Oil-resistant modified vulcanized silicone rubber and preparation process thereof

Abstract

This invention belongs to the field of polymer materials technology and discloses an oil-resistant modified vulcanized silicone rubber and its preparation process. This preparation process introduces fluorinated ester-type dynamic covalent bonds into the crosslinking network. The material is composed of fluorinated vinyl siloxane copolymers, carboxyl-functionalized siloxane oligomers, and fluorinated silanol crosslinking agents, etc., maintaining excellent oil resistance and high / low temperature resistance while endowing the material with self-healing and hot-press reprocessing capabilities. This invention extends the service life of seals under harsh operating conditions; utilizes the reversible thermal response of dynamic bonds to achieve hot-press reprocessing of the material, making thermosetting rubber recyclable; employs in-situ generation of dynamic crosslinking points to ensure the long-term reliability of the material; and maintains mechanical property balance over a wide temperature range, making it suitable for high-end applications such as aerospace engine seals, new energy vehicle battery pack gaskets, and deep-sea oil drilling equipment seals.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology and relates to an oil-resistant modified vulcanized silicone rubber and its preparation process. Background Technology

[0002] Fluorosilicone rubber, due to its unique molecular structure—a main chain with a siloxane skeleton and side chains with fluorinated organic groups—combines the excellent high and low temperature resistance of silicone rubber with the superior oil and solvent resistance of fluororubber. It can maintain a stable physical sealing function for a long time in complex media environments, preventing the penetration and corrosion of fuel, lubricating oil or organic solvents.

[0003] Traditional fluorosilicone rubber forms a three-dimensional covalent cross-linked network through peroxide or addition vulcanization systems. This network structure endows the material with high elastic modulus, low compression set, and excellent chemical inertness, thereby effectively ensuring the integrity of the seal during its service life.

[0004] While the C–C or Si–C type permanent covalent cross-links constructed by traditional vulcanization processes provide excellent thermodynamic stability, they fundamentally deprive the material of dynamic reversibility. Once the product develops micro-cracks or even macro-cracks due to mechanical stress, fatigue, or accidental impact during use, the cross-linked network undergoes irreversible breakage, the local sealing function is rapidly lost, and due to the lack of chain segment rearrangement and interface reconstruction capabilities, the damage cannot be repaired autonomously.

[0005] These thermosetting materials are difficult to reshape using conventional thermal processing methods after their service life, making closed-loop recycling and degradation impossible. This not only wastes resources but also contradicts the current development trends of green manufacturing and the circular economy. The reason for this is that the topological structure of the permanently cross-linked network freezes the freedom of movement of the polymer chains, making the material macroscopically exhibit single-use properties. Even if its chemical composition itself has excellent resistance to various media, the sustainability of its engineering applications is fundamentally limited. Summary of the Invention

[0006] To achieve the above-mentioned objectives, this invention provides an oil-resistant modified vulcanized silicone rubber and its preparation process. The oil-resistant modified vulcanized silicone rubber, while maintaining the inherent high and low temperature resistance and oil and solvent resistance of fluorosilicone rubber, introduces dynamic covalent bonds with specific structures into the crosslinking network, enabling the material to have self-healing ability after damage and end-stage hot pressing reprocessing performance, thereby solving the problem of irreversible functional failure and non-recyclability caused by permanent crosslinking of traditional fluorosilicone rubber.

[0007] The oil-resistant modified vulcanized silicone rubber of this invention is composed of the following components: a fluorinated vinyl siloxane copolymer, a carboxyl-functionalized siloxane oligomer, a crosslinking agent with a fluorinated silanol structure, a dynamic accelerator, a reinforcing filler, a structure control agent, and a catalyst; wherein, the fluorinated vinyl siloxane copolymer serves as the main chain backbone, and its repeating units include dimethylsiloxane units, methyltrifluoropropylsiloxane units, and vinyl-terminated units, with a vinyl molar content of 0.8%-1.5% and a weight-average molecular weight of 400,000-800,000; the carboxyl-functionalized siloxane oligomer is a polydimethylsiloxane with carboxyl groups at both ends or on the side chains, with a number-average molecular weight of 2,000-8,000 and a carboxyl group content of 1-3 per molecule; the crosslinking agent with a fluorinated silanol structure is a polydimethylsiloxane with the general formula R f –(CH2) n –Si(OH)3 compounds, where R f The polymer is a C1 to C6 perfluoroalkyl group, where n is an integer from 1 to 4; the dynamic accelerator is an organotin compound, specifically dibutyltin dilaurate, added at an amount of 0.1%-0.5% of the main chain polymer mass; the reinforcing filler is fumed silica with a specific surface area of ​​200-300 m² / g. 2 / g, the addition amount is 20%-40% of the main chain polymer mass; the structure control agent is hexamethyldisilazane, the addition amount is 3%-8% of the reinforcing filler mass; the catalyst is isopropanol chloroplatinate solution, the platinum content is 1000ppm, the addition amount is 5-20ppm of the main chain polymer mass based on platinum element.

[0008] The core of this invention lies in the fact that, in the presence of a catalyst and a dynamic promoter, the carboxyl-functionalized siloxane oligomer and a crosslinking agent with a fluorinated silanol structure form fluorinated ester-type dynamic covalent crosslinking points in situ during the vulcanization process. These crosslinking points have the following chemical structure: –COO–(CH2). n –Si(R f )(O–)2–, where R f It is a C1 to C6 perfluoroalkyl group, with n being an integer from 1 to 4. This fluorinated ester bond exhibits high bond energy and low exchange rate in the range of room temperature to 150°C, ensuring the mechanical stability and oil resistance of the material under normal service conditions. When the temperature rises above 180°C, a reversible transesterification reaction occurs under the catalysis of a dynamic accelerator, realizing the local dissociation and reconstruction of the cross-linked network, thereby endowing the material with hot pressing re-forming capability. Under conditions of 80-120°C, if there are micro-cracks on the material surface, the fluorinated ester bond can also undergo slow exchange at the interface, promoting the interdiffusion of molecular chains on the fracture surface and re-bonding, realizing the self-healing function.

[0009] The fluorinated vinyl siloxane copolymer is prepared by anionic ring-opening polymerization. The raw materials include octamethylcyclotetrasiloxane, 1,3-bis(3,3,3-trifluoropropyl)tetramethyldisiloxane, and 1,3-divinyltetramethyldisiloxane. The polymerization reaction is carried out at 120°C for 4 hours under nitrogen protection, followed by hexamethyldisilazane end-capping. After removal of low-molecular-weight byproducts, the target copolymer is obtained. The trifluoropropyl group introduction density in this copolymer is 15-25 trifluoropropyl groups per 100 siloxane units, ensuring that the volume swelling rate of the material to aliphatic hydrocarbons, aromatic hydrocarbons, and synthetic lubricating oils is less than 15%.

[0010] In a preferred embodiment of the present invention, the carboxyl-functionalized siloxane oligomer is prepared by an amidation-hydrolysis reaction of γ-aminopropyl-terminated polydimethylsiloxane and succinic anhydride. The carboxyl groups in the molecular chain are located at the chain ends and separated from the main chain by propylene groups. This structure ensures the reactivity of the carboxyl groups while avoiding steric hindrance that could inhibit subsequent esterification reactions. During the mixing stage, the oligomer is uniformly dispersed with the main-chain copolymer, and its flexible segments simultaneously act as internal plasticizers, reducing the material's compression set.

[0011] In another preferred embodiment of the present invention, the crosslinking agent with the fluorinated silanol structure is 3,3,3-trifluoropropyltrihydroxysilane, which is added in the form of an ethanol solution at a concentration of 20 wt% before mixing to prevent self-condensation during storage. The three silanol groups in this crosslinking agent react with carboxyl groups on three different polymer chains to form three-dimensional crosslinking nodes, significantly increasing the network crosslinking density; simultaneously, its side-chain trifluoropropyl groups synergistically enhance the overall oleophobicity of the material.

[0012] The preparation process of the oil-resistant modified vulcanized silicone rubber of the present invention includes the following steps: Step 1: The fluorinated vinyl siloxane copolymer is put into a mixer and mixed at 100°C for 10 minutes. Then, fumed silica and hexamethyldisilazane are added, the temperature is raised to 150°C and mixed for another 30 minutes. After the glue is discharged, it is cooled to room temperature to obtain the base rubber compound. Step 2: Place the base rubber compound on a two-roll mill and add carboxyl-functionalized siloxane oligomer, ethanol solution of crosslinking agent with fluorinated silanol structure and dibutyltin dilaurate in sequence. Control the roller temperature at 40°C and pass through the mill 10 times to ensure that the components are evenly dispersed. Step 3: Dilute the isopropanol chloroplatinic acid solution 10 times with anhydrous isopropanol, spray it onto the surface of the above-mentioned compound, and continue to pass it through the thin tube 5 times to obtain the unvulcanized rubber compound. Step 4: Place the uncured rubber compound in the mold and vulcanize it at 170°C and 10MPa pressure for 15 minutes to complete the initial crosslinking and obtain oil-resistant modified vulcanized silicone rubber products. Step 5: When the product is damaged or needs to be reshaped, place it in a 180°C hot press and hold it under a pressure of 5MPa for 20 minutes. The fluorinated ester bonds undergo dynamic exchange, the material flows and re-densifies, and reprocessing is achieved.

[0013] In the above preparation process, two types of reactions occur simultaneously during sulfidation: one is the addition reaction of vinyl groups with silane bonds (catalyzed by a platinum catalyst), forming stable Si–CH2–CH2–Si type permanent crosslinking points; the other is the condensation reaction of carboxyl groups with fluorosilanols (promoted by organotin), forming –COO–(CH2)3–Si(CF2CF2CF3)(O–)2– type dynamic crosslinking points. Both types of crosslinking points coexist in the same network; the permanent crosslinking points provide basic mechanical strength and dimensional stability, while the dynamic crosslinking points impart reversibility to the material.

[0014] Furthermore, this invention enables precise customization of material properties by controlling the dynamic crosslinking point density and the ratio of permanent crosslinking points. Compared with existing technologies, the advantages of this invention are as follows: 1. By introducing fluorinated ester-type dynamic covalent bonds into the crosslinked network of fluorosilicone rubber, the material is endowed with self-healing ability after damage without sacrificing oil resistance and high and low temperature resistance, thus extending the service life of the seals under harsh working conditions. 2. By utilizing the reversible thermal response of dynamic bonds, the material can be reprocessed by hot pressing, breaking through the technical bottleneck of the traditional non-recyclable thermosetting rubber, which is in line with the concepts of green manufacturing and circular economy. 3. By adopting the strategy of generating dynamic cross-linking points in situ, the performance degradation caused by the migration and precipitation of external small molecule dynamic monomers is avoided, ensuring the reliability of the material for long-term use. 4. The composite cross-linked network structure balances the stability of permanent cross-linking with the reversibility of dynamic cross-linking, enabling the material to maintain a balance of mechanical properties over a wide temperature range. It is suitable for high-end applications such as sealing rings for aerospace engines, sealing gaskets for new energy vehicle battery packs, and sealing components for deep-sea oil drilling equipment. Detailed Implementation

[0015] This invention provides an oil-resistant modified vulcanized silicone rubber and its preparation process. The core of this invention lies in introducing fluorinated ester-type dynamic covalent bonds into the crosslinking network of fluorosilicone rubber through molecular design. This imbues the material with self-healing capabilities after damage and endows it with post-heat pressing reprocessing performance while maintaining its inherent high and low temperature resistance, oil resistance, and solvent resistance. The oil-resistant modified vulcanized silicone rubber of this invention consists of seven components: a fluorinated vinyl siloxane copolymer, a carboxyl-functionalized siloxane oligomer, a crosslinking agent with a fluorinated silanol structure, a dynamic accelerator, a reinforcing filler, a structure control agent, and a catalyst.

[0016] 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.

[0017] Example 1: Fluorinated vinyl siloxane copolymer with a weight average molecular weight of 600,000, a vinyl molar content of 1.2%, and 20 trifluoropropyl groups per 100 siloxane units; The number-average molecular weight of the carboxyl-functionalized siloxane oligomer is 5000, each molecule contains 2 carboxyl groups, the addition amount is 7.5%, and the dynamic crosslinking points account for 40% of the total crosslinking points; The crosslinking agent is a 20% ethanol solution of 3,3,3-trifluoropropyltrihydroxysilane; The reinforcing filler is fumed silica with a specific surface area of ​​250 m². 2 / g, addition amount 30%; The addition amount of the structure control agent hexamethyldisilazane is 5% of the filler mass; The dynamic accelerator, dibutyltin dilaurate, was added at a rate of 0.3%. The amount of platinum added to the chloroplatinic acid isopropanol solution was 12 ppm. Vulcanization process: Mix in an internal mixer at 100°C for 10 minutes, add silica and structure control agent, mix at 150°C for 30 minutes, cool → open mill at 40°C, add oligomer crosslinking agent solution and dynamic accelerator, pass through 10 times → spray diluted catalyst, pass through 5 times → vulcanize at 170°C and 10 MPa for 15 minutes → finished product. Preparation process: preparation of base rubber compound → mixing and dispersion of components → addition of catalyst → molding and vulcanization → self-healing / reprocessing test.

[0018] Example 2: The amount of carboxyl-functionalized siloxane oligomer added is 5%, the dynamic crosslinking point ratio is 30%, and the rest of the formulation and process are the same as in Example 1; Preparation process: Same as in Example 1 (adjustment of oligomer dosage).

[0019] Example 3: The amount of carboxyl-functionalized siloxane oligomer added is 10%, the dynamic crosslinking point ratio is 50%, and the rest of the formulation and process are the same as in Example 1; Preparation process: Same as in Example 1 (adjustment of oligomer dosage).

[0020] Example 4: Fumed silica addition of 20%, other formulations and processes are the same as in Example 1; Preparation process: Same as in Example 1 (with adjustment of filler dosage).

[0021] Example 5: Fumed silica addition of 40%, 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).

[0022] Example 6: Fluorinated vinyl siloxane copolymer containing 15 trifluoropropyl groups per 100 siloxane units; the rest of the formulation and process are the same as in Example 1. Preparation process: Same as in Example 1 (copolymer structure adjustment).

[0023] Example 7: Fluorinated vinyl siloxane copolymer containing 25 trifluoropropyl groups per 100 siloxane units; the rest of the formulation and process are the same as in Example 1. Preparation process: Same as in Example 1 (copolymer structure adjustment).

[0024] Example 8: The catalyst chloroplatinic acid isopropanol solution was added with 5 ppm of platinum. The rest of the formulation and process were the same as in Example 1. Preparation process: Same as in Example 1 (catalyst dosage adjusted).

[0025] Comparative Example 1: The carboxyl-functionalized siloxane oligomer and the fluorinated silanol crosslinking agent formed a permanent crosslink only through platinum-catalyzed vinyl-hydrogen bond addition; the rest of the formulation and process were the same as in Example 1; Preparation process: preparation of base rubber compound → mixing with traditional crosslinking agent and catalyst → vulcanization → finished product.

[0026] Comparative Example 2: The crosslinking agent was propyltrihydroxysilane with no fluorinated groups; 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).

[0027] Test method: Oil resistance test: Immersion in IRM903 standard oil at 70℃ for 72 hours to determine the volume change rate; assess resistance to aliphatic and aromatic hydrocarbons.

[0028] Mechanical and dynamic performance testing: tensile strength and elongation at break are measured using a universal testing machine; the strength recovery rate is calculated by holding the scratch at 100℃ for 2 hours; the strength retention rate is measured by three hot pressing processes (180℃, 5 MPa for 20 minutes); and the compression set test (25% deformation at 150℃ for 70 hours) is performed.

[0029] Stability performance test: observe whether cracks appear during cyclic thermal shock at -55-150℃; measure mechanical retention rate during long-term thermal aging (150℃ for 72 hours).

[0030] The test data comparisons are shown in Table 1 and Table 2.

[0031] Table 1 Comparison of Oil Immersion Volume Change Rate, Self-Healing Strength Recovery Rate, and Reprocessing Strength Retention Rate Test item Oil immersion volume change rate (%) Self-repairing strength recovery rate (%) Reprocessing strength retention rate (%) Example 1 11 93 89 Example 2 10 88 85 Example 3 12 95 92 Example 4 13 91 87 Example 5 9 90 86 Example 6 14 92 88 Example 7 8 94 90 Example 8 12 90 86 Comparative Example 1 13 10 25 Comparative Example 2 28 91 87 Table 2 Comparison of Tensile Strength, Elongation at Break, Compression Set, and Number of Thermal Shock Cycles Test item Tensile strength (MPa) Elongation at break (%) Compression set (%) Thermal shock cycle number (times) Example 1 8.6 330 15 50 Example 2 9 310 14 50 Example 3 8.2 340 16 50 Example 4 7.8 350 17 50 Example 5 9.5 300 13 50 Example 6 8.4 320 15 50 Example 7 8.7 315 14 50 Example 8 8.1 325 16 50 Comparative Example 1 8.5 300 18 15 Comparative Example 2 7.5 330 17 50 Examples 1-8 showed a self-healing recovery rate of ≥90%, a reprocessing retention rate of ≥86%, and an oil resistance volume change rate of ≤14%, which were far superior to the comparative examples. Comparative example 1 had no self-healing and reprocessing capabilities due to the lack of dynamic crosslinking, and comparative example 2 had extremely poor oil resistance due to the lack of fluorinated groups. This confirms that dynamic crosslinking of fluorinated ester bonds + fluorinated copolymers are the key to the synergistic effect of oil resistance and dynamic function.

[0032] The proportion of dynamic crosslinking points increases (Example 2→1→3), improving self-healing and reprocessing performance, while slightly decreasing mechanical strength; the amount of reinforcing filler increases (Example 4→1→5), optimizing tensile strength and oil resistance, while reducing elongation; the density of the copolymer trifluoropropyl increases (Example 6→1→7), significantly improving oil resistance, while maintaining basically stable dynamic performance.

[0033] The embodiment combines excellent oil resistance and dynamic function, can be efficiently repaired after damage, and can be reprocessed by hot pressing after being scrapped, thus achieving recycling; it has stable mechanical properties, low compression set, and is suitable for a wide temperature range; the preparation process is compatible with existing rubber processing equipment, requires no special modification, and is easy to industrialize.

[0034] Compared to traditional permanently cross-linked fluorosilicone rubber (Comparative Example 1), Example 1 showed an 830% increase in self-healing recovery rate and a 256% increase in reprocessing retention rate; compared to non-fluorinated dynamically cross-linked rubber (Comparative Example 2), the oil resistance volume change rate was reduced by 61%, solving the industry problem of traditional fluorosilicone rubber being unrepairable and unrecyclable, while maintaining excellent oil resistance.

[0035] In summary, the rubber described in this invention achieves multifunctional requirements such as oil resistance, self-healing, and reprocessing through dynamic cross-linking of fluorinated ester bonds and synergy with fluorinated structures, and can be used in high-end applications such as aerospace and automotive sealing, depending on the combination of different parameters.

[0036] 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. An oil-resistant modified vulcanized silicone rubber, characterized in that, It consists of the following components: Fluorinated vinyl siloxane copolymers; Carboxyl-functionalized siloxane oligomers; Crosslinking agents containing fluorinated silanol structures; Dynamic promoters; Reinforcing filler; Structure control agents and catalysts.

2. The oil-resistant modified vulcanized silicone rubber according to claim 1, characterized in that, The fluorinated vinyl siloxane copolymer serves as the main chain backbone, and its repeating units include dimethylsiloxane units, methyltrifluoropropylsiloxane units, and vinyl end-capping units, with a vinyl molar content of 0.8%-1.5%.

3. The oil-resistant modified vulcanized silicone rubber according to claim 1, characterized in that, The carboxyl-functionalized siloxane oligomer is a polydimethylsiloxane with carboxyl groups at both ends or on the side chains, and each molecule contains 1-3 carboxyl groups.

4. The oil-resistant modified vulcanized silicone rubber according to claim 1, characterized in that, The crosslinking agent with the fluorinated silanol structure is of general formula R. f –(CH2) n –Si(OH)3 compounds, where R f It is a C1 to C6 perfluoroalkyl group, where n is an integer from 1 to 4.

5. The oil-resistant modified vulcanized silicone rubber according to claim 1, characterized in that, The dynamic accelerator is dibutyltin dilaurate, and the addition amount is 0.1%-0.5% of the mass of the fluorinated vinyl siloxane copolymer; the reinforcing filler is fumed silica, and the addition amount is 20%-40% of the mass of the fluorinated vinyl siloxane copolymer.

6. The oil-resistant modified vulcanized silicone rubber according to claim 1, characterized in that, The structure control agent is hexamethyldisilazane, and the amount added is 3%-8% of the mass of the reinforcing filler; the catalyst is isopropanol chloroplatinate solution with a platinum content of 1000 ppm, and the amount added based on the elemental platinum is 5-20 ppm of the mass of the fluorinated vinyl siloxane copolymer.

7. The oil-resistant modified vulcanized silicone rubber according to claim 1, characterized in that, The crosslinking network of the oil-resistant modified vulcanized silicone rubber simultaneously includes Si–CH2–CH2–Si type permanent crosslinking points formed by the addition of vinyl groups to silane bonds and –COO–(CH2) formed in situ by the condensation of carboxyl groups with fluorosilanols. n –Si(R f (O–)2– type dynamic covalent crosslinking points.

8. The oil-resistant modified vulcanized silicone rubber according to claim 1, characterized in that, The trifluoropropyl group introduction density in the fluorinated vinyl siloxane copolymer is 15-25 trifluoropropyl groups per 100 siloxane units.

9. The oil-resistant modified vulcanized silicone rubber according to claim 1 or 3, characterized in that, The carboxyl-functionalized siloxane oligomer is prepared by amidation-hydrolysis reaction of γ-aminopropyl-terminated polydimethylsiloxane and succinic anhydride, wherein the carboxyl group is located at the end of the chain and is connected to the main chain by propylene groups.

10. The oil-resistant modified vulcanized silicone rubber according to claim 1, characterized in that, The crosslinking agent containing the fluorinated silanol structure is 3,3,3-trifluoropropyltrihydroxysilane, which is added in the form of a 20% by mass ethanol solution.