Viscosity index improvers with defined molecular weight distributions

1. A polyalkyl(meth)acrylate based comb polymer, consisting of:

(a) 10 to 25% by weight of an ester of (meth)acrylic acid and a hydroxylated hydrogenated polybutadiene;

(b) 0% to 5% by weight of at least one C 4-18 alkyl acrylate;

(c) 0% to 0.3% by weight of methyl methacrylate;

(d) 60% to 75% by weight of n-butyl methacrylate;

(e) 5% to 20% by weight of at least one C 10-30 alkyl (meth)acrylate; and

(f) 0% to 2% by weight of at least one styrene monomer,

wherein the polyalkyl(meth)acrylate based comb polymer has a weight-average molecular weight M w of 700,000 g/mol or greater and a number-average molecular weight M n of 130,000 g/mol or greater, determined by size exclusion chromatography (SEC) using a polymethylmethacrylate standard.

2. The polyalkyl(meth)acrylate based comb polymer according to claim 1 , wherein the weight-average molecular weight M w is from 700,000 to 2,000,000 g/mol and the number-average molecular weight M n is from 130,000 to 300,000 g/mol, determined by size exclusion chromatography (SEC) using a polymethylmethacrylate standard.

3. The polyalkyl(meth)acrylate based comb polymer according to claim 1 , having a value P of 1.5 or lower:

P

=

M

w

-

0.8

M

n

×

10

10

≤

1.5

.

4. A method of increasing KV 100 and in parallel decreasing HTHS 100 and HTHS 80 of a lubricating oil composition, the method comprising adding the polyalkyl(meth)acrylate based comb polymer according to claim 1 to a lubricating oil composition in need thereof.

5. An additive composition, comprising:

(A) 60 to 80% by weight of a base oil, and

(B) 20 to 40% by weight of a polyalkyl(meth)acrylate based comb polymer, which has a weight-average molecular weight M w of 700,000 g/mol or greater and a number-average molecular weight M n of 130,000 g/mol or greater, determined by size exclusion chromatography (SEC) using a polymethylmethacrylate standard,

wherein the polyalkyl(meth)acrylate based comb polymer (B) consists of the following monomers:

(a) 10 to 25% by weight of an ester of (meth)acrylic acid and a hydroxylated hydrogenated polybutadiene;

(b) 0% to 5% by weight of at least one C 4-18 alkyl acrylate;

(c) 0% to 0.3% by weight of methyl methacrylate;

(d) 60% to 75% by weight of n-butyl methacrylate;

(e) 5% to 20% by weight of at least one C 10-30 alkyl (meth)acrylate; and

(f) 0% to 2% by weight of at least one styrene monomer.

6. The additive composition according to claim 5 , wherein the weight-average molecular weight M w of component (B) is from 700,000 to 2,000,000 g/mol and the number-average molecular weight M n is from 130,000 to 300,000 g/mol, determined by size exclusion chromatography (SEC) using a polymethylmethacrylate standard.

7. A method of increasing KV 100 and in parallel decreasing HTHS 100 of a lubricating oil composition, the method comprising adding the additive composition according to claim 5 to a lubricating oil composition in need thereof.

8. A lubricating oil composition, comprising:

(A) 80 to 99.5% by weight of a base oil;

(B) 0.5 to 5% by weight of a polyalkyl(meth)acrylate based comb polymer, which has a weight-average molecular weight M w of 700,000 g/mol or greater and a number-average molecular weight M n of 130,000 g/mol or greater, determined by size exclusion chromatography (SEC) using a polymethylmethacrylate standard; and

(C) 0 to 15% by weight of one or more further additives,

wherein component (B) consists of:

(a) 10 to 25% by weight of an ester of (meth)acrylic acid and a hydroxylated hydrogenated polybutadiene;

(b) 0% to 5% by weight of at least one C 4-18 alkyl acrylate;

(c) 0% to 0.3% by weight of methyl methacrylate;

(d) 60% to 75% by weight of n-butyl methacrylate;

(e) 5% to 20% by weight of at least one C 10-30 alkyl (meth)acrylate; and

(f) 0% to 2% by weight of at least one styrene monomer.

9. The lubricating oil composition according to claim 8 , wherein the weight-average molecular weight M w of component (B) is from 700,000 to 2,000,000 g/mol and the number-average molecular weight M n is from 130,000 to 300,000 g/mol, determined by size exclusion chromatography (SEC) using a polymethylmethacrylate standard.

10. The lubricating oil composition according to claim 8 , wherein component (C) is at least one selected from the group consisting of conventional VI improvers, dispersants, defoamers, detergents, antioxidants, pour point depressants, antiwear additives, extreme pressure additives, friction modifiers, anticorrosion additives, dyes and mixtures thereof.

11. A process for preparing the polyalkyl(meth)acrylate based comb polymer according to claim 1 , the process comprising:

(a) preparing a reaction mixture comprising monomers and a first dilution oil, wherein the monomers are present in an amount of 40 to 65% by weight;

(b) heating 50% of the reaction mixture prepared under (a) to a first temperature of from 80 to 120° C.;

(c) adding 0.05 to 0.1%, based on the total amount of the monomers, of a first initiator to the reaction mixture as prepared under (b), the first initiator having a half-life T 1/2 of from 100 to 200 minutes, at the first temperature according to (b);

(d) adding a further amount of the reaction mixture prepared under and further 0.05 to 0.1% of the first initiator during a time of from 2 to 4 hours;

(e) maintaining the reaction mixture prepared under (d) for a time of 0.5 to 3 hours at the first temperature;

(f) diluting the reaction mixture prepared under (e) during a time of 0.5 to 3 hours to 30% with a second dilution oil, which can be the same or different than the first dilution oil, comprising a further amount of the first initiator;

(g) optionally adding further amount of the first initiator or a second initiator, which can be the same as or different than the first initiator, to the reaction mixture prepared under (e) and maintaining for at least 2 hours; and

(h) diluting the reaction mixture prepared under (g) by addition of the first dilution oil or the second dilution oil.

12. The process according to claim 11 , wherein the first and second initiators are the same or different and are each independently selected from the group consisting of azo initiators, and peroxy compounds.

13. The process according to claim 11 , wherein the first initiator is 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexan and the second initiator is tert-butylperoxy 2-ethylhexanoate or 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexan.

14. The process according to claim 11 , wherein the first and second dilution oils are the same or different and are each independently selected from the group consisting of API Group I, II, III, IV, V and mixtures thereof.

15. The process according to claim 12 , wherein the first and second initiators are each independently at least one selected from the group consisting of azobis-isobutyronitrile (AIBN), 2,2′-azobis(2-methylbutyronitrile) (AMBN), 1,1-azobiscyclohexanecarbonitrile, methyl ethyl ketone peroxide, acetylacetone peroxide, dilauryl peroxide, tert-butyl per-2-ethylhexanoate, ketone peroxide, tert-butyl peroctoate, methyl isobutyl ketone peroxide, cyclohexanone peroxide, dibenzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxyisopropylcarbonate, 2,5-bis(2-ethylhexanoylperoxy)-2,5-dimethylhexane, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, dicumyl peroxide, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, cumyl hydroperoxide, tert-butyl hydroperoxide and bis(4-tert-butylcyclohexyl) peroxydicarbonate.

16. The lubricating oil composition of claim 8 , having a KV 100 of at least 6.9 mm 2 /s.

17. The lubricating oil composition of claim 8 , having a KV 100 of at least 6.9 mm 2 /s and an HTHS 80 of 6.0 mPas or less.