Synthesis and radiocarbon evidence of terephthalate polyesters completely prepared from renewable resources

Article abstract of DOI:10.1039/c1gc15400a

Monomers used for the synthesis of terephthalate polyesters have been prepared starting from renewable resources. In particular, dimethyl terephthalate was synthesised starting from bio-limonene while butanediol was synthesised starting from bio-succinic acid. Using these bio-monomers it was possible to synthesise polyesters with the same chemical structure and molecular weight of commercially available polymers. Moreover, the polymers obtained from bio-based monomers, present the same thermal properties of the polyesters obtained using petrol-derived monomers. A poly(butylene terephthalate) completely obtained from renewable resources was also synthesised. The radiocarbon and isotope mass spectroscopy analysis confirmed that this polyester contains 94 ± 3% of bio-based material.

Full text of DOI:10.1039/c1gc15400a

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PAPER
Synthesis and radiocarbon evidence of terephthalate polyesters completely
prepared from renewable resources†
a
a
a
a
a
Martino Colonna,* Corrado Berti, Maurizio Fiorini, Enrico Binassi, Marzia Mazzacurati,
a
b
Micaela Vannini and Sreepadaraj Karanam
Received 12th April 2011, Accepted 27th June 2011
DOI: 10.1039/c1gc15400a
Monomers used for the synthesis of terephthalate polyesters have been prepared starting from
renewable resources. In particular, dimethyl terephthalate was synthesised starting from
bio-limonene while butanediol was synthesised starting from bio-succinic acid. Using these
bio-monomers it was possible to synthesise polyesters with the same chemical structure and
molecular weight of commercially available polymers. Moreover, the polymers obtained from
bio-based monomers, present the same thermal properties of the polyesters obtained using
petrol-derived monomers. A poly(butylene terephthalate) completely obtained from renewable
resources was also synthesised. The radiocarbon and isotope mass spectroscopy analysis
confirmed that this polyester contains 94 ± 3% of bio-based material.
1
. Introduction
has recently reported that starting from year 2012 they will use
only renewable resources for the production of PET bottles.
However, no information about the synthetic path that will be
1–3
Several scientific studies suggest that the oil feed stocks will
end around the year 2050 if the present consumption of fossil
stocks continues at a constant rate. The Kyoto protocol and
the desire to reduce the dependence on crude oil has directed
research attention toward the use of biomass as source of energy
and for commodity chemicals and polymers.
Thermoplastic polymer producers are focusing their atten-
tion in the preparation of polymers starting from renewable
resources. For example, Novamont produces polymers that use
7
used, is reported in their press-release. PBT is widely used
as engineering thermoplastic material in several applications
8
due to its good electrical insulation properties. PPT presents
intermediate properties between PBT and PET and is gaining
more importance in the last few years since the propanediol
that is used for its synthesis can be obtained from renewable
5
resources. Draths corporation has recently submitted a patent
application for the preparation of a variety of terephthalate
polyesters that employ bio-derived terephthalic acid obtained
4
starch as a component, and Dupont has introduced to the
market a poly(propylene terephthalate) (PPT) that uses bio-
propanediol obtained from corn. The interest in preparing
9
from muconic acid. However, no chemical characterization of
5
the polymers prepared is provided in the patent.
polymers from natural resources has become a major focus from
both an industrial and environmental point of view. However,
the natural feedstocks which can lead to the preparation of
aromatic groups are very few. Among semi-aromatic thermo-
plastic polymers, terephthalate polyesters such as poly(butylene
terephthalate) (PBT) and poly(ethylene terephthalate) (PET) are
widely used. For example, PET is used as material for water and
soft drinks bottles, for tyre cords and for textile fibres. PET
Terpenes have attracted a growing interest as natural and
sustainable supply of building blocks for the fine chemical
industry. Within this industry, they are important sources
of intermediates and ingredients for flavour and fragrances.
Terpenes are hydrocarbons that are formed by units of isoprene
ordered in a regular pattern and constitute a very promising
starting point for the preparation of chemicals from natural
10–12
sources. It is well reported in the literature
the possibility
6
production in 2009 was 12.7 million tons. PepsiCo company
to synthesise p-cymene from several terpenes. In particular, a
and b pinene (that are the main components of turpentine oil)
and limonene (main component of lemon essential oil) possess
a six member hydrocarbon ring and therefore can give rise,
by a dehydrogenation reaction, to six member ring aromatic
a
Dipartimento di Ingegneria Civile, Ambientale e dei Materiali, Via
Terracini 28, 40131, Bologna, Italy. E-mail: martino.colonna@unibo.it;
Fax: +39 0512090322
b
SABIC Innovative Plastics, Plasticslaan 1, 4600, AC Bergen op Zoom,
13
compounds such as p-cymene. World production of turpentine
Netherlands
oil amounts to some 350 000 tons per year while limonene
production is around 30 000 tons per year. These amounts are
not enough for the use of terpenes in the bio-fuels market but
†
Electronic supplementary information (ESI) available: NMR spectra
of DMT from limonene (a) and from non renewable resources (b). See
DOI: 10.1039/c1gc15400a
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Green Chem., 2011, 13, 2543–2548 | 2543

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can be very interesting for their use as building blocks for the
chemical industry. In his review on the use of renewable resources
in macromolecular science and technology, Gandini has recently
dark solution, limonene (742 mmol, 101 g) was added dropwise
into the mixture. The mixture was then heated to 100 C and
◦
held at this temperature for 8 h. The mixture was then cooled to
room temperature, diluted with water (300 mL) and extracted
two times with dichloromethane (DCM) (300 mL). The organic
solution was dried over magnesium sulphate and concentrated
using a rotary evaporator obtaining the crude product that was
13
reported that terpenes are very promising building blocks for
the preparation of monomers for polymers production.
2
Okkerse reports in his analysis on natural feedstocks for
polymer monomers, the possibility to prepare PET from
limonene or terpenes. However, his work is a pure speculation
of the different strategic routes for monomers preparation and
is not backed up by any experimental evidence. Although,
1
characterized by H NMR. Yield: 99%.
2.3 Synthesis of terephthalic acid form p-cymene
10–13
several papers and reviews report
the use of terpenes for
The oxidation stage was carried out in two steps.
A solution of p-cymene (742 mmol, 100 g) in water (400 mL)
the preparation of fine chemicals, the complete synthesis of
terephthalic acid using terpenes as starting materials has never
been reported before. Moreover, also the diol monomers used for
the preparation of terephthalate polyesters can be synthesised
from renewable resources. In addition to commercially available
and HNO 65% (2.97 mol, 288 g) was heated to reflux for 24 h.
3
The reaction mixture was then cooled to room temperature
and extracted twice with DCM (400 mL). The organic solution
was washed two times with water (100 mL) and the solvent
eliminated using a rotary evaporator.
NaOH (1.484 mol, 83.0 g) was added to the water (1 L)
solution of the crude product obtained from the oxidation of
p-cymene. The mixture was then stirred until the solid was
completely dissolved. Potassium permanganate (1.484 mol, 235
g) was then slowly added and the reaction mixture was heated to
reflux for 16 h. The slurry mixture was then filtered on celite pad
5
bio-propanediol, ethylene glycol (used for PET synthesis) can
be prepared from glucose via the formation of sorbitol as
14
intermediate, and butanediol (used for PBT synthesis) can be
15
prepared from succinic acid obtained from corn.
16
We have recently patented the production of terephthalate
polyesters synthesised using terephthalic acid obtained from bio-
available and renewable limonene. To the best of our knowledge,
the literature does not report any other scientific paper that
reports the characterization of terephthalate polyesters using
terephthalic acid synthesised using renewable resources.
The scope of this work is to illustrate a viable synthetic route
for the preparation of terephthalate polyesters (PBT, PET and
PPT) using dimethyl terephthalate derived from bio-limonene.
We have also prepared a poly(butylene terephthalate) com-
pletely obtained from renewable resources (DMT obtained from
bio-limonene and butanediol derived from bio-succinic acid).
In this paper we also report for the first time a comparison
of the main chemical, physical and thermal properties of the
polymers obtained using monomers from renewable resources
and commercially available polymers.
and washed with water. Concentrated H
2
SO (98%) was added
4
to the aqueous layer until the pH of the solution was 1. The
white solid was filtered and washed with water and DCM. The
◦
resulting white solid was dried at 80 C under vacuum and
1
characterized by H NMR. Total yield (2 steps): 85%.
2.4 Synthesis of dimethyl terephthalate
A solution of terephthalic acid (632 mmol, 105 g) in methanol
(6.32 mol, 2.086 L) and H SO (31.6 mmol, 3.23 mL) was stirred
2
4
for 24 h at reflux. The solvent was removed and the resulting solid
was dissolved in DCM (400 mL). The solution was washed with
water (200 mL) and then dried over magnesium sulphate. The
solvent was then eliminated using a rotary evaporator to obtain
the crude product. The solid was washed with cold methanol
2
. Experimental
◦
1
and dried at 90 C, for 12 h and characterized by H NMR and
melting temperature. Yield: 95%.
2.1 Reagents
Dimethyl terephthalate (DMT), 1,4-butanediol (BD), ethy-
lene glycol (EG), 1,3-propanediol (PD), ethylenediamine,
2.5 Synthesis of dimethyl succinate from succinic acid
FeCl
3
, sodium, titanium tetrabutoxide (TBT), dichloromethane,
SO (98%), potassium perman-
A solution of succinic acid (847 mmol, 100 g) in methanol (1.50
L) and H SO 98% (42.0 mmol, 4.33 g) was stirred for 15 h at
methanol, concentrated H
2
4
2
4
ganate, magnesium sulphate, diethyl ether, lithium aluminium
hydride, sodium hydroxide and chloroform were all purchased
from Aldrich Chemicals and not purified before use.
Bio-based limonene and bio-based succinic acid were pur-
chased from Aldrich Chemicals which certified that the limonene
and succinic acid used in this work were derived from natural
resources. Commercial PBT (VALOX315) was a gift from
SABIC-IP.
reflux. The solvent was removed under reduced pressure. The
obtained solid was dissolved in DCM (400 mL) and the organic
solution was extracted for 3 times with water (200 mL each time).
The solution was then dried over magnesium sulphate and the
solvent eliminated using a rotary evaporator obtaining the crude
product. Yield: 95%.
2.6 Synthesis of 1,4-butanediol from dimethyl succinate
A solution of dimethyl succinate (766 mmol, 112 g) in diethyl
2
.2 Synthesis of p-cymene from limonene
ether (100 mL) was added dropwise to a solution of LiAlH
4
95%
◦
A mixture of ethylenediamine (525 mmol, 31.6 g), anhydrous
FeCl
was heated to 50 C under N
started, as evidenced by hydrogen evolution and formation of a
(2.293 mol, 92.0 g) in diethyl ether (1.50 L) kept at 0 C (ice bath).
The addition was complete within 1 h and the reaction mixture
was warmed to room temperature over 1 h. The mixture was
3
(0.964 mmol, 0.160 g) and sodium (145 mmol, 3.34 g)
◦
2
. After sodium dissolution had
◦
then cooled at 0 C and quenched with water (20 mL) and with
2
544 | Green Chem., 2011, 13, 2543–2548
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a solution of NaOH 15% w/w (50 mL). After 30 min the slurry
was filtered and the salt residue was washed with chloroform
nitrogen cooled condenser. The second stage under vacuum was
performed in the same way as for PET synthesis.
(
2 L) 5 times. The solvent was then eliminated using a rotary
evaporator. Yield: 94%.
2.10 Instruments
1
H NMR spectra were recorded with a Varian Mercury 400 spec-
2
.7 PBT synthesis
trometer (chemical shifts are downfield from tetramethylsilane
(
TMS), using a CF
3
COOD/CDCl (1/4 v/v) mixture as solvent.
3
PBT was synthesised, using a standard two steps polycondensa-
tion process, using DMT obtained from limonene or from non-
renewable resources (100 mmol, 19.4 g) and BD (160 mmol, 14.4
g) (BD/DMT = 1.6 molar ratio) with TBT as catalyst (0.027 g,
The spectra have been recorded just after dissolution in order to
avoid esterification reaction of end groups with trifluoroacetic
acid.
Gel permeation chromatography (GPC) analysis was per-
formed by using a mixture of chloroform/hexafluoroisopro-
panol (HFIP) (95/5 v/v) as eluent (elution rate of 0.3 mL min )
on a HP 1100 Series apparatus equipped with a PL Gel 5 m Mini-
Mixed-C column and a UV detector. Calibration was performed
with polystyrene standards.
Differential scanning calorimetry (DSC) analysis was per-
formed using a Perkin Elmer DSC7. The instrument was
calibrated with high purity standards (indium and cyclohexane).
Dry nitrogen was used as purge gas. DSC heating and cooling
1
75 ppm as titanium with respect to the final polymer weight).
The monomers and the catalyst were introduced into the
-
1
reactor that was closed with a three-neck flat flange lid equipped
with a mechanical stirrer, a torque meter and a heating band
◦
at 90 C. The system was then connected to a water-cooled
◦
condenser and immersed in a thermostatic salt bath at 215 C
and the stirrer switched on at 140 rpm. After 2 h, the temperature
◦
was increased to 245 C, the lid was heated at a temperature of
◦
1
20 C and the reactor connected to a liquid nitrogen cooled
condenser. Dynamic vacuum was then applied to reduce the
pressure down to 0.2 mbar in 60 min. After 60 min the torque
meter signal reached the maximum value and the very viscous
and transparent melt was discharged from the reactor.
◦
rate were 20 C/min. All transitions have been measured after a
heating scan to 270 C and cooling down to room temperature
in order to delete previous thermal history.
◦
The thermogravimetric analyses (TGA) were performed using
-
1
a Perkin Elmer TGA7 apparatus in air (gas flow: 40 mL min )
at 10 C min heating rate, from 25 C to 800 C.
◦
-1
◦
◦
2
.8 PET synthesis
The bio-based content was measured according to the stan-
dard test ASTM D6886-06 by Beta Analytic Inc. 4985 SW
PET was synthesised using DMT obtained from limonene or
from non-renewable resources (120 mmol, 23.3 g) and EG
7
4 Court, Miami, Florida 33155 USA. The tests have been
(
264 mmol, 16.4 g) (EG/DMT = 2.2 molar ratio), with TBT
conducted using Radiocarbon and Isotope Mass Spectrome-
try Analysis. In particular, Isotope Ratio Mass Spectrometry
as catalyst (0.019 g, 100 ppm as titanium with respect to the
final polymer weight).
(IRMS), with an average error of 3%, has been used.
The monomers and the catalyst were introduced into the
reactor that was closed with a three-neck flat flange lid equipped
with a mechanical stirrer, a torque meter and a heating band
3
. Results and discussion
◦
at 90 C. The system was then connected to a water-cooled
Terephthalic acid has been produced in three steps starting from
limonene. The first step yields p-cymene (Scheme 1) that can
be further oxidized to terephthalic acid in two sequential steps
◦
condenser and immersed in a thermostatic salt bath at 210 C
and the stirrer switched on at 140 rpm. After 160 min, the
◦
temperature was increased to 280 C, the lid was heated at a
17,18
without intermediate purification.
◦
temperature of 120 C and the reactor connected to a liquid
nitrogen cooled condenser. The second stage under vacuum was
performed in the same way as for PBT synthesis except that the
polymerization was stopped after 90 min.
2
.9 PPT synthesis
PPT was synthesised using DMT obtained from limonene or
from non-renewable resources (100 mmol, 19.4 g) and PD
Scheme 1 Preparation p-cymene from limonene.
18,19
(
170 mmol, 13.2 g) (PD/DMT = 1.7 molar ratio), with TBT
Several procedures reported in the literature
have been
as catalyst (0.016 g, 100 ppm as titanium with respect to the
final polymer weight).
tested for the oxidation of p-cymene. The best results have
been obtained using concentrated nitric acid to achieve the
oxidation of the isopropyl moiety followed by the reaction with
potassium permanganate to obtain the complete oxidation of
the intermediate products (Scheme 2). The overall yield of the
three steps was 85% with respect to the starting limonene.
Terephthalic acid was then esterified with methanol to
produce dimethyl terephthalate (DMT) to be used in the
polymerization processes. The choice of DMT as monomer
was dictated by the difficulties associated with small-scale batch
The monomers and the catalyst were introduced into the
reactor that was closed with a three-neck flat flange lid equipped
with a mechanical stirrer, a torque meter and a heating band
◦
at 90 C. The system was then connected to a water-cooled
◦
condenser and immersed in a thermostatic salt bath at 205 C
and the stirrer switched on at 140 rpm. After 90 min, the
◦
temperature was increased to 245 C, the lid was heated at a
◦
temperature of 120 C and the reactor connected to a liquid
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recycled. Only a small part of the methanol (less than 1% using
our polymerization protocol) is present in the final polymer as
end-group. Moreover, methanol can be easily obtained from
24
renewable resources.
PBT, PET, and PPT have been prepared by standard two-
25
stages melt polycondensation (Scheme 4) of DMT prepared
from limonene with the respective glycols (BD, EG and PD),
using titanium butoxide as catalyst.
Scheme 2 Oxidation of p-cymene to terephthalic acid.
Table 1 Bio-based content of monomers measured using ASTM
D6886-06 testing
Monomer
Biomass (%)
Commercial TPA
Bio-TPA
Commercial DMT
Bio-DMT
Commercial BD
Bio-BD
0
93
0
81
0
81
polymerization using TPA. However, in continuous processes
under pressure, TPA can be directly used for the synthesis
20
of PET and PPT avoiding the esterification step to DMT.
On the contrary, DMT is always the preferred monomer for
PBT synthesis, since a consistent amount of tetrahydrofuran is
Scheme 4 Terephthalate polyesters polycondensation scheme.
21
1
formed using TPA as monomer. The H NMR spectrum of
DMT obtained from limonene is identical to that reported in
1
The H NMR spectra of commercial PBT (Valox315 from
8
Sabic-IP) and of PBT prepared from limonene are reported in
Fig. 1. NMR analysis shows that the chemical compositions of
both the repeating unit and the end groups of the two polymers
are identical. No side reactions as well as no catalyst deactivation
have been observed. In addition, no differences were observed
the literature for standard DMT.
Butanediol was prepared from bio-succinic acid. The synthe-
sis was performed in two steps (Scheme 3) via the intermediate
22
formation of dimethyl succinate since the direct reduction of
23
succinic acid does not afford BD in high yields.
1
when comparing the H NMR spectra of PET and PPT made
The butanediol obtained from bio-succinic acid did not
present any chemical or physical difference with respect to
commercial BD obtained from non-renewable resources as
1
indicated by H NMR and boiling point measurements.
The bio-based content of the monomers was measured ac-
cording to the standard test ASTM D6886-06 using radiocarbon
and Isotope Mass spectrometry Analysis taking into account the
1
4
C content. Radiocarbon is present in constant amounts in all
living things and it gradually fades away by radioactive decay
with a half life of approximately 5700 years.
1
4
Therefore, C is present only in bio-based products and not
in products deriving from fossil fuels. ASTM D6866 is the
method approved by the U.S. Department of Agriculture for the
determination of the renewable/bio-based content of natural
range materials like ethanol additives, bio-diesel additives, and
other bio-based products such as bio-polymers. The results
obtained for the commercial monomers and for the monomers
obtained from renewable resources are reported in Table 1.
Bio-TPA presents a higher amount of biomass since the
methanol used for the esterification of TPA was not from
renewable resources. However, methanol can be almost com-
pletely recovered during the polycondensation process and then
1
Fig. 1 H NMR of PBT made from commercial DMT (a) and from
DMT obtained from limonene (b).
Scheme 3 BD synthesis from succinic acid.
2
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Table 2 Molecular weight, thermal behaviour and thermal stability of terephthalate polyesters made from renewable resources and from standard
non-renewable monomers
a
◦
b
◦
c
◦
d
◦
Sample
M
w
M
n
T
D
( C)
T
ONSET ( C)
T
g
( C)
m
T ( C)
PBT (bio-DMT)
PBT
PET (bio-DMT)
PET
PPT (bio-DMT)
PPT
113 000
105 000
93 000
62 000
70 000
64 000
46 700
48 000
38 000
30 000
32 000
29 000
415
413
452
451
413
414
395
392
423
426
390
391
—
—
82
84
—
—
222
223
251
257
230
231
a
◦
b
T = temperature of the maximum degradation rate, measured in TGA under air flow at 10 C/min. TONSET = temperature of the beginning of
D
c
◦
d
degradation by TGA weight loss.
temperature measured in DSC during the 2nd heating scan at 20 C/min.
T
g
= glass transition temperature measured in DSC during the 2nd heating scan at 20 C/min.
T
m
= melting
◦
Table 3 Bio-based content of terephthalate polyesters
resources) is shorter for PET than it is for PPT and PBT. The
PBT obtained from bio-DMT and bio-BD presents an almost
complete bio-based composition (94 ± 3% biomass content as
confirmed by ASTM D6886-06 tests).
Polymer
Biomass (%)
PET
0
PPT
0
0
28
79
71
66
94
Commercial PBT
Bio-PBT (bio-BD)
Bio-PET (bio-DMT)
Bio-PPT (bio-DMT)
Bio-PBT (bio-DMT)
Bio-PBT (bio-DMT + bio-BD)
4
. Conclusions
We have proved that terephthalate polyesters can be prepared
starting from renewable resources. In particular, we have demon-
strated that starting from natural a-limonene it is possible to
prepare PBT, PPT and PET with the same chemical structure
and thermal properties of commercial products.
A PBT synthesised using bio-derived DMT and BD
monomers has also been prepared. All the synthetic steps
involved in the preparation of the bio-monomers present high
yields and can be scaled-up for commercial production.
The use of bio-based monomers has no effect on catalyst
activity and on all the polycondensation procedures. Thermal
transitions and thermal stability of the bio-based polymers are
not significantly different from those of commercial tereph-
thalate polyesters or of polyesters made from monomers not
obtained from renewable resources.
The radiocarbon and Isotope Mass Spectrometry Analysis
confirmed that the bio-PBT obtained has a bio-based content
up-to 94 ± 3%.
Further work is planned to verify the environmental advan-
tage of the production of terephthalate polyesters from natural
resources by measuring the overall carbon footprint and by life-
cycle analysis of all the synthetic routes reported in this paper.
The carbon footprint of the production of limonene will also be
studied.
from standard DMT, with those of the polymers obtained from
bio-limonene. The diethylene glycol (DEG) by-products content
1
26
(
measured by H NMR) was 1.5 mol% in PETs made by both
standard- and bio-DMT.
All the polymers synthesised have reached high molecular
weight and thermo-mechanical properties comparable to those
of standard and commercial terephthalate polyesters (Table 2).
The thermal transitions (glass transition and melting temper-
◦
ature) are always in the range ± 3 C with respect to the
commercial and standard polyesters and therefore within the
27
values reported in the literature for commercial polyesters.
Thermal stability (as measured by TGA) is not affected from
the source of DMT or BD. All these results indicate that it is
possible to obtain polymers form renewable resources that, from
a chemical-physical point of view, are identical to commercially
available polymers obtained from non-renewable resources.
A PBT prepared using standard DMT and bio-BD was also
prepared. Once again, the chemical structure of the polymer, its
molecular weight, and its thermal properties, were very similar
◦
◦
to those of commercial PBT (T = 223 C, Tonset = 393 C).
m
A PBT completely obtained from renewable resources was
also synthesised, using DMT obtained from bio-limonene and
BD prepared from bio-succinic acid. A high molecular weight
Acknowledgements
This work was financed by SABIC-IP.
polyester (M
properties (T
w
= 110 000, M
= 222 C, Tonset = 392 C) with respect to the
n
= 44300) with very close thermal
◦
◦
m
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The bio-based content of the polymers synthesised has been
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