Process for manufacturing vinyl-rich polybutadiene rubber

A process for manufacturing a vinyl-rich polybutadiene rubber, comprising polymerizing butadiene in a solvent using a catalyst system comprising an iron-based catalyst as catalyst and a phosphite as ligand, said catalyst system comprising:

• A) an organoiron compound;
• B) an organoaluminum compound;
• and
• C) a phosphite selected from a group consisting of dialkyl phosphite, trialkyl phosphite, diaryl phosphite, triaryl phosphite and mixtures thereof;
• wherein, the mole ratio of component B to component A is between 5 and 100;
• and that of component C to component A is between 0.5 and 10;
• and 80 wt % or more monomer units of macromolecules of the rubber have a vinyl group,
• wherein the organoiron compound is selected from the group consisting of iron acetyl acetone, iron naphthenate, iron neodecanoate and iron-i-octanoate, wherein the addition sequence of the catalyst components is in the following order:
• first A, then B or C, then aged first in the presence of butadiene for 10 to 15 min, then the other B or C added singly, wherein the mole ratio of butadiene to component A is between 5 and 100,
• wherein during the premixing of A and B or C, the component A is first added, and then butadiene.