Abstract: A process for preparing viscosity index improvers for lubricating oils consisting of thermally cracking a solution of an olefin copolymer in mineral oil at a temperature of between 250.degree. C. and 350.degree. C. in an inert atmosphere said solution containing free radical scavengers.

Abstract: Organic esters, to be employed to make up lubricating compositions are disclosed, said esters being the products of the reaction between a diol and a triol, on the one hand, and a mixture of saturated monocarboxylic acids, on the other hand. The ratios of the diol to the triol (molarly) and the structure and number of carbon atoms of the saturated monocarboxylic acids are critical. Critical values are given, as well as examples of practical use; the viscosity and viscosity index properties of the novel esters out do those of the conventional esters to a degree.

Abstract: An ester, adapted for use as a component of a multigrade lubricating oil, is prepared by reacting:A. A mixture of bifunctional and trifunctional polyols wherein the molar ratio of the bifunctional polyols to the trifunctional polyols is in the range of 1:2.5 to 1:10; andB. A mixture of linear monocarboxylic acids containing from 6 to 8 carbon atoms, wherein the molar average is C.sub.7, and of linear monocarboxylic acids containing from 12 to 18 carbon atoms, the molar ratio of the C.sub.6 to C.sub.8 acids and the C.sub.12 to C.sub.18 acids being in the range of from 4:1 to 19:1.

Abstract: A mineral or synthetic lubricating oil is protected against oxidation by dissolving therein, at a temperature not higher than 80.degree. C, a 3-aza-6a-thio-thiophthene or a 3,4-diaza-6a-thio-thiophthene represented by the general formulae: ##STR1## wherein, R, R.sub.1 and R.sub.2, the same or different, represent hydrogen, alkyl, cycloalkyl, aryl, alkylaryl, arylalkyl or aminoaryl.

Abstract: This invention relates to esters prepared by reactingA. a mixture of tri-, tetra- and hexafunctional polyols in which the molar ratio of the trifunctional polyol to the other polyols is from about 0.5:1 to 10:1 and in which the molar ratio of the hexafunctional polyol to the tetrafunctional polyol is from about 0 to 1.2:1, andB. a mixtue of linear alkyl monocarboxylic acids comprised of (i) one or more acids having from 7 to 8 carbon atoms and (ii) one or more acids having from 12 to 18 carbon atoms, the molar ratio of the acids (i) to the acids (ii) being from about 1.5:1 to 6:1.The invention also relates to lubricating compositions comprised of the esters.

Abstract: A composition comprising a poly-alkyleneglycol is stablized against molecular degradation and viscosity loss at elevated temperatures by about 0.1 to about 10% by weight of an arylhydroquinone such as p-acetylphenylhydroquinone.