Biorenewable polyethylene terephthalate mimics derived from lignin and acetic acid

Article abstract of DOI:10.1039/c0gc00150c

Lignin-based vanillin and acetic anhydride are subjected to the Perkin reaction and then hydrogenation to afford acetyldihydroferulic acid. Polymerization of this monomer yields poly(dihydroferulic acid), which exhibits thermal properties functionally similar to those of polyethylene terephthalate (PET).

Full text of DOI:10.1039/c0gc00150c

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Volume 12 | Number 10 | October 2010 | Pages 1677–1872
ISSN 1463-9262
COMMUNICATION
TUTORIAL REVIEW
Miller et al.
Frost and Mutton
Biorenewable polyethylene
terephthalate mimics derived from
lignin and acetic acid
Heterogeneous catalytic synthesis
using microreactor technology
1463-9262(2010)12:10;1-D

COMMUNICATION
www.rsc.org/greenchem | Green Chemistry
Biorenewable polyethylene terephthalate mimics derived from lignin
and acetic acid†
Laurent Mialon, Alexander G. Pemba and Stephen A. Miller*
Received 26th May 2010, Accepted 18th June 2010
DOI: 10.1039/c0gc00150c
Lignin-based vanillin and acetic anhydride are subjected
to the Perkin reaction and then hydrogenation to afford
acetyldihydroferulic acid. Polymerization of this monomer
yields poly(dihydroferulic acid), which exhibits thermal
properties functionally similar to those of polyethylene
terephthalate (PET).
Scheme 2 Aromatic aldehydes vanillin and syringaldehyde are by-
products of lignin extraction during the production of paper.
Polyethylene terephthalate (PET) is the third most common
synthetic polymer and accounts for about 18% of world polymer
production.1 This aromatic/aliphatic polyester possesses very
practical thermal properties that are not found in any all-
their extremely high melting temperatures usually limit their pro-
aliphatic commodity thermoplastic: a glass transition temp◦era-
ture (Tg) near 67 ◦C and a melting temperature (Tm) of 265 C.2
The key aromatic component of PET, terephthalic acid, is
derived from petroleum, while ethylene glycol is derived from
petroleum or natural gas (Scheme 1).
cessability (e.g., poly(p-hydroxybenzoic acid) with Tm = 350 ◦C).6
Also, several lignin-based polyesters have been synthesized, but
these generally do not match the thermal properties of PET
and employ an oxidized version of vanillin, vanillic acid, as
the feedstock.7 While the use of lignin-derived aromatics for
building polymers appears industrially sound, such materials
have not yet achieved commercial significance.8 Interestingly, the
pentose-derived aromatic furan-2,5-dicarboxylic acid has been
used as a successful replacement of terephthalic acid in a recent
PET analogue.9
Another important design strategy is the use of a single
monomer instead of two co-monomers; this avoids the necessity
of stoichiometric balance to achieve high molecular weights.
A final aspiration is main-chain ester functionality built from
aromatic alcohols instead of aliphatic alcohols (as in PET);
in this case, hydrolytic degradation should be more facile
because of the superior leaving group ability of aryloxides vs.
alkoxides. An ideal monomer that meets our design criteria
is acetyldihydroferulic acid.10 Scheme 3 depicts the two-step
synthesis of this monomer (69% and 85% yields, respectively)
from vanillin.
The first step employs acetic anhydride and sodium acetate—
although other bases can be used—to effect a Perkin reaction
on the aldehyde functional group of vanillin.11 Most acetic
acid currently derives from natural gas via carbonylation of
methanol but the requisite C1 feedstocks for this process can
readily be prepared from wood through anaerobic distillation—
first yielding wood alcohol (methanol). Alternatively, acetic
acid can be derived from sustainable fermentation processes.12
Concomitant with the Perkin reaction is an acetylation of the
hydroxyl group of vanillin. The obtained acetylferulic acid
is conjugated and yellow, but facile hydrogenation yields a
nearly colorless, aromatic/aliphatic monomer. Acetyldihydro-
ferulic acid has been investigated as a minor component of
an amorphous, liquid crystalline, random terpolymer,13 but its
homopolymer, poly(dihydroferulic acid), PHFA, has not been
reported.
Scheme 1 Polyethylene terephthalate derives from fossil fuel feedstocks
terephthalic acid and ethylene glycol.
The design of sustainable PET mimics will probably also
require aromatic components and the most abundant biorenew-
able source of aromatic compounds is lignin, which is found
in all vascular plants, is the second most abundant naturally-
occurring organic polymer, and makes up approximately 30%
of wood.3 The extraction of lignin from wood is common in the
paper pulping industry and can result in appreciable quantities
of the aromatic aldehydes vanillin and syringaldehyde – up to
5% and 8%, respectively (Scheme 2).4
Hence, our initial design of
a
fully sustainable5
aliphatic/aromatic polyester focused on incorporating aromat-
ics derived from vanillin and syringaldehyde into the main-chain,
while also including a short aliphatic component that provides
necessary flexibility. All-aromatic polyesters certainly exist, but
The George and Josephine Butler Laboratory for Polymer Research,
Department of Chemistry, University of Florida Gainesville, Florida,
32611-7200, USA. E-mail: miller@chem.ufl.edu;
Fax: +1-352-392-9741; Tel: +1-352-392-7773
† Electronic supplementary information (ESI) available: Synthetic
details and complete polymer characterization data. See DOI:
10.1039/c0gc00150c
1704 | Green Chem., 2010, 12, 1704–1706
This journal is
The Royal Society of Chemistry 2010
©

Table 1 Polymerization and characterization of poly(dihydroferulic acid) from acetyl dihydroferulic acid (1–6) and dihydroferulic acid (7)
Catalyst
(1 mol%) time/h time/h
Melt
Vacuum Stirring
stops/h yield (%)
Entry Tp/◦C
[h] a/mL g-1 Mv
DP c Mn
Tg/◦C Tm/◦C
T
50%/◦C d
b
c
1
2
3
4
5
6
7
200–220 none
200–220 Sb2O3
200–220 Zn(OAc)2
200–220 Zn(OAc)2
220–250 Zn(OAc)2
200–220 Zn(OAc)2
200–220 Sb2O3
2
2
2
2
2
2
5
2
2
2
6
6
0.17
6
1.5
0.5
0.5
0.5
0.5
—
83
67
82
91
68
75
~5
31
29
27
36
35
17
n.d.
12 900 27
12 000 23
11 000 38
15 500 50
4 800
4 100
6 800
8 900
74
73
73
67
243
234
234
231
216
240
—
471
462
461
464
456
452
n.d.
14 800 100 17 800 67
6 300
n.d.
17
3 000
65
—
—
3.5e 630e
a Intrinsic viscosity obtained with an Ubbelohde viscometer in a 1 : 2 solution of phenol/1,1,2,2-tetrachloroethane at 35 ◦C. b From [h]= 1.09 ¥ 10-2
Mv0.84, using Mark–Houwink–Sakurada parameters established for PET.14 c Degree of Polymerization and Mn by 1H NMR end group analysis. d The
temperature at which 50% mass loss is observed by thermogravimetric analysis, under nitrogen. e Gel permeation chromatography analysis.
Scheme 3 Synthetic scheme for preparing the aromatic/aliphatic polyester poly(dihydroferulic acid), PHFA, from biorenewable feedstocks vanillin
and acetic anhydride.
Efficient polymerization was accomplished in the melt (200–
220 ◦C) with Sb2O3 or Zn(OAc)2·2H2O as catalyst. Dynamic
vacuum effected removal of acetic acid as the by-product of this
condensation polymerization. Naturally, the evolved acetic acid
could be recycled back to the anhydride form. Table 1 describes
the various polymerizations as well as characterization data for
the obtained polymers. Note that a catalyst is not required to
achieve reasonable yields. But, a catalyst does appear to hasten
the reaction, as indicated by the time transpired before viscosity
impedes stirring.
The insolubility of the polymers in common organic solvents
precluded gel permeation chromatography analysis. Instead,
molecular weight information was obtained by viscometry. The
intrinsic viscosity was determined with an Ubbelohde viscome-
Fig. 1 1H NMR assignment and end group analysis of PHFA from
ter under conditions previously reported for PET analysis.14
Table 1, entry 3.
Since the Mark–Houwink–Sakurada parameters have not been
established for novel PHFA, the parameters reported for PET
([h]= 1.09 ¥ 10-2 Mv0.84) were applied instead in order to convert
group of the monomer. When dynamic vacuum is limited to
intrinsic viscosity to molecular weight. While this transfer of
MHS parameters from one polymer to another is not general,
the associated error is typically much less than an order of
magnitude when the polymeric structures are similar and the
solvent and temperature are matched.15
10 min (Table 1, entry 6), comparatively low molecular weight
polymer is obtained. When the acid/alcohol dihydroferulic acid
is employed (Table 1, entry 7), the reaction is remarkably sluggish
and yields only oligomers. Thus, the acetyl group installed by the
Perkin reaction is deemed a necessity and it allows for molecular
weights comparable to that of commercial PET (Mn = 15 000 to
40 000).
Additionally, molecular weight information was obtained by
1
1H NMR end group analysis. Fig. 1 shows the H NMR spec-
The Tm for a typical sample of PHFA is measured as 234 ◦C
and its Tg is measured as 73 ◦C (Fig. 2; Table 1, entry 3). Thus,
PHFA and PET have comparable glass transition temperatures,
but PHFA has a melting temperature that is lower by about
30 ◦C. PHFA has a cooling-cycle crystallization temperature up
to 17 ◦C higher (Tc = 207 ◦C for Table 1, entry 1) than that
trum of the PHFA from Table 1, entry 3. The methyl substituent
of the acetyl end group was located at 2.40 ppm. Comparative
integration suggests an average degree of polymeriation of 38.
1
Note that the H NMR end group analysis method provides
number-average molecular weight values generally lower than
the viscosity-average molecular weight values, as theoretically
predicted for polydisperse samples.16
◦
of PET (190 C), suggesting a faster rate of crystallization.17
The most important factors that contribute to high molecular
weight material are prolonged dynamic vacuum and the acetyl
Additionally, PHFA typically exhibits a peak decomposition
temperature near 462 ◦C (50% mass loss under nitrogen, as
This journal is
The Royal Society of Chemistry 2010
Green Chem., 2010, 12, 1704–1706 | 1705
©

Acknowledgements
This research was supported by the donors of the American
Chemical Society Petroleum Research Fund (#47951-AC7) and
the National Science Foundation (CHE-0848236).
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processability. Finally, preliminary crystallization temperature
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PET is excelled by PHFA.
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1706 | Green Chem., 2010, 12, 1704–1706
This journal is
The Royal Society of Chemistry 2010
©