Patent ID: 7030195

Claim:
A process for the preparation of polybutadiene with a low branching degree having the following characteristics: branching index value (gM) lower than 1; damping coefficient value (tans), 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% of strain, ranging from 0.80 to 1.40; Mooney viscosity lower than 49; M w /M n lower than 2.9; percentage of 1,4-cis units higher than 93%; the above process being effected by the polymerization of 1,3-butadiene in the presence of neodymium catalysts, the above process comprising: (a) a first polymerization step of butadiene in the presence of organic solvents and in the presence of a catalytic system comprising (a1) a derivative of neodymium selected from neodymium carboxylates with a molar ratio H 2 O/Nd lower than 1, and a molar ratio —COOH/Nd lower than 2; (a2) an aluminum alkyl having the general formula (I) AlR 1 R 2 R 3 wherein R 1 and R 2 , the same or different, are an alkyl radical containing from 1 to 10 carbon atoms or a hydrogen atom, R 3 is an alkyl radical containing from 1 to 10 carbon atoms; (a3) an organo aluminum derivative containing at least one halogen atom; the above first step being carried out up to a butadiene conversion ≧98% to give a linear polybutadiene (g M =1) with a content of 1,4-cis units greater than 93%, and an M w /M n ranging from 2.2 to 2.9; (b) treatment of the polymeric solution obtained at the end of step (a) with a peroxide until polybutadiene with a low branching degree is obtained; (c) recovery of the polybutadiene with a low branching degree obtained at the end of step (b).