Synthesis of methacrylate polymer bearing cyanate groups and its chemoselective reaction with amines

Article abstract of DOI:10.1002/pola.27053

A novel reactive polymer containing cyanate groups in the side chain was prepared by free radical polymerization of a cyanate-containing monomer, 2-(4-cyanatophenyl)ethyl methacrylate (1). The monomer 1 and its polymer, poly[2-(4-cyanatophenyl)ethyl methacrylate] (PCPMA), were stable under the air for a long period. The copolymerization of 1 and methyl methacrylate provided the corresponding copolymers with various cyanate contents. The availability of the cyanate-containing polymers as a reactive polymer was investigated. Model reaction using 4-cyanatotoluene revealed that a cyanate group reacted with aliphatic amines, whereas no reaction occurred in the presence of water, alcohols, and aromatic amines under mild conditions. Post-functionalization of PCPMA was demonstrated using aliphatic amines or diamines. Copyright

Full text of DOI:10.1002/pola.27053

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
Synthesis of Methacrylate Polymer Bearing Cyanate Groups and Its
Chemoselective Reaction with Amines
Kousuke Tsuchiya, Takeshi Endo
Molecular Engineering Institute, Kinki University, 11-6 Kayanomori, Iizuka, Fukuoka 820–8555, Japan
Correspondence to: T. Endo (E-mail: tendo@moleng.fuk.kindai.ac.jp)
Received 21 May 2013; accepted 3 December 2013; published online 16 December 2013
DOI: 10.1002/pola.27053
ABSTRACT: A novel reactive polymer containing cyanate groups in
the side chain was prepared by free radical polymerization of a
cyanate-containing monomer, 2-(4-cyanatophenyl)ethyl methacry-
late (1). The monomer 1 and its polymer, poly[2-(4-cyanatopheny-
l)ethyl methacrylate] (PCPMA), were stable under the air for a long
period. The copolymerization of 1 and methyl methacrylate pro-
vided the corresponding copolymers with various cyanate con-
tents. The availability of the cyanate-containing polymers as
4-cyanatotoluene revealed that a cyanate group reacted with ali-
phatic amines, whereas no reaction occurred in the presence of
water, alcohols, and aromatic amines under mild conditions. Post-
functionalization of PCPMA was demonstrated using aliphatic
C
V
amines or diamines. 2013 Wiley Periodicals, Inc. J. Polym. Sci.,
Part A: Polym. Chem. 2014, 52, 699–706
KEYWORDS: crosslinking; functionalization of polymers; radical
a
reactive polymer was investigated. Model reaction using
polymerization
ing thermoset materials known as cyanate ester resins.9 The
cyanate ester resins consist of densely networked polycyanu-
rates formed by cyclotrimerization of cyanate groups. Their
excellent thermal, mechanical, and dielectric properties offer
the industrial uses in aerospace, insulation, microelectronics,
and adhesive. Blending the cyanate resins with the other
type of thermosets such as epoxy and polybenzoxazine res-
ins was also demonstrated to control their properties.10–14
In the case of the epoxy/cyanate mixture resin, the tough-
ness of the cured materials was improved by decreasing the
glass transition temperature (Tg) compared to cyanate ester
resins.12
INTRODUCTION Polymers containing reactive functional
groups have widely been developed for various applications
such as adhesives, coatings, and emulsion paints.1,2 Post-
functionalization at the reactive moieties in such polymers
allows sophisticated control in the physical properties
required for the applications. For example, isocyanate is one
of the reactive functional groups and has been introduced in
polymer backbones as a moiety, which reacts with various
functional groups such as alcohols and amines in a benign
condition. Among them, 2-isocyanatoethyl (meth)acrylate is a
commercially available monomer, and its polymer has widely
used in academic researches and industrial materials. Key
functionalizations or crosslinking reactions at the isocyanate
groups have been demonstrated for a wide range of diverse
applications.3–6 However, the high reactivity of isocyanates,
which causes the deactivation and/or undesired crosslinking
by the reaction with aerobic water in an atmospheric
condition, reduces the storage stability of these reactive
polymers. Recently, it has been reported that copolymeriza-
tion with hydrophobic monomers suppresses the reactivity
of isocyanate at room temperature, which renders easy han-
dling and latent reactivity to the isocyanate-containing
copolymers.7,8
Very few were reported on polymers containing cyanate
groups at their side chain, and the availability as
a
prepolymer of polycyanurate thermosets was only dis-
cussed.15,16 Because cyanate group is known to show a
unique reactivity, the cyanate-containing polymers can be an
alternative of reactive polymers for post-functionalization.17
Here, we designed a novel reactive polymer containing
cyanate groups in the side chain. A methacrylate monomer
having a cyanate group was synthesized and polymerized
via free radical polymerization method. The reactivity of
cyanate groups on the polymer backbone with various
reactants was investigated by a model reaction using
4-cyanatotoluene and various nucleophiles. The feasibility of
post-functionalization and crosslinking reaction with ali-
phatic amines was discussed.
Cyanate group is a structural isomer of isocyanate containing
a carbon–nitrogen triple bond. The compounds containing
two or more cyanate groups have been applied to engineer-
Additional Supporting Information may be found in the online version of this article.
C
V
2013 Wiley Periodicals, Inc.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 699–706
699

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
EXPERIMENTAL
nitrogen. The solution was degassed by freeze-pump-thaw
cycles and stirred for 24 h at 60 C under nitrogen. The mix-
ꢀ
Materials
ture was cooled down to room temperature and poured into
20-fold amount of hexane/diethyl ether. The precipitation
was collected by filtration, dissolved in THF, and reprecipi-
tated with hexane. The white polymer was filtered and dried.
The yield was 0.269 g (54%).
Tetrahydrofuran (THF) and diethyl ether were distilled over
sodium and benzophenone. Toluene, acetonitrile, and
N-methyl-2-pyrrolidinone (NMP) were distilled over CaH2.
Triethylamine was distilled over KOH. Methyl ethyl ketone
(MEK) was dried over 4 Å molecular sieves. Methacryloyl
chloride and methyl methacrylate (MMA) were used as
freshly distilled under vacuum. 2-(4-Hydroxyphenyl)ethyl
methacrylate was prepared from 4-(2-hydroxyethyl)phenol
and methacryloyl chloride according to the literature.18
4-Cyanatotoluene was prepared from p-cresol and cyanogen
bromide by the modified procedure of the literature
method.19 The other reagents were used as received.
IR (neat): 2991, 2949, 2264, 2235, 1722, 1603, 1502, 1444,
1389, 1238, 1186, 1144, 987, 808, 750 cm21 1H NMR
.
(CDCl3): 7.39–7.20 (m, 4H), 4.13 (br, 2H), 3.58 (br, 3H), 2.96
(br, 2H), 2.08–1.54 (m, 4H), 1.50–0.46 (m, 6H).
Synthesis of 4-Cyanatotoluene (2) as a Model Compound
To a flask equipped with a stirring bar and an addition fun-
nel were added p-cresol (5.95 g, 55.0 mmol), triethylamine
(8.40 mL, 60.5 mmol), and dried diethyl ether (80 mL). A
solution of cyanogen bromide (3.0 M in diethyl ether,
20.0 mL, 60.0 mmol) was added dropwise at 210 ꢀC with
vigorous stirring, and the mixture was stirred for 1.5 h. After
the precipitated salt was filtered off and washed with diethyl
ether, the filtrate was washed with water and brine. The
organic layer was dried over MgSO4 and concentrated by a
rotary evaporator. The crude product was purified by silica
gel column chromatography eluted with hexane to give a col-
orless liquid. The yield was 4.92 g (67%).
Synthesis of 2-(4-Cyanatophenyl)ethyl Methacrylate (1)
To a flask equipped with a stirring bar and an addition
funnel were added 2-(4-hydroxyphenyl)ethyl methacrylate
(6.00 g, 29.1 mmol), triethylamine (8.1 mL, 58.2 mmol), and
dried diethyl ether (40 mL). A solution of cyanogen bromide
(3.0 M in diethyl ether, 10.7 mL, 32.0 mmol) was added
dropwise at 210 ꢀC with vigorous stirring, and the mixture
was stirred for 1.5 h. After the resulting mixture was washed
with water and brine, the organic layer was dried over
MgSO4 and concentrated by a rotary evaporator. The crude
product was purified by silica gel column chromatography
eluted with hexane and ethyl acetate (5/1 in volume ratio)
to give a colorless liquid. The yield was 2.77 g (41%).
IR (neat): 2928, 2260, 2235, 1604, 1498, 1184, 1163, 1084,
1
1016, 808, 731 cm21. H NMR (CDCl3): d 7.23 (d, 2H, J 5 8.8
Hz), 7.17 (d, 2H, J 5 8.8 Hz), 2.37 (s, 3H). 13C NMR (CDCl3):
d 151.06, 136.90, 130.93, 115.13, 109.19, 20.83.
IR (neat): 2958, 2262, 2235, 1715, 1635, 1501, 1320, 1295,
1155, 1014, 940, 812 cm21. H NMR (CDCl3): d 7.32 (d, 2H,
1
J 5 9.2 Hz), 7.24 (d, 2H, J 5 9.2 Hz), 6.06 (s, 1H), 5.56 (s,
1H), 4.35 (t, 2H, J 5 6.8 Hz), 3.01 (t, 2H, J 5 6.8 Hz), 1.91 (s,
3H). 13C NMR (CDCl3): d 167.40, 151.73, 137.20, 136.24,
130.99, 125.86, 115.45, 108.94, 64.76, 34.45, 18.39.
Model Reaction of a Cyanate Group Using 2 with Various
Nucleophiles
The reactions of cyanate ester 2 and various nucleophiles
were carried out by the same procedure as follows. To a
flask equipped with a stirring bar and a stopcock were
added 2 (0.133 g, 1.00 mmol) and THF (2 mL) under nitro-
gen. A nucleophile (1.00 mmol) was added to this solution
by a syringe, and the mixture was stirred for 24 h. An ali-
quot (20 lL) was taken out at different intervals, and each
sample was subjected to 1H NMR measurement in CDCl3.
The conversion was monitored by the consumption of 2 for
each sample.
Synthesis of Poly[2-(4-cyanatophenyl)ethyl methacrylate]
(PCPMA)
To a tube equipped with a stirring bar and a stopcock were
added 1 (1.00 g, 4.32 mmol), 2,20-azobis(2,4-dimethylvalero-
nitrile) (ADVN) (0.022 g, 0.086 mmol), and MEK (2.2 mL)
under nitrogen. The solution was degassed by freeze-pump-
thaw cycles and stirred for 24 h at 60 ꢀC under nitrogen.
The mixture was cooled down to room temperature and
poured into 20-fold amount of diethyl ether. The sticky pre-
cipitation was collected by decantation, dissolved in THF,
and reprecipitated with hexane. The white polymer was fil-
tered and dried. The yield was 0.95 g (95%).
Synthesis of N,N-Diisopropyl-O-(p-tolyl)isourea (4)
To a flask equipped with a stirring bar and a stopcock were
added 2 (0.133 g, 1.00 mmol) and THF (2 mL) under nitro-
gen. Diisopropylamine (0.14 mL, 1.0 mmol) was added to
this solution, and the mixture was stirred at room tempera-
ture for 24 h. After the solution was concentrated by a
rotary evaporator, the crude product was purified by silica
gel column chromatography eluted with hexane and ethyl
acetate (1/1 in volume ratio) containing 0.5 vol/vol % of
triethylamine to give a colorless liquid. The yield was 0.14 g
(60%).
IR (neat): 2956, 2264, 2237, 1728, 1604, 1504, 1448, 1167,
1086, 1016, 825, 750 cm21 1H NMR (CDCl3): d 7.38–7.17
.
(m, 4H), 4.11 (br, 2H), 2.94 (br, 2H), 1.94–1.48 (m, 2H),
1.03–0.45 (m, 3H).
Copolymerization of 1 with MMA
To a tube equipped with a stirring bar and a stopcock were
added 1 (0.347 g, 1.50 mmol), MMA (0.150 g, 1.50 mmol),
ADVN (14.9 mg, 0.060 mmol), and MEK (1.5 mL) under
IR (neat): 3342, 2968, 2928, 2872, 1630, 1508, 1429, 1365,
1313, 1209, 1161, 1134, 1082, 1034, 993, 889, 847, 816,
700
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 699–706

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
721 cm21
.
1H NMR (CDCl3): d 7.18 (d, 2H, J 5 8.0 Hz), 6.97
Functionalization of Cyanate Group in PCPMA with
(d, 2H, J 5 8.0 Hz), 4.80–4.00 (br, 1H), 4.05 (sep, 2H, J 5 6.8
Hz), 2.35 (s, 3H), 1.30 (d, 12H, J 5 6.8 Hz). 13C NMR (CDCl3):
d 160.47, 149.14, 135.07, 130.46, 122.06, 46.57, 21.51,
20.96.
n-Propylamine (8)
To a flask equipped with a stirring bar and a stopcock were
added PCPMA (0.050 g, 0.22 mmol of unit) and THF (0.5 mL)
under nitrogen. Propylamine (27.1 lL, 0.33 mmol) was added
to this solution, and the mixture was stirred at room tempera-
ture for 24 h. The solution was poured into hexane, and the
precipitate was collected by decantation. The polymer was
washed with hexane and dried. The yield was 0.06 g (94%).
Synthesis of Phosphonium Salt (5)
To a flask equipped with a stirring bar and a stopcock were
added 2 (0.133 g, 1.00 mmol) and THF (2 mL) under nitro-
gen. Triphenylphosphine (0.262 g, 1.0 mmol) was added to
this solution, and the mixture was stirred at room tempera-
ture for 24 h. The mixture was poured into excess amount
of hexane, and the precipitate was filtered. The crude
product was washed with hexane and dried. The yield was
0.095 g (24%).
IR (neat): 3352, 2956, 2875, 2178, 1722, 1651, 1615, 1592,
1515, 1455, 1223, 1149, 968, 823, 749 cm21
.
Functionalization of Cyanate Group in PCPMA with
Triphenylphosphine (9)
To a flask equipped with a stirring bar and a stopcock were
added PCPMA (0.050 g, 0.22 mmol of unit) and THF
(0.5 mL) under nitrogen. Triphenylphosphine (0.065 g,
0.248 mmol) was added to this solution, and the mixture
was stirred at room temperature for 24 h. The resulting mix-
ture was poured into hexane, and the precipitate was col-
lected by filtration. The polymer was washed with hexane
and dried. The yield was 0.067 g (58%).
IR (neat): 1684, 1546, 1505, 1483, 1436, 1308, 1241, 1196,
1111, 1057, 997, 878, 849, 748, 720, 692 cm21 1H NMR
.
(CDCl3): d 9.55 (s, 1H), 7.80–7.73 (m, 6H), 7.67–7.60 (m,
3H), 7.58–7.51 (m, 6H), 7.20 (d, 2H, J 5 8.4 Hz), 7.16 (d, 2H,
J 5 8.4 Hz), 2.35 (s, 3H).
Synthesis of Poly{2-[4-(N,N-
diisopropylcarbamimidoyloxy)phenyl]ethyl
methacrylate} (6)
IR (neat): 2953, 1722, 1614, 1592, 1514, 1436, 1236, 1155,
1115, 997, 825, 721, 691 cm21
.
To a flask equipped with a stirring bar and a stopcock were
added PCPMA (0.050 g, 0.22 mmol of unit) and THF
(0.5 mL) under nitrogen. Diisopropylamine (46.3 lL,
0.33 mmol) was added to this solution, and the mixture was
stirred at room temperature for 24 h. The solution was
poured into hexane, and the viscous precipitate was col-
lected by decantation. The polymer was washed with hexane
and dried. The yield was 0.064 g (88%).
General Procedure for Synthesis of Networked Polymers
To a flask equipped with a stirring bar and a stopcock were
added PCPMA (0.050 g, 0.22 mmol of unit) and THF (0.45 mL)
under nitrogen. A solution of diamine (0.044 mmol) in THF
(0.05 mL) was added by a syringe, and the mixture was stirred
at room temperature for 24 h. The resulting gel was poured into
hexane, filtered, washed by hexane, and dried at 100 ꢀC in vacuo.
Measurements
IR (neat): 3340, 2966, 2873, 1726, 1628, 1510, 1431, 1367,
1H and 13C NMR spectra were recorded on a JEOL JNM-ECS
400 spectrometer at 400 and 100 MHz, respectively. Deuter-
ated chloroform or dimethylsulfoxide was used as a solvent
with tetramethylsilane as an internal standard. IR spectra were
1315, 1213, 1136, 1034, 993, 891, 852 cm21 1H NMR
.
(CDCl3): d 7.22 (d, 2H, J 5 8.0 Hz), 7.00 (d, 2H, J 5 8.0 Hz),
4.80–3.90 (br, 1H), 4.14 (br, 2H), 4.02 (br, 2H), 2.91 (br, 2H),
2.10–1.70 (br, 2H), 1.27 (d, 12H, J 5 6.4 Hz), 1.15–0.65 (m,
3H).
Synthesis of Poly{2-[4-(N,N-
diethylcarbamimidoyloxy)phenyl]ethyl methacrylate} (7)
To a flask equipped with a stirring bar and a stopcock were
added PCPMA (0.050 g, 0.22 mmol of unit) and THF
(0.5 mL) under nitrogen. Diisopropylamine (34.1 lL,
0.33 mmol) was added to this solution, and the mixture was
stirred at room temperature for 24 h. The solution was
poured into hexane, and the viscous precipitate was col-
lected by decantation. The polymer was washed with hexane
and dried. The yield was 0.063 g (90%).
IR (neat): 3340, 2966, 2873, 1726, 1628, 1510, 1431, 1367,
1315, 1213, 1136, 1034, 993, 891, 852 cm21 1H NMR
.
(CDCl3): d 7.21 (d, 2H, J 5 8.0 Hz), 6.99 (d, 2H, J 5 8.0 Hz),
4.40 (s, 1H), 4.13 (br, 2H), 3.39 (d, 4H, J 5 7.2 Hz), 2.90 (br,
2H), 2.09–1.56 (br, 2H), 1.18 (t, 6H, J 5 7.2 Hz), 1.08–0.62
(m, 3H).
SCHEME 1 Synthesis of monomer 1 containing cyanate group.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 699–706
701

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 2 Free radical (co)polymerization of 1.
a heating and cooling rate of 10 ꢀC min21. Thermal gravimetric
analysis (TGA) was performed on a TG/DTA 6200 instrument
(Seiko Instruments) using an aluminum pan under 50 mL
min21 of nitrogen flow at a heating rate of 10 ꢀC min21
.
FIGURE 1 1H NMR spectrum of 1 in CDCl3.
RESULTS AND DISCUSSION
As a novel monomer containing a cyanate group, 2-(4-cyanato-
phenyl)ethyl methacrylate (1) was designed and synthesized
in two-step reactions (Scheme 1). Esterification of 4-(2-hydrox-
yethyl)phenol using methacryloyl chloride afforded a methac-
rylate containing a phenol moiety. Then, the phenolic hydroxyl
group was converted to a cyanate ester by the reaction with
cyanogen bromide to give the monomer 1. The chemical struc-
1
ture of 1 was confirmed by H NMR, 13C NMR, and IR spectra.
All the signals in the 1H NMR spectrum were reasonably
assigned as shown in Figure 1. A characteristic signal at
108.94 ppm derived from the carbon of the cyanate group
was observed in the 13C NMR spectrum of 1 (Fig. 2). The
introduction of the cyanate group was also confirmed by sharp
peaks at 2235 and 2262 cm21 derived from stretching vibra-
tion mode of CBN bond in the IR spectrum. After purification
by silica gel column chromatography, the monomer 1 was sta-
ble under the air for several months.
FIGURE 2 13C NMR spectrum of 1 in CDCl3.
obtained on a Nicolet iS10 spectrometer (Thermo Fisher Scien-
tific) equipped with a Smart iTR Sampling Accessory unit.
Number- and weight-average molecular weights (Mn and Mw)
were determined by gel permeation chromatography (GPC)
analyses using a HLC-8320GPC (Tosoh Corporation) equipped
with a TSKgel SuperHM-H column eluted with THF at a flow
rate of 0.5 mL min21 and calibrated by standard polystyrene
samples. Differential scanning calorimetry (DSC) analyses were
performed on a DSC 6200 instrument (Seiko Instruments)
using an aluminum pan under 20 mL min21 of nitrogen flow at
Free radical polymerization of 1 was conducted with ADVN
as an initiator in toluene or MEK at 60 ꢀC as shown in
Scheme 2. After the precipitation with diethyl ether and hex-
ane, poly[2-(4-cyanatophenyl)ethyl methacrylate] (PCPMA)
with number-average molecular weights (Mn) of 28,000 and
16,400 using toluene and MEK as a solvent, respectively, and
slightly broad molecular weight distributions (Mw/Mn) were
obtained (Table 1, Runs 1 and 2). The polymer structure was
confirmed by 1H NMR (Fig. 3) and IR spectra. The strong
peaks assignable to CBN bond were observed at 2237 and
TABLE 1 Free Radical Polymerization of 1 and Copolymerization with MMAa
Unit Ratioc (1/MMA)
b
b
b
d
Tg (ꢀC)
Run
Feed Ratio (1/MMA)
Solvent
Yield (%)
Mn
Mw
Mw/Mn
1
2
3
4
5
6
100/0
100/0
50/50
25/75
50/50
75/25
Toluene
MEK
67
95
54
86
54
70
28,000
16,400
15,000
6,900
106,000
66,400
85,000
15,000
20,000
35,000
3.79
4.04
5.71
2.12
2.28
2.46
–
66
65
77
65
73
85
–
Toluene
MEK
51/49
26/74
51/49
73/27
MEK
8,600
MEK
14,000
a
c
Polymerization was carried out using 2 mol % of ADVN at 60 ꢀC for
Determined by 1H NMR.
d
24 h.
b
Determined by DSC in the second heating scan.
Determined by GPC eluted with THF using polystyrene standards.
702
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 699–706

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
FIGURE 3 1H NMR spectrum of PCPMA in CDCl3.
SCHEME 3 Nucleophilic addition to
phosphines.
2
using amines and
2264 cm21 in the IR spectrum of PCPMA, which indicates
that cyanate group of 1 remained unreactive during the radi-
cal polymerization. The polymer showed good solubility in
common organic solvents such as acetone, ethyl acetate, tolu-
ene, THF, chloroform, DMSO, and N,N-dimethylformamide
(DMF). The glass transition temperature (Tg) of PCPMA was
requirements in their application. No spectral change in the
NMR spectra of PCPMA and the copolymers was observed
after settled under the air for several months, indicating that
the cyanate-containing polymers can be easily preserved
even under the moist condition.
ꢀ
determined as 66 C by DSC measurement. Copolymerization
of 1 and MMA with various feed ratios was also conducted
to provide poly{[2-(4-cyanatophenyl)ethyl methacrylate]-stat-
(methyl methacrylate)}, and the results are summarized in
Table 1. The unit ratios of 1 to MMA in the copolymers were
estimated by 1H NMR spectra, and found to be almost
same as feed ratios. This indicates that the content of
cyanate-containing unit in the copolymers can be tuned for
To investigate the reactivity of a cyanate group, a model
reaction with various nucleophiles was carried out using 4-
cyanatotoluene (2) as a model compound. The reaction was
examined by mixing 2 and an equimolar nucleophile in THF
at room temperature or 60 ꢀC. The conversion was moni-
tored by the consumption of 2, which was estimated by the
decrease in a signal at 7.23 ppm derived from the aromatic
proton in 1H NMR spectra. The results are summarized in
Table 2. No spectral change was observed when water was
added to the solution of 2 at both room temperature and 60
ꢀC. In addition, the cyanate group does not react with nucle-
ophiles containing a hydroxy group such as n-propanol and
phenol even at 60 ꢀC. This indicates that the polymer con-
taining cyanate groups can be stored and used in the pres-
ence of water and/or alcohols. On the other hand, the
consumption of 2 rapidly proceeded within 1 h on the addi-
tion of aliphatic amines such as n-propylamine and diethyl-
amine. Nucleophilic addition to the cyanate group
immediately took place using an aliphatic amine to generate
an isourea compound. However, aromatic amines such as
aniline gave no adduct with 2. In the case of primary amines
such as n-propylamine, using 0.5 equiv of the amine to 2
resulted in high conversion up to 90%, which revealed that
the 1:2 adduct 3 was generated by the reaction of the pri-
mary amine with 2 equiv of 2 as shown in Scheme 3 (not
isolated owing to the instability). The reaction with second-
ary amines provided the 1:1 adduct, and the reaction rate
was significantly influenced by the bulkiness of the amines.
Figure 4 shows the conversion curves of the reactions with
diethylamine and diisopropylamine. Because of the bulky
structure of diisopropylamine, the reaction rate decreased
TABLE 2 Model Reaction of 2 with Various Nucleophilesa
Nucleophiles
Temp. (ꢀC)
Time (h)
Conv.b (%)
H2O
r. t.
60
24
24
24
24
24
0.5
0.5
1
0
H2O
0
n-Propanol
r. t.
60
0
n-Propanol
0
Phenol
r. t.
r. t.
r. t.
r. t.
r. t.
r. t.
r. t.
r. t.
r. t.
r. t.
0
n-Propylamine
n-Propylaminec
Diethylamine
Diisopropylamine
Aniline
91
90
95
92
0
12
24
24
0.5
6
Acetic acid
0
Tricyclohexylphosphine
Triphenylphosphine
1-Octadecanethiol
>99
94
0
12
a
Reaction was carried out using 2 (1.0 mmol) and a nucleophile (1.0
mmol) in THF (0.5 M).
b
Conversion of 2 determined by 1H NMR.
c
Using 0.5 mmol.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 699–706
703

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 5 1H NMR spectrum of 6 in CDCl3.
FIGURE 4 Conversion curves of the model reaction with dieth-
ylamine and diisopropylamine using
PCPMA (open symbol).
2 (filled symbol) and
1H NMR spectrum (Fig. 5), all the signals were clearly
assigned to the polymer structure of 6, and the transforma-
tion of cyanate into isourea was found to be quantitative.
Figure 6 shows IR spectra of PCPMA and 6. The peaks
assignable to cyanate at 2264 and 2237 cm21 completely
disappeared for 6, and a new strong peak arose at 1628
cm21 according to the generation of the isourea group. The
reaction of PCPMA with diethylamine was carried out to pro-
vide an isourea polymer (7), and the reaction proceeded in a
very fast rate as shown in Figure 4. The isourea structure of
7 was confirmed by the assignment of all the signals in 1H
NMR spectrum (Supporting Information Fig. S1). When n-
propylamine was used instead of these secondary amines,
the resulting polymer (8) was almost insoluble in common
solvents because of the crosslinking reaction. The structure
of 8 was confirmed by IR spectrum (Supporting Information
Fig. S2). Although the peak at 1651 cm21 derived from C@N
bond in isourea group can be observed, the cyanate group
partially remained in spite of the excess use of n-propyla-
mine. This is due to the steric hindrance of the cyanate
group left in the networked structure. Triphenylphosphine
also reacted with PCPMA, and the pale yellow polymer (9)
was obtained. The polymer 9 was insoluble in any common
solvent. By the IR spectrum of 9 (Supporting Information
and the conversion moderately increased up to 92% for
12 h. The adduct of 2 with diisopropylamine was isolated
and the formation of the isourea compound 4 was confirmed
by NMR and IR spectra. Phosphines are other reactants giv-
ing high conversions for the reaction with 2. However, the
following decyanation occurred to give p-cresol as a main
product, especially for the reaction with tricyclohexylphos-
phine. In the case of triphenylphosphine, the adduct could
be isolated after precipitation in hexane in low yield (21%).
Characterization of the crude product by NMR revealed that
the hydrated phosphonium salt 5 was obtained (Scheme 3).
Finally, carboxylic acid and thiol compounds do not react
with the cyanate group at room temperature.
Based on the results of the model reaction, the structural
modification of PCPMA was performed by the reactions
with various nucleophiles in THF at room temperature
(Scheme 4). By the reaction with diisopropylamine, the poly-
mer bearing isourea groups in the side chain (6) was
obtained in a high yield (88%). The reaction proceeded
faster than using the model compound 2 as shown in Figure
4, which is probably due to the neighboring effect. In the
SCHEME 4 Functionalization of PCPMA with various nucleophiles.
704
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 699–706

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
FIGURE 6 IR spectra of (a) PCPMA and (b) 6.
Fig. S3), the transformation of cyanate group was assumed
to be complete according to the disappearance of the peak
at 2264 and 2237 cm21. However, 9 showed a very weak
peak corresponding to C@N bond compared to isourea poly-
mers. This result suggests that the elimination of phospho-
nium moiety partially occurred to afford phenol group as
indicated by the model reaction.
FIGURE 7 TGA profiles of (a) PCPMA and 6, and (b) net-
worked polymers; the crosslinker for 10: ethylenediamine, 11:
hexamethylenediamine, 12: m-xylylenediamine, and 13: N,N’-
diisopropylethylenediamine.
On the other hand, water and n-propanol were also used as
a nucleophile for the reaction of PCPMA in THF at room tem-
perature. These nucleophiles do not react with PCPMA, even
when fivefold excess of water or n-propanol was used, which
resulted in the recovery of PCPMA.
The formation of isourea polymers 6 and 7 was also evi-
denced by GPC measurement eluted by DMF. The chromato-
grams of 6 and 7 were similar profiles to that of PCPMA
with a slight increase of Mn (Supporting Information Fig. S4).
SCHEME 5 Synthesis of networked polymers based on PCPMA using diamines.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 699–706
705

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
The Mns of PCPMA, 6, and 7 were 13,500, 15,200, and
14,200, respectively. Therefore, it is assumed that the trans-
formation of the cyanate into isourea proceeded without any
undesired crosslinking and/or branching reactions.
used as a reactive polymer with long storage stability, which
is easily modified by the reaction with functionalized amine
agents.
As another example of functionalization using cyanate group,
the formation of networked polymers based on PCPMA by cross-
linking with aliphatic diamines was examined (Scheme 5). Ethyl-
enediamine, hexamethylenediamine, m-xylylenediamine, and
N,N0-diisopropylethylenediamine were used as a diamine cross-
linker. On adding the primary diamines (0.2 equiv to the cyanate
group) to the solution of PCPMA in THF, the gelation immedi-
ately occurred within 1 min. Using N,N0-diisopropylethylenedi-
amine, a secondary diamine with a bulky structure, retarded the
gelation time over 1 h as expected by the result of the model
reaction. All the networked polymers were quantitatively
obtained after reprecipitation into hexane. Thermal property of
these networked polymers was investigated by TGA under nitro-
gen atmosphere, and the profiles are shown in Figure 7. PCPMA
showed 5% weight loss temperature (Td) of 261 ꢀC, whereas
REFERENCES AND NOTES
1 M. A. Gauthier, M. I. Gibson, H.-A. Klok, Angew. Chem. Int.
Ed. 2009, 48, 48–58.
2 G. Tillet, B. Boutevin, B. Ameduri, Prog. Polym. Sci. 2011, 36,
191–217.
3 J. B. Beck, K. L. Killops, T. Kang, K. Sivanandan, A. Bayles,
M. E. Mackay, K. L. Wooley, C. J. Hawker, Macromolecules
2009, 42, 5629–5635.
4 J. D. Flores, J. Shin, C. E. Hoyle, C. L. McCormick, Polym.
Chem. 2010, 1, 213–220.
5 R. M. Hensarling, S. B. Rahane, A. P. LeBlanc, B. J. Sparks,
E. M. White, J. Locklin, D. L. Patton, Polym. Chem. 2011, 2,
88–90.
6 X. Piao, X. Zhang, Y. Mori, M. Koishi, A. Nakaya, S. Inoue, I.
Aoki, A. Otomo, S. Yokoyama, J. Polym. Sci. Part A: Polym.
Chem. 2011, 49, 47–54.
the decomposition of
6 began at lower temperature
ꢀ
(Td 5 180 C). The formation of network slightly increased the
Tds compared to PCPMA except for 10 (11: 263 ꢀC, 12: 274 ꢀC,
and 13: 278 ꢀC). The Td of 7 was observed at 230 ꢀC. In the case
that ethylenediamine was used as a crosslinker, the reaction pro-
ceeded too quickly to form a homogeneous network. The hetero-
geneity in the network structure probably caused a decrease in
the decomposition temperature of 10.
7 Y. Itagaki, A. Sudo, T. Endo, J. Polym. Sci. Part A: Polym.
Chem. 2006, 44, 681–685.
8 Y. Kamimura, O. Haba, T. Endo, J. Polym. Sci. Part A: Polym.
Chem. 2006, 44, 2448–2453.
9 I. Hamerton, J. N. Hay, Polym. Int. 1998, 47, 465–473.
10 C. A. Fyee, J. Niu, S. J. Retting, D. W. Wang, M. D. Poliks,
J. Polym. Sci. Part A: Polym. Chem. 1994, 32, 2203–2221.
11 C. A. Fyfe, J. Niu, K. Mok, J. Polym. Sci. Part A: Polym.
Chem. 1995, 33, 1191–1202.
CONCLUSIONS
12 C. H. Lin, K. Z. Yang, T. S. Leu, C. H. Lin, J. W. Sie,
J. Polym. Sci. Part A: Polym. Chem. 2006, 44, 3487–3502.
A novel reactive polymer PCPMA containing cyanate groups
in the side chain was successfully prepared by free radical
polymerization of methacrylate monomer 1. The composition
of cyanate-bearing unit was able to be controlled in
the copolymers with MMA. The model reaction using
4-cyanatotoluene revealed that the reaction of the cyanate
ester with aliphatic amines gives an isourea group quantita-
tively, whereas the cyanate group remains unreactive in the
presence of water, alcohols, or aromatic amines under mod-
erate conditions. By post-functionalization with aliphatic
amines, PCPMA was quantitatively converted to isourea-
containing polymers. The networked polymers based on
PCPMA were also prepared by the reaction with diamines as
the crosslinkers. These results indicate that PCPMA can be
13 K. S. Santhosh Kumar, C. P. Reghunadhan Nair, K. N.
Ninan, Eur. Polym. J. 2009, 45, 494–502.
14 X. Li, Y. Gu, Polym. Chem. 2011, 2, 2778–2781.
15 W. Kern, M. Cifrain, R. Schroder, K. Hummel, C. Mayer, M.
Hofstotter, Eur. Polym. J. 1998, 34, 987–995.
16 D. Mathew, C. P. R. Mair, K. N. Ninan, Eur. Polym. J. 2000,
36, 1195–1208.
€
17 E. Grigat, R. Putter, Angew. Chem. Int. Ed. Engl. 1967, 6,
206–218.
18 K. Ohno, T. Akashi, Y. Tsujii, M. Yamamoto, Y. Tabata, Bio-
macromolecules 2012, 13, 927–936.
19 K. Fukumoto, A. A. Dahy, T. Oya, K. Hayasaka, M. Itazaki, N.
Koga, H. Nakazawa, Organometallics 2012, 31, 787–790.
706
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 699–706