| abstract |
A polymer suitable for use as a viscosity index improver for lubricating oil compositions, comprising a hydrogenated linear polymer characterized by the formula (1) and a hydrogenated star polymer characterized by the formula: Formula 1 D'-PA-D " (2) (D'-PA-D ") n -X In this formula, D 'represents an "external" block derived from dienes having a number average molecular weight of from about 10,000 to about 120,000 daltons; PA represents a block derived from monoalkenyl arene having a number average molecular weight of from about 10,000 to about 50,000 daltons; Quot; D "represents an internal random number derived from diene having a number average molecular weight of from about 5,000 to about 60,000 daltons; and n represents a forming polymer formed by reaction of at least two moles of polyalkenyl coupling agent per mole of arm And X represents the nucleus of the polyalkenyl coupling agent. |