Symmetric and asymmetric spiro-type colorless poly(ester imide)s with low coefficients of thermal expansion, high glass transition temperatures, and excellent solution-processability

Article abstract of DOI:10.1016/j.polymer.2019.02.020

In this work, we present several new poly(ester imide)s (PEsIs) with low coefficients of thermal expansion (CTE), excellent optical transparency, very high heat resistance (T_g), film ductility, and solution-processability. Symmetric and asymmet

Full text of DOI:10.1016/j.polymer.2019.02.020

Accepted Manuscript
Symmetric and asymmetric spiro-type colorless poly(ester imide)s with low
coefficients of thermal expansion, high glass transition temperatures, and excellent
solution-processability
Masatoshi Hasegawa, Shinya Takahashi, Soichi Tsukuda, Tomoki Hirai, Junichi Ishii,
Yukari Yamashina, Yoshinori Kawamura
PII:
S0032-3861(19)30151-X
DOI:
https://doi.org/10.1016/j.polymer.2019.02.020
JPOL 21259
Reference:
To appear in: Polymer
Received Date: 2 November 2018
Revised Date: 9 January 2019
Accepted Date: 10 February 2019
Please cite this article as: Hasegawa M, Takahashi S, Tsukuda S, Hirai T, Ishii J, Yamashina Y,
Kawamura Y, Symmetric and asymmetric spiro-type colorless poly(ester imide)s with low coefficients of
thermal expansion, high glass transition temperatures, and excellent solution-processability, Polymer
(2019), doi: https://doi.org/10.1016/j.polymer.2019.02.020.
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ACCEPTED MANUSCRIPT
Graphical Abstract
Symmetric and asymmetric spiro-type colorless poly(ester imide)s with low coefficients of
thermal expansion, high glass transition temperatures, and excellent solution-processability
Masatoshi Hasegawa*, Shinya Takahashi, Soichi Tsukuda, Tomoki Hirai, Junichi Ishii
Yukari Yamashina, Yoshinori Kawamura
Solution casting of the material shown in the figure led to a colorless film with a low yellowness
–
1
index (3.4), a considerably low coefficient of thermal expansion (10.5 ppm K ), a very high T
g
(351 ºC), and a high tensile modulus (6.12 GPa).
Photo of the film
Backlight
Polarizer
TAC
&
LC cell
Optoelectronic Application
Plastic
substrate
Polarizer
TAC
&
Imagedisplaydevices

ACCEPTED MANUSCRIPT
POLYMER-18-2598 R1
Symmetric and asymmetric spiro-type colorless poly(ester imide)s with low coefficients of
thermal expansion, high glass transition temperatures, and excellent solution-processability
1
1
1
1
1
Masatoshi Hasegawa* , Shinya Takahashi , Soichi Tsukuda , Tomoki Hirai , Junichi Ishii
2
2
Yukari Yamashina , Yoshinori Kawamura
1
2
Department of Chemistry, Faculty of Science, Toho University,
2
-2-1 Miyama, Funabashi, Chiba 274-8510, Japan.
Taoka Chemical Co., Ltd.,
-2-11 Nishimikuni, Yodogawa, Osaka 532-0006, Japan.
4
----------------------------------------------------------------------------------------------------
*
Correspondence to: Masatoshi Hasegawa, Department of Chemistry, Faculty of Science, Toho
University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan.
E-mail: mhasegaw@chem.sci.toho-u.ac.jp
1

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Abstract
In this work, we present several new poly(ester imide)s (PEsIs) with low coefficients of
thermal expansion (CTE), excellent optical transparency, very high heat resistance (T ), film
g
ductility, and solution-processability. Symmetric and asymmetric spiro-type tetracarboxylic
dianhydrides containing ester linkages (TA-s-Spiro and TA-a-Spiro) and diamines (AB-s-Spiro
and AB-a-Spiro) were synthesized using xanthene-based isomeric bisphenols with a fluorenyl
side group. The chemically imidized PEsIs were highly soluble in various common solvents
including less polar non-amide solvents, and yielded stable solutions with high solid contents.
The properties of the spiro-type PEsIs were systematically investigated and compared with those
of the cardo-type counterparts. A PEsI derived from 1,2,3,4-cyclobutanetetraccarboxylic
dianhydride (CBDA), AB-a-Spiro, and 2,2′-bis(trifluoromethyl)benzidine (TFMB) achieved
−
1
outstanding combined properties, i.e., a very low CTE (10.5 ppm K ), excellent optical
transparency (YI = 3.4, T400 = 80.8%), a very high T (351 °C) and solution-processability. Thus,
g
the PEsIs are promising candidates as novel plastic substrates for use in image display devices.
The isomer effects on the properties were also investigated and a possible mechanism for these
effects is proposed.
Keywords: Poly(ester imide)s; Spiro structure; Cardo structure; Optical transparency;
Coefficient of thermal expansion (CTE); Solution processability; Heat-resistant plastic substrates
2

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1
. Introduction
Heat-resistant colorless polymers are key materials for use in optical and optoelectronic
applications. Colorless plastic substrate materials have been investigated as alternatives to current
inorganic glass substrates to allow the upsizing of display devices and concomitant weight saving,
as well as the realization of foldable or curved displays. These plastic substrates must have very
high short-term heat resistance (i.e., glass transition temperature: T > 300 °C, desirably > 350 or
g
4
00 °C) to support the high-temperature processes used in device fabrication. Therefore, even
poly(ether sulfone) (PES), which has the highest T (225 °C [1]) among commercially available
g
super-engineering plastics, is not always suitable as the plastic substrates. On the other hand,
wholly aromatic polyimides (PIs) are reliable heat-resistant polymers, and some have very high
Tg values, exceeding 350 °C [2–7]. However, wholly aromatic PI films are in general intensely
colored because of charge-transfer (CT) interactions [8], which often limit their optical and
optoelectronic applications. Therefore, optically transparent (colorless) PIs and other
high-temperature polymers have been studied in academia and industry as promising candidate
plastic substrates [9–32]. The most effective strategy for eliminating PI film coloration is to
disturb the CT interactions by using aliphatic (usually cycloaliphatic) monomers either diamines
or tetracarboxylic dianhydrides or both [8–27].
The plastic substrates for optoelectronics must also have excellent dimensional stability
3

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during the multiple thermal cycles used in the device fabrication processes; this can be achieved
by significantly reducing their linear coefficients of thermal expansion (CTE) in the film plane
(
X–Y) direction in the glassy temperature regions (< T ). However, non-stretched polymer films
g
prepared by solution casting or melt extrusion molding usually show high CTE values (50–120
–
1
ppm K [33] because of the practically three-dimensionally random chain orientation, which
causes significant thermal expansion–contraction behavior during thermal cycling. This causes
serious problems, such as misalignment and adhesion failure of various micro-components,
laminate warpage, and transparent electrode breakdown.
A low thermal expansion property is achieved when there is a high degree of chain alignment
in the X–Y direction (in-plane orientation), which prominently occurs during the thermal
imidization of PI precursor [poly(amic acid)s (PAAs)] films formed on substrates only when the
PI systems have linear and rigid backbone structures [34–37]. However, previously reported
cycloaliphatic monomers with structural linearity/planarity, which is favorable for inducing
prominent in-plane orientation, are practically limited to trans-1,4-cyclohexanediamine
(
t-CHDA) and 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA). For example, the
combination of t-CHDA and rigid aromatic tetracarboxylic dianhydrides [e.g.,
,3′4,4′-biphenyltetracarboxylic dianhydride (s-BPDA)] provides colorless PI films with very low
3
CTE values [38,39], as shown in Fig. 1. However, the use of t-CHDA causes the formation of
4

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poorly soluble salts in anhydrous solvents (usually amide solvents such as
N,N-dimethylacetamide (DMAc)] in the initial stages of the PAA polymerization process, which
often results in the termination of PAA polymerization or greatly extends the reaction periods
until the reaction mixture becomes homogeneous [21,27,39,40]. In contrast, there is no salt
formation problem when CBDA was combined with rigid aromatic diamines [typically,
2
,2′-bis(trifluoromethyl)benzidine (TFMB)], and this system leads to a colorless PI film with a
relatively low CTE through the conventional two-step process (PAA casting on a substrate +
thermal imidization) [38]. However, the imidized forms of these transparent low-CTE systems
are not soluble in common solvents.
We have previously revealed that a somewhat complicated film preparation method via
chemical imidization (i.e., chemical imidization at room temperature in solution + isolation of the
PI powder + re-dissolution in fresh solvents + coating/drying) is superior to the conventional
process (PAA solution coating/drying + thermal imidization at elevated temperatures) in terms of
achieving both optical transparency and a low CTE in the resultant PI films [27]. This means that
compatibility with the chemical imidization process holds the key to achieving our present goals.
The chemical imidization process can also be applied to highly soluble PI systems. Otherwise, on
the addition of a dehydrating agent [acetic anhydride (Ac O)/pyridine mixture] to PAA solutions
2
during chemical imidization, the reaction mixtures become inhomogeneous with gelation or
5

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precipitation of the half-imidized portion, and subsequent casting from a homogeneous PI
solution is inhibited. Unfortunately, the above-mentioned semi-aromatic transparent PIs are not
compatible with the chemical imidization process because of their insolubility.
A variety of solubility-improving groups, linkages, and structural units have been reported in
the literature, e.g., bulky and non-polarized substituents (CF [10,23,28,41–45], tert-butyl [46],
3
and phenyl side groups [47,48]), highly polar and bent connecting groups (–SO – groups [32,49]),
2
highly twisted/distorted units (2,2′-biphenyl group [50]), bent and asymmetric structural units
[51,52], non-planar cycloaliphatic units [19], and cardo structures [53,54]. However, these
approaches for solubility improvement mostly reduce in the chain linearity/rigidity, consequently
sacrificing the low CTE.
We have previously reported that poly(ester imide)s (PEsIs) obtained using ester-linked
cardo-type tetracarboxylic dianhydride with 9-fluorenyl (FL) side group (TA-BPFL, Fig. 1) show
enhanced solubility compared to the corresponding cardo-type poly(ether imide)s [55]. For
example, the combination of TA-BPFL and t-CHDA (Fig. 1) led to a PEsI soluble in hot
N-methyl-2-pyrrolidone (NMP) [55], even though t-CHDA-based PIs are usually quite insoluble.
The significantly improved solubility of TA-BPFL/t-CHDA is probably attributed to a combined
effect of the ester linkages and the bulky FL side group of TA-BPFL, which has a perpendicularly
directed molecular plane to the main chains, as shown in Fig. 1. However, the TA-BPFL/t-CHDA
6

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PEsI film did not show low CTE behavior, probably reflecting the “hinge” structure at the central
3
sp carbon atom of TA-BPFL (Fig. 1), which significantly reduces the overall chain linearity,
consequently, the in-plane chain orientation was disturbed. The results motivated us to modify
TA-BPFL to create a local coplanar structure by the formation of ether-bridge between the two
9
-phenolic groups on the FL unit [i.e., formation of a xanthene (XAN) unit with a spiro structure],
whereby the local molecular planarity/linearity can be enhanced.
One study [56] reported that poly(ether imide)s derived from an ether-linked spiro-type
diamine containing a XAN unit and common aromatic tetracarboxylic dianhydrides showed good
solubility and relatively high T values, although the CTE was not reported. As discussed later,
g
this type of poly(ether imide) does not usually have low CTE values owing to their decreased
overall main chain linearity. On the other hand, our target monomers, i.e., ester-linked spiro-type
monomers with a FL-pendant XAN unit have the potential to improve the low CTE property
while maintaining excellent solubility (i.e., compatibility with chemical imidization process). In
this study, we investigated the effects of symmetric spiro-type monomers with ester linkages on
the current target properties (transparency, solubility, CTE, and T ) and compared them with
g
those of the asymmetric counterparts. The results suggest that some of the spiro-type PEsIs
developed in this work are promising novel plastic substrate materials for use in image display
devices and other optoelectronic materials.
7

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2
2
2
. Experimental
.1. Materials
.1.1. Monomer synthesis
Spiro(fluorene-9,9′-xanthene]-3′,6′-diol (s-Spiro FLBP)
Spiro-type bisphenols and related monomers were synthesized using raw materials listed in
Supplementary Data 1. First, we carried out the synthesis of a symmetric spiro-type bisphenol
(s-Spiro FLBP, Fig. 2) without solvent [56] or in toluene [57]. The previously reported synthetic
procedures gave rise to an orange- or yellow-colored product, which was the mixtures of the
desired bisphenol and a minor fraction of a dimeric by-product estimated by liquid
chromatography–mass spectrometry (Fig. 2). The latter is probably responsible for the intense
coloration of the product. Then we carried out the synthesis by a sophisticated method using
water as a solvent [58]; 9-fluorenone (9-FLN, 39.12 mmol), resorcinol (RC, 313.79 mmol), and
1
5
5
-dodecanethiol (1.56 mmol) was suspended in water (5.75 mL) in a 300 mL-flask and heated at
5–60 °C. To the reaction mixture, conc. HCl (8.47 mL) was added very slowly, and refluxed at
5–60 °C for 8 h with continuous stirring. Subsequently, water (43.1 mL) was added and
neutralized with a NaOH aqueous solution in an ice bath. The pale pink precipitate formed was
collected by filtration, washed with water, and dried at 120 °C for 12 h under vacuum. The
8

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product was dissolved in 2-propanol, and an undissolved portion was filtered out. Subsequently,
the product was recrystallized from a mixed solvent (2-propanol/water, 4/1, v/v), and dried at
1
00 °C for 12 h under vacuum (total yield: 74 %). The analytical data of the product is as follows.
–
1
FT-IR (KBr plate method, cm ): 3505/3405 (O–H), 3061/3036 (Carom–H), 1262/1171 (Carom–O–
1
Carom). H-NMR [400 MHz, dimethyl sulfoxide (DMSO)-d ,
δ
, ppm]: 9.61 [s, 2H (the measured
6
relative integrated intensity: 2.00H), OH], 7.92 [d, 2H(2.04H), J = 7.6 Hz, 4,5-protons of the
fluorene (FL) unit], 7.37 [t, 2H (2.07H), J = 7.4 Hz, 3,6-protons of FL], 7.22 [t, 2H (2.07H), J =
7
.5 Hz, 2,7-protons of FL], 7.02 [d, 2H (2.03H), J = 7.6 Hz, 1,8-protons of FL], 6.58 [sd, 2H
2.04H), J = 2.4 Hz, 4,5-protons of the xanthene (XAN) unit], 6.26 [dd, 2H (2.01H), J = 8.6, 2.4
Hz, 2,7-protons of XAN], 6.03 [d, 2H (2.00H), J = 8.6 Hz, 1,8-protons of XAN]. Elemental
(
−
1
analysis: Calcd. (%) for C H O (364.40 g mol ): C, 82.40; H, 4.43, Found: C, 82.47; H, 4.52.
25
16
3
Melting point determined from an endothermic peak by differentia scanning calorimetry (DSC):
65 °C. These data confirmed that the product is the desired 3,6-dihydroxy-substituted form
s-Spiro FLBP) shown below.
2
(
s-Spiro FLBP
9

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Spiro(fluorene-9,9′-xanthene)-2′,6′-diol (a-Spiro FLBP)
An asymmetric-type isomer of s-Spiro FLBP, a-Spiro FLBP, was synthesized using 9-FLN
(32 mmol), RC (157 mmol), and hydroquinone (HQ, 157 mmol) in the same way as the
procedures for the synthesis of s-Spiro FLBP. Thin-layer chromatography (TLC) using silica gel
and CHCl /ethyl acetate (6/1, v/v) as an eluent for the product showed four spots with the Rf
3
values of 0.67 (obscure), 0.58, 0.39, and 0 (obscure), which correspond to 2,7-, 2,6-, and
3
,6-dihydroxy-substituted compounds, and predicted dimeric compound, respectively (Fig. 2).
Column chromatography (Wakogel C-300, = 40–64 m) using a mixed eluent (CHCl /ethyl
ϕ
µ
3
acetate, 12/1, v/v) was effective for isolating the desired 2,6-dihydroxy-substituted form (a-Spiro
FLBP); a single spot (R = 0.58) was observed on TLC after this procedure. An oily product was
f
obtained after solvent evaporation of the separated fraction. The oily product turned into a
powder form by addition of n-hexane and successive solvent removal. The solid product was
washed with water and dried at 100 °C for 12 h under vacuum. The analytical data of the
–
1
pale-yellow product obtained is as follows. FT-IR (KBr plate method, cm ): 3512/3446 (O–H),
1
3
059/3034/3010 (Carom–H), 1240 (Carom–O–Carom). H-NMR [400 MHz, DMSO-d ,
δ
, ppm]: 9.59
6
[
s, 1H (1.00H), 6-OH], 8.91 [s, 1H (1.07H), 2-OH], 7.95 [d, 2H (2.07H), J = 7.6 Hz, 4,5-protons
of FL], 7.39 [t, 2H (2.07H), J = 7.5 Hz, 3,6-protons of FL], 7.24 [t, 2H (2.05H), J = 7.5 Hz,
,7-protons of FL], 7.09–7.05 [m, 3H (3.09H), 1,8-protons of FL + 4-proton of XAN], 6.61 [dd,
2
1
0

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1
H (1.06H), J = 8.8, 2.9 Hz, 3-protons of XAN], 6.57 [sd, 1H (1.08H), J = 2.4 Hz, 5-protons of
XAN], 6.25 [dd, 1H (1.07H), J = 8.4, 2.3 Hz, 7-protons of XAN], 6.03 [d, 1H (1.03H), J = 8.6 Hz,
-protons of XAN], 5.65 [sd, 1H (1.08), J = 2.9 Hz, 1-proton of XAN]. Elemental analysis: Calcd.
8
−
1
(
%) for C H O (364.40 g mol ): C, 82.40; H, 4.43, Found: C, 82.00; H, 4.50. Melting point
25 16 3
(DSC): 228 °C. These data confirmed that the product is the desired 2,6-dihydroxy-substituted
form (a-Spiro FLBP) shown below.
a-Spiro FLBP
Ester-linked s-spiro-type tetracarboxylic dianhydride (TA-s-Spiro)
An ester-linked s-spiro-type tetracarboxylic dianhydride was synthesized according to the
reaction scheme shown in Fig. 3. s-Spiro FLBP (10.01 mmol) was dissolved in anhydrous
tetrahydrofuran (THF, 47.1 mL) in the presence of pyridine (60 mmol, 4.85 mL) as an HCl
acceptor in a sealed flask with a septum cap. In a separate sealed flask, trimellitic anhydride
chloride (TMAC, 30.09 mmol) was dissolved in THF (16.6 mL). To the TMAC solution cooled at
0
°C, the s-Spiro FLBP solution was slowly added using a syringe with continuous magnetic
stirring, after which the reaction mixture was stirred at room temperature for 12 h. The precipitate
11

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formed was collected by filtration and washed with THF and subsequently water. The white
product was dried at 160 °C for 12 h to ensure cyclodehydration of a hydrolyzed portion (yield:
–
1
6
7%). The analytical data of the product is as follows. FT-IR (KBr plate method, cm ): 3066
(Carom–H), 1856/1782 (anhydride C=O), 1739 (ester C=O), 1493 (phenyl), 1224/1168 (Carom–O–
–
1
Carom), and the absence of the absorption bands at 3400–3500 cm (O–H) from the unreacted
–
1
s-Spiro FLBP and ~2600 cm (hydrogen-bonded carboxylic acid O–H) from the hydrolyzed
1
product. H-NMR [400 MHz, DMSO-d ,
δ
, ppm]: 8.62–8.58 [m, 4H (4.01H), 3,3′- + 5,5′-protons
6
of the phthalic anhydride (PAn) unit], 8.27 [d, 2H (2.02H), J = 7.8 Hz, 6,6′-protons of PAn], 8.04
d, 2H (2.00H), J = 7.8 Hz, 4,5-protons of FL], 7.49–7.46 [m, 4H (4.01H), 3,6-protons of FL +
,5-protons of XAN], 7.32 [t, 2H (2.02H), J = 7.6 Hz, 2,7-protons of FL], 7.21 [d, 2H (2.02H), J
7.6 Hz, 1,8-protons of FL], 6.94 [d, 2H (2.00H), J = 8.6 Hz, 2,7-protons of XAN], 6.40 [d, 2H
2.03H), J = 8.6 Hz, 1,8-protons of XAN]. Elemental analysis: Calcd. (%) for C H O (712.63
[
4
=
(
4
3
20 11
−
1
g mol ): C, 72.47; H, 2.83, Found: C, 72.61; H, 2.96. Melting point (DSC): 331 °C. These data
confirmed that the product is the desired compound (TA-s-Spiro) shown below.
TA-s-Spiro
1
2

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The abbreviations, purification methods, and melting points for all the spiro-type monomers
synthesized in this work are summarized in Supplementary Data 2.
For a comparison, ester-linked cardo-type counterpart (TA-Cardo, Fig. 3) was also
synthesized in a similar manner. The analytical data are shown in Supplementary Data 3.
Ester-linked a-spiro-type tetracarboxylic dianhydride (TA-a-Spiro)
An isomer of TA-s-Spiro, TA-a-Spiro (Fig. 3), was synthesized from a-Spiro FLBP (5.03
mmol) and TMAC (15.01 mmol) in anhydrous acetone in the presence of pyridine. After the
reaction, the solvent was removed, and the pale-yellow solid obtained was washed with toluene
and subsequently water, and dried at 200 °C for 12 h under vacuum. The crude product was
recrystallized from a mixed solvent (toluene/acetic anhydride, 25/2, v/v), and vacuum-dried at
–
2
00 °C for 12 h (total yield: 50%). The analytical data is follows. FT-IR (KBr plate method, cm
1
): 3066 (Carom–H), 1863/1780 (anhydride C=O), 1760/1736 (ester C=O), 1488 (phenyl), 1223
–
1
(ester C–O), 1163 (Carom–O–Carom), and the absence of the absorption bands at 3400–3500 cm
–
1
(
O–H) from the unreacted a-Spiro FLBP and ~2600 cm (hydrogen-bonded carboxylic acid O–
1
H) from the hydrolyzed product. H-NMR [400 MHz, DMSO-d ,
δ
, ppm]: 8.62–8.59 [m, 2H
6
(2.09H), 3,6-protons of PAn], 8.48–4.44 [m, 2H (2.02H), 3′,6′-protons of PAn], 8.27 [d,
1
H(1.07H), J = 7.8 Hz, 5-proton of PAn], 8.15 [d, 1H (1.00H), J = 7.8 Hz, 5′-proton of PAn],
1
3

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8
.01 [d, 2H (2.00H), J = 7.6 Hz, 4,5-protons of FL], 7.49–7.44 [m, 4H (4.03H), 3,6-protons of FL
+
3,5-protons of XAN], 7.36–7.30 [m, 3H (3.05H), 2,7-protons of FL + 4-proton of XAN], 7.22
d, 2H (2.04H), J = 7.6 Hz, 1,8-protons of FL], 6.92 [dd, 1H (1.00H), J = 8.6, 2.3 Hz, 7-proton of
XAN], 6.36–6.34 [m, 2H (2.01H), 1,8-protons of XAN]. Elemental analysis: Calcd. (%) for
[
−
1
C H O (712.63 g mol ): C, 72.47; H, 2.83, Found: C, 72.44; H, 3.16. Melting point (DSC):
43
20 11
2
94 °C. These data confirmed that the product is the desired compound (TA-a-Spiro) shown
below.
TA-a-Spiro
Ester-linked s-spiro-type diamine (AB-s-Spiro)
AB-s-Spiro was synthesized according to the reaction scheme shown in Fig. 3. The detailed
procedures are as follows. 4-Nitrobenzoyl chloride (4-NBC, 30.0 mmol) was dissolved in
anhydrous THF (9.4 mL) in a sealed flask. In another sealed flask, s-Spiro FLBP (10.02 mmol)
was dissolved in anhydrous THF (47.1 mL) in the presence of pyridine (60 mmol). To the 4-NBC
solution cooled to 0 °C, the s-Spiro FLBP solution was slowly added using a syringe with
continuous magnetic stirring, after which the reaction mixture was stirred at room temperature for
1
4

ACCEPTED MANUSCRIPT
1
2 h. The pale-yellow precipitate formed was collected by filtration and washed with a small
quantity of THF, a large quantity of water, and methanol, and vacuum-dried at 120 °C for 12 h
–
1
(
yield: 68%). The analytical data of the product as follows. FT-IR (KBr plate method, cm ):
3
075 (Carom–H), 1742 (ester C=O), 1522/1347 (NO ), 1486 (phenyl), 1239/1152 (Carom–O–Carom),
2
and the absence of the absorption bands at 3400–3500 (O–H) from unreacted s-Spiro FLBP.
1
H-NMR [400 MHz, DMSO-d6, δ, ppm]: 8.41 [d, 4H (4.04H), J = 9.0 Hz, 2,2′,6,6′-protons of the
nitrobenzene (NB) unit], 8.34 [d, 4H (4.03H), J = 9.0 Hz, 3,3′,5,5′-protons of NB], 8.04 [d, 2H
(
2.01H), J = 7.6 Hz, 4,5-protons of FL], 7.47 [t, 2H (2.04H), J = 7.5 Hz, 3,6-protons of FL], 7.42
sd, 2H (2.03H), J = 2.4 Hz, 4,5-protons of XAN], 7.31 [t, 2H (2.04H), J = 7.5 Hz, 2,7-protons of
[
FL], 7.20 [d, 2H (2.00H), J = 7.5 Hz, 1,8-protons of FL], 6.89 [dd, 2H (2.05H), J = 8.6, 2.4 Hz,
,7-protons of XAN], 6.39 [d, 2H (2.00H), J = 8.6 Hz, 1,8-protons of XAN]. Melting point
2
(DSC): 292 °C. These data confirmed that the product is the desired dinitro compound
(NB-s-Spiro) shown below.
NB-s-Spiro
The nitro groups of NB-s-Spiro were reduced as follows. NB-Spiro (5.80 mmol) was
1
5

ACCEPTED MANUSCRIPT
dissolved in N,N-dimethylformamide (DMF, 100 mL) and Pd/C (0.424 g) as a catalyst was added
to this solution. The reaction mixture was refluxed at 100 °C for 4 h in a hydrogen atmosphere
and cooled to room temperature. After the catalyst residue was filtered out, the filtrate was
concentrated by an evaporator, and water (200 mL) was added to the flask. The white precipitate
formed was collected by filtration, washed with water and methanol, and dried at 120 °C for 12 h
under vacuum (yield: 81%). The analytical data of the product as follows. FT-IR (KBr plate
–
1
method, cm ): 3480/3375/3218 (amine N–H), 3066 (Carom–H), 1708 (ester C=O), 1628 (NH2,
1
deformation), 1517/1489 (phenyl), 1237/1172 (Carom–O–Carom). H-NMR [400 MHz, DMSO-d ,
6
δ, ppm]: 8.01 [d, 2H (2.01H), J = 7.5 Hz, 4,5-protons of FL], 7.77 [d, 4H (4.05H), J = 8.7 Hz,
3,3′,5,5′-protons of the aniline (AN) unit], 7.46 [t, 2H (2.03H), J = 7.4 Hz, 3,6-protons of FL],
7.31 [t, 2H (2.04H), J = 7.5 Hz, 2,7-protons of FL], 7.20 [sd, 2H (2.02H), J = 2.3 Hz, 4,5-protons
of XAN], 7.17 [d, 2H (2.02H), J = 7.6 Hz, 1,8-protons of FL], 6.74 [dd, 2H (2.02H), J = 8.5, 2.3
Hz, 2,7-protons of XAN], 6.62 [d, 4H (4.04H), J = 8.7 Hz, 2,2′,6,6′-protons of AN], 6.32 [d, 2H
(
2.03H), J = 8.6 Hz, 1,8-protons of XAN], 6.19 [s, 4H (4.00H), NH ]. Elemental analysis: Calcd.
2
−
1
(
%) for C H O N (602.65 g mol ): C, 77.73; H, 4.35; N, 4.65, Found: C, 77.52; H, 4.50; N,
39 26 5 2
4
.67. Melting point (DSC): 274 °C. These data confirmed that the product is the desired diamine
(AB-s-Spiro) shown below.
1
6

ACCEPTED MANUSCRIPT
AB-s-Spiro
For a comparison, ester-linked cardo-type counterpart (AB-Cardo, Fig. 3) was also
synthesized in a similar manner. The analytical data are shown in Supplementary Data 4.
Ester-linked a-spiro-type diamine (AB-a-Spiro)
An isomer of AB-s-Spiro, AB-a-Spiro (Fig. 3), was synthesized using a-Spiro FLBP in a
similar manner to that in the synthesis of the symmetric counterpart. A pale-yellow product was
obtained from a-Spiro FLBP and 4-NBC with a yield of 70%. The analytical data of the product
–
1
is as follows. FT-IR (KBr plate method, cm ): 3076 (Carom–H), 1737 (ester C=O), 1524/1348
(
NO ), 1490 (phenyl), 1177 (Carom–O–Carom), and the absence of the absorption bands at 3400–
2
1
3
500 (O–H) from unreacted a-Spiro FLBP. H-NMR [400 MHz, DMSO-d ,
δ
, ppm]: 8.42 [d, 2H
6
(2.05H), J = 8.9 Hz, 2,6-protons of NB], 8.34 [d, 2H (2.02H), J = 8.9 Hz, 3,5-protons of NB],
8
3
.29 [d, 2H (2.01H), J = 8.8 Hz, 2′,6′-protons of NB], 8.19 [d, 2H (2.02H), J = 9.0 Hz,
′,5′-protons of NB], 8.01 [d, 2H (2.05H), J = 7.6 Hz, 4,5-protons of FL], 7.48–7.43 [m, 3H
(3.02H), 3,6-protons of FL + 3-proton of XAN], 7.41 [sd, 1H (1.02H), J = 2.4 Hz, 5-proton of
1
7

ACCEPTED MANUSCRIPT
XAN], 7.33–7.29 [m, 3H (3.05H), 2,7-protons of FL + 4-proton of XAN], 7.21 [d, 2H (2.03H), J
=
7.6 Hz, 1,8-protons of FL], 6.88 [dd, 1H (1.04H), J = 8.6, 2.4 Hz, 7-proton of XAN], 6.35 [d,
1
H (1.01H), J = 8.6 Hz, 8-proton of XAN], 6.27 [sd, 1H (1.00H), J = 2.8 Hz, 1-proton of XAN].
Melting point (DSC): 301 °C. These data confirmed that the product is the desired dinitro
compound (NB-a-Spiro) shown below.
2
NO2
1
3
4
1
0
4
5
O
O
6
6
3
O
5
3
'
2
O
2
'
'
4
'
9
9
7
O
1
8
1
8
5
'
1
O N
2
2
7
6'
3
6
4
5
NB-a-Spiro
The catalytic reduction of NB-a-Spiro was carried out in the same way as the procedures used
for the symmetric counterpart and a white product was obtained with a yield of 86%. The
–
1
analytical data of the product is as follows. FT-IR (KBr plate method, cm ): 3459/3363/3217
(
amine N–H), 3060 (Carom–H), 1714 (ester C=O), 1631 (NH , deformation), 1516/1479 (phenyl),
2
1
1
167 (Carom–O–Carom). H-NMR [400 MHz, DMSO-d ,
δ
, ppm]: 7.99 [d, 2H (2.06H), J = 7.5 Hz,
6
4
8
,5-protons of FL], 7.77 [d, 2H (2.05H), J = 8.7 Hz, 3,5-protons of AN], 7.52 [d, 2H (2.02H), J =
.8 Hz, 3′,5′-protons of AN], 7.44 [t, 2H (2.05H), J = 7.5 Hz, 3,6-protons of FL], 7.39 [d, 1H
(
1.02H), J = 8.9 Hz, 4-proton of XAN], 7.30 [t, 2H (2.01H), J = 7.6 Hz, 2,7-protons of FL], 7.22
sd, 1H (1.01H), J = 2.4 Hz, 5-protons of XAN], 7.19 [d, 2H (2.03H), J = 7.5 Hz, 1,8-protons of
[
1
8

ACCEPTED MANUSCRIPT
FL], 7.15 [dd, 1H (1.07H), J = 8.9, 2.7 Hz, 3-proton of XAN], 6.73 [dd, 1H (1.02H), J = 8.6, 2.4
Hz, 7-protons of XAN], 6.63 [d, 2H (2.01H), J = 8.8 Hz, 2,6-protons of AN], 6.52 [d, 2H (2.08H),
J = 8.8 Hz, 2′,6′-protons of AN], 6.29 [d, 1H (1.02H), J = 8.5 Hz, 8-proton of XAN], 6.20 [s, 2H
(
2.00H), 1-NH ], 6.13 [s, 2H (2.05H), 1′-NH ], 6.03 [sd, 1H (1.00H), J = 2.7 Hz, 1-proton of
2
2
−
1
XAN]. Elemental analysis: Calcd. (%) for C H O N (602.65 g mol ): C, 77.73; H, 4.35; N,
3
9
26
5
2
4
.65, Found: C, 77.25; H, 4.48; N, 4.78. Melting point (DSC): 292 °C. These data confirmed that
the product is the desired diamine (AB-a-Spiro) shown below.
AB-a-Spiro
Ether-linked s-spiro-type diamine (AP-s-Spiro)
For comparison with ester-linked s-spiro-type diamine, an ether-linked counterpart was
synthesized according to the reaction scheme shown in Supplementary Data 5. The detailed
procedures are as follows. s-Spiro-FLBP (12.66 mmol) and 4-fluoronitrobenzene (4-FNB) were
dissolved in DMAc (30 mL) in the presence of K CO (29.60 mmol), and refluxed at 160 °C for
2
3
4
h in a nitrogen atmosphere. The reaction mixture was slowly poured into a large quantity of
water. The pale-yellow precipitate formed was collected by filtration, washed with water, and
1
9

ACCEPTED MANUSCRIPT
dried at 120 °C for 12 h under vacuum (yield: 98%). The analytical data of the product is as
–
1
follows. FT-IR (KBr plate method, cm ): 3070 (C –H), 1522/1343 (NO ), 1483 (phenyl),
arom
2
1
230/1150 (Carom–O–Carom), and the absence of the absorption bands at 3400–3500 (O–H) from
1
unreacted s-Spiro FLBP. H-NMR [400 MHz, DMSO-d ,
δ
, ppm]: 8.26 [d, 4H (4.06H), J = 9.3
6
Hz, 2,2′,6,6′-protons of NB], 8.02 [d, 2H (2.00H), J = 7.6 Hz, 4,5-protons of FL], 7.46 [t, 2H
1.99H), J = 7.5 Hz, 3,6-protons of FL], 7.32 [t, 2H (1.90H), J = 7.6 Hz, 2,7-protons of FL],
.21–7.17 [m, 6H (6.05H), 3,3′,5,5′-protons of NB + 1,8-protons of FL], 7.13 [sd, 2H (2.05H), J
2.5 Hz, 4,5-protons of XAN], 6.72 [dd, 2H (2.05H), J = 8.6, 2.5 Hz, 2,7-protons of XAN], 6.37
d, 2H (2.04H), J = 8.6 Hz, 1,8-protons of XAN]. Melting point (DSC): 190 °C. These data
confirmed that the product is the desired dinitro compound (NP-s-Spiro) shown below.
(
7
=
[
NP-s-Spiro
NP-Spiro (12.4 mmol) was dissolved in 1,4-dioxane (75 mL) in the presence of Pd/C (0.746
g), and refluxed at 80 °C for 8 h in a hydrogen atmosphere. After the catalyst residue was filtered
out, the filtrate was slowly poured into a large quantity of water. The white precipitate formed
was collected by filtration, washed with water and methanol, and recrystallized from toluene
2
0

ACCEPTED MANUSCRIPT
–
1
(
yield: 42%). The analytical data of the product as follows. FT-IR (KBr plate method, cm ):
3
431/3353/3216 (amine N–H), 3044/3011 (Carom–H), 1609 (NH , deformation), 1509/1489
2
1
(
(
[
phenyl), 1210/1168 (Carom–O–Carom). H-NMR [400 MHz, DMSO-d ,
δ
, ppm]: 7.95 [d, 2H
6
2.00H), J = 7.5 Hz, 4,5-protons of FL], 7.40 [t, 2H (2.04H), J = 7.4 Hz, 3,6-protons of FL], 7.24
t, 2H (1.99H), J = 7.5 Hz, 2,7-protons of FL], 7.07 [d, 2H (1.91H), J = 7.5 Hz, 1,8-protons of
FL], 6.77 [d, 4H (3.94H), J = 6.7 Hz, 3,3′,5,5′-protons of AN], 6.61–6.56 [m, 6H (5.87H),
,5-protons of XAN + 2,2′,6,6′-protons of AN], 6.38 [dd, 2H (1.96H), J = 8.6, 2.5 Hz, 2,7-protons
of XAN], 6.15 [d, 2H (1.99H), J = 8.7 Hz, 1,8-protons of XAN], 5.02 [s, 4H (3.75H), NH2].
4
−
1
Elemental analysis: Calcd. (%) for C H O N (546.63 g mol ): C, 81.30; H, 4.79; N, 5.12,
3
7
26
3
2
Found: C, 81.67; H, 4.92; N, 5.15. Melting point (DSC): 233 °C. These data confirmed that the
product is the desired diamine (AP-s-Spiro) shown below.
AP-s-Spiro
For a comparison, ether-linked cardo-type counterpart (AP-Cardo, Supplementary Data 5)
was also synthesized in a similar manner. The analytical data are shown in Supplementary Data
6
.
Commercially available common monomers (Fig. 4) were also used in this study. These
2
1

ACCEPTED MANUSCRIPT
abbreviations, commercial sources, purification methods, and melting points are summarized in
Supplementary Data 1.
2
.1.2. Polyaddition, imidization, and film preparation
The polymerization of PAAs, imidization, and PI film preparation were carried out according
to the schemes shown in Fig. 5. A typical procedure for the polyaddition is as follows.
Tetracarboxylic dianhydride powder (5 mmol) was added to an N,N-dimethylacetamide (DMAc)
of diamine (5 mmol) with continuous stirring in a sealed bottle. The reaction mixture (initial
solute content: 30 wt%) was stirred at room temperature, if necessary, while conducting multiple
dilution with a minimal quantity of DMAc at each step, and a homogeneous/viscous PAA
solution was obtained after 72 h.
Chemical imidization was carried out by slowly adding a dehydrating agent (Ac O/pyridine,
2
7
/3, v/v) to an adequately diluted PAA solution at a fixed feed ratio of [Ac O]/[COOH]
= 5
2
PAA
with continuous vigorous stirring, followed by stirring at room temperature for 24 h in a sealed
bottle. The homogenous reaction mixture obtained was adequately with DMAc and very slowly
poured into a large amount of poor solvent (methanol or water) to form fibrous precipitates, and
collected by filtration, washed with methanol, and dried at 100 °C for 12 h under vacuum. The
chemically imidized powder samples were dissolved in a fresh anhydrous solvent [e.g.,
2
2

ACCEPTED MANUSCRIPT
cyclopentanone (CPN), DMAc, or N-methyl-2-pyrrolidone (NMP)] at a solid content of 8–20
wt%, if necessary, while warming to facilitate dissolution. The homogeneous PEsI solutions
obtained were coated on a glass substrate, and dried at 60 °C for 2 h (for CPN and DMAc) or
8
0 °C for 3 h [for γ-butyrolactone (GBL) and NMP] in an air convection oven, followed by
vacuum-drying at 200 °C for 1 h on the substrate. After being peeling off from the substrate, the
PEsI films (typically 20 µm thick) were heated at an annealing temperature [T , typically at
ann
2
50 °C (or 300 °C)] for 1 h under vacuum to remove residual stress. These thermal conditions
during the film preparation were adjusted to obtain better-quality films.
For some insoluble systems, PEsI films were prepared upon thermal imidization as follows.
PAA solution was coated on a substrate, dried 60 °C for 2 h, heated typically at 200 °C for 1 h +
3
00 °C for 1 h under vacuum on the substrate, followed by annealing at 300 °C (or 330 °C) for 1
h under vacuum without the substrate. These thermal conditions were also adjusted to obtain
better-quality films.
In this paper, the chemical compositions of PEsI systems are represented with the
abbreviations of the monomer components used [tetracarboxylic dianhydrides (A) and diamines
(
B)] as A/B for homopolymers and A ;A / B ;B for copolymers.
1
2
1
2
2
.2. Measurements
2
3

ACCEPTED MANUSCRIPT
2
.2.1. Inherent viscosity and molecular weight
The reduced viscosities ( red) of PAAs and chemically imidized PEsIs were measured in
η
DMAc at a solid content of 0.5 wt% at 30 °C on an Ostwald viscometer. The polyelectrolyte
effect of PAAs disturbs to determine the inherent viscosities (ηinh) from the extrapolation to zero
concentration. Therefore, the ηred values of PAAs are often treated as the ηinh values. For highly
soluble PEsI systems in THF, the number- (M ) and weight- (M ) average molecular weights
n
w
were determined by gel permeation chromatography (GPC) using THF as an eluent at room
temperature on a Jasco, LC-2000 Plus HPLC system with a GPC column (Shodex, KF-806L) at a
–
1
flow rate of 1 mL min by ultraviolet-visible detection at 300 nm (Jasco, UV-2075). The
calibration was performed using standard polystyrenes (Shodex, SM-105).
2
.2.2. Linear coefficient of thermal expansion
The CTE values along the film plane (X–Y) direction for PEsI specimens (15 mm long, 5 mm
wide, and typically 20 µm thick) in the glassy region were measured by the thermomechanical
–
1
analysis (TMA) as an average in the range of 100–200 °C at a heating rate of 5 °C min on a
thermomechanical analyzer (Netzsch, TMA 4000) with a fixed static load (0.5 g per unit film
thickness in
µm, i.e., 10 g load for 20 µm-thick films) in a dry nitrogen atmosphere. In this case,
after the preliminary first heating run up to 120 °C and successive cooling to room temperature in
2
4

ACCEPTED MANUSCRIPT
the TMA chamber, the data were collected from the second heating run to remove an influence of
adsorbed water. The TMA curve was also used for determining the T of PEsI films, as mentioned
g
later.
2
.2.3. Heat resistance
The storage modulus (E′) and loss energy (E″) of PEsI films were measured by the dynamic
–
1
mechanical analysis (DMA) at a heating rate of 5 °C min at a sinusoidal load frequency of 0.1
Hz with an amplitude of 15 gf in a nitrogen atmosphere on the TMA instrument (as before). The
Tg of PEsI films was determined from the peak temperature of the E″ curve (method-1). The Tg
was also determined from an inflection point of the TMA curve measured under a fixed static
load, where the specimens started to abruptly elongate, as an intersection of two tangential lines
(method-2).
5
The thermal stability of PEsI films was evaluated from the 5% weight loss temperatures (T )
d
by the thermogravimetric analysis (TGA) on a thermo-balance (Netzsch, TG-DTA2000). TGA
–
1
was performed at a heating rate of 10 °C min in dry nitrogen and air atmosphere. A small
weight loss due to the desorbed water from the samples was observed around 100 °C in the TGA
curves. It was compensated by off-set at 150 °C to 0% weight loss for the data analysis.
2
5

ACCEPTED MANUSCRIPT
2
.2.4. Optical properties
The light transmission spectra of PEsI films (typically 20 µm thick) were recorded on an
ultraviolet-visible spectrophotometer (Jasco, V-530) in the wavelength ( ) range of 200–800 nm.
The light transmittance at 400 nm (T ) and the cut-off wavelength (λcut) at which the
λ
4
00
transmittance becomes practically null were determined from the spectra. In this work, the
transmittance data at longer wavelengths (e.g., 450 and 500 nm) themselves were not discussed
because they are often less informative for evaluating the film coloration; the films are not always
colorless even if the T500 value was very high (T500 > 80%). The yellowness indices (YI, ASTM E
3
13) for PEsI films were also determined from the spectra under a standard illuminant of D65
and a standard observer function of 2° using a color calculation software (Jasco) on the basis of
the relationship:
YI = 100 (1.2985x – 1.1335z) / y
(1)
where x, y, and z are the CIE tristimulus values. YI takes zero for an ideal white/transparent
sample. The total light transmittance (T , JIS K 7361-1) and the diffuse transmittance (T , JIS
tot
diff
K 7136) of PEsI films were measured on a double-beam haze meter equipped with an integrating
sphere (Nippon Denshoku Industries, NDH 4000). The haze (turbidity) of PEsI films was
calculated from the relationship:
Haze = (Tdiff / T ) × 100
(2)
tot
2
6

ACCEPTED MANUSCRIPT
The in-plane (n or n ) and out-of-plane (n or n ) refractive indices of PEsI films were
in
xy
out
z
measured with a sodium lamp at 589.3 nm (D-line) on an Abbe refractometer (Atago, 4T, nD
range: 1.47–1.87) equipped with a polarizer by using a contact liquid (sulfur-saturated methylene
iodide n = 1.78–1.80) and a test piece (n = 1.92). The birefringence of PEsI films, which
D
D
indicates the relative extent of chain alignment in the X–Y direction, was calculated from the
relationship:
∆
n = n – n
(3)
th
in
out
2
.2.5. Mechanical properties
The tensile modulus (E), tensile strength (σb), and elongation at break ( b
ε
) of PEsI films were
measured using specimens free of any defects such as fine bubbles (30 mm long, 3 mm wide,
typically 20 µm thick) on a mechanical testing machine (A & D, Tensilon UTM-II) at a cross
–
1
head speed of 8 mm min at room temperature. The data analysis was carried out on a data
processing program (Softbrain, UtpsAcS Ver. 4.09) and averaged for the valid run numbers (n >
1
5) unless stated otherwise.
2
.2.6. Solubility
The solubility of PEsIs was qualitatively examined using chemically imidized powder
2
7

ACCEPTED MANUSCRIPT
samples by observing whether the samples (10 mg) were completely dissolved in various solvents
(1 mL) in a test tube at room temperature (1st step). The insoluble samples were heated at an
established temperature for each solvent (2nd step). For the samples that were dissolved by
heating, the solution homogeneity was monitored after cooling to room temperature.
3
. Results and discussion
3
.1. PEsIs from symmetric spiro-type tetracarboxylic dianhydride (TA-s-Spiro)
To ascertain the potential of TA-s-Spiro, which has a unique feature, a “locally planar and
bulky” structure, we first investigated homo-PEsIs derived from TA-s-Spiro and common
diamines. The results are summarized in Table 1. TA-s-Spiro had sufficient PAA polymerizability
with 4,4′-oxydianiline (4,4′-ODA), p-phenylenediamine (p-PDA), 4,4′-diaminobenzanilide
(DABA), and TFMB, as suggested by the relatively high ηinh values ranging from 0.96–1.53 dL
–
1
g . These PAAs were chemically imidized and maintained a homogeneous state during the
reaction, except for the system using p-PDA. The results reflect the good solubility of the
imidized forms, which arises because the bulky FL side groups act to inhibit chain flocculation. A
1
typical H-NMR spectrum for the chemically imidized samples is shown in Fig. 6. Chemical
imidization occurred quantitatively, as suggested from the absence of signals corresponding to the
NHCO protons at
δ = 10–11 ppm and COOH protons at δ = 13–14 ppm, which should be
2
8