Note: Descriptions are shown in the official language in which they were submitted.
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PREPARATION OF ALKALI-SOLUBLE (METH)ACRYLATE-BASED COPOLYMERS
5 The present invention relates to a process for preparing
(meth)acrylate-based copolymers which are soluble in the alkaline
range by free-radical emulsion polymerization at a pH <4 and to
the copolymers obtainable by this process, and their use.
10 (Meth)acrylate-based copolymers which are soluble in water in the
alkaline range are frequently employed in the field of
cosmetology as hairsetting agents. For example, EP-A-379 082
describes hairsetting compositions which as film former comprise
copolymers having a K value of from 10 to 50 which are composed
15 of from 75 to 99 % by weight of t-butyl acrylate and/or t-butyl
methacrylate, from 1 to 25 % by weight of acrylic acid and~or
methacrylic acid, and from 0 to 10 % by weight of a further
free-radically copolymerizable monomer. For use in cosmetology,
all or some of the copolymer carboxyls are neutralized by means
20 of amines.
DE-A-43 14 305 describes hairsetting compositions whose film
former comprises copolymers of the type specified in EP-A-379 082
composed of from 30 to 72 ~ by weight of t-butyl acrylate and/or
25 t-butyl methacrylate, from 10 to 28 % by weight of acrylic acid
and/or methacrylic acid, and from ~ to 60 % by weight of a
free-radically copolymerizable monomer or of a free-radically
copolymerizable monomeric mixture, at least one of these monomers
producing a homopolymer having a glass transition temperature
30 <30~C.
EP-A-646 606 describes alkali-soluble copolymers of low molecular
weight which are composed of from 25 to 75 % by weight of a
water-insoluble monoethylenically unsaturated aromatic monomer
35 and from 25 to 75 % by weight of (meth)acrylic acid. Copolymers
of this type are used in printing pastes, surface treatment
compositions, coating compositions, adhesive compositions and
paper-coating compositions. These copolymers are prepared by
emulsion polymerization at a pH c4.5 using a molecular weight
40 regulator.
If the abovementioned copolymers are to be employed as
hairsetting agents, they must wash off readily from the hair.
This is generally achieved by making the copolymers soluble in
water through neutralization of some or all of the carboxyls,
generally using an alkali metal hydroxide or, preferably, an
organic amine. The pH of a solution of a partially or completely
CA 02203686 1997-04-24
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neutralized copolymer is, in general, in the range from 8.0 to
9.5.
The copolymers can be prepared by solution, suspension or
S emulsion polymerization, the latter having the advantage that the
resulting dispersion can be freed from residual monomers and
odorous substances by means of physical deodorization, for
example by passing steam into the dispersion.
However, the dispersions obtained by emulsion polymerization have
the following two disadvantages:
a) Their shear stability is inadequate. In the industrial
apparatus commonly used for physical deodorization, the
dispersion is subject to strong shear. In insufficiently
shear-stable dispersions this has the consequence of partial
or complete coagulation and/or sedimentation and/or of
deposits in the apparatus.
b) The dispersions obtained by polymerization are acidic, owing
to the presence of the carboxyls, and in the course of
6-month storage tests show a reduction in pH by about 0.3
units. In practice this is undesirable and unacceptable.
It is an object of the present invention to provide a process for
25 preparing alkali-soluble (meth)acrylate-based copolymers by
free-radical emulsion polymerization which provides a copolymer
dispersion of sufficient stability. In particular, it is intended
that the copolymer dispersion will have better shear stability
and storage stability than the prior art dispersions.
We have found that this object is achieved, surprisingly, if the
pH of the dispersion obtained on polymerization is adjusted to a
level within the range from 4 to 7.
The present invention accordingly provides a process for
preparing alkali-soluble ~meth)acrylate-based copolymers by
free-radical emulsion polymerization at a pH <4, which comprises
adjusting the pH of the dispersion after polymerization to a
40 level within the range from 4 to 7 by adding a base.
Polymerization starts from a monomer mixture containing at least
one acrylate and/or methacrylate or a mixture thereof and at
least one monomer which is copolymerizable therewith and includes
45 at least one carboxyl.
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Suitable acrylates and methacrylates are those which lend
themselves to emulsion polymerization, especially esters of
acrylic or methacrylic acid with Cl-C6 alcohols such as methanol,
ethanol, i~opropanol, n-propanol, n-butanol, sec-butanol,
5 iso-butanol, tert-butanol and the like. Preference is given to
t-butyl acrylate or t-butyl methacrylate.
The carboxyl-containing monomers are preferably acrylic,
methacrylic, maleic, itaconic or crotonic acid.
Particular preference is given to acrylic acid, methacrylic acid
or a mixture thereof.
15 To modify the properties of the copolymer it is also possible, if
desired, to copolymerize at least one further monomer. This
monomer, or at least one of these monomers, should produce a
homopolymer having a glass transition temperature 530 ~C.
Preferred such monomers are C1-Cl8-alkyl acrylates or Cl-Cl8-alkyl
20 (meth)acrylates or N-Cl-Cl8-alkylacrylamides or N-Cl-Cl8-alkyl
(meth)acrylamides, especially N-Cl-C4-alkylacrylamides or
-methacrylamides or mixtures of two or more of these monomers.
Cl-C4-alkyl in the abovementioned (meth)acrylates and
(meth)acrylamides is suitably methyl, ethyl, n-propyl, isopropyl,
25 n-butyl, isobutyl, sec-butyl or t-butyl. Particularly preferred
monomers are ethyl acrylate or a mixture thereof with
N-t-butylacrylamide.
In a particularly preferred embodiment, the copolymers are
30 obtained by free-radical polymerization of
a) from 30 to 72 % by weight of t-butyl acrylate or t-butyl
methacrylate or a mixture thereof,
b) from lO to 28 % by weight of acrylic acid or methacrylic acid
or a mixture thereof, and
c) from 0 to 60 % by weight of a free-radically copolymerizable
monomer or mixture of monomers, at least one of these
monomers producing a homopolymer with a glass transition
temperature 530~C.
It is preferred to use from 50 to 72 % by weight and, in
particular, from 60 to 70 % by weight of the monomer a),
from 10 to 25 % by weight and, in particular, from 15 to 23 ~ by
45 weight of the monomer b), and
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from 3 to 38 % by weight and, in particular, from 7 to 25 % by
weight of the monomer c).
The particularly preferred copolymers are described in DE-A-43 14
5 305, the entire content of which is incorporated herein by
reference.
The K values of the novel polymers are generally in the range
10 from 10 to 90, preferably from 10 to 60 and, in particular, from
15 to 50. The desired K value can be established conventionally
by choosing the polymerization conditions, for example the
temperature of polymerization and the concentration of initiator.
The K value can also be reduced by using regulators, such as
15 aldehydes, halogen or sulfur compounds, examples being
formaldehyde, acetaldehyde, bromotrichloromethane,
mercaptoethanol, 2-ethylhexyl thioglycolate, thioglycolic acid or
dodecyl mercaptan. The amounts of regulators, based on the
monomers to be polymerized, are generally up to 10 % by weight,
20 preferably from 0.1 to 5 % by weight.
The K values are measured by the method of Fikentscher,
Cellulosechemie, Volume 13 (1932) 58-64 at 25~C in 1 ~ strength by
weight solution in ethanol and are a measure of the molecular
25 Weight.
The glass transition temperature of the novel copolymers is
usually in the range from 50 to 130~C, in particular from 60 to
100~C.
Copolymers are prepared conventionally using initiators such as
peroxo or azo compounds, examples being dibenzoyl peroxide,
t-butyl perpivalate, t-butyl per-2-ethylhexanoate, di-t-butyl
peroxide, t-butyl hydroperoxide,
35 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, alkali metal or
ammonium persulfates, azobisisobutyronitrile,
2,2'-azobis(2-methylbutyronitrile),
2,2'-azobis(2,4-dimethylvaleronitrile),
l,l'-azobis~ l-cyelohexane~arbonitrile)~
40 2,2'-azobis(2-amidinopropane) salts, 4,4~-azobis(4-cyanovaleric
acid) or 2-(carbamoylazo)isobutyronitrile, etc., hydrogen
peroxide or redox initiators. These initiators are usually
employed in amounts of up to 10 % by weight, preferably from 0.02
to 5 ~ by weight, based on the monomers to be polymerized.
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The polymerization is to be carried out in the presence of a
protective colloid and/or emulsifier suitable for such purposes.
Examples of suitable protective colloids are polyvinyl alcohols,
cellulose derivatives or polyvinylpyrrolidones. The emulsifiers
5 may be anionic, cationic or nonionic. Examples of suitable
emulsifiers are ethoxylated mono-, di- and trialkylphenols,
ethoxylated fatty alcohols or sorbitan esters, alkali metal and
ammonium salts of alkyl sulfates or alkyl ether sulfates, of
alkylsulfonic acids, of ligninsulfonic acid and of
10 alkylarylsulfonic acids or alkyldiphenyl oxidesulfonates.
The emulsion polymerization is conventionally carried out with
the exclusion of oxygen and at from 20 to 200~C, either
continuously or batchwise.
The amounts of monomers and dispersant are expediently chosen so
as to give a copolymer dispersion with a concentration of from 30
to 80 % by weight.
Preferably, at least some of the monomers, initiators and, if
used, regulators are metered uniformly into the reaction vessel
in the course of polymerization. However, it is also possible to
charge the monomers and the initiator to the reactor and then
25 carry out polymerization, cooling if necessary.
In accordance with one preferred embodiment, the polymerization
is carried out using a seed latex, which is expediently prepared
in a conventional manner from the monomers which are to be
30 polymerized, in the first polymerization phase. Subsequently, the
remaining portion of the monomer mixture is added, preferably by
metered addition (feed technique).
After the end of polymerization, the residual monomer content can
35 be reduced by carrying out a conventional after-polymerization
with the addition of appropriate initiators. If desired, physical
deodorization can also take place in a conventional manner by,
for example, passing steam into the batch.
The pH of the dispersion is adjusted to 4-7, preferably 5-7 and
especially 5.5-7 by addition of customary bases, for example an
alkali metal hydroxide, such as NaOH, ammonia or organic amines,
preferably those which are also used for subsequent
45 neutralization of the carboxyls, in order to make the copolymer
easy to wash out. Examples of suitable amines are mono-, di- or
trialkanolamines, such as mono-, di- or triethanolamine,
triisopropanolamine or 2-amino-2-methylpropanol,
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alkanediolamines, such as 2-amino-2-ethylpropane-1,3-diol, or
primary, secondary or tertiary alkylamines, such as
N,N-diethylpropylamine.
5 The adjustment of the pH to 4-7 may also, if desired, be
accomplished by adding a buffer solution. Preferred buffers are
based on alkali metal and/or ammonium carbonate or bicarbonate.
10 The bases and/or buffers are preferably added to the dispersion
in the form of dilute aqueous solutions.
The novel copolymers are particularly useful in cosmetology, as
film formers. They exhibit a good hairsetting effect and are
15 notable for causing virtually no sticking together of the hairs.
The copolymer dispersion obtainable by the novel process can
either be incorporated directly into an aqueous hairsetting
formulation or can be dried, for example by spray drying, so that
20 the copolymer can be used as a powder and incorporated into a
hair treatment composition.
Powders obtained by drying novel dispersions should preferably be
soluble in ethanol so as to be suitable for use in cosmetic
25 formulations for hair.
For use in hair treatment compositions, all or some of the
carboxyls in the polymer are neutralized with an alkali metal
30 hydroxide or an amine, expediently to a level of from 30 to
lO0 %, preferably from 50 to lO0 %. Amines which can be used are
those mentioned above.
The examples which follow illustrate the invention without
35 limiting it. The test data indicated below were obtained as
follows:
Shear stability:
40 A sample of the dispersion was stirred for 15 minutes at a speed
of 9000 rpm. As a measure of the shear stability, the particle
size distribution, measured by light scattering, was determined.
If a dispersion is shear-stable, there is no significant change
in the particle size distribution as a result of the shearing
45 imparted by stirring. If the difference is more than 5 %, the
dispersion is unstable to shearing.
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Solubility in ethanol:
A sample of the dispersion is converted by freeze-drying or
spray-drying into a powder, which is dissolved in ethanol (5 %
5 w/w) and neutralized to the extent of 100 % using
2-amino-2-methylpropanol.
The test for solubility is made visually. The assessment levels
10 are: clear, almost clear, cloudy and highly cloudy. From the
applications standpoint, the classifications clear and almost
clear denote acceptability.
Solubility in water:
The test is similar to that for solubility in ethanol.
pH stability on storage:
20 The pH of the dispersion is measured after storage for 6 months
at 25~C. The dispersion is said to be stable on storage if the pH
has changed by not more than 0.15 pH units.
Proporti~n of coagulum:
The proportion of coagulum in the dispersion, based on the
initial weight of monomer, is determined by filtration. Formation
of coagulum is deemed to have taken place if the proportion of
coagulum is 20.1 %.
For the Examples and Comparison Examples described below, a
dispersion was prepared as follows:
35 1 g of sodium lauryl sulfate, 6.7 g of a commercial nonionic
emulsifier, 100 g of water, 1.3 g of ethylhexyl thioglycolate,
60 g of methacrylic acid, 210 g of tert-butyl acrylate and 30 g
of ethyl acrylate are used to prepare an emulsion which was
metered by the feed technique, over the course of about 2 hours
40 and at about 75 - 85~C, into a polymerization vessel containing
500 g of water. At the same time the initiator, 1 g of sodium
persulfate dissolved in water, was likewise run in continuously.
After the end of addition, post-polymerization is carried out for
1 - 2 h at the temperature stated.
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This process is modified in accordance with Examples 1 to 5 and
Comparison Examples 1 to 4 below.
Example 1
After the end of polymerization, 2 g of ammonia in the form of an
aqueous solution were added to the dispersion. The pH of the
solution was 5.8.
Example 2
After the end of polymerization, 2 g of ammonia in the form of an
aqueous solution of ammonium hydrogen carbonate were added to the
15 dispersion. The pH of the solution was 5.8.
Example 3
20 After the end of polymerization, 1.8 g of ammonia were added to
the dispersion in the form of an aqueous ammonium carbonate
solution. The pH of the solution was 5.7.
Example 4
After the end of polymerization, 8.5 g of
2-amino-2-methylpropanol were added to the dispersion in the form
of an aqueous solution. The pH of the solution was 5.9.
30 Example 5
At the beginning of the polymerization, about 10 % of the monomer
emulsion employed was included in the initial charge, and a seed
35 latex was prepared from this using the appropriate portion of
initiator solution, in the first polymerization phase. In the
second polymerization phase, the remaining monomer mixture and
the .~ ~ining initiator solution were metered continuously but
separately into the initial charge. After the end of
40 polymerization, the pH was adjusted to ~5 by adding 2.0 g of
ammonia in the form of an aqueous solution.
Comparison Example 1
45 A dispersion was prepared as described in DE-A-43 14 305, Example
2, without any modification to the pH.
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Comparison Example 2
2 g of ammonia in the form of an aqueous solution were added to
the emulsion feed stream.
Comparison Example 3
2 g of ammonia in the form of an aqueous solution were included
10 in the initial charge.
Comparison Example 4
1 g each of ammonia in the form of an aqueous solution was added
15 to the emulsion feed stream and to the initial charge.
Using the dispersions obtained in accordance with the Examples
and Comparison Examples, the tests described above were carried
20 out. The results obtained are shown in the table:
Table
Example Shear Solubility Solubility ~ pH Coagulum
25 No. stability in ethanolin water
1 stable almost clear < 0.2 < 0.1%
clear
2 stable almost clear < 0.2 < 0.1%
clear
3 stable almost clear < 0.2 < 0.1%
clear
4 stable almost clear < 0.2 ~ 0.1%
clear
stable clear clear < 0.2 < 0.1%
Comp.
Ex.
1 unstable almost clear 0.3 < 0.1%
clear
2 stable highly highly C 0.2 > 3%
cloudy cloudy
3 stable highly cloudy < O . 2 > 3%
cloudy
4 stable highly highly < 0.2 > 3%
c loudy c loudy
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Comparison Example 1 represents the process described in the
prior art (DE-A-43 14 305 and EP-A-646 606). It is evident that
this dispersion, although meeting the requirements as regards
solubility and the formation of coagulum, is neverthele~s
5 inadequate in terms of its shear stability and pH stability.
Comparison Examples 2, 3 and 4 show that, by increasing the pH
during the polymerization, it is indeed possible to achieve the
desired shear stability and pH stability but only at the expense
10 of a situation where the solubility of the copolymers and the
formation of coagulum are no longer in accordance with what is
required.
15 In contrast, the dispersions obtained in accordance with the
novel process are shear-stable and pH-stable, sufficiently
soluble in water and ethanol, and with no coagulum formed.
Consequently, requirements which appear mutually contradictory
are met simultaneously.
