New application for metallocene catalysts in olefin polymerization

Abstract

Metallocenes and other transition metal complexes, activated by methylaluminoxane allow the synthesis of polyolefins with a highly defined microstructure, tacticity, and stereoregularity. New copolymers, long chain branched polymers, and polyolefin nanocomposites are produced by these highly active catalysts. A better understanding of the structure of active sites for the olefin polymerization will lead to findings of new and simpler co-catalysts. Ethene or propene can be copolymerized with 1-olefin macromers with chain lengths up to 12,000 g mol(-1) as well as with cyclic olefins. Polypropenes of high molecular weight and filled with multi-walled carbon nanotubes show exciting new physical and mechanical properties and are prepared by in situ polymerization. These, and other polyolefin specialities, will be new future materials in a wide range of applications.

Revisiting the Stereochemistry of Propylene Isotactic Polymerization Reaction Mechanism on C2 Symmetric [SiH2(Ind)2ZrCH3]+ and [SiH2(Ind)2ZrCH3]+[CH3B(C6F5)3]−

“…However, the interaction of CA affects the relatively weak agostic interaction as we observed that the α agostic ZrH distance is slightly increased (maximum of 0.07 ¡) in the presence of CA. It is also noted that the CH 3 group of CA in these TSs is projecting towards the CH 3 Zr fragment when CA is in the trans position and towards the CH 2 group of propylene when CA is in the cis position.…”

“…31 These agostic interactions have been experimentally and theoretically examined. Erker experimentally investigated the stereochemistry for first propylene insertion in [rac-Me 2 Si-(Ind) 2 ]Zr(®-C 4 H 6 )B(C 6 F 5 ) 3 and observed that α agostic metal CH interaction could be a reason for the isoselective nature of propylene attack. 32 The αCH agostic interaction might decrease the activation energy for insertion and give more space for propylene attack.…”

“…4547 To the best of our knowledge, the pathway of first insertions to second insertions through proper agostic resting states in propagation is not appropriately discussed anywhere due to the various possibilities of the insertion products. It remains unclear, (i) how and from which insertion products the agostic resting catalysts are originally generated, (ii) why so many resting catalysts or epimers are formed during the reaction and how the system avoids the stereoirregularities, (iii) what is the role of counter anion (CA) such as [CH 3 B(C 6 F 5 ) 3 ]…”

Supported Single-Site Organometallic Catalysts for the Synthesis of High-Performance Polyolefins

“…In the 1950s, the first olefin polymerization catalyst was reported by Phillips Petroleum constituted essentially of Cr/silica or by Walter Kaminsky [13][14][15]. A methylaluminoxane (MAO, Fig.…”

“…3) [13][14][15]. This highly active homogeneous system allows for tuning of the product polymer microstructure (M w , PDI, % comonomer incorporation, tacticity) exclusively by varying the organic ancillary ligands surrounding the group 4 metal [14,[16][17][18][19][20][21][22][23][24].…”