Tough epoxy casting resins based on polybutadiene-polyoxyalkleneglycol copolymers

Curable compositions containing PA0 A) an epoxy resin having on average more than one epoxy group per molecule, PA0 B) a carboxylic anhydride curing agent for component A) and PA0 C) about 5 to 40% by weight, relative to the amount of the components A), B) and C), of a liquid mixture of C1) a polyalkylene glycol based on polypropylene glycol or polybutylene glycol having two to about six hydroxyl, carboxyl, carboxylic anhydride or glycidyl end groups and of C2) an elastomeric copolymer based on butadiene, a polar, ethylenically unsaturated comonomer and, if appropriate, further ethylenically unsaturated comonomers having carboxylic acid, hydroxyl, mercapto or glycidyl ether end groups are described. Components C1) and C2) can also occur together in a segmented copolymer.

The present invention relates to novel castable epoxy resin compositions 
and to the cured products obtainable therefrom. 
Additives for modifying epoxy resins are already known. Thus, for example, 
DE-A 2,631,108 describes polymer compositions which are curable and 
castable at room temperature and contain a non-cycloaliphatic epoxy resin 
and a selected liquid amine-terminated polymer, such as a 
butadiene/acrylonitrile rubber. These compositions are resistant to 
hydrolysis and generally require no additional crosslinking agent. 
Compositions of matter containing a cycloaliphatic epoxy resin, a selected 
liquid amine-terminated polymer, such as a butadiene/acrylonitrile rubber, 
and an anhydride are described in DE-A 2,706,693. These mixtures can be 
cured to produce a thermoplastic, elastomeric intermediate state and can 
then be converted via a molten state into a heat-cured, elastomeric, 
tack-free end product. 
The preparation of rubber-elastic mouldings is described in DE-A 2,447,036. 
The process disclosed therein is characterized by the casting and curing 
of compositions containing a polyether having an average molecular weight 
of 1,000 and 20,000, a 1,2-dicarboxylic anhydride, a bis-epoxide and, if 
appropriate, a polar, high-molecular rubber. 
Improving the incorporation of synthetic rubber in epoxy resins by using a 
nonionic or anionic surface-active agent is suggested in DE-A 3,740,183. 
This enables the rubber to be dispersed uniformly and permanently in the 
epoxy resin, which results in improved processability, and products having 
a low fluctuation in peel strength can be obtained. 
According to EP-A 169,066 combinations of glycidyl ethers and 
amino-terminated aliphatic polyethers can be modified by adding a 
combination of a polymeric toughening agent and a curing catalyst in such 
a way that rapidly curable compositions are obtained which can be 
converted into cured products having a high tensile shear strength and a 
high peel strength. 
It has been found that the use of polyethers in epoxy resins often results 
in reduced strength properties, such as tensile strength, tensile shear 
strength and flexural strength, in the cured products. Furthermore, the 
modulus of elasticity and the glass transition temperature of the cured 
products are, as a rule, reduced. Loss of strength can, as a rule, be 
avoided by adding butadiene elastomers. However, additives of this type 
frequently result in an undesirable increase in the viscosity of the 
curable mixture, and the impact strength and fracture toughness of the 
cured products as a rule leave something to be desired. 
Castable and heat-curable epoxy compositions of increased toughness which 
can be processed to give cured products of high strength and high glass 
transition temperatures are provided by the invention. The compositions 
according to the invention are distinguished particularly by surprisingly 
high impact strength and fracture toughness and by high values of 
elongation at break. 
The invention relates to curable compositions comprising 
A) an epoxy resin having on average more than one epoxy group per molecule, 
B) a carboxylic anhydride curing agent for component A) and 
C) about 5 to 40% by weight, relative to the amount of the components A), 
B) and C), of a liquid mixture of C1) a polyalkylene glycol based on 
polypropylene glycol or polybutylene glycol having two to about six 
hydroxyl, carboxyl, carboxylic anhydride or glycidyl end groups and of C2) 
an elastomeric copolymer based on butadiene, a polar, ethylenically 
unsaturated comonomer and, if appropriate, further ethylenically 
unsaturated comonomers having carboxylic acid, hydroxyl, mercapto or 
glycidyl ether end groups. 
The polyalkylene glycol and the elastomeric copolymer can also occur 
together in a segmented copolymer. This embodiment is preferred, since as 
a rule it enables even higher toughness values to be achieved in the cured 
product without significant losses in strength. 
The invention also relates, therefore, to curable compositions comprising 
A) an epoxy resin having on average more than one epoxy group per molecule, 
B) a carboxylic anhydride curing agent for component A) and 
C) about 5 to 40% by weight, relative to the amount of the components A), 
B) and C), of a liquid, segmented copolymer having hydroxyl, carboxyl, 
carboxylic anhydride or glycidyl end groups and containing at least one 
block derived from a polyalkylene glycol based on polypropylene glycol or 
polybutylene glycol and at least one block derived from an elastomeric 
copolymer based on butadiene, a polar, ethylenically unsaturated comonomer 
and, if appropriate, further ethylenically unsaturated comonomers, the 
said blocks being attached via identical or different functional groups 
--CO--X-- or --Y--CH.sub.2 --CH(OH)--CH.sub.2 --O-- in which X is --O--, 
--S-- or --NR.sub.1 --, Y is --O--, --S--, --NR.sub.1 -- or --CO--O-- and 
R.sub.1 is hydrogen, alkyl, cycloalkyl, aryl or aralkyl. 
As alkyl, R.sub.1 can be linear or branched. Linear C.sub.1 -C.sub.6 alkyl, 
in particular methyl, is preferred. As cycloalkyl, R.sub.1 preferably has 
5 or 6 ring carbon atoms. It is preferably cyclohexyl. As aryl, R.sub.1 is 
preferably a mononuclear or dinuclear carbocyclic-aromatic radical, in 
particular phenyl. As aralkyl, R.sub.1 is preferably a radical containing 
a mononuclear carbocyclic-aromatic radical, in particular benzyl. 
Virtually any epoxide resin having on average at least two 1,2-epoxide 
groups per molecule is suitable as the component A) in the compositions 
according to the invention. The following are examples of these: 
I) polyglycidyl and poly-(.beta.-methylglycidyl) esters which can be 
obtained, for example, by reacting a compound containing at least two 
carboxyl groups in the molecule with epichlorohydrin, glycerol 
dichlorohydrin or .beta.-methyl epichlorohydrin in the presence of bases. 
Examples of compounds having at least two carboxyl groups in the molecule 
are saturated aliphatic dicarboxylic acids, such as oxalic acid, malonic 
acid, succinic acid, .alpha.-methylsuccinic acid, glutaric acid, adipic 
acid, pimelic acid, azelaic acid, sebacic acid or dimerized linoleic acid; 
or unsaturated aliphatic dicarboxylic acids, such as maleic acid, 
mesaconic acid, citraconic acid, glutaconic acid or itaconic acid; or 
cycloaliphatic dicarboxylic acids, such as hexahydrophthalic, 
hexahydroisophthalic or hexahydrotererphthalic acid or tetrahydrophthalic, 
tetrahydroisophthalic or tetrahydroterephthalic acid or 
4-methyltetrahydrophthalic acid, 4-methylhexahydrophthalic acid or 
endomethylenetetrahydrophthalic acid; or aromatic dicarboxylic acids, such 
as phthalic, isophthalic or terephthalic acid; or copolymers of 
(meth)acrylic acid with copolymerizable vinyl monomers, for example the 
1:1 copolymers of methacrylic acid with styrene or with methyl 
methacrylate. Examples of tricarboxylic and higher carboxylic acids are 
especially aromatic tricarboxylic or tetracarboxylic acids, such as 
trimellitic acid, trimesic acid, pyromellitic acid or 
benzophenonetetracarboxylic acid, and also dimerized or trimerized fatty 
acids such as are available commercially, for example, under the name 
Pripol.RTM.. 
II) Polyglycidyl and poly-(.beta.-methylglycidyl) ethers which can be 
obtained, for example, by reacting a compound containing at least two 
alcoholic hydroxyl groups and/or phenolic hydroxyl groups in the molecule 
with epichlorohydrin, glycerol dichlorohydrin or .beta.-methyl 
epichlorohydrin under alkaline conditions or in the presence of an acid 
catalyst with subsequent treatment with alkali. Examples of compounds 
having at least two alcoholic hydroxyl groups and/or phenolic hydroxyl 
groups in the molecule are aliphatic alcohols, such as ethylene glycol, 
diethylene glycol and higher poly-(oxyethylene) glycols, propane-1,2-diol, 
propane-1,3-diol or higher poly-(oxypropylene) glycols, butane-1,4-diol or 
higher poly-(oxybutylene) glycols, pentane-1,5-diol, neopentyl glycol 
(2,2-dimethylpropanediol), hexane-1,6-diol, octane-1,8-diol, 
decane-1,10-diol or dodecane-1,12-diol; hexane-2,4,6-triol, glycerol, 
1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, pentaerythritol, 
sorbitol or polyepichlorohydrins; or cycloaliphatic alcohols, such as 
1,3-dihydroxycyclohexane, 1,4-dihydroxycyclohexane, 
1,4-cyclohexanedimethanol, bis-(4-hydroxycyclohexyl)-methane, 
2,2-bis-(4-hydroxycyclohexyl)-propane or 
1,1-bis-(hydroxymethyl)-cyclohex-3-ene; or alcohols containing aromatic 
groups, such as N,N-bis-(2-hydroxyethyl)-aniline or 
p,p'-bis-(2-hydroxyethylamino)-diphenylmethane; or mononuclear or 
polynuclear polyphenols, such as resorcinol, hydroquinone, 
bis-(4-hydroxyphenyl)-methane, 2,2-bis-(4-hydroxyphenyl)-propane, 
brominated 2,2-bis-(4-hydroxyphenyl)-propane, bis-(4-hydroxyphenyl) ether, 
bis-(4-hydroxyphenyl) sulfone, 1,1,2,2-tetrakis-(4-hydroxyphenyl)-ethane 
or novolaks which are obtainable by the condensation of aldehydes, such as 
formaldehyde, acetaldehyde, chloral or furfuraldehyde, with phenols which 
are unsubstituted or substituted by alkyl or halogen, such as phenol, the 
bisphenols described above, 2-methylphenol, 4-methylphenol, 
4-tert-butylphenol, p-nonylphenol or 4-chlorophenol. 
III) Poly-(N-glycidyl) compounds which can be prepared, for example, by 
dehydrochlorinating reaction products of epichlorohydrin with amines 
containing at least two amino hydrogen atoms. Examples of amines on which 
such epoxy resins are based are aliphatic amines, such as 
hexamethylenediamine or n-butylamine; cycloaliphatic amines, such as 
1,4-diaminocyclohexane or bis-aminomethylene-1,4-cyclohexane; aromatic 
amines, such as aniline, p-toluidine, bis-(4-aminophenyl)-methane, 
bis-(4-aminophenyl) ether, bis-(4-aminophenyl) sulfone, 
4,4'-diaminobiphenyl or 3,3'-diaminobiphenyl; or araliphatic amines, such 
as m-xylylenediamine. The poly-(N-glycidyl) compounds also include, 
however, triglycidyl isocyanurate, N,N'-diglycidyl derivatives of 
cycloalkyleneureas, such as ethyleneurea or 1,3-propyleneurea, and 
N,N'-diglycidyl derivatives of hydantoins, such as 5,5-dimethylhydantoin. 
IV) Poly-(S-glycidyl) compounds, for example di-S-glycidyl derivatives 
derived from dithiols, such as ethane-1,2-dithiol or 
bis-(4-mercaptomethylphenyl) ether. 
V) Cycloaliphatic epoxy resins or epoxidation products of dienes or 
polyenes, such as cycloaliphatic epoxy resins which can be prepared, for 
example, by epoxidation of ethylenically unsaturated cycloaliphatic 
compounds. Examples of these are 1,2-bis-(2,3-epoxycyclopentyloxy)-ethane, 
2,3-epoxycyclopentyl glycidyl ether, diglycidyl 
cyclohexane-1,2-dicarboxylate, 3,4-epoxycyclohexyl glycidyl ether, 
bis-(2,3-epoxycyclopentyl) ether, bis-(3,4-epoxycyclohexyl) ether, 
5(6)-glycidyl-2-(1,2-epoxyethyl)-bicyclo[2.2.1]heptane, dicyclopentadiene 
dioxide, cyclohexa-1,3-diene dioxide, 3,4-epoxy-6-methylcyclohexylmethyl 
3',4'-epoxy-6'-methylcyclohexanecarboxylate or 3,4-epoxycyclohexylmethyl 
3',4'-epoxycyclohexanecarboxylate. It is also possible, however, to use 
epoxy resins in which the 1,2-epoxy groups are attached to various 
heteroatoms or functional groups; such compounds include, for example, the 
N,N,O-triglycidyl derivative of 4-aminophenol, the N,N,O-triglycidyl 
derivative of 3-aminophenol, the glycidyl ether/glycidyl ester of 
salicylic acid, N-glycidyl-N'-(2-glycidyloxypropyl)-5,5-dimethylhydantoin 
or 2-glycidyloxy-1,3-bis-(5,5-dimethyl-1-glycidylhydantoin-3-yl)-propane. 
Preferred components A) are cycloaliphatic epoxy resins, for example the 
compounds listed earlier in the text and polyglycidyl ethers, in 
particular diglycidyl ethers based on a bisphenol, such as bisphenol F or 
especially bisphenol A. 
Components A) which are very particularly preferred are liquid diglycidyl 
ethers based on bisphenol A. 
In general, all anhydride curing agents for epoxy resins are suitable as 
the component B) in the compositions according to the invention. These 
curing agents include anhydrides of aliphatic, cycloaliphatic, aromatic or 
araliphatic polycarboxylic acids, for example anhydrides of the 
polycarboxylic acids enumerated earlier in the text as components for the 
formation of polyglycidyl esters. 
Preferred components B) are anhydrides of aliphatic, cycloaliphatic or 
aromatic dicarboxylic acids. 
Anydrides of dicarboxylic acids or mixtures of these anhydrides which are 
liquid at temperatures below 40.degree. C. are very particularly 
preferred. Anhydride curing agents of this type are known per se to those 
skilled in the art in the field of epoxide curing and are described, for 
example, in the "Epoxy Handbook" by Lee and Neville (McGraw Hill, 1967). 
Specific examples of preferred anhydride curing agents B) are maleic 
anhydride, succinic anhydride, dodecylsuccinic anhydride, 
tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 
hexachloroendomethylenetetrahydrophthalic anhydride, phthalic anhydride, 
pyromellitic dianhydride, benzophenone-3,3',4,4'-tetracarboxylic 
dianhydride, bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride (nadic 
anhydride) or methylbicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride 
(methylnadic anhydride). 
Component C) of the compositions according to the invention is either a 
combination of the components C1) and C2) defined above or a segmented 
copolymer containing blocks based on these components C1) and C2). 
Component C1) is a selected polyalkylene glycol based on polypropylene 
glycol or polybutylene glycol and having two to about six hydroxyl, 
carboxyl, carboxylic anhydride or glycidyl end groups. In general, these 
polymers have an average molecular weight (number average) of about 500 to 
10,000, in particular between 1,000 and 5,000. 
As a rule, the polyalkylene glycol segments have a minimum length of about 
five recurring structural units in order to impart adequate flexibility to 
the composition according to the invention. It is also possible for 
mixtures of different polypropylene glycols or polybutylene glycols within 
the compositions according to the invention or within a segmented 
copolymer C) to be present; components C1) or copolyether segments 
composed of polypropylene glycol and polybutylene glycol units can also be 
used. In this embodiment it is also possible for up to 30% by weight of 
ethylene glycol units to be co-condensed into the copolyether radical. 
Hydroxyl-terminated polyalkylene glycols can be obtained, for example, by 
anionic polymerization, copolymerization or block copolymerization of 
propylene oxide or butylene oxide, if appropriate in combination with 
ethylene oxide, with difunctional or polyfunctional alcohols, such as, 
1,2-ethanediol, 1,4-butanediol, 1,1,1-trimethylolethane, 
1,1,1-trimethylolpropane, 1,2,6-hexanetriol, glycerol, pentaerythritol or 
sorbitol, or with difunctional or polyfunctional phenols, such as 
bisphenol A or novolaks, or with amines, such as methylamine, 
ethylenediamine or 1,6-hexamethylenediamine, as initiation components, or 
by cationic polymerization or copolymerization of cyclic ethers, such as 
tetrahydrofuran or propylene oxide, if appropriate together with ethylene 
oxide, using acid catalysts, such as BF.sub.3 etherate, or by 
polycondensation of glycols which can be polycondensed with the 
elimination of water, such as 1,3-propanediol or 1,4-butanediol, in the 
presence of acid etherification catalysts, such as p-toluenesulfonic acid. 
It is also possible to use oxalkylation products of phosphoric or 
phosphorous acid with tetrahydrofuran or propylene oxide, if appropriate 
together with ethylene oxide. Polypropylene oxide oligomers can be 
terminated with ethylene oxide. Other hydroxyl-terminated polyalkylene 
glycols can be obtained, for example, by masking hydroxyl-terminated or 
amino-terminated polypropylene glycols or polybutylene glycols with 
aromatic hydroxycarboxylic acids, for example hydroxybenzoic acid. 
Carboxyl-terminated or carboxylic anhydride-terminated components C1) can 
be obtained, for example, by masking hydroxyl-terminated polypropylene 
glycols or polybutylene glycols with polycarboxylic acids, anhydrides 
thereof or other ester-forming derivatives. Examples of possible masking 
components are the polycarboxylic acids enumerated earlier in the text as 
components for the formation of polyglycidyl esters. 
Glycidyl-terminated components C1) can be prepared, for example, by 
reacting hydroxyl-terminated polypropylene glycols or polybutylene glycols 
with epichlorohydrin or .beta.-methyl epichlorohydrin in the manner 
described earlier in the text in regard to the preparation of glycidyl 
ethers. In addition, polypropylene glycols or polybutylene glycols which 
are terminated with aromatic hydroxycarboxylic acids can be glycidylated 
in the manner described above. 
Preferred components C1) are trihydric and particularly dihydric 
carboxyl-terminated, carboxylic anhydride-terminated, glycidyl-terminated 
and especially hydroxyl-terminated polypropylene glycols or polybutylene 
glycols. The average molecular weights (number average) of these preferred 
components C1) are between 500 and 5,000, in particular between 1,000 and 
2,500. 
Components C1) which are very particularly preferred are compounds of the 
formulae I to V 
##STR1## 
in which y is 5 to 90, in particular 10 to 90, z is 10 to 40, R.sub.2 is a 
radical of an aliphatic diol or bisphenol after the two OH groups have 
been removed, R.sub.3 is a radical of an aliphatic triol or trisphenol 
after the three OH groups have been removed and Z is a radical selected 
from the group consisting of 
##STR2## 
and --O--R.sub.7, in which R.sub.4 is the radical of an aliphatic, 
cycloaliphatic or aromatic dicarboxylic acid after the two carboxyl groups 
have been removed, R.sub.5 is the radical of an aromatic tricarboxylic 
acid after the three carboxyl groups have been removed, R.sub.6 is the 
radical of an aromatic hydroxycarboxylic acid after the carboxyl group and 
the phenolic hydroxyl group have been removed and R.sub.7 is hydrogen or 
a group of the formula 
##STR3## 
Examples of R.sub.4 as aliphatic, cycloaliphatic or aromatic dicarboxylic 
acids are listed earlier in the text as components for the formation of 
glycidyl esters A). 
R.sub.4 is preferably an unbranched C.sub.2 -C.sub.12 alkylene radical, an 
unsubstituted or methyl-substituted phenylene radical or an unsubstituted 
naphthalene radical. 
R.sub.5 is preferably a radical of trimesic acid or especially a radical of 
trimellitic acid. 
R.sub.6 is preferably an unsubstituted or methyl-substituted phenylene 
radical or an unsubstituted naphthalene radical. 
Any desired elastomeric carboxyl-terminated, hydroxyl-terminated, 
mercapto-terminated or glycidyl ether-terminated copolymers based on 
butadiene, a polar, ethylenically unsaturated comonomer and, if 
appropriate, further ethylenically unsaturated comonomers can be used as 
component C2) of the compositions according to the invention. 
Examples of polar, ethylenically unsaturated comonomers for the preparation 
of component C2) are acrylic acid, methacrylic acid, esters of acrylic or 
methacrylic acid, for example the methyl or ethyl esters, amides of 
acrylic or methacrylic acid, and also fumaric acid, itaconic acid, maleic 
acid or esters and half-esters thereof or maleic anhydride or itaconic 
anhydride; vinyl esters, for example vinyl acetate; polar styrenes, such 
as styrenes chlorinated or brominated in the nucleus; or methacrylonitrile 
or, in particular, acrylonitrile. 
As well as polar, ethylenically unsaturated comonomers, further non-polar, 
ethylenically unsaturated comonomers can also be employed for the 
preparation of component C2). Examples of these are ethylene, propylene or 
especially styrene or substituted styrenes, such as vinyltoluene. 
Component C2) can be statistical copolymers, block copolymers or graft 
copolymers. This component can be solid, especially pulverulent, or 
liquid, provided that a liquid mixture can be prepared with it in 
combination with component C1). In general, component C2) is an elastomer 
or a thermoplastic elastomer. It is very particularly preferable for 
component C2) to be a liquid elastomer. 
The average molecular weights (number average) of the preferred liquid 
butadiene copolymers are, in general, 500-10,000, in particular 
1,000-5,000. 
Preferred components C2) are carboxyl-terminated, hydroxyl-terminated, 
mercapto-terminated or glycidyl ether-terminated, liquid, elastomeric 
copolymers based on butadiene and acrylonitrile. Examples of such 
compounds are rubbers of the Hycar.RTM. type made by B.F. Goodrich. 
Carboxyl-terminated or carboxylic anhydride-terminated components C2) can 
also be obtained by masking hydroxyl-terminated butadiene copolymers C2) 
with polycarboxylic acids, anhydrides thereof or other ester-forming 
derivatives. Examples of possible masking components are the 
polycarboxylic acids enumerated earlier in the text as components for the 
formation of polyglycidyl esters. 
Glycidyl-terminated components C2) can also be prepared by reacting 
hydroxyl-terminated butadiene copolymers C2) with epichlorohydrin or 
.beta.-methyl epichlorohydrin in the manner described earlier in the text 
in regard to the preparation of glycidyl ethers. 
Preferred types of liquid butadiene elastomers C2) contain the structural 
elements of the formulae VIa to VId and the end groups Q 
##STR4## 
in which R.sub.8 is hydrogen or methyl, R.sub.9 is --COOH, --COOR.sub.10 
or --CONH.sub.2, R.sub.10 is an aliphatic radical, preferably methyl, and 
Q is selected from the group consisting of --R.sub.11 --COOH and 
--R.sub.11 --OH in which R.sub.11 is an alkylene or arylene radical; the 
proportion of the radicals VIa and VIb is preferably 5 to 50% by weight, 
the proportion of the radicals VIc is preferably 5-50% by weight and the 
proportion of the radicals VId is preferably 0-10% by weight, the figures 
relating to the total amount of the radicals VIa to VId. 
In general, the acrylonitrile content of the preferred liquid butadiene 
copolymers is less than 50% by weight, in particular 8 to 30% by weight, 
relative to the total monomer content. 
Component C2) can also be employed in the form of an adduct, onto an epoxy 
resin, of a butadiene/acrylonitrile copolymer containing the functional 
groups, described above, reactive towards epoxy groups. 
The preparation of such adducts is effected in a manner known per se by 
heating the reactive butadiene elastomer and the epoxy resin, if 
appropriate with a catalyst, such as triphenylphosphine, a tertiary amine, 
a tertiary ammonium or phosphonium salt or chromium acetylacetonate, so 
that a fusible, but still curable, pre-condensate is formed. 
The proportion of the comonomers to one another in component C2) can vary 
within wide ranges. This component is so selected that it is compatible 
with the epoxy resin A) and the curing agent B). In this regard it is 
generally necessary for the difference between the solubility parameters 
of the constituents of the mixture to be less than 1.0, in particular less 
than 0.6. Solubility parameters of this type can be calculated, for 
example, by Small's method [J. Appl. Chem., 3, 71 (1953)]. The use of 
solubility parameters in determining the compatibility of polymer mixtures 
has been described, for example, by C. B. Bucknall in "Toughened 
Plastics", chapter 2, Applied Science Publishers Ltd., London, 1977. 
Components C) which are very particularly preferred are segmented 
copolymers having hydroxyl, carboxyl, carboxylic anhydride or glycidyl end 
groups containing blocks based on the components C1) and C2), which are 
attached to one another via the functional groups defined earlier in the 
text. 
These copolymers generally have an average molecular weight (number 
average) of 1,000 to 20,000, preferably 3,000 to 10,000. 
Segmented copolymers C) which are attached to one another via --CO--X-- 
groups can be obtained by reacting carboxyl-terminated or carboxylic 
anhydride-terminated components C1) with hydroxyl-terminated, 
mercapto-terminated or amino-terminated components C2) or by reacting 
hydroxyl/terminated, mercapto-terminated or amino-terminated components 
C1) with carboxyl-terminated or carboxylic anhydride-terminated components 
C2). 
Segmented copolymers C) which are attached to one another via --Y--CH.sub.2 
--CH(OH)--CH.sub.2 --O-- groups can be obtained by reacting 
carboxyl-terminated, carboxylic anhydride-terminated, hydroxyl-terminated, 
mercapto-terminated or amino-terminated components C1) with glycidyl 
ether-terminated components C2) or by reacting glycidyl ether-terminated 
components C1) with carboxyl-terminated, carboxylic anhydride-terminated, 
hydroxyl-terminated, mercapto-terminated or amino-terminated components 
C2). 
In these reactions the proportions of the reactants are generally so chosen 
that the reactive groups of one of the components is essentially consumed 
by the reaction, whereas the reactive groups of the other component are in 
part preserved, and form the end groups of the component C) or are 
converted into the end groups according to the definition by masking with 
a masking agent. 
In general, the reactions are carried out by heating the components for the 
formation of the segmented copolymers in the presence or absence of an 
inert solvent. 
Depending on the functionality of these components, the components C1) and 
C2) to be reacted with one another are so chosen that a segmented 
copolymer which is liquid at temperatures up to about 40.degree. C. is 
obtained. Thus, if a difunctional component is present, another component 
of higher functionality can be used, whereas combinations of several 
polyfunctional components as a rule result in excessive crosslinking and 
the formation of gels. The criteria of selection for the preparation of 
the component C) to the specification indicated above are known per se to 
those skilled in the art in the field of polymerization. 
The carboxyl-terminated, carboxylic anhydride-terminated, 
hydroxyl-terminated, mercapto-terminated, glycidyl ether-terminated or 
amino-terminated starting materials for the preparation of the segmented 
copolymers C) are known per se or can be obtained by processes known per 
se. 
The preparation of carboxyl-terminated, carboxylic anhydride-terminated, 
hydroxyl-terminated or glycidyl ether-terminated polyalkylene glycols is 
described earlier in the text in regard to the preparation of component 
C1). 
Amino-terminated polyalkylene glycols are derived, for example, from the 
hydroxyl-terminated polyalkylene glycols described above by reacting 
compounds of this type containing primary hydroxyl groups, for example 
polybutylene glycol, with acrylonitrile and then hydrogenating the 
products, or by reacting compounds of this type containing secondary 
hydroxyl groups with ammonia. Suitable amino-terminated polypropylene 
glycols are the products obtainable commerically under the name 
"Jeffamine.RTM." from Texaco. 
Mercapto-terminated polyalkylene glycols can be obtained, for example, by 
reacting the corresponding hydroxyl-terminated or amino-terminated 
polyalkylene glycols with mercaptocarboxylic acids or esters thereof, such 
as mercaptoacetic acid (esters), or by adding on episulfides onto 
hydroxyl-terminated or amino-terminated polyalkylene glycols. 
The preparation of carboxyl-terminated, carboxylic anhydride-terminated, 
hydroxyl-terminated or glycidyl ether-terminated butadiene copolymers is 
described earlier in the text in regard to the preparation of component 
C2). Mercapto-terminated and amino-terminated butadiene copolymers are in 
part commerically available and can be prepared analogously to the 
polyalkylene glycol derivatives by masking hydroxyl-terminated 
derivatives. 
Preferred segmented polymers C) are derived from essentially difunctional 
components C1) and C2). 
Segmented copolymers C) which are very particularly preferred are compounds 
containing blocks derived from liquid butadiene/acrylonitrile copolymers 
and containing blocks derived from difunctional polybutylene glycols or 
from trifunctional, or especially difunctional, polypropylene glycols. 
It is very particularly preferable to use segmented copolymers C) of the 
formula VI 
EQU Z--PAG--X.sub.1 --BDC].sub.n X.sub.1 --PAG--Z (VI), 
in which n is an integer from 1 to 10, in particular 1, PAG is the radical 
of a difunctional polypropylene glycol or polybutylene glycol after the 
functional groups have been removed, BDC is the radical of a difunctional 
liquid butadiene/acrylonitrile copolymer after the functional groups have 
been removed, X.sub.1 is a bridge group of the formulae --CO--X-- and/or 
--X--CO-- or --Y--CH.sub.2 --CH(OH)--CH.sub.2 --O-- and/or --O--CH.sub.2 
--CH(OH)--CH.sub.2 --Y-- in which X, Y and the end groups Z are as defined 
above. 
Components A), B) and C) in the compositions according to the invention 
should be compatible with one another. In general, these components are so 
selected that no visible phase separation takes place in the curable 
mixture. Components B) and C) should dissolve in the epoxy resin A) at 
least at an elevated temperature. Components A), B) and C) are preferably 
so selected that a multi-phase system is formed when the composition is 
cured. 
In order to achieve products having a high strength, glass transition 
temperature, peel strength, impact strength and resistance to crack 
propagation (fracture toughness), the proportion of the component C), 
relative to the amount of A), B) and C), will generally not exceed 40% by 
weight. The lower limit depends on the desired properties, for example the 
peel strength. As a rule, component C) should make up more than 5% by 
weight, preferably more than 10% by weight. Compositions having a content 
of the component C) of about 10 to about 30% by weight, relative to the 
amount of A), B) and C), are preferred. 
The ratio by weight of C1) to C2) or the ratio by weight of the 
polyalkylene glycol segments and the elastomeric copolymer segments in the 
copolymer C) can be varied within wide ranges. The preferred range for C1) 
to C2) or for the polyalkylene glycol segments to the elastomeric 
copolymer segments is 50:1 to 1:50, in particular 5:1 to 1:5. 
The amount of the curing agent B), relative to the epoxy resin A), 
generally depends on the type of curing agent used and is known per se to 
those skilled in the art. As a rule the amounts of component B) employed 
will be such that there is about 0.7 to 0.8 of anhydride groups of the 
curing agent to one epoxy group. 
If appropriate, the compositions according to the invention also contain a 
curing accelerator D). As a rule, the nature and amount of the component 
D) depend on the type of curing agent used and are known per se to those 
skilled in the art in the field of epoxide curing. Details are to be found 
in the "Epoxy Handbook" by Lee and Neville (McGraw Hill, New York 1967). 
The preferred curing accelerators are tertiary amines, such as 
benzyldimethylamine. 
The compositions according to the invention can be prepared by mixing their 
components in the devices customary for this process. 
The curing temperatures of the compositions according to the invention are 
preferably between 80.degree. and 280.degree. C., particularly preferably 
between 100.degree. and 200.degree. C. 
If desired, curing can also be carried out in two stages, for example by 
interrupting the curing process or by allowing the curable mixture to cure 
in part at fairly low temperatures. The products obtained in this way are 
pre-condensates which are still fusible and soluble (so-called "B-stage 
resins") and are suitable for use, for example, as compression moulding 
materials or sintering powders or for the production of prepregs. 
If desired, reactive thinners, for example styrene oxide, butyl glycidyl 
ether, 2,2,4-trimethylpentyl glycidyl ether, phenyl glycidyl ether, cresyl 
glycidyl ether or glycidyl esters of synthetic, highly branched, 
principally tertiary, aliphatic monocarboxylic acids can be added to the 
curable mixtures to lower the viscosity. Further customary additives which 
can also be present in the mixtures according to the invention are 
plasticizers, extenders, fillers and reinforcing agents, for example coal 
tar, bitumen, textile fibres, glass fibres, asbestos fibres, boron fibres, 
carbon fibres, mineral silicates, mica, quartz powder, hydrated aluminium 
oxide, bentonites, wollastonite, kaolin, silica aerogel or metal powders, 
for example aluminium powder or iron powder, and also pigments and dyes, 
such as carbon black, oxide colours and titanium dioxide, and also 
fire-retarding agents, thixotropic agents, flow control agents (which can 
in some cases also be used as mould release agents), such as silicones, 
waves and stearates, or adhesion promoters, antioxidants and light 
stabilizers. 
The compositions according to the invention can be employed very generally 
as casting resins for the production of cured products, and can be used in 
the formulation suited to the particular field of application, for example 
as adhesives, matrix resins, electrical casting resins or surface coating 
agents. 
The curable compositions according to the invention are liquid at room 
temperature as a rule. They can in every case be cast at temperatures of 
40.degree. C. 
The curable compositions according to the invention are particularly 
suitable for casting and encapsulating electrical and electronic 
components or for the production of composite materials. 
The invention also relates to the use of the curable mixtures for the 
purposes mentioned above. 
The cured products are distinguished by the advantageous and surprising 
properties described initially. The invention therefore also relates to 
the products obtainable by heating the compositions according to the 
invention. 
The following examples illustrate the invention.