Polymerization process for fluorosilicone polymers

Details Polymerization process for fluorosilicone polymers Polymerization process for fluorosilicone polymers

1998-12-31

2001-05-15

Dawson, Robert (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

C528S021000, C528S033000, C528S034000, C528S036000, C528S042000, C556S450000, C556S451000, C556S453000, C556S460000, C556S462000, C556S467000

Reexamination Certificate

active

06232425

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a process for producing fluorosilicone polymers.
BRIEF DESCRIPTION OF THE RELATED ART
Fluorosilicone polymers are used in a variety of applications such as for silicone greases, hydraulic fluids, anti-foam composition and paper-release compositions.
Previously, fluorosilicone oil was produced by a cumbersome and expensive process that resulted in low yield of product and significant waste. U.S. Pat. No. 4,267,298 to Blustein discloses a process for producing triorganosilyl end-stopped diorganopolysiloxane fluids by polymerizing fluoro-substituted cyclic trisiloxane with itself, or by reacting it with other cyclo-trisiloxanes in the presence of potassium hydroxide and water, or silanol end-stopped siloxane. The resulting disilanol stopped fluorosilicone oil is then treated with a large excess of trimethylchlorosilane to provide trimethylsiloxy termination. The excess chlorosilane and hydrochloric acid byproduct from chain stopping are removed by adding excess methanol to the reaction and then stripping the methanol, HCI and trimethoxysilane from the product.
The Bluestein process produces a significant amount of waste acidic methanol and only about 85% oil and 15% volatiles. The process is also inconsistent and it is difficult to achieve a product with a desired target viscosity. As a result, separate batches of fluorosilicone fluid are typically blended to achieve a final viscosity specification. U.S. Pat. No. 3,607,899 to Brown discloses a method for producing fluorosilicone oil in which fluorosilicone trimer is reacted with hexamethyldisiloxane in the presence of an acid-activated clay. This process is also cumbersome in that a first reaction occurs at a temperature of 75-90° C., followed by a subsequent reaction at 120-140° C. Then, the reaction is cooled and the acid-activated clay must be removed by filtration. For products exceeding about 1,000 cps, the removal of the acid-activated clay is difficult. Such products first must be dissolved in a solvent, the solution must then be filtered to remove the clay, and the solvent subsequently removed by stripping. The yield of product after a long strip of high temperature described as between 68-82%. The process also generates unusable fluorosilicone volatile waste, adding to the expense and difficulty of the process.
U.S. Pat. No. 5,514,828 to Evans discloses a method for making a polyfluoroalkylsiloxane fluid by polymerizing a fluorosilicone trimer in the presence of water in combination with a strong acid catalyst. The polymer is not subjected to a condensation reaction in which the water of condensation is removed to drive polymerization of the polymer, resulting in a polymer with a high silanol content.
There is a need in the art to produce fluorosilicone oil in high yield in an efficient manner, in which the process yields a large amount of product and limited waste.
SUMMARY OF THE INVENTION
The process of the invention comprises reacting a fluorosilicone trimer and organic end-stopping compound in the presence of a catalytic amount of linear phosphonitrilic chloride (LPNC) to form end-stopped diorganopolysiloxane fluid, and stopping the reaction by inactivating the LPNC. Optionally, the resulting end-stopped diorganopolysiloxane fluid may be stripped of volatiles.
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention comprises reacting a fluorosilicone trimer and organic end-stopping compound in the presence of a catalytic amount of linear phosphonitrilic chloride (LPNC) to form end-stopped diorganopolysiloxane fluid, and stopping the reaction by inactivating the LPNC. Optionally, the resulting end-stopped diorganopolysiloxane fluid may be stripped of volatiles by heating and removing the volatiles by a method such as applying a vacuum or by a nitrogen purge.
The fluorosilicone trimer used in the present invention has the general formula (I):
wherein R
1
is a monovalent hydrocarbon of 1-8 carbon atoms, and R
2
is a perfluoroalkylethylenyl radical of 3-8 carbon atoms. Of the trifluorosilicone trimers useful in the present invention, 1,3,5-tris(3,3,3-trifluoropropyl)-1,3,5-trimethylcyclotrisiloxane is preferred.
The organic end-stopping compounds that may be used with the present invention include, but are not limited to hexaorganodisiloxanes, organic anhydrides, halogenated silanes and mixtures thereof.
The hexaorganodisiloxanes suitable for use in the present invention are of the general formula (II):
wherein the R groups are independently hydrogen, hydroxyl, alkyls of 1-8 carbon atoms, and vinyl groups of 2-8 carbon atoms. Examples of the hexaorganodisiloxanes, suitable for use in the present invention include, but are not limited to hexamethyldisiloxane, tetramethyldisiloxane, and divinyltetramethyidisiloxane.
The halogenated silanes suitable for use in the present invention have the general formula R
3
SiX, wherein R is a monovalent alkyl radical of 1-8 carbon atoms, an alkenyl radical of 2-8 carbon atoms, a cycloalkyl radical of 4-8 carbon atoms, a mononuclear aryl radical of 6-8 carbon atoms, or a perfluoroalkylethylenyl radical of 3-8 carbon atoms; and X is a halogen, preferably, chlorine. Examples of the halogenated silanes that are suitable for use in the present invention include, but are not limited to trimethylchlorosilane, vinyidimethylchlorosilane, 3,3,3-trifluropropyldimethylchlorosilane, and phenyidimethylchlorosilane.
In one embodiment of the invention, fluorosilicone trimer is reacted with a hexaorganodisiloxane in the presence of a catalytic amount of linear phosphonitrilic chloride (LPNC). A catalytic amount of LNPC is generally about 50 ppm or more LPNC. The reaction can be performed at a temperature from about room temperature to about 130° C., more preferably from about 55-120° C., most preferably from about 70-100° C. At this temperature range, a smooth reaction occurs in which the viscosity of the product approaches the equilibrium viscosity over a period of about 2-4 hours.
LPNC is generally in the form of a solution in which LPNC is dissolved in methylene chloride. Typically a 2% solution of LPNC in methylene chloride is used as a stock solution. The concentration of LPNC in methylene chloride is such that the final concentration of LPNC when added to the reaction is at least 50 ppm.
The reaction is stopped by inactivation of LPNC. Volatiles content is influenced by the formation of cyclic hexamer, which has a high boiling point. It may or may not be necessary to remove the cyclic hexamer, based on whether pure polymer is desired. For low temperature applications, the hexamer will not evaporate and it may not be necessary to remove the cyclic hexamer. Of the cyclic molecules formed in the reaction, 1-2% of the cyclic molecules are tetramers & pentamers, which will come off in a stripping process. However, 5-6% are cyclic hexamers, which may not come off in the stripping process, or require much higher temperatures for stripping. Yield determinations are generally based on weight loss. This is performed by heating a sample to 135° C. at 15 mmHg for 45 minutes. The remaining weight is considered polymer. However, calculations of polymer yield based on weight loss are not accurate for polymer solutions containing cyclic hexamers. Although longer reaction times can lead to a volatiles content of up to about 8%, such long reaction times may be easily avoided.
LPNC may be inactivated by neutralizing the LPNC with the addition of a base. Any strong base is suitable for use in the present invention. Examples of based that are suitable for use include, but are not limited to sodium carbonate, sodium hydroxide, calcium carbonate, any amine, and the like. When inactivating the catalyst with a base, it is preferred not to use excess base as a strong base is a depolymerization catalyst. A preferred method of inactivation is hexamethyidisilizane in 2-5 fold excess. The silizane leads to the formation of insoluble ammonium chloride that makes the product hazy. Using a high temperature strip such as 250° C. at 20 mm Hg will strip out the a

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