Transition-metal Alkyl and Related Catalysts

4 Transition-Metal Alkji and Related Catalysts There continues to be a lively interest in the use of transition-metal alkyl compounds as polymerization catalysts both in the absence and in the presence of alkylaluminium cocatalysts. Hie more active catalysts of this type are invariably supported sterns and indeed it is of some interest that many non-supported transition metal alkyls do not polymerize propylene at all. Sinc this field has been extensively reviewed in recent years by Ballard and also features in an article by Yermakov only the most recent publications will be mentioned in this Report. 

The kinetic behaviour of the system Bz Ti-AlEtsCI-ethytene without a support was similar to that reported earlier for Cp TiClr-AlMejCl- thylenc, both systems showing initially high overall rates of polymerization which then decayed rapidly with time. Chien has postulated that the decay in rate is due to the reduction reaction 

The relatively slow increase in the rate of polymerization when titanium alkyls are supported on Mg(OH)Cl was believed to indicate that the active species was a tervalent titanium compound. 

Izinni, S. Ikeda, and T. Keii, Makromot. Chem., 1977,178, 337. 

The proceedings of the Fourth International Symposium on Cationic Polymerization were published inunediateiy before the period of this Report and are an excellent introduction to the state-of-the-art at the beginning of 1977. 

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