Catalysts based on transition metal complexes with a well-defined structure and their behavior in the homo- and copolymerization of 1,3-dienes

The research activity carried out in recent years in the field of stereospecific polymerization of conjugated dienes has shown that catalytic systems based on organometallic complexes with a well-defined structure are capable of polymerizing conjugated dienes exhibiting a high catalytic activity. Catalytic selectivity was also found to be very high, and strongly dependent on the catalytic structure (nature of the ligand on the metal atom) and on the monomer structure: the same catalyst can provide polymers with different structure from different monomers, and the same monomer can provide polymers with different structure from different catalysts1,2. But these characteristics are not the only ones that we have encountered, as in some cases these catalytic systems have highlighted living features. Therefore, exploiting these peculiarities, i.e. different selectivity as a function of the catalytic and monomeric structure, and living characteristics, we have now prepared stereo-block polymers and co-polymers of the type - (M1)x  (M2)y  in which M1 and M2 can be monomeric units of the same monomer but with different structure (e.g., cis-1,4 or 1,2) or monomeric units of different monomers (e.g., butadiene, isoprene and myrcene). These new polymeric materials are constituted by two stereoregular polymeric blocks, one amorphous and one crystalline, joined through a single junction point, with different thermal properties: the characteristics of these products are those typical of thermoplastic elastomers, with excellent mechanical properties of ductility and elasticity, such as to allow an expansion of the application spectrum of diene-based polymeric materials.