Initiation and propagation steps in the equibinary polymerization of butadiene by bis( h 3 ‐allylnickel trifluoroacetate)

Polymerization of butadiene by bis( h 3 ‐allylnickel trifluoroacetate) in benzene and o ‐dichlorobenzene solvents yields an equibinary 1,4‐polybutadiene, containing equal amounts of cis and trans isomers. Initiation proceeds by addition of the allylic moiety of the initiator to a butadiene molecule. The rate of initiation is high enough to ensure complete consumption of the catalyst for a monomer/catalyst molar ratio of about 10 at 5°C. The propagation exhibits the characteristics of a “living” polymerization: the molecular weight is proportional to the conversion, and at the end of the reaction, the average degree of polymerization is equal to the monomer/catalyst molar ratio. Living polybutadienyl‐nickel trifluoroacetate is able to reinitiate not only butadiene polymerization but also allene polymerization. However, for high [monomer]/[catalyst] ratios, conversion‐dependent transfer reactions limit the molecular weight to 7000 in benzene and to 70,000 in bulk polymerization in the presence of small amounts of o ‐dichlorobenzene.