The subject invention relates to a process for preparing a catalyst system that comprises the sequential steps of (I) reacting an organometalic compound that contains a metal from Group III-B of the Periodic System with an organoaluminum compound at a temperature which is within the range of 50.degree. C. to 100.degree. C. to produce an aluminum modified Group III-B metal containing catalyst component, and (II) mixing the aluminum modified Group III-B metal containing catalyst component with a halogen containing compound to produce the Group III-B metal containing catalyst system, wherein the catalyst system is void of compounds selected from the group consisting of aliphatic alcohols, cycloaliphatic alcohols, aliphatic thiols, cycloaliphatic thiols, trialkyl silanols, and triaryl silanols, wherein the organometalic compound that contains a metal from Group III-B of the Periodic System is reacted with the organoaluminum compound in the absence of conjugated diene monomers, and wherein the catalyst system is prepared in the absence of compounds that contain labile halogen atoms.