Process for preparing low sulfur dispersant polymers

1. A process for preparing a grafted polyalkyl (meth)acrylate copolymer (A),

the process comprising:

(a) charging a first mineral oil having a sulfur content of less than 50 ppm to a reaction vessel;

(b) preparing a monomer mixture of monomer units (A2) to (A4), an optional monomer unit (A1), and a first reaction initiator:

(A1) one or more ethylenically unsaturated ester compounds of formula (I)

where

R is H or CH 3 ,

R 1 represents a linear or branched, saturated or unsaturated alkyl group with 1 to 5 carbon atoms or a cycloalkyl group with 3 to 5 carbon atoms,

R 2 and R 3 independently represent H or a —COOR′ group, where R′ is H or a linear or branched, saturated or unsaturated alkyl group with 1 to 5 carbon atoms or a cycloakyl group with 3 to 5 carbon atoms,

(A2) one or more ethylenically unsaturated ester compounds of formula (II)

where

R is H or CH 3 ,

R 4 represents a linear or branched, saturated or unsaturated alkyl group with 6 to 15 carbon atoms,

R 5 and R 6 independently represent H or a —COOR″ group, where R″ is H or a linear or branched, saturated or unsaturated alkyl group with 6 to 15 carbon atoms,

(A3) one or more ethylenically unsaturated ester compounds of formula (III)

where

R is H or CH 3 ,

R 7 represents a linear or branched, saturated or unsaturated alkyl group with 16 to 30 carbon atoms,

R 8 and R 9 independently represent H or a —COOR′″ group where R′″ is H or a linear or branched, saturated or unsaturated alkyl group with 16 to 30 carbon atoms, and

(A4) at least one N-dispersant monomer selected from the group consisting of vinyl pyridine, N-vinyl imidazole, N-vinyl pyrrolidone (NVP), morpholinoethyl methacrylate, N-vinyl caprolactam, N,N-dimethylaminoethyl methacrylate (DMAEMA), tert-butyl aminoethyl methacrylate, N,N-dimethylaminopropylmethacrylamide (DMAPMAm), dimethylaminopropylacrylamide, and dimethylaminoethylacrylamide;

(c) adding the monomer mixture to the first mineral oil to obtain a mixture;

(d) polymerizing the mixture obtained in (c) to obtain a polymer;

(e) optionally isolating the polymer obtained in (d);

(f) adding at least one N-dispersant monomer unit (A5) selected from the group consisting of vinyl pyridine, N-vinyl imidazole, N-vinyl pyrrolidone (NVP), morpholinoethyl methacrylate, N-vinyl caprolactam, N,N-dimethylaminoethyl methacrylate (DMAEMA), tert-butyl aminoethyl methacrylate, N,N-dimethylaminopropylmethacrylamide (DMAPMAm), dimethylaminopropylacrylamide, and dimethylaminoethylacrylamide;

(g) adding a second reaction initiator to obtain a mixture;

(h) polymerizing the mixture obtained in (g) to obtain the grafted polyalkyl (meth)acrylate copolymer (A);

(i) optionally isolating the grafted polyalkyl (meth)acrylate copolymer (A) to obtain an isolated grafted polyalkyl (meth)acrylate copolymer (A); and/or

(j) diluting the grafted polyalkyl (meth)acrylate copolymer (A), or when the isolating (i) is performed, the isolated grafted polyalkyl (meth)acrylate copolymer (A), with a second mineral oil having a sulfur content of less than 50 ppm,

wherein

the first mineral oil and the second mineral oil are the same or different, and

the grafted polyalkyl (meth)acrylate copolymer (A) comprises

a polymer backbone comprising: 0% to 40% by weight of the monomer unit (A1), 20% to 93.5% by weight of the monomer unit (A2), 5% to 60% by weight of the monomer unit (A3), and 1% to 40% by weight of the monomer unit (A4), where the monomer units (A1) to (A4) add up to 100% by weight based on a total weight of the polymer backbone; and

0.5% to 10% by weight of at least one grafted side chain, which is the monomer unit (A5) grafted onto the polymer backbone, based on a total weight of the grafted polyalkyl(meth)acrylate copolymer (A).

2. The process according to claim 1 , wherein the monomer unit (A1) is used in the process and R 2 and R 3 in the formula (I) are hydrogen.

3. The process according to claim 1 , wherein R 5 and R 6 in the formula (II) are hydrogen.

4. The process according to claim 1 , wherein R 8 and R 9 in the formula (III) are hydrogen.

5. The process according to claim 1 , wherein the N-dispersant monomer (A4) is N-vinyl pyrrolidone (NVP).

6. The process according to claim 1 , wherein the N-dispersant monomer (A5) is N-vinyl pyrrolidone (NVP).

7. The process according to claim 1 , wherein the grafted polyalkyl(meth)acrylate copolymer (A) has a number average molecular weight M n of from 3000 to 150000 g/mol.

8. The process according to claim 1 , wherein the first reaction initiator and the second reaction initiator are the same.

9. The process according to claim 1 , wherein the first reaction initiator is added in an amount of from 0.5% to 1.5% by weight, based on a total amount of the monomer units (A1) to (A4).

10. The process according to claim 1 , wherein the second reaction initiator is added in an amount of from 5% to 15% by weight, based on a total amount of the monomer unit (A5).

11. The process according to claim 1 , wherein the first reaction initiator and the second reaction initiator are different.

12. The process according to claim 1 , wherein the first mineral oil has a sulfur content of less than 10 ppm.

13. The process according to claim 1 , wherein the adding (c) is done over a course of 1 to 5 hours.

14. The process according to claim 1 , wherein the adding (c) is done over a course of 2 to 3 hours.

15. The process according to claim 1 , wherein the polymerizing (d) occurs in the absence of a chain transfer agent.

16. The process according to claim 1 , wherein the monomer unit (A1) is used in (b).

17. The process according to claim 1 , wherein the process comprises (e).

18. The process according to claim 1 , wherein the process comprises (i).

19. The process according to claim 1 , wherein the polymerizing (d) occurs in the presence of a sulfur free chain transfer agent.