Polymerizations of butadiene (BD) with transition metals (MtX) and methylaluminoxane (MAO) catalysts were studied. Among the catalysts examined, nickel(I1) acetylacetonate [Ni(acach] in combination with MA0 revealed the highest catalytic activities for the polymerization of BD, giving high molecular weight polymers consisting of mainly cis-1,4-units in the microstructure. With Ni(aca~)~-MA0 catalyst, the overall activation energy for the polymerization of BD between 0°C and 60°C was estimated to be 18 kJ/mol. From a kinetic study, the rate equation for the polymerization of BD with the Ni(acac),-MA0 catalyst at 30°C can be expressed as follows: R, = [BD]'.* [Ni(a~ac)~-MA0]'.'. The polymerization mechanism of the polymerization of BD with the Ni(acac),-MA0 catalyst is discussed.

Copolymerization of styrene (St) and butadiene (Bd) with nickel(II) acetylacetonate [Ni(acac)2]‐methylaluminoxane (MAO) catalyst was investigated. Among the metal acetylacetonates [Mt(acac)x] examined, Ni(acac)2 showed a high activity for the copolymerization of St and Bd giving copolymers having high cis‐1,4‐microstructure in Bd units in the copolymer. The effect of alkylaluminum as a cocatalyst on the copolymerization of St and Bd with the Ni(acac)2‐MAO catalyst was observed, and MAO was found to be the most effective cocatalyst for the copolymerization. The monomer reactivity ratios for the copolymerization of St and Bd with the Ni(acac)2‐MAO catalyst were determined to be rSt = 0.07 and rBd = 3.6. Based on the obtained results, it was presumed that the random copolymers with high cis‐1,4‐microstructure in Bd units could be synthesized with the Ni(acac)2‐MAO catalyst without formation of each homopolymer. The polymerization mechanism with the Ni(acac)2‐MAO catalyst was also discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3838–3844, 1999

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