A method for purifying trimethoxy (pentamethylcyclopentadienyl) titanium

Abstract

This invention belongs to the field of chemical production technology, specifically disclosing a purification method for trimethoxy(pentamethylcyclopentadienyl)titanium, comprising the following steps: vacuum distillation of crude trimethoxy(pentamethylcyclopentadienyl)titanium raw material to obtain a crude distillate; adding 5-20 parts by mass of a modifier to 100 parts by mass of the crude distillate, wherein the modifier is at least one selected from triethylene glycol dibutyl ether, tetraethylene glycol dibutyl ether, n-heptadecane, n-octadecane, and mineral oil, and then distilling to obtain the product. This invention achieves large-scale purification of Star-Ti, achieving a distillation yield of over 75%, with a maximum of over 95%, and obtaining a high-purity product with an organic purity of over 99.5%, solving the problems of difficult large-scale purification, difficulty in purity improvement, and low recovery rate of Star-Ti in existing technologies.

Description

Technical Field

[0001] This invention belongs to the field of chemical production technology, and specifically discloses a method for purifying trimethoxy (pentamethylcyclopentadienyl) titanium. Background Technology

[0002] Trimethoxy (pentamethylcyclopentadienyl)titanium (molecular formula: Me5CpTi(OMe)3, abbreviated as Star-Ti) is an important precursor for preparing titanium thin films (such as titanium nitride, strontium titanate, titanium dioxide, etc.) using atomic layer deposition (ALD) and chemical vapor deposition (CVD) techniques. It has broad application prospects in fields such as dielectric layers of DRAM capacitors, diffusion barrier layers of copper interconnects, gate electrode materials, and optical thin films. As the feature size of semiconductor devices continues to shrink, downstream manufacturers have extremely stringent requirements for the purity of Star-Ti precursors, typically requiring a metal purity of 5N (99.999%) or higher and an organic purity of 99.5% or higher.

[0003] Currently, there are several reported synthetic routes for Star-Ti. For example, J. Organometal. Chem. 340 (1988) 37-40 reported the preparation of (pentamethylcyclopentadienyl)titanium trichloride by reacting pentamethylcyclopentadienyllithium with titanium tetrachloride, followed by reaction with sodium methoxide to generate Star-Ti. However, this route has a low overall yield (only about 15%) and lengthy reaction steps. Chinese patent CN117946187A discloses a method for synthesizing Star-Ti by reacting tetramethyl titanate and titanium tetrachloride with pentamethylcyclopentadienyl potassium. This route shortens the reaction steps and achieves higher metal purity. However, all of the above synthetic methods share a common problem: the crude Star-Ti product contains residual high-boiling-point organic impurities (such as by-reaction products), which are difficult to effectively remove by conventional distillation or single distillation operations. More challenging is that these impurities cause significant changes in the physical properties of the distillation system (such as relative volatility and vapor-liquid equilibrium constant) during the distillation process, leading to a sharp deterioration in separation efficiency. Even with a taller distillation column and a larger reflux ratio, it is impossible to obtain a high-purity product while maintaining the yield. For example, when using conventional vacuum distillation to directly purify crude Star-Ti, the product yield is usually below 55%, and the organic purity is difficult to consistently reach above 99.0%.

[0004] Therefore, the existing Star-Ti purification methods have the following main drawbacks: (1) Conventional vacuum distillation or rectification cannot effectively remove high-boiling-point impurities, resulting in insufficient organic purity of the product.

[0005] (2) Impurities during distillation cause changes in the physical properties of the system, resulting in low separation efficiency and low yield (usually less than 55%).

[0006] (3) It is difficult to achieve large-scale (kilogram level or above) stable production of high-purity (organic purity ≥99.5%) Star-Ti.

[0007] Therefore, there is an urgent need to provide a Star-Ti purified product with high yield and high purity that can meet the needs of large-scale process production. Summary of the Invention

[0008] The purpose of this invention is to provide a purification method for trimethoxy(pentamethylcyclopentadienyl)titanium. This invention enables the large-scale purification of Star-Ti, significantly improves the distillation yield (up to 95% or more), and obtains a high-purity product with an organic purity of 99.5% or more. This solves the problems of difficult large-scale purification of Star-Ti, difficulty in improving purity, and low recovery rate in the prior art.

[0009] To achieve the above objectives, the present invention employs the following technical solution: a method for purifying trimethoxy(pentamethylcyclopentadienyl)titanium, comprising the following steps: S1. Distillation of crude trimethoxy(pentamethylcyclopentadienyl)titanium under reduced pressure to obtain crude distillate; S2. Add a modifier to the crude distillate at a mass ratio of 100:(5-20). The modifier is at least one of triethylene glycol dibutyl ether, tetraethylene glycol dibutyl ether, n-heptadecane, n-octadecane, and mineral oil. Distill under an inert gas atmosphere to obtain a purified product.

[0010] A further improvement to the purification method for trimethoxy(pentamethylcyclopentadienyl) titanium: Preferably, the pressure of the vacuum distillation is 20-100 Pa, and the distillation temperature is 130-180℃.

[0011] Preferably, in step S2, 7-15 parts by mass of a modifier are added to 100 parts by mass of the crude distillate.

[0012] Preferably, in step S2, 8-12 parts by mass of a modifier are added to 100 parts by mass of the crude distillate.

[0013] Preferably, in step S2, the temperature of the distillation process is ≤160℃, the distillation pressure is 3-100 Pa, the reflux ratio is 1:(2-4), and the height of the distillation column is ≥1 m.

[0014] Preferably, in step S2, the temperature of the distillation process is 120-160℃ and the distillation pressure is 10-80 Pa.

[0015] Preferably, in step S2, the temperature of the distillation process is 140-160℃ and the distillation pressure is 30-60 Pa.

[0016] Preferably, in step S2, the distillation process uses a distillation column with a height of 1.5 m, 2 m, 3 m, 4 m, or 5 m.

[0017] Preferably, in step S2, the packing material in the distillation column is at least one of Raschig rings, spiral rings, ceramic corrugated packing, metal corrugated packing, metal wire mesh packing, glass spring packing, stainless steel spring packing, and Sitta ring packing.

[0018] Preferably, the modifier is at least one of triethylene glycol dibutyl ether and tetraethylene glycol dibutyl ether.

[0019] The design concept of this invention is as follows: This invention adds specific modifiers (such as high-boiling-point ethers, high-boiling-point alkanes, or mixtures of high-boiling-point hydrocarbons) before distillation to significantly improve the purification yield of trimethoxy(pentamethylcyclopentadienyl)titanium (Star-Ti) and achieve large-scale production. The selection of modifiers in this invention is based on the following points: First, to change the macroscopic properties of the distillation system. Experiments have shown that high-boiling impurities and unreacted materials during crude product distillation can lead to changes in the macroscopic properties of the distillation system, such as significantly reduced fluidity and decreased mass transfer efficiency. Adding high-boiling-point, thermally stable modifiers can dilute and homogenize the system, and the modifiers can act as a continuous phase to uniformly disperse local hot spots, ensuring stable distillation. Second, to retain heavy components and high-boiling impurities in the crude product. The boiling point of the modifier is much higher than the distillation temperature, allowing it to act as a solvent for dissolving impurities, causing them to be retained in the modifier and separated from the product. Third, to utilize the modifier to change the intermolecular forces between Star-Ti and various impurities, achieving a selective retention effect. Star-Ti and impurities in the crude product, such as unreacted ligands, oligomeric titanyl alkane, halide byproducts, or polymers of these substances, exhibit strong intermolecular forces, forming stable associative compounds. The apparent boiling points of these associative compounds are extremely close to those of the Star-Ti monomer, sometimes even exhibiting azeotropy, thus preventing separation by conventional distillation or rectification. Selecting specific modifiers can preferentially coordinate with impurity molecules or induce stronger intermolecular interactions, disrupting the original associative compound structure. However, the interaction between these modifiers and Star-Ti monomer molecules is weaker, leading to easier breakage and stable product release, effectively improving separation efficiency. The initial distillation removes light components and a small amount of heavy components, providing a controllable feedstock state for subsequent rectification. Using specific types of modifiers allows for property regulation and selective association, further matching the specified rectification temperature and pressure, altering the properties of high-boiling impurities, ensuring better selective association, preventing precursor decomposition, and effectively improving purification yield and efficiency. This approach is highly suitable for large-scale purification processes.

[0020] The advantages of this invention compared to the prior art are as follows: 1. Existing technologies cannot effectively remove high-boiling-point impurities with similar boiling points or strong interactions, and these impurities can cause changes in the physical properties of the distillation system, leading to low separation efficiency and hindering large-scale production. This invention breaks away from the traditional technical bias in the semiconductor purification field of "avoiding the introduction of foreign substances that lead to excess impurities." It creatively introduces modifiers into the distillation process. These modifiers not only improve the phase changes of the system through dilution and homogenization but also retain high-boiling-point impurities, increasing the purification yield. By selecting specific modifiers, the intermolecular interactions between impurities and Star-Ti monomers can be readjusted, achieving an organic purity of over 99.5%, thus realizing the effective separation of impurities and products that cannot be removed by ordinary distillation or rectification.

[0021] 2. This invention utilizes distillation, modification of the distillation system by a modifier, and a specific distillation process. These three aspects work together to effectively improve distillation efficiency, save distillation time, and achieve a purification yield of up to 95% or more. This enables large-scale synthesis and effectively improves the economic benefits of the process.

[0022] 3. The Star-Ti purified product prepared by the purification method of this invention has a metal purity of ≥99.9999% and an organic purity of ≥99.5%, which has good competitiveness and market value in high-end application fields such as semiconductor, photovoltaic and new energy fields. Attached Figure Description

[0023] Figure 1 The crude raw material obtained for the preparation example 1 H NMR spectrum.

[0024] Figure 2 The crude distillate from Example 1 1 H NMR spectrum.

[0025] Figure 3 The purified product in Example 1 1 H NMR spectrum.

[0026] Figure 4 For the purified product in Comparative Example 3 1 H NMR spectrum. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0028] Preparation Example Under nitrogen protection, 5.16 kg (30 mol) of tetramethyl titanate and 100 L of tetrahydrofuran were added to a reaction flask. Then, while stirring, 1.9 kg (10 mol) of titanium tetrachloride was added to the reaction system. The temperature was then slowly increased to reflux, and the reaction was continued under reflux for 12 h. The reaction temperature was then lowered to room temperature, and another 10 L of tetrahydrofuran was added to the reaction system. Then, while stirring, 1.74 kg (10 mol) of potassium pentamethylcyclopentadienyl was added, and the reaction was continued under reflux for 12 h. The reaction temperature was then lowered, and solid impurities were filtered out in a glove box. The liquid was collected, and the solvent was distilled off, yielding crude trimethoxy(pentamethylcyclopentadienyl)titanium. Testing revealed that... 1 The purity of H NMR is 70.53%.

[0029] Example 1 This embodiment provides a method for purifying trimethoxy(pentamethylcyclopentadienyl) titanium, including the following steps: S1. Take 3.2 kg of crude trimethoxy(pentamethylcyclopentadienyl)titanium from the preparation example and distill it under reduced pressure at 100 Pa and 140 °C to obtain 2.80 kg of crude distillate. S2. Add tetraethylene glycol dibutyl ether (TEGD) as a modifier to the crude distillate at a mass ratio of 100:10 to obtain a mixture. Prepare a 1 m high distillation column filled with stainless steel spring packing. Distill the mixture under inert gas protection at a temperature of 150 °C, a pressure of 40 Pa, and a reflux ratio of 1:2 to obtain 2.66 kg of purified product. The calculated distillation yield is 95%.

[0030] Example 2 This embodiment provides a method for purifying trimethoxy(pentamethylcyclopentadienyl) titanium, including the following steps: S1. Take 3.2 kg of crude trimethoxy(pentamethylcyclopentadienyl)titanium from the preparation example and distill it under reduced pressure at 100 Pa and 150 °C to obtain 2.91 kg of crude distillate. S2. Add tetraethylene glycol dibutyl ether (TEGD) as a modifier to the crude distillate at a mass ratio of 100:7 to obtain a mixture. Prepare a 1.5 m high distillation column filled with stainless steel spring packing. Distill the mixture under inert gas protection at a temperature of 150 °C, a pressure of 55 Pa, and a reflux ratio of 1:2 to obtain 2.64 kg of purified product. The calculated distillation yield is 90.7%.

[0031] Example 3 This embodiment provides a method for purifying trimethoxy(pentamethylcyclopentadienyl) titanium, including the following steps: S1. Take 3.2 kg of crude trimethoxy(pentamethylcyclopentadienyl)titanium from the preparation example and distill it under reduced pressure at 80 Pa and 140 °C to obtain 2.69 kg of crude distillate. S2. Add tetraethylene glycol dibutyl ether (TEGD) as a modifier to the crude distillate at a mass ratio of 100:20 to obtain a mixture. Prepare a 1 m high distillation column filled with stainless steel spring packing. Distill the mixture under inert gas protection at a temperature of 160 °C, a pressure of 60 Pa, and a reflux ratio of 1:4 to obtain 2.35 kg of purified product. The calculated distillation yield is 87.4%.

[0032] Example 4 This embodiment provides a method for purifying trimethoxy(pentamethylcyclopentadienyl) titanium, including the following steps: S1. Take 3.2 kg of crude trimethoxy(pentamethylcyclopentadienyl)titanium raw material from the preparation example and distill it under reduced pressure at 100 Pa and 160 °C to obtain 2.93 kg of crude distillate. S2. Add tetraethylene glycol dibutyl ether (TEGD) as a modifier to the crude distillate at a mass ratio of 100:15 to obtain a mixture. Prepare a 1.5 m high distillation column filled with stainless steel spring packing. Distill the mixture under inert gas protection at a temperature of 155 °C, a pressure of 30 Pa, and a reflux ratio of 1:3 to obtain 2.47 kg of purified product. The calculated distillation yield is 84.3%.

[0033] Example 5 This embodiment provides a method for purifying trimethoxy(pentamethylcyclopentadienyl) titanium, including the following steps: S1. Take 3.2 kg of crude trimethoxy(pentamethylcyclopentadienyl)titanium from the preparation example and distill it under reduced pressure at 20 Pa and 130 °C to obtain 2.82 kg of crude distillate. S2. Add the modifier triethylene glycol dibutyl ether to the crude distillate at a mass ratio of 100:5 to obtain a mixture. Prepare a 2 m high distillation column filled with wire mesh packing. Distill the mixture under inert gas protection at a temperature of 140℃, a pressure of 3 Pa, and a reflux ratio of 1:2 to obtain 2.34 kg of purified product. The distillation yield is calculated to be 83.0%.

[0034] Example 6 This embodiment provides a method for purifying trimethoxy(pentamethylcyclopentadienyl) titanium, including the following steps: S1. Take 3.2 kg of crude trimethoxy(pentamethylcyclopentadienyl)titanium from the preparation example and distill it under reduced pressure at 60 Pa and 180 °C to obtain 2.85 kg of crude distillate. S2. Add the modifier n-heptadecane to the crude distillate at a mass ratio of 100:18 to obtain a mixture. Prepare a 1 m high distillation column filled with stainless steel spring packing. Distill the mixture under inert gas protection at a distillation temperature of 150℃, a distillation pressure of 100 Pa, and a reflux ratio of 1:3 to obtain 2.44 kg of purified product. The calculated distillation yield is 85.6%.

[0035] Example 7 This embodiment provides a method for purifying trimethoxy(pentamethylcyclopentadienyl) titanium, including the following steps: S1. Take 3.2 kg of crude trimethoxy(pentamethylcyclopentadienyl)titanium raw material from the preparation example and distill it under reduced pressure at 50 Pa and 150 °C to obtain 2.73 kg of crude distillate. S2. A modifier, a mixture of n-octadecane and mineral oil in a 1:1 mass ratio, is added to the crude distillate at a mass ratio of 100:12 to obtain a mixture. A 3 m high distillation column is prepared and filled with ceramic corrugated packing. The mixture is distilled under inert gas protection at a temperature of 130 °C, a pressure of 50 Pa, and a reflux ratio of 1:2.5, yielding 2.18 kg of purified product. The calculated distillation yield is 79.9%.

[0036] Example 8 This embodiment provides a method for purifying trimethoxy(pentamethylcyclopentadienyl) titanium, including the following steps: S1. Take 3.2 kg of crude trimethoxy(pentamethylcyclopentadienyl)titanium from the preparation example and distill it under reduced pressure at 80 Pa and 140 °C to obtain 2.76 kg of crude distillate. S2. Add mineral oil as a modifier to the crude distillate at a mass ratio of 100:8 to obtain a mixture. Prepare a 5 m high distillation column filled with glass spring packing. Distill the mixture under inert gas protection at a temperature of 120℃, a pressure of 80 Pa, and a reflux ratio of 1:4 to obtain 2.11 kg of purified product. The calculated distillation yield is 76.4%.

[0037] Comparative Example 1 This comparative example provides a method for purifying trimethoxy(pentamethylcyclopentadienyl) titanium, the specific steps of which are as follows: 2.8 kg of crude trimethoxy(pentamethylcyclopentadienyl)titanium from the preparation example was taken. A 1 m high distillation column was prepared, filled entirely with stainless steel spring packing. The crude product was directly distilled under inert gas protection at a temperature of 150 °C, a pressure of 40 Pa, and a reflux ratio of 1:2, yielding 1.30 kg of purified product. The calculated distillation yield was 46%.

[0038] Comparative Example 2 This comparative example provides a method for purifying trimethoxy(pentamethylcyclopentadienyl) titanium, the specific steps of which are as follows: 2.9 kg of crude trimethoxy(pentamethylcyclopentadienyl)titanium from the preparation example was taken. A 2 m high distillation column was prepared, filled entirely with stainless steel spring packing. The crude feedstock was directly distilled under inert gas protection at a temperature of 150 °C, a pressure of 40 Pa, and a reflux ratio of 1:2, yielding 1.60 kg of purified product. The calculated distillation yield was 55%.

[0039] Comparative Example 3 This comparative example provides a purification method for trimethoxy(pentamethylcyclopentadienyl)titanium, with the specific steps referring to Example 1, except that tetraethylene glycol dibutyl ether is not added in step S2. A final product of 1.81 kg was obtained, with a calculated distillation yield of 64.6%.

[0040] Comparative Example 4 This comparative example provides a method for purifying trimethoxy(pentamethylcyclopentadienyl)titanium. The specific steps are the same as in Example 1, except that tetraethylene glycol dibutyl ether is replaced with tetrahydrofuran in step S2. A total of 1.95 kg of purified product was obtained, with a calculated distillation yield of 69.6%.

[0041] Comparative Example 5 This comparative example provides a method for purifying trimethoxy(pentamethylcyclopentadienyl)titanium. The specific steps are the same as in Example 1, except that in step S2, tetraethylene glycol dibutyl ether is replaced with toluene. A total of 2.08 kg of purified product was obtained, with a calculated distillation yield of 74.3%.

[0042] Performance testing: Appendix Figure 1 The crude raw material obtained for the preparation example 1 H NMR spectrum; attached Figure 2 For the crude distillate of Example 1 1 H NMR spectrum; attached Figure 3 Purified product of Example 1 1 HNMR spectrum. (Attached) Figure 1-3The comparison shows that distillation cannot remove high-boiling-point impurities, and high-boiling-point substances have a significant impact on the yield and purity of the qualified product (the core influencing factor on the yield of the qualified product is the distillation yield, which is calculated as: Distillation yield = Purified product quality / Distilled crude product quality). 100%.

[0043] Take the purified products from Examples 1-4 and Comparative Examples 1-5 above, and use... 1 Organic purity was determined by 1H NMR, and metal purity was determined by ICP-MS / MS. The test results are shown in Table 1.

[0044] Table 1. Process yield and purity tests for Examples 1-8 and Comparative Examples 1-5

[0045] The test results in Table 1 above show that: (1) Compared with Example 1, the process of Comparative Example 1 did not use vacuum distillation and added modifier, which greatly reduced the product yield, made it difficult to remove high-boiling impurities, and the impurities were not completely removed, resulting in poor product purity (see Table 1); in ICP-MS / MS testing, the contents of some metal elements such as Na, K, Ca and Zn were significantly exceeded.

[0046] (2) Compared with the purification process of Comparative Example 1, Comparative Example 2, by increasing the height of the distillation column to 2m, although it is beneficial to improve the separation degree of the product and impurities, still cannot completely remove the impurities. Its yield and purity are far inferior to the solution of the example.

[0047] (3) Compared to Example 1, Comparative Example 3 did not add a modifier during the distillation process, resulting in a lower yield and lower product purity. Appendix Figure 4 Purification of the product for Comparative Example 3 1 H NMR characterization map, and Figure 3 Example 1: Purification of the product 1 A comparison of the H NMR spectra shows that the technical solution in Comparative Example 3 cannot completely remove high-boiling impurities.

[0048] (4) Compared with Example 1, Comparative Example 4 replaced the modifier with tetrahydrofuran. However, tetrahydrofuran has a low boiling point and cannot retain high-boiling impurities well, so the distillation yield and product purity are still not as good as in Example 1.

[0049] (5) Compared with Comparative Example 1, Comparative Example 5, which replaced the modifier with toluene, showed a decrease in both process yield and product purity. This confirms that the modifier not only produces dilution homogenization and dissolves and retains high-boiling-point impurities, but may also change the association state of the distillation system through selective intermolecular interactions with high-boiling impurities and Star-Ti, making it more difficult for high-boiling impurities to be removed and easier for Star-Ti to be removed, thereby achieving a distillation yield and product purity that are difficult to achieve with existing technologies.

[0050] In summary, this invention employs a process that combines distillation, the addition of a specific modifier, and rectification. These three processes work synergistically to effectively improve rectification efficiency, save rectification time, and achieve a rectification yield of up to 95%. This enables large-scale synthesis and effectively improves the economic benefits of the process.

[0051] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method for purifying trimethoxy(pentamethylcyclopentadienyl)titanium, characterized in that, Includes the following steps: S1. Distillation of crude trimethoxy(pentamethylcyclopentadienyl)titanium under reduced pressure to obtain crude distillate; S2. Add a modifier to the crude distillate at a mass ratio of 100:(5-20). The modifier is at least one of triethylene glycol dibutyl ether, tetraethylene glycol dibutyl ether, n-heptadecane, n-octadecane, and mineral oil. Distill under an inert gas atmosphere to obtain a purified product.

2. The purification method for trimethoxy(pentamethylcyclopentadienyl)titanium according to claim 1, characterized in that, The pressure of the vacuum distillation is 20-100 Pa, and the distillation temperature is 130-180℃.

3. The purification method for trimethoxy(pentamethylcyclopentadienyl)titanium according to claim 1, characterized in that, In step S2, 7-15 parts by mass of modifier are added to 100 parts by mass of crude distillate.

4. The purification method for trimethoxy(pentamethylcyclopentadienyl) titanium according to claim 3, characterized in that, In step S2, 8-12 parts by mass of modifier are added to 100 parts by mass of crude distillate.

5. The purification method for trimethoxy(pentamethylcyclopentadienyl)titanium according to claim 1, characterized in that, In step S2, the temperature of the distillation process is ≤160℃, the distillation pressure is 3-100 Pa, the reflux ratio is 1:(2-4), and the height of the distillation column is ≥1 m.

6. The purification method for trimethoxy(pentamethylcyclopentadienyl) titanium according to claim 5, characterized in that, In step S2, the temperature of the distillation process is 120-160℃ and the distillation pressure is 10-80 Pa.

7. The purification method for trimethoxy(pentamethylcyclopentadienyl)titanium according to claim 6, characterized in that, In step S2, the temperature of the distillation process is 140-160℃ and the distillation pressure is 30-60 Pa.

8. The purification method for trimethoxy(pentamethylcyclopentadienyl)titanium according to claim 5, characterized in that, In step S2, the distillation process uses a distillation column with a height of 1.5 m, 2 m, 3 m, 4 m, or 5 m.

9. The purification method for trimethoxy(pentamethylcyclopentadienyl)titanium according to claim 1, characterized in that, In step S2, the packing material in the distillation column is at least one of Raschig rings, spiral rings, ceramic corrugated packing, metal corrugated packing, metal wire mesh packing, glass spring packing, stainless steel spring packing, and Sitta ring packing.

10. The purification method for trimethoxy(pentamethylcyclopentadienyl)titanium according to claim 1, characterized in that, The modifier is preferably at least one of triethylene glycol dibutyl ether and tetraethylene glycol dibutyl ether.

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