A highly efficient catalyst for hydrosilylation reactions and its preparation method

Abstract

This application relates to the field of hydrosilylation, and in particular to a highly efficient catalyst for hydrosilylation reactions and its preparation method. This application provides a method for preparing a microcapsule-form catalyst, which first modifies methyl-terminated hydroxyl silicone oil with silazane, and then forms a microcapsule coating system with paraffin, thereby improving the release performance of the microcapsule coating system, so that the catalyst has low reactivity in the early stage of release, thereby improving the uniformity of the reaction process inside the silicone rubber, and thus improving the transparency and overall strength of the silicone rubber.

Description

Technical Field

[0001] This application relates to the field of hydrosilylation, and in particular to a highly efficient catalyst for hydrosilylation reactions and a method for preparing the same. Background Technology

[0002] Hydrosilylation is a reaction between silicon and unsaturated organic compounds such as olefins via silicon-hydrogen bonds. It is primarily used in the preparation of silicone rubber from hydrogen-containing silicone oils and vinyl silicone oils. Industrially, hydrosilylation mainly employs platinum-based catalysts, such as Karstedt catalysts or chloroplatinic acid.

[0003] Because silicone rubber is sensitive to components such as water vapor during catalytic reactions, catalyst deactivation often occurs during long-term storage. Therefore, existing technologies have developed methods such as microencapsulation to encapsulate and protect the catalyst, thereby improving the weather resistance of silicone rubber raw materials. For example, invention CN105665014A discloses a supported platinum catalyst for hydrosilylation and its preparation method, which involves microencapsulating the platinum catalyst on an organosilicon support and releasing the platinum catalyst upon heating.

[0004] Based on most existing technologies, the encapsulation of catalysts in the form of microcapsules adopts the method of heat release. After heat treatment, the microcapsules are broken and the catalyst is released, which then reacts with hydrogen-containing silicone oil or vinyl silicone oil. However, because the catalyst is more reactive under heating, the reaction rate between different parts of the silicone rubber is different during the catalytic process. This leads to uneven curing structure inside the silicone rubber, affecting the overall strength and transparency of the silicone rubber. Summary of the Invention

[0005] Based on the above problems, the purpose of this application is to improve the release process of catalysts in microcapsule form, so that the catalyst is less likely to be locally enriched due to the presence of microcapsules, thereby improving the strength and transparency of the prepared silicone rubber.

[0006] In a first aspect, this application provides a method for preparing a highly efficient catalyst for hydrosilylation reactions, comprising the following steps:

[0007] S1. Silicone oil containing hydroxyl groups on its side chains is modified with silazane, wherein the molar ratio of silazane to hydroxyl groups is 0.1 to 0.4:1, to obtain silazane-modified methyl-terminated hydroxyl silicone oil.

[0008] S2. Under an oxygen-free environment, the catalyst compound, methyl-terminated hydroxyl silicone oil modified with silazane, and liquid paraffin are mixed to obtain the first mixed system;

[0009] S3. Prepare solid paraffin wax, heat it to melt, and do not exceed 100°C. While maintaining a shear rate of 5000-10000 rpm, add the solid paraffin wax in batches to the first mixing system within 1-5 minutes. Then continue to emulsify it thoroughly until homogeneous to obtain the second mixing system.

[0010] S4. The mixture in step S3 is prepared into microcapsules by spray cooling;

[0011] The mass of the liquid paraffin is 0.1 to 0.3 times the mass of the solid paraffin;

[0012] The total mass of the liquid and solid paraffin is 10 to 20 times the mass of the catalyst compound.

[0013] In the above scheme, a microcapsule structure system with paraffin as the main component is provided. Overall, the packaging material uses two main components: methyl-terminated hydroxyl silicone oil modified with silazane and paraffin. The paraffin is mainly solid paraffin with some liquid paraffin added. The main purpose is to provide a lower thermal decomposition temperature and also to provide a good barrier effect.

[0014] In this application, methyl-terminated hydroxyl silicone oil refers to silicone oil with hydroxyl groups on its branches. Preferably, the hydroxyl content of the methyl-terminated hydroxyl silicone oil is 1.5–2.0 mg / g, where the hydroxyl content refers to the mass of hydroxyl groups per gram of methyl-terminated hydroxyl silicone oil being 1.5–2.0 mg. Overall, it belongs to methyl-terminated hydroxyl silicone oil with a relatively low hydroxyl content. The main purposes of using methyl-terminated hydroxyl silicone oil in this system are as follows: First, methyl-terminated hydroxyl silicone oil has a certain degree of coordination, thus effectively controlling the diffusion rate of the catalyst and reducing its activity during the encapsulation process. However, excessive hydroxyl content in methyl-terminated hydroxyl silicone oil can lead to excessively strong coordination with the catalyst, resulting in catalyst poisoning. Simultaneously, methyl-terminated hydroxyl silicone oil provides a certain degree of hydrophilicity, which can better control the formation of the interface during microcapsule molding. It can also disrupt paraffin crystallization to provide better heat release effects. Furthermore, in the early stages of release, it can improve the dispersion of the catalyst, making local micro-reactions more uniform.

[0015] Building upon the above, methyl-terminated hydroxyl silicone oil is modified with silazane to enhance hydrophobicity at some hydroxyl groups. The primary purpose is to improve the coordination effect of the methyl-terminated hydroxyl silicone oil with the catalyst. Small-scale modification of the methyl-terminated hydroxyl silicone oil can significantly improve the catalytic performance without affecting its microcapsule release performance, reducing the impact of the methyl-terminated hydroxyl silicone oil on the catalyst. Simultaneously, silazane modification can provide further perturbation at the branched chains, improving the dispersibility of microcapsules in the silicone rubber raw material system, and also improving the transparency and strength of the molded product. In contrast, directly using methyl-terminated hydroxyl silicone oil with a lower hydroxyl value, compared to modifying it with silazane to achieve a higher hydroxyl content, results in less overall steric hindrance and a stronger coordination effect. This leads to a more severe inhibition of the catalyst, resulting in a significant weakening of the silicone rubber's curing effect. The preferred mass of methyl-terminated hydroxyl silicone oil is 2 to 5 times the mass of the catalyst, and generally less than the mass of paraffin. It also helps improve the strength of the silicone rubber system. Excessive methyl-terminated hydroxyl silicone oil, besides significantly increasing the system cost, also leads to a significant increase in the rupture temperature of the microcapsule system. This may be because, despite the modification with silazane, residual hydroxyl groups in the system still form a cross-linked system through hydrogen bonds, thus affecting the release performance of the system. The preferred silazane is HMDS, which provides good reactivity and coating properties. Furthermore, its modification of the methyl-terminated hydroxyl silicone oil improves the overall dispersibility of the microcapsules in the silicone rubber system, further improving the dispersibility of the catalyst itself.

[0016] The process involves initially mixing methyl-terminated hydroxyl silicone oil modified with silazane, liquid paraffin, and a catalyst to form an initial dispersion structure, which provides a certain protective effect during subsequent processing. Then, the liquid paraffin and the modified methyl-terminated hydroxyl silicone oil are slowly dispersed into the molten liquid paraffin system. A coating system is formed through high-speed shearing and then through atomization spraying. Compared with the emulsion method, this approach can be carried out in a completely anhydrous environment, reducing the impact on the catalyst. At the same time, almost no solvent is used throughout the process, thus reducing waste liquid discharge and resulting in better overall industrial production efficiency.

[0017] Based on the above, the preferred melting point of solid paraffin is 50-60℃, which allows for melting and atomization at a relatively low overall temperature. In addition, the use of paraffin with a lower melting point in this scheme is mainly aimed at reducing the temperature requirements for heating the silicone sealant during the curing process, improving the release effect of the catalyst, and thus achieving a better curing process.

[0018] Preferably, in step S3, microcrystalline wax is also added, wherein the mass of the microcrystalline wax is 0.05 to 0.2 times the mass of the solid paraffin wax;

[0019] And / or,

[0020] In step S3, the heating temperature is 15-30°C higher than the melting point of solid paraffin.

[0021] In the above scheme, a small amount of microcrystalline wax is introduced. The overall purpose is to improve the coating performance and the overall strength of the formed microcapsules. On the one hand, it reduces catalyst deactivation caused by wall material damage during long-term storage or stirring. On the other hand, it also helps the overall coating and forming. At the same time, the small amount of microcrystalline wax coating will not affect the heat release performance, and can also provide better moisture resistance and weather resistance.

[0022] Preferably, in step S2, 5-15% by weight of a nonionic surfactant is added to the liquid paraffin.

[0023] The main purpose of nonionic surfactants is to improve the uniformity of catalyst dispersion in the system. Considering that the catalyst itself has strong polarity, adding a certain amount of nonionic surfactant helps to improve the uniformity of the encapsulation system.

[0024] Preferably, step S1 is as follows:

[0025] Methyl-terminated hydroxyl silicone oil is dissolved in benzene or alkyl-substituted benzene solvent, heated to 60-90°C, and silazane is uniformly added to the system over 10-30 minutes under an anaerobic environment. After the addition is complete, the reaction continues for 4-8 hours. Subsequently, the solvent and residual silazane are removed by vacuum distillation, and the residual NH3 is removed by an adsorbent. The solution is then ready for use.

[0026] Since silazane produces NH3 during the reaction, which can severely affect the activity of the catalyst, the above scheme adopts a dual purification step. First, the solvent and residual ammonia are removed by vacuum distillation. At the same time, residual ammonia is further removed by an adsorbent (such as magnesium sulfate or molecular sieve). After the above treatment, the impact on the catalyst is minimal, allowing the catalyst to form a good catalytic effect.

[0027] Preferably, in step S2, an inhibitor is also added, wherein the inhibitor is 1 to 3 times the mass of the catalyst compound.

[0028] The addition of inhibitors can further control the catalytic effect of the catalyst. Since the overall content of the added inhibitors is low, they will only inhibit the catalytic activity of the catalyst when the microcapsules are initially broken. After the catalyst is evenly distributed in the system, due to its low dosage, it will not have an adverse effect on the curing process. Overall, it further improves the uniformity of the silicone rubber curing process.

[0029] In addition, this application also relates to the high-efficiency catalyst prepared by the above preparation method, which, when incorporated into the silicone rubber system, is basically not damaged by high-speed stirring or other mechanical behavior. It will only be damaged by microcapsule rupture under heating conditions, releasing the catalyst. This improves the weather resistance of the catalyst while ensuring good curing performance. At the same time, it can also provide more uniform curing performance in the silicone rubber to improve the strength and transparency of the good silicone rubber.

[0030] In summary, this application provides a method for preparing a microcapsule catalyst. First, methyl-terminated hydroxyl silicone oil is modified with silazane, and then it is combined with paraffin to form a microcapsule coating system. This improves the release performance of the microcapsule coating system, allowing the catalyst to have low reactivity in the initial stage of release, thereby improving the uniformity of the reaction process inside the silicone rubber, and thus improving the transparency and overall strength of the silicone rubber. Detailed Implementation

[0031] The technical solution of this application will be further described through the following specific embodiments.

[0032] While Karstedt platinum catalysts or other platinum catalysts are widely used in silicone rubber reaction systems, their application in microencapsulation systems has not been widely reported in the market. Microencapsulation can effectively improve the weather resistance of catalysts and reduce catalyst poisoning during long-term storage. However, the release process can lead to localized catalyst concentration, and because microcapsule rupture requires high temperatures, it can cause localized silicone rubber reactions to be too rapid, affecting overall uniformity.

[0033] To address the aforementioned issues, the following embodiments employ a special coating material to coat the Karstedt platinum catalyst, thereby suppressing its catalytic activity as early as possible without affecting overall curing performance and providing better transparency. It should be noted that the method described in this application is also applicable to the coating of other platinum catalysts.

[0034] Example 1: In this example, a microcapsule system was prepared using the Karstedt platinum catalyst, specifically including the following steps:

[0035] S1, silazane-modified methyl-terminated hydroxyl silicone oil:

[0036] Under dry nitrogen protection, methyl-terminated hydroxyl silicone oil (hydroxyl content 1.8 mg / g, viscosity 50 mm² / s at 25℃) was dissolved in toluene at a ratio of 1:5. The mixture was heated to 80℃, and then, over 20 minutes while stirring, HMDS was slowly added dropwise to the methyl-terminated hydroxyl silicone oil at a molar ratio of 0.25:1 (i.e., the mass ratio of HMDS to methyl-terminated hydroxyl silicone oil was 0.0043:1). (If the amount of HMDS is too small to add dropwise, a small amount of toluene can be used to dissolve it first. After the addition was complete, the reaction was continued at 80℃ for 6 hours. Then, toluene was removed by vacuum distillation at 60℃ (vacuum distillation time 40 minutes), and residual NH3 was removed by adsorption treatment with 3A-grade molecular sieves.

[0037] S2, Initial dispersion of catalyst:

[0038] Weigh each material according to the following mass proportions:

[0039] 1 part Karstedt platinum catalyst

[0040] Liquid paraffin (density 0.831 g / cm³) 2.5 parts

[0041] 3 parts of silazane-modified methyl-terminated hydroxyl silicone oil (based on unmodified)

[0042] Nonionic surfactant (Span-80) 0.3 parts

[0043] Inhibitor (dimethyl maleate) 2 parts

[0044] The above system was mixed at 500 rpm for 30 minutes in a strictly anaerobic environment to obtain a premixed system.

[0045] S3, wall material overmolding

[0046] Based on the above mass ratio, the following mass parts of material are further weighed per 1 part by mass of Karstedt platinum catalyst:

[0047] Solid paraffin wax (melting point 57.4℃) 12.5 parts

[0048] Microcrystalline wax (70#, melting point 69.2℃) 1.25 parts

[0049] The mixture of solid paraffin wax and microcrystalline wax was heated to 80°C, melted and stirred evenly. The premixed system obtained in step S2 was then transferred to a high-speed emulsifier. Under a strictly oxygen-free and water-free environment (dry nitrogen protection), emulsification was started at 80°C and 8000 rpm. The molten solid paraffin wax and microcrystalline wax system was added to the emulsifier in five batches within 5 minutes. Emulsification was then continued for 15 minutes to obtain a stable system.

[0050] S4. The stable system obtained in step S3 is spray-dried into granules using a spray dryer, with the inlet temperature controlled at 25°C. The granules are then passed through a 50-mesh sieve for later use.

[0051] Example 2 differs from Example 1 in that, in step S2, the mass fraction of liquid paraffin is 3.5 parts and the mass fraction of solid paraffin is 11.5 parts.

[0052] Example 3 differs from Example 1 in that, in step S2, the mass fraction of liquid paraffin is 1.5 parts and the mass fraction of solid paraffin is 13.5 parts.

[0053] Example 4 differs from Example 1 in that microcrystalline wax is not added in step S2 or step S3.

[0054] Example 5 differs from Example 1 in that, in step S2 and step S3, the mass fraction of microcrystalline wax added is 2.5 parts.

[0055] Example 6 differs from Example 1 in that, in step S2 and step S3, the mass fraction of microcrystalline wax added is 4 parts.

[0056] Examples 7-21: In this series, different methyl-terminated hydroxyl silicone oils were used, and different amounts of silazane were added to the methyl-terminated hydroxyl silicone oils, as shown in Table 1.

[0057]

[0058] In Comparative Example 1, based on Example 1, step S1 was omitted. In step S2, unmodified methyl-terminated hydroxyl silicone oil (hydroxyl content 1.8 mg / g, viscosity 50 mm² / s at 25°C) was directly added.

[0059] Comparative Example 2: Based on Example 1, step S1 is omitted in this comparative example. In step S2, the methyl-terminated hydroxyl silicone oil is replaced with low-viscosity methyl silicone oil (viscosity 100 mm² / s at 25°C).

[0060] Compared with Example 3, based on Example 1, step S1 is omitted, and in step S2, methyl-terminated hydroxyl silicone oil is not added. Liquid paraffin is used directly for premixing.

[0061] Compared with Example 4, based on Example 1, in step S2, the mass fraction of liquid paraffin is adjusted to 7.5 parts by mass, the mass fraction of solid paraffin is adjusted to 7.5 parts by mass, and the mass fraction of microcrystalline wax is adjusted to 0.75 parts by mass.

[0062] Compared with Example 1, Example 5 differs in that liquid paraffin is not added in step S2, and the mass of solid paraffin is adjusted to 15 parts in step S3, while the mass of microcrystalline wax remains unchanged.

[0063] The experimental results for the above catalyst were verified using the following silicone rubber system:

[0064] Vinyl silicone oil (vinyl content 0.15%, viscosity at 25°C 5000 mPa·s) 100 parts by weight;

[0065] 3.5 parts of hydrogen-containing silicone oil (hydrogen content 0.18%, viscosity 30 mPa·s);

[0066] 10 parts of nano-fumed silica (50nm particle size)

[0067] Catalyst 15 ppm (calculated as platinum).

[0068] The overall preparation method is as follows:

[0069] Vinyl silicone oil and hydrogen-containing silicone oil were mixed at 25°C, then a catalyst was added and stirred until homogeneous. The mixture was then poured into a mold. Three experimental groups were designed and heated to 60°C, 80°C and 100°C respectively. Every 1 minute, a glass rod tip was used to slide the mixture until it could no longer flow. The gelation time at different temperatures was recorded.

[0070] In addition, a control example 6 was set up in which Karstedt platinum catalyst was added directly to the same system at a platinum content of 15 ppm without coating, while keeping other conditions unchanged. This method was cured at 60°C, and the tensile strength and transmittance of the system were measured to compare with Example 1, in order to verify that the method in this application does not affect the catalytic performance of the catalyst.

[0071] Meanwhile, for the samples fully cured at 60℃, referring to "GB / T 528-2009 Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber", the samples were cut into type 2 specimens using a universal testing machine, and the tensile strength of the prepared samples was measured. Referring to "GB / T 2410-2008 Determination of Light Transmittance and Haze of Transparent Plastics", the light transmittance of the samples (thickness 5mm) was measured using a spectrophotometer.

[0072] In addition, after the catalyst was prepared, it was placed in an environment of 80% relative humidity and 25°C for 24 hours, and the gel time of the above system for curing silicone rubber at 60°C was measured again.

[0073] The overall experimental results for the above embodiments and control examples are shown in Table 2.

[0074]

[0075] In Table 2, " / " indicates that no measurement was performed.

[0076] Note ①: In Comparative Example 5, since the product could not be fully solidified at 60°C, the tensile strength and elongation at break were measured on the product after it was cured at 80°C.

[0077] By comparing Example 1 and the Comparative Example, it can be seen that the catalyst prepared in this application has similar tensile strength and transparency to the Comparative Example 6 after catalysis. This indicates that the microencapsulation method used in Example 1 to encapsulate the catalyst has virtually no adverse effect on the catalytic effect, and the introduction of small amounts of paraffin and methyl-terminated hydroxyl silicone oil does not affect the strength of the silicone rubber. Referring to Examples 2-6 and Comparative Examples 4 and 5, the direct use of solid paraffin in Comparative Example 5 leads to a deterioration in the system's heat release performance. It cannot fully solidify at 60°C and only exhibits good reactivity at 80°C. Furthermore, at higher temperatures, its transparency and strength significantly decrease. In Comparative Example 4, the excessive addition of liquid paraffin results in insufficient overall wall strength, negating the purpose of encapsulation and causing significant catalyst deactivation under high humidity conditions. Furthermore, the amount of microcrystalline wax in the system was adjusted in Examples 4-6. Excessive addition of microcrystalline wax can also lead to a decrease in the uniformity of the system. This may be because microcrystalline wax makes it more difficult for the microcapsules to undergo thermal decomposition, and after thermal decomposition, the microcrystalline wax itself is prone to crystallization within the system, resulting in more severe light scattering. However, in Example 4, the absence of microcrystalline wax generally leads to a decrease in encapsulation performance, and some catalyst deactivation still occurs under high humidity conditions, resulting in a prolonged gelation time after high humidity treatment.

[0078] In Examples 7-21 and Comparative Examples 1-3, the parameters of the methyl-terminated hydroxyl silicone oil and its modification were adjusted. First, in Comparative Example 1, the absence of hydroxyl modification resulted in a significant decrease in catalyst activity, failing to cure within 2 hours at both 60°C and 80°C. In Comparative Example 2, replacing the methyl-terminated hydroxyl silicone oil with ordinary silicone oil, while allowing for normal coating, still resulted in excessively strong early-stage catalytic activity, leading to a significant decrease in system transparency. Comparative Example 3 yielded similar experimental results to Comparative Example 2, demonstrating that the methyl-terminated hydroxyl silicone oil's inhibitory catalytic effect in localized areas significantly improves reaction uniformity. However, Examples 16-18 also show that excessive hydroxyl content in the methyl-terminated hydroxyl silicone oil can prolong the overall curing time and negatively impact overall strength. Furthermore, excessive addition of methyl-terminated hydroxyl silicone oil can lead to the presence of crystalline methyl-terminated hydroxyl silicone oil in the system, affecting transparency. Additionally, the interactions of the methyl-terminated hydroxyl silicone oil make the microcapsule system more difficult to break, resulting in a longer gel time at 60–80°C. Excessive addition of silazane also has some adverse effects. Due to the increased branching of the methyl-terminated hydroxyl silicone oil, the encapsulation performance is weakened, making the catalyst more easily exposed in humid environments. However, its strong hydrophobicity somewhat compensates for these defects, so the curing time is only slightly extended under high humidity exposure. On the other hand, excessive silazane can reduce the inhibitory effect of methyl-terminated hydroxyl silicone oil on catalyst activity, thus affecting overall transparency.

[0079] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a highly efficient catalyst for hydrosilylation reactions, characterized in that, Includes the following steps: S1. Modify the methyl-terminated hydroxyl silicone oil on the side chain with silazane, wherein the molar ratio of silazane to hydroxyl group is 0.1 to 0.4:1, to obtain silazane-modified methyl-terminated hydroxyl silicone oil; S2. Under an oxygen-free environment, the catalyst compound, methyl-terminated hydroxyl silicone oil modified with silazane, and liquid paraffin are mixed to obtain the first mixed system; S3. Prepare solid paraffin wax, heat it to melt, and do not exceed 100°C. While maintaining a shear rate of 5000-10000 rpm, add the solid paraffin wax in batches to the first mixing system within 1-5 minutes. Then continue to emulsify it thoroughly until homogeneous to obtain the second mixing system. S4. The mixture in step S3 is prepared into microcapsules by spray cooling; The mass of the liquid paraffin is 0.1 to 0.3 times the mass of the solid paraffin; The total mass of the liquid and solid paraffin is 10 to 20 times the mass of the catalyst compound; The methyl-terminated hydroxyl silicone oil has a hydroxyl content of 1.5–2.0 mg / g. The mass of the methyl-terminated hydroxyl silicone oil is 2 to 5 times the mass of the catalyst compound; The silazane is HMDS; In step S3, microcrystalline wax is also added, wherein the mass of the microcrystalline wax is 0.05 to 0.2 times the mass of the solid paraffin wax.

2. The method for preparing a highly efficient catalyst for hydrosilylation reactions according to claim 1, characterized in that, The melting point of the solid paraffin is 50-60℃.

3. The method for preparing a highly efficient catalyst for hydrosilylation reactions according to claim 1, characterized in that, In step S3, the heating temperature is 15-30°C higher than the melting point of solid paraffin.

4. The method for preparing a highly efficient catalyst for hydrosilylation reactions according to claim 1, characterized in that, In step S2, 5-15% by weight of liquid paraffin and a nonionic surfactant are also added.

5. The method for preparing a highly efficient catalyst for hydrosilylation reactions according to claim 1, characterized in that, Step S1 is as follows: Methyl-terminated hydroxyl silicone oil is dissolved in benzene or alkyl-substituted benzene solvent, heated to 60-90°C, and silazane is uniformly added to the system over 10-30 minutes under an anaerobic environment. After the addition is complete, the reaction continues for 4-8 hours. Subsequently, the solvent and residual silazane are removed by vacuum distillation, and the residual NH3 is removed by an adsorbent. The solution is then ready for use.

6. The method for preparing a highly efficient catalyst for hydrosilylation reactions according to claim 1, characterized in that, In step S2, an inhibitor is also added, wherein the inhibitor is 1 to 3 times the mass of the catalyst, and the inhibitor is dimethyl maleate.

7. The high-efficiency catalyst prepared by the preparation method according to any one of claims 1 to 6.

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