Background Information Homogeneous polyethylenes and EPRs are elastomeric copolymers and terpolymers used in such applications as hose and tubing, wire and cable, gaskets, and single ply roofing. They are usually formulated with fillers, oils, processing aids, and stabilizing agents.

The EPRs are presently manufactured commercially in solution and slurry processes with soluble vanadium catalysts. These processes are very expensive to run, requiring solvent removal and steam stripping steps. Improvement in these processes would be desirable and, particularly, the development of a gas phase process to produce these same products would be more economically attractive because little post-reaction cost will be incurred, and particle morphology would, expectedly, be improved.

One of the catalyst systems selected to produce these polymers in the gas phase is described in United States patent 4,508,. 842. Typically, the catalyst system is comprised of a catalyst precursor, which is the reaction product of vanadium trichloride and an electron donor, the precursor being reacted with an aluminum containing modifier, and impregnated into a silica support; a promoter such as chloroform; and a triisobutylaluminum cocatalyst. This catalyst system produces a compositionally heterogeneous resin. It does achieve good particle morphology, but the non-uniform composition and broad molecular weight distribution results in polyethylene products with poor transparency and poor heat-sealing properties. In addition, EPRs made with this catalyst exhibit poor cure and contain much high temperature crystallinity. This is believed to be the result of poorly distributed propylene, and, in the case of the EPDMs, poorly distributed diene.

In United States patent application serial no. 08/083,664 filed on June 28,1993 by Bai et al, a process is provided for the production of homogeneous polyethylenes and EPRs, which are relatively free of these deficiencies. This is accomplished by a process comprising contacting a mixture comprising ethylene, one or more alpha-olefins, and, optionally, a diene, under polymerization conditions, with a catalyst system comprising: (A) a catalyst precursor comprising: (i) a vanadium compound, which is the reaction product of (a) VX3 wherein each X is independently chlorine, bromine, or iodine; and (b) an electron donor, which is a liquid, organic Lewis base in which VX3 is soluble; (ii) a modifier having the formula BX3 or AlR (3-a) Xa wherein each R is independently alkyl having 1 to 14 carbon atoms; each X is as defined above; and a is 0,1, or 2; and (iii) a support for said vanadium compound and modifier, said catalyst precursor being in an independent or prepolymerized state, (B) a cocatalyst consisting of a compound having the formula AlR (3-a) Xa wherein R and X are as defined above and a is 1 or 2; and (C) a promoter consisting of a saturated or an unsaturated aliphatic halocarbon having at least 3 carbon atoms and at least 6 halogen atoms, or a haloalkyl substituted aromatic hydrocarbon wherein the haloalkyl substituent has at least 3 halogen atoms.

While this process is certainly advantageous, it is found that, when the process is carried out at low temperatures, e. g., temperatures in the 35° to 65° C range, whether the catalyst precursor is in the independent or the prepolymerized state, the resin produced is a mixture of both the desirable compositionally homogeneous resin and, in this case, the undesirable compositionally heterogeneous resin, and, further, catalyst activity is relatively low. The alternative was to operate at higher temperatures, about 85° C or higher, to obtain essentially all of the homogeneous type.

The demands of industry, however, are in the direction of operating at relatively lower temperatures while producing compositionally homogeneous polymer to the exclusion of the heterogeneous at relatively high catalyst activity levels.

Disclosure of the Invention An object of this invention, therefore, is to provide a low temperature process for the production of homogeneous polyethylenes and EPRs, which are essentially free of heterogeneous resin, and, in which process, catalyst activity is relatively high. Other objects and advantages will become apparent hereinafter.

According to the present invention, the above object is met by a process comprising contacting a mixture comprising ethylene, one or more alpha-olefins, and, optionally, a diene, under polymerization conditions, in one reactor or two reactors connected in series, with a catalyst system comprising: (A) a vanadium based catalyst precursor; (B) a cocatalyst consisting of a compound having the formula AlR (3 a) Xa wherein R is independently alkyl having 1 to 14 carbon atoms; each X is independently chlorine, bromine, or iodine; and a is 1 or 2; and (C) a promoter consisting of a saturated or an unsaturated aliphatic halocarbon having at least 3 carbon atoms and at least 6 halogen atoms, or a haloalkyl substituted aromatic hydrocarbon wherein the haloalkyl substituent has at least 3 halogen atoms with the proviso that (i) if one reactor is used, the precursor is prepolymerized at a temperature of at least about 80° C and the polymerization conditions include a polymerization temperature no higher than about 65° C; and (ii) if two reactors are used, the polymerization temperature in the first reactor in the series is at least about 80° C and the polymerization temperature in the second reactor in the series is no higher than about 80° C.

Description of the Preferred Embodiment (s) The vanadium compound can be any of the group of vanadium compounds well known to be useful as or in catalyst precursors in olefin polymerization processes. Examples are vanadium acetylacetonates, vanadium trihalides, vanadium tetrahalides, and vanadium oxyhalides. The halides are generally chlorides, bromides, or iodides, or mixtures thereof. More specific examples of these compounds are VCl3, VCl4, vanadium oxychloride, vanadium (acetylacetonate) 3, vanadyl triacetylacetonate, VO (OC2H5) C12, VOC1 (OC2H5) 2, VO (OC2H5) 3, and VO (OC4Hg) 3.

A typical vanadium catalyst precursor in the unprepolymerized state and a process for preparing same are described in United States patent 4,508,842. This precursor is described above. It includes an electron donor, a modifier, and a support, all of which are optional in the vanadium based catalyst precursor used in the process of this invention. If used, the electron donor is a liquid, organic Lewis base in which the vanadium trihalide is soluble. The electron donor is, generally, liquid at temperatures in the range of about 0°C to about 200°. The electron donor can be an alkyl ester of an aliphatic or aromatic carboxylic acid, an aliphatic ketone, an aliphatic amine, an aliphatic alcohol, an alkyl or cycloalkyl ether, or mixtures thereof, each electron donor having 2 to 20 carbon atoms. Among these electron donors, the preferred are alkyl and cycloalkyl ethers having 2 to 20 carbon atoms; dialkyl, diaryl, and alkylaryl ketones having 3 to 20 carbon atoms; and alkyl, alkoxy, and alkylalkoxy esters of alkyl and aryl carboxylic acids having 2 to 20 carbon atoms. The most preferred electron donor is tetrahydrofuran.

Other examples of suitable electron donors are methyl formate, ethyl acetate, butyl acetate, ethyl ether, dioxane, di-n-propyl ether, dibutyl ether, ethyl formate, methyl acetate, ethyl anisate, ethylene carbonate, tetrahydropyran, and ethyl propionate.

While an excess of electron donor is used initially to provide the reaction product of vanadium compound and electron donor, the reaction product finally contains about 1 to about 20 moles of electron donor per mole of vanadium compound and preferably about 1 to about 10 moles of electron donor per mole of vanadium compound.

The modifier has the formula BX3 or AlR (3 a) Xa wherein each R is independently alkyl having 1 to 14 carbon atoms; each X is independently chlorine, bromine, or iodine; and a is 0,1, or 2. One or more modifiers can be used. Preferred modifiers include alkylaluminum mono-and dichlorides wherein each alkyl radical has 1 to 6 carbon atoms; boron trichloride; and the trialkylaluminums.

About 0.1 to about 10 moles, and preferably about 0.2 to about 2.5 moles, of modifier can be used per mole of electron donor. The molar ratio of modifier to vanadium can be in the range of about 1: 1 to about 10: 1 and is preferably in the range of about 2: 1 to about 5: 1.

The promoter can be a saturated aliphatic halocarbon having the formula C3 (X) a (F) b (H) c wherein each X is independently chlorine, bromine, or iodine; a is an integer from 6 to 8; b and c are integers from 0 to 2; and a+b+c equal 8. Examples of these halocarbon promoters are hexachloropropane, heptachloropropane, and octachloropropane. These saturated halocarbon promoters are mentioned in United States patent 4,892,853. The promoter can also be an unsaturated aliphatic halocarbon such as perchloropropene or any unsaturated halocarbon having a CX3 group attached to a C= C group wherein each X is independently chlorine, bromine, or iodine.

Finally, the promoter can be a haloalkyl substituted aromatic hydrocarbon wherein the haloalkyl substituent has at least 3 halogen atoms such as trichlorotoluene and trichloroxylene. Again, the halogen can be chlorine, bromine, or iodine. The number of carbon atoms in the halocarbon or the haloalkyl substituent can be 1 to 14, and the number of benzene rings in the halocarbon or the aromatic hydrocarbon can be 1 to 3, but is preferably one. About 0.01 to about 10 moles, and preferably about 0.2 to about 1 mole, of promoter can be used per mole of cocatalyst.

The cocatalyst can be a compound having the formula AlR (3-a) Xa wherein each R is independently alkyl having 1 to 14 carbon atoms; each X is independently chlorine, bromine, or iodine; and a is lor 2. The cocatalyst can be present in the catalyst system in an amount of about 10 to about 500 moles of cocatalyst per gram atom of vanadium, and is preferably introduced in an amount of about 30 to about 150 moles of cocatalyst per gram atom of vanadium.

Examples of halogen containing modifiers and cocatalysts are di-n-butylaluminum chloride; diethylaluminum chloride; diisobutylaluminum chloride; ethylaluminum sesquichloride; methylaluminum sesquichloride; isobutylaluminum sesquichloride; dimethylaluminum chloride; di-n-propylaluminum chloride; methylaluminum dichloride; and isobutylaluminum dichloride.

Examples of trialkylaluminum modifiers are triisobutylaluminum, trihexylaluminum, di-isobutylhexylaluminum, isobutyldihexylaluminum, trimethylaluminum, triethylaluminum, tripropylaluminum, triisopropylaluminum, tri-n-butylaluminum, trioctylaluminum, tridecylaluminum, and tridodecylaluminum.

The support can be inorganic or organic such as silica, alumina, or polymeric; silica is preferred. Examples of polymeric supports are porous crosslinked polystyrene and polypropylene. A typical silica or alumina support is a solid, particulate, porous material essentially inert to the polymerization. It is used as a dry powder having an average particle size of about 10 to about 250 microns and preferably about 30 to about 100 microns; a surface area of at least 200 square meters per gram and preferably at least about 250 square meters per gram; and a pore size of at least about 100 angstroms and preferably at least about 200 angstroms. Generally, the amount of support used is that which will provide about 0.1 to about 1.0 millimole of vanadium per gram of support and preferably about 0.4 to about 0.9 millimole of vanadium per gram of support. Impregnation of the above mentioned catalyst precursor into a silica support is accomplished by mixing the precursor and silica gel in the electron donor solvent or other solvent followed by solvent removal under reduced pressure.

The modifier is usually dissolved in an organic solvent such as isopentane and impregnated into the support following impregnation of the precursor, after which the supported catalyst precursor is dried. The promoter can also be impregnated into the support in similar fashion, if desired. The cocatalyst and promoter are preferably added separately neat or as solutions in an inert solvent, such as isopentane, to the polymerization reactor at the same time as the flow of ethylene is initiated.

In one embodiment of this invention, the catalyst precursor described above must be used in prepolymer form. A technique for prepolymerization can be found in United States patent In the present process, however, the temperature under which the prepolymerization is carried out is at least about 80° C; it can be in the range of about 80° to about 100°, and preferably the temperature is in the range of about 85° C to about 95° C. Typically, the prepolymerization is carried out in the liquid phase in a similar manner to a diluent slurry polymerization. The catalyst system used in the prepolymerization is the same one that will be used in the fluidized bed polymerization. The difference lies in the monomers used and weight ratio of monomer (s) to catalyst precursor, which is at least about 10: 1, and is usually about 50: 1 to about 300: 1. It should be pointed out that the numbers vary with the particular catalyst system selected. Examples of suitable prepolymers are homoprepolymers of ethylene, ethylene/propylene coprepolymers, ethylene/1-hexene coprepolymers, ethylene/propylene/1-hexene terprepolymers, and ethylene/propylene/diene terprepolymers. The prepolymer does not have to be the same as the resin product of the main polymerization.

The amount of prepolymer formed, in terms of grams of prepolymer per gram of catalyst precursor, generally depends on the composition of the prepolymer, the composition of the polymer being produced, and the productivity of the catalyst employed. The prepolymer loading is chosen so as to minimize prepolymer residue in the product resin.

A typical prepolymerization can be carried out in a slurry prepolymerizer. The equipment includes a monomer feed system, a reaction vessel, and an inert screener. The reactor is a jacketed pressure vessel with a helical ribbon agitator to give good solids mixing, and with a bottom cone to facilitate solids discharge. Ethylene is fed from cylinders, with the pressure regulated, through 4A or 13X molecular sieves to remove impurities, and then through a flow meter to measure flow rate. Other olefins, if required, are fed from cylinders via a dip tube with nitrogen pressure supplied to the cylinder headspace. They also pass through 4A or 13X molecular sieves and through a flow meter. The monomers can be fed to either the reactor headspace or subsurface, with subsurface preferred as it increases the reaction rate by eliminating one mass transfer step. Temperature is controlled with a closed loop tempered water system. Pressure is controlled with a vent/make-up system.

The finished prepolymerized catalyst is screened to remove skins, agglomerates, and other types of oversize particles that could cause feeding difficulties into the gas phase reactor. The screening is done with a vibratory screener with a 20 mesh screen. The screener is kept under a nitrogen atmosphere to maintain the prepolymerized catalyst activity. Oversize material is collected for disposition. The desired undersize fraction is discharged into a cylinder for storage and shipping.

As noted, the typical prepolymerization is a slurry polymerization of ethylene and, optionally, a comonomer. Isopentane, hexane, and heptane can be used as the solvent, with isopentane preferred for its higher volatility. In this invention, the prepolymerization temperatures are as stated above, i. e., at least about 80° C. Monomer partial pressures are about 15 to about 40 psi, and levels of cocatalyst and catalyst promoter are about 1 to about 5 moles per mole of vanadium. The prepolymer loading ranges from about 10 to about 500 grams per gram of supported catalyst precursor, preferably from about 50 to about 300 grams per gram. The comonomer content of the prepolymer ranges from 0 to 15 weight percent. Hydrogen, or other chain transfer agents, can be added at the start of polymerization or throughout the polymerization to control molecular weight. Additional olefins or dienes may also be added.

When the polymerization is complete, the agitator is stopped and the solids are allowed to settle so that the excess solvent can be removed by decanting. The remaining solvent is removed by drying, using low temperatures to avoid catalyst decay. The dried prepolymer catalyst is discharged to a storage cylinder through an inert screener, to remove oversize (+20 mesh) material.

The polymerization can be conducted in a solution or in a slurry as described above for the prepolymerization, or in the gas phase, preferably in a fluidized bed. As noted above, one reactor or two reactors connected in series can be used. The fluidized bed can be a stirred fluidized bed reactor or a fluidized bed reactor, which is not stirred. In terms of the fluidized bed, a superficial velocity of about 1 to about 4.5 feet per second and preferably about 1.5 to about 3. 5 feet per second can be used. The total reactor pressure can be in the range of about 150 to about 600 psia and is preferably in the range of about 250 to about 500 psia. The ethylene partial pressure can be in the range of about 25 psi to about 350 psi and is preferably in the range of about 80 psi to about 250 psi. In the prepolymer embodiment, the temperature of the polymerization using the prepolymerized catalyst precursor is no greater than about 65° C, but can be in the range of about 0° C to about 65° C. The preferred temperature is in the range of about 35° C to about 60° C. Temperatures used in the two reactor (stage) embodiment are discussed below. The gaseous feed streams of ethylene, alpha-olefin, and hydrogen (or another chain transfer agent) are preferably fed to the reactor recycle line while liquid ethylidene norbornene or another diene, if used, and the cocatalyst solution are preferably fed directly to the fluidized bed reactor to enhance mixing and dispersion. The prepolymer containing the catalyst precursor is transferred into the fluidized bed from the catalyst feeder. The composition of the polymer product can be varied by changing the alpha-olefin/ethylene molar ratio in the gas phase and the diene (if used) concentration in the fluidized bed. The product is intermittently discharged from the reactor as the bed level builds up with polymerization. The production rate is controlled by adjusting the catalyst feed rate.

Two types of polymers are considered here, polyethylenes and EPRs. The polyethylenes are, generally, homopolymers of ethylene and copolymers of ethylene and one or more alpha-olefins having 3 to 12 carbon atoms, and preferably 3 to 8 carbon atoms.

Examples of the alpha-olefins are propylene, 1-butene, 1-hexene, 4- methyl-1-pentene, and 1-octene. A diene, such as those mentioned below, may be introduced into the polyethylene, if desired. As noted, these are homogeneous polyethylenes. The polyethylenes are characterized by narrow molecular weight distributions, e. g., Mw/Mn ratios of about 2 or 3, and narrow comonomer distributions, i. e., preferably as close to uniform as possible. The EPRs are either copolymers of ethylene and propylene or terpolymers of ethylene, propylene, and a diene such as ethylidene norbornene, 1,4-pentadiene, 1, 3-hexadiene, and 1,4-octadiene.

The molar ratio of monomers in the reactor will be different for different catalyst systems, as is well-known to those skilled in the art. The alpha-olefin/ethylene molar ratio is adjusted to control the level of alpha-olefin incorporated into the polymer. The propylene/ethylene ratio can be in the range of about 0.05: 1 to about 1 and is preferably in the range of about 0.25: 1 to about 1.5: 1.

The 1-hexene/ethylene molar ratio can be in the range of about 1 to about 0.050: 1 and is preferably in the range of about 0.008: 1 to about 0.012: 1. The hydrogen/ethylene molar ratio is adjusted to control average molecular weights of the terpolymer. The level of diene in the bed, if used, is in the range of about 1 to about 15 weight percent based on the weight of the bed, and is preferably in the range of about 2 to about 10 weight percent. Examples of useful dienes, in addition to ethylidene norbornene (ENB), are 1,4-hexadiene and dicyclopentadiene dimer.

Steps can be taken to reduce agglomeration. For example, fluidization aids can be provided as described in United States patent 4, 994, 534. Also, the product discharge line between the reactor and the product pot is often plugged up with chunks between intervals of product drops. A continuous purge flow of nitrogen in the line prevents the plugging problem. Also, coating the reactor surface with a low surface energy material is shown to be beneficial to slow-down the rate of fouling build up. In addition, control of the electrostatic level in the bed prevents static induced particle agglomeration. Static can be adjusted to a satisfactory level by controlled use of reaction rate, quick change of gas composition, selective use of static-neutralizing chemicals, and surface passivation with aluminum alkyls.

Static can also be controlled by using small amounts of an inert conductive particulate material such as carbon black. The amount of inert particulate material is that which is sufficient to control static, i. e., about 0.5 to about 1.5 percent by weight based on the weight of the fluidized bed. Carbon black is the preferred antistatic material. The mean particle size of the inert conductive particulate material is in the range of about 0.01 to about 150 microns, preferably to about 10 microns. The mean particle size can refer to the particle per se or to an aggregate as in the case of carbon black. The carbon black materials employed can have a primary particle size of about 10 to about 100 nanometers and an average size of aggregate (primary structure) of about 0.1 to about 10 microns. The surface area of the carbon black can be about 30 to about 1500 square meters per gram and can display a dibutylphthalate (DBP) absorption of about 80 to about 350 cubic centimeters per 100 grams. It is preferred to treat the particulate material prior to its introduction into the reactor to remove traces of moisture and oxygen. This can be accomplished by purging the material with nitrogen gas, and heating using conventional procedures. Other antistatic agents are also found to be effective in keeping the static level under control as mentioned, for example, in United States patent 5,194,526.

The residence time of the mixture of comonomers, resin, catalyst, and liquid in the fluidized bed can be up about 8 hours and is preferably no more than about 4 hours. The final product can contain the following amounts of reacted comonomers: about 35 to about 80 percent by weight ethylene; about 18 to about 50 percent by weight alpha-olefin; and about 0 to about 15 percent by weight diene. The EPR crystallinity, also in weight percent based on the total weight of the resin product, can be in the range of zero (essentially amorphous) to about 15 percent by weight (nearly amorphous). The Mooney viscosity can be in the range of about 10 to about 150 and is preferably about 30 to about 100. The Mooney viscosity is measured by introducing the polymer into a vessel with a large rotor, preheating for one minute at 100°C, and then stirring for four minutes at the same temperature. The viscosity is measured at 100°C in the usual manner.

The fluidized bed reactor can be the one described in United States patent 4,482,687 or another conventional reactor for the gas phase production of, for example, polyethylene. The bed is usually made up of the same granular resin that is to be produced in the reactor. Thus, during the course of the polymerization, the bed comprises formed polymer particles, growing polymer particles, and catalyst particles fluidized by polymerizable and modifying gaseous components introduced at a flow rate or velocity sufficient to cause the particles to separate and act as a fluid. The fluidizing gas is made up of the initial feed, make-up feed, and cycle (recycle) gas, i. e., monomer and, if desired, modifiers and/or an inert carrier gas. A typical cycle gas is comprised of ethylene, nitrogen, hydrogen, and propylene, either alone or in combination. The process can be carried out in a batch or continuous mode, the latter being preferred. The essential parts of the first reactor are the vessel, the bed, the gas distribution plate, inlet and outlet piping, a compressor, a cycle gas cooler, and a product discharge system. In the vessel, above the bed, there is a velocity reduction zone, and in the bed, a reaction zone. Both are above the gas distribution plate.

Variations in the reactor can be introduced if desired. One involves the relocation of the cycle gas compressor from upstream to downstream of the cooler and another involves the addition of a vent line from the top of the product discharge vessel (stirred product tank) back to the top of the reactor to improve the fill level of the product discharge vessel.

As noted, the process of this invention can also be carried out in two reactors connected in series, also referred to as staged reactors.

It will be understood that the definition of"two reactors connected in series"includes one reactor operated in two stages. All of the conditions of the prepolymer embodiment apply to the staged reactor embodiment except that the catalyst precursor doe not have to be prepolymerized; the temperature in the first reactor in the series is at least about 80° C. The temperature can be in the range of about 80° to <BR> <BR> <BR> about 100° C and is preferably in the range of about 85° to about 95 ° C. The temperature in the second reactor in the series is no greater than about 80° C. It can be in the range of about 0° to about 80° C and is preferably in the range of about 35° C to about 60° C. In these reactors, a high melt index resin is made in one or more of the reactors, and a low melt index resin is made in the other reactor (s), and bimodal resin blend is produced. An exemplary process is described in United States patent application serial number 73,173, filed on June 8,1993 by Daniel et al. Briefly, this particular process comprises continuously contacting with a catalyst, under polymerization conditions, ethylene or a mixture comprising ethylene and one or more alpha-olefins in a first fluidized bed reactor and a mixture comprising ethylene and one or more alpha-olefins in a second fluidized bed reactor, the first and second reactors being connected in series, said catalyst comprising: (A) a catalyst precursor comprising: (i) a vanadium compound, which is the reaction product of (a) VX3 wherein each X is independently chlorine, bromine, or iodine; and (b) an electron donor, which is a liquid, organic Lewis base in which VX3 is soluble; (ii) as a modifier, either BX3 or AlXaR (3-a) wherein each X is as defined above; each R is independently alkyl having 1 to 14 carbon atoms; and a is 1 or 2; and (iii) a silica or alumina support for said vanadium compound and modifier; (B) a cocatalyst; and (C) a promoter, wherein, in the first reactor, (1) optionally, alpha-olefin is present in a ratio of about 0.002 to about 0.01 mole of alpha-olefin per mole of ethylene; and (2) hydrogen is present in a ratio of about 0.05 to about 0.15 mole of hydrogen per mole of ethylene to produce a homopolymer or copolymer having a relatively high melt index in the range of about 1 to about 100 grams per 10 minutes; a density of at least 0.950 gram per cubic centimeter; and a melt flow ratio in the range of about 20 to about 100; and (3) the said polymer is admixed with active catalyst and the mixture is transferred to the second reactor wherein: (1) said alpha-olefin is present in a ratio of about 0.005 to about 0.03 mole of alpha-olefin per mole of ethylene; (2) hydrogen is present in a ratio of about 0.002 to about 0.02 mole of hydrogen per mole of ethylene; (3) additional cocatalyst is introduced into the second reactor in an amount sufficient to restore the activity of the catalyst transferred from the first reactor to produce a copolymer having a relatively low melt index in the range of about 0.001 to about 0.01 gram per 10 minutes; a density of at least 0.925 gram per cubic centimeter; and a melt flow ratio in the range of about 20 to about 100 with the said relatively high melt index polymer produced in said first reactor in intimate admixture therewith.

In the two stage embodiment of the present invention as in the prepolymer embodiment, the vanadium compound is more broadly defined, and the electron donor, the modifier, and the support are optional. In both embodiments, the cocatalyst and the promoter are particularly defined, however.

The advantages of the prior invention are found in the production of homogeneous polyethylene resins having narrow molecular weight distributions, the products of which have very good transparency and heat-sealing properties; in the production of EPRs having improved cure performance and improved high temperature crystallinity; and in the provision of a polymerization process, which is equal to or better than commercially available solution processes for the production of EPM and EPDM, and results in good particle morphology.

The advantages of this invention, not only incorporate the advantages of the prior invention, but permit compositionally homogeneous polyethylenes and EPRs to be produced to the essential exclusion of the corresponding compositionally heterogeneous resins at relatively low temperatures while maintaining a relatively high level of catalyst activity. Further, these advantages can be achieved in a single reactor or in two or more staged reactors. The two stage embodiment of this invention produces bimodal molecular weight distribution resins with homogeneous compositional distribution. This results in superior resin strength and extrusion characteristics in addition to the good transparency and heat sealing properties.

The patents and patent applications mentioned in this application are incorporated by reference herein.

The invention is illustrated by the following examples.

Examples 1 to 9 In examples 1 and 2, the polymerization is carried out in one reactor, but in the two stage mode. This simulates two reactors connected in series. In these examples, the catalyst precursor is not prepolymerized. In exampes 3 to 6, a single reactor is used. In examples 7 to 9, the prepolymerization and the polymerization are each carried out in one reactor. In all of the examples, the reactors used for the preparation of the catalyst precursor, the prepolymerization, and the polymerization are stirred reactors. The prepolymerization and the polymerization are carried out in a hexane slurry.

The catalyst system for the polymerization includes a vanadium based catalyst precursor; a cocatalyst ; and a promoter. The catalyst precursor is first prepared using conventional procedures such as the procedure described in United States patent 4, 508, 842, i. e., the reaction product of vanadium trichloride and an electron donor (tetrahydrofuran) are supported on dehydrated silica followed by a modification step to reduce the supported precursor with diethylaluminum chloride (DEAC).

Polymerization: To a one liter stirred batch reactor is charged, under nitrogen, 500 milliliters of dry hexane. The catalyst precursor is then charged, followed by a one time batch charge of 1- hexene, and hydrogen for molecular weight control. The reactor is pressurized at a first stage polymerization temperature (examples 1 and 2), at desired polymerization temperatures (examples 3 to 6), and at prepolymerization temperatures (examples 7 to 9). The promoter is charged and the reactor solution temperature is lowered 5 to 10 degrees C before the addition of the cocatalyst. The cocatalyst is added and the reactor solution is brought up to the desired temperature.

Ethylene is continuously fed so as to maintain the prescribed reactor pressure. In all of the examples, at the end of the reaction period, ethanol is injected into the reaction solution to quench the polymerization reaction. The polymer is isolated by coagulation in methanol followed by filtration.

Catalyst activity is determined by mass balance, and the polymer composition is determined by NMR (nuclear magnetic resonance) analysis. Process variables and various properties of the resin product are set forth in the Table.

Table (continued) Example FI Mw/Mn density MP (g/10 (g/cc)(°C) min) 1 13 7.8 0.9142 107 2 8 7.9 0.919-9 114 3 44 3 0.9125 106 4--------0.9232 116 & 124 5------------116 & 126 6 110 & 118 7 0.7--------106 8 29--------96 9 72--------100 Notes to Examples and Table: 1. DEAC = diethylaluminum chloride PCP = perchloropropene or perchloropropylene llmol = micromole mmol = millimole 2. Catalyst activity = the grams of C2/C6 copolymer produced per millimole of vanadium per hour per 100 psi of C2.

3. FI (g/10 min) = flow index is reported in grams per 10 minutes. It is determined under ASTM D-1238, Condition F, at 190° C and 21.6 kilograms.

4. Mw/Mn = polydispersity, a measure of the breadth of the molecular weight distribution. The ratio represents weight average molecular weight divided by number average molecular weight.

5. In example 1, polymerization is carried out in the first stage at 85° C for 10 minutes, and in the second stage at 35° C for 20 minutes. After the first stage, the ethylene flow is stopped and the temperature is lowered to the second stage temperature. The ethylene feed is then reinitiated and the polymerization is continued for 20 minutes. The catalyst activity is relatively high and is about the same as in example 3, and the resin is compositionally homogeneous as indicated by the single and low melting point. Further, the molecular weight distribution is found to be broad and bimodal.

Example 2 is similar to example 1 except that the temperature in the second stage is 50° C.

Examples 3 to 6 are each conducted in a single reactor.

Example 3, carried out at 85° C, is compositionally homogeneous; has a narrower molecular weight distribution than examples 1 and 2; is monomodal; and has a relatively high catalyst activity. Examples 4 to 6, conducted at 50° C, 35° C, and 6ã° C, respectively, have relatively low catalyst activities, and are compositionally heterogeneous as indicated by the two melting points.

Examples 7 to 9 are each carried out in a single reactor with a catalyst precursor, which has been prepolymerized at 85° C for 3 minutes. The prepolymerization is controlled to provide less than 5 percent by weight of prepolymer in the final product. Polymerization is effected for 60 minutes at 35, 50, and 65 degrees C, respectively. The product resins are compositionally homogeneous as indicated by the single and low melting points. While the catalyst activities are relatively higher than those of examples 4 and 5, they are similar to that of example 6.