A method for preparing a high temperature resistant silicone elastomer

Abstract

The application relates to the technical field of organic silicon elastic material preparation, in particular to a preparation method of a high-temperature-resistant organic silicon elastic material, which comprises the following steps: ring-opening copolymerization of cyclic dimethyl siloxane, cyclic 3,3,3-trifluoropropyl methyl siloxane and cyclic methyl vinyl siloxane in an inert environment to obtain a vinyl fluorosiloxane base polymer containing trimethyl siloxy end groups, and the methyl vinyl siloxane unit is not higher than 2 mol%; dispersing surface-treated fumed silica in the base polymer to form a filler dispersion base; dissolving vinyl-functionalized polyhedral oligomeric silsesquioxane in tetrahydrofuran to form a pre-dispersion liquid, the vinyl ratio is not less than 50%, and the addition amount is 0.5-2.5 parts by mass; mixing the filler dispersion base, the pre-dispersion liquid and a hydrogen-containing fluorosiloxane crosslinking agent, so that the ratio of the total moles of silicon hydride groups to the total moles of vinyl groups is 1:1; adding a platinum-based catalyst after pressure reduction, and obtaining the organic silicon elastic material through hot pressing and post-curing.

Description

Technical Field

[0001] This invention relates to the field of organosilicon elastic material preparation technology, and in particular to a method for preparing a high-temperature resistant organosilicon elastic material. Background Technology

[0002] Organosilicon elastic materials, such as fluorosilicone rubber, possess good high and low temperature resistance, weather resistance, and chemical stability, making them widely used in sealing, aerospace, automotive, and high-temperature protection fields. However, with increasing operating temperature and duration, their molecular chains may still undergo rearrangement, depolymerization, and side group breakage, leading to accelerated weight loss and decreased mechanical properties. Existing technologies typically improve high-temperature resistance by adding heat-resistant fillers, nano-metal oxides, adjusting the vulcanization system, or introducing inorganic silicon structures.

[0003] For example, patent application No. 2020100120297, entitled "A High-Temperature Resistant Fluorosilicone Rubber Material", uses components such as silica, phenyl silicone oil, and nano-oxides to mix with fluorosilicone rubber raw rubber to improve the material's performance at higher temperatures; patent application No. 2023114498312, entitled "A Long-Term High-Temperature Resistant Silicone Rubber and Its Preparation Method and Application", uses fumed silica, nano-high-temperature resistant agents, and a composite vulcanization system to improve the long-term heat resistance of silicone rubber; and patent application No. 2019113667779, entitled "A Fluorosilicone Rubber Composition and Preparation Method", introduces a fluorinated cage-type polysilsesquioxane structure into the fluorosilicone rubber system and combines it with silica, high-vinyl fluorosilicone oil, and peroxide vulcanizing agents to improve the material's mechanical properties, processing properties, and heat resistance.

[0004] As can be seen from the above technologies, existing high-temperature resistant silicone elastic materials largely rely on heat-resistant additives, inorganic fillers, or peroxide vulcanization systems to improve material properties. However, there is still insufficient consideration of the coordination between the structural stability of polysiloxanes themselves, the interfacial activity of fillers, and the formation mode of crosslinking networks. Under high-temperature conditions, active end groups and active groups on the filler surface may promote polysiloxane chain rearrangement and depolymerization, while changes in vinyl content and crosslinking structure can also affect the initial thermal degradation and subsequent degradation rate of the material. Therefore, it is still necessary to coordinate the design of polymer structure, filler interface, and crosslinking network formation process to further improve the high-temperature stability of silicone elastic materials. Summary of the Invention

[0005] In view of the above technical problems, the present invention provides a method for preparing a high-temperature resistant organosilicon elastic material, which aims to improve the problems of existing organosilicon elastic materials being prone to chain segment rearrangement and depolymerization under high temperature conditions, as well as the insufficient synergistic effect of filler interface and cross-linking structure on heat resistance stability.

[0006] Other features and advantages of the invention will become apparent from the following detailed description, or may be learned in part by practice of the invention.

[0007] According to one aspect of the present invention, a method for preparing a high-temperature resistant organosilicon elastic material is provided, comprising the following steps: In an inert environment, cyclic dimethylsiloxane, cyclic 3,3,3-trifluoropropylmethylsiloxane, and cyclic methylvinylsiloxane undergo ring-opening copolymerization to obtain a vinyl fluorosiloxane-based polymer with trimethylsiloxy end groups. In this vinyl fluorosiloxane-based polymer, the molar content of dimethylsiloxane units is higher than that of methylvinylsiloxane units but lower than that of 3,3,3-trifluoropropylmethylsiloxane units, and the molar fraction of methylvinylsiloxane units among all siloxane units is not higher than 2 mol%. Surface-treated fumed silica is dispersed in the vinyl fluorosiloxane-based polymer to obtain a filler dispersion base material; Vinyl-functionalized polyhedral oligomeric silsesquioxane is dissolved in tetrahydrofuran to obtain a polyhedral oligomeric silsesquioxane pre-dispersion. The proportion of vinyl groups in the organic substituents of the vinyl-functionalized polyhedral oligomeric silsesquioxane is not less than 50%, and the amount of the vinyl-functionalized polyhedral oligomeric silsesquioxane added relative to 100 parts by weight of the vinyl-containing fluorosiloxane base polymer is 0.5-2.5 parts by weight. The filler dispersion is added to the polyhedral oligomeric silsesquioxane predispersant and mixed. Then, a hydrofluorosiloxane crosslinking agent is added. The amount of hydrofluorosiloxane crosslinking agent added is adjusted according to the total molar ratio of vinyl groups in the vinyl-functionalized polyhedral oligomeric silsesquioxane base polymer and the vinyl group, so that the ratio of silanol groups in the hydrofluorosiloxane crosslinking agent to the total molar ratio of vinyl groups is 1:1, thereby obtaining a crosslinkable mixture. The crosslinkable mixture was subjected to reduced pressure treatment, followed by the addition of a platinum-based addition catalyst to obtain the molding compound. The adhesive to be molded is subjected to hot-press curing, so that the silane groups in the hydrofluorosiloxane crosslinking agent undergo hydrosilylation crosslinking with the vinyl groups in the vinyl-containing fluorosiloxane base polymer and the vinyl-functionalized polyhedral oligomeric silsesquioxane, respectively. The adhesive obtained by hot-press curing is then post-cured to obtain an organosilicon elastic material.

[0008] Furthermore, in the vinyl fluorosiloxane-based polymer, dimethylsiloxane units account for 8-13 mol% of all siloxane units, methyl vinylsiloxane units account for 1.25-2 mol% of all siloxane units, and the remaining 3,3,3-trifluoropropylmethylsiloxane units are the balance.

[0009] Furthermore, the ring-opening copolymerization is carried out under nitrogen atmosphere, and the resulting vinyl fluorosiloxane-containing base polymer is precipitated with methanol and washed, then dried under reduced pressure to remove residual cyclic siloxanes and low-boiling components.

[0010] Furthermore, the vinyl-functionalized polyhedral oligomeric silsesquioxane is a T8 cage-type polyhedral oligomeric silsesquioxane composed of eight RSiO1.5 structural units, wherein R is vinyl or methyl, and the proportion of vinyl in the organic substituents of the vinyl-functionalized polyhedral oligomeric silsesquioxane is 50%-100%.

[0011] Furthermore, the vinyl-functionalized polyhedral oligomeric silsesquioxane is prepared by acid-catalyzed co-hydrolysis and co-condensation of vinyltrimethoxysilane and methyltrimethoxysilane, and is subsequently subjected to filtration, washing, recrystallization and drying.

[0012] Furthermore, the decompression treatment is carried out at 100°C for 2 hours.

[0013] Furthermore, the platinum-based addition reaction catalyst is a Karstedt catalyst, and the hot pressing curing is carried out at 140°C for 5 minutes.

[0014] Furthermore, the post-curing is carried out at 200°C for 4 hours.

[0015] The technical solution of the present invention has the following beneficial effects: This invention reduces the adverse effects of polysiloxane chain rearrangement and depolymerization under high temperature conditions by controlling the chain structure and end group state of the vinyl fluorosiloxane-based polymer and combining it with surface-treated fumed silica. Vinyl functionalized polyhedral oligomeric silsesquioxanes participate in hydrosilylation crosslinking, which improves the stability of the crosslinking network and introduces a heat-resistant cage-like silicon-oxygen structure, thereby improving the high-temperature stability of organosilicon elastic materials. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating a method for preparing a high-temperature resistant organosilicon elastic material as described in the embodiments of this specification. Figure 2 This is a schematic diagram of the structure of a vinyl fluorosiloxane-based polymer according to an embodiment of the present invention. Figure 3 This is a schematic diagram illustrating the composition principle of the crosslinkable mixture according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the hydrosilylation crosslinking network structure according to an embodiment of the present invention. Detailed Implementation

[0017] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make the invention more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of embodiments of the invention. However, those skilled in the art will recognize that the technical solutions of the invention may be practiced with one or more of these specific details omitted, or other methods, components, apparatus, steps, etc., may be employed. In other instances, well-known technical solutions are not shown or described in detail to avoid obscuring various aspects of the invention.

[0018] Example 1 This invention provides a method for preparing a high-temperature resistant organosilicon elastic material. (Refer to...) Figure 1 The diagram shown is a flowchart illustrating a method for preparing a high-temperature resistant organosilicon elastic material according to an embodiment of the present invention.

[0019] The method specifically includes: In a nitrogen atmosphere, cyclic dimethylsiloxane, cyclic 3,3,3-trifluoropropylmethylsiloxane, and cyclic methylvinylsiloxane undergo ring-opening copolymerization to obtain a vinyl fluorosiloxane-based polymer with trimethylsiloxy end groups. In this vinyl fluorosiloxane-based polymer, dimethylsiloxane units account for 8 mol% of all siloxane units, methylvinylsiloxane units account for 2 mol%, and 3,3,3-trifluoropropylmethylsiloxane units account for 90 mol%. By retaining a low content of methylvinylsiloxane units in the vinyl fluorosiloxane-based polymer, the polymer chain has vinyl reaction sites required for subsequent crosslinking, while avoiding excessive vinyl content. The trimethylsiloxy end groups in the vinyl fluorosiloxane-based polymer reduce the tendency for bite-back depolymerization caused by active chain ends under high-temperature conditions.

[0020] After ring-opening copolymerization, the vinyl fluorosiloxane-containing base polymer is precipitated and washed with methanol, and then dried under reduced pressure to remove residual cyclic siloxanes and low-boiling components. This purification process is performed before filler dispersion and crosslinking treatment, ensuring that the base polymer used in subsequent batching processes has a relatively stable composition and reducing the impact of residual low-molecular-weight components on subsequent mixing and curing processes.

[0021] Surface-treated fumed silica is dispersed in the vinyl fluorosiloxane-containing base polymer and then compounded to obtain a filler dispersion. The surface-treated fumed silica, dispersed in the polymer matrix, restricts polymer chain movement. Simultaneously, the pre-treatment reduces the surface activity of the silica, thereby mitigating the adverse effects of the surface-active groups on the stability of the polysiloxane chains under high-temperature conditions. Pre-forming the filler dispersion with the surface-treated fumed silica and the vinyl fluorosiloxane-containing base polymer also facilitates subsequent uniform mixing with the polyhedral oligomeric silsesquioxane pre-dispersion.

[0022] Vinyl-functionalized polyhedral oligomeric silsesquioxanes were prepared separately. Acid-catalyzed co-hydrolysis and co-condensation of vinyltrimethoxysilane and methyltrimethoxysilane were used to form a T8 cage-like polyhedral oligomeric silsesquioxane composed of eight RSiO1.5 structural units, where R is vinyl or methyl. After the reaction, the product was sequentially filtered, washed, recrystallized, and dried to obtain POSS-V4. The proportion of vinyl groups in the organic substituents of POSS-V4 was 50%. Purification of the co-hydrolysis and co-condensation product reduced the possibility of unreacted components and residual small molecules entering the subsequent crosslinking system.

[0023] Based on 100 parts by weight of the vinyl fluorosiloxane-containing base polymer, 0.5 parts by weight of the POSS-V4 were taken and dissolved in tetrahydrofuran to obtain a polyhedral oligomeric silsesquioxane pre-dispersion. Pre-dispersing POSS-V4 in tetrahydrofuran helps it form a more uniform dispersion before entering the polymer system, reducing the possibility of local aggregation when directly added to a high-viscosity polymer system.

[0024] The filler dispersion is added to the polyhedral oligomeric silsesquioxane pre-dispersion and mixed, followed by the addition of a hydrofluorosiloxane crosslinking agent. The amount of hydrofluorosiloxane crosslinking agent added is adjusted according to the sum of the molar number of vinyl groups in the vinyl-containing fluorosiloxane base polymer and the vinyl groups in POSS-V4, so that the ratio of the molar number of silanium groups in the hydrofluorosiloxane crosslinking agent to the sum of the molar number of vinyl groups in the vinyl-containing fluorosiloxane base polymer and the vinyl groups in POSS-V4 is 1:1, thus obtaining a crosslinkable mixture.

[0025] In the above formulation process, the vinyl-containing fluorosiloxane base polymer and the vinyl group in POSS-V4 are used together as the reaction targets of the hydrofluorosiloxane crosslinking agent, enabling the vinyl group in POSS-V4 to participate in the subsequent hydrosilylation reaction. Therefore, POSS-V4 is not only dispersed in the material as a physical filler, but it can also participate in the formation of the crosslinking network through its own vinyl group.

[0026] The crosslinkable mixture was subjected to a reduced pressure treatment at 100°C for 2 hours. This reduced pressure treatment was performed before the addition of the platinum-based addition catalyst to reduce residual moisture and air bubbles in the mixture and to treat the rubber compound formed in the aforementioned mixing process. After the reduced pressure treatment, the Karstedt catalyst was added to the crosslinkable mixture, and the mixture was then mixed to obtain the rubber compound to be molded.

[0027] The adhesive to be molded was hot-pressed and cured at 140°C for 5 minutes. Under the action of Karstedt catalyst, the silane groups in the hydrofluorosiloxane crosslinking agent underwent hydrosilylation reactions with the vinyl groups in the vinyl-containing fluorosiloxane base polymer and the vinyl groups in POSS-V4, respectively, to form chemical crosslinks between different polysiloxane molecular chains. At the same time, POSS-V4 was bound to the crosslinking network through its vinyl reaction sites.

[0028] After hot-press curing, the resulting adhesive is post-cured at 200℃ for 4 hours to obtain a high-temperature resistant silicone elastic material. Post-curing is used to further complete the cross-linking and structural stabilization of the hot-pressed adhesive, making the formed cross-linked network more stable.

[0029] In the obtained high-temperature resistant organosilicon elastic material, the vinyl fluorosiloxane-based polymer constitutes the main body of the organosilicon elastic material, and surface-treated fumed silica is dispersed in the main body, restricting the movement of polymer chain segments. A hydrofluorosiloxane crosslinking agent connects the vinyl reaction sites in the vinyl fluorosiloxane-based polymer and the vinyl reaction sites in POSS-V4 through a hydrosilylation reaction, allowing POSS-V4 to participate in the formation of the crosslinking network. The T8 cage-like silicon-oxygen structure of POSS-V4 has a high proportion of inorganic Si-O structures and is chemically bonded to the polysiloxane crosslinking network, which is beneficial to improving the structural stability of the crosslinking network under high-temperature conditions. Simultaneously, the trimethylsiloxy end groups are used to reduce the tendency for chain-end biting depolymerization, and the surface-treated fumed silica is used to reduce the adverse effects of the active filler interface on the high-temperature stability of the polysiloxane, thereby improving the high-temperature stability of the obtained organosilicon elastic material.

[0030] Example 2 This embodiment provides a method for preparing a high-temperature resistant organosilicon elastic material. The overall preparation route of this embodiment is the same as that of Embodiment 1, with the main differences being the composition of the vinyl-containing fluorosiloxane base polymer, the vinyl ratio of the vinyl-functionalized polyhedral oligomeric silsesquioxane, and the amount added.

[0031] Under a nitrogen atmosphere, cyclic dimethylsiloxane, cyclic 3,3,3-trifluoropropylmethylsiloxane, and cyclic methylvinylsiloxane undergo ring-opening copolymerization to obtain a vinyl fluorosiloxane-containing base polymer with trimethylsiloxy end groups. In this base polymer, dimethylsiloxane units comprise 10 mol% of all siloxane units, methylvinylsiloxane units comprise 2 mol%, and 3,3,3-trifluoropropylmethylsiloxane units comprise 88 mol%. Maintaining a low content of methylvinylsiloxane units ensures the base polymer has the vinyl reaction sites required for subsequent crosslinking, while avoiding excessive vinyl content. The trimethylsiloxy end groups are used to reduce the tendency for bite-back depolymerization caused by active chain ends under high-temperature conditions.

[0032] After ring-opening copolymerization, the vinyl fluorosiloxane-containing base polymer is precipitated and washed with methanol, and dried under reduced pressure to remove residual cyclic siloxanes and low-boiling components, so that the base polymer is purified before entering the subsequent filler dispersion and crosslinking processes.

[0033] Surface-treated fumed silica is dispersed in the vinyl fluorosiloxane-containing base polymer and then compounded to obtain a filler dispersion. The surface-treated fumed silica, once dispersed in the base polymer, restricts polymer chain movement and reduces the adverse effects of the filler interface on the stability of the polysiloxane chain under high-temperature conditions by decreasing the activity of the filler surface. Pre-forming the filler dispersion also facilitates subsequent mixing with the polyhedral oligomeric silsesquioxane pre-dispersion.

[0034] Vinyl-functionalized polyhedral oligomeric silsesquioxanes were prepared separately. Acid-catalyzed co-hydrolysis and co-condensation of vinyltrimethoxysilane and methyltrimethoxysilane were used to form a T8 cage-like polyhedral oligomeric silsesquioxane composed of eight RSiO1.5 structural units, where R is vinyl or methyl. After the reaction was completed, the mixture was sequentially filtered, washed, recrystallized, and dried to obtain POSS-V6. The vinyl content of the organic substituents in POSS-V6 was 75%.

[0035] Based on 100 parts by mass of the vinyl fluorosiloxane-containing base polymer, 1 part by mass of the POSS-V6 was taken and dissolved in tetrahydrofuran to obtain a polyhedral oligomeric silsesquioxane pre-dispersion. By pre-dispersing POSS-V6 in tetrahydrofuran, it forms a more uniform dispersion before entering the polymer system, thereby reducing the possibility of local aggregation when directly added to a high-viscosity polymer system.

[0036] The filler dispersion is added to the polyhedral oligomeric silsesquioxane pre-dispersion and mixed, followed by the addition of a hydrofluorosiloxane crosslinking agent. The amount of hydrofluorosiloxane crosslinking agent added is adjusted according to the sum of the molar number of vinyl groups in the vinyl-containing fluorosiloxane base polymer and the vinyl groups in POSS-V6, so that the ratio of the molar number of silanium groups in the hydrofluorosiloxane crosslinking agent to the sum of the molar number of vinyl groups in the vinyl-containing fluorosiloxane base polymer and the vinyl groups in POSS-V6 is 1:1, thus obtaining a crosslinkable mixture.

[0037] Compared to POSS-V4 used in Example 1, POSS-V6 in this example has more vinyl substituents, thus providing more vinyl sites that can participate in the hydrosilylation reaction. Therefore, when determining the amount of hydrofluorosiloxane crosslinking agent added, the vinyl groups in the base polymer and the vinyl groups in POSS-V6 are taken into account, so that the hydrofluorosiloxane crosslinking agent can simultaneously undergo subsequent hydrosilylation reactions with both types of vinyl groups. POSS-V6 thus enters the crosslinking network as a component that can participate in chemical crosslinking, rather than merely existing as a physical filler.

[0038] The crosslinkable mixture was subjected to reduced pressure treatment at 100°C for 2 hours to reduce residual moisture and air bubbles. After the reduced pressure treatment, Karstedt catalyst was added and mixed to obtain the molding compound.

[0039] The adhesive to be molded was hot-pressed and cured at 140°C for 5 minutes. Under the action of Karstedt catalyst, the silane groups in the hydrofluorosiloxane crosslinking agent underwent hydrosilylation reactions with the vinyl groups in the vinyl-containing fluorosiloxane base polymer and the vinyl groups in POSS-V6, respectively, to form chemical crosslinks between different polysiloxane molecular chains, and POSS-V6 was bound to the crosslinking network through its own vinyl reaction sites.

[0040] After hot-press curing, the resulting adhesive is post-cured at 200℃ for 4 hours to obtain a high-temperature resistant silicone elastic material. Post-curing is used to further complete the cross-linking and structural stabilization of the hot-pressed adhesive, making the formed cross-linked network more stable.

[0041] In the obtained high-temperature resistant organosilicon elastic material, a vinyl fluorosiloxane-based polymer constitutes the material matrix, with surface-treated fumed silica dispersed within the matrix. A hydrofluorosiloxane crosslinking agent forms a polysiloxane crosslinking network through a hydrosilylation reaction, while POSS-V6 is incorporated into the crosslinking network through its vinyl reaction sites. The T8 cage-like silicon-oxygen structure and multiple vinyl sites that can participate in crosslinking of POSS-V6 facilitate the formation of a crosslinking network containing POSS structural nodes. Furthermore, the combination of trimethylsiloxy end groups and surface-treated fumed silica enhances the structural stability of the obtained organosilicon elastic material under high-temperature conditions.

[0042] Example 3 This embodiment provides a method for preparing a high-temperature resistant organosilicon elastic material. The overall preparation route of this embodiment is the same as that of Embodiment 1, with the main differences being the composition of the vinyl-containing fluorosiloxane base polymer, the vinyl ratio of the vinyl-functionalized polyhedral oligomeric silsesquioxane, and the amount added.

[0043] Under a nitrogen atmosphere, cyclic dimethylsiloxane, cyclic 3,3,3-trifluoropropylmethylsiloxane, and cyclic methylvinylsiloxane undergo ring-opening copolymerization to obtain a vinyl fluorosiloxane-containing basic polymer with trimethylsiloxy end groups. In this vinyl fluorosiloxane-containing basic polymer, dimethylsiloxane units account for 13 mol% of all siloxane units, methylvinylsiloxane units account for 2 mol%, and 3,3,3-trifluoropropylmethylsiloxane units account for 85 mol%. The dimethylsiloxane units are used to regulate the chain structure of the basic polymer, while the methylvinylsiloxane units are kept at a low content to provide the vinyl reaction sites required for subsequent crosslinking, while avoiding excessive vinyl content in the basic polymer. The trimethylsiloxy end groups are used to reduce the tendency for bite-back depolymerization caused by active chain ends under high-temperature conditions.

[0044] After ring-opening copolymerization, the vinyl fluorosiloxane-containing base polymer is precipitated and washed with methanol, and dried under reduced pressure to remove residual cyclic siloxanes and low-boiling components, so that the vinyl fluorosiloxane-containing base polymer is purified before entering the subsequent filler dispersion and crosslinking process.

[0045] Surface-treated fumed silica is dispersed in the vinyl fluorosiloxane-containing base polymer and then compounded to obtain a filler dispersion. The surface-treated fumed silica, after being dispersed in the base polymer, restricts the movement of polymer chain segments and, by reducing the activity of the filler surface, mitigates the adverse effects of the filler interface on the stability of the polysiloxane chain under high-temperature conditions. By pre-forming the filler dispersion, the fumed silica is first dispersed in the base polymer before being mixed with the subsequent polyhedral oligomeric silsesquioxane pre-dispersion.

[0046] Vinyl-functionalized polyhedral oligomeric silsesquioxanes were prepared separately. Acid-catalyzed co-hydrolysis and co-condensation of vinyltrimethoxysilane and methyltrimethoxysilane were used to form a T8 cage-like polyhedral oligomeric silsesquioxane composed of eight RSiO1.5 structural units, where R is vinyl or methyl. After the reaction was completed, the mixture was sequentially filtered, washed, recrystallized, and dried to obtain POSS-V8. The vinyl groups in the organic substituents of POSS-V8 accounted for 100%, giving POSS-V8 multiple vinyl reaction sites capable of participating in subsequent hydrosilylation reactions.

[0047] Based on 100 parts by mass of the vinyl fluorosiloxane-containing base polymer, 2.5 parts by mass of the POSS-V8 were dissolved in tetrahydrofuran to obtain a polyhedral oligomeric silsesquioxane pre-dispersion. By first dispersing POSS-V8 in tetrahydrofuran, it forms a more uniform dispersion before entering the polymer system, reducing the possibility of local aggregation after direct addition to a high-viscosity polymer system. Using 2.5 parts by mass of POSS-V8 can increase the number of POSS structures and their vinyl reaction sites involved in subsequent crosslinking within a given formulation range, while also ensuring its dispersion in the polymer system.

[0048] The filler dispersion is added to the polyhedral oligomeric silsesquioxane pre-dispersion and mixed, followed by the addition of a hydrofluorosiloxane crosslinking agent. The amount of hydrofluorosiloxane crosslinking agent added is adjusted according to the sum of the molar number of vinyl groups in the vinyl-containing fluorosiloxane base polymer and the molar number of vinyl groups in POSS-V8, so that the ratio of the molar number of silanium groups in the hydrofluorosiloxane crosslinking agent to the sum of the molar number of vinyl groups in the vinyl-containing fluorosiloxane base polymer and the molar number of vinyl groups in POSS-V8 is 1:1, thus obtaining a crosslinkable mixture.

[0049] Since the vinyl content of the organic substituents in POSS-V8 used in this embodiment is 100%, it can provide a large number of vinyl sites that can participate in the hydrosilylation reaction. Therefore, when determining the amount of hydrofluorosiloxane crosslinking agent added, the vinyl groups in the base polymer and the vinyl groups in POSS-V8 are taken into account together, so that the hydrofluorosiloxane crosslinking agent can simultaneously undergo hydrosilylation reactions with both types of vinyl groups, allowing POSS-V8 to participate in the formation of the crosslinking network through its own vinyl reaction sites.

[0050] The crosslinkable mixture was subjected to a reduced pressure treatment at 100°C for 2 hours to reduce residual moisture and air bubbles. After the reduced pressure treatment, Karstedt catalyst was added to the crosslinkable mixture and mixed to obtain the molding compound.

[0051] The adhesive to be molded was hot-pressed and cured at 140°C for 5 minutes. Under the action of Karstedt catalyst, the silane groups in the hydrofluorosiloxane crosslinking agent underwent hydrosilylation reactions with the vinyl groups in the vinyl-containing fluorosiloxane base polymer and the vinyl groups in POSS-V8, respectively, resulting in chemical crosslinking between different polysiloxane molecular chains. POSS-V8 was then incorporated into the crosslinking network through its multiple vinyl reaction sites. POSS-V8 has high vinyl functionality, providing numerous reaction sites for the crosslinking reaction, which is beneficial for forming a crosslinking network containing POSS structural nodes.

[0052] After hot-press curing, the resulting adhesive is post-cured at 200℃ for 4 hours to obtain a high-temperature resistant silicone elastic material. Post-curing is used to further complete the cross-linking and structural stabilization of the hot-pressed adhesive, making the formed cross-linked network more stable.

[0053] In the obtained high-temperature resistant organosilicon elastic material, a vinyl fluorosiloxane-based polymer constitutes the material matrix. Surface-treated fumed silica is dispersed within the matrix and restricts the movement of polymer chain segments. A hydrofluorosiloxane crosslinking agent forms a polysiloxane crosslinking network through a hydrosilylation reaction, with POSS-V8 acting as a chemical crosslinking node within this network. The T8 cage-like silicon-oxygen structure and multiple vinyl reaction sites of POSS-V8 contribute to improving the structural stability of the crosslinking network. Furthermore, the combination of trimethylsiloxy end groups and surface-treated fumed silica reduces the tendency for polysiloxane chain rearrangement and depolymerization under high-temperature conditions, thereby enhancing the high-temperature structural stability of the obtained organosilicon elastic material.

[0054] In summary, such as Figure 2As shown, the vinyl fluorosiloxane-based polymer 1 includes a dimethylsiloxane unit 2, a 3,3,3-trifluoropropylmethylsiloxane unit 3, and a methylvinylsiloxane unit 4, and has a trimethylsiloxy end group 5. The dimethylsiloxane unit 2 is used to regulate the polymer chain structure, the methylvinylsiloxane unit 4 provides the vinyl reaction site required for subsequent hydrosilylation, and the trimethylsiloxy end group 5 is used to reduce the tendency of backbiting depolymerization caused by the active chain end under high temperature conditions.

[0055] like Figure 3 As shown, surface-treated fumed silica 6 is dispersed in vinyl fluorosiloxane-based polymer 1 to obtain filler dispersion 10; vinyl functionalized polyhedral oligomeric silsesquioxane 7 is dissolved in tetrahydrofuran to form polyhedral oligomeric silsesquioxane pre-dispersion 9; then filler dispersion 10 is added to polyhedral oligomeric silsesquioxane pre-dispersion 9 and mixed, and then hydrofluorosiloxane crosslinking agent 8 is added. The amount of hydrofluorosiloxane crosslinking agent 8 added is adjusted according to the sum of the number of vinyl moles in vinyl-based polymer 1 and vinyl functionalized polyhedral oligomeric silsesquioxane 7, so that the components are mixed to form a crosslinkable mixture 12.

[0056] like Figure 4 As shown, the crosslinkable mixture 12 is subjected to reduced pressure treatment and a platinum-based addition reaction catalyst is added. After hot pressing and post-curing, the silane groups in the hydrofluorosiloxane crosslinking agent 8 undergo hydrosilylation reactions with the vinyl groups in the methyl vinylsiloxane unit 4 and the vinyl groups in the vinyl-functionalized polyhedral oligomeric silsesquioxane 7, forming a hydrosilylation crosslinking network 11. The vinyl-functionalized polyhedral oligomeric silsesquioxane 7 acts as a crosslinking node in the hydrosilylation crosslinking network 11, and the surface-treated fumed silica 6 is dispersed within the hydrosilylation crosslinking network 11, thereby obtaining a high-temperature resistant organosilicon elastic material.

[0057] Beneficial effects: This invention reduces the adverse effects of polysiloxane chain rearrangement and depolymerization under high temperature conditions by controlling the chain structure and end group state of the vinyl fluorosiloxane-based polymer and combining it with surface-treated fumed silica. Vinyl functionalized polyhedral oligomeric silsesquioxanes participate in hydrosilylation crosslinking, which improves the stability of the crosslinking network and introduces a heat-resistant cage-like silicon-oxygen structure, thereby improving the high-temperature stability of organosilicon elastic materials.

[0058] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the claims.

[0059] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method for preparing a high-temperature resistant organosilicon elastic material, characterized in that, Includes the following steps: In an inert environment, cyclic dimethylsiloxane, cyclic 3,3,3-trifluoropropylmethylsiloxane, and cyclic methylvinylsiloxane undergo ring-opening copolymerization to obtain a vinyl fluorosiloxane-based polymer with trimethylsiloxy end groups. In this vinyl fluorosiloxane-based polymer, the molar content of dimethylsiloxane units is higher than that of methylvinylsiloxane units but lower than that of 3,3,3-trifluoropropylmethylsiloxane units, and the molar fraction of methylvinylsiloxane units among all siloxane units is not higher than 2 mol%. Surface-treated fumed silica is dispersed in the vinyl fluorosiloxane-based polymer to obtain a filler dispersion base material; Vinyl-functionalized polyhedral oligomeric silsesquioxane is dissolved in tetrahydrofuran to obtain a polyhedral oligomeric silsesquioxane pre-dispersion. The proportion of vinyl groups in the organic substituents of the vinyl-functionalized polyhedral oligomeric silsesquioxane is not less than 50%, and the amount of the vinyl-functionalized polyhedral oligomeric silsesquioxane added relative to 100 parts by weight of the vinyl-containing fluorosiloxane base polymer is 0.5-2.5 parts by weight. The filler dispersion is added to the polyhedral oligomeric silsesquioxane predispersant and mixed. Then, a hydrofluorosiloxane crosslinking agent is added. The amount of hydrofluorosiloxane crosslinking agent added is adjusted according to the total molar ratio of vinyl groups in the vinyl-functionalized polyhedral oligomeric silsesquioxane base polymer and the vinyl group, so that the ratio of silanol groups in the hydrofluorosiloxane crosslinking agent to the total molar ratio of vinyl groups is 1:1, thereby obtaining a crosslinkable mixture. The crosslinkable mixture was subjected to reduced pressure treatment, followed by the addition of a platinum-based addition catalyst to obtain the molding compound. The adhesive to be molded is subjected to hot-press curing, so that the silane groups in the hydrofluorosiloxane crosslinking agent undergo hydrosilylation crosslinking with the vinyl groups in the vinyl-containing fluorosiloxane base polymer and the vinyl-functionalized polyhedral oligomeric silsesquioxane, respectively. The adhesive obtained by hot-press curing is then post-cured to obtain an organosilicon elastic material.

2. The method for preparing the high-temperature resistant organosilicon elastic material according to claim 1, characterized in that, In the vinyl fluorosiloxane-based polymer, dimethylsiloxane units account for 8-13 mol% of all siloxane units, methyl vinylsiloxane units account for 1.25-2 mol% of all siloxane units, and the remaining 3,3,3-trifluoropropylmethylsiloxane units are the balance.

3. The method for preparing the high-temperature resistant organosilicon elastic material according to claim 1, characterized in that, The ring-opening copolymerization was carried out under nitrogen atmosphere. The resulting vinyl fluorosiloxane-containing base polymer was precipitated with methanol and washed, and then dried under reduced pressure to remove residual cyclic siloxanes and low-boiling components.

4. The method for preparing the high-temperature resistant organosilicon elastic material according to claim 1, characterized in that, The vinyl-functionalized polyhedral oligosilsesquioxane is composed of eight RSiO₂ groups. 1.5 The T8 cage-like polyhedral oligomeric silsesquioxane is composed of structural units, wherein R is vinyl or methyl, and the proportion of vinyl in the organic substituents of the vinyl-functionalized polyhedral oligomeric silsesquioxane is 50%-100%.

5. The method for preparing the high-temperature resistant organosilicon elastic material according to claim 4, characterized in that, The vinyl-functionalized polyhedral oligomeric silsesquioxane is prepared by acid-catalyzed co-hydrolysis and co-condensation of vinyltrimethoxysilane and methyltrimethoxysilane, and is subsequently subjected to filtration, washing, recrystallization and drying.

6. The method for preparing the high-temperature resistant organosilicon elastic material according to claim 1, characterized in that, The decompression treatment was carried out at 100°C for 2 hours.

7. The method for preparing the high-temperature resistant organosilicon elastic material according to claim 1, characterized in that, The platinum-based addition reaction catalyst is a Karstedt catalyst, and the hot pressing curing is carried out at 140°C for 5 minutes.

8. The method for preparing the high-temperature resistant organosilicon elastic material according to claim 1, characterized in that, The post-curing process was carried out at 200°C for 4 hours.

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