Process for preparing low sulfur dispersant polymers

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 CH3,
• R1 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,
• R2 and R3 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 CH3,
• R4 represents a linear or branched, saturated or unsaturated alkyl group with 6 to 15 carbon atoms,
• R5 and R6 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 CH3,
• R7 represents a linear or branched, saturated or unsaturated alkyl group with 16 to 30 carbon atoms,
• R8 and R9 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).