Synthesis of poly(decahydro-2-naphthyl methacrylate)s with different geometric structures and effects of side-group dynamics on polymer properties investigated by thermal and dynamic mechanical analyses and DFT calculations

Article abstract of DOI:10.1021/ma400254d

We prepared the geometric isomers of decahydro-2-naphthols as the source materials for the synthesis of poly(decahydro-2-naphthyl methacrylate)s [poly(DNMA)-I, -II, -III, and -IV] including alicyclic ester groups with different geometric structures. The geometry and conformational dynamics of the decahydro-2-naphthyl moieties were investigated by NMR spectroscopy and DFT calculations. We synthesized each isomer of the methacrylic monomers, polymerized them, and investigated the optical, thermal, and mechanical properties of poly(DNMA)s with different isomer compositions. The T_g values of the poly(DNMA)s were in the following order: 139.3 C for poly(DNMA)-II < 142.7 C for poly(DNMA)-I < 146.2 C for poly(DNMA)-III < 152.9 C for poly(DNMA)-III/IV. On the basis of the dynamic motion of the alicyclic substituents determined by dynamic mechanical analysis, the tan δ peaks due to the β-relaxation for the a conformation change of the side group were observed for poly(DNMA)-I, while no peak was observed for poly(DNMA)-III. The activation energies for the β-relaxation were 65 kJ/mol for poly(DNMA)-I and 56-63 kJ/mol for the poly(DNMA)s including the four isomeric ester groups with various compositions. An increase in the DNMA-II content in the repeating units accelerated a dynamic conformation change, resulting in a decrease in the tan δ peak temperature and the activation energy value, as well as the glass transition temperature of the polymers. The optical property of the resulting polymers as the transparent polymer materials was also investigated. The density, refractive index value, and Abbe number of poly(DNMA)s were 1.04-1.10 cm³/g, 1.489, and 42-44, respectively.

Full text of DOI:10.1021/ma400254d

Article
pubs.acs.org/Macromolecules
Synthesis of Poly(decahydro-2-naphthyl methacrylate)s with
Different Geometric Structures and Effects of Side-Group Dynamics
on Polymer Properties Investigated by Thermal and Dynamic
Mechanical Analyses and DFT Calculations
Anri Ozaki, Koha Sumita, Kunihiro Goto, and Akikazu Matsumoto*
Department of Applied Chemistry and Bioengineering, Graduate School of Engineering, Osaka City University, 3-3-138, Sugimoto,
Sumiyoshi-ku, Osaka 558-8585, Japan
S
* Supporting Information
ABSTRACT: We prepared the geometric isomers of
decahydro-2-naphthols as the source materials for the
synthesis of poly(decahydro-2-naphthyl methacrylate)s [poly-
(DNMA)-I, -II, -III, and -IV] including alicyclic ester groups
with different geometric structures. The geometry and
conformational dynamics of the decahydro-2-naphthyl moi-
eties were investigated by NMR spectroscopy and DFT
calculations. We synthesized each isomer of the methacrylic
monomers, polymerized them, and investigated the optical,
thermal, and mechanical properties of poly(DNMA)s with
different isomer compositions. The Tg values of the poly-
(DNMA)s were in the following order: 139.3 °C for
poly(DNMA)-II < 142.7 °C for poly(DNMA)-I < 146.2 °C for poly(DNMA)-III < 152.9 °C for poly(DNMA)-III/IV. On
the basis of the dynamic motion of the alicyclic substituents determined by dynamic mechanical analysis, the tan δ peaks due to
the β-relaxation for the a conformation change of the side group were observed for poly(DNMA)-I, while no peak was observed
for poly(DNMA)-III. The activation energies for the β-relaxation were 65 kJ/mol for poly(DNMA)-I and 56−63 kJ/mol for the
poly(DNMA)s including the four isomeric ester groups with various compositions. An increase in the DNMA-II content in the
repeating units accelerated a dynamic conformation change, resulting in a decrease in the tan δ peak temperature and the
activation energy value, as well as the glass transition temperature of the polymers. The optical property of the resulting polymers
as the transparent polymer materials was also investigated. The density, refractive index value, and Abbe number of
poly(DNMA)s were 1.04−1.10 cm3/g, 1.489, and 42−44, respectively.
values of poly(4-tert-butylcyclohexy methacrylate) sensitively
depended on the geometric position of the tert-butyl group; the
Tg value varied over the temperature range from 130 to 178 °C,
according to the cis/trans content of the ester alkyl groups.30,31
Poly(2-tert-butylcyclohexy methacrylate) similarly exhibited
higher Tg values in the range of 163-214 °C.32 These polymers
have a cyclohexyl ring with a fixed conformation due to the
presence of the bulky tert-butyl group, but an increase in the
bulkiness of the side-group substituents simultaneously induced
an alternative problem of mechanical strength. The selection of
the most favorable geometric structure is important for the
rational molecular design of high-temperature and transparent
polymer materials. The Tg value of poly(decahydro-2-naphthyl
methacrylate) [poly(DNMA)] was previously reported to be
145 °C, which was evaluated using a poly(DNMA) containing
four kinds of geometric isomers in the ester alkyl groups.33 In
INTRODUCTION
■
Transparent polymers with a high glass transition temperature
(Tg) and excellent mechanical properties are one of the key
materials for electronic and photonic applications, and
therefore, various types of polymers and their composites
have been developed as high-performance transparent materi-
als.1−12 They exhibit excellent transparency, low birefringence,
and low water absorption as well as their high thermal resistant
and they are used as the new polymer materials alternative to
conventional poly(methyl methacrylate) [poly(MMA)] and
polycarbonates. Another approach to the design of transparent
polymers with a high Tg value is the introduction of a bulky
substituent in the side group of acrylic polymers.13−23 Poly(1-
adamantyl methacrylate) [poly(AdMA)] has an extremely high
Tg value (more than 200 °C) because chain mobility is reduced
due to the bulk ester group, while the Tg value of
poly(cyclohexyl methacrylate) [poly(CHMA)] is similar to
that of poly(MMA).24−29 The dynamic motion of the
cycloalkyl moieties is important and the Tg is closely related
to the free volume of the polymers. We reported that the Tg
Received: February 4, 2013
Revised: March 20, 2013
Published: April 2, 2013
© 2013 American Chemical Society
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B3LYP level of theory with the base function of 6-311G*. The
dynamic mechanical properties were determined using a Seiko DMS-
6100 dynamic mechanical analyzer under atmospheric conditions and
temperature control. The measurements were carried out using the
flexural mode at frequencies of 0.5−10 Hz and the heating rate of 2
°C/min in the temperature range of −150 to 150 °C. The strain
amplitude and the initial amplitude were 5 μm and 10 mN,
respectively. The apparent activation energy was evaluated for the β-
relaxations using the peak tan δ temperatures and the applied
frequency. The sample for the DMA measurements was prepared by
compression of the polymer powders with an applied pressure at 25 g/
cm2 with a guide made of a poly(tetrafluoroethylene) sheet (1-mm
thickness) in vacuo at a temperature over each Tg for 1 h. The
obtained polymer sheets were cut into sample sizes of 40 mm ×10 mm
×1 mm for the measurement.
this study, we prepared each isomer for the precursor
alcohols34−38 (DNOHs) and then synthesized the correspond-
ing poly(DNMA)s with different geometric structures, as
shown in Scheme 1. The structures of the ester alkyl groups of
Scheme 1
Materials. All reagents used for monomer synthesis were
purchased from Tokyo Chemical Industry Co., Ltd., Wako Pure
Chemical Industries, Ltd., and Sigma-Aldrich, Japan, and used without
further purification. Solvents were used after distillation.
(2R*,4aR*,8aS*)-Decahydro-2-naphthol (DNOH-I). Recrystallized
from the n-hexane solution of the commercial isomeric mixture, mp
1
89−90 °C. H NMR (400 MHz, CDCl3): δ 3.63−3.57 (m, CHOH),
1.80−1.18 (m, others, 16H). 13C NMR (100 MHz, CDCl3): δ 71.60
(COH), 35.44, 34.90, 34.68, 31.76, 30.42, 30.11, 26.75, 25.83, and
21.02 (others).
Synthesis of (2R*,4aS*,8aR*)-Decahydro-2-naphthol (DNOH-II)
(Scheme 2). (2R*,4aR*,8aS*)-Decahydro-2-naphthyl Tosylate. To
poly(DNMA)s with different geometric structures as well as
their thermal, mechanical, and optical properties were
investigated. The effects of the conformation and the dynamic
motion of the alicyclic substituents in the side group are
discussed based on the results of NMR measurements, dynamic
mechanical analysis, and DFT calculations.
Scheme 2
EXPERIMENTAL SECTION
■
General Procedures. The NMR spectra were recorded using
Bruker AV300N and JEOL JNM-A400 spectrometers in CDCl3. The
number-average molecular weight (Mn), weight-average molecular
weight (Mw), and polydispersity (Mw/Mn) were determined by size
exclusion chromatography (SEC) in tetrahydrofuran (THF) as the
eluent using a Tosoh CCPD RE-8020 system and calibration with
standard polystyrenes. The FT-IR spectra were recorded by a JASCO
FT/IR 430 spectrometer using the KBr pellet method. The
thermogravimetric and differential thermal analyses (TG/DTA) were
carried out using a Seiko TG/DTA 6200 with a nitrogen stream at the
heating rate of 10 °C/min. The onset temperature of decomposition
was evaluated as the 5% weight-loss temperature (Td5) in the TG
analysis. The maximum temperature of decomposition (Tmax) was
determined using the derivatives of the TG curves. Differential
scanning calorimetry (DSC) was carried out using a Seiko DSC-6200
at the heating rate of 10 °C/min in order to determine the Tg. The
UV−vis spectra were recorded using a JASCO V-550 spectropho-
tometer. The refractive indices (nD, nF, and nC) were measured at the
wavelengths of 486, 589, and 656 nm, respectively, using an Abbe-type
refractometer (Atago DR-M2, 1-bromonaphthalene, a halogen lamp).
The Abbe number (νD) was calculated as follows.
the DNOH-I (7.70 g, 50 mmol) in 30 mL of pyridine, p-
toluenesulfonyl chloride (9.53 g, 50 mmol) in 30 mL of pyridine
was added at 0 °C. After the reaction was stirred at room temperature
for 1 day, the precipitated pyridine hydrochloride salt was filtered. The
filtrate was washed with sodium hydrogen carbonate and a saturated
saline solution and then dried on sodium sulfate. The pyridine was
evaporated under reduced pressure, and the crude product was
recrystallized from a mixture of chloroform and n-hexane to obtain
colorless and powdery crystals. Yield: 10.9 g (71%); mp 62−63 °C. 1H
NMR (400 MHz, CDCl3): δ 7.83−7.73 (m, Ar, 2H), 7.36−7.30 (m,
Ar, 2H), 4.52−4.41 (m, OCH, 1H), 2.45 (s, CH3, 3H), 1.88−1.16 (m,
others, 16H). 13C NMR (100 MHz, CDCl3): δ 144.28 (CH3), 134.68
(Ar), 129.67 (Ar), 127.51 (Ar), 82.96 (OC), 34.58, 34.30, 32.49,
31.02, 29.24, 27.59, 26.07, 21.57, and 21.07 (others).
(2R*,4aS*,8aR*)-Decahydro-2-naphthyl Acetate. A mixture of
(2R*,4aR*,8aS)-decahydro-2-naphthyl tosylate (10.7 g, 35 mmol) and
sodium acetate (5.74 g, 70 mmol) in acetic acid (150 mL) was stirred
at 50 °C for 2 days. After the reaction, 800 mL of water was added and
the products were extracted with 450 mL of diethyl ether (150 mL ×
3). The ether layers were collected and washed with sodium hydrogen
carbonate and dried on sodium sulfate. The ether was evaporated
under reduced pressure, and the crude product was distilled under
reduced pressure. Yield: 0.55 g (8%); bp 95 °C (0.5 mmHg). 1H NMR
(400 MHz, CDCl3): δ 4.93 (s, OCH, 1H), 2.02 (s, CH3, 3H), 1.97−
1.19 (m, others, 16H). 13C NMR (100 MHz, CDCl3): δ 170.35 (C
O), 70.16 (OC), 35.10, 34.81, 34.66, 34.32, 29.19, 27.73, 25.85, 24.81,
23.06, and 21.23 (others).
νD = (nD − 1)/(nF − nC)
(1)
Single-crystal X-ray diffraction data were collected at −150 °C using a
Rigaku RAXIS RAPID imaging plate diffractometer with Mo Kα
radiation (λ = 0.71073 Å, 40 kV, 40 mA) monochromated by graphite.
The crystal structures were solved by a direct method using SIR92 and
refined by the full-matrix least-squares method on F2 with anisotropic
displacement parameters for non-hydrogen atoms using SHELXL-97.
All the DFT calculations were carried out using the Spartan’08
software package (Wave function, Inc.). A semiempirical molecular
orbital method was used for the estimation of candidates of initial
preferred conformations for the calculations, and then a optimized
structure and an energy for each conformer were calculated at the
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(2R*,4aS*,8aR)-Decahydro-2-naphthol (DNOH-II). To methanol
(30 mL) containing 5 wt % potassium hydroxide was added
(2R*,4aS*,8aR)-decahydro-2-naphthyl acetate (0.55 g) and the
reaction then refluxed for 10 h. After the reaction, 150 mL of water
was added to the solution, and the products were extracted with 450
mL of diethyl ether (150 mL × 3). The ether layers were collected and
washed with a saturated saline solution and dried on sodium sulfate.
The ether was evaporated under reduced pressure to obtain the crude
Scheme 4
1
product. Yield 0.43 g (99%); colorless liquid. H NMR (400 MHz,
CDCl3): δ 3.74−3.94 (br, CHOH, 1H), 1.17−1.99 (m, others, 16H).
13C NMR (100 MHz, CDCl3): δ 66.47 (COH), 35.21, 34.74, 34.49,
31.58, 30.12, 29.17, 25.82, 24.64, and 20.44 (others).
Synthesis of (2R*,4aR*,8aR)- and (2R*,4aS*,8aS)-Decahydro-2-
naphthols39,40 (DNOHs-III and -IV). cis-2,3,5,6,9,10-Hexahydro-1,4-
naphthoquinone (Scheme 3). In a Pyrex glass ampule, p-
added dropwise at 0 °C. The solution was diluted with 11 mL of
chloroform and washed with 10% sodium hydrogen sulfite and water,
and then dried on sodium sulfate. The chloroform was evaporated
under reduced pressure and the recrystallization from ethanol was
repeated three times to obtain trans-octalin dibromide as a colorless
Scheme 3
1
powder. Yield: 18%. H NMR (CDCl3, 300 MHz): δ 4.64−4.62 (m,
BrCH, 2H), 2.15−0.99 (m, others, 14H). 13C NMR (CDCl3, 75
MHz): δ 53.81 (CBr), 36.76 (CH), 35.37 (CHCH2CBr), 32.54
(CHCH2CH2), 26.25 (CHCH2CH2).
trans-Octalin. The trans-octalin dibromide (0.97 g, 33 mmol) was
added to 7.8 mL of the ethanol suspension of zinc powder (2.0 g, 10
mmol), and the reaction mixture was stirred at room temperature for
1.5 h and then at 65 °C for 2.5 h. After the reaction, pyridine (2.4 mL,
31 mmol) was added, and the solution was filtered. The products were
extracted with diethyl ether, and the obtained ether solution was
washed with a saturated saline solution and dried on sodium sulfate.
The ether was evaporated under reduced pressure to obtain trans-
octalin as a colorless liquid. Yield: 45%. 1H NMR (CDCl3, 300 MHz)
δ 5.64−5.62 (m, CHCH, 2H), 2.04−0.91 (m, others, 14H); 13C
NMR (CDCl3, 75 MHz) δ 126.57 (CHCH), 38.26 (CH), 34.00
(CHCHCH2), 33.22 (CHCH2CH2), 26.54 (CHCH2CH2)
benzoquinone (2.5 g, 23 mmol),1,3-butadiene (6 mL, 69 mmol),
and acetic acid (20 mL) were charged and degassed, and then the
ampule was sealed. The mixture was stirred at room temperature for 2
days. After the ampule was opened, Zn powder (2.7 g) and 12 mL of
acetone were added at 0 °C and stirred for 3 h. The suspension was
filtered, and the solvent was evaporated under reduced pressure. The
obtained crude solids were dissolved in chloroform and washed with
sodium hydrogen carbonate and water, and dried on sodium sulfate.
The chloroform was evaporated under reduced pressure, and the
residue was recrystallized from methanol to obtain cis-2,3,5,6,9,10-
hexahydro-1,4-naphthoquinone as colorless and powdery crystals.
Yield: 64%. 1H NMR (CDCl3, 300 MHz): δ 5.66 (m, CHCH, 2H),
3.09−3.02 (m, CH, 2H), 2.90−2.63 (m, CH2CO, 4H), 2.41−2.14 (m,
CHCHCH2, 4H). 13C NMR (CDCl3, 75 MHz): δ 209.20 (CO),
124.43 (CHCH), 44.87 (CH), 35.84 (CH2CO), 23.50 (CH
CHCH2).
(2R*,4aR*,8aR)- and (2R*,4aS*,8aS)-Decahydro-2-naphthols
(DNOHs-III and -IV) (Scheme 5). Into a flask purged with argon,
Scheme 5
were charged trans-octalin (0.21g, 16 mmol) and dry THF (2 mL),
and a THF solution of borane (1 mol/L, 1.6 mL) was added dropwise.
After being stirred at 0 °C for 30 min, the solution was further stirred
at room temperature for 4 h. After the mixture was cooled to 0 °C
again, 3.0 mol/L aqueous sodium hydroxide solution (0.52 mL, 1.55
mmol) and 10% hydrogen peroxide solution (0.26 mL) were added,
and the mixture was then stirred at room temperature for 12 h. The
products were extracted with diethyl ether, and the obtained ether
solution was dried on sodium sulfate. The ether was evaporated under
reduced pressure to obtain a DNOHs-III and -IV mixture as a colorless
liquid, which was further distilled under reduced pressure using a glass
tube oven. Yield: 86%. 1H NMR (CDCl3, 300 MHz): δ 4.12−4.07 (m,
OCH, 1H), 2.00−0.77 (m, others, 16H). 13C NMR: δ 70.40 and 66.57
(CHOH), 42.96, 42.16, 41.05, 40.17, 36.22, 35.52, 33.72, 33.66, 33.61,
33.13, 32.69, 31.88, 31.43, 27.38, 26.48, 26.40, 26.15, 22.50, and 13.96
(others).
Octalin (cis- and trans-Mixture)41 (Scheme 3). To the solution of
cis-2,3,5,6,9,10-hexahydro-1,4-naphthoquinone (4.8 g, 29 mmol) and
potassium hydroxide (5.3 g, 94 mmol) in 38 mL of triethylene glycol
(38 mL) was added hydrazine monohydrate (7.0 mL) and the mixture
heated at 120 °C for 90 min. The temperature was gradually raised to
evaporate the excess hydrazine monohydrate and further reacted at
190 °C for 4 h. After the reaction, 50 mL of water was added to the
solution and the products were extracted with diethyl ether, washed
with a saturated saline solution, and dried on sodium sulfate. The ether
was evaporated under reduced pressure to obtain a mixture of trans-
1
and cis-octalins as a colorless liquid product. Yield: 63%. H NMR
(CDCl3, 300 MHz): δ 5.67−5.54 (m, CHCH, 2H), 2.09−0.90 (m,
others, 14H). 13C NMR (CDCl3, 75 MHz): δ 126.54 (trans, CH
CH), 125.04 (cis, CHCH), 38.25 (trans, CH), 34.00 (trans,
CHCHCH2), 33.21 (trans, CHCH2CH2), 26.54 (trans, CHCH2CH2),
33.00 (cis, CH), 29.20 (cis, CHCHCH2), 28.66 (cis, CHCH2CH2),
23.65 (cis, CHCH2CH2).
trans-Octalin (Scheme 4). trans-Octalin Dibromide. To a solution
of the mixture of trans- and cis-octalins (2.5 g, 18 mmol) in 7.7 mL of
chloroform, bromine (1.9 mL, 36 mmol) in 4 mL of chloroform was
Synthesis of Decahydro-2-naphthyl Methacrylates (DNMAs). To
the solution of DNOHs (1.54 g, 10 mmol) and triethylamine (1.51 g,
15 mmol) in dichloromethane (20 mL), methacryloyl chloride (1.57 g,
15 mmol) was added dropwise at 0 °C. After the mixture was stirred at
room temperature overnight, the resulting triethylamine hydrochloride
as the precipitated salt was filtered out and the dichloromethane
solution was washed with a saturated sodium bicarbonate, water, and a
saturated saline solution, and then dried on sodium sulfate. The
dichloromethane was evaporated under reduced pressure, and the
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products were purified by silica gel chromatography using n-hexane
45.12, and 44.79 (CH2C(CH3)(CO2CH3)), 21.26, 19.19, 18.95, and
16.90 (α-CH3).
and ethyl acetate (9/1 volume ratio).
1
DNMA Mixture. Yield: 88%; a colorless liquid. H NMR (CDCl3,
300 MHz): δ 6.11−6.06 and 5.55−5.50 (m, CH2C, 2H), 5.15−5.13
(m, OCH), 4.95−5.10 (broad, OCH), 4.85−4.72 (m, OCH), 2.05−
0.80 (m, others, 16H).
RESULTS AND DISCUSSION
■
Separation and Structure Determination of the DNOH
Isomers. Decahydro-2-naphthols (DNOHs) are commercially
available as a mixture of four kinds of diastereomeric isomers,
i.e., (2R*,4aR*,8aS)-DNOH (DNOH-I), (2R*, 4aS*,8aR)-
DNOH (DNOH-II), (2R*,4aR*,8aR)-DNOH (DNOH-III),
and (2R*,4aS*,8aS)-DNOH (DNOH-VI) (Scheme 1), because
they are industrially synthesized by the hydrogenation of 2-
naphthol using platinum group metal catalysts.42 In the 2D
NMR (HSQC) spectrum of the DNOH mixture in Figure 1,
DNMA-I. Yield: 77%; a colorless liquid. 1H NMR (CDCl3, 300
MHz): δ 6.09−6.08 and 5.53−5.52 (m, CH2C, 2H), 4.85−4.75 (m,
OCH, 1H), 2.04−0.88 (m, others, 16H). 13C NMR (CDCl3, 75
MHz): δ 166.98 (CO), 137.02 (CH2C), 124.83 (CH2C),
74.17 (OCH), 18.38 (CH2CCH3), 34.91, 34.55, 31.77, 31.33, 29.17,
26.89, 26.28, 24.79, 21.38, and 21.06 (others).
1
DNMA-II. Yield: 59%; a colorless liquid. H NMR (CDCl3, 400
MHz): δ 6.11−6.07 and 5.54−5.51 (m, CH2C, 2H), 5.08−4.97
(broad, OCH, 1H), 2.02−1.23 (m, others, 16H).
1
DNMA-III. Yield: 68%; a colorless liquid. H NMR (CDCl3, 300
MHz): δ 6.10−6.06 and 5.55−5.50 (m, CH2C, 2H), 4.85−4.77 (m,
OCH, 1H), 2.05−0.80 (m, others, 16H). 13C NMR (CDCl3, 75
MHz): δ 166.98 (CO), 136.97 (CH2C), 124.82 (CH2C),
73.46 (OCH), 18.34 (CH2CCH3), 42.33, 41.03, 39.11, 34.22, 33.17,
31.73, 31.60, 26.76, 26.50, and 26.22 (others).
DNMA-III and DNMA-IV Mixture. A colorless liquid. 13C NMR
(CDCl3, 75 MHz): δ 166.98 and 166.83 (CO), 137,17 and 136.97
(CH2C), 124.87 and 124.82 (CH2C), 73.46 and 70.55 (OCH),
18.38 and 18.34 (CH2CCH3), 42.81, 42.33, 41.03, 39.11, 37.42,
34.22, 33.72, 33.17, 31.87, 31.73, 31.60, 30.19,28.38, 26.76, 26.57,
26.50, 26.22, and 14.13 (others).
Polymerization. DNMAs (1.0 mol/L), 2,2′-azobis-
(isobutyronitrile) (AIBN, 1.0 mmol/L), and toluene (5−50 mL)
were placed in a glass ampule, the solution was degassed by the
freeze−thaw technique three times, and finally the ampule was sealed.
After polymerization for a given time at 60 °C, the polymerization
mixture was poured into a large amount of methanol. The polymer
was filtered out, washed with methanol, and then dried in vacuo at
room temperature. The yield of the polymers was gravimetrically
determined.
Figure 1. 2D NMR (HSQC) spectrum of the DNOH mixture in
CDCl3 (for the C2 methine carbon and hydrogen).
Hydrolysis of Poly(DNMA)s and the Subsequent Methyl-
ation (Scheme 6). Poly(DNMA)s (0.5 g) were dissolved in
four cross-peaks corresponding to the methine carbon and
hydrogen adjacent to a hydroxy substituent at the C2 position
were observed. The peaks at 4.07−4.12 and 3.74−3.92 ppm in
the 1H NMR spectrum are correlated with an apparently single
peak at 66.5 ppm in the 13C NMR spectrum, and the protons at
3.52−3.68 ppm have relations to both peaks observed at 70.4
and 71.6 ppm for the carbons. The major components in the
DNOH mixture were expected to include a cis-decalin ring
structure because the hydrogenation of naphthalene derivatives
with the metal catalysts preferentially produces the correspond-
ing cis-decalin derivatives.42,43 As a result, a pure isomer was
isolated from the mixture by recrystallization using n-hexane as
the solvent and assigned as the DNOH-I isomer based on the
1H and 13C NMR chemical shifts (3.54−3.68 and 71.6 ppm,
respectively) shown in Figure 2. The assignment of the NMR
spectra for each isomer is discussed in the next section, together
with the DFT calculation results. We derived an alternative
isomer from the isolated DNOH-I, because the other isomers
were hardly separated from the mixture. We used an inversion
reaction of the stereocenter during the transformation of the
tosylate of the alcohol to the corresponding acetate, as shown
in Scheme 2. The stereochemistry of the obtained DNOH-II
was confirmed based on the NMR spectroscopic results; δ =
3.74−3.92 ppm (1H NMR) and 66.47 ppm (13C NMR).
For the preparation of the other isomers, DNOH-III and
DNOH-IV, we selected the synthetic pathway shown in
Scheme 3. First, octalin was synthesized by the Diels−Alder
reaction of p-benzoquinone and 1,3-butadiene, followed by
selective hydrogenation to the conjugate CC using zinc and
Scheme 6
concentrated sulfuric acid (30 mL) and left at room temperature for
3 h. The reaction mixture was poured into ice−water and the
precipitated polymer was filtered out and washed with cold water. The
recovered poly(methacrylic acid) was dissolved in methanol and
precipitated with diethyl ether. The polymer was filtered out and dried
in vacuo. The yield of poly(methacrylic acid) was 180 mg. The
obtained poly(methacrylic acid) was dissolved in a mixture of toluene
and methanol (4/1 in volume) and methylation was carried out using
a diethyl ether solution of (trimethylsilyl)diazomethane (2.0 mol/L,
3.75 mL) by dropwise addition at room temperature. After the
reaction was stirred at room temperature for 12 h, a small amount of
acetic acid was added, and the solution was washed with water and
then dried on sodium sulfate. The solvents were evaporated under
reduced pressure and the poly(MMA) as the product was precipitated
with chloroform and methanol. Yield: 144 mg.
Poly(MMA). 1H NMR (CDCl3, 300 MHz): δ 3.60 (OCH3), 2.10−
1.76 (CH2), 1.30−0.80 (α-CH3). 13C NMR (CDCl3, 75 MHz): δ
178.18, 177.89, 177.61,177.01, 176.82, 176.07, and 166.57 (CO),
54.67, 57.62, 54.48, 54.23, and 52.67 (CH2), 51.59 (OCH3), 45.72,
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Figure 3. Structure of the DNOH-III isomer determined by X-ray
single crystal structure analysis. Packing structure is viewed down
along the b-axis of the crystal.
1
Figure 2. Partial H and 13C NMR spectra of the isolated DNOH-I
(measured in CDCl3).
acetic acid and the Wolff−Kishner reduction of the ketone to
yield octalin as the product. The syn-addition exclusively
occurred during the Diels−Alder addition in the first step
reaction in Scheme 3, resulting in the formation of a product
with cis configuration.41 While the configuration was retained
during the following hydrogenation, the Wolff−Kishner
reduction under alkaline conditions with reflux induced a
partial configuration change to a trans one, which is
thermodynamically more stable. The 13C NMR spectrum of
the 2,3,5,8,9,10-hexahydro-1,4-naphthoquinone evidenced the
production of both the cis- and trans-octalins and the latter was
the major product (Figure S1, Supporting Information). The
racemization might occur via the formation of an enolate anion
produced by hydrogen elimination at the 9- and 10-positions of
hexahydro-1,4-naphthoquinone during the reduction.
The direct separation of each isomer from the cis- and trans-
octalin mixture was difficult, but we successfully isolated the
trans isomer from the mixture by recrystallization after these
compounds were derived to the octalin dibromides (Scheme
4). The 13C NMR spectra of the isolated trans-octalin
dibromide and the trans-octalin, which was derived by
reduction with zinc, confirmed that both compounds contained
no contamination of the corresponding cis isomers (Figure S2,
Supporting Information).
1
Figure 4. (a) H NMR spectrum of the DNOH-III and DNOH-IV
mixture (measured in CDCl3). (b) Partial 1H and 13C NMR spectra of
the isolated DNOH-III (measured in CDCl3).
Conformation Dynamics Investigated by DFT Calcu-
lations. We carried out the DFT calculations for the
determination of favored conformational structures for the
geometric isomers and the estimation of their thermodynamic
stability at the B3LYP/6-311G* level of theory. The optimized
structures and their energies were determined for each DNOH
isomer as well as those of the esters derived from the DNOHs.
The results are shown in Table 1. For DNOH-I and DNOH-II,
two stable conformers exist because two kinds of chair−chair
conformations are possible (Figure 5). One of the conformers
includes a hydroxy group at the equatorial position, while the
other includes at the axial one. The former is energetically
favorable with a difference in the energy (ΔΔE) of 2.1 and 0.3
kcal/mol for DNOH-I and DNOH-II, respectively. The
DNOH-III and DNOH-IV isomers exhibited a single con-
former due to the fixed conformation of the ring skeletons,
being similar to the conformation changes observed for cis- and
trans-decalins.44,45 The thermodynamic stability was in the
following order: III > IV > IIa or Ia > IIb > Ib for all the series
including not only the DNOHs but also the acrylic (DNAs),
methacrylic (DNMAs), and pivalic esters (DNPs). The most
stable III-isomers contain no axial substituents, while the other
The hydroboration of trans-octalin and the subsequent
oxidation led to the mixture of DNOH-III and DNOH-IV due
to no stereoselectivity during the hydroboration reaction, as
shown in Scheme 5. In the NMR spectra of the products, the
peaks due to both DNOH isomers were observed; i.e., 3.5−3.7
1
and 4.1 ppm and 66.6 and 70.4 ppm for the H and 13C NMR
spectra, respectively. Fortunately, single crystals grew during
the slow evaporation of the solvent from the chloroform
solution of the mixture of DNOH-III and DNOH-IV at room
temperature and were provided for X-ray single crystal
structure analysis. The crystal structure analysis undoubtedly
indicated that the isomer separated by recrystallization is
DNOH-III (Figure 3, see also Table S1, Supporting
Information). We further succeeded in the preparation of a
large amount of crystals of the pure isomer by recrystallization
from n-hexane in the presence of a trace amount of the isolated
single crystals as the seed for crystal growth. Consequently, we
concluded that the peaks observed at 3.60 and 70.4 ppm in the
1H and 13C NMR spectra, respectively, are assigned as those for
DNOH-III (Figure 4).
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a
Table 1. Energy Differences for the DNOHs and Their Ester Derivatives Determined by DFT Calculations
ΔE (kcal/mol)
isomer
DNOHs
DNMAs
DNAs
DNPs
Ia
3.23
3.06
3.19
3.33
Ib
5.32 (ΔΔE = 2.09)
4.49 (ΔΔE = 1.43)
4.35 (ΔΔE = 0.84)
5.19 (ΔΔE = 1.86)
IIa
IIb
III
IV
3.09
3.41
3.59
3.45
3.41 (ΔΔE = 0.32)
0
4.18 (ΔΔE = 0.77)
0
3.71 (ΔΔE = 0.12)
0
4.02 (ΔΔE = 0.57)
0
0.75
0.45
0.45
1.21
a
The values for the most stable isomer IIIs were used as standard (ΔE = 0) for each derivative. The ΔΔE value is energy difference between the ΔE
values for conformers a and b. DNOH: decahydro-2-naphthol. DNMA: decahydro-2-naphthyl methacrylate. DNA: decahydro-2-naphthyl acrylate.
DNP: decahydro-2-naphthyl pivalate.
isomers have cyclohexane rings with one or two groups at the
axial positions.
The calculated chemical shift values for the DNOHs are
summarized in Table 2. The order of the chemical shifts were
as follows; III (δ = 3.89 ppm) ∼ I (3.90) < II (4.12) < IV
1
(4.27) for the H NMR spectra and II (72.63) < IV (73.54) <
III (76.48) < I (77.28) for the 13C NMR spectra. This order
agreed well with the observed results, and a linear relationship
was observed between the observed and calculated chemical
shifts (Figure S4, Supporting Information).
Synthesis and Characterization of Poly(DNMA)s. The
decahydro-2-naphthyl methacrylate monomers (DNMAs) were
prepared using three kinds of the isolated alcohols (DNOH-I,
-II, and -III) and the DNOH mixture. The composition of the
isomers in the synthesized DNMAs was determined by NMR
1
spectroscopy, similar to the case of the DNOHs. In the H
NMR spectrum of the DNMA mixture, the methine protons
observed at 4.72−4.85, 4.95−5.10, and 5.13−5.15 ppm were
assigned as those for the mixture of DNMA-I and DNMA-III,
DNMA-II, and DNMA-IV, respectively.46 The radical polymer-
ization of the DNMAs was carried out in toluene at 60 °C in
the presence of AIBN as the initiator. The results of the
polymerization are shown in Table 3. The composition of the
isomeric units in the obtained polymers was determined as the
1
ratio of (I + III)/II/IV based on the peak intensity in their H
NMR spectra (Figure 6). The poly(DNMA)-M was produced
during the polymerization of the DNMA mixture. The isomer
composition in the polymer was as follows; (I + III)/II/IV =
41/51/8. The polymerization using both DNMA-I and the
DNMA mixture at the same time was carried out to obtain the
poly(DNMA)s with different isomeric compositions; (I + III)/
II/IV = 68/28/4 and 55/40/5 for poly(DNMA)-I45/M55 and
poly(DNMA)-I25/M75, respectively. The random copolymer
Figure 5. (a) Thermodynamically favored conformations for the
DNOH isomers determined by the DFT calculations at the BYLP/6-
311G* level and (b) the chemical structures of DNOHs and their ester
derivatives.
1
Table 2. Observed and Calculated H and 13C NMR Chemical Shifts for the DNOH Isomers
observed chemical shifts δ (ppm)
calculated chemical shifts δ (ppm)
isomers
1H NMR
13C NMR
1H NMR
13C NMR
abundance at 25 °C
a
a
DNOH-I
3.61
71.60
3.89
77.28
Ia/Ib = 97.1/2.9
3.88 (for Ia)
4.21 (for Ib)
77.39 (for Ia)
73.55 (for Ib)
a
a
DNOH-II
3.83
66.47
4.12
72.63
IIa/IIb = 36.9/63.1
4.30 (for IIa)
4.02 (for IIb)
3.90
73.95 (for IIa)
71.86 (for IIb)
76.48
DNOH-III
DNOH-IV
3.60
4.10
70.40
66.57
100
100
4.27
73.54
a
Estimated based on the isomer abundance at 25 °C.
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a
Table 3. Preparation and Characterization of Poly(DNMA)s
polymer
yield (%)
77
Mw/105
Mw/Mn
Tg (°C)
Td5 (°C)
Tmax (°C)
poly(DNMA)-I
2.9
5.5
2.4
2.5
3.2
4.2
3.6
2.2
1.9
1.9
1.9
1.6
2.9
2.3
2.6
2.9
142.7
139.3
146.2
152.9
140.7
139.4
133.4
126.4
221.2
259.5
220.3
213.3
237.9
225.2
231.8
229.3
347.5
345.1
355.9
352.1
346.0
346.4
345.9
347.9
b
poly(DNMA)-II
poly(DNMA)-III
poly(DNMA)-III/IV
9
86
65
66
70
81
86
c
d
e
poly(DNMA)-I45/M55
poly(DNMA)-I25/M75
f
poly(DNMA)-M
g
poly(DNMA-co-MMA)
a
b
c
d
[DNMA] = 1 mol/L, [AIBN] 1 mmol/L in toluene at 60 °C for 24 h. Polymerized for 1 h. III/IV = 61/39 in the polymer. (I + III)/II/IV = 68/
e
f
g
28/4 in the polymer. (I + III)/II/IV = 55/40/5 in the polymer.. (I + III)/II/IV = 41/51/8 in the polymer.. Random copolymer, DNMA mol % in
the copolymer =17.4, (I + III)/II/IV = 41/51/8 in the polymer.
poly(DNMA)-I and poly(DNMA)-III were 1.04 and 1.10 cm3/
g, respectively, being slightly smaller than that of poly(MMA).
The water absorption property was also examined after the
polymers were immersed in water at room temperature for 7
days. The maximum water absorption was 0.3, 1.1, and 1.4% for
poly(DNMA)-M, poly(DNMA-co-MMA), and poly(MMA),
respectively (Figure S5, Supporting Information). These results
indicate that the high water absorption of poly(MMA) as a
demerit for applications can be effectively improved by
introduction of the DNMA units with bulky alkyl ester groups.
In contrast to the constant optical properties, the Tg values
sensitively depended on the isomeric compositions; 139.3 °C
for poly(DNMA)-II < 142.7 °C for poly(DNMA)-I < 146.2 °C
for poly(DNMA)-III < 152.9 °C for poly(DNMA)-III/IV
1
Figure 6. H NMR spectrum of poly(DNMA) in CDCl3.
(Table 3). The poly(DNMA)s containing the isomers at
various compositions also showed similar results; the greater
the content of the isomers I and III in the poly(DNMA)s, the
higher the Tg values of the polymers from 133.4 °C for
poly(DNMA)-M to 142.7 °C for poly(DNMA)-I. Because the
isomer II was the major component in the poly(DNMA)
repeating units, the change in the Tg values for the
poly(DNMA)s simultaneously reflects the effect of the
DNMA-II unit, which has the lower ΔΔE values between
two possible conformers (Table 1). The side group of the
DNMA-II repeating units may most frequently change their
conformation and the free volume in the polymer is assumed to
be greater. This causes the lowering of the Tg values. It is noted
that the poly(DNMA)s containing a trans-decalin skeleton with
a fixed conformation in the ester alkyl groups exhibit a high Tg
value, although the role of the conformation change in the side
group on the polymer mechanical properties is discussed later.
We examined the tacticity of the obtained poly(DNMA)s
because it is well-known that the Tg values of polymethacrylates
significantly depend on their tacticity.13 The tacticity of the
poly(DNMA)s used in this study was determined after they
of DNMA and MMA was also prepared and the DNMA
content in the copolymer was 17.4 mol %.
The polymers with a molecular weight higher than 105 were
obtained in a high yield (65−86%) during the 24-h polymer-
ization, irrespective of the composition of the DNMA isomers.
The composition of the repeating unit structure was assumed
to be similar to the monomer compositions in the feed by the
assumption of a small difference in the monomer reactivity for
the isomers. The poly(DNMA)s were soluble in toluene, THF,
chloroform, cyclohexanone, and cyclohexane, and insoluble in
n-hexane, acetone, dimethylformamide, and methanol. Trans-
parent and flexible films were obtained by casting the solutions
of poly(DNMA)s. The transmittance of the poly(DNMA) films
(thickness of 60 μm) was as high as 97% at 380 nm. The nD
and νD values were 1.489 and 42−44, respectively (Table 4).
The determined optical parameters were insensitive to the
geometric structure of the polymer side groups and similar to
the values for poly(MMA), poly(CHMA), and other acrylic
polymers including adamantly ester groups. The densities of
Table 4. Physical and Optical Properties of poly(DNMA)s
refractive indices
polymer
density (g/cm3)
nF
nD
nC
νD
transmittance at 380 nm (%)
poly(DNMA)-I
poly(DNMA)-III
poly(MMA)
1.04
1.4968
1.4969
1.4954
1.4894
1.4891
1.4895
1.5064
1.512
1.4858
1.4854
1.4861
44
42
53
97
97
96
1.10
1.14
a
poly(CHMA)
1.100
1.052
b
poly(DMAdMA)
c
poly(AdA)
1.4977
1.4914
1.4869
45
a
b
c
Poly(cyclohexyl methacrylate).47 Poly(3,5-dimethyl-1-adamantyl methacrylate).48 Poly(1-adamantyl acrylate).
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were derived to poly(MMA) by hydrolysis in conc. H2SO4 at
room temperature for 3 h and the subsequent methylation by
(trimethylsilyl)diazomethane (Scheme 6). The triad tacticity
values for the poly(DNMA)s were mm = 2−4%, mr = 28−33%,
and rr = 63−68%, irrespective of the isomeric compositions, as
summarized in Table 5. The syndiotacticity of the poly-
(DNMA)s was slightly greater than that of poly(MMA) and
similar to that of poly(AdMA).24,29
(depolymerization) in competition with the side-group
degradation accompanying the olefin elimination from the
ester alkyl groups. The latter reactions finally led to the
formation of carboxylic acid anhydride units, which are
thermally stable and further decompose over a temperature
range higher than 400 °C. The effect of the configuration of the
ester alkyl groups was negligible for the thermal degradation
behavior.
Next, we investigated the dynamic mechanical properties of
the polymers. Figure 7 shows the temperature dependences of
storage moduli (E′), loss moduli (E″), and the tan δ values
determined by the dynamic mechanical analysis of poly-
(DNMA)-I and poly(DNMA)-III at frequencies of 0.5−10 Hz
over a temperature range from −150 to 150 °C. The tan δ
peaks due to the β-relaxation were observed at −30 to 0 °C for
poly(DNMA)-I depending on the applied frequency as shown
in the expanded spectra. This relaxation corresponds to a
conformation change between two conformers of the ester alkyl
groups,19,49−52 similar to that of the mutual transformation
between Ia and Ib in Figure 5. In contrast, no peak was
observed for poly(DNMA)-III, of which the trans-decalin
moiety adopted a fixed conformation.44 A similar relaxation
process was expected to be observed for poly(DNMA)-II, but
we could not directly confirm it because of the difficulty of large
mass production of the corresponding monomer. Therefore, we
speculated the effect of the introduction of the DNMA-II units
based on the β-relaxation processes observed for the poly-
(DNMA)s with various compositions of the isomeric units
(Table 6 and Figure S7, Supporting Information). The peak
Table 5. Tacticity of Poly(DNMA)s Determined by 1H NMR
Spectroscopy after Transformation to Poly(MMA)
triad fraction (%)
polymer
mm
mr
rr
poly(DNMA)-I
4
33
63
a
c
b
b
b
poly(DNMA)-I45/M55
poly(DNMA)-I25/M75
2 (3)
31 (32)
28
67 (65)
68
3
2
d
poly(DNMA)-M
31
67
e
poly(MMA)
4
34
62
ef
,
b
b
b
poly(AdMA)
3 (5)
30 (29)
67 (66)
a
b
(I + III)/II/IV = 68/28/4 in the polymer. The values in parentheses
c
indicate the results determined by 13C NMR spectroscopy. (I + III)/
II/IV = 55/40/5 in the polymer. (I + III)/II/IV = 41/51/8 in the
polymer. Reference 24. Poly(1-adamantyl methacrylate).
d
e
f
The thermal degradation of the poly(DNMA)s started at a
temperature over 200 °C via a complicated mechanism (Table
3 and Figure S6, Supporting Information), in which the main-
chain scission was followed by the zipper degradation
Figure 7. Temperature dependence of storage modulus (E′), loss modulus (E″), and tan δ values determined by dynamic mechanical analysis at
frequencies of 0.5, 1, 2, 5, and 10 Hz for (a) poly(DNMA)-I and (b) poly(DNMA)-III. The bottoms are expanded over the β-relaxation temperature
range.
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Table 6. Dynamic Mechanical Properties of Poly(DNMA)s at a Frequency of 1 Hz
data at 25 °C
tan δ peak for β relaxation
polymer
E′ (MPa)
tan δ
temp (°C)
intensity
Ea (kJ/mol)
poly(DNMA)-I
10.38
9.61
9.83
9.83
0.0567
0.0567
0.0495
0.0445
−21.7
−26.5
−28.0
−30.4
0.0929
0.0750
0.0569
0.0595
65
63
61
56
a
b
poly(DNMA)-I45/M55
poly(DNMA)-I25/M75
c
poly(DNMA)-M
a
b
c
(I + III)/II/IV = 68/28/4. (I + III)/II/IV = 55/40/5. (I + III)/II/IV = 41/51/8.
temperature decreased with an increase in the content of the
DNMA-II isomer. The activation energy (Ea) for the β-
relaxation was estimated based on the frequency dependence of
the tan δ peak temperatures (Table 6 and Figure S8,
Supporting Information). The Ea value was 65 kJ/mol for
poly(DNMA)-I and 56−63 kJ/mol for the poly(DNMA)
mixtures. The existence of the DNMA-II unit tends to
accelerate the dynamic conformation changes of the side
groups and the polymer main chain, resulting in the decrease in
the tan δ peak temperature and the Ea value for the β-relaxation
(Table 6) as well as the decrease in the Tg values of the
polymers (Table 3). These results agree well with the
conclusions obtained from the DFT calculations.
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*(A.M.) Fax: +81-6-6605-2981. E-mail: matsumoto@a-chem.
eng.osaka-cu.ac.jp.
Notes
The authors declare no competing financial interest.
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CONCLUSIONS
■
Using commercially available decahydro-2-naphthols
(DNOHs) as a mixture of four kinds of diastereomeric isomers
and several synthetic procedures, we prepared poly(decahydro-
2-naphthyl methacrylate)s [poly(DNMA)s] including alicyclic
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* Supporting Information
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