DE19735225A1 - Controlled production of aqueous polymer dispersion - Google Patents

Abstract

Production of aqueous polymer dispersions by radical initiated aqueous emulsion polymerisation of ethylenically unsaturated monomer(s) (I) comprises emulsifying (a) a mixture of (I) with radical initiator(s) and stable N-oxyl radical(s) or (b) a mixture of (I) with compound(s) which decompose on heating to give stable N-oxyl radicals and polymerisation initiating radical partners, with the aid of dispersants to give an aqueous emulsion with a disperse phase mainly comprising droplets with a diameter \} 500 nm, and then polymerising the emulsion at elevated temperature. Also claimed are the aqueous polymer dispersions.

Description

The present invention relates to a process of free-radically initiated aqueous emulsion polymerization for the preparation of an aqueous polymer dispersion, in which compounds (monomers) having at least one ethylenically unsaturated group are emulsified by means of dispersants in an aqueous medium and by means of a free-radical polymerization initiator in the presence of an N-oxyl radical ( a connection that has at least one

N - O •

Has a group) derived from a secondary amine, which has no hydrogen atoms on the α-C atoms (i.e. the N-oxyl groups are derived from corresponding secondary ones Amino groups from), with the formation of an aqueous polymer dispersion polymerizes. In this document, the aforementioned are intended N-oxyl radicals are called stable N-oxyl radicals.

Aqueous polymer dispersions are fluid systems which as disperse phase in aqueous dispersion medium polymer particles in stable (storage stability usually ≧ 24 h, normally ≧ 2-3 days, mostly ≧ 1 week) disperse distribution contain. The number average diameter of the polymer particles is usually 0.01 to 1 µm.

Just like polymer solutions when the solution evaporates by means of aqueous polymer dispersions on evaporation of the aqueous dispersion medium, polymer Form films, which is why aqueous polymer dispersions in a lot times directly as a binder, e.g. B. for paints or compositions for coating leather.

Often, however, the dispersed polymer is also dispersed Coagulation separated and as a component in polymer blends Modification of the mechanical properties used. This will the polymer separated from the aqueous polymer dispersion sat for example with other thermoplastics and if necessary the usual additives such as colorants, pigments, lubricants medium, stabilizers or fillers, extruded.  

Aqueous polymer dispersions are usually produced by radically initiated aqueous emulsion polymerization of having at least one ethylenically unsaturated group Connections at temperatures below 100 ° C. Here are the monomers to be polymerized, which are predominantly only are hardly water-soluble, without great effort, e.g. B. by usual stirring, with the addition of dispersant in aqueous Medium emulsified and by the action of radical poly polymerization initiators polymerized.

The radical polymerization initiators are usually around water-soluble peroxides, hydroperoxides and / or Azo compounds that, above a certain temperature, which is usually ≦ 100 ° C, break down into reactive radicals, that trigger the polymerization.

The term emulsion expresses that the monomers and the water as a system of two liquids that are only slightly soluble in each other in which the liquids are present in more or less fine distribution. The labeling aqueous emulsion expresses that the aqueous phase is the continuous phase forms. Requires for the preparation of an aqueous monomer emulsion it usually involves the addition of dispersants (e.g. Ullmann's Encyclopedia of Technical Chemistry, Vol. 10, 4th edition, Verlag Chemie, Weinheim (1975), p. 449), the immediate Union of two randomly colliding monomers prevent droplets in the aqueous emulsion and stability ensure the resulting aqueous polymer dispersion.

As a result of the low distribution effort, the radical aqueous emulsion polymerization used aqueous monomer emulsion usually mainly Monomer droplets with a diameter <1 µm.

Like all radical-initiated polymerizations of compounds having at least one ethylenically unsaturated group, the method of radical-initiated aqueous emulsion polymerization also has the disadvantage that the molecular weight of the polymer chains does not normally increase with the polymerization conversion and that the polymer chains of the resulting polymer generally do not have uniform molecular weight. Ie, the available polymer is usually not monodisperse with regard to the molecular weight property, but usually has a related polydispersity index PDI of ≧ 2 (PDI = M _w / M _n , with M _w = weight average molecular weight and M _n = number average molecular weight), which is attributed in particular to termination reactions as a result of an irreversible combination of growing free radical polymer chain ends.

Another disadvantage of the radically initiated aqueous Emulsion polymerization is that during the Polymerization carried out change of the to be polymerized Monomers generally do not form segmented copolymers (Block polymers) but usually too disperous gated core-shell polymer particles, the core of which leads from the one and its shell made up of the other type of monomer is, with the core and shell essentially not chemical but are only physically bound to each other.

From TRIP Vol. 4, No. 6, June 1996, p. 183 ff, US-A 5,322,912, WO 96/24620, US-A-4,581,429, US-A 5,412,047, EP-A 135 280 and from the earlier application DE-A 19602539 it is known that the Implementation of radical initiated polymerizations Temperatures above 100 ° C in the presence of a stable (essentially non-initiating) N-oxyl radical some control of the radical initiated polymerization enables.

The underlying mechanism of action is probably in it establishes that the stable N-oxyl radicals are reactive radicals Ends of a growing polymer chain at elevated temperatures do not terminate irreversibly, but only temporarily To block. This results in a reduction in stationary Concentration of growing free radical polymer chains end what the possibility for an irreversible termination of the Chain growth through the combination of two growing polymers chain ends reduced. This leads on average to the poly merization conversion (ideally linear) growing polymer chains. The latter depends on the polymerization conversion (in Ideally linear) growing average molecular weight of the formed polymer with a polydisper at 1 sity index.

According to US Pat. No. 5,322,912, column 10, line 65 ff, the reaction is medium for such a controlled radical initiated Polymerization also considered an emulsion. More extensive Information on the implementation of such a radically initiated US Pat. No. 5,322,912 does not make emulsion polymerization. The the same applies to DE-A 19602539. US-A 5,412,047 recommends in column 18, lines 54 ff in the event that the radical initiated polymerization takes place in a multi-phase system, as is the case with the radically initiated aqueous emulsion poly merization is the case, only, stable N-oxyl radicals too  use that in water a particularly low solubility exhibit.

The availability of a simple to do controlled radically initiated aqueous emulsion poly merization for the preparation of an aqueous polymer dispersion would be beneficial in that it is a controlled mindset the molecular weight of the resulting, in disperse distribution located, would enable polymer. The same is stoned e.g. B. Cohesion and adhesion of the resulting film of the aqueous Polymer dispersion. With increasing molecular weight grows in usually cohesion, promoting a decreasing molecular weight usually the surface stickiness of the film. Furthermore, open net access to aqueous dispersions of bespoke block copolymers because the free radicals polymer chain ends are not destroyed by combination, but are only reversibly blocked. That is, according to Ver If a first type of monomer is required, the polymerization can be carried out Addition of further types of monomers to be continued.

In Macromolecules 1997, 30, pp. 324-326 it is recommended that Her position of an aqueous polymer dispersion by controlled initiated aqueous emulsion polymerization to reali the latter sieren that a preformed aqueous polymer dispersion (a so-called seed latex) in a polymerization vessel sets and the template the monomers to be polymerized as well a hydrophobic compound that under the influence of heat into a stable N-oxyl radical and into one the polymerization initiating radical partner disintegrates, adds. Then over if the reaction mixture is left to stand at room temperature, to both the monomers to be polymerized and the hydro phobic compound diffusion into the seed polymer particles to enable (swelling). After swelling is completed Temperature increase (<100 ° C) the polymerization below atmospheric pressure. A disadvantage of this Ver driving style is that it is the pre-production of the comparative wise complicated hydrophobic compound as well as the extremely slow swelling process is required. It is also essential the pre-production of a seed latex.

The object of the present invention was therefore an advantageous one procedure of a controlled radical initiated aqueous emulsion polymerization for production to provide aqueous polymer dispersions.  

Accordingly, a process of free-radically initiated aqueous emulsion polymerization for the preparation of an aqueous polymer dispersion has been found, in which compounds containing at least one ethylenically unsaturated group are emulsified by means of dispersants in an aqueous medium and radically polymerized in the presence of a stable N-oxyl radical, which is characterized in that that one from a mixture comprising

• a) the at least one ethylenically unsaturated group containing compounds, at least one radical polymerization initiator and at least one stable N-oxyl radical,
  or
• b) the at least one ethylenically unsaturated group pointing compounds and at least one compounds that under the action of heat in a stable N-oxyl radical and into a radical initiating the polymerization Partner disintegrates,

produces an aqueous emulsion, the disperse phase mainly consists of droplets with a diameter of ≦ 500 nm, and the aqueous Emulsion polymerized by increasing the temperature.

Suitable stable N-oxyl radicals according to the invention are all those considered in EP-A 135 280, the older Application DE-A 19651307, US-A 5,322,912, US-A 4,581,429, WO 96/24620, US-A 5,412,047 and the earlier application DE-A 19602539 are mentioned.

Such suitable, derived from a secondary amine, stable N-oxyl radicals are e.g. B. those of the general formula I.

With
R ¹ , R ² , R ⁵ and R ⁶ = the same or different straight or branched chain, optionally substituted alkyl groups and
R ³ and R ⁴ = the same or different straight or branched chain, optionally substituted alkyl groups or
R ³ CNCR ⁴ = an optionally substituted, cyclic structure.

Particularly suitable compounds I are those which in EP-A 135 280, the older application DE-A 19651307, the US-A 5,322,912, US-A 5,412,047, US-A 4,581,429, the DE-A 16 18 141, CN-A 1052847, US-A 4,670,131, US-A 5,322,960 and the earlier application DE-A 19602539 are mentioned.

Examples of these are those stable N-oxyl radicals of the general formula I in which R ¹ , R ² , R ⁵ and R ^{6 represent} (same or different) methyl, ethyl, n-propyl, iso-propyl, , n-butyl, iso-butyl, tert-butyl, linear or branched pentyl, phenyl or substituted groups thereof and R ³ and R ⁴ for (same or different) methyl, ethyl, n-propyl -, Iso-propyl, n-butyl, iso-butyl, tert-butyl, linear or branched pentyl, substituted groups thereof or together with CNC the cyclic structure

where n is an integer from 1 to 10 (often 1 to 6), including substituted such cyclic structures, stand. 2,2,6,6-tetrams are exemplary examples thyl-1-oxyl-piperidine, 2,2,5,5-tetramethyl-1-oxyl-pyrrolidine and 4-Oxo-2,2,6,6-tetramethyl-1-oxyl-piperidine called.

The stable N-oxyl radicals can be derived from the corresponding secondary amines by oxidation, e.g. B. with hydrogen peroxide, produce. As a rule, they can be represented as pure substances.

Suitable stable N-oxyl radicals according to the invention are e.g. B. those whose molar solubility in water at 25 ° C and 1 bar ≦ 10⁻ ¹ mol / kg. That is, the aforementioned molar solubility can also be ≦ 10⁻ ³ mol / kg or ≦ 10⁻ ⁴ mol / kg or ≦ 10⁻ ⁵ mol / kg or ≦ 10⁻ ⁶ mol / kg.

The stable N-oxyl radicals suitable according to the invention include, in particular, carboxylated, phosphonated, sulfonated and / or hydroxylated piperidine- or pyrrolidine-N-oxyls and di-N-oxyls of the following general formulas II to IX:

With
m = 2 to 10,
R ⁷ , R ⁸ , R ⁹ = independently of one another

with the proviso that at least one of the existing substituents R ⁷ , R ⁸ or R ^{9 is} different from hydrogen and M ^{⊕ is} a hydrogen or an alkali metal ion (in particular K ^⊕ or Na ^⊕ ),
q = an integer from 1 to 10,
R ^{1 '} , R ^2' , R ^{5 '} , R ^6' = independently of one another and independently of R ¹ , R ² , R ⁵ , R ^{6 the} same groups as R ¹ ,
R ¹⁰ = C ₁ to C ₄ alkyl, -CH = CH ₂ , -C∼CH, -CN,

-COO ^⊖ M ^⊕ , -COOCH ₃ or -COOC ₂ H ₅ ,
R ¹¹ = an organic radical which has at least one primary, secondary (e.g. -NHR ¹ ) or tertiary amino group (e.g. -NR ¹ R ² ) or at least one ammonium group -N ^⊖ R ¹⁴ R ¹⁵ R ^{16 has} X ^⊖ , with X ^⊖ = F ^⊖ , Cl ^⊖ , Br ^⊖ , HSO ₄ ^⊖ , SO ₄ ^⊖ , H ₂ PO ₄ ^⊖ , HPO ₄ ^{2 ⊖} of PO ₄ ^{3 ⊖} and R ¹⁴ , R ¹⁵ , R ¹⁶ mutually independent organic radicals (e.g. independently of one another and independently of R ^{1 the} same groups as R ¹ ),
R ¹² = independently of R ^{11 the} same groups as R ¹¹ or -H, -OH, C ₁ - to C ₄ -alkyl, -COO ^⊖ M ^⊕ , -C∼CH,

hydroxy substituted C ₁ to C ₄ alkyl (e.g. hydroxyethyl or hydroxypropyl) or
R ¹¹ , R ¹² = together the oxygen of a carboxyl group and
R ¹³ = -H, -CH ₃ or

Preferably R ¹ = R ² = R ⁵ = R ⁶ = R ^{1 '} = R ^2' = R ^{5 '} = R ^6' = -CH ₃ .

If the stable N-oxyl radical as a functional group a has acidic or basic group, the solubility of the N-oxyl radical in the aqueous polymerization medium Adjust the pH value of the same.

Examples of representatives of stable N-oxyl radicals which are suitable according to the invention are
4-hydroxy-2,2,6,6-tetramethyl-1-oxyl-piperidine,
4-hydroxy-2,6-diphenyl-2,6-dimethyl-1-oxyl-piperidine,
4-carboxy-2,2,6,6-tetramethyl-1-oxyl-piperidine,
4-carboxy-2,6-diphenyl-2,6-dimethyl-1-oxyl-piperidine,
3-carboxy-2,2,5,5-tetramethyl-1-oxyl-pyrrolidine,
3-carboxy-2,5-diphenyl-2,5-dimethyl-1-oxyl-pyrrolidine and the sodium or potassium salt of the sulfuric acid half-ester of
4-Hydroxy-2,2,6,6-tetramethyl-1-oxyl-piperidine called.

The preparation of 3-carboxy-2,2,5,5-tetramethyl-1-oxyl-pyrroli din is found e.g. B. in Romanelli, M .; Ottaviani, M.F .; Martini, G.; Kevan, L., JPCH J: Phys. Chem., EN, 93, 1, 1989, Pp. 317-322.

Compounds (VI) and (VII) can be prepared according to US-A 4665185 (e.g. Example 7) and DE-A 19510184 can be obtained.  

Other suitable representative representatives are:

Mixtures of stable N-oxyl radicals can be used.

As according to the invention in combination with the stable N-oxyl-radi kalen (inventive variant a)) radicals to be used In principle, polymerization initiators all come in Consider that are capable of radical polymerization trigger. It can be both peroxides and hydroperoxides as well as azo compounds. They can both be oil-soluble be water soluble as well.

Examples of suitable radical polymerization initiators are benzoyl peroxide, peroxodisulfuric acid and their ammonium and Alkali metal salts as well as hydrogen peroxide or hydroper oxides such as tert-butyl hydroperoxide. As azo compounds such. B. 4,4'-azo-bis-cyanovaleric acid into consideration. Of course can as such water-soluble, radical polymer onsinitiators also combined systems consisting of at least one Reducing agent and at least one peroxide and / or hydro  peroxide (hereinafter redox initiators called) can be used.

Examples of such combinations are e.g. B. tert-butyl hydro peroxide / sodium metal salt of hydroxymethanesulfinic acid and hydrogen peroxide / ascorbic acid. Frequently, the combined systems additionally comprise a small amount of a metal compound which is soluble in the aqueous medium and whose metallic component can occur in several valence levels. examples for
such systems are e.g. B. ascorbic acid / iron (II) sulfate / hydrogen peroxide or sodium sulfite / iron (II) sulfate / hydrogen peroxide. Of course, the sodium metal salt of hydroxymethanesulfinic acid, sodium bisulfite or sodium metal bisulfite can also be used in the aforementioned systems instead of ascorbic acid. Furthermore, tert-butyl hydroperoxide or alkali metal peroxydisulfates and / or ammonium peroxydisulfates can be used in the aforementioned systems instead of hydrogen peroxide. Instead of a water-soluble iron (II) salt, a combination of water-soluble Fe / V salts is often used.

Based on the molar amount of free-radical monomers to be polymerized, the amount of radical polymerization initiator employed in the present process is generally from 10⁻ ⁶ to 2 mol%, most 10⁻ ⁴ to 1 mol%, and depends in a manner known per se by the desired molecular weight of the resulting polymer in disperse distribution.

The molar ratio between stable N-oxyl radicals and radical polymerization initiator is within the Process variant a) according to the invention normally 0.5 to 5, preferably 0.8 to 4.

By adding organic acids such as camphorsulfonic acid or p-toluenesulfonic acid (US-A 5,322,912) or by adding Dimethyl sulfoxide (US-A 5,412,047), 2-fluoropyridine-1-metho-p-to luenesulfonate, 4-3-indolyl-butyric acid or indonylacetic acid to the polymerization mixture, the polymerization rate can be speed of the method a) generally increased will.

As compounds which, under the action of heat, break down into a stable N-oxyl radical and initiate the polymerization, the radical partner (hereinafter called N-oxyl radical generator) and are therefore suitable for variant b) according to the invention, come z. B. Compounds of the general formula X

into consideration
wherein R ¹⁷ , R ¹⁸ and R ^{19 are the} same or different and represent hydrogen or an alkyl (C ₁ - to C ₄ -), phenyl, cyano or carboxylic acid group or substituted groups thereof.

Compounds of the general formula X are e.g. B. published in EP-B 135 280. Connections of this type are in a simple manner, for. B. also obtainable by radically polymerizing a small amount of monomers by means of a radical polymerization initiator in the presence of compounds I to IX and then cleaning the polymerization product by reprecipitation. Based on the molar amount of free-radically polymerized monomer is according to the invention to ver-turning amount of N-oxyl radical formers usually 10⁻ ⁶ to 2 mol%, most 10⁻ ⁴ to 1 mol%.

Suitable monomers to be polymerized according to the invention are all those at least one ethylenically unsaturated group of pointing compounds which are usually used in the context of free-radical aqueous emulsion polymerizations. These monomers include olefins, such as. B. ethylene, vinyl aromatic monomers such as styrene, α-methyl styrene, o-chlorostyrene or vinyl toluenes, vinyl and vinylidene halides such as vinyl and vinylidene chloride, esters of vinyl alcohol and monocarboxylic acids containing 1 to 12 carbon atoms such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl laurate and commercially available monomers VEOVA® 9-11 (VEOVA X is a trade name of Shell and stands for vinyl esters of carboxylic acids, which are also known as Versatic® X acids), esters from allyl alcohol and 1 to Monocarboxylic acids containing 12 carbon atoms, such as allyl acetate, allyl propionate, allyl n-butyrate and allyl laurate, esters of α, β-monoethylenically unsaturated mono- and dicarboxylic acids, preferably having 3 to 6 carbon atoms, such as, in particular, acrylic acid, methacrylic acid, maleic acid, Fumaric acid and itaconic acid, with alkanols generally having 1 to 12, preferably 1 to 8 and in particular 1 to 4 carbon atoms, such as, in particular, methyl, ethyl, acrylic acid and methacrylic acid, -n-butyl-, -iso-butyl- and -2-ethylhexyl ester, maleic acid dimethyl ester or maleic acid n-butyl ester, nitriles α, β-monoethylenically unsaturated ter carboxylic acids such as acrylonitrile and C _4-8 conjugated dienes such as 1,3-butadiene and isoprene.

The monomers mentioned generally form the main monomers, which, based on the total amount of polymerized Monomers, normally more than 50% by weight to unite. Monomers that polymerize on their own usually Homopolymers result in increased water solubility have, are usually only as modifying Monomers in amounts, based on the total amount of polymeri based monomers, of less than 50 wt .-%, usually 0.5 up to 20, preferably 1 to 10 wt .-%, co-polymerized.

Examples of such monomers are 3 to 6 carbon atoms α, β-monoethylenically unsaturated mono- and dicarboxylic acids and whose amides such as B. acrylic acid, methacrylic acid, maleic acid, Fumaric acid, itaconic acid, acrylamide and methacrylamide, further Vinyl sulfonic acid and its water-soluble salts and N-vinyl pyrrolidone.

Monomers, which usually increase the internal strength of the films of the aqueous polymer dispersions, are generally also co-polymerized only in minor amounts, usually 0.5 to 10% by weight, based on the total amount of the monomers to be polymerized. Such monomers normally have an epoxy, hydroxy, N-methylol, carbonyl or at least two non-conjugated ethylenically unsaturated double bonds. Examples of these are N-alkylolamides of α, β-monoethylenically unsaturated carboxylic acids having 3 to 10 carbon atoms and their esters with alkanols having 1 to 4 carbon atoms, among which the N-methylolacrylamide and the N-methylolmethacrylamide are very particularly preferred , two monomers having vinyl residues, two monomers having vinylidene residues and two monomers having alkenyl residues. The di-esters of dihydric alcohols with α, β-mono ethylenically unsaturated monocarboxylic acids are particularly suitable, among which in turn acrylic and methacrylic acid are preferably used. Examples of such two nonconjugated ethylenically unge saturated double bonds are alkylene glycol monomers diacrylate- and dimethacrylates such as ethylene glycol, 1,3-butylene glycol diacrylate, 1,4-butylene glycol diacrylate and propylene glycol diacrylate, divinylbenzene, vinyl methacrylate, vinyl acrylate, allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate, methylenebisacrylamide, cyclopentadienyl acrylate or tri allyl cyanurate. Of particular importance in this context are the methacrylic acid and acrylic acid C ₁ -C ₈ hydroxyalkyl esters such as n-hydroxyethyl, n-hydroxypropyl or n-hydroxybutyl acrylate and methacrylate, and compounds such as diacetone acrylamide and acetylacetoxyethyacrylate or methacrylate .

The process according to the invention is preferably applicable to the monomers styrene, vinyl toluene, C ₁ - to C ₈ -alkyl (meth) acrylates, in particular n-butyl acrylate, 2-ethylhexyl acrylate or methyl methacrylate, and acrylonitrile and to monomer mixtures which do not contain at least 85% by weight. -% are composed of the aforementioned monomers or mixtures of the aforementioned monomers.

Particularly suitable dispersants according to the invention are the emulsifiers customarily used in the context of free-radically initiated aqueous emulsion polymerizations. These are e.g. B. block copolymers of ethylene oxide and propylene oxide, ethoxylated mono-, di- and tri-alkylphenols (e.g. EO grade: 3 to 50 and alkyl radical: C ₄ - to C ₉ ), ethoxylated fatty alcohols (e.g. EO Grade: 3 to 50 and alkyl radical: C ₈ to C ₃₆ ), and alkali and ammonium salts of alkyl sulfates (e.g. alkyl radical: C ₈ to C ₃₀ ), of sulfuric acid semiesters of ethoxylated alkanols (e.g. EO Degree: 4 to 30 and alkyl radical: C ₁₂ to C ₃₀ ) and ethoxylated alkylphenols (e.g. EO degree: 3 to 50 and alkyl radical: C ₄ to C ₁₅ ), of alkyl sulfonic acids (e.g. B. alkyl radical: C ₁₂ - to C ₃₅ ) and alkylaryl sulfonic acids (z. B. alkyl radical C ₉ - to C ₃₅ ). The group of emulsifiers suitable according to the invention furthermore includes the sulfosuccinates (sulfosuccinic acid esters) of C ₈ -C ₁₈ -alkanols and the water-soluble salts of these sulfosuccinates, in particular the alkali metal salts, among which the sodium salt is preferred.

Other suitable dispersants are compounds of the general formula XI

wherein V and W are hydrogen or C ₄ - to C ₁₄ -alkyl and are not simultaneously hydrogen, and G and H can be alkali metal ions and / or ammonium ions. V, W are preferably linear or branched alkyl radicals having 6 to 18 carbon atoms or hydrogen and in particular having 6, 12 and 16 carbon atoms, where V and W are not both hydrogen at the same time. G and H are preferably sodium, potassium or ammonium ions, with sodium being particularly preferred. Compounds XI in which G and H are sodium, V is a branched alkyl radical having 12 C atoms and W is hydrogen or V are particularly advantageous. Technical mixtures are frequently used which have a proportion of 50 to 90% by weight of the monoalkylated product, for example Dowfax® 2A1 (trademark of the Dow Chemical Company). The compounds XI are generally known, e.g. B. from US-A 4,269,749, and commercially available. The amount of emulsifier is appropriately chosen according to the invention so that the critical micelle formation concentration of the emulsifiers used is essentially not exceeded in the aqueous phase of the aqueous emulsion to be polymerized. Based on the monomers contained in the emulsion, the amount of emulsifier is generally 0.1 to 5% by weight. Of course, protective colloids can be added to the side of the emulsifiers, which are able to stabilize the disperse distribution of the ultimately resulting aqueous polymer dispersion.

To produce the aqueous required according to the invention Emulsion, the disperse phase of which consists mainly of droplets Diameter ≦ 500 nm, is expediently first in in a manner known per se from the constituents of the emulsion conventional aqueous emulsion, a macro emulsion, (e.g. the monomers, the stable N-oxyl radical, the radical one Polymerization initiator, water and the emulsifier under convention mix with each other; or the monomers, one N-oxyl radical generator, water and the emulsifier under convention mix together with each other; due to the low Distribution effort consists of the resulting aqueous emulsion mainly from droplets with a diameter ≧ 1000 nm).

This can then be necessary for the invention aqueous emulsion can be homogenized (see P.L. Tang, E.D. Sudol, C.A. Silebi and M.S. El-Aasser in the Journal of Applied Polymer Science, Vol. 43, pp. 1059-1066 [1991]). Usually high-pressure homogenizers are used. The Feinver In these machines, the components are divided by a achieved high local energy input. There are two variants especially proven in this regard.  

In the first variant, the aqueous macroemulsion is over a Piston pump compressed to over 1000 bar and then by relaxed a narrow gap. The effect here is based on one Interplay of high shear and pressure gradients and Kavita tion in the gap. An example of a high pressure homogenizer, the Working on this principle is the Niro-Soavi high pressure Homogenizer type NS1001L Panda.

In the second variant, the compressed aqueous macro emulsion through two opposing nozzles in a mixing chamber relaxed. The fine distribution effect is especially important here depend on the hydrodynamic conditions in the mixing pit gig. An example of this type of homogenizer is the microflui dizer type M 120 E from Microfluidics Corp. In this high pressure The aqueous macroemulsion is homogenized using a pneu matically operated piston pump at pressures of up to 1200 atm compressed and via a so-called "interaction chamber", ent tense. In the "interaction chamber" the emulsion jet is in a microchannel system divided into two beams, the below 180 ° C are brought together. Another example of one The homogenizer working according to this type of homogenization is the Nanojet type Expo from Nanojet Engineering GmbH. However with Nanojet instead of a fixed channel system two homogenizers built-in valves that can be adjusted mechanically.

In addition to the principles mentioned above, homogenization but e.g. B. also by using ultrasound (e.g. Branson Sonifier II 450) can be generated. The fine distribution is based here on cavitation mechanisms. The degree of division of the sound field generated aqueous emulsion depends not only on the brought sound power, but also by other factors, such as B. the intensity distribution of ultrasound in the mix chamber, the residence time, the temperature and the physical Properties of the substances to be emulsified, for example of Toughness, interfacial tension and vapor pressure. The resulting droplet size depends on a. from the Konzen tration of the emulsifier and of the homogenization registered energy and is z. B. by appropriate Ver Change in the homogenization pressure or the corresponding one Ultrasound energy selectively adjustable.

The average size of the droplets of the disperse phase of the aqueous emulsion I to be used according to the invention can be determined according to the principle of quasi-elastic dynamic light scattering (the so-called z-average droplet diameter d _{z of} the unimodal analysis of the autocorrelation function; see examples).

According to the invention, the values for d _z determined in this way on aqueous emulsions to be used according to the invention are normally ≦ 500 nm, frequently ≦ 400 nm. According to the invention, the d _z range from 100 nm to 300 nm or from 100 nm to 200 nm is favorable Normally, d _{z of} the aqueous emulsion to be used according to the invention is ≧ 40 nm.

Favorable for the stability of the droplet size distribution of the The aqueous emulsion to be used according to the invention is when the organic phase contains at least one compound, the sol in water, based on the saturated aqueous solution, at 25 ° C and 1 atm essentially less than 0.001% by weight amounts (ensures reduced Ostwald ripening). This little At least one compound can be both a monomer and a N-oxyl radical or an N-oxyl radical generator. Has none of the components of the Ge to be polymerized mix over the low water solubility required above, it is recommended to use a non-radically polymerizable one organic compound with correspondingly low water solubility into the organic droplets of those to be used according to the invention to incorporate aqueous emulsion.

Examples of monomers that are as required above have low water solubility, are p-tert-butylstyrene, Esters of 3 to 6 carbon atoms having α, β-monoethylenic unsaturated carboxylic acids and ≧ 12 carbon atoms (usually up to 30 C atoms) containing alkanols such as. B. lauryl acrylate and Stearyl acrylate. But also esters from vinyl alcohol or allyl alcohol and ≧ 9 C atoms (usually up to 30 C atoms) send alkane carboxylic acids such. B. vinyl nonanoate (VEOVA 9), Vinyl decanoate (VEOVA 10), vinyl laurate and vinyl stearate such monomers. But also macromonomers such as oligopropene acrylate are such monomers (in general macromonomers are polymers or oligomeric compounds, the at least one, mostly have an ethylenically unsaturated double bond; your rela tives number average molecular weight should be used Availability as the least water-soluble monomer preferably not be more than 100,000; usually this becomes relative number average molecular weight 1000 to 50 000 or 2000 to Amount to 50,000; Macromonomers are known to the person skilled in the art; your Manufacturing is in Makromol, for example. Chem. 223 (1994) Pp. 29 to 46;). Generally come as least Water soluble monomers are considered all those whose molar Solubility at 25 ° C and 1 atm in water less than the ent speaking solubility of lauryl acrylate is. Such monomers are z. B. also the methacryloyl polybutyl acrylate AB-6 and that Methacryloyl polystyrene A5-6 from Toa Gosei Kagaku KK (JP),  both of which have a number average molecular weight of 6000 exhibit. But also Polyol 130 from Hüls AG (a stereospecific fishy, low-viscosity polybutadiene (75% 1,4-cis, 24% 1,4-trans, 1% vinyl), its dynamic viscosity at 20 ° C 3000 mPa.s) and Polyol 110 from Hüls AG (one stereo specific, low-viscosity polybutadiene (75% 1,4-cis, 24% 1,4-trans, 1% vinyl), its dynamic viscosity at 20 ° C 3000 mPa.s) form as macromonomers with less Compounds that can be used in water solubility.

Examples of non-polymerizable compounds with low water solubility which can be used according to the invention are Acronal® A 150 F, a poly-n-butyl acrylate from BASF AG, whose 50% strength by weight solution in ethyl acetate at 23 ° C. and 1 atm has a viscosity (determined according to ISO 3219, DIN 53 019, at 250 s⁻ ¹ ) of 33 mPa.s.

But also PnBa, a high temperature (120 ° C) solution (isopropanol) poly Merisat the n-butyl acrylate with one at 25 ° C in isopropanol certain K value of 24 comes as such Ostwald ripening reducing connection into consideration. The K value is a relative one Viscosity number, which is determined in analogy to DIN 53 726. He includes the flow rate of the pure solvent relative to the flow rate of the 0.1 wt .-% solution of Polymers in the same solvent (see also cellulose chemistry, Vol. 13 (1932), pp. 58-64, and Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 23, pp. 967-968). The K value is a Measure of the average molecular weight of a polymer. A high K value corresponds to a high average molecular Weight.

However, connections that reduce the maturation of the Ostwald are also possible Resins such as rosin resins (cf. Ullmanns Encycl. Techn. Chem., 4th edition (1976), vol. 12, pp. 525-538) and hydrocarbon resins (cf. Encycl. Polym. Sci. Eng. (1987) Vol. 7, pp. 758-782), such as B. Kristalex F 85 from Hercules. Exemplary Foral® 85 E, a glycerol ester of highly hydrogenated Rosin resin (softening point: 86 ° C) from Hercules. Continue such compounds are polystyrenes (cf. CM. Miller et al., J. Polym. Sci .: Part A: Polym. Chem. 32, 2365-2376, 1994).

But also other water-insoluble, oil-soluble substances such as aliphatic and aromatic hydrocarbons (e.g. hexadecane), Film forming aids or plasticizers such as Plastilit® 3060 (a Polypropylene glycol alkylphenyl ether plasticizers) come as possible Compounds that reduce ripening in the Eastern Forest (which are often in the form of of mixtures are used).  

Preferably contain the aqueous to be used according to the invention Emulsions, based on the monomers contained, at least 0.5% by weight of a minimal water as described above soluble connection.

An upper bound on the amount obtained in this way contained, slightly insoluble in water, There are no connections. This statement applies especially if if they are exclusively monomers. If it is used a slight water Solubilizing compound around no monomer and around no N-oxyl radical generator, the latter is obtained as above However, the content normally does not exceed 200% by weight and often ≦ 100% by weight. Embodiments according to the invention are also those in which the content referred to above these compounds 1 to 50% by weight or 2 to 30% by weight or 5 to 15 wt .-% is.

The aqueous emulsions as described above are in one most technically to bring to the polymerization by in a polymerization vessel to the polymerization temperature warmed up. According to the invention, the latter is advantageously <100 ° C. to 180 ° C. Temperatures of 120 to 150 ° C. are particularly advantageous.

The polymerization is preferably carried out at a pressure leads, which is above the vapor pressure of the polymerization mixture at the corresponding polymerization temperature. He can <1 bar to 1000 bar. The poly is advantageous Merization pressure 2 to 20 bar. Is particularly advantageous a polymerization pressure of 4 to 10 or 5 to 7 bar.

In a simple manner, the desired pressure ratios can be set in that, in the polymerization reactor, prior to heating the polymerization mixture to the desired polymerization temperature, using inert gases such as, for. B. methane, CO ₂ , CO, Ar, He or N ₂ sets a form. Typically, such a form z. B. 3 to 5 bar. The closed polymerization reactor (pressure reactor) is then brought to the polymerization temperature. The free-radically initiated aqueous emulsion polymerization according to the invention is usually carried out with the exclusion of molecular oxygen.

Of course, but also in the presence of molecular Oxygen are polymerized. That is, the desired form can e.g. B. can also be adjusted by means of air. But also gas shaped monomers such as butadiene or ethylene, optionally in  Mixture with the aforementioned gases, can be used to set the pre-pressure be used. The pre-pressure setting is usually carried out at temperatures <100 ° C. Usually it is at Tempe temperatures from 0 ° C to 75 ° C or 25 ° C to 75 ° C.

In process variant a) according to the invention, the Temperature of the aqueous to be polymerized according to the invention Emulsion initially set to a value of 50 ° C to <100 ° C, to disintegrate the radical polymerization initiator to solve. At the actual polymerization temperature then warmed.

It is essential according to the invention that the product is a pseudo living aqueous polymer dispersion is obtained. This means, new is added to the aqueous polymer dispersion obtained Monomers (just stir in) and then raise the temperature the polymerization continued without the addition of radical polymerization initiator is required. The dispersed Particles of the previously obtained aqueous polymer dispersion act as polymerization sites.

This way it can be compared in a more controlled manner Form both statistical, alternating and segmented Copolymers, especially two- and three-block copolymers, produce. All that is required is a correspondingly more frequent one Wise change of the supplied monomer type.

By appropriately controlling the feed to be polymerized Monomers can also be gradient polymers, i.e. i.e., polymers with increasing or decreasing comonomer content along the polymer chain can be made. For three-block copolymers A-Block-B-Block-C-Block can blocks A and C from the same or ver different monomers. The glass transition temperature the blocks can be chosen at will. For example the chemical composition of blocks A, C can be chosen so that their glass transition temperature is ≧ 0 ° C. At the same time the chemical composition of block B should be chosen so that whose glass transition temperature is <0 ° C.

The block B z. B. more than 70 wt .-% of C ₁ - to C ₈ - (meth) acrylates in polymerized form. Block B is often composed of n-butyl acrylate, 2-ethylhexyl acrylate or mixtures thereof in polymerized form.

Of course, such monomers can also be used as comonomers be siert that have more than one vinyl group. As a result Crosslinked polymers are not obtained. According to the invention  The production of aqueous polymer is particularly advantageous dispersions whose dispersed polymer particles form a core / Have shell morphology. The advantage results in particular from an improved connection of the shell to the Core. A core / shell morphology is usually available then when a change of monomer occurs with the duration of the polymerization completed and at the same time a new formation of dispersed Polymer particles is essentially suppressed. Preferential Monomers which have a crosslinking action are copoly merized. For example, the core made of polystyrene or poly methyl methacrylate or from a copolymer of styrene and Acrylonitrile and a glass transition temperature ≧ 25 ° C exhibit. The first shell can be made of polybutadiene, Poly-n-alkyl acrylate such as poly-n-butyl acrylate or from copolymers Saten exist with a glass transition temperature Tg <0 ° C. That one or more other hard shells (e.g. made of poly styrene, polymethyl methacrylate or poly-styrene-acrylonitrile-co polymer) with a Tg ≧ 25 ° C.

Such core-shell polymer particles can according to their Iso lation as additives for modifying other plastics be set.

The molecular weight of those obtainable according to the invention in aq dispersed in the medium, polymers is in a easily adjustable by having one at the desired time point lowers the polymerization temperature and thus the blockage the growing polymer chain ends through the stable N-oxyl-Ra dical freezes. As a rule, this occurs below 100 ° C lying temperatures. By increasing the temperature, a such blockade can be removed. Another possibility speed to adjust the molecular weight consists in the loading limit the amount of monomers to be polymerized. A crazy one versible molecular weight adjustment allows the addition of classic molecular weight regulators such as esters made of thioglycol acid and 2-ethylhexanol or tert-dodecyl mercaptan. Your addition terminates the growing polymer chain ends irreversibly and frees the polymer chains from the stable N-oxyl radicals, the following z. B. by to be carried out in a suitable manner Extraction can be eliminated.

According to the invention, aqueous dispersions of polymers are thus obtained in a simple manner, the weight-average molecular weight M _{w of which is} specifically from ≧ 1000 to 250,000 or ≧ 10,000 to 250,000. The polydispersity indices of the molecular weight can be <2, often <1.5. In the case of block copolymers, this also applies to the individual segments.

After the polymerization, the particle size of the disper gated polymer particles z. B. by chemical agglomeration or be coarsened by pressure agglomeration. Subsequently can the aqueous polymer dispersion by evaporation of Dispersing medium are concentrated. They are so fictional can be prepared according to aqueous polymer dispersions, the solid substance content, based on the aqueous polymer dispersion, 10 to 50 vol .-% and if necessary up to 75 vol .-%.

According to the invention, aqueous polymer dispersions are available whose dispersed polymer particles consist of polymer of the following structure:

With
I = radical of the radical polymerization initiator and = branched or linear copolymer.

If you use a radical polymerization initiator that develops fragments with more than one radical functionality during thermal decay, the following structures are also possible:

with m = 1 to 4.

Similar structures are possible if multivalent stable N-oxyl radicals are used, i.e. H. Connections that more have as an N-oxyl radical group.  

It is

 a block copolymer a hydrophobic and a hydrophilic block, are the aforementioned Structures suitable as dispersants (cf. the older one Application DE-A 19648029).

A disadvantage of the radical initiated according to the invention aqueous emulsion polymerization is partially comparative wise slow response. With this in mind it may be appropriate to carry out the procedure according to the invention with a classic radically initiated aqueous emulsion to combine polymerization. This can be done, for example done that you start according to the invention and then classic continues.

In this case, for example, is considered to be appropriate Radical polymerization initiator in excess (relative to the amount of N-oxyl radical contained) added. In usually you will add the initiator with a monomer and If necessary, accompany the emulsifier additive.

The polydispersity of the resulting polymer is then elevated. Of course, the method according to the invention can also realized in the feed procedure according to DE-A 19 628 143 will.

Examples General

The determination of the average size of the droplets of the disperse phase of the aqueous emulsions to be used according to the invention, as well as the determination of the average size of the polymer particles in disperse distribution in the resulting aqueous polymer dispersion, was carried out using the principle of quasi-elastic dynamic light scattering (the so-called z -mean diameter d _{z of} the unimodal analysis of the autocorrelation function). A Coulter N4 Plus Particle Analyzer from Coulter Scientific Instruments was used (1 bar, 25 ° C). The measurements were carried out on dilute aqueous emulsions or dispersions whose content of non-aqueous constituents was 0.01% by weight. In the case of the aqueous polymer dispersions, the dilution was carried out using water and in the case of the aqueous emulsions using water which was saturated on the non-aqueous phase. The latter measure should prevent a change in the droplet diameter associated with the dilution.

Determination of the solids content of the resulting aqueous Polymer dispersions were carried out gravimetrically based on DIN 53 216 (drying time: 30 min, drying temperature: 140 ° C).

The molecular weights were determined by means of GPC (gel permeation chromatography graph) determined. The calibration was carried out using polystyrene Standards, tetrahydrofuran was chosen as the mobile phase and the detection was based on the refractive index.

To detect a block structure, ultrathin steps were removed from the film of the aqueous polymer dispersion using an Ultracut E (from Reichert Jung) at room temperature. The sections were transferred to Cu mesh and contrasted in OsO ₄ vapor (butadiene reacts with OsO ₄ ). Subsequently, images were taken on the contrasted section in the transmission electron microscope (TEM) (the heavy osmium nuclei capture the electrons, the other atomic nuclei let the electrons pass).

The glass transition temperature Tg was determined according to the differential scanning calorimetry method (DSC, midpoint temperature) on the films of the aqueous polymer dispersion.

The polymerization vessels were filled before the start of the Polymerization at 25 ° C.

Production of N-oxyl radical formers

• A) 4.5 g of benzoyl peroxide hydrate (25% by weight of water), 0.938 g of 2,2,6,6-tetramethyl-1-oxylpiperidine (TEMPO) and 1.5 g of camphorsulfonic acid were added to 750 g of styrene at 25 ° C. (CSA) stirred in. The mixture was then heated to 135 ° C. and held at this temperature for 4.5 hours. The reaction mixture was then cooled and dried at 30 ° C. and reduced pressure. The mixture was then taken up in toluene and reprecipitated twice in methanol (ten times the mass of methanol was used based on toluene). 545 g of a macromolecular N-oxyl radical generator A were obtained. Table 1 shows its M _w , M _n and PDI.
• B) 1.29 g of benzoyl peroxide hydrate (25% by weight of water), 0.938 g of TEMPO and 0.32 g of CSA were stirred into 208.3 g of styrene at 25 ° C. The mixture was then heated to 125 ° C. and held at this temperature for 6 h. The reaction mixture was then cooled and dissolved in toluene at 25 ° C. Then it was reprecipitated twice in methanol (ten times the mass of methanol was used based on toluene). 63 g of a macro-molecular N-oxyl radical generator B were obtained. Table 1 shows its M _w , M _n and PDI.

Table 1

Comparative example

19.5 g of the N-oxyl radical generator B were mixed with 84.75 g of styrene, 2.54 g of an 80% strength by weight aqueous solution of the sodium salt of the dihexyl ester of sulfosuccinic acid (Aerosol® MA80 from Dow Chemical Inc., Emulsifier solution 1) and 716.1 g of water mixed with stirring. The aqueous emulsion obtained was then placed in a stirred 3 liter pressure vessel. Using molecular nitrogen, a pre-pressure of 5 bar and the aqueous emulsion (d _z << 500 nm) were heated to 130 ° C. in the same and kept at this temperature for 3 hours. Then 57.59 g of acrylonitrile, 29.35 g of styrene and 2.17 g of emulsifier solution were added to the pressure vessel and the mixture was stirred for a further 4 h at 130 ° C. under a corresponding excess pressure. The reaction mixture was then cooled to 25 ° C. and analyzed. Essentially no polymer formation was found.

example 1

19.5 g of the N-oxyl radical generator B were mixed with 84.75 g of styrene, 2.54 g of emulsifier solution 1 and 716.8 g of water with stirring. The mixture obtained was then homogenized by using ultrasound (Branson Sonifier II 450) for 20 minutes to give an aqueous emulsion with d _z = 169 nm. The resulting aqueous emulsion was then placed in a stirred 3 liter pressure vessel. Using molecular nitrogen, a pre-pressure of 5 bar was set in the same and then the aqueous emulsion was heated to 130 ° C. and held at this temperature for 3 hours. A sample was then taken and analyzed. A stable aqueous polymer dispersion was present, which is characterized in Table 2. Finally, 57.59 g of acrylonitrile, 29.35 g of styrene and 2.17 g of emulsifier solution 1 were added to the pressure vessel as in the comparative example, and the mixture was stirred for a further 4 h at 130 ° C. under a corresponding excess pressure. Then the reaction mixture was cooled to 25 ° C. A stable aqueous polymer dispersion was obtained, which is characterized in Table 2.

Table 2

Example 2

0.12 g of TEMPO, 0.09 g of benzoyl proxy hydrate (25% by weight of water), 96.51 g of styrene, 4.83 g of hexadecane, 2.54 g of emulsifier solution 1 and 716 g of water were mixed with stirring. The mixture obtained was then homogenized by application of ultrasound (Branson Sonifier II 450) to an aqueous emulsion with d _z = 188 nm. The aqueous emulsion obtained was then placed in a stirred 3 liter pressure vessel. Using molecular nitrogen, a pre-pressure of 5 bar was set in the same and then the aqueous emulsion was heated to 130 ° C. and held at this temperature for 3 hours. Then 57.59 g of acrylonitrile, 29.35 g of styrene and 2.17 g of emulsifier solution 1 were added to the pressure vessel and the mixture was stirred for a further 4 h at 130 ° C. under a corresponding excess pressure. Then the reaction mixture was cooled to 25 ° C. A stable aqueous polymer dispersion was obtained which is characterized in Table 3. In addition, Table 3 shows the result of the analysis on various samples taken as a function of the polymerization time.

Table 3

Example 3

33 g of the N-oxyl radical generator A were mixed with 165 g of styrene, 7.07 g of a 35% strength by weight aqueous solution of the sodium salt, the sulfuric acid half-ester of ethoxylated nonylphenol [EO grade: 25] (Emulphor®NPS from BASF Aktiengesellschaft, Emulsifier solution 2, 1.65 g of a 50% by weight aqueous solution of the sodium salt of the dioctyl ester of sulfosuccinic acid (Lumiten® I-RA from BASF Aktiengesellschaft, emulsifier solution 3) and 800 g of water were mixed with stirring, and the mixture obtained was then applied homogenized by ultrasound (Branson Sonifier II 450) to form an aqueous emulsion with d _z = 185 nm, the resulting aqueous emulsion was then placed in a stirred 3 liter pressure vessel, and a form pressure of 1 bar was set in the same using molecular nitrogen then the aqueous emulsion was heated to 130 ° C. and held at this temperature for 24 hours, after which the reaction mixture was cooled to 25 ° C. A stable aqueous polymer dispersion became obtained, which is characterized in Table 4. In addition, Table 4 shows the result of the analysis on various samples taken as a function of the polymerization time.

Comparative example

As example 3, but instead of the N-oxyl radical generator A, 33 g of polystyrene were used, which were prepared by anionic polymerization using n-butyllithium in cyclohexane in a manner known per se (M _w = 45350, M _w / M _n = 1 , 15). After a polymerization time of only 2 h, the PDI was 2.53 at M _w = 111930. After a polymerization time of 7 h, the PDI was 4.11.

Example 4

16.4 g of the N-oxyl radical generator A were mixed with 41 g of styrene, 41 g of n-butyl acrylate, 2.05 g of emulsifier solution 1 and 400 g of water with stirring. The mixture was then homogenized by using ultrasound (Branson Sonifier II 450) to form an aqueous emulsion with d _z = 205 nm. The aqueous emulsion obtained was then placed in a stirred 3 liter pressure vessel and diluted there with 485 g of water. Using molecular nitrogen, a pre-pressure of 1 bar was set in the pressure vessel and the aqueous emulsion was then heated to 130 ° C. and held at this temperature for 25 h. The reaction mixture was then cooled to 25 ° C. A stable aqueous polymer dispersion was obtained, which is characterized in Table 5. In addition, Table 5 shows the result of the analysis on various samples taken as a function of the polymerization time.

Table 5

Example 5

16.4 g of the N-oxyl radical generator A were mixed with 82 g of vinyl toluene, 2.05 g of emulsifier solution 1 and 400 g of water with stirring. The mixture was then homogenized by using ultrasound (Branson Sonifier II 450) to form an aqueous emulsion with d _z = 194 nm. The aqueous emulsion obtained was then placed in a stirred 3 l pressure vessel and diluted there with 485 g of water. Using molecular nitrogen, a pre-pressure of 2 bar was set in the pressure vessel and then the aqueous emulsion was heated to 124 ° C. and held at this temperature for 42 hours. The reaction mixture was then cooled to 25 ° C. A stable aqueous polymer dispersion was obtained, which is characterized in Table 6. In addition, Table 6 shows the result of the analysis on various samples taken as a function of the polymerization time.

Table 6

Example 6

16.4 g of the N-oxyl radical generator B were mixed with 24.6 g of styrene, 55.76 g of n-butyl acrylate, 1.64 g of dicyclopentadienyl acrylate, 2.05 g of emulsifier solution 1 and 400 g of water with stirring. The mixture was then homogenized using ultrasound (Branson Sonifier II 450) to form an aqueous emulsion with d _z = 171 nm. The aqueous emulsion obtained was then placed in a stirred 3 liter pressure vessel and diluted there with 485 g of water. Using molecular nitrogen, a pre-pressure of 2 bar was set in the pressure vessel and then the aqueous emulsion was heated to 130 ° C. and held at this temperature for 24 hours. The reaction mixture was then cooled to 25 ° C. A stable aqueous polymer dispersion was obtained, which is characterized in Table 7. In addition, Table 7 shows the result of the analysis on various samples taken as a function of the polymerization time.

Table 7

Example 7

16.4 g of the N-oxyl radical generator A were mixed with 82 g of styrene, 2.05 g of emulsifier solution 1 and 400 g of water with stirring. The mixture was then homogenized by using ultrasound (Branson Sonifier II 450) to form an aqueous emulsion with d _z = 211 nm. The aqueous emulsion obtained was then placed in a stirred 3 liter pressure vessel and diluted there with 485 g of water. Using molecular nitrogen, a pre-pressure of 1 bar was set in the pressure vessel and then the aqueous emulsion was heated to 130 ° C. and held at this temperature for 6 hours. Subsequently, 38 g of butadiene were added to the pressure vessel and the polymerization was continued for a further 21 h at 130 ° C. and the corresponding excess pressure. The reaction mixture was then cooled to 25 ° C. A stable aqueous polymer dispersion was obtained, which is characterized in Table 8. In addition, Table 8 shows the result of the analysis on a sample taken after 6 hours. TEM images of sections of the film of the resulting aqueous polymer dispersion contrasted with OsO ₄ show the expected block copolymer formation within the dispersed polymer particles.

Table 8

Example 8

11.3 g of the N-oxyl radical generator B were mixed with 56.50 g of styrene, 1.51 g of emulsifier solution 1 and 275.4 g of water with stirring. The mixture was then homogenized by using ultrasound (Branson Sonifier II 450) to form an aqueous emulsion with d _z = 229 nm. The aqueous emulsion obtained was then placed in a stirred 3 liter pressure vessel and a pre-pressure of 2 bar was set in the same by means of molecular nitrogen. The aqueous emulsion was then heated to 130 ° C. and held at this temperature for 4 hours. Then 38 g of butadiene were added to the pressure vessel and the polymerization was continued for a further 20 h at 130 ° C. and the corresponding excess pressure. The reaction mixture was then cooled to 25 ° C. A stable aqueous polymer dispersion was obtained, which is characterized in Table 9. In addition, Table 9 shows the result of the analyzes on samples taken after 4 h and 7 h of polymerization.

Table 9

Example 9

11.3 g of the N-oxyl radical generator B were mixed with 56.50 g of styrene, 1.41 g of emulsifier solution 1 and 275.4 g of water with stirring. The mixture was then homogenized by using ultrasound (Branson Sonifier II 450) to form an aqueous emulsion with d _z = 229 nm.

Thereafter, the aqueous emulsion obtained was stirred 3 l pressure vessel and in using molecular nitrogen a pre-pressure of 2 bar is set. Then the aqueous emulsion heated to 130 ° C and 4 h at this temperature held. Then 53 g of butadiene were added to the pressure vessel and the polymerization for a further 20 h at 130 ° C and the like the overpressure continued. Then using a molecular stick a pressure of 10 bar and then to 4 bar relaxed (this process was repeated 9 times). After that 80 g of styrene added to the pressure vessel and the polymerization for corresponding for a further 4 h at 130 ° C and a pre-pressure of 2 bar Overpressure continued. Then the reaction mixture was brought to 25 ° C cooled t.

A stable aqueous polymer dispersion was obtained, which is characterized in Table 10.

In addition, Table 10 shows the analysis result according to various polymerization times.

Table 10

The film of the aqueous polymer dispersion obtained was Completely soluble in tetrahydrofuran, which is at best showed low degree of crosslinking.

Example 10

16.4 g of the N-oxyl radical generator B were mixed with 82 g of styrene, 2.05 g of emulsifier solution 1 and 400 g of water with stirring. The mixture was then homogenized by using ultrasound (Branson Sonifier II 450) to form an aqueous emulsion with d _z = 231 nm. The aqueous emulsion obtained was placed in a stirred 3 liter pressure vessel and diluted in the same with 485 g of water. A pre-pressure of 1 bar was then set in the pressure vessel using molecular nitrogen and the aqueous emulsion was heated to 130 ° C. and held at this temperature for 4 hours. Then 38 g of n-butyl acrylate were added to the pressure vessel and the polymerization was continued for a further 2 h at 130 ° C. and the corresponding excess pressure. Finally, the reaction mixture was cooled to 25 ° C. A stable aqueous polymer dispersion was obtained, which is characterized in Table 1. In addition, Table 1 shows the analysis result after different polymerisation times.

Table 11

Example 11

40 g of the N-oxyl radical generator B were mixed with 93 g of styrene, 2.66 g of emulsifier solution 1 and 645.1 g of water with stirring. The mixture was then homogenized by using ultrasound (Branson Sonifier II 450) to form an aqueous emulsion with d _z = 200 nm. The aqueous emulsion obtained was placed in a stirred 3 l pressure vessel and a pre-pressure of 5 bar was set in the same with molecular nitrogen. The aqueous emulsion was then heated to 130 ° C. and held at this temperature for 2 hours. 118 g of n-butyl acrylate, 20.05 g of styrene and 2.76 g of emulsifier solution 1 were then added to the pressure vessel and the polymerization was continued for a further 4 h at 130 ° C. and the corresponding excess pressure. Finally, the reaction mixture was cooled to 25 ° C. A stable aqueous polymer dispersion was obtained, which is characterized in Table 12. In addition, Table 12 shows the analysis result after 2 hours of polymerization.

Table 12

Example 12

35.55 g of the N-oxyl radical generator B were mixed with 82.65 g of styrene, 2.96 g of emulsifier solution 1 and 572.15 g of water with stirring. The mixture was then homogenized using ultrasound (Branson Sonifier II 450) to form an aqueous emulsion with d _z = 212 nm. The aqueous emulsion obtained was placed in a stirred 3 liter pressure vessel and a pre-pressure of 5 bar was set in the same with molecular nitrogen. The aqueous emulsion was then heated to 130 ° C. and held at this temperature for 3 hours. 104.9 g of n-butyl acrylate, 17.82 g of styrene and 3.07 g of emulsifier solution 1 were then added to the pressure vessel and the polymerization was continued for a further 4 h at 130 ° C. and the corresponding excess pressure. Then a solution of 0.45 g of sodium peroxodisulfate in 15 g of water was added to the pressure vessel and polymerized for 1.5 h at 130 ° C. and the corresponding excess pressure. Finally, the reaction mixture was cooled to 25 ° C. A stable aqueous polymer dispersion was obtained, which is characterized in Table 13 and had a residual monomer content, determined by gas chromatography, of <100 ppm by weight, which indicated an almost quantitative polymerization conversion. In addition, Table 13 shows the analysis result after 3 and 7 hours of polymerization (while after 7 hours of polymerization the molecular weight distribution was still monomedal, after 8.5 hours it was bimodal, with a first maximum at around 90,000 g / mol and a second maximum at about 600,000 g / mol).

Table 13

Claims (2)

1. A process of free-radically initiated aqueous emulsion polymerization for the preparation of an aqueous polymer dispersion, in which at least one compound having ethylenically unsaturated groups is emulsified by means of a dispersing agent in an aqueous medium and polymerized radically in the presence of a stable N-oxyl radical, characterized in that that one from a mixture comprising

• a) the at least one ethylenically unsaturated group containing compounds, at least one radical polymerization initiator and at least one stable N-oxyl radical,
  or
• b) the compounds having at least one ethylenically unsaturated group and at least one compound which, under the action of heat, breaks down into a stable N-oxyl radical and into a radical partner initiating the polymerization,

generates an aqueous emulsion, the disperse phase mainly consists of droplets with a diameter of ≦ 500 nm, and polymerizes the aqueous emulsion by increasing the temperature. 2. Aqueous polymer dispersion obtainable by a process according to claim 1.