A transitional metal component comprising at least one zirconocene of the formula I and at least one zirconocene of the formula Ia or alternatively, at least two zirconocenes of the formula I ##STR19## in which R1 and R2 are identical or different and are a hydrogen atom, a C1 -C10 -alkyl group, a C1 -C10 -alkoxy group, a C6 -C10 -aryl group, a C6 -C10 -aryloxy group, a C2 -C10 -alkenyl group, a C