9,9-diaryl-4,5-diazafluorene-based cardo polymer; Synthesis and characteristic properties

Article abstract of DOI:10.1002/pola.26870

To open out new aspects of 9,9-diarylfluorene (DAF)-based polymers with high performances, 9,9-(4-hydroxyphenyl)-4,5-diazafluorene (N-BPF) was designed as a new cardo structure and the properties of poly(ether ketone)s (N-PEKs) containing N-BPF skeletons were examined in detail. N-PEKs were synthesized in high yields via polycondensation of N-BPF with difluoroarenes. N-PEKs showed cardo polymer-specific properties such as high thermal stability and high solubility in organic solvents. The addition of p-toluenesulfonic acid (TsOH) to N-PEK resulted in the formation of network polymer based on interchain hydrogen bonds. It turned out that the films of network polymer are flexible and transparent and exhibit high refractive index and low birefringence. The effects of feed ratio of TsOH to N-PEK were also evaluated on the mechanical properties of network polymer.

Full text of DOI:10.1002/pola.26870

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9
,9-Diaryl-4,5-diazafluorene-Based Cardo Polymer;
Synthesis and Characteristic Properties
1
1
2
1
Hitoshi Okuda, Yasuhito Koyama, Takahiro Kojima, Toshikazu Takata
1
Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1 (H-126), Ookayama,
Meguro, Tokyo 152-8552, Japan
2
Production Engineering Research Laboratory, Canon Inc., 70-1, Yanagi-cho, Saiwai, Kawasaki,
Kanagawa 212-8602, Japan
Correspondence to: T. Takata (E-mail: ttakata@polymer.titech.ac.jp)
Received 16 May 2013; accepted 29 June 2013; published online 30 July 2013
DOI: 10.1002/pola.26870
ABSTRACT: To open out new aspects of 9,9-diarylfluorene
DAF)-based polymers with high performances, 9,9-(4-hydroxy-
on interchain hydrogen bonds. It turned out that the films of
network polymer are flexible and transparent and exhibit high
refractive index and low birefringence. The effects of feed ratio
of TsOH to N-PEK were also evaluated on the mechanical prop-
(
phenyl)-4,5-diazafluorene (N-BPF) was designed as a new cardo
structure and the properties of poly(ether ketone)s (N-PEKs)
containing N-BPF skeletons were examined in detail. N-PEKs
were synthesized in high yields via polycondensation of N-BPF
with difluoroarenes. N-PEKs showed cardo polymer-specific
properties such as high thermal stability and high solubility in
organic solvents. The addition of p-toluenesulfonic acid (TsOH)
to N-PEK resulted in the formation of network polymer based
erties of network polymer.
V
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2013 Wiley Periodicals, Inc. J.
Polym. Sci., Part A: Polym. Chem. 2013, 51, 4541–4549
KEYWORDS: cardo structure; heteroatom-containing polymers;
high-performance polymers; poly(ether ketones); refractive
index; low birefringence
INTRODUCTION As 9,9-diarylfluorene (DAF)-based polymers
exhibit unique properties such as high thermal stability,
high solubility in organic solvents, amorphous nature, high
filler-dispersing ability, high refractive index, and low bire-
fringence, they have attracted considerable interests in the
field of high-performance polymer materials such as optical
nitrogen functionality seem interesting from new aspects of
DAF-based polymers. In this article, we describe the synthe-
sis and properties of N-BPF-based cardo polymers and the
network polymers obtained by interchain hydrogen bonds
of N-BPF.
1
–6
7–9
materials,
gas permselective film,
heat-resistance resin,
These excellent properties are attributed to the
high filler dispersi-
EXPERIMENTAL
1
0–12
13–21
ble matrix polymer,
and so
Materials
2
2–29
forth.
39
4
,5-Diazafluorenone (1),
1,4-bis(4-fluorobenzoyl)benzene
cardo structure of DAF in which aryl substituents at the
quaternary carbon center of alicyclic moiety occupy differ-
ent planes [Fig. 1(a)]. To explore the useful derivatives of
DAF-based polymers, we have previously reported the syn-
thesis of modified cardo structure-based polymers such as
40
41
(2a),
5-tert-butyl-1,3-bis(4-fluorobenzoyl)benzene (2b),
42
2,5-bis(4-fluorophenyl)21,3,4-oxazole (2d), and 1,5-bis(4-
43
fluorobenzoyl)22,6-dimethylnaphthalene (2e)
pared according to the literature. 4,4 -Difluorobenzophenone
were pre-
0
(
2c) available from TCIVR was purified by recrystallization
3
0
silafluorene-type cardo polymer,
mers,
sulfur-containing poly-
from EtOH. Other commercially available materials were
used without further purification.
3
,19
0
31–34
9,9 -spirobifluorene-based polymers,
and their
excellent properties such as higher thermal stability, higher
refractive index, and lower birefringence than those of the
corresponding DAF-containing polymers. We have recently
Measurements
H (400 MHz) and
1
13
C NMR (100 MHz) spectra were
3
5–
focused our attention on the fusion of 4,5-diazafluorene
recorded on a JEOL AL-400 spectrometer using CDCl3,
3
8
into a new cardo structure. Because the cardo polymer
DMSO-d , and CD OD as the solvent and tetramethylsilane as
6
3
consisting of 4,5-diazafluorene-based cardo units (N-BPF)
has the regularly arranged nitrogens in the side chain, the
applications of N-BPF that use the characteristics of the
an internal standard. The viscosity of N-PEKs was evaluated
by Ostwald viscometer in N-methypyrrolidone (NMP) solu-
tion (0.50 g dL ) at 30 C. Tensile testing (stress–strain)
2
1
ꢀ
Additional Supporting Information may be found in the online version of this article.
2013 Wiley Periodicals, Inc.
V
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FIGURE 1 Structures and the space-filling models of DFT-optimized geometries (B3LPY, 6–31G**) of (a) 9,9-Diarylfluorene DAF
and (b) 9,9-bis(4-hydroxyphenyl)24,5-diazafluorene N-BPF. [Color figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
was conducted in a Shimadzu AG-IS test machine by using
5.0 mm 3 20.0 mm) specimens at a strain rate of 10 mm
MeOH or DMF–H O to give a white cotton solid (6.31 g,
82%).
2
(
21
g
min . The glass transition temperatures (T ) were meas-
ꢀ
1
3
m.p. > 314 C (decomp.); H NMR (400 MHz, CD OD, d): 8.56
ured with a Shimadzu DSC-60 instrument at a heating rate
ꢀ
21
21
(dd, J 5 4.9, 1.5 Hz, 2H), 7.85 (dd, J 5 7.8, 1.5 Hz, 2H), 7.35 (dd,
of 10 C min under a nitrogen (flow rate 50 mL min ).
Thermo gravimetric analysis (TGA) was performed with a
J 5 4.9, 1.5 Hz, 2H), 6.78 (d, J 5 8.6 Hz, 4H), 6.47 (d, J 5 8.6 Hz,
1
ꢀ
2H) ppm; H NMR (400 MHz, DMSO-d , d): 9.41 (s, 2H), 8.66
Shimadzu TGA-50 instrument at a heating rate of 10
min under a nitrogen atmosphere and on air atmosphere
flow rate 50 mL min ). The solubility of polymers was
C
6
21
(d, J 5 4.6 Hz, 2H), 7.90 (d, J 5 8.1 Hz, 2H), 7.40 (dd, J 5 8.1,
4.6 Hz, 2H), 6.90 (d, J 5 8.5 Hz, 4H), 6.64 (d, J 5 8.5 Hz, 4H)
2
1
(
1
3
ppm; C NMR (100 MHz, CD
1
3
OD, d): ꢁ162.2, 157.9, 150.1,
evaluated by using 3 mg of polymer to 1 mL of solvent. Fou-
rier transform infrared spectroscopy (FTIR) spectra were
recorded on a JASCO FT/IR-460 Plus spectrophotometer.
Melting points were measured with a Stuart Scientific SMP3.
Ultraviolet-visible (UV-vis) spectra were recorded on a JASCO
V-550 UV-vis spectrometer. The refractive indices of the poly-
mers were measured with an Abbe refractometer (DR-M2/
49.9, 135.9, 133.0 129.8, 125.0 117.9, 39.5 ppm; IR (KBr):
m 5 3222 (br), 1612, 1511, 1208, 1043, 735 cm
2
1
.
38 1
lit.
(
H NMR (DMSO-d , d): 9.44 (s, 2H), 8.67 (d, 2H), 7.93
6
13
d, 2H), 7.42 (dd, 2H), 6.92 (d, 4H), 6.66 (d, 4H) ppm;
C
NMR (DMSO-d , d): 164.1, 163.2, 160.8, 131.6, 129.2, 128.6,
6
126.4, 123.5, 116.1, 114.0 ppm.
1550, ATAGO Co.). The birefringence values of the films were
evaluated by taking the pictures of films placed between two
cross-axis polarizing films. Retardations were measured
using a polarized optical microscope (OPTIPHOTO-POL,
Nikon Co.) under the cross-Nicols (588 nm). Transmittance
of the films was evaluated with a UV-vis spectrophotometer
Typical Procedure of Synthesis of N-PEK:
Synthesis of N-PEK1
Bis(4-hydroxyphenyl)-4,5-diazafluorene (150 mg, 425 mmol),
K CO (118 mg, 850 mmol), and diphenylsulfone (1.7 g) was
2
3
placed in a 50 mL round-bottom flask under argon atmos-
(JASCO V-550) across a scanning range of 300 to 700 nm.
ꢀ
phere. The mixture was heated at 170 C for 2 h and cooled
to room temperature. 1,4-Bis(4-fluorophenylbenzoyl)benzene
4
0
Film Preparation
2a (137 mg, 425 mmol) was added to the mixture, and
ꢀ
Polymer films of the N-PEKs were prepared for the evalua-
tion of refractive index and birefringence with a casting
method using the NMP solutions of the corresponding poly-
then, the mixture was heated at 220 C for 2 h. The mixture
was cooled to room temperature, poured into MeOH, and the
resulting precipitates were collected by filtration and washed
with MeOH. The crude polymer was dissolved with CHCl
and the solution was filtered through a Celite
trate was reprecipitated into MeOH to give solids, which
were collected by filtration and dried in vacuo overnight to
give the corresponding polymer N-PEK1 (245 mg, 91%) as a
white solid.
ꢀ
mers at 150 C. The films used for the evaluation of trans-
,
3
VR pad. The fil-
parency were prepared by a casting method using the NMP
solutions of the corresponding polymers and annealed
ꢀ
gently at 100 C for long time enough to remove the
solvent.
Synthesis of N-BPF
N-PEK1
3
9
1
A solution of 4,5-diazafluorenone 1 (4.00 g, 22.0 mmol),
phenol (9.28 g, 98.6 mmol), 3-mercaptopropionic acid (200
mL, 2.4 mmol), and methanesulfonic acid (5.6 mL, 86 mmol)
H NMR (400 MHz, CDCl , d): 8.76 (br, 2H), 7.82–7.79 (m,
3
10H), 7.34–7.31 (m, 2H), 7.22 (d, J 5 8.4 Hz, 4H), 7.03 (d,
J 5 8.5 Hz, 4H), 6.98 (d, J 5 8.4 Hz, 4H) ppm; IR (KBr):
m 5 3056, 1656, 1591, 1495, 1401, 1242, 994 cm
ꢀ
21
in chlorobenzene (40 mL) was heated at 90 C for 7 h under
.
argon atmosphere. The mixture was cooled to room temper-
ature and concentrated in vacuo to remove chlorobenzene.
N-PEK2
1
The residue was poured into sat. aq. NaHCO . The resulting
H NMR (400 MHz, CDCl , d): 8.75 (d, J 5 3.4 Hz, 2H), 7.98
3
3
precipitates were filtered off and washed with MeOH and
(br, 2H), 7.86 (br, 1H), 7.80–7.79 (m, 6H), 7.32–7.29 (m, 2H),
CHCl . The crude was purified by recrystalization from DMF–
7.20 (d, J 5 8.8 Hz, 4H), 7.00 (d, J 5 8.8 Hz, 4H), 6.97 (d,
3
4
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SCHEME 1 Synthesis of N-BPF.
TABLE 1 Synthesis of N-PEKs
a
21
Entry
Spacer
Products
Solvent
Temperature (Time)
Yield (%)
g
inh (dL g
)
ꢀ
ꢀ
b
b
1
2
3
4
5
6
7
2a
2a
2a
2b
2c
2d
2e
2e
N-PEK1
N-PEK1
N-PEK1
N-PEK2
N-PEK3
N-PEK4
N-PEK5
co-N-PEK5
DMAc
140 C, 2 h ! 170 C, 3 h
–
–
ꢀ
ꢀ
NMP
140 C, 2 h ! 170 C, 4 h
75
91
89
80
88
99
99
0.25
0.24
0.25
0.27
0.32
0.35
0.29
ꢀ
ꢀ
Diphenylsulfone
Diphenylsulfone
Diphenylsulfone
Diphenylsulfone
Diphenylsulfone
Diphenylsulfone
170 C, 2 h ! 220 C, 2 h
ꢀ
ꢀ
170 C, 2 h ! 220 C, 2 h
ꢀ
ꢀ
170 C, 2 h ! 220 C, 2 h
ꢀ
ꢀ
170 C, 2 h ! 220 C, 2 h
ꢀ
ꢀ
170 C, 2 h ! 220 C, 2 h
c
d
ꢀ
ꢀ
8
170 C, 2 h ! 220 C, 2 h
a
d
The viscosity was measured by using
a
polymer solutions (0.50
Composition of BPF and N-BPF was estimated to 12:88.
21
ꢀ
g dL ) in NMP at 30 C.
b
Polymer was not obtained.
c
Polymerization was performed with 5e (1.0 equiv), BPF (0.9 equiv),
CO (1.0 eq).
and N-BPF (0.1 equiv) in the presence of K
2
3
J 5 8.8 Hz, 4H), 1.85 (s, 9H) ppm; IR (KBr): m 5 2969, 1653,
N-PEK5
2
1
1
1591, 1498, 1244, 1163, 953 cm
.
H NMR (400 MHz, CDCl , d): 8.75 (d, J 5 4.6 Hz, 4H), 7.77–
3
7
7
.75 (m, 6H), 7.45 (d, J 5 8.5 Hz, 2H), 7.31–7.29 (m, 2H),
.22 (d, J 5 8.5 Hz, 2H), 7.18 (d, J 5 8.5 Hz, 4H), 6.95 (d,
N-PEK3
1
H NMR (400 MHz, CDCl , d): 8.75 (br, 2H), 7.79 (d, J 5 8.2
Hz, 2H), 7.79–7.41 (m, 4H), 7.31–7.29 (m, 2H), 7.19 (d,
J 5 8.4 Hz, 4H), 7.00 (d, J 5 8.2 Hz, 4H), 6.97 (d, J 5 8.4 Hz,
3
J 5 9.0 Hz, 4H), 6.93 (d, J 5 8.5 Hz, 4H), 2.25 (s, 6H) ppm; IR
21
(
KBr): m 5 3056, 2963, 1663, 1590, 1496, 1243, 1154 cm
.
4
H) ppm; IR (KBr): m 5 1653, 1593, 1497, 1399, 1240, 1161,
Preparation of Network-Polymer Film
N-PEK (10 mg) was dissolved in NMP (300 mL) in 5 mL
flask. A solution of p-toluenesulfonic acid monohydrate
2
1
1014, 928 cm
.
N-PEK4
TsOHꢂH O in NMP (100 mL) was added to the polymer solu-
2
1
H NMR (400 MHz, CDCl , d): 8.78 (br, 2H), 8.05 (d, J 5 8.5
3
tion, and the mixture was stirred for 5 min. The resulting
Hz, 4H), 7.80 (d, J 5 8.3 Hz, 2H), 7.34–7.30 (m, 2H), 7.20 (d,
J 5 8.5 Hz, 4H), 7.08 (d, J 5 8.5 Hz, 4H), 6.96 (d, J 5 8.5 Hz,
ꢀ
solution was casted to a glass plate, heated at 100 C for 24
ꢀ
h, dried in vacuo at 80 C under vacuum for 12 h to give the
4H) ppm; IR (KBr): m 5 3058, 1598, 1488, 1400, 1242, 1168,
corresponding network film.
2
1
1013, 749 cm
.
SCHEME 2 Synthesis of N-PEKs.
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FIGURE 2 H NMR spectra (400 MHz, 298 K) of (a) N-BPF in DMSO-d
6
(b) 2a in CDCl
3
3
, and (c) N-PEK1 in CDCl .
TABLE 2 Solubility of N-PEKs
Entry
CH
2
Cl
2
CHCl
3
THF
DMF
DMAc
NMP
NMP
DMSO
Toluene
Conc. HCl aq
N-PEK1
N-PEK2
N-PEK3
N-PEK4
N-PEK5
PEK1
11
11
11
11
11
11
11
11
11
11
11
11
6
6
6
6
6
6
6
11
11
11
11
11
11
11
11
11
11
11
11
6
2
6
2
2
2
2
6
6
6
6
6
2
11
11
11
11
11
11
11
6
12
6
6
6
6
6
6
6
Solubility was evaluated by dissolving 3 mg polymer in 1 mL solvent. Key: 11, soluble; 12, soluble on heating; 6, partially soluble on heating;
, insoluble.
2
Synthesis of 9,9-Bis(4-methoxyphenyl)24,5-
diazafluorene 3
and conc. sulfuric acid (2.9 g, 1.6 mol) were placed in a 100
mL round-bottom-flask. The mixture was stirred at room
temperature for 30 min, followed by heating at 65 C for 5
ꢀ
4
5
,5-Diazafluorenone (1.00 g, 5.49 mmol), anisole (3.55 g,
4.9 mmol), 3-mercaptopropionic acid (2.9 mL, 33 mmol),
h. The resulting mixture was poured into 10% aq. NaOH to
FIGURE 3 Chemical Structures of N-PEKs and PEK1.
4
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TABLE 3 Thermal Properties of N-PEKs
fluorenone 1 and phenol to result in a low yield of N-BPF
40%). After considerable efforts, it turned out that the use
of methanesulfonic acid in place of HCl gas afforded 82%
(
b
ꢀ
b
ꢀ
T
d5 ( C)
T
d10 ( C)
a
ꢀ
yield of N-BPF in the presence of 3-mercaptopropionic acid
Polymer
T
g
( C)
N
2
Air
N
2
Air
(
Scheme 1).
N-PEK1
N-PEK2
N-PEK3
N-PEK4
N-PEK5
234
220
261
290
539
494
535
497
454
528
494
510
493
448
560
521
555
516
467
549
519
544
517
575
Synthesis of N-BPF-Based Cardo Polymer (N-PEK)
We have previously reported the synthesis of DAF-containing
poly(ether ketone) (PEK) to the main chain and its excellent
chemical and thermal stability. Building on the previous
work, the polymerizations of N-BPF and difluoroarenes 2a–
c
2
–
2
a
Glass transition temperatures were evaluated at a heating rate of 10
e were examined (Scheme 2), and the results were summar-
ized in Table 1.
ꢀ
b
21
21
C min under nitrogen (50 mL min ).
5
% Decomposition temperatures were measured at a heating rate of
ꢀ
21
1
c
0
C min under nitrogen or in air.
Not determined.
At first, the polycondensation condition of N-BPF was inves-
tigated by using 2a as a coupling partner (Entries 1–3). Dur-
ing polymerization in N,N-dimethylacetamide (DMAc) that is
a good solvent of both N-BPF and 2a (Entry 1), the polymers
with low molecular weights deposited soon as white solids.
Thus, we decided to use NMP or diphenylsulfone as the sol-
vent, because these solvents show high solubility for not
only N-BPF and 2a but also the precipitated polymer. As a
result, N-PEK1 with high viscosity was obtained in both
cases (Entries 2 and 3), in which it found that diphenylsul-
fone was the best solvent to afford a high yield of the poly-
precipitate a white solid, which was collected by filtration,
washed with Et O, and dried in vacuo to give 3 (1.72 g,
2
82%).
ꢀ
1
m.p. 262.0–263.3 C; H NMR (400 MHz, CDCl
J 5 4.6, 1.2 Hz, 2H), 7.44 (dd, J 5 7.8, 1.2 Hz, 2H), 7.27 (dd,
J 5 7.8, 4.6 Hz, 2H), 7.08 (d, J 5 8.9 Hz, 4H), 6.77 (d, J 5 8.9
3
, d): 8.72 (dd,
1
3
Hz, 4H), 3.76 (s, 6H) ppm; C NMR (100 MHz, CDCl , d):
3
1
6
1
58.7, 157.3, 150.0, 146.2, 135.6, 133.5, 128.8, 123.4, 113.8,
0.2, 55.2 ppm; IR (KBr): m 5 2949, 2829, 1606, 1562, 1508,
401, 1249, 1178, 1039, 813, 746 cm
1
mer. Figure 2 shows the H NMR spectra of N-BPF, 2a, and
N-PEK1. No terminal signal was observed in the H NMR
21
.
1
3
8
ꢀ
1
spectrum of N-PEK1, suggesting the formation of high-
molecular weight polymer. On the other hand, the molecular
weight of the polymer could be not estimated by an SEC
measurement, probably because of the strong interaction
between the nitrogen atoms in the 4,5-diazafluorene moi-
eties of polymer and the SEC filler gel.
lit, m.p. 275–276 C; H NMR (CDCl , d): ꢁ8.75 (m, 2H),
3
8
.13 (m, 4H), 8.07 (d, 4H), 7.80 (d, 2H), 7.54 (m, 2H), 7.52
m, 2H), 7.32 (dd, 2H), 7.08 (m, 4H), 7.06 (d, 4H), 6.79 (d,
H), 3.62 (s, 6H) ppm.
(
4
RESULTS AND DISCUSSION
According to the same manner, the polycondensation reac-
tions of N-BPF with various difluoroarenes 2b–e were pre-
formed to give the corresponding polymers with high
viscosity in high yields (Entries 4–7). Copolymerization of
BPF and N-BPF (90:10) with 5e was also performed to give
the corresponding copolymer (co-N-PEK5) quantitatively.
Synthesis of 9,9-(4-Hydroxyphenyl)-4,5-diazafluorene (N-
BPF)
According to the literature, the synthesis of N-BPF was
3
8
performed by bubbling HCl gas to a mixture of 4,5-diaza-
1
Through the integral ratio of the H NMR spectrum of co-N-
PEK5 (Supporting Information Fig. S15), the composition of
BPF and N-BPF was determined as 88:12. The structures of
TABLE 4 Optical Properties of N-PEKs
Refractive Index (n)
Birefringence
a
Polymer
484 nm
588 nm
656 nm
(Dnp2s)
b
b
b
b
b
PEK1
1.6962
1.6871
1.6719
1.6618
1.6621
1.6521
–
–
–
–
–
N-PEK1
N-PEK2
N-PEK3
N-PEK4
N-PEK5
b
b
b
–
–
–
1.6982
1.6947
1.6845
1.6719
1.6674
1.6559
1.6640
1.6570
1.6452
0.0009
FIGURE 4 Transmittance of N-PEKs films measured by a UV-vis
spectrometer (thickness 6–24 mm). [Color figure can be viewed in
the online issue, which is available at wileyonlinelibrary.com.]
a
Retardation was measured by polarizing optical microscopy under
crossed Nicols with a light wavelength of 588 nm.
b
Not determined.
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N-PEKs were characterized by IR and H NMR spectroscopy.
The IR spectra of N-PEKs except for N-PEK4 showed car-
2
1
bonyl absorption peaks at 1653–1663 cm , while the
absorption band attributed to the AC@NA (diazafluorene)
2
1
stretching at 1590–1593 cm appeared at all IR spectra of
N-PEKs. The structure of N-PEK4 was confirmed by the
2
1
presence of the characteristic peak at 1013 cm based on
@
CAOAC@ stretching of the oxadiazole ring. In the spec-
21
trum of N-PEK4, the absorption band at 1598 cm attribut-
able to the AC@NA (oxadiazole) stretching was overlapped
with that of the AC@NA stretching on the diazafluorene
moiety.
FIGURE 5 Transmittance of N-PEK1ꢂTsOH network films meas-
ured by a UV-vis spectrometer (thickness: 14–55 mm). [Color
figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
Solubility
Solubility of N-PEKs in various solvents was evaluated by
dissolving 3 mg polymer in 1 mL solvent and is summarized
in Table 2. All N-PEKs showed cardo structure-specific high
solubility in CHCl , DMAc, and NMP, which is a good contrast
3
with the low solubility of typical poly(ether ketone) such as
PEEK-HTVR in common organic solvents. In addition, N-PEKs
were partially soluble even in conc. aq. HCl, which is prob-
ably caused by the protonation of diazafluorene moieties on
the polymer. Such solubility of N-PEK1 was hardly different
to that of 9,9-diarylfluorene-type polymer (PEK1, Fig. 3)
except for the column of conc. aq. HCl in Table 2.
Thermal Stability
Thermal properties of N-PEKs were evaluated by TGA and
differential scanning calorimetry (DSC) (Table 3). The weight
d
loss temperatures (T s) of N-PEKs were in a range of 448–
FIGURE 6 IR spectra (NaCl) of (a) N-PEK1, and the network
polymers of N-PEK1 with (b) 50 mol %, (c) 100 mol %, and (d)
ꢀ
5
28 C in air atmosphere, and the glass transition tempera-
ꢀ
tures (T s) were in a range of 220–294 C, respectively. The
g
200 mol % of TsOH.
high thermal stability would come from the rigid backbone
of polymer containing cardo moieties in the main chain. On
FIGURE 7 (a) UV-vis spectral change of 3 on addition of TsOH (CH
2
Cl
2
, 0.1 mM, 298 K); and (b) Benesi-Hildebrand plot of absorb-
21
21
21
0
ance at 337 nm (blue, (A–A )
versus [TsOH] plot; red, mol % of TsOH versus [TsOH] plot). [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
4
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the other hand, no melting point was observed in all N-
PEKs, which indicated the amorphous nature of N-PEKs.
drop cast using an NMP solution of N-PEK1 with arbitrary
amounts of TsOH. It was found that no precipitation of TsOH
was observed, even when 200 mol % of TsOH per the
repeating unit was added to the polymer. After the removal
of solvent, the swelling ability of the polymers was examined
to evaluate a network formation. The polymers were swollen
without any degradation in CHCl3 and NMP that are good
solvents for the original polymers (Supporting Information
Fig. S21). These results strongly indicate the formation of
network polymer.
Transparency
The transparency of the casting films of N-PEK1, N-PEK2,
and N-PEK5 reached over 80% at 400 nm (Fig. 4). This high
transparency can be attributed to their amorphous nature of
N-PEKs. On the other hand, the films of N-PEK3 and N-
PEK4 showed relatively low transparency, probably because
of the aggregation between the polymer chains of N-PEK3
and N-PEK4 with rigid spacer moieties.
Figure 5 shows the transparency of the films. The obtained
films were remarkably flexible and transparent. In the case
of a mixture of 9,9-diarylfluorene-type polymer PEK1 and
TsOH, opaque film was obtained (Supporting Information
Fig. S20), indicating that the diazafluorene moieties of N-
PEK behave as a dispersant of TsOH. In IR spectra of the
network polymer N-PEKꢂTsOH, stretching modes of pyridine
Refractive Index and Birefringence
Optical properties were summarized in Table 4. Refractive
indices were sufficiently high (1.65–1.67 at 588 nm), which
would be attributed to the high content of aromatic groups.
Intriguingly, the refractive index of N-PEK1 was nearly same
as PEK1 with the same spacer, despite N-PEK has C@N
4
4
2
1
bonds with high atom refraction. N-PEK5 exhibited very
low birefringence attributed to the structural property of
cardo skeleton, although birefringence values of other poly-
mers could not be measured, because of the poor film form-
ing properties of N-PEKs.
and pyridinium ring were observed at 1590 and 1698 cm
,
respectively (Fig. 6). Interestingly, the former band remained
as a broaden peak even upon the addition of excess amount
of TsOH, which indicates that all pyridine moieties are not
protonated. We evaluated a UV-vis spectral change of mono-
mer 3 by a manipulation of feed ratio of TsOH. The UV-vis
spectra of 3 substantially changed on the addition of TsOH.
The UV-vis titration results are shown in Figure 7(a). It
turned out that the spectral change reached ceiling on the
addition of more than 100 mol % TsOH. In addition, clear
one isobestic point was observed. The reciprocals of the
absorbance at around 337 nm were calculated and plotted
Preparation of Hydrogen-Bond Network Polymer
To prepare the chemically stable network polymer of N-PEK,
p-toluenesulfonic acid (TsOH) was used as a proton source,
because of the nonvolatility and low pK constant of TsOH.
Several network polymer films were prepared at 100 C by a
a
ꢀ
2
1
against [TsOH]
7
to make the Benesi-Hildebrand plot [Fig.
4
5
(b)]. These plots were fitted well with a straight line
ranging from the point of 0 to 100 mol % of TsOH added,
indicating that only one nitrogen atom was protonated and
the other was not (Scheme 3). The binding constant was
3
21
determined to be 1.5 3 10
M
. These results could
SCHEME 3 Protonation of model Compound 3.
TABLE 5 Optical Properties of Network Polymers
strongly support the formation of hydrogen bonds between
pyridinium and pyridine ring to give the network structure.
Network
Polymer
TsOH
Refractive
Birefringence
Refractive Index and Birefringence
a
b
(mol %)
Index (n)
(Dnp–s)
Table 5 summarizes the optical properties of the network
films. As the feed ratio of TsOH increased, the refractive indi-
ces (n) of the polymer decreased, probably because of the
c
N-PEK1
N-PEK3
0
1.6618
1.6746
1.6530
1.6077
1.6719
1.6716
1.6509
1.6193
1.6674
1.6670
1.6640
–
1
5
1
0
1
5
1
0
5
1
0
0.0038
c
0
–
c
00
–
c
–
0
0.0035
0.0006
0.0001
0
00
c
N-PEK5
–
0
0.0003
0.0003
00
a
Refractive index was measured at 588 nm.
b
FIGURE 8 Bent film of network polymer (N-PEK5 with 1 mol %
TsOH). [Color figure can be viewed in the online issue, which
is available at wileyonlinelibrary.com.]
Retardation was measured by polarizing optical microscopy under
crossed Nicols with a light wavelength of 588 nm.
c
Not determined.
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good agreement to the increase of weak hydrogen bonds
between pyridine and pyridinium moieties in the network
polymer. It is noted that the network polymers prepared
from co-N-PEK5 also showed the increase of flexibility and
elongation at rupture; Young’s modulus: 110.9 MPa (1 mol
%
TsOH) and 64.7 MPa (2 mol % TsOH) [Fig. 9(b)], strongly
suggesting that only a few composition of N-BPF is crucial
to modify the mechanical properties of the polymer.
CONCLUSIONS
A new series of N-BPF-based cardo polymer (N-PEKs) were
synthesized in high yields by polymerization of a new cardo
monomer (N-BPF) with various difluoroarenes (2), and the
network polymers were prepared by the addition of TsOH.
N-PEKs exhibited high thermal properties and high solubility
in various organic solvents. These excellent properties come
from cardo structure of N-BPF. The network polymer films
showed not only high flexibility and transparency but also
low birefringence. Additionally, co-N-PEK5 copolymerized by
BPF and N-BPF with 2 exhibited the increase of flexibility
on the addition of TsOH. This study demonstrated that the
hybridization of heteroaromatics to cardo structure enables
the creation of new cardo monomer for the production of
high-performance polymers with excellent properties.
Because 4,5-diazafluorene skeleton has been widely
exploited as a ligand similar to 1,10-phenanthlorine, directed
toward electron injection layers, electron transporting layers,
organic light emitting materials, dye sensitizers, and so forth,
N-BPF and the related polymers would become a good can-
didate of these materials.
21
FIGURE 9 Stress–strain curves (thickness 10 mm, 10 mm min
)
of (a) N-PEK5 and network polymer prepared with TsOH; (b) net-
work polymer prepared from co-N-PEK5 with TsOH.
ACKNOWLEDGMENTS
The work was financially supported by a Grant-in-Aid for Scien-
tific Research (A) (No. 23245031) from the Ministry of Educa-
tion, Culture, Sports, Science and Technology, Japan. A
fellowship to H.O. from JSPS for Young Japanese Scientists is
gratefully acknowledged.
low refractive index of TsOH (n 1.56 at 589 nm) and the
decrease in the polymer density attributed to the introduc-
tion of ionic bonds with long distance between atoms. On
the other hand, the birefringence value (Dn) also decreased
along the increase of the feed ratio of TsOH, which would be
attributed to the defect of ordered aggregation of polymer
chain by the formation of hydrogen bonds and/or the exis-
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