EP4630521A1 - Sulfur-free dispersant polymers for industrial applications - Google Patents

Abstract

The present invention is directed to lubricants comprising small amounts of dispersant polymers and their use to avoid particle formation and deposits in industrial machine equipment.

Description

Sulfur-free dispersant polymers for industrial applications

The present invention is directed to lubricants comprising small amounts of dispersant polymers and their use to avoid particle formation and deposits in industrial machine equipment.

The invention relates to the preparation of statistical alkyl (meth)acrylate copolymers useful in industrial lubricant applications that are more resistant to aging. As lubricants and oil formulations are used, they will oxidize and darken because of prolonged exposure to high temperature and oxygen. If an oil has increased susceptibility to this aging process, the useful life of the oil formulation will drastically decrease thereby increasing cost of the equipment by requiring increased services. The aging process not only darkens the oil, but it also forms oxidative side products that can cause unwanted sludge or varnish that can build up and damage machine parts. Using polymeric additives that tend to cause sludge or varnish will require shorter service intervals and oil changes thereby increasing cost to the user. Being able to extend service intervals is something of high value to the consumer and is general industry desire.

It was an object of the present invention to provide an additive for an industrial oil formulation, preferably a compressor oil, a turbine oil, a hydraulic fluid or a gear oil, more preferably a compressor oil, that is able to disperse particles that arise during equipment in use, e.g. from oil ageing, and to keep them dispersed in the oil, avoid particle separation and to avoid sludge, gum and lacquer formation.

Common compressors belong to the groups of rotating or reciprocating machines. They compress a variety of gases, e.g. air, carbon dioxide, other chemical gases or other refrigerants. Small refrigeration compressors are used in domestic refrigerators, larger compressors are e.g. used to cool warehouses.

Additives are well known in the lubricant industry to be able to deliver performance benefits, like e.g. wear and corrosion protection, improved oxidation stability or to cure sealing problems.

Commonly used are inter alia polyalkyl (meth)acrylates. Polyalkyl (meth)acrylates are well-known additives that are used in different applications like engine oils, transmission oils, gear oils, hydraulic oils, shock absorber oils and greases.

The use of dispersant polyalkyl (meth)acrylates as additives in compressor oils to avoid particle formation and deposits has so far not been reported. WO 2022/139687 A1 relates to a soot dispersant comprising an A-B type block copolymer. The A block is a soot anchoring unit and comprises an N-dispersant monomer as well as styrene or benzyl methacrylate.

US 2006/0189490 A1 relates to lubricant oil compositions comprising friction-modifying additives. Such friction-modifying additives are block copolymers.

EP 4 015604 A1 relates to acrylate-olefin copolymers and their use as lubricant additives or synthetic base fluids.

It was surprisingly found that low molecular weight statistical alkyl (meth)acrylate copolymers with a sulfur content of below 50 ppm (so called sulfur-free alkyl (meth)acrylate copolymers) and comprising at least 1000 ppm of nitrogen allow to formulate fluids with better oxidation stability and corrosion stability. The purpose of the inventive polymer in formulations is to disperse particles that arise during equipment in use, e.g. from oil ageing, and to keep them dispersed in the oil, avoid particle separation and to avoid sludge, gum and lacquer formation. This property was improved without sulfur, and the inventive sulfur-free products did also allow to pass the other requirements as mentioned above.

Detailed Description of the Invention

A first object of the present invention is directed to a method for avoiding the formation of particles and deposits in industrial oil formulations, the method comprising the steps of:

(i) preparing a sulfur-free statistical alkyl (meth)acrylate copolymer comprising:

(a) 41 wt% to 99 wt%, preferably 46 wt% to 99 wt%, more preferably 48.5 wt% to 99 wt%, of C8-18 alkyl (meth)acrylates, preferably C10-15 alkyl (meth)acrylates;

(b) 1 wt% to 10 wt%, preferably 1 wt% to 5 wt%, more preferably 2.5 wt% to 3.5 wt%, of N-dispersing monomers or hydroxy-substituted C2-4 alkyl (meth)acrylates;

(c) 0 wt% to 2 wt% of methyl methacrylate; and

(d) 0 wt% to 49 wt% of alpha-olefins comprising C8-16 carbon atoms, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight Mw of 5,000 g/mol to 50,000 g/mol;

(ii) adding 0.05 wt% to 1 .0 wt% of the sulfur-free alkyl (meth)acrylate copolymer prepared under step (i) to a base oil or a base oil mixture;

(iii) optionally adding one or more further additives; and

(iv) applying the industrial oil formulation prepared under step (ii) or (iii) to a compressor, a turbine, a hydraulic machine or an industrial gear, preferably to a compressor. The content of each component (a), (b) (c) and (d) is based on the total composition of the statistical alkyl (meth)acrylate copolymer. In a particular embodiment, the proportions of components (a), (b), (c) and (d) add up to 100% by weight.

A further object is directed to the method as mentioned further above, wherein the sulfur-free statistical alkyl (meth)acrylate copolymer comprises:

(a) 88 wt% to 99 wt%, preferably 93 wt% to 99 wt%, more preferably 94.5 wt% to 97.5 wt%, of C8-18 alkyl (meth)acrylates, preferably C10-15 alkyl (meth)acrylates;

(b) 1 wt% to 10 wt%, preferably 1 wt% to 5 wt%, more preferably 2.5 wt% to 3.5 wt%, of N- dispersing monomers or hydroxy-substituted C2-4 alkyl (meth)acrylates, preferably N- dispersing monomers; and

(c) 0 wt% to 2 wt% of methyl methacrylate.

A further object is directed to the method as mentioned further above, wherein the sulfur-free statistical alkyl (meth)acrylate copolymer comprises:

(a) 90 wt% to 99 wt%, preferably 95 wt% to 99 wt%, more preferably 96.5 wt% to 97.5 wt%, of C8-18 alkyl (meth)acrylates, preferably C10-15 alkyl (meth)acrylates;

(b) 1 wt% to 10 wt%, preferably 1 wt% to 5 wt%, more preferably 2.5 wt% to 3.5 wt%, of N- dispersing monomers or hydroxy-substituted C2-4 alkyl (meth)acrylates, preferably N- dispersing monomers; and

(c) 0 wt% to 2 wt% of methyl methacrylate.

The content of each component (a), (b) and (c) is based on the total composition of the statistical alkyl (meth)acrylate copolymer. In a particular embodiment, the proportions of components (a), (b) and (c) add up to 100% by weight.

A further object is directed to the method as mentioned further above, wherein the sulfur-free statistical alkyl (meth)acrylate copolymer comprises:

(a) 94.5 wt% to 97.5 et%, preferably 96.5 wt% to 97.5 wt% of C8-18 alkyl (meth)acrylates, preferably C10-15 alkyl (meth)acrylates;

(b) 2.5 wt% to 3.5 wt% of N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm); and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight M_w of 10,000 g/mol to 30,000 g/mol.

The content of each component (a), (b) and (c) is based on the total composition of the statistical alkyl (meth)acrylate copolymer. In a particular embodiment, the proportions of components (a), (b) and (c) add up to 100% by weight. In the context of the present invention, the term "sulfur-free" statistical alkyl (meth)acrylate copolymers means that the alkyl (meth)acrylate copolymers comprise less than 300 ppm, preferably less than 100 ppm, more preferably less than 50 ppm of sulfur.

The weight-average molecular weight Mw of the statistical alkyl (meth)acrylate copolymers according to the present invention is preferably in the range of 10,000 g/mol to 30,000 g/mol, more preferably 15,000 g/mol to 30,000 g/mol.

Mw is determined by size exclusion chromatography (SEC) using commercially available polymethylmethacrylate standards. The determination is affected by gel permeation chromatography with THF as eluent.

The term "(meth)acrylate" refers to both, esters of acrylic acid and esters of methacrylic acid. In accordance with the present invention, methacrylates are preferred.

The C8-18 alkyl (meth)acrylates for use in accordance with the invention are esters of (meth)acrylic acid and straight chain or branched alcohols having 8 to 18 carbon atoms. The term "C8-18 alkyl (meth)acrylates" encompasses individual (meth)acrylic esters with an alcohol of a particular length, and likewise mixtures of (meth)acrylic esters with alcohols of different lengths.

Suitable C8-18 alkyl (meth)acrylates include, for example, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, /so-decyl (meth)acrylate, 2-propylheptyl (meth)acrylate, undecyl (meth)acrylate, 5-methylundecyl (meth)acrylate, dodecyl (meth)acrylate, 2- methyldodecyl (meth)acrylate, tridecyl (meth)acrylate, 5-methyltridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, and octadecyl (meth)acrylate.

The C10-15 alkyl (meth)acrylates for use in accordance with the invention are esters of (meth)acrylic acid and straight chain or branched alcohols having 10 to 15 carbon atoms. The term "C10-15 alkyl (meth)acrylates" encompasses individual (meth)acrylic esters with an alcohol of a particular length, and likewise mixtures of (meth)acrylic esters with alcohols of different lengths. Suitable C10-15 alkyl (meth)acrylates include, for example, decyl (meth)acrylate, /so-decyl (meth)acrylate, 2-propylheptyl (meth)acrylate, undecyl (meth)acrylate, 5-methylundecyl (meth)acrylate, dodecyl (meth)acrylate, 2-methyldodecyl (meth)acrylate, tridecyl (meth)acrylate, 5-methyltridecyl (meth)acrylate, tetradecyl (meth)acrylate, and pentadecyl (meth)acrylate. Preferably, at least 30 wt% of the C10-15 alkyl (meth)acrylates are esters of (meth)acrylic acid and branched alcohols having 10 to 15 carbon atoms. The N-dispersing monomers for use in accordance with the invention are selected from the group consisting of N,N-dimethylaminoethyl methacrylate (DMAEMA), N-(3-(dimethylamino)propyl)- methacrylamide (DMAPMAm) and N-vinylpyrrolidinone (NVP); preferred is N-(3- (dimethylamino)propyl)-methacrylamide (DMAPMAm).

The hydroxy-substituted C2-4 alkyl (meth)acrylates for use in accordance with the invention are selected from the group consisting of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl acrylate and 2-hydroxypropyl methacrylate; preferred is 2-hydroxyethyl methacrylate (HEMA).

A further object is directed to the method as mentioned further above, wherein the sulfur-free statistical alkyl (meth)acrylate copolymer is selected from the group consisting of:

Polymer 1 , consisting of 97 wt% of a mixture of C12-C15-alkyl methacrylates and 3 wt% of an N-dispersing monomer, preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm),

Polymer 2, consisting of 99 wt% of a mixture of C12-C15-alkyl methacrylates and 1 wt% of an N-dispersing monomer, preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm),

Polymer 3, consisting of 95 wt% of a mixture of C12-C15-alkyl methacrylates and 5 wt% of an N-dispersing monomer, preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm),

Polymer 4, consisting of 0.2 wt% of methyl methacrylate (MMA), 96.8 wt% of a mixture of C12-C15-alkyl methacrylates and 3 wt% of an N-dispersing monomer, preferably N-(3- (dimethylamino)propyl)-methacrylamide (DMAPMAm), wherein the alkyl (meth)acrylate copolymers have a weight-average molecular weight Mw of 15,000 g/mol to 30,000 g/mol.

A further object is directed to the method as mentioned further above, wherein the sulfur-free statistical alkyl (meth)acrylate copolymer is selected from the group consisting of:

Polymer 1 , consisting of 97 wt% of a mixture of C12-C15-alkyl methacrylates and 3 wt% of an N-dispersing monomer, preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm), and having a weight-average molecular weight Mw in the range of 18,160 g/mol ± 20%, i.e. in the range of 27,240 g/mol to 24,970 g/mol.

Polymer 2, consisting of 99 wt% of a mixture of C12-C15-alkyl methacrylates and 1 wt% of an N-dispersing monomer, preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm), and having a weight-average molecular weight Mw in the range of 25,520 g/mol ± 20%, i.e. in the range of 20,416 g/mol to 30,624 g/mol.

Polymer 3, consisting of 95 wt% of a mixture of C12-C15-alkyl methacrylates and 5 wt% of an N-dispersing monomer, preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm), and having a weight-average molecular weight Mw in the range of 24,900 g/mol ± 20%, i.e. in the range of 19,920 g/mol to 29,880 g/mol. Polymer 4, consisting of 0.2 wt% of methyl methacrylate (MMA), 96.8 wt% of a mixture of C12-C15-alkyl methacrylates and 3 wt% of an N-dispersing monomer, preferably N-(3- (dimethylamino)propyl)-methacrylamide (DMAPMAm), and having a weight-average molecular weight Mw in the range of 22,300 g/mol ± 20%, i.e. in the range of 17,840 g/mol to 26,760 g/mol.

A second object of the present invention is directed to an industrial oil formulation, comprising:

(A) 85 wt% to 99.95 wt% of a base oil;

(B) 0.05 wt% to 1 .0 wt%, preferably 0.05 wt% to 0.5 wt%, more preferably 0.1 wt% to 0.5 wt%, of a sulfur-free statistical alkyl (meth)acrylate copolymer comprising:

(a) 41 wt% to 99 wt%, preferably 46 wt% to 99 wt%, more preferably 48.5 wt% to 99 wt%, of C8-18 alkyl (meth)acrylates, preferably C10-15 alkyl (meth)acrylates;

(b) 1 wt% to 10 wt%, preferably 1 wt% to 5 wt%, more preferably 2.5 wt% to 3.5 wt% of N-dispersing monomers or hydroxy-substituted C2-4 alkyl (meth)acrylates;

(c) 0 wt% to 2 wt% of methyl methacrylate; and

(d) 0 wt% to 49 wt% of alpha-olefins comprising C8-16 carbon atoms, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight Mw of 5,000 g/mol to 50,000 g/mol; and

(C) 0 wt% to 15 wt% of one or more further additives.

The content of each component (A), (B) and (C) is based on the total composition of the industrial oil formulation. In a particular embodiment, the proportions of components (A), (B) and (C) add up to 100% by weight.

The content of each component (a), (b), (c) and (d) is based on the total composition of the statistical alkyl (meth)acrylate copolymer. In a particular embodiment, the proportions of components (a), (b), (c) and (d) add up to 100% by weight.

A further second object of the present invention is directed to an industrial oil formulation as mentioned further above, wherein the statistical alkyl (meth)acrylate copolymer (B) comprises:

(a) 88 wt% to 99 wt%, preferably 93 wt% to 99 wt%, more preferably 94.5 wt% to 97.5 wt%, of C8-18 alkyl (meth)acrylates, preferably C10-15 alkyl (meth)acrylates;

(b) 1 wt% to 10 wt%, preferably 1 wt% to 5 wt%, more preferably 2.5 wt% to 3.5 wt%, of N- dispersing monomers or hydroxy-substituted C2-4 alkyl (meth)acrylates, preferably N- dispersing monomers, more preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm); and

(c) 0 wt% to 2 wt% of methyl methacrylate.

A further second object of the present invention is directed to an industrial oil formulation as mentioned further above, wherein the statistical alkyl (meth)acrylate copolymer (B) comprises: (a) 90 wt% to 99 wt%, preferably 95 wt% to 99 wt%, more preferably 96.5 wt% to 97.5 wt%, of C8-18 alkyl (meth)acrylates, preferably C10-15 alkyl (meth)acrylates;

(b) 1 wt% to 10 wt%, preferably 1 wt% to 5 wt%, more preferably 2.5 wt% to 3.5 wt%, of N- dispersing monomers or hydroxy-substituted C2-4 alkyl (meth)acrylates, preferably N- dispersing monomers, more preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm); and

(c) 0 wt% to 2 wt% of methyl methacrylate.

The content of each component (a), (b) and (c) is based on the total composition of the statistical alkyl (meth)acrylate copolymer. In a particular embodiment, the proportions of components (a), (b) and (c) add up to 100% by weight.

A further second object of the present invention is directed to an industrial oil formulation as mentioned further above, comprising:

(A) 85 wt% to 99.95 wt% of a base oil;

(B) 0.05 wt% to 1 .0 wt% of a sulfur-free statistical alkyl (meth)acrylate copolymer comprising:

(a) 94.5 wt% to 97.5 wt%, preferably 96.5 wt% to 97.5 wt% of C10-15 alkyl (meth)acrylates;

(b) 2.5 wt% to 3.5 wt% of N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm); and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight M_w of 10,000 g/mol to 30,000 g/mol; and

(C) 0 wt% to 15 wt% of one or more further additives.

The content of each component (A), (B) and (C) is based on the total composition of the industrial oil formulation. In a particular embodiment, the proportions of components (A), (B) and (C) add up to 100% by weight.

The content of each component (a), (b) and (c) is based on the total composition of the statistical alkyl (meth)acrylate copolymer. In a particular embodiment, the proportions of components (a), (b) and (c) add up to 100% by weight.

A third object of the present invention is directed to a sulfur-free statistical alkyl (meth)acrylate copolymer comprising:

(a) 88 wt% to 99 wt%, preferably 90 wt% to 99 wt% of C10-15 alkyl (meth)acrylates;

(b) 1 wt% to 10 wt% of N-dispersing monomers; and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight Mw of 5,000 g/mol to 50,000 g/mol.

The content of each component (a), (b) and (c) is based on the total composition of the alkyl (meth)acrylate copolymer. In a particular embodiment, the proportions of components (a), (b) and (c) add up to 100% by weight.

A further third object of the present invention is directed to a sulfur-free statistical alkyl (meth)acrylate copolymer comprising:

(a) 93 wt% to 99 wt%, preferably 95 wt% to 99 wt% of C10-15 alkyl (meth)acrylates;

(b) 1 wt% to 5 wt% of N-dispersing monomers; and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight M_w of 5,000 g/mol to 50,000 g/mol.

The content of each component (a), (b) and (c) is based on the total composition of the statistical alkyl (meth)acrylate copolymer. In a particular embodiment, the proportions of components (a), (b) and (c) add up to 100% by weight.

A further third object of the present invention is directed to a sulfur-free statistical alkyl (meth)acrylate copolymer comprising:

(a) 94.5 wt% to 97.5 wt%, preferably 96.5 wt% to 97.5 wt% of C10-15 alkyl (meth)acrylates;

(b) 2.5 wt% to 3.5 wt% of N-dispersing monomers; and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight Mw of 10,000 g/mol to 30,000 g/mol.

The content of each component (a), (b) and (c) is based on the total composition of the alkyl (meth)acrylate copolymer. In a particular embodiment, the proportions of components (a), (b) and (c) add up to 100% by weight.

A further third object is directed to the sulfur-free statistical alkyl (meth)acrylate copolymers selected from the group consisting of:

Polymer 1 , consisting of 97 wt% of a mixture of C12-C15-alkyl methacrylates and 3 wt% of an N-dispersing monomer, preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm),

Polymer 2, consisting of 99 wt% of a mixture of C12-C15-alkyl methacrylates and 1 wt% of an N-dispersing monomer, preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm), Polymer 3, consisting of 95 wt% of a mixture of C12-C15-alkyl methacrylates and 5 wt% of an N-dispersing monomer, preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm),

Polymer 4, consisting of 0.2 wt% of methyl methacrylate (MMA), 96.8 wt% of a mixture of C12-C15-alkyl methacrylates and 3 wt% of an N-dispersing monomer, preferably N-(3- (dimethylamino)propyl)-methacrylamide (DMAPMAm), wherein the alkyl (meth)acrylate copolymers have a weight-average molecular weight Mw of 15,000 g/mol to 30,000 g/mol.

A further object is directed to the sulfur-free statistical alkyl (meth)acrylate copolymers selected from the group consisting of:

Polymer 1 , consisting of 97 wt% of a mixture of C12-C15-alkyl methacrylates and 3 wt% of an N-dispersing monomer, preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm), and having a weight-average molecular weight Mw in the range of 18,160 g/mol ± 20%, i.e. in the range of 27,240 g/mol to 24,970 g/mol.

Polymer 2, consisting of 99 wt% of a mixture of C12-C15-alkyl methacrylates and 1 wt% of an N-dispersing monomer, preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm), and having a weight-average molecular weight Mw in the range of 25,520 g/mol ± 20%, i.e. in the range of 20,416 g/mol to 30,624 g/mol.

Polymer 3, consisting of 95 wt% of a mixture of C12-C15-alkyl methacrylates and 5 wt% of an N-dispersing monomer, preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm), and having a weight-average molecular weight Mw in the range of 24,900 g/mol ± 20%, i.e. in the range of 19,920 g/mol to 29,880 g/mol.

Polymer 4, consisting of 0.2 wt% of methyl methacrylate (MMA), 96.8 wt% of a mixture of C12-C15-alkyl methacrylates and 3 wt% of an N-dispersing monomer, preferably N-(3- (dimethylamino)propyl)-methacrylamide (DMAPMAm), and having a weight-average molecular weight Mw in the range of 22,300 g/mol ± 20%, i.e. in the range of 17,840 g/mol to 26,760 g/mol.

According to the present invention, the sulfur-free statistical alkyl(meth)acrylate copolymer is prepared by a process comprising at least the steps of:

(i) providing the monomer composition as described above, and

(ii) initiating radical polymerization of the monomer composition.

The radical polymerization of the present invention may be carried out in the absence (working examples) or presence (comparative examples) of one or more sulfur-free chain transfer agents as described above. Standard free-radical polymerization is detailed, inter alia, in Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition. In general, a polymerization initiator and optionally a chain transfer agent are used for this purpose.

For the synthesis of the alkyl(meth)acrylate copolymer, the monomer mixtures described above can be polymerized by any known method. Conventional radical initiators can be used to perform a free radical polymerization. These initiators are well known in the art. Non-limiting examples for these radical initiators are azo initiators like 2,2'-azodiisobutyronitrile (AIBN), 2,2'-azobis(2- methylbutyronitrile) and 1 ,1-azo-biscyclohexane carbonitrile; peroxide compounds, e.g. methyl ethyl ketone peroxide, acetyl acetone peroxide, dilauryl peroxide, te/Y-butylperoxy-2-ethyl hexanoate, te/Y-amylperoxy-2-ethyl hexanoate, methyl isobutyl ketone peroxide, cyclohexanone peroxide, dibenzoyl peroxide, te/Y-butylperoxy-benzoate, te/Y-butylperoxy isopropyl carbonate, 2,5- bis(2-ethylhexanoyl-peroxy)-2,5-dimethyl hexane, te/Y-amylperoxy-3,5,5-trimethyl hexanoate, tert- butylperoxy-3,5,5-trimethyl hexanoate, dicumene peroxide, 1 ,1 bis(te/Y-butylperoxy) cyclohexane, 1 ,1 bis(te/Y-butylperoxy) 3,3,5-trimethyl cyclohexane, cumene hydroperoxide and te/Y-butyl hydroperoxide.

Poly(meth)acrylates with a lower molecular weight can be obtained by using chain transfer agents. This technology is ubiquitously known and practiced in the polymer industry and is de-scribed in Odian, Principles of Polymerization, 1991.

Furthermore, novel polymerization techniques such as ATRP (Atom Transfer Radical Polymerization) and or RAFT (Reversible Addition Fragmentation Chain Transfer) can be applied to obtain useful polymers derived from alkyl esters. These methods are well known. The ATRP reaction method is described, for example, by J-S. Wang, et al., J. Am. Chem. Soc., Vol. 117, pp. 5614-5615 (1995), and by Matyjaszewski, Macromolecules, Vol. 28, pp. 7901-7910 (1995). Moreover, the patent applications WO 96/30421 , WO 97/47661 , WO 97/18247, WO 98/40415 and WO 99/10387 disclose variations of the ATRP explained above to which reference is expressly made for purposes of the disclosure. The RAFT method is extensively presented in WO 98/01478, for example, to which reference is expressly made for purposes of the disclosure.

The polymerization can be carried out at normal pressure, reduced pressure or elevated pressure. The polymerization temperature is in the range of -20 to 200°C, preferably 60 to 120°C, without any limitation intended by this. The polymerization can be carried out with or without solvents. The term solvent is to be broadly understood here. According to a preferred embodiment, the polymer is obtainable by a polymerization in API Group I, II or III mineral oil or in API group IV synthetic oil. According to the present invention, the poly alkyl(meth)acrylate copolymers are prepared preferably without using any sulfur-containing chain transfer agent. However, when sulfur - containing CTA such as n-dodecyl mercaptan or 2-mercaptoethanol is used for the radical polymerization of the monomer composition, the content thereof should be less than 0.05 wt.-% based on the total weight of the monomer composition.

Preferably, sulfur-containing chain transfer agent is not comprised in the monomer composition of the present invention or not used or added in the radical polymerization of the monomer composition in order to obtain the sulfur-free poly alky(meth)acrylate of the present invention.

The copolymers retrieved are statistical copolymers.

The base oil to be used in the industrial oil formulations comprises an oil of lubricating viscosity. Such oils include natural and synthetic oils, oils derived from hydrocracking, hydrogenation, and hydro-finishing, unrefined, refined, re-refined oils or mixtures thereof.

The base oil may also be defined as specified by the American Petroleum Institute (API) (see April 2008 version of "Appendix E-API Base Oil Interchangeability Guidelines for Passenger Car Motor Oils and Diesel Engine Oils", section 1.3 Subheading 1.3. "Base Stock Categories").

The API currently defines five groups of lubricant base stocks (API 1509, Annex E - API Base Oil Interchangeability Guidelines for Passenger Car Motor Oils and Diesel Engine Oils, September 2011). Groups I, II and III are mineral oils which are classified by the amount of saturates and sulfur they contain and by their viscosity indices; Group IV are polyalphaolefins; and Group V are all others, including e.g. ester oils. The table below illustrates these API classifications.

The kinematic viscosity at 100°C (KV100) of appropriate base oils used to prepare the industrial oil formulations in accordance with the present invention is preferably in the range of 0.7 mm²/s to 20 mm²/s, more preferably in the range of 2 mm²/s to 10 mm²/s, determined to ASTM D445. Particularly preferred industrial oil formulations of the present invention comprise at least one base oil selected from the group consisting of API Group II oils, API Group III oils, API Group IV oils and mixtures thereof.

Further base oils which can be used in accordance with the present invention are Group Il-Ill Fischer-Tropsch derived base oils.

Fischer-Tropsch derived base oils are known in the art. By the term "Fischer-Tropsch derived" is meant that a base oil is, or is derived from, a synthesis product of a Fischer-Tropsch process. A Fischer-Tropsch derived base oil may also be referred to as a GTL (Gas-To-Liquids) base oil. Suitable Fischer-Tropsch derived base oils that may be conveniently used as the base oil in the industrial oil formulations of the present invention are those as for example disclosed in EP 0 776 959, EP 0668 342, WO 97/21788, WO 00/15736, WO 00/14188, WO 00/14187, WO 00/14183, WO 00/14179, WO 00/08115, WO 99/41332, EP 1 029 029, WO 01/18156, WO 01/57166 and WO 2013/189951.

The industrial oil formulations used according to the present invention may also contain one or more further additives selected from the group consisting of pour point depressants, dispersants, defoamers, detergents, demulsifiers, antioxidants, antiwear additives, extreme pressure additives, friction modifiers, anticorrosion additives, metal deactivators and metal passivators and mixtures thereof; preferably antiwear additives, anticorrosion additives and antioxidants.

The industrial oil formulations used according to the present invention may preferably comprise up to 2.5% by weight, preferably 0.5% to 1 .5% by weight, of a performance package containing at least an antiwear agent, an anticorrosion agent and an antioxidant.

The performance package is preferably a zinc-free performance package, more preferably fully ashless.

Preferred pour point depressants are, for example, selected from the group consisting of alkylated naphthalene and phenolic polymers, polyalkyl methacrylates different than those of the present invention, maleate copolymer esters and fumarate copolymer esters, which may conveniently be used as effective pour point depressants. The industrial oil formulation may contain 0.1% by weight to 0.5% by weight of a pour point depressant. Preferably, not more than 0.3% by weight of a pour point depressant is used.

Appropriate dispersants include poly(isobutylene) derivatives, for example poly(isobutylene)succinimides (PIBSIs), including borated PIBSIs; and ethylene-propylene oligomers having N/O functionalities. The industrial oil formulation may contain up to 5% by weight of at least one dispersant, based on the total weight of the industrial oil formulation. Suitable defoaming agents include, for example, silicone oils, fluorosilicone oils, and fluoroalkyl ethers. The industrial oil formulation may contain 0.01% to 0.02% by weight of at least one defoaming agent, based on the total weight of the industrial oil formulation.

The detergents include metal-containing compounds, for example phenoxides; salicylates; thiophosphonates, especially thiopyrophosphonates, thiophosphonates and phosphonates; sulfonates and carbonates. These compounds may preferably be used in neutral or overbased form.

Preferred demulsifiers include alkyleneoxide copolymers and (meth)acrylates including polar functions.

The suitable antioxidants include, for example, phenols, for example 2,6-di-te/Y-butylphenol (2,6- DTB), 2,6-di-te/Y-butyl-4-ethylphenol, butylated hydroxytoluene (BHT), 2,6-di-te/Y-butyl-4- methylphenol, 4,4'-methylenebis(2,6-di-te/Y-butylphenol); aromatic amines, especially alkylated diphenylamines, N-phenyl-1 -naphthylamine (PNA), N,N'-di-phenyl-p-phenylenediamine, polymeric 2,2,4-trimethyldihydroquinone (TMQ); "OOS triesters" = reaction products of dithiophosphoric acid with activated double bonds from olefins, cyclopentadiene, norbornadiene, a-pinene, polybutene, acrylic esters, maleic esters (ashless on combustion); organophosphorus compounds, for example triaryl and trialkyl phosphites; organocopper compounds and overbased calcium- and magnesium- based phenoxides and salicylates. The industrial oil formulation may contain 0.05% to 5% by weight of at least one antioxidant, based on the total weight of the industrial oil formulation.

The preferred antiwear and extreme pressure additives include phosphorus compounds, for example trialkyl phosphates, triaryl phosphates, e.g. tricresyl phosphate, amine-neutralized mono- and dialkyl phosphates, ethoxylated mono- and dialkyl phosphates, phosphites, phosphonates or phosphines. The industrial oil formulations may contain 0.05% to 3% by weight of at least one antiwear and extreme pressure additive, based on the total weight of the industrial oil formulations.

Examples of the metal deactivators include triazoles, thiadiazoles and salicylidenes, like e.g. N,N'- disalicyliden-1 ,2-diaminopropane.

Rust inhibitors are widely used. Common chemistries are carboxylates like succinic acid half esters, sulfonates, alkyl amines and phosphates, e.g. amine neutralized phosphate esters.

Friction modifiers used may include mechanically active compounds, for example molybdenum disulfide, graphite (including fluorinated graphite), poly(trifluoroethylene), polyamide, polyimide; compounds that form adsorption layers, for example long-chain carboxylic acids, fatty acid esters, ethers, alcohols, amines, amides, imides; compounds which form layers through tribochemical reactions, for example saturated fatty acids, phosphoric acid and thiophosphoric esters, xanthogenates, sulfurized fatty acids; compounds that form polymer-like layers, for example ethoxylated dicarboxylic partial esters, dialkyl phthalates, methacrylates, unsaturated fatty acids, and sulfurized olefins.

The above-detailed additives are described in detail, inter alia, in T. Mang, W. Dresel (eds.): "Lubricants and Lubrication", Wiley-VCH, Weinheim 2001 ; R. M. Mortier, S. T. Orszulik (eds.): "Chemistry and Technology of Lubricants".

The invention is further illustrated by the following non-limiting examples and comparative examples. The examples below serve for further explanation of preferred embodiments according to the present invention but are not intended to restrict the invention.

Experimental Part

Abbreviations

BV100 kinematic bulk viscosity measured @100°C to ASTM D445

DMAPMAm N-(3-dimethylaminopropyl)methacrylamide

KV100 kinematic viscosity measured @100°C to ASTM D445

LIMA mixture of C12-C15-alkyl methacrylates (average carbon number = 13.4),

60% branched

M_n number-average molecular weight

Mw weight-average molecular weight nDDM n-dodecyl mercaptan

PDI polydispersity index, molecular weight distribution calculated via ratio Mw/Mn

Test Methods

Molecular weight

The alkyl (meth)acrylate copolymers according to the present invention and the comparative examples were characterized with respect to their molecular weight and PDI.

Molecular weights were determined by size exclusion chromatography (SEC) using commercially available polymethylmethacrylate (PMMA) standards. For polymers that do not contain N- dispersing monomers (such as CE1), molecular weight was determined by gel permeation chromatography with THF as eluent (flow rate: 1 mL/min; injected volume: 100 pl) using the following conditions:

Columns: 5 SDV Columns 8 x 300 mm resp. 8 x 50 mm (company PSS at Mainz)

1 Solvent-Peak Separation Column 8 x100 mm (company Shodex)

No. Type Dimension Serial no.

Precolumn SDV 10p 8 X 50 mm 91121224

1 SDV LXL 10p 8 X 300 mm 6013101

2 SDV LinL 10p 8 X 300 mm 6082302

3 SDV 100A 10p 8 X 300 mm 0071401

4 SDV 100A 10p 8 X 300 mm 0070508

5 KF-800D 8 X 100 mm 2007012

Instruments: Agilent 1100 Series Pump G1310A PSS SECcurity Inline-Degaser 409-0024 Agilent 1260 Series Autosampler G1329B Agilent 1260 Series UV-Detector G1314B Agilent 1100 Series Rl-Detector G1362A Agilent 1100 Series Control-Module G1323B Techlab Column oven K-5

Oven: Temperature 35°C

Eluent: Tetrahydrofuran

Eluent is continuously distilled and circulated by pump

Flow rate: 1 ml I min

Injected volume: 100 pl

Detection: Rl: Temperature 35°C

UV: Wavelength 239 nm

Delay volume: 0.175 ml (between UV- and Rl-signal)

Software: PSS WinGPC-Software

Concentration sample solution: 2 g/L (Mw > 10⁶: 1 g/L ... 0.5 g/L)

Standards: PMMA (for example PSS (Mainz) or Polymer Laboratories)

Concentration standard solution: 1 g/l (for Mw > 10⁶: 0.5 g/l, Mw > 2*10⁶: 0.25 g/l) (narrow distribution)

Internal standard: 1 ,2-Dichlorobenzene 0.2 pL to 99.8 pL Sample For polymers that do contain N-dispersing monomers (such as Inventive Examples 1-4 and CE2-5), molecular weight was determined by gel permeation chromatography with THF + 0.02 Mol 2-(diethylamino)ethylamine as eluent (flow rate: 1 mL/min; injected volume: 100 pl) using the following conditions:

Columns: 5 SDV Columns 8 x 300 mm resp. 8 x 50 mm (company PSS at Mainz)

No. Type Dimension Serial no.

Precolumn SDV 10³A 10p 8 X 50 mm 3051510

1 SDV 10³A 10p 8 X 300 mm 3051502

2 SDV 10³A 10p 8 X 300 mm 3051505

3 SDV 10³A 10p 8 X 300 mm 3051512

4 SDV 10³A 10p 8 X 300 mm 3051512

Instruments: Agilent 1100 Series Pump G1312A PSS SECcurity Inline-Degaser 409-0024 Agilent 1100 Series Autosampler G131313A Agilent 1260 Series Rl-Detector G1362A Agilent 1200 Series Control-Module G4208A PSS SECurity Column oven TCC6000

Oven: Temperature 35°C

Eluent: Tetra hydrofuran + 0.02 Mol DEAEA (2-(Diethylamino)ethylamine

Flow rate: 1 ml I min

Injected volume: 100 pl

Detection: Rl: Temperature 35°C

UV: Wavelength 239 nm

Delay volume: 0.175 ml (between UV- and Rl-signal)

Software: PSS WinGPC-Software

Concentration sample solution: 2 g/L (Mw > 10⁶: 1 g/L ... 0.5 g/L)

Standards: PMMA (ReadyCal from PSS Mainz)

Concentration standard solution: 1 g/L (for Mw > 10⁶: 0.5 g/L, Mw > 2*10⁶: 0.25 g/L) (narrow distribution)

Internal standard: 1 ,2-Dichlorobenzene 0.2 pL to 99.8 pL Sample

Sulfur content and Nitrogen content

Sulfur and nitrogen content were calculated using the molecular formulas of the monomers and chain transfer agents used to synthesize the polymers and by using the mass of component added.

Values were rounded to the nearest 100 ppm. Viscosities

The alkyl (meth)acrylate copolymers according to the present invention and comparative examples were received as compositions in oil which were characterized with respect to bulk kinematic viscosity at 100°C according to ASTM D445.

To determine thickening of the polymeric product, the kinematic viscosity at 100°C (KV100) was measured on a blend of 25 wt% of the example in a Group I oil. The Group I oil had a starting viscosity at 100°C of 5.4 cSt. The blend was prepared by blending 25 g of the example and 75 g of the group I oil for 30 minutes at 80°C. The KV100 was then measured according to ASTM D445.

Deposits test / Aging Test

The aging test was carried out by blending 0.5 wt% of the polymer into an ISO 220 fluid. 10 g of the mixture was placed in a test tube and stored uncovered in a 150°C oven for 30 days. After 30 days, the fluid was removed and visually observed for color change. After recording the observed color/darkening of the fluid, the fluid was passed through a filter paper to check for sludge formation. The amount of sludge that was formed was recorded using a scale of no deposits, minimum deposits, medium deposits, or major deposits.

Preparation of Example 1 :

100 g of ShellsolA150 ND were placed in a 1 L 4-necked round bottom flask. In a separate beaker, the reaction mixture was mixed by placing 485 g of LIMA, 15 g of DMAPMAm, and 15 g of tert- butylperoxy-2-ethylhexanoate. The round bottom flask containing 100 g of ShellsolA150ND was heated to 115°C, mixed using a C-stirring rod, and inerted with nitrogen. Once the reactor reached the set-point temperature, the reaction mixture was fed into the reactor at a rate of 1 .7 g/min. After the reaction mixture was completely added to the reactor, the reactor was held at 110°C for 60 minutes.

As all monomers used as starting materials are mixed together prior to starting the polymerization, the retrieved polymer is a statistical copolymer.

Example 2, Example 3 and Example 4 were prepared in the same way as Example 1 , except that the weight ratios of reaction components were changed according to the following Table 1 .

Table 1 : Amounts of monomers used to prepare Examples 1-4. Preparation of Comparative Example 1 :

485 g of LIMA, 15 g of DMAPMAm, and 2.75 g of nDDM were placed in a 1 L 4-necked round bottom flask. The reactor was heated to 120°C, mixed using a C-stirring rod, and inerted with nitrogen. Once the reactor reached the set-point temperature, 2.25 g of tert-butylperoxy-2- ethylhexanoate were fed into the reactor using the following dosing profile: 0.15 g in the first 60 minutes, 0.3 g in the next 60 minutes, and 0.9 g in the next 60 minutes. The reaction was allowed to continue stirring for 1 hour, and then the final 0.9 g of initiator fed into the reactor. The reactor was held at 110°C for 60 minutes.

As all monomers used as starting materials are mixed together prior to starting the polymerization, the retrieved copolymers are statistical copolymers.

Comparative Examples 2-4 were prepared in the same way as Comparative Example 1 , except that the weight ratios of reaction components were changed according to the following Table 2.

Table 2: Net composition of the examples and comparative examples

"CE" means comparative example

Examples 1-4 are in accordance with the present invention and contain no sulfur. They contain nitrogen in the range of 1600 ppm to 8200 ppm and were prepared in the absence of any sulfur- containing regulator.

Comparative Examples 1-5 do either not contain any nitrogen (CE1) and/or were prepared in the presence of a sulfur-containing regulator nDDM (CE2-CE5).

The sulfur and nitrogen values were calculated based on raw material data.

Characterizing data as molecular weights, PDIs, bulk viscosities and KV100 are outlined in the following Table 3.

Table 3: Characteristic data

"CE" means comparative example

The alkyl (meth)acrylate copolymers according to the present invention show weight-average molecular weights in the range of 20,000 g/mol to 30,000 g/mol. Their kinematic bulk viscosities at 100°C are in the range of 190 mm²/s to 210 mm²/s and the KV100 data are between 12 mm²/s and 13 mm²/s.

Aging test results are presented in the following Table 4.

Table 4: Aging test results

"CE" means comparative example

Examples 1-3 demonstrate that oil aging can be greatly reduced using polymers that contain <50 ppm of sulfur and at least 1000 ppm of nitrogen. The aging test conducted using these polymers show no deposit formation after a 30 day-aging cycle and no visible deposit on the filter paper test.

Comparative Example 1 does not contain any of the nitrogen-containing monomers, and although the deposits are minor the oil shows susceptibility to aging by a drastic change in color.

Comparative examples 2-5 contain varying amounts of sulfur and nitrogen, and all show severe darkening of the fluid as well as major numbers of deposits formed.

Table 5 below also shows aging of the ISO VG 220 fluid without any polymeric additive present. Table 5: Untreated oil versus treated oil

The ISO VG 220 oil darkens drastically to a brown color over the 4 weeks, whereas the oil treated with Inventive Example 1 only darkens to a light amber color. The fluid treated with Comparative Example 2 darkens the most and also has visible sludge that was formed.

Claims

Claims

1 . Method for avoiding the formation of particles and deposits in industrial oil formulations, the method comprising the steps of:

(i) preparing a sulfur-free statistical alkyl (meth)acrylate copolymer comprising:

(a) 93 wt% to 99 wt%, preferably 95 wt% to 99 wt% of C10-15 alkyl (meth)acrylates;

(b) 1 wt% to 5 wt% of N-dispersing monomers; and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight Mw of 5,000 g/mol to 50,000 g/mol, preferably of 10,000 g/mol to 30,000 g/mol, more preferably 15,000 g/mol to 30,000 g/mol;

(ii) adding 0.05 wt% to 1 .0 wt% of the sulfur-free alkyl (meth)acrylate copolymer prepared under step (i) to a base oil or a base oil mixture;

(iii) optionally adding one or more further additives; and

(iv) applying the industrial oil formulation prepared under step (ii) or (iii) to a compressor, a turbine, a hydraulic machine or an industrial gear, preferably to a compressor.

2. The method according to claim 1 , wherein the sulfur-free statistical alkyl (meth)acrylate copolymer comprises:

(a) 94.5 wt% to 97.5 wt%of C10-15 alkyl (meth)acrylates;

(b) 2.5 wt% to 3.5 wt% of N-dispersing monomers; and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight Mw of 10,000 g/mol to 30,000 g/mol.

3. The method according to claim 1 , wherein the sulfur-free statistical alkyl (meth)acrylate copolymer comprises:

(a) 96.5 wt% to 97.5 wt%of C10-15 alkyl (meth)acrylates;

(b) 2.5 wt% to 3.5 wt% of N-dispersing monomers; and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight Mw of 10,000 g/mol to 30,000 g/mol.

4. The method according to claim 1 , 2 or 3, wherein the N-dispersing monomers are selected from the group consisting of N,N-dimethylaminoethyl methacrylate (DMAEMA), N-(3- (dimethylamino)propyl)-methacrylamide (DMAPMAm) and N-vinylpyrrolidinone (NVP); preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm).

5. The method according to claim 1 , 2, 3 or 4, wherein at least 30 wt% of the C10-15 alkyl (meth)acrylates of component (a) are branched.

6. Industrial oil formulation, comprising:

(A) 85 wt% to 99.95 wt% of a base oil selected from the group consisting of API Group II, III and IV oils and mixtures thereof;

(B) 0.05 wt% to 1 .0 wt%, preferably 0.05 wt% to 0.5 wt%, more preferably 0.1 wt% to 0.5 wt%, of a sulfur-free statistical alkyl (meth)acrylate copolymer comprising:

(a) 93 wt% to 99 wt%, preferably 95 wt% to 99 wt% of C10-15 alkyl (meth)acrylates;

(b) 1 wt% to 5 wt% of N-dispersing monomers; and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight Mw of 5,000 g/mol to 50,000 g/mol, preferably of 10,000 g/mol to 30,000 g/mol, more preferably 15,000 g/mol to 30,000 g/mol; and

(C) 0 wt% to 15 wt% of one or more further additives.

7. The industrial oil formulation according to claim 6, wherein the statistical alkyl (meth)acrylate copolymer (B) comprises:

(a) 94.5 wt% to 97.5 wt% of C10-15 alkyl (meth)acrylates;

(b) 2.5 wt% to 3.5 wt% of N-dispersing monomers, more preferably N-(3- (dimethylamino)propyl)-methacrylamide (DMAPMAm); and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight Mw of 10,000 g/mol to 30,000 g/mol.

8. The industrial oil formulation according to claim 6, wherein the statistical alkyl (meth)acrylate copolymer (B) comprises:

(a) 96.5 wt% to 97.5 wt% of C10-15 alkyl (meth)acrylates;

(b) 2.5 wt% to 3.5 wt% of N-dispersing monomers, more preferably N-(3- (dimethylamino)propyl)-methacrylamide (DMAPMAm); and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight Mw of 10,000 g/mol to 30,000 g/mol.

9. The industrial oil formulation according to claim 7 or 8, wherein the N-dispersing monomers of component (b) are selected from the group consisting of N,N-dimethylaminoethyl methacrylate (DMAEMA), N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm) and N-vinylpyrrolidinone (NVP); preferably N-(3-(dimethylamino)propyl)-methacrylamide (DMAPMAm).

10. The industrial oil formulation according to claim 6, 7, 8 or 9, wherein the industrial oil formulation is selected from compressor oils, turbine oils, hydraulic fluids and gear oils; preferably compressor oils.

11 . Sulfur-free statistical alkyl (meth)acrylate copolymer comprising:

(a) 93 wt% to 99 wt% of C10-15 alkyl (meth)acrylates;

(b) 1 wt% to 5 wt% of N-dispersing monomers; and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight Mw of 5,000 g/mol to 50,000 g/mol, preferably of 10,000 g/mol to 30,000 g/mol, more preferably 15,000 g/mol to 30,000 g/mol .

12. Sulfur-free statistical alkyl (meth)acrylate copolymer according to claim 16, comprising:

(a) 95 wt% to 99 wt% of C10-15 alkyl (meth)acrylates;

(b) 1 wt% to 5 wt% of N-dispersing monomers; and

(c) 0 wt% to 2 wt% of methyl methacrylate.

13. Sulfur-free statistical alkyl (meth)acrylate copolymer according to claim 11 or 12, wherein the N-dispersing monomer is selected from the group consisting of N,N-dimethylaminoethyl- methacrylate, N-(3-(dimethylamino)propyl)-methacrylamide and N-vinylpyrrolidone; preferably N-(3- (dimethylamino)propyl)-methacrylamide.

14. Sulfur-free statistical alkyl (meth)acrylate copolymer according to claim 11 , 12 or 13, comprising:

(a) 94.5 wt% to 97.5 wt% of C10-15 alkyl (meth)acrylates;

(b) 2.5 wt% to 3.5 wt% of N-dispersing monomers; and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight Mw of 10,000 g/mol to 30,000 g/mol.

15. Sulfur-free statistical alkyl (meth)acrylate copolymer according to claim 11 or 12, comprising:

(a) 96.5 wt% to 97.5 wt% of C10-15 alkyl (meth)acrylates; (b) 2.5 wt% to 3.5 wt% of N-dispersing monomers; and

(c) 0 wt% to 2 wt% of methyl methacrylate, wherein the alkyl (meth)acrylate copolymer has a weight-average molecular weight M_w of 10,000 g/mol to 30,000 g/mol.