Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
21~8826
Redispersible, pulverulent core-~hell polymers, their
preparation and use
Polymers based on butadiene, vinyl acetate, vinyl
chloride, vinylidene chloride and acrylic esters which
are used as an additive to hydraulic binders are already
known from the literature.
To produce flexible, extendable cement-polymer compos-
ites, preference is given to using soft polymers having
glass transition temperatures or freezing temperatures
below 0C. Thus, for example, DE-A 25 24 064 describes
aqueous dispersions of copolymers having a glass transi-
tion temperature of from -15C to -75C and comprising at
least one ester of acrylic or methacrylic acid, vinyl
acetate, at most 1.5% by weight of 2-acrylamido-2-methyl-
propanesulfonic acid and further monomers such as acrylo-
nitrile, styrene and vinyl chloride. These polymer
dispersions serve as adhesives in pressure-sensitive
adhesive tapes which adhere well to resin surfaces, paper
and metal. The disadvantage of these dispersions is
primarily in their poor cement compatibility.
Polymer dispersions obtained by emulsion polymerization
of esters of unsaturated carboxylic acids, styrene or
vinyltoluene and an olefinically unsaturated sulfonic
acid based on acrylic acid or methacrylic acid are known
from DE-A 38 38 294. A particularly suitable combination
is 2-ethylhexyl acrylate, styrene and 2-acrylamido-
2,2-dimethyle~hanesulfonic acid.
The polymers are used in mixtures with cement, sand and
further ayyleyates for coatings, crack-bridging coating
compositions and jointing compounds. However, building
material compositions produced in this way have only a
very low strength.
Furthermore, EP-A1-348 565 discloses dispersions
comprising so-called core-shell polymers-based on alkyl
acrylates or alkyl methacrylates having free carboxylic
acid groups.
However, the disadvantage of these dispersions
and also of the above-described dispersions ~ and all
-` 216882~
..
-- 2
previously known dispersions comprising polymers having
a glass transition temperature of less than 10C is that
they can be converted into powder form only with diffi-
culty and with addition of large amounts of fillers.
Furthermore, the powders thus obtained have a poor
redispersibility in water.
It is accordingly an object of the invention to
find a polymer which can easily be converted into a
pow~er which is redispersible in a neutral and also inan acid or
~ alkaline medium and which, due to its excellent
compatibility, is suitable as additive to hydraulic
binders while simultaneously ensuring the strength,
flexibility and water resistance of the latter.
Unexpectedly, this object can be achieved by
means of a core-shell polymer based on acrylates, if
desired in combination with styrene compounds, which
polymer has a different content of an ethylenically
unsaturated sulfonic acid compound in the core and in the
shell.
The present invention accordingly provides a
redispersible pulverulent core-shell polymer comprising
a) a core polymer comprising from 80 to 100% by weight
of mon~mers from the group of acrylates, if desired
in combination with monomers from the group of
styrenes, and from 0 to 20% by weight of ethyleni-
cally unsaturated sulfonic acid compound and
b) a shell polymer comprising from 60 to 95% by weight
of monomers from the group of acrylates, if desired
in combination with mo~m-rs from the group of
styrenes, and from 5 to 40% by weight of ethyleni-
cally unsaturated sulfonic acid compound, with the
content of sulfonic acid compound in the shell being
greater than the content of sulfonic acid compound
in the core.
The group of acrylates here encompasses acryloni-
trile, acrylic acid, methacrylic acid, acrylamide,
methacrylamide and acrylic and methacrylic esters having
from 1 to 12 carbon atoms in the ester part. The monomers
from this group can be unsubstituted or substituted, for
- 2168~26
- 3
instance by hydroxy or halogen.
Examples of such monomers are methyl acrylate, ethyl
acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl
acrylate, decyl acrylate, n-dodecyl acrylate, methyl
5 methacrylate, ethyl methacrylate, 2-chloroethyl acrylate,
butyl methacrylate, l~yd o~yethyl methacrylate, methylol-
acrylamide and hydroxypropyl methacrylate. Preferred
monomers from the group of acrylates are acrylic and
methacrylic esters ha~ring from 1 to 12 carbon atoms in
10 the ester part.
Particular preference is given to those esters having
from 1 to 8 carbon atoms in the ester part.
The polymer of the present invention can, both in
the core and in the shell, be built up of only one
15 monomer from this group but also of a combination of two
or more of these monomers.
Furthermore, it is possible to use, both for the core
polymer and for the shell polymer, one or more monomers
from the group of styrenes in addition to the monomers
20 from the group of acrylates. The group of styrenes here
encompasses styrene and substituted styrenes or styrene
derivatives such as, for example, alpha-methylstyrene,
vinyltoluenes such as 2-methylstyrene, 3-methylstyrene,
4-methylstyrene or chlorostyrenes such as 2-chloro-
25 styrene, 3-chlorostyrene, 2,4-dichlorostyrene,
2,5-dichlorostyrene and 2,6-dichlorostyrene. In the
polymer of the present invention, the core polymer is
built up of from 80 to 100% by weight, preferably from 90
to 99.5% by weight, of monomers from the group of
30 acrylates, if desired in combination with mor~omers from
the group of styrenes. The shell polymer is built up of
from 60 to 95% by weight, preferably 75 - 93% by weight,
of one or more of the above-described m~ omers.
For the purposes of the present invention, ethylenically
35 unsaturated sulfonic acid compounds are monomers contain-
ing sulfonic acid groups and having at least one
ethylenic double bond. These are preferably compounds of
the formula
~168826
,
- 4 -
--S--0~
Il
where R is an acrylate, methacrylate, vinyl, allyl or
styrene group.
Examples of such compounds are vinylsulfonic
acid, 4-styrenesulfonic acid, 3-sulfopropyl acrylate,
3-sulfopropyl methacrylate, 2-sulfoethyl acrylate,
2-sulfoethyl methacrylate, 2-acrylamidopropanesulfonic
acid, 2-acrylamido-2-methyl-1-propanesulfonic acid,
2-methacrylamido-2-methyl-1-propanesulfonic acid. A
particularly preferred ethylenically unsaturated sulfonic
acid co~u~d is 2-acrylamido-2-methyl-1-propanesulfonic
acid.
The ethylenically unsaturated sulfonic acid
compound is used in an amount of 0 - 20% by weight,
preferably 0.5 - 10% by weight, for preparing the core
polymer and in an amount of from 5 to 40% by weight,
preferably 7 - 25% by weight, for preparing the shell
polymer, in addition to the abovementioned monQmers.
The content of sulfonic acid compound in the shell
polymer is here always greater than the content of
sulfonic acid compound in the core polymer.
The mo~o~-rs and their distribution on a weight
basis are preferably selected in such a way that the core
polymer has a glass transition temperature of from about
-65C to +30C and the shell polymer has a glass transi-
tion temperature of over +40C. Preferably, the glass
transition temperature of the core polymer should be
between -45C and 0C and the glass transition tempera-
ture of the shell polymer should be over +60C.
The weight ratio of core polymer to shell polymer
is between 95:5 and 60:40 in the core-shell polymers of
the present invention.
The polymers of the present invention are pre-
pared by a 2-stage emulsion polymerization in an aqueous
medium in the pre~ence of initiators, di~per~ants,
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emulsifiers and, if desired, regulators and protective
colloids. The polymerization is preferably carried out in
the form of a feed stream process. In this process, a
monomer emulsion of the monomers suitable for preparing
S the core polymer in combination with the abovementioned
auxiliaries customary for emulsion polymerization is
prepared in the first step. Part of this polymerization
mixture and an aqueous initiator solution is initially
charged in water heated to the reaction temperature and
after commencement of the polymerization the rema;n;ng
monomer emulsion on the one hand and an additional
initiator solution, as well as, if appropriate, further
polymerization auxiliaries, on the other hand are contin-
uously fed in from separate reservoirs. The streams are
fed in over a period of from about 1 to 4 hours, prefera-
bly from 1.5 to 2.5 hours, with the reaction temperature
being kept constant within a range of a few degrees. The
reaction mixture is subsequently held in this temperature
range for a further period of from about 5 to 60 minutes,
preferably from 10 to 20 minutes. During this time, a
second mon~ or emulsion comprising the monomers suitable
for preparing the shell polymer in combination with the
abovementioned polymerization auxiliaries is prepared.
The second monomer emulsion is then added to the latex
obtained in the 1st polymerization step over a period of
from about 20 minutes to 2 hours, preferably from about
30 minutes to 1.5 hours. At the same time, an aqueous
initiator solution is again allowed to run in via a
separate inlet. After addition i8 complete, the reaction
mixture is, if appropriate, held at the reaction tempera-
ture for a further few minutes to complete the reaction,
subsequently cooled or allowed to cool to room tempera-
ture and the latex thus obtained is filtered off.
The polymerization temperature is here between about 20
and 100C, preferably between about 40 and 90C. The
polymerization temperature is set 80 that the initiators
used decompose sufficiently quickly into the reactive
free radicals required for the reaction. The amount of
free-radical-forming initiators is, in each step, from
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about 0.1 to 1~ by weight, based on the total amount of
the monomers used in the respective step. Particularly
suitable initiators are water-soluble inorganic perox-
ides, of which peroxodisulfates such as sodium, potassium
or ammonium peroxodisulfate are particularly preferred.
If desired, the initiators are used in combination with
reducing agents such as sodium formaldehyde-sulfoxylate,
sodium hydrogen sulfite, sodium pyrosulfite, sodium
dithionite, sodium thiosulfate and/or ascorbic acid,
hydroxylamine or hydrazine. The reducing agent can
additionally be combined with an effective amount of a
heavy metal salt such as an iron, cobalt, cerium or
vanadyl salts as accelerator. To complete the conversion
and to lower the amount of residual monomers, additional
amounts of initiator or combined systems can subsequently
be added. An example of a system suitable for this
purpose is tert-butyl hydroperoxide in combination with
sodium formaldehyde-sulfoxylate.
The mean molecular weight of the dispersed core-
shell polymer is, in addition to the glass transition
temperature and the cro88l; nk; ng density, the most
important molecular parameter for influencing decisive
use properties of the products such as, for example,
tack, adhesion, viscoelasticity or tensile strength. If
the desired range of the molecular weight is not achieved
by alteration of the polymerization temperature or the
amount of initiator, use can be made of additional
substances which regulate the molecular weight, for
example n-butyl mercaptan, tert-butyl mercaptan,
n-dodecyl mercaptan, thioglycol, thioglycolic acid, etc.,
in an amount in each case of up to about 2% by weight,
based on the total amount of the monomers used in the
respective step. The regulator i8 added as desired, but
it is preferably added to the respective monomer emul-
sions.
In the polymerization process of the present invention,anionic or nonionic emulsifiers customary in emulsion
polymerization or their compatible mixtures can be used,
provided that they are sufficiently soluble both in the
- 2168826
aqueous phase and in the monomer phase and no interfering
interactions with the monomers and other additives occur.
Ionic emulsifiers used are preferably anionic surfac-
tants. Emulsifiers which have been found to be particu-
larly useful are those prepared by ethoxylation andsulfation of C~-C10-alkylphenols. They are derived, for
example, from nonylphenol, isononylphenol, isooctyl-
phenol, triisobutylphenol and tri-tert-butylphenol and
bear from 3 to 30 ethylene oxide (E0) units. Further
examples of possible anionic emulsifiers are AlkAl; metal
salts of alkylsulfonic acid~ such as sodium dodecyl-
sulfonate, alkylaryl~ulfonic acids such as sodium
dodecylbenzenesulfonate and also ethoxylated and sulfo-
nated fatty alcohols having a C8-C2s-alkyl radical and a
degree of ethoxylation of from 3 to 50, for example
sodium lauryl alcohol ether sulfate contA;n;ng 3 E0
units. As nonionic emulsifiers, preference is given to
using reaction products of Ca-C10-alkylphenols contA~; n; n~
from 3 to 30 mol of ethylene oxide.
Also suitable are ethoxylation products of
C10-C20-alkanols such as lauryl alcohol polyglycol ether
and reaction products of polypropylene glycol and ethyl-
ene oxide. Based on the amount of monomer in the respec-
tive step, from about 0.2 to 5% by weight, preferably
from 0.5 to 2% by weight, of emulsifier are used per
step.
To prepare the water-free, pulverulent core-shell
polymers, the polymer latex prepared as described above
is, if desired, mixed with a suitable anticaking agent
such as microsilica, silicates or calcium carbonate and
diluted to a solids content of from about 10 to 50%,
preferably from 20 to 40%. If desired, the free acid
groups can then be neutralized. Suitable neutralization
agents are bases such as ammonia, triethylamine, mono-
ethanolamine, dimethylaminoethanol, and also hydroxidesor carbonates of the alkali metals and alkaline earth
metals. Preference is given to using hydroxides and
carbonates of the alkaline earth metals, particularly
preferably calcium or magne~ium hydroxide. This is
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-- 8
followed by spray drying, whereby the redispersible
pulverulent core-shell polymers of the present invention
are obtA i n~ .
The present invention accordingly further pro-
vides a 2-stage process for preparing redispersible,
pulverulent core-shell polymers, which comprises
a) in the 1st step, preparing a monomer mixture of from
80 to 100% by weight of monomers from the group of
acrylates, if desired in combination with monomers
from the group of styrenes, and from 0 to 20% by
weight of ethylenically unsaturated sulfonic acid
compound and polymerizing the monomer mixture by
emulsion polymerization to form the core polymer,
meanwhile
b) preparing a monomer mixture of from 60 to 95% by
weight of monomers from the group of acrylates, if
desired in combination with monomers from the group
of styrenes, and from 5 to 40% by weight of
ethylenically un~aturated sulfonic acid compound,
then
c) in the 2nd step, A~;ng the monomer mixture from b)
to the polymer emulsion obtained in the 1st step and
polymerizing the mixture by emulsion polymerization
to form the shell polymer, thereby obtA;n;ng an
aqueous emulsion of a core-shell polymer, and
d) if desired after neutralization of the free acid
groups, converting this emulsion into powder form by
spray drying.
The pulverulent core-shell polymers of the
present invention are suitable as additives to hydraulic
binders. They are redispersible both in neutral and in
acid or alkaline media and are particularly compatible
with hydraulic binders such as cement, lime, plaster of
Paris or anhydrite and can therefore be advantageously
used in building material compositions which can addi-
tionally contain other inorganic and/or organic constitu-
ents such as gravel, sand, reinforcing fibers. Such
building material compositions based on hydraulic binder~
containing polymers of the present invention have
- 216882~
improved processibility, adhesion, flexibility or
elasticity even at low temperatures and are suitable, for
example, as repair compositions, coating compositions,
building adhesives, building materials, jointing com-
pounds, sealing compounds, road surfacing compositions,intermediate layers and leveling layers.
The polymers of the present invention are partic-
ularly suitable as binders in cement-cont~;n;ng composi-
tions. To prepare such compositions, for example, the
appropriate amount of hydraulic binders, for example
cement, preferably Portland cement, is initially charged
and, if desired, pr~mixed dry with further ingredients
such as sand, polymer fibers, etc.
This is followed by the addition of the redispersed core-
shell polymer of the present invention. However, it is
also possible to initially charge the polymer of the
present invention in powder form together with the
hydraulic binder. Based on the amount of the hydraulic
binder, preference is given to using from 5 to 100% by
weight, particularly preferably from 15 to 50% by weight,
of the core-shell polymer of the present invention,
calculated as solid resins. This corresponds to a ratio
of polymer to inorganic binder of from 0.05 to 1Ø
Example 1: Preparation of a core-shell polymer latex
a) To prepare the core polymer, a monomer emulsion
having the following composition was prepared (pre-
emulsion 1)
DI water (DI = deionized) 210 g
30% strength sodium lauryl sulfate (SLS) 14 g
solution
25% strength ethoxylated nonylphenol, 18.3 g
15 E0 (NP15) solution
Butyl acrylate (BA) 415 g
Methyl methacrylate (MMA) 71.5 g
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.
- 10 -
2-Acrylamido-2-methyl-1-propanesulfonicS g
acid (AMPS)
n-Dodecyl mercaptan (nDSH) 0.6 g
A 2 1 round-bottom flask equipped with mechanical
stirrer, reflux con~nRer, thermometer, N2 inlet and
inlets for the initiator solution and the pre-
emulsion was initially charged with 770 g of deion-
ized water and the water was heated.
After reaching the reaction temperature of
82 - 84C, the following solutions were added:
Initiator solution: G onium persulfate/DI water
1.1 g/58.0 g
Preemulsion 1: 30 g
After the commencement of polymerization (exothermic
peak), the remaining preemulsion 1 and an additional
initiator solution comprising 1 g of G onium per-
sulfate in 55 g of DI water was allowed to run in
over a period of 120 minutes.
During this phase, the temperature was held in a
range of 81 - 83C. Subsequent to the addition, the
reaction mixture was held in this temperature range
for a further 15 minutes.
b) To prepare the shell polymer, a further monomer
emulsion having the following composition was pre-
pared (preemulsion 2)
DI water 40 g
30% strength SLS solution 2.5 g
25% strength NP 15 solution 3.9 g
BA 29.5 g
MMA 100 g
AMPS 27 g
nDSH 1.3 g
~168826
.
After the 15 minutes, the preemulsion 2 was metered
into the flask cont~;n;ng the core polymer latex
over a period of 60 minutes.
Simultaneously, over the same period of time, a
further initiator solution comprising 0.5 g of
ammonium persulfate in 40 g of DI water was allowed
to run in. After addition was complete, the core-
shell polymer latex was held at the reaction
temperature for a further 15 minutes, subseguently
allowed to cool to room temperature and filtered
off.
The product obt~;neA had a solids content of 42% and
a pH of 1.2. The Brookfield viscosity was (at
100 rpm) 40 mPa-s.
ExamPle 2: Preparation of a core-shell polymer latex
cont~;n;ng carboxylic acid
The preparation of the polymer latex was carried
out in a manner similar to Example 1, except that AMPS
was replaced in both preemulsions by an equimolar amount
of methacrylic acid (MAA).
The latex obtained had a solids content of 41.5% and a pH
of 2.2. The Brookfield ~iscosity was (at 100 rpm)
34 mPa-s.
Example 3:
Random copolymers 3a) cont~;n;ng AMPS and 3b)
containing MAA were prepared by a single-stage emulsion
polymerization using the monomer composition of the
combination of preemulsions 1 and 2 from Examples 1 and
2.
Example 4:
Further AMPS-containing core-shell polymers
having different monomer emulsion compositions and
core/shell weight ratios were prepared in a manner
~imilar to Example 1.
The respective compositions are shown in Table 1.
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Preemulsion 1 4a 4b 4c 4d 4e 4f
(g) (g)(g) (g) (g) (g)
BA 44.0 44.044.0 62.244.0 44.2
MMA 20.2 5.220.2 25.020.2 19.9
STY 15.0
ANæS 0.5 0.5 0.5 0.5 1.0
SEMA 0.4
Preemulsion 2
BA 6.6 6.66.6 6.6 6.6
MMA 25.4 25.425.5 9.026.1 21.8
AMPS 3.3 3.3 3.3 2.6 6.5
SEMA 3.2
meq/g 1.8 1.81.8 1.8 1.5 3.6
Core/shell 65/35 65/3565/3588/1265/3565/35
STY: Styrene
SEMA: CH2C(CH3)COOCH2CH2SO3H
meq/g: milliequivalents of acid groups/g of solid polymer
ExamPle 5: Preparation of redispersible powders
The latices from Examples 1 to 4 were mixed with
anticaking agent (calcium carbonate, 5% by weight) and
diluted to a solids content of 30%. Two test samples were
used per polymer latex, with one test sample of each
having the acid groups neutralized with calcium hydrox-
ide.
The dispersions were then converted into powder form by
spray drying using a LAB-PLANI SD04 laboratory-scale
spray dryer.
The powders thus obtained were then tested for redis-
persibility.
For this purpose, 1 g of dry powder was added to
100 ml of DI water and stirred for 5 minutes. The mixture
obtained was transferred to a sedimentation tube (IMOF
cone). The formation of a latex phase was observed and
the amount of sediment formed after 6 hours was measured
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,.
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to determine the water redispersibility.
The results are shown in Table 2.
Ex. Structure Acid Acid Ion Redisp. pH
group (meq/g)
1 Core/shell AMPS1.8 H ++ 1.85
Ca ++ 10.8
2 Core/shell MAA1.8 H -- 2.7
Ca ++ 9.2
3a) Random AMPS 1.8 H - 1.9
Ca + 8.5
3b) Random MAA 1.8 H -- 3.0
Ca - 9.8
4c) Core/shell SEMA1.8 H + 1.9
Ca ++ 8.7
Redisp. Redispersibility obtained
10 ++ Latex phase is easily obt~; ne~, sedimentation
volume after 6 hours ~ 1.5 ml
+ Latex phase is obtained, sedimentation volume
after 6 hours ~ 3 ml
- Latex phase is obtained only with difficulty,
sedimentation volume after 6 hours ~ 3 ml
-- Latex phase is not obtained.
Example 6: Use in Portland cement
Various powders from Example 5 were added to a
mixture of 3 parts of sand/1 part of cement (Italian
Portland cement grade 425) in such an amount as to
achieve a polymer/cement ratio of 0.10.
Sub~equently, water and antifoaming agent (Lumitin
IP3108, from BASF) were added in such an amount that a
water/cement ratio of 0.50 and an antifoam/cement ratio
of 0.01 was achieved. A Hobart-type mixer was used to
obtain a mortar having a wet density of 2.1 kg/dm3 which
was used to produce 4 x 4 x 16 cm mortar briquettes which
were te~ted for compressive strength (CS), flexural
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- 14 -
strength (FS) and water absorption (WA) (measured after
contact with water for 7 days).
For comparison, test specimens cont~;n;n~ no
polymer addition (C1) or cont~;n;ng a commercial acrylic
copolymer latex (Acryl 60, from Thoro) (C2) without
sulfonic acid monomers were examined.
The results are summarized in Table 3.
Ex. Ion CS FS WA
(NPa) (MPa) (%)
1 H 40.0 9.0 4.5
1 Ca 42.0 9.2 3.5
C1 40.0 7.0 8.5
C2 41.0 8.5 5.0
