Polymerization of propylene over isospecific catalysts
immobilized on MAO-pretreated supports with triisobutylaluminum as activator
Polimery 2000, No 5, 328
SummaryThe effect of support type on the activity of zirconocene—triisobutylaluminum (TIBA) systems was studied in the polymerization of propylene, and on the properties of the resulting PP. Three zirconocenes were used: Me2SiInd2ZrX2 (X = Cl or Me) and Ph2CCpFluZrCl2; and three supports were used: (i) SiO2 (spec. area Ssp = 300 m2/g); (ii) SiO2-gr-PAAc [i.e. SiO2 modified with poly(acrylic acid) by radiative grafting]; (iii) PE-gr-PAAc (i.e. functionalized by radiative grafting, Ssp = 4 m2/g). Propylene was polymerized in the liquid monomer. The supports were made to react with methylaluminoxane (MAO) and the product was used to immobilize a zirconocene compound to produce a supported catalyst. With TIBA as cocatalyst, the resulting PP constituted a replica of catalyst particles; the bulk density of PP was high, up to 0.5 g/cm3. As the Zr content in the catalyst was increased, the specific productivity (g PP/g catalyst) rose to attain a maximum, characteristic for a given support. Catalyst activity and M of PP were studied in relation to TIBA concentration. The type of MAO-modified support had little effect on the PP properties. Modification of the SiO2/MAO/Me2SiInd2ZrCl2 catalyst with a boron compound, CPh3B(C6F5)4, did not affect PP properties but reduced the activity of the catalyst system at AlTIBA/Zr > 500.