Atom transfer radical polymerizations of styrene and butadiene as ...

Atom transfer radical polymerizations of styrene and butadiene as well as their copolymerization 45
Fig. 5 Dependences of M n , GPC and M w /M n on the conversion in the
ATRP of butadiene.The conditions were the same as in Fig. 3. Unfilled
circles, M n ; filled circles, M w /M n ; line, theoretical value M th
(assuming “living” conditions)
only a trace amount of product, irrespective of the reaction
parameters used [22]. At the same time, the polydispersity
of the product was around 2.0. In this paper, the conversion
of polybutadiene reached 23.6% after 15.5 h at 120°C. The
polydispersity of this system was lower than 2.0.
The contents of cis-1,4-, trans-1,4- and 1,2-butadiene
structural units were 22.1%, 58.4% and 19.5%, as elucidated
using the FTIR spectrum of the polybutadiene. These
results were similar to those obtained from 1 H NMR of the
PBd (the content of 1,4-butadiene was 83.1% and that of
1,2-butadiene was 16.9%, as calculated according to [23]).
The microstructure of the PBd obtained here was similar to
that of PBd obtained by conventional free radical polymerization
[24].
Copolymerization of styrene and butadiene
It was interesting to investigate whether styrene and
butadiene copolymer can be obtained through ATRP
initiated by this novel initiator system, C 6 H 5·CH 2 Cl /
MoCl 3 (OC 8 H 17 ) 2 / PPh 3 . The copolymerization of Bd and
St was studied in this regard.
Table 2 The influence of the initiator system on conversion, M n , GPC
and M w /M n in the polymerization of butadiene
Conditions C 6 H 5·CH 2 Cl /
MoCl 3 (OC 8 H 17 ) 2 :P(Ph) 3 :
Bd=1:1:3:200
C 6 H 5·CH 2 Cl :
Bd=1:200
Polymerization 15.50 62.27 62.27
time (h)
Conversion (%) 23.60 4.80 4.80
M n ×10 −4 1.24 9.88 8.86
M w /M n 1.75 2.44 2.58
Conditions: [Bd] 0 =2.19 M; T=120°C; solution was toluene
Bd
Fig. 6 Relationship between ln([M 0 ]/[M]) and polymerization time
for the copolymerization of St and Bd in toluene. [St+Bd] 0 =4.69 M;
T=90°C
The kinetics of the copolymerization of St and Bd in
toluene at 90°C, initiated by the C 6 H 5·CH 2 Cl / MoCl 3
(OC 8 H 17 ) 2 / PPh 3 initiator system, are shown in Fig. 6.
The molar ratio of C 6 H 5·CH 2 Cl/MoCl 3 (OC 8 H 17 ) 2 /PPh 3 /
(St+Bd) was 1/1/3/200, and that of St/Bd was 2/1. It was
found that a semilogarithmic kinetics plot of ln([M 0 ]/[M])
versus time gave a straight line. Figure 7 shows that there
is a linear dependence of M n on the monomer conversion
and a decrease in M w /M n with monomer conversion.
Figure 7.
The microstructure of the copolymer was characterized by
IR, 13 C NMR and 1 H NMR. In the IR spectrum of the
copolymer (Fig. 8), absorptions at 738, 911 and 967 cm −1
were characteristic of cis-1,4-, 1,2- and trans-1,4 butadiene
structural units, respectively, and the peaks at 3023∼3085 cm −1
were assigned to the aromatic C–H stretching of styrene units
in the copolymer. It was also found that the characteristic
Mn
25000
20000
15000
10000
5000
0
0 10 20 30 40 50 60
Conversion%
Fig. 7 Dependence of M n , GPC and M w /M n on conversion during the
copolymerization of St and Bd in toluene. The conditions were the
same as in Fig. 1. Squares, M n ; triangles, M w /M n
2.4
2.2
2.0
1.8
1.6
Mw/Mn