Synthesis of high-performance polyurethanes with rigid 5-6-5-fused ring system in the main chain from naturally occurring myo-inositol

Article abstract of DOI:10.1002/pola.26805

A bisketal of myo-inositol was used as a diol-type monomer for synthesis of polyurethanes. The monomer was obtained by treatment of myo-inositol with 1,1-dimethoxycyclohexane in the presence of p-toluenesulfonic acid as a catalyst. The ketalization resulted in the formation of a 5-6-5-fused ring system, which endowed the diol-type monomer with high rigidity. The diol readily reacted with diisocyanate to give the corresponding polyurethane, which exhibited excellent heat resistance due to the rigid 5-6-5 system in the main chain. Copyright

Full text of DOI:10.1002/pola.26805

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Synthesis of High-Performance Polyurethanes with Rigid 5-6-5-Fused
Ring System in the Main Chain from Naturally Occurring myo-Inositol
Atsushi Sudo, Yoshiya Shibata, Ayano Miyamoto
Department of Applied Chemistry, Faculty of Science and Engineering, Kinki University, Higashi Osaka, Osaka 577–8502, Japan
Correspondence to: A. Sudo (E-mail: asudo@apch.kindai.ac.jp)
Received 25 March 2013; accepted 1 June 2013; published online
DOI: 10.1002/pola.26805
ABSTRACT: A bisketal of myo-inositol was used as a diol-type
monomer for synthesis of polyurethanes. The monomer was
obtained by treatment of myo-inositol with 1,1-dimethoxycy-
clohexane in the presence of p-toluenesulfonic acid as a cata-
lyst. The ketalization resulted in the formation of a 5-6-5-fused
ring system, which endowed the diol-type monomer with high
rigidity. The diol readily reacted with diisocyanate to give the
corresponding polyurethane, which exhibited excellent heat
resistance due to the rigid 5-6-5 system in the main chain.
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2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym.
Chem. 2013, 00, 000–000
KEYWORDS:
bisketal; myo-inositol; polyurethanes; renewable
resources; step-growth polymerization
INTRODUCTION Development of monomers with highly rigid
structures and their use in polymerizations is a promising
approach to high-performance polymer materials that exhibit
with cyclohexanone or its derivatives, is one of such deriva-
tives that has been conveniently used for synthesizing vari-
2
4–26,28
ous inositol derivatives.
We have focused our interest
1
–6
excellent heat resistance and mechanical strength.
Bifunc-
on this molecule as an intriguing monomer for polymer syn-
thesis from the following two viewpoints (Scheme 1): (1)
Bisketal 1 is a diol-type monomer that can be used for vari-
ous polyaddition and polycondensation systems. (2) Bisketal
1 has a rigid 5-6-5-fused ring system of which incorporation
into main chains of polymers will endow these polymers
with high thermal stability and mechanical strength. Praefcke
tional monomers involving diols bearing nonaromatic and
rigid cyclic cores with conformational restriction are of high
interest because of their facile and versatile applications to
polycondensation and polyaddition systems that permit
7
,8
diverse designs of high-performance polymers.
Recently,
derivation of sugars into conformationally rigid monomers
via selective transformation of their functional groups has
gained increasing interest, because this strategy meets the
current demands for polymer synthesis from nonfossil and
2
9
et al. have disclosed their conception of utilization of 1 for
synthesis of polycondensates in their patent application:
What they intended was to synthesize polymers inheriting
the hydroxyl groups from myo-inositol via polycondensation
of bisketal 1 as a protected inositol followed by successive
deprotection of the ketal moieties in the polymer side
chains; however, there is no description on experimental
details and properties of polymers.
9
,10
renewable feed stocks.
1,4:3,6-Dianhydrohexitols includ-
ing isosorbide and their derivatives are such a class of
1
1–15
bifunctional monomers derived from monosaccharides.
Bisketals of sugars with bicyclic structures such as those of
mannitol are also a class of rigid monomers of which utiliza-
tion for synthesizing several polycondensates exhibiting
1
6,17
The present contribution describes the details of our investi-
gation on the utilization of racemic 1 as a diol-type mono-
mer for polyurethane synthesis.
excellent thermal properties has been demonstrated.
myo-Inositol is a naturally occurring cyclic hexaol that exists
in organs as its phosphate derivatives such as phosphatidyl
EXPERIMENTAL
1
8,19
inositol and phytic acid.
So far, various bioactive mole-
cules bearing inositol-derived components have been targets
of precise synthesis, and thus several efficient strategies
for regioselective protection of inositol have been devel-
Materials
myo-Inositol, 1,1-dimethoxycyclohexane, p-toluenesulfonic
acid were purchased from Kishida Chemical and used as
received. Phenyl isocyanate, hexamethylene diisocyanate
(HMDI), isophorone diisocyanate (IPDI), methylenediphenyl
2
0–28
oped.
DL-1,2:4,5-Di-O-cyclohexylidene-myo-inositol (1),
which can be synthesized easily by treating myo-inositol
Additional Supporting Information may be found in the online version of this article.
2013 Wiley Periodicals, Inc.
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concentrated under reduced pressure. The resulting residue
was dissolved in 30 mL, and to the resulting solution, hexane
(
300 mL) was added slowly. The resulting precipitates were
isolated by filtration with suction and dried under vacuum
0
to obtain a mixture of 1 and its isomer 1 . The mixture of 1
0
and 1 was recrystallized from a mixture of hexane (70 mL)
and ethyl acetate (50 mL) to obtain pure 1 (11.8 g, 34.7
ꢀ
mmol; 21%) as a colorless crystal: mp, 180.6–181.8 C.
1
H-NMR (400 MHz, CDCl , at rt, d): 4.48 (t, J 5 4.6, 1H),
3
4
2
2
1
3
.12–3.98 (m, 2H), 3.92–3.79 (m, 2H), 3.32 (t, J 5 10.3, 1H),
.79 (d, J 5 2.0, 1H), 2.52 (d, J 5 9.3, 1H), 1.80–1.34 (m,
1
0H); H-NMR (400 MHz, DMSO-d , at rt, d): 5.42 (d, J 5 5.4,
6
H), 5.25 (d, J 5 6.3, 1H), 4.20 (t, J 5 2.3, 1H), 3.85 (m, 2H),
.62 (t, J 5 5.0, 1H), 3.51 (m, 1H), 3.20 (t, J 5 5.4, 1H), 1.50
1
3
ꢀ
(m, 20H); C-NMR (100 MHz, DMSO-d , at 60 C) d 110.72,
6
1
3
2
08.68, 81.46, 78.36, 78.09, 77.01, 73.84, 68.17, 37.65,
SCHEME 1 Concept of this work: Derivation of myo-inositol
6.19, 34.84, 24.59, 23.62, 23.40, 23.31; IR (KBr): m 5 2937,
into
a
rigid diol by ketalization and its use for polymer
21
861, 1452, 1371, 1080 cm
.
synthesis.
0
1
was isolated by column chromatography (silica gel,
0
4
,4 -diisocyanate (MDI), and 2,6-tolylenediisocyanate (TDI)
eluent 5 hexane 1 ethyl acetate in 3:1) as a white solid.
were purchased from Tokyo Chemical Industry and distilled
under vacuum prior to use. N,N-Dimethylformamide (DMF)
was purchased from Wako Pure Chemical Industries, dried
over calcium hydride, and distilled prior to use for the polyur-
ethane synthesis. Other reagents and solvents were purchased
from Wako Pure Chemical Industries and used as received.
1
H-NMR (400 MHz, CDCl , at rt, d): 4.64 (dd, J 5 2.9, 5.4,
H), 4.20 (t, J 5 5.8, 1H), 3.97 (t, J 5 9.7, 1H), 3.80–3.68 (m,
H), 3.13 (br s, 1H), 1.81–1.32 (m, 20H).
3
1
3
Reaction of 1 with Phenyl Isocyanate
In a 20-mL two-necked flask, 1 (1.00 g, 2.94 mmol) and
dibutyltin dilaurate (DBTDL) (0.19 g, 0.30 mmol) were
placed. DMF (3.0 mL) was added to dissolve these com-
pounds, and the flask was flushed with argon. To the solu-
tion, phenyl isocyanate (709 mg, 5.95 mmol) was added. The
Instruments
1
13
NMR spectra (400 MHz for H; 100.6 MHz for C) were
recorded on a JEOL NMR spectrometer model JNM-AL400.
Chemical shift d and coupling constant J are given in ppm
and Hz, respectively. IR spectra were obtained on a JASCO
FT/IR-470 and wave number m is given in cm . Number
average molecular weight (M ) and weight average molecular
ꢀ
resulting solution was stirred at 60 C for 24 h. After cool-
2
1
ing, DMF was removed under reduced pressure, and the
resulting residue was fractionated by silica gel column chro-
matography (eluent 5 hexane 1 ethyl acetate in 1:1) to
obtain the corresponding adduct 2 (1.55 g, 2.68 mmol; 91%)
n
weight (M ) were estimated by size exclusion chromatogra-
w
phy (SEC), performed on a Tosoh chromatograph model
HLC-8120GPC equipped with Tosoh TSK gel-Super HM-H
styrogel columns (6.0 mm x 15 cm), using DMF containing 1
wt % of lithium bromide as an eluent at a flow rate of 0.6
mL/min after calibration with polystyrene standards. Ther-
mogravimetric analysis (TGA) and differential scanning calo-
rimetry (DSC) were performed with a SEIKO Instruments
model EXSTAR6000 under a nitrogen flow.
ꢀ
as a colorless crystal: mp, 250.0–250.3 C.
1
H-NMR (400 MHz, DMSO-d , at rt, d): 10.1 (s, 1H), 9.85 (s,
6
1
H), 7.50 (t, J 5 9.2, 4H), 7.29 (t, J 5 7.7, 4H), 7.01 (t, J 5 7.3,
H), 5.36 (dd, J 5 10.5, 4.1, 1H), 5.17 (dd, J 5 11.0, 7.1, 1H),
.59 (t, J 5 4.4, 1H), 4.35 (t, J 5 5.7, 1H), 4.09 (t, J 5 10.0,
2
4
1
1
3
H), 3.87 (t, J 5 10.1, 1H), 1.85–1.20 (m, 20H); C-NMR
ꢀ
(100 MHz, DMSO-d , at 60 C, d): 152.45, 138.94, 138.83,
6
1
7
2
1
6
28.81, 122.66, 122.54, 118.18, 112.41, 110.05, 78.69, 75.37,
4.97, 74.74, 74.48, 70.20, 36.92, 35.81, 34.96, 24.33, 24.29,
3.49, 23.31. 23.30, 23.25; IR (KBr): m 5 3384, 2940, 1719,
Synthesis
Synthesis of Diol-type Monomer 1
To a suspension of myo-Inositol (30.0 g, 167 mmol) in DMF
2
1
526, 1445 cm . Anal. calcd. for C H N O : C 66.42, H
3
2 38 2 8
(
210 mL), cyclohexanone dimethylacetal (75 mL, 520 mmol)
.62, N 4.84; found: C 66.33, H 6.58, N 4.83.
and p-toluenesulfonic acid (843 mg, 4.43 mmol) were added.
The resulting mixture was heated at 100 C for 3 h to obtain
ꢀ
When the reaction was performed at ambient temperature, a
:1 adduct of diol 1 and phenyl isocyanate was given. The
a solution. After cooling, triethylamine (2.5 mL) was added
and the volatiles were removed under reduced pressure. The
resulting residual solid was dissolved in ethyl acetate (200
mL) and washed with 5% aqueous solution of sodium car-
bonate (100 mL) twice and water (100 mL). The ethyl ace-
tate layer was dried over sodium sulfate, filtered, and
1
adduct 3 was isolated by column chromatography (eluent 5
hexane 1 ethyl acetate in 1:2): mp, 229.3–230.1 C.
ꢀ
1
H-NMR (400 MHz, DMSO-d , at rt, d): 9.75 (s, 1H), 7.45 (d,
6
J 5 8.3, 2H), 7.27 (t, J 5 7.8, 2H), 6.98 (t, J 5 7.4,1H), 5.45
2
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ꢀ
(d, J 5 6.4, 1H), 5.06 (dd, J 5 11.1, 7.2, 1H), 4.28 (t, J 5 4.4,
d6, at 60 C, d): 153.26, 152.27, 136.81, 136.71, 136.18,
136.01, 130.05, 115.73, 112.19, 112.15, 112.11, 109.80,
109.75, 109.70, 109.64, 78.46, 75.00, 74.82, 74.64, 70.41,
70.21, 36.80, 35.69, 34.64, 24.21, 23.29, 23.07, 16.69; IR
1
H), 4.14 (dd, J 5 7.1, 4.6, 1H), 4.04–3.97 (m, 1H), 3.81 (t,
1
3
J 5 9.8,1H), 3.50 (t, J 5 10.1, 1H), 1.76–1.22 (m, 20H); C-
NMR (100 MHz, DMSO-d , at rt, d): 152.51, 138.97, 128.78,
6
2
1
122.53, 118.15, 111.67, 109.45, 78.41, 78.34, 77.69, 75.09,
(KBr): m 5 2937, 1732, 1532, 1225, 1063 cm
.
7
4.95, 37.17, 36.08, 35.87, 34.93, 24.43, 23.50, 23.41, 23.31,
21
23.22; IR (KBr): m 5 3493, 3382, 2942, 1718, 1529 cm
.
Polyaddition of Trans-1,4-cyclohexanediol and
Diisocyanates
Anal. calcd. for C H NO : C 65.34, H 7.24, N 3.05; found: C
2
5
33
7
65.19, H 7.29, N 3.00.
In a 20-mL two-necked flask, CHD (499 mg, 4.30 mmol),
hexamethylene diisocyanate (723 mg, 3.00 mmol) and
DBTDL (0.27 g, 0.22 mmol) were placed and flushed with
argon. DMF (4.3 mL) was added, and the resulting solution
Polyaddition of 1 and Diisocyanates
In a 20-mL two-necked flask, 1 (1.02 g, 3.00 mmol), hexam-
ethylene diisocyanate (505 mg, 3.00 mmol), and DBTDL
ꢀ
was stirred at 60 C for 24 h. After cooling, the reaction mix-
(
0.19 g, 0.30 mmol) were placed and flushed with argon.
ture was poured into methanol (150 mL) to obtain the cor-
responding polyurethane 5a (1.21 g, 99%) as a colorless
solid. 5a was insoluble in chloroform, THF, DMF, and DMSO
and thus its NMR and SEC analyses were not available.
DMF (3.0 mL) was added, and the resulting solution was
stirred at 60 C for 24 h. After cooling, the solution was
poured into methanol (150 mL) to obtain the corresponding
ꢀ
polyurethane 4a (1.51 g, 99%) as a colorless solid.
With using other diisocyanates (IPDI, MDI, and TDI) in the
same way, the corresponding polyurethanes 5b, 5c, and 5d
were obtained in 35, 99, and 98%, respectively. The spectro-
scopic data of the polyurethanes are shown below.
With using other diisocyanates (IPDI, MDI, and TDI) in the
same way, the corresponding polyurethanes 4b, 4c, and 4d
were obtained, respectively. The spectroscopic data of the
polyurethanes are shown below.
2
1
5a: IR (Kbr): m 5 2940, 2863, 1689, 1533, 1261 cm
.
1
ꢀ
a: H-NMR (400 MHz, DMSO-d , at 60 C, d): 7.30 (s, 1H),
6
4
1
ꢀ
5
b: H-NMR (400 MHz, DMSO-d , at 60 C, d): 6.9–6.4 (br m,
6
6
(
.99 (s, 1H), 5.07–4.96 (m, 2H), 4.48 (t, J 5 6.0 Hz, 1H), 4.16
t, J 5 5.9 Hz, 1H), 3.93 (t, J 5 5.9 Hz, 1H), 3.63 (t, J 5 10 Hz,
H), 2.98 (t, J 5 10 Hz, 1H), 2.50 (d, J 5 5.6 Hz, 4H), 1.67–
2
H), 4.54 (br s, 2H), 3.59 (br s, 1H), 2.74 (br s, 2H), 1.88 (br
1
3
s, 4H), 1.44 (br s, 6H), 1.15–0.78 (br m, 11H); C-NMR (100
MHz, DMSO-d , at 60 C, d): 154.60, 70.09, 35.89, 34.59,
1
1
1
4
2
1
ꢀ
1
3
ꢀ
6
.26 (m, 28H); C-NMR (100 MHz, DMSO-d , at 60 C, d):
6
31.00, 27.90, 27.11, 22.75. In addition to these major signals,
54.87, 111.85, 109.35, 78.61, 75.15, 74.75, 74.15, 69.78,
8.35, 36.73, 35.74, 35.65, 34.68, 29.09, 28.99, 25.70, 25.65,
4.20, 23.23, 23.08, 22.99; IR (KBr): m 5 2939, 2861, 1715,
several small signals were observed. IR (KBr): m 5 2946,
2
1
1698, 1507, 1238, 1042 cm
.
2
1
521, 1239 cm
.
1
5
c: H-NMR (400 MHz, DMSO-d
6
, at rt, d): 9.21 (s, 2H), 7.36
1
ꢀ
(d, J 5 7.7, 4H), 7.08 (d, J 5 7.7, 4H), 4.71 (s, 2H), 3.81 (s,
4
2
(
3
1
4
2
2
b: H-NMR (400 MHZ, DMSO-d , at 60 C, d): 7.36–6.75 (m,
6
1
3
2
H), 2.01 (s, 4H), 1.57 (s, 4H); C-NMR (100 MHz, DMSO-d6,
H), 5.08–4.89 (br, 2H), 4.45 (s, 1H), 4.14 (s, 1H), 3.96–3.85
br, 1H), 3.59 (br, 2H), 2.84–2.60 (br, 1H), 1.70–0.70 (m,
4H); C-NMR (100 MHz, DMSO-d , at 60 C, d): 155.69,
54.29, 111.69, 109.31, 78.5, 75.2, 74.7, 74.2, 69.9, 54.5,
6.4, 45.5, 44.03, 41.3, 36.7, 36.2, 35.8, 34.65, 30.90, 27.19,
6.66, 24.20, 23.22, 23.07, 22.79, 22.71; IR (KBr): m 5 2937,
ꢀ
at 60 C, d): 152.72, 136.75, 135.06, 128.37, 118.27, 70.60,
27.92; IR (KBr): m 5 2946, 1702, 1523, 1230, 1058 cm
2
1
1
3
ꢀ
.
6
1
5
d: H-NMR (400 MHz, DMSO-d , at rt, d): 9.33 (s, 1H), 8.57
6
(
s, 1H), 7.53 (s, 1H), 7.16 (d, J 5 8.3, 1H), 7.05 (d, J 5 8.3,
1
1
H), 4.70 (br s, 2H), 2.13 (br s, 3H), 2.02 (br d, J 5 7.0, 4H),
2
1
863, 1731, 1508, 1232 cm
.
13
ꢀ
.58 (br s, 4H); C-NMR (100 MHz, DMSO-d , at 60 C, d):
6
1
ꢀ
153.57, 152.83, 136.98, 136.27, 129.86, 125.53, 115.08,
0.83, 28.00, 16.77; IR (KBr): m 5 2948, 1704, 1535, 1234,
4
c: H-NMR (400 MHz, DMSO-d , at 60 C, d): 9.76 (s, 1H),
6
7
9
5
1
.53 (s, 1H), 7.35 (t, J 5 8.4 Hz, 4H), 7.07 (d, J 5 8.5 Hz, 4H),
.25 (dd, J 5 14.6 10.5 Hz, 1H), 5.10 (dd, J 5 15.4 10.8 Hz,
H), 4.56 (t, J 5 4.5 Hz, 1H), 4.28 (t, J 5 5.9 Hz, 1H), 4.03 (t,
21
1052 cm
.
J 5 9.8 Hz, 1H), 3.72 (s, 2H), 3.76 (t, J 5 10.1 Hz, 4H), 1.76–
RESULTS AND DISCUSSION
1
3
ꢀ
1
1
1
.20 (m, 20H); C-NMR (100 MHz, DMSO-d , at 60 C, d):
52.29, 136.67, 136.55, 135.50, 135.40, 128.58, 118.41,
18.36, 112.09, 109.75, 78.53, 75.11, 74.77, 74.71, 74.53,
6
Synthesis of Diol-type Monomer 1
The ketalization of myo-inositol was performed with using
1
,1-dimethoxycyclohexane according to the procedure
7
0.12, 36.70, 35.65, 35.60, 34.67, 24.12, 24.09, 23.22, 23.04,
2
6
2
1
reported by Suzuki et al. (Scheme 2). The reaction gave a
22.95; IR (KBr): m 5 2946, 1702, 1523, 1230, 1058 cm
.
0
mixture of bisketal 1 and its isomer 1 at an approximate
1
ꢀ
4
d: H-NMR (400 MHz, DMSO-d , at 60 C, d): 9.83 (s, 0.6H),
ratio of 2:1. Other isomers and monoketals were not
detected by thin-layer chromatography. Recrystallization of
the mixture gave 1 selectively as a colorless crystal. The
6
9
1
4
.60 (s, 0.4H), 9.13 (s, 0.6H), 8.84 (s, 0.4H), 7.62-7.46 (m,
H), 7.28–7.05 (m, 2H), 5.32–5.10 (m, 2H), 4.64 (br s, 1H),
.33 (br s, 1H), 4.09 (t, J 5 9.8, 1H), 3.80 (br m, 1H), 2.17
1
structure of 1 was confirmed by comparing its H-NMR data
1
3
28
0
(br s, 3H), 1.82–1.20 (m, 20H); C-NMR (100 MHz, DMSO-
with the reported one. The isomer 1 was isolated by
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TABLE 1 Reaction of 1 with Phenyl Isocyanate (2.0 eq)
[
1]
0
Amount of
Temp.
Yield
21
ꢀ
a
Run
(mol L
)
DBTDL (mol%)
( C)
(%)
1
2
3
4
0.3
0.3
0.3
1.0
0.5
0.5
5
rt
32
64
81
91
60
60
60
5
a
Isolated yield (by column chromatography).
room temperature. The resulting mixture was analyzed by
thin-layer chromatography, with using a 1:1 mixture of hex-
ane and ethyl acetate as the eluent. The chromatogram con-
firmed complete consumption of diol 1. Three spots were
observed, and these were attributed to the bisurethane-type
SCHEME 2 Synthesis of diol-type monomer 1 by ketalization
of myo-inositol.
0
adduct 2 (Rf 5 0.6), N,N -diphenylurea (DPU) (Rf 5 0.5), and
column chromatography. Its 1H-NMR spectrum was com-
pared with the reported data28 to determine its structure.
an unknown compound (Rf 5 0.2). The presence of DPU
implied that phenyl isocyanate was not consumed com-
pletely: DPU can be formed from phenyl isocyanate through
its hydrolysis into aniline followed by the addition reaction
of aniline to phenyl isocyanate. The complete consumption
Model Reaction
Prior to performing the polyaddition of diol 1 with diisocya-
nates, we performed a relevant model reaction to evaluate
the reactivity of the hydroxyl groups of 1. As a model for
polyaddition of the obtained diol 1 with diisocyanates, the
reaction of 1 with a 2 equivalent amount of phenyl isocya-
nate was investigated to optimize reaction conditions such
as initial concentration of 1, amount of DBTDL, and reaction
temperature (Scheme 3). Although this reaction looks quite
simple, it was not easy to achieve high efficiency, presumably
owing to the steric hindrance around the secondary hydroxyl
groups. Table 1 summarizes the conditions and the corre-
sponding results. In Run 1, the reaction was performed at
1
FIGURE 1 H-NMR spectra (400 MHz, in DMSO-d
6
) of model
SCHEME 3 Reaction of 1 with phenyl isocyanate.
compound 2 and polyurethane 4c.
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1
3
6
FIGURE 2 C-NMR spectra (100 MHz, in DMSO-d ) of model compound 2 and polyurethane 4c.
of 1 and incomplete consumption of phenyl isocyanate let us
predict that the unknown compound was monourethane 3.
moieties were observed at 112 and 110 ppm. The presence
of the urethane moieties was also confirmed by IR analysis,
In Run 2, the reaction was performed at higher temperature,
where a strong absorption attributable to the urethanes was
ꢀ
21
60 C. As a result, the yield of 2 was remarkably improved.
observed at 1719 cm
.
Further improvement of the yield was achieved by increasing
the amount of the tin catalyst from 0.5 to 5 mol % (Run 3).
Finally, 91% of isolated yield of 2 was achieved by increas-
ing the initial concentration of 1 from 0.3 to 1.0 M. In this
case, monourethane 3 was not detected.
1
13
The H- and C-NMR spectra of monourethane 3 are shown
in Supporting Information Figure S1. The spectra supported
that 3 was a 1:1 adduct of 1 and phenyl isocyanate. The
regioselectivity in the addition reaction is not clear at pres-
ent, however, the reported regioselectivity in various reac-
tions allowed us to presume that 3 was formed by the
The chemical structure of bisurethane 2 was confirmed by
1
13
20
H- and C-NMR spectrometry. The spectra are shown in
predominant reaction of the C1-OH with phenyl isocyanate.
The isomer of 3, which can be obtained by the reaction of
C4-OH with phenyl isocyanate, was not detected.
1
Figures 1 and 2, respectively. In the H-NMR spectrum, two
singlet signals attributable to the two urethane protons, sig-
nals attributable to the phenyl groups, six signals attribut-
able to the six protons on the inositol-derived core, and
broad signals attributable to the cyclohexylidene moieties
were observed with the integral ratios that agreed with the
Polyaddition
Under the same conditions as those optimized for the model
reaction, the polyaddition of diol 1 and four diisocyanates
was performed to obtain the corresponding polyurethanes 4
(Scheme 4). The initially homogeneous reaction mixture
became gradually viscous and finally turned into a gel,
1
3
structure of 2. In the C-NMR, one signal attributable to the
two urethane groups was observed at 152 ppm and two sig-
nals attributable to the two quaternary carbons in the ketal
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FIGURE 3 Stereochemistry in polyurethanes 4.
the polymer chain, there can be four isomeric unit–unit
sequences (Fig. 3).
SCHEME 4 Polyaddition of 1 with diisocyanates.
Besides, polyaddition of trans21,4-cyclohexanediol (CHD)
with the diisocyanates was performed (Scheme 5). The cor-
responding products were polyurethanes 5 bearing 1,4-
cyclohexylene moieties in the main chain of which thermal
properties were compared with those of 4 to clarify the
influence of the structural differences between 4 and 5 on
the differences in thermal properties between them (vide
suggesting the formation of 4. The polyurethanes 4 thus
formed were isolated as methanol-insoluble parts in good
yields. The yields and molecular weights of the obtained pol-
yurethanes are listed in Table 2. Although polyurethanes 4
were insoluble in pure DMF, they were successfully solubi-
lized by adding lithium bromide, permitting their SEC analy-
1
infra). In Supporting Information Figures S5–S7, the H- and
1
13
sis. H- and C-NMR analyses of these polymers confirmed
their chemical structures. As a representative example, the
13
C-NMR of polyurethanes 5b–5d are shown. Polyurethane
5a was not soluble in DMF or DMSO and thus its NMR analy-
1
H-NMR spectrum of 4c obtained by the polyaddition of 1
sis was not available. Polyurethanes 5b–5d were not soluble
in DMF although lithium bromide was added to prohibit
their SEC analysis.
and MDI is shown in Figure 1 along with that of the model
1
3
compound 2. In addition, the C-NMR spectrum of 4c is
shown in Figure 2 along with that of the model compound
2
. These spectra clarified the structural commonality
Properties of the Polyurethanes
1
13
between the repeating unit of 4c and 2. The H- and C-
NMR of the other three polyurethanes are shown in Support-
ing Information Figures S2–S4. As the monomer was racemic
and it can be inserted with two possible orientations along
The polyurethanes 4 were soluble in DMSO. On the other
hand, 5a obtained by the polyaddition of CHD and HMDI
was insoluble in DMSO, whereas 5b, 5c, and 5d were barely
soluble in DMSO. In total, 4 were more soluble than 5, pre-
sumably because of the incorporation of the cyclohexylidene
groups in the side chain.
TABLE 2 Synthesis of Polyurethanes 4 by Polyaddition of 1
and Diisocyanates
Yield
a
b
Run
Diisocyanate
Polyurethane
(%)
n w n
M (M /M )
1
2
3
4
HMDI
IPDI
MDI
TDI
4a
4b
4c
4d
99
73
87
84
61,600 (1.56)
41,300 (1.53)
21,400 (2.53)
19,300 (2.13)
a
Methanol-insoluble parts.
b
Estimated by SEC (eluent 5 DMF 1 1% LiBr, polystyrene standards).
SCHEME 5 Polyaddition of CHD with diisocyanates.
6
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TABLE 3 Properties of the Polyurethanes
than those of the polyurethanes 5 obtained by the polyaddi-
tion of CHD and diisocyanates. The higher heat resistance of
the myo-inositol-derived polyurethanes 4 than that of the
CHD-derived ones 5 proved the contribution of the rigid 5-6-
Polyurethane
T
d5
T
d10
T
g
T
m
ꢀ
a
ꢀ
a
ꢀ
b
ꢀ
b
Run
(Used Monomers)
( C)
( C)
( C)
( C)
5
-fused ring system inherited from the diol monomer 1 to
1
2
3
4
5
6
7
8
4a (1 1HMDI)
4b (1 1 IPDI)
302
283
302
296
258
198
274
270
316
301
309
303
275
242
287
282
143
159
248
250
199
225
265
265
the efficient restriction of the motion of the polymers. Fur-
ther applications of the diol monomer 1 to other polymeriza-
tion systems to develop various high-performance polymers
are currently under investigation.
4c (1 1 MDI)
4d (1 1 TDI)
c
c
5a (CHD 1 HMDI)
5b (CHD 1 IPDI)
5c (CHD 1 MDI)
5d (CHD 1 TDI)
–
–
c
ACKNOWLEDGMENT
119
–
c
c
–
–
This research was partially supported by the Grants-in-Aid for
Scientific Research (C) (No. 24550262) from Japan Society for
the Promotion of Science (JSPS).
218
229
a
Determined by TGA.
b
c
Determined by DSC.
Not observed.
REFERENCES AND NOTES
1
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g
1
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naturally occurring compounds: For example, the reported
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4
6, 384–394.
1
3 L. Jasinska-Walc, D. Dudenko, A. Rozanski, S. Thiyagarajan,
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ꢀ
10
C, respectively. Another comparative example is the poly-
1
7
urethanes obtained from a bisketal of D-mannitol. The poly-
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1
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CONCLUSIONS
A highly rigid diol 1 obtained by ketalization of myo-inositol
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corresponding polyurethanes 4. The thermal properties of 4
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degradation temperatures and glass transition temperatures
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