Ethylene/Propylene Copolymerization Over Three Conventional C2-Symmetric Metallocene Catalysts: Correlation Between Catalyst Configuration and Copolymer Microstructure

This work reports on a correlation between catalyst configuration and copolymer microstructure for ethylene/propylene (E/P) copolymerization using three conventional C-2-symmetric metallocene catalysts, namely, rac-Et(Ind)(2)ZrCl2 (EBI), rac-Me2Si(2-Me-4-Ph-Ind)(2)ZrCl2 (SiPh), and rac-CH2(3-tBu-Ind)(2)ZrCl2 (MBu), with MAO as a common cocatalyst. Copolymerization reactions were conducted in toluene at three different temperatures with varied E/P ratios. Some typically obtained copolymers were characterized in detail using C-13-NMR spectroscopy, by which triad distribution data were elaborated in a statistical method to determine the reactivity ratios (r(E) and r(P)) of the comonomers, which were also obtained by Fineman-Rose estimation. The production of alternating-like copolymers from EBI is attributed to the rapid interconversion between two conformation states of the active site, one of which favors the incorporation of propylene but the other one does not. Both SiPh and MBu are structurally more rigid and of larger dihedral angles than EBI; however, SiPh which owns open active site conformation tend to produce random copolymers at all studied temperatures, and for MBu, sterically hindered catalyst, block-like copolymers were obtained. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 3218-3226, 2010