Macromolecules
Article
1,3-Butadien-2-ylmagnesium Chloride. Magnesium turnings
(7.97 g) (328 mmol) and anhydrous THF (120 mL) were placed in a
two-necked round bottom flask equipped with a reflux condenser
under N2 gas. Prior to use, the magnesium surface was activated with
1 mL of 1,2-dibromoethane. After the activation was completed,
ZnCl2 (2.71 g) (19.9 mmol) was added to the mixture. A mixture of
chloroprene (19.35 g) (219 mmol), anhydrous THF (80 mL), and a
small amount of 1,2-dibromoethane was added dropwise with gently
heating the flask. Then, the mixture was refluxed at 90 °C for 1 h.
(Z)-1-Phenyl[3]dendralene. (Z)-β-Bromostyrene (20.04 g)
(109.3 mmol), Ni(dppp)Cl2 (1.32 g) (2.42 mmol), and anhydrous
THF (70 mL) were placed in a two-necked round bottom flask under
N2 gas. 1,3-Butadien-2-ylmagnesium chloride (ca. 219 mmol) was
added dropwise over 1 h at 0 °C. The mixture was then stirred for 1 h
at the same temperature. The resulting mixture was treated with ice
water and extracted using ethyl ether. The combined organic layer
was washed with 1 M HCl, sat. NaHCO3 aq., and brine. The washed
mixture was dried over magnesium sulfate and concentrated in vacuo.
Finally, 1Z-P3D was isolated by fractional distillation. (yield 63%,
clear liquid, bp 54.5 °C/4 mmHg) 1H NMR (CDCl3): δ = 5.19−5.13
(3H, m, Hc, Hd, Hg), 5.38 (1H, d, J = 17.4 Hz, Hf), 6.21 (1H, d, J =
12.3 Hz, Hb), 6.48 (1H, dd, J = 17.4, 10.5 Hz, He), 6.59 (1H, d, J =
12.3 Hz, Ha), 7.21−7.41 (5H, m, Hh, Hi, Hj), 13C NMR (CDCl3): δ =
115.6, 118.1, 127.0, 127.9, 128.0, 128.8, 131.7, 136.8, 137.6, 143.9
(Scheme 3).
Measurements. All NMR spectra were recorded in CDCl3 using a
JEOL JNM-AL-400 spectrometer. The solvent peak was used as a
1
reference. One-dimensional H and 13C spectra were obtained with
32 768 data points, 15 and 220 ppm spectral widths, 45 and 30° pulse
widths, and 7 and 5 s repetition times, respectively. A 2D H−H
COSY spectrum was obtained with 1024 raw data points and 256
column data points with zero filling. A 2D C−H HMQC spectrum
was obtained with 512 raw data points and 512 column data points.
GC-MS spectra were obtained using a Shimadzu QP-2010plus
instrument with electron impact ionization. A size-exclusion
chromatogram (SEC) was obtained at 40 °C using a TOSOH
HLC-8220 instrument equipped with three polystyrene gel columns
(TOSOH TSKgel G4000HHR, G3000HHR, and G2000HHR (7.8 mm
× 30 cm)), UV (254 nm), and refractive index (RI) detectors. THF
was used as the carrier solvent at a flow rate of 1 mL/min.
RESULTS AND DISCUSSION
■
Anionic Polymerization of 1Z-P3D. The anionic
polymerization of 1Z-P3D was carried out in THF using K-
Naph as an initiator. Upon addition of 1Z-P3D, the
characteristic green color of K-Naph immediately changed to
dark red. This color was unchanged and disappeared only
when a small amount of ethanol was added to terminate the
reaction. The polymer was obtained by pouring the solution
into a large excess of methanol; no insoluble fraction was
formed during polymerization. Table 1 summarizes the results
of the anionic polymerization of 1Z-P3D under various
conditions. Polymers of predictable molecular weights based
on the monomer-to-initiator ratio were obtained at −78 °C,
with narrow molecular-weight distribution (Mw/Mn < 1.26).
The conversion increased with time and 24 h were required to
achieve quantitative conversion. Although a slight increase in
Mw/Mn was observed with time, the shape of the SEC
chromatogram remained unimodal. It is worth noting that the
polymerization rate of 1Z-P3D was significantly lower than
that of P3D. According to a previous study, the anionic
polymerization of P3D was complete in ∼90 min under THF/
K-Naph conditions at −78 °C. The SEC chromatograms of
poly(1Z-P3D)s produced under different conditions (Figure
2) showed that the molecular-weight distributions remained
unimodal during 24 h in the polymerizations carried out at
−78 °C. This indicated that side reactions, such as nucleophilic
addition of a propagating carbanion to a conjugated double
bond in the polymer chain, did not occur. Surprisingly, the
polymerization of 1Z-P3D proceeded without broadening of
the molecular-weight distribution, even at −40 and 0 °C,
Scheme 3. Chemical Structure of 1Z-P3D
Anionic Polymerization. The synthesized monomer was purified
by distillation under high vacuum in the presence of phenyl-
magnesium bromide, diluted with THF, and then sealed in ampules
with breakable seals. All anionic polymerizations were carried out
under high vacuum using the break-seal method.24 First, a THF
solution of the initiator (K-Naph) was introduced into the reactor and
cooled to −78 °C. Then, the entire monomer solution was added to
the reactor at the same temperature, and the reactor was placed in an
aimed constant-temperature bath and held for a fixed time. Finally,
degassed ethanol was added to terminate the polymerization.
Table 1. Anionic Polymerization of 1Z-P3D in THF with K-Naph
1Z-P3D
K-Naph
Mn (kg/mol)
a
b
mol/L
mmol
mol/L
mmol
[M]/[I]
temp. (°C)
time (h)
conv. (%)
calcd
SEC
Mw/Mn
0.576
0.576
0.576
0.576
0.576
0.576
0.576
0.576
0.669
4.33
4.98
6.12
7.08
6.15
6.34
6.99
7.73
10.4
0.0702
0.0702
0.0702
0.0702
0.0702
0.0702
0.0719
0.0719
0.0719
0.143
0.206
0.199
0.278
0.229
0.194
0.270
0.154
0.070
30
24
31
25
27
33
26
50
149
−78
−78
−78
−78
−40
0
40
−78
−78
1
6
12
24
6
6
6
48
168
57
94
95
100
97
99
100
100
100
5.4
7.1
9.2
7.9
8.1
10.1
8.1
15.7
46.3
5.2
7.4
9.4
8.2
8.3
9.3
3.2
16.3
68.7
1.19
1.22
1.21
1.26
1.17
1.16
1.68
1.21
1.23
c
c
a
b
Calculated from the amount of residual 1Z-P3D estimated by GC in a methanol solution after precipitation. Mn (calcd) = 2 × [M]/[I] × (MW
c
of 1Z-P3D) × (conversion)/100. For low-molecular-weight samples, other polystyrene gel columns (TOSOH TSKgel G3000HHR, G2000HHR
and G1000HHR) were used.
,
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Macromolecules 2021, 54, 4326−4332