Linear semicrystalline polyesters from fatty acids by complete feedstock molecule utilization

Article abstract of DOI:10.1002/anie.201001510

(Figure Presented) Complete and linear incorporation of fatty acids into polyesters is achieved by isomerizing carbonylation to give polymerization- quality diesters and their polycondensation with the corresponding diols obtained by reduction. The strictly linear and long-chain hydrocarbon nature of these polyesters results in a high degree of crystallinity and melting behavior akin to common thermoplastics.

Full text of DOI:10.1002/anie.201001510

Communications
DOI: 10.1002/anie.201001510
Renewable Resources
Linear Semicrystalline Polyesters from Fatty Acids by Complete
Feedstock Molecule Utilization**
Dorothee Quinzler and Stefan Mecking*
Dedicated to Hans Brintzinger on the occasion of his 75th birthday
Thermoplastic polymers are currently prepared almost exclu-
sively from fossil feedstocks. In view of the limited availability
of such feedstocks, alternative renewable resources are
carbohydrates by microorganisms or enzymes. Entirely chem-
ical synthetic routes in which the original molecular structure
of the utilized plant biomass is substantially retained are an
interesting alternative to such biotechnological routes, as they
can be efficient in terms of feedstock utilization and reaction
space–time yields, and also provide novel properties. Plant
[1,2]
desirable in the long term.
Polymer production from a
renewable resource ideally allows for a complete molecular
utilization of the feedstock and carries its molecular structure
over into the resulting polymers, providing them with specific
desirable properties. In this regard, fatty acids from plant oils
are attractive substrates as they contain long-chain linear
segments. They also possess two functional groups, as
required in principle for the generation of thermoplastics by
step-growth polymerization. However, the double bond is
located in the center of the molecule. For complete utilization
of fatty acids in the generation of crystallizable linear
polymers, a functionalization at the chain end is required
[
5–7]
oils
are in principle attractive substrates for semicrystalline
long-chain polyesters, as the substrate already provides
relatively long (CH ) crystallizable segments. This is illus-
2
n
trated by preparation of the difunctional monomer sebacic
[8]
acid from ricinoleic acid, which is converted into aliphatic
polyamides such as nylon-6,10 with a beneficially low water
uptake. Herein, only one side of the fatty acid chain with
respect to the double bond is incorporated into the monomer
and ultimately the polymer. For longer-chain aliphatic
polyesters, a complete incorporation (Scheme 1) is also of
particular importance to achieve sufficient melt and crystal-
lization temperatures for thermoplastic processing and appli-
cations. Known aliphatic polyesters based on adipic or higher
acids suffer from low melting
(
Scheme 1). Herein we report the preparation and properties
of novel semicrystalline polyesters with long-chain hydro-
carbon segments based on complete linear incorporation of
oleic acid and erucic acid.
[
9–12]
points.
An efficient and highly
regio- as well as chemoselec-
tive conversion of an internal
double bond into a terminal
functional group is a chal-
lenge for synthetic chemis-
[
13]
try.
m(II) complexes of very bulky
substituted electron-rich
diphosphines catalyze the
To this end, palladiu-
Scheme 1. Complete conversion of unsaturated fatty acids into long-chain linear polyesters (x=1: oleic acid,
x=5: erucic acid).
Polyesters are one of the most important classes of organic
polymers, and indeed the more recently developed and
commercialized biomass-based polymers are thermoplastic
polyesters, namely polylactides and short-chain polyhydroxy-
reaction of ethylene with carbon monoxide and methanol to
methylpropionate (methoxycarbonylation) with high
[
14,15]
rates.
Remarkably, these catalysts methoxycarbonylate
[
16]
internal octenes to the linear carboxylic acid esters. They
have been noted to be compatible with fatty acids; however,
from the gas chromatographic data of the reaction mixture
presented it appears that the carbonylation products were not
formed or isolated with a purity sufficient for utilization as a
[
1–4]
alkanoates.
Their preparation involves conversion of
[*] D. Quinzler, Prof. Dr. S. Mecking
[
17–20]
Chair of Chemical Materials Science
difunctional monomer for polycondensation.
This point
Department of Chemistry, University of Konstanz
Universitꢀtsstrasse 10, 78457 Konstanz (Germany)
Fax: (+49)7531-88-5152
E-mail: stefan.mecking@uni-konstanz.de
Homepage: http://www.chemie.uni-konstanz.de/agmeck/
is critical as highly pure monomers are a prerequisite for
achieving any substantial molecular weights in subsequent
polycondensation reactions, owing to the correlation DP =
n
1
/(1Àp) between the degree of polymerization (DP ) and the
n
[
21]
functional group conversion (p).
[**] We thank Lars Bolk for DSC and GPC analysis and Marina Krumova
for WAXS.
Exposure of methyl oleate to carbon monoxide and
methanol in the presence of catalytic amounts of Pd(OAc)2/
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201001510.
1,2-bis[(di-tert-butylphosphino)methyl]benzene
(dtbpx)/
4
306
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2010, 49, 4306 –4308

Angewandte
Chemie
methanesulfonic acid (Pd/oleic acid 1:60) under optimized
conditions with respect to concentration of the reactants and
temperature (908C; 20 bar CO; methanol) resulted in vir-
tually complete and selective conversion of the unsaturated
fatty acid ester (for details, see the Supporting Information).
The desired product, dimethyl-1,19-nonadecanedioate, crys-
tallizes from this reaction mixture in more than 99% purity, as
revealed by gas chromatography and NMR spectroscopy of
the isolated material (see the Supporting Information). A
corresponding long-chain diol component was obtained by
reduction of the ester, affording more than 99%-pure non-
adecane-1,19-diol. Polycondensation of stoichiometric
amounts of dimethyl-1,19-nonadecandioate and nonade-
cane-1,19-diol catalyzed by titanium alkoxides afforded the
novel polyester 1 (Scheme 1, x = 1). GPC reveals molecular
4
À1
weights M of typically 2 ꢀ 10 gmol (M /M = 2); this data
w
w
n
1
agrees with Mn determined from H NMR spectroscopic
analysis of the end groups. This value approaches typical
[22]
molecular weights of commercial polyesters. The material
melts with a peak temperature of T = 1038C and crystallizes
m
À1
at T = 878C, with an enthalpy of DH = 140 Jg . These
c
m
properties compare for example with the ubiquitous thermo-
plastic low-density polyethylene (LDPE).
Erucic acid is of particular interest for the concept
presented herein, as it has an unusually long carbon chain.
It is readily available from appropriate rape seed oils, or
crambe. Methyl erucate is insufficiently soluble in methanol
under the aforementioned conditions, and forms a heteroge-
neous mixture. This issue can be resolved by employing
higher alcohols. Carbonylation of ethyl erucate proceeded
smoothly in ethanol to afford diethyl-1,23-tricosanedioate in
more than 99% isolated purity. The ethyl ester was employed
as a starting material to circumvent formation of a mixture of
three different methyl and ethyl esters, as transesterification
may occur under the conditions of carbonylation, which
would complicate adjusting the exact stoichiometry in the
polycondensation. Reduction afforded more than 99%-pure
tricosane-1,23-diol. Polycondensation of stoichiometric
amounts of the linear terminal C23 diacid ester and diol,
Figure 1. Characterization of poly(1,23-tricosadiyl-1,23-tricosanedioate).
a) GPC trace and b) DSC trace. Top: first heating obscured by second
heating (black); bottom: first cooling (gray).
esters and diols are obviously of further interest for combi-
nation with established condensation monomers (some of
which can also be generated entirely from renewable
resources) to novel materials.
Experimental Section
Preparative procedures are exemplified by erucic acid ethyl ester (for
full analytical data and procedures, see the Supporting Information).
respectively, yielded polyester 2 (Scheme 1, x = 5), with M =
Diethyl-1,23-tricosanedioate: Pd(OAc) (0.079 mmol), 1,2-bis[(di-
2
w
4
À1
tert-butylphosphino)methyl]benzene (0.395 mmol), erucic acid ethyl
ester (4.93 mmol), methanesulfonic acid (0.79 mmol), and ethanol
2
ꢀ 10 gmol (M /M = 2) according to GPC (Figure 1), and
w n
[10,23]
T = 998C; T = 848C and a high
melt enthalpy DH =
m
m
c
(10 mL) were added into a dry Schlenk tube equipped with a
À1
1
80 Jg . Wide-angle X-ray scattering (WAXS; Supporting
Information) yields a high degree of crystallinity c of about
5% (ca. 70% for 1). These properties also approach those of
magnetic stirring bar using standard Schlenk and drybox techniques.
Vigorous stirring afforded a homogeneous reaction mixture that was
transferred by cannula into a 20 mL stainless-steel magnetically
stirred pressure reactor equipped with a glass inlay placed in a heating
block. The reactor was closed, pressurized with carbon monoxide
(20 bar) and then heated to 908C. After 22 h, the reactor was cooled
to room temperature and vented. After retrieving the reaction
mixture from the reactor, ethanol was removed in vacuo. The crude
product was dissolved in dichloromethane and filtrated over a
Bꢁchner funnel. Dichloromethane was removed in vacuo. The
diethyl-1,23-tricosanedioate thus obtained was recrystallized from
ethanol to yield the product in more than 99% purity in 79% yield.
Tricosane-1,23-diol: Diethyl-1,23-tricosanedioate (5.22 mmol) was
dissolved in tetrahydrofuran (20 mL). This solution was slowly
7
linear polyethylene in terms of enthalpy per mass associated
with melting, reflecting the predominantly hydrocarbon
[
23]
nature of the polymers.
The approach presented allows an efficient and complete
incorporation of fatty acids into semicrystalline polyconden-
sates, and is demonstrated herein for polyesters. This com-
plete molecular incorporation in a linear fashion is also
beneficial for achieving substantial melting points of the
aliphatic polyesters. The generic reaction types employed,
[
15]
[24]
namely carbonylation,
reduction,
and polycondensa-
added to a stirred and cooled suspension of LiAlH (13.2 mmol) in
[
22]
4
tion, are proven on a large industrial scale. The concept is
demonstrated herein for two low-cost fatty acids available
from a variety of sources. Beyond the novel linear largely
hydrocarbon polyesters studied, the long-chain a,w-diacid
tetrahydrofuran (40 mL). After further addition of tetrahydrofuran
(10 mL), the stirred mixture was heated to reflux for 1 hour and then
stirred overnight at room temperature. The reaction was quenched by
slowly adding water (0.5 mL), 15% aqueous NaOH (0.5 mL), and
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www.angewandte.org 4307

Communications
then more water (1.5 mL). The reaction mixture was filtrated at 408C,
and the solvent was removed from the filtrate in vacuo. The resulting
tricosane-1,23-diol was recrystallized from toluene to yield 1.62 g
moto, U. Witt, G. Skupin, D. Beimborn, R.-J. Mꢁller in
Biopolymers, Vol. 4 (Eds. A. Steinbꢁchel, Y. Doi), Wiley-VCH,
Weinheim, 2002, pp. 299 – 311.
(
87%) of the pure product. Poly(1,23-tricosadiyl-1,23-tricosane-
dioate): In 10 mL Schlenk tube, diethyl-1,23-tricosanedioate
1.13 mmol), tricosane-1,23-diol (1.13 mmol), and Ti(OBu)4
0.13 mmol) were heated from 1108C to 1508C at 0.01 mbar over
[13] For enzymatic w-oxidation of (saturated) fatty acids cf.; a) S.
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2009, 81, 1797 – 1808; b) U. Schoerken, P. Kempers, Eur. J. Lipid
Sci. Technol. 2009, 111, 627 – 645.
a
(
(
the course of 17 h. After cooling, a white solid was obtained in
quantitative yield.
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Received: March 12, 2010
Published online: May 7, 2010
[
Keywords: crystallinity · homogeneous catalysis ·
.
[18] C. Jimꢃnez-Rodriguez, Ph.D. thesis, University of St.Andrews,
004.
[
polycondensation · polyesters · renewable resources
2
19] Remarkably, the multiple unsaturated linoleate and linolenate
are also converted into the saturated, linear a,w-diester, which is
advantageous for the utilization of technical-grade fatty acid
[
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[
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[
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[
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[
23] From DHm (determined by DSC) and c (determined by WAXS),
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an enthalpy of fusion DH of the crystalline portion of about
u
[
[
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À1
À1
2
00 Jg (1) and 240 Jg (2) is estimated by comparison to
DH = 293 Jg for linear polyethylene. Poly(decamethylene
À1
u
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[
[
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À1
from currently accessible monomers melts with DH 148 Jg
u
[10]
(
T = 808C).
m
[
24] In this work, reduction of diacid esters to diols was performed
with inorganic hydrides, as this is convenient on a laboratory
scale. Industrially, catalytic reduction of esters to alcohols with
hydrogen as a reagent is an established reaction.
[
10] L. Mandelkern, R. G. Alamo in Physical Properties of Polymers
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[
[
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12] This is underlined by the resulting necessity of incorporation of
fossil-feedstock based aromatic diacid comonomers: M. Yama-
4
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