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.

The disclosure relates to viscosity improver concentrates comprising a bio-based liquid decarboxylated rosin acid as a solubilizer, and a viscosity index improver. The viscosity improver concentrate is used in lubricating oil compositions comprising base oil and optional additives. The decarboxylated rosin acid component has at least one or more of: one or more CC groups, and 40-100 wt. % of tricyclic compounds having 18-20 carbon atoms; a sum of tricyclic compounds as aromatic and cycloaliphatic of 50-100 wt. %, based on total weight of the decarboxylated rosin acid; and an amount of cycloaliphatic compounds of 15-100 wt. %, based on total weight of the decarboxylated rosin acid. The viscosity improver concentrates comprising the solubilizer have comparable properties, including compatibility, kinematic viscosity, and viscosity index, to other commonly used fossil based solubilizers.

Provided are functional polymers based on functionalized styrenic monomers including a nitrogen-containing moiety, other than as pendant to the phenyl ring that are polymerized from addition-polymerizable monomer compositions including amine-derivatized alpha-methyl styrene (ADAMS) monomers according to structure (I).

##STR00001##

wherein k is an integer from 1 to 3, preferably 2; wherein R.sub.1 is a methyl group or a phenyl group and R.sub.2 is a benzyl group, or wherein R.sub.1 and R.sub.2 are connected to form a moiety containing one 6-membered ring, with four carbons, bearing an O or NCH.sub.3 group at the 4-position of the 6-membered ring; wherein R, in structure (I), is hydrogen, a phenyl ring co-attached at two neighboring ring carbon positions with the phenyl ring shown so as to form a naphthalene assembly, a phenyl group attached at a single carbon of the phenyl ring shown, a C.sub.1-C.sub.4 hydrocarbyl group (such as a methyl group), a C.sub.1-C.sub.6 hydrocarbyl group containing 1 to 4 additional heteroatoms (such as O, N, S, P, Se, and combinations thereof). Also provided are methods of using such functional polymers in lubricating oil compositions.

A lipophilic copolymer including polar multi-blocks having general formula (I):
[(B.sub.yA.sub.k).sub.s].sub.t(A.sub.jC.sub.m)(I)
wherein: B represents at least one monomer unit deriving from a lipophilic monomer having general formula (II): ##STR00001## wherein: X represents a hydrogen atom; or a methyl group; R is selected from C.sub.1-C.sub.50 alkyl groups, linear or branched; A represents at least one monomer unit deriving from a polar monomer selected from: (a) compounds having general formula (III): ##STR00002## wherein X represents a hydrogen atom or a methyl group and n represents an integer comprised between 0 and 4; (b) (meth)acrylamide or (meth)acrylamides substituted on the nitrogen atom with one or two C.sub.1-C.sub.4 alkyl groups linear or branched; (c) di-(C.sub.1-C.sub.4)-alkylamino-(C.sub.1-C.sub.4)-alkyl (meth)acrylates; C represents at least one monomer unit deriving from a polar polyfunctional monomer having general formula (IV):
Z(W).sub.p(IV) wherein: Z represents a group containing carbon, hydrogen and, optionally, oxygen; and W represents a function able to react covalently with an alkyl radical.

A lipophilic copolymer including polar multi-blocks having general formula (I):

##STR00001##

wherein: B represents at least one monomer unit deriving from a lipophilic monomer having general formula (II):

##STR00002## wherein: X represents a hydrogen atom; or a methyl group; R is selected from C.sub.1-C.sub.50 alkyl groups, preferably C.sub.1-C.sub.30, linear or branched; A represents at least one monomer unit deriving from a polar monomer selected from: (a) compounds having general formula (III):

##STR00003## wherein X represents a hydrogen atom or a methyl group and n represents an integer comprised between 0 and 4; (b) (meth)acrylamide or (meth)acrylamides substituted on the nitrogen atom with one or two C.sub.1-C.sub.4 alkyl groups, linear or branched; (c) di-(C.sub.1-C.sub.4)-alkylamino-(C.sub.1-C.sub.4)-alkyl (meth)acrylates; C represents at least one monomer unit deriving from a polar polyfunctional monomer having general formula (IV):

##STR00004## wherein: Z represents a group containing carbon, hydrogen and, optionally, oxygen; and W represents a function able to react covalently with an alkyl radical.

A lubricating oil composition may include a base oil (A), succinimide (B) which has not been modified with boron, succinimide (C) modified with boron, a metallic detergent (D), and an antioxidant (E), wherein the ratio of the content of boron atoms derived from ingredient (C) to the content of nitrogen atoms derived from ingredients (B) and (C), B/N, is 0.30 or less by mass, the lubricating oil composition satisfying requirement (I) and/or requirement (II). Requirement (I): Ingredient (D) includes a metallic detergent (D1) having a base value less than 100 mgKOH/g. Requirement (II): Ingredient (E) includes an amine-based antioxidant (E1), the content of ingredient (E1) being 1.00 mass % or less.