A compounded catalyst containing phenolic hydroxyl and imidazole structure catalyst, cyanate ester resin system

Abstract

This invention relates to a composite catalyst containing phenolic hydroxyl and imidazole structures, and a cyanate ester resin system. The catalyst system of this invention comprises compounds containing imidazole and phenolic structures, along with transition metal compounds. The compounds containing imidazole and phenolic structures serve as the hydrogen source for the active hydrogen catalyst and as the support for the transition metal compound catalyst. The cyanate ester resin system of this invention is prepared by mixing cyanate ester resin, a toughening agent, and a high-efficiency catalyst. By using the catalyst, the curing reaction of the cyanate ester resin system is completed under medium-low temperature curing conditions while maintaining the excellent heat resistance of the cyanate ester resin. This cyanate ester resin system can be widely used in aerospace, military, and other fields such as projectile transparent covers, radar domes, satellite solar panels, and space support structures.

Description

Technical Field

[0001] This invention belongs to the field of thermosetting resin and polymer material preparation technology, and relates to a composite catalyst containing phenolic hydroxyl and imidazole structure catalysts and a cyanate ester resin system. This high-efficiency catalyst system can significantly reduce the curing temperature of cyanate esters. The resin system configured with cyanate ester resin can be widely used in aerospace, military industry and other fields such as projectile transparent covers, radar covers, satellite battery panels and space bearing structures. Background Technology

[0002] Cyanate ester resins (CE) refer to phenolic derivatives containing two or more cyanate ester groups (-OCN). Under high temperature or catalytic conditions, cyanate ester resins can undergo cyclotrimerization to form a highly symmetrical triazine ring structure, endowing the material with excellent dielectric and heat resistance properties. The ether bonds in the network structure also contribute to the material's toughness. Without a catalyst, cyanate ester resins require extremely high temperatures (>220℃) and long curing times to achieve a high degree of crosslinking. Because the energy required for pure cyanate ester molecules to rise from the monomer energy level to the activated state is extremely high, for example, with bisphenol A cyanate ester, heating at 150℃ for 48 hours results in a monomer conversion rate of less than 50%; heating at 200℃ for 6 hours only achieves a conversion rate of 70%–80%. Furthermore, prolonged curing at excessively high temperatures can lead to significant residual stress within the product, causing large deformations and reducing the stability of its service performance, severely restricting the development and large-scale application of cyanate ester resins and their composites. Given the drawbacks of cyanate ester resins, such as high reaction temperature, long curing time, and impact on finished products, research on efficient catalytic reactions of cyanate ester resins is urgently needed and has great value and potential.

[0003] Commonly used catalysts for cyanate ester resin systems include phenolic compounds such as nonylphenol and phenol containing active hydrogen, transition metal acetylacetonates and (cyclo)alkanoates, and organotin compounds. Phenolic catalysts containing active hydrogen are effective in the later stages of curing, improving the degree of curing, but their catalytic effect is not high, and their effect on lowering the curing temperature is generally limited. Transition metal salts such as acetylacetonates, (cyclo)alkanoates, and dibutyl dilaurate, and their oxides, are effective in the gel stage, the early stages of curing, significantly reducing the resin curing temperature, but their effect on improving the degree of curing in the later stages is difficult. Therefore, using these catalysts alone results in a still high curing temperature and unsatisfactory catalytic effect. Furthermore, transition metal salts and their oxides are usually solid at room temperature and have high melting points, making it difficult to uniformly disperse in the cyanate ester resin system. This can cause localized burst polymerization and low degree of curing, thus affecting the catalytic effect, material properties, and the preparation of subsequent related products. To achieve better catalytic performance and address the catalyst dispersion issue in resin systems, patent CN202211110509.2 discloses a low-temperature, rapidly curable imidazole-containing cyanate ester resin and its preparation method, which discloses a catalyst containing both cyano and imidazole structures. Both the catalyst and the cyanate ester resin contain cyano groups, exhibiting good compatibility. The imidazole exerts its catalytic effect, thus solving the catalytic and dispersion problems. However, this catalyst system requires a large amount of organic solvent, necessitating specialized equipment for solvent evaporation, making the preparation process complex, environmentally unfriendly, and requiring a large catalyst dosage. Furthermore, the cyano group in the catalyst structure, as the main reactive structure of the cyanate ester resin, participates in curing, hindering the catalyst's free movement within the resin system and affecting the realization of the imidazole structure's catalytic effect. Summary of the Invention

[0004] This invention proposes a composite catalyst and cyanate ester resin system containing phenolic hydroxyl and imidazole structures, solving the problems of high curing temperature, long curing time, low temperature resistance, and environmental impact of existing cyanate ester resin systems. It provides a highly efficient catalyst system, a cyanate ester resin system, and its preparation method. The highly efficient catalyst requires fewer raw materials, is simple to formulate, and the resin system has a low curing temperature, short curing time, and high heat resistance. The use of compounds containing active hydrogen in conjunction with metal complexes can improve the solubility of the metal complex in the monomer. Furthermore, after the gel point, the curing reaction is a diffusion-controlled process, with low metal ion mobility and high active hydrogen mobility. The catalytic efficiency of active hydrogen is much higher than that of metal ions, and the two can synergistically achieve low-temperature curing and high degree of curing. The catalytic effect of the active hydrogen-containing catalyst is related to the content and activity of active hydrogen. To obtain more efficient catalytic effects at low addition levels and for safety and environmental considerations, other compounds with higher active hydrogen content, those that can enhance active hydrogen activity, or those with inherent catalytic potential can be selected for use in conjunction with the metal complex. Therefore, this invention innovatively selects compounds containing both phenol and various imidazole structures in their molecular structure as hydrogen sources for active hydrogen catalysts and supports for transition metal compound catalysts.

[0005] This invention is achieved through the following technical solution:

[0006] This invention provides a composite catalyst containing phenolic hydroxyl and imidazole structures, comprising compounds containing imidazole and phenolic structures and transition metal compounds;

[0007] The structural formulas of compounds containing imidazole and phenolic structures are shown in Formula I or Formula II:

[0008] ,

[0009] Formula I and Formula II;

[0010] in,

[0011] R1 is one of -CH2-, -C2H4-, -C3H6-, or -C(CH2)-.

[0012] R2, R3, and R4 are H or C1-C5 alkyl groups.

[0013] As one embodiment of the present invention, R1 is preferably one of -CH2- and -C(CH2)-.

[0014] As one embodiment of the present invention, R2 is one of H, -CH3, and -C2H5; R3 is one of H, -CH3, and -C2H5; and R4 is one of H, -CH3, and -C2H5.

[0015] The imidazole structure in this invention can provide active hydrogen itself, increasing the active hydrogen content; it can also increase the activity of active hydrogen in phenolic hydroxyl groups; and it can also self-catalyze cyanate esters.

[0016] Formula I represents an imidazole structure linked to a phenolic structure via R1, with the linkage position being one of the ortho, meta, or para positions of the phenolic hydroxyl group. Formula II represents an imidazole structure linked to a phenolic structure, with the linkage position being one of the ortho, meta, or para positions of the phenolic hydroxyl group.

[0017] Preferably, the compound containing an imidazole structure and a phenolic structure has one of the following structural formulas (1) to (12):

[0018]

[0019] In one embodiment of the present invention, the transition metal compound is one or more of the acetylacetonate, alkanoate, dibutyl dilaurate, or oxide of a transition metal. The transition metal includes one of Cr, Mn, Fe, Co, Ni, Zn, Cu, and Sn.

[0020] As one embodiment of the present invention, the mass ratio of the compound containing the imidazole structure and the phenolic structure to the transition metal compound is 1:0.01~100, preferably 1:1~3, and more preferably 1:1.5~2.5.

[0021] As one embodiment of the present invention, the composite catalyst is preferably a combination of 4-(imidazol-1-yl)phenol, zinc naphthenate, and dibutyltin dilaurate. This composite catalyst can reduce the peak curing temperature to below 110°C.

[0022] This invention also provides a method for preparing a composite catalyst containing phenolic hydroxyl and imidazole structures, comprising the following steps:

[0023] Compounds containing imidazole and phenolic structures are heated and mixed with transition metal compounds at 50–100 °C to obtain a transparent liquid, which is a composite catalyst for cyanate ester resin systems. This composite catalyst is liquid at room temperature after preparation.

[0024] The present invention also provides a cyanate ester resin system comprising the aforementioned composite catalyst, comprising, by mass parts:

[0025] 100 parts of cyanate ester resin;

[0026] Toughening agent 1-20 parts;

[0027] 0.001~2 parts of compound catalyst.

[0028] The preferred amount of the compound catalyst is 0.001 to 1 part, and more preferably 0.1 to 0.4 parts.

[0029] The cyanate resin includes one or more of the following: bisphenol A type cyanate resin, bisphenol E type cyanate resin, bisphenol F type cyanate resin, bisphenol M type cyanate resin, bisphenol AF type cyanate resin, phenolic type cyanate resin, and dicyclopentadienol type cyanate resin.

[0030] The toughening agent includes one or more of the following: polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyaryletherketone (PAEK), polyphenylene sulfide (PPS), polyethersulfone (PES), polyetherimide (PEI), polyphenylene sulfone (PPSU), polysulfone (PSU), polyamide imide (PAI), polyimide (PI), bismaleimide (BMI), phenolic resin, phenolic epoxy resin, high-temperature resistant epoxy resin, and silicone resin.

[0031] The preparation method of the cyanate ester resin system includes the following steps:

[0032] S1. The cyanate ester resin and toughening agent are stirred and mixed evenly at 100~140℃ to obtain component A;

[0033] S2. Add the compounded catalyst to component A at 80~100℃ and stir to mix evenly to obtain a cyanate ester resin that can be used in the prepreg system, thus obtaining the cyanate ester resin system.

[0034] The present invention also provides the application of the cyanate ester resin system in the aerospace and military industries.

[0035] The applications are in projectile transparent covers, radar domes, satellite solar panels, and space-borne structures.

[0036] The application involves curing the prepared cyanate ester resin system at ≤170℃.

[0037] Curing is performed using a temperature gradient: cure at 60-105℃ for 0.5-2 hours, then at 110-135℃ for 0.5-2 hours, and finally at 140-170℃ for 0.5-2 hours. The total curing time is 2-6 hours.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] This invention utilizes compounds containing both phenol and various imidazole structures in their molecular structure as the hydrogen source for an active hydrogen catalyst and as a support for a transition metal compound catalyst. Since both phenolic hydroxyl groups and imidazoles contain active hydrogen, the active hydrogen content is increased, and the imidazole groups can enhance the activity of the active hydrogen in the phenolic hydroxyl groups, possessing catalytic potential themselves. When combined with transition metal compounds, the catalyst addition is low, resulting in high catalytic efficiency and a resin system curing temperature ≤160℃. This catalyst requires fewer raw materials, is simple to prepare, and is healthier and more environmentally friendly compared to nonylphenol and organic solvents. Using this catalyst, the curing reaction of the cyanate ester resin system is completed under medium-low temperature curing conditions while maintaining the excellent heat resistance of the cyanate ester resin, with a Tg ≥290℃. This cyanate ester resin system can be widely used in aerospace, military, and other fields such as projectile transparent covers, radar domes, satellite solar panels, and load-bearing structures. Attached Figure Description

[0040] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0041] Figure 1 The Tg curves are for the cured resin systems of Examples 1-4. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, providing detailed implementation methods and specific operating procedures, which will help those skilled in the art to further understand the present invention. It should be noted that the scope of protection of the present invention is not limited to the following embodiments; any adjustments and improvements made under the concept of the present invention are all within the scope of protection of the present invention.

[0043] This invention relates to a highly efficient catalyst system containing phenolic hydroxyl and imidazole structures. It utilizes compounds containing both phenolic and various imidazole structures in their molecular structure as the hydrogen source for active hydrogen catalysts and as a support for transition metal compound catalysts. A novel, highly efficient catalyst is obtained by compounding this compound with transition metal compounds in a specific ratio. This catalyst has the advantages of requiring fewer raw materials, simple preparation, being environmentally friendly, requiring low dosage, and exhibiting high catalytic efficiency. The cyanate ester resin system of this invention is prepared by mixing cyanate ester resin, toughening agent, and highly efficient catalyst according to a specific ratio and process. Using the catalyst, the curing reaction of the cyanate ester resin system is completed under medium-low temperature curing conditions while maintaining the excellent heat resistance of the cyanate ester resin. The advantages of this cyanate ester resin system are: low curing temperature, short curing time, and high Tg of the cured product. This cyanate ester resin system can be widely used in aerospace, military, and other fields such as projectile transparent covers, radar domes, satellite solar panels, and space support structures.

[0044] The preparation method of the cyanate ester resin system includes the following steps:

[0045] S1: By mass fraction, compounds containing imidazole and phenolic structures are mixed with transition metal compounds at a ratio of 0.01~1:0.01~1 and heated at 50~100℃ to obtain a highly efficient catalyst.

[0046] S2: By mass, 100 parts of cyanate ester resin and 1-20 parts of toughening agent are stirred and mixed evenly at 100-140℃ to obtain component A.

[0047] S3: Add 0.001 to 2 parts by mass of the high-efficiency catalyst to component A at 80 to 100°C and stir until homogeneous to obtain a cyanate ester resin that can be used in prepreg systems.

[0048] S4: The prepared resin system is cured at ≤170℃ in a temperature gradient for 2~6 hours.

[0049] Example 1

[0050] S1: By mass, 0.1 parts of 4-(imidazol-1-yl)phenol of formula (1) and 0.2 parts of dibutyltin dilaurate are stirred and mixed evenly at 90°C to obtain a high-efficiency catalyst.

[0051] S2: According to the mass fraction, 100 parts of bisphenol A cyanate resin and 5 parts of polyetherimide (PEI) are stirred and mixed evenly at 140°C to obtain component A.

[0052] S3: Add 0.3 parts by mass of the high-efficiency catalyst to component A at 100°C and stir until homogeneous to obtain a cyanate ester resin that can be used in prepreg systems.

[0053] S4: The prepared resin system is first cured at 78℃ for 2 hours, then cured at 108℃ for 2 hours, and finally cured at 141℃ for 2 hours.

[0054] Example 2

[0055] S1: By mass, 0.1 parts of 4-(imidazol-1-yl)phenol of formula (1) and 0.2 parts of tin isooctanoate are stirred and mixed evenly at 90°C to obtain a high-efficiency catalyst.

[0056] S2: According to the mass fraction, 100 parts of bisphenol A cyanate resin and 5 parts of polyetherimide (PEI) are stirred and mixed evenly at 140°C to obtain component A.

[0057] S3: Add 0.3 parts by mass of the high-efficiency catalyst to component A at 100°C and stir until homogeneous to obtain a cyanate ester resin that can be used in prepreg systems.

[0058] S4: The prepared resin system is first cured at 92℃ for 2 hours, then cured at 123℃ for 2 hours, and finally cured at 156℃ for 2 hours.

[0059] Example 3

[0060] S1: By mass, 0.1 parts of 4-(imidazol-1-yl)phenol of formula (1) and 0.2 parts of zinc isooctanoate are stirred and mixed evenly at 90°C to obtain a high-efficiency catalyst.

[0061] S2: According to the mass fraction, 100 parts of bisphenol A cyanate resin and 5 parts of polyetherimide (PEI) are stirred and mixed evenly at 140°C to obtain component A.

[0062] S3: According to the mass fraction, add 0.2 parts of high-efficiency catalyst to component A at 100°C and stir to mix evenly to obtain cyanate ester resin that can be used in prepreg system.

[0063] S4: The prepared resin system is first cured at 88℃ for 2 hours, then cured at 121℃ for 2 hours, and finally cured at 154℃ for 2 hours.

[0064] Example 4

[0065] S1: By mass, 0.1 parts of 4-(imidazol-1-yl)phenol of formula (1) and 0.2 parts of zinc naphthenate are stirred and mixed evenly at 90°C to obtain a high-efficiency catalyst.

[0066] S2: According to the mass fraction, 100 parts of bisphenol A cyanate resin and 5 parts of polyetherimide (PEI) are stirred and mixed evenly at 140°C to obtain component A.

[0067] S3: Add 0.3 parts by mass of the high-efficiency catalyst to component A at 100°C and stir until homogeneous to obtain a cyanate ester resin that can be used in prepreg systems.

[0068] S4: The prepared resin system is first cured at 72℃ for 2 hours, then cured at 108℃ for 2 hours, and finally cured at 143℃ for 2 hours.

[0069] Example 5

[0070] S1: By mass, 0.1 parts of 4-(2-methyl-1H-imidazol-1-yl)phenol of formula (10) and 0.2 parts of dibutyltin dilaurate are stirred and mixed evenly at 100°C to obtain a high-efficiency catalyst.

[0071] S2: According to the mass fraction, 100 parts of bisphenol A cyanate resin and 5 parts of polyetherimide (PEI) are stirred and mixed evenly at 140°C to obtain component A.

[0072] S3: Add 0.3 parts by mass of the high-efficiency catalyst to component A at 100°C and stir until homogeneous to obtain a cyanate ester resin that can be used in prepreg systems.

[0073] S4: The prepared resin system is first cured at 98℃ for 2 hours, then cured at 130℃ for 2 hours, and finally cured at 154℃ for 2 hours.

[0074] Example 6

[0075] S1: By mass, 0.1 parts of 4-[(1H-imidazol-4-yl)methyl]phenol of formula (11) and 0.2 parts of dibutyltin dilaurate are stirred and mixed evenly at 100°C to obtain a high-efficiency catalyst.

[0076] S2: According to the mass fraction, 100 parts of bisphenol A cyanate resin and 5 parts of polyetherimide (PEI) are stirred and mixed evenly at 140°C to obtain component A.

[0077] S3: Add 0.3 parts by mass of the high-efficiency catalyst to component A at 100°C and stir until homogeneous to obtain a cyanate ester resin that can be used in prepreg systems.

[0078] S4: The prepared resin system is first cured at 103℃ for 2 hours, then cured at 130℃ for 2 hours, and finally cured at 146℃ for 2 hours.

[0079] Comparative Example 1

[0080] The preparation method of this comparative example is basically the same as that of Example 1, except that the high-efficiency catalyst obtained by combining 0.1 parts of 4-(imidazol-1-yl)phenol of formula (1) and 0.2 parts of dibutyltin dilaurate is replaced with 0.3 parts of 4-(imidazol-1-yl)phenol of formula (1).

[0081] Specifically, S1: Take 0.3 parts of 4-(imidazol-1-yl)phenol of the formula (1) according to the mass fraction to obtain the catalyst.

[0082] Comparative Example 2

[0083] The preparation method of this comparative example is basically the same as that of Example 1, except that the high-efficiency catalyst obtained by combining 0.1 parts of 4-(imidazol-1-yl)phenol of formula (1) and 0.2 parts of dibutyltin dilaurate is replaced with 0.3 parts of dibutyltin dilaurate.

[0084] Specifically, S1: Take 0.3 parts by mass of dibutyltin dilaurate to obtain the catalyst.

[0085] Comparative Example 3

[0086] The preparation method of this comparative example is basically the same as that of Example 1, except that the amount of high-efficiency catalyst added in S3 is 2 parts. The experimental results show that the system undergoes explosive polymerization during the catalyst mixing process at 80°C, but it also indicates that the formulation system can solidify at a lower temperature.

[0087] Comparative Example 4

[0088] The preparation method of this comparative example is basically the same as that of Example 1, except that the catalyst in S3 is 2 parts of 4-(imidazol-1-yl)phenol with the structure of formula (1).

[0089] Excessive use of a single catalyst, while lowering the curing temperature to some extent, also degrades resin properties. For example, excessive use of catalysts containing active hydrogen reduces the crosslinking density of the material, thereby lowering the glass transition temperature, but also leading to performance degradation. Similarly, excessive use of metal ion catalysts reduces the heat resistance of the cured product, mainly because metal ion catalysts catalyze the formation of the byproduct urethane while catalyzing the curing of cyanate esters.

[0090] Comparative Example 5

[0091] The preparation method of this comparative example is basically the same as that of Example 1, except that the compound with the structure of formula (1) is replaced with nonylphenol.

[0092] Performance testing:

[0093] The catalytic effect of the high-efficiency catalyst was determined by non-isothermal DSC analysis of the curing kinetics of the cyanate ester resin system. The curing process of the resin system was characterized by heating rates (β) of 2.5, 5, 10, 15, and 20 K / min. The curing temperature was determined by extrapolating the data to a heating rate β=0, thus evaluating the catalyst's effectiveness. The test results are shown in Table 1.

[0094] Table 1. DSC curing temperature data of resin systems in Examples 1-6 and Comparative Examples 1 and 2

[0095]

[0096] The thermal properties of the resin system were determined using a non-isothermal DSC method to measure the Tg of the cured product. The cyanate ester resin system was cured according to the specified curing regime, and the Tg of the cured product was tested at a heating rate of 10 K / min. The test results are as follows: Figure 1 As shown in Table 2.

[0097] Table 2. Glass transition data of resin systems in Examples 1-4

[0098]

[0099] As shown in Tables 1 and 2, the compounded catalyst has excellent promoting effect, can catalyze the curing of cyanate ester system at temperatures below 170℃, and has short curing time, good heat resistance of cured product, and Tg of cured product is above 250℃.

[0100] The mechanical properties of the samples obtained after curing in the examples and comparative examples are comparable to those of samples obtained by high-temperature curing with conventional catalysts.

[0101] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0102] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A cyanate ester resin system comprising a compound catalyst, characterized in that, By mass parts, it includes the following components: 100 parts of cyanate ester resin; Toughening agent 1-20 parts; 0.001~2 parts of compound catalyst; The composite catalyst includes compounds containing imidazole and phenolic structures and transition metal compounds; The structural formulas of compounds containing imidazole and phenolic structures are shown in Formula I or Formula II: 、 Formula I and Formula II; in, R1 is one of -CH2-, -C2H4-, -C3H6-, and -C(CH2)-; R2 is one of H, -CH3, and -C2H5; R3 is one of H, -CH3, and -C2H5; R4 is one of H, -CH3, and -C2H5. The transition metal compound is one or more of the acetylacetonate, alkanoate, dibutyl dilaurate, and oxide of the transition metal; the transition metal includes one of Cr, Mn, Fe, Co, Ni, Zn, Cu, and Sn; The mass ratio of compounds containing imidazole and phenolic structures to transition metal compounds is 1:0.01~100.

2. The cyanate ester resin system according to claim 1, characterized in that, The cyanate resin includes one or more of the following: bisphenol A type cyanate resin, bisphenol E type cyanate resin, bisphenol F type cyanate resin, bisphenol M type cyanate resin, bisphenol AF type cyanate resin, phenolic type cyanate resin, and dicyclopentadienol type cyanate resin.

3. The cyanate ester resin system according to claim 1, characterized in that, The toughening agent includes one or more of the following: polyetheretherketone, polyetherketoneketone, polyaryletherketone, polyphenylene sulfide, polysulfone, polyamide-imide, polyimide, bismaleimide, phenolic resin, phenolic epoxy resin, high-temperature resistant epoxy resin, and silicone resin.

4. A method for preparing the cyanate ester resin system as described in claim 1, comprising the following steps: S1. The cyanate ester resin and toughening agent are stirred and mixed evenly at 100~140℃ to obtain component A; S2. Add the compounded catalyst to component A at 80~100℃ and stir to mix evenly to obtain a cyanate ester resin that can be used in the prepreg system, thus obtaining the cyanate ester resin system.

5. The application of the cyanate ester resin system as described in claim 1 in the preparation of projectile transparent covers, radar domes, satellite solar panels, and space bearing structures in the aerospace and military industries.

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