PROCESS FOR THE POLYMERIZATION OF PROPYLENE

摘要

The invention relates to a process for the preparation of polypropylene having - a molecular weight (Mw) of 450,000-950,000, - a molecular weight distribution of 3-6, - a melt flow in the range of 7-14 dg/min measured with a load of 21.6 kg at 230 °C or 0.05-2 dg/min measured with a load of 2.16 kg at 230 °C and - a xylene soluble content of 2-6 wt% by converting propylene into the polypropylene without pre-polymerization in the presence of a polymerization catalyst under a condition where the volume ratio of H2 to propylene is at most 0.0020, wherein the catalyst comprises a catalyst component, a co-catalyst and an external donor, wherein the catalyst component is obtained by a process wherein a compound with formula Mg(OAlk)xCly wherein x is larger than 0 and smaller than 2, y equals 2-x and each Alk, independently, represents an alkyl group, is contacted with a titanium tetraalkoxide and/or an alcohol in the presence of an inert dispersant to give an intermediate reaction product and wherein the intermediate reaction product is contacted with titanium tetrachloride in the presence of an internal donor, and wherein the molar ratio of the co-catalyst to the external donor is 3.3-5.2, preferably 3.8-4.4.