Ethylene polymerization, metallocene based

Table 12.7 Ethylene polymerization based on supported group 3 and lanthanide metallocene complexes-examples from relevant patents.

The active species in MAO cocatalyzed metallocene polymerization is likely a coordinatively unsaturated cationic complex, as in 9-24 (for a zirconium-based metallocene), where substituents on the metal atoms have been omitted for clarity. The Zr—O—A1 bond withdraws electron density from the Zr atom. The mechanism for ethylene polymerization is proposed to be as follows, where the monomer forms a t-complex with the transition metal [ 14] ... 

Resconi, L. Giannini, U. Dall Occo, T. MAO-free Metallocene Catalysts for Ethylene (Co)Polymerization. In Metallocene-based Polyolefins Preparation, Properties and Technology, Scheirs, J., Kaminsky, W., Eds. Wiley Chichester, 2000 Vol. 1, 69. 

The base-free dimethyl Sc complex 121 was a highly active catalyst precursor for ethylene polymerization under B(C6F5)3, trityl borate, or methylaluminoxane (MAO)-type activation. The catalytic activity of 121 was similar to those observed of Group 4 metallocene complexes [81]. Generally, cationic scandium complexes are believed to be the active species. Activation of the catalyst was studied by reacting 120 and 121 with various equivalences of B(C6F5)3. The monomeric bulky rBu-substituted dimethyl complex 121 reacted with 1 equiv of B(C6F5)3... 

EPM [poly(ethylene-co-propylene)] and EPDM [poly(ethylene-co-propylene-co-5-ethylidene-2-norbomene)P can be metallocene catalyst polymerized. Metallocene catalyst technologies include (1) Insite, a constrained geometry group of catalysts used to produce AfiGnity polyolefin plastomers (POP), Elite PE, Nordel EPDM, and Engage polyolefin elastomers (POP) and (2) Exxpol ionic metallocene catalyst compositions used to produce Exact plastomer octene copolymers.2 Insite technology produces EPDM-based Nordel IP with property consistency and predictability (see Sec. 3.2.2). 

Group NIB and f-BIOCk Metallocenes. The need for expensive cocatalysts has always hampered the development of metallocene catalysts for olefin polymerization. It was recognized early on that substitution of the Group IVB metal with a lanthanide or Group IIIB element in the -1-3, state would represent a cocatalyst-free analogue of the Kaminsky system. Active catalysts are indeed obtained from bis-Cp lanthanocenes and yttrium- and scandium-based congeners. The lutetium dimer 29 has an activity of >7 kg/mmol(Lu)/h/atm for ethylene polymerization in cyclohexane (95). (This remarkable compound can also break the C—H bonds of alkanes.)... 

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