Improvements in the production of stereo-specific poly-1,4-butadiene

Trans-1, 4-polybutadiene substantially free from the corresponding cis-polymer is made by polymerizing 1, 3-butadiene in the presence of a catalyst combination consisting of an organo-metallic aluminium compound and a zirconium halide which has been carefully purified from compounds of iron so that the halide contains less than 0.01% by weight of iron. The zirconium halide, preferably the tetrachloride, may be purified by sublimation or distillation over pure iron in an inert atmosphere. The aluminium compound may be triethyl, tri-isopropyl, or tri-isobutyl aluminium. The catalyst is preferably preformed. The polymerization reaction is preferably effected in a hydrocarbon solvent. In the examples the aluminium compound used is commercial aluminium tri-isobutyl which contains aluminium di-isobutyl hydride.