Stereoregular di-block polybutadienes and butadiene/isoprene copolymers by cobalt catalysis

Catalytic systems based on cobalt phosphine complexes are well known in the literature for providing polymers from butadiene with an essentially cis-1,4 or 1,2 structure depending on the type of phosphine ligand coordinated to the cobalt atom. Thus, for example, complex (I), in combination with methylaluminoxane, provides from butadiene a highly cis-1,4 polymer (97%), complex (II) an essentially 1,2 polymer (85%), and complex (III) a 1,2 polymer operating at low MAO/Co ratio (50-100) and an essentially cis-1,4 polymer operating at higher MAO/Co ratio (1000) . Furthermore, complex (II), in combination with methylaluminoxane, is also able to polymerize isoprene, providing a polymer with a perfectly alternating cis-1,4/3,4 structure. We have now found that such systems exhibit living characteristics, and that in some cases it is possible to modify their selectivity by replacing the ligand during polymerization, always maintaining their living character. By combining these features, we have now prepared butadiene based di- or tri-block stereoregular polymers, in which the different blocks, that can be amorphous or crystalline, are joined through a single junction point and present different thermal properties as a function of the type of monomer and the catalytic system used. The characteristics of these products are those typical of thermoplastic elastomers, which should allow to expand use of diene polymers outside the tire production field, to which today they are essentially confined.