ABSTRACT: Metallocenes with different symmetries in combination with methylaluminoxane (MAO), have been investigated at different propylene polymerization temperatures. The metallocenes rac-ethylene bis(h5-1-indenyl) zirconium dichloride, with C2 symmetry and isopropylidene (h5cyclopentadienyl)(h5-9-fluorenyl) zirconium dichloride, with Cs symmetry, produce isotactic and syndiotactic polypropylene respectively. The degree of tacticity of these polymers decreases with the increase of polymerization temperature. Only atactic polypropylene was formed with the unbridged zirconocenes bis(h5-cyclopentadienyl) zirconium dichloride and bis(h5-indenyl) zirconium dichloride at any temperature investigated. The polymer microtacticity was analysed by 13C NMR.
Metallocenes; zirconium; stereoselectivity; polypropylene; NMR
