in an inert nonpolymerizable solvent therefor and for the copolymer to be prepared in an I agitated reaction zone maintained at a pressure sufiicient to maintain the monomers in solution and at a temperature of 40 to 110 C. in the presence of a catalyst prepared by mixing (A) an organoaluminum halide R AlX- wherein R is an alkyl or aryl radical, n is not greater than 1.5 or less than 1.0 and X is