Selective nucleophilic additions to poly(methacrylate)s containing isothiocyanate moieties in the side chains and their application in cross-linking

Article abstract of DOI:10.1002/pola.27189

Reactivity of isothiocynate moieties in the side chain of polymethacrylate with amine, alcohol, or thiol was investigated, and the reactions were applied to preparation of networked polymers. Isothiocyanate of polymer side chain rapidly reacted with amines without a catalyst, to give the corresponding thioureas. However, it did not react with alcohols or thiols under the same conditions. Using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a catalyst, addition of alcohols or thiols to the isothiocyanate proceeded smoothly. Addition of amines, alcohols, and thiols to isothiocyanates moiety contained in the side chain of polymethacrylate also proceeded readily with or without the catalyst, respectively, to effectively give the corresponding side chain modified polymers. Occurrence of these additions was confirmed by ¹H NMR and IR measurements. Glass transition temperatures and thermal decomposition temperatures of the obtained polymers were investigated by differential scanning calorimetry and thermogravimetric analysis. Networked polymers were easily prepared by addition of 1,6-hexamethylenediamine or hexamethylene glycol to the polymethacrylate having isothiocyanato groups. Copyright

Full text of DOI:10.1002/pola.27189

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Selective Nucleophilic Additions to Poly(methacrylate)s Containing
Isothiocyanate Moieties in the Side Chains and their Application in Cross-
Linking
Ryota Seto,1 Kozo Matsumoto,1,2 Takeshi Endo1
1Molecular Engineering Institute, Kinki University, 11-6 Kayanomori, Iizuka, Fukuoka Prefecture 820–8555, Japan
2Department of Biological & Environmental Chemistry, Kinki University, 11-6 Kayanomori, Iizuka,
Fukuoka Prefecture 820–8555, Japan
Correspondence to: T. Endo (E-mail: tendo@moleng.fuk.kindai.ac.jp)
Received 18 December 2013; accepted 22 March 2014; published online 15 April 2014
DOI: 10.1002/pola.27189
ABSTRACT: Reactivity of isothiocynate moieties in the side
chain of polymethacrylate with amine, alcohol, or thiol was
investigated, and the reactions were applied to preparation of
networked polymers. Isothiocyanate of polymer side chain rap-
idly reacted with amines without a catalyst, to give the corre-
sponding thioureas. However, it did not react with alcohols or
thiols under the same conditions. Using 1,8-diazabicy-
clo[5.4.0]undec-7-ene (DBU) as a catalyst, addition of alcohols
or thiols to the isothiocyanate proceeded smoothly. Addition of
amines, alcohols, and thiols to isothiocyanates moiety con-
tained in the side chain of polymethacrylate also proceeded
readily with or without the catalyst, respectively, to effectively
give the corresponding side chain modified polymers. Occur-
rence of these additions was confirmed by 1H NMR and IR
measurements. Glass transition temperatures and thermal
decomposition temperatures of the obtained polymers were
investigated by differential scanning calorimetry and thermog-
ravimetric analysis. Networked polymers were easily prepared
by addition of 1,6-hexamethylenediamine or hexamethylene
glycol to the polymethacrylate having isothiocyanato groups.
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Chem. 2014, 52, 1832–1842
KEYWORDS: polymethacrylate; isothiocyanate; radical polymer-
ization; reactive polymer; cross-linking; heteroatom-containing
polymers
addition, fluorescein isothiocyanate (FITC) is used as fluores-
cent indicator of primary amines.5 Although there are a lot of
compounds having isothiocyanato groups, few polymers have
isothiocyanato groups in the side chains.6,7
INTRODUCTION Isothiocyanate (RAN@C@S) is a heterocumu-
lene that has cumulative double bonds between a carbon and
heteroatoms. It is structurally analogous to isocyanate
(RAN@C@O). The central carbon atom in the isothiocyanato
group is electron-deficient because of the existence of
electron-negative neighbor sulfur and nitrogen atoms. Isocya-
nates or isothiocyanates can readily undergo various reac-
tions; for instance, nucleophilic additions of amines, alcohols,
and thiols to the central carbon atom rapidly proceed under
mild conditions to give urea or thiourea, urethane, or thiour-
ethane, and thiocarbamate or dithiocarbamate, respectively.1
Diels–Alder type 4 1 2 cycloadditions with conjugated dienes
and nucleophilic cycloaddition with bifunctional compounds
were also reported.2,3 Isothiocyanate is particularly interest-
ing because of its high reactivity and high reaction selectivity.
Isothiocyanate reacts selectively with primary amino groups
on proteins, but does not react with hydroxyl groups of alco-
hols, carboxylic acids, or water. Using this reaction selectivity,
isothiocyanate is applied to structure determination of pro-
teins, which is known as the Edman degradation method.4 In
Isocyanate-containing monomers are popular monomers manu-
factured in an industrial scale, which are useful because one can
easily introduce reactive isocyanato groups into various vinyl
polymers by copolymerization, or transform various amines and
alcohols to polymerizable monomers by connecting at the iso-
cyanato moiety.8–10 However, isocyanate is highly labile to water
and difficult to handle. To precisely synthesize isocyanate-
containing homopolymers, completely dry solvents and special
techniques are necessary.11 Generally, protecting groups were
used to handle the isocyanate-containing monomers or poly-
mers in air or nucleophilic solvents.12 For example, Theato and
coworkers synthesized poly(4-vinylbenzoyl azide), which was
thermally transformed to the corresponding isocyanate-
containing polymer.13 Thus, a special method is needed to han-
dle the monomers or polymers having isocyanto groups.
Additional Supporting Information may be found in the online version of this article.
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1
Recently, we reported synthesis and polymerization of meth-
acrylic, acrylic, and styrene monomers having an isothiocya-
nato structure, 2-isothiocyanatoethyl methacrylate (ITEMA,
6), 2-isothiocyanatoethyl acrylate (ITEA), and 4-vinylbenzyl
isothiocyanate (VBIT) to obtain the corresponding homopol-
ymers, poly-ITEMA (1), poly-ITEA, or poly-VBIT.14,15 We
examined the reactivity of isothiocyanates and found that
isothiocyanate is less reactive toward water, alcohol, and car-
boxylic acid than the corresponding isocyanate. Isothiocya-
nate is stable enough in a usual air atmosphere or in a
hydrous solvent so that it can be easily handled and stored
without any strict dry conditions (see Supporting Informa-
tion, Fig. S4). Furthermore, isothiocyanate-containing mono-
mers can be copolymerized with monomers containing free
hydroxyl or carboxyl groups, which are difficult to be copoly-
merized with isocyanate-containing monomers. Taking
advantage of these characteristics, we copolymerized ITEMA
with 2-hydroxyethyl methacrylate (HEMA) or methacrylic
acid (MAA) to obtain corresponding copolymer, poly
(ITEMA-co-HEMA) or poly(ITEMA-co-MAA).16
resonance frequency of 300 and 75 MHz for H and 13C with
tetramethylsilane as an internal standard. NMR chemical
shifts were reported in delta unit (d). Infrared (IR) spectra
were recorded on a Thermo Scientific Nicolet iS10 spectrom-
eter equipped with a Smart iTR Sampling Accessory using
attenuated total reflection (ATR) method. Number-average
and weight-average molecular weights (Mn, Mw) and polydis-
persity indices (Mw/Mn) of the polymers were estimated by
size exclusion chromatography using N,N-dimethylformamide
(DMF) as the eluent at a flow rate of 0.6 mL/min at 40 ꢀC,
performed on a Tosoh TSKgel SuperHM-H styrogel columns
(3.0 mm u 3 15 cm, 3 and 5-mm bead sizes), UV-vis detector
(254 nm) and refractive index detector. The molecular
weight calibration curve was obtained with polystyrene
standards. Thermogravimetric analysis (TGA) was performed
on a Seiko Instrument TG-DTA 6200 with an aluminum pan
ꢀ
under a 100 mL/min N2 flow at a heating rate of 10 C/min.
Differential scanning calorimetry (DSC) was performed with
a Seiko Instrument. DSC-6200 using an aluminum pan under
ꢀ
a 50 mL/min N2 flow at the heating rate of 10 C/min. Melt-
ing points (mp) were measured with a Stuart Scientific
SMP3. High-resolution mass spectra (HRMS) were obtained
on a JEOL JMN-700 spectrometer using electron impact (EI)
ionization mode.
In this study, we demonstrated that an isothiocyanate-
containing polymethacrylate reacted with an amine, an alco-
hol, and a thiol to obtain the corresponding thiourea, thiour-
etane, and dithiocarbamate. These reactions were applied to
crosslink the polymers to prepare networked polymers using
bifunctional compounds. Fundamental properties of the
obtained polymers such as glass transition temperatures and
thermal decomposition temperatures were evaluated and
considered along with the reactivity of the isothiocyanato
groups in the polymer side chains.
Reaction of 1 and 2a
To a solution of 1 (103 mg) in THF (6.00 mL), 2a (72.2 mL,
70.7 mg, 0.66 mmol) was added at room temperature, and
the mixture was stirred for 3 h. The crude mixture was
poured into a large amount of diethyl ether (100 mL), and
the resulting precipitate was collected by filtration to give
142 mg of thiourea (3a, see Table 1) as a white powder in
85% yield.
EXPERIMENTAL
Tg 89 ꢀC; Td5 193 ꢀC; Mn 95,400, Mw 196,000, Mw/Mn 2.06;
1H NMR (400 MHz, 353 K, DMSO-d6, d): 8.04–7.70 (m, 1 H,
NAH), 7.58–7.36 (m, 1 H, NAH), 7.36–7.13 (m, 5 H, PhAH),
Materials
Polymer 1 was prepared from compound 6 according to the
reported procedures.14 2,20-Azobis(isobutyronitrile) (AIBN)
was purchased from Wako Pure Chemical Industry (Osaka,
Japan) and purified by recrystallization from methanol.
Methyl ethyl ketone (MEK) was purchased from Wako Pure
Chemical Industry (Osaka, Japan) and distilled over KMnO4
and distilled over CaH2 before use. Hexamethylene glycol
(4b), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), dimethyl
sulfoxide (DMSO), benzylamine (2a), and 2-aminoethanol
(2d) were purchased from Wako Pure Chemical Industries
(Osaka, Japan) and used as received. Benzyl alcohol (2b)
was purchased from Sigma-Aldrich, LLC. (St. Louis, MO) and
used as received. Benzyl mercaptan (2c), 2-mercaptethanol
(2e), and hexamethylenediamine (4a) were purchased from
Tokyo Chemical Industry (Tokyo, Japan) and used as
received. Triethylamine, acetone, tetrahydrofuran (THF), and
MgSO4 were purchased from Kanto Chemical (Tokyo, Japan)
and used as received.
4.83–4.52 (m,
2
H, ACH2Ph), 4.24–3.91 (m,
2
H,
AOCH2CH2A), 3.81–3.56 (m, 2 H, AOCH2CH2NHA), 2.24–
1.35 (m, 2 H, ACH2C(CH3)A), 1.35–0.52 (m, 3 H, ACH3)
ppm; IR (ATR): mmax 5 3258 (w, NAH), 2944 (w, CAH), 1728
(s, C@O), 1548 (s, CSNH), 1454 (m, Ph), 1344 (w, CSNH),
1230 (m, CAO), 1150 (s, CAO), 696 (s, Ph) cm21
.
Reaction of 1 and 2b
To a solution of 1 (103 mg) in THF (6.00 mL), 2b (68.0 mL,
71.4 mg, 0.66 mmol), and DBU (90.0 mL, 91.3 mg, 0.60
mmol) were added at room temperature, and the mixture
was stirred for 24 h. The crude mixture was poured into a
large amount of diethyl ether (100 mL), and the resulting
precipitate was collected by filtration to give 155 mg of thio-
uretane (3b, see Table 1) as a white powder in 92% yield.
Tg 58 ꢀC; Td5 154 ꢀC; Mn 27,800, Mw 64,400, Mw/Mn 2.32;
1H NMR (400 MHz, 353 K, DMSO-d6, d): 7.65–6.95 (m, 5 H,
PhAH), 5.71–4.98 (m, 2 H, ACH2Ph), 4.31–3.84 (m, 2 H,
AOCH2CH2A), 3.84–3.31 (m, 2 H, AOCH2CH2NHA), 2.27–
1.60 (m, 2 H, ACH2C(CH3)A), 1.34–0.28 (m, 3 H, ACH3)
ppm; IR (ATR): mmax 5 3291 (w, NAH), 2941 (w, CAH), 1723
Measurements
1H and 13C NMR spectra were recoded on a JEOL JNM-ECS
400 spectrometer at a resonance frequency of 400 and 100
1
MHz for H and 13C, and JEOL JMN-AL 300 spectrometer at a
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TABLE 1 Results of Reactions between Isothiocyanate-Containing Polymer 1 and Nucleophiles
Entry
1
Nucleophile
–
Catalyst
–
Time (h)
–
Product
Conversion (%)a
–
Tg (ꢀC)
Td5 (ꢀC)
55
277
b
2
3
4
None
DBUc
DBUd
3
98
99
95
89
58
68
193
154
154
24
12
e
5
6
a
None
DBUd
3
99
96
–
184
142
e
12
–
Calculated by absorption of IR spectra (2150 cm21 of N@C@S).
Polymer 1 as a starting material.
5 mol % to a nucleophile.
Not determined.
d
b
c
e
1.0 eq. to a nucleophile.
(s, C@O), 1645 (w, N@C), 1518 (m, CSNH), 1453 (m, Ph),
1399 (w, CSNH), 1243 (m, CAO), 1145 (s, CAO), 694 (m,
and the mixture was stirred for 3 h. The crude mixture was
poured into a large amount of diethyl ether (100 mL), and
the resulting precipitate was collected by filtration to give
132 mg of thiourea (3d, see Table 1) as a white powder in
95% yield.
Ph) cm21
.
Reaction of 1 and 2c
To a solution of 1 (103 mg) in THF (6.00 mL), 2c (77.3 mL,
82.0 mg, 0.66 mmol), and DBU (4.5 mL, 4.57 mg, 0.03 mmol)
were added at room temperature, and the mixture was
stirred for 12 h. The crude mixture was poured into a large
amount of diethyl ether (100 mL), and the resulting precipi-
tate was collected by filtration to give 155 mg of dithiocarba-
mate (3c, see Table 1) as a white powder in 87% yield.
Td5 184 ꢀC; Mn 42,000, Mw 75,500, Mw/Mn 1.80; 1H NMR
(400 MHz, 353 K, DMSO-d6, d): 7.53–7.20 (m, 2 H, NAH),
4.64–4.34 (m, 1 H, AOH), 4.16–3.84 (m, 2 H, AOCH2CH2A),
3.75–3.58 (m, 2 H, AOCH2CH2NHA), 3.58–3.47 (m, 2 H,
ANHCH2CH2OH), 3.47–3.35 (m, 2 H, ANHCH2CH2OH), 2.16–
1.34 (m, 2 H, ACH2C(CH3)A), 1.24–0.54 (m, 3 H, ACH3)
ppm; IR (ATR): mmax 5 3281 (w, NAH, OAH), 2935 (w, CAH),
1716 (s, C@O), 1652 (m, N@C), 1557 (m, CSNH), 1385 (w,
Tg 68 ꢀC; Td5 154 ꢀC; Mn 67,500, Mw 257,300, Mw/Mn 3.81; 1H
NMR (400 MHz, 353 K, DMSO-d6, d): 7.57–6.90 (m, 5 H,
PhAH), 4.71–4.32 (m, 2 H, ACH2Ph), 4.32–3.97 (m, 2 H,
AOCH2CH2A), 3.97–3.63 (m, 2 H, AOCH2CH2NHA), 2.28–1.32
(m, 2 H, ACH2C(CH3)A), 1.32–0.33 (m, 3 H, ACH3) ppm; IR
(ATR): mmax 5 3271 (w, NAH), 2936 (w, CAH), 1722 (s, C@O),
1645 (w, N@C), 1494 (m, CSNH), 1452 (m, Ph), 1381 (w,
CSNH), 1243 (m, CAO), 1150 (s, CAO) cm21
.
Reaction of 1 and 2e
To a solution of 1 (103 mg) in DMSO (6.00 mL), 2e (46.0
mL, 51.6 mg, 0.66 mmol) and DBU (4.5 mL, 4.57 mg, 0.03
mmol) were added at room temperature, and the mixture
was stirred for 12 h. The crude mixture was poured into a
large amount of diethyl ether (100 mL), and the resulting
precipitate was collected by filtration to give 142 mg of
dithiocarbamate (3e, see Table 1) as a white powder in 95%
yield.
CSNH), 1233 (m, CAO), 1148 (s, CAO), 696 (m, Ph) cm21
.
Reaction of 1 and 2d
To a solution of 1 (103 mg) in DMSO (6.00 mL), 2d (39.5
mL, 40.3 mg, 0.66 mmol) was added at room temperature,
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(4.4 mL, 4.5 mg, 0.029 mmol) in THF (0.293 mL, 0.1 mol/L)
was added at room temperature, and the mixture was stirred
for 24 h. The crude mixture was poured into a large amount
of diethyl ether (100 mL), and the resulting precipitate was
collected by filtration to give 71.6 mg of networked polymer
(5b, see Scheme 2) as a white powder.
ꢀ
ꢀ
Tg 90 C; Td5 129 C; IR (ATR): mmax 5 3436 (br, NAH), 2931
(w, CAH), 2210 (br, N@C@S), 2102 (br, N@C@S), 1736 (s,
C@O), 1542 (m, CSNH), 1350 (w, CSNH), 1146 (m, CAO)
SCHEME 1 Addition of nucleophiles to polymers having iso-
cm21
.
thiocyanato groups.
Td5 142 ꢀC; Mn 38,900, Mw 115,200, Mw/Mn 2.97; 1H NMR
Reaction of 6 and 2a
To a solution of 6 (1.00 g, 5.84 mmol) in THF (5.84 mL, 1.0
mol/L), 2a (702 mL, 688 mg, 6.42 mmol, 1.1 eq.) was added
at room temperature, and the mixture was stirred for 15
min. The crude mixture was purified by silica gel column
chromatography (eluent: ethyl acetate) to give 1.65 mg (5.92
mmol) of thiourea (7a, see Scheme 3) as a white solid in
99% yield.
(400 MHz, 353 K, DMSO-d6, d): 4.14–3.96 (m,
AOCH2CH2A), 3.91–3.74 (m, 2 H, AOCH2CH2NHA), 3.47–
3.35 (m, 2 H, ASCH2CH2OH), 3.53–3.36 (m, 1 H, AOH), 3.36–
2 H,
3.23 (m,
ACH2C(CH3)A), 1.20–0.61 (m, 3 H, ACH3) ppm; IR (ATR):
max 5 3209 (w, NAH, OAH), 2927 (w, CAH), 1716 (s, C@O),
1646 (m, N@C), 1506 (m, CSNH), 1384 (w, CSNH), 1234 (m,
CAO), 1150 (s, CAO) cm21
2
H, ASCH2CH2OH), 2.07–1.53 (m,
2
H,
m
.
Mp 70.8–73.9 ꢀC; Rf value 0.8 (eluent: ethyl acetate); 1H
NMR (400 MHz, 293 K, CDCl3, d): 7.39–7.30 (m, 5 H, PhAH),
6.29 (br, 1 H, ANHCH2Ph), 6.15 (br, 1 H, AOCH2CH2NHA),
6.04 (dq, J 5 1.5, 1.5 Hz, 1 H, CH2@C<), 5.58 (dq, J 5 1.5, 1.5
Hz, 1 H, CH2@C<), 4.57 (d, J 5 5.4 Hz, 2 H, ACH2Ph), 4.32 (t,
J 5 5.0 Hz, 2 H, AOCH2CH2A), 3.84 (dt, J 5 5.0, 5.0 Hz, 2 H,
AOCH2CH2NHA), 1.90 (dd, J 5 1.5, 1.5 Hz, 3 H, C@CACH3)
ppm; 13C NMR (100 MHz, 293 K, CDCl3, d): 182.3 (C@S),
167.8 (C@O), 136.8 (Ph), 135.6 (CH2@C<), 128.8 (Ph), 127.8
(Ph), 127.5 (Ph), 126.6 (CH2@C<), 63.2 (AOCH2A), 48.1
(ACH2Ph), 44.1 (ACH2NHA), 18.3 (ACH3) ppm; IR (ATR):
Cross-linking of 1 using 4a
To a solution of 1 (50 mg) in THF (0.293 mL), a solution of
4a (3.4 mg, 0.029 mmol) in THF (0.293 mL, 0.1 mol/L) was
added at room temperature, and the mixture was stirred for
1 min. The crude mixture was poured into a large amount of
diethyl ether (100 mL), and the resulting precipitate was col-
lected by filtration to give 58.9 mg of networked polymer
(5a, see Scheme 2) as a white powder.
ꢀ
ꢀ
Tg 75 C; Td5 168 C; IR (ATR): mmax 5 3366 (br, NAH), 2935
(w, CAH), 2214 (br, N@C@S), 2111 (br, N@C@S), 1735 (s,
C@O), 1545 (m, CSNH), 1347 (w, CSNH), 1146 (m, CAO)
mmax 5 3252 (w, NAH), 3062 (w, CAH), 1713 (s, C@O), 1635
(w, C@C), 1541 (s, CSNH), 1453 (w, Ph), 1292 (m, CSNH),
1154 (s, CAO), 695 (m, Ph) cm21; HRMS (EI, m/z): [m]1
calcd for C14H18N2O2S, 278.1089; found, 278.1086.
cm21
.
Cross-linking of 1 using Hexamethylene Glycol 4b
To a solution of 1 (50 mg) in THF (0.293 mL), 4b (3.5 mg,
0.029 mmol) was added at room temperature, and the mix-
ture was stirred for 5 min. To the mixture, a solution of DBU
Reaction of 6 and 2b
To a solution of 6 (1.00 g, 5.84 mmol) in THF (5.84 mL, 1.0
mol/L), 2b (661 mL, 694 mg, 6.42 mmol, 1.1 eq.), and DBU
SCHEME 2 Cross-linking of polymer 1 with a diamine or a diol.
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SCHEME 3 Reaction of 6 with 2a or 2b, and polymerization of the corresponding adducts.
(872 mL, 889 mg, 5.84 mmol, 100 mol %) were added at
room temperature, and the mixture was stirred for 15 min.
The crude mixture was purified by silica gel column chroma-
tography (eluent: ethyl acetate) to give 1.55 g (5.56 mmol)
of thiouretane (7b, see Scheme 3) as a white solid in 95%
yield.
ACH3) ppm; IR (ATR): mmax 5 3253 (w, NAH), 2944 (w,
CAH), 1723 (s, C@O), 1544 (s, CSNH), 1453 (w, Ph), 1342
(w, CSNH), 1151 (s, CAO) cm21
.
Polymerization of 7b
A monomer 7b (500 mg, 1.79 mmol), benzene (1 drop), and
AIBN (5.9 mg, 0.036 mmol, 2 mol %) were dissolved in MEK
(1.79 mL, 1.0 mol/L). After the solution was degassed
through three freeze-pump-thaw cycles, the ampoule tube
was sealed, and the mixture was stirred for 24 h at 60 ꢀC.
After cooling, the reaction mixture was poured into a large
amount of diethyl ether (200 mL), and the resulting precipi-
tate was collected by filtration to give 388 mg of polymer
(8b, see Scheme 3) as a white solid in 78% yield.
Mp 52.0–57.5 ꢀC; Rf value 0.7 (eluent: ethyl acetate); 1H
NMR (400 MHz, 293 K, CDCl3, d): 7.44–7.32 (m, 5 H, PhAH),
6.90 (br, 0.3 H, ANHA), 6.66 (br, 0.7 H, ANHA), 6.13 (dq,
J 5 1.4, 1.4 Hz, 1 H, CH2@C<), 5.61 (dq, J 5 1.4, 1.4 Hz, 1 H,
CH2@C<), 5.55 (s, 0.6 H, ACH2Ph), 5.49 (s, 1.4 H, ACH2Ph),
4.37 (t, J 5 5.0 Hz, 1.4 H, AOCH2CH2A), 4.23 (t, J 5 5.0 Hz,
0.6 H, AOCH2CH2A), 3.92 (dt, J 5 5.0, 5.0 Hz, 1.4 H,
AOCH2CH2NHA), 3.62 (dt, J 5 5.0, 5.0 Hz, 0.6 H,
AOCH2CH2NHA), 1.95 (dd, J 5 1.4, 1.4 Hz, 3 H, C@CACH3)
ppm; 13C NMR (100 MHz, 293 K, CDCl3, d): 190.7 (C@S),
190.0 (C@S), 167.5 (C@O), 167.3 (C@O), 135.9 (Ph), 135.8
(CH2@C<), 135.4 (Ph), 128.7 (Ph), 128.6 (Ph), 128.4 (Ph),
128.3 (Ph), 126.6 (Ph), 126.5 (CH2@C<), 126.0 (Ph), 73.4
(ACH2Ph), 72.2 (ACH2Ph), 66.5 (AOCH2A), 62.7 (AOCH2A),
44.6 (ACH2NHA), 42.2 (ACH2NHA), 18.5 (ACH3) ppm; IR
(ATR): mmax 5 3305 (w, NAH), 2925 (w, CAH), 1708 (s,
C@O), 1635 (w, C@C), 1520 (m, CSNH), 1453 (w, Ph), 1294
Mn 35,600; Mw 153,100; Mw/Mn 4.3; Tg 56 ꢀC; Td5 181 ꢀC;
1H NMR (400 MHz, 293 K, DMSO-d6, d): 9.32–8.70 (m, 1 H,
ANHA), 7.39–7.17 (m, 5 H, PhAH), 5.50–4.80 (m, 2 H,
ACH2Ph), 4.14–3.82 (m, 2 H, AOCH2CH2A), 3.70–3.29 (m, 2
H, AOCH2CH2NHA), 1.96–1.57 (m, 2 H, ACH2C(CH3)A),
1.02–0.64 (m, 3 H, ACH3) ppm; IR (ATR) mmax: 3294 (w,
NAH), 2935 (w, CAH), 1723 (s, C@O), 1520 (s, CSNH), 1453
(w, Ph), 1337 (w, CSNH), 1146 (s, CAO) cm21
.
(m, CSNH), 1150 (s, CAO), 942 (m, CAO), 694 (m, Ph) cm21
;
RESULTS AND DISCUSSION
HRMS (EI, m/z): [m]1 calcd for C14H17NO3S, 279.0929;
Polymer Reactions
Reaction of Isothiocyanate-Containing Polymer 1 with a
Primary Amine
found, 279.0930.
Polymerization of 7a
In advance of the polymer reactions, reactivity of a model
isothiocyanate was examined. The results of model reactions
were summarized in Supporting Information. Taking the data
of the model compound into consideration, reactivity of iso-
thiocyanate in polymer side chains with various nucleophiles
were investigated (Scheme 1). Reaction with a primary
amine was examined at first. A THF solution of 1 and 2a
was stirred at room temperature for 3 h (Table 1, entry 2),
and the resulting polymeric product was collected by precip-
itating in diethyl ether.
A monomer 7a (500 mg, 1.80 mmol), benzene (1 drop), and
AIBN (5.9 mg, 0.036 mmol, 2 mol %) were dissolved in MEK
(1.80 mL, 1.0 mol/L). After the solution was degassed
through three freeze-pump-thaw cycles, the ampoule tube
was sealed, and the mixture was stirred for 24 h at 60 ꢀC.
After cooling, the reaction mixture was poured into a large
amount of diethyl ether (200 mL), and the resulting precipi-
tate was collected by filtration to give 368 mg of polymer
(8a, see Scheme 3) as a white solid in 73% yield.
1
Mn 55,500; Mw 205,800; Mw/Mn 3.7; Tg 67 ꢀC; Td5 181 ꢀC;
1H NMR (400 MHz, 293 K, DMSO-d6, d): 7.86–7.77 (m, 1 H,
ANHCH2Ph), 7.47–7.35 (m, 1 H, AOCH2CH2NHA), 7.31–7.17
(m, 5 H, PhAH), 4.71–460 (m, 2 H, ACH2Ph), 4.08–3.94 (m,
2 H, AOCH2CH2A), 3.76–3.62 (m, 2 H, AOCH2CH2NHA),
1.97–1.70 (m, 2 H, ACH2C(CH3)A), 1.05–0.75 (m, 3 H,
Figure 1(b) shows a H NMR spectrum of the obtained poly-
mer. A broad signal h around 7.36–7.13 ppm assigned to the
phenyl protons of benzyl group was observed. Broad signals
f around 8.04–7.70 ppm and e around 7.58–7.36 ppm
assigned to a thiourea NAH protons were observed. A signal
of the methylene protons d adjacent to the thiourea group
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FIGURE 1 1H NMR spectra of (a) 1, (b) 3a, (c) 3b, (d) 3c, (e) 3d, (f) 3e. (400 MHz, DMSO-d6, 353 K)
were observed around 3.81–3.56 ppm. Figure 2(b) shows an
IR spectrum of 3a. A sharp absorption of C@S stretching of
the thiourea was observed at 1548 cm21 along with a weak
absorption of ANH bending at 1344 cm21. Absorption attrib-
uted to the N@C@S stretching of the stating material had
disappeared. These data indicate the occurrence of
FIGURE 2 IR spectra of (a) 1, (b) 3a, (c) 3b, (d) 3c, (e) 3d, (f) 3e. (ATR, 293 K)
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d adjacent to the thiourethane group were observed around
3.70 and 3.40 ppm. Because of the tautomerization of the
thiourethane, signals of the methylene protons adjacent to
thiourethane appeared at two positions.17 Figure 2(c) shows
an IR spectrum of 3b. A sharp absorption of C@S stretching
of the thiourethane was observed at 1518 cm21 along with a
weak absorption of ANH bending at 1399 cm21. Absorption
attributed to the N@C@S stretching completely disappeared.
These data suggested that the nucleophilic addition of 2b to
the isothiocyanate occurred quantitatively.
Thermal stability of 3b was examined by TGA (Fig. 3). Td5 of
ꢀ
the 3b was determined to be 154 C. Compared from the Td5
of the starting polymer 1, the Td5 of polymer was far lower.
This is probably due to thermal instability of the thiour-
ethane moiety. Thermal phase transition of 3b was exaꢀmined
by DSC. The glass transition of 3b was observed at 58 C.
FIGURE 3 TGA curves of polymers. [Color figure can be
viewed in the online issue, which is available at wileyonlineli-
brary.com.]
Reaction of Isothiocyanate-Containing Polymer 1 with a
Thiol
nucleophilic addition of 2a to the isothiocyanate in the poly-
mer side chain.
We investigated the reactivity of polymer 1 with benzyl mer-
captan. Before the polymer reactions, we examined the reac-
tivity of a model isothiocyanate. Like alcohols, thiols did not
react with isothiocyanate without a catalyst (see Supporting
Information, Fig. S6). So, we chose DBU as a catalyst for
nucleophilic addition of thiol to the isothiocyanate. A THF
solution of 1, 2c, and DBU (5 mol % to 2c) as catalyst was
stirred at room temperature for 12 h (Scheme 1, Table 1,
entry 4), and polymeric products were collected by precipi-
tation in diethyl ether.
Thermal stability of 3a was examined by TGꢀA (Fig. 3). The
polymer 3a was thermally stable before 180 C and showed
no decomposition. Td5 of the polymer 3a was determined to
be 193 ꢀC. Compared from the Td5 of unreacted polymer 1,
the Td5 of copolymer was far lower. This is probably due to
thermal instability of the thiourea moiety. Thiourea may
decompose at a lower temperature than the main chain of
the polymer and the isothiocyanato group. Thermal phase
transition of 3a was examined by DSC. The glass transition
of polymer 3a was observed and the glass transition temper-
ature (Tg) was determined to be 89 ꢀC. The Tg of 3a was
slightly higher than 1. This raise of Tg maybe due to the
bulkiness of the side chains composed of benzyl moieties
and the hydrogen bonding caused by the thioureas.
1
Figure 1(d) shows a H NMR spectrum of 3c. A broad signal
g around 7.57–6.90 ppm assigned to the phenyl protons of
benzyl group was observed. A signal of the methylene pro-
tons adjacent to dithiocarbamate d around 3.97–3.63 ppm
slight upfield sifted, because of electron density decrease
due to nucleophilic addition. Figure 2(d) shows an IR spec-
trum of 3c. A sharp absorption of C@S stretching of the
dithiocarbamate was observed at 1494 cm21 along with a
weak absorption of ANH bending at 1381 cm21. These data
suggested the nucleophilic addition of 2c to isothiocyanate
was occurred in polymer side chain.
Reaction of Isothiocyanate-Containing Polymer 1 with a
Primary Alcohol
We investigated the reactivity of isothiocyanate-containing
polymer 1 with a primary alcohol, 2b. In advance of the
polymer reactions, reactivity of a model isothiocyanate was
examined. No reaction ocꢀcurred between 2b and model iso-
thiocyanate in THF at 60 C for 3 days (see Supporting Infor-
mation, Fig. S5). Then, we examined the catalytic effect of
several Lewis bases or acids for the addition. The best con-
version of the isothiocyanate was achieved using DBU as a
catalyst (see Supporting Information Table S2). Based on
these results, we chose DBU as a catalyst for nucleophilic
additions of alcohols to the isothiocyanate. A THF solution of
1, 2b, and DBU (1.0 eq. to 2b) as catalyst was stirred at
room temperature for 24 h (Scheme 1, Table 1, entry 3), and
the resulting polymeric products were collected by precipita-
tion in diethyl ether.
Figure 3(e) shows the TGA curves for polymer 3c and Td5 of
ꢀ
3c was 154 C. The Td5 of 3c was far lower than that of the
starting polymer 1, which may be because thermal stability
of the dithiocarbamate is much lower than that of the iso-
thiocyanate. The glass transitions of 3c was observed at 68
ꢀC. The Tg of 3c was little higher than 1. This rise of Tg was
caused by bulky side chain of benzyl moieties and hydrogen
bonds of dithiocarbamate.
Reaction of Isothiocyanate-Containing Polymer 1 with 2-
Aminoethanol (2d)
Reaction of the polymer 1 and 2-aminoethanol (2d) was
examined in THF at room temperature (Scheme 1, Table 1,
1
1
Figure 1(c) shows a H NMR spectrum of 3b. A broad signal
entry 5). Figures 1(e) and 2(e) show a H NMR and IR spec-
g around 7.65–6.95 ppm assigned to phenyl protons of the
benzyl group was observed. Signals of the methylene protons
trum of the product. These data suggested that the nucleo-
philic addition of amine to isothiocyanate occurred in the
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FIGURE 4 IR spectra of (a) 1, (b) 5a, (c) 5b. (ATR, 293 K)
polymer side chain, with the alcohol moiety remaining
unreacted with the isothiocyanate.
Figure 4(b) shows an IR spectrum of the obtained net-
worked polymer 5a. A sharp absorption of C@S stretching of
the thiourea was observed at 1545 cm21 with a weak
absorption of ANH bending at 1347 cm21. Absorption attrib-
uted to the N@C@S stretching decreased. These data sug-
gested that nucleophilic addition of the amine to the
isothiocyanate occurred in the polymer side chain.
Reaction of Isothiocyanate-Containing Polymer 1 with 2-
Mercaptethanol (2e)
Reaction of polymer 1 and 2-mercaptoethanol (2e) was
examined by stirring a THF solution of the mixture with
DBU (5 mol % to 2e) at room temperature for 12 h. After
the reaction, the corresponding dithiocarbamate adduct poly-
mer 3e was selectively obtained (Scheme 1, Table 1, entry
Figure 5 shows the TGA curves for 5a, indicating that 5a
was thermally stable before 150 ꢀC. Td5 of 5a was deter-
1
ꢀ
6). Figures 1(f) and 2(f) show a H NMR and IR spectrum of
mined to be 168 C. However, if it is compared with the Td5
3e. These data suggested that the nucleophilic addition of
the thiol group to the isothiocyanate selectively occurred
without the occurrence of a reaction between hydroxyl group
and the isothiocyanate.
Cross-Linking of Isothiocyanate-Containing Polymer 1
Cross-Linking of Polymer 1 with a Diamine
The reactivity of nuclephiles to isothiocyanato groups in the
polymer side chains was applied to cross-linking of the poly-
mer. A THF solution of 1 and hexamethylenediamine (4a)
([NH2]/[isothiocyanate moiety of 1] 5 0.1) was stirred at
room temperature (Scheme 2). Viscosity of the mixture rap-
idly increased, and the magnetic stirring stopped in 1 min
after the addition of the diamine. After the reaction, the mix-
ture was poured into a large amount of diethyl ether, and
the resulting precipitate was collected and dried to afford
the networked polymer as a white solid. Supporting Informa-
tion, Figure S30 shows the photographs of the polymer mix-
tures before and after the cross-linking. A transparent gel
was formed after the cross-linking.
FIGURE 5 TGA curves of networked polymers. [Color figure
can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
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FIGURE 6 1H NMR spectrum of (a) 6 (b) 7a (c) 7b (d) 8a (e) 8b (400 MHz, CDCl3, 293 K for 6, 7a, and 7b, DMSO-d6, 353 K for 8a
and 8b). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
of 1, the Td5 of polymer 5a was far lower. This is probably
because of a thermal unstability of the thiourea linkage and
the network formation did not contribute much to increase
the thermal stability of the material in this case.
of 5b was determined to be 129 ꢀC. This unstability is due
to thermal unstability of the thiouarethane. However, this
unstability may be useful, when the networked polymers
need to be decomposed in a proactive manner.
Polymerization of Monomers Prepared from 2-
Isothiocyanatoethyl Methacrylate with Amine or Alcohol
Polymerization of Monomer Obtained from Benzylamine/
2-Isothiocyanatoethyl Metharylate
Monomer 7a was prepared by adding 2a to 6 in a similar
manner as the model reaction described previously (Scheme
3). The corresponding monomer 7a was easily obtained in
99% isolated yield. 1H NMR [Fig. 6(b)], 13C NMR [Fig. 7(b)],
and IR [Fig. 8(b)] spectra for the obtained 7a clearly showed
that the adduct was obtained.
Cross-Linking of Isothiocyanate-Containing Polymer 1
with a Diol
A THF solution of 1, hexamethylene glycol (4b) ([OH]/[iso-
thiocyanate moiety of 1] 5 0.1), and DBU (5 mol % to 4b) as
the catalyst was stirred at room temperature (Scheme 2).
After 12 h, the magnetic stirring stopped because of the sig-
nificant increase of the solution viscosity. After the reaction, a
mixture was poured into a large amount of diethyl ether, and
the resulting precipitates were collected and dried to afford
the networked polymer as a white solid. Supporting Informa-
tion, Figure S31 shows the photographs of the polymer solu-
tions in THF before and after the cross-linking. A transparent
self-standing gel was formed after the cross-linking with 4b.
Polymerization of 7a was performed in a similar manner as
6 (Scheme 3). After the polymerization, the mixture was rep-
recipitated and collected by filtration to yield corresponding
polymer 8a in 73%. 1H NMR and IR spectra of the polymer
8a are also shown in Figures 6(d) and 8(d), which are com-
pletely identical to those of the polymer 3a prepared by a
postpolymerization modification of polymer 1 with 2a. Fig-
ure 9 shows the TGA curves of polymer 8a. The Td5 of 8a
In the IR spectrum of 5b [Fig. 4(c)], a sharp absorption of
C@S stretching of the thiourea was observed at 1542 cm21
along with a weak absorption of ANH bending at 1350
cm21
. Absorption attributed to the N@C@S stretching
decreased. These data suggested that addition of the alcohol
to the isothiocyanate occurred.
ꢀ
was determined to be 181 C, which was little lower than 3a
ꢀ
(193 C). The glass transition of 8a was determined to be 67
ꢀ
TGA curves of the networked polymer 5b [Fig. 5(d)] indi-
cated that 5b was thermally unstable and that decomposi-
tion started just after the beginning of the heating. The Td5
ꢀC. The Tg of 8a was little lower than 3a (89 C). These dif-
ferences in thermal properties may be caused by the differ-
ence of molecular weight between 3a and 8a.
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FIGURE 7 13C NMR spectra of (a) 6 (b) 7a (c) 7b. (CDCl3, 100 MHz, 293 K). [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
FIGURE 8 IR spectra of (a) 6 (b) 7a (c) 7b (d) 8a (e) 8b. (ATR, 293 K)
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urea monomer 7a and thiourethane monomer 7b were pre-
pared from compound 6 with 2a or 2b, and they could be
polymerized to give the corresponding polymers 8a or 8b,
which were identical to polymers 3a or 3b. These results indi-
cated that isothiocyanate-containing polymer 1 can react with
various nucleophilies. Using this reactivity of isothiocyanate in
the side chain of polymer, various functional substituents such
as a fluorescent group or a catalytic group can be introduced
into the polymer side chain. The polymers containing isothiocy-
anate structures in the side chains are expected to be applica-
ble in a wide range of functional materials.
ACKNOWLEDGMENTS
This work was financially supported by JSR Corporation Inc.
High-resolution mass spectral measurement was performed
under the Cooperative Research Program of “Network Joint
Research Center for Materials and Devices.”
FIGURE 9 TGA curves of 1, 3a, 3b, 8a, and 8b. [Color figure
can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
Polymerization of Monomer Obtained from Benzyl
Alcohol/2-Isothiocyanatoethyl Metharylate
REFERENCES AND NOTES
Monomer 7b was also prepared by adding benzyl alcohol 2b to
compound 6 in the presence of DBU catalyst (Scheme 3). The
corresponding monomer 7b was obtained in 95% isolated
yield. 1H NMR [Fig. 6(c)], 13C NMR [Fig. 7(c)], and IR [Fig. 8(c)]
spectra clearly revealed the chemical structure of monomer 7b.
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Polymerization of 7b was performed in a similar manner as
6 (Scheme 3) to obtain the corresponding polymer 8b in
78% yield. 1H NMR [Fig. 6(e)] and IR [Fig. 8(e)] spectra of
the obtained polymer 8b were identical to those of the poly-
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Figure 9 shows the TGA curves for polymer 8b. The Td5 of 8b
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ꢀ
was determined to be 181 C, which was little higher than 3b
ꢀ
(154 C). The glass transiꢀtions of 8b was observed and the Tg
was determined to be 56 C. The Tg of 8b was little lower than
3b (58 ꢀC). These differences in thermal properties may be
caused by the difference in molecular weight between 3b and 8b.
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CONCLUSIONS
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In this study, we investigated the reactivity of isothiocyanate
groups in the side chain of polymethacrylate. The isothiocya-
nates reacted with amine without a catalyst to give the cor-
responding thiourea. Conversely, the isothiocyanates did not
react with alcohol and thiol without a catalyst. Addition of
alcohols or thiols to the isothiocyanates needed catalysts
such as DBU. The Tgs of the obtained polymers were slightly
higher than that of the original polymer. However, thermal
decomposition temperatures of the obtained polymers were
lower than that of the original polymer, which may be due to
thermal unstability of the thiourea, thiourethane, and dithio-
carbamate structure in the obtained polymers. Using this
reactivity of the isothiocyanate, networked polymers were syn-
thesized from polymer 1 and diamine 4a or diol 4b. Networked
polymers were synthesized simply and easily. In addition, thio-
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