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Y.-J. Jin et al. / Polymer 123 (2017) 81e86
during the synthesis of the corresponding monomers [6]. Since
then, silylene linkages have become a staple for the synthesis of
PDPA derivatives. Despite the fact that silicon has a larger atomic
radius and adopts higher coordination numbers than carbon, the
influences of the silylene linkage on the thermal stability, ther-
modynamic, and PL properties of PDPAs have never been examined
in detail. Although a new category of PDPA derivatives has recently
been synthesized with polymethylated ring moieties fused to the
pendant phenyl rings, their physical properties other than their gas
permeabilities were not examined [7]. In this study, we synthesized
a new PDPA derivative having a long alkyl side chain without a
silylene linkage (1 in Fig. 1) and compared its properties with those
of an analogous polymer containing a silylene linkage (2 in Fig. 1).
Herein, we describe the details of the resulting thermogravimetric,
thermodynamic, and spectroscopic analyses.
J ¼ 7.53 Hz, 2H),1.57 (m, 2H),1.34e1.19 (m, 31H), 0.88 (t, J ¼ 6.65 Hz,
3H).
2.2.2. 2-Methyl-4-(4-octadecylphenyl)-3-butyn-2-ol (4)
3 (2.00 g, 4.88 mmol), triphenylphosphine (257 mg, 0.98 mmol),
copper(I) iodide (278 mg, 1.46 mmol), Pd(PPh3)2Cl2 (175 mg,
0.25 mmol), and triethylamine (20 mL) were placed into a three-
necked flask equipped with a Dimroth condenser, three-way
stopcock, magnetic stirrer bar, and rubber septum. 2-Methyl-3-
butyn-2-ol (431 mg, 5.12 mmol) was then added to the solution.
The resulting mixture was refluxed and stirred for 24 h. After
removal of the solvent by evaporation, the crude residue was
extracted with diethyl ether, and the ether solution was washed
with 2 N HCl aq., sat. NaHCO3 aq., and brine and dried over anhy-
drous MgSO4. The solvent was evaporated and the obtained crude
product was purified by flash silica gel column chromatography
(eluent: hexane:ethyl acetate 4:1 v/v) to give 4 (704 mg, 35%) as a
2. Experimental section
white solid. 1H NMR (400 MHz, CDCl3)
d
7.32 (d, J ¼ 8.32 Hz, 2H),
7.11 (d, J ¼ 8.32 Hz, 2H), 2.58 (t, J ¼ 7.53 Hz, 2H), 2.00 (s, 1H, eOH),
1.61 (s, 6H), 1.60e1.56 (m, 2H), 1.34e1.19 (m, 31H), 0.88 (t, 3H,
J ¼ 6.64 Hz).
2.1. Materials
Polymer 2 was synthesized according to a method reported in
the literature [8]. The monomer of 1 (5 in Scheme 1) was synthe-
sized with reference to literature methods [9,10]. Pd(PPh3)2Cl2 was
prepared by mixing stoichiometric amounts of PdCl2 and triphe-
nylphosphine in hot DMF. Pd(dppf)Cl2 and other reagents were
purchased from TCI Co. and used without further purification.
Dehydrated solvents (THF and diethyl ether) were obtained from
Kanto Chemical Co. Other chemicals including solvents were pur-
chased from Aldrich and TCI and used as received.
2.2.3. 1-(4-Octadecylphenyl)-2-phenylacetylene (5)
A heterogeneous solution of 4 (660 mg, 1.60 mmol), bromo-
benzene (251 mg, 1.60 mmol), Pd(PPh3)2Cl2 (112 mg, 0.16 mmol),
copper(I) iodide (30 mg, 0.16 mmol), and tetrabutylammonium
iodide (59 mg, 0.16 mmol) in a mixture of toluene (1 mL) and 5 M
NaOH aq. (2.5 mL) was degassed by sonication under reduced
pressure for a short time. The mixture was heated at 80 ꢀC for 24 h,
and then cooled to ambient temperature. The reaction solution was
filtered through a silica gel pad, and the filtrate was concentrated
using a rotary evaporator. The crude product was purified by flash
silica gel column chromatography (eluent: hexane) to give the
desired product (290 mg, 42%) as a white solid. 1H NMR (400 MHz,
2.2. Synthesis of 1 (Scheme 1)
2.2.1. 1-Bromo-4-octadecylbenzene (3)
A three-necked flask was equipped with a Dimroth condenser,
dropping funnel, magnetic stirrer bar, and a three-way stopcock
then flushed with dry nitrogen. Magnesium turnings (0.63 g,
25.9 mmol), a catalytic amount of iodine, and dry THF (2 mL) were
placed in the flask. The mixture was then stirred until the brown
color of the iodine disappeared. 1-Bromooctadecane (8.63 g,
25.9 mmol) in dry THF (15 mL) was added dropwise at a rate suf-
ficient to cause gentle self-refluxing. When the addition was
finished, the reaction mixture was stirred for an additional
30 min at 40 ꢀC. Another three-necked flask was equipped with a
Dimroth condenser, magnetic stirrer bar, rubber septum, and three-
way stopcock and flushed with dry nitrogen. 1,4-Dibromobenzene
(6.11 g, 25.9 mmol), Pd(dppf)Cl2 (212 mg, 0.259 mmol), and dry
diethyl ether (15 mL) were placed in the flask and the solution was
warmed to 40 ꢀC. The above-synthesized 1-octadecylmagnesium
bromide was then slowly added through a Teflon® cannula at
40 ꢀC with stirring. The resulting mixture was refluxed for 2 days
and then poured into water. After removal of the catalyst residue by
filtration, the filtrate was extracted with diethyl ether. The organic
layer was washed with brine and dried over anhydrous MgSO4, and
the solvent was evaporated. The resulting crude product was pu-
rified by flash silica gel column chromatography (eluent: hexane) to
give 3 (5.27 g, 50%) as a white solid. 1H NMR (400 MHz, CDCl3)
CDCl3)
d
7.56e7.49 (m, 2H), 7.44 (d, J ¼ 8.24 Hz, 2H), 7.38e7.28 (m,
3H), 7.16 (d, J ¼ 8.24 Hz, 2H), 2.61 (t, J ¼ 7.53 Hz, 2H), 1.61 (m, 2H),
1.35e1.20 (m, 31H), 0.88 (t, J ¼ 6.70 Hz, 3H). 13C NMR (100 MHz,
CDCl3)
d 143.44, 131.53, 131.49, 128.45, 128.29, 128.04, 123.49,
120.34, 89.58, 88.69, 35.91, 31.92, 31.25, 29.70 ( ꢁ 4C), 29.66 ( ꢁ 5C),
29.57, 29.48, 29.36, 29.25, 22.69, 14.12. IR (KBr) 2918, 2848, 2359,
1463, 751, 723, 688 cmꢂ1. Anal. Calcd. for C32H46: C, 89.24; H, 10.76.
Found: C, 89.09; H, 10.97.
2.2.4. Poly[1-(4-Octadecylphenyl)-2-phenylacetylene] (1)
Polymerization of 5 was carried out under dry nitrogen using
the following conditions: [M]0 ¼ 0.16 M, [TaCl5] ¼ 20 mM, [n-
Bu4Sn] ¼ 40 mM, in toluene at 80 ꢀC for 48 h. The polymerization
procedure was as follows. A monomer solution was prepared in a
two-necked flask by mixing 5 (210 mg, 0.49 mmol) and toluene
(1.29 mL). Another two-necked flask was charged with TaCl5
(21.5 mg, 0.06 mmol), n-Bu4Sn (39
mL, 0.12 mmol), and toluene
(1.5 mL), and the catalyst solution was aged at 80 ꢀC for 15 min. The
monomer solution was then added to the catalyst solution and
stirred at 80 ꢀC for 48 h. The polymerization was quenched by
adding a small amount of methanol. The polymerization mixture
was diluted with toluene and poured into methanol while stirring
to precipitate the resulting polymer, 1, as yellow solid. The polymer
was isolated by filtration and dried. The polymer yield was deter-
mined to be 78% by gravimetry.
d
7.38 (d, J ¼ 8.36 Hz, 2H), 7.05 (d, J ¼ 8.36, Hz, 2H), 2.55 (t,
2.3. Instruments
1H and 13C NMR were recorded on a Varian 400-MR spec-
trometer, while infrared spectra were recorded on a JASCO FT/IR-
4200 spectrometer. Number-average molecular weight (Mn) and
Fig. 1. Chemical structures of PDPAs without (1) and with (2) a silylene linkage.