Acrylate resins as binders for color concentrates

Color concentrates comprising a colorant such as a pigment and a polymeric binder, and polymeric binders therefor, said polymeric binders comprising: PA0 (a) 70-90 percent of methyl methacrylate, by weight of the polymer; PA0 (b) 10-20 percent of methyl acrylate; and PA0 (c) from 0 to 10 percent of at least one free radically polymerizable monomer of the formula ##STR1## wherein R.sub.1 is hydrogen or methyl and R.sub.2 is a moiety carrying a functional group.

The present invention relates to color concentrates and to acrylate and 
methacrylate synthetic resins adaptable to use as binders for such color 
concentrates. 
Colorants which permit practically any desired coloring are available to 
the industry for the coloring of synthetic resins. Such resins are mainly 
colored either in bulk as they are produced or during the processing of 
the resins in powder or granular form. The coloring method is adapted to 
the particular resin. 
Color concentrates formed between colorants, particularly pigments, and 
binders and known as masterbatches are advantageously used for 
incorporating the colorants into synthetic resin monomers or prepolymers. 
Similar techniques are used to color plastics in powdered or granular 
form. 
The main difficulty usually lies in securing a uniform dispersion of the 
pigment in the pigment concentrates, which is a prerequisite for uniform 
pigment dispersion in the resin. Pigment agglomerations in resins 
invariably have an adverse effect on their mechanical and optical 
properties. 
The mechanical dispersion of colorants in synthetic resin has been dealt 
with in many patent publications. Published German patent application DOS 
No. 12 48 291 discloses pigment concentrates for the coloring of synthetic 
resins comprising polyvinyl chloride, in the preparation of which granular 
PVC and finely divided pigments and additives are subjected to high shear 
forces at temperatures below their melting point. 
According to published German patent application DOS No. 15 92 897, pigment 
masses for the coloring of thermoplastic resins are obtained inter alia by 
mixing the finely divided pigment in the aqueous phase with an emulsion or 
solution of the vehicle, with formation of an unagglomerated mixture, and 
then spray drying the latter. 
British patent No. 1,148,168 describes the production of specific types of 
solid color concentrates wherein a pigment in paste form (obtained by 
electrolytic precipitation from an aqueous dispersion) and a phenolic 
resin containing an unesterified rosin (obtained by precipitation from an 
aqueous salt solution) are mixed. 
According to U.S. Pat. No. 3,471,433, masterbatches are obtained from 
pigment dispersions in acrylate resins when a strong acid is mixed with 
formamide or acetamide, the pigment is dispersed therein, and a viscous 
acrylic polymer (for example, an acrylonitrile/vinyl acetate and 
methylvinylpyridine copolymer) is added with stirring. 
The emulsion polymerization of vinyl monomers such as butyl 
acrylate/acrylonitrile with the addition cf 0.1 to 20 percent of monoallyl 
maleate in an aqueous suspension of a pigment followed by grafting with 
vinyl monomers (styrene/acrylonitrile) yields pigment concentrates which 
can be processed with polymers such as ABS resins to give uniformly 
colored mixtures. (Japanese patent publication No. 50-092386.) 
According to published German patent application DOS No. 28 41 540, 
colorants for incorporation in plasticized polyvinyl chloride are obtained 
by the mechanical mixing of polymers of aromatic vinyl compounds, 
2-alkenecarboxylic acids or monoalkyl esters of 2-alkenecarboxylic acids, 
and alkyl acrylates or methacrylates in the molten state with pigments, 
kneading above 100.degree. C., cooling, and grinding. 
According to Czech patent No. 106,877, polymethyl methacrylate, titanium 
dioxide, and lead stearate are plasticized at about 170.degree. C. and the 
concentrate so obtained is suspended in methyl methacrylate. To produce 
colored acrylic glasses, defined herein as rigid homopolymers and 
copolymers of acrylate esters and/or methacrylate esters having a Vicat 
softening temperature of 80.degree.-120.degree. C. (as determined 
according to DIN 53460 or IS 306), the suspension is mixed with a 
prepolymer and completely polymerized in a mold. 
The prior art colorants for the coloring of acrylic glasses (as defined 
above) in bulk do not meet all the necessary requirements. These 
requirements relate both to the ease of incorporating the color 
concentrates and to the way the concentrates affect acrylic glasses 
colored therewith. 
For example, the color concentrates should be readily soluble in the 
monomers or prepolymers. Moreover, they should not adversely affect the 
course of polymerization or removal from the mold. The pigments should be 
well dispersed in the polymerization formulation. Above all, the disperse 
state of the pigments should be sufficiently stable, that is to say, no 
sedimentation or reagglomeration of the pigments should occur. A 
desideratum is that the dispersions prepared with the color concentrates 
be stable for a period of hours or even days. 
The colorants or pigments should be readily dispersible mechanically to 
give a color concentrate, for example a dry pigment concentrate. 
Further processing of the acrylic glasses following completion of 
polymerization, such as annealing, forming, stretching, etc., should not 
be adversely affected. 
The other mechanical properties of the colored acrylic glasses, their Vicat 
softening temperature, and their weatherability should not be inferior to 
those of regular acrylic glasses. 
It has been found that these requirements are fully satisfied by colorants 
prepared in accordance with the invention with polymeric binders 
comprising 
(a) 70-90 percent, by weight of the polymer, of methyl methacrylate, 
(b) 10-20 percent, by weight of the polymer, of methyl acrylate, and 
(c) 0-10 percent, by weight of the polymer, of at least one free radically 
polymerizable monomer of the formula 
##STR2## 
wherein R.sub.1 is hydrogen or methyl and R.sub.2 is (i) --OH, 
(ii) --NR.sub.3 R.sub.4, wherein R.sub.3 and R.sub.4, taken alone, are the 
same or different and are hydrogen or linear or branched alkyl having 1 to 
5 carbon atoms, and R.sub.3 and R.sub.4, taken together with the nitrogen 
atom to which they are bonded, form a 5- or 6-membered heterocycle or such 
a heterocycle containing further nitrogen or oxygen atoms, 
(iii) --Y--X--NR.sub.3 R.sub.4, wherein 
Y is oxygen or --NR.sub.5 --, 
X is linear or branched alkylene having 2 to 10 carbon atoms or is 
cycloalkylene, and 
R.sub.5 is hydrogen or alkyl having 1 to 6 carbon atoms, 
(iv) --Y--X--OH, 
(v) 
##STR3## 
wherein n is 0 or 1 and R.sub.6 is hydrogen or alkyl having 1 to 6 carbon 
atoms, 
(vi) --Y--X--Si--(OR.sub.7).sub.3, wherein R.sub.7 is alkyl having 1 to 6 
carbon atoms, or 
(vii) 
##STR4## 
The polymeric binders of the invention can readily be dispersed with the 
pigments, for example, by means of rolling and kneading equipment, to give 
a dry pigment concentrate. The polymer is composed predominantly of methyl 
methacrylate but includes also methyl acrylate. While preparations with a 
satisfactory degree of dispersion of the pigment or pigments can be 
obtained with polymers of this type when used in a weight ratio from 6:1 
to 3.3:1, mainly as a result of the shearing action of the dispersing 
equipment, the stability of the disperse state of the pigment mixtures in 
the polymer formulations, which consist essentially of methyl 
methacrylate/polymethacrylate, cannot always be maintained for the 
necessary length of time. 
However, adequate stability will always be secured when at least one 
further monomer component (c) is added to the methyl methacrylate and 
methyl acrylate components in an amount of at least 0.1 percent by weight 
of the polymer, preferably in an amount from 1 to 6 percent by weight. It 
may be hypothesized that the binder molecules are adsorbed in sufficient 
number on the pigment surface through functional groups and thus form a 
stabilizing envelope around the pigment particles which prevents their 
flocculation. 
Particularly preferred is the addition of nitrogen bearing monomers of the 
types (c) (ii) and (iii) identified above. Of special advantage is the 
presence of type (c) (iii) monomers with branching in the alkylene chain 
X, and particularly of type (c) (iii) monomers having a tertiary carbon 
atom in the alkylene chain. These include ccmpounds in which X represents 
2,2-dimethylpropyl, and particularly 
3-dialkylamino-2,2-dimethylpropyl-1-methacrylate, and more particularly 
the 3-dimethylamino and 3-diethylamino compounds. Binders containing these 
monomers are distinguished by ease of handling, among other things, 
particularly in removal from the mold, and generally meet the practical 
requirements set forth above particularly well. 
Polymeric binders in which component (c) is formed of or comprises at least 
one of the monomers: 
2-dimethylaminoethyl acrylate and/or methacrylate, 
2-diethylaminoethyl acrylate and/or methacrylate, 
2-dimethylaminopropyl acrylate and/or methacrylate, or 
2-diethylaminopropyl acrylate and/or methacrylate 
have also proved themselves. 
Combinations with one or more monomers containing hydroxyl groups, for 
example of the types (c) (i) or (c) (iv), are also advantageous. 
A weight ratio of (a):(b):(c) of 4.2.+-.0.7:1:0.3.+-.0.2 will serve as a 
guide. The polymers generally have a reduced viscosity .eta..sub.sp /c, 
ranging from 10 to 70, and preferably from 15 to 30, ml/g in CHCl.sub.3 at 
20.degree. C. The viscosity is determined in conformity with DIN 1342 by 
means of an Ubbelohde microviscometer. 
The colorants used to prepare the color concentrates from the binders of 
the invention are colorants which are suitable also for the coloring of 
the polymers, in other words, both inorganic and organic dyes and 
pigments. They are listed in the prior art for the coloring of specific 
polymers. (See Vieweg-Esser, Kunststoff-Handbuch ["Plastics Handbook"], 
vol. IX, Polymethacrylates, Carl Hanser Verlag, 1975.) 
Foremost among these are carbon black, yellow and red pigments comprising 
cadmium sulfide and/or calcium selenide, phthalocyanine blue and green, 
and the like. 
The concentration of colorant in the binders of the invention will 
generally range from 10 to 70 weight percent and preferably is from 30 to 
60 weight percent. The colorants may be incorporated in the binders of the 
invention conventionally by the use of sufficiently high shear forces. 
Suitable dispersing equipment includes kneaders, roller mills, and the 
like. 
The masterbatches (polymeric binders containing colorants) usually 
represent from 0.05 to 3 weight percent, and preferably from 0.1 to 1.5 
weight percent, of the total polymerization formulation, which generally 
consists of monomers, and preferably a prepolymer, binder, and optional 
additives. They may be incorporated in intermediates such as syrups, 
prepolymers, and/or in monomers which are used in the prior art for 
polymerization of acrylic or methacrylic resins (matrix polymers) in the 
usual manner, for example by being stirred into them. 
The subsequent steps, for example, pouring the syrup into polymerization 
cells serving as molds, the polymerization which follows, removal from the 
molds, etc., may be carried out in keeping with prior art methods. 
Surprisingly, it is also possible to carry out the incorporation by 
introducing a dispersion of the colorants in a polymeric binder formed 
only of components (a) and (b) into the polymerization intermediates of a 
methacrylic resin simultaneously with a sufficient amount of a polymeric 
binder formed of components (a), (b), and (c). The latter binder is 
evidently adsorbed rapidly enough on the pigment surface from the 
solution. Based on recognition of this fact, the coloring procedure for 
batches with different pigment preparations can be largely standardized 
since it will suffice always to add the same but adequate amount of a 
polymeric binder formed of (a), (b), and (c). 
The polymeric binders of the invention are suited primarily for 
incorporation into acrylic resins produced by bulk polymerization. 
Articles molded therefrom will find use particularly in industry, in 
sanitary applications, and in households, where resistance to common 
solvents and good mechanical properties are required. 
Such acrylic resins (matrix polymers) usually are composed entirely or to a 
large extent of esters of acrylic acid and of methacrylic acid, and 
particularly of methyl methacrylate, as monomers, and optionally also of 
other copolymerizable monomers in addition to methyl methacrylate. 
For example, matrix polymers comprising methyl methacrylate may further 
contain from 0 to 45 weight percent of other comonomers. These may be 
other esters of methacrylic acid or of acrylic acid, for example methyl 
acrylate, butyl acrylate, alpha-chloromethyl acrylate, or ethyl 
methacrylate, or may be optionally substituted amides of acrylic acid or 
of methacrylic acid, such as acrylamide, methacrylamide, 
methylolmethacrylamide, and methylolacrylamide, or may be acrylonitrile, 
styrene, or styrene derivatives such as alpha-methylstyrene, or may be 
vinyl esters of carboxylic acids, such as vinyl acetate and the like. 
The presence of crosslinking monomers such as ethylene glycol 
dimethacrylate, 1,4-butanediol dimethacrylate, triglycol dimethacrylate, 
or trimethylolpropane trimethacrylate, or of allyl compounds such as allyl 
methacrylate, triallyl cyanurate, or triallyl isocyanurate, is highly 
desirable. 
Polymerization may be carried out conventionally utilizing the practical 
experience of the art. (See H. Rauch-Puntigam and Th. Voker in "Acryl- und 
Methacrylverbindungen", Springer-Verlag, 1967, and J. Brandrup and E. H. 
Immergut, Polymer Handbook, 2nd ed., Wiley-Interscience, 1975.) 
Appropriate techniques have been outlined in German patent No. 639,095. 
The preparation of matrix polymers and of the resin binders of the 
invention is discussed below. 
For preparing the matrix polymer, peroxide or azo compounds may be employed 
in the usual amounts as initiators for the free radical polymerization of 
the monomers (such as acrylic monomers, styrene and styrene derivatives, 
and esters of vinyl compounds). For regulation of the molecular weight, 
conventional modifiers (chain transfer agents) such as organosulfur 
compounds may be employed in the usual concentrations. As is known, the 
degree of polymerization, and hence the molecular weight of the resin, can 
be controlled through the initiator concentration and/or the modifier 
concentration. In the polymerization of acrylic resins, from 0.01 to 1.0 
percent of initiator, by weight of the monomer, will normally be used, 
while the modifier added will generally range from 0.01 to 0.5 percent, 
and preferably from 0.05 to 0.2 percent, by weight of the monomers. As a 
rule, the molecular weight of the matrix polymers will range from 
2.times.10.sup.5 to 5.times.10.sup.6. In most cases, the matrix polymer 
will be weakly crosslinked. The Vicat softening temperature (determined in 
conformity with DIN 53460, procedure B) will usually be above 100.degree. 
C. The polymerization formulation may further contain conventional 
additives such as UV absorbers, plasticizers, light and heat stabilizers, 
antioxidants, flame retardants, etc. 
The polymeric binder may also be prepared by techniques based on prior art 
polymerization methods (cf. the discussion immediately above.) For 
example, polymerization may be carried out to advantage in foil pouches in 
accordance with Belgian patent No. 695,342. Polymerization is usually 
initiated by compounds forming free radiaals, and preferably by peroxide 
or azo compounds present in the usual amounts (normally between 0.02 and 
0.1 percent, by weight of the monomers). The known redox systems, 
accelerators, etc., may also be used to advantage. (See H. Rauch-Puntigam, 
"Acrylund Methacrylverbindungen", Springer-Verlag, 1967.) For regulation 
of the molecular weight, such known modifiers as organosulfur modifiers 
may also be used here in the usual concentrations. The amount of modifier 
added will generally range from 0.1 to 5 weight percent, and preferably 
from 0.5 to 3 weight percent. 
In the case of a polymer comprising components (a), (b), and, optionally, 
(c), the components along with the additives, plasticizers, and optional 
lubricants, etc., are advantageously mixed intensively by stirring and 
polymerized in a pouch made of a suitable plastic, for example, of a 
polyethylene terephthalate copolymer, in a layer several centimeters thick 
and at elevated temperature, for example about 50.degree..+-.10.degree. C. 
(water bath) for a sufficiently long period of time of up to two days, 
with 24 hours serving as a guide. For the final polymerization, the 
temperature is advantageously again raised, for example to about 
100.degree. C., for a period of about 16 hours. 
The polymer so obtained is removed from the mold and preferably comminuted, 
for example by grinding to a particle size appropriate to further 
processing. For the production of a dry pigment preparation, an average 
particle size of about 1 mm will serve as a guide. In this case, the 
molecular weight of the polymer should be on the order of 
40,000.+-.15,000. 
Dry pigment preparations can be produced from the binders of the invention 
by techniques based on prior art methods. 
The binder polymer, preferably in ground form, and the pigment are 
intensively mixed in a suitable mixing apparatus, for example a drum 
mixer. The pigment/polymer mixture is then charged to a suitable roller 
mill, for example a two-roll mill, and milled, usually at elevated 
temperature, for example 90.degree. to 100.degree. C., or dispersed in a 
kneader such as a ZSK kneader or also a pestle kneader. After the 
polymer/pigment mixture has become thermoplastic and the pigment is 
completely enclosed, the mixture is preferably milled once more, the 
masterbatch sheet is then taken off, allowed to cool, and ground to a 
powdery consistency. 
For the production of a colored acrylic glass panel for instance, here, 
too, a procedure based on prior art methods may be employed. For example, 
an acrylate prepolymer which has been mixed with the usual polymerization 
additives may be used as the starting material. The dry pigment 
preparation produced in accordance with the invention is then introduced 
into the formulation, which then is intensively mixed by means of an 
agitator for example, preferably allowed to stand for a while, and then 
poured into the polymerization cell. Polymerization is carried out in the 
usual manner and is normally followed by a final polymerization at 
elevated temperature, for example at about 120.degree. C. in an annealing 
cabinet. The colored acrylic glass panels removed from the molds exhibit 
optimum pigment dispersion and, after heating to forming temperature, and 
also after stretching, have flawless surfaces. 
The binders of the invention meet the practical requirements set forth 
earlier to a high degree. 
The color concentrates readily dissolve in the monomers or prepolymers. 
Adding them has no adverse effect on the course of polymerization. They 
offer substantial advantages over prior art color concentrates especially 
with regard to removal from the mold. For example, the fractures which are 
frequently encountered in removing the resin sheet from the mold are 
minimized or completely absent. Another advantage is the relative 
stability of the disperse state. 
The processing operations which follow the completion of polymerization, 
such as annealing, forming, stretching, etc., can readily be carried out. 
The mechanical and optical properties of the colored acrylic glass 
substitutes and their Vicat softening temperature and weatherability are 
comparable to those of regular acrylic glass substitutes.

A better understanding of the invention and of its many advantages will be 
had by referring to the following specific Examples, given by way of 
illustration. 
EXAMPLE 1 
Preparation of a polymeric binder containing components (a) and (b) 
Formulation 
828 g of methyl methacrylate; 
150 g of methyl acrylate; 
2 g of dilauroyl peroxide; and 
20 g of 2-ethylhexyl thioglycolate. 
The formulation is vigorously stirred and polymerized for 25 hours in a 
plastic pouch, made of a polyethylene terephthalate copolymer, in a layer 
from 1 to 2 cm thick, in a water bath at about 50.degree. C. Final 
polymerization is carried out for 10 hours at 100.degree. C. The polymer 
removed from the mold is colorless and clear and is then ground to an 
average particle size of less than about 1 mm. 
The molecular weight is about 40,000, and the reduced viscosity is 20.+-.2 
cm.sup.3 /g. 
EXAMPLE 2 
Preparation of a dry pigment composition 
200 g of the polymer binder of Example 1, ground, and 200 g of cadmium 
sulfide/selenide are vigorously mixed in a tumbling mixer. A two-roll mill 
is heated to from 90.degree. to 100.degree. C. and the pigment/polymer 
mixture is charged to the mill and milled. (Dispersing may optionally be 
carried out in a ZSK kneader or in a pestle kneader.) 
After the polymer/pigment mixture has become thermoplastic and the pigment 
has been completely enclosed, the mixture is milled for another 10 to 15 
minutes. Then the masterbatch sheet is taken off and allowed to cool. The 
sheet is then ground to a powder with a particle diameter of about 1 mm. 
EXAMPLE 3 
Production of a red acrylic glass panel 
Formulation 
984 g of methyl methacrylate prepolymer (about 1,000 cp); 
10 g of dry pigment preparation (red, produced according to Example 2); 
5 g of triallyl cyanurate; and 
1 g of 2,2-azobis-isobutyronitrile 
The dry pigment preparation is incorporated into the initially colorless 
formulation by stirring and is vigorously stirred in an agitator for 2 
hours, allowed to stand for 15 minutes, and then poured into a cell formed 
by two silicate glass plates spaced 3 mm apart and polymerized for 15 
hours at 45.degree. C. in a water bath. Final polymerization is carried 
out in an annealing cabinet at 120.degree. C. The nontransparent red 
acrylic glass panel obtained after cooling and removal from the mold 
exhibits optimum pigment dispersion and, after heating to forming 
temperature and after stretching, has a flawless surface. 
EXAMPLE 4 
Preparation of a polymeric binder containing components (a), (b), and (c) 
Formulation 
673 g of methyl methacrylate; 
200 g of methyl acrylate; 
1 g of 2,2'-azobis-isobutyronitrile; 
72 g of 2-hydroxyethyl methacrylate; 
29 g of 2-dimethylaminoethyl methacrylate; and 
2 g of dodecyl mercaptan. 
Preparation is carried out as in Example 1. 
EXAMPLE 5 
Preparation of a brown dry pigment composition 
Formulation 
242 g of the polymeric binder prepared as in Example 4, ground; 
150 g of titanium dioxide; 
43 g of cadmium selenide; 
10 g of beta-phthalocyanine blue; and 
39 g of iron oxide red. 
Production is carried out as described in Example 2. 
EXAMPLE 6 
Production of a dark-brown acrylic glass panel 
Formulation 
993.2 g of methyl methacrylate prepolymer (about 1,000 cp); 
5.0 g of brown pigment preparation according to Example 5; 
0.1 g of glycol dimethyacrylate; 
1.0 g of 2,2-azobis-isobutyronitrile; 
0.5 g of bis-2,2,6,6,-tetramethyl-4-piperidyl sebacate; and 
0.2 g of lecithin-based lubricant. 
Production is carried out as described in Example 3. The brown acrylic 
glass panel so obtained exhibits optimum pigment dispersion and an even 
more uniform surface and appearance than the panel obtained in Example 3. 
The preparations of the invention according to Example 5 thus make it 
possible to secure homogeneous dispersion of pigments of different 
particle sizes, particle shapes and particle densities and with a 
different particle size distribution within a PMMA panel. 
EXAMPLE 7 
Preparation of a polymeric binder containing components (a), (b), and (c) 
Formulation 
724 g of methyl methacrylate; 
200 g of methyl acrylate; 
50 g of 3-dimethylamino-2,2-dimethylpropyl-1-methacrylate; 
25 g of dodecyl mercaptan; and 
1 g of 2,2-azobis-isobutyronitrile. 
The same procedure is followed as in Example 4. 
EXAMPLE 8 
Preparation of a white dry pigment compositions 
Formulation 
242 g of the polymeric binder according to Example 7, ground and 
242 g of titanium dioxide. 
Production is carried out as described in Example 2. 
EXAMPLE 9 
Preparation of a white acrylic glass panel 
Formulation 
989 g of methyl methacrylate prepolymer (about 1,000 cp); 
10 g of white pigment preparation of Example 8; 
0.1 g of glycol dimethacrylate; 
1.0 g of 2,2-azobis-isobutyronitrile. 
Production is carried out as described in Example 3. 
EXAMPLE 10 
Preparation of a polymeric binder containing components (a), (b) and (c) 
Formulation 
778 g of methyl methacrylate, 
150 g of methyl acrylate, 
50 g of methacrylic acid, 
2 g of dilauroyl peroxide and 
20 g of 2-ethylhexyl thioglycolate. 
Preparation is carried out as in Example 1. 
EXAMPLE 11 
Preparation of a polymeric binder containing components (a), (b) and (c) 
Formulation 
769 g of methyl methacrylate, 
200 g of methyl acrylate, 
20 g of n-isopropyl-methacrylamide, 
10 g of thioglycol and 
1 g of 2,2-azobis-isobutyronitrile. 
Preparation is carried out as in Example 1. 
EXAMPLE 12 
Preparation of a polymeric binder containing components (a), (b) and (c) 
Formulation 
674 g of methyl methacrylate, 
200 g of methyl acrylate, 
100 g of 2,2,6,6,-tetramethyl-piperidyl-4-methacrylate, 
25 g of dodecyl mercaptane and 
1 g of 2,2-azobis-isobutyronitrile. 
Preparation is carried out as in Example 1. 
EXAMPLE 13 
Preparation of a polymeric binder containing components (a), (b) and (c) 
Formulation 
769 g of methyl methacrylate, 
200 g of methyl acrylate, 
20 g of .gamma.-methacryl-oxypropyl-trimethoxysilane, 
10 g of thioglycol and 
1 g of 2,2-azobis-isobutyronitrile. 
Preparation is carried out as in Example 1. 
EXAMPLE 14 
Preparation of a polymeric binder containing components (a), (b) and (c) 
Formulation 
739 g of methyl methacrylate, 
200 g of methyl acrylate, 
50 g of glycidyl methacrylate, 
10 g of thioglycol and 
1 g of 2,2-azobis-isobutyronitrile. 
Preparation is carried out as in Example 1.