Abstract: Lubricating oil compositions and viscosity index (VI) improver concentrates containing combinations of first polymers that are amorphous ethylene ?-olefin copolymers; and second polymers that are star polymers, the arms of which are derived from diene, and optionally vinyl aromatic hydrocarbon monomer, wherein the star polymers have a Shear Stability Index (SSI) of from about 1% to about 35% (30 cycle).

Abstract: Oil soluble viscosity index improver composition comprising a mixture of: (A) at least one molecular weight degraded copolymer of ethylene and at least one other alpha-olefin monomer; and (B) at least one substantially undegraded copolymer of ethylene and at least one other alpha-olefin monomer. The ethylene alpha-olefin copolymers before degradation can be polymerized by a variety of available technologies including Ziegler-Natta, metallocene and diimine catalysis, as well as batch, continuous stirred tank and tubular reactors to produce copolymers having both broad or narrow molecular weight and compositional distributions. Use of degraded/non-degraded copolymer mixtures facilitates the preparation of viscosity index improvers for oils having targeted levels of shear stability index.