LUBRICATING OIL COMPOSITIONS CONTAINING PRE-CERAMIC POLYMERS

Abstract

A lubricating composition comprises an oil of lubricating viscosity, a metal-free pre-ceramic polymer and one or more co-additives. The metal-free pre-ceramic polymer comprises a plurality of repeat units which do not contain oxygen. The pre-ceramic polymers provide the lubricating oil composition with antiwear properties. Also described is a method of lubricating an internal combustion engine and the use of a lubricating oil composition containing a pre-ceramic polymers to inhibit wear in an internal combustion engine.

Claims

1. A lubricating oil composition comprising a major amount of an oil of lubricating viscosity and a minor amount of a metal-free pre-ceramic polymer, wherein the pre-ceramic polymer comprises a plurality of repeat units which do not contain oxygen, and wherein the lubricating oil composition further comprises one or more co-additives.

2. A lubricating oil composition according to claim 1 wherein the metal-free pro-ceramic polymer comprises a silicon-containing pre-ceramic polymer.

3. A lubricating oil composition according to claim 2 wherein the metal-free pre-ceramic polymer comprises a polysilazane, a polyborosilane, a polycarbosilane, a polyborosilazane, a polysilylcarbodiimide, or a mixture thereof.

4. A lubricating oil composition according to claim 1 wherein the metal-free pre-ceramic polymer contains a repeat unit of formula (I): ##STR00011## where X is NH, NR, BR.sub.3 or R.sub.4; or wherein the metal-free pre-ceramic polymer contains a repeat unit of formula (II), (III), (IV): ##STR00012## where R, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6 and R.sub.7 are independently hydrocarbyl groups containing 1 to 30 carbon atoms.

5. A lubricating oil composition according to claim 4 wherein R, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6 and R.sub.7 are independently linear, branched or cyclic alkyl or alkenyl groups, or aryl groups containing 1 to 30 carbon atoms.

6. A lubricating oil composition according to claim 4 wherein the metal-free pre-ceramic polymer contains a repeat unit of formula (I) and where X is NH or NR.

7. A lubricating oil composition according to claim 4 wherein metal-free pre-ceramic polymer consists of units of formulae (I) to (IV).

8. A lubricating oil composition according to claim 4 wherein the metal-free pre-ceramic polymer includes additional units or groups.

9. A lubricating oil composition according to claim 8 wherein the metal-free pre-ceramic polymer is capped at one or both ends by a capping or chain-terminating group such as an amide group, an amine or polyamine, an ester, an ether, a thioether or a polymeric residue.

10. A lubricating oil composition according to claim 4 wherein the repeat units of formulae (I) to (VI) form a closed ring structure.

11. A lubricating oil composition according to claim 4 wherein the number of repeat units of formulae (I) to (IV) in the metal-free pre-ceramic polymer is in the range from 2 to 100.

12. A lubricating oil composition according to claim 4 to 11 wherein at least one of R, R.sub.1, R.sub.2, R.sub.3, R.sub.5, R.sub.6 and R.sub.7 contains at least 3 carbon atoms, and/or any capping or chain-terminating group contains such a group.

13. A lubricating oil composition according to claim 1 wherein the metal-free pre-ceramic polymer comprises a compound of structure (VII): ##STR00013## where R.sub.1, R.sub.2 and R.sub.8 are independently hydrocarbyl groups containing 1 to 30 carbon atoms, provided that at least one of R.sub.1, R.sub.2 and R.sub.8 contains at least 3.

14. A lubricating oil composition according to claim 1 wherein the metal-free pre-ceramic polymer comprises a compound of structure (VIII): ##STR00014## where R.sub.1 and R.sub.2 are independently hydrocarbyl groups containing 1 to 30 carbon atoms, provided that at least one of R.sub.1 and R.sub.2 contains at least 3 carbon atoms.

15. A lubricating oil composition according to claim 1 wherein the metal-free pre-ceramic polymer comprises a mixture of a compound of structure (VII): ##STR00015## where R.sub.1, R.sub.2 and R.sub.8 are independently hydrocarbyl groups containing 1 to 30 carbon atoms, provided that at least one of R.sub.1, R.sub.2 and R.sub.8 contains at least 3; and a compound of structure (VIII): ##STR00016## where R.sub.1 and R.sub.2 are independently hydrocarbyl groups containing 1 to 30 carbon atoms, provided that at least one of R.sub.1 and R.sub.2 contains at least 3 carbon atoms.

16. A lubricating oil composition according to any preceding claim 1 wherein the metal-free pre-ceramic polymer is present in the lubricating oil composition in an amount of between 0.001 and 10 percent by weight, based on the weight of the composition.

17. A lubricating oil composition according to claim 1 wherein the one or more co-additives comprises an antiwear additive, an oil-soluble or oil-dispersible molybdenum-containing compound, a metal-containing detergent, an ashless dispersant, an ashless friction modifier, a viscosity modifier, an anti-oxidant, a rust inhibitor, a copper and lead bearing corrosion inhibitor, a demulsifier or a pour point depressant.

18. A lubricating oil composition according to claim 18 wherein the one or more co-additives comprises a zinc dihydrocarbyl dithiophosphate in an amount sufficient to provide from greater than 800 ppm to 1200 ppm by mass of phosphorous to the lubricating oil composition, based upon the total mass of the lubricating oil composition, and as measured in accordance with ASTM D5185.

19. A lubricating oil composition according to claim 18 wherein the one or more co-additives comprises a zinc dihydrocarbyl dithiophosphate in an amount sufficient to provide no greater than 800 ppm by mass of phosphorous to the lubricating oil composition, based upon the total mass of the lubricating oil composition, and as measured in accordance with ASTM D5185.

20. A lubricating oil composition according to claim 18 which does not contain a zinc dihydrocarbyl dithiophosphate.

21. A method of lubricating a spark-ignited or compression-ignited internal combustion engine, the method comprising lubricating the engine with a lubricating oil composition according to claim 1.

Description

EXAMPLE SYNTHESIS OF POLYSILAZANE PRE-CERAMIC POLYMERS

[0152] Step 1: A 500 ml multi-necked, round-bottomed flask was fitted with a solid CO.sub.2-cooled cold-finger condenser having a nitrogen inlet, a pressure-equalising dropping funnel, a thermal probe and a magnetic stirrer. The inlet/outlet of the condenser was connected to a three-way tap to allow nitrogen inlet and also headspace gas outlet to a scrubber solution (HCl, 2M) contained in a 1 litre beaker. A solution of ammonia in 1,4-dioxane (0.5M, 200 ml) was charged to the flask and the flask was placed in a cold bath (ca. 0 C.) and the solution stirred. Triethylamine (0.2 mol, 20.2 g) was then added to the flask using a syringe. The dropping funnel was then charged with anhydrous THF (100 ml) together with di-isopropyldichlorosilane (0.1 mol, 12.9 g) and the resulting solution added dropwise to the ammonia solution in the flask. The rate of addition was controlled so as to maintain at most a steady reflux of ammonia from the cold-finger and taking care to limit the rate of temperature rise to no more than 5 C. per minute. The reaction proceeded with the precipitation of ammonium chloride. Once all of the di-isopropyldichlorosilane solution had been added to the flask and the precipitation of ammonium chloride had stopped, the solution was cooled to below 33 C. with stirring to permit the removal of the cold-finger. The flask was then fitted with a stopper and allowed to warm to room temperature while venting any excess ammonia to the scrubber solution.

[0153] Step 2: Oleamide (0.05 mol, 14.07 g) dissolved in THF (100 ml) was then added dropwise to the solution obtained from Step 1. This reaction produced a solid by-product which was separated from the solution by filtration. The resulting filtrate was distilled to remove the solvent and the final liquid product was dried under vacuum for several hours.

[0154] The above synthesis is represented in the following scheme:

##STR00010##

[0155] The polymer (B) produced from the above synthesis is labelled as Polymer P2 in the table below. Variation in groups R.sub.1 and R.sub.2 to produce analogous compounds was achieved by substituting the dialkyldichlorosilane starting material in Step 1 above (di-isopropyldichlorosilane in the case of P2) for a differently substituted compound (dichloro(methyl)(octadecyl)silane in the case of P3). Variation in group R.sub.8 was achieved by using a different amide in Step 2 (e.g. butyramide instead of oleamide). Polymer P1 was made using the same reactants as P3 but by omitting Step 2 of the process (product (A) in the scheme above). As will be appreciated, primary amines can be used in place of ammonia to provide analogous polymers where the nitrogen atoms (excepting those of the amide groups) carry alkyl groups rather than hydrogen atoms.

[0156] Four silicon-containing, metal-free pre-ceramic polymers were prepared using the synthesis outlined above, conforming to structures (VII) and (VIII) described herein. They are detailed in the table below:

TABLE-US-00002 Polymer Structure type Group R.sub.1 Group R.sub.2 Group R.sub.8 derived from P1 (VIII) methyl C.sub.18 - alkyl n/a P2 (VII) iso-propyl iso-propyl oleamide P3 (VII) methyl C.sub.18 - alkyl oleamide P4 (VII) iso-propyl iso-propyl butyramide

[0157] Six lubricating oils were formulated using an API Group III base stock. Details are shown in the table below. In addition to the anti-wear compounds listed in the table, all six lubricating oils contained similar amounts of an ashless dispersant, metal-containing detergents, a molybdenum-based friction modifier, anti-oxidants, a pour point depressant, a viscosity modifier and an anti-foaming component, all of the types and in amounts typically found in passenger car crankcase lubricating oils.

TABLE-US-00003 Oil Anti-wear compound/amount 1 none 2 ZDDP/to provide 800 ppm of phosphorus to the oil 3 P1/1 wt. % 4 P2/1 wt. % 5 P3/1 wt. % 6 P4/1 wt. %

[0158] Oils 1 and 2 were comparative examples and Oils 3, 4, 5 and 6 represent examples according to the present invention. None of Oils 3, 4, 5 and 6 contained any phosphorus.

[0159] Each oil was tested using a Mini Traction Machine MTM obtainable from PCS Instruments, London. In this test, a steel ball is loaded against the face of a steel disc and both the ball and the disc are driven independently to create a mixed rolling/sliding contact. Tests were run for a duration of 2 hours at an oil temperature of 100 C. The load between the ball and the disc was set at 50N giving a maximum contact pressure of 1.1 Gpa. The ball was driven at a speed of 200 mms.sup.1 over a stroke length of 4 mm and the disc frequency was 10 Hz. The measured wear scars obtained from each oil are set out in the table below.

TABLE-US-00004 Oil Wear scar/m.sup.3 1 61568 2 32260 3 32530 4 28147 5 12719 6 14156

[0160] The results show that as expected, an oil containing a conventional amount (800 ppm of phosphorus) of a phosphorus anti-wear additive (ZDDP) provides the lubricating oil with good wear protection (compare Oil 1 with Oil 2). However, the results also demonstrate that 1 wt. % of pre-ceramic polymer P1 is able to provide equivalent wear protection as the ZDDP (compare Oil 3 with Oil 2) and further that 1 wt. % of pre-ceramic polymers P2, P3 and P4 provide enhanced wear protection compared to the use of ZDDP (compare Oils 4, 5 and 6 with Oil 2). Especially advantageous wear protection is provided by pre-ceramic polymers P3 and P4. It has thus shown to be possible to entirely replace a conventional ZDDP anti-wear additive with a species that is phosphorus-free and metal-free without compromise to the ability of the oil to protect against wear.

[0161] The testing above was carried out on freshly formulated oils. While it is clearly important that a lubricating oil is able to protect contacting parts (e.g. in an engine) when the oil is new, it is also critical that the oil continues to provide protection from wear when the oil has been in use for a period of time. To investigate this, five further lubricating oils were formulated as shown in the table below. In addition to the anti-wear compounds listed in the table, all five lubricating oils contained similar amounts of an ashless dispersant, metal-containing detergents, anti-oxidants, and a viscosity modifier, all of the types and in amounts typically found in passenger car crankcase lubricating oils.

TABLE-US-00005 Oil Anti-wear compound/amount 7 none 8 ZDDP/to provide 400 ppm of phosphorus to the oil 9 ZDDP/to provide 800 ppm of phosphorus to the oil 10 P2/1 wt. % 11 ZDDP/to provide 400 ppm of phosphorus to the oil + P2/0.5 wt. %

[0162] Oils 10 and 11 are examples of the present invention. Oils 7, 8 and 9 are comparative examples, with Oils 8 and 9 being representative of common commercial lubricating oils. The oils were tested using a High Frequency Reciprocating Rig (HFRR) available from PCS Instruments, London. The testing regime used was as follows. [0163] a) Each oil was blended and the sample split into two portions. One portion of each oil was aged by heating to a temperature of 160 C. and blowing air through the oil at a rate of 10 litres/hour for 192 hours. [0164] b) A run-in procedure was performed whereby the fresh (un-aged) portion of the oil to be tested was used in the HFRR using standard steel substrates and balls: 200 g load, 20 Hz reciprocation, 1 mm stroke length at 100 C. for 30 minutes. [0165] c) Following the run-in procedure, the fresh oil portion was replaced by the aged portion and HFRR testing continued on the same substrates and balls as used in stage b) under the same conditions but for 90 minutes.

[0166] Each oil was tested in the same way a further two times and the average wear scar volume was calculated. Results are shown in the table below.

TABLE-US-00006 Oil HFRR wear scar volume/m.sup.3 7 671935 8 509640 9 186605 10 139855 11 190155

[0167] The results show that as expected, the conventional anti-wear additive (ZDDP) is effective to protect against wear, and an increased amount of ZDDP (in terms of phosphorus content) provided additional protection (compare Oils 7, 8 and 9). The oil containing 1 w.t % the of pre-ceramic polymer (Oil 10) provided enhanced wear protection compared to the oil containing the highest amount of phosphorus (Oil 9) showing that the improvement in wear exhibited for the fresh oils persisted into aged oils. Comparing the results for Oils 11 and 9 shows that equivalent wear performance can be achieved by replacing half of the ZDDP (in terms of phosphorus content) with only 0.5 wt. of a pre-ceramic polymer. Entire or partial replacement of ZDDP has thus shown to be possible without compromising wear performance.

[0168] SEM-EDX analysis of the wear scars formed during HFRR testing showed increased levels of silicon present in scars formed during fresh oil testing (step b) above) and during aged oil testing (step c) above).

[0169] Fresh (un-aged) samples of Oils 8, 9 and 11 were tested using a 4-ball wear tester. This is a higher pressure boundary lubrication test then either the MTM or the HFRR. Results are shown in the table below.

TABLE-US-00007 Oil Average 90 wear scar/mm 8 1.60 9 0.76 11 0.73

[0170] The results show that the oil containing 400 ppm of phosphorus (from ZDDP) and 0.5 wt. % of the pre-ceramic polymer (Oil 11) significantly outperformed the oil containing 400 ppm of phosphorus (Oil 8) and provided equivalent wear performance to an oil containing twice as much phosphorus (Oil 9).