A method suitable for analyzing the structure of liquid crystal polymer monomers

Abstract

The present invention provides a method suitable for analyzing the structure of liquid crystal polymer monomers, the analysis method comprising the steps of: S1-depolymerization: mixing a liquid crystal polymer sample and a depolymerization liquid matrix in a reactor for depolymerization treatment to obtain a depolymerization product; S2-separation: subjecting the depolymerization product to a three-step derivatization treatment to obtain a separated product; S3-detection: taking the separated product and dissolving it in mobile phase 1, and using liquid chromatography-mass spectrometry for detection; taking another separated product and dissolving it in mobile phase 2, and using nuclear magnetic resonance spectroscopy for detection. The method suitable for analyzing the structure of liquid crystal polymer monomers provided by the present invention derivatizes a macromolecular polymer into small molecular acids and alcohols through reverse depolymerization and pretreatment, so that the depolymerization is more complete and the separation is more thorough; at the same time, accurate qualitative and quantitative analysis is performed through liquid chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy, so that the analysis result has high completeness, high accuracy, and reliable data.

Description

Technical Field

[0001] The invention belongs to the field of chemical analysis, and in particular relates to a method suitable for analyzing the structure of liquid crystal polymer polymerization monomers. Background Art

[0002] Liquid crystal polymers, commonly known as LCP, refer to polymer compounds that can exist in liquid crystal phase under certain conditions. In terms of molecular structure, LCP has a rigid rod-like molecular chain structure, the molecular chains can be highly oriented, the structure is tightly stacked, and the interaction between macromolecules is relatively large. Therefore, compared with other polymer materials, LCP has many excellent properties, such as: high temperature resistance, high mechanical strength, excellent electrical properties (high dielectric, low loss), and good processing performance (small parts injection molding).

[0003] There are dozens of types of monomers that make up LCP, which are divided into Type I, Type II and Type III according to the synthetic monomers. Type I LCP is polymerized from monomers such as p-hydroxybenzoic acid, 4,4'-biphenol and terephthalic acid / isophthalic acid; Type II LCP is mainly polymerized from p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid as monomers, and has better processing performance and recyclability than Type I LCP; Type III LCP contains PET in its molecular structure, and the addition of flexible ester groups further reduces the heat resistance of the material, so it is mainly used in the production of connecting tubes and sensors.

[0004] In actual application, researchers will select several monomers for combination according to different purposes. However, since the formed LCP is difficult to dissolve, in order to understand the resin structure of the formed LCP, the existing technology often uses infrared spectroscopy and pyrolysis gas chromatography mass spectrometry for analysis. Due to the similarity of some monomer structures of LCP, it is impossible to make an accurate judgment of the monomer category when using infrared spectroscopy, and it is difficult to control the relevant conditions when using pyrolysis gas chromatography for monomer structure characterization, resulting in huge deviations in the actual qualitative and quantitative analysis results.

[0005] Invention patent CN 115616024 A invented a component analysis method for liquid crystal polyester. The invention uses a special solvent to dissolve the liquid crystal polyester sample, adopts the solvent peak suppression method, and performs quantitative nuclear magnetic resonance hydrogen spectrum characterization to achieve accurate quantification of liquid crystal polyester. However, the invention mainly achieves accurate quantification for type II LCP containing p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, and the qualitative and quantitative analysis of LCP containing other monomers is insufficient.

[0006] Therefore, it is particularly important to invent a method for rapid and efficient reverse depolymerization of liquid crystal polymers. Summary of the invention

[0007] In view of the defects of the prior art, the purpose of the present invention is to provide a method suitable for analyzing the structure of liquid crystal polymer polymerization monomers, which method enables liquid crystal polymers to be depolymerized economically and efficiently, and the separation is more thorough; at the same time, accurate qualitative and quantitative analysis is performed by combining liquid chromatography-mass spectrometry with nuclear magnetic resonance spectroscopy, so that the analysis results are highly complete, accurate, and the data are reliable.

[0008] The present invention provides a method suitable for analyzing the structure of a liquid crystal polymer monomer, the method comprising the steps of:

[0009] S1-depolymerization: mixing the liquid crystal polymer sample and the depolymerization liquid matrix in a reactor for depolymerization treatment to obtain a depolymerization product;

[0010] S2-Separation: The depolymerization product is subjected to a three-step derivatization treatment to obtain a separation product;

[0011] S3-Detection: Take the separated product and dissolve it in mobile phase 1, and use liquid chromatography-mass spectrometry for detection; take another separated product and dissolve it in mobile phase 2, and use nuclear magnetic resonance spectroscopy for detection;

[0012] The mobile phase 1 is a mixed mobile phase of mobile phase 1-1 and mobile phase 1-2;

[0013] The mobile phase 1-1 is one or more of water, methanol, acetonitrile and N,N-dimethylformamide, and the mobile phase 1-2 is acetonitrile.

[0014] Preferably, the liquid crystal polymer is a liquid crystal polymer containing any one of p-hydroxybenzoic acid, 4,4'-biphenol, terephthalic acid, isophthalic acid, 2-hydroxy-6-naphthoic acid, hydroquinone and ethylene glycol.

[0015] The method for analyzing the structure of liquid crystal polymer polymerization monomers proposed by the present invention has comprehensive application and strong applicability, and can realize efficient and accurate depolymerization and qualitative and quantitative analysis of monomers for liquid crystal polymers involved in the prior art.

[0016] Preferably, the depolymerization liquid matrix is ​​alkali and water;

[0017] More preferably, the base is sodium hydroxide.

[0018] Preferably, the mass ratio of the liquid crystal polymer sample, the alkali and the water is (0.1-2):(0.5-4):(11-16.4);

[0019] Further preferably, the mass ratio of the liquid crystal polymer sample, alkali and water is 1:2:14. The applicant controlled the amount of sodium hydroxide and water added and found that when the mass ratio of the liquid crystal polymer sample, alkali and water was 1:2:14, the liquid crystal polymer achieved a fast and efficient hydrolysis process. During the reaction, sodium hydroxide and the liquid crystal polymer sample continuously generated corresponding carboxylates and sodium phenolates and dissolved in water, achieving preliminary separation.

[0020] Preferably, the amount of the liquid crystal polymer sample and the depolymerization liquid matrix added in the S1-depolymerization is 2 / 3 to 3 / 4 of the volume of the reactor.

[0021] Preferably, the depolymerization treatment is performed at a temperature of 100 to 200°C, a time of 36 to 72 hours, and a pressure of 1.5 to 3 MPa;

[0022] Further preferably, the depolymerization treatment is carried out at a temperature of 160° C., a time of 48 h and a pressure of 2 MPa.

[0023] In the prior art, in addition to the depolymerization form and the depolymerization liquid matrix, the depolymerization volume, temperature, time and pressure of the depolymerization process will also affect the depolymerization efficiency and the purity of the depolymerization product. The applicant controls the amount of liquid crystal polymer sample and the depolymerization liquid matrix added to ensure the pressure of the depolymerization reaction, thereby avoiding the adverse effects of insufficient or excessive pressure on the depolymerization efficiency and safety of the product. Under the said ratio, the depolymerization reaction is more controllable, taking into account both the depolymerization efficiency and the depolymerization purity, and effectively avoiding the influence of excessive depolymerization byproducts on the subsequent separation and qualitative process.

[0024] Preferably, the three derivatization steps in the S2-separation are:

[0025] (1) filtering and separating the depolymerization products in the depolymerization of S1 to obtain soluble matter 1 and insoluble matter 1;

[0026] (2) taking the soluble matter 1 in step (1) and performing a reduction experiment, filtering and separating, to obtain a soluble matter 2 and an insoluble matter 2, wherein the soluble matter 2 is a first separation product;

[0027] (3) subjecting the insoluble matter 2 in step (2) to an esterification reaction to obtain a second separated product.

[0028] Preferably, the three derivatization steps in the S2-separation are:

[0029] (1) filtering and separating the depolymerization products in the depolymerization of S1 to obtain soluble matter 1 and insoluble matter 1;

[0030] (2) adding acid to the soluble matter 1 in step (1) to perform a reduction experiment, and performing membrane filtration to separate the soluble matter 2 and the insoluble matter 2, wherein the soluble matter 2 is the first separation product;

[0031] (3) Adding alcohol and an acid catalyst to the insoluble matter 2 in step (2) to carry out an esterification reaction to obtain a second separated product.

[0032] Further preferably, in step (1), the soluble matter 1 is a monomer and / or a sodium salt mixture of monomers, and the insoluble matter 1 is an impurity or an incompletely depolymerized liquid crystal polymer;

[0033] In step (2), the acid is formic acid and / or hydrochloric acid solution, the pore size of the filter membrane is 0.22 μm and / or 0.45 μm, the soluble matter 2 is a phenol / alcohol monomer, and the insoluble matter 2 is a carboxylic acid monomer;

[0034] In step (3), the alcohol is methanol and / or ethanol, and the acid catalyst is at least one of sulfuric acid, phosphoric acid and hydrochloric acid.

[0035] The applicant uses a three-step derivatization process to separate the depolymerization products in multiple steps. First, the monomers are separated by using the difference in acidity and alkalinity of the monomers, and then the inseparable monomers are derivatized into corresponding methyl esters and / or ethyl esters by esterification reaction to achieve separation, so that they can be well dissolved in the mobile phase. Compared with the prior art, the three-step derivatization process achieves complete separation of the depolymerized monomers. At the same time, the good solubility of the derivatized monomers in the mobile phase is also conducive to the qualitative and quantitative detection of subsequent tests, making the analysis results more complete and accurate.

[0036] More preferably, in step (2), formic acid and / or hydrochloric acid solution is added to adjust the pH to 2-7.

[0037] Preferably, the mobile phase 1-1 is N,N-dimethylformamide;

[0038] Preferably, the volume ratio of the mobile phase 1-1 to the mobile phase 1-2 is 1:(5-15);

[0039] Further preferably, the volume ratio of the mobile phase 1-1 to the mobile phase 1-2 is 1:10.

[0040] The applicant found that mixing mobile phase 1-1 and mobile phase 1-2 in a preferred ratio unexpectedly achieved complete dissolution of the monomer. The good solubility of the monomer in the preferred mixed solvent improved its response effect during the detection and analysis process, which was beneficial to the accurate qualitative and quantitative analysis of the monomer. The possible reason is that acetonitrile, as a highly polar organic solvent, can play a similar solubility role on most monomers containing polar functional groups; and the hydrogen bonds formed between hydrogen and nitrogen atoms in N, N-dimethylformamide molecules make it also have a strong solubility for non-polar or weakly polar functional groups, especially the formation of hydrogen bonds with negatively charged atoms in the monomer to enhance the interaction between molecules; at the same time, its molecular volume is relatively small and it is easy to enter gaps or cavities. Therefore, the mixed use of the two solvents at the preferred ratio can significantly improve the solubility of the monomer and achieve complete dissolution.

[0041] Preferably, the mobile phase 2 is one or more of deuterated water, deuterated chloroform, deuterated dimethyl sulfoxide and deuterated tetrahydrofuran.

[0042] Further preferably, the mobile phase 2 is deuterated water or deuterated dimethyl sulfoxide.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The method for analyzing the structure of liquid crystal polymer monomers provided by the present invention is comprehensive and has strong applicability. It can achieve efficient and accurate depolymerization and qualitative and quantitative analysis of monomers for the three types of liquid crystal polymers involved in the prior art.

[0045] (2) The method for structural analysis of liquid crystal polymer monomers provided by the present invention controls the ratio of depolymerization treatment conditions to make the depolymerization reaction more controllable, taking into account both depolymerization efficiency and depolymerization purity, and effectively avoiding the influence of excessive depolymerization by-products on the subsequent separation and qualitative process.

[0046] (3) The method provided by the present invention for structural analysis of liquid crystal polymer polymerization monomers adopts a three-step derivatization process to achieve complete separation of depolymerized monomers. At the same time, the good solubility of the derivatized monomers in the mobile phase is also beneficial to the subsequent qualitative and quantitative detection, making the analysis results more complete and accurate.

[0047] (4) The method for structural analysis of liquid crystal polymer polymerization monomers provided by the present invention provides a mixed mobile phase with a preferred ratio, which unexpectedly achieves complete dissolution of the monomer by utilizing the interaction of like dissolves like and intermolecular hydrogen bonds, effectively improves the response effect of the monomer during detection, and significantly improves the accuracy of monomer qualitative and quantitative analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of the liquid crystal polymer sample separation product in Example 1.

[0049] Figure 2 This is the liquid chromatography-mass spectrum of the liquid crystal polymer sample separation product in Example 1. DETAILED DESCRIPTION

[0050] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0051] The detection conditions of liquid chromatography-mass spectrometry in the following embodiments are as follows: the ion source is an electrospray source (ESI), the scanning range is 60 to 1000, the drying gas is nitrogen, the elution mode is isocratic elution, the injection volume is 3 μL, the chromatographic column is C18 1.7 μm, 2.1*50 mm, and the flow rate is 0.3 mL / min; the nuclear magnetic resonance spectrum is a nuclear magnetic resonance hydrogen spectrum, and the detection conditions of the nuclear magnetic resonance hydrogen spectrum are 400M. Unless otherwise specified, the mobile phase 2 is deuterated water.

[0052] Example 1

[0053] A method for analyzing the structure of a liquid crystal polymer monomer, the method comprising the steps of:

[0054] S1-depolymerization: 1 g of liquid crystal polymer sample, 2 g of sodium hydroxide and 14 mL of deionized water were mixed and added into a reactor, and depolymerization reaction was carried out at a temperature of 160 ° C and a pressure of 2 MPa. The depolymerization product was collected after 48 h of reaction;

[0055] S2-Separation: The depolymerization product is subjected to a three-step derivatization treatment to obtain a separation product, which specifically includes:

[0056] (1) filtering and separating the depolymerization product to obtain a mixture of p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, terephthalic acid and hydroquinone;

[0057] (2) taking the sodium salt mixture of p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, terephthalic acid and hydroquinone in step (1), adding formic acid to adjust and conduct a reduction experiment, filtering and separating through a filter membrane (0.22 μm), wherein the soluble matter is hydroquinone, the soluble matter is the first separation product, and the insoluble matter is p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid and terephthalic acid;

[0058] (3) 4.6 mL of methanol and 0.05 mL of phosphoric acid were added to a mixture of 5 g of p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid and terephthalic acid to carry out esterification reaction to obtain a second separated product.

[0059] S3-Detection: Take 0.02 mL of the second separated product and dissolve it in 22 mL of mobile phase 1, and use liquid chromatography-mass spectrometry for detection; take another 0.02 mL of the first separated product and 0.02 mL of the second separated product and dissolve them in 1 mL of mobile phase 2 and use nuclear magnetic resonance hydrogen spectrum for detection;

[0060] Mobile phase 1 is N,N-dimethylformamide and acetonitrile, with a volume ratio of V N,N-二甲基甲酰胺 :V 乙腈 =1:10.

[0061] Example 2

[0062] A method for analyzing the structure of a liquid crystal polymer monomer, the method comprising the steps of:

[0063] S1-depolymerization: 0.1 g of liquid crystal polymer sample, 0.5 g of sodium hydroxide and 16.4 mL of deionized water were mixed and added into a reactor, and depolymerization reaction was carried out at a temperature of 100 ° C and a pressure of 1.5 MPa. After the reaction time of 72 h, the depolymerization product was collected;

[0064] Steps S2-separation and S3-detection are the same as in Example 1.

[0065] Example 3

[0066] A method for analyzing the structure of a liquid crystal polymer monomer, the method comprising the steps of:

[0067] S1-depolymerization: 2 g of liquid crystal polymer sample, 4 g of sodium hydroxide and 11 mL of deionized water were mixed and added into a reactor, and depolymerization reaction was carried out at a temperature of 200 ° C and a pressure of 3 MPa. After 36 h of reaction, the depolymerization product was collected;

[0068] Steps S2-separation and S3-detection are the same as in Example 1.

[0069] Example 4

[0070] A method for analyzing the structure of a liquid crystal polymer monomer, the method comprising the steps of:

[0071] S1-depolymerization: 1 g of liquid crystal polymer sample, 2 g of sodium hydroxide and 14 mL of deionized water were mixed and added into a reactor, and depolymerization reaction was carried out at a temperature of 160 ° C and a pressure of 2 MPa. The depolymerization product was collected after 48 h of reaction;

[0072] S2-Separation is the same as in Example 1;

[0073] S3-Detection: Take 0.02 mL of the second separated product and dissolve it in 18 mL of mobile phase 1 and use liquid chromatography-mass spectrometry for detection; take another 0.02 mL of the first separated product and 0.02 mL of the second separated product and dissolve them in 1 mL of mobile phase 2 and use nuclear magnetic resonance hydrogen spectrum for detection;

[0074] Mobile phase 1 is N,N-dimethylformamide and acetonitrile, with a volume ratio of V N,N-二甲基甲酰胺 :V 乙腈 =1:5.

[0075] Example 5

[0076] A method for analyzing the structure of a liquid crystal polymer monomer, the method comprising the steps of:

[0077] S1-depolymerization: 1 g of liquid crystal polymer sample, 2 g of sodium hydroxide and 14 mL of deionized water were mixed and added into a reactor, and depolymerization reaction was carried out at a temperature of 160 ° C and a pressure of 2 MPa. The depolymerization product was collected after 48 h of reaction;

[0078] S2-Separation is the same as in Example 1;

[0079] S3-Detection: Take 0.02 mL of the second separated product and dissolve it in 20 mL of mobile phase 1 and use liquid chromatography-mass spectrometry for detection; take another 0.02 mL of the first separated product and 0.02 mL of the second separated product and dissolve them in 1 mL of mobile phase 2 and use nuclear magnetic resonance hydrogen spectrum for detection;

[0080] Mobile phase 1 is N,N-dimethylformamide and acetonitrile, with a volume ratio of V N,N-二甲基甲酰胺 :V 乙腈 =1:15.

[0081] Example 6

[0082] A method for analyzing the structure of a liquid crystal polymer monomer, the method comprising the steps of:

[0083] S1-depolymerization: 1 g of liquid crystal polymer sample, 2 g of sodium hydroxide and 14 mL of deionized water were mixed and added into a reactor, and depolymerization reaction was carried out at a temperature of 90 ° C and a pressure of 1.5 MPa. The depolymerization product was collected after 72 h of reaction;

[0084] S2-Separation is the same as in Example 1;

[0085] S3-Detection: Take 0.02 mL of the second separated product and dissolve it in 20 mL of mobile phase 1 and use liquid chromatography-mass spectrometry for detection; take another 0.02 mL of the first separated product and 0.02 mL of the second separated product and dissolve them in 1 mL of mobile phase 2 and use nuclear magnetic resonance hydrogen spectrum for detection;

[0086] Mobile phase 1 was acetonitrile.

[0087] Example 7

[0088] A method for analyzing the structure of a liquid crystal polymer monomer, the method comprising the steps of:

[0089] S1-depolymerization: 1 g of liquid crystal polymer sample, 2 g of sodium hydroxide and 14 mL of deionized water were mixed and added into a reactor, and depolymerization reaction was carried out at a temperature of 200 ° C and a pressure of 2 MPa. After 24 h of reaction, the depolymerization product was collected;

[0090] Steps S2-separation and S3-detection are the same as in Example 1.

[0091] Performance Testing

[0092] 1. Depolymerization rate: The depolymerization rate is calculated by the peak area ratio of the ester bond before and after depolymerization in the infrared absorption spectrum;

[0093] 2. Solubility: In step S3-detection, observe the solubility of the second separated product in mobile phase 1. If there is no obvious insoluble matter visible to the naked eye and the solution is clear and transparent, it is considered to be fully soluble;

[0094] 3. Calculation of the mass fraction of the monomer: The peak area integral calculation is performed based on the nuclear magnetic resonance hydrogen spectrum obtained in step S3-detection, and the internal standard is 10%wt sodium formate.

[0095] The above performance tests were performed on Examples 1-7, and the results are shown in Table 1.

[0096] Table 1

[0097]

[0098]

[0099] Depend on Figure 1 and Figure 2 The test results show that the analysis results of the liquid chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy of the embodiment 1 of the present invention on the liquid crystal polymer monomer are complete and the data reliability is high. Figure 1 The hydrogen nuclear magnetic resonance spectrum of the liquid crystal polymer sample separation product in Example 1, wherein: the peaks of 7.58-7.60 and 6.48-6.50 ppm are attributed to p-hydroxybenzoic acid monomer, the peaks of 8.16, 7.48-751, 6.92-6.95 and 6.81 ppm are attributed to 2-hydroxy-6-naphthoic acid monomer, the peak of 7.78 ppm is attributed to terephthalic acid monomer, the peaks of 7.05-7.09 and 6.55 ppm are attributed to phenol, and since hydroquinone is very easy to oxidize, the other peaks are attributed to the oxidation product of hydroquinone; Figure 2 It is the liquid chromatography-mass spectrum (m / z) of the liquid crystal polymer sample separation product in Example 1, wherein: 137 is the M-1 peak of p-hydroxybenzoic acid monomer, and 187 is the M-1 peak of 2-hydroxy-6-naphthoic acid monomer.

[0100] It can be seen from the performance test table 1 and the comparison of Examples 1-7 that the preferred depolymerization treatment conditions of the present method can achieve complete depolymerization (there is an error of 1% in the infrared absorption spectrometer). In Example 3, when more liquid crystal polymer is added to the reactor, even if the depolymerization treatment conditions are increased, the depolymerization reaction is incomplete due to approaching the reaction limit of the reactor, resulting in a decrease in the depolymerization rate, which affects the purity of the monomer. In Example 6, the depolymerization reaction is carried out at a temperature of 90°C and a pressure of 1.5MPa, and the depolymerization reaction is not complete after 72h of reaction, resulting in a decrease in the depolymerization rate.

[0101] By comparing Examples 4-6 with Examples 1-3, it can be seen that changing the mixing ratio of mobile phase 1 significantly affects the solubility. In particular, when the mixing ratio is too large, even if complete dissolution can be achieved, the signal interference of excessive organic solvent will also affect the signal response of the monomer, ultimately reducing the accuracy of monomer quantification.

[0102] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for analyzing the structure of a liquid crystal polymer monomer, characterized in that: The method comprises the steps of: S1-depolymerization: mixing the liquid crystal polymer sample and the depolymerization liquid matrix in a reactor for depolymerization treatment to obtain a depolymerization product; S2-Separation: The depolymerization product is subjected to a three-step derivatization treatment to obtain a separation product; S3-Detection: Take the separated product and dissolve it in mobile phase 1, and use liquid chromatography-mass spectrometry for detection; take another separated product and dissolve it in mobile phase 2, and use nuclear magnetic resonance spectroscopy for detection; The mobile phase 1 is a mixed mobile phase of mobile phase 1-1 and mobile phase 1-2; The mobile phase 1-1 is N,N-dimethylformamide, and the mobile phase 1-2 is acetonitrile; The liquid crystal polymer is a liquid crystal polymer containing any one of p-hydroxybenzoic acid, 4,4'-biphenol, terephthalic acid, isophthalic acid, 2-hydroxy-6-naphthoic acid, hydroquinone and ethylene glycol; The depolymerization liquid matrix is ​​alkali and water; The alkali is sodium hydroxide; The mass ratio of the liquid crystal polymer sample, alkali and water is (0.1-2):(0.5-4):(11-16.4); The depolymerization treatment is performed at a temperature of 100-200°C, a time of 36-72 hours, and a pressure of 1.5-3 MPa; The three-step derivatization process in the S2-separation is as follows: (1) filtering and separating the depolymerization products in the depolymerization of S1 to obtain soluble matter 1 and insoluble matter 1; (2) adding acid to the soluble matter 1 in step (1) to perform a reduction experiment, and performing membrane filtration to separate the soluble matter 2 and the insoluble matter 2, wherein the soluble matter 2 is the first separation product; (3) adding alcohol and an acid catalyst to the insoluble matter 2 in step (2) to carry out an esterification reaction to obtain a second separated product; The volume ratio of the mobile phase 1-1 to the mobile phase 1-2 is 1:(5-15); The mobile phase 2 is one or more of deuterated water, deuterated chloroform, deuterated dimethyl sulfoxide and deuterated tetrahydrofuran; The detection conditions of the liquid chromatography-mass spectrometry are as follows: the ion source is an electrospray source, the scanning range is 60-1000, the drying gas is nitrogen, the elution mode is isocratic elution, the injection volume is 3 μL, the chromatographic column is C18, 1.7 μm, 2.1*50 mm, and the flow rate is 0.3 mL / min; The nuclear magnetic resonance spectrum is a hydrogen nuclear magnetic resonance spectrum, and the detection condition of the hydrogen nuclear magnetic resonance spectrum is 400M.

2. The method for analyzing the structure of a liquid crystal polymer monomer according to claim 1, characterized in that: In the S1-depolymerization, the amount of the liquid crystal polymer sample and the depolymerization liquid matrix added is 2 / 3 to 3 / 4 of the volume of the reactor.

3. The method for analyzing the structure of a liquid crystal polymer monomer according to claim 1, characterized in that: The mass ratio of the liquid crystal polymer sample, alkali and water is 1:2:

14.

4. The method for analyzing the structure of a liquid crystal polymer monomer according to claim 1, characterized in that: The depolymerization treatment was performed at a temperature of 160° C., a time of 48 h, and a pressure of 2 MPa.

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