CA2041332A1

CA2041332A1 - Imidazolyl derivatives, their use as curing agents in epoxy-resin compositions, and curable epoxy-resin compositions and molded epoxy-resin articles incorporating said imidazolyl derivatives

Info

Publication number: CA2041332A1
Application number: CA 2041332
Authority: CA
Inventors: Christian Burba; Werner Mrotzek
Original assignee: Schering AG
Current assignee: Lanxess Organometallics GmbH
Priority date: 1990-05-18
Filing date: 1991-04-26
Publication date: 1991-11-19
Also published as: DE4015961A1; EP0457046A1; JPH04226962A

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to new compounds of the general formulas (I) and (II) where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20 carbon atoms and optionally containing ether groups;
R3 is -COOH, -CN, -COOC2H4-OH, -CONH-NH2 or -COOR4; R4 is an aliphatic hydrocarbon group having from 1 to 4 carbon atoms; n is 2 or 3; and R5 is hydrogen or a methyl group.

JMK-SCHERING:2505.APP

Description

The invention relates to new imidazolyl deriv-atives, their use as curing agents in epoxy-resin compositions, and curable epoxy-resin compositions incorporating said imidazolyl derivatives and comprising an epoxy resin and compounds of the general formula (I), and optionally commonly used curing agents and solvents, for the manufacture of molded articles.
In the manufacture of composite materials, two basic processes are employed today.
One of these is the wet-layup process, a one-step process in which reinforcing materials are impregnated with a curable mixture and heat-cured in one step to the thermoset final state.
In the other process, the two-step process, so-called prepregs are first produced from reinforcing materials and a curable mixture, and these prepregs are then processed into finished parts in a separate second step. With respect to operating procedure, a distinction is made between working with and without solvents.
The prepregs are normally produced in a continuous operation in which the reinforcing materials are passed through an impregnating bath of the resin/curing agent mixture being used, or the impregnant is mixed only just before it is applied to the base material and then spread thereon with a special device. The amount of impregnant to be applied to a given base-material web is controlled not only through the viscosity of the impregnant but also through squeeze rolls located downstream.
With solvent-containing systems, the solvent con-tained in the impregnating solution is evaporated through heat input after the impregnating operation, and the resin system is converted at the same time from JMK SC~EP~I NG: 2 5 0 5 . APP

2 ~

the A stage to the B stageO Depending on the operating conditions and the resin system used, the reinforcing materials impregnated with liquid to highly viscid impregnant are thus turned into a prepreg that is slightly tacky to almost dry. In this process step it is important that the solvent be completely eliminated from the impregnating mixture and that the latent curing agent needed to cure the prepreg in the second process step not be activated just yet, as this would cause the impregnated reinforcing materials to react completely, which is not desired.
With solventless systems, depending on the chemical composition of the resin system the material either also undergoes a short heat treatment after impregnation or the reinforcing materials are lined on both sides with release sheets immediately after impregnation, without any separate heat treatment, and placed into intermediate storage appropriate to the system. During this intermediate storage, either a gradual transition of the resin system to the B stage takes place or the impregnant is fixed on the base materials through physical effects alone and largely without chemical changes.
The prepregs so obtained can be stored and shipped as rolls before they are cut to size, as required for the intended end use, and stacked to the thickness of the finished part. Under the simultaneous action of pressure and heat, the prepreg stack is completely cuxed to give a high-strength molded part, the still low-molecular-weight, fluid resins being thus converted to the high-molecular-weight C stage of a thermoset.
While in the one-step process long open times and short cure times at low cure temperatures are required, prolonged storage stability of the prepregs is an JMX-SCH3~RING: 2505 . APP

additional reguirement in the two-step process.
Storage temperatures lower than room temperature have become steadily less acceptable in practice.
Of importance is further that, depending on the prepreg manufacturing method, the viscosity of the ready-to-use curable mixture remains substantially constant for as long a period as possible. This is necessary, especially when an impregnating bath of large volume is used, for achieving constant resin deposition and an invariant B stage since the manufacturing conditions cannot be continually adjusted to changing relationships within the curable mixture and since fluctuations in the viscosity would have an adverse effect on the physical properties of the full cured end product.
What is desired in practice is a curable mixture whose viscosity remains constant in the impregnating bath for an extended period of time and which can then be stored as a prepreg at room temperature for a long time without undergoing chemical changes.
Regardless of how they are manufactured, the prepregs should cure completely within a short time at the lowest possible temperature, the maximum temperature of the exothermic reaction should remain at a low level even with moderately thick layersl and the profile of physical properties of the finished products should meet practical requirements.
These requirements concerning curing behavior and profile of properties apply alss to epoxy-resin systems to be processed by the wet-layup method.
For certain applications, all that is required and, in fact, desired is a partial cure to the point where the molded articles are dimensionally stable, complete curing taking place, optionally after JMK-SCHERING: 2 505 . APP

2 ~ 3 ~

intermediate storage, in a subsequent tempering operation at the necessary temperatures. However, it is important that even during the partial cure, the thermal stability of the material increase to a level above the cure temperature or otherwise the temperature of the molded article will have to be lowered before it can be removed from the mold.
Dicyandiamide, long used as a latent curing agent in curable mixtures based on epoxy resins, is usually combined with co-curing agents and/or accelerators to obtain the desired properties. A great many suggestions for its use in this field are known from the literature.
While dicyandiamide solutions can be used to produce homogeneous substrates, the use of solvents gives rise to other problems.
Dicyandiamide is soluble in sufficient amounts in only a few solvents, particularly dimethylformamide and methyl glycol. However, these solvents are toxicologically hazardous and create problems both in the manufacture of the prepregs, that is, during impregnation of the reinforcing materials and conver-sion to the B stage, and in waste disposal.
Since dicyandiamide is only sparingly soluble, rather large amounts of solvents must be used, and these affect the impregnating viscosity in such a way that the binder content on the reinforcing materials cannot be chosen as desired.
! Inasmuch as these solvents canno~ be removed com-pletely during the cure, there is, moreover, the danger that when the finished parts are subjected to thermal stresses the material will fail prematurely and/or the solvents will be given off uncontrolled to the ambient air in the field.

JMR-SCHERING: 2 5 0 5 . APP

When solid crystalline dicyandiamide is used without solvents in liquid epoxy resins, the necessary amount of dicyandiamide is either dispersed directly in the epoxy resin or a highly filled dicyandiamide/epoxy resin paste is first prepared and later adjusted with the bulk of the epoxy resin to the desired resin/curing agent concentration.
In either case, preparation of the dispersions is not a simple matter. Moreover, when standing for an extended period of time, particularly under impregnating conditions, the dispersions tend to separate.
When solid crystalline dicyandiamide is used without solvents in epoxy resins which at room temperature are solid, a paste of dicyandiamide and liquid epoxy resins is also ~irst prepared and then worked into the solid-resin melt at elevated temperature.
Apart from the problems outlined, undesired amounts o~ liquid epoxy resins are introduced into the solid resin when this operating procedure is employed.
Moreover, when solid crystalline dicyandiamide is used, inhomogeneities which are due to undissolved and unreacted particles are observed in the cured substrates.
The present invention seeks to overcome the draw-backs of the prior art and to provide curable mixtures, based on epoxy compounds and latent curing agents soluble or homogeneously dispersible in the epoxy resins, which partially cure to the dimensionally stable state or completely cure to the thermoset final state at relatively low temperatures within a short time and without high peak exotherms, whose thermal - stability meets practical requirement~, and in which ' J~C--SC}I}~RING:2505.APP

,~
~,~

prepregs have adequate storage stability at low temperature.
This goal is attained through the use of a new curing agent, optionally with the concurrent use of conventional latent curing agents.
The invention thus, in one respect, relates to compounds of the general formulas 11 R5 o o R5 ~2 N = ~ ~ ~
¦ ~N-(CH2)~-N -C~-CH-C-0-R-0-C-~-c~2 N\C I (I) and 0 ~5 R5 R[-o-l-lH-~H2-N-CH2-~H-R3]2 2)n N (II) R -C C~
,1 ~-R2 where R is a divalent, optionally branched aliphatic, 10 cyclic or alicyclic hydrocarbon group having from 2 to 20, and more particularly from 4 to 8, carbon atoms and cptionally containing ether groups; R1 and R2 are, independently of one another, hydrogen, or aliphatic or aromatic hydrocarbon groups, and more particularly H, CH3 or C2H5; R3 is -COOH, CN, -COOC2H4-OH, ~CONH-NH2 or -CooR4; R4 is an aliphatic hydrocarbon group having~from JM}C-SCHERING: 2 505 . APP

l to 4 carbon atoms, and more particularly -CH2-CH2-OH;
n is 2 or 3; and R5 is hydrogen or a methyl group.
The invention further relates to curing agents for glycidyl compounds which can be prepared by reacting (A) imidazolyl compounds of the general formula CH =
H2N- (CH2) n~N
(III) C =
~1 where Rl and R2 are, independently of one another, aliphatic or aromatic hydrocarbon groups, and more particularly H, CH3 or C2H5, and n is 2 or preferably 3, with (B) diacrylates of the general formula R(-0-C-C=CH2)~ (IV) where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20, and more particularly from 4 ;~ to 8, carbon ats~ms, and R5 iS hydrogen or a methyl group, in a molar ratio of (A~ to (B) of from l:2 to 2:l, and optionally further reacting these addition compounds with (C) (l) acrylic acid or derivatives of acrylic acid of the JMX-SCHERING:2505.APP

general fsrmula CH2=C-R3 ~V) ~5 where R3 is -COOH, -CN, -CONH-NH2, -COOC2H4-OH or -CooR4 and R4 is an aliphatic hydrocarbon group having from 1 to 4 carbon atoms when the addition product of (A) and (B) contains free amine hydrogen atoms, or with (2) imidazoles of the general formula N ~ I
NH (VI) = CH

where Rl and R2 are, independently of one another, H, CH3, C2H5 or phenyl when the addition product of (A) and (B) has terminal double bonds (according to formula ;. [IV]), the compounds of step (C) being used in such amounts that all reactive amine hydrogen atoms or double bonds of the addition products of (A) and (B) are reacted.
One object of the invention is the use of compounds of the general formulas JM~C-SCHERING: 2 51:)5 . APP

Il R5 o ~ R5 ~2 ¦ ~C/N-(cH2)n-N -CH2-1H-~-O-R-O~ R-CH2-N~ ~ (I) 2 ~1 2 and ~ R5 R5 Rl-o~ -cH2-N-~2-~N-R3]2 (~2)n /~\ ~II) Rl-C CH
N _ ~-R2 where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20, and more particularly from 4 to 8, carbon atoms and optionally containing ether groups; R1 and R2 are, independently of one another, hydrogen, or aliphatic or aromatic hydrocarbon groups, and more particularly H, CH3 or C2H5; R3 is -COOH, -CN, -COOC2H4-OH, -CONH-NH2 or -CooR4; R4 is an aliphatic hydrocarbon group having from 1 to 4 carbon atoms, and more particularly -CH2-CH2-OH;
n is 2 or 3; and R5 is hydrogen or a methyl group, optionally with the concurrent use of commonly used nitrogen-containing heterocyclic amino compounds, as curing agents for epoxy resins.
The invention has as a further object molded epoxy-resin articles characterized in that in a first step the reinforcements or embedm~nts are impregnated J~5K-SCHERING: 2505 .APP

J

at room temperature with a binder, composed o~
(a) an epoxy resin with more than one epoxy group per molecule on the average;
(b) compounds of the general formulas Jl R5 o o R5 R2' N = \ ~ C~ = ~
~N-~C~2)n-N -~2-~H-~-O-R-o-~ c~2-N/ ~ (I) and o ~5 ~5 R[-o-J-CH-C~2-N-CH2-1~-R3]2 (IH2 ) n II III) Rl-C Cll : ~ J ~2 . 5 where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20, and more particularly from 4 to 8, carbon atoms and optionally containing ether YrOUP5; R1 and R2 are, independently of one another, hydrogen, or aliphatic or aromatic hydrocarbon groups, and more particularly H CH3 Or C2H5; R3 iS -COOH -CN COOC2H4-OH _CONH-NH2 or -CooR4; R4 is an aliphatic hydrocarbon group : having from 1 to 4 carbon atoms, and more particu-~ 15 larly -CH2-CH2-OH; n iS 2 or 3; and R5 is H or CH3;
~ and optionally JMK-SCHERING: 2505 .APP

2 ~

(c) commonly used solvents, fillers, reinforcements or embedments, pigments and auxiliaries; and optionally (d) commonly used nitrogen-containing heterocyclic amino compounds, and in a first step converted to the solid and dimensionally stable state and then, in a second step, fully cured at a temperature that is below the softening point of the molded articles formed in the first step.
Further objects of the .invention are set forth in the claims.
The imidazolyl compounds of the invention can be prepared by addition reactions, the acrylate compounds being reacted in a first step with N-aminoalkyl-imidazolyl compounds containing primary amino groups, in a ratio of mols of acrylate compound to mols of primary amino groups that may range from 1:2 to 2~
and, in a second step, acrylic acid or derivatives of acrylic acid being added to the secondary amino groups formed, and imidazolyl compounds of formula (VI3 to the freP double bonds. The addition reactions of the first and second steps generally are carriad out by known methods.
The acrylate compounds which, in accordance with the invention, are used in making the addition compounds are esterification or transesterification products of polyhydric alcohols and acrylic acids.
These reactions generally are carried out by known methods.
The alcohols here used may be straight- or branched-chain polyhydric aliphatic alcohols, and particularly diols such as butanediol, hexanediol, octanediol, neopentyl glycol or decanediol, or cyclic JMK-SCHERING: 2505 .APP

or alicyclic diols such as 1,4-cyclohexanediol or 1,4-dihydroxymethylcyclohexane, or diols containing ether groups, such as tetraethylene glycol or tri-propylene glycol.
The imidazolyl compounds which, in accordance with the invention, are used in making the addition products are compounds of the general formula CH =
H2N-(CH2)n~Ni ~ I (III~
C =

where R1 and R2 are, independently of one another, aliphatic or aromatic hydrocarbon groups, and more particularly H, CH3 or C2H5, and n is 2 or preferably 3.
From l to 2 mols of the imidazolyl compound of formula (III) are used per mol vf acrylate compound of the aforesaid acrylate compounds of formula (IV).
The acrylic acid or derivatives of acrylic acid used in accordance with the invention are compounds of the ~eneral formula CH2 ~ C-R3 (V) where R3 is -COOH, -CN, -COOC2H4-OH, -CONH-NH2 or -CooR4; and R4 is an aliphatic hydrocarbon group having from 1 to 4 carbon atoms, and more particularly CH3 or C2H5 .

SCHERING: 2 505 . APP

One mol of the acrylic acid compounds is used per secondary amino group of the addition compounds made in the first step.
The imidazolyl compounds containing only one amine hydrogen atom which, in accordance with the invention, are added to the addition compounds with free double bonds made in a first step are compounds of the general formula R
N
¦ NH (VI~

C~l ~2 where R1 and R2 are, independently of one another, H, CH3, C2H5 or phenyl. One mol of the compounds of formula (VI) is used per double bond.
The addition products of the invention which can be prepared by these process steps are compounds of the general formulas R1 RS O O ~5 N =, ~ ~ C~ -(CR2)n-N -CR2-~B-~-O-R-O~ B-C~2~N/ l (I) ~2 ~1 2 and o R5 R5 Rl-o-c-lH-cR2-N-c~2-l~-R3]2 (1~2)~
~ lII) / \
Rl_C CH
,1 ~-R2 where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to : 20, and more particularly from 4 to 8, carbon atoms and optionally containing ether groups; Rl and R2 are, independently of one another, hydrogen, or aliphatic or aromatic hydrocarbon groups, and more particularly H, CH3 or C2H5; R3 is -COOH, -CN, -COOC2H4-OH, -CONH-NH2 or -CooR4; R4 is an aliphatic hydrocarbon group having from 1 to 4 carbon atoms, and more particularly -CH2-CH2-OH;
n is 2 or 3; and R5 is hydrogen or a methyl group.
Apart from the preferred compounds of the general formulas (I) and (II), which are formed when the ratio between the imidazolyl compounds of formula (III) and the acrylate compounds of formula (IV) is an even-numbered 1:2 or 2:1, molar ratios between these values will yield structured products which contain the structural unit .

~_N_~H2_~H_I_O_R_O_~_~H_CH2_J m (1H~)n (VII) Rl-~ CH
d ~-R2 repeatedly (m) in the chain and have derivatives of either formula (V) or formula (VI) as end groups.
Both m, which is preferably between 1 and 5, and more particularly between 1 and 3, and the end groups can be determined at will through the choice of the molar ratios of compounds of formula (III) to compounds JM}C-SCHERING: 2 505 . APP

of formula (IV).
It thus becomes possible to control the catalytic activity (tertiary or total nitrogen content) and to adjust the viscosity from low-viscosity to high-viscosity to solid.
In a first step, the addition products of the imidazolyl compounds of formula (III) and the acrylate compounds of formula (IV) are prepared, in molar ratios that assure that no double bonds are present at the same time as tertiary aliphatic nitrogen, and in a second step the derivatives of acrylic acid of formula (V) are added.
Preferably, however, all components are reacted simultaneously. A statistical mixture is then obtained which usually is less homogeneous than is the case when a stepwise procedure is employed. Care should be taken to assure that there is no excess of acrylic acid or derivatives thereof while tertiary nitrogen is also present. No significant difference has been observed so far as suitability for the end uses contemplated by the invention is concerned.
The curing agents of the invention can be used singly or as a mixture at the rate of from 2 to 35 g, ; and more particularly from 4 to 25 g, but preferably from 5 to 20 g, of curing agent per 100 g of epoxy resin.
The imidazolyl compounds of the invention can also be used in the form of their salts. Use may here be made of the organic and inorganic salt formers known in this field. In accordance with the invention, however, mono- or polybasic organic carboxylic acids are preferred, branched-chain monocarboxylic acids having up to 10 carbon atoms, such as 2-ethylhexoic acid, being particularly well suited.

JM~C-SCHERING: 2505 . APP

The epoxy resins which, in accordance with the invention, are used as a binder constituent are glycidyl esters and ethers with two or more epoxy groups per molecule, and preferably glycidyl ethers based on mono- or polyhydric phenols. In accordance with the invention, glycidyl ethers of 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) with epoxy values of from 0.2 to 0.6, and particularly the compounds with epoxy values of from 0.45 to 0.55 which : 10 are liquid at room temperature, are preferred.
The glycidyl ethers based on bisphenol F and the novolacs have also proved advantageous.
~ Also usable are the commercial halogenated, and t more particularly brominated, epoxy resins based on the aforesaid phenols.
The amino compounds which, in accordance with the invention, may also be used are preferably commonly used nitrogen-containing heterocyclic amino compoun~s, that is, N-alkylimidazoles such as N-methyl- or : 20 N ethylimidazole, and/or imidazoline compounds of the general formula : tHINH-CH2-CH21X-N - C-~z R tVlII) where R is an optionally branched alkyl or alkylene group having fewer than 10 carbon atoms, and more particularly -CH3, -CHOH-CH3 or -(CHR~)y~ R' is H or -CH3, x is 1, 2 or 3, y is from 4 to 8, and z is equal to the valence of R, and particularly those where x is 1, z is 1, and R is -CH3 or -CH2-CH3. Other curing J2~5}C-SCHERING: 2 5 0 5 . APP

2 ~

agents commonly used in this field may also be used, if desired.
For modification of the properties of the end product, other epoxy resins may be used concurrently, as may modifiers or auxiliaries such as phenolic resins, melamine resins, silicone resins, inorganic and organic fillers such as quartz powders, titanium dioxide, carbon black, and silicone or butadiene rubber.
To obtain the desired viscosity, resins of di~ferent viscosities, diluents, or such commonly used solvents as dimethyl formamide, acetone, methyl ethyl ketone, methyl glycol or propylene glycol monomethyl ether, or mixtures thereof, may be used.
In prepregging, organic and inorganic fibers, nonwovens and woven fabrics based on aramid, carbon or cellulose, metals such as boron, steel, etc., ceramics and especially glass are used.
The solvent-containing prepregs are generally made by known methods, in which the base materials are impregnated with the reactive resin mixture in an impregnating bath and, after the excess resin has been squeezed off, continuously converted from the A stage to the B stage with input of energy (mostly heat) and simultaneous removal of the solvent. Depending on the desired preprey consistency (viscid to solid), the prepregs are then provided on both sides with a release sheet and wound into a roll for storage and shipping.
The further processing involves cutting the individual prepreg layers to size and assembling them into a stack, from which a highly crosslinked part is produced by shaping with simultaneous heat input.
The curing agents of the invention can als~ be used successfully in solventless prepregs based on JMR--SCHERING: 2505 .APP

2 ~ r3 ~3 epoxy resins and, optionally, commonly used curing agents. Here the base materials are impregnated at optionally elevated temperature and by conventional methods with the binder system and placed into storage appropriate to the system before they are processed further like solvent~containing systems.
Further examples of solventless systems are wet-layup laminates, base materials for the electrical industry, fiber-reinforced molded parts produced in situ, heat-curing one-component adhesives for the bonding of body sections in the automotive industry (flange-joint adhesives), for example, as well as epoxy-resin castings, epoxy-resin coatings and epoxy-resin filament- or tape-wound structures.
Both the imidazolyl compounds and the acrylates used in the examples are commercial products of BASF
AXtiengesellschaft, Ludwigshafen, and have been used in that technical grade.
EXAMPLES
(I) PREPARATION OF THE CURING AGENTS OF THE INVENTION
Example 1 41.7 g (0.33 mol) of 1-(3-aminopropyl)imidazole and S4.7 g (0.66 mol) of 2-methylimidazole are dissolved in 70.0 g of ethanol at about 60~ C and slowl~ mixed with 132.0 g ~0.66 mol) of butanediol diacrylate. The mixture is allowed to react for another hour at 70 C, and the ethanol is then drawn of~.
A product is obtained which has the following characteristics:
Amine value: 342-343 Viscosity/25~ C: 1.2 Pa s JMK-SCHERING: 2 505 . APP

ExamPle 2 250 g (2 mols) of 1-(3-aminopropyl)imi~azole is introduced as initial charge and slowly mixed at 60-80 C with 198 g (1 mol) of butanediol acrylate with cooling.
The addition product has the following characteristics:
Amine value: 494-497 Viscosity/25 C: 1.6 Pa-s 448 g of this addition product is slowly mixed at 60 C with 232 g (2 mols) of 2-hydroxyethyl acrylate with cooling.
The mixture is allowed to react for another hour at 80 C. A product is obtained which has the following characteristics:
Amine value: 326-327 Viscosity/25 C: 10.4 Pa-s Example 3 375 g ~3 mols) of 1-(3-aminopropyl)imidazole is introduced as initial charge and slowly mixed at 60-80 C with 396 g (2 mols) of butanediol acrylate with cooling.
The addition product has the folîowin~
ch~racteristics:

Amine value: 435-437 Viscosity/25 C: 5.1 Pa-s 385.5 g of this addition product is slowly mixed at Ç0 C with 116 g (1 mol) of 2-hydroxyethyl acrylate with cooling.
The mixture is allowed to react for another hour at 80 C. A product is obtained which has the following characteristics:

JMK-SCHERING: 2 51:) 5 . APP

.

Amine value: 335-337 Viscosity/25 C: 6.7 Pa s Example 4 125 g (1 mol) of 1-(3-aminopropyl)imidazole and 164 g (2 mols) of 2-methylimidazole are dissolved in 150 g of ethanol at about 60 C and slowly mixed with 452.6 g (2 mols) of hexanediol diacrylate at temperatures ranging from 60 to 80 C. The mixture is allowed to react for another hour at 70 C, and the ethanol is then drawn off.
A product is obtained which has the following characteristics:
Amine value: 299-301 Viscosity/25 C: 2.5 Pa s Example 5 300 g of the product of Example 4 is homogeneously mixed with 58.3 g of 2-ethylhexoic acid at 80 C. A
product is obtained which has the following characteristics:
Amine value: 252 Viscosity/25 C: 4.3 Pa-s Example 6 125 g (1 mol) of 1-(3-aminopropyl)imidazole is in-troduced as initial charge, and 198 g (1 mol~ of butanediol diacrylate is slowly added at temperatures ranging from 60 to 80 C. After the exothermic reaction has subsided, stirring is continued for 3 hr at 90 C. A product is obtained which has the following characteristics:
Amine Yalue: 345-346 Viscosity/2~ C: 1290 Pa-s J~K-SCHE~ING: 2 5 0 5 . APP

2~4~33~

(II) PREPARATIONnOF A PREPREG REACTION MIXTURE
Example 1 100 g of an epoxy resin (epoxide equivalent weight about 190) is mixed with 14 g of the inventive reaction product of Example (I) 1 and used to make prepregs.
This mixture has a viscosity at room temperature (25 C) of 11.6 Pa s and is workable even after 10 hours.
The prepregs are produced on the laboratory scale by spreading khe reaction mixture onto a glass-filament fabric in a satin weave, measuring about 0.1 m2, which after impregnation is lined on both sides with release sheets and then stored at room temperature.
Aftar 24-hour storage at room temperature, the material has aged sufficiently to be processed as a slightly tacky prepreg in several layers by the hot-press molding method at 0.1 bar and temperatures of from 100 to 120 C, in from 30 minutes to 1 hour, into high-strength molded articles. The finished product, fully cured in this manner, exhibits no flaws of any kind with respect to adhesion of the individual prepreg layers.
The storage-stability values given in Table 1 are determined on the basis o~ conditions duplicating those used in actual practice. The impregnated fabric is ~tored between two polyethylene sheets at 23 C under standard climatic conditions. A layer of a specimen is molded at 24-hour intervals under conditions duplicating those used in actual practice (1 hr, 120 C, 0.1 bar). The storage-stability value indicated is based on the last day on which the resin is fluid under hot-press molding conditions. The other ~torage-stability values given in Table 1 are determined in the same way as the one for Example 1.

J~K-SCHE~ING:2505.APP

Table 1 Storage stability of solventless prepregs _ -~
Example Curing Curing Epoxy Storage agent, agent, resin, stability, Example g 100 g days I .... _ ... _ 1 (I) 1 14 Bisphenol ~ 6 value _ 2 (I) 2 5 id. )25 3 (I~ 3 5 id. ~ 6 4 (I) 4 14 id. ~ 6 _ _ _ (I) 5 14 id. ~ 6 (III) DETERMINATION OF INFLUENCE OF CURING AGENT
To determine the properties of the curing agent as a function of structure, the mixtures, composed only of epoxy resin and curing agent so as to eliminate any distorting influences of reinforcements and additives, are fully cured and tested.
In the examples listed in Table 2, a glycidyl ether based on bisphenol A and having an epoxy value of 0O53 is used as epoxy resin.
~ o produce the test specimens, 100 g of epoxy r sin is mixed in each case at room temperature with the amount of curing agent indicated in Table l and , completely cured in a steel mold for 2 hr at ~20 C to give flat molded parts 4 mm thick. From these molded parts, test specimens are then taken by sawing or milling. On these specimens, the properties specified in Table 2 are determined in conformity with the test standards listed below.

JM~C--SCHERING: 2505 .APP

Test-specimen dimensions ~ . . _ .. . _.
Flexural DIN 53,452 80 x 10 x 4 mm strength i - ---__ Deflection DIN 53,452 80 x 10 x 4 mm Impact strength DIN 53,453 50 x 6 x 4 mm Tensile strength DIN 53,455 Dumbbell No. 3 =~ .__ _ Elongation DIN 53,455 Dumbbell No. 3 _ ~ _ ._ .__ ~T
Modulus of DIN 53,457 Dumbbell No. 3 elasticity Heat-distortion DIN 53,461 120 x 10 x 4 mm temperature Glass-transition DIN 53,445 80 x 10 x 1 mm temperature . _ Table 2 Thermal and mechanical properties .
IExample _ (unit? 1 2 3 4 5 ¦Flexural N/mm2 93 45 26 82 78 ¦strength I ~ _ ¦Deflection mm 13.74.3 4.8 8.3 7.8 ¦
¦Impact kJ/m2 12.5 3.03.1 8.55.5 ¦
Istrength I . _ ¦Tensile N/mm2 50 31 34 41 43 strength _ . I
Elongation ~ 2.21.2 1.2 1.7 1.8 _ l Modulus of N/mm2 28002850 2970 2850 2740 l elasticity __ , _ _ Heat- C 127 127127 127 122 distortion temperature _ ~
3G Glass C153 163151 153149 transition temperature _ JMK-SCHERING: 2 505 . APP

Claims

1. A compound of the general formula (I) where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20 carbon atoms and optionally containing ether groups;
R1 and R2 are, independently of one another, hydrogen, or aliphatic or aromatic hydrocarbon groups; n is 2 or 3; and R5 is hydrogen or a methyl group.

2. A compound of the general formula JMK-SCHERING:2505.APP

(II) where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20 carbon atoms and optionally containing ether groups;
R1 and R2 are, independently of one another, hydrogen, or aliphatic or aromatic hydrocarbon groups; R3 is -COOH, -CN, -COOC2H4-OH, -CONH-N2H or -COOR4; R4 is an aliphatic hydrocarbon group having from 1 to 4 carbon atoms; n is 2 or 3; and R5 is hydrogen or a methyl group.

3. A method for preparing a curing agent for glycidyl compounds which comprises reacting (A) an imidazolyl compound of the general formula (III) JMK-SCHERING:2505.APP

where R1 and R2 are, independently of one another, aliphatic or aromatic hydrocarbon groups and n is 2 or 3, and (B) a diacrylate of the general formula (IV) where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20 carbon atoms and optionally containing ether groups, and R5 is hydrogen or a methyl group, in a molar ratio of (A) to (B) of from 1:2 to 2:1.

4. The method for preparing a curing agent for glycidyl compounds as claimed in claim 3, which further comprises reacting the addition product formed from the reaction of (A) and (B) with (C) (1) acrylic acid or a derivative of acrylic acid or the general formula (V) JMK-SCHERING:2505.APP

where R3 is -COOH, -CN, -COOC2H4-OH, -CONH-NH2 or -COOR4, R4 is an aliphatic hydrocarbon group hav-ing from 1 to 4 carbon atoms, and R5 is hydrogen or a methyl group, when the addition product of (A) and (B) contains free amine hydrogen atoms, or with (2) an imidazole of the general formula (VI) where R1 and R2 are, independently of one another, H, CH3, C2H5 or phenyl when the addition product of (A) and (B) has free double bonds, the compound (C) being used in such amounts that all reactive amine hydrogen atoms or epoxy groups of the addition product of (A) and (B) are reacted.

5. A curable epoxy-resin composition which comprises (a) an epoxy resin with more than one epoxy group per molecule on the average;

JMK-SCHERING:2505.APP

(b) a compound of the general formula (I) or (II) or both, where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20 carbon atoms and optionally containing ether groups; R1 and R2 are, independently of one another, hydrogen, or ali-phatic or aromatic hydrocarbon groups; R3 is -COOH, -CN, -COOC2H4-OH, -CONH-NH2 or -COOR4; R4 is an aliphatic hydrocarbon group having from 1 to 4 carbon atoms; n is 2 or 3; and R5 is hydrogen or a methyl group;
(c) commonly used additives selected from the group consisting of solvents, fillers, reinforcements or embedments, pigments and auxiliaries; and optionally JMK-SCHERING:2505.APP

(d) commonly used nitrogen-containing heterocyclic amino compounds.

6. A curable epoxy-resin composition wherein reinforcements or embedments are impregnated at room temperature with a binder, which comprises (a) an epoxy resin with more than one epoxy group per molecule on the average;
(b) a compound of the general formula (I) or (II) or both, where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20 carbon atoms and optionally containing ether groups; R1 and R2 are, independently of one another, hydrogen, or ali-JMK-SCHERING:2505.APP

phatic or aromatic hydrocarbon groups; R3 is -COOH, -CN, -COOC2H4-OH, -CONH-NH2 or -COOR4; R4 is an aliphatic hydrocarbon group having from 1 to 4 carbon atoms; n is 2 or 3; and R5 is hydrogen or a methyl group; and optionally (c) commonly used additives selected from the group consisting of solvents, fillers, reinforcements or embedments, pigments and auxiliaries; and (d) commonly used nitrogen-containing heterocyclic amino compounds which are optionally converted at elevated temperature to the semisolid but still fusible state (B stage).

7. A curable epoxy-resin composition wherein reinforcements or embedments are impregnated at room temperature with a binder, which comprises (a) an epoxy resin with more than one epoxy group per molecule on the average; and (b) an imidazolyl compound prepared by reacting (A) an imidazolyl compound of the general formula (III) where R1 and R2 are, independently of one another, hydrogen, or aliphatic or aromatic hydrocarbon groups, and n is 2 or 3, and JMK-SCHERING:2505.APP

(B) a diacrylate of the general formula (IV) where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20 carbon atoms and optionally containing ether groups, and R5 may be hydrogen or a methyl group, in a molar ratio of (A) to (B) of from 1:2 to 2:1, and optionally by further reacting these addition compounds with (C) (1) acrylic acid, or a derivative of acrylic acid, of the general formula (V) where R3 is -COOH, -CN, -COOC2H4-OH, -CONH-NH2 or -COOR4, R4 is an aliphatic hydrocarbon group hav-ing from 1 to 4 carbon atoms, and R5 is hydrogen or a methyl group, when the addition product of (A) and (B) contains free amine hydrogen atoms, or with JMK-SCHERING:2505.APP

(2) an imidazole of the general formula (VI) where R1 and R2 are, independently of one another, H, CH3, C2H5 or phenyl when the addition product of (A) and (B) contains free double bonds, the compound (C) being used in such amounts that all reactive amine hydrogen atoms or double bonds of the addition compounds from (A) and (B) are reacted;
and optionally (c) commonly used additives selected from the group consisting of solvents, fillers, reinforcements or embedments, pigments and auxiliaries; and (d) commonly used nitrogen-containing heterocyclic amino compounds.

JMK-SCHERING:2505.APP

8. A molded epoxy-resin article, wherein the reinforcements or embedments are impregnated at room temperature with a binder, which comprises (a) an epoxy resin with more than one epoxy group per molecule on the average;
(b) a compound of the general formula (I) or (II) or both, where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20 carbon atoms and optionally containing ether groups; R1 and R2 are, independently of one another, hydrogen, or ali-phatic or aromatic hydrocarbon groups; R3 is -COOH, -CN, -COOC2H4-OH, -CONH-NH2 or -COOR4; R4 is JMK-SCHERING:2505.APP

an aliphatic hydrocarbon group having from 1 to 4 carbon atoms; n is 2 or 3; and R5 is hydrogen or a methyl group; and optionally (c) commonly used additives selected from the group consisting of solvents, fillers, reinforcements and embedments, pigments and auxiliaries; and (d) commonly used nitrogen-containing heterocyclic amino compounds which are optionally converted to the semisolid but still fusible state (B stage), and where moist laminates or prepregs are molded or placed between substrates to be bonded and fully cured at elevated temperature and by the use of pressure.

9. A molded epoxy-resin article, wherein reinforcements or embedments are impregnated at room temperature with a binder, which comprises (a) an epoxy resin with more than one epoxy group per molecule on the average;
(b) a compound of the general formula (I) or (II) or both, where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20 carbon atoms and optionally containing ether groups; R1 and R2 are, independently of one another, hydrogen, or ali-phatic or aromatic hydrocarbon groups; R3 is -COOH, -CN, -COOC2H4-OH, -CONH-NH2 or -COOR4; R4 is an aliphatic hydrocarbon group having from 1 to 4 carbon atoms; n is 2 or 3; and R5 is hydrogen or a methyl group; and optionally (c) commonly used additives selected from the group consisting of solvents, fillers, reinforcements or embedments, pigments and auxiliaries; and (d) commonly used nitrogen-containing heterocyclic amino compounds which are converted to the solid and dimensionally stable state and then fully cured at a temperature that is below the softening point of the molded articles already formed.

10. A molded epoxy-resin article, according to claim 9, which further comprises at least one curing agent prepared by reacting (A) an imidazolyl compound of the general formula (III) JMK-SCHERING:2505.APP

where R1 and R2 are, independently of one another, hydrogen, or aliphatic or aromatic hydrocarbon groups, and n is 2 or 3, and (B) a diacrylate of the general formula (IV) where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20 carbon atoms and optionally containing ether groups, and R5 may be hydrogen or a methyl group, in a molar ratio of (A) to (B) of from 1:2 to 2:1, and optionally by further reacting these addition compounds with (C) (1) acrylic acid, or a derivative of acrylic acid, of the general formula (V) JMK-SCHERING:2505.APP

where R3 is -COOH, -CN, -COOC2H4-OH, -CONH-NH2 or -COOR4, R4 is an aliphatic hydrocarbon group hav-ing from 1 to 4 carbon atoms, and R5 is hydrogen or a methyl group, when the addition product of (A) and (B) contains free amine hydrogen atoms, or with (2) an imidazole of the general formula (IV) where R1 and R2 are, independently of one another, H, CH3, C2H5 or phenyl when the addition product of (A) and (B) contains free double bonds, the compound (C) being used in such amounts that all reactive amine hydrogen atoms or double bonds of the addition compounds from (A) and (B) are reacted.

11. A process for manufacturing fiber-reinforced base materials for the electrical industry which comprises converting in a first step a reinforcing material impregnated with a binder based on epoxy resin and an amine curing agent to the B stage by the use of heat and optionally pressure and completely curing them at elevated temperature, wherein the curing agent used JMK-SCHERING:2505.APP

is a compound of the general formula (I) or (II) where R is a divalent, optionally branched aliphatic, cyclic or alicyclic hydrocarbon group having from 2 to 20 carbon atoms and optionally containing ether groups;
R1 and R2 are, independently of one another, hydrogen, or aliphatic or aromatic hydrocarbon groups; R3 is -COOH, -CN, -COOC2H4-OH, -CONH-NH2 or -COOR4; R4 is an aliphatic hydrocarbon group having from 1 to 4 carbon atoms; n is 2 or 3; and R5 may be hydrogen or a methyl group.

JMK-SCHERING:2505.APP