Highly crystalline propylene homopolymers

A process for the preparation of propylene homopolymers having from 0.4 wt percent to 0.6 wt percent xylene soluble fraction and a halogen content of 7.8 ppm to 10.1 ppm by polymerizing propylene at from 20 to 50° C. and from 1 to 100 bar in the presence of a Ziegler-Natta catalyst system containing, as active components, wherein the process comprises

• a) reacting a titanium halide with a chlorine-free magnesium alkyl compound, an inorganic oxide as a carrier, a C1–C8-alkanol and an electron donor compound by a method in which, in a first stage, a solution of the chlorine-free magnesium alkyl compound in an inert solvent is added to the inorganic oxide as a carrier, this mixture is allowed to react for from 0.5 to 5 hours at from 10 to 120° C. and then reacted, at from −20° to 80° C. with constant mixing, with a C1–C8-alkanol in at least a 1.3 fold molar excess, based on the compound of magnesium, to give a chlorine-free intermediate, the titanium halide and the electron donor compound are then added to said intermediate, the resulting mixture is allowed to react for at least 10 minutes at from 10 to 150° C. and the solid substance thus obtained is then filtered off as washed in a liquid alkane
• and, as cocatalyst,
• b) an aluminum compound and
• c) a further electron donor compound,
• the molar ratio of the aluminum compound b) to the further electron donor compound c) in the polymerization being from 1.5:1 to 9:1.