Patent ID: 7531607

Claim:
A process for producing at least two different propylene polymer grades, which comprises polymerizing propylene, optionally with comonomers, under polymerization conditions in the presence of hydrogen as a molecular weight controlling agent and a Ziegler-Natta catalyst system, said catalyst system comprising a catalyst component, and an external donor selected from a first and a second external donor, wherein the first external donor is used for producing a first polymer grade and is changed to the second external donor for producing a second polymer grade, but the hydrogen feed is changed at the most 5% from the volume used for producing the first polymer grade, during the transition of production from the first polymer grade to the second; and wherein the catalyst system comprises solid catalyst particles which exhibit active sites evenly distributed throughout the particles; wherein the catalyst particles are not supported on an external carrier; wherein the isotacticity of the second polymer grade is different than that of the first polymer grade while keeping the melt flow rate of the first and second polymer at the same, predetermined level of 0.01 to 1500 g/10 min during a transition of production from the first polymer grade to the second; and wherein said process is carried out in a polymerization arrangement comprising at least one polymerization reactor.