The mechanism of stereoregulation in diene polymerization on lanthanide catalytic systems

The main distinctive feature of lanthanide catalysts among others Ziegler-Natta catalysts is that they allow one to synthesize polydienes with a high content of cis-1,4-units. In most cases, lanthanides are used in the form of blends and concentrates. About 50% of lanthanides consumed worldwide are used for the production of catalysts for various chemical processes. The number of these processes can be increased by using lanthanide catalysts in the manufacture of synthetic rubbers. A great number of studies are devoted to polymerization of dienes with lanthanide catalytic systems. Many of these studies are concerned with the problems related to the mechanism that controls the microstructure of polydienes. Although not all aspects of stereoregulation have been clarified, many problems were solved and possible explanations were offered for some of others (1-4) The objective of this work was to review the basis results of research of diene (butadiene, isoprene, and piperylene) polymerization with the LnHal(3).nL-AlR3 (Ln = Ianthanide, L = tributylphosphate, AlR3 = triisobutylaluminum. and diisobutylaluminum hydride) catalytic system and to analyze the role of such factors as the electronic and geometric structure of bimetallic active centers, anti-syn and pi-sigma-transitions of the terminal units of the growing polymer chains, and the nature of the lanthanide, diene, and organoaluminum component in the mechanism of stereoregulation.