Patent ID: 7078466

Claim:
A process for the preparation of a polydiene which comprises the polymerization of a conjugated diene in the presence of a catalytic system which essentially consists in components (a) to (d), wherein: component (a): compound containing a rare-earth element having an atomic number from 57 to 71 in the Periodic Table, or a product obtained by reacting the above compound with a Lewis base; component (b): an organo aluminum derivative containing at least one halogen atom; component (c): an alumoxane; component (d): an organometallic compound of aluminum represented by general formula (I) AlR 1 R 2 R 3 wherein R 1 and R 2 , the same or different, are hydrocarbyl groups having from 1 to 10 carbon atoms or hydrogen, and R 3 is a hydrocarbyl group having from 1 to 10 carbon atoms; the above process being characterized in that it is effected under operating conditions selected from: (i) essentially isothermal conditions at a temperature ranging from 70° C. to 140° C.; (ii) essentially adiabatic conditions with an initial temperature ranging from 50° C. to 90° C. and a final temperature ranging from 100° C. to 150° C.; the above process being continued under conditions (i) or (ii) until a polydiene is obtained, having branching index values (measured with the GPC-MALLS technique) lower than 0.90 and α parameter values (also measured with the GPC-MALLS technique) ranging from 0.53 to 0.30.