Preparation of catalyst system

A process for the preparation of a supported catalyst system, wherein the catalyst system comprises:

• (i) a metallocene complex;
• (ii) a cocatalyst system comprising a boron containing cocatalyst and an aluminoxane cocatalyst;
• and
• (iii) a porous inorganic silica support;
• whereby the process comprises the steps of:
• a) treating the porous inorganic support with the aluminoxane cocatalyst in a hydrocarbon solvent, optionally followed by thermal treatment of the aluminoxane treated support;
• b) combining the metallocene complex with the boron containing cocatalyst and optionally with the aluminoxane cocatalyst in the hydrocarbon solvent;
• c) loading the solution of step b) onto the treated support of step a);
• wherein the amount of aluminoxane cocatalyst added in step a) is 75.0 to 100.0 wt % of the total amount of aluminoxane cocatalyst and the amount of aluminoxane cocatalyst added in step b) is 0.0 to 25.0 wt % of the total amount of aluminoxane cocatalyst;
• and
• wherein the metallocene complex is of formula (VI):
• wherein
• each X independently is a sigma-donor ligand,
• M is a group 4 metal;
• L is a carbon, silicon, or germanium based bridge in which one to four backbone atoms link the ligands;
• and
• each Ind is a substituted or unsubstituted indenyl, or a substituted or unsubstituted fused indenyl;
• and
• wherein the boron containing cocatalyst is either of formula (B) or a borate containing an anion of formula (C):
• BY3 (B)
• (Z)4B— (C)
• wherein
• each Y independently is a hydrogen atom, an alkyl group of from 1 to about 20 carbon atoms, an aryl group of from 6 to about 15 carbon atoms, alkylaryl, arylalkyl, haloalkyl or haloaryl each having from 1 to 10 carbon atoms in the alkyl radical and from 6-20 carbon atoms in the aryl radical or fluorine, chlorine, bromine or iodine;
• or
• Z is an optionally substituted phenyl derivative, said substituent being a halo-C1-6-alkyl or halo group, and as counterions protonated amine or aniline derivatives.