Synergetic Effect of a Nickel Diimine in Ethylene Polymerization with Immobilized Fe-, Cr-, and Ti-Based Catalysts on MgCl₂ Supports

Abstract

Significant increases in the productivity of iron-, chromium-, and titanium-based MgCl2-supported catalysts for ethylene polymerization have been obtained by incorporation of a limited amount of a nickel diimine catalyst giving branched polyethylene. Formation of the latter during the early stages of polymerization reduces the monomer diffusion limitation inherent in ethylene homopolymerization, thereby increasing the productivity of the main catalyst component. The final products are essentially linear, high-density polyethylenes containing very small amounts of branched polymer. As well being effective for catalysts prepared by coimmobilization of the Ni and Fe, Cr, or Ti component on the MgCl2 support, it is also shown that the productivity of preformed Ziegler−Natta catalysts can be improved significantly by impregnation with the nickel diimine component. In the latter case, more rapid increases in rate throughout the polymerization indicated easier fragmentation of the support in the presence of the nickel complex.

Characteristics of linear/branched polyethylene reactor blends synthesized by metallocene/late transitional metal hybrid catalysts

“…These catalysts are well known for production of respectively branched and linear polyethylene chains depending on the applied reaction conditions [34][35][36][37]. Both catalysts were supported on the TIBA-modified MgCl 2-nEtOH adduct, separately and concurrently, at different ratios.…”

“…Chadwick et al have discovered that Cp 2 TiCl 2 and other titanium-based single-site catalysts can be readily immobilized and activated on these supports, without the use of MAO or borate activators [36]. They have shown that through this method, a-diimine nickel catalysts could also be activated with traditional TEA activator, but immobilization may suppress chain walking and end in higher population of shorter methyl branches [42].…”

“…Likewise, Ahmadjo et al [33] have provided polyethylene with multimodal melting peaks using hybrid bis(imino)pyridine Fe/Ziegler-Natta catalysts. Many groups have utilized a-diimine nickel complexes in homogeneous or heterogeneous states in combination with Ziegler-Natta or metallocene catalysts in order to synthesize linear/branched polyethylene blend in one reactor [34][35][36][37]. Such blends are mainly produced by post-polymerization melt-mixing process.…”

“…Application of mixed as well as SiO 2 -supported hybrid LTM/metallocene catalysts for production of linear/branched polyethylene blends has been reported in the literature [34,35]. Others have reported synergistic effect of immobilization of LTM and metallocene catalysts on MgCl 2 adduct [36] supports and MCM nanoparticles [37]. Chadwick et al have attributed such a synergy to reduction in monomer diffusion restriction into crystalline structure of linear ethylene homopolymers as a result of introducing small fraction of less crystalline branched chain [36].…”

Iron-Based and Cobalt-Based Olefin Polymerisation Catalysts

“…In addition to other polystyrene [138] and silica supports [139,140,141,142,143,144] , iron and cobalt precatalysts have been immobilised on calcosilicate [145] , magnesium dichloride [146,147,148,149] , MCM-41 zeolite [150,151] , clay [152] and fluorotetrasilicic mica [153] . Supported systems have also been examined using alternative activators [154,155,156,157,158,159] .…”