CA1276369C - Reactive concentrated irradiated catalytic complexes as low temperature curing agents for organic resinous materials - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A reactive catalytic complex solution is formed between a mixture of carboxylic acid anhydride and an excess of a carbon containing cyclic solvent containing an electron deficient component, where the solution is concen-trated to a weight of from about 55% to about 90% of its original weight, to provide a concentrated reactive cata-lytic complex.

Description

7~i311Ei~3 - l - 73661-8 REACTIVE CONCENq'RATED IRRADIArrED CATALYq'lC
COMPLEXES AS LOW TEMPERATURE CURIN~
AGENTS FOR ORGANIC RESINOUS MATE'RIALS

BACKGROU~D OF THE INVENTION
Carboxylic acid anhydride curing agents have been found to be useful with epoxy resins for high voltage insulating applications. Usually, the addition of an accelerator is required to give reasonable gel times at elevated temperatures, but at room temperature, even with hiyh 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.
Smith et al., in U.S. Patent 4,020,017, used minor amounts of organotin compounds, such as triphenyl tin chloride, to form apparent complexes with reactive epoxide diluents, for use as :.
additives for cycloaliphatic and glycidyl ester epoxy resins, to provide resirour electrical .

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insulating compositions without usin~ acid anhydrides These compositions, however, required at least 120C curing temperatureS, In a later improvement, Smlth et al., in U.S. Patent 4,~73,914, fliscovered a low temperature, fast S curing epoxy insulating composition, which consists 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 penta-chloride, titanium ~etrachloride, boron trifluoride, tin tetrachloride, or triphenyl tin chloride, with a carbox-ylic acid anhydride. There, the catalyst and anhydride were simply pre-reacted at a reacting mass temperature of from 10C to about 45C. The complex allowed substantially complete cure of the epoxy resin at 25C in about 48 hours.
Von Brachel et al., in U.S. Patent 3,499,077, utilized a peroxide initiated, non-irradiated, free-radical chain reaction of maleic anhydride and straight chain polyalkylene ethers, at from about 80C to 160C, to provide addition products, noting that the literature showed successful reaction of maleic anhydride with tetra-hydrofuran, 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 ~rom 100C to about 130C
with epoxies and the like.
What is needed is a room temperature curing agent which will provide good gel and cure times, have extended shelf life, and which will help provide good electrical 30 insulating properties to the resins it cures.
SUMMARY OF THE INVENTION
Th~ above problems have heen solved and the aboveneeds met by admixing an organic resinous material, such as an epoxy resin or a vinyl resin, with a highly concentrated reactive catalytic complex produced by admixing: (a) a ~arboxylic acid anhydride, selected from halide or short chain alkyl substituted maleic anhydride, and preferably : ~ . .: - .
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citraconic anhydride or maleic anhydride, and their mix-tures, and (b) a carbon containing cyclic compound contain_ ing an electron deficient element, such as sulfur or preferably oxygen and their mixtures, selected from t~e group consisting of tetrahydrofuran, dioxane, trioxane, and sulfolane, and their mixtures. This latter material acts both as solvent and interactant. A reactive catalytic complex i9 then formed between (a) and a portion of (b), and then at least a part of the other portion of (b) is removed. The weight ratio of (carboxylic acid anhy-dride):(carbon containing cyclic compounfl) is preferably from about (1):(0.6 to 2). In the interaction to form the unconcentrated catalytic complex, no free radical initia-tors are used, and the temperature is preerably kept below about 40C.
The unconcentrated catalytic complex which will always contain excess solvent then has solvent removed, preferably without the use of heat in for example a vacuum chamber or other vacuum means, to reduce its weight to from about 55% to about 90% of its original weight. The highly concentrated, highly reactive catalytic complex, when added in a weight ratio of (resinous material~:(catalytic com-plex) of from about (1~:(0.2 to 1.5~, will effect substan-tially complete cure at 25C, in from about 2 hours to 144 hours. No additional curing agents are needed.
The irradiation that can be used to form th~
unconcentrated catalytic complex contains the wavele~gth ran~e of from~about 2,000 Angstrom units to 5,200 Angstrom units. The irradiation is effective only when both the .

selected carboxylic acid anhydride and the s~lected carbon containing cyclic compound are mixed togather, the irradia-tion of the mixed product solution producing an active species wh1ch is responsible for initiating resin polymer-ization at room temperature.
The resins incorporating these catalytic complex-es can be used to impregnate electrical coil insulation tapes, to encapsulato electrical articles, to act as an : ' .'; ,, ' , - . , . ~ '.. ' '., ' ~ . ~ , '. ',- ;
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insulating adhesiv~ for polyurethane and other type arti-cles, to act as a low viscosity room temperature curable resin, and particularlY, to insulate coil connection~ of high hors~power motors and similar hiyh voLta~e rotating apparatus. These highly concentrated complex catalyzed resins can be especially useful when insulatins temperature sensitive materials that might be melted by application of heat, or, with certain semiconductors, which might change their characteristics upon heating. Also, these highly concentrated complex catalyzed resins can be used where heating the resin to cure it would also unduly cause expansion of the wires or other components that are being bonded or insulated.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, reference may be made to the preferred embodiments, exem-plary of the invention, shown in ~he accompanying drawings, in which:
Figure 1 shows one type of apparatus that can be used to produce the catalytic complexes used in this invention;
Fig. 2 shows a wrapped, resin-impregnated coil made with the resinous composition of this invention;
Fig. 3 shows an encapsulated electrical article ! 25 made with the resinous composition of this invention; and Fig. 4 shows an illustration of the resinous composition of this invention used as a series coil connec-tion stub insulation in high voltage rotating apparatus.
DESCRIPTION OF_THE PREFERRED EMBODIMENTS
30 It has been found that selected carbon containing cyclic compounds, containing an electron deficient element, can effectively interact and complex with selected carbox-ylic acid anhydrides, through irradiation containing the radiation wavelength range of from about 2,000 Angstrom units to about 5,200 Angstrom units, preferably in the ultraviolet portion of that range, i.e., from about 2,000 Angstrom units to about 3,900 Angstrom units. Laser :

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51,803l irradiation, for example with ar~ Argon laser at about 3,600 Angstrom units, is a very concentrated and en~rgy efficient substitute for commol ult~aviolet (U-V-) lamp sources, and allows the reaction to proceed at about ~5C without cooling.
When a laser is used, 5 minutes to 60 minutes irradiation will provide an effective amount of reactive catalytic complex to cure organic resins; and when a 250 watt to 500 watt U.V. lamp is used, 15 minutes to 90 minutes will provide an effective amount of reactive catalytic complex to cure organic resins, when, in each case, the catalytic complex is to be further concentrated in its solvent solution. In the case of the U.V. lamp, the interacting mixture must usually be surrounded by a refrig-eration means, so that the heat of the U.V. lamp does notcause undue evaporation of the materials before the com-plexing is completed. In all cases, the temperature must be kept below about 40C, to prevent evaporation of the materials, for example, maleic anhydride has a sublimation temperature of about 52C and tetrahydrofuran has a boiling point of about 66C. These complexes formed by irradiation are reactive species that are particularly effective in curing epoxy, vinyl, polyester, and other organic resinous systems, at temperatures below about 30C, with no ionic contamination of the cured resin.
The useful carbon containing cyclic compounds ~or these complexes contain one or more sulfur and/or oxygen, preerably oxygen, electron deficient elements or compo-nents, where th~ electron deficient element or component ne~d not be present in the ring structure. Particularly useful compounds of this type include sulfolane, trioxane, and preferably dioxane (1,4 dioxane) a~d tetrahydrofuran, whose respective chemical structures are shown below:

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O o o O O
S/ \ / \ H C / \
H~C CH2 , O\ /O , H2C \ ~ ~ /C-C

H2C~CH CH2 o Use~ul carboxylic acid anhydrides for these complexes include a class of carboxylic acid anhydrides having the chemical formula:
C ~ o R'C'' ~
s- 1~ /o ~ C
~0 ;:
where R and R' = H, CH3, C2H5, Cl, Br or I, for example, R' can = Cl and R can = CH3.
Use of a higher alkyl than C2H5 as R or R' will slow the irradiation reaction with the carbon containing cyclic compound. The most preferred carboxylic acid anhydrid~s are those where R = H and R' - CH3, and where R
and R' - ~, i.e., citraconic anhydride, and preferably maleic anhydride, respectively:

C ~ C~O
CH C~' \ HC'~ \
11 , 11 ~
HC ~C / C
~0 ~o : 15 Other carboxylic acld anhydrides, such as hexa-hydrophthalic anhydride, succinic anhydride, and dodecenyl succinic anhydride, are not effective to provide catalytic reactive æpecies. The double bond opposite the central, single bonded oxygen, appears to be o critical importance in providing catalytic reactive species with the above described carbon containing cyclic compounds during irradi-ation. The carbon containing cyclic compounds act a5 a '. ' ~ ' ' ' ....................................... :

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solvent for the selected acid anhydrides which are usually in solid form. The most useful weight ran~e of (selected carboxylic acid anhydride):(selected carbon containing cyclic compound) is from about (1):(0.6 to 2), most preer-S ably from about (1):(0.8 to 2~. Less than 0.6 part/l partacid anhydride, a solution will not usually result, even with mild heating. Over 2 parts/l part acid ar~ydride, 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 25C to 30C, although they can be mixed at up to about 40C, until a solution results. At this point there is no interaction between the two ingredients other than solution formation, i.e., the produc~ of the mixture contains no complexes or reactive species. Then a reactive catalytic complex is formed between the aci~ anhydride and a part of the sol-vent. Preferably, 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 to form the reactive catalyt-ic complex. 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, attached to magnetic ~tirrer means 6, and having optionaL nitrogen bubbler means 7.
Upon irradiation of the solution, with the wavelength range containing radiation of about 2,000 3Q Angstrom units to about 5,200 Angstrom units, and prefera-bly from about 2,000 Angstrom units to about 3,900 Angstrom units, a complex forms. There will never be complete interaction and complexing betwe~n the two components, so that some solvent will always remain. Although applicants are not to be held to any particular theory, using the interaction between maleic anhydride and dioxane as an .:

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example, the possible interactionS that, it is thought might occur include:
HC ~ \ l ~ C~0 r , C~ *

H2C~ Ch ~ C~ ~ ~ hC ~ / ~ ~

O r C0 ,~0 HC ~ S
r ~ O ~ 0 O

~C C~O
/ ~ CH HC
. O I + I
2 .HC \ /
)C ~ ~ (II) ~O

12C ~ ~fCH2 (III) ~s shown in the previously described reactions, i~ is believed that Argon ion laser action on the product solution and mixture of maleic anhydride and dioxane in step (A) produces a si~glet excited species which goes to triplet excited state via step (B). The triplet excimer thUS produced reacts with another maleic anhydride unit in , .
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the ground state (step C) and produces a complex (after step C). This compl~x then abstract~ a hydrogen atom from dioxane. Th~s results in a color change between step (C) and step (D) to provide catalytic char~e trans~er complexes consisting essentially o reactive specieS, such as cation (I), radical anion (II) and a free radical (III) containing only an electron as a reactive component; which are capable of initiating a cationic polymerization in epoxies and a free radical polymerization in vinyl monomers. In addition to the re~c$ive species shown, it has tlOW been found that a substantial amount, i.e., from about 20% to about 50% of carbon containing cyclic compound added as solvent-interactant, i.e., such as dioxane, remains uncomplexed, and acts as an undesirable plasticizer. No deliberate heating is generally used, care being taken to react only up to about 40C, with no ca~alysts, or initiators being present, the complexing proceeding solely due to irradia-tion effects.
The uncomplexed, carbon containing cyclic com-pound remaining after catalytic complex production, be it dioxane, sulfolane or tetrahydrofuran, has now been found to provide a plasticizing effect on the resinous system it is used~ with, slowing resin cure at 25C. Continued irradiation has not been found to reduce substantially the 25 amount o~ carbon containing cyclic compound remaining.
Heating the catalytic complex over about 45C in an attempt to reduce the amount of unreacted, car~on containing cyclic compound usually causes decomposition of the already formed catalytic complex. A method to remove a substantial amount of the uncomplexed, r~maining carbon containing cyclic solvent compound without decomposing or deactivating any catalytic complex aIready foxmed, can involve passing a stream of nitrogen gas over the catalytic complex at 25C
under about 45C, or preferably using a vacuum chamber at 3~ under about 45C, to remove a substantial amount of the uncomplexed carbon containing cyclic solvent compound, and reduce substantially the plasticizing effect of the unre ' ' ' "

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acted solvent, allcwing extremely fast re~in gel times and commercially feasible cure times at 25C. It is also speculated that the concentration may open up some rings of the carbon containing cyclic compounds, proviclin~ addition-al reactive species.
The solvent solution of catalytic complex is concentrated to from about 55% to about 90%, preferably from about 65% to abou~ 75% of its original weight.
Concentration below about 55% is very difficult, and not concentrating below about ~0% does not yield much benefit in terms of gel and cure times to justify the expense of utilizing a concentrating means. Concentrating between 65%
and about 75% yields a very workable thick slurry material.
Concentration between about 55% and 65% yields a still useful material of incr~a ing solidity as 55% is ap-proached. The term "c~oncentrated" as used here means concentration of the irradiated complex solution, wherein a portion of the remaining carbon containing cyclic solvent is removed, genarally in the temperature range of from about 18C to about 45C, preferably below about 30C. The term X% concentrated as used herein is defined as concen-trated to X% of its original weight, i.e., 60% concentrated means that 40% of the original solvent solution weight has been evaporated. The solvent will evaporate but the complex will not evaporate or decompose under the tempera-ture conditions described above.
Epoxy resins are the preferred resinous materials used with the highly concentrated catalytic complexes previously described. One type of epoxy resin which may be used as the base resin in the invention, or usad in combi-nation with, for example, a cycloaliphatic epoxy, is a bisphenol type obtainable by reacting epichlorohydrin with a dihydric phenol in an alkaline medium at about 50C, using 1 to 2 or more moles of epichlorohydrin per mole of dihydric phenol. The heatin~ 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 .
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single simple compoun~, is generally a complex mixture of glycidyl polyethers, but the principal product may be represented by the chemical structural formula:

, CH2-CH-CE2-0(R-O-CH2-CHOH-CH2-O)n-R-O-CH2-CH-CH2 where n is an integer of the series, O, 1, 2, 3..., and R
represents the divalent hydrocarbon radical of the dihydric phenol. Typically R is:

to provide a diglycidyl ether of bisphenol A type epoxy resin or @~ C ~ ~.
H

to provide a diglyci~yl 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, refer-ence is made to the average number of 1,~ epoxy groups, : ~0~
C~2 c : ' . I
contained in the average molecule of the glycidylether.
Other epoxy resins that are useful in this invention include polyglycidylethers of a novolac. The polyglycidylethers of a novolac suitable for use in accor-dance With this invention are prepared by reacting an epihalohydrin with phenol formaldehyde condensates. While the bisphenol~based resins contain a maximum of two epoxy . :' . - . ~ .

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~roups 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 ~or the productlon of epoxy novolac resins.
Other useful epoxy resins include glycidyl esters, hydantoin epoxy resins, cycl~aliphatic epoxy resins and diglycidyl ethers of aliphatic diols. Of these latter four varieties of epoxies, cycloaliphatic epoxies are particularly useful, used alone or blended with the other epoxy types. The cycloaliphatic type epoxy resins that can be amployed 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 hydroyen peroxide or peracids such as peracetic acid and perhenæoic acid.
The organic peracids are generally prepared by reacting hydrogen peroxide with either carboxylic acids, acid chloride 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 cyclo-hexene dioxide (containing two epoxide groups, one of whichis part of a ring structure); and 3,4-epoxy-6-methylcyclo-hexyl methyl~3,4-epoxy-6-methylcyclohexane carboxylate.
All o~ these epoxy resins are well known in the art, and reference can be made to U.S. Patent 4,273,914 for addi~
tional de-tails in their production.
Other useful organic resinous materials that can be used with the catalytic complexes previously described include vinyl monomers, such as, styrene, 4-methoxy sty-rene, vinyl toluene, methyl methacrylate, methyl vinyl 3S ketone, or 1,1 diphenyl ethylene and the like, and their mixtures. Polyester resins should also work. Both of these classes of resins are well known in the art. The :' ' ' ' ' :' ' " ' . '~'' .

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most useful weight ratio t`ange of (organic resinous material):(concentrated catalytic complex) is from about (1):(0.2 to 1.5), mo5t preferabJ.y from about (1):(0.4 to 0.60). Use of less than 0.2 parts concentrated catalytic complex/l part organic resinous material will provide little gel or cure time improvement- Use of over 1.5 parts concentrated catalytic complex/l part organic resinous material will result in minimal pot life or working time, and air bubhles and voids .in the resin due to high exo-therms resulting in lowering electrical properties. Therange between about (1):(0.60 to 1.5) can be especially useful when a large quantity of filler is used, since filler inclusion seems to substantially delay gel time.
Natural oil extenders, such as epoxidized linseed or soybean oils, octyl epoxy tallate and reactive plasti-cizers such as the conventional phthalates and phosphates may also be used in small amounts, up to about 50 parts per 100 parts of resin to provide increased flexibility.
Thixotropic agents, such as fumed alumina or fumed silica, having particle sizes of from about 0.005 micron to 0.025 micron, and pigments, such as TiO2, may be used in minor amounts as aids in thickening the composition or enhancing the color tones of the ~ured resins.
Similarly, various inorganic particulate fillers, such as alumina trihydrate, silica, quartz, mica, chopped glass fibers, beryllium aluminum silicate, lithium aluminum ~ilicat~, mixtures thereof, ànd the like, in average particle sizes from about 5 microns to about 150 microns, may be employed in amounts up to about 400 parts per 100 parts of resin, to improve electrical properties of the resin formulation, to lower costs, and to provide thick casting or pasting compositions. Photoinitiatoxs are neither required nor desired, since they can provide an impurity element in the composition.
Referring now to ~ig. 2, a closed full coil 10 is shown which can be used in an electric motor or the like.
The coil comprises an end portion comprising a tangent 12, ., ~' , - ~' ' .

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a connecting loop ;4 and another tangent ~6 with bar leads 18 extending theref~om. Slot portions ~0 and 22 of the - coil which sometimes are hot pressed to precure the resin and to form them to predetermined s~lape and si7e are connected to the tan~ents lZ and 16, respectively. These slot portions are connected to other tangents 24 and 26 connected through another loop 28.
In the case of a motor, generally the entire motor con-taining the coils would be placed in an impreg-nating bath containing a low viscosity version of the resinof this invention, and vacuum impregnated. Thereafter the impregnated motor could be removed from the impregnating tank, drained, and air dried for about 100 hours.
Fig. 3 shows an insulated electrical member such as a coil 30, which has conductors 32, potted or encapsu-lated in a thick, cured, insulating casting 34, the casting being the resinous composition of this invention applied to the member in a casting or pasting operation and cured at room temperature.
.20 Tha resin of this invention can be used to adhesively bond coils together or adhesively bond plastic articles, such as polyurethane or other plastic mountings, to a variety of flat or tubular structures, without the use of heat for curing. With filler added, the composition can be used as a thick paste to coat a variety of articles.
Fig. 4 shows its use to bond coils together, where adjacent coils 40, grouped in series are ~hown, and the resinous insulation is used to saturate and coat tape fabric applied over the joint connections 41, to provide insulated stub 42.

Several batches of cataly~ic complex solutionwere made, each containing 50 grams (0.51 mole) of maleic anhydride (MAH) dissolved in 50 milliliters ~44.5 grams) of tetrahydrofuran (THF) solvent-interactant. 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 ~, . . .. . . .
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beaker was kept in a bath of ethylene glycol-water mixture.
Refri~erated ethylene glycol-water coolant, }cept at -20C
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 temper-ature was about 2C. During stirring, the mixture was subjected to U.V. irradiation from a 300 watt U.V.-D bulb having a wav~length band between 2,000 Angstrom units and 4,000 Angstrom units, with primary wavelengths between 10about 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 compo-nents would not evaporate before reaction. In all cases the temperature must be maintained below about 40C.
15After 30 seconds of irradiation, the mixture temperature increased from 18C to 35C, after which the D
bulb was shut off and the mixture was allowed to cool down to 18C over a ~ to 3 minute period. Then the solution was irradiated until a 35C temperature was reached, after which it was again cooled to 18C. This irradiation and cooling cycle was repeated until a total U.V. exposure time of 15 minutes was obtained. During the 15 minutes irradia-tion, the colorless MAH-THF solution turned to red, indi-cating 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 a~out 4,480 Angstrom units, were ormed.
The irradiated, highly fluid solution of MAH-THF, the unconcentrated charge transfer complex, was found to contain a substantial amount of uncomplexed tetrahydrofuran solvent, the carbo~ containing cyclic compound~ from about 20% to about 50% of the T~F added. The unconcentrated charge transfer complex solution was then placed in a small ~5 vacuum chamber apparatus, i.e., a vacuum desiccator at-tached to a vacuum line drawing 0.5 Torr to 1.0 Torr, until charge transfer complex solution weight was reduced to 65%

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of its original weiaht. This concentration was carried out at 25C, and produce~ a highly concentrated charge transfer complex solution having s~lbstantially all of the uncom-plexed THF removed without decomposin~ the already formed charge transfer complex. The highly concentrated charge transfer complex had a thick slurry consistency.
Varying amounts of the highly concentrated charge transfer complex were added to 3,4-epoxy cyclohexyl-methyl(3,~ epoxy)cyclohexane carboxylate, a cycloaliphatic epoxy resin having an epoxy equivalent weight of 133 and a viscosity at 25C of from 350 cps. to 450 cps. (sold commercially by Union Carbide Corporation under the trade name of ERL-4221), In several instances, filler, such as chopped mica or glass iber, was added to the composition.
lS The gel time at 25C and the cure time at 25C for the various compositions, which were placed in 2 inch diameter aluminum dishes, were recorded as set forth in Table 1 below:

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As can be seen, epoxy resins can be yelled at 2SC at very reasondble valu~s and reach an intermediate cure hardness, Shore D of 50, within reason~bLe commercial times. Initial cure times, i.~., to a Shore D hardness of 35 to 37, occurred much sooner for Samples 1 through 5.
For e~ample, Sample 3 reached a Shore D of 35 to 37 in about 23 hours and Sample 5 reached a Shore D of 35 to 37 in about 20 hours, both of which could be considered cured.
Upon further aging at 25C, all the Samples will. eventually reach a Shore D hardness of 85 to 90. Of course, post-curing for 3 to 5 hours at 75C to 125~C will bring the Shore D value to 85 to 90 much sooner. It must be remem bered, that, in most instances BF3 catalyzed epoxy resins require from 12 hours to 18 hours at 75C to cure at all.
Also, increasing the U~V. lamp irradiation time to 30, 45, or 90 minutes should provide a greater amount of reactive species which after concentration would remain and provide faster gel and cure times. In this example, an Argon laser, for example, a coherent CR-18 VSG Argon ion laser operated in the region of 3,600 Angstrom units, could be used to form the charge transfer complex solutions with equally good results as the U.V. lamp, in the fashion shown in Fig. l of the drawings.
Sample 2 resinous compositions were allowed to cure for 288 hours (12 days) at 25C, after which the electrical properties were determined and compared to ERL-4221 catalyzed by a mixture of 3 wt.% BF3 and methyl ethyl amine (MEA) and a 3 wt.% addition of triphenyl tin chloride (TPTCL), both of which are standard curing agents in those amounts for cycloaliphatic epoxy resins. The results are set forth in Table 2 below, where the higher the value, the better the electrical properties:

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19 51,803I

TABI.E ~
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DIELECTRIC
C~RE TI~IE & BREAKDOWN STRENGTH-:t-/' SAMPLE RESIN CATALYST TE~IPERATURE VOLTS/MII.__ ___ __ ____ 2 ERL-4221 MAH:THF 288 hrs. 2;C 435 _ _ _ _ , ~
6* ERL-4221 BF3/~lEA 15 hrs. 75C 285 .
__ __ ~
7~,~ ERL-4221 TPTCL 15 hrs. 75C 260 _ _ ~ .
: ~':Comparative Examples : *~Rate of voltage incre~se = 500 ~o1ts/second As can be seen, if the insulation can be applied in a situa~ion where a 2.5 hour gel period is practical and a storage time of 12 days is feasible, dramatic improve-ments in dielectric strength, at least a 50% increase, are possi~le. It was found that the catalytic curing activity of the complexes remained stable for over l year. In addition to polymerizing epoxies, these catalytic complexes were successfully used to initiate polymerization in vinyl monomers such as styrene, p-methoxy styrene and 1,1 di-phenyl ethylene. Hence, these catalytic complexes can be used to polymerize a wide variety of monomers at room temperature without exposing the epoxy or vinyl resin itself to radiation, or exposing the electrical components bonded or insulated with the complexed resins to excesses of halide action.

The same amounts of ingredients and processes were followed as in Example 1 to make the charge transfer complex, except that the charge transfer complex solution was concentrated to 75% of its original weight. The gel time at 25~C, and the cure time at 25C was recorded as set for-th in Table 3 below:

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21 51,803I
As can b~ seen, comparing the gel and cure times of Sample 8 with Sam~le 3 in Table 1, where the Sample 3 is a more concentrated solution, i.e., 65% concentrated--having 35% o~ the solution cold vaporized, the Sample 3 charge transfer complex provided improved values. In both Examples 1 and ~, the composition is considered to be gelled when it reaches a soft, tacky, gel consistency exhibiting no flow.

' ~ 10 One layer of Dacro~ polyethylene terephthalate) b felt tape, 0.010 inch thick, was dry half lap wrapped around the stub bar lead connections of cut adjacent motor coils, as shown in Fig. 4 of the drawing. The tape was then saturated with the insulating composition of Sample 3, from Example 1, by a dipping and painting process, to provide a total build of about 0.05 inch. The Sample 3 composition contained ERL-4221 resin and a 65% concentrated complex of MRH:THF, with a resin:concentrated complex weight ratio of 1:0.50. A similar tape was wrapped around a similar coil stub and saturated and painted with an insulating composition containing ERL-4221 resin and an alkyl amine catalyst, capable of providing room temperature epoxy cure. The Sample 3 composition was cured for 288 hours ~12 days) at 25C and the comparative Sample 9 25 composition was also cured for 288 hours at 25C. The dielectric strength of each Sample was then measured while immersed in a 5% salt solution--a very drastic test. The results are shown below in Table 4, where the higher the value, the better the electrical properties:

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22 51,803I
TA~LE 4 ____~___ __________ _ _ _ TOTAL ~ __ __ __ __ __ INSUL. DTELECTRIC
CURE TIME THICKNESS BREAKDOWN STRENGT}I**

5 SAMPLE RESIN CATALYST & TEMP. INC}IES VOLTS/MIL
___ , _ -,. . ~ __ _ 3 ERL-4221 MAH:THF 288 hours 0.05" 352.9 =.,. ___ ___ . _ 9~ ERL-4221 Alkyl 288 hours 0.05" 19.5 amine 25C
__ . _ _ . __ ,~ L _ ~Comparative Example ~Rate of increase = 500 volts/second As can be seen, the c~mposition of this invention provides outstanding insulating and electrical properties even under highly rigorous testing.

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.

Claims (8)

1. A method of making a concentrated, reactive catalytic complex comprising the steps:
(1) admixing:
(a) a carboxylic acid anhydride selected from the group consisting of citraconic anhydride and maleic anhydride, and (b) a carbon containing cyclic compound selected from the group consisting of sulfolane, trioxane, dioxane, tetrahydro-furan, and mixtures thereof, where the weight ratio of (carboxylic acid anhydride), (carbon containing cyclic compound) is from about (1):(0.6 to 2);
(2) irradiating the admixture of (a) and (b) with radiation having a wavelength effective to form a reactive catalytic complex between (a) and a portion of (b); and then (3) removing at least a part of the other portion of (b) without decomposing the reactive catalytic complex, so that the weight of the irradiated admixture is reduced to a weight of from about 55% to about 90% to its original weight.

2. The method of claim 1, where the irradiating in step (2) is with radiation which includes the wavelength range of from about 2,000 Angstrom units to about 5,200 Angstrom units.

3. A curable composition comprising the admixture of:
(1) an organic resinous material; and (2) a concentrated, reactive complex comprising the irradiated admixture of, (a) 1 part by weight of a carboxylic acid anhydride having the chemical formula, where R and R' = H, CH3, C2H5, Cl, Br or I; and (b) from about 0.6 part to about 2 parts by weight of a carbon containing cyclic compound containing an electron deficient element selected from the group consisting of sulfur, oxygen, and mixtures thereof; where during irradiation the complex forms between (a) and a portion of (b), and after the complex is formed at least a part of the other portion of (b) is removed so that the weight of the irradiated admixture is reduced to a weight of from about 55% to about 90% of its original weight.

4. The curable composition of claim 3, where the organic resinous material is selected from the group consisting of epoxy resin, vinyl resin, and polyester resin.

5. The curable composition of claim 3, where the carboxylic acid anhydride is selected from the group consisting of citraconic anhydride and maleic anhydride, the carbon containing cyclic compound is selected from the group consisting of sulfolane, trioxane, dioxane, tetrahydrofuran, and mixtures thereof, and the organic resinous material is selected from the group consisting of epoxy resin, vinyl resin, and polyester resin.

6. The curable composition of claim 3, where the carboxylic acid anhydride is maleic anhydride, the carbon containing cyclic compound is selected from the group consisting of dioxane, tetra-hydrofuran, and mixtures thereof, and the organic resinous material is a cycloaliphatic epoxy resin.

7. The curable composition of claim 3, where the weight ratio range of (organic resinous material):(concentrated reactive complex) is from about (1):(0.2 to 1.5).

8. The curable composition of claim 3, where the mixture of anhydride and cyclic compound is irradiated with radiation which includes the wavelength range of from about 2,000 Angstrom units to about 5,200 Angstrom units.