Multimodal polyethylene compositions

Abstract

Provided are multimodal polyethylene compositions, and geomembranes including the same. The multimodal polyethylene composition includes a first polyethylene component and a second polyethylene component, wherein the composition has a density of from 0.933 to 0.945 g / cm3; a high flow melt index (I21) of from 7.5 to 18.0 g / 10 min; a molecular weight distribution (Mw / Mn), measured by absolute GPC, of less than 15.0; and a strain hardening modulus of at least 50 MPa. The compositions according to embodiments disclosed herein can be formed into geomembranes and can exhibit desirable processability and slow growth crack performance, among other things.

Description

MULTIMODAL POLYETHYLENE COMPOSITIONSTECHNICAL FIELD

[0001] Embodiments of the present disclosure generally relate to multimodal polyethylene compositions, and geomembranes including the same.INTRODUCTION

[0002] Polyethylene compositions can be formed into useful articles such as films, liners, and geomembranes. Polymeric sheets such as geomembranes can be used as part of containment structures to provide barrier protection to the migration of materials into the environment. When extruding polyethylene compositions to form articles, it is generally desirable for the polyethylene compositions to have a lower molecular weight and lower viscosity, particularly under shear conditions for articles such as geomembranes, so that the polyethylene compositions can be more easily processed. However, lower molecular weight and viscosity can compromise slow growth crack resistance properties such as environmental stress crack resistance (ESCR) and notched constant tensile load (NCTL). These properties are of particular importance in polyethylene compositions used to form articles like geomembranes because longevity and anti-leak performance is required to address potential environmental protection concerns. In addition to processability and slow growth crack performance, polyethylene compositions formed into articles such as geomembranes must balance a number of other properties, including, for example, melt strength, tensile elongation, puncture resistance, low temperature flexibility, strong corrosion resistance, and good weldability.

[0003] Attempts to achieve a desirable balance of properties from polyethylene compositions include the introduction of narrow molecular weight distribution catalysts in dual reactor systems to produce multimodal polyethylene compositions. With multimodal compositions in dual reactor systems, it is possible, for example, to increase stress crack resistance by increasing the molecular weight or increasing the comonomer content of the high molecular weight fraction, which in turn decreases density. Altering properties of the higher molecular fraction, however, can lead to undesirable behavior such as an increase in viscosity. Moreover, producing multimodal compositions in a dual or multiple reactor system can be cost prohibitive and less sustainable due to the need for multiple reactors and multiple feeds, among other things. Accordingly, there remains a need for polyethylene compositions that can be produced in a single reactor and can exhibit a desirable balance of properties such as superiorslow growth crack resistance, good processability, and maintained tensile elongation properties.SUMMARY

[0004] Embodiments of the present disclosure meet one or more of the foregoing needs by providing a polyethylene composition that can be produced in a single reactor and can achieve desirable processability and slow growth crack resistance for applications such as geomembranes.

[0005] Disclosed herein is a multimodal polyethylene composition. In a first aspect, the multimodal polyethylene composition comprises from 20 to 45 wt.% of a first polyethylene component, based on the total weight of the multimodal polyethylene composition, and a second polyethylene component, wherein the first polyethylene component has a molecular weight greater than the second polyethylene component, and wherein the multimodal polyethylene composition has the following: a density of from 0.933 to 0.945 g / cm3; a high flow melt index (I21) of from 7.5 to 18.0 g / 10 min; a molecular weight distribution (Mw / Mn), measured by absolute GPC, of less than 15.0; and a strain hardening modulus of at least 50 MPa.

[0006] Disclosed herein are geomembranes. In a second aspect, the geomembrane comprises the multimodal composition according to the first aspect.

[0007] These and other embodiments are described in more detail in the Detailed Description.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 depicts a GPC chromatogram of an example according to the embodiments disclosed herein.DETAILED DESCRIPTION

[0009] Aspects of the disclosed multimodal polyethylene compositions are described in more detail below. The multimodal polyethylene compositions are suitable for use in forming geomembranes and can have a wide variety of applications, including, for example, liners, hoses, or the like.

[0010] As used herein, the term “polymer” means a polymeric compound prepared by polymerizing monomers, whether of the same or a different type. The generic term polymer thus embraces the term homopolymer (employed to refer to polymers prepared from only one type of monomer), and the term copolymer or interpolymer. Trace amounts of impurities (for example, catalyst residues) may be incorporated into and / or within the polymer. A polymer may be a single polymer, a polymer blend, or a polymer mixture, including mixtures of polymers that are formed in situ during polymerization.

[0011] As used herein, the term “copolymer” means a polymer formed by the polymerization reaction of at least two structurally different monomers. The term “copolymer” is inclusive of terpolymers.

[0012] As used herein, the terms “polyethylene” or “ethylene-based polymer” shall mean polymers comprising a majority amount (>50 mol %) of units which have been derived from ethylene monomer. This includes polyethylene homopolymers and copolymers (meaning units derived from two or more comonomers). The terms “ethylene-based polymer” and “polyethylene” may be used interchangeably. Generally, polyethylene may be produced in gas-phase, fluidized bed reactors, liquid phase slurry process reactors, or liquid phase solution process reactors, using a heterogeneous catalyst system, such as Ziegler-Natta catalyst, a homogeneous catalyst system, comprising Group 4 transition metals and ligand structures such as metallocene, non-metallocene metal-centered, heteroaryl, heterovalent aryloxyether, phosphinimine, and others. Combinations of heterogeneous and / or homogeneous catalysts also may be used in either single reactor or dual reactor configurations.

[0013] As used herein, the term “composition” refers to a mixture of materials which comprise the composition, as well as reaction products and decomposition products formed from the materials of the composition. By virtue of the composition disclosed herein having a first polyethylene and a second polyethylene component, it is a composition.

[0014] The term “multimodal” means compositions that can be characterized by having at least two (2) polyethylene components or subcomponents with different molecular weights and / or different comonomer contents. The term “bimodal” means compositions that can be characterized by having two (2) polyethylene components or subcomponents with different molecular weights and / or different comonomer contents. All GPC measurement values (e.g.,Mw, Mn, Mz) recited herein are Absolute GPC measurements provided in accordance with the test methods described below.

[0015] The terms “comprising,” “including,” “having,” and their derivatives, are not intended to exclude the presence of any additional component, step or procedure, whether or not the same is specifically disclosed. In order to avoid any doubt, all compositions claimed through use of the term “comprising” may include any additional additive, adjuvant, or compound, whether polymeric or otherwise, unless stated to the contrary. In contrast, the term, “consisting essentially of’ excludes from the scope of any succeeding recitation any other component, step or procedure, excepting those that are not essential to operability. The term “consisting of’ excludes any component, step or procedure not specifically delineated or listed.

[0016] Disclosed herein are multimodal polyethylene compositions. The multimodal polyethylene composition according to embodiments disclosed herein comprises a first polyethylene component and a second polyethylene component. The first polyethylene component has a molecular weight greater than the second polyethylene component. In some embodiments, the multimodal composition is a bimodal polyethylene composition (i.e., it has only two polyethylene components). In other embodiments, the multimodal composition has two, three, or more polyethylene components with different molecular weights and / or different comonomer contents.

[0017] In some embodiments, the first polyethylene component is a copolymer of ethylene and one or more alpha-olefin comonomers. In some embodiments, the second polyethylene component is also a copolymer of ethylene and one or more alpha-olefin comonomers. The alpha-olefin comonomers can have 3 to 10 carbon atoms or 3 to 8 carbon atoms. Exemplary alpha-olefin comonomers include, but are not limited to, propylene, 1 -butene, 1 -pentene, 1- hexene, 1 -heptene, 1 -octene, 1 -nonene, 1 -decene, and 4-m ethyl- 1 -pentene. In some embodiments, the alpha-olefin comonomers may be selected from the group consisting of 1- butene, 1 -hexene, and 1 -octene, or from the group consisting of 1 -butene and 1 -hexene, or from the group consisting of 1 -hexene and 1 -octene. In some embodiments, the first polyethylene component is a non-metallocene catalyzed ethylene copolymer. In some embodiments, the second polyethylene component is a metallocene catalyzed ethylene copolymer. As discussed below, the first polyethylene component and the second polyethylene component can be polymerized in a single reactor in the presence of bimodal catalyst system. In some embodiments, the first polyethylene component is a copolymer comprising ethylene and 1-hexene. In some embodiments, the second polyethylene component is a copolymer comprising ethylene and 1 -hexene. In some embodiments, the first polyethylene component and second polyethylene component comprise 1 -hexene or are void of comonomers other than 1 -hexene, or void of comonomers other 1 -hexene or 1 -octene.

[0018] The multimodal polyethylene composition comprises from 20 to 45 wt.% of a first polyethylene component, based on the total weight of the multimodal polyethylene composition. All individual values and subranges from 20 to 45 wt.% are disclosed and included herein. For example, the multimodal polyethylene composition can comprise from a lower limit of 20, 25, 30, 35, or 40 wt.% to an upper limit of 45, 40, 35, 30, or 25 wt.% of the first polyethylene component, based on the total weight of the multimodal polyethylene composition. In some embodiments, the multimodal polyethylene composition comprises from 55 to 80 wt.% of the second polyethylene component, based on the total weight of the multimodal polyethylene composition. For example, in some embodiments, the multimodal polyethylene composition can comprise from 55, 60, 65, 70, or 75 wt.% to 80, 75, 70, 65, or 60 wt.% of the second polyethylene component, based on the total weight of the multimodal polyethylene composition.

[0019] The multimodal polyethylene composition has a density of from 0.933 to 0.945 g / cm3. In some embodiments, the multimodal polyethylene composition can have a density from a lower limit of 0.934, 0.935, 0.936, 0.937, 0.938, 0.939, 0.940, 0.941, 0.942, 0.943, or 0.944 g / cm3to an upper limit of 0.935, 0.936, 0.937, 0.938, 0.939, 0.940, 0.941, 0.942, 0.943, 0.944, or 0.945 g / cm3.

[0020] The multimodal polyethylene composition has a high flow melt index (I21) of from 7.5 to 18.0 g / 10 min. In some embodiments, multimodal polyethylene composition can have a high flow melt index (I21) of from a lower limit of 7.5, 8.0. 8.5, 9.0, 9.5, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0 or 16.5 g / 10 min to an upper limit of 8.0. 8.5, 9.0, 9.5, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0,16.5, or 18.0 g / 10 min.

[0021] The multimodal polyethylene composition has a molecular weight distribution (Mw / Mn), measured by absolute GPC, of less than 15.0. In some embodiments, the multimodal polyethylene composition has a molecular weight distribution of less than 14.0, or less than 13.0, or less than 10.0. In some embodiments, the multimodal polyethylenecomposition has a molecular weight distribution of greater than 4.0, greater than 5.0, greater than 7.0, or greater than 10.0.

[0022] The multimodal polyethylene composition has a strain hardening modulus of at least 50 MPa. In some embodiments, the multimodal polyethylene composition can have a strain hardening modulus of at least 51, 52, 53, 54, 55, 56, or 57 MPa. In some embodiments, the multimodal polyethylene composition can have a strain hardening modulus of no more than 75, 74, 73, 72, 71, or 70 MPa. Without being bound by theory, the combination of strain hardening modulus in combination with the other characteristics, including weight percent of the firs polyethylene component, high flow melt index and molecular weight distribution, results in a composition having desirable processability and slow growth crack resistance suitable for use in geomembrane applications.

[0023] In some embodiments, the multimodal polyethylene composition has a PENT value as measured according to ASTM F1472 of at least 5,000 hours. In some embodiments, the multimodal polyethylene composition can have a PENT value as measured according to ASTM F1472 of at least 5,500 hours, at least 6,000 hours, or at least 6,300 hours.

[0024] In some embodiments, the multimodal polyethylene composition can have a I21 / I5 of greater than 15, or greater than 17, or greater than 19, or greater than 21, or greater than 23. In some embodiments, the multimodal polyethylene composition can have a I21 / I5 of less than 40, or less than 35, or less than 30.

[0025] In some embodiments, the multimodal polyethylene composition can have a I21 / I2 of greater than 50, or greater than 55, or greater than 60, or greater than 70, or greater than 80, or greater than 100, or greater than 110, or greater than 120, or greater than 130, or greater than 140, or greater than 150. In some embodiments the multimodal polyethylene composition can have a I21 / I2 of no more than 200, or no more than 180.

[0026] In some embodiments, the multimodal polyethylene composition can have a Mz of greater than 1,600,000 g / mol or greater than 1,700,000 g / mol, or greater than 1,800,000 g / mol. In some embodiments, the multimodal polyethylene composition can have a Mz of no more than 3,000,000 g / mol, or no more than 2,500,000 g / mol, or no more than 2,000,000 g / mol.

[0027] In some embodiments, the multimodal polyethylene composition can have a melt strength of greater than 12.0 cN, or greater than 12.5 cN, or greater than 13.0 cN. In someembodiments, the multimodal polyethylene composition can have a melt strength of no more than 25.0 cN, or no more than 20.0 cN.

[0028] In some embodiments, the multimodal polyethylene composition can have a molecular weight distribution from Absolute GPC, where the Absolute GPC molecular weight distribution has a first peak and a shoulder in a range of Log(molecular weight) of 3.5 to 7.0, wherein the first peak corresponds to the second polyethylene component and the shoulder corresponds to the first polyethylene component. The “shoulder” is defined herein and identified as a part of the GPC chromatogram subsequent to the first peak, whereby the slope increases to a point of less than zero (i.e., the curve does not form a second peak whereby the slope reaches zero) and then decreases (i.e., so as to form a “shoulder” visually on the GPC chromatogram). Figure 1 discloses a GPC chromatogram displaying a first peak and shoulder. A person of ordinary skill in the art understands that the GPC chromatogram relates to the molecular architecture of the multimodal polyethylene composition and is in part a result of the particular catalyst system used to form the composition. Without being bound by theory, it has been found that, according to embodiments disclosed herein, a particular type of catalyst is suitable for producing the multimodal polyethylene composition in a single reactor and, relatedly, delivering a specific GPC chromatogram, whereas prior art compositions with similar features or different catalyst systems cannot be made in a single reactor system, deliver the specific GPC chromatogram, and / or deliver the desirable properties disclosed herein. Also, without being bound by theory, the multimodal polyethylene composition has a first polyethylene component, as represented by the shoulder in the GPC chromatogram, which contributes to the compositions balance of desirable slow growth crack resistance, processability, and maintenance or improvement of mechanical and tensile properties. In some embodiments, the Absolute GPC chromatogram has a first peak in a range of Log(molecular weight) of from 3.5 to 5.8 or from 3.5 to 5.5.

[0029] In some embodiments, the multimodal polyethylene composition has a complex viscosity at 100 rad / s of less than 2,700 Pa.s, less than 2,500 Pa.s, or less than 2,300 Pa.s, or less than 2,100 Pa.s. The complex viscosity at 100 rad / s can be an indication of the processability of the multimodal polyethylene compositions for applications described herein.

[0030] The first and second polyethylene components can have distinct Mw, Mn, Mz, and Mw / Mn from each other. In some embodiments, the first polyethylene component (i.e., the component having a higher molecular weight than the second polyethylene component orHMW) can have at least one of the following: a weight average molecular weight (Mw) of greater than 800,000 g / mol or greater than 900,000 g / mol, and / or less than 100,000 g / mol; a number average molecular weight (Mn) of greater than 200,000 g / mol and / or less than 400,000 g / mol; a Mz value of greater than 2,000,000 g / mol, or greater than 2,200,000 g / mol, and / or less than 3,000,000 g / mol, or less than 2,800,000 g / mol; and a molecular weight distribution (Mw / Mn) in the range of from 2.0 to 6.0, or from 3.0 to 5.0, or from 3.5 to 4.5. In some embodiments, the second polyethylene component (i.e., the component having a lower molecular weight than the first polyethylene component or LMW) can have at least one of the following: a weight average molecular weight (Mw) of less than 100,000 g / mol, or less than 75,000 g / mol, and / or greater than 30,000 g / mol, or greater than 40,000 g / mol; a number average molecular weight (Mn) of less than 50,000 g / mol, or less than 40,000 g / mol, or less than 30,000 g / mol, and / or greater than 10,000 g / mol or greater than 20,000 g / mol; a Mz value of less than 200,000 g / mol, or less than 150,000 g / mol, and / or greater than 50,000 g / mol or greater than 75,000 g / mol; a molecular weight distribution (Mw / Mn) in the range of from 1.0 to 3.0, or from 1.5 to 3.0. The Mw, Mn, Mz, and Mw / Mn values of each of the components are measured in accordance with the test methods described below. In some embodiments, the first polyethylene component has a weight average molecular weight distribution at least 600,000 g / mol, at least 700,000 g / mol, at least 800,000 g / mol greater than the second polyethylene component. In some embodiments, the first polyethylene component has a Mw / Mn at least 1.0 greater than the second polyethylene component. In some embodiments, the first polyethylene component has a number average molecular weight (Mn) at least 150,000 g / mol greater than the second polyethylene component.

[0031] In some embodiments, when the multimodal polyethylene composition is formed into a geomembrane in accordance with the geomembrane fabrication method described below, the geomembrane can have a notched constant tensile load failure time at 30% yield stress, as measured according to ASTMD5397, of greater than 1,500 hours, or greater than 2,000 hours, or greater than 3,000 hours.

[0032] In some embodiments, in addition to the properties above, when the multimodal polyethylene composition is used to form a geomembrane as described in the geomembrane fabrication method described below, the geomembrane can exhibit at least one of the following properties: a yield strength of at least 2,300 psi (or at least 2,400 psi); a break strength of at least 4,000 psi (or at least 4,500 psi, or at least 49,00 psi); a yield elongation of at least 13% (orat least 14% or at least 14.5%); a break elongation of at least 700% (or at least 720%); a puncture strength of at least 2,000 Ib / inch (or at least 2,100 Ib / inch).

[0033] The multimodal polyethylene composition of the present invention is suitable for fabrication of geomembranes. A geomembrane is a low permeability barrier polymeric sheet used in any geotechnical applications to regulate the migration of a liquid or gas in industrial systems. Geomembranes can be used to receive or transmit fluids, gas, or solids and used to protect water or the environment from impurities or pollution. Geomembranes can be used as a hydraulic barrier in purification processes and as a gas barrier. Geomembranes generally must meet certain regulatory or industrial thresholds for performance such as Geosynthetic Institute’s GM- 13 standard.

[0034] In some embodiments, the multimodal polyethylene composition is formed into a geomembrane meeting or exceeding Geosynthetic Institute’s GM- 13 standard. The features of the multimodal high density polyethylene composition, including its density, melt flow properties, elongation properties, and modulus properties, contribute to making it particularly suitable for geomembranes. The geomembrane may be extruded by methods known to those skilled in the art and may be formed by methods known to those skilled in the art. For example, a geomembrane may formed by sealing, via heat or other means, polymeric sheets formed from polyethylene compositions, along one or more overlapping seams, to create a long, wide sheet with fused overlaps. A geomembrane may also be formed from polymeric sheets that are welded together.

[0035] The geomembrane according to embodiments disclosed herein may be a monolayer geomembrane and may comprise suitable additives used for extrusion or geomembrane applications. Such additives include colorants and materials suitable to protect the composition from adverse environmental effect, for example, oxidation during extrusion or degradation under service conditions. Suitable additives include process stabilizers, antioxidants, and pigments. In some embodiments, the geomembrane may comprise multiple layers wherein at least one layer comprises the composition according to the present invention. Additional polyolefins may be coextruded with other polymers such as polyamides, ethylene vinyl alcohol copolymers and polyesters.

[0036] The process for making a geomembrane comprises forming a multimodal high density polyethylene composition according to embodiments disclosed herein and extrudingthe multimodal polyethylene composition to form a geomembrane, wherein the multimodal polyethylene is formed by polymerizing ethylene monomer and an alpha-olefin comonomer in the presence of a bimodal catalyst system in a single gas phase polymerization (GPP); wherein the bimodal catalyst system consists essentially of a metallocene catalyst, a single-site nonmetallocene catalyst that is a bis((alkyl-substituted phenylamido)ethyl)amine catalyst, optionally a host material, and optionally an activator; wherein the host material, when present, is selected from at least one of an inert hydrocarbon liquid and a solid support; wherein the metallocene catalyst is an activation reaction product of contacting an activator with a metalligand complex of formula (Rt 2Cp)((alkyl)1 3Indenyl)MX2, wherein Ris hydrogen, methyl, or ethyl; each alkyl independently is a (C1-C4)alkyl; M is titanium, zirconium, or hafnium; and each X is independently a halide, a (Cxto C20)alkyl, a (C7to C20)aralkyl, a (Cxto C6)alkyl- substituted (C6to C12)aryl, or a (Ctto C6)alkyl-substituted benzyl; and wherein the bis((alkyl- substituted phenylamido)ethyl)amine catalyst is an activation reaction product of contacting an activator with a bis((alkyl-substituted phenylamido)ethyl)amine ZrR^, wherein each R1is independently selected from F, Cl, Br, I, benzyl, -CH2Si(CH3)3, a (C1-C5)alkyl, and a (C2- Cs)alkenyl. In some embodiments the metal-ligand complex of formula (I) is a compound wherein M is zirconium (Zr); R is H, alternatively methyl, alternatively ethyl; and each X is Cl, methyl, or benzyl; and thebis((alkyl-substituted phenylamido)ethyl)amineMR12 is abis(2- (pentamethylphenylamido)ethyl)-amine zirconium complex of formula (II):,(II), wherein M is Zr and each R1independently is Cl, Br, a (Ci toC2o)alkyl, a (Ci to C6)alkyl-substituted (Ce-Ci2)aryl, benzyl, or a (Ci to C6)alkyl-substituted benzyl. In some aspects the compound of formula (II) is bis(2- (pentamethylphenylamido)ethyl)-amine zirconium dibenzyl. In some embodiments each X and R1 is independently Cl, methyl, 2,2-dimethylpropyl, -CH2Si(CH3)3, or benzyl. In someembodiments the metal-ligand complex of formula (I) is (cyclopentadienyl)(l,5- dimethylindenyl)zirconium dimethyl. In some embodiments the metal-ligand complex of formula (I) is (methylcyclopentadienyl)(l,3-dimethyl-4,5,6,7-tetrahydroindenyl)zirconium dimethyl.Process for Making the Multimodal Composition

[0037] In some embodiments, the multimodal polyethylene composition is made by polymerizing ethylene and an alpha-olefin in the presence of a bimodal catalyst system in a single gas phase polymerization (GPP); wherein the bimodal catalyst system consists essentially of a metallocene catalyst, a single-site non-metallocene catalyst that is a bis((alkyl- substituted phenylamido)ethyl)amine catalyst, optionally a host material, and optionally an activator; wherein the host material, when present, is selected from at least one of an inert hydrocarbon liquid and a solid support; wherein the metallocene catalyst is an activation reaction product of contacting an activator with a metal-ligand complex of formula (Ri- 2Cp)((alkyl)i-3lndenyl)MX2, wherein R is hydrogen, methyl, or ethyl; each alkyl independently is a (Ci-C4)alkyl; M is titanium, zirconium, or hafnium; and each X is independently a halide, a (Ci to C2o)alkyl, a (C7 to C2o)aralkyl, a (Ci to C6)alkyl-substituted (Ce to Cn)aryl, or a (Ci to C6)alkyl-substituted benzyl; and wherein the bis((alkyl-substituted phenylamido)ethyl)amine catalyst is an activation reaction product of contacting an activator with a bis((alkyl-substituted phenylamido)ethyl)amine ZrR wherein each R1is independently selected from F, Cl, Br, I, benzyl, -CH2Si(CH3)3, a (Ci-Cs)alkyl, and a (C2-Cs)alkenyl.

[0038] In some embodiments, the multimodal polyethylene composition may be a polymerized reaction product of an ethylene monomer and at least one C3-C12 alpha-olefin comonomer. For example, embodiments of the composition may be a polymerized reaction product of an ethylene monomer and 1 -butene, 1 -hexene, or both. Alternatively, embodiments of the polyethylene composition may be a polymerized reaction product of an ethylene monomer and 1 -butene, 1 -octene, or both. Embodiments of the polyethylene composition may also be a polymerized reaction product of an ethylene monomer and 1 -hexene, 1 -octene, or both. In some embodiments, the C3-C12 alpha-olefin comonomer may not be propylene.

[0039] In some embodiments, the multimodal polyethylene composition may be produced with a catalyst system in a single reactor. As used herein, a “catalyst system” may comprise a main catalyst, a trim catalyst, and, optionally, at least one activator. Catalyst systems may alsoinclude other components, such as supports, and are not limited to a main catalyst, a trim catalyst, and, optionally, at least one activator. Embodiments of the catalyst system may comprise a main catalyst and a metallocene trim catalyst. Embodiments of the catalyst system may also comprise one or more additives commonly used in the art of olefin polymerization. For example, embodiments of the catalyst system may comprise one or more continuity additives, flow aids, and anti-static aids. In embodiments, the reactor may be a gas phase reactor, although slurry phase reactors may also be used.

[0040] Embodiments of the catalyst system may comprise at least one catalyst for producing the first polyethylene component (a higher molecular weight component) by polymerization (sometimes referred to herein as an “HMW catalyst”), and at least one catalyst compound for producing the second polyethylene component (a lower molecular weight component) by polymerization (sometimes referred to herein as an “LMW catalyst”).

[0041] Embodiments of the catalyst system may be referred to as a “bimodal catalyst system.” Such a catalyst system produces a polyethylene composition having separate, identifiable high molecular weight and low molecular weight distributions. The term “bimodal catalyst system” may comprise any formulation, mixture, or system that comprises at least two different catalyst compounds, each having the same or a different metal group, but generally different ligands or catalyst structure, including a “dual catalyst.” Alternatively, each different catalyst compound of the bimodal catalyst system resides on a single support particle, in which case a dual catalyst is considered to be a supported catalyst. However, the term “bimodal catalyst system” also broadly comprises a system or mixture in which one of the catalysts resides on one collection of support particles, and another catalyst resides on another collection of support particles. In such embodiments, the two supported catalysts are introduced to a single reactor, either simultaneously or sequentially, and polymerization is conducted in the presence of the two collections of supported catalysts. Alternatively, the bimodal catalyst system may comprise a mixture of unsupported catalysts in slurry form.

[0042] The single gas phase polymerization reactor may be a fluidized-bed gas phase polymerization (FB-GPP) reactor and the effective polymerization conditions may comprise conditions (a) to (e): (a) the FB-GPP reactor having a fluidized resin bed at a bed temperature from 80 to 110 degrees Celsius (°C), alternatively from 85 to 108°C, alternatively from 90 to 108°C, alternatively from 94 to 107°C, alternatively from 95 °C to 106°C; (b) the FB-GPP reactor receiving feeds of respective independently controlled amounts of ethylene, 1 -alkenecharacterized by a 1-alkene-to-ethylene (Cx / C2) molar ratio, the bimodal catalyst system, optionally a trim catalyst comprising a solution in an inert hydrocarbon liquid of a dissolved amount of unsupported form of the metallocene catalyst made from the metal-ligand complex of formula (I) and activator, optionally hydrogen gas (H2) characterized by a hydrogen-to- ethylene (H2 / C2) molar ratio or by a weight parts per million H2to mole percent C2ratio (H2ppm / C2mol%), and optionally an induced condensing agent (ICA) comprising a (C5- Cio)alkane(s), e.g., isopentane; wherein the (C6 / C2) molar ratio is from 0.0001 to 0.1, alternatively from 0.0002 to 0.03, alternately from 0.003 to 0.02; wherein when H2is fed, the H2 / C2molar ratio is from 0.0001 to 0.1, alternatively from 0.0002 to 0.0020, alternately from 0.0003 to 0.001, or the H2ppm / C2mol% ratio is from 1 to 1,000, alternatively from 2.0 to 20.0, alternately from 3.0 to 10.0; and wherein when the ICA is fed, the concentration of ICA in the reactor is from 1 to 25 mole percent (mol%), alternatively from 4 to 20 mol%, based on total moles of ethylene, 1 -alkene, and ICA in the reactor. The average residence time of the copolymer in the reactor may be from 1 to 6 hours, alternatively from 2 to 4 hours. A continuity additive may be used in the FB-GPP reactor during polymerization.

[0043] The bimodal catalyst system may be characterized by an inverse response to bed temperature such that when the bed temperature is increased, the viscoelastic property value of the resulting composition is decreased, and when the bed temperature is decreased, the viscoelastic property value of the resulting bimodal poly(ethylene-co-l -alkene) copolymer is increased. The bimodal catalyst system may be characterized by an inverse response to the H2 / C2ratio such that when the H2 / C2ratio is increased, the viscoelastic property value of the resulting bimodal poly(ethylene-co-l -alkene) copolymer is decreased, and when the H2 / C2ratio is decreased, the viscoelastic property value of the resulting composition is increased.

[0044] The composition comprises the higher molecular weight component (HMW component) and the lower molecular weight component (LMW component). In an illustrative pilot plant process for making the bimodal polyethylene polymer, a fluidized bed, gas-phase polymerization reactor (“FB-GPP reactor”) having a reaction zone dimensioned as 304.8 mm (twelve inch) internal diameter and a 2.4384 meter (8 feet) in straight-side height and containing a fluidized bed of granules of the composition. Configure the FB-GPP reactor with a recycle gas line for flowing a recycle gas stream. Fit the FB-GPP reactor with gas feed inlets and polymer product outlet. Introduce gaseous feed streams of ethylene and hydrogen togetherwith 1-alkene comonomer (e.g., 1-hexene) below the FB-GPP reactor bed into the recycle gas line. Measure the (C5-C20)alkane(s) total concentration in the gas / vapor effluent by sampling the gas / vapor effluent in the recycle gas line. Return the gas / vapor effluent (other than a small portion removed for sampling) to the FB-GPP reactor via the recycle gas line.

[0045] Polymerization operating conditions are any variable or combination of variables that may affect a polymerization reaction in the GPP reactor or a composition or property of a bimodal polyethylene copolymer made thereby. The variables may include reactor design and size, catalyst composition and amount; reactant composition and amount; molar ratio of two different reactants; presence or absence of feed gases such as H2and / or O2, molar ratio of feed gases versus reactants, absence or concentration of interfering materials (e.g., H2O), average polymer residence time in the reactor, partial pressures of constituents, feed rates of monomers, reactor bed temperature (e.g., fluidized bed temperature), nature or sequence of process steps, time periods for transitioning between steps. Variables other than that / those being described or changed by the method or use may be kept constant.

[0046] In operating the method, control individual flow rates of ethylene (“C2”), 1-alkene (“Cx”, e.g., 1-hexene or “C6” or “Cx” wherein x is 6), and any hydrogen (“H2”) to maintain a fixed comonomer to ethylene monomer gas molar ratio (Cx / C2, e.g., C6 / C2) equal to a described value, a constant hydrogen to ethylene gas molar ratio (“H2 / C2”) equal to a described value, and a constant ethylene (“C2”) partial pressure equal to a described value (e.g., 1,000 kPa). Alternately, individual flow rates of ethylene (“C2”), 1-alkene (“Cx”, e.g., 1-hexene or “C6” or “Cx” wherein x is 6), and any hydrogen (“H2”) to maintain a fixed comonomer to ethylene monomer gas flow ratio (Cx / C2flow ratio, e.g., kg C6 / kg C2FR) equal to a described value, a constant hydrogen to ethylene gas flow ratio (“H2 / C2flow ratio” e.g., kg H2 / kg C2FR) equal to a described value, and a constant ethylene (“C2”) partial pressure equal to a described value (e.g., 1,000 kPa). Measure concentrations of gases by an in-line gas chromatograph to understand and maintain composition in the recycle gas stream. Maintain a reacting bed of growing polymer particles in a fluidized state by continuously flowing a make-up feed and recycle gas through the reaction zone. Use a superficial gas velocity of 0.43 to 0.76 meter per second (m / sec) (1.4 to 2.5 feet per second (ft / sec)). Operate the FB-GPP reactor at a total pressure of about 2000 to about 2413 kilopascals (kPa) (about 290 to about 350 pounds persquare inch-gauge (psig)) and at a described reactor bed temperature RBT. Maintain the fluidized bed at a constant height by withdrawing a portion of the bed at a rate equal to the rate of production of particulate form of the bimodal polyethylene polymer, which production rate may be from 4,500 to 90,000 kilograms per hour (kg / hr), alternatively 9,000 to 80,000 kg / hr. Remove the produced bimodal poly(ethylene-co-l -alkene) copolymer semi-continuously via a series of valves into one or more fixed volume chambers, convey the resin to a product purge bin and contact the removed composition stepwise with a suitable purging medium to remove solubilized hydrocarbons and then contact the resin with a stream of humidified nitrogen (N2) gas to deactivate any trace quantities of residual catalysts.

[0047] The bimodal catalyst system may be fed into the polymerization reactor(s) in “dry mode” or “wet mode”, alternatively dry mode, alternatively wet mode. The dry mode is a dry powder or granules. The wet mode is a suspension in an inert liquid such as mineral oil or the (C5-C2o)alkane(s). In some aspects the composition is made by contacting the metal-ligand complex of formula (I) and the single-site non-metallocene catalyst with at least one activator in situ in the GPP reactor in the presence of olefin monomer and comonomer (e.g., ethylene and 1 -alkene) and growing polymer chains. These embodiments may be referred to herein as in .s / 7z / -contacting embodiments. In other aspects the metal-ligand complex of formula (I), the single-site non-metallocene catalyst, and the at least one activator are pre-mixed together for a period of time to make an activated bimodal catalyst system, and then the activated bimodal catalyst system is injected into the GPP reactor, where it contacts the olefin monomer and growing polymer chains. These latter embodiments pre-contact the metal-ligand complex of formula (I), the single-site non-metallocene catalyst, and the at least one activator together in the absence of olefin monomer (e.g., in absence of ethylene and alpha-olefin) and growing polymer chains, i.e., in an inert environment, and are referred to herein as pre-contacting embodiments. The pre-mixing period of time of the pre-contacting embodiments may be from 1 second to 10 minutes, alternatively from 30 seconds to 45 minutes, alternatively from 5 minutes to 30 minutes. The ICA may be fed separately into the FB-GPP reactor or as part of a mixture also containing the bimodal catalyst system. The ICA may be a (Cn-C2o)alkane, alternatively a (C5-Cio)alkane, alternatively a (C5)alkane, e.g., pentane or 2-methylbutane; a hexane; a heptane; an octane; a nonane; a decane; or a combination of any two or more thereof. The aspects of the polymerization method that use the ICA may be referred to as being an induced condensing mode operation (ICMO). ICMO is described in US 4,453,399; US4,588,790; US 4,994,534; US 5,352,749; US 5,462,999; and US 6,489,408. The concentration of ICA in the reactor is measured indirectly as total concentration of vented ICA in recycle line using gas chromatography by calibrating peak area percent to mole percent (mol%) with a gas mixture standard of known concentrations of ad rem gas phase components.

[0048] The method uses a gas-phase polymerization (GPP) reactor, such as a stirred-bed gas phase polymerization reactor (SB-GPP reactor) or a fluidized-bed gas-phase polymerization reactor (FB-GPP reactor), to make the composition disclosed herein. Such gas phase polymerization reactors and methods are generally well-known in the art. For example, the FB-GPP reactor / method may be as described in US 3,709,853; US 4,003,712; US 4,011,382; US 4,302,566; US 4,543,399; US 4,882,400; US 5,352,749; US 5,541,270; EP-A- 0 802 202; and Belgian Patent No. 839,380. These SB-GPP and FB-GPP polymerization reactors and processes either mechanically agitate or fluidize by continuous flow of gaseous monomer and diluent the polymerization medium inside the reactor, respectively. Other useful reactors / processes contemplated include series or multistage polymerization processes such as described in US 5,627,242; US 5,665,818; US 5,677,375; EP-A-0 794 200; EP-B1-0 649 992; EP-A-0 802 202; and EP-B-634421.

[0049] The polymerization conditions may further include one or more additives such as a chain transfer agent or a promoter. The chain transfer agents are well known and may be alkyl metal such as diethyl zinc. Promoters are known such as in US 4,988,783 and may include chloroform, CFCI3, tri chloroethane, and difluorotetrachloroethane. Prior to reactor start up, a scavenging agent may be used to react with moisture and during reactor transitions a scavenging agent may be used to react with excess activator. Scavenging agents may be a trialkylaluminum. Gas phase polymerizations may be operated free of (not deliberately added) scavenging agents. The polymerization conditions for gas phase polymerization reactor / method may further include an amount (e.g., 0.5 to 200 ppm based on all feeds into reactor) of a static control agent and / or a continuity additive such as aluminum stearate or polyethyleneimine. The static control agent may be added to the FB-GPP reactor to inhibit formation or buildup of static charge therein. The static control agent may be added to the FB- GPP reactor prior at a preset concentration prior to initiating the catalyst feed.

[0050] The method may use a fluidized bed gas phase polymerization reactor FB-GPP that comprises a reactor vessel containing a fluidized bed of a powder of the bimodal polyethylene polymer, and a distributor plate disposed above a bottom head, and defining a bottom gas inlet,and having an expanded section, or cyclone system, at the top of the reactor vessel to decrease amount of resin fines that may escape from the fluidized bed. The expanded section defines a gas outlet. The FB-GPP further comprises a compressor blower of sufficient power to continuously cycle or loop gas around from out of the gas outlet in the expanded section in the top of the reactor vessel down to and into the bottom gas inlet of the FB-GPP and through the distributor plate and fluidized bed. The FB-GPP further comprises a cooling system to remove heat of polymerization and maintain the fluidized bed at a target temperature. Compositions of gases such as ethylene, 1 -alkene (e.g., 1 -hexene), and hydrogen being fed into the Pilot Reactor are monitored by an in-line gas chromatograph in the cycle loop in order to maintain specific concentrations thereof that define and enable control of polymer properties. The bimodal catalyst system may be fed as a slurry or dry powder into the FB-GPP from high pressure devices, wherein the slurry is fed via a pump and the dry powder is fed via a metered disk. The bimodal catalyst system typically enters the fluidized bed in the lower 1 / 3 of its bed height. The FB-GPP further comprises a way of monitoring the weight of the fluidized bed and isolation ports (Product Discharge System) for discharging the powder of bimodal polyethylene polymer from the reactor vessel in response to an increase of the fluidized bed weight as polymerization reaction proceeds.

[0051] In some embodiments the FB-GPP reactor is a commercial scale reactor such as a UNIPOL™ reactor, which is available from Univation Technologies, LLC, a subsidiary of The Dow Chemical Company, Midland, Michigan, USA. In some embodiments, the bimodal catalyst system used in the method consists essentially of the metallocene catalyst and the bis((alkyl-substituted phenylamido)ethyl)amine ZrR^ catalyst, and, optionally, the host material; wherein the host material, when present, is selected from the at least one of the inert hydrocarbon liquid and the solid support; wherein the metallocene catalyst is an activation reaction product of contacting an activator with a metal-ligand complex of formula (I) described earlier; and wherein the bis((alkyl-substituted phenylamido)ethyl)amine catalyst is an activation reaction product of contacting an activator with the bis((alkyl-substituted phenylamido)ethyl)amine ZrR^ catalyst described earlier. The phrase consists essentially of means that the bimodal catalyst system and method using same is free of a third single-site catalyst (e.g., a different metallocene, a different amine catalyst, or a biphenylphenolic catalyst) and free of non-single site catalysts (e.g., free of Ziegler-Natta or chromium catalysts). The bimodal catalyst system may also consist essentially of the host material and / or at least oneactivator species, which is a by-product of reacting the metallocene catalyst or non-metallocene molecular catalyst with the activator(s).

[0052] Without being bound by theory, it is believed that the bis((alkyl-substituted phenylamido)ethyl)amine catalyst (e.g., the bis(2-(pentamethylphenylamido)ethyl)amine zirconium dibenzyl) is a substantially single-site non-metallocene catalyst that is effective for making the HMW component of the bimodal poly(ethylene-co-l -alkene) copolymer and the metallocene catalyst (made from the metal-ligand complex of formula (I)) is a substantially single-site catalyst that is independently effective for making the LMW component of the composition. The molar ratio of the two catalysts of the bimodal catalyst system may be based on the molar ratio of their respective catalytic metal atom (M, e.g., Zr) contents, which may be calculated from ingredient weights thereof or may be analytically measured. The molar ratio of the two catalysts may be varied in the polymerization method by way of using a different bimodal catalyst system formulation having different molar ratio thereof or by using a same bimodal catalyst system and the trim catalyst. Varying the molar ratio of the two catalysts during the polymerization method may be used to vary the particular properties of the bimodal poly(ethylene-co-l -alkene) copolymer within the limits of the described features thereof.

[0053] The catalysts of the bimodal catalyst system may be unsupported when contacted with an activator, which may be the same or different for the different catalysts. Alternatively, the catalysts may be disposed by spray-drying onto a solid support material prior to being contacted with the activator(s). The solid support material may be uncalcined or calcined prior to being contacted with the catalysts. The solid support material may be a hydrophobic fumed silica (e.g., a fumed silica treated with dimethyldichlorosilane). The bimodal (unsupported or supported) catalyst system may be in the form of a powdery, free-flowing particulate solid. Support material. The support material may be an inorganic oxide material. The terms “support” and “support material” are the same as used herein and refer to a porous inorganic substance or organic substance. In some embodiments, desirable support materials may be inorganic oxides that include Group 2, 3, 4, 5, 13 or 14 oxides, alternatively Group 13 or 14 atoms. Examples of inorganic oxide-type support materials are silica, alumina, titania, zirconia, thoria, and mixtures of any two or more of such inorganic oxides. Examples of such mixtures are silica-chromium, silica-alumina, and silica-titania.

[0054] The inorganic oxide support material is porous and has variable surface area, pore volume, and average particle size. In some embodiments, the surface area is from 50 to 1000square meter per gram (m^ / g) and the average particle size is from 20 to 300 micrometers (pm). Alternatively, the pore volume is from 0.5 to 6.0 cubic centimeters per gram (cm^ / g) and the surface area is from 200 to 600 m^ / g. Alternatively, the pore volume is from 1.1 to 1.8 cm^ / g and the surface area is from 245 to 375 m^ / g. Alternatively, the pore volume is from 2.4 to 3.7 cm^ / g and the surface area is from 410 to 620 m^ / g. Alternatively, the pore volume is from 0.9 to 1.4 cm^ / g and the surface area is from 390 to 590 m^ / g. Each of the above properties are measured using conventional techniques known in the art.

[0055] The support material may comprise silica, alternatively amorphous silica (not quartz), alternatively a high surface area amorphous silica (e.g., from 500 to 1000 m^ / g). Such silicas are commercially available from several sources including the Davison Chemical Division of W.R. Grace and Company (e.g., Davison 952 and Davison 955 products), and PQ Corporation (e.g., ES70 product). The silica may be in the form of spherical particles, which are obtained by a spray-drying process. Alternatively, MS3050 product is a silica from PQ Corporation that is not spray-dried. As procured, these silicas are not calcined (i.e., not dehydrated). Silica that is calcined prior to purchase may also be used as the support material.

[0056] Prior to being contacted with a catalyst, the support material may be pre-treated by heating the support material in air to give a calcined support material. The pre-treating comprises heating the support material at a peak temperature from 350° to 850° C., alternatively from 400° to 800°C., alternatively from 400° to 700°C., alternatively from 500° to 650°C. and for a time period from 2 to 24 hours, alternatively from 4 to 16 hours, alternatively from 8 to 12 hours, alternatively from 1 to 4 hours, thereby making a calcined support material. The support material may be a calcined support material.

[0057] The method may further employ a trim catalyst. The trim catalyst may be any one of the aforementioned metallocene catalysts made from the metal-ligand complex of formula (I) and activator. For convenience the trim catalyst is fed in solution in a hydrocarbon solvent (e.g., mineral oil or heptane). The hydrocarbon solvent may be the ICA. The trim catalyst may be made from the same metal-ligand complex of formula (I) as that used to make the metallocene catalyst of the bimodal catalyst system, alternatively the trim catalyst may be made from a different metal-ligand complex of formula (I) than that used to make the metallocene catalyst of the bimodal catalyst system. The trim catalyst may be used to vary, within limits, the amount of the metallocene catalyst used in the method relative to the amount of the single-site non-metallocene catalyst of the bimodal catalyst system. Each catalyst of the bimodal catalyst system is activated by contacting it with an activator. Any activator may be the same or different as another and independently may be a Lewis acid, a non-coordinating ionic activator, or an ionizing activator, or a Lewis base, an alkylaluminum, or an alkylaluminoxane (alkylalumoxane). The alkylaluminum may be a trialkylaluminum, alkylaluminum halide, or alkylaluminum alkoxide (diethylaluminum ethoxide). The trialkylaluminum may be trimethyl aluminum, triethylaluminum (“TEA1”), tripropylaluminum, or tris(2- methylpropyl)aluminum. The alkylaluminum halide may be diethylaluminum chloride. The alkylaluminum alkoxide may be diethylaluminum ethoxide. The alkylaluminoxane may be a methylaluminoxane (MAO), ethylaluminoxane, 2-methylpropyl-aluminoxane, or a modified methylaluminoxane (MMAO). Each alkyl of the alkylaluminum or alkylaluminoxane independently may be a (C C7)alkyl, alternatively a (Ci-Cg)alkyl, alternatively a (C C4)alkyl. The molar ratio of activator’s metal (Al) to a particular catalyst compound’s metal (catalytic metal, e.g., Zr) may be 1000: 1 to 0.5: 1, alternatively 300: 1 to 1 : 1, alternatively 150: 1 to 1 : 1. Suitable activators are commercially available.

[0058] Once the activator and the catalysts of the bimodal catalyst system contact each other, the catalysts of the bimodal catalyst system are activated and activator species may be made in situ. The activator species may have a different structure or composition than the catalyst and activator from which it is derived and may be a by-product of the activation of the catalyst or may be a derivative of the by-product. The corresponding activator species may be a derivative of the Lewis acid, non-coordinating ionic activator, ionizing activator, Lewis base, alkylaluminum, or alkylaluminoxane, respectively. An example of the derivative of the byproduct is a methylaluminoxane species that is formed by devolatilizing during spray-drying of a bimodal catalyst system made with methylaluminoxane.

[0059] Each contacting step between activator and catalyst independently may be done either in a separate vessel outside the GPP reactor (e.g., outside the FB-GPP reactor) or in a feed line to the GPP reactor. In option (a) the bimodal catalyst system, once its catalysts are activated, may be fed into the GPP reactor as a dry powder, alternatively as a slurry in a nonpolar, aprotic (hydrocarbon) solvent. The activator(s) may be fed into the reactor in “wet mode” in the form of a solution thereof in an inert liquid such as mineral oil or toluene, in slurry mode as a suspension, or in dry mode as a powder. Each contacting step may be done at the same or different times.

[0060] TEST METHODS

[0061] Density

[0062] Density is measured in accordance with ASTM D792, and expressed in grams / cm3(g / cm3or g / cc).

[0063] Melt Flow Rate (12, 15 and 121)

[0064] The procedure described in ASTM D1238 is followed to determine the melt flow rate. Method B of ASTM D1238 is used. Samples are ran with loads of 21.6 kg, 5.0 kg or 2.16 kg (i.e., 121, 15 or 12, respectively).

[0065] Absolute GPC (Molecular Weight Distribution)

[0066] The chromatographic system consists of a PolymerChar GPC-IR (Valencia, Spain) high temperature GPC chromatograph equipped with an internal IR5 infra-red detector (IR5) and 4-capillary viscometer (DV) coupled to a Precision Detectors (Now Agilent Technologies) 2-angle laser light scattering (LS) detector Model 2040. For all absolute Light scattering measurements, the 15 degree angle is used for measurement. The autosampler oven compartment was set at 160° Celsius and the column and detector compartment were set at 150° Celsius. The columns used were 4 Agilent “Mixed A” 30cm 20-micron linear mixed-bed columns. The chromatographic solvent used was 1,2,4 tri chlorobenzene and contained 200 ppm of butylated hydroxytoluene (BHT). The solvent source was nitrogen sparged. The injection volume used was 200 microliters and the flow rate was 1.0 milliliters / minute.

[0067] The total plate count of the GPC column set was performed with decane which was introduced into blank sample via a micropump controlled with the PolymerChar GPC-IR system. The plate count for the chromatographic system should be greater than 18,000 for the 4 Agilent “Mixed A” 30cm 20-micron linear mixed-bed columns.

[0068] Samples were prepared in a semi-automatic manner with the PolymerChar “Instrument Control” Software, wherein the samples were weight-targeted at 2 mg / ml, and the solvent (contained 200ppm BHT) was added to a pre nitrogen-sparged septa-capped vial, via the PolymerChar high temperature autosampler. The samples were dissolved for 2 hours at 160° Celsius under “low speed” shaking.

[0069] In order to monitor the deviations over time, a flowrate marker (decane) was introduced into each sample via a micropump controlled with the PolymerChar GPC-IR system. This flowrate marker (FM) was used to linearly correct the pump flowrate (Flowrate(nominal)) for each sample by RV alignment of the respective decane peak within the sample (RV(FM Sample)) to that of the decane peak within the narrow standards calibration (RV(FM Calibrated)). Any changes in the time of the decane marker peak are then assumed to be related to a linear-shift in flowrate (Flowrate(effective)) for the entire run. After calibrating the system based on a flow marker peak, the effective flowrate (with respect to the narrow standards calibration) is calculated as Equation 1. Processing of the flow marker peak was done via the PolymerChar GPCOne™ Software. Acceptable flowrate correction is such that the effective flowrate should be within + / -0.5% of the nombiinal flowrate.

[0070] Flowrate(effective) = Flowrate(nominal) * (RV(FM Calibrated) / RV(FM Sample)) (EQI)

[0071] For the determination of the viscometer and light scattering detector offsets from the IR5 detector, the Systematic Approach for the determination of multi -detector offsets is done in a manner consistent with that published by Balke, Mourey, et. al. (Mourey and Balke, Chromatography Polym. Chpt 12, (1992)) (Balke, Thitiratsakul, Lew, Cheung, Mourey, Chromatography Polym. Chpt 13, (1992)), optimizing triple detector log (MW and IV) results from a linear homopolymer polyethylene standard (3.5 > Mw / Mn > 2.2) with a molecular weight in the range of 115,000 to 125,000 g / mol to the narrow standard column calibration results from the narrow standards calibration curve using PolymerChar GPCOne™ Software.

[0072] The absolute molecular weight data was obtained in a manner consistent with that published by Zimm (Zimm, B.H., J. Chem. Phys., 16, 1099 (1948)) and Kratochvil (Kratochvil, P., Classical Light Scattering from Polymer Solutions, Elsevier, Oxford, NY (1987)) using PolymerChar GPCOne™ software. The overall injected concentration, used in the determination of the molecular weight, was obtained from the mass detector area and the mass detector constant, derived from a suitable linear polyethylene homopolymer, or one of the polyethylene standards of known weight-average molecular weight. The calculated molecular weights (using GPCOne™) were obtained using a light scattering constant, derived from one or more of the polyethylene standards mentioned below, and a refractive index concentration coefficient, dn / dc, of -0.104. Generally, the mass detector response (IR5) and the light scattering constant (determined using GPCOne™) should be determined from a linear standardwith a molecular weight in excess of about 50,000 g / mole. The viscometer calibration (determined using GPCOne™) can be accomplished using the methods described by the manufacturer, or, alternatively, by using the published values of suitable linear standards, such as Standard Reference Materials (SRM) 1475 (available from National Institute of Standards and Technology (NIST)). A viscometer constant (obtained using GPCOne™) is calculated which relates specific viscosity area (DV) and injected mass for the calibration standard to its intrinsic viscosity. The chromatographic concentrations are assumed low enough to eliminate addressing 2nd viral coefficient effects (concentration effects on molecular weight).

[0073] The absolute weight average molecular weight (MW(Abs)) is obtained (using GPCOne™) from the Area of the Light Scattering (LS) integrated chromatogram (factored by the light scattering constant) divided by the mass recovered from the mass constant and the mass detector (IR5) area. The molecular weight and intrinsic viscosity responses are linearly extrapolated at chromatographic ends where signal to noise becomes low (using GPCOne™). Other respective moments, Mn(Abs) and Mz(Abs) are be calculated according to the following equations:

[0074] Deconvolution of Absolute GPC Chromatogram

[0075] Deconvolution of Absolute GPC Chromatogram - The fitting of the absolute GPC chromatogram into a first component and second component fraction was accomplished using a Flory distribution which was broadened with a normal distribution function as follows: For the log M axis, 601 equally-spaced Log(M) points, spaced by 0.01, were established between2 and 8 representing the molecular weight range between 100 and 100,000,000 where Log is the logarithm function to the base 10. At any given Log (M), the population of the Flory distribution was in the form of Eq. 2:where Mw is the absolute weight-average molecular weight of the Flory distribution and M is the specific x-axis absolute molecular weight point, (10A[Log(M)]). The Flory distribution weight fraction was broadened at each 0.01 equally-spaced log(M) index according to a normal distribution function, of width expressed in Log(M), s; and current M index expressed as Log(M), m.

[0077] It should be noted that before and after the spreading function has been applied that the area of the distribution (dWf / dLogM) as a function of Log(M) is normalized to unity. Two weight-fraction distributions, dWf i and dWf2, for LMW and HMW components or components 1 and 2 were expressed with two unique Mw target values, Mwi and Mw2 and with overall component compositions Ai and A2. Both distributions were broadened with the same width, 5. The two distributions were summed as follows:where: A1+A2 = 1.

[0078] The weight fraction result of the measured absolute GPC molecular weight distribution was interpolated along 601 log M points using a 2nd-order polynomial. Microsoft Excel™ 2010 Solver was used to minimize the sum of squares of residuals for the equally-spaces range of 601 LogM points between the interpolated chromatographically determined molecular weight distribution and the two broadened Flory distribution components (.siand 2), weighted with their respective component compositions, Ai and A2. The iteration starting values for the components are as follows:Component 1 : Mwi = 60,000, s = 0.200, and Ai = 0.7.Component 2: Mw2 = 700,000, s = 0.200, and A2 = 1 - Ai.(Note 5i = 52 and Ai + A2= 1).

[0079] The bounds for components 1 and 2 are such that 5 is constrained such that 5 > 0.001, yielding an Mw / Mn of approximately 2.00 and 5 < 0.550, yielding a Mw / Mn of approximately 5.71. The composition, Ai, is constrained between 0.000 and 1.000. The Mwi is constrained between 2,500 and 2,000,000. The composition, A2, is constrained between0.000 and 1.000. The Mw2 is constrained between 2,500 and 2,000,000. The “GRG Nonlinear” engine was selected in Excel Solver™ and precision was set at 0.00001 and convergence was set at 0.0001. The solutions were obtained after convergence (in all cases shown, the solution converged within 60 iterations). The high molecular weight percent is the equal to the output of A2 from the above description.

[0080] Pennsylvania Notch Test (PENT)

[0081] PENT is measured in accordance with ASTM F1473 at 80°C and at 2.4 MPa. Results are reported in hours.

[0082] Strain Hardening Modulus

[0083] The ISO 18488 standard is followed to determine the strain hardening modulus. The samples are compression molded at 180°C with a preheating time of 5 to 15 minutes followed by 5 MPa full-pressure application for 5 minutes. A controlled 15°C / min cooling rate is used in the last step. The compression molded sheet is conditioned at 120°C for one hour followed by controlled cooling at a rate of 2°C / min to RT. Tensile bars are punched out of the compression molded sheets. The tensile test is conducted at 80°C. A non-contact extensometer is used to record the strain. As specified in ISO 18488, Neo-Hookean Strain Measure (NHSM) and the true stress plot is used to calculate the slope between a draw ratio of 8 and 12. If the failure occurred before a draw ratio of 12, then the draw ratio corresponding to the failure strain is considered as the upper limit of the slope. If the failure occurred before a draw ratio of 8.5, then the test is considered invalid.

[0084] Melt Strength

[0085] Melt strength is determined with a Gbttfert Rheotens unit model 71.9 in combination with a capillary rheometer (such as Rheotester 2000 from Gbttfert, e.g.). A polymer melt (about 20-30 grams, pellets) is extruded through a capillary die with a flat entrance angle (180 degrees) with a capillary diameter of 2.0 mm and an aspect ratio (capillary length / capillary diameter) of 15. After equilibrating the samples at 190° C. for 10 minutes, molten polymer is extruded out of the die at a constant volume flow rate corresponding to a theoretical average exit velocity of 9.5 mm / s and an apparent wall shear rate of 38.2 s'1. The wheels of the Rheotens were at standard laboratory temperature. The distance between the die exit and the wheels was 100 mm. The extruded strand was drawn by a set of standard smoothwheels with a 0.4 mm gap. The wheels were accelerated at a rate of 2.4 mm / s2and the tensile force recorded as a function of take-up speed until the filament broke. The velocity at break is a measure for the drawability of the polymer melt. Melt strength is defined as the plateau value of the force-velocity curve just before the strand broke and is reported in Newtons (N).

[0086] Complex Viscosity

[0087] Complex viscosities (q*) are calculated using Dynamic Mechanical Spectroscopy and are reported in pascal-seconds (Pa-s). Samples are compression-molded into a 9.75 inch x 10.25 inch x 1.85 mm thick rectangular plaque at 190 °C, for 6.5 minutes, under 25,000 psi pressure, in air. The sample is then taken out of the press, and allowed to cool. The resulting plaque is subjected to a 25mm diameter die cutter to extract disk-shaped samples for rheological testing. A constant temperature frequency sweep is performed using a TA Instruments “Advanced Rheometric Expansion System (ARES),” equipped with 25 mm (diameter) parallel plates, under a nitrogen purge. Samples are placed on the plate and allowed to melt for five minutes at 190 °C. The plates are then closed to a gap of “1.8 mm,” the samples trimmed (extra sample that extends beyond the circumference of the “25 mm diameter” plate was removed), and then the tests are started. The method had an additional five minute delay built in to allow for temperature equilibrium. The tests are performed at 190°C over a frequency range of from 0.1 radians per second (rad / s) to 100 rad / s at a constant strain amplitude of 10%.

[0088] Tensile / Tear / Puncture / NCTL on Geomembrane

[0089] Tensile, tear, and puncture tests are performed on geomembranes formed from the inventive and comparative multimodal compositions according to GM-13 standards for MDPE membranes. Tear strength is measured in accordance with ASTM D1004; puncture resistance is measured in accordance with ASTM D4833; single-point NCTL is measured in accordance with ASTM D5397; tensile properties (i.e., tensile yield strength, elongation at break, yield stress, and tensile strength) are measured in accordance with ASTM D6693.

[0090] Geomembrane Fabrication

[0091] Geomembranes are fabricated on Collin cast line from certain of the inventive and comparative multimodal compositions. Melt temperature is set at 240°C and the output rate is about 20 Ib / hr. A 60 mil thick and 8-inch-wide membrane is produced. A low winder speed of about 0.7 m / min is used to minimize orientation in machine direction.

[0092] EXAMPLES

[0093] Materials Used

[0094] The following materials are included in the examples discussed below.

[0095] DOW™ DGDA-5310 NT, a unimodal ethylene copolymer medium density polyethylene is used as Comparative Example (CE) 1 and is commercially available from The Dow Chemical Company (Midland, MI).

[0096] CONTINUUM™ DGDA-2420 NT, a bimodal ethylene copolymer medium density polyethylene is used as Comparative Example (CE) 2 and is commercially available from The Dow Chemical Company (Midland, MI).

[0097] Preparation of Comparative Examples 3-5

[0098] Example bimodal polyethylene compositions designated as Comparative Examples (CE) 3-5, are produced via gas phase polymerization in a single-reactor. A main catalyst was fed to a polyethylene reactor, commercially available as UNIPOL™ from Univation Technologies, via a 0.125 inch injection tube. The 0.125 inch injection tube was centered within a 0.250 inch shroud tube where a flow of isopentane and nitrogen was fed to assist in catalyst dispersion. A trim catalyst was also fed to the polyethylene reactor via the same 0.125 inch injection tube at a rate sufficient to provide the desired resin flow index. The reactor gas composition was controlled by metering the feeds to the polyethylene reactor at rates sufficient to maintain the desired ethylene partial pressure, molar ratio of comonomer to ethylene (C2), molar ratio of hydrogen gas (H2) to ethylene (C2), and amount of isopentane. An additive, commercially available as CA-300 from Univation Technologies, was fed separately to the polyethylene reactor at a rate sufficient to maintain an additive concentration of about 35-55 parts per million by weight (ppmw) based on the ethylene feed rate to the reactor. The polyethylene reactor temperature was maintained at a desired temperature and the reactor residence time was from about 1.8 hours to 2.5 hours. The reactor bed weight was maintained by discharging granular resin into a discharge tank, which was purged with nitrogen before being dumped into a fiberpack and purged again with a mixture of nitrogen and steam. Table 1 A lists the polymerization conditions for CE 3-5.

[0099] Table 1AaSpray-dried mixture of bis(2-pentamethylphenylamido)ethyl)amine zirconium dibenzyl, (1,3 -dimethyl -4, 5,6,7- tetrahydroindene)(methyl cyclopentadienyl)zirconium dimethyl, methylalumoxane (MAO), and fumed silica, commercially available as CAB-O-SIL® TS-610 from Cabot Corporation, in a mineral oil slurrybSpray-dried mixture of bis(2-pentamethylphenylamido)ethyl)amine zirconium dibenzyl, (cyclopentadienyl)(l ,5- dimethylindenyl)zirconium dimethyl, methylalumoxane (MAO), and fumed silica, commercially available as CAB-O-SIL® TS-610 from Cabot Corporation, in a mineral oil slurrycMixture of 0.04 wt.% (1,3 -dim ethyl- 4,5,6,7-tetrahydroindene)(methyl cyclopentadienyl)zirconium dimethyl bis(n-butylcyclopentadienyl)zirconium dimethyl in isopentanedMixture of 0.04 wt.% (cyclopentadienyl)(l,5-dimethylindenyl)zirconium dimethyl in isopentane

[0100] Inventive Examples 1 and 2 and Comparative Example 6

[0101] Bis(2-(pentamethylphenylamido)ethyl)amine zirconium dibenzyl is the compound of formula (II) wherein M is Zr and each R is benzyl (“Bn”). It may be made by procedures described in the art or obtained from Univation Technologies, LLC, Houston, Texas, USA, a wholly-owned entity of The Dow Chemical Company, Midland, Michigan, USA. Representative Group 15-containing metal compounds, including bis(2-(pentamethylphenylamido)ethyl)amine zirconium dibenzyl, and preparation thereof can be as discussed and described in U.S. Pat. Nos. 5,318,935, 5,889,128, 6,333,389; 6,271,325; 6,689,847, and 9,981,371; and WO Publications WO 99 / 01460, WO 98 / 46651; WO 2009 / 064404; WO 2009 / 064452; and WO 2009 / 064482.

[0102] (II) CA-300: a continuity additive available from Univation Technologies, LLC. Added to gas phase polymerization reactor to decrease static buildup.

[0103] 1 -hexene Comonomer: H2C=C(H)(CH2)3CH3. Comonomer co-polymerized with ethylene in the gas phase polymerization reactor. Ethylene (“C2”): CH2=CH2. Monomer polymerized in the gas phase polymerization reactor. When copolymerized with 1 -hexene, makes ethylene / 1 -hexene copolymer.

[0104] ICA: a mixture consisting essentially of at least 95%, alternatively at least 98% of 2-methylbutane (isopentane) and minor constituents that at least include pentane (043(042)3043). Molecular hydrogen gas: H2. Added to the gas phase polymerization reactor to alter molecular weight of the polyethylene produced therein. Mineral oil: Sonneborn HYDROB RITE 380 PO White. Used as a carrier liquid for feeding catalyst into a gas phase polymerization reactor.

[0105] Preparation 1 : synthesis of 3,6-dimethyl-U7-indene, of the formula. In a glove box, a 250-mL two-neck container fitted with a thermometer (side neck) and a solids addition funnel, was charged with tetrahydrofuran (25 mL) and methylmagnesium bromide (2 equivalents, 18.24 mL, 54.72 mmol). The contents of thecontainer were cooled in a freezer set at -35 °C for 40 minutes; when removed from the freezer, the contents of the container were measured to be -12 °C. While stirring, indanone [5-Methyl- 2,3-dihydro-lH-inden-l-one (catalog #HC-2282)] (1 equivalent, 4.000 g, 27.36 mmol) was added to the container as a solid in small portions and the temperature increased due to exothermic reaction; additions were controlled to keep the temperature at or below room temperature. Once the addition was complete, the funnel was removed, and the container was sealed (SUBA). The sealed container was moved to a fume hood (with the contents already at room temperature) and put under a nitrogen purge, then stirred for 3 hours. The nitrogen purge was removed, diethyl ether (25 mL) was added to the container to replace evaporated solvent, and then the reaction was cooled using an acetone / ice bath. A HC1 (15% volume) solution (9 equivalents, 50.67 mL, 246.3 mmol) was added to the contents of the container very slowly using an addition funnel, the temperature was maintained below 10 °C. Then, the contents of the container were warmed up slowly for approximately 12 hours (with the bath in place). Then, the contents of the container were transferred to a separatory funnel and the phases were isolated. The aqueous phase was washed with diethyl ether (3 times 25 mL). The combined organic phases were then washed with sodium bicarbonate (50 mL, saturated aqueous solution), water (50 mL), and brine (50 mL). The organic phase was dried over magnesium sulfate, filtered and the solvent removed by rotary evaporator. The resulting dark oil, confirmed as product by NMR, was dissolved in pentane (25 mL), then filtered through a short silica plug (pre-wetted with pentane) that was capped with sodium sulfate. Additional pentane (25-35 mL) was used to flush the plug, then were combined with the first. The solution was dried by rotary evaporator resulting in 2.87 g (74% yield) of 3,6-dimethyl-lH-indene that was confirmed as product by NMR. 1H NMR (C6D6): 5 7.18 (d, 1H), 7.09 (s, 1H), 7.08 (d, 1H), 5.93 (m, 1H), 3.07 (m, 2H), 2.27 (s, 3H), 2.01 (q, 3H).

[0106] Preparation 2: synthesis of (cyclopentadienyl)(l,5-dimethylindenyl)zirconium dimethyl, which is a compound of formula (I) wherein R is H and each X is methyl. In a glovebox under an anhydrous inert gas atmosphere (anhydrous nitrogen or argon gas), 3,6- dimethyl-lH-indene (1.000g, 6.94 moles) in dimethoxy ethane (10 mL) was added to a 120 mL (4-ounce (oz)) container, which was then capped, and the contents of the container were chilled to -35 °C. w-butyllithium (1.6M hexanes, 4.3 mL, 0.0069 mole) was added to the container and the contents were stirred for approximately 3 hours while heat was removed to maintain the contents of the container near -35 °C. Reaction progress was monitored by dissolving a small aliquot in d8-THF for NMR analysis; when the reaction was complete, solidcyclopentadienyl zirconium trichloride (CpZrC13) (1.821 g) was added in portions to the contents of the container while stirring. Reaction progress was monitored by dissolving a small aliquot in d8-THF for ' H NMR analysis; the reaction was complete after approximately 3 hours and the contents of the container were stirred for approximately 12 more hours. Then, methylmagnesium bromide (3.0M in ether, 4.6 mL) was added to the contents of the container, after the addition the contents of the container were stirred for approximately 12 hours. Then, solvent was removed in vacuo and the product was extracted into hexane (40 mL) and filtered through diatomaceous earth, washed with additional hexane (30 mL) and then dried in vacuo to provide the cyclopentadienyl(l,5-dimethylindenyl) zirconium dimethyl. (Cyclopentadienyl)(l,5-dimethylindenyl)zirconium dimethyl was confirmed by proton nuclear magnetic resonance spectroscopy ('H NMR) analysis. 'H NMR (CgDg): 5 7.26 (d, 1H), 6.92 (d, 1H), 6.83 (dd, 1H), 5.69 (d, 1H), 5.65 (m, 1H), 5.64 (s, 5H), 2.18 (s, 3H), 2.16 (s, 3H), - 0.34 (s, 3H), -0.62 (s, 3H).

[0107] Due to the rules of IUPAC nomenclature it is believed that the dimethyl numbering in the molecule 3,6-dimethyl-lJT-indene becomes, after deprotonation thereof, becomes in the conjugate anion 1,5-dimethylindenyl.

[0108] Preparation 3: Preparation of Bimodal Catalyst System 1 (AFS-BMCS1). Slurry 70.3 parts by weight of treated fumed silica (CABOSIL TS-610) in 1000 parts by weight of toluene, followed by adding 171 parts by weight of a 30 wt% solution of methylaluminoxane (MAO) in toluene, 3.54 parts by weight of the bis(2-(pentamethylphenylamido)ethyl)amine zirconium dibenzyl and 0.229 parts by weight of cyclopentadienyl(l,5-dimethylindenyl) zirconium dimethyl of Preparation 2 to give a mixture. Using a spray dryer set at 160° C. and with an outlet temperature at 70° to 80° C., introduce the mixture into an atomizing device of the spray dryer to produce droplets of the mixture, which are then contacted with a hot nitrogen gas stream to evaporate the liquid from the mixture to give a powder. Separate the powder from the gas mixture in a cyclone separator and discharge the separated powder into a container to give the Bimodal Catalyst System 1 (“BMCS1”) as a fine powder. Slurry the resultant powder form of BMCS1 to give an activator formulation slurry form of BMCS1 (“AFS-BMCS1”) of 22 wt% solids in 10 wt% isoparaffin fluid and 68 wt% mineral oil.

[0109] Preparation 4: preparation of Trim Catalyst Solution 1 (“TCS1”) comprising a trim solution of cyclopentadienyl(l,5-dimethylindenyl) zirconium dimethyl in n-hexane andisopentane. Charge (cyclopentadienyl)(l,5-dimethylindenyl)zirconium dimethyl of Preparation 2 and n-hexane into a first cylinder. Charge the resulting solution of (cyclopentadienyl)(l,5-dimethylindenyl)zirconium dimethyl solution in hexane from the first cylinder into a 106 liter (L; 28 gallons) second cylinder. The second cylinder contained 310 grams of 1.07 wt % (cyclopentadienyl)(l,5-dimethylindenyl)zirconium dimethyl. Added 7.98 kg (17.6 pounds) of high purity isopentane to the 106 L cylinder to yield the Trim Catalyst Solution 1 of 0.04 wt % (cyclopentadienyl)(l,5-dimethylindenyl)zirconium dimethyl in n- hexane and isopentane.

[0110] Polymerization Procedure. For Inventive Examples 1, 2 and CE 6 described below, copolymerized ethylene and 1-hexene using the Activator Formulation Slurry form of Bimodal Catalyst System 1 (AFS-BMCS1) and a controlled relative amount of the Trim Catalyst Solution 1 (TCS1) in a fluidized bed-gas phase polymerization (FB-GPP) reactor having a distribution grid to make an embodiment of the bimodal poly(ethylene-co-l -alkene) copolymer that is a bimodal poly(ethylene-co- 1-hexene) copolymer. Trim Catalyst Solution 1 (TCS1) mixed with isopentane carrier contacted Activator Formulation Slurry form of Bimodal Catalyst System 1 (AFS-BMCS1) in line on way to reactor, mixed with static mixer prior to injection into reactor with nitrogen carrier. Catalyst was fed via a 0.125 inch injection tube. The 0.125 inch injection tube was centered within a 0.250 inch shroud tube where a flow of isopentane and nitrogen was fed to assist in catalyst dispersion. A trim catalyst was also fed to the polyethylene reactor via the same 0.125 inch injection tube at a rate sufficient to provide the desired resin flow index. The FB-GPP reactor had a 0.35 meter (m) internal diameter and 2.3 m bed height and a fluidized bed composed of polymer granules. Flowed fluidization gas through a recycle gas loop comprising sequentially a recycle gas compressor and a shell-and- tube heat exchanger having a water side and a gas side. The fluidization gas flows through the compressor, then the water side of the shell-and-tube heat exchanger, then into the FB-GPP reactor below the distribution grid. Fluidization gas velocity in the bed is about 0.58 to 0.61 meter per second (m / s, 1.9 to 2.0 feet per second). The fluidization gas then exits the FB-GPP reactor through a nozzle in the top of the reactor, and is recirculated continuously through the recycle gas loop. Maintained a constant fluidized bed temperature of 95° C. by continuously adjusting the temperature of the water on the shell side of the shell-and-tube heat exchanger. Introduced feed streams of ethylene, nitrogen, and hydrogen together with the 1-hexene comonomer into the recycle gas line. Operated the FB-GPP reactor at a total pressure of about 2413 kPa gauge, and vented reactor gases to a flare to control the total pressure. Adjustedindividual flow rates of ethylene, nitrogen, hydrogen and the 1 -hexene to maintain their respective gas composition targets. Set ethylene partial pressure to 1.52 megapascal (MPa, 220 pounds per square inch (psi)), and set the Cg / C2 molar ratio and the H2 / C2 molar ratio per Table 1. Maintained isopentane (ICA) concentration at about 10.5 mol%. Average copolymer residence time was about 2.3 to 2.5 hours. Measured concentrations of all gasses using an online gas chromatograph. Maintained the fluidized bed at constant height by withdrawing a portion of the bed at a rate equal to the rate of formation of particulate product bimodal poly(ethylene-co-l -hexene) copolymer. Product was removed semi-continuously via a series of valves into a fixed volume chamber. A nitrogen purge removed a significant portion of entrained and dissolved hydrocarbons in the fixed volume chamber. After purging, the product was discharged from the fixed volume chamber into a fiber pack for collection. The product was further treated with a small stream of humidified nitrogen to deactivate any trace quantities of residual catalyst and cocatalyst. Set the ratio feed of trim catalyst solution TCS1 to the feed of the bimodal catalyst system AFS-BMCS1 to adjust the HLMI (I21) of the produced bimodal poly(ethylene-co-l -hexene) copolymer in the reactor to target values. Set the catalyst feeds at rates sufficient to maintain a production rate of about 17 to about 21 kg / hour (about 38 to about 46 Ibs / hr) of the bimodal poly(ethylene-co-l -hexene) copolymer.

[0111] Inventive Example 1 to 2 (IE1, IE2) and Comparative Example 6 (CE6): synthesized an embodiment of the inventive copolymer using the Polymerization Procedure described above, wherein 1-alkene comonomer is 1-hexene, and Activator Formulation Slurry form of Bimodal Catalyst System 1 (AFS-BMCS1) and Trim Catalyst Solution 1 (TCS1). The polymerization conditions and process results are described in Table 1 below.

[0112] Table 1 : Polymerization Conditions of IE1, IE2 and CE6.

[0113] Polyethylene compositional properties are measured in accordance with the test methods described above. Geomembranes are formed from certain of the polyethylene compositions in accordance with the geomembrane fabrication process described above.

[0114] Table 2A - Properties of Comparative Examples 1-5

[0115] Table 2B - Properties of IE 1 and 2 and CE 6

[0116] As can be seen from Tables 2A and 2B, the inventive examples display a desirable balance of PENT, strain hardening, melt strength, and processability as indicated by viscosity, melt flow rates, and molecular weight distribution over the comparative examples, and provide desirable tensile properties for when the compositions are formed into geomembranes.

Claims

We Claim:

1. A multimodal polyethylene composition comprising from 20 to 45 wt.% of a first polyethylene component, based on the total weight of the multimodal polyethylene composition, and a second polyethylene component, wherein the first polyethylene component has a molecular weight greater than the second polyethylene component, and wherein the multimodal polyethylene composition has the following:(a) a density of from 0.933 to 0.945 g / cm3;(b) a high flow melt index (I21) of from 7.5 to 18.0 g / 10 min;(c) a molecular weight distribution (Mw / Mn), measured by absolute GPC, of less than 15.0; and(d) a strain hardening modulus of at least 50 MPa.

2. The multimodal polyethylene composition of any preceding claim, wherein the multimodal composition has a PENT value as measured according to ASTM Fl 472 of at least 5,000 hours.

3. The multimodal polyethylene composition of any preceding claim, wherein the composition has a I21 / I5 of greater than 15.

4. The multimodal polyethylene composition of any preceding claim, wherein the composition has a I21 / I2 of greater than 50.

5. The multimodal polyethylene composition of any preceding claim, wherein the composition has a Mz of greater than 1,600,000 g / mol.

6. The multimodal polyethylene composition of any preceding claim, wherein the composition has a melt strength of greater than 12.0 cN.

7. The multimodal polyethylene composition of any preceding claim, wherein the composition has a complex viscosity at 100 rad / s of less than 2,700 Pa.s.

8. The multimodal polyethylene composition of any preceding claim, wherein the composition is a bimodal polyethylene composition.

9. The multimodal polyethylene composition of any preceding claim, wherein the composition has a molecular weight distribution from Absolute GPC, where the Absolute GPC molecular weight distribution has a first peak and a shoulder in a range of Log(molecular weight) of 3.5 to 7.0, wherein the first peak corresponds to the second polyethylene component and the shoulder corresponds to the first polyethylene component.

10. The multimodal polyethylene composition of any preceding claim, wherein the composition, when formed into a geomembrane, the geomembrane exhibits at least one of the following properties: a yield strength of at least 2,300 psi (or at least 2,400 psi); a break strength of at least 4,000 psi (or at least 4,500 psi, or at least 49,00 psi); a yield elongation of at least 13% (or at least 14% or at least 14.5%); a break elongation of at least 700% (or at least 720%); a puncture strength of at least 2,000 Ib / inch (or at least 2,100 Ib / inch).

11. The multimodal polyethylene composition of any preceding claim, wherein the composition, when formed into a geomembrane, the geomembrane has a notched constant tensile load failure time at 30% yield stress, as measured according to ASTMD5397 of greater than 1,000 hours.

12. The multimodal polyethylene composition of any preceding claim, wherein the composition is made in a single reactor in the presence of a bimodal catalyst system, wherein the bimodal catalyst system consists essentially of a metallocene catalyst, a single-site nonmetallocene catalyst that is a bis((alkyl-substituted phenylamido)ethyl)amine catalyst, optionally a host material, and optionally an activator; wherein the host material, when present, is selected from at least one of an inert hydrocarbon liquid and a solid support; wherein the metallocene catalyst is an activation reaction product of contacting an activator with a metalligand complex of formula (R^.2Cp)((alkyl)j_3lndenyl)MX2, wherein R is hydrogen, methyl, or ethyl; each alkyl independently is a (Cj-C^alkyl; M is titanium, zirconium, or hafnium; and each X is independently a halide, a (Cj to C2o)alkyl, a (C7 to C2o)aralkyl, a (Cj to Cg)alkyl- substituted (Cg to C ^2)aryl, or a (C | to C^alkyl-substituted benzyl; and wherein the bis((alkyl- substituted phenylamido)ethyl)amine catalyst is an activation reaction product of contacting anactivator with a bis((alkyl-substituted phenylamido)ethyl)amine ZrR^, wherein each R1 is independently selected from F, Cl, Br, I, benzyl, -CH2Si(CH3)3, a (Cj-C5)alkyl, and a (C2- C5)alkenyl.

13. The multimodal polyethylene composition of any preceding claim, wherein the first polyethylene component and second polyethylene component comprise 1 -hexene.

14. A geomembrane comprising the multimodal polyethylene composition of any preceding claim.

15. The geomembrane of claim 14, wherein the geomembrane has a notched constant tensile load failure time at 30% yield stress, as measured according to ASTMD5397, of greater than 1,500 hours.

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