Stereospecific bulk polymerization of propylene over ansa-zirconocene catalysts
Polimery 2000, No 5, 333
SummaryBulk polymerization of propylene was studied over four ansa-zirconocene catalysts, viz., Me2SiInd2ZrCl2 (1), Me2Si(4-Ph-2-Et-Ind)2ZrCl2 (2) (rac:meso = 1:2), Ph2C(CpFlu)ZrCl2 (3), and Me2C(3-Me-CpFlu)ZrCl2 (4), which were characterized by different symmetries (C1, C2, Cs). The structure of the metallocene affected the structure of PP. Upon reactions with methylaluminoxane (MAO) or triisobutylaluminum (TIBA), compounds 1–4 produced very active catalytic systems which catalyzed the polymerization to yield various structures of PP. Catalysts 1 and 2 gave isotactic PP, catalyst 3 gave syndiotactic PP and catalyst 4 gave hemiisotactic PP. Hemiiso-PP was similar in structure to amorphous PP and had no melting point. The catalytic activity of the system and molecular weight and stereospecificity of PP were studied in relation to the mode of preparation of the catalyst. Kinetic parameteres were evaluated, viz., time of insertion of the propylene molecule (0.001–0.0001 s) and the time of growth of a single PP macromolecule (3–6 s), and from these data the minimum degree of polymerization was determined. Activation energies were evaluated for the polymerization carried out over each catalyst system. Young's modulus, molecular weight and stereoregularity of the PP prepared were determined.