Method for manufacturing of butadiene-propylene copolymers

A method for manufacturing a high molecular weight elastomeric butadiene-propylene random copolymer whose propylene unit content is in the range of 3 to 45 mol% and wherein no propylene unit chain exists in the resulting copolymer chain, which comprises copolymerizing, in an inert solvent, butadiene and propylene in the mol ratio ranging from one to ten at a temperature ranging from 0.degree.C to 80.degree.C, in the presence of a catalyst system consisting of (1) at least one compound selected from the group consisting of titanium tetrachloride, titanium tetrabromide, titanium tetraiodide and vanadyl trichloride, (2) an organoaluminum compound having the formula, AlR.sup.1 R.sup.2 R.sup.3 wherein R.sup.1, R.sup.2 and R.sup.3 represent a hydrocarbon radical having 1 to 18 carbon atoms each of which may be the same or different, and (3) phosgene, in which said components (2) and (3) are mixed at room temperature prior to the addition of other catalysts and of monomers, the mol ratio of said component (1) to said component (2) being one to ten, the mol ratio of said component (2) to said component (3) being ten to one, said component (1) being used in the amount of 0.05 to 15 mmol based on 100 gr of the total amount of the monomers as charged.