GB1592472A - Preparation of hydrocarbon solutions of ethylene polymers - Google Patents

Description

(54) PREPARATION OF HYDROCARBON SOLUTIONS OF ETHYLENE POLYMERS (71) We, GULF OIL CORPORATION, a corporation organized and existing under the laws of the State of Delaware, United States of America, of P.O. Box 1166, Pittsburgh, Pennsylvania 15230, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the production of a hydrocarbon solution of an ethylene polymer.

British Patent 1,372,116 describes the preparation of fibre-like materials suitable for use in manufacture of sheet material. Such products are prepared from high molecular weight ethylene polymers and are referred to as fibrils. In the preparation of such fibrils the high molecular weight ethylene polymer, having an inherent viscosity of at least 3.5, is dissolved in a hydrocarbon at a temperature of at least about 1300C and is the starting material from which such fibrils are prepared.

The preparation of such ethylene polymer solutions presents technical problems. By reason of the very high molecular weight of the ethylene polymers employed in the process, such polymer solutions have high viscosities, even at low concentrations of the ethylene polymer. The high viscosities of such polymer solutions makes it difficult to provide adequate stirring to dissolve all of the ethylene polymer particles. This presents serious problems in that it also has been observed that the quality of the ultimately-obtained fibrils is adversely affected, if undissolved polymer solids are present in the ethylene polymer solution employed in the process.

The preparation of such ethylene polymer solutions is costly and energy-intensive in that very large quantities of the hydrocarbon solvent are required to dissolve the ethylene polymer. Typically, 96 parts by weight of hydrocarbon solvent are required to dissolve four parts by weight of the ethylene polymer. In the preparation of the fibrils, the heated polymer solution is subsequently cooled to precipitate the ethylene polymer therefrom. Upon recycling, the hydrocarbon then must be reheated.

In view of the considerations noted above, it would appear to be desirable to prepare a hot hydrocarbon solution of an ethylene polymer by polymerizing ethylene in the hydrocarbon solvent. Such an approach would reduce the total energy requirement for preparing the ultimately-desired fibrils, in that the ethylene polymer would not be cooled and reheated.

Moreover, the heat of polymerization of the ethylene would provide a substantial portion of the energy required to prepare the hot ethylene polymer solution. It has not been possible up to this time to directly prepare such hot solutions of ethylene polymers of high molecular weight by direct polymerization of ethylene in a hydrocarbon solvent. The difficulty that has been presented is the well-recognized fact that the molecular weight of an ethylene polymer decreases as the temperature employed in the polymerization is increased. With presently known catalysts, it has not been possible to prepare ethylene polymers having an inherent viscosity of at least 3.5 in a hydrocarbon solvent by carrying out the polymerization at temperatures above 100"C.

The present invention provides a method of preparing a hot hydrocarbon solution of an ethylene polymer, the said polymer having an intrinsic viscosity of at least 3.5, comprising contacting ethylene with a polymerisation initiator comprising a supported chemicallymodified transition metal component and an alkyl aluminium compound in a liquid hydrocarbon medium at a temperature of at least 1300C; said liquid hydrocarbon having a boiling range such that its vapour pressure at 1300C is not higher than 5 atmospheres, in which said supported component is prepared by a method comprising the sequential steps of: (a) suspending a finely divided organic thermoplastic or thermosetting polymer in an alkanol of from 1 to 4 carbon atoms having dissolved therein a magnesium compound which has the formula MgX2.n H20, in which X is an atom of chlorine, bromine, iodine or fluorine or a group selected from NO3, OCH3, OCOCH3 and OOCH, and n is not greater than 6, whereby the magnesium compound complexes with the alkanol; (b) evaporating the alkanol from the suspension of step (a) to deposit the complex on the polymer; (c) suspending the product of step (b) in a liquid hydrocarbon of boiling point above 1300C and adding thereto an aluminium alkyl compound selected from dialkyl aluminium hydrides, dialkyl aluminium halides and trialkyl aluminiums; and (d) adding a transitional metal chloride to the suspension of step (c); in which; the polymer employed in step (a) consists of particles having at least one dimension not exceeding 600 microns; the magnesium compound employed in step (a) constitutes from 5 to 25% by weight of the combined weight of the finely divided polymer and the magnesium compound; the quantity of the aluminium alkyl compound employed in step (c) is not in excess of the quantity that will react with the complex carried on the polymeric support; the transition metal chloride is titanium tetrachloride or vanadium oxytrichloride; the quantity of the said transition metal chloride employed in step (d) is at least molarly equivalent to the quantity of the aluminium alkyl compound employed in step (c).

Hot hydrocarbon solutions of an ethylene polymer, said polymer having an intrinsic viscosity of at least 3.5 are prepared by contacting ethylene with a special type of polymerisation initiator in a high boiling liquid hydrocarbon at a temperature of at least 1300C. The polymerisation initiator employed in the process is the reaction product of (1) an aluminium alkyl selected from dialkyl aluminium hydrides, dialkyl aluminium halides and trialkyl aluminiums, and, (2) a supported chemically-modified transition metal chloride product prepared by the above-defined multistep process.

The special polymerization initiators employed in the process of the present invention are described and claimed in our copending application 13038/77 (Serial No. 1586071).

The aluminum alkyl employed in the preparation of the special polymerization initiator is a dialkyl aluminum hydride, a dialkyl aluminum halide, or a trialkyl aluminum. Typical examples of suitable alkyl aluminums include tirethyl aluminum, triisobutyl aluminum, diethyl aluminum hydride, and diethyl aluminum chloride. Such alkyl aluminums should be of the purity and quality conventionally employed in the preparation of Ziegler-type polymerization initiators.

The supported, chemically-modified transition metal chloride product employed as the second component in the preparation of the special polymerization initiators of the invention is prepared by a multistep process.

In the first step of the preparation of the supported, chemically-modified, transition metal chloride compound, a finely-divided polymeric support is suspended in an alkanol solution of a particular class of magnesium compounds. The polymeric support may be either an organic thermosetting polymer, or preferably an organic thermoplastic polymer. The polymeric support should be in a finely-divided particulate form which has at least one dimension not exceeding 600 microns and preferably having one dimension falling within the range of about 1 to 200 microns. The polymeric support may be of any desired shape such as spheres, rods, or cylinders. Suitable polymeric materials include poly (triallyisocyanurate), polyethylene, polypropylene, poly (3-methylbutene), poly (4-methylpentene), polyamides, polyesters, polyacrylamides, polyacrylonitriles, polycarbonates, and cellulose. While essentially any polymer not soluble in an alkanol can be employed for this purpose, it is preferred to employ an ethylene polymer, particularly an ethylene polymer having an inherent viscosity of at least 3.5.

The alkanol solution of a magnesium compound employed in the treatment of the polymeric support in the first step of the preparation is an alkanol solution of a magnesium compound having the structure: MgX2nH20 where X is an anion which imparts solubility of at least 1% in a lower alkanol (C4 or less), and n is not greater than 6, X being Cl, F, Br, I, NO3, OCOCH3, or OCOH.

Magnesium compounds found to be particularly suitable in the practice of the invention include magnesium chloride, magnesium methoxide, magnesium nitrate, and magnesium acetate. The alkanol in which the magnesium compound will be dissolved is an alcohol containing 1-4 carbon atoms such as methanol, isopropanol and butanol. The alkanol solution should preferably contain a relatively high concentration of the magnesium compound, e.g., desirably at least 5% by weight, by reason of the fact that the alkanol subsequently will be removed from the process by vaporization.

In carrying out the first step of the process, the polymeric support may be suspended in a sufficient quantity of the alkanol solution of the magnesium compound so that the magnesium compound contained therein will constitute 1-60 weight % and preferably 5-25 weight % of the combined weight of the polymeric support and the magnesium compound.

The polymeric carrier should be stirred with the alkanol solution of the magnesium compound to the extent required to thoroughly wet and impregnate the polymeric carrier with the alkanol solution.

In the second step of the process, the alkanol is evaporafrotlie suspension of the polymeric carrier in the alkanol solution so as to deposit the magnesium compound uniformly over the polymeric carrier. The magnesium compound is deposited on the carrier in the form of a complex with the alkanol. The precise structure of the complex has not been established, but it is believed to contain 1-4 mols of alkanol per mol of magnesium compound. It is observed, however, that the magnesium compound-alkanol complex is in a highly active state particularly suitable for use in the preparation of the chemically-modified, transition metal chloride compounds in the subsequent steps of the process. To the extent that is practically feasible, all of the alkanol, except that complexed with the magnesium compound, should be removed as any excess alkanol will react with and consume the aluminum alkyl compound employed in the next step of the process.

The alkanol is removed by simply evaporating the alkanol from the suspension of the polymeric carrier in the alkanol solution. The or evaporation is preferably carried out under reduced pressure. Care should be excersied to remove the alkanol solution at moderate temperatures not exceeding 1500C and preferably not exceeding 75"C. Frequently the evaporation of the alkanol can be accelerated by passing an inert sweep gas such as nitrogen or argon over the surface of the alkanol solution. When a sweep gas is employed, it should be free of water, oxygen and other compounds recognized as having a deleterious effect upon Ziegler-type catalysts.

While a simple evaporation as described above can be used to remove the alkanol, somewhat better results are obtained if at least the final portions of the alkanol are removed by codistillation with an inert hydrocarbon. In this procedure, after a portion of the alkanol is removed as described previously, a liquid hydrocarbon such as heptane, will be added to the reaction vessel. The hydrocarbon then will be distilled from the system under atmospheric or preferably reduced pressure. So long as any free, uncomplexed alkanol remains in the system, the distillate being removed from the system will be a mixture of the hydrocarbon and alkanol. When the final traces of the uncomplexed alkanol are removed from the system, the vapor temperature of the distillate will rise to the boiling point of the hydrocarbon at the prevailing pressure employed in the distillation. Thus, the observed boiling point of the distillate serves as a criterion for determining when the removal of the alkanol is completed.

The hydrocarbon employed for removal of the alkanol may be of any of the hydrocarbon types conventionally employed in the preparation of Ziegler-type Catalysts. Predominantly aliphatic hydrocarbons such as heptanes and cotanes are preferred. The hydrocarbon employed should be purified in a manner so as to remove therefrom moisture and other materials known to have a deleterious effect upon the activity of Ziegler-type catalysts.

In the next step of the process, the polymeric carrier with the magnesium compound deposited thereon is suspended in the liquid hydrocarbon to form a slurry. Normally, such a slurry already will have been prepared, particularly where the final traces of the alkanol are removed by codistillation as described above. A suitable aluminum alkyl compound such as diethyl aluminum chloride is then added to the slurry. The aluminum alkyl reacts with the magnesium compound-alkanol complex carried on the polymeric support. The mechanism by which the two components react and the structure of the resulting reaction product have not been fully established. The evidence that a chemical reaction takes place is that a gas, possibly an alkane, is formed when the aluminum alkyl is added to the reaction mixture. The reaction product formed in this step of the process is firmly bonded to the polymeric support.

The aluminum alkyl employed in the step of the process described immediately above may be a dialkyl halide, a dialkyl aluminum hydride, or a trialkyl aluminum, with the dialkyl aluminum halides being preferred. Typical examples of suitable alkyl aluminums include triethyl aluminum, triisobutyl aluminum, diethyl aluminum hydride and diethyl aluminum chloride.

The aluminum alkyl should preferably be employed in a quantity such that all of the aluminum alkyl added to the reaction mixture will react with the magnesium compoundalkanol complex carried on the polymeric support and so that the reaction system, after completion of this step of the process, contains little or no unreacted aluminum alkyl in the hydrocarbon phase of the reaction mixture. If an excess of the aluminum alkyl is employed, the remaining free, unreacted aluminum alkyl will react with the transition metal chloride employed in the next step of the process to form a more conventional Ziegler-type catalyst as a coproduct. The presence of such conventional Ziegler-type catalyst will tend to reduce the advantages obtained with the present invention.

The precise quantity of the aluminum alkyl to be employed will be somewhat dependent upon the completeness with which uncomplexed alkanol is removed from earlier steps of the process. This results from the fact that any free, uncomplexed alkanol present in the reaction system will react with the aluminum alkyl compound. Ordinarily, the applicant prefers to employ 0.1-2.0 mols and preferably 0.25-0.5 mol of the aluminum alkyl for each mol of the magnesium compound present in the reaction system. If desired or believed to be necessary, the presence of unreacted aluminum alkyl can be determined either qualitatively or quantitively by removing a sample from the reaction system; filtering the solids from the slurry and measuring the concentration (if any) of the aluminum alkyl present in the hydrocarbon filtrate. Analytical methods for measuring the concentration of aluminum alkyls in hydrocarbons are known in the art.

The use of less than the stoichiometrically required quantity of the alkyl aluminum has no serious effect upon the quality of the ultimate product. If the supported reaction product contains unreacted magnesium compound, the unreacted magnesium compound will react with the transition metal chloride in the next step of the process to provide a reaction product which will be converted into a slightly different polymerization catalyst in subsequent processing steps.

In the next step of the process, a transition metal chloride of the group consisting of titanium tetrachloride and vanadium oxytrichloride is added to the reaction mixture of the previous step, which contains as the active reactant the reaction product formed between the supported magnesium compound-alkanol complex and the aluminum alkyl. The transition metal chloride reacts with the previously prepared reaction product and is reduced to a lower valence state. This supported, chemically-modified, transisition metal chloride compound is the ultimately desired catalyst component and is insoluble in the hydrocarbon reaction medium. The structure of the product has not been established, but probably is complex.

Virtually all of the titanium becomes bound to the polymeric support, probably by reason of formation of a chemical or physical complex with the magnesium compound.

In this step of the process, from 1 to 2 mols of the transition metal chloride will normally be employed for each mol of aluminum alkyl employed in the previous step of the process. Not more than 2 mols of the transition metal chloride compound can be reduced by 1 mol of the previously-prepared reaction product, and any quantity of transition metal chloride added in excess of this quantity serves principally to drive the reaction to completion in the shortest possible period of time.

As the supported, chemically-modified, transition metal chloride product is insoluble in the hydrocarbon medium, it can be recovered by filtration and stored for future use if desired.

If the product is recovered in this manner for storage, the hydrocarbon filtrate containing unconsumed transisition metal chloride can be recovered and reused in the subsequent production of additional product. The recovered solid reaction product should preferably be washed with hydrocarbon to free it from any occluded unreacted transition metal chloride compound.

It is frequently desirable, however, to use the supported, chemically-modified, transition metal chloride product shortly after it is prepared. In such situations, it is usually desirable to employ the product in the slurry in which it is prepared. In such situations, it is desirable to remove any unreacted transition metal chloride from the system. Such removal can be effected by simply distilling the hydrocarbon from the slurry at either atmospheric or reduced pressure. The unreacted transition metal chloride codistills with the hydrocarbon. The distillation is continued until the distillate gives a negative test for chloride.

To prepare the special polymerization initiator used for the polymerization of ethylene; the supported, chemically-modified transition metal chloride product is reacted with an aluminum alkyl compound in a hydrocarbon medium, preferably the same hydrocarbon that will be used in the subsequent polymerization. The reaction is carried out in a manner generally equivalent to that employed to prepare more conventional Ziegler-type catalysts.

The supported, chemically-modified transition metal chloride product is employed in the same molar proportions as conventional transisition metal chlorides are employed in their reactions with aluminum alkyls. Typically, the two components are employed in proportions to provide an Al/Ti atomic ratio of from 0.5 - 10:1, or preferably 1.0 - 5.0:1. While dialkyl aluminum hydrides and dialkyl aluminum halides can be employed for this purpose, the trialkyl aluminums and particularly triethyl aluminum and triisobutyl aluminum are the preferred aluminum alkyls to be employed in the preparation of such polymerization initiators.

The special polymerization initiators prepared as described above have a number of features which make them particularly effective and desirable for use in the polymerization of ethylene by the method of the present invention. Initially, it will be noted that the magnesium compound, the transition metal compound, and the aluminum alkyl compounds may be employed in the precise quantities (The transition metal chloride may be employed in slight excess of that stoichiometrically required for reasons previously discussed.) required in the final polymerisation initiator. Thus, no expensive compounds are employed in excess of their actual need. The polymerization initiators have high productivity rates and provide low production costs for the ethylene polymers produced. In addition, by reason of the high catalyst productivities, the finished polymers contain very low concentrations of metallic catalyst residues so that, for most purposes, they need not be removed from the polymers. Yet another advantage of the polymerization initiators is that they have a specific gravity substantially the same as the hydrocarbon solvent employed in the ethylene polymerization process. Thus, a uniform dispersion of the polymerization catalyst in the polymerization solvent is more easily obtained than is the case with more conventional Ziegler-type catalysts.

The polymerization of ethylene is carried out by suspending the special polymerization initiator in an appropriate high-boiling liquid hydrzcarbon, heating the hydrocarbon to the desired reaction temperature, and feeding polymerization-grade ethylene to the reaction zone. If the polymerization is carried out batchwise, the polymerization is continued until the concentration of the ethylene polymer reaches the desired level. Ordinarily, the polymerization is carried to the point at which the ethylene polymer reaches a concentration of at least 3 weight %, and preferably 4-7 weight %. Ordinarily, the polymerization cannot be carried beyond the point at which the ethylene polymer constitutes more than about 7 weight % of the reaction mixture. This process limitation is set by the practical consideration that higher solids solutions are too viscous for easy handling; the high viscosity resulting from the very high molecular weight of the ethylene polymer produced in the process. It is preferred to carry out the polymerization by a continuous process with ethylene, the special polymerization initiator, and the hydrocarbon being continuously fed to the reaction zone with a polymer solution being continuously withdrawn from the reaction zone. The feed rate and the withdrawal rate are selected so that the residence time of ethylene in the reaction zone is such that the polymer solution being withdrawn from the reactor has an ethylene polymer content within the desired range previously noted.

The hydrocarbon employed in the process should have a boiling point range such that its vapor pressure at 1300C is not higher than 5 atmospheres and preferably less than 2 atmospheres. It is preferred to employ a predominantly aliphatic hydrocarbon mixture such as kerosene, but the hydrocarbon employed may contain modest percentages of aromatic and cycloaliphatic hydrocarbons without adversely affecting the process. The hydrocarbon employed should be carefully dried, as it is well-known that water acts to poison or deactivate Ziegler-type polymerization initiators. Depending upon the source of the hydrocarbon, additional treatments may be required to remove organic compounds containing nitrogen, oxygen, or sulfur atoms, as it is known that such compounds also tend to deactivate Zieglertype polymerization initiators.

The polymerization initiator should be employed in the process at a concentration within the range of 0.01 to 4 grams per liter of reactor volume. The polymerization will be carried out at a temperature of at least 1 300C, and no advantages are obtained by carrying out the polymerization at a temperature above 150"C. The polymerization normally will be carried out at a superatomospheric pressure of at least 2 and preferably at least 30 atmospheres to maintain a sufficient concentration of ethylene in the reaction medium to provide reasonable rates of polymerization.

The polymerization temperature, the concentration of polymerization initiator, and concentration of ethylene (controlled by the ethylene partial pressure) are maintained in appropriate balance to produce an ethylene polymer having inherent viscosity of at least 3.5.

Methods for determining the inherent viscosities of ethylene polymers are set forth in the art, e.g., see British Patent 1,372,116. The most unexpected and unique characteristic of the process of the invention is that ethylene polymers of such high inherent viscosity can be produced at the high temperatures employed in this process. It is well recognized in the art that increasing the polymerization temperature in a process ordinarily reduces the molecular weight and the inherent viscosity of the ethylene polymers produced. Moreover, most Ziegler-type catalysts are deactivated at the temperature employed in the process of the present invention.

The process of the invention provides very high yields of polymer based on the polymerization initiator employed. Typically the process provides minimum yields of the order of about 1200 grams of polymer per gram of titanium per hour. As a result of the high yield, the polymers produced contain a sufficiently low level of catalyst residues that no post polymerization treatment is required to remove such residues.

While the process of the invention is designed principally to produce homopolymers of ethylene, it is also possible to produce copolymers of ethylene with C3 and higher monoolefins, such as propylene and butylene. It is preferred, however, to limit the concentration of any higher olefin comonomer in the monomer mixture to a level not more than about 25 mol % of the ethylene employed in the process. Minor concentrations of hydrogen can be employed in the process to modify the molecular weight of the ethylene polymers produced in the process.

The following examples are set forth to illustrate more clearly the principle and practice of this invention to those skilled in the art.

Examples 1-3 Three polymerization initiators were prepared for use in the polymerization of ethylene by the process of this invention.

Part A Preparation or support ofSuppo rt A 4-liter reaction vessel fitted with a stirrer, a reflux condenser, a dropping funnel, and heating and cooling means; was charged with methanolic solution of magnesium chloride prepared by dissolving 75 grams of magnesium chloride in 1 liter of methanol. Six hundred seventy grams of a finely-divided powder of high density polyethylene having an average particle diameter of less than 40 microns was slurried in the methanolic solution of magnesium chloride. The slurry was heated to a temperature of 55"C over a period of 30 minutes and stirring at this temperature was continued for another 30 minutes. This pressure then was reduced to about 10 mm of Hg to remove methanol from the system. Heating was continued for two hours under these conditions to assure removal of all methanol which did not form a complex with the magnesium chloride deposited on the polyethylene support. The powder was removed from the reaction vessel and ground to pass through a 40-mesh U.S. screen.

Part B Preparation ofChemically-Modified Transition Metal Chloride Compound The magnesium chloride treated polyethylene powder prepared as described above in the amount of 200 grams, an appropriate quantity of diethyl aluminum chloride, was charged to a 4-liter reactor equipped as described above. This reaction mixture was stirred for one hour while maintaining the temperature at 25"C. Evolution of a gas was noted. At this point in the reaction, it is believed that the charged diethyl aluminum chloride has been chemically bonded to the polymeric support or one of the chemicals carried thereon. The reaction mixture then was heated to 800C and an appropriate quantity of TiCl4 was added to the reaction mixture from the dropping funnel over a period of one hour. The reaction mixture then was stirred for an additional 16-20 hours, while maintaining the temperature at 800C to assure complete reaction between the TiCl4 and the components carried on the support. Prior to the addition of the Tic4, the solids present in the slurry were light yellow in color, but the color changed to a purple-red shortly after the addition of the TiCl4. The liquid present in the slurry was removed by decantation, and the solids were washed with several aliquots of heptane until the heptane gave no test for the presence of chlorides. The solids then were recovered and dried under vacuum at ambient temperature.

Part C Preparation ofPolymerization Initiator Two parts of a product prepared in Part B were suspended in 500 parts of heptane.

Thirty-six parts of triethyl aluminum (added as a 25% solution heptane) then were added over a period of 10 minutes with stirring. This dispersion of polymerization initiator was stored under rigorously anhydrous conditions for use in the polymerization of ethylene.

In all of the procedures described above, care was exercised to carry out all reactions under rigorously anhydrous conditions. All reactants employed were purified grades and contained no identifiable concentrations of water or reactive hydrogen compounds known to have a deleterious effect upon Ziegler-type polymerization reactions.

In Table I, Section A shows the proportions of re

Table I Section A Preparation of Thermically-Modifed Transition Metal Chloride Compound Example Catalyst Heptane DEAC(I) TiC14 No. Support, gms ml gms gms 1 200 400 72 663 2 200 300 36 345 3 200 300 36 345 Section B Catalyst Analysis Total Example Magnesium Aluminum Chlorine Titanium Inorganic No. wt% wt% wt% wt% wt% 1 1.7 0.3 9.7 2.0 13.7 2 2.0 4.1 15.9 2.6 24.6 3 1.7 2.7 15.1 2.8 22.3 Example 4 Sixty-seven grams of particulate high density polyethylene, having a particle size less than 40 microns, was suspended in 100 ml of methanol containing 7.5 grams of dissolved magnesium chloride in a 1-liter reaction vessel equipped as described in Example 1. Two hundred fifty ml of heptane then was added to the reactor and the reaction mixture was heated to take off an overhead fraction having a boiling point of 59-60 C. After about 175 ml of distillate was recovered, the temperature of the distillate rose to the atmospheric boiling point of heptane.

The reactor was cooled to room temperature and 70 ml of a heptane solution containing 12.7 grams of diethyl aluminum chloride was added to the reactor dropwise over a period of 15 minutes. A colorless gas was liberated and vented during this addition. Thereafter, the reaction mixture was heted to 80 C and 138 grams of TiCl4 was added dropwise to the reaction system. At the start of the addition of TiCl4 the reaction mixture was a straw yellow in color, but about 15 minutes after the addition of the TiCl4 had been completed, the solids in the reaction system changed to a purple-red color. Heating was continued with stirring for another 16 hours. Thereafter the reactor was cooled and the catalyst solids were recovered by filtration. The recovered solids were washed with aliquots of dry heptane until the wash heptane gave a negative test for soluble chlorides.

A total of 0.2 gram of catalyst component described in the paragraph above was suspended in 50 ml of heptane having dissolved therein 0.36 gram of triethyl aluminum.

EXAMPLES A five-gallon stirred reactor was charged with 12.3 kg of kerosene (Gulfsol 20) and a slurry of 2 grams of the catalyst of Example 2 in 40 ml of heptane. The reactor was heated to a temperature of 145 C over a period of about one hour with a bleed in the reactor being opened periodically to vent the minor amount of heptane charged to the reactor. Polymerization grade ethylene then was fed to the reactor until the reactor pressure increased to 200 psig. Controls then were set to feed the ethylene to the reactor at a rate of 0.3 pound per hour.

Ethylene gas was fed to the reactor over a period of 3.5 hours. After the feed of ethylene was cut off, stirring was continued for an additional hour at 1450C to convert the remaining ethylene to polymer. The final reaction product consisted of a hydrocarbon solution containing 3 weight % of ethylene polymer.

The polymer solution was cooled to room temperature to precipitate the ethylene polymer therefrom. Ther recovered polymer solids were washed with several aliquots of heptnae and dried overnight in a vacuum oven at a temperature of about 50 C. The inherent viscosity of the recovered polymer, measured by the method as set forth in British patent 1,372,116, was greater than 3.5. The polymer's high load melt index, determined by ASTM 1238-70 (Condition F), was less than 0.02.

EXAMPLE 6 Example 5 was repeated and the hot polymer solution was employed directly to prepare fibrils by the method of British Patent 1,372,116. The recovered fibrils were of better quality than a control lot of fibrils prepared from a 3% solution of ethylene polymer having a substantially identical inherent viscosity which was dissolved in the same kerosene employed in Example 5.

As the two polymers employed had substantially identical inherent viscosities and were employed in the same concentration in the same kerosene solvent, it is believed that the improved quality of the fibrils resulted by reason of the fact that, in the preparation of the control hydrocarbon solution, monor quantities of the ethylene polymer were not completely dissolved and gave rise to imperfections in the final fibrils.

EXAMPLES 7-9 Three additional solutions of high molecular weight ethylene polymer were prepared by the method described in Example 5, except that the polymerization initiator employed was, respectively, the polymerization initiator prepared in Examples 1, 3 and 4. In each instance, the polymerization ran smoothly and provided an ethylene polymer having an inherent viscosity in excess of 3.5, as determined by the method set forth in British patent 1,372,116.

Claims (11)

WHAT WE CLAIM IS:

1. A process for preparing a hot hydrocarbon solution of an ethylene polymer, the said polymer having an intrinsic viscosity of at least 3.5, comprising contacting ethylene with a polymerisation initiator comprising a supported chemically-modified transition metal component and an aluminium alkyl compound initiator in a liquid hydrocarbon medium at a temperature of at least 1 300C; said liquid hydrocarbon having a boiling point range such that its vapour pressure at 1300C is not higher than 5 atmospheres, in which said supported component is prepared by a method comprising the sequential steps of: (a) suspending a finely divided organic thermoplastic or thermosetting polymer in an alkanol of from 1 to 4 carbon atoms having dissolved therein a magnesium compound which has the formula MgX2.n H2O, in which Xis an atom of chlorine, bromine, iodine or fluorine or a group selected from NO3, OCH3, OCOCH3, and OCOH, and n is not greater than 6, whereby the magnesium compound complexes with the alkanol; (b) evaporating the alkanol from the suspension of step (a) to deposit the complex on the surface of the polymer; (c) suspending the product of the step (b) in a liquid hydrocarbon and adding thereto an aluminium alkyl compound selected from dialkyl aluminium hydrides, dialkyl aluminium halides and trialkyl aluminiums; and (d) adding a transition metal chloride compound to the suspension of step (c); in which the polymer employed in step (a) consists of the particles having at least one dimension not exceeding 600 microns; the magnesium compound employed in step (a) constitutes 5-25 weight % of the combined weight of the finely-divided polymer and the magnesium compound; the quantity of the aluminium alkyl employed in step (c) is not in excess of the quantity that will react with the magnesium compound-alkanol complex carried on the polymeric support; the transition metal chloride employed in step (d) is titanium tetrachloride or vanadium oxytrichloride; and the quantity of the transition metal chloride compound employed in step (d) is at least molarly equivalent to the quantity of the aluminium alkyl compound employed in step (c).

2. A process according to claim 1, in which the alkanol is evaporated in step (d) by distillation directly from the suspension.

3. A process according to claim 1, in which a hydrocarbon is added to the suspension formed in step (a) and the alkanol is vaporized in step (b) by co-distillation with the hydrocarbon.

4. A process according to any preceding claim, in which said magnesium compound is magnesium chloride, magnesium methoxide, magnesium acetate or magnesium nitrate.

5. A process according to any preceding claim, in which said support is an organic thermoplastic polymer.

6. A process of claim 5 in which the organic thermoplastic polymer is an ethylene polymer.

7. A process according to any preceding claim in which the ethylene is contacted with the polymerization initiator at a temperature of l450C.

8. A process according to any preceding claim, in which the liquid hydrocarbon medium is kerosene.

9. A process according to claim 1, for the preparation of a hydrocarbon solution of an ethylene polymer according to any one of Examples 5 and 7 to 9 hereinbefore.

10. A process according to claim 1, substantially as hereinbefore described.

11. A hot hydrocarbon solution of an ethylene polymer whenever prepared by the process claimed in any one of claims 1 to 10 EITZPATRICKS