High efficiency synthesis of isotactic polypropylene and linear polyethylene using a new C₂-symmetric carbon-bridged zirconocene catalyst

Abstract

Ansa-Cyclohexyl-bis(4,5,6,7-tertrahydro-1-indenyl) zirconium dichloride (5) was used as catalyst for propylene and ethylene polymerization together with methyl aluminoxane (MAO) as the cocatalyst. Isotactic polypropylene (PP) was obtained with the highest activity of 6.37×10⁷g PP (molZr)⁻¹h⁻¹. The meso-meso (mmmmm) pentads sequence content of PP was determined by ¹³C NMR spectroscopy. The dependence of the microstructure on the reaction temperature and the Al/Zr molar ratio was examined and the catalytic activity of complex 5 was compared with that of the similar ansa-zirconocene 3. The high activity of the new zirconocene 5 for propylene isospectic polymerization at high temperature (60 °C) is the result of its unique bridged-group structure. Complex 5/MAO displays also high catalytic activity of 0.46×10⁶ to 9.87×10⁶g PE(molZr)⁻¹h⁻¹ in the homo-polymerization of ethylene. The visometric molecular weight of PE ranges from 0.97×10⁴ to 11.16×10⁴ g·mol⁻¹ under the given conditions.¹³C NMR spectroscopy analysis proves the PE to be linear polyethylene (LPE).

Keywords

ansa-zirconocene / propylene polymerization / isotactic polypropylene / ethylene polymerization

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