Synthesis and characterization of a renewable polyester containing oxabicyclic dicarboxylate derived from furfural

Article abstract of DOI:10.1039/c3gc36938b

Techniques using biomass-based materials have become important to reduce the impacts of global warming and the depletion of petroleum resources. Changing biomass from edible to inedible is essential to solve global food issues. Furan derivatives are ideal chemicals for green chemistry because they are produced from inedible biomass resources. Here, we report the preparation of a biomass-based oxabicyclic dicarboxylic anhydride derived from furan derivatives and its polymerization with several α,ω-diols to polyoxabicyclates. ¹H NMR spectra and MALDI-TOF MS measurements verified the chemical structure of the polyoxabicyclates. Polyoxabicyclates prepared using 1,3-propanediol or 1,4-butanediol could be moulded into elastic films by melt pressing. Tensile strength testing of the films indicated that they were highly elastic. Furthermore, the films had good transparency in the visible region.

Full text of DOI:10.1039/c3gc36938b

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Synthesis and characterization of a renewable
polyester containing oxabicyclic dicarboxylate derived
from furfural
Cite this: DOI: 10.1039/c3gc36938b
Yuya Tachibana, Masayuki Yamahata and Ken-ichi Kasuya*
Techniques using biomass-based materials have become important to reduce the impacts of global
warming and the depletion of petroleum resources. Changing biomass from edible to inedible is essen-
tial to solve global food issues. Furan derivatives are ideal chemicals for green chemistry because they are
produced from inedible biomass resources. Here, we report the preparation of a biomass-based oxabicyc-
lic dicarboxylic anhydride derived from furan derivatives and its polymerization with several α,ω-diols to
polyoxabicyclates. 1H NMR spectra and MALDI-TOF MS measurements verified the chemical structure of
the polyoxabicyclates. Polyoxabicyclates prepared using 1,3-propanediol or 1,4-butanediol could be
moulded into elastic films by melt pressing. Tensile strength testing of the films indicated that they were
highly elastic. Furthermore, the films had good transparency in the visible region.
Received 3rd December 2012,
Accepted 12th March 2013
DOI: 10.1039/c3gc36938b
www.rsc.org/greenchem
of forming a poly(ethylene terephthalate) analogue.9 HMF is
Introduction
often used as a Diels–Alder unit to form reversible polymers.10
Producing chemicals and other materials from biomass
resources has become an emerging research field.1 Although
glucose and starch have often been used as biomass resources
for commercially available biomass-based polymers such as
poly(lactic acid),2 poly(hydroxyl alkanoates)3 and bio-polyethyl-
ene via bio-ethanol,4 they are edible resources which should be
used as food resources to solve global food issues. Ligno-
cellulose, composed of lignin, cellulose and hemicellulose, is
the most abundant inedible biomass resource. Therefore,
lignocellulose biorefinery techniques have been developed by
many companies and researchers, and many chemicals have
been produced from it.5
We have focused on furan derivatives produced from cellu-
lose and hemicellulose for use as biomass resources to
produce polymers. Furan derivatives, such as 5-hydroxyl
methyl furfural (HMF), furfural, furfuryl alcohol and furan, are
produced from biomass resources and used industrially as
organic solvents or resins.6 The U.S. Department of Energy
(DOE) has stated that they are the most value-added chemicals
derived from biomass.7 Therefore, much effort has been put
into their efficient conversion from biomass resources.8 To
increase their use, furan derivatives have been tested as func-
tional precursors for polymers. 2,5-Furandicarboxylic acid has
been polymerized with a diol to form a polyester, with the aim
It has also been noted that furan derivatives are valuable as
building blocks for polymers. However, furan derivatives in
such polymers have been used as only one unit, while the other
units were supplied from petroleum and/or other biomass
resources. We have converted furfural into monomers (i.e. succi-
nic acid, fumaric acid, maleic acid, dimethyl fumaric acid,
dimethyl succinic acid and 1,4-butanediol) and synthesized
poly(butylene succinate) (PBS) from them.11 It is possible to
convert only these compounds produced from furfural into
more complex compounds. The Diels–Alder reaction of maleate
derivatives and furan produces Diels–Alder adducts with reac-
tive groups (i.e. a double bonded moiety, a dicarboxylic anhy-
dride moiety and a bulky oxabicyclic (OBC) alkene).12 The
Diels–Alder adduct has been used as a monomer for olefin
metathesis polymerization using a double bonded moiety.13
Polyester derived from the Diels–Alder adduct was hardly syn-
thesized because of the retro-Diels–Alder reaction of the double
bond and an OBC alkene. Hydrogenation of the double bond
prevents the retro-Diels–Alder reaction of the double bond and
an OBC alkene and produces a thermally stable OBC dicarb-
oxylic anhydride (OBCA), known as norcantharidin, which is an
anti-cancer drug.14 OBCAs have an alicyclic OBC, which gives
useful high solubility and transparency properties, and can
become a diacid polyester moiety with several diols. Neverthe-
less, such polyesters have not been produced from OBCAs.
In this paper, we report the synthesis of an OBCA monomer
derived from furan derivatives and its polymerization with
diols to form biomass-based polyoxabicyclates (POBCs). The
Department of Chemistry and Chemical Biology, Graduate School of Engineering,
Gunma University, 1-5-1 Tenjin, Kiryu, Gunma 376-8515, Japan.
E-mail: kkasuya@gunma-u.ac.jp; Fax: +81-27730-1409; Tel: +81-27730-1481
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characteristics of the unique OBC structure were evaluated by melt-pressed film was immediately cooled to room tempera-
gel permeation chromatography (GPC), 1H nuclear magnetic ture using cold water. The film was cut into specimens
resonance (NMR) and 13C NMR spectrometry, differential scan- (20 mm long, 2.0 mm wide, 0.10 mm deep). The strength and
ning calorimetry (DSC), thermal gravimetric analysis (TGA) strain of the specimens at breaking point were measured using
and ultraviolet-visible (UV-vis) spectrometry. The mechanical tensile strength tests carried out using a universal material
properties of the moulded specimens were assessed by their testing machine (EZ-test; Shimadzu) with the test specimens at
tensile strength. We found that POBCs derived from furfural room temperature. The grip distance was 10 mm and the
had excellent flexibility and transparency.
tensile strength test speed rate was 10 mm min−1. The tensile
strength was determined as the maximum strength required to
break the materials on the stress–strain curve. The tensile
strain at the breaking point was determined to be the
maximum strain on the stress–strain curve. An average value
was taken from the five sample measurements under the same
conditions for each specimen. Transparency was measured
using a Shimadzu UV-1700 UV-vis spectrophotometer in the
wavelength range 190–1100 nm, using 0.10 mm thick films.
Experimental section
Materials
1,2-Ethanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexane-
diol, 1,8-octanediol, 1,10-decanediol, titanium tetraiso-
propoxide, palladium/carbon and succinic anhydride were
purchased from Wako Pure Chemical Industries (Osaka,
Japan) and, when appropriate, used after distillation under
reduced pressure. Furfural and furan were purchased from
Wako Pure Chemical Industries and verified as biomass-based
chemicals as previously reported.11a Furfural was used after
distillation under reduced pressure. Other chemicals were of
reagent grade and used without further purification. Low-
density polyethylene (LDPE) was purchased from Seisannip-
ponsha Ltd (Tokyo, Japan).
Synthesis
Oxidation of furfural to fumaric acid and maleic acid.11,15
Furfural (60.2 g, 626 mmol) was added dropwise to a solution
of sodium chlorate (135 g, 1.27 mol) and vanadium pentoxide
(638 mg, 3.51 mmol) in water (300 mL) at 90 °C for 3 h, and
the mixture was stirred at 80 °C for 10 h. The mixture was
allowed to stand at room temperature for 11 h and a white pre-
cipitate was obtained. The precipitate was filtered and dried to
Characterization
1H NMR spectra were recorded on a 600 MHz NMR spectro- give 42.3 g (58%) of a mixture of fumaric acid and maleic acid
meter (JNM-ECX600; JEOL, Tokyo, Japan) using deuterated as white crystals.
chloroform or deuterated dimethyl sulfoxide as the solvent
and tetramethylsilane as an internal standard. Mass spectra fumaric acid), 6.04 (2H, s, –CHv of maleic acid) ppm.
were recorded on a matrix assisted laser desorption ionization- Dehydration of fumaric acid and maleic acid to anhydrous
1H NMR (600 MHz, DMSO-d6) δ 6.63 (2H, s, –CHv of
time of flight mass spectrometry (MALDI-TOF MS) spectro- maleic acid.16 A mixture of fumaric acid and maleic acid
meter (AXIMA Performance; Shimadzu Co., Kyoto, Japan) (1.27 g, 1.0 mmol) was added to a sublimation apparatus. After
equipped with a nitrogen laser (λ = 337 nm). The spectrometer the addition of diphosphorus pentoxide (5.21 g, 36.7 mmol),
was operated in reflectron positive ion mode with pulsed ion the mixture was heated at 155 °C and 8 kPa for 2 h. The result-
extraction. Tetrahydrofuran (THF) solutions of a polymer ing sublimate was collected to give 0.866 g (81%) of anhydrous
sample (100 mg mL−1), 2,5-dihydroxybenzoic acid (DHBA) maleic acid as white crystals.
(100 mg mL−1) and sodium trifluoroacetate (100 mg mL−1
)
M.p. 52.7–54.7 °C. 1H NMR (600 MHz, CDCl3) δ 7.05 (2H, s,
were mixed (in equal volumes), and a 2 μL portion of the –CHv) ppm.
mixture was deposited onto a sample target plate. The mole-
Diels–Alder reaction of anhydrous maleic acid and
cular weight of POBCs was determined by GPC with a refractive furan.17
A mixture of anhydrous maleic acid (10.2 g,
index detector and a combination of two columns (TSK, 104 mmol) and furan (36 ml, 498 mmol) was stirred at room
GMHXL; Tosoh Co., Tokyo, Japan). The columns were eluted temperature for 12 h. The resulting precipitate was collected to
with chloroform (0.5 mL min−1 flow rate, at 40 °C) and the give 16.4 g (96%) of the Diels–Alder adduct as white crystals.
molecular weights were calibrated with polystyrene standards.
Thermal properties were determined by differential scanning s, –CHv), 5.46 (2H, s, –CH–O–), 3.18 (2H, s, –CH–) ppm.
calorimetry (SSC/5520; Seiko Instruments Inc., Chiba, Japan). Hydrogenation of the Diels–Alder adduct to the oxabicyclic
M.p. 126.9–128.8 °C. 1H NMR (600 MHz, CDCl3) δ 6.58 (2H,
After the sample was heated to 120 °C and cooled to −120 °C dicarboxylic anhydride.18 The Diels–Alder adduct (10.2 g,
at a rate of 10 °C min−1, it was then heated from −120 °C to 36.3 mmol), 5% palladium/carbon (154 mg) and ethyl acetate
120 °C at a rate of 10 °C min−1 as the second heating scan. (170 mL) were added to a round bottom flask. After purging
The glass transition temperature of the polymer was recorded the flask with hydrogen, a balloon (6 L) was connected to it.
from the second heating scan. The polymer was compressed to The reaction mixture was stirred at room temperature for
a 20 × 20 × 0.1 mm film at 15 MPa using a hot-pressing 6 h. The resulting mixture was filtered through a glass filter,
machine (Mini Press Test 10; Toyo Seiki Seisaku-sho Ltd, and the solution was distilled under a vacuum to give 6.05 g
Tokyo, Japan) at 110 °C for 1 min. After compressing, the (99%) of OBCA as a white solid.
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M.p. 115.8–117.7 °C. 1H NMR (600 MHz, CDCl3) δ 5.04 (2H, purification of the mixture. Because fumaric acid can be iso-
dd, J = 2.4 and 3.3 Hz, –CH–O–), 3.19 (2H, s, –CH–), 1.93–1.88 merized to maleic acid during the reaction with phosphoric
(2H, m), 1.66–1.62 (2H, m) ppm.
acid (as a catalyst),19 the mixture quantitatively gave only
Transesterification polycondensation of OBCA and maleic anhydride. The Diels–Alder reaction of maleic anhy-
α,ω-diols.11 OBCA (1.01 mmol) and an excess of the α,ω-diol dride and furan smoothly gave OBC alkene. The melting point
(2.10 mmol) were added to a 10 mL flask. The reaction mixture indicated that the exo-Diels–Alder adduct was formed, the
was heated to 160 °C for 3 h under dry N2 flow to remove the thermal stability of which is well known. The double bond in
α,ω-diol by-product of esterification. After cooling to room the exo-Diels–Alder adduct was hydrogenated using a palla-
temperature, titanium tetraisopropoxide (1.7 mg, 6.0 μmol) dium/carbon catalyst to give the OBCA monomer. As men-
catalyst was added to the mixture. Polycondensation was tioned above, furfural was produced from the conversion of
carried out at 10 Pa at 180 °C for 5 h. The resulting solid was hemicellulose and furan was produced from the furfural.
dissolved in chloroform (5 mL) and the solution was poured Therefore, OBCA was produced only from biomass-based
into methanol (50 mL). The precipitate was filtered and dried resources.
under a vacuum at 80 °C to give a white solid (OBCA-a, b, c) or
a highly viscous liquid (OBCA-d, e, f, and PBCH).
Polymerization to polyoxabicyclate
The polymerization of OBCA and α,ω-diols was carried out fol-
lowing the stepwise reaction shown in Scheme 1. First, the
esterification of OBCA and an excess of α,ω-diol was carried
out at 160 °C and atmospheric pressure for 3 h, yielding a
polyester precursor. Then, after the addition of titanium tetra-
Results and discussion
Synthesis of biomass-based monomers
The OBCA monomer synthesis pathway is shown in Scheme 1.
Furfural was oxidized to a mixture of fumaric acid and maleic
acid with sodium chlorate and vanadium oxide catalyst. The
ratio of fumaric acid to maleic acid was 5 : 1, determined from
isopropoxide as a catalyst, polycondensation proceeded under
reduced pressure, with the removal of H2O and excess α,ω-diol,
to give POBC. The resulting POBC was obtained by reprecipita-
tion in methanol. The POBC yields and molecular weights are
shown in Table 1.
1
the H NMR spectrum. A dehydration reaction of the mixture
was carried out using phosphorus pentoxide without further
Polymerization with 1,2-ethanediol gave POBC-a, having a
yield, number average molecular weight (Mn) and polydisper-
sity (Mw/Mn) of 61%, 1.88 × 104 and 1.67, respectively. Polymeri-
zation with 1,3-propanediol gave POBC-b, having a yield, Mn
and Mw/Mn of 38%, 1.69 × 104 and 1.41, respectively. Polymeri-
zation with 1,4-butanediol gave POBC-c, having a yield, Mn and
Mw/Mn of 53%, 2.32 × 104 and 1.38, respectively. Polymeri-
zation with 1,6-butanediol gave POBC-d, having a yield, Mn
and Mw/Mn of 30%, 2.44 × 104 and 1.27, respectively. Polymeri-
zation with 1,8-octanediol gave POBC-e, having a yield, Mn and
Mw/Mn of 38%, 1.81 × 104 and 1.20, respectively. Polymeri-
zation with 1,10-octanediol gave POBC-f, having a yield, Mn
and Mw/Mn of 15%, 1.15 × 104 and 1.31, respectively. For com-
parison with POBC-c, cis-1,2-cyclohexanedicarboxylic anhy-
dride without an OBC moiety was polymerized with 1,4-
butanediol to give poly(butylene cyclohexyldicarboxylate)
PBCH, having a yield, Mn and Mw/Mn of 33%, 1.00 × 104 and
2.66, respectively.
All POBCs could not be obtained in good yields. Esterifica-
tion in the first step was monitored using thin layer chromato-
graphy (TLC), confirming that OBCA was quantitatively
converted to the precursor after 3 h. However, OBCA sublimed
during polymerization under reduced pressure. The results
mean that POBC changed to OBCA with reversible reaction,
giving a low POBC yield. We also assumed that the low yield
and low molecular weight of POBC-f were caused by the rela-
tively high boiling point of 1,10-decanediol, which was
difficult to remove under reduced pressure.
POBCs were found to be amorphous polymers because they
showed no endothermic or exothermic peaks. The glass
transition temperature of POBC-c was higher than room
Scheme 1
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Table 1 Synthesis of POBCs and cyclohexyl polyestersa
Yieldb/%
Mn × 10−4 c
Mw/Mn
Tg d/°C
c
Run
Acid anhydride
Diol
Polyester
1
2
3
4
5
6
7
OBCA
OBCA
OBCA
OBCA
OBCA
OBCA
CHAe
1,2-Ethanediol
1,3-Propanediol
1,4-Butanediol
1,6-Hexanediol
1,8-Octanediol
1,10-Decanediol
1,4-Butanediol
POBC-a
POBC-b
POBC-c
POBC-d
POBC-e
POBC-f
PBCHf
61
38
53
30
38
15
33
1.88
1.69
2.32
2.44
1.81
1.15
1.00
1.67
1.41
1.38
1.27
1.20
1.31
2.66
19.3
13.8
28.4
−16.2
−10.1
−16.1
−29.1
a Reaction condition is at 160 °C and atmospheric pressure for 3 h, and then at 180 °C under 10 Pa for 7 h. b Methanol-insoluble parts.
c Estimated by GPC (eluent : THF) calibrated with polystyrene standards. d Measured by thermal gravity analysis. e cis-1,2-Cyclohexanedicarboxylic
anhydride. f Poly(butylene cyclohexanecarboxylate).
Fig. 1 (a) 1H NMR spectrum (600 MHz, CDCl3) of POBC-c, (b) 13C NMR spectrum (151 MHz, CDCl3) of POBC-c, (c) DEPT135 spectrum (151 MHz, CDCl3) of POBC-c.
The chemical drawing style of POBC-c was altered to clarify its stereochemistry.
temperature, but those of other POBCs were below room temp- of the multiplet peaks at 1.82–1.80, 1.73–1.65 and
erature. POBC-e, POBC-f and POBC-g had particularly low glass 1.55–1.50 ppm was 2 : 4 : 2, and the peaks were assigned as Hc,
transition temperatures. The different glass transition temp- Hd, Hg and Hh methylene protons, they still could not be fully
eratures affected the physical properties, as described below.
assigned. Several pulse sequence NMRs were adapted to assign
the peaks.
The 1H–1H correlation spectroscopy (COSY) spectrum is
shown in Fig. 2a. Due to the strong correlation between the
peaks at 1.73–1.65 and the He or Hf peaks around 4.19–4.10
and 4.05–4.01 ppm, the multiplet peaks at 1.73–1.65 were
assigned as two Hg and Hh methylene protons. The magnetic
environments of the Hg and Hh protons were almost the
same.
Chemical structure of POBC
The 1H NMR, 13C NMR and distortionless enhancement by
polarization transfer (DEPT) 135 spectra of POBC-c, for repre-
senting POBCs, are shown in Fig. 1. There were seven major
peaks in the 1H NMR spectrum. Because of the stereo-
chemistry and rigidity of the OBC moiety, two methylene
protons, Hc–Hd and He–Hf, were split. The peak at 4.88 ppm
was assigned to two Hb methine protons on the carbon of the
OBC ether moiety. Although multiplet peaks at 4.19–4.10 ppm
and 4.05–4.01 ppm were assigned as two He and two Hf
methylene protons attached to the same carbon, the assigning
of specific protons to which peaks was not possible. The peak
at 3.01–2.95 ppm was assigned as two Ha methine protons,
α-protons of the carbonyl group. Although the integration ratio
There were six main peaks in the 13C NMR spectrum, and
there were correlations in the 1H–13C heteronuclear multiple
quantum coherence (HMQC) spectrum, shown in Fig. 2b. The
peak at 171.1 ppm was assigned to the C1 carbonyl carbon.
Because the peak at 78.5 ppm was positive in the DEPT135
spectrum and correlated with the Hb protons, it was assigned
to the C3 carbon. The peak at 64.41 ppm was negative in the
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Fig. 3 1H NMR spectra (600 Hz, CDCl3) of POBC-a, POBC-b, POBC-c, POBC-d,
POBC-e and POBC-f.
Fig. 2 (a) Partial 1H–1H COSY spectrum of POBC-c. (b) Partial 1H–13C HMQC
spectrum of POBC-c. The F1 axis is the observation wave frequency of 1H and
the F2 axis is the irradiation wave frequency of 13C. The DEPT135 spectrum on
the F2 axis clarifies the carbon peaks. (c) Partial 1H–1H NOESY spectrum of the
polymer. The F1 axis is limited from 1.4 ppm to 1.9 ppm. The F2 axis is limited
from 3.9 ppm to 4.9 ppm. (d) Partial 1H–1H NOESY spectrum of the polymer.
The F1 axis is limited from 3.9 ppm to 4.3 ppm. The F2 axis is limited from
3.8 ppm to 5.0 ppm.
DEPT135 spectrum and correlated with the He and Hf
protons, so it was assigned to the C5 carbon. The peaks at
52.2 ppm were positive in the DEPT135 spectrum and corre-
lated with the Ha protons, so were assigned to the C2 carbon.
The peaks at 29.1 ppm were negative in the DEPT135 spectrum
and correlated with the Hc and Hd protons, so were assigned
to the C4 carbon. The peaks at 25.2 ppm were negative in the
DEPT135 spectrum and correlated with the Hg and Hh
protons, so were assigned to the C6 carbon.
Fig. 4 MALDI-TOF MS spectrum of POBC-c.
1H–1H nuclear Overhauser effect spectroscopy (NOESY)
spectra are shown in Fig. 2c and 2d. Because of the stereo- of the peaks at 4.19–4.10 ppm was due to the shielding effect
chemistry and rigidity of the OBC moiety, Hc is directed to the of the carbonyl double bond, and the bulky OBC moiety pre-
same side of the ether oxygen on the OBC moiety and its vented the ester bond from rotating, giving shielded and
chemical shift was moved to a lower magnetic field by the unshielded protons.
effect of the ether oxygen. Hb is directed to the same side as
Additionally, a number of minor peaks at 4.86, 4.14–4.19,
Hc. We assumed that there should have been a correlation 3.76–3.75, 3.53–3.52, 3.07, 2.63, 2.62, 1.82–1.80, 1.73–1.62 and
between Hb and Hc in the 1H–1H NOESY, but the peaks at 1.55–1.50 ppm were observed. All POBCs had the same minor
1.73–1.65 ppm correlated more strongly with the Hb proton peaks, as shown in Fig. 3. However, these peaks were not from
peak at 4.88 ppm than with the peaks at 1.52–1.51 ppm. There- the end-groups of POBCs, because the integral ratio between
fore, the peaks at 1.73–1.65 ppm were assigned as Hc and the major and minor peaks did not coincide with the mole-
those at 1.52–1.51 ppm were assigned as Hd. Although the cular weight. Particularly, for POBC-a, the integral ratio
peaks at 4.19–4.10 and 4.05–4.01 ppm correspond to He and between the major peaks at 4.91 ppm and the minor peaks at
Hf, which should be equivalent because of the ester bond 4.86–4.85 ppm was about 1 : 3. MALDI-TOF MS was used to
rotation, the peaks were split with a chemical shift of 0.9 ppm. examine the chemical structure of POBC-c in detail.
The peaks at 4.19–4.10 ppm correlated more strongly with the
The MALDI-TOF MS spectrum of POBC-c is shown in Fig. 4.
Hb proton peak at 4.88 ppm than with the peaks at Two kinds of repeating peaks were observed in the MALDI-TOF
4.05–4.01 ppm. We assume that the lower magnetic field shift MS spectrum, both having a repeating m/z of 240, which
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acid catalyst allowed this reaction to give POBC-c′. The same
ring-opening mass series were observed for each POBC. There-
fore, the ring-opening reaction of the OBC moiety is common
to the polymerization of each OBCA and α,ω-diol. Because the
ring-opening structure of the OBC moiety was irregular, POBC
could not crystallize and thus behaved as an amorphous
material. The irregular structure would also give unique prop-
erties to POBCs.
Mechanical properties of the polyesters
The mechanical properties of POBCs were evaluated after
moulding each POBC by melt-pressing into a film at 110 °C
and 15 MPa for 1 min. Although POBC-b and POBC-c formed
into elastic films, POBC-d, POBC-e, POBC-f and PBCH could
not be formed into films because of their high viscosities. This
physical aspect matches their glass transition temperatures,
i.e. POBC-d, POBC-e, POBC-f and PBCH had low glass tran-
sition temperatures and were viscous liquids that could not be
moulded. POBC-b and POBC-c had relatively high glass tran-
sition temperatures and were elastic. The POBC-a film was
brittle and heterogeneous because of its low fluidity, even
though its glass transition temperature was only slightly low
and its molecular weight was the same as that of other POBCs.
As shown in Fig. 3, the relative peak size of the POBC-a ring-
opening structure at 4.88–4.82 ppm was larger than other
equivalent POBCs. The ring-opening reaction of the OBC
moiety would cause the cross-linking and branching reactions
of POBC-a, although cross-linked and branched structures
could not be confirmed in the MALDI-TOF-MS and NMR
spectra. Polymer chain entanglement would occur through
irregular structures such as macrocyclic, cross-linked and
branched structures. It appears that the irregular ring-opening
structure of POBC-a causes its low fluidity.
Fig. 5 Proposed chemical structure of (a) POBC-c, as n = 5 in the series 240 × n
+ 113, (b) POBC-c’, as n = 5 in the series 240 × n + 95.
corresponds with the POBC-c unit mass, as shown in Fig. 4
(the exact mass of C12H16O5 is 240.1). The major repeating
peaks represent a series of ‘m/z = 240 × n + 113’ and there were
minor repeating peaks representing a series of ‘m/z = 240 × n +
95’. These series represent the repeating unit mass (240) and
the residual mass (113 and 95). Because sodium trifluoro-
acetate was used as the ionization reagent, the sodium cation
(m/z = 22.9) was attached to the polymer during ionization. There-
fore, the residual mass for the major peaks was recalculated to
be ‘23 + 90’ and that for the minor peaks was recalculated to
be ‘23 + 72’.
The residual mass of 90 corresponds to the end-group with
–O(CH2)4OH and –H, i.e. both end-groups together are 1,4-
butanediol, as shown in Fig. 5a. The monoisotopic mass of the
pentamers of POBC-c and the sodium cation is 1073.5
(C52H74O22Na), which corresponds to a peak at m/z = 1073.3.
This structure could be expected due to polymerization con-
ditions. The following was the POBC-c synthetic strategy; after
an excess of 1,4-butanediol was reacted with the acid anhy-
dride to give the di-ester with a 1,4-butanediol moiety attached
to both carboxyl groups, the 1,4-butanediol was eliminated at
reduced pressure to give POBC-c with a 1,4-butanediol at both
end-groups.
The tensile strengths of specimens (20 × 2 × 0.10 mm) of
POBC-b and POBC-c were measured, and the stress–strain
curves of POBC-b and POBC-c are shown in Fig. 6. The tensile
strength and strain at the breaking point of POBC-b were 0.12
0.03 N mm−2 and 1970
282%, respectively. The tensile
The residual mass of the minor peaks was 18 mass units
lesser than that of the major peaks. In general, an m/z of 18
corresponds to the H2O molecule, indicating that H2O was
eliminated from POBC-c during the polymerization reaction.
Although several structures can be proposed for the minor
structure, we suppose that the structure was caused by the
ring-opening reaction of the OBC moiety and the ring for-
mation of two macrocyclic ethers, as shown in Fig. 5b. The
monoisotopic mass of the ring-opening POBC-c′ and a sodium
cation is 1295.5 (C64H88O26Na), which corresponds to a peak at
m/z = 1295.7. The ring-opening reaction of the OBC moiety
with an acid catalyst, giving a polyether, has been reported.20
For POBC, we suppose that titanium tetraisopropoxide as the
Fig. 6 Stress–strain curves for POBC-a and POBC-c.
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strength and strain at the breaking point of POBC-c were 4.75 spectra and MALDI-TOF MS measurements showed that the
0.6 N mm−2 and 324 85%, respectively. These results indi- OBC moiety formed an irregular structure which was based on
cate that POBC-b was a soft, highly elastic material, whereas a ring-opening reaction yielding a macrocyclic polyether.
POBC-c was a tough, elastic material. PBCH could not be POBC-b and POBC-c could be moulded into elastic films by
moulded into a film because it was a viscous liquid. It seems melt pressing, and mechanical property testing of the films
that the mechanical properties of POBC-c were improved by showed that they were highly elastic materials. The films
the OBC moiety, making it an elastic material. In comparison showed good transparency in the visible region. Therefore, we
with POBCs, PBS with an Mn, Mw/Mn and melting temperature demonstrated that the biomass-based OBCA acted as a dicarb-
of 3.11 × 104, 1.76 and 114 °C, respectively, and a commercially oxylate unit to produce novel polyesters, which could replace
available LDPE with a melting temperature of 104 °C were the commercially available transparent elastic polymers. The
used. The tensile strengths of LDPE and PBS specimens (20 × ring-opening reaction of OBC units indicates that the polymer
2 × 0.10 mm) were measured. The tensile strength and strain having OBC units is available as a reactive polymer, and the
at the breaking point of LDPE were 10.2 0.8 N mm−2 and 555 polymer properties could be controlled by the generation of
41%, respectively, while those of PBS were 20.5 0.8 N mm−2 the irregular structure from a soft material to a hard cured
and 10 0.6%, respectively. Although the chemical structure resin. POBCs could find applications as unique optical
of POBC-c is similar to PBS, the mechanical properties of materials on the basis of their rigid structure and the irregular
POBC-c and LDPE are almost the same.
structure of OBC units. The optical materials could be used in
electrical devices such as optical lenses and optical filters as
well as a cured resin replacing epoxy resin. Additionally,
POBCs consisting of 1,2-ethanediol, 1,3-propanediol or 1,4-
butanediol can be produced purely from biomass resources
available from a number of companies, and we have already
reported the synthesis of 1,4-butanediol from furfural. POBCs
are fully biomass-based polymers and can be derived entirely
from furfural. Furthermore, OBCAs synthesized from furan
derivatives become new building blocks of polymers such as
polyamide, polycarbonate and polyether. The polymers having
the OBC moiety could show elasticity, transparency and reac-
tivity. Finally, we suggest that furfural produced from inedible
biomass resources can be a precursor for novel polymers.
Transparency
Bicyclic moieties usually lead to amorphous polymers and
polymers with bicyclic moieties in the main chain usually
show good transparency.21 To evaluate the transparency of
POBCs, 0.10 mm thick melt-pressed films were measured by
UV-vis spectrometry. The UV-vis spectrum of POBC-c is shown
in Fig. 7. The melt-pressed POBC-c film was very transparent,
as shown in the photograph in Fig. 7. The POBC-c film was
more than 80% transparent from 1100 nm to 350 nm and no
specific absorption bands were observed in this range. POBC-c
had good transparency because it was amorphous and had no
functional groups with absorption bands higher than a wave-
length of 350 nm.
Acknowledgements
Conclusions
This work was supported by a JSPS KAKENHI Grant-in-Aid for
Research Activity Start-up Number 23810003 and a Grant-in-
Aid for Young Scientists (B) Number 24710087.
We successfully prepared biomass-based polyesters consisting
of α,ω-diol and OBCAs, which were derived from furfural and
had not previously been used as a polyester unit. 1H NMR
References
1 (a) J. Rincones, A. Zeidler, M. C. Grassi, M. Carazzolle and
G. Pereira, Polym. Rev., 2009, 49, 85–106; (b) G.-Q. Chen
and M. K. Patel, Chem. Rev., 2012, 112, 2082–2099.
2 (a) J. Lunt, Polym. Degrad. Stab., 1998, 59, 145–152;
(b) E. T. H. Vink, K. R. Rábago, D. A. Glassner and
P. R. Gruber, Polym. Degrad. Stab., 2003, 80, 403–419.
3 K. Sudesh, H. Abe and Y. Doi, Prog. Polym. Sci., 2000, 25,
1503–1555.
4 (a) A. Morschbacker, Polym. Rev., 2009, 49, 79–84;
(b) A. U. B. Queiroz and F. P. Collares-Queiroz, Polym. Rev.,
2009, 49, 65–78.
5 (a) A. Effendi, H. Gerhauser and A. V. Bridgwater, Renew.
Sust. Energ. Rev., 2008, 12, 2092–2116; (b) L. Petrus and
M. A. Noordermeer, Green Chem., 2006, 8, 861;
(c) M. Funaoka, Macromol. Symp., 2003, 201, 213–222.
Fig. 7 UV-vis spectrum and photograph of POBC-c. The POBC-c film (0.10 mm
thick) covers the right half of the photograph.
This journal is © The Royal Society of Chemistry 2013
Green Chem.

View Article Online
Paper
Green Chemistry
6 (a) F. Trimble, Ind. Eng. Chem., 1941, 33, 660–662; 12 D. J. Cott, K. J. Ziegler, V. P. Owens, J. D. Glennon,
(b) J. P. Trickey, C. S. Miner and H. J. Brownlee, Ind. Eng. A. E. Graham and J. D. Holmes, Green Chem., 2005, 7, 105.
Chem., 1923, 15, 65–66; (c) O. W. Cass, Ind. Eng. Chem. Res., 13 (a) J. G. Hamilton, D. G. Marquess, T. J. O’Neill and
1948, 40, 216–219; (d) W. J. Mckillip, in Adhesives from
Renewable Resources, ed. R. W. Hemingway, A. H. Conner,
and S. J. Branham, ACS Symp. Ser. 385, American Chemical
Society, Washington, DC, 1989, pp. 408–423.
J. J. Rooney, J. Chem. Soc., Chem. Commun., 1990, 119;
(b) A. E. Madkour, J. M. Grolman and G. N. Tew, Polym.
Chem., 2011, 2, 114; (c) S. F. Alfred, K. Lienkamp,
A. E. Madkour and G. N. Tew, J. Polym. Sci., A: Polym.
Chem., 2008, 46, 6672–6676.
7 J. J. Bozell and G. R. Petersen, Green Chem., 2010, 12, 539.
8 (a) X. Tong, Y. Ma and Y. Li, Appl. Catal. A: Gen., 2010, 385, 14 (a) H. Kwart and I. Burchuk, J. Am. Chem. Soc., 1952, 74,
1–13; (b) R. Weingarten, J. Cho, W. C. Conner Jr. and
G. W. Huber, Green Chem., 2010, 12, 1423; (c) P. L. Dhepe
3094–3097; (b) A. McCluskey and J. A. Sakoff, Mini-Rev.
Med. Chem., 2001, 1, 43–55.
and R. Sahu, Green Chem., 2010, 12, 2153; (d) A. Cukalovic 15 (a) N. A. Milas, Org. Synth., 1931, 11, 46; (b) C. F. Cross,
and C. V. Stevens, Green Chem., 2010, 12, 1201.
9 (a) J. Moore and J. Kelly, Macromolecules, 1978, 11, 568–
E. J. Bevan and J. F. Briggs, Chem. Ber., 1900, 33, 3132–3138;
(c) N. A. Milas, J. Am. Chem. Soc., 1927, 49, 2005–2011.
573; (b) A. Gandini, A. J. D. Silvestre, C. P. Neto, A. F. Sousa 16 R. F. Nystrom, Y. Loo and J. C. Leak, J. Am. Chem. Soc.,
and M. Gomes, J. Polym. Sci., Part A: Polym. Chem., 2009, 1952, 74, 3434–3435.
47, 295–298; (c) L. Wu, R. Mincheva, Y. Xu, J.-M. Raquez 17 H. Kwart and I. Burchuk, J. Am. Chem. Soc., 1952, 74, 3094–
and P. Dubois, Biomacromolecules, 2012, 13, 2973–2981. 3097.
10 (a) M. Watanabe and N. Yoshie, Polymer, 2006, 47, 4946– 18 N. a. O’Connor, A. J. Berro, J. R. Lancaster, X. Gu,
4952; (b) N. Teramoto, Y. Arai and M. Shibata, Carbohydr.
Polym., 2006, 64, 78–84; (c) A. Gandini, D. Coelho,
M. Gomes, B. Reis and A. Silvestre, J. Mater. Chem., 2009,
19, 8656.
S. Jockusch, T. Nagai, T. Ogata, S. Lee, P. Zimmerman,
C. G. Willson and N. J. Turro, Chem. Mater., 2008, 20,
7374–7376.
19 K. Nozaki and R. Ogg, J. Am. Chem. Soc., 1941, 63, 2583–
11 (a) Y. Tachibana, T. Masuda, M. Funabashi and
2586.
M. Kunioka, Biomacromolecules, 2010, 11, 2760–2765; 20 (a) Y. Yokoyama and H. K. Hall Jr., Adv. Polym. Sci., 1982,
(b) Y. Tachibana, T. Masuda, M. Funabashi, K. Kasuya and
M. Kunioka, in Biobased Monomers, Polymers, and
42, 107138; (b) F. Andruzzi, G. Pilcher and Y. Virmani, Mak-
romol. Chem., 1977, 178, 2367–2373.
Materials, ed. K. C. Khemani and C. Scholz, ACS Sym. Ser. 21 (a) T. Kohara, Macromol. Symp., 1996, 101, 571–579;
1105, American Chemical Society, Washington, DC, 2012,
pp. 91–110.
(b) T. Otsuki, K. Goto and Z. Komiya, J. Polym. Sci., Part A:
Polym. Chem., 2000, 38, 4661–4668.
Green Chem.
This journal is © The Royal Society of Chemistry 2013