The nature of the active centres and the stereospecific effect of benzyl derivatives of four valent titanium in polymerization of Butadiene

Abstract

A study has been made of the stereospecific effect of tetrabenzyltitanium and its halide derivatives in polymerization of butadiene. The proportion of 1,2-units decreases and of 1·4- cis-units in the polymers increases in the order of the series of catalysts (C 6H 5CH 2) 4Ti, (C 6H 5CH 2) 3TiCl, (C 6H 5CH 2) 3TiBr and (C 6H 5CH 2) 3TiI. Tribenzyltitanium iodide has a high stereospecific effect for formation of 1·4- cis-units, the concentration of which reaches 94–97%. By determination of the number of benzyl groups attached to titanium at various degrees of conversion, it is shown that the active centre formed from tetrabenzyltitanium contains three benzyl groups and one polymer chain. In the case of tribenzyltitanium iodide the active centre contains two benzyl groups, an iodine atom and a polymer chain, attached to the titanium atom. Electron donors alter the stereospecific effect of tribenzyltitanium iodide considerably. In the presence of these the proportion of 1,2-units in the polymer increases to 68%.