Introducing multicomponent reactions to polymer science: Passerini reactions of renewable monomers

Article abstract of DOI:10.1021/ja1113003

Combination of the Passerini three component-reaction (3CR) and olefin metathesis led to the formation of poly[1-(alkyl carbamoyl)alkyl alkanoates], a new class of polyesters with amide moieties in their side chain, from renewable resources. Two different

Full text of DOI:10.1021/ja1113003

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Introducing Multicomponent Reactions to Polymer Science:
Passerini Reactions of Renewable Monomers
Oliver Kreye,†,‡ Tommy Tꢀoth,‡ and Michael A. R. Meier*,†,‡
†Laboratory of Applied Chemistry, Institute of Organic Chemistry, Karlsruhe Institute of Technology, D-76131 Karlsruhe, Germany
‡Laboratory for Sustainable Organic Synthesis, Institute of Chemistry, University of Potsdam, D-14476 Golm/Potsdam, Germany
S Supporting Information
b
ABSTRACT: Combination of the Passerini three compo-
nent-reaction (3CR) and olefin metathesis led to the for-
mation of poly[1-(alkyl carbamoyl)alkyl alkanoates], a new
class of polyesters with amide moieties in their side chain,
from renewable resources. Two different approaches were
studied and compared to each other. First, monomers were
synthesized by the Passerini-3CR and then polymerized via
acyclic diene metathesis. Alternatively, bifunctional mono-
mers were synthesized by self-metathesis and then poly-
merized by Passerini-3CR. Both approaches led to the
formation of high-molecular-weight polymers. Moreover,
Passerini-3CRs were shown to be a versatile grafting-onto
method. The results clearly demonstrate that the Passerini-
3CR offers an interesting new access to monomers and
polymers and thus broadens the synthetic portfolio of
polymer science.
Figure 1. Products of pyrolysis of ricinoleic acid (1), their use for
Passerini-3CRs to prepare monomers 6a-d, and subsequent ADMET
polymerization of these monomers.
renewable polyamide on the market today.6 To expand the
possibilities for application of 2, we started to investigate the
behavior of 2 and its reduced product 10-undecenal (4) in
IMCRs to yield novel ADMET monomers (Figure 1).
asserini described the first isonitrile-based multicomponent
reaction (IMCR) in 1921, in which carboxylic acids and
P
aldehydes undergo an addition reaction with isonitriles to obtain
1-(alkyl carbamoyl)alkyl alkanoates.1,2 Today, the Passerini three-
component reaction (3CR) and the more famous Ugi four-
component reaction (4CR) play important roles in combinator-
ial chemistry, for drug discovery as well as natural product syn-
thesis.3,4 The use of IMCRs in the syntheses of polymers has
been, until now, only described in one example, from 2003 by
Wright et al., who performed ring-opening metathesis polymer-
ization (ROMP) with products derived from Ugi-4CR with
norbornenyl starting materials.5 The combination of IMCRs
and acyclic diene metathesis (ADMET) polymerization has not
yet been described in the literature, and, more importantly, the
use of IMCRs for direct polymer synthesis via polycondensation,
as described in this Communication, is a completely new
approach in polymer science. Thus, in order to investigate a
new method for the preparation of a new class of polymers, we
studied Passerini-3CRs with 2 and 4 in combination with olefin
metathesis. As can be seen from Figure 1, ricinoleic acid (1,
(9Z,12R)-12-hydroxyoctadec-9-enoic acid), the major fatty acid
of castor oil triglycerides (content up to 95%),6 is industrially
pyrolyzed to yield 10-undecenoic acid (2) and heptanal (3).6 2
was already shown to be of high value for the synthesis of a large
variety of polymers from renewable resources.7 Moreover, 2 is
used industrially for the synthesis of polyamide 11, the only fully
The Passerini-3CRs of 2 and 4 were thus performed with four
different isonitriles (5a-d, Figure 1). After 2 and 4 were stirred
with 5a in a small amount of THF at room temperature for about
1 day, the crude product could be easily purified by recrystalliza-
tion from hexane. 6a was obtained as colorless crystals in a yield
of 74%. The use of 5b yielded 6b as a colorless oil after puri-
fication by column chromatography. The commercially available
tert-butyl isocyanoacetate 5c, derived from glycine, was also
successfully subjected to the Passerini-3CR to yield 6c in a yield
of 73%. Moreover, the Passerini-3CR of 5d with 2 and 4 led to
the formation of 6d in a yield of 83%. Products 6c,d are especially
interesting since they offer further derivatization possibilities due
to their ester functional group.
Subsequently, the behavior of the obtained R,ω-unsaturated
compounds 6a-d as monomers for ADMET polymerization
was investigated. In a screening experiment, eight ruthenium-
based olefin metathesis catalysts (see Supporting Information for
structures) were tested for the polymerization of 6a (Figure 1) in
order to investigate their functional group tolerance toward this
Received: January 3, 2011
Published: January 25, 2011
r
2011 American Chemical Society
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Table 1. GPC Results (after Precipitation) of ADMET
Polymerizations of Monomers 6a-d with 1% Loading of C3a
entry
monomer
Mn, g/mol
PDI (Mw/Mn)
P10
P28
P30
P32
6a
6b
6c
6d
21 650
16 500
11 450
17 800
1.35
1.45
1.40
1.44
a Conditions: neat/1,4-benzoquinone (3 equiv per Ru catalyst)/
80 °C/4 h reaction time/N2-purged.
Figure 3. Passerini-3CR with dialdehyde 8, dicarboxylic acid 9, and
isonitriles 5a,b,d.
Table 2. Results of Polycondensation of 8 and 9 via Passerini-
3CRa
entry
isonitrile
THF solvent, mL
Mn, g/mol
PDI (Mw/Mn)
P44
P45
P46
P49
P50
P51
5a
5a
5a
5a
5a
5b
2.0
1.0
0.5
0.3
0.2
0.5
8 000
29 900
50 500
55 550
56 450
42 250
1.40
1.53
1.46
1.62
1.42
1.60
Figure 2. Saponification and subsequent grafting-onto reaction via
Passerini-3CR.
novel class of monomers. It is known that double bonds with
a high “distance” to functional groups are tolerated during
ADMET polymerization.8 Thus, all catalysts polymerized 6a
quite well at 80, 100, and 120 °C and catalyst amounts of 2.0, 1.0,
and 0.5 mol %. C3, the Hoveyda-Grubbs second-generation
catalyst, gave the highest molecular weights, and C4-C8 also
showed high molecular weights (10-19 kDa; see Table 1 of the
Supporting Information). Only the Grubbs first-generation
catalyst C1 showed a significantly lower activity in the ADMET
polymerization of 6a. The poly[1-(alkyl carbamoyl)undecyl
undecenoates] P1-P27 thus obtained behaved as sticky, rub-
bery substances, with good solubility in THF, chloroform, and
dichloromethane.
a Conditions: 40 °C/1 day reaction time/N2-purged.
Based on these promising results, the Passerini-3CR was
also investigated as a direct polymerization method by study-
ing the self-metathesis products of 2 and 4, namely 8 (after
saponification) and 9 (Figure 3), in polymerizations with 5a to
directly obtain poly[1-(alkyl carbamoyl)undecyl undecenoates]
(Figure 3). It should be noted here that the polymer architecture
of these polymers is different from that of the polymers obtained
from 6a-d via ADMET, since ADMET allows head-to-tail,
head-to-head, and tail-to-tail additions, whereas the reaction of
8 and 9 with isonitriles leads to a more regular repeat unit struc-
ture. The polymerization experiments showed that reducing the
amount of solvent led to the formation of higher molecular
weight polymers (up to ∼56 kDa for P49 and P50, Table 2)
at reaction temperatures of only 40 °C. Therefore, the poly-
Passerini-3CR seems to be a very powerful new approach for
polymer synthesis, starting from two bifunctional building
blocks, in this case of renewable origin. Increasing the tempera-
ture to 50 °C led to polymers with lower molecular weights
(P48). If dichloromethane was used, dissolution of the starting
materials 8 and 9 was incomplete, but high molecular weight
could be obtained (P42).
In conclusion, IMCRs, in this case Passerini-3CRs, offer
manifold new possibilities for polymer chemistry, as demon-
strated with the synthesis of monomers and grafting-onto
reactions as well as direct polymerizations. Thus, a new class
of polyester offering high molecular weights was prepared that
should open interesting possibilities for applications due to the
amide side chain. It is also important to note that the prepared
polymers are mainly of renewable origin and might thus con-
tribute to a sustainable development. In the future, it will be
interesting to see if this approach can be generalized to other
dicarboxylic acids and dialdehydes in order to achieve a large
variety of new polymer properties via this new polymerization
approach. Moreover, the variation of the isonitrile component
will be an interesting approach to tune the properties of these
polymers.
Having learned about the polymerization behavior of 6a, we
next polymerized 6b-d with the catalysts C3 and C8 (1.0 mol %)
at 80 °C, and the results were similar with those for 6a
(Table 1 and Supporting Information). The obtained polymers
P28-P33 showed molecular weights between 11 and 18 kDa
and polydispersity indexes (PDIs) between 1.4 and 1.5, as deter-
mined by gel permeation chromatography (GPC). Identical to
the polymers derived from 6a, 6b-6d were sticky, rubbery subs-
tances. Determination of the exact degree of polymerization
(DP) by 1H NMR was not possible, since terminal double bonds
were not observed, even in high enlargement. Thus, 7 was used as
a chain-stopper to produce telechelics with defined end groups.
This study clearly showed that the investigated polymers possess
significantly higher molecular weights than determined by GPC
(see Supporting Information section 1.4.5 and Table 3).
To demonstrate the possibilities of postmodifications, the tert-
butyl ester of P33 was hydrolyzed with trifluoroacetic acid (TFA)
to obtain the polycarboxylic acid derivative P39 (Figure 2).
The free carboxylic acid groups of P39 should undergo
additional IMCRs to generate diverse substructures in the side
chain of these polymers and thus versatile and adjustable polymer
properties. As an example, the Passerini-3CR of P39 with 5a and
3 (see Figures 1 and 2) led to the formation of P40. In contrast to
P39, which was insoluble in chloroform, P40 shows a high solu-
1
bility in this solvent. Analysis of P40 via H NMR revealed a
complete conversion of all carboxyl groups, thus showing that
IMCRs can also be used for efficient grafting-onto reactions.
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’ ASSOCIATED CONTENT
S
Supporting Information. Experimental details, synthesis
b
procedures, and additional results (GPC, NMR, and DSC). This
material is available free of charge via the Internet at http://pubs.
acs.org.
’ AUTHOR INFORMATION
Corresponding Author
m.a.r.meier@kit.edu
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