Vinyl ester / (meth) acrylate polymer dispersions

Abstract

The invention relates to a method for producing a polymer dispersion and to an aqueous polymer dispersion obtained by such a method and to the use of the aqueous polymer dispersion. Furthermore, in particular but not exclusively, the present invention relates to redispersible polymer powders and uses of the redispersible polymer powders, and building materials comprising such aqueous polymer dispersions or redispersible polymer powders.

Description

Technical Field

[0001] The present invention relates to a method for preparing a polymer dispersion and an aqueous polymer dispersion obtained by this method and the use of the aqueous polymer dispersion. In addition, in particular but not exclusively, the present invention relates to a redispersible polymer powder and the use of the redispersible polymer powder, as well as a building material comprising such an aqueous polymer dispersion or redispersible polymer powder. Background Art

[0002] For many years, waterborne polymer dispersions and the corresponding redispersible powders have been indispensable additives in applications in the construction industry, such as for renders, mortars, reinforcing compositions, self-leveling compositions, tile adhesives, paints and composite insulation systems. Especially for high-quality renders, the increasing use of binders can provide, for example, better mechanical properties, better weathering resistance and lower susceptibility tosoiling.

[0003] To date, these polymer dispersions have been preferably prepared using protective colloid-stabilized polymerization of vinyl ester monomers and (meth)acrylate monomers. However, plasticizers and coalescing agents are usually required to maintain the flexibility of the film. These plasticizers and coalescing agents are undesirable because they may increase the volatile organic compound (VOC) content of the product. Since plasticizers and coalescing agents are not permanently bound to the polymer structure, migration of these plasticizers and coalescing agents may occur.

[0004] Furthermore, due to the different reactivity ratios between the monomers and the different grafting reaction rates of the monomers with the protective colloid, it is difficult to polymerize different vinyl ester monomers and (meth)acrylate monomers to prepare a polymer dispersion that can be dried to form a redispersible powder. This may result in deteriorated stability of the polymer dispersion and reduced polymer properties.

[0005] EP 1 262 465 A2 relates to the use of copolymers derived from vinyl esters, (meth)acrylates and optionally ethylene comonomers and stabilized with protective colloids in the form of aqueous dispersions thereof or redispersible polymer powders and their use in building materials.

[0006] Surprisingly, it was found that the process of the present invention enables the formation of polymer dispersions having a low glass transition temperature (which provides film flexibility and film formation at low temperatures) while having enhanced chemical resistance. In addition, the process of the present invention enables the formation of polymer dispersions having high resistance to degradation in water without compromising re-wetting. The process also enables the formation of polymer dispersions having a low VOC content. The present process also provides for the formation of polymer dispersions having a wide range of compositions, which allows tailoring of polymer dispersion properties to accommodate a wide range of possible applications. Summary of the invention

[0007] The following clauses summarize some aspects of the invention.

[0008] According to a first aspect, the present invention relates to a process for preparing a polymer dispersion by free-radical emulsion or suspension polymerization of a mixture of ethylenically unsaturated monomers, comprising the following steps:

[0009] (i) providing an aqueous composition comprising a first mixture of ethylenically unsaturated monomers, the first mixture comprising:

[0010] (a) vinyl alkanoate having the following structural formula:

[0011] ,

[0012] Where R 1 is H or CH3; R 2 and R 3 is an alkyl group containing 6 to 8 carbon atoms in total; and

[0013] (b) an alkanoic acid vinyl ester different from the alkanoic acid vinyl ester (a);

[0014] and polymerizing the mixture of ethylenically unsaturated monomers in the presence of a protective colloid to obtain seed particles;

[0015] (ii) adding to the aqueous composition after step (i) a second mixture of ethylenically unsaturated monomers comprising:

[0016] (a) vinyl alkanoate having the following structural formula:

[0017] ,

[0018] Where R 1 is H or CH3; R 2 and R 3is an alkyl group containing 6 to 8 carbon atoms in total; and

[0019] (b) an alkanoic acid vinyl ester different from the alkanoic acid vinyl ester (a);

[0020] and polymerizing the mixture of ethylenically unsaturated monomers in the presence of a protective colloid;

[0021] (iii) adding a third mixture of ethylenically unsaturated monomers comprising the following to the aqueous composition after step (ii):

[0022] (a) vinyl alkanoate having the following structural formula:

[0023] ,

[0024] Where R 1 is H or CH3; R 2 and R 3 is an alkyl group containing 6 to 8 carbon atoms in total; and

[0025] (b) (Meth)acrylates;

[0026] and polymerizing the mixture of ethylenically unsaturated monomers;

[0027] (iv) adding a fourth mixture of ethylenically unsaturated monomers comprising vinyl alkanoate to the aqueous composition after step (iii); and polymerizing the mixture of ethylenically unsaturated monomers.

[0028] The vinyl alkanoate (a) in one, more than one or all, preferably all, of the first to third mixtures of ethylenically unsaturated monomers may have the following structural formula:

[0029]

[0030] Where R 1 is H or CH3; R 2 and R 3 The alkyl group contains 6 or 7 carbon atoms in total.

[0031] The vinyl alkanoate (a) in one, more than one or all, preferably all, of the first to third mixtures of ethylenically unsaturated monomers may have the following structural formula:

[0032] ,

[0033] Where R 1 CH3; R 2 and R 3 The alkyl group contains 7 carbon atoms in total.

[0034] The vinyl alkanoate (a) in one, more than one or all, preferably all, of the first to third mixtures of ethylenically unsaturated monomers may have the following structural formula:

[0035] ,

[0036] Where R 1 H; R 2 and R 3 An alkyl group having a total of 6 carbon atoms.

[0037] The alkanoic acid vinyl ester (b) different from the alkanoic acid vinyl ester (a) in one, more than one or all, preferably all, of the first to third mixtures of ethylenically unsaturated monomers may include vinyl acetate, 1-methylvinyl acetate, vinyl propionate, vinyl butyrate, vinyl laurate, vinyl pivalate and combinations thereof, preferably vinyl acetate.

[0038] The vinyl alkanoate of the fourth mixture of ethylenically unsaturated monomers may include vinyl acetate, 1-methylvinyl acetate, vinyl propionate, vinyl butyrate, vinyl laurate, vinyl pivalate, and combinations thereof, preferably vinyl acetate.

[0039] The first mixture of ethylenically unsaturated monomers may include:

[0040] (a) 10 to 90 wt %, preferably 20 to 80 wt %, more preferably 20 to 70 wt % of vinyl alkanoate; and

[0041] (b) 10 to 90 weight percent, preferably 20 to 80 weight percent, more preferably 30 to 80 weight percent of a vinyl alkanoate different from the vinyl alkanoate (a); the weight percentages are based on the total weight of the monomers in the first mixture of ethylenically unsaturated monomers.

[0042] The second mixture of ethylenically unsaturated monomers may include:

[0043] (a) 10 to 70 wt %, preferably 15 to 60 wt %, more preferably 20 to 50 wt % of vinyl alkanoate; and

[0044] (b) 30 to 90 weight percent, preferably 40 to 85 weight percent, more preferably 50 to 80 weight percent of a vinyl alkanoate different from the vinyl alkanoate (a); the weight percentages are based on the total weight of the monomers in the second mixture of ethylenically unsaturated monomers.

[0045] The third mixture of ethylenically unsaturated monomers may include:

[0046] (a) 10 to 70 wt %, preferably 15 to 60 wt %, more preferably 30 to 50 wt % of vinyl alkanoate; and

[0047] (b) 35 to 90 wt %, preferably 40 to 85 wt %, more preferably 50 to 80 wt % of (meth)acrylate; the weight percentages are based on the total weight of the monomers in the third mixture of ethylenically unsaturated monomers.

[0048] The (meth)acrylate can be selected from methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, 4-methyl-2-pentyl (meth)acrylate, 2-methylbutyl (meth)acrylate, 3,5,5-trimethylhexyl (meth)acrylate and combinations thereof, preferably butyl (meth)acrylate and combinations thereof.

[0049] The median particle size of the seed particles in step (i) may be in the range of 100 nm to 300 nm.

[0050] The protective colloid in the first step (i) and / or the second step (ii), preferably in the first step (i) and the second step (ii), may include polyvinyl alcohol, polyvinyl alcohol copolymers and combinations thereof, preferably polyvinyl alcohol.

[0051] The degree of hydrolysis of the polyvinyl alcohol can be in the range of 80 mol % to 99 mol %, preferably in the range of 80 mol % to 95 mol %, more preferably in the range of 85 mol % to 94 mol %; and the viscosity of the polyvinyl alcohol can be in the range of 1 mPa·s to 56 mPa·s, preferably in the range of 2 mPa·s to 50 mPa·s, more preferably in the range of 3 mPa·s to 40 mPa·s, the viscosity being measured by a Hoppler falling ball viscometer according to DIN 53015:2019 at 20°C for a 4 wt % aqueous solution of polyvinyl alcohol.

[0052] The protective colloid may be added in the first step (i) in an amount ranging from 2.0 wt % to 11.0 wt %, the weight percentage being based on the total weight of the monomers in the first to fourth mixtures of ethylenically unsaturated monomers.

[0053] The first mixture of ethylenically unsaturated monomers may further comprise a chain transfer agent, wherein the chain transfer agent is preferably selected from n-dodecyl mercaptan, carbon tetrachloride, carbon tetrabromide, bromotrichloromethane, 4-methylbenzenethiol, isooctyl 3-mercaptopropionate, tert-nonyl mercaptan, 4,4'-thiobisbenzenethiol, tert-dodecyl mercaptan, α-methylstyrene dimer, thioglycolic acid, 2-ethylhexyl thioglycolate, butyl 3-mercaptopropionate, 1,8-dimercapto-3,6-dioxaoctane, and combinations thereof.

[0054] The second mixture of ethylenically unsaturated monomers may be added continuously in step (ii) such that the reaction temperature is in the range of 70°C to 90°C.

[0055] When no new seed particles are formed in step (ii), step (iii) can be started.

[0056] The third mixture of ethylenically unsaturated monomers may be added continuously in step (iii) such that the reaction temperature is in the range of 70°C to 90°C.

[0057] The first mixture of ethylenically unsaturated monomers (i) may comprise from 1 wt% to 15 wt% of ethylenically unsaturated monomers;

[0058] The second mixture of ethylenically unsaturated monomers (ii) may comprise from 35% to 90% by weight of ethylenically unsaturated monomers;

[0059] The third mixture of ethylenically unsaturated monomers (iii) may comprise from 8 to 50 wt% of ethylenically unsaturated monomers; and

[0060] The fourth mixture of ethylenically unsaturated monomers (iv) may comprise from 1 wt% to 20 wt% of ethylenically unsaturated monomers;

[0061] The weight percentages are based on the total weight of the ethylenically unsaturated monomers of the first through fourth mixtures of ethylenically unsaturated monomers.

[0062] Mixtures of ethylenically unsaturated monomers can be polymerized by free radical emulsion polymerization.

[0063] According to another aspect of the present invention, the present invention relates to an aqueous polymer dispersion obtained by the above method.

[0064] Furthermore, another aspect of the present invention relates to a redispersible polymer powder obtained by drying the aqueous polymer dispersion as described above.

[0065] Drying can be achieved by fluid bed drying, freeze drying or spray drying.

[0066] Another aspect of the present invention relates to the use of the above aqueous polymer dispersion or the above redispersible polymer powder in building materials such as building adhesives, plasters, fillers, floor fillers, sealing slurries, grouts and paints.

[0067] A further aspect of the invention relates to a building material comprising an aqueous polymer dispersion as described above or a redispersible polymer powder as described above.

[0068] The building material may be selected from cement-based tile adhesives; self-leveling substrates; thermal insulation systems (ETICS); repair mortars; cement-based grouts; joint fillers; plasters and plasters; joint compounds; fillers; or waterproofing compounds. DETAILED DESCRIPTION

[0069] The present invention relates to a method for preparing a polymer dispersion by free radical emulsion polymerization or free radical suspension polymerization of a mixture of ethylenically unsaturated monomers. The method of the present invention comprises the following steps: (i) providing an aqueous composition comprising a first mixture of ethylenically unsaturated monomers, and polymerizing the mixture of ethylenically unsaturated monomers in the presence of a protective colloid to obtain seed particles; (ii) adding a second mixture of ethylenically unsaturated monomers to the aqueous composition after step (i); and polymerizing the mixture of ethylenically unsaturated monomers in the presence of a protective colloid; (iii) adding a third mixture of ethylenically unsaturated monomers to the aqueous composition after step (ii); and polymerizing the mixture of ethylenically unsaturated monomers; and (iv) adding a fourth mixture of ethylenically unsaturated monomers, and polymerizing the mixture of ethylenically unsaturated monomers.

[0070] As used herein, the term "aqueous" refers to a medium consisting only of water or a medium mainly including water (e.g., at least 50% by weight of water) and a non-aqueous solvent combination. If desired, a non-aqueous solvent can be used in a small amount in an aqueous composition of the present invention. Based on the gross weight of water and the non-aqueous solvent, the content of the non-aqueous solvent can be less than 3% by weight, preferably less than 2% by weight, more preferably less than 1.5% by weight, most preferably less than 1% by weight, specifically less than 0.5% by weight. The example of suitable non-aqueous solvent includes but is not limited to toluene, acetone, methyl ethyl ketone, cyclohexane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ether, dimethyl formamide, dimethyl sulfoxide, monohydric alcohols such as methanol and ethanol, and polyols. Aqueous composition preferably does not contain a non-aqueous solvent.

[0071] The first mixture of ethylenically unsaturated monomers (i) comprises: (a) an alkanoic acid vinyl ester having the formula:

[0072] ,

[0073] Where R 1 is H or CH3; R 2 and R 3 is an alkyl group having a total of 6 to 8 carbon atoms, preferably 6 or 7 carbon atoms; and (b) an alkanoic acid vinyl ester different from the alkanoic acid vinyl ester (a).

[0074] The vinyl alkanoate (a) of the first mixture of ethylenically unsaturated monomers (i) may have the following structural formula:

[0075]

[0076] Where R 1 CH3; R 2 and R 3 The alkyl group contains 7 carbon atoms in total.

[0077] The vinyl alkanoate (a) of the first mixture of ethylenically unsaturated monomers (i) may have the following structural formula:

[0078]

[0079] Where R 1 H; R 2 and R 3 is an alkyl group containing 6 carbon atoms in total, wherein R 2 Ethyl, R 3 It is butyl.

[0080] Suitable examples of the alkanoic acid vinyl esters (a) of the first mixture (i) of ethylenically unsaturated monomers that can be used according to the present invention can be exemplified by VeoVa grade vinyl esters commercially available from Hexion Inc. (USA), such as VeoVa 9 vinyl ester, VeoVa 10 vinyl ester and Veova EH vinyl ester.

[0081] According to the present invention, the first mixture (i) of ethylenically unsaturated monomers can include at least 10 weight %, such as at least 13 weight %, or at least 15 weight %, or at least 18 weight %, or at least 20 weight %, or at least 23 weight % or at least 25 weight % of alkanoic acid vinyl ester (a). The first mixture (i) of ethylenically unsaturated monomers can include less than 90 weight %, such as less than 85 weight %, or less than 80 weight %, or less than 75 weight %, or less than 70 weight % or less than 65 weight % of alkanoic acid vinyl ester (a). Those skilled in the art will appreciate that any scope between any clearly disclosed lower limit and upper limit is disclosed herein. Thus, the first mixture (i) of ethylenically unsaturated monomers can include 10 weight % to 90 weight %, preferably 20 weight % to 80 weight %, more preferably 20 weight % to 70 weight % of alkanoic acid vinyl ester (a). The weight percentage is based on the gross weight of monomers in the first mixture of ethylenically unsaturated monomers.

[0082] The alkanoic acid vinyl ester (b) different from the alkanoic acid vinyl ester (a) in the first mixture (i) of ethylenically unsaturated monomers may include vinyl acetate, 1-methylvinyl acetate, vinyl propionate, vinyl butyrate, vinyl laurate, vinyl pivalate, and combinations thereof. Preferably, the alkanoic acid vinyl ester (b) includes vinyl acetate.

[0083] According to the present invention, the first mixture (i) of ethylenically unsaturated monomers may contain at least 10% by weight, such as at least 13% by weight, or at least 15% by weight, or at least 18% by weight, or at least 20% by weight, or at least 23% by weight, or at least 25% by weight, or at least 30% by weight, or at least 35% by weight of vinyl alkanoate (b) that is different from vinyl alkanoate (a). The first mixture (i) of ethylenically unsaturated monomers may contain less than 90% by weight, such as less than 88% by weight, or less than 85% by weight, or less than 83% by weight, or less than 80% by weight, or less than 78% by weight, or less than 75% by weight of vinyl alkanoate (b) that is different from vinyl alkanoate (a). It will be appreciated by those skilled in the art that any range between any explicitly disclosed lower and upper limits is disclosed herein. Thus, the first mixture of ethylenically unsaturated monomers (i) may contain 10 to 90 wt %, preferably 20 to 80 wt %, more preferably 30 to 80 wt % of vinyl alkanoate (b) different from vinyl alkanoate (a). The weight percentages are based on the total weight of the monomers in the first mixture of ethylenically unsaturated monomers.

[0084] According to the present invention, the first mixture of ethylenically unsaturated monomers (i) may contain 10% to 90% by weight, preferably 20% to 80% by weight, more preferably 20% to 70% by weight of vinyl alkanoate (a); and 10% to 90% by weight, preferably 20% to 80% by weight, more preferably 30% to 80% by weight of vinyl alkanoate (b) different from vinyl alkanoate (a). The weight percentages are based on the total weight of the monomers in the first mixture of ethylenically unsaturated monomers.

[0085] According to the present invention, the first mixture of ethylenically unsaturated monomers is polymerized in the presence of a protective colloid. As used herein, the term "protective colloid" generally refers to a water-soluble polymer compound used to stabilize finely dispersed polymer particles. The protective colloid is usually attached to the particles by grafting during the polymerization process, and can surround the particles with a film, and due to its spatial extension, for example, it can prevent the particles from approaching each other, thereby preventing flocculation or coagulation. The protective colloid of the first step (i) may include polyvinyl alcohol, polyvinyl alcohol copolymers and combinations thereof. Preferably, the protective colloid may include polyvinyl alcohol. As used herein, the term "polyvinyl alcohol" is generally considered in the art to be fully hydrolyzed or partially hydrolyzed polyvinyl acetate. Suitable polyvinyl alcohol copolymers may include hydrophobic copolymers of polyvinyl alcohol with the following substances: isopropenyl acetate, vinyl pivalate, vinyl ethylhexanoate, vinyl esters of saturated α-branched monocarboxylic acids having 5 or 9 to 11 carbon atoms, dialkyl maleates, dialkyl fumarates, vinyl chloride, vinyl alkyl ethers such as vinyl butyl ether, olefins such as ethylene and decene, and combinations thereof. The proportion of the hydrophobic units is preferably from 0.1% to 10% by weight, based on the total weight of the polyvinyl alcohol.

[0086] The degree of hydrolysis of polyvinyl alcohol can be at least 80 mol %, such as at least 82 mol % or at least 80 mol %. According to the present invention, the degree of hydrolysis of polyvinyl alcohol can be below 99 mol %, such as below 98 mol %, or below 97 mol %, or below 96 mol %, or below 95 mol %, or below 94 mol % or below 93 mol %. It will be appreciated by those skilled in the art that any scope between any clearly disclosed lower limit and upper limit is disclosed herein. Thus, the degree of hydrolysis of polyvinyl alcohol can be in the range of 80 mol % to 99 mol %, preferably in the range of 80 mol % to 95 mol %, more preferably in the range of 85 mol % to 94 mol %. The degree of hydrolysis should be understood as an average value, which means that a mixture of polyvinyl alcohol with less hydrolysis and more hydrolysis can be used.

[0087] According to the present invention, the viscosity of polyvinyl alcohol may be at least 1mPa s, such as at least 2mPa s or at least 3mPa s. The viscosity of the polyvinyl alcohol of the present invention may be 56mPa s or less, such as 50mPa s or less, or 45mPa s or less, or 40mPa s or less, or 35mPa s or less, or 30mPa s or less. The viscosity can be measured by a Hoppler falling ball viscometer according to DIN 53015:2019 at 20 ° C for a 4 wt % polyvinyl alcohol aqueous solution. It will be understood by those skilled in the art that any range between the explicitly disclosed lower and upper limits is disclosed herein. Thus, the viscosity of polyvinyl alcohol may be in the range of 1mPa s to 56mPa s, preferably in the range of 2mPa s to 50mPa s, and more preferably in the range of 3mPa s to 40mPa s.

[0088] The degree of hydrolysis of the polyvinyl alcohol of the present invention can be in the range of 80 mol % to 99 mol %, preferably in the range of 80 mol % to 95 mol %, and more preferably in the range of 85 mol % to 94 mol %; the viscosity of the polyvinyl alcohol of the present invention is in the range of 1 mPa·s to 56 mPa·s, preferably in the range of 2 mPa·s to 50 mPa·s, and more preferably in the range of 3 mPa·s to 40 mPa·s, and the viscosity is measured by a Hoppler falling ball viscometer according to DIN 53015:2019 at 20°C for a 4 wt % aqueous solution of polyvinyl alcohol.

[0089] Suitable examples of polyvinyl alcohol include, but are not limited to, Poval grade polyvinyl alcohol and Exceval grade polyvinyl alcohol, both commercially available from Kuraray (Japan), and Mowiol grade polyvinyl alcohol, commercially available from Clariant GmbH (Germany).

[0090] The aqueous composition may include at least 1.5 wt %, such as at least 1.8 wt %, or at least 2.0 wt %, or at least 2.2 wt % or at least 2.5 wt % of protective colloid. The aqueous composition may include less than 13.0 wt %, such as less than 12.5 wt %, or less than 12.0 wt %, or less than 11.5 wt %, or less than 11.0 wt %, or less than 10.5 wt % or less than 10.0 wt % of protective colloid. It will be appreciated by those skilled in the art that any range between any explicitly disclosed lower and upper limits is disclosed herein. Thus, the aqueous composition may include 1.5 wt % to 11.0 wt %, preferably 2.0 wt % to 11.0 wt % of protective colloid. The weight percentage is based on the total weight of monomers in the first mixture to the fourth mixture of ethylenically unsaturated monomers. The protective colloid may be dissolved in the aqueous composition at high temperatures, such as in a temperature range of 65° C. to 90° C., preferably 70° C. to 90° C.

[0091] The aqueous composition can include at least 1.5 weight %, for example, at least 1.8 weight %, or at least 2.0 weight %, or at least 2.2 weight % or at least 2.5 weight % of polyvinyl alcohol. The aqueous composition can include less than 13.0 weight %, for example, less than 12.5 weight %, or less than 12.0 weight %, or less than 11.5 weight %, or less than 11.0 weight %, or less than 10.5 weight % or less than 10.0 weight % of polyvinyl alcohol. It will be appreciated by those skilled in the art that any scope between any clearly disclosed lower limit and upper limit is disclosed herein. Thus, the aqueous composition can include 1.5 weight % to 11.0 weight %, preferably 2.0 weight % to 11.0 weight % of polyvinyl alcohol. Percentage by weight is the gross weight of monomers in the first mixture to the fourth mixture based on ethylenically unsaturated monomers.

[0092] All protective colloids can be added at the beginning, or a portion of protective colloids can be added at the beginning, and the remainder is metered into the aqueous composition. Preferably, the protective colloid can be added to the aqueous composition in step (i) at the beginning, and preferably added before the first mixture of ethylenically unsaturated monomers is added. Protective colloids can be added in the first step (i) with a content in the range of 1.5 wt % to 11.0 wt %, preferably 2.0 wt % to 11.0 wt %, and the weight percentage is based on the total weight of monomers in the first mixture to the fourth mixture of ethylenically unsaturated monomers. In the step (i) of the method of the present invention, the ethylenically unsaturated monomers of the first monomer mixture can be grafted onto the protective colloid forming the seed particles. The median particle size of the seed particles obtained in step (i) can be at least 50nm, for example at least 60nm, or at least 70nm, or at least 80nm, or at least 90nm or at least 100nm. According to the present invention, the median particle size of the seed particles obtained in step (i) can be less than 350nm, such as less than 330nm or less than 300nm or less than 280nm. It will be appreciated by those skilled in the art that any range between any clearly disclosed lower limit and upper limit is disclosed herein. Thus, the median particle size of the seed particles obtained in step (i) can be in the range of 50nm to 300nm, preferably 100nm to 300nm. The median particle size can be measured by dynamic light scattering according to ISO 22412:2017 using a dynamic light scattering instrument Mastersizer 2000 (Malvern Panalytical (UK)).

[0093] The first mixture of ethylenically unsaturated monomers may further comprise a chain transfer agent. According to the present invention, the chain transfer agent may be selected from n-dodecyl mercaptan, carbon tetrachloride, carbon tetrabromide, bromotrichloromethane, 4-methylbenzenethiol, 3-isooctyl mercaptopropionate, tert-nonyl mercaptan, 4,4'-thiobisbenzenethiol, tert-dodecyl mercaptan, α-methylstyrene dimer, mercaptoacetic acid, 2-ethylhexyl mercaptoacetate, 3-butyl mercaptopropionate, 1,8-dimercapto-3,6-dioxaoctane, and combinations thereof. If a chain transfer agent is used, the chain transfer agent may be used in an amount of at least 0.01 wt%, such as at least 0.03 wt%, or at least 0.05 wt%, or at least 0.07 wt%, or at least 0.10 wt%, or at least 0.12 wt%, or at least 0.15 wt%. If a chain transfer agent is used, it can be used in an amount of 3.0 wt % or less, such as 2.8 wt % or less, or 2.5 wt % or less, or 2.3 wt % or less, or 2.0 wt % or less, or 1.8 wt % or less, or 1.5 wt % or less. It will be appreciated by those skilled in the art that any range between any explicitly disclosed lower and upper limits is disclosed herein. If a chain transfer agent is used, it can be used in an amount of 0.01 wt % to 3.0 wt %, 0.05 wt % to 2.0 wt %. The weight percentage is the total weight of the ethylenically unsaturated monomers based on all mixtures of ethylenically unsaturated monomers.

[0094] The polymerization of the ethylenically unsaturated monomer mixture in step (i) of the method of the present invention can be carried out in the form of batch polymerization or semi-continuous polymerization. As used herein, the term "batch polymerization" refers to a polymerization in which all monomers are added at the beginning of the polymerization reaction. The term "semi-continuous polymerization" refers to a polymerization in which monomers are added continuously. Preferably, the polymerization of the ethylenically unsaturated monomer mixture in step (i) of the method of the present invention is carried out in the form of batch polymerization. Typically, the polymerization in step (i) is an exothermic reaction, i.e., the reaction releases heat. The polymerization temperature in step (i) can be in the range of 65°C to 90°C, preferably in the range of 70°C to 90°C.

[0095] The second mixture of ethylenically unsaturated monomers (ii) comprises: (a) an alkanoic acid vinyl ester having the formula:

[0096] ,

[0097] Where R 1 is H or CH3; R 2 and R 3 is an alkyl group having a total of 6 to 8 carbon atoms, preferably 6 or 7 carbon atoms; and (b) an alkanoic acid vinyl ester different from the alkanoic acid vinyl ester (a).

[0098] When the exothermic reaction in step (i) is completed, i.e. when the polymerization temperature in step (i) is reduced, the second mixture of ethylenically unsaturated monomers (ii) can be added to the aqueous composition. Preferably, when the polymerization temperature in step (i) is reduced by 3° C., preferably 5° C., the second mixture of ethylenically unsaturated monomers (ii) can be added to the aqueous composition.

[0099] The alkanoic acid vinyl ester (a) of the second mixture of ethylenically unsaturated monomers (ii) may have the following structural formula:

[0100]

[0101] Where R 1 CH3; R 2 and R 3 The alkyl group contains 7 carbon atoms in total.

[0102] The alkanoic acid vinyl ester (a) of the second mixture of ethylenically unsaturated monomers (ii) may have the following structural formula:

[0103]

[0104] Where R 1 H; R 2 and R 3 is an alkyl group containing 6 carbon atoms in total, wherein R 2 Ethyl, R 3 It is butyl.

[0105] Suitable examples of the alkanoic acid vinyl esters (a) of the second mixture (ii) of ethylenically unsaturated monomers that can be used according to the present invention can be exemplified by VeoVa grade vinyl esters commercially available from Hexion Inc. (USA), such as VeoVa 9 vinyl ester, VeoVa 10 vinyl ester and Veova EH vinyl ester.

[0106] According to the present invention, the second mixture (ii) of ethylenically unsaturated monomers can include at least 10 weight %, for example, at least 13 weight %, or at least 15 weight %, or at least 18 weight %, or at least 20 weight %, or at least 23 weight % or at least 25 weight % of alkanoic acid vinyl ester (a). The second mixture (ii) of ethylenically unsaturated monomers can include less than 70 weight %, for example, less than 65 weight %, or less than 60 weight %, or less than 55 weight %, or less than 50 weight % or less than 45 weight % of alkanoic acid vinyl ester (a). Those skilled in the art will appreciate that any scope between any clearly disclosed lower limit and upper limit is disclosed herein. Thus, the second mixture (ii) of ethylenically unsaturated monomers can include 10 weight % to 70 weight %, preferably 15 weight % to 60 weight %, more preferably 20 weight % to 50 weight % of alkanoic acid vinyl ester (a). The weight percentage is based on the gross weight of monomers in the second mixture of ethylenically unsaturated monomers.

[0107] The alkanoic acid vinyl ester (b) different from the alkanoic acid vinyl ester (a) in the second mixture (ii) of ethylenically unsaturated monomers may include vinyl acetate, 1-methylvinyl acetate, vinyl propionate, vinyl butyrate, vinyl laurate, vinyl pivalate, and combinations thereof. Preferably, the alkanoic acid vinyl ester (b) includes vinyl acetate.

[0108] According to the present invention, the second mixture (ii) of ethylenically unsaturated monomers may include at least 30% by weight, such as at least 33% by weight, or at least 35% by weight, or at least 38% by weight, or at least 40% by weight, or at least 43% by weight, or at least 45% by weight, or at least 48% by weight, or at least 50% by weight or at least 55% by weight of vinyl alkanoate (b) that is different from vinyl alkanoate (a). The second mixture (ii) of ethylenically unsaturated monomers may include less than 90% by weight, such as less than 88% by weight, or less than 85% by weight, or less than 83% by weight, or less than 80% by weight, or less than 78% by weight or less than 75% by weight of vinyl alkanoate (b) that is different from vinyl alkanoate (a). It will be appreciated by those skilled in the art that any range between any clearly disclosed lower and upper limits is disclosed herein. Thus, the second mixture of ethylenically unsaturated monomers (ii) may contain 30% to 90% by weight, preferably 40% to 85% by weight, more preferably 50% to 80% by weight of vinyl alkanoate (b) different from vinyl alkanoate (a). The weight percentages are based on the total weight of the monomers in the second mixture of ethylenically unsaturated monomers.

[0109] According to the present invention, the second mixture of ethylenically unsaturated monomers (ii) may contain 10% to 70% by weight, preferably 15% to 60% by weight, more preferably 20% to 50% by weight of vinyl alkanoate (a); and 30% to 90% by weight, preferably 40% to 85% by weight, more preferably 50% to 80% by weight of vinyl alkanoate (b) different from vinyl alkanoate (a). The weight percentages are based on the total weight of the monomers in the second mixture of ethylenically unsaturated monomers.

[0110] As discussed above for the protective colloid of step (i), the protective colloid of step (ii) may include polyvinyl alcohol, polyvinyl alcohol copolymers and combinations thereof. Preferably, the protective colloid may include polyvinyl alcohol. Preferably, the protective colloid is added to the aqueous composition in step (i).

[0111] In step (ii) of the method of the present invention, the second mixture of ethylenically unsaturated monomers may be added in its entirety or may be added continuously, preferably continuously. Typically, the polymerization in step (ii) is an exothermic reaction, i.e., the reaction releases heat. Preferably, the second mixture of ethylenically unsaturated monomers is added continuously so that the reaction temperature in step (ii) does not exceed 90°C. The second mixture of ethylenically unsaturated monomers may be added continuously so that the reaction temperature in step (ii) is in the range of 65°C to 90°C, preferably in the range of 70°C to 90°C. In addition, the polymerization temperature may be controlled in the range of 65°C to 90°C, preferably in the range of 70°C to 90°C, by, for example, cooling the aqueous composition with a water-cooled jacket. Typically, the second mixture of ethylenically unsaturated monomers may be added continuously in the range of 2 hours to 8 hours, preferably in the range of 2 hours to 6 hours. Continuous addition may be performed using a dropping funnel, a syringe pump or a peristaltic pump.

[0112] The third mixture of ethylenically unsaturated monomers (iii) comprises: (a) an alkanoic acid vinyl ester having the formula:

[0113] ,

[0114] Where R 1 is H or CH3; R 2 and R 3 is an alkyl group having a total of 6 to 8 carbon atoms, preferably 6 or 7 carbon atoms; and (b) (meth)acrylate.

[0115] In step (ii) of the method of the present invention, the ethylenically unsaturated monomers of the second monomer mixture can be grafted onto the protective colloid to further form seed particles. In addition, the ethylenically unsaturated monomers of the second monomer mixture can be polymerized onto the seed particles and increase the particle size of the polymer particles.

[0116] When no new seed particles are formed in step (ii), the third mixture of ethylenically unsaturated monomers (iii) can be added to the aqueous composition. Generally, when no new seed particles are formed, the median particle size of the polymer particles increases, and the number of particles (N) in the aqueous composition increases. p ) will decrease. The formation of new polymer (seed) particles can be monitored during the polymerization process. Here, the median particle size of the obtained polymer dispersion can be determined by dynamic light scattering, for example, with a dynamic light scattering instrument Mastersizer 2000 (Malvern Panalytical (UK)) according to ISO 22412:2017. The number of particles (N) in the aqueous composition can be determined by dividing the total mass of the polymerizable components added at any point in the process by the average particle volume. p ), and the average particle volume is calculated based on the average particle size. When the median particle size of the polymer dispersion in step (ii) increases, preferably by 5% of the median particle size of the seed particles formed in step (i), the third mixture of ethylenically unsaturated monomers (iii) can be added to the aqueous composition. Usually, the formation of new seed particles is complete when the protective colloid is fully incorporated.

[0117] The alkanoic acid vinyl ester (a) of the third mixture of ethylenically unsaturated monomers (iii) may have the following structural formula:

[0118]

[0119] Where R 1 CH3; R 2 and R 3 The alkyl group contains 7 carbon atoms in total.

[0120] The alkanoic acid vinyl ester (a) of the third mixture of ethylenically unsaturated monomers (iii) may have the following structural formula:

[0121]

[0122] Where R 1 H; R 2 and R 3 is an alkyl group containing 6 carbon atoms in total, wherein R 2 Ethyl, R 3 It is butyl.

[0123] Suitable examples of the alkanoic acid vinyl esters (a) of the third mixture (iii) of ethylenically unsaturated monomers that can be used according to the present invention can be exemplified by VeoVa grade vinyl esters commercially available from Hexion Inc. (USA), such as VeoVa 9 vinyl ester, VeoVa 10 vinyl ester and Veova EH vinyl ester.

[0124] According to the present invention, the third mixture (iii) of ethylenically unsaturated monomers can include at least 10 weight %, such as at least 13 weight %, or at least 15 weight %, or at least 18 weight %, or at least 20 weight %, or at least 23 weight %, or at least 25 weight %, or at least 28 weight %, or at least 30 weight %, or at least 32 weight % or at least 35 weight % of alkanoic acid vinyl ester (a). The third mixture (iii) of ethylenically unsaturated monomers can include less than 70 weight %, such as less than 65 weight %, or less than 60 weight %, or less than 55 weight %, or less than 50 weight % or less than 45 weight % of alkanoic acid vinyl ester (a). Those skilled in the art will appreciate that any scope between any clearly disclosed lower limit and upper limit is disclosed herein. Thus, the third mixture (iii) of ethylenically unsaturated monomers can include 10 weight % to 70 weight %, preferably 15 weight % to 60 weight %, more preferably 30 weight % to 50 weight % of alkanoic acid vinyl ester (a). The weight percentage is based on the gross weight of monomers in the third mixture of ethylenically unsaturated monomers.

[0125] According to the present invention, (meth)acrylate can be selected from methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, 4-methyl-2-pentyl (meth)acrylate, 2-methylbutyl (meth)acrylate, 3,5,5-trimethylhexyl (meth)acrylate and combinations thereof. Preferably, (meth)acrylate can be selected from butyl (meth)acrylate and combinations thereof.

[0126] According to the present invention, the third mixture (iii) of ethylenically unsaturated monomers can include at least 30% by weight, such as at least 33% by weight, or at least 35% by weight, or at least 38% by weight, or at least 40% by weight, or at least 43% by weight, or at least 45% by weight, or at least 48% by weight, or at least 50% by weight or at least 55% by weight of (meth) acrylate. The third mixture (iii) of ethylenically unsaturated monomers can include less than 90% by weight, such as less than 88% by weight, or less than 85% by weight, or less than 83% by weight, or less than 80% by weight, or less than 78% by weight, or less than 75% by weight of (meth) acrylate. Those skilled in the art will appreciate that any range between any clearly disclosed lower and upper limits is disclosed herein. Thus, the third mixture (iii) of ethylenically unsaturated monomers can include 35% to 90% by weight, preferably 40% to 85% by weight, and more preferably 50% to 80% by weight of (meth) acrylate. The weight percentage is based on the total weight of the monomers in the third mixture of ethylenically unsaturated monomers.

[0127] According to the present invention, the third mixture of ethylenically unsaturated monomers (iii) may include 10% to 70% by weight, preferably 15% to 60% by weight, more preferably 30% to 50% by weight of vinyl alkanoate (a); and 35% to 90% by weight, preferably 40% to 85% by weight, more preferably 50% to 80% by weight of (meth)acrylate. The weight percentages are based on the total weight of the monomers in the third mixture of ethylenically unsaturated monomers.

[0128] The third mixture (iii) of ethylenically unsaturated monomers may not contain any vinyl esters other than vinyl alkanoate (a). The third mixture (iii) of ethylenically unsaturated monomers may be polymerized in the absence of a dissolved protective colloid in the aqueous composition. As used herein, the term "in the absence of a dissolved protective colloid" means that the content of the protective colloid is less than 0.05% by weight, preferably less than 0.01% by weight, and the weight percentage is based on the total weight of the monomers in the first to fourth mixtures of ethylenically unsaturated monomers. In fact, this may be a stage where no new particles are generated.

[0129] In step (iii) of the method of the present invention, the third mixture of ethylenically unsaturated monomers can be added in full or the third mixture of ethylenically unsaturated monomers can be added continuously, preferably continuously. Typically, the polymerization in step (iii) is an exothermic reaction, i.e., the reaction releases heat. Preferably, the third mixture of ethylenically unsaturated monomers is added continuously so that the reaction temperature in step (iii) does not exceed 90°C. The third mixture of ethylenically unsaturated monomers can be added continuously so that the reaction temperature in step (iii) is in the range of 70°C to 90°C. In addition, the polymerization temperature can also be controlled in the range of 65°C to 90°C, preferably in the range of 70°C to 90°C, by, for example, cooling the aqueous composition with a water-cooling jacket. Typically, the third mixture of ethylenically unsaturated monomers can be added continuously in the range of 20 minutes to 8 hours, preferably in the range of 20 minutes to 6 hours. Continuous addition can be performed with a dropping funnel, a syringe pump or a peristaltic pump.

[0130] According to the present invention, the fourth mixture (iv) of ethylenically unsaturated monomers comprises vinyl alkanoate. The vinyl alkanoate of the fourth mixture (iv) of ethylenically unsaturated monomers may include vinyl acetate, 1-methyl vinyl acetate, vinyl propionate, vinyl butyrate, vinyl laurate, vinyl pivalate and combinations thereof. Preferably, the vinyl alkanoate of the fourth mixture (iv) of ethylenically unsaturated monomers may include vinyl acetate.

[0131] When the exothermic reaction in step (iii) is complete, i.e. when the polymerization temperature in step (iii) is reduced, the fourth mixture of ethylenically unsaturated monomers (iv) may be added to the aqueous composition. Preferably, when the polymerization temperature in step (i) is reduced by 3° C., preferably 5° C., the second mixture of ethylenically unsaturated monomers (iii) may be added to the aqueous composition. Preferably, when the monomer conversion in step (iii) is in the range of 94 wt % to 99 wt %, the fourth mixture of ethylenically unsaturated monomers (iv) may be added to the aqueous composition.

[0132] In step (iv) of the method of the present invention, the fourth mixture of ethylenically unsaturated monomers may be added in full or the fourth mixture of ethylenically unsaturated monomers may be added continuously, preferably continuously. Typically, the polymerization in step (iv) is an exothermic reaction, i.e., the reaction releases heat. Preferably, the fourth mixture of ethylenically unsaturated monomers is added continuously so that the reaction temperature in step (iv) does not exceed 90°C. The fourth mixture of ethylenically unsaturated monomers may be added continuously so that the reaction temperature in step (iv) is in the range of 65°C to 90°C, preferably in the range of 70°C to 90°C. In addition, the polymerization temperature may be controlled in the range of 65°C to 90°C, preferably in the range of 70°C to 90°C, by, for example, cooling the aqueous composition with a water cooling jacket. Typically, the fourth mixture of ethylenically unsaturated monomers may be added continuously in the range of 2 hours to 8 hours, preferably in the range of 2 hours to 6 hours. Continuous addition may be performed with a dropping funnel, a syringe pump or a peristaltic pump.

[0133] The first mixture (i) of ethylenically unsaturated monomers can include at least 0.5 wt %, such as at least 1.0 wt %, or at least 1.5 wt %, or at least 2.0 wt % or at least 2.5 wt % of ethylenically unsaturated monomers. The first mixture (i) of ethylenically unsaturated monomers can include less than 20 wt %, such as less than 15 wt %, or less than 15 wt %, or less than 13 wt % or less than 10 wt % of ethylenically unsaturated monomers. It will be appreciated by those skilled in the art that any scope between any clearly disclosed lower limit and upper limit is disclosed herein. Thus, the first mixture (i) of ethylenically unsaturated monomers can include 0.5 wt % to 15 wt %, preferably 1 wt % to 15 wt % of ethylenically unsaturated monomers. The weight percentage is the total weight of the ethylenically unsaturated monomers of the first mixture to the fourth mixture based on ethylenically unsaturated monomers.

[0134] The second mixture (ii) of ethylenically unsaturated monomers can include at least 30 wt %, such as at least 35 wt %, or at least 45 wt %, or at least 50 wt %, or at least 55 wt %, or at least 60 wt % or at least 65 wt % of ethylenically unsaturated monomers. The second mixture (ii) of ethylenically unsaturated monomers can include less than 92 wt %, such as less than 90 wt %, or less than 88 wt %, or less than 85 wt % or less than 82 wt % of ethylenically unsaturated monomers. It will be appreciated by those skilled in the art that any scope between any clearly disclosed lower limit and upper limit is disclosed herein. Thus, the second mixture (ii) of ethylenically unsaturated monomers can include 35 wt % to 92 wt %, preferably 35 wt % to 90 wt % of ethylenically unsaturated monomers. Percentage by weight is the total weight of the ethylenically unsaturated monomers of the first mixture to the fourth mixture based on ethylenically unsaturated monomers.

[0135] The third mixture (iii) of ethylenically unsaturated monomers can include at least 5 weight %, for example, at least 8 weight %, or at least 10 weight %, or at least 12 weight % or at least 15 weight % of ethylenically unsaturated monomers. The third mixture (iii) of ethylenically unsaturated monomers can include less than 50 weight %, for example, less than 48 weight %, or less than 45 weight %, or less than 42 weight % or less than 40 weight % of ethylenically unsaturated monomers. It will be appreciated by those skilled in the art that any scope between any clearly disclosed lower limit and upper limit is disclosed herein. Thus, the third mixture (iii) of ethylenically unsaturated monomers can include 8 weight % to 50 weight %, preferably 10 weight % to 50 weight % of ethylenically unsaturated monomers. Percentage by weight is the gross weight of the ethylenically unsaturated monomers of the first mixture to the fourth mixture based on ethylenically unsaturated monomers.

[0136] The 4th mixture (iv) of ethylenically unsaturated monomers can include at least 0.5 wt %, such as at least 1.0 wt %, or at least 1.5 wt %, or at least 2.0 wt % or at least 2.5 wt % of ethylenically unsaturated monomers. The 4th mixture (iv) of ethylenically unsaturated monomers can include less than 25 wt %, such as less than 20 wt %, or less than 15 wt % or less than 10 wt % of ethylenically unsaturated monomers. It will be appreciated by those skilled in the art that any scope between any clearly disclosed lower limit and upper limit is disclosed herein. Thus, the 4th mixture (iv) of ethylenically unsaturated monomers can include 0.5 wt % to 20 wt %, preferably 1 wt % to 20 wt % of ethylenically unsaturated monomers. Percentage by weight is the total weight of the ethylenically unsaturated monomers of the first mixture to the 4th mixture based on ethylenically unsaturated monomers.

[0137] According to the present invention, the first mixture of ethylenically unsaturated monomers (i) may contain 1% to 15% by weight of ethylenically unsaturated monomers; the second mixture of ethylenically unsaturated monomers (ii) may contain 35% to 90% by weight of ethylenically unsaturated monomers; the third mixture of ethylenically unsaturated monomers (iii) may contain 8% to 50% by weight of ethylenically unsaturated monomers; and the fourth mixture of ethylenically unsaturated monomers (iv) may contain 1% to 20% by weight of ethylenically unsaturated monomers. The weight percentages are based on the total weight of the ethylenically unsaturated monomers of the first to fourth mixtures of ethylenically unsaturated monomers.

[0138] The selection of any of the ethylenically unsaturated monomers in the first to fourth mixtures of ethylenically unsaturated monomers and the proportions of the ethylenically unsaturated monomers can be carried out in such a way that the glass transition temperature (Tg) of the polymer dispersion is below 120°C, preferably in the range of -50°C to 60°C, more preferably in the range of -30°C to 40°C, most preferably in the range of -15°C to 20°C. The glass transition temperature can be determined by differential scanning calorimetry (DSC). In this context, the person skilled in the art knows that DSC is sufficiently conclusive only if, after an initial heating cycle to a temperature at least 25°C above the highest glass transition temperature or melting temperature of the material but at least 20°C below the lowest decomposition temperature of the material, a sample of the material is kept at this temperature for at least 2 minutes. The sample is then cooled to a temperature at least 20°C below the lowest glass transition temperature or melting temperature to be determined, wherein the cooling rate should be a maximum of 20°C / min, preferably a maximum of 10°C / min. After a further waiting time of several minutes, the actual measurement then begins, during which the sample is heated at a heating rate of typically less than 10°C / min to at least 20°C above the highest melting temperature or glass transition temperature. The corresponding upper and lower limiting temperatures can be roughly ascertained by simple preliminary measurements with individual samples.

[0139] Surprisingly, it has been found that the process according to the invention for preparing a polymer dispersion enables a homogeneous distribution of the monomers despite the different reactivity ratios of the alkanoic acid vinyl ester (a), the alkanoic acid vinyl ester (b) different from the alkanoic acid vinyl ester (a) and the (meth)acrylate. The mixture of ethylenically unsaturated monomers is polymerized by free radical emulsion polymerization or free radical suspension polymerization. Preferably, the mixture of ethylenically unsaturated monomers is polymerized by free radical emulsion polymerization.

[0140] The process of the present invention for preparing a polymer dispersion can be carried out at a temperature of 0 to 130° C., preferably 40 to 100° C., more preferably 60 to 90° C. This temperature includes all values ​​and subvalues ​​therebetween, specifically including 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120 and 125° C.

[0141] Initiators can be used to initiate polymerization. Initiators that can be used in the practice of the present invention can include water-soluble initiators and / or oil-soluble initiators that are effective for polymerization purposes. Representative initiators are well known in the art and include, for example, azo compounds (such as AIBN, AMBN, and cyanovaleric acid) and inorganic peroxy compounds (such as hydrogen peroxide, sodium persulfate, potassium persulfate, and ammonium persulfate, peroxycarbonates, and peroxyborates), and organic peroxy compounds (such as alkyl hydroperoxides, dialkyl peroxides, acyl hydroperoxides, and diacyl peroxides), and esters such as tert-butyl perbenzoate, and combinations of inorganic and organic initiators.Suitable initiators may be selected from 2,3-dimethyl-2,3-diphenylbutane, tert-butyl hydroperoxide, tert-amyl hydroperoxide, cumyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, isopropyl cumyl hydroperoxide, p-menthane hydroperoxide, 2,5-di(tert-butylperoxy)-2,5-dimethyl-3-hexyne, 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxynonane, di(tert-butyl)peroxide, 2,5-dimethyl -2,5-di(tert-butylperoxy)hexane, di(tert-butylperoxyisopropyl)benzene, tert-butylcumyl peroxide, di(tert-amyl)peroxide, dicumyl peroxide, 4,4-di(tert-butylperoxy)butyl valerate, tert-butyl peroxybenzoate, 2,2-di(tert-butylperoxy)butane, tert-amyl peroxybenzoate, tert-butyl peroxyacetate, tert-butyl peroxy(2-ethylhexyl)carbonate, tert-butyl peroxyisopropylcarbonate, tert-butyl peroxy-3,5,5-trimethylhexanoate, 1,1-di(tert-butylperoxy)cyclohexane, tert-Amyl peroxyacetate, tert-Amyl peroxy-(2-ethylhexyl) carbonate, 1,1-di(tert-butylperoxy)-3,5,5-trimethylcyclohexane, 1,1-di(tert-amylperoxy)cyclohexane, tert-butyl monoperoxymaleate, 1,1'-azobis(hexahydrobenzonitrile), tert-butyl peroxyisobutyrate, tert-butyl peroxydiethylacetate, tert-butyl peroxy-2-ethylhexanoate, dibenzoyl peroxide, tert-amyl peroxy-2-ethylhexanoate, di(4-methylbenzoyl)peroxide, 1,1,3-dihydro-2-ethylhexanoate ,3-tetramethylbutyl peroxide, ammonium peroxydisulfate, 2,5-dimethyl-2,5-di(2-ethylhexanoyl peroxy)hexane, 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(isobutyronitrile), didecanoyl peroxide, potassium persulfate, dilauroyl peroxide, di(3,5,5-trimethylhexanoyl) peroxide, tert-amyl peroxypivalate, tert-butyl peroxyneoheptanoate, 1,1,3,3-tetramethylbutyl peroxypivalate, tert-butyl peroxypivalate, di(hexadecyl) peroxydicarbonate (dicetyl peroxydicarbonate), dimyristyl peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, di(4-tert-butylcyclohexyl) peroxydicarbonate, diisopropyl peroxydicarbonate, tert-butyl peroxyneodecanoate, di-sec-butyl peroxydicarbonate, tert-amyl peroxyneodecanoate, cumyl peroxyneoheptanoate, di(3-methoxybutyl) peroxydicarbonate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, cumyl peroxyneodecanoate, diisobutyryl peroxide and mixtures thereof.

[0142] Initiators can be used in sufficient amounts to initiate polymerization at a desired rate. Generally speaking, it is sufficient to include initiators in an amount of 0.01% to 5% by weight, preferably 0.1% to 4% by weight, based on the total weight of the monomers in the corresponding monomer mixture. The content of initiators is most preferably 0.01% to 2% by weight, based on the total weight of the monomers in the corresponding monomer mixture. The content of initiators includes all values ​​and subvalues ​​therebetween, specifically including 0.01, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 4 and 4.5% by weight, based on the total weight of the monomers in the monomer mixture.

[0143] As is well known in the art, the inorganic peroxy compounds and organic peroxy compounds mentioned above may also be used alone or in combination with one or more suitable reducing agents. Examples of such reducing agents may include sulfur dioxide, alkali metal disulfites, alkali metal bisulfites and ammonium bisulfites, thiosulfates, dithionites and formaldehyde sulfoxylates, as well as hydroxylamine hydrochloride, hydrazine sulfate, iron (II) sulfate, cuprous naphthanate, glucose, sulfonic acid compounds such as sodium methanesulfonate, amine compounds such as dimethylaniline and ascorbic acid. The amount of the reducing agent is preferably 0.03 to 10 parts by weight per part by weight of the polymerization initiator.

[0144] Polymerization according to the present invention is preferably carried out without adding surfactant or emulsifier. In special cases, it is advantageous to add a small amount of surfactant or emulsifier, for example, 1 wt % to 5 wt % of the total weight of the monomers in the whole monomer mixture is added. Surfactants or emulsifiers suitable for stabilizing dispersed polymers may include those conventional surfactants used in polymerization techniques. One or more surfactants may be added to water and / or monomer phase. Representative surfactants include saturated sulfonic acids and ethylenically unsaturated sulfonic acids or their salts, including, for example, unsaturated hydrocarbon sulfonic acids, such as vinyl sulfonic acid, allyl sulfonic acid and methallyl sulfonic acid and their salts; aromatic sulfonic acids, such as p-styrene sulfonic acid, isopropenylbenzenesulfonic acid and vinyloxybenzenesulfonic acid and their salts; sulfoalkyl esters of acrylic acid and sulfoalkyl esters of methacrylic acid, such as sulfoethyl methacrylate and sulfopropyl methacrylate and their salts, and 2-acrylamido-2-methylpropanesulfonic acid and their salts; alkylated diphenyl oxide disulfonates, sodium dodecylbenzenesulfonate and dihexyl or dioctyl esters of sodium sulfosuccinate, sodium alkyl esters of sulfonic acid, ethoxylated alkylphenols and ethoxylated alcohols; fatty alcohol sulfates and fatty alcohol (poly) ether sulfates.

[0145] After the polymerization in step (iv) is completed, residual monomers can be removed by after-polymerization by known methods, for example by after-polymerization initiated by a redox initiator. The redox initiator can be any of the inorganic peroxy compounds and organic peroxy compounds mentioned above in combination with one or more suitable reducing agents. Volatile residual monomers can also be removed by distillation, preferably under reduced pressure, if necessary, by passing an inert stripping gas such as air, nitrogen or steam through or over the dispersion.

[0146] The present invention relates to an aqueous polymer dispersion obtained by the method of the present invention as described above. The solid content of the aqueous polymer dispersion of the present invention may be 30% to 75% by weight, preferably 40% to 70% by weight, more preferably 50% to 65% by weight.

[0147] The glass transition temperature (Tg) of the polymer dispersion may be below 120° C., preferably in the range of −50° C. to 60° C., more preferably in the range of −30° C. to 40° C., most preferably in the range of −15° C. to 20° C. The glass transition temperature may be determined by differential scanning calorimetry (DSC) as described above.

[0148] Furthermore, the present invention relates to a redispersible polymer powder obtained by drying the aqueous polymer dispersion of the present invention. Drying can be achieved by fluidized bed drying, freeze drying or spray drying. Preferably, drying is achieved by spray drying. Spray drying can be carried out in a conventional spray dryer and atomization can be achieved by means of a single-fluid nozzle, a two-fluid nozzle or a multi-fluid nozzle or by means of a rotating disk. The outlet temperature is generally set in the range of 45° C. to 120° C., preferably 60° C. to 90° C. The aqueous polymer dispersion can be dried by spray drying after adding a spraying aid such as a protective colloid.

[0149] Suitable spraying aids are polyvinyl alcohol; polyvinyl pyrrolidone; water-soluble polysaccharides, i.e. starch (such as amylose and amylopectin), cellulose and its carboxymethyl derivatives, methyl derivatives, hydroxyethyl derivatives and hydroxypropyl derivatives; proteins, such as casein or caseinates, soy protein, gelatin; lignin sulfonates; synthetic polymers, such as poly(meth)acrylic acid, copolymers of (meth)acrylates with carboxyl-functional comonomer units, poly(meth)acrylamide, polyvinylsulfonic acid and water-soluble copolymers thereof; melamine-formaldehyde sulfonates, naphthalene-formaldehyde sulfonates, styrene-maleic acid copolymers and vinyl ether-maleic acid copolymers, preferably polyvinyl alcohol. If added, the spraying aid can be added to the aqueous polymer dispersion of the present invention in an amount of 3% to 30% by weight, for example 5% to 20% by weight, based on the total weight of the solids content of the aqueous polymer dispersion.

[0150] The aqueous polymer dispersion to be dried by spray drying of the present invention may have a viscosity of less than 500 mPa·s, preferably less than 350 mPa·s, more preferably less than 250 mPa·s at 23° C. The viscosity may be measured at 23° C. using a Brookfield type DV-II+ viscometer (commercially available from Brookfield Engineering Laboratories, Inc. (USA)) and a No. 0 or 1 spindle according to ASTM D-3236.

[0151] The invention furthermore relates to the use of the aqueous polymer dispersions according to the invention or the redispersible polymer powders according to the invention in building materials such as construction adhesives, plasters, fillers, floor fillers, sealing slurries, grouts and paints.

[0152] Furthermore, the present invention relates to a building material comprising an aqueous polymer dispersion according to the invention or a redispersible polymer powder according to the invention. According to the invention, the building material can be selected from cement-based tile adhesives; self-leveling substrates; thermal insulation systems (ETICS); repair mortars; cement-based grouts; joint fillers; plasters and gypsum; joint compounds; fillers; or waterproofing compounds.

[0153] The present invention will be further described with reference to the following examples.

[0154] Example:

[0155] Unless otherwise indicated, all parts and percentages hereinafter are by weight.

[0156] Preparation of polymer dispersions by multi-step polymerization

[0157] The polymer dispersions were prepared by free radical emulsion polymerization in a sealed water / oil jacketed glass vessel equipped with a water cooled condenser and stirring. The amounts used for the multi-step polymerizations of the present invention are listed in Table 1.

[0158] Table 1: Example 1

[0159]

[0160] 1 Mowiol® 4-88 (commercially available from Clariant GmbH (Germany))

[0161] 2 Commercially available from Hexion Inc. (USA)

[0162] At a temperature of 75°C, 5 pphm (parts by weight based on 100 parts of total monomer weight) of polyvinyl alcohol is dissolved in water in an amount of 10% (weight / weight). A monomer mixture of vinyl acetate and VeoVa 10 vinyl ester (step (i)) is added to the aqueous composition. Afterwards, n-dodecyl mercaptan and sodium bicarbonate are added to the aqueous mixture. The polymerization reaction is initiated by adding a 5% (weight / weight) potassium persulfate aqueous solution. The reaction mixture is heated to a temperature of 75°C to 85°C. Seed particles having a median particle size of 100nm to 300nm are obtained, and the median particle size is measured by dynamic light scattering using a dynamic light scattering instrument Mastersizer2000 (Malvern Panalytical (UK)) according to ISO 22412:2017. When the reaction temperature is stable, i.e. no longer rising, a monomer mixture of vinyl acetate and VeoVa 10 vinyl ester (step (ii)) and a 5% (weight / weight) potassium persulfate aqueous solution are added simultaneously and continuously to the reaction. The addition rate is controlled to maintain the temperature in the range of 70°C to 90°C. After the addition (step (ii)) is completed, the polymerization is continued and the median particle size of the formed particles of the aqueous reaction mixture is recorded by dynamic light scattering measurement using a dynamic light scattering instrument Mastersizer 2000 (Malvern Panalytical (UK)) according to ISO 22412:2017. When no new polymer particles are formed and the median particle size of the formed particles is increased by 5% compared to the seed particles formed in the polymerization process, a monomer mixture of VeoVa 10 vinyl ester and butyl acrylate (step (iii)) is continuously added to the aqueous reaction mixture. At the same time, a 5% (weight / weight) potassium persulfate aqueous solution is continuously added to the reaction. The addition rate is controlled to maintain the temperature in the range of 70°C to 90°C. After the addition is completed, polymerization is continued. When the reaction temperature is stable, i.e. no longer increases, vinyl acetate and 5% (weight / weight) potassium persulfate aqueous solution are continuously added to the reaction mixture. The reaction mixture is polymerized until the residual monomer level reaches less than 1000ppm. The residual monomer level is determined by gas chromatography. The solid content of the polymer dispersion is 50%, and the median particle size is 500nm to 5000nm. The median particle size is measured by dynamic light scattering using a dynamic light scattering instrument Mastersizer 2000 (Malvern Panalytical (UK)) according to ISO 22412:2017.

[0163] Preparation of polymer dispersions by standard polymerization

[0164] The polymer dispersions were prepared by free radical emulsion polymerization in a sealed water / oil jacketed glass vessel equipped with a water-cooled condenser and stirring. The amounts used for the standard polymerization are listed in Table 2.

[0165] Table 2: Example 2

[0166]

[0167] 1 Mowiol® 4-88 (commercially available from Clariant GmbH (Germany))

[0168] 2 Commercially available from Hexion Inc. (USA)

[0169] At a temperature of 75°C, 5 pphm (parts by weight based on 100 parts of total monomer weight) of polyvinyl alcohol was dissolved in water in an amount of 10% (weight / weight). A monomer mixture of 7.5 pphm of vinyl acetate and 2.5 pphm of VeoVa 10 vinyl ester was added to an aqueous composition. Afterwards, n-dodecyl mercaptan and sodium bicarbonate were added to the aqueous mixture. The polymerization reaction was initiated by adding 5% (weight / weight) potassium persulfate solution (0.1 pphm). The reaction mixture was heated to a temperature of 75°C to 85°C. Seed particles with a median particle size of 100 nm to 300 nm were obtained, which was measured by dynamic light scattering using a dynamic light scattering instrument Mastersizer 2000 (Malvern Panalytical (UK)) according to ISO 22412:2017. After 0.5 hours, a monomer mixture of 52.5pphm of vinyl acetate, 22.5pphm of VeoVa 10 vinyl ester and 15pphm of butyl acrylate was continuously added to the aqueous reaction mixture. At the same time, a 5% (weight / weight) potassium persulfate aqueous solution (0.1pphm) was continuously added to the reaction. The addition rate was controlled to maintain the temperature in the range of 70°C to 90°C. Polymerization was continued until no more polymerization heat was observed. The solid content of the polymer dispersion was 50%, and the median particle size was 500nm to 5000nm. The median particle size was measured by dynamic light scattering using a dynamic light scattering instrument Mastersizer 2000 (Malvern Panalytical (UK)) according to ISO 22412:2017.

[0170] Additional polymer dispersions of standard polymerizations were prepared using the amounts listed in Tables 3 and 4.

[0171] Table 3: Example 3

[0172]

[0173] 1 Mowiol® 4-88 (commercially available from Clariant GmbH (Germany))

[0174] 2 Commercially available from Hexion Inc. (USA)

[0175] 5 pphm (parts by weight based on 100 parts by weight of total monomers) of polyvinyl alcohol was dissolved in water in an amount of 10 wt% (w / w) at a temperature of 75°C.

[0176] 7pphm of vinyl acetate and 3pphm of VeoVa 10 vinyl ester were added to the aqueous composition. Afterwards, n-dodecyl mercaptan and sodium bicarbonate were added to the aqueous mixture. The polymerization reaction was initiated by adding a 5% (weight / weight) potassium persulfate aqueous solution (0.1pphm). The reaction mixture was heated to a temperature of 75°C to 85°C. Seed particles with a median particle size of 100nm to 300nm were obtained, which was measured by dynamic light scattering using a dynamic light scattering instrument Mastersizer 2000 (Malvern Panalytical (UK)) according to ISO 22412:2017. After 0.5 hours, a monomer mixture of 63pphm of vinyl acetate and 27pphm of VeoVa 10 vinyl ester was continuously added to the aqueous reaction mixture. At the same time, a 5% (weight / weight) potassium persulfate solution (0.1pphm) was continuously added to the reaction. The addition rate was controlled to maintain the temperature in the range of 70°C to 90°C. Polymerization was continued until no more polymerization heat was observed. The solid content of the polymer dispersion was 50% and the median particle size was 500nm to 5000nm. The median particle size was measured by dynamic light scattering using a dynamic light scattering instrument Mastersizer 2000 (Malvern Panalytical (UK)) according to ISO 22412:2017.

[0177] Table 4: Example 4

[0178]

[0179] 1 Mowiol® 4-88 (commercially available from Clariant GmbH (Germany))

[0180] 2 Commercially available from Hexion Inc. (USA)

[0181] The same steps as described in Example 4 were applied, except that after the formation of the seed particles, a monomer mixture of 73 pphm of vinyl acetate and 17 pphm of VeoVa 10 vinyl ester was continuously added to the aqueous reaction mixture. The solid content of the polymer dispersion was 50%, and the median particle size was 500 nm to 5000 nm. The median particle size was measured by dynamic light scattering using a dynamic light scattering instrument Mastersizer 2000 (Malvern Panalytical (UK)) according to ISO 22412:2017.

[0182] Preparation of redispersible polymer powders

[0183] A 10% formulation was prepared by mixing the polymer dispersions of Examples 1 to 4 (weight 10 g) with 1 g of Mowiol® 4-88 (commercially available from Clariant GmbH (Germany)) and diluting with water at 23°C to a dilute viscosity of 250 mPa·s. The viscosity was measured at 23°C using a Brookfield DV-II+ viscometer (commercially available from Brookfield Engineering Laboratories, Inc. (USA)) and a No. 0-1 rotor according to ASTM D-3236. The dispersion was then spray dried by means of a two-fluid nozzle spinning disk atomizer. The dispersion was dried using a 4×10 5 The droplets were dried in concurrent air heated to 125°C.

[0184] Determination of wet adhesion

[0185] To determine the wet adhesion of the polymer dispersions, tile adhesive mortar mixes were prepared according to the formulations in Table 5.

[0186] Table 5: Tile bonding mortar

[0187]

[0188] 1 Commercially available from HeidelbergCement AG (Germany)

[0189] 2 Commercially available from Quarzwerke (Germany)

[0190] 3 Commercially available from Ashland Inc. (USA)

[0191] The cement mixture was prepared using the redispersible polymer powders of Examples 1 to 4 and VINNAPAS® 7220E (commercially available from Wacker Chemie AG (Germany). VINNAPAS® eco 7220E is based on a copolymer of vinyl acetate, ethylene and methyl methacrylate.

[0192] The tile adhesive mortar was mixed with water in an amount of 24 g of water per 100 g of dry mortar. The bond strength was determined after water storage according to DIN EN 1348:2007 (item 8.3) and the measured bond strength of each example was normalized to the bond strength of example 3. The results are listed in Table 6.

[0193] Table 6: Normalized bond strength

[0194]

[0195] As can be seen from Table 6, Example 1 prepared by multi-step polymerization provides improved wet adhesion compared to Examples 2 to 4 prepared by standard polymerization. Example 2 prepared by standard polymerization provides an inhomogeneous block distribution of VeoVa 10 vinyl ester in the vinyl acetate / VeoVa 10 vinyl ester / butyl acrylate copolymer, which results in poor chemical resistance and impaired wet adhesion.

Claims

1. A method for preparing a polymer dispersion by free radical emulsion polymerization or free radical suspension polymerization of a mixture of ethylenically unsaturated monomers, comprising the following steps: (i) providing an aqueous composition comprising a first mixture of ethylenically unsaturated monomers, the first mixture comprising: (a) vinyl alkanoate having the structural formula: ， Where R 1 is H or CH3; R 2 and R 3 is an alkyl group containing 6 to 8 carbon atoms in total; and (b) an alkanoic acid vinyl ester different from the alkanoic acid vinyl ester (a); and polymerizing the mixture of ethylenically unsaturated monomers in the presence of a protective colloid to obtain seed particles; (ii) adding to the aqueous composition after step (i) a second mixture of ethylenically unsaturated monomers comprising: (a) vinyl alkanoate having the structural formula: ， Where R 1 is H or CH3; R 2 and R 3 is an alkyl group containing 6 to 8 carbon atoms in total; and (b) an alkanoic acid vinyl ester different from the alkanoic acid vinyl ester (a); and polymerizing the mixture of ethylenically unsaturated monomers in the presence of a protective colloid; (iii) adding a third mixture of ethylenically unsaturated monomers comprising the following to the aqueous composition after step (ii): (a) vinyl alkanoate having the structural formula: ， Where R 1 is H or CH3; R 2 and R 3 is an alkyl group containing 6 to 8 carbon atoms in total; and (b) (Meth)acrylates; and polymerizing the mixture of ethylenically unsaturated monomers; (iv) adding a fourth mixture of ethylenically unsaturated monomers comprising vinyl alkanoate to the aqueous composition after step (iii); and polymerizing the mixture of ethylenically unsaturated monomers.

2. The method according to claim 1, wherein the vinyl alkanoate (a) in one, more than one or all, preferably all of the first to third mixtures of ethylenically unsaturated monomers has the following structural formula: Where R 1 is H or CH3; R 2 and R 3 The alkyl group contains 6 or 7 carbon atoms in total.

3. The method according to claim 1 or claim 2, wherein the vinyl alkanoate (a) in one, more than one or all, preferably all of the first to third mixtures of ethylenically unsaturated monomers has the following structural formula: ， Where R 1 CH3; R 2 and R 3 is an alkyl group containing 7 carbon atoms in total; or The alkanoic acid vinyl ester (a) in one, more than one or all, preferably all of the first to third mixtures of ethylenically unsaturated monomers has the following structural formula: ， Where R 1 H; R 2 and R 3 An alkyl group having a total of 6 carbon atoms.

4. The method according to any one of claims 1 to 3, wherein the alkanoic acid vinyl ester (b) different from the alkanoic acid vinyl ester (a) in one, more than one or all, preferably all, of the first to third mixtures of ethylenically unsaturated monomers comprises vinyl acetate, 1-methylvinyl acetate, vinyl propionate, vinyl butyrate, vinyl laurate, vinyl pivalate and combinations thereof, preferably vinyl acetate; and / or The alkanoic acid vinyl ester of the fourth mixture of ethylenically unsaturated monomers includes vinyl acetate, 1-methylvinyl acetate, vinyl propionate, vinyl butyrate, vinyl laurate, vinyl pivalate and combinations thereof, preferably vinyl acetate.

5. The method of any one of claims 1 to 4, wherein the first mixture of ethylenically unsaturated monomers comprises: (a) 10 to 90 wt %, preferably 20 to 80 wt %, more preferably 20 to 70 wt % of vinyl alkanoate; and (b) 10 to 90% by weight, preferably 20 to 80% by weight, more preferably 30 to 80% by weight, of a vinyl alkanoate different from the vinyl alkanoate (a); The weight percentages are based on the total weight of the monomers in the first mixture of ethylenically unsaturated monomers; and / or The second mixture of ethylenically unsaturated monomers comprises: (a) 10 to 70 wt %, preferably 15 to 60 wt %, more preferably 20 to 50 wt % of vinyl alkanoate; and (b) 30 to 90 weight percent, preferably 40 to 85 weight percent, more preferably 50 to 80 weight percent of a vinyl alkanoate different from the vinyl alkanoate (a); the weight percentages are based on the total weight of the monomers in the second mixture of ethylenically unsaturated monomers.

6. The method of any one of claims 1 to 5, wherein the third mixture of ethylenically unsaturated monomers comprises: (a) 10 to 70 wt %, preferably 15 to 60 wt %, more preferably 30 to 50 wt % of vinyl alkanoate; and (b) 35 to 90% by weight, preferably 40 to 85% by weight, more preferably 50 to 80% by weight of (meth)acrylate; The weight percentages are based on the total weight of monomers in the third mixture of ethylenically unsaturated monomers; and / or The (meth)acrylate is selected from methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, 4-methyl-2-pentyl (meth)acrylate, 2-methylbutyl (meth)acrylate, 3,5,5-trimethylhexyl (meth)acrylate and combinations thereof, preferably butyl (meth)acrylate and combinations thereof.

7. The method according to any one of claims 1 to claim 6, wherein the median particle size of the seed particles in step (i) is in the range of 100 nm to 300 nm.

8. The method according to any one of claims 1 to 7, wherein the protective colloid of the first step (i) and / or the second step (ii), preferably the first step (i) and the second step (ii) comprises polyvinyl alcohol, polyvinyl alcohol copolymers and combinations thereof, preferably polyvinyl alcohol; and / or Wherein the protective colloid is added in the first step (i) in an amount ranging from 2.0 wt % to 11.0 wt %, the weight percentage being based on the total weight of the monomers in the first to fourth mixtures of ethylenically unsaturated monomers.

9. The method according to claim 8, wherein the degree of hydrolysis of the polyvinyl alcohol is in the range of 80 mol % to 99 mol %, preferably in the range of 80 mol % to 95 mol %, more preferably in the range of 85 mol % to 94 mol %; and The viscosity of the polyvinyl alcohol is in the range of 1 mPa·s to 56 mPa·s, preferably in the range of 2 mPa·s to 50 mPa·s, and more preferably in the range of 3 mPa·s to 40 mPa·s, and the viscosity is measured by a Hoppler falling ball viscometer according to DIN 53015:2019 at 20° C. for a 4 wt % aqueous solution of polyvinyl alcohol.

10. The method according to any one of claims 1 to 9, wherein the first mixture of ethylenically unsaturated monomers further comprises a chain transfer agent, wherein the chain transfer agent is preferably selected from n-dodecyl mercaptan, carbon tetrachloride, carbon tetrabromide, bromotrichloromethane, 4-methylbenzenethiol, isooctyl 3-mercaptopropionate, tert-nonyl mercaptan, 4,4'-thiobisbenzenethiol, tert-dodecyl mercaptan, α-methylstyrene dimer, thioglycolic acid, 2-ethylhexyl thioglycolate, butyl 3-mercaptopropionate, 1,8-dimercapto-3,6-dioxaoctane, and combinations thereof.

11. The process according to any one of claims 1 to 10, wherein in step (ii) the second mixture of ethylenically unsaturated monomers is added continuously such that the reaction temperature is in the range of 70°C to 90°C; and / or When no new seed particles are formed in step (ii), step (iii) is started.

12. The process according to any one of claims 1 to 11, wherein in step (iii) the third mixture of ethylenically unsaturated monomers is added continuously such that the reaction temperature is in the range of 70°C to 90°C; and / or The mixture of ethylenically unsaturated monomers is polymerized by free radical emulsion polymerization.

13. The method according to any one of claims 1 to 12, wherein (i) the first mixture of ethylenically unsaturated monomers comprises from 1 wt % to 15 wt % of ethylenically unsaturated monomers; (ii) the second mixture of ethylenically unsaturated monomers comprises from 35% to 90% by weight of the ethylenically unsaturated monomers; (iii) the third mixture of ethylenically unsaturated monomers comprises from 8 wt% to 50 wt% of ethylenically unsaturated monomers; and (iv) the fourth mixture of ethylenically unsaturated monomers comprises from 1 wt% to 20 wt% of the ethylenically unsaturated monomers; The weight percentages are based on the total weight of the ethylenically unsaturated monomers of the first through fourth mixtures of ethylenically unsaturated monomers.

14. An aqueous polymer dispersion obtainable by the process according to any one of claims 1 to 13.

15. A redispersible polymer powder obtained by drying the aqueous polymer dispersion according to claim 14; The drying is preferably achieved by fluidized bed drying, freeze drying or spray drying.

16. Use of the aqueous polymer dispersion according to claim 14 or the redispersible polymer powder according to claim 15 in building materials such as construction adhesives, plasters, fillers, floor fillers, sealing slurries, grouts and paints.

17. A building material comprising the aqueous polymer dispersion according to claim 14 or the redispersible polymer powder according to claim 15; The building material is preferably selected from cement-based tile adhesives; self-leveling substrates; thermal insulation systems (ETICS); repair mortars; cement-based grouts; joint fillers; plasters and gypsum; joint compounds; fillers; or waterproofing compounds.

Images