Method for preparing copolymers

1. A method for the preparation of copolymers of ethylene and α-olefins having a fraction (%) of the molecular weight component of >1,000,000 of less than 6% said method comprising polymerising ethylene and an α-olefin in the presence of a supported polymerisation catalyst system comprising

(a) a transition metal compound,

(b) a porous support material, and

(c) an activator,

characterized in that the support material has been

(i) dried at a temperature in the range 0° C. to 195° C. in an inert atmosphere, and

(ii) treated with an organometallic compound.

2. A method according to claim 1 wherein the fraction (%) of the molecular weight component of >1,000,000 is less than 4%.

3. A method according to claim 1 wherein the fraction (%) of the molecular weight component of >1,000,000 is less than 2.5%.

4. A method according to claim 1 wherein the support material has been heated at a temperature in the range 25° C. to 195° C.

5. A method according to claim 1 wherein the support material has been heated at a temperature in the range 30° C. to 180° C.

6. A method according to claim 1 wherein the support material has been heated at a temperature in the range 30° C. to 95° C.

7. A method according to claim 1 wherein the support material is silica.

8. A method according to claim 1 wherein the organometallic compound is an organoaluminium compound.

9. A method according to claim 8 wherein the organoaluminium compound is a trialkylaluminium compound.

10. A method according to claim 9 wherein the trialkylaluminium compound is trisisobutylaluminium.

11. A method according to claim 1 wherein the support material is treated with the organometallic compound at a temperature in the range 20° C. to 100° C.

12. A method according to claim 11 wherein the support material is treated with the organometallic compound at room temperature.

13. A method according to claim 1 wherein the transition metal compound is a metallocene.

14. A method according to claim 13 wherein the metallocene has the general formula

wherein:—

R′ each occurrence is independently selected from hydrogen, hydrocarbyl, silyl, germyl, halo, cyano, and combinations thereof, said R′ having up to 20 nonhydrogen atoms, and optionally, two R′ groups (where R′ is not hydrogen, halo or cyano) together form a divalent derivative thereof connected to adjacent positions of the cyclopentadienyl ring to form a fused ring structure;

X is a neutral η 4 bonded diene group having up to 30 non-hydrogen atoms, which forms a π-complex with M;

Y is —O—, —S—, —NR*—, —PR*—,

M is titanium or zirconium in the +2 formal oxidation state;

Z* is SiR* 2 , CR* 2 , SiR* 2 SIR* 2 , CR* 2 CR* 2 , CR*═CR*, CR* 2 SiR* 2 , or

GeR* 2 , wherein:

R* each occurrence is independently hydrogen, or a member selected from hydrocarbyl, silyl, halogenated alkyl, halogenated aryl, and combinations thereof, said

R* having up to 10 non-hydrogen atoms, and optionally, two R* groups from Z* (when R* is not hydrogen), or an R* group from Z* and an R* group from Y form a ring system.

15. A method for the preparation of a supported polymerization catalyst system suitable for use in the method according to claim 13 said method comprising the following steps:

(i) drying a porous support material at a temperature in the range 0° C. to 195° C. in an inert atmosphere,

(ii) addition of an organometallic compound in a suitable solvent,

(iii) removal of the solvent,

(iv) addition of an activator in a suitable solvent to the support material,

(v) addition of a metallocene in a suitable solvent, and

(vi) removal of the solvent.

16. A method according to claim 1 wherein the α-olefin is 1-butene, 1-hexene, 4-methyl-1-pentene or 1-octene.

17. A method according to claim 1 wherein the ethylene and α-olefin are polymerized in the slurry or the gas phase.