MXPA06007871A - Ultra high molecular weight polyethylene fractions having narrow molecular weight distributions and methods of making and using the same - Google Patents

Abstract

Polymer fractions such as polyethylene fractions can be produced that have a PDT less than 2.3 and a M,âÇ×greater than 1,000,000 g/mol, 3,000,000 g/mol, or 6,000,000 g/mol. Such polyethylene fractions are separated from a UHMWPE parent polymer by first dissolving the parent polymer in a relatively good solvent. The conditions employed for such dissolution are selected to reduce the degradation of the parent polymer. The resulting parent solution is transported into a fractionation column in which a support is disposed. The fractionation column is thereafter operated at conditions effective to form a precipitate on the support comprising the desired polyethylene fraction. The polyethylene fraction may then be recovered from the fractionation column by repeatedly displacing a solvent/non-solvent mixture into the column to dissolve the polyethylene fraction. The relative concentrations of the solvent and the non-solvent are based on a solvent gradient profile of the polyethylene parent polymer.

Description

FRACTIONS D? POLOXYTI ENO MOLECULAR WEIGHT ULTRA HIGH THEY HAVE DISTRIBUTIONS OF SCARCE MOLECULAR WEIGHT AND METHODS TO OBTAIN AND USE THE SAME FIELD OF THE INVENTION The present invention relates to the characterization and production of polymer, and more particularly, to produce ultra high weight polyethylene fractions (ÜHMWPE) having sparse molecular weight distributions for use as reference standards in analytical tools such as a tool of permeation chromatography on gei.

BACKGROUND OF THE INVENTION There is a continuing need to develop and optimize polymeric materials for a wide range of applications. Several polymer characterization techniques have been developed to determine the properties and compositions of said polymeric materials. For example, gel permeation chromatography (GPC) is a type of size exclusion chromatography (SEC) that is commonly used to evaluate the molecular mass and molecular weight distributions of polymers. Differential scanning calorimetry (DSC) is a technique used to study thermal transitions such as the transition of glass that a polymer experiences as its temperature changes. Many other techniques known in the art exist to evaluate the performance of polymeric materials such as rheology measurement techniques and light scattering techniques. Reference standards are required to calibrate and test the instruments used for such polymer characterization techniques. The most useful reference standards for calibrating instruments such as gel permeation chromatographs have relatively low molecular weight distributions. Unfortunately, it has been found that minimizing the molecular weight distribution of polyethylene, which is one of the most widely used polymers, is very difficult. The lack of good reference standards of polyethylene limits the ability of researchers to determine exactly the properties of polymeric materials. Therefore, it is necessary to develop polymer fractions, for example, polyolefin fractions, and more specifically, polyethylene fractions, which would serve as good reference standards for polymer characterization instruments. In particular, it is desired to develop the polyethylene fractions that have the smallest molecular weight distributions. Fractions or compositions of the polymer can be produced, and in particular the polyethylene fractions, which have a polydispersity index (PDI) less than 2.3 and a weight average molecular weight (Mw) ~ greater than 1,000,000 g / mol, 3,000,000 g / mol, or 6,000,000 g / mol. Such fractions or compositions may have an Mw in the range of 1,000,000 to 100,000,000; 1,000,000 to 50,000,000 or 1,000,000 to 10,000,000. Such polyethylene fractions are separated from a primary polymer of ultra high molecular weight polyethylene (UHMWPE) by first dissolving the primary polymer in a relatively good solvent to form a primary polyethylene solution. The conditions used for said solution to reduce the degradation of the primary polymer UHMWPE are selected. In particular, the primary polymer UHMWPE and the solvent can be stirred at a speed of 55 rpm at 65 rpm while heating the mixture to a temperature with a temperature range of the melting point of the primary polymer UHMWPE at 30 ° C above its Melting point temperature. This stirring and heating of the mixture can be developed for an effective period to dissolve substantially all of the primary UHMWPE polymer in the solvent. After this dissolution step, the resulting primary solution is then transported to a fractionation column in which a support is placed, for example, glass spherules. The fractionation column can be scaled upwards in size to produce relatively large amounts of polyethylene fractions.

SUMMARY D? THE INVENTION Subsequently, the fractionation column is operated under effective conditions to form a precipitate in the support comprising one or more desired polyethylene fractions. That is, the temperature of the column is reduced to a temperature below 40 ° C at a rate from 1 ° C / hr to 0.5 ° C / hr. The polyethylene fractions can then be recovered from the fractionation column by placing a mixture of non-solvent / recovery solvent in the column. The relative concentrations of the solvent and the non-solvent are based on a solvent gradient profile of the polyethylene primary polymer. The temperature of the column is raised to a temperature between the melting point of the primary polymer UHMWPE at 30 ° C above its melting point, thereby heating the non-solvent / solvent mixture. The fractionation column is maintained at that temperature while allowing a part of the polyethylene primary polymer to dissolve in the non-solvent / solvent mixture. Subsequently, the mixture in the fractionation column can be displaced and combined with a precipitation agent to recover the polyethylene fraction dissolved therein. The above steps related to the recovery of the polyethylene fractions may be repeated until the non-solvent / solvent mixture leaving the fractionation column does not substantially contain the polyethylene precipitate.

BRIEF DESCRIPTION OF THE FIGURES The invention, together with the additional advantages thereof, can be better understood by referring to the following description, which is considered together with the attached figures in which: Figure 1 illustrates a lateral flat view of a system modality fractionation used to produce a UHMWPE fraction that has a relatively low molecular weight distribution, where the fractionation system is shown as it appears during loading of a primary polyethylene solution.

Figure 2 illustrates a side planar view of the fractionation system as it appears during the recovery of the UHMWPE fraction from the fractionation column. Figure 3 illustrates a solvent gradient curve used to produce the UHMWPE fraction, where the logarithm of Mw of the UHMWPE fraction is determined as a function of the amount of TCB solvent in a non-solvent / solvent mixture used to recover the fraction UHMWPE. Figure 4 illustrates a solvent gradient curve used to produce a UHMWPE fraction, wherein the total amount of UHMWPE produced is determined as a function of the amount of TCB solvent in a non-solvent / solvent mixture used to recover the UHMWPE fraction. .

DETAILED DESCRIPTION OF THE INVENTION According to an aspect of the invention, a polymer fraction or composition, for example, a polyolefin fraction, and more specifically, polyethylene fraction suitable for use as a reference standard having a lower polydispersity index (PDI) to 2.3, alternatively less than 2.2, alternatively less than 2.1, alternatively less than 2.0, alternatively less than 1.9, alternatively less than 1.8, alternatively less than 1.7, alternatively less than 1.6, or alternatively less than 1.5. In one aspect, a polyethylene fraction suitable for use as a reference standard has a polydispersity index (PDI) LESS THAN 2. Therefore, it will be understood that the description of the present invention can be applied to a variety of crystallines or polymers. Semi-crystalline (e.g., primary polymers), most of the description is focused on the embodiments to produce one or more polymer fractions, e.g., polyolefins or polyethylene. In order to explain it better, the invention will be described for polyethylene, however, any polymer or polyolefin can be tried. As used in the present invention, the term "polyethylene fraction" refers to an isolated fraction or "cut" of a polyethylene primary polymer - which is a part, as defined by PDI and molecular weight, of polyethylene polymer that is less than that polymer primary polyethylene complete. The PDI is an amplitude index of the molecular weight distribution (MWD) of a polymer and is equivalent to the molecular weight of the average polymer weight divided by the molecular weight of the average polymer number (ie, Mw / Mn). In one aspect, the polyethylene fraction is a fraction of ultra high molecular weight polyethylene (UHMWPE) having a molecular weight greater than 1,000,000 g / mol, alternatively higher than 3,000,000 g / mol, or alternatively higher than 6,000,000 g / mol. In one embodiment, one or more UHMWPE fractions of a polyethylene primary polymer can be produced using the fractionation system shown in Figures 1 and 2. As shown in Figure 1, the fractionation system includes a fractionation column 8 having a cooling / heating jacket 10 and a cooling / heating bath 12. In one embodiment, the fractionation column 8 may be a column that is scaled in an upward direction, for example, a cylindrical column. As used in the present invention, "climbing up" refers to the size of the column that is sufficient to produce more than 1 gram of one or more UHMWPE fractions, alternatively greater than 2 grams of one or more UHMWPE fractions. , alternatively greater than 3 grams of one or more UHMWPE fractions. The fractionation system also includes a jacketed dissolution vessel 14 and a corresponding heating bath 16, a charging pump 18, an embossed vessel 20, a solvent cooling unit 22, a solvent vessel 24. and a pump fractionation 26. The cooling unit 22 contains a means for cooling the solvent such as the coil refrigerator. The fractionation of a primary polyethylene polymer into one or more UHMWPE fractions first comprises charging the primary polymer into the fractionation system. A mixture of a primary polymer UHMWPE and a solvent is placed in the dissolution vessel 14 to dissolve the primary polymer UHMWPE in the solvent. In one embodiment, the amount of primary polymer UHMWPE contained in the mixture is in the range of 7.5 grams / liter of the solvent to 25 grams / liter of the solvent. As used in the present invention, the primary polymer UHMWPE is defined as a crystalline or semi-crystalline polyethylene which may be a homopolymer or copolymer, may be linear or branched, and has an Mw greater than 1,000,000 g / mol. In a further embodiment described in the present invention, the primary polymer is a UHMWPE homopolymer. The UHMWPE homopolymer, which has a PDI greater than 2, serves as a "primary" of one or more UHMWPE fractions that have a PDI of less than 2. An example of an appropriate linear UHMWPE homopolymer to be used as the primary of the UHMWPE fractions is polyethylene Natta Ziegler GÜR4150, which is commercially available from Ticona LLC: Physical properties are listed in Table 1.

TABLE 1 The solvent in which the polyethylene Natta Ziegler GUR4150 desirably dissolves has a boiling point temperature higher than the melting point temperature of the UHMWPE homopolymer. For UHMWPE having a density in the range of 0.9564 to 0.9620 g / cc, a melting point temperature in the range of 128 to 132 ° C, and a crystallinity in the range of 83 to 85%, examples of suitable solvents include hydrocarbons recovered from the derivatization of petroleum, halo derivatives of said hydrocarbons, or combinations thereof. The solvent may comprise, for example, trichlorobenzene (TCB).

To initiate the dissolution of the UHMWPE homopolymer in the solvent, a stirring paddle or paddle is placed in the dissolution vessel and connected to a stirring motor (not shown). The lid of the solution vessel 14 is closed, and the nitrogen is allowed to flow through the lid in the vessel 14 through a nitrogen line. The conditions used to dissolve the UHMWPE homopolymer in the solvent are selected to reduce the degree of degradation of the UHMWPE homopolymer during dissolution. Otherwise, a particular UHMWPE fraction that is to be isolated during dissolution could be destroyed. The UHMWPE solvent / homopolymer mixture can be heated to a temperature in the range of the melting point temperature of the UHMWPE homopolymer to less than the boiling point of the solvent, for example, at 30 ° C above the melting point temperature of the solvent. UHMWPE homopolymer. This heating of the mixture can be achieved by circulating a known heat transfer fluid such as ethylene glycol in the heating bath 16 through the jacket of the dissolution vessel 14. The heating bath 16 can be heated to the target temperature using, for example, a heat exchanger. The mixture is also stirred with the stirring blade at a speed of 55 rpm at 65 rpm while it is heating. The heating and stirring of the mixture can be developed for an effective period to dissolve substantially all of the UHMWPE homopolymer in the solvent. In one modality, this period can be, for example, at least 4 days. The operation of the fractionation system shown in Figure 1 then includes preheating the fractionation system and loading the embossed container 20 with a solvent, for example, by placing a solvent contained in the solvent container 24 into the embossed container 20 operating the fractionation pump. 26 for pumping solvent towards the solution vessel 14. This solvent is the same as that used in the UHMWPE primary solution and is heated to a temperature ranging from the melting point temperature of the UHMWPE to 160 ° C. In one embodiment, the solvent is heated above the melting point temperature, for example, by heating the solvent in a storage container or by heating the solvent during circulation with heat exchangers or other heating means such as heat straps placed along the circulation path. More specifically, the solvent is pumped into the solvent container 24 through the fractionation pump 26 through a suction line 50 and subsequently through lines 54 and 40 to the fractionation column 8. Subsequently, it is pumped. through fractionation column 8 to embossed vessel 20 through lines 28 and 32. Valves 52, 56 and 34 are opened in lines 50, 54 and 32, respectively, to allow passage of the solvent while valves 46 and 48 on line 44 and valve 30 on line 28 are closed. Fractionation pump 26 is operated until a desired amount of solvent is transferred into embossed container 20, and subsequently closed. In one embodiment, the solvent is further pumped through line 28 into the dissolution vessel 14 through the reverse charge pump., in this way, the rest of the fractionation system is heated and the existing air is removed. The embossed container 20, the fractionation pump 26, the column 8, and the loading pump 18, and thereby, heat the lines existing therebetween by means of the solvent at a temperature above the melting point temperature of the UHMWPE. In one embodiment, the transfer lines (eg, line 28) can be additionally or alternatively heated to charge the polymer from the dissolution vessel 14 to the column 8 by other heating means, for example, through a heating jacket or heating tapes. During loading, the fractionation column 8 is also operated at a temperature comprising the melting point temperature of the UHMWPE at 160 ° C, for example, 30 ° C above the melting point temperature. The fractionation column 8 can also be preheated by circulating a heat transfer fluid such as ethylene glycol from the cooling / heating bath 12, which is maintained at the desired temperature, through the jacket 10 of the column 8. Preheat the heating system. Fractionation helps prevent the cooling of the UHMWPE primary solution, which could result in unwanted early precipitation of the polymer, for example, resulting in clogging of the transfer lines. After loading the embossed container 20 with solvent and preheating the fractionation system, the primary solution UHMWPE of the dissolution container 14 can be charged to the column 8. After closing the valves 34, 52, and 56, open the valve 30, and opening the valve 46 lightly, the charging pump 18 can be started. Subsequently, all of the primary UHMWPE solution contained in the dissolution vessel 14 is placed on top of the fractionation column 7 by pumping the solution through the suction line 17 and the feed line 28. In this way, the drive column 8, which contains a support, is loaded with the primary UHMWPE solution while maintaining its temperature high enough to prevent the polyethylene from precipitating out of the solution . The valve 48 can be opened to allow the hot solution of the primary solution UHMWPE to flow through line 28, fractionation column 8, line 40, line 42, cooling unit 22, and line 44 to the container of the solvent 24. The opening of the valve 46 can be controlled to maintain a desired back pressure in the system, for example, 3 psig. The system pressure can be maintained at atmospheric pressure or slightly above atmospheric pressure during the production of the UHMWPE fractions. The charge pump 18 can be turned off after loading the fractionation column 8 with the primary solution UHMWPE. The solvent of the embossed container 20 can then be introduced through line 32 and valve 34 into column 8. Subsequently, the fractionation column 8 containing the primary solution UHMWPE can be operated at effective conditions to cause the molecules of the fraction to precipitate. Remove the polymer from the solution and deposit it in the support placed in the column 8. In particular, the temperature of the fractionation column 8 can be reduced to less than 40 ° C at a rate of 1 ° C / hr to 0.5 ° C / hr cooling the cooling / heating bath 12 using, for example, a heat exchanger (not shown). In one embodiment, computerized control is used to control the cooling rate of column 8 and the primary UHMWPE solution existing therein. The support in the fractionation column 8 can be a fixed bed of relatively small objects having solid surfaces on which the precipitate can be deposited. The support is inert in the presence of the UHMWPE primary solution under operating conditions of the fractionation column 8. Its presence in the fractionation column 8 helps to distribute the molecules of the precipitated polymer along the length of the column, in this way, the polymer molecules are prevented from clumping or sticking together. Examples of suitable support materials include glass balls, steel balls, and combinations thereof. As shown in Figure 2, the embossed container 20, cooling unit 22, charging pump 18, and the lines associated therewith of the fractionation system can be disconnected after the formation of the precipitate in the support. Additionally, a receiving container 62 can be connected to the top of the column 8 via the line 60. The solvent container 24 can be filled with a non-solvent, i.e., a liquid in which the HMWPE is insoluble. Examples of suitable non-solvents include 2-ethoxyethanol, 2-butoxyethanol, ethylene glycol, monoethyl ether, ethanol, acetone, triethylene glycol, or combinations thereof. Subsequently, valves 52 and 56 are opened, followed by fractionation pump 26 running to displace the non-solvent through suction line 50, feed line 54, and fractionation column 8. As a result of this displacement, the solvent used to create the primary UHMWPE solution is removed from the fractionation column 8. The non-solvent is also displaced through the fractionation column 8 and line 60 to the receiving vessel 62. After all the primary solution is washed UHMWPE of the fractionation system and transported to the receiving vessel 62, the fractionation pump 26 can be turned off. Subsequently, a fractionation technique is used to recover one or more UHMWPE fractions or cuts from the homopolymer precipitate placed in the fractionation column 8. The fractionation technique includes at least one and typically a plurality of wash steps where the homopoxide precipitate is washed. a non-solvent / solvent mixture, where each wash is designed to dissolve, and in that way, isolate a particular UHMWPE fraction. Subsequently, the non-solvent / solvent mixture can be recovered, and the UHMWPE fraction contained therein is precipitated out of the mixture and recovered. By using successive washes with a non-solvent / solvent mixture containing an iteratively increased amount of solvent to non-solvent, a corresponding number of UHMWPE fractions can be recovered. That is, the homopolymer precipitate can be washed with a first non-solvent / solvent mixture corresponding to a desired first UHMWPE cut, after which the homopolymer precipitate can be washed with a second non-solvent / solvent mixture corresponding to a second cut. UHMWPE desired, and so continuously with non-solvent / solvent mixtures that are recovered between washes and the corresponding UHMWPE fraction that precipitates therefrom. The relative amounts of the solvent and the non-solvent are based on the first and successive wash mixtures in the solvent gradient curves for the UHMWPE homopolymer, examples of which are shown in Figures 3 and 4 for the UHMWPE GUR4150 homopolymer. In Figure 3, the logarithm of Mw of the UHMWPE fraction is shown as a function of the amount of TCB in the non-solvent / solvent mixture at a temperature of 140 ° C. In Figure 4, the amount of the UHMWPE fraction produced as a function of the amount of TCB in the non-solvent / solvent mixture at a temperature of 140 ° C is shown. The same solvents suitable for use in the UHMWPE primary solution are suitable for use in washing mixtures. Also, the same non-solvents suitable for being used to wash the solvent from column 8 as those described above, are suitable for use in the washing mixtures. In one embodiment, the solvent is TCB, and the non-solvent is 2-butoxyethanol. A first non-solvent / solvent mixture corresponding to a first UHMWPE fraction is placed in the solvent container 24. After having combined the non-solvent / solvent mixture in the solvent container 24, the mixture can be placed in the fractionation column 8, the fractionation pump 26 can be turned off and the valves 52 and 56 can be closed. Before, during, or after filling the fractionation column 8 with the non-solvent / solvent mixture , the temperature of the fractionation column 8 can be increased to a temperature ranging from the melting point temperature of the UHMWPE to 160 ° C, for example, 30 ° C above the melting point temperature by heating the cooling bath / heating 12 using, for example, a heat exchanger. The fractionation column 8 can be maintained at this temperature for a sufficient period to allow the non-solvent / solvent mixture contained therein to reach a state of equilibrium at which point the solvent and the non-solvent are separated into two phases. In one embodiment, the non-solvent / solvent mixture can be maintained in the fractionation column 8 for 16 hours or more. During this period, the first UHMWPE fraction is dissolved in the solvent phase. The first non-solvent / solvent mixture can be removed and the non-solvent / subsequent solvent mixtures can be successively placed in the solvent container 24 to remove the successive cuts of the homopolymer in fractionation column 8. Valves 52 and 56 can be opened and the fractionation pump 26 can be operated to place the second non-solvent / solvent mixture (and successive) in the fractionation column 8, while simultaneously placing the first non-solvent / solvent mixture of the column 8 to the receiving vessel 62 through of line 36. This pumping can be developed at a relatively low speed, for example, less than 40 ml / min, to reduce the amount of mixing at the interface between the two mixtures. A precipitating agent can be added which has the ability to cause the first UHMWPE fraction to separate out of the non-solvent / solvent mixture into the receiving vessel 62. Examples of suitable precipitating agents include acetone, CH3OH, and other low boiling solvents. and polar boiling. Subsequently, the first UHMWPE fraction of receiver vessel 62 can be analyzed by GPC to determine its MW / Mn, and PDI values. The process of placing a non-solvent / solvent mixture in the solvent container 24, placing the mixture in the fractionation column 8, allows the corresponding UHMWPE fraction to dissolve in the mixture, and the placement of the mixture in the mixture can be repeated. receiving vessel 62 until substantially all of the UHMWPE homopolymer precipitate is recovered from column 8. In one embodiment, the amount of solvent used in the non-solvent / solvent mixture can be increased between washes by selecting an amount that is in a gradient curve of solvent of the UHMWPE fraction. In one embodiment, a wash step may be repeated one or more times with the same non-solvent / solvent mixture to totally isolate a particular fraction before changing the non-solvent / solvent ratio of the wash mixture to isolate another fraction. Likewise, the total number of wash steps and the composition of the non-solvent / solvent wash mixture can be selected and optimized based on the initial homopolymer material and the desired polymer fractions to be isolated and recovered therefrom. . The solvent gradient curves, such as those shown in Figures 3 and 4 for a given UHMWPE homopolymer can be developed by carrying out the above procedure based on a wide range of solvent concentrations and analyzing the recovered UHMWPE fractions to determine their PDI values. Subsequently, those fractions that have a PDI less than 2 are shown to form solvent gradient curves for the UHMWPE homopolymer. Due to the sparse MWD, several UHMWPE fractions can serve as an excellent reference standard for an instrument or analytical tool used to characterize polymer molecules. The use of such UHMWPE fractions as reference standards improves the accuracy with which the instruments can measure the properties of the polymer molecules. With the knowledge of said properties, researchers can better evaluate, among other things, how to use and optimize the polymers they have developed. For example, ÜHMWPE fractions can be used as a reference standard for calibrating exclusion chromatography (SEC) tools such as a gel permeation chromatography (GPC) tool, providing a more accurate determination of the Mw of the polymer molecules . The additional description regarding GPC can be found in the patent E.Ü.A. No. 6,294,388, which is incorporated by reference in its entirety in the present invention. UHMWPE fractions can also be used as a reference standard for the differential scanning calorimetry (DSC) tool in such a way that the behavior of the polyethylene molecules in response to heating can be determined more accurately. Additionally, UHMWPE fractions can be used as a reference standard to establish a baseline for linear polymers in rheology measurements using rheology instruments such as a viscometer. Other examples of analytical tools for which UHMWPE fractions can be used as a reference standard include light scattering tools such as a static light scattering detector (SLS) and a dynamic light scattering detector (DLS). ). An SLS detector can be used to measure Mw and radius of gyration (Rg) of a polymer in dilute solution. A DLS detector can be used to measure fluctuations in the dispersion signal as a function of time to determine the diffusion constant of the polymer chains in dilute solution or polymer particles in an emulsion. The additional description related to the light scattering tools can be found in the patent E.U.A. No. 6,294, 388 mentioned above and in Helmstedt et al., 42 (9) Polymeror p. 4163-4172 (2001), which is incorporated by reference in its entirety in the present invention. Other analytical tools for which UHMWPE fractions can be used as a reference standard can also be found in US Patent No. No. 6,294,388. It is also contemplated that the UHMWPE fractions could be used in a polymeric material such as a polymer blend to study the effect of high Mw on the properties and / or processing of the polymeric material. EXAMPLES Since the invention has been described in general form, the following examples are provided as particular embodiments of the invention and to demonstrate the practice and advantages thereof. It is understood that the examples are provided as a form of illustration and are not intended to limit the specification or the claims below in any way. The fractionation system and the general procedure were used to use the fractionation system described above to produce a plurality of UHMWPE fractions. A cylindrical fractionation column containing glass mats was used as the support and they have a height of 6 feet (182.88 cm) and a foot diameter (15.24 cm). First, 60 grams (g) of the homopolymerc UHMWPE GUR4150 and 8 liters (L) of TCB solvent were added to the dissolution vessel which was a round bottom flask equipped with a stirring blade. The TCB / UHMWPE homopolymer mixture was stirred using the stirring paddle for 3 days at a speed of 60 rpm while heating the dissolution vessel to 160 ° C, thereby dissolving the UHMWPE homopolymer in the TCB and forming a primary UHMWPE solution. While the fractionation system was preheated to 150 ° C, the primary solution was placed in the fractionation column using the loading pump. Subsequently, the fractionation column was slowly cooled at the rate of 0.7 ° C / hr at a temperature of 40 ° C, resulting in the precipitation of polymer molecules of different compositions out of the primary solution in the glass mats. Later, the solvent was removed from the fractionation column by filling the solvent container with a non-solvent, i.e., 2-butoxyethanol, and pumped through the fractionation column using the fractionation pump. The solvent container was a 15-L round bottom flask. Subsequently, a first (non-solvent) 2-butoxyethanol / (solvent) TCB mixture was placed in the solvent container, and the mixture was subsequently pumped into the fractionation column, thereby displacing the non-solvent from the column of fractionation. The amount of TCB in the first mixture (as subsequent mixtures) is set in Table 2 and selected based on the solvent gradient curves shown in Figures 3 and 4. Since the first 2-butoxyethanol / mixture was placed. TCB in the fractionation column, the temperature of the column was raised to 140 ° C and maintained at that temperature overnight for 15 hours to allow a fraction of the precipitated UHMWPE homopolymer to dissolve in the mixture. Subsequently, another mixture of 2-butoxyethanol / TCB was placed in the solvent container. A second mixture of 2-butoxyethanol / TCB was then placed in the fractionation column using the fractionation pump such that the first 2-butoxyethanol / TCB mixture was placed from the column into the recipient vessel. Acetone was added to the receiver vessel to cause the first UHMWPE fraction to precipitate out of the first 2-butoxyethanol / TCB mixture. The first UHMWPE fraction of the first 2-butoxyethanol / TCB mixture was then isolated and analyzed using GPC to determine its Mw, MOr PDI and Mp (ie, the ultra high molecular weight). The second 2-butoxyethanol / TCB mixture was also heated at 140 ° C in the fractionation column overnight for 15 hours, to allow more of the second UHMWPE fraction to dissolve in the mixture. The steps for placing a mixture of 2-butoxyethanol / TCB in the solvent container, placing the mixture in the fractionation column while simultaneously placing another 2-butoxyethanol / TCB mixture from the column to the recipient vessel to recover the UHMWPE fraction, and the heating of the mixture in the column was repeated at 140 ° C for 15 hours until substantially all of the UHMWPE homopolymer precipitate had been removed from the column. As shown in Table 2 below, the concentration of TCB, i.e., the solvent, was increased in the 2-butoxyethanol / TCB mixture each time the step was repeated. Also shown is the amount of the UHMWPE fraction recovered with each wash step and the M ", M / PDI and Mp of the UHMWPE fraction recovered in Table 2, where RT-35 represents the fraction recovered at 35 ° C in 100 ° C. % TCB. As desired, the recovered UHMWPE fractions had Mw values greater than 1,000 g / mol, and some were greater than 3,000 kg / mol, and one was even greater than 6,000 kg / mol. In addition, several of the UHMWPE fractions had PDI values less than 2, some were less than 1.5. Therefore, such UHMWPE fractions would be useful as reference standards for analytical tools such as GPC, DSC, rheology and light scattering tools.

TABLE 2 Since preference modalities have been shown and described, those skilled in the art can make the modifications thereto without departing from the spirit and teachings of the invention. The embodiments described in the present invention are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention described in the present invention are possible and are within the scope of the invention. The use of the term "optionally" with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. Accordingly, the scope of protection is not limited by the description set forth above, but is limited only by means of the claims that follow up on the scope that includes all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the preferred embodiments of the present invention. The mention of a reference in the Detailed Description of the Invention is not an admission that is about the prior art of the present invention, especially any reference that may have a publication date subsequent to the priority date of this application. The descriptions of all patents, patent applications, and publications mentioned in the present invention are incorporated herein by reference, insofar as they provide examples, procedures or other details supplementary to those set forth in the present invention. 2/4 Ü.C v 39.00 39.50 40.00 40.50 41.00 41.50 42.00 Amount of TCB (% by weight) . 00 36.00 37.00 38.00 39.00 40.00 41.00 42.00 43.00 Amount of TCB (% by weight)

Claims (41)

NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following is claimed as a priority: CLAIMS

1. - A polyethylene composition that has a PDI less than or equal to 2.3.

2. The polyethylene composition according to claim 1, characterized in that it has an Mw greater than 1,000,000 g / mol.

3. The polyethylene composition according to claim 1, characterized in that it has an Mw greater than 3,000,000 g / mol.

4. The polyethylene composition according to claim 1, characterized in that it has an Mw greater than 6,000,000 g / mol.

5. - The polyethylene composition according to claim 1, characterized in that the polyethylene composition has the ability to be used as a reference standard in an analytical tool.

6. - The polyethylene composition according to claim 5, characterized in that the analytical tool comprises a SEC tool, a DSC tool, a light scattering tool, a viscosity measuring tool, or combinations thereof.

7.- A polyethylene reference standard that has a PDI of less than 2 and a Mw greater than 1,000,000 g / mol.

8. A method for producing a polyethylene fraction, comprising: (a) dissolving a primary UHMWPE polymer in a solvent to form a primary polyethylene solution; (b) transporting the primary polyethylene solution to a fractionation column in which a support is placed; (c) operating the fractionation column under effective conditions to form a precipitate comprising the polyethylene fraction in the support; and (d) recover the polyethylene fraction from the fractionation column, the polyethylene fraction that has a PDI less than 2.3.

9. The method according to claim 8, characterized in that the polyethylene fraction has an Mw greater than 1,000,000 g / mol.

10. The method according to claim 8, characterized in that an amount of the primary polymer UHMWPE dissolved in the solvent is in the range of 7.5 grams / liter of solvent to 25 grams / liter of solvent.

11. The method according to claim 8, characterized in that the primary polymer UHMWPE comprises a homopolymer.

12. The method according to claim 11, characterized in that the homopolymer comprises polyethylene GUR4150.

13. The method according to claim 8, characterized in that said solution comprises heating and stirring a mixture comprising the primary polymer UHMWPE for a period sufficient to dissolve substantially all the primary polymer UHMWPE in the solvent, characterized in that the mixture is heated at a temperature comprised of a melting point temperature of the primary polymer UHMWPE at 30 ° C above the melting point temperature, and characterized in that the mixture is stirred at a speed of 55 rpm at 65 rpm.

14. The method according to claim 13, characterized in that the period is at least 1 day.

15. The method according to claim 8, characterized in that the solvent comprises a hydrocarbon recovered from the derivation of the oil, a halo-derivative of the hydrocarbon, or combinations thereof.

16. The method according to claim 8, characterized in that the solvent comprises trichlorobenzene.

17. The method according to claim 8, characterized in that said transportation comprises pumping the primary polyethylene solution in the fractionation column.

18. The method according to claim 8, characterized in that said operation comprises decreasing a temperature of the fractionation column at a temperature lower than 40 ° C at a rate of 1 ° C / hr to 0.5 ° C / hr.

19. The method according to claim 8, characterized in that the support comprises glass mats, steel balls, or combinations thereof.

20. The method according to claim 8, characterized in that said recovery comprises placing a non-solvent / solvent mixture recovered in the fractionation column, raising a temperature of the column to a temperature in a range of a temperature of the point of melting the polyethylene fraction at 160 ° C above the melting point temperature, and allowing a portion of the polyethylene fraction to dissolve in the recovered non-solvent / solvent mixture.

21. The method according to claim 20, characterized in that the solvent recovered comprises a hydrocarbon recovered from the derivation of the oil, a halo-derivative of the hydrocarbon, or combinations thereof.

22. The method according to claim 20, characterized in that the recovered solvent comprises trichlorobenzene.

23. The method according to claim 20, characterized in that the non-solvent comprises 2-ethoxyethanol, 2-butoxyethanol, ethylene glycol, monoethyl ether, ethanol, acetone, triethylene glycol, or combinations thereof.

24. The method according to claim 20, characterized in that said recovery further comprises placing the non-solvent / solvent mixture recovered from the fractionation column and introducing a precipitation agent into the mixture.

25. The method according to claim 24, further comprises repeating said recovery until the recovered non-solvent / solvent mixture leaving the fractionation column is substantially absent from the polyethylene precipitate.

26. The method according to claim 20, characterized in that a concentration of the solvent recovered in the recovered non-solvent / solvent mixture is based on a solvent gradient profile of the polyethylene primary polymer.

27. The method according to claim 8, characterized in that the fractionation column comprises a column scaled in an upward direction.

28.- A method to use a polyethylene fraction, includes: using the polyethylene fraction as a reference standard in an analytical tool, the polyethylene fraction that has a PDI of less than 2.

29.- The method of compliance with claim 28, characterized in that the analytical tool comprises a SEC tool, a DSC tool, a light scattering tool, a viscosity measuring tool, or combinations thereof.

30. The method according to claim 28, characterized in that the polyethylene fraction has an M "greater than 1,000,000 g / mol.

31. - The method according to claim 28, characterized in that the polyethylene fraction has an Mw greater than 3,000,000 g / mol.

32. The method according to claim 28, characterized in that the polyethylene fraction has an Mw greater than 6,000,000 g / mol.

33.- The method according to claim 8, characterized in that the polyethylene fraction is produced in an amount equal to or greater than 1 gram.

34.- A polyolefin composition that has a PDI less than or equal to 2.3.

35. A method for producing a polyolefin fraction comprises: (a) dissolving a primary UHMWPE polymer in a solvent to form a primary polyolefin solution; (b) transporting the primary polyolefin solution to a fractionation column in which a support is placed; (c) operating the fractionation column under effective conditions to form a precipitate comprising the polyolefin fraction in the support; and (d) recovering the polyolefin fraction from the fractionation column, the polyolefin fraction that has a PDI less than 2.3. 36.- A method for using a polyolefin fraction, comprises: using the polyolefin fraction as a reference standard in an analytical tool, the polyolefin fraction that has a POI less than 2. 37.- The composition in accordance with Claim 1 or 34 that has a PDI ranging from less than 1.5 to 2.3. 38.- The composition according to claim 1 or 34 that has a PDI that comprises from 0.1 to 2.3. 39.- The composition according to claim 1 or 34 that has a PDI of 0.5 to 2.0. 40.- A polyethylene fraction produced by a method defined in any of claims 8 to 33. 41.- The use of a polyethylene fraction that has a PDI of less than about 2 as a reference standard in an analytical tool.