Compositions containing a mixture of a polyhydric alcohol and charge transfer complex of irradiated anhydrides and cyclic ethers, used to cure epoxy resins

A curing agent is made by admixing (a) an irradiated mixture of carboxylic acid anhydride and carbon containing cyclic compound and (b) a polyhhydric alcohol, where the curing agent can be added to a resin such as an epoxy resin, applied to the surface of an article, and cured.

BACKGROUND OF THE INVENTION 
Carboxylic acid anhydrides, Lewis Acids, and boron trifluoride:amine 
complexes are curing agents that have been found to be useful with epoxy 
resins for insulating applications, as described by Lee and Neville in the 
Handbook of Epoxy Resins, McGraw Hill, 1967, pages 11-1 to 11-8 and 12-1 
to 12-27. Usually, the addition of an accelerator is required to give 
reasonable gel times at elevated temperatures, but at room temperature, 
even with high concentrations of accelerators, very slow gel times are 
experienced. Considerable effort has been devoted in recent years to 
developing improved room temperature curing agents for epoxy-anhydride 
resins. 
Ecke et al., in U.S. Pat. No. 3,114,752, taught the reaction of 
tetrahydrofuran with maleic acid in the presence of a free radical 
initiator to produce monomeric 1:1 adducts. Free radical initiators were 
taught to include ultraviolet light and various persulfates, peroxides and 
nitrides. The compounds formed were bonded adducts rather than 
disassociated species such as free radicals, and were taught as useful 
plasticizers and curing agents for epoxy resins. Smith et al., in U.S. 
Pat. No. 4,273,914, discovered a low temperature, fast curing epoxy 
insulating composition, which consisted of an epoxy resin and a carboxylic 
acid anhydride complex. The anhydride complex was made by the low 
temperature reaction of a selected Lewis Acid catalyst, such as antimony 
pentrachloride, titanium tetrachloride, boron trifluoride, tin 
tetrachloride, or triphenyl tin chloride, with a carboxylic acid 
anhydride. There, the catalyst and anhydride were simply pre-reacted at a 
reacting mass temperature of from 10.degree. C. to about 45.degree. C. The 
complex allowed substantially complete cure of the epoxy resin at 
25.degree. C. in about 48 hours. 
Von Brachel et al., in U.S. Pat. No. 3,499,007, utilized a peroxide 
initiated, non-irradiated, free-radical chain reaction of maleic anhydride 
and straight chain polyalkylene ethers, at from about 80.degree. C. to 
160.degree. C., to provide addition products, noting that the literature 
showed successful reaction of maleic anhydride with tetrahydrofuran, but 
not dioxane, in the presence of radical initiators. These addition 
products were found useful as raw materials for lacquers, and as surface 
active anhydride components in the production of polyesters. These 
addition products were usually reacted at from 100.degree. C. to about 
130.degree. C. with epoxies and the like. 
Charge-transfer systems have recently been shown capable of polymerizing 
monomer and epoxy resins. Williamson et al., J. Polm. Sci., Polm. Chem. 
Ed., Vol. 20, pp. 1875-1884, 1982, "Laser-Initiated Polymerization of 
Charge-Transfer Monomer Systems" describe polymer formation after laser 
exposure in three successful systems: 9-vinylanthracene/diethylfumarate; 
2-vinylnaphthalene/fumaronitrile, in methylene chloride solvent; and 
2-vinylnaphthalene/fumaronitrile, in sulfolane solvent. Another article, 
"Laser Initiated Polymerization of Charge Transfer Monomer Systems: 
Copolymerization of Maleic Anhydride with Styrene, Vinyltoluene and 
t-Butylstyrene", by R. K. Sadhir et al., Polym. Prepr. Am. Chem. Soc. Div. 
Polym. Chem., Vol. 23 No. 1, pp. 291-292, March 1982, describes 
vinyl-maleic anhydride systems and a theoretical discussion of 3,600 
Angstrom Unit laser irradiation of such systems to form charge transfer 
systems. 
Later articles, "Laser-initiated Copolymerization of Maleic Anhydride with 
Styrene, Vinyltoluene, and t-Butylstyrene", by R. K. Sadhir et al., J. 
Polym. Sci. Polym. Chem. Ed., Vol. 21, No. 5, pp. 1315-1329, May 1983, and 
"Laser-Initiated Polymerization of Epoxies in the Presence of Maleic 
Anhydride", by R. K. Sadhir et al., J. Polym. Sci. Polym. Chem. Ed., Vol. 
23, pp. 411-427, 1985, give a more detailed description of laser-initiated 
polymerization of styrene, vinyltoluene and t-butystyrene in the presence 
of maleic anhydride, and laser-initiated polymerization of cyclohexene 
oxide in the presence of maleic anhydride, respectively. 
Sadhir et al., in U.S. Patent Application Ser. No. 731,745, filed on May 7, 
1985, utilized a reactive, irradiated catalytic complex as a low 
temperature curing agent for organic resins. The complex was produced by 
U.V. or laser irradiating a mixture of carboxylic acid anhydride and at 
least one of a cyclic compound selected from tetrahydrofuran, dioxane, 
trioxane and sulfolane, with no use of catalysts or initiators. Another 
application in the area is Sadhir et al., U.S. Patent Application Ser. No. 
703,165, filed on Feb. 19, 1985, which used additional catalysts. 
Sadhir et al., in U.S. Patent Application Ser. No. 739,242 filed on May 30, 
1985, cold concentrated these irradiated catalytic complexes to improve 
reactivity. These concentrated catalytic complexes were described as sole 
room temperature catalysts with epoxy resins and vinyl monomers, to 
provide impregnating, potting, or protective encapsulating resins for 
motor coils, or coil connection insulators for high voltage rotating 
apparatus. Examples showed a quick room temperature cure with 
cycloaliphatic epoxy resins. It had been found, however, that these 
complexes provided a slower room temperature cure with bisphenol A epoxy 
resins than with cycloaliphatic epoxy resins. 
Since the bisphenol A epoxy is the most commonly used and inexpensive type 
of epoxy resin, it is highly desirable to find a fast acting catalyst for 
them which is useful at room temperature, and to provide fast, room 
temperature curable bisphenol A epoxy coating compositions. It would also 
be highly desirable to be able to fast cure cycloaliphatic epoxy resins at 
times below 3 minutes at room temperature, for fast production line, thin 
coating of a variety of articles. 
As a further improvement, Saunders et al., in U.S. Patent Application Ser. 
No. 926,304, filed on Nov. 3, 1986, utilized a boron trihalide complex in 
the concentrated catalytic complexes of Sadhir et al., to lower room 
temperature cure time. Inclusion of such complexes tended however to lower 
electrical properties of the cured composition somewhat. Additionally, in 
the cases involving concentrated catalytic complexes, crystallization in 
the solution can occur in the range of about 10% to 15% concentration 
after 6 hours to 10 hours, limiting storage life and mixing ability. What 
is needed is a means to concentrate the catalytic complexes without 
crystallization and to modify their structure to provide an extremely 
reactive curing agent for resin systems. 
SUMMARY OF THE INVENTION 
The above problems have been solved and the above needs met by providing a 
curing agent particularly effective for epoxy resins, containing the 
admixture of: (1) a charge transfer complex (CTC) produced by mixing and 
irradiating a combination of: (a) a carboxylic acid anhydride, selected 
from halide or short chain alkyl substituted carboxylic anhydride, and 
preferably citraconic anhydride or maleic anhydride, and their mixtures, 
and (b) a carbon containing cyclic compound containing an electron 
deficient element, such as sulfur or preferably oxygen and their mixtures, 
selected from the group consisting of tetrahydrofuran, dioxane, trioxane, 
and sulfolane, and their mixtures, and (2) a polyhydric alcohol, i.e., one 
containing two, three or four hydroxyl groups, such as 1,4 butane diol, 
trimethylol propane, or pentaerythritol. Preferably, the irradiated 
mixture of carboxylic acid anhydride and carbon containing cyclic compound 
is concentrated before mixing with the polyhydric alcohol. 
The preferred weight ratio of carboxylic acid anydride:carbon containing 
cyclic compound in the catalytic complex is from about 1:0.8 to 2. In the 
reaction to form the unconcentrated charge transfer complex, no free 
radical initiators are used, and the temperature is preferably kept below 
about 45.degree. C. The weight ratio of charge transfer complex:polyhydric 
alcohol can generally be from about 2 to 50:1. 
The charge transfer complex can be concentrated without the use of heat, 
in, for example, a vacuum chamber or other vacuum means, to from about 55% 
to about 90% of its original weight, to remove plasticizing compounds. The 
highly reactive mixture of concentrated charge transfer complex and 
polyhydric alcohol, is the curing agent of this invention. When, for 
example, it is added in a weight ratio of epoxy resin:curing agent of from 
about 1:0.2 to 0.8, it will effect substantially complete cure at 
25.degree. C. of thick coatings of epoxy resins in a short time. No 
additional curing agents are needed. 
In a preferred embodiment of this invention, the polyhydric alcohol is 
added to a concentrated charge transfer complex at temperatures ranging 
from about 20.degree. C. to 85.degree. C. The polyhydric alcohol has been 
found to react with radical anion or cation anhydride groups in the charge 
transfer complex and with unreacted carboxylic acid anhydride, resulting 
in a slightly higher molecular weight material less prone to 
crystallization. The polyhydric alcohol reacts with anhydride to produce 
ester groups, and also carboxyl groups which are more reactive toward 
epoxy than corresponding anhydrides. The reaction can slowly continue to 
form long chain oligomers at 25.degree. C. to 40.degree. C. 
The irradiation to form the unconcentrated charge transfer complex can be, 
for example, from a laser or a U.V. lamp, and contains radiation within 
the wavelength range of from about 100 Angstrom units to about 7,000 
Angstrom units. The irradiation is effective only when both the selected 
carboxylic acid anhydride and the selected carbon containing cyclic 
compound are mixed together, the irradiation of the mixed product solution 
producing an active species which is responsible for helping to initiate 
resin polymerization at room temperature. The resins incorporating these 
curing agents can be used to encapsulate electrical articles, to act as an 
insulating adhesive, and to act as room temperature curable surface 
coating paints of 0.02 inch thickness or less, for steel, other metals, 
wood, and plastics.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
It has been found that selected carbon containing cyclic compounds, 
containing an electron deficient element, can effectively interact and 
complex with selected carboxylic acid anhydrides, through irradiation 
containing radiation within the radiation wavelength range of from about 
100 Angstrom units to about 7,000 Angstrom units, preferably in the range, 
of from about 2,000 Angstrom units to about 7,000 Angstrom units, and most 
preferably from about 2,000 Angstrom units to about 3,900 Angstrom units. 
The irradiation need not be wide band, but can be any portion within the 
band. Laser irradiation, for example with an Argon laser at about 3,600 
Angstrom units, is a very concentrated and energy efficient substitute for 
common ultraviolet (U.V.) lamp sources, and allows the reaction to proceed 
at about 25.degree. C. without the need for cooling. 
When a laser is used, 5 minutes to 60 minutes irradiation will provide an 
effective amount of reactive species, which when mixed with a polyhydric 
alcohol can be used to cure epoxy resins. When a 250 watt to 500 watt U.V. 
lamp is used, 15 minutes to 90 minutes will provide an effective amount of 
reactive species, which when mixed with a polyhydric alcohol can be used 
to quick cure epoxy resins. Preferably, especially if bisphenol A epoxies 
are to be used, the charge transfer complex will be further concentrated. 
In the case of the U.V. lamp, the reacting mixture is preferably 
surrounded by a refrigeration means, so that the heat of the U.V. lamp 
does not cause undue evaporation of the reactants before the reaction is 
completed. In all cases, the temperature should be kept below about 
45.degree. C., to prevent evaporation of reactants, for example, maleic 
anhydride has a sublimation temperature of about 52.degree. C. and 
tetrahydrofuran has a boiling point of about 66.degree. C. 
The useful carbon containing cyclic compounds for the cyclic charge 
transfer complex (CTC) component of the curing agent of this invention 
contain one or more sulfur and/or oxygen, preferably oxygen, electron 
deficient elements or components, where the electron deficient element or 
component need not be present in the ring structure. Particularly useful 
compounds of this type include sulfolane, trioxane, and preferably dioxane 
(1,4-dioxane) and tetrahydrofuran, whose respective chemical structures 
are shown below: 
##STR1## 
Useful carboxylic acid anhydrides for these complexes include a class of 
carboxylic acid anhydrides having the chemical formula: 
##STR2## 
where R and R'=H, CH.sub.3, C.sub.2 H.sub.5, Cl, Br or I, for example, R' 
can =Cl and R can =CH.sub.3. 
Use of a higher alkyl than C.sub.2 H.sub.5 as R or R' will slow the 
irradiation reaction with the carbon containing cyclic compound. The most 
preferred carboxylic acid anhydrides are those where R=H and R'=CH.sub.3, 
and where R and R'=H, i.e., citraconic anhydride, and preferably maleic 
anhydride, respectively: 
##STR3## 
Other carboxylic acid anhydrides, such as hexahydrophthalic anhydride, 
succinic anhydride, and dodecenyl succinic anhydride, are not effective to 
provide catalytic reactive species. The double bond opposite the central, 
single bonded oxygen, appears to be of critical importance in providing 
catalytic reactive species with the above-described carbon containing 
cyclic compounds during irradiation. The carbon containing cyclic 
compounds act as a solvent for the selected acid anhydrides which are 
usually in solid form. The preferred weight range of (selected carboxylic 
acid anhydride):(selected carbon containing cyclic compound) is from about 
(1):(0.8 to 2). Less than 0.8 part/1 part acid anhydride, a solution will 
not result. Over 2 parts/1 part acid anhydride, the complex may not form. 
Usually, the selected acid anhydride is added to the selected liquid carbon 
containing cyclic compound, acting as solvent, and mixed, at about 
25.degree. C. to 30.degree. C., until a solution results. At this point 
there is no interaction between the two ingredients other than solution 
formation, i.e., the product of the mixture contains no complexes or 
reactive species. Then a source of irradiation, such as a bank of U.V. 
lamps or, for example, an Argon ion laser beam, which provides 
concentrated radiation and fast interaction, is directed into the 
solution. FIG. 1 of the Drawings, shows the use of a coherent CR-18 Argon 
ion laser to produce useful complexes for curing resins. In FIG. 1, 
mirrors 1 reflect laser beam 2, from laser source 3, through convex lens 4 
into monomer solution 5, in contact with magnetic stirrer means 6, and 
having optional nitrogen bubbler means 7. 
Upon irradiation of the solution, preferably with radiation containing the 
wavelength range of from about 2,000 Angstrom units to about 5,200 
Angstrom units, and most preferably within the range of from about 2,000 
Angstrom units to about 3,900 Angstrom units, a charge transfer complex 
forms. Although applicants are not to be held to any particular theory, 
using the interaction between maleic anhydride and dioxane as an example, 
the possible reactions that, it is thought, might occur include: 
##STR4## 
As shown in the previously described reactions, it is believed that argon 
ion laser action on the product solution and mixture of maleic anhydride 
and dioxane in step (A) produces a singlet excited species which goes to 
triplet excited state via step (B). The triplet excimer thus produced 
reacts with another maleic anhydride unit in the ground state (step C) and 
produces a reactive charge transfer complex (after step C). This charge 
transfer complex then abstracts a hydrogen atom from dioxane. This results 
in a color change between step (C) and step (D) indicating the presence of 
catalytic complexes, consisting essentially of reactive species such as 
cation (I), radical anion (II) and a free radical (III) containing only an 
electron as a reactive component. The catalytic complexes are capable of 
initiating cationic polymerization in epoxies. 
In addition to the reactive species shown, it has been found that a 
substantial amount, i.e., from about 20% to about 50% of carbon containing 
cyclic compound added, i.e., such as dioxane, remains unreacted. 
Additionally, it has been found that a substantial amount of carboxylic 
acid anhydride also remains unreacted. No deliberate heating is used, care 
being taken to react only up to about 45.degree. C., with no catalysts, or 
initiators being present, the reaction proceeding solely due to 
irradiation effects. 
The unreacted, carbon containing cyclic compound remaining after charge 
transfer complex production, be it dioxane, sulfolane or tetrahydrofuran, 
has been found to provide a plasticizing effect on epoxy resins, slowing 
resin cure at 25.degree. C. Continued irradiation has not been found to 
reduce substantially the plasticizing effect of the unconcentrated charge 
transfer complex. Heating the charge transfer complex in an attempt to 
reduce the amount of unreacted, carbon containing cyclic compound may 
cause decomposition of the already formed complex. A means to cold 
concentrate the charge transfer complex, such as passing a stream of 
nitrogen gas over the catalytic complex at 25.degree. C., or preferably 
using a vacuum chamber at 25.degree. C., has been found useful to remove 
substantially all of the unreacted, carbon containing cyclic compound and 
reduce substantially the plasticizing effect of the complex. It is also 
speculated that the concentration may open up some rings of the carbon 
containing cyclic compounds, providing additional reactive species. 
Unreacted carboxylic acid anhydride remains even after cold concentration. 
Addition of polyhydric alcohol causes a reaction not only with the 
anhydride groups in the charge transfer complex but also with anhydride 
which has not reacted, producing carboxyl end groups which are more 
reactive toward epoxy resins than corresponding anhydrides, thus helping 
to increase the reactivity of the curing agent. Also, this reaction forms 
a more viscous material having a slightly higher molecular weight which 
inhibits crystallization. It is thought that one hydrogen from the 
polyhydric alcohol attaches to the oxygen of the opened anhydride ring, 
while the remaining --O--C.sub.n --H.sub.2n --OH group attaches to the 
carbon, forming an ester linkage, shown as the addition product: 
##STR5## 
Where the anhydride type reactant is the charged radical anion or cation 
form (II) and (I) of the charge transfer complex, described previously, it 
is believed that the charge remains on the addition product. At low 
concentrations of polyol, i.e., about 8 to 50:1 of CTC:polyol, a 
substantial amount of unreacted anhydride and charge transfer complex 
radical anion or cation anhydride remain. This material will have a long 
pot life yet control crystallization. The curing agent itself will 
initially contain: (a) charge transfer complex, (b) polyol reaction 
products of radical anion or cation portions of the charge transfer 
complex, (c) polyol reaction products of previously unreacted anhydride, 
(d) unreacted polyol, (e) unreacted anhydride, and possibly (f) some 
unremoved carbon containing cyclic compound such as dioxane. As time 
passes more and more polyol will slowly react with both the unreacted 
anhydride and the radical anion and cation forms of the charge transfer 
complex. 
The term "polyhydric alcohol", i.e. polyol, as used herein, is defined as 
an alcohol having a carbon chain containing from C.sub.2 to C.sub.15 atoms 
preferably C.sub.2 to C.sub.6 atoms and containing two, three or four 
hydroxyl (--OH) groups. Use of over C.sub.15 atoms in the carbon chain of 
the polyol would make the cured resin too flexible and detract from its 
physical strength properties. The preferred polyhydric alcohols contain 
three hydroxyl groups, such as trimethylol propane (hexaglycerol) C.sub.2 
H.sub.5 C(CH.sub.2 OH).sub.3, glycerol C.sub.3 H.sub.5 (OH).sub.3, and the 
like. Polyhydric alcohols containing four hydroxyl groups are useful, such 
as pentaerythritol C(CH.sub.2 OH).sub.4, and the like. Polyhydric alcohols 
containing two hydroxyl groups are also useful, such as 1,6 hexane diol 
CH.sub.2 OH(CH.sub.2).sub.4 CH.sub.2 OH; 2,3 hexane diol CH.sub.3 
(CH.sub.2).sub.2 (CHOH).sub.2 CH.sub.3 ; 1,2 propane diol (propylene 
glycol); 1,3 propane diol (trimethylene glycol); 1,2 pentane diol; 1,4 
pentane diol; 1,5 pentane diol; 2,3 pentane diol; 1,2 butane diol; 1,3 
butane diol; 1,4 butane diol; 2,3 butane diol; ethylene glycol CH.sub.2 
OHCH.sub.2 OH; and the like, particularly ethylene glycol and propane 
diol. Mixtures of polyhydric alcohols are also useful in the invention. 
The weight ratio of charge transfer complex: polyhydric alcohol can 
generally be from about 2 to 50:1, i.e., one part polyhydric alcohol to 
from 2 parts to 50 parts charge transfer complex. Concentrations of 
polyhydric alcohol greater than one part alcohol to 2 parts charge 
transfer complex may cause too much flexibility in the cured resin and 
result in an undesirable excess of polyol. Concentrations of polyhydric 
alcohol less than one part alcohol to 50 parts charge transfer complex may 
not help much in increasing reactivity and reducing crystallization. 
Concentration of the charge transfer complex mixture can be from about 55% 
to 90% , preferably from about 65% to 85% of its original weight. 
Concentration below about 60% is very difficult, and not concentrating 
below about 90% does not yield much benefit in terms of gel and cure times 
to justify the expense of utilizing a cold concentrating means. 
Concentrating between 65% and about 80% yields a very workable thick 
slurry material. Concentration between about 55% and 65% yields a still 
useful material of increasing solidity as 55% is approached. The term 
"cold concentration" as used herein is defined as concentration in the 
temperature range of from about 18.degree. C. to about 30.degree. C. The 
term "X% concentrated" as used herein is defined as concentrated to X% of 
its original weight, i.e., 85% concentrated means that 15% of the original 
weight has been evaporated. 
Bisphenol based epoxy resins are useful in this invention, especially with 
the preferred, highly concentrated curing agents previously described. 
These resins may be used as the base resin in the invention, or used in 
combination with, for example, a cycloaliphatic epoxy. A bisphenol type 
resin is obtainable by reacting epichlorohydrin with a dihydric phenol in 
an alkaline medium at about 50.degree. C., using 1 to 2 or more moles of 
epichlorohydrin per mole of dihydric phenol. The heating is continued for 
several hours to effect the reaction and the product is then washed free 
of salt and base. The product, instead of being a single simple compound, 
is generally a complex mixture of glycidyl polyethers, but the principal 
product may be represented by the chemical structural formula: 
##STR6## 
where n is an integer of the series, 0, 1, 2, 3 . . . , and R represents 
the divalent hydrocarbon radical of the dihydric phenol. Typically R is: 
##STR7## 
to provide a diglycidyl ether of bisphenol A type epoxy resin or 
##STR8## 
to provide a diglycidyl ether of bisphenol F type epoxy resin. 
The bisphenol epoxy resins used in the invention have a 1, 2 epoxy 
equivalency greater than one. They will generally be diepoxides. By the 
epoxy equivalency, reference is made to the average number of 1, 2 epoxy 
groups, 
##STR9## 
contained in the average molecule of the dlycidylether. 
Other epoxy resins that are particularly useful alone or in admixture with 
bisphenol epoxy resins are epoxy novolacs. The polyglycidylethers of a 
novolac suitable for use in accordance with this invention are prepared by 
reacting an epihalohydrin with phenol formaldehyde condensates. While the 
bisphenol-based resins contain a maximum of two epoxy groups per molecule, 
the epoxy novolacs may contain as many as seven or more epoxy groups per 
molecule. In addition to phenol, alkyl-substituted phenols such as 
o-cresol may be used as a starting point for the production of epoxy 
novolac resins. 
Other epoxy resins useful alone or in mixture with bisphenol types include 
glycidyl esters, hydantoin epoxy resins, cycloaliphatic epoxy resins and 
diglycidyl ethers of aliphatic diols. Of these latter four varieties of 
epoxies, cycloaliphatic epoxies are most useful. The cycloaliphatic type 
epoxy resins that can be employed as the resin ingredient in the invention 
are selected from nonglycidyl ether epoxy resins containing more than one 
1,2 epoxy group per molecule. These are generally prepared by epoxidizing 
unsaturated hydrocarbon compounds, such as cyclo-olefins, using hydrogen 
peroxide or peracids such as peracetic acid and perbenzoic acid. The 
organic peracids are generally prepared by reacting hydrogen peroxide with 
either carboxylic acids, acid chlorides ketones to give the compound 
R--COOOH. 
Examples of cycloaliphatic epoxy resins would include: 
3,4-epoxycyclohexylmethyl-3, 4-epoxycyclohexane carboxylate (containing 
two epoxide groups which are part of ring structures, and an ester 
linkage); vinyl cyclohexene dioxide (containing two epoxide groups, one of 
which is part of a ring structure); and 3,4-epoxy-6-methylcyclohexyl 
methyl-3,4-epoxy-6-methylcyclohexane carboxylate. All of these types of 
epoxy resins described previously are well known in the art, and reference 
can be made to U.S. Pat. No. 4,273,914 for additional details in their 
production. Cycloaliphatic epoxy resins used alone do not require cold 
concentrating of the dual curing agent admixture of this invention. 
Other useful organic resins that can be used in this invention, generally 
in minor amounts with the epoxies and the curing agents previously 
described, include vinyl monomers, such as, styrene, 4-methoxy styrene, 
vinyl toluene, methyl methacrylate, methyl vinyl ketone, or 1,1 diphenyl 
ethylene and the like, and their mixtures. These resins are well known in 
the art. 
The preferred weight ratio range of epoxy resin: curing agent is from about 
1:0.2 to 0.8, preferably from about 1:0.3 to 0.6. Use of less than about 
0.2 part curing agent/1 part epoxy resin will provide little gel or cure 
time improvement. Use of over 0.8 part curing agent/1 part epoxy resin 
will result in minimal pot life or working time. The range between about 
1:0.60 to 0.8 can be especially useful when a filler is used, since filler 
inclusion often seems to substantially delay gel time. 
Natural oil extenders, such as epoxidized linseed or soy bean oils, may 
also be used in small amounts as epoxy resin additives. Polyhydric 
alcohols, having carbon chains from C.sub.2 to C.sub.15, can also be added 
directly to the epoxy resin, acting as a cross-linking agent when the 
carbon chain is from C.sub.2 to C.sub.5, or as a flexibilizer when the 
carbon chain is from C.sub.6 to C.sub.15, helping to tailor heat 
distortion temperature and flexibility. They can be added in amounts up to 
1:1 epoxy:polyol for certain paint applications. Thixotropic agents, such 
as fumed alumina or fumed silica, having particle sizes of from about 
0.005 micron to 0.025 micron, and coloring pigments, such as titanium 
dioxide, zinc chromate, zinc oxide, zinc sulfide, zirconium oxide, iron 
oxide, and the like may be used in minor amounts as aids in enhancing the 
color tones of the cured resins and making paint like compositions. 
Similarly, various inorganic particulate fillers, such as alumina 
trihydrate, silica, quartz, mica, chopped glass fibers, beryllium aluminum 
silicate, magnesium silicate, lithium aluminum silicate, mixtures thereof, 
and the like, in average particle sizes from about 5 microns to about 150 
microns, may be employed in amounts up to about 50 parts per 100 parts of 
resin, to improve electrical properties of the resin formulation, and to 
lower costs. Photoinitiators are neither required nor desired, since they 
can provide an impurity element in the composition. 
Referring now to FIG. 2 of the Drawings, a metal substrate 20 is coated 
with a thin coating 21 of the resinous composition of this invention. 
Substrates can include aluminum, copper and other metals, wood, plastic, 
and the like. These compositions can be coated in thickness of 0.02 inch 
or less. Thin films, from about 0.0005 inch to 0.005 inch thick, can be 
cured in air at from about 25.degree. C. to about 30.degree. C., to 
provide coatings which are quite flexible and have excellent adhesion and 
electrical insulating properties. 
EXAMPLE 1 
A batch of charge transfer complex (CTC) solution was first made, 
containing 50 grams (0.51 mole) of maleic anhydride (MAH) dissolved in 50 
milliliters (44.5 grams) of tetrahydrofuran (THF). The MAH and THF were 
well mixed in a stainless steel beaker with a magnetic stirrer. The beaker 
was wrapped with copper tubing and the beaker was kept in a bath of 
ethylene glycol-water mixture. Refrigerated ethylene glycol-water coolant, 
kept at -20.degree. C. using an Endocol, Neslab refrigeration unit, was 
circulated through the copper coil wrapped around the beaker and also 
dipped in the ethylene glycol-water bath. The bath temperature was about 
2.degree. C. During stirring, the mixture was subjected to U.V. 
irradiation from a 300 watt U.V.-D bulb having a wavelength band between 
2,000 Angstrom units and 4,000 Angstrom units, with primary wavelengths 
between about 3,600 Angstrom units and 3,900 Angstrom units. The cooling 
arrangement was necessary to dissipate the heat energy generated by the D 
bulb, so that the mixture components would not evaporate before reaction. 
In all cases the temperature must be maintained below about 40.degree. C. 
After 30 seconds of irradiation, the mixture temperature increased from 
18.degree. C. to 35.degree. C., after which the D bulb was shut off and 
the mixture was allowed to cool down to 18.degree. C. over a 2 minute to 3 
minute period. Then the solution was irradiated until a 35.degree. C. 
temperature was reached, after which it was again cooled to 18.degree. C. 
This irradiation and cooling cycle was repeated until a total U.V. 
exposure time of 15 minutes was obtained. During the 15 minutes 
irradiation, the colorless MAH-THF solution was turned to red, indicating 
some interaction between the MAH and the THF. The development of color was 
followed spectrophotometrically. In the MAH-THF mixture, charge transfer 
complexes, having an absorption maxima at about 4,480 Angstrom units were 
formed. The irradiated, highly fluid solution of MAH-THF, the charge 
transfer complex, was found to contain a substantial amount of unreacted 
material from about 20% to about 50% of the THF added as well as from 
about 10% to 15% of the maleic anhydride added, as determined by gel 
permeation chromatography. 
This unconcentrated charge transfer complex was then placed in a small 
vacuum chamber apparatus, i.e., a vacuum dessicator attached to a vacuum 
line drawing 0.5 Torr to 1.0 Torr., until its weight was reduced to 85% of 
its original weight, i.e., 15% concentrated. This concentration was 
carried out at 25.degree. C., and produced a concentrated, solution having 
substantially all of the unreacted THF removed without decomposing the 
already formed charge transfer complex. The concentrated charge transfer 
complex was still in liquid form and still contained unreacted maleic 
anhydride. 
Various amounts of different polyhydric alcohols were then quickly admixed 
with samples of the concentrated charge transfer complex solution, 
containing unreacted maleic anhydride, at about 25.degree. C., except that 
trimethylol propane inclusion required 5 minutes of stirring at 35.degree. 
C. In all cases, after admixing to form the dual curing agent, an increase 
in viscosity occurred, indicating addition reactions of polyol and 
anhydride types. These samples, including one control sample containing no 
polyhydric alcohol, were later added to 
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, a 
cycloaliphatic epoxy resin having a viscosity at 25.degree. C. of 350 cps. 
to 400 cps. and an Epoxy Equivalent Weight of 133 (sold commercially by 
Union Carbide under the Tradename ERL-4221). A dual curing agent 
containing concentrated charge transfer complex and ethylene glycol was 
also added to a mixture of 75 parts ERL-4221 and 25 parts of a liquid 
diglycidyl ether of bisphenol A resin, having a viscosity at 25.degree. C. 
of 10,000 cps. to 16,000 cps. and an Epoxy Equivalent Weight of 185-192 
(sold commercially by Shell Chemical under the Tradenan Epon-828). 
In all cases the curing agents and control sample were allowed to sit about 
1 week before addition to the epoxy resins. During this time only the 
polyhydric alcohol free control sample showed visible evidence of a 
crystallization problem. The control sample was also difficult to mix into 
the epoxy resin, and did not provide a homogeneous admixture with the 
epoxy resin. These mixtures of epoxy resin-control curing agent and curing 
agent containing concentrated charge transfer complex and polyhydric 
alcohol were then coated on 3".times.6".times.0.1" steel strips and left 
to cure at 25.degree. C. for 24 hours, to provide 1 mil (0.001") thick 
coatings. Electrical properties, impact strength, and flexibility 
properties were determined and are shown below in Table 1: 
TABLE 1 
__________________________________________________________________________ 
Dual Curing Agent Flexibility: 
Dissipation 
Wt. Ratio ConCTC: 
Wt. Ratio Resin: 
Impart Mandrel Conical 
100 Tan .delta. 
Sample 
Resin Polyhydric Alcohol 
Dual Curing Agent 
Strength 
Bend Test 
25.degree. C. 
100.degree. 
125.degree. 
__________________________________________________________________________ 
C. 
1. ERL-4221 
9:1 ethylene glycol 
10:4 20 in-lb 
&gt;11/2 in. 
0.2 6.5 
8.9 
(C.sub.2 carbon chain) 
2. ERL-4221 
9:1 propylene glycol 
10:4 -- -- 0.2 16.5 
-- 
(C.sub.3 carbon chain) 
3. ERL-4221 
9:1 1,4 butane diol 
10:4 50 in-lb. 
5/8 in. 
2.8 54.5 
-- 
(C.sub.4 carbon chain) 
4. ERL-4221 
9:1 pentane diol 
10:4 -- -- 4.6 26.5 
-- 
(C.sub.5 carbon chain) 
5. ERL-4221 
9:1 hexane diol 
10:4 100 in-lb. 
1/4 in. 
3.1 60+ -- 
(C.sub.6 carbon chain) 
6. ERL-4221 
9:1 trimethylol propane 
10:4 20 in-lb. 
11/2 in. 
0.2 5.2 
7.7 
(C.sub.4 carbon chain) 
7. ERL-4221 
8:2 trimethylol 
10:4 10 in-lb. 
&gt;11/2 in. 
0.2 5.3 
5.0 
propane 
(C.sub.4 carbon chain) 
8. ERL-4221 
20:10 trimethylol 
10:4 -- -- 0.2 5.5 
4.8 
propane 
(C.sub.4 carbon chain) 
9. ERL-4221 + 
9:1 ethylene glycol 
10:4 40 in-lb. 
3/4 in. 
-- -- -- 
EPON-828 
(C.sub.4 carbon chain) 
10.* 
ERL-4221 
1:0 10:4 &lt;10 in-lb. 
&gt;11/2 in. 
0.2 3.8 
17.0 
__________________________________________________________________________ 
*Control Sample no added polyol 
ERL4221 is a cycloaliphatic epoxy resin and EPON828 is a bisphenol A epox 
resin. 
As can be seen from Table 1, trimethylol propane and ethylene glycol 
exhibited better overall electrical properties than the control, evident 
at 125.degree. C. The other samples would be useful for non-electrical 
encapsulation. The best overall candidates were trimethylol propane, 
ethylene glycol and propylene glycol. Samples 1, 3, 5, 6 and 9 were highly 
flexible showing outstanding high impact strength and ability to bend 
around small diameter mandrels. Very importantly, the dual curing agent 
component had good storage and mixing properties, and samples 1 through 9 
all had gel times equal to or better than the control sample. Using the 
dual curing agents of this invention, epoxy resin compositions can be made 
using the dual curing agents of this invention with a 25% concentrated 
charge transfer complex component, where the dual curing agent would 
exhibit excellent stability and mixability. 
Additionally, these curing agents can be used with epoxy resin based paint 
formulations. The paint formulation would generally contain resin such as 
epoxy resin, pigment, filler, and thixotropic agent highly ball milled 
together. Preferably, the paint formulation and the curing agent would be 
put into separate feed containers in a two component air pressure spray 
gun, which would mix the two components in a mixing chamber just before 
the spray head. This type apparatus could be used advantageously for fast, 
room temperature, production line coating.