π-Allyl-type polymerization

π-allyl type polymerization is becoming increasingly important as many results in the field of the stereospecific polymerization reveal the general formation of π-allylic intermediates when conjugated dienes are polymerized by means of transition metal derivatives. The catalytic activity of simple π-allyl complexes of transition metals, as well as the structure of the polymers produced, are determined by the nature of the active center as a whole and are strongly influenced by both the transition metal itself and the ligands bound to the metal atom. In particular, the counter ion in the catalytic complex and some electron accepting or donating additives have been shown to control, with high precision and versatility, the overall reaction rate and the stereospecificity of the polymerization process. At the same time, the use of appropriate ligands yields a new type of stereoregular polydienes - e.g., the "equibinary" polymers. Kinetic data on π-allyl-type polymerization are briefly discussed, and tentative propagation is suggested to explain the significant experimental results now available.