SUMMARY: Monocyclopentadienyl compounds, CpMCl 3 (M = Ti, Zr) supported on activated MgCl 2 were used for the polymerizations of ethylene in the presence of methylaluminoxane (MAO) or a common alkylaluminium as a cocatalyst. By supporting CpMCl 3 on MgCl 2 , the catalyst activity was increased drastically to show high activity similar to MgCl 2 -supported TiCl 4 catalysts. The activity of the CpZrCl 3 /MgCl 2 catalyst was higher than that of the CpTiCl 3 /MgCl 2 one. Both catalysts gave polymers with high molecular weight (M
Propene polymerization was conducted by a
MgCl2/diisobutyl phthalate/TiCl4
catalyst
combined with AlEt3 as cocatalyst. The polymerization
was quenched by oxygen gas, and the polymer
was fractionated into atactic and isotactic parts with boiling heptane.
Each part was analyzed by 1H
NMR. The spectra showed the resonances of vinylidene, vinyl, and
hydroxymethylene groups, whose
intensities were strongly dependent on the polymerization temperature
and the stereoregularity. Raising
the polymerization temperature increased the intensity of the
hydroxymethylene group in both parts.
The relative intensity of the hydroxymethylene to that of the
vinylidene group was much higher in the
atactic parts. These results suggest that the rates of
β-hydrogen transfer and transfer by AlEt3
should
be affected by the stereospecificity of the active species as well as
polymerization conditions. Heat
treatment at 120 °C in the presence of 1-octene quantitatively
converted the terminal aluminum−carbon
bond to a vinylidene group.
The effect of different external silane donors on the activity and isotacticity of polypropylene prepared by using Mg(OEt) 2 -phthalate ester-TiCl 4 -AlEt 3 -alkoxy disilane catalyst systems has been investigated. In the case of catalyst systems containing (trimethylsilyl)methylalkyldimethoxysilanes [Me 3 SiCH 2 Si(OMe) 2 R] as external donors, the bulky Me 3 SiCH 2 -group was effective in converting aspecific sites into isospecific ones, followed by the increase of activity and isospecificity of the obtained polymer. Catalyst activity and isotacticity of the polymer increased with the decrease of the number of alkoxy groups in the substituted alkoxy disilanes. The effect of alkoxy groups between alkoxy disilanes and alkylaluminum as cocatalyst on the active sites of the catalyst and the influence of the size of alkoxy groups in disilane compounds were examined, respectively. Some correlation between molecular weight, molecular weight distribution, and isospecificity was also observed.
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