Title - BIMODAL MEDIUM-DENSITY POLYETHYLENE COMPOSITIONS SUITABLE FOR USE AS MICRO-IRRIGATION DRIP TAPES

Abstract

Bimodal medium-density polyethylene (MDD) compositions and micro-irrigation drip tapes incorporating them are provided. MDD compositions can be extruded at high line speeds while maintaining other desirable properties. These compositions include a high-molecular-weight (HMW) polyethylene component and a low-molecular-weight (LMW) polyethylene component. The MDD composition has a density of 0.937 to 0.946 g / cm³; a high-load melt index (I21) of 7 to 20 g / 10 min; a G'=G'' intersection of 30 to 50 kPa; a constant-load tensile failure time with notches at 30% yield strength, as measured according to ASTM D5397, of more than 700 hours; and a strain-hardening modulus of more than 65 MPa.

Description

84321-AR-NP BIMODAL MEDIUM DENSITY POLYETHYLENE COMPOSITIONS SUITABLE FOR USE AS DRIP TAPES MICROIRRIGATION TECHNICAL FIELD Embodiments of the present disclosure generally relate to bimodal medium density polyethylene compositions, and microirrigation drip tapes including them. INTRODUCTION A microirrigation drip tape is a tube for transporting and dripping water, fertilizer, and / or nutrients in irrigation systems. The annual U.S. market consumption of microirrigation drip tapes exceeds 120 million pounds of polyethylene resins. Currently, microirrigation drip tapes are primarily formed from unimodal polyethylene resins with densities of 0.939 to 0.944 g / cm3, a melt index (I2) of 0.2 to 0.3 g / 10 min, and a molecular weight distribution of more than 15. However, existing polyethylene resins have limited processability because the resins lack properties that do not allow processors to produce microirrigation drip tapes with adequate wall thickness while maintaining tensile strength, strain-hardening modulus, and service life.Accordingly, there remains a need for polyethylene compositions suitable for use in microirrigation drip tapes that have desirable processability and have maintained or improved storage hardening modulus, tensile strength, and service life as indicated by notched constant tensile load failure time. 2152541 of 51 84321-AR-NP SUMMARY Embodiments of the present disclosure meet one or more of the foregoing needs by providing a bimodal medium density polyethylene composition that can be processed at high extrusion rates and can exhibit improved or maintained tensile strength, storage hardening modulus, and notched constant tensile load failure time. Without being limited by any theory, in some embodiments, the bimodal medium density polyethylene composition has specific properties, including a G'=G'' intersection (which is indicative of melt elasticity) and short average chain branching in the low molecular weight polyethylene component, that can allow the composition to be extruded at high rates and exhibit maintained or improved storage hardening modulus and notched constant tensile load failure time. Disclosed herein are bimodal medium density polyethylene compositions. In one or more embodiments, the bimodal medium density polyethylene composition comprises (i) a high molecular weight (HMW) polyethylene component comprising an ethene^-olefin copolymer and (ii) a low molecular weight (LMW) polyethylene component comprising an ethene^-olefin copolymer; the bimodal medium density polyethylene composition having: (a) a density of 0.937 to 0.946 g / cm3; (b) a high load melt index (I21) of 7 to 20 g / 10 min; (c) a G'=G'' intercept of 30 to 50 kPa; (d) a notched constant tensile loading failure time at 30% yield strength, as measured in accordance with ASTM D5397, of greater than 700 hours; (e) a strain hardening modulus of more than 65 MPa; 2152541 of 51 84321-AR-NP wherein the LMW polyethylene component has an average short chain branching frequency of greater than 0.9 SCB per 1000 carbons; wherein the HMW polyethylene component has a weight average molecular weight, Mw, of 300,000 to 600,000 g / mol; and wherein the HMW polyethylene component is present in an amount of 45 to 60% by weight, based on the total weight of the bimodal medium density polyethylene composition. Microirrigation drip tapes are described herein. The microirrigation drip tapes comprise the bimodal medium-density polyethylene composition described herein. These and other modalities are described in more detail in the Detailed Description. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a perspective view of a microirrigation drip tape with a round cross section. Figure 2 is an absolute GPC chromatogram of certain inventive and comparative Examples showing local maxima for the LMW and HMW polyethylene component peaks and a local minimum between the LMW and HMW polyethylene component peaks. DETAILED DESCRIPTION Aspects of the disclosed bimodal medium density polyethylene compositions are described in greater detail below. The compositions 2152541 of 51 84321-AR-NP bimodal medium-density polyethylene are suitable for use as micro-irrigation drip tapes and can have a wide variety of applications, including, for example, pipes, tubes, hoses, tapes, or the like. However, this disclosure should not be construed as a limitation on the embodiments set forth below, as this disclosure is an illustrative implementation of the embodiments described herein. As used herein, the term "polymer" means a polymeric compound prepared by the polymerization of monomers, whether of the same or different types. The generic term "polymer" thus encompasses the term "homopolymer" (used to refer to polymers prepared from a single type of monomer) and the term "copolymer" or "interpolymer." Minor amounts of impurities (e.g., catalyst residues) may be incorporated into and / or within the polymer. A polymer may be a single polymer or a blend of polymers, including polymer blends formed in situ during polymerization. As used herein, the term “copolymer” means a polymer formed by the polymerization reaction of at least two structurally different monomers. The term “copolymer” includes terpolymers. As used herein, the term “polyethylene” or “ethylene-based polymer” shall mean polymers comprising a majority amount (>50 mol %) of units derived from ethylene monomer. This includes polyethylene homopolymers and copolymers (i.e., 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. 2152541 of 51 84321-AR-NP by a heterogeneous catalyst system, such as a Ziegler-Natta catalyst, a homogeneous catalyst system comprising Group 4 transition metals and ligand structures such as metallocene, metal-centered non-metallocene heteroaryl, heterovalent aryloxyether, phosphinimine, and others. Combinations of heterogeneous and / or homogeneous catalysts can also be used in single-reactor or dual-reactor configurations. As used herein, the term “composition” refers to a mixture of materials comprising the composition, as well as reaction products and decomposition products formed from the materials of the composition. As used herein, the term “bimodal catalyst” refers to a catalyst system containing two different catalysts for catalyzing the polymerization of ethylene copolymers and producing a bimodal copolymer composition.The two catalysts generally differ from each other in at least one of the following characteristics: (a) their catalytic metals are different (such as Ti versus Zr, Zr versus Hf, Ti versus Hf; non-activating metals such as Al); (b) one catalyst has a functional ligand bound to its catalytic metal and the other catalyst is free of functional ligands bound to its catalytic metal; (c) both catalysts have functional ligands bound to their catalytic metal and the structure of at least one functional ligand of one catalyst is different from the structure of the functional ligands of the other catalyst; and (d) for catalysts arranged on a support material, the compositions of the support materials are different.Two catalysts in a bimodal catalyst system can be mounted on the same support material, either on the same particles of the same support material or on different particles of the same support material. When a catalyst system includes the same catalyst, the catalyst system is 2152541 of 51 84321-AR-NP of catalytic metal and ligands, wherein a portion thereof is disposed on a support material and a different portion thereof is dissolved in an inert solvent, the different portions not constituting by themselves a bimodal catalyst system. As used herein, the term “backbone” refers to the longest continuous polymer chain of a polymer. All other polymer chains are referred to as side chains, branches, or graft polymer chains. As used herein, the term “short chains” or “short chain branching” (SCB) refers to branches of the backbone that result from the polymerization of monomers containing three or more carbons. The terms “comprising,” “including,” “having,” and their derivatives do not exclude the presence of any additional component, step, or process, whether specifically described or not. For the avoidance of doubt, all compositions claimed using the term “comprising” may include any additional additive, adjuvant, or compound, whether polymeric or otherwise, unless otherwise indicated. Conversely, the term “consisting essentially of” excludes from the scope of any subsequent recitation any other component, step, or process, except those not essential to operability. The term “consisting of” excludes any component, step, or process not specifically outlined or enumerated. Disclosed herein are bimodal medium density polyethylene compositions. As used herein, a medium density polyethylene composition is a polyethylene composition having a density of 0.937 to 0.946 g / cm3. The bimodal medium density polyethylene composition according to the embodiments disclosed herein comprises a high molecular weight (HMW) polyethylene component and a low molecular weight (HMW) polyethylene component. 2152541 of 51 84321-AR-NP Low molecular weight (LMW). The HMW polyethylene component has a higher molecular weight than the LMW polyethylene component. The bimodal medium density polyethylene composition according to the embodiments described herein is bimodal. A “bimodal” polyethylene composition contains two polyethylene fractions (e.g., an HMW polyethylene component and an LMW polyethylene component) that were produced under copolymerization conditions in a polymerization reactor, by contacting ethylene (monomer) and α-olefin (comonomer) with a mixture of a bimodal catalyst system and a trimming solution in the presence of molecular hydrogen gas (H2) and an induced condensation agent (ICA), resulting in different molecular weights and / or different comonomer contents for the fractions as demonstrated by the bimodality test method described below. For the avoidance of doubt, the bimodal medium density polyethylene composition described herein excludes and is not a unimodal polyethylene having a single polyethylene fraction. HMW polyethylene component The bimodal medium-density polyethylene composition comprises an HMW polyethylene component. In some embodiments, the HMW polyethylene component comprises an ethylene / α-olefin copolymer. In some embodiments, the ethylene / α-olefin copolymer of the HMW polyethylene component comprises ethylene and an α-olefin comonomer. Non-limiting examples of suitable α-olefins include C3-C20 α-olefins, or C4-C20 α-olefins, or C3-C10 α-olefins, or C4-C10 α-olefins, or C4-C8 α-olefins. Representative α-olefins include propylene, 1-butene, 1-pentene, 2152541 of 51 84321-AR-NP 1-hexene, 1-heptene, and 1-octene. In one embodiment, the ethylene / α-olefin copolymer does not contain an aromatic comonomer polymerized therein. In a further embodiment, the ethylene / α-olefin copolymer is an ethylene / 1-hexene copolymer. In one embodiment, the ethylene / α-olefin copolymer consists of ethylene, the C4-C8 α-olefin comonomer, and an optional additive. In one embodiment, the ethylene / α-olefin copolymer contains greater than 50% by weight of units derived from ethylene, or from 51% by weight, or 55% by weight, or 60% by weight to 70% by weight, or 80% by weight, or 90% by weight, or 95% by weight, or 99% by weight of units derived from ethylene, based on the weight of the ethylene / α-olefin copolymer. In one embodiment, the ethylene / α-olefin copolymer contains a reciprocal amount of units derived from α-olefin comonomer, or from less than 50 wt. %, or 49 wt. %, or 45 wt. %, or 40 wt. % to 30 wt. %, or 20 wt. %, or 10 wt. %, or 5 wt. %, or 1 wt. % of units derived from an α-olefin comonomer, based on the weight of the ethylene^-olefin copolymer. The comonomer content can be measured by any suitable technique, such as techniques based on nuclear magnetic resonance (“NMR”) spectroscopy and, for example, by 13C NMR analysis as described in U.S. Pat. No. 7,498.282, which is incorporated herein by reference. In some embodiments, the HMW polyethylene component has an average short chain branching frequency of greater than 1.4 SCB per 1000 carbons. All individual values ​​and subranges of greater than 1.4 SCB per 1000 carbons are included and described herein. For example, the HMW polyethylene component may have an average short chain branching frequency of greater than 1.5 SCB per 1000 carbons, or greater than 1.6 SCB per 1000 carbons. 2152541 of 51 84321-AR-NP carbons, or more than 1.7 SCB per 1000 carbons, or more than 1.8 SCB per 1000 carbons; or in the range of 1.4 to 4.0 SCB per 1000 carbons, or 1.5 to 3.9 SCB per 1000 carbons, or 1.6 to 3.8 SCB per 1000 carbons, or 1.7 to 3.7 SCB per 1000 carbons, or 1.8 to 3.6 SCB per 1000 carbons. The average short chain branching frequency of the HMW polyethylene component may be measured according to the test method described below. In some embodiments, the HMW polyethylene component is present in an amount of 45 to 60% by weight, based on the total weight of the bimodal medium density polyethylene composition. All individual values ​​and subranges of 45 to 60% by weight are included and described herein. For example, the HMW polyethylene component may be present in an amount of 45 to 60% by weight, 50 to 60% by weight, 53 to 60% by weight, 50 to 58% by weight, 50 to 56% by weight, 52 to 58% by weight, 53 to 57% by weight, or 52 to 56% by weight, based on the total weight of the bimodal medium density polyethylene composition. The presence of the HMW polyethylene component may also be expressed as a weight fraction rather than a weight percentage. For example, 50% by weight can be expressed as 0.50 weight fraction, 60% by weight can be expressed as 0.60 weight fraction, etc. In some embodiments, the HMW polyethylene component has a weight average molecular weight, Mw, of 300,000 to 600,000 g / mol. All individual values ​​and subranges of 300,000 to 600,000 g / cc are described and included herein. For example, the HMW polyethylene component may have a weight average molecular weight, Mw, of 325,000 to 575,000 g / mol, 350,000 to 550,000 g / mol, 375,000 to 525,000 g / mol, 375,000 to 500,000 g / mol, 375,000 to 475,000 g / mol, or 375,000 to 450,000 g / mol. The 2152541 of 51 84321-AR-NP weight average molecular weight, Mw, can be measured according to the GPC test method described below. Polyethylene component of LMW The bimodal medium-density polyethylene composition comprises an LMW polyethylene component. In some embodiments, the LMW polyethylene component comprises an ethylene / α-olefin copolymer. In some embodiments, the ethylene / α-olefin copolymer of the LMW polyethylene component comprises ethylene and an α-olefin comonomer. Non-limiting examples of suitable α-olefins include C3-C20 α-olefins, or C4-C20 α-olefins, or C3-C10 α-olefins, or C4-C10 α-olefins, or C4-C8 α-olefins. Representative α-olefins include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene. In one embodiment, the ethylene / α-olefin copolymer does not contain an aromatic comonomer polymerized therein. In a further embodiment, the ethylene^-olefin copolymer is an ethylene / 1-hexene copolymer. In one embodiment, the ethylene / α-olefin copolymer consists of ethylene, the C4-C8 α-olefin comonomer, and an optional additive. In one embodiment, the ethene^-olefin copolymer of the LMW polyethylene component contains greater than 50% by weight of units derived from ethylene, or from 51% by weight, or 55% by weight, or 60% by weight to 70% by weight, or 80% by weight, or 90% by weight, or 95% by weight, or 99% by weight of units derived from ethylene, based on the weight of the ethene^-olefin copolymer. In one embodiment, the ethene^-olefin copolymer contains a reciprocal amount of units derived from α-olefin comonomer, or from less than 50% by weight, or 49% by weight, or 45% by weight, or 40% by weight to 30% by weight, or 20% by weight, 2152541 of 51 84321-AR-NP or 10% by weight, or 5% by weight, or 1% by weight of units derived from an α-olefin comonomer, based on the weight of the ethylene / α-olefin copolymer. In some embodiments, the LMW polyethylene component has an average short chain branching frequency of greater than 0.9 SCB per 1000 carbons. All individual values ​​and subranges of greater than 0.9 SCB per 1000 carbons are included and described herein. For example, the LMW polyethylene component may have an average short chain branching frequency of greater than 0.9 SCB per 1000 carbons, or greater than 1.0 SCB per 1000 carbons, or greater than 1.1 SCB per 1000 carbons, or in the range of 1.0 to 2.5 SCB per 1000 carbons, 1.0 to 2.2 SCB per 1000 carbons, or 1.0 to 2.0 SCB per 1000 carbons. The average short chain branching frequency of the LMW polyethylene component can be measured according to the test method described below. The ethylene / α-olefin copolymer of the LMW polyethylene component and the ethylene / α-olefin copolymer of the HMW polyethylene component differ by at least the molecular weight of the respective component. In one embodiment, the LMW polyethylene component has a weight average molecular weight, Mw, that is lower than the weight average molecular weight, Mw, of the HMW polyethylene component, and the LMW polyethylene component has a density that is greater than the density of the HMW polyethylene component. In some embodiments, the ratio of the weight average molecular weight, Mw, of the HMW polyethylene component to the weight average molecular weight, Mw, of the HMW polyethylene component is 16 to 27. All individual values ​​and subranges of 16 to 27 are included and described herein. For example, the ratio of the weight average molecular weight, Mw, of 2152541 of 51 84321-AR-NP HMW polyethylene component with respect to the weight average molecular weight, Mw, of the LMW polyethylene component may be 17 to 26, 18 to 25, or 20 to 25. The weight average molecular weight, Mw, may be measured according to the GPC test method described below. Composition characteristics of medium density polyethylene In some embodiments, the bimodal medium density polyethylene composition has a density of 0.937 to 0.946 g / cm3, a high load melt index (I21) of 7 to 20 g / 10 min, a notched constant tensile load (NCTL) failure time at 30% yield strength, as measured in accordance with ASTM D5397, of greater than 700 hours, and a strain hardening modulus of greater than 65 MPa. In some embodiments, the bimodal medium density polyethylene composition has a density of 0.937 to 0.946 g / cm3. All individual values ​​and subranges of 0.937 to 0.946 g / cm3 are described and included herein. For example, the bimodal medium density polyethylene composition may have a density of 0.938 to 0.946 g / cm3, 0.939 to 0.946 g / cm3, 0.940 to 0.946 g / cm3, 0.941 to 0.946 g / cm3, 0.938 to 0.946 g / cm3, 0.938 to 0.945 g / cm3, 0.940 to 0.943 g / cm3, or 0.940 to 0.942 g / cm3, where the density is measured in accordance with ASTM D792. In embodiments, the bimodal medium density polyethylene composition has a high load melt index (I21) of 7 to 20 g / 10 min. All individual values ​​and subranges of 7 to 20 g / 10 min are included and described herein. For example, the bimodal medium density polyethylene composition may have a total high load melt index (I21) of 8 to 20 g / 10 min, 9 to 20 g / 10 min, 8 to 19 g / 10 min, 9 to 19 g / 10 min, 10 to 20 g / 10 2152541 of 51 84321-AR-NP min, 10 to 19 g / 10 min, or 10 to 18 g / 10 min, where a high load melt index (I21) of the bimodal medium density polyethylene composition is measured in accordance with ASTM D1238 (190 °C / 21.6 kg). In some embodiments, the bimodal medium density polyethylene composition has a G'=G'' intercept of 30 to 50 kPa. All individual values ​​and subranges of 30 to 50 kPa are described and included herein. For example, the bimodal medium density polyethylene composition may have a G'=G'' intercept of 32 to 48 kPa, 33 to 48 kPa, 34 to 48 kPa, or 34 to 47 kPa, where the G'=G'' intercept is measured according to the test method described below. In some embodiments, the HMW polyethylene component has an average short chain branching frequency (HMW SCB / 1000C), and the following equation is solved: 3094 HMW wt % - 30.52 G'=G Intercept - 160.1 (LMW SCB / 1000C / HMW SCB / 1000C) - 211.7 > 0 (Eq. A) where “HMW wt %” is the weight percent of HWM polyethylene present in the bimodal medium density polyethylene composition, based on the total weight of the bimodal medium density polyethylene composition, “G'=G'' Intercept” is the G'=G'' Intercept of the bimodal medium density polyethylene composition, “LMW SCB / 1000C” is the average short chain branching frequency of the LMW polyethylene component, and “HMW SCB / 1000C” is the 2152541 of 51 84321-AR-NP average short chain branching of the HMW polyethylene component. In some embodiments, the left-hand side of Equation A above is equal to or greater than 5, equal to or greater than 10, or equal to or greater than 15. In some embodiments, the bimodal medium density polyethylene composition has a molecular weight distribution, Mw / Mn, of 12 to 30. All individual values ​​and subranges of 12 to 30 are included herein. For example, the bimodal medium density polyethylene composition may have a molecular weight distribution, Mw / Mn, of 12 to 28, 12 to 26, 12 to 24, 12 to 22, 12 to 20, 14 to 28, 14 to 26, 14 to 24, 14 to 22, or 14 to 20, wherein the molecular weight distribution, Mw / Mn, can be measured according to the test method described below. In embodiments, the bimodal medium density polyethylene composition has a notched constant tensile load (NCTL) failure time at 30% yield stress of greater than 700 hours. In some embodiments, the bimodal medium density polyethylene composition has an NCTL failure time at 30% yield stress of greater than 750 hours, or 800 hours, or 850 hours, or 900 hours, or 950 hours, where the NCTL failure time at 30% yield stress is measured according to the test method described below. In some embodiments, the bimodal medium density polyethylene composition has a strain hardening modulus of greater than 65 MPa. All individual values ​​and subranges of greater than 65 MPa are described and included herein. For example, the bimodal medium density polyethylene composition may have a strain hardening modulus of greater than 2152541 of 51 84321-AR-NP of 68 MPa, or more than 70 MPa, or in the range of 65 to 100 MPa, 70 to 95 MPa, 70 to 90 MPa. The strain-hardening modulus can be measured according to the test method described below. In some embodiments, the bimodal medium density polyethylene composition has a tensile yield strength of 19 to 30 MPa. All individual values ​​and subranges of 19 to 30 MPa are described and included herein. For example, the bimodal medium density polyethylene composition may have a tensile yield strength of 19 to 27 MPa, 19 to 26 MPa, 19 to 25 MPa, 19 to 24 MPa, 20 to 27 MPa, 20 to 26 MPa, 20 to 25 MPa, or 20 to 24 MPa, where the tensile yield strength is measured according to the test method described below. In some embodiments, the bimodal medium density polyethylene composition has a resolved bimodality (resolved molecular weight distribution) shown in a gel permeation chromatography (GPC) chromatogram of the bimodal medium density polyethylene composition, wherein the chromatogram shows a peak representing the HMW polyethylene component, a peak representing the LMW polyethylene component, and a local minimum in a Log (molecular weight) (“Log (MW)”) range of 3.0 to 7.0 between the peak representing the HMW polyethylene component and the peak representing the LMW polyethylene component, as measured in accordance with the bimodality test method described below. In some embodiments, the bimodal medium density polyethylene composition can be extruded at process speeds of greater than 300 m / min. In some embodiments, the bimodal medium density polyethylene composition can be extruded at process speeds of greater than 325 m / min, or greater than 350 m / min. 2152541 of 51 84321-AR-NP m / min, or more than 375 m / min. The extrusion line speed can be measured according to the test method described below. The bimodal medium-density polyethylene composition can be prepared by polymerizing ethylene monomer and the α-olefin comonomer in a reactor with a catalyst and, optionally, other reactants and diluents. The polymerization can take place in the liquid phase, slurry phase, or gas phase, but preferably in the gas phase. To produce the bimodal molecular weight distribution, the copolymers can be produced in a two-stage polymerization or a one-stage polymerization, but are preferably made in a one-stage polymerization. In a two-stage polymerization, the higher molecular weight polyethylene component is polymerized by a first catalyst in a first reactor under a first set of process conditions and the lower molecular weight polyethylene component is made by a second catalyst in a second reactor under a second set of process conditions. Examples of such production are described in the following patent publications, which are incorporated herein by reference: US 5,627,242; US 5,665,818; US 5,677,375; US 2007 / 0043177 A1, EP-A-0 794 200; EP-B1-0 649 992; EP-A-0 802 202; EP-B-634421 and WO 2009 / 148,487 A1. In a single-stage polymerization, the higher molecular weight polyethylene component and the lower molecular weight polyethylene component are polymerized in a single reactor using a bimodal catalyst. The single-stage polymerization preferably takes place in a fluidized bed gas phase polymerization reactor (FB-GPP reactor) using a bimodal catalyst. Such reactors and methods are known in the art. 2152541 of 51 84321-AR-NP example, the FB-GPP methods and reactors are as described in the following patent publications, which are incorporated herein by reference: 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; US 2020 / 0024376 A1, US 2020 / 024376 A1, US 2018 / 0155473 A1 and WO 2016 / 172279 A1. The best operating conditions for producing the polymers of this invention vary depending on the reactor used, the catalyst system used, and the specific properties desired for the copolymer. The following discussion describes typical conditions for common FB-GPP reactors using the bimodal catalyst described below: The molar ratio (Cx / C2) of comonomer and ethylene fed to the reactor is preferably at least 0.0001, more preferably at least 0.0002, and most preferably at least 0.0004. The molar ratio (Cx / C2) of comonomer and ethylene fed to the reactor is preferably at most 0.1, more preferably at most 0.05, and most preferably at most 0.02. The partial pressure of ethylene in the reactor is preferably at least 690 kPa (100 psia), more preferably at least 830 kPa (120 psia), and most preferably at least 1300 kPa (190 psia). The partial pressure of ethylene in the reactor is preferably at most 2070 kPa (300 psia), more preferably at most 1720 kPa (250 psia), and most preferably at most 1590 kPa (230 psia). The molar ratio of hydrogen to ethylene (H2 / C2) in the reactor varies depending on the molecular weights of the polymers being produced. The molar ratio of hydrogen to ethylene (H2 / C2) is preferably at least 0.0003 and more preferably at least 0.001. The molar ratio of hydrogen 2152541 of 51 84321-AR-NP with respect to ethylene (H2 / C2) is preferably at most 0.01 and more preferably at most about 0.006. The catalyst system (described below) can be fed to a polymerization reactor in either "dry mode" or "wet mode." Dry mode is a dry powder or granules. Wet mode is a suspension in an inert liquid such as mineral oil. Preferably, the catalyst system is fed in wet mode. Optionally, the catalyst system may comprise the primary catalyst plus a “trimming catalyst” that provides additional control over the ratio of the higher molecular weight polyethylene component to the lower molecular weight polyethylene component in the final copolymer. For example, the trimming catalyst may contain catalytic material that supplements the formation of either the higher molecular weight polyethylene component or the lower molecular weight polyethylene component of the composition. The use of trimming catalysts is described in greater detail in PCT patent publications WO 2015 / 123172A1 and WO 2015 / 123179A1, which are incorporated herein by reference. The bed temperature in the reactor is preferably at least 70 °C, more preferably at least 80 °C, and most preferably at least 85 °C. The bed temperature in the reactor is preferably at most 110 °C, more preferably at most 100 °C, and most preferably at most 95 °C. The flow of reactants through the reactor is preferably at a velocity sufficient to maintain the reactor bed in a fluidized state. Optionally, an inert liquid (called an induced condensation agent (ICA)) can be added to the reactor to help cool the reactor. 2152541 of 51 84321-AR-NP the reactor. The ICA is preferably a (C5 to C20) alkane, more preferably a (C5 to C10) alkane, and most preferably pentane or 2-methylbutane (i.e., isopentane). The use of ICA is described in the following patent publications, which are incorporated herein by reference: U.S. Pat. No. 4,453,399; U.S. Pat. No. 4,588,790; U.S. Pat. No. 4,994,534; U.S. Pat. No. 5,352,749; U.S. Pat. No. 5,462,999; and U.S. Pat. No. 6,489,408. The ICA concentration is preferably at least 1 mole percent, and more preferably at least 3 mole percent. The ICA concentration is preferably at most 20 mole percent, and most preferably at most 8 mole percent. Optionally, a continuity additive can be added to the reactor to control lamination in the reactor. Suitable continuity additives are commercially available from Univation Technologies LLC as CA-200 and CA-300. The concentration of the continuity additive is preferably at least 0.5 ppm by weight and more preferably at least 30 ppm by weight. The concentration of the continuity additive is preferably at most 200 ppm by weight and most preferably at most 80 ppm by weight. The polymerization conditions may further include one or more additives such as a chain transfer agent or a promoter. Chain transfer agents are well known and may be metal alkyl such as diethylzinc. Promoters are known as in US 4,988,783 and may include chloroform, CFCl3, trichloroethane, 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 can be operated without scavenging agents (not deliberately added). 2152541 of 51 84321-AR-NP polymerization conditions for the gas phase polymerization reactor / method may further include an amount (e.g., 0.5 to 200 ppm based on all feeds to the reactor) of a static control agent and / or a continuity additive such as aluminum stearate or polyethyleneimine. Static control agents may be added to the FB-GPP reactor to inhibit the formation or buildup of static charge in the present disclosure. The start-up of a restarted FB-GPP reactor (cold start-up) or the restart of a transitioning FB-GPP reactor (hot start-up) includes a period of time before steady-state polymerization conditions are reached. The start-up or restart may include the use of a pre-filled polymer seed in the fluidized bed reactor. The polymer seed may be composed of polyethylene powder; preferably, it is a bimodal copolymer similar to the bimodal medium-density polyethylene composition being produced. Startup or restart of the FB-GPP reactor may also include gas atmosphere transitions comprising purge air or other unwanted reactor gases with a dry (anhydrous) inert purge gas, followed by purging the dry inert purge gas from the FB-GPP reactor with dry ethylene gas. The dry inert purge gas may consist essentially of molecular nitrogen (N2), argon, helium, or a mixture of any two or more of these. When not in operation, prior to start-up (cold start), the FB-GPP reactor contains an atmosphere of air. The dry inert purge gas may be used to sweep air from an FB-GPP reactor that was restarted during the early stages of start-up to provide an FB-GPP reactor having an atmosphere consisting of the dry inert purge gas. 2152541 of 51 84321-AR-NP Before restarting (e.g., after a seedbed change), a transitioning FB-GPP reactor may contain an atmosphere of unwanted ICA or other unwanted gas or vapor. The dry inert purge gas may be used to sweep unwanted vapor or gas from the transitioning FB-GPP reactor during the early stages of restart to provide the FB-GPP reactor with an atmosphere consisting of the dry inert purge gas. Any dry inert purge gas may in turn be swept from the FB-GPP reactor with the dry ethylene gas. The dry ethylene gas may also contain molecular hydrogen gas, such that the dry ethylene gas is fed to the fluidized bed reactor as a mixture of these. Alternatively, the dry molecular hydrogen gas may be introduced separately and after the fluidized bed reactor atmosphere has been converted to ethylene.Gas atmosphere transitions can be performed before, during or after heating the FB-GPP reactor to the reaction temperature of polymerization conditions. The start-up or restart of the FB-GPP reactor also includes the introduction of reactant and reagent feeds into the reactor. Reactants include ethylene and alpha-olefin (e.g., 1-hexene). Reactants fed to the fluidized bed reactor include molecular hydrogen gas and the induced condensation agent (ICA), the bimodal catalyst system, and the trimming catalyst. Two-reactor polymerizations of bimodal copolymers can be carried out using conventional catalyst systems. One-reactor polymerizations of bimodal copolymers are typically carried out using a bimodal catalyst that has a catalyst component especially suited for producing the higher molecular weight (HMW) polyethylene fraction. 2152541 21 of 51 84321-AR-NP of the composition and another that is especially suitable for making the lower molecular weight (LMW) polyethylene fraction of the composition. Preferred bimodal catalyst systems preferentially direct a greater portion of the α-olefin comonomer into the higher molecular weight fraction; such bimodal catalysts (and processes for making them) are described in the following patent publications, which are incorporated herein by reference: US 2020 / 048379 A1 , US 2020 / 024376 A1 , US 2018 / 0155473 A1 , WO 2016 / 172279 A1. Bimodal catalyst systems that are particularly useful for producing the copolymers are described in U.S. patent application No. 62 / 880,826, entitled “Bimodal Poly(ethylene-co-1-alkene) Copolymer Bimodal Poly(ethylene-co-1-alkene) Copolymer” and filed July 31, 2019; U.S. patent application 62 / 990,549, entitled “Metal-Ligand Complexes” and filed March 17, 2020; and application PCT / US20 / 30033, entitled “Metal-Ligand Complexes” and filed April 27, 2020, which are incorporated herein by reference. Preferred catalyst systems comprise a bis(2-(pentamethylphenylamido)ethyl)-amine zirconium dibenzyl component and a (cyclopentadienyl)(1,5-dimethylindenyl)zirconium (X)2 component, wherein X is an entity that completes the valency of zirconium. X is preferably a halide or an alkyl group containing 1-4 carbon atoms and is more preferably a methyl group. Without being limited by theory, it is believed that bis(2-(pentamethylphenylamido)ethyl)-amine zirconium dibenzyl is effective in making the HMW polyethylene component of the bimodal copolymer and (cyclopentadienyl)(1,5-dimethylindenyl)zirconium dimethyl is effective in making the LMW polyethylene component of the bimodal copolymer. 2152541 of 51 84321-AR-NP The HMW catalyst and the LMW catalyst in the bimodal catalyst system can be kept separate until they are added to the reactor, in which case each catalyst can be unsupported or deposited on its own support. Preferably, the HMW catalyst and the LMW catalyst in the bimodal catalyst system are deposited together on a single support. Preferably, the catalysts of the bimodal catalyst system are applied onto a solid support material, such as by spray drying. The support material preferably comprises a porous inorganic substance or organic substance. More preferably, it comprises a Group 2, 3, 4, 5, 13 or 14 metal oxide, and most preferably a Group 13 or 14 metal oxide. Examples of inorganic oxide support materials are silica, alumina, titania, zirconia, thoria, and mixtures of any two or more such inorganic oxides. The solid support material is most preferably a hydrophobic fumed silica (e.g., dimethyldichlorosilane-treated fumed silica). The inorganic oxide support material is porous and has varying surface area, pore volume, and average particle size. In some embodiments, the surface area is 50 to 1000 square meters per gram (m2 / g) and the average particle size is 20 to 300 micrometers (pm). Alternatively, the pore volume is 0.5 to 6.0 cubic centimeters per gram (cm3 / g) and the surface area is 200 to 600 m2 / g. Alternatively, the pore volume is 1.1 to 1.8 cm3 / g and the surface area is 245 to 375 m2 / g. Alternatively, the pore volume is 2.4 to 3.7 cm3 / g and the surface area is 410 to 620 m2 / g. Alternatively, the pore volume is 0.9 to 1.4 cm3 / g and the surface area is 390 to 590 m2 / g. Each of the above properties is measured using conventional techniques known in the art. 2152541 23 of 51 84321-AR-NP Before contacting with a catalyst, the support material may be pretreated by heating the support material in air to obtain a calcined support material. The pretreatment comprises heating the support material to a maximum temperature of 350 to 850 °C, alternatively, 400 to 800 °C, alternatively, 400 to 700 °C, alternatively, 500 to 650 °C and for a period of time of 2 to 24 hours, alternatively, 4 to 16 hours, alternatively, 8 to 12 hours, alternatively, 1 to 4 hours, which forms a calcined support material. In some aspects, the support material is a calcined support material. Most preferably, the bimodal catalyst system comprises 1.0 to 5.0 weight percent of bis(2-(pentamethylphenylamido)ethyl)amine zirconium dibenzyl and 0.1 to 2.0 weight percent of (cyclopentadienyl)(1,5-dimethylindenyl)zirconium dimethyl or (1,3-dimethyl-4,5,6,7-tetrahydroindene)(methyl cyclopentadienyl)zirconium dimethyl, applied to a fumed silica support. The trimming catalyst may be an HMW catalyst or an LMW catalyst. The trimming catalyst is preferably the same as the HMW catalyst or the LMW catalyst in the bimodal catalyst system. For the most preferred catalyst system, the trimming catalyst is preferably (cyclopentadienyl)(1,5-dimethylindenyl)zirconium dimethyl or (1,3-dimethyl-4,5,6,7-tetrahydroindene)(methyl cyclopentadienyl)zirconium dimethyl bis(n-butylcyclopentadienyl)zirconium dimethyl. For convenience, the clipping catalyst is preferably fed to the reactor in solution in a hydrocarbon solvent. The hydrocarbon solvent may be an alkane, or a mixture of alkanes, wherein each alkane independently has 5 to 20 carbon atoms, alternatively 5 to 12 carbon atoms, 2152541 of 51 84321-AR-NP alternatively of 5 to 10 carbon atoms. Each alkane, independently, can be acyclic or cyclic. Each acyclic alkane can independently be straight chain or branched chain. Examples of acyclic alkane include pentane, 1-methylbutane (isopentane), hexane, 1-methylpentane (isohexane), heptane, 1-methylhexane (isoheptane), octane, nonane, decane, or a mixture of two or more of these. Examples of cyclic alkane include cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, methycyclopentane, methylcyclohexane, dimethylcyclopentane, or a mixture of two or more of these.Each catalyst in the bimodal catalyst system and the clipping catalyst is preferably activated by contact with at least one activator. The activators are preferably a Lewis acid, a non-coordinating ionic activator, or an ionizing activator, or a Lewis base, an alkylaluminum, or an alkylaluminoxane (alkylalumoxane). The alkylaluminum can be a trialkylaluminum, an alkylaluminum halide, or an alkylaluminum alkoxide (diethylaluminum ethoxide). The trialkylaluminum can be trimethylaluminum, triethylaluminum (“TEAL”), tripropylaluminum, or tris(2-methylpropyl)aluminum. The alkylaluminum halide can be diethylaluminum chloride. The alkylaluminum alkoxide can be diethylaluminum ethoxide. The alkylaluminoxane can be methylaluminoxane (MAO), ethylaluminoxane, 2-methylpropylaluminoxane, or modified methylaluminoxane (MMAO).Each alkyl of the alkylaluminum or alkylaluminoxane may independently be a (Ci to C7)alkyl, alternatively a (Ci to C6)alkyl, alternatively a (Ci to C4)alkyl. The molar ratio of the activator metal (Al) to the metal of a particular catalyst compound (catalytic metal, e.g., Zr) may be 1000:1 a. 2152541 of 51 84321-AR-NP 0.5:1, alternatively 300:1 to 1:1, alternatively 150:1 to 1:1. Suitable activators are commercially available. Each contacting step between the activator and the catalyst can be carried out independently (a) in a separate vessel outside the GPP reactor (e.g., outside the FB-GPP reactor), (b) in a feed line to the GPP reactor, and / or (c) within the GPP reactor (in situ). In option (a), the bimodal catalyst system, once its catalysts are activated, can be fed to the GPP reactor as a dry powder, alternatively as a suspension in a non-polar aprotic (hydrocarbon) solvent. In option (c), the bimodal catalyst system can be fed to the reactor prior to activation via a first feed line, the first activator can be fed to the reactor via a second feed line, the trimming catalyst can be fed to the reactor via a third feed line, and the second activator can be fed to the reactor via a fourth feed line.Any two of the first and fourth feed lines may be the same or different. The activator(s) may be fed to the reactor in "wet mode" as a solution thereof in an inert liquid such as mineral oil or toluene, in slurry mode as a slurry, or in dry mode as a powder. Each contacting step may be performed in separate vessels, feed lines, or reactors at the same time or at different times, or in the same vessel, feed line, or reactor at different times, to separately provide the bimodal catalyst system and the clipping catalyst. Alternatively, the contacting steps may be performed in the same vessel, feed line, or reactor at the same time to provide a mixture of the bimodal catalyst system and the clipping catalyst in situ. 2152541 26 of 51 84321-AR-NP The bimodal medium density polyethylene composition may comprise two or more embodiments explained herein. Also described herein is a micro-irrigation drip tape. The micro-irrigation drip tape comprises the bimodal medium density polyethylene composition described herein. A “micro-irrigation drip tape” is an extruded structure having an annular wall composed of the bimodal medium density polyethylene composition, wherein the annular wall defines an annular passageway. In other words, the micro-irrigation drip tape is a tube through which water or other liquid may pass. Figure 1 depicts a micro-irrigation drip tape 10 having an annular wall 12 defining an annular passageway 14. The annular wall 12 has an outer surface 16 and an inner surface 18. In one embodiment, the annular wall 12 of the micro-irrigation drip tape 10 is composed solely of the bimodal medium density polyethylene composition. Emitters 20 are arranged at intervals along the inner surface 18 of the annular wall 12. An “emitter” is an insert that controls the rate at which water or other liquid passes through an opening 22 (e.g., a hole, slot, or perforation) made in the annular wall by mechanical drilling, cutting, or laser cutting. The emitter 20 is located on the inner surface 18 of the annular wall 12 after the micro-irrigation drip tape 10 exits the extruder while the formulation is in transition from a molten state to a rigid state, allowing the emitter 20 to be adhered to the micro-irrigation drip tape 10 by welding. The adhesion of the emitter 20 to the annular wall 12 is sufficient to hold the emitter 20 in a fixed position, and to maintain a leak-proof seal between the annular wall 12 and the emitter 20. 2152541 of 51 84321-AR-NP Microirrigation drip tape has a cross-sectional shape. Non-limiting examples of suitable cross-sectional shapes for microirrigation drip tape include ellipse, polygon, and combinations of these. A "polygon" is a closed plane figure bounded by at least three sides. The polygon can be a regular polygon or an irregular polygon having three, four, five, six, seven, eight, nine, ten, or more sides. Non-limiting examples of suitable polygonal shapes include triangle, square, rectangle, diamond, trapezoid, parallelogram, hexagon, and octagon. An "ellipse" is a plane curve where the sum of the distances of every point on its periphery from two fixed points, the foci, are equal. The ellipse has a center that is the midpoint of the line segment joining the two foci. The ellipse has a principal axis (the longest diameter through the center). The secondary axis is the shortest line through the center.The center of the ellipse is the intersection of the primary and secondary axes. A "circle" is a specific ellipse shape where the two focal points are in the same location (at the center of the circle). Non-limiting examples of ellipse shapes include circle, oval, and ovoid. Figure 1 depicts a microirrigation drip tape 10 that has a circular cross-section. Test methods Density Density is measured according to ASTM D792 and is expressed in grams / cm3 (g / cm3 or g / cc). 2152541 of 51 84321-AR-NP Melt flow rate (I2, I5 and I21) The procedure outlined in ASTM D1238 is followed to determine melt flow index. This test method covers the determination of the extrusion rate of molten thermoplastic resins by using an extrusion plastometer. After a specified preheat time of 7 (+ / - 0.5) min, the resin is extruded through a die with a specified orifice length and diameter under prescribed conditions of temperature, load, and ram position in the barrel. Method B of ASTM D1238 is used. Method B is an automatically timed method. Here, the sample is extruded from the melt index machine, and the ram travel is timed over a predetermined distance; timing is automatically accomplished by a movable arm position beneath the loading frame. The predetermined distance is 0.25 in (6.35 mm) for an I2 up to 10 g / 10 min and 1 in (25.4 mm) for an I2 >10 g / 10 min.The extrudate weight is determined from the volume (orifice distance x area) and the melt density. The melt density is assumed to be 0.7636 g / cm3 for polyethylene. Data are reported as MFR in g / 10 min or dg / min. Samples can be processed at loads of 21.6 kg, 5.0 kg, or 2.16 kg (i.e., I21, I5, or I2, respectively). Notched Constant Tensile Load (NCTL) The notched constant tensile load (NCTL) failure time in hours is measured at a yield strength of 30% according to ASTM D5397. This test is evaluated at 50°C with a 10% aqueous solution of Igepal. The specimen thickness is 0.075" and is notched to a depth of 20%. 2152541 29 of 51 84321-AR-NP of the thickness. The applied stress is equal to 30% of the resin's yield strength measured at room temperature. Tensile yield strength The tensile yield strength of the bimodal medium density polyethylene composition in MPa is measured using samples prepared by pellet compression molding according to ASTM D638 (2 in / min crosshead speed, 5.08 cm / min crosshead speed). Strain hardening modulus The strain hardening modulus of the bimodal medium high-density polyethylene composition in MPa is measured using samples prepared by pellet compression molding according to ISO 18488:2015 (sample thickness 0.3 mm, crosshead speed 20 mm / min, test temperature 80 °C). Dynamic mechanical spectroscopy (G'=G'' intersection) Each sample was compression molded into a disc shape for rheology measurement. The discs were prepared by pressing the samples into 3.0 mm thick plates and then cutting them into 25 mm diameter discs. Resin rheology was measured on a TA Instruments ARES-G2 rheometer. The ARES is a strain-controlled rheometer. A rotary actuator (servo motor) applies shear strain in the form of stress to a sample. In response, the sample generates torque, which is measured by the transducer. The stress and torque are used to calculate dynamic mechanical properties, such as 2152541 of 51 84321-AR-NP Modulus and Viscosity. The viscoelastic properties of the sample were measured, in the melt, using a 25 mm diameter parallel plate configuration, at 190 °C, and as a function of variable frequency (range 0.01 s-1 to 100 s-1). A small constant strain (5%) was applied to ensure that the measurement was in the linear viscoelastic region. The storage modulus (G'), loss modulus (G), tan delta (G / G'), and complex viscosity (eta) of the resin were determined. The intersection G'=G" is recorded in kPa as a measure of melt elasticity, where a lower value indicates greater melt elasticity. Absolute GPC (molecular weight distribution) The chromatographic system consisted of a PolymerChar GPC-IR high-temperature chromatograph (Valencia, Spain), equipped with an IR5 internal infrared detector (IR5) coupled to a Precision Detectors (now Agilent Technologies) model 2040 two-angle laser light scattering (LS) detector. For all light scattering measurements, a 15-degree angle was used. The autosampler oven compartment was set at 160° Celsius, and the column compartment and detectors were set at 150° Celsius. The columns used were four Agilent “Mixed A” 20-micron, 30-cm linear mixed-bed columns. The chromatographic solvent used was 1,2,4-trichlorobenzene, containing 200 ppm butylated hydroxytoluene (BHT). The solvent source was sparged with nitrogen. The injection volume used was 200 microliters and the flow rate was 1.0 milliliter / minute. The calibration of the GPC column set was performed with 21 narrow molecular weight distribution polystyrene standards with molecular weights ranging from 580 to 8,400,000 g / mol, and were arranged in 6 mixtures. 2152541 of 51 84321-AR-NP of “cocktails” with at least a decade between the individual molecular weights. Standards were purchased from Agilent Technologies. Polystyrene standards were prepared at 0.025 grams in 50 milliliters of solvent for molecular weights equal to or greater than 1,000,000 g / mol, and at 0.05 grams in 50 milliliters of solvent for molecular weights less than 1,000,000 g / mol. The polystyrene standards were dissolved at 80 °C with gentle stirring for 30 minutes. The peak molecular weights of the polystyrene standard were converted to ethylene-based polymer molecular weights using Eq. 2 (as described in Williams and Ward, J. Polym. Sci., Polym. Let., 6, 621 (1968)). Mpolyethylene = AX (Mpolystyrene) Eq. 2 where M is the molecular weight, A has a value of 0.4315 and B is equal to 1.0. A fifth-order polynomial was used to fit the respective ethylene-based polymer equivalent calibration points. Total plate counts from the GPC column array were performed with decane without further dilution. Plate count (Eq. 3) and symmetry (Eq. 4) were measured in a 200-microliter injection according to the following equations: Plate count = 5.54 X __________RVpeakmax__________ Peak width at mid-height Eq. 3 2152541 of 51 84321-AR-NP where RV is the retention volume in milliliters, peak width is in milliliters, peak maximum is the maximum peak height, and half-height is one-half of the maximum peak height. Symmetry = (Posterior peak RV one-tenth of height Max peak RV) (Max peak RV—Peak|anterior RV one-tenth of height) Eq.4 where RV is the retention volume in milliliters and peak width is in milliliters, peak maximum is the peak position, one-tenth of peak height is one-tenth of the peak height, and where peak back refers to the peak tail at retention volumes later than the peak maximum, and where peak front refers to the peak front at retention volumes before the peak maximum. The plate count for the chromatographic system should be greater than 18,000 and the symmetry should be between 0.98 and 1.22. Samples were prepared semi-automatically using PolymerChar's Instrument Control software. The target sample weight was 2 mg / ml, and the solvent (containing 200 ppm BHT) was added to a septum-capped vial previously sparged with nitrogen using the PolymerChar high-temperature autosampler. Samples were dissolved for 3 hours at 160°C with low-speed stirring. To monitor deviations over time, a flow rate marker (decane) was introduced into each sample via a micropump controlled by the PolymerChar GPC-IR system. This flow rate marker (FM) was used to linearly correct the pump flow rate (Nominal Flow Rate) for each sample. 2152541 of 51 84321-AR-NP by aligning the RV of the respective decane peak within the sample (RV(sample FM)) with that of the decane peak within the narrow calibration standards (RV(calibrated FM)). Any change in the timing of the decane marker peak is assumed to be related to a linear change in flow rate (Effective Flow Rate) over the entire run. To facilitate maximum accuracy of an RV measurement of the flow marker peak, a least-squares fitting routine is used to fit the flow marker concentration chromatogram peak to a quadratic equation. The first derivative of the quadratic equation is then used to solve for the true peak position. After calibrating the system based on a flow marker peak, the effective flow rate (with respect to the narrow calibration standards) is calculated as Eq. 5.The flow marker peak was processed using PolymerChar's GPCOne™ software. The acceptable flow rate correction is such that the effective flow rate should be within 0.5% of the nominal flow rate. Effective flow rate = FNominal flow rate X (RV(FMcalibrated) / RV(FMSample))£c.5 The systematic approach to determining multi-detector shifts is consistent with that published by Balke, Mourey et al. (Mourey and Balke, Chromatography Polym. Chapter 12, (1992)) (Balke, Thitiratsakul, Lew, Cheung, Mourey, Chromatography Polym. Chapter 13, (1992)), by optimizing the triple detector log (MW and IV) results from a wide homopolymer polyethylene standard (Mw / Mn >3) to the results 2152541 of 51 84321-AR-NP Narrow Standard Column Calibration of the narrow standards calibration curve using PolymerChar GPCOne™ software. Absolute molecular weight data were obtained in a manner consistent with those 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 GPCOne™ software from PolymerChar. The overall injected concentration used in the molecular weight determination was obtained from the mass detector area, and mass detector constant, derived from a suitable linear polyethylene homopolymer, or one of the known weight average molecular weight polyethylene standards. Calculated molecular weights (by using GPCOne™) were obtained by 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™) must be determined from a linear standard with a molecular weight greater than about 50,000 g / mol. Viscometer calibration (determined using GPCone™) can be performed by methods described by the manufacturer or alternatively by using published values ​​of suitable linear standards such as Standard Reference Materials (SRM) 1475a (available through the National Institute of Standards and Technology (NIST). A viscometer constant (obtained using GPCone™) is calculated that relates the specific viscosity (DV) area and injected mass for the calibration standard to its intrinsic viscosity. Concentrations are assumed to be... 2152541 35 of 51 84321-AR-NP chromatographic values ​​are low enough to eliminate the effects of the second viral coefficient (effects of concentration on molecular weight). The absolute weight average molecular weight (MW(Abs)) is obtained (using GPCOne™) from the integrated light scattering (LS) area chromatogram (factored by the light scattering constant) divided by the recovered mass from the mass constant and the mass detector area (IR5). The molecular weight and intrinsic viscosity responses are extrapolated at the chromatographic extremes where the signal-to-noise ratio becomes low (using GPCOne™). The absolute number average molecular weight (Mn(Abs)), weight average (Mw(Abs)) and absolute z average molecular weight (Mz(Abs)) are calculated according to Eqs. 6-8 as follows: Mn(Abs') = riRiΣΜ / ) V AMAbsoluteJ Eq.6 Mw(Abs) = %l(jRi * ^Absolutej) WR) Ec.7 Mz(Abs) = Tf(IRi * ^Absolute?'} lÍ(lRi*MAbsomtoi) Ec. 8 Average short chain branching frequency A calibration for the IR5 detector rationing was performed using at least ten ethylene-based polymer standards (ethylene-based polymer homopolymer and ethylene / octene copolymers) of known short chain branching (SCB) frequency (the comonomer content of the reference materials is determined using 13C NMR analysis of 2152541 of 51 84321-AR-NP in accordance with the techniques described, for example, in U.S. Patent No. 5,292,845 (Kawasaki, et al.) and by J.C. Randall in Rev. Chem. Phys., C29, 201317, which are incorporated herein by reference), ranging from homopolymer (0 SCB / 1000 total C) to about 50 SCB / 1000 total C, wherein the total C is equal to the carbons in the backbone plus the carbons in the branches. Each standard had a weight average molecular weight of 36,000 g / mol to 126,000 g / mol and had a molecular weight distribution of 2.0 to 2.5 as determined by GPC. The “IR5 height ratio (or “IR5methyl channel height / IR5measurement channel height”)” of “the baseline subtracted height response of the IR5 methyl channel sensor” to “the baseline subtracted area response of the IR5 measurement channel sensor” (standard filters and filter wheel supplied by PolymerChar: part number IR5_FWM01 included as part of the GPC-IR instrument) was calculated for each of the “copolymer” standards. A linear fit of wt% comonomer frequency versus “IR5 height ratio” is constructed in the form of the following Eq. 9: % by weight of comonomer = A0 + [A1(IR5Measuring channel area| of methyl / IR5Measuring channel area)]fC.9with coefficients A0= -47.94 and Ai = 239.0. Thus, a GPC-CC (comonomer content per GPC) plot (wt% comonomer vs. lgMW) can be obtained. End group correction of the wt% comonomer data can be performed through knowledge of the termination mechanism if there is significant spectral overlap with the comonomer termination (methyls) at 2152541 37 of 51 84321-AR-NP through the molecular weight determined in each chromatographic cut. The SCB frequency for each cut, sCBi of lgMwi, can be calculated using the ratio SCBi =Σ'» ,8 * % by weight of comonomer i) Eq. 10 for ethylene-octene copolymers and SCB, Σ(0.6 * weight % of comonomer f) Eq. 11 for ethylene-hexene copolymers. The average SCB frequency across the entire distribution can then be calculated. Average SCB = Σ (wtGPCi * SCBt). Eq.12 Deconvolution of the GPC chromatogram The fitting of the chromatogram into a high molecular weight (HMW) and low molecular weight (LMW) component fraction was achieved using a Flory distribution that was extended with a normal distribution function as follows: For the log M axis, 501 equally spaced Log(M) points, spaced by 0.01, were set between 2 and 7 representing the molecular weight range between 100 and 10,000,000 where Log is the logarithmic function to the base 10. 2152541 of 51 84321-AR-NP At any given Log(M), the population of the Flory distribution was in the form of Eq. 13: Mw 0.868588961964 ) M2e(2M / MW) Eq. 13 / where Mw is the weight average molecular weight of the Flory distribution and M is the specific x-axis molecular weight point, (10Λ[Log(M)]). The Flory distribution weight fraction was broadened at every 0.01 equally spaced log(M) index according to a normal distribution function, with width expressed as Log(M), σ; and the current M index expressed as Log(M), μ. (LogM- μ)2e 2σ2ftLogM.^a) = ^' 14 It is worth noting that before and after the spread function has been applied, the area of ​​the distribution (dWf / dLogM) based on Log(M) is normalized to unity. Two weight fraction distributions, dWf 1 and dWf 2, for LMW and HMW components or components 1 and 2 were expressed with two single Mw target values, Mw1 and Mw2, and with overall component compositions A1 and A2. Both distributions were scaled to the same width, σ. The two distributions were summed as follows: dWf= A1 dWf1+ A2dWf2Eq. 15 2152541 of 51 84321-AR-NP where: A1+A2 = 1 The resulting weight fraction of the measured GPC molecular weight distribution (from conventional GPC) was interpolated across the 501 logM points using a 2nd order polynomial. Microsoft Excel™ 2010 Solver was used to minimize the sum of squares of the residuals for the equally spaced range of 501 LogM points between the chromatographically determined interpolated molecular weight distribution and the two extended Flory distribution components (σi and σ2), weighed with their respective component compositions, A1 and A2. The iteration start values ​​for the components are as follows: Component 1: Mw = 30,000, σ = 0.300, and A = 0.475 Component 2: Mw = 250,000, σ = 0.300, and A = 0.475 (Note σi = σ2 and Ai + A2 = 1) The limits for components 1 and 2 are such that σ is constrained such that σ > 0.001, yielding a Mw / Mn of about 2.00, and σ < 0.450, yielding a Mw / Mn of about 5.71. The composition, A, is constrained between 0.000 and 1.000. The Mw is constrained between 2500 and 2,000,000. The composition, A, is constrained between 0.000 and 1.000. The Mw is constrained between 2500 and 2,000,000. The “nonlinear GRG” engine was selected in Excel Solver™, with precision set to 0.00001 and convergence set to 0.0001. Solutions were obtained after convergence (in all cases shown, the solution converged within 60 iterations). 2152541 of 51 84321-AR-NP The average short chain branching frequency distributions for the LMW and HMW components are calculated by dosing the short chain branching based on the weight fraction distribution of the two components, dWf 1 and dWf 2, obtained from the deconvolution described above and averaged for each component. Bimodality Test Method The presence or absence of resolved bimodality is determined by plotting dWf / dLogM (mass detector response) on the y-axis against LogM on the x-axis to obtain a GPC chromatogram curve containing local maxima of log(MW) for the LMW and HMW polyethylene component peaks, and noting the presence or absence of a local minimum between the LMW and HMW polyethylene component peaks. The dWf is the change in weight fraction, dLogM is also known as dLog(MW) and is the change in logarithm of molecular weight, and LogM is also known as Log(MW) and is the logarithm of molecular weight. Figure 2 shows the absolute GPC chromatogram of certain inventive and comparative Examples showing local maxima for the LMW and HMW polyethylene component peaks and a local minimum between the LMW and HMW polyethylene component peaks to illustrate the points for the bimodality test method. Extrusion line speed Extrusion line speed is a key parameter in the production of micro-drip irrigation, as it determines machine capacity per unit produced. Therefore, a high line speed is beneficial for the tape manufacturer. The line was optimized for pin and die geometry. 2152541 of 51 84321-AR-NP to allow for the highest possible line speed. To measure the maximum extrusion line speed, the line speed is gradually increased from 200 m / min to 250, 300, 350, and 400 m / min. The line speed is recorded using the extrusion parameters displayed by the control unit. The highest line speed, where the belt runs stably for several minutes, e.g., 30 minutes, is recorded and considered the maximum extrusion line speed for the example. In the event of an extrusion break at this speed, the lower line speed—where the product still runs stably—is considered the maximum extrusion line speed. Examples Materials used The following materials were included in the examples analyzed below. FINGERPRINT™ DFDC 7525, a unimodal ethylene / 1-hexene copolymer medium density polyethylene, is used as Comparative Example (CE) 1 and is commercially available from The Dow Chemical Company (Midland, MI). Preparation of Comparative Examples 2-4 and Inventive Examples 5-7 The exemplary bimodal medium density polyethylene compositions designated as Comparative Examples (CE) 2, 3 and 4, and Inventive Examples (IE) 5, 6 and 7 are produced by gas phase polymerization in a single reactor. A main catalyst was fed to a commercially available polyethylene reactor. 2152541 of 51 84321-AR-NP as UNIPOL™ from Univation Technologies, through a 0.25 inch injection tube (). A trim catalyst was also fed to the polyethylene reactor through the same 0.25 injection tube at a rate sufficient to provide the desired resin flow rate. The reactor gas composition was controlled by metering the feeds to the polyethylene reactor at rates sufficient to maintain the desired ethylene partial pressure, comonomer to ethylene (C2) mole ratio, hydrogen gas (H2) to ethylene (C2) mole ratio, and amount of isopentane. An additive, commercially available as CA-300 from Univation Technologies, was separately fed to the polyethylene reactor at a rate sufficient to maintain an additive concentration of approximately 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 approximately 1.8 to 2.5 hours. The reactor bed weight was maintained by discharging the granular resin into a dump tank, which was purged with nitrogen before being disposed of in a fiber pack and further purged with a nitrogen-steam mixture. Table 1A lists the polymerization conditions for CE 2, CE3, and CE4. Table 1B lists the polymerization conditions for IE 5, IE 6, and IE 7. The product is blended with additives (500 ppm calcium stearate, 1300 ppm Irganox™ 1010 and 1300 ppm Irgafos™ 168) and fed into a continuous mixer (LCM-100 continuous mixer from Kobe Steel, Ltd.), which is closed together with a gear pump, and equipped with a melt filtration device and an underwater pelletizing system. The properties of the Comparative Examples and the Inventive Examples are provided below in Tables 2A and 2B. In Tables 2A and 2B, “HMW” 2152541 of 51 84321-AR-NP refers to the high molecular weight polyethylene component and “LMW” refers to the low molecular weight polyethylene component. Microirrigation drip tapes are formed from bimodal medium-density polyethylene composition using a Maillefer International Oy MXC 60-36D extruder with a diameter of 60 mm and a length / diameter (L / D) ratio of 36. The extruder uses a suitable temperature profile to achieve a melt temperature of 240 °C. The extruder is equipped with an annular die with a diameter of 34.5 mm and a pin with a diameter of 32.5 mm (1 mm gap). Each microirrigation drip tape has an internal diameter of 16 mm. The annular wall thickness is adjusted by changing the extruder rotations per minute (rpm) and the extruder line speed. Each microirrigation drip tape is then calibrated and water-quenched. During cooling of the tape, just after leaving the extruder, the emitters are placed on the inner surface of the annular wall.Later in the line, perforations are made in-line in the annular wall of the emitters before winding the tape using a mechanical perforation device or laser cutting. The extrusion line speeds are given in Tables 2A and 2B. High-speed tape processing is a key property and requires efficient irrigation tape production. Processing trials were carried out on a Maillefer PIL032-miniFT test line. This line represents an entry-level model for the drip irrigation market, readily available from Maillefer upon request. The line was modified with a belt-drive system, type RCI 32, capable of higher line speeds of 300 to 400 m / min for development purposes. For calibration, a Maillefer BRI 32-16 m vacuum channel with dryer was used. 2152541 of 51 84321-AR-NP Inventive Examples 5, 6, and 7 were processed at line speeds up to 400 m / min with line and process configurations according to the following table: For Inventive Examples 5 and 6, 8 mil tapes were produced. Two different thicknesses of Inventive Example 7.8 mil (0.20 mm) (referred to as IE 7A) and 6 mil (0.15 mm) (referred to as IE 7B) were produced in thickness. The process parameters for the Inventive Examples are shown in Table A below. Table A - Process parameters for microirrigation tapes Inventive examples IE 5 IE 6 IE 7A IE 7B Temperature settings °C Zone 1 150 150 150 150 Zone 2 210 210 210 210 Zone 3 225 225 225 225 Zone 4 230 230 230 230 Zone 5 230 230 230 230 Zone 6 250 250 250 250 Adapter 250 250 250 250 Head 2 250 250 250 250 Head 3 250 250 250 250 Head 4 250 250 250 250 Rpm 1 / min 73.8 75.2 70 54.7 Torque Nm 266.4 253.4 240.1 218.6 Current ratio % 68 64.6 61.4 55.7 Head pressure Bar 373.5 346.2 322.5 295.9 Head pressure Bar 273.8 253 230.1 213.7 Melt temperature °C 234.8 241.9 241 241.5 Line speed m / min 400 399.992 399.911 399.98 Yield g / m kg / h 9.22 g / m 221.28 kg / h 9.67 g / m 232.07535 kg / h 9.09 g / m 218.11 kg / h 7.04 g / m 168.95 kg / h Average diameter mm 15.72 16.56 15.96 15.98 Water temperature °C 17.1 19.5 24.1 26.2 Tape thickness Mil 8 mil 8 mil 8 mil 6 mil Die / pin mm 34.5 / 32.5 34.5 / 32.5 34.5 / 32.5 34.5 / 32.5 2152541 of 51 84321-AR-NP Table 1A - Polymerization Conditions of Comparative Examples 2-4 CE2 CE3 CE4 Bed temperature (°C) 95 95 95 Reactor pressure (kPa) 2406 2406 2406 Partial pressure of C2 (kPa) 1517 1517 1517 H2 / C2 molar ratio 0.0037 0.0037 0.0034 C6 / C2 molar ratio 0.0067 0.0061 0.0080 Condensing agent induced (mol%) 1-methylbutane (10.6) 1-methylbutane (11.4) 1-methylbutane (13.0) Superficial gas velocity (m / sec) 0.55 0.52 0.55 Main catalyst MC-1a MC-1a MC-2b Trimming catalyst TC-1c TC-1c TC-2d Catalyst flow rate (g / hr) 7.5 7.9 6.3 Trim / cat. (1.5 wt. % trim) 0.26 0.18 0.16 Continuity additive CA-300 (ppm) 53 51 38 Conc. Zr catalyst (wt. %) 0.51 0.51 0.43 Conc. Al catalyst (% by weight) 20.8 20.8 18.9 Initial seedbed = granular HDPE resin Pre-charged Pre-charged Pre-charged Fluidized bed weight (kg) 30 29 38 Copolymer production rate (kg / hour) 17 15 19 Copolymer residence time (hour) 1.8 1.9 2.0 Copolymer fluid bulk density, (kg / m3) 178 175 245 aSpray-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 slurry. bSpray-dried mixture of bis(2-pentamethylphenylamido)ethyl)amine zirconium dibenzyl, (cyclopentadienyl)(1,5-dimethylindenyl)zirconium dimethyl, methylalumoxane (MAO), and fumed silica, commercially available as CAB-O-SIL® TS-610 from Cabot Corporation, in a mineral oil slurry. cBlend of 0.04% by weight of (1,3-dimethyl-4,5,6,7-tetrahydroindene)(methyl cyclopentadienyl)zirconium dimethyl bis(n-butylcyclopentadienyl)zirconium dimethyl in isopentaned Mixture of 0.04% by weight of (cyclopentadienyl)(1,5-dimethylindenyl)zirconium in isopentane Table 1B - Polymerization conditions of inventive examples 5-7 IE5 IE6 IE7 Bed temperature (°C) 95 95 95 Reactor pressure (kPa) 2413 2413 2413 Partial pressure of C2 (kPa) 1517 1517 1517 H2 / C2 molar ratio 0.0037 0.0037 0.0034 C6 / C2 molar ratio 0.0146 0.0150 0.0146 Induced condensation agent (% mol) 1-methylbutane (6.4) 1-methylbutane (6.4) 1-methylbutane (6.9) 2152541 of 51 84321-AR-NP Superficial Gas Velocity (m / sec) 0.55 0.55 0.58 Primary Catalyst MC-1a MC-1a MC-2b Trim Catalyst TC-1c TC-1c TC-2d Catalyst Flow Rate (g / hr) 7.4 9.0 5.7 Trim / cat. (1.5 wt % trim) 0.16 0.14 0.11 Continuity Additive CA-300 (ppm) 35 38 44 Conc. Zr Catalyst (wt %) 0.51 0.51 0.43 Conc. Al Catalyst (% by weight) 20.8 20.8 18.9 Initial seedbed = granular HDPE resin Pre-charged Pre-charged Pre-charged Fluidized bed weight (kg) 39 38 41 Copolymer production rate (kg / hour) 21 19 16 Copolymer residence time (hour) 1.9 2.0 2.5 Bulk density of copolymer fluid, (kg / m3) 258 242 255 aSpray-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 slurry. bSpray-dried mixture of bis(2-pentamethylphenylamido)ethyl)amine zirconium dibenzyl, (cyclopentadienyl)(1,5-dimethylindenyl)zirconium dimethyl, methylalumoxane (MAO), and fumed silica, commercially available as CAB-O-SIL® TS-610 from Cabot Corporation, in a mineral oil slurry. cBlend of 0.04% by weight of (1,3-dimethyl-4,5,6,7-tetrahydroindene)(methyl cyclopentadienyl)zirconium dimethyl bis(n-butylcyclopentadienyl)zirconium dimethyl in isopentaned Mixture of 0.04% by weight of (cyclopentadienyl)(1,5-dimethylindenyl)zirconium in isopentane Table 2A - Properties of Comparative Examples 1-4 CE 1 CE 2 CE 3 CE 4 Unimodal Bimodal Bimodal Bimodal Density (g / cm3) 0.939 0.950 0.950 0.952 I21 (dg / min) 22 16 11 17 (MFR2) 31 18 M21 / I2 (g / mol) 10,270 14,833 15,598 10,388 Mw (g / mol) 240,550 204,466 21,836 229,925 Mz (g / mol) 1,267,304 Mw / Mn 23.42 13.78 13.97 22.13 SCB / 1000C2 NM1 1.1 1.0 0.6 LMW Mw (g / mol) N / A3 20.078 19.481 (M3.A / M20.mol) 388,788 393,342 463,631 HMW Mw / LMW Mw N / A3 19.4 20.19 22.9 Weight fraction of HMW N / A3 0.576 0.541 0.467 LMW 393,6M / H1000C SCB / 1000C2 N / A3 1.3 1.2 0.5 Tensile strength (MPa) 19.3 25.2 24.8 25.7 2152541 of 51 84321-AR-NP NCTL Failure Time at 30% Yield Strength (hrs) 560 >1000 >1000 416 Strain Hardening Modulus (MPa) NM1 59.3 61.8 51.3 G'=G Intercept kPa 14.8 41.7 45.3 35.4 3094 HMW Wt% - 30.52 G'=G Intercept - 160.1 ( LMW SCB / 1000C / HMW SCB / 1000C) - 211.7 N / A3 -18.23 -30.85 -18.16 Maximum Extrusion Line Speed ​​(m / min) 400 Frequent Breaks Frequent Breaks Not Processable 1NM = not measured. 2SCB / 1000C = average short chain branching frequency per 1000 carbons3Comparative Example 1 is a unimodal resin and therefore these parameters are not applicable. Table 2B - Properties of Inventive Examples 5-7 IE 5 IE 6 IE 7 Mode Bimodal Bimodal Bimodal Density (g / cm3) 0.942 0.942 0.941 I21 (dg / min) 11 15 18 (MFR2) I21 / I2 93 NM1 124 Mn (g / mol) 16.165 16.145 12.575 Mw (g / mol) 209,232 206,598 208,507 Mz (g / mol) 1,032,727 1,150,292 1,106,758 Mw / Mn 12.94 12.80 16.58 SCB / 1000C2 1.46 1.85 2.49 LMW Mw (g / mol) 20,750 21,138 21,324 HMW Mw (g / mol) 374,420 376,936 409,578 HMW Mw / LMW Mw 18.04 17.83 19.21 HMW Weight Fraction 0.546 0.525 0.477 LMW SCB / 1000C2 0.94 1.27 2.23 HMW SCB / 1000C2 1.93 2.42 2.87 Tensile Yield Strength (MPa) 20.9 20.1 19.8 NCTL Failure Time at 30% Yield Strength (hrs) >1000 >1000 >1000 Strain Hardening Modulus (MPa) 92.2 86.4 71.7 Intersection G'=G kPa 45.3 41.4 36.8 3094 HMW % by weight - 30.52 Intersection G'=G - 160.1 ( LMW SCB / 1000C / HMW SCB / 1000C) - 211.7 18.02 65.73 17.17 2152541 of 51 84321-AR-NP Maximum speed of the extrusion line (m / min) 400 400 4003 1NM = not measured. 2SCB / 1000C = average short chain branching frequency per 1000 carbons3Maximum extrusion line speed for Inventive Example 7A (8 mil) and 7B (6 mil) As can be seen in Tables 2A and 2B, the inventive examples have an NCTL failure time of > 1000 hours, a strain hardening modulus of more than 65 MPa, and maximum extrusion line speeds of 400 m / min. None of the comparative examples have a combination of these parameters. Each document cited herein, if any, including any related or cross-referenced patent or application and any patent application or patent to which the present application claims priority or the benefit thereof, is incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. Citation of any document is not an admission that it is prior art with respect to any invention described or claimed herein or that alone, or in any combination with any other reference(s), teaches, suggests, or describes any such invention. Furthermore, to the extent that any meaning or definition of a term herein conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term herein shall control. While particular embodiments of the present invention have been illustrated and described, it will be obvious to those skilled in the art that various other changes and modifications may be made without departing from the spirit and scope of the invention. 2152541 of 51 84321-AR-NP Therefore, the appended claims are intended to cover all such changes and modifications which are within the scope of this invention. 2152541 of 51 Alejandra Aoun - 27184140328 Digitally signed by PORTALTRAMITES - INPI Date: 2023.02.06 14:43:23 -03:00 Reason: Digitally signed by the INPI Location: Buenos Aires, Argentina 2152541

Claims

1. A bimodal medium-density polyethylene composition comprising (i) a high molecular weight (HMW) polyethylene component comprising an ethylene / α-olefin copolymer and (ii) a low molecular weight (LMW) polyethylene component comprising an ethylene / α-olefin copolymer; the bimodal medium-density polyethylene composition having the following: (a) a density of 0.937 to 0.946 g / cm3; (b) a high load melt index (I21) of 7 to 20 g / 10 min; (c) an intersection G'=G” of 30 to 50 kPa; (d) a notched constant tensile load failure time to 30% yield strength, as measured in accordance with ASTMD5397, of more than 700 hours; (e) a strain hardening modulus of more than 65 MPa; and wherein the LMW polyethylene component has an average short-chain branching frequency of more than 0.9 SCB per 1000 carbons;wherein the HMW polyethylene component has a weight average molecular weight, Mw, of 300,000 to 600,000 g / mol; and wherein the HMW polyethylene component is present in an amount of 45 to 60% by weight, based on the total weight of the bimodal medium-density polyethylene composition. Six claims follow;