Emulsion polymerization with solketal (meth)acrylate.

Abstract

1. A process for preparing an aqueous polymer latex by polymerizing a monomer composition containing solketal (meth)acrylate by radical emulsion polymerization in an aqueous polymerization medium in the presence of an acidic-acting radical polymerization initiator, optionally in the presence of a seed latex, wherein the monomer composition comprises a) 0.1 to 100% by weight of solketal (meth)acrylate, b) 0 to 99.9% by weight of one or more further ethylenically unsaturated monomers, and wherein an essentially neutral pH in the range of 6 to 8 is maintained in the aqueous polymerization medium during the radical emulsion polymerization reaction by the presence of a basic compound.

Description

[Technical field]

[0001] The present invention relates to a process for the preparation of an aqueous polymer latex containing solketal (meth)acrylate as monomer by radical emulsion polymerization, as well as to the aqueous polymer latex obtained thereby and its uses. [Background technology]

[0002] Solketal acrylate, also known as (2,2-dimethyl-1,3-dioxolan-4-yl)methyl acrylate, IPGA, is known as a reactive diluent in curable compositions, such as printing inks, preferably inkjet printing inks. Solketal acrylate can be prepared by transesterification of ethyl acrylate with solketal, as described in WO 2018 / 146258.

[0003] Solketal (meth)acrylates are of increasing interest as monomers for the preparation of aqueous polymer latexes by radical emulsion polymerization in a variety of applications, such as water-based coatings, films, paints and various adhesives. Further application areas for the polymer latexes are, for example, pigment printing, road markings, flooring or oil drilling fluids.

[0004] Zhen et al., Atom Transfer Radical Polymerization of Solketal Acrylate Using Cyclohexanone as the Solvent, Macromolecular Chemistry and Physics 206(5), pp.607-612, describes the homopolymerization of solketal acrylate by atom transfer radical polymerization (ATRP) using CuBr / pentamethyldiethylenetriamine as catalyst and cyclohexanone as solvent. The prepared bromine-terminated homopolymer was used as a macroinitiator to initiate the polymerization of tert-butyl acrylate under similar ATRP conditions to produce a diblock copolymer with controlled molecular weight and low polydispersity.

[0005] Pham et al., Glycerol-based co-oligomers by free-radical chain transfer polymerization: Towards reactive polymers bearing acetal and / or carbonate groups with enhanced properties, European Polymer Journal 95(2017), pp.491-502, reported the synthesis of solvent-soluble oligomers from glycerol carbonate acrylate and solketal acrylate by free radical chain transfer polymerization using 2-mercaptoethanol as a chain transfer agent.

[0006] WO 2017 / 191167 discloses an aqueous polymer latex for use as a binder in an aqueous coating composition containing titanium dioxide pigment. The aqueous polymer latex is obtained by polymerizing a monomer composition M by radical emulsion polymerization using a specific supply method, the monomer composition M being a) 80 to 99.95% by weight of an ethylenically unsaturated monomer M1 based on the total weight of the monomer composition M, 20 -C5-C alkyl esters and methacrylic acid20 - a mixture of at least one monomer M1a selected from the group consisting of alkyl esters; and at least one monomer M1b selected from vinyl aromatic monomers and C1-C4-alkyl esters of methacrylic acid; b) 0.05 to 5 wt. %, based on the total weight of the monomer composition M, of one or more monoethylenically unsaturated monomers M2 selected from monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms and monoethylenically unsaturated dicarboxylic acids having 4 to 6 carbon atoms; c) 0 to 20% by weight of non-ionic monomers M3 different from the monomers M1, such as hydroxy-C2-C4-alkyl esters of acrylic and methacrylic acid. It consists of:

[0007] The aqueous polymer latex is used as a binder in an aqueous coating composition containing titanium dioxide pigment.

[0008] Aqueous emulsion polymerization initiated by free radicals is initiated by free radical polymerization initiators (free radical initiators). These are, as a rule, peroxides, persulfates, azo compounds and redox initiator systems. The peroxides can be inorganic or organic peroxides. Some radical polymerization initiators, especially inorganic persulfates, react acidically on contact with water. They, when dissolved in the aqueous reaction medium, give rise to an acidic pH below 6, especially at elevated temperatures. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2018 / 146258 Brochure [Patent Document 2] International Publication No. 2017 / 191167 Brochure [Non-patent literature]

[0010] [Non-Patent Document 1] Zhen et al., Atom Transfer Radical Polymerization of Solketal Acrylate Using Cyclohexanone as the Solvent,Macromolecular Chemistry and Physics 206(5),pp.607-612 [Non-Patent Document 2] Pham et al., Glycerol-based co-oligomers by free-radical chain transfer polymerization: Towards reactive polymers bearing acetal and / or carbonate groups with enhanced properties, European Polymer Journal 95(2017), pp. 491-502 Summary of the Invention [Problem to be solved by the invention]

[0011] It is an object of the present invention to provide a process for preparing aqueous polymer latexes containing solketal (meth)acrylate as monomer by radical emulsion polymerization using acid-working polymerization initiators, such as persulfates. [Means for solving the problem]

[0012] This problem is solved by a method for preparing an aqueous polymer latex by polymerizing a monomer composition containing solketal (meth)acrylate by radical emulsion polymerization in an aqueous polymerization medium in the presence of an acidic-acting radical polymerization initiator, optionally in the presence of a seed latex, wherein the monomer composition a) 0.1 to 100% by weight of solketal (meth)acrylate; b) 0 to 99.9% by weight of one or more further ethylenically unsaturated monomers Including, The present invention is characterized in that the pH of the aqueous polymerization medium is maintained essentially neutral in the range of 6 to 8 during the radical emulsion polymerization reaction by the presence of a basic compound. is solved by the method.

[0013] Solketal (meth)acrylate is an abbreviation for solketal acrylate and solketal methacrylate. Solketal acrylate is preferred.

[0014] Further ethylenically unsaturated monomers are C1-C of acrylic acid or methacrylic acid. 20 - alkyl esters.

[0015] C1~C 20The term alkyl refers to a group of straight or branched or cyclic saturated hydrocarbon radicals having from 1 to 20 carbon atoms. Examples of alkyl include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, secbutyl, isobutyl, tert-butyl, pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2 dimethylpropyl, 1-ethylpropyl, hexyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 1 methylpentyl, 2-methylpentyl, 3 methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2 dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3 dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylbutyl, 1,2-trimethylbutyl, 1,3 ... ethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, 1-ethyl-2-methylpropyl, n-heptyl, 2-heptyl, n-octyl, 2-octyl, isooctyl, 2-ethylhexyl, 2-propylheptyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyldocosyl, and in the case of nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyldocosyl, their isomers; Examples include cyclopentyl, cyclohexyl, methylcyclohexyl, dimethylcyclohexyl, cycloheptyl, cyclooctyl, cyclododecyl, cyclohexadecyl, norbornyl (=bicyclo[2.2.1]heptyl) and isobornyl (=1,7,7-trimethylbicyclo[2.2.1]heptyl).

[0016] In particular, tert-butyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-propyl-heptyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, 2-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, methyl (meth)acrylate are used as monomers b1). (Meth)acrylate is an abbreviation for acrylate and methacrylate.

[0017] Further ethylenically unsaturated monomers may be selected from the group b2) consisting of vinyl esters, in particular vinyl acetate, vinyl propionate, vinyl laurate, vinyl neodecanoate, vinyl esters of versatic acid and vinyl esters of 2-ethylhexanoic acid.

[0018] Further ethylenically unsaturated monomers may be selected from the group b3) consisting of vinyl aromatic monomers, in particular styrene.

[0019] Further ethylenically unsaturated monomers include - monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms, such as, for example, acrylic acid, methacrylic acid, crotonic acid, 2-ethylpropenoic acid, 2-propylpropenoic acid, 2-acryloxyacetic acid and 2-methacryloxyacetic acid; - monoethylenically unsaturated dicarboxylic acids having 4 to 6 carbon atoms, such as itaconic acid, citraconic acid, maleic acid and fumaric acid; - semiesters of monoethylenically unsaturated dicarboxylic acids having 4 to 6 carbon atoms with C1-C4 alkanols, such as methanol or ethanol, such as, for example, the semiesters of itaconic acid, citraconic acid, maleic acid or fumaric acid with methanol or ethanol; monoethylenically unsaturated sulfonic acids, such as vinylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, etc.; monoethylenically unsaturated phosphonic acids, such as vinylphosphonic acid, allylphosphonic acid, styrenephosphonic acid and 2-acrylamido-2-methylpropanephosphonic acid; and monoethylenically unsaturated phosphoric acids, such as, for example, monophosphates of hydroxyalkyl acrylates, monophosphates of hydroxyalkyl methacrylates, monophosphates of alkoxylated hydroxyalkyl acrylates and monophosphates of alkoxylated hydroxyalkyl methacrylates, in particular monophosphates of hydroxyethyl acrylate, hydroxypropyl acrylate or hydroxybutyl acrylate, monophosphates of hydroxyethyl methacrylate, hydroxypropyl methacrylate or hydroxybutyl methacrylate, monophosphates of ethoxylated hydroxy-C2-C4-alkyl acrylates, monophosphates of propoxylated hydroxy-C2-C4-alkyl acrylates, monophosphates of ethoxylated hydroxy-C2-C4-alkyl methacrylates and monophosphates of propoxylated hydroxy-C2-C4-alkyl methacrylates, may be selected from the group b4) consisting of:

[0020] Preferred monomers b4) are acrylic acid, methacrylic acid, maleic acid, the half-methyl ester of maleic acid, the half-ethyl ester of maleic acid, citraconic acid, the half-methyl ester of citraconic acid, itaconic acid, the half-methyl ester of itaconic acid, fumaric acid, the half-methyl ester of fumaric acid and the half-ethyl ester of fumaric acid.

[0021] Further ethylenically unsaturated monomers include - primary amides of monoethylenically unsaturated monocarboxylic acids having 3 to 8 carbon atoms, such as, for example, acrylamide and methacrylamide; -N-C1-C of monoethylenically unsaturated monocarboxylic acids having 3-6 carbon atoms 10 Alkylamides, especially N-C1 to C of acrylic or methacrylic acid 10Alkyl amides, such as N-methylacrylamide, N-ethylacrylamide, N-propylacrylamide, N-isopropylacrylamide, N-butylacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-propylmethacrylamide, N-isopropylmethacrylamide and N-butylmethacrylamide; -N-Hydroxy-C1-C of monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms 10 Alkylamides, especially N-hydroxy-C1-C of acrylic or methacrylic acid 10 Alkyl amides, such as N-hydroxymethyl acrylamide, Monoethylenically unsaturated monomers having urea or keto groups, such as 2-(2-oxo-imidazolidin-1-yl)ethyl (meth)acrylate, 2-ureido (meth)acrylate, N-[2-(2-oxooxazolidin-3-yl)ethyl]methacrylate, ethyl acetoacetoxyacrylate, acetoacetoxypropyl methacrylate, acetoacetoxybutyl methacrylate, 2-(acetoacetoxy)ethyl methacrylate, diacetone acrylamide (DAAM) and diacetone methacrylamide; hydroxyalkyl esters of monoethylenically unsaturated C3-C6 monocarboxylic acids, in particular the hydroxyalkyl esters of acrylic acid and the hydroxyalkyl esters of methacrylic acid, also called hydroxyalkyl (meth)acrylates below, in particular the hydroxy-C2-C4 alkyl esters of acrylic acid and the hydroxy-C2-C4 alkyl esters of methacrylic acid, such as 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate and 4-hydroxybutyl methacrylate; and Monoethylenically unsaturated monomers having at least one tri-C1-C4-alkoxysilane group, such as vinyltrimethoxysilane, vinyltriethoxysilane, methacryloxyethyltrimethoxysilane, methacryloxyethyltriethoxysilane, etc. may be selected from the group b5) consisting of:

[0022] Preferred monomers b5) are acrylamide, methacrylamide, N-hydroxymethylacrylamide, 2-hydroxyethyl acrylate, ureido methacrylate and 4-hydroxybutyl acrylate.

[0023] Further ethylenically unsaturated monomers include diesters of monoethylenically unsaturated C3-C6 monocarboxylic acids with saturated aliphatic or cycloaliphatic diols, in particular diesters of acrylic or methacrylic acid, such as the diacrylates and dimethacrylates of ethylene glycol (1,2-ethanediol), propylene glycol (1,2-propanediol), 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol (2,2-dimethyl-1,3-propanediol) and 1,2-cyclohexanediol; - monoesters of monoethylenically unsaturated C3-C6 monocarboxylic acids with monoethylenically unsaturated aliphatic or alicyclic monohydroxy compounds, such as the acrylates and methacrylates of vinyl alcohol (ethenol), allyl alcohol (2-propen-1-ol), 2-cyclohexen-1-ol or norbornenol; and - Divinyl aromatic compounds, such as 1,3-divinylbenzene and 1,4-divinylbenzene may be selected from the group b6) consisting of:

[0024] In some embodiments, the monomer composition comprises: a) 1 to 99% by weight of solketal (meth)acrylate; b) 1 to 99% by weight of one or more further ethylenically unsaturated monomers Includes.

[0025] In some particular embodiments, the monomer composition comprises: a) 5 to 50% by weight of solketal (meth)acrylate; b) 50 to 95% by weight of one or more further ethylenically unsaturated monomers Includes.

[0026] In some other particular embodiments, the monomer composition comprises: a) 1 to 20% by weight of solketal (meth)acrylate; b) 80 to 99% by weight of one or more further ethylenically unsaturated monomers Includes.

[0027] In some other particular embodiments, the monomer composition comprises: a) 50 to 95% by weight of solketal (meth)acrylate; b) 5 to 50% by weight of one or more further ethylenically unsaturated monomers Includes.

[0028] In some other particular embodiments, the monomer composition comprises: a) 80 to 99% by weight of solketal (meth)acrylate; b) 1 to 20% by weight of one or more further ethylenically unsaturated monomers Includes.

[0029] In some particular embodiments, the further ethylenically unsaturated monomer is selected from one or more of the groups b1), b2), b3), b4), b5), and b6).

[0030] The preparation process of the polymer latex is carried out according to well-known processes of the radical emulsion polymerization technique. The conditions necessary for carrying out the free-radical emulsion polymerization of monomers are described, for example, in the first cited prior art and in “Emulsions-polymerisation” [Emulsion Polymerisation] in Encyclopedia of Polymer Science and Engineering, vol. 8, pages 659 ff. (1987); DC 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, Interscience Publishers, New York (1965); DE-A-40 03 422 and Dispersionen synthetischer Hochpolymere [Dispersions of Synthetic High Polymers], F. Holscher, Springer-Verlag, Berlin (1969), are well known to those skilled in the art.

[0031] However, according to the present invention, it is essential that the radical emulsion polymerization is carried out by maintaining an essentially neutral pH in the aqueous polymerization medium, between pH 6 and 8, preferably between pH 6.5 and 7.5, during the course of the polymerization reaction due to the presence of a basic compound in the aqueous polymerization medium.

[0032] Free-radical initiated aqueous emulsion polymerizations are initiated by free-radical polymerization initiators (free-radical initiators). These are, as a rule, peroxides, persulfates, azo compounds and redox initiator systems.

[0033] According to the present invention, the free radical polymerization initiator is an acid-acting polymerization initiator which when dissolved in water generally leads to an acidic pH < 6, preferably ≦ 4, for example an acidic pH of 2 to 4. The free radical polymerization initiator may be acidic, especially at elevated temperatures.

[0034] The preferred acid-acting radical polymerization initiators used according to the present invention are persulfates.Preferred persulfates are sodium persulfate, potassium persulfate and ammonium persulfate.They are inexpensive and commonly used in industrial processes.

[0035] Generally, an essentially neutral pH in the aqueous polymerization medium is maintained during the polymerization reaction by adding a basic compound to the aqueous polymerization medium. In some embodiments of the process of the present invention, a partial or total amount of the basic compound is initially charged to the reaction vessel with the aqueous polymerization medium.

[0036] 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 such as ammonia or water-soluble organic amines, e.g. lower aliphatic amines, are also possible.

[0037] Preferred basic compounds are sodium, potassium and ammonium hydroxides, sodium and potassium carbonates, and sodium and potassium hydrogen carbonates (bicarbonates).

[0038] The basic compound is preferably dissolved in water.

[0039] In one embodiment, the amount of free radical initiator for emulsion polymerization is initially charged completely to the polymerization vessel. However, it is preferred that the acid-acting free radical initiator is not charged or is charged only partially, for example 40% by weight or less, in particular 15% by weight or less, based on the total amount of free radical initiator required for the aqueous polymerization medium.

[0040] A basic compound or a portion of the basic compound may also be initially charged to the polymerization vessel to achieve an essentially neutral pH of 6-8 in the aqueous reaction mixture, if desired. This is generally not necessary if no free radical initiator is charged and the pH of the initially charged reaction mixture is already pH 6-8. Then, under polymerization conditions, during the free radical emulsion polymerization of the monomers, the total or residual amount of the basic component is added batchwise in one or more portions, depending on the consumption, or continuously at a constant or variable flow rate to maintain a substantially neutral pH of 6-8 in the aqueous polymerization medium.

[0041] Preferably, the basic compound is dissolved in water and added as an aqueous solution as described above.

[0042] In another preferred embodiment, the free radical aqueous emulsion polymerization of the present invention is carried out at a temperature in the range of 0 to 170° C.; more preferably in the range of 50 to 100° C., most preferably in the range of 60 to 100° C., and in particular, the free radical aqueous emulsion polymerization of the present invention is carried out at a temperature in the range of 70 to 100° C. The free radical aqueous emulsion polymerization can be carried out at a pressure of less than 1 atmosphere (101325 Pa), 1 atmosphere, or greater than 1 atmosphere.

[0043] In certain embodiments, the polymerization is carried out in the presence of a chain transfer agent. Chain transfer agents are aliphatic and / or araliphatic halogen compounds, such as 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, such as ethanethiol, n-propanethiol, 2-propanethiol, n-butanethiol, 2-butanethiol, 2-methyl-2-propanethiol, n-pentanethiol, 2-pentanethiol, 3-pentanethiol, 2-methyl-2-butanethiol, 3-methyl-2-butanethiol, n-hexanethiol, 2-hexanethiol, 3-hexanethiol, 2-methyl-2-pentanethiol, 3-methyl-2-pentanethiol, 4-methyl-2-pentanethiol. , 2-methyl-3-pentanethiol, 3-methyl-3-pentanethiol, 2-ethylbutanethiol, 2-ethyl-2-butanethiol, n-heptanethiol and its isomers, n-octanethiol and its isomers, n-nonanethiol and its isomers, n-decanethiol and its isomers, n-undecanethiol and its isomers, n-dodecanethiol and its isomers, n-tridecanethiol and its isomers, substituted thiols such as 2-hydroxyethanethiol, aromatic thiols such as benzenethiol, ortho-, meta- or para-methylbenzenethiol, alkyl esters of mercaptoacetic acid (thioglycolic acid), such as 2-ethylhexyl thioglycolate, alkyl esters of mercaptopropionic acid, such as octyl mercaptopropionate, and also those described in Polymer Handbook, 3rd edition, 1989, J. Brandrup and EHImmergut, John Wiley & Sons, section II, pages 133-141, and aliphatic and / or aromatic aldehydes, such as acetaldehyde, propionaldehyde and / or benzaldehyde, unsaturated fatty acids, such as oleic acid, dienes with non-conjugated double bonds, such as divinylmethane or vinylcyclohexane, or hydrocarbons with easily abstractable hydrogen atoms, such as toluene.

[0044] Generally, the total amount of chain transfer agents, if present, will not exceed 1% by weight, based on the total amount of monomers.

[0045] Generally, radical emulsion polymerization is carried out in the presence of a surfactant. The surfactant can be selected from emulsifiers and protective colloids. Protective colloids are understood to mean polymeric compounds with a molecular weight of more than 2000 Daltons, in contrast to emulsifiers, while emulsifiers typically have a lower molecular weight. The surfactant can be anionic or nonionic, or a mixture of nonionic and anionic surfactants.

[0046] Anionic surfactants generally have at least one anionic group selected from phosphate group, phosphonate group, sulfate group and sulfonate group.Anionic surfactants having at least one anionic group are typically used in the form of their alkali metal salts, particularly their sodium salts, or in the form of their ammonium salts.

[0047] In a preferred embodiment, the anionic surfactant is an anionic emulsifier, in particular having at least one sulfate or sulfonate group. Similarly, an anionic emulsifier having at least one phosphoric or phosphonic acid group can be used as the only anionic emulsifier or in combination with one or more anionic emulsifiers having at least one sulfate or sulfonate group. Examples of anionic emulsifiers having at least one sulfate or sulfonate group are, for example, alkyl sulfates, in particular C8-C 22 - the salts of alkylsulfuric acids, in particular the alkali metal and ammonium salts, preferably the sulfate monoesters of ethoxylated alkanols, with an ethoxylation level (EO level) ranging from 2 to 40, in particular the ethoxylated C8-C 22 - Salts of sulfuric acid monoesters of alkanols, in particular the alkali metal and ammonium salts, and sulfuric acid monoesters of ethoxylated alkylphenols, in particular the ethoxylated C4-C 18 - salts of sulfuric acid monoesters of alkylphenols (EO level preferably 3-40), in particular the alkali metal and ammonium salts, alkylsulfonic acids, in particular C8-C 22 -Salts of alkylsulfonic acids, in particular the alkali metal and ammonium salts, dialkyl esters, in particular di-C1-C2 sulfosuccinic acids 18 - Salts of alkyl esters, in particular the alkali metal and ammonium salts, alkylbenzenesulfonic acids, in particular C4-C 22 - the salts of alkylbenzenesulfonic acids, in particular the alkali metal and ammonium salts, and mono- or disulfonated alkyl-substituted diphenyl ethers, e.g. those containing C4-C on one or both aromatic rings; 24 -alkyl groups, particularly the alkali metal and ammonium salts. Examples are described in U.S. Patent No. 4,269,749 and Dowfax® 2A1 (Dow Chemical Company).

[0048] In a particularly preferred embodiment, the anionic surfactant is an anionic emulsifier selected from the following group: Alkyl sulfates, especially C8-C22 the salts of alkyl sulfates, in particular the alkali metal and ammonium salts; Sulfuric acid monoesters of ethoxylated alkanols, especially ethoxylated C8-C 22 - Salts of sulfuric acid monoesters of alkanols, in particular alkali metal salts (preferably with an ethoxylation level (EO level) in the range of 2 to 40) Sulfuric acid monoesters of ethoxylated alkylphenols, especially ethoxylated C4-C 18 - Sulfuric acid monoesters of alkylphenols (EO level preferably 3-40), alkylbenzenesulfonic acids, especially C4-C 22 -sulfuric acid monoesters of alkylbenzenesulfonic acids, and Mono- or disulfonated alkyl-substituted diphenyl ethers, e.g., C4-C on one or both aromatic rings 24 -Bis(phenylsulfonic acid) ethers having alkyl groups.

[0049] Examples of anionic emulsifiers having phosphoric or phosphonic acid groups include, but are not limited to, the following salts selected from the following group: Mono- and dialkyl phosphates, especially C8-C 22 the salts of alkyl phosphates, in particular the alkali metal and ammonium salts, Phosphoric acid monoesters of C2-C3-alkoxylated alkanols, preferably having an alkoxylation level in the range from 2 to 40, in particular in the range from 3 to 30, such as ethoxylated C8-C 22 - Phosphate monoesters of alkanols (preferably with an ethoxylation level (EO level) in the range of 2 to 40), propoxylated C8-C 22 - Phosphate monoesters of alkanols (preferably with a propoxylation level (PO level) of 2-40) and ethoxylated-co-propoxylated C8-C 22 the salts, in particular the alkali metal and ammonium salts, of phosphoric acid monoesters of alkanols, preferably having an ethoxylation level (EO level) in the range from 1 to 20 and a propoxylation level of 1 to 20; Phosphate monoesters of ethoxylated alkylphenols, especially ethoxylated C4-C 18 the salts, in particular the alkali metal and ammonium salts, of phosphoric acid monoesters of alkylphenols (with an EO level preferably between 3 and 40); Alkylphosphonic acids, especially C8-C 22 the salts of alkylphosphonic acids, in particular the alkali metal and ammonium salts, Alkylbenzene phosphonic acids, especially C4-C 22 - The salts of alkylbenzenephosphonic acids, in particular the alkali metal and ammonium salts.

[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, p. 192-208.

[0051] In another preferred embodiment, the surfactant comprises at least one anionic emulsifier having at least one sulfate or sulfonate group. The at least one anionic emulsifier having at least one sulfate or sulfonate group may be the only type of anionic emulsifier. However, a mixture of at least one anionic emulsifier having at least one sulfate or sulfonate group and at least one anionic emulsifier having at least one phosphoric acid or phosphonic acid group may also be used. In such a mixture, the amount of at least one anionic emulsifier having at least one sulfate or sulfonate group is preferably at least 50% by weight based on the total weight of the anionic surfactant used in the method of the present invention. In particular, the amount of the anionic emulsifier having at least one phosphoric acid or phosphonic acid group does not exceed 20% by weight based on the total weight of the anionic surfactant used in the method of the present invention.

[0052] In another preferred embodiment, the surfactant may also comprise one or more non-ionic surface active substances, in particular selected from non-ionic emulsifiers. Suitable non-ionic emulsifiers are, for example, aromatic aliphatic or aliphatic non-ionic emulsifiers, such as ethoxylated mono-, di- and trialkylphenols (EO level: 3-50, alkyl chain: C4-C5, ethylene glycol, propylene ... 10 ), ethoxylates of long-chain alcohols (EO level: 3-100, alkyl chain: C8-C 36 ), as well as polyethylene oxide / polypropylene oxide homopolymers and copolymers. These may contain alkylene oxide units copolymerized in random distribution or in the form of blocks. Very suitable examples are EO / PO block copolymers. Ethoxylates of long-chain alkanols (alkyl chain C1-C 30 , average ethoxylation level 5 to 100) are preferred, and among these, C 12 ~C 20 Particularly preferred are those with alkyl chains and average ethoxylation levels of 5 to 20, as well as ethoxylated monoalkylphenols.Preferably, the surfactant used in the process of the invention comprises less than 60% by weight, in particular not more than 50% by weight, of non-ionic surfactant, based on the total amount of surfactant used in the process of the invention.

[0053] In another embodiment, the surfactant used in the method of the present invention comprises at least one anionic surfactant and at least one nonionic surfactant, and the ratio of anionic surfactant to nonionic surfactant is typically in the range of 0.5:1 to 10:1, in particular 1:1 to 5:1.

[0054] In another preferred embodiment, the surfactant(s) are used in an amount such that the amount of the surfactant(s) is in the range of 0.2% to 5% by weight, in particular in the range of 0.5% to 3% by weight, based on the monomers to be polymerized.

[0055] The aqueous reaction medium in the polymerization may in principle also contain small amounts (≦5% by weight) of water-soluble organic solvents, such as methanol, ethanol, isopropanol, butanol, pentanol, but also acetone, etc. Preferably, however, the process of the invention is carried out in the absence of such solvents.

[0056] Generally, the resulting aqueous polymer dispersion has a polymer solids content in the range of 10% to 70% by weight, preferably 20% to 65% by weight, more preferably 30% to 60% by weight, and most preferably 40% to 60% by weight, in each case based on the total weight of the aqueous polymer dispersion.

[0057] It has been found to be advantageous to carry out the free radical emulsion polymerization in the presence of a seed latex. The seed latex is a polymer latex that is present in the aqueous polymerization medium before the metering of the solketal (meth)acrylate and optionally further monomers is started. The seed latex can help to better control the particle size of the final polymer latex obtained in the free radical emulsion polymerization of the present invention.

[0058] Basically, any polymer latex can serve as a seed latex. For the purposes of the present invention, seed latexes in which the polymer particles have a relatively small particle size are preferred. The Z-average particle size of the polymer particles of the seed latex, determined by dynamic light scattering at 20° C., is preferably in the range of 10-80 nm, in particular 10-50 nm. Preferably, the polymer particles of the seed latex are made of ethylenically unsaturated monomers, which are at least 95% by weight, based on the total weight of the monomers forming the seed latex, of C2-C acrylic acid. 10 - alkyl esters, in particular ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, C1-C4-alkyl esters of methacrylic acid, in particular methyl methacrylate, and vinyl aromatic monomers, in particular styrene.

[0059] For this purpose, the seed latex is usually charged to the polymerization vessel before the metering of the solketal (meth)acrylate and optionally further monomers is started. In particular, the seed latex is charged to the polymerization vessel, followed by the establishment of polymerization conditions and the charging of at least a portion of the free radical initiator to the polymerization vessel before the metering of the solketal (meth)acrylate and optionally further monomers is started.

[0060] The amount of seed latex, calculated as solids, may range from 0.1 to 10% by weight, in particular from 0.5 to 5% by weight, based on the total weight of the monomers to be polymerized.

[0061] Generally, the reactor is initially charged with none, some or all of the free radical initiator, none, some or all of the basic compound, optionally some or all of the surfactant, optionally some or all of the solketal (meth)acrylate, and optionally one or more additional ethylenically unsaturated monomers.

[0062] In a preferred embodiment, the free radical emulsion polymerization is carried out by adding one or more feeds containing solketal (meth)acrylate, optionally one or more further ethylenically unsaturated monomers, and optionally a surfactant, one feed containing an acid-acting polymerization initiator, and one feed containing a basic compound to a reactor containing an aqueous reaction medium.

[0063] In a more preferred embodiment, a portion of the free radical initiator, a portion of the basic compound, optionally a portion of the surfactant, optionally a portion of the solketal (meth)acrylate, and optionally one or more additional ethylenically unsaturated monomers are initially charged to the reactor.

[0064] Thus, in a more preferred embodiment, the radical emulsion polymerization is carried out by first charging a portion of the free radical initiator, a portion of the basic compound, optionally a portion of the surfactant, and optionally a portion of the solketal (meth)acrylate and any one or more additional ethylenically unsaturated monomers to a reaction vessel, and adding one or more feeds containing the (remaining) solketal (meth)acrylate, optionally the (remaining) one or more additional ethylenically unsaturated monomers and optionally the (remaining) surfactant, one feed containing the remaining acid-acting polymerization initiator, and one feed containing the basic compound.

[0065] The present invention also relates to the polymer latex obtained by the method of the present invention and its use.The preferred application of the polymer latex is in coating, film, paint and various adhesives.Further application fields of the polymer latex are, for example, pigment printing, road marking, flooring or oil drilling fluid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] The present invention will now be described in more detail by the following examples. EXAMPLES

[0067] Example E1 Hydrolysis studies using solketal acrylate under acidic conditions Mix 5 g of Solketal acrylate, 0.4 g of sodium dodecyl sulfate, 0.025 g of methylhydroquinone (MeHQ) and 0.025 g of phenothiazine (PTZ) with 45 g of deionized water and stir. The pH value is adjusted as follows: a) 2.5 b) 3.8 c) 7.0 In cases a) and b), an aqueous HCl solution (5 wt. % solution) is used, and in case c), an aqueous sodium bicarbonate solution (10 wt. %) is used. The mixture is stirred at 90° C. for 3 h. In case c), the pH is kept at pH 7 by successive addition of drops of an aqueous sodium bicarbonate solution (10 wt. %). The mixture is then cooled to room temperature. In cases a) and b), the pH is adjusted to pH 7 using an aqueous sodium hydroxide solution (10 wt. % solution).

[0068] The degree of hydrolysis of solketal acrylate is determined by GC analysis. Degree of hydrolysis: a)>99.8% b)>99.8% c) <0.01%

[0069] Example E2 Emulsion polymerization with solketal acrylate under neutral conditions. A reactor equipped with stirrer, temperature control, nitrogen inlet and several inlets is charged with 500 g deionized water, 11 g sodium lauryl sulfate and 0.4 g potassium persulfate. The reaction mixture is purged with nitrogen, heated to 85 °C and adjusted to pH 7 with Feed 3. At 85 °C, Feed 1 is added in 80 min and Feed 2 is added in 90 min. The pH is kept between pH 6.5 and 7.5 by continuous dropwise addition of Feed 3 (Feed 3 is not necessarily added completely). Feed 1: 350 g deionized water, 5 g sodium lauryl sulfate, 196.25 g methyl methacrylate, 196.25 g n-butyl acrylate, 392.5 g solketal acrylate. Feed 2: 3 g potassium persulfate in 60 g deionized water. Feed 3: 10 g sodium bicarbonate in 70 g deionized water. The reaction mixture is post-polymerized for 60 minutes at 85° C. The reaction mixture is then cooled to ambient temperature.

[0070] No coagulum is observed.

[0071] Examples E3 to E5 Emulsion polymerization with solketal acrylate under neutral conditions. Emulsion polymerizations E3–E5 were prepared similarly to the protocol for E2, substituting the monomers with their respective relative amounts given in weight % (based on total monomers, BOTM) and are summarized in Table 1 .

[0072] No coagulum is observed.

[0073] Comparative Example C1 Emulsion polymerization using solketal acrylate under acidic conditions without pH adjustment. A reactor equipped with stirrer, temperature control, nitrogen inlet and several inlets is charged with 500 g deionized water, 11 g sodium lauryl sulfate and 0.4 g potassium persulfate. The reaction mixture is purged with nitrogen and heated to 85° C. At 85° C., feed 1 is added in 80 minutes and feed 2 is added in 90 minutes. Feed 1: 350 g deionized water, 5 g sodium lauryl sulfate, 196.25 g methyl methacrylate, 196.25 g n-butyl acrylate, 392.5 g solketal acrylate. Feed 2: 3 g potassium persulfate in 60 g deionized water. The reaction mixture is post-polymerized at 85° C. for 60 minutes. The reaction mixture is then cooled to ambient temperature.

[0074] Complete coagulation is observed. No dispersion is formed.

[0075] Comparative Example C2 Solketal acrylate-free emulsion polymerization under neutral conditions. The emulsion polymerization of C2 was prepared similarly to the protocol for E2, substituting the monomers with their relative amounts given in weight % (based on total monomers, BOTM) and are summarized in Table 1.

[0076] No coagulum is observed.

[0077] The results of the experiment are summarized in Table 1.

[0078] [Table 1]

Claims

1. 1. A process for preparing an aqueous polymer latex by polymerizing a monomer composition containing solketal (meth)acrylate in an aqueous polymerization medium in the presence of an acid-acting radical polymerization initiator by radical emulsion polymerization, optionally in the presence of a seed latex, comprising: The monomer composition comprises: a) 0.1 to 100% by weight of solketal (meth)acrylate; b) 0 to 99.9% by weight of one or more further ethylenically unsaturated monomers Including, A process characterized in that an essentially neutral pH in the range of 6 to 8 is maintained in said aqueous polymerization medium during the free radical emulsion polymerization reaction by the presence of a basic compound.

2. 2. The method of claim 1, wherein the acid-working radical polymerization initiator is a persulfate.

3. 3. The process of claim 1 or 2, wherein said essentially neutral pH in said aqueous polymerization medium is maintained during said free radical emulsion polymerization reaction by adding a basic compound to said aqueous polymerization medium.

4. 4. The method of claim 3, wherein the basic compound is selected from the group consisting of water-soluble alkali or alkaline earth metal or ammonium hydroxides, oxides, carbonates, hydrogen carbonates (bicarbonates), acetates, citrates, borates phosphates and hydrogen phosphates, ammonia, and water-soluble organic amines.

5. 5. The method of claim 4, wherein the basic compound is selected from the group consisting of sodium, potassium and ammonium hydroxides, sodium and potassium carbonates and sodium and potassium hydrogen carbonates (bicarbonates).

6. The process according to any one of claims 1 to 5, wherein the free-radical emulsion polymerization is carried out in the presence of a surfactant.

7. The radical emulsion polymerization one or more feeds comprising solketal (meth)acrylate, optionally one or more additional ethylenically unsaturated monomers, and optionally a surfactant; one feed comprising the acid-working radical polymerization initiator, and One feed containing the basic compound 7. The process of claim 1 , wherein the process is carried out by adding to a reactor containing an aqueous reaction medium.

8. 8. The method of claim 7, wherein a portion of the free radical initiator, a portion of the basic compound, optionally a portion of the surfactant, optionally a portion of the solketal (meth)acrylate, and any one or more additional ethylenically unsaturated monomers are initially charged to the reactor.

9. A polymer latex obtainable by the process according to any one of claims 1 to 8.

10. 10. Use of the polymer latex according to claim 9 in coatings, films, paints, adhesives and for pigment printing, road markings, flooring or oil drilling.

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