Disclosed is a star copolymer (C) including at least 10 wt. % of units derived from styrene monomer and including arms that include a statistical copolymer (EP) including ethylene units and propylene units, and the method for preparing same. Also disclosed is the use thereof in lubricating compositions, in particular for improving the viscosity index, to the lubricating compositions thus obtained and to the uses thereof.

The present invention provides a process for preparing a polymer, employing the steps of: (1) contacting a free radical initiator; a chain transfer agent containing a thiocarbonyl thio group and a free radical leaving group; and a radically polymerisable monomer, to form a polymer chain; and (2) contacting the polymer chain of step (1) with at least one of a polyvalent coupling agent, a polymerisation inhibitor, a grafting acylating agent, an amine and an oil of lubricating viscosity. The invention further provides compositions and uses for the polymer.

An engine oil composition includes a star polymer (A) and a poly(alkyl (meth)acrylate) (B) as a viscosity index improver, and has a viscosity index of 185 to 230, the star polymer (A) having a star structure and having a weight average molecular weight of 100,000 to 1,000,000, the star structure being a structure in which polymer chains branch from a center of the polymer, the polymer chains being obtained by copolymerization and hydrogenation of an aromatic vinyl compound monomer and a conjugated diene monomer, the poly(alkyl (meth)acrylate) (B) having a weight average molecular weight of 200,000 to 600,000, the content (M.sub.A) of the star polymer (A) in the engine oil composition being 0.10 to 2.00 mass % based on the total mass of the engine oil composition, the content (M.sub.B) of the poly(alkyl (meth)acrylate) (B) in the engine oil composition being 0.50 to 6.00 mass % based on the total mass of the engine oil composition, and the ratio M.sub.A/M.sub.B being 0.10 to 1.00. The engine oil composition can significantly improve fuel efficiency, and is suitably used for a diesel engine.

A viscosity index improver containing, in diluent oil, one or more optionally functionalized linear block copolymers having at least one block derived from alkenyl arene covalently linked to at least one block derived from diene in an amount that is greater than the critical overlap concentration (c.sub.h*), in mass %, for the linear block copolymers in the diluent oil; and ester base stock and/or at least one star (or radial) polymer, the star polymer being present in an amount such that the c/c.sub.h* value of the star polymer in the concentrate falls within the range of from 0.01 to about 1.6, wherein c is the concentration in mass % of star polymer in the concentrate and c.sub.h* is the critical overlap concentration in mass % for the star polymer in the diluent oil used to form the concentrate.

A lubricant composition comprising (a) an oil of lubricating viscosity; (b) a (meth)-acrylate-containing polymer comprising a multiplicity of arms containing at least 20 carbon atoms, said arms being attached to a multivalent organic moiety; and (c) an ethylene/olefin copolymer having a weight average molecular weight of about 10,000 to about 250,000, wherein the copolymer comprises about 40 to about 70 weight percent polymerized ethylene monomers and optionally further comprises polymerized propylene monomers; exhibits good viscometric and antiwear properties.

The invention provides a method of lubricating an internal combustion engine equipped with a centrifugal oil mist separator, wherein the lubricant contains 0.1 wt % to 8 wt % soot resulting from operation of the engine, and wherein the lubricant composition comprises an oil of lubricating viscosity, and 0.2 wt % to 3 wt % of a soot dispersing additive having a shear stability index of 0 to 25, wherein the soot dispersing additive comprises a block copolymer comprising (i) a vinyl aromatic monomer block and (ii), a conjugated diene olefin monomer block.

The invention provides a composition comprising: (a) a star polymer comprising: (i) a core portion comprising a polyvalent (meth) acrylic monomer, oligomer or polymer thereof or a polyvalent divinyl non-acrylic monomer, oligomer or polymer thereof; and (ii) at least two arms of polymerized alkyl (meth)acrylate ester; and (b) an oil of lubricating viscosity, wherein the core portion further comprises a functional group of formula (I):

CH.sub.2C(R.sup.1)(C(O)A)-Y(I)

wherein R.sup.1 is hydrogen, a linear or branched alkyl group containing 1 to 5 carbon atoms; A is nitrogen or oxygen; and Y is a free radical leaving group selected from the group consisting of one or more atoms or groups of atoms which may be transferred by a radical mechanism under the polymerisation conditions, a halogen, an ON group and an SC(S) group. The invention further provides the use of the composition in an oil of lubricating viscosity as a dispersant, a viscosity modifier or a precursor to a dispersant viscosity modifier.

This invention relates to a lubricating oil composition, or concentrate therefor, comprising or resulting from the admixing of: (i) base oil, (ii) one or more styrenic block copolymers having a radial structure where one or more blocks derived from conjugated diene monomers are distal to the radial center and one more blocks derived from vinyl aromatic monomers that are proximal to the radial center, and (iii) optionally one or more dispersants and or detergents.

The present application relates to the use of a lubricant composition comprising a base oil and a hydrogenated diene styrene polymer to reduce engine particulate emissions.

Hydrogenated polymers with a radial structure having a core made up of calixarenes of the general formula (I), to the core of which is linked a number P of hydrogenated linear polymer segments selected from: hydrogenated homopolymers or copolymers of conjugated dienes; or hydrogenated copolymers of said conjugated dienes and monoalkenyl arenes, and mixtures thereof said formula (I) in which: R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently selected from hydrogen; a group containing carbon and hydrogen; a group also containing heteroatoms in addition to carbon and hydrogen; a group also containing silicon in addition to carbon, hydrogen and heteroatoms; one of the two substituents R.sub.5 and R.sub.6 is hydrogen, while the other may be hydrogen or alkyl, with a number of carbon atoms between 1 and 6, preferably methyl and ethyl; n is an integer in the range between 4 and 16.

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