Ethylene and propylene were copolymerized with 10-undecen-1-ol,
using stereorigid
Et[Ind]2ZrCl2,
Me2Si[Ind]2ZrCl2,
Me2Si[2-MeInd]2ZrCl2,
and
Me2Si[2-Me-4,5-BenzoInd]2ZrCl2
catalysts
activated with methylaluminoxane (MAO). As a reference, ethylene
copolymerization was also carried
out with the nonstereospecific catalyst
[Ind]2ZrCl2/MAO. Characterization of the
copolymers by 13C and
1H NMR spectroscopy revealed that the polymerization
product was a true copolymer and that the
conversion of the polar comonomer was strongly favored by the chiral
geometry of the catalyst. The
pretreatment of 10-undecen-1-ol with MAO before initiating the
copolymerization increased the ethylene
polymerization rate markedly and slightly improved the reactivity of
the polar comonomer. A major
improvement in the polymerization rate of 10-undecen-1-ol was obtained
when the polymerization
temperature and Al/Zr mole ratio were increased.
In the solid-state structure of the Schiff base salen [salen ) N, N′-ethylenebis(salicylideneiminato)] zirconium dichloride complex Zr(salen)Cl2(THF), C20H22Cl2N2O3Zr, a quadridentate ligand, occupies four sites in the pseudopentagonal bipyramidal coordination. The coordination sphere is completed by one THF molecule, and two chloride ions are forced into the trans-position. Removal of THF, while Zr(salen)Cl2(THF) is heated in toluene, leads to a six-coordinated complex with the two chloride ligands assuming the cis-position. This property was successfully utilized in the preparation of a homogeneous Zr(salen)Cl2 catalyst precursor. Heating of Zr(salen)Cl2(THF) in toluene in the presence of SiO2 causes deposition of Zr(salen)Cl2 on to the silica support, producing a heterogeneous catalyst, which shows an acceptable activity in ethylene polymerization at 80 °C and at low ethylene pressures in the presence of the cocatalyst methylaluminoxane.
A homogeneous titanium halide catalyst containing one bulky phenoxy ligand was synthesized by the reaction of a lithium salt of 2,6-di-tert-butylphenol and TiC1 4 • The complex was tested, with methylaluminoxane as cocatalyst, in the copolymerization of ethylene and styrene. The reaction product was not a copolymer but a mixture of polyethylene and atactic polystyrene. The formation of two fractions may indicate the presence of several active species in the catalyst or a different polymerization mechanism for the two monomers.
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