Patent ID: 7112632

Claim:
A process for the preparation of low branch content polybutadiene having the following characteristics: a branch index value (g M ) of less than 1; a damping coefficient (tan δ) value, defined as the trigonometric tangent of the ratio between the viscous modulus (G″) and the elastic modulus (G′) [tan δ=G″/G′] measured at 0.01 Hz, 100° C. and 1% strain, from 0.80 to 1.40; a Mooney viscosity of less than 49; M w /M n less than 2.5; a 1,4-cis unit percentage greater than 93%; the aforementioned process comprising the following stages: (a) polymerisation of the butadiene in the presence of organic solvents and in the presence of a catalytic system comprising (a1) a neodymium derivative selected from neodymium carboxylates, the aforesaid neodymium carboxylates being devoid of water and —COOH groups; (a2) an aluminium alkyl of general formula (Ia) AlR 4 3 or (Ib) AlH n R 4 3−n wherein “n” is from 1 to 2 and R 4 , being either identical or differing from one another, represent an alkyl radical containing from 1 to 10 carbon atoms; (a3) an organo-aluminium derivative containing at least one halogen atom; the aforesaid first stage giving rise to a linear polybutadiene (g M =1) with a 1,4-cis unit content greater than 93%, and a M w /M n ratio of less than 2.5; (b) treatment of the polymer solution obtained upon completion of stage (a) with a coupling agent, thus obtaining low branch content polybutadiene having the above mentioned characteristics; (c) recovery of the low branch content polybutadiene obtained upon completion of stage (b); the aforementioned process being characterised in that the coupling agent is selected from: (i) unsaturated natural oils; (ii) butadiene and/or isoprene oligomers; (iii) butadiene and/or isoprene copolymers with vinylarene monomers; the unsaturations present in compounds (i)–(iii) being at least partially substituted with groups selected from epoxides, anhydrides and esters.