Copolymer Of An Alkene, An Alkyl Ester Of An Unsaturated Carboxylic Acid And A Hydroxyalkyl Ester Of An Unsaturated Carboxylic Acid

Abstract

Lubricating oil compositions containing a copolymer of (1) ethylene, (2) an alkyl ester of an unsaturated monocarboxylic acid and (3) a hydroxyalkyl ester of an unsaturated carboxylic acid exhibit excellent properties relative to thermal stability, viscosity index improvement and dispersant activity. 4 Claims, No Drawings

Parent Case Text

This is a divisional application of Ser. No 721,092, filed Apr. 12, 1968, and now Pat. No. 3,518,197.

Description

This invention relates to novel lubricant compositions containing polymeric compounds which have dispersant properties and viscosity-improving characteristics. This invention further relates to novel polymeric compounds which are suitable for use as lubricant additives.

In the past a number of polymeric compounds have been proposed which proved capable of imparting dispersant properties to a lubricating oil in addition to improving the viscosity of the lubricating oil. A drawback of most of these compounds is that they possess a low thermal stability. If the lubricant in which they have been incorporated is exposed to high temperature, they are decomposed, whereby their favorable reaction is greatly reduced or disappears entirely. In those cases where the lubricants are exposed to high temperature, for example as lubricating oils in combustion engines, it is desirable that the additives incorporated in the lubricants possess a sufficiently high thermal stability, so that their favorable action is retained at high temperature.

A class of polymeric compounds has now been found which impart dispersant properties to a lubricating oil, improve the viscosity characteristics of the lubricating oil and in addition possess a very high thermal stability. These novel polymeric compounds are those which have been obtained by copolymerization of one or more olefins containing from two to six carbon atoms per molecule with one or more alkyl esters of unsaturated carboxylic acids and one or more esters of unsaturated carboxylic acids containing at least one free hydroxyl group located in the part of the molecule derived from the alcohol.

The invention therefore relates to novel lubricant compositions containing one or more lubricants and polymeric compounds which have been obtained by copolymerization of one or more olefins containing two carbon atoms per molecule with one or more alkyl esters of unsaturated carboxylic acids and with one or more esters of unsaturated carboxylic acids containing at least one free hydroxyl group located in the part of the molecule derived from the alcohol.

By an appropriate choice of the molar ratio of the olefins to the esters of the unsaturated carboxylic acids in the mixture to be polymerized and by the use of alkyl esters with a suitable alkyl-chain length one may obtain thermally stable copolymers which are not only active as dispersants and VI improvers and/or thickeners but are also capable of depressing the pour point of the lubricating oils into which they have been incorporated.

The preparation of the present polymers may be accomplished in two manners. The polymers may be prepared directly by copolymerization of a monomer mixture consisting of one or more olefins with two to six carbon atoms per molecule, one or more alkyl esters of unsaturated carboxylic acids and one or more esters of unsaturated carboxylic acids which contain at least one free hydroxyl group located in the part of the molecule derived from the alcohol. However, the polymers are preferably prepared by an indirect route comprising copolymerization of a monomer mixture consisting of one or more olefins having two to six carbon atoms per molecule, one or more unsaturated carboxylic acids and one or more alkyl esters of unsaturated carboxylic acids, followed by after-treatment of the acid copolymers so obtained in which the carboxyl groups are converted into --COOR groups, in which R represents a monovalent alkyl radical containing at least one free hydroxyl group.

The olefins suitable for use as monomers in the preparation of the present copolymers may be either monoolefins or diolefins. Mixtures of olefins may also be used. Examples of suitable monoolefins are ethylene, propylene, butene and pentene. Examples of suitable diolefins are, among others, butadiene, isoprene and dimethylbutadiene. Copolymers prepared with the aid of ethylene are preferred. Copolymers which have been prepared by copolymerization with diolefins may be used for the preparation of lubricant compositions as such or may be hydrogenated, thereby saturating at least part of the olefinically unsaturated bonds with hydrogen.

The alkyl esters of unsaturated carboxylic acids suitable for use as monomers in the preparation of the present copolymers may be either alkyl esters of unsaturated monobasic carboxylic acids of alkyl esters of unsaturated polybasic carboxylic acids. Mixtures of esters of unsaturated carboxylic acids can be used as well. Examples of suitable alkyl esters of unsaturated monobasic carboxylic acids which may be mentioned are methyl methacrylate, isobutyl acrylate, lauryl methacrylate and stearyl methacrylate. Some examples of suitable alkyl esters of unsaturated polybasic carboxylic acids are diethyl maleate, dioctyl fumarate and di(2-ethylhexyl)itaconate. Preference is given to polymers prepared with the aid of alkyl esters of monobasic carboxylic acids wherein the alkyl group contains eight or more carbon atoms, in particular lauryl methacrylate or a mixture of lauryl and stearyl methacrylate.

The esters of unsaturated carboxylic acids, wherein the part of the molecule derived from the alcohol contains at least one free hydroxyl group may be esters of both monobasic carboxylic acids and polybasic carboxylic acids. Mixtures of these esters are useful also. Examples of such esters are partial esters of polyvalent alcohols, such as glycol, glycerol, trimethylolpropane, pentaerythritol and p-dimethylolbenzene, with monobasic carboxylic acids, such as acrylic acid and methacrylic acid, or with polybasic carboxylic acids, such as maleic acid, fumaric acid and itaconic acid, in which partial esters part of the hydroxyl groups originally present in the polyvalent alcohols remains as such. Other examples of such esters are products of the reaction of cyclic ethers wherein the ring contains an oxygen atom and two or three carbon atoms, such as ethylene oxide and trimethylene oxide, with unsaturated monobasic carboxylic acids, such as acrylic acid and methacrylic acid, or with unsaturated polybasic carboxylic acids, such as maleic acid, fumaric acid and itaconic acid, in which reaction products the part of the molecule derived from the cyclic ether contains a free hydroxyl group. Preference is given to copolymers which have been derived from one or more hydroxyalkyl esters of unsaturated monocarboxylic acids, in particular from .beta.-hydroxyethyl methacrylate.

If the preparation of the present copolymers takes place along the indirect route by copolymerization of a monomer mixture consisting of one or more olefins having two to six carbon atoms per molecule, one or more unsaturated carboxylic acids and one or more alkyl esters of unsaturated carboxylic acids followed by aftertreatment of the copolymers so obtained, the unsaturated carboxylic acids may be either monobasic or polybasic carboxylic acids. Mixtures of unsaturated carboxylic acids may also be used. Examples of suitable unsaturated monobasic carboxylic acids are acrylic acid and methacrylic acid. Examples of appropriate unsaturated polybasic carboxylic acids are fumaric acid, maleic acid and itaconic acid. Preferred copolymers are those prepared by the indirect route using one or more unsaturated monocarboxylic acids. Particularly preferred are copolymers prepared using methacrylic acid.

The aftertreatment of the copolymers containing free carboxyl groups may be carried out in different ways. What is important is that the carboxyl groups are converted into --COOR groups, in which R represents a monovalent alkyl radical containing at least one free hydroxyl group. For example, the copolymers containing free carboxyl groups may be caused to react with polyvalent alcohols such as glycol, glycerol, trimethylolpropane, pentaerythritol or p-dimethylolbenzene. The aftertreatment is preferably carried out by reacting the copolymers containing free carboxyl groups with cyclic ethers wherein the ring contains an oxygen atom and two or three carbon atoms, i.e., ethylene oxide and trimethylene oxide. Ethylene oxide is especially preferred.

The copolymerization of olefins with unsaturated carboxylic acids and alkyl esters of unsaturated carboxylic acids is preferably carried out in solution in the presence of a free radical initiator, such as an azo compound or a peroxide.

The ratio in which the monomers are incorporated into a growing copolymer molecule depends on the reactivity of the monomers involved. If there are differences in reactivity, the molar ratio of the monomers in the mixture to be polymerized will be subject to considerable changes as the copolymerization proceeds, since the more reactive monomer is incorporated more rapidly. As a result, the composition of the copolymer also changes continually. As a general rule it may be said that, if in the polymerization of monomers which differ strongly in reactivity no special measures are taken, the products obtained are of an extremely heterogeneous composition. Such a case arises in the copolymerization of olefins, unsaturated carboxylic acids and alkyl esters of unsaturated carboxylic acids, since three types of monomers are involved which differ in reactivity. In the copolymerization of unsaturated carboxylic acids with alkyl esters of unsaturated carboxylic acids it has been found that the rates of incorporation or reaction of these monomers can be equalized by conducting the copolymerizations in the presence of a substance which associates with the unsaturated carboxylic acid. Since the rates of the incorporated monomers becomes equal to that of the monomers in the starting mixture. Associating substances which may be used are aliphatic compounds containing an oxygen atom attached to carbon, such as alcohols, ethers, ketones and carboxylic acids. Preference is given to lower aliphatic alcohols, such am methanol, ethanol, isopropanol and, in particular, to tert-butanol. The solvent in which the copolymerizations are carried out may be an aromatic solvent such as benzene, toluene or xylene, with benzene being preferred. In the preparation of copolymers of olefins, unsaturated carboxylic acids and alkyl esters thereof in the presence of the aforementioned associating substances the number of monomers with different reactivity is in principle reduced by one, since the unsaturated carboxylic acids and the alkyl esters thereof behave as monomers with the same reactivity.

In the copolymerization of olefins with unsaturated carboxylic acids and alkyl esters thereof it has been found that, despite the very different reactivity of these monomers, it is nevertheless possible to prepare copolymers of uniform composition. To accomplish this care must be taken that the ratio between the concentrations of the monomers in the mixture to be polymerized remain constant during the copolymerization. For example, the more reactive monomer or a mixture of monomers rich in the more reactive monomer may be added gradually to the mixture to be polymerized. This method is known as programmed copolymerization. It is also possible to stop the polymerization at a time when the concentrations of the monomers in the mixture to be polymerized remain substantially unchanged. This is called copolymerization to low conversion. The polymerizations may be conducted both batchwise and continuously. Continuous polymerization may take place in a tubular reactor or by continuously adding all reaction components in the ratio in which they are consumed in the process to a reaction mixture whose composition is kept homogenous, for example by intensive stirring, while simultaneously discharging part of the reaction mixture.

The aftertreatment of the copolymers containing free carboxyl groups, in which the carboxyl groups are converted into --COOR groups in which R represents a monovalent alkyl radical containing at least one free hydroxyl group, is preferably carried out with the aid of a cyclic ether, and in particular, ethylene oxide. This conversion may take place under the influence of a substance giving an alkaline reaction as a catalyst. Suitable substances giving an alkaline reaction are alkali metals, alkali metal oxides, alkali metal hydroxides, alkaline earth metals, alkaline earth metal oxides, alkaline earth metal hydroxides and organic compounds, such as trimethylamine, N-methylmorpholine, pyridine, quinoline and .beta.-picoline. By preference a lithium compound is employed as a catalyst. Examples of suitable lithium compounds are lithium hydroxide, lithium hydride, lithium alkoxides, lithium carbonate and lithium acetate. Very favorable results may be obtained by using lithium hydroxide as a catalyst.

In an alternative aftertreatment process the reaction of the acid polymer with the cyclic ether is not conducted in the presence of a substance giving an alkaline reaction as a catalyst. Rather this catalyst is incorporated in the acid polymer beforehand. Incorporation of the catalyst in the acid polymer may take place by first combining one or more salts of substances giving an alkaline reaction with unsaturated carboxylic acids in the monomer mixture from which the acid polymer is prepared. The acid copolymer obtained by polymerization of this monomer mixture may then be reacted with a cyclic ether without using an additional catalyst. In this process, too, lithium salts are preferred.

The reaction of the acid copolymer with the cyclic ether may take place at room temperature, but is preferably conducted at elevated temperatures between about 95.degree. and 130.degree. C. If the final product is liquid, the reaction may proceed without a solvent. The solvent, if employed, may be either polar or nonpolar. The polymer containing free carboxyl groups tends to form intramolecular hydrogen bridges, especially in a nonpolar solvent, as a result of which the viscosity greatly increases. The reaction with the cyclic ether is therefore preferably carried out in the presence of a polar substance which prevents the formation of intramolecular hydrogen bridges. For this purpose a low-boiling aliphatic alcohol is preferred. A very suitable medium for the reaction to be carried out is a mixture of a low-boiling aliphatic alcohol and an aromatic hydrocarbon such as benzene or toluene.

In the preparation of the present polymeric compounds by copolymerization to acid polymers followed by after treatment with a cyclic ether it is not necessary that the acid copolymers be isolated before they are caused to react with the cyclic ether. The cyclic ether may be added directly to the reaction mixture obtained in the copolymerization. If, in the preparation of the acid copolymer, an alcohol was used as an associating substance, this one-step procedure offers the additional advantage that the alcohol present in the reaction mixture prevents the formation of intramolecular hydrogen bridges in the acid copolymer.

The molecular weight of the copolymers according to the invention may vary between wide limits. The invention relates in particular to lubricant compositions containing copolymers with a molecular weight (M.sub.n) between 5,000 and 150,000 and in particular to lubricant compositions containing copolymers with a molecular weight between 15,000 and 100,000. The ratio of monomers in the copolymer may also vary between wide limits. In general copolymers having a molecular ratio of 11 to 300 moles of olefin, 10 moles of an alkyl ester of unsaturated carboxylic acids and 1 to 15 moles of a hydroxyalkyl ester of unsaturated carboxylic acids may be used.

The invention relates in general to lubricant compositions containing polymeric compounds which have been obtained by copolymerization of one or more olefins containing from two to six carbon atoms per molecule with one or more alkyl esters of unsaturated carboxylic acids and with one or more esters of unsaturated carboxylic acids in which the part of the molecule derived from the alcohol contains at least one free hydroxyl group.

The invention relates in particular to lubricant compositions containing polymeric compounds which have been obtained by copolymerization of ethylene with one or more alkyl esters of C.sub.3 --C.sub.4 unsaturated monocarboxylic acids, in which the alkyl group contains eight to 20 carbon atoms, and with one or more hydroxyalkyl esters of C.sub.3 --C.sub.4 unsaturated monocarboxylic acids in which the hydroxyalkyl group contains two to three carbon atoms. Favorable results were obtained by application of the following copolymers of this type in a mineral lubricating oil: 1. ethylene/lauryl methacrylate/.beta.-hydroxyethylmethacrylate copolymers; 2. ethylene/lauryl methacrylate/stearyl methacrylate/.beta.-hydroxyethyl methacrylate copolymers. These copolymers were prepared by ethoxylating ethylene/lauryl methacrylate/methacrylic acid copolymers and ethylene/lauryl methacrylate/stearyl methacrylate/methacrylic acid copolymers, respectively, with ethylene oxide. The ethylene/lauryl methacrylate/methacrylic acid copolymers and the ethylene/lauryl methacrylate/stearyl methacrylate/methacrylic acid copolymers as well as the ethylene/lauryl methacrylate/.beta. -hydroxyethyl methacrylate copolymers and the ethylene/lauryl methacrylate/stearyl methacrylate/.beta.-hydroxyethyl methacrylate copolymers, respectively, obtained therefrom by ethoxylation are novel substances.

The base oils suitable for the preparation of the lubricant compositions according to the invention may be mineral lubricating oils of varying viscosity, and also synthetic lubricating oils or lubricating oils containing fatty oils. The present lubricant additives may also be incorporated into lubricating greases. The invention is of particular importance in improving the quality of mineral lubricating oils or mixtures thereof. The polymeric compounds may be added to the lubricant as such or in the form of a concentrate obtained, by mixing the polymeric compounds with a small quantity of oil. The concentration of the present polymers in the lubricants may vary between wide limits. In general, the desired dispersant action and improvement of the viscometric properties is obtained when the quantity added is from 0.1 to 10 percent by weight and, in particular, when this quantity is from 0.5 to 5 percent by weight of the lubricating oil composition.

In addition to the present polymers, the lubricant compositions according to the invention may also contain other additives, such as antioxidants, anticorrosive agents, antifoaming agents, agents to improve the lubricating action and other substances which are usually added to lubricants.

The invention will now be further described with the aid of the following examples which are considered to be illustrative only.

EXAMPLE I

Five copolymers of ethylene, methacrylic acid stearyl methacrylate and lauryl methacrylate and four copolymers of ethylene, methacrylic acid and lauryl methacrylate (designated as polymers 1-9 were prepared as follows: A specific mixture of methacrylic esters, methacrylic acid, azodiisobutyronitrile, 300 g. of tert-butanol and 100 g. of benzene was passed into a 2-liter autoclave. After the air had been expelled from the autoclave with the aid of pure nitrogen, ethylene was introduced into the autoclave at room temperature under a pressure of up to 170 to 200 atm. The mixture was heated for a specified period, during which the pressure increased to 380- 480 atm. After the pressure had been released, the mixture was discharged and concentrated by partial evaporation of the solvent. The polymer was purified by precipitating three times in methanol. Finally the polymer was dissolved in benzene, the solution filtered and the polymer separated by freeze-drying.

Further details on the copolymerizations described above and the resulting acid polymers are tabulated in tables I and II.----------------------------------------------------------------------- ----TABLE II Molar Ratio of the Monomers in the Acid Copolymer Lauryl Stearyl Methacrylic Polymer Methacrylate Methacrylate Acid Ethylene _________________________________________________________________________ _ 1 5 5 3.1 22 2 5 5 2.8 20 3 5 5 3.0 21 4 5 5 3.7 19 5 5 5 3.9 12 6 10 2.6 30 7 10 3.7 19 8 10 2.9 27 9 10 2.7 44 _________________________________________________________________________ _

EXAMPLE II

The acid copolymers (1 to 9) from example I were converted into polymers I- IX according to the invention as follows:

To a solution composed of 20 g. of the acid copolymer and 48 mg. of lithium hydroxide in a solvent mixture comprising 9 g. of toluene and 71 g. of methanol, ethylene oxide was added at room temperature. The solution was kept at 95.degree. for 24 hours and subsequently cooled down to room temperature. The ethoxylated polymer was purified by precipitating two times in methanol. Further details on the ethyoxylation described above are collected in table III. ##SPC1##

EXAMPLE III

In order to assess the viscometric behavior of the polymers I- IX according to the invention they were dissolved in a concentration of 1.5 percent weight in a paraffinic base oil. The results of the viscometric determinations are listed in table IV. ##SPC2##

the above results definitely show the advantages of the polymers of the present invention with regards to improvement in viscosity index (VI) of a lubricating oil composition.

EXAMPLE IV

The thermal stabilities of the polymers according to the invention are recorded in table V. They were determined in vacuum at a rate of heating of 3.degree. C./min. The values T.sub.10, t.sub.20 and T.sub.50 represent the temperatures at which 10, 20 and 50 percent weight loss, respectively, of the polymer was attained. To test the present polymers as dispersants they were subjected to a peptization test. In this test the lowest concentration of additive is determined that is capable of keeping 0.015 percent weight of carbon in mineral oil in suspension for 15 minutes at 250.degree. C. Concentrations below 0.008 are considered favorable. The results of these peptization tests are also listed in table V.------------------------------------------------------------------ ---------TABLE V Polymer T.sub.10 T.sub.20 T.sub.50 Peptization Test, %w _________________________________________________________________________ _ I 330 355 390 0.001- 0.003 II 325 350 380 0.001- 0.003 III 350 375 405 0.004 IV 345 360 390 0.001- 0.003 V 335 360 390 0.003 VI 360 385 420 0.001- 0.003 VII 340 365 395 0.001- 0.003 VIII 340 365 395 0.005 IX 340 365 395 0.005 _________________________________________________________________________ _

the results of the peptization tests (in all cases <0.005 percent weight) may be considered very favorable.

From the above it is evident that the polymers of the present invention impart excellent dispersancy and viscosity index characteristics to lubricating oil as well as possessing excellent thermal stability.

Claims

1. An oil-soluble copolymer of ethylene with one or more C.sub.8.sub.-20 alkyl methacrylates and .beta.-hydroxyethyl methacrylate, said copolymer having an average molecular weight between 5,000 and 150,000 and in which the molecular ratios of monomers in the copolymer are 11- 300 moles ethylene to 10 moles C.sub.8.sub.-20 alkyl methacrylates to 1- 15 moles

2. The copolymer of claim 1 in which the copolymer is a copolymer of ethylene, a member selected from the group consisting of lauryl methacrylate and stearyl methacrylate and mixtures thereof, and

3. The copolymer of claim 1 in which the copolymer is a copolymer of

4. The copolymer of claim 1 in which the copolymer is a copolymer of ethylene, lauryl methacrylate, stearyl methacrylate and .beta.-hydroxyethyl methacrylate.