Syndiotactic 1,2‐polybutadiene with Co‐CS2 catalyst system. II. Catalysts for stereospecific polymerization of butadiene to syndiotactic 1,2‐polybutadiene

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Abstract
Butadiene is polymerized by cobalt compound–organoaluminum–CS2 catalysts to give highly crystalline syndiotactic 1,2‐polybutadiene (s‐PB) having melting point up to 216°C. An aluminum‐free catalyst, Co(C4H6)(C8H13)‐CS2, is also effective. Syndiotactic polymerization with Co(C4H6)(C8H13)‐CS2 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‐AlEt2Cl or tetraethylaluminoxane increases the molecular weight, stereoregularity, and yield of the polymer. In the presence of CS2 a mixture of cis‐PB and s‐PB was obtained by using Co(octoate)2‐AlEt2Cl‐H2O, with molar ratio H2O/Co less than unity. In the case of H2O/Co > 1, only cis‐PB was obtained. By the addition of donor substances such as ester, ether, nitrile, and AlEt3, s‐PB was obtained even when H2O/Co > 1. The amount and ratio of cis‐PB and s‐PB are dependent upon the nature and amount of the additives.