Click-dendronized poly(amide-triazole)s-effect of dendron size and polymer backbone symmetry on self-assembling and gelation properties

Article abstract of DOI:10.1002/chem.201101045

Nine dendronized poly(amide-triazole)s 2-Gm Gn (m=1-3, n=1-3), were prepared by the 1:1 copolymerization between AA-type dendritic diazides 4-Gm (m=1-3) and BB-type dendritic diacetylenes 5-Gn (n=1-3) under the copper(I)-mediated click coupling conditions

Full text of DOI:10.1002/chem.201101045

FULL PAPER
DOI: 10.1002/chem.201101045
Click-Dendronized Poly(amide–triACTHNUTRGNEUGNazole)s—Effect of Dendron Size and
Polymer Backbone Symmetry on Self-Assembling and Gelation Properties
Hak-Fun Chow,*[a, b, c, d] Kwun-Ngai Lau,[a] and Man-Chor Chan[a]
Abstract: Nine dendronized poly(am-
ide–triazole)s 2-GmGn (m=1–3, n=
1–3), were prepared by the 1:1 copoly-
merization between AA-type dendritic
diazides 4-Gm (m=1–3) and BB-type
dendritic diacetylenes 5-Gn (n=1–3)
under the copper(I)-mediated click
coupling conditions. The degree of
polymerization value of the polymers
was found to range from 15–50, and
decreased with increasing size of the
dendron, suggesting steric hindrance
had a retardation role on the copoly-
merization efficiency. Based on FT-IR
was present in the solution state after
copolymerization, whereas the mono-
mers 4-Gm and 5-Gn were devoid of
any intermolecular hydrogen-bonding
interaction. Hence a positive allosteric
hydrogen-bonding effect was observed
after polymerization, and could be ra-
tionalized by the zip effect. The
strength of the interchain association in
polymers 2-GmGn was found to de-
crease with increasing size of the den-
G3G1>2-G2G3ꢀ2-G3G2>2-
G3G3). Among the nine polymers,
only 2-G1G2 and 2-G2G1 were good
organogelators for aromatic solvents,
while the 2-G2G2 polymer, bearing
the closest structural resemblance to
the previously reported organogelator
1-G2 prepared from the polymerization
of AB-type monomers, was devoid of
gelating power. Careful analysis of
structures of the present polymer series
2-GmGn and the previously reported
series 1-Gn suggested that the polymer
backbone symmetry played a subtle
role in controlling their self-assembling
and gelating properties.
dron
(i.e.,
2-G1G1>2-G1G2>2-
G2G1ꢀ2-G2G2>2-G1G3ꢀ2-
1
and H NMR studies, it was found that
significantly strong, interchain hydro-
gen bonding between the amide units
Keywords: click chemistry · den-
drimers · gels · self-assembly
Introduction
exhibit some interesting conformational and supramolecular
properties.[4] For example, oligotriazoles have been reported
as hosts for anions,[5] and to form double helical structures
when replacing the phosphodiester linkages in an DNA oli-
The copper(I)-catalyzed cycloaddition (CuAAC) reaction[1]
between acetylenes and azides has become an important
synthetic tool in many research disciplines and in polymer
chemistry.[2,3] While it is a useful and universal ligation tech-
nique that can link various types of molecules together, the
product functionality, that is, the triazole unit, and its associ-
ated properties generated from this reaction have also been
the subject of increasing interest. In particular, emerging ex-
gomer.[6] Poly
ACTHUNRTGNE(GNU triazole)s are also known to function as
hydro-[7] as well as organogelators.[8] We earlier reported the
interesting self-assembling properties of a series of click-
dendronized poly(amide–triazole)s 1-Gm (m=1–3) pre-
pared from the polymerization of AB-type monomers 3-
Gm, in which a synergistic cooperative hydrogen-bonding
effect and dendrimer-generation-specific organogelating
properties were found.[9,10] Despite these findings, the mech-
anism by which triazole and the dendritic units, as well as
the polymer backbone, exert their control on the supra-
molecular properties still deserve further investigations.
Herein, we disclose additional research findings based on
the study of a new series of click-dendronized poly(amide–
triazole)s 2-GmGn (m=1–3; n=1–3) bearing alternating
dendritic side chains of different size, and provided addition-
al insights of the structural factors on their organogelating
and self-assembling properties. These new dendronized
polymers were synthesized by a copolymerization reaction
between AA-type diazide 4-Gm and BB-type diacetylene 5-
Gn monomers. In contrast to our earlier report in which
only three dendronized polymers were subjected to our in-
vestigation, here a total number of nine dendronized copoly-
mers of different dendritic side-chain combination were
probed in a systematic manner, and hence a broader picture
amples indicate that oligo- and polyACTHNUTRGNEUNG(triazole) compounds
[a] Prof. Dr. H.-F. Chow, Dr. K.-N. Lau, Prof. Dr. M.-C. Chan
Department of Chemistry
The Chinese University of Hong Kong
Shatin NT (Hong Kong)
Fax : (+852)26035057
E-mail: hfchow@cuhk.edu.hk
[b] Prof. Dr. H.-F. Chow
The Center of Novel Functional Molecules
The Chinese University of Hong Kong
Shatin NT (Hong Kong)
[c] Prof. Dr. H.-F. Chow
Institute of Molecular Functional Materials
Areas of Excellent Scheme
University Grants Committee (Hong Kong)
[d] Prof. Dr. H.-F. Chow
State Key Laboratory on Synthetic Chemistry (Hong Kong)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201101045.
Chem. Eur. J. 2011, 17, 8395 – 8403
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
8395

of the structure–property relationships is revealed. Despite
their structural similarities, there are subtle differences be-
tween these two series of dendronized polymers 1-Gm and
2-GmGn. In our previous reported polymers 1-Gm, the un-
symmetrical repeating units of the polymer backbone are
connected in a head-to-tail manner, and hence the corre-
Results and Discussion
Synthesis: The dendronized copolymers 2-GmGn were pre-
pared by the AABB-type click copolymerizations between
diazides 4-Gm (m=1–3) and diacetylene dendritic macro-
monomers 5-Gn (n=1–3; Scheme 2). Despite their structur-
al simplicities, direct bis-functionalization of the known di-
carboxylic acid dendrons 6-Gm (m=1–3)[11] with propargyl
sponding dipoles are aligned in
a
parallel fashion
(Scheme 1). On the other hand, the same backbone repeat-
ing units are arranged either in a head-to-head or tail-to-tail
arrangement in 2-GmGn. As a result, any two neighboring
backbone dipoles are aligned in an antiparallel manner. Sur-
prisingly, while only 1-G2 showed gelation properties in our
previous study, its closest structural analogue 2-G2G2 in
this present series is non-gelating. Hence the results ob-
tained here suggest that the parallel and antiparallel ar-
rangements of these backbone dipoles can also exert sub-
stantial influence on the polymer gelaton properties.
Scheme 2. Synthesis of bifunctional monomers 4-Gm and 5-Gm and
dendronized periodic polymers 2-GmGn. Reagents and conditions: i)
ꢁ
HC CCH2NH2, EDCI (or DCC, cat. DMAP), HOBt, CH2Cl2; ii) KOH
(2m), THF, MeOH; iii) 4-(azidomethyl)benzylamine, EDCI (or DCC and
cat. DMAP), HOBt, CH2Cl2; iv) 5-Gn (1 equiv), CuSO4·5H2O, sodium
ascorbate, THF/DMF/H2O (v/v/v 1:1:1).
amine or 4-(azidomethyl)benzyl amine using dicyclohexyl-
carbodiimide (DCC) or 1-[3-(dimethylamino)propyl]-3-eth-
ylcarbodiimide methiodide (EDCI) failed to give any prod-
ucts. Reactions using the corresponding diacid chlorides,
however, led to a complex mixture of products. Hence, se-
quential introduction of the azide or acetylene functionali-
ties was used. The known monoacid monoesters 7-Gm[9]
were first coupled to propargyl amine in the presence of 1-
hydroxybenzotriazole (HOBt) and a coupling reagent to
produce the propargyl amides 8-Gm in 80–92% yield. It was
found that EDCI was useful for preparation of the first-gen-
eration (G1) dendrimer. On the other hand, DCC plus a cat-
alytic amount of N,N-dimethylaminopyridine (DMAP) were
better suited for the second- and thrid-generation (G2 and
G3, respectively) dendrimers. The ester functionality in
compounds 8-Gm was then hydrolyzed under basic condi-
tions to give the corresponding carboxylic acids 9-Gm in 77–
92% yield. Finally, coupling of the acids with propargyl
amine again under the same coupling conditions afforded
the target diacetylenes 5-Gm in 80–94% yield. The target
diazides 4-Gm were similarly prepared in 67–79% by react-
ing the known acids 10-Gm[9] with 4-(azidomethyl)benzyl
amine under the standard coupling conditions. The struc-
Scheme 1. Click dendronized poly(amide–triazole)s 1-Gm from polymeri-
zation of AB-type monomers 3-Gm, and 2-GmGn from copolymeriza-
tion of AA-type 4-Gm + BB-type 5-Gn monomers.
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Click-Dendronized Poly(amide–triazole)s
FULL PAPER
tures of all compounds were fully characterized and con-
firmed by 1H and 13C NMR spectroscopy and mass spec-
trometry. Their purities were also assessed by size exclusion
chromatography (SEC), and all of them gave a major sigmo-
dial peak with a polydispersity index (PDI) of less than 1.03
(see Supporting Information for details).
Click copolymerizations: The procedure for the 1:1 click
polymerizations between 4-Gm and 5-Gn was the same as
that described for the preparation of dendronized polymers
1-Gm.[9] To ensure good polymerization efficiency, a 1:1:1
mixture of THF, DMF, and water was required to maintain
homogeneous conditions, at least in the initial stage of the
polymerization. After stirring at 258C for four days, the
polymer was isolated either by precipitation in aqueous
HCl, or by extraction with CH2Cl2 followed by solvent evap-
oration. A total of nine dendronized polymers was prepared
in yields from 84–99%. It should be noted that dendronized
polymer 2-GmGn was structurally different from 2-GnGm.
The structure of the various dendronized polymers was
first characterized by 1H NMR spectroscopy. To minimize
the degree of aggregations, [D8]THF was employed as the
solvent for analysis except for 2-G1G1, which was only solu-
ble in [D6]DMSO. Both the acetylene and methylene proton
signals adjacent to the azide functionality disappeared, and
hence this suggested that the copolymerization reactions
Figure 1. Stacked partial 1H NMR (400 MHz, [D8]THF, 258C) spectra of
dendronized polymers 2-GmG2. For clarity, the spectral portion due to
the aliphatic hydrocarbon dendron was not shown.
carbonyl moiety were located at about d=172.5–174.0 ppm.
In the cases of 2-G1G1 and 2-G2G1 dendronized polymers,
only one 13C carbonyl signal was found, but up to five sig-
nals were noted in the case of 2-G3G3 (Figure 2). Hence,
one could conclude that dendronized polymers constructed
from monomers bearing G1 dendrons showed a high struc-
tural homogeneity with respect to those from monomers of
G2 and G3 dendrons, indicating that the steric bulkiness of
the dendritic appendage lowered the copolymerization effi-
ciency. This finding is also consistent with the results ob-
tained from size exclusion chromatographic (SEC) analysis
(vide infra).
1
were very efficient. The H signals of the aliphatic hydrocar-
bon dendrons remained almost unchanged, but a certain
degree of peak broadening was observed. Two methylene
1H signals (ArCH2Triaz and ArCH2N) appeared at d=4.2–
4.5 ppm, whereas the third (NCH2Triaz) was located at d=
5.2–5.7 ppm. All three methylene 1H signals were shifted
1
downfield relative to their corresponding H signals in the
monomers. The aromatic signals of all dendronized poly-
mers appeared at around d=7.0–7.3 ppm either as a broad
1
singlet or multiplets, while the H signal of the triazole ring
was situated at about d=7.4–7.8 ppm.
À
The position of the N H signals of this new series of
dendronized polymers deserved further comments. As 2-
À
G1G1 is only soluble in DMSO, the N H signals appeared
at a relatively downfield region at about d=8.5–9.0 ppm
(see Supporting Information for details). For the remaining
eight soluble dendronized polymers, at least three sets of
1
amide H signals at about d=7.4–8.5 ppm could be identi-
fied (Figure 1). This was in sharp contrast to the spectral
properties of the previously reported 1-G2, which was found
to be a good organogelator in THF, wherein the NH signals
were significantly shifted downfield to d=10.5–10.7 ppm. As
it turned out, none of the nine new dendronized polymers,
including the closest structural isomer of 1-G2 (i.e., 2-
G2G2), were able to gel THF, highlighting that a subtle
change of polymer backbone could significantly alter their
self-assembling and organogelating properties.
The 13C NMR signals of all nine dendronized polymers 2-
GmGn were well resolved. Hence, two sp2-hybridized 13C
signals due to the triazole appeared as two distinctive peaks
at about d=123.0 and 147.0 ppm. The 13C signals due to the
Figure 2. Stacked partial 13C NMR (100 MHz, [D8]THF, 258C) spectra of
dendronized polymers 2-G3G3, 2-G2G2 and 2-G2G1. Only the C=O, ar-
omatic and triazole 13C signals were shown.
Chem. Eur. J. 2011, 17, 8395 – 8403
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8397

H.-F. Chow et al.
Table 2. MGC values [mgmLÀ1] of 2-G1G2 and 2-G2G1 dendronized
The dendronized polymers 2-GmGn were then character-
ized by SEC analysis. Similar to 1-G1, the poor solubility
properties of 2-G1G1 in THF precluded its SEC examina-
tion. In addition to the expected polymer peak, the SEC
chromatograms of all examined dendronized polymers also
showed the presence of many low-molecular-weight (LMW)
peaks, suggesting the formation of cyclic oligomers during
the copolymerization process[9] (see Supporting Information
for details). The calculated Mw, PDI, degree of polymeri-
zation (DP) values, and weight percentage of LMW oligo-
mers (up to [3+3]mer) are given in Table 1. One point that
polymers in various organic solvents.[a]
Solvent
2-G1G2 2-G2G1 Solvent
2-G1G2 2-G2G1
n-hexane
CHCl3
EtOAc
acetone
EtOH
– (I)
– (S)
50 (OG)
– (S)
– (S)
– (S)
– (I)
– (S)
– (S)
– (S)
– (S)
– (S)
toluene
20 (CG) 30 (CG)
10 (CG) 50 (CG)
20 (CG) 50 (CG)
20 (CG) 30 (CG)
o-xylene
m-xylene
p-xylene
o-dichlorobenzene 10 (CG) 20 (CG)
anisole 20 (CG) 50 (CG)
50 (TG) – (S)
THF
benzene 50 (CG) 20 (CG) nitrobenzene
[a] CG=transparent gel; OG=opaque gel; TG=translucent gel; S=
soluble (>50 mgmLÀ1); I=insoluble.
Table 1. SEC data of dendronized polymers 2-GmGn.[a]
contrast to dendronized polymer 1-G2, polymers 2-G1G2
and 2-G2G1 formed organogels specifically with aromatic
solvents, but did not form gel in other non-aromatic organic
solvents. In addition, the gelation speed of organogels origi-
nated from polymers 2-G1G2 (ꢀ20 min) and 2-G2G1
(ꢀ1 h) were slower than that from 1-G2 (ꢀ5 min). More-
over, the minimum gelation concentrations (MGC) for both
of them were higher than those of polymer 1-G2, and hence
one could conclude that the presence series of dendronized
polymers 2-G1G2 and 2-G2G1 had a lower gelation power.
The thermotropic behavior of the gels from polymers 1-
G2, 2-G1G2, and 2-G2G1 in p-xylene were studied by using
the dropping ball method. For the gel derived from
dendronized polymer 2-G2G1, the steel ball sank immedi-
ately to the bottom of the vial when it was placed on the gel
surface before heating. This indicated that polymer 2-G2G1
was the weakest organogelator among the three. For
dendronized polymer 2-G1G2, as a 8% (w/v) gel, the Tg
was near to the boiling point of p-xylene (1368C). However,
when the concentration was reduced to 7% (w/v), the Tg de-
creased significantly (1248C). A Tg temperature plateau at
1248C was observed from 7% (w/v) to 2.5% (w/v), followed
by an abrupt drop to 728C as the concentration was lowered
to 2% (w/v). On the other hand, the gel derived from poly-
mer 1-G2 showed significantly higher Tg (1308C) than poly-
mer 2-G1G2 even at a lower concentration range (1.5–3%
w/v). This again showed that 2-G1G2 was a weaker organo-
gelator than 1-G2, even though the former possessed a
higher DP and a larger Mw value.
Mw
PDI
DP
Weight% of
LMW fraction[b]
2-G1G1[c]
2-G1G2
2-G1G3
2-G2G1
2-G2G2
2-G2G3
2-G3G1
2-G3G2
2-G3G3
–
–
–
–
1
5
2
4
8
5
5
8
56000
33000
43000
39000
27000
41000
46000
45000
2.3
1.6
1.9
2.1
1.5
1.7
2.0
1.9
51
21
39
29
15
26
25
19
[a] All experiments were conducted in THF at 408C using polystyrenes
as calibration standards. [b] Low MW fraction up to [3+3]mer. [c] Not
determined because of poor solubility in THF.
should be mentioned here was that the DP values were cal-
culated based on the molecular weight of one repeating
unit. For 2-GmGn, one repeating unit actually consists of
two dendron anchorage points, and thus the DP values
should be doubled if we want to directly compare them with
the results obtained from 1-Gm. Taking this into consider-
ation, it was noted that there was little difference in terms
of the PDI and DP values, and also in the weight% of
LMW fraction between polymers 1-Gm and 2-GmGn bear-
ing dendritic appendages of the same generation.
Gelation properties: In the present study, nine compounds
were synthesized with a broader structural spectrum in
order to have a better understanding of the size of the den-
drons on the self-assembling and gelation properties. Recall
that in our previous series of dendronized polymers 1-Gm,
three compounds were prepared and only the G2-dendron-
ized polymer 1-G2 could form gels with organic solvents. To
our surprise, its closest structural analogue 2-G2G2 could
not form gels with any organic solvents. Among the nine
compounds, only 2-G1G2 and 2-G2G1 were good organo-
gelators. Other dendronized polymers just simply dissolved
in most organic solvents, while 2-G1G1 was not soluble in
most nonpolar organic solvents.
Gelation mechanism: To unveil the mechanism of the self-
assembling process, FT-IR spectroscopy was used to probe
the extent of hydrogen bonding in all dendronized mono-
mers 4-Gm and 5-Gn and the click polymers 2-GmGn
(Table 3). For both the diazides 4-Gm and the diacetylenes
5-Gn, the C=O stretching frequencies were located at about
1679 and 1682 cmÀ1, respectively. These values are typical of
non-hydrogen-bonded C=O stretching frequency. Further-
À
more, two N H absorptions were observed at about 3433
The gelation properties of 2-G1G2 and 2-G2G1 were fur-
ther examined in various solvents (Table 2). One point that
should be mentioned was that experiments were conducted
on polymer samples after treatment with ethylenediaminete-
traacetic acid (EDTA) to remove trace of the Cu ions. In
and 3280 cmÀ1 in all generations of monomers. While the
one at 3433 cmÀ1 was characteristic of a non-hydrogen-
bonded secondary amide, the one at 3280 cmÀ1 appeared to
À
be due to hydrogen-bonded N H stretching. However, this
assignment contradicted other experimental evidence. First,
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Click-Dendronized Poly(amide–triazole)s
FULL PAPER
Table 3. FT-IR data [cmÀ1] of 4-Gm, 5-Gn monomers and dendronized
polymers 2-GmGn in different physical states.[a]
of the symmetrical 4-Gm and 5-Gn monomers was due to
band splitting and not hydrogen bonding. In other words, all
monomers 4-Gm and 5-Gn are non-hydrogen-bonded in the
solution state. This was consistent with what was found with
the unsymmetrical monomers 3-Gm.
For the IR spectra of the dendronized polymers 2-GmGn,
some showed the presence of a residual N3 absorption peak
(e.g., 2-G2G3 and 2-G3G1 in the solid state, 2-G2G3 and
2-G3G3 in the solution state). Hence, this suggested that
either the polymerization was not 100% complete, and/or
the degree of polymerization was low. The former situation
would lead to the presence of residue diazide and/or diace-
tylene monomers, while the latter would render the higher
percentage of the azide or alkyne end groups detectable by
À
ꢁ À
C H
–
–
–
3306
3310
3311
–
–
–
–
–
–
–
–
–
–
State
N H
N3
C=O
4-G1
4-G2
4-G3
5-G1
5-G2
5-G3
2-G1G1
2-G1G2
solution[b]
solution[b]
solution[b]
solution[b]
solution[b]
solution[b]
solid
3433, 3276
3433, 3279
3433, 3277
3434, ꢀ3290[c]
3433, ꢀ3290[c]
3434, ꢀ3290[c]
3341
3334
3341
3336
3341
3341
3337
3344
3344
3337
3341
3345
3342
2099
2099
2099
–
–
–
–
–
–
–
–
–
–
1679
1679
1679
1682
1682
1682
1663
1640
1643
1643
1666
1652
1649
1643
1648
1647
1673
1647
1665
1643
1673
1676
dried gel
gel[d]
2-G1G3
2-G2G1
2-G2G2
2-G2G3
2-G3G1
2-G3G2
2-G3G3
solid
solution[d]
dried gel
gel[d]
solid
–
ꢁ À
IR spectroscopy. Unfortunately, the residual C H peak, if
solution[d]
solid
–
–
–
–
À
[e]
any, was obscured by the broader N H signals and could
1
solution[d]
solid
–
–
–
–
–
–
[e]
not be observed. Apparently, H NMR spectroscopy was a
[e]
less sensitive tool to monitor the extent of the polymeri-
zation, as no acetylenic proton signals could be observed in
all the 1H NMR spectra of the polymers 2-GmGn (see
above). The presence of the N3 absorption peaks revealed
that the efficiency of the AABB-type copolymerization
were inferior to that of the AB-type polymerization involv-
ing the unsymmetrical monomers 3-Gm. Nonetheless, we
could not absolutely rule out this was the result due to a
weighing error of the monomers, as this type of AABB-type
polymerization required an exact 1:1 reactant stoichiometry.
solution[d]
solid
–
–
–
3335
3345
3346
solution[d]
solution[d]
[e]
–
[a] Spectra were recorded at 2 cmÀ1 resolution. [b] 35 mm solution in tolu-
ene. [c] Exact frequency of the latter number could not be determined
ꢁ À
due to overlapping with C H stretching. [d] ꢀ4% w/v in toluene. [e] A
residual N3 absorption peak was found at 2099 cmÀ1
.
1
this was inconsistent with the H NMR results, in which the
For the solid-state FT-IR spectra, all dendronized poly-
À1
À
À
N H signal appeared at an upfield position (d=7.4–
mers gave one broad N H peak between 3335–3345 cm
7.5 ppm) for all the dendritic monomers, which indicated
little or no hydrogen bonding in the solution state. Second,
and a C=O peak between 1643–1663 cmÀ1 (see Supporting
Information for details). Both signals were redshifted rela-
tive to those of the monomers in toluene, and were indica-
tive of the presence of intra- and/or interchain hydrogen
1
a H NMR concentration-dependent study was carried out
À
using diazide 4-G3 in [D8]toluene. No significant shift in N
À
H signal (Ddꢂ0.05 ppm) was found in concentrations in the
bonds between the N H and C=O moieties. Furthermore,
À1
À
À
range 35–0.78 mm. Third, if N H hydrogen bonding was
the non-hydrogen-bonded N H peak (ꢀ3430 cm ) origi-
present in the monomers, the C=O stretching band should
be redshifted. However, all the C=O stretching bands ap-
peared at about 1680 cmÀ1, a region that corresponded to
non-hydrogen-bonded C=O stretching. It should be noted
that the IR absorption band at 3280 cmÀ1 could not be
found in all the asymmetrical AB-type dendritic monomers
3-Gm used in the preparation of 1-Gm, while this peak was
observed in all the symmetrical 4-Gm and 5-Gn monomers.
Careful examination of the literature suggested that two
nally present in the monomers disappeared. These findings
À
were in accord to the observed red shifts of C=O and N H
signals in the solid-state FT-IR spectra of most secondary
amides.
The solution FT-IR spectra of the non-gelating dendron-
ized polymers (except 2-G1G1 because of its poor solubili-
ty) and the toluene gel FT-IR spectra of the two gelating 2-
G1G2 and 2-G2G1 polymers were also measured in ꢀ4%
toluene solution (see Supporting Information for details).
À
À
types of N H stretching modes were possible for the sym-
Several interesting findings were noted. First, the N H
metrical AA-type 4-Gm and BB-type 5-Gn monomers,
namely symmetrical and asymmetrical. Strictly speaking,
only those bonds with the same symmetry can be coupled to
give this kind of interactions in IR spectroscopy. Taking this
into consideration, it could be easily rationalized why the
previous AB-type monomers 3-Gm did not show this kind
signal of all dendronized polymers was redshifted
(ꢀ130 cmÀ1) to about 3341–3346 cmÀ1, indicating the pres-
ence of hydrogen bonding in the solution state. Second,
there was the presence of a shoulder peak at around
3430 cmÀ1 in dendronized polymers that contained the
larger G2 and G3 dendrons (i.e., 2-G2G3, 2-G3G2, 2-
G3G3), but this was not observed in dendronized polymers
not bearing the largest G3 dendron such as 2-G2G1
(Figure 3). This indicated that the interpolymer chain hydro-
gen bonding became weaker once the largest G3 dendron
was attached to the polymer backbone. Third, in line with
this finding, the extent of the C=O red shift was found to re-
À
of band splitting, as the two N H bonds did not have the
À
same symmetry. In fact, the N H stretchings of symmetrical
malonamide[12] were found to split into two bands (3375 and
3162 cmÀ1) in the solid state, attributable to the asymmetric
À
and symmetric N H stretchings, respectively. It could there-
fore be concluded that N H stretching signal at ꢀ3280 cm
À1
À
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H.-F. Chow et al.
enced red shift values that were comparable to those ob-
served in the gel state.
In summary, the FT-IR experimental results reinforced
our earlier proposed concept of synergistic binding of the
amide units upon polymerization. In addition, the effect of
increasing dendron size on impeding the self-assembly prop-
erties of such amide-containing dendrimers was clearly re-
vealed. In terms of gelation properties, only dendronized
polymers (i.e., 2-G1G2 and 2-G2G1) bearing dendrons of
moderate size were good organogelators. However, what
still remained perplexing was why gelation was specific to 2-
G1G2 and 2-G2G1, but not to 2-G2G2. This last dendron-
ized polymer evidently possesses the closest structural re-
semblance to the uniquely organogelating 1-G2 in the AB-
type dendronized polymers.
In our previous work,[9] we proposed that the strength of
polymer self-assembly was controlled by 1) the synergistic
association originated from the zip-effect after polymeri-
zation, and 2) the size of the dendritic appendage. In order
to rationalize the gelation property of 2-G1G2 and 2-G2G1
and also the lack of gelation property of 2-G2G2, we specu-
lated that there was a third factor involved, namely the
polymer backbone symmetry. Careful examination of 1-G2
and 2-G2G2 revealed one subtle structural difference be-
tween them. Due to its unsymmetrical nature, the polymer
backbone segment between the two dendritic anchorage
points should possess a net dipole moment (grey arrows in
Figure 5). Based on the studies by Schlꢁter,[13] it is likely
that such dendronized polymers, especially those bearing
the G2 and G3 dendrons, will adopt a rigid cylindrical struc-
ture. Hence, in the AB-type dendronized polymers 1-Gm,
the adjacent dipoles should be aligned more or less along
the same direction (i.e., parallel orientation), resulting in a
net polymer backbone dipole. On the other hand, in the
AABB-type dendronized polymers 2-GmGn, the adjacent
Figure 3. Stacked partial FT-IR spectra of dendronized polymers (from
top to bottom) 2-G2G1, 2-G2G3, 2-G3G2 and 2-G3G3. The asterisks
(*) indicate the shoulder peak at 3430 cmÀ1
.
flect the increasing degree of hydrogen-bonding interactions
with decreasing dendron size (Figure 4). For 2-G2G3, 2-
G3G3, and 2-G3G2-dendronized polymers, the position of
Figure 4. Stacked partial FT-IR spectra of dendronized polymers 2-
GmGn, showing the gradual increase of C=O red-shift with decreasing
size of dendritic appendage. From top to bottom: 2-G2G1, 2-G2G1, 2-
G2G2, 2-G1G3, 2-G3G1, 2-G2G3, 2-G3G2, and 2-G3G3.
the C=O signal was between 1673–1676 cmÀ1, representing a
red shift of 5–10 cmÀ1 as compared to that of the non-hydro-
gen-bonded dendronized monomers (spectral resolution at
2 cmÀ1). The red shift value was increased to 15 cmÀ1 for 2-
G1G3 and 2-G3G1. For the non-gelating 2-G2G2 and the
weaker gelating dendronized polymer 2-G2G1, a red shift
of ꢀ20 cmÀ1 was found. This shift was further increased to
25 cmÀ1 in the stronger gelating dendronized polymer 2-
G1G2. The freeze-dried gel FT-IR spectra of the two
dendronized polymers 2-G1G2 and 2-G2G1 were also re-
Figure 5. The arrangement of backbone dipoles (shown as arrows) in the
À
corded. As expected, both the N H and C=O bands experi-
AB-type 1-Gm and AABB-type 2-GmGn dendronized polymers.
8400
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Chem. Eur. J. 2011, 17, 8395 – 8403

Click-Dendronized Poly(amide–triazole)s
FULL PAPER
(400 MHz, CDCl3): d=0.81 (d, J=6.8 Hz, 12H; CH3), 1.00–1.12 (m, 4H;
CH2), 1.44 (septet, J=6.8 Hz, 2H; CHMe2), 1.79–1.91 (m, 4H; CCH2),
4.32 (s, 4H; CH2N3), 4.46 (d, J=6 Hz, 4H; NHCH2), 7.27 (d, J=8 Hz,
4H; ArH), 7.32 (d, J=8 Hz, 4H; ArH), 7.51 ppm (t, J=6 Hz, 2H; NH);
13C NMR (100 MHz, CDCl3): d=22.3, 28.1, 33.7, 36.0, 42.9, 54.2, 56.5,
127.8, 128.3, 134.3, 138.5, 173.5 ppm; SEC: Rt =34.69 min; MS (ESI): m/z
(%): 555 (100) [M+Na+]; HRMS (ESI) calcd for C29H40N8O2 +Na+:
555.3166; found: 555.3153; elemental analysis calcd (%) for C29H40N8O2:
C 65.39, H 7.57, N 21.03; found: C 65.43, H 7.76, N 21.04.
dipoles are aligned in antiparallel fashion, and this type of
polymer is expected to have a diminishing overall dipole
moment due to the cancellation effect of the antiparallel ar-
rangement. Hence, the interchain interaction between the
parallel-type polymer chains (i.e., 1-Gn) should be stronger
than that between the antiparallel-type polymer chains (i.e.,
2-GmGn), because of the presence of extra dipole–dipole
interaction. Hence, the absence of a dipole–dipole interac-
tion in case of 2-G2G2, as compared to the presence of
dipole–dipole interaction in 1-G2, weakened the interchain
association, making it a poor organogelator. In order to
become an effective organogelator, the interchain hydrogen-
bonding interaction must be strengthened, and this could be
realized by decreasing the size of the appending dendrons.
Hence, both 2-G1G2 and 2-G2G1 are good organogelators,
as one of the dendrons is smaller and this can promote
stronger interchain association and compensate for the di-
minishing polymer dipole–dipole interaction.
G2-Diazide 4-G2: DCC (0.72 g, 3.49 mmol) was added to a stirred solu-
tion of 10-G2 (1.60 g, 2.50 mmol), 4-(azidomethyl)benzylamine (0.56 g,
3.45 mmol), HOBt (0.47 g, 3.48 mmol), and DMAP (2 mg) in CH2Cl2
(30 mL). The reaction mixture was stirred at 258C for 2 h and concentrat-
ed under reduced pressure. The residue was purified by flash chromatog-
raphy on silica gel (eluent: hexane/EtOAc 8:1) to afford 4-G2 (1.41 g,
72%) as a white solid. M.p. 74–768C; Rf =0.13 (hexane/EtOAc 8:1);
1H NMR (400 MHz, CDCl3): d=0.85 (d, J=6.8 Hz, 24H; CH3), 1.03–
1.24 (m, 26H), 1.45 (septet, J=6.8 Hz, 4H; CHMe2), 1.78–1.88 (m, 4H;
CCH2), 4.32 (s, 4H; CH2N3), 4.47 (d, J=5.6 Hz, 4H; NHCH2), 7.27 (brs,
8H; ArH), 7.49 ppm (t, J=5.6 Hz, 2H; NH); 13C NMR (100 MHz,
CDCl3): d=22.4, 22.8, 22.9, 28.5, 31.2, 34.1, 35.9, 37.8, 38.4, 43.4, 54.5,
57.2, 128.1, 128.7, 134.7, 138.5, 173.4 ppm; SEC: Rt =33.28 min. MS
(ESI): m/z (%): 808 (100) [M+Na+]; HRMS (ESI) calcd for
C47H76N8O2 +Na+: 807.5983; found: 807.5977; elemental analysis calcd
(%) for C47H76N8O3: C 71.90, H 9.76, N 14.26; found: C 71.95, H 10.08, N
14.19.
Conclusion
G3-Diazide 4-G3: DCC (0.61 g, 2.96 mmol) was added to a stirred solu-
tion of 10-G3 (1.91 g, 1.67 mmol), 4-(azidomethyl)benzylamine (0.48 g,
2.96 mmol), HOBt (0.37 g, 2.74 mmol), and DMAP (2 mg) in CH2Cl2
(30 mL). The reaction mixture was stirred at 258C for 2 h and concentrat-
ed under reduced pressure. The residue was purified by flash chromatog-
raphy on silica gel (eluent: hexane/EtOAc 15:1) to afford 4-G3 (1.45 g,
67%) as a pale yellow oil. Rf =0.25 (hexane/EtOAc 12:1); 1H NMR
(400 MHz, CDCl3): d=0.87 (d, J=6.4 Hz, 48H; CH3), 1.05–1.30 (m,
70H), 1.48 (septet, J=6.8 Hz, 8H; CHMe2), 1.78–1.89 (m, 4H; CCH2),
4.32 (s, 4H; CH2N3), 4.47 (d, J=5.6 Hz, 4H; NHCH2), 7.27 (brs, 8H;
ArH), 7.50 ppm (t, J=5.6 Hz, 2H; NH); 13C NMR (100 MHz, CDCl3):
d=22.4, 22.87, 22.89, 23.8, 28.5, 31.3, 31.4, 34.0, 34.3, 36.0, 36.1, 37.4, 38.0,
38.4, 43.4, 54.5, 57.2, 128.1, 128.7, 134.7, 138.5, 173.4 ppm; SEC: Rt =
31.72 min; HRMS (ESI) calcd for C83H148N8O2 +Na+: 1312.1622; found:
1312.1675; elemental analysis calcd (%) for C83H148N8O2: C 77.27, H
11.56, N 8.68; found: C 77.34, H 11.90, N 8.69.
A new series of click poly(amide–triazole) dendronized
polymers 2-GmGn was prepared by the 1:1 copolymeriza-
tion of AA-type diazides 4-Gm and BB-type diacetylenes 5-
Gn. The DP values of the polymer obtained were compara-
ble to those of the previously reported 1-Gn dendronized
polymers, and were found to decrease with increasing den-
dron size. The strength of polymer interchain self-associa-
tion was found to be influenced by three factors. First, a syn-
ergistic hydrogen-bonding interaction, arising due to the
presence of many amide units in close proximity and in high
spatial regularity along the polymer chain, was identified.
Second, the strength of intermolecular self-association was
found to decrease with increasing dendron size, indicating
that steric repulsion between the polymer side chains also
played an important role in defining the binding strength.
Third, the polymer backbone symmetry, which can deter-
mine the presence or absence of an overall polymer dipole
moment, contributes an extra binding factor through the
polymer dipole–dipole interaction. Among the nine newly
prepared dendronized polymers, only 2-G1G2 and 2-G2G1
were good organogelators for aromatic solvents. In contrast,
2-G2G2, which possessed the closest structural similarity to
the previously reported organogelator 1-G2, was non-gelat-
ing. This differential gelating property could be rationalized
in terms of the difference in polymer backbone symmetry.
G1-Diacetylene 5-G1: EDCI (0.46 g, 1.51 mmol) was added to a stirred
solution of 9-G1 (0.32 g, 1.14 mmol), propargylamine (0.16 mL,
2.50 mmol), and HOBt (0.20 g, 1.48 mmol) in CH2Cl2 (20 mL). The reac-
tion mixture was stirred at 258C for 2 h and concentrated under reduced
pressure. The residue was purified by flash chromatography on silica gel
(eluent: hexane/EtOAc 3:1) to afford 5-G1 (0.29 g, 80%) as a white
solid. M.p. 123.5–1268C; Rf =0.39 (hexane/EtOAc 3:1); 1H NMR
(400 MHz, CDCl3): d=0.86 (d, J=6.4 Hz, 12H; CH3), 1.00–1.20 (m, 4H;
CH2), 1.48 (septet, J=6.4 Hz, 2H; CHMe2), 1.75–1.95 (m, 4H; CCH2),
ꢁ
ꢁ
2.22 (t, J=2.4 Hz, 2H; C CH), 4.06 (dd, J=5.2, 2.4 Hz, 4H; CH2C C),
7.40 ppm (brs, 2H; NH); 13C NMR (100 MHz, CDCl3): d=22.5, 28.2,
29.2, 33.7, 36.3, 56.7, 71.4, 79.5, 173.4 ppm; SEC: Rt =35.18 min; MS
(ESI): m/z (%): 341 (100) [M+Na+]; HRMS (ESI) calcd for
C19H30N2O2 +Na+: 341.2199; found: 341.2207; elemental analysis calcd
(%) for C19H30N2O2: C 71.66, H 9.49, N 8.79; found: C 71.62, H 9.89, N
8.70.
G2-Diacetylene 5-G2: DCC (0.09 g, 0.44 mmol) was added to a stirred
solution of 9-G2 (0.16 g, 0.30 mmol), propargylamine (0.06 mL,
0.94 mmol), HOBt (0.06 g, 0.44 mmol), and DMAP (2 mg) in CH2Cl2
(15 mL). The reaction mixture was stirred at 258C for 2 h and concentrat-
ed under reduced pressure. The residue was purified by flash chromatog-
raphy on silica gel (eluent: hexane/EtOAc 8:1) to afford 5-G2 (0.16 g,
94%) as a white solid. M.p. 68–698C; Rf =0.42 (hexane/EtOAc 8:1);
1H NMR (400 MHz, CDCl3): d=0.85 (d, J=6.4 Hz, 24H; CH3), 1.03–
1.26 (m, 26H), 1.44 (septet, J=6.4 Hz, 4H; CHMe2), 1.74–1.86 (m, 4H;
Experimental Section
G1-Diazide 4-G1: EDCI (0.70 g, 2.36 mmol) was added to a stirred solu-
tion of 10-G1 (0.70 g, 1.80 mmol), 4-(azidomethyl)benzylamine (0.38 g,
2.34 mmol), and HOBt (0.32 g, 2.37 mmol) in CH2Cl2 (30 mL). The reac-
tion mixture was stirred at 258C for 2 h and concentrated under reduced
pressure. The residue was purified by flash chromatography on silica gel
(eluent: hexane/EtOAc 4:1) to afford 4-G1 (0.76 g, 79%) as a white
solid. M.p. 126–1288C; Rf =0.16 (hexane/EtOAc 4:1); 1H NMR
ꢁ
CCH2), 2.19 (t, J=2.4 Hz, 2H; C CH), 4.05 (dd, J=5.2, 2.4 Hz, 4H;
Chem. Eur. J. 2011, 17, 8395 – 8403
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H.-F. Chow et al.
CH2C C), 7.41 ppm (t, J=5.2 Hz, 2H; NH); 13C NMR (100 MHz,
1H NMR (400 MHz, [D8]THF): d=0.50–0.75 (m, 14H), 0.75–1.00 (m,
30H), 1.00–1.37 (m, 22H), 1.38–1.59 (m, 6H; CHMe2), 1.77–2.10 (m, 8H;
CCH2), 3.83–4.50 (m, 8H; TriazCH2Ar, NHCH2Ar), 5.20–5.60 (m, 4H;
NHCH2Triaz), 7.00–7.30 (m, 8H; ArH), 7.52–7.94 (m, 2H; TriazH), 8.00–
8.70 ppm (m, 4H; NH); 13C NMR (100 MHz, [D8]THF): d=23.1, 23.4,
29.3, 29.5, 32.2, 34.5, 35.1, 35.6, 36.9, 38.7, 43.7, 54.1, 57.6, 58.0, 123.7,
128.7, 129.1, 135.6, 141.0, 146.6, 174.0 ppm.
ꢁ
CDCl3): d=22.0, 22.68, 22.72, 28.3, 29.1, 31.0, 33.8, 35.7, 37.5, 38.7, 56.8,
71.2, 79.4, 173.3 ppm; SEC: Rt =33.66 min; HRMS (ESI) calcd for
C37H66N2O2 +H+: 571.5202; found: 571.5239; elemental analysis calcd
(%) for C37H66N2O2: C 77.84, H 11.65, N 4.90; found: C 78.06, H 12.22, N
4.91.
G3-Diacetylene 5-G3: DCC (0.05 g, 0.24 mmol) was added to a stirred
solution of 9-G3 (0.18 g, 0.17 mmol), propargylamine (0.1 mL,
1.56 mmol), HOBt (0.04 g, 0.30 mmol), and DMAP (2 mg) in CH2Cl2
(15 mL). The reaction mixture was stirred at 258C for 2 h and concentrat-
ed under reduced pressure. The residue was purified by flash chromatog-
raphy on silica gel (eluent: hexane/EtOAc 18:1) to afford 5-G3 (0.16 g,
Polymer 2-G2G2: Sodium ascorbate (40 mg, 0.20 mmol) and
CuSO4·5H2O (10 mg, 0.04 mmol) were added to a solution of 4-G2
(325 mg, 0.41 mmol) and 5-G2 (236 mg, 0.41 mmol) in THF/DMF/H2O
(v/v/v 1:1:1, 6 mL). The reaction mixture was stirred at 258C for 4 d.
Aqueous HCl (25 mL, 0.2m) was added to the solution and the precipi-
tate was filtered off to give the polymer as a yellow solid (527 mg, 94%).
1H NMR (400 MHz, [D8]THF): d=0.70–1.00 (m, 48H; CH3), 1.01–1.38
(m, 52H), 1.39–1.63 (m, 8H; CHMe2), 1.75–2.16 (m, 8H; CCH2), 4.00–
4.50 (m, 8H; TriazCH2Ar, NHCH2Ar), 5.35–5.65 (m, 4H; NHCH2Triaz),
7.00–7.30 (m, 8H; ArH), 7.50–7.78 (m, 2H; TriazH), 7.79–7.90 (m, 2H;
NH), 8.10–8.25 (m, 1H; NH), 8.25–8.40 ppm (m, 1H; NH); 13C NMR
(100 MHz, [D8]THF): d=22.3, 22.4, 22.6, 23.0, 23.4, 29.5, 32.2, 34.4, 34.6,
35.2, 36.0, 36.3, 36.9, 38.56, 38.64, 43.7, 53.9, 54.1, 57.9, 58.2, 123.3, 128.6,
128.8, 129.0, 135.7, 135.9, 140.9, 146.6, 173.3, 173.7, 174.0 ppm.
88%) as
a
colorless oil. Rf =0.17 (hexane/EtOAc 18:1). 1H NMR
(400 MHz, CDCl3): d=0.87 (d, J=6.4 Hz, 48H; CH3), 1.05–1.30 (m,
70H), 1.47 (septet, J=6.4 Hz, 8H; CHMe2), 1.75–1.85 (m, 4H; CCH2),
ꢁ
ꢁ
2.19 (t, J=2.4 Hz, 2H; C CH), 4.06 (dd, J=5.2, 2.4 Hz, 2H; CH2C C),
7.40 ppm (t, J=5.2 Hz, 2H; NH); 13C NMR (100 MHz, CDCl3): d=22.2,
22.80, 22.82, 23.7, 28.4, 29.2, 31.25, 31.30, 33.9, 34.2, 34.3, 35.9, 36.0, 37.3,
37.8, 38.8, 56.9, 71.3, 79.5, 173.2 ppm; SEC: Rt =31.87 min. MS (ESI):
m/z (%): 1098 (100) [M+Na+]; HRMS (ESI) calcd for C73H138N2O2 +
Na+: 1098.0651; found: 1098.0634; elemental analysis calcd (%) for
C73H138N2O2: C 81.49, H 12.93, N 2.60; found: C 81.72, H 13.00, N 2.78.
Polymer 2-G2G3: Sodium ascorbate (14 mg, 0.07 mmol) and
Polymer 2-G1G1: Sodium ascorbate (30 mg, 0.15 mmol) and
CuSO4·5H2O (3 mg, 0.01 mmol) were added to
a solution of 4-G2
CuSO4·5H2O (8 mg, 0.03 mmol) were added to
a solution of 4-G1
(108 mg, 0.14 mmol) and 5-G3 (148 mg, 0.14 mmol) in THF/DMF/H2O
(v/v/v 1:1:1, 6 mL). The reaction mixture was stirred at 258C for 4 d and
then extracted with CH2Cl2 (3ꢂ20 mL). The combined extracts were
washed with brine, dried (Mg2SO4), filtered, and evaporated in vacuo to
(164 mg, 0.31 mmol) and 5-G1 (98 mg, 0.31 mmol) in THF/DMF/H2O
(v/v/v 1:1:1, 6 mL). The mixture was stirred at 258C for 4 d. Aqueous
HCl (25 mL, 0.2m) was added to the solution and the precipitate was fil-
tered off to give the polymer as a yellow solid (240 mg, 92%). 1H NMR
(400 MHz, [D6]DMSO): d=0.50–1.00 (m, 32H; CH2, CH3), 1.11–1.50 (m,
4H; CHMe2), 1.60–2.00 (m, 8H; CCH2), 4.00–4.60 (m, 8H; TriazCH2Ar,
NHCH2Ar), 5.30–5.70 (m, 4H; NHCH2Triaz), 7.00–7.40 (m, 8H; ArH),
7.80–8.10 (m, 2H; TriazH), 8.60–9.10 ppm (m, 4H; NH); 13C NMR
(100 MHz, [D6]DMSO): d=22.2, 27.5, 27.7, 32.9, 33.0, 34.3, 41.9, 52.4,
56.0, 123.1, 127.2, 127.4, 127.7, 128.1, 133.8, 134.2, 139.4, 139.6, 172.7 ppm.
give the polymer as
a
pale yellow solid (223 mg, 87%). 1H NMR
(400 MHz, [D8]THF): d=0.85–0.95 (m, 72H; CH3), 1.10–1.39 (m, 96H),
1.41–1.57 (m, 12H; CHMe2), 1.74–1.95 (m, 8H; CCH2), 4.25–4.45 (m,
8H; TriazCH2Ar, NHCH2Ar), 5.40–5.60 (m, 4H; NHCH2Triaz), 7.05–
7.28 (m, 8H; ArH), 7.56–7.60 and 7.80–7.83 (m, 2H; TriazH), 7.70–7.80
(m, 1H; NH), 8.00–8.10 (m, 1H; NH), 8.40–8.50 ppm (m, 2H; NH);
13C NMR (100 MHz, [D8]THF): d=22.4, 23.1, 23.4, 24.7, 29.5, 30.8, 32.2,
32.3, 32.4, 34.4, 34.6, 34.9, 35.1, 35.2, 35.3, 35.49, 35.54, 36.0, 36.3, 36.9,
37.0, 38.0, 38.2, 38.6, 38.7, 39.0, 43.7, 53.9, 54.1, 57.9, 58.20, 58.24, 123.2,
123.3, 128.6, 128.7, 128.8, 129.0, 135.8, 135.9, 140.9, 141.0, 146.5, 146.6,
173.3, 173.4, 173.6, 174.1 ppm.
Polymer 2-G1G2: Sodium ascorbate (55 mg, 0.28 mmol) and
CuSO4·5H2O (14 mg, 0.06 mmol) were added to a solution of 4-G1
(295 mg, 0.55 mmol) and 5-G2 (316 mg, 0.55 mmol) in THF/DMF/H2O
(v/v/v 1:1:1, 6 mL). The reaction mixture was stirred at 258C for 4 d.
Aqueous HCl (25 mL, 0.2m) was added to the solution and the precipi-
tate was filtered off to give the polymer as a yellow solid (595 mg, 97%).
1H NMR (400 MHz, [D8]THF): d=0.60–0.94 (m, 36H; CH3), 0.94–1.30
(m, 30H), 1.31–1.58 (m, 6H; CHMe2), 1.76–2.00 (m, 8H; CCH2), 4.00–
4.50 (m, 8H; TriazCH2Ar, NHCH2Ar), 5.30–5.60 (m, 4H; NHCH2Triaz),
6.95–7.42 (m, 8H; ArH), 7.50–7.80 (m, 2H; TriazH), 7.88–8.30 (m, 2H;
NH), 8.40–8.65 ppm (m, 2H; NH); 13C NMR (100 MHz, [D8]THF): d=
22.6, 23.2, 23.4, 26.5, 29.5, 32.1, 34.8, 35.1, 36.0, 36.8, 38.6, 43.6, 54.1, 57.6,
58.0, 123.4, 129.0, 135.7, 141.0, 146.6, 173.6, 174.2 ppm.
Polymer 2-G3G1: Sodium ascorbate (37 mg, 0.19 mmol) and
CuSO4·5H2O (11 mg, 0.04 mmol) were added to a solution of 4-G3
(485 mg, 0.38 mmol) and 5-G1 (120 mg, 0.38 mmol) in THF/DMF/H2O
(v/v/v 1:1:1, 6 mL). The reaction mixture was stirred at 258C for 4 d.
Aqueous HCl (25 mL, 0.2m) was added to the solution and the precipi-
tate was filtered off to give the polymer as a yellow solid (542 mg, 92%).
1H NMR (400 MHz, [D8]THF): d=0.68–0.79 (m, 48H; CH3), 0.80–1.00
(m, 12H), 1.07–1.42 (m, 74H), 1.43–1.63 (m, 10H; CHMe2), 1.75–2.11
(m, 8H; CCH2), 4.20–4.45 (m, 8H; TriazCH2Ar, NHCH2Ar), 5.40–5.55
(m, 4H; NHCH2Triaz), 7.08–7.28 (m, 8H; ArH), 7.60–7.80 (m, 2H;
TriazH), 7.90–8.00 (m, 1H; NH), 8.10–8.20 (m, 2H; NH), 8.35–8.55 ppm
(m, 1H; NH); 13C NMR (100 MHz, [D8]THF): d=23.1, 23.4, 24.7, 29.35,
29.44, 29.5, 29.7, 30.8, 32.3, 32.4, 34.5, 34.6, 35.0, 35.3, 35.5, 35.8, 37.0,
38.16, 38.22, 39.0, 43.7, 53.9, 54.1, 57.4, 57.7, 58.0, 58.1, 123.4, 128.5, 128.8,
128.9, 129.0, 129.2, 135.7, 135.8, 140.9, 141.0, 146.6, 173.4, 173.6, 173.8,
174.1 ppm.
Polymer 2-G1G3: Sodium ascorbate (29 mg, 0.15 mmol) and
CuSO4·5H2O (7 mg, 0.03 mmol) were added to
a solution of 4-G1
(154 mg, 0.29 mmol) and 5-G3 (311 mg, 0.29 mmol) in THF/DMF/H2O
(v/v/v 1:1:1, 6 mL). The reaction mixture was stirred at 258C for 4 d.
Aqueous HCl (25 mL, 0.2m) was added to the solution and the precipi-
tate was filtered off to give the polymer as a yellow solid (425 mg, 91%).
1H NMR (400 MHz, [D8]THF): d=0.70–0.95 (m, 60H; CH3), 0.96–1.07
(m, 4H; CH2), 1.08–1.37 (m, 70H), 1.41–1.61 (m, 10H; CHMe2), 1.75–
1.95 (m, 8H; CCH2), 4.20–4.50 (m, 8H; TriazCH2Ar, NHCH2Ar), 5.30–
5.60 (m, 4H; NHCH2Triaz), 7.10–7.30 (m, 8H; ArH), 7.60–7.82 (m, 2H;
TriazH), 7.84–7.97 (m, 1H; NH), 8.00–8.15 (m, 1H; NH), 8.45–8.60 ppm
(m, 2H; NH); 13C NMR (100 MHz, [D8]THF): d=22.6, 23.2, 23.4, 24.7,
29.5, 29.7, 30.8, 32.3, 32.4, 34.5, 35.0, 35.3, 35.5, 35.9, 37.0, 38.2, 39.1, 43.6,
54.0, 54.1, 57.6, 57.8, 58.0, 58.1, 123.3, 128.8, 128.9, 129.0, 130.4, 135.7,
135.8, 141.1, 146.7, 173.5, 173.6, 174.2 ppm.
Polymer 2-G3G2: Sodium ascorbate (30 mg, 0.15 mmol) and
CuSO4·5H2O (8 mg, 0.03 mmol) were added to
a solution of 4-G3
(395 mg, 0.31 mmol) and 5-G2 (175 mg, 0.31 mmol) in THF/DMF/H2O
(v/v/v 1:1:1, 6 mL). The reaction mixture was stirred at 258C for 4 d and
then extracted with CH2Cl2 (3ꢂ20 mL). The combined extracts were
washed with brine, dried (Mg2SO4), filtered and evaporated in vacuo to
give the polymer as
a
pale yellow solid (526 mg, 92%). 1H NMR
(400 MHz, [D8]THF): d=0.80–0.99 (m, 72H; CH3), 1.00–1.41 (m, 96H),
1.42–1.62 (m, 12H; CHMe2), 1.75–2.02 (m, 8H; CCH2), 4.10–4.50 (m,
8H; TriazCH2Ar and NHCH2Ar), 5.35–5.70 (m, 4H; NHCH2Triaz), 7.00–
7.25 (m, 8H; ArH), 7.55–7.71 (m, 2H; TriazH), 7.72–7.90 (m, 2H; NH),
8.10–8.30 ppm (m, 2H; NH); 13C NMR (100 MHz, [D8]THF): d=22.2,
22.4, 22.5, 22.9, 23.4, 24.7, 29.5, 32.1, 32.2, 32.3, 35.0, 35.2, 35.3, 35.4, 35.5,
36.8, 37.0, 38.2, 38.50, 38.54, 39.0, 43.8, 53.9, 54.1, 57.9, 58.0, 58.3, 123.3,
Polymer 2-G2G1: Sodium ascorbate (52 mg, 0.26 mmol) and
CuSO4·5H2O (13 mg, 0.05 mmol) were added to a solution of 4-G2
(409 mg, 0.52 mmol) and 5-G1(166 mg, 0.52 mmol) in THF/DMF/H2O
(v/v/v 1:1:1, 6 mL). The reaction mixture was stirred at 258C for 4 d.
Aqueous HCl (25 mL, 0.2m) was added to the solution and the precipi-
tate was filtered off to give the polymer as a yellow solid (567 mg, 99%).
8402
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 8395 – 8403

Click-Dendronized Poly(amide–triazole)s
FULL PAPER
128.6, 128.8, 129.0, 129.6, 135.5, 135.6, 135.8, 140.8, 141.0, 146.5, 173.2,
173.3, 173.6, 173.76, 173.84 ppm.
V. V. Fokin, Aldrichimica Acta 2007, 40, 7; d) W. H. Binder, R. Sach-
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Polymer 2-G3G3: Sodium ascorbate (10 mg, 0.05 mmol) and
CuSO4·5H2O (3 mg, 0.01 mmol) were added to
a solution of 4-G3
(126 mg, 0.10 mmol) and 5-G3 (106 mg, 0.10 mmol) in THF/DMF/H2O
(v/v/v 1:1:1, 6 mL). The reaction mixture was stirred at 258C for 8 d and
then extracted with CH2Cl2 (3ꢂ20 mL). The combined extracts were
washed with brine, dried (Mg2SO4), filtered and evaporated in vacuo to
give the polymer as
a
pale yellow solid (196 mg, 84%). 1H NMR
(400 MHz, [D8]THF): d=0.89 (d, J=6.8 Hz, 96H; CH3), 1.10–1.40 (m,
140H), 1.50 (septet, J=6.8 Hz, 16H; CHMe2), 1.76–1.99 (m, 8H; CCH2),
4.25–4.45 (m, 8H; TriazCH2Ar, NHCH2Ar), 5.40–5.60 (m, 4H;
NHCH2Triaz), 7.05–7.30 (m, 8H; ArH), 7.55–7.71 (m, 2H; TriazH), 7.80–
7.90 (m, 2H; NH), 8.10–8.20 (m, 1H; NH), 8.30–8.48 ppm (m, 1H; NH);
13C NMR (100 MHz, [D8]THF): d=22.5, 23.4, 24.7, 29.6, 32.36, 32.39,
35.0, 35.3, 35.6, 37.1, 38.2, 39.1, 43.8, 53.9, 54.1, 58.0, 58.25, 58.30, 123.1,
123.4, 128.6, 128.7, 128.9, 129.0, 129.2, 135.8, 135.9, 141.0, 141.1, 146.6,
173.1, 173.2, 173.7, 174.0 ppm.
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Partridge, D. K. Smith, G. M. Dykes, P. T. McGrail, Chem. Commun.
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Zhou, Y. Wei, Angew. Chem. 2005, 117, 6179; Angew. Chem. Int.
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Chem. Rev. 2010, 110, 1857.
Acknowledgements
We thank the Research Grants Council, Hong Kong SAR, for financial
support (Project No: 400810).
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Received: April 6, 2011
Published online: June 16, 2011
Chem. Eur. J. 2011, 17, 8395 – 8403
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8403