HOMO- AND COPOLYMERIZATION OF ETHYLENE CATALYZED BY ANSA-METALLOCENES WITH DOUBLY HETERO-BRIDGES

Abstract

Three ansa-metallocenes (Me2C)(Me2Si)Cp2TiCl2(1), [(CH2)5C](Me2Si)Cp2TiCl2(2) and (Me2C)(Me2Si)Cp2ZrCl2(3) with larger dihedral angles and longer distance from metal to the center of Cp planes were synthesized and used as catalysts for ethylene polymerization in the presence of methylaluminoxane (MAO). In the case of ethylene polymerization, compared the feature structures of unbridged metallocenes, singly bridged metallocenes and doubly bridged metallocenes 1, 2, 3, there exhibit the relationship between structural characteristics and the catalytic properties with behavior of polymers. And the view that the dimensions of the short dimethylsilylene and isopropylidene bridges of metallocene 3 do not match the co-ordination requirement of the larger zirconium atom can also explain the result for ethylene polymerization. Catalyzed by complexes 1 and 2 respectively, the copolymerizations of ethylene with 1-hexene, 1-octene, especially the long chain α-olefins (1-tetradecene, 1-hexadecene) were investigated, and showed high incorporations and comonomer effects in almost all the examples. The melting points of the copolymers are approximately 4%–31% below those of the homopolymers, and the enthalpies of fusion decrease greatly due to the lower crystallinity. The microstructures of the copolymer were analyzed with 13C-NMR to determine the comonomer sequence distributions and number–average sequence lengths. Comparison between results for the complexes 1 and 2 with different bridging groups respectively showed that the nature of the bridge has a significant effect on both the incorporation and sequence distribution of the α-olefin. Because of the bridges in ansa-metallocene complexes, the copolymerization behavior was different in using catalyst 1 and catalyst 2.