COMPOSITIONS FOR ROTOMOLDING WITH RELATIVE LOW ELASTICITY

Abstract

High-density polyethylene compositions with a high melt flow index and bimodal composition provide an excellent combination of processability, stiffness, and ductility in rotomolded articles. These compositions have a relatively low elasticity (G' / G'', measured at 0.05 rad / s) of less than 0.03.

Description

COMPOSITIONS FOR ROTOMOLDING WITH RELATIVE LOW ELASTICITY Field of Invention The present invention relates to high-density polyethylene compositions for use in rotomolded articles. The compositions have high rigidity and ductility. They also have a high flow index, which facilitates molding, especially for parts with complex shapes and geometries. The compositions have a relatively low elasticity (G' / G). Background of the Invention There are a number of different considerations when manufacturing a resin suitable for use in rotomolding manufacturing; non-limiting examples include the following: the resin must be capable of being produced at commercially acceptable production rates; the resin must be suitable for use in the rotomolding process (e.g., for example, having a suitable sintering temperature and a suitable cooling rate for removal from the mold); and the final rotomolded parts must have properties suitable for the end-use applications. U.S. Patents Nos. 5,382,630 and 5,382,631, granted on January 17, 1995, to Stehling and assigned to Exxon, disclose bimodal resins having superior physical properties. The patent requires that the mixture have QJ ίΖίη / ΖΖΠΖ / Β / ΥΙΛΙ Ref. 337551 two or more components, each with a polydispersity (Mw / Mn) less than 3 and the mixture having a polydispersity greater than 3 and no component of the mixture having a relatively higher molecular weight and lower comonomer content (i.e., comonomer incorporation is reversed). U.S. Patent No. 6,969,741, granted on November 29, 2005, to Lustiger et al. and assigned to ExxonMobil, discloses a polyethylene blend suitable for rotomolding. The patent states that the difference in density of each component is not less than 0.030 g / cm³. The difference in the densities of the component polymers in the present composition is less than 0.030 g / cm³. U.S. Patent No. 8,486,323, granted on July 16, 2013, to Davis and assigned to Dow Global Technologies Inc., discloses polymer blends used in rotomolded articles that have high impact resistance. The blends have a residual unsaturation of less than 0.06 per 1000 carbon atoms. Summary of the Invention One embodiment of the invention provides: a bimodal polyethylene composition having 1) a molecular weight distribution, Mw / Mn, from 2.3 to 5.5; 2) a density of 0.940 to 0.957 g / cc; 3) a melting index, I2, measured by ASTM D1238 at 190°C QJ ίΖίη / ΖΖΠΖ / Β / ΥΙΛΙ using a 2.16 kg load of 4 to 10 grams for 10 minutes; and 4) a relative elasticity, G' / G when measured at 190°C and 0.05 rad / second of less than 0.03 rad / second, wherein the bimodal polyethylene composition comprises: A. 10 to 70% by weight of a first ethylene copolymer having: Ai. a melting index, I2, measured by ASTM D1238 at 190°C using a 2.16 kg load of 0.4 to 5 grams for 10 minutes; A.ii. a molecular weight distribution, Mw / Mn, from 1.8 to 3.0; and A.iii. a density of 0.920 to 0.950 g / cc; B. 90 to 30% by weight of a second ethylene copolymer having: Bi. a melting index, I2, measured by ASTM D1238 at 190°C using a 2.16 kg load of 4 to 1500 grams for 10 minutes; Bi i. a molecular weight distribution, Mw / Mn, from 2.3 to 6.0; and Bi ii. a density higher than the density of the first ethylene copolymer but lower than 0.967 g / cc; provided that the density of the first ethylene copolymer is less than the density of the second ethylene copolymer by an amount of 0.010 to 0.035 g / cc. Another embodiment provides a process for the production of hollow polyolefin articles, comprising loading the bimodal polyethylene composition of claim 1 into a mold, heating this mold in an oven above 280°C so that the stabilized polyolefin fuses, rotating the mold about at least 2 axes, the plastic material spreading towards the walls, cooling the mold while it continues to rotate, opening it and removing the resulting hollow object. Another embodiment provides a process for making a bimodal polyethylene composition as above, comprising feeding ethylene and one or more C4-g comonomers to two sequential solution-phase reactors, in the presence of a single-site catalyst comprising a phosphinimine ligand together with one or more activators in the first reactor and a Ziegler Naphtha (ZN) catalyst in the second reactor. In one embodiment, the single catalyst is defined by the formula: (PDm I (L)n— M — (Y)pen where M is selected from the group consisting of Ti, Zr and Hf; PI is a phosphinimine ligand of the formula: R21\ r21 - p = N / QJ ίΖίη / ΖΖΠΖ / Β / ΥΙΛΙ R21 wherein each R21 is independently selected from the group consisting of a hydrogen atom; a halogen atom; hydrocarbyl radicals, typically Ci-io, which are either unsubstituted or further substituted by a halogen atom; alkoxy radicals Ci-s; aryl or aryloxy radicals Cg_io; amido radicals; silyl radicals of formula: --Si-- (R22)3 where each R22 is independently selected from the group consisting of hydrogen, an alkyl or alkoxy radical Ci-g and aryl or aryloxy radicals Ce-io / and a germanyl radical of formula: —Ge-(R22)3 where R22 is as defined above; L is a monoanionic cyclopentadienyl-type ligand selected independently from the group consisting of cyclopentadienyl-type ligands, Y is selected independently from the group consisting of activatable ligands; m is 1 or 2; n is 0 or 1; p is an integer and the sum of m+n+p is equal to the valency state of M. An additional embodiment provides a rotomolded part consisting essentially of the bimodal polyethylene composition described above. In another embodiment, rotomolded parts manufactured from the bimodal polyethylene composition described above exhibit ductile failure. Brief Description of the Figures Figure 1 shows the deconvolution of Example 1. The experimentally measured GPC chromatogram was deconvolved into a first and second ethylene interpolymer based on the predictions of the kinetic model. Figure 2 shows the deconvolution of Example 2. The experimentally measured GPC chromatogram was deconvolved into a first and second ethylene interpolymer (based on the predictions of the kinetic model). Figure 3 is a graph of the molecular weight distribution obtained by gel permeation chromatography (GPC) of the resin from examples 1, 2, 3 and 4. Figure 4 is a graph of the molecular weight distribution obtained by gel permeation chromatography (GPC) of the resin from examples 1, 8, 9 and 10. Figure 5 is a graph of the molecular weight distribution obtained by gel permeation chromatography (GPC) and the short chain branching distribution determined from GPC-FTIR of the resin from examples 3 and 4. Figure 6 is a graph of the molecular weight distribution obtained by gel permeation chromatography (GPC) and the short chain branching distribution determined from GPC-FTIR of the resin from examples 5, 6, 8 and 9. Detailed Description of the Invention Number intervals Except in operational examples or where otherwise stated, all numbers or expressions relating to quantities of ingredients, reaction conditions, etc., used in the description and claims shall be understood to be modified in all cases by the term "approximately." Consequently, unless otherwise stated, the numerical parameters stated in the following description and appended claims are approximations that may vary depending on the desired properties of the described embodiments. At a minimum, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter shall be interpreted at least in light of the number of significant digits reported and by applying ordinary rounding techniques. Although the numerical ranges and parameters that define the broad scope of this description are approximations, the numerical values ​​stated in the specific examples are reported as accurately as possible. However, any numerical value inherently contains certain errors that necessarily result from the standard deviation found in its respective test measurements. Furthermore, it should be understood that any numerical interval mentioned in this document is intended to include all subintervals within it. For example, an interval from 1 to 10 is intended to include all subintervals between and including the stated minimum value of 1 and the stated maximum value of 10; that is, any interval with a minimum value equal to or greater than 1 and a maximum value equal to or less than 10. Because the numerical intervals described are continuous, they include all values ​​between the minimum and maximum values. Unless expressly stated otherwise, the various numerical intervals specified in this application are approximations. All composition ranges expressed in this document are limited in total and do not exceed 100 percent (volume percent or weight percent) in practice. When multiple components may be present in a composition, the sum of the maximum amounts of each component may exceed 100 percent, with the understanding that, and as readily understood by persons experienced in the art, the amounts of the components actually used will conform to the 100 percent maximum. The compositions of the present invention are bimodal polyethylene and can be unscrewed into two distinct components. This is generally demonstrated by the presence of a ridge on the right side of a gel permeation chromatography (GPC) curve (Figure 1). In the present case, there is a small ridge on the right side of the GPC curve, as shown in Figure 2, indicating a small amount of a lower molecular weight, lower-density component. The high molecular weight component has a melting index of 0.4 to 5 and is present in an amount of approximately 10 to approximately 70% by weight of the total composition, preferably from approximately 15 to approximately 50% by weight. The lower molecular weight component is present in corresponding amounts of approximately 90 to approximately 30% by weight of the total composition, preferably from approximately 85 to approximately 50% by weight based on the weight of the entire composition. In one embodiment, the highest molecular weight component has a weight-average molecular weight (Mw) of approximately 70,000 to approximately 150,000, as determined using gel permeation chromatography (GPC). The highest molecular weight component has a polydispersity (Mw / Mn: weight-average molecular weight / number-average molecular weight) of 1.8 to 3.0. The melting index, I3, of the overall composition is approximately 4 to 10. The component with the highest molecular weight has a lower density than the component with the lowest molecular weight. The density of the highest molecular weight component in the composition may range from approximately 0.920 to approximately 0.950 g / cm³. The density of the component, or of any other component or the overall composition, is a function of the degree of incorporation of the comonomer. The highest molecular weight component preferably has no long-chain branching. The component with the lowest molecular weight has a melting index of 4 to 1,500. In one modality, the molecular weight (Mw) is approximately 28,000 to approximately 72,000, as determined using gel permeation chromatography (GPC), and a polydispersity (Mw / Mn) of 2.3 to 5.0. The lower molecular weight component has a density 0.010 to 0.030 g / cc greater than the higher molecular weight component. The catalysts used to produce the bimodal polyethylene compositions preferably do not produce long chain branching. The general properties of bimodal polyethylene compositions include the following: density of approximately 0.940 to approximately 0.957 g / cm3; QJ ίΖίη / ZZΖΠZ / Β / YΥΙΛΙ index of melt under a load of 2.16 kg (I2) at a temperature of 190°C as determined by ASTM 1238 of approximately 4 to approximately 10; and a relative elasticity G' / G, measured at 190 and 0.05 rad / second, less than 0.03 (especially from 0.01 to 0.03). In one modality, polyethylene compositions generally have a comonomer content of less than 1.2% by mol as measured by Fourier Transform Infrared Spectrometry (FTIR). The polymer can be prepared using a solution polymerization technique. In the solution polymerization of ethylene with one or more comonomers, non-limiting examples of comonomers include C3-8 α-olefins; in some cases, 1-hexene or 1-octene are preferred; in other cases, 1-octene is preferred. The monomers are typically dissolved in an inert hydrocarbon solvent, usually a C5-12 hydrocarbon, which may or may not be substituted with a C1-4 alkyl group, such as pentane, methylpentane, hexane, heptane, octane, cyclohexane, methylcyclohexane, and hydrogenated naphtha. An example of a suitable solvent that is commercially available is Isopar E (Cg-12 aliphatic solvent, Exxon Chemical Co.). The catalyst and activators are also dissolved in the solvent or suspended in a diluent miscible with the solvent under the reaction conditions. Catalysts In one embodiment, the single-site catalyst is a compound of formula (PDm I (Dn — M — (Y)p) where M is selected from the group consisting of Ti, Zr, and Hf; PI is a phosphinimine ligand of formula: R21 R21 _ p= N_ / R21 wherein each R21 is independently selected from the group consisting of a hydrogen atom; a halogen atom; hydrocarbyl radicals, typically Ci-io, which are either unsubstituted or further substituted by a halogen atom; alkoxy radicals Ci-s; aryl or aryloxy radicals Cc-io / amido radicals; silyl radicals of formula: --Si-- (R22)3 where each R22 is independently selected from the group consisting of hydrogen, an alkyl or alkoxy radical Ci-g and aryl or aryloxy radicals Ce-io / and a germanyl radical of formula: QJ ίΖίη / ZZΖΠZ / Β / YΥΙΛΙ —Ge— (R22)3 where R22 is as defined above; L is a monoanionic cyclopentadienyl-type ligand selected independently from the group consisting of cyclopentadienyl-type ligands, Y is selected independently from the group consisting of activatable ligands; m is 1 or 2; n is 0 or 1; p is an integer and the sum of m+n+p is equal to the valency state of M. Suitable phosphinimines are those in which each R21 is a hydrocarbyl radical, preferably a C1-e hydrocarbyl radical, more preferably a C1-4 hydrocarbyl radical. The term cyclopentadienyl refers to a 5-membered carbon ring that has a delocalized bond within the ring and is typically attached to the active catalyst site, usually a group 4 (M) metal, via δ-5 linkages. The cyclopentadienyl ligand may be unsubstituted or fully substituted with one or more substituents selected from the group consisting of C1-10 hydrocarbyl radicals that are either unsubstituted or further substituted with one or more substituents selected from the group consisting of a halogen atom and a C1-4 alkyl radical; a halogen atom; a C1-θ alkoxy radical; a Cg-ium aryl or aryloxy radical; an unsubstituted or substituted amido radical; or an unsubstituted or substituted phosphide radical. QJ ίΖίη / ZZΖΠZ / Β / ΥΙΛΙ two Ci-g alkyl radicals; silyl radicals of formula -Si-(R) 3 wherein each R is independently selected from the group consisting of hydrogen, an alkyl or alkoxy Ci-g radical, aryl or aryloxy Cg-io radicals; and germanyl radicals of formula Ge-- (R) 3 wherein R is as defined above. The cyclopentadienyl-type ligand can be selected from the group consisting of a cyclopentadienyl radical, an indenyl radical, and a fluorenyl radical, the radicals of which are either unsubstituted or completely substituted by one or more substituents selected from the group consisting of a fluorine atom, a chlorine atom; Ci-4 alkyl radicals; and a phenyl or benzyl radical either unsubstituted or substituted by one or more fluorine atoms. Activatable ligands Y can be selected from the group consisting of a halogen atom, C1-4 alkyl radicals, C6-20 aryl radicals, C7-12 arylalkyl radicals, Cg-1θΛ phenoxy radicals, amido radicals that may be substituted by up to two C1-4 alkyl radicals, and C1-4 alkoxy radicals. In some cases, Y is selected from the group consisting of a chlorine atom, a methyl radical, an ethyl radical, and a benzyl radical. Suitable phosphinimine catalysts are Group 4 organometallic complexes containing a phosphinimine ligand (as described above) and a ligand of QJ ίΖίη / ΖΖΠΖ / Β / ΥΙΛΙ cyclopentadienyl type (L) and two activatable ligands. The catalysts are not bridged. Activators The activators for the catalyst are normally selected from the group consisting of aluminoxanes and ionic activators. Alumoxanes (also known as aluminoxanes) The suitable alumoxane may have the formula: (R4) 2A1O (R4A1O) mAl (R4) 2 where each R4 is independently selected from the group consisting of C1-20 hydrocarbyl radicals and m is from 0 to 50, preferably R4 is a C1-4 alkyl radical and m is from 5 to 30. A non-limiting example of a suitable alumoxane is methylalumoxane (or MAO) where each R is methyl. Alumoxanes are well known as cocatalysts, particularly for metallocene-type catalysts. They are also readily available commercial products. The use of an alumoxane cocatalyst generally requires a molar ratio of aluminum to the transition metal in the catalyst of approximately 20:1 to approximately 1000:1; or, in other cases, from approximately 50:1 to approximately 250:1. Commercially available MAO typically contains free alkyl aluminum (e.g., trimethylaluminum or TMA) which can reduce the QJ ίΖίη / ZZΖΠZ / Β / YΥΙΛΙ catalyst activity and / or broaden the molecular weight distribution of the polymer. If a polymer with a narrow molecular weight distribution is required, it is preferable to treat the commercially available MI0 with an additive that is capable of reacting with TMA; non-limiting examples of suitable additives include hindered alcohols or phenols. Ionic activating cocatalysts So-called ionic activators are also well known for metallocene catalysts. See, for example, U.S. Patent No. 5,198,401 (Hlatky and Turner) and U.S. Patent No. 5,132,380 (Stevens and Neithamer). While we do not wish to limit ourselves to any one theory, those experienced in the technique believe that ionic activators initially cause the abstraction of one or more of the activatable ligands in a way that ionizes the catalyst into a cation, then provide a bulky, labile, non-coordinating anion that stabilizes the catalyst in a cationic form. The bulky, non-coordinating anion allows the polymerization of definites to take place in the center of the cationic catalyst (presumably because the non-coordinating anion is labile enough to be displaced by the monomer that coordinates to the catalyst). Non-limiting examples of ionic activators are boron-containing ionic activators such as: compounds of formula [R5] + [B (R7) 4] ~ wherein B is a boron atom, R5 is an aromatic hydrocarbyl (e.g., triphenylmethyl cation) and each R7 is independently selected from the group consisting of phenyl radicals that are either unsubstituted or substituted with 3 to 5 substituents selected from the group consisting of a fluorine atom, an unsubstituted or fluorine-substituted C1-4 alkyl or alkoxy radical; and a silyl radical of formula -Si--(Rs)3; wherein each R9 is independently selected from the group consisting of a hydrogen atom and a C1-4 alkyl radical;and compounds of formula [(R8)tZH] + [B(R7)4] where B is a boron atom, H is a hydrogen atom, Z is a nitrogen or phosphorus atom, t is 2 or 3, and R8 is selected from the group consisting of C1-8 alkyl radicals, an unsubstituted or substituted phenyl radical with up to three C1-4 alkyl radicals, or an R8 taken together with the nitrogen atom can form an anilinium radical and R7 is as defined above; and compounds of formula B(R7)a where R7 is as defined above. In the above compounds, preferably R7 is a pentafluorophenyl radical and R5 is a triphenylmethyl cation, Z is a nitrogen atom and R8 is a C1-4 alkyl radical or R8 taken together with the nitrogen atom forms an anilinium radical that is substituted by two O-4 alkyl radicals. The ionic activator can abstract one or more activatable ligands to ionize the catalyst center into a cation but not to covalently bond with the catalyst and to provide a sufficient distance between the catalyst and the ionizing activator to allow a polymerizable olefin to enter the resulting active site. Examples of ionic activators include: triethylamonium tetra (phenyl)boron; tripropylamonium tetra (phenyl) boron; tetra(phenyl)boron de tri(n-butyl)ammonium; tetra(p-tolyl)trimethylammonium boron; tetra(o-tolyl)trimethylammonium boron; tetra(pentafluorophenyl) tributylammonium boron; tripropylamonium tetra(o,p-dimethylphenyl)boron; tetra(m,mdimethylphenyl) tributylammonium boron; tetra(ptrifluoromethylphenyl) tributylammonium boron; tetra(pentafluorophenyl) tributylammonium boron; tetra(otolyl)boron de tri(n-butyl)ammonium; N,Ndimethylanilinium tetra(phenyl)boron; N,N-diethylanilinium tetra(phenyl)boron; tetra(phenyl)n-butylboron of N,N-diethylanilinium; tetra(phenyl)boron of N,N-2,4,6-pentamethylanilinium; tetra(pentafluorophenyl)boron of di-(isopropyl)amonium; tetra(phenyl)boron of dicyclohexylamonium; tetra(phenyl)boron of triphenylphosphonium; tetra(phenyl)boron of tri(methylphenyl)phosphonium; tetra(phenyl)boron of tri(dimethylphenyl)phosphonium; tetrakispentafluorophenyl borate of tropylium; tetrakispentafluorophenyl triphenylmethyl borate; tetrakispentafluorophenyl benzene borate(diazonium); phenyltrispentafluorophenyl tropyl borate; phenyltrispentafluorophenyl triphenylmethyl borate; phenyltrispentafluorophenyl benzene borate(diazonium); tetrakis(2,3,5,6-tetrafluorophenyl) tropyl borate; tetrakis(2,3,5, 6-tetrafluorophenyl) triphenylmethyl borate; tetrakis(3,4,5-trifluorophenyl) benzene borate(diazonium); tetrakis(3,4,5-trifluorophenyl) tropyl borate; tetrakis(3,4,5-trifluorophenyl) benzene borate(diazonium); tetrakis(1,2,2-trifluoroethenyl) tropyl borate; tetrakis(1,2,2-trifluoroethenyl) triphenylmethyl borate; tetrakis(1,2,2-trifluoroethenyl)borate of benzene(diazonium); tetrakis(2,3,4,5-tetrafluorophenyl)borate of tropyl; tetrakis(2,3,4,5-tetrafluorophenyl)borate of triphenylmethyl; and tetrakis(2,3,4,5-tetrafluorophenyl)borate of benzene(diazonium). Commercially available ionic activators include: N,N-dimethylanilinium tetrakispentafluorophenyl borate; triphenylmethyl tetrakispentafluorophenyl borate; and trispentafluorophenyl borane. The ionic activator can be used in approximately molar equivalents of boron to group IV metal in the catalyst. Suitable molar ratios of the catalyst group IV metal to boron can be found in the range between approximately 1:1 and QJ ίΖίη / ZZΖΠZΖ / Β / YΥΙΛΙ approximately 3:1, in other cases, between approximately 1:1 and approximately 1:2. In some cases, the ionic activator can be used in combination with an alkylation activator (which can also serve as a scrubber). The ionic activator can be selected from the group consisting of (R3)MgX2-p where X is a halide and each R3 is independently selected from the group consisting of C1-io alkyl radicals and p is 1 or 2; R3Li where R3 is as defined above; (R3)qZnX2-q where R3 is as defined above, X is a halogen and q is 1 or 2; (R3)sAIX3-Sen where R3 is as defined above, X is a halogen and s is an integer from 1 to 3. Preferably, in the above compounds, R3 is a C1-4 alkyl radical and X is chlorine. Commercially available compounds include triethylaluminum (TEAL), diethylaluminum chloride (DEAC), dibutylmagnesium ((Bu)2Mg) and butylethylmagnesium (BuEtMg or BuMgEt). If the phosphinimine catalyst is activated with a combination of ionic activators (e.g., boron compounds) and an alkylating agent, the molar ratio of the group IV metal of the catalytic metalloid (boron) of the ionic activator:metal of the alkylating agent may be in the range of approximately 1:1:1 to approximately 1:3:10, in other cases from approximately 1:1.3:5 to approximately 1:1.5:3. Second catalyst In one embodiment, a ZN catalyst is used in the second reactor. Any ZN catalyst system that works well for solution polymerization of ethylene (optionally with one or more alpha olefin comonomers, especially 1-butene, 1-hexene, or 1-octene) is potentially suitable. The ZN catalysts described in U.S. Patents Nos. 10,023,706 and 9,695,309 are specific (but not limiting) examples. Polymerization process The temperature of the reactor(s) in a high-temperature solution polymerization process is approximately 80°C to approximately 300°C; in other cases, it ranges from approximately 120°C to 250°C. The upper temperature limit will be influenced by considerations well known to those experienced in the art, such as the desire to maximize the operating temperature (to reduce the solution viscosity) while maintaining good polymer properties (since increasing polymerization temperatures generally reduces the polymer's molecular weight). In general, the upper polymerization temperature can be between approximately 200°C and approximately 300°C. A process using two reactors can be carried out at two different temperatures, with the temperature of the second reactor being higher than that of the first. The most preferred reaction process is a pressure process. QJ L7 iΠ / 77Ω7 / B / YILI media, meaning that the pressure in the reactor or reactors is preferably less than approximately 6000 psi (approximately 42,000 kilopascals or kPa). Preferred pressures are from approximately 10,000 to approximately 40,000 kPa (1450-5800 psi), most preferably from approximately 14,000 to approximately 22,000 kPa (2,000 psi to 3,000 psi). In some reaction schemes, the pressure in the reactor system must be high enough to maintain the polymerization solution as a single-phase solution and provide the upstream pressure necessary to feed the polymer solution from the reactor system through a heat exchanger and a devolatilization system. Other systems allow the solvent to be separated into a polymer-rich stream and a polymer-poor stream to facilitate polymer separation. The solution polymerization process can be carried out in a stirred-tank reactor system comprising one or more stirred-tank reactors, one or more loop reactors, or a mixed stirred-tank and loop reactor system. The reactors can operate in tandem or in parallel. In a tandem double-reactor system, the first polymerization reactor preferably operates at a lower temperature. The residence time in each reactor will depend on the reactor design and capacity. In general, the reactors should be operated under conditions that ensure thorough mixing of the reactants. Furthermore, it is preferred that 20 to 60% by weight of the final polymer be polymerized in the first reactor, with the remainder being polymerized in the second reactor. A useful solution polymerization process uses at least two polymerization reactors in series. The polymerization temperature in the first reactor is approximately 80°C to approximately 180°C (in other cases, approximately 120°C to 160°C), and the second reactor is typically operated at a higher temperature (up to approximately 220°C). The most preferred reaction process is a medium-pressure process, meaning that the pressure in each reactor is preferably less than approximately 6000 psi (approximately 42,000 kilopascals or kPa), most preferably from approximately 2000 psi to approximately 3000 psi (approximately 14000 to approximately 22000 kPa). Examples Testing methods Mn, Mw, and Mz (g / mol) were determined by high-temperature gel permeation chromatography (GPC) with differential refractive index detection using universal calibration (ASTM-6467). The molecular weight distribution (MWD), also known to those experienced in the technique as polydispersity or polydispersity index, is the ratio between the weight average molecular weight (Mw) and QJ ίΖίη / ΖZΖΠΖ / Β / ΥΙΛΙ the number average molecular weight (Mn). GPC was used in combination with Fourier transform infrared spectroscopy (GPC-FTIR) to determine comonomer content as a function of molecular weight. After polymer separation by GPC, an online FTIR spectrometer measured the polymer concentration and the methyl end groups. The methyl end groups were used in branching frequency calculations. Conventional calibration allowed for the calculation of a molecular weight distribution. Mathematical deconvolutions were performed to estimate the relative amount of polymer, molecular weight, and comonomer content of the component manufactured in each reactor. The short-chain branching frequency (SCB per 1000 carbon atoms) of the copolymer samples was determined by Fourier transform infrared spectroscopy (FTIR) according to ASTM D6645-01. A Thermo-Nicolet 750 Magna-IR spectrophotometer was used for the measurement. FTIR was also used to determine the levels of internal, side-chain, and terminal unsaturation (also referred to as unsats for convenience). Comonomer content can also be measured using carbon-13 nuclear magnetic resonance (NMR) techniques QJ ίΖίη / ΖΖΠΖ / Β / ΥΙΛΙ as described in Randall Rev. Macromol. chemistry Phys., C29 (2 and 3), p. 285; US Patent No. 5,292,845 and WO 2005 / 121239. Information on the composition distribution was also obtained from temperature-raising elution fractionation (TREF). A polymer sample (80–100 mg) was introduced into the reactor vessel of the Polymer Char crystal-TREF unit. The reactor vessel was filled with 35 mL of 1,2,4-trichlorobenzene (TCB) and heated to the desired dissolution temperature (e.g., 150°C) for 2 hours. The solution (1.5 mL) was then loaded onto the TREF column filled with stainless steel beads. After allowing equilibration at a given stabilization temperature (e.g., 110°C) for 45 minutes, the polymer solution was allowed to crystallize with a temperature drop from the stabilization temperature to 30°C (0.090°C / minute). After equilibrating at 30°C for 30 minutes, the crystallized sample was eluted with TCB (0.75 ml / minute) with a temperature ramp from 30°C to the stabilization temperature (0.25°C / minute).The TREF column was cleaned at the end of the run for 30 minutes at the dissolution temperature. Data were processed using PolymerChar software, Excel spreadsheets, and the internally developed TREF software. CDBI is defined as the percentage of polymer whose composition is within 50% of the median comonomer composition. It is calculated from the composition distribution curing and the normalized cumulative integral of the composition distribution curve, as illustrated in U.S. Patent No. 5,376,439. The density of the polyethylene composition (g / cm3) was measured according to ASTM D792. The melting indices 12, 16, and I22 for the polyethylene composition were measured according to ASTM D1238. For clarity: I2 is measured at 190°C with a load of 2.16 kilograms; I2i is measured at the same temperature with a load of 21.6 kilograms. The density and melt index of the first and second ethylene polymers comprising the polyethylene composition were determined based on composition models. The following equations were used to calculate the density and melt index I2 (reference to U.S. Patent 8,022,143 B2, Wang, assigned to NOVA Chemicals and published September 20, 2011): Density = 0.979363 - 5.95308 x 10-3) - 3.83133 x iiooacv w A \0·25 10'4[logi0(A / rA3- 5.77986 x ) + 5.57395 x ΙΟ3' ) log10(Fusion index = 22.326528 + 3.467 x 10-3[logi0GO3- 4.322582 - 1.80061 x 10-i[logLOGWzF2-h 2.6478 X W2[logi0GWz)]3 QJ ίΖίη / ZZΖΠZ / Β / YΙΛΙ where Mη, Mw, Mz and SCB / 1000C are the deconvoluted values ​​of the individual ethylene polymer components, obtained from the results of the deconvolution described above. The primary melting peak (°C), heat of fusion (J / g), and crystallinity (%) were determined using differential scanning calorimetry (DSC) as follows: the instrument was first calibrated with indium; then a polymer sample was equilibrated at 0°C; the temperature was increased to 200°C at a heating rate of 10°C / min; the melt was then held at that temperature for five minutes; the melt was then cooled to 0°C at a cooling rate of 10°C / min and held at 0°C for five minutes; the sample was then heated a second time to 200°C at a heating rate of 10°C / min. The reported melting peak (Tm), heat of fusion, and crystallinity are calculated based on the second heating. RHEOLOGY - RESISTANCE TO FUSION BY CAPILLARY RHEOMETRY The molten polymer is extruded through a capillary die at a constant extrusion rate. The extruded chain is stretched at an increasing draw rate. The melt pull force is continuously monitored, and the maximum constant value of the force level at or before chain breakage is defined as the melt strength. The ratio of the draw rate to the extrusion rate at the die exit is defined as the draw ratio. Melt strength is measured using a capillary rheometer (cylinder diameter = 15 mm) with a 2 mm diameter flat die, L / D ratio 10:1, at 190°C. Pressure transducer: 10,000 psi (68.95 MPa). Piston speed: 5.33 mm / min. Drag angle: 52°. Incremental drag speed: 50 m / min² or 65 ± 15 m / min². A polymer melt is extruded through a capillary die at a constant speed, and then the polymer chain is pulled at an increasing pull speed until it breaks. The maximum stable force value in the plateau region of a force-versus-time curve is defined as the polymer's melt strength. The melt stretch ratio is defined as the ratio of the speed at the pulley to the speed at the die exit. RHEOLOGY - DMA Rheological properties were determined using frequency sweep test measurements on a rotational rheometer. A sample (in the form of a compression-molded disc) is placed in an environmental test chamber between two test geometries: the upper geometry attached to the drive shaft and the lower geometry attached to a base. The analysis is performed over a frequency range, at a fixed strain and a constant temperature. The rheometer was a commercially available instrument (sold under the name DHR-3 by TI Instruments). This testing technique provides the opportunity to study the various characteristics of a polymer melt where the elastic and viscous modulus (G' and G), complex viscosity, complex modulus (G*), loss tangent, dynamic viscosity, out-of-phase component of the complex modulus, phase angle, and other rheological properties as a function of oscillation frequency are generated to provide information on rheological behavior in correlation with molecular architecture. The rheological parameters derived from the test data are: crossover frequency, crossover modulus, three Ellis model constants: Ellis constant C1 (or zero shear viscosity), Ellis constant C2 (or reciprocal of the characteristic relaxation time), Ellis constant C3 (or power law exponent), Dow rheology index (DRI), relaxation spectrum index (RSI), melt elasticity index (G' @ G = 500 Pa), viscosity ratio, Cole-Cole diagrams and VGP. Relative elasticity, defined as the ratio of G' to G at a frequency of 0.05 rad / s. Without intending to limit ourselves to theory, it has been observed that a relatively low relative elasticity correlates with powder densification during the rotomolding process. The Izod impact test was performed in accordance with ASTM D256-10E1. The tensile impact test was performed in accordance with ASTM D1822-13. The rotomolded parts were prepared on a rotational molding machine sold under the trade name Rotospeed RS3-160 by Ferry Industries Inc. The machine has two arms that rotate around a central axis inside a closed oven. The arms are equipped with platens that rotate about an axis approximately perpendicular to the arm's axis of rotation. Each arm is equipped with six cast aluminum molds that produce plastic cubes with dimensions of 12.5 in. (31.8 cm) x 12.5 in. x 12.5 in. The arm rotation was set to approximately 8 revolutions per minute (rpm), and the platen rotation was set to approximately 2 rpm. These molds produce parts that have a nominal thickness of approximately 0.25 in. (0.64 cm) when initially filled with a standard charge of approximately 3.7 kg of powdered polyethylene resin (US 35 mesh size).The temperature inside the closed oven was maintained at 560°F (293°C). The molds and their contents were heated for a specific period of time until complete densification of the powder was achieved. The molds were then cooled in a controlled environment before the parts were removed. Specimens of the molded parts were collected for density and color measurements. The ARM impact test was performed in accordance with ASTM D5628 at a test temperature of -40°C. The test specimens to be impacted must be rotationally molded from a single piece. The test specimens must be conditioned to achieve uniform cooling of the sample cross-section to no less than -40°F ± 3.5°F (-40°C ± 2°C). The impact testing technique for a rotationally molded part is commonly called the Bruceton ladder method or the up-and-down method. The procedure establishes the height of a specific dart that will cause 50% of the specimens to fail. The percentage of ductility represents the percentage of failures that exhibited ductile characteristics. Specimens are subjected to impact testing using a drop-weight impact tester. If the specimen does not fail at a predetermined height / weight, the height or weight is gradually increased until failure occurs. Once failure has occurred, the height / weight is reduced in the same increment, and the process is repeated until all specimens have been used. The falling dart must impact the surface of the part that was in contact with the mold when it was molded. For polyethylene, ductile failure is the desired failure mode that generally occurs in properly processed specimens.A brittleness failure or fragmentation failure generally indicates that the optimal properties have not been obtained by the processing parameters used. Ductile: indicated by the dart penetrating through the specimen, leaving a hole with filamentous fibers at the point of failure rather than cracking outward from the point of failure. The area beneath the dart has elongated and thinned at the point of failure. Brittle: means that the piece physically separates or cracks at the point of impact. The sample has very little or no elongation. As used in this document, the term ductility index refers to the percentage of parts in a multi-part test that exhibit ductile failure. For example, if 10 pieces are tested and 8 of them exhibit ductile failure (i.e., 80% of the pieces exhibit ductile failure), then the test result is reported to have a ductility index of 80%. The Resin Bimodal polyethylene compositions were prepared in a dual-reactor pilot plant. In this dual-reactor process, the contents of the first reactor flow into the second reactor, both thoroughly mixed. The process operates using continuous feed streams. The catalyst (cyclopentadienyl tri(butyl tertiary)phosphinimine titanium dichloride) [note: this catalyst is referred to as Pl-cat in tables describing experimental polymerizations] with activator was fed to the first reactor, and a ZN catalyst to the second. The overall production rate was approximately 90 kg / h. The polymerization conditions are provided in Table 1. The polymer compositions prepared at the pilot plant were stabilized using a conventional additive package for rotomolding applications before plate testing. Rotomolding compositions typically contain an additive package to protect the polyethylene from degradation during processing and to subsequently protect the rotomolded part from atmospheric exposure. The compositions described here are not intended to be limited to the use of any specific additive package.The inventive compositions shown in the examples contained the following additives (all quantities are shown in parts per million by weight relative to the weight of polyethylene): 500 ppm of hindered phenol (CAS Registry Number 2082-79-3); 550 ppm of phosphite (CAS Registry Number 31570-04-4); 450 ppm of diphosphite (CAS Registry Number 154862-43-8); 250 ppm of hydroxylamine (CAS Registry Number 143925-92-2); 750 ppm of hindered amine light stabilizer (HALS)-1 (CAS Registry Number 70624-189); 750 ppm of HALS-2 (CAS Registry Number 65447-77-0); and 750 ppm of zinc oxide. Table 2 describes the GPC deconvolution results, in which Examples 1 and 2 were mathematically deconvolved into a first ethylene polymer (synthesized in reactor 1) and a second ethylene polymer (synthesized in reactor 2). The density and melt index of the first and second ethylene polymers were calculated based on fundamental kinetic models (with kinetic constants specific to each catalyst formulation), as well as the feed and reactor conditions. The equations used to calculate the densities and melt indices were described earlier (and in U.S. Patent No. 8,022,143). The simulation was based on the dual-reactor solution pilot plant configuration described earlier. The first ethylene interpolymer was fitted to a distribution based on a fundamental kinetic model describing the behavior of the single-site catalyst formulation.The second ethylene interpolymer was fitted to a distribution based on a fundamental kinetic model describing the behavior of the heterogeneous catalyst formulation. As shown in Table 2, in the case of Example 1, the first plus the second ethylene polymer comprise 88 wt% of Example 1; the remainder of Example 1 (12 wt%) was synthesized in the junction reactor of tubes 1 and 2 (<3 wt%, with the same composition as the first ethylene polymer) and the tube following reactor 2 (<10 wt%, with the same composition as the second ethylene polymer) before the catalyst deactivator was added. The properties of the pressed plates of the rotomolding resins described herein (Examples 1 to 4) are shown in Table 3a; the comparative resins are shown in Table 3b (Comparative Examples 5 to 8). The properties of the rotomolded parts as well as the pressed plates manufactured from the polyethylene compositions described herein are shown in Table 4a; and comparative properties are shown in Tables 4b and 4c. Resins with higher density generally do not perform well in rotomolding applications that also require good toughness. Examples 1 and 2 show superior performance to the comparative examples with a combination of high density, good toughness (ductility >50%), and high mean failure energy under optimal molding conditions. Without limiting ourselves to theory, high density translates into greater stiffness and allows the use of less material to achieve a TABLE 1 - CONTINUED Conditions of manufacture QJ I 7 I η / 77Π7 / Β / ΥΙΛΙ Comparative Example 8 Comparative Example 9 Comparative Example 10 Catalyst in R1 Pl-cat Pl-cat Pl-cat Catalyst in R2 ZN Pl-cat Pl-cat Ethylene partition between the first reactor (R1), the second reactor (R2) and the third reactor (R3) 0.25 / 0.75 / 0 0.30 / 0.70 / 0 Octene partition between the first reactor (R1), the second reactor (R2) and the third reactor (R3) 1 / 0 / 0 1 / 0 / 0 Octene / ethylene ratio in the fresh feed 0.135 0.144 Hydrogen in reactor 1 (ppm) 1.2 0.9 Hydrogen in reactor 2 (ppm) 24.3 2.9 Temperature of reactor 1 (°C) 138 138 Temperature of reactor 2 (°C) 212 210 Conversion in the reactor 1 (%) 91.5 89.6 Conversion in reactor 2 (%) 91.9 88.0 Catalyst feed in reactor 1 - (ppm of Ti) 0.21 0.14 SSC - Al / Group 3 metal in reactor 1 (mol / mol) SSC - B / Group 4 metal in reactor 1 (mol / mol) 0.69 Catalyst feed in reactor 2 - Pl (ppm of Ti) 4.7 Catalyst feed in reactor 2 - (ppm of Ti) 2.0 Catalyst feed in reactor 2 - tert-butyl chloride / butyl(ethyl) magnesium (mol / mol) 1.4 Catalyst feed in reactor 2 - Diethylaluminum ethoxide / Titanium tetrachloride (mol / mol) 0.4 Catalyst feed in reactor 2 Triethylaluminum / Titanium tetrachloride (mol / mol) 7.0 Polyethylene production rate (kg / h) 94.1. TABLE 2 Deconvolution results to describe the global molecular weight distribution QJ ίΖίη / ΖΖΠΖ / Β / ΥΙΛΙ Example 1 Example 2 1st ETHYLENE POLYMER (R1 - Deconvolution Studies) Catalyst System Pl-cat Pl-cat Weight Fraction (%) 29% 26% Mn 53.915 50.107 Mw 107.831 100.214 Mz 161.747 150.321 Polydispersity Index (Mw / Mn) 2.0 2.0 Branching Frequency / 1000C (SCB1) 1.4 3.6 Density Estimate (g / cm3) (d1) Equation (1) 0.9370 0.9316 Melting Index Estimate I2 (g / 10 min) Equation (2) 0.63 0.83 2nd ETHYLENE POLYMER (R2 - Deconvolution Studies) Catalyst System ZN ZN Weight fraction (%) 71% 74% Mn 19,974 19,875 Mw 49,054 49,062 Mz 94,329 94,638 Polydispersity index (Mw / Mn) 2.5 2.5 Branching frequency / 1000C (SCB2) 0.4 1.0 Density estimate (g / cm3) (d2) Equation (1) 0.9514 0.9491 Melting index estimate I2 (g / 10 min) Equation (2) 13.49 13.48 GENERAL ETHYLENE POLYMER (Deconvolution studies) Mn 23,453 22,709 Mw 63,840 60,416 Mz 119,603 112,405 index polydispersity (Mw / Mn) 2.7 2.7 TABLE 3a Resin characteristics QJ ΤΖΙΝ / ΖΖΠΖ / Β / ΥΙΙΛΙ Example 1 Example 2 Example 3 Example 4 Density (g / cm3) 0.9506 0.9452 0.9412 0.9422 Melting index l2 (g / 10 min) 6.4 6.4 6.7 7.75 Melting index I21 (g / 10 min) 129 133 136 184 Strain exponent 1.19 1.20 1.18 1.23 Melting flux ratio (I21 / I2) 20.3 20.9 20.1 23.8 CTREF / CTREF SLOW High elution peak (°C) 95.1 94.9 Low elution peak (°C) 85.9 86.0 CDBI50 62.8 68.8 Branching frequency - FTIR Frequency of Branching / 1000C 1.9 3.5 4.2 4.4 Comonomer ID octene octene octene octene Comonomer content (mol %) 0.4 0.7 0.8 0.9 Comonomer content (wt %) 1.5 2.7 3.3 3.4 Internal Unsaturation / 100C 0 0.001 0.002 0.003 Unsaturation side chain / 1 OOC 0 0 0.001 0.001 Unsaturation terminal / 100C 0.043 0.043 0.054 0.056 GPC - Conventional Mn 20,349 22,923 22,572 23,948 Mw 67,425 94,999 62,322 62,255 Mz 136,239 247,612 117,398 125,666 polydispersity index (Mw / Mn) 3.31 4.14 2.8 2.6 index (Mz / Mw) 2.0 2.6 1.9 2.0 Branching frequency GPC-FTIR Comonomer distribution Inverse Inverse Inverse Inverse Rheology Zero shear viscosity - 190°C (Pa-s) 1396 1401 1266 1152 Relative elasticity G' / G at 0.05 rad / s 190°C 0.022 0.017 0.013 0.014 Average melting strength - 190°C (cN) 1.02 0.94 0.68 0.66 Average stretch ratio - 190°C (%) 1388.8 1502.5 1440.7 1581.7. TABLE 3b Resin characteristics Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Density (g / cm3) 0.9477 0.9436 0.9408 0.9381 Melt Index L (g / 10 min) 6.94 5.99 6.63 4.56 Melt Index I21 (g / 10 min) 205 154 156 108 Strain Exponent 1.31 1.27 1.24 1.24 Melt Flow Ratio (I21 / I2) 29.5 25.6 23.5 23.7 CTREF / CTREF SLOW High Elution Peak (°C) 97.5 97.6 95.6 Low Elution Peak (°C) 83.3 CDBI50 Terpolymer 42.2 52.3 Frequency Branching - FTIR Branching frequency / 1000C C4 (1-butene) and C8 (1-octene) 5.9 5.4 5.1 Comonomer ID C4 and C8 Hexene hexene octene Comonomer content (molar %) C4 and C8 1.2 1.1 1.0 Comonomer content (weight %) C4 and C8 3.4 3.2 3.8 Internal unsaturation / 100C 0.001 0 0.001 0.003 Unsaturated side chain / 100C 0 0.004 0.001 0.000 Unsaturated terminal / 100C 0.011 0.011 0.015 0.054 GPC - Conventional Mn 22,081 15,603 25,692 24,649 Mw 72,138 69,049 69,741 66,330 Mz 177,243 171,744 166,490 131,250 polydispersity index (Mw / Mn) 3.3 4.43 2.7 2.7 Index (Mz / Mw) 2.5 2.5 2.4 2.0 Branching frequency GPCFTIR Comonomer distribution Inverse Normal Normal Inverse Rheology Zero shear viscosity 190°C(Pa-s) 1639 1383 2013 Relative elasticity G7G at 0.05 rad / s - 190°C 0.046 0.020 0.019 Average melt strength 190°C (cN) 0.79 Average stretch ratio 190°C(%) 1813.4. TABLE 3c Resin characteristics QJ I 7 I Π / 77Π7 / Β / YILI Comparative Example 9 Comparative Example 10 Density (g / cm3) 0.9365 0.937 I2 Melting Index (g / 10 min) 5.03 5.06 I21 Melting Index (g / 10 min) 160 249 Strain Exponent 1.34 1.48 Melting Flux Ratio (I21 / I2) 31.8 49.2 CTREF / CTREF SLOW High Elution Peak (°C) 89.1 89.2 Low Elution Peak (°C) 85.3 84.3 CDBI50 82 86.5 Branching Frequency - FTIR Branching Frequency / 1000C 6.2 6.7 Comonomer ID octene octene Comonomer Content (% mol) 1.2 1.3 Comonomer Content (% wt) 4.8 5.2 Internal Unsaturation / 100°C 0.027 0.018 Unsaturated Side Chain / 1 OOC 0.005 0.004 Unsaturated Terminal / 1 OOC 0.017 0.013 GPC - Conventional Mn 27,251 23,655 Mw 68,845 71,156 Mz 154,100 212,486 Polydispersity Index (Mw / Mn) 2.5 3.0 Index (Mz / Mw) 2.2 3.0 Branching Frequency GPC-FTIR Comonomer Distribution Inverse Inverse Rheology Zero shear viscosity - 190°C (Pa-s) 2069 2322 Relative elasticity G' / G at 0.05 rad / s - 190°C 0.023 0.032 Average melt strength - 190°C (cN) Average stretch ratio - 190°C (%) QJ ίΖίη / ΖΖΠΖ / Β / ΥΙΛΙ TABLE 4a Results of tests performed on compression-molded plates and rotomolded specimens Example 1 Example 2 Example 3 Example 4 Tensile and Flexural Properties (Plates) Elastic Tensile Strength (MPa) 27.5 23.9 21.5 21.8 Maximum Tensile Strength Stress until rupture (MPa) 30.5 30.5 29.3 16.2 Modulus of Section 1% Tensile Strength (MPa) 1279.6 1074 856 886 Modulus Flexural Dryness 1% (MPa) 1136 946 840 841 Impact Properties (Plates) Izod Impact [m-kg / cm (ft-lb / in)] 0.081646 (1.5) 0.059874 (1.1) 0.136077 (2.5) 0.087089 (1.6) Tensile Impact [m-kg / cm2 (ft-lb / in2)] 1.9672 (91.8) 2.4151 (112.7) 2.8865 (134.7) 2.5844 (120.6) Environmental Stress Cracking Resistance ESCR Cond. B at 10% CO630 (hrs) 21 21 5-22 5-16 ESCR Cond. B at 100% CO630 (hrs) 17 25 51 55 Rotomolding Performance (Thinness of molded part of 6.35 mm (1 / 4'j) Optimal times (min) at 293.33°C (560°F) oven temperature 18-20 18-20 18-20 18-20 Average Failure Energy [m-kg (ft.Lb)] under optimal conditions 24.8-26.13 (180189) 25.9-25.02 (188 181) 21.4-26.68 (155-193) 24.8-26.68 (180-193) Ductility (%) under optimal conditions 100-100 100-100 100-91 100-91 As well as density (g / cm3) under optimal conditions 0.9540 - 0.9439 0.9475 - 0.9476 0.9428 - 0.9425 0.9430 - 0.9423. TABLE 4b Results of tests performed on compression-molded plates and rotomolded samples QJ ίΖίη / ΖΖΠΖ / Β / ΥΙΛΙ Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Tensile and Flexural Properties (plates) Tensile Yield Strength (MPa) 22.5 22.7 21.7 20.7 Ultimate Tensile Strength (MPa) 16.5 15.9 14.1 29.3 Sequence Modulus of Tension 1% (MPa) 961 1017.9 909.8 864 Sequence Modulus of Flexure 1% (MPa) 933 952 897 814 Impact Properties (plates) Izod Impact [m-kg / in] (ft-lb / in) 0.08164 (1.5) 0.07620 (1.4) Tensile Impact [m-kg / cm2] (ft-lb / in2) 1.9715 (92.0) 1.6950 (79.1) Environmental Stress Cracking Resistance ESCRCond. Bal 10% of CO630 (hrs) 42 189 7-22 92 ESCR Cond. B at 100% CO630 (hrs) 15 81 30 >1000 Rotomolding Performance (molded part thickness of 6.35 mm (1 / 4'j)) Optimal times (min) at 293.33°C (560°F) oven temperature 18-20 20-22 18-20 20-22 Average Failure Energy (ft.lb) under optimal conditions 22.67-25.438 (164- 184) 8.018-15.208 (58-110) 7.88-11.613 (57-84) 23.779 - 25.30 (172-183) Ductility (%) under optimal conditions 63-75 0-7 0-0 100-100 As well as density (g / cm3) under optimal conditions 0.9514 - 0.9512 0.9445 - 0.9442 0.9401 - 0.9397 0.9422 0.9422. TABLE 4 c Results of Tests Performed on Molded Plates by Compression and Rotomolded Specimens QJ ίΖίη / ΖΖΠΖ / Β / ΥΙΛΙ Comparative Example 9 Comparative Example 10 Tensile and Flexural Properties (plates) Elastic Tensile Strength (MPa) 21.6 19.6 Ultimate Tensile Strength - Breaking Strength (MPa) 14.3 15.3 Secular Modulus of Tension 1% (MPa) 875 780 Secular Modulus of Flexure 1% (MPa) 784 694 Impact Properties (Plates) Izod Impact [m-kg / cm (ft-lb / in)] Tensile Impact [m-kg / cm2] (ft-lb / in2) Environmental Stress Cracking Resistance ESCR Cond. B at 10% CO630 (hrs) 79 144 ESCR Cond. B at 100% CO630 (hrs) >1008 >1006 Rotomolding Performance (Molded part thickness of 6.35 mm (1 / 4")) Optimal times (min) at 293.33°C (560°F) oven temperature 18-20 18-20 Mean Failure Energy [m-kg (ft.lb)] under optimal conditions 23.641 -25.853 (171-187) 22.674-23.918 (164-173) Ductility (%) under optimal conditions 100-100 60-27 As well as density (g / cm3) under optimal conditions 0.9392 - 0.9391 0.9397 - 0.9397 INDUSTRIAL APPLICABILITY High-density polyethylene compositions are provided that offer high rigidity and ductility and can be useful in the preparation of rotomolded articles. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. A bimodal polyethylene composition, characterized in that it has 1) a molecular weight distribution, Mw / Mn, of 2.3 to 5.5; 2) a density of 0.940 to 0.957 g / cc; 3) a melting index, I2, measured per ASTM D1238 at 190°C using a 2.16 kg load of 4 to 10 grams for 10 minutes; and 4) a relative elasticity, G' / G when measured at 190°C and 0.05 rad / second of less than 0.03 rad / second, wherein the bimodal polyethylene composition comprises: A. 10 to 70 wt% of a first ethylene copolymer having: Ai. a melt index, I2, measured by ASTM D1238 at 190°C using a 2.16 kg load of 0.4 to 5 grams for 10 minutes; Aii. a molecular weight distribution, Mw / Mn, of 1.8 to 3.0; and Aiii. a density of 0.920 to 0.950 g / cc; B. 90 to 30 wt% of a second ethylene copolymer having: Bi. a melting index, I2, measured by ASTM D1238 at QJ ίΖίη / ZZΖΠZ / Β / YΥΙΛΙ 190°C using a 2.16 kg load of 4 to 1500 grams for 10 minutes; Bi i. a molecular weight distribution, Mw / Mn, of 2.3 to 6.0; and Bi ii. a density greater than the density of the first ethylene copolymer but less than 0.967 g / cc; provided that the density of the first ethylene copolymer is less than the density of the second ethylene copolymer by an amount of 0.010 to 0.035 g / cc.

2. The polyethylene composition according to claim 1, characterized in that the first ethylene copolymer is further characterized by having A.iv. a number-average molecular weight, Mn, of 35,000 to 80,000; A.v. a weight-average molecular weight, Mw, of 70,000 to 150,000; A.vi. an Mz of 120,000 to 250,000; A.vii. an Mw / Mn ratio of 2 to 3; A.viii. a number of short-chain branches (SCB1) per thousand carbon atoms of 1 to 5; and A.ix. a melting index, I2, measured by ASTM D1238 at 190°C using a 2.16 kg load of 0.5 to 4.0 grams for 10 minutes.

3. The polyethylene composition according to claim 1 or 2, characterized in that the second QJ ίΖίη / ZZΖΠZ / Β / YΥΙΛΙ ethylene copolymer is further characterized by having: A.iv.A number-average molecular weight, Mn, of 12,000 to 30,000; A weight-average molecular weight, Mw, of 28,000 to 72,000; A.vi. an Mz of 70,000 to 150,000; A.vii. an Mw / Mn of 2.3 to 5.0; A.viii. a number of short-chain branches (SCB2) per thousand carbon atoms of 0.1 to 2; B. ix. a density greater than the density of the first ethylene copolymer but less than 0.965 g / cc; Bx a melt index, I2, measured by ASTM D1238 at 190°C using a 2.16 kg load of 4 to 100 grams for 10 minutes; provided that the density of the first ethylene copolymer is less than the density of the second ethylene copolymer by an amount of 0.010 to 0.030 g / cc.

4. A rotomolded part, characterized in that it is prepared with a polyethylene composition according to claim 1, 2 or 3.

5. A rotomolded part according to claim 4, characterized in that it has a ductility index of 80 to 100%. 6.The rotomolded part according to claim 5, characterized in that it has an average failure energy greater than 16.59 m-kg (120 ft-lb) on 6.35 mm (0.250 in) thick specimens tested in accordance with ASTM D5628 at a test temperature of -40°C.

7. A rotomolded part according to claim 4 or 5, characterized in that the first ethylene copolymer is prepared with a single-site catalyst and the second ethylene copolymer is prepared with a Ziegler-Natta catalyst.

8. The polyethylene composition according to claim 1, characterized in that it has a comonomer content of less than 1.2 mol%, as determined by the FTIR method.

9. The polyethylene composition according to claim 1, characterized in that the first and second ethylene copolymers are copolymers of ethylene and 1-octene. 10.The polyethylene composition according to claim 1, characterized in that it is prepared by contacting ethylene and an alpha-olefin with a polymerization catalyst under solution polymerization conditions in at least two polymerization reactors.

11. A process for the production of hollow polyolefin articles, characterized in that it comprises loading the bimodal polyethylene composition according to claim 1 into a mold, heating this mold in an oven to more than 280°C, so that the stabilized polyolefin melts, rotating the mold about at least two axes, spreading the plastic material towards the walls, cooling the mold while it continues to rotate, opening it, and removing the resulting hollow article 5.