Ultrahigh performance bio-based polyimides from 4,4′-diaminostilbene

Article abstract of DOI:10.1016/j.polymer.2015.12.008

We have developed a novel route for the synthesis of high-performance bio-polyimides (PIs) microbially-derived from photo-responsive aromatic diamine 4,4′-diaminostilbene (DAS) and its reduced counterpart 4, 4′-(ethane-1,2-diyl)dianiline (EDDA). DAS and EDDA were condensed with various commercially-available dianhydrides to obtain a series of poly(amic acid)s (PAAs) and PIs which were characterized in terms of their thermal, mechanical, and photo-functions. These bio-based PAAs showed a very high viscosity of 6.62 dL/g, and the PIs showed ultrahigh thermal resistance with T_d10 values over 600 °C, which were higher than that of any bio-based plastic reported thus far. They also showed T_g values above 250 °C, and tensile strength of over 132 MPa, which is higher than that of Kapton. The PIs also showed photo-functional behavior based on stilbene-based photoreactions.

Full text of DOI:10.1016/j.polymer.2015.12.008

Accepted Manuscript
Ultrahigh performance bio-based polyimides from 4,4’-diaminostilbene
Amit Kumar, Seiji Tateyama, Katsuaki Yasaki, Mohammad Asif Ali, Naoki Takaya,
Rajeev Singh, Tatsuo Kaneko
PII:
S0032-3861(15)30422-5
10.1016/j.polymer.2015.12.008
JPOL 18303
DOI:
Reference:
To appear in: Polymer
Received Date: 29 August 2015
Revised Date: 29 November 2015
Accepted Date: 8 December 2015
Please cite this article as: Kumar A, Tateyama S, Yasaki K, Ali MA, Takaya N, Singh R, Kaneko T,
Ultrahigh performance bio-based polyimides from 4,4’-diaminostilbene, Polymer (2016), doi: 10.1016/
j.polymer.2015.12.008.
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ACCEPTED MANUSCRIPT
Graphical abstract
For
Ultrahigh performance bio-based polyimides from
4,4’-diaminostilbene
Amit Kumar1,3ǁ, Seiji Tateyama1,4ǁ, Katsuaki Yasaki1, Mohammad Asif Ali1, Naoki Takaya2,4,
Rajeev Singh3 and Tatsuo Kaneko*,1, 4
1School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST),
1-1 Asahidai, Nomi-shi, Ishikawa, 923-1292, Japan
2Faculty of Life and Environmental Sciences, University of Tsukuba, Ibaraki, 305-8572,
Japan
3Material/ Organometallics Laboratory, Department of Chemistry, ARSD College, University
of Delhi-110021, India
4JST, ALCA
ǁ Equal contribution to this paper
*Email: kaneko@jaist.ac.jp, Telephone: +81-761-51-1633, Fax: +81-761-51-1635.

ACCEPTED MANUSCRIPT
Ultrahigh performance bio-based polyimides from 4,4’-
diaminostilbene
Amit Kumar1,3ǁ, Seiji Tateyama1,4ǁ, Katsuaki Yasaki1, Mohammad Asif Ali1, Naoki Takaya2,4,
Rajeev Singh3 and Tatsuo Kaneko*,1, 4
1School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST),
1-1 Asahidai, Nomi-shi, Ishikawa, 923-1292, Japan
2Faculty of Life and Environmental Sciences, University of Tsukuba, Ibaraki, 305-8572,
Japan
3Material/ Organometallics Laboratory, Department of Chemistry, ARSD College, University
of Delhi-110021, India
4JST, ALCA
ǁ Equal contribution to this paper
*Email: kaneko@jaist.ac.jp, Telephone: +81-761-51-1633, Fax: +81-761-51-1635.
ABSTRACT: We have developed a novel route for the synthesis of high-performance bio-
polyimides (PIs) microbially-derived from photo-responsive aromatic diamine 4,4′-
diaminostilbene (DAS) and its reduced counterpart 4,4'-(ethane-1,2-diyl)dianiline (EDDA).
DAS and EDDA were condensed with various commercially-available dianhydrides to obtain
a series of poly(amic acid)s (PAAs) and PIs which were characterized in terms of their
thermal, mechanical, and photo-functions. These bio-based PAAs showed a very high
viscosity of 6.62 dL/g, and the PIs showed ultrahigh thermal resistance with Td10 values over
600 °C, which were higher than that of any bio-based plastic reported thus far. They also
showed Tg values above 250 °C, and tensile strength of over 132 MPa, which is higher than
that of KaptonTM. The PIs also showed photo-functional behavior based on stilbene-based
photoreactions.

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KEYWORDS: stilbenes, polyimides, high performances, photofunctions, aromatic diamines.
1. Introduction
Development of renewable polymer materials such as bio-based plastics is indispensable in
the creation of a sustainable society [1]. Although bio-based polymers such as polyurethanes,
polyesters, and polyamides have been synthesized using bio-available aliphatic molecules,
however low thermal and mechanical properties restrict their application as high performance
materials[2-9]. High-performance plastics are in demand due to their exceptionally high
thermal and mechanical properties that fulfill the requirements of various industrial
applications such as their use in electronic insulation, automobiles parts, transportation and
aviation materials[10]. Introduction of aromatic rings in the backbone of the polymer chain
improves performance and we have prepared high-performance aromatic biopolyesters from
phenolic acids [9]. However polyesters showed a fatal limitation of thermodegradation at
around 300 oC, which forced us to change the molecular design [5-12]
.
We have reported polyimides (PIs), which are a special class of polymers with intrinsically
high thermal and mechanical properties[13,14], by bio-based aromatic diamines which had
never been developed by bio-processing [15-17]
.
In previous reports, an exotic aromatic amino acid, 4-aminocinnamic acid (4ACA), was
produced using recombinant Escherichia coli from glucose via 4-aminophenylalanine
(4APhe)[18-21]. 4ACA dimerization can give bio-based aromatic diamine monomers and then
4ACA photoreactivity was utilized to prepare photodimer, 4,4’-diaminotruxillic acid.
However, the cyclobutane moiety of truxillate backbone is less thermally stable than an
aromatic ring or double bond. Therefore, we tried to develop another 4ACA dimerization
method by metathesis catalysis to produce stilbene [22-24]
.

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In this report, we describe the novel synthetic route of 4,4’-diaminostylbene (DAS) and its
derivative from bio-based 4ACA by utilizing Grubb’s olefin metathesis as a key step. Then,
we synthesized bio-based polyimides from DAS by reactions with different dianhydrides,
which show excellent thermo-mechanical properties.
2. Experimental Section
2.1 Materials
4-aminocinnamic acid which was used for the synthesis of the diamine monomers preparation
was obtained via two routes: 1) fermentation using genetically-manipulated Escherichia
coli[25]; and 2) purchase from TCI (Tokyo, Japan). Pyromellitic anhydride (PMDA) was
purchased from Kanto Chemical Co. Inc. 3,3′,4,4′-benzophenone tetracarboxylic dianhydride
(BTDA), 3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride (DSDA), 3,4,3′,4′-
biphenyltetracarboxylic dianhydride (BPDA), 4,4′-oxidiphthalic anhydride (OPDA), 1,2,3,4-
tetracarboxycyclobutane dianhydride (CBDA) and trimethylsilyl chloride (TMSCl) were
purchased from Aldrich. N,N-dimethylacetamide (DMAc) (99.8% anhydrous) was purchased
from Kanto Chemical and was used as received. All of the dianhydrides were purified before
using by refluxing with acetic anhydride for 6 h, and cooling to 0-5 °C. The crystals were
carefully collected by filtration, washed in hot dioxane, and dried in vacuo.
2.2 Instrumentation and Characterizations
1H nuclear magnetic resonance (1H-NMR) and 13C-NMR were performed on a Bruker
Biospin AG 400 and 100 MHz spectrometer respectively using DMSO-d6 as a solvent at 23.1
oC with 16 accumulation scans, using the proton resonance of residual non-deuterated DMSO
as an internal standard (2.55 ppm). The FT-IR spectra were recorded with a Perkin-Elmer
Spectrum One spectrometer between 4000 and 400 cm−1 using a diamond-attenuated total

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reflection (ATR) accessory. The mass spectra were measured using a Fourier transform ion
cyclotron resonance mass spectrometer (FT-ICR MS, Solarix) and scanned from m/z 50 to
m/z 1000. The ultraviolet−visible (UV−vis) optical absorption spectra were recorded on a
Perkin-Elmer Lambda 25 UV/vis spectrophotometer at room temperature. The inherent
viscosities were measured using an Ubbelohde viscometer at 30 °C in DMAc at a polymer
concentration of 0.5 g/dL. Thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC) were performed on Seiko Instruments SII, SSC/5200 and Seiko
Instruments SII, X-DSC7000T, respectively, at a heating rate of 10 °C/min under a nitrogen
atmosphere. The tensile measurements were carried out at an elongation speed of 0.5
mm/min on a tensiometer (Instron 3365) at room temperature. The number-average
molecular weight (Mn), weight-average molecular weight (Mw) and the molecular weight
distribution (PDI) were determined by gel permeation chromatography (GPC; Shodex GPC-
101 with a connection column system of 803 and 807, concentration 5 g/L, DMF eluant) after
calibration with pullulan standards. The solubility of the polymers was investigated using 1
mg of sample in 1 mL of solvent at room temperature and at 50 °C.
2.3 Monomer syntheses
2.3.1 Syntheses of diamines
The systematic representation of synthesis of DAS and its reduced counterparts 4,4'-(ethane-
1,2-diyl)dianiline (EDDA) from 4ACA is shown in Scheme 1. cm-1

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A)
O
OH
Starting material
NH2
NHAc
OH
O
OH
O
OCH3
OH
CA
1. Me3SiCl, MeOH
2. NH3 (aq)
1. HCl/MeOH
2. NH3 aq.
LiAlH4
THF
Grubb's
metathesis
Ac2O
MeOH
O
OH
NHAc
NH2
NH2
NH2
IV
I
II
III
NH2
4-ACA
Methyl-4ACA
4-aminocinnamyl N-acetyl-4-amino
NH2
NHAc
alcohol
cinnamyl alcohol
V
VI
DAS
N,N'-diacetyl-DAS
NH2
4APhe
B)
NH2
NH2
Pd/C, H2
MeOH
H2N
H2N
VII
EDDA
VI
DAS
Scheme 1. Synthesis of DAS and EDDA monomers from 4ACA.
a)
Preparation of methyl-4-aminocinnamic acid ester (methyl-4ACA) from 4ACA. 30
mmol of 4ACA (5.00 g, 30.64 mmol) was mixed methanol (50 ml) in a two neck flask round
bottom flask under nitrogen, to obtain a mixture in suspended state. TMSCl (6.2 g 7.6 mL, 60
mmol) was added dropwise with constant stirring at room temperature. The mixture became
clear after complete addition of TMSCl and after some time the solid started separating out.
The mixture was stirred for 12 h at room temperature. The solvent was evaporated and crude
sample was dried under vacuum. Thus prepared compound was treated with ammonia and the
compound was extracted with ethyl acetate. The collecting ethyl acetate organic layer was
dried over MgSO4, and it was then evaporated. Thus compound obtained was found to be
1
methyl-4-ACA in 99 % yield. The specifications were as follow: H NMR (400 MHz,
DMSO-d6, δ, ppm): 3.67 (s, 3H), 5.78(s, 2H), 6.23 (d, 1H, J = 8 Hz), 6.56 (d, 2H J = 16 Hz),
7.37 (d, 2H, J = 8 Hz), 7.47 (d, 1H J = 16 Hz). 13C NMR (100 MHz, DMSO-d6, δ, ppm):
51.5, 111.0, 114.0, 121.7, 130.7, 146.0, 152.0, 167.9. Mass: m/z = 178.08617 (experimental),
177.0790 (calculated). Melting point: 129 °C

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b)
Preparation of 4-amino-cinnamyl alcohol from 4-aminomethylcinnamate. LiAlH4 (4.5
g, 117.5 mmol) and anhydrous THF (40 ml) was mixed in a two neck round bottom flask
under nitrogen atmosphere. A solution of methyl-4-ACA (4.18 g, 23.5 mmol) in anhydrous
THF (20 ml) was slowly added into the LiAlH4/THF mixture. After complete addition the
reaction mixture was stirred for 90 mins. The reaction was quenched by addition of ethanol
and then water followed by the filtration. The compound was extracted by ethylacetate (40
ml) 3 times and the organic layer was dried over MgSO4, which was then evaporated. The
crude compound was purified by column chromatography using silica and 10 % ethylacetate/
petroleum ether as eluent. Compound thus obtained was found to be 60 % yield (purity > 95
%) with some residual impurity which was eliminated during purification after acetylation of
4-aminocinnamyl alcohol. The specifications were as follow: 1H NMR (400 MHz, DMSO-d6,
δ, ppm): 4.04 (t, 2H), 4.69 (t, OH), 5.15 (s, 2H), 6.01 (td triplet of doublet) 1H, J = 16 Hz),
13
6.33 (d, 1H, J = 16 Hz), 6.50 (d, 2H J = 8 Hz), 7.08 (d, 2H, J = 8 Hz). C NMR (100 MHz,
DMSO-d6, δ, ppm): 61.9, 113.9, 124.6, 124.8, 127.0, 129.6, 148.1. Mass: m/z = 150.09133
(experimental), 149.0841 (calculated). Melting point: 38 °C
c)
Preparation of N-acetyl-4-aminomethylcinnamyl alcohol from 4-aminocinnamyl
alcohol. 4-aminocinnamyl alcohol (2.01 g, 13.4 mmol) was mixed with methanol (30 ml) in a
two neck round bottom flask under nitrogen atmosphere. Acetic anhydride (5.5 g, 5 ml, 53.6
mmol) was added to the reaction mixture. The mixture was stirred overnight, evaporated and
purified via column chromatography using silica gel and 10 % ethyl acetate/petroleum ether
as eluent. The 100 % purified compound was obtained in 80 % yield. The specifications were
1
as follow: H NMR (400 MHz, DMSO-d6, δ, ppm): 2.03 (s, 3H), 4.09 (t, 2H), 4.82 (t, 1H)
6.26 (td, 1H, J = 16 Hz), 6.47 (d,1H, J = 16 Hz), 7.33 (d, 2H, J = 8 Hz), 7.53 (d, 2H, J = 8
Hz), 9.94 (s, 1H). 13C NMR (100 MHz, DMSO-d6, δ, ppm): 23.9, 61.6, 118.9, 126.4, 128.2,

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129.1, 131.2, 138.4, 168.1. Mass: m/z = 192.10182 (experimental), 191.0946 (calculated).
Melting point: 135 °C
d)
Preparation of N,N’-diacetyl-4,4’-diaminostilbene from N-acetyl-4-aminocinnamyl
alcohol using Grubb’s catalyst. N-acetyl-4-aminocinnamyl alcohol (1 g, 5.2 mmol,) and
Grubb’s second generation catalyst (5 mole percent, 0.27 mmol, 233 mg) was taken in a
round bottom flask followed by addition of 30 ml THF under nitrogen atmosphere. The
mixture was refluxed at 70 °C for 24 h. The solvent was evaporated and the compound was
separate by column chromatography using silica gel and 10 % ethyl acetate/petroleum ether.
The compound was obtained in 30 % yield (collected), however the conversion was
1
determined as ca. 100 % by NMR studies. The specifications were as follow: H NMR (400
MHz, DMSO-d6, δ, ppm): 2.05 (s, 3H), 7.06 (s, 1H), 7.49 (d, 2H, J = 8 Hz), 7.57 (d, 2H, J =
8 Hz), 9.98 (s, 1H). 13C NMR (100 MHz, DMSO-d6, δ, ppm): 24.5, 119.5, 127.0, 127.1,
132.5, 139.1, 168.7. Mass: m/z = 295.14403 (experimental), 294.1368 (calculated). Melting
point: 218 °C
e)
Preparation of DAS from N,N’-diacetyl-DAS. N,N’-diacetyl-DAS (0.25 g, 0.85 mmol)
was mixed with methanol (5 ml) in a two neck round bottom flask under nitrogen. HCl conc
(1.5 ml) was added and the mixture was stirred for 6 h. The solvent was evaporated under
vacuum followed by the addition of ammonia solution and then extracted using ethyl acetate
3 times (10 ml). The collected ethyl acetate organic layer was dried over MgSO4, and it was
then evaporated. The compound was obtained in 82 % yield. The specifications were as
1
follow: H NMR (400 MHz, DMSO-d6, δ, ppm): 5.15 (s, 4H), 6.56 (d, 2H, J = 8 Hz), 6.74 (s,
2H), 7.20 (d, 4H, J = 8 Hz). 13C NMR (100 MHz, DMSO-d6, δ, ppm): 114.0, 123.8, 125.8,
126.8, 147.7. Mass: m/z = 211.12286 (experimental), 210.1157 (calculated). Melting point:
207 °C

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f)
Preparation of EDDA from DAS. DAS (0.1 g, 0.48 mmol) and 10 % Pd/C (0.22 g)
was mixed with methanol (5 ml) in a two neck round bottom flask and H2 gas was bubbled
into the mixture while stirring. After 5 h the reaction mixture turned pink from orange. The
reaction mixture was filtered and solvent was evaporated to get shiny pinkish crude product
in 99 % yield which was recrystallized using ethanol to get pink colored crystal. The
1
specifications were as follow: H NMR (400 MHz, DMSO-d6, δ, ppm): 2.61 (s, 4H), 4.79 (s,
2H), 6.49 (d, 2H, J = 8 Hz), 6.85 (d, 2H). 13C NMR (100 MHz, DMSO-d6, δ, ppm): 37.1,
113.9, 128.7, 129.0, 146.3. Mass: m/z = 213.14217 (experimental), 212.1313 (calculated).
Melting point: 137 °C
2.3.2 PAAs and PIs syntheses
Poly(amic acid)s (PAAs) are synthesized by a reaction of prepared diamines such as DAS
with equimolar amounts of dianhydrides as shown in Scheme 2. The general procedure for
the synthesis of PAA is as follows. DAS (0.252 g, 1.2 mmol) was dissolved in DMAc (2.4 ml,
0.5 M) in a 10 mL flask under nitrogen atmosphere. Dianhydrides such as CBDA (0.235 g,
1.2 mmol), PMDA (0.261 g, 1.2 mmol), BPDA (0.353 g, 1.2 mmol), BTDA (0.387 g, 1.2
mmol), OPDA (0.372 g, 1.2 mmol) and DSDA (0.430 g, 1.2 mmol) were then added into the
diamine solution which produced a yellowish solution. The reaction mixture was vigorously
stirred by a mechanical stirrer with a propeller at room temperature for 48 h to yield a viscous
PAA solution. The PAA solution was diluted by suitable amount of DMAc, and then added
dropwise into water/methanol/acetone to precipitate as solid fibrils PAA which were
collected by filtration, washed thoroughly with warm water and dried in a vacuum. PAA film
of thickness 30-45 µm was obtained by dissolving polymer fibrils in DMAc/DMF forming a
yellow solution, poured on a silicon wafer / aluminum plate by spin coating (spin rate = 100
rpm for 2 min, 200 rpm for 2 min, 500 rpm for 1 min, MS-A100 Spincoater, Misaka Co.,
Ltd.) and dried by heating over hot plate. Polyimide (PI) films were obtained by stepwise

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thermal imidization of the PAAs film in an oven for 1 h each at 100, 150, 200 and 250 °C,
respectively, under vacuum. Similar procedure was repeated to get PAAs and PIs using
EDDA diamine and different dianhydride.
Scheme 2. Synthesis of bio-based PAAs and PIs from 4ACA derived monomers DAS and EDDA.
3. Results and Discussion
3.1 Monomer Synthesis
Olefin metathesis enables the redistribution of fragments of alkenes by scission and
regeneration of carbon-carbon double bonds[26]. In particular, Grubbs' catalysts are air-
tolerant and compatible with a wide range of solvents[27-31]. We developed a novel synthesis
route for aromatic diamines using Grubbs olefin metathesis reaction with the 4ACA
derivative which is bioavailable by microbial deamination using recombinant Escherichia
coli to possess the phenylalanine ammonia lyase activity[25, 32-34]
.
Initially, we tried to prepare DAS directly from the 4ACA metathesis reaction, but the
reaction did not proceed smoothly. Then, we protected the amine group and reduced the

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carboxyl group to alcohol, and then started a metathesis reaction. In order to reduce carboxyl
readily, the corresponding carboxylic acid was esterified by methanol in the presence of
TMSCl. LiAlH4 was utilized to reduce methyl ester to alcohol. The product 4-
aminocinnamyl alcohol was purified by repeated column chromatography. The product purity
was only 95 % due to the presence of inseparable impurities, which were removed in the next
step of the process. The free amine group of methyl-4-aminocinnamyl alcohol was acetylated
using acetic anhydride to avoid it from interfering in Grubbs olefin metathesis. The resulting
N-acetyl-4-aminocinnamyl alcohol was used for olefin metathesis along with Grubbs 2nd
generation catalyst and N,N’-deacetyl-DAS was successfully prepared with moderate yield.
The free diamine monomer DAS was prepared by deacetylation using HCl in methanol
followed by neutralization by ammonia. The diamine EDDA was prepared from DAS by
reducing the double bond using Pd/C and H2. The structures of all intermediates were
confirmed using 1H NMR, 13C NMR and FT-IR (Figures S1, S2 and S3).
Table 1: The yield, observation during polymerization, inherent viscosity (ηinh ), molecular
weight, and film properties of PAAs.
a
ηinh
Film
property
b
b
Polymer
Yield (%)
Mn
Mw
PDIb
(dL/g)
PAA-1a
PAA-2a
PAA-1b
PAA-1c
PAA-2c
PAA-1d
PAA-1e
PAA-1f
PAA-1fc
PAA-1fd
PAA-2f
96
94
96
98
98
90
91
92
91
92
92
6.62
2.50 X 105 4.04 X 105 1.62
3.07 X 105 4.71 X 105 1.53
1.72 X 105 2.21 X 105 1.29
2.48 X 105 3.82 X 105 1.57
2.35 X 105 3.84 X 105 1.63
2.22 X 105 3.23 X 105 1.48
1.83 X 105 2.95 X 105 1.61
2.43 X 105 3.73 X 105 1.53
2.82 X 105 4.30 X 105 1.52
2.86 X 105 4.42 X 105 1.54
2.15 X 105 3.27 X 105 1.51
Flexible
0.52
0.54
1.04
0.48
0.41
0.51
0.49
0.53
0.55
0.41
Flexible
Flexible
Flexible
Flexible
Flexible
Flexible
Flexible
Flexible
Flexible
Flexible
aηinh refers to inherent viscosities which are measured at a concentration 0.5 g/dL in DMAc at
b
30 °C, Mw, Mn, and PDI refer to the weight-average molecular weight, the number-average
molecular weight, and the distribution of polymer molecular weight of PAA, respectively,
which are measured using GPC. cPolymerization time is 8 h, dPolymerization time is 24 h.

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3.2 Polymer Syntheses
PAAs were prepared by polycondensation of the prepared diamine of DAS or EDDA with
stoichiometric amounts of the dianhydride CBDA, PMDA, BTDA, OPDA, BPDA, or DSDA
(Scheme 2). The resulting PAAs were abbreviated as PAA-1a, PAA-1b, PAA-1c, PAA-1d,
PAA-1e, and PAA-1f for DAS-based PAAs, and PAA-2a, PAA-2c, and PAA-2f for EDDA-
based PAAs as shown in Table 1. The structures of the PAAs were confirmed by NMR study
and conversion to PI was confirmed by IR spectroscopy (see Figures 1, 2 and 3 in Ref 38).
Highly viscous solutions were obtained after polymerization for each case except for PAA-
1a, which showed gel formation due to its ultrahigh viscosity. The weight-average molecular
weight (Mw), the number average molecular weight (Mn) and the molecular weight
distribution (PDI) were determined using GPC by dissolving PAAs in a suitable amount of
DMF and the results are summarized in Table 1. PAAs exhibited high molecular weights of
2.2 x 105 – 4.4 x105 g/mol for Mw and 1.7 x 105 – 2.8 x105 g/mol for Mn and PDI ranged from
1.29 to 1.61. Inherent viscosities of PAA solutions were determined at a concentration of 0.5
g/dL and were found to range from 0.41 to 6.62 dL/g at 30 °C thereby confirming the high
molecular weights of the PAAs (Table 1). Of all the bio-based PAAs, PAA-1a formed a gel
after polymerization and showed the highest viscosity possibly due to the aliphatic
cyclobutane ring of CBDA. Carboxylic acid attached to the CBDA ring in PAA-1 has a
higher reactivity than an aromatic acid, occasionally causing the addition of COOH to the
central double bond of stilbene moiety in PAA-1a, resulting in cross-linking of the polymer
chains. If the reaction occurred with only 1 % probability, the viscosity would be increased.
PAA films were then cast from the DMAc solution by spin-coating and evaporating the
solvent at 60-70 °C (Figure 1). DAS-based PAA films were yellow/orange colored while
EDDA-based films were colorless to light yellow. The PI films were obtained by stepwise
thermal imidization of PAA at 100, 150, 200, and 250 °C for 1 h at each step in a vacuum

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oven. The film color changed from yellow to dark orange after imidization due to more
efficient charge transfer between the diamine-based benzenes compared to the benzoic amic
acids, leading to the color change in resulting benzimides [35]. The complete imidization was
confirmed by FT-IR spectra. The PIs were represented as PI-1a, PI-2a, PI-1b, PI-1c, PI-2c,
PI-1d, PI-1e, PI-1f and PI-2f.
Figure 1. PAAs fibrils [(a) PAA-1a, (b) PAA-1c and (c) PAA-1f], PAAs film [(d)PAA-1a,
(e) PAA-1c and (f) PAA-1f] and PIs [(g) PI-1a, (h)PI-1c and (i) PI-1f]
3.3 Solubility
The solubility of all the prepared polymers was investigated in various solvents as shown in
Table S1. The solubility of the polymers was tested by dissolving them in three groups of
solvents at room temperature and at 50 °C. For those solvents whose boiling point was below
50 °C the solubility was checked at room temperature and at their boiling point. The three
groups of solvents were: (A) nonpolar solvents such as hexane, benzene, toluene,
dichloromethane (DCM), chloroform and diethyl ether, (B) polar protic solvents such as

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distilled water, methanol, ethanol, and concentrated sulfuric acid, and (C) polar aprotic
solvents such as acetone, acetonitrile, ethyl acetate, THF, DMF, DMAc, NMP and DMSO.
All of the PAAs prepared here were only soluble in polar aprotic solvents such NMP, DMAc,
DMF, and DMSO at room temperature. It was found that DAS-derived PIs were insoluble
even at 50 °C in all of the solvents shown above, while EDDA-derived PIs were soluble in
conc. H2SO4.
3.4 Thermal Properties
3.4.1 Thermogravimetric analysis (TGA)
Thermogravimetric analysis (TGA) was utilized in order to investigate the thermal
degradation of PIs. TGA was carried out under nitrogen atmosphere at a heating rate of 10
°C/min. Td5 and Td10 represents the 5% and 10% weight-loss temperatures, respectively, and
the results are summarized in Table 2 and shown in Figure 2. The Td5 values ranged between
397-550 °C while Td10 ranged between 406 and 600 °C, which indicates a high degree
resistance to thermal degradation. DAS-based PIs such as PI-1a, PI-1c, and PI-1f showed
higher Td5 and Td10 values compared to their respective EDDA-based PIs such as PI-2a, PI-2c
and PI-2f due to the extended conjugation in DAS-based PIs. PI-1d showed the highest Td10
value of 600 °C, while CBDA-derived PIs such as PI-1a and PI-2a showed Td10 values less
than 500 °C since they had fewer aromatics (i.e. benzene rings) than the others. PIs prepared
here showed higher Td10 values and high degree of thermal resistance than conventional bio-
based polymers reported thus far. Changing the atmosphere from pure nitrogen to air did not
significantly affect the stability of the PIs since air contains much more nitrogen than oxygen.
The PIs maintained their stability towards oxidative thermal degradation in nitrogen and air.
However, Td10 was found to drop by 20-50 °C under a pure oxygen atmosphere due to high
oxidative thermal degradation. Representative results of the TGA in different atmosphere of
PI-1f are shown in Figure 2B. Overall, PIs showed good thermal stability under nitrogen, air

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and oxygen atmospheres. TGA were carried out upto 650 °C as this temperature is high
enough to evaluate the thermal stability. However, TGA upto 800 °C was also carried out for
PI-1f to evaluate the residual weight which was found to be nearly 20 %.
100
90
80
70
60
50
40
30
20
PI-1a
PI-1b
PI-1c
PI-1d
PI-1e
PI-1f
PI-2a
PI-2c
PI-2f
100
200
300
400
500
600
Temperature (°C)
(A)
100
90
80
70
60
50
40
30
20
PI-1f-Nitrogen
PI-1f-Air
PI-1f-oxygen
100
200
300
400
500
600
Temperature (°C)
(B)
Figure 2. TGA curves of PI films measured under a nitrogen atmosphere (A) and TGA
curves of PI-1f in different atmosphere (B) at a heating rate of 10 °C/min
3.4.2 Differential scanning calorimetry (DSC)
Differential scanning calorimetry (DSC) was used to determine the Tg values of the PIs under
a nitrogen atmosphere and the data are summarized in Table 2. The backbone structure of

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dianhydride plays an important role in the Tg values of the PIs[36,37]. The Tg values of PI-1b
and PI-1e were determined to be 330 °C and 250 °C, respectively. None of the PIs had Tg
values below 350 °C, meaning that they could not show Tg values due to their decomposition
temperature was lower than Tg. The charge transfer from the electron rich bio-derived
diamine to the electron deficient dianhydride and the high stability of the 5-membered imide
ring due to extended n−π conjugation between the carbonyl group and the lone pair of
nitrogen atom could be the reasons for the high Tg values. Materials with high Tg values are
suitable for application as super-engineering plastics.
Table 2. Thermo-mechanical properties of bio-based PIs
TGA (°C)c
Tensile strength
at break
(MPa)a
Young’s
modulus
(GPa)a
ND
Elongation at
break
Tg
(°C)b
(%)a
Td5
Td10
PI-1a
PI-2a
PI-1b
PI-1c
PI-2c
PI-1d
PI-1e
PI-1f
PI-1fd
ND
ND
ND
ND
330
ND
ND
ND
250
ND
ND
400
400
445
550
535
540
490
445
440
460
435
565
585
575
600
580
500
500
24
ND
60
70
54
65
81
106
2.27
ND
2.3
2.82
2.4
4.3
3
1.1
ND
2.6
2.5
2.2
1.5
7.8
3.9
2.8
PI-1fe
132
ND
120
2.4
ND
0.3
5.6
ND
15.8
ND
ND
ND
440
395
430
495
405
555
PI-2f
TM
Kapton
aTensile strength at break, Young’s modulus, and elongation at break were measured using
b
tensiometer at room temperature, Tg referring to glass transition temperature was measured
by DSC at a heating rate of 10 °C/min under N2 atmosphere. Td5 , Td10 referring to
c
temperatures at 5 % and 10 % weight loss, respectively, which were measured using TGA at
a heating rate of 10 °C/min under N2, . ND refers to not determined., dPolymerization time is
8 h, ePolymerization time is 24 h.
3.5 Mechanical Properties
The mechanical properties such as tensile strength at break, Young’s modulus, and elongation
at break were determined using a tensiometer at an elongation speed of 0.5 mm/min at room

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temperature. The results are summarized in Table 2. As the degree of elongation at break
measures flexibility, PI-1f was found to be more flexible than the other PIs due the flexible
and kinked sulfone unit in the DSDA-derived moiety. PI-1a and PI-1b prepared from DAS
diamine and dianhydride PMDA and CBDA, respectively, were found to be brittle due to the
rigidity of their dianhydride-derived moieties. The brittleness made it impossible to prepare
PI films for tensile strength tests. The PI films had tensile strength at break values in the
range of 54-132 MPa, Young’s moduli in the range of 2.3-4.3 GPa, and elongation at break
values in the range of 1.5-7.8 %. Of all the films prepared here, the PI-1f film was the
strongest and toughest. PI-1f prepared by long agitation for 24 h showed an increased tensile
strength of 132 MPa, Young’s modulus of 2.4 GPa, and elongation at break of 5.6 %. The
tensile strength of PI-1f was found to be more than that of the commercially available, best
known and extensively used polyimide KaptonTM. Totally bio-based PI-1a was too brittle to
be examined for its tensile properties due to its highly rigid dianhydride CBDA and diamine
DAS. PI-2a was flexible enough but showed lower than expected mechanical properties.
3.6 UV-vis absorbance
UV-vis spectroscopy was carried out by dissolving suitable amounts of PAA in DMF. λmax of
the PAAs derived from DAS were found to be in the visible range due to the extended
conjugation by unsaturation as expected in compounds containing the stilbene moiety. The
λmax ranged from 348 to 358 nm depending on the type of dianhydride used. However,
complete saturation led to no extended conjugation in EDDA-derived PAAs and thus no
absorbance in the visible region (Figure 3). The
and 357 nm respectively) were found to be higher than those of other PAAs. The high values
of max could be due to the rigidity in the dianhydride structure and thus in their respective
PAAs. The max of PAA-1e was the lowest (348 nm) due to the presence of a carbonyl linker
between the two phenyl rings in BTDA. The max values of PAA-1d and PAA-1f were both
λmax values of PAA-1b and PAA 1c (358 nm
λ
λ
λ

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354 nm. Since the PIs were insoluble in any of the solvent PI films were used in order to
determine the transmittance. Figure 4 shows the wavelength dependence of transmittance of
the PI films, where the transmittance ranges from 38 to 72 %.
1
0.8
0.6
0.4
0.2
0
PAA-1a
PAA-1b
PAA-1c
PAA-1d
PAA-1e
PAA-1f
PAA-2f
300
350
400
450
500
550
600
Wavelength (cm)
Figure 3. UV-vis spectra of PAAs showing the
λ
max nearly about 354 nm for DAS based
PAAs.
100
80
60
40
20
0
PI-2a
PI-1a
PI-1b
PI-2c
PI-1c
PI-1d
PI-1e
PI-2f
PI-1f
PI-1f-24h
PI-1f-8h
200
300
400
500
600
700
800
Wavelength (nm)
Figure 4. Transmittance spectra of total bio-based and semi bio-based PIs showing no
transmittance upto 450 nm.

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4. Conclusion
A new method was employed to utilize the bio-derived material 4-aminocinnamic acid for the
synthesis of diamine monomers of polyimides via a series of reactions utilizing Grubb’s
olefin metathesis. The prepared diamine was utilized and a series of different PAA and PI
polymers were synthesized and found to be thermally and mechanically stronger than
conventional polyimides. PI-1f prepared by 24 h polymerization showed higher mechanical
properties than KaptonTM, which is a commercially available polyimide used extensively.
1
Supporting Information Available: Figure S1: H NMR spectra of (a) 4ACA, (b) methyl-
4ATA, (c) 4-aminocinnamyl alcohol, (d) N-acetyl-4-aminocinnamyl, (e) N,N’-diacteyl-DAC,
(f) DAS (g) EDDA. Figure S2: 13C NMR NMR spectra of (a) EDDA, (b) DAS, (c) N,N’-
diacteyl-DAC, (d) N-acetyl-4-aminocinnamyl, (e) 4-aminocinnamyl alcohol, (f) Methyl-
4ACA (g) 4ACA. Figure S3: FT-IR spectra of (a) Methyl-4ATA 4ACA, (b), (c) 4-
aminocinnamyl alcohol, (d) N-acetyl-4-aminocinnamyl, (e) N,N’-diacteyl-DAC, (f) DAS (g)
EDDA. Figure S4: GPC chromatogram of various representative polyamides. Figure S5:
TGA curves of PI-1f measured under a nitrogen atmosphere at a heating rate of 10 °C/min.
Table S1: Solubility of biobased PAAs and PIs in various solvents.
Acknowledgement
The research was financially supported by Advanced Low Carbon Technology Research and
Development Program (JST ALCA, 5100270), Tokyo, Japan and MEXT.
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Research highlights
•
Novel synthetic route for the synthesis of aromatic diamines from biomass based
material were developed fro.
•
•
Novel Semi and fully bio-based polyimides were prepared and characterized.
Ultrahigh tensile strength polyimide was developed.