Patent Publication Number: US-7906603-B2

Title: Polymers having broad molecular weight distributions and methods of making the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a Divisional Application of U.S. patent application Ser. No. 11/929,448 filed Oct. 30, 2007, published as US 2008-0051545A1, which is a divisional application of U.S. patent application Ser. No. 10/829,842, issued as U.S. Pat. No. 7,307,133 on Dec. 11, 2007, all entitled “Polymers Having Broad Molecular Weight Distributions and Methods of Making the Same.” The present application is related to U.S. Pat. No. 6,977,235, issued on Dec. 20, 2005 and entitled “Catalyst System Comprising a Chromium Catalyst and a Non-Transition Metal Cyclopentadienyl Cocatalyst.” Each of the patents and patent application is hereby incorporated by reference herein in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not applicable. 
     FIELD OF THE INVENTION 
     The present invention generally relates to polymers, and more particularly to polymers having relatively broad molecular weight distributions and methods of making the same using a chromium-based catalyst and a non-transition metal cyclopentadienyl cocatalyst. 
     BACKGROUND OF THE INVENTION 
     The production of polyolefins using chromium-based catalysts is well known in the art. Various supports have been employed for such chromium-based catalysts. Silica supports have primarily been used due to their ability to form highly active polymerization catalysts. Other examples of supports that have been used for such chromium-based catalysts include alumina and aluminophosphates. Supported chromium-based catalysts were initially employed in solution polymerization processes. However, slurry polymerization soon became known as the more economical route to many commercial grades of polyolefins using such catalysts. 
     A polyolefin exhibits various physical, and in particular, mechanical properties that are highly affected by its molecular weight distribution (MWD). The molecular weight distribution can be determined by means of a curve obtained by gel permeation chromatography (GPC). It can be described by a parameter known as the polydispersity index (PDI), which indicates the breadth of the molecular weight distribution and is equivalent to the weight-average molecular weight of a polymer divided by the number-average molecular weight of the polymer (i.e., M W /M N ). A broadening in the molecular weight distribution of a polyolefin tends to improve the flow of the polyolefin when it is being processed at high rates of shear. 
     The polymerization of olefins using chromium-based catalysts is often performed in the presence of hydrogen to produce polyolefins having relatively low molecular weights. However, although hydrogen can be used to regulate the molecular weight, the breadth of the molecular weight distribution of a polyolefin tends to be limited by the choice of catalyst. A need therefore exists to broaden the molecular weight distributions of polyolefins produced using chromium-based catalysts. 
     SUMMARY OF THE INVENTION 
     Methods of polymerizing at least one olefin include contacting the olefin with a catalyst comprising chromium and with a cocatalyst comprising a non-transition metal cyclopentadienyl (Cp) compound. The polymerization may be performed in the presence of hydrogen. Using the cocatalyst in conjunction with the catalyst increases several properties, such as the high load melt index (HLMI), the M W , and the M N , of the polymers produced by this polymerization method. 
     Polymer compositions produced by such methods have various unique properties. In one embodiment, the polymer compositions have a M W  greater than about 600,000 g/mol and a HLMI in a range of from about 0.01 g/10 min to about 10 g/10 min. In another embodiment, the polymer compositions have a M W  greater than about 400,000 g/mol and a zero shear viscosity (E o ) less than about 10 8  Pa·s. In yet another embodiment, the polymer compositions have a rheological breadth parameter greater than about 0.15 and a PDI greater than about 30. Additional embodiments include polymer compositions having other properties, and articles of manufacture or end use articles formed from the foregoing polymer compositions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a graph illustrating the molecular weight distributions of polyethylene resins formed using a chromium-based catalyst and different non-transition metal cyclopentadienyl cocatalysts and of a polyethylene resin formed using a chromium-based catalyst but no cocatalyst. 
         FIG. 2  depicts a graph illustrating the molecular weight distributions of polyethylene resins formed using a chromium-based catalyst and different concentrations of a dicyclopentadienyl magnesium cocatalyst and of a polyethylene resin formed using a chromium-based catalyst and a triethylaluminum cocatalyst. 
         FIG. 3  depicts a graph illustrating the molecular weight distributions of two polyethylene resins formed using a chromium-based catalyst, wherein one is formed with a cyclopentadienyl lithium cocatalyst and one is formed without a cocatalyst. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A catalyst system suitable for use in polymerizing olefins includes at least one chromium-based catalyst and at least one non-transition metal cyclopentadienyl (Cp) compound as a cocatalyst. A mole ratio of the non-transition metal Cp compound to the chromium in the catalyst system may range from about 0.001 to about 20, from about 0.001 to about 10, from about 0.003 to about 20, from about 0.01 to about 3, or from about 0.02 to about 2. The non-transition metal Cp compound typically constitutes from about 0.01 to about 50 ppm by weight of the reaction zone contents, alternatively from about 0.1 to about 20 ppm, or alternatively from about 0.1 to about 10 ppm by weight of the contents of a reaction zone in which the catalyst system is used for polymerization. 
     The non-transition metal Cp cocatalyst contains a non-transition metal bonded to a Cp group. Examples of suitable non-transition metals include a Group I metal such as lithium (Li) and sodium (Na), a Group II metal such as magnesium (Mg), and a Group III metal such as aluminum. Examples of suitable Cp groups include cyclopentadienyl, a fluorenyl group, and an indenyl group. The Cp group may be substituted or unsubstituted. For example, the Cp group may be substituted with an alkyl group, an aryl group, an alkylaryl group, an alkoxy group, an aryloxy group, an alkylsilyl group, or combinations thereof. In an embodiment, the metal Cp cocatalyst is cyclopentadienyl lithium (CpLi), dicyclopentadienyl magnesium (Cp 2 Mg), a lithium aluminum cyclopentadienyl trialkyl, or combinations thereof. If the metal is a divalent or trivalent metal, other anions may accompany the Cp group, such as halides, alkoxides, or organic radicals. For example, the metal Cp cocatalyst may also be cyclopentadienyl magnesium ethoxide (CpMgOC 2 H 5 ), indenyl aluminum dibutyl (IndAl(C 4 H 9 ) 2 ) or fluorenyl ethyl boron chloride (FluBClC 2 H 5 ). The metal Cp cocatalyst may also be a complex salt of two metals such as lithium aluminum cyclopentadienyl triethyl (LiAlCp(C 2 H 5 ) 3 ). 
     The chromium-based catalyst includes chromium on a support that serves as a carrier for the chromium. The support may primarily include an inorganic oxide such as silica, alumina, aluminophosphates, and mixtures thereof. In an embodiment, the support contains greater than about 50 percent (%) silica, alternatively greater than about 80% silica, by weight of the support. The support may further include additional components that do not adversely affect the catalyst system, such as titania, zirconia, alumina, boria, thoria, magnesia, and mixtures thereof. The support has a specific surface area and a specific pore volume effective to provide for an active catalyst. A Quantachrome Autosorb-6 Nitrogen Pore Size Distribution Instrument, which is commercially available from the Quantachrome Corporation of Syosset, N.Y., may be used to determine the specific surface area (hereinafter “surface area”) and specific pore volume (hereinafter “pore volume”) of the support. The surface area of the support may range from about 100 square meters per gram (m 2 /g) to about 1,000 m 2 /g, alternatively from about 200 m 2 /g to about 800 m 2 /g, or from about 250 m 2 /g to about 700 m 2 /g. Further, the pore volume of the support, i.e., an indicator of the amount of liquid it can absorb, may range from about 0.5 cubic centimeters per gram (cc/g) to about 3.5 cc/g or alternatively from about 0.8 cc/g to about 3 cc/g. 
     The chromium may be loaded on the support using any method known in the art. In one embodiment, a coprecipitated cogel of chromium and of one or more support components is made. As used herein, cogel refers to the product resulting from the gelation of two or more components. In another embodiment, the support is impregnated with an aqueous solution containing a water-soluble chromium compound. Examples of water-soluble chromium compounds include chromium oxide, chromium trioxide, chromium acetate, chromium nitrate, or combinations thereof. In yet another embodiment, the support is impregnated with a hydrocarbon solution in which a chromium compound is dissolved after removing water from the support by, e.g., spray dying or azeotropically drying it. Examples of hydrocarbon soluble chromium compounds include tertiary butyl chromate, a diarene chromium compound, biscyclopentadienyl chromium(II), chromium acetylacetonate, or combinations thereof. The amount of chromium present in the ensuing catalyst may range from about 0.01% to about 10% by weight of the catalyst, alternatively from about 0.2% to about 5%, or from about 0.5% to about 2%. 
     In an embodiment, chromium-based catalyst grades 963, 964, 969, or combinations thereof may be obtained from any commercial source such as the Grace Davison catalysts of W.R. Grace &amp; Company of Columbia, Md. Especially suitable are those catalysts comprising chromium oxide supported by a high porosity silica-titania as are described in U.S. Pat. Nos. 3,887,494 and 3,119,569, both of which are incorporated by reference herein in their entirety. By way of example, the support may be produced by simultaneous gellation of silica, titania, and chromia. Such gellation may be performed by contacting an alkali metal silicate such as sodium silicate with an acid solution containing a titanium salt such as a sulfuric acid titanyl sulfate solution containing chromium, thereby forming a cogel, also known as a hydrogel. After gellation, the cogel may be aged at a pH of from about 7 to about 8 for several hours at 80° C. It may then be azeotropically dried in an organic solvent such as hexanol to form a xerogel. The titanium content of this support may range from about 1% to about 10% by weight of the catalyst. The surface area of this support is typically about 550 m 2 /g, and the pore volume of the support is typically in the range of from about 2.2 cc/g to about 2.5 cc/g. 
     Additional disclosure regarding chromium-based catalysts supported by silica/titania can be found in the following patents: U.S. Pat. Nos. 4,405,501 and 4,436,886 which relate to the aging process; U.S. Pat. Nos. 4,436,883 and 4,392,990 which relate to N 2  calcination; U.S. Pat. Nos. 4,081,407 and 4,152,503 which relate to azeotropic drying using hexanol; U.S. Pat. No. 4,981,831; U.S. Pat. Nos. 4,294,724, 4,382,022, 4,402,864, and 4,405,768, and 4,424,320 which relate to titanation; and U.S. Pat. Nos. 2,825,721, 4,382,022, 4,402,864, 4,405,768, 3,622,521, 3,625,864 which relate to silica-titania, all of the foregoing patents being incorporated by reference herein in their entirety. Aluminophosphate supported catalysts are described in U.S. Pat. Nos. 4,364,842, 4,444,965, 4,364,855, 4,504,638, 4,364,854, 4,444,964, 4,444,962, each of which is incorporated by reference herein in its entirety. Phosphated alumina supported catalysts are described U.S. Pat. Nos. 4,444,966, 4,397,765, and 4,900,704, each of which is incorporated by reference herein in its entirety. 
     The chromium-based catalyst may be activated using any known technique after introducing the chromium to the support. In one embodiment, the catalyst is activated via calcination by heating it in an oxidizing environment. For example, the support may be heated in the presence of air at a temperature in the range of from about 400° C. to about 1,000° C., alternatively from about 600° C. to about 900° C. Optionally, the calcination may be followed by a reduction step. The reduction step may be performed by, for example, heating the support in the presence of carbon monoxide (CO) at a temperature in the range of from about 200° C. to about 800° C. In another embodiment, the catalyst is activated via a reduction and reoxidation process. Suitable reduction and reoxidation processes are disclosed in U.S. Pat. Nos. 4,151,122, 4,177,162, 4,247,421, 4,248,735, 4,297,460, 4,397,769, 4,460,756, 4,182,815, 4,277,587, each of which is incorporated by reference herein in its entirety. 
     In an embodiment, the non-transition metal Cp cocatalyst is co-supported with the chromium-based catalyst. The metal Cp cocatalyst is loaded onto the support after activating it. The Cp cocatalyst may be combined with the support by, for example, impregnating the already activated chromium-based catalyst with an organic (preferably hydrocarbon) solution comprising the metal Cp cocatalyst. The resulting Cr/metal Cp catalyst may then be fed to a polymerization reactor. In another embodiment, the activated chromium-based catalyst and the non-transition metal Cp are separately fed to a polymerization zone. In yet another embodiment, the Cr catalyst and Cp compound can both be continuously fed into a contacting vessel where they react for a period of from about 1 minute to about 10 hours, and from there the contacted ingredients are fed into the polymerization zone. The two feeds can thus be accurately and continuously controlled during the polymerization to determine the correct molar Cp/Cr ratio which in turn controls polymer properties. In this way adjustments to the catalyst-cocatalyst recipe can be made as the polymers are produced. 
     Polymer compositions may be formed by polymerizing at least one monomer in the presence of the foregoing catalyst system comprising a chromium-based catalyst and a non-transition metal Cp cocatalyst. Examples of suitable monomers include unsaturated hydrocarbons having from 2 to 20 carbon atoms such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, and mixtures thereof. The chromium-based catalyst is particularly suitable for producing polyethylene homopolymers, and copolymers of ethylene monomer and 1-hexene comonomer. The polymer density of such copolymers may be controlled by varying the comonomer to monomer ratio in the reactor. 
     Any suitable polymerization methods known in the art may be used, such as solution polymerization, slurry polymerization, and gas phase polymerization. Any polymerization reactor known in the art that is capable of polymerizing olefin monomers to produce the homopolymers or copolymers described herein also may be used. Such reactors can comprise slurry reactors, gas-phase reactors, solution reactors or any combination thereof. Gas phase reactors can comprise fluidized bed reactors or tubular reactors. Slurry reactors can comprise vertical loops or horizontal loops. Solution reactors can comprise stirred tank or autoclave reactors. Such reactors can be combined into multiple reactor systems operated in parallel or in series. 
     Any manner known in the art may be employed to contact the monomer with the catalyst in the reaction zone. As mentioned previously, the cocatalyst may be co-supported with the catalyst, or it may alternatively be separately introduced to a reaction zone. Suitable contact methods include fluidized bed, gravitating bed, and fixed bed methods. In one embodiment, the catalyst and the cocatalyst streams are both continuously fed into a pre-contacting reaction zone prior to adding the mixture into the polymerization reactor. In this pre-contacting reaction zone, the two components react with each other at temperatures ranging from about −10° C. to about 100° C. during residence times typically ranging from about 1 minute to about 2 hours. After the two components have contacted each other for the specified duration, the combination is then fed continuously into the polymerization reactor. 
     In one embodiment, the polymerization is carried out using a plurality of stirred tank reactors either in series, parallel, or combinations thereof. Different reaction conditions may be used in the different reactors. In another embodiment, the polymerization is conducted in a loop reactor using slurry polymerization. Suitable loop reactors are disclosed in U.S. Pat. Nos. 3,248,179, 5,565,175 and 6,239,235, which are incorporated by reference herein in their entirety. Within the loop reactor, the catalyst and the cocatalyst are suspended in an inert diluent and agitated to maintain them in suspension throughout the polymerization process. The diluent is a medium in which the polymer being formed does not readily dissolve. In an embodiment, the diluent is isobutane in which the polymer tends to swell less than in other diluents. It is understood that other diluents may be utilized as deemed appropriate by one skilled in the art. In an embodiment in which ethylene is polymerized in the loop reactor, the amount of ethylene present is in the range of from about 1% to about 20% by the weight of the diluent, or alternatively from about 3% to about 8%. When a comonomer such as 1-butene or 1-hexene is used, it is added to the reactor in an amount sufficient to yield a polymer having a desired density, which is usually in the range of from about 0.92 to about 0.96 g/cc. In a loop reactor this amount is typically in the range of from about 0.1% to about 20% by weight of the diluent. 
     The slurry polymerization conditions are selected to ensure that the polymer being produced has certain desirable properties and is in the form of solid particles. The polymerization is desirably carried out below a temperature at which the polymer swells or goes into solution. For example, the polymerization temperature may be less than about 110° C., alternatively in the range of from about 85° C. to about 110° C. The catalyst system is contacted with the at least one monomer at a pressure sufficient to maintain the diluent and at least a portion of the monomer in the liquid phase. That is, the pressure within the loop reactor may be maintained in the range of from about 110 psi to about 700 psi or higher. Suitable slurry polymerization processes are disclosed in U.S. Pat. Nos. 4,424,341, 4,501,855, and 4,613,484, 4,589,957, 4,737,280, 5,597,892, and 5,575,979, each of which is incorporated by reference herein in its entirety. The activity and the productivity of the catalyst system are relatively high. As used herein, the activity refers to the grams of polymer produced per gram of solid catalyst charged per hour, and the productivity refers to the grams of polymer produced per gram of solid catalyst charged. 
     Additional details regarding chromium-based catalysts and/or slurry polymerization processes can be found in U.S. Pat. Nos. 3,887,494, 3,900,457, 3,947,433, 4,053,436, 4,081,407, 4,151,122, 4,294,724, 4,296,001, 4,345,055, 4,364,839, 4,364,841, 4,364,842, 4,364,854, 4,364,855, 4,392,990, 4,397,765, 4,402,864, and 4,405,501, each of which is incorporated by reference herein in its entirety. 
     According to an embodiment, hydrogen (H 2 ) may be introduced to the polymerization reaction zone to control molecular weight. The H 2  may be employed at concentrations of equal to or less than about 3 mole % based on the total number of moles of the diluent in a loop reactor, alternatively from about 0.1 mole % to about 2 mole %. Polymerizing the olefin in the presence of the cocatalyst and the hydrogen broadens the molecular weight distribution of the polymer and generally improves the properties of the polymer. For example, the use of the cocatalyst in conjunction with the hydrogen results in an increase in the melt index (MI) and the high-load melt index (HLMI) of the polymer produced, whereas the MI and the HLMI of the polymer drop when the cocatalyst is used without any hydrogen present. Without intending to be limited by theory, it is believed that the presence of the cocatalyst causes the sites on the catalyst that usually produce low molecular weight polymer to convert to chromocenyl sites that reject the comonomer, e.g., hexene, and are more sensitive to H 2 . 
     When the metal Cp cocatalyst is included in the catalyst system added to the reactor in the presence of hydrogen, the weight average molecular weight (M W ) of the polymer formed therein increases while the number average molecular weight (M N ) decreases substantially, as compared to using the same catalyst system run under the same reactor conditions in the presence of the same amount of hydrogen, but without the metal Cp cocatalyst. Typically, the M W  may increase by equal to or greater than about 25%, alternatively by equal to or greater than about 50%, or alternatively by equal to or greater than about 80%. Increases of equal to or greater than about 100% also may result, depending on the catalyst type and the amount of hydrogen and metal Cp catalyst used. Further, the M N  may decrease by equal to or greater than about 20%, alternatively by equal to or greater than about 40%, alternatively by equal to or greater than about 50%, or alternatively on occasion by equal to or greater than about 60%. 
     Likewise, the MI and HLMI of the polymer produced increase when the metal Cp cocatalyst is added to the reactor to which hydrogen is also added, as compared to the same polymer made with the same catalyst under the same reactor conditions but in the absence of the metal Cp cocatalyst. The MI or HLMI typically increases by equal to or greater than about 50%, alternatively by equal to or greater than about 100%, or alternatively by equal to or greater than about 500%. They may even increase by equal to or greater than ten fold, depending on the catalyst type, the amount of metal Cp cocatalyst used, and the amount of hydrogen used. 
     Polymer compositions or resins produced using the chromium-based catalyst in conjunction with the non-transition metal Cp cocatalyst have unique properties. Examples of the polymer compositions include polyethylene homopolymers and copolymers of ethylene monomer and 1-hexene comonomer. For example, the polymer compositions have a weight-average molecular weight greater than about 100,000 g/mol. Alternatively, the M W  may be greater than about 250,000 g/mol, greater than about 400,000 g/mol, greater than about 500,000 g/mol, or greater than about 600,000 g/mol. Also, the polymer compositions have broad MWD&#39;s as indicated by PDI values greater than about 20. In some embodiments, the polymer compositions have PDI values, greater than about 30, greater than about 40, greater than about 50, greater than about 70, or greater than about 90. 
     The molecular weights and the molecular weight distributions of the polymer compositions are obtained using a Waters 150 CV gel permeation chromatograph with trichlorobenzene (TCB) as the solvent using a flow rate of 1 mL/min at a temperature of 140° C. The TCB is stabilized using 2,6-Di-t-butyl-4-methylphenol (BHT) at a concentration of 1.0 g/L. An injection volume of 220 microliters is used with a nominal polymer concentration of 0.3 g/L at room temperature. The polymer sample is dissolved in stabilized TCB by heating it at about 160 to 170° C. for 20 hours while performing occasional gentle agitation. The gel permeation chromatograph includes two Waters HT-6E columns (7.8 mm×300 mm). The columns are calibrated with a broad linear polyethylene standard (Phillips Marlex® BHB 5003 resin) for which the molecular weight has been determined. 
     Rheological breadth refers to the breadth of the transition region between Newtonian and power-law type shear rate for a polymer or the frequency dependence of the viscosity of the polymer. The rheological breadth is a function of the relaxation time distribution of a polymer resin, which in turn is a function of the resin molecular structure or architecture. Assuming the Cox-Merz rule, the rheological breadth may be calculated by fitting flow curves generated in linear-viscoelastic dynamic oscillatory frequency sweep experiments with a modified Carreau-Yasuda (CY) model, which is represented by the following equation: 
     
       
         
           
             E 
             = 
             
               
                 
                   E 
                   o 
                 
                 ⁡ 
                 
                   [ 
                   
                     1 
                     + 
                     
                       
                         ( 
                         
                           
                             T 
                             ξ 
                           
                           ⁢ 
                           
                             γ 
                             . 
                           
                         
                         ) 
                       
                       a 
                     
                   
                   ] 
                 
               
               
                 
                   n 
                   - 
                   1 
                 
                 a 
               
             
           
         
       
     
     where 
     E=viscosity (Pa·s) 
     {dot over (γ)}=shear rate (1/s) 
     “a”=rheological breadth parameter 
     T ξ =relaxation time (s) [describes the location in time of the transition region] 
     E o =zero shear viscosity (Pa·s) [defines the Newtonian plateau] 
     n=power law constant [defines the final slope of the high shear rate region] 
     To facilitate model fitting, the power law constant is held at a constant value. Details of the significance and interpretation of the CY model and derived parameters may be found in: C. A. Hieber and H. H. Chiang,  Rheol. Acta,  28, 321 (1989); C. A. Hieber and H. H. Chiang,  Polym. Eng. Sci.,  32, 931 (1992); and R. B. Bird, R. C. Armstrong and O. Hasseger,  Dynamics of Polymeric Liquids, Volume  1,  Fluid Mechanics,  2nd Edition, John Wiley &amp; Sons (1987), each of which is incorporated by reference herein in its entirety. The polymer compositions have rheological breadth parameters, i.e., “a” parameters, greater than about 0.15, as determined at a temperature of 190° C. Alternatively, the “a” parameters are greater than about 0.18, greater than about 0.19, or greater than about 0.20. 
     In addition, the zero shear viscosity (E o ) values, of the polymer compositions are less than about 10 8  Pa·s. In one embodiment, the E o  values are greater than about 10 5  Pa·s and less than about 10 8  Pa·s. In yet another embodiment, the E o  values greater than about 10 5  Pa·s and less than about 5×10 7  Pa·s. In still another embodiment, the E o  values are greater than about 10 5  Pa·s and less than about 10 7  Pa·s. In another embodiment, the E o  values are greater than about 10 5  Pa·s and less than about 5×10 6  Pa·s. 
     Polymer compositions having the previously described properties may be formed into articles of manufacture or end use articles using techniques known in the art such as extrusion, blow molding, injection molding, fiber spinning, thermoforming, and casting. For example, a polymer resin may be extruded into a sheet, which is then thermoformed into an end use article such as a container, a cup, a tray, a pallet, a toy, or a component of another product. Examples of other end use articles into which the polymer resins may be formed include pipes, drums, films, bottles, fibers, and so forth. Additional end use articles would be apparent to those skilled in the art. 
     In an embodiment, pipes are formed from the foregoing polymer compositions using, for example, extrusion. The densities of the polymer pipes range from about 0.92 g/cc to about 0.97 g/cc. Alternatively, the densities range from about 0.93 g/cc to about 0.965 g/cc, from about 0.94 g/cc to about 0.96 g/cc, or from about 0.945 g/cc to about 0.955 g/cc. Polymer density is determined in grams per cubic centimeter (g/cc) on a compression molded sample that is cooled at about 15° C. per hour and conditioned for about 40 hours at room temperature in accordance with ASTM D1505 and ASTM D1928, procedure C. 
     The melt index of a polymer resin represents the rate of flow of a molten resin through an orifice of 0.0825 inch diameter when subjected to a force of 2,160 grams at 190° C. Further, the high load melt index of a polymer resin represents the rate of flow of a molten resin through an orifice of 0.0825 inch diameter when subjected to a force of 21,600 grams at 190° C. The MI values of the polymer pipes are in a range of from about 0.01 g/10 min to about 10 g/10 min, alternatively from about 0.1 to about 10 g/10 min. Alternatively, the polymer pipes may have MI values in the range of from about 0.05 g/10 min to about 5 g/10 min, from about 0.1 g/10 min to about 1.0 g/10 min, or from about 0.2 g/10 min to about 0.5 g/10 min. The MI values are determined in accordance with ASTM D1238. The polymer pipes have HLMI values in the range of from about 0.1 to about 100 g/10 min, from about 1 to about 10 g/10 min, from about 1 to about 50 g/10 min, from about 2 to about 20 g/10 min, or from about 4 to about 15 g/10 min. The HLMI values are determined in accordance with ASTM D1238 condition E. In addition, the shear ratio (HLMI/MI) values of the polymer pipes are greater than about 80, greater than about 100, greater than about 150, or greater than about 200. 
     Charpy impact testing is one method of predicting the pipe&#39;s resistance to rapid crack growth at low temperatures. In this test, compression molded plastic bars are cooled to various temperatures, and subjected to an impact test. The temperature at which a crack in a bar transitions from ductile to brittle failure is recorded, as well as the total energy at each temperature required to break the bar. Details of the test can be found in ASTM F2231. Results are usually reported as 1) the ductile to brittle transition temperature T db  (i.e., the Charpy critical temperature), and 2) the specific energy of breakage at a certain reference temperature, usually 0° C. (i.e., the Charpy impact energy). The lower the T db  and the higher the impact energy, the better the resin&#39;s resistance to rapid crack growth. The polymer pipes described herein have a low T db  less than about 0° C. and a Charpy impact energy greater than about 50 J/m. Alternatively, the T db  is less than about −5° C., less than about −10° C., or less than about −20° C. Alternatively, the Charpy impact energy is greater than about 75 J/m, greater than about 100 J/m, or greater than about 125 J/m. 
     The resistance of a pipe to slow crack growth is measured by pressurizing a section of a notched pipe (ASTM F1474; ISO 13479). The resistance of a pipe material to slow crack growth is well studied and documented. Typically, the resistance to slow crack growth of pipe products improves with increasing molecular weight, decreasing crystallinity (or density) of the starting resin, and proper placement of short chain branching in the molecular weight distribution. The inherent resistance of a pipe to slow crack growth is measured in tests such as the Pennsylvania notched-tensile test (PENT; ASTM F1473) using compression-molded specimens. Sample bars are subjected to a constant load at 80° C. until they finally break. The polymer pipes described herein display high Pent values of greater than about 500 h, greater than about 700 h, or greater than about 1,000 hours. 
     In another embodiment, the previously described polymer compositions are blow molded into bottles. The MI values of the blow molded bottles are in the range of from about 0.01 to about 10 g/10 min, alternatively from about 0.1 to about 10 g/10 min. Alternatively, the blow molded bottles may have MI values in the range of from about 0.1 g/10 min to about 1 g/10 min, from about 0.15 g/10 min to about 0.5 g/10 min, or from about 0.18 g/10 min to about 0.4 g/10 min. The blow molded bottles also have HLMI values in the range of from about 1 to about 1,000 g/10 min, from about 1 to about 10 g/10 min, from about 5 to about 100 g/10 min, from about 10 to about 80 g/10 min, from about 15 to about 50 g/10 min, or from about 18 to about 35 g/10 min. 
     Environmental Stress Crack Resistance (ESCR) measures a polymer&#39;s resistance to chemical attack and can be determined using ASTM D 1693, condition A and condition B. For blow molded bottles having HLMI values ranging from about 15 to about 30 g/10 min and densities greater than or equal to about 0.952, both their ESCR-A values and their ESCR-B values are greater than about 250, greater than about 500, greater than about 800, or greater than about 1,000. 
     A polymer often tends to swell during blow molding extrusion. Percent weight swell measures the amount the molten resin expands immediately as it exits the die. It is a measure of the “memory” of the polymer chains as they seek to relax and thus reform the polymer shape. Weight swell is an important parameter as it determines how tight the die gap must be adjusted to provide a constant bottle weight. If a resin has high weight swell, the die gap required will be tighter to make the proper part weight. In so doing, it will require higher stress to push the resin through the die than a lower weight swell resin. Weight swell is defined as the ratio of the die gap to the final bottle wall thickness. The weight swell values of the polymer compositions described herein are usually less than about 700, less than about 500, less than about 450, or less than about 400. 
     As a polymer is subjected to increasing shear rates during extrusion, it eventually slips or experiences a so-called melt fracture. In an embodiment, the shear rates at the onset of melt fracture for the blow molded polymers are greater than about 22,000/sec. Alternatively, the shear rates are greater than about 24,000/sec, greater than about 26,000/sec, or greater than about 28,000/sec. 
     EXAMPLES 
     The invention having been generally described, the following examples are given as particular embodiments of the invention and to demonstrate the practice and advantages thereof. It is understood that the examples are given by way of illustration and are not intended to limit the specification or the claims to follow in any manner. 
     Example 1 
     A grade 963 chromium oxide/silica-titania catalyst obtained from W.R. Grace Corporation was activated in air at 800° C. To activate the catalyst, about 10 grams were placed in a 1.75 inch quartz tube fitted with a sintered quartz disk at the bottom. While the catalyst was supported on the disk, dry air was blown up through the disk at the linear rate of from about 1.6 to about 1.8 standard cubic feet per hour. An electric furnace around the quartz tube was then turned on and the temperature was raised at the rate of 400° C. per hour to the indicated temperature, i.e., 800° C. At that temperature the catalyst was allowed to fluidize for three hours in the dry air. The temperature was then lowered to 350° C. where the air was flushed out with dry nitrogen, and then the catalyst was reduced in the presence of carbon monoxide (CO) for 30 minutes. After a final flushing out of the CO with nitrogen, the catalyst was collected and stored under dry nitrogen, where it was protected from the atmosphere until ready for testing. It was never allowed to experience any exposure to the atmosphere. 
     The catalyst was then employed in four different runs to polymerize ethylene. The polymerization runs were made in a 2.2 liter steel reactor equipped with a marine stirrer running at 400 rpm. The reactor was surrounded by a steel jacket containing boiling methanol and connected to a steel condenser. The boiling point of the methanol was controlled by varying nitrogen pressure applied to the condenser and jacket, which permitted precise temperature control to within half a degree centigrade, with the help of electronic control instruments. 
     Unless otherwise stated, a small amount (normally 0.01 to 0.10 grams) of the catalyst was first charged under nitrogen to the dry reactor. Next 0.6 liter of isobutane liquid was added to the reactor, followed by a solution containing the non-transition metal Cp cocatalyst, and finally by another 0.6 liter of isobutane liquid. Then the reactor was heated up to 95° C., followed by the addition of 30 psig of hydrogen gas (H 2 ). Finally ethylene was added to the reactor to equal a fixed pressure of 550 psig. The reaction mixture was stirred for about one hour. As ethylene was consumed, more ethylene flowed into the reactor to maintain the pressure. The activity was noted by recording the flow of ethylene into the reactor to maintain the set pressure. 
     After the allotted time, the ethylene flow was stopped and the reactor was slowly depressurized and opened to recover a granular polymer powder. In all cases, the reactor was clean with no indication of any wall scale, coating, or other forms of fouling. The polymer powder was then removed and weighed. The activity was specified as grams of polymer produced per gram of solid oxide component charged per hour. 
     Run 1 was performed in the absence of a cocatalyst, runs 2 and 3 were run using different amounts of the trimethylsilylcyclopentadienyl lithium (TMS-Cp-Li) as a cocatalyst, and run 4 was run using biscyclopentadienyl magnesium (Cp 2 Mg) as a cocatalyst. Table 1 below provides details regarding each run and the MI, HLMI, HLMI/MI, M N , M W , and PDI values of the polymer resin produced in each run. The methods used to determine such values are disclosed above. As shown in Table 1, the MI and HLMI values increased substantially when a non-transition metal Cp cocatalyst was used with H 2 . When used without H 2 , the melt index actually dropped, thus supporting the theory that chromocenyl sites form on the catalyst when the cocatalyst and H 2  are used. In addition, the breadth of the MWD, i.e., the PDI, increased when the cocatalyst was used with H 2 . 
     Example 2 
     A 969 MPI grade Cr/silica-titania catalyst was obtained from W.R. Grace and activated in air at 650° C. in the same manner as described in Example 1. It was then reduced in the presence of CO at a temperature of about 370° C. The catalyst was then employed in several runs to polymerize ethylene at 95° C. as described in Example 1. Most but not all of the runs were performed in the presence of H 2 . Some runs were performed using no cocatalyst, and some runs were performed using Cp 2 Mg cocatalyst, one of which additionally used triethylaluminum (TEA) cocatalyst. Other runs were performed using CpLi cocatalyst. Table 2 below provides details regarding each run and the MI, HLMI, HLMI/MI, M N , M W , and PDI values of the polymer resins produced in each run. The methods used to determine such values are disclosed above. As shown in Table 2, the MI and HLMI values generally increased when a non-transition metal Cp cocatalyst was used with H 2 . In addition, the breadth of the MWD, i.e., the PDI, increased when the cocatalyst was used with H 2 . 
     Example 3 
     A 963 grade Cr/silica-titania catalyst obtained from W.R. Grace Corp., was calcined in air at 650° C. as described above in Example 1. It was then reduced in the presence of CO at a temperature of about 370° C. The catalyst was then employed in two different runs to polymerize ethylene as described in Example 1. One run was performed in the absence of a cocatalyst and in the absence of H 2 . The other run was performed using Cp 2 Mg as a cocatalyst and in the presence of H 2 . Table 3 below provides details regarding each run and the MI, HLMI, HLMI/MI, M N , M W , and PDI values of the polymer resin produced in each run. The methods used to determine such values are disclosed above. As shown in Table 3, the MI and HLMI values increased substantially when the Cp 2 Mg cocatalyst was used with H 2 . In addition, the breadth of the MWD, i.e., the PDI, increased when the cocatalyst was used with H 2 . 
     Example 4 
     A 969 MPI grade Cr/silica-titania catalyst was obtained from W.R. Grace Corp. and calcined in air at 650° C. as described in Example 1. The catalyst and 4 ppm of Cp 2 Mg cocatalyst based on the weight of the isobutane added were then employed in three runs to polymerize ethylene in the presence of H 2  at 95° C. and 30 psig. The catalyst was reduced in the presence of CO at a temperature of about 371° C. before two of the three runs. A triethylaluminum cocatalyst was additionally used in one of these runs. The catalyst and the cocatalyst(s) were suspended in an isobutane diluent within a pipe loop reactor during these different runs. Table 4 below provides details regarding each run and the MI, HLMI, HLMI/MI values of the polymer resins produced in each run. The methods used to determine such values are disclosed above. These values improved when TEA cocatalyst was used to supplement the Cp 2 Mg catalyst. In the run in which the catalyst had not been reduced beforehand, the catalyst exhibited little activity. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Non- 
                 Catalyst 
                   
                 Run 
                   
                   
                 MI 
                 HLMI 
                   
                   
                   
                   
               
               
                   
                 Transition Metal 
                 Charge 
                 Yield 
                 Time 
                 Prod. 
                 Activity 
                 (g/10 
                 (g/10 
                 HLMI/ 
                 M N   
                 M W   
               
               
                 Run # 
                 Cp Treatment 
                 (g) 
                 (g) 
                 (min.) 
                 (g/g) 
                 (g/g/h) 
                 min.) 
                 min.) 
                 MI 
                 (kg/mol) 
                 (kg/mol) 
                 PDI 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 none 
                 0.0452 
                 69.5 
                 74.5 
                 1538 
                 1238 
                 0.12 
                 7.6 
                 63 
                 15.4 
                 165.2 
                 10.7 
               
               
                 2 
                 4 ppm TMS-Cp-Li 
                 0.1796 
                 279 
                 54 
                 1553 
                 1726 
                 0.18 
                 25.4 
                 141 
                 6.3 
                 367.5 
                 58.2 
               
               
                 3 
                 11.3 ppm TMS-Cp-Li 
                 0.1176 
                 155 
                 50 
                 1318 
                 1582 
                 0.945 
                 107.6 
                 114 
                 5.1 
                 238.5 
                 46.6 
               
               
                 4 
                 4 ppm Cp 2 Mg 
                 0.0891 
                 74.5 
                 77.1 
                 836 
                 651 
                 1.58 
                 224.3 
                 142 
                 4.3 
                 255.0 
                 59.3 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Non- 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                   
                 Transition 
                 H 2 , 
                 Catalyst 
                   
                 Run 
                   
                   
                 MI 
                 HLMI 
               
               
                   
                 Metal Cp 
                 psig on 
                 Charge 
                 Yield 
                 Time 
                 Prod. 
                 Activity 
                 (g/10 
                 (g/10 
                 HLMI/ 
                 M N   
                 M W   
               
               
                 Run # 
                 Treatment 
                 Rx 
                 (g) 
                 (g) 
                 (min.) 
                 (g/g) 
                 (g/g/h) 
                 min.) 
                 min.) 
                 MI 
                 (kg/mol) 
                 (kg/mol) 
                 PDI 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 5 
                 none 
                 0 
                 0.0536 
                 133 
                 62 
                 2481 
                 2401 
                 0 
                 0.4 
                   
                 32.8 
                 724.4 
                 22.0 
               
               
                 6 
                 none 
                 30 
                 0.0848 
                 267 
                 68 
                 2624 
                 2315 
                 0 
                 0.81 
                   
                 33.4 
                 641.0 
                 19.2 
               
               
                 7 
                 1 ppm Cp 2 Mg 
                 30 
                 0.1054 
                 208 
                 60 
                 1973 
                 1973 
                 0 
                 0.95 
                   
                 21.7 
                 812.3 
                 37.5 
               
               
                 8 
                 2 ppm Cp 2 Mg 
                 30 
                 0.1045 
                 143 
                 70 
                 1368 
                 1173 
                 0 
                 2.05 
                   
                 15.6 
                 851.2 
                 54.7 
               
               
                 9 
                 4 ppm Cp 2 Mg 
                 30 
                 0.0798 
                 61 
                 64 
                 764 
                 717 
                 0 
                 4.6 
                   
                 13.0 
                 753.6 
                 58.0 
               
               
                 10 
                 5.4 ppm Cp 2 Mg 
                 30 
                 0.1042 
                 50 
                 60 
                 480 
                 480 
                 0.017 
                 6.92 
                 407 
                 10.2 
                 574.9 
                 56.4 
               
               
                 11 
                 4 ppm Cp 2 Mg + 
                 30 
                 0.0998 
                 105 
                 65 
                 1052 
                 971 
                 0.033 
                 8.7 
                 263 
                 10.4 
                 554.5 
                 53.2 
               
               
                   
                 8 ppm TEA 
               
               
                 12 
                 6 ppm Cp 2 Mg 
                 0 
                 0.0982 
                 50 
                 60 
                 509 
                 509 
                 0 
                 0 
               
               
                 13 
                 1 ppm CpLi 
                 30 
                 0.0942 
                 61 
                 68 
                 648 
                 571 
                 0 
                 1.52 
                   
                 20.2 
                 675.4 
                 33.5 
               
               
                 14 
                 4 ppm CpLi 
                 30 
                 0.1014 
                 27 
                 63 
                 266 
                 254 
                 0 
                 2.84 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Non- 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                   
                 Transition 
                 H 2 , 
                 Catalyst 
                   
                 Run 
                   
                   
                 MI 
                 HLMI 
               
               
                   
                 Metal Cp 
                 psig on 
                 Charge 
                 Yield 
                 Time 
                 Prod. 
                 Activity 
                 (g/10 
                 (g/10 
                 HLMI/ 
                 M N   
                 M W   
               
               
                 Run # 
                 Treatment 
                 Rx 
                 (g) 
                 (g) 
                 (min.) 
                 (g/g) 
                 (g/g/h) 
                 min.) 
                 min.) 
                 MI 
                 (kg/mol) 
                 (kg/mol) 
                 PDI 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 15 
                 none 
                 0 
                 0.0436 
                 168 
                 94 
                 3853 
                 2459 
                 0 
                 0.79 
                   
                 20.2 
                 736.0 
                 36.4 
               
               
                 16 
                 1 ppm Cp 2 Mg 
                 30 
                 0.0566 
                 70 
                 60 
                 1237 
                 1237 
                 0.0254 
                 6.55 
                 258 
                 7.2 
                 838.5 
                 116.3 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                 Catalyst 
                   
                 Run 
                   
                   
                 MI 
                 HLMI 
                   
               
               
                   
                 CO 
                 Other 
                 Charge 
                 Yield 
                 Time 
                 Prod. 
                 Activity 
                 (g/10 
                 (g/10 
                 HLMI/ 
               
               
                 Run # 
                 Reduction 
                 Cocatalyst 
                 (g) 
                 (g) 
                 (min.) 
                 (g/g) 
                 (g/g/h) 
                 min.) 
                 min.) 
                 MI 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 17 
                 none 
                 none 
                 0.0873 
                 2 
                 53 
                 23 
                 26 
                   
                   
                   
               
               
                 18 
                 371C 
                 none 
                 0.0798 
                 61 
                 64 
                 764 
                 717 
                 0 
                 4.6 
               
               
                 19 
                 371C 
                 8 ppm TEA 
                 0.0998 
                 105 
                 65 
                 1052 
                 971 
                 0.033 
                 8.7 
                 263 
               
               
                   
               
            
           
         
       
     
     Example 5 
     A 963 grade Cr/silica-titania catalyst was calcined in air at 800° C. and reduced in the presence of CO at a temperature of about 370° C., as described in Example 1. The catalyst was then employed in three different runs to polymerize ethylene in the presence of H 2  at 95° C. and 30 psig, again as described in Example 1. A first run was performed using TMS-Cp-Li as the cocatalyst, a second run was performed using Cp 2 Mg as the cocatalyst, and a third run was performed using no cocatalyst.  FIG. 1  illustrates the molecular weight distributions of the polymer resins produced in these runs. The breadths of the molecular weight distributions of the polymer resins produced using the non-transition metal Cp cocatalysts were greater than that of the polymer resin produced in the absence of such cocatalyst. They were also shifted to the left, indicating an exaggerated effect of H 2  due to the influence of the Cp compound. 
     Example 6 
     A 969 MPI Cr/silica-titania catalyst was calcined in air at 650° C. as described in Example 1. It was then reduced in the presence of CO at a temperature of about 370° C. The catalyst was then employed in several runs to polymerize ethylene in the presence of H 2  at 95° C. and 30 psig, again as described in Example 1. All runs but one were performed using Cp 2 Mg cocatalyst, and one additional run was performed using 8 ppm of TEA cocatalyst along with the Cp 2 Mg cocatalyst.  FIG. 2  illustrates the molecular weight distributions of the polymer resins produced in these runs. Again, the breadths of the molecular weight distributions of the polymer resins produced using the non-transition metal Cp cocatalysts were greater than that of the polymer resin produced in the absence of such cocatalyst. They were also shifted to the left, indicating the effect of H 2 . 
     Example 7 
     A 969 MPI grade Cr/silica-titania catalyst was calcined in air at 600° C. and reduced in the presence of CO at a temperature of about 370° C. as described in Example 1 The catalyst was then employed in two different runs to polymerize ethylene in the presence of H 2  at 95° C. and 30 psig as described in example 1. A first run was performed using CpLi as the cocatalyst, and a second run was performed using no cocatalyst.  FIG. 3  illustrates the molecular weight distributions of the polymer resins produced in these runs. The breadth of the molecular weight distribution of the polymer resin produced using the CpLi cocatalyst was slightly greater than that of the polymer resin produced in the absence of such cocatalyst. Again, it was shifted to the left, indicating that the effect of H 2  was exaggerated by the cocatalyst. 
     Example 8 
     The following procedure was followed to produce polymer resins in a pilot plant reactor. Larger quantities of grade 964 Cr/silica-titania catalyst than in previous examples were activated by calcination in air at 650° C. for use in a 23-gallon loop reactor. Then 1.5 pounds of the catalyst were charged to a 6-inch diameter stainless steel furnace, which was heated by electric heating coils surrounding it. Dry air rose up through a sintered metal grid plate at the rate of 0.12 to 0.20 linear feet per second to fluidize the catalyst. The catalyst was heated up to the desired temperature, i.e., 650° C. in this example, over a period of about five hours. It was held at that temperature for another six hours. The catalyst was given a final treatment in carbon monoxide (CO) before being discharged from the furnace and stored under nitrogen. This was done in order to reduce the hexavalent chromium to its divalent state. This was accomplished by cooling down the catalyst from 650° C. to 370° C. while fluidizing the catalyst in dry air. The air was then replaced by nitrogen for about 10 minutes, and then about 10% CO by volume of the total gas was added. This CO treatment lasted 1 hour, after which the catalyst was flushed clean with nitrogen for about 1 hour and cooled down to room temperature and stored under dry nitrogen until being used. About 65% to 85% of the catalyst weight charged was recovered. The lost weight was water and very fine material. 
     While the original hexavalent catalysts were usually orange or yellow, this reduced divalent catalyst appeared blue and chemiluminesced brightly when exposed to oxygen. 
     The activated catalyst was employed in various runs with different amounts of Cp 2 Mg cocatalyst to polymerize ethylene that had been dried over activated alumina. Liquid isobutane that had been degassed by fractionation and dried over alumina was used as the diluent. 
     The reactor was a 15.2 cm diameter pipe loop filled with liquid and having a volume of 23 gallons (87 liters). The reactor pressure was about 600 psig. The reactor temperature was varied over the range of 88° C. to 94° C. The reactor was operated to have a residence time of 1.25 hours. The catalyst was added through a 0.35 cc circulating ball-check feeder. At steady state conditions the isobutane feed rate was about 46 L/hr and the ethylene feed rate was about 30 lbs/hr. The ethylene concentration in the diluent was 8 to 12 mole %. Hydrogen was added in concentrations ranging from 0.4 to 1.1 mole % based on the total moles of the diluent. The Cp 2 Mg cocatalyst was added in concentrations ranging from 0.25 to 1.1 parts per million by weight of the diluent. The Cp 2 Mg cocatalyst was added as a hydrocarbon stream into a pre-contacting vessel into which the catalyst was also added continuously. The isobutane flow through the pre-contacting vessel was adjusted so that the contact time between the catalyst and cocatalyst was about 20 minutes on average. After that amount of time, the contacted catalyst and cocatalyst are then fed into the reactor. To prevent static buildup in the reactor, a small amount (&lt;5 ppm of diluent) of STADIS 450 antistatic agent sold by Octel Corp. was usually added. The polymer was removed from the reactor at a rate of about 25 lbs/hour and recovered in a flash chamber. A Vulcan dryer was used to dry the polymer under nitrogen at about 60 to 80° C. 
     The polymers produced in these runs were blown into 1 mil (0.001 inch)-thick films on a high density processing line. The line used was a 1.5 inch diameter Davis-Standard extruder with L/D of 24:1, having a barrel temperature of from 210° C. to 230° C., a screw speed of 30 rpm, and an output of 17 to 18 pounds per hour, feeding a 2 inch diameter Sano die having a 35 mil gap. Films of typically 0.001-0.0005 inch (1 to 0.5 mil) thickness were blown on a 4:1 blow-p ratio and a production rate of 65 ft/min. Frostline heights were usually 14 inches. After cooling, the film passed through an A-frame with a resultant flattened width of 12.5 inches. 
     Various properties of the films produced using the Cp 2 Mg cocatalyst were tested and compared to the same properties of a 1 mil (0.001 inch) thick film produced from a commercial high density film resin sold by Chevron Phillips Chemical Company LLC and its licensees as TR-130 resin. The results of these tests are shown in Table 5 below. In particular, the density and melt index of each film resin was determined in the manner described previously. Each film was subjected to the dart impact test in accordance with ASTM D 1709-75. The dart impact test is a standard test method for determining the impact resistance of polyethylene films. It is the energy needed to rupture a one millimeter thick film upon impact of a free falling dart. This method establishes the weight of the dart dropped from a height of 26 inches, which causes 50% of the samples to break. All but one of the Cp 2 Mg produced films had dart impacts higher than or comparable to the TR-130 produced film. Another measure of film toughness is the Spencer Impact resistance (also known as the pendulum impact strength). The Spencer Impact resistance of each film was also determined in accordance with ASTM D 3420. These values of the Cp 2 Mg produced films were higher than or similar to that of the TR-130 produced film. 
     Each film was further subjected to a tear resistance test in accordance with ASTM D 1922. This test is a standard test method for determining the propagation tear resistance of a polymer film and is a modification of the Elmendorf tear test used for paper. The method determines the average energy in grams required to propagate a tear through 2.5 inches of film in the machine extrusion direction (MD) or transverse direction (TD) as indicated. The MD and TD tear resistances of the Cp 2 Mg produced films were substantially higher than those of the TR-130 produced film. 
     Table 5 also shows the motor load in amperes and the die pressure in psig generated while processing the film. They indicate the amount of resistance the molten polymer offered against the screw. One can see that the polymers produced with a metal Cp cocatalyst in general processed with greater ease than the control polymer, even though many of them had higher melt viscosity values (lower melt index values). The ease of processing can determine the rate at which film can be processed and thus the capacity of a film line. 
     Example 9 
     As shown in Table 6, Cr/silica-titania catalyst grades 963 and 964 from W.R. Grace were used to produce polymer resins in a pilot plant reactor as described above in Example 8. The catalysts were activated at 600° C. and 650° C., followed in many cases by reduction in CO at 370° C. The reactor temperature was 82 to 91° C., the ethylene concentration was 10 to 14% by moles of the diluent, and the hydrogen concentration was 0.3 to 0.4% by moles of the diluent. As indicated in Table 6, a Cp 2 Mg cocatalyst was used in most of the runs in concentrations ranging from 0.25 to 1 ppm based on the weight of the diluent. However, one run was performed with no cocatalyst and another run was performed with TEB as the cocatalyst. 
     The polymer resins produced in these runs were extruded into pipes. The pipe extrusion was performed by melting and conveying polyethylene pellets into an annular shape and solidifying that shape during a cooling process. All pipe products tested in this study were made using a 2 inch Davis-Standard Single Screw Extruder (smoothbore) and a 220° C. set temperature on the extruder and die. The samples were extruded at 150 lb/hr using a Barrier screw. The melt temperatures ranged from 232 to 238° C. A two inch die was used. To cool the pipe and “freeze in” the desired dimensions, cooling was accomplished by the use of several water tanks where the pipe was sprayed with water on the pipe exterior. Thus, the pipe was cooled from the outside surface to the inside surface. Per D2513 “Standard Specification for Thermoplastic Gas Pressure Pipe, Tubing, and Fittings”, the maximum wall thickness eccentricity is 12% and the maximum ovality is 5%. The resins produced using metal Cp cocatalysts fell within those values. 
     A TR-480 pipe resin sold by Chevron Phillips Chemical Company and made from a chromium-based catalyst was tested as the control. Also, an H516 polyethylene resin sold by Chevron Phillips Chemical Company was tested as a control. It was made using a Ziegler-Natta catalyst in a bimodal process. A third control resin was produced using the same catalyst but a different cocatalyst, i.e., triethylboron, was used. 
     Various properties of the pipes were tested, and the results of these tests are shown in Table 6. The HLMI, density, M W , M N , and PDI of each resin, and the Charpy critical temperature, Charpy energy, and PENT of each pipe were tested using the methods described previously. Normally PENT increases as the density of the resin decreases. However, one can see in the table that some of the polymers described herein, despite having higher densities, also have higher PENT values than the control resins that are even equivalent to the bimodal grade H516 resin, which is more difficult to make and to process into pipe. The Charpy critical temperatures were also much lower for the polymers described herein, which indicates high resistance to rapid crack propagation. The total energy adsorbed (at 25° C. Charpy Impact) was also very high for all of the polymers described herein relative to the control resins. 
     Standard PE-100 screening hoop stress tests were also run on these polymers. In this test, a two foot length of pipe was pressured to the indicated pressure and then immersed in a water bath set at the indicated temperature. The duration of time that each pipe lasted (the average of three) was then recorded. 
     Example 10 
     A grade 964 Cr/silica-titania catalyst from W.R. Grace was used to produce polymer resins in a pilot plant reactor as described above in Example 8. The catalyst was activated at 650° C. and reduced in the presence of CO at a temperature of about 370° C. The catalyst was employed with different amounts of the Cp 2 Mg cocatalyst in various runs to polymerize ethylene at 94 to 102° C. in the presence of 0.3 to 0.4 mol % H 2  based on the isobutane diluent. The ethylene content in the reactor was 10 mol % ethylene based on the isobutane diluent. The resulting polymers and their properties are shown in Table 7. 
     The polymers produced are useful for blow molding applications. Blow molding evaluations were conducted by blowing a one gallon (105.1 grams) bottle on a UNILOY 2016 single head blow molding machine (sold by Uniloy Milacron Inc.) using a 2.5 inch diameter die, 20 degree diverging die, 32% accumulator position, 8.5 second blow time, 0.10 second blow delay, 0.75 second pre-blow delay and a 45° F. mold temperature. A reciprocating screw speed of 45 rpm was used, providing parison extrusion at shear rates greater than 10,000/sec through the die. 
     The polymers&#39; ease of processing during blow molding was determined using known measurements. The first measure, listed as “Output” in Table 7, was calculated from the cycle time of the machine and the weight of the bottle and flashing. This measure describes the rate of bottle output in lbs of polymer per hour at which the resin in question was blow molded into bottles during normal operation, and it would describe the commercial rate of bottle production. The second measure was the cycle time, i.e., the time needed to make the bottle and was measured in seconds. Another measure of processing ease is the head pressure, which measures the maximum pressure at the die plate during the extrusion of the bottle. In other words, it is the pressure at the die plate as the bottles are being blown. 
     The previously discussed weight swell values for the polymers during blow molding were also determined as shown in Table 7. Another measurement of the swell is the die swell or the diameter swell, which is the ratio of the parison diameter to the die diameter. These numbers were referenced to a standard commercial blow molding polyethylene resin known as MARLEX® 5502BN resin, which was obtained from Chevron Phillips Chemical Company. 
     The onset of melt fracture of each resin was evaluated on the same UNILOY machine by opening the die gap and extruding the resin. The shear rate was increased steadily by increasing the screw rpm. The onset was the rpm at which the parison showed visible signs of melt fracture, such as a shark skin appearance or a distorted surface. This rate was then translated into the shear rate listed in Table 7. A high value indicated that the polymer could be processed at high rates without melt fracture. 
     Environmental stress crack resistance was also tested using ten 1-gallon bottles made as described above on a UNILOY 2016 machine. The bottles were filled with a 10% Orvus-K detergent solution, capped, and placed in a 140° F. hot room. Bottle failures were noted each day until all had broken, and a 50% mean failure time was calculated for each set. 
     The bottle toughness of the ten 1-gallon bottles was measured by the Izod impact test (Izod Impact, notched (kJ/m2): ASTM D256(a)-84). A higher number indicated greater toughness. Drop impact tests were also performed to measure bottle toughness by filling the 1-gallon bottles completely full of water and then sealing the bottles by means of a screw cap. These liquid filled bottles were then dropped from a vertical position onto a flat surface from progressively higher levels up to 12 feet high or until the bottle ruptured upon impact. A new bottle was used for each drop. 
     Based on the results shown in Table 7, various properties of the bottles produced using the Cp 2 Mg cocatalyst (the polymers disclosed herein) were found to be superior when compared to the same properties of bottles produced from the standard MARLEX® HHM 5502BN polyethylene resin sold by Chevron Phillips Chemical Company. This resin, which has been sold for 35 years, has become a standard of the industry because of its excellent processing characteristics. However, one can see in Table 7 from the cycle times, output rates, melt fracture shear rates, and head pressure that the polymers disclosed herein processed better. One can also see that the polymers disclosed herein had superior ESCR and impact properties. Their ESCR values were more than ten times greater than those values for the MARLEX® HHM 5502BN resin. The polymers disclosed herein further exhibited a lower swell. 
     A commercially available resin known as ALATHON® L54400S bimodal resin, which is sold by Equistar Chemicals, LP, was also compared. This bimodal resin is known for its high ESCR. The results in Table 7 below indicate that the polymers produced using the metal Cp cocatalyst also exhibited high ESCR values. In fact, both the ASTM ESCR values and the bottle ESCR of these polymers were quite surprising. The Izod impact and bottle drop properties of the polymers produced using the metal Cp cocatalyst were also very good compared to the control resins. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 Resin 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 MgCp 2  Added (ppm) 
                 0.25 
                 0.25 
                 0.5 
                 1.1 
                 1.1 
                 Commercial 
               
               
                   
                   
                   
                   
                   
                   
                 TR130 
               
               
                 Density (g/cc) 
                 0.937 
                 0.936 
                 0.937 
                 0.938 
                 0.934 
                 0.937 
               
               
                 MI (g/10 min) 
                 0.31 
                 0.33 
                 0.28 
                 0.29 
                 0.16 
                 0.28 
               
               
                 M N  (kg/mol) 
                 13.97 
                 10.05 
                 15.67 
                 7.1 
                 10.14 
                 13.8 
               
               
                 M W  (kg/mol) 
                 197.49 
                 226.16 
                 114.23 
                 168.41 
                 283.86 
                 227.00 
               
               
                 M W /M N   
                 14.14 
                 22.50 
                 7.29 
                 23.72 
                 28.0 
                 16.5 
               
               
                 Eta(0) (Pa · s) 
                 3.08E+05 
                 5.13E+05 
                 8.65E+05 
                 1.36E+06 
                 2.95E+06 
                 4.56E+05 
               
               
                 Tau (s) 
                 6.75E−01 
                 1.34E+00 
                 2.40E+00 
                 8.07E+00 
                 1.45E+01 
                 1.34 
               
               
                 CY-“a” parameter 
                 1.75E−01 
                 0.1606 
                 1.55E−01 
                 1.57E−01 
                 0.1473 
                 0.1729 
               
               
                 Dart Impact (g) 
                 83 
                 80 
                 90 
                 50 
                 113 
                 81 
               
               
                 Spencer Impact (J) 
                 0.45 
                 0.63 
                 0.48 
                 0.51 
                 0.91 
                 0.45 
               
               
                 MD Tear Resistance (g) 
                 63 
                 100 
                 59 
                 89 
                 70 
                 52 
               
               
                 TD Tear Resistance (g) 
                 704 
                 712 
                 843 
                 781 
                 918 
                 672 
               
               
                 Pressure (psig) 
                 1600 
                 1150 
                 1150 
                 1100 
                 1250 
                 1200 
               
               
                 Motor Load (amp) 
                 5.7 
                 5.1 
                 5.1 
                 4.1 
                 5.6 
                 5.9 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                 Sample 
                 7 
                 8 
                 9 
                 10 
                 11 
                 12 
                 13 
                 14 
               
               
                   
               
             
            
               
                 Catalyst 
                 964, 650° C. 
                 963, 650° C. 
                 964, 650° C. 
                 964, 650° C. 
                 964, 650° C. 
                 963, 600° C. 
                 963, 600° C. 
                 H516 
               
               
                   
                 CO Reduced 
                 CO Reduced 
                 CO Reduced 
                 CO Reduced 
                 CO Reduced 
               
               
                 Cp 2 Mg added 
                 0.25 ppm 
                 1 ppm 
                 0.5 ppm 
                 1 ppm 
                 1 ppm 
                 none 
                 5 ppm TEB 
                 ZN Bimodal 
               
               
                 HLMI 
                 6.7 
                 5.4 
                 6.9 
                 10 
                 11 
                 10 
                 8.5 
                 8 
               
               
                 (g/10 min.) 
               
               
                 Density (g/cc) 
                 0.9503 
                 0.9502 
                 0.9497 
                 0.9490 
                 0.9539 
                 0.945 
                 0.9503 
                 0.95 
               
               
                 M W   
                 377.05 
                 511.37 
                 417.88 
                 466.25 
                 472.18 
                 243.3 
                 319.6 
                 256.5 
               
               
                 (kg/mol) 
               
               
                 M N   
                 14.06 
                 10.14 
                 11.42 
                 8.57 
                 7.96 
                 22.5 
                 8.72 
                 20.1 
               
               
                 (kg/mol) 
               
               
                 PDI 
                 27 
                 50 
                 37 
                 54 
                 59 
                 16.8 
                 36.7 
                 12.8 
               
               
                 Eta(0) (Pa · s) 
                 4.08 × 10{circumflex over ( )}6 
                 2.62 × 10{circumflex over ( )}7 
                 5.78 × 10{circumflex over ( )}6 
                 1.50 × 10{circumflex over ( )}7 
                 2.49 × 10{circumflex over ( )}7 
                 1.54 × 10{circumflex over ( )}6 
                 4.6 × 10{circumflex over ( )}6 
                 2.74 × 10{circumflex over ( )}5 
               
               
                 Tau (s) 
                 26.8 
                 48 
                 53 
                 269 
                 537 
                 5.2 
                 55 
                 1.9 
               
               
                 CY-“a” parameter 
                 0.1840 
                 0.1965 
                 0.1918 
                 0.1889 
                 0.1815 
                 0.1629 
                 0.205 
                 0.3093 
               
               
                 Charpy 
               
               
                 Critical Temp.° C. 
                 −24.2 
                 −24.3 
                 −25.3 
                 −3.0 
                 −2.4 
                 −3.4 
                 −4.4 
                 −22.0 
               
               
                 Total Energy at 
                 128 
                 144 
                 144 
                 98 
                 86 
                 36 
                 69 
                 129 
               
               
                 23° C. (J/m) 
               
               
                 PENT (h) 
                 27 (D) 
                 &gt;750 
                 84 (D) 
                 &gt;750 
                 &gt;750 
                 13 
                 456 
                 &gt;750 
               
               
                 Hoop Stress 
               
               
                 20° C., 12.4 (Mpa) 
                   
                 30, 44, 67 
                 35, 66, 92 
                 63, 116, 157 
                   
                 1000 
                 36 
                 65 
               
               
                   
                   
                 (D) 
                 (D) 
                 (D) 
               
               
                 80° C., 5.5 (Mpa) 
                   
                 25, 137, 163 
                 130, 183, 197 
                 2, 3, 8 
                   
                 200 
                 22 
                 932 
               
               
                   
                   
                 (D) 
                 (B) 
                 (B) 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 7 
               
               
                   
               
             
            
               
                   
                   
                 MARLEX 
                   
                   
               
               
                   
                   
                 HHM 
                 ALATHON 
               
               
                 Resin ID 
                   
                 5502BN 
                 L54400S 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Sample 
                   
                 15 
                 16 
                 17 
                 18 
                 19 
               
               
                 Cp 2 Mg 
                 (ppm) 
                   
                   
                 1.1 
                 0.5 
                 0.5 
               
               
                 MI 
                 (g/10 min) 
                 0.39 
                 0.34 
                 0.15 
                 0.19 
                 0.21 
               
               
                 HLMI 
                 (g/10 min) 
                 34.98 
                 33.08 
                 22.56 
                 18.81 
                 21.10 
               
            
           
           
               
               
               
               
               
               
            
               
                 HLMI/MI 
                 89.7 
                 97.3 
                 150.4 
                 99.0 
                 100.5 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Density 
                 (g/cc) 
                 0.9537 
                 0.9545 
                 0.9530 
                 0.9499 
                 0.9536 
               
               
                 M W   
                 (kg/mol) 
                 168.52 
                 191.55 
                 413.7 
                 329.0 
                 340.6 
               
               
                 M Z   
                 (kg/mol) 
                 2143 
                 1869 
                 8788 
                 6748 
                 6617 
               
            
           
           
               
               
               
               
               
               
            
               
                 PDI 
                 8.042 
                 10.475 
                 37.148 
                 24.745 
                 25.730 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 E o   
                 (Pa · s) 
                 621600 
                 1486000 
                 14280000 
                 1566000 
                 1365000 
               
               
                 T ξ   
                 (s) 
                 1.348 
                 2.323 
                 151.1 
                 5.948 
                 5.338 
               
               
                 CY-“a” parameter 
                 0.1432 
                 0.1254 
                 0.1348 
                 0.1525 
                 0.1539 
                 0.1667 
               
               
                 Notched Izod 
                 (ft-lb/in) 
                 2.295 P 
                 1.572 P 
                 1.609 P 
                 2.133 P 
                 2.237 P 
               
               
                 Tensile Impact 
                 (ft-lb/in 2 ) 
                 53.4 
                 71.9 
                 62.0 
                 75.3 
                 69.0 
               
               
                 ESCR A, F50 
                 (hr) 
                 34 
                 142 
                 &gt;1000 
                 &gt;1000 
                 &gt;1000 
               
               
                 ESCR B, F50 
                 (hr) 
                 31 
                 124 
                 &gt;1000 
                 &gt;1000 
                 &gt;1000 
               
               
                 Bottle ESCR, 
                 (hr) 
                 213 
                 165 
                 &gt;1175 
                 &gt;1175 
                 &gt;1175 
               
               
                 10% Joy F50 
               
               
                 Bottle Drop Impact 
                 (ft) 
                 &gt;12 
                 10.5 
                 10.7 
                 11.5 
                 &gt;12 
               
               
                 Part Weight 
                 (g) 
                 168 
                 161 
                 179 
                 157 
                 153 
               
               
                 Cycle Time 
                 (s) 
                 11.7 
                 11.6 
                 15.5 
                 11.4 
                 11.8 
               
               
                 Die Gap 
                 (in) 
                 0.0159 
                 0.0200 
                 0.0120 
                 0.0154 
                 0.0151 
               
               
                 Weight Swell 
                 (%) 
                 450 
                 320 
                 676 
                 433 
                 429 
               
               
                 Diameter Swell 
                 (%) 
                 33.6 
                 32.4 
                 39.0 
                 36.0 
                 41.6 
               
               
                 Melt Temperature 
                 (° F.) 
                 381 
                 381 
                 381 
                 381 
                 381 
               
               
                 Head Pressure 
                 (psi) 
                 5160 
                 4650 
                 5360 
                 5730 
                 5700 
               
               
                 Output 
                 (lb/hr) 
                 113.9 
                 110.1 
                 91.6 
                 109.2 
                 102.8 
               
               
                 Shear Rate 
                 (l/s) 
                 26274 
                 15770 
                 29298 
                 23890 
                 25863 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Resin ID 
               
               
                   
                   
               
               
                   
                 Sample 
                   
                 20 
                 21 
                 22 
                 23 
               
               
                   
                 Cp 2 Mg 
                 (ppm) 
                 0.25 
                 0.25 
                 0.25 
                 0.25 
               
               
                   
                 MI 
                 (g/10 min) 
                 0.20 
                 0.31 
                 0.31 
                 0.31 
               
               
                   
                 HLMI 
                 (g/10 min) 
                 16.63 
                 21.44 
                 21.00 
                 19.54 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 HLMI/MI 
                 83.2 
                 69.2 
                 67.7 
                 63.0 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Density 
                 (g/cc) 
                 0.9535 
                 0.9548 
                 0.9540 
                 0.9541 
               
               
                   
                 M W   
                 (kg/mol) 
                 337.7 
                 253.0 
                 230.4 
                 258.2 
               
               
                   
                 M Z   
                 (kg/mol) 
                 7112 
                 4233 
                 2937 
                 3783 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 PDI 
                 21.119 
                 14.939 
                 13.993 
                 15.341 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 E o   
                 (Pa · s) 
                 717700 
                 289400 
                 325600 
                 419000 
               
               
                   
                 T ξ   
                 (s) 
                 2.119 
                 0.633 
                 0.6893 
                 0.9632 
               
               
                   
                 CY-“a” parameter 
                 0.1432 
                 0.1754 
                 0.1714 
                 0.1689 
                 0.1432 
               
               
                   
                 Notched Izod 
                 (ft-lb/in) 
                 2.848 P 
                 2.775 P 
                 2.719 P 
                 2.524 P 
               
               
                   
                 Tensile Impact 
                 (ft-lb/in 2 ) 
                 97.0 
                 78.6 
                 75.9 
                 72.4 
               
               
                   
                 ESCR A, F50 
                 (hr) 
                 506 
                 183 
                 269 
                 259 
               
               
                   
                 ESCR B, F50 
                 (hr) 
                 722 
                 154 
                 244 
                 310 
               
               
                   
                 Bottle ESCR, 
                 (hr) 
                 832 
                 647 
                 991 
                 439 
               
               
                   
                 10% Joy F50 
               
               
                   
                 Bottle Drop Impact 
                 (ft) 
                 &gt;12 
                 &gt;12 
                 &gt;12 
                 &gt;12 
               
               
                   
                 Part Weight 
                 (g) 
                 160 
                 164 
                 157 
                 158 
               
               
                   
                 Cycle Time 
                 (s) 
                 11.4 
                 11.4 
                 11.4 
                 11.5 
               
               
                   
                 Die Gap 
                 (in) 
                 0.0174 
                 0.0166 
                 0.0161 
                 0.0166 
               
               
                   
                 Weight Swell 
                 (%) 
                 378 
                 414 
                 408 
                 396 
               
               
                   
                 Diameter Swell 
                 (%) 
                 47.7 
                 48.5 
                 47.7 
                 46.7 
               
               
                   
                 Melt Temperature 
                 (° F.) 
                 381 
                 382 
                 381 
                 381 
               
               
                   
                 Head Pressure 
                 (psi) 
                 5570 
                 5370 
                 5440 
                 5370 
               
               
                   
                 Output 
                 (lb/hr) 
                 111.3 
                 114.1 
                 109.2 
                 108.9 
               
               
                   
                 Shear Rate 
                 (l/s) 
                 20185 
                 22308 
                 23582 
                 22731 
               
               
                   
                   
               
            
           
         
       
     
     While preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Use of the term “optionally” with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. 
     Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the preferred embodiments of the present invention. The discussion of a reference herein is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent that they provide exemplary, procedural, or other details supplementary to those set forth herein.