Preparation method and application of high-temperature-resistant transparent modified polyester

Abstract

The invention relates to the field of high polymer materials, and discloses a preparation method and application of high-temperature-resistant transparent modified polyester. The preparation method comprises the following steps: 1) blending 9, 9-di-[(4-phenylphenoxy) dibenzoic acid] fluorene with diacid and dihydric alcohol, and carrying out esterification reaction; and 2) carrying out condensation polymerization on the esterification product to obtain the high-temperature-resistant transparent modified polyester with the glass transition temperature of more than 70 DEG C. According to the invention, 9, 9-di-[(4-phenylphenoxy) dibenzoic acid] fluorene is used as a modification monomer, and is copolymerized with other dibasic acids and dihydric alcohols to synthesize the modified polyester, and the modified polyester has high transparency and still has good mechanical properties and dimensional stability at high temperature. Therefore, the high-temperature-resistant transparent modified polyester is applicable to the application fields of optical films, optical lenses, reflective protective films, optical fibers or liquid crystal displays and the like.

Description

Technical Field

[0001] The present invention relates to the field of polymer materials, and particularly to a preparation method and application of a high-temperature resistant transparent modified polyester. Background Art

[0002] Due to their excellent mechanical properties, abrasion resistance, and dimensional stability, polyester materials are widely used in fields such as fibers, films, and engineering plastics. However, traditional polyester materials such as polyethylene terephthalate (PET) have a certain degree of crystallinity. In the PET molecular structure, the benzene ring of terephthalic acid is rigid and can form regular packing in the polymer chain, thus promoting the crystallization process. This orderliness of packing is one of the key factors for PET crystallization. Due to the packing of the benzene rings of terephthalic acid, PET exhibits a relatively high degree of crystallinity during processing and use. Although this helps to improve the strength and rigidity of the material, it also leads to a decrease in transparency and flexibility, thereby limiting its application fields. For example, in the field of optical applications, due to the crystallization phenomenon of polyester, the transparency decreases and a birefringence effect occurs, especially posing a severe challenge in the application of liquid crystal display technology.

[0003] Optical grade polyester materials play an important role in modern industry, especially in fields such as display screens, touch panels, and precision optical components. Among them, optical grade polyester films are widely used in fields such as smartphones, tablet computers, and automotive interiors. Due to the characteristics of their application scenarios, optical grade polyester films generally require properties such as high transparency, high thermal stability, high dimensional stability, and high flexibility. To improve the transparency of polyester, traditional technologies often use isophthalic acid as a modifying monomer to reduce the crystallinity and birefringence of polyester (for example, CN119101218A), but a high content of isophthalic acid will also reduce the mechanical properties and glass transition temperature (Tg) of polyester, resulting in poor thermal stability of the material.

[0004] Therefore, the existing technologies still lack polyester materials that simultaneously possess high transparency, low birefringence, high thermal stability, and good mechanical properties. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a preparation method and application of a high-temperature resistant transparent modified polyester. The present invention uses 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene as a modifying monomer, and after copolymerization with other dibasic acids and diols, a modified polyester can be synthesized, which not only has high transparency but also has good mechanical properties and dimensional stability at high temperatures. Therefore, the high-temperature resistant transparent modified polyester of the present invention is suitable for application fields such as optical films, optical lenses, reflective protective films, optical fibers, or liquid crystal displays.

[0006] The specific technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing a high-temperature resistant transparent modified polyester, which comprises the following steps: 1) Blending 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene with a dicarboxylic acid and a diol, and carrying out an esterification reaction.

[0007] The 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene accounts for 0.01-99 mol% of the total amount of it and the dicarboxylic acid.

[0008] 2) Continuing the polycondensation reaction of the esterification product to obtain a high-temperature resistant transparent modified polyester with a glass transition temperature > 70°C.

[0009] The present invention uses 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene (structural formula as follows) as a modified monomer of the polyester, and after copolymerizing with other dicarboxylic acids and diols, a high-temperature resistant transparent modified polyester material can be synthesized.

[0010] As can be seen from the above structural formula: First, each of the two benzene rings in the molecular structure of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene is connected with a carboxyl group, so it can participate in the copolymerization of the polyester as a dicarboxylic acid monomer, thus providing a premise for being a polyester modified monomer. Second, this compound contains a phenyl ether structure. The present invention finds that when this compound participates in the polyester copolymerization as a modified monomer, the obtained polyester simultaneously has the following excellent optical and mechanical properties: (1) High transparency: The rigid structure of the benzene ring and the non-polar characteristics of the ether bond can reduce the disordered stacking of molecular chains, reduce Rayleigh scattering, and improve transparency; (2) Low birefringence: The symmetrical structure of the benzene ring and the ether bond can reduce the molecular chain orientation and reduce the birefringence of the polymer; (3) High thermal stability: The benzene ring structure can enhance the heat resistance of the polymer and increase the glass transition temperature (Tg) and melting point; (4) Good mechanical properties: The presence of the benzene ring and the ether bond can promote the close packing of molecular chains and improve the tensile strength and flexural modulus; (4) Flexibility: By adjusting the ratio of phenyl ether diacid to flexible diol, the flexibility of the polyester can be regulated to meet different application requirements.

[0011] In step 1), the 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene accounts for 5-60 mol% of the total amount of it and the dicarboxylic acid.

[0012] In order to further improve the modification effect of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene, its content should not be too low, otherwise the modification effect will not be obvious enough. Through experiments, it is found that when its content accounts for more than 5 mol% of the total amount of dibasic acid, the polymer Tg can be significantly increased and the crystallinity can be reduced. Theoretically, in polycondensation reactions, the collision frequency of end groups is closely related to the mobility of polymer segments. Due to its rigid structure, traditional fluorene-based dibasic acids often cause the reaction kinetics to become slow due to limited segmental movement in the later stage of the reaction, resulting in the inability to further increase the molecular weight. Therefore, in the synthesis of polyesters, the dosage of most modifying monomers should not be too much, otherwise it will bring a series of negative impacts (such as mechanical properties and fluidity decline, etc.). The flexible phenylene ether segment in the modifying monomer of the present invention can significantly improve the flexibility of the entire molecular chain while not losing the inherent high modulus effect of the fluorene skeleton, so that the end groups can still maintain a high collision frequency during the formation of high molecular weight. This design can extend the effective reaction period of the polycondensation reaction, promote the formation of high molecular weight polymers, enable the overall molecular weight to reach a higher level, and at the same time reduce the reaction stagnation phenomenon caused by insufficient diffusion effect in the final stage of the reaction. In addition, on the basis of retaining the high modulus and heat resistance of the polymer given by the fluorene structure, the present invention reduces the rigidity of the entire molecular chain, thereby improving the fluidity of the polyester in the molten state and further improving the thermal processing performance. Therefore, even in the case of a relatively high content of the modifying monomer, the present invention can still achieve the balance between high modulus and flexibility of the polyester material, enabling the final product to simultaneously possess excellent mechanical properties, impact resistance and processing suitability, and expanding its application potential in high-performance engineering plastics, electronics, optoelectronics and other fields.

[0013] Preferably, in step 1), the synthesis route of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene is as follows: Furthermore, the synthesis method of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene includes the following steps a) Mix bisphenol fluorene, alkali and organic solvent evenly, heat for reaction, cool and then add 4-chlorobenzonitrile for reaction; after cooling the reaction product, add it to acid for precipitation, purification and drying to obtain dicyanide.

[0014] b) Mix dicyanide, alkali and organic solvent evenly, heat for reaction; after cooling the reaction product, add it to acid, stir, filter, disperse the obtained aromatic dibasic acid in acid, perform heat treatment, filter, rinse and dry, and recrystallize to obtain 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene.

[0015] Preferably, in step a), the molar ratio of bisphenol fluorene to 4-chlorobenzonitrile is 1∶(2 - 3).

[0016] Preferably, in step a), the temperature of the heating reaction is 105 - 115 °C.

[0017] Preferably, in step a), the first cooling is to cool to 98 - 102 °C; the second cooling is to cool to room temperature.

[0018] Preferably, in step a), after adding 4 - chlorobenzonitrile, the reaction continues for 2 - 4 h.

[0019] Preferably, in step b), the temperature of the heating reaction is 150 - 170 °C and the time is 1.5 - 2.5 h.

[0020] Preferably, in step b), the temperature of the heat treatment is 75 - 85 °C.

[0021] Preferably, in step b), the solvent for recrystallization is dioxin.

[0022] Preferably, in step 1), the dibasic acid is selected from aromatic dibasic acids and aliphatic dibasic acids; the diol is selected from straight - chain alkyl diols with C2 - C12.

[0023] More preferably, in step 1), the dibasic acid is selected from one or more of terephthalic acid, isophthalic acid, and naphthalene dicarboxylic acid; the diol is selected from one or more of ethylene glycol, propylene glycol, 1,4 - butanediol, and 1,6 - hexanediol.

[0024] Preferably, in step 1), the molar ratio of the total amount of 9,9 - bis - [(4 - phenoxyphenyl)dibenzoic acid]fluorene and dibasic acid to the diol is 1:(0.5 - 1.5).

[0025] Preferably, in step 1), the temperature of the esterification reaction is 240 - 250 °C; in step 2), the temperature of the polycondensation reaction is 270 - 290 °C.

[0026] In a second aspect, the present invention provides the use of the high - temperature - resistant transparent modified polyester obtained by the above - mentioned preparation method in preparing polyester materials such as optical films, optical lenses, reflective protective films, optical fibers, or liquid crystal displays, which have special requirements for transparency, high - temperature resistance, or flexibility.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) After using 9,9 - bis - [(4 - phenoxyphenyl)dibenzoic acid]fluorene as a modified monomer of polyester to participate in polyester copolymerization, the obtained polyester simultaneously has the following excellent optical and mechanical properties: (a) high transparency; (b) low birefringence; (c) high thermal stability; (d) good mechanical properties; (e) flexibility.

[0028] (2) The high-temperature resistant transparent modified polyester of the present invention is applicable to fields with special requirements for transparency, high-temperature resistance or flexibility, such as optical films, optical lenses, reflective protective films, optical fibers or liquid crystal displays, etc. Description of the Drawings

[0029] Figure 1 It is the DSC diagram of the polyester obtained in Example 1.

[0030] Figure 2 It is the DSC diagram of the polyester obtained in Example 2.

[0031] Figure 3 It is the DSC diagram of the polyester obtained in Comparative Example 1. Detailed Embodiments

[0032] The present invention will be further described below in conjunction with embodiments.

[0033] The synthesis of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene includes the following steps: a) Mix bisphenol fluorene, an alkali and an organic solvent evenly, heat for reaction, cool, and then add 4-chlorobenzonitrile for reaction; after the reaction product is cooled, add it to an acid for precipitation, purification, and drying to obtain a dicyanide.

[0034] In some preferred embodiments, in step a), the molar ratio of bisphenol fluorene to 4-chlorobenzonitrile is 1:(2 - 3).

[0035] In some preferred embodiments, in step a), the temperature of the heating reaction is 105 - 115°C.

[0036] In some preferred embodiments, in step a), the first cooling is to cool to 98 - 102°C; the second cooling is to cool to room temperature.

[0037] In some preferred embodiments, in step a), after adding 4-chlorobenzonitrile, continue the reaction for 2 - 4 h.

[0038] b) Mix the dicyanide, an alkali and an organic solvent evenly, heat for reaction; after the reaction product is cooled, add it to an acid, stir, filter, disperse the obtained aromatic dicarboxylic acid in the acid, perform heat treatment, filter, rinse, dry, and recrystallize to obtain 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene.

[0039] In some preferred embodiments, in step b), the temperature of the heating reaction is 150 - 170°C and the time is 1.5 - 2.5 h.

[0040] In some preferred embodiments, in step b), the temperature of the heat treatment is 75 - 85°C.

[0041] In some preferred embodiments, in step b), the solvent for recrystallization is dioxin.

[0042] A method for preparing a high-temperature resistant transparent modified polyester, comprising the following steps: 1) Blending 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene with a dicarboxylic acid and a diol, and carrying out an esterification reaction. Among them, the 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene accounts for 0.01-99 mo1% of the total amount of it and the dicarboxylic acid.

[0043] In some preferred embodiments, in step 1), the 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene accounts for 5-60 mo1% of the total amount of it and the dicarboxylic acid.

[0044] In some preferred embodiments, in step 1), the dicarboxylic acid is selected from aromatic dicarboxylic acids and aliphatic dicarboxylic acids; the diol is selected from straight-chain alkyl diols with C2-C12; further preferably, the dicarboxylic acid is selected from one or more of terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid; the diol is selected from one or more of ethylene glycol, propylene glycol, 1,4-butanediol, and 1,6-hexanediol.

[0045] In some preferred embodiments, in step 1), the molar ratio of the total amount of the 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene and the dicarboxylic acid (i.e., the total acid amount) to the diol ranges from 1:(0.5-1:5).

[0046] In some preferred embodiments, in step 1), the temperature of the esterification reaction is 240-250°C.

[0047] 2) Continuing the polycondensation reaction on the esterification product to obtain a high-temperature resistant transparent modified polyester with a glass transition temperature >70°C.

[0048] In some preferred embodiments, in step 2), the temperature of the polycondensation reaction is 270-290°C.

[0049] In some preferred embodiments, in step 2), a catalyst and / or an antioxidant is added to the reaction system before the polycondensation reaction.

[0050] In some preferred embodiments, in step 2), the antioxidant is diethyl phosphite.

[0051] In some preferred embodiments, in step 2), the catalyst is antimony trioxide.

[0052] Specific examples and comparative examples.

[0053] Example 1 (1) Synthesis of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene: Step 1: Pour 74.64 g (0.213 mol) of bisphenol fluorene, 29.90 g (0.533 mol) of potassium hydroxide, 50 g of toluene, and 790 g of dimethylformamide into a 2-liter four-necked flask equipped with a stirrer, thermometer, Dean-Stark trap, and reflux condenser. While stirring the mixture, keep the system under a nitrogen atmosphere and heat the system to 110 °C to distill out the generated water together with toluene in an azeotropic form. After the distillation of water is completed, lower the system temperature to 100 °C. Add 73.3 g (0.533 mol) of 4-chlorobenzonitrile to the flask and carry out the reaction at this temperature for 3 hours. After the reaction is completed, cool the reaction product mixture to room temperature and then pour it into 1500 g of 5% hydrochloric acid solution. The precipitated crystals are collected by filtration. The collected crude crystals are rinsed with 1000 g of water and then filtered to remove the residual inorganic salts. Rinse the crystals with water again and filter. Then rinse the crystals with 500 g of methanol and filter. After repeating the methanol rinsing and drying, the crystals are dried to obtain 80.97 g of the dicyanide compound. The yield of the dicyanide is 88.3%.

[0054] Step 2: Pour 27.85 g (0.188 mol) of the dicyanide, 104 g of potassium hydroxide, and 832 g of ethylene glycol into a 2-liter four-necked flask equipped with a stirrer, thermometer, and reflux condenser. React the mixture at 160 °C for 2 hours. After the reaction is completed, cool the reaction product mixture and pour it into 3 liters of 10% sulfuric acid solution. Stir at room temperature for 1 hour. Then, separate the free aromatic dicarboxylic acid by filtration. Disperse the aromatic dicarboxylic acid in 1.5 liters of 10% sulfuric acid solution and carry out heat treatment at 80 °C. Filter the mixture, separate the solid aromatic dicarboxylic acid, and rinse it twice with 1.5 liters of boiling distilled water. The obtained aromatic dicarboxylic acid is dried by hot air and recrystallized using 400 g of dioxane to obtain 79.27 g of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene. The yield of the product based on the dicyanide is 90.0%.

[0055] (2) Synthesis of polyester: Put 2.5 kg of materials, 1.266 kg of terephthalic acid, 0.996 kg of ethylene glycol and 0.236 kg of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene into the reaction kettle, heat up to 245 °C and stir to carry out the esterification reaction. Maintain the pressure at 3 kg for 3 hours and leave it at normal pressure for 12 hours. A distillation column is involved in the esterification process. After the esterification reaction is completed, add 0.66 g of antimony trioxide and 0.56 g of antioxidant (diethyl phosphite) for mixing. Vacuum the air pressure from 760 torr to 0.1 torr within 30 minutes and continue stirring, and carry out the polymerization reaction at a temperature of 280 °C. After the polymerization reaction reaches a specific torque value, take out the product from the reaction kettle and granulate it to make polyester particles. Figure 1 It is the DSC diagram of the polyester obtained in Example 1. It can be known from the DSC graph that the glass transition temperature of this polyester particle is 76.62 °C and the crystallization peak temperature is 158.86 °C.

[0056] Example 2 (1) Synthesis of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene: The same as in Example 1.

[0057] (2) Synthesis of polyester: Put 2.5 kg of materials, 0.885 kg of terephthalic acid, 0.827 kg of ethylene glycol and 0.786 kg of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene (Example 1) into the reaction kettle, heat up to 245 °C and stir to carry out the esterification reaction. Maintain the pressure at 3 kg for 3 hours and leave it at normal pressure for 12 hours. A distillation column is involved in the esterification process. After the esterification reaction is completed, add 0.66 g of antimony trioxide and 0.56 g of antioxidant (diethyl phosphite) for mixing. Vacuum the air pressure from 760 torr to 0.1 torr within 30 minutes and continue stirring, and carry out the polymerization reaction at a temperature of 280 °C. After the polymerization reaction reaches a specific torque value, take out the product from the reaction kettle and granulate it to make polyester particles. Figure 2 It is the DSC diagram of the polyester obtained in Example 2. It can be known from the DSC graph that the glass transition temperature of this polyester particle is 96.47 °C and the crystallization peak completely disappears.

[0058] Example 3 (1) Synthesis of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene: The same as in Example 1.

[0059] (2) Synthesis of polyester: 2.5 kg of materials were charged. 0.541 kg of terephthalic acid, 0.674 kg of ethylene glycol and 1.283 kg of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene (Example 1) were charged into the reaction kettle. The temperature was raised to 245 °C and stirred to carry out the esterification reaction. The pressure was maintained at 3 kg for 3 hours and left at atmospheric pressure for 12 hours. A distillation column was involved in the esterification process. After the esterification reaction was completed, 0.66 g of antimony trioxide and 0.56 g of antioxidant (diethyl phosphite) were added and mixed. The air pressure was evacuated from 760 torr to 0.1 torr within 30 minutes and continuously stirred. The polymerization reaction was carried out at a temperature of 280 °C. After the polymerization reaction reached a specific torque value, the product was taken out of the reaction kettle and granulated to make polyester particles. The glass transition temperature of this polyester particle was 108.71 °C, and the crystallization peak completely disappeared.

[0060] Example 4 (1) Synthesis of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene: The same as Example 1.

[0061] (2) Synthesis of polyester: 2.5 kg of materials were charged. 0.305 kg of terephthalic acid, 0.569 kg of ethylene glycol and 1.625 kg of 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene (Example 1) were charged into the reaction kettle. The temperature was raised to 245 °C and stirred to carry out the esterification reaction. The pressure was maintained at 3 kg for 3 hours and left at atmospheric pressure for 12 hours. A distillation column was involved in the esterification process. After the esterification reaction was completed, 0.66 g of antimony trioxide and 0.56 g of antioxidant (diethyl phosphite) were added and mixed. The air pressure was evacuated from 760 torr to 0.1 torr within 30 minutes and continuously stirred. The polymerization reaction was carried out at a temperature of 280 °C. After the polymerization reaction reached a specific torque value, the product was taken out of the reaction kettle and granulated to make polyester particles. The glass transition temperature of this polyester particle was 124.71 °C, and the crystallization peak completely disappeared.

[0062] Comparative Example 1 2.5 kg of materials were charged. 1.430 kg of terephthalic acid and 1.069 kg of ethylene glycol were charged into the reaction kettle. The temperature was raised to 245 °C and stirred to carry out the esterification reaction. The pressure was maintained at 3 kg for 3 hours and left at atmospheric pressure for 12 hours. A distillation column was involved in the esterification process. After the esterification reaction was completed, 0.66 g of antimony trioxide and 0.56 g of antioxidant (diethyl phosphite) were added and mixed. The air pressure was evacuated from 760 torr to 0.1 torr within 30 minutes and continuously stirred. The polymerization reaction was carried out at a temperature of 280 °C. After the polymerization reaction reached a specific torque value, the product was taken out of the reaction kettle and granulated. Figure 3It is the DSC graph of the polyester obtained in Comparative Example 1. From the DSC graph, it can be known that the glass transition temperature of this polyester particle is 68.15 °C, and the crystallization peak temperature is 126.29 °C.

[0063] Comparative Example 2 (the modified monomer is 9,9-bis[(4-hydroxyethoxyphenyl)fluorene]) Put 2.5 kg of materials, put 0.942 kg of terephthalic acid, 0.563 kg of ethylene glycol and 0.994 kg of 9,9-bis[(4-hydroxyethoxyphenyl)fluorene] into the reaction kettle, heat up to 245 °C and stir to carry out the esterification reaction. The pressure of 3 kg is maintained for 3 hours and left at normal pressure for 12 hours. A distillation column is involved in the esterification process. After the esterification reaction is completed, 0.66 g of antimony trioxide and 0.56 g of antioxidant (diethyl phosphite) are put in for mixing. The air pressure is evacuated from 760 torr to 0.1 torr within 30 minutes and continuous stirring is carried out, and the polymerization reaction is carried out at a temperature of 280 °C. After the polymerization reaction reaches a specific torque value, the product is taken out from the reaction kettle and granulated to make polyester particles. The glass transition temperature of this polyester particle is 90.15 °C, and the crystallization peak completely disappears.

[0064] Comparative Example 3 (the modified monomer is 1,4-cyclohexanedimethanol) Put 2.5 kg of materials, put 1.285 kg of terephthalic acid, 0.768 kg of ethylene glycol and 0.446 kg of 1,4-cyclohexanedimethanol into the reaction kettle, heat up to 245 °C and stir to carry out the esterification reaction. The pressure of 3 kg is maintained for 3 hours and left at normal pressure for 12 hours. A distillation column is involved in the esterification process. After the esterification reaction is completed, 0.66 g of antimony trioxide and 0.56 g of antioxidant (diethyl phosphite) are put in for mixing. The air pressure is evacuated from 760 torr to 0.1 torr within 30 minutes and continuous stirring is carried out, and the polymerization reaction is carried out at a temperature of 280 °C. After the polymerization reaction reaches a specific torque value, the product is taken out from the reaction kettle and granulated to make polyester particles. The glass transition temperature of this polyester particle is 80.82 °C, and the crystallization peak completely disappears.

[0065] Performance Test The polyester particles prepared in the above-mentioned examples and comparative examples were subjected to various performance tests, and the test results are shown in Table 1 and Table 2: Table 1: The effects of different modified monomer contents and types on the crystallization peak, Tg and transparency of polyester Case Proportion of modified monomer in total dibasic acid Whether there is a crystallization peak Tg (°C) Transparency (%) Comparative Example 1 0 mol% Yes 68.15 87.27 Example 1 9,9 - bis - [(4 - phenylphenoxy)dibenzoic acid]fluorene 5 mol% Yes 76.62 86.75 Example 2 9,9 - bis - [(4 - phenylphenoxy)dibenzoic acid]fluorene 20 mol% No 96.47 67.32 Example 3 9,9 - bis - [(4 - phenylphenoxy)dibenzoic acid]fluorene 40 mol% No 108.71 35.38 Example 4 9,9 - bis - [(4 - phenylphenoxy)dibenzoic acid]fluorene 60 mol% No 124.71 29.12 Comparative Example 2 9,9 - bis - [(4 - hydroxyethoxyphenyl)]fluorene 20 mol% No 90.15 83.98 Comparative Example 3 1,4 - cyclohexanedimethanol 20 mol% No 80.82 87.78 Table 2: The effects of different modified monomer contents and types on the mechanical properties of polyester It can be known from the data comparison in Table 1 and Table 2 that: (1) The main difference between Comparative Example 1 and Examples 1-4 lies in the different proportions of 9,9-bis[(4-phenylphenoxy)dibenzoic acid] fluorene in the total amount of dibasic acids. Comparative Example 1 does not contain this modified monomer of 9,9-bis[(4-phenylphenoxy)dibenzoic acid], and the resulting polyester has a crystallization peak, and the glass transition temperature is the lowest, and the data of these indicators such as transparency and flexibility are the worst. In Examples 1-3, as the content of the modified monomer increases, the crystallization peak gradually does not appear in the resulting polyester, indicating that the crystallinity is reduced, and at the same time the glass transition temperature continuously increases, and the flexibility and other indicators of the resulting polyester are also at a better level.

[0066] Theoretically, the collision frequency of end groups in polycondensation reactions is closely related to the mobility of polymer segments. Due to its rigid structure, traditional fluorene-based dibasic acids often cause the reaction kinetics to become slow due to limited segment mobility in the later stage of the reaction, resulting in the inability to further increase the molecular weight. Therefore, in the synthesis of polyesters, the dosage of most modified monomers should not be too much, otherwise it will bring a series of negative impacts (such as a decrease in mechanical properties and fluidity). The flexible phenylene ether segment in the modified monomer of the present invention can significantly improve the flexibility of the entire molecular chain while not losing the inherent high modulus effect of the fluorene backbone, so that the end groups can still maintain a high collision frequency during the formation of high molecular weight. This design can extend the effective reaction period of the polycondensation reaction, promote the formation of high molecular weight polymers, make the overall molecular weight reach a higher level, and at the same time reduce the reaction stagnation phenomenon caused by insufficient diffusion effect at the end of the reaction. In addition, on the basis of retaining the high modulus and heat resistance given by the fluorene structure to the polymer, the present invention reduces the rigidity of the entire molecular chain, thereby improving the fluidity of the polyester in the molten state and further improving the hot processing performance. Therefore, even in the case of a relatively high content of the modified monomer, the present invention can still achieve a balance between high modulus and flexibility of the polyester material, so that the final product has excellent mechanical properties and processing suitability at the same time.

[0067] (2) The difference between Comparative Examples 2 and 3 and Example 1 lies in the use of other modified monomers. The results show that both of the two modified monomers in Comparative Examples 2-3 exist in the form of diols, which have an excellent effect on the crystallization destruction of the polyester structure, but are slightly insufficient in terms of the increase in Tg temperature and mechanical properties.

[0068] The present invention relates to 9,9-bis[(4-phenylphenoxy)dibenzoic acid]fluorene and its application technology in the synthesis of novel polyesters, aiming to overcome the deficiencies of traditional fluorene-containing polyesters in polycondensation reaction kinetics, molecular weight growth, and thermal processing performance. Although polyesters synthesized using fluorene diacid as a monomer can enhance the modulus and heat resistance of materials due to the high rigidity of the fluorene backbone, the large cardo group results in excessive molecular chain rigidity, often leading to problems such as restricted diffusion of reaction end groups, stagnant molecular weight growth, and high melt viscosity, which limit the development of such materials in thermal processing and practical applications. The present invention addresses the above problems by introducing a flexible linker segment (such as an alkyl chain, ether chain, or other flexible functional groups) into the molecular backbone of fluorene diacid to adjust the rigidity-flexibility balance of the entire molecular chain, retaining the characteristics of the fluorene structure that endow the polymer with high modulus and heat resistance, while significantly improving the segmental mobility in the polycondensation reaction, promoting effective collision of end groups, thereby obtaining high molecular weight polyesters, and reducing the viscosity in the molten state and improving thermal processing performance.

[0069] The preparation of traditional polyesters mainly involves using terephthalic acid (or its derivatives) and ethylene glycol, followed by polycondensation reaction to further extend the molecular chain after esterification or transesterification. Although introducing fluorene diacid can utilize its rigid structure to enhance the modulus and heat resistance of the polymer, due to the steric hindrance effect of the fluorene structure itself, the polycondensation reaction in the later stage will be restricted: when the molecular chain gradually grows, it is difficult for the end groups to fully collide due to steric hindrance, resulting in difficulty in forming high molecular weight; at the same time, the increased rigidity of the polymer chain will also reduce the fluidity in the molten state, further affecting processability. Therefore, how to improve the reaction kinetics and thermal processing performance without sacrificing high modulus and heat resistance has become a major challenge in the design of polyester materials.

[0070] Unless otherwise specified, the raw materials and equipment used in the present invention are common raw materials and equipment in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0071] The above are only preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A preparation method of a high-temperature resistant transparent modified polyester, characterized in that Comprising: 1) Blending 9,9-bis[(4-phenylphenoxy)dibenzoic acid] fluorene with a dicarboxylic acid and a diol, and carrying out an esterification reaction; The 9,9-bis[(4-phenylphenoxy)dibenzoic acid] fluorene accounts for 0.01 - 99 mol% of the total amount of it and the dicarboxylic acid; 2) Continuing the polycondensation reaction on the esterification product to obtain a high-temperature resistant transparent modified polyester with a glass transition temperature > 70 °C.

2. The preparation method according to claim 1, characterized in that: In step 1), the 9,9-bis[(4-phenylphenoxy)dibenzoic acid] fluorene accounts for 5 - 60 mol% of the total amount of it and the dicarboxylic acid.

3. The preparation method according to claim 1, wherein: In step 1), the synthesis method of the 9,9-bis[(4-phenylphenoxy)dibenzoic acid] fluorene includes: a) Mixing bisphenol fluorene, a base and an organic solvent uniformly, heating for reaction, cooling, and then adding 4-chlorobenzonitrile for reaction; after cooling the reaction product, adding it to an acid for precipitation, purification, and drying to obtain a dicyanide; b) Mixing the dicyanide, a base and an organic solvent uniformly, heating for reaction; after cooling the reaction product, adding it to an acid, stirring, filtering, dispersing the obtained aromatic dicarboxylic acid in the acid, performing heat treatment, filtering, rinsing, drying, and recrystallizing to obtain 9,9-bis[(4-phenylphenoxy)dibenzoic acid] fluorene.

4. The preparation method according to claim 3, wherein: In step a), The temperature of the heating reaction is 105 - 115 °C; The first cooling is to cool to 98 - 102 °C; The molar ratio of bisphenol fluorene to 4-chlorobenzonitrile is 1:(2 - 3); Continue the reaction for 2 - 4 h after adding 4-chlorobenzonitrile; The second cooling is to cool to room temperature.

5. The preparation method according to claim 3, characterized in that: In step b), The temperature of the heating reaction is 150 - 170 °C, and the time is 1.5 - 2.5 h; The temperature of the heat treatment is 75 - 85 °C; The solvent for recrystallization is dioxin.

6. The preparation method according to claim 1 or 2, characterized in that: In step 1), The dicarboxylic acid is selected from aromatic dicarboxylic acids and aliphatic dicarboxylic acids; The diol is selected from straight-chain alkyl diols with C2 - C12.

7. The preparation method according to claim 6, characterized in that: In step 1), The dicarboxylic acid is selected from one or more of terephthalic acid, isophthalic acid, and naphthalene dicarboxylic acid; The diol is selected from one or more of ethylene glycol, propylene glycol, 1,4-butanediol, and 1,6-hexanediol.

8. The preparation method according to claim 1, characterized in that: In step 1), the molar ratio of the total amount of 9,9-bis[(4-phenylphenoxy)dibenzoic acid] fluorene and the dicarboxylic acid to the diol is 1:(0.5 - 1.5).

9. According to the preparation method described in claim 1, characterized in that: In step 1), the temperature of the esterification reaction is 240 - 250 °C; In step 2), the temperature of the polycondensation reaction is 270 - 290 °C.

10. Application of the high-temperature resistant transparent modified polyester obtained by the preparation method according to any one of claims 1 - 9 in the preparation of optical films, optical lenses, reflective protective films, optical fibers, or liquid crystal displays.

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