Thermal-crosslinkable all-aryl polynaphthyl ester and preparation method thereof

Abstract

The preparation method comprises the following steps: by taking p-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, terephthalic acid and 4-(4-acetamidophenoxy) phthalonitrile as raw materials, carrying out heat-crosslinking reaction on the raw materials, so as to obtain the thermo-crosslinkable all-aryl polynaphthyl ester. Under the action of a catalyst and an antioxidant, low-molecular-weight all-aromatic polynaphthyl ester with the end capped by phthalonitrile is firstly prepared, and then the polynaphthyl ester is prepared through a heating reaction. The melting temperature is regulated and controlled by controlling the ratio of p-acetoxybenzoic acid to 6-acetoxy-2-naphthoic acid, the molecular weight is regulated and controlled by controlling the amount of terephthalic acid to change the excessive degree of carboxyl in a reaction system, and the crosslinking degree is further regulated and controlled by controlling the thermal crosslinking temperature. The preparation process provided by the invention avoids the problem of thermal oxidation degradation in the later stage of traditional melt polymerization, has excellent flowability, and can realize a cross-linking reaction through subsequent heating, thereby further improving the performance of the material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer materials, in particular to a heat-crosslinkable wholly aromatic poly naphthalene ester and a preparation method thereof. BACKGROUND

[0002] Poly naphthalene ester is a high-performance polymer material with rigid naphthalene ring as the skeleton structure. The naphthalene ring structure in the molecular chain endows the material with extremely high main chain rigidity, thereby exhibiting excellent mechanical properties, heat resistance, barrier properties and radiation resistance. Based on these characteristics, poly naphthalene ester can be processed into fibers, films and sheets and other forms, and is widely used in high-end application fields such as aerospace and atomic energy industry. Among them, poly naphthalene ester fibers can be used in high-end fields such as high-speed tires, ropes, special protection, etc. due to their outstanding strength, thermal stability and fatigue resistance. Due to the rigid molecular structure, when heated to above the melting temperature, the molecular chain can be easily oriented along the flow direction by applying a small shear force, the melt viscosity is low, and the processing performance is excellent. When it is blended and modified with other thermoplastic resins, not only can the melt viscosity be reduced to improve the melt flowability of the blend, but also the wholly aromatic poly naphthalene ester can be formed into fibers during processing to form in-situ fiber-forming composites, thereby greatly improving the strength of thermoplastic plastics.

[0003] However, the realization of the above-mentioned excellent performance depends to a great extent on the preparation of high-quality poly naphthalene ester resin. At present, the preparation routes of poly naphthalene ester resin include direct esterification method and ester exchange method. The direct esterification method is similar to the reaction of PET, but due to the presence of naphthalene ring, the steric hindrance effect is increased, the reaction conditions are extremely harsh, and the purity of the monomer is extremely high, so far industrial application has not been realized. The ester exchange method is the most widely used method in current industry, but this process has inherent bottlenecks: first, in the late stage of melt ester exchange, as the molecular weight increases, the melt viscosity of the system rises sharply, leading to serious deterioration of heat transfer and mass transfer, which easily causes uneven molecular weight distribution, local carbonization and poor batch stability; second, in the subsequent solid phase polycondensation stage, although the molecular weight can be further improved, it needs to be treated at high temperature and high vacuum for tens of hours, which not only has long reaction period, high energy consumption and strict requirements for equipment, but also long-term high-temperature treatment easily leads to thermal oxidative degradation of the polymer, directly affecting the performance stability of the final resin.

[0004] Therefore, the traditional melt polymerization process has become a key obstacle restricting the development and application of high-performance poly naphthalene ester resin. In order to break through this bottleneck, it has become a technical problem urgently to be solved in the field to develop a wholly aromatic poly naphthalene ester oligomer with controllable molecular weight and capable of realizing thermal curing after processing. SUMMARY

[0005] In view of the defects in the preparation process of the poly naphthalene resin, the present application aims to precisely control the molecular weight of the oligomer and develop a high-efficiency post-thermal curing process to avoid the defects of the traditional process and expand the application of poly naphthalene in a wider field.

[0006] To achieve the above-mentioned purpose, the present application provides a preparation method of a heat-crosslinkable wholly aromatic poly naphthalene, characterized in that, with p-acetoxybenzoic acid, 6-acetoxy-2-naphthalene carboxylic acid, terephthalic acid and 4-(4-acetylamino phenoxy) phthalonitrile as raw materials, a low-molecular-weight wholly aromatic poly naphthalene with phthalonitrile end-capping is first prepared under the action of a catalyst and an antioxidant, and then the poly naphthalene is prepared through heating reaction.

[0007] In a preferred mode, the method comprises the following steps:

[0008] S1, prepolymer preparation: p-acetoxybenzoic acid, 6-acetoxy-2-naphthalene carboxylic acid, terephthalic acid, a catalyst and an antioxidant are reacted at 200-220℃ for 1-3h under an inert atmosphere, then the temperature is continuously raised to 240-260℃ for 1-3h, and then 4-(4-acetylamino phenoxy) phthalonitrile is added after the temperature is raised to 280-320℃ for 0.5-3h, and then the low-molecular-weight wholly aromatic poly naphthalene with phthalonitrile end-capping is obtained after discharging, crushing and drying;

[0009] S2, hot-press crosslinking: the wholly aromatic poly naphthalene prepared in S1 is hot-pressed and formed at 280-320℃ and subjected to crosslinking reaction treatment under vacuum for 0.5-5h, and then the temperature is raised to 340-380℃ for continuous reaction for 0.5-5h to further promote the thermal crosslinking of phthalonitrile, and the poly naphthalene is obtained.

[0010] In a preferred mode, the content of the p-acetoxybenzoic acid is 40-70mol%, the content of the 6-acetoxy-2-naphthalene carboxylic acid is 25-50mol%, the content of the terephthalic acid is 0-10mol%, and the content of the 4-(4-acetylamino phenoxy) phthalonitrile is 0-20mol% in terms of molar fraction.

[0011] In a preferred mode, the molar ratio of the terephthalic acid to the 4-(4-acetylamino phenoxy) phthalonitrile is 1:2.

[0012] In a preferred mode, the p-acetoxybenzoic acid is prepared by acetylation reaction of p-hydroxybenzoic acid and acetic anhydride.

[0013] In a preferred mode, the molar ratio of the acetic anhydride to the p-hydroxybenzoic acid is 1.5~3:1, and the acetic anhydride and the p-hydroxybenzoic acid are reacted at 100-140℃ for 2-4h.

[0014] In a preferred embodiment, the molar ratio of the acetic anhydride to the p-hydroxybenzoic acid is 1.5.

[0015] In a preferred embodiment, the 6-acetoxy-2-naphthoic acid is prepared from 6-hydroxy-2-naphthoic acid and acetic anhydride by acetylation.

[0016] In a preferred embodiment, the molar ratio of the acetic anhydride to the 6-hydroxy-2-naphthoic acid is 1.5-3:1, and the acetic anhydride and the 6-hydroxy-2-naphthoic acid are reacted at 100-140°C for 2-4h.

[0017] In a preferred embodiment, the molar ratio of the acetic anhydride to the 6-hydroxy-2-naphthoic acid is 1.5.

[0018] In a preferred embodiment, the 4-(4-acetylamino phenoxy) phthalonitrile is prepared from 4-(4-amino phenoxy) phthalonitrile and acetic anhydride by acetylamination.

[0019] In a preferred embodiment, the molar ratio of the acetic anhydride to the 4-(4-amino phenoxy) phthalonitrile is 1.5-3:1, and the acetic anhydride and the 4-(4-amino phenoxy) phthalonitrile are reacted at 100-140°C for 2-4h.

[0020] In a preferred embodiment, the molar ratio of the acetic anhydride to the 4-(4-amino phenoxy) phthalonitrile is 1.5.

[0021] In a preferred embodiment, the catalyst is selected from one or more of titanium dioxide, titanium ethylene glycolate, titanium acetylacetonate, n-butyl titanate, isopropyl titanate, antimony ethylene glycolate, antimony trioxide, stannous octoate, stannous oxalate, dibutyl tin oxide, dibutyl tin dilaurate, butyl tin acid, lithium acetate, potassium acetate, calcium acetate, magnesium acetate, barium acetate, zinc acetate, cobalt acetate, antimony acetate, lead acetate, manganese acetate, triisopropoxyaluminum, zinc oxide, stannous chloride, concentrated sulfuric acid, p-toluenesulfonic acid, zinc chloride, lithium chloride, germanium chloride, tin tetrachloride, potassium carbonate, triethylenediamine, triethylamine, and zinc lactate.

[0022] In a preferred embodiment, the antioxidant is selected from one or more of antioxidant BHT, antioxidant 1010, antioxidant 168, triphenyl phosphite, dilauryl thiodipropionate.

[0023] In a preferred embodiment, the catalyst is added in an amount of 40-450 ppm based on the total weight of the p-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, terephthalic acid, and 4-(4-acetylamino phenoxy) phthalonitrile.

[0024] In a preferred embodiment, the amount of antioxidant added is 0.05 to 0.5 wt% of the total weight of p-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, terephthalic acid, and 4-(4-acetaminophenoxy)phthalonitrile.

[0025] In a preferred embodiment, the reaction in step S1 is carried out in a Hastelloy polymerization reactor.

[0026] In a preferred embodiment, the inert atmosphere in step S1 is nitrogen.

[0027] In a preferred embodiment, the hot pressing and thermal cross-linking processes in step S2 are performed in a vacuum hot pressing apparatus.

[0028] In a preferred embodiment, the pressure in the hot pressing and thermal crosslinking process of step S2 is 10-80 MPa.

[0029] In a preferred embodiment, the vacuum level in step S2 is 0.06-0.1 MPa.

[0030] The present invention also provides a low dielectric thermal crosslinked polynaphthalene ester, which is prepared by the above preparation method.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] 1. This invention utilizes melt transesterification under conditions of slight excess terephthalic acid to first generate carboxyl-terminated all-aromatic polynaphthalene ester oligomers. Then, by employing the amidation reaction between the carboxyl group and the amino group in 4-(4-aminophenoxy)phthalonitrile, phthalonitrile groups are precisely introduced at both ends of the oligomer chain as crosslinking sites. This design endows the polynaphthalene ester oligomers with the ability to undergo crosslinking reactions at high temperatures, generating a stable three-dimensional network structure dominated by aromatic heterocycles such as isoindole and triazine rings, thereby significantly improving the material's heat resistance and mechanical properties.

[0033] 2. This invention separates the "polymerization" and "crosslinking" processes of polymers by synthesizing oligomers that can be subsequently crosslinked. This method effectively avoids the problems of heat and mass transfer deterioration and thermo-oxidative degradation caused by excessively high melt viscosity in the later stages of traditional melt polycondensation, fundamentally ensuring the regularity of the resin structure and the stability of its performance. Simultaneously, by controlling the amount of terephthalic acid added, precise control of the oligomer molecular weight can be easily achieved, resulting in good process repeatability.

[0034] 3. The phthalonitrile-terminated polynaphthalene oligomer prepared by this invention has low melt viscosity and excellent processability before crosslinking and curing. After subsequent heating and curing, it can be further transformed into a high-performance material with high crosslinking density. By controlling the degree of crosslinking, the processability and final performance of the material can be balanced within a certain range, making it show great application potential in high-end fields such as high-speed tires, ropes, and special protection. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The illustrative embodiments and descriptions of this invention are for illustrative purposes only and are not intended to limit the invention. The embodiments described below are some, but not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0036] Example 1

[0037] 1380 g (10 mol) of p-hydroxybenzoic acid and 1531.4 g (15 mol) of acetic anhydride were weighed and added to a 5 L reactor equipped with a stirrer, thermometer, and reflux condenser. The mixture was refluxed at 120 °C for 3 h to obtain a p-acetoxybenzoic acid solution. The solution was poured into cold water, washed and filtered more than 3 times, and dried at 140 °C for 20 h to obtain purified p-acetoxybenzoic acid with a purity of 98.8% and a yield of 96%.

[0038] 1881.8 g (10 mol) of 6-hydroxy-2-naphthoic acid and 1531.4 g (15 mol) of acetic anhydride were weighed and added to a 5 L reactor equipped with a stirrer, thermometer, and reflux condenser. The mixture was refluxed at 140 °C for 3 h to obtain a 6-acetoxy-2-naphthoic acid solution. The solution was poured into cold water, washed and filtered more than 3 times, and dried at 140 °C for 20 h to obtain purified 6-acetoxy-2-naphthoic acid with a purity of 98.5% and a yield of 95%.

[0039] 2352.4 g (10 mol) of 4-(4-aminophenoxy)phthalonitrile and 1531.4 g (15 mol) of acetic anhydride were weighed and added to a 5 L reactor equipped with a stirrer, thermometer, and reflux condenser. The mixture was refluxed at 140 °C for 3 h to obtain a 4-(4-acetaminophenoxy)phthalonitrile solution. The solution was poured into cold water, washed and filtered more than 3 times, and dried at 120 °C for 20 h to obtain purified 4-(4-acetaminophenoxy)phthalonitrile with a purity of 97.8% and a yield of 91%.

[0040] 630.6 g (3.5 mol) of purified p-acetoxybenzoic acid, 345.3 g (1.5 mol) of purified 6-acetoxy-2-naphthoic acid, 16.6 g (0.1 mol) of terephthalic acid, 80 ppm of magnesium acetate catalyst, and 0.1 wt% of antioxidant 1010 were weighed and added to a 5 L Hastelloy reactor equipped with a mechanical stirrer and reflux condenser. Nitrogen gas was then introduced, and the temperature was raised to 220 °C. After reflux reaction for 2 hours, the small molecule acetic acid was discharged, and then the temperature was raised to 2... The reaction was carried out at 50℃ for 2 hours, and the temperature was further increased to 280℃. 58.6 g (0.2 mol) of purified 4-(4-acetamidophenoxy)phthalonitrile was added and reacted for 1 hour. The product was then discharged, pulverized, and dried to obtain phthalic acid-terminated low molecular weight fully aromatic polynaphthalene ester. The above polynaphthalene ester was placed in a vacuum press for hot pressing to carry out a crosslinking reaction. The vacuum degree was maintained at 0.08 MPa and the hot pressing pressure was 50 MPa. The product was hot-pressed at 310℃ for 2 hours and then at 340℃ for 2 hours to obtain crosslinked fully aromatic polynaphthalene ester resin.

[0041] Solutions of phthalic acid-terminated low-molecular-weight fully aromatic polynaphthalene ester and high-molecular-weight crosslinked fully aromatic polynaphthalene ester resin, respectively, were prepared using pentafluorophenol at 0.1 g / dL. At 60°C, the intrinsic viscosity before and after crosslinking was measured using an Ubbelohde viscometer, showing values ​​of 0.63 and 4.27, respectively. This indicates a significant change in molecular weight before and after crosslinking, with the crosslinked polynaphthalene ester exhibiting a higher molecular weight. Thermal properties of the crosslinked fully aromatic polynaphthalene ester resin, measured by DSC and TGA, showed a melting point of 262°C and a thermal decomposition temperature of 483°C, indicating good heat resistance. The tensile strength was 159 MPa, and the tensile modulus was 8.9 GPa, demonstrating excellent mechanical properties. The water absorption rate after immersion in water for 24 hours was only 0.02%.

[0042] Example 2

[0043] 1380 g (10 mol) of p-hydroxybenzoic acid and 1531.4 g (15 mol) of acetic anhydride were weighed and added to a 5 L reactor equipped with a stirrer, thermometer, and reflux condenser. The mixture was refluxed at 125 °C for 3 h to obtain a p-acetoxybenzoic acid solution. The solution was poured into cold water, washed and filtered more than 3 times, and dried at 140 °C for 20 h to obtain purified p-acetoxybenzoic acid with a purity of 98.6% and a yield of 96.3%.

[0044] 1881.8 g (10 mol) of 6-hydroxy-2-naphthoic acid and 1531.4 g (15 mol) of acetic anhydride were weighed and added to a 5 L reactor equipped with a stirrer, thermometer, and reflux condenser. The mixture was refluxed at 138 °C for 3 h to obtain a 6-acetoxy-2-naphthoic acid solution. The solution was poured into cold water, washed and filtered more than 3 times, and dried at 140 °C for 20 h to obtain purified 6-acetoxy-2-naphthoic acid with a purity of 98.4% and a yield of 95.1%.

[0045] 2352.4 g (10 mol) of 4-(4-aminophenoxy)phthalonitrile and 1531.4 g (15 mol) of acetic anhydride were weighed and added to a 5 L reactor equipped with a stirrer, thermometer, and reflux condenser. The mixture was refluxed at 139 °C for 3 h to obtain a 4-(4-acetaminophenoxy)phthalonitrile solution. The solution was poured into cold water, washed and filtered more than 3 times, and dried at 120 °C for 20 h to obtain purified 4-(4-acetaminophenoxy)phthalonitrile with a purity of 97.9% and a yield of 91.3%.

[0046] 630.6 g (3.5 mol) of purified p-acetoxybenzoic acid, 345.3 g (1.5 mol) of purified 6-acetoxy-2-naphthoic acid, 24.9 g (0.15 mol) of terephthalic acid, 80 ppm of magnesium acetate catalyst, and 0.1 wt% of antioxidant 1010 were weighed and added to a 5 L Hastelloy reactor equipped with a mechanical stirrer and reflux condenser. Nitrogen gas was then introduced, and the temperature was raised to 220 °C and refluxed for 2 hours. After removing the small molecule acetic acid, the temperature was raised to 25 °C. The reaction was carried out at 0℃ for 2 hours, and the temperature was further increased to 280℃. 87.9 g (0.3 mol) of purified 4-(4-acetamidophenoxy)phthalonitrile was added and reacted for 1 hour. The product was then discharged, pulverized, and dried to obtain phthalic acid-terminated low molecular weight fully aromatic polynaphthalene ester. The above polynaphthalene ester was placed in a vacuum press for hot pressing to carry out a crosslinking reaction. The vacuum degree was maintained at 0.08 MPa, the hot pressing pressure was 40 MPa, and the hot pressing was carried out at 300℃ for 1 hour and at 340℃ for 1.5 hours to obtain crosslinked fully aromatic polynaphthalene ester resin.

[0047] Solutions of phthalic acid-terminated low-molecular-weight fully aromatic polynaphthalene ester and high-molecular-weight crosslinked fully aromatic polynaphthalene ester resin, respectively, were prepared using pentafluorophenol. At 60°C, the intrinsic viscosity before and after crosslinking was measured using an Ubbelohde viscometer to be 0.47 and 5.32, respectively, indicating a significant change in molecular weight before and after crosslinking. The crosslinked polynaphthalene ester already possesses a high molecular weight. Thermal properties of the crosslinked fully aromatic polynaphthalene ester resin, measured by DSC and TGA, showed a melting point of up to 260°C and a thermal decomposition temperature of up to 486°C, exhibiting good heat resistance. The tensile strength was 162 MPa, and the tensile modulus was 9.2 GPa, demonstrating excellent mechanical properties. The water absorption rate after immersion in water for 24 hours was only 0.013%.

[0048] Example 3

[0049] 1380 g (10 mol) of p-hydroxybenzoic acid and 1531.4 g (15 mol) of acetic anhydride were weighed and added to a 5 L reactor equipped with a stirrer, thermometer, and reflux condenser. The mixture was refluxed at 125 °C for 3 h to obtain a p-acetoxybenzoic acid solution. The solution was poured into cold water, washed and filtered more than 3 times, and dried at 140 °C for 20 h to obtain purified p-acetoxybenzoic acid with a purity of 98.6% and a yield of 96.3%.

[0050] 1881.8 g (10 mol) of 6-hydroxy-2-naphthoic acid and 1531.4 g (15 mol) of acetic anhydride were weighed and added to a 5 L reactor equipped with a stirrer, thermometer, and reflux condenser. The mixture was refluxed at 138 °C for 3 h to obtain a 6-acetoxy-2-naphthoic acid solution. The solution was poured into cold water, washed and filtered more than 3 times, and dried at 140 °C for 20 h to obtain purified 6-acetoxy-2-naphthoic acid with a purity of 98.4% and a yield of 95.1%.

[0051] 2352.4 g (10 mol) of 4-(4-aminophenoxy)phthalonitrile and 1531.4 g (15 mol) of acetic anhydride were weighed and added to a 5 L reactor equipped with a stirrer, thermometer, and reflux condenser. The mixture was refluxed at 139 °C for 3 h to obtain a 4-(4-acetaminophenoxy)phthalonitrile solution. The solution was poured into cold water, washed and filtered more than 3 times, and dried at 120 °C for 20 h to obtain purified 4-(4-acetaminophenoxy)phthalonitrile with a purity of 97.9% and a yield of 91.3%.

[0052] Weigh 540.5 g (3 mol) of purified p-acetoxybenzoic acid, 460.4 g (2 mol) of purified 6-acetoxy-2-naphthoic acid, 33.2 g (0.2 mol) of terephthalic acid, 80 ppm of magnesium acetate catalyst, and 0.1 wt% of antioxidant 1010 and add them to a 5 L Hastelloy reactor equipped with a mechanical stirrer and reflux condenser. Then, nitrogen gas is introduced, the temperature is raised to 210 °C, and the reaction is refluxed for 2.5 h. After removing the small molecule acetic acid, the temperature is raised to 240 °C and the reaction is continued. After 3 hours, the temperature was further increased to 290℃, and 117.3 g (0.4 mol) of purified 4-(4-acetamidophenoxy)phthalonitrile was added. After reacting for 0.5 hours, the product was discharged, pulverized, and dried to obtain phthalic acid-terminated low molecular weight fully aromatic polynaphthalene ester. The above polynaphthalene ester was placed in a vacuum press for hot pressing to carry out crosslinking reaction. The vacuum degree was maintained at 0.08 MPa, the hot pressing pressure was 45 MPa, and the hot pressing was carried out at 300℃ for 1.5 hours and at 330℃ for 1.5 hours to obtain crosslinked fully aromatic polynaphthalene ester resin.

[0053] Solutions of phthalic acid-terminated low-molecular-weight fully aromatic polynaphthalene ester and high-molecular-weight crosslinked fully aromatic polynaphthalene ester resin, respectively, were prepared using pentafluorophenol at 0.1 g / dL. At 60°C, the intrinsic viscosity before and after crosslinking was measured using an Ubbelohde viscometer to be 0.41 and 5.43, respectively, indicating a significant change in molecular weight before and after crosslinking. The crosslinked polynaphthalene ester already possesses a high molecular weight. Thermal properties of the crosslinked fully aromatic polynaphthalene ester resin, measured by DSC and TGA, showed a melting point of up to 250°C and a thermal decomposition temperature of up to 479°C, exhibiting good heat resistance. The tensile strength was 167 MPa, and the tensile modulus was 9.3 GPa, demonstrating excellent mechanical properties. The water absorption rate after immersion in water for 24 hours was only 0.012%.

[0054] Comparative Example 1

[0055] 1380 g (10 mol) of p-hydroxybenzoic acid and 1531.4 g (15 mol) of acetic anhydride were weighed and added to a 5 L reactor equipped with a stirrer, thermometer, and reflux condenser. The mixture was refluxed at 125 °C for 3 h to obtain a p-acetoxybenzoic acid solution. The solution was poured into cold water, washed and filtered more than 3 times, and dried at 140 °C for 20 h to obtain purified p-acetoxybenzoic acid with a purity of 98.6% and a yield of 96.3%.

[0056] 1881.8 g (10 mol) of 6-hydroxy-2-naphthoic acid and 1531.4 g (15 mol) of acetic anhydride were weighed and added to a 5 L reactor equipped with a stirrer, thermometer, and reflux condenser. The mixture was refluxed at 138 °C for 3 h to obtain a 6-acetoxy-2-naphthoic acid solution. The solution was poured into cold water, washed and filtered more than 3 times, and dried at 140 °C for 20 h to obtain purified 6-acetoxy-2-naphthoic acid with a purity of 98.4% and a yield of 95.1%.

[0057] 2352.4 g (10 mol) of 4-(4-aminophenoxy)phthalonitrile and 1531.4 g (15 mol) of acetic anhydride were weighed and added to a 5 L reactor equipped with a stirrer, thermometer, and reflux condenser. The mixture was refluxed at 139 °C for 3 h to obtain a 4-(4-acetaminophenoxy)phthalonitrile solution. The solution was poured into cold water, washed and filtered more than 3 times, and dried at 120 °C for 20 h to obtain purified 4-(4-acetaminophenoxy)phthalonitrile with a purity of 97.9% and a yield of 91.3%.

[0058] Weigh 720.6 g (4 mol) of purified p-acetoxybenzoic acid, 230.2 g (1 mol) of purified 6-acetoxy-2-naphthoic acid, 33.2 g (0.2 mol) of terephthalic acid, 80 ppm of magnesium acetate catalyst, and 0.1 wt% of antioxidant 1010 and add them to a 5 L Hastelloy reactor equipped with a mechanical stirrer and reflux condenser. Then, nitrogen gas is introduced and the temperature is raised to 220 °C and refluxed for 2 h. After that, the small molecule acetic acid is discharged. Then, the temperature is raised to 260 °C and reacted for 2 h. The temperature is then raised to 330 °C and 117.3 g (0.4 mol) of purified 4-(4-acetaminophenoxy)phthalonitrile is added and reacted for 1 h before being discharged. When the ratio of p-acetoxybenzoic acid to 6-acetoxy-2-naphthoic acid is 4:1, the polymer has a melting point of 325°C. At this temperature, the addition of 4-(4-aminophenoxy)phthalonitrile will cause thermal cross-linking, making it impossible to extract or process the material, and thus it lacks the ability to be processed and molded.

[0059] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a thermally crosslinkable all-aryl polynaphthalene ester, characterized in that, Using acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, terephthalic acid, and 4-(4-acetaminophenoxy)phthalonitrile as raw materials, a low molecular weight fully aromatic polynaphthalene ester with phthalic acid end capping is first prepared under the action of a catalyst and an antioxidant, and then the polynaphthalene ester is obtained by heating reaction.

2. The method for preparing a thermally crosslinkable all-aryl polynaphthalene ester according to claim 1, characterized in that, Includes the following steps: S1. Preparation of prepolymer: P-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, terephthalic acid, catalyst and antioxidant are reacted at 200-220℃ for 1-3h under an inert atmosphere, the temperature is further increased to 240-260℃ for 1-3h, and then the temperature is increased to 280-320℃ and 4-(4-acetamidophenoxy)phthalonitrile is added and reacted for 0.5-3h. After discharge, crushing and drying, low molecular weight fully aromatic polynaphthalene ester with phthalic acid end caps is obtained. S2, Hot-press crosslinking: The all-aromatic polynaphthalene ester obtained in S1 is hot-pressed at 280-320℃ and subjected to crosslinking reaction treatment under vacuum for 0.5-5h. The temperature is then increased to 340-380℃ and the reaction continues for another 0.5-5h to further promote the thermal crosslinking of phthalic acid, thereby obtaining the polynaphthalene ester.

3. The method for preparing a thermally crosslinkable all-aryl polynaphthalene ester according to claim 1 or 2, characterized in that, The content of p-acetoxybenzoic acid is 40-70 mol%, the content of 6-acetoxy-2-naphthoic acid is 25-50 mol%, the content of terephthalic acid is 0-10 mol%, the content of 4-(4-acetaminophenoxy)phthalonitrile is 0-20 mol%, and the molar ratio of terephthalic acid to 4-(4-acetaminophenoxy)phthalonitrile is 1:

2.

4. The method for preparing a thermally crosslinkable all-aryl polynaphthalene ester according to claim 1 or 2, characterized in that, The p-acetoxybenzoic acid is prepared by acetylation reaction of p-hydroxybenzoic acid and acetic anhydride. The 6-acetoxy-2-naphthoic acid is prepared by acetylation reaction of 6-hydroxy-2-naphthoic acid and acetic anhydride. The 4-(4-acetaminophenoxy)phthalonitrile is prepared by acetylation reaction of 4-(4-aminophenoxy)phthalonitrile and acetic anhydride.

5. The method for preparing a thermally crosslinkable all-aryl polynaphthalene ester according to claim 4, characterized in that, The molar ratio of acetic anhydride to p-hydroxybenzoic acid is 1.5~3:1, and the acetic anhydride and p-hydroxybenzoic acid react at 100-140℃ for 2-4 hours. The molar ratio of acetic anhydride to 6-hydroxy-2-naphthoic acid is 1.5~3:1, and the acetic anhydride and 6-hydroxy-2-naphthoic acid react at 100-140℃ for 2-4 hours. The molar ratio of acetic anhydride to 4-(4-aminophenoxy)phthalonitrile is 1.5~3:1, and the acetic anhydride and 4-(4-aminophenoxy)phthalonitrile react at 100-140℃ for 2-4 hours.

6. The method for preparing a thermally crosslinkable all-aryl polynaphthalene ester according to claim 5, characterized in that, The molar ratio of acetic anhydride to p-hydroxybenzoic acid is 1.5, the molar ratio of acetic anhydride to 6-hydroxy-2-naphthoic acid is 1.5, and the molar ratio of acetic anhydride to 4-(4-aminophenoxy)phthalonitrile is 1.

5.

7. The method for preparing a thermally crosslinkable all-aryl polynaphthalene ester according to claim 1 or 2, characterized in that, The catalyst is selected from one or more of the following: titanium dioxide, titanium glycol, titanium acetylacetonate, n-butyl titanate, isopropyl titanate, antimony glycolate, antimony trioxide, stannous octoate, stannous oxalate, dibutyltin oxide, dibutyltin dilaurate, butylstannic acid, lithium acetate, potassium acetate, calcium acetate, magnesium acetate, barium acetate, zinc acetate, cobalt acetate, antimony acetate, lead acetate, manganese acetate, aluminum triisopropoxy, zinc oxide, stannous chloride, concentrated sulfuric acid, p-toluenesulfonic acid, zinc chloride, lithium chloride, germanium chloride, stannous tetrachloride, potassium carbonate, triethylenediamine, triethylamine, and zinc lactate. The antioxidant is selected from one or more of the following: antioxidant BHT, antioxidant 1010, antioxidant 168, triphenyl phosphite, and dilauryl thiodipropionate.

8. A method for preparing a thermally crosslinkable all-aryl polynaphthalene ester according to claim 1 or 2, characterized in that, The catalyst is added at a rate of 40 to 450 ppm of the total weight of p-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, terephthalic acid, and 4-(4-acetaminophenoxy)phthalonitrile, and the antioxidant is added at a rate of 0.05 to 0.5 wt% of the total weight of p-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, terephthalic acid, and 4-(4-acetaminophenoxy)phthalonitrile.

9. A method for preparing a thermally crosslinkable all-aryl polynaphthalene ester according to any one of claims 2, characterized in that, The reaction in step S1 is carried out in a Hastelloy polymerization reactor under an inert atmosphere of nitrogen; the hot pressing and thermal cross-linking processes in step S2 are carried out in a vacuum hot pressing device at a pressure of 10-80 MPa and a vacuum degree of 0.06-0.1 MPa.

10. A thermally crosslinkable all-aryl polynaphthalene ester, prepared by the preparation method according to any one of claims 1-9.