Hafnium bases

Observations Metallocene-driven terpolymeration usually relies upon hafnium-based... 

The transition metal has, in addition to ligand substitution and interan-nular bridge, a distinctive effect on the copolymerisation behaviour. Hafnium-based metallocenes are considered to exhibit higher comonomer response than zirconium based ones [45]. 

Symyx-Dow A process for making polyolefins using a hafnium-based metallocene catalyst that had been identified by the Symyx combinatorial method. Not commercialized in 2003. 

A separation of zirconium and hafnium based on difference in rates of reaction of the tetrachlorides with molecular oxygen has been devised. The activation energies for the reaction... 

Recently, a series of soluble, highly isospecific catalysts were developed for propylene polymerization. These materials are zirconium, titanium, or hafnium based metallocenes, such as... 

ELECTROCHEMICAL PRODUCTION OF HAFNIUM-BASED COMPOSITE MATERIALS... 

This chapter describes the advances and new findings on organic reactions using zirconium and hafnium as Lewis acids from 1998 to 2006. Literatures published before 1998 were reviewed in the previous edition of this book [la] and the others [Ib-dj. Among the vast reports, the reactions in which zirconium or hafnium-based Lewis acids played an important role or showed significant advantages were chosen in this manuscript, but olefin polymerization catalysis was not included. 

Now the vented combustion calorimetry (VCC) method shows that the experimental reaction enthalpy increases about asymptotically with increasing velocity. At low impact speed, the hafnium-based formulation outperforms any other composition and already reaches an efficiency of 52%, whereas the other formulations barely deHver a quarter of the reaction enthalpy. The tantalum-based composition is exceptionally poor as only about 3% of the theoretically stored energy is released. The situation changes at higher speeds (1800-2400 ms ) and shows the gravimetric superiority of Al/PTFE over the other formulations (Figure 13.13). 

Tobisch S, Ziegler T Catalytic ohgomerization of ethylene to higher hnear a-olefins promoted by cationic group 4 cyclopentadienyl-arene active catalysts toward the computational design of zirconium- and hafnium-based ethylene trimerization catalysts, Organometallics 24(2) 256-265, 2005. 

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