One-pot synthesis of precise polyisoxazoles by click polymerization: Copper (I)-catalyzed 1,3-dipolar cycloaddition of nitrile oxides with alkynes

Article abstract of DOI:10.1002/pola.26537

This article reports a new one-pot method for polymer preparation, which involves double click chemistry. In one pot, two click reactions take place sequentially by adding the reactants step by step. The first click reaction is to produce the monomer for

Full text of DOI:10.1002/pola.26537

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One-Pot Synthesis of Precise Polyisoxazoles by Click Polymerization:
Copper (I)-Catalyzed 1,3-Dipolar Cycloaddition of Nitrile Oxides with
Alkynes
1
1,2
Yan Li, Bin Cheng
1
Key Laboratory of Beijing City on Preparation and Processing of Novel Polymer Materials, Beijing University of Chemical
Technology, Beijing 100029, China
2
Analysis and Testing Center, Beijing University of Chemical Technology, Beijing 100029, China
Correspondence to: B. Cheng (E-mail: chengb@mail.buct.edu.cn)
Received 3 November 2012; accepted 17 December 2012; published online 12 January 2013
DOI: 10.1002/pola.26537
ABSTRACT: This article reports a new one-pot method for poly-
mer preparation, which involves double click chemistry. In one
pot, two click reactions take place sequentially by adding the
reactants step by step. The first click reaction is to produce the
monomer for the second click reaction for polymerization. The
click polymerization differs from the general click polymerization
with the reaction of diazides and dialkynes. Nitrile oxides, pro-
duced in situ by the first click reaction of the formation of aldox-
ime, instead azides, avoiding the poisonousness and
explosiveness of azides and being much safer and easy to oper-
ate. And 3,5-disubstitute polyisoxazoles are produced by the
copper(I)-catalyzed the 1,3-dipolar cycloaddition of nitrile oxides
with alkynes in high yields by our one-pot method. The resulting
polyisoxazoles agree well with the structural assignment
1
obtained by the H NMR and IR analyses, with high molecular
w n
weights, narrow molecular weight distribution (M /M < 1.2)
and high regioregularity. The poor solubility of these polymers
is found to be caused by their crystallization. Improvement of
solubility is achieved by modifying the structures of alkyne
monomers. All the polymers are thermally stable, losing little of
ꢁ
their weights when heated to ꢀ350 C. VC 2013 Wiley Periodicals,
Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 1645–1650
KEYWORDS: stereospecific polymers; click polymerization;
metal-organic catalysts; nitrile oxides; one-pot; crystal struc-
ture; heteroatom-containing polymer
INTRODUCTION Synthesis of complex molecules needs highly
reliable and selective reactions. ‘‘Click reaction,’’ coined by
Sharpless et al. in 2001, has caught the interest of synthetic
chemists because of its remarkable efficiency, high regiose-
lectivity, mild reaction conditions, and easy product isola-
1,3-dipolar cycloaddition of nitrile oxide and diynes with mo-
lecular sieves 4 Å to prepare polyisoxazoles. Although many
6
nitrile oxides react with alkynes at appreciable rates without
ꢁ
a catalyst (reaction time from several hours at 60–70 C to
7
several days), both isoxazole regioisomers are usually
1
tion. Polymer chemists have attempted to use the click reac-
tion to carry out polymerization. The copper(I)-catalyzed
obtained. We found that copper(I) was an efficient catalyst
8
for this system. Nitrile oxides are best prepared from the
1
,3-dipolar cycloaddition of diazide and dialkyne has been
corresponding aldoximes by halogenations/dehydrohalogena-
tion (via imidoyl chlorides) immediately before use, because
2
,3
9
used to prepare polytrizoles since 2004. Much progress on
the click polymerization of azides and alkynes has been
achieved in recent years. However, further success has been
limited by several drawbacks. The azides are toxic and explo-
sive. In addition, the copper(I)-catalyzed polymerizations of
arylenediazides and arylenediynes are sluggish, taking as
some of them, especially the aliphatic series, cannot be
8
stored for extended periods of time. Herein, we report an
experimentally convenient one-pot three-step process for the
regioselective synthesis of 3,5-disubstituted polyisoxazoles. A
dialdehyde was first converted to the corresponding aldox-
ime. Without isolation, the aldoxime was transformed to the
corresponding nitrile oxide using a halogenating agent and a
base for halogenation and dehydrohalogenation, respectively.
Finally, the in situ generated nitrile oxide undergoes 1,3-
dipolar polycycloaddtion with diynes catalyzed by copper(I)
which was obtained in situ by reduction of copper(II) sulfate
4
long as 7–10 days to finish. To address these problems,
new click polymerization reaction is needed.
We used nitrile oxides as the substitutes for azides, which
allows efficient [2 þ 3]cycloaddition with both alkenes and
alkynes to selectively produce the corresponding nitrogen-
5
containing heterocycles. Lee et al. succeeded in using the
Additional Supporting Information may be found in the online version of this article.
2013 Wiley Periodicals, Inc.
V
C
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IR spectrophotometer. Wide angle X-Ray diffraction patterns
were obtained at room temperature on a Rigaku D/Max-
2
500 VB2þ/PL powder diffractometer with scanning speed
ꢁ
of 10 /min, and the patterns were recorded in the 2y range
of 5–90 . TLC was performed on silica gel plates and prepa-
ꢁ
rative chromatography was carried out on silica gel column
(
200–300 mesh).
Monomer Preparation
Due to the limited sources of diyne monomers, we prepared
arylpropargyl ethers by simple etherification of different aro-
matic phenols and propargyl bromide under reflux in ace-
tone (Scheme 2). Detailed procedures for the preparation of
1
,4-bis(prop-2-ynyloxy)benzene 2 are given below as an
SCHEME 1 One-pot synthesis of polyisoxazoles.
example.
with ascorbate (Scheme 1). In our one pot, two click chemis-
try took place sequentially by adding the reactants step by
step. No isolation of intermediate products was needed. It is
much safer and easy to operate.
Acetone was dried with K CO overnight and distilled. Into
2 3
250 mL round-bottom flask were added hydroquinone (5.5
g, 50 mmol) and anhydrous potassium carbonate (27.6 g,
200 mmol) in 150 mL of dry acetone. The mixture was
stirred at ambient temperature for 0.5 h. Then propargyl
bromide (13 g, 110 mmol) was added dropwise within 0.5 h
under stirring. Afterwards, the mixture was refluxed for an
additional 24 h. The mixture was cooled to room tempera-
ture and filtered, and the filtrate was concentrated on a ro-
tary evaporator. The residue was dissolved in 150 mL DCM
and washed with 150 mL of water three times and 100 mL
of saturated brine once. The organic phase was dried over
EXPERIMENTAL
General Information
All the solvents used in this study were purchased from Bei-
jing Chemical Industry Factory, including dimethylformamide
(
DMF), acetone, tetrahydrofuran (THF), petroleum ether,
dichloromethane (DCM), ethyl acetate, triethylamine, etc.
Other reagents include terephthalaldehyde (Alfa Aesar, 98%),
hydroxylamine hydrochloride (Beijing Chemical Industry), N-
chlorosuccinimide (NCS) (Tianjin Guangfu Fine Chemicals
Institute, 99%), hydroquinol (Tianjin Guangfu Fine Chemicals
Institute, 99%), bisphenol A (Tianjin Fuchen Chemical Rea-
gent), and propargyl bromide (Alfa Aesar, 80% in toluene,
stab. with MgO). Unless otherwise stated, these commercially
available solvents and reagents were directly used without
further purification.
MgSO . After filtration and evaporation, the crude product
4
was purified on a silica gel column using petroleum ether/
ethyl acetate (5:1 by volume) as the eluent. A white solid
1
was obtained in 85% yield (7.9 g). H NMR (400 MHz, 298
K, CDCl
3
), d (TMS, ppm): 6.93 (s, 2H, Ar H), 4.65 (s, 2H, J ¼
13
2
.40 Hz, OCH ), 2.51 (s, 1H, J ¼ 2.40 Hz, CCH). C NMR
2
(
100 MHz, 298 K, CDCl ), d (TMS, ppm): 152.6, 116.3 (ArC),
3
ꢃ1
79.1, 75.6 (CCH), 56.7(OCH2). IR (KBr),
m
(cm ):
3275(BCAH), 2130(CBC), 1507, 1450 (OACH2), 1378,
1
13
1283, 1222, 827.
H NMR (400 MHz) and C (100 MHz) were recorded on a
Bruker AV-400 spectrometer using CDCl , acetone-d , and
0
3
6
4,4 -(Propane-2,2-diyl)bis(prop-2-ynyloxyl)benzene 4 (Scheme
DMSO-d as the solvents and tetramethylsilane (TMS; d ¼ 0)
6
2). This monomer was prepared from the reaction of bisphe-
nol A with propargyl bromide by the similar synthetic proce-
dures. A white solid was obtained in 89% yield. H NMR (400
as the internal standard. IR spectra were obtained on a Ther-
mal Electron Corporation Nicolet 8700/Continuum XL FT-IR
spectrophotometer. Relative molecular weight and molecular
weight distribution were estimated by a gel permeation
chromatography system equipped with an Agilent 1260 re-
fractive index detector and an Agilent PL1110-6530 column,
which has a 5 lm bead size with measurable molecular
1
2
weight range from 1000 to 40,000, 7.5 ꢂ 300 mm . DMF
was used as the eluent at a flow rate of 1 mL/min and a set
of monodisperse linear polystyrenes as the calibration stand-
ards. Thermal stabilities were evaluated by thermogravimet-
ric analysis (TGA), which were carried out under nitrogen
(
flow rate 45 mL/min) on a Perkin Elmer TGA analyzer at a
ꢁ
ꢁ
heating rate of 10 C/min from 25 to 400 C. Differential
scanning calorimetry (DSC) was performed with a NETZSCH
DSC 204 F1 at a heating rate of 20 C/min and a flow rate
ꢁ
of 50 mL/min under N2 atmosphere. TGA-IR was operated
on a Mettler Toledo TGA/DSC1/1100SF and Nicolet 6700 FT-
SCHEME 2 Alkyne monomers and the synthesis of monomer
2, 4, and 8.
1
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MHz, 298 K, CDCl ), d (TMS, ppm): 7.14 (s, 2H, Ar H), 6.86(s,
alkaline environment, 10 mmol triethylamine was added to
the mixture. The reaction proceeded for 48 h at mild tem-
perature 40 C with stirring. The resulting mixture was
3
2
H, H ArAO), 4.66(s, 2H, J ¼ 2.40 Hz, OCH
2
), 2.51(s, 1H, J ¼
1
3
ꢁ
2
.40 Hz, CCH), 1.64(s, 3H, CH ). C NMR (100 MHz, 298 K,
3
CDCl ), d (TMS, ppm): 155.6, 144.1, 128.0, 114.4 (ArC), 79.0,
poured into 300 mL water, and 20 mL concentrated ammo-
nia was added to remove all copper salts. The precipitates
were collected by filtration and dried overnight in a temper-
3
7
5.5 (CCH), 56.0 (OCH ), 42.0 (CCH ), 31.2 (CH ). IR (KBr), m
2 3 3
ꢃ1
(
cm ): 3284 (BCAH), 3035, 2970 (CH ), 2874, 2119 (CBC),
3
ꢁ
1
1
604, 1506, 1450 (OACH ), 1385, 1366, 1287, 1263, 1217,
182, 1019, 832.
ature controlled drier at 45 C to a constant weight. The cor-
2
responding polymer P was thereby obtained.
I
4-(Prop-2-ynyloxyl)benzaldehyde 8 (Scheme 2). This mono-
Characterization Data of PI
mer was prepared from parahydroxybenzaldehyde and pro-
pargyl bromide by the similar synthetic procedures. The only
difference between 8 and 2, 4 is that 8 contain both an alde-
hyde group and an alkynyl group. Compound 8 was there-
Off-white powder; 69.5% yield. Mw 9239; Mn 8566; M /Mn
w
1
.079 (GPC, polystyrene calibration). 10% weight loss temper-
ꢁ
ꢁ
1
ature was at 325 C. Most weight loss occurred at 350 C. H
NMR (400 MHz, 298 K, DMSO-d ), d (TMS, ppm): 8.04, 7.26,
7
6
fore marked as AB-type monomer while 2 and 4 as B -type
13
2
.05, 6.95, 5.30, 4.74, 3.54, 2.95. C NMR (100 MHz, 298 K,
monomers and dialdehyde as A -type monomer. A white
2
1
DMSO-d ), d (TMS, ppm): 161.33, 127.37, 115.92, 102.33,
6
solid was obtained in 80% yield. H NMR (400 MHz, 298 K,
ꢃ1
7
8.04, 61.00, 55.83. IR (KBr), m (cm ): 3291 (BCAH), 3129
CDCl ), d (TMS, ppm): 9.91(s, 1H, CHO), 7.85(s, 2H, Ar H),
3
(
2
CAH, aromatic), 2924 (CAH, str, asym), 2865 (CAH, str, sym),
135 (CBC), 1612, 1506 (C ¼¼ C), 1227 (phenylAOACH2).
7
¼
.11(s, 2H, Ar H), 4.78(s, 2H, J ¼ 2.4 Hz, OCH ), 2.56(s, 1H, J
2
13
2.40 Hz, CCH). C NMR (100 MHz, 298 K, CDCl ), d (TMS,
3
The polymer PII was prepared from nitrile oxide 1 and 4
using the same one–pot procedure (Table 1, entry 2). The
polymer PIII was prepared by polymerization of 1 and 1,7-
Octadyne 6 in the same fashion (Table 1, entry 3).
ppm): 190.7 (CHO), 162.4, 131.9, 130.6, 115.2 (ArC), 77.5,
ꢃ1
7
6.4 (CCH), 56.0 (OCH ). IR (KBr), m (cm ): 3207 (BCAH),
2
3
1
072, 2928, 2836, 2121 (CBC), 1680 (CHO), 1600, 1576,
508, 1427 (OACH ), 1385, 1247, 1172, 1021, 835.
2
(
ii) The procedure for the synthesis of polymer PIV from AB-
One-Pot Synthesis of Polyisoxazoles
monomer 8 is as follows. To a solution of 4 mmol of 8 in 30 mL
DMF was added 6 mmol of hydroxylamine hydrochloride. After
reaction at 30 C for 3 h under stirring, 6 mmol of NCS was
added. The mixture was stirred at the same temperature for
another 4 h. Afterwards, sodium ascorbate (0.4 mmol in 600
lL water, 20 mol %) was added to the solution, followed by
copper(II) sulfate pentahydrate (0.1 mmol in 400 lL water, 5
mol %). To create an alkaline environment, 10 mmol triethyl-
amine was added to the mixture. The reaction proceeded for
Scheme 1 shows the three steps in this one-pot synthesis.
The first two steps involving the synthesis of nitrile oxide
precursors are discussed together. The last step is the syn-
thesis of polyisoxazoles with the addition of the catalyst sys-
tem, the base, and the alkynes.
ꢁ
Synthesis of Nitrile Oxide Precursor
Typical procedure for synthesizing nitrile oxide precursor, as
exemplified by benzene-1,4-dicarbohydroxamoyl dichloride,
is as follows. To a solution of 2 mmol of terephthalaldehyde
in DMF (20 mL) was added 6 mmol of hydroxylamine hydro-
chloride. Oxime formation was complete after reaction at 30
ꢁ
48 h at mild temperature 40 C with stirring. The resulting
mixture was poured into 300 mL water, and 20 mL concen-
trated ammonia was added to remove all copper salts. The pre-
cipitates were collected by filtration and dried. The polymer
PIV was obtained in 73% yield, Mw 8380; M 7684; M /M
1.091 (GPC, polystyrene calibration). Ten percent weight loss
temperature was at 330 C. Most weight loss took place at 350
ꢁ
ꢁ
C for 2 h under constant stirring, as indicated by the TLC
analysis. Then 6 mmol of NCS was added to the solution.
The mixture was stirred at the same temperature for another
n
w
n
ꢁ
4
h. TLC analysis indicated most oxime was converted to
1
imidoyl chloride intermediate. The imidoyl chloride would
become nitrile oxide by dehydrohalogenation in an alkaline
environment and immediately participate in the next reac-
tion. In an additional experiment, benzene-1,4-dicarbohy-
droxamoyl dichloride was obtained by precipitation with
plenty of water, and its yield was 90%.
C. H NMR (400 MHz, 298 K, DMSO-d ), d (TMS, ppm): 7.88,
6
13
7.21, 7.17, 7.11, 5.42, 4.88. C NMR (100 MHz, 298 K, DMSO-
d ), d (TMS, ppm): 168.0, 161.47, 138.9, 128.11, 115.19,
102.28, 78.52, 60.52, 55.54. IR (KBr), m (cm ): 3291 (BCAH),
3129 (CAH, aromatic), 2922 (CAH, str, asym), 2870 (CAH, str,
sym), 2126 (CBC), 1245 (phenylAOACH2).
6
ꢃ1
Polymer Synthesis
RESULTS AND DISCUSSION
(
i) Click polymerization reactions of diyne monomers with
nitrile oxides by polycycloaddition were carried out in an
open atmosphere. Typical procedures for the click polymer-
Monomer Synthesis
A - and B - type monomers of dialdehyde and diyne were
2
2
ization of nitrile oxide 1 with B - monomer 2 are given
below as an example. In a small beaker, 1.8 mmol of 2 was
dissolved in 10 mL DMF. Under stirring, sodium ascorbate
designed to realize the planned A þ B approach to polyisoxa-
2
2
2
zoles. Considering the tendency to produce insoluble gels by
the click polymerization of 1 and diyne 2 with rigid structures,
flexible alkyl chains were introduced into the diyne monomers.
The diyne 4 were prepared and the diyne 6 were used to
improve the solubility of the linear polyisoxazoles. We also
synthesized AB- type monomers with one terminal aldehyde
(
0.4 mmol in 600 lL water, 20 mol %) was added, followed
by copper(II) sulfate pentahydrate (0.1 mmol in 400 lL
water, 5 mol %). The mixture was immediately added to the
solution of imidoyl chloride mentioned above. To create an
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a
TABLE 1 Synthesis of Polyisoxazoles via Click Polymerization
Entry
1
Alkyne Monomer
Products
Yield/%
69.5
2
3
78.4
46
4
73
a
Polymerization conditions:[Diyne]:[Dialdehyde] ¼ 0.9:1, 48 h, 40 ꢁC, in 30 mL DMF.
group and the other alkynyl group like 8. The monomer 8 can
harmful and unstable hydroximoyl chlorides are avoided, as
10
undergo three steps (Scheme 1) to form P . It indicates that
nitrile oxides are obtained directly from oximes.
The
IV
the two click reactions (carbonyl chemistry of the ‘‘non-aldol’’
type and 1,3-dipolar cycloaddition reaction) involved in this
process are independent and do not affect each other.
reagents used in excess including hydroxylamine hydrochlor-
ide and NCS are water soluble, which ensures the maximiza-
tion of the extent of the reactions and simplified product pu-
rification. The potentially versatile sequence is tolerant of
most functional groups and performs well in mild environ-
ment without the need for oxygen protection. It is reliable
for synthetic applications of many heterocyclic polymers by
1
One-Pot Synthesis of Polyisoxazoles by Click
Polymerization
Scheme 1 shows the one-pot procedure for rapid preparation
of polyisoxazoles. The isolation and handling of potentially
1,3-dipolar cycloaddition.
In the experiments, several bifunctional terminal acetylenic
TABLE 2 Molecular Weight and Crystallization Properties of the
monomers (2, 4, 6) were employed to demonstrate the
Polyisoxazole
c
d
d
T
g
ꢁ
Crystallinity
R
a
w
a
a
Polymer
M
M
n
M
w
/M
n
( C) (%)
(%)
b
e
P
P
P
P
a
I
9239 8566 1.079
10,354 9200 1.125
9919 9215 1.076
8380 7684 1.091
47.79
3.00
2.67
2.77
3.84
II
III
28
e
12.29
55.51
49.11
b
b
e
IV
w n
M , weight-average molecular weight; M , number-average molecular
weight were estimated by gel permeation chromatography (DMF, on
the basis of polystyrene standards).
b
I
P , PII, and PIV were not completely soluble in DMF with the concentra-
tion from 5 to 10 mg/mL. The molecule weight may be the one of the
soluble part polymer.
c
Glass transition temperatures (T
g
) were obtained at a heating rate of
ꢁ
ꢁ
2
d
0
C/min under N
2
(flow rate 50 mL/min) from ꢃ100 to 100 C.
Crystallinity values were measured on a powder diffractometer at a
ꢁ
ꢁ
scanning speed of 10 /min in the 2y range of 5–90 ; R is the Residue
Error of Fit in data processing by MDI Jade software. The smaller this
value is the better.
I
FIGURE 1 TGA thermograms of P -PIV recorded under nitrogen
e
ꢁ
Not estimated.
at a heating rate of 10 C/min.
1
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to form the isoxazole rings in the polymer. Figure 3 shows
1
the H NMR spectra of nitrile oxide precursor imidoyl chlo-
ride (obtained in an independent experiment), monomer 2
and polymer P . The new resonance peaks of the heteroaro-
I
matic protons at 7.26 ppm (f) and benzyl protons at 5.30
ppm (g) were observed in the spectrum of P . The downfield
I
shift of the benzyl proton signal d of 2 and significant
I
FIGURE 2 IR spectra of monomer 2 (A) and its polymers P (B).
usefulness of the one-pot strategy. The results are summar-
ized in Tables 1 and 2. All the polyisoxazoles were obtained
in high yields, with high molecular weights and narrow mo-
lecular weight distribution (Table 1), and in high regioregu-
1
0
larities with 3,5-disubstituted isoxazole unit. It was certi-
1
fied by H-NMR spectrum only containing the signal of
proton of 3,5-disubstituted isoxazole. It was found the poly-
mers P were not totally soluble in commonly used solvent
I
like DCM, THF, acetone, and even DMF. They were also found
to have high crystallinities (Table 2). One possible explana-
tion is that these polymers were crystallized and precipitated
when the reaction mixture were poured into plenty of water
at the end of the reaction. As expected, the solubility of PII is
I
better than P because of the introduction of alkyl group. PII
is totally soluble in commonly used organic solvents such as
chloroform, THF, and DMF. Therefore, it can be concluded
that the insolubility problem of the polymer prepared by
click polymerization can be solved by new designs of the
monomer structures.
The thermal properties of the polymers were evaluated by
DSC (Table 2) and TGA (Fig. 1). The glass transition tempera-
tures of P
I
, PIII, PIV were not estimated under the given con-
ꢁ
ditions. PII have a low glass transition temperature of 28 C.
All the polymers (P –P ) were thermally stable. As shown in
I
IV
Figure 1, most of the polyisoxazoles lose about 10% of their
ꢁ
ꢁ
weights at a temperature as high as 300–350 C. Supposedly,
the isoxazole moieties decompose at ꢀ350 C because the
ꢁ
maximum rate of weight loss occurs at about 350 C and a
large amount of carbon dioxide and water vapor are formed
as detected by TG-IR. A small weight loss at lower tempera-
ture (Fig. 1) can be attributed to the decomposition of slight
residual small molecular weight materials.
1
FIGURE 3 H NMR spectra of benzene-1,4-dicarbohydroxamoyl
The structures of the polyisoxazoles were determined by IR
and H NMR analyses. Examples of IR spectra of monomer 2
dichloride in DMSO-d
6
(A), and monomer 2 in CDCl
3
(B), and
1
their polymer P in DMSO-d
I
6
(C). The nitrile oxide precursor
and polymer P are given in Figure 2. As shown in Figure 2,
I
benzene-1,4-dicarbohydroxamoyl dichloride were obtained at
the end of the second reaction of the one-pot process.
the very weak absorption bands associated with the vibra-
ꢃ1
13
1
13
tional stretching of BCAH at 3275 cm and CBC at 2130
C NMR spectra of monomer 2 and PI, H and C NMR spec-
tra of 4, 8, P - P , and IR spectra of 4 and P , 8 and PIV, and PIII
ꢃ1
cm
indicate that most of the acetylene groups of the
II
IV
II
monomers have undergone the polycycloaddition reactions
are found in the supporting information.
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reduction of the ethynyl proton signal e of 2 along with the
reduction of the OH signal b of benzene-1,4-dicarbohydroxa-
homoditopic nitrile oxides and diynes would be a useful syn-
thetic entry of new polymers.
moyl dichloride clearly suggested the formation of P . Only
one type of heteroaromatic proton signal indicated that only
I
It is anticipated that further optimization of polymerization
reactions and new efforts in molecular structure design will
make the click polymerization an even more versatile syn-
thetic tool for the generation of new advanced materials
with multifaceted functionalities.
3,5-disubsituted polyisoxazoles were produced.
CONCLUSIONS
REFENRENCE AND NOTES
In this work, we succeed in establishing an effective, regiose-
lective, experimentally convenient new one-pot copper (I)-
catalyzed synthetic route to polyisoxazoles. In one pot, two
click reactions take place sequentially by adding the reac-
tants step by step. The first click reaction is to produce the
monomer for the second click reaction for polymerization.
1 H. C. Kolb, M. G. Finn, K. B. Sharpless, Angew. Chem., Int.
Ed. Engl. 2001, 40, 2004–2021.
2 A. J. Sheel, H. Komber, B. Voit, Macromol. Rapid Commun.
2
004, 25, 1175–1180.
3
(a) A. J. Qin, J. W. Y. Lam, B. Z. Tang, Chem. Soc. Rev. 2010,
8
39, 2533–2544; (b) B. S. Sumerlin, A. P. Vogt, Macromolecules
The isolation and handling of the unstable intermediates
2
010, 43, 1–13.
such as oximes and hydroximoyl chlorides are avoided.
Results also show the applicability of this new click polymer-
ization reaction that exploits a homo ditopic nitrile oxide as
a bifunctional 1,3-dipole formed in situ from the correspond-
4
(a) D. J. V. C. van Steenis, O. R. P. David, G. P. F. van Strij-
donck, J. H. van Maareseveen, J. N. H. Reek, Chem. Commun.
005, 4333–4335; (b) S. Bakbak, P. J. Leech, B. E. Carson, S.
Saxena, W. P. King, U. H. F. Bunz, Macromolecues 2006, 39,
2
6
ing bifunctional hydroxamoyl chloride. This one-pot syn-
6
793–6795.
thetic system for polyisoxazoles is fast and insensitive to air
and moisture. It can produce polymers with high molecular
weights, narrow molecular weight distribution and high
regioregularities in high yields. The polymers are thermally
5
For selected review on isoxazoles, see: S. A. Lang, Y. I. Lin,
In Comprehensive Heterocyclic Chemistry; A. R. Katritzky, C.
W. Rees, Eds.; Pergamon: Oxford, 2000; Vol. 6, pp 1–144.
6 Y. G. Lee, Y. Koyama, M. Yonekawa, T. Takata, Macromole-
cules 2009, 42, 7709–7717.
ꢁ
stable, losing little of their weights when heated to ꢀ350 C.
7
(a) R. Huisgen, In 1,3-Dipolar Cycloaddition Chemistry; A.
These click polymerization reactions based on 1,3-dipolar
polycycloaddition of the nitrile oxide with alkynes have the
following advantages. (1) No explosive and poisonous mate-
rials were involved, which was different from general click
Padwa, Ed.; Wiley: New York, 1984; Vol. 1, pp 1–176; (b) V. J a€ ger,
P. A. Colinas, In Heterocyclic Compounds; A. Padwa, W. H. Per-
son, Eds.; Wiley: New York, 2002; Vol. 59, pp 363–461.
8
F. Himo, T. Lovell, R. Hilgraf, V. V. Rostovtsev, L. Noodleman,
1
1
polymerization using azides. (2) Dipolarophiles used in the
reaction can be versatile. Both dialkyne and dialkene are
K. B. Sharpless, V. V. Forkin, J. Am. Chem. Soc. 2005, 127,
210–216.
6
available although this work only dealt with dialkynes. (3)
9
K. Hallig, K. B. G. Torssell, R. G. Hazell, Acta Chem. Scand.
1991, 45, 736–741.
0 T. V. Hansen, P. Wu, V. V. Forkin, J. Org. Chem. 2005, 70,
The synthesized heterocyclic polymer containing nitrogen
and oxygen may be biocompatible. (4) The resulted polymers
can be transformed into reactive polymers with useful func-
tional groups such as aldol, diketone, b-aminoalcohol, and b-
1
7761–7764.
11 A. J. Qin, W. Y. Lam, B. Z. Tang, Macromolecules 2010, 43,
8693–8702.
6
aminoenone. The present new click polymerization using
1
650
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