Group 4 Metallocenes: Supported and Unsupported

The global thermoplastics industry is made up of 74% commodity resins, one-third of which is accounted for by polyethylene alone [1]. It was only in 1933 that polyethylene was discovered by Fawcett and Gibson [2] and it was not until 1953 that Karl Ziegler [3–5], Guilio Natta [6–8], and Paul Hogen [9] discovered the revolutionary first-generation Ziegler-Natta transition metal catalyst system. The second-generation MgCI, and/or donorsupported Ziegler-Natta transition metal catalyst system, which was at least 100 times more active, led to the development of the low-pressure polymerization process for polyolefins and synthetic elastomers [10]. This revolutionary catalyst system resulted in the development of simplified gas-phase low-pressure polymerization plant operation without the need for the removal of residual trace catalyst from the polymer.