Chemistry Reference
In-Depth Information
Butadiene can be polymerized with chromium oxide catalyst on support to form solid
homopolymers. The products, however, tend to coat the catalyst within a few hours after the start
of the reaction and interfere with further polymerization. Polybutadiene can also be prepared in the
presence of molybdenum catalyst promoted by calcium hydride. The product contains 80% of
1,4 units and 20% of 1,2 units. Of the 1,4 units, 62.5% are
cis
and 37.5% are
trans
[
110
].
Cobalt oxide on silica-alumina in the presence of alkyl aluminum also yields high
cis-
1,4 structure
polymers. An all 1,2 polybutadiene can be prepared with
n
-butyllithium modified with bis-piperidino
5 to +20
C temperature [
111
]. The 100%
1,2 placement was postulated to proceed according to the following scheme [
111
]. First a complex
forms between the base and butyllithium:
ethane. The atactic polymer can be formed in hexane at
N
Li
N
The above complex reacts with butadiene to form a new complex:
N
Li
N
This is followed by insertion of butadiene into the carbon-lithium bond:
N
Li
N
Annunziata et al. [
114
] reported that Group 4 metals complexes bearing anilidomethylpyridine
ligands were prepared by them. After activation by AlBu
2
H and methylalumoxane, the catalysts were
tested in 1,3-butadiene and
-olefin polymerization. The zirconium complexes showed higher activity
than the titanium analogous. Polymerization of ethylene resulted in all cases in the production of high
molecular weight linear polyethylene. On the other hand, propylene polymerization tests provided
a
