A calixarene-modified high-carbon-forming carborolynol resin, and a method for preparing the same

Abstract

The present application relates to the technical field of modified phenolic resin, in particular to a calixarene modified high carbon yield boron phenolic resin and a preparation method thereof, wherein the preparation method comprises the following steps: uniformly mixing phenol, aldehyde and calixarene, adding a catalyst to adjust the pH to 7-9, and reacting at 50-90 DEG C for 1-3 h, then adding a boron compound, heating to 90-150 DEG C and reacting for 0.5-4 h, and finally performing vacuum and reduced pressure dehydration to obtain the calixarene modified boron phenolic resin. The resin has high ortho-ortho methylene and para-para methylene structures, and the initial decomposition temperature and carbon yield of the resin cured product are significantly improved. The calixarene modified high carbon yield boron phenolic resin has excellent heat resistance, mechanical properties and ablation performance, and can be used for preparing high-temperature-resistant high-performance resin matrix composites.

Description

Technical Field

[0001] This invention relates to the field of modified phenolic resin technology, and particularly to a calixarane-modified high-carbon boron phenolic resin and its preparation method. Background Technology

[0002] Phenolic resins have long been used as the resin matrix for ablation-resistant composite materials, friction materials, and thermal protection materials due to their advantages such as readily available raw materials, mature molding processes, good flame retardancy, and high char yield. However, as the aerospace thermal protection environment evolves towards higher heat flux, higher erosion, and longer service life, the heat resistance and char formation efficiency of traditional phenolic resins are no longer sufficient to meet higher requirements.

[0003] Boron modification is an effective way to improve the heat resistance and char yield of phenolic resins. Boron can block some active phenolic hydroxyl groups by forming high-bond-energy structures such as BOC and BOB, and generate a B2O3 protective layer during pyrolysis, thereby inhibiting the escape of volatile small molecules, reducing char layer defects, and promoting the structural stabilization of char products. Related studies have shown that the phenylboron ester bonds formed in boron phenolic resins play an important role in improving the char yield and the structure of pyrolyzed char. Existing work, such as patents CN101805435B, CN103289033A, and CN105732924A, mainly focuses on the synergistic modification of boron source type, boron content, or inorganic fillers. Its advantage lies in significantly improving the char yield and heat resistance, but there is a general lack of research on the correlation between the intrinsic crosslinking network of the resin, especially the methylene bridging configuration, and pyrolysis behavior.

[0004] Compared to simply introducing boron, the methylene bridging mechanism, aromatic ring arrangement, and cross-linking network structure directly affect the pyrolysis pathway and char evolution of the resin. Phenolic resins undergo complex reactions during high-temperature pyrolysis, including further cross-linking, bond breaking, aromatization, and char rearrangement. The phenolic hydroxyl group and methylene bridging structure are key structural factors influencing thermal stability and char yield. In particular, the phenolic hydroxyl group can form active free radicals and promote the pyrolysis of phenolic resin to generate oxygen-containing small molecules such as CO, CO2, and H2O, while the breaking of methylene bridges is one of the important reasons for resin skeleton degradation. Currently, the regulation of methylene bridging in phenolic resins mainly focuses on high ortho-position connections, while the combined regulation of high ortho-ortho (o-o') and para-para (p-p') methylene combinations is rarely studied. High ortho-position bridging is beneficial for char yield but reduces the initial decomposition temperature, while high para-position bridging is beneficial for increasing the initial decomposition temperature but reducing the char yield, making it difficult for thermal protection materials to simultaneously achieve high initial decomposition temperature and high char yield. Therefore, regulating the structure of boron phenolic resin at the molecular level is key to further improving its heat resistance and char-forming properties. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a method for preparing calixarene and its modified boron phenolic resin, aiming to improve the heat resistance and char-forming properties of boron phenolic resin.

[0006] The technical solution of this application is as follows: In a first aspect, this application provides a calixarene-modified high-carbon boron phenolic resin, wherein the main molecular chain of the resin contains calixarene structural units, ortho-ortho-methylene bridges and para-para-methylene bridges, and the molar content of the ortho-ortho-methylene bridges accounts for more than 20% of the total molar content of all methylene bridges, and the molar content of the para-para-methylene bridges accounts for more than 20% of the total molar content of all methylene bridges.

[0007] The calixarene-modified high carbon-forming boron phenolic resin provided in this application contains calixarene structural units in its molecular backbone, compared with the prior art. Since the calixarene modifier is rich in aromatic ring structure and does not contain heteroatoms, it can be introduced into the resin skeleton through chemical bonding, which helps to improve the high-temperature carbonization rate and carbon layer density of the resin.

[0008] Furthermore, the high ortho-ortho and para-para methylene structures in the resin's molecular structure help to improve the char formation rate and initial decomposition temperature of phenolic resin, thereby enhancing the heat resistance and char formation performance of boron phenolic resin. It is expected to be used in high-tech fields such as aerospace, and has good application prospects in refractory materials, coated sand and other fields.

[0009] Furthermore, the sum of the molar contents of the ortho-ortho-methylene bridges and the para-para-methylene bridges accounts for more than 50% of the total molar contents of all methylene bridges.

[0010] Based on the calixarene-modified high-carbon boron phenolic resin provided in this embodiment, compared with the prior art where the sum of the molar contents of ortho-ortho-methylene bridges and para-para-methylene bridges accounts for only about 30% of the total molar contents of methylene bridges, the calixarene-modified high-carbon boron phenolic resin provided in this application has a sum of ortho-ortho-methylene bridges and para-para-methylene bridges accounting for more than 50% of the total molar contents of methylene bridges. Thus, since high ortho-bridges are beneficial to the char formation rate, and high para-bridges are beneficial to increasing the initial decomposition temperature, the calixarene-modified high-carbon boron phenolic resin provided in this application has very good heat resistance and char formation performance compared with the prior art.

[0011] For example, in some embodiments of this application, the molar content of ortho-ortho-methylene bridges accounts for about 30% of the total molar content of methylene bridges, and the molar content of para-para-methylene bridges accounts for about 40% of the total molar content of methylene bridges.

[0012] Furthermore, the calixarene structural unit is derived from resorcinol calixarene.

[0013] Furthermore, the resin has a carbon residue rate of ≥78% under a nitrogen atmosphere at 800°C, and the temperature corresponding to a 5% thermal weight loss is ≥480°C.

[0014] Secondly, based on the same inventive concept, this application also provides a method for preparing a calixarane-modified high-carbon boron phenolic resin, comprising the following steps: S1) Take the selected proportions of phenol, aldehyde, and calixarene, mix them evenly, add a catalyst to adjust the pH to 7-9, and react at 50-90℃ for 1-3 hours to obtain the intermediate product; S2) Add a selected amount of boron compound to the intermediate product and react at 90-140°C for 0.5-4 hours; S3) Remove the water generated in the reaction by vacuum distillation. When the resin gels at 180±1℃ for 80-400s, the reaction ends and calixarane-modified high-carbon boron phenolic resin is obtained.

[0015] Specifically, step S1) is mainly an addition reaction of phenol and aldehyde to form hydroxymethyl substituted phenol; step S2) is mainly a condensation reaction of hydroxymethyl and phenol to form methylene bridged bond; in addition, step S2) also involves the reaction of boron compound with hydroxymethyl / phenol hydroxyl group to generate BOC bond; step S3) mainly removes water generated in the reaction process and further condenses hydroxymethyl with phenol / boron compound.

[0016] In summary, the method for preparing high-carbon-forming boron phenolic resin modified with calixarene, as provided in the second aspect, introduces calixarene into the skeletal structure of boron phenolic resin through in-situ synthesis. Because the calixarene modifier is rich in aromatic ring structures and contains no heteroatoms, it effectively improves the high-temperature carbonization rate and carbon layer density of the resin. Furthermore, the introduction of the calixarene structure successfully achieves the directional regulation of the ortho-ortho, ortho-para, and para-para methylene structures in the boron phenolic resin, resulting in a resin with high ortho-ortho and para-para methylene structures, which helps to improve the carbonization rate and initial decomposition temperature of the phenolic resin.

[0017] Furthermore, in the preparation of calixarene-modified high-carbon boron phenolic resin, the reactants, by molar parts, are: phenol 10-200 parts; aldehyde 12-350 parts; calixarene 0.1-10 parts; boron compound 0.1-40 parts.

[0018] Furthermore, the phenol is one or both of monohydric phenols and dihydric phenols.

[0019] For example, the monohydric phenol is one or more of phenol, o-phenylcresol, m-phenylcresol, p-phenylcresol, α-naphthol, β-naphthol, and 4-hydroxymethylphenol; the dihydric phenol is one or more of catechol, resorcinol, hydroquinone, bisphenol A, and bisphenol F.

[0020] Furthermore, the aldehyde is one or more of formaldehyde, acetaldehyde, butyraldehyde, glutaraldehyde, trioxymethylene, and paraformaldehyde.

[0021] Furthermore, the boron compound is at least one of boric acid and boric acid derivatives.

[0022] For example, boric acid derivatives include one or more of phenylboronic acid, hydroxymethylphenylboronic acid, hydroxyphenylboronic acid, biphenylboronic acid, borax, sodium borate, diphenylboronic acid, methylphenylboronic acid, dimethylphenylboronic acid, methoxyphenylboronic acid, isopropylphenylboronic acid, ethoxyphenylboronic acid, 1,4-phenyldiboronic acid, ethylphenylboronic acid, butylphenylboronic acid, 2,4,6-triphenylcycloboronic acid, and 3-hydroxyphenylboronic acid.

[0023] Furthermore, the calixarene is resorcinol calixarene.

[0024] Furthermore, in some embodiments of this application, the preparation method of resorcinol calixarene is as follows: Take the selected proportions of resorcinol, aldehyde, ethanol, and deionized water and place them in a three-necked flask equipped with a mechanical stirrer. Stir to form a clear solution, add a certain proportion of concentrated hydrochloric acid dropwise, and heat to 75°C for 1-20 hours. After the product cools to room temperature, wash with 5-10 times the amount of deionized water / ethanol mixed solvent and filter until the pH of the filtrate is in the range of 6-7. Take the precipitate and dry it in an oven to constant weight to obtain resorcinol-type calixarene.

[0025] It should be noted that the method for preparing resorcinol calixarene provided in this application is only one method for preparing resorcinol calixarene. In addition to being prepared by this method, the resorcinol calixarene used in this application can also be obtained by purchase.

[0026] Furthermore, the catalyst used in the preparation of calixarene-modified high-carbon boron phenolic resin is one or more of NaOH, NH3·H2O, and Ba(OH)2. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the calixarane-modified high-carbon boron phenolic resin prepared in Example 2 of the present invention.

[0028] Figure 2 The image shows a comparison of the ¹³C NMR spectra of the cured boron phenolic resins of Example 2 and Comparative Example 1.

[0029] Figure 3 The TGA curves of the boron phenolic resin cured products prepared in Example 2 and Comparative Example 1 of this invention under a nitrogen atmosphere are shown.

[0030] Figure 4The mechanical data are for the carbon fiber composite materials prepared from boron phenolic resin in Example 2 and Comparative Example 1 of this invention.

[0031] Figure 5 The data provided are ablation data of the carbon fiber composite materials prepared from boron phenolic resin in Example 2 and Comparative Example 1 of this invention.

[0032] Figure 6 The results of the pyrolysis gas chromatography-mass spectrometry test of boron phenolic resin in Example 2 and Comparative Example 1 of this invention are shown. Detailed Implementation

[0033] Unless otherwise specified, the experimental methods used in the following implementation examples are all conventional methods.

[0034] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0035] Example 1 Preparation of resorcinol calixarene: Take the selected proportions of resorcinol, aldehyde, ethanol, and deionized water and place them in a three-necked flask equipped with a mechanical stirrer. Stir to form a clear solution, add a certain proportion of concentrated hydrochloric acid dropwise, and heat to 75°C for 1-20 h. After the product cools to room temperature, wash with 5-10 times the amount of deionized water / ethanol mixed solvent and filter until the pH of the filtrate is in the range of 6-7. Take the precipitate and dry it in an oven to constant weight to obtain resorcinol-type calixarene.

[0036] It should be noted that the preparation method of resorcinol calixarene used in this application is a commonly used existing method. The raw material ratio and reaction conditions are the same as those in existing methods and will not be repeated here. The ratio of 5-10 times is by mass, and the purpose is to add a large amount of water to wash away hydrochloric acid and non-cyclic impurities.

[0037] Calcifera-modified high-carbon boron phenolic resin: 94 g of phenol was added to a 250 mL three-necked flask equipped with a stirrer, thermometer, and condenser. The mixture was heated until melted, then 2.72 g of resorcinol calixarene was added. After stirring and mixing for 0.5 h, 33.0 g of paraformaldehyde was added, followed by the addition of sodium hydroxide to adjust the pH to 7.2. The temperature was slowly increased to 50 °C and the reaction was carried out for 1 h. After the reaction was complete, 2.8 g of boric acid was added, and the mixture was refluxed at 90 °C for 0.5 h. Subsequently, the water generated in the reaction was removed by vacuum distillation at 90 °C. The reaction was terminated when the gel time of the resin at 180±1 °C reached 380 s, yielding calixarene-modified high-carbon boron phenolic resin.

[0038] Example 2 94 g of phenol was added to a 250 mL three-necked flask equipped with a stirrer, thermometer, and condenser. The mixture was heated until melted, then 5.44 g of resorcinol calixarene was added. After stirring and mixing for 1 h, 33.0 g of formaldehyde was added, followed by ammonia to adjust the pH to 7.5. The temperature was slowly raised to 60 °C, and the reaction was allowed to proceed for 1.5 h. After the reaction was complete, 4.70 g of boric acid was added, and the mixture was refluxed at 110 °C for 1.5 h. Subsequently, the water generated during the reaction was removed by vacuum distillation at 100 °C. The reaction was terminated when the resin gelled at 180 ± 1 °C for 300 s, yielding a calixarene-modified high-carbon boron phenolic resin. The preparation method of resorcinol calixarene was the same as in Example 1.

[0039] Example 3 After heating to a melt state, 7.52 g of resorcinol calixarene was added, and the mixture was stirred for 2 h. Then, 42.12 g of acetaldehyde was added, followed by the addition of barium hydroxide to adjust the pH of the system to 7.8. The temperature was slowly increased to 80 °C, and the reaction was allowed to proceed for 2 h. After the reaction was complete, 7.52 g of zinc borate was added, and the mixture was refluxed at 140 °C for 3 h. Subsequently, the water generated in the reaction was removed by vacuum distillation at 120 °C. The reaction was terminated when the resin gelled at 180 ± 1 °C for 180 s, yielding calixarene-modified high-carbon boron phenolic resin. The preparation method of resorcinol calixarene was the same as in Example 1.

[0040] Example 4 94 g of phenol was added to a 250 mL three-necked flask equipped with a stirrer, thermometer, and condenser. The mixture was heated until melted, then 2.72 g of resorcinol calixarene was added. After stirring and mixing for 1 h, 39.16 g of paraformaldehyde was added, followed by the addition of barium hydroxide to adjust the pH to 7.3. The temperature was slowly increased to 55 °C, and the reaction was allowed to proceed for 1 h. After the reaction was complete, 4.70 g of methylphenylboronic acid was added, and the mixture was refluxed at 100 °C for 1 h. Subsequently, the water generated during the reaction was removed by vacuum distillation at 95 °C. The reaction was terminated when the resin gelled at 180 ± 1 °C for 330 s, yielding a calixarene-modified high-carbon boron phenolic resin. The preparation method of resorcinol calixarene was the same as in Example 1.

[0041] Example 5 94 g of p-cresol was added to a 250 mL three-necked flask equipped with a stirrer, thermometer, and condenser. After melting, 5.44 g of resorcinol-type calixarene was added, and the mixture was stirred for 1.5 h. Then, 94.02 g of butyraldehyde was added, followed by the addition of sodium hydroxide to adjust the pH to 7.6. The temperature was slowly increased to 65 °C, and the reaction was allowed to proceed for 1.5 h. After the reaction was complete, 7.52 g of borax was added, and the mixture was refluxed at 120 °C for 2 h. Subsequently, the water generated during the reaction was removed by vacuum distillation at 105 °C. The reaction was terminated when the resin gelled at 180 ± 1 °C for 240 s, yielding a calixarene-modified high-carbon boron phenolic resin. The preparation method of the resorcinol calixarene was the same as in Example 1.

[0042] Example 6 94 g of resorcinol was added to a 250 mL three-necked flask equipped with a stirrer, thermometer, and condenser. The mixture was heated until melted, then 7.52 g of resorcinol calixarene was added. After stirring and mixing for 0.5 h, 38.45 g of paraformaldehyde was added, followed by the addition of ammonia to adjust the pH to 8.0. The temperature was slowly increased to 75 °C, and the reaction was allowed to proceed for 2 h. After the reaction was complete, 2.4 g of sodium borate was added, and the mixture was refluxed at 120 °C for 2.5 h. Subsequently, the water generated during the reaction was removed by vacuum distillation at 115 °C. The reaction was terminated when the resin gelled at 180 ± 1 °C for 160 s, yielding a calixarene-modified high-carbon boron phenolic resin. The preparation method of the resorcinol calixarene was the same as in Example 1.

[0043] Example 7 94 g of catechol was added to a 250 mL three-necked flask equipped with a stirrer, thermometer, and condenser. The mixture was heated until melted, then 2.72 g of resorcinol calixarene was added. After stirring and mixing for 2 h, 46.15 g of paraformaldehyde was added. Ammonia was then added to adjust the pH to 7.4, and the temperature was slowly raised to 60 °C, reacting for 1 h. After the reaction was complete, 7.52 g of 4-hydroxyphenylboronic acid was added, and the mixture was refluxed at 110 °C for 1 h. Subsequently, the water generated in the reaction was removed by vacuum distillation at 100 °C. The reaction was terminated when the resin gelled at 180 ± 1 °C for 280 s, yielding calixarene-modified high-carbon boron phenolic resin.

[0044] Example 8 94 g of hydroquinone was added to a 250 mL three-necked flask equipped with a stirrer, thermometer, and condenser. The mixture was heated until melted, then 5.44 g of resorcinol calixarene was added. After stirring and mixing for 1 h, 67.69 g of acetaldehyde was added, followed by the addition of barium hydroxide to adjust the pH to 7.7. The temperature was slowly raised to 70 °C, and the reaction was allowed to proceed for 1.5 h. After the reaction was complete, 3.47 g of boric acid was added, and the mixture was refluxed at 90 °C for 2 h. Subsequently, the water generated during the reaction was removed by vacuum distillation at 110 °C. The reaction was terminated when the resin gelled at 180 ± 1 °C for 220 s, yielding a calixarene-modified high-carbon boron phenolic resin. The preparation method of resorcinol calixarene was the same as in Example 1.

[0045] Example 9 94 g of α-naphthol was added to a 250 mL three-necked flask equipped with a stirrer, thermometer, and condenser. The mixture was heated until melted, then 7.52 g of resorcinol calixarene was added. After stirring and mixing for 1.5 h, 35.24 g of paraformaldehyde was added, followed by the addition of sodium hydroxide to adjust the pH to 7.1. The temperature was slowly increased to 80 °C, and the reaction was allowed to proceed for 2 h. After the reaction was complete, 4.70 g of hydroxymethylphenylboronic acid was added, and the mixture was refluxed at 140 °C for 3 h. Subsequently, the water generated during the reaction was removed by vacuum distillation at 120 °C. The reaction was terminated when the resin gelled at 180 ± 1 °C for 120 s, yielding a calixarene-modified high-carbon boron phenolic resin. The preparation method of resorcinol calixarene was the same as in Example 1.

[0046] Example 10 94 g of β-naphthol was added to a 250 mL three-necked flask equipped with a stirrer, thermometer, and condenser. After heating to melt, 5.44 g of resorcinol calixarene was added, and the mixture was stirred for 0.5 h. Then, 51.72 g of butyraldehyde was added, followed by the addition of sodium hydroxide to adjust the pH to 7.5. The temperature was slowly increased to 70 °C, and the reaction was allowed to proceed for 1 h. After the reaction was complete, 7.52 g of methoxyphenylboronic acid was added, and the mixture was refluxed at 100 °C for 0.5 h. Subsequently, the water generated during the reaction was removed by vacuum distillation at 95 °C. The reaction was terminated when the resin gelled at 180 ± 1 °C for 340 s, yielding a calixarene-modified high-carbon boron phenolic resin. The preparation method of resorcinol calixarene was the same as in Example 1.

[0047] Example 11 94 g of bisphenol F was added to a 250 mL three-necked flask equipped with a stirrer, thermometer, and condenser. After heating to melt, 7.52 g of resorcinol calixarene was added, and the mixture was stirred for 0.5 h. Then, 22.75 g of acetaldehyde was added, followed by the addition of barium hydroxide to adjust the pH to 7.4. The temperature was slowly increased to 55 °C, and the reaction was allowed to proceed for 1.5 h. After the reaction was complete, 4.70 g of diphenylboronic acid was added, and the mixture was refluxed at 110 °C for 2.5 h. Subsequently, the water generated during the reaction was removed by vacuum distillation at 105 °C. The reaction was terminated when the resin gelled at 180 ± 1 °C for 260 s, yielding a calixarene-modified high-carbon boron phenolic resin. The preparation method of resorcinol calixarene was the same as in Example 1.

[0048] Example 12 94 g of phenol was added to a 250 mL three-necked flask equipped with a stirrer, thermometer, and condenser. The mixture was heated until melted, then 5.44 g of resorcinol calixarene was added. After stirring and mixing for 1.5 h, 150.00 g of glutaraldehyde was added, followed by the addition of barium hydroxide to adjust the pH to 7.6. The temperature was slowly increased to 75 °C, and the reaction was allowed to proceed for 1 h. After the reaction was complete, 3.47 g of 3-hydroxyphenylboronic acid was added, and the mixture was refluxed at 90 °C for 2.0 h. Subsequently, the water generated during the reaction was removed by vacuum distillation at 100 °C. The reaction was terminated when the resin gelled at 180 ± 1 °C for 310 s, yielding a calixarene-modified high-carbon boron phenolic resin. The preparation method of resorcinol calixarene was the same as in Example 1.

[0049] Example 13 94 g of 4-hydroxymethylphenol was added to a 250 mL three-necked flask equipped with a stirrer, thermometer, and condenser. The mixture was heated until melted, then 2.72 g of resorcinol calixarene was added. After stirring and mixing for 1 h, 34.11 g of paraformaldehyde was added, followed by the addition of ammonia to adjust the pH to 7.2. The temperature was slowly increased to 50 °C, and the reaction was allowed to proceed for 2 h. After the reaction was complete, 3.47 g of ethylboric acid was added, and the mixture was refluxed at 120 °C for 1.5 h. Subsequently, the water generated during the reaction was removed by vacuum distillation at 90 °C. The reaction was terminated when the resin gelled at 180 ± 1 °C for 400 s, yielding a calixarene-modified high-carbon boron phenolic resin. The preparation method of resorcinol calixarene was the same as in Example 1.

[0050] Comparative Example 1 The boron phenolic resin in this comparative example has the same composition as that in Example 1, except that no calixarene was added and it was prepared using the same method as in Example 1.

[0051] Comparative Example 2 The boron phenolic resin in this comparative example has the same composition as that in Example 4, except that no calixarene was added and it was prepared using the same method as in Example 4.

[0052] Structural characterization and effect verification examples Figure 1 This is a schematic diagram of the structure of the calixarane-modified high-carbon boron phenolic resin prepared in Example 2 of the present invention. Figure 2 The image shows a comparison of the ¹³C NMR spectra of the cured boron phenolic resins of Example 2 and Comparative Example 1. The positions of the P-P', op, and o-o' methylene groups in the resin are indicated, and the results are obtained through integration. The percentage of the integration results is shown in Table 1.

[0053] Table 1: The chemical shift ranges of 39~42ppm, 34~36ppm, and 29~32ppm correspond to the three characteristic methylene bridging bonds of phenolic aldehydes: p-p', op, and o-o', respectively. Figure 2 The inset is a magnified view of the 20-40 ppm region. Combined with Table 2, it can be seen that in Comparative Example 1, the dominant asymmetric bridging bonds are the op (op-para) bonds, accounting for 65.5%, while p-p' and o-o' bonds account for only 20.2% and 14.2%, respectively. The black carbon spectrum curve also shows a prominent op signal peak intensity at 34-36 ppm. However, Example 2, after modification and regulation, shows a significant change. The proportion of op bridging bonds drops sharply to 12.7%, while the proportions of regular and symmetrical o-o' and p-p' bonds increase to 49.1% and 38.2%, respectively. Correspondingly, the characteristic peak signals at 29-32 ppm and 39-42 ppm in the red carbon spectrum curve are significantly enhanced, while the peak signal at 34-36 ppm is significantly weakened. This demonstrates that the preparation process of this invention can effectively regulate the structure of phenolic resin, reduce the formation of disordered asymmetric op-para bridging bonds, and significantly increase the molar proportion of o-o' and p-p' symmetrical bridging bonds.

[0054] To verify the technical effect of the calixarene-modified high-carbon boron phenolic resin described in this invention, the boron phenolic resins prepared in Examples 1-6, Comparative Example 1, and Comparative Example 2 were used for the following experiments: Take the boron phenolic resin to be tested, and after curing, test the residual carbon rate of the resin at 800℃ using a thermogravimetric analyzer (TG) to simply determine the thermal stability of the resin.

[0055] The thermal and mechanical properties of the resin matrix in the examples and comparative examples were measured. The boron phenolic resin to be tested was pressed into carbon fiber composite material according to the national standard GB / T9341-2008, and the impact strength and tensile strength of the prepared composite material were tested on a universal testing machine.

[0056]

[0057] The experimental results are shown in Table 2 below: As shown in Table 2, compared to the boron phenolic resin without calixarene modification, the resins in the examples modified with calixarene exhibited significantly improved 5% thermal decomposition temperature, char residue, impact strength, and flexural strength. The comparative examples showed an average 5% thermal decomposition temperature of approximately 420.5℃, a char residue of 74.75%, an impact strength of 2.45 MPa, and a flexural strength of 51.35 MPa. Overall, the properties of the examples modified with calixarene were significantly improved. This demonstrates that the introduction of calixarene can optimize the resin and improve its thermal stability, char formation ability, and mechanical properties.

[0058] Thermogravimetric curves of the residual amount of boron phenolic resin used in Example 2 and Comparative Example 1 under nitrogen atmosphere as a function of temperature are shown below. Figure 3 As shown, by Figure 3 It can be seen that the modification with calixarene affects the residual carbon content and T of the resin at 800℃. 5％ Both have seen significant improvements.

[0059] The resin-pressed carbon fiber composite materials prepared in Example 2 and Comparative Example 1 of this invention were used to test the mechanical properties of the composite materials using a multi-functional testing machine. The data are as follows: Figure 4 As shown. By Figure 4 It can be seen that the interlaminar shear strength and flexural strength of the boron phenolic resin matrix modified with calixarene are significantly improved.

[0060] The resin-pressed carbon fiber composites prepared in Example 2 and Comparative Example 1 of this invention were used to test the ablation properties of the fiber composites. The data are as follows: Figure 5 As shown. By Figure 5 It can be seen that the ablation resistance of the composite material in Example 2 has been effectively improved.

[0061] Figure 6 These are the gas chromatography-mass spectrometry (GC-MS) results of the pyrolysis of boron phenolic resin in Example 2 and Comparative Example 1 of this invention. Figure 6 As can be seen, at 300℃, the comparative example showed a large number of pyrolysis products such as phenol, methylphenol, and phenolic dimers, while Example 2 showed almost no obvious volatile components. Upon heating to 450℃ and 600℃, the content of pyrolysis products in the resins prepared in both Comparative Example 1 and Example 2 increased, but at the same temperature, the relative content of various phenolic pyrolysis products in the resin prepared in Example 2 was significantly lower. This result indicates that the boron phenolic resin modified with calixarene has a higher thermal decomposition temperature.

[0062] Combining Table 1 and Table 2, Figure 1 , Figure 2 and Figure 6The high o-o' methylene structure formed in Example 2 is beneficial to the formation of fused ring structures in the early stage of resin pyrolysis. The oxanthracene structure is generated at 300°C. This structure can not only reduce the volatilization of small molecules such as CO and CO2 in the early stage of pyrolysis and fix more carbon elements in the resin, but also reduce the phenolic hydroxyl structure in the resin, reduce oxygen-containing free radicals, and delay the further oxidative cracking of the resin. These two effects synergistically improve the carbonization rate of the resin, and increase the mass retention rate of the resin at 800°C from 74.2% in Comparative Example 1 to 80.2% in Example 2. The high p-p' methylene structure has a higher fracture temperature than the o-o' and op-methylene structures, which increases the initial decomposition temperature of the resin from 419°C in Comparative Example 1 to 516°C in Example 2.

[0063] The above description only illustrates some embodiments of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All modifications made within the scope of the independent claims of this invention are also within the scope of protection of this invention.

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A calixarane-modified high-carbon boron phenolic resin, characterized in that, The main molecular chain of the resin contains calixarene structural units, ortho-ortho-methylene bridges and para-para-methylene bridges, wherein the molar content of ortho-ortho-methylene bridges accounts for more than 20% of the total molar content of all methylene bridges, and the molar content of para-para-methylene bridges accounts for more than 20% of the total molar content of all methylene bridges.

2. The resin according to claim 1, characterized in that, The sum of the molar contents of the ortho-ortho-methylene bridges and the para-para-methylene bridges accounts for more than 50% of the total molar contents of all methylene bridges.

3. The resin according to claim 1 or 2, characterized in that, The calixarene structural unit is derived from resorcinol calixarene.

4. The resin according to claim 1 or 2, characterized in that, The resin has a carbon residue rate of ≥78% under a nitrogen atmosphere at 800℃, and the temperature corresponding to a 5% thermal weight loss is ≥480℃.

5. A method for preparing a calixarane-modified high-carbon boron phenolic resin, characterized in that, Includes the following steps: S1) Take the selected proportions of phenol, aldehyde, and calixarene, mix them evenly, add a catalyst to adjust the pH to 7-9, and react at 50-90℃ for 1-3 hours to obtain the intermediate product; S2) Add a selected amount of boron compound to the intermediate product and react at 90-140°C for 0.5-4 hours; S3) Remove the water generated in the reaction by vacuum distillation. When the resin gels at 180±1℃ for 80-400s, the reaction ends and calixarene-modified high-carbon boron phenolic resin is obtained.

6. The method for preparing calixarane-modified high-carbon boron phenolic resin according to claim 5, characterized in that, During preparation, the reactants, by molar amounts, are: phenol 10-200 parts; aldehyde 12-350 parts; calixarene 0.1-10 parts; boron compounds 0.1-40 parts.

7. The method for preparing calixarane-modified high-carbon boron phenolic resin according to claim 5, characterized in that, The phenol is one or both of monohydric phenols and dihydric phenols.

8. The method for preparing calixarane-modified high-carbon boron phenolic resin according to claim 5, characterized in that, The aldehyde is one or more of formaldehyde, acetaldehyde, butyraldehyde, glutaraldehyde, trioxymethylene, and paraformaldehyde.

9. The method for preparing calixarane-modified high-carbon boron phenolic resin according to claim 5, characterized in that, The boron compound is at least one of boric acid and boric acid derivatives.

10. The method for preparing calixarane-modified high-carbon boron phenolic resin according to any one of claims 5 to 9, characterized in that, The calixarene is resorcinol calixarene.

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