Poly (meth)acrylate star polymers for lubricant additive applications

1. A poly(meth)acrylate star polymer comprising a polymer of Formula I

[(PMA)-Q-R 1 —C(O)—O—CH 2 ] m —C-A n   (Formula I)

wherein

PMA is a polymeric chain with randomly polymerized (meth)acrylate monomer units including from about 20 to about 35 mole percent short chain alkyl (meth)acrylate monomer units with alkyl chain lengths of 1 to 4 carbons, about 60 to about 80 mole percent long chain alkyl (meth)acrylate monomer units with alkyl chain lengths of 12 to 20 carbons, and optionally about 5 to about 10 mole percent oxygen-functional alkyl (meth)acrylate monomer units with hydroxy alkyl chains including 2 to 7 carbons;

each Q is independently a sulfur atom;

R 1 is an alkylene group of 1 to 10 carbons;

A is hydrogen, an alkyl group, or a group independently selected from Formula A1, A2, or A3:

—O—C(O)—R 1 -Q-(PMA)  (Formula A1);

—C(A1)CH 2 —O—C(O)—R 1 -Q-(PMA)  (Formula A2);

—CH 2 —O—CH2—C—[CH 2 —O—C(O)-Q-(PMA)] r   (Formula A3);

m is an integer from 1 to 4 and if m is less than 4, then A includes at least one group independently selected from the hydrogen, the alkyl group or the Formulas A1, A2, or A3;

n is 0 or an integer from 1 to 4;

r is an integer from 1 to 3;

wherein the groups associated with the m integer, A, and the groups associated with the r integer are bonded only to the carbon atom adjacent thereto;

wherein the poly(meth)acrylate star polymer has a weight average molecular weight of about 20 to about 500 Kg/mol and a polydispersity index of greater than 1.1 to about 4.0.

2. The poly(meth)acrylate star polymer of claim 1 , wherein the short chain alkyl (meth)acrylate monomers include about 10 to about 30 mole percent of a dispersant monomer.

3. The poly(meth)acrylate star polymer of claim 2 , wherein the dispersant monomer is a (meth)acrylate monomer of the formula

wherein R 3 is a hydrogen or methyl, p is an integer from 1 to 6, R 4 is independently a C 1 to C 4 alkyl group, and A is —O— or —NH—.

4. The poly(meth)acrylate star polymer of claim 1 , wherein the polymer exhibits a viscosity index of about 200 or greater.

5. The poly(meth)acrylate star polymer of claim 1 , wherein n is 0, and m is 4.

6. The poly (meth)acrylate star polymer of claim 1 , wherein the oxygen-functional alkyl (meth)acrylate monomers are selected from hydroxy ethyl (meth)acrylate, hydroxy propyl (meth)acrylate, 1-hydroxy propyl (meth)acrylate, 2-hydroxy propyl (meth)acrylate, and combinations thereof.

7. A poly (meth)acrylate star polymer comprising;

a free radical polymerization product of a polyfunctional thiol core and (meth)acrylate monomers wherein the polymerization product has a weight average molecular weight of about 20 to about 500 Kg/mol and a polydispersity index of greater than 1.5 to about 4.0;

the polyfunctional thiol core obtained from a reaction product of a tri- to hexa-functional alcohol and a mercaptocarboxylic acid;

the (meth)acrylate monomers include about 20 to about 35 mole percent short chain alkyl (meth)acrylate monomers with alkyl chain lengths of 1 to 4 carbons, about 60 to about 80 mole percent long chain alkyl (meth)acrylate monomers with alkyl chain lengths of 12 to 20 carbons, and optionally about 5 to about 10 mole percent oxygen-functional alkyl (meth)acrylate monomers with hydroxyl alky chains including 2 to 7 carbons.

8. The poly (meth)acrylate star polymer of claim 7 , wherein the tri- to hexa-functional alcohol forming the polyfunctional thiol core is selected from glycerol, pentaerythritol, dipentaerythritol, tripentaerythritol, trimethylolethane, trimethylolpropane, pentahydroxypentane, and mixtures thereof.

9. The poly (meth)acrylate star polymer of claim 7 , wherein the mercaptocarboxylic acid is selected from mercaptoacetic acid, mercaptopropionic acid, mercaptobutyric acid, mercaptopentanoic acid, mercaptohexanoic acid, mercaptodecanoic acid, and combinations thereof.

10. The poly (meth)acrylate star polymer of claim 7 , wherein the oxygen-functional alkyl (meth)acrylate monomers are selected from hydroxy ethyl (meth)acrylate, hydroxy propyl (meth)acrylate, 1-hydroxy propyl (meth)acrylate, 2-hydroxy propyl (meth)acrylate, and combinations thereof.

11. The poly (meth)acrylate star polymer of claim 7 , wherein the weight average molecular weight is about 40 to about 300 Kg/mol.

12. The poly (meth)acrylate star polymer of claim 7 , wherein the polymer has a kinematic viscosity at 100° C. of about 50 to about 1500 cSt.

13. A lubricating oil composition comprising:

a major amount of a lubricating oil;

a viscosity index improving polymer including a polymerization product of a polyfunctional thiol and (meth)acrylate monomers forming the polymer of Formula I

[(PMA)-Q-R 1 —C(O)—O—CH 2 ] m —C-A n   (Formula I)

wherein

PMA is a polymeric chain with randomly polymerized (meth)acrylate monomer units including about 20 to about 35 mole percent short chain alkyl (meth)acrylate monomer units with alkyl chain lengths of 1 to 4 carbons, about 60 to about 80 mole percent long chain alkyl (meth)acrylate monomer units with alkyl chain lengths of 12 to 20 carbons, and optionally about 5 to about 10 mole percent oxygen-functional alkyl (meth)acrylate monomer units with hydroxy alkyl chains including 2 to 7 carbons;

each Q is independently a sulfur atom;

R 1 is an alkylene group of 1 to 10 carbons;

A is hydrogen, an alkyl group, or a group independently selected from Formula A1, A2, or A3:

—O—C(O)—R 1 -Q-(PMA)  (Formula A1);

—C(A1)CH 2 —O—C(O)—R 1 -Q-(PMA)  (Formula A2);

—CH 2 —O—CH2—C—[CH 2 —O—C(O)-Q-(PMA)] r   (Formula A3);

m is an integer from 1 to 4 and if m is less than 4, then A includes at least one group independently selected from the hydrogen, the alkyl group, or the Formulas A1, A2, or A3;

n is 0 or an integer from 1 to 4;

r is an integer from 1 to 3;

wherein the groups associated with the m integer, A, and the groups associated with the r integer are bonded only to the carbon atom adjacent thereto;

wherein the lubricating oil composition includes, on an active basis, no more than about 10 weight percent viscosity index improving polymer; and

wherein a thickening VI of the lubricating oil composition is about 45 to about 65 viscosity index units per weight percent polymer in the lubricating oil composition.

14. The lubricating oil composition of claim 13 , wherein the short chain alkyl (meth)acrylate monomers include about 10 to about 30 mole percent of a dispersant monomer.

15. The lubricating oil composition of claim 13 , wherein n is 0, and m is 4.

16. The lubricating oil composition of claim 15 , wherein the weight average molecular weight is about 20 to about 500 Kg/mol.

17. The lubricating oil composition of claim 13 , wherein the composition has a viscosity index of about 200 to about 350.