Synthesis and thermoreversible gelation properties of main-chain poly(pyridine-2,6-dicarboxamide-triazole)s

Article abstract of DOI:10.1002/chem.201203684

A series of main-chain poly(amide-triazole)s were prepared by copper(I)-catalyzed alkyne-azide AABB-type copolymerizatons between five structurally similar diacetylenes 1-5 with the same diazide 6. The acetylene units in monomers 1-5 possessed different degrees of conformational flexibility due to the different number of intramolecular hydrogen bonds built inside the monomer architecture. Our study showed that the conformational freedom of the monomer had a profound effect on the polymerization efficiency and the thermoreversible gelation properties of the resulting copolymers. Among all five diacetylene monomers, only the one, that is, 1-Py(NH)₂ which possesses the pyridine-2,6-dicarboxamide unit with two built-in intramolecular H bonds could produce the corresponding poly(amide-triazole) Poly-(PyNH) ₂ with a significantly higher degree of polymerization (DP) than other monomers with a lesser number of intramolecular H bonds. In addition, it was found that only this polymer exhibited excellent thermoreversible gelation ability in aromatic solvents. A self-assembling model of the organogelating polymer Poly-(PyNH)₂ was proposed based on FTIR spectroscopy, XRD, and SEM analyses, in which H bonding, π-π aromatic stacking, hydrophobic interactions, and the structural rigidity of the polymer backbone were identified as the main driving forces for the polymer self-assembly process. Supramolecular chemistry: The presence of an intramolecular hydrogen-bonding pyridine-2,6-dicarboxamide unit inside a diacetylene monomer promoted its AABB click copolymerization efficiency with a diazide by reducing the amount of low molecular weight oligomers; this structural motif also conferred excellent thermoreversible gelating properties to the resulting poly(amide-triazole) compound (see scheme). Copyright

Full text of DOI:10.1002/chem.201203684

FULL PAPER
DOI: 10.1002/chem.201203684
Synthesis and Thermoreversible Gelation Properties of Main-Chain
Poly(pyridine-2,6-dicarboxamide-triACTHNUTRGNEUGaN zole)s
Sui-Lung Yim,[a, b] Hak-Fun Chow,*[a, b] Man-Chor Chan,[a] Chi-Ming Che,[c] and
Kam-Hung Low[c]
Abstract: A series of main-chain poly-
(amide-triazole)s were prepared
N
lesser number of intramolecular H
E
bonds. In addition, it was found that
only this polymer exhibited excellent
thermoreversible gelation ability in ar-
by copper(I)-catalyzed alkyne–azide
AABB-type copolymerizatons between
five structurally similar diacetylenes 1–
5 with the same diazide 6. The acety-
lene units in monomers 1–5 possessed
different degrees of conformational
flexibility due to the different number
of intramolecular hydrogen bonds built
inside the monomer architecture. Our
study showed that the conformational
freedom of the monomer had a pro-
found effect on the polymerization effi-
ciency and the thermoreversible gela-
ACHTUNGTRENNUNG
omatic solvents.
A
self-assembling
model of the organogelating polymer
Poly-(PyNH)2 was proposed based on
FTIR spectroscopy, XRD, and SEM
analyses, in which H bonding, p–p aro-
matic stacking, hydrophobic interac-
tions, and the structural rigidity of the
polymer backbone were identified as
the main driving forces for the polymer
self-assembly process.
Keywords: catalysis · click chemis-
try · copper · polymers · supramo-
lecular chemistry
Introduction
also begun to attract a lot of research attention. Various ex-
amples have shown that oligo- and polytriazole compounds
exhibited interesting conformational and supramolecular
properties.[5] For example, oligotriazoles could act as hosts
for anions[6] and were capable of forming head-to-tail dimer-
ic structures,[7] whereas polytriazoles were able to act as
hydro-[8] and organogelators.[9] Due to its bioisostericity with
the amide functionality,[10] the triazole moiety can be used to
replace some of the amide units in a polyamide chain and
The introduction of the ꢀclick chemistryꢁ concept by Sharp-
less in 2001[1] has led to discovery of new chemical reactions
that allow the coupling of basic chemistry building blocks in
an extremely effective manner.[2] One of the most popular
methods is the copper(I)-catalyzed azide–alkyne cycloaddi-
tion (CuAAC) between azides and alkynes, which results in
the formation of 1,4-disubstituted 1,2,3-triazoles[3] in high
yields and with excellent regioselectivity. This method has
been employed extensively in polymer synthesis.[4] At the
same time, the properties of the product triazole unit have
produce a new class of hybrid molecule poly(amide-tri
ACHTUNGTRENNUNGaz-
AHCTUNGTRENNUNG
Earlier we reported the synthesis of several dendronized
poly(amide-triazole)s and exemplified the effect of the den-
dron side chain, the H bonding amide unit, and the relative
orientation of triazole motifs on the self-assembling and
thermoreversible gelation properties,[11] which demonstrates
that the interplay between the amide and triazole function-
alities was a key factor for such poly(amide-triazole)s to dis-
play rich chemistry. However, the preparation of triazole-
rich polymers is not without challenge. One key issue was
the formation of cyclic oligomeric byproducts from structur-
ally flexible monomers.[12] This led to poor polymerization
efficiencies and most often polymers with low DP values
were formed.[13] Herein we wish to report the synthesis of a
new class of poly(pyridine-2,6-dicarboxamide-triazole) 1-
Py(NH)2 with intramolecularly H-bonded, structurally rigid
pyridine-2,6-dicarboxamide units along the polymer main
chain. It was shown that this structurally rigid motif, in com-
parison to other structurally more flexible dicarboxamide
[a] S.-L. Yim, Prof. H.-F. Chow, Prof. M.-C. Chan
Department of Chemistry
The Chinese University of Hong Kong
Shatin, HKSAR
Fax : (+852)26035057
E-mail: hfchow@cuhk.edu.hk
[b] S.-L. Yim, Prof. H.-F. Chow
Center of Novel Functional Molecules and
Institute of Molecular Functional Materials (UGC-AoE Scheme)
CUHK, Shatin, HKSAR
[c] Prof. C.-M. Che, Dr. K.-H. Low
Department of Chemistry
The University of Hong Kong and
Institute of Molecular Functional Materials (UGC-AoE Scheme)
HKU, Pokfulam Road, HKSAR
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203684.
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motifs (i.e. 2–5), produced the corresponding polymer Poly-
Py(NH)2 with a significantly higher DP value. Furthermore,
it was also found that only this polymer Poly-Py(NH)2 could
form strong thermoreversible polymer gels[14] with aromatic
solvents. The other structurally closely related polymer,
Poly-Ar(NH)2, despite containing the same number of car-
boxamide and triazole units along the main chain but
devoid of two intramolecular H bonds, in sharp contrast,
was nongelating. It was proposed that the two intramolecu-
lar H-bonds in the pyridine-2,6-dicarboxamide moieties
were responsible for holding the polymer chain in an ex-
tended conformation to facilitate its self-assembling into a
three-dimensional network gel structure. This work further
highlights new and additional factors in the self-assembly of
multifunctional polymers, and should offer insights to the
design and preparation of new polymer-based physical gelat-
ing materials.
nitrogen atom,[15] amongst the monomers 1–3, the conforma-
tional flexibility of the two acetylene functionalities should
follow the order: 1-Py(NH)2 <2-PyNHNMe<3-PyACHTUNGTRENNUNG(NMe)2.
To further demonstrate the importance of the pyridyl nitro-
gen atom on the self-assembling properties, the correspond-
ing benzene-1,3-dicarboxamide analogues of 1 and 3 (i.e. 4-
Ar(NH)2 and 5-Ar
ACHTUNGRTENN(UNG NMe)2, respectively) were also prepared
and subjected to the same click copolymerization reaction.
Due to the inherent poor solubility of polyACHTNUTRGNEUNG(triazole)s, a hy-
drophobic aliphatic side chain[16] (R1) was anchored to the
monomers to improve the solubility of the resulting poly-
mers.
Preparation of monomers: The various diacetylene 1–5 and
diazide 6 monomers were readily prepared from commer-
cially available starting materials by simple functional-group
transformations (Scheme 1). Hence, the pyridine-2,6-dicar-
boxamide monomers 1 and 3 could be obtained from di-
methyl chelidamate 7 in 65 and 63% yields, respectively,
whereas the benzene-1,3-dicarboxamide monomers 4 and 5
were synthesized in 75 and 72% yields, respectively, from
dimethyl isophthalate 12. For the unsymmetrical monomer
2-PyNHNMe, a reaction sequence involving the sequential
introduction of the propargyl amine and N-methylpropargyl
Results and Discussion
To investigate whether the conformational flexibility of the
monomers could exert any effects on CuAAC polymeriza-
tion efficiency, AA-type diacetylene monomers 1–5 with dif-
ferent extents of intramolecular H bonding were prepared
and click copolymerized with a BB-type diazide 6 to form
the corresponding copolymers Poly-Py(NH)2, Poly-
PyNHNMe, Poly-Py
(NMe)2, respectively. Due to the presence of the intramolec-
ular H bond between the carboxamide NH and the pyridyl
ACHTUGNTERN(NUNG NMe)2, Poly-Ar(NH)2, and Poly-Ar-
ACHTUNGTRENNUNG
Scheme 1. Synthesis of diacetylene monomers 1–5.
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Properties of Main-Chain Poly(pyridine-2,6-dicarboxamide-triazole)s
FULL PAPER
amine was carried out, and the overall yield was 66% from
compound 9. On the other hand, the diazide monomer 6
could be prepared from diethyl 2,5-dihydroxyterephthalate
20 in 75% yield in four steps (Scheme 2). Details of the syn-
thetic preparations and characterization data of monomers
1–6 can be found in the Supporting Information.
Figure 1. Partial stacked 1H NMR spectra (400 MHz, [D8]THF, 258C) of
(from top to bottom) Poly-Ar(NH)2, 4-Ar(NH)2, Poly-Py(NH)2, and 1-
Py(NH)2. All spectra were recorded at the same total NH concentration
(60 mm).
tramolecular H bonding due to the presence of multiple NH
and triazole units in close proximity, a synergistic zip-tem-
plating effect that has been reported by Hunter[17] and us[11]
before.
The weight-average molecular weight (Mw), polydispersity
index (PDI), and DP values of the click polymers were then
determined by SEC analysis (Table 1 and Figure 2). No no-
table difference in the SEC chromatograms was observed
Table 1. SEC data of the click polymers.[a]
Scheme 2. Synthesis of diazide monomer 6.
Polymer
Mw
[kD]
PDI DP Weight % of LMW Yield
fraction[b]
[%]
Copolymerizations and polymer characterizations: The click
1:1 copolymerizations between 1–5 and 6 were carried out
under optimized conditions (~100 mm, CuSO4, sodium as-
corbate, DMF/H2O 9:1, 258C). The copolymerizations were
repeated two-to-six times and the results were reproducible
as confirmed by size-exclusion chromatographic analysis
(SEC). After polymerization, the product was isolated by
dissolving the mixture in a small amount of DMF followed
by precipitation with water. Their structures were character-
ized by H NMR spectroscopy and SEC. In all the H NMR
spectra, the original acetylenic proton signal (d=2.2–
2.6 ppm) due to the diacetylene monomers disappeared,
which confirmed that the copolymerization proceeded to a
high degree (>98%) of conversion. Incidentally, the appear-
ance of the triazolyl proton signal at around d=7.2–8.0 ppm
was noted. Moreover, a significant downfield shift of the
NH resonance signal was observed for the polymeric com-
Poly-Py(NH)2
Poly-PyNHNMe
37
14
13
13
8
2.2 45 <0.4
84
85
83
85
83
84
1.3 17
1.3 15
1.3 16
1.1 10
1.6 25
3
5
7
23
2
Poly-Py
Poly-Ar(NH)2
Poly-Ar(NMe)2
Poly([Py(NH)2]4-ran-
[Py(NMe)2]1)
Poly([Py(NH)2]1-ran-
[Py(NMe)2]1)
ACHTUNGERTN(NUNG NMe)2
T
21
AHCTUNGTRENNUNG
16
1.4 20
3
82
AHCTUNGTRENNUNG
[a] All SEC measurements were performed in THF at 408C by using
poly
styrene standards for calibrations. [b] LMW fraction with Mw ꢀ4 kD.
1
1
ACHTUNGTRENNUNG
with samples of Poly-Py(NH)2 of 20 times difference in con-
centration (i.e. 1.0 and 0.05 mgmLÀ1), which indicated that
the samples were free of aggregation under the SEC experi-
mental conditions. Several interesting findings deserved at-
tention. First, low molecular weight (LWM) oligomers (arbi-
trarily defined as Mw ꢀ4 kD) were found in various amounts
(<0.4–23%), but the relative % was strongly dependent on
the structure of the diacetylene monomer. Hence, the struc-
turally more rigid Poly-Py(NH)2 contained <0.4% of such
LWM oligomers, whereas the one without intramolecular H-
pounds when compared to that of the corresponding di
ACHTUNGTNERaNUNG cet-
ACHTUNGTRENNUNG
the intramolecular H-bonded NH signal of 1-Py(NH)2, ini-
tially located at d=9.1 ppm, was further downfield shifted
to d=9.2–10.9 ppm in Poly-Py(NH)2 (Figure 1). The non-H
bonded NH signal of 4-Ar(NH)2, which was initially at d=
8.1 ppm, was similarly shifted to d=8.3–8.5 ppm. Such a
downfield shift of the NH resonance signals upon polymeri-
zation could be attributed to a strengthening of inter- or in-
bonds on the polymer backbone (i.e. Poly-ArACTHNUGTRENUNG(NMe)2) con-
sisted of 23% weight of LWM oligomers. As the molecular
masses of the cyclic oligomers are exactly the same as those
of the corresponding linear oligomers, we were unable to
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H.-F. Chow et al.
To further evaluate the effect of the pyridine-2,6-dicar-
boxamide H bonding unit on the polymerization, two
random copolymers, Poly-([Py(NH)2]4-ran-[Py
ACHTUNGTRNEN(UNG NMe)2]1) and
Poly-([Py(NH)2]4-ran-[Py(NMe)2]1), with reduced intramo-
AHCTUNGTRENNUNG
lecular H bonding content, were prepared by mixing 4:1 and
1:1 molar ratios of 1-Py(NH)2 and 3-Py(NMe)2, respectively,
Figure 2. Stacked SEC chromatograms of (top) Poly-Py(NH)2, Poly-
PyNHNMe, Poly-Py(NMe)2 and (bottom) Poly-Ar(NH)2, Poly-Ar-
(NMe)2. The relative % of LMW oligomers is exaggerated in the plot as
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
and copolymerized with 1.0 equivalent of diazide 6. The
structure of the copolymers and the relative amount of NH
versus NMe functionality in them, were confirmed by
1H NMR spectroscopy (see the Supporting Information for
details). The Mw of these two polymers were found to be in
the x-axis is on a logarithm scale of polymer Mw.
provide conclusive proof that these were cyclic oligomers by
MS analysis. However, judging from the complete absence
1
of the acetylenic H NMR spectroscopic signals in the NMR
between Poly-Py(NH)2 and Poly-PyACTHNGUTERN(NUG NMe)2, and increased
spectra and the lack of N3 absorption from the IR spectra, it
was likely that these were cyclic oligomers as those reported
earlier by other groups.[12] This finding also highlighted the
inherent cyclic oligomerization problem associated with
such structurally flexible monomers. In our case, flexible
monomers 2–5 were simply poor candidates for click linear
polymerizations. This could also be reflected in the signifi-
cant deviation of their corresponding polymer PDI values
(1.1–1.3) from the theoretical value (2.0) typical of a step-
growth polymerization process. It should be noted that once
cyclization occurred, no further addition of monomer was
possible. Second, monomers containing more H-bonded NH
functionalities produced the corresponding polymer with a
higher DP value. Hence, for the pyridine series, the DP
value of Poly-Py(NH)2 was higher than that of Poly-
PyNHNMe, which in turn was higher than that of Poly-Py-
with increasing 1-Py(NH)2 content, further proving that the
rigidity of the pyridine-2,6-dicarboxamide H-bonding unit
did improve the DP value.
Thermoreversible gelating properties: Other than better po-
ACHUTNGERNlNUG ymAHCTUNGTRNENeUGN rization efficiency, it was also found that only Poly-
Py(NH)2 was able to form physical gels in aromatic solvents.
The polymer sample was extracted with Na2EDTA (sodium
ethylenediaminetetraacetic acid) solution to remove trace
amounts of Cu salt that might interfere with the gelation
process.[19] The minimum gelation concentration (MGC) was
in the range of 0.5–2% w/v (Table 2). As the polymer exhib-
Table 2. MGC values of Poly-Py(NH)2.[a]
Solvent
MGC[b]
Solvent
MGC
benzene
toluene
o-xylene
m-xylene
p-xylene
o-dichlorobenzene
10 (CG)
5 (CG)
10 (CG)
10 (CG)
5 (CG)
ethanol
acetone
THF
CH2Cl2
DMF
P
P
S
S
S
I
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
of the pyridine series was consistently higher than that of
the benzene series bearing the same number of NH moiet-
ies. Among the five diacetylene monomers, 1-Py(NH)2 was
found to form the corresponding polymer Poly-Py(NH)2
with the highest Mw and DP values. On the other hand,
20 (CG)
n-hexane
[a] CG=transparent gel, P=precipitated upon cooling, S=solubility
ꢁ50 mgmLÀ1, I=insoluble. [b] MGC value was expressed in mgmLÀ1
.
monomer 2-PyACHTUNGTRENNUNG(NHNMe), containing only one intramolecu-
lar H bond, and 4-Ar(NH)2, containing two NH groups but
lacking the pyridyl nitrogen atom required for intramolecu-
lar H bonding, polymerized with significantly lower efficien-
cies. All these results indicated that the polymerization effi-
ciency could be significantly enhanced by imposing confor-
mational rigidity by intramolecular H bonding on the mono-
mer. It should be mentioned here that previous literature
examples involving structurally preorganized monomers
generally led to the preferential formation of LMW cyclic
oligomers,[18] in contrast to the results we encountered here.
ited excellent gelation power only in aromatic solvents,
which implied p–p stacking interactions might play a signifi-
cant role in the gelation process. In contrast, the di-NMe an-
alogues, Poly-PyACTHNUTRGENN(UG NMe)2 and Poly-ArCAHTUNGTRNEN(UGN NMe)2, simply dis-
solved in most of the common organic solvents, whereas
Poly-Ar(NH)2 showed poor solubilities in most organic sol-
vents. Interestingly, the two random copolymers were also
found to be nongelating (up to 50 mgmLÀ1) even though
they contained a certain percentage of pyridine-2,6-dicar-
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Properties of Main-Chain Poly(pyridine-2,6-dicarboxamide-triazole)s
FULL PAPER
and 19.598) were found, which
corresponded to a regular spac-
ing of 22.1 and 4.5 ꢃ, respec-
tively (Figure 4). The d spacing
of 4.5 ꢃ falls within the range
of p–p stacking interaromatic
distance,[23] and could be as-
signed to the distance between
the backbones of two neighbor-
ing polymer chains. Meanwhile,
the d spacing of 22.1 ꢃ was
roughly two times equal to the
span of the hydrophobic side
chain. Based on this informa-
tion, a packing model of Poly-
Py(NH)2
was
proposed
Figure 3. Stacked FTIR spectra of (top to bottom) 10% gel of Poly-Py(NH)2 in toluene; 0.5% toluene solution
of Poly-Py(NH)2; 1% toluene solution of 1-Py(NH)2; and 1% toluene solution of 4-Ar(NH)2.
(Figure 5). Because of the pres-
ence of the two intramolecular
H bonds that hold the polymer
chain in extended conforma-
boxamide intramolecular H-bond motif in their backbone
structure.
tion, the backbone of the polymer will be stiffened to adopt
a wormlike structure. The polymer chains are then stacked
onto each other with a spacing of approximately 4.5 ꢃ by in-
terchain p–p aromatic stacking and H-bonding interactions
FTIR studies were performed to reveal the extent of H
bonding in monomers 1-Py(NH)2, 4-Ar(NH)2, and the gelat-
ing polymer Poly-Py(NH)2 in various physical states
(Figure 3). As expected, in 1% toluene solution, both mono-
mers 1 and 4 did not exhibit any intermolecular H bonding.
Hence, the NH (3420, 3290 cmÀ1) and C=O (1678,
1689 cmÀ1) stretching frequencies were located at typical
non-H-bonded regions. The NH stretching at 3290 cmÀ1 was
due to band splitting but not H bonding, and was a typical
IR spectral characteristic of symmetrical AA-type diacety-
lene monomers.[11b,20] It should be noted that although 1-
Py(NH)2 was involved in intramolecular H bonding, the NH
stretching frequency was not significantly redshifted because
of the nonlinear alignment of the N–H···N H-bonding
system. On the other hand, the intramolecular H-bonding
nature of 1-Py(NH)2 could be revealed by examining the
NH bending frequency (1518 cmÀ1), which was blueshifted[21]
relative to that of the non-H-bonded 4-Ar(NH)2
(1508 cmÀ1). Incidentally, both the NH (from 3420 to 3370/
3310 cmÀ1) and C=O stretching frequencies (from 1689 to
1674 cmÀ1) experienced redshift, whereas the NH bending
exhibited blueshift (from 1518 to 1534 cmÀ1) in both the sol-
ution and gel IR spectra of Poly-Py(NH)2, which indicated
that the presence of strong intermolecular H-bonding inter-
actions in the polymer and gel state. It was also noted
that part of the C=O stretching remained unchanged
(ꢂ1684 cmÀ1) in Poly-Py(NH)2, which suggested some C=O
moieties might not be involved in the intermolecular H
bonding in the gel state. In fact, it had been reported that
only one of the carbonyl groups was involved in H bonding
in the crystal structure of N,N’-dimethylpyridine-2,6-dicar-
boxamide.[22]
XRD analyses were carried out to gain further insight on
the packing arrangement of Poly-Py(NH)2. For the freeze-
dried sample of the 1% gel in toluene, two peaks (2q=4.00
Figure 4. Powder XRD diffractograms of (top) freeze-dried Poly-
Py(NH)2 from 1% gel in toluene and (bottom) Poly-Py(NH)2 gel in 1%
toluene inside a capillary tube.
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H.-F. Chow et al.
tural rigidity of the intramolecularly H-bonded motif along
the polymer backbone could promote the polymerization ef-
ficiency by suppressing LMW oligomers formation, and fa-
cilitate the packing of the rigidified polymer chain into a
three dimensional gel network. More interestingly, the mere
presence of secondary amide and triazole functionalities in a
polymer does not guarantee it to become gelating, as judg-
ing from the nongelating examples of Poly-PyNHNMe and
Poly-Ar(NH)2. In addition to the side-chain steric effect[11a]
and polymer backbone symmetry effect[11b] reported earlier
by us, here in this present work it was found out that the
backbone rigidity could also play an important factor in con-
trolling their thermoreversible gelating and self-assembling
properties. These new findings should help us in further un-
derstanding and unveiling the fundamental factors of poly-
mer self-assembling behavior.
Figure 5. Proposed stacking structure of Poly-Py(NH)2: a) Formation of
the sandwich structure by H-bonding and p–p stacking interactions;
b) package arrangement of the sandwich structures in the freeze-dried
gel state; c) package arrangement of the sandwich structures in 1% tol-
uene gel.
Experimental Section
All reactions were carried out under N2 at 258C unless otherwise stated.
The progress of the reactions was monitored by TLC analysis performed
on Merck pre-coated silica gel 60F254 plates, and compounds were visual-
ized by using a spray of 5% (w/v) dodecamolybdophosphoric acid in
ethanol followed by subsequent heating. Flash column chromatography
was carried out on columns of Merck Kwiselgel 60 (230–400 mesh). All
reagents were purchased from commercial suppliers and used without
further purification unless otherwise stated. THF was freshly distilled
prior to use from sodium/benzophenone ketyl under N2. Dichloro-
(Figure 5a). Due to the highly hydrophobic nature of the
side chains, they would segregate from the polar poly-
ACHTUNGTRENNUNG(amide-triazole) backbone and form sandwichlike structures.
These sandwichlike layers then stacked onto each other with
a spacing of 22.1 ꢃ separated by a thickness of two nonpolar
layers (Figure 5b). On the other hand, only one diffraction
pattern at 2q=18.308 could be observed when a 1% gel
sample of Poly-Py(NH)2 was analyzed inside a capillary
tube. This translated to a d spacing of 4.8 ꢃ that could simi-
larly be attributed to the interchain p–p aromatic stacking
distance. This suggested that in the gel state, the polymer
chains could still pack in a side by side manner with a slight-
ly lengthened interchain distance of 4.8 ꢃ, whereas the
weaker van der Waals interaction between the nonpolar
layers was disrupted in the presence of nonpolar aromatic
solvents (Figure 5c).[24] Incidentally, SEM images of the
freeze-dried gel showed the presence of fiberlike structures
with a diameter of 5–10 nm (see the Supporting Information
for details). The results further confirmed that these fibers
were formed by the regular stacking of the polymer chains
by a combination of H bonding, p–p aromatic stacking, and
hydrophobic interactions. Based on all these studies, it was
proposed that intramolecular H bonding in Poly-Py(NH)2
induced a preorganization of the polymer backbone, and al-
lowed it to pack in an orderly manner to facilitate their fur-
ther self-assembly. On the other hand, no discernible XRD
peaks could be identified in all the other non-gelating poly-
mers.
AHCTUNGRTENmGNUN ethane was freshly distilled from CaH2 under N2.
Compound 1-Py(NH)2: Oxalyl chloride (1.50 mL, 17.29 mmol) in CH2Cl2
(3 mL) was added dropwise to a stirred solution of the diacid 10 (2.19 g,
5.77 mmol) in CH2Cl2 (20 mL) at 08C followed by the addition of one
drop of DMF. The reaction mixture was stirred for 4 h from 0 to 258C,
and then concentrated under reduced pressure to give the diacyl chloride
11 as a yellow solid. Compound 11 was then used directly by mixing with
triethylamine (10 mL) at 08C. After the mixture had been stirred for
10 min, a solution of propargylamine (1.00 mL, 15.61 mmol) in CH2Cl2
(5 mL) was added dropwise at 08C. The reaction mixture was allowed to
stir for 10 h at 258C, and was then quenched with aqueous HCl (30 mL,
1.2m). The two layers were separated and the aqueous layer was extract-
ed with CH2Cl2 (2ꢄ30 mL). The combined organic extracts were washed
with saturated NaCl solution, dried (Na2SO4), filtered, and evaporated
under reduced pressure to give a brown oil. The oil was purified by flash
column chromatography (hexane/EtOAc 3:1 gradient to 1:1) to generate
1-Py(NH)2 (2.14 g, 4.72 mmol, 82% in two steps) as a pale-yellow oil. Rf:
0.50 (hexane/EtOAc 2:1); 1H NMR: d=0.87 (12H, d, J=6.8 Hz; CH3),
1.08–1.18 (4H, m; CH2), 1.18–1.31 (5H, m; CH2, CH2CHCH2), 1.31–1.42
(2H, m; CH2), 1.41–1.53 (2H, m; CHMe2), 1.72–1.82 (2H, m;
OCH2CH2), 2.25 (2H, brs; CꢃCH), 4.08 (2H, t, J=6.4 Hz; OCH2), 4.29
(4H, dd, J=5.6, 2.4 Hz, NHCH2CꢃCH), 7.84 (2H, m; ArH), 8.05–
8.15 ppm (2H, brs; NH); 13C NMR: d=22.6, 25.8, 28.2, 29.0, 29.4, 30.9,
35.6, 37.4, 69.4, 71.1, 79.3, 111.4, 150.3, 164.0, 167.8 ppm; ESI: m/z (%):
476 [M+Na]+ (100); HRMS (ESI): m/z: calcd for C27H39N3O3 +Na+:
476.2884; found: 476.2891.
Compound 2-PyNHNMe: Benzotriazol-1-yl-oxytripyrrolidinophosphoni-
um hexafluorophosphate (PyBOP; 180 mg, 0.37 mmol) was added to a
stirred solution of 19 (103 mg, 0.25 mmol) and N-methylpropargylamine
(0.10 mL, 1.18 mmol) in DMSO (5 mL). Triethylamine (0.1 mL) was then
added to the solution mixture. After 10 h, EtOAc (15 mL) and H2O
(15 mL) were added to quench the reaction. The organic layer was sepa-
rated and the aqueous layer was extracted with EtOAc (2ꢄ15 mL). The
combined organic extracts were washed with saturated NaCl, dried
(Na2SO4), and concentrated under reduced pressure to afford the target
Conclusion
In summary, we reported here the synthesis and novel orga-
nogelating properties of a new class of poly(pyridine-2,6-di-
carboxamide-triazole) compounds, Poly-Py(NH)2. The struc-
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Properties of Main-Chain Poly(pyridine-2,6-dicarboxamide-triazole)s
FULL PAPER
compound 2-PyNHNMe (106 mg, 0.23 mmol, 94%) as a pale-yellow oil.
Rf =0.42 (hexane/EtOAc 2:1); 2-PyNHNMe exists as a mixture of rota-
Compound 5-ArACTHUNGTERNNU(G NMe)2: The diacyl chloride 15 was prepared from
diacid 14 (201 mg, 0.53 mmol) by using the same procedure as described
previously. Triethylamine (1 mL) in CH2Cl2 (1 mL) was added dropwise
to a stirred solution of 15 in CH2Cl2 (5 mL) at 08C. After 15 min, a solu-
tion of N-methylpropargylamine (0.10 mL, 1.18 mmol) in CH2Cl2 (3 mL)
was added dropwise at 08C. The reaction mixture was stirred for 10 h at
258C and quenched by the addition of aqueous HCl (10 mL, 1.2m). The
two layers were separated and the aqueous layer was extracted with
CH2Cl2 (2ꢄ10 mL). The combined organic extracts were washed with sa-
turated NaCl solution, dried (Na2SO4), filtered, and concentrated under
reduced pressure to give a brown liquid which was then purified by flash
column chromatography (hexane/EtOAc 3:1 gradient to 1:1) to produce
1
tional isomers which causes complications of the signal splitting in the H
1
and 13C NMR spectra; H NMR: d=0.87 (12H, d, J=6.8 Hz; CH3), 1.09–
1.19 (4H, m; CH2), 1.19–1.33 (5H, m; CH2, CH2CHCH2), 1.33–1.42 (2H,
m; CH2), 1.42–1.53 (2H, m; CHMe2), 1.73–1.83 (2H, m; OCH2CH2),
2.23–2.53 (total 2H, m; CꢃCH), 3.12, 3.22 (total 3H, s; NCH3). 4.09
(2H, t, J=6.4 Hz; OCH2), 4.15–4.45 (4H, m; CH2CꢃC), 7.23–7.42 (total
1H, m; ArH), 7.74–7.78 (total 1H, m; ArH), 8.04, 8.49 ppm (total 1H, t,
J=5 Hz; NH); 13C NMR: d=22.8, 26.0, 28.4, 29.1, 29.3, 29.6, 31.1, 34.0,
35.9, 36.2, 36.8, 37.5, 41.7, 69.4, 71.7, 71.8, 72.6, 73.1, 78.1, 79.3, 79.5, 79.9,
109.5, 110.2, 112.8, 113.7, 149.7, 150.2, 153.0, 153.9, 163.4, 167.2, 167.5,
167.7, 167.8 ppm; MS (ESI): m/z (%): 468 [M+H]+ (100); HRMS (ESI):
m/z: calcd for C28H41N3O3 +H+: 468.3221; found: 468.3231.
5-Ar
ACHTUNGTRENNUNG
liquid. Rf =0.48 (hexane/EtOAc 2:1); 5-ArACHTUNGTRENNNUG
three rotational isomers which causes the complication of the unequal
sized splitting in the 1H and 13C NMR spectra; 1H NMR: d=0.87 (12H,
d, J=6.4 Hz; CCH3), 1.09–1.19 (4H, m; CH2), 1.19–1.33 (5H, m; CH2,
CH2CHCH2), 1.33–1.42 (2H, m; CH2), 1.42–1.53 (2H, m; CHMe2), 1.70–
1.80 (2H, m; OCH2CH2), 2.20–2.40 (total, 2H, m; CꢃCH), 3.00–3.20
(total, 6H, m; NCH3), 3.97 (2H, t, J=6.4 Hz; OCH2), 3.95–4.40 (total
4H, m; CH2CꢃC), 7.00–7.15 ppm (total 3H, m; ArH); 13C NMR: d=
22.6, 26.6, 28.4, 30.1, 31.3, 31.5, 33.9, 34.4, 35.1, 35.3, 36.1, 37.8, 39.3, 69.2,
72.8, 73.4, 73.6, 78.4, 115.0, 117.5, 137.4, 159.5, 170.1 ppm; MS (ESI): m/z
(%): 481 [M+H]+ (100); HRMS (ESI): m/z: calcd for C30H44N2O3 +H+:
481.3425; found: 481.3414.
Compound 3-PyACHTUNGTRENNUNG(NMe)2: Compound 11 was prepared from the diacid 10
(641 mg, 1.69 mmol) by using the same procedure as above. Triethyla-
mine (2 mL) in CH2Cl2 (5 mL) was added dropwise to a stirred solution
of 11 in CH2Cl2 (5 mL) at 08C. After 15 min, a solution of N-methylpro-
pargylamine (0.40 mL, 4.74 mmol) in CH2Cl2 (3 mL) was added dropwise
at 08C. The reaction mixture was stirred for 10 h at 258C and quenched
with aqueous HCl (10 mL, 1.2m). The two layers were separated and the
aqueous layer was extracted with CH2Cl2 (2ꢄ10 mL). The combined or-
ganic extracts were washed with saturated NaCl solution, dried (Na2SO4),
filtered, and concentrated under reduced pressure to give a brown liquid.
The brown liquid was then purified by flash column chromatography
Compound 6: A solution of compound 22 (2.04 g, 6.57 mmol) in THF
(10 mL) was added dropwise to a solution of SOCl2 (5 mL) in THF
(10 mL) at 08C. The reaction mixture was stirred for 2 h and then poured
into iced water (20 mL). The mixture was extracted with diethyl ether
(3ꢄ20 mL) and the combined organic extracts were washed with saturat-
ed Na2CO3 and saturated NaCl, dried (MgSO4), and concentrated under
reduced pressure to give the dichloride 23 (2.19 g, 6.31 mmol, 96%) as a
pale-yellow solid. Rf =0.95 (hexane/EtOAc 2:1); compound 23 was found
to be unstable in the presence of silica gel and was, therefore, used di-
rectly without further purification. A mixture of sodium azide (1.40 g,
21.5 mmol) and 23 (2.19 g, 6.31 mmol) in DMF (15 mL) was stirred for
48 h. Water (20 mL) was added to quench the reaction and the mixture
was extracted with diethyl ether (3ꢄ20 mL). The combined organic ex-
tracts were washed with saturated NaCl, dried (MgSO4), and then con-
centrated under reduced pressure to give a yellow solid. The solid was
then purified by flash column chromatography (hexane/CH2Cl2 6:1 gradi-
ent to 4:1) to afford the desired diazide monomer 6 (2.08 g, 5.74 mmol,
91%) as a pale-yellow solid. M.p. 47–488C; Rf =0.40 (hexane/CH2Cl2
4:1); 1H NMR: 0.97 (12H, d, J=6.4 Hz; CH3), 1.69 (4H, q, J=6.4 Hz;
CH2CH2CH), 1.77–1.92 (2H, m; CHMe2), 3.99 (4H, t, J=6.8 Hz; OCH2),
4.36 (4H, s; ArCH2N3), 6.83 ppm (2H, s; ArH); 13C NMR: d=22.7, 25.2,
38.2, 50.1, 67.3, 113.5, 124.8, 150.8 ppm; MS (ESI): m/z (%): 383
[M+Na]+ (50); HRMS (ESI): m/z: calcd for C18H28N6O2 +K+: 399.1905;
found: 399.1905.
(hexane/EtOAc 3:1 gradient to 1:1) to produce 3-Py
1.36 mmol, 80% in two steps) as a pale-brown liquid. Rf =0.35 (hexane/
EtOAc 2:1). Compound 3-Py(NMe)2 exists as a mixture of three rota-
ACHTUNGRTENUN(NG NMe)2 (654 mg,
AHCTUNGTRENNUNG
tional isomers which causes the complication of unequal sized splitting in
the 1H and 13C NMR spectra; 1H NMR: d=0.87 (12H, d, J=6.8 Hz;
CH3), 1.07–1.18 (4H, m; CH2), 1.18–1.32 (5H, m; CH2, CH2CHCH2),
1.32–1.42 (2H, m; CH2), 1.42–1.53 (2H, m; CHMe2), 1.72–1.82 (2H, m;
OCH2CH2), 2.23–2.36 (total 2H, m; CꢃCH), 3.12, 3.15, 3.17 (total 6H,
s; NMe), 4.05 (2H, t, J=6.4 Hz), 4.28–4.40 (total 4H, m; CH2CꢃC),
7.27–7.30 ppm (total 2H, m; ArH); 13C NMR: d=22.6, 25.9, 28.3, 29.5,
31.0, 33.4, 35.7, 36.1, 36.2, 36.79, 36.84, 37.3, 40.7, 69.1, 72.28, 72.33, 72.86,
72.89, 78.09, 78.11, 78.26, 111.1, 111.5, 111.6, 153.6, 153.9, 154.0, 166.7,
166.8, 166.9, 167.52, 167.57, 167.63, 167.7 ppm; MS (ESI): m/z (%): 482
[M+H]+ (100); HRMS (ESI): m/z: calcd for C29H43N3O3 +H+: 482.3377;
found: 482.3374.
Compound 4-Ar(NH)2: Oxalyl chloride (0.11 mL, 1.29 mmol) in CH2Cl2
(1 mL) was added dropwise to a stirred solution of diacid 14 (222 mg,
0.59 mmol) in CH2Cl2 (5 mL) at 08C followed by the addition of one
drop of DMF. The reaction mixture was allowed to stir for 4 h at 0–258C
and concentrated under reduced pressure to give compound 15 as a
deep-orange solid which was then used directly without purification. Trie-
thylamine (1 mL) in CH2Cl2 (1 mL) was added dropwise to a stirred solu-
tion of 15 in CH2Cl2 (5 mL) at 08C. After 10 min, a solution of propargyl-
amine (0.10 mL, 1.56 mmol) in CH2Cl2 (5 mL) was added dropwise at
08C. The reaction mixture was allowed to stir for 10 h at 258C and then
quenched by the addition of aqueous HCl (10 mL, 1.2m). The two layers
were separated and the aqueous layer was extracted with CH2Cl2 (2ꢄ
10 mL). The combined organic extracts were washed with saturated NaCl
solution, dried (Na2SO4), filtered, and evaporated under reduced pressure
to give a deep-brown liquid. The liquid was purified by flash column
chromatography (hexane/EtOAc 3:1 gradient to 1:1) to generate 4-
Ar(NH)2 (239 mg, 0.53 mmol, 90% in two steps) as a white solid. M.p.
67–698C; Rf =0.62 (hexane/EtOAc 2:1); 1H NMR: d=0.87 (12H, d, J=
6.4 Hz; CH3), 1.09–1.19 (4H, m; CH2), 1.19–1.34 (5H, m; CH2,
CH2CHCH2), 1.34–1.42 (2H, m; CH2), 1.42–1.54 (2H, m; CHMe2), 1.71–
1.81 (2H, m; OCH2CH2), 2.29 (2H, t, J=2.4 Hz; CꢃCH), 4.00 (2H, t,
J=6.4 Hz; OCH2), 4.24 (4H, dd, J=2.4, 4.8 Hz; CH2CꢃC), 6.50–6.62
(2H, brs; NH), 7.46 (2H, brs; ArH), 7.73 ppm (1H, brs; ArH);
13C NMR: 22.7, 26.3, 28.4, 29.8, 29.9, 31.0, 35.8, 37.6, 69.0, 71.9, 79.4,
116.9, 117.3, 135.2, 159.5, 166.8 ppm; MS (ESI): m/z (%): 453 [M+H]+
(100); HRMS (ESI): m/z: calcd for C28H40N2O3 +H+: 453.3112; found:
453.3111; elemental analysis calcd (%) for C28H40N2O3: C 74.30, H 8.91,
N 6.19; found: C 73.99, H 9.14, N 6.13.
Compound Poly-Py(NH)2: Aqueous CuSO4 (0.50 mL, 0.056m) was added
to
a stirred solution of 1-Py(NH)2 (194 mg, 0.43 mmol), 6 (154 mg,
0.43 mmol), and sodium ascorbate (10 mg, 0.05 mmol) in DMF (4.5 mL).
The CuAAC polymerization was allowed to proceed for 24 h. DMF was
added to the solution mixture to form a clear solution and the solution
was poured into water (30 mL). The solid was then filtered and dried
under reduced pressure to give Poly-Py(NH)2 (292 mg, 84%) as a pale-
1
yellow powder. H NMR ([d8]THF): d=0.70–1.02 (24H, m; CCH3), 1.14–
1.94 (21H, m), 3.70–4.04 (4H, m; OCH2), 4.07–4.25 (2H, m; OCH2),
4.37–4.80 (4H, m; NCH2Triaz), 5.30–5.65 (4H, m; ArCH2Triaz), 6.74–
7.02 (2H, m; ArH), 7.02–7.14, 7.25–7.33, 7.78–7.90 (total 2H, m; TriazH),
7.60–7.80 (2H, m; ArH), 8.77–8.90, 9.10–9.60, 10.85–10.95 ppm (total 2H,
m; NH).
Compound Poly-Py
ACHTUNGTRENNUNG
added to a stirred solution of 3-PyAHCUTNGTRENNUNG
0.11 mmol), and sodium ascorbate (5 mg, 0.03 mmol) in DMF (0.9 mL).
The CuAAC polymerization was allowed to proceed for 24 h. DMF was
added to the solution mixture to give a clear solution, and then the solu-
tion mixture was poured into water (10 mL). The solid was then filtered
Chem. Eur. J. 2013, 00, 0 – 0
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H.-F. Chow et al.
and dried under reduced pressure to give Poly-Py
(NMe)2 (75 mg, 83%)
m; ArCH2Triaz), 6.72–7.00 (10H, m; ArH), 7.00–7.33 (10H, m; TriazH),
7.57–7.93 (10H, m; ArH), 8.77–8.84, 9.14–9.54, 9.97–10.01 ppm (total 8H,
m; NH).
as a pale-yellow glassy solid. 1H NMR ([d8]THF): d=0.80–1.00 (24H, m;
CCH3), 1.14–1.90 (21H, m), 2.60–3.10 (6H, m; NCH3), 3.74–4.02 (4H, m;
OCH2), 4.02–4.22 (2H, m; OCH2), 4.31–4.76 (4H, m; NCH2Triaz), 5.25–
5.75 (4H, m; ArCH2Triaz), 6.66–6.99 (2H, m; ArH), 7.00–7.44 (2H, m;
TriazH), 7.60–7.90 ppm (2H, m; ArH).
Compound Poly-Ar(NH)2: Aqueous CuSO4 (0.50 mL, 0.056m) was added
to a stirred solution of 4-Ar(NH)2 (179 mg, 0.40 mmol), 6 (143 mg,
0.40 mmol), and sodium ascorbate (10 mg, 0.05 mmol) in DMF (4.5 mL).
The CuAAC polymerization was allowed to proceed for 24 h. DMF was
added to the solution mixture until a clear solution was obtained, and
then the solution mixture was poured into water (30 mL). The solid was
then filtered and dried under reduced pressure to give Poly-Py(NH)2
(274 mg, 85%) as a pale-yellow powder. 1H NMR: ([d8]THF): 0.75–1.10
(24H, m; CCH3), 1.14–1.90 (21H, m), 3.87–4.10 (6H, m; OCH2), 4.37–
4.70 (4H, m; NCH2Triaz), 5.25–5.75 (4H, m; ArCH2Triaz), 6.77–6.97
(2H, m; ArH), 7.45–7.56 (2H, m; ArH), 7.67–7.78 (1H, m; ArH), 7.78–
7.94 (2H, m; TriazH), 8.20–8.55 ppm (2H, m; NH).
Acknowledgements
This research is supported by a grant from the RGC (CUHK 400810)
and partially by a grant from the UGC (project no. AoE/P-03/08) of
HKSAR, China.
[1] H. C. Kolb, M. G. Finn, K. B. Sharpless, Angew. Chem. 2001, 113,
2056–2075; Angew. Chem. Int. Ed. 2001, 40, 2004–2021.
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Compound Poly-Ar
added to a stirred solution of 5-Ar
G
[3] a) V. V. Rostovtsev, L. G. Green, V. V. Fokin, K. B. Sharpless,
Angew. Chem. 2002, 114, 2708–2711; Angew. Chem. Int. Ed. 2002,
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29, 952–981; e) P. L. Golas, K. Matyjaszewski, Chem. Soc. Rev. 2010,
AHCTUNGTRENNUNG
0.10 mmol), and sodium ascorbate (5 mg, 0.03 mmol) in DMF (0.9 mL).
After 24 h, DMF was added to the mixture until a clear solution was ob-
tained, and the solution mixture was poured into water (10 mL). The
solid was then filtered and dried under reduced pressure to give Poly-Ar-
ACHTUNGTRENNUNG
(NMe)2 (71 mg, 84%) as a pale-yellow glassy solid. 1H NMR ([d8]THF):
d=0.80–1.02 (24H, m; CCH3), 1.12–1.95 (21H, m), 2.55–3.10 (6H, m;
NCH3), 3.75–4.12 (6H, m; OCH2), 4.16–4.71 (4H, m; NCH2Triaz), 5.25–
5.75 (4H, m; ArCH2Triaz), 6.77–6.92 (2H, m; ArH), 6.92–7.00 (1H, m;
ArH), 7.00–7.52 (2H, m; TriazH), 7.52–8.20 ppm (2H, m; ArH).
ˇ
39, 1338–1354; f) M. Jurꢅcek, P. H. Kouwer, A. E. Rowan, Chem.
Compound Poly-PyNHNMe: Aqueous CuSO4 (0.15 mL, 0.070m) was
added to a stirred solution of 2-PyNHNMe (76 mg, 0.16 mmol), 6 (58 mg,
0.16 mmol), and sodium ascorbate (5 mg, 0.03 mmol) in DMF (1.4 mL).
The CuAAC polymerization was allowed to proceed for 24 h. DMF was
added to the solution mixture until a clear solution was formed, and then
the solution mixture was poured into water (10 mL). The solid was then
filtered and dried under reduced pressure to give Poly-PyNHNMe
(114 mg, 85%) as a pale-yellow powder. 1H NMR ([d8]THF): d=0.70–
1.00 (24H, m; CCH3), 1.14–1.94 (21H, m), 2.81–3.10 (3H, m; NCH3),
3.80–4.04 (4H, m; OCH2), 4.04–4.24 (2H, m; OCH2), 4.46–4.88 (4H, m;
NCH2Triaz), 5.32–5.70 (4H, m; ArCH2Triaz), 6.70–6.94 (2H, m; ArH),
7.14–7.24, 7.36–7.46 (total 2H, m; TriazH), 7.60–7.90 (2H, m; ArH),
8.65–8.75, 9.48–9.62 ppm (total 1H, m; NH).
Commun. 2011, 47, 8740–8749.
[5] For reviews, see: a) H.-F. Chow, K.-N. Lau, Z. Ke, Y. Liang, C.-M.
Lo, Chem. Commun. 2010, 46, 3437–3453; b) A. C. Fahrenbach, J. F.
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2658.
[9] D. D. Dꢅaz, K. Rajagopal, E. Strable, J. Schneider, M. G. Finn, J.
Am. Chem. Soc. 2006, 128, 6056–6057.
Compound
(0.10 mL, 0.070m) was added to a stirred solution of 1-Py(NH)2 (38.5 mg,
0.085 mmol), 3-Py(NMe)2 (41.0 mg, 0.085 mmol), 6 (61.1 mg, 0.17 mmol),
Poly([Py(NH)2]1-ran-[Py(NMe)2]1):
Aqueous
CuSO4
[10] a) G. Appendino, S. Bacchiega, A. Minassi, M. G. Cascio, L. De Pe-
trocellis, V. Di Marzo, Angew. Chem. 2007, 119, 9472–9475; Angew.
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Billington, P. L. Canonico, G. Sorba, A. A. Genazzani, Med. Res.
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8395–8403.
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4138–4140.
ACHTUNGTRENNUNG
and sodium ascorbate (5 mg, 0.03 mmol) in DMF (0.9 mL). The CuAAC
polymerization was allowed to proceed for 24 h. DMF was added to the
solution mixture until a clear solution was formed, and then the solution
mixture was poured into water (10 mL). The solid was then filtered and
dried under reduced pressure to give Poly([Py(NH)2]1-ran-[PyACHTNUGTRNEUNG(NMe)2]1)
(115 mg, 82%) as a pale-yellow powder. 1H NMR ([d8]THF): d=0.72–
1.10 (48H, m; CCH3), 1.14–1.90 (42H, m), 2.70–3.15 (6H, m; NCH3),
3.75–4.03 (8H, m; OCH2), 4.03–4.24 (4H, m; OCH2), 4.36–4.90 (8H, m;
NCH2Triaz), 5.35–5.70 (8H, m; ArCH2Triaz), 6.38–7.00 (4H, m; ArH),
7.00–7.42 (4H, m; TriazH), 7.90–7.93 (4H, m; ArH), 8.77–8.84, 9.14–9.54,
9.97–10.01 ppm (total 2H, m; NH).
Compound
(0.20 mL, 0.070m) was added to
(100.2 mg, 0.221 mmol), 3-Py(NMe)2 (26.6 mg, 0.055 mmol), 6 (99.6 mg,
0.276 mmol), and sodium ascorbate (10 mg, 0.05 mmol) in DMF
(1.8 mL). The CuAAC polymerization was allowed to proceed for 24 h.
DMF was added to the solution mixture until a clear solution was
formed, and then the solution mixture was poured into water (20 mL).
The solid was then filtered and dried under reduced pressure to give
Poly([Py(NH)2]4-ran-[Py
G
Aqueous
CuSO4
[13] A. R. Katritzky, N. K. Meher, S. Hanci, R. Gyanda, S. R. Tala, S.
Mathai, R. S. Duran, S. Bernard, F. Sabri, S. K. Singh, J. Doskocz,
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a
AHCTUNGTRENNUNG
ˇ
ˇ
mers and biopolymers, see: a) J. Spevꢆcek, B. Schneider, Adv. Col-
loid Interface Sci. 1987, 27, 81–150; b) J.-M. Guenet, Thermoreversi-
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ACHTUNGTRENNUNGPoly([Py(NH)2]4-ran-[PyACHTUNGTRENNUNG(NMe)2]1) (190 mg, 84%) as a pale-yellow
powder. 1H NMR ([d8]THF): d= 0.72–1.10 (120H, m; CCH3), 1.14–1.90
(105H, m), 2.70–3.10 (6H, m; NCH3), 3.75–4.04 (20H, m; OCH2), 4.04–
4.25 (10H, m; OCH2), 4.36–4.80 (20H, m; NCH2Triaz), 5.25–5.70 (20H,
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Properties of Main-Chain Poly(pyridine-2,6-dicarboxamide-triazole)s
FULL PAPER
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cules 1988, 21, 1752–1756; b) M. Klein, A. Brꢈlet, J.-M. Guenet,
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frutos, M. Ortega-MuÇoz, J. Lopez-Jaramillo, F. Hernandez-Mateo,
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dron Lett. 2008, 49, 1340–1343.
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Received: October 16, 2012
Revised: November 12, 2012
Published online: && &&, 0000
Chem. Eur. J. 2013, 00, 0 – 0
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H.-F. Chow et al.
Click Chemistry
S.-L. Yim, H.-F. Chow,* M.-C. Chan,
C.-M. Che, K.-H. Low ......... &&& — &&&
Synthesis and Thermoreversible
Gelation Properties of Main-Chain
Poly(pyridine-2,6-dicarboxamide-tri-
Supramolecular chemistry: The pres-
ence of an intramolecular hydrogen-
bonding pyridine-2,6-dicarboxamide
unit inside a diacetylene monomer
promoted its AABB click copolymeri-
zation efficiency with a diazide by
reducing the amount of low molecular
weight oligomers; this structural motif
also conferred excellent thermoreversi-
ble gelating properties to the resulting
poly(amide-triazole) compound (see
scheme).
ACHTUNGTRENNUNGazole)s
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These are not the final page numbers!