Monomers and their polymers derived from saturated fatty acid methyl esters and dimethyl carbonate

Article abstract of DOI:10.1039/c2gc35793c

In this study, we exploit the alpha-acidity of saturated fatty acid methyl esters (FAMEs) for the direct conversion of these renewable raw materials to malonate derivatives. After deprotonation with sodium hydride in dimethyl carbonate (DMC) as reactive solvent, the ester enolates react with DMC to give the desired products with up to 80% isolated yield. These malonate derivatives, bearing a long aliphatic chain with chain lengths of C₆-C ₁₆, were then polymerized to yield polyesters and polyamides. The polyesters were obtained by copolymerization with 1,6-hexanediol and titanium isopropoxide as a catalyst. For the polyamides, 1,6-hexanediamine was used with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a catalyst. The obtained polyesters are highly viscous and tacky materials with low melting points and a molecular weight range of 9-17 kDa. The polyamides, on the other hand, are high melting polymers with molecular weights from 7-15 kDa.

Full text of DOI:10.1039/c2gc35793c

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PAPER
Monomers and their polymers derived from saturated fatty acid methyl esters
and dimethyl carbonate
Nicolai Kolb and Michael A. R. Meier*
Received 22nd May 2012, Accepted 26th June 2012
DOI: 10.1039/c2gc35793c
In this study, we exploit the alpha-acidity of saturated fatty acid methyl esters (FAMEs) for the direct
conversion of these renewable raw materials to malonate derivatives. After deprotonation with sodium
hydride in dimethyl carbonate (DMC) as reactive solvent, the ester enolates react with DMC to give the
desired products with up to 80% isolated yield. These malonate derivatives, bearing a long aliphatic chain
with chain lengths of C –C , were then polymerized to yield polyesters and polyamides. The polyesters
6
16
were obtained by copolymerization with 1,6-hexanediol and titanium isopropoxide as a catalyst. For the
polyamides, 1,6-hexanediamine was used with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a catalyst.
The obtained polyesters are highly viscous and tacky materials with low melting points and a molecular
weight range of 9–17 kDa. The polyamides, on the other hand, are high melting polymers with molecular
weights from 7–15 kDa.
2
4
Introduction
enolates which then undergo a Claisen-condensation. Our idea
was to perform this reaction in dimethyl carbonate (DMC) where
the formed enolate should attack DMC to obtain the malonate
derivative bearing an aliphatic residue (Scheme 1) and suppress
the Claisen-condensation. One advantage of this approach is that
DMC can be synthesized from carbon dioxide and methanol as
Due to the limitation of fossil resources, one of today’s biggest
challenges in chemistry is to develop new routes towards renew-
able and bio-based commodity chemicals. Within this context,
fatty acids have been shown to be an optimal resource for polymer
1,2
2
5
chemistry. A large number of reactions of fatty acids have been
reported; for instance, they were converted to renewable mono-
renewable materials. Also, DMC is a non-toxic solvent com-
pared to other common organic solvents. It is well established
that malonates can be polymerized to yield semi-crystalline poly-
26
3
–8
9–14
mers by (cross-) olefin-metathesis,
isomerization catalysis where the double bond within the chain is
isomerized to the chain end and modified subsequently,
mention only a few examples. However, all of these conversions
rely on the use of unsaturated fatty acids, since the double bond in
the chain is a prerequisite for the reaction. On the other hand, for
saturated fatty acids far fewer routes for their functionalization are
reported. For instance, enzymatic pathways allow the synthesis of
thiol-ene reactions
or
27–31
esters for various applications.
However, fatty acid derived
15,16
to
malonates bearing long aliphatic residues have so far not been
employed for polymerization reactions nor have they been syn-
thesized directly from fatty acid methyl esters.
Results and discussion
1
7
ω-hydroxy fatty acids very efficiently. Other methods focus on
Synthesis of malonate derivatives
the synthesis of vinyl- or norbornyl-esters that can be polymerized
18
19
radically or via ring-opening metathesis polymerization. More-
The first challenge of this study was to find suitable conditions
over, it has been reported that saturated fatty acid methyl esters
for the synthesis of malonate derivatives from saturated fatty acid
2
0
(
FAMEs) can be dimerized by oxidative coupling or by Kolbe-
21,22
electrolysis
in very efficient manners. Furthermore, substi-
tution reactions with chlorine were carried out on stearic acid
2
3
revealing a certain selectivity towards the ω-position.
The aim of this study is to modify saturated fatty acid esters
towards renewable monomers directly. We had in mind that
esters can be deprotonated with strong bases, such as sodium
hydride (NaH) or lithium diisopropylamide (LDA), to form
Karlsruhe Institute of Technology, Institute of Organic Chemistry,
Fritz-Haber-Weg-6, Building 30.42, 76131 Karlsruhe, Germany.
E-mail: m.a.r.meier@kit.edu; http://www.meier-michael.com;
Fax: (+49)-721-608-46800; Tel: (+49 )-721-608-48326
Scheme 1 Synthesis of malonate derivatives based on dimethyl malo-
nate (classic way) or saturated fatty acid methyl esters (our approach).
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methyl esters in DMC. We had in mind that strong bases and an
excess of DMC are required in order to suppress the Claisen-
condensation. In an initial investigation of the reaction con-
ditions, we found that the best base for this reaction is sodium
hydride (NaH, 60 wt% dispersion in mineral oil). Other bases
like sodium hydroxide, potassium hydroxide, potassium carbon-
ate or trimethylamine gave no or very low conversion. When
LDA (2 M in THF) was used, the reaction proceeded but only
with disappointing yields since after a short reaction time the
reaction mixture became gel-like and stirring was thus hindered.
The best results with LDA (73.7% GC-conversion with 62.1%
product selectivity) were obtained with 2.0 eq of LDA in 2.0 eq
of DMC at 60 °C. With a higher DMC concentration of 10.0 eq,
only 53.0% conversion were obtained with a product selectivity
of 66.6%. Moreover, LDA considerably promoted the Claisen-
condensation (see Scheme 2). The reaction conditions were then
further investigated using NaH as base. NaH was used in the
range of 1.0–3.0 eq and DMC from 5.0–20.0 eq. During our
investigations, we also observed that anhydrous DMF can
accelerate the deprotonation considerably and therefore DMF
was added to most reactions (compare Table 1) as an additive.
This increased the conversion significantly (compare Table 1,
entries 2 and 3). Since similar reactions are carried out in pure
DMF, we consider that the effect is a better solvation of reactants
that the reaction proceeded well with 3.0 eq NaH in 5.0 eq
DMC. However, a significant amount of the Claisen-conden-
sation side-product was formed under these conditions (Table 1,
entry 4). This can be suppressed by a larger excess of DMC of
10 or 20 eq. However, due to the large dilution, the yields were
lower (Table 1, entries 6 and 7). This problem was solved by
prolonging the reaction time to 8 h; under these conditions also
2.5 eq of base gave very good conversion with almost no
Claisen-condensation side-product (Table 1, entries 10 and 11).
The optimal conditions were found to be 2.5 eq NaH in 20.0 eq
DMC with 1.0 eq DMF as an additive at 60 °C for at least 8 h
reaction time, yielding almost quantitative conversions in GC
analysis (Table 1, entry 11). A drawback of this reaction in terms
of sustainability and safety is the use of an excess of NaH. This
excess, however, was required since the malonate derivatives are
more acidic than the starting esters and are thus preferentially
deprotonated. Thus, base loadings lower than 2.0 eq resulted in
very low conversions (Table 1, entry 12).
With these results in hand, we synthesized the malonate
derivatives of different saturated fatty acids (C –C ) in higher
8
18
scale for the further characterizations (Scheme 3). For monomers
M1–M4, 8 h reaction time gave an almost quantitative conver-
sion as with the small-scale reactions, for M5 and M6 the reac-
tion time needed to be increased to 12 h in order to obtain
similar results. This might be due to a slightly lower solubility
with the increase of the aliphatic chain length. All malonate
derivatives were purified by vacuum distillation to give the
desired products with good purity and yields of 59% to 82%.
However, with long-chain fatty acids the purification of the pro-
ducts was far more challenging since their chemical and physical
32
and/or intermediates and therefore increased reactivity.
However, doubling the concentration of DMF had no consider-
able effect on the conversion (Table 1, entry 5). We observed
Scheme 2 Possible Claisen-condensation during the synthesis of
dimethyl 2-decylmalonate from methyl dodecanoate.
Scheme 3 Overview of the synthesized malonate-derived monomers.
Table 1 Condition screening and optimization of malonate synthesis
a
a
a
Entry
NaH (eq)
DMC (eq)
DMF (eq)
Time (h)
% Conv.
% Product
% Claisen
1
2
3
4
5
6
7
8
9
1.0
2.0
2.0
3.0
3.0
3.0
3.0
2.0
2.0
2.5
2.5
1.5
5
5
5
5
None
None
1.0
1.0
2.0
1.0
1.0
1.0
1.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
8.0
8.0
8.0
8.0
10.0
4.7
22.7
63.1
95.5
93.6
90.3
46.8
79.7
74.5
97.6
97.2
29.8
56.7
62.4
71.0
85.6
91.7
43.3
37.6
29.0
14.4
8.3
5.0
0.0
0.0
0.0
2.3
1.0
5
10
20
10
20
10
20
10
95.0
100.0
100.0
100.0
97.7
99.0
100.0
1
0
1.0
1.0
1.0
1
1
1
2
0.0
a
Estimated by GC assuming similar response factors for product, by-product and starting material.
2430 | Green Chem., 2012, 14, 2429–2435
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properties were almost the same if compared to the starting
material. Therefore, the isolated yields, with an acceptable
purity, were only about 60% for M5 and M6.
Further studies showed that the catalyst performs best with a con-
centration of 1 mol% at 120 °C giving a high molecular weight
polymer with the expected PDI value of ∼2 (Table 2, entry 14).
For a reaction temperature of 100 °C, the molecular weights
were significantly lower. Surprisingly, it seems that higher con-
centrations of the catalyst had a reverse effect on the polymeri-
zation, which also resulted in higher PDI values (Table 2, entries
5, 8 and 13).
With these results in hand we performed the polycondensation
on a large scale of the respective monomer (5.0 mmol) with
slightly optimized reaction conditions (see Experimental
section). The crude and precipitated polymers were analysed via
Polycondensation of the malonate derivatives
Having optimized the malonate synthesis from saturated fatty
acid methyl esters, the next step of this study was to polymerize
the obtained monomers to polyesters and polyamides in order to
investigate their polymerization behaviour and the properties of
the corresponding polymers. First, we were interested in the syn-
thesis of polyesters using 1,6-hexanediol as comonomer giving
polyesters with aliphatic side-chains (Scheme 4). In the begin-
ning, we investigated three different polymerization catalysts:
p-toluenesulfonic acid (p-TsOH), 1,5,7-triazabicyclo[4.4.0]dec-
GPC after 24 h. The number average molecular weights (M ) of
n
the polyesters were between 9–17 kDa (see Table 3 and Fig. 1
for GPC data).
Except for PE6, which is a rubbery material, all polyesters
were yellowish, highly viscous and sticky materials, which were
well soluble in almost every organic solvent.
The thermal properties of the precipitated polyesters were
studied by differential scanning calorimetric analysis (DSC)
within a temperature range of −90 to 200 °C (Fig. 2). Polyesters
PE1 and PE2 did exhibit a glass transition around −65 °C, but
no melting transition within that range. The longer the aliphatic
side-chains of the polyesters, the higher the melting point of the
5
-ene (TBD) and titanium(IV) isopropoxide (Ti(OiPr )). Using
4
relatively high concentrations of 10 mol% catalyst relative to the
employed monomer, comparable results at 80 or 100 °C were
observed for all three catalysts (Table 2, entries 1–6). However,
when the catalyst loading was reduced to 2 mol%, only Ti-
(
OiPr ) gave good results, whereas TBD and p-TsOH gave only
4
oligomers under similar conditions (Table 2, entries 7–9). There-
fore, Ti(OiPr)4 was chosen as the polycondensation catalyst.
Scheme 4 Malonate-derived polyesters (PE1–PE6) and polyamides (PA1–PA6).
Table 2 Condition screening for the polymerization of dimethyl 2-decylmalonate with 1,6-hexanediol
a
Entry
Temp. (°C)
Cat.
mol%
M
n
(kDa)
M
w
(kDa)
w n
PDI (M /M )
1
2
3
4
5
6
7
8
9
80
80
80
TBD
10
10
10
10
10
10
2
2
2
1
0.5
2
4.0
3.7
1.6
4.6
4.8
6.0
7.1
2.2
7.1
14.1
8.6
1.50
1.94
1.40
1.55
2.93
1.78
Ti(OiPr)
p-TsOH
TBD
Ti(OiPr)
p-TsOH
TBD
Ti(OiPr)
p-TsOH
Ti(OiPr)
Ti(OiPr)
Ti(OiPr)
Ti(OiPr)
Ti(OiPr)
4
4
4
100
100
100
100
100
100
100
100
120
120
120
4.8
b
N.P.
15.2
N.P.
11.8
14.5
17.0
22.1
15.7
44.0
2.89
1
1
4
4
4
4
4
24.6
29.3
50.8
44.6
33.9
2.08
2.02
2.99
2.02
2.17
1
1
1
1
2
3
4
5
1
0.5
a
b
GPC analysis was performed from the crude reaction mixture without precipitation. N.P. = no polymer.
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Table 3 Molecular weight data and thermal behaviour of the
polyesters PE1–PE6
Table 4 Molecular weight distribution and thermal behaviour of the
polyamides PA1–PA6
Entry
M
n
(kDa)
M
W
(kDa)
PDI
T
m
(°C)
T
g
(°C)
Entry
M
n
(kDa)
M
w
(kDa)
PDI
m
T (°C)
PE1
PE2
PE3
PE4
PE5
PE6
16.0
11.1
12.2
9.4
12.8
17.0
23.8
19.3
24.1
17.4
28.3
32.0
1.49
1.73
1.97
1.84
2.21
1.88
—
—
−35.7
−6.4
11.4
−65.1
−68.0
—
—
—
PA1
PA2
PA3
PA4
PA5
PA6
15.4
8.9
8.4
8.3
6.9
7.0
23.2
13.2
11.6
11.7
9.4
1.51
1.48
1.38
1.41
1.36
1.13
128.8
113.6
139.2
128.2
140.6
158.5
26.8
—
7.9
However, in general the synthesis of polyamides is quite challen-
ging because of the poor solubility of the resulting polymers and
the usually high melting points. Therefore, we performed the
polycondensation in ortho-xylene to keep the mixture stirrable
as long as possible. Also, we applied a temperature gradient,
raising the reaction temperature in 3 steps from 120 to 180 °C
(see Experimental section for details) with the change from a
stream of argon to high vacuum (∼2 mbar). After the polymer-
ization, the polymers were clear, transparent to yellowish solids,
which were dissolved in hexafluoroisopropanol (HFIP) and pre-
cipitated into diethyl ether. It is noteworthy that the longer the
side-chain is, the worse is the solubility of the polyamides in
HFIP. Aside from HFIP, the polyamides were only soluble in
boiling DMSO and boiling DMF. GPC analysis of these poly-
amides was performed in HFIP (Table 4). It was apparent that
the side-chain length had a strong influence on the molecular
weight. While PA1 had a molecular weight of almost 16 kDa,
the polyamide with the longest side-chains PA6 had only a mo-
lecular weight of about 5 kDa. We believe that this is because of
the bad solubility of the polyamides in general and the even
worse solubility with a longer side-chain. This did not change
with higher temperatures and longer reaction times, as we tested
for polyamides PA1 and PA5 by modifying our polymerization
procedure to 20 h of heating at 200 °C as the last step. The mo-
Fig. 1 GPC traces of polyesters PE1–PE6 after precipitation.
lecular weights changed only marginally (M of 18.6 kDa for
n
PA1 and 8.6 kDa for PA5 for the precipitated polymers) with
almost no change in the PDI value.
As for the polyesters, the DSC analysis of the precipitated
polyamides was carried out from −90 to 200 °C. We found that
the best results were obtained with a relatively high heating rate
of 20 °C min− . With slower heating rates the peaks could not be
identified clearly.
1
The precipitated polyamides were found to be high melting
polymers with melting points ranging from 120 to 160 °C
Fig. 2 DSC analysis of precipitated polyesters PE1–PE6.
(Fig. 3). Interestingly, it was observed that for PA2, with an
8
-carbon side-chain, the melting point was the lowest, whereas
resulting polymers ranging from −35.7 to 26.8 °C. PE6 is the
only polyester that was obtained as a solid at room temperature,
but it is still very tacky and rubbery. These results suggest that
the side-chain length and the resulting non-polar interactions are
the main driving force for the crystallinity of the obtained
polyesters.
for the other polyamides the melting points increased with
longer side-chains. Also, the melting point of PA1, with a
6-carbon side-chain, is significantly higher than for PA2. This
shows the important impact of the aliphatic side-chain on the
ability of the polyamide to crystallize. We consider that with
longer side-chains, the non-polar interactions contribute to a
better packing and therefore crystallinity. In addition, below a
Having established some basic properties of our polyesters,
we were also interested in malonate derived polyamides. There-
fore, we used 1,6-hexanediamine as comonomer (Scheme 4)
with 5.0 mol% of TBD as catalyst since we had good experience
certain length (in this case C for PA1) shortening the chain
6
length contributes to the crystallinity of the polyamide because
of the decreased steric hindrance of the side-chains. PA1 is
33
using these conditions with other fatty acid derived monomers.
also the only polyamide sample which shows a clear T
.
g
2432 | Green Chem., 2012, 14, 2429–2435
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General methods
The small scale malonate synthesis and polymerization reactions
were performed using a Radleys Carousel™ 12 Plus (RR98072,
Radleys Discovery Technologies, UK); large-scale malonate syn-
thesis was performed with a Radleys Carousel™ 6 Plus (Radleys
Discovery Technologies, UK) equipped with 250 mL round
bottom flasks.
Nuclear magnetic resonance (NMR) measurements were per-
formed on a Bruker AVANCE DPX system at 300 MHz for
1
13
H-NMR and 75 MHz for C-NMR. The chemical shifts (δ) are
given in ppm relative to tetramethylsilane (TMS, δ = 0.00 ppm)
as the internal standard.
Polymer molecular weight (GPC) analysis was performed on
different systems for polyesters and polyamides. For polyesters,
a LC-20A system from Shimadzu was used, which was equipped
with an SIL-20A autosampler and an RID-10A refractive index
detector in THF with a flow rate of 1 mL min− at 50 °C.
The analysis was performed on the following column system:
PLgel 5 μm MIXED-D column (Varian, 300 mm × 7.5 mm,
10 000 Å) with a SDV gel 5 μm pre-column (PSS, 50 mm ×
Fig. 3 DSC analysis of precipitated polyamides PA1–PA6.
1
This correlates with results of another study on polyamides,
where a pendant pentadecyl chain had a strong influence on the
3
4
thermal properties of the resulting polymers which was
described as an internal plasticizer.
8
.0 mm). For polyamides a Tosoh EcoSEC HLC-8320 GPC
system with HFIP containing 0.1 wt% potassium trifluoroacetate
Moreover, we tried to analyze the obtained polyamides
by H-NMR spectroscopy. In order to make them soluble
1
1
as the solvent was used. The solvent flow was 0.40 mL min− at
3
0 °C. The analysis was performed on a 3-column system: PSS
we derivatized them with trifluoroacetic anhydride (TFAA) in
3
3
PFG Micro precolumn (3.0 × 0.46 cm, 10 000 Å), PSS
PFG Micro (25.0 × 0.46 cm, 1000 Å) and PSS PFG Micro
deuterated chloroform, but the analysis still proved to be
difficult. Nevertheless, it was possible to assign most of the
peaks, which confirmed the general structure of the obtained
polyamides.
(25.0 × 0.46 cm, 100 Å). Both systems were calibrated with
linear poly(methyl methacrylate) standards (Polymer Standard
Service, M 102–981 000 Da).
p
Differential scanning calorimetry (DSC) experiments were
carried out under a nitrogen atmosphere at a heating rate of
5
Conclusion
°C min− for polyesters and 20 °C min for polyamides start-
1
−1
In conclusion, we have found a straightforward and high yield-
ing route for the conversion of saturated fatty acid methyl
esters to malonate derivatives bearing long aliphatic chains.
These malonates can be polymerized quite easily to polyesters
and polyamides with moderate to high molecular weights.
Whereas the polyesters are highly viscous and sticky materials
with low melting points, the polyamides have very high melting
points.
ing from −90 °C with a DSC821e (Mettler Toledo) calorimeter
up to a temperature of 200 °C using a sample mass in the
range of 20–30 mg. The data from second heating scans are
reported.
Gas chromatography (GC) analysis of the synthesized
malonates was performed on a Bruker 430 GC instrument
equipped with a capillary column FactorFour™ VF-5 ms
(30.0 m × 0.25 mm × 0.25 μm), using flame ionization detection.
The oven temperature program was: initial temperature 95 °C,
−1
hold for 1 min, ramp at 15 °C min to 220 °C, hold for 4 min,
−1
Experimental
ramp at 15 °C min to 300 °C, hold for 2 min, ramp at
1
1
5 °C min− to 325 °C, hold for 3 min. Measurements were
Materials
performed in split–split mode using hydrogen as the carrier gas
1
(
flow rate 30 mL min− ).
All solvents and chemicals were used as received. Sodium
hydride (NaH, 60 wt% dispersion in mineral oil), trifluoro-
acetic anhydride (TFAA, 99%), 1,5,7-triazabicyclo[4.4.0]dec-
Condition screening malonate synthesis
5
-ene (TBD, 98%), potassium trifluoroacetate (98%), p-toluene-
sulfonic acid monohydrate (p-TsOH, 98.5%) and 1,6-hexane-
diamine (98%) were purchased from Sigma Aldrich. N,N-
In a typical experiment, 0.50 mL of methyl dodecanoate
(2.0 mmol) were mixed with different amounts of DMC and
NaH. For most reactions, DMF was added as an additive.
The suspensions were then heated to 60 °C for different reaction
times. To stop the reaction, 10 mL of diluted hydrochloric
acid was added resulting in an immediate separation of
the organic phase. The conversions were then analysed by GC
of the organic phase. For detailed amounts and results see
Table 1.
Dimethylformamide (DMF, 99.8%, extra dry), Ti(OiPr ) (98%),
4
1
,6-hexanediol (97%) and dimethyl carbonate (DMC, 99%)
were from Fisher Scientific. Hexafluoroisopropanol (HFIP,
9.9%) was purchased from Chempur. Fatty acid methyl
9
esters were either bought directly or synthesized from the
corresponding fatty acids (Fisher Scientific) using standard
procedures.
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General procedure for upscale synthesis of malonate derivatives
For large scale synthesis of the malonate derivatives, 0.1 mol of
the fatty acid methyl ester was mixed with 170 mL DMC
(20.0 eq), 10.0 g NaH (60 wt% dispersion in mineral oil equals
6
g NaH, 2.5 eq) and 7.7 mL DMF (1.0 eq). The mixtures were
heated to 60 °C for 8 h, in the case of methyl palmitate and
stearate for 12 h. To stop the reaction, the suspensions were
added slowly to 200 mL diluted hydrochloric acid. The organic
phase was isolated and concentrated under reduced vacuum.
Thus, non-reacted DMC could be recovered. All malonate
derivatives were isolated by high vacuum distillation.
Scheme 5 Assignment of polyester NMR-signals.
(
CH ), 28.85 (CH ), 27.33 (CH ), 22.67 (CH ), 14.09 (CH );
2 2 2 2 3
MS (EI): m/z = 328.3 ([M], calc. 328.23).
Dimethyl 2-hexadecylmalonate (M6). 21.8 g (61.1%) of the
1
Dimethyl 2-hexylmalonate (M1). 15.8 g (72.9%) of the
product was obtained as a white wax. H NMR (300 MHz,
1
product was obtained as a clear oil. H NMR (300 MHz, CDCl )
CDCl
CH OOCCHRCOOCH
1.18 (s, 28H, chain), 0.80 (t, J = 6.0 Hz, 3H, CH
(75 MHz, CDCl3) δ 169.84 (COOCH ), 52.25 (CH
CHR–COOCH ), 51.64 (COOCH ), 31.88 (CH ), 29.84–28.94
(CH ), 28.80 (CH ), 27.29 (CH ), 22.63 (CH ), 14.02 (CH );
3
) δ 3.66 (s, 6H, OCH
3
), 3.28 (t, J = 7.5 Hz, 1H,
3
δ 3.66 (s, 6H, OCH ), 3.29 (t, J = 7.5 Hz, 1H, CH OOCCHR-
3
3
), 1.82 (m, J = 14.0, 7.0 Hz, 2H, β-H),
3
3
1
3
COOCH ), 1.82 (m, J = 14.0, 7.0 Hz, 2H, β-H), 1.22 (m, J =
3
); C NMR
OOC–
3
1
3
6
.2 Hz, 8H, chain), 0.80 (t, J = 6.4 Hz, 3H, CH3); C NMR
3
3
(
75 MHz, CDCl ) δ 169.81 (COOCH ), 52.21 (CH OOC–
3
3
2
3
3
3
CHR–COOCH ), 51.59 (COOCH ), 31.38 (CH ), 28.74 (CH ),
2
2
2
2
3
3
3
2
2
2
7.18 (CH ), 22.40 (CH ), 13.85 (CH ); MS (EI): m/z = 217.2
MS (EI): m/z = 356.3 ([M], calc. 356.29).
2
2
3
+
([M + H] , calc. 217.14).
Condition screening for polyester synthesis
Dimethyl 2-octylmalonate (M2). 17.7 g (72.7%) of the
1
product was obtained as a clear oil. H NMR (300 MHz, CDCl )
3
In a typical reaction 0.5 mL dimethyl 2-decylmalonate (M2,
2.0 mmol) were mixed with 236.0 mg 1,6-hexanediol
(2.0 mmol) and different catalysts in different amounts. The
mixtures were then heated to different temperatures for 24 h and
then analysed by GPC without precipitation. For detailed
amounts and results see Table 3.
δ 3.66 (s, 6H, OCH ), 3.28 (t, J = 7.5 Hz, 1H, CH OOCCHR-
3
3
COOCH ), 1.82 (m, J = 14.0, 7.0 Hz, 2H, β-H), 1.21 (m,
3
J = 10.9 Hz, 12H, chain), 0.80 (t, J = 6.4 Hz, 3H, CH );
3
1
3
C NMR (75 MHz, CDCl ) δ 169.82 (COOCH ), 52.21
3
3
(
2
1
CH OOC–CHR–COOCH ), 51.60 (COOCH ), 31.71 (CH ),
3 3 3 2
9.39–28.94 (CH ), 28.76 (CH ), 27.23 (CH ), 22.53 (CH ),
2 2 2 2
+
3.93 (CH ); MS (EI): m/z = 245.2 ([M + H] , calc. 245.17).
3
Preparation of polyesters
Dimethyl 2-decylmalonate (M3). 22.1 g (81.3%) of the
product was obtained as a yellowish oil. H NMR (300 MHz,
1
After optimizing the polyester condensation, the reaction con-
ditions were adapted with little modifications on a large scale
with different malonates. In a typical reaction 5.0 mmol malo-
nate derivative (M1–M6) was mixed with 591.0 mg 1,6-hexane-
CDCl ) δ 3.61 (s, 6H, OCH ), 3.24 (t, J = 7.5 Hz, 1H,
3
3
CH OOCCHRCOOCH ), 1.78 (m, J = 14.0, 7.0 Hz, 2H, β-H),
3
3
1
3
1
(
.15 (s, 16H, chain), 0.77 (t, J = 6.2 Hz, 3H, CH3); C NMR
diol (5.0 mmol) and 15.0 μL Ti(OiPr ) (1 mol%). Afterwards,
4
75 MHz, CDCl ) δ 169.64 (COOCH ), 52.03 (CH OOC–
3
3
3
2
.0 mL THF was added to homogenize the mixture, which was
CHR–COOCH ), 51.47 (COOCH ), 31.75 (CH ), 29.80–28.82
3
3
2
consequently heated to 120 °C for 1 h under a stream of argon
where the THF evaporated after 1–2 min and afterwards 23 h
under high vacuum. After the complete reaction the polymers
were solved in THF and precipitated in methanol at room temp-
erature. Because of the good solubility and due to the sticky
nature of all polymers, the isolation of the precipitated polyesters
was not complete.
(
CH ), 28.68 (CH ), 27.17 (CH ), 22.51 (CH ), 13.86 (CH );
2 2 2 2 3
+
MS (EI): m/z = 273.3 ([M + H] , calc. 273.21).
Dimethyl 2-dodecylmalonate (M4). 24.5 g (81.6%) of the
1
product was obtained as a clear oil. H NMR (300 MHz, CDCl )
δ 3.68 (s, 6H, OCH ), 3.30 (t, J = 7.5 Hz, 1H, CH OOCCHR-
COOCH ), 1.84 (m, J = 14.0, 7.0 Hz, 2H, β-H), 1.22 (s 20H,
chain), 0.82 (t, J = 6.5 Hz, 3H, CH3); C NMR (75 MHz,
CDCl3) 169.76 (COOCH3), 52.16 (CH OOC–CHR–
COOCH ), 51.59 (COOCH ), 31.83 (CH ), 29.79–28.83 (CH ),
3
3
3
3
1
3
1
Poly(hexyl 2-hexylmalonate) (PE1). H NMR (300 MHz,
δ
3
CDCl ) δ 4.05 (t, J = 6.6 Hz, e), 3.25 (t, J = 7.5 Hz, a), 1.81 (m,
3
3
3
2
2
b), 1.56 (m, f), 1.29 (s, g), 1.22 (s, c), 0.80 (t, J = 6.4 Hz, d);
2
8.75 (CH ), 27.24 (CH ), 22.58 (CH ), 13.95 (CH ); MS (EI):
13
2
2
2
3
C NMR (75 MHz, CDCl ) δ 169.55 (COOR), 65.09 (e),
3
m/z = 300.3 ([M], calc. 300.23).
5
2.03 (a), 31.49 (CH ), 28.82 (CH ), 28.38 (CH ), 27.28 (CH ),
2 2 2 2
2
5.41 (CH ), 22.48 (CH ), 13.98 (d).
2
2
Dimethyl 2-tetradecylmalonate (M5). 19.4 g (59.1%) of the
product was obtained as a white wax. H NMR (300 MHz,
1
1
Poly(hexyl 2-octylmalonate) (PE2). H NMR (300 MHz,
CDCl ) δ 3.67 (s, 6H, OCH ), 3.29 (t, J = 7.5 Hz, 1H,
CDCl ) δ 4.05 (t, J = 6.5 Hz, e), 3.25 (t, J = 7.4 Hz, a), 1.81
3
3
3
CH OOCCHRCOOCH ), 1.82 (m, J = 14.0, 7.0 Hz, 2H, β-H),
(m, b), 1.57 (m, f), 1.29 (s, g), 1.19 (s, c), 0.81 (t, J = 6.4 Hz,
3
3
1
3
13
1
.18 (s, 24H, chain), 0.81 (t, J = 6.4 Hz, 3H, CH3); C NMR
d); C NMR (75 MHz, CDCl ) δ 169.55 (COOR), 65.09 (e),
3
(
75 MHz, CDCl ) δ 169.97 (COOCH ), 52.40 (CH OOC–
52.03 (a), 31.78 (CH ), 29.45–28.98 (CH ), 28.80 (CH ), 28.38
3
3
3
2
2
2
CHR–COOCH ), 51.72 (COOCH ), 31.91 (CH ), 29.86–28.99
(CH ), 27.34 (CH ), 25.41 (CH ), 22.60 (CH ), 14.04 (d).
2 2 2 2
3
3
2
2434 | Green Chem., 2012, 14, 2429–2435
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1
Poly(hexyl 2-decylmalonate) (PE3). H NMR (300 MHz,
References
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3
1
3
3
(
(
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3
C NMR (75 MHz, CDCl ) δ 169.55 (COOR), 65.09 (e), 52.05
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3
(
(
a), 31.90 (CH ), 29.44 (CH ), 28.39 (CH ), 27.37 (CH ), 25.41
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2
2
2
13 M. Desroches, S. Caillol, R. Auvergne, B. Boutevin and G. David,
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3
(
s, b), 1.57 (s, f), 1.30 (s, g), 1.18 (s, c), 0.81 (t, J = 6.0 Hz, d);
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1
3
3
(
(
2
2
2
2
1
1
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1
1
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3
1
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Acknowledgements
N.K. would like to thank the German Environmental Foundation
1019–1025.
(Deutsche Bundesstiftung Umwelt, www.dbu.de) for financial
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557–567.
support.
This journal is © The Royal Society of Chemistry 2012
Green Chem., 2012, 14, 2429–2435 | 2435