Ethylene polymerization catalysts

Recently some information became available on a new type of highly active one-component ethylene polymerization catalyst. This catalyst is prepared by supporting organometallic compounds of transition metals containing different types of organic ligands [e.g. benzyl compounds of titanium and zirconium 9a, 132), 7r-allyl compounds of various transition metals 8, 9a, 133), 7r-arene 134, 185) and 71-cyclopentadienyl 9, 136) complexes of chromium]. 

Discuss to what extent the Phillips ethylene polymerization catalyst satisfies all of the criteria that define a catalyst. Compare this polymerization catalyst with the FCC catalyst and Pt-based reforming catalysts. 

Anatomy of Catalytic Centers in PhUlips Ethylene Polymerization Catalyst... 

Zecchina A, Groppo E, Damin A, Prestipino C (2005) Anatomy of Catalytic Centers in Phillips Ethylene Polymerization Catalyst. 16 1-35 Ziegler T, see Michalak A (2005) 12 145-186... 

As described in Section 9.1.2.2.3, several lanthanocene alkyls are known to be ethylene polymerization catalysts.221,226-229 Both (188) and (190) have been reported to catalyze the block copolymerization of ethylene with MMA (as well as with other polar monomers including MA, EA and lactones).229 The reaction is only successful if the olefin is polymerized first reversing the order of monomer addition, i.e., polymerizing MMA first, then adding ethylene only affords PMMA homopolymer. In order to keep the PE block soluble the Mn of the prepolymer is restricted to <12,000. Several other lanthanide complexes have also been reported to catalyze the preparation of PE-b-PMMA,474 76 as well as the copolymer of MMA with higher olefins such as 1-hexene.477... 

Although chromium-based ethylene polymerization catalysts have already been developed commercially, these processes are based on a heterogeneous catalyst... 

A large number of transition metal complexes whose cationic complexes are 10- to 16-electron species (including those with the ligands summarized in Fig. 7) were investigated to determine their potential as ethylene polymerization catalysts with methyaluminoxane (MAO) activation at 25 °C under atmospheric pressure. As a result, we discovered a number of high-activity catalysts for ethylene polymerization that contain electronically flexible ligands [11]. 

The silica-supported chromate can be activated directly to a very efficient ethylene polymerization catalyst by ethylene itself or by reduction under CO, to yield active Cr(ll) bisiloxy species, ](=SiO)2Cr] [8]. While the silsesquioxane Cr derivative on its own does not lead to an active polymerization catalyst under ethylene (albeit only low ethylene pressure were tested), the silsesquioxane chromate ester can yield an active polymerization catalyst by addition of methyl-aluminoxane as co-catalyst. Comparison between the two catalytic systems is therefore possible but suffers from the lack of molecular definition of the active homogeneous species obtained after activation with the alkylating agent (Scheme 14.11). 

Cr-based catalysts have been utilized for the synthesis of specific a-olefms, such as 1-hexene, and have been further developed by the use of ligands with novel structures. " Very recently, unprecedented selective tetramer-ization of ethylene was reported by Bollmann e/a/. to form 1-octene at >70% selectivity by using Gr(iii) precursors in conjunction with diphosphinamine ligands activated with MAO F12-10. Hessen and co-workers discovered that a hemilabile aryl group incorporated into the mono-Gp based Ti complexes F12-11 induced the unusual transformation of Ti complexes from ethylene-polymerization catalysts to selective trimerization catalysts. ... 

In an earlier investigation by the authors (1) ethylene polymerization catalysts were prepared consisting of (C4H9MgCl)o.3 (MgC ), 2-ethylhexanol, ethyl aluminum chloride, and titanium tetrachloride. 

The disproportionation activity in the supported species is parallel to the increased activity of ethylene polymerization on supported catalysts. Many of the steps in the reaction may be identical for example, the initial coordination of olefin to the metal center will be common to both systems. Indeed, some of these catalysts are also ethylene polymerization catalysts (see Table IV) although their activities are much less than the corresponding zirconium derivatives. A possible intermediate common to both disproportionation and polymerization could be the hydrocarbyl-olefin species (Structure I). Olefin disproportionation would result if the metal favored /3-hydrogen elimination to give the diolefin intermediate (Structure II) which is thought to be necessary for olefin disproportionation. Thus, the similarity between the mechanism and activation of olefin disproportionation and polymerization is suggested. 

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