Post metallocenes

For more general overviews of post-metallocene a-olefin polymerisation catalysts, the reader is referred to a series of reviews [8, 9, 10, 11, 12], while recent reviews pertaining to the importance of 2,6-bis(imino)pyridines and to iron and cobalt systems per se have also been documented [13, 14],... 

Ethylene-higher-a-olefin co-polymers, via post-metallocene... 

Tt-Olefins, with Ru and Os half-sandwiches, 6, 512 Olefin—styrene, co-polymerizations with post-metallocenes, 4, 1145... 

A zirconium-based post-metallocene catalyst can produce PP-fo-PE. This has been reported as 13C NMR evidence of the real block nature for a polyolefin based materials [139]. 

Ligands which have recently been explored in post-metallocene chemistry are presently being adopted for Nd-catalysts. For example Thiele, Wilson and co-workers (Dow Global Technologies Inc.) recently filed a patent and published a paper on neodymium diimine and diiminopyridine complexes which yield poly(diene)s with high cis- 1,4-contents (95-97%) [345-347]. 

Dow Discovers New Class of Post-Metallocene Polyolefin Catalyst, PT, May 2003. 

Olefin co-polymerizations with post-metallocene catalysts 1143... 

Polystyrene and olefin-styrene co-polymerization with post-metallocene catalysts 1145... 

Effective ethylene-styrene co-polymerization with the post-metallocene catalysts has been achieved with the pentacoordinated complexes 195 and 196.159,1245 Pseudo-random ethylene-styrene co-polymers (i.e., co-polymers with no regioregularly arranged styrene-styrene units)642 were synthesized. The synthesis of an alternating crystalline co-polymer with isotactic styrene units and a Tm of 116 °C was also claimed. In these first studies, the importance of the S atom was noted, since the CH2-bridged complex 197 showed no co-polymerization activity. However, further studies demonstrated that the S atom is not fundamental, since complex 198 also promotes ethylene-styrene co-polymerization. Moreover, it was shown that complexes 195 and 196 incorporate a rather minor amount of styrene units (about 6-10 mol%) in the co-polymer relative to complex 198 (about 35 mol%), but they are roughly 1-2 order of magnitude more active than 198. 

One of the features of olefin copolymerization kinetics is the effect of comonomer on the rate of ethene or propene polymerization during ethene/a-olefin or propene/ a-olefin copolymerization, i.e., the so-called comonomer effect (CEF). The rate enhancement of ethene or propene polymerization in the presence of a comonomer is observed for conventional ZN catalysts [80, 113-123] and for homogeneous [124-133] and supported metallocenes [134—136] and post-metallocenes catalysts [137-140]. The increase in activity was remarked in the presence of such comonomers as propene, 2-methylpropene, 1-butene, 3-methylbutene,4-methylpentene-l, 1-hexene, l-octene,l-decene, cyclopentene, styrene, and dienes. 

The sheer size and value of the polyethylene industry ensure that there is continued research, progress, and development in catalysis, for their potential commercial impact. Although this whole subject is not within the scope of this chapter, we mention a couple of aspects of the progress, which offer the potential to impact this industry. In 1995, DuPont introduced work, carried out with them at the University of North Carolina—via the largest patent applicafion ever in the USA. They disclosed what are described as post-metallocene catalysts. These are transition and late transition metal complexes with di-imine ligands, which form part of the DuPont Versipol technology. Such catalysts create highly branched to exceptionally linear ethylene homopolymers and linear alpha-olefins. Late transition metals offer not only the potential for the incorporation of polar comonomers, which until now has only been possible in LDPE reactors, but also their controlled sequence distribution, compared to the random composition of free radical LDPE copolymers. Such copolymers account for over 1 million tons per annum [20]. Versipol has so far only been cross-licensed and used commercially by DuPont Dow Elastomers (a former joint venture, now dissolved) in an EPDM plant. 

Early Transition Metal-Based Post-Metallocene Catalysts...155... 

Beginning of the post-metallocene catalysis - the new ones often have imine ligand, but not Cp. They are characterized by high activity, a possibility of adjusting polymer MW and MWD as well as copolymerization of olefins with polar monomeric and macromeric species. A wide spectrum of catalysts based on fight and heavy transition metals have been published in open literature and patents. There are also several types of catalysts with intermediate stmcture - pseudo metallocene with a post-metallocene imine ligand. Unfortunately, the product shows poor thermal stability and is not ready for commercialization. 

PE mixtures constitute an important part of commercial blends. The information in Appendix, Table 18.12, suggests five major steps in the production of commercial PE, which result in different types of PE, commercially available at present, viz., 1935 - LDPE with LCB 1950 - LLDPE or HOPE catalyzed by, e.g., CraOg, NiO, M02O3, or CoO 1953 - the Ziegler-Natta (Z-N) catalysis for HOPE, UHMWPE, and LLDPE with a broad MWD and heterogeneous comonomer placement 1975 - the metallocene catalysis producing narrow MWD and homogeneously distributed SCB and 1997 - post-metallocene catalysis that leads to PE copolymers with adjustable MW and MWD as well as copolymerization of olefins with polar monomers and macromers. 

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