Efficient synthesis and properties of soluble aliphatic oligo(spiroorthocarbonate)s from pentaerythritol derivatives

Article abstract of DOI:10.1002/pola.29327

A series of soluble oligo(spiroorthocarbonate)s (OSOCs) were synthesized by polycondensation of tetraethylorthocarbonate with pentaerythritol derivatives. The pentaerythritol derivatives used herein were synthesized from pentaerythritol by attaching subst

Full text of DOI:10.1002/pola.29327

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Efficient Synthesis and Properties of Soluble Aliphatic
Oligo(spiroorthocarbonate)s from Pentaerythritol Derivatives
1
Yasuyuki Mori,1 Atsushi Sudo,1,2 Takeshi Endo
1Molecular Engineering Institute, Kindai University, 11-6 Kayanomori, Iizuka, Fukuoka 820-8555, Japan
2Department of Applied Chemistry, Faculty of Science and Engineering, Kindai University, Kowakae 3-4-1, Higashi-Osaka, Osaka
577-8502, Japan
Correspondence to: T. Endo (E-mail: tendo@moleng.fuk.kindai.ac.jp)
Received 7 December 2018; accepted 12 January 2019
DOI: 10.1002/pola.29327
ABSTRACT:
A series of soluble oligo(spiroorthocarbonate)s
confirmed by NMR spectroscopy and MALDI-TOF mass analysis.
© 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym.
Chem. 2019
(OSOCs) were synthesized by polycondensation of tetraethy-
lorthocarbonate with pentaerythritol derivatives. The pentaerythri-
tol derivatives used herein were synthesized from pentaerythritol
by attaching substituents on it to improve the solubility of them-
selves and the resulting OSOCs. The structures of the OSOCs were
KEYWORDS: spiroorthocarbonates; spiropolymers; pentaerythri-
tol; polycondensation
carbonate).9 Surprisingly, the polymerization accompanied
by 29% volume expansion.9
INTRODUCTION Spiropolymers are a subclass of ladder polymers
consisted of double-stranded main chains, which are expected to
be thermally and mechanically more stable than polymers with a
single main chain. Poly(spiroketal)s and poly(spiroorthocarbonate)
s (PSOCs) have been two major spiropolymers because of the sim-
plicity of their syntheses.1–6 Previously, we reported the synthesis
of aromatic poly(spiroorthocarbonate)s (PSOCs) by the poly-
condensation of 1,2,4,5-tetrahydroxybenzene (THB) with
2,2,6,6-tetrachlorobenzo [1,2-d;4,5-d’]bis[1,3]dioxol (TCBBD).4
The polymer exhibited high thermal stability (the temperature
In spite of these attractive features of aliphatic PSOCs as poten-
tial high performance and functional polymers, the structural
diversity is quite limited due to the lack of availability of tetra-
ols that can be used as monomers for synthesizing PSOCs.
Herein, we report an efficient synthesis of aliphatic OSOCs
using a series of pentaerythritol derivatives (Fig. 1). The syn-
thesis and the use of these derivatives bearing alkyl and phenyl
groups allowed us to access OSOCs with enhanced solubility, of
which chemical structures were studied intensively by NMR
spectroscopy and MALDI-TOF mass analysis.
ꢀ
of 10% weight loss was c.a. 400 C) as well as the good toler-
ance to acids and bases. By replacing THB by biscatechols bear-
ing cardo and bent structures, the corresponding PSOCs with
good solubility and excellent thermal stability were obtained.5
Aliphatic PSOCs are also attractive as candidate high-performance
materials because of the absence of UV absorbable moieties that
allow the potential high UV-resistance of PSOCs. Yaghi et al. have
reported a oligo(spiroorthocarbonate) (OSOC) that can be synthe-
sized by the polycondensation of pentaerythritol and tetraethy-
lorthocarbonate (TEOC).6 The OSOC thus obtained was insoluble
in common organic solvents due to the high crystallinity, which
was arisen by the spontaneous alignment of the rigid rod-
like oligomer chains into a bundle, preventing adequate
structural analyses. On the other hand, spiroorthocarbonates
undergo the double ring-opening polymerization with vol-
ume expansion.7,8 We revealed that the spiroorthocarbonate
moieties in the main chain of the OSOC underwent cationic
ring-opening polymerization to give a crosslinked poly(ether
EXPERIMENTAL
Materials
N, N-dimethylformamide (Wako Pure Chemical Co., Ltd., Kyoto,
Japan) was purchased as an anhydrous solvent and used without
further purification. Tetrahydrofuran (Wako Pure Chemical Co.,
Ltd.) was dried and distilled from benzophenone-sodium immedi-
ately prior to use under a nitrogen atmosphere. Dichloromethane
(Wako Pure Chemical Co., Ltd.) and triethylamine (Tokyo Chemi-
cal Industry Co., Ltd.) were dried over molecular sieves (MS 4A)
and used without further purification. Pentaerythritol, benzyl bro-
mide, dimethylsulfoxide, ethanol, sodium hydroxide, oxalyl chlo-
ride, Pd/C (10%), methansulfonic acid, tetraethylorthocarbonate
(Wako Pure Chemical Co., Ltd.), phenylmagnesium bromide
Additional supporting information may be found in the online version of this article.
© 2019 Wiley Periodicals, Inc.
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(1 M in THF), n-butylmagnesium chloride (2 M in THF), and
methylmagnesium bromide (1 M in THF) (Tokyo Chemical
Industry Co., Ltd.) were purchased and used without further
purification.
by adding 1 N HCl and extracted with CH2Cl2 three times. The
combined organic extracts were washed with brine and then
dried (MgSO4) and concentrated under reduced pressure. The
residue was purified by flash chromatography over silica gel
(hexane/ethyl acetate = 2/1, v/v) to give the corresponding alco-
hol S2 (9.85 g, 24.2 mmol, 81%) as a colorless oil: IR (neat):
Instruments
1H (400 MHz) and 13C (100 MHz) NMR spectra were obtained
3457, 3062, 3029, 2861, 1453, 1089, 1073, 1027, 733, 695 cm−1
;
1
on a JEOL ECS 400 spectrometer. Chemical shifts for H NMR
1H NMR (400 MHz, CDCl3): δ 2.82 (t, J = 6.4 Hz, 1 H), 3.57
(s, 6 H), 3.77 (d, J = 6.4 Hz, 2 H), 4.48 (s, 6 H), 7.25–7.33
(m, 15 H); 13C NMR (100 MHz, CDCl3) δ 45.1, 66.2, 70.9, 73.5,
127.4, 127.5, 128.3, 138.3; HRMS (FAB): m/z calcd for C26H31O4
[M + H]+: 407.2222; found: 407.2223.
are given in parts per million (ppm) relative to tetramethylsi-
lane (δ 0.00 ppm) or a residual solvent (δ 2.50 ppm for
DMSO-d6). Chemical shifts for 13C NMR are given in ppm rela-
tive to deuterated solvents (δ 77.0 ppm in CDCl3 or δ
39.52 ppm for DMSO-d6). Solid-state 13C CPMAS NMR spectra
were recorded with a JEOL ECX-400 spectrometer at a reso-
nance frequency of 100 MHz for 13C with adamantane as an
external standard. Infrared spectra were recorded on a
Thermo Fischer Scientific Nicolet iS10 spectrometer (Madison,
WI, USA) with attenuated total reflection (ATR) method. High-
resolution mass spectra (HRMS) were obtained on a JEOL
JMN-700 spectrometer using fast atom bombardment (FAB)
ionization mode. MALDI-TOF mass spectrometry was per-
formed on a Shimadzu Biotech AXIMA Confidence using
dithranol and sodium trifluoroacetate, as a matrix material
and a cationization agent, respectively. To prepare the sample
for MALDI-TOF mass analysis, the obtained oligomer (3 mg),
dithranol (10 mg), and sodium trifluoroacetate (10 mg) were
dissolved in tetrahydrofuran (THF) (1 mL). The resulting solu-
tion was deposited onto sample plate and allowed to air dry.
The resulting sample was irradiated at 337 nm by a nitrogen
laser and detected on positive mode at 20 kV. Size exclusion
chromatography (SEC) was carried out on a TOSOH HLC-8220
system equipped with three consecutive polystyrene gel col-
umns (TSK-gels [bead size, exclusion limited molecular wight];
super-AW4000 [6 μm, >4 × 105], super-AW3000 [4 μm,
>6 × 105], and super-AW2500 [4 μm, >2 × 103]) and refractive
index and ultraviolet detectors at 40 ꢀC. This system was oper-
ated using DMF containing 10 mM LiBr as eluent at a flow rate
of 0.5 mL/min. In the calibration, polystyrene standards were
used for the determination of their elution times. The molecular
weights of OSOCs were estimated based on the comparison of
their elution times with those of the standards. Thermogravi-
metric analysis (TGA) was carried out on a Seiko Instrument
Inc. TG-DTA 6200 with an aluminum pan under nitrogen flow
Synthesis of Aldehyde S3
A solution of DMSO (8.31 mL, 117.0 mmol) in CH2Cl2 (8 mL)
was added to
a solution of oxalyl chloride (5.05 mL,
58.5 mmol) in CH2Cl2 (30 mL) at −78 ꢀC. The mixture was
stirred for 5 min at −78 ꢀC and a solution of S2 (15.74 g,
38.7 mmol) in CH2Cl2 (40 mL) was added dropwise. After
stirring for 30 min, triethylamine (32.6 mL, 234.0 mmol) was
added and the reaction mixture was allowed to warm to room
temperature. A 1 N HCl was then added after 30 min and the
mixture was extracted with CH2Cl2 three times. The combined
organic extracts were washed with brine and then dried
(MgSO4) and concentrated under reduced pressure. The resi-
due was purified by flash chromatography over silica gel (hex-
ane/ethyl acetate = 5/1, v/v) to give the corresponding
aldehyde S3 (15.59 g, 38.5 mmol, 99.5%) as a pale yellow oil:
IR (neat): 3062, 3029, 2915, 2859, 1726, 1453, 1089, 1075,
734, 696 cm−1 1H NMR (400 MHz, CDCl3): δ 3.74 (s, 6 H),
;
4.47 (s, 6 H), 7.23–7.32 (m, 15 H), 9.72 (s, 1 H); 13C NMR
(100 MHz, CDCl3) δ 56.3, 68.0, 73.5, 127.4, 127.6, 128.3,
138.0, 203.8; HRMS (FAB): m/z calcd for C26H29O4 [M + H]+:
405.2066; found: 405.2067.
Synthesis of Alcohol S4
Typical Procedure: A solution of aldehyde S3 (8.10 g, 20.0 mmol)
in THF (40 mL) was added to a solution of MeMgBr (26 mL of
1 M solution in THF, 26.0 mmol) at 0 ꢀC. The reaction mixture
was allowed to warm to room temperature and then stirred for
3 h. The reaction mixture was quenched by adding 1 N HCl and
extracted with CH2Cl2 three times. The combined organic extracts
were washed with brine and then dried (MgSO4) and concen-
trated under reduced pressure. The residue was purified by flash
chromatography over silica gel (hexane/ethyl acetate = 10/1,
v/v) to give the corresponding alcohol S4b (8.30 g, 19.7 mmol,
99%) as a pale yellow oil: IR (neat): 3510, 3063, 3029, 2861,
ꢀ
rate of 200 mL/min at a heating rate of 10 C/min. Differential
scanning calorimetry (DSC) analysis was carried out on a Seiko
Instrument Inc. DSC-6200R with an aluminum pan under a
ꢀ
nitrogen flow rate of 50 mL/min at a heating rate of 10 C/min.
1453, 1089, 1069, 1023, 733, 695 cm−1 1H NMR (400 MHz,
;
The melting point was measured using a SRS MPA 100 auto-
mated melting point apparatus and was uncorrected.
CDCl3): δ 1.18 (d, J = 6.8 Hz, 3 H), 3.50 (d, J = 6.4 Hz, 1 H), 3.58
(d, J = 9.2 Hz, 3 H), 3.63 (d, J = 9.2 Hz, 3 H), 4.06 (quin,
J = 6.4 Hz, 1 H), 4.47 (s, 6 H), 7.25–7.34 (m, 15 H); 13C NMR
(100 MHz, CDCl3) δ 18.2, 46.7, 70.4, 70.5, 73.5, 127.4, 127.5,
128.3, 138.2; HRMS (FAB): m/z calcd for C27H33O4 [M + H]+:
421.2379; found: 421.2379.
Synthesis of Tribenzyl Ether S2
An aqueous solution of NaOH (12.5 M, 12.8 mL, 160.0 mmol)
was added to a solution of pentaerythritol (4.09 g, 30.0 mmol)
in DMSO (30.0 mL) at room temperature. After stirring for
30 min, benzyl bromide (27.80 g, 162.5 mmol) was added at
ꢀ
ꢀ
0 C and the reaction mixture was stirred for 1 h at 0 C. The
reaction mixture was allowed to warm to room temperature
and then stirred for 16 h. The reaction mixture was quenched
According to the typical procedure, the reaction of aldehyde
S3 (15.59 g, 38.5 mmol) with n-BuMgCl (25 mL of 2 M solu-
tion in THF, 50.0 mmol) was carried out to give the
2
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corresponding alcohol S4c (14.28 g, 30.9 mmol, 80%) as a
DMSO-d6): δ 0.86 (t, J = 6.8 Hz, 3 H), 1.12–1.38 (m, 4 H),
1.43–1.53 (m, 2 H), 3.42 (dd, J = 10.8, 5.2 Hz, 3 H), 3.47 (dd,
J = 10.8, 5.2 Hz, 3 H), 3.52 (ddd, J = 9.2, 6.4, 5.2 Hz, 1 H), 4.31
(t, J = 5.2 Hz, 3 H), 4.32 (d, J = 5.2 Hz, 1 H); 13C NMR
(100 MHz, DMSO-d6): δ 14.1, 22.3, 28.8, 30.8, 46.4, 61.4, 72.0;
HRMS (FAB): m/z calcd for C9H21O4 [M + H]+: 193.1440;
found: 193.1441.
pale yellow oil: IR (neat): 3513, 3063, 3029, 2923, 2858,
1
1453, 1071, 1028, 733, 696 cm−1; H NMR (400 MHz, CDCl3):
δ 0.89 (t, J = 7.6 Hz, 3 H), 1.23–1.64 (m, 6 H), 3.25 (d,
J = 6.8 Hz, 1 H), 3.58 (d, J = 9.2 Hz, 3 H), 3.62 (d, J = 9.2 Hz,
3 H), 3.80 (m, 1 H), 4.46 (s, 6 H), 7.23–7.34 (m, 15 H); 13C
NMR (100 MHz, CDCl3) δ 14.1, 22.7, 28.9, 31.6, 46.8, 70.5,
73.5, 74.4, 127.4, 127.5, 128.3, 138.3; HRMS (FAB): m/z calcd
for C30H39O4 [M + H]+: 463.2848; found: 463.2846.
According to the typical procedure, the reaction of alcohol S4d
(11.32 g, 23.5 mmol) in the presence of 10% Pd/C (3.91 g,
3.67 mmol based on Pd) under a hydrogen atmosphere was car-
ried out to give 1d (4.78 g, 22.5 mmol, 96%) as a white solid:
Mp: 101–102 ꢀC; IR (neat): 3317, 3031, 2935, 2889, 1453, 1429,
1021, 999, 702, 671 cm−1; 1H NMR (400 MHz, DMSO-d6): δ 3.34
(dd, J = 10.4, 4.8 Hz, 3 H), 3.48 (dd, J = 10.4, 4.8 Hz, 3 H), 4.48
(t, J = 4.8 Hz, 3 H), 4.83 (d, J = 5.2 Hz, 1 H), 5.46 (d, J = 4.8 Hz,
1 H), 7.20–7.36 (m, 5 H); 13C NMR (100 MHz, DMSO-d6): δ 46.6,
61.1, 74.1, 126.7, 127.3, 127.3, 142.4; HRMS (FAB): m/z calcd for
C11H17O4 [M + H]+: 213.1127; found: 213.1129.
According to the typical procedure, the reaction of aldehyde
S3 (16.75 g, 41.4 mmol) with PhMgBr (54 mL of 1 M solution
in THF, 54.0 mmol) was carried out to give the corresponding
alcohol S4d (19.64 g, 40.7 mmol, 98%) as a pale yellow oil:
IR (neat): 3475, 3061, 3029, 2914, 2865, 1495, 1452, 1071,
1027, 734, 696 cm−1 1H NMR (400 MHz, CDCl3): δ 3.49 (d,
;
J = 8.8 Hz, 3 H), 3.59 (d, J = 9.2 Hz, 3 H), 4.48 (s, 6 H), 4.54
(d, J = 7.2 Hz, 1 H), 5.05 (d, J = 7.2 Hz, 1 H), 7.22–7.34 (m,
20 H); 13C NMR (100 MHz, CDCl3) δ 47.5, 69.5, 73.5, 76.7,
127.1, 127.3, 127.5, 127.6, 127.7, 128.3, 138.1, 141.0; HRMS
(FAB): m/z calcd for C32H35O4 [M + H]+: 483.2535; found:
483.2536.
FIGURE 1 Development of soluble OSOCs based on introducing
substituent R in the side chain.
SCHEME 1 Synthetic route for pentaerythritol derivatives 1.
Synthesis of 1b, 1c, and 1d
Typical procedure: A suspension of S4b (8.30 g, 19.7 mmol)
and 10% Pd/C (3.40 g, 3.19 mmol based on Pd) in EtOH
(100 mL) in a 300 mL two-necked flask was degassed under
reduced pressure. The flask was filled with hydrogen, and the
suspension was vigorously stirred for 72 h at room tempera-
ture under a hydrogen atmosphere. The resulting mixture was
filtered through a membrane filter, and the filtrate was evapo-
rated in vacuo. The resulting crude product was recrystallized
from ethyl acetate to obtain pure 1b (2.82 g, 18.8 mmol,
95%) as a white solid: Mp: 149–150 ꢀC; IR (neat): 3242,
SCHEME
1 with TEOC.
2 Polycondensation of pentaerythritol derivatives
2937, 2883, 1472, 1327, 1057, 1002, 907 cm−1 1H NMR
;
Polycondensation of Pentaerythritol Derivatives 1 with
Tetraethylorthocarbonate
(400 MHz, DMSO-d6): δ 1.09 (d, J = 6.4 Hz, 3 H), 3.42 (dd,
J = 10.4, 4.0 Hz, 3 H), 3.47 (dd, J = 10.4, 4.4 Hz, 3 H), 3.78
(dq, J = 6.4, 5.6 Hz, 1 H), 4.30 (t, J = 5.2 Hz, 3 H), 4.46
(d, J = 5.2 Hz, 1 H); 13C NMR (100 MHz, DMSO-d6): δ 18.5,
46.3, 61.3, 68.1; HRMS (FAB): m/z calcd for C6H15O4
[M + H]+: 151.0970; found: 151.0970.
Typical procedure: Into a nitrogen-purged flask with pentaer-
ythritol (272.3 mg, 2.0 mmol) was introduced successively
anhydrous DMF (8 mL), tetraethylorthocarbonate (384.5 mg,
2.0 mmol), and methanesulfonic acid (13 μL, 0.2 mmol) via
syringe. The homogeneous mixture was stirred at room tem-
perature under 2 kPa. After 24 h, the mixture was filled with
a nitrogen. Triethylamine (200 μL) was added to the mixture,
and the resulting solution was poured into an aqueous solu-
tion of NaOH (1 M). After 0.5 h, the resulting precipitate was
collected by filtration and washed with distilled water. And
then, it was dried under vacuum to give the OSOC 2a
(282.5 mg, 98%) as a white powder: IR (ATR): 3430, 2932,
According to the typical procedure, the reaction of alcohol S4c
(7.89 g, 17.05 mmol) in the presence of 10% Pd/C (3.10 g,
2.91 mmol based on Pd) under a hydrogen atmosphere was
carried out to give 1c (2.96 g, 15.4 mmol, 90%) as a white
solid: Mp: 124–125 ꢀC; IR (neat): 3299, 2952, 2930, 2869,
1
1455, 1407, 1142, 1022, 1007, 911 cm−1; H NMR (400 MHz,
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2888, 1463, 1227, 1161, 1103, 995 cm−1 13C NMR (CPMAS):
;
TABLE 1 Yields and Properties of OSOCs 2
δ 31.8, 39.8, 65.8, 116.2.
Yield (%)a
Mn
Mw/Mn
T
d10 (ꢀC)c
b
b
Entry
2
R
According to the typical procedure, the polycondensation of 1b
(75.1 mg, 0.5 mmol) with tetraethylorthocarbonate (96.1 mg,
0.5 mmol) was carried out to give 2b (47.1 mg, 60%) as a white
powder: IR (ATR): 3415, 2945, 2891, 1459, 1373, 1220, 1161,
d
d
1
2
3
4
a
2a
2b
2c
2d
H
98
60
73
84
-
-
302
354
320
278
Me
n-Bu
Ph
1100
1300
1200
1.66
1.96
1.75
1
1107, 992 cm−1; H NMR (400 MHz, DMSO-d6): δ 1.04–1.18 (br,
3H), 3.57–4.63 (br, 7H); 13C NMR (CPMAS): δ 16.4, 34.6, 42.1,
63.0, 65.6, 67.3, 71.5, 75.5, 115.8.
1 M NaOH aq.-insoluble part.
b
Estimated by SEC (eluent = DMF with 10 mM LiBr, polystyrene
standards).
c
According to the typical procedure, the polycondensation of 1c
(196.3 mg, 1.0 mmol) with tetraethylorthocarbonate (192.3 mg,
1.0 mmol) was carried out to give 2c (147.1 mg, 73%) as a
white powder: IR (ATR): 3548, 2955, 2873, 1460, 1373, 1228,
Determined by TGA.
d
Not analyzed by SEC because of the insolubility of 2a.
The polycondensation of 1a with TEOC gave the correspond-
ing OSOC 2a. As has been reported,6 it was insoluble in com-
mon organic solvents and thus its molecular weight of the
oligomer could not be measured by SEC. The structure of
OSOC 2a was confirmed by solid state 13C NMR (CPMAS). In
the spectrum (Fig. S17 in the Supporting Information), a sig-
nal attributable to the quaternary carbon in the spiroorthocar-
bonate moiety was observed at 116 ppm.
1
1162, 1110, 1000, 985 cm−1; H NMR (400 MHz, CDCl3): δ 0.90
(br, 3H), 1.34–1.60 (br, 6H), 3.49–4.31 (br, 7H); 13C NMR
(100 MHz, CDCl3): δ 13.9, 14.0, 22.3, 22.5, 28.5, 29.0, 34.9, 35.3,
35.5, 35.8, 41.0, 41.3, 61.5, 61.7, 64.8, 65.3, 66.0, 66.4, 66.9, 75.4,
75.7, 76.1, 114.9, 115.2, 115.7.
According to the typical procedure, the polycondensation of 1d
(106.1 mg, 0.5 mmol) with tetraethylorthocarbonate (96.1 mg,
0.5 mmol) was carried out to give 2d (92.6 mg, 84%) as a
white powder: IR (ATR): 3550, 3061, 3031, 2957, 2891, 1606,
In contrast to OSOC 2a synthesized from pentaerythritol 1a,
the other OSOCs 2b, 2c, and 2d synthesized from the pentaery-
thritol derivatives bearing alkyl or phenyl group were partially
soluble or soluble in organic solvents (Table 2). Among these
three OSOCs, 2d bearing phenyl group in the side chain was
entirely or partially soluble in a wide range of solvents involving
aprotic highly polar solvents such as DMSO, ethyl acetate, ace-
tone, dichloromethane, and chloroform, implying that the bulki-
ness of the phenyl groups hindered aggregation of the rigid rod-
like OSOC molecules into bundles. The second most soluble was
2c bearing butyl group in the side chain, as expected from the
more sterically hindered and flexible natures of butyl group than
1
1455, 1375, 1216, 1163, 999, 700 cm−1; H NMR (400 MHz,
DMSO-d6): δ 3.17–5.54 (br, 7H), 6.78–7.31 (br, 5H); 13C NMR
(100 MHz, DMSO-d6): δ 34.6, 40.9, 41.4, 60.4, 61.5, 63.1,
64.1, 65.7, 75.7, 76.4, 113.7, 114.6, 115.2, 127.2, 127.6,
128.1, 134.8.
RESULTS AND DISCUSSION
Synthesis of Pentaerythritol Derivatives 1
The synthetic route for the C-mono-alkylated or arylated pen-
taerythritol derivatives used in this work is shown in
Scheme 1. Pentaerythritol (1a) was reacted with benzylbro-
mide to obtain tribenzyl ether S2, then S2 was oxidized into
the corresponding aldehyde S3. The aldehyde S3 readily
reacted with Grignard reagents to give the corresponding
alcohols S4 in good to high yields, then the benzyl groups
were removed by hydrogenation to obtain the desired pen-
taerythritol derivatives 1b-1d.
TABLE 2 Solubility of OSOCs 2
Solvent
MeOH
EtOH
2a
−
−
−
−
−
−
−
−
−
−
−
−
−
2b
−
−
+
2c
−
2d
−
−
−
DMSO
DMF
+
++
++
−
+
+
CH3CN
AcOEt
Acetone
THF
−
−
−
−
−
+
−
−
+
Polycondensation of Pentaerythritol Derivatives 1 with
Tetraethylorthocarbonate
−
+
The polycondensation of pentaerythritol 1a and its derivatives
1b-1d with TEOC was carried out using methanesulfonic acid as
a catalyst (Scheme 2).10 The polymerization was conducted in N,
N-dimethylformamide (DMF) under a reduced pressure. The role
of the reduced pressure is to ensure efficient removal of ethanol
formed by the transesterification. After 24 h, the reaction was
quenched by adding triethylamine, and the solution was poured
into a solution of 1 M aqueous sodium hydroxide to precipitate
OSOC 2. The yields of 2, their number-average molecular weights
(Mn) and their polydispersity indices (Mw/Mn) estimated by size
exclusion chromatography (SEC), are shown in Table 1.
+
+
Et2O
−
−
CH2Cl2
CHCl3
Toluene
Hexane
++
++
+
+
+
+
−
−
−
−
−
++: Soluble, +: partially soluble, −: insoluble. These categories of solubil-
ity were determined by visual observation. In the solubility test, 1 mL of
solvent was added to 2 mg of the oligomer and the mixture was stirred
at room temperature for 1 h.
4
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more decisive evidence for the formation of spiroorthocarbo-
nate structure, indicating a signal at 116 ppm attributable to
the quaternary carbon connecting to the four oxygen atoms.
The chemical structures of OSOCs 2b–2d were studied further
in detail with MALDI-TOF mass spectroscopy. Prior to the
analysis, OSOCs were treated with 1 M NaOH aq. to prevent
contamination of the spectra by signals attributable to OSOCs
bearing cyclic carbonate and hydroxycarbonate moieties at
their chain ends. The spectrum for 2c is shown in Figure 3.
The spectrum showed a series of signals differed by 200 Da,
which corresponded to the molecular weight of the repeating
unit of 2c. The mass numbers confirmed that 2c had diol moi-
eties at the both chain ends.11 Similarly, 2b and 2d were ana-
lyzed with MALDI-TOF MS to reveal their defect free main
chains and the presence of diol-type terminals. MALDI-TOF
MS analysis of 2a was also attempted; however, intensive
studies to ionize 2a with varying ionizing agent and matrix
resulted in failure, presumably due to the poor miscibility of
2a with the matrices.
Thermal Property of OSOCs 2
OSOCs 2 were subjected to TGA to evaluate their thermal
stability. The resulting thermograms are shown in the Sup-
porting Information Figure S24. The 10% weight loss tem-
peratures (Td10s) are summarized in Table 1. The Td10
values for 2a was 302 ꢀC, which was higher than that
reported, suggesting the present method for the synthesis
allowed the formation of 2a with higher molecular weight
than that reported and thus the thermal stability of OSOCs
is potentially high.6 Interestingly, the thermal stability of 2b
was much higher than 2a, while that of 2c was comparable
to that of 2a. For these differences in thermal stability, the
first factor would be the differences in molecular weight.
Because the alkyl-substituted pentaerythritol derivatives 1b
and 1c were more soluble than pentaerythritol 1a, the poly-
condensations of 1b and 1c with tetraethylorthocarbonate
would proceed more efficiently than that of 1a, leading to
the higher molecular weights of the corresponding OSOCs
2b and 2c than that of 2a. The second factor would be the
degree of spontaneous packing of oligomer chains that can
restrict motion of oligomer chains to enhance their thermal
stability. The butyl group in the side chain of 2c is bulkier
than the methyl group in the side chain of 2b to hamper
the packing of the polymer chains, leading to the lower
thermal stability of 2c than that of 2b. On the other hand,
the thermal stability of 2d was much lower than the other
OSOCs, presumably due to not only the high bulkiness of
the phenyl group in the side chain but also the thermally
induced scission of the benzyl ether linkage in the main
chain causing relatively stable benzyl cation and/or benzyl
radical.
FIGURE 2 1H (top) and 13C (bottom) NMR spectra of 2c (in CDCl3)
methyl group. OSOC 2c was soluble in dichloromethane and
chloroform. Presumably due to the nonpolar nature of butyl
group, 2c was less soluble in aprotic polar solvents than 2d,
whereas 2c was more soluble in toluene than 2d. All the OSOCs
were insoluble in water and alcohols.
The enhanced solubility of 2b-2d allowed the estimation of
their molecular weights by SEC. As shown in Table 1, their Mn
ranged from 1100 to 1300. From these values, the average
numbers of the repeating units in 2b, 2c, and 2d were esti-
mated to be 7.0, 6.5, and 5.4, respectively. It should be noted
that OSOCs 2b–2d were partially soluble in DMF used as the
eluent for the SEC analysis, and thus the Mn values shown
herein are only for the soluble parts.
Structure of OSOCs 2
The chemical structures of 2b-2d were successfully confirmed
by 1H and 13C NMR analyses of their solutions. As typical
examples, the spectra of 2c are shown in Figure 2. As for the
1H NMR spectrum, the main signals were assignable to the
repeating unit and the integral ratio of the signals agreed with
the assignments. In addition, the 13C NMR spectrum gave a
OSOCs 2 were also subjected to differential scanning calorime-
try (DSC). The resulting thermograms confirmed that they
exhibit neither glass transition nor melting in the range from
30 ꢀC to the temperatures at which OSOCs start to degrade,
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FIGURE 3 MALDI-TOF MS spectrum of 2b, 2c, and 2d
suggesting the constrain of the conformational change in the
OSOC main chain.
solubility in common organic solvents in contrast to the
pentaerythritol-derived OSOC that was persistently insoluble
in organic solvents. The soluble nature of OSOCs achieved by
the introduction of alkyl and phenyl substituents allowed the
detailed structural analysis of OSOCs by NMR and MALDI-TOF
analyses. In addition, the high 10% weight loss temperatures
OSOCs and the absence of glass transition behaviors below
200 ꢀC confirmed the potential applicability of OSOCs as
high-performance materials. Another feature of OSOCs as a
crosslinkable oligomers with volume expanding is under
investigation.
CONCLUSIONS
The polycondensation of alkyl- and phenyl-substituted
pentaerythritol derivatives with tetraethylorthocarbonate affo-
rded a series of the corresponding OSOCs. The polycondensa-
tion proceeded at room temperature using methanesulfonic
acid as the catalyst. The resulting OSOCs inheriting the alkyl
and phenyl substituents in the side chains exhibited improved
6
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ACKNOWLEDGMENTS
7 T. Takata, T. Endo, In Expanding Monomers; Synthesis, Char-
acterization, and Applications; R. K. Sadhir, R. M. Luck, Eds.;
CRC Press: Boca Raton, FL, 1992; Vol. 63.
This work was financially supported by JSR Corporation.
High-resolution mass spectral measurement was performed
under the Cooperative Research Program of “Network Joint
Research Center for Materials and Devices.”
8 W. J. Bailey, R. R. Sun, H. Katsuki, T. Endo, H. Iwama,
K. Tsushima, K. Saigo, M. Bitritto, In Ring-Opening Polymeriza-
tion with Expansion in Volume; ACS Symposium Series 59;
T. Saegusa, E. Goethals, Eds.; American Chemical Society:
Washington, DC, 1977; Vol. 38.
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10 We examined the polycondensation of pentaerythritol deriva-
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11 The partial ring-opening reaction of the spiroorthocarbonate
in the oligomers proceeded because the polycondensation
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