A Proposed Mechanism of the Stereospecific Polymerization of Butadiene with a Transition Metal Catalyst

Abstract

ABSTRACT The proposed mechanism is based upon an experimental study of nickel catalysts, quantum chemical considerations, and polymerization results with various transition metal catalysts. It is concluded that polymerization proceeds through a σ-allyl metal complex, at least in cis-1,4 polymerization and the energy level of the transition metal orbital which receives the π-electrons of butadiene is a decisive factor in determining the microstructure of the polymer. According to the mechanism, the polymer of predominantly cis-l,4 structure is obtained only in the case the energy level is in the vicinity of that of the highest occupied orbital of butadiene, and, in the case where the former level is sufficiently apart from the latter, predominantly 1,2 or trans-l,4 polymer is afforded. It is found that the polymerizations resulting with various catalysts are in line with the mechanism.