Abstract: A composition prepared by adding as the sliding properties improving agent a small amount of ethylene-&agr;-olefin random copolymer having polar groups to engineering plastics including polyacetal, ABS, and polyamide is suitable for the manufacture of gears, rotary shafts and bearings by way of exploiting its molding processibility including excellent mold release properties, and at the same time is capable of enhancing its friction/wear resistance. As the sliding properties improving agent, an oxidation-modified material produced from ethylene-&agr;-olefin random copolymer or a graft-modified material prepared by graft-copolymerizing an ethylenic unsaturated monomer having carboxylic acid group, hydroxyl group or the like with ethylene-&agr;-olefin random copolymer is particularly preferable.

Abstract: A lubricating oil composition comprising a major proportion of a lubricating oil, and an oil-soluble graft copolymer, said graft copolymer being prepared by grafting a small amount of a grafting monomer selected from saturated esters of unsaturated monocarboxylic acids, unsaturated esters of saturated carboxylic acids and unsaturated epoxy compounds to a trunk copolymer which is substantially free from an oxygen-containing functional group and a carbon-carbon double bond determined from its iodine value and has a number average molecular weight of about 5,000 to about 100,000, said trunk copolymer being selected from copolymers of alpha-olefins having 2 to 20 carbon atoms, copolymers of styrene and alpha-olefins having 2 to 20 carbon atoms and hydrogenated products of copolymers of styrene and diolefins. A process for preparation of said composition is also provided.