MXPA96001812A - Ethylene polymers having enhanced processability - Google Patents

Abstract

An ethylene polymer having a Polydispersity Index of at least about 3.0, a melt index, MI, and a Relaxation Spectrum Index, TSI, such that (RSI)(MI alpha) is greater than about 26 when alpha is about 0.7, and a Crystallizable Chain length Distribution Index, Lw/Ln, less than about 3 is provided, such ethylene polymer has processability equivalent or superior to even conventional high pressure polyethylene at similar melt index, yet need not be made under high pressure reaction conditions.

Description

"ETHYLENE POLYMERS THAT HAVE IMPROVED PROCESSABILITY" This invention relates to ethylene polymers having improved processability, particularly extrudability, and a limited comonomer distribution that can be advantageously carried out in a low pressure process. The melt extrusion properties of these ethylene polymers are superior to those of conventional linear low density polyethylene, and are equivalent to or superior to those of high pressure low density polyethylene at a similar melt index.

BACKGROUND Linear polyethylene can be easily produced in low pressure processes, for example in gas phase fluidized bed reactors. Its mechanical properties, such as stiffness, resistance to tension and elongation, are good. However, its processability is poor. Linear polyethylene has a tendency to fracture by melting and experience problems of continuous ribbon instability such as high drawdown and stretch resonance when rolling films are produced.

High pressure low density polyethylene, which is highly branched, is preferred to linear low density polyethylene for applications requiring ease of processing. High pressure low density polyethylene, for example, can easily be extruded into films without suffering from melt fracture, overheating, or continuous tape instability problems. However, conventional processes for producing these resins require tubular reactors or autoclaves operating at extremely high pressure (in the order of 2.109 to 3.127 kilograms per square centimeter) and high temperature (approximately 200 ° C to 350 ° C), and they are necessarily difficult and expensive to operate. In addition, due to its highly branched nature, the mechanical properties of high pressure low density polyethylene are inferior to those of linear low density polyethylene. Several researchers in the field have tried to address this issue of poor processability of linear polyethylene by introducing long chain branching into linear polyethylene. U.S. Patent Nos. 5,272,236; 5,380,810; and 5,278,272 issued to Lai et al., and PCT Application Number WO 93/08221, all assigned to The Dow Chemical Company, describe "essentially linear" olefin polymers having certain properties that lead to improved processability, including from about 0.01 to 3 long chain branches per 1000 carbon atoms of the main chain and a molecular weight distribution of about 1.5 to about 2.5. Similarly, PCT Application Number WO 94/07930 assigned to Exxon Chemical Patents Inc. discloses polymers having less than 5 long linear branches per 1000 carbon atoms of the main chain with at least some of the branches having a molecular weight greater than the critical molecular weight for the entanglement of the polymer. WO 94/07930 states that these polymers have superior processability as fusions and superior mechanical properties as solids. U.S. Patent No. 5,374,700 issued to Tsutsui et al. Discloses ethylene copolymers which are said to have limited compositional distributions and excellent fusion stress. The so-called melt flow regimes of these copolymers are 0.001 to 50 grams per 10 minutes, as measured at a temperature of 190 ° C and a load of 2.16 kilograms, that is, the same as the melt index. Finally, PCT Application Number W094 / 19381 assigned to Idemitsu Kosan Co., Ltd., relates to an ethylene copolymer derived from ethylene and an olefin of 3 to 20 carbon atoms which is said to have good processability and controllability with regarding various properties such as density, melting temperature and crystallinity. The copolymer is characterized by 1) the polymer backbone contains no quaternary carbon, 2) the melt flow activation energy (Ea) is 8-20 kilocalories per mole, and 3) when Huggins constant k of the copolymer it is compared with that of a linear polyethylene having the same limit viscosity as the copolymer, the measurement of the viscosity having been made in decalin at 135 ° C, the ratio is as follows: 1.12 <; kl / k2 < 5 (where kl is the Huggins constant of the copolymer and k2 is that of linear polyethylene). A new class of ethylene polymers having excellent processability that is equivalent to or exceeding that of high pressure low density polyethylene at a similar melt index has been discovered. These ethylene polymers possess a unique set of properties that are not found in the polyethylene resins of the prior art.

SUMMARY OF THE INVENTION The invention provides an ethylene polymer having a Polydispersity index of at least about 3.0; and a melt index, MI, and a Relaxation Spectrum Index, RSI, such that (RSI) (MIalfa) is greater than about 26 when alpha is approximately 0.7; and a Crystallizable Chain Length Distribution Index, Lw / Ln, less than about 3. The ethylene polymer is efficiently extruded showing lower loading pressure and amperage than those of conventional linear low density polyethylene or commercially produced metallocene polyethylene. obtainable The ethylene polymer, which may be an ethylene homopolymer or ethylene interpolymer, may be easily manufactured into a variety of useful articles such as general purpose films, clarity films, shrink films, extrusion coatings, wire and cable insulation. and outer sheathing or coating and insulation of cross-linked transmission cable, injection molded, blown or rotational molded articles, and semiconducting and coating insulation using methods well known in the art.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a trace of (RSI) (MIalfa) versus the melt index (MI) for ethylene polymers of the invention and various other polyethylenes. Figure 2 is a plot of the Crystallization Rate Constant (CRC) versus the density for the ethylene polymers of the invention and various other polyethylenes.

DETAILED DESCRIPTION OF THE INVENTION The ethylene polymers of the invention include ethylene homopolymers and linear or branched higher ethylene and alpha-olefin interpolymers containing from 3 to about 20 carbon atoms, with densities ranging from about 0.86 to about 0.95. Suitable higher alpha olefins include, for example, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene and 3,5,5-trimethyl-1-hexene. Dienes, particularly non-conjugated dienes, can also be polymerized with ethylene. Suitable non-conjugated dienes are linear, branched, or cyclic hydrocarbon dienes having from about 5 to about 20 carbon atoms. Especially preferred dienes include 1,5-hexadiene, 5-vinyl-2-norbornene, 1,7-octadiene and the like. Ethylene polymers also include, for example, ethylene / propylene rubbers (EPR's), ethylene / propylene / diene terpolymers (EPDM's) and the like. Aromatic compounds having vinyl unsaturation such as styrene and substituted styrenes can also be included as comonomers. Particularly preferred ethylene polymers comprise ethylene and from 1 percent to about 40 percent by weight of one or more comonomers described above. Ethylene polymers have indices of Polydispersity uncorrected for long chain branching of at least about 3.0, preferably at least about 4.0, indicating that these ethylene polymers have molecular weight distributions that are advantageously quite broad. The Polydispersity Index (PDI) of a polymer is defined as the ratio of the weight average molecular weight of the polymer to the number average molecular weight of the polymer (Mw / Mn). PDI, uncorrected for long chain branching, is determined using size exclusion chromatography (SEC) and a WATERS 150C GPC instrument operating at 140 ° C with 1,2,4-trichlorobenzene at a flow rate of 1 milliliter per minute. The pore size scale of the column set provides a MW separation that covers the scale of 200 to 10,000,000 Daltons. The NBS 1475 or 1496 polyethylene standard from the National Institute of Standards Technology is used as the calibration standard to obtain the uncorrected molecular weight distribution (presumably from the linear polymer). The ethylene polymers present have unique rheological properties that impart superior melt strength, shear stress behavior and excellent reduction allowing them to be processed extremely easily. This improved processability encompasses ease in both extrusion and manufacturing processes, such as in blown film, blow molding, extrusion coating and wire and cable extrusion operations. In particular, ethylene polymers have melt indexes, MI, and Relaxation Spectrum Indexes, RSI, in such a way, for a given ethylene polymer: (RSI) (MIalfa) > of about 26 when alpha is about 0.7.

Preferably, (RSI (MIalfa)> of about 30 when alpha is about 0.7 In the formulas immediately above, MI is the melt index of the polymer that is reported as grams per 10 minutes, determined according to the Method D-1238, condition E, of the American Society for the Testing of Materials, at 190 ° C and RSI is the Index of Relaxation Spectrum of the polymer in dimensional-free units.The RSI of the ethylene polymer is determined by first subjecting the polymer to a shear strain and measuring its response to deformation using a rheometer As is known in the art, based on the response of the polymer and the mechanics and geometry of the rheometer used, the relaxation module G (t) or the modules dynamics G1 (omega) and G "(omega) can be determined as functions of time to the omega frequency, respectively (See JJ Dealy and KF Wissbrun, Melt Rheology and Its Role in Plastics Pr ocessing, Van Nostrand Reinhold, 1990, pages 269 to 297). The mathematical connection between the dynamic and storage modules is an integral Fourier transformation relationship but one set of data can also be calculated from the other using the well-known relaxation spectrum (See SH Wasserman, J. Rheology, Volume 39, pages 601 to 625 (1995)). Using a classical mechanical model, a spectrum of discrete relaxation can be defined consisting of a series of relaxations or "modes", each with a characteristic intensity or "weight" and time of relaxation. Using this spectrum, the modules are re-expressed as: N G (t) =? G¡expH /? I) where N is the number of modes and g-¡and are the weight and time for each of the modes (See JD Ferry, Viscoelastic Properties of Polymers, John Wiley &Sons, 1980, pages 224 to 263) . A relaxation spectrum can be defined for the polymer using software such as the IRIS (R) rheological software, which can be obtained commercially from IRIS Development. Once the distribution of modes in the relaxation spectrum is calculated, the first and second moments of the distribution that are analogous to Mn and Mw, the first and second moments of the molecular weight distribution, are calculated as follows: S? =? 8¡ /? Si '? ¡I = l I i = J N I N 8p =? 8i? If 1 = 1 I =? RSI is defined as gjj / g. Because RSI is sensitive to these parameters as a molecular weight distribution of the polymer, molecular weight and long chain branching, it is a reliable indicator of the processability of a polymer. The higher the RSI value, the better the processability of the polymer. In addition, the ethylene polymers have a Crystallisable Chain Length Distribution Index, Lw / Ln, of less than about 3, preferably less than about 2, indicating that they have limited comonomer distributions and thus considerable composition homogeneity. The Crystallizable Chain Length Distribution Index is determined using the Temperature Elevation Elution Fractionation (TREF), as described in the article by Wild and others, J. Polymer Sci., Poly. Phys. Ed., Volume 20, pages 441 (1982). A dilute solution of the ethylene polymer in a solvent such as 1, 2, 4-trichlorobenzene, at 1 to 4 milligrams per milliliter, is loaded at high temperature into a packed column. The column is then allowed to cool slowly at 0.1 ° C per minute to room temperature, in a controlled manner so that the ethylene polymer crystallizes towards the packing in the order of increasing branching (or decreased crystallinity) with the temperature decreased. The column is then heated in a controlled manner at 0.7 ° C per minute to more than 140 ° C with a constant solvent flow at 2 milliliters per minute through the column. The polymer fractions as they elute have decreased branching (or increased crystallinity) with increased temperature. An infrared concentration detector is used to monitor the concentrations of the effluent. From the temperature data of TREF, the branching frequency for a given comonomer can be obtained. Consequently, the main chain lengths between the branches that are expressed as Lw and Ln can be calculated in the following manner. Lw is the average chain length in weight between branches: Lw = _} I WII and Ln is the average chain length in number between the branches: Jn = 1 / JJi (Wi i) where w-_ is the fraction by weight of the component of polymer i that has a separation L-de of chain of Average basic structure between two adjacent branch points. Optionally, the limited comonomer distributions of the ethylene polymers can be characterized using Differential Scanning Calorimetry (DSC). With the DSC, the melting temperature of a polymer is measured by Differential Scanning Calorimetry, such as the DSC 2920 that can be obtained commercially from Thermal Analysis Instruments, Inc. A polymer sample of approximately 5 milligrams sealed in an aluminum pen is heat first at 160 ° C at a rate of 10 ° C per minute and then cool to -20 ° C also at a rate of 10 ° C per minute. This is followed by a second heating at 160 ° C at a rate of 10 ° C per minute. The maximum melting temperature during the second endothermic fusion reaction is recorded as the melting temperature of the polymer. The DSC-related properties that preferably have the ethylene polymers present are 1) a DSC Homogeneity index, DSC-HI, of at least about 1, preferably at least about 9 and 2) a steady state Crystallization, CRC, equal to greater than 1.

The DSC-HI is defined as follows: DSC-HI = [(Tm ^ heterog. ~ Tm) '^ m, heterog. ~~ ^ m, homog. ) J l * -1 wherein Tm is the maximum melting temperature of the ethylene polymer and Tm, heterog > and Tm / homog. they are the maximum melting temperatures of the compositionally representative heterogeneous and compositionally homogeneous polyethylene, respectively, which have the same density as the ethylene polymer. The relationships between the melting temperature and the density used for heterogeneous and homogeneous representative polymers are: homogeneous: Tm = -6023.5 + 12475.3 (density) - 6314.6 (density) 2 heterogeneous: Tm = -49.6 + 189.1 (density) The CRC values of the ethylene polymers are preferably equal to or greater than 1. The CRC is a relative measure of the crystallization rate under a set of determined conditions and is defined: CRC (g / cc) = (density) (Tc / T] _ / 2) where Tc is the maximum crystallization temperature of the polymer, and T 2 is the temperature at which 50 percent by weight of the crystallizable fractions in the polymer they have crystallized. Both Tc and T? 2 are determined from the exothermic reaction of recrystallization obtained with DSC measurements of the non-isothermal recrystallization processes. The density of the polymer is measured according to Method D-1505 of the American Society for the Testing of Materials. Another preferred feature of the ethylene polymers present is that they contain at least about 0.3 long chain branches per 1000 carbon atoms of the main chain. This also contributes to its excellent processability. Preferably, the ethylene polymers contain at least about 0.5 long chain branches per 1000 carbon atoms of the main chain. Most preferably, the ethylene polymers contain at least about 0.7 long chain branches per 1000 carbon atoms of the main chain. The long chain or LCB branching is measured by size exclusion chromatography (SEC) with solution viscoetry using the Waters 150C GPC instrument (Waters Corporation) with an aligned differential viscometer manufactured by Viscotek Corporation using the same experimental conditions as describe anywhere else for normal size exclusion chromatography. It is used to obtain the calibration, a polyethylene standard of known molecular weight distribution and intrinsic viscosity in 1,2,4-trichlorobenzene at 140 ° C, such as NBS 1475 or 1496. The LCB values are derived from the ratio of viscosity of the branched polymer with respect to the linear polymer of the same molecular weight. (See F. M. Mirabella, Jr., and L. Wild, Polymer Characterization, Amer. Chem. Soc. Symp. Ser., 227, 1990, page 23). An epsilon value of 0.75 is used in relating the ratio of viscosity to the ratio of the radius of gyration of the quadratic medium of the branched polymer to the linear polymer also at the same molecular weight. (See G.N. Foster, T. MacRury, A.E. Hamielec, Liquid Chromatography of Polymer and Realted Materials II, Ed.- J. Cazes and X. Delamere, Marcel Dekker, New York). This ratio of rotating radii is used in LCB calculations by the Zimm-Stockmayer relationship (BH Zimm and WH Stockmayer, Phys., Volume 17, page 1301, 1949), as described in Developments in Polymer Characterization - 4, JV Dawkins, ed., Applied Science, Barking, 1993. Ethylene polymers can be produced by any conventional polymerization process of suspension, solution, slurry or gas phase, using reaction conditions well known in the art. A reactor or several reactors can be used in series. Gas phase polymerization is preferred using one or more fluidized bed reactors. Similarly, the catalyst compositions that can be used to produce the ethylene polymers of the invention are any of those known for the polymerization of ethylene, such as those comprising one or more conventional Ziegler-Natta catalysts, as well as the catalysts of most new metallocene, both of which are well documented in the literature. The use of a catalyst system mixed within or between the families of catalysts can also be used to produce the ethylene polymers of the invention. However, it has been found that a preferred process for preparing the ethylene polymers comprises contacting, under gas phase polymerization conditions, ethylene and optionally a higher alpha-olefin with a catalyst composition comprising: a) racemic and meso stereoisomers of a bridge metallocene catalyst containing two cycloalkadienyl coordinating groups linked by a bridge bond and complexed to a metal atom, each cycloalkadienyl coordinating group has facial chirality, and b) a cocatalyst which is selected from the group consisting of of methylaluminoxane and modified methylaluminoxane. Preferably, the metal atom is titanium, zirconium or hafnium. More preferably, the metal atom is zirconium. Each of the cycloalkalienyl coordinating groups of the bridge metallocene catalyst having facial chirality. Chirality is used to describe asymmetric coordinating molecules or groups whose mirror images are not capable of overlapping (that is, they do not remain "facing each other"). In non-cyclic molecules, there is a chiral center. In the following case, the chiral center is the carbon atom: specular In cyclic systems a plane of chirality can exist, giving rise to facial chirality. To illustrate the concept of facial chirality, the indenyl coordinating group is used as an example. An indenyl coordinating group can be seen as a cyclopentadienyl coordinating group that contains two substituents that are connected to form a ring of 6 carbon atoms. An unsubstituted indenyl coordinating group (ie, a cyclopentadienyl coordinating group containing only the two substituents that form the 6-membered ring) has no chirality. If a chiral substituent is attached to the indenyl coordinating group, the coordinating group is intended in terms of chirality of the chiral center of the substituent. However, if one or more substituents are attached to the indenyl coordinating group, and there is no plane of mirror symmetry, the substituted indenyl coordinating group (the cyclopentadienyl coordinating group containing the two connected substituents to form the 6-membered ring) plus one or more additional achiral substituents) then it is said to have facial chirality: speculate of 1-methylindenyl (facially prochiral) Therefore, the above-mentioned 2-methylidenyl coordinating group has no chirality (facial or otherwise) but the coordinating 1-methylindenyl group has facial pro-chirality. The term facial chirality implies that there is a plane of chirality that incorporates the indenyl coordinating group. A metal (M) can be coordinated with one of the two chiral faces of the 1- ethylindenyl coordinating group, forming a basis for discrimination between the two prochiral faces. This forms the enantiomers: enantiomers When there are two of these coordinating groups in a molecule, each having a facial chirality and coordinated with a metal, four possible stereoisomers can result: the metal can be coordinated with the R face of each coordinating group (R, R ') or the S face of each coordinating group (S, S ') or can be coordinated with one of each face (R, S' and S, R '), where R, R', S, and S 'refer to the absolute configurations of the coordinating groups. The stereoisomers R, R 'and S, S' are collectively called the racemic stereoisomers, while the stereoisomers R, S 'and S, R' are called the meso-stereoisomers. When the preferred catalyst composition comprising the bridging metallocene catalyst containing the cycloalkdienyl coordinating groups having facial chirality is used, it is necessary that both the racemic and meso stereoisomers are present in larger amounts than trivial amounts in the catalyst composition. Preferably, both racemic and meso stereoisomers are present during the polymerization in an amount greater than about 6, more preferably 10 weight percent of the total amount of bridging metallocene catalyst containing the cycloalkadienyl coordinating groups having facial chirality . This amount is independent of the ratio of the racemic stereoisomer to the meso stereoisomer present in the bridge metallocene catalyst containing cycloalkalienyl coordinating groups with facial chirality, before it is combined with the cocatalyst of methylaluminoxane or modified methylaluminoxane to form the catalyst composition activated In a preferred embodiment, the bridge metallocene catalyst containing two coordinating cycloalkalienyl groups with facial chirality has the formula: wherein R] _ to RQ are the same or different monovalent substituents selected from alkyl, aryl, alkylaryl, arylalkyl, hydrogen, halogen or hydrocarboxy and any two of R ^ to Rg can be connected to form a ring of 4 to 8 atoms of carbon, in such a way that if R] _ = R then R2 4 R3 and if R2 = R3 then R ^ R4, and if R5 = Rg then Rg R? , and if Rg = R7 then R5 Rg, the symbol "=" representing a chemical as well as a stereochemistry equivalence; Q is a divalent substituent selected from alkylidene, dialkylsilylene, dialkylgermylene, and cycloalkylidene; M is a transition metal selected from Group 4, and preferably zirconium or hafnium; and XX and X2 are the same or different, and are monovalent coordinating groups which are selected from alkyl, aryl, alkylaryl, arylalkyl, hydrogen, halogen, hydrocarboxy, aryloxy, dialkylamido, carboxylate, thiolate and thioaryloxy. The following compounds are illustrative but non-limiting examples of metallocene catalysts bridge containing two coordinating groups cycloalkadienyl with facial chirality: dichloride dimethylsilylenebis (indenyl) zirconium dichloride, ethylenebis (lindenil) zirconium dichloride, dimethylsilylenebis (4, 5, 6, 7-tetrahydroindenyl) zirconium; ethylenebis (4, 5, 6, 7-tetrahydroindenyl) zirconium dichloride, dimethylsilylenebis (2-methylindenyl) zirconium dichloride dimethylsilylenebis (2-methyl-4, 5, 6, 7-tetrahydroindenyl) zirconium dichloride metilfenilsililenbis ( 2-methylindenyl) zirconium dichloride dimethylsilylenebis (2, 4, 7-trimetilindenil) zirconium, ethylenebis (2-methylindenyl) zirconium dichloride, ethylenebis (2-methyl-4, 5, 6-7-tetrahydroindenyl) zirconium dichloride, dichloride dimethylsilylenebis (2-methylindenyl) zirconium dichloride dimethylsilylenebis (2-methyl-4-phenylindenyl) zirconium dichloride, dimethylsilylenebis (2-methyl-4-isopropylindenyl) zirconium dichloride, dimethylsilylenebis (2-methyl-4-naftilindenil) zirconium phenoxide of dimethylsilylenebis chloride (2-methylindenyl) diphenoxide zirconium dimethylsilylenebis (2-methylindenyl) zirconium bis (dimethylamide) dimethylsilylenebis (2-methylindenyl) zirconium bis (benzoate) dimethylsilylenebis (2-methylindenyl) zirconium), dimethyl chloride ethoxide ilsilylenebis (2-methylindenyl) zirconium, dimethylsilylenebis (2-methylindenyl) zirconium diethoxide, dimethylsilylenebis (2-methylindenyl) zirconium bis (cyclohexane oxide), dimethylsilylenebis (2-methylindenyl) zirconium catecolate, dimethylsilylenebis (2,4-dimethylcyclopentadienyl) dichloride ) zirconium, dimethylsilylenebis (2-methyl-4-t-butylcyclopentadienyl) zirconium dichloride, and ethylenebis (2,4-dimethylcyclopentadienyl) zirconium dichloride. Preferably, the bridge metallocene catalyst is dimethylsilylene-bis (2-methylindenyl) zirconium dichloride, which is defined by the formula immediately above when R and R5 each is methyl; R2 and R6 each is hydrogen; R3 and R4 are connected to form -CH = CH-CH = CH-; R7 and R8 are connected to form -CH = CH-CH = CH-; Q is di-ethylsilylene; M is zirconium; and X and X2 each one is chloride. The bridge metallocene catalyst can be produced by one of several methods. The manufacturing method is not critical. For example, see A. Razavi and J. Ferrara, J. Organomet. Chem., 435, 299 (1992) and of K. P. Reddy and J. L. Petersen, Organometallics, Q, 2107 (1989). One method comprises first reacting two equivalents of an optionally substituted cyclopentadiene with a metal deprotonation agent such as an alkyl lithium or potassium hydride in an organic solvent such as tetrahydrofuran, followed by reaction of this solution with a solution of one equivalent of a doubly halogenated compound such as dichlorodimethylsilane. The resulting coordinating group is then isolated by conventional methods known to those skilled in the art (such as distillation or liquid chromatography), reacted with two equivalents of a metal deprotonation agent as above, and then reacted with an equivalent of a titanium, zirconium or hafnium tetraeloride, optionally coordinated with the donor coordinator group molecules such as tetrahydrofuran, in an organic solvent. The resulting bridging metallocene catalyst is isolated by methods known to those skilled in the art, such as recrystallization or sublimation. Alternatively, the bridge metallocene catalyst can be produced by first reacting one equivalent of an optionally substituted cyclopentadiene with one equivalent of a metal deprotonation agent in an organic solvent as above followed by reaction with one equivalent of a molecule containing a ring of five unsaturated carbon atoms to which an exocyclic group susceptible to nucleophilic attack is attached, such as a dialquilfulvene. The reactive solution is then rapidly cooled with water and the coordinating group is isolated by conventional methods. An equivalent of the coordinating group is then reacted with two equivalents of the metal deprotonation agent as above, and the resulting solution in turn is reacted with an equiuvalent of a titanium, zirconium or hafnium tetraeloride optionally coordinated with the coordinating group molecules donor, such as tetrahydrofuran, in an organic solvent. The resulting bridging metallocene catalyst is isolated by methods known to those skilled in the art. The cocatalyst is methylaluminoxane (MAO) or modified methylaluminoxane (MMAO). Aluminoxanes are well known in the art and comprise oligomeric linear alkyl aluminoxanes represented by the formula: and oligomeric cyclic alkyl aluminoxanes of the formula: wherein s is from 1 to 40, preferably from 10 to 20; p is from 3 to 40, preferably from 3 to 20; and R *** is an alkyl group containing from 1 to 12 carbon atoms, preferably a methyl radical or an aryl radical such as a substituted or unsubstituted phenyl or naphthyl radical. In the case of methylaluminoxane, R *** in the two formulas immediately above is methyl. For the modified methylaluminoxane, R *** is a mixture of methyl and alkyl groups of 2 to 12 carbon atoms wherein the methyl comprises from about 20 to about 80 weight percent of the R *** groups. Aluminoxanes can be prepared in a variety of ways. In general, a mixture of linear and cyclic aluminoxanes is obtained in the preparation of aluminoxanes, for example trimethylaluminium and water. For example, an aluminum alkyl can be treated with water in the form of a wet solvent. Alternatively, an aluminum alkyl such as trimethylaluminum can be contacted with a hydrated salt, such as ferrous sulfate hydrate. The latter method comprises treating a dilute solution of trimethylaluminum, for example, in toluene with a suspension of ferrous sulfate heptahydrate. It is also possible to form the methylaluminoxanes by reacting a tetraalkyldialuminoxane containing alkyl groups of 2 carbon atoms or higher with an amount of trimethylaluminum which is less than a stoichiometric excess. The synthesis of the methylaluminoxanes can also be achieved by the reaction of a trialkylaluminum compound or a tetralkyldialuminoxane containing alkyl groups of 2 carbon atoms or higher with water to form a polyalkylaluminoxane, which is then reacted with the trimethylaluminum. Additional modified methylaluminoxanes containing both methyl groups and higher alkyl groups can be synthesized by reacting a polyalkylaluminoxane containing alkyl groups of 2 carbon atoms or higher with trimethylaluminum and then with water as disclosed, example, in U.S. Patent No. 5,041,584. The amount of the bridging metallocene catalyst and the cocatalyst employed usefully in the catalyst composition can vary over a wide scale. Preferably, the catalyst composition is present at a concentration sufficient to provide at least about 0.000001 percent, preferably at least about 0.000001 percent by weight of a transition metal based on the total weight of ethylene and other monomers. The molar ratio of the aluminum atoms contained in the methylaluminoxane or the modified methylaluminoxane with respect to the metal atoms contained in the bridging metallocene catalyst usually falls within the range of about 2: 1 to about 100,000: 1, preferably within the range of about 10: 1 to about 10,000: 1, and especially preferably within the range of about 30: 1 to about 2,000: 1. The catalyst composition can be supported or not supported. In the case of a supported catalyst composition, the bridge metallocene catalyst and the cocatalyst can be impregnated into or deposited on the surface of an inert substrate such as silicon dioxide, aluminum oxide, magnesium dichloride, polystyrene, polyethylene, polypropylene. or polycarbonate, such that the catalyst composition constitutes between 1 percent and 90 percent by weight of the total weight of the catalyst composition and the support. Polymerization in the gas phase in a fluidized bed or stirred reactor is preferably carried out using the equipment and procedures well known in the art. Preferably, superatmospheric pressures are used within the range of .0703 to 70.30 kilograms per square centimeter, preferably from 3.52 to 28.12 kilograms per square centimeter and more preferably from 7.03 to 21.09 kilograms per square centimeter, temperatures within the range of 30 ° to 130 ° C, preferably from 65 ° C to 110 ° C. The ethylene and other monomers, if used, are contacted with an effective amount of the catalyst composition at a temperature and pressure sufficient to initiate the polymerization. Suitable gas phase polymerization reaction systems comprise a reactor to which the monomer (s) and the catalyst composition can be added and which contain a bed to form polyethylene particles. The invention is not limited to any specific type of gas phase reaction system. As an example, a conventional fluidized bed process is carried out by passing a gaseous stream containing one or more monomers continuously through a fluidized bed reactor under reaction conditions and in the presence of a catalyst composition at a rate enough to keep the bed of solid particles in a suspended condition. The gaseous stream containing the unreacted gaseous monomer is continuously removed from the reactor, compressed, cooled and recycled to the reactor. The product is removed from the reactor and added to the recycle stream of the replenishing monomer. Conventional additives may be included in the process as long as they do not interfere with the epimerization of the racemic and meso stereoisomers of the bridge metallocene catalyst.

When hydrogen is used as a chain transfer agent in the process, it is used in amounts ranging from about 0.001 to about 10 moles of hydrogen per mole of the total monomer feed. Also, as desired for system temperature control, any inert gas to the catalyst composition and reagents may also be present in the gas stream. Organometallic compounds can be used as scrubbing agents for contaminants in order to increase the activity of the catalyst. Examples of these compounds are metal alkyls, preferably aluminum alkyls, more preferably tri-n-hexylaluminum triisobutylaluminum. The use of these scavenging agents is well known in the art. The ethylene polymers can be mixed with other polymers and resins as desired, using techniques known in the art. In addition, various additives and agents such as thermo- and photo-oxidation stabilizers including hindered phenolic antioxidants, hindered amine light stabilizers and aryl phosphites or phosphonites can be mixed with the ethylene polymer of the invention as desired. crosslinking agents including dicumyl peroxide, dyes including carbon blacks and titanium dioxide, lubricants including metal stearates, processing aids including fluoroelastomers, glidants including oleamide or erucamide, release agents or antiblocking agents including talc or silica in size of controlled particle, blowing agents, flame retardant agents and other conventional materials. The ethylene polymers of the invention useful for manufacturing in a variety of finished articles such as films including clarity films and shrink films, extrusion coatings, wire and cable insulation and coatings, cross-linked transmission cable insulation, molded articles produced by injection molding, blow molding or rotational molding, extrusions of pipe, tube, profiles and laminated materials and insulation and semiconductor coating and / or shielding. The methods for producing these articles are well known in the art.

EXAMPLES A series of ethylene polymers according to the invention (Examples 1 to 35) were compared with known polyethylene samples for a variety of properties, including the Polydispersity Index (PDI), the Crystallizable Chain Length Distribution Index (Lw). / Ln), the melting index (MI), the Relaxation Spectrum Index (RSI), and (RSI) (MIalfa) when alpha is approximately 0.7. In addition, the long-chain branching (LCB), the DSC Homogeneity index (DSC-HI), and the Crystallization Regimen Constant (CRC) were compared. The ethylene polymers in Examples 1 to 35 were made using a gas phase fluidized bed reactor of nominal diameter of 35.56 centimeters having a bed height of 3,048 meters. The catalyst composition used to produce each of these examples comprised the racemic and meso isomers of dimethylsilylenebis (2-methylindenyl) zirconium dichloride and the silica-supported methylaluminoxane cocatalyst. Examples of Comparison AE were certain AFFINITY Polyolefin Plastometers that can be obtained commercially from The Dow Chemical Company, as specified in Table 1. Comparative Examples FJ were certain EXACT Linear Ethylene Polymers, commercially available from Exxon Chemical as specified in Table 1.

Examples K-M Comparison were polyethylene produced by free radical high pressure polymerization. These low density polyethylenes were produced in a high pressure tubular reactor using multiple organic initiators, pressures up to 3000 atmospheres and temperatures up to 320 ° C. The process used to produce these high pressure low density polyethylenes was similar to that described in the article by Zabisky and others, Polymer, 33, Number 11, 2243, of 1992. Comparative Examples N and 0 were commercial linear low density polyethylenes produced by the UNIPOL (R) process (Union Carbide Corp.) using a phase-bed fluidized-bed reactor. gas. These polyethylenes were ethylene copolymers catalyzed with Ziegler-Natta either butene-1 or hexene-1 as described in US Pat. No. 4,302,565. Examples Comparison P-R were low density polyethylenes produced by a gas phase fluidized bed reaction in a step reactor configuration using the Ziegler-Natta catalysts. The Molecular Weights, the Molecular Weight Distribution, and the Long Chain Branch (LCB) were determined by size exclusion chromatography in the following manner. A WATERS 150C GPC chromatography apparatus equipped with mixed pore size columns for molecular weight measurements and a VISCOTEK 150R viscometer for aligned viscosity measurements were of course employed. For size exclusion chromatography (SEC), a 25-centimeter-long preliminary column of Polymer Labs having a nominal pore size of 50 angstrom units was used followed by three 25-centimeter long Shodex columns A-80 M / S (Showa) to effect a molecular weight separation for the linear ethylene polymer of about 200 to 10,000,000 Daltons. Both columns contained porous poly (styrene-divinylbenzene) packing. 1, 2, 4-trichlorobenzene was used as the solvent to prepare the polymer solutions and the chromatographic eluent. All measurements were made at a temperature of 140 + 0.2 ° C. The analog signals of the mass and viscosity detectors were collected in a computer system. The collected data were then processed using standard software that can be obtained commercially from various sources or sources (Waters Corporation and Viscotek Corporation) for an uncorrected molecular weight distribution. The calibration uses the MWD wide calibration method (See from WW Yau, JJ Kirkland and DD Bly, Modern Size-Exclusion Liquid Chromatography, Wiley, 1979, pages 289-313.) For the latter, two statistics related to MW such as the values The average molecular weight of number and weight must be known for the polymer calibrant, based on the molecular weight calibration, the volume of the elution is converted to molecular weight for the assumed linear ethylene polymer, a detailed discussion of the methodology of the The SEC-Viscometry technique and the equations used to convert the SEC and viscometry data into long-chain branching and corrected molecular weights are provided in the Mirabella and Wild article referred to above. DSC and TREF as described above.Rheological measurements were carried out through dynamic oscillatory shear experiments They are carried out with a new model of Weißenberg Rheogiometer that can be obtained commercially from TA Instruments. The experiments were carried out in a parallel plate mode under a nitrogen atmosphere at 190 ° C. The sample sizes varied from approximately 1100 to 1500 millimeters and were 4 centimeters in diameter. The frequency sweep experiments covered a frequency scale of 0.1 to 100 sec ~ with an effort amplitude of 2 percent. The response to torque was converted by the rheometer control software of TA Instruments into dynamic modules and a dynamic viscosity data at each frequency. The discrete relaxation spectra were adjusted to the data of the dynamic modules for each sample using the commercial software package IRIS (R). The results, which are disclosed in Table 1, demonstrate that only the ethylene polymers of the invention exhibit the unique combination of a Polydispersity index of at least about 3.0., a melt index, MI, and a Relaxation Spectrum Index, RSI, such that (RSI) (MIalfa) is greater than approximately 26 when alpha is approximately 0.7, and a Crystallisable Chain Length Distribution index , Lw / Ln, less than about 3. Figure 1 is a trace of (RSI) (MIa - * - fa) when alpha is approximately 0.7 versus the MI data in Table 1. In addition, only ethylene polymers of the invention had CRC values equal to or greater than 1. Figure 2 is a trace of CRC versus the densidated data in Table 1.

Table 1 Table 1 Table 1 Example: Corrected SEC Polymer 12 MFR DensiSEC Not Corrected Mn Mw PDI IV f. peers df dad Mn- Mw-PDI- Viscode min. SAEM sidad No No No IntrínLCB Corre- Corre- Correseca per (dL / g) 1000 gida gida gida B AFFINITY 2.50 0.00 0.9350 HF1030 60059 2.16 C AFFINITY 1.00 0.00 0.9080 PL1840 72588 2.22 D AFFINITY 3.50 - 0.00 0.9100 PL1845 57486 2.15 E AFFINITY 1.00 0.00 0.9020 PL1880 76481 2.3 F EXACT-2010 1.55 0.00 0.9250 G 47187 95790 2.03 EXACT-3006 1.50 0.00 0.9090 H 47525 84120 1.77 EXACT-4001 4.00 0.00 0.8950 I 32631 66240 2.03 EXACT-4003 9.20 0.00 0.8950 J 27395 54790 2 EXACT-4024 3.80 0.00 0.0000 K HP-LDPE 0.10 0.00 0.9200 L 20764 125000 6.02 HP-LDPE 0.20 0.00 0.9210 M HP- LDPE 18212 124390 6.83 1.90 0.00 2.7000 0.9230 N LLDPE 16207 70500 4.35 1.00 0.00 1.9 0.9180 0 LLDPE 1.00 0.00 0.9180 Table 1 Table 1 - Part 2 Ej emPolymer Tm Te Tm, plos Tm, (C) DSC-HI Indi- (O Lw Ln heterog RSI homog 10 = homog ce of (sec) to (RSI) (M_ ~) 0 = heterog. 190 ° C at «= 0.74 v IQ? ° P 1 Inverdon 93.07 81.24 2 121.97 Invention 97.20 113.14 10.0 103.55 2.30 16.53 36.23 3 125.36 Invec tion 113.38 95.16 10.0 84.04 1.021 1.98 4 122.29 18.53 Inven? ion 98.91 39.57 115.95 10.0 106.10 1.64 5 126.13 19.81 Invention 116.52 37.77 111.35 10.0 101.82 1.023 1.61 6 124.88 26.88 Invention 111.36 43.15 112.32 10.0 102.64 1.026 1.53 125.13 22.28 nverdicfh 112.42 34.35 7 I 108.13 10.0 97.91 1.024 124.05 1.45 21.35 .58 8 Inver & ón 107.62 35 111.64 9.7 102.70 1.022 1.26 125.15 20.54 112.50 31.67 9 Invention 108.12 10.0 97.97 1.026 1.67 124.03 21.40 107.54 34.34 Invendón 96.41 9.6 85.69 1.021 1.90 122.39 21.59 tion 99.41 29.10 11 Inven 111.75 10.0 102.96 1.77 125.03 23.97 112.02 33.89 12 Invention 112.48 10.0 103.38 1.025 1.63 124.96 36.91 111.69 34.15 13 Invention 113.46 9.4 100.82 1.016 2.04 63.88 26.30 14 Invention 113.08 100.22 2.05 15 Invention 112.86 100.22 1.63 16 125.05 Inven? Óh 112.10 112.14 9.4 99.81 1.82 17 Invention 1.59 18 Invention 108.45 95.81 1.45 24.08 40.14 19 Invention 1.67 20 Invention 96.27 92.05 21 122.41 Invention .99.51 10.0 1.60 22 Invention 12.63 49.59 23 Invention 11.49 41.98 24 InverPion 12.51 44.52 14.73 53.12 Table 1 - part 2 Example Polymer Tm Te Tm, Tm, DSC-HI indiLw / Ln RSI (RSIXMI0 *) plos (C) (O heterog homog 10 = homog «ce from (sec) to 0 = heterog. CC 190 ° C at oc = 0.74« and 190 ° C 1 EXACT-4003 83.60 65.61 119.64 83.74 10.0 0.955 1.10 J EXACT-4024 K HP-LDPE 126.51 23.18 L HP-LDPE 108.90 96.05 124.56 109.95 10.0 0.980 1.16 13.30 21.35 M HP-LDPE 109.20 97.38 124.94 111.61 10.0 0.982 1.42 44.49 13.59 N LLDPE 121.70 106.44 123.99 107.36 1.4 0.972 7.86 3.26 3.26 0 LLDPE 123.70 110.16 123.99 107.36 0.2 0.983 14.03 4.79 4.79 P Reactor PE 7.36 6.25 in Stages Q - Reactor PE 10.69 in Stages R Reactor PE in Stages Referring now to Table 2, the ethylene polymers of Examples 1 to 12, as well as the Comparative Examples A, C, E, F, L, M, 0 and P were each compared to determine their extrudability under blown film processing conditions. The ethylene polymers of the invention were each dry blended with 1000 parts per million of IRGANOX B-900 (Ciba-Geigy Corporation) and stirred in a 3.81 centimeter Killion Extrusion Apparatus with a normal LLDPE mixing screw (30). / 1 length to diameter) at a rate of 18.16 kilograms per hour (~ 90 revolutions per minute) with a graduated die temperature of 209 ° C. The granulated ethylene polymers and the polyethylenes of the Comparison Example were extruded into blown films using typical operating conditions. The blown film extrusion kit consisted of a 3.81-centimeter diameter Sterling extruder equipped with a general purpose LLDPE screw, 24: 1 L / D, (constant tilt, decreased depth, Maddox head screw) and a spiral pin matrix. The specific details of the matrices used and the extrusion rate and temperature conditions were as follows: Examples Speed Temperature Matrix Profile Screw ° C 1-12, M 98 rpm 5.59 cm flat spiral spiral profile, matrix spacing of .762 mm with a matrix diameter of 5.44 cm and matrix length of 7.92 mm 90 rpm 209, 218, 237, matrix spiral 237, 237, 237, 5.59 cm, spacing, matrix of .762 mm with a matrix diameter of 5.44 cm \ matrix length of 7.92 mm A, C, E, F, 90 rpm 193, 193, 195, spiral matrix and N 198, 204, 204, 7.62 cm, espa¬ 204 mm matrix of 2.03 mm, with a matrix diameter of 7.21 cm and matrix length of 3.20 cm 90 rpm 193, 193, 195, spiral matrix 198, 204, 204, 5.59 cm, matrix spacing. 762 mm with a matrix diameter of 5.44 cm and a matrix length of 7.92 mm Table 2 shows the loading pressure and amperage that were required to extrude each of the resins tested, as well as the standardized load and amperage pressure with respect to the matrix regime so that direct comparisons could be made. The data normalized in Table 2 shows that the charge and amperage pressures required to extrude the ethylene polymers of the invention were much lower than those needed to extrude the Comparison Examples when compared to a similar melt index. In addition, the ethylene polymers of the invention showed excellent reduction and extrusion ease as compared to high pressure low density polyethylene.

Table 2 BLOWED FILM PROCEPTION Examples Polymer Presidn Ampe- Reg of Pre-Ampe- < _e - rajes Matrix / raje / Head (Kg / sec / cm) DR DR 1 Invention 1390.0 6.00 347. 5 257.41 1.11 2 Invention 1200.0 7.20 424.7 181.82 1.09 3 Invention 1390.0 6.00 328. 2 272.55 1.18 4 Invention 1390.0 7.50 418. 3 213.85 1.15 5 Invention 1550.0 8.20 418. 3 238.46 1.26 6 Invention 1500.0 7.70 418. 3 230.77 1.18 7 Invention 1700.0 7.50 418. 3 261.54 1.15 8 Invention 1500.0 7.90 424. 7 227.27 1.20 9 Inversion 1700.0 7.20 405.4 269.84 1.14 10 Investment 1590.0 6.20 347. 5 294.44 1.15 11 Invention 1450.0 7.10 431. 1 216.42 1.06 12 Invention 2100.0 9.80 424.7 318.18 1.48 A AFFINITY 1900.0 12.2000 225.2 542.86 3.49 FM1570 C AFFINITY 1960.0 11.6000 184.0 685.31 4.06 PL1840 E AFFINITY 1960.0 11.7000 187. 9 671.23 4.01 PL1880 F EXACT-2010 2560.0 17.2000 233.6 705.23 4.74 L HP-LDPE 2100.0 8.2000 379. 7 355.93 1.39 M HP-LDPE 2000.0. 7.9000 379.7 338.98 1.34 N LLDPE 0 LLDPE 2650.0 14.2000 218. 1 '781.71 4.19 P Reactor PE 2200.0 9.0000 368, 7 383.94 1.57 Stages

Claims (10)

CLAIMS:

1. An ethylene polymer having: a Polydispersity index of at least about 3.0; a melt index, MI, and an RSI Relaxation Spectrum index, such that (RSI) (MI * -1- "?) is greater than approximately 26; and a Crystallizable Chain Length Distribution index, Lw / Ln, less than about 3. The ethylene polymer according to claim 1, which further has a DSC Homogeneity index, DSC-HI, of at least about 7. 3. The ethylene polymer in accordance with claim 1, which also has at least about 0.3 long chain branching per 1000 carbon atoms of the main chain 4. The ethylene polymer according to claim 1, which further has a Regimen Constant Crystallisable, CRC, equal to or greater than 1. The ethylene polymer according to claim 1, which contains from about 1 percent to about 40 percent by weight of a linear or branched alpha-olefin having from 3 to about 20 carbon atoms. The ethylene polymer according to claim 1 containing from about 1 percent to 40 percent by weight of a comonomer that is selected from propylene, linear or branched alpha-olefins having from 4 to about 20 carbon atoms , and linear branched or cyclic hydrocarbon dienes and mixtures thereof. 7. A film, an extrusion coated layer, or molded articles comprising the ethylene polymer according to claim 1. 8. The wire and cable insulation and / or the coating comprising the ethylene polymer in accordance with claim 1. 9. A cross-linked transmission cable insulation comprising the ethylene polymer according to claim 1. 10. Insulation sleeves or liners and / or semiconductor sleeves and / or shields comprising the ethylene polymer in accordance with claim 1.