DEGREE OF STEREOCHEMICAL CONTROL OF RAC-ET[IND]2ZRCL2 MAO CATALYST AND PROPERTIES OF ANISOTACTIC POLYPROPYLENES

Polypropylenes had been obtained with racemic ethylenebis(indenyl)zirconium dichloride/ methyl aluminoxane (MAO) catalyst from -55 to +80 °C and Al/Zr ratios between 103 and 1.6 × 104. As the polymerization temperature increases, the polymers produced have progressively lower melting transition temperature, lower homosteric pentad sequence population, and higher solubility in low-boiling solvents, indicating frequent stereochemical inversion in monomer enchainment. Polymer fractions separated by solvent extraction are relatively crystalline (crystallinity >50%) favoring a thermally stable 7-modification. The13C NMR spectra also showed the presence of tetramethylene unit in acetone- and ether-soluble fractions. In addition, there is tail-to-tail enchainment in PP obtained at a low MAO to Zr ratio. The results indicate variations of degrees of stereochemical and regiochemical control by the rac-Et[Ind]2ZrCl2/MAO catalyst with polymerization temperature and catalyst composition. © 1990, American Chemical Society. All rights reserved.