Propylenepolymerization to high molecular weight atactic polypropylene and copolymerization with 1-hexene using monocyclopentadienyl titaniumcatalysts

Abstract

A number of cyclopentadienyltitanium aryloxide complexes, 1-Ar-2,3,4,5-Me₄-Cp(2,6-ⁱPr₂C₆H₃O)TiCl₂ (Ar = 4-Me₃SiPhenyl (5), 4-ⁱPrPhenyl (6), 4-MePhenyl (7), 3,5-(CF₃)₂Phenyl (8)) and (1-Ar-2,3,4,5-Me₄CpTiCl₂)₂(OAr′O) (Ar′ = 4,4′-(3,3′,5,5′-ⁱPr₄C₆H₂–C₆H₂), Ar = 4-SiMe₃Phenyl (9), 4-MePhenyl (10)) were synthesized from the reaction of a corresponding cyclopentadienyl titanium trichloride derivative with the lithium salt of a relevant phenol. The molecular structures of complexes 6, 7 and 8 were determined by X-ray crystallography. Upon activation with ⁱBu₃Al and Ph₃CB(C₆F₅)₄, all mononuclear complexes 5–8 exhibit good catalytic activities for propylene polymerization, whereas the binuclear complexes 9 and 10 show lower catalytic activities under the same polymerization conditions. ¹³C NMR, DSC and GPC analysis indicates the produced polymers are atactic polypropylene with relatively high molecular weight. It was found that the substituents on both the cyclopentadienyl and aryloxy ligands of these complexes show obvious influence on the molecular weight of the resultant polymers with complex 5 producing the highest molecular weight atactic polypropylene. Complexes 5, 6 and 7 were also tested as catalysts for copolymerization of propylene with 1-hexene and copolymers with 1.2–10.1% comonomer incorporation were obtained in reasonable catalytic activity.