RU2576311C1 - Method of producing polyorganosiloxanes - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemical engineering of organosilicon compounds. Disclosed is a method of producing polyorganosiloxanes by polycondensation of alkoxy silanes, which is carried out in an aqueous medium, saturated with carbon dioxide under pressure from 150 to 350 ATM in a temperature range from 20 to 110°C. As initial alkoxysilane used is a compound selected from alkoxy silanes of general formula R¹ _aR² _bSi(OR³)_4-(a+b), where R¹=C₁-C₄ alkyl or C₆H₅; R²=C₁-C₄ alkyl; R³=C₁-C₄ alkyl; a=0 or 1 or 2; b=0 or 1.

EFFECT: proposed method is producible, enables to obtain a required polyorganosiloxane with quantitative output at low process time and in the absence of an organic solvent.

1 cl, 4 dwg, 1 tbl, 8 ex

Description

The invention relates to the chemical technology of high molecular weight organosilicon compounds, and in particular to a method for producing polyorganosiloxanes by hydrolytic polycondensation of alkoxysilanes.

The invention can be used in the chemical industry for the production of polyorganosiloxanes, which form the basis of polymer composite materials for the production of sealants, compounds, adhesives, various coatings, etc., used in mechanical engineering, electronics, and other technical fields.

The method according to the invention allows to obtain polyorganosiloxanes of various structures, in particular linear or cyclic polydimethylsiloxanes, without solvent and the addition of catalysts.

It is known that polyorganosiloxanes of various structures are obtained by hydrolytic polycondensation of functionally substituted silanes. Hydrolytic polycondensation is a set of processes of hydrolysis of the functional groups of the initial monomer with water, followed by homo-and heterofunctional polycondensation formed during the hydrolysis of intermediates.

Known methods for producing polyorganosiloxanes by hydrolysis of organochlorosilanes [Andrianov, K.A. Organoelemental chemistry methods. Silicon / K.A. Andrianov. - M .: Nauka, 1968 .-- 699 p .; Sokolov, N.N. Methods for the synthesis of polyorganosiloxanes / N.N. Sokolov. - M .: Goskhimizdat, 1959. - 197 p .; Hydrolytic polycondensation of organochlorosilanes (review) / V.M. Kopylov, L.M. Khananashvili, O.V. Schoolboy A.G. Ivanov // Naval Forces (A) - 1995. - T. 37, No. 3. - S. 394-416; Khananashvili, L.M. Chemistry and technology of organoelement monomers and polymers / L.M. Khananashvili. - M.: Chemistry, 1998. - 528 p.].

Processes using organochlorosilanes proceed quickly, but are characterized by the complexity of management and technological design, the presence of intermediate stages of filtration and neutralization of products, the formation of a large amount of hydrochloric acid waste, including washing water, which are difficult to dispose of.

Known methods for producing polyorganosiloxanes by hydrolytic polycondensation of alkoxysilanes [Hook, R.J. A 29 Si NMR study of the sol-gel polymerization rates of substituted ethoxysilanes / R.J. Hook // J. of Non-Cryst. Sol. - 1996. - V. 195. - P. 1-15; Schmidt, H. Principles of Hydrolysis and Condensation Reaction of Alkoxysilanes / H. Schmidt, H. Scholze, A. Kaiser. // J. Non-Cryst. Sol. - 1984. - V. 63. - P. 1-11; Chemical modification of TEOS with acetic acid / A. Campero, R. Arroyo, C. Sanchez, J. Livage. // Utrastructure processing of advanced ceramics. Edit J.D. Mackenzie, D.R. Ulrich. - John Wyley & Sons, 1988 .-- P. 327-332; Tsai, M.T. Hydrolysis and condensation of forsterite precursor alkoxides: modification of the molecular gel structure by acetic acid / M.T. Tsai // J. of Non-Cryst. Sol. - 2002. - V. 298. - P. 116-130; Polycondensation of alkoxysilanes in an active medium - a universal method for producing polyorganosiloxanes / E.V. Egorova, N.G. Vasilenko, N.V. Demchenko [et al.] // DAN. - 2009. - T. 424, No. 2. - S. 200-204].

Methods that use alkoxysilanes as monomers have several advantages: the environmental load is reduced due to the absence of a large amount of hydrochloric acid waste, there is no need to use expensive corrosion-resistant equipment.

However, the hydrolysis of alkoxysilyl groups occurs much more slowly than the hydrolysis of chlorosilyl groups; therefore, the use of catalysts is necessary to accelerate such processes.

Known methods for producing polyorganosiloxanes by hydrolysis of alkoxysilanes in the presence of acids and bases, however, these methods are characterized by incomplete conversion of monomer and alkoxysilyl groups, the need to use solvents, the absence of selective processes for the formation of products of a given structure in the case of hydrolysis of diorganodialcoxysilanes, the presence of additional stages of purification of products from catalysts ( neutralization, filtration, washing), which leads to a decrease in the yield and quality of the target Product [Rankin, S. 29 Si NMR study of base-catalyzed polymerization of dimethyldiethoxysilane / S. Rankin, A.V. McCormick // Magn. Reson. Chem. - 1999. - V. 37. - P. s27-s37; Sanchez, J. 29 Si NMR Kinetic Study of Tetraethoxysilane and Ethyl-Substituted Ethoxysilane Polymerization in Acidic Conditions / J. Sanchez, S.E. Rankin, A.V. McCormick // Ind. Eng. Chem. Res. - 1996. - V. 35. - P. 117-129; Zhang, Z. Hydrolysis and Polymerization of Dimethyldiethoxysilane, Methyltrimethoxysilane and Tetramethoxysilane in Presence of Aluminum Acetylacetonate. A Complex Catalyst for the Formation of Siloxanes / Z. Zhang, S. Sakka. // J. Sol-Gel Sci. Technol. - 1999. - V. 16. - P. 209-220; Performance enhancement of polybenzoxazine by hybridization with polysiloxane / H. Ardhyananta, M. Wahid, M. Sasaki, T. Agag // Polymer. - 2008. - V. 49. - P. 4585-4591].

A known method of producing linear organopolysiloxanes with terminal hydroxyl groups by hydrolysis of dialkoxysilane in the presence of hydrochloric acid for 1 hour, followed by the addition of metal oxides to neutralize the catalyst, drying the product over magnesium sulfate and removing alcohol from the product (JP Patent JP 2652307).

The disadvantages of the method are multi-stage, the presence of waste, incomplete conversion of the monomer, the lack of selectivity of the process.

The known two-stage method for producing polyorganosiloxanes with terminal hydroxysilyl groups (Japanese patent JP 3079939), where in the first stage hydrolytic polycondensation of organoalkoxysilanes is carried out in the presence of sulfocationite for 4 hours and products with terminal ethoxysilyl groups are obtained, in the second stage, hydrolysis of these products is carried out, adding an additional amount water.

The disadvantages of the method are the incomplete conversion of the monomer, the low molecular weight of the product, the presence of additional stages of purification and isolation of the product.

A known method of producing polyorganosiloxanes, which consists in carrying out the polycondensation of organoalkoxysilanes in formic acid using an ion exchange resin as a catalyst (European patent EP 0431409).

The disadvantages of this method are: low molecular weight of the product, the lack of complete conversion of alkoxy groups, the duration of the process for 3-4 days, the inability to control the structure and composition of the product.

Known methods for the hydrolysis of tetraalkoxysilanes under conditions of supercritical CO ₂ in the presence of inorganic and organic acid catalysts where supercritical CO ₂ acts as a solvent, which is an advantage of these methods, since after depressurization, gaseous CO ₂ escapes and additional solvent removal steps are not required in contrast to the methods described above (Moner-Girona, M .; Roig, A .; Molins, EJ Sol-Gel Route to Direct Formation of Silica Aerogel Microparticles Using Supercritical Solvents Sol-Gel Sci. Technol. 2003, 26, 645; A Rao, D. Bhagat Solid State Sciences 6 (2004) 945-952; U.S. Patent US 6,670,402). However, CO ₂ in these methods is not a reagent and does not participate in the polycondensation process, its key role is to dry the gel formed by the interaction of tetraalkoxysilane and catalyst, and to obtain the so-called airgel. Methods that employ supercritical CO ₂ have not been used to produce substituted polyorganosiloxanes.

A known method for producing polyorganosiloxanes by hydrolytic polycondensation of alkoxysilanes in an active medium, which is a carboxylic acid, which simultaneously acts as a reagent, catalyst and solvent, or a mixture of carboxylic acid and solvent (RU 2006113775; E.V. Egorova, N.G. Vasilenko, N.V. Demchenko [et al.] // DAN. - 2009. - T. 424, No. 2. - S. 200-204). The amount of carboxylic acid is from 3 to 20 mol per 1 mol of alkoxysilane, and the amount of solvent used in the reaction mixture is from 10 to 90 vol. % The duration of the process varies from 5 to 20 hours, depending on the number of alkoxy groups of the monomer. Isolation of the product in the specified method is carried out by distillation of volatile components. This method is closest to the proposed method in technical essence and can be considered as a prototype.

The disadvantages of this method are: the presence of by-products - alcohol, water, carboxylic acid ester, which complicates and slows the release of the target organopolysiloxane, the need to use large volumes of carboxylic acid, solvent and a longer process compared to the duration of hydrolytic polycondensation of organochlorosilanes, which proceeds in continuous mode.

The objective of the invention is the creation of an effective technological method for producing polyorganosiloxanes from alkoxysilanes, which would ensure complete conversion of the monomer with a short process time and in the absence of an organic solvent.

The problem is solved by the claimed method of producing polyorganosiloxanes by polycondensation of alkoxysilane, and the polycondensation is carried out in an aqueous medium saturated with carbon dioxide, under a pressure of from 150 to 350 atm in a temperature range from 20 to 110 ° C. As the starting alkoxysilane, an alkoxysilane selected from compounds of the general formula R ¹ _a R ² _b Si (OR ³ ) _{4- (a + b) is used} , where

R ¹ is C ₁ -C ₄ alkyl or C ₆ H ₅ ;

R ² is C ₁ -C ₄ alkyl;

R ³ is C ₁ -C ₄ alkyl;

and is 0, or 1, or 2;

b is 0 or 1.

The time of polycondensation depends on the structure of the initial alkoxysilane and ranges from 10 minutes to 3 hours (table 1).

In contrast to the prototype method, where the hydrolytic polycondensation of alkoxysilanes is carried out in excess of carboxylic acid (RU 2006113775), in the claimed method, the polycondensation of alkoxysilanes is carried out in an aqueous medium saturated with carbon dioxide, under a pressure of from 150 to 350 atm and a temperature of from 20 to 110 ° C . A solution of carbon dioxide in water at such temperature and pressure values is characterized by a pH value in the range from 2.8 to 3.9, that is, it is carbonic acid, which acts as a catalyst for the hydrolytic polycondensation of the monomer.

In general, the hydrolytic polycondensation of alkoxysilanes in carbonic acid can be represented by the following summary scheme:

where: R ¹ is C ₁ -C ₄ alkyl or C ₆ H ₅ ; R ² is C ₁ -C ₄ alkyl; R ³ is C ₁ -C ₄ alkyl; and is 0, or 1, or 2; b is 0 or 1; n denotes the number of elementary chain links.

The duration of hydrolytic polycondensation of alkoxysilane in such conditions is not more than three hours, whereas in the prototype - from 5 to 20 hours. The final polycondensation product consists of polyorganosiloxane, alcohol, water and carbon dioxide, which simplifies the isolation of the target product. Carbon dioxide spontaneously is removed from the reactor when the pressure is released, the remaining components are a heterophasic system consisting of the target organopolysiloxane and a water-alcohol layer. After separation of the water-alcohol layer, the siloxane layer is analyzed by GLC, GPC, IR and NMR spectroscopy. Thus, the selection of the target product does not require operations associated with the removal of solvent and a large excess of acid (as in the prototype). The desired polyorganosiloxane is obtained in quantitative yield. Using difunctional alkoxysilanes as an example, the possibility of controlling the structure of the product is shown. Thus, an increase in the polycondensation temperature of dimethyldiethoxysilane from 60 ° C (example 1, table 1) to 110 ° C (example 5, table 1) leads to an increase in the yield of linear organopolysiloxanes from 57 to 88%.

The technical result achieved in the claimed invention is to significantly reduce the duration of the process with complete conversion of the monomer; polycondensation without the use of an organic solvent; in less time-consuming selection of the target product and the ability to control the structure of the resulting product.

Product analysis after depressurization and separation of the water-alcohol layer was performed by GLC, GPC, IR and ¹ H NMR spectroscopy.

In FIG. 1 shows ¹ H NMR spectrum of the reaction mixture obtained in Example 1 after depressurization. To determine the number of terminal hydroxyl groups, the resulting product was blocked with dimethylvinylchlorosilane under conditions ensuring their complete conversion.

In FIG. Figure 2 shows the ¹ H NMR spectrum of the blocked polydimethylsiloxane from Example 4. The content of vinyl dimethylsilyl groups and, accordingly, hydroxyl groups is determined by the ratio of the integrated signal intensities of the protons of the methyl groups of silicon atoms in the region δ = 0.06 ppm. and protons of vinyl groups in the region δ = 5.9 ppm

The molecular weight distribution of the obtained samples was determined by GPC analysis of the samples, and the composition of volatile polyorganosiloxanes was determined by GLC. As an example in FIG. 3 shows the GLC curve for example 3, which is typical for examples 1-6. In FIG. 4 shows the GPC curves of the products obtained in examples 4 and 5.

The conditions of preparation and the results of the study of the obtained polyorganosiloxanes are presented in Table 1.

The invention is illustrated by the following examples of its implementation.

Example 1. Polycondensation of (CH ₃ ) ₂ Si (OC ₂ H ₅ ) ₂ in a carbonic acid medium.

10 ml of dimethyldiethoxysilane and 5 ml of Milli-Q water are placed in a 20 ml autoclave. Then, CO _{2 is} supplied to the autoclave at a pressure of 150 atm. Using an electronic thermostat, the temperature inside the autoclave is set to 60 ° C. The process is carried out for 3 hours. Then the pressure is released, the water-alcohol layer is separated. The siloxane layer is analyzed by GLC, GPC, IR and NMR spectroscopy. The yield of polydimethylsiloxane is quantitative. GLC: [(CH _{3) 2} SiO] _33%, [(CH _{3) 2} SiO] ₄ - 33%, [(CH _{3) 2} SiO] ₅ - 7%, HO - [(CH _{3) 2} SiO ] _n -H is 57%. GPC: M _p = 500. According to ¹ H NMR, the product contains 1.2 mass. % residual EtO-groups (according to the ratio of signals of CH ₃ C H ₂ OSi- and CH ₃ Si-groups). IR (CCl ₄ ), v / cm ^-1 : 3300 (SiOH). The number of hydroxyl groups, determined after blocking with dimethylvinylchlorosilane, is 9.2 mass. %

Examples 2-8. The polycondensation of alkoxylans in examples 2-8 is carried out according to the method similar to that described in Example 1. The conditions for the preparation and results of the study of the obtained organopolysiloxanes are presented in Table 1.

Thus, the proposed method has the following advantages:

- it allows you to get polyorganosiloxanes of various structures, in particular linear or cyclic polydimethylsiloxanes and to regulate the structure of the resulting product;

- this significantly reduces the time of polycondensation;

- there is no need to add an organic solvent and catalyst;

- less time-consuming selection of the target product;

- the method is more technological than the prototype.

Claims (1)

A method of producing polyorganosiloxanes by polycondensation of an alkoxysilane selected from alkoxysilanes of the general formula R ¹ _a R ² _b Si (OR ³ ) _{4- (a + b)} , where
R ¹ is C ₁ -C ₄ alkyl or C ₆ H ₅ ;
R ² is C ₁ -C ₄ alkyl;
R ³ is C ₁ -C ₄ alkyl;
and is 0, or 1, or 2;
b is 0 or 1,
characterized in that the polycondensation is carried out in an aqueous medium saturated with carbon dioxide, under a pressure of from 150 to 350 atmospheres in a temperature range of from 20 to 110 ° C.

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