Phenolic resin, preparation method and application thereof

Abstract

The invention discloses phenolic resin as well as a preparation method and application thereof, and belongs to the field of macromolecules. Aiming at the problems that existing phenolic resin is poor in heat resistance and limited in application, the preparation method of the phenolic resin comprises the steps that raw material pretreatment is conducted, specifically, naphthol, biphenyl dimethyl ether and p-benzene dimethyl ether are mixed and heated to be molten at the first preset temperature, and a molten liquid mixture is obtained; carrying out synthesis reaction: putting the liquid mixture under an acidic condition, and carrying out synthesis reaction at a second preset temperature to obtain a resin monomer; and obtaining a finished product: removing unreacted naphthol from the resin monomer to obtain the finished phenolic resin. The naphthol is simultaneously mixed with two dimethyl ethers which are similar in structure but different in property to prepare the resin which is good in heat resistance, high in flame retardance and low in moisture absorption; the raw materials are heated and melted, so that subsequent mixing with a catalyst is facilitated, and sufficient reaction is ensured; and finally, the application range of the phenolic resin is expanded.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and more specifically, relates to a phenolic resin, its preparation method, and its application. Background Technology

[0002] Phenolic resin is a general term for resins formed by the reaction of phenols and aldehydes in the presence of a catalyst. It was one of the earliest industrially produced polymer materials, possessing excellent dimensional stability, flame retardancy, acid resistance, mechanical properties, and heat resistance, and is widely used in electronic packaging. However, in recent years, advancements in advanced materials have demanded the development of higher-performance phenolic resins. For example, in the field of electronic components, with the development of high-frequency technology, reducing transmission loss requires circuit boards and other related materials to have unprecedentedly low dielectric loss tangents. Furthermore, the miniaturization and thinning of communication devices, exemplified by mobile devices, have led to increasingly thinner insulating materials such as circuit boards. This makes them prone to heat-induced warping, necessitating measures to achieve high heat resistance and low CTE. Against this backdrop, phenolic resins used in circuit board materials need to simultaneously meet multiple characteristics, including low dielectric loss tangent, high heat resistance, and low CTE. Because common phenolic resins are very brittle, have poor toughness, and poor heat resistance, phenolic resin products have low impact strength and short service life, increasing costs in copper-clad laminate applications and significantly limiting their application.

[0003] Corresponding improvements have been made to address the aforementioned issues. For example, Chinese Patent Application No. CN202211287420.3, published on December 13, 2022, discloses a method for preparing naphthol biphenyl aralkyl type epoxy resin. This invention uses pure water instead of toxic organic solvents to synthesize naphthol phenolic monomers, reducing environmental pollution. Simultaneously, unreacted 1% phenolic resin is separated by extraction. Naphthol is used to improve the purity of naphthol phenolic monomers. A two-step synthesis of naphthol biphenyl aralkyl type epoxy resin is employed, resulting in a simple process under mild conditions. The product exhibits low epoxy equivalent and low viscosity, along with good heat resistance, high flame retardancy, and low hygroscopicity, making it suitable for applications in chip packaging materials and integrated circuit packaging, thus expanding the application range of epoxy resins. However, this patent has some drawbacks: while p-toluenesulfonic acid, as an acidic catalyst, can improve reaction selectivity, its high solubility in the reaction system leads to difficulties in recovery and increased costs; furthermore, the heat resistance of the naphthol phenolic monomer is relatively poor.

[0004] For example, Chinese patent application CN202110254328.6, published on June 15, 2021, discloses a phenolic resin and its preparation method. The method involves adding 4-R-methylphenol and paraformaldehyde to a high-pressure reactor, adding an acidic catalyst to adjust the pH of the system, heating under reflux in a water bath, and allowing the reactants to undergo an addition-condensation reaction with paraformaldehyde under the action of the acidic catalyst to obtain a product. The product is then washed with water and dried to obtain the phenolic resin. The drawback of this patent is that the condensation product of 4-R-methylphenol and paraformaldehyde mainly forms a linear or branched structure with methylene bridges, resulting in relatively low thermal stability. Summary of the Invention

[0005] 1. The problem to be solved To address the problems of poor heat resistance and limited applications of existing phenolic resins, this application provides a phenolic resin, its preparation method, and its applications. This invention prepares a resin with good heat resistance, high flame retardancy, and low moisture absorption by simultaneously mixing naphthol with two structurally similar but differently soluble dimethyl ethers. Furthermore, heating and melting the raw materials facilitates subsequent mixing with a catalyst, ensuring a complete reaction. Ultimately, this expands the application range of phenolic resins.

[0006] 2. Technical Solution To solve the above problems, the present invention adopts the following technical solution.

[0007] A method for preparing a phenolic resin includes the following steps: S1: Raw material pretreatment: Naphthol, biphenyl dimethyl ether and p-phenylenediamine are mixed and heated to melt at a first preset temperature to obtain a melted liquid mixture; S2: Synthesis reaction: The liquid mixture is placed under acidic conditions and a synthesis reaction is carried out at a second preset temperature to obtain resin monomers; S3: Obtain the finished product: After removing unreacted naphthol from the resin monomer, the finished phenolic resin is obtained.

[0008] The first key aspect of the above technical solution is the first-time simultaneous mixing of naphthol with two structurally similar but differently functionally distinct dimethyl ethers. This fully utilizes the characteristics of each component, achieving a better synergistic effect. It overcomes the drawbacks of naphthol reacting alone with dimethyl biphenyl ether, resulting in a high resin softening point and excessive rigidity, which is detrimental to the processing performance of subsequent materials. It also avoids the drawbacks of naphthol reacting alone with dimethyl terephthalate, leading to a low hydroxyl equivalent and poor heat resistance in the resin. By simultaneously introducing the biphenyl and terephthalic acid structures into the resin framework, this application results in a final phenolic resin with high heat resistance and a low dielectric loss tangent, without hindering the processing of subsequent materials. The second key step is to preheat and melt the raw materials. Considering that naphthol, biphenyl dimethyl ether, and terephthalic dimethyl ether are all solids at room temperature, directly reacting with the catalyst would result in a large amount of catalyst used, increasing costs, and the catalyst would not be evenly dispersed in the raw materials, leading to incomplete reactions and slow reaction efficiency, thus prolonging the entire preparation cycle. Therefore, heating the raw materials to a liquid mixture facilitates subsequent mixing with the catalyst, ensuring a complete reaction and reducing unnecessary cost inputs. The entire preparation method is simple to operate. The pretreatment step ensures the sufficiency and uniformity of the reaction, while the removal step ensures the purity of the product. This method not only solves the problems of low raw material utilization and incomplete reaction in the traditional preparation process of phenolic resin, but also significantly improves the heat resistance and processability of phenolic resin, thus greatly expanding the application range of phenolic resin.

[0009] Furthermore, in step S1, the weight parts of naphthol and diphenyl dimethyl ether differ by an order of magnitude; the weight parts of naphthol are greater than the weight parts of diphenyl dimethyl ether, and the weight parts of diphenyl dimethyl ether are greater than the weight parts of terephthalic dimethyl ether.

[0010] Using the above technical solution, naphthol, as a phenolic monomer, has the largest weight proportion, ensuring the preferential formation of the basic skeleton of the phenolic resin and providing the resin with basic thermal and chemical stability. The ether bonds and benzene rings in the biphenyl dimethyl ether structure can participate in the cross-linking reaction of the resin, forming a three-dimensional network structure, enhancing the resin's thermal stability and mechanical properties. The methoxy group in the terephthalic dimethyl ether structure can react with the phenolic hydroxyl groups of naphthol, adjusting the hydroxyl equivalent of the resin. Biphenyl dimethyl ether and terephthalic dimethyl ether act as modifiers, finely controlling the resin's performance. If their weight proportions are too high, it will increase the cost and decrease the performance. Increasing the amount of biphenyl dimethyl ether can improve thermal stability, but excessive amounts will lead to excessive rigidity. Increasing the amount of terephthalic dimethyl ether can improve processing performance, but excessive amounts will reduce heat resistance. Therefore, through this ratio design, the final prepared phenolic resin has excellent thermal stability, mechanical properties, and processing performance.

[0011] Furthermore, the weight parts of naphthol are in the unit of "hundred"; the weight parts of biphenyl dimethyl ether are in the unit of "ten"; and the weight parts of terephthalic dimethyl ether are in the unit of "ten" or "piece"; and the weight parts of biphenyl dimethyl ether are twice the weight parts of terephthalic dimethyl ether.

[0012] Using the above technical solution, the biphenyl dimethyl ether molecule does not contain active hydroxyl groups. Using a high proportion can reduce hydroxyl consumption and maintain a high hydroxyl equivalent in the resin, thereby improving heat resistance. In the reaction, the methyl ether group in diphenyl ether is converted into hydroxymethyl, which forms a flexible methylene ether bond with the phenolic hydroxyl group of naphthol. This moderately increases the mobility of the molecular chain, avoiding processing difficulties caused by excessive rigidity, and moderately reduces the hydroxyl equivalent, avoiding increased hygroscopicity or decreased thermal stability caused by excessive hydroxyl, thus achieving synergistic optimization of heat resistance and other properties. By presenting the two in a two-fold ratio, the thermal stability and processability are balanced. By enhancing thermal stability with biphenyl dimethyl ether and improving toughness with diphenyl ether, the contradiction between traditional phenolic resins being hard and brittle or soft and weak can be resolved, thus broadening the application fields.

[0013] Furthermore, in step S1, by weight, the following proportions are used: 100-120 parts of naphthol; 12-20 parts of biphenyl dimethyl ether; 6-10 parts of p-phenylenediamine; and the first preset temperature is 110℃-120℃.

[0014] Furthermore, step S2 specifically includes the following steps: S21: Add acidic catalyst dropwise to the liquid mixture while simultaneously raising the temperature to 140℃~150℃ and pre-reacting at this temperature range for 2h~3h; S22: After the pre-reaction is completed, the temperature is raised again to 160℃~165℃, and the reaction continues for 1h~2h within this temperature range; S23: After the reaction is completed, resin monomer is obtained.

[0015] Using the above technical solution, the second preset temperature is carried out in two stages in the synthesis reaction. The early stage of the reaction is highly exothermic and the reaction rate is fast, resulting in the production of a large amount of methanol as a byproduct. If the synthesis is carried out directly at a fixed temperature, the methanol will evaporate too quickly if the temperature is too high, making it difficult to control the temperature. A large amount of methanol will be carried out as naphthol in the reaction, causing changes in the feed ratio. Therefore, this application ensures that the reactants are fully mixed and activated by using a long low temperature for the pre-reaction, and then continues the reaction at a high temperature for a short time, which efficiently completes the crosslinking and avoids energy waste and byproduct generation.

[0016] Furthermore, in step S3, the resin monomer is heated and unreacted naphthol is removed by distillation; and when the naphthol content in the resin monomer is less than 1%, the removal operation is terminated to obtain the finished phenolic resin.

[0017] Using the above technical solution, unreacted naphthol is a small molecule monomer with poor compatibility with high molecular weight phenolic resin. It is easy to preferentially volatilize as a low-boiling-point component during distillation, thereby achieving efficient separation. Moreover, the distillation step can be directly coupled with the reaction step to achieve integrated reaction-removal treatment, simplifying the process flow. Furthermore, by strictly controlling the naphthol content in the resin monomer, the thermal stability and mechanical properties of the final phenolic resin can be significantly improved.

[0018] Furthermore, in step S21, the acidic catalyst is methanesulfonic acid, and the dripping time of methanesulfonic acid is 60 min to 80 min, and the weight fraction of methanesulfonic acid is 0.2 to 1 part.

[0019] By adopting the above technical solution, the side reactions caused by excessively high local concentrations can be avoided by slowly adding methanesulfonic acid. Furthermore, the addition of the catalyst during the pre-reaction stage ensures the catalyst activity and prevents premature volatilization or decomposition of naphthol. At the same time, strict control of the catalyst addition time facilitates molecular weight control and avoids excessively short addition times, which can easily lead to heat accumulation and rapid temperature rise. Excessively long delivery times can easily prolong the entire preparation cycle of phenolic resin.

[0020] A phenolic resin is prepared by any of the methods described above.

[0021] An application of phenolic resin in the circuit board material industry. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the process of the present invention; Figure 2 This is the GPC diagram of the product in Example 1; Figure 3 This is the GPC diagram of the product in Example 2; Figure 4 This is the GPC diagram of the product in Example 3; Figure 5 This is the GPC diagram for Comparative Example 1. Figure 6 This is the GPC diagram for Comparative Example 2; Figure 7 The product GPC diagram for Comparative Example 3; Figure 8 The product GPC diagram for Comparative Example 4; Figure 9 This is the GPC diagram for Comparative Example 5. Detailed Implementation

[0023] The present invention will now be further described with reference to specific embodiments and accompanying drawings.

[0024] like Figure 1 As shown, a method for preparing a phenolic resin includes the following steps: S1: Raw material pretreatment: Naphthol, biphenyl dimethyl ether and p-phenylenediamine are mixed and heated to melt at a first preset temperature to obtain a melted liquid mixture; S2: Synthesis reaction: The liquid mixture is placed under acidic conditions and a synthesis reaction is carried out at a second preset temperature to obtain the resin monomer; the reaction in this step is as follows:

[0025] Where n = 2~3; S3: Obtain the finished product: After removing unreacted naphthol from the resin monomer, the finished phenolic resin is obtained.

[0026] In this embodiment, the inventors of this application have, for the first time, creatively reacted naphthol with both diphenyl ether and terephthalic ether simultaneously. Naphthol forms the main chain, while diphenyl ether forms crosslinking points in localized areas. The ether bonds and benzene rings in the structure of diphenyl ether can participate in the crosslinking reaction of the resin, forming a three-dimensional network structure that enhances the resin's thermal stability and mechanical properties. The methoxy group in the structure of terephthalic ether can react with the phenolic hydroxyl groups of naphthol, adjusting the hydroxyl equivalent of the resin and avoiding performance degradation caused by excessively low hydroxyl equivalents. This results in a phenolic resin that possesses both high heat resistance and mechanical properties, meets the requirements for subsequent processing, and is easy to process.

[0027] The applicant wishes to emphasize that the mainstream method for preparing phenolic resins in the prior art involves the reaction of phenols and aldehydes in the presence of a catalyst. However, the resulting phenolic resins typically do not meet performance requirements. Other methods involve reacting phenols with ethers, but usually only a single ether compound is used, as in patent application number "TW101135961," which can achieve some performance improvements. However, through continuous research and experimentation, the inventors of this application have discovered that: the reaction of naphthol alone with a diphenyl ether structure results in a resin with a high softening point and excessive rigidity, which is detrimental to the processing performance of subsequent materials; the reaction of naphthol alone with a diphenyl ether structure results in a resin with a low hydroxyl equivalent and poor heat resistance. In other words, the reaction of naphthol with a single ether compound cannot simultaneously achieve both processing performance and heat resistance, greatly limiting the application of phenolic resins.

[0028] Therefore, based on this, the inventors for the first time mixed naphthol with two dimethyl ethers that have similar structures but different properties, making full use of the characteristics of each component and achieving a better synergistic effect. By introducing biphenyl and paraben structures into the resin skeleton at the same time, the final phenolic resin has high heat resistance and low dielectric loss tangent, and will not cause problems for the subsequent processing of materials, thus achieving a balance between heat resistance, physical properties and processing performance.

[0029] Secondly, when introducing two structurally similar but different dimethyl ethers and naphthol to react, considering that all three raw materials are solid at room temperature, directly reacting with the catalyst would result in excessive catalyst usage, increased costs, and uneven catalyst dispersion in the raw materials, leading to incomplete reaction and slow reaction efficiency, thus prolonging the entire preparation cycle. Therefore, heating the raw materials to a liquid mixture facilitates subsequent mixing with the catalyst, ensuring a thorough reaction, sufficient mixing between the raw materials, and thorough and uniform mixing with the catalyst, reducing unnecessary cost inputs and ensuring a complete reaction, thus providing a good guarantee for the subsequent preparation of phenolic resin.

[0030] Third, the two different dimethyl ether raw materials react with phenol at different rates under acidic conditions. The reaction rate of biphenyl dimethyl dimethyl ether is much higher than that of terephthalic dimethyl ether. Therefore, in the synthesis process, it is extremely important to select a suitable catalyst, the order of feeding, and the ratio of the two substances.

[0031] Therefore, the entire preparation method in this embodiment is simple to operate, the pretreatment step ensures the sufficiency and uniformity of the reaction, and the removal step ensures the purity of the product. This method not only solves the problems of low raw material utilization and insufficient reaction in the traditional preparation process of phenolic resin, but also significantly improves the heat resistance and processability of phenolic resin, which greatly expands the application range of phenolic resin.

[0032] In one specific embodiment, in step S1, the weight parts of naphthol and diphenyl dimethyl ether differ by an order of magnitude; the weight parts of naphthol are greater than the weight parts of diphenyl dimethyl ether, and the weight parts of diphenyl dimethyl ether are greater than the weight parts of terephthalic acid. It should be noted that: a difference of an order of magnitude means that if the weight parts of naphthol are several hundred, then the weight parts of diphenyl dimethyl ether are several tens; if the weight parts of naphthol are several tens, then the weight parts of diphenyl dimethyl ether are several parts, and so on.

[0033] Specifically, in this embodiment, the weight percentages of naphthol, diphenyl ether, and terephthalic ether were further limited. Naphthol had the highest weight percentage because, as a phenolic monomer, its larger amount ensured the rapid formation of the basic framework of the phenolic resin, providing the resin with basic thermal and chemical stability. Diphenyl ether had the second highest weight percentage, with a difference of one order of magnitude, because excessive diphenyl ether could lead to a high softening point and excessive rigidity in the resin, which would be detrimental to subsequent processing performance. Terephthalic ether had the lowest weight percentage because, although the ether bonds in terephthalic ether improve processability, excessive amounts would dilute the aromatic ring density. Therefore, by strictly controlling the content of the three components and keeping them within a certain range, the heat-resistant framework and reactivity could be guaranteed, achieving a balance of high heat resistance, good processability, and mechanical toughness. This made the prepared phenolic resin particularly suitable for high-end electronic packaging and aerospace composite materials.

[0034] In one specific embodiment, the weight parts of naphthol are in the unit of "hundred"; the weight parts of biphenyl dimethyl ether are in the unit of "ten"; the weight parts of terephthalic dimethyl ether are in the unit of "ten" or "piece"; and the weight parts of biphenyl dimethyl ether are twice the weight parts of terephthalic dimethyl ether.

[0035] In this embodiment, the weight percentage of biphenyl dimethyl ether is further limited to twice that of terephthalic acid dimethyl ether. This is because: twice the amount ensures that enough cross-linking points are formed in the resin to construct a three-dimensional rigid network, which significantly improves the thermal stability of the resin; while terephthalic acid dimethyl ether only performs a fine-tuning function, and its content is kept at a low level to avoid increased brittleness caused by excessive cross-linking. At the same time, it improves the toughness of the resin through flexible segments, balancing rigidity and processing performance.

[0036] In other words, biphenyl dimethyl ether (BDE) molecules do not contain active hydroxyl groups. Its high proportion reduces the consumption of phenolic hydroxyl groups, maintaining a high hydroxyl equivalent in the resin, thereby reducing hygroscopicity and retaining more aromatic ring structures. Simultaneously, its methoxy group is converted to hydroxymethyl during the reaction, forming a flexible methylene ether bond with the phenolic hydroxyl group of naphthol, moderately increasing the molecular chain mobility and avoiding processing difficulties caused by excessive rigidity. Ultimately, BDE achieves synergistic optimization of heat resistance, low hygroscopicity, and processability through a dual mechanism of rigid framework reinforcement and flexible connecting bonds.

[0037] In one specific embodiment, in step S1, by weight, the following proportions are used: 100-120 parts naphthol; 12-20 parts diphenyl ether; 6-10 parts terephthalic ether; and the first preset temperature is 110°C-120°C. The raw materials within this range balance cost and performance.

[0038] In one specific embodiment, step S2 specifically includes the following steps: S21: Add acidic catalyst dropwise to the liquid mixture while simultaneously raising the temperature to 140℃~150℃ and pre-reacting at this temperature range for 2h~3h; S22: After the pre-reaction is completed, the temperature is raised again to 160℃~165℃, and the reaction continues for 1h~2h within this temperature range; S23: After the reaction is completed, resin monomer is obtained.

[0039] In this embodiment, the second preset temperature is carried out in two stages during the synthesis reaction. The reaction is highly exothermic and fast in the early stage, resulting in the production of a large amount of methanol as a byproduct. If the synthesis is carried out directly at a fixed temperature, the methanol will evaporate too quickly and the temperature will be difficult to control. A large amount of methanol will be carried out as naphthol in the reaction, causing changes in the feed ratio. Therefore, this application ensures that the reactants are fully mixed and activated by using a long low temperature for the pre-reaction, and then continues the reaction at a short high temperature to efficiently complete the crosslinking and avoid energy waste and byproduct generation.

[0040] In one specific embodiment, the acidic catalyst in step S21 is methanesulfonic acid, and the addition time of methanesulfonic acid is 60-80 minutes. By slowly adding methanesulfonic acid, side reactions caused by excessively high local concentrations can be avoided. Adding the catalyst during the pre-reaction stage ensures catalyst activity and prevents premature volatilization or decomposition of naphthol. At the same time, strictly controlling the catalyst addition time facilitates molecular weight control and avoids excessively short addition times, which can easily lead to heat accumulation and rapid temperature rise. Excessively long addition times can easily prolong the entire preparation cycle of phenolic resin.

[0041] In one specific embodiment, in step S3, the resin monomer is heated, and unreacted naphthol is removed by distillation. The removal operation terminates when the naphthol content in the resin monomer is less than 1%, yielding the final phenolic resin. Unreacted naphthol is a small molecule monomer with poor compatibility with high molecular weight phenolic resin. It readily volatilizes preferentially as a low-boiling-point component during distillation, thus achieving efficient separation. Furthermore, the distillation step can be directly coupled with the reaction step, achieving integrated reaction-removal processing and simplifying the process flow. Strict control of the naphthol content in the resin monomer significantly improves the thermal stability and mechanical properties of the final phenolic resin.

[0042] In one specific embodiment, a phenolic resin is prepared using a method for preparing a phenolic resin as described in any of the above embodiments. The phenolic resin in this embodiment exhibits heat resistance stability and low dielectric loss tangent characteristics; and the naphthol resin, based on the area ratio determined by GPC, contains at least 16% of the component with n=5 or more, preferably at least 20%. Furthermore, the component with n=0 is at least 30%, preferably at least 27%. By containing at least 15% of the component with n=5 or more as a multifunctional organism, the crosslinking density is increased, thereby improving heat resistance; on the other hand, when the component with n=0, which cannot form a three-dimensional structure during curing, increases, the heat resistance decreases, therefore it is necessary to suppress it to 30% or less.

[0043] In one specific embodiment, the phenolic resin as described above is applied in the circuit board material industry. Because the phenolic resin prepared using the above-described method exhibits significantly improved heat resistance, it also meets multiple characteristics such as low dielectric loss tangent and low CTE, making it suitable for use in circuit boards.

[0044] To further facilitate understanding of the technical solution of this application, the following embodiments and comparative examples are also provided: Example 1 Under a nitrogen atmosphere, 100 parts of naphthol, 16 parts of biphenyl dimethyl ether, 8 parts of terephthalic acid, and 0.67 parts of methanesulfonic acid catalyst were added to a reaction vessel. The mixture was then heated to 110-120°C to melt the raw materials. Methanesulfonic acid catalyst was slowly added dropwise over 60 minutes. The temperature was then raised to 140-150°C to initiate the reaction for 2-3 hours, followed by a further increase to 160-165°C and maintaining this temperature for 1-2 hours. After the reaction was complete, the temperature was increased to 230°C to evaporate excess naphthol until the naphthol content was less than 1%, yielding a resin monomer with a softening point of 98°C. The resin was then cooled and discharged, with a GPC spectrum showing 27% n=0 and 24% n=5.

[0045] Example 2 Under a nitrogen atmosphere, 120 parts of naphthol, 20 parts of biphenyl dimethyl ether, 8 parts of terephthalic acid, and 0.67 parts of methanesulfonic acid catalyst were added to a reaction vessel. The mixture was then heated to 110-120°C to melt the raw materials. Methanesulfonic acid catalyst was slowly added dropwise over 60 minutes. The temperature was then raised to 140-150°C to initiate the reaction for 2-3 hours, followed by a further increase to 160-165°C and maintaining this temperature for 1-2 hours. After the reaction was complete, the temperature was increased to 230°C to evaporate excess naphthol until the naphthol content was less than 1%, yielding a resin monomer with a softening point of 98°C. The resin was cooled and discharged, and its GPC spectrum showed a 31% proportion for n=0 and a 19% proportion for n=5.

[0046] Example 3 Under a nitrogen atmosphere, 110 parts of naphthol, 16 parts of biphenyl dimethyl ether, 10 parts of terephthalic dimethyl ether, and 0.67 parts of methanesulfonic acid catalyst were added to a reaction vessel. The mixture was then heated to 110-120°C to melt the raw materials. Methanesulfonic acid catalyst was slowly added dropwise over 60 minutes. The temperature was then raised to 140-150°C to initiate the reaction for 2-3 hours, followed by a further increase to 160-165°C and maintaining this temperature for 1-2 hours. After the reaction was complete, the temperature was increased to 230°C to evaporate excess naphthol until the naphthol content was less than 1%, yielding a resin monomer with a softening point of 98°C. The resin was then cooled and discharged. Its GPC spectrum showed that n=0 was 15% and n=5 was 31%.

[0047] Comparative Example 1 The process is basically the same as in Example 1, except that the raw materials are only 100 parts of naphthol and 16 parts of biphenyl dimethyl ether. The other steps and parameters are the same. The proportion of its GPC spectrum with n=0 is 19% and with n=5 is 16%.

[0048] Comparative Example 2 The process is basically the same as in Example 1, except that the raw materials are only 100 parts of naphthol and 12 parts of p-phenylenedimethyl ether. The other steps and parameters are the same. The proportion of its GPC spectrum with n=0 is 29% and with n=5 is 21%.

[0049] Comparative Example 3 The basic process is the same as in Example 1, except that the raw materials are naphthol, biphenyl dimethyl ether and terephthalic dimethyl ether. However, the naphthol is 100 parts, and the biphenyl dimethyl ether and terephthalic dimethyl ether are kept in the same number of parts, that is, 16 parts each. The remaining steps and parameters are the same. The GPC spectrum shows that the proportion is 21% when n=0 and 13% when n=5.

[0050] Comparative Example 4 The process is basically the same as in Example 1, except that the raw materials are naphthol, biphenyl dimethyl ether, and terephthalic dimethyl ether. However, the amount of naphthol is 100 parts, the amount of biphenyl dimethyl ether is less than the amount of terephthalic dimethyl ether, the amount of biphenyl dimethyl ether is 8 parts, and the amount of terephthalic dimethyl ether is 16 parts. The remaining steps and parameters are the same. The proportion of n=0 in the GPC spectrum is 11%, and the proportion of n=5 is 33%.

[0051] Comparative Example 5 The process is basically the same as in Example 1, except that the raw materials are naphthol, biphenyl dimethyl ether, and terephthalic dimethyl ether. However, the amount of naphthol is 100 parts, and the amount of biphenyl dimethyl ether is much greater than the amount of terephthalic dimethyl ether. The amount of biphenyl dimethyl ether is 16 parts, and the amount of terephthalic dimethyl ether is 4 parts. The remaining steps and parameters are the same. The proportion of n=0 in the GPC spectrum is 14%, and the proportion of n=5 is 28%.

[0052] Thermogravimetric analysis was performed on the resin monomers obtained in Examples 1-3 and Comparative Examples 1-5, and the results are shown in Table 1 below: Table 1. Experimental data for TGA

[0053] Biphenyl dimethyl ether itself has high thermal stability due to the rigidity of the biphenyl structure and the conjugated system. Although terephthalic dimethyl ether has good thermal stability, its relatively small molecular size results in a lower thermal decomposition temperature. As can be seen, the resin synthesized in Example 1 has high thermal stability and relatively high residue at 600 degrees Celsius. This is because the resin skeleton is mainly composed of biphenyl structure, which is relatively regular and has strong thermal stability.

[0054] The examples described herein are merely preferred embodiments of the invention and are not intended to limit the concept and scope of the invention. Any modifications and improvements made by those skilled in the art to the technical solutions of the invention without departing from the design concept of the invention should fall within the protection scope of the invention.

Claims

1. A method for preparing a phenolic resin, characterized in that: Includes the following steps: S1: Raw material pretreatment: Naphthol, biphenyl dimethyl ether and terephthalic dimethyl ether are mixed and heated to melt at a first preset temperature to obtain a melted liquid mixture; and the weight of biphenyl dimethyl ether is twice the weight of terephthalic dimethyl ether. S2: Synthesis reaction: The liquid mixture is placed under acidic conditions and a synthesis reaction is carried out at a second preset temperature to obtain resin monomers; S3: Obtain the finished product: After removing unreacted naphthol from the resin monomer, the finished phenolic resin is obtained.

2. The method for preparing a phenolic resin according to claim 1, characterized in that: In step S1, the weight parts of naphthol and diphenyl dimethyl ether differ by an order of magnitude; the weight parts of naphthol are greater than the weight parts of diphenyl dimethyl ether, and the weight parts of diphenyl dimethyl ether are greater than the weight parts of terephthalic dimethyl ether.

3. The method for preparing a phenolic resin according to claim 2, characterized in that: Naphthol is expressed in parts by weight in "hundreds"; biphenyl dimethyl ether is expressed in parts by weight in "tens"; and p-phenylenediamine is expressed in parts by weight in "tens" or "pieces".

4. A method for preparing a phenolic resin according to claim 2 or 3, characterized in that: In step S1, by weight parts: naphthol 100-120 parts; biphenyl dimethyl ether 12-20 parts; p-phenylenediamine 6-10 parts; and the first preset temperature is 110℃-120℃.

5. The method for preparing a phenolic resin according to claim 1, characterized in that: Step S2 specifically includes the following steps: S21: Add an acidic catalyst dropwise to the liquid mixture while simultaneously raising the temperature to 140℃~150℃ and pre-reacting at this temperature range for 2h~3h; S22: After the pre-reaction is completed, the temperature is raised again to 160℃~165℃, and the reaction continues for 1h~2h within this temperature range; S23: After the reaction is completed, resin monomer is obtained.

6. The method for preparing a phenolic resin according to claim 5, characterized in that: In step S21, the acidic catalyst is methanesulfonic acid, and the dripping time of methanesulfonic acid is 60 min to 80 min, and the weight fraction of methanesulfonic acid is 0.2 to 1 part.

7. The method for preparing a phenolic resin according to claim 1, characterized in that: In step S3, the resin monomer is heated and unreacted naphthol is removed by distillation; and when the naphthol content in the resin monomer is less than 1%, the removal operation is terminated to obtain the finished phenolic resin.

8. A phenolic resin, characterized in that: It is prepared by the method for preparing a phenolic resin as described in any one of claims 1-7.

9. An application of the phenolic resin as described in claim 8, characterized in that: It is used in the circuit board material industry.

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