US2753365A - Silicone fluids of improved lubricity - Google Patents

Description

United States Patent SILICONE FLUIDS 0F IMPROVED LUBRICITY Simon W. Kantor and Robert C. Osthofi, Schenectady,

N. Y., assignors to General Electric Company, a corporation of New York Application December 28, 1954, Serial No. 478,180

4 Claims. (Cl. 260-4482) No Drawing.

radicals, and (2) sodium in the presence of an inert.

solvent. This invention is also concerned with the products prepared by the above process. e In the past, many attempts have been made to discover materials which have good lubricating properties but which do not have the deficiencies of the typical hydrocarbon lubricants and organo metallic salts commonly used as lubricants. The disadvantage of these hydrocarbon lubricants and organometallic salts is that they provide satisfactory lubricity only within a very narrow temperature range. Thus, when these typical lubricants are employed at temperatures of the order of 100 C. and higher, decomposition of the hydrocarbon material occurs at a rapid rate, destroying the lubricating etfect of these materials. Also, when an attempt is made to use these hydrocarbon lubricants and organometallic compounds at low temperatures (e.g., temperatures much below 0 C.) the lubricants become extremely viscous and again lose their lubricating effect. The term lubricity as used in the present application refers to the property of a material which diminishes the friction between two moving members. 7

One group of lubricants which has been developed to replace the hydrocarbon lubricants are the organopolysiloxane, particularly methylpolysiloxane, lubricants which are operable from temperatures as low as 60 C. to temperatures as high as 150-250 C. Over this entire operating range these silicones remain fluid without extreme changes in viscosity and are not decomposed by' the high temperatures encountered in this range. However, the known organopolysiloxane fluids are not as efiicient as hydrocarbon lubricants or organometallic compounds in that the lubricity of these silicone fluids is not as high as the lubricity of the earlier lubricating compounds.

The conventional organopolysiloxane fluids, described above, are generally prepared by equilibrating a cyclic organopolysiloxane, such as octamethylcyclotetrasiloxane, with a short chain linear organopolysiloxane, such as hexamethyldisiloxane, in the presence of a strong acid such as sulfuric acid. The method of preparing these conventional organopolysiloxane fluids is described in detail in Patnode Patents 2,469,888 and 2,469,890. Unexpectedly, we have found that organocyclopolysiloxanes, particularly the cyclic derivatives of dimethylsiloxanes which contain at least one chloromethyl group attached to siliconthrough a silicon-carbon linkage may 2,753,365 Patented July 3, 1956 fluids. We have discovered that these organopolysiloxane fluids have lubricating properties superior to the lubricating properties of the conventional organopolysiloxanes such as are described in the aforementioned Patnode patents.

The organocyclopolysiloxanes containing at least one chloromethyl radical attached to silicon through a siliconcarbon linkage, referred to hereinafter, for the sake of brevity, as chlorinated methylcyclopolysiloxanes, may comprise methylcyclopolysiloxanes, such as the tetramer or pentamer of dimethylsiloxane having the formula CH3 n where one or more carbon-bonded hydrogens of one or more of the methyl groups is replaced with a carbonbonded chlorine and where n is an integer equal to, e. g., from 4 to 10 or more, but preferably is equal to from 4 or 5. Some of these chlorinated cyclic derivatives are more particularly described in McGregor et a1.

' reaction.

be reacted with sodium to form organopolysiloxane Patent 2,522,053 and include cyclic chlorinated dimethyl siloxane containing from 1 to 10 or more carbon-bonded chlorine atoms per cyclic unit.

Various methods may be employed for preparing th different chlorinated methylcyclopolysiloxanes described above. In this connection, attention is directed to patents such as Kohl Patent 2,530,202; Goodwin Patents 2,527,807; 2,527,809; 2,511,812; and 2,483,972; Fletcher et a1. Patent 2,528,355; Gilliam Patent 2,474,578; Nordlander Patent 2,439,669; Sommer Patent 2,512,390; Elliott et al. Patents 2,513,924 and 2,457,539; Speier Patents 2,527,591; 2,510,148; and 2,510,149; and McGregor et al. Patents 2,507,316; 2,522,053; 2,384,384; and-2,435,148. These various colorinated methylpolysiloxanes may be prepared, for instance, from the methylcyclopolysiloxanes by merely passing the requisite amount of chlorine into the polymer to be treated in the presence of light, for instance. The chlorine becomes attached to the carbon atoms of one or more of the methyl radicals bonded to silicon atoms by displacement of hydrogen therefrom. The use of ultraviolet light as a means for effecting chlorination of the groups attached to the silicon atoms has been very helpful as shown in Nordlander Patent 2,439,669. We do not intend to be limited to any particular number of chlorine atoms since one or more chlorine atoms may be substituted on one or more of the methyl radicals. Typical chlorinated methylpolysiloxanes are chloromethylheptamethylcyclotetrasiloxane, 1,1-di-(chloromethyl)-octamethylcyclopentasiloxane, 1,5 (chloromethyl) hexamethylcyclotetrasiloxane, etc.

The reaction of the present invention is carried out by merely contacting the chlorinated methylcyclopolysiloxane with metallic sodium in a suitable solvent. The proportions of reactants are not critical, but we prefer to react the ingredients in such a proportion that about one mole of sodium is present for each mole of-chlorine present in the chlorinated methylcyclopolysiloxane. Since the reaction is substantially quantitative, the use of equimolar proportions of the two reactants tends to facilitate the separation and purification of the product after the reaction is completed. The particular solvent employed in the reaction is not critical, as long as an inert solvent is used. By the term inert solvent we mean a solvent which is inert to the reactants under the conditions of the Among the many solvents which may be employed are included, for example, aromatic hydrocarbons such as benzene, toluene, xylene, aliphatic hydrocarbons such as, for example, pentane, hexane, heptane, octane, nonane, cycloaliphatic and substituted cycloaliphatic hydrocarbons such as, for example, cyclohexane, cycloheptane,

ethylcyclopentane, etc.; petroleum hydrocarbon fractions, such as petroleum ether, gasoline, kerosene, etc.; aliphatic ethers, such as, for example, n-propyl ether, n-amyl ether, n-butyl ether, methylpropyl ether, propylbutyl ether, 1,4- dioxane, etc. A convenient solvent to employ in the reaction is one which is liquid in the temperature range from room temperature (about 25 C.) up to about 150 C., or a solvent may be employed which is liquid at room temperature and which has a boiling point of from about 100-150 C. The reaction is eifected by contacting the chlorinated methylcyclopolysiloxane and the sodium in suspended form in the solvent until reaction has been eifected. Since the rate of reaction increases with increasing temperatures, we prefer to effect the reaction at temperatures of from about 100-150 C. Where a solvent is employed which has a boiling point within this latter range, it is convenient to effect the reaction in a re-refluxing solution of the solvent. The amount of solvent employed is not critical and we employ amounts at least sufficient to keep the sodium metal in suspension while dissolving the chlorinated methylcyclopolysiloxane and the resulting silicone fluid.

After the reaction has been completed it is generally found that the silicone fluid product is dissolved in the solvent phase and this phase may be separated and the solvent removed to yield the methylsilicone fluid product.

In order to determine whether a particular silicone fluid has a desirable lubricity, it is customary to measure the lubricating effect of the material in question and also the lubricating eifect of a standard material to determine whether the material in question has a desirable lubricity. In the present application, lubricity is measured as the wear scar in a Sheel Four Ball Wear Tester which comprises a device for holding three rigidly clamped one-half inch metal balls submerged in a lubricant in a metal cup. A fourth rotating ball of the same diameter is then thrust into contact with the three stationary balls by an adjustable loading arm and allowed to run for one hour. The contact points on the three stationary balls grow to circular scars as the Wear progresses. The average diameter of these scars in millimeters after one hours run at 600 R. P. M., with a specified load, with the rotating ball of steel and the stationary balls of bronze or steel is taken as the measurement of wear. Where the stationary balls are of steel, the lubricity is referred to as the steelon-steel lubricity. Where the stationary balls are bronze, the lubricity is taken as the steel-on-bronze lubricity.

From the above description, it is obvious that the lower the wear scar, the better the lubricity of the material being tested. We have found that the silicone fluids prepared by the method of the present invention have a lower Wear scar than those of conventional methyl silicone fluids in both the steel-on-steel lubricity test and the steel-on-bronze lubricity test.

The following examples are illustrative of the practice of our invention and are not inserted for purposes of limitation.

Example 1 A solution of 166 grams (0.5 mole) of chloromethylheptamethylcyclotetrasiloxane in 100 ml. of dry toluene was added to a stirred suspension of 12.7 grams (0.55 mole) of sodium metal in 300 ml. of refluxing toluene over a period of about 2 hours. The reaction mixture was stirred and refluxed (at about 110 C.) for 17 hours. After the solution had cooled to room temperature, about 20 ml. of methanol was added; however, there was no indication of reaction or hydrogen evolution showing that all of the sodium had reacted with the chloromethylheptamethylcyclotetrasiloxane. The reaction mixture was then stirred with 100 ml. of water and the toluene layer was again washed with water, dried over calcium sulfate, and distilled. The residual oil obtained after removal of the toluene was stripped of low boilers until the vapor temperature reached 148 C. at 3 mm. mercury. This resulted in a clear fluid having a refractive index 11 1.4260. Analysis of this fluid showed: Si, 36.8%; C, 32.6%; H, 8.1%. The theoretical values for dimethylsiloxane units are: Si, 37.8%; C, 32.4%; H, 8.2%. This fluid had a viscosity of 95.3 centistokes at F. and 25.5 centistokes at 210 F. Although the ultimate structure of this oil is not known, infra-red examination indicates that the oil contains silylmethylene linkages (ESiCHZSiE). An organic group analysis on the oil using the method of Burkhard and Norton Anal. Chem. 21, 304 (1949) indicated that no ethylene linkages were present. The infra-red absorption spectrum of the material and chemical analysis indicate that no carbon-chlorine bonds remain. The lubricity of the oil prepared in this example and the lubricity of a conventional methylsilicone oil prepared by the method of the aforementioned Patnode patents and having a viscosity of 100 centistokes at 100 F. were measured on the Sheel Four Ball Wear Tester described above to give the results listed below.

Lubricity (Wear Scar, mm.)

Steel-0n- Bronze, 10

Kg. Load Kg. Load Fluid of Example 1 Methylsilicone fluid Example 2 Following the procedure of Example 1 a silicone fluid of improved viscosity may be prepared by adding a solution of 1,5-di-(chloromethyl)-octamethylcyclopentasiloxane in kerosene to a suspension of sodium in kerosene. This solution can be maintained at a temperature of about C. with stirring for about ten hours to complete the reaction. The product may be removed from the kerosene by washing the kerosene layer with water and separating the product from the kerosene layer by distillation.

Although the examples have illustrated the method of the present invention using substantially equimolar amounts of the chlorine atom and sodium, it should be understood that the proportions of the ingredients may be changed so that more or less than equimolar proportions are present. It should also be understood that temperatures above and below those illustrated in the examples may also be employed. In selecting the particular chlorinated methylpolysiloxane employed, consideration should be given to the viscosity desired in the final silicone fluid. In general, the greater the ratio of chloromethyl or polychloromethyl radicals to silicon, the greater is the viscosity of the resulting oil.

The silicone fluids prepared by the method of our invention are particularly suitable for lubrication under oxidizing conditions at elevated temperatures, at very low temperatures, and in locations where wide temperature fluctuations are experienced. These fluids are also valuable for use as heat transfer media, hydraulic fluids, and as additives to hydrocarbon lubricating materials.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. The process of preparing a silicone fluid of improved lubricity which comprises effecting reaction between (1) a cyclic diorganosiloxane in which at least one of the organo groups is a chloromethyl group and in which the remaining organo groups are methyl and (2) sodium in the presence of an inert solvent.

2. A silicone fluid of improved lubricity prepared by the process of claim 1.

3. The process of preparing a silicone fluid of improved lubricity which comprises elfecting reaction between chloromethylheptamethylcyclotetrasiloxane and sodium in the presence of an inert solvent.

4. A silicone fluid of improved lubricity prepared by the method of claim 3.

No references cited.

Claims (1)

1. THE PROCESS OF PREPARING A SILICONE FLUID OF IMPROVED LUBRICITY WHICH COMPRISES EFFECTING REACTION BETWEEN (1) A CYCLIC DIORGANOSILOXANE IN WHICH AT LEAST ONE OF THE ORGANO GROUPS IS A CHLOROMETHYL GROUP AND IN WHICH THE REMAINING ORGANO GROUPS ARE METHYL AND (2) SODIUM IN THE PRESENCE OF AN INERT SOLVENT.