High-temperature-resistant fluorinated silicone rubber and vulcanization preparation method thereof

Abstract

The invention belongs to the technical field of high polymer materials, and discloses high-temperature-resistant fluorinated silicone rubber and a vulcanization preparation method thereof. According to the preparation method, a cyclic olefin structural unit is introduced into a fluorine-silicon main chain side group, and a tetrazole or thiol polyfunctional crosslinking agent is adopted to carry out click chemical reaction, so that a nanoring crosslinking structure with a heat shielding function is formed in situ. The core technical problems of insufficient cross-linked network thermal stability, non-uniform structure and sudden decline of mechanical properties of the existing fluorosilicone rubber in a high-temperature service environment are solved. The vulcanization preparation method is mild in process, does not need a noble metal catalyst, avoids the problem of platinum poisoning, and is suitable for one-time forming of products with complex shapes. After being used for a long time in an air environment of 300 DEG C, the obtained fluorosilicone rubber still keeps the elastomer characteristics, has no obvious hardening, pulverization or cracking phenomena, and meets the application requirements of extreme working conditions such as aero-engine sealing rings, deep well drilling O-shaped rings and high-power IGBT module packaging gaskets.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology and relates to a high-temperature resistant fluorosilicone rubber and its vulcanization preparation method. Background Technology

[0002] Fluorosilicone rubber is widely used in aerospace, automotive sealing, electronic packaging and special industrial fields because it combines the high and low temperature resistance of organosilicon materials with the oil resistance, solvent resistance and chemical stability of fluoropolymers. It shows irreplaceable value, especially in extreme working conditions such as high temperature and strong corrosion.

[0003] To achieve the transformation from raw rubber to elastomer, vulcanization crosslinking is a key process. The chemical structure and topological uniformity of the crosslinking network directly determine the thermal stability, mechanical properties, and service life of the final product.

[0004] Existing technologies primarily rely on peroxide-induced free radical crosslinking or platinum-catalyzed hydrosilylation reactions (i.e., platinum vulcanization) to construct three-dimensional networks. The former forms carbon-carbon crosslinks by abstracting hydrogen atoms from the main chain, while the latter generates stable Si-C bonds between Si–H and vinyl groups. Both methods exhibit good process adaptability and physical properties within the conventional operating temperature range (typically below 200°C), and have effectively supported the large-scale application of fluorosilicone rubber in low- and medium-temperature sealing applications.

[0005] While carbon-carbon crosslinking points formed by peroxide sulfidation in traditional sulfidation systems possess a certain degree of thermal stability, their formation process is accompanied by numerous free radical side reactions, easily leading to random chain breakage, resulting in a decrease in molecular weight and a sharp decline in mechanical properties. Although platinum sulfidation offers controllable reactions and fewer byproducts, the resulting Si–C bonds still exhibit a tendency for thermal dissociation at high temperatures. Furthermore, due to the sensitivity of hydrosilylation reactions to functional group distribution, the actual crosslinking process often results in heterogeneous network structures and the formation of hotspot regions due to local functional group concentration differences or limited diffusion. These regions are the first to experience crosslinking point fracture under thermal stress cycling, subsequently inducing microcrack propagation and macroscopic failure. Such heterogeneous networks struggle to effectively transfer and disperse stress under load, causing localized stress concentrations and significantly reducing the material's fatigue life and dimensional stability. Summary of the Invention

[0006] To achieve the above-mentioned objectives, this invention provides a high-temperature resistant fluorosilicone rubber and its vulcanization preparation method. The high-temperature resistant fluorosilicone rubber introduces cyclic olefin structural units into the side groups of the fluorosilicone main chain and constructs a crosslinking network using highly selective click chemistry. This results in the in-situ formation of nano-ring protective structures with spatial rigidity and thermal shielding function at the crosslinking points, thereby significantly improving the material's long-term thermal stability, mechanical retention, and dimensional stability in thermo-oxidative environments above 250°C.

[0007] The high-temperature resistant fluorosilicone rubber of this invention is composed of the following components: (1) Fluorosilicone raw rubber with cyclic olefins in the side chain; (2) A multifunctional crosslinking agent, the molecule of which contains at least two complementary functional groups that can undergo click chemistry with the cyclic olefin; (3) Optional catalyst or initiator; (4) Optional fillers, additives and stabilizers.

[0008] The cyclic olefin is a saturated or partially unsaturated alicyclic structure with strained double bonds, preferably norbornene, dicyclopentadiene, cyclooctene or their derivatives; the complementary functional group is a tetrazolium group or a thiol group.

[0009] The repeating unit structure of the fluorosilicone raw rubber with cyclic olefins in the side chain is shown in the following formula: –[R f –Si(CH3)2–O–] m –[R nb –Si(CH3)2–O–] n –; Among them, R f It is a fluorinated alkyl group, selected from –(CH2)3–(CF2). p –CF3, p is an integer from 1 to 8; R nb It is a cyclic olefinic group linked by alkylene spacers, with the general structural formula –(CH2). q –C7H9, q is an integer from 1 to 4, C7H9 represents norbornene-2-yl; the molar ratio of m to n is (90:10) to (70:30), preferably 85:15.

[0010] This fluorosilicone raw rubber is prepared by co-hydrolysis condensation polymerization: methyltrimethoxysilane, γ-trifluoropropylmethyldimethoxysilane and γ-(norbornen-2-yl)propylmethyldimethoxysilane are mixed in a predetermined molar ratio and stirred in an acidic aqueous solution at 40°C for 6 hours. Then the temperature is raised to 80°C and the reaction continues for 2 hours. After neutralization, washing and drying, a colorless and transparent raw rubber is obtained with a number average molecular weight of 300,000-600,000 and a vinyl content of 0.8-1.5 mmol / g.

[0011] The multifunctional crosslinking agents are classified into two categories based on the click reaction type used: The first type is a tetrazolium-based crosslinking agent, whose molecular structure contains at least two 1,3-dipolar tetrazolium rings, preferably 1,4-bis(1H-tetrazole-5-yl)benzene, 1,3,5-tris(1H-tetrazole-5-yl)benzene, or tetra(1H-tetrazole-5-ylmethyl)methane. This type of crosslinking agent undergoes a strain-promoted [3+2] cycloaddition reaction with cyclic olefins under heating conditions to generate a stable pyrazoline ring structure. The reaction temperature is 80-150℃, and no metal catalyst is required.

[0012] The second type is thiol-type crosslinking agents, whose molecular structure contains at least two thiol groups (–SH), preferably pentaerythritol tetra(3-mercaptopropionate), trimethylolpropane tri(3-mercaptopropionate), or 1,6-hexanedithiol. In the presence of a free radical initiator, this type of crosslinking agent undergoes a thiol-olefin click addition reaction with cyclic olefins at 60-120°C to generate a crosslinked network linked by thioether bonds.

[0013] When using a tetrazolium-type crosslinking agent, no catalyst is added to the vulcanization system; when using a thiol-type crosslinking agent, a free radical initiator needs to be added. The free radical initiator is an azo or peroxide compound, specifically 2,2'-azobis(2-methylpropionitrile), dicumyl peroxide, or tert-butyl hydroperoxide, and its dosage is 0.1%-1.0% of the mass of the fluorosilicone raw rubber.

[0014] The sulfurization preparation method includes the following steps: Step 1: Plasticize the fluorosilicone raw rubber containing cyclic olefins in the side chain on a two-roll mill at 30°C for 5 minutes, add a multifunctional crosslinking agent and an optional free radical initiator, mix evenly to obtain an uncured rubber compound. Step 2: Place the uncured rubber compound in the mold and pre-cur it at 100-150℃ for 10 minutes on a flat vulcanizing machine, then heat it to 180℃ for 30 minutes to complete the crosslinking reaction; Step 3: The vulcanized product is subjected to a second vulcanization at 200°C for 4 hours to eliminate residual stress and improve the integrity of the cross-linked network.

[0015] During the crosslinking reaction, the strained double bonds of the cyclic olefin undergo a highly selective and high-conversion addition reaction with tetrazolium or thiol, with a conversion rate exceeding 95%. Because the double bonds of the cyclic olefin open while the cyclic skeleton remains after the reaction, the resulting crosslinking points are surrounded by a rigid alicyclic structure, forming a nanoring protective layer with a diameter of approximately 0.7-1.2 nm.

[0016] This structure has a dual function: Firstly, the steric hindrance effect effectively shields the direct attack of thermo-oxidative stress on cross-linking bonds, inhibiting the thermal oxidative breakage of Si–C or C–S bonds. Secondly, the localized rigidity enhancement improves the stress transmission efficiency of the cross-linked network, avoiding stress concentration at traditional flexible cross-linking points under thermo-mechanical coupling loads.

[0017] In a preferred embodiment of the present invention, R in the fluorosilicone raw rubber nb The molar content of the group is 15%, and the crosslinking agent used is 1,3,5-tris(1H-tetrazole-5-yl)benzene, with an amount of 1.05 moles of tetrazolium groups per mole of cyclic olefin. The vulcanization conditions are 120℃×10 minutes + 180℃×30 minutes.

[0018] As another preferred embodiment of the present invention, a thiol-type crosslinking system is adopted: R in fluorosilicone raw rubber nb The content is 12%, the crosslinking agent is pentaerythritol tetra(3-mercaptopropionate), the free radical initiator is 2,2'-azobis(2-methylpropionitrile), and the amount is 0.5% of the raw rubber mass. The vulcanization conditions are 90℃×15 minutes + 170℃×40 minutes.

[0019] The present invention further specifies that the filler is fumed silica produced by surface fluorination, and its specific surface area is 200 m². 2 / g, surface hydroxyl density less than 0.5OH / nm 2 The addition amount is 20%-40% of the mass of the fluorosilicone raw rubber. This filler has excellent interfacial compatibility with the fluorosilicone matrix and can effectively inhibit the performance degradation caused by filler-polymer interface debonding at high temperatures.

[0020] The crosslinked network of the high-temperature resistant fluorosilicone rubber described in this invention exhibits high chemical homogeneity and topological regularity. Due to the orthogonality and high selectivity of the click chemistry reaction, it avoids the main chain breakage side reaction caused by free radical chain transfer in traditional peroxide vulcanization, and also overcomes the crosslinking density fluctuations caused by uneven functional group diffusion in platinum vulcanization.

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention introduces cyclic olefins as functional side groups into the main chain through molecular design and couples them with a click chemistry crosslinking strategy, achieving self-reinforcement and self-protection of the crosslinking points. This solves the core technical problems of insufficient thermal stability, structural inhomogeneity, and rapid degradation of mechanical properties in existing fluorosilicone rubber crosslinking networks under high-temperature service conditions. 2. The vulcanization preparation method of the present invention has a wide process window, mild reaction conditions, no need for precious metal catalysts, avoids platinum poisoning problems, and is suitable for one-time molding of complex shaped products; 3. The obtained fluorosilicone rubber retains its elastomer properties after long-term use in an air environment at 300℃, without significant hardening, powdering or cracking, meeting the application requirements of extreme working conditions such as aero-engine sealing rings, deep well drilling O-rings and high-power IGBT module packaging gaskets. 4. By constructing a three-in-one technology system with cyclic olefins as reaction sites, click chemistry as the crosslinking mechanism, and nanoring structures as protective units, the high-temperature durability of fluorosilicone rubber is fundamentally improved. Detailed Implementation

[0022] This invention provides a high-temperature resistant fluorosilicone rubber and its vulcanization preparation method. By introducing cyclic olefin structural units into the side groups of the fluorosilicone main chain and constructing a crosslinking network using highly selective click chemistry, a nano-ring protective structure with spatial rigidity and thermal shielding function is formed in situ at the crosslinking points. This significantly improves the long-term thermal stability, mechanical retention, and dimensional stability of the material in a thermo-oxidative environment above 250°C. The high-temperature resistant fluorosilicone rubber of this invention is composed of the following components: fluorosilicone raw rubber with cyclic olefins in the side chains, a multifunctional crosslinking agent, an optional catalyst or initiator, and optional fillers, additives, and stabilizers. The cyclic olefins are saturated or partially unsaturated alicyclic structures with strained double bonds, preferably norbornene, dicyclopentadiene, cyclooctene, or derivatives thereof; the complementary functional groups are tetrazolium groups or thiol groups.

[0023] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples, so as to ensure that those skilled in the art can fully understand and implement the present invention.

[0024] Example 1: Fluorosilicone raw rubber m:n molar ratio 85:15, R f In the case of p=3, R nb In the case of q=3, the number-average molecular weight is 450,000; The crosslinking agent is 1,3,5-tris(1H-tetrazole-5-yl)benzene, and the amount used is 1.05 moles of tetrazolium groups per mole of cyclic olefin; The filler is 30% surface-fluorinated fumed silica with a specific surface area of ​​200 m². 2 / g; The vulcanization process involves plasticizing at 30°C for 5 minutes on a two-roll mill, adding the crosslinking agent in three equal portions with a 1-minute interval between each addition, mixing thoroughly, then applying a mold closing pressure of 10MPa, pre-vulcanizing at 120°C for 10 minutes, followed by post-treatment at 180°C for 30 minutes, and then secondary vulcanization at 200°C for 4 hours with a heating rate of 3°C / minute and slow cooling to 80°C at a wind speed of 0.5m / s. Preparation process: Plasticizing of fluorosilicone raw rubber → Adding crosslinking agent and filler and mixing evenly → Molding and segmented vulcanization → Secondary vulcanization to eliminate residual stress → Finished product.

[0025] Example 2: Fluorosilicone raw rubber with a m:n molar ratio of 90:10; other formulations and processes are the same as in Example 1. Preparation process: Same as in Example 1 (adjustment of raw rubber ratio).

[0026] Example 3: Fluorosilicone raw rubber with a m:n molar ratio of 70:30; other formulations and processes are the same as in Example 1. Preparation process: Same as in Example 1 (adjustment of raw rubber ratio).

[0027] Example 4: The crosslinking agent was replaced with 1,4-bis(1H-tetrazole-5-yl)benzene; the rest of the formulation and process were the same as in Example 1. Preparation process: Same as in Example 1 (with crosslinking agent adjusted).

[0028] Example 5: The crosslinking agent was pentaerythritol tetra(3-mercaptopropionate), and the free radical initiator was 2,2-azobis(2-methylpropionitrile), with a dosage of 0.5%; pre-curing was carried out at 90°C for 15 minutes, followed by treatment at 170°C for 40 minutes; the remaining formulation was the same as in Example 1. Preparation process: Same as in Example 1 (adjustment of crosslinking system and vulcanization parameters).

[0029] Example 6: The filler addition amount is 20%, and the rest of the formulation and process are the same as in Example 1; Preparation process: Same as in Example 1 (with adjustment of filler dosage).

[0030] Example 7: The filler addition amount is 40%, and the rest of the formulation and process are the same as in Example 1; Preparation process: Same as in Example 1 (with adjustment of filler dosage).

[0031] Example 8: Pre-vulcanization at 150°C for 8 minutes; the rest of the formula and process are the same as in Example 1. Preparation process: Same as in Example 1 (with adjustment of vulcanization parameters).

[0032] Comparative Example 1: Fluorosilicone raw rubber with acyclic olefin side chains containing vinyl groups; the crosslinking agent is a hydrogen-containing silicone oil platinum catalyst; the rest of the formulation and process are the same as in Example 1; Preparation process: raw rubber plasticizing → mixing with crosslinking agent and catalyst → vulcanization → secondary vulcanization → finished product.

[0033] Comparative Example 2: Fluorosilicone raw rubber with acyclic olefin side chains; crosslinking agent is dicumyl peroxide; the rest of the formulation and process are the same as in Example 1; Preparation process: raw rubber plasticizing → mixing with crosslinking agent → vulcanization → secondary vulcanization → finished product.

[0034] Test method: High-temperature stability test: Tensile strength and elongation retention rate are measured by aging at 300℃ or 280℃ in a thermal aging chamber; storage modulus retention rate is measured at 250℃ using a dynamic mechanical analyzer; compression set is evaluated.

[0035] Mechanical and durability testing: Universal testing machine to measure tensile strength and elongation at break; hardness tester to measure hardness change after aging; cyclic thermal shock test to evaluate resistance to temperature changes.

[0036] Structural testing: Observe the integrity of the nanoring structure; detect the uniformity of the crosslinked network; verify the compatibility of the filler and matrix interface.

[0037] The test data comparisons are shown in Table 1 and Table 2.

[0038] Table 1. Comparison of tensile retention rate, elongation retention rate, and energy storage modulus retention rate at 300℃ and 250℃. Test Project Tensile retention rate after aging at 300℃ (%) Elongation retention rate after aging at 300℃ (%) Energy storage modulus retention rate at 250℃ (%) Example 1 82 76 75 Example 2 78 72 70 Example 3 85 78 80 Example 4 80 74 73 Example 5 - - 72 Example 6 79 75 68 Example 7 86 74 82 Example 8 81 73 74 Comparative Example 1 40 35 45 Comparative Example 2 35 30 40 Table 2 Comparison of Compression Permanent Deformation, Number of Thermal Shock Cycles, and Hardness Changes After Aging Test Project Compression set (%) Number of thermal shock cycles (times) Changes in hardness after aging (ShoreA) Example 1 18 50 2 Example 2 20 50 3 Example 3 16 50 2 Example 4 19 50 2 Example 5 21 50 3 Example 6 22 50 3 Example 7 15 50 1 Example 8 17 50 2 Comparative Example 1 45 10 8 Comparative Example 2 50 8 10 Examples 1-8 showed a high-temperature aging retention rate of ≥72% and no cracks after 50 thermal shock cycles, which is far superior to the comparative examples. The traditional vulcanization system in Comparative Examples 1-2 lacks nano-ring protection, and the crosslinking network is easily degraded at high temperatures, confirming that the cyclic olefin side chain + click chemical crosslinking is the key to high-temperature resistance.

[0039] Increased cyclic olefin content in raw rubber (Examples 2→1→3) improves high-temperature stability; increased filler addition (Examples 6→1→7) optimizes storage modulus and compression set; both tetrazolium-based and thiol-based crosslinking systems are compatible, with the former exhibiting superior high-temperature performance.

[0040] The embodiments exhibit long-term stability at 300°C, making them suitable for extreme high-temperature conditions; they demonstrate high mechanical property retention and excellent elasticity and dimensional stability; the vulcanization process is mild, requiring no precious metal catalysts and avoiding platinum poisoning; the preparation process is compatible with existing equipment and is easily industrialized.

[0041] Compared to traditional platinum vulcanization (Comparative Example 1), Example 1 showed a 105% increase in tensile retention at 300°C and a 60% reduction in compression set; compared to peroxide vulcanization (Comparative Example 2), the tensile retention was increased by 134% and the thermal shock resistance was increased by 525%, solving the industry problem of a sharp drop in the high-temperature performance of traditional fluorosilicone rubber.

[0042] In summary, the fluorosilicone rubber described in this invention achieves excellent high-temperature resistance through the synergistic effect of nano-ring protection structure and click chemical crosslinking, and is suitable for extreme scenarios such as aerospace and deep well drilling.

[0043] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-temperature resistant fluorosilicone rubber, characterized in that, The fluorosilicone rubber is composed of the following components: (1) Fluorosilicone raw rubber with cyclic olefins in the side chain; (2) A multifunctional crosslinking agent, the molecule of which contains at least two complementary functional groups that can undergo click chemistry with the cyclic olefin; (3) Free radical initiators; (4) Fillers, additives and stabilizers.

2. The high-temperature resistant fluorosilicone rubber according to claim 1, characterized in that, The repeating unit structure of the fluorosilicone raw rubber with cyclic olefins in its side chains is –[R f –Si(CH3)2–O–] m –[R nb –Si(CH3)2–O–] n –; Among them, R f It is –(CH2)3–(CF2) p –CF3, p is an integer from 1 to 8; R nb For –(CH2) q –C7H9, q is an integer from 1 to 4, C7H9 represents norbornen-2-yl; the molar ratio of m to n is 90:10 to 70:

30.

3. The high-temperature resistant fluorosilicone rubber according to claim 1, characterized in that, The cyclic olefin is an alicyclic structure with strained double bonds, and the complementary functional group is a tetrazolium group or a thiol group.

4. The high-temperature resistant fluorosilicone rubber according to claim 1, characterized in that, The multifunctional crosslinking agent is an aromatic compound containing at least two tetrazolium groups, or a polythiol compound containing at least two thiol groups.

5. The high-temperature resistant fluorosilicone rubber according to claim 1, characterized in that, After vulcanization, the fluorosilicone rubber forms a nano-ring protective structure with a diameter of 0.7-1.2 nm at the crosslinking points, which is composed of a rigid alicyclic skeleton.

6. The high-temperature resistant fluorosilicone rubber according to claim 2, characterized in that, The R f p is 3, R nb In this case, q is 3, and the molar ratio of m to n is 85:

15.

7. The high-temperature resistant fluorosilicone rubber according to claim 1 or 4, characterized in that, The multifunctional crosslinking agent is 1,3,5-tris(1H-tetrazole-5-yl)benzene, 1,4-bis(1H-tetrazole-5-yl)benzene, or tetra(1H-tetrazole-5-ylmethyl)methane.

8. The high-temperature resistant fluorosilicone rubber according to claim 1 or 4, characterized in that, The multifunctional crosslinking agent is pentaerythritol tetra(3-mercaptopropionate), trimethylolpropane tri(3-mercaptopropionate), or 1,6-hexanedithiol, and the system contains a free radical initiator, which is 2,2'-azobis(2-methylpropionitrile), dicumyl peroxide, or tert-butyl hydroperoxide, and its amount is 0.1%-1.0% of the mass of the fluorosilicone raw rubber.

9. The high-temperature resistant fluorosilicone rubber according to claim 1, characterized in that, The filler is fumed silica with surface fluorination treatment, and the amount added is 20%-40% of the mass of fluorosilicone raw rubber. It is prepared by reacting hexafluoropropylene oxide vapor with the hydroxyl groups on the surface of the silica at 200°C, and its surface end-capping group is –CF(CF3)OCF2–.

10. A vulcanization preparation method for high-temperature resistant fluorosilicone rubber as described in any one of claims 1-9, characterized in that, Includes the following steps: S1: Plasticize the fluorosilicone raw rubber containing cyclic olefins in the side chain on a two-roll mill, add a multifunctional crosslinking agent and an optional free radical initiator, mix evenly to obtain an uncured rubber compound. S2: Place the uncured rubber compound in a mold, pre-cur it on a flat vulcanizing machine, and then heat it to complete the cross-linking reaction; S3: Perform secondary vulcanization on the vulcanized product.