THE NATURE OF ACTIVE-CENTERS AND KEY STAG ES IN DIENE POLYMERIZATION WITH LANTHANIDE CATALYTIC-SYSTEMS

The data on the mechanism of stereoregulation in diene polymerization with the LnHal(3) . nL-AlR(3) catalytic systems (L - tributyl phosphat e, AlR(3) - triisobutylaluminum, diisobutylaluminum hydride) are analy zed. On the basis of experimental data and using the results of quantu m-chemical calculations, it is shown that the role of each structural element of the active center manifests itself through various factors, and the possible mechanisms of their realization are considered. The key point that determines the importance of one or another factor in t he mechanism of stereoregulation is the relationship between the chara cteristic times, such as the time of occurrence of the terminal units in pi- and sigma-states, time of elementary acts of insertion and isom erization, and time interval between two successive additions of the d iene molecules to the polymer chain. Special attention is given to ana lysis of the mechanism of cis-stereoregulation.