Random butadiene-isoprene copolymers with a trans-1, 4 structure

1. Random butadiene-isoprene copolymers with a 1,4-trans structure, having a butadiene/isoprene molar composition ranging from 98/2 to 32/68, the above copolymers being crystalline or amorphous depending on the isoprene content, 1,4-cis and vinyl structure not being detected by 13 CNMR techniques.

2. The copolymers according to claim 1 , having a butadiene/isoprene molar composition ranging from 80/20 to 32/68, which are amorphous and have a glass transition temperature ranging from −75° C. to −67° C.

3. The copolymers according to claim 1 , having a butadiene/isoprene molar composition ranging from 85/15 to 98/2, which are crystalline and have a melting point ranging from 100° C. to 50° C.

4. The copolymers according to claim 1 , which have an M w value ranging from 200×10 3 to 500×10 3 and an M w /M n value ranging from 1.7 to 4.

5. The copolymers according to claim 4 , which have an M w value ranging from 250×10 3 to 400×20 10 3 and an M w /M n value ranging from 2.0 to 3.0.

6. A process for the preparation of random butadiene-isoprene copolymers with a 1,4-trans structure, comprising copolymerization of 1,3-butadiene and isoprene, in the presence of one or more solvents and a catalytic system, wherein the catalytic system comprises:

(a) a first component consisting of a vanadium compound selected from the group consisting of:

(a1) compounds having general formula (Ia) VO(L) n (X) m wherein n is an integer from 1 to 3 and m ranges from zero to 2, n+m being equal to 2 or 3; and

(a2) compounds having general formula (Ib) V(L) p (X) q wherein p is an integer from 1 to 4, q ranges from zero to 3, the sum of p+q being equal to 3 or 4;

wherein L is a bidentate ligand and X is a halogen; and

(b) a second component selected from the group consisting of aluminoxanes.

7. The process according to claim 6 , wherein the vanadium compound is selected from the (a2) group of compounds.

8. The process according to claim 7 , wherein the vanadium compound is vanadium acetylacetonate.

9. The process according to claim 6 , wherein the molar ratio aluminum/vanadium ranges from 10/1 to 10000/1.

10. The process according to claim 9 , wherein the molar ratio aluminum/vanadium ranges from 100/1 to 1000/1.

11. The process according to claim 6 , wherein the molar ratio monomers/vanadium ranges from 1×10 3 /1 to 1×10 5 /1.

12. The process according to claim 11 , wherein the molar ratio monomers/vanadium ranges from 20×10 3 /1 to 50×10 3 /1.

13. The process according to claim 6 , wherein the solvent is selected from the group consisting of aliphatic hydrocarbons, cycloaliphatic hydrocarbons, aromatic hydrocarbons and mixtures thereof.

14. The process according to claim 13 , wherein the solvent is selected from the group consisting of C 4 –C 8 aliphatic hydrocarbons, C 5 –C 10 cycloaliphatic hydrocarbons, aromatic hydrocarbons and mixtures thereof.

15. The process according to claim 6 , which is carried out at a temperature ranging from −50° C. to +60° C.

16. The process according to claim 15 , which is carried out at a temperature ranging from −20° C. to +20° C.

17. The process according to claim 6 , wherein X is chlorine.

18. The process according to claim 14 , wherein the solvent is toluene.