Temperature-resistant organic silicon adhesive prepared from phenolic hydroxyl group-containing double-layer silsesquioxane and use method of temperature-resistant organic silicon adhesive

Abstract

The invention relates to a temperature-resistant organic silicon adhesive prepared from phenolic hydroxyl group-containing double-layer silsesquioxane and a use method of the temperature-resistant organic silicon adhesive. The phenolic hydroxyl group-containing double-layer silsesquioxane is used as a phenol source, aniline is used as an amine source, and the phenolic hydroxyl group-containing double-layer silsesquioxane is used as an amine source; and carrying out Mannich reaction on the benzoxazine group-containing double-layer silsesquioxane and an aldehyde compound to prepare the benzoxazine group-containing double-layer silsesquioxane type temperature-resistant organic silicon adhesive. According to the preparation method, the defect that the high temperature resistance is damaged by residual silicon-hydrogen bonds easily caused by a preparation route of hydrosilylation reaction can be avoided, the temperature resistance of the obtained organic silicon adhesive is improved, and the adhesive property at high temperature is improved.

Description

Technical Field

[0001] The present invention relates to a heat-resistant silicone adhesive prepared from phenolic hydroxyl-containing double-layer silsesquioxane and its usage method, belonging to the field of preparation and application of polymer materials. Background Art

[0002] Silicone materials are renowned for their excellent heat resistance, which enables them to exhibit outstanding stability in a variety of harsh environments. Whether it is for long-term use at continuous high temperatures or short-term exposure to transient high temperatures, silicone materials can maintain their physical and chemical properties without degradation or performance decline. This characteristic makes silicone materials an ideal choice in multiple fields such as aerospace, automotive manufacturing, electronics and electrical, especially in critical applications that require tolerance to extreme temperature conditions, such as the thermal protection system of spacecraft, the sealing and heat insulation of automotive engine components, and the high-temperature protection coating in electronic devices.

[0003] The heat resistance of silicone adhesives is particularly important in many application scenarios. Such adhesives can provide reliable bonding strength at high temperatures, ensuring a firm connection between components. In industrial production, many equipment and devices need to work in high-temperature environments, such as the fixation of automotive exhaust systems and the assembly inside ovens, which pose extremely high requirements for bonding materials. Thanks to their excellent heat-resistant characteristics, silicone adhesives can not only meet these needs but also significantly improve the durability and reliability of products, reduce the risk of bonding failure caused by high temperatures, and thus ensure the safe and efficient operation of related facilities and equipment.

[0004] According to the curing conditions and application characteristics, silicone adhesives are mainly divided into two major categories: room-temperature curing type and high-temperature curing type. Room-temperature curing silicone adhesives can be cured at room temperature, with simple operation and a wide range of applications, suitable for bonding various materials such as plastics, metals, and glasses. Their greatest advantage lies in their convenience of use, without the need for additional heating equipment, especially suitable for on-site construction. However, a significant disadvantage of this type of adhesive is its poor high-temperature resistance. Most products will show a significant decrease in bonding strength and weakening of physical properties when used in a high-temperature environment above 200°C for a long time. In addition, the curing speed of room-temperature curing silicone adhesives is relatively slow, which significantly restricts the operating efficiency of continuous production processes. High-temperature curing silicone adhesives exhibit excellent heat resistance after curing, and some products can even maintain a stable bonding effect in extreme environments above 300°C. However, high-temperature curing silicone adhesives also have obvious deficiencies: the curing temperature is high, usually reaching above 200°C, resulting in high energy consumption during the curing process and being unsuitable for temperature-sensitive materials. At the same time, the cured bonded parts usually have relatively low mechanical strength, which may be an important limiting factor in some applications that require high-strength bonding.

[0005] The silsesquioxane structure is a structure with excellent heat resistance. Existing literature and patents have reported that silicone materials containing the silsesquioxane structure exhibit excellent heat resistance. For example, patent document US201615206423A describes a benzoxazine material containing the silsesquioxane structure. The 5% thermal weight loss temperature of this material after curing is as high as 500.1 °C, but this patent does not mention the specific adhesion performance and requires curing at a high temperature of 240 °C. Another patent document KR1020220171013 reports a silsesquioxane-modified highly heat-resistant polyimide-based adhesive resin with a 5% thermal weight loss temperature higher than 410 °C, and its adhesion to copper plates can reach 14.9 N / cm. However, the preparation processes of these materials are complex and the adhesion effects are not satisfactory, which limits their wide promotion in practical applications.

[0006] In addition, CN103788123A discloses a bifunctional benzoxazine resin containing double-tower silsesquioxane, its preparation method, and a resin composition containing the same. Through a hydrosilylation reaction, a double-silyl-hydrogen double-tower silsesquioxane is added to a benzoxazine compound having one benzoxazine unit in the molecular structure and one carbon-carbon double bond in the side chain to obtain a benzoxazine resin containing double-tower silsesquioxane. However, the preparation route of this patent is to prepare the product by hydrosilylation reaction of a hydrogen-terminated double-layer silsesquioxane and vinyl-containing benzoxazine, which has the defect that incomplete hydrosilylation reaction leads to residual silicon-hydrogen bonds damaging the high-temperature resistance performance.

[0007] In summary, although the above-mentioned many technical solutions have improved the heat resistance of adhesives to a certain extent, in terms of key core issues such as medium and low temperature curing performance, high heat resistance performance, and excellent adhesion performance, further improvement is still needed to meet more stringent application requirements. Summary of the Invention

[0008] In view of the above-mentioned status of the prior art, especially aiming at the defect that the preparation route using hydrosilylation reaction in the prior art easily leads to residual silicon-hydrogen bonds damaging the high-temperature resistance performance. The inventors of the present invention have conducted in-depth and extensive research in the field of heat-resistant silicone adhesives containing silsesquioxane, and found that using a double-layer silsesquioxane containing phenolic hydroxyl groups as the phenol source, aniline as the amine source, and reacting with aldehyde compounds through the Mannich reaction route can not only avoid the defect that the preparation route of hydrosilylation reaction easily leads to residual silicon-hydrogen bonds damaging the high-temperature resistance performance, but also improve the heat resistance of the obtained silicone adhesive and improve the adhesion performance at high temperatures. The present invention is completed based on the above discovery.

[0009] Therefore, an object of the present invention is to provide a method for preparing a temperature-resistant silicone adhesive starting from a phenolic hydroxyl-containing double-layer sesquisiloxane. This method has mild conditions, is easy to control, and has high synthesis efficiency.

[0010] The second object of the present invention is to provide the temperature-resistant silicone adhesive obtained by this preparation method and a temperature-resistant silicone adhesive composition containing this adhesive. The temperature-resistant silicone adhesive prepared by the present invention can be directly used as an adhesive with high bonding strength; it can also be used as a basic formulation and used as an adhesive after adding other fillers; it can also be used as a primer to meet different requirements in various special occasions.

[0011] The third object of the present invention is to provide a method for using the temperature-resistant silicone adhesive obtained by this preparation method.

[0012] The technical solutions for achieving the above-mentioned invention objects can be summarized as follows:

[0013] A method for preparing a temperature-resistant silicone adhesive starting from a phenolic hydroxyl-containing double-layer sesquisiloxane uses the phenolic hydroxyl-containing double-layer sesquisiloxane as the phenolic source, aniline as the amine source, and reacts with an aldehyde compound through the Mannich reaction to prepare a double-layer sesquisiloxane-based temperature-resistant silicone adhesive containing benzoxazine groups.

[0014] According to the present invention, preferably, the reaction is carried out under the condition of using a solvent, and the phenolic hydroxyl-containing double-layer sesquisiloxane is mixed with aniline and an aldehyde compound for reaction to obtain a double-layer sesquisiloxane-based temperature-resistant silicone adhesive containing benzoxazine groups.

[0015] According to the present invention, preferably, the solvent is toluene, tetrahydrofuran, chloroform, methanol, diphenyl ether, dimethyl sulfoxide, N,N-dimethylformamide, dioxane; more preferably, toluene, tetrahydrofuran, dioxane.

[0016] According to the present invention, preferably, the aldehyde compound is a small molecule aldehyde compound or a cyclic acetal; more preferably, the aldehyde compound is formaldehyde or trioxymethylene.

[0017] According to the present invention, preferably, the molar ratio of the phenolic hydroxyl-containing double-layer sesquisiloxane, aniline, and the aldehyde compound is 1:(0.1 - 10):(0.2 - 20), and further preferably 1:(2 - 10):(2 - 10).

[0018] According to the present invention, preferably, the reaction temperature of the phenolic hydroxyl-containing double-layer sesquisiloxane, aniline, and the aldehyde compound is 30 - 180 °C, and further preferably 40 - 80 °C.

[0019] According to the present invention, preferably, the reaction time of the phenolic hydroxyl group-containing double-layer sesquisiloxane, aniline and aldehyde compound is 1-24 h.

[0020] According to the present invention, there is also provided a temperature-resistant silicone adhesive composition based on a sesquisiloxane structure, comprising the following components in parts by mass:

[0021] 100 parts of the above temperature-resistant silicone adhesive, 0-10 parts of a catalyst, 0-400 parts of a filler, and 0-200 parts of an auxiliary agent.

[0022] According to the present invention, preferably, the catalyst is benzenesulfonic acid, acetic acid, sodium hydroxide or hexamethylenediamine. The amount of the catalyst used is preferably 1-3 parts.

[0023] According to the present invention, preferably, the filler is fumed silica, precipitated silica, carbon black, calcium carbonate, aluminum hydroxide or / and magnesium hydroxide, and various treated compounds thereof, more preferably silica treated with silazane. The amount of the filler used is preferably 1-200 parts, more preferably 2-30 parts.

[0024] According to the present invention, preferably, the auxiliary agent is a thermal oxygen stabilizer, a flame retardant, a conductive agent, a foaming agent, a deep curing agent, a pigment or / and a plasticizer, further preferably iron oxide red; the amount of the auxiliary agent used is preferably 1-10 parts.

[0025] According to the present invention, preferably, the temperature-resistant silicone adhesive composition based on a sesquisiloxane structure comprises the following components in parts by mass:

[0026] 100 parts of the above temperature-resistant silicone adhesive, 1-9 parts of a catalyst, 1-50 parts of a filler, and 1-20 parts of an auxiliary agent.

[0027] According to the present invention, preferably, the temperature-resistant silicone adhesive composition based on a sesquisiloxane structure comprises the following components in parts by mass:

[0028] 100 parts of the above temperature-resistant silicone adhesive, 2-5 parts of hexamethylenediamine, 3-10 parts of M-5 type silica treated with silazane, and 3-10 parts of silane coupling agent KH570.

[0029] According to the present invention, the usage method of the above temperature-resistant silicone adhesive containing benzoxazine group double-layer sesquisiloxane type comprises the following steps:

[0030] Directly used as an adhesive;

[0031] Or used in combination with a catalyst, a filler and an auxiliary agent added.

[0032] According to the present invention, preferably, when directly used as an adhesive, the double-layered silsesquioxane-based high-temperature-resistant silicone adhesive containing benzoxazine groups is directly coated and used.

[0033] According to the present invention, preferably, when used in combination with a catalyst, fillers, and additives, the double-layered silsesquioxane-based high-temperature-resistant silicone adhesive containing benzoxazine groups is used as a basic formulation, and a catalyst, fillers, and additives are added for compounding and mixed evenly; then the mixture is placed at the bonding interface, and good bonding is achieved through programmed temperature rise.

[0034] According to the present invention, preferably, the programmed temperature rise is a heating process from an initial temperature to a final temperature with a temperature difference as a gradient through a "heating - constant temperature" cycle. The temperature difference is any temperature difference between 5°C and 100°C. In the "heating - constant temperature" cycle, the heating rate is any heating rate between 0.1°C / min and 20°C / min; in the "heating - constant temperature" cycle, the constant temperature time is any time between 1 minute and 180 minutes.

[0035] The beneficial effects of the present invention are as follows:

[0036] 1. The reaction route of the present invention abandons the route of preparing products by hydrosilylation reaction of hydrogen-terminated double-layered silsesquioxane and vinyl-containing benzoxazine in the prior art, avoiding the damage to the high-temperature resistance performance caused by incomplete hydrosilylation reaction and residual silicon-hydrogen bonds. The reaction route of the present invention ingeniously combines the double-layered silsesquioxane and benzoxazine together, utilizes the high-temperature resistance performance of silsesquioxane, and combines the characteristics of no volume shrinkage during the curing ring-opening process of benzoxazine groups and the generation of phenolic hydroxyl groups during the curing process, thereby realizing the preparation of a high-temperature-resistant adhesive with high bonding strength, which is particularly suitable for bonding requirements in high-temperature environments.

[0037] 2. The synthesis process of the double-layered silsesquioxane-based high-temperature-resistant silicone adhesive containing benzoxazine groups of the present invention is simple, easy to operate, and suitable for large-scale production. The core of this adhesive is the silsesquioxane structure in the molecular center, which is bridged by silicon-oxygen bonds from two cyclotetrasiloxanes, showing extremely high structural stability. The eight phenyl groups connected to the silicon atoms in the double-layered silsesquioxane further enhance the rigidity of the structure, significantly improving the high-temperature resistance performance of the adhesive. It has wide adaptability and a large application range, not only expanding its usage conditions but also improving its practical value.

[0038] 3. The double-layered silsesquioxane-based high-temperature-resistant silicone adhesive containing benzoxazine groups of the present invention can be directly used as an adhesive, can also be used as a primer, or can be used as an adhesive after compounding with other substances, and has various usage methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The infrared spectrum of the silicone adhesive prepared in Example 1.

[0040] Figure 2 The NMR spectrum of the silicone adhesive prepared in Example 4.

[0041] Figure 3 The DSC graph of the silicone adhesive prepared in Example 1.

[0042] Figure 4 The thermogravimetric graph of the silicone adhesive after bonding and curing prepared in Example 1. Detailed implementation manners

[0043] The present invention provides a heat-resistant silicone adhesive prepared starting from a phenolic hydroxyl group-containing double-layered silsesquioxane and its usage method. Using the phenolic hydroxyl group-containing double-layered silsesquioxane as the phenol source, aniline as the amine source, and reacting with an aldehyde compound through the Mannich reaction to prepare a heat-resistant silicone adhesive of double-layered silsesquioxane type containing benzoxazine groups; the prepared heat-resistant silicone adhesive can be directly used as an adhesive, can also be used as a primer, and can also be used as a basic formulation and used as an adhesive after adding other fillers to meet the bonding requirements of various special occasions.

[0044] The corresponding reaction equation for preparing the heat-resistant silicone adhesive of double-layered silsesquioxane type containing benzoxazine groups in the present invention is as follows:

[0045]

[0046] The method for preparing a heat-resistant silicone adhesive starting from a phenolic hydroxyl group-containing double-layered silsesquioxane in the present invention uses the phenolic hydroxyl group-containing double-layered silsesquioxane as the phenol source, aniline as the amine source, and reacts with an aldehyde compound through the Mannich reaction to prepare a heat-resistant silicone adhesive of double-layered silsesquioxane type containing benzoxazine groups.

[0047] In one or more preferred embodiments, the reaction is carried out under the condition of using a solvent. The phenolic hydroxyl group-containing double-layered silsesquioxane is mixed with aniline and an aldehyde compound for reaction to prepare a heat-resistant silicone adhesive of double-layered silsesquioxane type containing benzoxazine groups.

[0048] According to the present invention, the solvent is various polar or non-polar solvents that can dissolve the reactants and do not react chemically with the reactants; in one or more preferred embodiments, the solvent is toluene, tetrahydrofuran, chloroform, methanol, diphenyl ether, dimethyl sulfoxide, N,N-dimethylformamide, dioxane; more preferably, toluene, tetrahydrofuran, dioxane.

[0049] According to the present invention, the aldehyde compound is various aldehyde organic compounds that can dissolve in this system; in one or more preferred embodiments, the aldehyde compound is a small molecule aldehyde compound or a cyclic acetal; more preferably, the aldehyde compound is formaldehyde or trioxane.

[0050] According to the present invention, the double-decker silsesquioxane containing phenolic hydroxyl groups has the following structure:

[0051]

[0052] This compound is prepared from hydrogen-terminated double-decker silsesquioxane and eugenol as raw materials (see the paper "Preparation, characterization, and properties of poly(aryl ether sulfone) systems with double-decker silsesquioxane in the main chains by reactive blending", Journal of Polymer Science Part A: Polymer Chemistry, 2014, 52(6): 780-788).

[0053] In one or more preferred embodiments, the molar ratio of the double-decker silsesquioxane containing phenolic hydroxyl groups, aniline, and the aldehyde compound is 1:(0.1-10):(0.2-20), preferably 1:(2-10):(2-10).

[0054] In one or more preferred embodiments, the reaction temperature of the double-decker silsesquioxane containing phenolic hydroxyl groups, aniline, and the aldehyde compound is 30-180°C, preferably 40-80°C.

[0055] In one or more preferred embodiments, the reaction time of the double-decker silsesquioxane containing phenolic hydroxyl groups, aniline, and the aldehyde compound is 1-24 h.

[0056] According to the present invention, a temperature-resistant silicone adhesive composition based on a silsesquioxane structure is also provided, which includes the following components in parts by mass:

[0057] 100 parts of the above temperature-resistant silicone adhesive, 0-10 parts of a catalyst, 0-400 parts of a filler, and 0-200 parts of an auxiliary agent.

[0058] According to the present invention, the use of a catalyst can accelerate the ring-opening crosslinking of benzoxazine groups, reduce the reaction temperature and shorten the reaction time. Both generalized Lewis acids and generalized Lewis bases can promote this ring-opening process. In one or more preferred embodiments, the catalyst is benzenesulfonic acid, acetic acid, sodium hydroxide, and hexamethylenediamine. Excessive use of the catalyst will cause the crosslinking reaction to be too fast, resulting in internal defects in the adhesive system. Therefore, the amount of the catalyst added should not be excessive. The amount of the catalyst used is preferably 1-3 parts.

[0059] According to the present invention, the filler is various additives used to improve the performance of this type of adhesive; in one or more preferred embodiments, the filler is fumed silica, precipitated silica, carbon black, calcium carbonate, aluminum hydroxide, and / or magnesium hydroxide, as well as various treated compounds thereof, more preferably silica treated with silazane. The amount of the filler used is preferably 1-200 parts, more preferably 2-30 parts.

[0060] According to the present invention, the auxiliary agent is various auxiliary agents that do not significantly reduce the performance of the high-temperature-resistant adhesive after being added, including various functional components and non-functional components; in one or more preferred embodiments, the auxiliary agent is a thermal-oxidative stabilizer, a flame retardant, a conductive agent, a foaming agent, a deep-curing agent, a pigment, and / or a plasticizer, preferably iron oxide red; the amount of the auxiliary agent used is preferably 1-10 parts.

[0061] According to the present invention, preferably, the high-temperature-resistant organosilicon adhesive composition based on the silsesquioxane structure comprises the following components in parts by mass:

[0062] 100 parts of the above-mentioned high-temperature-resistant organosilicon adhesive, 1-9 parts of the catalyst, 1-50 parts of the filler, and 1-20 parts of the auxiliary agent.

[0063] In one or more preferred embodiments, the high-temperature-resistant organosilicon adhesive composition based on the silsesquioxane structure comprises the following components in parts by mass:

[0064] 100 parts of the above-mentioned high-temperature-resistant organosilicon adhesive, 2-5 parts of hexamethylenediamine, 3-10 parts of M-5 type silica treated with silazane, and 3-10 parts of silane coupling agent KH570.

[0065] According to the present invention, the method for using the above-mentioned high-temperature-resistant organosilicon adhesive of the double-layer silsesquioxane type containing benzoxazine groups comprises the following steps:

[0066] Directly used as an adhesive;

[0067] Or used in combination with a catalyst, a filler, and an auxiliary agent.

[0068] The double-layered silsesquioxane-based high-temperature resistant silicone adhesive containing benzoxazine groups prepared by the present invention can be directly used as an adhesive. However, the performance of this type of adhesive is greatly affected by the silsesquioxane structure and can only achieve bonding in specific situations. By compounding it with various additives (including various fillers and auxiliaries), the comprehensive performance of the adhesive can be greatly improved, thus meeting the bonding requirements in various situations.

[0069] In one or more preferred embodiments, when directly used as an adhesive, the double-layered silsesquioxane-based high-temperature resistant silicone adhesive containing benzoxazine groups is directly applied by coating.

[0070] In one or more preferred embodiments, when used in combination with a catalyst, fillers, and auxiliaries, the double-layered silsesquioxane-based high-temperature resistant silicone adhesive containing benzoxazine groups is used as the basic formulation, and a catalyst, fillers, and auxiliaries are added for compounding and mixed evenly; then the mixture is placed at the bonding interface, and good bonding is achieved through programmed temperature increase.

[0071] According to the present invention, using various fillers, especially reinforcing fillers, can preferably improve the mechanical properties of such adhesives. Since the raw material double-layered silsesquioxane used in the present invention contains both phenyl groups and silicon-oxygen bonds, it can exhibit the characteristics of fast powder absorption, good compatibility, and high reinforcing efficiency for various inorganic fillers and organic polar fillers. To further improve the performance of the adhesive during use at high temperatures, the present invention further preferably uses silica treated with phenyl group-containing compounds for reinforcement to slow down the softening and thermal degradation phenomena during use at high temperatures.

[0072] According to the present invention, adding various auxiliaries can further improve its performance and expand its applications, such as heat-oxygen stabilizers, flame retardants, conductive agents, foaming agents, deep curing agents, pigments, plasticizers, etc. Some auxiliaries can play multiple roles. For example, iron oxide red can simultaneously act as a heat-oxygen stabilizer, a pigment, and a reinforcing filler. Adding special polymers can improve the wetting performance of such adhesives with specific interfaces. Adding special coupling agents can improve the adhesion performance of such adhesives with special interfaces. In short, by changing the dosage of auxiliaries and using multiple auxiliaries together, high-performance adhesives that meet the needs of various situations can be prepared, with broad application prospects and good market prospects.

[0073] According to the present invention, the programmed temperature rise is a temperature rise process from an initial temperature to a termination temperature via multiple "temperature rise - constant temperature" cycles with a certain temperature difference as the gradient. Among them, the temperature difference is a temperature gradient that is allowed in the bonding situation and can be controlled under conditions; in one or more preferred embodiments, the temperature difference is any temperature difference between 5°C and 100°C, preferably 10°C; in one or more preferred embodiments, in the "temperature rise - constant temperature" cycle, the heating rate is any heating rate between 0.1°C / min and 20°C / min, preferably 10°C / min; in one or more preferred embodiments, in the "temperature rise - constant temperature" cycle, the constant temperature time is any time between 1 minute and 180 minutes, preferably any time between 30 minutes and 120 minutes, more preferably 60 minutes. The initial temperature is any temperature between room temperature and the termination temperature, preferably 100°C; the termination temperature is a temperature that is allowed in the bonding situation and can achieve the best bonding performance of the adhesive in this bonding situation, including a certain optimal bonding temperature obtained through actual tests between 100°C and 200°C.

[0074] For those not elaborated in the present invention, they shall follow the prior art.

[0075] Principle of the present invention:

[0076] The reaction route of the present invention abandons the route reported in the previous literature (Patent CN103788123A) of preparing products by hydrosilylation reaction of hydrogen - terminated double - layer - structured silsesquioxane and vinyl - containing benzoxazine, which can avoid the damage to the high - temperature resistance performance caused by incomplete hydrosilylation reaction resulting in residual silicon - hydrogen bonds. The reaction route of the present invention cleverly combines double - layer - structured silsesquioxane and benzoxazine together. By utilizing the high - temperature resistance performance of silsesquioxane and combining the characteristics of no volume shrinkage during the curing ring - opening process of benzoxazine groups and the generation of phenolic hydroxyl groups during the curing process, the preparation of a high - bonding - strength high - temperature - resistant adhesive is realized, which is particularly suitable for the bonding requirements in high - temperature environments.

[0077] The high - temperature - resistant organosilicon adhesive of double - layer silsesquioxane type containing benzoxazine groups synthesized by the present invention has a simple synthesis process, is easy to operate, and is suitable for large - scale production. The core of this adhesive is the silsesquioxane structure in the molecular center, which is bridged by siloxane bonds from two cyclotetrasiloxanes, showing extremely high structural stability. The eight phenyl groups connected to the silicon atoms in the double - layer - structured silsesquioxane further enhance the rigidity of the structure, significantly improving the high - temperature resistance performance of the adhesive. In addition, the special structural design enables this adhesive to cure under medium - and low - temperature conditions (the initial temperature for ring - opening curing is 123°C, see the appendix Figure 3), significantly lower than the curing temperature of traditional heat-resistant silicone resins (the curing temperature is above 150 °C, see the paper "Synthesis of High-Temperature-Resistant Organosilicon Resins and Their Heat Resistance and Curing Properties", Journal of Aeronautical Materials, 2005, 25(01): 25-29), with wide adaptability and a large application range. This not only innovatively expands its usage conditions but also improves its practical value.

[0078] The heat-resistant organosilicon adhesive of double-layered silsesquioxane type containing benzoxazine groups synthesized in the present invention can be directly used as an adhesive, can also be used as a primer, or can be used as an adhesive after being compounded with other substances. Since this type of adhesive contains benzoxazine groups, which have the advantage of zero volume shrinkage during ring-opening copolymerization, such adhesives are mainly crosslinked through the ring-opening copolymerization of benzoxazine groups. The ring-opening process of benzoxazine groups can generally be achieved by heating. To ensure that the adhesive has good adhesive properties, a programmed temperature increase method is generally used to gradually increase the temperature to achieve crosslinking.

[0079] The following further illustrates the present invention through specific examples, but is not limited thereto.

[0080] The raw materials used in the examples are all conventional commercially available raw materials or are synthesized according to the methods in the reference documents.

[0081] The molar ratio described in the examples is the ratio of the amount of substance, and the parts ratio described is the mass ratio.

[0082] Example 1

[0083] Using dioxane as a solvent, the double-layer silsesquioxane with terminal phenolic hydroxyl groups, paraformaldehyde, and aniline were mixed in a molar ratio of 1:4:2, and the temperature was raised to 80 °C and reacted for 6 h. After purification, a heat-resistant organosilicon adhesive of double-layered silsesquioxane type containing benzoxazine groups was obtained, and the reaction yield reached 81.3%. The infrared spectrum is as Figure 1 shown, and the signal peaks of the benzoxazine ring appear at 1498, 1232, and 937 cm -1 −1. The NMR data are as follows: 1H NMR (ppm, CDCl 3 3): 0.31 (s, 6H, Si-C H 3 ), 0.78 (t, 4H, SiC H 2 H 2 C 2 H 2 -), 1.74 (sext, 4H, SiCH H 2 2 2 C 2CH 2 C H 2 -), 3.88 (s, 6H, C H 3 -O), 4.54 (s, 4H, Ar-C H 2 -N), 5.44 (s, 4H, O-C H 2 -N), 6.30 - 6.50 (m, 4H, Ar H of BZ), 6.60 - 6.90 (m, 10H, Ar H ), 7.00 - 7.60 (m, 40H, Ar H of Si-Ph). The DSC diagram is as Figure 3 shown.

[0084] Example 2

[0085] Using dioxane as the solvent, the double-layered silsesquioxane with terminal phenolic hydroxyl groups was mixed with paraformaldehyde and aniline in a molar ratio of 1:2:4, and the temperature was raised to 40 °C and reacted for 12 h. After purification, a double-layered silsesquioxane-based heat-resistant silicone adhesive containing benzoxazine groups was obtained.

[0086] Example 3

[0087] Using dioxane as the solvent, the double-layered silsesquioxane with terminal phenolic hydroxyl groups was mixed with paraformaldehyde and aniline in a molar ratio of 1:4:4, and the temperature was raised to 60 °C and reacted for 8 h. After purification, a double-layered silsesquioxane-based heat-resistant silicone adhesive containing benzoxazine groups was obtained.

[0088] Example 4

[0089] Using dioxane as the solvent, the double-layered silsesquioxane with terminal phenolic hydroxyl groups was mixed with trioxane and aniline in a molar ratio of 1:2:4, and the temperature was raised to 80 °C and reacted for 6 h. After purification, a double-layered silsesquioxane-based heat-resistant silicone adhesive containing benzoxazine groups was obtained. The 1H NMR spectrum is as Figure 2 shown.

[0090] Example 5

[0091] Using tetrahydrofuran as the solvent, the double-layered silsesquioxane with terminal phenolic hydroxyl groups was mixed with aqueous formaldehyde solution and aniline in a molar ratio of 1:4:2, and the temperature was raised to 80 °C and reacted for 6 h. After purification, a double-layered silsesquioxane-based heat-resistant silicone adhesive containing benzoxazine groups was obtained.

[0092] Example 6

[0093] According to "Determination of Tensile Shear Strength of Adhesives (Rigid Material to Rigid Material)" (National Standard: GB / T 7124-2008), the double-layered silsesquioxane-based temperature-resistant silicone adhesive containing benzoxazine groups obtained in Example 1 was directly brush-coated on an iron plate with the dimensions specified in the national standard. Then, the two plates were overlapped, and the overlapped parts were thermally cured under certain conditions (the curing conditions were heating at 100 °C for 1 h, 110 °C for 1 h, 120 °C for 1 h, 130 °C for 1 h, 140 °C for 1 h, 150 °C for 1 h, 160 °C for 1 h, 170 °C for 1 h, 180 °C for 1 h, 190 °C for 1 h, 200 °C for 1 h). After curing, it was left for 1 day. Then, a tensile testing machine was used to measure its performance.

[0094] Example 7

[0095] According to "Determination of Tensile Shear Strength of Adhesives (Rigid Material to Rigid Material)" (National Standard: GB / T 7124-2008), a tetrahydrofuran solution of the double-layered silsesquioxane-based temperature-resistant silicone adhesive containing benzoxazine groups obtained in Example 1 was brush-coated on a polytetrafluoroethylene plate with the dimensions specified in the national standard. After the solvent evaporated, heat treatment was carried out under certain conditions (i.e., the thermal curing process of the adhesive, and the curing conditions were heating at 100 °C for 1 h, 110 °C for 1 h, 120 °C for 1 h, 130 °C for 1 h, 140 °C for 1 h, 150 °C for 1 h, 160 °C for 1 h, 170 °C for 1 h, 180 °C for 1 h, 190 °C for 1 h, 200 °C for 1 h). Subsequently, two polytetrafluoroethylene plates with a cured layer of silicone adhesive were bonded with a commercially available 502 adhesive. After the 502 adhesive cured, it was left for 1 day. Then, a tensile testing machine was used to measure its performance.

[0096] Example 8

[0097] Taking the double-layered silsesquioxane-based temperature-resistant silicone adhesive containing benzoxazine groups obtained in Example 1 as the basic formula, hexamethylenediamine (2 parts), M-5 type silica white treated with silazane (5 parts), and silane coupling agent KH570 (3 parts) were added for compounding and mixing evenly to obtain a temperature-resistant silicone adhesive composition based on the silsesquioxane structure. According to "Determination of Tensile Shear Strength of Adhesives (Rigid Material to Rigid Material)" (National Standard: GB / T 7124-2008), the mixture was evenly coated on a steel plate and thermally cured under certain conditions (the curing conditions were heating at 90 °C for 1 h, 100 °C for 1 h, 110 °C for 1 h, 120 °C for 1 h, 130 °C for 1 h), and then the steel plate bonding could be achieved. After curing, it was left for 1 day, and then a tensile testing machine was used to measure its performance.

[0098] Test Example 1

[0099] According to "Determination of Tensile Shear Strength of Adhesives (Rigid Material to Rigid Material)" (National Standard: GB / T 7124-2008), the bonding strength between the adhesive in Example 6 and the iron plate was tested, and the results are shown in Table 1.

[0100] Table 1 Bonding Strength under Different Test Environments

[0101]

[0102] *Note: The bonding data of Comparative Example 1, Comparative Example 2, and Comparative Example 3 are the bonding data of Example 5, Example 4, and Example 1 in the patent (Publication No.: CN117567978A), respectively.

[0103] As can be seen from Table 1, the strength of the double-layered silsesquioxane-based temperature-resistant silicone adhesive containing benzoxazine groups bonding to the iron plate in Example 6 of the present invention reached 1.40 MPa, which indicates that both the self-strength (cohesion) of the adhesive prepared in the present invention and the bonding strength between the adhesive and metallic iron reached 1.40 MPa. Compared with the adhesive containing benzoxazine groups reported in the literature (1.27 MPa), the adhesive of the present invention demonstrated significant advantages and improvements.

[0104] The DSC diagram of the silicone adhesive prepared in Test Example 1 is as Figure 3 shown. As can be Figure 3 seen, the initial curing temperature of the present invention is 123 °C, meeting the requirements of medium and low-temperature curing. At the same time, the present invention still has bonding performance at high temperatures, and the bonding strengths at 300 °C (1.25 MPa) and 350 °C (1.00 MPa) are good.

[0105] The thermogravimetric diagram of the silicone adhesive prepared in Test Example 1 after bonding and curing is as Figure 4 shown. As can be Figure 4 seen, the temperature-resistant silicone adhesive of the present invention has good high-temperature resistance, and the data are shown in Table 2.

[0106] Table 2 High-Temperature Resistance Performance Data

[0107]

[0108] **Note: Comparative Example 4 is the high-temperature resistance performance data of Example 6 in the patent (Publication No.: CN103788123A).

[0109] ***Note: Comparative Example 2 and Comparative Example 3 are the high-temperature resistance performance data of Example 4 and Example 1 in the patent (Publication No.: CN117567978A), respectively.

[0110] As can be seen from Table 2, the temperature (389 °C) at which the double-layer silsesquioxane-based heat-resistant silicone adhesive containing benzoxazine groups in Example 6 of the present invention has a 5% thermal weight loss is much higher than that of the adhesives containing benzoxazine groups mentioned in Table 1 (312 °C, 294 °C). At the same time, compared with the compound (Comparative Example 4) with a molecular structure similar to that of the present invention reported in the literature, the temperature (389 °C) at which the heat-resistant silicone adhesive of the present invention has a 5% thermal weight loss is higher than that of Comparative Example 4 (353 °C). At the same time, the char residue rate (75.1%) of the heat-resistant silicone adhesive of the present invention at 800 °C is higher than that of Comparative Example 4 (68.8%). This shows that even if the molecular structures of the target compounds are similar, the heat-resistant properties of the products obtained by different synthesis methods can vary greatly. Further comparative analysis shows that different synthesis methods will produce different impurities, and the heat-resistant properties of the material are closely related to the impurities in the system. When the heat-resistant properties of the impurities are poor, it will cause a significant decrease in the heat-resistant properties of the material. The data comparison in the above table shows that the technical route adopted in the present invention has significant advantages.

[0111] According to the existing literature records, there have been no other research reports on the adhesive properties of compounds with molecular structures similar to those of the silicone adhesives based on silsesquioxane structures prepared in the present invention. Combining the superiority of the present invention in the preparation process described above further demonstrates the creativity of the present invention.

Claims

1. A method for preparing a heat-resistant silicone adhesive from a double-layer silsesquioxane containing phenolic hydroxyl groups, characterized in that: The method uses a double-layer silsesquioxane containing phenolic hydroxyl groups as a phenol source, aniline as an amine source, and aldehyde compounds through a Mannich reaction to prepare a double-layer silsesquioxane type heat-resistant silicone adhesive containing benzoxazine groups.

2. The method for preparing a heat-resistant silicone adhesive from a double-layer silsesquioxane containing phenolic hydroxyl groups according to claim 1, characterized in that: The reaction is carried out under the condition of using a solvent, and the double-layer silsesquioxane containing phenolic hydroxyl groups is mixed with aniline and aldehyde compounds to react, so as to prepare a double-layer silsesquioxane type heat-resistant silicone adhesive containing benzoxazine groups; Preferably, the solvent is toluene, tetrahydrofuran, chloroform, methanol, diphenyl ether, dimethyl sulfoxide, N,N-dimethylformamide or dioxane; Preferably, the aldehyde compound is a small molecule aldehyde compound or a cyclic acetal.

3. The method for preparing a heat-resistant silicone adhesive from a double-layer silsesquioxane containing phenolic hydroxyl groups according to claim 1, characterized in that: The molar ratio of the double-layer silsesquioxane containing phenolic hydroxyl groups to the aniline and aldehyde compounds is 1:(0.1-10):(0.2-20).

4. The method for preparing a heat-resistant silicone adhesive from a double-layer silsesquioxane containing phenolic hydroxyl groups according to claim 1, characterized in that: The reaction temperature of the double-layer silsesquioxane containing phenolic hydroxyl group, aniline and aldehyde compound is 30-180°C.

5. A heat-resistant organosilicon adhesive composition based on a silsesquioxane structure, comprising a double-layer silsesquioxane-type heat-resistant organosilicon adhesive containing a benzoxazine group prepared by any one of claims 1 to 4, characterized in that: The composition comprises the following components in parts by weight: 100 parts of a double-layer silsesquioxane-type heat-resistant silicone adhesive containing a benzoxazine group, 0-10 parts of a catalyst, 0-400 parts of a filler, and 0-200 parts of an auxiliary agent.

6. The heat-resistant silicone adhesive composition based on the silsesquioxane structure according to claim 5, characterized in that: The catalyst is benzenesulfonic acid, acetic acid, sodium hydroxide or hexamethylenediamine, and the amount of the catalyst used is preferably 1-3 parts; Preferably, the filler is fumed silica, precipitated silica, carbon black, calcium carbonate, aluminum hydroxide and / or magnesium hydroxide and various treated compounds thereof; the amount of filler used is preferably 2-30 parts; Preferably, the auxiliary agent is a thermal oxygen stabilizer, a flame retardant, a conductive agent, a foaming agent, a deep curing agent, a pigment and / or a plasticizer; the auxiliary agent is preferably used in an amount of 1-10 parts.

7. The heat-resistant silicone adhesive composition based on a silsesquioxane structure according to claim 5, characterized in that: The composition comprises the following components in parts by weight: 100 parts of a double-layer silsesquioxane-type heat-resistant silicone adhesive containing a benzoxazine group, 2-5 parts of hexamethylenediamine, 3-10 parts of M-5 type white carbon black treated with silazane, and 3-10 parts of a silane coupling agent KH570.

8. A method for using the double-layer silsesquioxane-type heat-resistant silicone adhesive containing benzoxazine groups prepared according to any one of claims 1 to 4, comprising the following steps: Used directly as an adhesive; Or add catalysts, fillers and additives for use in combination.

9. The method of use according to claim 8, characterized in that: When used directly as an adhesive, a double-layer silsesquioxane-type heat-resistant silicone adhesive containing a benzoxazine group is directly applied and used; When a catalyst, filler and additive are added for use, a double-layer silsesquioxane-type heat-resistant silicone adhesive containing a benzoxazine group is used as a basic formula, and the catalyst, filler and additive are added for compounding and mixing evenly; the mixture is then placed at the bonding interface, and good bonding is achieved through programmed temperature increase.

10. The method of use according to claim 9, characterized in that: The programmed temperature rise is a temperature rise process that takes the temperature difference as the gradient, and gradually rises from the initial temperature to the final temperature through the "temperature rise-constant temperature" link. The temperature difference is any temperature difference between 5°C and 100°C. In the "temperature rise-constant temperature" link, the temperature rise rate is any temperature rise rate between 0.1°C / min and 20°C / min; in the "temperature rise-constant temperature" link, the constant temperature time is any time between 1 minute and 180 minutes.

Images