Viscosity index improver for lubricant compositions

1. A lubricant composition comprising:

(i) a base oil; and

(ii) an ethylene/α-olefin interpolymer comprising a hard segment and a soft segment, wherein the ethylene/α-olefin interpolymer:

(a) has a Mw/Mn from about 1.7 to about 3.5;

(b) has an ethylene content in the hard segment in the range of from 70 wt % to 85 wt % based on total monomer content in hard segment;

(c) (i) has a hard segment composition of at least 40%, at least one melting point, Tm, in degrees Celsius and an amount of ethylene in weight percent, wt % C 2 , wherein the numerical values of Tm and wt % C 2 correspond to the relationship:

90° C.≧ Tm≧ 4.1276(wt % C 2 )−244.76; or

(ii) has a hard segment composition of less than 40%, at least one melting point, Tm, in degrees Celsius and an amount of ethylene in weight percent, wt % C 2 , wherein the numerical values of Tm and wt % C 2 correspond to the relationship:

80° C.≧ Tm≦ 4.1276(wt % C 2 )−264.95; or

(iii) is characterized by an average block index greater than zero and up to about 1.0; or

(iv) has a molecular fraction which elutes between 0° C. and 130° C. when fractionated using low temperature TREF, characterized in that the fraction has a molar comonomer content of at least 5 percent higher than that of a comparable random ethylene interpolymer fraction eluting between the same temperatures, wherein said comparable random ethylene interpolymer has the same comonomer(s) and has a melt index, density, and molar comonomer content (based on the whole polymer) within 10 percent of that of the ethylene/α-olefin interpolymer; or

(v) has a relationship between ethylene content in wt % and log molecular weight such that a line plotted of ethylene content vs log molecular weight as measured by GPC-IR has an absolute slope, m, of equal to or less than 4 ; and,

(d) has a turbidity measurement of a 1.0 wt % solution of the ethylene/α-olefin interpolymer in oil or a 1.5 wt % solution in dodecane of less than or equal to that of a comparable copolymer wherein the comparable copolymer has the same DSC enthalpy (J/g) at greater than 55° C. within ±5 J/g, and the same overall ethylene content within 10%; and

wherein the soft segment comprises 35 wt % to 80 wt % comonomer.

2. The lubricant composition of claim 1 , wherein the α-olefin is styrene, propylene, 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene, norbonene, 1-decene, 1,5-hexadiene, or a combination thereof.

3. The lubricant composition of claim 1 or 2 , wherein the base oil is selected from the group consisting of the base stocks of API Groups I, II, III, IV and V and combinations thereof.

4. The lubricant composition of claim 1 , wherein the base oil is a natural oil, a synthetic oil or a combination thereof.

5. The lubricant composition of claim 1 , wherein the lubricant composition further comprises at least an additive.

6. The lubricant composition of claim 5 , wherein the additive is a detergent, a dispersant, a friction modifier, a pour point depressant, a demulsifier, an anti-foam, a corrosion inhibitor, an anti-wear agent, an antioxidant, a rust inhibitor, a thickener or a combination thereof.

7. The lubricant composition of claim 1 , wherein the lubricant composition is a motor oil, a transmission fluid, a gear oil, a power steering fluid, a shock absorber fluid, a brake fluid, a hydraulic fluid or a grease.

8. The lubricant composition of claim 7 , wherein the lubricant composition is a motor oil.

9. The lubricant composition of claim 8 , wherein the motor oil further comprises a pour point depressant, a detergent, a dispersant, an anti-wear, an antioxidant, a friction modifier, a rust inhibitor or a combination thereof.

10. The lubricant composition of claim 7 , wherein the lubricant composition is a transmission fluid.

11. The lubricant composition of claim 10 , wherein the transmission fluid further comprises a friction modifier, a detergent, a dispersant, an antioxidant, an anti-wear agent, an extreme pressure agent, a pour point depressant, an anti-foam, a corrosion inhibitor or a combination thereof.

12. The lubricant composition of claim 7 , wherein the lubricant composition is a gear oil.

13. The lubricant composition of claim 12 , wherein the gear oil further comprises an anti-wear, an extreme pressure agent, a rust inhibitor or a combination thereof.

14. The lubricant composition of claim 7 , wherein the lubricant composition is a grease.

15. The lubricant composition of claim 14 , wherein the grease further comprises a thickener, a complexing agent, an antioxidant, an anti- wear agent, an extreme pressure agent, an anti-foam, a corrosion inhibitor or a mixture thereof.