Diphenolic 9,9-diarylfluorene trimers and derivatives possessing flexible alkylene chain spacers: Synthesis of the monomers, their polymerization, and properties of the resulting polymers

Article abstract of DOI:10.1021/ma901841y

9,9-Diarylfluorene-based monomers capable of controlling the thermal properties of the corresponding polymers were synthesized. The monomers possess flexible alkylene chains linking 9,9-diarylfluorene units with diphenol, dialcohol, and diamine terminal u

Full text of DOI:10.1021/ma901841y

Macromolecules 2010, 43, 131–136 131
DOI: 10.1021/ma901841y
Diphenolic 9,9-Diarylfluorene Trimers and Derivatives Possessing Flexible
Alkylene Chain Spacers: Synthesis of the Monomers, Their
Polymerization, and Properties of the Resulting Polymers
Toshihide Hasegawa,† Yasuhito Koyama,† Ryota Seto,† Takahiro Kojima,‡
Katsumoto Hosokawa,‡ and Toshikazu Takata*,†
†Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro,
Tokyo 152-8552, Japan and ‡Canon, Inc., Production Engineering Research Laboratory, 70-1, Yanagi-cho,
Saiwa-ku, Kawasaki-shi, Kanagawa 212-8602, Japan
Received August 18, 2009; Revised Manuscript Received November 19, 2009
ABSTRACT: 9,9-Diarylfluorene-based monomers capable of controlling the thermal properties of the
corresponding polymers were synthesized. The monomers possess flexible alkylene chains linking
9,9-diarylfluorene units with diphenol, dialcohol, and diamine terminal units. All of these terminal units
were synthesized from a common trimeric tert-alcohol-functionalized intermediate. Polycarbonates consist-
ing of the 9,9-diarylfluorene trimer structure in the main chains were synthesized by interfacial polyconden-
sation with triphosgene. The polymerizability of the diphenolic trimer was sufficiently high to afford a
polycarbonate with a high molecular weight (Mw 334 000). The thermal properties (Tg and Td) of the
polymers were easily controlled by adjusting the feed ratio of the 9,9-diarylfluorene trimer to 9,9-bis-
(4-hydroxyphenyl)fluorene. The resulting highly transparent polymers showed high refractive indices and
low birefringence values originating from the cardo structure.
Introduction
inherent properties and polymerizability. Herein, we describe a
new concept for the modification of the cardo structure based on
9,9-Diarylfluorene-based polymers are intriguing materials for
optical use: they combine transparency with high refractive index
and low birefringence.1 Their optical properties can be attributed
to the cardo structure of 9,9-diarylfluorene, in which each
aromatic ring occupies different planes to disturb the one-direc-
tional folding and eliminate the optical anisotropy. In addition,
such polymers exhibit other characteristic properties, including
fine dispersing ability for inorganic fillers,2 good solubility in
organic solvents,3 high thermal stability,4 and so on.5,6 Whereas
various 9,9-diarylfluorene-containing polymers with excellent
properties have been reported, polymers with finely tuned pro-
perties are strongly desired in actual use. The most straightfor-
ward way to attain such polymers with desired properties, for
example, favorable thermal properties, is to modify the polymer
main chain structure through the monomer structure change or
the copolymerization with suitable comonomer. In fact, we
previously attempted to synthesize a polycarbonate with lowered
Tg by the copolymerization of 9,9-bis(4-hydroxyphenyl)fluorene
(BPF, 1) with 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene
(BPEF, 2) as an alkylene-chain-containing related comonomer.
However, we got any copolymers by neither direct polycondensa-
tion with carbonyl sources such as diphenylcarbonate nor inter-
facial polycondensation with triphosgene. The reason why no
copolymer was formed is clear because their hydroxy groups are
essentially different in reactivity from each other: one is phenolic,
and the other is alcoholic. Focusing on the development of
monomer designing to settle such problems, we thought of
exploiting an oligomer of a 9,9-diarylfluorene-based cardo mono-
mer connected by flexible alkylene segments (R group, Figure 1)
for controlling thermal properties without sacrificing their
C2 symmetric trimerization of the 9,9-diarylfluorene structure.
The polycarbonates are synthesized by polymerization of the new
monomer.
Experimental Section
General. 1H spectra were recorded on a JEOL AL-400 NMR
spectrometer (400 MHz) in CDCl3 with tetramethylsilane as an
internal standard. 13C NMR spectra were recorded on the JEOL
AL-400 NMR spectrometer operating at 100 MHz. IR spectra
were recorded on a JASCO FT/IR-460 plus spectrometer.
Molecular weight and molecular-weight distribution were esti-
mated by gel permeation chromatography using a JASCO HSS-
1500 system equipped with consecutive TOSOH TSK-gel
GMHXL and G5000HXL eluted with CHCl3 at a flow rate of
1.0 mL/min calibrated by polystyrene standards. The decom-
position temperature was obtained using a Shimadzu TGA-50
instrument at a heating rate of 10 °C/min. DSC was performed
on a Shimadzu DSC-60 instrument at a heating rate of 10 °C/
min under N2 atmosphere at a flow rate of 50 mL/min. The
glass-transition temperature was taken as the temperature in the
middle of the thermal transition from the second heating scan.
UV-vis spectra were recorded on a JASCO V-550 UV/vis
spectrophotometer. Refractive indices and retardations of poly-
mers were measured using a Kalnew precision refractometer
(KPR-30, Shimadzu). The elementary analyses and FAB
HRMS spectra were obtained at National University Corpora-
tion Tokyo Institute of Technology Center for Advanced
Materials Analysis on request.
Dichloromethane was dried over freshly activated 4A molec-
ular sieves (MS 4A). 9,9-Bis(4-hydroxyphenyl)fluorene (BPF, 1)
and 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene (BPEF, 2)
were provided by Osaka Gas and were used without further
*Corresponding author. E-mail: ttakata@polymer.titech.ac.jp.
r 2009 American Chemical Society
Published on Web 12/14/2009
pubs.acs.org/Macromolecules

132 Macromolecules, Vol. 43, No. 1, 2010
Hasegawa et al.
gel (CHCl3-Et2O 20:1) to yield product 5 (31.1 g, 82%) as a
fluffy pale-yellow powder. 1H NMR (400 MHz, CDCl3, 298 K,
δ): 7.73 (d, J = 7.4 Hz, 2H, ArH), 7.66 (d, J = 7.6 Hz, 4H, ArH),
7.21-7.38 (m, 22H, ArH), 7.09 (d, J = 8.8 Hz, 4H, ArH), 6.81
(d, J = 8.8 Hz, 4H, ArH), 6.76 (d, J = 8.8 Hz, 4H, ArH), 4.22 (s,
8H, OCH2CH2O), 2.40 (s, 2H, OH). 13C NMR (100 MHz,
CDCl3, 298 K, δ): 157.7, 157.2, 151.6, 150.4, 139.8, 139.3, 138.4,
135.6, 129.1, 128.9, 128.3, 127.6, 127.3, 126.5, 125.9, 124.6,
120.1, 120.0, 114.21, 114.15, 83.2, 66.2, 64.1. IR (KBr) υ:
3449, 3060, 3037, 2927, 2879, 1606, 1507, 1448, 1241, 1178,
1033, 918, 826, 769, 749, 734, 641. HRMS (FAB) [M]þ calcd for
C67H50O6, 950.3607; found, 950.3622.
Figure 1. Synthetic strategy of 9,9-diarylfluorene trimer.
General Procedure for Incorporating Aromatics. Synthesis of
9,9-Diarylfluorene-trimer 6. BF3 OEt2 (3.50 mL, 28.4 mmol)
purification. Other chemicals were of reagent grade and were
used without further purification.
3
was added to a solution of bistritylalcohol 5 (9.00 g, 9.46 mmol)
and phenol (2.14 g, 22.7 mmol) in CH2Cl2 (90 mL) at 0 °C. The
mixture was stirred for 1.5 h at the same temperature and
quenched by the addition of H2O. The products were repeatedly
extracted with CHCl3. The combined organic layer was dried
over MgSO4, filtered, and concentrated in vacuo. The crude
materials were purified by column chromatography on silica gel
(CHCl3-Et2O 10:1) to afford the corresponding 9,9-diaryl-
fluorene-trimer 6 (10.1 g, 97%) as a fluffy white powder. (See
Scheme 1.) 1H NMR (400 MHz, CDCl3, 298 K, δ): 7.74 (d, J =
7.5 Hz, 6H, ArH), 7.38-7.30 (m, 12H, ArH), 7.28-7.21 (m, 6H,
ArH), 7.09 (d, J = 8.8 Hz, 4H, ArH), 7.08 (d, J = 8.8 Hz, 4H,
ArH), 7.05 (d, J = 8.7 Hz, 4H, ArH), 6.75 (d, J = 8.8 Hz, 4H,
ArH), 6.74 (d, J = 8.8 Hz, 4H, ArH), 6.66 (d, J = 8.7 Hz, 4H,
ArH), 4.70 (s, 2H, OH), 4.20 (s, 8H, OCH2CH2O). 13C NMR
(100 MHz, CDCl3, 298 K, δ): 157.09, 157.07, 154.2, 151.62,
151.58, 139.8, 138.5, 138.4, 138.0, 136.7, 129.2, 129.1, 127.6,
127.3, 125.9, 120.1, 115.0, 114.2, 66.2, 64.0. IR (KBr) υ: 3422,
3060, 3034, 2927, 2875, 1607, 1507, 1447, 1241, 1176, 1068, 916,
824, 746, 730, 629, 588, 524. HRMS (FAB): [M þNa]þ calcd for
C79H50O6, 1125.4131; found, 1125.4142.
General Procedure for the Synthesis of Polycarbonate Poly-12
Using Triphosgene.7 A solution of NaOH (65.3 mg, 1.63 mmol)
in H2O (5 mL) was cooled by a mixture of crushed ice and NaCl.
To this solution, a solution of 6 (300 mg, 0.272 mmol) in CH2Cl2
(3 mL) was added dropwise, and then a solution of triphosgene
(54.1 mg, 0.182 mmol) in CH2Cl2 (2 mL) was added. A catalytic
amount of Et3N (3.8 μL, 0.027 mmol) was added to the water
phase, and the resulting mixture was stirred vigorously for 15 min.
Later, the resulting mixture was warmed to room temperature and
stirred for 45 min. It was then diluted with CH2Cl2 (10 mL) and
H2O (50 mL), and the two phases were separated. The aqueous
phase was extracted with CH2Cl2 (30 mL ꢀ 2). The combined
organic layers were washed with H2O (50 mL ꢀ 2), dried over
MgSO4, filtered, and concentrated in vacuo to 50 mL. The crude
product was precipitated by the addition to MeOH (200 mL) to
yield a white solid, which was collected by filtration to afford the
polycarbonate in a quantitative yield. The polymer was purified by
gel permeation chromatography to afford poly-12 (206.4 mg) as a
white solid in 67% yield: Mw 334 000; Mn 165 000; Mw/Mn 2.0; Tg
221 °C; Td5 435 °C. 1H NMR (400 MHz, CDCl3, 298 K) 7.77-7.69
(m, 6H, ArH), 7.38-7.28 (m, 12H, ArH), 7.28-7.17 (m, 10H,
ArH), 7.12-7.03 (m, 12H, ArH), 6.78-6.69 (m, 8H, ArH), 4.17 (s,
8H, OCH2CH2O). IR (film) υ: 3063, 3035, 3018, 2925, 2871, 1773,
1605, 1505, 1447, 1239, 1189, 1163, 1068, 1012, 915, 823, 745.
Film Preparation. Polymer films of the polycarbonates were
prepared by a hot-press method (150 °C, 15 min) using the
corresponding polymers plasticized by NMP for the evaluation
of refractive index and retardation. The films for the evaluation of
transmittance were prepared by a casting method using a chloro-
form solution of the corresponding polymers at room temperature.
Synthesis of Bistosylate 3. TsCl (28.7 g, 150.5 mmol) was
added to a solution of BPEF 2 (30.0 g, 68.4 mmol) and Et3N
(22.9 mL, 164 mmol) in THF (150 mL) at 0 °C. The mixture was
warmed to room temperature and stirred. To this mixture,
additional TsCl (7.83 g, 90.3 mmol) and Et3N (28.6 mL, 205
mmol) were added incrementally over a 5 day period. The
reaction was quenched by the addition of sat. aq NaHCO3.
The products were extracted repeatedly with CH2Cl2. The
combined organic layer was dried over MgSO4, filtered, and
concentrated in vacuo. SiO2 (200 g) was added to the crude
materials diluted with hexane-CHCl3 (1:1, 300 mL) at 0 °C. The
mixture was warmed to room temperature, stirred for 1 h,
filtered, and concentrated in vacuo to yield the bistosylate 3
(47.7 g, 93%) as a white solid. 1H NMR (400 MHz, CDCl3, 298
K, δ): 7.78 (d, J = 8.3 Hz, 4H, ArH), 7.75 (d, J = 7.5 Hz, 2H,
ArH), 7.37-7.31 (m, 4H, ArH), 7.31-7.23 (m, 6H, ArH), 7.05
(d, J = 8.7 Hz, 4H, ArH), 6.61 (d, J = 8.7 Hz, 4H, ArH),
4.34-4.29 (m, 4H, CH2), 4.10-4.05 (m, 4H, CH2), 2.39 (s, 6H,
CH3). 13C NMR (100 MHz, CDCl3, 298 K, δ): 156.7, 151.4,
144.9, 139.8, 138.7, 132.7, 129.8, 129.0, 127.9, 127.7, 127.4,
125.9, 120.1, 114.1, 68.1, 65.3, 64.0, 21.5. IR (KBr) υ: 3449,
3063, 3039, 2955, 2925, 2871, 1508, 1358, 1249, 1176, 1021, 931,
817, 749, 663, 577, 554. HRMS (FAB): [M]þ calcd for
C43H38O8S2, 746.2008; found, 746.2002.
Synthesis of Bis(4-bromophenyl) Derivative 4. K2CO3 (45.3 g,
0.327 mol) was added to a solution of bistosylate 3 (81.5 g, 0.109
mol) and 4-bromophenol (39.7 g, 0.229 mol) in DMF (300 mL)
at room temperature. The resulting mixture was warmed to
80 °C and stirred overnight. The reaction was performed at
room temperature and quenched by the addition of sat. aq
NaHCO3. The products were extracted with CH2Cl2, and the
combined organic layer was washed with H2O. The organic
layer was dried over MgSO4, filtered, and concentrated in
vacuo. The crude materials were washed with Et2O to afford
white solids, which were isolated by filtration to yield product 4
(72.3 g, 89%) as a white solid. 1H NMR (400 MHz, CDCl3, 298
K, δ): 7.75 (d, J = 7.5 Hz, 2H, ArH), 7.39-7.32 (m, 8H, ArH),
7.29-7.23 (m, 2H, ArH), 7.12 (d, J = 8.7 Hz, 4H, ArH), 6.80 (d,
J = 9.0 Hz, 4H, ArH), 6.79 (d, J = 8.7 Hz, 4H, ArH), 4.24 (s,
8H, OCH2CH2O). 13C NMR (100 MHz, CDCl3, 298 K, δ):
157.6, 157.2, 151.6, 139.9, 138.6, 132.2, 129.2, 127.7, 127.4,
125.9, 120.1, 116.4, 114.2, 113.2, 66.6, 66.2, 64.1. IR (KBr) υ:
3060, 3038, 2937, 2874, 1608, 1578, 1508, 1487, 1454, 1287, 1240,
1182, 1065, 945, 822, 750, 653, 508. HRMS (FAB): [M]þ calcd
for C41H32Br2O4, 746.0667; found, 746.0672.
Synthesis of Bis(tert-alcohol) Derivative 5. BuLi (1.6 M in
hexane, 52.6 mL, 84.2 mmol) was added dropwise to a solution
of bis(4-bromophenol) 4 (30.0 g, 40.1 mol) in THF (300 mL) at
-78 °C over 40 min. After stirring for 1 h at the same tempera-
ture, a solution of fluorenone (15.1 g, 84.2 mmol) in THF (150
mL) was added dropwise to the mixture over a 1.5 h period. The
resulting mixture was warmed to room temperature overnight
and quenched by the addition of sat. aq NH4Cl; the products
were extracted with CHCl3. The combined organic layer was
dried over MgSO4, filtered, and concentrated in vacuo. The
crude product was purified by column chromatography on silica
Results and Discussion
Monomer Synthesis. C2 Symmetric 9,9-diarylfluorene tri-
merization started with commercially available 9,9-bis(4-
(2-hydroxyethoxy)phenyl)fluorene 2 (BPEF) (Scheme 1).

Article
Macromolecules, Vol. 43, No. 1, 2010 133
Scheme 1. Synthesis of 9,9-Diarylfluorene-trimer 6a
a Reagents and conditions: (a) TsCl (2.8 equiv), Et3N (7.8 equiv), CH2Cl2, RT, 5 d, 93%; (b) 4-bromophenol (2.2 equiv), Cs2CO3 (4.8 equiv), DMF,
80 °C, overnight, 89%; (c) BuLi (2.2 equiv), fluorenone (2.2 equiv), THF, -78 °C, overnight, 82%; (d) phenol (2.2 equiv), BF3 OEt2 (3.0 equiv), CH2Cl2,
3
0 °C, 1.5 h, 82%.
Scheme 2. Synthesis of 9,9-Diarylfluorene-Based Polycarbonatesa
a Reagents and conditions: (a) triphosgene (0.67 equiv), NaOH (6.0 equiv), Et3N (0.1 equiv), CH2Cl2-H2O (1:1), 0 °C, 15 min, then RT, 45 min.
Treatment of BPEF 2 with tosylchloride in the presence of
Et3N afforded the bistosylate 3 in a high yield, followed by an
SN2 reaction with 4-bromophenol to yield the corresponding
bromophenylether 4. The crude material was pure enough to
be used for the next reaction (i.e., did not required further
purification, such as by column chromatography). The
resulting compound was reacted with BuLi in THF to
undergo a Br-lithium exchange. To this solution, fluorene
was added to afford a bis(tert-alcohol) derivative 5 in 82%
yield. Having the key compound 5 in hand, we investigated
the introduction of various nucleophilic aromatics to 6 via
Friedel-Crafts alkylation reaction. After considerable ef-
Table 1 summarizes the results of the synthesis of the 9,9-
diarylfluorene trimers, which were prepared in a similar
manner as 6. Phenol derivatives such as o-cresol, phenox-
yethanol, and 2-naphthol regioselectively reacted with 5 to
afford the corresponding trimers 7, 8, and 9, respectively, in
high yield. The introduction of an aniline moiety was also
successful, affording Bisamine-terminated trimer 10 in 20%
yield. These results suggested the versatility and generality of
the present functionalization method using the key inter-
mediate 5.9
Polymer Syntheses. Scheme 2 features the polymerization
and copolymerization of 9,9-bis(4-hydroxyphenyl)fluorene
(BPF) 1 and trimer 6 to polycarbonates using the known
method of interfacial polycondensation.7 Treatment of 1
with triphosgene (0.67 equiv) and NaOH (6.0 equiv) in
CH2Cl2-H2O (1:1) in the presence of a catalytic amount of
Et3N (0 °C, 15 min, then RT, 45 min) afforded the
corresponding polycarbonate poly-11 in 92% yield. The
molecular weight and molecular-weight distribution were
estimated by SEC on the basis of PSt standards (Mw 32 000,
fort, the synthesis was achieved using BF3 OEt2 in CH2Cl2 in
3
the presence of the aromatics to yield the 9,9-diarylfluorene
trimers.8 When a phenol was used as a nucleophilic aromatic,
the corresponding diphenolic 9,9-diarylfluorene trimer 5 was
obtained in 82% yield. The structure of 6 was determined by
1H NMR, IR, and FAB HRMS spectra. The 1H NMR
spectrum of 6 is shown in Figure 2 and is discussed later in
this study.

134 Macromolecules, Vol. 43, No. 1, 2010
Table 1. Syntheses of 9,9-Diarylfluorene Trimers
Hasegawa et al.
Mw/Mn 2.3). In the present polycondensation process, a
prolonged reaction time or higher temperature resulted in a
decrease in yield and lowering of the molecular weight,
probably because of the cleavage of the labile diarylcarbo-
nate linkage by hydrolysis. Given this knowledge, the po-
lymerization of 6 was performed with a limited reaction time
similar to that of 1 to afford the corresponding polycarbo-
nate poly-12 in quantitative yield. For a detailed evaluation
of properties, the polymer was purified by gel permeation
chromatography to afford poly-12 in 67% yield (Mw 334 000,
Mw/Mn 2.0). To evaluate the reactivity of 6 and the proper-
ties of the resultant polymer, the copolymerization reaction
of 6 and 1 (feed ratio, 6:1 = 1:9) was also performed, and
copolymer copoly-13 (Mw 74 000, Mw/Mn 2.5) was obtained
in 99% yield. Although the reason is not clear, trimer 6 seems
to have sufficiently high reactivity under interfacial poly-
condensation conditions despite its higher molecular weight.
It reacted especially well in homopolymerization, judging
from the high molecular weight of the product (poly-12, Mw
334 000).
agreement with those of BPF 1 (C-F). The signals of the
phenyl ether moieties (a, b, a0, and b0) were split into two
couplets, which come from terminal phenol moieties and
four phenyl ether moieties, strongly supporting the structur-
al identification of trimer 6. All aromatic signals of the
polymers were sharp enough to confirm the formation of
high-molecular-weight polymers with a low degree of dis-
order in the polymer structures. The signals (A and a00) of
phenolic ortho-position protons of 1 and 6 shifted downfield
from 6.7 to 7.2 ppm, indicating carbonate bond formation in
poly-11 and poly-12. The copolymer composition of copoly-
13 was (6:1 = 8:92), as evaluated by the integral ratio of the
1H NMR spectrum.
Thermal Properties. Thermal properties of the polycarbo-
nates were determined by DSC and TGA (Table 2). The
glass-transition temperature (Tg) of poly-12 was observed at
221 °C, which was 32 °C lower than that of poly-11 as a
consequence of the presence of the flexible spacer. The
slightly lowered Tg of poly-13 (248 °C) was reasonable given
the copolymer composition. The temperature at which de-
composition occurred (Td5) was 456 °C for poly-11 and 404
°C for poly-12, indicating that the spacer chains reduced the
thermal stability. Furthermore, the incorporation of como-
nomer 6 in the polycarbonate structure lowered both Tg and
Structural Characterization. Figure 2 shows 1H NMR
spectra of monomers 1 and 6 and the three polycarbonates.
1
In the H NMR spectrum of 6 (b), the signals (c-f and
c0-f0) originating from the fluorene skeleton were in good
T
d5 of copoly-13.

Article
Macromolecules, Vol. 43, No. 1, 2010 135
Figure 2. 1H NMR spectra of monomers and polymers (400 MHz,
CDCl3, 298 K): (a) 1, (b) 6, (c) poly-11, (d) poly-12, and (e) copoly-13.
Figure 3. Transmittance of poly-12 and copoly-13 films measured by a
UV-vis spectrometer (film thickness: 15 to 16 μm).
Table 2. Polymerization Results and Properties of the Polymers
Table 3. Refractive Index and Birefringence Values of Polycarbonates
Tg (°C)b Td5 (°C)c
polycarbonate
refractive index (n)
Δnp-s
a
a
a
polycarbonate yield (%)
Mw
Mw/Mn
486 nm
588 nm
656 nm
poly-11
poly-12
copoly-13
92
67
99
32 000
334 000
74 000
2.3
2.0
2.5
253
221
248
456
435
447
b
poly-11
poly-12
copoly-13
1.667
1.674
1.666
1.646
1.653
1.645
1.637
1.645
1.637
0.0008
0.0009
a Estimated by SEC on the basis of polystyrene standards. b Glass-
transition temperature was obtained at a heating rate of 10 °C/min under
nitrogen (50 mL/min). c 5% decomposition temperature was obtained at
a heating rate of 10 °C/min under nitrogen (50 mL/min).
a Retardation was measured by a polarizing optical microscopy under
the crossed Nicols with a light wavelength of 588 nm. b Not determined.
The degree of retardation of visible light at 588 nm was
0.0008 (poly-12) and 0.0009 (poly-13) nm. The remarkably
low birefringence must be also attributed to the cardo
structure in the main chain that largely reduces the optical
anisotropy.
Solubility and Transparency. Although the three poly-
mers mostly consist of aromatic units, they were highly
soluble in typical organic solvents such as toluene, CH2Cl2,
CHCl3, and THF. The exceptionally high solubility comes
from the cardo structure in the main chain. This cardo
structure comprises 9,9-diarylfluorene units, as previously
reported.1i,j,n,o
Conclusions
This article has revealed the synthesis and polymerization of
9,9-diarylfluorene trimer-related monomers linked by flexible
alkylene spacers. These monomers are capable of controlling
the thermal properties of 9,9-diarylfluorene-based polymers
while retaining their high reactivity in polymerization. The
present synthetic protocol based on the C2 symmetric trimeriza-
tion through a bis(tert-alcohol) derivative 5 as the common
intermediate was successful in the preparation of versatile mono-
mers such as diphenol, diol, and diamine monomers. The
diphenolic monomer possessing two flexible alkylene spacers
was polymerized to the corresponding polycarbonate with a high
molecular weight and low Tg in high yield. Copolymerization of
the diphenolic monomer with BPF clearly decreased the glass-
transition temperature of the corresponding copolycarbonate as
compared with the fluorene homopolymer to an extent depen-
dent on the feed ratio. The resulting transparent films exhibited
remarkably high refractive indices in the range of 1.646 to 1.653
but showed low birefringence. The results obtained in this study
demonstrate the usefulness of the flexible spacer-linked monomer
as a highly reactive phenolic monomer. Meanwhile, the present
new concept would allow us to access polymers with versatile
properties by altering the spacer structure of the monomer.
The transmittance of the films (poly-12 and copoly-13)
reached 90% over 360 nm and gradually increased over the
visible light region with increasing wavelength (Figure 3).
The high transparency of the films results from their amor-
phous nature and is consistent with the greatly reduced
interchromophore interaction between or within the poly-
mer chains.
Optical Properties. Thin films of the polycarbonates for
the evaluation of refractive index and birefringence were
prepared by a hot-press method (150 °C, 15 min) using the
NMP solution. When the film of poly-11 was cooled to room
temperature, several cracks were observed despite the high
molecular weight of the polymer, making it impossible to
evaluate the retardation index. The poor film-forming cap-
ability is probably caused by the rigid polymer structure of
poly-11, which possibly prevents the formation of entangle-
ments of the polymer chains. In contrast, both poly-12 and
copoly-13 with the flexible alkylene spacers allowed the
formation of the corresponding colorless freestanding films
with sufficient dimensional stability to evaluate the optical
properties.
Table 3 summarizes the refractive index and birefringence
values of the polycarbonates (poly-11, poly-12, and copoly-
13). The refractive index value at a typical wavelength of 588
nm was quite high for polymers consisting only of C, H, and
O atoms: 1.646 (poly-11), 1.653 (poly-12), and 1.645 (copoly-
13). The present high refractive indices would be attributable
not only to the polynuclear aromatic main chain, but also to
the dense packing of the polymer chains permitted by the
presence of the flexible alkylene segments and the cardo
structure in the main chain. The birefringences of the poly-
mers were evaluated using similar films in the undrawn state.
Supporting Information Available: Experimental details.
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http://pubs.acs.org.
References and Notes
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