Method for producing modified methylaluminoxane

Abstract

To provide a method for producing a modified methylaluminoxane capable of producing the modified methylaluminoxane with high yield.SOLUTION: There is provided a method for producing a modified methylaluminoxane having a number of constituent units represented by formula (I) of x and a number of constituent units represented by formula (II) of y, wherein the method comprises a step (b) of adding water in an amount equivalent to 1.10 mol or more based on the amount of trimethylaluminum to a mixture containing trialkyl aluminum represented by R3Al (where R is the same as R in formula (II)) and trimethyl aluminum to partially hydrolyze the trialkyl aluminum and the trimethyl aluminum. (R is an alkyl group of C2 to 10; * represents a binding site; x and y are each independently positive real numbers; provided that the ratio of x / y is between 0.1 and 25; when there are multiple R's in the modified methylaluminoxane, the multiple R's may be the same or different.)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing modified methylaluminoxane. [Background technology]

[0002] Aluminoxanes are generally condensation products prepared by partial hydrolysis of organoaluminum compounds with water, and are useful as co-catalyst components that efficiently activate transition metal compounds, which serve as the main catalyst in the production of polyolefins (olefin polymers).

[0003] In recent years, proposals have been made regarding aluminoxanes, such as modified methylaluminoxanes having a methyl group and an alkyl group having two or more carbon atoms (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-119278 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-119279 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-119280 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Documents 1 to 3 propose methods for synthesizing modified methylaluminoxanes by mixing a tetraalkyldialuminoxane having an alkyl group with two or more carbon atoms with trimethylaluminum, followed by a hydrolysis reaction. The modified methylaluminoxanes obtained by these synthesis methods are soluble not only in aromatic hydrocarbon solvents but also in aliphatic hydrocarbon solvents, and can therefore be widely used in the production of polyolefins for food applications, etc., where the inclusion of aromatic solvents is restricted. Furthermore, these synthesis methods involve mild synthetic reactions that are easy to control, and the resulting modified methylaluminoxanes exhibit good storage stability.

[0006] However, even with the above synthesis method, a portion of the trimethylaluminum is excessively hydrolyzed to form an insoluble gel, resulting in a decrease in the yield of aluminoxane. Therefore, there has been a demand for a method for producing modified methylaluminoxane with a higher yield.

[0007] An object of one aspect of the present invention is to provide a method for producing modified methylaluminoxane, which can produce modified methylaluminoxane in high yield.

[0008] As previously mentioned, the formation of insoluble gel, which reduces the yield of aluminoxane, occurs during the hydrolysis of trimethylaluminum. Therefore, in order to suppress the formation of insoluble gel, a conventional method for reducing the amount of water added in the presence of trimethylaluminum has been to partially hydrolyze a trialkylaluminum having an alkyl group containing two or more carbon atoms prior to the partial hydrolysis of trimethylaluminum (see, for example, the Examples in Patent Documents 1 to 3). Surprisingly, the present inventors conducted extensive research and surprisingly discovered that adding a predetermined amount of water to a mixture containing trialkylaluminum having an alkyl group containing two or more carbon atoms and trimethylaluminum can suppress the formation of insoluble gel and increase the yield of aluminoxane. Even more surprisingly, it was also discovered that the modified methylaluminoxane thus obtained has a low residual amount of trimethylaluminum. Regarding trimethylaluminum, when a metallocene is used as the main catalyst in the production of polyolefins, trimethylaluminum is known to convert the metallocene into a dormant species. Therefore, modified methylaluminoxanes with a small amount of residual trimethylaluminum are desirable as cocatalysts in the production of polyolefins. [Means for solving the problem]

[0009] That is, one aspect of the present invention is as follows. [1] A method for producing a modified methylaluminoxane having a structural unit represented by the following formula (I) in a structural unit number x and a structural unit represented by the following formula (II) in a structural unit number y, [ka] (In the above formula, R represents an alkyl group having 2 to 10 carbon atoms, and * represents a bonding position. x and y each independently represent a positive real number, with the proviso that the x / y ratio is 0.1 to 25. When multiple Rs are present in the modified methylaluminoxane, the multiple Rs may be the same or different. The structural units in the modified methylaluminoxane, where x is the number of structural units, and the structural units in the number y is the number of structural units, may be arranged in any order.) The above production method includes a step (b) of adding 1.10 or more molar equivalents of water relative to the amount of trimethylaluminum to a mixture containing a trialkylaluminum represented by R3Al (R has the same meaning as R in formula (II)) and trimethylaluminum, thereby partially hydrolyzing the trialkylaluminum and trimethylaluminum. [2] The production method according to [1], wherein R represents an isobutyl group in formula (II). [3] The manufacturing method according to [1] or [2], wherein the step (b) further comprises preparing the mixture by adding trimethylaluminum to a composition containing a trialkylaluminum represented by R3Al. [4] before the step (b), a step (a) of preparing the composition containing trialkylaluminum represented by R3Al; and The manufacturing method according to [3], wherein water is not added in the step (a). [5] before the step (b), a step (a) of preparing the composition containing a trialkylaluminum represented by R3Al; and The production method according to [3], wherein in the step (a), less than 0.60 molar equivalents of water are added relative to the amount of trialkylaluminum represented by R3Al. [6] The method according to any one of [1] to [5], wherein the modified methylaluminoxane has an integral ratio of 0.950 or more. [Effects of the Invention]

[0010] According to one aspect of the present invention, there is provided a method for producing modified methylaluminoxane, which can produce modified methylaluminoxane in high yield. DETAILED DESCRIPTION OF THE INVENTION

[0011] One aspect of the present invention relates to a method for producing a modified methylaluminoxane having x number of structural units represented by the following formula (I) and y number of structural units represented by the following formula (II):

[0012] [ka]

[0013] In the above formula, R represents an alkyl group having 2 to 10 carbon atoms, and * represents a bonding position. x and y each independently represent a positive real number, with the x / y ratio being 0.1 to 25. When multiple Rs are present in the modified methylaluminoxane, the multiple Rs may be the same or different. The structural units of the number x of structural units and the number y of structural units in the modified methylaluminoxane may be arranged in any order. The modified methylaluminoxane contained in the composition may have a molecular weight distribution. Therefore, x and y represent the average value of x and the average value of y of the modified methylaluminoxane contained in the composition.

[0014] [Modified methylaluminoxane] The modified methylaluminoxane will be described in more detail below.

[0015] In formula (II), R represents an alkyl group having 2 to 10 carbon atoms. Since R is included in the structural unit of the structural unit number y, when there are multiple R in the modified methylaluminoxane, the multiple R may be the same or different.

[0016] The alkyl group represented by R can be a linear alkyl group or a branched alkyl group. Specific examples of the alkyl group represented by R include an ethyl group, a propyl group, an n-butyl group, an isobutyl group, a t-butyl group, an amyl group, an isoamyl group, an n-hexyl group, an isohexyl group, an n-octyl group, and an isooctyl group. The alkyl group represented by R can be an unsubstituted alkyl group or a substituted alkyl group. Specific examples of the substituent possessed by the substituted alkyl group include halogen atoms such as a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. In the alkyl group substituted with a halogen atom, the number of halogen atoms contained as a substituent can be, for example, 1 or more and 10 or less.

[0017] From the viewpoint of availability, the number of carbon atoms in the alkyl group represented by R is preferably 2 or more and 6 or less. The alkyl group represented by R may preferably be an ethyl group, an n-butyl group, an isobutyl group, or an n-hexyl group.

[0018] The number of structural units x of the structural unit represented by formula (I) and the number of structural units y of the structural unit represented by formula (II) each independently represent a positive real number. However, if the x / y ratio is below 0.1, the polymerization activity decreases significantly, and if the x / y ratio exceeds 25, the solubility in the solvent decreases, so the x / y ratio is 0.1 or more and 25 or less. From the viewpoint of suppressing a decrease in polymerization activity, the x / y ratio is preferably 0.5 or more. From the viewpoint of suppressing a decrease in solubility in the solvent, the x / y ratio is preferably 20 or less.

[0019] From the viewpoint of fully exhibiting catalytic performance, the sum of x and y (x+y) is preferably 2 or more, and more preferably 5 or more. From the above viewpoint, the sum of x and y (x+y) is preferably 50 or less, and more preferably 30 or less.

[0020] In formula (I) and formula (II), * represents a bonding position. The structural unit represented by formula (I) can be bonded, for example, to a structural unit represented by formula (I), to a structural unit represented by formula (II), or to an end group of the modified methylaluminoxane at the bonding position. The structural unit represented by formula (II) can be bonded, for example, to a structural unit represented by formula (I), to a structural unit represented by formula (II), or to an end group of the modified methylaluminoxane at the bonding position. In the above modified methylaluminoxane, the structural units represented by formula (I) and the structural units represented by formula (II) can be arranged in any manner. For example, the structural units represented by formula (I) and the structural units represented by formula (II) may be arranged consecutively, alternately, or randomly.

[0021] [Step (b)] The above-described production method includes at least step (b) for producing the modified methylaluminoxane described above. In step (b), 1.10 or more molar equivalents of water relative to the amount of trimethylaluminum are added to a mixture containing a trialkylaluminum represented by RAl (where R has the same meaning as R in formula (II)) and trimethylaluminum, thereby partially hydrolyzing the trialkylaluminum and trimethylaluminum. By adding 1.10 or more molar equivalents of water relative to the amount of trimethylaluminum in step (b), it is possible to suppress the formation of an insoluble gel and increase the yield of aluminoxane. Furthermore, it is possible to reduce the amount of residual trimethylaluminum in the resulting modified methylaluminoxane. From the viewpoint of further improving the yield of aluminoxane and further reducing the amount of residual trimethylaluminum, the amount of water added in step (b) is preferably 1.12 or more molar equivalents relative to the amount of trimethylaluminum, with 1.14 or more, 1.20 or more, 1.25 or more, and 1.30 or more being more preferred in that order. The amount of water in step (b) can be, for example, 3.00 equivalents or less, 2.50 equivalents or less, 2.00 equivalents or less, or 1.50 equivalents or less on a molar basis relative to the amount of trimethylaluminum.

[0022] <Preparation of the mixture> Step (b) can further include a step of preparing the mixture to which water is added, i.e., a mixture containing trialkylaluminum represented by R3Al and trimethylaluminum, by adding trimethylaluminum to a composition containing trialkylaluminum represented by R3Al. The composition containing trialkylaluminum represented by R3Al will be described in more detail below. Trimethylaluminum may be added alone, or as a solution in which trimethylaluminum is mixed with an organic solvent. The concentration of trimethylaluminum in such a solution is not particularly limited. The amounts of trialkylaluminum and trimethylaluminum used may be determined depending on the values of x and y of the modified methylaluminoxane to be produced.

[0023] When trimethylaluminum is added as a solution, examples of organic solvents that can be mixed with trimethylaluminum to prepare this solution include electron-donating organic solvents, hydrocarbon compounds, and mixtures of two or more of these organic solvents.

[0024] Specific examples of the electron-donating organic solvent include ether solvents such as 1,2-diethoxyethane, 1,2-dibutoxyethane, diethyl ether, di-n-propyl ether, diisopropyl ether, dibutyl ether, cyclopentyl methyl ether, tetrahydrofuran, dioxane, glyme, diglyme, triglyme, anisole, and methoxytoluene; amine solvents such as N,N-diisopropylethylamine and triethylamine; and chain or cyclic amide compounds such as N,N-dimethylformamide, N,N-diethylformamide, 1,1,3,3-tetramethylurea, N-methyl-2-pyrrolidone, 1,3-dimethyl-imidazolidinone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

[0025] Examples of the hydrocarbon compound include linear hydrocarbon compounds, branched hydrocarbon compounds, or cyclic hydrocarbon compounds having 5 to 20 carbon atoms (preferably 6 to 12 carbon atoms), aromatic hydrocarbon compounds having 6 to 20 carbon atoms (preferably 6 to 12 carbon atoms), and mixtures thereof.

[0026] Specific examples of the hydrocarbon compound include aliphatic hydrocarbons such as pentane, hexane, heptane, isohexane, methylpentane, octane, 2,2,4-trimethylpentane (isooctane), n-nonane, n-decane, n-hexadecane, octadecane, eicosane, methylheptane, 2,2-dimethylhexane, and 2-methyloctane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclohexane, and ethylcyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene, cumene, and trimethylbenzene; and hydrocarbon solvents such as mineral spirits, solvent naphtha, kerosene, and petroleum ether.

[0027] <Adding water> The addition of water to the mixture in step (b) can be carried out without mixing water with another solvent, or after mixing water with another solvent. The addition of water can be carried out over a period of time ranging from 60 seconds to 10 hours, depending on the scale of the reaction. The internal temperature during the addition can be, for example, in the range of -90 to 150°C, and from the viewpoint of the reactivity of the hydrolysis reaction, it is preferable that the temperature be in the range of -15 to 30°C. In the present invention and this specification, the term "internal temperature" refers to the temperature of the composition (e.g., the mixture to which water is added).

[0028] After the addition of water, in order to further promote the hydrolysis reaction, the mixture to which water has been added can be left to stand without stirring for 1 minute to 48 hours, or can be stirred. The internal temperature here can be, for example, in the range of -90 to 150°C, and preferably in the range of -15 to 80°C. The internal temperature can be maintained at a constant temperature or within a predetermined range, or can be raised and / or lowered as appropriate. For example, the internal temperature after the addition of water can be raised and then maintained at a constant temperature or within a predetermined range, and then lowered, and this process can be carried out once or multiple times. Maintaining the internal temperature at a constant temperature or within a predetermined range is called "aging."

[0029] In step (b), a hydrolysis reaction proceeds in the mixture after adding water, and the trialkylaluminum and trimethylaluminum represented by R3Al are partially hydrolyzed to produce the modified methylaluminoxane. In the modified methylaluminoxane, the structural unit represented by formula (I) is derived from the partial hydrolysis product of trimethylaluminum, and the structural unit represented by formula (II) is derived from the trialkylaluminum represented by R3Al. Therefore, R in R3Al has the same meaning as R in formula (II). In R3Al, the three Rs may be the same or different.

[0030] [Process (a)] As described above, step (b) can further include a step of preparing a mixture to which water is added, i.e., a mixture containing trialkylaluminum represented by R3Al and trimethylaluminum, by adding trimethylaluminum to a composition containing trialkylaluminum represented by R3Al. Step (a) is a step of preparing a composition to which trimethylaluminum is added in this step. The above production method can include step (a) before step (b).

[0031] In one embodiment of step (a), water is not added. In this case, a composition containing a trialkylaluminum represented by R3Al can be prepared, for example, by mixing the trialkylaluminum with an organic solvent, and does not contain trimethylaluminum. However, water is not added to the composition thus prepared. Not adding water in step (a) is preferable from the viewpoint of further improving the yield of modified methylaluminoxane. For details of the organic solvent, please refer to the above description regarding the organic solvent that can be mixed with trimethylaluminum. The concentration of the trialkylaluminum in the composition thus prepared is not particularly limited.

[0032] Another embodiment of step (a) involves adding less than 0.60 molar equivalents of water relative to the amount of trialkylaluminum represented by RAl. In this case, for example, water can be added to a composition obtained by mixing a trialkylaluminum represented by RAl with an organic solvent. The composition to which water is added is as described above. When water is added in step (a), it is preferable to add less than 0.60 molar equivalents relative to the amount of trialkylaluminum in order to prevent a decrease in the yield of modified methylaluminoxane. From the above perspective, the amount of water added in step (a) is preferably 0.58 molar equivalents or less, more preferably 0.55 molar equivalents or less, relative to the amount of trialkylaluminum. When water is added in step (a), the amount of water added is more than 0.00 molar equivalents relative to the amount of trialkylaluminum, and can be 0.10 molar equivalents or more, 0.20 molar equivalents or more, or 0.30 molar equivalents or more.

[0033] For details of the addition of water in step (a) (internal temperature and time), please refer to the above description of the addition of water in step (b). When water is added in step (a), polyalkylaluminoxane can be produced by partial hydrolysis of trialkylaluminum represented by RAl.

[0034] In the above production method, the total amount of water added in step (a) and step (b) can be, for example, 0.50 equivalents or more, 0.60 equivalents or more, or 0.70 equivalents or more, based on the total amount of trialkylaluminum represented by RAl and trimethylaluminum, on a molar basis. It can also be, for example, 1.00 equivalents or less, 0.95 equivalents or less, or 0.90 equivalents or less. When no water is added in step (a) as described above, the amount of water added in step (a) is zero.

[0035] For the modified methylaluminoxane obtained by the above production method, the methylaluminoxane integral ratio determined by the method described below can be used as an indicator of the residual trimethylaluminum content. A higher methylaluminoxane integral ratio indicates a lower residual trimethylaluminum content. In one embodiment, the modified methylaluminoxane obtained by the above production method can exhibit a methylaluminoxane integral ratio of 0.950 or more or 0.960 or more. In one embodiment, the methylaluminoxane integral ratio of the modified methylaluminoxane obtained by the above production method can be 1.000 or less or less than 1.000. When the residual trimethylaluminum content is zero, the methylaluminoxane integral ratio is 1.000. [Example]

[0036] The present invention will be described below based on examples, but the present invention is not limited to the embodiments shown in the examples.

[0037] In the following, "triisobutylaluminum" will be abbreviated as "TIBAL," "trimethylaluminum" as "TMAL," "methylcyclohexane" as "MCH," and "methylaluminoxane" as "MAO." The "equivalents" listed below are on a molar basis. "eq" is an abbreviation for equivalent.

[0038] The "Al content of the insoluble gel" described below was calculated by weighing the total mass of the insoluble gel obtained by filtration and drying, sampling a portion of this, and multiplying it by the Al concentration (mass%) in the insoluble gel, which was quantified by chelating titration (a solution hydrolyzed with 0.5 N aqueous sulfuric acid was added with an excess amount of disodium ethylenediaminetetraacetate, and then back-titrated with zinc sulfate using dithizone as an indicator). The calculated Al content of the insoluble gel is shown in the "Insoluble gel [mol %]" column in the table below.

[0039] The "MAO integral ratio" described below was calculated as the ratio of the integral value of modified methylaluminoxane to the methyl group signals detected in the range of -0.2 ppm to -1.1 ppm in the NMR analysis results in THF-d8 measured using an ECA500 manufactured by JEOL Ltd., excluding the sharp signal detected in the range of -0.9 ppm to -1.0 ppm (attributed to unreacted TMAL). Each peak can be easily extracted by curve fitting, baseline collection, etc.

[0040] [Example 1] Step (a): TIBAL (1.78 mol) and hexane (0.53 kg) were weighed and mixed in a 5 L separable flask to obtain a mixture (a composition containing trialkylaluminum). Step (b): A solution of TMAL (2.84 mol) mixed with hexane (1.02 kg) was added to the above mixture, and water (3.73 mol = 1.31 equivalents relative to TMAL) was added over 9 hours while maintaining the internal temperature at 1±2°C. The internal temperature was then raised to 50±2°C over 35 minutes, aged at the same temperature for 1 hour, and then cooled to 30°C. The insoluble gel in the resulting composition had an Al content of 1.71 g, equivalent to 2.2 mol% of the TMAL used. NMR analysis of the liquid phase of the resulting composition revealed that the methyl group signals were modified methylaluminoxane: unreacted TMAL = 0.969:0.031. Therefore, the MAO integral ratio was 0.969, and the yield of soluble modified methylaluminoxane was calculated to be 95%.

[0041] [Example 2] Step (a): TIBAL (1.76 mol) and MCH (0.53 kg) were weighed and mixed in a 5 L separable flask to obtain a mixture (a composition containing trialkylaluminum). Step (b): A solution of TMAL (2.83 mol) mixed with MCH (1.02 kg) was added to the above mixture, and water (3.71 mol = 1.31 equivalents relative to TMAL) was added over 10 hours while maintaining the internal temperature at 1±2°C. The internal temperature was then raised to 50±2°C over 50 minutes, aged at the same temperature for 1 hour, and then cooled to 30°C. The insoluble gel in the resulting composition had an Al content of 1.48 g, equivalent to 1.9 mol% of the TMAL used. NMR analysis of the liquid phase of the resulting composition revealed that the methyl group signals were modified methylaluminoxane: unreacted TMAL = 0.951:0.049. Therefore, the MAO integral ratio was 0.951, and the yield of soluble modified methylaluminoxane was calculated to be 93%. Polymerization activity evaluation: The reaction product (modified methylaluminoxane composition) obtained in Example 2 was diluted with toluene to an Al concentration of 0.6 M to prepare a cocatalyst solution. Toluene (1.0 L) was added to a 1.5 L autoclave under an ethylene atmosphere, and triethylaluminum (0.50 mmol, 0.5 M hexane solution) was added. The internal temperature was raised to 40 ± 2 °C, and the main catalyst bis(1-butyl-3-methylcyclopentadienyl)zirconium dichloride (2.5 μmol, 3.0 mM toluene solution) and the cocatalyst solution (0.50 mmol as Al) were sequentially added. Ethylene was then introduced at a flow rate of 5.0 L / min to increase the gauge pressure to 0.8 MPa, and the mixture was stirred at 50 ± 2 °C for 1 hour. The ethylene introduction was then stopped, and the mixture was replaced with a nitrogen atmosphere and allowed to cool. The resulting polyethylene was collected by suction filtration and dried. The polymerization activity was calculated from its dry mass and the amount of ethylene consumed, and was found to be 21.2 kg-PE / mmol-Zr. The polymerization activity is calculated using the following formula. Note that the mass [kg] of consumed ethylene was quantified using a mass flow meter, and the same results were obtained by using this as the mass [kg] of the resulting polymer. Mass of the obtained polymer (PE: polyethylene) [kg] / Amount of the main catalyst added [mmol] = Polymerization activity [kg-PE / mmol-Zr (main catalyst)]

[0042] [Example 3] Step (a): TIBAL (1.76 mol) and MCH (1.40 kg) were weighed and mixed in a 5 L separable flask to obtain a mixture (a composition containing trialkylaluminum). Water (0.528 mol) was added to the mixture over 100 minutes while maintaining the internal temperature at 1±2°C, and the mixture was aged at the same temperature for 1 hour. The internal temperature was then raised to 20±2°C over 1 hour to obtain a polyisobutylaluminoxane composition. Step (b): A solution of TMAL (2.82 mol) mixed with MCH (150 g) was added to the polyisobutylaluminoxane composition, and water (3.18 mol = 1.13 equivalents relative to TMAL) was added over 6.75 hours while maintaining the internal temperature at 1±2°C. The internal temperature was then raised to 50±2°C over 50 minutes, aged at the same temperature for 1 hour, and then cooled to 30°C. The insoluble gel in the resulting composition had an Al content of 3.70 g, equivalent to 4.9 mol% of the TMAL used. NMR analysis of the liquid phase of the resulting composition revealed that the methyl group signals were modified methylaluminoxane: unreacted TMAL = 0.961:0.039. Therefore, the MAO integral ratio was 0.961, and the yield of soluble modified methylaluminoxane was calculated to be 91%. Ethylene polymerization was carried out by the method described in Example 2 using the composition obtained in Example 3, and the polymerization activity was calculated to be 21.3 kg-PE / mmol-Zr.

[0043] GC analysis was performed on the modified methylaluminoxane compositions obtained in Examples 1 to 3. From the results obtained, it was determined that the x and y of the modified methylaluminoxane contained in the modified methylaluminoxane composition obtained in each Example were each independently a positive real number, and the x / y ratio was 0.1 or more and 25 or less.

[0044] [Comparative Example 1] Step (a): TIBAL (1.77 mol) and hexane (1.40 kg) were weighed and mixed in a 5 L separable flask to obtain a mixture (a composition containing trialkylaluminum). Water (1.24 mol) was added to the mixture over 3.5 hours while maintaining the internal temperature at 1±2°C, and the mixture was aged at the same temperature for 1 hour. The internal temperature was then raised to 20±2°C over 1 hour to obtain a polyisobutylaluminoxane composition. Step (b): A solution of TMAL (2.82 mol) mixed with hexane (150 g) was added to the polyisobutylaluminoxane composition, and the internal temperature was then raised to 50±2°C over 40 minutes, aged at the same temperature for 1 hour, and cooled to 30°C. Subsequently, water (2.48 mol = 0.88 equivalents relative to TMAL) was added over 6 hours while maintaining the internal temperature at 1±2°C, and the internal temperature was then raised to 50±2°C over 35 minutes, aged at the same temperature for 1 hour, and cooled to 30°C. The insoluble gel in the resulting composition had an Al content of 6.86 g, equivalent to 9.0 mol% of the TMAL used. NMR analysis of the liquid phase of the resulting composition revealed that the methyl group signal breakdown was modified methylaluminoxane: unreacted TMAL = 0.935:0.065. Therefore, the MAO integral ratio was 0.935, and the yield of soluble modified methylaluminoxane was calculated to be 85%.

[0045] Comparative Example 2 Step (a): TIBAL (1.77 mol) and MCH (1.41 kg) were weighed and mixed in a 5 L separable flask to obtain a mixture (a composition containing trialkylaluminum). Water (1.24 mol) was added to the mixture over 3.5 hours while maintaining the internal temperature at 1±2°C, and the mixture was aged at the same temperature for 1 hour. The internal temperature was then raised to 20±2°C over 1 hour to obtain a polyisobutylaluminoxane composition. Step (b): A solution of TMAL (2.84±0.02 mol) mixed with MCH (150 g) was added to the polyisobutylaluminoxane composition, and the internal temperature was then raised to 50±2°C over 30 minutes, aged at the same temperature for 1 hour, and cooled to 30°C. Subsequently, water (2.50 mol = 0.88 equivalents relative to TMAL) was added over 5 hours while maintaining the internal temperature at 1±2°C, and the internal temperature was then raised to 50±2°C over 30 minutes, aged at the same temperature for 1 hour, and cooled to 30°C. The insoluble gel in the resulting composition had an Al content of 8.28 g, equivalent to 10.8 mol% of the TMAL used. NMR analysis of the liquid phase of the resulting composition revealed that the methyl group signals were modified methylaluminoxane: unreacted TMAL = 0.903:0.097. Therefore, the MAO integral ratio was 0.903, and the yield of soluble modified methylaluminoxane was calculated to be 81%.

[0046] Comparative Example 3 The procedure described for Comparative Example 2 was repeated, except that the amount of water added in step (b) was changed to 2.06 mol (0.72 equivalents relative to TMAL). The insoluble gel in the resulting composition had an Al component content of 4.51 g, equivalent to 5.8 mol% of the TMAL charged. NMR analysis of the liquid phase of the resulting composition revealed that the breakdown of methyl group signals was modified methylaluminoxane: unreacted TMAL = 0.856:0.144. Therefore, the MAO integral ratio was 0.856, and the yield of soluble modified methylaluminoxane was calculated to be 81%.

[0047] Comparative Example 4 The procedure described for Comparative Example 2 was repeated, except that the amount of water added in step (b) was changed to 1.78 mol (0.63 equivalents relative to TMAL). The insoluble gel in the resulting composition had an Al content of 4.52 g, equivalent to 5.9 mol% of the TMAL charged. NMR analysis of the liquid phase of the resulting composition revealed that the breakdown of methyl group signals was modified methylaluminoxane: unreacted TMAL = 0.758:0.242. Therefore, the MAO integral ratio was 0.758, and the yield of soluble modified methylaluminoxane was calculated to be 71%.

[0048] Comparative Example 5 As a reproduction experiment of Examples 48 to 50 of Patent Document 1 (Japanese Patent Laid-Open Publication No. 2000-119278), modified methylaluminoxane was prepared by the following method. Step (a): In a 500 mL flask, water (0.267 mol) was added to a mixture of TIBAL (0.300 mol) and toluene (178 g) over 2.5 hours while maintaining the internal temperature at 12° C. or below. The internal temperature was then raised to 75±5° C., and after the bubbling of isobutane gas had subsided, the temperature was allowed to naturally cool (20±5° C.). Step (b): Next, TMAL (0.150 mol) was added, and the internal temperature was raised to 75±5°C over 30 minutes. The mixture was then aged at this temperature for 1 hour and then allowed to cool naturally (20±5°C). Water (0.134 mol = 0.89 equivalents relative to TMAL) was added to this composition while maintaining the internal temperature at 5±5°C. A large amount of white solid was formed at the end of the reaction. Samples were taken at 0.047 mol (0.31 equivalents relative to TMAL) and 0.078 mol (0.52 equivalents relative to TMAL) of water added during the reaction and analyzed by NMR. The ratio of the integral value of the methyl group signal accounted for by the modified methylaluminoxane (i.e., the MAO integral ratio) was 0.663 at 0.047 mol and 0.763 at 0.078 mol. The insoluble gel contained 0.33 g of Al, equivalent to 8.2 mol% of the TMAL added.

[0049] Comparative Example 6 A modified methylaluminoxane was prepared by carrying out the same method as in Example 49 of Patent Document 1 (JP-A No. 2000-119278) in MCH solvent as follows. Step (a): In a 500 mL flask, water (0.267 mol) was added to a mixture of TIBAL (0.300 mol) and MCH (158 g) over 2.5 hours while maintaining the internal temperature at 12° C. or less. The internal temperature was then raised to 73±2° C., and after the bubbling of isobutane gas had subsided, the temperature was allowed to naturally cool (25±5° C.). Step (b): Next, TMAL (0.150 mol) was added, and the internal temperature was raised to 75±2°C over 10 minutes. The mixture was then aged at the same temperature for 1 hour, and then allowed to cool naturally (25±5°C). Water (0.134 mol = 0.89 equivalents relative to TMAL) was added to this composition while maintaining the internal temperature at 5±5°C. The resulting insoluble gel had an Al content of 0.55 g, equivalent to 13.5 mol% of the TMAL added. NMR analysis of the liquid phase of the resulting composition revealed a breakdown of the methyl group signals: modified methylaluminoxane: unreacted TMAL = 0.907:0.093. Therefore, the MAO integral ratio was 0.907, and the yield of soluble modified methylaluminoxane was calculated to be 78%.

[0050] The results are shown in the table below.

[0051] [Table 1]

[0052] From the results shown in Table 1, it can be confirmed that in Examples 1 to 3, modified methylaluminoxane was produced in high yield and the amount of residual TMAL in the obtained modified methylaluminoxane was small. The results of Example 2 compared to Example 1 and the results of Comparative Example 2 compared to Comparative Example 1 show that the yield and MAO integral ratio (an index of the amount of TMAL remaining) are lower in MCH than in hexane. However, the fact that the yield and MAO integral ratio of Example 2 (solvent: MCH) exceed those of Comparative Example 1 (solvent: hexane) indicates the advantage of adding water in the amount equal to or greater than the above-mentioned predetermined amount in step (b), regardless of the type of solvent. On the other hand, a comparison with Comparative Examples 2 to 4 reveals that when the amount of water added in step (b) is below the predetermined amount described above, the amount of insoluble gel increases as the amount of water added in step (b) increases, and the yield plateaus. Regarding Comparative Example 5, according to the disclosure of Examples 48 to 50 of Patent Document 1 (JP 2000-119278 A), when the amount of water added in step (b) was 0.31 equivalents, 99.5% was soluble, and when the amount was 0.52 equivalents, 93.3% was soluble (paragraph 0027 of Patent Document 1 (JP 2000-119278 A)). However, the MAO integral ratios of Comparative Example 5, which were performed as a reproduction experiment, were 0.663 and 0.763, respectively, which were significantly lower than those of Examples 1 to 3. In Comparative Example 5, when the amount of water added in step (b) was increased to 0.89 equivalents, the MAO integral ratio improved to 0.940, but the amount of insoluble gel increased and the yield decreased. The same was true for Comparative Example 6, in which the solvent type was changed to the same as in Examples 2 and 3. This shows that conventional methods such as the method described in Patent Document 1 (JP 2000-119278 A) do not achieve an improvement in yield. [Industrial Applicability]

[0053] One aspect of the present invention is useful in the art of olefin polymerization.

Claims

1. A method for producing a modified methylaluminoxane having a structural unit represented by the following formula (I) in a number x of structural units and a structural unit represented by the following formula (II) in a number y of structural units, 【Chemical 1】 (In the above formula, R represents an alkyl group having 2 to 10 carbon atoms, * represents a bonding position, x and y each independently represent a positive real number, provided that the x / y ratio is 0.1 to 25. When a plurality of R's are present in the modified methylaluminoxane, the plurality of R's may be the same or different. The structural unit represented by formula (I) and the structural unit represented by formula (II) may be arranged in any order in the modified methylaluminoxane.) R ３ and (b) adding 1.10 or more molar equivalents of water relative to the amount of trimethylaluminum to a mixture containing a trialkylaluminum represented by formula (II) Al (R has the same meaning as R in formula (II)) and trimethylaluminum, thereby partially hydrolyzing the trialkylaluminum and trimethylaluminum.

2. The method according to claim 1, wherein in formula (II), R represents an isobutyl group.

3. The step (b) is a step of subjecting the mixture to a reaction with R ３ 3. The method of claim 1 or 2, further comprising preparing the composition by adding trimethylaluminum to a composition containing a trialkylaluminum represented by Al.

4. Before the step (b), R ３ (a) preparing the composition comprising a trialkylaluminum represented by Al; and The method according to claim 3, wherein no water is added in step (a).

5. Before the step (b), R ３ (a) preparing the composition comprising a trialkylaluminum represented by Al; and In the step (a), R ３ The method according to claim 3, wherein water is added in an amount of less than 0.60 equivalents on a molar basis relative to the amount of trialkylaluminum represented by Al.

6. The method according to claim 1 or 2, wherein the modified methylaluminoxane has a methylaluminoxane integral ratio of 0.950 or more.

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