NOVEL MULTISTEP METHOD OF PRODUCING POLYPROPYLENE Russian patent published in 2014 - IPC C08F110/06 C08F10/06 C08F2/00 C08F4/6592 C08L23/10 

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 MFR₂ (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 C₂-C₁₀ α-olefin different from the propylene. The polypropylene composition has melt flow rate MFR₂ (230°C) of more than 2.0 g/10 min and the melt flow rate MFR₂ (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 m²/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