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The separated organic phase was washed with water (3 ꢂ 60
mL) and dried over anhydrous Na SO . Aer removal of the
2
. Experimental
2
4
2.1 Materials
solvent, the crude product was obtained, which was puried by
All starting chemicals were purchased from Aldrich and used as a ash column chromatography on SiO using a mixture of
received. Benzocyclobutene-4-boronic acid was purchased from petroleum ether and CH Cl as the eluent (10 : 1 v/v). Pure 2 was
Chemtarget Technologies Co., Ltd, China, and puried by obtained as a colorless oil with a yield of 84%. H NMR (400
column chromatography on SiO
using a mixture of ethyl MHz, CDCl , ppm) d 7.56 (d, 2H), 7.45 (d, 4H), 7.04 (d, 4H), 6.76
acetate and n-hexane (40 : 1, v/v) as the eluent. The obtained (d, 4H), 3.90 (s, 4H), 1.73 (d, 4H), 1.37 (d, 12H), 0.91 (d, 6H).
compound showed a purity of 98.7% (HPLC). Dimethylsulfone NMR (100 MHz, CDCl , ppm) d 158.28, 153.81, 137.88, 136.28,
DMSO) was dried over CaH2 and distilled under reduced 130.76, 129.32, 129.03, 121.86, 121.55, 114.39, 67.95, 64.44,
2
2
2
1
2
3
1
3
C
3
(
+
pressure before use.
31.62, 29.28, 25.78, 22.66, 14.11. EI-MS (m/z): M ¼ 676.1
100%).
Synthesis of 2,7-dibenzocyclobutene-9,9-bis(4-hexyloxyphe-
(
2.2 Measurement
nyl)uorene (FB). To a mixture of 2 (0.68 g, 1 mmol), benzocy-
clobutene-4-boronic acid (0.44 g, 3 mmol), tetrakis-(triphenyl-
1
13
H NMR and C NMR spectra were recorded on a Bruker 400
spectrometer. FT-IR spectra were run on a Nicolet spectrometer
with KBr pellets. Differential scanning calorimetry (DSC) was
determined with TA Instrument DSC (Q200) at a heating rate of
phosphine)palladium (Pd(PPh
3 4
) ) (0.0058 g, 0.05 mmol) and
toluene (10 mL) was added aq. K
2
CO
3
solution (5 mL, 2 M)
ꢀ
under argon. The mixture was heated to 75 C and maintained
at the temperature for 12 h. Aer being cooled to room
temperature, the mixture was diluted with ethyl acetate (30 mL),
and ltered. The separated organic phase was washed with
ꢁ1
ꢁ1
10 K min under nitrogen ow with a rate of 50 mL min . The
DSC measurement was performed for 3 times for each sample.
For each test, the Tzero aluminum pans were used and the lled
amount of the sample was 4–7 mg. Thermogravimetric analysis
water (3 ꢂ 60 mL), and dried over anhydrous Na
and concentrated. The obtained residue was puried by ash
column chromatography on SiO using a mixture solvent of
petroleum ether and CH Cl as the eluent (20 : 1 v/v) to give FB
as a white solid with a yield of 85% and a purity of 99.3%
2 4
SO , ltered,
(TGA) was performed on a TG209F1 apparatus at a heating rate
ꢁ
1
of 10 K min in a nitrogen atmosphere or air with a ow rate of
ꢁ1
2
30 mL min . The TGA measurement was performed for 3 times
2
2
for each sample. For each experiment, platinum boats were
used, and grinded powder-like samples with a lled amount of
near 10 mg were employed.
The dielectric constant (k) of the cured samples was
measured ranging from 0.15 MHz to 30 MHz on cured cylindric
samples (average diameters were 10 mm and thicknesses were
1
(
(
(
(
HPLC). H NMR (400 MHz, acetone-d , ppm) d 7.94 (d, 2H), 7.62
6
d, 4H), 7.42 (d, 2H), 7.27 (s, 2H), 7.21 (d, 4H), 7.09 (d, 2H), 6.81
d, 4H), 3.91 (t, 4H), 3.17 (s, 8H), 1.75–1.63 (m, 4H), 1.45–1.27
m, 12H), 0.87 (t, 6H). C NMR (100 MHz, CDCl
1
3
3
, ppm) d
1
1
6
57.88, 152.74, 146.22, 144.88, 141.75, 140.58, 138.58, 137.97,
29.26, 126.64, 126.16, 125.04, 122.73, 121.59, 120.30, 114.13,
2–3 mm, respectively) at room temperature using a 4294A
Precision Impedance Analyzer (Agilent). Before each measure-
ment the samples were thoroughly dried under vacuum.
7.90, 64.36, 31.61, 29.49, 29.43, 29.29, 25.77, 22.64, 14.08. EI-
+
MS (m/z): M ¼ 722.4 (100%).
2.3 Synthesis
2.4 Sample preparation
Synthesis of 2,7-dibromo-9,9-bis(4-hydroxyphenyl)uorene
29
(
1). A solution of 2,7-dibromouoren-9-one (14.0 g, 41.0
mmol), phenol (23.8 g, 246 mmol), and methansulfonic acid
50 mL) was stirred at room temperature for overnight. Then the
mixture was poured into water, and the obtained solid was
ltered and washed with water. The crude 1 thus prepared. To
FB (5.0 g) was placed in a at-bottomed glass tube with a
diameter of 10 mm and a highness of 85 mm under argon
(
ꢀ
atmosphere. The tube was heated to 130 C and kept at the
temperature for 30 min so that a transparent melting liquid was
ꢀ
obtained. The temperature was then elevated and kept at 150 C
purify 1, a solution of crude 1 in ethyl acetate was added drop
wise to n-hexane to obtain a precipitate. The precipitate was
ꢀ
ꢀ
ꢀ
ꢀ
for 1 h, 170 C for 1 h, 210 C for 5 h, 240 C for 5 h, and 280 C
for 5 h respectively. Thus, a completely cured sample was
obtained.
ltrated and dried under reduced pressure to give pure 1 as a
1
white powder with a yield of 90%. H NMR (400 MHz, acetone-
d , ppm) d 8.33 (s, 2H), 7.85 (d, 2H), 7.56 (d, 4H), 7.02 (d, 4H),
6
1
3
6
1
1
6
.76 (d, 4H). C NMR (100 MHz, acetone-d , ppm) d 156.53,
3
. Results and discussion
54.34, 137.99, 135.36, 130.68, 129.05, 128.98, 122.21, 121.29,
15.24, 64.46. EI-MS (m/z): M ¼ 508 (100%).
+
3.1 Synthesis and characterization
Synthesis of 2,7-dibromo-9,9-bis(4-hexyloxyphenyl)uorene The procedure for the synthesis of FB is shown in Scheme 2. As
29
(
2). A mixture of 1 (10.16 g, 20.0 mmol), K
2
ꢀ
CO
3
(6.22 g, 45.0 shown in Scheme 2, the monomer FB was prepared in a yield of
mmol), and DMSO (50 mL) was stirred at 75 C for 0.5 h under 85% by using the standard Suzuki coupling reaction between
argon atmosphere. To the obtained solution was added 1-bro- 2,7-dibromo-9,9-bis(4-hexyloxyphenyl)uorene (2) and benzo-
mohexane (6.00 g, 36.3 mmol) through syringe. The mixture was cyclobutene-4-boronic acid. The obtained monomer showed a
ꢀ
stirred at 75 C for overnight. Aer being cooled to room purity of 99.3% (HPLC), implying that it can meet the require-
temperature, the solution was diluted by ethyl acetate (100 mL). ment of the polymerization.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 39884–39888 | 39885