JP7136001B2 - Method for producing organopolysiloxane raw rubber - Google Patents

Description

The present invention relates to a method for producing organopolysiloxane raw rubber.

In general, silicone rubber is excellent in weather resistance, durability, heat resistance, colorability, and is physiologically inactive. in use.

As a method for producing a linear organopolysiloxane used as a raw material for silicone rubber, a low-molecular-weight cyclic or linear organopolysiloxane is subjected to an equilibration reaction using an acidic or basic catalyst. Methods for polymerizing are known. However, in this polymerization method, as a result of simultaneous formation and cleavage of siloxane bonds, the resulting high-molecular-weight straight-chain organopolysiloxane contains a large amount of low-molecular-weight cyclic siloxanes.

Under the current chemical substance regulations, it is common to evaluate accumulation by BCF (Bioconcentration Factor). Accurate evaluation of accumulation in the natural world is possible by collecting data in the actual environment. Laboratory data are used as indicators of accumulation.

BCF is a method to test how much chemical substances accumulate in fish in water, and the experiment is conducted under a constant concentration of chemical substances. Therefore, this method is not suitable for evaluating the accumulation of poorly water-soluble substances and highly volatile substances. Tetramer, pentamer and hexamer low-molecular-weight cyclic siloxanes (D4-6) have been shown to have low accumulation and little toxicity in actual environments, but their BCF values are high. and is subject to regulation.

In Europe, D4-6 is designated as SVHC (Substances of Very High Concern). D5, which had sufficient data in Japan, was not designated as a monitoring chemical substance, but D4 and D6, which lacked data, were designated as monitoring chemical substances. In such a worldwide trend of chemical substance regulation, reduction of low-molecular-weight cyclic siloxane is required.

In Patent Document 1, a hydroxide selected from magnesium hydroxide, calcium hydroxide, strontium hydroxide and barium hydroxide is added to an organopolysiloxane having at least one hydroxyl group at the molecular end, and polycondensation is performed. A method of obtaining the polymer is disclosed. However, by this method, the degree of polymerization of the product obtained is low, and it is difficult to obtain a crude rubber-like substance.

Patent Document 2 discloses a method for obtaining a polymer by adding a silane or siloxane having a difunctional dialkylaminosilyl group to an organopolysiloxane or triorganosilanol having a silanol group at both ends of the molecular chain and conducting a polycondensation reaction. ing. However, in this method, an amino compound, which is difficult to remove, is produced as a by-product during neutralization and remains in the product.

Patent Literature 3 discloses a method of obtaining a polymer by adding a specific acidic compound to an organopolysiloxane having hydroxyl groups at both ends of the molecule and conducting a polycondensation reaction. However, in this method, a fluorine compound is produced as a by-product during neutralization, so there is a problem that the use of the resulting linear organopolysiloxane may be limited.

Patent No. 2857202 Patent No. 2824953 Patent No. 2838352

Regarding the method of distilling off low-molecular-weight cyclic siloxanes, if low-molecular-weight cyclic siloxanes are contained in the main oily component, they can be distilled off by performing high-temperature, low-pressure treatment. If the high polymer contains low-molecular-weight cyclic siloxane, the treatment must be carried out for a long period of time, which poses an industrial problem.

The present invention has been devised in view of the above circumstances, and it is an object of the present invention to provide a method for polymerizing linear organopolysiloxane that is industrially advantageous and has no odor, with little by-production of low-molecular-weight cyclic siloxanes or fluorine compounds. With the goal.

As a result of intensive studies to achieve the above object, the present inventors have found that a hydroxyl group-containing organopolysiloxane having a total content of low-molecular-weight cyclic siloxanes (D3 to D20) of 500 ppm or less is added with sodium hydroxide or A method for producing an organopolysiloxane raw rubber containing 1,000 ppm or less of each of low-molecular cyclic siloxanes D4, D5 and D6 by conducting a polycondensation reaction in the presence of an organosilanolate of sodium has been found.

Accordingly, the present invention provides the following method for producing organopolysiloxane raw rubber.

[1]
A method for producing an organopolysiloxane raw rubber having an average degree of polymerization of 3,000 to 10,000, comprising:
(A) has at least two silicon-bonded hydroxy groups in one molecule, has a viscosity of 100 to 100,000 mPa·s at 25° C., and contains low-molecular-weight cyclic siloxanes (D3 to D20) Organopolysiloxane whose amount is 500 ppm or less in component (A),
(B) polycondensation in the presence of a sodium hydroxide catalyst or a sodium organosilanolate catalyst,
A method for producing organopolysiloxane crude rubber, wherein the contents of cyclic siloxanes D4, D5 and D6 are each 1,000 ppm or less.
[2]
The method for producing organopolysiloxane gum according to [1], wherein the total content of low-molecular-weight cyclic siloxanes (D3 to D20) in the resulting organopolysiloxane gum is 5,000 ppm or less.
[3]
The method for producing an organopolysiloxane raw rubber according to [1] or [2], wherein the condensation polymerization temperature is 80 to 120°C.

In the present invention, room temperature or room temperature means 20°C ± 10°C, particularly 25°C. Raw rubber is a non-liquid substance (solid or pasty substance) having an average degree of polymerization of organopolysiloxane of 3,000 to 10,000 and having no (or almost no) self-fluidity at room temperature. means

In the present invention, the viscosity is the viscosity at 25° C. measured by the method described in JIS K 7117-1:1999, and is the value measured with a BH-type rotational viscometer.
In addition, in the present invention, a cyclic siloxane having X silicon atoms is represented as "DX".

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an industrially advantageous method for polymerizing a colorless, transparent, odor-free linear organopolysiloxane that hardly produces low-molecular-weight cyclic siloxanes or fluorine compounds by-products.

The present invention will be described in more detail below.

I. (A) has at least two silicon-bonded hydroxy groups in one molecule, has a viscosity of 100 to 100,000 mPa·s at 25° C., and has a total content of low-molecular-weight cyclic siloxanes D3 to D20 of 500 ppm or less. Production of hydroxy group-containing organopolysiloxane

（式（２）中、Ｒ²は互いに独立に非置換又は置換の炭素数１～１０の1価炭化水素基を表し、ｎは３～８の整数である。）

上記一般式（２）中、Ｒ²は互いに独立に非置換又は置換の炭素数１～１０の、好ましくは炭素数１～６の１価炭化水素基を表す。例えば、メチル基、エチル基、ブチル基等のアルキル基、シクロヘキシル基、シクロペンチル基等のシクロアルキル基、ビニル基、アリル基等のアルケニル基、フェニル基、キシリル基等のアリール基、ベンジル基等のアラルキル基などやこれらの基の水素原子の一部又は全部がハロゲン原子、メルカプト基、グリシド基、（メタ）アクリロキシ基、アミノ基等で置換され基が挙げられる。Ｒ²は、好ましくは、メチル基、ビニル基、フェニル基であり、一般式（２）で表される化合物としては、一分子中の全Ｒ²のうち、好ましくは２５～１００％、より好ましくは５０～１００％がメチル基である化合物が好ましい。ｎは３～８の整数、好ましくは３～５の整数である。 Component (A) can be obtained by a known method, for example, by polymerizing a cyclic organosiloxane and water in the presence of an alkaline catalyst. Specifically, the polymerization is carried out by adding a small amount of an alkaline catalyst to a cyclic organosiloxane and water, or adding an aqueous solution containing a small amount of an alkaline catalyst to a cyclic organosiloxane and equilibrating under sealed conditions at 100-180°C. by reacting. By appropriately adjusting the amount of water during the equilibration reaction, the desired organopolysiloxane having at least two silicon-bonded hydroxyl groups per molecule and a viscosity of 100 to 100,000 mPa·s can be obtained. be done.
Here, examples of the cyclic organosiloxane include those represented by the following formula (2).

(In formula (2), R ² independently represents an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, and n is an integer of 3 to 8.)

In general formula (2) above, each R ² independently represents an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms. For example, alkyl groups such as methyl group, ethyl group and butyl group; cycloalkyl groups such as cyclohexyl group and cyclopentyl group; alkenyl groups such as vinyl group and allyl group; aryl groups such as phenyl group and xylyl group; Examples include aralkyl groups and groups in which some or all of the hydrogen atoms of these groups are substituted with halogen atoms, mercapto groups, glycide groups, (meth)acryloxy groups, amino groups and the like. R ² is preferably a methyl group, a vinyl group, or a phenyl group, and the compound represented by the general formula (2) preferably accounts for 25 to 100%, more preferably 25 to 100% of all R ² in one molecule. is preferably a compound in which 50 to 100% are methyl groups. n is an integer of 3-8, preferably an integer of 3-5.

One of the cyclic organosiloxanes may be used alone, or two or more of them may be used in combination. When two or more cyclic organosiloxanes are used in combination, a compound in which all R ² are methyl groups in the general formula (2), preferably 25 to 100%, more preferably 50 to 100%, of all R ² A compound in which R 2 is a methyl group and the remaining R ² is an alkenyl group such as a vinyl group, and a compound in which 25 to 100%, more preferably 50 to 100% of the total R ² is a methyl group and the remaining R ² is a phenyl group It is preferable to appropriately combine compounds that are aryl groups such as

Examples of alkaline catalysts include alkali metal compounds such as sodium hydroxide, potassium hydroxide and cesium hydroxide, or silanolates thereof. _In addition, these catalysts may be deactivated by an acidic neutralizing agent, but at a high temperature of 130 to 150° C., they _decompose and lose activity. Quaternary ammoniums such as ( _CH3 ) _4NOH or their silanolates can also be used. In addition, in the equilibration reaction, it is preferable to use the alkaline catalyst in the form of an aqueous solution.

The content of the alkaline catalyst is preferably 1 to 1,000 ppm, particularly 10 to 500 ppm, based on the cyclic organosiloxane. Within the above range, sufficient polymerizability can be obtained.

The equilibration reaction can be carried out under normal conditions, for example, preferably at 100 to 180° C. for 30 minutes to 6 hours under sealed or pressure-regulated conditions.

After the above reaction, the alkaline catalyst is neutralized with an acidic neutralizing agent such as hydrochloric acid, ethylene chlorohydrin, acetic acid, carbon dioxide, etc., or deactivated by thermal decomposition. Moreover, it is preferable to distill off a low volatile matter after that.

The viscosity of component (A) is 100 to 100,000 mPa·s, preferably 100 to 50,000 mPa·s, more preferably 100 to 30,000 mPa·s. If the viscosity is less than 100 mPa, the target product may also be distilled off when the low volatile matter is distilled off. Low-molecular-weight siloxane may remain in raw rubber.

The low-molecular-weight cyclic siloxane (D3 to D20) in component (A) is 500 ppm or less, preferably 450 ppm or less, more preferably 400 ppm or less. By setting the total content of cyclic siloxanes in component (A) to 500 ppm or less, it is possible to reduce the content of low-molecular-weight cyclic siloxanes in raw rubber after condensation polymerization. If the amount of low-molecular-weight cyclic siloxane in component (A) exceeds 500 ppm, the low-molecular-weight cyclic siloxane remains in the crude rubber after polycondensation to obtain raw rubber, making it difficult to remove. In the present invention, the amount of the low-molecular-weight cyclic siloxane is a value determined by gas chromatography analysis.

When the total content of low-molecular-weight cyclic siloxanes D3 to D20 in the organopolysiloxane to be subjected to the production method of the present invention exceeds 500 ppm, the following method is used to reduce the total content of low-molecular-weight cyclic siloxanes to 500 ppm or less. to reduce Methods for removing the low-molecular-weight cyclic siloxane include a heating distillation method, a vacuum distillation method, a thin film distillation method, and the like. In order to efficiently remove low-molecular-weight cyclic siloxanes, it is preferable that the system pressure is low and the temperature is high. °C is preferred. Among the above methods, the thin-film distillation method is preferable because the organopolysiloxane is not exposed to high temperatures for a long time and the siloxane chains are less likely to be cut. Two or more methods for removing low-molecular-weight cyclic siloxane may be combined. For example, thin-film distillation may be performed after crude distillation by heating under reduced pressure.

Conditions for thin film distillation are, for example, a temperature of 150 to 300° C., preferably 200 to 300° C., more preferably 260° C., and a pressure of 10×10 ⁻² mmHg or less, preferably 5×10 ⁻² mmHg. Below. A vacuum pump used for reducing the pressure may be selected as appropriate, and examples thereof include rotary pumps, diffusion pumps, turbo pumps, and the like.

(B) Sodium hydroxide or sodium organosilanolate Component (B) acts as a catalyst for the polycondensation reaction of the present invention, and either sodium hydroxide or sodium organosilanolate can be used. There are no restrictions. The organosilanolate of sodium can be prepared by a known method. For example, sodium hydroxide is added to polydialkylsiloxane having hydroxyl groups at both ends, and water is distilled off by blowing an inert gas or the like. Equilibration reaction is carried out at 100-150° C. for 3-6 hours. After completion of the reaction, low volatile matter is distilled off under reduced pressure at 100 to 150° C. for 6 to 10 hours to obtain sodium silanolate. Moreover, you may use organic solvents, such as toluene, for the said reaction.

II. The present invention provides (A) a low-molecular-weight cyclic siloxane containing at least two silicon-bonded hydroxyl groups per molecule and having a viscosity of 100 to 100,000 mPa·s. An organopolysiloxane having a total content of D3 to D20 of 500 ppm or less is (B) polycondensed in the presence of sodium hydroxide or a sodium organosilanolate catalyst to obtain low-molecular-weight cyclic siloxanes D4, D5 and D6. An organopolysiloxane raw rubber is obtained in which the amount of each is less than 1,000 ppm.

The amount of component (B) blended is preferably 1 to 1,000 ppm, particularly preferably 10 to 500 ppm, relative to the total amount of hydroxy group-containing organopolysiloxane (A). can get. It is also possible to shorten the reaction time by increasing the amount of catalyst used within the above range.

The temperature of the polycondensation reaction is preferably 80 to 120°C, more preferably 90 to 110°C. If the reaction temperature is less than 80°C, the desired polycondensation reaction proceeds slowly, and if the reaction temperature exceeds 120°C, the equilibration reaction may proceed.

The polymerization reaction time is usually in the range of 1 to 12 hours, preferably 3 to 9 hours.

The polycondensation reaction may be carried out under normal pressure or under reduced pressure, but it is preferable to carry out under reduced pressure in order to remove water generated during polycondensation and to remove low volatile matter contained in the raw materials. When the condensation polymerization reaction is performed under reduced pressure, the pressure is 20 mmHg or less, preferably 10 mmHg or less.

After the above reaction, the sodium hydroxide or sodium organosilanolate is neutralized and deactivated with an acidic neutralizing agent such as hydrochloric acid, ethylene chlorohydrin, acetic acid, carbon dioxide and the like. The amount of the neutralizing agent to be added is 1 to 20 times by mol, preferably 2 to 10 times by mol, the amount of sodium in component (B). Within the above range, it is possible to sufficiently neutralize the catalyst.

Moreover, it is preferable to distill off a low volatile matter after that. The conditions for distilling off low volatile matter are a temperature of 100 to 170° C., preferably 120 to 150° C., and a time of 1 to 4 hours. The reaction for distilling off the low volatile matter may be carried out under normal pressure or reduced pressure.

The polymerization process of the present invention may be carried out as a batch process or as a continuous process.

Low-molecular-weight cyclic siloxanes D4, D5 and D6 in the obtained organopolysiloxane raw rubber are each less than 1,000 ppm. If each of the low-molecular-weight cyclic siloxanes D4 to D6 exceeds 1,000 ppm, it may be regulated from the viewpoint of chemical substance regulation.

Examples of the present invention are shown below. The present invention is by no means limited by the following examples.
The average degree of polymerization referred to in the present invention is obtained as the number average degree of polymerization in terms of polystyrene in gel permeation chromatography (GPC) analysis using tetrahydrofuran (THF) as a developing solvent under the following measurement conditions.

[Measurement condition]
Developing solvent: tetrahydrofuran (THF)
Flow rate: 0.6mL/min
Detector: Differential Refractive Index Detector (RI)
Column: TSK Guard column SuperH-L
TSKgel Super H4000 (6.0mm ID x 15cm x 1)
TSKgel Super H3000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH2000 (6.0mm I.D. x 15cm x 2)
(both manufactured by Tosoh Corporation)
Column temperature: 40°C
Sample injection volume: 20 μL (THF solution with a concentration of 0.5% by weight)

Low-molecular-weight cyclic siloxanes (D3 to D20) with a polymerization degree of 3 to 20 contained in the organopolysiloxanes produced in the following examples were measured under the following measurement conditions.

[Measurement condition]
Apparatus: Shimadzu Gas Chromatograph Nexis GC-2030
Fluid: air, hydrogen, helium Flow rate: 0.6 mL/min
Detector: Hydrogen flame ionization detector Column: DB-5MS
(both manufactured by Shimadzu Corporation)
Column temperature: 320°C
Sample injection volume: 1.0 μL

Preparation example 1
Synthesis of 2% sodium silanolate Into a 300 ml separable flask equipped with a stirrer, a reflux condenser and a thermometer, 171 g of polydimethylsiloxane (viscosity of 5,000 mPa s) having hydroxyl groups at both ends and 23.3 g of toluene were added. Further, 4.0 g of sodium hydroxide was added, nitrogen gas was blown in, and an equilibration reaction was carried out at 150° C. for 3 hours while water was distilled off. After completion of the reaction, low volatile matter was distilled off at 150° C. and 5 mmHg or less for 6 hours while blowing nitrogen gas to obtain 105 g of 2% sodium silanolate.

Preparation example 2
Synthesis of 3% potassium silanolate Into a 300 ml separable flask equipped with a stirrer, a reflux condenser and a thermometer, 171 g of polydimethylsiloxane (viscosity of 5,000 mPa s) having hydroxyl groups at both ends and 23.3 g of toluene were added. Further, 4.0 g of potassium hydroxide was added, nitrogen gas was blown in, and an equilibration reaction was carried out at 150° C. for 3 hours while water was distilled off. After completion of the reaction, low volatile matter was distilled off at 150° C. and 5 mmHg or less for 6 hours while blowing nitrogen gas to obtain 112 g of 3% potassium silanolate.

Preparation example 3
Synthesis of organopolysiloxane (A) In a 3 L separable flask equipped with a stirrer, reflux condenser, dropping funnel and thermometer, 1,986 g of octamethylcyclotetrasiloxane and 1,3,5,7-tetramethyl-1 were added. ,3,5,7-tetravinylcyclosiloxane 2.9 g, 0.5% potassium hydroxide aqueous solution 9.5 g was added, and equilibration reaction was carried out at 150° C. for 6 hours under closed conditions. let me
After completion of the reaction, the mixture was cooled to 80°C, 0.53 g of ethylene chlorohydrin was added, and neutralized at 150°C for 2 hours under closed conditions. After completion of neutralization, crude distillation is performed at 150°C and 20 mmHg or less for about 6 hours, and the obtained product is subjected to a thin-film molecular distillation apparatus three times at 260°C and 5×10 ^-2 mmHg or less for 9 minutes. was used to distill off the low volatiles.
The resulting organopolysiloxane (A), 1,521 g, contained 99.850 mol% of dimethylsiloxane units, 0.125 mol% of methylvinylsiloxane units, and 0.025 mol% of dimethylhydroxysiloxane units, and had an average The degree of polymerization was 243, the viscosity was 1.08 Pa·s, the total content of low-molecular-weight cyclic siloxanes (D3 to D20) was 20 ppm, and it was colorless and transparent.

Example 1
Synthesis of Organopolysiloxane Gum Into a 200 ml separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer, 100 g of organopolysiloxane (A) and 0.64 g of 0.5% sodium hydroxide aqueous solution were added, The polycondensation reaction was carried out at 100° C. and 20 mmHg or less for 5 hours. After completion of the reaction, the mixture was cooled to 80°C, 0.06 g of ethylene chlorohydrin was added, and neutralized at 150°C for 1 hour under closed conditions. After completion of neutralization, low volatile matter was distilled off under conditions of 150° C. and 10 mmHg or less for 1 hour to obtain 87 g of organopolysiloxane raw rubber.
The resulting organopolysiloxane raw rubber had a viscosity of 12,000 Pa·s, an average degree of polymerization of 4,500, contents of D4, D5 and D6 of 287 ppm, 166 ppm and 893 ppm, respectively, and a total content of D3 to D20 of It was 3,268 ppm, and was colorless, transparent, and odorless. Table 1 shows the results of measuring the average degree of polymerization and the amount of low-molecular-weight cyclic siloxanes (D3 to D20).

Example 2
100 g of organopolysiloxane (A) and 0.16 g of 2% Na silanolate obtained in Preparation Example 1 were added to a 200 ml separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer. The polycondensation reaction was carried out for 5 hours under conditions of 20 mmHg or less. After completion of the reaction, the mixture was cooled to 80°C, 0.06 g of ethylene chlorohydrin was added, and neutralized at 150°C for 1 hour under closed conditions. After the neutralization was completed, low volatile matter was distilled off under conditions of 150° C. and 10 mmHg or less for 1 hour to obtain 88 g of organopolysiloxane raw rubber.
The resulting organopolysiloxane raw rubber had a viscosity of 10,000 Pa·s, an average degree of polymerization of 4,300, contents of D4, D5 and D6 of 287 ppm, 179 ppm and 879 ppm, respectively, and a total content of D3 to D20 of 3. It was 896 ppm and was colorless, transparent, and odorless. Table 1 shows the results of measuring the average degree of polymerization and the amount of low-molecular-weight cyclic siloxanes (D3 to D20).

Comparative example 1
100 g of organopolysiloxane (A) and 0.18 g of 3% potassium silanolate were added to a 200 ml separable flask equipped with a stirrer, reflux condenser, dropping funnel and thermometer, and the mixture was stirred at 100° C. and 20 mmHg or less. Time condensation polymerization reaction was carried out. After completion of the reaction, the mixture was cooled to 80°C, 0.06 g of ethylene chlorohydrin was added, and neutralized at 150°C for 1 hour under closed conditions. After completion of neutralization, low volatile matter was distilled off under conditions of 150° C. and 20 mmHg or less for 1 hour to obtain 87 g of organopolysiloxane raw rubber.
The obtained organopolysiloxane crude rubber had a viscosity of 12,500 Pa·s and an average degree of polymerization of 5,500, and the contents of D4, D5 and D6 were 1,487 ppm, 1,368 ppm, 2,121 ppm, and D3 to D20, respectively. was 30,818 ppm, colorless, transparent and odorless. Table 1 shows the results of measuring the average degree of polymerization and the amount of low-molecular-weight cyclic siloxanes (D3 to D20).

Comparative example 2
100 g of organopolysiloxane (A) and 0.64 g of 0.5% lithium hydroxide aqueous solution were added to a 200 ml separable flask equipped with a stirrer, reflux condenser, dropping funnel and thermometer, and the temperature was maintained at 100° C. under 20 mmHg or less. The polycondensation reaction was carried out for 5 hours under these conditions. An average degree of polymerization of 243 and sufficient polymerizability were not obtained, and a liquid product was obtained.

Comparative example 3
100 g of organopolysiloxane (A) and 0.64 g of 0.5% strontium hydroxide aqueous solution were added to a 200 ml separable flask equipped with a stirrer, reflux condenser, dropping funnel and thermometer, and the temperature was maintained at 100° C. under 20 mmHg or less. The polycondensation reaction was carried out for 5 hours under these conditions. An average degree of polymerization of 282 and sufficient polymerizability were not obtained, and a liquid product was obtained.

Comparative example 4
100 g of organopolysiloxane (A) and 0.64 g of 0.5% barium hydroxide aqueous solution were added to a 200 ml separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer, and the temperature was maintained at 100° C. under 20 mmHg or less. The polycondensation reaction was carried out for 5 hours under these conditions. An average degree of polymerization of 420 and sufficient polymerizability were not obtained, and a liquid product was obtained.

Comparative example 5
In a 200 mL separable flask equipped with a stirrer, reflux condenser, dropping funnel and thermometer, 126 g of octamethylcyclotetrasiloxane, 0.050 g of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane and To a mixture consisting of 0.18 g of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclosiloxa was added 0.0 of dimethylpolysiloxanate of 10% tetra-n-butylphosphonium hydroxide. 21 g was added and polymerized at 110° C. for 1 hour. After the polymerization reaction, the temperature is maintained at 150°C for 2 hours to thermally decompose the tetra-n-butylphosphonium hydroxide, and then the temperature is maintained at 140 to 150°C under reduced pressure for about 5 hours until the temperature reaches 2 mmHg or less, and the low volatile content is removed. After distilling off, 113 g of organopolysiloxane crude rubber was obtained.
The resulting organopolysiloxane crude rubber had a viscosity of 14,000 Pa·s, an average degree of polymerization of 5,000, and contents of D4, D5 and D6 of 1,624 ppm, 1,546 ppm, 2,452 ppm, and D3 to The total D20 content was 34,548 ppm, and it was colorless, transparent, and odorless. Table 1 shows the results of measuring the average degree of polymerization and the amount of low-molecular-weight cyclic siloxanes (D3 to D20).

Claims (3)

A method for producing an organopolysiloxane raw rubber having an average degree of polymerization of 3,000 to 10,000, comprising:
(A) has at least two silicon-bonded hydroxy groups in one molecule, has a viscosity of 100 to 100,000 mPa·s at 25° C., and contains low-molecular-weight cyclic siloxanes (D3 to D20) Organopolysiloxane whose amount is 500 ppm or less in component (A),
(B) polycondensation in the presence of a sodium hydroxide catalyst or a sodium organosilanolate catalyst,
A method for producing organopolysiloxane raw rubber, wherein the content of each of cyclic siloxanes D4, D5 and D6 is 1,000 ppm or less, and the total content of low-molecular-weight cyclic siloxanes (D3 to D20) is 5,000 ppm or less . 2. The method for producing organopolysiloxane raw rubber according to claim 1 , wherein the polymerization reaction time is 1 to 12 hours . 3. The method for producing an organopolysiloxane raw rubber according to claim 1, wherein the condensation polymerization temperature is 80 to 120.degree.