A high-toughness methyl silicone resin and a method for preparing the same

Abstract

The application provides a high-toughness methyl silicone resin and a preparation method thereof. The high-toughness methyl silicone resin comprises the following raw materials in parts by mass: 100 parts of methyltrimethoxysilane; 18-24 parts of dimethyldimethoxysilane; 10-12 parts of a polyhydroxy steric-modified agent; 20-26 parts of water; 36-44 parts of an organic solvent; 0.1-0.3 parts of a titanate catalyst; and 0.1-0.3 parts of an organic tin catalyst. The polyhydroxy steric-modified agent is a topological structure compound containing at least two active hydroxyl groups, which is prepared by an addition reaction of a multifunctional aliphatic polyol and an unsaturated bridged cyclic alicyclic compound under the catalysis of a Lewis acid, and the active hydroxyl group content of the topological structure compound is 3.5-4 mmol / g. The high-toughness methyl silicone resin is applied in the preparation of a flexible sealing material or a heat-resistant coating material for a heating pipe.

Description

Technical Field

[0001] This application relates to the field of organosilicon polymer materials technology, specifically to a high-toughness methylsilicone resin and its preparation method. Background Technology

[0002] Traditional methyl silicone resin is mainly formed by the hydrolysis and condensation of trifunctional siloxane monomers. It has an extremely high crosslinking density, and the cured methyl silicone resin exhibits a highly three-dimensional network structure. Although this structure brings high hardness and high heat resistance, it also leads to high internal stress, hard and brittle texture, and poor toughness. Under mechanical impact, bending, or thermal shock environments with alternating hot and cold temperatures, the chemical layer is prone to cracking and peeling, losing its sealing or protective function. It is difficult to meet the actual needs in applications such as flexible sealing of heating pipes and heat-resistant coating materials that require a certain degree of flexibility and thermal stability.

[0003] To improve the above-mentioned defects, the following methods are usually adopted:

[0004] Introducing difunctional monomers: linear segments such as dimethyldimethoxysilane are introduced through co-condensation; although this can reduce the crosslinking density to some extent, it is prone to depolymerization at high temperatures, resulting in a significant decrease in the heat resistance and mechanical strength of the material, and the toughening effect is limited.

[0005] Introducing phenyl-containing monomers: While the introduction of phenyl-containing monomers can indeed improve the brittleness of resins by increasing free volume, phenyl groups, as rigid planar side groups, lack the deformation buffering capacity of flexible chain segments. Their toughening mechanism is mainly based on hindering chain segment stacking rather than providing molecular chain flexibility. Therefore, they cannot fundamentally solve the problem of high internal stress and poor crack resistance in methyl silicone resins under high crosslinking density.

[0006] Organic resin modification: Physical blending or chemical modification using organic resins such as epoxy, acrylic or polyester; mainly relying on the physical plasticizing effect of long chains, while improving flexibility, it significantly sacrifices mechanical strength and resilience, making it difficult to meet the application requirements of heating pipe sealing for both high modulus and high toughness.

[0007] Therefore, there is an urgent need to develop a new type of methyl silicone resin material that combines high toughness and thermal stability to meet the needs of high-performance sealing and encapsulation applications. Summary of the Invention

[0008] This invention provides a high-toughness methyl silicone resin and its preparation method, which improves toughness and thermal shock resistance without sacrificing the original excellent heat resistance of methyl silicone resin.

[0009] In a first aspect, this application provides a high-toughness methyl silicone resin comprising the following raw materials in parts by weight: 100 parts methyltrimethoxysilane; 18-24 parts dimethyldimethoxysilane; 10-12 parts polyhydroxy steric hindrance modifier; 20-26 parts water; 36-44 parts organic solvent; 0.1-0.3 parts titanate catalyst; 0.1-0.3 parts organotin catalyst; wherein the polyhydroxy steric hindrance modifier is a topologically structured compound containing at least two active hydroxyl groups, obtained by addition reaction of a multifunctional aliphatic polyol with an unsaturated bridged alicyclic compound under Lewis acid catalysis, and the content of its active hydroxyl groups is 3.5-4 mmol / g.

[0010] According to this application, a polyhydroxy steric hindrance modifier is co-hydrolyzed and polycondensed with methyltrimethoxysilane and dimethyldimethoxysilane to construct a hybrid polysiloxane backbone with a specific topological structure, which is embedded in the main chain of the polysiloxane formed by methyltrimethoxysilane and dimethyldimethoxysilane. This endows the final cured high-toughness methylsiloxane resin with excellent heat resistance, high toughness and thermal shock resistance.

[0011] Specifically, through the co-condensation of the active hydroxyl groups in the polyhydroxyl steric hindrance modifier with methyltrimethoxysilane and dimethyldimethoxysilane, the polyhydroxyl steric hindrance modifier is embedded into the hybrid polysiloxane backbone mentioned above; the aliphatic polyol segments in the polyhydroxyl steric hindrance modifier serve as flexible segments, introducing elastic buffers to the brittle hybrid polysiloxane backbone and improving the elongation at break;

[0012] The three-dimensional cage-like topology of the unsaturated bridged alicyclic groups in the side groups of the polyhydroxy steric hindrance modifier generates a significant steric hindrance effect. This steric hindrance effect effectively inhibits the dense packing of the hybrid polysiloxane backbone during the curing process, thereby retaining a large free volume inside the finally formed cured high-toughness methyl silicone resin, thus reducing the volume curing shrinkage rate. In addition, this free volume promotes the relaxation and dissipation of internal stress during thermal cycling, endowing the cured high-toughness methyl silicone resin with excellent dimensional stability and thermal shock resistance.

[0013] Furthermore, the free volume refers to the microscopic gaps in the cured high-toughness methyl silicone resin that are not occupied by the atomic entities of the hybrid polysiloxane backbone and are available for the molecular chain segments to undergo thermal motion and conformational adjustment.

[0014] In some embodiments, the polyhydroxy steric hindrance modifier is prepared by the following method:

[0015] Multifunctional aliphatic polyols, Lewis acid catalysts, and polymerization inhibitors are mixed in an organic solvent, and then an unsaturated bridged alicyclic compound is added. The double bonds of the unsaturated bridged alicyclic compound undergo an addition reaction with the hydroxyl groups of the multifunctional aliphatic polyol to form a topologically linked compound with ether bonds, thus obtaining a multihydroxyl steric hindrance modifier.

[0016] The multifunctional aliphatic polyol includes at least one of bis(trimethylol)propane, bispentaerythritol, trimethylolpropane, and trimethylolethane; the unsaturated bridged alicyclic compound includes at least one of norbornene, 5-vinyl-2-norbornene, and ethylidene norbornene; the Lewis acid catalyst includes at least one of trifluoromethanesulfonic acid and montmorillonite; the polymerization inhibitor includes at least one of 2,6-di-tert-butyl-4-methylphenol and p-hydroxyanisole; and the organic solvent includes at least one of propylene glycol methyl ether acetate, xylene, and n-butyl acetate.

[0017] Through the above embodiments, a polyhydroxyl steric hindrance modifier with high steric hindrance effect is constructed by the addition reaction of the double bond of the unsaturated bridged alicyclic compound with the hydroxyl group of the multifunctional aliphatic polyol. Specifically, the introduction of the unsaturated bridged alicyclic skeleton forms a certain steric shielding protection for the active sites of the multifunctional aliphatic polyol, effectively isolating the sensitive bonding sites of the hybrid polysiloxane backbone from nucleophilic attacks. At the same time, the high steric hindrance effect enables the polyhydroxyl steric hindrance modifier to exhibit a controllable reaction rate when participating in subsequent crosslinking reactions.

[0018] Furthermore, the polyhydroxy steric hindrance modifier is prepared by the following method:

[0019] Mix 100 parts of multifunctional aliphatic polyol, 0.1-3 parts of Lewis acid catalyst, and 0.01-0.1 parts of polymerization inhibitor in 200-400 parts of organic solvent. Then, add 80-150 parts of unsaturated bridged alicyclic compound at a constant rate under conditions of 95-105℃ and 300-500rpm for 1-2 hours. Continue the reaction for 3-5 hours to obtain a polyhydroxy steric hindrance modifier.

[0020] By limiting the reaction parameters and material ratios as described above, while ensuring high conversion rate and product purity, side reactions and gelation are effectively suppressed, achieving a stable and controllable preparation process and the construction of a multi-hydroxyl steric hindrance modifier structure.

[0021] In some embodiments, the organic solvent includes at least one of ethanol, isopropanol, n-butanol, ethyl acetate, butyl acetate, and propylene glycol methyl ether acetate.

[0022] The above-described embodiments can effectively improve the compatibility of the reaction components, and can also control the reaction temperature and gradient evaporation rate by compounding organic solvents.

[0023] In some embodiments, the titanate catalyst includes at least one of tetrabutyl titanate and tetraisopropyl titanate; the organotin catalyst includes at least one of stannous octoate and dibutyltin dilaurate.

[0024] Through the above embodiments, titanate catalysts mainly promote alcoholysis condensation reactions, can gently initiate the hydrolysis of siloxane groups, and promote the prepolymerization of polyhydroxy steric hindrance modifiers and silane monomers in the early stage; organotin catalysts are highly efficient polycondensation catalysts; the synergy of the two can improve reaction efficiency, promote the improvement of the high-toughness methyl silicone resin network structure, and effectively avoid local gelation.

[0025] Secondly, this application provides a method for preparing a high-toughness methyl silicone resin, comprising:

[0026] S1: Provide raw materials for the high-toughness methyl silicone resin according to any embodiment of the first aspect;

[0027] S2: Methyltrimethoxysilane, a polyhydroxy steric hindrance modifier, and a titanate catalyst are mixed to allow the methoxy group of methyltrimethoxysilane to undergo an alcoholysis condensation reaction with the hydroxyl group of the polyhydroxy steric hindrance modifier, and the low molecular weight alcohol generated in the reaction is continuously removed to obtain a modified silane intermediate.

[0028] S3: The modified silane intermediate, dimethyldimethoxysilane, and organic solvent are mixed, and then 25%-45% (by weight) of an organic alcohol aqueous solution is added dropwise to allow the modified silane intermediate and dimethyldimethoxysilane to undergo a co-hydrolysis and polycondensation reaction to obtain a hybrid prepolymer; the organic alcohol includes at least one of isopropanol and n-butanol.

[0029] S4: An organotin catalyst is added to the hybrid prepolymer to cause the silanol groups in the hybrid prepolymer to undergo a polycondensation reaction, and a high-toughness methyl silicone resin is obtained after post-treatment.

[0030] Through the above implementation method, step S1 ensures that each functional raw material can play a full role in subsequent steps by scientifically selecting and proportioning the raw materials, thus laying the foundation for the preparation of high-toughness methyl silicone resin.

[0031] In step S2, methyltrimethoxysilane and a polyhydroxy steric hindrance modifier undergo an alcoholysis condensation reaction under the catalysis of a titanate catalyst. Because the polyhydroxy steric hindrance modifier has significant steric hindrance, direct hydrolysis and polycondensation cannot provide sufficient activation energy for its integration into the main chain. By utilizing an anhydrous alcoholysis condensation reaction, the active hydroxyl groups of the polyhydroxy steric hindrance modifier react with the methoxy groups of the silane to generate a modified silane intermediate. This fundamentally solves the problem of large steric hindrance molecules being unable to enter the dense methylsilicone resin network, ensuring that the polyhydroxy steric hindrance modifier is firmly bonded through chemical bonds rather than physical doping.

[0032] In step S3, the local instantaneous concentration of water dropped into the system is reduced by using a 25%-45% (by mass) organic alcohol aqueous solution, which slows down the conversion rate of titanate catalyst to TiO2, allowing it to still assist the modified silane intermediate in preliminary hydrolysis before complete deactivation. The modified silane intermediate, as a macromonomer containing active silane functional groups, is hydrolyzed in synergistic manner with dimethyldimethoxysilane. By converting the heterogeneous polyhydroxy steric hindrance modifier into a homogeneous silane precursor, the difference in hydrolysis rate between components is effectively eliminated, allowing each component to be more uniformly embedded in the methyl silicone resin backbone, thereby forming a hybrid prepolymer without phase separation defects.

[0033] In step S4, an organotin catalyst is introduced to exert its highly efficient catalytic effect on the silanol condensation reaction, thereby promoting the final preparation of high-toughness methyl silicone resin.

[0034] In summary, by adopting a phased and targeted catalytic strategy, explosive polymerization or premature gelation caused by excessive catalytic activity can be effectively avoided, thus keeping the reaction process stable and controllable.

[0035] Furthermore, the alcoholysis condensation reaction conditions in step S2 are: stirring rate of 300-500 rpm, temperature of 70-85℃, and reaction time of 1.5-3h.

[0036] The above implementation methods can effectively avoid the occurrence of side reactions while ensuring a suitable reaction rate.

[0037] Furthermore, the hydrolysis-condensation reaction conditions in step S3 are as follows: stirring speed of 300-500 rpm, temperature of 40-60℃, dropwise addition time of 25%-45% organic alcohol aqueous solution controlled at 30-60 min, and after dropwise addition, the reaction is kept at 60-70℃ for 2-4 h.

[0038] The above-described implementation methods enable more precise control over the hydrolysis-condensation process.

[0039] Furthermore, the polycondensation reaction conditions in step S4 are as follows: vacuum distillation is carried out at 55-65℃ and -0.09MPa to -0.08MPa until no obvious liquid distillation occurs; then a dehydrating agent is added, the stirring rate is 300-500rpm, the temperature is 85-95℃, and the reaction time is 1-2h; the post-treatment conditions are: a dehydrating agent is added, azeotropic dehydration is performed, and after dehydration, the solvent is removed by vacuum distillation or organic solvent is added to adjust the solid content of the system to 40-60% to obtain high-toughness methyl silicone resin;

[0040] The water-removing agent includes at least one of butyl acetate and propylene glycol methyl ether acetate;

[0041] The organic solvent includes at least one of isopropanol and n-butanol.

[0042] Through the above-described embodiments, pre-vacuum distillation avoids interference from organic solvents such as ethanol, isopropanol, n-butanol, and ethyl acetate with the binary azeotropic system formed by the dehydrating agent and water, allowing the residual silanol groups in the system to undergo more thorough dehydration and polycondensation at higher temperatures. Introducing at least one solvent selected from butyl acetate and propylene glycol methyl ether acetate as a dehydrating agent into the polycondensation reaction system promotes the continuous removal of water and alcohol byproducts generated during hydrolysis and polycondensation, allowing the dehydration and polycondensation reaction between silanol groups to proceed in the forward direction, thereby increasing the crosslinking rate and crosslinking density, and avoiding problems such as bubbles, pores, or incomplete crosslinking caused by the retention of water and alcohol byproducts. Furthermore, the dilution effect of the dehydrating agent and the constant reflux temperature effectively suppress the easy occurrence of local overheating and explosive self-accelerated polymerization. Combined with the vacuum concentration after dehydration or the adjustment method of adding alcohol solvents such as isopropanol and n-butanol, a high-toughness methyl silicone resin existing in the form of a highly stable resin solution is obtained, effectively ensuring the uniformity of film formation on complex substrate surfaces.

[0043] Thirdly, this application provides an application of the high-toughness methyl silicone resin according to the first aspect or the high-toughness methyl silicone resin prepared according to the method of the second aspect in a flexible sealing material or heat-resistant coating material for heating pipes.

[0044] Compared with the prior art, the beneficial effects of this application are at least as follows:

[0045] This application introduces a polyhydroxy steric hindrance modifier and embeds it into the polysiloxane backbone of a high-toughness methyl silicone resin under alcoholysis condensation reaction conditions. The steric hindrance effect generated by the three-dimensional cage-like topology of the side groups of the polyhydroxy steric hindrance modifier effectively inhibits the dense stacking of the polysiloxane backbone during the curing process, retaining a large free volume. This free volume not only reduces the volume curing shrinkage rate and improves dimensional stability, but also promotes the relaxation and dissipation of internal stress during thermal cycling, thereby improving thermal shock resistance. The resulting high-toughness methyl silicone resin has excellent heat resistance, toughness, and thermal shock resistance, significantly improving the reliability of flexible sealing materials and heat-resistant coating conditions under high-temperature and complex working conditions such as heating pipes and heat exchange systems. Detailed Implementation

[0046] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0047] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0048] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0049] In this specification, unless otherwise specified, "parts" refers to "parts by weight".

[0050] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0051] Preparation Example

[0052] Preparation of polyhydroxy steric hindrance modifiers:

[0053] 100 parts of bis(trimethylol)propane, 0.2 parts of trifluoromethanesulfonic acid, and 0.05 parts of 2,6-di-tert-butyl-4-methylphenol were mixed in 300 parts of xylene. Then, 100 parts of norbornene were added uniformly at 100℃ and 400 rpm for 2 hours. The reaction continued for 4 hours. A saturated ammonium bicarbonate solution was added dropwise to adjust the pH to 7. The mixture was allowed to stand and separated. The organic phase was filtered through a 0.45 μm filter and then subjected to gradual vacuum distillation at 55℃ and -0.08 MPa. Further vacuum distillation was then carried out at 85℃ and -0.09 MPa to obtain a polyhydroxy sterically hindered modifier. The active hydroxyl content was determined to be approximately 3.76 mmol / g by the acetic anhydride-pyridine reflux method.

[0054] Example 1

[0055] Used in the preparation of a high-toughness methyl silicone resin:

[0056] S1: Provides 100 parts methyltrimethoxysilane; 20 parts dimethyldimethoxysilane; 11 parts polyhydroxy steric hindrance modifier; 24 parts water; 40 parts isopropanol; 0.15 parts tetrabutyl titanate; 0.15 parts stannous octoate;

[0057] S2: Methyltrimethoxysilane, polyhydroxy steric hindrance modifier, and tetrabutyl titanate were mixed and heated to 75°C under stirring at 400 rpm for 2.5 h to obtain a modified silane intermediate.

[0058] S3: Mix the modified silane intermediate, dimethyldimethoxysilane, and isopropanol, heat to 50°C while stirring at 400 rpm, add 30% isopropanol aqueous solution dropwise at a uniform rate for 40 min, and then keep the mixture at 65°C for 3 h to obtain the hybrid prepolymer.

[0059] S4: Add stannous octoate to the hybrid prepolymer, then add 40 parts of butyl acetate, and react for 1.5 h at 400 rpm and 90 °C; perform vacuum distillation at 60 °C and -0.09 MPa until no obvious liquid distills off; then add 50 parts of butyl acetate, and perform azeotropic dehydration until the distillation temperature stabilizes at the boiling point of butyl acetate; then remove the solvent at 70 °C and -0.095 MPa until the solid content of the system is 50%, to obtain high-toughness methyl silicone resin;

[0060] The obtained high-toughness methyl silicone resin is a stable high-toughness methyl silicone resin prepolymer solution. During the application process, the prepolymer first achieves preliminary film formation through solvent evaporation. Then, under the action of the organotin catalyst remaining in the system, the silanol groups are further dehydrated and polycondensed through high-temperature treatment, and finally a highly cross-linked cured network structure is constructed.

[0061] Comparative Example 1

[0062] Preparation of a methyl silicone resin:

[0063] It is largely the same as Example 1, except that 11 parts of the polyhydroxy steric hindrance modifier were not added.

[0064] Comparative Example 2

[0065] The process is largely the same as in Example 1, except that 11 parts of the polyhydroxy steric hindrance modifier are replaced with 2.59 parts of bis(trimethylolpropane) (which is equivalent to the molar amount of active hydroxyl groups in the polyhydroxy steric hindrance modifier in Example 1).

[0066] Comparative Example 3

[0067] The results are largely the same as in Example 1, except that 11 parts of the polyhydroxy steric hindrance modifier are replaced with 2.44 parts of 1,6-hexanediol (which is equivalent to the molar amount of active hydroxyl groups in the polyhydroxy steric hindrance modifier in Example 1).

[0068] Comparative Example 4

[0069] Preparation of a high-toughness methyl silicone resin by direct co-hydrolysis and polycondensation:

[0070] S1: Same as S1 in Example 1;

[0071] S2: Methyltrimethoxysilane, dimethyldimethoxysilane, polyhydroxy steric hindrance modifier, isopropanol, and tetrabutyl titanate were mixed and heated to 75°C under stirring at 400 rpm for 2.5 h; then 30% isopropanol aqueous solution was added dropwise at a uniform rate for 40 min. After the addition was complete, the mixture was kept at 65°C for 3 h to obtain the hybrid prepolymer.

[0072] S3: Same as S4 in Example 1.

[0073] Comparative Example 5

[0074] The results are largely the same as in Example 1, except that 11 parts of the polyhydroxy steric hindrance modifier are replaced with 7.25 parts of bisphenol fluorene (which is equivalent to the molar amount of active hydroxyl groups in the polyhydroxy steric hindrance modifier in Example 1).

[0075] Comparative Example 6

[0076] The results are largely the same as in Example 1, except that 11 parts of the polyhydroxy steric hindrance modifier are replaced with 19.64 parts of 1,2-propanediol isobutyl-POSS (which is equivalent to the molar amount of active hydroxyl groups in the polyhydroxy steric hindrance modifier in Example 1).

[0077] Test section

[0078] Testing of flexible sealing materials for heating pipes:

[0079] An annular gasket (3.0 mm thick) made of high-toughness methyl silicone resin was placed between two flat steel plates. A 25% compressive strain was applied at 200°C, and the load was removed after 24 hours of holding at that temperature. After cooling to room temperature and standing for 30 minutes, the recovered thickness was measured. The compressive permanent deformation rate (Cs) was calculated according to the following formula:

[0080]

[0081] t0: Initial thickness of the gasket before the test;

[0082] t r Thickness under compression;

[0083] t n The thickness recovered after unloading and cooling;

[0084] Used for testing the flexibility of heat-resistant coating materials:

[0085] Sample preparation:

[0086] High-toughness methyl silicone resin was diluted with isopropanol and its application viscosity was adjusted to 20s (Ford-4 cup, 25℃). It was then uniformly applied to the outer surface of a sandblasted and cleaned 304 stainless steel heating pipe by spraying, with the dry film thickness controlled to be 100μm. The coated pipe was then heat-aged at 200℃ for 48 hours and cooled to room temperature to obtain the sample.

[0087] Flexibility test:

[0088] The flexibility of the samples was tested using the mandrel bending method. The mandrel diameter was gradually reduced, and the minimum non-cracking mandrel diameter D for which the coating did not crack was recorded.

[0089] Thermal shock cycling test:

[0090] Place the sample in a low-temperature test chamber at a cooling rate of 8℃ / min, and hold it at -55℃ for 30 minutes. Remove the sample and quickly transfer it to a high-temperature test chamber at a heating rate of 8℃ / min, and hold it at 200℃ for 30 minutes. Repeat this cycle and record the number of times the sample cracks or peels off.

[0091] The test results are shown in Table 1:

[0092] Table 1

[0093]

[0094] As shown in Table 1, the compression set Cs and minimum non-cracking mandrel diameter D of the high-toughness methyl silicone resin prepared in Example 1 are smaller than those of the comparative example, but larger than those of the comparative example in thermal shock cycle test. The reason may be that the crosslinking density of the pure methyl silicone resin system in Comparative Example 1 is extremely high, forming a rigid and brittle network structure after curing. Under high temperature compression, the rigid network lacks flexibility and is prone to fracture or plastic deformation. Moreover, due to the extremely small number of free bodies inside, the chain segments cannot undergo effective conformational adjustment and stress relaxation, resulting in severe stress concentration under alternating hot and cold thermal shock environments.

[0095] In Comparative Example 2, although bis(trimethylol)propane provides the organic framework, it has four highly active hydroxyl groups, which actually act as a strong crosslinking agent. This further increases the crosslinking density of the system, making the methyl silicone resin network too dense and lacking stress relaxation space. The high crosslinking density leads to a reduction in the free volume inside the material, restricting the conformational adjustment and rotation of molecular chain segments, making it difficult to release or dissipate stress.

[0096] In Comparative Example 3, 1,6-hexanediol is a linear flexible molecule; the flexible long chain does improve bending performance; however, due to the lack of side group steric hindrance, the linear molecular chain is prone to slippage and creep under high temperature and pressure; and it is mainly embedded in the siloxane network in a linear manner, making it difficult to form an effective spatial shielding effect or provide additional free volume. Therefore, the interaction between molecular chain segments is weak when under stress, which easily leads to stress concentration and structural relaxation.

[0097] In Comparative Example 4, a direct co-hydrolysis polycondensation method was used, in which the hydrolysis polycondensation rate of small molecule silane was much faster than the reaction rate of the sterically hindered chain extender. This resulted in the polyhydroxy steric hindrance modifier failing to effectively enter the main network of methyl silicone resin, and it mostly existed in the form of physical doping or local self-polymerization. The overall cross-linking structure of the system lacked the synergistic effect of steric hindrance buffer and flexible chain segments, and the material still exhibited a high cross-linking density and limited free volume.

[0098] In Comparative Example 5, bisphenol fluorene contains a rigid caldo ring structure with high steric hindrance and strong rigidity, thus exhibiting good resistance to compression deformation. However, due to the lack of sufficient aliphatic flexible segments, the rigid skeleton of bisphenol fluorene mainly provides structural support and compressive stability in the siloxane network, but it is difficult to provide segment extensibility and stress dissipation channels during the stress process.

[0099] The core of the 1,2-propanediol isobutyl-POSS cage-like silsesquioxane used in Comparative Example 6 is an inorganic siloxane skeleton with extremely high rigidity. Moreover, its cage-like structure itself lacks the necessary intramolecular rotational freedom, which limits its stress dissipation ability under stress deformation. Although the POSS structure can improve the thermal stability and dimensional stability of the material to a certain extent, its excessive rigidity makes it difficult for the system to achieve flexible stretching and stress relaxation of the chain segments under high temperature compression and bending conditions.

[0100] The high-toughness methyl silicone resin prepared in Example 1 was tested according to the sample preparation method for testing the flexibility of heat-resistant coating materials and achieved a V-0 level after vertical burning rating test according to GB / T 2408-2008.

[0101] The high-toughness methyl silicone resin prepared in Example 1 was subjected to 100 thermal shock cycles according to the sample preparation method for testing the flexibility of heat-resistant coating materials, and then the flexibility was tested by the mandrel bending method. The minimum non-cracked mandrel diameter D' for coating without cracks was recorded as 3.8 mm.

[0102] In addition, the density change of the high-toughness methyl silicone resin before and after curing was measured separately;

[0103] Test procedure: Measure the density ρ of high-toughness methyl silicone resin at 25℃ using a precision densitometer. l Then, based on the sample preparation method used for testing the flexibility of heat-resistant coating materials, the density ρ of the sample at 25℃ was measured. s According to the formula:

[0104] S v ×100%

[0105] Calculate the volumetric curing shrinkage rate S v S in Example 1 v It was 1.62%, compared to S in comparative examples 1-6. v The percentages were 5.84%, 4.92%, 3.15%, 3.88%, 2.55%, and 2.18%, respectively; this result strongly supports the argument that "the three-dimensional cage-like topology produces a significant spatial steric hindrance effect".

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A high-toughness methyl silicone resin, characterized in that, The raw materials include the following parts by weight: 100 parts methyltrimethoxysilane; 18-24 parts dimethyldimethoxysilane; 10-12 parts of a polyhydroxy steric hindrance modifier; 20-26 parts of water; 36-44 parts of organic solvent; 0.1-0.3 parts of titanate catalyst; 0.1-0.3 parts of organotin catalyst; wherein the polyhydroxy steric hindrance modifier is a topologically structured compound containing at least two active hydroxyl groups, prepared by addition reaction of a multifunctional aliphatic polyol with an unsaturated bridged alicyclic compound under Lewis acid catalysis, and the content of active hydroxyl groups is 3.5-4 mmol / g; The polyhydroxy steric hindrance modifier was prepared by the following method: A multifunctional aliphatic polyol, a Lewis acid catalyst, and a polymerization inhibitor are mixed in a first organic solvent, and then an unsaturated bridged alicyclic compound is added. The double bond of the unsaturated bridged alicyclic compound reacts with the hydroxyl group of the multifunctional aliphatic polyol to form a compound with a topological structure linked by ether bonds, thus obtaining a multihydroxyl steric hindrance modifier. The multifunctional aliphatic polyol includes at least one of bis(trimethylol)propane, bispentaerythritol, trimethylolpropane, and trimethylolethane; the unsaturated bridged alicyclic compound includes at least one of norbornene, 5-vinyl-2-norbornene, and ethylidene norbornene. The high-toughness methyl silicone resin includes the following preparation steps: S1: Provides raw materials for high-toughness methyl silicone resin; S2: Methyltrimethoxysilane, a polyhydroxy steric hindrance modifier, and a titanate catalyst are mixed to allow the methoxy group of methyltrimethoxysilane to undergo an alcoholysis condensation reaction with the hydroxyl group of the polyhydroxy steric hindrance modifier, and the low molecular weight alcohol generated in the reaction is continuously removed to obtain a modified silane intermediate. S3: The modified silane intermediate, dimethyldimethoxysilane, and a second organic solvent are mixed, and then 25%-45% (by weight) of an organic alcohol aqueous solution is added dropwise to allow the modified silane intermediate and dimethyldimethoxysilane to undergo a co-hydrolysis and polycondensation reaction to obtain a hybrid prepolymer; the organic alcohol includes isopropanol and n-butanol; S4: An organotin catalyst is added to the hybrid prepolymer to cause the silanol groups in the hybrid prepolymer to undergo a polycondensation reaction, and a high-toughness methyl silicone resin is obtained after post-treatment.

2. The high-toughness methyl silicone resin according to claim 1, characterized in that, The polyhydroxy steric hindrance modifier was prepared by the following method: Mix 100 parts of a multifunctional aliphatic polyol, 0.1-3 parts of a Lewis acid catalyst, and 0.01-0.1 parts of a polymerization inhibitor in 200-400 parts of a first organic solvent. Then, add 80-150 parts of an unsaturated bridged alicyclic compound at a constant rate under conditions of 95-105℃ and 300-500 rpm for 1-2 hours. Continue the reaction for 3-5 hours to obtain a polyhydroxy steric hindrance modifier. The Lewis acid catalyst includes at least one of trifluoromethanesulfonic acid and montmorillonite; the polymerization inhibitor includes at least one of 2,6-di-tert-butyl-4-methylphenol and p-hydroxyanisole; the first organic solvent includes at least one of propylene glycol methyl ether acetate, xylene, and n-butyl acetate.

3. The high-toughness methyl silicone resin according to claim 1, characterized in that, The organic solvent includes at least one of ethanol, isopropanol, n-butanol, ethyl acetate, butyl acetate, and propylene glycol methyl ether acetate.

4. The high-toughness methyl silicone resin according to claim 1, characterized in that, The titanate catalyst includes at least one of tetrabutyl titanate and tetraisopropyl titanate; the organotin catalyst includes at least one of stannous octoate and dibutyltin dilaurate.

5. The high-toughness methyl silicone resin according to claim 1, characterized in that, The alcoholysis condensation reaction conditions in step S2 are: stirring rate of 300-500 rpm, temperature of 70-85℃, and reaction time of 1.5-3h.

6. The high-toughness methyl silicone resin according to claim 1, characterized in that, The hydrolysis-condensation reaction conditions in step S3 are as follows: stirring speed of 300-500 rpm, temperature of 40-60℃, dropwise addition time of 25%-45% organic alcohol aqueous solution controlled at 30-60 min, and after dropwise addition, the reaction is kept at 60-70℃ for 2-4 h.

7. The high-toughness methyl silicone resin according to claim 1, characterized in that, The polycondensation reaction conditions in step S4 are as follows: vacuum distillation is carried out at 55-65℃ and -0.09MPa to -0.08MPa until no obvious liquid distillation occurs; then a dehydrating agent is added, the stirring rate is 300-500rpm, the temperature is 85-95℃, and the reaction time is 1-2h; the post-treatment conditions are: a dehydrating agent is added, azeotropic dehydration is performed, and after dehydration, the solvent is removed by vacuum distillation or a second organic solvent is added to adjust the solid content of the system to 40-60% to obtain high-toughness methyl silicone resin; The water-removing agent includes at least one of butyl acetate and propylene glycol methyl ether acetate; The second organic solvent includes at least one of isopropanol and n-butanol.

8. The application of the high-toughness methyl silicone resin according to any one of claims 1-7 in the flexible sealing material or heat-resistant coating material of heating pipes.

Images