Storage-stable, silane-modified core-shell copolymers are provided comprising a shell-forming copolymer I of PA0 a) from 70 to 95% by weight, based on the overall weight of the shell, of acrylic and/or methacrylic C.sub.1 - to C.sub.10 -alkyl esters of which from 20 to 80% by weight have a water solubility of not more than 2 g/l and from 80 to 20% by weight, based in each case on the comonomers a), have a water solubility of at least 10 g/l, and PA0 b) from 5 to 30% by weight, based on the overall weight of the shell, of one or more ethylenically unsaturated, functional and water-soluble monomers including a proportion of from 25 to 100% by weight, based on the comonomers b), of unsaturated carboxylic acids, and a core-forming copolymer II of one or more monomers c) from the group of the vinyl esters, monoolefinically unsaturated mono- or dicarboxylic esters, vinylaromatic compounds, olefins, 1,3-dienes and vinyl halides, wherein the shell contains no silane compounds and the core comprises one or more silane compounds d) from the group of the mercaptosilanes alone or in combination with olefinically unsaturated, hydrolyzable silicon compounds.

BACKGROUND OF THE INVENTION 
1) Field of the Invention 
The invention relates to storage-stable, silane-modified core-shell 
copolymers, to processes for preparing storage-stable, silane-modified 
core-shell copolymer dispersions and powders, and to their use. 
2) Background Art 
Alkoxysilane-functional copolymers are frequently employed in practice as 
building adhesives (DE-B 2148456=GB-A 1407827) or for preparing emulsion 
paints and polymer-based plasters (DE-A 2148457=GB-A 1407827, EP-A 
327006=U.S. Pat. No. 5,576,384). The alkoxysilane groups are incorporated 
by polymerization into the copolymers in order to improve the wet adhesion 
and the water resistance in the case of use as coating materials, and to 
improve the adhesion to mineral substrates in the case of use as building 
adhesives or tile adhesives. 
A problem when using alkoxysilane-functional copolymers, especially in the 
form of their aqueous dispersions, is their tendency to premature 
crosslinking through hydrolytic condensation reactions of the alkoxysilane 
groups. As a consequence, aqueous dispersions of alkoxysilane-functional 
copolymers frequently possess inadequate stability on storage and when 
stored for several months lose their very good binder properties. 
EP-B 687277 discloses aqueous dispersions of core-shell copolymers which 
are obtainable by a procedure in which the alkoxysilane-functional 
comonomers are reacted with a small amount of predominantly hydrophilic 
comonomers to give a water-swellable or water-soluble addition polymer 
which subsequently, in the polymerization of the major amount of 
hydrophobic comonomer, envelops the hydrophobic core formed in the 
polymerization. This gives core-shell polymers in which the 
alkoxysilane-functional comonomer units are present externally in the 
shell, with the effect that very good adhesion properties result with 
relatively small amounts of alkoxysilane-functional comonomer. A 
disadvantage, however, is that after these dispersions have been stored 
for six months the very good binder properties (adhesive strengths under 
tension following dry and wet storage) in dispersion tile adhesives and 
plasters are no longer achieved. 
EP-A 444827 discloses silane-modified core-shell copolymer dispersions, for 
preparing elastic coatings, which comprise a core of vinyl 
ester-olefin-acrylate-vinylsilane copolymer and a vinyl ester-olefin 
shell. For their preparation, part of a mixture of vinyl ester, a acrylate 
and vinylsilane is introduced as initial charge, ethylene is injected, and 
the remainder of the comonomer mixture is metered in. After the end of the 
metered addition of silane-containing monomer, a second metered, 
silane-free vinyl ester addition is started. This process achieves the 
formation of a silane-containing, hydrophobic core, which has particular 
strength owing to crosslinking by way of the silane functions, and the 
formation of a silane-free shell. Although the silane component of these 
core-shell polymers is concentrated in the core and surrounded by a shell, 
the tensile adhesion values achieved following wet storage with this 
system when used as a tile adhesive are extremely poor. 
From EP-A 366969 (U.S. Pat. No. 5,100,948) it is known that ceramic tile 
adhesives based on aqueous dispersions of polymers comprising 
mercaptosilane rather than vinylsilane units exhibit greater water 
resistance in the solidified state than do vinylsilane-containing polymer 
dispersions. 
The object, therefore, starting from the silane-modified core-shell 
copolymers of EP-A 687277, was to provide storage-stable, silane-modified 
core-shell copolymer dispersions with which high-grade binder properties 
are obtained via the crosslinking of the silane functions even after 
storage at room temperature for 12 months. 
SUMMARY OF THE INVENTION 
It has surprisingly been found that the polymerized incorporation of 
hydrolyzable organosilicon polymerization regulators, such as 
mercaptosilanes, in the core polymer gives core-shell polymers which have 
very good binder properties even after 12 months of storage. It has also 
been found that the combination of mercaptosilanes and olefinically 
unsaturated silicon compounds in the core polymer achieves a further 
marked improvement in the profile of properties. 
The invention provides storage-stable, silane-modified core-shell 
copolymers comprising a shell-forming copolymer I of 
a) from 70 to 95% by weight, based on the overall weight of the shell, of 
acrylic and/or methacrylic C.sub.1 - to C.sub.10 -alkyl esters of which 
from 20 to 80% by weight have a water solubility of not more than 2 g/l 
and from 80 to 20% by weight, based in each case on the comonomers a), 
have a water solubility of at least 10 g/l, and 
b) from 5 to 30% by weight, based on the overall weight of the shell, of 
one or more ethylenically unsaturated, functional and water-soluble 
monomers including a proportion of from 25 to 100% by weight, based on the 
comonomers b), of unsaturated carboxylic acids, and a core-forming 
copolymer II of one or more monomers c) from the group of the vinyl 
esters, monoolefinically unsaturated mono- or dicarboxylic esters, 
vinylaromatic compounds, olefins, 1,3-dienes and vinyl halides, 
wherein the shell contains no silane compounds and the core comprises one 
or more silane compounds d) from the group of the mercaptosilanes alone or 
in combination with olefinically unsaturated, hydrolyzable silicon 
compounds. 
The invention also provides a process for preparing storage-stable, 
silane-modified core-shell copolymer dispersions and powders by 
free-radical emulsion polymerization of a comonomer mixture I comprising 
a) from 70 to 95% by weight, based on the overall weight of the comonomer 
mixture I, of acrylic and/or methacrylic C.sub.1 - to C.sub.10 -alkyl 
esters of which from 20 to 80% by weight have a water solubility of not 
more than 2 g/l and from 80 to 20% by weight, based in each case on the 
comonomers a), have a water solubility of at least 10 g/l, and 
b) from 5 to 30% by weight, based on the overall weight of the comonomer 
mixture I, of one or more ethylenically unsaturated, functional and 
water-soluble monomers including a proportion of from 25 to 100% by 
weight, based on the comonomers b), of unsaturated carboxylic acids, and 
the comonomer mixture I is introduced into a reactor together with water 
and emulsifier at a pH of from 2 to 5, polymerization is started by adding 
an initiator at a temperature of from 40.degree. C. to 90.degree. C. and, 
at a conversion of at least 40% of the comonomer mixture I, a comonomer 
mixture II comprising one or more monomers c) from the group of the vinyl 
esters, monoolefinically unsaturated mono- or dicarboxylic esters, 
vinylaromatic compounds, olefins, 1,3-dienes and vinyl halides is metered 
in, alone or with further emulsifier and initiator, and the resulting 
copolymer dispersion is dried if desired, 
wherein the comonomer mixture I contains no silane compounds and the 
comonomer mixture II comprises one or more silane compounds d) from the 
group of the mercaptosilanes alone or in combination with one or more 
olefinically unsaturated, hydrolyzable silicon compounds. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The proportion of the comonomer mixture I and hence the proportion of the 
shell polymer I is from 2 to 25% by weight, based on the overall weight of 
the core-shell copolymer. Suitable constituents of the mixture a) are the 
esters of acrylic and/or methacrylic acid with straight-chain or branched 
aliphatic C.sub.1 to C.sub.10 alcohols, alone or in combination with the 
corresponding diesters of fumaric or maleic acid. A table relating to the 
water solubility of these esters is given in "Vinyl and Diene Monomers, 
Part 1", E. C. Leonard Ed., Wiley-Interscience, New York (1970) p. 149 ff. 
Examples of suitable esters of acrylic, methacrylic, fumaric or maleic acid 
having a water solubility of not more than 2 g/l are butyl acrylate, 
ethylhexyl acrylate, ethyl methacrylate, butyl methacrylate, dibutyl 
maleate or fumarate and diethylhexyl maleate or fumarate. It is preferred 
to use butyl acrylate and/or ethylhexyl acrylate. If desired, said esters 
of acrylic, methacrylic, fumaric and maleic acid can also be replaced in 
part by one or more monomers from the group of the vinyl esters of 
branched or unbranched monocarboxylic acids having 1 to 12 carbon atoms, 
such as vinyl acetate, vinylaromatic compounds, such as styrene, olefins, 
such as ethylene, 1,3-dienes, such as 1,3-butadiene, and vinyl chloride. 
Examples of suitable esters having a water solubility of more than 10 g/l 
are methyl acrylate, methyl acrylate and ethyl acrylate. Particular 
preference is given to ethyl acrylate and/or methyl methacrylate. 
Suitable water-soluble monomers b) are acrylic, methacrylic, itaconic, 
fumaric and/or maleic acid and/or the corresponding alkali metal and 
ammonium salts; the monoamides and possibly diamides thereof, which may be 
substituted on the nitrogen once or twice by the methylol group; the 
monoesters of said dicarboxylic acids with C.sub.1 to C.sub.3 alcohols; 
the vinylsulfonates, the sulfonate-group-substituted esters of unsaturated 
carboxylic acids, such as sulfoethyl methacrylate or sulfopropyl 
methacrylate, the sulfonate-group-substituted amides of unsaturated 
carboxylic acids, such as acrylamidomethylpropanesulfonic acid, 
sulfonate-group-substituted styrenes, such as styrenesulfonic acid; 
N-vinylpyrrolidone, N-vinylformamide and the hydroxyl-substituted esters 
of unsaturated carboxylic acids. By water solubility here is meant that 
under standard conditions more than 10 g/l are soluble in water. 
Preferred water-soluble monomers b) are acrylic acid, methacrylic acid and 
the alkali metal and ammonium salts thereof, acrylamide, methacrylamide, 
N-methylolacrylamide, N-methylolmethacrylamide, hydroxyethyl acrylate, 
vinyl sulfonate, and sulfonate-group-substituted esters and amides of 
acrylic and methacrylic acid, such as sulfoethyl and sulfopropyl 
methacrylate and acrylamidomethylpropanesulfonic acid. Particular 
preference is given to acrylic acid, methacrylic acid, acrylamide and 
methacrylamide. Particular preference is also given to embodiments in 
which alongside the comonomers specified as being of particular preference 
there is copolymerized from 0.01 to 10% by weight, based on the overall 
weight of the shell polymer I, of comonomers comprising sulfonate groups, 
such as vinyl sulfonate, sulfoethyl and sulfopropyl methacrylate, 
styrenesulfonic acid, allyl sulfonate, methallyl sulfonate and 
acrylamidomethylpropanesulfonic acid. 
The proportion of the comonomer mixture II and hence the proportion of the 
core polymer is from 75 to 98% by weight, based on the overall weight of 
the core-shell copolymer. The core polymer, or the comonomer mixture II 
used to prepare it, comprises one or more monomers c) from the group cf 
the vinyl esters of branched and unbranched carboxylic acids having 1 to 
12 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl pivalate, 
vinyl ethylhexanoate, VeoVa9.RTM. and VeoVa10.RTM. (trademark of Shell 
Corporation's vinyl esters of alpha-branched carboxylic acids having 9 to 
10 carbon atoms), vinyl 2-ethylhexanoate and vinyl pivalate; 
monoolefinically unsaturated mono- or dicarboxylic esters whose acid 
component consists of 3 to carbon atoms and whose alcohol component 
consists of 1 to 8 carbon atoms, examples being acrylic and methacrylic 
esters of methanol, ethanol, butanol and 2-ethylhexanol, such as methyl 
methacrylate, butyl acrylate, 2-ethylhexyl acrylate; vinylaromatic 
compounds, such as styrene and vinyltoluene; olefins, such as ethylene and 
propylene; 1,3-dienes, such as butadiene and isoprene; and vinyl halides, 
such as vinyl chloride. 
In minor amounts it is also possible for polyethylenically unsaturated 
monomers to be employed, such as allyl methacrylate, divinyl adipate, 
butanediol diacrylate and triallyl cyanurate in amounts of from 0 to 2% by 
weight, preferably from 0.05 to 0.5% by weight, based in each case on the 
overall weight of the comonomer mixture II. 
Suitable silane compounds d) are one or more mercaptosilanes of the general 
formula HS--CR.sub.2 --SiR'.sub.3 in which R is identical or different at 
each occurrence and has the definition H and C.sub.1 - to C.sub.6 -alkyl 
group, R' is identical or different at each occurrence and has the 
definition C.sub.1 - to C.sub.6 -alkyl group and C.sub.1 - to C.sub.6 
-alkoxy group, at least one of the radicals R' being an alkoxy group. 
Preference is given to 3-mercaptopropyltriethoxysilane, 
3-mercaptopropyltrimethoxysilane and 
3-mercaptopropylmethyldimethoxysilane. The mercaptosilanes are generally 
present in an amount of from 0.01 to 10% by weight, based on the overall 
weight of the core polymer II. 
Also suitable as silane compound d) in combination with said 
mercaptosilanes are one or more olefinically unsaturated, hydrolyzable 
silicon compounds of the general formula R.sup.1 Si(CH.sub.3).sub.0-2 
(OR.sup.2).sub.3-1 where R.sup.1 has the definition CH.sub.2 .dbd.CR.sup.3 
--(CH.sub.2).sub.0-1 or CH.sub.2 .dbd.CR.sup.3 CO.sub.2 
(CH.sub.2).sub.1-3, R.sup.2 is an unbranched or branched, unsubstituted or 
substituted alkyl radical having 3 to 12 carbon atoms which can if desired 
be interrupted by an ether group, and R.sup.3 is H or CH.sub.3. The 
olefinically unsaturated, hydrolyzable silicon compounds can be 
copolymerized additionally to the mercaptosilane component in an amount of 
from 0.01 to 10% by weight, based on the overall weight of the core 
polymer II. Preference is given to gamma-acryl- and/or 
gamma-methacryloxypropyltri(alkoxy)silanes, vinylalkyldialkoxysilanes and 
vinyltrialkoxysilanes, examples of alkoxy groups which can be employed 
being methoxy, ethoxy, methoxyethylene, ethoxyethylene, methoxypropylene 
glycol ether and ethoxypropylene glycol ether radicals. It is also 
possible to use trisacetoxyvinylsilane. Particular preference is given to 
vinyltriethoxysilane, gamma-methacryloxypropyltriethoxysilane and 
trisacetoxyvinylsilane. 
As silane compound d) present in the core polymer II preference is given to 
exclusively from 0.01 to 5% by weight of mercaptosilane, based on the 
overall weight of the core polymer II. Maximum preference is given to core 
polymers II including from 0.01 to 5% by weight, based on the overall 
weight of the core polymer II, of at least one mercaptosilane and at least 
one olefinically unsaturated silane. The weight ratio of mercaptosilane to 
olefinically unsaturated silane in this case is preferably from 20:1 to 
1:20. 
Preference is given to core-shell copolymers including from 5 to 15% by 
weight of a shell copolymer I of 
a) from 80 to 95% by weight, based on the overall weight of the shell, of 
comonomer a), of which from 30 to 70% by weight is butyl acrylate and/or 
ethylhexyl acrylate and from 30 to 70% by weight, based in each case on 
the overall weight of the comonomers a), is ethyl acrylate and/or methyl 
methacrylate, 
b) from 4.5 to 19.5% by weight, based on the overall weight of the shell, 
of acrylic acid and/or methacrylic acid, alone or together with acrylamide 
and/or methacrylamide, and 
c) from 0.01 to 10% by weight, based on the overall weight of the shell, of 
one or more sulfonate-functional monomers from the group vinyl sulfonate, 
sulfoethyl and sulfopropyl methacrylate, styrenesulfonic acid, allyl 
sulfonate, methallyl sulfonate and acrylamidomethylpropanesulfonic acid. 
Preference is also given to core-shell copolymers including from 85 to 95% 
by weight of a core polymer II which is based on vinyl chloride-ethylene, 
vinyl chloride-ethylene-vinyl acetate, vinyl 
chloride-ethylene-VeoVa9.RTM., vinyl chloride-ethylene-VeoVa10.RTM., vinyl 
acetate-ethylene, vinyl acetate-VeoVa9.RTM., vinyl acetate-VeoVa10.RTM., 
methyl methacrylate-2-ethylhexyl acrylate, methyl methacrylate-butyl 
acrylate, methyl methacrylate-butyl acrylate-VeoVa9.RTM., methyl 
methacrylate-butyl acrylate-VeoVa10.RTM., styrene-butyl acrylate, 
styrene-butyl acrylate-VeoVa9.RTM., styrene-butyl acrylate-VeoVa10.RTM., 
styrene-2-ethylhexyl acrylate, styrene-2-ethylhexyl acrylate-VeoVa9.RTM., 
styrene-2-ethylhexyl acrylate-VeoVa10.RTM., and styrene-1,3-butadiene 
mixtures. The proportions in these mixtures are chosen so as to give core 
polymers having a glass transition temperature Tg of from -60.degree. C. 
to +100.degree. C. The glass transition temperature Tg of the polymers can 
be determined in known manner by means of differential scanning 
calorimetry (DSC). The Tg can also be calculated approximately in advance 
by means of the Fox equation (Fox, T. G., Bull. Am. Physics Soc. 1, 3, 
page 123, 1956). Tg values for homopolymers are listed in Polymer Handbook 
2nd Edition, J. Wiley and Sons, New York (1975). 
In these preferred embodiments of the core polymer II there is also from 
0.01 to 10, preferably from 0.01 to 5% by weight of mercaptosilanes from 
the group 3-mercaptopropyltriethoxysilane, 
3-mercaptopropyltrimethoxysilane and 
3-mercaptopropylmethyldimethoxysilane, or from 0.01 to 10% by weight, 
preferably from 0.01 to 5% by weight, based on the overall weight of the 
core polymer II, of at least one of said mercaptosilanes and at least one 
olefinically unsaturated silane from the group gamma-acryl- and 
gamma-methacryloxypropyltri(alkoxy)silanes, vinyltrialkoxysilanes and 
trisacetoxyvinylsilane in a weight ratio of from 20:1 to 1:20. 
The process can be carried out such that the polymerization of the 
comonomer mixture II together with the required emulsifier and/or 
initiator either takes place directly following the preparation of the 
alkali-soluble protective colloid of the first stage, in other words 
directly after the end of the metered addition of the comonomer mixture I, 
or is carried out subsequently in a separate stage. 
Suitable emulsifiers are non-ionic and/or anionic surfactants, examples 
being: 
1) Alkyl sulfates, especially those having a chain length of 8 to 18 carbon 
atoms, and alkyl and alkylaryl ether sulfates having 8 to 18 carbon atoms 
in the hydrophobic radical and 1 to 50 ethylene oxide units. 
2) Sulfonates, especially alkylsulfonates having 8 to 18 carbon atoms, 
alkylarylsulfonates having 8 to 18 carbon atoms, esters and monoesters of 
sulfosuccinic acid with monohydric alcohols or alkylphenols having 4 to 15 
carbon atoms in the alkyl radical; if desired, these alcohols or 
alkylphenols may also be ethoxylated with from 1 to 40 ethylene oxide 
units. 
3) Phosphoric acid partial esters and the alkali metal and ammonium salts 
thereof, especially alkyl and alkylaryl phosphates having 8 to 20 carbon 
atoms in the organic radical, alkyl ether and alkylaryl ether phosphates 
having 8 to 20 carbon atoms in the alkyl or alkylaryl radical and from 1 
to 50 EO units. 
4) Alkyl polyglycol ethers preferably comprising 8 to 40 EO units and alkyl 
radicals having 8 to 20 carbon atoms. 
5) Alkylaryl polyglycol ethers preferably comprising 8 to 40 EO units and 8 
to 20 carbon atoms in the alkyl and aryl radicals. 
6) Ethylene oxide/propylene oxide (EO/PO) block copolymers preferably 
having from 8 to 40 EO and/or PO units. 
Preferred anionic emulsifiers in the polymerization of the comonomer 
mixture I and on addition of the comonomer mixture II are the ethoxylated 
representatives of groups 1 to 5. Particular preference is given to the 
ethoxylated representatives of group 1. 
The polymerization is started by the methods commonly employed. 
Particularly suitable compounds are at least partially water-soluble, 
preferably totally water-soluble, inorganic or organic peroxide compounds, 
such as peroxo compounds, hydroperoxides and peresters, and also 
water-soluble azo compounds. Mention may be made of alkali metal or 
ammonium peroxo(di)sulfates or -phosphates, hydrogen peroxide, 
tertiary-butyl hydroperoxide, azobiscyanovaleric acid and tertiary-butyl 
permaleate. Said peroxides can also be combined if desired with reducing 
agents in a known manner. Examples of suitable reducing agents are alkali 
metal formaldehydesulfoxylates (BRUGGOLIT.RTM., RONGALIT.RTM.), alkali 
metal sulfites and alkali metal bisulfites, alkali metal thiosulfates and 
ascorbic acid. In that case, in a known manner, the use of small amounts 
of heavy metal salts is also frequently appropriate, examples being 
iron(II) salts. Particular preference is given to thermal polymerization 
with alkali metal or ammonium peroxo(di)sulfates. The amount of initiator 
employed is preferably from 0.01 to 1.0% by weight, based on the overall 
weight of the comonomers. 
It is possible to employ further customary auxiliaries, such as buffer 
substances, regulators or inhibitors of premature polymerization. In a 
preferred embodiment the comonomer mixtures I and II are polymerized in 
the presence of polymerization regulators in the customary amounts; for 
example, in the presence of n-dodecyl mercaptan, t-dodecyl mercaptan, 
mercaptopropionic acid, methyl mercaptopropionate, isopropanol or 
acetaldehyde. 
The text below describes in more detail a particularly preferred embodiment 
of the process: 
The monomers of the comonomer mixture I that is specified under b) are 
charged to a reaction vessel together with deionized water, from 0.5 to 
10% by weight, preferably from 1 to 5% by weight, based in each case on 
comonomer mixture I, of a preferably anionic emulsifier or emulsifier 
mixture and, if desired, further customary additives, such as buffers, 
regulators and inhibitors, and a pH of from 2 to 5, preferably from 2.5 to 
4, is established by adding preferably volatile acids or bases such as 
formic acid or ammonia, for example. Following the addition of the 
monomers specified under a) and establishment of the polymerization 
temperature of from 40.degree. C. to 90.degree. C., preferably from 
60.degree. C. to 80.degree. C., the polymerization is started by adding an 
initiator. 
As soon as the monomers of the comonomer mixture I have undergone from 40 
to 99%, preferably from 50 to 95%, conversion, the metered addition of the 
comonomer mixture II, of the remaining emulsifier and of the remaining 
water in the form of a preemulsion is begun; if desired, ethylene is 
injected. In the case of the copolymerization of ethylene the ethylene 
pressure is preferably maintained at from 8 to 80 bar during the 
polymerization and allowed to drop toward the end of polymerization by 
shutting off the ethylene supply. After the end of the addition of the 
comonomer mixture II the supply of initiator is maintained until the 
monomers employed have undergone more than 90%, preferably more than 99%, 
conversion, except for any ethylene used. Subsequently, the pH of the 
dispersion is adjusted to levels of between 6 and 10, preferably between 7 
and 9, any overpressure present is released, and the dispersion is 
degassed by applying reduced pressure, subjected to conventional stripping 
if desired, and then cooled. 
Especially when ethylene is copolymerized into the core polymer, from 1 to 
10% by weight of the comonomer mixture II is introduced into the reaction 
vessel together with the monomers of the comonomer mixture I as a swelling 
agent which features little or no copolymerizability with the comonomers 
a) and b). For this purpose it is possible to employ only those comonomers 
c) which, under the conditions of the polymerization of the shell polymer, 
undergo little or no copolymerization with the monomers a) and b). These 
are vinyl acetate and vinyl esters of carboxylic acids having 5 to 10 
carbon atoms, such as vinyl pivalate, vinyl ethylhexanoate, VeoVa9.RTM., 
VeoVa10.RTM.. 
The aqueous dispersions obtainable with the process of the invention have a 
solids content of from 30 to 75% by weight, preferably from 40 to 65% by 
weight. To prepare water-redispersible polymer powders the aqueous 
dispersions can be dried by means, for example, of fluidized-bed drying, 
freeze drying or spray drying. The dispersions are preferably spray dried. 
Spray drying takes place in this case in customary spray drying units, 
with atomization taking place by means of single-, dual- or 
multi-substance nozzles or with a rotating disc. The exit temperature is 
generally chosen in the range from 55.degree. C. to 100.degree. C., 
preferably from 70.degree. C. to 90.degree. C., depending on the unit, 
resin Tg and desired degree of drying. 
To ensure redispersibility, protective colloids are added to the dispersion 
as an atomizing aid prior to drying. In general the atomizing aid is 
employed in an amount of from 5 to 25% by weight, based on the polymeric 
constituents of the dispersion. Suitable atomizing aids are known to the 
skilled worker. Preference is given to partially hydrolyzed polyvinyl 
acetates, polyvinylpyrrolidones; polysaccharides in water-soluble form, 
such as starches, celluloses and their carboxymethyl, methyl, hydroxyethyl 
and hydroxypropyl derivatives; proteins, such as casein or caseinate; 
ligninsulfonates; synthetic polymers, such as poly(meth)acrylic acid, 
copolymers of (meth)acrylates with carboxyl-functional comonomer units, 
poly(meth)acrylamide, polyvinylsulfonic acids and water-soluble copolymers 
thereof; melamine-formaldehydesulfonates, 
naphthalene-formaldehydesulfonates, styrene-maleic acid copolymers and 
vinyl ether-maleic acid copolymers. 
At the atomization stage, a content of up to 1.5% by weight of antifoam, 
based on the base polymer, has frequently been found favorable. In order 
to increase the storage life by improving the blocking stability, 
especially in the case of powders of low glass transition temperature, an 
antiblocking (anticaking) agent can be added to the resulting powder, 
preferably in an amount of up to 30% by weight based on the overall weight 
of polymeric constituents. Examples of antiblocking agents are Ca and Mg 
carbonate, talc, gypsum, silica and silicates having particle sizes 
preferably in the range from 10 nm to 10 .mu.m. 
The aqueous dispersions and the water-redispersible dispersion powders of 
the core-shell copolymers are suitable for preparing polymer-bound 
plasters having good water resistance, full heat insulation systems, and 
interior and exterior paints having good abrasion resistance. The 
dispersions are particularly suitable, in addition, for preparing of 
water-resistant dispersion tile adhesives. 
The examples which follow serve to illustrate the invention.

EXAMPLE 1 
170 ml of deionized water, 28 g of a 15% strength y weight aqueous solution 
of sodium alkylbenzene-sulfonate, 9 g of an aqueous 30% strength by weight 
solution of acrylamide, 9 g of an aqueous 58% strength by weight solution 
of acrylamidomethyl-propanesulfonic acid and 8.5 g of methacrylic acid 
were placed in a stirred autoclave having a capacity of about 2 l. The pH 
was adjusted to 3.5 with dilute ammonia. The autoclave was then evacuated, 
flushed with nitrogen and evacuated again, and a mixture of 39 g of butyl 
acrylate and 43 g of methyl methacrylate was introduced under suction. 
After heating to 70.degree. C., 30 ml of an aqueous 3% strength by weight 
solution of ammonium persulfate were added over the course of 3 minutes. 
45 minutes later, the monomers introduced initially had undergone 90% 
conversion. At this point in time the pH of the initial latex was adjusted 
to 8-10 and 15 bar of ethylene were injected. At the same time, the 
metered addition of a 3% strength by weight aqueous solution of tert-butyl 
hydroperoxide was begun at a rate of 36 ml/h and of a 3% strength by 
weight aqueous solution of Bruggolit (alkali metal 
formaldehydesulfoxylate) at a rate of 36 ml/h, together with a preemulsion 
consisting of 510 g of water, 105 g of a 35% strength by weight aqueous 
solution of a nonylphenol polyethylene oxide sulfate with about 25 mol of 
ethylene oxide per mole of emulsifier, 262 g of VeoVas.RTM.10, 689 g of 
vinyl acetate, 2.2 g of 3-mercaptopropyltrimethoxysilane (Silan GF70 from 
Wacker-Chemie) and 7.6 g of vinyltriethoxysilane (Silan GF 56 from 
Wacker-Chemie). During this period, the pH was maintained at between 5 to 
6 by adding NH.sub.3 and the ethylene pressure was maintained at 15 bar. 
After the end of the metered addition of preemulsion, the metering of 
ethylene was stopped. After one hour at 70.degree. C., the metered 
addition of initiator was stopped, the pH was adjusted to 8.5 by adding 
ammonia, ethylene was blown off, and the dispersion was stirred under 
reduced pressure for 1 hour more. 
Analysis revealed an ethylene content of 4%, a solids content of 49.8% and 
a viscosity (Brookfield viscometer, 20.degree. C., 20 rpm) of 250 mPas. 
The product showed a minimum film-forming temperature of 16.degree. C. 
EXAMPLE 2 (COMATIVE) 
The procedure of Example 1 was repeated with the difference that only 9.8 g 
of vinyltriethoxysilane were employed in the monomer feed for the core 
instead of the mixture of 2.2 g of 3-mercaptopropyltrimethoxysilane and 
7.6 g of vinyltriethoxysilane. 
EXAMPLE 3 
The procedure of Example 1 was repeated with the difference that 7.6 g of 
3-mercaptopropyl-trimethoxysilane and 2.2 g of vinyltriethoxysilane were 
employed in the monomer feed (proportion inverted relative to that in 
Example 1). 
EXAMPLE 4 
The procedure of Example 1 was repeated with the difference that only 9.8 g 
of 3-mercaptopropyltrimethoxysilane and no vinyl triethoxysilane were 
employed in the monomer feed. 
EXAMPLE 5 (COMATIVE) 
The procedure of Example 1 was repeated with the difference that no 
3-mercaptopropyltrimethoxysilane and no vinyltriethoxysilane were employed 
in the monomer feed. 
EXAMPLE 6 (COMATIVE) 
The procedure of Example 1 was repeated with the difference that, instead 
of the metered addition of 2.2 g of 3-mercaptopropyltrimethoxysilane and 
7.6 g of vinyltriethoxysilane, 9.8 g of 3-mercaptopropyltrimethoxysilane 
were copolymerized in the initial charge (shell). 
EXAMPLE 7 (COMATIVE) 
The procedure of Example 1 was repeated with the difference that, instead 
of the metered addition of 2.2 g of 3-mercaptopropyltrimethoxysilane and 
7.6 g of vinyltriethoxysilane, 9.8 g of vinyltriethoxysilane were 
copolymerized in the initial charge (shell). 
Performance testing: 
For applications-related testing, the dispersions from the inventive 
examples and comparative examples were tested in a formulation for tile 
adhesives. Test formulation for dispersion tile adhesives: 
______________________________________ 
Parts Substance 
______________________________________ 
0.20 water 
0.10 preservative (Parmetol DF 12) 
0.15 dispersant (Styrodex PK 90) 
0.20 thickener (Tylose MHP 30000yp) 
0.25 thickener (Rohagit SD 15) 
0.05 dispersing auxiliary (AMP 90) 
0.15 ammonia 
0.15 defoamer (Agitan 281) 
51.80 CaCO.sub.3 filler (Durcal 40) 
8.50 CaCO.sub.3 filler (Durcal 10) 
37.75 dispersion (solids content 50% by weight) 
______________________________________ 
The adhesives of the above formulation were adjusted using film-forming 
auxiliary (1:1 mixture of Dowanol DPnB and Dowanol PnB) to a minimum 
film-forming temperature of 0.degree. C. 
The dispersions obtained in the inventive and comparative examples were 
stored for 1 week, 6 months and 12 months and thereafter used to produce 
adhesives of the above formulation with which ceramic tiles were bonded to 
concrete. The tensile adhesion strength of the bonded tiles was tested in 
accordance with DIN 18156 after 28 days' storage under standard climatic 
conditions (dry) and after 28 days' storage under standard climatic 
conditions with an additional 21 days of storage in water (wet). The test 
results are summarized in Table 1. 
The test results show that, with the combination of mercaptosilane units 
and vinylsilane units in the core polymer, good wet adhesion is still 
obtained even after 12 months (Example 1, Example 3). If the core contains 
only mercaptosilane, the wet adhesion following a 12-month storage period 
drops sharply (Example 4). Where the core contains only vinylsilane units 
(Comparative Example 2) or neither mercaptosilane nor vinylsilane 
(Comparative Example 5) wet adhesion is no longer achieved after only 6 
months. If the mercaptosilane units are incorporated only into the shell 
(Comparative Example 6) the results are even poorer than in the case of 
silane-free polymers (Comparative Example 5). If vinylsilane is 
incorporated into the shell, wet adhesion is no longer obtained after 6 
months (Comparative Example 7). 
TABLE 1 
______________________________________ 
Tensile adhesion strength [N/mm.sup.2] 
1 week 6 months 12 months 
dry wet dry wet dry wet 
______________________________________ 
Ex. 1 2.31 0.55 2.17 0.51 2.19 0.42 
C.Ex. 2 1.98 0.16 2.12 --* 2.03 --* 
Ex. 3 2.09 0.37 2.03 0.36 2.13 0.32 
Ex. 4 2.14 0.31 2.17 0.25 2.08 0.11 
C.Ex. 5 2.16 0.11 2.02 --** 2.12 --** 
C.Ex. 6 1.89 --* 1.93 --* 1.76 --* 
C.Ex. 7 2.12 0.16 1.87 --** --** 
______________________________________ 
*= tiles fell off; **adhesion too low for measurement range