Butadiene copolymers having controlled electrical life and controlled resistivity are described. A method is disclosed for enhancing the electrical life of butadiene copolymers having solubilized conductivity control agents incorporated therein by varying specified quantities of terminally unsaturated hydrocarbon nitriles in copolymers of the butadiene and the specified nitriles by using mixtures of such copolymers having conductivity control agents therein. The method and polymers are useful for enhancing the electrical life and polymer stability in xerographic devices where control of conductivity and/or relaxation behavior is important, e.g., in bias transfer rolls.