Triallyl monomer bearing adamantane-like core derived from naturally occurring myo-inositol: Synthesis and polyaddition with dithiols

Article abstract of DOI:10.1002/pola.27106

This paper deals with a triallyl monomer bearing a rigid adamantane-like core derived from myo-inositol, a naturally occurring cyclic hexaol. The core structure of the monomer can be readily constructed by orthoesterification of myo-inositol. The polyaddition of the triallyl monomer with dithiols based on the thermally induced radical thiol-ene reaction gives the corresponding networked polymers. These networked polymers exhibit much higher thermal stability than the comparative networked polymers obtained from a triallyl monomer bearing less rigid cyclohexyl core. 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1193-1199 Naturally occurring myo-inositol is transformed into the corresponding triallyl monomer bearing a rigid adamantane-like core. The polyaddition of the triallyl monomer with dithiol gives the corresponding networked polymers bearing the adamantane-like structure at the crosslinking points, which exhibit higher heat resistance than those bearing a more flexible cyclohexyl structure at the crosslinking points. Copyright

Full text of DOI:10.1002/pola.27106

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Triallyl Monomer Bearing Adamantane-like Core Derived from Naturally
Occurring myo-Inositol: Synthesis and Polyaddition with Dithiols
Atsushi Sudo, Tomio Sakue
Department of Applied Chemistry, Faculty of Science and Engineering, Kinki University, Kowakae 3-4-1, Higashi-Osaka,
Osaka 577-8502, Japan
Correspondence to: A. Sudo (E-mail: asudo@apch.kindai.ac.jp)
Received 10 October 2013; accepted 18 January 2014; published online 4 February 2014
DOI: 10.1002/pola.27106
ABSTRACT: This paper deals with a triallyl monomer bearing a
rigid adamantane-like core derived from myo-inositol, a natu-
rally occurring cyclic hexaol. The core structure of the mono-
mer can be readily constructed by orthoesterification of myo-
inositol. The polyaddition of the triallyl monomer with dithiols
based on the thermally induced radical thiol-ene reaction gives
the corresponding networked polymers. These networked
polymers exhibit much higher thermal stability than the com-
parative networked polymers obtained from a triallyl monomer
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bearing less rigid cyclohexyl core.
2014 Wiley Periodicals,
Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1193–1199
KEYWORDS: myo-inositol; networks; orthoester; renewable
resources; step-growth polymerization
adamantane-like rigid compounds that are functionalized with
three hydroxyl groups, of which selective chemical transforma-
tions give a wide range of myo-inositol-derivatives.16–19 Upon
looking at the adamantane-like molecular structure of myo-ino-
sitol 1,3,5-orthoesters, we envisaged its utilization as a precur-
sor for synthesizing various trifunctional monomers with a
rigid core. So far, only a few examples of polymers with myo-
inositol 1,3,5-orthoester moieties have been reported:20–22 In
some of these examples, the orthoester pendants were hydro-
lyzed under acidic conditions to obtain cyclic polyol moieties,
and their hydroxyl groups were phosphorylated to obtain poly-
mer materials with metal ion-absorbing function.20,21 On the
other hand, Holmes et al. have reported efficient use of myo-
inositol 1,3,5-orthoester as a rigid scaffold to design a
bis(styryl)-type monomer.22 The two styryl moieties of the
monomer were oriented so that the monomer underwent the
cyclopolymerization to give a linear polystyrene derivative.
Finn et al. have reported a tris(propargylether) bearing myo-
inositol 1,3,5-orthoester core.23 With the azide-alkyne coupling
chemistry, this monomer was converted into a networked poly-
mer with high adhesion performance. However, the influence of
the rigidity of the core on the properties of the networked poly-
mers is not clarified therein.
INTRODUCTION Molecular design of multifunctional mono-
mers for synthesis of networked polymers involves (1)
design of their core structures, (2) choice of reactive func-
tions to be attached on the cores, and (3) choice of the num-
ber of the reactive functions. By combining these factors
appropriately, properties of the corresponding networked
polymers can be adjusted specifically depending on various
demands in practical applications. Particularly, rigidity of
core structures of monomers, which will be introduced into
the crosslinking points of the networked polymers, is a criti-
cal factor to determine the properties of the networked poly-
mers. In general, the employment of monomers with rigid
cores gives us an effective approach to obtain polymer mate-
rials with heat resistance and mechanical strength.1–5
Recently, our research interest has been focused on utiliza-
tion of naturally occurring myo-inositol as a starting material
for polymer synthesis,6 with aiming that such investigation
would contribute to the current progress in the development
of bio-based polymers.7–11 myo-Inositol is a cyclic hexaol
that exists in organs as its phosphate derivatives such as
phosphatidyl inositol and phytic acid.12,13 A wide range of
myo-inositol derivatives have been synthesized through vari-
ous protocols of selective protection of hydroxyl groups.14
Among those protocols, the orthoesterification of myo-inosi-
tol has been most frequently used for the selective and
straightforward protection of the three hydroxyl groups at 1-,
3-, and 5-positions at once.15 The resulting orthoesters are
The designed monomer for the present work is a tris(ally-
lether)-type compound 2 that can be easily synthesized from
myo-inositol 1,3,5-orthoacetaete 1. The reasons for the choice
of allyl group as the reactive site of the monomer are (1) its facile
Additional Supporting Information may be found in the online version of this article.
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introduction under basic conditions that are compatible with the
orthoester moiety and (2) its versatility that allows us to use it
for various bond formation chemistries, such as hydrosilylation,
metathesis, and thiol-ene chemistry. Currently, thiol-ene reac-
tion, that is, radical addition of thiol to CAC double bond, is used
as one of the “click” reactions for combining two components
into one molecule quickly and quantitatively.24,25 Its expanding
application field includes polymers and polymeric biomateri-
als26–28 and synthesis of functionalized monomers.29–31
Recently, the exploitation of the thiol-ene reaction has opened a
new access to networked polymers.32–37
p-toluenesulfonic acid monohydrate (1.0 g; 5.8 mmol) were
added. The resulting mixture was heated at 100 C for 2–3 h
ꢀ
until the mixture became homogeneous. After cooling, trie-
thylamine (4.0 mL) was added to the solution. The solution
was evaporated to dryness under a reduced pressure, and
the resulting residue was dissolved in a minimum amount of
ethyl acetate and chromatographed on a short silica gel col-
umn with eluting with ethyl acetate. The resulting solution
was concentrated under a reduced pressure, and the result-
ing residual solid was recrystallized from methanol to obtain
myo-inositol 1,3,5-orthoacetate (1) (9.57 g; 46.3 mmol; 70%)
as a colorless crystal.
Herein, we report the details of the synthesis of tris(ally-
lether)-type monomer 2 and its radically mediated polyaddi-
tion with dithiols to afford networked polymers with rigid
myo-inositol orthoester cores. Their thermal stability was
compared with that of comparative networked polymers
with less rigid cyclohexyl cores to clarify the influence of
rigidity of cores on thermal stability.
Synthesis of 2,4,6-Tri-O-Allyl-myo-Inositol 1,3,5-
Orthoacetate (2)
Sodium hydride in mineral oil (60%; 4.0 g; 0.10 mol) was
washed with hexane (10 mL) twice, dried under vacuum, and
then dispersed in DMF (20 mL). To the resulting dispersion, a
solution of myo-inositol 1,3,5-orthoacetate (1) (4.15 g; 20.0
mmol) in DMF (30 mL) was added dropwise for 30 min at room
ꢀ
EXPERIMENTAL
temperature. After cooling to 0 C, allyl bromide (6.1 mL; 70
mmol) was added to the mixture dropwise for 10 min. The
resulting mixture was allowed to warm to room temperature
and was stirred for 3 h. Water (15 mL) was added to the mix-
ture carefully, and the resulting mixture was extracted with
ethyl acetate (100 mL) three times. The combined organic
layers were dried over sodium sulfate, filtered, and concen-
trated under a reduced pressure. The resulting residue was dis-
tilled under vacuum to obtain 2,4,6-tri-O-allyl-myo-inositol
1,3,5-orthoacetate (2) (5.27 g; 16.2 mmol; 81%) as a colorless
oil: 1H-NMR (in CDCl3, at rt) 6.04–5.93 (m, 1H), 5.92–5.83 (m,
2H), 5.35–5.26 (m, 3H), 5.23–5.17 (m, 3H), 4.35–3.30 (m, 3H),
3.23 (t, J 5 3.7, 2H), 4.18 (d, J 5 5.6, 2H), 4.13–4.01 (m, 4H),
3.85 (t, J 5 1.6, 1H), 1.46 (s, 3H); 13C-NMR (in CDCl3, at rt)
134.71, 134.13, 117.49, 117.24, 108.92, 73.58, 71.25, 70.55,
70.47, 68.06, 66.32, 24.27; IR (on a NaCl plate) 3080, 3012,
2955, 2865, 1645 cm21. Anal. calcd. for C17H24O6: C 62.94, H
7.46, N 0.00; found: C 62.60, H 7.56, N 0.00.
Chemicals
myo-Inositol (99.0%), allyl bromide (>99.0%), azobisisobutyr-
onitrile (AIBN) (>98%), 1,6-hexanedithiol, 1,4-butanedithiol,
bis(3-mercaptopropionyl)ethylene glycol were purchased from
Wako Pure Chemical Industries Co., and used as received. p-
Toluenesulfonic acid monohydrate (98.0%) and trimethyl
orthoacetate (98.0%) were purchased from Tokyo Chemical
Industry Co. and used as received. Triethylamine (99.0%) and
60% sodium hydride in mineral oil were purchased from
Kishida Chemical Co. and used as received.
N,N-Dimethylformamide (DMF) (>95.5%) was purchased
from Wako Pure Chemical Industries Co., dried over calcium
hydride, and distilled under a reduced pressure prior to use.
1,4-Dioxane was purchased from Kishida Chemical Co. dried
over calcium hydride, and distilled prior to use.
Instruments
NMR spectra (400 MHz for 1H; 100.6 MHz for 13C) 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 cm21. Thermo-
gravimetric analysis (TGA) was performed under a nitrogen
Synthesis of 2,4,6-Tri-O-Allyl-myo-Inositol (3)
To a solution of 2 (1.62 g; 5.00 mmol) in ethanol (10 mL),
1M HCl aq (10 mL) was added, and the resulting mixture
was heated with refluxing. After 24, the mixture was concen-
trated under a reduced pressure, and the resulting residue
was chromatographed on a silica gel column [eluent 5
hexane 1 ethyl acetate (1:1)] to obtain 2,4,6-tri-O-allyl-myo-
inositol (3) (1.45 g; 4.83 mmol; 97%) as a white solid: 1H-
NMR (in CDCl3, at rt) 6.04–5.88 (m, 3H), 5.35-5.24 (m, 3H),
5.23-5.26 (m, 3H), 4.42-4.29 (m, 6H), 3.91 (s, 1H), 3.60-3.35
(m, 5H), 2.62 (s, 1H), 2.46 (d, J 5 2.3, 2H); 13C-NMR (in
CDCl3 at rt) 134.99, 134.89, 117.23, 116.90, 81.63, 79.09,
74.68, 74.23, 73.90, 72.30; IR (KBr) 3414, 3076, 2922, 1132,
ꢀ
ꢀ
flow in a range from 50 to 500 C at a heating rate of 10 C
min21 with a RIGAKU model Thermo plus EVO II TG-DTA.
Differential scanning calorimetry (DSC) was performed
under a nitrogen flow in a range from 2100 to 50 ꢀC at a
21
ꢀ
heating rate of 10 C min with a SEIKO Instruments model
EXSTAR6000. From the resulting DSC profiles, the glass tran-
sition temperatures (Tg) were obtained as the extrapolated
onset temperatures.
714 cm21
.
Synthesis
Synthesis of 1,3,5-Tri-O-Methyl-2,4,6-Tri-O-Allyl-myo-
Inositol (4)
Sodium hydride in mineral oil (60%; 0.82 g; 20 mmol) was
washed with hexane (5 mL) twice, dried under vacuum, and
Synthesis of myo-Inositol 1,3,5-Orthoacetate (1)
To a suspension of myo-inositol (12.0 g; 66.6 mmol) in DMF
(100 mL), trimethyl orthoacetate (12.0 mL; 94.3 mmol) and
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then dispersed in DMF (10 mL). To the resulting dispersion,
a solution of 3 (1.20 g; 4.00 mmol) in DMF (24 mL) was
added drꢀopwise for 10 min at room temperature. After cool-
ing to 0 C, dimethyl sulfate (2.3 g; 18 mmol) was added to
the mixture dropwise for 10 min. The resulting mixture was
allowed to warm to room temperature and was stirred for
24 h. Water (6 mL) was added to the mixture carefully, and
the resulting mixture was extracted with ethyl acetate (30
mL) three times. The combined organic layers were dried
over sodium sulfate, filtered, and concentrated under a
reduced pressure. The resulting residual oil was chromato-
graphed on a silica gel column (eluent 5 hexane 1 ethyl ace-
tate (5:1)) to obtain 1,3,5-tri-O-methyl-2,4,6-tri-O-allyl-myo-
inositol (4) (1.14 g; 3.34 mmol; 84%) as a colorless oil: 1H-
NMR (in CDCl3 at rt) 6.05–5.85 (m, 3H), 5.33–5.22 (m, 3H),
5.28–5.23 (m,3H), 4.35–4.21 (m, 6H), 4.00 (t, J 5 2. 4, 1H),
3.63 (t, J 5 9.5, 2H), 3.62 (s, 3H), 3.46 (s, 6H), 3.02 (t, J 5 9.2,
1H), 2.99,2.96 (dd, J 5 2.2, 2.4, 2H); 13C-NMR (in CDCl3, at
rt) 135.55, 116.48, 116.30, 85.43, 82.57, 81.27, 74.24, 73.00,
72.34, 61.27, 58.49; IR (on a NaCl plate) 3078, 2980, 2930,
1728, 1131, 721 cm21. Anal. calcd. for C18H30O6: C 63.14, H
8.83, N 0.00; found: C 62.93, H 8.80, N 0.00.
SCHEME 1 Synthesis of triallyl monomer 2.
(282 mg; 2.31 mmol) was carried out to obtain networked
polymer 6a (652 mg; 76%): IR 2932, 2850, 1302, 1106,
863 cm21
.
According to the typical procedure, the reaction of triallyl
monomer 2 (497 mg; 1.50 mmol) and bis(3-mercaptopro-
pionic acid) ethylene glycol (551 mg; 2.31 mmol) was per-
formed to obtain the corresponding networked polymer
6c (990 mg; 94%): IR 2950, 2873, 1735, 1112, 1280,
Radical Addition of 1-Octanethiol to Triallyl Monomer 2
Triallyl monomer 2 (496 mg; 1.53 mmol), AIBN (23 mg, 0.14
mmol) and 1-octanethiol (746 mg, 5.10 mmol) were placed
in a vessel. To the mixture, 1,4-dioxane (3.1 mL) was added,
and the reaction vessel was flushed with argon. The resulting
solution was stirred at 65 ꢀC for 4 h. The volatiles were
removed under a reduced pressure, and the resulting residue
was chromatographed on a silica gel column (eluent: hexa-
ne 1 ethyl acetate 20:1 1 2% triethylamine) to obtain a mix-
ture of target 5 and its isomers (1.09 g; 1.43 mmol; 93%) as
867 cm21
.
Polyaddition of Triallyl Monomer 4 and Dithiols
Typical procedure: Triallyl monomer 4 (514 mg; 1.50 mmol),
AIBN (0.338 g; 2.25 mmol), and 1,6-hexanedithiol (338 mg;
2.25 mmol) were placed in a vessel. To the mixture, 1,4-diox-
ane (3.1 mL) was added, and the reaction vessel wasꢀflushed
with argon. The resulting solution was stirred at 65 C for 4
h to obtain a transparent gel. The gel was crushed into pieces
and washed with diethyl ether (10 mL). The resulting rubbery
solid was isolated by filtration with suction and dried under
vacuum at 60 ꢀC for 24 h to obtain networked polymer 7b
1
a slightly yellow oil: H-NMR (in CDCl3 at, rt) 4.32 (d, J 5 3.2,
3H), 4.16 (t, J 5 3.7, 2H), 3.70 (t, J 5 6.3, 3H), 3.66–3.54 (m,
4H), 2.64 (t, J 5 7.2, 2H), 2.57 (t, J 5 7.1, 4H), 2.53–2.44 (m,
6H), 1.98–1.91 (m, 4H), 1.91–1.70 (m, 4H), 1.66–1.50 (m,
6H), 1.43–1.31 (m, 6H), 1.31–1.18 (m, 24H), 0.88 (t, J 5 6.8,
9H); 13C-NMR (in CDCl3, at rt) 108.82, 74.31, 70.78, 68.13,
67.78, 67.63, 66.93, 31.93, 31.66, 29.60, 29.53, 29.49, 29.05,
28.80, 28.47, 28.37, 24.23, 22.48, 13.93; IR (on a NaCl plate)
(836 mg; 98%): IR 2918, 2850, 1129, 1094, 703 cm21
.
According to the typical procedure, the reaction of triallyl
monomer 4 (527 mg; 1.54 mmol) and 1,4-butanedithiol (282
mg; 2.31 mmol) was carried out to obtain networked poly-
mer 7a (598 mg; 74%): IR 2926, 2807, 1130, 1095,
2924, 2854, 1302, 1117, 867 cm21
.
711 cm21
.
Polyaddition of Triallyl Monomer 2 and Dithiols
Typical procedure: Triallyl monomer 2 (497 mg; 1.50 mmol),
AIBN (23 mg, 0.14 mmol), and 1,6-hexanedithiol (346 mg;
2.30 mmol) were placed in a vessel. To the mixture, 1,4-diox-
ane (3.1 mL) was added, and the reaction vessel wasꢀflushed
with argon. The resulting solution was stirred at 65 C for 4
h to obtain a transparent gel. After adding triethylamine
(1 mL), the gel was crushed into pieces and washed with
diethyl ether (10 mL). The resulting rubbery solid was iso-
lated by filtration with suction and dried under vacuum at
60 ꢀC for 24 h to obtain networked polymer 6b (0.787 g;
According to the typical procedure, the reaction of triallyl
monomer 4 (527 mg; 1.54 mmol) and bis(3-mercaptopro-
pionic acid) ethylene glycol (551 mg; 2.31 mmol) was per-
formed to obtain the corresponding networked polymer 7c
(1.00 g; 93%): IR 2931, 1738, 1131, 1095, 711 cm21
.
RESULTS AND DISCUSSION
Synthesis of Triallyl Monomer
Scheme 1 shows the synthetic route to the triallyl monomer
2. Treatment of myo-inositol with trimethyl orthoacetate in
the presence of a catalytic amount of p-toluenesulfonic acid
resulted in the selective orthoesterification of myo-inositol.
The resulting triol 1 with a rigid core was isolated in 70%
96%): IR 2923, 2854, 1301, 1109, 865 cm21
.
According to the typical procedure, the reaction of triallyl
monomer 2 (497 mg; 1.50 mmol) and 1,4-butanedithiol
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revealed complete consumption of 2 within 4 h and forma-
tion of the corresponding adduct 5. Besides the formation of
5, those of minor products were detected. These products
were quite similar to 5 in terms of polarity and thus were
considered to be regioisomers that were formed as a result
of the incomplete control in regioselectivity in the radical
addition of thiol to CAC double bond. Since it was difficult
to separate them by column chromatography, 5 and its iso-
mers were collected in one fraction and the mixture was
analyzed by NMR spectroscopy. The resulting 1H-NMR spec-
trum is shown in Figure 1.
Besides the set of major signals attributable to 5, the spec-
trum also showed some small signals attributable to the iso-
mers formed by the addition of thiol to the center carbon of
the allyl group.38,39 A list of the possible regioisomers is
shown in Figure S4 in Supporting Information. The 13C-NMR
spectrum, which also supported the structure of 5, is shown
in Figure S5 in Supporting Information. In addition, the sig-
nal assignments were supported by CAH COSY spectroscopy
(Fig. S6 in Supporting Information).
SCHEME 2 Synthesis of triallyl monomer 4.
by recrystallization from methanol. The next reaction step,
allylation of the hydroxyl groups of 1, was achieved by a
standard protocol, that is, transformation of hydroxyl group
into sodium alkoxide with sodium hydride and successive
treatment with allyl bromide. The reaction proceeded quanti-
tatively and the resulting 2 was isolated in a pure form by
1
Synthesis of Networked Polymers
distillation under vacuum. Its structure was confirmed by H
and 13C-NMR spectroscopies (Fig. S1 in Supporting Informa-
Scheme 4 shows the reaction of triallyl monomers 2 and 4
with dithiols to synthesize networked polymers. Table 1 sum-
marizes the results. The conditions for the reaction were
same as those for the model reactions with using monothiols.
1
tion): The H-NMR spectrum indicated a singlet signal attrib-
utable to the methyl group at 1.46 ppm and signals for the
vinyl protons in a range from 5 to 6 ppm. The integration
ratio between these signals agreed with the monomer struc-
ture bearing one orthoester core and three allyl moieties.
The 13C-NMR spectrum indicated a signal at 109 ppm attrib-
utable to the carbon connecting to the three oxygen atoms
in the orthoester structure. In addition, the signal assign-
ments were supported by C-H COSY spectroscopy (Fig. S2 in
Supporting Information).
The reactions of 2 with 1,4-butanedithiol (BDT), 1,6-hexane-
dithiol (HDT), and bis(3-mercaptopropionic acid) ethylene
glycol (BMPEG) gave the corresponding networked polymers
6a, 6b, and 6c, respectively. In a similar manner, the reac-
tions of triallyl monomer 4 with the dithiols were performed
to obtain a series of the corresponding networked polymers
7. In all the cases, the reaction gave a transparent gel. From
Synthesis of a Comparative Triallyl Monomer with a Less
Rigid Structure
Besides the triallyl monomer 1 with a rigid orthoester core,
another triallyl monomer 4 with a less rigid structure was
prepared (Sch. 2). The starting material used herein was the
triallyl monomer 2. Its orthoester core was hydrolyzed under
acidic conditions to obtain triol 3. The three hydroxyl groups
of 3 were transformed into the corresponding methyl ether
using sodium hydride and dimethyl sulfate to obtain 4. The
triallyl monomer 4 was isolated successfully by column chro-
1
matography. Its structure was confirmed by H and 13C-NMR
spectroscopy (Fig. S3 in Supporting Information).
Model Reaction
Next, we investigated radical addition of monofunctional
thiol to the allyl groups of 2 to clarify the efficiency of the
reaction and the stability of the orthoester moiety under the
conditions (Sch. 3).
With employing AIBN as a radical source, the reaction of 2
and 1-octanethiol was carried out in 1,4-dioxane at 65 ꢀC.
Monitoring the reaction with thin layer chromatography
SCHEME 3 Radical addition reaction of monothiols to the allyl
moieties of triallyl monomer 2.
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FIGURE 1 1H-NMR spectrum of compound 5.
this gel, the networked polymers were isolated as diethyl
ether-insoluble fractions.
Supporting Information. From the corresponding thermal
profiles, 5% weight loss temperature (Td5) and 10% weight
loss temperature (Td10) were extracted (Table 1). The Td5
and Td10 values for the networked polymers 6 were higher
than 300 and 330 ꢀC, respectively. In contrast to these val-
ues, those for the networked polymers 7 were much lower,
to clarify the higher thermal stability of 6 than 7.
As shown in Table 1, the yields of the networked polymers
that were isolated as ether-insoluble fractions were excellent
when the triallyl monomers were reacted with HDT and
BMPEG (entries 2 and 3, entries 5 and 6). In contrast, the
yields of 6a and 7a that were synthesized using BDT were
moderate (entries 1 and 4), to imply that the chain length of
BDT was less suitable for efficient intermolecular polyaddition
(Fig. S7 in Supporting Information). As a result, intramolecular
addition was enhanced to give increased amount of macrocy-
clic structures, leading to the decrease in crosslinking density.
The difference in thermal stability between 6 and 7 can be
attributable to the difference in conformational freedom
between the two different inositol-derived cores. As shown
in Scheme 5, the inositol-derived six-membered ring in the
networked polymers 7 is allowed to have two chair-like con-
formations (Chairs A and B), and these two chairs are inter-
mediated by boat-like conformations. One of the boat-like
conformations depicted in Scheme 5 is favorable for ther-
mally induced syn-elimination to give fragmented polymers
Thermal Properties of the Networked Polymers
The obtained networked polymers were subjected to TGA.
The resulting TGA traces are shown in Figure S8 in
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SCHEME 5 Possible mechanism for the thermal degradation of
networked polymer 7.
obtained in a similar way implies the higher efficiency in
growth of networked structure in 6b than that in 6a, and
this tendency is in a good agreement with the much higher
thermal stability of 6b than 6a. On the other hand, the net-
worked polymer 6c obtained using BMPEG was thermally
less stable than 6b, although the high yield of 6c suggests
efficient growth of the networked structure. The lower sta-
bility of 6c would be due to the longer chain length of the
BMPEG-derived tether between the two sulfur atoms and
presence of the ester linkage in the tether that can be ther-
mally less stable than the other linkages such as ether and
thioether ones. These discussions on the order of thermal
stability, 6b > 6c > 6a, can be adopted also to that of the
thermal stability of the networked polymers 7, 7b > 7c > 7a.
SCHEME 4 Synthesis of networked polymers.
with hydroxyl terminal. Further conformational change of
the six-membered ring allows stepwise elimination of alco-
hols that causes thermal degradation of the networked poly-
mers. On the other hand, the orthoester-type core of 6 is
highly rigid to prohibit its conformational change into boat-
like one. This efficient “conformation freeze” contributed to
the enhanced thermal stability of the networked polymers 6.
Among the networked polymers 6, 6b obtained using HMDT
as dithiol monomer was thermally most stable. It was much
more stable than 6a obtained by using another alkyl dithiol,
BDT. This difference in thermal stability between these net-
worked polymers is attributable to the difference in cross-
linking density. As has been already discussed above, the
intermolecular reaction between triallyl monomer 2 and
dithiols leading to the formation of crosslinking points is
competed by the intramolecular reaction that terminate the
growth of networked structure. The much higher yield of 6b
that was obtained as ether-insoluble fraction than that of 6a
For further clarification of the influence of rigidity of core
structure on the properties of the networked polymers, the
networked polymers 6 and 7 were subjected to DSC analysis.
The resulting DSC profiles are shown in Figure S9 (Support-
ing Information). From these profiles, the Tg values were
obtained and listed in Table 1. As was expected from the
rubbery nature of the networked polymers, all the Tg values
TABLE 1 Synthesis of Networked Polymers and their Thermal Stability.
Triallyl
Networked
polymer
Entry
monomer
Dithiol
Yield (%)a
Td5 (ꢀC)b
Td10 (ꢀC)b
Tg (ꢀC)c
1
2
3
4
5
6
2
2
2
4
4
4
BDT
6a
6b
6c
7a
7b
7c
76
93
94
74
98
93
302
327
310
269
307
295
330
339
334
293
329
309
1
HDT
1
BMPEG
BDT
210
210
26
227
HDT
BMPEG
a
c
Ether-insoluble parts.
Determined by TGA.
Determined by DSC.
b
1198
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were lower than ambient temperature. The Tg values of the
networked polymers 6 bearing the adamantane-like struc-
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networked polymers 7 bearing the cyclohexyl structure at
the crosslinking points, implying that the difference in the Tg
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triallyl compound with a rigid adamantane-like core via a
sequence of two reaction steps: (1) 1,3,5-orthoesterification
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