Diene polymerisation

1. A process for producing homopolymers or copolymers of conjugated dienes comprising contacting monomeric material comprising at least one conjugated diene with a catalyst system comprising two or more different transition metal compounds comprising (i) a first transition metal selected from the group consisting of complexes containing neutral, monoanionic or dianionic ligands wherein the ligands comprise at least one N donor atom and wherein the metal is selected from the group consisting of Cr, Mo and W; (ii) a second transition metal selected from the group consisting of complexes containing neutral, monoanionic or dianionic ligands wherein the ligands comprise at least one N donor atom and wherein the metal is selected from the group consisting of Fe, Co, and Ni; and optionally (iii) one or more activators.

2. A process as claimed in claim 1 wherein the ligands of the first transition metal complex or the second transition metal complex are monodentate, bidentate, tridentate or tetradentate.

3. A process as claimed in claim 1 wherein the ligands of the first transition metal complex or the second transition metal complex comprise at least one heteroatom selected from the group consisting of N, P, O and S.

4. A process as claimed in claim 1 wherein the transition metals comprise cobalt and chromium.

5. A process as claimed in claim 1 wherein the amount of each of the transition metal compounds is such that the concentration of any one of these compounds is >0.01 moles % based on total moles of transition metal compound employed as catalyst.

6. A process as claimed in claim wherein the amount of each of the transition metal compounds is such that the concentration of any one of these compounds is at least 0.10 moles % based on total moles of transition metal compound employed as catalyst.

7. A process as claimed in claim 1 wherein at least one of the transition metal compounds is a metallocene.

8. A process as claimed in claim 1 wherein at least one of the transition metal compounds has the following Formula A

wherein in the five-membered heterocyclic group K, which can be saturated or unsaturated and unsubstituted or substituted by halide or hydrocarbyl groups, the atoms A 1 to A 4 comprise at least 2 carbon atoms and at least one atom selected from N, O, P and S, the remaining atom in said ring, if any, being selected from nitrogen and carbon; any 2 or more of A 1 to A 4 can form part of one or more further ring systems; M is a metal selected from the group consisting of Cr, Mo, W, Fe, Co and Ni; E 1 and E 2 are atoms or groups bearing single and or double bond connections and being independently selected from the group consisting of substituted carbon, unsubstituted carbon atom, (i) aliphatic hydrocarbyl, (ii) alicyclic hydrocarbyl, (iii) aromatic hydrocarbyl, (iv) alkyl substituted aromatic hydrocarbyl, (v) heterocyclic groups and (vi) heterosubstituted derivatives of said groups (i) to (v); J is a group comprising one or more carbon atoms and optionally one or more atoms selected from the group consisting of N, O, P and S each of which can be substituted or unsubstituted by halogen or hydrocarbyl groups; D 1 and D 2 are donor atoms or groups; X is an anionic group, L is a neutral donor group; m, n and p are independently 0 or 1; y and z are independently zero or integers such that the number of X and L groups satisfy the valency and oxidation state of the metal M.

9. A process as claimed in claim 5 wherein D 2 and K are identical imidazole containing groups.

10. A process as claimed in claim 5 wherein the imidazole-containing group K is a group selected from the group consisting of Formulae Ia, IIa, IIIa, IVa, Va and VIa:

wherein the groups R 2 to R 11 are independently hydrogen or a monovalent (i) aliphatic hydrocarbyl, (ii) alicyclic hydrocarbyl, (iii) aromatic hydrocarbyl, (iv) alkyl substituted aromatic hydrocarbyl (v) heterocyclic groups, (vi) heterosubstituted derivatives of said groups (i) to (v), and (vii) hydrocarbyl-substituted heteroatom groups.

11. A process as claimed in claim 5 wherein the transition metal compound is selected from the group of cobalt complexes consisting of:

12. A process as claimed in claim 5 wherein the transition metal compound is selected from the group of chromium complexes consisting of:

13. A process as claimed in claim 1 wherein at least one of the transition metal compounds is supported on a support material.

14. A process as claimed in claim 1 wherein the catalyst system comprises at least two transition metal compounds and an activator supported on the same support material.

15. A process as claimed in claim 13 wherein the support material is selected from the group consisting of silica, alumina, zirconia, magnesia, magnesium chloride, polymer and prepolymer.