Stereoregular diblock polybutadienes having a 1,4-cis/syndiotactic 1,2 structure from stereospecific polymerization

A stereoregular diblock polybutadiene, having formula (i):

• PB1—PB2 (I)
• wherein:
• PB1 represents a polybutadiene block comprising a 1,4-cis structure;
• PB2 represents a polybutadiene block comprising a 1,2 syndiotactic structure having a content of syndiotactic triads ranging from 60% to 80%;
• a molar quantity of 1,4-trans units in the stereoregular diblock polybutadiene is less than 3 mol % with respect to a total molar quantity of butadiene units in the stereoregular diblock polybutadiene;
• and
• the stereoregular diblock polybutadiene is obtained by a process comprising:
• subjecting 1,3-butadiene to total or partial stereospecific polymerization in the presence of a catalytic system comprising at least one phosphine ligand selected from the group consisting of a hindered aliphatic phosphine and a bidentate phosphine to obtain polybutadiene with a 1,4-cis living structure;
• and adding at least one monodentate aromatic phosphine and optionally 1,3-butadiene, and continuing said stereospecific polymerization to obtain the stereoregular diblock polybutadiene.