Document Type: Review
CNR - Istituto per lo Studio delle Macromolecole (ISMAC), via E. Bassini 15, I-20133 Milano (Italy)
The stereospecific polymerization of conjugated dienes began in 1954 with the first catalysts obtained by combining TiCl4 or TiCl3 with aluminum-alkyls, i.e. the catalytic systems previously employed for ethylene and propylene polymerizations. Subsequently, many other catalytic systems were obtained and examined by a combination of transition metal or lanthanide compounds with appropriate alkylating agents. With the advent of MAO as alkylating agent, at the beginning of the 1980s, new catalytic systems were introduced, in some cases much more active and stereospecific than those based on common aluminum-alkyls. Starting from the 2000s, in the wake of what happened in the case of mono-olefins, a new generation of catalysts based on complexes of transition ,metals and lanthanides with various ligands containing donor atoms such as P, N, O (e.g., phosphines, imines imino-pyridines, cheto-imines) has been introduced. These systems have proved particularly active and able to (provide polymers with controlled microstructure (i.e., cis-1,4; 1,2; mixed cis-1,4/1,2 with a variable 1,2 content ,from several types of 1,3-dienes, permitting indeed to establish new correlations between the catalyst structure the monomer structure and the polymer microstructure, and to improve our knowledge on the polymerization mechanism of 1,3-dienes. This paper provides an exhaustive overview of the latest developments in the field of stereospecific polymerization of 1,3-butadiene.