Catalyst-free click cascade functionalization of unsaturated-bond- containing polymers using masked-ketene-tethering nitrile N-oxide

Article abstract of DOI:10.1016/j.polymer.2013.06.020

We developed a facile protocol for grafting-onto and cross-linking unsaturated-bond-containing common polymers via the formation of masked-ketene-functionalized polymers. The protocol utilizes a cascade functionalization agent 1 that has nitrile N-oxide and masked ketene functionalities. Through the model ligation reactions using 1, it turned out that the 1 facilitates the catalyst-free click introduction of masked ketene moieties to the unsaturated bonds such as CN and CC bonds, capable of undergoing catalyst-free ligation with not only a nucleophilic amine but also a neutral alcohol with low nucleophilicity. On the basis of these results, the catalyst-free grafting reactions of PEG onto EPDM and PAN using 1 were performed to afford the corresponding graft copolymers in excellent conversion yields. In addition, it was also revealed that heating of both PAN and NR with masked ketene moieties at 250 C for 1 h without catalyst enables the efficient conversion to give the respective cross-linked polymers.

Full text of DOI:10.1016/j.polymer.2013.06.020

Polymer 54 (2013) 4501e4510
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Catalyst-free click cascade functionalization of unsaturated-bond-
containing polymers using masked-ketene-tethering nitrile N-oxide
,
a
a,
Sumitra Cheawchan a, Yasuhito Koyama b , Satoshi Uchida , Toshikazu Takata
*
**
a Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1-(H-126), Ookayama, Meguro, Tokyo 152-8552, Japan
b Catalysis Research Center, Hokkaido University, N21 W10, Kita-ku, Sapporo 001-0021, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
We developed
a facile protocol for grafting-onto and cross-linking unsaturated-bond-containing
Received 20 April 2013
Received in revised form
6 June 2013
Accepted 12 June 2013
Available online 20 June 2013
common polymers via the formation of masked-ketene-functionalized polymers. The protocol utilizes a
cascade functionalization agent 1 that has nitrile N-oxide and masked ketene functionalities. Through the
model ligation reactions using 1, it turned out that the 1 facilitates the catalyst-free click introduction of
masked ketene moieties to the unsaturated bonds such as C^N and C]C bonds, capable of undergoing
catalyst-free ligation with not only a nucleophilic amine but also a neutral alcohol with low nucleo-
philicity. On the basis of these results, the catalyst-free grafting reactions of PEG onto EPDM and PAN
using 1 were performed to afford the corresponding graft copolymers in excellent conversion yields. In
addition, it was also revealed that heating of both PAN and NR with masked ketene moieties at 250 ꢀC for
1 h without catalyst enables the efficient conversion to give the respective cross-linked polymers.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Nitrile N-oxide
Cascade functionalization
Catalyst-free grafting onto and cross-linking
reaction
1. Introduction
applications, we developed a new protocol to directly form MKPs
from common polymers using nitrile N-oxide agents.
Among various modification or functionalization methods of
polymers, the stepwise protocol using a cascade functionalization
tool is beneficial owing to the remarkable versatility of functional
groups and a high functionalization ratio. However, it is inferior to
direct methods in terms of the number of reactions employed. A
masked-ketene-functionalized polymer (MKP) [1e10] is a potential
reactive polymers that can be used for the post-modification of
processed materials toward the development of advanced mate-
rials. The MKP skeleton includes ketene equivalents, such as
Meldrum’s acid derivatives and benzodioxinones, to generate a
ketene functionality by external stimuli, e.g., heating [11,12] and
photoirradiation [13]. The resulting ketene is highly reactive to
various nucleophiles and provides the corresponding adducts
without any catalyst [14e16]. The ketene gradually dimerizes in the
absence of nucleophiles to give cyclobutadione [17]. Therefore,
MKP exhibits dual reactivity to produce both polymers function-
alized with nucleophiles and cross-linked polymers by self-
Recently, we reported a new cascade functionalization agent for
common polymers, consisting of an ambident agent having both
nitrile N-oxide and epoxide functionalities [22]. This agent enables
the easy molecular integration of various nucleophiles onto C]C-,
C^C-, and C^N-containing polymers in the presence of an
appropriate catalyst. Building on our previous reports [23e32], in
this study, we describe a convenient protocol to introduce a masked
ketene moiety to unsaturated-bond-containing common polymers
via a catalyst-free click reaction. Central to this method is the use of
a new ambident agent that possesses both nitrile N-oxide and
masked ketene functionalities (Fig. 1). Heating of the resulting
MKPs enables both a catalyst-free grafting-onto reaction with a
nucleophilic polymer and a catalyst-free cross-linking reaction.
2. Experimental section
2.1. Materials
ꢀ
reaction. In light of Yagci’s [18e20] and Hawker’s pioneering
reports [21] of the synthesis of MKP based on the polymerization of
masked-ketene-containing monomers for general materials
For NMR analyses, deuterated solvents with trimethylsilane by
Across Organics Inc. were used. Wako GelÒ C-400HG (Wako
Chemical Inc.) was used for silica gel chromatography. Meldrum’s
acid was purchased from Wako Chemical Inc. All compounds given
below bear the same formula numbers as used in the main body.
Compounds unlabeled in the main body are labeled with letters
* Corresponding author. Tel.: þ81 11 706 9157; fax: þ81 11 706 9156.
** Corresponding author.
E-mail address: yasuhito.koyama@cat.hokudai.ac.jp (Y. Koyama).
0032-3861/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2013.06.020

4502
S. Cheawchan et al. / Polymer 54 (2013) 4501e4510
Fig. 1. Synthetic strategy for MKP and its subsequent modification to enable grafting and cross-linking using an ambident agent having nitrile N-oxide and masked ketene
functionalities.
[AeE]. Compound A was prepared according to the literature [33].
Other reagents and solvents commercially available were used
without further purification unless otherwise noted.
columns TOSO TSK gel GMHXL and G5000HXL at 30 ꢀC. TGAs were
carried out on a Shimadzu TGA-50 instrument at N2 atmosphere
(flow rate of 50 mL/min) to determine 5% weight decomposition
temperature (Td5) at which 5% weight loss was observed. DSC an-
alyses were carried out with a Shimadzu DSC-60 instrument at N2
atmosphere (flow rate of 50 mL/min) with liquid N2 as a refrigerant
to determine glass transition temperature (Tg).
2.2. Characterization
1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were
recorded on a JEOL AL-400 spectrometers using tetramethylsilane
as an internal standard. MALDIeTOF MS spectra were measured
with a Shimadzu AXIMA-CFR mass spectrometer using a dithranol
matrix. Melting points were measured with a Stuart Scientific
SMP3. SEC analyses were carried out on JASCO PU-2080 plus pump
with a JASCO UV-1570 (UV detector) and JASCO RI-1530 (RI
detector) equipped with a consecutive linear polystyrene gel
2.3. Synthesis of new cascade functionalization agent 1
2.3.1. Synthesis of alcohol B
2-Hydroxy-1-naphthaldehyde (5.00 g, 29.0 mmol) was
dissolved in DMF (146 mL) at room temperature. K2CO3 (4.81 g,
35.0 mmol) and 6-chlorohexanol (4.50 mL, 32.0 mmol) were
O
OH
Cl
Cl
CHO
CHO
CHO
O
K2CO3
Et3N
OH
O
O
OH
O
CH2Cl2
rt, 10 min
88%
DMF, 100 °C, 5.5 h
86%
B
C
O
O
OH
N
O
O
A
NH2OH·HCl
CHO
O
O
O
NaOAc
CH3COONa
O
O
O
O
O
O
O
THF–i-PrOH (2:1)
rt, 1.5 h
t-BuOH, 60 °C, 31 h
O
O
99%
O
O
99%
D
E
O–
N
C
NCS
Et3N
O
O
CHCl3
0 °C, 3.5 h
95%
O
O
O
O
O
1
Scheme 1. Synthetic pathway of 1.

S. Cheawchan et al. / Polymer 54 (2013) 4501e4510
4503
added into the solution and the mixture was stirred at 100 ꢀC for
5.5 h, and cooled to room temperature. The mixture was diluted
with CH2Cl2 and washed with water. The products were extracted
with CH2Cl2 (200 mL, 3 times). The combined organic layer was
washed with brine, dried over MgSO4, filtered, and concentrated in
vacuo. The crude was purified by a flash column chromatography
on silica gel (hexane:ethyl acetate ¼ 1:1) to afford the product (B)
as bright brown solids (2.8 g, 69% yield); m.p. 81.1e83.4 ꢀC; 1H NMR
conjugated with aromatic)), 1512 (CH2(alkane)), 1269-1155 (CeO,
as, Ar-O-R) cmꢁ1; MALDIeTOF MS (m/z) calc’d for C33H36O8Naþ
[M þ Na]þ, 583.23; found, 583.11.
2.3.4. Synthesis of oxime E
Compound D (2.0 g, 3.57 mmol) was dissolved in a mixed
solvent of THF and i-PrOH (2:1, 30.6 mL). A solution of hydrox-
ylammonium chloride (281.1 mg, 3.92 mmol) and sodium acetate
trihydrate (542.1 mg, 3.92 mmol) in water (5.1 mL) was added
dropwise into the solution of D at 0 ꢀC during stirring for 30 min.
The mixture was warmed to room temperature and stirred for 1 h.
The mixture was diluted with EtOAc (30 mL), and washed with
water three times. The organic layer was washed with brine, dried
over MgSO4, filtered, and concentrated in vacuo to give E as yellow
(400 MHz, CDCl3, 298 K)
d
10.93 (s, 1H), 9.28 (d, J ¼ 8.6 Hz, 1H), 8.04
(d, J ¼ 9.0 Hz, 1H), 7.77 (d, J ¼ 8.0 Hz, 1H), 7.62 (dd, J ¼ 8.6, 7.1 Hz,
1H), 7.42 (dd, J ¼ 8.0, 7.1 Hz, 1H), 7.28 (d, J ¼ 9.0 Hz, 1H), 4.24 (t,
J ¼ 6.4 Hz, 2H), 3.68 (t, J ¼ 6.4 Hz, 2H), 1.95e1.44 (m, 8H) ppm; 13C
NMR (100 MHz, CDCl3, 298 K)
d 192.2, 163.5, 137.5, 131.5, 128.4,
128.2, 124.9, 124.7, 119.0, 116.2, 113.5, 69.7, 62.8, 42.6, 39.3, 25.9,
25.5 ppm; IR (NaCl) 3416 (OeH), 2936 (CeH(aromatic)), 2865 (Ce
y
solids (2.03 g, 99% yield); 1H NMR (400 MHz, CDCl3, 298 K)
d 8.88 (s,
H(aliphatic)), 2800 (CeH, aldehyde), 1669 (C]O(ether)), 1513
(CH2(alkane)), 1246 (CeO, as, Ar-O-R) cmꢁ1; MALDIeTOF MS (m/z)
calc’d for C17H20O3Na [M þ Na]þ, 295.13; found, 294.49.
1H), 8.77 (d, J ¼ 8.8 Hz, 1H), 7.85 (d, J ¼ 9.0 Hz, 1H), 7.77 (d,
J ¼ 8.0 Hz, 1H), 7.51 (dd, J ¼ 8.8, 7.1 Hz, 1H), 7.38 (dd, J ¼ 8.0, 7.1 Hz,
1H), 7.27e7.17 (m, 6H), 4.17e4.09 (m, 4H), 3.34 (s, 2H), 2.49 (t,
J ¼ 8.9 Hz, 2H), 2.37 (t, J ¼ 8.9 Hz, 2H), 1.88e1.46 (m, 11H), 0.65 (s,
2.3.2. Synthesis of acrylate C
3H) ppm; 13C NMR
d (100 MHz, CDCl3, 298K) d 171.5, 168.6, 156.5,
To a solution of alcohol B (3.00 g, 11 mmol) and acryloyl chloride
(1.80 mL, 22 mmol) in CH2Cl2 (15 mL) was added dropwise Et3N
(3.06 mL, 22 mmol) by dropping at 0 ꢀC. The solution was stirred at
room temperature for 10 min. The reaction was quenched by the
addition of sat. aq. NaHCO3. The products were extracted with
CH2Cl2. The combined organic layer was dried over MgSO4, filtered,
and concentrated in vacuo. The crude was purified by a flash col-
umn chromatography on silica gel (hexane:ethyl acetate ¼ 1:1) to
give the product C as bright yellow solids (2.37 g, 88% yield); m.p.
148.0, 135.1, 132.2, 131.8, 130.6, 129.2, 129.1, 128.5, 125.7, 125.7,
124.2, 114.7, 114.0, 106.3, 106.3 69.6, 65.1, 56.6, 43.8, 30.2, 29.5, 29.4,
28.9, 28.6, 28.0, 26.0, 25.8 ppm; IR (NaCl) y 3445 (OeH), 2940 (CeH
(aromatic)), 2868 (CeH (aliphatic)), 1770, 1733 (C]O(ester)), 1652
(C]N), 1270 (CeO, as, Ar-O-R) cmꢁ1; MALDIeTOF MS (m/z) calc’d
for C33H37NO8Naþ [M þ Na]þ, 598.24; found, 597.39.
2.3.5. Synthesis of cascade functionalization agent 1
Compound E (2.03 g, 3.53 mmol) was dissolved in CHCl3 (35 mL)
41.8e42.9 ꢀC; 1H NMR (400 MHz, CDCl3, 298 K)
d
10.93 (s, 1H), 9.28
at 0 ꢀC. Et3N (690
mL) was added to the mixture. N-Chlor-
(d, J ¼ 8.6 Hz, 1H), 8.04 (d, J ¼ 9.0 Hz, 1H), 7.77 (d, J ¼ 8.0 Hz, 1H),
7.62 (dd, J ¼ 8.6, 7.1 Hz, 1H), 7.42 (dd, J ¼ 8.0, 7.1 Hz, 1H), 7.28 (d,
J ¼ 9.0 Hz, 1H), 6.43 (d, J ¼ 9.0 Hz, 1H), 6.38 (dd, J ¼ 12.0 Hz, 1H),
5.82 (d, J ¼ 9.0 Hz, 1H), 4.24e4.17 (m, 4H), 1.93e1.48 (m, 8H) ppm;
osuccinimide (577.9 mg, 4.24 mmol) was portionwised into the
solution, and the mixture was continually stirred at 0 ꢀC for 3.5 h.
The reaction was quenched by pouring into water (30 mL). The
products were extracted with CHCl3. The combined organic layer
was washed with water 2 times, brine, dried over MgSO4, filtered,
and concentrated in vacuo to obtain 1 as a bright yellow oil (1.92 g,
13C NMR (100 MHz, CDCl3, 298 K)
d 192.6, 166.8, 164.0, 138.1, 132.0,
131.1, 130.3, 129.3, 129.0, 127.3, 125.4, 117.1, 117.1, 113.9, 69.8, 64.9,
29.7, 29.0, 28.2, 26.2 ppm; IR (NaCl) 2940 (CeH(aromatic)), 2865
y
95% yield); 1H NMR (400 MHz, CDCl3, 298 K)
d
7.98 (d, J ¼ 8.8 Hz,
(CeH(aliphatic)), 2800 (CeH, aldehyde), 1730 (C]O(ester conju-
gated with C]C)), 1671 (C]O(aldehyde conjugated with aro-
1H), 7.93 (d, J ¼ 9.0 Hz, 1H), 7.82 (d, J ¼ 8.3 Hz, 1H), 7.60 (dd, J ¼ 8.9,
7.1 Hz, 1H), 7.43 (dd, J ¼ 8.3, 7.0 Hz, 1H), 7.27e7.17 (m, 6H), 4.22 (t,
J ¼ 6.6 Hz, 2H), 4.11 (t, J ¼ 6.8 Hz, 2H), 3.34 (s, 2H), 2.50 (t, J ¼ 8.8 Hz,
2H), 2.38 (t, J ¼ 8.1 Hz, 2H), 1.93e1.47 (m, 11H), 0.67 (s, 3H) ppm; 13C
matic)), 1512 (CH2(alkane)), 1246e1153 (CeO, as, Ar-O-R) cmꢁ1
;
MALDIeTOF MS (m/z) calc’d for C20H22O4Na [M þ Na]þ, 349.14;
found, 348.69.
NMR (100 MHz, CDCl3, 298 K) d 171.5, 168.6, 161.0, 135.2, 132.9,
130.6, 130.6, 129.1, 128.9, 128.5, 128.1, 128.1, 125.1, 124.1, 113.4, 106.2,
106.2, 69.6, 65.1, 56.6, 43.8, 30.2, 29.5, 29.2, 28.9, 28.6, 28.6, 25.8,
2.3.3. Synthesis of aldehyde D
Compound C (2.41 g, 7.39 mmol) and Meldrum’s acid derivative
(A) (4.31 g, 18.4 mmol) were dissolved in t-BuOH (15 mL). Sodium
acetate trihydrate (5.03 g, 37.0 mmol) was added to the mixture and
the mixture was stirred at 60 ꢀC for 31 h. The mixture was cooled to
room temperature, and poured into EtOAc. The solution was
washed with water and the aqueous layer was extracted with
EtOAc. The combined organic layer was washed with brine, dried
over by MgSO4, filtered, and concentrated in vacuo. The crude was
25.8 ppm; IR (NaCl) y 2941 (CeH(aromatic)), 2868 (CeH(aliphatic)),
2292 (C^N), 1771, 1739 (C]O(ester)), 1274 (CeO, as, Ar-O-R) cmꢁ1
;
MALDIeTOF MS (m/z) calc’d for C33H35NO8Naþ [M þ Na]þ, 596.23;
found, 595.38 .
2.4. Synthesis of model compounds obtained by using cascade
functionalization agent 1
purified by
a
flash column chromatography on silica gel
2.4.1. Synthesis of oxadiazole 2
(hexane:EtOAc ¼ 5:3) to give D as bright yellow solids (4.12 g, 99%
Compound 1 (50 mg, 87.2 mmol) was dissolved in CHCl3 (0.5 mL).
yield); m.p. 107.0e107.5 ꢀC; 1H NMR (400 MHz, CDCl3, 298 K)
Isobutyronitrile (78.3 mL, 872 mmol) was added to the mixture. The
d
10.93 (s, 1H), 9.28 (d, J ¼ 8.6 Hz, 1H), 8.04 (d, J ¼ 9.0 Hz, 1H), 7.77
mixture was stirred at 60 ꢀC for 1 d, cooled to room temperature,
(d, J ¼ 8.0 Hz, 1H), 7.62 (dd, J ¼ 8.6, 7.1 Hz, 1H), 7.42 (dd, J ¼ 8.0,
7.1 Hz, 1H), 7.30e7.17 (m, 6H), 4.24 (t, J ¼ 6.3 Hz, 2H), 4.11 (t,
J ¼ 6.8 Hz, 2H), 3.34 (s, 2H), 2.50 (t, J ¼ 7.3 Hz, 2H), 2.38 (t, J ¼ 7.3 Hz,
2H), 1.94e1.46 (m, 11H), 0.67 (s, 3H) ppm; 13C NMR (100 MHz,
and concentrated in vacuo to give 2 (56.0 mg, 92% yield) as an
yellow oil; 1H NMR (400 MHz, CDCl3, 298 K)
d
7.95 (d, J ¼ 9.2 Hz,
1H), 7.81 (d, J ¼ 8.1 Hz, 1H), 7.62 (d, J ¼ 8.6 Hz, 1H), 7.44 (dd, J ¼ 8.1,
7.0 Hz, 1H), 7.39e7.17 (m, 7H), 4.13 (t, J ¼ 6.5 Hz, 2H), 4.06 (t,
J ¼ 6.5 Hz, 2H), 3.41e3.34 (m, 1H), 3.34 (s, 2H), 2.49 (t, J ¼ 8.7 Hz,
2H), 2.36 (t, J ¼ 8.7 Hz, 2H),1.75e1.36 (m,17H), 0.65 (s, 3H) ppm; 13C
CDCl3, 298 K)
d 192.2, 171.5, 168.5, 163.8, 137.7, 135.1, 130.5, 130.5,
129.0, 129.0, 128.4, 128.1, 125.1, 124.9, 113.6, 133.6, 133.6, 106.2, 69.5,
65.0, 56.6, 43.8, 30.1, 29.5, 29.4, 28.9, 28.6, 27.9, 25.9, 25.8 ppm; IR
NMR (100 MHz, CDCl3, 298 K)
d 183.6, 171.3, 168.4, 165.4, 155.9,
(NaCl)
y
2941 (CeH(aromatic)), 2868 (CeH(aliphatic)), 2798 (CeH,
135.0, 133.2, 132.2, 132.2, 130.4, 128.9, 128.7, 128.0, 127.5, 127.4,
124.1, 114.4, 110.8, 106.1, 69.5, 65.0, 56.5, 43.6, 35.3, 30.0, 30.0, 29.4,
aldehyde), 1770, 1733 (C]O(ester)), 1673 (C]O(aldehyde

4504
S. Cheawchan et al. / Polymer 54 (2013) 4501e4510
O–
N
C
O
N
N
Ph
O
Ph
O
C
N
O
O
O
O
O
O
O
O
O
O
CHCl3
60 °C, 1 d
92%
O
O
1
2
catalyst-free
TMS
TMS
O
N
CHCl3, 60 °C, 1 d
90%
O
OMe
O
H2N
catalyst-free
O
Ph
OMe
Ph
O
DMF
NH
160 °C, 12 h
4
TMS
O
N
85%
catalyst-free
Ph
O
O
O
O
O
O
O
TMS
3
O
N
O
O
O
HO
O
O
O
DMF
160 °C, 6 h
60%
O
5
catalyst-free
O
O
Scheme 2. Catalyst-free ligation between unsaturated bond and nucleophile using 1.
29.1, 28.8, 28.5, 27.6, 25.6, 20.3 ppm; IR (NaCl)
y
2938 (CeH(aro-
in to give 4 as a bright yellow oil (35.7 mg, 85% yield); 1H NMR
(400 MHz, CDCl3, 298 K)
8.02 (d, J ¼ 8.6 Hz, 1H), 7.87 (d, J ¼ 9.0 Hz,
matic)), 2867 (CeH(aliphatic)),1772,1738 (C]O(ester)),1271 (CeO,
as, Ar-O-R), 1624 (C]N) cmꢁ1; MALDIeTOF MS (m/z) calc’d for
C37H42N2O8Naþ [M þ Na]þ, 665.28; found, 665.41.
d
1H), 7.78 (d, J ¼ 8.2 Hz, 1H), 7.47 (dd, J ¼ 7.0, 8.6 Hz, 1H), 7.36 (dd,
J ¼ 7.0, 8.2 Hz, 1H), 7.27e7.13 (m, 6H), 6.87 (d, J ¼ 8.8 Hz, 2H), 6.74
(d, J ¼ 8.8 Hz, 2H), 4.93e4.88 (m, 1H), 4.33 (d, J ¼ 6.2 Hz, 2H), 4.30
(d, J ¼ 6.2 Hz, 2H), 4.13 (t, J ¼ 6.7 Hz, 2H), 4.05 (t, J ¼ 4.2 Hz, 2H), 3.77
(s, 3H), 3.41 (dddd, J ¼ 2.5, 2.5, 2.4, 2.4 Hz, 1H), 3.01e2.90 (m, 3H),
2.75 (d, J ¼ 6.2 Hz, 2H), 2.72 (d, J ¼ 6.2 Hz, 2H), 2.42e2.36 (m, 2H),
2.32e2.23 (m, 1H), 2.06e2.02 (m, 2H), 1.84e0.86 (m, 10H), 0.11 (s,
2.4.2. Synthesis of isoxazoline 3
Compound 1 (50 mg, 87.2
Allytrimethysilane (141.3
m
mol) was dissolved in CHCl3 (0.5 mL).
m
L) was added to the mixture. The
mixture was stirred at 60 ꢀC for 1 d, cooled to room temperature,
and concentrated in vacuo to give 3 as a mixture of the target
product (3) (59.3 mg, 90% yield) and the regio-isomer (10%). 3: 1H
3H), ppm; 13C NMR (100 MHz, CDCl3, 298 K)
d 174.7, 174.3, 154.4,
137.7,137.0,135.0,132.1,130.1,130.0,129.9,129.9,129.4,129.4,129.0,
128.3, 127.3, 125.4, 125.0, 114.8, 114.8, 80.6, 70.2, 65.4, 56.5, 54.4,
50.0, 47.0, 43.8, 40.1, 32.9, 30.7, 30.4, 29.5, 28.9, 26.8, 25.1, 0.0 ppm;
NMR (400 MHz, CDCl3, 298 K)
d
8.04 (d, J ¼ 8.8 Hz, 1H), 7.87 (d,
J ¼ 9.0 Hz, 1H), 7.78 (d, J ¼ 8.0 Hz, 1H), 7.48 (dd, J ¼ 8.8, 7.3 Hz, 1H),
7.43 (dd, J ¼ 8.0, 7.3 Hz, 1H), 7.27e7.17 (m, 6H), 5.29e4.87 (m, 1H),
4.16e4.07 (m, 4H), 3.42 (dd, J ¼ 9.4, 9.3 Hz, 2H), 3.33 (s, 2H), 2.99
(dd, J ¼ 9.4, 9.3 Hz, 2H), 2.49 (t, J ¼ 7.2 Hz, 2H), 2.37 (t, J ¼ 7.2 Hz,
2H), 1.86e1.39 (m, 12H), 1.14 (dd, J ¼ 8.9, 8.8 Hz, 1H), 0.67 (s, 3H),
IR (NaCl)
y 3300 (NeH), 2931 (CeH(aromatic)), 2849 (Ce
H(aliphatic)), 1733 (C]O(ester)), 1646 (C]O(amide)), 1248 (CeO)
cmꢁ1; MALDIeTOF MS (m/z) calc’d for C43H54N2O6SiNaþ [M þ Na]þ,
745.37; found, 745.29.
0.12 (s, 9H) ppm; 13C NMR (100 MHz, CDCl3, 298 K)
d 172.2, 169.4,
156.2, 155.8, 135.9, 133.6, 132.1, 131.4, 131.4, 129.9, 129.9, 128.9,
128.3, 125.4, 124.9, 114.8, 114.7, 107.1, 80.6, 70.1, 65.9, 57.4, 47.2, 44.6,
2.4.4. Synthesis of 5
Isoxazoline 3 (25 mg, 36.4
mmol) was dissolved in DMF (374
mL).
36.2, 30.3, 29.7, 26.8, 26.8, 26.7, 26.7, 25.1, 25.1, 0.0 ppm; IR (NaCl)
y
Diethylene glycol monomethyl ether (42.8
m
L, 364 mol) was added
m
2940 (CeH(aromatic)), 2859 (CeH(aliphatic)), 1769, 1742 (C]
O(ester)),1270 (CeO, as, Ar-O-R) cmꢁ1; MALDIeTOF MS (m/z) calc’d
for C39H49NO8SiNaþ [M þ Na]þ, 710.31; found; Td5 248 ꢀC.
to the mixture. The mixture was refluxed for 8 h, cooled to room
temperature, and concentrated in vacuo. The crude was purified by
a flash column chromatography on silica gel (CH2Cl2) in to give 5 as
a bright yellow oil (15.4 mg, 60% yield); 1H NMR (400 MHz, CDCl3,
2.4.3. Synthesis of 4
Isoxazoline 3 (40 mg, 58.2
4-Methoxybenzylamine (76.0
mixture. The mixture was refluxed for 12 h, cooled to room tem-
perature, and concentrated in vacuo. The crude was purified by a
flash column chromatography on silica gel (CH2Cl2:MeOH ¼ 10:1)
298 K)
d
8.04 (d, J ¼ 8.3 Hz, 1H), 7.87 (d, J ¼ 9.0 Hz, 1H), 7.78 (d,
m
mol) was dissolved in DMF (116
m
L).
J ¼ 8.3 Hz, 1H), 7.48 (dd, J ¼ 8.3, 7.3 Hz, 1H), 7.36 (dd, J ¼ 8.3, 7.3 Hz,
1H), 7.26e7.15 (m, 6H), 4.95e4.87 (m, 1H), 4.18 (t, J ¼ 4.6 Hz, 2H),
4.13 (t, J ¼ 6.4 Hz, 2H), 4.06 (t, J ¼ 6.6 Hz, 2H), 3.59e3.50 (m, 9H),
3.36 (s, 3H), 3.01e2.95 (m, 1H), 2.78 (t, J ¼ 6.1 Hz, 2H), 2.38e2.30
(m, 1H), 1.85e0.88 (m, 12H), 0.12 (s, 9H), ppm; 13C NMR (100 MHz,
m
L, 582 mol) was added to the
m

S. Cheawchan et al. / Polymer 54 (2013) 4501e4510
4505
CDCl3, 298 K)
d
175.7, 173.9, 156.2, 155.8, 139.8, 133.6, 132.0, 129.9,
room temperature, and dissolved with CHCl3, and poured into
MeOH to give precipitates. The precipitates were collected by
filtration and dried in vacuo to give the Meldrum’s acid-function-
alized EPDM (99% yield, 64% conversion) as an yellow rubber; 1H
129.9, 129.4, 129.0, 128.3, 127.4, 125.4, 125.0, 114.8, 114.5, 80.6, 72.8,
71.4, 70.2, 70.0, 65.4, 64.4, 60.1, 47.6, 47.0, 39.3, 32.8, 30.7, 30.7, 30.4,
29.6, 27.8, 26.8, 0.0 ppm; IR (NaCl)
y 2924 (CeH(aromatic)), 2849
(CeH(aliphatic)), 1733 (C]O(ester)), 1248 (CeO, as, Ar-O-R) cmꢁ1
;
NMR (400 MHz, CDCl3, 298 K) d 8.07e7.17 (m), 5.25e5.02 (m),
MALDIeTOF MS (m/z) calc’d for C40H55NO8SiNaþ [M þ Na]þ,
4.22e4.11 (m), 3.34 (s), 2.47e0.83 (m), 0.66 (s) ppm; IR (KBr) y 1735
728.36; found, 728.18.
(C]O(ester)), 1261 (CeO, as, Ar-O-R) cmꢁ1; Td5 309 ꢀC; Tg ꢁ17 ꢀC.
2.5. Typical procedure for polymer modification using 1
2.6. Typical procedure for grafting-onto reaction
2.5.1. Typical procedure for modification of PAN with 1 under
solution reaction (Table 1, entry 2)
2.6.1. Typical procedure for grafting reaction of PEG onto EPDM
Meldrum’s acid-functionalized EPDM (25 mg, 19.8
conversion) was dissolved in mesitylene (632 L). To the solution
was added MeOPEGOH (Mn 350) (63.4 L, 19 mol) and CaSO4
mmol, 64%
A solution of PAN (Mw 150,000) (50 mg, 943.4
mmol) and 1
m
(54.0 mg, 94.2
m
mol) in DMF (2.0 mL) was stirred at 60 ꢀC for 3 d.
m
m
The mixture was cooled to room temperature, and precipitated into
H2O, washed again with CHCl3. The precipitates were collected by
filtration and dried in vacuo to give the Meldrum’s acid-function-
alized PAN (99% yield, 35% conversion) as a white solid; 1H NMR
(63.2 mg). The mixture was stirred at room temperature for 1 h and
heated at 160 ꢀC for 9 h. The solution was cooled to room tem-
perature, and poured into water to give precipitates. The pre-
cipitates were collected by filtration, and the filtrate was washed
with H2O and MeOH and dried in vacuo to give the PEG-grafted
EPDM (99% yield, 98% conversion of Meldrum’s acid); 1H NMR
(400 MHz, DMSO, 298 K)
d 8.03e7.03 (m), 4.12e4.39 (m), 3.32 (m),
3.25e3.13 (m), 2.65 (s), 2.44e2.02 (m), 1.67e1.23 (m), 0.70 (s) ppm;
IR (KBr)
y 2243 (C^N), 1735 (C]O(ester)), 1453 (He C^N), 1270
(400 MHz, CDCl3, 298 K) d 8.14e6.95 (m), 5.25e5.02 (m), 4.34e4.23
(CeO, as, Ar-O-R) cmꢁ1; Td5 287 ꢀC; Tg 105 ꢀC.
(m), 3.92e3.46 (m), 2.45e0.88 (m) ppm; IR (KBr)
y 1260 (CeO, as,
Ar-O-R), cmꢁ1; Td5 217 ꢀC; Tg ꢁ18 ꢀC.
2.5.2. Typical procedure for modification of NR with 1 under
solution reaction (entry 4)
2.6.2. Typical procedure for one-pot grafting reaction of PEG onto
PAN
NR (Mw 1,250,000) (50 mg, 0.735 mmol) was dissolved in CHCl3
(0.5 mL) overnight. Compound 1 (42.1 mg, 74 mmol) was added to
A mixture of PAN (50 mg, 943.4
m
mol), 1 (54.1 mg, 94.3
mmol),
the mixture. The solution was stirred at 60 ꢀC for 3 d. The solution
was cooled to room temperature, and poured into MeOH to give
precipitates. The precipitates were collected by filtration and dried
in vacuo to give the Meldrum’s acid-functionalized NR (99% yield,
MeOPEGOH (Mn 350, 330.2 L, 943.4
m
mmol), and CaSO4 (100 mg) in
DMF (1.0 mL) was stirred at room temperature for 1 h. The mixture
was warmed to 60 ꢀC and stirred for 1 d. The reaction temperature
was elevated to 160 ꢀC and stirred for 12 h. The mixture was cooled
to room temperature, filtered, and poured into water to give
precipitates. The precipitates were collected by filtration and the
filtrate was washed with H2O and CHCl3 and dried in vacuo to give
the PEG-grafted PAN (249.2 mg, 99% yield, 27% conversion for the
1,3-dipolar cycloaddition, 97% conversion for the grafting reaction);
16% conversion); 1H NMR (400 MHz, CDCl3, 298 K)
d
8.08e7.19 (m),
5.12 (s), 4.22e4.11 (m), 3.34 (s), 2.47e1.25 (m), 0.66 (s) ppm; IR
(NaCl)
y
1737 (C]O(ester)), 1270 (CeO, as, Ar-O-R) cmꢁ1; Td5
213 ꢀC; Tg ꢁ23 ꢀC.
1H NMR (400 MHz, DMSO, 298 K)
3.59 (s), 3.48e3.12 (m), 2.75 (s), 2.44e2.02 (m), 1.67e1.23 (m) ppm;
d 8.31e7.17 (m), 4.12e4.03 (m),
2.5.3. Typical procedure for modification of NR with 1 under solid-
state reaction (entry 7)
NR (Mw 1,250,000) (50 mg, 735 mmol) and 1 (42.1 mg, 74 mmol)
IR (KBr)
y 2243 (C^N), 1600 (C]O(ester)), 1453 (HeC^N), 1270
were ground in a mortar at 70 ꢀC for 2 h. The mixture was cooled to
room temperature, and dissolved with CHCl3, and poured into
MeOH to give precipitates. The precipitates were collected by
filtration and dried in vacuo to give the Meldrum’s acid-function-
alized NR (99% yield, 37% conversion) as a yellow solid; 1H NMR
(CeO, as, Ar-O-R) cmꢁ1; Td5 292 ꢀC; Tg 133 ꢀC.
2.7. Typical procedure for cross-linking reaction of Meldrum’s acid-
functionalized polymer: synthesis of cross-linked NR
(400 MHz, CDCl3, 298 K)
d 8.08e7.19 (m), 5.12 (s), 4.22e4.11 (m),
NR with 16% Meldrum’s acid functionality (15.0 mg, 0.1 mmol)
was dissolved in CHCl3. The mixture was placed to Teflon plate and
heated at 40 ꢀC to give a self-standing film. The film was heated at
250 ꢀC for 1 h under N2 to give the cross-linked polymer. The cross-
linked polymer was purified by swelling in toluene to remove the
unreacted materials, and gently dried at room temperature for 1 d to
give the corresponding cross-linked NR (11.4 mg). To evaluate the
cross-linking efficiency, the cross-linked polymer was immersed into
toluene overnight to give the swollen gel (swelling ratio: 1300%). The
cross-linking density (v, mol/cm3) was calculated by the modified
FloryeRehner equation [34] to evaluate that the interchain reaction
efficiency of Meldrum’s acid moieties on the cross-linking reaction
was 25%: By the following FloryeRehner equation, the cross-linking
density (v) was calculated to be 1.31 ꢂ 10ꢁ5 mol/cm3.
3.34 (s), 2.47e1.25 (m), 0.66 (s) ppm; IR (KBr) y 1737 (C]O(ester)),
1270 (CeO, as, Ar-O-R) cmꢁ1; Td5 213 ꢀC; Tg ꢁ23 ꢀC.
2.5.4. Typical procedure for modification of NBR with 1 under solid-
state reaction (entry 8)
NBR (acrylonitrile: 33%, 50 mg, 930.7
mmol) and 1 (53.4 mg,
93.7
m
mol) were ground in a mortar at 70 ꢀC for 2 h. The mixture
was cooled to room temperature, and dissolved with CHCl3, and
poured into MeOH to give precipitates. The precipitates were
collected by filtration and dried in vacuo to give the Meldrum’s
acid-functionalized NBR (99% yield, 85% conversion) as an yellow
solid; 1H NMR (400 MHz, CDCl3, 298 K)
d
7.97e7.18 (m), 5.54e5.41
(m), 5.11e4.97 (m), 4.15e4.09 (m), 3.66e3.49 (m), 3.33 (s), 2.59e
1.16 (m), 0.66 (s) ppm; IR (KBr)
y 2235 (C^N), 1739 (C]O(ester)),
1267 (CeO, as, Ar-O-R) cmꢁ1; Td5 332 ꢀC; Tg ꢁ3.4 ꢀC.
"
#
ꢀ
ꢁ
ln 1 ꢁ VR þ VR þ
m
VR2
g
V
v ¼ ꢁ
;
2.5.5. Typical procedure for modification of EPDM with 1 under
solid-state reaction (entry 9)
g2=3VR2=3 ꢁ VR=2
EPDM (ENB: 10%, 50 mg, 115
mmol) and 1 (38.2 mg, 115
m
mol)
where v, V, g,
volume of the solvent (toluene: 106.3 cm3/mol), volume fraction of
m
, and VR are cross-linking density (mol/cm3), molar
were ground in a mortar at 70 ꢀC for 2 h. The mixture was cooled to

4506
S. Cheawchan et al. / Polymer 54 (2013) 4501e4510
Fig. 2. 1H NMR spectra of (A) 1, (B) 3, and (C) 5 (400 MHz, CDCl3, 298 K).
cross-linked gel (1.003), interaction parameter between polymer
and solvent (natural rubberetoluene: 0.39), and volume fraction of
polymer in the gel (6.19 ꢂ 10ꢁ2), respectively. Therefore, the
interchain reaction efficiency of Meldrum’s acid moieties on the
cross-linking reaction would be described with the following
equation:
corresponding adducts 4 and 5 in high yields without a catalyst.
It should be noted that 1 enables catalyst-free ligation between
the unsaturated bond and not only a nucleophilic amine but also
a neutral alcohol with low nucleophilicity. Fig. 2 shows 1H NMR
spectra of (A) 1, (B) 3, and (C) 5. In the spectrum (B), the
appearance of the signals originating from the isoxazoline
ꢂ
ꢀ
ꢁꢃ
ꢂ
ꢀ
ꢁꢃ
observed cross-linking density mol=cm3 ꢂ sample volume cm3
½expected mol of cross-linking point as 100% efficiency ðmolÞꢃ
interchain reaction efficiency ð%Þ ¼
ꢂ ½yieldꢃ
3. Results and discussion
skeleton protons and TMS protons afforded the direct evidence
for the formation of 3. In the spectrum (C), the characteristic
3.1. Model study of 1
signals of diethylene glycol monomethyl ether (a, b, g, d, and
OMe) along with the disappearance of signals of geminal
dimethyl protons of Meldrum’s acid moiety support the for-
mation of 5. The ratio of 1H NMR integrals of TMS protons, the
isoxazoline protons, and the protons from the alcohol as a
nucleophile clearly indicates that the cascade functionalization
agent 1 served as a molecular glue to mediate successfully the
ligation reaction between allyltrimethylsilane and diethylene
glycol monomethyl ether.
Before investigating the utility of 1 as an attachment tool for
common polymers, we performed model ligation reactions to
evaluate its reactivity toward the 1,3-dipolar cycloaddition reaction
of C]C and C^N groups and the subsequent nucleophilic substi-
tution to the thermally generated ketene moiety, as shown in
Scheme 2.
The treatment of
1
with isobutyronitrile or allyl-
trimethylsilane at 60 ꢀC without a catalyst produced the corre-
sponding heteroaromatics 2 and 3 in high yields, indicating
adequate reactivity of the nitrile N-oxide moiety of 1 to C^N
and C]C bonds. The subsequent catalyst-free nucleophilic
attack at the thermally generated ketene of 3 was examined
using an amine and an alcohol. Since the gradual weight loss of
3 (attributed to the elimination of acetone and CO2 from the
masked ketene moiety [35]) was observed at around 160 ꢀC by
thermogravimetric analysis (TGA), we conducted the nucleo-
philic modification at this temperature. As a result, refluxing a
3.2. Synthesis of functionalized polymers
On the basis of these results, we next investigated the
reactions of various unsaturated-bond-containing polymers with 1
(Scheme 3). The results are summarized in Table 1.
The reaction in DMF using 0.1 equiv of 1 per repeating unit of
polyacrylonitrile (PAN) at 60 ꢀC for 24 h resulted in the formation of
oxadiazole-containing polymer (Table 1, entries 1 and 2). Increasing
the reaction time increased the conversion percentage for the
cycloaddition reaction but only up to a maximum of 35% (entry 2).
mixture of
3 and the nucleophiles in DMF produced the

S. Cheawchan et al. / Polymer 54 (2013) 4501e4510
4507
C
N
C
N
O
N
O
N
N
O
N
N
R
Ph
O
R
C
N
Ph
O
C
N
R
Ph
O
O
O
O
O
O
O
O
O
O
polyacrylonitrile
(PAN, Mw 150 kDa)
nitrile–butadiene rubber
(NBR, Mw 350 kDa)
O
R
Functionalized PAN
Functionalized NBR
1 (0.1 equiv)
catalyst-free
O
O
O
N
O
N
R
Ph
O
O
natural rubber
(NR, Mw 1,250 kDa)
ethylene–propylene–diene
terpolymer
(EPDM, Mw 350 kDa)
R
Ph
O
O
O
O
O
O
Functionalized EPDM
Functionalized NR
Scheme 3. Catalyst-free functionalization of unsaturated-bond-containing polymers using 1.
Table 1
The cycloaddition of 1 to natural rubber (NR) in CHCl3 gave the
corresponding functionalized NR in low conversion yields (entries 3
and 4), probably because of the low reactivity (caused by steric
hindrance) of the trisubstituted internal olefin in NR [22]. Through
considerable effort, it was found that the solvent-free press-
grinding of a mixture of NR and 1 enabled a more rapid cycload-
dition reaction with higher conversion of NR (21%) than in the
solution reactions (entries 3 and 4), even when the reaction is
performed at room temperature (entry 5).
In addition, a prolonged reaction time at room temperature or
an elevated reaction temperature (70 ꢀC) increased the conver-
sion yields (entry 6: 59%, entry 7: 37%). The reactions of two
commercially available elastomers, acrylonitrile-butadiene rub-
ber (NBR) and ethyleneepropyleneediene terpolymer (EPDM),
gave the corresponding modified polymers in high conversion
yields (entries 8 and 9). Such high conversion yields are probably
Functionalization of various polymers with 1.
Entry Polymer Reaction Temp. Time Conversion for
Functionalization
media
(ꢀC)
(h)
cycloadditiona (%) ratio of polymer
(%)
1b
2b
3b
4b
5b
6b
7b
8b
9d
PAN
PAN
NR
NR
NR
NR
NR
NBR
EPDM
DMF
DMF
CHCl3
CHCl3
ec
60
60
60
60
rt
24
72
24
72
2
72
2
2
25
35
12
16
21
59
37
2.5
3.5
1.2
1.6
2.1
5.9
3.7
ec
rt
ec
70
70
70
ec
Olefin: 90, CN: 76 Olefin: 9.0, CN: 7.6
64 64
ec
2
a
Estimated by 1H NMR.
Reaction was performed by using 0.1 equiv of 1.
Reaction was performed in the solid state.
1.0 equiv of 1 was used.
b
c
d
(i)
MeO
OH
PEG
(M 350, 10 equiv)
n
CaSO4
co
co
co
co
co
co
mesitylene
160 °C, 9 h
36
O
N
36
O
N
99% yield
98% conv.
for grafting reaction
R
Ph
O
R
O
O
Ph
OPEG
O
O
Functionalized EPDM
PEG-Graft EPDM
64
64
(0.1 equiv)
(ii)
1
MeO
OH
PEG
co
(M 350, 10 equiv)
n
CaSO4
C
N
O
N
N
DMF
C
N
60 °C, 1 d
then 160 °C, 12 h
R
PAN
O
99% yield
Ph
27% conv. for cycloaddition
OPEG
97% conv. for grafting reaction
PEG-Graft PAN
Scheme 4. (i) Catalyst-free grafting of PEG (Mn 350) onto masked-ketene-functionalized EPDM and (ii) one-pot grafting of PEG onto PAN.

4508
S. Cheawchan et al. / Polymer 54 (2013) 4501e4510
Fig. 3. 1H NMR spectra of (a) PAN, (b) functionalized PAN with 3% functionalization ratio, and (c) PEG-grafted PAN (400 MHz, DMSO-d6, 298 K).
attributed to the higher reactivity of the disubstituted olefin in
NBR and the exo-olefin in EPDM to the nitrile N-oxide of 1 in
comparison with the trisubstituted olefin in NR.
Having produced several masked-ketene-containing poly-
mers, we demonstrated the grafting reaction using monomethyl-
terminated polyethylene glycol (Scheme 4). We attempted the
treatment of masked-ketene-functionalized EPDM (64% conver-
sion) with 10 equiv of PEG in mesitylene at 160 ꢀC for 9 h. The
corresponding PEG-grafted EPDM was obtained with 50% graft-
ing conversion. On the other hand, when CaSO4 was added to the
In addition, we examined a one-pot grafting reaction of PEG
onto PAN. The step-by-step heating of a mixture of PAN, 0.1 equiv of
1, and PEG (60 ꢀC,1 d then 160 ꢀC) without a catalyst was performed
and the latter process at 160 ꢀC was monitored by using the SEC
profiles (Fig. 5). As a result, we found that the SEC change finished
in 12 h, indicating the completion of the addition reaction of PEG to
the polymer backbone. The longer reaction time of grafting reaction
than that from 3 to 5 (6 h, Scheme 1) could be probably attributed
to the steric repulsion between PEG as a nucleophile and PAN as a
trunk polymer.
reaction mixture as
reaction produced PEG-grafted EPDM in an excellent conver-
sion yield (98%).
a
dehydrating agent, the grafting-onto
Finally, we investigated the catalyst-free thermal cross-linking
of MKPs (Scheme 5). The cross-linking reactions of both PAN and
NR with masked ketene moieties efficiently proceeded at 250 ꢀC
(1 h) to give the respective cross-linked polymers as a solvent-
insoluble part. In the case of cross-linked NR, the density of the
network chain, cross-linking ratio, and efficiency of the cross-
linking reaction were estimated by a modified FloryeRehner
equation [34], based on the swelling ratio of the insoluble
polymer in toluene. As a result, it turned out that the interchain
reaction efficiency of Meldrum’s acid moieties on functionalized
NR was 25%.
The structure of PEG-grafted EPDM was determined by 1H NMR,
IR spectral analysis, and SEC. Fig. 3 shows 1H NMR spectra of (a)
PAN, (b) functionalized PAN with 3% functionalization ratio, and (c)
PEG-grafted PAN. In the spectrum (c), the signals originating from
PAN, the skeleton of 1, and PEG along with disappearance of the
protons attributed to the Meldrum’s acid moieties are in good
accordance with the formation of PEG-grafted PAN. From the in-
tegral ratio between the protons from 1 and the main chain protons
of PAN, we determined that the conversion for cycloaddition re-
action was 27%. In addition, we determined the conversion for
grafting reaction of PEG was 97%, which was calculated from the
integral ratio between the protons from 1 and the protons of PEG
considering the number average molecular weight of PEG (Mn 350).
It is noted that the conversion for the cycloaddition during the one-
pot grafting reaction is in a good agreement with that in the
absence of MeOePEGeOH (Table 1, entry 1, 25%), emphasizing that
the 1,3-dipolar cycloaddition of nitrile N-oxide and nucleophilic
substitution of PEG to the thermally generated ketene are not
competitive.
The SEC profiles of EPDM and PEG-grafted EPDM are shown in
Fig. 4. PEG-grafted EPDM appeared as a monomodal peak at an
elution time later than that of unreacted EPDM. This result indicates
a distinct structural change in EPDM, and it is consistent with a
stronger interaction between the polar graft chains on the polymer
and the SEC stationary phase.
Fig. 4. SEC profiles of EPDM (black line) and PEG-grafted EPDM (red line) (eluent:
DMF, 303 K). (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article.)

S. Cheawchan et al. / Polymer 54 (2013) 4501e4510
4509
Fig. 5. Time-dependent SEC change of PEG-Graft PAN during the one-pot grafting reaction of PEG onto PAN using 1 at 160 ꢀC (eluent: DMF, 303 K).
Scheme 5. Catalyst-free cross-linking of MKPs.
4. Conclusion
cascade functionalization agent possessing both nitrile N-oxide and
masked ketene functionalities serves as a molecular glue to mediate
the ligation reaction between unsaturated bonds and nucleophiles.
Theagentprovedcapableofcatalyst-freeclickintroductionofmasked
ketene moieties to the unsaturated bond-containing common poly-
mers to give the MKPs. Heating of the resulting MKPs in the presence
We have designed and developed a facile and widely applicable
protocol for obtaining MKPs from unsaturated-bond-containing
polymers via a catalyst-free click reaction and its subsequent modi-
fication to enable grafting and cross-linking. In this protocol, the

4510
S. Cheawchan et al. / Polymer 54 (2013) 4501e4510
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without a catalyst. On the other hand, heating of the MKPs in the
absence of nucleophile resulted in the formation of cross-linked
polymer based on the interchain dimerization reaction of Mel-
drum’s acid moieties to give cyclobutadiones at the cross-linking
points. The outcome would have broad applications not only to
post-modification and surface modification of highly processed
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Appendix A. Supplementary material
Supplementary material associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.polymer.
2013.06.020.
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