| 摘要 |
FIELD: chemistry.SUBSTANCE: invention relates to a multistep method of producing polypropylene by polymerisation. The method includes using at least two series-connected reactors. At step (A) a first polypropylene fraction is obtained in a first reactor. At step (B) the first polypropylene fraction fed into a second reactor. At step (C) a second polypropylene fraction is polymerised in the second reactor in the presence of the first polypropylene fraction to obtain a polypropylene composition. The first polypropylene fraction has melt flow rate MFR(230°C) of not more than 1.5 g/10 min or more than 2.0 g/10 min, and includes propylene units and optionally at least one C-C?-olefin different from the propylene. The polypropylene composition has melt flow rate MFR(230°C) of more than 2.0 g/10 min and the melt flow rate MFR(230°C) of the polypropylene composition is different from that of the first polypropylene fraction. In the first and second reactor, polymerisation takes place in the presence of a solid catalyst system. The catalyst system has porosity of less than 1.40 ml/g and/or surface area of less than 25 m/g and includes a catalyst which is an organozirconium compound of formula (I).EFFECT: obtaining pure polypropylene substantially free from undesirable residues and characterised by excellent hardness and high heat resistance.14 cl, 9 tbl, 5 ex |
