Supported polymerisation catalysts

Supported ionic metallocene catalyst systems may be prepared by a method comprising the following steps: i) mixing together in a suitable solvent: a) an organometallic compound, and b) an ionic activator comprising a cation and an anion; ii) addition of the mixture from step (i) to a support material; iii) addition of a metallocene complex in a suitable solvent; iv) further addition of an organometallic compound in a suitable solvent; and v) removal of the solvent. The preferred supported catalysts comprise a constrained geometry metallocene complex for example (t-butylamido)(tetramethyl--> -cyclopentadienyl) dimethyl silanetitanium--> -1,3-pentadiene and are particularly suitable for the polymerisation of ethylene or the copolymerisation of ethylene and alpha-olefins having from 3 to 10 carbons in the gas phase. The supported metallocene catalysts of the present invention show improved productivity compared to supported ionic metallocene catalyst systems of the prior art particularly when used in the gas pha