Synthesis and properties of novel triptycene-based polyimides

Article abstract of DOI:10.1002/pola.24748

Two new triptycene-containing bis(ether amine)s, 1,4-bis(4-aminophenoxy) triptycene (4) and 1,4-bis(4-amino-2-trifluoromethylphenoxy)triptycene (6), were synthesized, respectively, from the nucleophilic chloro-displacement reactions of p-chloronitrobenzene and 2-chloro-5-nitrobenzotrifluoride with 1,4-dihydroxytriptycene in the presence of potassium carbonate, followed by palladium-catalyzed hydrazine reduction of the dinitro intermediates. The bis(ether amine)s were polymerized with six commercially available aromatic tetracarboxylic dianhydrides to obtain two series of novel triptycene-based polyimides 8a-f and 9a-f by using a conventional two-step synthetic method via thermal and chemical imidizations. All the resulting polyimides exhibited high enough molecular weights to permit the casting of flexible and strong films with good mechanical properties. Incorporation of trifluoromethyl groups in the polyimide backbones improves their solubility and decreases their dielectric constants. The fluorinated polyimides 9d and 9f derived from diamine 6 with 4,4′-oxydiphthalic anhydride and 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), respectively, could afford almost colorless thin films.

Full text of DOI:10.1002/pola.24748

Synthesis and Properties of Novel Triptycene-Based Polyimides
SHENG-HUEI HSIAO,1 HUI-MIN WANG,1 WEN-JENG CHEN,1 TZONG-MING LEE,2 CHYI-MING LEU2
1Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei, Taiwan
2Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan
Received 23 March 2011; accepted 23 April 2011
DOI: 10.1002/pola.24748
Published online 18 May 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Two new triptycene-containing bis(ether amine)s,
1,4-bis(4-aminophenoxy)triptycene (4) and 1,4-bis(4-amino-2-tri-
fluoromethylphenoxy)triptycene (6), were synthesized, respec-
tively, from the nucleophilic chloro-displacement reactions of
p-chloronitrobenzene and 2-chloro-5-nitrobenzotrifluoride with
1,4-dihydroxytriptycene in the presence of potassium carbon-
ate, followed by palladium-catalyzed hydrazine reduction of the
dinitro intermediates. The bis(ether amine)s were polymerized
with six commercially available aromatic tetracarboxylic dia-
nhydrides to obtain two series of novel triptycene-based polyi-
weights to permit the casting of flexible and strong films with
good mechanical properties. Incorporation of trifluoromethyl
groups in the polyimide backbones improves their solubility
and decreases their dielectric constants. The fluorinated poly-
imides 9d and 9f derived from diamine 6 with 4,40-oxydiphthalic
anhydride and 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane
dianhydride (6FDA), respectively, could afford almost colorless
C
V
thin films.
2011 Wiley Periodicals, Inc. J Polym Sci Part A:
Polym Chem 49: 3109–3120, 2011
mides 8a–f and 9a–f by using
a
conventional two-step
KEYWORDS: dielectric properties; optical transparency; poly-
imides; structure-property relations; thermal properties; tripty-
cene; trifluoromethyl group
synthetic method via thermal and chemical imidizations. All
the resulting polyimides exhibited high enough molecular
INTRODUCTION Aromatic polyimides are well-known high-
performance polymeric materials for their excellent thermal,
mechanical, and electrical properties.1–3 Despite their out-
standing properties, most of the conventional aromatic polyi-
mides have high-melting or glass-transition temperatures
(Tg) and limited solubility in most organic solvents because
of their rigid backbones and strong interchain interactions.
Thus, polyimide processing is generally carried out via
poly(amic acid) precursor and then converted to polyimide
by vigorous thermal or chemical cyclodehydration. However,
this process has inherent problems such as emission of vola-
tile byproducts and storage instability of poly(amic acid)
solution. To overcome these problems, many attempts have
been made to the synthesis of soluble and processable polyi-
mides in fully imidized form while maintaining their excel-
lent properties.4 It has been generally recognized that aryl-
ether linkage imparts properties such as better solubility,
melt processing characteristics, and improved toughness in
comparison with those polymers without an aryl-ether link-
age.5–10 However, the decrease in mechanical properties on
heating is almost always a consequence of the reduced chain
stiffness or Tgs. The introduction of bulky, rigid units in the
polymer main chain or as pendent groups can impart an
increase in Tgs by restricting the segmental mobility, while
providing an enhanced solubility because of decreased pack-
ing density and crystallinity.11,12 Thus, combining these two
structural modifications minimized the trade-off between the
processability and the useful/positive properties of aromatic
polyimides.13–28
Iptycenes are a class of structurally unique compounds that
consist of a number of arene rings joined together to form
the bridges of [2.2.2] bicyclic ring systems.29 The name ipty-
cene originated from the basic unit triptycene, which was
first synthesized and named by Bartlett and coworkers in
1942.30 Later, triptycene has become readily available thanks
to the well known work of Wittig31,32 on the preparation of
dehydrobenzene (benzyne) and its interaction with anthra-
cene. The chemistry of triptycene has been studied in com-
parative detail and has been summarized in an earlier
review article reported by the Russian researchers.33 Tripty-
cene is a rigid molecular unit with three blades each com-
posed of a benzene ring. Its rigid, three-dimensional frame-
work has been incorporated in molecular rotors,34–37
molecular cages,38–40 and supramolecular architectures.41–43
In addition, triptycene and other iptycene units have been
used to design a variety of high performance polymers.44
Perhaps the earliest efforts in the study of triptycene poly-
mers were made at Eastman Kodak and DuPont in the late
1960s wherein bifunctional, bridgehead-substituted tripty-
cenes were synthesized and used to prepare a series of trip-
tycene polymers, including polyesters, polyamides, polyur-
ethanes, and a polyoxadiazole.45,46 The use of triptycene
Additional Supporting Information can be viewed in the online issue of this article. Correspondence to: S.-H. Hsiao (E-mail: shhsiao@ntut.edu.tw)
C
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Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 3109–3120 (2011) 2011 Wiley Periodicals, Inc.
TRIPTYCENE-BASED POLYIMIDES, HSIAO ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
moiety as a rigid and shape-persistent component is a
method to introduce molecular-scale free volume into a poly-
mer film. Polymers with high triptycene content were found
to be interesting low-k dielectric materials owing to the high
degree of internal free volume.47 Incorporation of triptycene
units into polyesters was also found to significantly enhance
the mechanical performance of film samples through molecu-
lar threading and interlocking.48,49 Additionally, it was
shown that triptycene-containing polycarbonates displayed
improvements in mechanical properties at both low- and
high-strain rates.50
(3,4-dicarboxyphenyl)hexafluoropropane diaꢀnhydride (6FDA;
7f) (Hoechst Celanese) were heated at 250 C in vacuum for
3 h before use. N,N-Dimethylacetamide (DMAc) was purified
by distillation under reduced pressure over calcium hydride
and stored over 4 Å molecular sieves. N,N-Dimethylforma-
mide (DMF; Fluka), acetic anhydride (Ac2O; Fluka), N-methy-
2-pyrrolidone (NMP; Fluka), dimethyl sulfoxide (DMSO;
Acros), tetrahydrofuran (THF; Acros), and pyridine (Py;
Wako) were used as received from commercial sources.
Synthesis of 1,4-Bis(4-aminophenoxy)triptycene (4)
1,4-Dihydroxytriptycene (or 9,10-Dihydro-9,10-[o]-
The work reported by Kasashima et al. seems to be the first
article dealing with the incorporation of triptycene moieties
into the backbone of the polyimides.51 Recently, some new
triptycene polyimides have also been synthesized.52–55
Because of the presence of rigid, packing-disruptive tripty-
cene unit, the polyimides exhibited good solubility in com-
mon organic solvents while preserving moderately high Tg
and good thermal stability. In view of the structural feature
of triptycene, synthesizing and characterizing new polyi-
mides bearing triptycene moieties in the backbone are
interesting enough to be investigated further. Therefore, in
this work we decided to synthesize and characterize two
new triptycene-based diamine monomers, 1,4-bis(4-amino-
phenoxy)triptycene (4) and 1,4-bis(4-amino-2-trifluorome-
thylphenoxy)triptycene (6), as well as their derived polyi-
mides with triptycene structure in the main chain. The
rigid, three-dimensional triptycene units may decrease
interchain interactions and hinder close chain packing.
Thus, it was expected that the introduction of triptycene
structure into the polymer backbone could improve the sol-
ubility, decrease the color intensity, and preserve moder-
ately high Tg values of the polyimides. On the other hand, it
is well known that polyimides with bulky trifluoromethyl
(ACF3) pendant groups are generally soluble and high-tem-
perature resistant polymer materials with low moisture
uptake, low dielectric constant, and high optical transpar-
ency.56–66 Therefore, the attachment of bulky, electron-with-
drawing trifluoromthyl groups on the polyimide backbone
through the use of diamine monomer 6 was expected to
give an extra enhanced solubility and reduced color inten-
sity of the polyimides.
benzenoanthracene-1,4-diol; Triptycenehydroquinone) (2)
p-Benzoquinone (12.1 g, 112.0 mmol) and anthracene (10.0
g, 56.0 mmol) were refluxed in dry toluene (100 mL) under
nitrogen for 4 h. The reaction mixture was cooled to room
temperature, filtered, and the residue was washed with tolu-
ene (2 ꢁ 5 mL). The residue was dried in oven overnight.
The resulting crude hydroquinone (14.2 g) was dissolved in
hot acetic acid (350 mL) and 48% aq. HBr (4 mL) was added
dropwise to the solution. An off-white color precipitate was
developed immediately. The residue was washed with acetic
acid (15 mL) and hexane (30 mL) and dried in air to give
compound 2 (12.8 g, 80%); mp ¼ 340–342 ꢀC.
IR (KBr; see Supporting Information Figure S1): 3260 cmꢂ1
(AOH stretch). 1H NMR (500 MHz, DMSO-d6, d, ppm) (Sup-
porting Information Figure S2): 8.80 (s, 2H, AOH), 7.38 (dd,
4H), 6.96 (dd, 4H), 6.32 (s, 2H), 5.81 (s, 2H). 13C NMR (125
MHz, DMSO-d6, d, ppm): 145.7, 144.7, 131.8, 124.5, 123.4,
112.8, 46.5.
1,4-Bis(4-nitrophenoxy)triptycene (3)
1,4-Dihydroxytriptycene (5.4 g, 19 mmol) and p-chloronitro-
benzene (6.0 g, 38 mmol) were dissolved in 50 mL of DMF
in a 100-mL flask. Then, potassium carbonate (5.6 g, 40
mmol) was added, and the reaction mixture was heated to a
reflux temperature and held at that temperature for 8 h. The
obtained mixture was poured into 200 mL of methanol/
water (1:1 by volume) to precipitate a light yellow solid,
which was collected by filtration, washed thoroughly with
methanol, and dried. The crude product (8.6 g, 82%) could
be further purified by crystallization from DMF/methanol
(10:1 by volume) as fine pale-yellow needles.
IR (KBr): 1594, 1310 (ANO2 stretch).
EXPERIMENTAL
1,4-Bis(4-aminophenoxy)triptycene (4)
Materials
In a 100-mL three-neck round-bottom flask equipped with a
stirring bar, 5.5 g (11.7 mmol) of dinitro compound 3 and
0.2 g of 10% Pd/C were dissolved/suspended in 50 mL of
DMF. The reaction solution was stirred at room temperature
and bubbled with a hydrogen gas stream. After reaction for
3 days, the solution was filtered into methanol to precipitate
an off-white fine crystal. The product was collected by filtra-
tion and dried in vacuum at 100 ꢀC to give 4.1 g (yield,
76%) of pure diamine compound 4; mp ¼ 254–255 ꢀC (by
The bis(ether amine)s 4 and 6 were synthesized from the
chloro-displacement reaction of p-chloronitrobenzene (Acros)
and 2-chloro-5-nitrobenzotrifluoride (Acros) with 1,4-dihy-
droxytriptcene in the presence of potassium carbonate
(K2CO3; Fluka), followed by Pd/C-catalyzed hydrazine reduc-
tion. Pyromellitic dianhydride (PMDA; 7a; Aldrich) and
3,30,4,40-benzophenonetetracarboxylic dianhydride (BTDA;
7c; Aldrich) were purified by recrystallization from acetic
anhydride.
3,30,4,40-Biphenyltetracarboxylic
dianhydride
DSC at a heating rate of 2 C minꢂ1).
ꢀ
(BPDA; 7b; Oxychem), 3,30,4,40-diphenylsulfonetetracarbox-
ylic dianhydride (DSDA; 7d; New Japan Chemical), 4,40-oxy-
diphthalic dianhydride (ODPA; 7e) (Oxychem), and 2,2-bis
IR (KBr): 3465, 3372 cmꢂ1 (NAH stretch). 1H NMR (500
MHz, DMSO-d6, d, ppm): 7.40 (dd, J ¼ 5.3 and 3.2 Hz, 4H,
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ARTICLE
drazine monohydrate (4 mL) was gradually added to the
stirred mixture. After a further 8-h reflux, the reaction solu-
tion was filtered hot to remove Pd/C. After cooling, the off-
white crystals were collected by filtration and dried in vac-
uum at 100 ꢀC overnight to afford 6.1 g (88%) of pure dia-
ꢀ
mine 6; mp ¼ 245–247 C.
IR (KBr): 3465, 3372 cmꢂ1 (NAH stretch), 1263, 1143 cmꢂ1
(CAF and CAO stretch). 1H NMR (500 MHz, DMSO-d6, d,
ppm) (For the peak assignments, see Fig. 2): 7.32 (dd, J ¼
5.3, 3.2 Hz, 4H, Hd), 7.02 (dd, J ¼ 5.3 and 3.2 Hz, 4H, Hc)
7.00 (s, J ¼ 2.5 Hz, 2H, Hg), 6.74 (dd, J ¼ 8.8 and 2.5 Hz, 2H,
Hf), 6.58 (d, J ¼ 8.8 Hz, 2H, He), 6.48 (s, 2H, Ha), 5.79 (s, 2H,
Hb), 5.39 (s, 4H, ANH2). 13C NMR (125 MHz, DMSO-d6, d,
ppm): 147.5 (C2), 145.1 (C11), 144.6 (C5), 143.8 (C8), 137.0
1
(C3), 125.2 (C6), 123.8 (C7), 123.7 (quartet, JCAF ¼ 271 Hz,
2
C14; ACF3), 121.0 (C9), 120.0 (quartet, JCAF ¼ 30 Hz, C13),
118.4 (C10), 115.5 (C1), 111.0 (C12), 47.0 (C4).
Synthesis of Polyimides
Polyimides 8a–8f and 9a–9f were synthesized from diamines
4 and 6, respectively, with commercially available dianhy-
drides 7a–f by the conventional two-step technique via the
thermal or chemical imidization method. The synthesis of
polyimide 9a is used as an example to illustrate the general
synthetic route. The diamine monomer 6 (0.7349 g, 1.22
mmol) was dissolved in 9.5 mL of DMAc in a 50-mL round-
bottom flask. Then 7a, PMDA (0.2651 g, 1.22 mmol) was
added to the diamine solution in one portion. Thus, the solid
FIGURE 1 (a) 1H and (b) 13C NMR spectra of diamine 4 in DMSO-
d6. [Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
Hd), 7.00 (dd, J ¼ 5.3 and 3.2 Hz, 4H, Hc) 6.69 (d, J ¼ 8.8 Hz,
4H, He), 6.58 (d, J ¼ 8.8 Hz, 4H, Hf), 6.47 (s, 2H, Ha), 5.88 (s,
2H, Hb), 4.90 (s, 4H, ANH2). 13C NMR (125 MHz, DMSO-d6,
d, ppm): 145.9 (C2), 145.8 (C8), 144.4 (C5), 144.3 (C11),
137.5 (C3), 125.0 (C6), 124.0 (C7), 119.0 (C9), 116.0 (C1),
115.0 (C10), 46.5 (C4). The peak assignments for this diamine
compound are shown in Figure 1.
Synthesis of 1,4-Bis(4-amino-2-
trifluoromethylphenoxy)triptycene (6)
1,4-Bis(4-nitro-2-trifluoromethylphenoxy)triptycene (5)
1,4-Dihydroxytriptycene (5.7 g, 20 mmol) and 2-chloro-5-
nitrobenzotrifluoride (9.0 g, 40 mmol) were dissolved in 50
mL of DMF in a 100-mL flask with stirring. Into this mixture
solution, potassium carbonate (5.6 g, 40 mmol) was added,
and the reaction mixture was heated at 100 ꢀC for 8 h. The
reaction solution was poured into 200 mL of methanol/
water (1:1 by volume), and the precipitated light yellow
solid was collected by filtration and washed thoroughly with
methanol and water. The yield of the crude product was
11.8 g (89%), which can be further purified by crystalliza-
tion from DMF/methanol to afford light yellow fine needles.
IR (KBr): 1500, 1310 (ANO2 stretch), 1265, 1124 cmꢂ1
(CAF and CAO stretch).
1,4-Bis(4-amino-2-trifluoromethylphenoxy)triptycene (6)
The dinitro compound 5 (7.0 g, 13 mmol) and 10% Pd/C
(0.1 g) were suspended in ethanol (100 mL) in a 300-mL
flask. The suspension solution was heated to reflux, and hy-
FIGURE 2 (a) 1H and (b) 13C NMR spectra of diamine 6 in
DMSO-d6. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
TRIPTYCENE-BASED POLYIMIDES, HSIAO ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
content of the solution is ꢃ10 wt %. The mixture was
stirred at room temperature for about 10 h to yield a viscous
poly(amic acid) solution. The inherent viscosity of the result-
ing poly(amic acid) was 0.86 dL gꢂ1, measured in DMAc at a
Weight-average molecular weights (Mw) and number-average
molecular weights (Mn) were obtained via gel permeation
chromatography (GPC) on the basis of polystyrene calibra-
tion using Waters 2410 as an apparatus and THF as the elu-
ent. The mechanical properties of the films were measured
with an Instron model 1130 tensile tester with a 5 kg load
cell at a crosshead speed of 5 mm minꢂ1 on strips approxi-
mately 40–60 lm thick and 0.5 cm wide with a 2 cm gauge
length. An average of at least five individual determinations
was used. Wide-angle X-ray diffraction (WAXD) measure-
concentration of 0.5 g dLꢂ1 at 30 C. The poly(amic acid) film
ꢀ
was obtained by casting from the reaction polymer solution
onto a glass Petri dish and dried at 80 ꢀC overnight. The
poly(amic acid) in the form of sold film was converted to
ꢀ
polyimide 9a by the successꢀive heating at 150 C for 30 min,
ꢀ
200 C for 30 min, and 250 C for 1 h. The IR spectrum of 9a
ꢀ
(film) exhibited characteristic imide absorption bands at 1780
(asymetrical C¼¼O stretch) and 1740 cmꢂ1 (symmetrical C¼¼O
stretch).
ments were performed at room temperature (ca. 25 C) on a
Shimadzu XRD-6000 X-ray diffractometer (40 kV, 20 mA),
using graphite-monochromatized Cu-Ka radiation. Ultravio-
let–visible (UV–vis) spectra of the polymer films were
recorded on Agilent 8453 UV-Visible diode array spectropho-
tometer. Color intensity of the polymers was evaluated on an
Admesy brontes colorimeter. Measurements were performed
for the films at an observational angle of 45ꢀ and a standard
D65 light source with the CIE LAB values. DSC analyses were
performed ꢂo1n a Perkin-Elmer Pyris 1 DSC at a scan rate of
20 ꢀC min in flowing nitrogen. Glass-transition tempera-
tures (Tgs) were read as the midpoint temperature of the
heat capacity jump and were taken from the second heating
scan after a quick cooling down from 400 ꢀC to room tem-
perature. Thermogravimetric analysis (TGA) was performed
with a Perkin-Elmer Pyris 1 TGA. Measurements were car-
For the chemical imidization method, 4 mL of acetic anhy-
dride and 2 mL of pyridine were added to a poly(amic acid)
obtained by a similar process as above, and the mixture was
heated at 100 ꢀC for 1 h to effect a complete imidization.
The homogeneous polymer solution was poured slowly into
200 mL of stirring methanol giving rise to yellow precipitate
that was collected by filtration, washed thoroughly with hot
water and methanol, and dried in oven. A polymer solution
was made by the dissolution of about 0.7 g of the chemically
imidized polyimide sample in 10 mL of hot DMAc. The ho-
mogeneous solution was poured into a 7-cm glass Petri dish,
which was placed in a 80 ꢀC oven overnight for the slow
release of the solvent, and then the film was stripped off
from the glass substrate.
ried out on 3–5 mg film samples heated in flowing nitrogen
3
or air (90 cm /min) at a heating rate of 20 C minꢂ1. Ther-
ꢀ
momechanical analysis (TMA) was conducꢂte1d with a Perkin-
Elmer TMA 7 at a scan rate of 10 ꢀC min with a penetra-
tion probe of 1.0 mm diameter under an applied constant
load of 10 mN. Dielectric property of the polymer films was
tested using an Agilent 4291B RF Impedance/Material
Analyzer.
Measurements
IR spectra were recorded on a Horiba FT-720 Fourier trans-
form infrared (FTIR) spectrometer. 1H and 13C NMR spectra
were measured on a Bruker AVANCE 500 MHz FT-NMR spec-
trometer. The inherent viscosities were determined at a 0.5 g
dLꢂ1 concentration with an Ubbelohde viscometer at 30 ꢀC.
SCHEME 1 Synthetic route to the triptycene bis(ether amine)s.
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ARTICLE
SCHEME 2 Synthesis of triptycene polyimides.
broad absorption in the region of 3000ꢃ3500 cmꢂ1, charac-
teristic of the hydrogen-bonded hydroxyl group. Bands rep-
resentative of the nitro functionality for the dinitro com-
pounds 3 and 5 appeared near 1590 and 1350 cmꢂ1. After
reduction, the characteristic absorptions of the nitro group
disappeared and the amino groups of 4 and 6 showed the
typical NAH stretching absorption pair in the region of
RESULTS AND DISCUSSION
Monomer Synthesis
The new triptycene bis(ether amine)s 4 and 6 were syn-
thesized via the synthetic route shown in Scheme 1.
According to a reported method,67 the triptycene-hydroqui-
none (TPHQ) 2 was obtained in a good yield starting from
the Diels–Alder reaction of p-benzoquinone and anthracene
and subsequent rearrangement reaction using acetic acid/
HBr as catalyst. As reported in the literature,68 colorless
single crystal of TPHQ could be obtained by slow crystalli-
zation from acetonitrile solution of the compound. Crystal-
lographic analysis indicated that the crystal has a pseudo-
center of symmetry and seemingly suggests space group
P63/m. The dinitro intermediates 3 and 5 were prepared
by the nucleophilic aromatic substitution reactions of p-
chloronitrobenzene and 2-chloro-5-nitrobenzotrifluoride,
respectively, with the potassium salt of TPHQ 2 formed in
situ by treatment of potassium carbonate in DMF. Both the
para nitro group and ortho trifluoromethyl group activate
the chlorine for displacement; therefore, the chloro-dis-
placement reaction of 2-chloro-5-nitrobenzotrifluoride by
the potassium phenolate of 2 can be carried out at a
milder condition; the reaction could proceed very well
even at room temperature. Subsequent reduction of the
dinitro compounds 3 and 5 by using hydrogen or hydra-
zine as reducing reagent in the presence of Pd/C catalyst
could readily give triptycene-bis(ether amine)s 4 and 6,
respectively. The yields in each step were reasonable, and
the molecular structures of the synthesized compounds
could be confirmed by spectroscopic techniques.
3300–3500 cmꢂ1. The strong bands at 1100–1300 cmꢂ1
,
assigned to the CAO and CAF stretching, were also appa-
rent in the FTIR spectra of the CF3-substituted compounds
5 and 6.
The structures were also confirmed by high-resolution NMR
1
spectra. Figures 1 and 2 illustrate the H NMR and 13C NMR
spectra of diamine monomers 4 and 6, respectively. Assign-
ments of each carbon and proton were assisted by the two-
dimensional (2D) NMR spectra shown in Supporting Infor-
mation Figures S3 and S4, and the spectra are in good agree-
ment with the proposed molecular structures of triptycene
bis(ether amine)s 4 and 6. The 13C NMR spectrum of 6
shows two clear quartets due to the heteronuclear 13C–19
F
coupling. The larger quartet centered at about 123.7 ppm
peculiar to the CF3 carbon (C-14). The one-bond CAF cou-
pling constant in this case was about 271 Hz. The CF3-
attached carbon (C-13) also displayed a clear quartet cen-
tered at 120.0 ppm with a smaller coupling constant of 30
Hz due to two-bond CAF coupling.
Polymer Synthesis
Two series of novel polyimides (8a–f and 9a–f) containing
the triptycene unit in the main chain were, respectively, pre-
pared from the triptycene-based bis(ether amine)s 4 and 6
with six commonly used aromatic dianhydrides (7a–f) to
form poly(amic acid)s, followed by the thermal or chemical
The FTIR spectra of obtained compounds are depicted in
the Supporting Information Figure S1. The TPHQ showed a
TRIPTYCENE-BASED POLYIMIDES, HSIAO ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
and S6. In the 1H NMR spectra, all the aromatic protons of
8f and 9d resonated in the region of d 6.8–8.3 ppm. The sig-
nals appearing in the range 5.5ꢃ6.0 ppm were assigned to
the bridgehead protons of the triptycene units. Assignments
of each proton are in good agreement with the structures of
their repeating units.
TABLE 1 Inherent Viscosity and GPC Data of Polyimides
GPC Data of
Polyimidesc
ginh (dL gꢂ1
)
b
Polymera
Code
Poly(amic
acid)s
Polyimides
Mw
Mn
PDI
d
e
8a
8b
8c
8d
8e
8f
1.49
0.90
0.81
0.77
1.24
0.81
1.08
0.86
0.78
0.50
0.77
0.64
–
–
–
–
–
–
–
–
–
–
–
–
Polymer Properties
Organosolubility
–
–
The solubility properties of all the new triptycene-containing
polyimides synthesized by both of thermal and chemical
imidization methods are reported in Table 2. The solubility
of these polyimdes varies depending on the dianhydride
used. For the 8 series polyimides, only 8e and 8f showed
moderate solubility in organic solvents. This result clearly
indicates that just incorporating a triptycene unit into the
polyimide backbone, even with flexible ether linkage, does
not result in organosoluble polyimides. Polymers using more
rigid dianhydrides such as PMDA and BPDA as the dianhy-
dride component are still insoluble. However, the solubility
of these triptycene-polyimides could be improved by further
attaching of bulky trifluoromethyl (ACF3) groups on the
polymer chain. As shown in Table 2, all the 9 series trifluor-
omethylated polyimides, except 9b, revealed a reasonable or
excellent solubility in the solvents tested. It is worth noting,
but difficult to explain, that the fluorinated polyimide 9b
from BPDA did not exhibit a good solubility as that of 9a
from PMDA. Although the reason is not very clear, it may be
caused by the rigid biphenyl structure and perhaps better
chain packing for the polyimide 9b. In addition, the chemi-
cally imidized samples generally revealed a higher solubility
than those prepared by the thermal imidization method. The
lower solubility of thermally cured polyimide may be attrib-
uted to the presence of partial interchain crosslinking or an
aggregation of the polymer chains during thermal curing
process. Thus, the 9 series polyimides containing both tripty-
cene and ACF3 groups, especially for that prepared by the
chemical imidization methods, are readily soluble in amide-
type dipolar solvents such as NMP and DMAc and even in
less polar THF. The enhancement in solubility is clearly
attributed to the additional effect arising from the bulky
ACF3 unit, which increased the disorder in the chains and
hindered close chain packing, and thus, reducing interchain
interactions. The good solubility of these polymers in low-
boiling point solvents is a benefit to prepare the polymer
films or coatings at low processing temperatures.
–
–
–
–
–
–
0.68
0.52
–
79,000
49,500
–
55,500
23,500
–
1.42
2.10
–
9a
9b
9c
9d
9e
9f
0.64
0.45
0.51
0.61
65,000
40,000
40,000
77,000
38,000
32,500
20,000
47,000
1.71
1.23
2.00
1.63
a
The polyimide samples were prepared via chemical imidization.
Measured at a polymer concentration of 0.5 g dLꢂ1 in DMAc at 30 ꢀC.
Determined in THF relative to polystyrene standards.
Insoluble in DMAc.
b
c
d
e
Insoluble in THF.
cyclodehydration (Scheme 2). In the first step, the viscosities
of the reaction mixtures became very high as poly(amic
acid)s were formed, indicating the formation of high-molecu-
lar weight polymers. As shown in Table 1, the poly(amic
acid) precursors had inherent viscosities in the range of
0.50–1.26 dL/g. The resulting viscous poly(amic acid) solu-
tions were poured into a clean glass Petri dish and dried to
form thin solid films. The thermal conversion to polyimides
was carried out by step-by-step heating of the poly(amic
acid) films to 250 ꢀC. The poly(amic acid) precursors also
could be chemically dehydrated to the polyimides by treat-
ment with acetic anhydride and pyridine. All these two se-
ries polyimides could afford flexible and tough films via ther-
mal imidization of their poly(amic acid) films. For the
organosoluble polyimides such as 8f and most of the 9 se-
ries, polyimides could be solution cast to flexible films in the
fully imidized form. The polyimides that are soluble in THF
were characterized by GPC, and the relative data are also
included in Table 1. The weight-average molecular weights
(Mws) and number-average molecular weights (Mns) were
recorded in the ranges of 40,000ꢃ79,000 and 20,000ꢃ55,500,
respectively, relative to polystyrene standards. For the com-
parative purpose, a series of corresponding polyimides (10a–
f) based on l,4-bis(4-aminophenoxy)benzene (BAPB) were
also prepared and characterized.
Tensile Properties
The tensile properties of the polyimide films prepared by
thermal curing are summarized in Table 3. All these polymer
films possess good tensile strengths indicating that they are
strong materials. The films had strengths at break of 91–128
MPa, an elongation at break of 5–9%, initial modulus of 1.3–
2.1 GPa. Generally, the casting films of the 9 series polyi-
mides exhibited slightly lower strengths than those of the 8
series ones, possibly because of increased free volume and
reduced cohesive force caused by the ACF3 group. These
results indicate that the incorporation of the ACF3 group
All the polyimides showed the characteristic absorption
bands of the imide ring near 1780 (asymmetric C¼¼O
stretching) and 1730 cmꢂ1 (symmetric C¼¼O stretching).
Typical IR and 1H NMR spectra of the representative polyi-
mides are included in Supporting Information Figures S5
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ARTICLE
TABLE 2 Solubility Properties of Polyimides
Solubility in Various Solventsa
Polymer Code
NMP
DMAc
DMF
DMSO
m-Cresol
THF
CH2Cl2
Toluene
8a(H)
8a(C)
8b(H)
8b(C)
8c(H)
8c(C)
8d(H)
8d(C)
8e(H)
8e(C)
8f(H)
8f(C)
9a(H)
9a(C)
9b(H)
9b(C)
9c(H)
9c(C)
9d(H)
9d(C)
9e(H)
9e(C)
9f(H)
9f(C)
a
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
þ
þ
þ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
þþ
þþ
þþ
þ
þþ
þþ
þþ
þþ
þþ
ꢂ
þþ
þþ
þþ
þꢂ
þþ
ꢂ
þþ
þ
þ
þꢂ
þþ
þþ
þþ
þþ
ꢂ
ꢂ
ꢂ
þ
þþ
þþ
þꢂ
þꢂ
ꢂ
þ
þþ
þ
þþ
þꢂ
þ
þ
þꢂ
ꢂ
þþ
ꢂ
þꢂ
þ
þþ
þ
þþ
þ
þþ
ꢂ
ꢂ
ꢂ
ꢂ
þ
ꢂ
þ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
þ
þ
þꢂ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
ꢂ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þ
þ
þꢂ
þþ
þþ
þꢂ
þꢂ
þþ
þþ
ꢂ
þ
þ
þ
þþ
þ
þþ
þþ
þþ
þþ
þþ
þ
ꢂ
þþ
þþ
þþ
þþ
þ
þþ
ꢂ
þþ
þþ
The qualitative solubility was tested with 10 mg of a sample in 1 mL of stirred solvent. þþ, soluble at room temperature; þ, solu-
ble on heating; þꢂ, partially soluble; ꢂ, insoluble even on heating.
TABLE 3 Tensile Properties of the Polyimide Films
Tensile
Elongation
Initial
Polymer Code
Strength (MPa)
at Break (%)
Modulus (GPa)
8a
8b
8c
8d
8e
8f
101
128
96
6
9
6
8
6
5
5
6
6
6
5
5
1.7
1.5
1.8
1.3
1.7
1.8
2.1
2.0
1.9
1.7
1.9
1.8
108
96
97
9a
9b
9c
9d
9e
9f
105
120
109
99
93
91
TRIPTYCENE-BASED POLYIMIDES, HSIAO ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 3 Wide-angle X-ray diffraction patterns of thin films of some typical polyimides. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
into the structure of polyimides not only improves solubility
but also retains the good mechanical properties.
X-Ray Diffraction Data
All the polyimide films were characterized by WAXD studies.
The diffraction patterns of some typical polyimides of the 8,
9, and 10 series are illustrated in Figure 3. The polyimides
10a–c derived from BAPB showed a semicrystalline WAXD
pattern, and the result is similar to that reported
TABLE 4 Thermal Properties of the Polyimides
Td at 10%
Weight Loss
(ꢀC)d
Polymera
Code
Char
Tg (ꢀC)b Ts (ꢀC)c In N2 In Air Yield (wt %)e
8a
8b
8c
8d
8e
8f
354
312
298
284
312
301
335
303
289
272
298
290
331
294
273
265
302
275
296
274
262
252
282
266
610
617
595
621
555
590
626
629
619
630
546
584
582
611
595
607
581
572
596
603
589
605
558
570
69
73
67
69
63
66
59
65
66
64
61
59
9a
9b
9c
9d
9e
9f
a
The polymer film samples were heated at 300 ꢀC for 30 min before all
the thermal analyses.
b
Midpoint temperature of the baseline shift on the second DSC heating
trace (rate ¼ 20 ꢀC minꢂ1) of the sample after quenching from 400 to 50
ꢀC (cooling rate ¼ ꢂ200 ꢀC minꢂ1) in nitrogen.
FIGURE 4 (a) DSC curves of polyimides 8b, 9b, and 10b. (b)
TGA curves of polyimides 8c and 9c in both air and nitrogen
atmospheres. (c) TMA curves of polyimides 8a and 9a. [Color
figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
c
Softening temperature measured by TꢂM1A with a constant applied load
of 10 mN at a heating rate of 10 ꢀC min
d
.
Decomposition temperature at which a 10% weight loss was recorded by
TGA at a heating rate of 20 ꢀC minꢂ1 and a gas flow rate of 20 cm3 minꢂ1
e
.
Residual weight percentage at 800 ꢀC in nitrogen.
3116
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ARTICLE
TABLE 5 Optical Properties and Dielectric Constants of the Polyimides
Color
Coordinatesa
Polymer
Code
Film Thickness
80% Transmission
Wavelength (nm)
Dielectric
(lm)
a*
0.5
b*
L*
k0 (nm)b
Constant (at 1 MHz)
8a
63
67
64
85
84
85
58
59
50
47
50
50
37
94.7
37.1
86.5
23.5
54.9
23.4
51.8
11.6
38.5
10.2
12.5
1.8
78.1
82.3
82.5
82.6
79.1
82.6
86.9
87.8
89.9
91.3
85.2
92.2
82.4
457
426
457
402
434
401
432
407
422
381
403
375
462
608
611
621
608
623
580
540
576
514
487
472
431
657
3.12
3.25
3.42
3.36
3.59
3.14
2.84
2.67
2.82
2.28
2.89
2.05
3.37
8b
ꢂ3.0
ꢂ5.3
1.3
8c
8d
8e
ꢂ3.9
2.2
8f
9a
ꢂ10.7
ꢂ1.1
ꢂ10.8
ꢂ2.4
ꢂ2.9
ꢂ0.7
0.7
9b
9c
9d
9e
9f
PMDA/ODAc
99.1
a
The color parameters were calculated according to a CIE LAB equation. L* is the lightness, where 100 means white and 0 implies black. A positive
a* means a red color, and a negative a* indicates a green color. A positive b* means a yellow color, and a negative b* implies a blue color.
Absorption edge from the UV–vis spectra of the polymer thin films.
A reference polyimide, which has the same structure of commercial Kapton polyimide, was prepared from pyromellitic dianhydride and 4,40-oxy-
b
c
dianiline (ODA). The poly(amic acid) precursor has an inherent viscosity of 2.50 dL gꢂ1
.
previously.69 In contrast, the triptycene-containing polyi-
mides 8a–c and 9a–c exhibited a somewhat reduced level of
crystallinity. This was reasonable because the polyimides
contained laterally attached, rigid, and three-dimensional
triptycene units that sterically disrupted the chain packing
and inhibited significant chain–chain interactions. In addi-
tion, the amorphous nature of the 9 series polyimides could
be attributed in part to the presence of the bulky ACF3
4(a). The triptycene-containing polyimides 8b and 9b
showed higher Tg values than the BAPB-based polyimide
10b. The result can be attributed to bulky triptycene units
thus restricting the segmental mobility. Moreover, slightly
lower Tgs for the 9 series in comparison with the 8 series
might be a result of reduced chain-to-chain charge transfer
interactions and poor chain packing due to the bulky pend-
ant ACF3 groups.
groups, which resulted in
structure.
a less dense chain packing
The thermal and thermo-oxidative stabilities of the polyi-
mides were evaluated by TGA in both nitrogen and air
atmospheres. Typical TGA curves for polyimides 8c and 9c
in both air and nitrogen atmospheres are illustrated in
Figure 4(b). The temperatures for 10% weight loss (T10) of
the 8 series polyimideꢀs in nitrogen and air atmospheres
polyimides within 546–630 ꢀC andꢀ558–605 ꢀC. They left
more than a 59% char yield at 800 C in nitrogen. The TGA
data indicated that the fluorinated polyimides 9a–f had fairly
high-thermal stability regardless of the introduction of the
CF3 groups.
Thermal Properties
Thermal properties of the polyimides were evaluated by dif-
ferential scanning calorimetry (DSC), thermogravimetric
analysis (TGA), and thermomechanical analysis (TMA). The
thermal behavior data of all the polyimides prepared by
thermal curing are summarized in Table 4. DSꢂC1experiments
ꢀ
stayed within 555–621 C and 572–611 C, and for 9 series
ꢀ
were conducted at a heating rate of 20 C min in nitrogen.
Rapid cooling from 400 ꢀC to room temperature produced
predominantly amorphous samples, so the glass transition
temperatures (Tgs) of all the polyimides could be easily read
in the subsequent heating DSC traces. The Tg values of these
two series polyimides 8a–f and 9a–f were in the range of
284–354 ꢀC and 272–335 ꢀC, respectively. The decreasing
order of Tg generally correlated with that of chain flexibility.
As expected, the polyimides 8d and 9d obtained from ODPA
showed the lowest Tg in each series due to the presence of a
flexible ether linkage between the phthalimide units, and the
polyimide 8a and 9a derived from PMDA exhibited the high-
est Tg due to the rigid pyromellitimide unit. Typical DSC
curves of polyimide 8b, 9b, and 10b are shown in Figure
The softening temperatures (Ts; may be referred to as appa-
rent Tg) of the polymer film samples were determined by the
TMA method with a loaded penetration probe. They were
obtained from the onset temperature of the probe displace-
ment on the TMA trace. As a representative example, the TMA
traces of polyimides 8a and 9a are depicted in Figure 4(c).
The Ts values obtained by TMA were recorded in the 252–
331 ꢀC range, and the trend of Ts variation with the chain
stiffness is similar to that of Tg observed in the DSC experi-
ments. The Ts values of the polyimide films were slightly
TRIPTYCENE-BASED POLYIMIDES, HSIAO ET AL.
3117

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
lowered than the Tg values obtained by DSC. This may indi-
cate that a higher degree of plasticity near Tg due to the
increased free volume by the triptycene unit in both series
polyimides and the ACF3 substituent in the
9 series
polyimides.
Optical and Colorimetric Properties
The color intensities of the polyimides were elucidated from
the yellowness (b*) or redness (a*) indices observed by a col-
orimeter. For comparison, a standard polyimide from PMDA
and ODA was also prepared and characterized by its color in-
tensity. The color coordinates of these polyimides are given in
Table 5. The results indicate that all the 9 series polyimides
showed a lower b* value in comparison with the 8 series ana-
logs without the CF3 substituents. In general, the cast films of
chemically treated polyimide samples showed a lower yellow-
ness index. Moreover, thin films were measured for optical
transparency using UV–vis spectroscopy. Figure 5 shows the
UV–vis transmittance spectra of some representative polyi-
mide films, and the wavelengths at absorption edge (k0) and
80% transmittance from the UV–vis spectra are also listed in
Table 5. The films of the 9 series polyimides also exhibited a
higher % transmittance value than those from the 8 and 10
series. As shown in Figure 6, the solution-cast film of 9f is
essentially colorless and reveals lighter color intensity than
the structurally related 8f and 10f and standard PMDA/ODA
(Kapton) films. The 6FDA and ODPA produced fairly transpar-
ent and nearly colorless polyimide films in contrast to other
dianhydrides. The less colored polyimide film could be attrib-
uted to the reduction of the intermolecular charge-transfer
complexing (CTC) between alternating electron donor (dia-
mine residue) and electron acceptor (dianhydride residue)
moieties. Low color of the 6FDA-derived polyimide films (8f,
9f, and 10f) could be explained by that the hexafluoroisopro-
pylidene moiety can separate the chromophoric groups and
reduce electronic interaction. The light color of the polyimides
FIGURE 5 Transmission UV–vis spectra of (a) BTDA, (b) ODPA
and (c) 6FDA polyimide films (film thickness ¼ 50–80 lm).
[Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
FIGURE 6 Photographs of the
thin films (ꢃ50 lm thick) of polyi-
mides 8f, 9f, 10f, and PMDA/ODA
(Kapton).
3118
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ARTICLE
4 De Abajo, J.; de la Campa J. G. Adv Polym Sci 1999, 140, 23–59.
with the ACF3 groups in their diamine components also can
be explained from the decreased interchain interactions. The
bulky and electron-withdrawing ACF3 group in diamine 6
was effective in decreasing CTC formation between polymer
chains through steric hindrance and the inductive effect (by
decreasing the electron-donating property of diamine moi-
eties). An additional positive effect of the ACF3 groups on
the film transparency is the weakened chain–chain dispersion
forces due to low polarization of the CAF bond. The decrease
in intermolecular CTC formation is understandable also from
the significant solubility of the polyimides prepared from flu-
orinated bis(ether amine) 6.
5 Takekoshi, T.; Kochanowski, J. E.; Manello, J. S.; Webber, M.
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8 Hsiao, S.-H.; Yu, C.-H. Polym J 1997, 29, 944–948.
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10 Shao, Y.; Li, Y.-F.; Zhao, X.; Ma, T.; Gong, C.-L.; Yang, F.-C.
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Dielectric Constants
The dielectric constants of the polyimide films are also
included in Table 5. Fluorinated polyimides 9a–f revealed
lower dielectric constants (2.05–2.89 at 1 MHz) than the
nonfluorinated one 8a–f (3.12–3.59) and the standard
PMDA/ODA polyimide (3.37). The decreased dielectric con-
stants could be attributed to the presence of bulky CF3
groups, which resulted in less efficient chain packing and
increased free volume. In addition, the strong electronegativ-
ity of fluorine atoms results in permanent dipole moments
of the CF3 groups, thus decreasing the dielectric constant.
Therefore, the 6FDA-derived polyimide 9f exhibited the low-
est dielectric constant of 2.05 at 1 MHz due to the higher
free volume and fluorine content.
13 Eastmond, G. C.; Paprotny, J. Eur Polym
J 1999, 35,
2097–2106.
14 Xu, J.; He, C.; Chung, T.-S. J Polym Sci Part A: Polym Chem
2001, 39, 2998–3007.
15 Reddy, D. S.; Chou, C.-H.; Shu, C.-F.; Lee, G.-H. Polymer
2003, 44, 557–563.
16 Myung, B. Y.; Kim, J. S.; Kim, J. J.; Yoon, T. H. J Polym Sci
Part A: Polym Chem 2003, 41, 3361–3374.
17 Hsiao, S.-H.; Huang, T.-L. J Polym Res 2004, 11, 9–21.
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Two novel triptycene-based bis(ether amine)s, 1,4-bis(4-ami-
nophenoxy)triptycene (4), and 1,4-bis(4-amino-2-trifluoro-
methylphenoxy)triptycene (6), have been successfully syn-
thesized and reacted with various aromatic tetracarboxylic
dianhydrides leading to several new triptycene-containing
polyimides by two-step thermal or chemical imidization
method. All the polyimides afforded transparent, flexible, and
strong films. Most of the fluorinated polyimides derived from
6 exhibited very good solubility in organic solvents and
could be solution-cast to pale yellow to nearly colorless films
directly in their fully imidized form. The enhanced solubility
and decreased color intensity in aromatic polyimides have
been achieved at little sacrifice in thermal stability, flexibility,
or mechanical properties. In addition, the fluorinated polyi-
mides also exhibited low dielectric constants. Thus, these
properties suggest the potential usefulness of these novel
polyimides in microelectronics and optoelectronics
applications.
20 Chen, Y.-Y.; Yang, C.-P.; Hsiao, S.-H. Macromol Chem Phys
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21 Lin, C. H.; Lin, C. H. J Polym Sci Part A: Polym Chem 2007,
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22 Chang, C. W.; Lin, C. H.; Cheng, P. W.; Hwang, H. J.; Dai, S.
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23 Lin, C. H.; Chang, S. L.; Cheng, P. W. J Polym Sci Part A:
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24 Chern, Y.-T.; Tsai, J.-Y. Macromolecules 2008, 41,
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25 Chern, Y.-T.; Wang, J.-J. J Polym Sci Part A: Polym Chem
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