A crystalline form of bis(4-mellitic anhydride) ethylene glycol ester and a method of making the same

Abstract

This invention provides a crystal form of bis(4-triphenyltriamic anhydride)ethylene glycol ester and its preparation method, belonging to the fields of organic synthesis and crystal engineering. The bis(4-triphenyltriamic anhydride)ethylene glycol ester crystal form provided by this invention possesses technical advantages such as a high melting point of 178.5~179.5°C, high crystal purity, excellent thermodynamic stability, and no crystal transformation during storage. It is suitable for the synthesis of high-performance polymers such as polyimides and has good prospects for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis and crystal engineering, and specifically relates to a crystal form of bis(4-triphenyltrihydric anhydride) ethylene glycol ester and its preparation method. Background Technology

[0002] bis(4-trimellitate anhydride) ethylene glycol ester, also known as ethylene glycol bis(4-trimellitate anhydride) (TMEG for short), CAS Registry No. 1732-96-3, molecular formula C 20 H 10 O 10 With a relative molecular mass of 410.3, its molecular structure consists of two trimellitic anhydride functional groups connected by an ethylene glycol bridge (-O-CH2-CH2-O-), making it an important aromatic dianhydride monomer.

[0003] TMEG is primarily used to synthesize high-performance specialty polymers such as polyesterimide (PEI) and polyamideimide (PAI). These materials, with their excellent high-temperature resistance, insulation, and mechanical properties, are widely used in high-end fields such as electronic-grade insulating materials, high-temperature resistant anti-corrosion coatings, and specialty engineering plastics. During the polymerization reaction, the purity, crystal morphology, and melt behavior of TMEG monomers directly affect the polymerization rate, the degree of side reactions, and further determine the molecular weight distribution, heat distortion temperature, and processing window of the final polymer. Therefore, providing TMEG monomers with high melting points, uniform crystal forms, and good thermal stability is a crucial foundation for the preparation of high-grade polymer materials and remains a key area of ​​ongoing research in this field.

[0004] Regarding the synthesis and crystallization process of TMEG, various technical solutions have been proposed, which can be summarized into three categories according to the synthetic route. The first category is the direct esterification / one-pot method. US Patent 3277117A (published in 1966) was an early disclosure of a method for synthesizing TMEG, using trimellitic anhydride and ethylene glycol as raw materials to prepare the target product via esterification, followed by recrystallization purification using butanone. This literature further points out that acetic anhydride has a significant impact on the crystallization behavior of TMEG: without the addition of acetic anhydride, the product melting point is only about 157℃ and effective recrystallization is difficult to achieve; with the addition of acetic anhydride, the product melting point ranges from 157℃ to 171℃. This route is relatively simple to operate, but the product melting point fluctuates significantly, resulting in insufficient batch-to-batch stability of crystal quality. The second category is the acyl chloride condensation method. European patent EP0308270A2 (published in 1989) describes the preparation of TMEG via a condensation reaction of trimellitic anhydride acyl chloride and ethylene glycol in the presence of a pyridine-binding acid agent. After two recrystallizations with acetic anhydride, the product's melting point reaches 173℃~175℃, with a yield of 75.3%. This route improves the product's melting point, but the acyl chloride raw material is highly corrosive, generates a large amount of waste, and has poor environmental friendliness. The third method is catalytic esterification. Chinese patent CN102477021A (published in 2011) uses a composite catalyst composed of metal acetate and p-toluenesulfonic acid to catalyze the reaction of trimellitic anhydride and ethylene glycol diacetate to synthesize TMEG. After recrystallization with acetone, the product's crystal purity reaches over 99%, but the melting point needs further improvement. This document also points out that the type of catalyst directly affects the product's crystallinity; using sodium acetate or potassium acetate alone as a catalyst only yields a low-crystallinity product with a melting point of 155℃~156℃. This route currently represents the technical solution with the highest melting point for TMEG crystals reported in public media.

[0005] Although existing technologies have explored the preparation and purification of TMEG to varying degrees in terms of synthetic routes, catalyst screening, and recrystallization solvent optimization, the following technical shortcomings remain: First, there is a technical bottleneck in improving the product's melting point. This, to some extent, restricts the development of downstream polymer materials with higher heat resistance. Second, there is a lack of systematic crystal form characterization methods. Existing technologies all use melting point as the main, or even the sole, indicator for evaluating crystal quality, and none employ modern crystallographic characterization methods such as X-ray powder diffraction, differential scanning calorimetry, and thermogravimetric analysis to identify the crystal form of the obtained product, making it impossible to confirm whether the product is a single crystal form or a mixed crystal system. In practice, the phenomenon in early literature where the product's melting point range was large and small changes in process parameters significantly affected the crystallization effect actually suggested that TMEG might have polymorphism, but existing technologies lack in-depth understanding and systematic research on this. Third, research on the controllability and stability of crystal form is lacking. Existing technologies only passively improve the crystallization effect by adjusting process parameters such as solvents and catalysts, and have not yet established an active control method for the target crystal form. The melting point of the product fluctuates significantly between different batches, and the crystal form purity is difficult to guarantee stably. Furthermore, existing technologies do not assess the long-term storage stability and thermal stability of the products, making it difficult to meet the stringent requirements for batch consistency and shelf life of monomer raw materials in high-end electronics, aerospace, and specialty engineering plastics fields.

[0006] In summary, there is an urgent need in this field to develop a new TMEG crystal form with a higher melting point, higher crystal purity, and excellent thermal stability, and to establish a corresponding controllable preparation method. This is of great technical value and industrial significance for improving the quality of TMEG products and expanding their application in the field of high-end polymer materials. Summary of the Invention

[0007] This invention aims to provide a novel crystalline form of ethylene glycol bis(triphenylene glycol) (TMEG) with high stability, high crystal purity, and controllable preparation process, to address the technical shortcomings of existing crystalline forms, such as melting point drift, impurities in X-ray diffraction (XRD) patterns, and purity degradation during storage. Existing TMEG crystalline forms (such as those reported in US3277117A) suffer from the following problems: different preparation methods yield products with varying melting points (157°C~171°C), resulting in poor crystal form consistency; some crystalline forms are prone to crystal transformation or degradation during storage, leading to melting point changes and impurities in the XRD patterns.

[0008] To achieve the above objectives, the specific technical solution of the present invention is as follows: This invention provides a crystalline form (named crystalline form W) of bis(4-triphenyltriamic anhydride) ethylene glycol ester (TMEG), the structure of which is shown in formula (I); in the X-ray powder diffraction pattern of the crystalline form, characteristic diffraction peaks are observed at 2θ diffraction angles of 26.76°±0.2°, 16.86°±0.2°, 17.88°±0.2°, and 19.94°±0.2°. Formula (I).

[0009] The molecular formula of this compound is C2. 20 H 10 O 10 .

[0010] Furthermore, in the X-ray powder diffraction pattern of the crystal form, the 2θ diffraction angles have characteristic diffraction peaks at 26.76±0.2°, 16.86±0.2°, 17.88±0.2°, 19.94±0.2°, 18.02±0.2°, 23.14±0.2°, 20.10±0.2°, and 36.06±0.2°.

[0011] Furthermore, in the X-ray powder diffraction pattern of the crystal form, the 2θ diffraction angles have characteristic diffraction peaks at 11.54±0.2°, 16.86±0.2°, 17.88±0.2°, 18.02±0.2°, 18.40±0.2°, 19.94±0.2°, 20.10±0.2°, 21.94±0.2°, 23.14±0.2°, 24.16±0.2°, 26.10±0.2°, 26.76±0.2°, 27.32±0.2°, 33.68±0.2°, and 36.06±0.2° (Table 1).

[0012] Furthermore, in the X-ray powder diffraction pattern of the crystal form, the relative intensity values ​​of the characteristic peaks at the 2θ diffraction angle are: Table 1. XRD characteristic diffraction peak data of crystal form W .

[0013] Furthermore, the melting point of the crystal form is 178.5~179.5℃.

[0014] Furthermore, the X-ray powder diffraction pattern of the crystal form is as follows: Figure 2 As shown.

[0015] This invention also provides a method for preparing the crystal form of the above-mentioned bis(4-triphenyltriacyl anhydride) ethylene glycol ester, the method comprising the following steps: reacting trimellitic anhydride with ethylene glycol diacetate under a composite catalysis of acetate-p-toluenesulfonic acid to obtain a reaction mixture; adding acetic anhydride to the reaction mixture; stirring and then adding ice water to precipitate crude bis(4-triphenyltriacyl anhydride) ethylene glycol ester; purifying and crystallizing the crude bis(4-triphenyltriacyl anhydride) ethylene glycol ester to obtain the crystal form of bis(4-triphenyltriacyl anhydride) ethylene glycol ester; The purification and crystallization process is selected from any one of solvent crystallization, high vacuum distillation crystallization, sublimation crystallization, or volatile crystallization.

[0016] Further, the solvent crystallization method includes: adding the crude bis(4-triphenyltrihydric anhydride) glycol ester to an organic solvent, heating to dissolve at 40~100°C, filtering while hot, cooling to -10~30°C to crystallize for 1~48 hours, separating, washing, and drying to obtain the crystal form.

[0017] Preferably, the organic solvent is acetone; the heating and dissolving temperature is 50~80℃; the cooling and crystallization temperature is 0~20℃; and the crystallization time is 1~12 hours.

[0018] Further, the organic solvent is selected from at least one of acetone and toluene; before cooling and crystallization, the aforementioned crystal form is added to the filtrate as a seed crystal, and the amount of the seed crystal added is 0.01~5 wt% of the crude mass, preferably 0.1~1 wt% of the crude mass.

[0019] Furthermore, the drying temperature is 40~80°C, preferably 40~60°C.

[0020] Further, the high-vacuum distillation crystallization method includes: placing crude bis(4-triphenyltrihydric anhydride) ethylene glycol ester in a high-vacuum distillation apparatus, performing vacuum distillation at 170~220°C and a vacuum degree <50 Pa, collecting the main fraction at 180~210°C, and slowly cooling and crystallizing at a rate of 0.5~2°C / min under nitrogen protection to obtain the crystal form.

[0021] Further, the sublimation deposition method includes: placing crude bis(4-triphenyltriglyceride) glycol ester in a sublimation apparatus, heating it at a constant temperature of 4 to 120 hours under vacuum conditions <20 Pa and temperature >130°C, and depositing it in a cold trap region at 40 to 60°C to obtain the crystal form.

[0022] Further, the method of volatile crystallization includes: adding crude bis(4-triphenyltriglyceride) glycol ester to toluene, heating to dissolve at 50-60°C, filtering while hot, cooling, and then allowing it to stand at a constant temperature of 20-30°C for 5-7 days to volatilize and crystallize. The crystal form is then separated, washed, and dried to obtain the crystal form.

[0023] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. Thermodynamic stability of crystal form W The TMEG crystal forms reported in the prior art (US3277117A, EP0308270A2, CN102477021A, CN118580207A, etc., named Form-A, Form-B, Form-C, Form-T, Form-D) have substantial differences in melting point, crystallization method and X-ray powder diffraction characteristic peaks. A detailed comparison is shown in Table 2.

[0024] Table 2. Comparison of characteristics of different TMEG crystal forms After being placed at 40°C / 75% RH for 6 months, the XRPD pattern of the W crystal form of this invention was consistent with the initial pattern, no crystal transformation occurred, and the melting point remained unchanged, confirming that it has excellent thermodynamic stability and is suitable for long-term storage and industrial application.

[0025] 2. Technical advantages of crystal form W in polyimide preparation (1) High purity ensures high molecular weight. Polyimide polycondensation requires a 1:1 equimolar ratio, and impurities will disrupt this ratio, thus limiting the molecular weight. The melting point range of crystal form W is 178.5~179.5°C, and the amount of lattice defects and impurities is low, which is conducive to obtaining high-purity monomers.

[0026] (2) Single crystalline phase ensures batch consistency. The characteristic peak of crystal form W at 2θ=26.76° in the XRD pattern does not overlap with any known crystal forms, which can ensure accurate identification of a single pure phase. Mixed crystal TMEG will have uneven concentration and a wider polymer dispersibility index (PDI) in the early stage of polymerization due to differences in dissolution rate, while crystal form W can ensure a high degree of consistency of physical properties between batches.

[0027] (3) Low metal content ensures high-frequency performance. Metal ions lead to increased dielectric loss and decreased breakdown voltage of PI. Electronic grade TMEG requires a total metal ion content of <30ppb, while crystal form W can achieve a total metal ion content of <10ppb through high-purity crystallization process, supporting low dielectric loss PI films for 5G / 6G.

[0028] (4) Low water content protects the activity of anhydride groups. Every 100 ppm of water consumes 0.1 mol% of anhydride groups, reducing the molecular weight of PI by about 10%. The compact lattice of crystal form W results in a lower surface adsorbed water content than other crystal forms, protecting chain growth from the first step of feeding.

[0029] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0030] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following embodiments. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0031] Figure 1 The XRPD comparison spectra of the crystal form W of this invention before and after accelerated storage at 40℃ / 75% RH for 6 months are shown.

[0032] Figure 2 The XRPD spectrum of crystal form W of this invention was obtained after being placed at 30°C for 6 months.

[0033] Figure 3 The XRPD spectrum of crystal form D in Example 2 of CN102477021A was obtained after being placed at 30°C for 6 months.

[0034] Figure 4 The XRPD spectrum of crystal form D in Example 2 of CN102477021A after being placed at 30°C for 6 months under accelerated conditions is shown.

[0035] Figure 5 This is the high-performance liquid chromatography (HPLC) spectrum of crystal form W of the present invention.

[0036] Figure 6 This is the differential scanning calorimetry (DSC) spectrum of crystal form W of the present invention.

[0037] Figure 7 The DSC spectrum of crystal form D in Example 2 of CN102477021A is shown. Detailed Implementation

[0038] The raw materials and equipment used in this invention are all known products, obtained by purchasing commercially available products.

[0039] Example 1: Preparation of crystal form W (high vacuum distillation crystallization method) 1. Preparation of crude ethylene glycol divinyltriglyceridate (TMEG) Trimeric triglyceride (TMA, 23.4 g), ethylene glycol diacetate (EGDA, 8.9 g), sodium acetate (0.47 g), and p-toluenesulfonic acid (0.12 g) were added to a 250 mL three-necked flask. The mixture was heated to 180–190°C under N2 protection and stirred for 4–6 h to distill off the byproduct acetic acid. After cooling to 100°C, 5 mL of acetic anhydride was added and stirred for 30 min. The mixture was then poured into ice water to precipitate crude TMEG.

[0040] 2. Preparation of crystal form W The crude TMEG obtained in the above steps was placed in a high-vacuum distillation apparatus and subjected to reduced-pressure distillation at 170–220°C and a vacuum degree <50 Pa. The main fraction, a colorless to pale yellow melt, was collected at 180–210°C. Under nitrogen protection, the melt was slowly cooled to room temperature at a rate of 0.5–2°C / min, allowing TMEG to crystallize directly from the melt. After drying, crystalline form W was obtained. This process involves no solvent and completes purification and crystallization in one step.

[0041] Example 2: Preparation of crystal form W (solvent crystallization method) (1) Add the crude TMEG obtained in Example 1 to acetone (about 200-250 mL) solvent and heat to 50-80°C while stirring to dissolve; (2) Filter the above solution while it is hot and retain the filtrate.

[0042] (3) Add the seed crystal of crystal form W obtained by the method described in Example 1, with a content of 0.1~1 wt% of the crude mass.

[0043] (4) Cool down to 0~20°C and continue stirring for 1~12 hours to allow for slow crystallization; (5) The crystals were filtered and washed with acetone and dried under vacuum at 40-60°C to constant weight to obtain TMEG crystal form W, about 22-26 g (yield ~75-85%).

[0044] Example 3: Preparation of crystal form W (sublimation-condensation method) The crude TMEG obtained in Example 1 was placed in the feed pan of a sublimation apparatus and heated at a constant temperature of <20 Pa and >130°C for 4–120 hours, causing TMEG to sublimate directly from a solid to vapor. The vapor condensed and precipitated in the cold trap region (40–60°C) of the apparatus, yielding white needle-like or plate-like crystals. The condensation product was collected to obtain crystal form W.

[0045] Example 4: Preparation of crystal form W (volatile crystallization method) 2.0 g of crude TMEG obtained in Example 1 was added to 15 mL of toluene, heated to 50-60°C and stirred to dissolve. The mixture was then filtered while hot. After the filtrate was cooled to room temperature, it was sealed with two layers of sealing film with 2-3 small holes punched in it. The mixture was then placed in a constant temperature environment at 25°C for 5-7 days to allow it to evaporate. After the crystals precipitated, the mixture was filtered under reduced pressure, washed with a small amount of cold toluene, and dried under vacuum at 60-80°C for 12 hours to obtain crystal form W.

[0046] The following is a comparison example.

[0047] Compare with Example 1, Preparation of Crystal Form D The Form-D crystal form (abbreviated as crystal form D) was prepared by referring to the method described in Example 2 of CN102477021A (i.e., paragraph 0021 of the specification).

[0048] The following experimental examples demonstrate the beneficial effects of the present invention.

[0049] Experimental Example 1: Characterization and Stability Testing of Crystal Forms The crystal forms prepared in Examples 1-4 have the same XRPD pattern. In Experiment 1, the crystal form W prepared in Example 2 was used for characterization and stability testing.

[0050] 1. Experimental Methods 1) X-ray powder diffraction (XRPD) test: Instrument: Rigaku Ultima IV (185mm); Test conditions: Cu Kα rays (λ=1.5406Å), scanning range 5°~90°, step size 0.02°.

[0051] Accelerated stability test: Crystal form W and crystal form D samples were placed in constant temperature and humidity chambers and stored at 30°C or 40°C / 75% RH. Samples were taken at specified time points, and the melting point was determined by DSC and the crystal form change was determined by XRPD.

[0052] 2) Differential Scanning Calorimetry (DSC) Test: Instrument Model: METTLER DSC 3 / 500 / Fan; Starting Temperature: 30℃; Finish temperature: 300℃; heating rate: 10℃ / min; gas: nitrogen; gas flow rate: 50mL / min.

[0053] Experimental procedure: Weigh an appropriate amount of sample and add it to an aluminum crucible. Cover the crucible, compact it, and leave a small hole at the top. Place the crucible into the instrument for testing.

[0054] 3) High Performance Liquid Chromatography (HPLC) Test: Instrument Model: Agilent 1100; Column: C18 4.6×150mm 4μm; Flow Rate: 0.6mL / min; Column Temperature: 30℃; Injection Volume: 5μL; Wavelength: 210nm; Mobile Phase: Acetonitrile; Diluent: ACN; The concentration of the test solution is 0.2 mg / mL.

[0055] 2. Experimental Results (1) Crystallographic characteristics of crystal form W The crystal form W of this invention is designated as Form-W, with a melting point of 178.5~179.5℃. The XRD characteristic diffraction peak data for crystal form W are shown in Table 3.

[0056] Table 3. XRD characteristic diffraction peak data of crystal form W The characteristic peaks for crystal form identification are: 2θ = 26.76 ± 0.2° (100%), 16.86 ± 0.2° (29.1%), 17.88 ± 0.2° (25.0%), and 19.94 ± 0.2° (18.9%).

[0057] After accelerated storage at 40°C / 75% RH for 6 months, the XRPD pattern of the W crystal form of this invention is consistent with the initial pattern. Figure 1 The crystallization did not occur, and the melting point remained unchanged, confirming its excellent thermodynamic stability, making it suitable for long-term storage and industrial applications.

[0058] (2) Comparison of accelerated stability between crystal form W and crystal form D The stability of the crystal form W of this invention and the prior art crystal form D (prepared according to Example 2 of CN102477021A, with a measured melting point of 173.09℃) was investigated under the same conditions (stored at a constant temperature of 30℃). The melting point of the samples at each time point was determined by DSC. The XRPD spectrum of crystal form W before storage is shown in [reference needed]. Figure 2 The XRPD spectra of crystal form D before and after storage are shown in the figures below. Figure 3 and Figure 4 The melting point test results are shown in Table 4. Figure 6 and Figure 7 .

[0059] Table 4 Comparison of accelerated stability melting points between crystal form W and crystal form D As shown in Table 4, under constant temperature storage conditions of 30℃, the melting point of crystal form W of the present invention changed from -0.81℃ to -0.15℃ relative to the initial temperature during a 6-month storage period, reaching 178.8℃ after 6 months, with a change of -0.50℃ relative to the initial temperature. In contrast, the melting point of crystal form D continuously decreased during the 6-month storage period, reaching 167.18℃ after 6 months, with a change of -5.91℃ relative to the initial temperature. These results indicate that the thermodynamic stability of crystal form W of the present invention is significantly better than that of the prior art crystal form D.

[0060] Furthermore, a comparative analysis of the XRPD spectra of crystal form W and crystal form D before and after storage was conducted. Under the same conditions, compared with crystal form D, the peak positions, relative intensities, and peak shapes of all characteristic diffraction peaks in the XRPD spectra of crystal form W remained consistent before and after 6 months of storage. No new peaks were observed to appear or existing characteristic peaks to disappear, indicating that crystal form W did not undergo crystal transformation during storage and its crystal structure remained intact. The XRPD analysis results corroborated the DSC melting point data, further confirming that crystal form W possesses excellent thermodynamic stability.

[0061] (3) Purity detection of crystal form W The purity of crystal form W of this invention was determined to be 99.96% by high-performance liquid chromatography (HPLC chromatogram shown in [reference needed]). Figure 5 ).

[0062] In summary, this invention provides a crystal form of bis(4-triphenyltriamic anhydride) ethylene glycol ester and its preparation method. The TMEG crystal form W provided by this invention has technical advantages such as high melting point (178.5~179.5°C), high crystal purity, excellent thermodynamic stability, and no crystal transformation during storage. It is suitable for the synthesis of high-performance polymers such as polyimides and has good prospects for industrial application.

Claims

1. A crystal form of bis(4-triphenyltrihydric anhydride) glycol ester, characterized in that: The structure of the bis(4-triphenyltrianic anhydride) ethylene glycol ester is shown in formula (I); in the X-ray powder diffraction pattern of the crystal form, the 2θ diffraction angles have characteristic diffraction peaks at 26.76°±0.2°, 16.86°±0.2°, 17.88°±0.2°, and 19.94°±0.2°. Formula (I).

2. The crystal form according to claim 1, characterized in that: In the X-ray powder diffraction pattern of the crystal form, the 2θ diffraction angles have characteristic diffraction peaks at 11.54±0.2°, 16.86±0.2°, 17.88±0.2°, 18.02±0.2°, 18.40±0.2°, 19.94±0.2°, 20.10±0.2°, 21.94±0.2°, 23.14±0.2°, 24.16±0.2°, 26.10±0.2°, 26.76±0.2°, 27.32±0.2°, 33.68±0.2°, and 36.06±0.2°.

3. The crystal form according to claim 1, characterized in that: In the X-ray powder diffraction pattern of the crystal form, the relative intensity values ​​of the characteristic peaks at the 2θ diffraction angle are: 。 4. The crystal form according to claim 1, characterized in that: The melting point of the crystal form is 178.5~179.5℃.

5. A method for preparing the crystal form of bis(4-triphenyltrihydric anhydride) ethylene glycol ester according to any one of claims 1 to 4, characterized in that: The method includes the following steps: reacting trimellitic anhydride with ethylene glycol diacetate under a combined catalysis of acetate and p-toluenesulfonic acid to obtain a reaction mixture; adding acetic anhydride to the reaction mixture; stirring and then adding ice water to precipitate crude bis(4-trimeric anhydride) ethylene glycol ester; purifying and crystallizing the crude bis(4-trimeric anhydride) ethylene glycol ester to obtain the crystalline form of bis(4-trimeric anhydride) ethylene glycol ester. The purification and crystallization process is selected from any one of solvent crystallization, high vacuum distillation crystallization, sublimation crystallization, or volatile crystallization.

6. The preparation method according to claim 5, characterized in that: The solvent crystallization method includes: adding the crude bis(4-triphenyltrihydric anhydride) glycol ester to an organic solvent, heating to dissolve at 40~100°C, filtering while hot, cooling to -10~30°C to crystallize for 1~48 hours, separating, washing, and drying to obtain the crystal form.

7. The preparation method according to claim 6, characterized in that: The organic solvent is selected from at least one of acetone and toluene; before cooling and crystallization, the crystal form described in any one of claims 1 to 4 is added to the filtrate as a seed crystal, and the amount of the seed crystal added is 0.01 to 5 wt% of the crude mass.

8. The preparation method according to claim 5, characterized in that: The high-vacuum distillation crystallization method includes: placing crude bis(4-triphenyltrihydric anhydride) ethylene glycol ester in a high-vacuum distillation apparatus, performing vacuum distillation at 170~220°C and a vacuum degree <50 Pa, collecting the main fraction at 180~210°C, and slowly cooling and crystallizing at a rate of 0.5~2°C / min under nitrogen protection to obtain the crystal form.

9. The preparation method according to claim 5, characterized in that: The sublimation-deposition method includes: placing crude bis(4-triphenyltriglyceride) glycol ester in a sublimation apparatus and heating it at a constant temperature of 4-120 hours under vacuum conditions <20 Pa and temperature >130°C, and then depositing it in a cold trap region at 40-60°C to obtain the crystal form.

10. The preparation method according to claim 5, characterized in that: The method of volatilization crystallization includes: adding crude bis(4-triphenyltriglyceride) glycol ester to toluene, heating to dissolve at 50-60°C, filtering while hot, cooling and then allowing it to stand at a constant temperature of 20-30°C for 5-7 days to volatilize and crystallize, separating, washing and drying to obtain the crystal form.

Images