Aqueous emulsion polymerization with long alkyl chain acrylates and methacrylates

Abstract

The invention is directed to a process for preparing an aqueous polymer dispersion by polymerization, in particular by free-radical emulsion polymerization, of a monomer composition in an aqueous composition and in presence of a polymerization initiator, wherein the aqueous composition comprises 10.0 wt.-% to 60.0 wt.-% of the monomer composition, referring to the total aqueous composition, wherein the monomer composition comprises: 90.0 wt.-% to 100.0 wt.-% of at least one C16-C22-alkyl (meth)acrylate, 0 wt.-% to 10.0 wt.-% of (meth)acrylic acid, referring to the total monomer composition; 40.0 wt.-% to 90.0 wt.-% of an aqueous reaction medium, referring to the total aqueous composition, wherein the aqueous reaction medium comprises: 70.0 wt.-% to 98.9 wt.-% of water, 1.0 wt.-% to 25.0 wt.-% of a glycol, in particular propane-1,2-diol, 0.1 wt.-% to 5.0 wt.-% of a buffer salt, referring to the total aqueous reaction medium, wherein the pH value is adjusted to a range from 7 to 8, preferably from 7 to 7.5. The invention is further directed to an aqueous polymer dispersion obtainable or obtained by the process and the use thereof.

Description

[0001] Aqueous emulsion polymerization with long alkyl chain acrylates and methacrylates

[0002] Description

[0003] The present invention relates to a process for preparing an aqueous polymer dispersion by polymerization of a monomer composition in an aqueous composition and in presence of a polymerization initiator, wherein the aqueous composition comprises a monomer composition of at least one Ci6-C22-al ky I (meth)acrylate and an aqueous reaction medium. The present invention further relates to the resulting aqueous polymer dispersion and the use thereof.

[0004] Aqueous emulsion polymers with (meth)acrylates having long alkyl chains, also referred to as fatty alcohol (meth)acrylates, as for example stearyl (meth)acrylate, are desired materials for example in the textile, oil and coating sectors. Polystearyl (meth)acrylate or polybehenyl (meth)acrylate for example are not regarded as substances of concern and are produced at least partially based on renewable raw materials, as stearyl, and behenyl alcohol are gained from bio-based natural sources.

[0005] Long alkyl chain poly(meth)acrylates have excellent water-repellent properties and are regarded as very promising sustainable materials in the ongoing substitution process of per- and polyfluoroalkyl substances (PFAS) in e.g. functional textiles. Especially aqueous emulsion polymers of long alkyl chain poly(meth)acrylates are of interest for example as PFAS-free, non-toxic, (partially) bio-based, sustainable, water-repellent impregnation or coating materials for functional textiles. Further application fields of long alkyl chain poly(meth)acrylate emulsion polymers can be for example the use as flow improvers for diverse oils.

[0006] However, due to the hydrophobic nature of the long alkyl chain (meth)acrylates, the aqueous emulsion polymerization of these monomers is challenging. During conventional emulsion polymerization as addressed by the present application the monomers and oligomers transfer from a dispersed phase comprising the monomer through the aqueous phase into micelles where the polymerization occurs. The hydrophobicity of long alkyl chain (meth)acrylate monomers like stearyl (meth)acrylate hinders the migration through the water phase. Especially homopolymerization of long chain alkyl (meth)acrylates leads to instable dispersions due to phase-separation and / or partial or complete coagulation by formation of undesired coarse polymer particles. For example in copolymerizations small amounts of long alkyl chain (meth)acrylates can be successfully polymerized with less hydrophobic comonomers as reaction partner in a conventional emulsion polymerization process.

[0007] Known alternative approaches for the preparation of polymer dispersions from hydrophobic monomers are suspension polymerization or miniemulsion techniques as described for example by Vivaldo-Lima et al. in Industrial & Engineering Chemistry Research 1997, Vol. 36, Issue 4, pages 939 to 965 and Crespy et al. in Beilstein Journal of Organic Chemistry 2010, Vol. 6, pages 1132 to 1148, wherein the polymerization takes place within the dispersed phase of the monomers such that no monomer diffusion through the water is required. However, for miniemulsion polymerization techniques an ultrasonic treatment is applied. For suspension polymerization the resulting particle size and distribution vary significantly from the conventional emulsion polymerization. In addition, the technical up- scaling of miniemulsion polymerization is challenging, expensive and still under development. Often, these techniques are no suitable alternatives to conventional emulsion polymerization, in particular on industrial scale where a feasible and reliable scale up at reasonable costs in a reasonable time frame is required. Applying conventional polymer production assets such as stirred tank reactors is desired.

[0008] Fleischhaker et al. in Emulsion polymerization of hydrophobic monomers such as Heptadecyl Acrylate C17A, 2016, IPCOM000247314D, describe the addition of the volatile water miscible organic additive isopropanol in order to enable the aqueous emulsion polymerization of the hydrophobic heptadecyl acrylate. The volatile additive isopropanol is removed from the resulting polymer dispersion by distillation.

[0009] WO 2021 / 191348 A1 is directed to polymer dispersions made from (meth)acrylates having long side chains, wherein the polymer dispersions contain copolymers derived from both (meth)acrylates and ethylenically unsaturated carboxylic acids. A surfactant system comprising at least two different surfactants is applied to accomplish the emulsion polymerization.

[0010] It is an object of the present invention to provide a process for the preparation of an aqueous polymer dispersion from at least one Ci6 - C22 (meth)acry late, which leads to a stable (no phase separation) and not coagulated polymer dispersion and wherein a non-toxic and less volatile additive is applied. The process should further be easily scalable and operable in conventional production equipment.

[0011] This object is achieved by a process for preparing an aqueous polymer dispersion by polymerization, in particular by free-radical emulsion polymerization, of a monomer composition in an aqueous composition and in presence of a polymerization initiator, wherein the aqueous composition comprises

[0012] 10.0 wt.-% to 60.0 wt.-% of the monomer composition, referring to the total aqueous composition, wherein the monomer composition comprises:

[0013] 90.0 wt.-% to 100.0 wt.-% of at least one Ci6-C22-alkyl (meth)acrylate, 0 wt.-% to 10.0 wt.-% of (meth)acrylic acid, referring to the total monomer composition;

[0014] 40.0 wt.-% to 90.0 wt.-% of an aqueous reaction medium, referring to the total aqueous composition, wherein the aqueous reaction medium comprises:

[0015] 70.0 wt.-% to 98.9 wt.-%, in particular 70.0 wt.-% to 94.9 wt.-%, of water,

[0016] 1.0 wt.-% to 25.0 wt.-%, in particular 5.0 wt.-% to 25.0 wt.-%, of a glycol, in particular propane-1, 2-diol, 0.1 wt.-% to 5.0 wt.-% of a buffer salt, referring to the total aqueous reaction medium, wherein the pH value is adjusted to a range from 7 to 8, preferably from 7 to 7.5.

[0017] With the process of the present invention stable, not coagulated dispersions, without formation of undesired coarse polymer particles and without phase-separation, are obtained. Due to the presence of the water-soluble, non-toxic and high-boiling glycol additive, in particular propane-1 , 2-diol, also referred to as propylene glycol, the aqueous reaction medium is rendered more hydrophobic and the migration of the hydrophobic long alkyl chain (meth)acrylates through the aqueous reaction medium is facilitated. Emulsion homopolymerization as known for short chain (meth)acrylates is now enabled for long chain Ci6 - C22 (meth)acrylates, wherein technical shortcomings inherent to other techniques as described above, in particular related to suspension polymerization or miniemulsion and the application of ultrasonic waves are avoided.

[0018] At neutral pH in the range from 7 to 8, the resulting aqueous polymer dispersion, also referred to as aqueous polymer dispersion, can be stored for at least several months. The pH value of the aqueous composition can be adjusted. Preferably, the pH value of the, in particular resulting, aqueous polymer dispersion is adjusted to a range from 7 to 8, preferably from 7 to 7.5.

[0019] (Meth)acrylate is an abbreviation for acrylate and / or methacrylate. (Meth)acrylic acid is an abbreviation for acrylic acid and / or methacrylic acid.

[0020] The term C16-C22 alkyl denominates a group of linear, branched or cyclic saturated hydrocarbon radicals with 16 to 22 carbon atoms. The Ci6-C22-alkyl (meth)acrylate is preferably a Ci6-Ci8-alkyl (meth)acrylate with an alkyl chain of 16 to 18 carbon atoms, in particular of 16 and / or 18 carbon atoms, also referred to as stearyl (meth)acrylate. The C16- Ci8-alkyl (meth)acrylate is, in particular, octadecan-1 -yl (meth)acrylate and / or hexadecan- 1-y I (meth)acrylate, especially octadecan-1 -yl (meth)acrylate or a mixture of octadecan- 1-y I (meth)acrylate and hexadecan- 1-y I (meth)acry- late. The Ci6-C22-alkyl (meth)acrylate can consist of octadecan- 1-y I (meth)acrylate. Stearyl (meth)acrylate is an abbreviation for stearyl acrylate and / or stearyl methacrylate. Stearyl (meth)acrylate is understood to be a Ci8-alkyl (meth)acrylate with an alkyl chain having 18 carbon atoms or a mixture of Ci6-Ci8-alkyl (meth)acrylates with alkyl chains having 16 or 18 carbon atoms, respectively. Stearyl (meth)acrylate can be produced for example by esterification as described in JP 2007 / 001886 A or by transesterification as described in DE 2317226 A1 , respectively.

[0021] Preferably, the monomer composition consists to more than 95.0 wt.-%, more preferably to more than 99.0 wt.-%, more preferably to more than 99.5 wt.-% and even more preferably to more than 99.9 wt.-% of the at least one (meth)acry late, in particular of stearyl (meth)acry I ate, referring to the total monomer composition. In particular, the aqueous composition comprises less than 1 .0 wt.-%, more preferably less than 0.5 wt.-%, even more preferably less than 0.1 wt.-% of (meth)acrylic acid, referring to the total aqueous composition. The aqueous composition can be free of (meth)acrylic acid. In particular, the monomer composition comprises less than 1.0 wt.-%, more preferably less than 0.5 wt.-%, even more preferably less than 0.1 wt.-% of (meth)acrylic acid, referring to the total monomer composition. The monomer composition can be free of (meth)acrylic acid.

[0022] In general, the emulsion polymerization is conducted in the presence of a surfactant. Preferably, the aqueous reaction medium comprises at least one surfactant.

[0023] Preferably, the aqueous composition comprises

[0024] 20.0 wt.-% to 40.0 wt.-% of the monomer composition, referring to the total aqueous composition, wherein the monomer composition comprises:

[0025] 95.0 wt.-% to 100.0 wt.-% of at least one Ci6-C22-alkyl (meth)acrylate,

[0026] 0 wt.-% to 5.0 wt.-% of (meth)acrylic acid, referring to the total monomer composition;

[0027] 20.0 wt.-% to 80.0 wt.-%, more preferably 60.0 wt.-% to 80.0 wt.-%, of an aqueous reaction medium, referring to the total aqueous composition, wherein the aqueous reaction medium comprises:

[0028] 70.0 wt.-% to 94.9 wt.-%, in particular 70.0 wt.-% to 89.9 wt.-%, of water,

[0029] 5.0 wt.-% to 20.0 wt.-%, in particular 10.0 wt.-% to 20.0 wt.-%, of a glycol, in particular propane-1 , 2- diol,

[0030] 0.1 wt.-% to 2.0 wt.-% of a buffer salt,

[0031] 0.0 wt.-% to 10.0 wt.-%, more preferably 1 .0 wt.-% to 10.0 wt.-%, of at least one surfactant, referring to the total aqueous reaction medium.

[0032] Preferably, the buffer salt comprises a citrate, carbonate, borate and / or phosphate salt. More preferably, the buffer salt comprises a phosphate salt selected from the group consisting of alkali dihydrogen phosphate, alkali hydrogen phosphate, alkali phosphate, alkali di-phosphate, alkali tri-phosphate, alkali poly-phosphate, alkali meta-phosphate and mixtures thereof. In particular, the buffer salt is sodium di-phosphate and / or sodium hydrogen phosphate, such as sodium di-phosphate decahydrate and / or sodium hydrogen phosphate heptahydrate. Sodium di-phosphate is also referred to as sodium pyrophosphate. With these buffer salts the tendency of coagulate formation during emulsion polymerization of the monomer composition described above is reduced.

[0033] The polymerization initiator is preferably selected from the group consisting of peroxides such as organic hydroperoxides; peracids; azo compounds; redox initiator systems and persulfates, in particular persulfates.

[0034] The at least one surfactant may be anionic or non-ionic or a mixture of non-ionic and anionic surfactants. The at least one surfactant is preferably an anionic surfactant. The at least one surfactant is preferably selected from gemini surfactants, which are quasi-dimers of conventional surfactants, that are linked with a molecular spacer with each other. They additionally support the migration of the long alkyl chain (meth)acrylates through the aqueous reaction medium. The at least one surfactant is more preferably selected from sulfosuccinates, in particular from bis(alkyl) sulfosuccinates, such as di-Ci-Ci8-alkyl sulfosuccinates. Even more preferably, the at least one surfactant is sodium dioctylsulfosuccinate and / or sodium ditridecylsulfosuccinate. With these surfactants the tendency of coagulate formation during emulsion polymerization of the monomer composition described above is reduced.

[0035] In certain embodiments, the emulsion polymerization is conducted in the presence of a chain transfer agent. The chain transfer agent is preferably selected from the group consisting of aliphatic and / or araliphatic halogen compounds, for example n-butyl chloride, n-butyl bromide, n-butyl iodide, methylene chloride, ethylene dichloride, chloroform, bromoform, bromotrichloromethane, dibromodichloromethane, carbon tetrachloride, carbon tetrabromide, benzyl chloride, benzyl bromide; organic thio compounds such as primary, secondary or tertiary aliphatic thiols, for example ethanethiol, n-propanethiol, 2-propanethiol, n-butanethiol, 2-butanethiol, 2-methyl-2-propanethiol, n-pen- tanethiol, 2-pentanethiol, 3-pentanethiol, 2-methyl-2-butanethiol, 3-methyl-2-butanethiol, n-hexanethiol, 2-hex- anethiol, 3-hexanethiol, 2-methyl-2-pentanethiol, 3-methyl-2- pentanethiol, 4-methyl-2-pentanethiol, 2-methyl-3-pen- tanethiol, 3-methyl- 3-pentanethiol, 2-ethylbutanethiol, 2-ethyl-2-butanethiol, n-heptanethiol and the isomeric compounds thereof, n-octanethiol and the isomeric compounds thereof, n-nonanethiol and the isomeric compounds thereof, n-decanethiol and the isomeric compounds thereof, n-undecanethiol and the isomeric compounds thereof, n- dodecanethiol and the isomeric compounds thereof, n-tridecanethiol and isomeric compounds thereof, substituted thiols, for example 2-hydroxyethanethiol, aromatic thiols such as benzenethiol, ortho-, meta- or para-methylben- zenethiol, alkylesters of mercaptoa-cetic acid (thioglycolic acid) such as 2-ethylhexyl thioglycolate, alkylesters of mercaptopropionic acid such as octyl mercapto propionate, and also further sulfur compounds described in Polymer Handbook, 3rd edition, 1989, J. Brandrup and E.H. Immergut, John Wiley & Sons, section II, pages 133 to 141 , and aliphatic and / or aromatic aldehydes such as acetaldehyde, propionaldehyde and / or benzaldehyde, unsaturated fatty acids such as oleic acid, dienes having nonconjugated double bonds, such as divinylmethane or vinylcyclohexane, or hydrocarbons having readily abstractable hydrogen atoms, for example toluene.

[0036] In general, the total amount of chain transfer agents, if present, does not exceed 1 wt.-%, based on the total amount of monomer composition.

[0037] Preferably, the aqueous reaction medium comprises at least one chain transfer agent. The at least one chain transfer agent is more preferably selected from alkylthiols. Even more preferably, the at least one chain transfer agent is dodecanethiol.

[0038] Anionic surfactants usually bear at least one anionic group, which is for example selected from phosphate, phospho- nate, sulfate and sulfonate groups. The anionic surfactants such as sulfosuccinates, which bear at least one anionic group, are typically used in the form of their alkali metal salts, especially of their sodium salts or in the form of their ammonium salts. The at least one surfactant can be selected from anionic surfactants, which bear in particular at least one sulfate or sulfonate group. Likewise, anionic surfactants, which bear at least one phosphate or phosphonate group may be used, either as sole anionic surfactants or in combination with one or more anionic surfactants, which bear at least one sulfate or sulfonate group. Examples of anionic surfactants, which bear at least one sulfate or sulfonate group, are, for example, the salts, especially the alkali metal and ammonium salts, of sulfosuccinates, alkyl sulfates, especially of Cs-C22-al ky I sulfates, the salts, especially the alkali metal and ammonium salts, of sulfuric monoesters of ethoxylated alkanols, especially of sulfuric monoesters of ethoxylated C8-C22- alkanols, preferably having an ethoxylation level (EO level) in the range from 2 to 40, the salts, especially the alkali metal and ammonium salts, of sulfuric monoesters of ethoxylated alkylphenols, especially of sulfuric monoesters of ethoxylated C4-Cis-alky Iphenols (EO level preferably from 3 to 40), the salts, especially the alkali metal and ammonium salts, of alkylsulfonic acids, especially of C8-C22-alkylsulfonic acids, the salts, especially the alkali metal and ammonium salts, of dialkyl esters, especially di- Ci-Ci8-alkyl esters of sulfosuccinic acid, the salts, especially the alkali metal and ammonium salts, of alkylbenzenesulfonic acids, especially of C4-C22-alkylbenzenesulfonic acids, and the salts, especially the alkali metal and ammonium salts, of mono- or disulfonated, alkyl-substituted diphenyl ethers, for example of bis(phenylsulfonic acid) ethers bearing a C4-C24-alkyl group on one or both aromatic rings. Examples are described in US-A 4,269,749, such as Dowfax® (Dow Chemical Company).

[0039] The anionic surfactants can be selected from the following groups:

[0040] • the salts, especially the alkali metal salts, of di-Ci-Ci8-alkyl sulfosuccinates,

[0041] • the salts, especially the alkali metal and ammonium salts, of alkyl sulfates, especially of Cs-C22-al ky I sulfates,

[0042] • the salts, especially the alkali metal salts, of sulfuric monoesters of ethoxylated alkanols, especially of sulfuric monoesters of ethoxylated C8-C22-alkanols, preferably having an ethoxylation level (EO level) in the range from 2 to 40,

[0043] • sulfuric monoesters of ethoxylated alkylphenols, especially of sulfuric monoesters of ethoxylated C4-Cis-al- kyl phenols (EO level preferably from 3 to 40), of alkylbenzenesulfonic acids, especially of C4-C22-al kyl benzenesulfonic acids, and

[0044] • mono- or disulfonated, alkyl-substituted diphenyl ethers, for example of bis(pheny Isulfonic acid) ethers bearing a C4-C24-alky I group on one or both aromatic rings.

[0045] Examples of anionic surfactants, which bear a phosphate or phosphonate group, include, but are not limited to the following salts are selected from the following groups: • the salts, especially the alkali metal and ammonium salts, of mono- and dialkyl phosphates, especially C8-C22- alkyl phosphates,

[0046] • the salts, especially the alkali metal and ammonium salts, of phosphoric monoesters of C2-C3-alkoxylated alkanols, preferably having an alkoxylation level in the range from 2 to 40, especially in the range from 3 to 30, for example phosphoric monoesters of ethoxylated C8-C22-alkanols, preferably having an ethoxylation level (EO level) in the range from 2 to 40, phosphoric monoesters of propoxylated C8-C22-alkanols, preferably having a propoxylation level (PO level) in the range from 2 to 40, and phosphoric monoesters of ethoxylated-co- propoxylated C8-C22-alkanols, preferably having an ethoxylation level (EO level) in the range from 1 to 20 and a propoxylation level of 1 to 20,

[0047] • the salts, especially the alkali metal and ammonium salts, of phosphoric monoesters of ethoxylated alkylphenols, especially phosphoric monoesters of ethoxylated C4-Cis-alky I phenols (EO level preferably from 3 to 40),

[0048] • the salts, especially the alkali metal and ammonium salts, of alkylphosphonic acids, espe-cially Cs-C22-al- kylphosphonic acids, and

[0049] • the salts, especially the alkali metal and ammonium salts, of alkylbenzenephosphonic acids, especially C4- C22-alkylbenzenephosphonic acids.

[0050] Further suitable anionic surfactants can be found in Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], volume XIV / 1, Makromolekulare Stoffe [Macromolecular Substances], Georg-Thieme-Verlag, Stuttgart, 1961 , pages 192 to 208.

[0051] In other preferred embodiments, the surfactant may also comprise one or more nonionic surfactant. Suitable nonionic surfactants are e.g. araliphatic or aliphatic nonionic surfactants, for example ethoxylated mono-, di- and trialkylphenols (EO level from 3 to 50, alkylchain: C4-C10), ethoxylates of long-chain alcohols (EO level: from 3 to 100, alkyl chain: Cs-C e), and polyethylene oxide / polypropylene oxide homo- and copolymers. These may comprise the alkylene oxide units copolymerized in random distribution or in the form of blocks. Very suitable examples are the EO / PO block copolymers. Preference is given to ethoxylates of long-chain alkanols (alkyl chain C1-C30, mean ethoxylation level from 5 to 100) and, among these, particular preference is given to those having a C12-C20 alkyl chain and a mean ethoxylation level of 5 to 20, and also to ethoxylated mono-alkylphenols.

[0052] In other preferred embodiments, the at least one surfactant will be used in such an amount that the amounts of the at least one surfactant are in the range from 0.1 wt.-% to 25 wt.-%, especially in the range from 1.0 wt.-% to 15 wt.-%, based on the total monomer composition. The aqueous reaction medium in the polymerization may in principle also comprise in addition to the glycol, which is in particular propane-1 ,2-diol, minor amounts, in particular of 5 wt.-% or less of water-soluble organic solvents, for example methanol, ethanol, isopropanol, butanols, pentanols, and / or acetone, referring to the total aqueous reaction medium. Preferably, however, the process of the invention is conducted in the absence of such additional organic solvents.

[0053] The polymerization according to the invention is also referred to as emulsion polymerization. The process for the preparation of the aqueous polymer dispersion can generally be performed in line with well-known processes of, in particular radical, emulsion polymerisation technology. The conditions required for the performance of the emulsion polymerization of the monomers are familiar to those skilled in the art, for example from the prior art cited at the outset and from "Emulsions polymerisation" [Emulsion Polymerization] in Encyclopedia of Polymer Science and Engineering, vol. 8, pages 659 ff. (1987); D. C. Blackley, in High Polymer Latices, vol. 1 , pages 35 ff. (1966); H. Warson, The Applications of Synthetic Resin Emulsions, chapter 5, pages 246 ff. (1972); D. Diederich, Chemie in unserer Zeit, 24, pages 135 to 142 (1990); Emulsion Polymerisation, Inter-science Publishers, New York (1965); DE-A 40 03 422 and Dispersionen synthetischer Hochpolymere [Dispersions of Synthetic High Polymers], F. Holscher, Springer- Verlag, Berlin (1969).

[0054] The polymerization according to the invention is preferably conducted under stirring. Typically, the polymerization as described herein is an emulsion polymerization and conducted in absence of ultrasonic waves and, more particularly, without ultrasonic pretreatment. It is an advantage of the present invention that the polymerization takes place within the micelles and reduction of the monomer droplet size of the dispersed monomer phase by means of ultrasonic treatment is not required. Therefore, the inventive process is readily scalable.

[0055] The monomer composition is typically present in form of a dispersed phase, preferably having a mean average droplet diameter D of more than 10 nm, more preferably more than 50 nm, even more preferably more than 100 nm, even more preferably more than 500 nm. The mean average droplet diameter D of the monomer composition is preferably less than 100 pm, more preferably less than 50pm and even more preferably less than 10 pm, for example 1 pm. The mean average droplet diameter D can be determined for example by dynamic light scattering (DLS) according to ISO 22412:2017. The droplets of the monomer composition can also be referred to as reservoir for the monomers to be polymerized in the micelles. With progress of the polymerization the monomer composition is consumed and the monomers are converted into polymers within the micelles.

[0056] However, according to the present invention, it is essential to use glycol, in particular propane-1, 2-diol, as additive and that the pH value is adjusted to a range from 7 to 8, in particular at the end of the polymerization. The emulsion polymerization is initiated by means of the polymerization initiator. The polymerization initiator in emulsion polymerization possesses typically hydrophilic properties. Preferably, the polymerization initiator is a hydrophilic polymerization initiator. Radical aqueous emulsion polymerization is triggered by means of a free-radical polymerization initiator. For example polymerization initiators encompass peroxides such as persulfates, azo compounds and redox initiator systems. The peroxides can be inorganic peroxides or organic peroxides. Advantageously, the type and amount of the polymerization initiator, polymerization temperature and polymerization pressure are selected such that a sufficient amount of initiating radicals is always present to initiate or to maintain the polymerization reaction. Some of these free-radical polymerization initiators, especially inorganic persulfates, react acidic when they are contacted with water: They typically produce an acidic pH value of below 6 when dissolved in an aqueous reaction medium, especially under elevated temperatures.

[0057] Preferably, the polymerization initiator is a persulfate. More preferably, the polymerization initiator is sodium persulfate, potassium persulfate or ammonium persulfate, in particular potassium persulfate. Persulfates are inexpensive and commonly used in industrial processes.

[0058] Preferably, at least part of the monomer composition is fed to the aqueous composition during polymerization. The total monomer composition can be fed to the aqueous composition during polymerization. The process of the present invention is preferably a semi-batch process. Under polymerization conditions, during the emulsion polymerization of the monomers, the remaining residual amount of the monomer composition can be added batchwise in one or more portions or continuously with constant or varying flow rates. More preferably, at least part of the monomer composition is fed to the aqueous composition during polymerization together with a part of the aqueous reaction medium. For example, 30 wt.-% to 100 wt.-%, in particular 30 wt.-% to 80 wt.-%, of the total amount of the aqueous reaction medium is fed to the aqueous composition during polymerization.

[0059] In some embodiments of the inventive process, only part or the entire amount of the aqueous composition is initially charged to a reaction vessel. Preferably, at least part of the entire amount of the aqueous reaction medium is initially charged to the reaction vessel before the monomer composition is added or fed. In particular, at least part of the entire amount of glycol, in particular of propane-1, 2-diol, is initially charged to the reaction vessel before the monomer composition is added. Further preferably, at least part of the entire amount of glycol, in particular of propane-1 , 2-diol, at least part of the entire amount of the buffer salt and at least part of the entire amount of the surfactant are initially charged to the reaction vessel before the monomer composition is added.

[0060] In general, none, part or the entire amount of the aqueous reaction medium is initially charged to the reaction vessel. Preferably, at least part of the entire amount of glycol, in particular of propane-1, 2-diol, at least part of the entire amount of the buffer salt and at least part of the entire amount of surfactant are initially charged to the reaction vessel before the monomer composition is added. In a preferred embodiment, the total amount of the polymerization initiator for the emulsion polymerization is added to the reaction vessel in one portion. Alternatively, it is also possible to add part of the entire amount of the polymerization initiator batchwise in one or more portions or continuously with constant or varying flow rates during the emulsion polymerization.

[0061] In preferred embodiments, the emulsion polymerization is carried out by adding a feed stream comprising at least part of the monomer composition to the reaction vessel during the emulsion polymerization, wherein the reaction vessel contains at least part of the aqueous reaction medium.

[0062] In a preferred embodiment, the emulsion polymerization of the invention is conducted at a reaction temperature in the range from 0°C to 170°C, more preferably in the range from 50°C to 95°C, most preferably in the range from 75°C to 95°C and in particularly the emulsion polymerization of the invention is conducted a temperature in the range from 80°C to 90°C. The emulsion polymerization can be conducted at a pressure of less than, equal to or greater than 1 atm (101325 Pa). Preferably, the emulsion polymerization is conducted at a pressure of 0.20 MPa or less, more preferably of 0.15 MPa or less. In particular, the emulsion polymerization is conducted at a pressure in a range from 0.05 MPa to 0.20 MPa, more particularly from 0.08 MPa to 0.13 MPa.

[0063] Preferably, after addition of the monomer composition, the reaction is post-polymerized for up to 3.0 hours, more preferably for a time range of 0.5 hours to 2.5 hours, in particular 2.0 hours. The term post-polymerization denotes the continued reaction after all feeds, in particular the monomer composition, are added to the reaction mixture. During post-polymerization the aqueous composition is preferably stirred at an elevated temperature, in particular at a post-polymerizing temperature in the range from 0°C to 170°C, more preferably in the range from 50°C to 95°C, most preferably in the range from 75°C to 95°C.

[0064] In a preferred embodiment, the polymerization and optionally the post-polymerization are carried out at a polymerization temperature in a range from 50°C to 95°C, the resulting aqueous polymer dispersion is cooled to a storage temperature of 45°C or less and then the pH value, in particular of the aqueous polymer dispersion, is adjusted to a range from 7 to 8, in particular from 7.0 to 7.5.

[0065] Preferably, the at least part of the monomer composition being fed to the aqueous composition during polymerization, and optionally the part of the aqueous reaction medium, are preheated to a preheating temperature of 25°C or more before being fed to the aqueous composition. More preferably, the preheating temperature is in a range from 30°C to 40°C.

[0066] Further, the emulsion polymerization can be conducted in presence of protective colloids. The protective colloids are understood to mean polymeric compounds having molecular weights above 2000 Daltons. Optionally, the emulsion polymerization can be performed in the presence of a seed latex. A seed latex is a polymer latex which is present in the aqueous reaction medium before the metering of the monomer composition is started. The seed latex may help to better adjust the particle size of the final aqueous polymer dispersion obtained in the emulsion polymerization of the invention.

[0067] Principally every polymer latex may serve as a seed latex. Preference is given to seed latices, where the particle size of the polymer particles is comparatively small. The Z average particle diameter of the polymer particles of the seed latex, as determined by dynamic light scattering at 20°C is preferably in the range from 10 nm to 80 nm, in particular from 10 nm to 50 nm. Preferably, the polymer particles of the seed latex are made of ethylenically unsaturated monomers, which comprise at least 95% by weight, based on the total weight of the monomers forming the seed latex, of one or more monomers selected from C2-Cio-alkyl esters of acrylic acid, in particular ethyl acrylate, n-butyl acrylate, 2-ethyl-hexyl acrylate, Ci-C4-alkyl esters of methacrylic acid, in particular methyl methacrylate, and vinylaromatic monomers, in particular styrene.

[0068] For this, the seed latex is usually charged into the reaction vessel before the metering of the monomer composition is started. In particular, the seed latex is charged into the reaction vessel followed by establishing the polymerization conditions and charging at least a portion of the polymerization initiator into the reaction vessel before the metering of the monomer composition is started.

[0069] The amount of seed latex, calculated as solids, may frequently be in the range from 0.1 wt.-% to 10.0 wt.-%, in particular from 0.5 wt.-% to 5 wt.-% by weight, based on the total weight of the monomer composition.

[0070] Preferably, the resulting aqueous polymer dispersion is neutralized to an essentially neutral pH value in the range from 7 to 8, in particular after the polymerization reaction, preferably after the polymerization reaction is accomplished to a conversion of at least 99 % by weight, by adding a basic compound.

[0071] Preferably, the basic compound is selected from water-soluble hydroxides, oxides, carbonates, hydrogen carbonates (bicarbonates), acetates, citrates, borates, phosphates, hydrogen phosphates of alkali or alkaline earth metals or ammonium. Other basic compounds are also possible, like ammonia or water-soluble organic amines such as lower aliphatic amines.

[0072] Preferred basic compounds are the hydroxides of sodium, potassium and ammonium, the carbonates of sodium and potassium and hydrogen carbonates (bicarbonates) of sodium and potassium. The basic compound is more preferably ammonium, in particular aqueous ammonium. The basic compound is preferably dissolved in water. Preferably, the pH value of the aqueous polymer dispersion is adjusted by addition of an aqueous ammonia solution and / or alkali hydroxides. The present invention also concerns the aqueous polymer dispersions obtainable or obtained by the process of the invention as well as their use. The aqueous polymer dispersion preferably has a pH value in a range from 7 to 8, more preferably from 7.0 to 7.5.

[0073] The glycol, in particular propane-1 , 2-diol, as additive can remain in the aqueous polymer dispersion. Thus, the aqueous polymer dispersion preferably comprises the glycol, in particular propane-1 , 2-diol. The aqueous polymer dispersion preferably comprises 0.5 wt.-% to 20.0 wt.-%, more preferably 1 .0 wt.-% to 15.0 wt.-%, of the glycol, in particular propane-1 , 2-diol, referring to the total aqueous polymer dispersion.

[0074] In general, the aqueous polymer dispersion obtained has a polymer solid content in the range from 10 wt.-% to 60 wt.-%, preferably 20 wt.-% to 55 wt.-%, more preferably 25 wt.-% to 50 wt.-%, and most preferably 30 wt.-% to 40 wt.-%, based in each case on the total weight of the aqueous polymer dispersion.

[0075] In general, the aqueous polymer dispersion obtained comprises polymer particles with a mean average particle diameter DPof less than 10 m, preferably less than 1 pm, more preferably less than 800 nm, even more preferably less than 500 nm. Typically, the aqueous polymer dispersion obtained comprises polymer particles with a mean average particle diameter DP of at least 10 nm, preferably at least 50 nm, more preferably at least 100 nm. The mean average particle diameter DP of the polymer particles comprised in the obtained aqueous polymer dispersion is for example in a range from 100 nm to 400 nm. The mean average particle diameter DP can be determined by dynamic light scattering (DLS) according to ISO 22412:2017.

[0076] Preferred uses of the aqueous polymer dispersions are the use for hydrophobic coatings, textile functionalization such as for water repellency of textiles; and / or as flow aids for oils. The obtained aqueous polymer dispersions, in particular, can serve as sustainable substitution for PFAS containing impregnations.

[0077] The invention is explained in more detail by the following examples and comparative examples.

[0078] Examples and comparative examples

[0079] Example 1

[0080] Emulsion homopolymerization of stearyl acrylate

[0081] A glass reactor with a volume of 2 L and equipped with a stirrer moving at 220 rpm, temperature control, nitrogen inlet and reflux condenser was charged with 100.0 g deionized water, 20.0 g propane-1 , 2-diol, 0.9 g sodium di-phos- phate decahydrate, 4.0 g Aerosol® TR-70, purchased from Solvay (sodium ditridecylsulfosuccinate) and 3.7 g Aerosol® OT-75, purchased from Solvay (sodium dioctylsulfosuccinate). This first part of the aqueous reaction medium was purged with nitrogen and heated to 80°C. The temperature was maintained at 80°C and 1.0 g potassium persulfate dissolved in 20 g deionized water was added in one portion. A mixture of 169.0 g stearyl acrylate (SA 18 from BASF), 0.5 g dodecanethiol, 150.0 g deionized water, 30.0 g propane-1, 2-diol, 1.4 g sodium di-phosphate decahydrate, 6.0 g Aerosol® TR-70, 5.6 g Aerosol® OT-75 was heated to a temperature between 30°C and 40°C and then fed with this temperature to the reactor within 1 hour under stirring. Subsequently, the aqueous composition was stirred for 2 hours at 80°C, then cooled to 20°C, neutralized by addition of aqueous ammonia solution, comprising 5 wt.-% of ammonia, to a pH value of 7.0 and filtered over filter with a pore size of 125 pm.

[0082] A stable, not coagulated aqueous polymer dispersion was obtained having a solid content of 34.6 wt.-%, referring to the total aqueous polymer dispersion, and an average particle diameter of 193 nm. For determination of the solid content throughout the invention, 2 g of the polymer dispersion were dried at 100°C in a vacuum drying cabinet until a constant weight was reached in an aluminum crucible with a diameter of 5 cm. The average particle size of the polymer dispersion was determined by dynamic light scattering with a Zetasizer Nano analyser, purchased from Malvern Panalytical GmbH.

[0083] The aqueous polymer dispersion was stored at 20°C for 2 months. No optical changes, coagulation or remarkable changes in particle size were observed.

[0084] Example 2

[0085] Emulsion copolymerization of stearyl acrylate and acrylic acid

[0086] A glass reactor with a volume of 2 L and equipped with a stirrer moving at 220 rpm, temperature control, nitrogen inlet and reflux condenser was charged with 100.0 g deionized water, 20.0 g propane-1, 2-diol, 0.9 g sodium di-phos- phate decahydrate, 4.0 g Aerosol® TR-70, purchased from Solvay (sodium ditridecylsulfosuccinate) and 3.7 g Aerosol® OT-75, purchased from Solvay (sodium dioctylsulfosuccinate). This first part of the aqueous reaction medium was purged with nitrogen and heated to 80°C. The temperature was maintained at 80°C and 1.0 g potassium persulfate dissolved in 20 g deionized water was added in one portion. A mixture of 165.7 g stearyl acrylate (SA 18 from BASF), 3.2 g acrylic acid, 0.5 g dodecanethiol, 150.0 g deionized water, 30.0 g propane-1, 2-diol, 1.4 g sodium diphosphate decahydrate, 6.0 g Aerosol® TR-70, 5.6 g Aerosol® OT-75 was heated to a temperature between 30°C and 40°C and then fed with this temperature to the reactor within 1 hour under stirring. Subsequently, the aqueous composition was stirred for 2 hours at 80°C, then cooled to 20°C, neutralized by addition of aqueous ammonia solution, comprising 5 wt.-% of ammonia, to a pH value of 7.0 and filtered over filter with a pore size of 125 pm.

[0087] A stable, not coagulated aqueous polymer dispersion was obtained having a solid content of 33.5 wt.-%, referring to the total aqueous polymer dispersion, and an average particle diameter of 303 nm. The aqueous polymer dispersion was stored at 20°C for 2 months. No optical changes, coagulation or remarkable changes in particle size were observed.

[0088] Example 3

[0089] Emulsion homopolymerization of stearyl methacrylate

[0090] A glass reactor with a volume of 2 L and equipped with a stirrer moving at 220 rpm, temperature control, nitrogen inlet and reflux condenser was charged with 100.0 g deionized water, 20.0 g propane-1 , 2-diol, 0.9 g sodium di-phos- phate decahydrate, 4.0 g Aerosol® TR-70, purchased from Solvay (sodium ditridecylsulfosuccinate) and 3.7 g Aerosol® OT-75, purchased from Solvay (sodium dioctylsulfosuccinate). This first part of the aqueous reaction medium was purged with nitrogen and heated to 80°C. The temperature was maintained at 80°C and 1.0 g potassium persulfate dissolved in 20 g deionized water was added in one portion. A mixture of 169.0 g stearyl methacrylate (SMA 1618 from BASF), 0.5 g dodecanethiol, 150.0 g deionized water, 30.0 g propane-1 , 2-diol, 1.4 g sodium di-phosphate decahydrate, 6.0 g Aerosol® TR-70, 5.6 g Aerosol® OT-75 was fed to the reactor within 1 hour under stirring. Subsequently, the aqueous composition was stirred for 2 hours at 80°C, then cooled to 20°C, neutralized by addition of aqueous ammonia solution, comprising 5 wt.-% of ammonia, to a pH value of 7.5 and filtered over filter with a pore size of 125 m.

[0091] A stable, not coagulated aqueous polymer dispersion was obtained having a solid content of 35.5 wt.-%, referring to the total aqueous polymer dispersion, and an average particle diameter of 336 nm.

[0092] The aqueous polymer dispersion was stored at 20°C for 2 months. No optical changes, coagulation or remarkable changes in particle size were observed.

[0093] Example 4

[0094] Emulsion copolymerization of stearyl methacrylate and methacrylic acid

[0095] A glass reactor with a volume of 2 L and equipped with a stirrer moving at 220 rpm, temperature control, nitrogen inlet and reflux condenser was charged with 100.0 g deionized water, 20.0 g propane-1 , 2-diol, 0.9 g sodium di-phos- phate decahydrate, 4.0 g Aerosol® TR-70, purchased from Solvay (sodium ditridecylsulfosuccinate) and 3.7 g Aerosol® OT-75, purchased from Solvay (sodium dioctylsulfosuccinate). This first part of the aqueous reaction medium was purged with nitrogen and heated to 80°C. The temperature was maintained at 80°C and 1.0 g potassium persulfate dissolved in 20 g deionized water was added in one portion. A mixture of 165.7 g stearyl methacrylate (SMA 1618 from BASF), 3.2 g methacrylic acid, 0.5 g dodecanethiol, 150.0 g deionized water, 30.0 g propane-1 , 2-diol, 1.4 g sodium di-phosphate decahydrate, 6.0 g Aerosol® TR-70, 5.6 g Aerosol® OT-75 was fed to the reactor within 1 hour under stirring. Subsequently, the aqueous composition was stirred for 2 hours at 80°C, then cooled to 20°C, neutralized by addition of aqueous ammonia solution, comprising 5 wt.-% of ammonia, to a pH value of 7.5 and filtered over filter with a pore size of 125 pm.

[0096] A stable, not coagulated aqueous polymer dispersion was obtained having a solid content of 36.2 wt.-%, referring to the total aqueous polymer dispersion, and an average particle diameter of 194 nm.

[0097] The aqueous polymer dispersion was stored at 20°C for 2 months. No optical changes, coagulation or remarkable changes in particle size were observed.

[0098] Example 5

[0099] Emulsion homopolymerization of stearyl acrylate

[0100] A glass reactor with a volume of 2 L and equipped with a stirrer moving at 220 rpm, temperature control, nitrogen inlet and reflux condenser was charged with 100.0 g deionized water, 20.0 g propane-1, 2-diol, 0.8 g sodium hydrogen phosphate heptahydrate, 4.0 g Aerosol® TR-70, purchased from Solvay (sodium ditridecylsulfosuccinate) and 3.7 g Aerosol® OT-75, purchased from Solvay (sodium dioctylsulfosuccinate). This first part of the aqueous reaction medium was purged with nitrogen and heated to 80°C. The temperature was maintained at 80°C and 1.0 g potassium persulfate dissolved in 20 g deionized water was added in one portion. A mixture of 169.0 g stearyl acrylate (SA 18 from BASF), 0.5 g dodecanethiol, 150.0 g deionized water, 30.0 g propane-1, 2-diol, 1.2 g sodium hydrogen phosphate heptahydrate, 6.0 g Aerosol® TR-70, 5.6 g Aerosol® OT-75 was heated to a temperature between 30°C and 40°C and then fed with this temperature to the reactor within 1 hour under stirring. Subsequently, the aqueous composition was stirred for 2 hours at 80°C, then cooled to 20°C, neutralized by addition of aqueous ammonia solution, comprising 5 wt.-% of ammonia, to a pH value of 7.5 and filtered over filter with a pore size of 125 pm.

[0101] A stable, not coagulated aqueous polymer dispersion was obtained having a solid content of 34.5 wt.-%, referring to the total aqueous polymer dispersion, and an average particle diameter of 243 nm.

[0102] The aqueous polymer dispersion was stored at 20°C for 2 months. No optical changes, coagulation or remarkable changes in particle size were observed.

[0103] Example 6

[0104] Emulsion copolymerization of stearyl acrylate and acrylic acid

[0105] A glass reactor with a volume of 2 L and equipped with a stirrer moving at 220 rpm, temperature control, nitrogen inlet and reflux condenser was charged with 100.0 g deionized water, 20.0 g propane-1, 2-diol, 0.8 g sodium hydrogen phosphate heptahydrate, 4.0 g Aerosol® TR-70, purchased from Solvay (sodium ditridecylsulfosuccinate) and 3.7 g Aerosol® OT-75, purchased from Solvay (sodium dioctylsulfosuccinate). This first part of the aqueous reaction medium was purged with nitrogen and heated to 80°C. The temperature was maintained at 80°C and 1.0 g potassium persulfate dissolved in 20 g deionized water was added in one portion. A mixture of 165.7 g stearyl acrylate (SA 18 from BASF), 3.2 g acrylic acid, 0.5 g dodecanethiol, 150.0 g deionized water, 30.0 g propane-1, 2-diol, 1.2 g sodium hydrogen phosphate heptahydrate, 6.0 g Aerosol® TR-70, 5.6 g Aerosol® OT-75 was heated to a temperature between 30°C and 40°C and then fed with this temperature to the reactor within 1 hour under stirring. Subsequently, the aqueous composition was stirred for 2 hours at 80°C, then cooled to 20°C, neutralized by addition of aqueous ammonia solution, comprising 5 wt.-% of ammonia, to a pH value of 7.5 and filtered over filter with a pore size of 125 pm.

[0106] A stable, not coagulated aqueous polymer dispersion was obtained having a solid content of 35.7 wt.-%, referring to the total aqueous polymer dispersion, and an average particle diameter of 273 nm.

[0107] The aqueous polymer dispersion was stored at 20°C for 2 months. No optical changes, coagulation or remarkable changes in particle size were observed.

[0108] Example 7

[0109] Emulsion homopolymerization of stearyl methacrylate

[0110] A glass reactor with a volume of 2 L and equipped with a stirrer moving at 220 rpm, temperature control, nitrogen inlet and reflux condenser was charged with 100.0 g deionized water, 20.0 g propane-1, 2-diol, 0.8 g sodium hydrogen phosphate heptahydrate, 4.0 g Aerosol® TR-70, purchased from Solvay (sodium ditridecylsulfosuccinate) and 3.7 g Aerosol® OT-75, purchased from Solvay (sodium dioctylsulfosuccinate). This first part of the aqueous reaction medium was purged with nitrogen and heated to 80°C. The temperature was maintained at 80°C and 1.0 g potassium persulfate dissolved in 20 g deionized water was added in one portion. A mixture of 169.0 g stearyl methacrylate (SMA 1618 from BASF), 0.5 g dodecanethiol, 150.0 g deionized water, 30.0 g propane-1, 2-diol, 1.2 g sodium hydrogen phosphate heptahydrate, 6.0 g Aerosol® TR-70, 5.6 g Aerosol® OT-75 was fed to the reactor within 1 hour under stirring. Subsequently, the aqueous composition was stirred for 2 hours at 80°C, then cooled to 20°C, neutralized by addition of aqueous ammonia solution, comprising 5 wt.-% of ammonia, to a pH value of 7.5 and filtered over filter with a pore size of 125 pm.

[0111] A stable, not coagulated aqueous polymer dispersion was obtained having a solid content of 36.7 wt.-%, referring to the total aqueous polymer dispersion, and an average particle diameter of 209 nm.

[0112] The aqueous polymer dispersion was stored at 20°C for 2 months. No optical changes, coagulation or remarkable changes in particle size were observed.

[0113] Example 8 Emulsion copolymerization of stearyl methacrylate and methacrylic acid

[0114] A glass reactor with a volume of 2 L and equipped with a stirrer moving at 220 rpm, temperature control, nitrogen inlet and reflux condenser was charged with 100.0 g deionized water, 20.0 g propane-1, 2-diol, 0.8 g sodium hydrogen phosphate heptahydrate, 4.0 g Aerosol® TR-70, purchased from Solvay (sodium ditridecylsulfosuccinate) and 3.7 g Aerosol® OT-75, purchased from Solvay (sodium dioctylsulfosuccinate). This first part of the aqueous reaction medium was purged with nitrogen and heated to 80°C. The temperature was maintained at 80°C and 1.0 g potassium persulfate dissolved in 20 g deionized water was added in one portion. A mixture of 165.7 g stearyl methacrylate (SMA 1618 from BASF), 3.2 g methacrylic acid, 0.5 g dodecanethiol, 150.0 g deionized water, 30.0 g propane- 1, 2-diol, 1.2 g sodium hydrogen phosphate heptahydrate, 6.0 g Aerosol® TR-70, 5.6 g Aerosol® OT-75 was ted to the reactor within 1 hour under stirring. Subsequently, the aqueous composition was stirred for 2 hours at 80°C, then cooled to 20°C, neutralized by addition of aqueous ammonia solution, comprising 5 wt.-% of ammonia, to a pH value of 7.5 and filtered over filter with a pore size of 125 pm.

[0115] A stable, not coagulated aqueous polymer dispersion was obtained having a solid content of 34.9 wt.-%, referring to the total aqueous polymer dispersion, and an average particle diameter of 174 nm.

[0116] The aqueous polymer dispersion was stored at 20°C for 2 months. No optical changes, coagulation or remarkable changes in particle size were observed.

[0117] Comparative example 1

[0118] Emulsion copolymerization of stearyl acrylate and acrylic acid

[0119] The emulsion polymerization was carried out according to example 2 with the difference that no aqueous ammonia solution was added and thus the pH was not adjusted to pH 7.0.

[0120] No stable polymer dispersion was obtained.

[0121] Comparative example 2

[0122] Emulsion homopolymerization of stearyl methacrylate

[0123] The emulsion polymerization was carried out according to example 3 with the difference that no aqueous ammonia solution was added and thus the pH was not adjusted to pH 7.5.

[0124] No stable polymer dispersion was obtained. Comparative example 3

[0125] Emulsion copolymerization of stearyl methacrylate and methacrylic acid

[0126] The emulsion polymerization was carried out according to example 4 with the difference that no aqueous ammonia solution was added and thus the pH was not adjusted to pH 7.5.

[0127] No stable polymer dispersion was obtained.

[0128] Comparative example 4

[0129] Emulsion copolymerization of stearyl acrylate and acrylic acid

[0130] The emulsion polymerization was carried out according to example 1 with the difference that no sodium di-phosphate decahydrate was added.

[0131] Coagulation is observed. No dispersion is formed.

[0132] Comparative example 5

[0133] Emulsion copolymerization of stearyl acrylate and acrylic acid

[0134] The emulsion polymerization was carried out according to example 2 with the difference that no sodium di-phosphate decahydrate was added.

[0135] Coagulation is observed. No dispersion is formed.

[0136] Comparative example 6

[0137] Emulsion homopolymerization of stearyl methacrylate

[0138] The emulsion polymerization was carried out according to example 3 with the difference that no sodium di-phosphate decahydrate was added.

[0139] Coagulation is observed. No dispersion is formed.

Claims

Claims1. Process for preparing an aqueous polymer dispersion by polymerization, in particular by free-radical emulsion polymerization, of a monomer composition in an aqueous composition and in presence of a polymerization initiator, wherein the aqueous composition comprises10.0 wt.-% to 60.0 wt.-% of the monomer composition, referring to the total aqueous composition, wherein the monomer composition comprises:90.0 wt.-% to 100.0 wt.-% of at least one Ci6-C22-alkyl (meth)acrylate, in particular at least one C16-C18- alkyl (meth)acrylate,0 wt.-% to 10.0 wt.-% of (meth)acrylic acid, referring to the total monomer composition;40.0 wt.-% to 90.0 wt.-% of an aqueous reaction medium, referring to the total aqueous composition, wherein the aqueous reaction medium comprises:70.0 wt.-% to 98.9 wt.-% of water,1.0 wt.-% to 25.0 wt.-% of a glycol, in particular propane-1 , 2-diol,0.1 wt.-% to 5.0 wt.-% of a buffer salt, referring to the total aqueous reaction medium, wherein the pH value is adjusted to a range from 7 to 8.

2. Process according to claim 1 , wherein at least part of the monomer composition is fed to the aqueous composition during polymerization.

3. Process according to claim 1 or 2, wherein at least part of the monomer composition is fed to the aqueous composition during polymerization together with a part of the aqueous reaction medium.

4. Process according to any of claims 1 to 3, wherein 30 wt.-% to 80 wt.-% of the total aqueous reaction medium is fed to the aqueous composition during polymerization.

5. Process according to any of claims 1 to 4, wherein the monomer composition consists to more than 95.0 wt.-% of the at least one (meth)acry I ate, referring to the total monomer composition.

6. Process according to any of claims 1 to 5, wherein the at least one (meth)acrylate is stearyl (meth)acrylate.

7. Process according to any of claims 1 to 6, wherein the buffer salt comprises a citrate, carbonate, borate and / or phosphate salt.

8. Process according to claim 7, wherein the buffer salt comprises a phosphate salt selected from the group consisting of alkali dihydrogen phosphate, alkali hydrogen phosphate, alkali phosphate, alkali di-phosphate, alkali tri-phosphate, alkali poly-phosphate, alkali meta-phosphate and mixtures thereof, in particular from sodium diphosphate and / or sodium hydrogen phosphate.

9. Process according to any of claims 1 to 8, wherein the polymerization initiator is selected from the group consisting of peroxides such as organic hydroperoxides; peracids; azo compounds; redox initiator systems and persulfates, in particular persulfates.

10. Process according to any of claims 1 to 9, wherein the aqueous reaction medium comprises at least one surfactant, in particular at least one sulfosuccinate such as bis(alkyl) sulfosuccinate, in particular sodium dioctylsulfosuccinate and / or sodium ditridecylsulfosuccinate; and / or at least one chain transfer agent, in particular an alkylthiol.11 . Process according to any of claims 1 to 10, wherein the pH value of the aqueous polymer dispersion is adjusted by addition of an aqueous ammonia solution and / or alkali hydroxides.

12. Process according to any of claims 1 to 11, wherein the polymerization is carried out at a polymerization temperature in a range from 50°C to 95°C, the resulting aqueous polymer dispersion is cooled to a storage temperature of 45°C or less and then the pH value of the aqueous polymer dispersion is adjusted to a range from 7 to 8.

13. Process according to any of claims 2 to 12, wherein the least part of the monomer composition being fed to the aqueous composition during polymerization and optionally the part of the aqueous reaction medium are preheated to a preheating temperature of 25°C or more before being fed to the aqueous composition.

14. An aqueous polymer dispersion obtainable or obtained by the process of any of claims 1 to 13, having a pH value in a range from 7 to 8 and in particular comprising the glycol such as propane-1, 2-diol.

15. Use of the aqueous polymer dispersion of claim 14 in coatings, in particular for hydrophobic coatings; for textile functionalization such as for water repellency of textiles; and / or as flow aids for oils.