A method capable of stably performing continuous production of a propylene polymer with high productivity while reducing generation of agglomerates is described. In the method, a monomer(s) containing propylene is/are (co)polymerized in a presence of an olefin polymerization catalyst with a polymerization system containing two or more gas phase polymerization reactors or a polymerization system containing a liquid phase polymerization reactor(s) and a gas phase polymerization reactor(s) such that that the total number of liquid phase polymerization reactor(s) and gas phase polymerization reactor(s) is three or more. In at least one gas phase polymerization reactor, an average retention time τ.sub.G [hour] in the gas phase polymerization, an average particle diameter D.sub.pi [μm] of fed powder, and a total amount C.sub.o [wt %] of an ethylene-derived structural unit and C4-C12 α-olefin-derived structural units in a polymer in discharged powder are in a predetermined relationship.

A method capable of stably performing continuous production of a propylene polymer with high productivity while reducing generation of agglomerates is described. In the method, a monomer(s) containing propylene is/are (co)polymerized in a presence of an olefin polymerization catalyst with a polymerization system containing two or more gas phase polymerization reactors or a polymerization system containing a liquid phase polymerization reactor(s) and a gas phase polymerization reactor(s) such that that the total number of liquid phase polymerization reactor(s) and gas phase polymerization reactor(s) is three or more. In at least one gas phase polymerization reactor, an average retention time τ.sub.G [hour] in the gas phase polymerization, an average particle diameter D.sub.pi [μm] of fed powder, and a total amount C.sub.o [wt %] of an ethylene-derived structural unit and C4-C12 α-olefin-derived structural units in a polymer in discharged powder are in a predetermined relationship.

A method is disclosed for producing a catalyst, which suppresses a decrease in polymerization activity due to early deactivation of the active site after the catalyst has been formed, exhibits excellent catalyst activity at the time of polymerization of olefins, and can produce polymers of olefins, which are excellent in stereoregularity. The method for producing a catalyst includes contacting a solid catalyst component (A) containing magnesium, titanium, halogen and an internal electron-donating compound, and a specific organoaluminum compound (B) represented by the general formula (I), with each other, wherein at least one selected from the solid catalyst component (A) and the organoaluminum compound (B) is previously subjected to contact treatment with a hydrocarbon compound having one or more vinyl groups, in an organic solvent containing 30% by mass or more of one or more compounds selected from saturated aliphatic hydrocarbon compounds having 20 or more carbon atoms.

A method is disclosed for producing a catalyst, which suppresses a decrease in polymerization activity due to early deactivation of the active site after the catalyst has been formed, exhibits excellent catalyst activity at the time of polymerization of olefins, and can produce polymers of olefins, which are excellent in stereoregularity. The method for producing a catalyst includes contacting a solid catalyst component (A) containing magnesium, titanium, halogen and an internal electron-donating compound, and a specific organoaluminum compound (B) represented by the general formula (I), with each other, wherein at least one selected from the solid catalyst component (A) and the organoaluminum compound (B) is previously subjected to contact treatment with a hydrocarbon compound having one or more vinyl groups, in an organic solvent containing 30% by mass or more of one or more compounds selected from saturated aliphatic hydrocarbon compounds having 20 or more carbon atoms.

The present invention provides a method for producing a catalyst for polymerization of an olefin, which suppresses a decrease in polymerization activity due to early deactivation of the active site after the catalyst has been formed, exhibits excellent catalyst activity at the time of polymerization of olefins, and can produce polymers of olefins, which are excellent in stereoregularity. The method for producing a catalyst for polymerization of an olefin includes contacting a solid catalyst component (A) containing magnesium, titanium, halogen and an internal electron-donating compound, and a specific organoaluminum compound (B) represented by the general formula (I), with each other, wherein at least one selected from the solid catalyst component (A) and the organoaluminum compound (B) is previously subjected to contact treatment with a hydrocarbon compound having one or more vinyl groups.

The present invention provides a method for producing a catalyst for polymerization of an olefin, which suppresses a decrease in polymerization activity due to early deactivation of the active site after the catalyst has been formed, exhibits excellent catalyst activity at the time of polymerization of olefins, and can produce polymers of olefins, which are excellent in stereoregularity. The method for producing a catalyst for polymerization of an olefin includes contacting a solid catalyst component (A) containing magnesium, titanium, halogen and an internal electron-donating compound, and a specific organoaluminum compound (B) represented by the general formula (I), with each other, wherein at least one selected from the solid catalyst component (A) and the organoaluminum compound (B) is previously subjected to contact treatment with a hydrocarbon compound having one or more vinyl groups.

A multimodal polyethylene composition having a lower molecular weight (LMW) ethylene homo or copolymer component (A) and a higher molecular weight ethylene copolymer component (B); wherein the lower molecular weight component comprises: (ai) a first fraction which comprises an ethylene homo or copolymer of ethylene and one or more C3-10 alpha olefins; and (aii) a N second fraction which comprises a different ethylene homo or copolymer of ethylene and one or more C3-10 alpha olefins; wherein the multimodal polymer composition has a density of 930 kg/m.sup.3 or more (ISO1183), such as 938 to 955 kg/m.sup.3, an MFR2 (ISO1133 at 190° C. and 2.16 kg load) in the range of 0.05 to 10 g/10 min, and a flexural modulus of up to 800 MPa, such as 300 to 800 MPa (ISO 178:2010).

A multimodal polyethylene composition having a lower molecular weight (LMW) ethylene homo or copolymer component (A) and a higher molecular weight ethylene copolymer component (B); wherein the lower molecular weight component comprises: (ai) a first fraction which comprises an ethylene homo or copolymer of ethylene and one or more C3-10 alpha olefins; and (aii) a N second fraction which comprises a different ethylene homo or copolymer of ethylene and one or more C3-10 alpha olefins; wherein the multimodal polymer composition has a density of 930 kg/m.sup.3 or more (ISO1183), such as 938 to 955 kg/m.sup.3, an MFR2 (ISO1133 at 190° C. and 2.16 kg load) in the range of 0.05 to 10 g/10 min, and a flexural modulus of up to 800 MPa, such as 300 to 800 MPa (ISO 178:2010).

A process for propylene preliminary polymerization in liquid phase that occurs in a continuous preliminary polymerization reactor may include feeding a propylene monomer and a Ziegler-Natta catalyst system having (a) a pro-catalyst having an internal electron donor comprising a substituted phenylene aromatic diester, (b) a catalyst activator and optionally (c) an external donor, into the continuous preliminary polymerization reactor, wherein the feeding is carried out without pre-contact of the pro-catalyst with the catalyst activator, and also without pre-contact of the catalyst activator with the propylene monomer before entering the continuous preliminary polymerization reactor.

A process for propylene preliminary polymerization in liquid phase that occurs in a continuous preliminary polymerization reactor may include feeding a propylene monomer and a Ziegler-Natta catalyst system having (a) a pro-catalyst having an internal electron donor comprising a substituted phenylene aromatic diester, (b) a catalyst activator and optionally (c) an external donor, into the continuous preliminary polymerization reactor, wherein the feeding is carried out without pre-contact of the pro-catalyst with the catalyst activator, and also without pre-contact of the catalyst activator with the propylene monomer before entering the continuous preliminary polymerization reactor.