Hydrogen effects in the polymerization of propylene with C2 symmetric metallocene catalysts

Propylene was polymerized with two C-2 symmetric metallocene catalysts, ethylene bis(indenyl)zirconium dichloride and dimethylsilyl bis(2-methyl-benz(e) indenyl) zirconium dichloride, in the presence of increasing amounts of hydrogen. The hydrogen influenced the molecular weight significantly, as was expected. The degree of isotacticity of the polypropylene was influenced by the level of hydrogen added during polymerization, and the amount and type of stereoerrors as determined by C-13 NMR increased as hydrogen levels were increased. Results indicated that efficiency of enantiomorphic site control is dependent on the length of the growing polymer chain during polymerization.