Polymerization process for fluorosilicone polymers

A process for making organosilyl end-stopped diorganopolysiloxane fluid is provided comprising the steps of reacting an organic end-stopping compound with a fluorosilicone trimer in the presence of a catalytic amount of linear phosphonitrilic acid, and inactivating the linear phosphonitrilic acid, thereby forming organosilyl end-stopped diorganopolysiloxane fluid.

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.degree. C., followed by a subsequent reaction at
 120-140.degree. 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):
 ##STR1##
 wherein R.sup.1 is a monovalent hydrocarbon of 1-8 carbon atoms, and
 R.sup.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):
 ##STR2##
 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.sub.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.degree. C., more preferably from
 about 55-120.degree. C., most preferably from about 70-100.degree. 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.degree. 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.degree. C. at 20 mm Hg will strip out the ammonium chloride to give a
 clear product. Inactivation with NaHCO.sub.3 or NaOH leads to the
 formation of insoluble salts that cannot be stripped out, but need to be
 filtered from the product, and therefore, are not preferred.
 Alternatively, the LPNC catalyst may be inactivated by heat. Heat
 inactivation is preferable to base inactivation. Inactivation by heat is
 preferred because it prevents the accumulation of salt. Inactivation by
 heat may be accomplished by heating the reaction to a temperature of at
 least about 150.degree. C. for about 1 hour.
 Inactivation by heat will result in a concentration of volatiles of about
 5-8% as heat inactivation requires a longer cycle time than the optimum
 cycle time for the highest yield of product. However, the amount of
 volatiles can be reduced by subjecting the reaction product to a high
 temperature strip to approach a yield of about 99% product. While a high
 temperature strip is required to achieve a reduction in volatiles to about
 1%, the amount of expensive and unusable fluorosilicone waste streams is
 considerably reduced by this process. Moreover, viscosities of about
 50-100,000 cps or more can be achieved.
 Temperatures for the strip are generally from about 150-250.degree. C. More
 preferably, the temperature range is from about 175-230.degree. C. Most
 preferably, the temperature range is from about 190-220.degree. C. The
 temperature selected is also in consideration of the pressure at which the
 strip is performed. Typically, the strip is conducted at a pressure of 3
 mm Hg and a temperature of about 220.degree. C.
 In another embodiment of the invention, fluorosilicone trimer is reacted
 with an organic anhydride in the presence of a catalytic amount of LPNC to
 yield a diacetoxy-terminated fluorosilicone oil. In this embodiment,
 suitable organic anhydrides include acetic anhydride, maleic anhydride,
 itaconic anhydride, propionic anhydride, butyric anhydride, and the like.
 In another embodiment, fluorosilicone trimer is reacted with acetoxysilane
 in the presence of a catalytic amount of LPNC. Suitable acetoxysilanes
 include methyltriacetoxysilane, dimethyldiacetoxysilane and their dimers.

EXAMPLES
 Example 1
 400 g of fluorosilicone cyclic trimer and 12 g of hexamethyldisiloxane were
 placed in a flask with an agitator. The batch was heated to 100.degree. C.
 and 4 g of a 2% solution of linear phosphonitrillic chloride (LNPC)
 catalyst dissolved in methylene chloride was added. After 5 hours of
 polymerization, 5 drops of hexamethyidisilazane was added to deactivate
 the LPNC. The batch was heated to 220.degree. C. at 3 mm Hg, and 60 g of
 volatiles were removed. Fluorosilicone oil in an amount of 335 g with a
 viscosity of 1060 cps and a 0.67% final weight loss was obtained.
 Example 2
 103 g of fluorotrimer and 3.6 g of trimethylchlorosilane were added to a
 flask equipped with a stirrer and a condenser and heated to 70.degree. C.
 0.4 g of a 2% solution of LPNC catalyst was added to the batch. Within 10
 minutes the batch temperature rose to 75.degree. C. from the exotherm
 resulting from the ring opening polymerization of the trimer. The batch
 temperature was raised to 80.degree. C. and samples taken after 1, 2, and
 3 hours. The weight loss of the samples at 135.degree. C., 2 mm for 45
 minutes were 36%, 12%, and 10% respectively. After 4 hours from time of
 catalyst addition, the batch was cooled to 25.degree. C., and 5.3 g of
 hexamethyidisilazane was added to the reaction and the temperature rose to
 29.degree. C. The product was quite hazy from the formation of ammonium
 chloride. The reaction contents were agitated at high rpm and a vacuum of
 4 mm was applied. The batch temperature was raised to 260.degree. C. for
 20 minutes to remove volatile components. A clear product oil (87.5 g) was
 isolated with a viscosity of 1220 cps, and a weight loss of 0.25%
 (135.degree. C., 2 mm, 45 minutes).
 Those of ordinary skill in the art appreciate that many variations and
 substitutions may be made without departing from the spirit of the
 invention. It should be understood that the foregoing examples are
 intended as illustrations of the invention and are not to be interpreted
 as limitations or restrictions on the scope of the invention, which is
 defined in the appended claims.