SynopsisButadiene is polymerized by cobalt compound-organoaluminum-CSz catalysts to give highly crystalline syndiotactic 1,2-polybutadiene (s-PB) having melting point up to 216OC. An aluminum-free catalyst, CO(C4H6)(C8H13)-CS2, is also effective. Syndiotactic polymerization with C O ( C~H~) ( C~H~& C S~ is not interrupted by the addition of protic substances such as water and alcohol, but is influenced by donor or acceptor substances. The donor molecule, e.g., dimethylsulfoxide or dimethylformamide, decreases the stereoregularity, i.e., syndiotacticity and 1,2 content. An acceptor molecule of organoaluminum with appropriate acidity such as AlEt3-AlEtzCl or tetraethylaluminoxane increases the molecular weight, stereoregularity, and yield of the polymer. In the presence of CSz a mixture of cis-PB and s-PB was obtained by using Co(octoate)z-AlEtzCl-HzO, with molar ratio H20/Co less than unity. In the case of HzO/Co > 1, only cis-PB was obtained. By the addition of donor substances such as ester, ether, nitrile, and U t 3 , s-PB was obtained even when H20/Co > 1. The amount and ratio of cis-PB and s-PB are dependent upon the nature and amount of the additives. [43& = [7]gg&,, = 8.18 x 1 0 -5~~o . w a Polymerization conditions: benzene 860 mL, butadiene 85 g, at 4OoC with HzO (variable)-AlEta (3.0 mmol)-Co(acac)3 (0.045 mmol)-CSz (0.13 mmol) as the catalyst.

SynopsisA mechanism is proposed for the polymerization of syndiotactic 1,2-polybutadiene (s-PB) with soluble cobalt-organoaluminum-CS2. The proposed active species have structures which consist of side-on coordination of CS2 to cobalt, anti-r-ally1 growing end, cisoid bidentate coordination of butadiene, and activation by complex formation with organoaluminum at the nonbonded sulfur of the coordinated CS2. This proposal is based on findings for the aluminum-free catalyst CO(C.&)(C&I~&CS~. It is tentatively interpreted that syndiotactic 1,2 polymerization proceeds under the influence of the side-on coordinated CS2, by which the reactivity between the terminal carbons of butadiene and the C3 of the s-ally1 end is enhanced.

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