Preparation method of diethoxy organic group terminated polydimethylsiloxane

Abstract

The invention discloses a preparation method of diethoxy organic group terminated polydimethylsiloxane, which comprises the following steps: (1) mixing alpha, omega-dihydroxy polydimethylsiloxane, an ethoxy siloxane cross-linking agent and a phosphate catalyst, and stirring for 30-150 minutes under the condition that the temperature is 35-75 DEG C and the humidity is isolated; (2) detecting that no thickening or gelling exists through titanium isopropoxide, and adding an inactivating agent; and (3) under the condition that the temperature is 35 to 75 DEG C, carrying out vacuum defoaming and mixing for 15 to 90 minutes, so as to obtain the diethoxy organic group terminated polydimethylsiloxane. According to the preparation method disclosed by the invention, the polydimethylsiloxane with thorough ethyoxyl end capping is obtained through the efficient catalytic action of the phosphate catalyst; the ethanol solution of sodium ethoxide is used as an inactivating agent, so that the side effect of the catalyst in rearrangement and degradation of high polymers can be greatly reduced, the storage time of the diethoxy organic group terminated polydimethylsiloxane is prolonged, and high-quality base rubber is provided for preparing non-toxic and ethanol-removed RTV-1 silicone rubber.

Description

Technical Field

[0001] The present invention relates to the field of silicone polymer synthesis, and particularly to a method for preparing diethoxy organo-terminated polydimethylsiloxane. Background Art

[0002] Room temperature curable silicone rubber adhesives have characteristics such as low toxicity, high transparency, chemical inertness, excellent weather resistance, and good electrical insulation. They can still maintain good physical and chemical properties in harsh environments and are widely used in many fields, such as the construction, automotive, electronics, and chemical industries. Among various room temperature curable silicone rubber adhesives, one-component room temperature curable (RTV-1) silicone rubber adhesives are increasingly favored because of their convenience in use, no need for high-temperature curing, and non-toxic and harmless properties.

[0003] During the curing process of alcohol-free one-component room temperature curable (RTV-1) silicone rubber, alcohols are released, with no pungent smell and good comprehensive performance. Its environmental protection characteristics meet the future market application requirements. However, current research and production mainly focus on the production of methanol-free RTV-1 silicone rubber. In the current "maximum allowable concentration of harmful substances in the air" standard in China, it is 200 mg / m³ (equivalent to 260 ppm). However, in methanol production plants or specific industrial environments, this value may be more stringent, such as 50 mg / m³. Ethanol has corresponding values in the national air quality standard for harmful substances, but its specific emission concentration limits will vary based on local environmental protection regulations and industry characteristics. At present and for some time to come, ethanol-free products are more environmentally friendly and long-lasting.

[0004] The patent JPH09-110988A proposes using α,ω-dihydroxy polydimethylsiloxane as the base rubber, methoxysilanes such as vinyltrimethoxysilane and methyltrimethoxysilane as the end-capping agents, acidic phosphates as the catalysts, and silazanes or triethylamine as the quenching agents to prepare methoxy-terminated polydimethylsiloxane at room temperature. However, this method is only applicable to the preparation of methoxy-terminated polydimethylsiloxane. At the same time, hexamethyldisilazane has a large steric hindrance and it is difficult to quench acidic phosphates. Rearrangement reactions will occur in the stored high polymer later, resulting in cracking and viscosity reduction.

[0005] The patent JPH04-359061A proposes reacting aminoalkyl-terminated polydimethylsiloxane with isocyanatopropyltriethoxysilane to prepare diethoxy organo-terminated polydimethylsiloxane. The RTV-1 silicone rubber formulated with this polymer has a fast curing speed and good adhesion. However, both the basic high polymer and the silane involved need to be customized. For economic reasons, this method is generally not the first choice. Summary of the Invention

[0006] Based on this, it is necessary to provide a preparation method of diethoxy organo-capped polydimethylsiloxane for the above-mentioned technical problems.

[0007] To achieve the above object, the present invention provides a preparation method of diethoxy organo-capped polydimethylsiloxane, which includes the following steps: (1) Mix α,ω-dihydroxy polydimethylsiloxane, ethoxysiloxane crosslinking agent, and phosphate catalyst, and stir for 30 - 150 min under moisture isolation at a temperature of 35 - 75 °C to obtain a reaction product; (2) Mix the reaction product with isopropyl titanate at a weight ratio of 100:(4 - 6). After observing no thickening or gelation, then add an inactivator; (3) Under the condition of a temperature of 35 - 75 °C, perform vacuum degassing and mixing for 15 - 90 min to obtain diethoxy organo-capped polydimethylsiloxane; Among them, the mass ratio of α,ω-dihydroxy polydimethylsiloxane, ethoxysiloxane crosslinking agent, phosphate catalyst, and inactivator is (100 - 600):(1 - 10):(0.1 - 2):(0.02 - 2); the inactivator is an ethanol solution of sodium ethoxide with a concentration of 17.5 - 21%. Diethoxy organo-capped polydimethylsiloxane can be used to prepare alcohol-free RTV-1 silicone rubber.

[0008] Preferably, the organic group of the diethoxy organo-capped polydimethylsiloxane is vinyl, and the structural formula is: CH2=CH-Si(OCH2CH3)2-O-[Si(CH3)2-O]n-Si(OCH2CH3)2-CH=CH2.

[0009] Preferably, the organic group of the diethoxy organo-capped polydimethylsiloxane is methyl, and the structural formula is: CH3-Si(OCH2CH3)2-O-[Si(CH3)2-O]n-Si(OCH2CH3)2-CH3.

[0010] Preferably, the viscosity of the α,ω-dihydroxy polydimethylsiloxane at 25 °C is 2000 - 80000 mPa·s.

[0011] Preferably, the ethoxysiloxane crosslinking agent is one or a mixture of more than one of methyltriethoxysilane, propyltriethoxysilane, vinyltriethoxysilane, and tetraethyl orthosilicate.

[0012] Preferably, the phosphate catalyst is one or a mixture of more than one of monoalkyl phosphate, dialkyl phosphate, and trialkyl phosphate. For example, dibutyl phosphate, bis(2-ethylhexyl) phosphate, mono(2-ethylhexyl) phosphate, bis(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphate, tributyl phosphate, and trioctyl phosphate.

[0013] Preferably, the inactivator is an ethanol solution containing 20% sodium ethoxide.

[0014] Preferably, in the step (1), α,ω-dihydroxypolydimethylsiloxane, ethoxysiloxane crosslinking agent, and phosphate catalyst are mixed and stirred for 80 - 100 min under moisture isolation at a temperature of 55 - 65°C, and the rotation speed is controlled at 500 - 800 rpm.

[0015] Preferably, in the step (1), α,ω-dihydroxypolydimethylsiloxane, ethoxysiloxane crosslinking agent, and catalyst are stirred and mixed in a high-speed disperser.

[0016] Preferably, in the step (3), the vacuum degassing mixing temperature is 50 - 55°C, and the vacuum degree is -0.06 - -0.099 MPa.

[0017] Compared with the prior art, the present technical solution has at least one of the following beneficial effects: 1. Through the efficient catalytic action of the phosphate catalyst, ethoxy-terminated polydimethylsiloxane is obtained in the present invention. 2. By using an ethanol solution of sodium ethoxide as the inactivator, the side effect of the catalyst rearranging and degrading the polymer is greatly reduced, and the storage time of diethoxy organo-terminated polydimethylsiloxane is increased. 3. The preparation method provided by the present invention can significantly improve the storage stability of diethoxy organo-terminated polydimethylsiloxane, and provides a high-quality base rubber for preparing non-toxic and ethanol-free RTV-1 silicone rubber. Specific Embodiments

[0018] The present invention will be further described below in conjunction with embodiments. All chemicals and reagents used in the embodiments are commercially available unless otherwise specified. However, the present invention can be implemented in many other ways different from those described herein. Those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0019] Example 1

[0020] This example provides a preparation method of diethoxy organo-terminated polydimethylsiloxane, and the specific steps are as follows: 500 g of α,ω-dihydroxypolydimethylsiloxane with a viscosity of 50,000 mPa·s, 10 g of vinyltriethoxysilane, and 2 g of bis(2-ethylhexyl) phosphate were added to a high-speed disperser. The rotation speed was controlled at 500 rpm, and the temperature was raised to 55 °C. The reaction was carried out for 90 min under moisture-proof conditions to obtain a reaction product. The reaction product was mixed with isopropyl titanate in a weight ratio of 100:5. After detecting that the isopropyl titanate did not thicken or gel, 2.1 g of an ethanol solution containing 20% sodium ethoxide was added, and the mixture was stirred for 30 min under a vacuum of -0.09 Mpa to remove low-boiling substances, obtaining α,ω-bis(vinyl diethoxysilyl)polydimethylsiloxane, or more simply, the industrial name: vinyl diethoxy-capped polydimethylsiloxane.

[0021] Structural formula: CH2=CH-Si(OCH2CH3)2-O-[Si(CH3)2-O]n-Si(OCH2CH3)2-CH=CH2.

[0022] The above α,ω-bis(vinyl diethoxysilyl)polydimethylsiloxane is one of the diethoxy organo-capped polydimethylsiloxanes.

[0023] Example 2

[0024] This example provides a preparation method of diethoxy organo-capped polydimethylsiloxane. The specific steps are as follows: 500 g of α,ω-dihydroxypolydimethylsiloxane with a viscosity of 50,000 mPa·s, 10 g of methyltriethoxysilane, and 3 g of bis(2-ethylhexyl) phosphate were added to a high-speed disperser. The rotation speed was controlled at 500 rpm, and the temperature was raised to 55 °C. The reaction was carried out for 90 min under moisture-proof conditions to obtain a reaction product. The reaction product was mixed with isopropyl titanate in a weight ratio of 100:5. After detecting that the isopropyl titanate did not thicken or gel, 3.1 g of an ethanol solution containing 20% sodium ethoxide was added, and the mixture was stirred for 30 min under a vacuum of -0.09 Mpa to remove low-boiling substances, obtaining α,ω-bis(methyl diethoxy)capped polydimethylsiloxane, or the common industrial name: methyl diethoxy double-capped polydimethylsiloxane.

[0025] Structural formula: CH3-Si(OCH2CH3)2-O-[Si(CH3)2-O]n-Si(OCH2CH3)2-CH3.

[0026] The above α,ω-bis(methyl diethoxy)capped polydimethylsiloxane is the other one of the diethoxy organo-capped polydimethylsiloxanes relative to α,ω-bis(vinyl diethoxysilyl)polydimethylsiloxane.

[0027] Example 3

[0028] This example provides a preparation method of diethoxy organo-terminated polydimethylsiloxane, and the specific steps are as follows: Add 500 g of α,ω-dihydroxy polydimethylsiloxane with a viscosity of 20000 mPa·s, 10 g of methyltriethoxysilane, and 3 g of bis(2-ethylhexyl) phosphate into a high-speed disperser, control the rotation speed at 500 rpm, heat up to 55 °C, and react for 90 min under moisture-proof conditions to obtain a reaction product; mix the reaction product with isopropyl titanate according to a weight ratio of 100:5. After detecting that the isopropyl titanate has no thickening or gelation, add 2.1 g of an ethanol solution containing 20% sodium ethoxide, and stir for 30 min under a vacuum of -0.09 Mpa to remove low-boiling substances, obtaining α,ω-bis(methyldiethoxy)-terminated polydimethylsiloxane.

[0029] Example 4

[0030] This example provides a preparation method of diethoxy organo-terminated polydimethylsiloxane, and the specific steps are as follows: Add 500 g of α,ω-dihydroxy polydimethylsiloxane with a viscosity of 50000 mPa·s, 10 g of methyltriethoxysilane, and 1.5 g of bis(2-ethylhexyl) phosphate into a high-speed disperser, control the rotation speed at 500 rpm, heat up to 55 °C, and react for 120 min under moisture-proof conditions to obtain a reaction product; mix the reaction product with isopropyl titanate according to a weight ratio of 100:5. After detecting that the isopropyl titanate has no thickening or gelation, add 1.5 g of an ethanol solution containing 20% sodium ethoxide, and stir for 30 min under a vacuum of -0.09 Mpa to remove low-boiling substances, obtaining α,ω-bis(methyldiethoxy)-terminated polydimethylsiloxane.

[0031] Comparative Example 1 This comparative example provides a preparation method of diethoxy organo-terminated polydimethylsiloxane, and the specific steps are as follows: Add 500 g of α,ω-dihydroxy polydimethylsiloxane with a viscosity of 50000 mPa·s, 10 g of vinyltriethoxysilane, and 2 g of bis(2-ethylhexyl) phosphate into a high-speed disperser, control the rotation speed at 500 rpm, heat up to 55 °C, and react for 90 min under moisture-proof conditions to obtain a reaction product; mix the reaction product with isopropyl titanate according to a weight ratio of 100:5. After detecting that the isopropyl titanate has no thickening or gelation, add 1 g of hexamethyldisilazane, and stir for 30 min under moisture-proof conditions to obtain α,ω-bis(vinyl diethoxysilyl) polydimethylsiloxane.

[0032] Comparative Example 2 This comparative example provides a method for preparing diethoxy organically terminated polydimethylsiloxane, and the specific steps are as follows: 500 g of α,ω-dihydroxy polydimethylsiloxane with a viscosity of 50,000 mPa·s, 10 g of methyltriethoxysilane, and 3 g of bis(2-ethylhexyl) phosphate are added to a high-speed disperser, the rotation speed is controlled at 500 rpm, the temperature is raised to 55 °C, and the reaction is carried out for 90 min under moisture-proof conditions to obtain a reaction product; the reaction product is mixed with isopropyl titanate according to a weight ratio of 100:5. After detecting that there is no thickening or gelation of isopropyl titanate, 0.63 g of triethylamine is added, and the mixture is stirred for 30 min under moisture-proof conditions to obtain α,ω-bis(methyldiethoxy) terminated polydimethylsiloxane.

[0033] Comparative Example 3 This comparative example provides a method for preparing diethoxy organically terminated polydimethylsiloxane, and the specific steps are as follows: 500 g of α,ω-dihydroxy polydimethylsiloxane with a viscosity of 20,000 mPa·s, 10 g of methyltriethoxysilane, and 3 g of bis(2-ethylhexyl) phosphate are added to a high-speed disperser, the rotation speed is controlled at 500 rpm, the temperature is raised to 55 °C, and the reaction is carried out for 90 min under moisture-proof conditions to obtain a reaction product; the reaction product is mixed with isopropyl titanate according to a weight ratio of 100:5. After detecting that there is no thickening or gelation of isopropyl titanate, 0.63 g of triethylamine is added, and the mixture is stirred for 30 min under a vacuum of -0.09 Mpa to remove low-boiling substances, obtaining α,ω-bis(methyldiethoxy) terminated polydimethylsiloxane.

[0034] Comparative Example 4 This comparative example provides a method for preparing diethoxy organically terminated polydimethylsiloxane, and the specific steps are as follows: 500 g of α,ω-dihydroxy polydimethylsiloxane with a viscosity of 50,000 mPa·s, 10 g of methyltriethoxysilane, and 1.5 g of bis(2-ethylhexyl) phosphate are added to a high-speed disperser, the rotation speed is controlled at 500 rpm, the temperature is raised to 55 °C, and the reaction is carried out for 90 min under moisture-proof conditions to obtain a reaction product; the reaction product is mixed with isopropyl titanate according to a weight ratio of 100:5. After detecting that there is no thickening or gelation of isopropyl titanate, 0.45 g of triethylamine is added, and the mixture is stirred for 30 min under a vacuum of -0.09 Mpa to remove low-boiling substances, obtaining α,ω-bis(methyldiethoxy) terminated polydimethylsiloxane.

[0035] Diethoxy organically terminated polydimethylsiloxane is used for preparing alcohol-cured RTV-1 silicone rubber.

[0036] The storage aging performance test was carried out on the diethoxy organically terminated polydimethylsiloxane prepared in Examples 1 to 4 and Comparative Examples 1 to 4. The specific method is as follows: The prepared diethoxy organically terminated polydimethylsiloxane was accelerated aging at 100 °C for 24 h and 168 h respectively, and then the viscosity of the diethoxy organically terminated polydimethylsiloxane after aging was detected.

[0037] The detection results are shown in Table 1.

[0038]

[0039] Except for replacing the inactivator, the preparation method and raw materials of Comparative Example 1 were the same as those of Example 1. Except for replacing the inactivator, the preparation method and raw materials of Comparative Example 2 were the same as those of Example 2.

[0040] Except for replacing the inactivator, the preparation method and raw materials of Comparative Example 3 were the same as those of Example 3. Except for replacing the inactivator, the preparation method and raw materials of Comparative Example 4 were the same as those of Example 4.

[0041] By comparing the experimental data of Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, Example 3 and Comparative Example 3, Example 4 and Comparative Example 4 in Table 1, it can be seen that the ethanol-eliminating type polydimethylsiloxane prepared using acidic phosphate can all pass the titanate test, that is, the conversion of hydroxyl groups to alkoxy groups is completed under the specified material ratio and reaction conditions of the patent. The titanate test methods for each test are the same.

[0042] However, after the accelerated aging experiment at 100 °C, the viscosity of the diethoxy organically terminated polydimethylsiloxane prepared in each example and each comparative example changed after 24 h, and was more obvious after accelerating aging at 100 °C for 168 h. After accelerating aging at 100 °C, it can be found by comparison that the stability of the silicone rubber prepared by the method disclosed in the present invention is significantly better than that of the comparative example.

[0043] This shows that the preparation method provided by the present invention can significantly improve the storage stability of diethoxy organically terminated polydimethylsiloxane.

[0044] It should be noted that the stable diethoxy organically terminated polydimethylsiloxane is a necessary condition for preparing ethanol-eliminating RTV-1, but not a sufficient condition.

[0045] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing diethoxy organic-terminated polydimethylsiloxane, characterized in that: The steps include: Mixing α,ω-dihydroxy polydimethylsiloxane, ethoxysiloxane crosslinking agent, and phosphate catalyst, stirring for 30 to 150 minutes under the condition of temperature of 35 to 75° C. and moisture isolation to obtain a reaction product; The reaction product is mixed with isopropyl titanate in a weight ratio of 100:(4-6), and then an inactivator is added; Under the condition of temperature of 35-75°C, vacuum degassing and mixing for 15-90 minutes to obtain diethoxy organic-terminated polydimethylsiloxane; Among them, the mass ratio of α,ω-dihydroxypolydimethylsiloxane, ethoxysiloxane crosslinking agent, phosphate catalyst and inactivator is (100~600):(1~10):(0.1~2):(0.02~2); the inactivator is an ethanol solution of sodium ethoxide with a concentration of 17.5~21%.

2. The method for preparing a diethoxy organic-terminated polydimethylsiloxane according to claim 1, characterized in that: The organic group of the diethoxy organic-terminated polydimethylsiloxane is vinyl, and the structural formula is: CH2=CH-Si(OCH2CH3)2-O-[Si(CH3)2-O]n-Si(OCH2CH3)2-CH=CH2.

3. The method for preparing a diethoxy organic-terminated polydimethylsiloxane according to claim 1, characterized in that: The organic group of the diethoxy organic-terminated polydimethylsiloxane is methyl, and the structural formula is: CH3-Si(OCH2CH3)2-O-[Si(CH3)2-O]n-Si(OCH2CH3)2-CH3.

4. The method for preparing a diethoxy organic-terminated polydimethylsiloxane according to claim 1, characterized in that: The viscosity of the α,ω-dihydroxy polydimethylsiloxane at 25° C. is 2000-80000 mPa·s.

5. The method for preparing a diethoxy organic-terminated polydimethylsiloxane according to claim 1, characterized in that: The ethoxysiloxane crosslinking agent is a mixture of one or more of methyltriethoxysilane, propyltriethoxysilane, vinyltriethoxysilane and ethyl orthosilicate.

6. The method for preparing a diethoxy organic-terminated polydimethylsiloxane according to claim 1, characterized in that: The phosphate catalyst is a mixture of one or more of monophosphate, diester and triester.

7. The method for preparing a diethoxy organic-terminated polydimethylsiloxane according to claim 1, characterized in that: The inactivator is an ethanol solution with a concentration of 20% sodium ethoxide.

8. The method for preparing a diethoxy organic-terminated polydimethylsiloxane according to claim 1, characterized in that: In the step (1), α,ω-dihydroxypolydimethylsiloxane, ethoxysiloxane crosslinking agent and phosphate catalyst are mixed and stirred at a temperature of 55-65° C. in a moisture-proof environment for 80-100 minutes, with the rotation speed controlled at 500-800 rpm.

9. The method for preparing a diethoxy organic-terminated polydimethylsiloxane according to claim 8, characterized in that: In the step (1), α,ω-dihydroxypolydimethylsiloxane, ethoxysiloxane crosslinking agent and catalyst are stirred and mixed in a high-speed disperser.

10. The method for preparing a diethoxy organic-terminated polydimethylsiloxane according to claim 1, characterized in that: In the step (3), the vacuum degassing mixing temperature is 50-55° C., and the vacuum degree is -0.06-0.099 MPa.

Images