Design and synthesis of unsymmetric phosphinated diamines for high-T g, transparent polyimides

Article abstract of DOI:10.1016/j.polymer.2012.02.037

Two phosphinated diamines, 1-(4-aminophenyl)-1-(3-t-butyl-4-aminophenyl) -1- (6-oxido-6H -dibenz <1,2> oxaphosphorin-6-yl)ethane (1) and 1-(4-aminophenyl) -1-(3-methxoy-4-aminophenyl)-1-(6-oxido-6H -dibenz <1,2> oxaphosphorin-6-yl)ethane (2),

Full text of DOI:10.1016/j.polymer.2012.02.037

Polymer 53 (2012) 1651e1658
Contents lists available at SciVerse ScienceDirect
Polymer
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Design and synthesis of unsymmetric phosphinated diamines for high-Tg,
transparent polyimides
,
b,
Hou Chien Chang a, Sheng Lung Chang a, Ching Hsuan Lin a , Sinn Wen Chen
*
**
a Department of Chemical Engineering, National Chung Hsing University, Taichung, Taiwan
b Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
Two phosphinated diamines, 1-(4-aminophenyl)-1-(3-t-butyl-4-aminophenyl) -1- (6-oxido-6H -dibenz
<c,e> <1,2> oxaphosphorin-6-yl)ethane (1) and 1-(4-aminophenyl) -1-(3-methxoy-4-aminophenyl)-1-
(6-oxido-6H -dibenz <c,e> <1,2> oxaphosphorin-6-yl)ethane (2), were prepared via a facile, one-pot
reaction of DOPO, 4-aminoacetophenone and 2-tertbutylaniline or 2-anisidine in the presence of p-
toluenesulfonic acid. Based on diamines (1e2), a series of unsymmetric polyimides (3e4) were prepared
in NMP/xylene by high-temperature solution polymerization. Transparency polyimides 3e4 with flexi-
bility, organo-solubility, high-Tg values (310e384 ꢀC), and moderate thermal properties (Td 5 wt%,
nitrogen: 461e477 ꢀC; air, 456e474 ꢀC) can be achieved. We found that the transparency of polyimide
films is related with the orientation of the biphenylene phosphinate pendant, and the orientation is
influenced by the bulkiness of the ortho-substituted substituent.
Received 29 November 2011
Received in revised form
14 February 2012
Accepted 19 February 2012
Available online 27 February 2012
Keywords:
Polyimides
Orientation
Transparency
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
bulky diphenylphosphine oxide-containing, space environmentally
stable PIs, in which low color is preferred for low solar absorptivity
Aromatic polyimides (PIs) are well-known as high performance
material because of their excellent thermal and mechanical prop-
erties [1e3]. They are widely applied in electronics and aerospace
industries [4,5]. Despite their outstanding properties, most PIs are
typically yellow to amber in color because of the conjugation of the
polymer chain and the formation of intermolecular/intramolecular
charge transfer complex (CTC) [6]. This feature limits their appli-
cation in optics such as flexible solar radiation protectors and
orientation films in liquid crystal display devices [7e10]. Studies
have reported that the incorporation of bulky pendants can reduce
the CTC effect. For example, Swager et al. prepared triptycene PIs
based on 2,6-diaminotriptycene. The resulting PIs exhibit high
transparency and extremely low dielectric constants due to the
increased free volume resulting from the triptycene structure [11].
Triptycene polyetherimides (PEIs) based on triptycene-containing
dietheranhydride [12] and dietheramine [13] have been reported
by Zhang et al, and Hsiao et al, respectively. Ando et al. [14,15],
Harris et al. [16,17], Yang et al. [18e20], Shu et al. [21,22], Kim et al.
[23,24] and Liaw et al. [25] prepared transparent fluorinated PI
based on bulky trifluoromethyl pendants. Connell et al. prepared
[26,27]. Another benefit of bulky groups is that they improve the
solubility of PIs [28e36].
In our previous work, we reported a facile approach for
preparing phosphinated diamines [37]. A series of PIs with high-Tg
and good flame retardancy were prepared. Although they exhibited
a bulky phosphinate pendant, the solubilities of the resulting PIs
were not good enough due to the rigid polymer chains. In the
second paper of this series [38], we introduced the unsymmetric
concept to enhance the solubility. Unsymmetric diamines with
ortho-dimethyl or diethyl substitution were designed, and the
corresponding PIs exhibited high-Tg characteristics and good
organo-solubility. Although a bulky phosphinate and two alkyl
pendants were present to reduce the well-staking of the PI chains,
the resulting PIs were even darker than the reference PI, [37], in
which no alkyl groups were present. X-ray single crystal diffracto-
gram showed the unusual orientation of the phosphinate pendant
[38]. Instead of being distant from the dialkyl groups to reduce the
steric and electronic repulsion, the phosphinate inclined toward
the diethyl groups. It was speculated that the unusual orientation
was resulted from the intramolecular interaction between
electron-deficient phosphorus and electron-donating dialkyl
groups. Moreover, the intramolecular interaction was probably
responsible for the darker colors of the resulting PIs.
* Corresponding author.
We thought that if the dimethyl or diethyl substitution were
replaced by a bulkier group, the phosphinate pendant might incline
** Corresponding author.
E-mail address: linch@nchu.edu.tw (C.H. Lin).
0032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2012.02.037

1652
H.C. Chang et al. / Polymer 53 (2012) 1651e1658
Scheme 1. Synthesis of diamines (1e2).
toward the unsbustituted 4-aminophenyl linkage due to the larger
steric and electronic repulsion. This would reduce the intra-
molecular interaction and therefore lighten the color of the PI films.
In the third part of this series, we prepared two phosphinated
diamines, 1-(4-aminophenyl) -1-(3-t-butyl-4-aminophenyl)-1-(6-
oxido-6H -dibenz <c,e> <1,2> oxaphosphorin-6-yl)ethane (1)
and 1-(4-aminophenyl) -1-(3-methxoy-4-aminophenyl)- 1-(6-
oxido-6H -dibenz <c,e> <1,2> oxaphosphorin-6-yl)ethane (2),
for PIs with low color characteristics. The X-ray single crystal
diffractions of diamines (1e2) showed that the orientation of the
phosphinate pendant, as thought, was inclined toward the unsub-
stitued 4-amino phenyl linkage, and the color of the resulting PI
films was clearly reduced. The detailed synthesis and the structure-
property relationship are reported in this work.
used are commercial products (HPLC grade) and were used without
further purification.
2.2. Characterization
NMR measurements were performed using a Varian Inova 600
NMR in DMSO-d6, and the chemical shift was calibrated by setting
the chemical shift of DMSO-d6 as 2.49 ppm. IR Spectra were ob-
tained in the standard wavenumber range of 400e4000 cmꢁ1 by
a PerkineElmer RX1 infrared spectrophotometer. High-resolution
mass (HRMS) measurements were performed by a Finnigan/
Thermo Quest MAT 95XL mass spectrometer by fast atom
bombardment. Elemental analysis was performed on an Elementar
Vario EL III. Wide-angle X-ray diffraction measurements were
performed at room temperature by an MAC Science DMAX2000 X-
ray diffractometer with monochromatic Cu Ka radiation
2. Experimental
(
l
¼ 1.5418 Å, operating at 40 kV and 30 mA). The scanning rate was
conducted at 3ꢀ/min over a range of 2
q
¼ 5e40ꢀ. Differential
2.1. Materials
scanning calorimeter (DSC) scans were obtained by a PerkineElmer
DSC 7 in a nitrogen atmosphere at a heating rate of 20 ꢀC/min.
Dynamic mechanical analysis (DMA) was performed with a Per-
9,10-Dihydro-oxa-10-phosphaphenanthrene-10-oxide (DOPO,
TCI), 4-aminoacetophenone (Acros), 2-tertbutylaniline (Acros), 2-
anisidine (Acros), p-toluenesulfonic acid monohydrate (p-TSA,
Showa) were used as received. Pyromellitic dianhydride (PMDA,
Acros) was dried at 170 ꢀC overnight before use. 3,30,4,40-Benzo-
phenonetetracarboxylic dianhydride (BTDA, Acros), 4,40-oxy-
kineElmer Pyris Diamond DMA with
a
sample size of
5.0 ꢂ 1.0 ꢂ 0.002 cm. The storage modulus E0 and tan
d were
determined as the sample was subjected to the temperature scan
mode at a programmed heating rate of 5 ꢀC/min at a frequency of
1 Hz. The test was performed by tension mode with an amplitude of
diphthalic
anhydride
(ODPA,
Chriskev),
3,30,4,40-
25 mm. Thermo mechanical analysis (TMA) was performed by a SII
biphenyltetracarboxylic dianhydride (BPDA, Chriskev), and 2,2-
bis(3,4-dicarboxyphenyl)hexafluoropropane.dianhydride (6FDA,
Chriskev) were recrystallized from acetic anhydride. The solvents
TMA/SS6100 at a heating rate of 5 ꢀC/min. Thermal gravimetric
analysis (TGA) was performed by a PerkineElmer TGA 7 at a heating
rate of 20 ꢀC/min in a nitrogen atmosphere from 105 ꢀC to 800 ꢀC.
Scheme 2. Synthesis of PIs 3e4.

H.C. Chang et al. / Polymer 53 (2012) 1651e1658
1653
Gel permeation chromatography (GPC) was carried out on a Per-
kineElmer series 200a with an RI detector using THF as the
eluent at 60 ꢀC with a flow rate of 1.0 mL/min. The data were
calibrated with polystyrene standards.
white crystal (62% yield) with a melting point of 248 ꢀC (DSC) was
obtained. The synthetic equation of diamine (1) is shown in Scheme
1. HR-MS(FABþ) m/z : Calcd. for C30H31N2O2P 482.2123; Anal.,
483.2213
for
C30H32N2O2P.
1H-NMR
(DMSO-d6),
d
¼ 1.20(9H,(CH3)3), 1.58(6H,H22), 4.63(2H,NH2), 5.23(2H,NH2), 6.35
(1H,H16), 6.43(2H,H23), 6.73(1H,H15), 7.04(2H,H22), 7.07(1H,H4),
7.14(2H,H6, H20), 7.22(1H,H7), 7.34(1H,H16), 7.34(2H,H3, H8),
7.65(1H,H2), 7.93(1H,H5), 8.04(1H,H1). 13C-NMR (DMSO-d6),
2.3. Synthesis of (1)
DOPO 4.80
g (22.21 mmol), 4-aminoacetophenone 3.0 g
d
¼ 24.39 (CH3), 29.09 ((CH3)3), 33.95 (C19), 51.32 (C13), 51.93 (C13),
(22.21 mol), 2-tertbutylaniline 9.94 g (66.63 mmol), and p-TSA
0.192 g (4 wt% based on DOPO) were introduced into a 100-mL
round-bottom glass flask equipped with a nitrogen inlet and
a magnetic stirrer. The reaction mixture was stirred at 90 ꢀC for
12 h. After that, the precipitate was filtered and recrystallized from
methanol, and then dried in a vacuum oven at 120 ꢀC for 8 h. Light
113.08 (C23), 116.13 (C16), 118.81 (C4), 120.95 (C11), 122.69 (C10),
123.23 (C1), 123.43 (C10), 123.66 (C6), 125.28 (C5), 126.18 (C20),
126.53 (C12), 17.04 (C15), 127.61 (C8), 129.40 (C14), 129.97 (C22),
130.43 (C3), 130.74 (C21), 131.83 (C7), 132.97 (C2), 135.93 (C18), 144.15
(C17), 147.27 (C24), 150.72 (C9). The single crystal data is shown as
Fig. 1. (a) 1H and (b) 13C NMR spectra of diamine (1).

1654
H.C. Chang et al. / Polymer 53 (2012) 1651e1658
Table 1
GPC and solubility data of PIs 3e4.
PIs
GPC Dataa
Solubility datac
Mnb (ꢂ104)
Mw (ꢂ104)
NMP
DMAc
DMSO
m-cresol
CHCl3
CH2Cl2
THF
3a
3b
3c
3d
3e
4a
4b
4c
4d
4e
e
e
þ
þ
þ
þ
þ
þ
ꢃ
þ
þ
þ
þ
þh
þ
þh
þ
þh
þ
þ
þ
þ
ꢃ
þ
þ
þ
þ
þ
þ
þ
þ
þ
ꢃ
þ
þ
ꢃ
þ
ꢃ
þ
ꢃ
ꢃ
þ
e
ꢃ
e
e
þ
4.7
e
8.3
e
þ
þ
þ
þ
e
e
þ
þh
þ
þ
4.6
e
7.9
e
þ
þ
þh
þ
ꢃ
þh
þ
e
e
ꢃ
e
e
þ
þh
ꢃ
þ
e
e
þh
þ
þh
þ
6.6
9.0
þ
a
Relative to polystyrene standard, using THF as eluent.
b
c
Mn: number-average molecular weight, Mw: weight-average molecular weight.
Solubility was tested with a 5 mg sample in 0.5 g of solvent at room temperature. þ, soluble; þh, soluble on heating; ꢃ, partially soluble on heating; -, insoluble on heating.
follows: C30H31N2O2P, 0.51 ꢂ 0.45 ꢂ 0.11 mm3, monoclinic with
2.5. Preparation of PIs
a ¼ 9.1227(8) Å, b ¼ 9.4038(9) Å, c ¼ 15.6412(15) Å,
a
¼ 80.957(2) ,
b
¼ 76.915(2) ,
g
¼ 74.222(2) with Dc ¼ 1.281 mg/m3 for Z ¼ 2,
PIs syntheses are exemplified by the synthesis of 3a from the
condensation of (1) and PMDA. To a 50-mL round-bottom flask
equipped with a magnetic stirrer, a DeaneStark trap with
V ¼ 1251.2(2) Å [3], T ¼ 297(2) K, ¼ 0.71073 Å, F(000) ¼ 512, final R
l
indices: R1 ¼ 0.0464, WR2 ¼ 0.1293.
condenser, a nitrogen inlet. (1) 1.4477 g (3 mmol), PMDA 0.6544 g
(3 mmol) and NMP 8.5 g were added. After the monomer had
dissolved completely, xylene 5 g was added. The reaction was
carried out at reflux temperature for 12 h. Then, the viscous PIs
solution was casted on glass by an automatic film applicator, and
dried at 80 ꢀC overnight and 100 ꢀC (1 h), 200 ꢀC (2 h), respectively.
The other PIs (3be3d, 4ae4d) were similarly prepared. The
synthetic equation of PIs 3e4 is shown in Scheme 2.
3. Results and discussion
2.4. Synthesis of (2)
3.1. Synthesis of (1e2)
Diamine (2) was synthesized with a procedure similar to (1)
using 2-anisidine as the starting material. White crystal (70% yield)
with a melting point of 237 ꢀC (DSC) was obtained. The synthetic
equation of diamine (2) is shown in Scheme 1. HR-MS(FABþ) m/z :
Calcd. for C27H25N2O3P 456.1603; Anal., 457.1691 for C27H26N2O3P.
Unsymmetric diamine (1-2) with the t-butyl/methoxy substit-
uent were prepared by
a one-pot reaction of DOPO, 4-
aminoacetophenone in excess 2-tertbutylaniline (or 2-anisidine)
using p-TSA as the catalyst (Scheme 1).
1H-NMR (DMSO-d6),
d
¼ 1.57(3H,CH3), 3.58(3H,H19), 4.63(2H,NH2),
The excess 2-tertbutylaniline (or 2-anisidine) played the roles of
both reactant and reaction medium. Initially, a similar reaction
condition (130 ꢀC for 24 h) [37,38] was applied to prepare
unsymmetric diamines (1e2). However, judging from the NMR
spectra, complicated products were obtained. It is speculated the t-
5.04(2H, NH2), 6.41(2H, H23), 6.45(1H, H16), 6.71(1H,H15),
6.88(1H,H20), 6.99(2H,H22), 7.12(1H,H4), 7.16(1H,H6), 7.17(1H,H7),
7.33(1H,H8), 7.35(1H,H3), 7.65(1H,H2), 7.99(1H,H5), 8.07(1H,H1).
13C-NMR (DMSO-d6),
d
¼ 24.26 (CH3), 51.44 (C13), 51.05 (C13), 51.35
(C5), 55.0 (C19), 111.2 (C20), 113.03 (C16, C23), 118.93 (C4), 120.89 (C11),
121.22 (C15), 122.59 (C10), 123.27 (C1), 123.32 (C10), 123.78 (C6),
125.31 (C5), 125.94 (C12), 127.68 (C8), 130.06 (C22), 130.34 (C14),
130.51 (C3), 131.85 (C7), 133.06 (C2), 135.86 (C21), 136.10 (C17), 145.49
(C24), 147.40 (C18), 150.64 (C9). The Single crystal data is as follows:
C27H25N2O3P, 0.32
ꢂ
0.25
ꢂ
0.15 mm3, monoclinic with
a ¼ 9.3407(4) Å, b ¼ 9.9427(3) Å, c ¼ 12.8449(5) Å,
a
¼ 78.401(3)o,
b
¼ 83.937(3)o,
g
¼ 79.619(3)o with Dc ¼ 1.322 mg/m3 for Z ¼ 2,
V ¼ 1146.46(7) Å [3], T ¼ 297(2) K, ¼ 0.71073 Å, F(000) ¼ 480, final
l
R indices: R1 ¼ 0.0404, WR2 ¼ 0.1064.
Fig. 2. WXRD diffraction of PIs 3.

H.C. Chang et al. / Polymer 53 (2012) 1651e1658
1655
Fig. 3. Picture of PI 3a, 4a, and ref PI.
butyl/methoxy and amine group are both para-directed substitu-
ents. Electrophilic substitution might occur at two position sites,
resulting in complicated products at high temperatures. After
changing to a mild reaction condition (90 ꢀC, 12 h), diamines (1e2)
were successfully synthesized. Therefore, the reaction temperature
is crucial for the electrophilic substitution of compounds with two
electron-donating groups.
1H-13C HETCOR NMR spectra (Figure S3-S5), and the assignments of
each peaks support the structure and purity.
3.3. PI synthesis
PIs 3e4 were prepared by reacting (1e2) with equal molar
dianhydrides (aed) in NMP/xylene by high-temperature solution
polymerization (Scheme 2).
Initially, we attempted to prepare PIs 3e4 via the standard two-
step procedure: polycondensation at a low temperature, followed
by high-temperature thermal imidization. However, the viscosity of
poly(amic acid) in the first step was not very high. It is speculated
that the steric hindrance resulting from the ortho-substituted t-
butyl/methoxy group reduced the reactivity. Therefore, a high-
temperature solution polymerization was applied to overcome
the steric hindrance. No precipitate was formed during the poly-
merizaiton, so PIs with moderate-to-high molecular weight were
expected. Table 1 lists the GPC data of the resulting PIs. The
number-average molecular weights range from 4.6 to 6.6 ꢂ 104 g/
mol, and the weight-average molecular weights range from 7.9 to
9.0 ꢂ 104 g/mol, demonstrating moderate-to-high molecular
weight.
3.2. Characterization of (1e2)
Fig. 1 shows the (a) 1H-NMR and (b) 13C-NMR spectra of (1). Two
amino signals were observed at 4.63 and 5.23 ppm, confirming the
unsymmetric structure of diamine (1). A t-butyl signal at 1.20 ppm
and a methyl doublet at 1.58 ppm were observed. The splitting of
3
methyl signal is due to the JPeH coupling, and the coupling
constant is 10.2 Hz. The assignment of AreH, assisted by the
correlations in the 1He1H COSY NMR spectrum (Figure S1),
confirms the structure of (1). The signals of aliphatic carbon adja-
cent to phosphorus (C13) were split into two peaks at 51.3 and
51.9 ppm with a coupling constant of 92 Hz due to the PeC 1J
coupling. The signals of aromatic carbon adjacent to phosphorus
(C10) were also split into two peaks at 122.7 and 123.4 ppm with
a coupling constant of 111 Hz for the same reason. The assignment
of AreC, assisted by the correlations in the 1H-13C HETCOR NMR
spectrum (Figure S2), also confirms the structure of (1). Unsym-
metric diamine (2) was characterized by 1H, 13C, 1H-1H COSY and
3.4. Organosolubility and crystallinity
Table 1 also lists the solubility data of PIs 3e4. Except for 4a, all
PIs display good solubility in NMP, DMAc, DMSO, m-cresol and
CHCl3. PIs 3b, 3e, and 4e are even soluble in THF. If one compares
the solubility data of PIs 3 with those of PIs 4, one can find that PIs 3
show better solubility. It is probably because the bulkiness of t-
butyl is higher than that of the methoxy group. Fig. 2 shows the
wide-angle X-ray diffraction pattern of PIs 3. All PIs are amorphous.
Although polyimides are generally amorphous, the bulky biphe-
nylene phosphinate and unsymmetric linkage, which prevents PI
chains from packing well, further enhance the amorphous charac-
teristic of the resulting PIs.
3.5. Film quality and color
Fig. 3 shows a picture of PI 3a, 4a, and ref PI (the structure of ref
PI is shown in the Figure). Fig. 4 shows UVeVis spectra of PIs 3a, 4a
and ref PI with thickness of 40 mm. As shown in Figs. 3and 4, PI 3a
shows much lower cutoff wavelength and higher transparency than
ref PI.
We speculated that the (1) intramolecular interaction between
electron-donating dialkyl and electron-deficiant phosphorus, and
(2) the
p.pinteraction between phenylene and biphenylene
Fig. 4. UVeVis spectra of PI 3a, 4a, and ref PI.
resulted in the dark color of the PI films in previous work [38]. In

1656
H.C. Chang et al. / Polymer 53 (2012) 1651e1658
Fig. 5. Single crystal diffractograms of (1e2).
this work, the bulky t-butyl group was introduced in diamine (1) to
increase the steric and electronic repulsion to prevent the intra-
molecular interaction. X-ray single crystal diffraction of (1) (Fig. 5)
shows the orientation of the phosphinate pendant inclines toward
the unsubstitued 4-aminophenyl linkage, which has conformation
that is completely different from that of a diethyl substituted
4e, respectively (Fig. 6). The higher bulkiness of t-butyl group,
which leads to not only less intramolecular but also intermolecular
interaction, might be responsible for this phenomenon. In partic-
ular, the cutoff wavelengths of 3b and 3e are 369 and 362 nm,
respectively, which are comparable with those of fluorinated
diamine-based PIs with the same dianhydride moiety [39,40].
diamine [38]. The orientation reduces thep.pinteraction, and PIs
with much better transparency are achieved. However, a detailed
analysis is required to confirm the speculation.
3.6. Thermal properties
A similar orientation was observed in diamine (2). PI 4a, as
shown in Figs. 3and 4, also shows much better transparency than
the ref PI. If one compares 3a and 4a, one can find that 3a shows
slightly better transparency. Similar results can also be observed for
the higher transparencies of 3b and 3e compared to those of 4b and
Since PIs 3e4 are flexible and foldable, DMA was applied to
evaluate their thermal mechanical properties. Fig. 7 shows the DMA
thermograms of PIs 3, and detailed data are listed in Table 2. Tgs
obtained from the peak temperature of tan(delta) range from 312 to
384 ꢀC. Generally, Tg is correlated with the stiffness and
Fig. 6. UVeVis spectra of PIs 3b, 3e, 4b and 4e.

H.C. Chang et al. / Polymer 53 (2012) 1651e1658
1657
4.5
10
conformation of polymer chain. Thus, the highest Tg value of 3a
may be attributed to the rigidity of PMDA moiety. In contrast, the
lowest Tg value of 3b may be due to the flexible ether linkage of
OPDA moiety. A similar trend can also be observed in the 4 series.
Fig. 8 shows the TMA curves of the 3 series, and the results are
listed in Table 2. Tgs of PIs 3 measured by TMA range from 279 to
353 ꢀC, and the trend is the same as that observed in DMA
measurement. The thermal stability of PIs 3e4 was evaluated by
TGA. The 5 wt% degradation temperatures range from 461 to 477 ꢀC
in a nitrogen atmosphere and range from 456 to 474 ꢀC in an air
atmosphere, demonstrating moderate-to-high thermal properties.
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
10
4a
4b
4c
4d
4e
10
10
10
10
10
10
4. Conclusions
Two phosphinated diamines (1e2), designed to reduce the
intermolecular interaction, were successfully prepared. PIs based
on (1e2) were prepared in NMP/xylene by high-temperature
solution polymerization. PIs with an ortho t-butyl or methoxy
substitution display much higher transparency and lower cutoff
wavelengths than those with ortho-dialkyl substituted PIs [38]. X-
ray single crystal diffractograms of (1e2) show the orientation of
the phosphinate pendant inclines toward the unsubstitued 4-
aminophenyl linkage, which has conformation with much smaller
intramolecular interaction than that of a diethyl substituted
diamine [38]. It is thought that the improved transparency of PIs
3e4 is related with the reduced intramolecular interaction. To the
best of our knowledge, this is the first study discussing the effect of
orientation of a bulky pendant on the transparency of PI films. In
addition to good transparency, PIs 3e4 display flexibility, good
organo-solubility, high-Tg values, and moderate thermal properties.
The combination of these characteristics makes PIs 3e4 attractive
for applications in microelectronic and optical devices.
50
100
150
200
250
300
350
400
450
Temperature oC
Fig. 7. DMA thermograms of PIs 3.
Table 2
Thermal and mechanical properties of PIs 3e4.
Sample Film
E0(GPa)a Tg (ꢀC) Tg (ꢀC) Td5%( oC)d
Char yielde
quality
(DMA)b (TMA)c
N2
air
N2
air
3a
3b
3c
3d
3e
4a
4b
4c
4d
4e
Foldable 4.0
Foldable 3.7
Foldable 3.7
Foldable 4.3
Foldable 3.9
Foldable 4.0
Foldable 2.4
Foldable 3.5
Foldable 4.5
Foldable 2.3
384
312
322
343
328
391
293
310
332
310
353
279
284
318
292
358
262
276
304
281
477
465
456
461
464
467
461
464
469
466
460
458
456
462
457
466
460
456
474
469
52
53
54
49
47
54
56
55
59
48
46
38
37
45
1
39
43
37
47
4
Appendix. Supporting information
a
Measured by DMA; heating rate, 5 ꢀC/min; storage modulus (E0) are recorded at
50 ꢀC.
Supplementary data related to this article can be found online at
doi:10.1016/j.polymer.2012.02.037.
b
c
Measured by DMA; the peak temperature of the Tan
Measured by TMA; heating rate, 5 ꢀC/min.
The 5% decomposition temperature.
Residual wt% at 800 ꢀC in nitrogen.
d
curve.
d
e
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