Abstract: In a process for producing syndiotactic-1,2-polybutadiene by suspension polymerization wherein a mixture composed of 1,3-butadiene, a cobalt compound, and an organometallic compound or metal hydride containing a metal of group I, II or III of the periodic table is contacted with an initiator selected from the group consisting of carbon disulfide, phenyl isothiocyanate and xanthogenic compounds in an aqueous medium, the improvement comprising, after the preparation of the mixture, adding thereto an anti gelling agent selected from the group consisting of alcohols, aldehydes, ketones, carboxylic acid esters, nitriles, sulfoxides, amides and phosphoric acid esters, whereby the formation of a rubber-like gelation product in the mixture is inhibited.

Abstract: A 1,2-polybutadiene composition having an excellent reinforcing effect for rubber and synthetic resin materials including at least two polybutadiene components different in melting point from each other and each having, as a main structure, a 1,2-polybutadiene structure, produced by polymerizing a 1,3-butadiene-containing monomer in a water-containing polymerization system in the presence of a catalyst comprising a transition metal compound, an organic compound of one of the Group I to III metals, and one of carbon disulfide, phenyl isothiocyanate, and xanthic acid compounds, while adding a melting point-regulating agent comprising at least one of ketones, aldehydes, alcohols, esters, nitriles, sulfoxides, amides, and phosphoric acid esters in one or two or more separate adding operations or a continuous adding operation.