Hafnocene catalysts molecular weights

In a time when prices for oil are continuously rising, hafnocene catalysts enable production of high-tech materials in a relatively cheap way. Hafnocenes are the key to a family of high and ultrahigh molecular weight polypropylenes whose material properties can be individually and simply varied. To help comprehend the importance... 

Collins et al. reported in 1995 that catalysts based on hafnium are desirable for the production of elastomeric polypropylene in that they polymerize propylene to a high molecular weight polymer and are indefinitely stable under typical polymerization conditions [8], Based on the theory that hafnium as a catalytic center leads to a significant increase of molecular weight in propene polymerization compared with the zirconium-based catalyst, Rieger et al. searched for hafnocene systems to obtain polymers with new properties. 

Rieger B, Troll C, Preuschen J (2002) Ultrahigh molecular weight polypropylene elastomers by high activity dual-side hafnocene catalysts. Macromolecules 35 5742-5743... 

Rieger B, Troll C, Hild S, Cobzaru C, Deisenhofer S, Hearley A (2005) Novel high and ult-rahigh molecular weight poly(propylene) plastomers by asymmetric hafnocene catalysts. Macromol Chem Phys 206 1231-1240... 

Collins and co-workers later developed a series of related C,-symmetric hafnocene and zirconocene catalysts shown in Figure 22.11 that formed elastomeric poljq)ropylene possessing narrow molecular weight distributions (M /M = 1.7-2.1) when activated with MAO at 25 The catalysts containing a silicon bridge produced relatively high... 

Cobzaru, C. Deisenhofer, S. Harley, A. Troll, C. Hild, S. Rieger, B. Novel high and ultrahigh molecular weight polypropylene plastomers by asymmetric hafnocene catalysts. Macromol. Chem. Phys. 2005, 206,1231-1240. 

With hafnocene catalysts, higher molecular weight and slightly more stereoregular polymers were produced compared to those produced with zirconocene catalysts, although the catalytic activity was very low. 

---