Process for preparing a fluoroorganopolysiloxane

Abstract: A process for preparing a fluoroorganopolysiloxane having a fluorine-containing organic group represented by the following formula: F-(-C g F 2g O-) d -C h F 2h CH₂- where d represents an integer of from 1 to 5, g represents an integer of from 1 to 3, and h is 1 or 2, comprising the steps of: polymerizing a monomer comprising a fluorine-­ containing cyclotrisiloxane having the following formula (II): wherein R¹ represents the above fluorine-containing organic group, R² is a fluorine-free hydrocarbon group, and R³ is a fluorine-free divalent hydrocarbon group, in the presence of an acidic catalyst or a basic catalyst, and in the presence of water at a temperature of not high­ er than 80°C, and neutralising the resulting polymerization product. This process can produce the above polymer containing little low molecular weight compounds and having a desired polymerization degree in a good yield.

Description: BACKGROUND OF INVENTION 1. Field of the Invention The present invention relates to a novel process for preparing a fluoroorganopolysiloxane 2. Description of the Prior art Organopolysiloxanes have low surface tension and low refractive indexes, and are excellent in properties such as heat resistance, cold resistance, electrical insulation properties, water repellency, release properties, defoaming properties and chemical resistance; hence they are nowadays used in extensive industries. However, the recent progress of technology requires development of organopolysiloxanes excellent in various properties capable of satisfying high level of requirements. In attempt to satisfying the requirements, for example, organopolysiloxanes having a fluorine-containing organic group were proposed. Examples are described in Specifications JP-A-62 47 605 and GB-A-2 065 153. The present inventors intended to produce an organopolysiloxane having a perfluoroalkylether group as the fluorine-containing group. Heretofore, as a conventional process of preparing an organopolysiloxane, there is known a process in which an organotrisiloxane having a desired pendant organic group is polymerized in the presence of such a catalyst as silanolates of alkali, e.g., Li, Na, K and Cs at 100 to 180°C. However, if this process is applied to an organotrisiloxane having said perfluoroalkylether group, polymerization proceeds with difficulty, and depolymerization also occur to produce a considerable amount of low molecular weight compounds; hence it is impossible to produce a polymer with an intended polymerization degree in a good yield. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a novel process for preparing a fluoroorganopolysiloxane having a perfluoroalkylether group, containing little molecular weight compounds and having a desired polymerization degree. Thus, the present invention provides a novel process for preparing a fluoroorganopolysiloxane having the following general formula (I): wherein R¹ represents a fluorine-containing organic group represented by the following formula: F-(-C g F 2g O-) d -C h F 2h CH-₂ where d represents an integer from 1 to 5, g represents an integer from 1 to 3, and h is 1 or 2, R² represents a divalent substituted or unsubstituted hydrocarbon group having 3 to 10 carbon atoms and containing no fluorine atom, R³ represents a substituted or unsubstituted hydrocarbon group containing 1 to 10 carbon atoms and containing no fluorine atom, R⁴ represents a hydrogen atom, m is an integer of at least 2, and typically an integer of from 10 to 2,500, and n is an integer of not less than 1, and typically an integer of from 10 to 2,500, provided m≧2n, said process comprising the steps of: polymerizing a fluorine-containing cyclotrisiloxane having the following formula (II): wherein R¹, R² and R³ are as defined above, or a mixture of said fluorine-containing cyclosiloxane of the formula (III) and a cyclosiloxane having the following formula (III): wherein R³ is as defined above, in the presence, as catalyst, of a quaternary phosphonium hydroxide or a silanolate thereof, and in the presence of water at a temperature of not higher than 80°C, and neutralizing the resulting polymerization product with an acidic substance. According to the process of the present invention, it is possible to produce a fluoroorganopolysiloxane having a perfluoroalkylether group which contains little low molecular weight compounds and has an intended polymerization degree. This fluoroorganopolysiloxane is expected to satisfy some of recent requirements to raw materials for high-level functional materials. BRIEF DESCRIPTION OF DRAWINGS Figs. 1, 2 and 3 show the GPC chart, IR absorption spectrum, and ¹H-NNR spectrum respectively, of the fluoroorganopolysiloxane obtained in Example 1. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Fluoroorganopolysiloxane In the general formula (I) of the fluoroorganopolysiloxane of the present invention, R¹ is a fluorine-containing organic group containing the perfluoroalkylether group having the following formula: F-(-C g F 2g O-) d -C h F 2h CH 2 - where g represents an integer of from 1 to 3, d represents an integer of from 1 to 5, and h is 1 or 2. Typically, R¹ has normally from 3 to 18 carbon atoms, and more typically has from 6 to 15 carbon atoms. The perfluoroalkylether group having too small a number of carbon atoms may impair the properties of the present polymer, such as release properties, low surface energy, etc. The fluorine-containing organic group includes, for example, the groups having the following formulas: CF₃CF₂CF₂O-(CF₂CF₂CF₂O)-CF₂CF₂CH₂-, and CF₃CF₂O-(CF₂CF₂O)₂-(CF₂O)-CF₂CH₂-. R² is a divalent substituted or unsubstituted hydrocarbon group having from 3 to 10 carbon atoms, and it includes, for example, alkylene groups such as a trimethylene group, a propylene group, and a 2-methyltrimethylene group; and alkylene groups substituted partly by a phenylene radical, such as R³ is a substituted or unsubstituted hydrocarbon group having from 1 to 10 carbon atoms and containing no fluorine atom. It includes, for example, alkyl groups such as a methyl group, an ethyl group, and a propyl group; aliphatic unsaturated hydrocarbon groups such as a vinyl group, an allyl group, and hexenyl group; aromatic hydrocarbon groups such as a phenyl group, a tolyl group, and a xylyl group; and corresponding substituted hydrocarbon groups having a substituent such as a halogen atom, cyano group, alkoxyl group, acryloyloxy group, methacryloyloxy group, and silyl group, including, e.g., a chloroethyl group, chloropropyl group, cyanoethyl group, and methoxyethyl group, -C₃H₆OCO-C(-R⁶)=CH₂, - C₂H₄Si(OR⁷)3, -C₂H₄Si(OR⁷)₃, -CH₂CH(-R⁶)-COOC₃H₆Si(OR⁷)₃, wherein R⁷ is a C₁ to C₅ alkyl group, or a C₂ to C₅ alkoxyalkyl group or alkenyl group, and R⁶ is a hydrogen atom or a methyl group. The symbol a is a number of from 0.001 to 0.34, b is a number of from 1.64 to 2.34, c is a number of from 0 to 0.67, and a+b+c ranges from 1.90 to 2.67. There is no limitation on the amount of the aliphatic unsaturated hydrocarbon groups contained as R³ in the molecule of the fluoroorganopolysiloxane of the present invention. When the fluoroorganopolysiloxane of the present invention is used as an ingredient of a fluorosilicone rubber, the amount of the aliphatic unsaturated groups is suitably adjusted according to requirements, and normally ranges from 0.2 to 30 mol% of all the pendant groups bonded to silicon atoms. When it is used as a silicone gel, it may contain less than two aliphatic unsaturated groups on average in the molecule, because it is required that the molar ratio of silicon-bonded hydrogen atoms of an organohydrogenpolysiloxane used in combination to the silicon-bonded aliphatic unsaturated groups in the fluoroorganopolysiloxane of the invention ranges from 1 to 1.5. Typical examples of the fluoroorganopolysiloxane represented by the above general formula (I) of the present invention include compounds wherein m+n ranges from 3 to 2,000. The viscosity of the fluoroorganopolysiloxane produced by the present process is not particularly limited. However, it normally has a viscosity of not more than 1x10⁶ cP at 25°C. Starting materials The fluorine-containing cyclotrisiloxane of the formula (II) includes, for example, the compounds represented by the following formulas: wherein R¹ is as defined above. The cyclotrisiloxane of the formula (III) includes, for example, the compounds represented by the following formulas: wherein R⁶ and R⁷ are as defined above. In the case where a mixture of the fluorine-containing cyclotrisiloxane of said formula (II) and the cyclotrisiloxane of the formula (III) is used in the preparation of the fluoroorganopolysiloxane of the present invention, the mixing ratio of the fluorine-containing cyclotrisiloxane of said formula (II) to the cyclotrisiloxane of said formula (III) is decided suitably according to an intended fluoroorganopolysiloxane of the formula (I), and it normally ranges from 99.9/0.1 to 0.1/99.9, by weight. The fluorine-containing cyclotrisiloxane of the above formula (II) can be prepared, for example, by the process using a perfluoroalkylene oxide, exemplified below, as a starting material. First, as shown in the equation (a) below, a perfluoroalkylene oxide having the formula (V) is polymerized in the presence of a catalyst in a non-protonic polar solvent to produce an acid fluoride having the formula (VI). (See H.S. Eleuterio, J. Macromol Sci-Chem., A6(6), 1027 (1979); U.S. Patent No. 3,250,808; and Japanese pre-examination patent publication (KOKAI) No. 195345/1987). wherein j is an integer of from 2 to 6. The non-protonic solvent used in this reaction includes, for example, tetraglyme. The catalyst includes, for example, cesium fluoride CsF, potassium fluoride, and the like. Subsequently, the acid fluoride of the formula (VI) obtained is reduced with a reducing agent such as, e.g., LiAlH₄ and NaBH₄, following by hydrolysis to produce a perfluoroalkyl polyether alcohol represented by the following formula (VII): (See U.S. Patent No. 3,293,306). The perfluoroalkylpolyetheralcohol of the formula (VII) is reacted with a halogenated alkene, e.g., allyl bromide to produce, for example, an ether compound having a vinyl group at its end represented by the following formula (VIII): (see the specification of Japanese Patent Publication (KOKOKU) No. 253044/1988). In order to allow this reaction to proceed smoothly, for example, a basic substance such as sodium hydroxide, or a phase-transfer catalyst such as tetrabutyl ammounium-hydrogen-sulfuric acid may be used. The ether compound of the formula (VIII) and methyldichlorosilane are subjected to addition reaction in the presence of a platinum catalyst according to the following equation (b) to produce a silane compound of the formula (IX). (See the specification of Japanese Patent Publication (KOKOKU) No. 255288/1988). Subsequently, the silane compound of the formula (IX) and tetramethyldisiloxane diol are subjected to dehydrochlorination to produce a fluorine-containing cyclotrisiloxane having the formula (IIa): (See the specification of Japanese Patent Application No. 71887/1989). The dehydrochlorination agent which may be used includes, for example, tertiary amines such as triethylamine and active hydrogen-free cyclic amines such as pyridine. In the foregoing description, the preparation of the fluorine-containing cyclotrisiloxane of the formula (II) are described based on a particular example. However, selection of a starting material corresponding to an intended fluorine-containing cyclotrisiloxane of the formula (II) makes it possible to produce a variety of fluorine-containing cyclotrisiloxanes of the formula (II). Particularly, change of the starting perfluoroalkylene oxide and the preparation process can provide an acid fluoride having a structure differing from that of the above formula (VI). (see Japanese Patent Publication No. 11164/1971). From the acid fluorides with a different structure, fluoroorganopolysiloxanes various perfluoroalkylether groups can be prepared. In the case of the preparation process described above, use of a mixed starting material containing various perfluoroalkylene oxides can bring about a mixture of various fluorine-containing cyclotrisiloxanes having different perfluoroalkylether groups. Polymerization step The fluorine-containing cyclotrisiloxane of the formula (II) obtained as described above, or a mixture of it with the cyclotrisiloxane of the formula (III) is polymerized in the presence of a basic catalyst and in the presence of a stopper to produce the fluoroorganopolysiloxane of the present invention. The basic catalyst used is a quaternary phosphonium hydroxide or a silanolate thereof. The quaternary phosphonium hydroxides include, for example, the compounds having the formulas: (C₄H₉)₄P-OH , Silanolation of the quaternary phosphonium hydroxide can be performed, for example, by heating an aqueous solution of it with octamethycyclotetrasiloxane at from 50 to 60°C under stirring, with water being distilled under reduced pressure. The amount of the catalyst is not particularly limited. Normally, the catalyst is preferably used in an amount such that the molar ratio of all the Si in the fluorine-containing cyclotrisiloxane of said formula (III) and the cyclotrisiloxane of the formula (IV) to the catalyst molecule may range from about 500 to 3,000. If the catalyst is used in too large an amount, neutralization treatment after the polymerization become harder, and salts formed by the neutralization may exert bad influence upon the properties of the resulting fluoroorganopolysiloxane. The stopper to be used is water. Polymerization is normally carried out at 80°C or lower, preferably at from 10 to 80°C, and more preferably at from 20 to 60 °C. At too high a temperature, formation of low molecular weight cyclic compounds may be promoted by equilibration reaction. Polymerization time can be set to within a time of for from several minutes to several ten minutes as required. Preferably, the polymerization time is set to from 30 minutes to several hours by regulating the catalyst amount and/or polymerization temperature so that a fluoroorganopolysiloxane with a desired polymerization degree may be prepared. As a solvent for polymerization, for example, non-protonic solvents such as tetrahydrofrun, dioxane, diglyme, tetraglyme, dimethylformamide, and acetonitrile, or inert solvents such as frons may be used. Neutralization step In the neutralization step, the neutralizing agent to be used is selected according to the catalyst used in the polymerization step. Thus, since the polymerization is carried out in the presence of a basic catalyst and water, which is the stopper, the resulting polymerization catalyst is neutralized with an acidic substance, whereby, the fluoroorganopolysiloxane is produced as one terminated with the group having the formula: where R³ is as defined above. The acidic substance used includes, for example, mineral acids such as dilute sulfuric acid, dilute hydrochloric acid and phosphoric acid. Normally, the acidic substance is preferably used in an amount 0.8 to 3 times by equivalent weight that of the basic catalyst used. After the neutralization treatment, salts and the excess acidic substance are preferably removed. Other conditions In the preparation of the fluoroorganopolysiloxane of the present invention, in order to make easier the stirring during polymerization, neutralization, the dissolving or dispersing of the neutralizing agent, or removal by filtration of salts formed by neutralization, an inert solvent may be used as required. Such inert solvents include, for example, fluorine solvents such as fron 113, and m-xylene hexafluoride, chlorine solvents such as methylene chloride and trichloroethane. Uses The fluoroorganopolysiloxane of the present invention has a low surface tension and refractive index, and is excellent in properties such as cold resistance and oil resistance. Hence, it is expected to be also used for release agents, fiber modifiers, liquid rubbers, and heat-cure rubbers. EXAMPLES The present invention will be described in detail by way of working examples and comparative examples below. In the description below, the fluorine-containing cyclotrisiloxane having the formula (IIb): which is an example of the fluorine-containing cyclotrisiloxane of said formula (II) is abbreviated to D₂F d , where d is as defined above, i.e., an integer of from 1 to 5. The viscosities were measured at 25°C. Example 1 In a four-necked flask, 56.4 g of D₂F¹ was charged, and then the inside was replaced with a dry nitrogen gas by passing a stream thereof through the flask at 40°C for 30 minutes. Then, 2.7 g of 1 % water solution in dioxane was added, and the contents in the flask was uniformly mixed. Subsequently, 0.33 g of a catalyst consisting of dimethylsilanolate of (C₄H₉)₄POH ((C₄H₉)₄POH content: 10 %) (hereinafter, referred to as "TBPH catalyst") was added thereto so that the molar ratio of Si/P in the reaction system might become 2,500. Thereafter, polymerization was initiated at 40°C under a stream of nitrogen. The reaction mixture was transparent, and reaction proceeded at a relatively slow rate. After 2 hours, 3.6 g of 0.49 % sulfuric acid solution in water/dioxane (weight ratio: 1/1) was added, and neutralization was carried out for 1 hour. After the heater was taken away, 0.8 g of a 0.7 % aqueous ammonia was added to the reaction mixture thus treated to neutralize the excess sulfuric acid therein. The reaction mixture was then diluted with 70 g of fron 113, 10 g of Na₂SO₄ and 0.56 g of active charcoal were added thereto, and treatments of dehydration and adsorption were carried out for 1 hour, followed by filtration. The resulting transparent filtrate was subjected to stripping by heating at 80°C under a reduced pressure of 700 mmHg. Finally, stripping was carried out at 80°C under a pressure of 5 mmHg with a nitrogen gas being bubbled therethrough, resulting in 51.0 g of a colorless transparent fluoroorganopolysiloxane terminated with silanol groups. Incidentally, no distillation of siloxanes was observed when the stripping was carried out. The viscosity, specific gravity, refractive index, and silanol group content of the fluoroorganopolysiloxane obtained were measured to be 6,500 cP, 1.29, 1.3643, and 0.008 mol/100 g, respectively. The viscosity after aging at 70°C for 24 hours was measured to be 7,000 cP, indicating that the polymer had a relatively good stability. The fluoroorganopolysiloxane was analyzed by GPC and the result is shown in Fig 1. The peak represents high molecular weight compounds, and it was found that the polymer contained hardly any low molecular weight compounds. Further, the IR absorption spectrum and ¹H-NMR spectrum were measured. The results obtained are as shown below. IR absorption spectrum: The spectrum is as shown in Fig. 2. Main characteristic absorption bands are as follows. 1,000 to 1,130 cm⁻¹ (Si-O-Si) 2,970, 1,260, 810 cm⁻¹ (Si-CH₃) 1,000 to 1,400 cm⁻¹ (C-F) ¹H-NMR: The spectrum shown in Fig. 3 was obtained (20 % solution in fron 113; internal standard: Si-CH₃) δ: 3.70-4.05 ppm (d, 2H) 3.29-3.60 ppm (t, -OC H ₂CH₂CH₂, 2H) 1.34-1.87 ppm (m,-CH₂C H ₂CH₂-, 2H) 0.29-0.67 ppm (m, -C H ₂-Si, 2H) Example 2 In a four-necked flask, 243.3 g of D₂F² (purity: 99.4 %) was charged and polymerized, and the fluoroorganopolysiloxane obtained was subjected to the treatments of neutralization, dehydration and adsorption in the same manner as in Example 1, provided under the conditions described below. Amount of 1 % water solution in dioxane 9.0 g Amount of TBPH catalyst 1.90 g Polymerization temperature 40°C 0.49 % sulfuric acid solution in water/dioxane 8.26 g 2.8 % aqueous ammonia 0.42 g Na₂SO₄ for dehydration treatment 23 g Active charcoal for adsorption treatment 3.6 g The fluoroorganopolysiloxane obtained was colorless and transparent. The viscosity, specific gravity and refractive index (n D ²⁵) were measured to be 13,000 cP, 1.38, and 1.3526, respectively. This fluoroorganopolysiloxane did not dissolve in tetrahydrofuran.

Claims: A process for preparing a fluoroorganopolysiloxane having the following general formula (I): wherein R¹ represents a fluorine-containing organic group represented by the following formula: F-(-C g F 2g O-) d -C h F 2h CH₂- where d represents an integer from 1 to 5, g represents an integer from 1 to 3, and h is 1 or 2, R² represents a divalent substituted or unsubstituted hydrocarbon group having 3 to 10 carbon atoms and containing no fluorine atom, R³ represents a substituted or unsubstituted hydrocarbon group containing 1 to 10 carbon atoms and containing no fluorine atom, R⁴ represents a hydrogen atom, m is an integer of at least 2, and n is an integer of not less than 1, provided m≧2n, said process comprising the steps of: polymerizing a fluorine-containing cyclotrisiloxane having the following formula (II): wherein R¹, R² and R³ are as defined above, or a mixture of said fluorine-containing cyclosiloxane of the formula (II) and a cyclosiloxane having the following formula (III): wherein R³ is as defined above, in the presence, as catalyst, of a quaternary phosphonium hydroxide or a silanolate thereof, and in the presence of water at a temperature of not higher than 80°C, and neutralizing the resulting polymerization product with an acidic substance.

Inventors: INOMATA HIROSHI, TARUMI YASUO, INOMATA, HIROSHI, TARUMI, YASUO
Applicants: SHINETSU CHEMICAL CO, SHIN-ETSU CHEMICAL CO., LTD.
Application year: 1990
Main classification: C08G77
IPC codes: C08G77, C07F7