Macromolecules
Article
dendritic nanoparticles have many applications such as in optical
instruments, selective oxidation and dehydrogenation, catalysis,
electrocatalysis, and sensors.21
Table 1. Synthesis of the Homopolymer VBPPy via Anionic
Polymerization Using Various Initiators in THF at −78 °C
homopolymer
The self-assembly process is a common phenomenon in nature
and synthetic materials science. Generally, block copolymers with
hydrophilic and hydrophobic moieties form amphiphilic assem-
blies such as microphase-separated nanostructures, hollow mi-
celles, and vesicles in selective solvent. Recently, polymer super-
structures with a miktoarm graft copolymer containing carboxylic
acid as a hydrophilic moiety and benzyl as a hydrophobic moiety
in both a polar and a nonpolar solvent have been reported.22−25
More recently, stimuli-sensitive vesicles, which act as a reservoir
for both hydrophobic and hydrophilic molecules individually,
were successfully formed through a one-step process with the
controlled amphiphilic homopolymer PVPPy.26,27 In this pro-
spective, the unique micellization behaviors of the homopolymer
PVBPPy are also predicted in view of the fact that it contains
hydrophilic (pyridyl) and hydrophobic (biphenyl) moieties in the
same monomer like the micellization behaviors of PVPPy.
Comparing P2VP with PVPPy as an amphiphilic homopoly-
mer, PVPPy has the chemical structure of both polystyrene
and P2VP. It is known that homopolymers with hydrophilic
and hydrophobic moieties can also form vesicles and micelles
similar to amphiphilic block copolymers. Additionally, the block
copolymer of P2VP-b-PVPPy allowed the formation of flower
micelles and bimetallic dendritic nanoparticles of Pt−Au by
the different reactivity of the pyridine in the P2VP and the
PVPPy blocks. Accordingly, to generate the different reactivity
from P2VP and PVPPy, a new pyridine-containing mono-
mer of 2-(4′-vinylbiphenyl-4-yl)pyridine (VBPPy) was designed
by introducing biphenyl between the vinyl and pyridine moieties
based on the structure of 2-vinylpyridine and the addition of
biphenyl between vinyl and pyridine units could make more
rigidity and hydrophobicity than P2VP and PVPPy. The VBPPy
was synthesized by the Suzuki coupling reaction, and the possi-
bility of anionic polymerization of 2-(4′-vinylbiphenyl-4-yl)-
pyridine (VBPPy) was evaluated using various reaction condi-
tions for optimal results. The reactivity of living poly(2-(4′-
vinylbiphenyl-4-yl)pyridine) (PVBPPy) containing biphenyl
units was compared with that of P2VP and PVPPy by the
block copolymerization of VBPPy with various monomers. More-
over, a phase-separated PVBPPy-b-PMMA (f VBPPy = 0.23)
diblock film was used as a template to form a nanocomposite in
which gold (Au) nanoparticles (NPs) were present only in
PVBPPy.
Mn × 10−3
initiator VBPPy additive time
yield
(%)
a
b
b
(mmol) (mmol) (mmol) (min) calcd obsd Mw/Mn
s-BuLi
0.055
0.099
2.08
2.14
360
360
9.8
6.7
30.1
5.9
1.72
1.21
15.9
97.2
α-MeSt
0.34
DPE
0.17
0.090
0.036
2.14
3.32
390
390
6.1
8.3
5.7
1.17
1.23
10.0
24.0
c
0.18
23.8
DPM-K
0.092
3.10
2.92
2.02
2.77
2.56
2.50
5.32
4.52
4.95
8.86
180
300
330
360
360
360
360
360
360
360
8.0
16.5
7.6
10.2
18.2
8.2
1.06
1.26
1.29
1.21
1.26
1.25
1.24
1.27
1.24
1.24
48.0
90.7
97.5
100
100
100
100
100
100
100
0.041
0.068
c
0.117
6.1
6.5
c
0.065
10.1
11.5
19.6
32.3
41.1
54.3
10.5
12.2
20.2
32.6
42.1
55.2
0.056
c
0.070
c
0.036
c
0.031
c
0.042
a
Mn(calcd) = (MW of VBPPy) × [VBPPy]/[initiator] × yield of
b
polymers (%). Mn(obsd) and Mw/Mn were obtained by SEC
calibration using a polystyrene standard in tetrahydrofuran (THF)
containing 2% triethylamine (C2H5)3N as an eluent at 40 °C. α-MeSt:
c
α-methylstyrene; DPE: 1,1-diphenylenthylene. The concentration of
the solution of VBPPy in THF is 0.15 mol/mL.
3.0 mol %) in THF were reacted at 80 °C for 2 h under a nitrogen
atmosphere, and then 4-bromophenylboronic acid (10.0 g, 42.7 mmol)
was slowly added dropwise over 30 min. After the reaction was com-
plete, the solvent was evaporated under reduced pressure. The excess
unreacted 2-bromopyridine was distilled at 110 °C at 1.0 mmHg and
2-(4-bromophenyl)pyridine at 180 °C at 1.0 mmHg as a white crystal.
1
The yield was 72%. H NMR spectra (CDCl3, 400 MHz), δ (ppm):
8.69 (d, 1H, −NCH−C= of pyridyl), 7.95 (d, 2H, Cl−CCH−
CH= of phenyl), 7.74 (m, 2H, N−CCH−CH= of phenyl), 7.45
(d, 2H, −CHCCl−CH= of phenyl), 7.24 (t, 1H, −NCH−CH=
of pyridyl).
Synthesis of VBPPy. 4-Vinylphenylboronic acid (10.0 g, 67.6 mmol),
2-(4-bromophenyl)pyridine (13.9 g, 87.9 mmol), 2 M potassium
carbonate (K2CO3, 14.0 g) in H2O (50 mL), and tetrakis(triphenyl-
phosphine)palladium(0) (Pd(PPh3)4, 3.0 mol %) in THF were reacted
at 80 °C for 24 h under a nitrogen atmosphere. After the reaction was
complete, the mixture was evaporated and extracted with ether/H2O.
The concentrated mixtures were purified by column chromatography
with hexane/ethyl acetate = 7/3 to obtain a yellowish-white solid and
then recrystallized from acetone. The yield was 78.0%. Melting point
(mp) = 142.5 °C. Elemental analysis: calcd C(88.68%), H (5.88%), N
(5.44%). Found: C (89.14%), H (5.49%), N (5.37%). 1H NMR
spectra (CDCl3, 400 MHz), δ (ppm): 8.64 (d, 1H, −NCH−C= of
pyridyl), 8.09 (d, 2H, N−C−CCH− of phenyl), 7.89 (m, 2H,
N−C−CCH−CH− of phenyl), 7.73 (d, 2H, CH2CH-CCH−
CH = of phenyl), 7.62 (d, 2H, N−CCH−CH = of pyridyl), 7.52
(d, 2H, CH2CH−CCH− of phenyl), 7.25 (t, 1H, −NCH−
CH= of pyridyl), 6.76 (q, 1H, CH2CH− of vinyl), 5.83 (d, 1H,
CH2CH− of vinyl), 5.30 (d, 1H, CH2CH− of vinyl). 13C NMR
(CDCl3, 75 MHz), δ (ppm): 114.1, 136.8 (vinyl-), 136.4, 126.7, 127.2,
139.9 (vinyl-phenyl), 136.9, 127.3, 127.2, 138.3 (-phenyl-pyridine),
157.0, 120.4, 141.2, 122.1, 149.7 (pyridine). FT-IR (KBr, cm−1): 3150
and 3050 (vinyl C−H, aromatic C−H), 1627 (vinyl CC), 1588,
1472, 1439 (aromatic amine CN, aromatic CC).
EXPERIMENTAL SECTION
■
Materials. 4-Vinylphenylboronic acid (Aldrich), 4-bromophenyl-
boronic acid, 2-bromopyridine (Aldrich, 99%), and tetrakis(triphenyl-
phosphine)palladium(0) (Pd(PPh3)4, Aldrich) were used as received.
A 2 M solution of K2CO3 (Aldrich, 99%) in distilled water was
prepared. As-received s-BuLi (Aldrich, 1.4 M in cyclohexane) and
naphthalenide potassium (Naph-K) prepared with naphthalene and
potassium metal were stored at −30 °C in ampules equipped with
break-seals. 2-Vinylpyridine (2VP, Aldrich, 97%) and methyl meth-
acrylate (MMA, Aldrich, 99%) were passed through an alumina
column, dried for 24 h over anhydrous CaH2, and distilled under re-
duced pressure. Tetrahydrofuran (THF, Fisher, GR grade) was
distilled under N2 after refluxing with sodium for 5 h. DPM-K was pre-
pared according to a previously reported procedure.28,29 The efficiency
of DPM-K was determined by titration with octyl alcohol.
2-(4-Bromophenyl)pyridine (BrPPy). 2-Bromopyridine (20.0 g,
126.7 mmol), 2 M potassium carbonate (K2CO3, 14.0 g) in H2O
(50.0 mL), and tetrakis(triphenylphosphine)palladium(0) (Pd(PPh3)4,
6707
dx.doi.org/10.1021/ma500974m | Macromolecules 2014, 47, 6706−6714