| abstract |
Polymers suitable for use as a viscosity index improver for lubricating oil compositions including linear polymers characterized by the formula: n D′-PA-D″;n and star polymers characterized by the formula: nn (D′-PA-D″) n -X;n wherein D′ represents an “outer” block derived from diene 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; D″ represents an inner random derived from diene having a number average molecular weight of from about 5,000 to about 60,000 daltons; n represents the average number of arms per star polymer formed by the reaction of 2 or more moles of a polyalkenyl coupling agent per mole of arms; and X represents a nucleus of a polyalkenyl coupling agent. |