Process for manufacture of low emission homopolymer or random polypropylene

A process for the preparation of preparing a propylene homopolymer or a propylene a-olefin random copolymer comprising the steps of:

• a) preparing a propylene homopolymer or a propylene α-olefin random copolymer, wherein the α-olefin is chosen from the group consisting of ethylene and α-olefins having 4 to 10 carbon atoms, by contacting at least the propylene and optionally α-olefin with a catalyst in a single gas-phase reactor at a temperature T1 and a pressure P1,
• wherein T1 is chosen in the range from 78 to 83° C.;
• wherein P1 is chosen in the range from 22 to 30 bar;
• to prepare a propylene homopolymer (A′) or a propylene α-olefin random copolymer (A′);
• and
• b) visbreaking the propylene homopolymer (A′) or the propylene α-olefin random copolymer (A′) to obtain a propylene homopolymer (A) or a propylene α-olefin random copolymer (A), wherein the propylene homopolymer (A) respectively the propylene α-olefin random copolymer (A) has a melt flow rate that is higher than the melt flow rate of the propylene homopolymer (A′) respectively propylene α-olefin random copolymer (A′) as measured according to ISO1133 (2.16 kg, 230° C.);
• wherein the catalyst is a catalyst system comprising a magnesium catalyst and an electron donor;
• wherein the magnesium catalyst is prepared by reacting titanium tetrachloride, diisobutyl phthalate, and magnesium diethoxide to form a solid material, slurrying the solid material and titanium tetrachloride, and collecting the magnesium catalyst from the slurry;
• and
• wherein the electron donor comprises n-propyltriethoxysilane;
• and
• wherein the FOG value of the propylene homopolymer (A′) or the propylene α-olefin random copolymer (A′) after the visbreaking and before any subsequent processing step is at most 400 μg/g, as determined by VDA 278.