Water on Homogeneous Catalysts

In systems completely free of chloride, complex formation between the titanium or zirconium compound and the trialkylaluminum was not detected by either NMR or UV spectroscopy 191), or by cryoscopy (189). Such systems were thus assumed to be inactive for polymerization. However, NMR-spectroscopic studies in the presence of ethylene revealed a weak but lasting insertion of ethylene, with formation of polyethylene. 

Addition of traces of chloride in the form of bis(cyclopentadienyl)-titanium dichloride lowered the yield of polyethylene and initiated the known reduction reaction (129). Finally, it was found that polyethylene formation was caused by traces of water ( 10-8 mol%). Consequently, the yield increased to 500,000 g polyethylene per gram of titanium when two equivalents of trimethyl- or triethylaluminum previously treated with one equivalent of water was added to dimethylbis(cyclopentadienyl)ti-tanium (Table VII). 

Mejzlik et al. (204) reported an increase of activity on adding water to other well-known catalytic systems based on bis(cyclopentadienyl)-titanium(IV) containing chloride [(T75-C5H5)2TiEtCl-AlEtCl2]. 

Ethylene Polymerization with the System Bis(tj5-cyclopentadienyl)dimethyltitanium(IV), Trimethylaluminum, and 

Control of Molecular Weight by Regulation of Temperature in the Polymerization of Ethylene with Tri(cyclopentadienyl)zirconium-Aluminum Compounds 

---