PREPARATION OF HIGH CIS-1,4-POLYBUTADIENE

PREPARATION OF HIGH CIS-1,4-POLYBUTADIENE There is disclosed a polymerization process of the regulation of a molecular weight of a high cis-1,4-polybutadiene which is prepared by polymerizing 1,3butadiene under solution polymerization conditions employing as a catalyst (1) at least one organoaluminum compound; (2) at least one organonickel compound selected from the group consisting of nickel salts of carboxylic acids, organic complex compounds of nickel and nickel tetracarbonyl; and (3) hydrogen fluoride or a hydrogen fluoride complex prepared by complexing hydrogen fluoride with a complexing compound of the group consisting of ketones, aldehydes, nitriles, esters, ethers, alcohols, phenols, mineral acids containing oxygen, and water or mixtures thereof, wherein the mole ratio of the organoaluminum compound to the organonickel compounds is within 26/1 to 70/1, the hydrogen fluoride or the hydrogen fluoride complex to the nickel compound is within the mole ratio of 86/1 to 121/1, wherein the hydrogen fluoride to the complexing compound ranges from 4/1 to 1/1, wherein the nickel compound is employed in an amount ranging from 0.004 to 0.010 parts per 100 parts of butadiene in the polymerization system, wherein the temperature of the polymerization is controlled from about 68.degree.C to about 107.degree.C, said polymerization being conducted in the presence of small amounts of an olefin selected from the group consisting of ethylene, propylene, 1-butene, cis and trans 2-butene, 1,5-hexadiene, 1,4-hexadiene, 1,4-pentadiene, 1,6heptadiene per 100 parts of butadiene charged, and where the polymerization is a continuous process. The amount of branching and microgel produced in the polybutadiene is controlled through the selection of the two variables, the nickel compound levels employed in the catalyst system and the reaction temperature. The lower nickel compound levels and the lower temperatures (Cont.) produce a more linear polymer which has been shown to result in improved tire performance when employed in automobile tires.