Catalyst system, the catalyst system comprising (i) at least one metallocene complex of formula (I) wherein Mt1 is Hf, X is a sigma-donor ligand, R.sup.1, R.sup.2, R.sup.3 are the same or different from each other and can be hydrogen or a saturated linear or branched C.sub.1-C.sub.10 alkyl, whereby the alkyl group can optionally contain up to 2 heteroatoms belonging to groups 14-16 of the periodic table, or R.sup.1 and R.sup.2 or R.sup.2 and R.sup.3 can form a ring having 4 to 6 C-atoms and 1 to 3 double bonds, R.sup.4 and R.sup.5 are the same or different from each other and can be saturated linear or branched C.sub.1-C.sub.10 alkyl, C.sub.5-C.sub.10 aryl, C.sub.6-C.sub.20 alkylaryl or C.sub.6-C.sub.20 arylalkyl groups, which can optionally contain up to 2 heteroatoms belonging to groups 14-16 of the periodic table, n can be 1 to 5, Ar is a C.sub.6-C.sub.20-aryl or -heteroaryl group, which can be unsubstituted or substituted by 1 to 5 linear or branched C.sub.1-C.sub.10 alkyl group(s), and (ii) an aluminoxane cocatalyst and (iii) optionally an aluminium alkyl compound AI(R.sup.7).sub.3, with R.sup.7 being a linear or branched C.sub.2-C.sub.8-alkyl group. ##STR00001##

A bimodal polymer composition comprising a lower molecular weight homopolymer and a higher molecular weight copolymer wherein the bimodal polymer composition has a density of from about 0.930 gram per cubic centimeter (g/cc) to about 0.970 g/cc, a ratio of high load melt index:melt index of from about 10 to about 150 and an Environmental Stress Crack Resistance (ESCR) of from about 25 hours to about 300 hours when measured in accordance with ASTM D1693 or ASTM D2561. A chromium-catalyzed polymer composition comprising (i) a lower molecular weight homopolymer and (ii) a higher molecular weight copolymer, wherein the bimodal polymer composition has an Environmental Stress Crack Resistance (ESCR) of from about 25 hours to about 300 hours when measured in accordance with ASTM D1693 or ASTM D2561.

A bimodal polymer composition comprising a lower molecular weight homopolymer and a higher molecular weight copolymer wherein the bimodal polymer composition has a density of from about 0.930 gram per cubic centimeter (g/cc) to about 0.970 g/cc, a ratio of high load melt index:melt index of from about 10 to about 150 and an Environmental Stress Crack Resistance (ESCR) of from about 25 hours to about 300 hours when measured in accordance with ASTM D1693 or ASTM D2561. A chromium-catalyzed polymer composition comprising (i) a lower molecular weight homopolymer and (ii) a higher molecular weight copolymer, wherein the bimodal polymer composition has an Environmental Stress Crack Resistance (ESCR) of from about 25 hours to about 300 hours when measured in accordance with ASTM D1693 or ASTM D2561.

The polyethylene according to the present invention has narrow particle size distribution, and can minimize a change in the crystal structure, and thus, it can be reacted with chlorine to prepare chlorinated polyethylene having excellent chlorination productivity and thermal stability.

The polyethylene according to the present invention has narrow particle size distribution, and can minimize a change in the crystal structure, and thus, it can be reacted with chlorine to prepare chlorinated polyethylene having excellent chlorination productivity and thermal stability.

In some embodiments, a polyethylene composition includes has 80 wt % to 99.9 wt % ethylene content and 20 wt % to 0.1 wt % a C3 to C40 α-olefin comonomer content, based on ethylene content plus comonomer content. The composition has a Mw/Mn of 15 to 45, a density of 0.93 g/cm.sup.3 to 0.97 g/cm.sup.3, a complex viscosity (at 628 rad/s, 190° C.) of 600 Pa*s or less, a zero shear viscosity by Cross model of 150,000 Pa*s to 350,000 Pa*s. It may also have a V index of less than 7. In some embodiments, an article includes the polyethylene composition. In some embodiments, the article is a pipe.

In some embodiments, a polyethylene composition includes has 80 wt % to 99.9 wt % ethylene content and 20 wt % to 0.1 wt % a C3 to C40 α-olefin comonomer content, based on ethylene content plus comonomer content. The composition has a Mw/Mn of 15 to 45, a density of 0.93 g/cm.sup.3 to 0.97 g/cm.sup.3, a complex viscosity (at 628 rad/s, 190° C.) of 600 Pa*s or less, a zero shear viscosity by Cross model of 150,000 Pa*s to 350,000 Pa*s. It may also have a V index of less than 7. In some embodiments, an article includes the polyethylene composition. In some embodiments, the article is a pipe.

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).

It is provided a process for producing an ethylene copolymer comprising compressing ethylene monomer at a certain pressure; adding a fresh comonomer in liquid form and, optionally, a fresh modifier in liquid form at a certain pressure to the compressed ethylene monomer; introducing the resulting compressed mixture into an autoclave reactor having a first reaction zone and at least one more reaction zone, the first reaction zone having a volume that is greater than 50% of the total reactor volume, and, optionally, at least one additional reactor; adding at least one free radical initiator in order to start a polymerization reaction; and separating the ethylene copolymer from the reaction mixture; wherein all the compressed ethylene monomer or the compressed mixture are introduced into the first reaction zone of the autoclave reactor, and wherein the compressed mixture is introduced into the autoclave reactor and, optionally, into the at least one additional reactor at a temperature from −20° C. to 70° C.