ada, respectively).[39]
mantyl group more pro-
nounced. The proton signals
from the adamantyl group also
3262
www.chemasianj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 3260 – 3269

Thermoresponsive Supramolecular Dendronized Polymers
resolution, and only chemical shifts of the protons from ada-
mantyl moieties shifted downfield (compare (c) with (a) in
Figure 2). For example, the characteristic adamantyl proton
signals at about d=1.50 and 1.80–1.90 ppm were shifted
downfield to d=1.69 and 2.08–2.20 ppm, respectively. The
signal broadness in spectrum (b) in comparison with (c) in
Figure 2 is assigned to the macromolecular effect.
1H NMR titration measurements were carried out to in-
vestigate the supramolecular formation in detail. The molar
ratio of CD to adamantane moieties is between 0.2 and 1.5,
and the typical spectra are summarized in Figure 3. When
0.2 equivalents of poly(5) (based on CD moiety) were ini-
tially added to the G2-Ada solution, the proton signals from
the adamantyl group became broader and their intensity de-
creased, and proton signals from the OEG dendron also
changed slightly. With successive addition of poly(5), all
proton signals from G2-Ada gradually became broader, and
the intensities decreased. When 0.8 equivalents of poly(5)
were introduced, the signals from the aromatic ring (at d=
6.98 ppm) and from the adamantyl group (at d=1.50 and
1.90 ppm) almost disappeared. The signal intensity from
other protons also decreased significantly. Further addition
of poly(5) caused the 1H NMR spectrum to change only
slightly and tended to remain unchanged once the guest/
host molar ratio reached 1. This phenomenon demonstrated
that, with the addition of host polymer poly(5) to the G2-
Ada aqueous solution, more and more guest molecules
change from the free state to the polymeric state owing to
the inclusion. When the guest/
Scheme 2. Synthesis procedures for the host polymer poly(5). Reagents
and conditions: a) 3, 4, DiPEA, DMF/MeOH, À15–258C, overnight,
53%; b) 5, AIBN, DMF, 608C, 12 h, 40%.
shift downfield. These demonstrate that the adamantane
moiety was included inside the CD cavity[42] and the den-
drons were attached onto the host polymer to form SDPs.
In contrast, for the complex formed from the guest dendron
G2-Ada with individual b-CD, all the proton signals from
both G2-Ada and b-CD were clearly shown and in sharp
host molar ratio reaches 1,
nearly all the guest molecules
were complexed with CD poly-
mer. One thing is necessary to
address here: the signal at d=
1.9 ppm from the adamantyl
group is monomodal in all these
cases, irrespective of the ratio of
host and guest units, which sug-
gests that the complexation is in
a fast dynamic.[43]
Dynamic
light
scattering
measurements were carried out
to investigate the supramolec-
ular formation from G2-Ada
and poly(5). The hydrodynamic
radius (Rh) value of free
poly(5) in water was determined
to be approximately 7 nm, while
upon complexation with G2-
Ada, it increased to approxi-
mately 12 nm (see Figure S2 in
the Supporting Information for
details). This indicates that the
size of the polymer increased
significantly after the attach-
ment of dendrons onto its side
chains.
Figure 2. 1H NMR spectra at room temperature in D2O (with the same G2-Ada concentration at 1.6ꢁ
10À2 molLÀ1) of a) pure G2-Ada, b) the mixture of 1 equivalent of G2-Ada and poly(5), and c) the mixture of
1 equivalent of G2-Ada and b-CD. The dotted lines are a guide for the eyes.
Chem. Asian J. 2011, 6, 3260 – 3269
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3263

P. Wu, A. Zhang et al.
FULL PAPERS
termined to be 28.2, 38.1, 52.7,
and 34.48C, respectively. The
phase transition temperature of
SPG2 is especially attractive as
it is close to the bodyꢂs temper-
ature. The phase transition
curves demonstrate that the
phase transitions are quite fast
and sharp, and the hysteresis is
very small (around 18C). These
thermoresponsive behaviors are
quite similar to the correspond-
ing OEG-based first- (PG1)
and second-generation (PG2)
dendronized polymers formed
through covalent linkages.[36] In-
terestingly, the LCST of SPG1
is much higher than that of the
corresponding dendritic guest,
while the LCST of SPG2 is a
little lower than that of the cor-
responding dendritic guest. Fur-
thermore, the phase transitions
of SPG1 and SPG2 are sharper
than their corresponding den-
Figure 3. 1H NMR spectra of complex from G2-Ada (at the same concentration of 1.6ꢁ10À2 molL À1) and
poly(5) with different molar ratio (based on CD moieties).
Thermoresponsive Behavior of Supramolecular
dritic guests alone. These results demonstrate that: (1) the
hydrophobic adamantyl moiety within G1-Ada contributes
more significantly to its thermally-induced phase transitions
(both heating and cooling) than the case for G2-Ada. The
reason arises from the smaller dendron size of G1-Ada than
that of G2-Ada, thus the hydrophobic adamantyl moiety oc-
cupies a higher percentage in the dendron, which leads to
the decrease of the overall hydrophobicity of the guest mol-
ecule; (2) the polar interior (CD moieties) of the supra-
molecular polymers contributes significantly to the thermal-
ly-induced phase transitions for SPG1, but for SPG2, this
effect is negligible. As proven in our previous report, the in-
terior part of dendronized polymers shows less contribution
to the polymerꢂs thermoresponsiveness when OEG outer
units are dense enough to cover the polymer periphery.[37]
The result here suggests that the size of the second genera-
tion OEG dendron is big enough to cover the surface of the
individual supramolecular polymer, which shields the hydro-
philic CD moieties; (3) the sharper phase transitions of
supramolecular polymers than that of their corresponding
guest molecules should arise from the macromolecular
crowding effect, which facilitates the dehydration and aggre-
gation kinetics of OEG units. Another factor for the fast
phase transitions is the absence of strong hydrogen bonding
in these OEG-based polymer systems when compared to
the conventional thermoresponsive polymer poly(N-isopro-
pylacrylamide). These have also been demonstrated in the
covalent PG1 and PG2.[44]
Dendronized Polymers
First- (SPG1) and second-generation (SPG2) supramolec-
ular dendronized polymers formed from the CD polymer
poly(5) with the corresponding G1-Ada and G2-Ada are
water-soluble at room temperature, but show interesting
thermoresponsive behavior at elevated temperature owing
to the dehydration of the OEG units.[37] Interestingly, den-
dritic guests G1-Ada and G2-Ada themselves also show
thermoresponsiveness. The thermoresponsive behavior of
these dendritic guests and their corresponding supramolec-
ular polymers was thus investigated by turbidity measure-
ments using UV/Vis spectroscopy, and the typical turbidity
curves are shown in Figure 4. From these curves the appar-
ent LCST of G1-Ada, G2-Ada, SPG1, and SPG2 were de-
The effects of concentration and molar ratio of host/guest
on the thermoresponsiveness of SDPs were further exam-
ined. For comparison, supramolecular complex (SM2),
formed from G2-Ada and individual b-CD, was also investi-
Figure 4. Plots of transmittance versus temperature for 0.25 wt% aqueous
solution G1-Ada, G2-Ada, SPG1, and SPG2.
3264
www.chemasianj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 3260 – 3269

Thermoresponsive Supramolecular Dendronized Polymers
gated. The LCSTs from one equivalent of G2-Ada with
poly(5) or b-CD at different concentrations were measured,
and the results are plotted in Figure 5a. With a concentra-
tion decrease from 1 wt% to 0.05 wt%, the LCST for SPG2
increases from 33.38C to 36.68C (D=3.38C), while the
LCST for SM2 increased from 40.78C to 51.28C (D=
10.58C), hence the latter case shows a much higher concen-
tration dependence. This result suggests that the LCST of
supramolecular polymers is less sensitive to the solution
concentration when compared with the corresponding supra-
molecular monomers or derivatives. This observation is also
in good agreement with thermoresponsive dendronized
polymers formed through covalent linkages.[36] The effect of
the host/guest molar ratio (at the same concentration of G2-
Ada) on the LCST was investigated, and the results are
shown in Figure 5b. For SPG2, with an increase of host/
guest molar ratio, the LCST decreased first, and then
tended to remain unchanged at about 348C when the host/
guest molar ratio reached 1. Even when the host/guest
molar ratio exceeded 1, existence of uncomplexed hydro-
philic CD units showed negligible influence on the LCST.
However, for SM2, the values of LCST increased with the
host/guest molar ratio, and this tendency was kept when the
host/guest molar ratio exceeded 1. This result demonstrates
that the supramolecular polymer shows a different entropy-
driven association process than its dendritic guest.
Temperature dependent 1H NMR spectroscopy was uti-
lized to investigate the thermally induced dehydration pro-
cess of the supramolecular dendronized polymers in aque-
1
ous solution. H NMR spectra of SPG2, formed from equal
equivalents of G2-Ada and poly(5), were recorded at 218C,
368C, and 458C (Figure 6). As expected, when the solution
temperature was increased to 368C, which is slightly above
the phase transition temperature (34.48C), proton signals
from OEG units (d=3.2–4.5 ppm) became broader and
their intensities decreased because of the dehydration. With
a further increase of temperature (such as for 458C), these
signal intensities decreased even more. The exception is that
the signal intensities from the adamantyl group slightly in-
creased (see inset within Figure 6); this indicates the in-
crease in mobility of the adamantane moieties with solution
temperature. This mobility increase suggests adamantane
moieties may (partially) escape from the cavity of CD in the
supramolecular polymer when the solution temperature in-
creases, thus causing decomplexation.[45]
Decomplexation Related to Thermally Induced Chain
Collapse
1
Based on the temperature dependent H NMR spectra dis-
cussed above, supramolecular dendronized polymers start to
decompose as the temperature approaches their LCSTs.
Several factors may be responsible for this dissociation:
(1) the inclusion constant of adamantane into b-CD decreas-
es with an increase in the solution temperature,[19f] therefore,
the inclusion complex becomes less stable at high tempera-
ture; (2) the hydrophobic domains formed from dehydration
of OEG chains compete with the hydrophobic adamantane
to form an inclusion complex with CD; (3) the hydrophobic
domains formed from dehydration of OEG chains compete
against the hydrophobic cavity within CD to take the hydro-
phobic adamantane; (4) aggregation of the hydrophobic do-
Figure 6. Temperature-dependent 1H NMR spectra of SPG2: a) 218C,
b) 368C, c) 45 8C. The inset shows partial spectrum in the range of d=
1.0–2.5 ppm.
Figure 5. LCST dependence of SPG2 and SM2 on concentrations a) and
host/guest molar ratio b) ([G2-Ada]=9.7ꢁ10À4 molL À1).
Chem. Asian J. 2011, 6, 3260 – 3269
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3265

P. Wu, A. Zhang et al.
FULL PAPERS
mains formed from the dehydrated OEG units causes steric
hindrance, which prevent the guests from inclusion.[45a] In
order to examine whether any or all of these possibilities
really contribute to the dissociation, proton NMR spectros-
copy is a convenient tool. However, owing to the inherent
broad NMR signals from supramolecular polymers, it is not
easy to accurately monitor and investigate the decomplexa-
tion process involved in thermally-induced phase transitions
on the polymer level. Instead, we choose the supramolecular
complex (SM2) from G2-Ada and b-CD as the model
system, and the typical spectra in the range of 1.0–2.7 ppm
are shown in Figure 7a (for full spectra see Figure S3 in the
Supporting Information). At room temperature (218C),
proton signals from the supramolecular complex are time-
averaged and well-resolved, because the complexation ki-
netics are a rapid exchange process relative to the NMR
time scale. However, as the solution temperature is in-
creased to 368C, which correlates to the temperature for the
OEG chain collapse[44] and is just below the phase transition
temperature of the inclusion complex (398C), a series of
new split proton signals appeared. For example, characteris-
tic proton signals from adamantane, peripheral methyl, and
the aromatic ring split into two groups, respectively. This
tendency is enhanced when the solution temperature is fur-
ther increased. The proton signal splitting suggests the com-
plexation kinetics become a slow exchange process relative
to the NMR timescale once dehydration occurs. By compari-
son with the spectra from native G2-Ada solution at the
same temperature (Figure S4 in the Supporting Informa-
tion), these new split proton signals come from the decom-
plexed (free) G2-Ada. By comparing the signal intensities,
the percentage of decomplexed species can be roughly cal-
culated, and the results are plotted in Figure 7b.[46] For the
case of 1 wt% aqueous solution of SM2, the decomplexation
starts around 368C with a percentage of decomplexed spe-
cies around 6%, which increased to 87% at 508C. As in-
creasing the concentration of the inclusion complex reduces
its phase transition temperature slightly, a high concentra-
tion solution (6 wt%) of SM2 is used for comparison (Fig-
ure 7b). It shows a similar decomplexation tendency as the
1 wt% case, but the dissociation starts slightly earlier
(348C) as expected. In conclusion, the supramolecular com-
plex between G2-Ada and b-CD decomplexes when the so-
lution temperature increases to the point at which OEG
units just start to dehydrate, forming the hydrophobic
micro-domains. The percentage of decomplexed species in-
creases linearly with temperature, and at a high temperature
such as 508C, the majority of G2-Ada in the system be-
comes uncomplexed. This linear increase surprisingly sug-
gests the phase transition following the aggregation does not
contribute significantly to the dissociation. As for the case
reported by Yamaguchi and co-workers,[45a] the decrease of
binding constant between the host and the guest, together
with the steric hindrance formed from the dehydrated hy-
drophobic domains are main factors responsible for the dis-
sociation. Based on the above observation, we can conclude
that increase of SDP solution temperature shows a dual
effect of favoring the dissociation of dendrons and inducing
the aggregation of free dendrons within loops of the main
chains (Figure 1, step two). Similar observations have also
been reported extensively for the supramolecular polymers
formed by electrostatic interactions.[11]
Conclusions
In summary, supramolecular dendronized polymers were
prepared by host–guest inclusion complexation in aqueous
solutions between OEG-based dendritic guests and b-CD
decorated polymers. Both these dendritic guests and the cor-
responding supramolecular polymers are water-soluble at
room temperature, but show thermoresponsive behavior in
water. The supramolecular polymers show much sharper
phase transitions with smaller hysteresis than the dendritic
guests alone; the phase transition temperatures from the
former show less dependence on the guest/host ratios and
the concentrations than those from the latter. All these arise
from a positive macromolecular effect. Temperature varied
1H NMR spectroscopy shows that the supramolecular poly-
mers start to decompose upon their chain dehydration (just
Figure 7. a) Temperature-dependent 1H NMR spectra of 1 wt% aqueous
solution of SM2. The dotted lines are a guide for the eyes. b) Plots of
transmittance and dissociation percentage versus temperature for 1 wt%
and 6 wt% aqueous solutions of SM2 (the solid lines between the plots
are a guide for the eyes).
3266
www.chemasianj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 3260 – 3269

Thermoresponsive Supramolecular Dendronized Polymers
General Procedure for Amide Coupling with EDC/HOBt (B)
below the phase transition temperature), and this tendency
enhances with an increase of solution temperature. Thus, in-
crease of SDP solution temperature can show a dual effect
of favoring the dissociation of dendrons and inducing the ag-
gregation of free dendrons within loops of the main chains.
With the supramolecular complex (SM2), formed from G2-
Ada and b-CD as the model, the decomplexation process is
followed and surprisingly, it is observed that this dissociation
process is independent of the aggregation induced by the de-
hydration. Interestingly, this dissociation does not contribute
significantly to the thermoresponsive behavior. This work
provides a novel strategy to fabricate thermoresponsive
bulky polymers with easy structural variability but with less
synthetic effort, which would find applications in developing
stimuli-responsive biomaterials and sensors.
EDC was added into a solution of the acid, TEA, and HOBt in dry
DCM at À158C. After the mixture became a clear solution, 1-adamanta-
neamine in DCM was dropped into the solution at À158C, and the mix-
ture was allowed to rise to room temperature and stirred overnight. The
mixture was washed successively with NaHCO3 and brine, and all aque-
ous phases were triply extracted with DCM. The combined organic
phases were dried over MgSO4. After filtration, the solvent was evaporat-
ed under vacuum. Purification with column chromatography afforded the
product.
3,4,5-Tris(2-(2-(2-ethoxyethoxy)ethoxy)ethoxy)benzoic acid (1b)
According to general procedure A, from LiOH·H2O (1.30 g, 30.98 mmol)
and compound 1a (2.0 g, 3.01 mmol) in MeOH (40 mL) and H2O
(10 mL), 1b was yielded as
a
colorless oil (1.9 g, 97%). 1H NMR
(CD2Cl2): d=1.13–1.16 (m, 9H; CH3), 3.46–3.48 (m, 6H; CH2), 3.53–3.68
(m, 24H; CH2), 3.71–3.79 (t, 2H; CH2), 3.85–3.87 (m, 4H, CH2), 4.16–
4.21 (m, 6H; CH2), 7.32 ppm (s, 2H; CH). 13C NMR (CD2Cl2): d=15.04,
15.10, 61.71, 66.55, 68.99, 69.74, 69.96, 70.42, 70.62, 70.68, 70.75, 70.88,
72.60, 109.23, 124.59, 143.05, 152.47, 169.81 ppm. HR-MS: m/z calcd. for
C32H56O14 [M+Na]+ 687.37; found 687.3572.
Experimental Section
Materials
1-Adamantyl 3,4,5-tris(2-(2-(2-ethoxyethoxy)ethoxy)ethoxy)benzamide
(G1-Ada)
OEG-based dendrons 1a and 2a were synthesized according to the previ-
ous reports.[37] Mono-6-deoxy-6-amino-b-CD (3) was prepared according
to the literature method.[47] 2-(4-Nitro-phenoxycarbonyloxy) ethyl metha-
crylate (4) was synthesized directly from 2-hydroxyethyl methacrylate
and 4-nitrophenyl chloroformate in the presence of triethylamine
(TEA).[48] Azobisisobutyronitrile (AIBN) was recrystallized from metha-
nol. TEA was dried over NaOH pellets. Tetrahydrofuran (THF) was re-
fluxed over lithium aluminium hydride (LAH) and dichloromethane
(DCM) was distilled from CaH2 for drying. Pure water was redistilled.
Other reagents and solvents were purchased at reagent grade and used
without further purification.
According to general procedure B, from 1b (0.50 g, 0.77 mmol), 1-ada-
mantaneamine (0.24 g, 1.59 mmol), TEA (0.39 g, 3.85 mmol), EDC
(0.22 g, 1.15 mmol), and HOBt (0.16 g, 1.18 mmol) in DCM (20 mL), G1-
Ada was yielded as a colorless oil (0.35 g, 56%). 1H NMR (CDCl3): d=
1.19–1.22 (m, 9H, CH3), 1.68–1.73 (m, 6H, 3CH2 in adamantane), 2.11
(br, 9H, 3CH2 and 3CH in adamantane), 3.50–3.54 (m, 6H, CH2), 3.57–
3.73 (m, 24H, CH2), 3.78–3.86 (m, 6H, CH2), 4.17–4.21 (m, 6H, CH2),
5.80 (s, 1H, NH), 6.98 ppm (s, 2H, CH). 13C NMR (CDCl3): d=15.14,
29.48, 36.38, 41.58, 52.33, 66.62, 69.09, 69.72, 69.79, 70.49, 70.59, 70.62,
70.64, 70.73, 72.34, 107.08, 131.32, 141.16, 152.37, 166.17 ppm. HR-MS:
m/z calcd. for C41H69NO13 [M+Na]+ 806.48; found 806.5306.
Instrumentation and Measurements
1H and 13C NMR spectra were recorded on a Bruker AV 500 (1H:
500 MHz; 13C: 125 MHz) spectrometer. High resolution MALDI-TOF-
MS analyses were performed on IonSpec Ultra instruments. Gel permea-
tion chromatography (GPC) measurements were carried out on a Water
GPC e2695 instrument with 3 column set (Styragel HR3+HR4+HR5)
equipped with refractive index detector (Waters 2414) and DMF (con-
taining 1 gLÀ1 LiBr) as eluent at 458C. UV/Vis turbidity measurements
were carried out for the lower critical solution temperature (LCST) de-
termination on a PE UV/Vis spectrophotometer Lambda 35 equipped
with a thermostatically regulated bath. Aqueous polymer solutions were
placed in the spectrophotometer (pathlength: 1 cm) and heated or cooled
at a rate of 0.28CminÀ1. The absorptions of the solution at l=500 nm
were recorded every five seconds. The LCST is determined as the tem-
perature at which the transmittance at l=500 nm had reached 50% of
its initial value. Dynamic light scattering (DLS) measurements were per-
formed on an ALV/DLS/SLS-5022F spectrometer equipped with a multi-
t digital time correlation (ALV5000) and a cylindrical 22 mW He–Ne
laser (l0 =632 nm, UNIPHASE) as the light source.
3,4,5-Tris(2-(2-(2-(3,4,5-tris(2-(2-(2-ethoxyethoxy)ethoxy)ethoxy)benzyl-
oxy)ethoxy) ethoxy)ethoxy)benzoic acid (2b)
According to general procedure A, from LiOH·H2O (0.70 g, 16.68 mmol)
and compound 2a (2.0 g, 0.82 mmol) in MeOH (40 mL) and H2O
(10 mL), 2b was yielded as colorless oil (1.5 g, 75%). 1H and 13C NMR
spectra and HR-MS data are the same as previously reported.[37]
1-Adamantyl 3,4,5-tris(2-(2-(2-(3,4,5-tris(2-(2-(2-ethoxyethoxy)ethoxy)
ethoxy) benzyloxy)ethoxy)ethoxy)ethoxy)benzamide (G2-Ada)
According to general procedure B, from 2b (0.40 g, 0.17 mmol), 1-ada-
mantaneamine (0.05 g, 0.33 mmol), TEA (0.10 g, 1.00 mmol), EDC
(0.06 g, 0.31 mmol), and HOBt (0.03 g, 0.22 mmol) in DCM (10 mL), G2-
Ada was yielded as a colorless oil (0.30 g, 71%). 1H NMR (CDCl3): d=
1.21–1.24 (m, 27H, CH3), 1.68–1.74 (m, 6H, 3CH2 in adamantane), 2.11
(br, 9H, 3CH2 and 3CH in adamantane), 3.51–3.87 (m, 138H, CH2),
4.12–4.22 (m, 24H, CH2), 4.45 (s, 6H, CH2), 5.81 (s, 1H, NH), 6.58 (s,
6H, CH), 7.00 ppm (s, 2H, CH). 13C NMR (CDCl3): d=15.15, 29.48,
36.38, 41.57, 52.34, 66.62, 68.75, 69.04, 69.30, 69.71, 69.80, 70.47, 70.50,
70.63, 70.66, 70.71, 70.78, 72.27, 72.34, 73.22, 107.10, 131.37, 133.72,
137.69, 141.12, 152.37, 152.58, 166.12 ppm. HR-MS: m/z calcd. for
C128H219NO49 [M+Na]+ 2577.47; found 2577.5908.
General Procedure for Saponification of Methyl Ester by LiOH (A)
LiOH·H2O was added into a solution of methyl ester in a mixed solvent
of methanol and water (5:1, v/v) at À58C with stirring, and then the reac-
tion temperature was allowed to rise to room temperature. After stirring
for 6 h, the solvents were evaporated in vacuo at room temperature, and
the residue was dissolved with DCM. The pH value of the solution was
adjusted carefully to around 5–6 with 10% KHSO4 aqueous solution.
The organic phase was washed with brine. All aqueous phase was triply
extracted with DCM. The combined organic phase was dried over
MgSO4. After filtration, the solvent was evaporated in vacuo. Purification
by column chromatography afforded the corresponding acid.
Compound 5
Compound 4 (0.26 g, 0.88 mmol) in DMF was dropped into the solution
of
3 (0.5 g, 0.44 mmol) and diisopropylethylamine (DiPEA; 0.3 g,
2.32 mmol) in DMF (5 mL) and MeOH (0.5 mL) at À158C. After stirring
for 1 h, the mixture was allowed to rise to room temperature and stirred
overnight. Precipitation in diethyl ether three times yielded b-CD mono-
mer 5 as a slightly yellow powder (0.3 g, 53%). 1H NMR (D2O): d=1.95
(s, 3H, CH3), 2.80–2.85 (m, CH2, 1H), 3.22–3.27 (m, CH2, 1H), 3.45–3.96
(m, CH+CH2, 40H), 4.09–4.43 (m, 4H, partly overlapped with b-CD
Chem. Asian J. 2011, 6, 3260 – 3269
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3267

P. Wu, A. Zhang et al.
FULL PAPERS
protons), 4.96–4.98 (m, CH, 7H), 5.84 (s, 1H, CH), 6.11 ppm (s, 1H,
CH). 13C NMR ([D6]DMSO): d=18.41, 60.37, 62.17, 63.67, 72.50, 72.62,
72.87, 73.43, 73.51, 81.98, 102.40, 126.42, 136.12, 156.54, 166.92 ppm. HR-
MS: m/z calcd. for C49H79NO38 [M+Na]+ 1312.43; found 1312.4956.
[15] K. A. Connors, Chem. Rev. 1997, 97, 1325–1357.
[16] a) X. Liao, G. Chen, X. Liu, W. Chen, F. Chen, M. Jiang, Angew.
Chem. 2010, 122, 4511–4515; Angew. Chem. Int. Ed. 2010, 49, 4409–
4413; b) Q. Yan, J. Yuan, Z. Cai, Y. Xin, Y. Kang, Y. Yin, J. Am.
Chem. Soc. 2010, 132, 9268–9270.
Poly(5)
[17] J. Li, Adv. Polym. Sci. 2009, 222, 79–113.
[18] J. Li, X. J. Loh, Adv. Drug Delivery Rev. 2008, 60, 1000–1017.
[19] Stimuli-responsive inclusion polymers reported to date are mostly
based on decomplexation of the supramolecular polymers. For inclu-
sion of CD decorated polylysines with guests, see: a) H.-S. Choi, N.
Yui, Prog. Polym. Sci. 2006, 31, 121–144. For reversible inclusion of
adamantane with b-CD to form supramolecular thermoresponsive
copolymers, see: b) H. Ritter, O. Sadowski, E. Tepper, Angew.
Chem. 2003, 115, 3279–3281; Angew. Chem. Int. Ed. 2003, 42, 3171–
3173; c) S. Schmitz, H. Ritter, Angew. Chem. 2005, 117, 5803–5806;
Angew. Chem. Int. Ed. 2005, 44, 5658–5661; d) O. Kretschmann,
S. W. Choi, M. Miyauchi, I. Tomatsu, A. Harada, H. Ritter, Angew.
Chem. 2006, 118, 4468–4472; Angew. Chem. Int. Ed. 2006, 45, 4361–
4365; e) O. Kretschmann, C. Steffens, H. Ritter, Angew. Chem.
2007, 119, 2764–2767; Angew. Chem. Int. Ed. 2007, 46, 2708–2711;
f) S. Amajjahe, H. Ritter, Macromolecules 2008, 41, 3250–3253. For
CD-assisted assembly of stimuli-responsive polymers in aqueous
media, see: g) F. Yuen, K.-C. Tam, Soft Matter 2010, 6, 4613–4630.
For chemical-responsive supramolecular hydrogels, see: h) W. Deng,
H. Yamaguchi, Y. Takashima, A. Harada, Chem. Asian J. 2008, 3,
687–695. For selectively helical induction, see: i) K. Maeda, H. Mo-
chizuki, K. Osato, E. Yashima, Macromolecules 2011, 44, 3217–
3226.
Monomer 5 (0.5 g) and AIBN (2.5 mg) were dissolved in DMF (0.4 mL)
in a Schlenk tube. The solution was thoroughly deoxygenated by several
freeze—pump–thaw cycles and then stirred at 608C for 16 h. After cool-
ing to RT, the polymer was dissolved in water and dialyzed against deion-
ized water (MWCO: 8000–10000) for three days. After evaporation of
water in vacuo, the title polymer was yielded as a colorless solid (0.2 g,
1
40%). H NMR ([D6]DMSO): d=3.28–3.95 (m), 4.85 (br, CH2), 4.48 (br,
CH2), 5.73 (br).
Acknowledgements
Prof. Guangzhao Zhang, Dr. Xiaodong Ye, and Mr. Chunliang Li (all
from University of Science and Technology of China) are cordially
thanked for their support on the DLS measurements. Dr. Hongmei Deng
from the Instrumental Analysis of Research Center (Shanghai Universi-
ty) is thanked for her assistance in NMR measurements. We gratefully
thank one of the referees for helpful suggestion. This work is financially
supported by National Natural Science Foundation of China (Nos.
21034004, 211040403, and 20974020) and the Science and Technology
Commission of Shanghai (No. 10520500300).
[20] a) A. Zhang, Prog. Chem. 2005, 17, 157–171; b) A. D. Schlꢆter, Top.
Curr. Chem. 2005, 245, 151–191; c) Y. Chen, X. Xiong, Chem.
Commun. 2010, 46, 5049–5060; d) B. M. Rosen, C. J. Wilson, D. A.
Wilson, M. Peterca, M. R. Imam, V. Percec, Chem. Rev. 2009, 109,
6275–6540.
[21] a) A. Zhang, L. Okrasa, T. Pakula, A. D. Schlꢆter, J. Am. Chem.
Soc. 2004, 126, 6658–6666; b) A. Zhang, J. Barner, I. Goessl, J. P.
Rabe, A. D. Schlꢆter, Angew. Chem. 2004, 116, 5297–5300; Angew.
Chem. Int. Ed. 2004, 43, 5185–5188; c) E. Kasꢇmi, W. Zhuang, J. P.
Rabe, K. Fischer, M. Schmidt, M. Colussi, H. Keul, D. Yi, H.
Cçlfen, A. D. Schlꢆter, J. Am. Chem. Soc. 2006, 128, 5091–5099.
[22] I. Gçssl, L. Shu, A. D. Schlꢆter, J. P. Rabe, J. Am. Chem. Soc. 2002,
124, 6860–6865.
[23] a) J. G. Rudick, V. Percec, Acc. Chem. Res. 2008, 41, 1641–1652;
b) V. Percec, J. G. Rudick, M. Peterca, P. A. Heiney, J. Am. Chem.
Soc. 2008, 130, 7503–7508; c) A. Zhang, F. Rodrꢄguez-Ropero, D.
Zanuy, C. Alemꢃn, E. W. Meijer, A. D. Schlꢆter, Chem. Eur. J. 2008,
14, 6924–6934; d) A. Zhang, Macromol. Rapid Commun. 2008, 29,
839–845.
[24] a) C.-X. Cheng, R.-P. Tang, F. Xi, J. Polym. Sci. Part A 2005, 43,
2291–2297; b) C.-X. Cheng, Y. Tian, Y. Qiao, R.-P. Tang, F. Xi,
Langmuir 2005, 21, 6576–6581; c) C.-X. Cheng, Y. Tian, Y. Shi, R.-
P. Tang, F. Xi, Macromol. Rapid Commun. 2005, 26, 1266–1272;
d) C.-X. Cheng, T.-F. Jiao, R.-P. Tang, E.-Q. Chen, M.-H. Liu, F. Xi,
Macromolecules 2006, 39, 6327–6330; e) Q. Jiao, Z. Yi, Y. Chen, F.
Xi, Polymer 2008, 49, 1520–1526.
[1] a) J.-M. Lehn, Angew. Chem. 1988, 100, 91–116; Angew. Chem. Int.
Ed. Engl. 1988, 27, 89–112; b) L. Brunsveld, B. J. B. Folmer, E. W.
Meijer, R. P. Sijbesma, Chem. Rev. 2001, 101, 4071–4097; c) O.
Ikkala, G. ten Brinke, Science 2002, 295, 2407–2409; d) J.-L. Li, X.-
Y. Liu, Adv. Funct. Mater. 2010, 20, 3196–3216.
[2] a) J.-M. Lehn, Supramolecular Chemistry, Wiley-VCH, Weinheim,
1995; b) S. K. Yang, A. V. Ambade, M. Weck, Chem. Soc. Rev. 2011,
40, 129–137.
[3] J. M. Pollino, M. Weck, Chem. Soc. Rev. 2005, 34, 193–207.
[4] a) T. F. A. de Greef, E. W. Meijer, Aust. J. Chem. 2010, 63, 596–598;
b) R. J. Wojtecki, M. A. Meador, S. J. Rowan, Nat. Mater. 2011, 10,
14–27.
[5] M. Burnworth, L. Tang, J. R. Kumpfer, A. J. Duncan, F. L. Beyer,
G. L. Fiore, S. J. Rowan, C. Weder, Nature 2011, 472, 334–338.
[6] G. R. Whittell, M. D. Hager, U. S. Schubert, I. Manners, Nat. Mater.
2011, 10, 176–188.
[7] a) L. A. Estroff, A. D. Hamilton, Chem. Rev. 2004, 104, 1201–1217;
b) W. T. Truong, Y. Su, J. T. Meijer, P. Thordarson, F. Braet, Chem.
Asian J. 2011, 6, 30–42.
[8] H.-J. Yoon, W.-D. Jang, J. Mater. Chem. 2010, 20, 211–222.
[9] a) G. ten Brinke, J. Ruokolainen, O. Ikkala, Adv. Polym. Sci. 2007,
207, 113–177; b) D. Gonzꢃlez-Rodrꢄguez, A. P. H. J. Schenning,
Chem. Mater. 2011, 23, 310–325.
[10] Y. Yamamoto, T. Fukushima, Y. Suna, N. Ishii, A. Saeki, S. Seki, S.
Tagawa, M. Taniguchi, T. Kawai, T. Aida, Science 2006, 314, 1761–
1764.
[11] a) A. Perico, A. Ciferri, Chem. Eur. J. 2009, 15, 6312–6320; b) A.
Ciferri, Chem. Eur. J. 2010, 16, 10930–10945.
[25] a) C. O. Liang, B. Helms, C. J. Hawker, J. M. J. Frꢅchet, Chem.
Commun. 2003, 2524–2525; b) B. M. J. M. Suijkerbuijk, L. Shu,
R. J. M. Klein Gebbink, A. D. Schlꢆter, G. van Koten, Organometal-
lics 2003, 22, 4175–4177.
[26] A. C. Grimsdale, K. Mꢆllen, Angew. Chem. 2005, 117, 5732–5772;
Angew. Chem. Int. Ed. 2005, 44, 5592–5629.
[27] a) A. Zhang, L. Shu, Z. Bo, A. D. Schlꢆter, Macromol. Chem. Phys.
2003, 204, 328–339; b) A. Zhang, B. Zhang, M. Schmidt, A. D.
Schlꢆter, Chem. Eur. J. 2003, 9, 6083–6092.
[28] Y. Guo, J. D. van Beek, B. Zhang, M. Colussi, P. Walde, A. Zhang,
M. Krçger, A. Halperin, A. D. Schlꢆter, J. Am. Chem. Soc. 2009,
131, 11841–11854.
[29] For supramolecular dendronized polymer formed with metal coordi-
nation, see: a) H.-F. Chow, C.-F. Leung, W. Li, K.-W. Wong, L. Xi,
Angew. Chem. 2003, 115, 5069–5073; Angew. Chem. Int. Ed. 2003,
[12] A. Arnaud, J. Belleney, F. Bouꢅ, L. Bouteiller, G. Carrot, V. Wint-
gens, Angew. Chem. 2004, 116, 1750–1753; Angew. Chem. Int. Ed.
2004, 43, 1718–1721.
[13] a) G. Wenz, Angew. Chem. 1994, 106, 851–870; Angew. Chem. Int.
Ed. Engl. 1994, 33, 803–822; b) A. Harada, A. Hashidzume, H. Ya-
maguchi, Y. Takashima, Chem. Rev. 2009, 109, 5974–6023; c) F. van
de Manakker, T. Vermonden, C. F. van Nostrum, W. E. Hennink,
Biomacromolecules 2009, 10, 3157–3175; d) G. Chen, M. Jiang,
Chem. Soc. Rev. 2011, 40, 2254–2266.
[14] I. Dimitrov, B. Trzebicka, A. H. E. Mꢆller, A. Dworak, C. B. Tsveta-
nov, Prog. Polym. Sci. 2007, 32, 1275–1343.
3268
www.chemasianj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 3260 – 3269

Thermoresponsive Supramolecular Dendronized Polymers
42, 4919–4923; b) Y. Kim, M. F. Mayer, S. Zimmerman, Angew.
Chem. 2003, 115, 1153–1158; Angew. Chem. Int. Ed. 2003, 42, 1121–
1126; c) H.-J. Kim, W.-C. Zin, M. Lee, J. Am. Chem. Soc. 2004, 126,
7009–7014; d) H.-J. Kim, E. Lee, H.-s. Park, M. Lee, J. Am. Chem.
Soc. 2007, 129, 10994–10995; e) H.-J. Kim, J.-H. Lee, M. Lee,
Angew. Chem. 2005, 117, 5960–5964; Angew. Chem. Int. Ed. 2005,
44, 5810–5814; f) H.-J. Kim, E. Lee, M. G. Kim, M.-C. Kim, M. Lee,
E. Sim, Chem. Eur. J. 2008, 14, 3883–3888; g) F. Wꢆrthner, V. Stepa-
nenko, A. Sautter, Angew. Chem. 2006, 118, 1973–1976; Angew.
Chem. Int. Ed. 2006, 45, 1939–1942.
[35] W. Li, A. Zhang, Y. Chen, K. Feldman, H. Wu, A. D. Schlꢆter,
Chem. Commun. 2008, 5948–5950.
[36] a) W. Li, A. Zhang, K. Feldman, P. Walde, A. D. Schlꢆter, Macromo-
lecules 2008, 41, 3659–3667; b) W. Li, A. Zhang, A. D. Schlꢆter,
Macromolecules 2008, 41, 43–49; c) W. Li, D. Wu, A. D. Schlꢆter,
A. Zhang, J. Polym. Sci. Part A 2009, 47, 6630–6640.
[37] W. Li, A. Zhang, A. D. Schlꢆter, Chem. Commun. 2008, 5523–5525.
[38] M. J. N. Junk, W. Li, A. D. Schlꢆter, G. Wegner, H. W. Spiess, A.
Zhang, D. Hinderberger, Angew. Chem. 2010, 122, 5818–5823;
Angew. Chem. Int. Ed. 2010, 49, 5683–5687.
[30] For supramolecular dendronized polymer formed with acid–base in-
teraction, see: a) K. C.-F. Leung, P. M. Mendes, S. N. Magonov, B. H.
Northrop, S. Kim, K. Patel, A. H. Flood, H.-R. Tseng, J. F. Stoddart,
J. Am. Chem. Soc. 2006, 128, 10707–10715; b) X. Zhu, U. Beginn,
M. Mçller, R. I. Gearba, D. V. Anokhin, D. A. Ivanov, J. Am. Chem.
Soc. 2006, 128, 16928–16937; c) D. Xie, M. Jiang, G. Zhang, D.
Chen, Chem. Eur. J. 2007, 13, 3346–3353; d) X. Zhang, Y. Wang, W.
Wang, Langmuir 2009, 25, 2075–2080; e) Z. Cheng, B. Ren, H.
Shan, X. Liu, Z. Tong, Macromolecules 2008, 41, 2656–2662; f) Z.
Zhang, M. Yang, X. Zhang, L. Zhang, B. Liu, P. Zheng, W. Wang,
Chem. Eur. J. 2009, 15, 2352–2361; g) P.-J. Yang, C.-W. Wu, D. Sahu,
H.-C. Lin, Macromolecules 2008, 41, 9692–9703; h) Y. Kamikawa, T.
Kato, H. Onouchi, D. Kashiwagi, k. Maeda, E. Yahsima, J. Polym.
Sci. Part A 2004, 42, 4580–4586; i) C. Li, A. D. Schlꢆter, A. Zhang,
R. Mezzenga, Adv. Mater. 2008, 20, 4530–4534.
[31] a) H. G. Schild, Prog. Polym. Sci. 1992, 17, 163–249; b) E. S. Gil,
S. M. Hudson, Prog. Polym. Sci. 2004, 29, 1173–1222; c) C. de la-
s Heras Alarcꢈn, S. Pennadam, C. Alexander, Chem. Soc. Rev. 2005,
34, 276–285.
[32] a) D. Schmaljohann, Adv. Drug Delivery Rev. 2006, 58, 1655–1670;
b) J. Xu, S. Liu, Soft Matter 2008, 4, 1745–1749; c) C. Li, N. Gunari,
K. Fischer, A. Janshoff, M. Schmidt, Angew. Chem. 2004, 116, 1121–
1124; Angew. Chem. Int. Ed. 2004, 43, 1101–1104; d) H. Hatakeya-
ma, A. Kikuchi, M. Yamato, T. Okano, Biomaterials 2007, 28, 3632–
3643; e) T. Gillich, E. M. Benetti, E. Rakhmatullina, R. Konradi, W.
Li, A. Zhang, A. D. Schlꢆter, M. Textor, J. Am. Chem. Soc. 2011,
133, 10940–10950.
[39] Abbreviations: Ada=adamantyl, AIBN=azobis(isobutyronitrile),
CD=cyclodextrin, DCM=dichloromethane, DiPEA=diisopropyle-
thylamine, DMF=N,N-dimethylformamide, EDC=1-(3-dimethyla-
minopropyl)-3-ethylcarbo-diimide hydrochloride, G1=first genera-
tion, G2=second generation, HOBt=N-hydroxybenzotriazole,
LAH=lithium aluminum hydride, LCST=lower critical solution
temperature, OEG=oligoethylene glycol, SDP=supramolecular
dendronized polymers, TEA=triethylamine.
[40] A. Zhang, S. Vetter, A. D. Schlꢆter, Macromol. Chem. Phys. 2001,
202, 3301–3315.
[41] F. Yhaya, A. M. Gregory, M. H. Stenzel, Aust. J. Chem. 2010, 63,
195–210.
[42] K. Ohga, Y. Takashima, H. Takahashi, Y. Kawaguchi, H. Yamagu-
chi, A. Harada, Macromolecules 2005, 38, 5897–5904.
[43] G. Wenz, B. H. Han, A. Mꢆller, Chem. Rev. 2006, 106, 782–817.
[44] a) S. Bolisetty, C. Schneider, F. Polzer, M. Ballauff, W. Li, A. Zhang,
A. D. Schlꢆter, Macromolecules 2009, 42, 7122–7128; b) M. J. N.
Junk, W. Li, A. D. Schlꢆter, G. Wegner, H. W. Spiess, A. Zhang, D.
Hinderberger, J. Am. Chem. Soc. 2011, 133, 10832–10838.
[45] This dissociation phenomenon has also been reported by others,
see: Refs [19b,c,f], and also a) H. Ohashi, Y. Hiraoka, T. Yamagu-
chi, Macromolecules 2006, 39, 2614–2620; b) J. Bigot, M. Bria, S. T.
Caldwell, F. Cazaux, A. Cooper, B. Charleux, G. Cooke, B. Fitzpa-
trick, D. Fournier, J. Lyskawa, M. Nutley, F. Stoffelbach, P. Woisel,
Chem. Commun. 2009, 5266–5268.
[46] Comparing the split pick areas from adamantyl moieties (at d=2.3–
2.5 and 2.2–2.3 ppm) or those from methyl groups (at d=1.26–1.46
and 1.20–1.36 ppm), respectively, which leads to the similar percent-
age results for the dissociation.
[33] A. Ciferri, Supramolecular Polymers, 2nd ed., 2005, CRC press,
p. 44.
[34] a) G. Lapienis, Prog. Polym. Sci. 2009, 34, 852–892; b) S. Han, M.
Hagiwara, T. Ishizone, Macromolecules 2003, 36, 8312–8319; c) F.
Hua, X. Jiang, D. Li, B. Zhao, J. Polym. Sci. Part A 2006, 44, 2454–
2467; d) J.-F. Lutz, J. Polym. Sci. Part A 2008, 46, 3459–3470; e) H.
Morinaga, H. Morikawa, Y. M. Wang, A. Sudo, T. Endo, Macromo-
lecules 2009, 42, 2229–2235; f) X. Gao, N. Kucerka, M.-P. Nieh, J.
Katsaras, S. Zhu, J. L. Brash, H. Sheardown, Langmuir 2009, 25,
10271–10278.
[47] K. Hamasaki, H. Ikeda, A. Nakamura, A. Ueno, F. Toda, I. Suzuki,
T. Osa, J. Am. Chem. Soc. 1993, 115, 5035–5040.
[48] D. Popescu, H. Keul, M. Mçller, React. Funct. Polym. 2010, 70, 767–
774.
Received: June 11, 2011
Published online: September 8, 2011
Chem. Asian J. 2011, 6, 3260 – 3269
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3269