Abstract: Factors governing the microstructure of 1, 2-polybutadienes preparedwith molybdenum catalysts have been stedied. It was found that the vinylcontent of the 1,2-polybutadienes could be regulated by addition cf allylhalide and the order of addition of the catalyst components as well as thepolymerization temperature. Allyl bromide appeared more effective for theregulation of 1,2-stereoisomer and the sequence distribution as. well.