Synthesis of polypropylene using bis(2-alkylindenyl)zirconium dichloride/MAO systems

Elastomeric polypropylene was prepared using bis(2-alkylindenyl)zirconium dichloride(alkyl=methyl, i-propyl, n-butyl, benzyl, and cyclohexyl) as a catalyst. The nature of the alkyl substituent exerted stronger influence upon the catalytic activity for propylene polymerization rather than upon that corresponding to ethylene polymerization. The rate of propylene polymerization decreased in the following order; (2-MeInd)2ZrCl2 > (2-n-BuInd)2ZrCl2 > (2-CyInd)2ZrCl2 > (2-i-PrInd)2ZrCl2 > (2-BzInd)2ZrCl2. Molecular weight of PP increased as the polymerization temperature decreased. Among the five catalysts, (2-MeInd)2ZrCl2 produced the highest molecular weight-PP, and (2-BzInd)2ZrCl2 yielded PP with the lowest molecular weight. Meanwhile, PP produced over (2-BzInd)2ZrCl2, which contained the highest [mmmm] pentad fraction, showed lower tensile strength, tensile modulus, elongation and elastic recovery compared to those obtained by the other catalysts, presumably due to its lower molecular weight. When PP had molecular weights high enough so that the mechanical properties were in the plateau region, [mmmm] pentad fraction influenced PP from (2-n-BuInd)2ZrCl2 to exhibit higher tensile strength and tensile modulus but lower elongation and tensile set after elongation compared to PP from (2-MeInd)2ZrCl2.