JP2010270027A - Method for producing hydroxy group-containing diorganosiloxane having low polymerization degree - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a straight-chain diorganosiloxane containing hydroxy groups at both terminals of the molecular chain and having a low polymerization degree, which has a small residual amount of an unreacted alkoxy group. <P>SOLUTION: The method for producing the straight-chain diorganosiloxane containing hydroxy groups at both terminals and having a low polymerization degree includes (a) a step of mixing a dialkoxysilane represented by formula (1): Si(R<SP>1</SP>)(R<SP>2</SP>)(OR<SP>3</SP>)<SB>2</SB>[wherein R<SP>1</SP>and R<SP>2</SP>are each independently substituted or unsubstituted alkyl, alkenyl, aryl or aralkyl; R<SP>3</SP>is methyl or ethyl] with an aqueous solution of an acid that contains water in an amount of ≥1.0 mol based on the alkoxy group of the dialkoxysilane and has a pH of 1.0-6.0 and carrying out hydrolysis and condensation while removing the alcohol produced and (b) a step of adding a metal oxide to the reaction mixture obtained by the step (a). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention provides a simple production of a low-degree-of-polymerization organosiloxane having a hydroxyl group, in particular, a linear low-degree-of-polymerization diorganopolysiloxane containing hydroxyl groups (silanol groups) bonded to silicon atoms at both ends of the molecular chain. Regarding the method.

  Linear organosiloxanes having hydroxyl groups bonded to silicon atoms at both ends of the molecular chain (that is, silanol groups) are effective as dispersants (wetters) in the production of silicone rubber compounds, and various such organosiloxane dispersants Is used. The effectiveness as a dispersant is proportional to the hydroxyl group content per mass, and siloxanes with a large hydroxyl group content, i.e., linear organosiloxanes having silanol groups at both terminal groups, have a dispersion effect as the degree of polymerization decreases. It is large and uses less. It is also effective in that the processability of the silicone rubber compound is not impaired.

  Various methods have been studied for synthesizing a low-polymerization linear organosiloxane having hydroxyl groups at both ends, that is, a low polymerization degree. As a laboratory production method, a solution using a buffer solution or the like is used. A method of hydrolyzing alkoxysilane or the like while maintaining a neutral state is known, but this method is industrially difficult.

  Also known is a method in which dimethoxysilane is mixed with excess neutral distilled water and refluxed, but the yield is low. Currently, the above-mentioned linear organosiloxane is industrially produced by hydrolyzing a linear organochlorosiloxane or chlorosilane having chlorine atoms at both ends with a weak alkaline aqueous solution so as not to form a ring. ing. A method of acetoxylating organochloropolysiloxane with acetic acid and hydrolyzing it is also known. However, in this method, it is difficult to carry out the hydrolysis completely, and there is a problem that an acetoxy group remains in the product. Such organopolysiloxanes are not preferred as dispersants for the production of silicone rubber compounds.

  In Patent Document 1, D3 (hexamethylcyclotrisiloxane), methanol, formic acid, and water are reacted to synthesize a low-polymerization linear polyorganosiloxane having a silanol end group in which some methoxy groups remain. Although a method is described, it is expensive to use a relatively expensive D3. Furthermore, diorganosiloxanes having silanol end groups with fewer than 3 D units (ie dimethylsiloxy units) cannot be produced. Therefore, there is a limit to the hydroxyl content of the product.

  Patent Document 2 discloses production of linear dihydroxyorganotetrasiloxane containing hydroxyl groups at both ends, including hydrolysis of dihalotetrasiloxane in the presence of an epoxy compound such as propylene oxide and butylene oxide. A method is described. In addition to the cost problem of using relatively expensive D3 as a raw material for dihalotetrasiloxane and the restriction that the product is limited to tetrasiloxane, this method also has a low boiling point. There were safety problems such as electrostatic ignition.

  Furthermore, as a document disclosing a method for producing an organopolysiloxane having a hydroxyl group at the terminal, there is Patent Document 3, in which an alkoxysilane is hydrolyzed and condensed using an acidic solution, and then a metal oxide is added to adjust the pH. A method is described for removing water and by-product alcohol after adjusting. However, in this method, a linear organopolysiloxane having a hydroxyl group at the end of the molecular chain is obtained, but there is a problem that a large amount of polysiloxane having an alkoxy group not hydrolyzed at the end remains.

US Pat. No. 3,925,285 US Pat. No. 5,057,620 Japanese Patent No. 2652307

  An object of the present invention is to produce an organosiloxane having a hydroxyl group by hydrolyzing alkoxysilane, without using a relatively expensive starting material such as D3, and the amount of unreacted alkoxy group remaining. Another object of the present invention is to provide a method for producing a linear diorganosiloxane having a low degree of polymerization and having hydroxyl groups at both ends of the molecular chain, which is significantly less than the conventional method.

  As a result of intensive studies in order to achieve the above object, the present inventors have conducted hydrolysis reactions while removing the alcohol produced under normal pressure or reduced pressure, preferably under reduced pressure, in the alkoxysilane hydrolysis step. As a result, it was found that diorganosiloxane having a low degree of polymerization and having hydroxyl groups at both ends of the molecular chain with few remaining alkoxy groups was obtained, and the present invention was achieved.

That is, according to the present invention,
(A) General formula (1):
Si (R ¹ ) (R ² ) (OR ³ ) ₂ (1)
[Wherein, R ¹ and R ² are each independently a substituted or unsubstituted alkyl group, alkenyl group, aryl group or aralkyl group, and R ³ is a methyl group or an ethyl group]
A dialkoxysilane represented by the formula is mixed with an acid aqueous solution having a pH of 1.0 to 6.0 containing water (H ₂ O) in an amount of 1.0 times mol or more with respect to the alkoxy group of the dialkoxysilane. A step of performing hydrolysis and condensation while removing alcohol under normal pressure or reduced pressure;
(B) providing a method for producing a linear diorganosiloxane having a low degree of polymerization having hydroxyl groups at both ends, comprising the step of adding a metal oxide to the reaction mixture obtained in step (a) Is done.

  According to the present invention, a relatively low-cost dialkoxysilane such as dimethoxydimethylsilane has a hydroxyl group at both ends of the molecular chain and the remaining alkoxy group is extremely less than conventional methods without using expensive raw materials. A small and low degree of polymerization, that is, a dimer to 10-mer linear diorganosiloxane can be easily produced.

<Dialkoxysilane>
In the present invention, the dialkoxysilane used as a starting material is a diorganodialkoxysilane represented by the general formula (1). This dialkoxysilane is relatively inexpensive and it is very economically advantageous to use it as a starting material industrially.

In the general formula (1), R ¹ and R ² are usually substituted or unsubstituted ones having 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms. Valent hydrocarbon group, specifically, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, 2-ethylhexyl group Alkyl groups such as octyl group, decyl group and dodecyl group; alkenyl groups such as vinyl group, allyl group, propenyl group and isopropenyl group; aryl groups such as phenyl group and tolyl group; aralkyl groups such as β-phenylethyl group A group in which at least a part of the hydrogen atoms bonded to the carbon atoms of these hydrocarbon groups are substituted with a halogen atom such as fluorine or a cyano group, such as 3,3,3-trifluoropro A pill group, a cyanoethyl group, etc. can be mentioned. Of these, a methyl group, a vinyl group, and a phenyl group are preferable. R ³ is independently a methyl group or an ethyl group, and the two R ³ groups may be the same or different.

  In the present invention, the diorganodialkoxysilane particularly preferably used as a starting material is not limited to this, but examples thereof include dimethyldimethoxysilane, phenylmethyldimethoxysilane, methylvinyldimethoxysilane, and dimethyldiethoxysilane. And phenylmethyldiethoxysilane, methylvinyldiethoxysilane, dimethylmethoxyethoxysilane, phenylmethylmethoxyethoxysilane, methylvinylmethoxyethoxysilane, and the like. The above dialkoxysilanes can be used alone or in combination of two or more. However, when plural kinds of dialkoxysilanes are mixed and used, care must be taken because different dialkoxysilanes have different hydrolysis rates and may not react uniformly.

<Acid aqueous solution>
In the method of the present invention, the alkoxy group is converted into a silanol group (that is, a hydroxyl group bonded to a silicon atom) by hydrolysis of dialkoxysilane, but most of the generated silanol group is condensed almost simultaneously with the generation. Therefore, it can be said that these hydrolysis and condensation reactions proceed almost simultaneously. This hydrolysis and condensation reaction is carried out using an acid aqueous solution having a pH of 1.0 to 6.0, preferably 3.0 to 5.0. If the pH is too low, hydrolysis occurs rapidly, making it difficult to obtain a product having a low polymerization degree, and cyclization occurs preferentially, which is inappropriate. On the other hand, if the pH is too high, the catalytic action necessary for hydrolysis cannot be obtained, and hydrolysis does not proceed. Examples of the acidic compound used to adjust the pH include inorganic acids such as hydrogen chloride, sulfuric acid, and nitric acid, and organic acids such as formic acid and acetic acid. Among them, hydrogen chloride is an aqueous solution (hydrochloric acid water, That is, it is most preferably used as hydrochloric acid. The amount of the aqueous acid solution used is such that the amount of water (H ₂ O) in the aqueous solution is 1.0 times mol or more (usually 1.0 to 2.0 times mol), preferably 1.0 to mol of the alkoxy group in the alkoxysilane. 1.5 mol. When this amount is less than the above range, the alkoxy group is not completely hydrolyzed and only a few hydroxyl groups are formed. If the amount is too large, a special step is required to remove excess water.

<Reaction>
By mixing the alkoxysilane and the acid aqueous solution, hydrolysis and condensation reactions proceed to produce alcohol and water. By performing hydrolysis and condensation while removing this alcohol under reduced pressure or normal pressure, preferably under reduced pressure, a diorganosiloxane having hydroxyl groups at both ends with a low content of unreacted alkoxy groups can be obtained. it can. Therefore, the alcohol produced by the hydrolysis reaction is removed before the acid aqueous solution is neutralized with the metal oxide. The above reaction while removing the alcohol is usually carried out by heating to 60 to 100 ° C., preferably 60 to 70 ° C., depending on the type of alcohol produced by hydrolysis under reduced pressure or normal pressure. The reaction is preferably carried out while stirring the reaction system in order to allow the reaction to proceed uniformly. The reaction time is usually 60 to 600 minutes, preferably 120 to 360 minutes.

<Metal oxide>
The metal oxide used in the step (b) of the present invention acts as a reaction terminator. By adding this metal oxide, the acidic compound in the acid aqueous solution used in the step (a) is medium. The hydrolysis and condensation reaction of the alkoxysilane or its partial hydrolyzate is stopped. If such a metal oxide is not added, the hydroxyl group of the produced organosiloxane is unstable to acid and alkali, and further condensation occurs, so that the desired diorganosiloxane having a low polymerization degree cannot be obtained.

  As this metal oxide, for example, magnesium oxide, manganese oxide, calcium oxide and the like can be used singly or in combination of two or more, but preferably magnesium oxide is used. The amount of the metal oxide is 1.0 times mol or more of the amount of the acidic compound in the acid aqueous solution used in the hydrolysis in the step (a), and may be used in excess, but usually 1.0 to 100 times mol, It is preferably used in an amount of 1 to 10 moles.

After the addition of the metal oxide, the excess metal oxide and the produced neutralized salt can be removed by filtration or the like to obtain the target diorganosiloxane.
The removal of water may be performed either before or after the filtration step. Usually, after adding a neutralizing agent such as the metal oxide, a dehydrating agent such as bow glass is added for dehydration. Later, it is desirable to filter at the same time.

[Example 1]
A 200 ml flask equipped with a thermometer and a stirrer and purged with nitrogen was charged with 100 g (0.832 mol) of dimethyldimethoxysilane, and 32.9 g of hydrochloric acid (ie, aqueous HCl) adjusted to pH 4.5 (1.828 as water (H ₂ O)). mol) was added to form a two-phase system, and the two-phase mixture was vigorously stirred and mixed at room temperature. After 10 minutes from the start of stirring, the mixture became homogeneous. This mixture was heated to 60-70 ° C. under normal pressure, and reacted for 340 minutes while removing formed methanol. After cooling the reaction solution to room temperature, 1.0 g (0.0248 mol) of magnesium oxide was added and stirred for 30 minutes to neutralize hydrochloric acid as a catalyst. Subsequently, excess magnesium oxide, produced neutralized salts and the like were removed by filtration. In this way, 55.6 g of a colorless and transparent oily substance was obtained. The results of GC (gas chromatography) measurement of this oily substance are shown in Table 1.

[Example 2]
The same operation as in Example 1 was performed except that the amount of hydrochloric acid added to dimethyldimethoxysilane and adjusted to pH 4.5 was changed to 44.9 g (2.494 mol as H ₂ O). 51.4 g of a colorless transparent oily substance was obtained. Table 1 shows the GC measurement results of the oily substance.

[Example 3]
The amount of hydrochloric acid adjusted to pH 4.5 added to dimethyldimethoxysilane was 44.9 g (2.494 mol as H ₂ O), and the reaction of the mixture of dimethyldimethoxysilane and hydrochloric acid was heated to 60 to 70 ° C. under reduced pressure. A colorless and transparent oily substance (54.5 g) was obtained in the same manner as in Example 1 except that methanol was removed under the condition of 240 minutes. Table 1 shows the GC measurement results of the oily substance.

[Comparative Example 1]
To a 200 ml flask equipped with a thermometer and stirrer and purged with nitrogen, 100 g (0.832 mol) of dimethyldimethoxysilane and 32.9 g of hydrochloric acid adjusted to pH 4.5 (1.828 mol as H ₂ O) were added. And the biphasic mixture was vigorously stirred and mixed at room temperature. After 10 minutes from the start of stirring, the mixture became homogeneous. The mixture was heated to 60-70 ° C. under normal pressure and reacted for 340 minutes. After cooling the reaction solution to room temperature, 1.0 g (0.0248 mol) of magnesium oxide was added and stirred for 30 minutes, and then the reaction solution was filtered. Subsequently, methanol was removed from the reaction solution under reduced pressure to obtain 54.8 g of a colorless transparent oily substance. Table 1 shows the GC measurement results of the oily substance. The numerical values in Table 1 indicate mass%.

  From the results shown in Table 1, when methanol was removed while performing hydrolysis as in Examples 1 to 3, the remaining alkoxy was compared to the case where methanol was removed after addition of the metal oxide as in Comparative Example 1. It can be seen that diorganosiloxane having a low degree of polymerization and having a hydroxyl group at both ends with few groups can be obtained.

  The linear organosiloxane having hydroxyl groups at both ends of the present invention is useful as a dispersant for producing a silicone rubber compound.

Claims (5)

(A) General formula (1):
Si (R ¹ ) (R ² ) (OR ³ ) ₂ (1)
[Wherein, R ¹ and R ² are each independently a substituted or unsubstituted alkyl group, alkenyl group, aryl group or aralkyl group, and R ³ is a methyl group or an ethyl group]
Is mixed with an acid aqueous solution having a pH of 1.0 to 6.0 containing water in an amount of 1.0-fold mol or more with respect to the alkoxy group of the dialkoxysilane, and the generated alcohol is removed. Performing hydrolysis and condensation;
(B) A process for adding a metal oxide to the reaction mixture obtained in the step (a), and a method for producing a low-polymerization linear diorganosiloxane having hydroxyl groups at both ends.   The method according to claim 1, wherein the dialkoxysilane is dimethyldimethoxysilane.   The manufacturing method according to claim 1 or 2, wherein the metal oxide is magnesium oxide, manganese oxide, calcium oxide, or a combination of two or more thereof.   The production method according to any one of claims 1 to 3, wherein in the step (a), the generated alcohol is removed under reduced pressure or normal pressure.   The production according to any one of claims 1 to 4, wherein the metal oxide added in the step (b) is 1.0 mol or more of the amount of the acidic compound in the acid aqueous solution used in the step (a). Method.