GB2144430A - Hydrogenated modified star-shaped polymers - Google Patents

Abstract

A process for the preparation of an oil-soluble, star-shaped product having viscosity index-improving and dispersant properties, comprises: (a) solution polymerizing one or more conjugated dienes and optionally one or more monoalkenyl arene monomers under polymerization conditions with an organolithium compound, forming living polymeric arms, (b) contacting said living polymeric arms with a polyalkenyl aromatic coupling agent forming a coupled polymer having a poly(polyalkenyl aromatic) nucleus and attached polymeric arms, and (c) optionally contacting said coupled polymer with a nitrogen-containing polar monomer, attaching poly(nitrogen-containing polar monomer) arms to said nucleus, characterized in that (d) the resulting product is contacted with a carbonyl group containing organic compound, e.g. acetaldehyde or acetone, and (e) the product resulting from step (d) is reduced by hydrogenation. n

Description

SPECIFICATION Process for the preparation of oil-soluble hydrogenated modified star-shaped polymers This invention relates to a process for the preparation of an oil-soluble, star-shaped product having viscosity index-improving and dispersant properties, comprising: (a) solution polymerizing one or more conjugated dienes and optionally one or more monoalkenyl arene monomers under polymerization conditions with an organolithium compound, forming living polymeric arms, (b) contacting said living polymeric arms with a polyalkenyl aromatic coupling agent forming a coupled polymer having a poly (polyalkenyl aromatic) nucleus and attached polymeric arms, and (c) optionally contacting said coupled polymer with a nitrogen-containing polar monomer, attaching poly (nitrogen-containing polar monomer) arms to said nucleus.

Such a process, wherein step (c) is essential, is known from European patent specification 82574 and the contents of this publication are incorporated in this specification. From this publication it is furthermore known to reduce the resulting product by hydrogenation of at least 80% of the aliphatic unsaturation of the polymeric arms while preferably reducing less than 20% of the aromatic unsaturation.

It appeared to be difficult and time-consuming to hydrogenate such nitrogen-modified star-shaped polymers.

It has now been found that hydrogenation can be made easy and fast, even somewhat faster than of the non-modified star-shaped polymers, by reaction, before hydrogenation, with one or more carbonyl group containing compounds, instead of nitrogen-containing monomers in order to introduce dispersant properties.

This invention therefore relates to the above-mentioned process, characterized in, that (d) the resulting product of step (b) and optionally step (c) is contacted with a carbonyl group containing organic compound, and (e) the product resulting from step (d) is reduced by hydrogenation of at least 80% of the aliphatic unsaturation of the polymeric arms while preferably reducing less than 20% of the aromatic unsaturation.

This invention furthermore relates to the resulting products and to oil compositions, in particular lubricating oil compositions or concentrates containing them.

Suitable conjugated dienes have 4 to 12 carbon atoms, such as butadiene and isoprene.

A preferred monalkenyl arene monomer is styrene.

A suitable organolithium compound is secondary-butyllithium.

A preferred polyalkenyl aromatic coupling-agent is divinylbenzene. This coupling-agent may also be considered as a comonomer.

The star-shaped polymer comprises preferably 5 to 15 polymeric arms, preferably at least 10 arms. The number average molecular weight (Mn) of each of the polymeric arms is from 5,000 to 150,000, preferably at least 35,000. The number average molecular weight of the star-shaped polymer is preferably from 25,000 to 1,500,000, more preferably above 300,000, e.g. 350,000 to 1,500,000, in particular 350,000 to 1,000,000.

Star-shaped polymers wherein each polymeric arm is a polyisoprene homopolymer are preferred.

The optional nitrogen-containing polar monomers preferably are 2- and 4-vinylpyridine. Other suitable compounds are described in European patent specification 82574.

Suitable carbonyl group containing compounds are saturated or unsaturated, linear or branched, aldehydes, ketones and esters.

Suitable aldehydes are acetaldehyde, propionaldehyde, aldehydes prepared via the Oxo-process, etc. The aldehydes may contain up to e.g. 30 carbon atoms, such as up to 20 carbon atoms.

Suitable ketones are acetones, methyl ethyl keton, methyl isopropyl ketone, etc. They may also contain up to e.g. 30 carbon atoms, such as up to 20 carbon atoms.

Suitable esters are esters of monoalkanols or polyols and mono- or poly carboxylic acids.

Suitable alcohols are (1-30 alkanols. Suitable polyols are diols such as glycols or polyglycols, triols such as trimethylolpropane, tetraols such as pentaerythritol.

Suitable acids are C1-30 fatty acids, such stearic acid or distearid acid.

Mixtures of these compounds can also be used.

Preferred compounds are acetaldehyde and acetone.

The preparation of the star-shaped polymers is well-known see e.g. European patent specification 82574.

In step (b) the polyalkenyl coupling agent should be added to the living polymer after the polymerization of the monomers is substantially complete, i.e., the agent should only be added after substantially all of the diene and optionally the monalkenyl arene monomer has been converted to living polymers.

The amount of polyalkenyl coupling agent added may vary between wide limits but preferably at least 0.5 mole is used per mole of unsaturated living polymer. Amounts of from 1 to 15 moles, preferably from 1.5 to 5 moles are preferred. The amount, which may be added in two or more stages, is usually such so as to convert at least 80 or 85%w of the living polymers into star-shaped polymers.

Step (b) may be carried out in the same solvents as for reaction step (a), preferably in cyclohexane. The temperature may vary between wide limits, e.g., from 0 to 150"C, preferably from 20 to 120"C. The reaction may take place in an inert atmosphere, e.g., nitrogen and under pressure, e.g., a pressure of from 0.5 to 10 bars.

The star-shaped polymers prepared in step (b) are characterized by having a dense centre or nucleus or cross-linked poly(polyalkenyl coupling agent) and a number of arms of substantially linear unsaturated polymers extending outwardly therefrom. The number of arms may vary considerably but is typically between 3 and 25, preferably from about 7 to about 15. Star-shaped homopolymers may be represented by the formula A-x A )n and star-shaped copolymers may be represented by the formula A-B-xS B-A )n wherein n is an integer, usually between 2 and 24 and x is the poly(polyalkenyl coupling agent)nucleus. From the above it can be seen that xis preferably a poly(polyvinyl aromatic coupling agent)nucleus and more preferably a poly-(divinylbenzene)nucleus.As stated above it is believed that the nuclei are cross-linked.

It has been found that the greater number of arms employed in the instant invention significantly improve both the thickening efficiency and the shear stability of the polymer since it is then possible to prepare a VI-improver having a high molecular weight (resulting in increased thickening efficiency) without the necessity of excessively long arms (resulting in improved shear stability).

In step (c), if applied, the star-shaped polymer is contacted with a nitrogen-containing polar compound monomer, resulting in the attachment of at least one polymer arm directly to the poly(polyvinyl aromatic)nucleus. If step (c) is applied the advantage of a fast hydrogenation is no longer obtained. Still, step (c) may be used if the introduction of nitrogen atoms is desired.

In the interests of simplicity, reference will now be made of vinylpyridine instead of nitrogen-containing polar compound.

After contacting the star-shaped polymer with the vinylpyridine monomer, the resulting star-shaped copolymer contains about 0.1 to about 10 per cent by weightvinylpyridine, preferably about 0.1 to about 5.0 per cent by weight. The number of poly(vinylpyridine)arms is typically between one and about 10, preferably between one and about 5. Accordingly, the molecular weight of the poly(vinylpyridine) arms is between about 105 and about 10,000, preferably between about 105 and about 1000.

The addition of the polar compound, preferably 2-vinylpyridine, to the poly(polyalkenyl aromatic)nucleus occurs at temperatures between -78OC and +80"C, preferably between 25"C and 60or, preferably in a solvent such as cyclohexane.

In step (d) the living star-shaped polymer resulting of either step (b) or (c), i.e. a polymer which contains lithium ions, is reacted with one or more of the carbonyl group containing compounds. This reaction results in replacing each living end by one secondary or tertiary OH-group, simultaneously terminating the active sites.

The resulting stars have the polar groups attached to their cores. Contrary to the reaction with the vinyl pyridines the OH-groups do not adversely affect the rates of the subsequent hydrogenation step (e). The maximum number of OH-groups which can be introduced by reaction with carbonyl groups is limited by the number of living ends.

Step (d), which may take less than e.g. 15 minutes, may be carried out in the same solvent as used in step (b), preferably cyclohexane and at the same temperature as used in step (b), e.g. at O150tC, preferably 20 to 120aC. The molar ratio carbonyl groups: Li ionsise.g. between 10:1 and 1 :10, preferably about 1:1. A slight excess of carbonyl groups, e.g. up to 10 mole % is preferred. An alcohol such as methanol, ethanol, isopropanol or higher alcohols, such as 2-ethyl hexanol, may be added to kill any remaining Li ions. Small amounts, e.g. up to 1 0%w on polymer, are usually sufficient. Higher alcohols mix better with solvents such as cyclohexane.

In step (e), the star-shaped polymers are hydrogenated by any suitable technique e.g. such as described in European patent specification 82754. Suitable at least 80%, preferably 90 to 98%, more preferably 95-98% of the original olefinic unsaturation is hydrogenated. If the star-shaped polymer is partly derived from a monoalkenyl arene compound, then the amount of aromatic unsaturation which is hydrogenated, if any, will depend on the hydrogenation conditions used. However, preferably less than 20%, more preferably less than 5% of such aromatic unsaturation is hydrogenated. If the poly(polyaikenyl coupling agent)nucleus is a poly(polyalkenyl aromatic coupling agent)nucleus,then the aromatic unsaturation of the nucleus may or may not be hydrogenated again depending upon the hydrogenation conditions used.

Although linear polymers can be modified as described herein, the shear stability will be lower than the present modified star-shaped polymers as explained hereinbefore.

The reaction product of this invention can be incorporated in oil compositions, in particular lubricating oil compositions, e.g., automotive crankcase oils, in concentrations with the range of 0.001 to 15, in particular 0.1 to 15 preferably 0.1 to 3 %w based on weight of the total compositions. The lubricating oils to which the additives of the invention can be added include not only mineral lubricating oils, but synthetic oils also.

Synthetic hydrocarbon lubricating oils may also be employed, as well as non-hydrocarbon synthetic oils including dibasic acid esters such as di-2-ethyl hexyl sebacate, carbonate esters, phosphate esters, halogenated hydrocarbons, polysilicones, polyglycols, glycol esters such as C13 oxo acid diesters of tetraethylene glycol, etc. Mixtures of these oils, in particular of mineral lubricating oils, including hydrogenated oils, and synthetic lubricating oil, can also be used.

When used in gasoline or fuel oil, e.g., diesel fuel, etc., then usually 0.001 to 0.5 %w, based on the weight of the total composition of the reaction product will be used.

Concentrates comprising a minor proportion, e.g., 15 to 45 O/ow of said reaction product in a major amount of hydrocarbon diluent, e.g., 85 to 55 O/ow mineral lubricating oil, with or without other additives present, can also be prepared for ease of handling.

In the above compositions or concentrates, other conventional additives may also be present, including dyes, pour point depressants, antiwear, e.g., tricresyl phosphate, zinc dialkyl dithiophosphate of 3 to 8 carbon atoms, antioxidants such as phenyl-alpha-naphthyl-amine, tert-octylphenol suiphide, bisphenols such as 4,4'-methylene bis(3,6-di-tert-butylphenol), viscosity index improvers such as the ethylene-higher olefin copolymer, polymethylacrylates, polyisobutylene, alkyl fumaratevinyl acetate copolymers, and the like as well as other ashless dispersants or detergents such as overbased sulphonates.

The invention is further illustrated by the following Examples.

Example 1 Preparation of an acetone-terminated star polymer.

850 g of isoprene in 3400 g of dry cyclohexane were polymerized under nitrogen with Li-sec-butyl between 72-80 C to a "living" polyisoprene with Mn =35000. 113 g of this solution were withdrawn for analytical purposes.

Then 3.2 equivalents/Li of dry technical grade divinylbenzene (DVB) (78.3 ml of a solution in cyclohexane containing 0.964 mol/l) were added and the coupling reaction was allowed to proceed for 2 hours. After cooling to 500C a sample of 110 g was saved for analysis followed by the addition of 291.8 ml of a dry solution of 0.0869 mol/l of acetone in cyclohexane which caused the colour of the solution to change from orange/brown to pale yellow. Then 51.5 ml of a solution of 0.407 mol/l of 2-ethyl-hexanol in cyclohexane were added and a sample was saved for analysis.

Hydrogenation was effected as usual applying a catalyst prepared from aluminium triethyl and Ni-octoate (1.16g Ni/kg of polymer). Degree of hydrogenation of aliphatic double bonds: 99.5 % (by ozone titration after 4.4 hrs).

Molecular weights All molecular weights were determined by GPC (gel permeation chromatography): 1) MR of linear polyisoprene 36.000 2) M(peak) of star after reaction with acetone 379.000 3) Coupling yield; % : 94 4) M(peak) of hydrogenated star : 442.000 Viscometry The viscometric evaluation was carried out in a 10V2/50 super motor oil formulation containing 1.64 %w of the functionalized star polymer, 15 %w of a commercial addition package and 0.3 %w of a polyalkyl methacrylate pour point depressant in HVI-oil Kuwait (V.k. 4.9 cSt at 1000C), (HVI= high viscosity index Vk= kinematic viscosity): Vk(100 C) 19.6cSt Vk (40 C) 131.0 cSt Vk(150 C) : 7.63cSt Vi (viscosity index) 171 V(-180C) 2.18 Pa.s Shearloss DIN 51382; % : 4 Example 2 Preparation of an acetaldehyde-terminated star polymer.

The same "living" star polymer was prepared under the same conditions. After the first step 113 grams of solution were taken for analysis. Coupling was effected with 73.6 ml of a solution of 0.964 mol/l of divinyl benzene in cyclohexane applying the same reaction conditions reported above for the coupling step. A 140 g sample was saved for analysis. The "living" star shaped polyisoprene was then reacted with 28.9 ml of a 0.95 molar solution of dry accetaldehyde in cyclohexane. During the reaction the colour of the solution changed from orange/brown to pale-yellow. After saving of a 186 gram sample 82.2 ml of a 0.407 molar solution of 2-ethyl-hexanol-1 in cyclohexane were added.

Hydrogenation was carried out under the conditions described for the acetone-modified star polymer.

Degree of hydrogenation: 99.6 (by ozone titration after 3.8 hrs).

Molecular weights All molecular weights are by GPC.(gel permeation chromatography): 1) Mri of linear polyisoprene : 35.000 2) M(peak) of star after reaction with acetaldehyde : 397.000 3) coupling yield; % : 94 4) M(peak) of hydrogenated star : 416.000 Viscometry The viscometric evaluation was carried out using (1.64) %w of polymer.in the same formulation as above: Vk(100"C) 19.35 cSt Vk (40"C) . 130.3 cSt Vk(150 C) : 7.82 cSt Vl 169 Shearloss DIN 51382: % : 3.6 Sequence - VD performance Ail formulations contained identical percentages of V!-improver and a dispersant/detergent package containing a reduced percentage of ashless dispersant in order to make the engine performance of the blends more sensitive to changes of dispersancy due to the presence of a dispersant/VI-improver.

Non-modified hydrogenated star polymer Ex. 2 of of polymer : 1.5 1.5 average sludge : 8.4 9.1 piston skirt varnish : 7.3 6.2 average engine varnish : 4.1 3.6 average cam lobe wear; micron 55 10

Claims (6)

1. A process for the preparation of an oil-soluble, star-shaped product having viscosity index-improving and dispersant properties, comprising: (a) solution polymerizing one or more conjugated dienes and optionally one or more monoalkenyl arene monomers under polymerization conditions with an organolithium compound, forming living polymeric arms, (b) contacting said living polymeric arms with 3 polyalkenyl aromatic coupling agent forming a coupled polymer having a poly(polyalkenyl aromatic)nucleus and attached polymeric arms; and (c) optionally contacting said coupled polymer with a nitrogen-containng polar monomer, attaching poly(nitrogen-containng polar monomer) arms to said nucleus, characterized in, that (d) the resulting product is contacted with a carbonyl group containing organic compound, and (e) the product resulting from step (d) is reduced by hydrogenation of at least 80% of the aliphatic unsaturation of the polymeric arms while preferably reducing less than 20% of the aromatic unsaturation.

2. A process as claimed in claim 1, wherein the carbonyl group containing compound is acetaldehyde or acetone.

3. A process as claimed in claim 1 or 2, wherein step (d) is carried out at 20-120 C.

4. A process as claimed in claim 1, substantially as hereinbefore described with special reference to the Examples.

5. A product whenever prepared according to the process as claimed in any one of claims 1-4.

6. An oil composition, in particular a lubricating oil composition or concentrate, comprising an oil and 0.001-45 %w of a product as claimed in clairn 5.