CS240826B1 - Process for preparing organosilicon polymers for defoaming liquids - Google Patents

Abstract

A method for preparing organosilicon polymers for defoaming liquids by cohydrolysis of dimethyldichlorosilane and methyltrichlorosilane, subsequent polymerization with the addition of an aqueous solution of a quaternary ammonium base and removal of volatile components at a temperature of 200 to 290 °C by subjecting dimethyldichlorosilane and methyltrichlorosilane with a CH ratio of 1.80 to Si 1.98 to cohydrolysis. The polymers obtained have good defoaming properties due to good thermal stability and low surface tension.

Description

The obtained polymers have good defoaming properties due to good thermal stability and low surface tension.

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The invention relates to a method for preparing organosilicon polymers for foaming synthetic oils and hydraulic fluids.

For defoaming of the above liquids, liquid organosilicon high molecular weight polymers or fluorinated polymers are most often used. These are polymers prepared by polymerization of dialkyl-polycyclosiloxanes, where the alkyl groups are methyl, or part of the methyl groups is replaced by a vinyl group or trifluoropropylene.

These polymers have good thermal stability and low surface tension. These properties give them the prerequisite for defoaming ability.

Foaming of liquids has not yet been theoretically mastered. Mixing liquids results in synergistic or antagonistic effects on foaming that cannot be predicted. In general, it can be stated that liquids with high surface tension can be more easily defoamed, or their foaming reduced, with silicone or fluorocarbon polymers.

The surface tension of methylpolysiloxanes is 20 methyltrifluoropropylpolysiloxanes 18.8 wV.fcH bis-2-ethylsebacate 32.8 ιηΐν,μ<1 mineral oil 42.00

When measuring the foaming capacity of individual liquids and their mixtures, the following values were found, which are listed in Table I (foaming capacity measured according to ČSN 656 238).

- 2 Table I

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Liquid at 25°C at 95 °C | foam ml ftÓŤ&fs foam ml m ...... collapse and/ methylphenylpolysiloxane oil 167 4 '30 35 1 '20 b/ bis-2-ethylhexyl sebacate 8 0 '13 15 0 '30 c/ phenyltris-2-ethylhex- oxysilane 0 - - d/ • a + b in the ratio 1:1 185 9 '30 60 2'15 e/ a + b + c in the ratio 5:4:1 220 10 '30'' 53 2 *13

For defoaming of the liquid ad e/, a commercial polymer dimethylpolysiloxane Z - diol with a viscosity at 50 °C of 65 Pa.s in an amount of 0.02% by weight relative to the liquid was used, which was dispersed in the liquid on a colloid mill. The liquid thus treated did not foam at all at 25 °C, but at 95 °C its foaming was 3 times greater than that of the untreated liquid. The ineffectiveness of the mentioned polymer can probably be explained by its increased solubility at elevated temperatures.

Another requirement for the defoaming polymer is that it should not be soluble over the entire operating temperature range.

For these reasons, the preparation of so-called branched polymers with a higher molecular weight and lower solubility was addressed by the method according to the invention.

The method of preparing organosilicon polymers for defoaming liquids by cohydrolysis of dimethyldichlorosilane and methyltrichlorosilane, followed by polymerization with the addition of an aqueous solution of a quaternary _ammonium base, volatile components at a temperature of 200 to 290 °C consists in cohydrolysis of diethyldichlorosilane and methyltrichlorosilane with a CH-2 ratio of 1.80 to 1.98.

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A sticky, stiff, elastic polymer was obtained, which after grinding was stripped of volatile components in a dryer and partially crosslinked by oxidation.

Liquid ad e/ was treated with these polymers in a colloid mill and after treatment tested for foamability as shown in Table II.

Table II

Polymer heating time in the dryer at 25°C foaming _ft at 95 C ml collapse 1 hour at 250 °C does not foam 95 3'30 3 hours at 275 C does not foam 45 1 *10 3 hours at 290 °C lightly foams 25 0 '30

The results show that the crosslinked polymer reduces foaming at 95 °C, which can be explained by lower solubility.

The examples below illustrate the implementation of the method according to the invention.

- 4 ^{Example 1}

A mixture consisting of 180g of dimethyldichlorosilane (1.39 mol),

30 g of methyltrichlorosilane (0.2 mol) with a CH2 ratio of 1.87 was added to 1 l of water with stirring and cooling for 15 min. at a temperature of 39 °C max. After separation of hydrochloric acid, the cohydrolyzate was neutralized with a soda solution. 2 ml of a 20% aqueous solution of tetramethylammonium hydroxide were added to the cohydrolyzate, the mixture was heated to 80 °C with stirring. When the temperature was increased to 90 °C, rapid polymerization occurred. A friable, non-sticky, elastic polymer was obtained. The polymer was ground in a mortar and freed from volatile components in a drying oven at 250 °C for 1 h. 64 g of a loose, homogeneous elastic polymer was obtained.

The liquid ad e/ was treated with this polymer. The foaming result is shown in Table III.

Table III

foaminess ml foam collapse at 25°C 8 0 '17 95°C 23 0 '25

A longer time or higher temperature in the dryer did not bring any improvement in the removal of volatile components from polymers.

Example 2

Similar to Example 1, a polymer with a higher methyltrichlorosilane content with a ratio of 1.80 was prepared. Practically the same results were achieved with this polymer.

Claims (1)

SUBJECT OF THE INVENTION Process for preparing organosilicon polymers for antifoaming of liquids by cosdrolysis of dimethyldichlorosilane and methyltrichlorosilane by addition of aqueous quaternary ammonium base solution and removal of volatiles at 200 to 290 ° C. , 98 ·