High-efficiency platinum catalyst, preparation method and application thereof

Abstract

This invention belongs to the field of catalyst technology, and discloses a high-efficiency platinum catalyst, its preparation method, and its application. The preparation of the high-efficiency platinum catalyst of this invention includes mixing and stirring a Karstedt catalyst, a ligand, and a catalyst, adding vinyl-terminated polydimethylsiloxane, and fully dissolving it to obtain the high-efficiency platinum catalyst. The obtained catalyst is used to prepare filler-free flame-retardant silicone rubber, which comprises the following raw materials in parts by weight: 80-100 parts vinyl-terminated polydimethylsiloxane, 2-4 parts crosslinking agent, 2-10 parts of the high-efficiency platinum catalyst of this invention, and 0.2-0.3 parts polymerization inhibitor. This invention provides a novel modified platinum catalyst for silicone rubber, which enhances the anti-sintering properties of Pt at high temperatures through the nitrogen-containing carbene ring and the Pt ligand, thereby improving the flame-retardant properties of silicone rubber brought by the platinum catalyst.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and specifically relates to a high-efficiency platinum catalyst, its preparation method, and its application. Background Technology

[0002] Silicone rubber is formed by crosslinking and curing vinyl-terminated polydimethylsiloxane and polymethylhydrosiloxane under the action of Karstedt catalyst. Typical flame-retardant silicone rubber requires the addition of a large amount of inorganic fillers to the matrix to improve its flame retardancy. For example, the glass powder and titanium dioxide added in Chinese patent publication text CN115491038A will greatly affect the transparency of the silicone rubber itself, which limits its application in some high-end fields.

[0003] The derivative ceramics formed from silicone rubber without inorganic fillers at high temperatures are relatively loose and exhibit low ceramic conversion rates. This is because while the Karstedt catalyst has extremely high catalytic efficiency for hydrosilylation, its thermal stability is poor. At high temperatures, Pt in the Karstedt gradually dissolves to form a yellow Pt colloid, which eventually sintersects to form black Pt nanoparticles with low catalytic efficiency. To address this issue, previous studies have often used strong ligands to modify the Karstedt catalyst to improve its catalytic activity at high temperatures. However, while strong ligands provide thermal stability to the Pt catalyst, they also significantly degrade its hydrosilylation rate. Therefore, the aforementioned studies all require a dual-curing system that can only be carried out under high temperature and high pressure, and this complex curing condition limits the application of platinum catalysts in coatings. Summary of the Invention

[0004] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing a highly efficient platinum catalyst.

[0005] Another object of the present invention is to provide a highly efficient platinum catalyst prepared by the above method.

[0006] Another objective of this invention is to provide the application of the above-mentioned highly efficient platinum catalyst in the preparation of flame-retardant silicone rubber.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned flame-retardant silicone rubber.

[0008] Another object of the present invention is to provide the application of the above-mentioned flame-retardant silicone rubber in flame-retardant materials.

[0009] The objective of this invention is achieved through the following solution:

[0010] A method for preparing a high-efficiency platinum catalyst includes the following steps: mixing and stirring a Karstedt catalyst, a ligand and a catalyst, adding vinyl-terminated polydimethylsiloxane, and dissolving it completely to obtain a high-efficiency platinum catalyst.

[0011] The ligand is at least one of 1,3-dimethylimidazolium iodide, 1,3-dimethylbenzimidazolium iodide, and 1,3-diphenylbenzimidazolium iodide.

[0012] The catalyst is at least one of potassium tert-butoxide, potassium methoxide, and sodium ethoxide.

[0013] The mass ratio of the Karstedt catalyst, modified ligand, and catalyst is 39:100 to 200:65.

[0014] The amount of vinyl-terminated polydimethylsiloxane used satisfies the following condition: the mass concentration of Pt in the modified Pt catalyst is 1000ppm to 3000ppm.

[0015] The mixing speed is 500rpm-1500rpm; the mixing time is 10-40min.

[0016] A highly efficient platinum catalyst prepared by the above method.

[0017] A flame-retardant silicone rubber comprises the following raw materials in parts by weight: 80-100 parts of vinyl-terminated polydimethylsiloxane, 2-4 parts of crosslinking agent, 2-10 parts of the above-mentioned high-efficiency platinum catalyst, and 0.2-0.3 parts of polymerization inhibitor.

[0018] The crosslinking agent in the raw material is 2.5-4 parts, preferably 2.5-3.5 parts.

[0019] The crosslinking agent includes at least one of polymethylhydrosiloxane and poly(dimethylsiloxane) hydride end-capping.

[0020] The polymerization inhibitor includes at least one of 1-ethynylcyclohexanol and diallyl maleate.

[0021] The vinyl-terminated polydimethylsiloxane has a vinyl content of 1.0-1.5% by mass; and the crosslinking agent has a hydrogen content of 0.97-1.03% by mass percentage.

[0022] The preparation method of the above-mentioned flame-retardant silicone rubber includes the following steps:

[0023] (1) Mix vinyl-terminated polydimethylsiloxane, crosslinking agent and polymerization inhibitor, then add modified Pt catalyst, stir, and vacuum degas to obtain silicone rubber prepolymer;

[0024] (2) Add the organosilicon prepolymer obtained in step (1) into a rectangular mold, let it stand and cure to obtain filler-free flame-retardant silicone rubber.

[0025] The stirring speed in step (1) is 500 rpm to 1500 rpm, and the stirring time is 10 to 40 minutes.

[0026] The step (2) of letting the plant stand overnight in a ventilated place.

[0027] The curing step (2) involves curing at 80℃~130℃ for 10~40min.

[0028] The above-mentioned application of flame-retardant silicone rubber in flame-retardant materials.

[0029] Mechanism of the invention:

[0030] This invention utilizes a ligand-modified Pt catalyst method to introduce strong ligand groups into the Karstedt catalyst, thereby reducing the temperature sensitivity of the Pt catalyst by stabilizing the single-atom Pt catalyst. A novel silicone rubber prepared from a ligand-modified platinum catalyst exhibits high transparency and flame retardancy at a level of ul94V-0. This provides a theoretical basis and new solutions for the development of novel catalysts, and offers technical parameters and references for accelerating the promotion and application of flame-retardant silicone rubber.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] (1) This invention provides a novel modified platinum catalyst for silicone rubber, which enhances the anti-sintering properties of Pt at high temperatures through the ligand of the nitrogen-containing carbene ring and Pt, thereby improving the flame retardant properties of silicone rubber brought by the platinum catalyst.

[0033] (2) Unlike Pt catalysts modified with strong ligands such as N, the Pt catalyst modified with nitrogen-containing carbene rings in this invention can improve the anti-sintering ability of Pt without significantly affecting its hydrosilylation activity. Therefore, silicone rubber prepared using the platinum catalyst of this invention still has excellent mechanical properties.

[0034] (3) The use of ligand modification to improve the flame retardant properties of platinum catalysts on silicone rubber does not require the addition of additional inorganic flame retardant fillers to silicone rubber, thus it has excellent transparency, which expands its application in handicrafts, heritage preservation and high-end furniture.

[0035] (4) The modified platinum catalyst for silicone rubber developed in this invention has a very simple preparation process, fewer components, strong process practicality, and can be applied to more scenarios. Attached Figure Description

[0036] Figure 1 This is a comparison of the catalytic activity of the catalysts obtained in Example 1 of the present invention and Comparative Examples 1-2.

[0037] Figure 2 This is a comparison of the thermal stability of the silicone rubber obtained in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0039] Unless otherwise specified, all reagents used in the examples are commercially available.

[0040] In this embodiment of the invention, the following components are used: vinyl-terminated polydimethylsiloxane (vinyl content 1.15 wt%, Guangzhou Chemical Industry Co., Ltd., Chinese Academy of Sciences), crosslinking agent (polymethylhydrosiloxane, hydride content 1 wt%, Guangzhou Chemical Industry Co., Ltd., Chinese Academy of Sciences), Karstedt catalyst (Pt: 19 wt%, Guangzhou Chemical Industry Co., Ltd., Chinese Academy of Sciences), ligand (1,3-dimethylimidazolium iodide, content ≥99 wt%, Aladdin Co., Ltd.), and polymerization inhibitor (1-ethynylcycloethanol, purity ≥99 wt%, Aladdin Co., Ltd.).

[0041] Comparative Example 1

[0042] (1) Preparation of platinum catalyst: Take 39 mg of Karstedt catalyst mother liquor, and then add vinyl-terminated polydimethylsiloxane solvent to obtain a Pt catalyst with a Pt mass concentration of 1000 ppm in the solution.

[0043] (2) Preparation of silicone rubber prepolymer: 0.2g of Pt catalyst obtained in step (1) was added to a mixture of 10g vinyl-terminated polydimethylsiloxane, 0.25g polymethylhydrosiloxane and 0.03g polymerization inhibitor. The mixture was magnetically stirred at room temperature for 40min at a stirring speed of 1500rpm. After vacuum degassing, silicone rubber prepolymer was obtained.

[0044] (3) Preparation of flame-retardant silicone rubber: The organosilicon prepolymer obtained in step (2) is added into a rectangular mold, left to stand overnight in a fume hood, and then placed in a 130°C oven to cure for 10 minutes to obtain transparent flame-retardant silicone rubber.

[0045] Comparative Example 2

[0046] (1) Modification of platinum catalyst: Take 39 mg of Karstedt catalyst mother liquor, 157 mg of 3-aminopropyltriethoxysilane and 65 mg of potassium tert-butoxide catalyst, adjust the magnetic stirrer to 1000 rpm and the magnetic stirring time to 15 min, filter out the potassium tert-butoxide catalyst, and obtain a homogeneous and fully plasticized modified Pt catalyst mother liquor. Then add vinyl-terminated polydimethylsiloxane solvent to obtain a modified Pt catalyst with a Pt mass concentration of 1000 ppm in the solution.

[0047] (2) Preparation of silicone rubber prepolymer: 0.2g of the modified Pt catalyst obtained in step (1) was added to a mixture of 10g of vinyl-terminated polydimethylsiloxane, 0.25g of polymethylhydrosiloxane and 0.03g of 1-ethynylcyclohexanol. The mixture was magnetically stirred at room temperature for 40min at a stirring speed of 1500rpm. After vacuum degassing, silicone rubber prepolymer was obtained.

[0048] (3) Preparation of flame-retardant silicone rubber: The organosilicon prepolymer obtained in step (2) is added into a rectangular mold, left to stand overnight in a fume hood, and then placed in a 130°C oven to cure for 10 minutes to obtain transparent flame-retardant silicone rubber.

[0049] Example 1

[0050] (1) Modification of platinum catalyst: Take 39 mg of Karstedt catalyst mother liquor, 157 mg of 1,3-dimethylimidazolium iodide and 65 mg of potassium tert-butoxide catalyst, adjust the magnetic stirrer to 1000 rpm and the magnetic stirring time to 15 min, filter out the potassium tert-butoxide catalyst, and obtain a homogeneous and fully plasticized modified Pt catalyst mother liquor. Then add vinyl-terminated polydimethylsiloxane solvent to obtain a modified Pt catalyst with a Pt mass concentration of 1000 ppm in the solution.

[0051] (2) Preparation of silicone rubber prepolymer: 0.2g of the modified Pt catalyst obtained in step (1) was added to a mixture of 10g of vinyl-terminated polydimethylsiloxane, 0.25g of polymethylhydrosiloxane and 0.03g of 1-ethynylcyclohexanol. The mixture was stirred at room temperature for 40min at a stirring speed of 1500rpm. After vacuum degassing, silicone rubber prepolymer was obtained.

[0052] (3) Preparation of flame-retardant silicone rubber: The organosilicon prepolymer obtained in step (2) is added into a rectangular mold, left to stand overnight in a fume hood, and then placed in a 130°C oven to cure for 10 minutes to obtain transparent flame-retardant silicone rubber.

[0053] Example 2

[0054] (1) Modification of platinum catalyst: Take 39 mg of Karstedt catalyst mother liquor, 157 mg of 1,3-dimethylimidazolium iodide and 65 mg of potassium tert-butoxide catalyst, adjust the magnetic stirrer to 1000 rpm and the magnetic stirring time to 15 min, filter out the potassium tert-butoxide catalyst, and obtain a homogeneous and fully plasticized modified Pt catalyst mother liquor. Then add vinyl-terminated polydimethylsiloxane solvent to obtain a modified Pt catalyst with a Pt mass concentration of 1000 ppm in the solution.

[0055] (2) Preparation of silicone rubber prepolymer: 0.4g of the modified Pt catalyst obtained in step (1) was added to a mixture of 10g of vinyl-terminated polydimethylsiloxane, 0.25g of polymethylhydrosiloxane and 0.03g of 1-ethynylcyclohexanol. The mixture was magnetically stirred at room temperature for 40min at a stirring speed of 1500rpm. After vacuum degassing, silicone rubber prepolymer was obtained.

[0056] (3) Preparation of flame-retardant silicone rubber: The organosilicon prepolymer obtained in step (2) is added into a rectangular mold, left to stand overnight in a fume hood, and then placed in a 130°C oven to cure for 10 minutes to obtain transparent flame-retardant silicone rubber.

[0057] Example 3

[0058] (1) Modification of platinum catalyst: Take 39 mg of Karstedt catalyst mother liquor, 157 mg of 1,3-dimethylimidazolium iodide and 65 mg of potassium tert-butoxide catalyst, adjust the magnetic stirrer to 1000 rpm and the magnetic stirring time to 15 min, filter out the potassium tert-butoxide catalyst, and obtain a homogeneous and fully plasticized modified Pt catalyst mother liquor. Then add vinyl-terminated polydimethylsiloxane solvent to obtain a modified Pt catalyst with a Pt mass concentration of 1000 ppm in the solution.

[0059] (2) Preparation of silicone rubber prepolymer: 0.6g of the modified Pt catalyst obtained in step (1) was added to a mixture of 10g of vinyl-terminated polydimethylsiloxane, 0.25g of polymethylhydrosiloxane and 0.03g of 1-ethynylcyclohexanol. The mixture was magnetically stirred at room temperature for 40min at a stirring speed of 1500rpm. After vacuum degassing, silicone rubber prepolymer was obtained.

[0060] (3) Preparation of flame-retardant silicone rubber: The organosilicon prepolymer obtained in step (2) is added into a rectangular mold, left to stand overnight in a fume hood, and then placed in a 130°C oven to cure for 10 minutes to obtain transparent flame-retardant silicone rubber.

[0061] Example 4

[0062] (1) Modification of platinum catalyst: Take 39 mg of Karstedt catalyst mother liquor, 157 mg of 1,3-dimethylimidazolium iodide and 65 mg of potassium tert-butoxide catalyst, adjust the magnetic stirrer to 1000 rpm and the magnetic stirring time to 15 min, filter out the potassium tert-butoxide catalyst, and obtain a homogeneous and fully plasticized modified Pt catalyst mother liquor. Then add vinyl-terminated polydimethylsiloxane solvent to obtain a modified Pt catalyst with a Pt mass concentration of 1000 ppm in the solution.

[0063] (2) Preparation of silicone rubber prepolymer: 0.8g of the modified Pt catalyst obtained in step (1) was added to a mixture of 10g of vinyl-terminated polydimethylsiloxane, 0.25g of polymethylhydrosiloxane and 0.03g of 1-ethynylcyclohexanol. The mixture was magnetically stirred at room temperature for 40min at a stirring speed of 1500rpm. After vacuum degassing, silicone rubber prepolymer was obtained.

[0064] (3) Preparation of flame-retardant silicone rubber: The organosilicon prepolymer obtained in step (2) is added into a rectangular mold, left to stand overnight in a fume hood, and then placed in a 130°C oven to cure for 10 minutes to obtain transparent flame-retardant silicone rubber.

[0065] Example 5

[0066] (1) Modification of platinum catalyst: Take 39 mg of Karstedt catalyst mother liquor, 157 mg of 1,3-dimethylimidazolium iodide and 65 mg of potassium tert-butoxide catalyst, adjust the magnetic stirrer to 1000 rpm and the magnetic stirring time to 15 min, filter out the potassium tert-butoxide catalyst, and obtain a homogeneous and fully plasticized modified Pt catalyst mother liquor. Then add vinyl-terminated polydimethylsiloxane solvent to obtain a modified Pt catalyst with a Pt mass concentration of 1000 ppm in the solution.

[0067] (2) Preparation of silicone rubber prepolymer: 1.0g of the modified Pt catalyst obtained in step (1) was added to a mixture of 10g of vinyl-terminated polydimethylsiloxane, 0.25g of polymethylhydrosiloxane and 0.03g of 1-ethynylcyclohexanol. The mixture was magnetically stirred at room temperature for 40min at a stirring speed of 1500rpm. After vacuum degassing, silicone rubber prepolymer was obtained.

[0068] (3) Preparation of flame-retardant silicone rubber: The organosilicon prepolymer obtained in step (2) is added into a rectangular mold, left to stand overnight in a fume hood, and then placed in a 130°C oven to cure for 10 minutes to obtain transparent flame-retardant silicone rubber.

[0069] Example 6

[0070] (1) Modification of platinum catalyst: Take 39 mg of Karstedt catalyst mother liquor, 157 mg of 1,3-dimethylimidazolium iodide and 65 mg of potassium tert-butoxide catalyst, adjust the magnetic stirrer to 1000 rpm and the magnetic stirring time to 15 min, filter out the potassium tert-butoxide catalyst, and obtain a homogeneous and fully plasticized modified Pt catalyst mother liquor. Then add vinyl-terminated polydimethylsiloxane solvent to obtain a modified Pt catalyst with a Pt mass concentration of 1000 ppm in the solution.

[0071] (2) Preparation of silicone rubber prepolymer: 0.2g of the modified Pt catalyst obtained in step (1) was added to a mixture of 10g of vinyl-terminated polydimethylsiloxane, 0.2g of polymethylhydrosiloxane and 0.03g of 1-ethynylcyclohexanol. The mixture was magnetically stirred at room temperature for 40min at a stirring speed of 1500rpm. After vacuum degassing, silicone rubber prepolymer was obtained.

[0072] (3) Preparation of flame-retardant silicone rubber: The organosilicon prepolymer obtained in step (2) is added into a rectangular mold, left to stand overnight in a fume hood, and then placed in a 130°C oven to cure for 10 minutes to obtain transparent flame-retardant silicone rubber.

[0073] Example 7

[0074] (1) Modification of platinum catalyst: Take 39 mg of Karstedt catalyst mother liquor, 157 mg of 1,3-dimethylimidazolium iodide and 65 mg of potassium tert-butoxide catalyst, adjust the magnetic stirrer to 1000 rpm and the magnetic stirring time to 15 min, filter out the potassium tert-butoxide catalyst, and obtain a homogeneous and fully plasticized modified Pt catalyst mother liquor. Then add vinyl-terminated polydimethylsiloxane solvent to obtain a modified Pt catalyst with a Pt mass concentration of 1000 ppm in the solution.

[0075] (2) Preparation of silicone rubber prepolymer: 0.2g of the modified Pt catalyst obtained in step (1) was added to a mixture of 10g of vinyl-terminated polydimethylsiloxane, 0.3g of polymethylhydrosiloxane and 0.03g of 1-ethynylcyclohexanol. The mixture was magnetically stirred at room temperature for 40min at a stirring speed of 1500rpm. After vacuum degassing, silicone rubber prepolymer was obtained.

[0076] (3) Preparation of flame-retardant silicone rubber: The organosilicon prepolymer obtained in step (2) is added into a rectangular mold, left to stand overnight in a fume hood, and then placed in a 130°C oven to cure for 10 minutes to obtain transparent flame-retardant silicone rubber.

[0077] Example 8

[0078] (1) Modification of platinum catalyst: Take 39 mg of Karstedt catalyst mother liquor, 157 mg of 1,3-dimethylimidazolium iodide and 65 mg of potassium tert-butoxide catalyst, adjust the magnetic stirrer to 1000 rpm and the magnetic stirring time to 15 min, filter out the potassium tert-butoxide catalyst, and obtain a homogeneous and fully plasticized modified Pt catalyst mother liquor. Then add vinyl-terminated polydimethylsiloxane solvent to obtain a modified Pt catalyst with a Pt mass concentration of 1000 ppm in the solution.

[0079] (2) Preparation of silicone rubber prepolymer: 0.2g of the modified Pt catalyst obtained in step (1) was added to a mixture of 10g of vinyl-terminated polydimethylsiloxane, 0.35g of polymethylhydrosiloxane and 0.03g of 1-ethynylcyclohexanol. The mixture was magnetically stirred at room temperature for 40min at a stirring speed of 1500rpm. After vacuum degassing, silicone rubber prepolymer was obtained.

[0080] (3) Preparation of flame-retardant silicone rubber: The organosilicon prepolymer obtained in step (2) is added into a rectangular mold, left to stand overnight in a fume hood, and then placed in a 130°C oven to cure for 10 minutes to obtain transparent flame-retardant silicone rubber.

[0081] Example 9

[0082] (1) Modification of platinum catalyst: Take 39 mg of Karstedt catalyst mother liquor, 157 mg of 1,3-dimethylimidazolium iodide and 65 mg of potassium tert-butoxide catalyst, adjust the magnetic stirrer to 1000 rpm and the magnetic stirring time to 15 min, filter out the potassium tert-butoxide catalyst, and obtain a homogeneous and fully plasticized modified Pt catalyst mother liquor. Then add vinyl-terminated polydimethylsiloxane solvent to obtain a modified Pt catalyst with a Pt mass concentration of 1000 ppm in the solution.

[0083] (2) Preparation of silicone rubber prepolymer: 0.2g of the modified Pt catalyst obtained in step (1) was added to a mixture of 10g of vinyl-terminated polydimethylsiloxane, 0.4g of polymethylhydrosiloxane and 0.03g of 1-ethynylcyclohexanol. The mixture was magnetically stirred at room temperature for 40min at a stirring speed of 1500rpm. After vacuum degassing, silicone rubber prepolymer was obtained.

[0084] (3) Preparation of flame-retardant silicone rubber: The organosilicon prepolymer obtained in step (2) is added into a rectangular mold, left to stand overnight in a fume hood, and then placed in a 130°C oven to cure for 10 minutes to obtain transparent flame-retardant silicone rubber.

[0085] Table 1: Performance Comparison of the Invention with Conventional Silicone Rubber

[0086] Limiting oxygen ul94 tensile strength Young's modulus hardness Residual carbon rate Comparative Example 1 26.7％ V-1 0.23MPa 2.91MPa 32.5HA 47.71％ Example 1 28.0％ V-0 0.21MPa 2.81MPa 32HA 50.02％

[0087] Comparative Example 1 and Example 1 used the same base rubber formulation but different Pt catalysts. Clearly, the silicone rubber prepared by the Pt catalyst modified with nitrogen-based carbene heterocyclic ligands exhibited significantly enhanced flame retardant properties while maintaining similar mechanical properties. Table 1 shows that the silicone rubber prepared with the modified platinum catalyst obtained in this embodiment of the invention has strength, hardness, and char residue comparable to commercially available silicone rubbers. Furthermore, the tensile strength and elongation at break of the silicone rubber prepared with the modified platinum catalyst did not show a significant decrease in mechanical properties compared to the unmodified platinum catalyst silicone rubber. Simultaneously, the limiting oxygen index (LOI) of the silicone rubber prepared with the ligand-modified Pt catalyst reached 28.0%, classifying it as a flame-retardant material; while the LIO of the silicone rubber prepared with the unmodified Pt catalyst was 26.7%, classifying it as a combustible material. In addition, the vertical flammability rating of the silicone rubber prepared with the ligand-modified catalyst improved from V-1 to V-0. Therefore, the novel ligand-modified platinum catalyst prepared by this invention can effectively improve the thermal stability of Pt catalysts, thereby effectively improving the flame retardant properties of silicone rubber. Thus, it can be widely applied and promoted, and can replace traditional platinum catalysts for silicone rubber.

[0088] Method for testing the limiting oxygen index of silicone rubber:

[0089] Mount the conditioned sample (i.e., the sample after compression into strips) onto the sample holder, then place the holder vertically in the center of the combustion chamber, ensuring the sample is at least 100 mm below the top of the glass combustion chamber and the lowest exposed part of the sample is at least 100 mm above the top of the gas distribution device. Adjust the gas control knob to use a mixture of gas with appropriate oxygen concentration, and purge the combustion chamber at a rate of 10 mm / s for at least 30 seconds (to expel any remaining air in the combustion chamber). Then, insert the igniter nozzle into the combustion chamber, ensuring the outer flame of the flame contacts the top of the sample and covers the entire top surface. Remove the flame approximately every 5 seconds to check if the entire top surface of the sample is ignited. If ignition is confirmed, immediately remove the igniter and begin timing or observing the length of the sample's combustion. If the sample cannot be ignited within 5 seconds, the ignition time can be appropriately extended, but the maximum time is 30 seconds. If the sample cannot be ignited within 30 seconds, the oxygen concentration should be increased until the sample ignites within 30 seconds. If the afterburning time exceeds 180s or the afterburning length exceeds 50mm after the sample is ignited, the oxygen concentration should be reduced by about 0.2%. If the above requirements are met, the oxygen concentration should be increased by about 0.2%. Through a series of tests, a set of results of "compliant -0" and "non-compliant -X" can be obtained around the initial oxygen concentration value. The K value can be obtained by looking up the table and the LOI value can be calculated.

[0090] Test method for residual carbon content of silicone rubber:

[0091] The transparent flame-retardant silicone rubber obtained in step (3) of each embodiment was placed in a muffle furnace and heated to 800°C at a heating rate of 20°C / min, and heated at this temperature for one hour, then cooled to room temperature with the furnace. The residual mass after heat treatment was used to measure the ceramic conversion efficiency of the flame-retardant silicone rubber.

[0092] Table 2: Comparison of the properties of flame-retardant silicone rubbers obtained at different Pt concentrations

[0093] Example 1 Example 2 Example 3 Example 4 Example 5 Residual carbon rate 50.02％ 51.50％ 54.64％ 55.51％ 56.63％

[0094] Table 3: Comparison of the properties of flame-retardant silicone rubbers obtained with different amounts of crosslinking agent

[0095] Example 6 Example 1 Example 7 Example 8 Example 9 Residual carbon rate 21.50％ 50.02％ 56.63％ 62.58％ 67.24％

[0096] Depend on Figure 1 It can be seen that the ligand-modified platinum catalyst prepared in this invention exhibits similar catalytic activity to the common Karstedt catalyst in the hydrosilylation catalytic field, without reducing its practical performance in curing silicone rubber. In Example 1, the modification with a nitrogen-containing heterocyclic carbene resulted in a slight decrease in catalytic activity compared to the Karstedt catalyst, but a similar torque value was observed at the end of the curve. This indicates that, upon complete curing, the silicone rubber prepared with the modified platinum catalyst has a similar crosslinking density to that prepared with a conventional Karstedt catalyst. This also explains why the silicone rubber prepared with the modified Pt catalyst has similar mechanical properties to that prepared with the Karstedt catalyst. In Comparative Example 2, the catalytic activity of the Pt catalyst modified with 3-aminopropyltriethoxysilane was significantly reduced, and the torque value at the catalytic endpoint was much lower than that of the silicone rubber prepared with the Karstedt catalyst. This indicates that, upon complete curing, the silicone rubber network prepared with a conventional nitrogen-containing silane-modified Karstedt catalyst is incompletely crosslinked and almost impossible to cure under normal temperature and pressure.

[0097] In addition, by Figure 2 It can be seen that the modified Pt catalyst prepared by this invention has stronger thermal stability. Figure 2 Figure a) shows that the silicone rubber prepared using the modified Pt catalyst has stronger thermal stability and higher char residue, and the modified Pt catalyst also exhibits enhanced thermal stability compared to the Karstedt catalyst. Figure 2 As can be seen in b), Pt black in the modified Pt catalyst is more difficult to dissolve under high temperature conditions. This is because the modified Pt catalyst uses nitrogen-based carbene ligands to modify Pt, which enhances Pt's anti-sintering properties, thereby improving its catalytic activity at high temperatures. This, in turn, results in a faster formation rate of the thermal barrier layer at high temperatures, and finally enhances the flame retardancy of the silicone rubber.

[0098] As shown in Table 2, the char residue of silicone rubber prepared with the platinum catalyst obtained in this invention increases slowly with the increase of the amount of modified Pt catalyst added. Table 3 shows that the char residue of silicone rubber prepared with the platinum catalyst obtained in this invention increases significantly with the increase of the crosslinking agent dosage. In Example 6, due to the low amount of crosslinking agent, the crosslinking network of the cured silicone rubber was incomplete, resulting in a low crosslinking density. The crosslinking density of silicone rubber is directly proportional to its thermal stability. When the crosslinking agent concentration continues to increase, the crosslinking network of the silicone rubber is basically completed, and further addition of crosslinking agent has little effect on increasing the crosslinking density, thus also having little effect on improving its char residue. This is because the thermal stability of silicone rubber is closely related to the crosslinking density, which in turn is closely related to the flame retardancy of silicone rubber. A crosslinking network with a high crosslinking density is more prone to free radical coupling reactions at high temperatures, thereby transforming the silicone rubber elastomer network into high-temperature resistant silicon carbide ceramic, thus increasing the char residue.

[0099] At high temperatures, silicone rubber undergoes an organic-inorganic transformation under the action of a Pt catalyst, forming a ceramic layer that is stable at 1000°C. This layer hinders heat and mass transfer between the internal materials and the flame, forming a thermal protection barrier and thus achieving a flame-retardant effect. Furthermore, the Pt catalyst prepared in this invention enhances the catalytic activity of the Pt catalyst at high temperatures while maintaining the crosslinking density of the silicone rubber, thereby improving the flame retardancy of the silicone rubber.

[0100] In summary, using vinyl-terminated polydimethyl silicone oil as the base rubber and polymethylhydrosilicone oil as the crosslinking agent, and 1,3-dimethylimidazolium iodide as a Pt catalyst modifier, a highly flame-retardant silicone rubber material was obtained. This material exhibits high flame retardancy, good transparency, and stronger thermal stability, and its overall performance is comparable to that of conventional silicone rubber. Given its above properties and excellent flame retardant performance, the novel platinum flame-retardant / catalytic flame-retardant rubber developed in this invention can be considered as a replacement for flame-retardant rubbers with low transparency on the market and can be applied in fields such as flame-retardant protective coatings, showing significant application prospects and value.

[0101] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A filler-free flame-retardant silicone rubber, characterized in that, The raw materials include the following parts by weight: 80-100 parts of vinyl-terminated polydimethylsiloxane, 2-4 parts of crosslinking agent, 2-10 parts of high-efficiency platinum catalyst, and 0.2-0.3 parts of polymerization inhibitor; The preparation of the high-efficiency platinum catalyst includes the following steps: mixing and stirring the Karstedt catalyst, ligand, and catalyst; adding vinyl-terminated polydimethylsiloxane; and fully dissolving to obtain the high-efficiency platinum catalyst; wherein the ligand is at least one of 1,3-dimethylimidazolium iodide, 1,3-dimethylbenzimidazolium iodide, and 1,3-diphenylbenzimidazolium iodide; wherein the mass ratio of the Karstedt catalyst, modified ligand, and catalyst is 39:100~200:65; and wherein the amount of vinyl-terminated polydimethylsiloxane is such that the mass concentration of Pt in the modified Pt catalyst is 1000-3000 ppm.

2. The filler-free flame-retardant silicone rubber according to claim 1, characterized in that: The catalyst is at least one of potassium tert-butoxide, potassium methoxide, and sodium ethoxide.

3. The filler-free flame-retardant silicone rubber according to claim 1, characterized in that: The mixing speed is 500rpm-1500rpm; the mixing time is 10-40min.

4. The flame-retardant silicone rubber according to claim 1, characterized in that: The crosslinking agent includes at least one of polymethylhydrosiloxane and poly(dimethylsiloxane) hydride end-capping; The polymerization inhibitor includes at least one of 1-ethynylcyclohexanol and diallyl maleate. The vinyl-terminated polydimethylsiloxane has a vinyl content of 1.0-1.5% by mass; and the crosslinking agent has a hydrogen content of 0.97-1.03% by mass percentage.

5. A method for preparing the fillerless flame-retardant silicone rubber according to any one of claims 1 to 4, comprising the following steps: (1) Mix vinyl-terminated polydimethylsiloxane, crosslinking agent and polymerization inhibitor, then add modified Pt catalyst, stir, and vacuum degas to obtain silicone rubber prepolymer; (2) Add the organosilicon prepolymer obtained in step (1) into a rectangular mold, let it stand and cure to obtain filler-free flame-retardant silicone rubber.

6. The method for preparing filler-free flame-retardant silicone rubber according to claim 5, characterized in that: The stirring speed in step (1) is 500 rpm-1500 rpm, and the stirring time is 10-40 min; The step (2) of letting the plant stand overnight in a ventilated place; The curing step (2) involves curing at 80°C to 130°C for 10 to 40 minutes.

7. The application of the fillerless flame-retardant silicone rubber according to any one of claims 1 to 4 in flame-retardant materials.

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