MXPA01003510A - Process for the polymerization of olefins - Google Patents

Abstract

A process for the polymerization of olefins is provided. The process involves contacting at least one olefin with a Ziegler-Natta catalyst in the presence of dinitrogen monoxide in the production of polymeric products having a narrower molecular weight distribution. A process for narrowing molecular weight distribution of polyolefins utilizing dinitrogen monoxide is also provided.

Description

PROCESS FOR THE POLYMERIZATION OF OLEFINS DESCRIPTION OF THE INVENTION The present invention relates to a process for the polymerization of olefins and reduction of the molecular weight distribution (MWD) of polyolefins. The polyethylenes produced according to the process of the present invention are generally characterized as additionally having a reduced polymer fraction "soluble in n-hexane." Catalyst systems for the polymerization of olefins are well known in the art and have been known at least from US Pat. No. 3,113,115 is issued, and many patents have been issued referring to new or improved Ziegler-Natta catalysts. Examples of such patents are US Patents 3,594,330, 3,676,415, 3,644,318, 3,917,575, 4,105,847, 4,148,754, 4,256,866; 4,298,713, 4,311,752, 4,363,904, 4,481,301 and Reissued 33,683 These patents describe Ziegler-Natta catalysts which are well known since they typically consist of a transition metal component and a co-catalyst which is typically an organoaluminum compound. used with activating catalysts such as hydrocarbon Uros, halogenated and activity modifiers such as electron donors.

The use of hydrocarbons, halogenated with Ziegler-Natta polymerization catalysts based on titanium in the production of polyethylene is described in European Patent Applications EP A 0 529 977 Al and EP 0 703 246 Al. As described, halogenated hydrocarbons can reduce the rate of formation of ethane, improve the efficiency of the catalyst, or provide other effects. Typical of such halogenated hydrocarbons are monohalogen and polyhalogen substitutes of saturated or unsaturated aliphatic, alicyclic or aromatic hydrocarbons having from 1 to 12 carbon atoms. Examples of aliphatic compounds include methyl chloride, methyl bromide, methyl iodide, methylene chloride, methylene bromide, methylene iodide, chloroform, bromoform, iodoform, carbon tetrachloride, carbon tetrabromide, carbon tetraiodide, ethyl chloride , ethyl bromide, 1,2-dichloroethane, 1,2-dibromoethane, methyl chloroform, perchlorethylene and the like. Examples of alicyclic compounds include chlorocyclopropane, tetrachlorocyclopentane and the like. Examples of aromatic compounds include chlorobenzene, hexabromobenzene, benzotrichloride and the like. These compounds can be used individually or as mixtures thereof. It is well known, also, in the polymerization of olefins, particularly where Ziegler-Natta catalysts are used, to optionally use electron donors. Such electron donors often help to increase the efficiency of the catalyst and / or to control the stereospecificity of the polymer when an olefin, other than ethylene, is polymerized. Electron donors, typically known as Lewis Bases, may be employed during the catalyst preparation step, referred to as internal electron donors, or during the polymerization reaction when the catalyst is contacted with the olefin or olefins, referred to as external electron donors. The use of electron donors in the field of propylene polymerization is well known and is used primarily to reduce the atactic form of the polymer and increase the production of the iostactic polymers. However, while improving the production of isotactic polypropylene, electron donors tend, generally, to reduce the productivity of the Ziegler-Natta catalyst. In the field of ethylene polymerization, where ethylene constitutes at least about 50% by weight of the "total monomers present in the polymer, electron donors are used to control the molecular weight (MD) distribution of the polymer and the activity of the catalyst in the polymerization medium.

Examples of patents that describe the use of internal electron donors to produce polyethylene are U.S. Patent Nos. 3,917,575; 4,187,385; 4,256,866; 4,293,673; 4,296,223; Reissued 33,683; 4,302,565; 4,302,566; and 5,470,812. The use of an external electron donor to control the molecular weight distribution ~ is shown in US Patent no. 5,055,535; and the use of external electron donors to control the reactivity of the catalyst particles is described in U.S. Patent No. 5,410,002. Illustrative examples of electron donors include carboxylic acids, carboxylic acid esters, alcohols, ethers, ketones, amines, amides, nitriles, aldehydes, alcoholates, thioethers, thioesters, carbonic esters, organosilicon compounds containing oxygen atoms, and phosphorus, arsenic or antimony linked to an organic group through a carbon or oxygen atom. The process of the present invention comprises polymerizing at least one olefin in the presence of at least one Ziegler-Natta catalyst comprised of a component comprising at least one transition metal and a cocatalyst comprising at least one organometallic compound, and an amount enough of dinitrogen monoxide (N20) to obtain a homopolymer or olfin interpolymer having a lower molecular weight distribution than would be obtained in the absence of dinitrogen monoxide. Also provided is a process for reducing the molecular weight distribution of a polymer comprising at least one or more olefins comprising contacting under polymerization conditions, at least one or more olefins with at least one Ziegler-Natta catalyst comprised of a component comprising at least one transition metal and a co-catalyst comprising at least one organometallic compound, and dinitrogen monoxide (N20), wherein the dinitrogen monoxide is present in an amount sufficient for the molecular weight distribution of the resulting polymer product is smaller than that which would be obtained in the absence of dinitrogens monoxide. All mention in the present to elements of Groups of the Periodic Table are made with reference to the Periodic Table of the Elements, as published in "Chemical and Engineering News", 63 (5), 27, 1985. In this format, the Groups are numbered from 1 to 18. In carrying out the novel polymerization process of the present invention, any electron donors and / or any halogenated hydrocarbon compounds can optionally be added.

The process of the present invention comprises polymerizing at least one olefin in the presence of at least one Ziegler-Natta catalyst comprised of a component comprising at least one transition metal and a co-catalyst comprising at least one organometallic compound, and a sufficient amount of dinitrogen monoxide (N20) to obtain an olefin homopolymer or interpolymer having a lower molecular weight distribution than would be obtained in the absence of dinitrogen monoxide. Also provided is a process for reducing the molecular weight distribution of a polymer comprising at least one or more olefins comprising contacting under polymerization conditions, at least one or more olefins with at least one Ziegler-Natta catalyst comprised of a component comprising at least one transition metal and a co-catalyst comprising at least one organometallic compound, and dinitrogen monoxide (N20), wherein the dinitrogen monoxide is present in an amount sufficient for the molecular weight distribution of the resulting polymer product is more reduced than would be obtained in the absence of dinitrogen monoxide. The polymerization of at least one olefin herein can be carried out using any suitable process. For example, polymerization in suspension, in solution or in gas phase media can be used. All of these polymerization processes are well known in the art. A particularly desirable method for producing polyethylene polymers according to the present invention is a gas phase polymerization process. This type of process and the means for operating the polymerization reactor are well known and fully described in U.S. Patent Nos. 3,709,853.; 4,003,712; 4,011,382; 4,012,573; 4,302,566; 4,543,399; 4,882,400; 5,352,749; 5,541,270; Canadian Patent No. 991,798 and Belgian Patent No. 839,380. These patents describe gas phase polymerization processes in which the polymerization zone is mechanically stirred or fluidized by the continuous flow of the gaseous monomer and diluent. The complete contents of these patents are incorporated herein by reference. In general, the polymerization process of the present invention can be carried out as a continuous process in the gas phase such as a fluid bed process. A fluid bed reactor for use in the process of the present invention typically comprises a reaction zone and a so-called rate reduction zone. The reaction zone comprises a bed of growing polymer particles, polymer particles formed and a smaller amount of catalyst particles fluidized by the continuous flow of the gaseous monomer and the diluent to remove heat of polymerization through the reaction zone. Optionally, some of the recirculated gases can be cooled and compressed to form liquids that increase the heat removal capacity of the circulating gas stream when it is readmitted to the reaction zone. An adequate rate of gas flow can be easily determined by a simple experiment. The collection of the gaseous monomer with the circulating gas stream is at a rate equal to the rate at which the particular polymer product and the associated monomer is withdrawn therefrom from the reactor and the composition of the gas passing through the reactor is adjusted to maintain an essentially continuous state of gaseous composition within the reaction zone. The gas that leaves the reaction zone is passed to the zone of speed reduction where the dispatched particles are removed. The finer particles dispensed and the powder can be removed in a cyclone and / or fine filter. The gas is passed through a heat exchanger where the heat of polymerization is removed, compressed in a compressor and then returned to the reaction zone. In more detail, the reactor temperature of the fluid bed process herein ranges from about 30 ° C to about 150 ° C. In general, the temperature of the reactor is operated at the highest temperature that is feasible taking into account the embedding temperatures of the polymer product within the reactor. The process of the present invention is suitable for the polymerization of at least one or more olefins. Olefins, for example, may contain from 2 to 16 carbon atoms. Included herein are the homopolymers, copolymers, terpolymers, and the like of the monomeric olefin units. Particularly preferred for preparation herein by the process of the present invention are polyethylenes. Such polyethylenes are defined as ethylene homopolymers and copolymers of ethylene and at least one alpha olefin wherein the ethylene content is at least about 50% by weight of the total monomers involved. Examples of alpha olefins that can be used herein are propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octane, 4-methyl-1-pentene, 1-decene, 1-dodecene, 1 -hexadecene and the like. Polyenes such as 1, 3-hexadiene, 1, -hexadiene, 1,5-hexadiene, cyclopentadiene, dicyclopentadiene, 4-vinylcyclohex-1-ene, 1,5-cyclooctadiene, 5-vinylidene-2- are also usable herein. norbornene, 5-vinyl-2-norbornene, and olefins formed in situ in the polymerization medium. When the olefins are formed in situ in the polymerization medium, the formation of polyethylenes containing branched long chain can occur. The polymerization reaction of the present invention is carried out in the presence of at least one Ziegler-Natta catalyst. In the process of the invention, the catalyst can be introduced in any manner known in the art. For example, the catalyst can be introduced directly into the fluidized bed reactor in the form of a solution, a suspension or a dry powder that flows freely. The catalyst can also be used in the form of a deactivated catalyst, or in the form of a prepolymer obtained by contacting the catalyst with one or more olefins. The Ziegler-Natta catalyst used in the present are well known in the industry. The Ziegler-Natta catalysts in the simplest form are comprised of a component comprising at least one transition metal and a co-catalyst comprising at least one organometallic compound. The metal of the transition metal component is a metal of Groups 4, 5, 6, 7, 8, 9 and 10 of the Periodic Table of the Elements, as published in "Chemical and Engineering News", 63 (5) , 27, 1985. In this format, groups are listed from 1-18. Examples of such transition metals are. titanium, zirconium, vanadium, chromium, manganese, iron, cobalt, nickel, and the like, and mixtures thereof. In a preferred embodiment, the transition metal is selected from the group consisting of titanium, zirconium, vanadium and chromium, and in a still further preferred embodiment, the transition metal is titanium. The Ziegler-Natta catalyst may optionally contain magnesium and / or chlorine. Such catalysts containing magnesium and chlorine can be prepared by any form known in the art. The co-catalyst used in the process of the present invention can be any organometallic compound, or mixtures thereof, which can activate the transition metal component in a Ziegler-Natta catalyst in the polymerization of olefins. In particular, the organometallic co-catalyst compound which is reacted with the transition metal component contains a metal of Groups 1, 2, 11, 12, 13 and / or 14 of the Periodic Table of the Elements described above. Examples of such metals are lithium, magnesium, copper, zinc, boron, silicon and the like, and mixtures thereof. Preferably the co-catalyst is at least one compound of the formula, XnER-n, or mixtures thereof, wherein, X is hydrogen, halogen, or mixtures of halogens, selected from fluorine, chlorine, bromine and iodine; n varies from 0 to 2; E is an element of Group 13 of the Periodic Table of the Elements such as boron, aluminum and gallium; and R is a hydrocarbon group, containing from 1 to 100 carbon atoms and from 0 to 10 oxygen atoms, attached to the Group 13 element by a carbon or oxygen bond. Examples of the group R suitable for use herein are C? _ ?ooalkyl, Ci-ioo alkoxy, C2-? ?o or C d ?oo dienyl alkenyl / C3_ ?cyclo cycloalkyl, C3-100 cycloalkoxy / cycloalkenyl of C3-100, cyclodienyl of C4-100, aryl of Cg-ioo, aralkyl of C7-100 'aralkoxy of C7_I0O? and alkaryl of C7-? oo- Hydrocarbons containing from 1 to 100 carbon atoms and from 1 to 10 oxygen atoms are also examples of the group R. Example of co-catalyst used in the process of the present invention wherein n = 0 are trimethylaluminum; triethylborane; triethylgalane; triethylaluminium; tri-n-propylaluminium; tri-n-butylaluminum; tri-n-pentylaluminum; triisoprenylaluminium; tri-n-hexylaluminum; tri-n-heptylalu inium; tri-n-octylaluminum; triisopropylaluminum; triisobutylaluminum; tris (cylxylmethyl) aluminum; dimethylaluminum methoxide; dimethylaluminum ethoxide; diethylaluminum ethoxide and the like. Examples of compounds wherein n = 1 are dimethylaluminum chloride; diethylaluminum chloride; di-n-propylaluminum chloride; di-n-butylaluminum chloride; di-n-pentylaluminum chloride; diisoprenyl aluminum chloride; di-n-hexylaluminum chloride; di-n-heptylaluminum chloride; di-n-octylaluminum chloride; diisopropylaluminum chloride; diisobutylaluminum chloride; bis (cylxylmethyl) aluminum chloride; diethylaluminum fluoride; diethylaluminum bromide; di-ethylaluminum iodide; dimethylaluminum hydride; diethylaluminum hydride; di-n-propylaluminum hydride; di-n-butylaluminum hydride; di-n-pentylaluminum hydride; diisoprenylaluminum hydride; di-n-hexylaluminum hydride; di-n-heptylaluminum hydride; di-n-octylaluminum hydride; diisopropylaluminum hydride; diisobutylaluminum hydride; bis (cylxylmethyl) aluminum hydride; chloromethylaluminum methoxide, chloromethylaluminum ethoxide; chloroethylaluminum ethoxide and the like. Examples of compounds wherein n = 2 are methylaluminum dichloride; ethylaluminum dichloride; n-propylaluminum dichloride; n-butylaluminum dichloride; n-pentylaluminum dichloride; isoprenylaluminum dichloride; n-hexylaluminum dichloride; n-heptylaluminum dichloride; n-octylaluminum dichloride; isopropyl aluminum dichloride; isobutylaluminum dichloride; (Cylxylmethyl) aluminum dichloride and the like. Also are sesquialkoxides of alkylaluminium such as methylaluminum sesquimethoxide; ethylaluminum sesquiethoxide; n-butylaluminum sesqui-n-butoxide and the like. Also examples are alkylaluminum sesquihalides such as methylaluminum sesquichloride; ethylaluminum sesquichloride; isobutylaluminum sesquichloride; ethylaluminum sesquifluoride; ethylaluminum sesquibromide; ethylaluminum sesquiodide and the like. Preferred for use herein as co-catalysts are trialkylaluminum such as trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, triisobutylaluminum, tri-n-hexylaluminum, triisohexylaluminum, tri-2-methylpentylaluminum, tri-n- octylaluminum, tri-n-decylaluminum; and dialkylaluminum halides such as dimethylaluminum chloride, diethylaluminum chloride, dibutylaluminum chloride, diisobutylaluminum chloride, diethylaluminum bromide and diethylaluminum iodide; and alkylaluminum sesquihalides such as methylaluminum sesquichloride, ethylaluminum sesquichloride, n-butylaluminum sesquichloride, isobutylaluminum sesquichloride, ethylaluminum sesquifluoride, ethylaluminum sesquibromide, and ethylaluminum sesquiodide. More preferred for use herein as co-catalysts are trialkylaluminums such as trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, triisobutylaluminum, tri-n-hexylaluminum, triisohexylaluminum, tri-2-methylpentylaluminum, tri-n-octylaluminum and dialkylaluminum halides such as dimethylaluminum chloride, diethylaluminum chloride, dibutylaluminum chloride, diisobutylaluminum chloride and alkylaluminum sesquihalides such as sesquichloride of methylaluminum, ethylaluminum sesquichloride, n-butylaluminum sesquichloride and isobutylaluminum sesquichloride. Mixtures of compounds of the above formula XnER3_n can also be used herein as the cocatalyst. Any or all of the components of the Zregler-Natta catalyst can be supported on a carrier. The carrier can be any particulate organic or inorganic material. Preferably the particle size of the carrier should not be larger than about 200 microns in diameter. The most preferred particle size of the carrier material can be easily established by experiment. Preferably, the carrier should have an average particle size of 5 to 200 microns in diameter, more preferably 10 to 150 microns and more preferably 20 to 100 microns. Examples of suitable inorganic carriers include metal oxides, metal hydroxides, metal halides - and other metal salts such as sulfates, carbonates, phosphates, nitrates and silicates. Examples of inorganic carriers suitable for use herein are the metal compounds of Groups 1 and 2 of the Periodic Table of the Elements, such as sodium or potassium salts and oxides or magnesium or calcium salts, for example chlorides, sulfates, carbonates, phosphates or silicates of sodium, potassium, magnesium or calcium and the oxides or hydroxides of, for example, magnesium or calcium. Also suitable for use are inorganic oxides such as silica, titania, alumina, zirconia, chromia, boron oxide, silanized silica, silica hydrogels, siliceous xerogels, silica aerogels, and mixed oxides such as talcs, silica / chromia, silica / chromia / titania, silica / alumina, silica / titania, silica / magnesia, silica / magnesia / titania, aluminum phosphate gels, silica co-gels and the like. Inorganic oxides may contain small amounts of carbonates, nitrates, sulfates and oxides such as Na2C03, -K2C03, CaC03, MgC03, Na2S04, A12 (S04) 3, BaSO4, KN03, Mg (N03) 2, A1 (N03) 3, Na20, K20 and Li20. Preferred carriers are those containing at least one component selected from the group consisting of MgCl2, SiO2, A1203 or mixtures thereof as a major component. Examples of suitable organic carriers include polymers such as, for example, polyethylene, polypropylene, interpolymers of ethylene and alpha-olefins, polystyrene, functionalized polystyrene, polyamides and polyesters. In the event that the Ziegler-Natta catalyst is used in the form of a prepolymer, the co-catalyst used to form the prepolymer can be any organometallic compound comprising a metal of Groups 1, 2, 11, 12, 13 and 14 of the Periodic Table of the Elements described above. Examples of such metals are lithium, magnesium, copper, zinc, boron, silicon and the like. When a prepolymer is used in the polymerization medium, the additional co-catalysts, if used, can be the same or different than that used to prepare the prepolymer. When used, an external electron donor and / or hydrocarbon or halogenated hydrocarbon donor or donor may be added to the prepolymer. The Ziegler-Natta catalyst can contain conventional components in addition to the transition metal component and the co-catalyst. For example, any compound of magnesium, halogenated hydrocarbon and the like can be added. In addition, any electron donor can be added to the Ziegler-Natta catalyst. The electron donor compound is preferably selected from the group consisting of carboxylic acid esters, anhydrides, acid halides, ethers, thioethers, aldehydes, ketones, imines, amines, amides, nitriles, isonitriles, cyanates, isocyanates, thiocyanates, isothiocyanates, thioesters, dithioesters, carbonic esters, hydrocarbylcarbamates, hydrocarbyl carbonates, hydrocarbyldithiocarbamates, urethanes, sulfoxides, sulfones, sulfonamides, organosilicon containing at least one oxygen atom and nitrogen, phosphorus, arsenic or antimony compounds bound to an organic group through a carbon or oxygen atom. More preferred as electron donors are compounds containing from 1 to 50 carbon atoms and from 1 to 30 heteroatoms of an element, or mixtures thereof, selected from Groups 14, 15, 16 and 17 of the Periodic Table of The elements. The Ziegler-Natta catalyst can be prepared by any method known in the art. The catalyst may be in the form of a solution, a suspension or a dry powder that flows freely. The amount of Ziegler-Natta catalyst used is that which is sufficient to allow the production of the desired amount of the polyolefin. The polymerization reaction is carried out in the presence of dinitrogen monoxide (N20). It is essential that the dinitrogen monoxide be used in an amount that will be sufficient to result in the production of polyolefins characterized by having a lower molecular weight distribution than would be obtained in the absence of the use of nitrogen monoxide in the amount specified The. The molecular weight distribution of the polyolefins herein is evidenced by the melt flow ratio (MFR) values of the polyolefins. In the process of the present invention it has been found suitable to add, generally, to the polymerization medium dinitrogen monoxide (N20) in an amount of about 1 ppm to about 10,000 ppm by volume to produce polyolefins having reduced molecular weight distributions. The polyethylenes produced by the present process are not only characterized by lower molecular weight distribution, but also, generally, by a polymer fraction soluble in reduced n-hexane. By carrying out the polymerization reaction of the present process, other conventional additives generally used in processes for polymerizing olefins can be added. Specifically, any halogenated hydrocarbon, including those mentioned above, and preferably chloroform, can be added. Additionally, any internal electron donors, or mixtures of electron donors, such as those mentioned above, and preferably, tetrahydrofuran can be added. Examples of the polymers that can be produced by the process of the present invention include the following: A. Homopolymers of ethylene and interpolymers of ethylene and at least one or more alpha-olefins having from 3 to 16 carbon atoms wherein the ethylene comprises at least about 50% by weight of the total monomers involved; B. Interpolymers of ethylene and l-hexene wherein the ethylene comprises at least about 50% by weight of the copolymer and has a melt transition temperature by differential scanning calorimetry (DSC), Tm, from about 116 ° C to about 123 ° C, a density of about 0.880g / cc to about 0.930g / cc, an extractable of n-hexane from 0 to about 6 weight percent, and a melt flow ratio of about 26 to about 34; C. Interpolymers of ethylene and l-hexene having a melt transition temperature DSC, Tm, from about 119 ° C to about 121 ° C, a density from about 0.905 g / cc to about 0.920 g / cc, an extractable- of n-hexane from 0 to about 3 weight percent, and a melt flow ratio of from about 26 to about 32; D. Interpolymers of ethylene and an olefin having from 3 to 16 carbon atoms, wherein the ethylene comprises at least 99% by weight of the copolymer, and the interpolymer has a molten flux ratio of from about 22 to about 26; and E. Interpolymers of ethylene and at least one or more olefins having from 5 to 16 carbon atoms, wherein the ethylene comprises at least about 50% by weight of the interpolymer having a DSC melt transition temperature of about 116 °. C at about 123 ° C, a density of about 0.880g / cc to about 0.930g / cc, an extractable in n-hexane of from 0 to about 6 weight percent, and a melt flow ratio of about 26 to about 34 Any conventional additive can be added to the polyolefins obtained by the present invention. Examples of the additives include nucleating agents, heat stabilizers, antioxidants of the phenol type, sulfur type and phosphorus type, lubricants, antistatic agents, dispersants, copper damage inhibitors, neutralizing agents, foaming agents, plasticizers, anti-foaming agents, flame retardants, crosslinking agents, flow improvers such as peroxides, ultraviolet light absorbers, light stabilizers, wear stabilizers, weld strength improvers, slip agents, antiblocking agents, anti-fog agents, dyes, pigments, natural oils, synthetic oils, waxes, fillers and rubber ingredients. The polyethylenes of the present invention can be made into films by any technique known in the art. For example, films can be produced by the well-known techniques of cast film, blown film and extrusion coating. Additionally, polyethylenes can be manufactured into other articles of manufacture, such as molded articles, by any of the well-known techniques. The invention will be more readily understood with reference to the following examples. There are, of course, many other forms of this invention, which will become obvious to one skilled in the art, once the invention has been fully described, and it will be recognized accordingly that these examples are given for the purpose of illustration only. , should not be construed as limiting the scope of this invention in any way. Examples In the following examples the test procedures listed below were used to evaluate the analytical properties of the polyolefins herein and in the evaluation of the physical properties of the films of the examples. - a) Dart Impact is determined in accordance with ASTM D-1709, Method A; with a dart of 38.1 mm, and a height of fall of 0.66 meters. Thickness of the film of approximately 1 thousandth; b) The density ge determined in accordance with ASTM D-4883 of a plate made in accordance with ASTM D1928; c) the Fusion Index (MI), I2, is determined in accordance with ASTM D-1238, condition E, measured at 190 ° C, and reported as decigrams per minute; d) the High Load Melt Index (HLMI), I21, is measured in accordance with ASTM D-1238, condition F, measured at 10.0 times the weight used in the previous melt index test; e) Melt Flow Ratio (MFR) = I2? / I2 or High Load Fusion index / Fusion index; and f) The n-Hexane extractable - is determined in accordance with 21 CFR 177.1520 (option 2). More particularly, a film test specimen of about 1 square inch having a thickness of = 4 thousandths weighing 2,510.05 grams is placed in a calibrated sample basket and precisely weighed to the nearest 0.1 milligram. The sample basket containing the test specimen is then placed in a 2 liter extraction vessel containing approximately 1 liter of n-hexane. The basket is placed in such a way that it is completely below the level of the n-hexane solvent. The sample resin film is extracted for 2 hours at 49.5 ± 0.5 ° C and then the basket is raised above the level of the solvent to drain momentarily. The basket is removed and the contents washed by immersing several times in fresh n-hexane. The basket is left to dry between washing. The excess solvent is removed by blowing briefly into the basket with a stream of nitrogen or dry air. The basket is placed in the vacuum oven for 2 hours at 80 ± 5 ° C. After 2 hours, it is removed and placed in a desiccator to cool to room temperature (approximately 1 hour). After cooling, the basket is reweighed to the nearest 0.1 milligram. The content of stractibles in n-hexane is calculated after the weight loss of the original sample. g) DSC (TM) Melting Transition Temperature was determined in accordance with ASTM D-3418-97. The transition, TM, was measured in the second heating cycle. The Ziegler-Natta catalyst used in Examples 1-7 herein was prepared according to Example 1-A of European Patent Application EP 0 703 246 Al. The prepolymer used in Examples 1-7 herein was prepared according to Example 1-b of European Patent Application EP 0 703 246 Al. Thus, a prepolymer containing approximately 34 grams of polyethylene per millimol of titanium was obtained, with a molar ratio of tri-n-octylaluminum ( TnOA) to titanium of approximately 1.1. The polymerization process used in Examples 1-7 here was carried out in a fluidized bed reactor for gas phase polymerization, consisting of a vertical cylinder of 0.74 meters in diameter and 7 meters in height and topped by a speed reduction camera. The reactor is provided in its lower part with a fluidizing grid and with an external line for the recycled gas, which joins the top of the speed reduction chamber with the lower part of the reactor, at a point below the grid. fluidization. The recycling line is equipped with a compressor to circulate gas and a heat transfer medium such as a heat exchanger. In particular, the lines for supplying ethylene, l-hexene, hydrogen and nitrogen, which represent the main constituents of the gaseous reaction mixture passing through the fluidized bed, are fed into the recycling line. Above the fluidization grid, the reactor contains a fluidized bed consisting of approximately 800 pounds of a linear low density polyethylene powder made of particles with an average weight diameter of about 0.7 mm. The gaseous reaction mixture, which contains ethylene, l-hexene, hydrogen nitrogen, and minor amounts of other components, it passes through the fluidized bed under a pressure of about 295 psig with an ascending fluidization rate of about 1.9 ft / second. A catalyst it is introduced intermittently into the reactor, containing the catalyst magnesium, chlorine and titanium and which has been previously converted to a prepolymer, as described above, containing approximately 34 grams of polyethylene per millimole of titanium and an amount of tri-n-octylaluminum (TnOA) such that the molar ratio, Al / Ti, is equal to approximately 1.1. The rate of introduction of the prepolymer into the reactor is adjusted to achieve the desired production speed. During the polymerization, a solution of trimethylaluminum (TMA) in n-hexane, at a concentration of about 2 weight percent, is continuously introduced into the line to recycle the gas reaction mixture, to a point downstream of the medium of heat transfer. The feed rate of TMA is expressed as a molar ratio of TMA to titanium (TMA / Ti), and is defined as the ratio of the feed rate TMA (in moles of TMA per hour) to the feed rate of the prepolymer ( in moles of titanium per hour). Simultaneously, a solution of chloroform (CHC13) in n-hexane, at a concentration of about 0.5 weight percent, is continuously introduced into the line to recycle the gaseous reaction mixture. The feed rate of CHCl3 is expressed as a molar ratio of CHC13 to titanium (CHCl3 / Ti), and is defined as the ratio of the feed rate of CHC13 (in moles of CHCl3 per hour) to the prepolymer feed rate (in moles of titanium per hour). In the same way, a solution of tetrahydrofuran (THF) in n-hexane, at a concentration of about 1 weight percent, can be continuously introduced into the line to recycle the gaseous reaction mixture. The feed rate of THF is expressed as a molar ratio of THF to titanium (THF / Ti), and is defined as the ratio of the feed rate THF (in moles of THF per hour) to the feed rate of prepolymer ( in moles of titanium per hour). In Examples 3-7 herein, dinitrogen monoxide (N20) was added as a gas to the line to recycle the gaseous reaction mixture in amounts sufficient to reduce the molecular weight distribution of the polyethylene. The concentration of N20 in the gas phase polymerization medium is expressed in units of parts per million (ppm) by volume. The ethylene and l-hexene copolymers, having densities of 0.917 g / cc, were manufactured at a rate of about 150 to about 200 pounds per hour in the following examples. The productivity of the prepolymer (Productivity) is the ratio of pounds of polyethylene produced per pound of prepolymer added to the reactor. The activity of the catalyst is expressed as grams of polyethylene per millimol of titanium per hour per 100 psia of ethylene pressure.

EXAMPLE 1 The process conditions of the gas phase are given in Table 1 and the properties of the resin are given in Table 2. The molar ratio of trimethylaluminum (TMA) to titanium (TMA / Ti) was 3. The ratio molar of chloroform (CHC13) to titanium (CHC13 / Ti) was 0.03. The operation was conducted without the addition of an external electron donor. Hexene was used as a comonomer. Under these conditions a polyethylene free of agglomerates from the reactor was removed at a rate of 150 lb / h (pounds per hour). The productivity of the prepolymer was 375 pounds of polyethylene per pound of prepolymer which corresponds to an activity of 2311 grams of polyethylene per millimol of titanium per hour per 100 psia of partial pressure of ethylene [gPE / (mmolTi • h • 100Pc2)] • The polyethylene had a density of 0.917 g / cc and a melting index MI2.?g, I2, of 0.9 dg / minute. The Melt Flow Ratio, I2? / I2, was 33 and the extractables in n-hexane were 2.6% by weight. The DSC melting transition temperature (Tm) was 124.5 ° C. EXAMPLE 2 The process conditions of the gas phase are given in Table 1 and the properties of the resin are given in Table 2. The molar ratio TMA / Ti was 7. The molar ratio of CHCl3 / Ti was 0.06. The molar ratio of tetrahydrofuran (THF) to titanium (THF / Ti) was 1. 1-Hexene was used as the comonomer. Under these conditions a free polyethylene was removed from the reactor agglomerate at a rate of 192 lb / h. The productivity of the prepolymer was 231 pounds of polyethylene per pound of prepolymer which corresponds to an activity of 1800 [gPE / (mmolTi • h • 100PC2)]. The polyethylene had a density of 0.917 g / cc and a melt index MI2.i6, I2, of 0.9 dg / min. The Melt Flow Ratio, I2? / I2 / was 31 and the extractables in n-hexane were 2.0% by weight. The melting transition temperature DSC (Tm) was 123.9 ° C. EXAMPLE 3 The process conditions of the gas phase are given in Table 1 and the properties of the resin are given in Table 2. The molar ratio TMA / Ti was 7. The molar ratio of CHC13 / Ti was 0.06. The molar ratio of THF / Ti was 1. The concentration of dinitrogen monoxide (N20) in the polymerization medium was 70 ppm by volume. 1-Hexene was used as the comonomer. Under these conditions, a free polyethylene was removed from the reactor agglomerate at a rate of 180 Ib / h. The productivity of the prepolymer was 79 pounds of polyethylene per pound of prepolymer which corresponds to an activity of 609 [gPE / (mmolTi • h • 100PC2)]. The polyethylene had a density of 0.917 g / cc and a MI2 fusion index., I2, of 0.9 dg / min. The Melt Flow Ratio, I2? / I2, was 28 and the extractables in n-hexane were 1.1% by weight. The DSC melting transition temperature (Tm) was 122.3 ° C. EXAMPLE 4 The process conditions of the gas phase are given in Table 1 and the properties of the resin are given in Table 2. The molar ratio TMA / Ti was 7. The molar ratio of CHC13 / Ti was 0.06. The molar ratio of THF / Ti was 0. The concentration of N20 in the polymerization medium was 130 ppm by volume. 1-Hexene was used as the comonomer. Under these conditions a free polyethylene was removed from the reactor agglomerate at a rate of 211 lb / h. The productivity of the prepolymer was 121 pounds of polyethylene per pound of prepolymer which corresponds to an activity of 1116 [gPE / (mmolTi • h • 100PC2)]. The polyethylene had a density of 0.917 g / cc and a melting index MI2.?6, I2, of 0.9 dg / min. The Melt Flow Ratio, I2X / I2A was 28 and the extractables in n-hexane were 1.6% by weight. The DSC melt transition temperature (Tm) was 122.7 ° C. EXAMPLE 5 The process conditions of the gas phase are given in Table 1 and the properties of the resin are given in Table 2. The molar ratio TMA / Ti was 7. The molar ratio of CHCl3 / Ti was 0.06. The molar ratio of THF / Ti was 0. The concentration of N20 in the polymerization medium was 210 ppm by volume. 1-Hexene was used as the comonomer. Under these conditions, a free polyethylene was removed from the reactor agglomerate at a rate of 194 lb / h. The productivity of the prepolymer was 124 pounds of polyethylene per pound of prepolymer which corresponds to an activity of 1038 [gPE / (mmolTi • h • 100PC2)] - The polyethylene had a density of 0.917 g / cc and an MI2 melt index .15, I2, of 0.9 dg / min. The Melt Flow Ratio, I2? / L2r was 28 and the extractables in n-hexane were 1.1% by weight. The DSC melting transition temperature (Tm) was 122.2 ° C. EXAMPLE 6 The process conditions of the gas phase are given in Table 1 and the properties of the resin are given in Table 2. The molar ratio TMA / Ti was 7. The molar ratio of CHC13 / Ti was 0.06. The molar ratio of THF / Ti was 0.3. The concentration of N20 in the polymerization medium was 300 ppm by volume. 1-Hexene was used as the comonomer. Under these conditions a free polyethylene was removed from the reactor agglomerate at a rate of 192 lb / h. The productivity of the prepolymer was 83 pounds of polyethylene per pound of prepolymer which corresponds to an activity of 471 [gPE / (mmolTi-h-100Pc2)]. The polyethylene had a density of 0.917 g / cc and a melt index MI2.I6A I2, of 0.9 dg / min. The Melt Flow Ratio, I2? / I2, was 27 and the extractables in n-hexane were 0.8% by weight. The DSC melting transition temperature (Tm) was 120.0 ° C. EXAMPLE 7 The process conditions of the gas phase are given in Table 1 and the properties of the resin are given in Table 2. The molar ratio TMA / Ti was 7. The molar ratio of CHC13 / Ti was 0.06. The molar ratio of THF / Ti was 0.3. The concentration of N20 in the polymerization medium was 300 ppm by volume. 1-Hexene was used as the comonomer. Under these conditions a free polyethylene was removed from the reactor agglomerate at a rate of 174 lb / h. The productivity of the prepolymer was 91 pounds of polyethylene per pound of prepolymer which corresponds to an activity of 470 [gPE / (mmolTi • h • 100PC2)] - The polyethylene had a density of 0.917 g / cc and an MI2 melt index .? e, I2, of 0.6 dg / min. The Melt Flow Ratio, I2? / I2, was 28 and the extractables in n-hexane were 0.5% by weight. The DSC melting transition temperature (Tm) was 119.5 ° C. Table 1: Reactor Conditions for Examples 1 to 7 Example 1 7 Reactor Pressure (psig) 290 296 295 294 295 297 296 Reactor Temperature (° C) 84 84 84 84 84 86 86 Fluidization Speed (ft / sec) 1.8 1.9 1.9 1.9 1.9 1.8 1.8 Fluidized bulk density (Ib / ft3) 17.0 17.8 17.1 17.5 16.7 15.2 14.9 Height of the reactor bed (foot) 9.4 10.2 10.2 10.0 10.4 12.8 12.9 Ethylene (mole%) 38 32 32 32 32 41 41 H2 / C2 (molar ratio) 0.178 0.157 0.140 0.113 0.110 0.080 0.063 C6 / C2 (molar ratio) 0.191 0.153 0.138 0.128 0.124 0.115 0.112 TMA / Ti (molar ratio) 3 7 7 7 7 7 7 CHCI3 / Ti 0.03 0.06 0.06 0.06 0.06 0.06 0.06 THF / Ti (molar ratio) 0 1 1 0 0 0.3 0.3 N20 (ppm by volume) 0 0 70 130 210 300 300 Prepolymer speed (Ib / h) 0.4 0.83 2.29 1.74 1.56 2.30 1.92 Production speed (Ib / h) 150 192 180 211 194 192 174 Productivity (mass ratio) 375 231 79 121 124 83 91 Performance space time (lb / h-ft3) 3.6 4.0 3.8 4.6 4.0 3.2 2.9 Activity * 2311 1800 609 1116 1038 471 470 Residual titanium (ppm) 3.8 5.9 17.5 11.3 11.0 16.9 15.6 ^ units of grams PE / (mmolTi-h-100Pc2) Table 2: Properties of Resin for LLDPE prepared in the E j ustoms 7 Example 1 6 7 Desity (g / cc) 0.917 0.917 0.917 0.917 0.917 0.917 0.917 Fusion index, 12 (dg / min) 0.9 0.9 0.9 0.9 0.9 0.9 0.6 Melt Flow Ratio (I?) '33 31 28 28 28 27 28 Extractibles in n-hexane (% by weight) 2.9 2.0 1.1 1.6 1.1 0.8 0.5 DSC Fusion Transition, TM (° C) 124.5 123.9 122.3 122.7 122.2 120.0 119.5 Dart Impact (g / thousand) 200 330 380 400 580 1750 > 2000 From the above data in the Examples and Tables 1 and 2 the following observations can be made. The addition of N20 caused a reduction in the molecular weight distribution as evidenced by the reduction in the values of the molten flux ratio (I21 / I2) caused a reduction in the soluble polymer fraction in n-hexane (% by weight of the extractable), and caused a reduction in the melting transition temperature DSC (Tm) of the polyethylenes. The combination of reduced molecular weight distribution, reduced n-hexane extractables, and reduced DCS fusion transition temperature (Tm) is indicative of a reduction of the compositional heterogeneity in the polyethylene. The films prepared from the polyethylenes of the present invention are generally characterized as having improved optical properties and improved strength properties which are particularly shown by the Dart Impact values in Table 2. Any conventional additive can be added to the polyolefins obtained by the present invention.

Examples of the additives include nucleating agents, heat stabilizers, antioxidants of the phenol type, sulfur type and phosphorus type, lubricants, antistatic agents, dispersants, copper damage inhibitors, neutralizing agents, foaming agents, plasticizers, anti-foaming agents, flame retardants, crosslinking agents, flow improvers such as peroxides, ultraviolet light absorbers, light stabilizers, wear stabilizers, weld strength improvers, slip agents, antiblocking agents, anti-fog agents, dyes, pigments, natural oils, synthetic oils, waxes, fillers and rubber ingredients. Articles such as molded objects can also be prepared from the polyethylenes of the present invention. Similarly, polyolefins can be produced using any of the other compounds described herein. It is expected that the resulting polyolefins will exhibit reduced molecular weight distributions in the same way. It should be clearly understood that the forms of the invention described herein are illustrative only and are not intended to limit the scope of the invention. The present invention includes all modifications that fall within the scope of the following claims.

Claims (26)

1. CLAIMS 1. A process for polymerizing at least one or more olefins comprising contacting, under polymerization conditions, at least one or more olefins with at least one Ziegler-Natta catalyst comprised of a component comprising at least one metal transition and a co-catalyst comprising at least one organometallic compound, and dinitrogen monoxide (N20), characterized in that the dinitrogen monoxide is present in an amount sufficient for the resulting molecular weight distribution of the resulting polymer product to be lower than the that would be obtained in the absence of dinitrogen monoxide. 2. The process in accordance with the claim 1, characterized in that at least one transition metal is selected from Groups 4, 5, 6, 7, 8, 9 and 10 of the Table
2. Periodic of the Elements, as defined herein.
3. 3. The process in accordance with the claim 2, characterized in that the transition metal is selected from the group consisting of titanium, zirconium, vanadium, iron, chromium, nickel and mixtures thereof.
4. 4. The process according to claim 1, characterized in that the metal of at least one organometallic compound is selected from Groups 1, 2, 11, 12, 13 and 14 of the Periodic Table of the Elements, as defined in I presented.
5. 5. The process according to claim 4, characterized in that at least one organometallic compound has the formula XnER3_n, or mixtures thereof, wherein X is hydrogen, halogen, or mixtures of halogens, selected from fluorine, chlorine, bromine and iodine; n varies from 0 to 2; E is an element of Group 13 of the Periodic Table of the Elements, and R is a hydrocarbon group, containing from 1 to 100 carbon atoms and from 0 to 10 oxygen atoms, attached to the Group 13 element by a hydrogen bond. carbon or oxygen.
6. 6. The process in accordance with the claim 4, characterized in that the organometallic compound is selected from the group consisting of trialkylaluminums, dialkylaluminum halides and alkylaluminum sesquihalides.
7. 7. The process in accordance with the claim 6, characterized in that the trialkylaluminum is selected from the group consisting of trimethylaluminum and triethylaluminum.
8. 8. The process in accordance with the claim 1, characterized in that it additionally comprises the presence of at least one electron donor and at least one halogenated hydrocarbon.
9. 9. The process in accordance with the claim 8, characterized in that the co-catalyst is trimethylaluminum, the electron donor is tetrahydrofuran and the halogenated hydrocarbon is chloroform.
10. 10. The process in accordance with the claim 9, characterized in that the transition metal is titanium.
11. 11. The process according to claim 1, characterized in that the dinitrogen monoxide is present in the polymerization medium in an amount ranging from about 1 ppm to about 10,000 ppm by volume.
12. 12. The process according to claim 1, characterized in that the polymerization conditions are gas phase.
13. 13. The process according to claim 1, characterized in that at least one olefin is ethylene.
14. 14. A process for reducing the molecular weight distribution of a polymer comprising at least one or more olefins comprising contacting, under polymerization conditions, at least one or more olefins with at least one Ziegler-Natta catalyst comprised of a component comprising at least one transition metal and a co-catalyst comprising at least one organometallic compound, and dinitrogen monoxide (N20), characterized in that the dinitrogen monoxide is present in an amount sufficient for the molecular weight distribution of the resulting polymer product is more reduced than would be obtained in the absence of dinitrogen monoxide.
15. 15. The process in accordance with the claim 14, characterized in that at least one transition metal is selected from Groups 4, 5, 6, 7, 8, 9 and 10 of the Periodic Table of the Elements, as defined herein.
16. 16. The process according to claim 15, characterized in that the transition metal is selected from the group consisting of titanium, zirconium, vanadium, iron, chromium, nickel and mixtures thereof. The process according to claim 14, characterized in that the metal of at least one organometallic compound is selected from Groups 1, 2, 11, 12, 13 and 14 of the Periodic Table of the Elements, as defined in I presented. 18. The process according to claim 17, characterized in that at least one organometallic compound has the formula XnER3-n, or mixtures thereof, wherein X is hydrogen, halogen, or mixtures of halogens, selected from fluorine, chlorine, bromine and iodine; • n varies from 0 to 2; E is an element of Group 13 of the Periodic Table of the Elements, and R is a hydrocarbon group, containing from 1 to 100 carbon atoms and from 0 to 10 oxygen atoms, attached to the Group 13 element by a hydrogen bond. carbon or oxygen. 19. The process in accordance with the claim 18, characterized in that the organometallic compound is selected from the group consisting of trialkylaluminums, dialkylaluminum halides and alkylaluminum sesquihalides. 20. The process in accordance with the claim 19, characterized in that the trialkylaluminum is selected from the group consisting of trimethylaluminum and triethylaluminum. 21. The process in accordance with the claim 14, characterized in that it additionally comprises the presence of at least one electron donor and at least one halogenated hydrocarbon. 22. The process according to claim 21, characterized in that the organometallic co-catalyst compound is trimethylaluminum, the electron donor is tetrahydrofuran and the halogenated hydrocarbon is chloroform. 23. The process according to claim 22, characterized in that the transition metal is titanium. 24. The process according to claim 14, characterized in that the dinitrogen monoxide is present in the polymerization medium in an amount ranging from about 1 ppm to about 10,000 ppm by volume. 25. The process according to claim 14, characterized in that the polymerization conditions are gas phase. 26. The process according to claim 14, characterized in that at least one olefin is ethylene.