CN112250848B - A kind of thermotropic flame retardant and anti-droplet aromatic liquid crystal copolyester material and preparation method thereof - Google Patents

Abstract

The invention relates to the field of polyester materials, and the invention discloses a thermotropic, flame-retardant, anti-droplet aromatic liquid crystal copolyester material and a preparation method thereof. The preparation method includes: (1) adding a fully aromatic diphenol monomer to , wholly aromatic diacid monomer, AB type wholly aromatic monomer containing both terminal carboxyl group A and terminal hydroxyl group B, active terminal compound, polyester particles, acetic anhydride and catalyst under inert gas protection, 120 ~ 150 ℃ Acetylation reaction; (2) heat up to 300-340 ℃, transesterification reaction occurs; (3) further react under the conditions of 300-320 ℃, 1-3 mbar; (4) cool in an inert gas atmosphere, and grind the obtained product It is converted into powder, and then subjected to post-polycondensation reaction under the conditions of 200-260° C. and 1-3 mbar to obtain the target product. The thermotropic flame-retardant and anti-droplet aromatic liquid crystal copolyester material of the present invention has the advantages of low melting point, anti-droplet property and no harmful gas generated during combustion.

Description

A kind of thermotropic flame retardant and anti-droplet aromatic liquid crystal copolyester material and preparation method thereof

technical field

The invention relates to the field of polyester materials, in particular to a thermotropic, flame-retardant, anti-droplet aromatic liquid crystal copolyester material and a preparation method thereof.

Background technique

Semi-aromatic polyester, as a widely used polymer material, has been widely used in civil and industrial fields since it was launched, with the characteristics of high strength, high modulus and low water absorption. Polyester fiber, also known as polyester, occupies the majority of the chemical fiber industry. The types of polyester that have been marketed include PET, PBT, PTT, etc. Because the polymer will undergo oxidation, degradation and other reactions at high temperature, once it is burned, it is easy to form a fire, which will seriously affect the safety of people's lives and properties. Therefore, it is of great significance to improve the flame retardant properties of polyester materials.

The more mature polyester flame retardant modification technology is to use polyester and phosphorus flame retardants to blend or copolymerize to give polyester flame retardant properties. Patent CN107938014A discloses a flame retardant thermotropic polyarylate liquid crystal fiber. The preparation method comprises the following steps: introducing phosphorus-containing aromatic units into the main chain to obtain thermotropic liquid crystal polyarylate slices, then melting and extruding the slices into filaments, and finally preparing the flame-retardant thermotropic polyarylate liquid crystal fibers through post-processing. This process is simple and the fiber has good flame retardant effect, but due to the phosphorus-based flame retardant, white smoke and molten droplets will be released when burning. Therefore, in order to reduce the flame retardant polyester fiber droplets and the harm to the human body, it is urgent to study new phosphorus-free flame retardant polyester materials.

On the other hand, if the main chain of the liquid crystal polyarylate is a rigid linear structure, it needs to be melted at a higher temperature (above 300°C) before it can be formed, and the liquid crystal polyarylate monomer is relatively expensive, which will further increase production. cost.

To sum up, it is expected to become a topic with great application value to study how to improve the anti-droplet properties of polyester while reducing the production cost of polyarylate liquid crystal materials.

SUMMARY OF THE INVENTION

In order to solve the technical problems of the high melting point of phosphorus-based flame-retardant polyester, the generation of molten droplets and the generation of harmful gases in the prior art, the present invention provides a thermotropic flame-retardant and anti-melt-dropping aromatic liquid crystal copolyester material and its preparation method. The thermotropic flame-retardant and anti-droplet aromatic liquid crystal copolyester material of the present invention has a low melting point, has anti-droplet properties, and does not generate harmful gas during combustion.

The specific technical scheme of the present invention is:

In a first aspect, the present invention provides a thermotropic flame-retardant and anti-droplet aromatic liquid crystal copolyester material, which has one of the following chemical structural formulas:

Wherein, n=2-20, m=90-100; R is (CH ₂ )x, X=2-4.

The rigid main chain mesogens of the thermotropic flame retardant and anti-melting aromatic liquid crystal copolyester material of the present invention are composed of AA, BB or AB monomers containing ester bonds, amide bonds, imide bonds or ether bonds or It is composed of a combination of rigid monomers and polyester pellets that are copolymerized, and capped with active groups such as phenylacetylene or norbornene acetylene. Thermotropic flame retardant is obtained by one-pot melt polycondensation. Anti-dripping aromatic liquid crystal copolyester material. The naphthalene monomers are introduced into the molecular chain of the obtained copolymer to destroy the linearity of the main chain, the molecular chain is semi-aromatic structure, and compared with the straight-chain fully aromatic liquid crystal material, it has a lower melting processing temperature. On the other hand, both ends of the molecular chain are capped by thermally curable active groups such as phenylacetylenes or norbornene acetylenes, and cycloaddition reactions will occur in the high temperature environment (350-500 °C) during combustion. The cured cross-linked network structure has a certain covering ability during the formation process of the cross-linked network structure, which can effectively reduce the phenomenon of dripping during combustion. Finally, the material of the present invention does not contain phosphorus-based flame retardants, so no harmful gas is generated during combustion.

Preferably, the molecular weight of the liquid crystal copolyester material is between 1000-10000 g/mol.

In the second aspect, the present invention provides a preparation method of a thermotropic flame retardant and anti-melting droplet aromatic liquid crystal copolyester material, comprising the following steps:

(1) Combine wholly aromatic diphenol monomers, wholly aromatic diacid monomers, AB type wholly aromatic monomers containing both terminal carboxyl groups A and terminal hydroxyl groups B, polyester particles, active terminal compounds, acetic anhydride and The catalyst is added into the reactor; the acetylation reaction is carried out under the protection of inert gas at 120-150°C.

In this stage of the reaction, the phenolic hydroxyl groups in the diphenol monomer and the AB-type fully aromatic monomer are acetylated to generate the corresponding aromatic ester, and part of the acetic acid is generated to avoid the sublimation of the AB-type monomer at this temperature. Condensation on the vessel wall leads to the reduction of raw materials involved in the reaction, and at the same time prepares for the next step of transesterification.

(2) The temperature is raised to 300 to 340° C., and the transesterification reaction occurs.

The degree of transesterification at about 300°C is relatively high, and a large amount of acetic acid is generated in the transesterification reaction, and because the viscosity of the system gradually increases, the small molecules generated by the reaction are difficult to discharge, which restricts the increase of the degree of polymerization. Vacuum pushes out small molecules to increase molecular weight.

(3) The reaction is further carried out under the conditions of a temperature of 300-320° C. and a vacuum degree of 1-3 mbar.

The small molecules of acetic acid in the system are discharged under vacuum conditions, and the viscosity of the system is further increased. When no more acetic acid is generated in the system, the transesterification reaction basically ends.

(4) After the reaction is completed, cool in an inert gas atmosphere, grind the obtained product into powder, and then perform a post-polycondensation reaction under the conditions of a temperature of 200 to 260 ° C and a vacuum of 1 to 3 mbar to further increase the molecular weight of the product, and finally A thermotropic flame retardant and anti-droplet aromatic liquid crystal copolyester material is obtained.

Preferably, in step (1), the fully aromatic diphenol monomer is one or more of 4,4'-biphenol, hydroquinone and resorcinol.

Preferably, in step (1), the fully aromatic diacid monomer is one or more of 1,4-terephthalic acid, 1,7-naphthalenedicarboxylic acid and 2,6-naphthalenedicarboxylic acid .

Preferably, in step (1), the AB-type fully aromatic monomer containing both terminal carboxyl group A and terminal hydroxyl group B is 4-hydroxybenzoic acid, 4'-hydroxybiphenyl-4-carboxylic acid and 6-hydroxybenzoic acid. One or more of hydroxy-2-naphthoic acid.

Preferably, in step (1), the active end group compound is one or more of the following compounds:

Wherein, Y is amino or imino; Z is hydroxyl, carboxyl, ester or carbonyl.

Preferably, in step (1), the catalyst is one or more of sodium acetate, potassium acetate, zinc acetate, antimony trioxide, tetrabutyl titanate and germanium dioxide.

Preferably, in step (1), the polyester particles are polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT) and polybutylene terephthalate (PBT) ) one or more of.

Preferably, in step (1), the wholly aromatic diphenol monomer, wholly aromatic diacid monomer, AB type wholly aromatic monomer containing both terminal carboxyl group A and terminal hydroxyl group B, polyester particles, active The molar ratio of the terminal compound ranges from 10 to 40: 10 to 40: 80 to 20: 100 to 500: 2 to 8;

The molar amount of acetic anhydride is in excess of 50-100% relative to the total amount of hydroxyl groups in the raw material, and the catalyst molar amount is 0.1-0.5% of the total molar amount of the raw material.

AB-type monomer, as a common monomer of liquid crystal polymer, has low price and high reactivity, so it is used as the main component of the liquid crystal copolyester. Whole aromatic diphenols and wholly aromatic diacids usually use a small part of nonlinear structural monomers to destroy the linearity of liquid crystal copolyesters and reduce the melting point to facilitate processing. The amount of reactive end group compound is then calculated based on the molecular weight of the liquid crystal copolyester desired to be synthesized. The larger the proportion of polyester particles in the liquid crystal copolyester, the lower the melting point of the liquid crystal copolyester, but the worse its thermal stability, so its dosage needs to be strictly controlled within a certain range. To ensure that all the hydroxyl groups in the monomer are acetylated, acetic anhydride is usually 50-100% excess over the amount of hydroxyl groups. The amount of the catalyst should ensure the catalytic reaction and at the same time the influence on the reaction will be minimized, usually 0.1-0.5% of the total molar amount of the raw materials.

Preferably, in step (1), the acetylation reaction time is 30-60 min.

Preferably, in step (2), the transesterification reaction time is 1-3h; the heating rate is 0.5-1.5°C/min;

Preferably, in step (3), the reaction time is 10-30 min.

Preferably, in step (4), cooling to room temperature in an inert gas atmosphere, and the post-polycondensation reaction time is 18-36 h.

Compared with the prior art, the present invention has the following technical effects:

(1) The polymer chain of the thermotropic flame-retardant and anti-droplet aromatic liquid crystal copolyester material of the present invention has a semi-aromatic structure, and has a lower melting processing temperature than the straight-chain fully aromatic liquid crystal material. . In addition, the cross-linked network structure formed by the thermal curing reaction of active end groups has excellent flame retardant and anti-droplet properties, which can effectively reduce the loss of life and property caused by fire, so it has a wide range of application prospects in the field of civil textiles and high-temperature protective materials. .

(2) The molecular weight of the aromatic liquid crystal copolyester of the present invention is controllable during the polymerization process, and materials with different molecular weights can be obtained as required.

(3) The aromatic liquid crystal copolyester prepared by the present invention itself does not contain any solvent, and no small molecules are generated during its curing process, and thermotropic liquid crystal polyarylate sheets and fibers can be prepared by hot pressing or melt spinning , no desolvation is required in the process, making the preparation process simpler, more efficient and environmentally friendly;

(4) The aromatic liquid crystal copolyester prepared by the present invention does not contain phosphorus-based flame retardants, so no harmful gas is generated during combustion.

Description of drawings

Fig. 1 is the polarized light microscope photograph of the hot stage of the product obtained in Example 1 of the present invention;

FIG. 2 is a DSC curve diagram of Comparative Example 1 and Examples 1-3 of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the examples.

General Example

A thermotropic flame-retardant and anti-droplet aromatic liquid crystal copolyester material, which has one of the following chemical structural formulas:

Wherein, n=2-20, m=90-100; R is (CH ₂ )x, X=2-4. Preferably, the molecular weight of the liquid crystal copolyester material is between 1000-10000 g/mol.

A preparation method of a thermotropic flame-retardant and anti-melting-dropping aromatic liquid crystal copolyester material, comprising the following steps:

(1) According to the molar ratio of 10～40:10～40:80～20:100～500:2～8, mix the wholly aromatic diphenol monomer, the wholly aromatic diacid monomer, the terminal carboxyl group A and the terminal carboxyl group at the same time AB-type fully aromatic monomers of hydroxyl B, polyester particles, active end-group compounds, and an appropriate amount of acetic anhydride (the molar amount is in excess of 50-100% relative to the total amount of hydroxyl groups in the raw material) and catalyst (the molar amount is the total molar amount of the raw material). 0.1-0.5% of the amount) was added to the reactor; the acetylation reaction was carried out for 30-60 min under the protection of inert gas at 120-150°C.

(2) The temperature is raised to 300-340°C at a heating rate of 0.5-1.5°C/min, and the transesterification reaction is carried out for 1-3h.

(3) further react for 10-30 min under the conditions of a temperature of 300-320° C. and a vacuum degree of 1-3 mbar.

(4) After the reaction is completed, cool down to room temperature in an inert gas atmosphere, grind the obtained product into powder, and then perform a post-polycondensation reaction for 18-36 h under the conditions of a temperature of 200-260° C. and a vacuum degree of 1-3 mbar to obtain Thermotropic flame retardant anti-droplet aromatic liquid crystal copolyester material.

The wholly aromatic diphenol monomer is one or more of 4,4'-biphenol, hydroquinone and resorcinol.

The fully aromatic diacid monomer is one or more of 1,4-terephthalic acid, 1,7-naphthalenedicarboxylic acid and 2,6-naphthalenedicarboxylic acid.

The AB-type fully aromatic monomer containing both terminal carboxyl group A and terminal hydroxyl group B is one of 4-hydroxybenzoic acid, 4'-hydroxybiphenyl-4-carboxylic acid and 6-hydroxy-2-naphthoic acid. one or more.

The active end group compound is one or more of the following compounds:

Wherein, Y is amino or imino; Z is hydroxyl, carboxyl, ester or carbonyl.

The catalyst is one or more of sodium acetate, potassium acetate, zinc acetate, antimony trioxide, tetrabutyl titanate and germanium dioxide.

The polyester particles are one or more of polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT) and polybutylene terephthalate (PBT).

Example 1

Preparation of thermotropic flame retardant and anti-droplet aromatic liquid crystal copolyester material: add 4 in a molar ratio of 100:80:20:800:1000:80:80:1800:4 in a 250ml three-necked round bottom flask, 4'-Dihydroxybiphenyl, terephthalic acid, 2,6-naphthalenedicarboxylic acid, p-hydroxybenzoic acid, PET pellets, N-(3-carboxyphenyl)-4-phenylethynylphthalidene Amine, N-(3-hydroxyphenyl)-4-phenylethynylphthalimide, and acetic anhydride and potassium acetate. The flask was equipped with a sealed glass paddle stirrer, a nitrogen inlet tube and an insulated distillation head. A moderate nitrogen flow was introduced, the reaction mixture was acetylated at 120 °C for 30 min in a quicksand bath, and then increased to 340 °C at a heating rate of 1.5 °C/min for 1 h of transesterification. At this time, the reaction system was slowly evacuated to a vacuum degree of 1 mbar and the temperature was set to 300° C. and maintained for 10 min. The opaque melt was cooled to room temperature and the product was removed from the flask and ground to a fine powder. The target product is obtained by solid-state polycondensation reaction at 260° C. and vacuum degree of 3 mbar for 36 hours.

Example 2

Preparation of Thermotropic Flame Retardant Anti-Droplet Aromatic Liquid Crystal Copolyester Material: Add p-benzene in a molar ratio of 200:160:40:600:5000:20:20:1200:36 in a 250ml three-necked round bottom flask Diphenol, terephthalic acid, 1,7-naphthalenedicarboxylic acid, 6-hydroxy-2-naphthoic acid, PBT particles, 3-ethynylaniline, 2-(3-ethynylphenyl)-1,3-di Oxyisoindole-5-carboxylic acid, and acetic anhydride and zinc acetate. The flask was equipped with a sealed glass paddle stirrer, a nitrogen inlet tube and an insulated distillation head. A moderate nitrogen flow was introduced, the reaction mixture was acetylated at 150 °C for 60 min in a quicksand bath, and then increased to 320 °C at a heating rate of 1.5 °C/min for 3 h of transesterification. At this time, the reaction system was slowly evacuated to a vacuum degree of 3 mbar and the temperature was set to 320° C. and maintained for 30 min. The opaque melt was cooled to room temperature and the product was removed from the flask and ground to a fine powder. The target product was obtained by solid-state polycondensation reaction at 200° C. and a vacuum of 1 mbar for 18 hours.

Example 3

Preparation of Thermotropic Flame Retardant Anti-Droplet Aromatic Liquid Crystal Copolyester Materials: In a 250ml three-neck round bottom flask, m Diphenol, terephthalic acid, 1,7-naphthalenedicarboxylic acid, 4'-hydroxybiphenyl-4-carboxylic acid, PTT particles, acetic acid 4-(1,3-dioxo-1,3,3a, 4,7,7a-Hexahydro-2H-4,7-methylisoindol-2-yl) phenylacetate, 4-(1,3-dioxo-1,3,3a,4,7, 7a-hexahydro-2H-4,7-methylisoindol-2-yl)benzoic acid, and acetic anhydride and sodium acetate. The flask was equipped with a sealed glass paddle stirrer, a nitrogen inlet tube and an insulated distillation head. A moderate nitrogen flow was introduced, and the reaction mixture was acetylated at 140 °C for 40 min in a quicksand bath, and then increased to 300 °C at a heating rate of 0.5 °C/min for 2 h of transesterification. At this time, the reaction system was slowly evacuated to a vacuum degree of 2 mbar and the temperature was set to 310° C. and maintained for 20 min. The opaque melt was cooled to room temperature and the product was removed from the flask and ground to a fine powder. The target product was obtained by solid-state polycondensation reaction at 230° C. and vacuum degree of 2 mbar for 18 h.

Example 4

Preparation of thermotropic flame retardant and anti-droplet aromatic liquid crystal copolyester material: add 4 in a 250 ml three-necked round bottom flask in a molar ratio of 300:200:100:400:4000:70:70:1190:12, 4'-Dihydroxybiphenyl, terephthalic acid, 2,6-naphthalenedicarboxylic acid, p-hydroxybenzoic acid, PET pellets, N-(3-carboxyphenyl)-4-phenylethynylphthalidene Amine, N-(3-hydroxyphenyl)-4-phenylethynylphthalimide, and acetic anhydride and titanium trioxide. The flask was equipped with a sealed glass paddle stirrer, a nitrogen inlet tube and an insulated distillation head. A moderate nitrogen flow was introduced, the reaction mixture was acetylated at 140 °C for 40 min in a quicksand bath, and then increased to 310 °C at a heating rate of 1 °C/min for 3 h of transesterification. At this time, the reaction system was slowly evacuated to a vacuum degree of 3 mbar and a temperature of 310° C. and maintained for 20 min. The opaque melt was cooled to room temperature and the product was removed from the flask and ground to a fine powder. The target product is obtained by solid-state polycondensation reaction at 240° C. and vacuum degree of 2 mbar for 24 hours.

Example 5

Preparation of Thermotropic Flame Retardant Anti-Droplet Aromatic Liquid Crystal Copolyester Materials: In a 250ml three-necked round bottom flask, add p-benzene in a molar ratio of 100:80:20:800:1000:80:80:1530:7 Diphenol, terephthalic acid, 1,7-naphthalenedicarboxylic acid, 6-hydroxy-2-naphthoic acid, PBT particles, 3-ethynylaniline, 2-(3-ethynylphenyl)-1,3-di Oxyisoindole-5-carboxylic acid, and acetic anhydride and germanium dioxide. The flask was equipped with a sealed glass paddle stirrer, a nitrogen inlet tube and an insulated distillation head. A moderate nitrogen flow was introduced, and the reaction mixture was acetylated at 140 °C for 40 min in a quicksand bath, and then increased to 300 °C at a heating rate of 0.5 °C/min for 2 h of transesterification. At this time, the reaction system was slowly evacuated to a vacuum degree of 2 mbar and the temperature was set to 310° C. and maintained for 20 min. The opaque melt was cooled to room temperature and the product was removed from the flask and ground to a fine powder. The target product was obtained by solid-state polycondensation reaction at 230° C. and vacuum degree of 2 mbar for 24 hours.

Comparative Example 1

Preparation of pure thermotropic flame retardant aromatic liquid crystal polymer: In a 250 ml three-necked round bottom flask, 4,4'-dihydroxyl Benzene, terephthalic acid, 2,6-naphthalenedicarboxylic acid, p-hydroxybenzoic acid, N-(3-carboxyphenyl)-4-phenylethynylphthalimide, N-(3-hydroxybenzene yl)-4-phenylethynylphthalimide, and acetic anhydride and potassium acetate. The flask was equipped with a sealed glass paddle stirrer, a nitrogen inlet tube and an insulated distillation head. A moderate nitrogen flow was introduced, and the reaction mixture was acetylated at 140 °C for 40 min in a quicksand bath, and then increased to 300 °C at a heating rate of 0.5 °C/min for 2 h of transesterification. At this time, the reaction system was slowly evacuated to a vacuum degree of 2 mbar and the temperature was set to 310° C. and maintained for 20 min. The opaque melt was cooled to room temperature and the product was removed from the flask and ground to a fine powder. The target product was obtained by solid-state polycondensation reaction at 230° C. and vacuum degree of 2 mbar for 24 hours.

Comparative Example 2

Preparation of pure thermotropic phosphorus-containing flame retardant aromatic liquid crystal polymer: add 4,4'-dihydroxybiphenyl, 4,4'-dihydroxybiphenyl, 4,4'-(phenoxyphosphorus)-dibenzoic acid, 2,6-naphthalenedicarboxylic acid, p-hydroxybenzoic acid, and acetic anhydride and potassium acetate. The flask was equipped with a sealed glass paddle stirrer, a nitrogen inlet tube and an insulated distillation head. A moderate nitrogen flow was introduced, and the reaction mixture was acetylated at 140 °C for 40 min in a quicksand bath, and then increased to 300 °C at a heating rate of 0.5 °C/min for 2 h of transesterification. At this time, the reaction system was slowly evacuated to a vacuum degree of 2 mbar and the temperature was set to 310° C. and maintained for 20 min. The opaque melt was cooled to room temperature and the product was removed from the flask and ground to a fine powder. The target product was obtained by solid-state polycondensation reaction at 230° C. and vacuum degree of 2 mbar for 24 hours.

Performance Testing

The liquid crystallinity of Example 1 was measured by a hot-stage polarizing microscope (see Figure 1); the thermal properties of the product were tested by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and the vertical combustion of the test product was used to determine the Its flame retardant performance is also tested for the intrinsic viscosity of the product, thermal properties, flame retardancy and intrinsic viscosity test results are shown in Table 1 and Table 2, respectively, and the DSC curves of Comparative Example 1 and Examples 1-3 are shown in Figure 2.

It can be seen from Fig. 1 that the obvious band-like texture is shown, indicating that the product of Example 1 has a nematic liquid crystal texture and belongs to the liquid crystal copolyester. Combining Figure 2 and Table 1, it can be seen that the melting point of the pure thermotropic liquid crystal polymer of Comparative Example 1 is 267°C, while the melting point of the copolymers of Examples 1 to 5 is relative to that of Comparative Example 1 and PET (T _m =250 ~ 260 ℃), which can reduce the cost of copolyester material molding to a certain extent; at the same time, the thermal decomposition temperature T _d5% of the liquid crystal copolyester of the present invention is all above 370 ℃, and has a relatively high thermal conductivity. stability.

Table 1

As shown in Table 2, the vertical combustion grade of Comparative Example 2 reached V-0, but accompanied by molten droplets and white smoke, while the flame retardant grades of the liquid crystal copolyesters obtained in Examples 1-5 all reached V-0 grade. There are no molten droplets and white smoke during burning, indicating that the liquid crystal copolyester obtained by the present invention still has good flame retardancy and anti-melting droplet performance without phosphorus flame retardant.

Table 2

The raw materials and equipment used in the present invention, unless otherwise specified, are the common raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are the conventional methods in the art.

The above are only preferred embodiments of the present invention and do not limit the present invention. Any simple modifications, changes and equivalent transformations made to the above embodiments according to the technical essence of the present invention still belong to the technical solutions of the present invention. scope of protection.

Claims (8)

1. a preparation method of thermotropic flame retardant anti-dropping aromatic liquid crystal copolyester material, is characterized in that comprising the steps: (1) Combine wholly aromatic diphenol monomers, wholly aromatic diacid monomers, AB type wholly aromatic monomers containing both terminal carboxyl groups A and terminal hydroxyl groups B, polyester particles, active terminal compounds, acetic anhydride and The catalyst is added to the reactor; the acetylation reaction is carried out under the protection of inert gas at 120-150°C; The wholly aromatic diphenol monomer is one or more of 4,4'-biphenol, hydroquinone and resorcinol; the wholly aromatic diacid monomer is 1,4 -one or more of terephthalic acid, 1,7-naphthalenedicarboxylic acid and 2,6-naphthalenedicarboxylic acid; the AB-type fully aromatic monomer containing both terminal carboxyl group A and terminal hydroxyl group B is 4 -One or more of hydroxybenzoic acid, 4'-hydroxybiphenyl-4-carboxylic acid and 6-hydroxy-2-naphthoic acid; the active end group compound is one or more of the following compounds :

Wherein, Y is amino or imino; Z is hydroxyl, carboxyl, ester or carbonyl; The molar ratio of the wholly aromatic diphenol monomer, wholly aromatic diacid monomer, AB type wholly aromatic monomer containing both terminal carboxyl group A and terminal hydroxyl group B, polyester particles, and active terminal compound is 10～ 40:10～40:80～20:100～500:2～8; (2) be warming up to 300～340 ℃, transesterification reaction; (3) further react under the condition that the temperature is 300～320 ℃, and the vacuum degree is 1～3mbar; (4) After the reaction is completed, cool in an inert gas atmosphere, grind the obtained product into powder, and then perform a post-polycondensation reaction under the conditions of a temperature of 200-260° C. and a vacuum degree of 1-3 mbar to obtain a thermotropic flame retardant Anti-dripping aromatic liquid crystal copolyester material. 2. preparation method as claimed in claim 1 is characterized in that: in step (1), described catalyst is in sodium acetate, potassium acetate, zinc acetate, antimony trioxide, tetrabutyl titanate and germanium dioxide one or more of. 3. preparation method as claimed in claim 1 is characterized in that: in step (1), described polyester particle is polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT) ) and one or more of polybutylene terephthalate (PBT). 4. preparation method as claimed in claim 1 is characterized in that: in step (1), described acetic anhydride molar amount is excessive 50-100% with respect to the total amount of hydroxyl groups in the raw material, and the catalyst molar amount is 50-100% of the raw material molar amount 0.1-0.5%. 5. preparation method as claimed in claim 1 is characterized in that: in step (1), acetylation reaction time is 30～60min. 6. The preparation method according to claim 1, characterized in that: in step (2), the reaction time of transesterification is 1-3h; the heating rate is 0.5-1.5°C/min. 7. preparation method as claimed in claim 1 is characterized in that: in step (3), reaction time is 10～30min. 8 . The preparation method according to claim 1 , wherein in step (4), cooling to room temperature in an inert gas atmosphere, and the post-polycondensation reaction time is 18-36 h. 9 .

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