US3479290A - Phosphorous-containing organopolysiloxane lubricant - Google Patents

Description

United States Patent 3,479,290 PHOSPHOROUS-CONTAINING ORGANOPOLY- SILOXANE LUBRICANT Edgar D. Brown, In, Schenectady, N.Y., assignor to general Electric Company, a corporation of New ork No Drawing. Filed Dec. 12, 1966, Ser. No. 600,757 Int. Cl. C10m 1/44, [/50 US. Cl. 252-49.9 7 Claims ABSTRACT OF THE DISCLOSURE An organopolysiloxane lubricating composition comprising (A) an organopolysiloxane having the formula:

cum. f

SIiO snow); CH3 CH3 b and (B) from 1 to percent by weight, based on the weight of said organopolysiloxane, of tricresyl phosphate, where R is an alkyl radical containing from 8 to 18 carbon atoms, inclusive, n has a value of from 2 to 6, inclusive, a has an average value of at least 1, b has an average value of at least about 2.9, the sum of a plus b is equal to from about 4 to 40, inclusive, and the ratio of a to the sum of a plus b is equal to from 0.1 to 0.4, inclusive.

The present invention is directed to a new class of organopolysiloxane lubricants in which extreme pressure lubricating characteristics are imparted by certain phosphorous compounds.

In my copending application Ser. No. 421,588, filed Dec. 28, 1964, now US. Patent No. 3,418,353 granted Dec. 24, 1968 and assigned to the same assignee as the present invention, there is described a class of organopolysiloxanes useful for many purposes, which comprises triorganosilyl chain-stopped diorganopolysiloxanes in which each of the diorganosiloxane units contains a siliconbonded higher alkyl radical. Examination of these materials shows that they have very good lubricating properties under moderate pressure conditions. However, when the pressure under which these compositions are to operate is increased, it is found that the fluids do not have as high a lubricating characteristic as desired. This is particularly true with respect to the lubrication of stainless steel parts.

In my copending application Ser. No. 600,768 filed concurrently herewith and assigned to the same assignee as the present invention, there is described a class of organopolysiloxane liquids of improved lubricating characteristics which are trimethylsilyl chain-stopped copolymers of methylchloroalkylsiloxane units and methyl higher alkylsiloxane units. While these copolymers have improved lubricating characteristics, the lubricating characteristics are still not as good as desired, particularly under extreme pressure lubricating conditions. While these copolymer fluids of my aforementioned copending application Ser. No. 600,768 have been useful in many applications, there have been many engineering designs which would normally have made use of the corrosion-resistance of stainless steel but which, because of the inability to lubricate satisfactorily stainless steel under extreme pressure conditions, has required the use of other materials.

The present invention is based on my discovery of a lubricating composition which contains both methylchloroalkylsiloxane units and methyl higher alkylsiloxane units, and which also contain tricresyl phosphate. This combination of components provides a lubricating composition which has improved high temperature stainless steel extreme pressure lubricating characteristics.

Patented Nov. 18, 1969 The compositions of the present invention comprise (A) an organopolysiloxane fluid having the average formula:

R Si(CH3)3 C 3 1: C 3 1:

where R is an alkyl radical containing at least 8 carbon atoms, e.g., from 8 to 18 carbon atoms, 11 is equal to from 2 to 6, inclusive, a has an average value of at least 1, b has an average value of at least 2.9, the sum of a plus b is equal to from about 4 to 40, inclusive, and the ratio of a to the sum of a plus b is equal to from 0.1 to 0.4, inclusive, and (B) from 1 to 15 percent by weight, based on the weight of the polysiloxane, of tricresyl phosphate.

The fact that tricresyl phosphate will increase the stainless steel lubricating characteristics of the compositions of Formula 1 is completely unexpected and unpredictable from the art, since the addition of tricresyl phosphate to a methyl higher alkyl polysiloxane fluid of the type described in my aforementioned copending application Ser. No. 421,588, or the addition of tricresyl phosphate to a trimethylsilyl chain-stopped methylchloroalkylpolysiloxane fluid fails to increase the lubricating characteristics of such fluids. On the other hand, the addition of the tricresyl phosphate to the compositions of the present invention has a dramatic effect in increasing the lubricating characteristics of the composition.

The organopolysiloxane fluids within the scope of Formula 1 can be copolymers in which the average molecule contains both methylchloroalkylsiloxane units and methyl higher alkylsiloxane units or can be a blend of two fluids, one of which is a trimethylsilyl chain-stopped methylchloroalkylsiloxane fluid having the formula:

c1 u Zn onmsio l orrmsio suoHm when n is as previously defined and c has a value of from about 4 to 40, inclusive, and the other of which is a trimethylsilyl chain-stopped methyl higher alkylpolysiloxane having the formula:

where R is as previously defined and d has a value of from about 4 to 40, inclusive.

The trimethylsilyl chain-stopped methylchloroalkylpolysiloxane fluids of Formula 2 are formed by the relatively straightforward hydrolysis and condensation of trimethylchlorosilane and a methylchloroalkyldichlorosilane having the formula:

(4) (CH (C1C H )SiCl Where n is as previously described. Generally, this hydrolysis and condensation is effected by mixing the stoichiometric amounts of the trimethylchlorosilane and the methyl higher alkyldichlorosilane, adding the resulting mixture to a stirred excess of ice water to eifect the hydrolysis and condensation, allowing the reaction mixture to separate into an upper silicone phase and a lower aqueous phase, separating the phases, washing with water to remove all acidic by-products, and drying the resulting product to form the polysiloxane within the scope of Formula 2.

As is obvious from the definition of the organopolysiloxane of Formula 2, the methylchloroalkyldichlorosilane of Formula 4 includes compounds in which the chloroalkyl radical can vary from chloroethyl to chlorohexyl. While it is preferred that the chlorine atom of the chloroalkyl radical be attached to the omega-carbon atom of a normal alkyl radical, it is also possible for the chlorine atom to be attached to any other carbon atom of the alkyl radical and it is also possible for the alkyl radical to be other than a normal alkyl radical. In any event, it is preferred that the chlorine atom be attached to a carbon atom other than the carbon atom attached to silicon. In the preferred embodiment of my invention, the chloroalkyl radical is the chloropropyl radical.

The trimethylsilyl chain-stopped methyl higher alkylsiloxane of Formula 3 is prepared from the corresponding trimethylsilyl chain-stopped methyl hydrogen polysiloxane which has the formula:

(5) III (CH3)3S O[sIlO :Isnomn on, d

This fluid is well known in the art and is prepared by the hydrolysis and condensation of trimethylchlorosilane and methyl hydrogen dichlorosilane in the proper proportions. The fluid within the scope of Formula 3 is then prepared by the general method described in my aforementioned copending application Ser. No. 421,588, by the addition of a suitable alpha-olefin to the methyl hydrogen polysiloxane fluid of Formula 5. In general, the preferred alpha-olefin is tetradecene-l, but any other alphaolefin having from about 8 to 18 carbon atoms can be employed, for example, octene-l, decylene-l, dodecylene- 1, tetradecylene-l, hexadecylene-l, and octadecylene-l.

My aforementioned copending application Ser. No. 421,588 is incorporated by reference into the present application for a disclosure of methods of forming the compositions within the scope of Formula 3. In general, the reaction involves one molecule of the alpha-olefin for each silicon-bonded hydrogen atom in the polysiloxane of Formula 5 and this is the ratio of components employed in the reaction. However, sometimes it is advantageous to add the alpha-olefin in a to 20% molar excess. The reaction is carried out in the presence of conventional SiH-olefin addition catalysts, with the preferred type being the elemental platinum catalysts of the type described in Patent 2,970,150-Bailey, as well as the platinum compound catalysts described in Patents 2,823,- 218Speier et al.; 3,159,60lAshby; 3,159,662Ashby; and 3,220,972-Lamoreaux.

The amount of SiH-olefin addition catalyst employed in effecting reaction between the polysiloxane of Formula 5 and the alpha-olefin can vary within wide limits. Generally, the catalyst is employed in an amount suflicient to provide one mole of platinum per 1,000 moles of alphaolefin to one mole of catalyst per million moles of alphaol efin. Generally, a mixture is formed of the hydrogencontaining polysiloxane of Formula 5 and a portion of the alpha-olefin and the' catalyst is added, the temperature of the reaction mixture is increased until the rate of temperature rise becomes greater than that supplied by the heating element, and thereafter the temperature is maintained by controlling the rate of addition of the remaining alpha-olefin. Generally, the reaction temperature is maintained at about to C. When an excess of the alpha-olefin is employed, it is removed from the reaction mixture by distillation.

The organopolysiloxane fluids within the scope of Formula 1 which are copolymers in which the average molecule contains both the methylchloroalkylsiloxane unit and the methyl higher alkylsiloxane unit are prepared by the process described in my aforementioned copending application Ser. No. 600,768, which is incorporated by reference into the present application for details of the technique for the preparation of such copolymers. In general, the procedure for preparing the copolymers of Formula 1 is to first form a trimethylsilyl chain-stopped copolymer of methylchloroalkylsiloxane units and methyl hydrogen siloxane units having the formula:

ohm. f (OHmSiO siro worn CH3 3 CH3 b where a, b and n are as previously defined. This copolymer of Formula 6 is prepared by the cohydrolysis and co-condensation of a mixture of trimethylchlorosilane, methyl hydrogen dichlorosilane, and a methylchloroalkyldichlorosilane within the scope of Formula 4. The process for forming the composition of Formula 6 is conventional, with the appropriate chlorosilanes being mixed together in the proper ratios, and added to an excess of ice water, with the subsequent isolation of the product.

Following the procedure previously described for preparation of the trimethylsilyl chain-stopped methyl higher alkylpolysiloxane of Formula 3, the methyl hydrogencontaining polysiloxane of Formula 6 is reacted with the appropriate alpha-olefin employing a platinum compound or elemental platinum catalyst to produce the composition within the scope of Formula 1 which is a copolymer hav ing both the methyl higher alkylpolysiloxane unit and the methylchloropropylsiloxane unit present in the same molecule.

When the composition of Formula 1 comprises a blend of a fluid of Formula 2 and a fluid of Formula 3, the two fluids are merely mixed together with agitation, and the tricresyl phosphate is added in the desired amount. The tricresyl phosphate is generally soluble in one or both of the organopolysiloxane fluids in the blend, and the tricresyl phosphate in the blend is merely stirred until the tricresyl phosphate goes into solution.

In addition to copolymeric organopolysiloxanes within the scope of Formula 1 and blends of methylchloroalkylpolysiloxane fluids of Formula 2 with methyl higher alkylpolysiloxanes of Formula 3 which result in an average blend composition within the scope of Formula 1, it should also be understood that within the contemplation Of the present invention are blends of copolymers within the scope of Formula 1 with either methylchloropropylpolysiloxanes within the scope of Formula 2 or methyl higher alkylpolysiloxanes within the scope of Formula 3, so long as the resulting composition has an average formula which falls within Formula 1. Likewise, it is possible to employ blends of copolymers of Formula 1 with both methylchloropropylpolysiloxanes of Formula 2 and methyl higher alkylpolysiloxanes of Formula 3, so long as the resulting blend has the average composition of Formula 1.

The tricresyl phosphate employed in the practice of the present invention has the formula:

and, as is well known in the art, can comprise a number of isomers. Thus, the methyl groups in the cresyl radicals can be ortho, meta, or para to the oxygen atom in the radical. In general, commercial tricresyl phosphate is a random mixture of the various tricresyl phosphate isomers and this random mixture was employed in the practice of the present invention. However, it should be understood that within the scope of the present invention are single isomers of tricresyl phosphate, in addition to the random mixture of such isomers.

The copolymeric siloxanes within the scope of Formula 1 are good solvents for tricresyl phosphate, for the methylchloroalkylpolysiloxane of Formula 2, and for the'methyl higher alkylpolysiloxane of Formula 3. Therefore, in the preferred embodiment of my invention, the composition within the scope of Formula 1 includes a copolymer within the scope of Formula 1 even though the composition can also contain the polysiloxane of Formula 2 or of For mula 3. In preparing the compositions of the present invention which contain copolymers within the scope of Formula 1, the tricresyl phosphate is merely added to the other components of the composition in the appropriate ratio and a uniform solution is obtained.

Because the methylchloroalkylpolysiloxane of Formula 2 is not completely miscible with the methyl higher alkylpoysiloxane of Formula 3, when the composition of the present invention is a blend of these two polysiloxanes with the tricresyl phosphate added, the resulting material is a two-phase mixture and conventional precautions are employed to insure that the compositions are uniformly and constantly mixed. Therefore, these compositions are most often employed in dynamic lubrication environments.

In order to evaluate the lubricating characteristics of the compositions of the present invention, they were subjected to the conventional Shell Four-Ball Wear test in which three rigidly clamped /2" 302 stainless steel balls in a metal cup are covered with the lubricant under evaluation. A fourth rotating 302 stainless steel ball of the same diameter is then pressed into contact with the three stationary balls by an adjustable loading arm. The fourth ball rotates at a speed of 600 r.p.m. at ambient temperature for one hour. The contact points between the rotatable ball and the three stationary balls grow to circular scars as wear progresses. The average diameter of these scars in millimeters, after the one hour run, is taken as the measure of wear. The better the lubricity of the fluid, the lower is the wear scar.

The following examples are illustrative of the practice of my invention and are not intended for purposes of limitation. All parts are by weight.

EXAMPLE 1 A methylchloropropylpolysiloxane fluid within the scope of Formula 2 was prepared by mixing g. (0.92 mole) trimethylchlorosilane with 197 g. (1.0 mole) methy1chloropropyldichlorosilane and the mixture was added to 600 g. of water and stirred for one hour. At the end of this time, the two layers were separated and the upper methylpolysiloxane layer was washed with water three times until neutral and then dried over sodium sulfate to produce a polysiloxane within the scope of Formula 2 where n is 3, and c has a value of about 25. Following the procedure of my copending application Ser. No. 421,588, a methyltetradecylpolysiloxane fluid was prepared by slowly adding 196 g. of tetradecene-1 to 63 g. of a trimethylsilyl chainstopped methyl hydrogen polysiloxane within the scope of Formula 5, where c was equal to 40. This resulted in a trimethylsilyl chain-stopped methyltetradecylpolysiloxane within the scope of Formula 3 in which R is tetradecyl and d is 40. A mixture was prepared of 92 parts of the methyltetradecylpolysiloxane and 8 parts of the methylchloropropylpolysiloxane. This blend was within the scope of Formula 1 when n was equal to 3, R is equal to tetradecyl, and the average value of a was 6 and the average value of b was 32. To 100 parts of this blend was added 5 parts of tricresyl phosphate and the wear scar was determined with type 302 stainless steel balls at 600 r.p.m., at ambient temperature, and under loads of 10 kg. and 20 kg: The wear scar at 10 kg. was 0.36 mm. and at 20 kg. was 0.43 mm. In comparison to this, the wear scar of a mixture of 100 parts of the methyltetradecylpolysiloxane and 8 parts of the methylchloropropylpolysiloxane at 10 kg. was 2.4 mm. In contrast also, the wear scar of a solution of 5 parts of tricresyl phosphate in 100 parts of the methyltetradecylpolysiloxane fluid was 2.6 mm. Also in contrast to this, the wear scar of a solution of 5 parts of tricresyl phosphate in 100 parts of the methylchloropropylpolysiloxane fluid was 2.5 mm. With the methyltetradecylpolysiloxane fluid, destructive failure occurred after minutes and the test could not be run for a full hour. Thus, the data of Example 1 show that with a polysiloxane fluid containing both the methyltetradecylsiloxane groups and methylchloropropyl-siloxane groups and the tricresyl phosphate, satisfactory lubrication occurred under loads 6 of 10 kg. and 20 kg. In contrast to this, when any of the three components was omitted from the reaction mixture, the wear scar increased drastically.

EXAMPLE 2 Following the procedure of my aforementioned copending application Ser. No. 600,768, a trimethylsilyl chainstopped copolymer of methylchloropropylsiloxane units and methyl hydrogen polysiloxane units within the scope of Formula 6, when n is 3, a is 8, and b is 32 (-20- copolymer), was prepared by the hydrolysis and condensation of a mixture of trimethylchlorosilane, methylchloropropyldichlorosilane, and methyl hydrogen dich1orosilane. This polymer was then reacted with tetradecene-l following the procedure of the same application, to produce a copolymer within the scope of Formula 1 in which n is 3, a is 8, b is 32, and R is tetradecyl. To parts of this fluid was added 5 parts of tricresyl phosphate and evaluation of this material in the lubrication of type 302 stainless steel showed a wear scar at 10 kgs. of 0.37 mm.

EXAMPLE 3 A mixture was prepared from 29.7 parts of the methyltetradecylpolysiloxane described in Example 1, and 100 parts of the copolymer containing methyltetradecylsiloxane units and methylchloropropylsiloxane units of Exam ple 2, to produce a polysiloxane blend within the scope of Formula 1 corresponding to the average composition in which n is 3, R is tetradecyl, a is 6 and b is 32, and then 5 parts tricresyl phosphate was added. Evaluation of this material in the Shell Four Ball Wear tester gave identical results to the results obtained in Example 1. The wear scar at 10 kg. was 0.36 mm. and the wear scar at 20 kg. was 0.43 mm.

EXAMPLE 4 A mixture was prepared to 216 g. (0.2 mole) trimethylchlorosilane, 93.2 g. (0.4 mole) methylchlorohexyldichlorosilane, 69 g. (0.6 mole) methyl hydrogen dichlorosilane. This mixture was slowly added to 500 g. of stirred ice water and allowed to stand for two hours. The upper silicone layer was separated and washed and dried as previously described to produce a polysiloxane within the scope of Formula 6, where n is 6, a is 4, and b is 6. To this silicone fluid was added suflicient chloroplatinic acid hexahydrate to provide one gram atom of platinum per 1,000 gram atoms of silicon-bonded hydrogen and 78.4 g. (0.7 mole) of octene-l was slowly added to the reac tion mixture which was maintained at a temperature of 75 C. At the end of this addition reaction, the reaction mixture was placed under a vacuum of 10 mm. to remove unreacted octene-l and to produce a copolymer within the scope of Formula 1 in which n is 6, R is octyl, a is 4, and b is 6. When 100 part portions of this copolymer are mixed, respectively, with 3 parts, 5 parts, and 15 parts of tricresyl phosphate, the resulting product exhibits a wear scar below 0.40 mm. under a 10 kg. load.

While the tricresyl phosphate-containing compositions of the present invention have been described as liquid materials useful in the lubrication of stainless steel parts and other materials in the liquid form, it should be understood that these compositions can also be employed as lubricating greases. For example, very useful lubricating greases are obtained by mixing 100 parts of the silicone fluid-tricresyl phosphate compositions of the present invention with from 5 to 15 parts by weight of finely divided silica to form a grease-like lubricating composition which can be used in conventional fashion. When the compositions of the present invention are employed in the manufacture of greases by the addition of finely divided silica or other fillers, the question of miscibility of the methylchloroalkylpolysiloxane of Formula 2 and the methyl higher alkylpolysiloxane of Formula 3 is unimportant, since the resulting grease can be maintained without difficulty in a homogeneous state.

While the foregoing examples have illustrated many of the embodiments of my invention, it should be understood that my invention relates broadly to the use of liquid organopolysiloxane compositions containing methylchloroalkylsiloxane units of the type described, methyl higher alkyl polysiloxane units of the type previously described and from 1 to 15 percent by weight, based on the weight of siloxanes, of tricresyl phosphate. The chloroalkyl groups and the higher alkyl groups, as well as the chain length of the polysiloxanes and the ratio of the various siloxane units can vary within the full range previously described.

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

1. An organopolysiloxane lubricating composition comprising (A) an organopolysiloxane having the formula:

and (B) from 1 to 15 percent by weight, based on the Weight of said organopolysiloxane, of tricresyl phosphate, where R is an alkyl radical containing from 8 to 18 carbon atoms, inclusive, n has a value of from 2 to 6, inclusive, a has an average value of at least 1, b has an average value of at least about 2.9, the sum of a plus b is equal to from about 4 to 40, inclusive, and the ratio of a to the sum of a: plus b is equal to form 0.1 to 0.4 inclusive.

2. A composition of claim 1 in which said organopolysiloxane is a copolymeric organopolysiloxane.

3. The composition of claim 1 in which said organopolysiloxane comprises a blend of a methylchloroalkylpolysiloxane having the formula:

Cl n h n Zn (CHa)3SiO i swans and a methyl higher alkyl polysiloxane having the formula:

R (CH SiO(S iO )Si( CH l a a References Cited UNITED STATES PATENTS 2,467,178 4/ 1949 Zimmer et a1. 25249.9 2,768,193 10/1956 Gilbert 2S2-46.7 X 2,970,150 1/1961 Bailey 25249.6 X 3,011,987 12/1961 Walton et a1. 260448.2 X 3,053,873 9/1962 Pepe 260448.2 3,386,917 6/1968 Schiefer 25249.9

DANIEL E. WYMAN, Primary Examiner W. CANNON, Assistant Examiner US. Cl. X.R.