Nature of active centers and stereospecificity of tetravalent titanium benzyl derivatives in polymerization of butadiene

Stereospecificity of tetrabenzyltitanium and its halogeno-derivatives in the polymerization of butadiene has been investigated. The content of 1,2-units decreases while the content of 1,4-cis-units increases in the resulting polybutadiene for the series (C₆H₅CH₂)₄Ti, (C₆H₅CH₂)₃TiCl, (C₆H₅CH₂)₃TiBr, (C₆H₅CH₂)₃Til. Tribenzyltitanium iodide exhibits high stereospecificity for the formation of 1,4-cis-units and their content reaches 94–97%. By determining the number of benzyl groups linked with titanium at different degrees of conversion, it has been shown that the active centre formed from tetrabenzyltitanium contains three benzyl groups and one polymer chain. Two benzyl groups, one iodine atom and one polymer chain are attached to a titanium atom in the active centre for the case of tribenzyltitanium iodide. Electron donors sharply change the stereospecificity of tribenzyltitanium iodide: the content of 1,2-units in the polymer rises to 68%.