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Synthesis of Hydroxyfluorosilicone Oil
info：m.wvchemicalgroup.com | Release time：2023-06-29
Synthesis of Hydroxyfluorosilicone Oil
Wang Bingchang
(Shanghai Institute of Organic Fluorine Materials)
1 Preface
Polymethyl (3,3,3-trifluoropropyl) siloxane fluids with silicon hydroxyl groups as end groups are generally referred to as hydroxyfluorosilicone oils
When n=1, it is the final product,
When n=2-10, it is an oily substance.
Hydroxyfluorosilicone oil not only has the high and low temperature resistance and fuel resistance characteristics of general fluorosilicone polymers, but also has a wide range of applications due to the presence of a large number of silicon hydroxyl groups and high chemical reactivity. As an intermediate and molecular weight regulator of fluorosilicone rubber, it can be grafted with organic monomers to form copolymers with special properties, as well as used as a structural control agent for thermosetting fluorosilicone rubber, a finishing agent for fabric hydrophobicity and oleophobicity, an defoamer for organic solvents, and an additive in cosmetics. Because the molecular weight of hydroxyfluorosilicone oil is very low and the polymerization degree is generally below 10, it can be synthesized using different raw materials and methods. One is to use methyl (3,3,3-trifluoropropyl) dichlorosilane as raw material, and obtain hydroxyfluorosilicone oil through hydrolysis and condensation:
Another method is to use tris (3,3,3-trifluoropropyl) trimethylsilsesquioxane (D3F) as the raw material to catalyze the opening and shrinking of hydroxyl fluorosilicone oil:
2 Synthesis methods
2.1 (3,3,3-trifluoropropyl) dichlorosilane hydrolysis and condensation synthesis method
In the mid-1960s, a single component hydroxymethyl (3,3,3-trifluoropropyl) siloxane was synthesized using α, ω - dichloromethyl (3,3,3-trifluoropropyl) siloxane abroad
Fluorosilicone oil, the method is:
(1) D3F and hydrogen chloride (HCI) are cracked under high pressure to synthesize α, ω - dichloropolymethyl (3,3,3-trifluoropropyl) siloxane;
(2) The α, ω - dichloromethyl (3,3,3-trifluoropropyl) siloxane obtained from (1) was purified by fractional distillation, dissolved in polar solvents, and hydrolyzed below 0 ℃ to obtain the desired product. The physical and chemical properties can be seen in Table 1.
Alternatively, α, ω - dichloro poly (3,3,3-trifluoropropyl) siloxane can be reacted with acetic anhydride under the action of ferric chloride to generate α, ω - diacyloxy poly (methyl) (333 trifluoropropyl) siloxane, which can then be further hydrolyzed. Because the reaction conditions are milder, a single hydroxyl fluorosilicone oil can be obtained.
Due to the long route and complex technical requirements of the above synthesis method, and the fact that a single composition of hydroxy fluorosilicone oil is generally not required in practical applications, this synthesis method has not been widely promoted or applied.
Since the 1970s, we have used a more convenient method to directly hydrolyze methyl (3,3,3-trifluoropropyl) dichlorosilane as raw material, and have also synthesized various hydroxyl fluorosilicone oils with different hydroxyl values:
Firstly, the hydroxyl value of hydroxyfluorosilicone oil is related to the acidity and alkalinity of the hydrolysis medium. High hydroxyl value hydroxyfluorosilicone oil can be obtained when pH=7.
Secondly, under the condition of maintaining near neutrality in the hydrolysis medium, the hydroxyl value of hydroxyfluorosilicone oil is related to the concentration of the hydrolysis product. That is, within a certain range, the lower the concentration, the higher the hydroxyl value until the final product with a polymerization degree of n=1 (HO%=19-5) is obtained.
2.2D Ring opening Condensation Synthesis Method
Due to the fact that Si-O bonds can form d π - P π coordination bonds with high bond energies, it is generally impossible for homolysis to occur under normal conditions However, due to the polarity of Si+- O - (electronegative Si: 1.8, O: 3.5) bonds, they are easily broken under the catalysis of ionic media such as acids and bases, especially tension ring structures like D3F, which are more prone to ring opening and become bond like polymers:
The ring opening synthesis of hydroxyfluorosilicone oil by D3F in the presence of anionic catalysts is generally carried out in NaOH or NHOH at lower temperatures under the promotion of oxygen-containing or nitrogen-containing compounds. However, even so, the D3F opening reaction is extremely fast and rapidly condenses into high viscosity polymers, making the reaction difficult to control. Therefore, this method is generally not used for the synthesis of hydroxyfluorosilicone oil.
The synthesis of low molecular weight organic silicon polymers is often carried out using cation catalysis, with acid as the catalyst. The reaction is relatively mild and easy to control. Therefore, this method is commonly used for the synthesis of hydroxy fluorosilicone oil. The reported catalysts of this type include cation exchange resin hydrochloric acid, acidic clay, etc., with acidic clay being particularly good because it meets the four requirements as an ideal catalyst:
(1) High activity, low concentration;
(2) Easy to remove from the product;
(3) Stable use and storage:
(4) Low price and easy to obtain.
G.E. Co. in the United States successfully synthesized hydroxyfluorosilicone oil using acidified clay Filtrol No.20. Similarly, based on the actual situation in China, we also synthesized hydroxyfluorosilicone oil that meets practical requirements using domestically produced acidified clay, laying the foundation for the continuous production of hydroxyfluorosilicone oil.
2.3 Comparison of Two Synthesis Methods:
Both the hydrolysis condensation method of methyl (3,3,3-trifluoropropyl) dichlorosilane and the D3F ring opening condensation method can yield the desired hydroxyfluorosilicone oil. Similar results were obtained as a structural control agent for hot vulcanized fluorosilicone rubber.
However, due to different synthesis methods and reaction mechanisms, the composition of the hydroxyfluorosilicone oil obtained is also different, resulting in differences in the properties of the hydroxyfluorosilicone oil obtained by the two synthesis methods (see Table 4).
3 Conclusion
The hydroxyl fluorosilicone oil obtained by direct hydrolysis condensation of methyl (3,3,3-trifluoropropyl) dichlorosilane and ring opening condensation of D3F has the same effect as a structural control agent for high-temperature vulcanized fluorosilicone rubber, but other applications are still to be developed. The hydrolysis condensation method of methyl (3,3,3-trifluoropropyl) dichlorosilane has high hydroxyl value, low cost, and good economic benefits; D3F open-loop compression method has high cost but good storage performance. Therefore, the choice of use should be based on specific circumstances.
Wang Bingchang
(Shanghai Institute of Organic Fluorine Materials)
1 Preface
Polymethyl (3,3,3-trifluoropropyl) siloxane fluids with silicon hydroxyl groups as end groups are generally referred to as hydroxyfluorosilicone oils
When n=1, it is the final product,
When n=2-10, it is an oily substance.
Hydroxyfluorosilicone oil not only has the high and low temperature resistance and fuel resistance characteristics of general fluorosilicone polymers, but also has a wide range of applications due to the presence of a large number of silicon hydroxyl groups and high chemical reactivity. As an intermediate and molecular weight regulator of fluorosilicone rubber, it can be grafted with organic monomers to form copolymers with special properties, as well as used as a structural control agent for thermosetting fluorosilicone rubber, a finishing agent for fabric hydrophobicity and oleophobicity, an defoamer for organic solvents, and an additive in cosmetics. Because the molecular weight of hydroxyfluorosilicone oil is very low and the polymerization degree is generally below 10, it can be synthesized using different raw materials and methods. One is to use methyl (3,3,3-trifluoropropyl) dichlorosilane as raw material, and obtain hydroxyfluorosilicone oil through hydrolysis and condensation:
Another method is to use tris (3,3,3-trifluoropropyl) trimethylsilsesquioxane (D3F) as the raw material to catalyze the opening and shrinking of hydroxyl fluorosilicone oil:
2 Synthesis methods
2.1 (3,3,3-trifluoropropyl) dichlorosilane hydrolysis and condensation synthesis method
In the mid-1960s, a single component hydroxymethyl (3,3,3-trifluoropropyl) siloxane was synthesized using α, ω - dichloromethyl (3,3,3-trifluoropropyl) siloxane abroad
Fluorosilicone oil, the method is:
(1) D3F and hydrogen chloride (HCI) are cracked under high pressure to synthesize α, ω - dichloropolymethyl (3,3,3-trifluoropropyl) siloxane;
(2) The α, ω - dichloromethyl (3,3,3-trifluoropropyl) siloxane obtained from (1) was purified by fractional distillation, dissolved in polar solvents, and hydrolyzed below 0 ℃ to obtain the desired product. The physical and chemical properties can be seen in Table 1.
Alternatively, α, ω - dichloro poly (3,3,3-trifluoropropyl) siloxane can be reacted with acetic anhydride under the action of ferric chloride to generate α, ω - diacyloxy poly (methyl) (333 trifluoropropyl) siloxane, which can then be further hydrolyzed. Because the reaction conditions are milder, a single hydroxyl fluorosilicone oil can be obtained.
Due to the long route and complex technical requirements of the above synthesis method, and the fact that a single composition of hydroxy fluorosilicone oil is generally not required in practical applications, this synthesis method has not been widely promoted or applied.
Since the 1970s, we have used a more convenient method to directly hydrolyze methyl (3,3,3-trifluoropropyl) dichlorosilane as raw material, and have also synthesized various hydroxyl fluorosilicone oils with different hydroxyl values:
Firstly, the hydroxyl value of hydroxyfluorosilicone oil is related to the acidity and alkalinity of the hydrolysis medium. High hydroxyl value hydroxyfluorosilicone oil can be obtained when pH=7.
Secondly, under the condition of maintaining near neutrality in the hydrolysis medium, the hydroxyl value of hydroxyfluorosilicone oil is related to the concentration of the hydrolysis product. That is, within a certain range, the lower the concentration, the higher the hydroxyl value until the final product with a polymerization degree of n=1 (HO%=19-5) is obtained.
2.2D Ring opening Condensation Synthesis Method
Due to the fact that Si-O bonds can form d π - P π coordination bonds with high bond energies, it is generally impossible for homolysis to occur under normal conditions However, due to the polarity of Si+- O - (electronegative Si: 1.8, O: 3.5) bonds, they are easily broken under the catalysis of ionic media such as acids and bases, especially tension ring structures like D3F, which are more prone to ring opening and become bond like polymers:
The ring opening synthesis of hydroxyfluorosilicone oil by D3F in the presence of anionic catalysts is generally carried out in NaOH or NHOH at lower temperatures under the promotion of oxygen-containing or nitrogen-containing compounds. However, even so, the D3F opening reaction is extremely fast and rapidly condenses into high viscosity polymers, making the reaction difficult to control. Therefore, this method is generally not used for the synthesis of hydroxyfluorosilicone oil.
The synthesis of low molecular weight organic silicon polymers is often carried out using cation catalysis, with acid as the catalyst. The reaction is relatively mild and easy to control. Therefore, this method is commonly used for the synthesis of hydroxy fluorosilicone oil. The reported catalysts of this type include cation exchange resin hydrochloric acid, acidic clay, etc., with acidic clay being particularly good because it meets the four requirements as an ideal catalyst:
(1) High activity, low concentration;
(2) Easy to remove from the product;
(3) Stable use and storage:
(4) Low price and easy to obtain.
G.E. Co. in the United States successfully synthesized hydroxyfluorosilicone oil using acidified clay Filtrol No.20. Similarly, based on the actual situation in China, we also synthesized hydroxyfluorosilicone oil that meets practical requirements using domestically produced acidified clay, laying the foundation for the continuous production of hydroxyfluorosilicone oil.
2.3 Comparison of Two Synthesis Methods:
Both the hydrolysis condensation method of methyl (3,3,3-trifluoropropyl) dichlorosilane and the D3F ring opening condensation method can yield the desired hydroxyfluorosilicone oil. Similar results were obtained as a structural control agent for hot vulcanized fluorosilicone rubber.
However, due to different synthesis methods and reaction mechanisms, the composition of the hydroxyfluorosilicone oil obtained is also different, resulting in differences in the properties of the hydroxyfluorosilicone oil obtained by the two synthesis methods (see Table 4).
3 Conclusion
The hydroxyl fluorosilicone oil obtained by direct hydrolysis condensation of methyl (3,3,3-trifluoropropyl) dichlorosilane and ring opening condensation of D3F has the same effect as a structural control agent for high-temperature vulcanized fluorosilicone rubber, but other applications are still to be developed. The hydrolysis condensation method of methyl (3,3,3-trifluoropropyl) dichlorosilane has high hydroxyl value, low cost, and good economic benefits; D3F open-loop compression method has high cost but good storage performance. Therefore, the choice of use should be based on specific circumstances.
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