Ultrastrong, Transparent Polytruxillamides Derived from Microbial Photodimers

Article abstract of DOI:10.1021/acs.macromol.6b00220

Ultrastrong and transparent bioplastics are generated from fermented microbial monomers. An exotic aromatic amino acid, 4-aminocinnamic acid, was prepared from a biomass using recombinant bacteria, and quantitatively photodimerized, and diacid and diamino monomers that were both characterized by a rigid α-truxillate structure were generated. These two monomers were polycondensed to create the polyamides with a phenylenecyclobutane repeating backbone such as poly{(4,4′-diyl-α-truxillic acid dimethyl ester) 4,4′-diacetamido-α-truxillamide} which was processed into amorphous fibers and plastic films having high transparency. In spite of noncrystalline structure, mechanical strength of the fiber is 407 MPa at maximum higher than those of other transparent plastics and borosilicate glasses, presumably due to the tentative molecular spring function of the phenylenecyclobutanyl backbone.

Full text of DOI:10.1021/acs.macromol.6b00220

Article
pubs.acs.org/Macromolecules
Ultrastrong, Transparent Polytruxillamides Derived from Microbial
Photodimers
Seiji Tateyama,† Shunsuke Masuo,‡ Phruetchika Suvannasara,†,§ Yuuki Oka,† Akio Miyazato,†
Katsuaki Yasaki,† Thapong Teerawatananond,§ Nongnuj Muangsin,§ Shengmin Zhou,‡ Yukie Kawasaki,‡
Longbao Zhu,∥ Zhemin Zhou,∥ Naoki Takaya,*,‡ and Tatsuo Kaneko*,†
†School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292 Japan
‡Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Ten-nodai, Tsukuba, Ibaraki 305-8572, Japan
§Bioorganic Chemistry and Biomaterials Research Group, Department of Chemistry, Faculty of Science, Chulalongkorn University,
254 Pathumwan, Bangkok 10330, Thailand
∥Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122,
China
S
* Supporting Information
ABSTRACT: Ultrastrong and transparent bioplastics are
generated from fermented microbial monomers. An exotic
aromatic amino acid, 4-aminocinnamic acid, was prepared
from a biomass using recombinant bacteria, and quantitatively
photodimerized, and diacid and diamino monomers that were
both characterized by a rigid α-truxillate structure were
generated. These two monomers were polycondensed to
create the polyamides with a phenylenecyclobutane repeating backbone such as poly{(4,4′-diyl-α-truxillic acid dimethyl ester)
4,4′-diacetamido-α-truxillamide} which was processed into amorphous fibers and plastic films having high transparency. In spite
of noncrystalline structure, mechanical strength of the fiber is 407 MPa at maximum higher than those of other transparent
plastics and borosilicate glasses, presumably due to the tentative molecular spring function of the phenylenecyclobutanyl
backbone.
tautomerization to produce ultrastrong and transparent
polyamides having higher mechanical strength than heavy
materials such as glasses and even gold, silver, copper, and so
forth. Our improvement of fermentation efficiency of 4ACA is
of advantage for producing the biopolyamides in a large scale.
INTRODUCTION
■
Weight saving of industrial materials is indispensable for
establishment of sustainable societies. Utilization of plastics
instead of hard and heavy materials such as metals and glasses is
very effective on weight saving. Most plastics, however, have
less thermomechanical performances than the heavy materials.1
Especially, transparent plastics such as polycarbonates are
expected to alternate glass materials, but their thermomechan-
ical performances were too low to apply in wide fields of
electronics and optics. We have synthesized functional aromatic
polymers2−4 and recently produced the functional polyimide
films5 with good transparency and very high thermoresistance
from the less toxic aromatic monoamine 4-aminocinnamic acid
(4ACA, compound 1) using genetically engineered microbial
cells from 4-aminophenylalanine, which is an intermediate of
chloramphenicol synthesis.5 Other researchers have also
prepared transparent polymers with high thermoresistance.
However, their mechanical strengths were not high enough to
alternate conventional heavy inorganic materials. This should
be attributed to a serious dilemma in molecular design that
amorphous structure is indispensable for the good transparency
but effectively reduces the mechanical strengths.
RESULTS AND DISCUSSION
■
Syntheses. The dianiline monomers of the aimed
polyamides were synthesized by an analogous method to the
previously reported polyimide syntheses,5 where natural 4-
aminophenylalalnine was bioconverted to 4ACA at a low
efficiency of 0.13 g/L, and a direct photoirradiation of its
hydrochloride salt (compound 2) powder without agitation
generated a milligram scale of the 4ACA dimer (compound 3).
Here, we biosynthesized 4ACA by using glucose biomass as a
starting material at a remarkably improved efficiency of 2.2 g/L
(detailed data sets are summarized in the Supporting
Information) and made a 100 g scaled synthesis of the
photodimer 3 in a benzene-dispersion state under magnetic
agitation. The three-dimensional structure deduced from X-ray
diffraction of the single crystal showed that the main backbone
Here we overcome the dilemma using truxillamide backbone
comprising rigid phenylenes and their connecting cyclobutanes
(CB) behaving as a molecular spring showing possible
Received: January 30, 2016
Revised: April 1, 2016
© XXXX American Chemical Society
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Scheme 1. Synthetic Route of Bio-Based Aromatic Polyamide from 4-Aminocinnamic Acid via Two α-Truxillic Acid Derivatives
Figure 1. Structural analysis and pictures of bio-based aromatic polyamide 7. (A) 1H NMR spectrum of aromatic polyamide 7. (B) Left, as-prepared
fibrils; center, cast film; right, spun fiber.
comprised an α-truxillic acid group formed as a result of head-
to-tail antiaddition of two cinnamoyls, and the phenylenes and
carboxyls were oppositely oriented (Figure S3). Following
methylation was made by the procedure shown in the previous
report to create 4,4′-diamino-α-truxillic acid dimethyl ester
(compound 4). These photochemical and chemical procedures
were quite simple and yielded over 90 wt % of aromatic
diamine 4 from 1.
In order to synthesize the diacid monomer, we acetylated 1
to give compound 5 and then investigated its photodimeriza-
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Figure 2. Transparency and mechanical properties of prepared polyamides. (A) Transmittance curve of polymers 7, 8, and 10. (B) Representative
stress−strain curve of polymer 7. (C) Structures of polymers 8, 9, and 10. (D) Tentative tautomerization of cyclobutanedioyl-4,4′-truxillamide
backbone.
tion in various organic solvents (Table S6). The photoreaction
in dispersions of benzene and dichloromethane resulted in the
formation of 4,4′-diacetoamido-α-truxillic acid (compound 6)
with a perfect yield. On the other hand, photoirradiation in
solutions of acetonitrile and DMSO, which were both good
solvents for 5, produced its cis-isomer. Schmidt’s rule states that
[2 + 2] photocyclization reactions occur in the solid state, since
the distance between molecules in the double bond should be
<4.2 Å.6,7 This explains why the homogeneous solution of 5 in
acetonitrile or DMSO did not create the targeted aromatic
diacid 6, which had two carboxyl groups that were used as a
diacid monomer for polyamide synthesis without further
chemical manipulation. The yield in the overall chemical
processes was over 80 wt %. Thus, the aromatic diacid 6 and
diamine 4 were synthesized from bioderived compound 1 in a
high efficiency.
shown in Scheme 1. The polyamide synthesis route from only
one bio-based amino acid 1 via two different dimerizations to
successive polycondensation of these two monomers had an
advantage in terms of bioresource efficiency. The polyconden-
sation of monomers 4 and 6 catalyzed by conventional
triphenyl phosphite and pyridine produced a polyamide 7,
1
whose structure was confirmed by the H NMR study (Figure
1A). The estimated number- and weight-average molecular
weight of 7 determined by gel permeation chromatography
(GPC) were 1.0 × 104 and 2.1 × 104, respectively. This
polyamide is notable since the repeating unit should be
regarded as a tetramer of 1 and modified by bioavailable acetic
acid and methanol.
Thermomechanical Properties and Transparency. The
polyamide was soluble in aprotic polar solvents, and a
transparent film and fiber were easily prepared from polymer
7 in dimethylformamide (Figure 1B). The wavelength depend-
ence of transparency is shown in Figure 2A showing high
transparency 89% at 400 nm, which is comparable to those of
A bio-based aromatic polyamide, poly{(4,4′-diyl-α-truxillic
acid dimethyl ester) 4,4′-diacetamido-α-truxillamide} (com-
pound 7), was synthesized from 4 and 6 via the procedures
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Table 1. Mechanical and Thermal Properties of Aromatic Polyamides and Other Materials
e
transparency (%)
Young’s
d
d
Mn
Mw
modulus, Einit
strength, σ
elongation at
d
a
a
a
b
c
materials
(×10−4
)
(×10−4
)
PDI
2.06
Td10 (°C)
Tg (°C)
(GPa)
(MPa)
break, ε (%) 400 nm 450 nm
7
8
9
1
2.1
5.4
370
355
273
198
11.4 1.6
8.0 0.3
356 33
163 71
ND
7.2 3.7
89
93
(336 nm)
2.7
1.99
13.6 6.8
71
81
(391 nm)
4.1−5.4
5.5
5.1−9.1
6.5
1.24−1.69
365−370
359
151−159
243
ND
ND
ND
74
ND
87
10-C6
10-C7
10-C8
1.18
12.1 4.1
407 188
284 42
223 36
36.9 19.1
(373 nm)
5
6.2
2.9
6.5
1.26
1.9
358
356
250
252
10.7 1.0
8.7 1.0
17.3 7.6
7.7 2.7
71
83
(370 nm)
2.5
2.5
87
90
(350 nm)
polyamide 11
2.6
29
1.3
3.3
2.4
67
f
fluoropolyimide 1
292
309
114
129
86
1
87
17
fluoropolyimide
g
2
fluoropolyimide
327
2.9
122
76
87
h
3
polycarbonate
PMMA
1.2
5.9
3.1
9.3
2.64
1.58
150
121
140
1.9
2.3
2.4
13
62
200
3.1
87
85
90
88
89
90
91
90
60
ZEONEX
63
nanocellulose
223
(ca. 310 nm)
a
The weight-average molecular weight, Mw, the number-average molecular weight, Mn, and the distribution of polymer molecular weight, PDI, of
b
polyamides were measured by GPC. 10% weight loss temperature, T10, was obtained from TGA curve scanned at a heating rate of 10 °C/min under
a nitrogen atmosphere. Glass transition temperature, Tg, which was measured by DSC thermogram scanned at a heating rate of 10 °C/min under a
nitrogen atmosphere. Tensile strength at break, Young’s moduli, and elongation at break were obtained from tensiometer at room temperature. ND
refers to not determined. Transmittances were measured as transparency by UV/vis spectrophotometer. UV cutoff wavelengths, λ0, meaning the
c
d
e
f
wavelength at 50% transmittance are shown in parentheses. Fluoropolyimide 1 refers to the polyimides derived from hexafluoroisopropylidene
diphthalic anhydrides and 2,5-diamino-2,5-dideoxy-1,4:3,6-dianhydrosorbitol.19 Fluoropolyimide 2 refers to the polyimides derived from 1,4-
g
bis(3,4-dicarboxytrifluorophenoxy)tetrafluorobenzene dianhydride and tetrafluoro-m-phenylenediamine.19 Fluoropolyimide 3 refers to the
h
polyimides derived from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride and 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl.20
conventional and newly developed transparent resins (Table 1).
Cutoff wavelength was in the range of ultraviolet region. The
thermogravimetry revealed no weight loss at temperatures
below 300 °C and 10% weight loss at 367 °C (weight loss
temperature, Td10). The Td10 value of polymer 7 was not so
high because of the methyl ester moiety limits their thermal
degradation properties. Differential scanning calorimetry
(DSC) showed that the glass transition temperature, Tg, of
the polymer was 273 °C. These thermal properties are lower
than those of previous biopolymers2 but are higher than those
of bio-based plastics reported other researchers. The both
values of Tg and T10 were sufficient for application of polymer 7
as an industrial plastic with high thermoresistant performance.8
The stress−strain curve of polymer 7 was also investigated
(Figure 2B), and the maximum tensile strength and Young’s
modulus were σ = 356 33 MPa and E = 11.4 1.6 GPa,
respectively (n = 5). The σ value of polymer 7 was much higher
than those of transparent resins such as conventional
polycarbonate, poly(ethylene terephthalate), poly(vinyl ac-
etate), and poly(methyl methacrylate) ranging 62, 73, 50, and
60 MPa, respectively,9,10 and recently developed transparent
resin, ZEONEX, showing 63 MPa.11 Notably, σ of polyamide 7
was also much higher than those of conventional bio-related
polyamides such as polyamide 11 (PA11)12,13 and of protein
fibers such as collagen, keratin, elastin, and titin.14−18 According
to recent scientific reports on transparent resins, fluorinated
aromatic polyimides show high σ values ranging 114−129
MPa19,20 and bio-derived films of nanocelluloses show 223
MPa,21 but the present biopolyamides showed much higher
values than them. Furthermore, mechanical strength of the
polyamide 7 exceeded those of borosilicate glasses (40−100
MPa).22 The polyamide 7 was amorphous as a result of wide-
angle X-ray studies (representative X-ray diffraction diagram is
shown in Figure S5) while their mechanical strengths were very
high in spite of no reinforcement by crystalline domains. Such
high mechanical strength is presumably derived from the
adequate deformation of CB ring with a nonplanar structure
just like as a V-shaped spring to avoid the stress concentration
during elongation. Additionally, the backbones of cyclo-
butanedioyl-4,4′-truxillamide have a rigid tautomerized struc-
ture with coplanarity drawn on the right of Figure 2D. If the
coplanar structure was formed under mechanical stress, the
most stressed parts of the macromolecular chains could be
quite rigid to tolerate against the stress-focusing, and the
original softer chains around this parts could be deformed to
impart the toughness to the materials. In order to confirm the
mechanochemical change of polymer backbones, we made IR/
ATR studies on the polyamide film under strong pressure and
found a small change in IR peak around 1550 cm−1 which was
assigned to overlapped vibrations of amide II and carbon−
carbon double bond stretching. This change suggests that the
mechanical stress to the film can affect the structural change of
amide and benzenes, possibly relating with proposed
tautomerization.
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Figure 3. Photonic and hydrolytic degradation of polyamides. (A) Chemical pathways of degradation. (B) Change of 1H NMR spectra of polyamide
7 by photoirradiation. (C) UV-irradiation time dependence of conversion ratio into 4ACA dimer from polyamide 7.
We assessed polycondensation of the bio-based aromatic
diamines 4 with bio-derived diacids including aliphatic diacids
(dicarboxylic derivatives of fatty acids) and 2,5-furan-
dicarboxylic acid. The direct amidation of compound 4 and
the synthesis of poly{(4,4′-diyl-α-truxillic acid dimethylester)
2,5-frandicarboxylamide} (8) from 2,5-furandicarboxylic acid
proceeded as described in the experimental section (Supporting
Information).
The syntheses of aromatic−aliphatic poly{(4,4′-diyl-α-
truxillic acid dimethyl ester) α,ω-alkyloylamide} (9) where
alkyloyls are hexyloyl (C6), heptyloyl (C7), and octyloyl (C8))
polyamides using compound 4 with aliphatic diacids proceeded
using the corresponding linear alkylene carboxylic chlorides
(Figure 2C). Table 1 summarizes the thermomechanical
properties of these polyamides. The tensile strength and
Young’s modulus of polyamide 8 were lower than those of
polyamide 7 and polyamides 9 in any carbon number of
aliphatic chains showed mechanical brittleness, either. As a
consequence, the double α-truxillic moiety comprising cyclo-
butanedioyl-4,4′-truxillamide was indispensable for inducing
high mechanical strength, which supports the above-mentioned
effects of tautomerized coplanar structures on the mechanical
strength increase (Figure 2D).
double α-truxillic moiety in the backbone. The structure and
compositions of terpolymers were determined by NMR
spectroscopy that were nearly equal to in-feed composition of
CB (x) and alkylene (y) moiety as shown in the Supporting
Information. As a result of mechanical test, these terpolyamides
10-C6, 10-C7, and 10-C8 kept high mechanical strength
(stress−strain curves are shown in the Supporting Informa-
tion). The incorporation of aliphatic chains increased
elongation at break with keeping high values of σ and E. In
addition, the elongation values of these terpolymides were
decreased with increasing in the carbon number of aliphatic
groups, which might be attributed to the entanglement more
efficiently induced by the longer alkyl chains. The results
indicate the good acceptability of cyclobutanedioyl-4,4′-
truxillamide structure for third components, which is very
important to control the physical properties by the additional
third component and/or to impart some functions of the third
component.
Degradation of Fully Bio-Based Aromatic Polyamide
7. The degradability of bio-derived polymers into monomers is
important in terms of sustainability because it enables their
chemical recycling. No enrichment culture using the powdered
polyamide 7 as a sole carbon source resulted in microorganism
that grew under the conditions. No soil bacteria were obtained
by streaking soil suspension on plates that degrades polyamide
7. These results indicated that the polymer is stable in nature
We then attempted to synthesize terpolyamides using third
monomers with aliphatic chains (10-Cn) (n refers to the
number of carbon atoms in the aliphatic diacids), with keeping
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although this conclusion awaits future investigation on the
polyamide-degrading microorganisms. A system comprising
hydrolysis and photodegradation was tested to accomplish this
since polyamide 7 had such a chemically stable backbone with
aromatic rings and amide bonds that typical hydration methods
such as biodegradation would be ineffective. This degradation
system was predicted to generate compound 1 from 7.
recyclable superengineering bioplastics which was first prepared
and would be widely applied in materials of automobile parts,
medical instruments, and electronic devices.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications Web site. The Supporting Information is
available free of charge on the ACS Publications website at
DOI: 10.1021/acs.macromol.6b00220.
Since polyamide 7 has CB rings cleavable by UV-irradiation,
photodegradation of the polymer backbone was carried out as
shown in path A of Figure 3A. If the photodegradation reaction
of polyamide 7 proceeds quantitatively, 4ACA dimer shown in
path A of Figure 3A should be formed. By UV-irradiation with a
main wavelength of 254 nm, broad signals assigned to
phenylenes and CB of polyamide 7 around 7.00−7.50 and
3.68−4.42 ppm, respectively, became weaker with longer
irradiation time. After 36 h irradiation or longer, the NMR
spectrum of polyamide 7 was overlapped by signals appearing
at 6.71 and 6.53 ppm assigned to allylic protons on trans-
vinylene structure of 4ACA-dimer (top of Figure 3B) which
was synthesized by a condensation of 4ACA methyl ester and
compound 5. After UV irradiation for 96 h, the conversion ratio
attained to 84.9% calculated from peak area of allylic and
aromatic protons as shown in Figure 3C. In addition, GPC
chromatography shown in Figure S6 demonstrated the decrease
in the polyamide molecular weight into 670 g/mol, which
demonstrated photodegradation of polyamide 7 into oligomers.
Besides the polyamide 7 powders were effectively hydrolyzed
in concentrated HCl at reflux temperature for 8 h (path B of
Figure 3A) (NMR in Supporting Information), and the needle
crystal appeared by successive cooling. The recovery rate of 3
was 97 wt % vs 7, and the mass spectrum of the product
confirmed its high purity. 4ACA was then obtained by
photocleavage of the CB ring of recovered compound 3 via 1
h irradiation of a Xe lamp whose wavelength was filtrated
around a 254 nm by band-pass filter. We then polymerized the
recovered resource 2 to get polyamide 7 again.
Experimental section; Figures S1−S9 and Tables S1−S6
(PDF)
AUTHOR INFORMATION
Corresponding Authors
■
*(T.K.) E-mail kaneko@jaist.ac.jp; Tel +81-761-51-1631.
*(N.T.) E-mail takaya.naoki.ge@u.tsukuba.ac.jp; Tel +81-029-
853-4937.
Author Contributions
S.T. and S.M. made equal contributions. T.K. and N.T.
designed studies and prepared the manuscript with S.T. and
S.M. S.M., S.Z., and Z.Z. designed and performed biological
experiments. S.T. and A. M. designed chemical experiments.
S.T., A. M., K.Y, P.S., and Y.O. performed chemical
experiments. L.Z. and Y.K. performed the experiments.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This study has been financially supported by Advanced Low
Carbon Technology Research and Development Program
(5100270) and Super highway project from Japan Science
and Technology Agency [JST-ALCA].
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■
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