Polysiloxane as well as preparation method and application thereof

Abstract

The invention discloses polysiloxane as well as a preparation method and application thereof. The preparation method comprises the following steps: 1) adding a siloxane ring body and an organic solvent into a reaction kettle, adding an alkyl lithium catalyst, and reacting at 10-50 DEG C for 3-24 hours; 2) adding silane containing chloroalkyl and alkoxy as an end-capping reagent, and reacting at 30-60 DEG C for 5-20 hours; and removing the solvent, and filtering to obtain a target product. According to the invention, polysiloxane with low hydroxyl content and narrow molecular weight distribution is prepared, and the polysiloxane has excellent powder treatment capacity and has better application in the aspect of powder treatment of organosilicone heat-conducting products.

Description

Technical Field

[0001] The present invention relates to an asymmetric silicone oil, and particularly to a polysiloxane, a preparation method thereof, and an application thereof. Background Art

[0002] The polysiloxane with an alkoxy group at one end is a commonly used powder treatment agent in the silicone field and is widely used in the powder treatment in the heat conduction field. This silicone oil reacts with the hydroxyl groups on the surface of the powder through the alkoxy group at its one end to improve the compatibility between the powder and the silicone system. The inventors of the present invention have continuously studied and found that the presence of silanol groups will reduce the reaction activity of the siloxane, resulting in problems such as the precipitation of silicone oil and the caking of powder, affecting the performance of heat conduction products; at the same time, the narrower the molecular weight distribution of the polysiloxane, the more accurate the addition amount during powder treatment, and the better the treatment effect.

[0003] Patent CN112608480B discloses a preparation method and an application of an asymmetric silicone oil. An asymmetric silicone oil is prepared using alkyllithium as a catalyst under solvent conditions and is applied to the treatment of heat conduction fillers, achieving good application effects. However, the high-reactivity chlorosilane used as a reaction raw material will generate HCl, which needs to be removed by washing with water and further promotes the formation of silanol groups, and is extremely likely to cause the cleavage and rearrangement of silicon-oxygen bonds, resulting in a wider molecular weight distribution.

[0004] Patent CN114763413A discloses a preparation method of an alkyl methoxy silicone oil. Using N-heterocyclic carbene iron as a catalyst effectively reduces the catalyst cost, but does not study the hydroxyl content and molecular weight distribution that affect the performance of this silicone oil.

[0005] Patent CN114854021A discloses a preparation method of a one-sided reaction type functional group-terminated silicone oil. The reaction efficiency is improved by using a microchannel reactor, and the control method of hydroxyl content and the control method of molecular weight distribution are not mentioned either.

[0006] In summary, the existing technologies for the preparation method of polysiloxane with an alkoxy group at one end still stay in aspects such as reaction process optimization and catalyst optimization, and the existing technology processes all use hydrogen-containing chlorosilane as raw materials, affecting the product performance. There are no research results on the control of hydroxyl content and molecular weight distribution in the disclosed technologies. Summary of the Invention

[0007] To solve the above technical problems, the present invention first proposes a preparation method of a polysiloxane.

[0008] The present invention also relates to a polysiloxane, which has both a lower hydroxyl value and a narrower molecular weight distribution, and has better application performance.

[0009] The present invention also relates to the application of polysiloxane in the technical field of silicone thermal conductive materials, especially as a surface treatment agent for thermal conductive fillers.

[0010] A preparation method of polysiloxane includes the following steps:

[0011] 1) Add siloxane cyclic body and organic solvent into a reaction kettle, and add an alkyllithium catalyst, and react at 10 - 50 °C for 3 - 24 h;

[0012] 2) Add a silane containing a chlorohydrocarbon group and an alkoxy group as a terminator, and react at 30 - 60 °C for 5 - 20 h; Remove the solvent, filter, and obtain the target product.

[0013] The present invention uses a chlorohydrocarbon group silane with relatively mild reaction activity as a terminator. Not only will no HCl be generated in the system, so there is no need for water washing and thus no introduction of silanol groups, eliminating the subsequent operations of water washing and water removal, but also it will not cause the cleavage and rearrangement of silicon - oxygen bonds, having the advantage of a narrower molecular weight distribution. Through continuous research by the inventors, polysiloxane with a low silanol group content and a narrow molecular weight distribution has more excellent applications in the surface treatment of silicone thermal conductive fillers.

[0014] As a preferred embodiment of the present invention, the siloxane cyclic body is selected from one or more of hexamethylcyclotrisiloxane, hexaethylcyclotrisiloxane, 2,4,6 - trivinyl - 2,4,6 - trimethylcyclotrisiloxane, and hexaphenylcyclotrisiloxane.

[0015] As a preferred embodiment of the present invention, the alkyllithium catalyst is one or more of methyllithium, ethyllithium, tert - butyllithium, n - butyllithium, and sec - butyllithium;

[0016] Preferably, the dosage of the alkyllithium catalyst is 0.1 - 5% of the mass of the siloxane cyclic body, preferably 0.5 - 2.5%.

[0017] As a preferred embodiment of the present invention, the terminator is selected from one or more of chloropropyltrimethoxysilane, chloropropyltriethoxysilane, chloropropylmethyldimethoxysilane, chloropropylmethyldiethoxysilane, and chloromethyltrimethoxysilane;

[0018] Preferably, the dosage of the terminator is 5 - 20% of the mass of the siloxane cyclic body, preferably 8 - 17%.

[0019] As a preferred embodiment of the present invention, the organic solvent is one or more of toluene, xylene, cyclohexane, n - hexane, and n - heptane;

[0020] Preferably, the dosage of the organic solvent is 1 - 10 times the mass of the siloxane cyclic body, preferably 1 - 5 times.

[0021] As a preferred embodiment of the present invention, in step 1), after the siloxane cyclic body and the organic solvent are added to the reaction kettle, the system is first dehydrated, and used after the water content is tested to be <10 ppm. The present invention preferably controls the water content of the raw materials, which can minimize the water content introduced into the reaction system, thereby further reducing the possibility of side reactions to generate silanol groups.

[0022] As a preferred embodiment of the present invention, the dehydration method in step 1) is any one of nitrogen stripping, solvent reflux, azeotropic water removal, and water absorption by an absorbent.

[0023] It should be noted that after the reaction is completed, for safety considerations, the solvent can be removed first and then filtered, but in terms of process feasibility, it is also feasible to filter first and then remove the solvent. The present invention does not impose any restrictions on the operation sequence of the two.

[0024] The present invention also provides a polysiloxane prepared by the method as described above, the hydroxyl content of which is less than 5 mol%, and the M w / M n ratio is less than 1.2.

[0025] The present invention also provides an application of the polysiloxane prepared by the method as described above or the polysiloxane as described above in the technical field of silicone thermal conductive materials, especially as a surface treatment agent for thermal conductive fillers.

[0026] The present invention prepares a polysiloxane with a low hydroxyl content and a narrow molecular weight distribution. This polysiloxane has excellent powder handling ability and better application in the powder handling of silicone thermal conductive products. Detailed Embodiments

[0027] The following further illustrates the present invention through specific examples. The examples described in the present invention are only for the illustration of the present invention and do not limit the scope of the present invention.

[0028] In the present invention, raw materials and reagents can be obtained through commercial channels without special instructions.

[0029] The main test methods involved in the following solutions of the present invention are as follows:

[0030] Molecular weight test method: Test using an Agilent PL-GPC-50 gel chromatography, and the mobile phase is toluene;

[0031] Thermal conductivity test method: Test using a Hot disk thermal conductivity meter according to the ISO-CD22007-2 standard, and take the average value after measuring 3 times;

[0032] Thermal resistance test method: The test was carried out using an LW-9389 thermal resistance meter in accordance with ASTM D 5470 standard. During the test, the hot-end temperature was 60 °C, the pressure was 40 psi, and the test duration was 10 minutes.

[0033] Example 1

[0034] 100 g of hexamethylcyclotrisiloxane and 100 g of cyclohexane solvent were added to a 1-liter four-necked flask and mixed evenly. The moisture in the system was removed by nitrogen stripping. The water content was tested to be < 10 ppm. 15 g of n-butyllithium hexane solution (1.6 mol / L) was added and reacted at 20 °C for 12 h. Then 10 g of chloropropyltrimethoxysilane was added and reacted at 30 °C for 18 h. After removing the solvent by vacuum distillation and filtering, polysiloxane product 1 was obtained. The molecular weight and hydroxyl content were tested, as shown in Table 1.

[0035] Example 2

[0036] 100 g of hexamethylcyclotrisiloxane and 200 g of toluene solvent were added to a 1-liter four-necked flask and mixed evenly. The moisture in the system was removed by toluene reflux. The water content was tested to be < 10 ppm. 20 g of tert-butyllithium hexane solution (1.6 mol / L) was added and reacted at 10 °C for 20 h. Then 20 g of chloropropylmethyldimethoxysilane was added and reacted at 40 °C for 12 h. After removing the solvent by vacuum distillation and filtering, polysiloxane product 2 was obtained. The molecular weight and hydroxyl content were tested, as shown in Table 1.

[0037] Example 3

[0038] 100 g of hexamethylcyclotrisiloxane and 100 g of xylene solvent were added to a 1-liter four-necked flask and mixed evenly. Excess moisture in the system was absorbed using anhydrous sodium sulfate. The water content was tested to be < 10 ppm. Then 5 g of methyllithium hexane solution (1.6 mol / L) was added and reacted at 30 °C for 12 h. Then 15 g of chloropropyltrimethoxysilane was added and reacted at 60 °C for 10 h. After removing the solvent by vacuum distillation and filtering, polysiloxane product 3 was obtained. The molecular weight and hydroxyl content were tested, as shown in Table 1.

[0039] Example 4

[0040] 100 g of hexamethylcyclotrisiloxane and 100 g of n-hexane solvent were added to a 1-liter four-necked flask and mixed evenly. Excess moisture in the system was absorbed using anhydrous sodium sulfate. The water content was tested to be < 10 ppm. Then 8 g of n-butyllithium hexane solution (1.6 mol / L) was added and reacted at 45 °C for 12 h. Then 13 g of chloropropyltrimethoxysilane was added and reacted at 55 °C for 10 h. After removing the solvent by vacuum distillation and filtering, polysiloxane product 4 was obtained. The molecular weight and hydroxyl content were tested, as shown in Table 1.

[0041] Comparative Example 1

[0042] Prepare an asymmetric silicone oil by referring to the method in Example 1 of Patent CN112608480B, that is:

[0043] In a four-necked flask equipped with mechanical stirring, nitrogen, a thermometer, and a rubber stopper, add 115.80 g (0.52 mol) of hexamethylcyclotrisiloxane and 180 ml of n-hexane. After all the raw material monomers are dissolved, use a syringe to suck 9 ml of a n-hexane solution of n-butyllithium (1.6 mol / L) and add it to the reaction flask through the rubber stopper; stir at room temperature for 1 h, then add 30 ml of tetrahydrofuran, react at 40 °C for 6 h, and then cool to room temperature; add 2.0 ml of dimethylchlorosilane (the molar ratio of n-butyllithium to dimethylchlorosilane is 1:1.25), stir at room temperature for 2 h, wash three times with water until neutral, add anhydrous magnesium sulfate to the organic phase to dry overnight, and then rotary evaporate (100 °C, 10 mbar) to remove the solvent and the remaining monomers to obtain an intermediate. Take 50 g of the above intermediate, add 2 g of vinyltrimethoxysilane and 5 μL of Karstedt catalyst (the platinum element dosage is 1.5 ppm), react at 60 °C for 6 h, and then rotary evaporate (110 °C, 10 mbar) to remove the excess raw materials to obtain polysiloxane sample 5. Test the molecular weight and hydroxyl content, as shown in Table 1.

[0044] Comparative Example 2

[0045] Prepare a polysiloxane by referring to the method in Comparative Example 1, and the difference is only in adjusting the raw material dosage to obtain products with different molecular weights, specifically as follows:

[0046] In a four-necked flask equipped with mechanical stirring, nitrogen, a thermometer, and a rubber stopper, add 115.80 g (0.52 mol) of hexamethylcyclotrisiloxane and 180 ml of n-hexane. After all the raw material monomers are dissolved, use a syringe to suck 11 ml of a n-hexane solution of n-butyllithium (1.6 mol / L) and add it to the reaction flask through the rubber stopper; stir at room temperature for 1 h, then add 30 ml of tetrahydrofuran, react at 40 °C for 6 h, and then cool to room temperature; add 2.0 ml of dimethylchlorosilane (the molar ratio of n-butyllithium to dimethylchlorosilane is 1:1.25), stir at room temperature for 2 h, wash three times with water until neutral, add anhydrous magnesium sulfate to the organic phase to dry overnight, and then rotary evaporate (100 °C, 10 mbar) to remove the solvent and the remaining monomers to obtain an intermediate. Take 50 g of the above intermediate, add 2 g of vinyltrimethoxysilane and 5 μL of Karstedt catalyst (the platinum element dosage is 1.5 ppm), react at 60 °C for 6 h, and then rotary evaporate (110 °C, 10 mbar) to remove the excess raw materials to obtain polysiloxane sample 6. Test the molecular weight and hydroxyl content, as shown in Table 1.

[0047] Table 1. Indexes of polysiloxane samples prepared in each example and comparative example

[0048]

[0049]

Application Example

[0050] Taking the polysiloxane samples prepared in each of the examples and comparative examples as treatment agents, the thermal conductive silicone grease was prepared according to the following method, and the thermal conductivity, thermal resistance and viscosity of the silicone grease were tested for performance. The test results are shown in Table 2.

[0051] By mass, 100 parts of aluminum powder with a particle size of 1 - 2 μm, 200 parts of aluminum powder with a particle size of 9 - 10 μm, 150 parts of zinc oxide powder with a particle size of 0.5 - 1 μm, 30 parts of the polysiloxane sample, and 20 parts of methyl silicone oil with a viscosity of 100 mPa·s were mixed with a high-speed disperser for 20 min to form a uniform paste, heated to 150 °C and stirred under vacuum for 90 min, and then cooled to below 40 °C to obtain the thermally conductive silicone resin.

[0052] Table 2. Test Results of the Performance of the Thermally Conductive Silicone Resin

[0053]

[0054] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the method of the present invention, several improvements and supplements can be made, and these improvements and supplements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing polysiloxane, characterized in that, it comprises the following steps: 1) Add siloxane cyclic body and organic solvent into a reaction kettle, and add an alkyllithium catalyst, and react at 10 - 50 °C for 3 - 24 h; 2) Add a silane containing a chlorohydrocarbon group and an alkoxy group as a terminator, and react at 30 - 60 °C for 5 - 20 h; Remove the solvent, filter, and obtain the target product.

2. The method for preparing polysiloxane according to claim 1, characterized in that, the siloxane cyclic body is selected from one or more of hexamethylcyclotrisiloxane, hexaethylcyclotrisiloxane, 2,4,6 - trivinyl - 2,4,6 - trimethylcyclotrisiloxane, and hexaphenylcyclotrisiloxane.

3. The method for preparing polysiloxane according to claim 1 or 2, characterized in that, the alkyllithium catalyst is one or more of methyllithium, ethyllithium, tert - butyllithium, n - butyllithium, and sec - butyllithium; Preferably, the dosage of the alkyllithium catalyst is 0.1 - 5% of the mass of the siloxane cyclic body, preferably 0.5 - 2.5%.

4. The method for preparing polysiloxane according to any one of claims 1 - 3, characterized in that, the terminator is selected from one or more of chloropropyltrimethoxysilane, chloropropyltriethoxysilane, chloropropylmethyldimethoxysilane, chloropropylmethyldiethoxysilane, and chloromethyltrimethoxysilane; Preferably, the dosage of the terminator is 5 - 20% of the mass of the siloxane cyclic body, preferably 8 - 17%.

5. The method for preparing polysiloxane according to any one of claims 1 - 4, characterized in that, the organic solvent is one or more of toluene, xylene, cyclohexane, n - hexane, and n - heptane; Preferably, the dosage of the organic solvent is 1 - 10 times the mass of the siloxane cyclic body, preferably 1 - 5 times.

6. The method for preparing polysiloxane according to any one of claims 1 - 5, characterized in that, in step 1), after the siloxane cyclic body and the organic solvent are added into the reaction kettle, the system is first dehydrated, and used after testing that the water content < 10 ppm.

7. The method for preparing polysiloxane according to claim 6, characterized in that, the dehydration method in step 1) is any one of nitrogen stripping, solvent reflux, azeotropic water removal, and water removal with a water absorbent.

8. A polysiloxane prepared by the method according to any one of claims 1 - 7, characterized in that, Its hydroxyl content is less than 5 mol%, and M w / M n The ratio is less than 1.

2.

9. An application of a polysiloxane prepared by the method according to any one of claims 1 - 7 or the polysiloxane according to claim 8 in the technical field of silicone thermal conductive materials.

Images