CS268216B1 - Process for producing modified branched ethoxypolysiloxanes - Google Patents

Abstract

2 method of producing modified branched ethoxypolysiloxanes consisting in treating branched ethoxypolysiloxanes containing 13.5 to 22 wt.% Si in the presence of acidic or basic catalysts with bexamethyldisiloxane or tetramethyldivinyldialoxane, optionally with the addition of octamethylcyclotetrasiloxane.

Description

The invention relates to a process for the preparation of modified branched ethoxypolysiloxanes.

Ethoxypolysiloxanes, sometimes referred to as silicic acid esters (generally referred to in the German literature as organooxysiloxanes, in technical practice as alkylsilicates) are an important group of organosilicon compounds which are widely used in the art (for more information see W. Noll: Chemie und Technologie der Silicone, Verlag Chemie, Weinheim, 1968). Their production is relatively simple and they are used mainly as hydraulic fluids, heat transfer fluids, hydrophobicizing agents, etc.

Since, in addition to stable Si (-OS groups, contain hydrolytically unstable Si-OC groups, it is desirable for some applications to replace these alkoxy-Si bonds with siloxane bonds. Such substances can be prepared by cohydrolysis of tetrachlorosilane, difunctional and monofunctional silanes However, cohydrolysis is very difficult because of the heterogeneous mixture of insoluble crosslinked resin and liquid polysiloxane, which is eliminated by the process for the preparation of modified branched ethoxypolysiloxanes, which comprises branching ethoxypolysiloxanes containing 13.5 to 22% by weight. It is treated in the presence of acidic or basic catalysts with tetramethyldivinyldisiloxane or hexamethyldisiloxane, optionally with the addition of octaraethylcyclotetrasiloxane.

This process has a number of advantages: on the one hand, hydrogen chloride is not released in this preparation of modified branched ethoxypolysiloxanes, production is not complicated by the formation of sparingly soluble resins and, last but not least, alkylsilicates are one of the cheapest and most accessible products in organosilicon chemistry.

The so-called ethylalicates, which are commonly sold as hydrophobicizing agents, are particularly suitable as starting materials. Their representatives are mainly ethyl silicate 29 and ethyl silicate 40. The essential component of the first substance is tetraethoxyslanate, after the hydrolysis of which approximately 29% of SiO 2 is formed. Ethyl silicate 40 is then a partially hydrolyzed form of the foregoing having a SiO 2 content of about 40%, it is a mixture of oligomers β with an average composition corresponding to a pentamer. In addition, the ethanol formed during the modification can be easily distilled off from the reaction mixture (preferably azeotropically in combination with an aromatic solvent). Although in principle the reaction can be carried out without a solvent, the presence of a solvent, preferably an aromatic one, facilitates the reaction.

Both acidic and basic catalysts can be used in the process described, and sulfonated styrene-divinylbenzene copolymers are preferred as acid catalysts. These can be removed from the reaction mixture by filtration after the reaction. Conversely, basic catalysts based on tetramethylammonis salts can be decomposed after the reaction by heating the reaction mixture to a temperature above 130 ° C. Stable water-soluble catalysts can be removed by washing the reaction mixture with water.

Although a wide variety of diplsloxanes can generally be used in the modification of ethoxypolysiloxanes, those which are technically available as hexanethyldisiloxane, hexaethyldislloxane or phenyl-containing disiloxanes are particularly preferred. Tetramethyldivinyldisiloxane is very preferred for the preparation of modified ethoxypolysiloxanes containing an unsaturated group.

The presence of water is not necessarily necessary, but its small proportions usually favor the course of the reaction as they aid in the hydrolysis of ethoxy groups. At the end of the reaction, water is usually distilled off together with the alcohol formed.

The addition of reagents containing difunctional siloxane units (for example, more broadly cyclosiloxanes or polysiloxanes) allows the properties of the resulting modified ethoxypolysiloxanes to be modified.

The reaction is expedient to be carried out at temperatures which allow the siloxane bonds to be cleaved in the presence of catalysts - usually at temperatures of 70 to 120 ° C.

CS 260216 B1 usual reaction time several hours. After the modification, it is advantageous to partially or completely distill off the lower boiling products, preferably using a lower pressure. The resulting modified ethoxypolysiloxanes show higher hydrolytic stability and, depending on the disiloxane used, may also contain groups allowing further chemical reactions.

The above examples denote the production method according to the invention without limiting or limiting it.

Example 1

104 parts of branched ethoxypolysiloxane Ethyl silicate 29, the essential component of which is tetraethoxysilane (content 29% SiO ₂ and 13.5% Si in partially hydrolyzed form, 47 parts tetramethyldivinyldisiloxane, 150 parts octamethylcyclotetrasiloxane and 5 parts tetramethylammonium siloxanol were stirred after stirring). Then 300 parts of toluene and 20 parts of water were added and the mixture was kept boiling for 2 hours, then toluene, ethanol and low-boiling parts were distilled off to obtain 67 parts of a modified branched alkoxypolysiloxane. the signal (<T <-88 to -113) belonging to the Si (-OSi) ^ groups was found and in the ¹ H NMR spectrum the signals belonging to the methyl and vinyl groups (J * »0.15 and (Γ« 5.6 to 6, 2) and in the infrared spectrum a wide typical band at 1060 cm ^-1 corresponding to the valence vibration> J (SiO) was found.

Example 2

100 parts of branched alkoxypolysiloxane Ethyl silicate 40, the essential component of which is pentamer Si (OH) ₄ (SiO ₂ content 40% and 18.7% Si, respectively), 50 parts hexane tyl disiloxane, 10 parts sulfonated styrene-divinylbenzene copolymer and 3 parts water were kept at reflux for 2 hours with stirring, then the ion exchanger was filtered off and the low-boiling fractions were distilled off to a bath temperature of 150 ° C and a vacuum of 10 kPa. 70 parts of a modified branched alkoxypolysiloxane were obtained, in the presence of which a broad multiplet belonging to the Si - (- O-S1) 2 groups (J "» -88 to -112) was found and in the IR spectrum a band at 1,060 cm -1. ¹ corresponding to the valence vibrationN (Si-0).

Example 3

100 parts of alkoxypolysiloxane Ethyl silicate 40 described in Example 2, 43 parts of tetramethyldivinyldisiloxane and 10 parts of sulfonated styrenedivinylbenzene copolymer and 5 parts of water were kept under stirring for 1 hour with stirring. Then 200 parts of toluene were added and the mixture was kept boiling for another 2 hours. after which the ion exchanger was filtered off and, as in Example 2, toluene and the lower-boiling components were distilled off. 70 parts of a modified branched alkoxypolysiloxane with an iodine value of 45 showing a considerable amount of vinyl groups were obtained. The signals described in Example 1 were found in the NMR spectra of the product, as well as in the infrared spectrum the band described in Example 1.

Claims (1)

OBJECT OF THE INVENTION Process for the preparation of modified branched ethoxypolysiloxanes, characterized in that branched ethoxypolysiloxanes containing 13.5 to 22 wt. It is treated in the presence of acidic or basic catalysts with tetramethyldivinyldisiloxane or hexamethyldisiloxane, optionally with the addition of octamethylcyclotetrasiloxane.