Process for the preparation of a polyolefin

1. A process comprising polymerizing at least one aliphatic C 2-20 hydrocarbyl mono- or multiolefin in the presence of a catalyst and an aluminum-comprising co-catalyst, wherein the catalyst is a composition comprising a metal-organic reagent, a spectator ligand and optionally at least one equivalent of a hydrocarbylating agent, and wherein the metal organic reagent is represented by ML j X p , where M is Ti, X is a monoanionic ligand bonded to M, L is a neutral ligand bonded to M, j represents an integer denoting the number of neutral ligands L, and p is the valence of the metal M, and wherein the spectator ligand is an imine ligand or an HA adduct thereof, wherein HA represents an acid of which H represents its proton and A represents its conjugate base.

2. Process according to claim 1 , wherein the hydrocarbylating agent comprises a metal or a metalloid chosen from group 1, 2, 11, 12, 13 or 13.

3. Process according to claim 2 , wherein the hydrocarbylating agent comprises Li, Mg, Zn or Al.

4. Process according to claim 3 , wherein the hydrocarbylating agent is a C 1 -C 20 trihydrocarbyl aluminum or aluminoxane.

5. Process according to claim 1 , which further comprises conducting polymerization in the presence of a base other than the hydrocarbylating agent.

6. Process according to claim 1 , wherein the metal-organic reagent comprises a cyclopentadienyl-comprising ligand.

7. Process according to claim 1 , which comprising conducting polymerization in the presence of between 5 to 10 equivalents of the spectator ligand.