Chemistry Reference
In-Depth Information
Table 6.7
Microstructures of polybutadienes prepared with some coordination catalysts
Microstructure (%)
Catalyst
Cis
-1,4
Trans
-1,4
1,2
TiI
4
/Al(C
2
H
5
)
3
95
2
3
TiBr
4
/Al(C
4
H
9
)
3
88
3
9
b
-TiCl
3
/Al(C
2
H
5
)
3
80
12
8
Ti(OC
4
H
9
)
4
/Al(
2
H
5
)
3
-
-
99-100
Ti(OC
6
H
5
)
4
/R
3
Al
90-100
-
-
(
p
-Cycloocatadiene)
2
Ni,CF
3
CO
2
H
100
-
-
Bis(
p
-Crotyl NiCl)
92
-
-
Bis(
p
-Crotyl NiI)
-
94
-
CoCl
2
/Al(C
2
H
5
)
2
Cl
96-97
2.5
1-1.5
CoCl
2
/Al(C
2
H
5
)
3
94
3
3
CoCl
2
/Al(C
2
H
5
)
3
/pyridine
90-97
-
-
Co
-stearate/AlR
2
Cl
98
1
1
VCl
3
/AlR
3
-
99
1
VOCl
3
/Al(C
2
H
5
)
3
-
97-9
2-3
VCl
4
/AlCl
3
-
95
-
Cr(C
6
H
5
CN)
6
/Al(C
2
H
5
)
3
100
-
-
MoO
2
(OR)
3
/Al(C
2
H
5
)
3
-
-
75
a
From various sources in the literature
6.6.1.2 High Molecular Weight Polybutadiene
High molecular weight polybutadiene homopolymers are prepared commercially with anionic
catalysts and with coordination ones. Polybutadiene formed with sodium dispersions was prepared
industrially in the former USSR, and perhaps might still be produced in that area today. This sodium-
catalyzed polybutadiene contains 65% of 1,2-adducts [
112
]. Many of the preparations by others,
however, utilize either alkyllithium or Ziegler-Natta type catalysts prepared with titanium tetra
iodide or preferably containing cobalt.
Because high molecular weight polybutadiene can be prepared by different catalytic systems, the
choice of catalyst is usually governed by the desired microstructure of the product. Alfin catalysts yield
very high molecular weight polymers with a large amount of
1,4 structures. Both the molecular
weight and microstructure can be affected significantly, however, by variations in the Alfin catalyst
components. These can be the alkyl groups of the organometallic compounds or alkoxide portions.
When butadiene is polymerized with lithium metal or with alkyllithium catalysts, inert solvents
like hexane or heptane must be used to obtain high
trans-
cis-
NMR spectra, 1,4-polybutadiene formed with
n-
butyllithium consists of blocks of
cis-
1,4 units and
trans-
1,4 units that are separated by isolated vinyl structures [
113
]:
z
y
x
The quantity of such units in the above polybutadienes is approximately 48-58%
trans-
1,4,
33-45%
1,4, and 7-10% 1,2 units [
112
]. There is little effect of the reaction temperatures upon
Reactions in tetrahydrofuran solvent result in 1,2 placement that can be as high as 87%.
The microstructures of polybutadienes prepared with Ziegler-Natta catalysts vary with catalyst
composition. It is possible to form polymers that are high either in 1,2 placement or in 1,4 units.
The catalysts and the type of placement are summarized in Table
6.7
.
cis-
