Polymer blends useful as viscosity modifiers

A composition, comprising:

• (I) an oil of lubricating viscosity;
• (II) a hydrogenated copolymer comprising at least one of block A and at least one of block B, block A comprising an olefin polymer block, block B comprising a vinyl aromatic polymer block, the mole ratio of monomer units in block A to monomer units in the combination of block A plus block B being in the range from 0.5 to 0.9;
• wherein from 40 to 75 mol % of the repeat units in block A contain alkyl branching groups, wherein the hydrogenated copolymer is not functionalized;
• and
• (III) a radial polymer comprising a core and from 3 to 12 polymeric arms extending from the core, each arm being derived from one or more conjugated dienes and one or more monoalkenyl aromatic hydrocarbons, each arm having a weight average molecular weight in the range from 40,000 to 200,000, each arm being hydrogenated at from 90 to 100% of the available double bonds, the radial polymer having a weight average molecular weight in the range from 300,000 to 2,500,000;
• wherein the composition is an engine oil, and wherein the composition has (a) a sulphur content of 0.5 wt % or less, (b) a phosphorus content of 0.1 wt % or less, and (c) a sulphated ash content of 1.5 wt % or less.