A process for the preparation of a solid catalyst component for the polymerization of CH.sub.2═CHR olefins, wherein R is hydrogen or hydrocarbyl radical with 1-12 carbon atoms, made from or containing a Ti compound on a Mg chloride based support, including the steps of (a) reacting a Mg based compound with a liquid medium made from or containing a Ti compound, at a temperature ranging from 0 to 150° C., thereby yielding solid particles; and (b) suspending the solid particles coming from step (a) in a liquid medium made from or containing hydrocarbons at a temperature ranging from 10 to 100° C., wherein step (a) or (b) is carried out in the presence of 0.2 to 20.0% by weight, with respect to the amount of Mg compound, of particles of a solid compound containing more than 50% by weight of SiO.sub.2 units and having average particle size from 1 to 100 μm.

A process for the preparation of a solid catalyst component for the polymerization of CH.sub.2═CHR olefins, wherein R is hydrogen or hydrocarbyl radical with 1-12 carbon atoms, made from or containing a Ti compound on a Mg chloride based support, including the steps of (a) reacting a Mg based compound with a liquid medium made from or containing a Ti compound, at a temperature ranging from 0 to 150° C., thereby yielding solid particles; and (b) suspending the solid particles coming from step (a) in a liquid medium made from or containing hydrocarbons at a temperature ranging from 10 to 100° C., wherein step (a) or (b) is carried out in the presence of 0.2 to 20.0% by weight, with respect to the amount of Mg compound, of particles of a solid compound containing more than 50% by weight of SiO.sub.2 units and having average particle size from 1 to 100 μm.

A catalyst mixture made from or containing (a) particles of a solid catalyst component comprising Ti, Mg, Cl, and (b) from 0.5 to 5.0% by weight, based upon the total weight of the mixture, of particles of a solid compound having particle size ranging from 0.1 μm to 1 mm containing more than 50% by weight of SiO.sub.2 units.

A magnesium-based solid, by means of determination based on a nitrogen adsorption method, has a multimodal pore distribution and a specific surface area of not less than 50 m.sup.2/g, and the pore size distribution of the solid is in a range of 1 nm to 300 nm. There is at least one peak within a pore size range of less than 10 nm, and there is at least another peak within a pore size range of not less than 10 nm. A catalyst is formed using the solid catalyst component is used for propylene polymerization.

The present invention relates to a multi-stage process for producing a C.sub.2 to C.sub.8 olefin polymer composition in a process comprising at least two reactors, wherein a pre-polymerized solid Ziegler-Natta catalyst is prepared by carrying out an off-line pre-polymerization of a solid Ziegler-Natta catalyst component with a C.sub.2 to C.sub.4 olefin monomer before feeding to the polymerization process.

The present invention relates to a polyethylene composition comprising a base resin having a density of from 952.0 kg/m.sup.3 to 960.0 kg/m.sup.3, determined according to ISO 1183, wherein the polyethylene composition has a melt flow rate MFR.sub.21 (190° C., 21.16 kg), of from 1.0 to 7.5 g/10 min, determined according to ISO 1133, a complex viscosity at a frequency of 0.05 rad/s eta0.05 of from 750 kPa #s to 1900 kPa #s, determined according to ISO 6721-1 and ISO 6721-10, and a white spot rating of not more than 12.0, determined according to ISO 18553, a polyethylene composition obtainable by a multi-stage process, a process for producing said polyethylene composition, an article, such as a pipe or pipe fitting, comprising said polyethylene composition and the use of said polyethylene composition for the production of an article.

A solid catalyst component for the polymerization of olefins CH.sub.2═CHR, wherein R is hydrogen or a hydrocarbon radical with 1-12 carbon atoms, made from or containing Mg, Ti, Bi, a halogen and an electron donor.

The present invention is concerned with a process for polymerizing ethylene or copolymerizing ethylene and at least one alpha-olefin comonomer in the presence of a supported polymerization catalyst in a multi-stage process in which the last polymerization stage is a gas phase reactor, the use of said process for reducing particle carry-over in the last polymerization stage and the use of a supported polymerization catalyst with a certain median particle size to polymerize an ethylene homo- or copolymer in said multi-stage process with a span of its particle size distribution which can be predicted from the median particle size of the catalyst.

The present invention is concerned with a process for polymerizing ethylene or copolymerizing ethylene and at least one alpha-olefin comonomer in the presence of a supported polymerization catalyst in a multi-stage process in which the last polymerization stage is a gas phase reactor, the use of said process for reducing particle carry-over in the last polymerization stage and the use of a supported polymerization catalyst with a certain median particle size to polymerize an ethylene homo- or copolymer in said multi-stage process with a span of its particle size distribution which can be predicted from the median particle size of the catalyst.

This invention relates to a non-phthalate catalyst system for olefin polymerization. The non-phthalate catalyst system comprises (a) a solid Ziegler-Natta catalyst composition comprising a transition metal, a Group 2 metal, and one or more halogens; and one or more internal electron donor compounds; and (b) one or more external electron donor compounds.