Preparation method of a structural control agent masterbatch for high-performance vulcanized silicone rubber

Abstract

The application discloses a preparation method of a structural control agent masterbatch for high-performance vulcanized silicone rubber and belongs to the technical field of silicone rubber materials, and comprises the following steps: condensing and copolymerizing hydroxyl-terminated linear dimethyl oligomeric siloxane, methyl vinyl dimethoxysilane and methyl phenyl dimethoxysilane under the catalysis of a weak acid catalyst to obtain a structural control agent; preparing polydopamine modified white carbon black; mixing methyl vinyl silicone rubber raw rubber with the structural control agent, adding the polydopamine modified white carbon black and a Lewis acid catalyst, performing low-vacuum removal, cooling and sheeting to obtain a structural control agent masterbatch. When the masterbatch is applied to the preparation of high-performance vulcanized silicone rubber, the polydopamine modified white carbon black is combined with the non-covalent interaction between the phenyl group and the vinyl group and the polydopamine to construct an interpenetrating network, the stability of an anchoring system in a strong acid and strong alkali medium is improved, and the vulcanized silicone rubber can maintain mechanical properties and processing stability under corrosive working conditions.

Description

Technical Field

[0001] This invention relates to the field of silicone rubber materials technology, and in particular to a method for preparing a high-performance structure control agent masterbatch for vulcanized silicone rubber. Background Technology

[0002] High-temperature vulcanized silicone rubber, with its excellent corrosion resistance, mechanical stability, high and low temperature resistance, weather resistance, and insulation properties, is widely used in electronic packaging, aerospace, chip manufacturing, and chemical corrosion protection. To obtain superior mechanical properties, reinforcing fillers such as silica are added to vulcanized silicone rubber. However, silica has a surface rich in active silanol groups, which readily react with the terminal hydroxyl groups or residual alkoxy groups in the raw silicone rubber through hydrogen bonding and condensation reactions. This leads to hardening and decreased plasticity of the compound during storage, resulting in a "structuring" phenomenon. Industrially, low molecular weight hydroxyl or alkoxy silicone oils are often introduced as structure control agents. Their active end groups react with the silica surface to inhibit structural formation.

[0003] Low molecular weight siloxane structure control agents are prone to volatilization and migration during high-temperature vulcanization or long-term thermal aging, leading to the failure of the filler interface protection and subsequent restructuring. Even when using macromolecular structure control agents to prepare masterbatches with in-situ anchoring of silica, only a small amount of silanol groups on the silica surface can be consumed through condensation reactions. A large number of untouched, highly active, isolated silanol groups remain on the silica surface, serving as core sites for adsorbing water molecules and acid / base ions. Under long-term contact with strong acid / base media, the residual active silanol groups on the silica surface promote the enrichment of water molecules and ions at the filler interface, weakening the interfacial bonding between the filler and the matrix, resulting in decreased mechanical properties, increased swelling, or poor processing stability of the compound.

[0004] Therefore, there is an urgent need to provide a method for preparing a high-performance structure control agent masterbatch for vulcanized silicone rubber, so that the structure control agent masterbatch can improve the structural stability and mechanical retention of silicone rubber under long-term immersion in strong acids and alkalis while ensuring the processing performance and storage stability of vulcanized silicone rubber, and meet the needs of industrial applications under extreme conditions. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides a method for preparing a high-performance structure control agent masterbatch for vulcanized silicone rubber.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing a high-performance structure control agent masterbatch for vulcanized silicone rubber, comprising the following steps:

[0007] S1. A hydroxyl-terminated linear dimethyl oligosiloxane, methyl vinyl dimethoxysilane, and methyl phenyl dimethoxysilane are mixed and a weak acidic condensation catalyst is added under nitrogen protection to carry out a condensation copolymerization reaction. After neutralization, vacuum descaling, and filtration, a structure control agent is obtained.

[0008] S2. Add silica and dopamine to a tris(hydroxymethyl)aminomethane buffer solution for self-polymerization reaction, and after washing and vacuum drying, obtain polydopamine-modified silica.

[0009] S3. The raw methyl vinyl silicone rubber and the structure control agent are put into a mixer and mixed until the components are uniformly dispersed; the polydopamine-modified silica is added in batches, the temperature is raised and Lewis acid catalyst is added to carry out condensation anchoring reaction; vacuum depressurization and cooling are performed to obtain the structure control agent masterbatch.

[0010] In a preferred embodiment of the present invention, in step S2, the main component of the structure control agent is α-hydroxy-ω-methoxy-terminated oligomeric (dimethyl-methylvinyl-methylphenyl)siloxane, with a viscosity of 20-80 mPa·s at 25°C, a hydroxyl content of 2-8 wt%, a vinyl content of 1-5 wt%, a phenyl content of 2-6 wt%, a number-average molecular weight of 1500-3000, and a molecular weight distribution index of 1.5-2.5.

[0011] In a preferred embodiment of the present invention, in step S1, by mass, the terminal hydroxyl linear dimethyl oligosiloxane is 60-70 parts, methyl vinyl dimethoxysilane is 12-20 parts, methyl phenyl dimethoxysilane is 6-10 parts, and the weak acidic condensation catalyst is 0.2-0.6 parts.

[0012] In a preferred embodiment of the present invention, in step S1, the terminal hydroxyl linear dimethyl oligosiloxane has a number-average molecular weight of 500-800, a viscosity of 10-30 mPa·s, and a hydroxyl content of 4-10 wt%.

[0013] In a preferred embodiment of the present invention, in step S1, the weakly acidic condensation catalyst is selected from one or more of p-toluenesulfonic acid, formic acid, and acetic acid; the neutralization reagent is selected from one or more of sodium carbonate, sodium bicarbonate, or ammonia water, and the pH of the system is adjusted to 6.5-7.5.

[0014] In a preferred embodiment of the present invention, in step S1, the reaction temperature of the condensation copolymerization reaction is 70-85°C, and the reaction time is 3-4 hours.

[0015] The vacuum de-lowering temperature is 100-120℃, and the de-lowering time is 1.0-1.5h. It is used to remove methanol, unreacted small molecule monomers and oligomer byproducts generated by condensation copolymerization reaction.

[0016] In a preferred embodiment of the present invention, in step S2, the concentration of the tris(hydroxymethyl)aminomethane buffer solution is 5-10 mmol / L, and the pH is 8.5-9.5; the mass ratio of the silica to the dopamine is 1:0.10-0.25; and the mass ratio of the silica to the tris(hydroxymethyl)aminomethane buffer solution is 1:100-300.

[0017] The self-polymerization reaction is carried out at a temperature of 25-30℃ for 1.5-2.5 hours.

[0018] A thin layer with a thickness of 1-5 nm is formed on the surface of the polydopamine-modified silica.

[0019] In a preferred embodiment of the present invention, in step S3, by weight, the raw methyl vinyl silicone rubber is 45-55 parts, the structure control agent is 35-45 parts, the polydopamine-modified silica is 6-12 parts, and the Lewis acid catalyst is 0.1-0.4 parts.

[0020] The Lewis acid catalyst is selected from one or more of dibutyltin oxide, dioctyltin oxide, and tetrabutyl titanate;

[0021] The mixing temperature is 40-60℃, the rotation speed is 30-60r / min, and the mixing time is 10-20min.

[0022] In a preferred embodiment of the present invention, in step S3, the reaction temperature of the condensation anchoring reaction is 80-90℃ and the reaction time is 30-60min.

[0023] In a preferred embodiment of the present invention, in step S3, the vacuum de-lowering temperature is 100-110°C and the de-lowering time is 50-70 min, used to remove methanol, residual water, unreacted small molecule monomers and easily hydrolyzed oligomers generated by condensation in the system.

[0024] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0025] (1) This invention constructs a structure control agent with both hydrophobic shielding and reaction anchoring functions by introducing methylphenyldimethoxysilane and methylvinyldimethoxysilane. The introduction of phenyl reduces the surface polarity of the masterbatch system, effectively inhibiting the adsorption and diffusion of water molecules and acid and alkali ions at the interface; the vinyl group can undergo a cross-linking reaction with the silicone rubber matrix during the vulcanization stage, allowing the structure control agent to be covalently integrated into the three-dimensional network of silicone rubber, reducing the possibility of the structure control agent being free, migrating or precipitating, and improving the stability and acid and alkali resistance of the filler interface.

[0026] (2) The present invention forms a nano-scale polydopamine thin layer on the surface of silica, which preferentially passivates the highly active isolated silanol groups on the surface of silica, thus blocking the inducing factors of structuring and hydrolysis; at the same time, it retains the low-activity homosilanol groups as sites for subsequent anchoring reactions, so that the structure control agent added later can form a stable chemical bond with silica, reducing the breakage of anchoring bonds due to acid and alkali media erosion.

[0027] (3) In the process of masterbatch preparation, the present invention relies on the π-π stacking, hydrogen bonding and polar-dipole interaction between phenyl, vinyl and polydopamine aromatic rings in the structure control agent to construct a dense three-dimensional interpenetrating network structure. Combined with the matrix covalent network formed by vinyl in vulcanization crosslinking, a double protective barrier is formed, which can effectively block the penetration channels of acid and alkali ions, avoid restructuring and mechanical decay, and ensure the mechanical property retention rate and service life of vulcanized silicone rubber in harsh environments. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a flowchart of the preparation process of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0032] Unless otherwise specified in the following examples, all raw materials are commercially available or prepared using conventional methods in the art. Specifically, the following materials are used: hydroxyl-terminated linear dimethyl oligosiloxane (Hesheng Silicon Industry Co., Ltd.); methyl vinyl dimethoxysilane (Hubei Siyuan New Material Technology Co., Ltd., purity ≥98%); methyl phenyl dimethoxysilane (Hubei Xinlantian New Material Co., Ltd., purity ≥99.0%); methyl vinyl silicone rubber raw material (Hesheng Silicon Industry Co., Ltd., vinyl content 0.1-0.3 mol%, hydroxyl content ≤0.05 wt%); and fumed silica (Jiangxi Black Cat Carbon Black Co., Ltd.).

[0033] like Figure 1 As shown, a method for preparing a high-performance structure control agent masterbatch for vulcanized silicone rubber includes the following steps:

[0034] S1. A hydroxyl-terminated linear dimethyl oligosiloxane, methyl vinyl dimethoxysilane, and methyl phenyl dimethoxysilane are mixed and a weak acidic condensation catalyst is added under nitrogen protection to carry out a condensation copolymerization reaction. After neutralization, vacuum descaling, and filtration, a structure control agent is obtained.

[0035] S2. Add silica and dopamine to a tris(hydroxymethyl)aminomethane buffer solution for self-polymerization reaction, and after washing and vacuum drying, obtain polydopamine-modified silica.

[0036] S3. Add methyl vinyl silicone rubber raw material and structure control agent to a mixer and mix until the components are evenly dispersed; add polydopamine-modified silica in batches, heat and add Lewis acid catalyst to carry out condensation anchoring reaction; vacuum depress and cool to obtain structure control agent masterbatch.

[0037] Specifically, in step S1, 60-70 parts by weight of terminal hydroxyl linear dimethyl oligosiloxane, 12-20 parts by weight of methyl vinyl dimethoxysilane, and 6-10 parts by weight of methyl phenyl dimethoxysilane are mixed and added to the reactor; under nitrogen protection, 0.2-0.6 parts by weight of weak acidic condensation catalyst are added; the reaction temperature is controlled at 70-85℃ and the reaction time is 3-4 hours.

[0038] Specifically, the number-average molecular weight of the hydroxyl-terminated linear dimethyl oligosilane is controlled at 500-800, the viscosity is 10-30 mPa·s, the hydroxyl content is 4-10 wt%, and the molecular backbone is a straight-chain Si-O-Si structure.

[0039] Specifically, methyl vinyl dimethoxysilane possesses both a methoxy-terminated structure and a vinyl active group, participating in structure control and molecular chain condensation and end-capping. It then participates in the peroxide vulcanization crosslinking of silicone rubber, covalently integrating the structure control agent into the silicone rubber network to prevent migration and precipitation.

[0040] Specifically, methylphenyldimethoxysilane introduces phenyl side groups and utilizes the large steric hindrance and hydrophobic effect of the benzene ring to enable the structure control agent molecular chain to have acid and alkali shielding ability, thereby reducing the adsorption of water molecules and acid and alkali ions.

[0041] Specifically, the weakly acidic condensation catalyst is selected from one or more of p-toluenesulfonic acid, formic acid, or acetic acid. The selected catalyst has mild acidity and catalyzes the de-alcoholization condensation reaction between silanol and methoxy groups.

[0042] Furthermore, after the condensation copolymerization reaction is completed, a weak alkaline neutralizing agent is added to the system to adjust the pH of the system to 6.5-7.5, neutralizing the residual weak acid and preventing the acid residue from accelerating the aging and degradation of silicone rubber. The weak alkaline neutralizing agent is selected from one or more of sodium carbonate, sodium bicarbonate, or ammonia water.

[0043] Further, the system is heated to 100-120℃ and vacuum de-polymerized for 1.0-1.5 hours to remove methanol, unreacted small molecule monomers, and oligomer byproducts generated during the condensation copolymerization reaction. After cooling and filtration, the structure control agent is obtained.

[0044] Specifically, the main component of the structure control agent is α-hydroxy-ω-methoxy-terminated oligomeric (dimethyl-methylvinyl-methylphenyl)siloxane, with a viscosity of 20-80 mPa·s at 25°C, a hydroxyl content of 2-8 wt%, a vinyl content of 1-5 wt%, a phenyl content of 2-6 wt%, a number-average molecular weight of 1500-3000, and a molecular weight distribution index of 1.5-2.5. The molecular chain of the structure control agent simultaneously possesses reactive end groups, sulfur-reactive vinyl groups, and hydrolysis-resistant phenyl side groups, providing a molecular structural basis for subsequent anchoring and acid / alkali resistance protection.

[0045] Furthermore, in step S2, a tris(hydroxymethyl)aminomethane buffer solution with a concentration of 5-10 mmol / L and a pH of 8.5-9.5 is prepared to provide a weakly alkaline environment and avoid uneven coating, excessive local thickness, or missing coating caused by pH fluctuations.

[0046] Further, dried silica and dopamine were added to a tris(hydroxymethyl)aminomethane buffer solution and stirred at 25-30°C for 1.5-2.5 h. Utilizing the oxidative self-polymerization properties of dopamine in a weakly alkaline environment, a polydopamine thin layer with a thickness of 1-5 nm was spontaneously formed on the surface of silica. After the reaction, the silica was washed with water until the filtrate was neutral. The silica was then vacuum dried at 100-110°C for 2-3 h to obtain polydopamine-modified silica.

[0047] The mass ratio of dried silica to dopamine is 1:0.10-0.25, and the mass ratio of silica to buffer solution is 1:100-300.

[0048] Specifically, the silica is selected from at least one of fumed silica and precipitated silica, preferably fumed silica, with a BET specific surface area of ​​150-300 m². 2 With a pH value of 3.5-4.5, the silica surface contains highly active isolated silanol groups and less active homologous silanol groups. The highly active silanols readily adsorb moisture and are easily corroded by acids and alkalis, which are the main causes of structuring and interfacial hydrolysis. A polydopamine thin layer covers or shields some of the active silanol groups on the silica surface, reducing its adsorption capacity for water molecules and acid / alkali ions. At the same time, by controlling the coating thickness, the silica surface still retains reaction sites that can participate in subsequent condensation anchoring.

[0049] Furthermore, in step S3, by weight, 45-55 parts of methyl vinyl silicone rubber raw rubber and 35-45 parts of structure control agent are added to an internal mixer, and the temperature is controlled at 40-60℃, the speed at 30-60 r / min, and the mixture is mixed for 10-20 min.

[0050] Specifically, during the mixing process, the terminal polar groups of the structure control agent form hydrogen bonds and polar-dipole interactions with the polar sites of the silicone rubber molecular chain, constructing a uniform and stable hydrogen bond association network precursor, achieving uniform dispersion of the two phases at the molecular level, and laying the foundation for a homogeneous system for the subsequent mixing and in-situ anchoring of polydopamine-modified silica.

[0051] Further, 6-12 parts of polydopamine-modified silica are added in batches to the internal mixer; the system is heated to 80-90℃, and 0.1-0.4 parts of Lewis acid catalyst are added, and the reaction is carried out under constant temperature and sealed for 30-60 minutes. The Lewis acid catalyst is selected from one or more of dibutyltin oxide, dioctyltin oxide, or tetrabutyl titanate.

[0052] Specifically, during the reaction, the terminal hydroxyl and methoxy groups of the structure control agent undergo dehydration condensation with the residual silanol groups on the surface of silica that are not coated with polydopamine, forming a strong Si-O-Si covalent anchoring bond, thus achieving chemical bonding and locking between the filler and the structure control agent. At the same time, the phenyl and vinyl groups in the molecular chain of the structure control agent spontaneously form a dense three-dimensional interpenetrating network with the polydopamine thin layer through π-π stacking, hydrogen bonding, and polar-dipole interactions. This effectively shields the diffusion and erosion of water molecules and acid and alkali ions into the anchoring interface and the interior of the molecular network, inhibiting the hydrolytic breakage of anchoring bonds and the re-structuring of the adhesive under strong acid and alkali conditions.

[0053] Furthermore, after the reaction is complete, the system temperature is raised to 100-110℃ and vacuum depressed for 50-70 minutes to remove methanol, residual moisture, unreacted small molecule monomers and easily hydrolyzed oligomers generated by condensation, reduce the volatile matter and small molecule migration of the masterbatch, and prevent residual impurities from forming defective channels under high-temperature processing or acid and alkali soaking.

[0054] Furthermore, after the de-lowering is completed, the material is naturally cooled to below 50°C before sheeting to avoid high-temperature sheeting causing the adhesive to stick together and the internal network structure to thermally relax and break down, thus obtaining the structure control agent masterbatch.

[0055] Example 1:

[0056] Step S1: By weight, 65 parts of terminal hydroxyl linear dimethyl oligosiloxane, 16 parts of methyl vinyl dimethoxysilane, and 6 parts of methyl phenyl dimethoxysilane were added to a reaction vessel and mixed. Under nitrogen protection, 0.4 parts of p-toluenesulfonic acid were added, the temperature was raised to 78°C, and the condensation copolymerization reaction was carried out at a constant temperature for 3.5 h. The pH of the system was adjusted to 7.0 using sodium bicarbonate, the temperature was raised to 110°C, and the mixture was vacuum degraded for 1.2 h. After cooling and filtration, the structure control agent was obtained. The viscosity of the structure control agent at 25°C was 35 mPa·s, the hydroxyl content was 5.2 wt%, the vinyl content was 3.8 wt%, the phenyl content was 2.5 wt%, the number average molecular weight was 2100, and the molecular weight distribution index was 1.9.

[0057] Step S2: Prepare a 7.5 mmol / L tris(hydroxymethyl)aminomethane buffer solution with a pH of 9.0; add dried fumed silica and dopamine to the tris(hydroxymethyl)aminomethane buffer solution, wherein the mass ratio of dried fumed silica to dopamine is 1:0.18 and the mass ratio of fumed silica to tris(hydroxymethyl)aminomethane buffer solution is 1:200. Stir the reaction at 28°C for 2 h, wash with water until the filtrate is neutral, and vacuum dry at 105°C for 2.5 h to obtain polydopamine-modified fumed silica, and form a 2 nm thick polydopamine thin layer on the surface of the fumed silica.

[0058] Step S3: By weight, add 50 parts of methyl vinyl silicone rubber raw rubber and 40 parts of structure control agent into an internal mixer, control the temperature at 50℃ and the speed at 45r / min, and mix for 15min; add 9 parts of polydopamine modified silica in batches, raise the temperature to 85℃, add 0.25 parts of dibutyltin oxide, and react at a constant temperature in a sealed environment for 45min; raise the temperature of the system to 105℃ and vacuum depress for 60min; let it cool naturally to 45℃ and sheet to obtain the structure control agent masterbatch.

[0059] Example 2:

[0060] Compared with Example 1, in this embodiment, in step S1, 63 parts by weight of terminal hydroxyl linear dimethyl oligosiloxane, 16 parts by weight of methyl vinyl dimethoxysilane, and 8 parts by weight of methyl phenyl dimethoxysilane are added to the reactor for mixing. The structure control agent has a viscosity of 42 mPa·s at 25°C, a hydroxyl content of 4.8 wt%, a vinyl content of 3.5 wt%, a phenyl content of 3.8 wt%, a number-average molecular weight of 2350, and a molecular weight distribution index of 1.8. The remaining raw material ratios, process operations, and parameters are completely consistent with those of Example 1.

[0061] Example 3:

[0062] Compared with Example 1, in this embodiment, in step S1, 61 parts by weight of terminal hydroxyl linear dimethyl oligosiloxane, 16 parts by weight of methyl vinyl dimethoxysilane, and 10 parts by weight of methyl phenyl dimethoxysilane are added to the reactor for mixing. The structure control agent has a viscosity of 48 mPa·s at 25°C, a hydroxyl content of 4.5 wt%, a vinyl content of 3.2 wt%, a phenyl content of 5.1 wt%, a number-average molecular weight of 2600, and a molecular weight distribution index of 1.7. The remaining raw material ratios, process operations, and parameters are completely consistent with those of Example 1.

[0063] Example 4:

[0064] Compared with Example 2, in this embodiment, the mass ratio of fumed silica to dopamine in step S2 is 1:0.10, and a polydopamine thin layer with a thickness of 1.2 nm is formed on the surface of fumed silica. The remaining raw material ratios, process operations, and parameters are completely consistent with those in Example 2.

[0065] Example 5:

[0066] Compared with Example 2, in this embodiment, the mass ratio of fumed silica to dopamine in step S2 is 1:0.25, and a 4.5 nm thick polydopamine thin layer is formed on the surface of fumed silica. The remaining raw material ratios, process operations, and parameters are completely consistent with those in Example 2.

[0067] Comparative Example 1:

[0068] Compared with Example 2, in step S1 of this comparative example, methylphenyldimethoxysilane is not added, and the corresponding missing parts are replaced with an equal amount of terminal hydroxyl linear dimethyl oligosiloxane. The remaining components and process conditions are completely consistent with those of Example 2.

[0069] Comparative Example 2:

[0070] Compared with Example 2, in step S2 of this comparative example, ordinary fumed silica was used, that is, the dopamine coating modification step was not performed. The amount of fumed silica added, the proportion of other raw materials, the process parameters, and the operation process are completely the same as those in Example 2.

[0071] Comparative Example 3:

[0072] Compared with Example 2, in step S2 of this comparative example, the mass ratio of fumed silica to dopamine is 1:0.4, the polymerization reaction time is 4h, and the remaining components and process conditions are completely the same as in Example 2. A polydopamine coating layer with a thickness of 9nm is formed on the surface of the silica.

[0073] Comparative Example 4:

[0074] Compared with Example 2, this comparative example replaces methyl vinyl dimethoxysilane in step S1 with an equal mass of terminal hydroxyl linear dimethyl oligosiloxane, while the remaining components and process conditions are completely consistent with Example 2.

[0075] Comparative Example 5:

[0076] Compared with Example 2, this comparative example does not add dibutyltin oxide Lewis acid catalyst in step S3, while the remaining components and process conditions are completely consistent with Example 2.

[0077] Experimental Example 1:

[0078] The structure control agent masterbatch prepared in the various embodiments and comparative examples of this invention was hot-pressed into a 2mm thick sheet on a flat vulcanizing machine at 120℃ and 5MPa pressure, and then naturally cooled to room temperature. Using a static water contact angle meter, at room temperature (25±1℃), 2μL of water was vertically dropped onto the surface of the sheet using a microsyringe. After the droplet stabilized for 10 seconds, the contact angle was measured. Five measurements were taken at different locations for each sample, and the arithmetic mean was calculated as the surface static water contact angle of that sample.

[0079] The structure control agent masterbatch prepared in each example and comparative example was cut into small pieces of approximately 5mm × 5mm × 2mm. The samples were completely immersed in 10% H2SO4 aqueous solution and 10% NaOH aqueous solution, respectively. The containers were sealed and soaked at a constant temperature of 40±1℃ for 30 days, with the soaking solution changed every 7 days. After soaking, the samples were removed, rinsed repeatedly with water until neutral, and dried in a vacuum drying oven at 80℃ to constant weight. The dried samples were placed in a Soxhlet extractor and extracted with toluene as solvent at 110℃ for 24 hours under reflux to remove organic components that were not chemically anchored or had been hydrolyzed. The residue after extraction was dried again to constant weight, and the residual mass was measured. Another sample of the same structure control agent masterbatch, which had not been soaked in acid or alkali, was extracted using a Soxhlet extractor and weighed to obtain the initial anchored organic matter mass. The anchoring retention rate was calculated using the formula: Anchoring retention rate = (Residual mass after acid and alkali soaking / Initial anchored organic matter mass) × 100%. Record the anchorage retention rate after acid immersion and the anchorage retention rate after alkali immersion respectively.

[0080] By weight, 100 parts by weight of methyl vinyl silicone rubber raw rubber were added to 20 parts by weight of structure control agent masterbatch, and the mixture was thoroughly mixed on a two-roll mill to obtain an uncured compound. Blank compound samples without structure control agent masterbatch, comparative compound samples with ordinary small-molecule hydroxyl silicone oil structure control agent, compound samples with structure control agent masterbatch from the example group, and compound samples with structure control agent masterbatch from the comparative example group were prepared. The initial Mooney viscosity of each group of samples was measured according to ML 1+4 mode at a test temperature of 125℃. The compound samples were then placed in a 70℃ constant temperature oven for 72 hours for accelerated storage. After storage, the Mooney viscosity was measured again under the same conditions, and the Mooney viscosity change rate was calculated.

[0081] Take the above four types of uncured rubber compounds and add 0.6 parts by weight of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane vulcanizing agent to each, and mix them evenly. Place the compounds in a flat vulcanizing mold and vulcanize at 180℃ and 18MPa pressure for 12 minutes. After demolding, allow them to cool naturally to room temperature to obtain blank rubber compound sample groups, control rubber compound sample groups, example groups, and comparative example groups of vulcanized silicone rubber test pieces with a thickness of 2 mm. Test the initial tensile strength at a tensile speed of 500 mm / min. Completely immerse the remaining test pieces in 10% H2SO4 aqueous solution and 10% NaOH aqueous solution, respectively, seal the containers, and soak them at a constant temperature of 40±1℃ for 30 days, changing the soaking solution every 7 days. After soaking, remove the test pieces, rinse them with water, and air dry them at room temperature for 24 hours. Test the tensile strength and calculate the tensile strength retention rate after acid soaking and alkali soaking.

[0082] The test results are shown in Tables 1 and 2.

[0083]

[0084]

[0085] As shown in Table 1, the water contact angles of Comparative Example 1 (without methylphenyl dimethoxysilane) and Comparative Example 2 (using unmodified ordinary fumed silica) were 76.2° and 68.5°, respectively, exhibiting hydrophilic or weakly hydrophobic properties. The contact angles of Examples 1-5 all reached over 96°, with Example 2 reaching as high as 104.5°. This is because the large steric hindrance effect of the phenyl group in the structure control agent and the π-π stacking interaction formed between the aromatic rings of polydopamine significantly reduced the interfacial polarity of the system, thereby inhibiting the adsorption and diffusion of water molecules and acid / base ions.

[0086] Although Comparative Example 3 improved the contact angle to 91.4° through excessive coating, it was still significantly lower than that of the other examples. The main reason is that a dense polydopamine layer with a thickness of about 9 nm was formed on the surface of the fumed silica in Comparative Example 3. Although it is hydrophobic, it caused subsequent anchoring failure because it blocked the silanol groups.

[0087] Regarding the retention rate of the masterbatch after acid and alkali immersion, Comparative Example 2, lacking dopamine modification, had an anchoring structure susceptible to acid and alkali corrosion, resulting in an anchoring retention rate of less than 30%. Comparative Example 4, lacking vinyl groups in its structure control agent, could not participate in vulcanization crosslinking and the formation of a non-covalent interpenetrating network, leading to easy dissociation of the anchoring structure at the interface and a lower anchoring retention rate compared to the other examples. In each example, the polydopamine layer selectively passivated highly active silanol groups, and by controlling the coating thickness, the surface of the silica retained reaction sites capable of participating in subsequent condensation anchoring. Combined with the vinyl groups in the structure control agent to construct a reinforcing network, the anchoring retention rate remained above 80% under both strong acid and strong alkali environments. Example 2, with an anchoring retention rate approaching 90%, demonstrated the dual protective effect of chemical bonding anchoring and physical network reinforcement, effectively blocking the penetration channels of corrosive media into the interface.

[0088] In terms of mechanical properties, the blank and control compound samples showed significant degradation in mechanical properties and low strength retention after acid and alkali immersion. In contrast, the embodiments of this invention maintained over 80% tensile strength retention after 30 days of continuous immersion in strong acids and alkalis. This further demonstrates that this invention, through the synergistic effects of phenyl hydrophobic shielding, dopamine selective passivation, and vinyl-reinforced interpenetrating network participation in vulcanization crosslinking, can significantly improve the structural integrity and mechanical strength retention of vulcanized silicone rubber under long-term immersion in strong acids and alkalis, while ensuring the processing flowability and storage stability of the compound.

[0089] Comparative Example 5, without the addition of a Lewis acid catalyst, had a contact angle of 103.5° in the initial state. However, due to the lack of catalyst-catalyzed Si-O-Si chemical bonding anchoring, the structure control agent was only physically adsorbed on the surface of fumed silica. After acid and alkali immersion, it was easily desorbed, causing its anchoring retention rate to plummet to about 45%, and its tensile strength retention rate to be only about 55%. This indicates that the Lewis acid catalyst plays a key role in achieving chemical bonding and preventing the migration and precipitation of the control agent.

[0090] As shown in Table 2, the initial Mooney viscosity of the blank compound sample without added structure control agent was as high as 72. After being stored at 70°C for 72 hours, it underwent significant structuring, and the Mooney viscosity increased significantly to 118, with a change rate of over 60%. The storage stability of each comparative example was inferior to that of the embodiments of the present invention.

[0091] The initial Mooney viscosity of each embodiment of the present invention is moderate, ranging from 48 to 52, and the viscosity change rate after accelerated storage is less than 12%. This indicates that the phenyl group in the structure control agent provides good lubrication, while the polydopamine modified layer effectively passivates the active sites on the surface of silica, preventing excessive formation of hydrogen bond networks. The comparative compound samples with the addition of common small molecule structure control agents can reduce the initial Mooney viscosity to some extent, but the Mooney viscosity still shows a significant rebound after long-term storage, indicating limited anti-structuralization effect. The Mooney change rate of Comparative Example 5 after storage is 59.2%, indicating that without chemical anchoring, physical mixing alone cannot maintain the low viscosity state of the rubber compound for a long time.

[0092] This invention achieves a synergistic effect through phenyl hydrophobic shielding, dopamine selective passivation, and vinyl-reinforced crosslinking network, which not only ensures the excellent processing flowability and storage stability of the compound, but also solves the technical problems of easy restructuring and rapid mechanical decay of silicone rubber under strong acid and alkali conditions, thus meeting the requirements of industrial applications under harsh conditions.

[0093] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a high-performance structure control agent masterbatch for vulcanized silicone rubber, characterized in that, Includes the following steps: S1. A hydroxyl-terminated linear dimethyl oligosiloxane, methyl vinyl dimethoxysilane, and methyl phenyl dimethoxysilane are mixed and a weak acidic condensation catalyst is added under nitrogen protection to carry out a condensation copolymerization reaction. After neutralization, vacuum descaling, and filtration, a structure control agent is obtained. S2. Add silica and dopamine to a tris(hydroxymethyl)aminomethane buffer solution for self-polymerization reaction, and after washing and vacuum drying, obtain polydopamine-modified silica. S3. The raw methyl vinyl silicone rubber and the structure control agent are put into a mixer and mixed until the components are uniformly dispersed; the polydopamine-modified silica is added in batches, the temperature is raised and Lewis acid catalyst is added to carry out condensation anchoring reaction; vacuum depressurization and cooling are performed to obtain the structure control agent masterbatch.

2. The method for preparing the high-performance structure control agent masterbatch for vulcanized silicone rubber according to claim 1, characterized in that: In step S1, the main component of the structure control agent is α-hydroxy-ω-methoxy-terminated oligomeric (dimethyl-methylvinyl-methylphenyl)siloxane, with a viscosity of 20-80 mPa·s at 25°C, a hydroxyl content of 2-8 wt%, a vinyl content of 1-5 wt%, a phenyl content of 2-6 wt%, a number-average molecular weight of 1500-3000, and a molecular weight distribution index of 1.5-2.

5.

3. The method for preparing the high-performance structure control agent masterbatch for vulcanized silicone rubber according to claim 1, characterized in that: In step S1, by mass, the terminal hydroxyl linear dimethyl oligosiloxane is 60-70 parts, methyl vinyl dimethoxysilane is 12-20 parts, methyl phenyl dimethoxysilane is 6-10 parts, and the weak acidic condensation catalyst is 0.2-0.6 parts.

4. The method for preparing the high-performance structure control agent masterbatch for vulcanized silicone rubber according to claim 1, characterized in that: In step S1, the hydroxyl-terminated linear dimethyl oligosiloxane has a number-average molecular weight of 500-800, a viscosity of 10-30 mPa·s, and a hydroxyl content of 4-10 wt%.

5. The method for preparing the high-performance structure control agent masterbatch for vulcanized silicone rubber according to claim 1, characterized in that: In step S1, the weakly acidic condensation catalyst is selected from one or more of p-toluenesulfonic acid, formic acid, and acetic acid; the neutralization reagent is selected from one or more of sodium carbonate, sodium bicarbonate, or ammonia water, and the pH of the system is adjusted to 6.5-7.

5.

6. The method for preparing the high-performance structure control agent masterbatch for vulcanized silicone rubber according to claim 1, characterized in that: In step S1, the reaction temperature of the condensation copolymerization reaction is 70-85℃, and the reaction time is 3-4h. The vacuum de-lowering temperature is 100-120℃, and the de-lowering time is 1.0-1.5h. It is used to remove methanol, unreacted small molecule monomers and oligomer byproducts generated by condensation copolymerization reaction.

7. The method for preparing the high-performance structure control agent masterbatch for vulcanized silicone rubber according to claim 1, characterized in that: In step S2, the concentration of the tris(hydroxymethyl)aminomethane buffer solution is 5-10 mmol / L, and the pH is 8.5-9.5; the mass ratio of the silica to the dopamine is 1:0.10-0.25; and the mass ratio of the silica to the tris(hydroxymethyl)aminomethane buffer solution is 1:100-300. The self-polymerization reaction is carried out at a temperature of 25-30℃ for 1.5-2.5 hours. A thin layer with a thickness of 1-5 nm is formed on the surface of the polydopamine-modified silica.

8. The method for preparing the high-performance structure control agent masterbatch for vulcanized silicone rubber according to claim 1, characterized in that: In step S3, by mass, the raw methyl vinyl silicone rubber is 45-55 parts, the structure control agent is 35-45 parts, the polydopamine modified silica is 6-12 parts, and the Lewis acid catalyst is 0.1-0.4 parts. The Lewis acid catalyst is selected from one or more of dibutyltin oxide, dioctyltin oxide, and tetrabutyl titanate; The mixing temperature is 40-60℃, the rotation speed is 30-60r / min, and the mixing time is 10-20min.

9. The method for preparing the high-performance structure control agent masterbatch for vulcanized silicone rubber according to claim 1, characterized in that: In step S3, the reaction temperature of the condensation anchoring reaction is 80-90℃, and the reaction time is 30-60min.

10. The method for preparing the high-performance structure control agent masterbatch for vulcanized silicone rubber according to claim 1, characterized in that: In step S3, the vacuum de-lowering temperature is 100-110℃ and the de-lowering time is 50-70min, which is used to remove methanol, residual water, unreacted small molecule monomers and easily hydrolyzed oligomers generated by condensation in the system.

Images