Access to amphiphilic cis-configurated polyamide-3 using alcohols as initiators

Article abstract of DOI:10.1021/acs.macromol.5b00272

The synthesis of polyamide-3 from 4a,5,8,8a-tetrahydro-1H-benzo[d][1,3]oxazine-2,4-dione (β-NCA, 1) using methanol, dye (Disperse Red 13), and poly(ethylene glycol) as initiator is described. The ring-opening polymerization under release of CO₂ produces polyamides-3 with definite terminal groups, high purity, and relatively narrow dispersity. This route was used for preparation of block copolymers from as an example.

Full text of DOI:10.1021/acs.macromol.5b00272

Article
pubs.acs.org/Macromolecules
Access to Amphiphilic Cis-Configurated Polyamide‑3 Using Alcohols
as Initiators
Olga Maiatska, Alexander Belkin, and Helmut Ritter*
Institute of Organic Chemistry and Macromolecular Chemistry, Heinrich Heine University of Duesseldorf, Universitaetsstrasse 1,
40225 Duesseldorf, Germany
S
* Supporting Information
ABSTRACT: The synthesis of polyamide-3 from 4a,5,8,8a-
tetrahydro-1H-benzo[d][1,3]oxazine-2,4-dione (β-NCA, 1)
using methanol, dye (Disperse Red 13), and poly(ethylene
glycol) as initiator is described. The ring-opening polymer-
ization under release of CO2 produces polyamides-3 with
definite terminal groups, high purity, and relatively narrow dispersity. This route was used for preparation of block copolymers
from as an example.
INTRODUCTION
RESULTS AND DISCUSSION
■
■
In the present work, the required monomer 4a,5,8,8a-
tetrahydro-1H-benzo[d][1,3]oxazine-2,4-dione (β-NCA, 1)
was prepared according to literature from cis-1,2,3,6-tetrahy-
drophthalic anhydride and trimethylsilyl azide (Scheme 1).13
For many decades, aliphatic polyamides have been of great
practical and scientific importance.1 Especially polyamide-6
(Perlon) or polyamide-66 (Nylon) are the main products. They
are produced worldwide in megatons via ring-opening
polymerization or via polycondensation, respectively. However,
polyamide-2 belongs generally to the group of proteins. The
synthesis can be conducted enzymatically via ring-opening
polymerization of N-carboxyanhydride of natural α-amino acids
step by step under irreversible release of CO2. This type of
polycondensation was the subject of many papers and was first
described by Curtius et al.2−4 and Wessely et al.5−12 In contrast
to that, the knowledge about preparation and properties of
polyamid-3 is relatively poor.13 Thus, it can be stated that the
required N-carboxyanhydrides of β-amino acids belong to the
group of “forgotten monomers”. Basically, polyamide-3 is a
polycondensate of 3-amino acids. It turned out that the
preparation polyamide-3 succeeds via ring-opening polymer-
ization of β-amino acid N-carboxyanhydrides (β-NCA’s) under
release of CO2 per monomer unit which is in analogy to the
preparation of polyamide-2 from α-amino acid N-carboxyanhy-
drides (α-NCA’s).14−16 The synthesis of β-NCA’s can be
conducted from cyclic anhydrides with trimethylsilyl azide via
rearrangement and final cyclization. This method was first
described in the early 1970s.17,18 The ring-opening polymer-
ization of β-NCAs to yield polyamide-3 can be catalyzed with
various amines, e.g., triethylamine, pyridine, or 4-bromoani-
line.13
Scheme 1. Synthesis of cis-β-NCA (1)
1
The structure of 1 was confirmed by H NMR spectroscopy
and characteristically by the FT-IR spectrum which exhibits
strong absorption bands of the carbonyl groups at 1784, 1746,
and 1724 cm−1. Since tetrahydrophthalic anhydride is prepared
in a technical scale from butadiene and maleic anhydride via a
typical Diels−Alder (2π + 4π) cycloaddition, the two carbonyl
groups are necessarily positioned in the 1,2-cis-configuration.
This means that, after Curtius rearrangement, the cis-
configuration is also retained. Accordingly, the bicyclic
compound 1 must be cis-configurated.19
The alcohol-initiated ring-opening polymerization of 1 was
accomplished by using of methanol (2a), Disperse Red 13
(2b), and methoxypolyethylene glycol 350 (2c) (Scheme 2).
Since the initiation step with alcohol is relatively slow
compared to propagation reactions with the terminal amines,
an excess of alcohol could be used quasi as solvents and
initiator. In the case of the solid dye 2b, toluene was used as
solvent. During the reaction, a release of bubbling carbon
dioxide can be observed. As mentioned above, this important
However, up to now, the use of alcohols as initiators for the
design of targeted end-groups of polyamide-3 has not been
described in the literature. According to our interest to
rediscover “forgotten monomers”, we were motivated to use
methanol and an OH group containing dye (Disperse Red 13 )
as model compounds and also poly(ethylene glycol) to obtain
amphiphilic block copolymers.
Received: February 11, 2015
Revised: March 30, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.macromol.5b00272
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Scheme 2. Ring-Opening Polymerization of β-NCA (1)
Starting from OH-Containing Derivatives
Figure 1. MALDI-TOF mass spectrum of polyamide 3a.
point was not described in the former literature.13Additionally,
as indicated in Scheme 2, the cis-configuration of the
incorporated monomer units is characteristic of the main
chain. This aspect was also not yet considered in former
investigations.13
Molecular weights of the 3a−d were determined by use of
GPC. The thermal properties were evaluated using differential
scanning calorimetry (DSC) measurements. Polymers 3a−3d
show a glass transition between 125 and 153 °C, depending on
the end-groups of polyamides. Block copolymers 3c and 3d
contain PEG residues and exhibit lower glass transition
compared to the 3a and 3b (Table 1).
chain can be prepared via Diels−Alder cyclization, ring
extension using a Curtius type rearrangement,20,21 and
subsequent ring-opening polymerization. The main novelty of
this investigation is use of alcohols as initiator which are
attached as ester end-groups. This opens the door for
preparation of e.g. amphiphilic block copolymers.
ASSOCIATED CONTENT
■
S
* Supporting Information
Description of the syntheses and spectroscopic data of the
obtained compounds. This material is available free of charge
via the Internet at http://pubs.acs.org.
Table 1. Characterization of Polymers 3a−3d
AUTHOR INFORMATION
Corresponding Author
*(H.R.) Tel (+49) 211 81-14760; Fax (+49) 211 8115840; e-
mail h.ritter@uni-duesseldorf.de.
■
a
b
c
sample alcohol/monomer molar ratio Mw [g mol−1
]
D
Tg [°C]
3a
3b
3c
3d
40/1
1/1
1/1
1/2
2300
6700
5800
8600
1.2
1.5
1.2
1.2
145
153
123
133
Notes
The authors declare no competing financial interest.
a
b
Determined by GPC (DMF) with polystyrene standards. D = Mw/
REFERENCES
c
■
289.
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The MALDI-TOF mass spectrum of 3a (Figure 1) also
clearly confirmed the formation of polyamide-3, showing the
mass difference of the repeating unit of 123 g mol −1. The
highest assignable degree of polymerization of 3a is n = 25
polymer which correspond to a molar mass of [M + Na]+ =
3131 m/z. Also, the formation of polymer 3b could be
confirmed by MALDI-TOF mass spectrometry (Supporting
Information).
CONCLUSION
It can be concluded from the above-described results that a
polyamide-3 containing trans-cyclohexene units in the main
■
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DOI: 10.1021/acs.macromol.5b00272
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
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C
DOI: 10.1021/acs.macromol.5b00272
Macromolecules XXXX, XXX, XXX−XXX