Highly phenylated polyimides containing 4,4′-diphenylether moiety

Article abstract of DOI:10.1016/j.reactfunctpolym.2014.02.010

A new aromatic diamine, 2,2′,6,6′-tetraphenyl-4,4′- oxydianiline (4PhODA, 4), has been synthesized by oxidation, bromination, Suzuki coupling and reduction of 4,4′-oxydianiline (4,4′-ODA). Highly phenylated polyimides PI7a-f were prepared from diamine 4 a

Full text of DOI:10.1016/j.reactfunctpolym.2014.02.010

Reactive & Functional Polymers 78 (2014) 23–31
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Highly phenylated polyimides containing 4,40-diphenylether moiety
a
a
b
Jyh-Chien Chen a, , Jin-An Wu , Shih-Wei Li , Shang-Chih Chou
⇑
a Department of Materials Science and Engineering, National Taiwan University of Science and Technology, No. 43, Sec. 4, Keelung Road, Taipei 106, Taiwan
b Department of Emerging Technology Research, Taiwan Textile Research Institute, New Taipei City 23674, Taiwan
a r t i c l e i n f o
a b s t r a c t
A new aromatic diamine, 2,20,6,60-tetraphenyl-4,40-oxydianiline (4PhODA, 4), has been synthesized by
oxidation, bromination, Suzuki coupling and reduction of 4,40-oxydianiline (4,40-ODA). Highly phenylated
polyimides PI7a-f were prepared from diamine 4 and six commercially available aromatic dianhydrides
by one-step method. The inherent viscosity of these polyimides ranged from 0.33 to 0.91 dL/g, measured
in a 0.5 g/dL of NMP or m-cresol solution at 30 °C. These highly phenylated polyimides showed excellent
solubility. Especially, polyimide PI7a derived from the rigid pyromellitic dianhydride (PMDA) was soluble
in DMAc, NMP at room temperature, and in DMF, chloroform, and m-cresol at 60 °C. Transparent, flexible
and tough films can be obtained by casting from their NMP or m-cresol solutions. They exhibited good
thermal stability, except PI7a containing pyromellitic diimide and PI7f containing nathphalenic diimide
(Tg > 350 °C), their glass transition temperatures measured by thermal mechanical analysis (TMA) ranged
from 298 to 340 °C. The decomposition temperatures at 5% weight loss under nitrogen were 506–542 °C.
They also showed excellent mechanical properties. The enhanced solubility combined with good thermal
stability could allow these phenylated polyimides to be further functionalized by various aromatic elec-
trophilic substitutions on four phenyl rings for polyelectrolyte applications.
Article history:
Received 23 September 2013
Received in revised form 25 January 2014
Accepted 26 February 2014
Available online 7 March 2014
Keywords:
Polyimides
Solubility
Phenylated
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
ages [13–15] and non-coplanar structures [16–18] into the
polymer backbone. Recently, even the solubility of the most intrac-
Aromatic polyimides are well known for their outstanding ther-
mal stability, chemical resistance, mechanical and electrical prop-
erties. They also exhibited good film-forming ability. They have
been exploited in various applications such as adhesives, gas sep-
aration membranes, proton exchange membranes for fuel cells,
composite matrices, and flexible substrates in the optoelectronic
and microelectronic industries [1–4]. However, polyimides have
very high melting or softening temperatures and poor solubility
in most organic solvents because of their high aromaticity,
heterocyclic imide linkage and the formation of strong inter- and
intramolecular charge transfer complex [5]. The processing of
polyimides has to be performed in their soluble polyamic acid
precursors, which are then imidized thermally or chemically. The
poor storage stability of polyamic acid, the tedious and high-tem-
perature process required for thermal imidization are undesirable
for some applications. In the last two decades, some attempts have
successfully developed various organo-soluble polyimides by
introducing bulky substituents [6–12], flexible or asymmetric link-
table polyimides derived from rigid pyromellitic dianhydride
(PMDA) has been improved to be soluble in common organic sol-
vents [13,19–21]. Among these approaches, the introduction of
bulky phenyl substituents have been proved to improve the solu-
bility without sacrificing their thermal stability. In addition to
Diels–Alder reaction, palladium catalyzed cross coupling reaction
(Suzuki coupling reaction) between phenylboronic acid or its
derivatives with aryl bromide is the most convenient and widely
used method to prepare phenylated monomers [7,9,22–25].
It is well known that 4,40-oxydianiline (4,40-ODA) is the diamine
used for commercial polyimide Kapton. Even though containing
flexible phenoxy linkage, 4,40-ODA alone is not enough to impart
organic solubility to the derived polyimides. In our previous study,
4,40-ODA based diamines with trifluoromethyl-substituted phenyl
or bromide at 2 and 20 positions were reported [26,27]. Polyimides
derived from these diamines all showed enhanced solubility over
those of 4,40-ODA based polyimides. Recently, we reported the syn-
thesis of four asymmetric 4,40-ODA based diamines with bromide
or phenyl at 2 or 2, 20, and 6 positions by controlling the equiva-
lents of brominating agent, N-bromosuccinimide (NBS), followed
by column chromatography [28]. Polyimides derived from these
four asymmetric diamines also showed outstanding solubility in
various common organic solvents.
⇑
Corresponding author. Tel.: +886 2 27376526.
E-mail addresses: jcchen@mail.ntust.edu.tw (J.-C. Chen), d9804013@mail.
ntust.edu.tw (J.-A. Wu), m10104126@mail.ntust.edu.tw (S.-W. Li), scchou.1213@
ttri.org.tw (S.-C. Chou).
http://dx.doi.org/10.1016/j.reactfunctpolym.2014.02.010
1381-5148/Ó 2014 Elsevier Ltd. All rights reserved.

24
J.-C. Chen et al. / Reactive & Functional Polymers 78 (2014) 23–31
In this study, we report the synthesis of a novel 4,40-ODA based
eluent and calibrated with polystyrene standards. Thermal gravi-
metric analyses (TGA) were performed in nitrogen with TA TGA Q
500 thermal gravimetric analyzer using a heating rate of 10 °C/
min. Glass transition temperatures (Tg) and coefficients of thermal
expansion (CTE) were determined by thermal mechanical analysis
(TMA) using TA TMA 2940 thermal mechanical analyzer with a ten-
sion mode (0.05 N) at a heating rate of 10 °C/min. The Tg was taken
as the temperature at which a change in slope of a plot of a film
dimension change versus temperature occurred. The CTE value
was taken as the mean of the dimension change between 50 and
150 °C. UV–Visible spectra were recorded on a Cary-100 UV–Visible
spectrometer at room temperature. The tensile properties of the
films were measured on a mechanical tester CHUN YEN at a
cross-head speed of 5 mm/min at 25 °C.
diamine with four bulky phenyl substituents at 2, 20, 6, and 60 posi-
tions, regardless of the possible steric hindrance. The effect of phen-
ylboronic acid equivalents used in Suzuki coupling reaction on the
yields of the diamine was examined. Highly phenylated polyimides
derived from this diamine and six commercially available dianhy-
drides were prepared by one-step method in m-cresol. The solubil-
ity, thermal stability, optical properties and mechanical properties
of the formed polyimides were investigated and discussed in detail.
2. Experimental section
2.1. Materials
Pyromellitic dianhydride (PMDA), 3,30,4,40-biphenyltetracarb-
oxylic dianhydride (BPDA), 4,40-oxydiphthalic anhydride (ODPA),
3,30,4,40-diphenylsulfonetetracarboxylic dianhydride (DSDA), 2,20-
2.3. Monomers synthesis
2.3.1. 2,20,6,60-Tetraphenyl-4,40-dinitrodiphenylether (3)
bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA),
and 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) were
purchased from Kriskev Co., dried at 150 °C and sublimated under
reduced pressure prior to use. 4,40-Oxydianiline (4,40-ODA) was ob-
tained from Kriskev Co. and used as received. 4,40-Dinitrodipheny-
lether (1), 2,20,6,60-tetrabromo-4,40-dinitrodiphenylether (2), and
2,20,6,60-tetrabromo-4,40-oxydianiline (5) were prepared according
to our previous publication [26]. m-Cresol (Lancaster Synthesis)
was dried with P2O5 and distilled under reduced pressure. Other
chemicals and solvents were used as received.
To a 100 mL, three-necked, round-bottomed flask equipped
with a nitrogen inlet, a thermometer and a condenser were added
2,20,6,60-tetrabromo-4,40-dinitrodiphenylether (2) (1.00 g, 1.75
mmol) and toluene (10 mL). The mixture was heated to 80 °C un-
der nitrogen.
A sodium carbonate aqueous solution (1.54 g,
14.52 mmol, in 6.4 mL of water) and Pd(PPh3)4 (0.24 g, 0.20 mmol)
were added. The mixture was vigorously stirred for 1 h under
nitrogen. A solution of phenylboronic acid (1.70 g, 14.00 mmol)
in ethanol (4.4 mL) was added. The mixture was heated at reflux
for 24 h under nitrogen. After cooling to room temperature, the
mixture was diluted with toluene and then filtered through a short
Celite pad to remove the insoluble components. The filtrate was
washed several times with a saturated NaCl aqueous solution
and dried with anhydrous magnesium sulfate. After solvent was
evaporated, the solid powder was washed with acetone (1–2 mL).
The insoluble solid power was purified by flash column chroma-
tography with a 70/30 (v/v) dichloromethane/n-hexane mixture
as the solvent then recrystallized in acetone to afford 0.49 g (50%
yield) of light yellow crystals; mp: 260–262 °C. 1H NMR
(500 MHz, DMSO-d6, d, ppm): 7.26 (d, J = 8.5 Hz, 8H, Hb), 7.42 (t,
J = 14.5 Hz, 4H, Hd), 7.50 (t, J = 14.5 Hz, 8H, Hc), 7.70 (s, 4H, Ha).
13C NMR (125 MHz, DMSO-d6, d, ppm): 125.0, 128.2, 128.4,
129.1, 133.5, 135.1, 142.7, 153.9. EIMS(m/z): Calcd. for
2.2. Measurements
All melting points were determined on a Mel-Temp capillary
melting point apparatus. Infrared spectra were obtained with a Dig-
ilab-FTS1000 FTIR spectrometer. 1H and 13C NMR measurements
were performed on a Bruker Avance-500 spectrometer operating
at 500 and 125 MHz, respectively. Mass spectrometry was con-
ducted on a Finnigan TSQ 700 mass spectrometer. Elemental anal-
yses were performed on a Heraeus Vario analyzer. Inherent
viscosity was measured using an Ubbelohde viscometer with a
0.5 g/dL NMP or m-cresol solution at 30 °C. High performance liquid
chromatography (HPLC) was performed on a JASCO HPLC system
equipped with a UV (254 nm) detector and a Thermo Hypersil
C
36H24N2O5, 564.2; Found, 564.1 [M]+. C36H24N2O5: Calcd.
C
column (250 mm ꢀ 4.6 mm, particle size 5
lm) with an 80/20 (v/
v) acetonitrile/water mixture as the eluent. Molecular weights were
76.63, H 4.28, N 4.96; Found: C 76.77, H 4.35, N 4.78.
measured on a JASCO GPC system (PU-980) equipped with an RI
2.3.2. 2,20,6,60-Tetraphenyl-4,40-oxydianiline (4PhODA, 4)
detector (RI-930),
a
Jordi Gel DVB Mixed Bed column
(250 mm ꢀ 10 mm), using dimethylacetamide (DMAc) as the

J.-C. Chen et al. / Reactive & Functional Polymers 78 (2014) 23–31
25
To a 500-mL, three-necked, round-bottomed flask were added
ethyl acetate (50 mL), ethanol (12 mL), and 2,20,6,60-tetraphenyl-
4,40-dinitrodiphenylether (3) (1.00 g, 1.77 mmol). The mixture
was vigorously stirred to become a homogeneous solution. After
ammonium formate (3.21 g, 50.90 mmol) and Pd/C (10 wt%)
(0.17 g, 1.59 mmol) were added, the mixture was stirred at room
temperature for 12 h. It was then filtered through a short Celite
pad to remove the insoluble components. The filtrate was collected
and washed several times with a saturated NaCl aqueous solution.
The combined organic solution was dried with anhydrous magne-
sium sulfate and evaporated under reduced pressure to afford
yellow oil. The crude product was purified by flash column chroma-
tography with a 50/50 (v/v) ethyl acetate/n-hexane mixture as the
solvent to afford 0.75 g (84% yield) of yellow power; mp: 106–
108 °C, 1H NMR (500 MHz, DMSO-d6, d, ppm): 4.59 (s, 4H, He),
6.09 (s, 4H, Ha), 7.20 (d, J = 9.5 Hz, 8H, Hb), 7.28 (t, J = 15.0 Hz, 4H,
Hd), 7.39 (t, J = 15.0 Hz, 8H, Hc). 13C NMR (125 MHz, DMSO-d6, d,
ppm): 115.7 (C1), 126.3 (C7), 127.1 (C6), 128.9 (C5), 132.1 (C2),
139.0 (C8), 141.7 (C4), 142.8 (C3). EIMS(m/z): Calcd. for
isoquinoline were added. The reaction mixture was further heated
at 200 °C for 24 h under nitrogen atmosphere. After cooled to room
temperature, the reaction mixture was poured slowly into stirred
methanol (200 mL). The fibrous precipitate was collected, ex-
tracted by hot ethanol for 12 h and dried under reduced pressure
at 200 °C for 12 h. Polyimides were obtained in quantitative yields
(>98%).
2.5. Preparation of polyimide films
Polyimide films were mostly prepared from their NMP solutions
(solid content around 10% w/v) while films of PI7b and PI7f were
prepared from their m-cresol solution. The formed clear polyimide
solution was filtered through a 0.45
TMA and mechanical strength measurements, polyimide films of
20–30 m in thickness were used. For UV–Visible transparency
test, the thickness of the polyimide films was controlled around
5–10 m. The polyimide films were dried in an air-circulated oven
lm Teflon syringe filter. For
l
l
at 50 °C for 1 h, 80 °C for 1 h, 150 °C for 1 h and 220 °C for 3 h.
C
36H28N2O, 504.2; Found, 504.1 [M]+. C36H28N2O: Calcd. C 85.75,
H 5.59, N 5.55; Found: C 85.59, H 5.53, N 5.41.
3. Results and discussion
2.4. Polyimide synthesis
3.1. Monomer synthesis
Polyimides PI7aꢁf were synthesized according to the following
The novel aromatic diamine 4 was prepared according to the
synthetic route shown in Scheme 1. First, 4,40-ODA was oxidized
by hydrogen peroxide to form a dinitro compound 1, which was
then brominated in the presence of 5 equivalents of N-bromosuc-
cinimide (NBS) to form a dinitro compound 2 with four bromides
at the 2, 20, 6, and 60 positions. From our previous report [26], it
is found that the aromatic ring of dinitro compound 1 is not so
electron-deficient. By controlling the amount of bromination agent
NBS, one to 7 bromides can be attached to the rings. The pure com-
pound 2 can be obtained by recrystallization in acetone.
procedure. To
a 50 mL, three-necked, round-bottomed flask
equipped with a mechanical stirrer, a condenser and a nitrogen in-
let were added 2,20,6,60-tetraphenyl-4,40-oxydianiline (4) (1.00 g,
1.98 mmol) and m-cresol. After diamine (4) was completely dis-
solved, the dianhydride (1.98 mmol) was added. The total solid
content was controlled at 10% w/v. The reaction mixture was
heated to 120 °C under nitrogen atmosphere and several drops of
The aryl bromides are important precursors that can be con-
verted to different functional groups by various organic reactions.
In this study, the Suzuki coupling reaction was used to convert bro-
mide into phenyl group. Thus, a dinitro compound 2 reacted with
phenylboronic acid in the presence of Pd(PPh3)4 and sodium car-
bonate to form a dinitro compound 3. When 4.4 equivalents of
phenylboronic acid were used, we found that the crude product
mainly consisted of the target compound (3a) together with 4,40-
dinitro-2,20,6-triphenyldiphenylether (3b), and 4,40-dinitro-2,20-
dibromo-6,60-phenyldiphenylether (3c) in a ratio of 30%, 40%, or
15%. Their chemical structures were confirmed by 1NMR spectros-
copy and the compositions were determined by HPLC. From the
presence of product 3b, it revealed that debromination could occur.
It could prohibit the formation of the target compound 3a. When
the amount of phenylboronic acid was increased to 6 equivalents,
the composition (3a:3b:3c) of the crude product changed to 42%,
28%, or 8%. Finally, 8 equivalents of phenylboronic acid were used,
the ratio changed to 55%, 19%, and 4%. This might be resulted from
the steric hindrance produced when three bromides of dinitro
compound 2 were converted into phenyl groups. It became more
inaccessible for the fourth bromide to react with phenylboronic
acid, leading to the unexpected debromination. It is therefore nec-
essary to use excess amount of phenylboronic acid in order to in-
crease the collision between bromide and phenylboronic acid
and result in higher yields. The pure compound 3a can be obtained
by column chromatography and recrystallization in acetone. The
dinitro compound 3a was then reduced by Pd/C and ammonium
formate in ethyl acetate/ethanol to form the diamine 4. Fig. 1
shows the 1H and 13C NMR spectra of diamine 4. Combined with
its HMQC spectrum as shown in Fig. 2, the corresponding peaks
were assigned accordingly. The formation of this diamine was
Fig. 1. (a) 1H and (b) 13C NMR spectra (DMSO-d6) of 4PhODA, 4.

26
J.-C. Chen et al. / Reactive & Functional Polymers 78 (2014) 23–31
Scheme 1. Synthetic route for 4PhODA, 4.
Fig. 2. HMQC spectra (DMSO-d6) of 4PhODA, 4.
confirmed by the assignments in the NMR spectra and the results
from element analysis and mass spectroscopy.
their 1H NMR spectrum as shown in Fig. 3. This can be explained by
the following reaction mechanism. Suzuki coupling reaction is pro-
posed to consist of three steps: oxidative addition, transmetalliza-
tion, and reductive elimination [29]. After oxidative addition with
Pd(PPh3)4, the aryl bromide acts as an electrophile in the next
transmetallization step [30]. In general, higher yields from the
coupling reactions can be expected if the aryl bromide contains
electron-withdrawing groups. Instead, using aryl bromide with
electron-donating amino groups as the starting material will be
An attempt to prepare the diamine 4 using Suzuki coupling
reaction between 2,20,6,60-tetrabromo-4,40-oxydianiline
5 and
phenylboronic acid was not successful (Scheme 2). Instead of
diamine 4, the diamine 6 containing two bromides at 2 and 20 posi-
tions and two phenyls at 6, and 60 positions was the major product
(about 60% yield), even though 8 equivalents of phenylboronic acid
were used. The chemical structure of diamine 6 was confirmed by

J.-C. Chen et al. / Reactive & Functional Polymers 78 (2014) 23–31
27
Scheme 2. Synthetic route for compound 6.
observed at 1715 cmꢂ1 and 1680 cmꢂ1 (carbonyl asymmetric and
symmetric stretching) [31]. Fig. 5 shows the 1H NMR spectrum
(in chloroform-d) of PI7e, derived from diamine 4 and DSDA. Be-
cause of the formation of the electron-withdrawing imide rings,
all the peaks of aromatic protons shifted to the deshielding region.
The aromatic protons in the dianhydride moiety appeared at the
farthest deshielding region (8.02, 8.37, and 8.41 ppm) in the spec-
trum. The aromatic protons in diamine moiety appeared in less
deshielding region (6.91, 7.36, and 7.39 ppm) because of the
electron-donating aromatic ether linkages. The 1H NMR spectra
combined with the characteristic peaks in their IR spectra
confirmed the chemical structures of these polyimides.
3.3. Properties of polyimides
Fig. 3. 1H NMR spectrum (DMSO-d6) of compound 6.
3.3.1. Molecular weights and solubility
The inherent viscosity of all the polyimides PI7aꢁe was deter-
mined in N-methyl-2-pyrrolidone (NMP) with a concentration of
0.5 g/dL at 30 °C, while that of PI7f, derived from NTDA, was mea-
sured in m-cresol with the same concentration and temperature.
The results together with GPC molecular weights of PI7aꢁf are
shown in Table 1. The inherent viscosity of PI7aꢁf was in the range
of 0.33–0.91 dL/g. The number-average molecular weights (Mn)
and weight-average molecular weights (Mw) were 32,000–83,000
and 42,000–163,000 g/mol, relative to polystyrene standards,
respectively. Flexible and transparent polyimide films can be ob-
tained by casting from their NMP or m-cresol (PI7b and PI17f)
solutions onto a glass plate and dried at appropriate temperatures.
The solubility of the polyimides was determined in various or-
ganic solvents with the concentration of 20 mg/mL at room tem-
perature. The results are summarized in Table 2. PI7f derived
from NTDA was only soluble in m-cresol and PI7b derived from
BPDA was soluble in NMP and m-cresol due to their chain rigidity.
The remaining polyimides were soluble in polar organic solvents
such as DMF, DMAc, NMP and m-cresol at room temperature or
upon heating at about 60 °C. PI7c, PI7d, and PI7e, derived from
6FDA, ODPA, and DSDA, respectively, were even soluble in chloro-
form at room temperature. In general, polyimides derived from ri-
gid PMDA are insoluble in common organic solvents. It is
surprising that PI7a derived from PMDA could be dissolved in
DMAc and NMP at room temperature and was soluble in DMF,
m-cresol and chloroform upon heating. Compared with polyimides
detrimental to the yield of Suzuki coupling reaction and in the
worst case the targeted product cannot be prepared.
3.2. Polyimides synthesis
Polyimides PI7aꢁf were prepared from diamine 4 with six com-
mercially available dianhydrides by one-step polycondensation
method as shown in Scheme 3. In this procedure, the diamine
and dianhydrides were polymerized in refluxing m-cresol and in
the presence of isoquinoline as the catalyst. Throughout the poly-
merization, all of the polyimides remained in m-cresol without any
premature precipitation. In addition, PI7a and PI7f, derived from
rigid PMDA and NTDA, exhibited thermally reversible gel forma-
tion. When the reaction mixtures were slowly cooled, they became
gel at temperature lower than 60 °C. The gel became a clear solu-
tion when it was heated up to 80 °C again. All the polyimides were
isolated in quantitative yields (>98%) by precipitating into metha-
nol, washing by hot ethanol and drying under reduced pressure.
The structures of the synthesized polyimides PI7aꢁf were char-
acterized using FTIR and NMR spectroscopy. As shown in Fig. 4,
PI7aꢁe exhibited characteristic absorption bands of phthalic imide
ring near 1780 cmꢂ1, 1720 cmꢂ1 (carbonyl asymmetric and sym-
metric stretching) and 1380 cmꢂ1 (C–N stretching). The character-
istic absorption bands of naphthalenic imide ring of PI7f were

28
J.-C. Chen et al. / Reactive & Functional Polymers 78 (2014) 23–31
Scheme 3. Synthesis of PI7aꢁf by one-step method.
functionalization on the phenyl substituents in solution state.
The functionalization can be achieved by reactions involving aro-
matic electrophilic substitution mechanism. Thus, it is possible to
conduct sulfonation or chloromethylation followed by amine
quarternization on the phenyl substituents. Our ongoing research
is preparing new polymer electrolytes from these highly phenylat-
ed polyimides PI7aꢁf.
3.3.2. Morphological structures
The crystallinity of all polyimides was investigated by wide an-
gle X-ray diffraction (WXRD). The diffraction patterns are shown in
Fig. 6. No crystalline peaks were observed, indicating that all the
polyimides were amorphous. The amorphous nature of these polyi-
mides could be attributed to the loose chain packing resulted from
the bulky phenyl substituents. It was well known that the polyim-
ide derived from 4,40-ODA and PMDA has high level of crystalline
characteristics due to its rigid pyromellitic structure [33]. How-
ever, the PI7a derived from PMDA and the new diamine 4 was
amorphous. It indicated that the introduction of four bulky phenyl
substituents at the 2, 20, 6, and 60 positions of 4,40-diphenylether
moiety effectively limited the polymer chain packing and led to
amorphous nature.
Fig. 4. FTIR spectra of PI7aꢁf.
prepared from 4,40-ODA with the same dianhydrides by two-step
method, polyimides PI7aꢁe exhibited much better solubility as
shown in Table 2. For example, polyimides prepared from 4,40-
ODA with PMDA and BPDA were insoluble in all tested solvents.
When ODPA or DSDA was used, ODA-polyimides can be soluble
only in hot NMP and m-cresol [32]. The improvement in solubility
demonstrated by PI7aꢁf could be resulted from incorporating four
bulky phenyl substituents. The polymer chain packing is hindered
by the presence of these bulky substituents, which also decreases
the intermolecular interaction. The increased free volume facili-
tates the penetration of small solvent molecules into polyimide
chain, leading to the good solubility. The enhanced solubility of
these highly phenylated polyimides is essential to allow further
3.3.3. Thermal properties
The thermal stability of polyimides PI7aꢁf was evaluated by
TMA and TGA. The results, including glass transition temperatures
(Tg), coefficients of thermal expansion (CTE), decomposition tem-
peratures at 5% (T5%) and 10% (T10%) weight loss, and residual
weight percent (Rw800) at 800 °C, are summarized in Table 3. The
glass transition of PI7a and PI7f containing rigid PMDA and NTDA
moieties cannot be detected at the temperature up to 350 °C. For
PI7bꢁe, the Tgs ranged from 298 to 340 °C. In general, bulky
substituents would lead to looser chain packing and weaker

J.-C. Chen et al. / Reactive & Functional Polymers 78 (2014) 23–31
29
Fig. 5. 1H NMR spectrum (chloroform-d) of PI7e.
counterpart was 295 °C. This might be attributed to the fact that
the incorporation of the phenyl substituents significantly en-
hanced the rotational barrier of the polymer chains. This effect
combined with high aromaticity of the four phenyl substituents
thus increased the Tgs of polyimides PI7aꢁf. Therefore, the good
solubility of these highly phenylated polyimides was achieved
without deteriorating their thermal stability.
The coefficients of thermal expansion (CTE) determined by TMA
at temperature between 50 and 150 °C are summarized in Table 3.
The CTEs of polyimides PI7aꢁf ranged between 47 and 65 ppm/°C.
Polyimides containing rigid BPDA and NTDA moieties such as PI7b
and PI7f, showed lower CTEs.
The thermal degradation temperatures (T5% at 5% and T10% at
10% weight loss) and residual weight percent at 800 °C (Rw800
)
determined by TGA in a nitrogen atmosphere are also summarized
in Table 3. Polyimides PI7aꢁf had T5% and T10% in the range of 506–
542 °C and 520–552 °C, respectively. Their Rw800 ranged from 53%
to 67%. Among them, PI7e containing DSDA moiety showed lowest
degradation temperatures both at 5% and 10% weight loss.
Fig. 6. WAXD patterns of PI7aꢁf.
intermolecular force, which should lower the glass transition tem-
peratures. However, polyimides PI7bꢁe containing four bulky phe-
nyl substituents had higher Tgs than those polyimides derived from
4,40-ODA as shown in Table 3. For example, the glass transition
temperature of polyimide PI7e derived from highly phenylated
diamine 4 and DSDA was 340 °C, while that of the non-phenylated
3.3.4. Mechanical and optical properties
Polyimides PI7aꢁf can be cast to form transparent and flexible
films from their NMP and m-cresol (PI7b and PI7f) solutions. The
tensile properties of these films are summarized in Table 4. All
polyimide films had high tensile strength of 40–86 MPa, elonga-
tions at break of 4.2–7.5% and initial moduli of 0.9–2.0 GPa. These
Table 1
Inherent viscosity and molecular weights of polyimides.
a
b
b
b
Polyimide
ginh (dL/g)
Mn ꢀ 10–3(g/mol)
Mw ꢀ 10ꢂ3(g/mol)
Mw/Mn
PI7a (4PhODA/PMDA)
PI7b (4PhODA/BPDA)
PI7c (4PhODA/6FDA)
PI7d (4PhODA/ODPA)
PI7e (4PhODA/DSDA)
PI7f (4PhODA/NTDA)
0.91
0.59
0.33
0.52
0.74
0.49c
83
163
NAd
42
1.96
NAd
1.31
1.57
1.59
NAd
NAd
32
42
66
61
97
NAd
NAd
a
b
c
Measured at a polymer concentration of 0.5 g/dL in NMP at 30 °C.
By GPC in DMAc (relative to polystyrene standards).
Measured at a polymer concentration of 0.5 g/dL in m-cresol at 30 °C.
Insoluble in DMAc.
d

30
J.-C. Chen et al. / Reactive & Functional Polymers 78 (2014) 23–31
Table 2
Solubility of polyimidesa.
Polymer
Solventb
Chloroform
Acetone
THF
DMF
DMAc
NMP
m-cresol
PI7a (4PhODA/PMDA)
PI7b (4PhODA/BPDA)
PI7c (4PhODA/6FDA)
PI7d (4PhODA/ODPA)
PI7e (4PhODA/DSDA)
PI7f (4PhODA/NTDA)
+
ꢂ
S
+
++
+ꢂ
++
++
++
+ꢂ
++
++
++
++
++
+ꢂ
+
+ꢂ
++
++
++
+ꢂ
ꢂ
+ꢂ
+ꢂ
++
+
++
+ꢂ
++
++
++
+
+ꢂ
ꢂ
+
+ꢂ
++
ꢂ
+ꢂ
ꢂ
++
ODA/PMDAc
ODA/BPDAc
ODA/6FDAc
ODA/ODPAc
ODA/DSDAc
NAd
NAd
NAd
NAd
NAd
NAd
NAd
NAd
NAd
NAd
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
++
ꢂ
ꢂ
ꢂ
ꢂ
+
ꢂ
ꢂ
++
+
ꢂ
ꢂ
+
+
+
ꢂ
ꢂ
+
a
The solubility was determined by using 20 mg of sample in 1 mL of stirred solvent. ++ = soluble at room temperature; + = soluble on heating; +ꢂ = partially soluble on
heating; S = swelling; ꢂ = insoluble even on heating.
b
THF: tetrahydrofuran; DMF: N,N-dimethylformamide; DMAc: N,N-dimethylacetamide; DMSO: dimethyl sulfoxide; NMP: N-methyl-2-pyrrolidone.
From Ref. [32] the test concentration was 10 mg of sample in 1 mL of stirred solvent.
Not available.
c
d
Table 3
Thermal properties of polyimides.
CTEb
(lm/m °C)
T5% (°C)
T10% (°C)
RW800 (%)
a
c
c
d
Polyimide
Tg (°C)
PI7a (4PhODA/PMDA)
PI7b (4PhODA/BPDA)
PI7c (4PhODA/6FDA)
PI7d (4PhODA/ODPA)
PI7e (4PhODA/DSDA)
PI7f (4PhODA/NTDA)
NDe
321
298
323
340
NDe
55
47
65
50
56
48
532
534
530
532
506
542
546
550
548
541
520
552
53
59
67
57
55
54
ODA/PMDAf
ODA/BPDAf
ODA/6FDAf
ODA/ODPAf
ODA/DSDAf
362
290
296
260
295
35g
61h
–
–
–
–
601
600
538
577
542
54
63
56
57
54
567
510
493
–
a
b
c
Measured by TMA (tension mode) at a heating rate of 10 °C/min.
Average values between 50 and 150 °C.
Measured by TGA at a heating rate of 10 °C/min in nitrogen.
Residual weight (%) when heated to 800 °C.
No Tg obtained before 350 °C.
From Ref. [26].
From Ref. [34].
From Ref. [35].
d
e
f
g
h
Table 4
Mechanical and optical properties of polyimides.
Polyimide
Tensile strength (MPa)
Elongation to break (%)
Initial modulus (GPa)
konset (nm)a
k80% (nm)a
PI7a (4PhODA/PMDA)
PI7b (4PhODA/BPDA)
PI7c (4PhODA/6FDA)
PI7d (4PhODA/ODPA)
PI7e (4PhODA/DSDA)
PI7f (4PhODA/NTDA)
55
51
40
43
41
86
5.1
4.6
4.2
4.8
4.5
7.5
1.6
1.5
1.1
0.9
1.8
2.0
385
398
344
351
361
434
607
499
457
532
568
709
a
Measured by UV–Visible spectroscopy with film thickness 5–10 lm.
values suggested that polyimides PIaꢁf are mechanically strong
enough for versatile film and membrane applications.
tively. Except PI7f, the polyimide films exhibited light yellow to
yellow color. PI7a derived from rigid PMDA showed yellow color,
whereas PI7c derived from 6FDA showed the lightest color as ex-
pected. The PI7f derived from NTDA showed orange color, which
was attributed to the naphthalenic imide moiety.
The optical transparency of all the polyimide films with a thick-
ness of 5–10
lm was measured using UV–Visible spectroscopy.
Two quantities, the wavelengths of the transmission onset (konset
)
and 80% transmission (k80%), were used to evaluate the transpar-
ency of the films. The smaller wavelengths for the transmission on-
set and the 80% transmission indicate higher optical transparency
of the polyimide films. The results are summarized in Table 4.
The transmission onset and 80% transmission of polyimide PI7aꢁf
occurred at wavelengths of 344–434 and 457–709 nm, respec-
4. Conclusions
In this study, we report the synthesis and properties of highly
phenylated polyimides. It was achieved by the use of a novel aro-
matic diamine which was prepared from 4,40-ODA as the starting

J.-C. Chen et al. / Reactive & Functional Polymers 78 (2014) 23–31
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